THE

AMERICAN NATURALIST

Vou. LI. January, 1917 No. 601

THE PERSONALITY, HEREDITY AND WORK OF

CHARLES OTIS WHITMAN, 1843-1910

DR. CHARLES B. DAVENPORT

COLD SPRING HARBOR

Ar Pinhook, in the town of Woodstock, Maine, was

born December 12, 1843,! a male child named by his par-

ents, Joseph and Marcia Whitman, Charles Otis. Some

time thereafter the parents and their children removed to

Waterford (where they were in the ’50s) and in 1861 to

Bryant’s Pond (Fig. 1). All of these places are in the

southern part of Oxford County, 50 miles or so from the

coast at Portland, in about the latitude of the Presidential

Range of the White Mountains—a country of high hills

and small mountains, covered with. pine and hardwood ©

forests, abounding in lakes with some fertile plains be-

tween; a country affording a stimulating environment to

a boy with an inherent love of nature. And a love of na-

ture was widespread in the boys of this country and in

their fathers. Take, for example, Jacob Whitman. Born

in Easton, Mass., twenty miles south of Boston and ten

miles north of Taunton it would appear that his lines had

been pleasantly cast. But? he had an adventurous spirit

and was perhaps ‘‘ very wilful.’’ He was with the ‘‘min-

1The date is given as December 14, 1842, by Lillie, yoy and Morse,

1912; also National Cyclopedia of American Biography, XI, p. 73. The

date given above is that of the Whitman Genealogy. It Es agrees with

that pasgain by Mrs. H. D. Smith (Mary Whitman) because her sister

as born September 10, 1843, and Charles O. was born the December

pes i

2Cole and Whitman, 1915, p. 42.

i Ee

6 THE AMERICAN NATURALIST [ Vou. LI

ute men”’ in 1775, probably fought at Bunker Hill, was at

Harlem Heights, stormed Stony Point, helped capture

Saratoga, and was at Trenton. He had married, 1777,

and, after the war, 1781, came to the frontier settlement

of Buckfield, Maine, which had been settled some four

years before. Fellow townsmen, by the name of Record,

had previously settled there and had told Jacob Whitman

about the town and their tales of conditions at Buckfield

evidently appealed to him, and induced him to migrate

thither.

He was a stout and musecularly built man ... and was inured to

hardship. . . . He was an industrious citizen and paid strict attention

to the clearing up of his lot, rearing a family and attaining a compe-

tence. He was often selected for road surveyor, school agent, and

‘school committee and his name was always kept in the jury box until

he got too old to attend to such service. He was a man of fierce spirit

when aroused and positive in his opinions and fond of argument.

No. 601] CHARLES OTIS WHITMAN 7

He declined to join the first church started at Buckfield

as he did not believe its creed. Of other founders and

early settlers of Buckfield it is known that they were

hunters and were attracted to the locality by observations

made on hunting expeditions. Such were Nathaniel Buck

‘fa man of great physical strength and endurance, and

noted for being an expert hunter and skilled in wood-

craft’; Thomas Allen, a deserter from the English army

to the side of the colonists, a man of adventurous disposi-

tion, fiery temper and obstinate in his opinions; and Ben-

jamin Spaulding who had retired from Chelmsford, near

Lowell, Mass., to this wilderness, partly to avoid certain

financial obligations and partly to trap and hunt.* Ox-

ford County was, indeed, as much a frontier of civiliza-

tion at the end of the eighteenth century as the Rocky

Mountains were fifty years later and attracted much the

same sort of adventurers, lovers of untouched nature, the

forests and wild animals. It was the sort of blood from

which naturalists might be expected to arise, and from

Oxford County and from the adjacent counties of Cum-

berland and York have arisen such men as A. E. Verrill,

of Greenwood, H. C. Bumpus, of Buckfield, and C. O.

Whitman, of Woodstock (Oxford Co.); E. S. Morse, of

Portland; A. S. Packard, of Brunswick (Cumberland

Co.) ; Geo. B. Emerson, of Wells, and Geo. L. Goodale, of

Saco (York Co.); and Elliot Coues from just over the

boundary at Portsmouth, N. H.

Charles Otis Whitman was born December 12, 1843, in

Woodstock, Me. As a boy he attended the town schools

at Woodstock and Waterford, and worked on the home

place. During the summers of 1857 and 1858, while at

Waterford, he helped his father’s brother, Elhanan, on

the farm, as Elhanan’s daughter, Mrs. H. D. Smith, of

Norway, Maine, recalls very well. He was a good-na-

tured boy and good company to his cousins. His cousin

can not recall that he was engrossed in birds at that time;

but by 1860 he had made a considerable collection which

3 Cole and Whitman, 1915, pp. 24-5.

IG. 3

FIG

r 9

Fre

FIG. 4

No. 601] CHARLES OTIS WHITMAN 9

Fie. 2. Charles O. Whitman, at the age of eighteen years. This picture

shows a great resemblance to his son, Carroll Whitman, at the time he entered

Cornell University. From a tintype contributed by Mrs. E. B. Reynolds (Myra

Whitman).

FIG Charles O. Whitman at the age of about twenty-one years. Re-

produced from gee PSA where it is hemp “1857, enlargement

type. Kindness of Professor E. B. Mor This wo

teen years. he cousin ai BD. iain: assures me that the correct age is as

stated.

G. 4. Charles O. Whitman at the age of twenty-five years. This is one

of a group d is probably of his regi = bene sree from Bowdoin College.

(Note the “class pin.”) Some of the of the gr are full-

bearded young men. From a silver er patar by his sister, Adrianna

Whitman Evans of Lynn.

Fie. 5. Charles O. Whitman at about thirty-nine years.

No. 601] CHARLES OTIS WHITMAN 11

Fic. 6. Solomon Leonard, the father of C. O. Whitman’s mother, from a

daguerreotype in the possession of Mrs. Myra Whitman Reynolds.

Fic. 7. Esther French, wife of Solomon Leonard and mother of C. O. Whit-

man’s mother. From a daguerreotype in the possession of Mrs. Reynolds.

Fic. 8. arcia Leonard, wife of Joseph Whitman and mother of C. O.

Whitman. Note the thick lower ns and sitehtty raised tip of nose. From a

photographic print; kindness of Mrs. Reynolds.

Fig. 9. Charles O. Whitman, at about twenty years, for comparison with

his mother. Note the restricted broad lip and the slightly raised tip of nose.

From a tintype; kindness of Mrs. Smith.

No. 601] CHARLES OTIS WHITMAN

Joseph Whitman (2d), father of via O. Whitman, shia the wide

nd w gra

nostrils, long tip of nose an y hair, turning

man, probably on his return from Germany, about

The hair of the head is now quite gray

Fig. 10.

Fic. 11. Charles O. Whitm

1878, age thirty-five years.

Fic. 12. Charles O. alap ern professor at hei cg of Chicago, probably

pring of 1900, Age

Fig. 13. “The Father,” about 1887.

THE AMERICAN NATURALIST [Vou. LI

Fie. 14. Handwriting of C. O. Whitman. Above, at Westbury Academy at

about the age of twenty-six years. Below, at fifty-six years.

he had mounted in two great glass cases, nearly covering

one side of the room. Lapham (1882, p. 166) says:

So artistically prepared were they, and so naturally mounted, that

they attracted much attention among ornithological students.

It is said that he was dissuaded from volunteering for the

Civil War by his father’s opposition; was drafted but re-

No. 601] CHARLES OTIS WHITMAN 15

jected after examination. In the autumns of 1861, ’62

and ’63 and in the spring of 1864 Charles attended the

Norway ‘‘Liberal Institute,’’ an academy of high school

grade, where his uncle, George F. Leonard, taught. It is

said that he taught winters to obtain the means for pay-

ing his school expenses.

He entered Bowdoin College as a sophomore in Sep-

tember, 1865, and was given the degree of B.A. in July,

1868. Lillie attributes Whitman’s strong views in favor

of the requirement of Latin for a college education to the

emphasis laid in his day on the classics at Bowdoin. He

participated in the student literary and debating inter-

ests. He ranked about ninth in a class of 23, his rank

having been decreased through the necessity he was under

of teaching to earn funds for his college expenses. The

following autumn he was appointed principal of the Acad-

emy at Westford, Massachusetts, and continued in this

capacity until the spring of 1872. Here he apparently

taught a variety of subjects. In September, 1872, he was

appointed sub-master at the English High School in Bos-

ton where his uncle, George F. Leonard, had been for some

years master. Here he taught general high school sub-

jects until the summer of 1875. Morse states that he dis-

tinguished himself there by his original methods in teach-

ing certain branches of elementary science.

‘While in Boston,’’ says Lillie, ‘‘Whitman came un-

der the influence of Louis Agassiz and was one of the 50

stndents who, in July and August, 1873, attended the

Anderson School of Natural History founded by Agassiz

on the island of Penikese.’’ Here he met Professor E.

S. Morse, one of the instructors, who became interested

in him because of his drawings, superior even to Morse’s

own. Whitman returned to Penikese in the summer of

1874, after which the laboratory was abandoned. The

short-lived Penikese laboratory greatly impressed those

who attended it and several of these became founders of

other marine laboratories—thus, Hyatt of a laboratory at

Annisauam, Whitman of one at Woods Hole, Franklin W.

Hoone~ of one at Cold Spring Harbor, David Starr Jor-

16 THE AMERICAN NATURALIST [ Vou. LI

dan of one on the Pacific coast at Pacific Grove, Califor-

nia. It was at Penikese, says Morse, that Whitman seri-

ously began his life work in science, for shortly after-

wards he went to Dr. Dohrn’s laboratory at Naples and

then to. Leipzig where, under the great Leuckart, he

learned methods of microtome section-eutting, staining of

tissues, and processes of preparation far ahead of those

used at Penikese; in short the modern methods of the em-

bryologist and morphologist.’’ He was in Germany for

three years, being on leave of absence all this time from

the Boston high school. In 1878, at the mature age of

thirty-five, he received the degree of doctor of philosophy

from the University of Leipzig and in the same year ap-

peared his doctor’s thesis, ‘‘The Embryology of Clep-

sine,’’ in the Quarterly Journal of Microscopical Science.

This paper of 100 pages introduced important new prin-

ciples, as well as facts, into embryological science and was

beautifully illustrated by his own drawings.

On his return to America Whitman took up again his

work at the Boston high school, teaching English; but at

the end of the year he had decided to become a zoologist,

applied for and received a fellowship in biology at Johns

Hopkins University and resigned from the English high

school. But during the summer of 1879 he received an

invitation from Professor Morse, who had been teaching

zoology at the Imperial University in Japan, to fill his

place. Accordingly Whitman set sail for Yokohama,

August 21, 1879, and taught at Tokyo until the summer

of 1881. Here he trained four investigators who all þe-

came professors of zoology in the university: conse-

quently he may properly be called the father of zoology in

Japan. He and the administration of the university be-

came estranged, as he would not adapt himself to what.

seemed to him a desire for official control of intellectual

property; also he felt that his work was insufficiently sup-

ported. As he left he published a somewhat harsh bro-

chure entitled ‘‘Zoology in the University of Tokyo.’’

Leaving Japan in August, 1881, Whitman worked at the

Zoological Station of Naples as a guest of Professor

No. 601] CHARLES OTIS WHITMAN 17

Dohrn, November, 1881, to May, 1882. He was interested

in, and recorded, the methods of microscopical research at

that station, and published an important paper on the em-

bryology, life-history and classification of Dicyemids,

which had some time earlier but, as Whitman proved,

without warrant been elevated to the position of a sub-

kingdom of animals, the Mesozoa.

Returning to America in the autumn of 1882 he was ap-

pointed assistant in zoology at the museum of compara-

tive zoology of Harvard University. While here he

worked in cooperation with Alexander Agassiz on the de-

velopment of pelagic fish eggs. Two papers were pub-

lished on this matter and plates prepared, but no text, for

another. At this time he published his book on ‘‘ Methods

of Research in Microscopical Anatomy and Embryology.’’

In 1886 Whitman was invited to take charge of a pri-

vate laboratory for biological and related research that

Edward Phelps Allis, Jr., had planned to found on the

Lake at Milwaukee, Wisconsin. With Allis’s cooperation

Whitman then started the Journal of Morphology, the

first of its kind in America and based on such high ideals

of quality and of beauty of plates that the eighteen vol-

umes published entailed considerable financial loss, so

that finally it had to be discontinued—although it was re-

vived, after a lapse of five years, under other auspices.

The three years, ’86-’89, at the Lake Laboratory saw the

beginning of some researches by Whitman, which were

mostly never completed, and by his associates, Howard

Ayers, William Patten, A. C. Eyeleshymer, as well by the

founder of the laboratory. Some of the published work

is of the finest quality.

In 1888 the Marine Biological Laboratory at Woods

- Hole was organized by certain residents of Boston and

Professor Whitman accepted their invitation to become its

director. It was in the development of this laboratory

that Whitman’s greatest work for science was done. For

he introduced and upheld ideals of cooperation and scien-

tific democracy which led to its loyal and devoted support

by a large body of the working biologists of the country.

18 THE AMERICAN NATURALIST [Vou. LI

In the year 1897 a disagreement occurred between Whit-

man and a minor, but influential, portion of the trustees.

The latter regarded him as extravagant, while he thought

they hampered the proper development and organization

of the laboratory. Some of the Boston supporters of the

‘laboratory thereupon withdrew from the board; however,

the development of the laboratory suffered no serious

interruption. At the end of twenty-one years as director

Whitman was led to resign, owing to the growing demands

upon his time of his researches.

It was in the early years of the Marine Biological Labo-

ratory that Whitman and some of his co-workers saw

the need of a technical zoological society and a call for

such a society was made by a committee of which he was

chairman. He served as president for the first four

years. At first known as the American Morphological

Society, it has been known since 1902 as ‘*The American

Society of Zoologists,’’ and is still the national society for

this science.

In 1889, Clark University having been organized exclu-

sively for graduate and research work, Whitman was

called from Milwaukee to become its professor of zoology.

He now took up again his work as a teacher which con-

tinued to his death. There gathered about him at Wor-

cester, Massachusetts, a small body of devoted zoological

investigators. What with the Journal of Morphology,

the Marine Laboratory and the organization of the new |

department his time was pretty well filled. He published

three short papers on the leech, Clepsine. But affairs at

Clark were not altogether to his liking and when a call to

the University of Chicago came in 1892 Whitman and the

heads of the departments of physics, chemistry, anatomy,

neurology and paleontology seceded from Clark Univer-

sity and formed the major portion of the scientific faculty

of the new university. Here at Chicago Whitman had

more graduate students than ever before, but as his re-

search grew more engrossing he kept more and more to

his home where his experiments were conducted. For a

period of fifteen years he bred pigeons to get at an under-

No. 601] CHARLES OTIS WHITMAN 19

standing of the evolution of their color markings. He

usually had about 500 individuals, representing about 40

wild species, in dovecotes surrounding his house. He

hybridized nearly 40 species, most of which had never

been crossed before. His work included the phylogeny

of pigeons, instinct and animal behavior, voice, fertility

and the nature of sex.

Professor Whitman suffered considerably from indi-

gestion for some years before his death. He contracted

a heavy cold while caring for his pigeons and died sud-

denly, December 6, 1910, at the age of 67, of pneumonia,

the same disease that his mother died of at the age of 57.

We have now to consider some of the personal charac-

teristics of Charles O. Whitman, and their distribution in

his family.

First, white hair. Charles Whitman’s hair turned

white unusually early. Morse quotes Judge Clarence

Hale of Portland as saying that his hair was perfectly

white when in college but his class portrait (Fig. 4) shows

his hair still dark. At the age of 39 (Fig. 5) the hair is

quite white. His father’s hair turned gray early ; Charles’s

brother at 49 has very gray hair. Early graying is ap-

parently a ‘‘ Whitman trait.’’

2.. Wave in hair is shown by his father (Fig. 10) and

as a dominant trait is doubtless inherited from this side.

3. Nostril. His father had broad nostrils (Fig. 10), but

the ridge is carried apically beyond the level of the nos-

tril. In Charles, as in his mother (Fig. 8), the apical

knob was lacking, hence the nostrils appeared unusually

full |

4. The lower lip is thick, especially near the median

plane. His mother’s portrait (Fig. 8) shows an excep-

tionally broad lower lip and this is exactly reproduced in

her daughter, Adrianna. The mother’s father (Fig. 6)

also has a broad lower lip. Charles gets the breadth of

lower lip from his mother’s side and its restriction to the

middle of this lip (Fig. 9) is doubtless due to another

factor.

5. The forehead is broad and full (Fig. 12) ; doubtless a

20 THE AMERICAN NATURALIST [ Von. LI

Whitman trait, as it is strikingly reproduced in his cousin,

Mrs. Smith. Moreover his grandfather Leonard had an

exceptionally fine head (Fig. 7).

6. The general slenderness of form is a Leonard trait.

His father and some of his sibs were stout, as is one of his

sisters, while his other sibs are slender, like himself.

Taste for Natural History.—This was, doubtless, in-

nate and it was very strong, developed very early, as we

have seen above, and led to his keeping animals and

mounting birds. Thus he kept, as a small boy, mud

turtles, rabbits, guinea pigs, woodchucks, and raccoons.

Later, his sister recalls, he kept two gray squirrels which

were so tame that they would go to sleep in his pockets.

He kept doves, which he would tend carefully and of which

he would watch the young after they were hatched. These

doves would cover him as he fed them. He was fond of

hunting. His stuffed eagle was especially famous. On

one occasion, at the age of twenty-four years, he was gone

two nights and a day after an owl. Mr. H. T. Libbey,

. of Bryant’s Pond, told me that on one occasion he went

out with Charles after a large bird and was gone all day.

It is interesting that the special objects of interest of his

early years should have been those of his late years. If

we seek for the origin of this strong taste in such an out-

of-the-way part of the world we find it, as stated above, in

the blood of the pioneer, adventurer, hunter and lover of

nature which sought the wilderness of Maine at the end

of the eighteenth century. Actually, one finds evidence of

love of hunting and of nature in close relatives, especially

on the father’s side. First, Charles’s sister, Adrianna,

was as fond of natural history as himself. She had a

tame bluejay which stayed about the house like a crow.

Charles’s uncle, Chauncey C. Whitman, was a farmer who

devoted himself, in his later years, particularly to the

raising of horses and cattle. Itis told of him‘ that, when

he was twenty-four, he joined his fellow townsmen on a

bear hunt and finally the bear was found in his den under

the roots of a large tree. Chauncey ‘‘had the temerity to

4 Lapham, 1882.

No. 601] CHARLES OTIS WHITMAN 21

thrust in his arm and catch hold of her hair, when she

quickly turned and came out before them all.” She had

two cubs. One was taken out alive and kept for several

months by Chauncey Whitman until, having become mis-

chievous, it was killed. Here we see the same love of

wild animals that Charles showed. This Chauncey had a

son, Albert, who is a hunter living in Oxford County.

He keeps squirrels, woodchucks, and other pets. Al-

bert’s brother, Thomas, had a poultry farm and his son

still carries on the business. Charles’s father’s father,

Joseph Whitman, father of Chauncey, was also a hunter

and told his grandchildren hunting stories, including ad-

ventures with bears and other animals, which are keenly

remembered to this day. It appears that the mother’s

father, Solomon Leonard, had a love of nature and took

pleasure in his trout brook. So Charles got his love of

nature from both sides of the house.

Scholarship.—But Charles had more than a love of na-

ture; he desired to study nature. This scholarship is a

family trait and comes to him from both sides of the

house. It is noteworthy that in Lapham’s ‘‘History of

Woodstock, Me.,’’ 1882, p. 56, it is stated:

Three Woodstock men have graduated from college, George F.

Leonard, Harrison S. Whitman and Charles O. Whitman.

The first is an uncle and the second a cousin of the third.

According to Cole and Whitman (1915, p. 707):

Judge Mitchell’s “History of Bridgewater” says that more persons

of this (Whitman) name in that town in early times received a college

edueation than any other. The next most numerous were Packards.

And Charles’s father’s father’s mother was Abigail Pack-

ard. It is worth while to consider in detail the direction

taken by the scholarship of the close relatives of Charles.

First, the mother’s father, Solomon Leonard, was a close

student of ancient history. But it was to the influence of

his mother’s brother, George F. Leonard, that the direc-

tion of Charles’s early life was chiefly due. George Leon-

ard graduated from Dartmouth with the class of 1859.

He adopted teaching as his profession and instructed in the academies.

in Norway and Paris, in Maine, and in Northbridge, Mass. He was

22 THE AMERICAN NATURALIST [ Von. LI

also a teacher in the English high school in Boston, following this occu-

pation for over twenty years. ... He is a profound scholar and suc-

ceeded well in his teaching.

It will be noted that Leonard was teaching at the English

high school, 1862-’82, at the time Charles O. Whitman

was there and had preceded him there probably ten years.

Leonard was especially interested in mathematics and

during the later years of his life devoted much time to

‘squaring the circle,’’ i. e., to determining if the relation 7

can be exactly expressed by a fraction. He is said to have

worked out the decimal to over 1,250 places. Relatives

say that George Leonard helped secure a college educa-

tion for Charles and his influence must have been great

in getting his parents to let Charles go instead of, as

eldest son, helping his father with his business. Leonard

graduated, 1859, and taught, probably 1859-’62, at the

academy in Norway and that at Paris only a mile or two

away; Charles studied at the Norway Academy, 1861—’64.

George Leonard, as we have seen, was already a veteran

at the English high when Charles came there to teach, re-

taining his connection with it for seven years, and during

this entire period his uncle taught there.

Another instance of scholasticism in this family is that

of Charles’s first cousin, Rev. Harrison Spofford Whit-

man, who was born 1844, a year or two later than Charles.

Harrison is the son of Harrison Whitman, who was a

farmer, at one time captain of an infantry company of

Woodstock that saw some service at the time when war

was threatened over the boundary of Maine; he was also

some time coroner of Oxford County, and died at the age

of thirty-one years, leaving a widow and three children.

Harrison, Jr., early showed remarkable aptitude in com-

position (as did his brother and sister); he wrote both

prose and poetry; he was fond of study, graduated at

Bowdoin in 1869, teaching school meanwhile to earn his

tuition and expenses, was for two years principal of the

Thomaston Academy, ’69-’71; then taught mathematics

and later classics at the Dean Academy, Franklin, Massa-

chusetts, ’71-’74; then he studied theology at Tufts Col-

No. 601] CHARLES OTIS WHITMAN 23

lege, graduating 1877. He has ever since taken a leading

position in the Universalist ministry of Maine, having

been pastor at Augusta and being now at Portland, Maine.

He is an able preacher and popular among his parish-

ioners.

This brief account of close relatives who have been dis-

tinguished scholars makes it clear how Charles O. Whit-

man found it natural to follow a scholarly career.

Thoughtfulness and Classicism.—Not all scholars are

of the same type. In one type (the hyperkinetic or ro-

mantic) there is a rich flow of brilliant ideas and a rapid

passage from one subject of interest to another. In the

other type (the hypokinetic or classic) there is a pro-

fundity of consideration of a subject and a persistence

of interest in it. Charles O. Whitman belonged to the

latter type. This type ordinarily shows a recessive in-

heritance. His mother apparently showed this type.

She was gentle and pleasant and never lost her even tem-

per; while in many of the Whitmans the temper was of

the periodically explosive sort; but there is evidence of

the classic temperament on the paternal side, e. g., in Har-

rison S. Whitman.

That Charles Whitman was of the classic type and was

thoughtful will be generally conceded; he was, indeed, one

of the best examples of this type that one could find.

He felt little pressure to express himself. His principal

biographer (Lillie, 1911) records only 67 titles of which 7

are his annual reports,—reports that, toward the end of

the series, were secured only, with much difficulty and

after long delay, and for the last twelve years not at all.

Of the remaining 60 there are hardly 20 that are to be

classed as typical professional papers, giving the final

results of finished observation. Some of the papers are

brief notices of technical methods (Methods in the Zoolog-

ical Station in Naples, 1882, with a French translation ;

treatment of pelagic fish eggs, 1883; means of differen-

tiating embryonic tissues, 1885; osmice acid and Merkel’s

fluid, 1886). Other papers are polemical (new facts

24 THE AMERICAN NATURALIST [ Vou. LI

about the Hirudinea critique of Apathy, 1888; Apathy’s

grief and consolation, 1899).

A group of papers (9) of a semi-popular sort relate to

the work and aims of the Biological Laboratory. Most of

the remaining non-technical papers are delightful essays,

chiefly upon philosophical biological matters. Such are:

“The Seat of Formative and Regenerative Energy,”

1887; ‘‘The Naturalist’s Occupation,’’ 1891; ‘‘The Inade-

quacy of the Cell Theory of Development,’’ 1893; ‘‘Gen-

eral Physiology and Its Relation to Morphology,’’ 1893;

‘Evolution and Epigenesis,’’ 1895; ‘‘Bonnet’s Theory of

Evolution; a System of Negations’’; also ‘‘The Palin-

genesia and the Germ Doctrine of Bonnet,’’ 1895; ‘‘ Ani-

mal Behavior,’’ 1899; ‘‘Myths in Animal Psychology,’’

1899.

The more strictly investigational papers fall into three

periods: (1) The invertebrate period—devoted chiefly to

the leech, Clepsine, which was the subject of his doctor’s

thesis and upon which he wrote more or less from 1878 to

1899—a period of 21 years. Here also belongs his Naples

work on Dicyemids. (2) The period of vertebrate em-

bryology, beginning with work done with Alexander

Agassiz on pelagic fish eggs, 1883-1889, on amphibian

eggs, 1888, and the ganoid fish, Amia, 1896. (3) The

period of genetics, foreshadowed in his note ‘‘Artificial

Production of Variation in Types,’’ 1892, and continued

with the pigeons to the end, 1910, in all eighteen years.

In his work with worms, amphibians and pigeons he was

led to reflections upon animal psychology and to the pub-

lication of his classic paper on animal behavior, 1898,

and his brief paper on myths in animal psychology, 1899.

Many of these papers are highly finished and give the

results of prolonged contemplation. Professor Whit-

man. especially in his later years, repeatedly spoke dis-

dainfully of rushing into print and making an annual

‘‘dump’’ of scientific gleanings—and these were the nat-

ural expressions of his own nature; perhaps he insuffi-

ciently recognized that all persons were not constituted

like himself and could not react in the same way. Whit-

No. 601] CHARLES OTIS WHITMAN 25

man, indeed, planned to publish far more than he did; he

had accumulated materials that were nearly ready for the

printer. But the absence of the hyperkinetic drive com-

bined with the manifold duties of the moment led to pro-

crastination for the more convenient period of prolonged

quiet which an overactive world never afforded him. On

the other hand, had it not been for the exceptional pres-

sure brought to bear on him for an address or a contribu-

tion we might have had less than we have from his pen.

Of his writings Lillie truly says (p. lxxiii):

His published papers, mostly short, are models of condensed thought,

written in a fine, polished, characteristic style. No less care was de-

voted to the form than to the substance, and some of his papers will

certainly endure as classics of the biology of his time. . . . He rarely

had occasion to correct any published statement, and even less rarely,

perhaps, to change in any radical way a point of view to which he had

once committed himself.

Conservatism, so frequently associated with hypoki-

nesis, was marked in Whitman. He was not very cordial

to developmental mechanics, and was critical of the en-

thusiastic rush to the mutation theory and Mendelism.

He could not easily abandon old ideas for new, and ally

himself with the latest biological fad.

A strong philosophic and argumentative tendency is

found on both sides of the house. His mother’s father

was much given to theological discussion, and was an ar-

dent adventist. Charles’s father, too, was argumenta-

tive. The philosophic tendency in Whitman was marked

in his writings. In one of his manuscripts of Westford

days, at the age of 26, he discusses the topic ‘‘Progress

Has No Goal” and again ‘‘Womanhood Suffrage,” of

which the tenor is shown by the concluding sentence:

Female suffrage . . . may meet with opposition, as indeed, every re-

form does, but all this opposition is but the alarm of the great ¿lock of

human progress, which is soon to strike the hour when all enlightened

nations shall recognize not only manhood but also womanhood suffrage.

This is quoted as an illustration of youthful style and not

a statement of his views in later life.

Whitman’s hypokinesis shows itself even in his hand-

writing. It altogether lacks the running dash of the

26 THE AMERICAN NATURALIST [ Von. LI

hyperkinetic. Each word is worked out with some effort.

It is interesting to compare his chirography of Westford

Academy days (when he was about twenty-six) and that

when he was fifty-six (Fig. 14). There is the same loop

from the end of the word to cross the ‘‘t’’ in ‘‘the’’; the

same scanting of the terminal ‘‘y’’; the same form of the

capital ‘‘I.’? In thirty and indeed in the course of

forty years his handwriting showed no important change.

Deliberateness.— Professor Whitman’s movements and

speech were characterized by deliberateness—another

characteristic of the classical type. It is, of course, a

mere caricature to say, as an unkind critic once did, that

his lectures consisted of pauses punctuated by sentences.

I mention this because it brings vividly to mind a way he

had in lecturing or addressing his seminar students to

pause frequently for some seconds looking pleasantly

over the room before beginning the next sentence. Even

in conversation he would turn a calm, thoughtful face to-

ward you and express himself clearly and deliberately.

So marked a deliberateness is not shown by his sibs,

but his brother shows something of it, and I am told that

his father was slow of speech.

Literary Ability.—While Whitman did not have a

strong internal impulse to write, what he published is

mostly characterized by high literary finish. Speaking of

cooperation between the organic and the inorganic sci-

ences he says (1895, p. iv):

Comparison of standpoints must benefit both sides. Cross fertiliza-

tion works rejuvenation in theories as in organisms. The biologist may

pause to see how the individual vanishes in the abyss of the universal,

and how self determination dissolves in the pressure of the physicist’s

fundamental postulate of inertia. The physicist may find it agreeable

from time to time to turn from the Nirvana where self and not self,

rocked ‘in blissful reciprocity of vibration, annul each other, to the

world where self asserts itself in organie determinations, issuing in pur-

poseful adaptations and eonscious, intelligent action.

Again, speaking of Bonnet he says:

With a zeal never daunted, and an ingenuity seldom baffled, never

defeated, he piled mountain upon mountain of negation, rolling Ossa

upon Olympus and Pelia upon Ossa, until the whole organie world

No. 601] CHARLES OTIS WHITMAN 27

seemed to be completely buried under a stupendous mass of negations,

blinding in one infinite negation—No Change.

Perhaps something of Whitman’s interesting and vivid

style may be referred to the influence of his teaching: of

English in the high school; but much of it appears in

papers written before the Boston days. In them, too,

he frequently uses the rhetorical question so often found

in his later writings (cf. Fig. 14, upper). I think we

must conclude that this literary ability has a constitu-

tional basis. We have seen above that his cousins, chil-

dren of Harrison Whitman, ‘‘early showed a remark-

able aptitude for composition both in prose and poetry.’’

A granddaughter of Chauncey Whitman, brother of

Charles’s father, was an authoress of poetry, for which

she found a market.

Pertinacity.—In Whitman’s combination of traits was

found an element of pertinacity that was at times very

formidable. Had it been less he could hardly have suc-

cessfully overcome the handicap of comparative poverty,

despite which he went through college. It showed itself

again when he insisted in Japan that his student’s papers

should be published under their own names: and, when,

since he was overruled, he resigned his professorship. It

showed itself again in his struggle with a minority of the

trustees of the Biological Laboratory, in which his views

prevailed. It showed itself still again in his relations

with Clark University, which led to his acceptance of the

offer to go to Chicago. In minor departmental and labo-

ratory affairs, as his colleagues well recall, this gentle-

mannered man would show at times uncommon resistance

to suggestion and persuasion. One, therefore, learns with

interest that his father also was set in his opinions and

could not readily be made to change his views. Indeed,

Charles is seen to be an interesting mixture of gentleness,

as shown also by his mother, and tenacity of purpose, as

shown also by his father, his mother’s father and other

members of the family. Closely akin to his insistence on

his ideals was his uncompromising disposition. As Lillie

well remarks,

_ It is questionable whether his life would have been so valuable, had :

his disposition been more pliable.

28 THE AMERICAN NATURALIST [Vou. LI

One other trait that sometimes showed itself, especially

in his writings, was his capacity for trenchant and satir-

ical criticism. Morse (1912, p. 283) has given some ex-

amples. It is characteristic of many hypokinetics to feel

deeply and to resent warmly. In weighing any criticism

we must always consider the personality of the critic.

Perhaps in this reaction of Whitman’s we see trace of a

Whitman ‘‘sternness’’ shown also by his father.

Artistic Taste.— Professor Whitman had a keen artis-

tic sense. This is proved by the success, in his boyhood,

of his mounts of birds. I think we may go back of this

and find evidence of an artistic sense in the appeal made

to him by natural beauty—the beauty of forests, flowers,

birds and beasts. To a person without the sense of

beauty natural forms have little attraction. Later this

sensitiveness to and love of form shows itself in the beau-

tiful drawings he made at Penikese, the exquisite plates

of leeches and the delicate pencil drawings of the Dicy-

emids. It is clear that the art of Japan appealed strongly

to him and he had in his house at Chicago many examples

of that art. It was love of form that made him a mor-

phologist and led him in the Journal of Morphology to in-

troduce a beauty of execution of plates exceeding any-

thing then current in America. It was this sense of

beauty that led him to select excellent Japanese artists to

draw and paint his pigeons. While I have not been able

to make an exhaustive study of the distribution of artistic

sense in his relatives, it appears that his father, who was

a carriage manufacturer, was an artistic one. The wood-

work of the finish was done very carefully, the wheels

made by hand and so artistically was the whole executed

that he once received a silver cup as prize for one of his

carriages at a competitive exhibition. On the other side

we find his mother’s father, Solomon Leonard, was also

an artisan. He established an iron foundry at Pinhook

and his kitchen ware was so satisfactory that ‘‘the name

of Solomon Leonard was known in every household.’’

When later he retired from business he maintained ‘‘a

small furnace at Bryant’s Pond, where he made small

castings to pass away the time.’’ So it seems probable

No. 601] CHARLES OTIS WHITMAN 29

that a taste for the beautiful in form and color had a con-

stitutional basis in Charles. :

Musical ability is frequent in the Whitman side of the

house. Nearly all of the Whitmans could sing; espe-

cially good were his father’s brothers. But Marcia Leon-

ard, the mother, could not carry a tune; and the children

were apparently not good singers. Charles tried to learn

to play the melodeon when he was a boy, but had no apti-

tude for it; his elder sister, however, plays well on the

piano and her son is a performer on the violin, of great

ability, and a brother of Charles plays the violin well.

Of mechanical ability Dr. Whitman had more than the

average man. His success in mounting birds (in his

father’s carriage shop) required manual dexterity. His

sister recalls that he made a martin house. This ability

shows itself again in his interest in methods of micro-

scopical research which culminated in a volume—the only

book he ever wrote—entitled: ‘‘Methods of Research in

Microscopical Anatomy and Embryology,’’ 255 pp., Bos-

ton, 1885. Of this book 55 pages are devoted to instru-

ments and methods of imbedding, including 28 figures of

machinery and apparatus, and pages of descriptions of

the principles and details of this apparatus. It is im-

probable that Whitman would have collected such ma-

terials and written such a book had he not been interested

in and had an insight into mechanical devices. This taste

he maintained to the end, and he tarried long over a stu-

dent who had invented some new instrument.” This me-

chanical insight enabled him to do things in ship-shape

fashion. His charts and general arrangements of his

laboratory and breeding pens showed this savoir faire.

With less mechanical skill the feat of moving his pigeons

to Woods Hole and back each year would hardly have

been feasible. Whitman came from a race of artisans on

both sides. His father was a carriage maker; his father’s

sister Loney had a son, Edwin, who is a machinist and an-

other, Edson, who is overseer in a fabric mill. One of

his uncle Cyprian Whitman’s sons is an engineer. Of

Elhanan Whitman’s sons, Austin was a farmer with more

5 Dr. Osear Riddle. ,

30 THE AMERICAN NATURALIST [Vou. LI

than average mechanical ability and Edgar was a carpen-

' ter and always ingenious. Even Elhanan’s daughter,

Mary, says she is handy with tools and so are all of her

sons. On the mother’s side we have doubtless mechan-

ical interests in at least the grandfather, Solomon Leon-

ard, the iron founder.

The social instinct was highly developed in Whitman.

While he rarely appeared at social functions and seemed

to shrink from exercising the presidential office to which

learned societies repeatedly elected him, yet he liked the

society of his younger colleagues, frequently had infor-

mal lunches or dinners and, after the excellent meal, would

encourage the guests to sit and talk on the matters that

were uppermost in the minds of such young and ardent

students of biology.

Given a young man of good health, fairly ambitious,

dogged, scholarly, gentle, friendly, philosophical, conserv-

ative, with an ardent love of natural objects, literary and

artistic ability of a high order, and with a savoir faire

and place him in an environment of a scholarly uncle who

is in a position to assist his nephew; of the stimulus of

magnetically charged biological atmospheres at Penikese

and at Leipzig; of an epoch when new machinery and new

methods are being rapidly introduced into a new science;

of a period in a young science that demanded organiza-

tion of laboratories, university departments, societies and

journals; and the reaction is that of the propositus; even

though handicapped (?) with a hypokinetic tempera-

ment, an uncompromising attitude and, in his earlier

years, an occasional tendency toward caustic criticism.

At any rate such was the man, such the environment that

provided the stimulus, and such the life history of Charles

Otis Whitman.

LITERATURE CITED

Cole, Alfred and C. F. Whitman, 1915. A History of Buckfield, Oxford

County, Maine. Buckfield, Me. 758 pp.

Farnam, C. H., 1889. Genealogy of Whitman Family.

Lapham, W. B., 1882. History of Woodstock, Maine.

Lillie, F. R., 1911. Charles Otis Whitman. Journal of Morphològy, XXII,

pp. š Č;

Morse, E. S., 1912. Biographical Memoir of Charles Otis Whitman, 1812-

1910. Nat. Acad. of Sci. Biographical Memoirs, Vol. VII, pp. 269-288.

MENDELIAN FACTOR DIFFERENCES VERSUS

REACTION SYSTEM CONTRASTS IN

HEREDITY!

T. H. GOODSPEED AND R. E. CLAUSEN

Durine recent years there has been a remarkable ad-

vance in our knowledge of Mendelian principles of hered-

ity. This advance has for the most part had its source in

the important and fundamental work of Morgan and his

associates (1915) in which they have been concerned with

the mutations of the common fruit fly, Drosophila ampe-

lophila. The results of other work, in so far as agreement

has permitted, have been brought into harmony with the

principles arrived at through these investigations. As a

result there has been developed a fairly clear and compre-

hensive conception of the constitution of the hereditary.

material and the nature of the mechanism by which it is

distributed in gametogenesis, a conception which fur-

nishes a consistent explanation of the products of Men-

delian studies.

Morgan has stated that the fundamental principle of

Mendelism may be reduced to this, that the units con-

tributed by two parents separate in the germ cells of the

offspring without having had any effect on each other.

This conception of the absence of any factorial variability

_ save that concerned in the discontinuous changes in fac-

tors involved in mutations has furnished the working hy-

pothesis for Morgan’s brilliant analysis of the germ

plasm of Drosophila. Although the results of the Droso-

phila investigations have been ably presented elsewhere

(Morgan et al., l. c.) it seems well briefly to review them

here especially as they are vital to the argument presented

in this paper.

1The investigations herein reported have been assisted by that portion

of the Adam’s fund granted to the department of botany by the depart-

ment of agriculture of the University of California.

| a

by 4 THE AMERICAN NATURALIST [ Vou. LI

The large amount of data which Morgan and his asso-

ciates have collected within the past six years has clearly

demonstrated that the chromosome mechanism furnishes

a basis upon which the behavior of Mendelian units may

be logically and consistently explained. In an investiga-

tion of Drosophila over a hundred factor mutations have

been discovered and studied, and these have been found

to fall into four groups with respect to the linkage rela-

tions they display with one another. These four groups

correspond to the four pairs of chromosomes. By deter-

mining the linkage values which are displayed within

groups it has been possible to demonstrate that there is a

consistent, invariable, linear arrangement of factors

within the chromosomes at some time in their history.

From this data Morgan and his associates have been able

to prepare a map of the relative positions of the factors

in the chromosomes. The complete conception, therefore,

pictures the chromosome at some stage in its history as a

linear series of loci. Whena change occurs in some locus,

a corresponding change of some sort may occur in soma-

togenesis, so that the individual which develops from such

a set of factors with the changed locus differs in some

particular way from an individual which develops from

the normal unchanged series of loci. The change in the

characters of the individual will depend not only upon the

particular locus which has been changed, but also upon

the particular way in which that locus has been changed.

A changed locus, however, maintains the same position.

with reference to the other loci as did the unchanged

locus, and this fact is the basis of Mendelian behavior, for

knowing the behavior of the chromosomes in reduction,

it enables us to gain a clear conception of the nature of

Mendelian segregation.

When now we consider the particular factors them-

selves, the changed loci of the system, we see clearly that

important physiological relations exist among the various

loci. It is an appreciation of this fact that has led many

investigators, among them Conklin (1908), Jennings

(1914), Morgan (1915 b), Pearl (1915), and Wilson (1914),

No. 601] § MENDELIAN FACTOR DIFFERENCES 33

to insist that the factors can not be regarded as deter-

miners in themselves; but rather that they are differenti-

ators, that working together with other factors in the

system a difference is produced in somatogenesis which

has its origin in some difference, some change in a locus

in the system. For when in Drosophila a change in the

locus W is produced, or in Y, such that the individuals

developing from systems with these changed loci are

white-eyed in the one case and yellow-bodied in the other,

it seems evident that the change is more profound than

the color of eyes or of body; that beyond these changes

there is an underlying, elusive, physiological change re-

sulting in individuals that are less vigorous and less fer-

tile than those which develop from the normal unchanged

system. The fact that a factor may have a primary,

simple, easily recognizable effect and secondary far reach-

ing effects, the latter to be attributed to the modified

physiological relations resulting from a change in one of

the members of a system, is one which has often been ob-

served and which is of fundamental significance in our

conception of the interrelations of the genetic factors.

There are, however, other instances which may be cited

of a somewhat similar nature, locus changes which pro-

duce certain characteristic effects under particular en-

vironmental conditions, but fail to disturb the normal

behavior of the factor system when these conditions are

not met.

It would, of course, be possible to recount almost in-

definitely the specific effects of particular locus changes,

whereas evidence concerning these far reaching effects of

single factors is too scanty to warrant further discussion

of this point. However, Morgan (1915 a) has been able to

establish the relations displayed by the factor for ab-

normal abdomen and to demonstrate that only under very

particular conditions is the presence of this genetic factor

manifested by its characteristic expression, and that when

these conditions are not present the product of somato-

genesis may not differ in appearance from the normal fly,

although differing from it both in genetic constitution and

34 THE AMERICAN NATURALIST [Vou. LI

hereditary behavior. We have thus a factor here which

evidently has such a relation to the other members of the

factor system that only under peculiar environmental con-

ditions does it disturb the normal course of somato-

genesis. Miles (1915) has likewise investigated a type of

chlorophyll reduction in maize in which the recessive

forms are yellow seedlings which usually show a dis-

tinct greenish tinge at the tips of the leaves. This type of

chlorophyll reduction displays normal Mendelian be-

havior in inheritance giving in the progeny of hetero-

zygous plants a ratio of approximately three seedlings

which are of the normal green coloration to one which is

of the yellowish type. The heterozygous plants possess

the normal depth of coloration and can not be distin-

guished from those which are homozygous for the produc-

tion of normal chlorophyll coloration. The yellow seed-

lings on the other hand form a distinct and easily recog-

nizable class with no tendency toward intergradation, an

observation which we have ourselves been able to con-

firm in independent mutations involving this locus. Usu-

ally these seedlings die as soon as the food material in the

endosperm is exhausted, for under ordinary conditions

the change in the locus is incompatible with a normal de-

velopment of the individual, it is too profound an altera-

tion to give a normally functioning factorial system.

Miles found, however, that when the yellow seedlings

were grown under particularly favorable conditions, they

developed a normal chlorophyll coloration and produced

plants which were able to go on through the cycle of

changes included in the normal development of the maize

plant. Now this behavior can not be referred to any

change of the reduction locus back to the original condi-

tion, for the progeny of such plants consisted entirely of

yellow seedlings; indeed, such a reversion would be incon-

ceivable. Obviously the explanation of the situation will

be found only through a consideration of the system with

the recessive reduction locus. Normally this unchanged

locus performs a definite function in determining the pro-

duction of chlorophyll in the plant, but this function is

No.601] § MENDELIAN FACTOR DIFFERENCES 35

performed in conjunction with a number, perhaps a very

great number or even all, of the other loci within the

system. With a change in this particular locus, how-

ever, comes a change in the normal course of events in

chlorophyll production, in that the rate at which the sys-

tem is able to produce chlorophyll has been altered.

Nevertheless, this change does not completely prevent the

system under favorable conditions from going on and

ultimately developing the same reaction end product

which would have developed in the normal unchanged

condition, but more rapidly.

Among such factors as have a profound influence upon

the interrelations within the systems of which they area

part are those which Morgan (1914) has called lethals.

Morgan’s work with lethals is particularly suggestive

because he has been able to demonstrate that they, like

other normal Mendelian factors, occupy a definite locus in

the chromatin system and display the same perfectly defi-

nite and consistent behavior with reference to the other

loci of the system as do all other changed loci which do

not interfere with the normal development of the indi-

vidual. It is entirely possible that some of the lethals,

like the chlorophyll reduction locus which we have dis-

cussed above, may yield systems which occasionally per-

mit of the normal development of the individual, at least

certain peculiar sex ratios which have been obtained

might indicate that fact (Morgan, l. c.) ; but the important

result of these investigations with lethal factors lies in

that fact that certain kinds of changes in some loci are

incompatible with normal functioning of the chromatin

system. It might in addition be noted that there seems to

be no particular reason why we should not include in the

same category with lethals, the type of chlorophyll reduc-

tion mentioned above and those other types in maize

which result from such profound factor changes that no

development is possible after the food supply of the endo-

sperm is exhausted.

Now giving the above results their broader and more

general interpretation, it would appear that the factors

36 THE AMERICAN NATURALIST [ Von, LI

make up a reaction system the elements of which bear a

more or less specific relationship to one another. It is

this specific interrelation of the factors of the reaction

system which determines that wheat produces wheat, and

corn, corn, and so on through the whole realm of living

matter. With this in mind it is at once apparent that

normal Mendelian behavior can not be considered as a

contrast of different reaction systems, but that in such

cases the two organisms contrasted must possess funda-

mentally the same reaction systems, only a relatively few

elements within the reaction system differing, and these

not in a fundamental fashion. Jn fact it seems entirely

logical in the light of modern Mendelian developments to

consider each particular locus as made up of a definite

nucleus, some complex organic compound perhaps, with

a number of end chains which may be altered in various

ways without changing the structure of the nucleus of the

locus. According to this conception the fundamental rela-

tion of the locus to the other elements of the reaction sys-

tem would remain unchanged, while the end product would

be altered in some particular manner. There is probably

no more striking confirmation of this conception than the

suggestive hypothesis of multiple allelomorphs which

Morgan and his associates (1915, J. c.) have developed.

Their results and those of others in this connection seem

to show clearly that the explanation of Mendelian differ-

ences on the basis of such a profound change as the drop-

ping out of an element from a delicately balanced reaction

system is practically out of the question. In multiple alle-

lomorphs we have not one, but several, changes within the

same locus. The similar effect which these changes have

on certain organs of the body, for example, that relation

shown in the locus W in Drosophila as a consequence of

which the normal red eye color may be changed to white,

eosin, or cherry depending upon a particular change in

the locus, are such as to indicate that these are probably

changes around the fringe of the molecule and not such

as fundamentally affect the structure of the entire locus.

Moreover, the relations thus exhibited again indicate that

No. 601] MENDELIAN FACTOR DIFFERENCES 37

the locus has a particular place and function in the reac-

tion system, that it bears a specific relation to the other

elements of the system.

It is true that investigation in plant breeding has not

yet progressed far enough to furnish a definite confirma-

tion all along the line of the work with Drosophila. The

reasons for this are very obvious and they lie in the tech-

nical difficulties involved in such work rather than in fun-

damental disagreements in principle. It has not as yet

been possible to study as many factors in any plant spe-

cies as have been investigated in Drosophila, nor to carry

the work through as many generations nor to employ as

large populations. Moreover, most plant material is

more difficult to handle from the standpoint of a chromo-

some analysis on account of the longer period of time

necessary to secure data and the greater amount of atten-

tion which must be given the cultures and the larger num-

ber of chromosomes which are usually involved in such

species. It must also be borne in mind that practically all

the Drosophila differences have arisen under observation

as simple factor mutations, and it has therefore been rela-

tively easy to determine their relations to the other fac-

tors in the system. In plants, on the other hand, the ma-

terial has presented itself as a confusing array of varieties

containing for the most part a large number of recessive

factors, and usually the original form from which they

were derived, corresponding to the normal fly of Morgan’s

work, has not been obtainable and would not have been

varticularly useful, had it been available. Nevertheless,

there appears to be no real difficulty in the way of accept-

ing the conception derived from the Drosophila studies as

a definite, consistent working hypothesis; for it is diffieult

to believe that the behavior of plant material should be

fundamentally different, and indeed points of correspond-

ence are not lacking to warrant us in viewing somewhat

sceptically any undue emphasis placed upon the differ-

ences which may seem to obtain.

We may now return to the conception of the reaction

system as a unit in itself in the sense that it is made up of

38 THE AMERICAN NATURALIST | Vou. Li

a large number of elements which bear a more or less spe-

cific relation to one another. This is the important physi-

ological conception which has grown out of the vast

amount of work which has been done in recent years in

the analysis of the hereditary material. This is no new

contention; it has been advanced and ably advocated by

many investigators, but we feel that certain consequences

of this conception have not been given the consideration

their importance deserves. For if this conception be

valid then it should not be possible, in certain cases at

least, to shift and recombine the elements from which

systems have been built up in the haphazard way that

some advocates of Mendelism have attempted to do. If,

for example, it is possible to obtain hybrids involving not

a contrast between factors within a single system, but a

contrast of systems all along the line, then it is obvious

that we must consider the phenomenon on a higher plane,

we must lift our point of consideration as it were from the

units of the system to the systems as units in themselves.

Our attention has been called to this extension of the

Mendelian conception by the behavior of species hybrids

of Nicotiana which have been studied at the University

of California during the past six years. This study has .

been concerned particularly with hybrids between N. syl-

vestris and varieties of N. Tabacum. These species, the

former represented in the collections of the University of

California Botanical Garden by a single type and the

latter by a considerable variety of distinct forms, belong

to entirely distinct sections of the genus Nicotiana and

differ in important particulars which have been described

elsewhere (Setchell, 1912). Goodspeed (1913) has studied

a large number of different reciprocal hybrids between

sylvestris and various of the distinct varieties of Taba-

cum. These hybrids are all partially sterile. It is pos-

sible to obtain a few viable seeds from open pollinated

flowers and from those pollinated with Tabacum and syl-

vestris, but it has never been found possible to obtain any

selfed seed. The phenomena displayed by these hybrids

in development and inheritance admit of a consistent ex-

No. 601] | MENDELIAN FACTOR DIFFERENCES 39

planation, if we regard them as the outcome of a contrast

of two distinct Mendelian reaction systems the elements

of which can not be freely interchanged without pro-

foundly affecting the general functions of the reaction

systems thereby resulting. We shall take up in very gen-

eral fashion the points which have inclined us to this view,

reserving for a later treatment the discussion of the hy-

pothesis in detail and also the presentation of the ex-

tended data.

When hybrids are obtained between sylvestris and the

various varieties of Tabacum they agree throughout in

F, in presenting the entire set of characters of the Taba-

cum parent to the exclusion of those of sylvestris. This

behavior may be definitely accounted for as a dominance

of the Tabacum reaction system as such over the sylves-

tris reaction system. For point by point and character

by character throughout, the correspondence between the

Tabacum variety and its F, sylvestris hybrid may be

demonstrated in a remarkable fashion and this irrespec-

tive of whether the factors concerned in these character

expressions in the Tabacum varieties are dominant or

recessive in varietal crosses. This correspondence is not

only apparent in general appearance, but it extends to

minute details of form and structure, and it is displayed

even in the more intangible characteristics generally in-

cluded under the term habit—i. e., such characteristic

varietal peculiarities of expression as the method of

branching, insertion and inclination of the leaves, the type

of inflorescence, and so on through a whole series of de-

tails. For example, when N. Tabacum var macrophylla

(Setchell, Z. c., p. 8) is the Tabacum parent, the F, hybrids

display the particular appearance and also the particular

characteristics of macrophylla, except that throughout

they are expressed on a very much enlarged scale (cf.

East and Hayes, 1912). The broad clasping leaf of mac-

rophylla with its distinctly pointed tip is faithfully repro-

duced in the hybrids. The flowers show no effect of the

very much elongated corolla tube and the lobing of the

limb peculiar to sylvestris, but display the macrophylla

40 THE AMERICAN NATURALIST [Von. LI

proportions throughout. The stout tube, swollen infun-

dibulum, and pentagonal limb are clearly derived from

macrophylla, and the color is rose red of approximately

the same depth and tone as that of macrophylla and in

striking contrast to the pure white of sylvestris. In habit

the hybrids resemble macrophylla. In early growth they

are not characterized by the long maintained rosette

which is so characteristic of sylvestris, and in leaf distri-

bution, branching, and type of inflorescence they again

correspond to their macrophylla parent.

When an entirely different set of characters is con-

cerned in the Tabacum parent the F, hybrid with syl-

vestris is still an exact replica of the particular Tabacum

used. For instance N. angustifolia (Setchell, l. c., p. 9)

and sylvestris give a hybrid which is entirely different in

general appearance and all details from that obtained

between macrophylla and sylvestris, and which displays

throughout the angustifolia characters. The leaves of the

hybrid are obliquely ovate-lanceolate and taper gradually

to a long, curved point. They are also distinctly petioled

like those of angustifolia. These characters are in strik-

ing contrast to those characteristic of the leaves of syl-

vestris, which are broad throughout, broadly pointed, and

have a broad clasping base. When flower characters are -

examined, angustifolia is again faithfully reproduced in

the F, hybrid for its flowers have the slender, straight

corolla tube with practically no suggestion of an infun-

dibulum and the deeply divided limb with narrow lobes

that taper into long slender tips, all so characteristic of

angustifolia. Like those of angustifolia the flowers are

pink. In habit these hybrids again resemble angustifolia.

This resemblance is displayed in a particularly striking

fashion in the graceful, drooping manner in which the

leaves are borne in marked contrast to the stiff, erect

manner in which the leaves are borne by sylvestris.

Throughout, macrophylla and angustifolia present a

strikingly contrasted set of characters, yet in each case

they are reproduced in their entirety in F, of the hybrid

with sylvestris,

No. 601] MENDELIAN FACTOR DIFFERENCES 41

When particular tagged Mendelian factors are con-

sidered the same behavior is displayed. Perhaps there is

no more striking instance of this than that shown by the

expression of the calycine flower type in these sylvestris

hybrids. When N. Tabacum var. calycina (Setchell, l. c.,

p. 6) with its peculiar split, hose-in-hose flowers is crossed

with Tabacum varieties of the normal flower type, the F,

hybrids display the normal flower form and segregation

occurs in F, into normal and ealycine in accordance with

simple Mendelian expectations. But when the -Tabacwm

reaction system carries the recessive calycine flower

factor into these species hybrids with sylvestris then

every flower on the F, plants displays a more or less caly-

cine structure. Similarly when the parthenocarpic char-

acteristics of N. Tabacum var. ‘‘ Cuba’’ (Goodspeed,

1915) are carried in by the Tabacum parent then the F,

hybrid, instead of shedding its capsules soon after anthe-

sis as is the case in all the other T'abacum-sylvestris hy-

brids, retains them indefinitely, in spite of the fact that no

good pollen is produced, and thus non-fertilization, the

stimulus for fruit abscission in Nicotiana, here also is the

rule. So far as present evidence indicates this character-

istic is rather strictly confined in Nicotiana to the variety

‘c Cuba.’’ This behavior of recessive factors of Tabacum

varieties in hybrids with sylvestris is a striking confirma-

tion of the conception that in such cases there is a con-

trast between distinct reaction systems rather than be-

tween certain factors as opposed to each other. In gen-

eral when Tabacum varieties of the type mentioned above

are crossed with each other the hybrids, especially with

respect to flower color, leaf shape, etc., are intermediate.

The contrast in this case is not one between two distinct

Mendelian reaction systems, but it is merely a contrast

of certain differences within a common system, and the

segregation in subsequent generations, although complex,

indicates a general accordance with normal Mendelian

expectation. But in the case of species hybrids between

Tabacum and sylvestris the contrast is between distinct

42 THE AMERICAN NATURALIST [ Vox. LI

Mendelian reaction systems and the consistent reproduc-

tion of all Tabacum characters, whether qualitative or

_ quantitative, indicates at one and the same time that these

are fundamentally of the same nature, depending essen-

tially for their expression on a complex set of Mendelian

factors, and, moreover, that the Tabacum system asa unit —

dominates the course of somatogenesis and determines the

reaction end products of the two systems.

This domination of the somatogenic processes by the

_ Tabacum reaction system is followed by important experi-

mental possibilities. If the species hybrids always dis-

play the Tabacum characteristics as completely as all our

present evidence indicates that they do, then they will

furnish a powerful method of attack on the problem of

Mendelian behavior in the Tabacum section of the genus

Nicotiana. For by crossing hybrids between Tabacum

varieties with sylvestris, it should be possible to secure in

the partially sterile hybrids resulting a phenotypic repro-

duction of the gametic series of the Tabacum parent.

This series would not be complicated by intergrading of

heterozygous forms, because the plants thus obtained

would exhibit the phenotypic characters of homozygotes,

and recessive factors as well as dominant ones would be

reproduced in their proper place in the Zabacum system.

Apparently it should be possible, therefore, to demon-

strate the fundamentally similar nature of linkage in

Nicotiana and Drosophila. Such an analysis will still be

very difficult in Nicotiana on account of its high chromo-

some number, but by the method of procedure outlined

above some distinct advance at least seems perfectly

feasible. These, however, are matters on which we have

as yet very little data.

Since, therefore, the Tabacum reaction system domi-

nates the somatogenic processes in the hybrid to nearly

or quite the exclusion of the sylvestris system, the ele-

ments of the two systems must be largely mutually in-

compatible. Free interchanges between the two systems

would not, therefore, necessarily result in the formation

No. 601] § MENDELIAN FACTOR DIFFERENCES 43

of functional Mendelian reaction systems. This high de-

gree of mutual incompatibility of the two reaction sys-

tems exhibits itself in the high degree of sterility of the

F, hybrids. As Goodspeed (1912, J. c.) has shown, how-

ever, this sterility is only partial and a few good ovules

are formed which produce viable seed in the case of open

pollination or when crossed back with the parents. In

evidence which is presented elsewhere (Goodspeed and

Ayres, 1916) it has been shown that, while it is experi-

mentally possible to modify the behavior of the F, plants

in such a manner that the fruits without pollination are

retained for a considerable period rather than falling

soon after anthesis, the percentage of good ovules pro-

duced can not be appreciably modified. This is an im-

portant point, for it indicates that the number of good

ovules produced is a function of the chromatin behavior

and not to be influenced by environmental factors, and

that they should, therefore, exhibit a consistent behavior

and lend themselves to a logical interpretation. In fact,

evidence at hand indicates that the small percentage of

functional ovules represents the Tabacum and sylvestris

extremes of a recombination series, and that, therefore,

the middle members of the series, which are made up of

relatively high proportions of both Tabacum and sylves-

tris elements, fail to function because they produce in-

compatible reaction systems. This is shown clearly by

back crosses which have been made with the parents,

although here portions of our evidence are not so well

controlled as we would prefer. When back crosses are

made with sylvestris as the pollen. parent there is pro-

duced a variety of forms many of which are highly ab-

normal, but among them there is a considerable propor-

tion of plants which are pure sylvestris in all characters.

These plants are fertile and have bred true to the sylves-

tris type for three generations. A number of the remain-

ing plants resemble sylvestris, but show contamination

. With other elements presumably derived from the Taba-

44 THE AMERICAN NATURALIST [Vou. LI

cum reaction system. These contaminations affect the

whole plant, not alone any particular character complex.

All plants except those which were of the pure sylvestris

type were sterile. Until this year we have not been able

to secure seed from back crosses with the Tabacum par-

ent, but from open pollinated seed a variety of forms is

produced, practically all of which are of the Tabacum

type in general appearance. This result is evidently due

to pollination of the F, flowers with pollen from the wide

series of Tabacum forms which, in predominating num-

bers, have always been grown in the cultures. Some of

these plants resulting from uncontrolled pollination were

likewise fertile. They have been grown for several gen-

erations and although displaying segregation, this segre-

gation has never involved the production of sylvestris

characters, but has been of a type normally found within

varietal hybrids of Tabacum. The sterile forms in this

series largely resembled the F, hybrids of Tabacum and

sylvestris, and the occurrence of a few aberrant and syl-

vestris forms which were obtained from the sowing of the

open pollinated seed are what would be expected, if pol-

lination was sometimes effected with sylvestris pollen.

It appears, therefore, that for these species hybrids the

conception of the factors as making up for each species

a reaction system in which the elements have a specific

relation to one another harmonizes the results obtained

with the more recent Mendelian developments. The ob-

jection which might be made that interchanges of factors

which behave normally in one system should not logically

be followed by such profound disturbances as to com-

pletely prevent the formation of a functional reaction

system is met by several counter considerations. In the

discussion of lethal factors it has been pointed out that `

Morgan (1914, l. c.) has demonstrated that changes in

many loci of the Drosophila system have been followed by

failure of the resulting individual to develop. It is en-

tirely conceivable that, if a certain factor A in one system -

No. 601] MENDELIAN FACTOR DIFFERENCES 45

be considered, the corresponding factor A’ in the other

system, if there be such a factor, might be just as differ-

ent from A as a lethal factor is different from its normal

allelomorph. Further, from a modern Mendelian view-

point there is no basis for assuming that recombinations

could be obtained involving only exchanges in isolated loci

in the systems. For if the behavior in segregation in the

F, hybrids corresponds to that in Drosophila then such

combinations as could be obtained would depend on the

shifting of entire choromosomes or in case of crossing-

over of relatively large portions of chromosomes. The

recombinations obtained in the hybrids between T'abacum

varieties and sylvestris, provided chromosome distribu-

tion takes place after the normal fashion in these hybrids,

would involve, therefore, for the most part, the formation

of systems containing either whole chromosomes or large

sections of chromosomes of opposing systems. Such

attempted reconstruction of systems might well fail in

cases of any marked specificity in the relations of the

factors of the opposing reaction systems, since any large

proportions of both systems in a gamete might conceiv-

ably destroy the continuity or the balanced relations neces-

sary for the continuance of system reactions. When the

proportions of one or the other system are relatively

small, the system reactions might be merely disturbed,

resulting in the production of the abnormal forms which

have been secured in our cultures. It is to such relations

between the two systems involved that we ascribe the

selective elimination of the greater portion of the possible

gametic combinations in the crosses between Tabacum

varieties and sylvestris, and which, therefore, results in

a high degree of sterility in these hybrids.

It is of course obvious that there are many categories

of sterility, in the hereditary sense as well as in the physi-

ological sense. The particular type herein considered is

that which results from relatively wide crossing such as is

involved in species hybrids. That certain types of steril-

46 THE AMERICAN NATURALIST [Von. LI

ity are due to specific factors which display consistent

Mendelian behavior has been demonstrated by Bateson

and Punnett (1908) and others and has been suggested by

Correns (1913) for cases which are concerned with the

specific category of normal self-sterility in Cardamine

pratensis. It appears, nevertheless, as Hast (1915) in

principle has suggested, that many cases in which sterility

has followed rather wide crossing would seem to be sus-

ceptible of a more logical treatment from the standpoint

of non-specific disturbances in the reaction systems

involved.

(To be continued)

COMPARATIVE RESISTANCE OF PRUNUS TO CROWN

GALL

Proressor CLAYTON O. SMITH

UNIVERSITY OF CALIFORNIA

In making a study of the plant disease popularly known as

crown gall, plant tumor, or plant cancer, it seemed desirable to

ascertain the relative resistance of the different species of Prunus

to this disease. It was soon evident that the usual methods em-

ployed in discovering disease resistance would be of little value.

The cause of the disease, life history and pathogenic nature of

the organism had already been studied by Dr. Erwin F. Smith?

and his assistants of the United States Department of Agricul-

ture. They showed, by artificial inoculations, the wide range of

plants susceptible to infection and.also found that some were

apparently resistant. Their experiments encouraged the writer

to follow with slight modifications the method of artificial inocu-

lations on a number of species and varieties of the genus Prunus.

It was hoped that suitable resistant stock might be discovered

that would be adapted to the propagation of the stone fruits.

Before considering in detail the methods employed, the general

characteristics of the disease will be briefly given. The affected

part of the tree, shrub or plant is generally found a little dis-

tance beneath the surface of the soil at the crown or point where

the roots are given off from the trunk. The disease is characterized

by an enlargement or gall more or less spherical in shape and

consisting of tissue that is usually much softer in texture than —

normal. The surface may or may not be covered with a normal

bark. This enlargement is now known to be caused by a stimulus

that comes from the presence of a definite motile bacterial organ-

ism known as Bacterium (Pseudomonas) tumefaciens, which lives

within certain of the plant cells in relatively small numbers. /

Considerable attention was given to perfecting methods for

1 Paper No. 28, Citrus Experiment Station, College of Agriculture, Uni-

versity of California, Riverside, California.

2 United States Department of Agriculture, Bureau of Plant Industry,

Bulletins No, 213 and 255, 1911, 1912.

48 THE AMERICAN NATURALIST [ Vou. LI

the determination of the relative resistance of the different spe-

cies of Prunus. Most of the different species and varieties were

budded or grafted on other stock, the scions or bud wood being

secured from several reliable sources, such as the Arnold Arbo-

retum, several of the larger nurseries. The methods used are

somewhat different from those usually employed in seeking for

disease resistance among plants. The plan was to artificially

inoculate with pure virulent laboratory cultures the different

kind of Prunus under experimentation. A number of suscep-

40 TE

+ e a <0" sae

mee iat a

a Cats

4 P

-M o

. 1. A bunch of galled peach stock as they often occur in the nursery.

Many of the other trees probably had incipient infections unrecognizable at the

time of digging, which later developed galls.

No. 601] RESISTANCE OF PRUNUS TO CROWN GALL 49

tible hosts were always included in the experiment, to act as a

check upon the virulence of the culture and any unfavorable

climatic condition. In each series of inoculation 5 or 10 punc-

tures were made upon vigorous growing twigs of the current

Fig. 2. Natural gall on English walnut in nursery. This gall appeared at

the point where the English walnut stock was grafted. It is common practice

to bank the dirt about the scions to prevent drying. The California black root

is much more resistant.

year’s growth. During the experiments of 1914, ten punctures

were always made. This number, being the same in all the ex-

periments, was of material aid in the final compilation of results.

Other check punctures were made in the same way as in the in-

oculations except that none of the organisms were placed in the

tissue. An ordinary steel needle in a cedar handle was used in

making the puncture inoculations. This was first flamed, then

used to convey some of the bacterial growth from the test tube

to the twig to be inoculated, the puncture being made through the

bark and wood of twig. The organism was grown in a medium

made as follows: 4 per cent. glucose, 4 per cent. sodium chloride,

$ per cent. meat extract, 1 per cent. peptone, 1 per cent. agar.

50 THE AMERICAN NATURALIST [ Von. LI

Fic: 3. Two aT roots naturally infected with numerous galls. Such stock

ould only make inferior trees

The tubes were incubated from twenty-four to thirty-six hours

before being used, at which time there was a vigorous, pearly

white, raised growth where the medium was inoculated. The

series of inoculations were made a week apart from May 1 to

about September 1, 1914. -The work of 1913, while similar in

nature, was not so extensive as that of 1914. The experiments

thus extended over the period of the year when the trees are

making their most rapid growth, and should be in their most

susceptible condition for infection. The trees were well cared

for and made rapid growth during the period the experiments

were in progress, and hence were in favorable condition for the

development of the disease. No effort was made to protect in

any way the punctures, as the use of wax or other covering stim-

ulates callus formation which could easily be confused with the

beginning stages of a young gall or with one that has not ma-

tured rapidly, as is often the case on inoculated trees showing

resistance.

The genus Prunus gives a wide range for investigation be-

cause of the large number of species and varieties. The follow-

ing are the species thus far tested by artificial inoculations:

No. 601] RESISTANCE OF PRUNUS TO CROWN GALL 51

Prunus Allegheniensis, P. Americana, P. Amygdalus, P. ander-

sonit, P. Armeniaca, P. Armeniaca, var. Mikado, P. Avium, P.

Besseyi, P. Caroliniana, P. cerasifera, P. cerasifera, var. divari-

cata, P. cerasifera, var. Planteriensis, P. domestica, several dif-

ferent varieties, P. eriogyna, P. glandulosa, P. hortulama, P. ilici-

folia, P. integrifolia, P. Japonica, P. maritima, P. Mahaleb, P.

Mitis, P. monticola, P. Mume, P. munsoniana, P. nigra, P. ortho-

sepala, P) Pennsylvanica, P. Persica, several varieties, P. platy-

carpa, P. pumila (Linn.), P. serotina, P. Simoni, P. Watsoni.

All the above hosts gave positive results from artificial inocu-

lation, except P. pumila, P. ilicifolia and P. Caroliniana. These

three hosts were inoculated during 1913 and 1914 and have

always showed negative results. P. ilicifolia and P. Caroliniana

were on their own roots and were not making very rapid growth

at the time of the experiment, but it seems almost impossible

that they should not have been in a susceptible condition some

time during the period from May to September. P. pumila made

rapid growth, as it was grafted on peach stock, but never showed

the least indication of gall formation, nor has it during the ex-

Fic. 4. Fie. 5.

Fig. 4. Artificial gall produced on pepper tree, Schinus Moll

a 5. rtific ag a made by inoculating sour orange seedlings. Citrus

ck is only rarely cted naturally with gall, but galls have been artifi-

cially produced on Ee ssa orange and shaddock.

52 THE AMERICAN NATURALIST [ Vou. LI

periments of 1915. Only a part of the kinds of Prunus just

mentioned were thoroughly tested out and these only are included

in tabulated results.

It will be noted that Tables II and III represent two varieties

of Prunus domestica. Not all varieties, however, are equally

resistant, but, in general, members of this group are much more

Fie. 6. Artificial galls on Prunus. (a) German prune, P, domestica, a

resistant variety. (b) Myrobolan, P. cerasifera, a priate: eda ir the

difference in size of galls and how in es susceptible kind the galls eventually

surround the twig

No. 601] RESISTANCE OF PRUNUS TO CROWN GALL

TABLE I

A TYPICAL EXPERIMENT WITH Bacterium tumefaciens, CULTURE No. 753 C

Y TO NOVEMBER 15, 1914), TO ILLUSTRATE GENERAL METHODS

(JUL

USED IN SEARCHING FOR A RESISTANT STOCK.

A SIMILAR EXPERIMENT

TO THIS WAS MADE EACH WEEK FROM MAY TO SEPTEMBER, 1914.

Experiment 20

Experiment No. of Positive Size of Galls

Serial No. |Inoculations Inoculations Host in Inches

745 10 2 German prune gt

746 10 0 German prune (old)

747 10 5 am 3-4

748 10 10 P. triflora w-

749 10 10 | Wic 43

750 10 9 Burbank 4-4

751 10 10 Myrobolan 3-3

752 10 10 P. Munsoniana 4-3

753 10 10 | P. davidiana 1

754 10 5 P. maritima 3—4

755 10 4 P carpa i-t

756 10 0 Golden drop (silver prune)

757 10 8 Reine Claude (green gage) 3s-

758 10 10 | P. Simonii 14

759 10 10 Royal apricot 4-4

760 10 10 Elberta peach 1-1}

761 10 0 Bitter almond

762 10 9 P. hortula 3-3

763 10 5 P. i as}

764 10 10 Schinus Molle 1-14

765 10 Positive, Oleander

766 10 0 P. pumila

767 10 0 P. Watsoni

768 10 8 | P. nigra 3-4

769 10 3 P. serotina ve-3

770 10 10 P. institia pendula 3-3

771 10 9 | P. mitis vs small

772 10 10 P. Mume 3-7

773 10 7 | P. Anders t

774 10 6 Duane (Tribble) a

775 10 2 nteriensis

776 10 8 Miyrobolan (Arnold) ys-t

ars: 10 9 M.yrobolan (sprouts) $-1

778 10 10 Viyrobolan (young sprouts) 3-3

779 10 10 dl Paso 3-7

780 10 0 Golden beauty

781 10 10 Arkansas 4-4

782 10 1 P. Virginiana %

783 10 7 P. cerasifera divarica -4

784 10 2 P. Besseyi ve

785 10 0 P. ilicifolia

786 10 0 P. Caroliniana

787 10 9 | P. orthosepala +

788 10 0 Olive

789 10 2 P. Armeniaca Mikado 3-3

790 10 5 Italian prune -$

54 THE AMERICAN NATURALIST [ Vou. LI

so than most other species of the genus. By comparison with

other tables, it will be found that the galls are of a much smaller

size than on most other hosts. The number of positive inocula-

TABLE II

SUMMARY OF ARTIFICIAL INOCULATIONS ON GERMAN PRUNE, Prunus domestica.

CONCLUDED NOVEMBER 15, 1914

Positiv: ize of Gal

EI eae Date No. of I lati focalationi a7 bt as

æ 500° 5/ 3/14 woo 0

532 5/25/14 10 0

559 6/18/14 10 0

zx 560 6/18/14 10 0

617 6/29/14 10 6. }-4

x 618 6/29/14 0

667 6/29/14 Check 0

679 7/ 6/14 6 3-4

zx 680 7/ 6/14 10 0

745 7/13/14 10 2 4-4

xz 746 7/13/14 10 0

æ 792 7/20/14 10 0

870 7/27/14 10 0

æ 871 7/27/14 10 0

934 8/ 3/14 Check 0

z 8/ 3/14 k 0

8/ 4/14 10 2 i-

| 4/14 10 0

A 15 8/10/14 10 0

A 87 8/15/14 10 0

2A 88 8/15/14 10 0

A125 8/17/14 10 0

A207 8/24/14 10 8 B-

2A208 8/24/14 10 0

242 8/31/14 10 0

2A243 8/31/ 10 0

240 24

tions as given in Tables II and III, is probably somewhat greater

than it should be, as in making the estimate of the number of

galls on these resistant stocks, any small enlargement was

counted, and subsequent examination has shown that many of

these small enlargements have not further increased in size..

When a gall becomes established in a resistant variety, it makes

rapid growth and eventually forms one of good size. These

large galls differ from similar galls on peach and many other

hosts in that the gall is attached to a relatively small circum-

ference of the infected twig. The gall growth is often nearly at

8 Numbers that are preceded by an x were made on rapid growing twigs

of the current year of a seven-year-old tree. The other inoculations in a

young tree two years old from the nursery.

No. 601] RESISTANCE OF PRUNUS TO CROWN GALL 55

TABLE III

SUMMARY OF ARTIFICIAL INOCULATIONS ON ITALIAN PRUNE (FELLENBERG)

Prunus domestica. CONCLUDED NOVEMBER, 1913

m vi Size of Galls

pegase me Date No. of I lati Porn in Inches

211 5/10/13 5 0

216 6/1 5 2 e e

252 6/13/13 5 0

264 6/16/13 5 0

270 6/17/13 5 0.

282 7/14 15 5 Tsis ie- re-te

292 7/13/13 5 0

315 7/19/13 6 2 Ts-ts

328 7/21/13 6 1 te

332 7/21/13 5 0

343 7/22/13 5 0

355 7/25/13 10 4 b-i- ik

366 7/30/13 10 0

259 6/ 9 0

375 7/30/13 10 ry

390 | 9/ 10 0

406 8/14/13 10 3 Ye-is-ts

420 8/14/13 5 0

127 17

right angles to the twig which makes these galls stand out for

considerable distance from the branch.

It is of interest to note that both of these are prunes that have

been under cultivation for many years. The German prune is

described as being one of the plums longest under cultivation and

the oldest of the prune type. Seedlings also come reasonably

true to type which might be of importance if grown from seed

for a stock. The Italian prune (Fellenberg) is the popular

prune of Oregon and has a history of over a century’s cultiva-

tion. Further experiments among varieties of the domestica

group are being carried on. The damson which is sometimes

included among the domesticas, shows considerable resistance to

artificial inoculation.

Prunus cerasifera, var. Planteriensis, Table VIII, is described

as a double flowering shrub and is the most gall resistant of any

of the tested varieties of cerasifera, although this resistance

should be again determined. Inoculations in the Arnold Ar-

boretum trees, Table IV, did not develop as many galls as those

of the larger Myrobolan tree, either because the former were not

4 A local commercial stock, propagated in California from sprouts, not the

true Duane eimh but a small blue plum having the flavor of a Damson,

but differing in

56 THE AMERICAN NATURALIST [Von. LI

TABLE IV

SUMMARY OF ARTIFICIAL INOCULATIONS ON Prunus cerasifera. CONCLUDED

NOVEMBER, 1914

Prunus cerasifera, Arnold Arboretum Type

"aan me ear Date No. of Inoculations ee: a Saar

595 6/20/14 10 10 4-4

646 6/29/14 10 8 is-is

709 6 10 9 i$-

776 7/13/14 10 8 gst

7/20/14 10 5 Is

7/27/14 8 4-4

963 / 3/1 Check 0

Á i 8/10/14 1 4 44

Alll 8/15/14 10 2 ie

A149 8/17/14 10 4 ts

A225 8/24/14 10 10 vs-'

A253 8/31/14 10 2 ‘5

110 70

Prunus cerasifera (large four year old seedling).

SAREH Datë Nö. ot Tioruiatiaan neers Z ao cula- Size Slaen in

5/ 5/14 10 10 li- 4

538 5/25/14 10 10 3

66 6/18/14 10 10

62 | 6/29/14 10 10 — t

6/29/14 10 10 ae

/ 6/14 10 10 -3

751 7/13/14 10 10 =%

821 7/20/14 10 10 waf T

901 7/27/14 1 10 i

962 8/ 3/14 Check 0

A / 4/14 10 10 4-3

8/10/14 10 10 4-4

A110 8/15/14 10 10 4 $

A148 8/17/14 1 10 3-4

A214 8/24/14 10 10

A251 8/31/14 10 10

150 150

growing as rapidly, or, judging from their shrub-like growth,

because they are of a different type possibly nearer to the wild

type than are those commonly imported from France by nursery-

men.

The variety known as Golden Beauty, P. hortulana, has thus

shown more marked resistance than other varieties of the

species thus far tested. It is interesting to remember that this

variety is supposed to have originated in western Texas some-

No. 601] RESISTANCE OF PRUNUS TO CROWN GALL 57

what out of the natural range of the species. P. hortulana and

P. americana are used as a stock for the native plums in the

middle west and east. P. hortulana does not sucker, fruits abun-

dantly and has a number of excellent qualities that would recom-

TABLE V

SUMMARY OF ARTIFICIAL INOCULATIONS ON GOLDEN BEAUTY, Prunus hor-

tulana. CONCLUDED NOVEMBER, 1914

i ize

rier ee i Date No. of Inoculations | Minn son pit g lag

600 6/20/14 10 | 7

651 6/29/14 10 | 3 vs very small

714 7/ 6/14 10 | 5 ys-t

780 7/13/14 10 0

826 7/20/14 10 4 ie

906 7/27/14 10 1 is

967 8/ 3/14 Check 0

Att 8/ 4/14 10 3 +

A 44 8/10/14 10

All4 8/15/14 10 1 ys

A152 8/17/14 0 1 is

A250 8/29/14 10 0

110 25

mend it as a stock. Further experiments with varieties of this

Species are being made and its adaptability to various of our

stone fruits carefully studied. |

TABLE VI

SUMMARY OF ARTIFICIAL INOCULATIONS ON Prunus pumila Linn. CoN-

UDED NOVEMBER 15, 1914

Experiment Serial No. Date No. of Inoculations Positive Inoculations

6/20/14 10 0

635 (29/1 10 0

766 7/13/14 10 0

849 7/20/1 10 0

88 7/27/14 10 0

94 / 3/1 Check 0

Rees 8/ 4/ 10 0

A 34 8/10/14 10 0

A106 8/15/14 10 0

Al44 8/17/14 10 0

A220 /24/ ; 10 0

A254 8/31/14 10 0

110

Further inoculations of P. pumila (thirteen experiments of

ten inoculations each or 130) made during the present year, 1915,

58 THE AMERICAN NATURALIST [ Vou. LI

in vigorous growing seedlings, gave negative results, agreeing

with the results of the two previous years. The experiments thus

far conducted show that the species is entirely resistant to arti-

ficial inoculations. P. Bessey, closely related to P. pumila, also

shows considerable resistance.

The two other species of Prunus referred to as being resistant

are P. ilicifolia and P. Caroliniana. They are evergreens and

are not now considered as strictly belonging to the genus Prunus.

They do not readily unite by grafting or budding with varieties

of the stone fruits. P. pumila is a shrub and while this stock

readily unites with many of the varieties of the stone fruits it

probably would dwarf the tree more or less and might sprout.

It is, however, readily grown from pits or cuttings.

TABLE VII

SuMMARY OF ARTIFICIAL INOCULATIONS ON Prunus. CONCLUDED OCTOBER

Species Variety | isins | imta Per Cent. g Bas"

P. domestica........ German prune 75 2 23 1-4

P. domestica........ German prune 50 5 10 fir

P. domestica........ | Italian prune 127 17 13 34-4}

P. domestica........ Green gage 17 4 23 Is-4

P bn oen 138 51 37 3-3

vba care Duane 37 15 40

P. persica Elberta 61 57 93 3-24

P. triflora X P. Wickson (hy-

Simoniti ve i 56- 64 98 4-1

P. triflora.........- Burbank 31 31 100 4-4

P. cerasifera. ccs: Myrobolan 8 8 100 4-1

In each of the inoculation experiments, ten punctures were

made, hence the number of inoculations divided by ten will give

the number of separate experiments made with the various hosts.

In the two tables, VII and VIII, where the inoculations of the

years 1913 and 1914 have been summarized, there is a reasonable

degree of consistency between the percentages shown for the dif-

ferent hosts. Other varieties of P. persica possibly should be

further tested, although such varieties as Elberta, Saucer or

Peento, Salway, Lovell and Muir seedlings have not shown any

marked resistance.

Any of the stock as listed in Tables VII and VIII that show

less than 50 per cent. infection are more or less promising, for in

the experimental work with artificial inoculations from virulent

No. 601] RESISTANCE OF PRUNUS TO CROWN GALL 59

TABLE VIII

SUMMARY OF INOCULATIONS MADE ON Prunus. CONCLUDED NOVEMBER 15,

1914

Species Variet oes phoned Cent. oț|Size of Galls

r ‘i lations | lations | Galls | in Inches

P. pumila.. ....| 2 varieties, Arnold 110 0 0

Arboretum

P. domestica,...... Italian prune 140 10 7 ps3

P. cerasifera....... P. planteriensis 40 3 73| tet

P. domestica....... German prune 240 24 10 | ye-4

P. insititi .....| Damson 120 13 10 3-4

P. Bessey 258: — 50 5 10 4-4

P. hortulana....... Golden Beauty 110 25 22 Is-4

P. amygdalust ....| Bitter almond 100 22 25 3—3

P. domestica....... Reine Claude (green gage) 90 25 26 | 354

P. Armeniaca...... Mikado 40 11 27| b

P. angustifolia.. ... Watsoni 50 15 30| 3—4

P. maritima....... Arnold Arboretum 140 48 34. i4

P. aema E apa Eei Arnold Arboretum 130 55 42| %2}

P. Miti .| Arnold Arboretum 32 53| ps4

P. pivot E ESN Arnold Arboret 110 70 63 | s+

P. Munsoniana.... ai eri SS 70 48 68 4-35

P. Munsoniana.... 90 70 77 | pe?

P. Americana...... poner y retum 100 83 83 | 3-

P. hortulana....... Arnold epee 130 | 108 83 4-3

PP. Ansa a Pendula 90 77 85 | 7-2

P. davidiana....... — 110 96 88 4-3

Schinus Molle... .. Pepper tree 110 97 88 ił- t

PSAP Rk Burbank 120 | 109 90 $-

Paata A a R eh Arnold Arboretum 60 56 90 4-3

P. orthosepala...... Arnold Arboret 80 72 90 | 3-4

aA eS Arnold Arboretum 100 9 91 1

P. Munsoniana....| Pi 140 | 130 92 | y-1}

P. cerasifera....... P. divaricata 00 94 $-

rE Piia. on Elberta 130 122 94 4-3

P. Armenica....... Royal apricot 120 117 97 E

Pi tiflora oe Arnold Arboretum J40. 137] OT -4

P. Munsoniana. ...| El Paso 100| 97| 97| 44

P. cerasifera....... Sprouts : 120 | 117 97 4-13

P. triflora X P

a Pre Ft 7 (hybrid) 140 138 98 4-3

cerasifera....... 150 | 150 : 100 14

P. monticola....... eon gerson Sta. 40 40 | 100 14

P. Simonii........ Arnold Arbo 130 | 130 | 100| 4-13

cultures, the different stocks were subject to a more severe test

than obtains under the usual field conditions. The more promis-

ing of these, the first seven in Table VIII, with the exception of

the damson, have already been considered after the various table

in which the results were summarized. The damson has often

5 Prunus Amygdalus was not growing well during the last part of the

season and no infections showed after that of July 6. Before this time a

large percentage of the inoculations were positive. This will be repeated

60 THE AMERICAN NATURALIST [Von. LI

been used as a stock, but is not popular on the Pacific coast be-

cause of its slow growth in the nursery and the difficulty of

working it with many of the stone fruits. Duane, P. domestica,

Table VII, is being used to some extent as a stock in California

and shows resistance to gall in old vineyard land where it has

been grown for six years. It makes as large a tree as the popular

Myrobolan stock. The seedlings are grown from suckers, which

give a root likely to sucker. Reine Claude (green gage) variety

has shown resistance and would without doubt be a good stock

for the domestic type of plums. P. Armeniaca, variety Mikado,

is an apricot that differs somewhat from the one commonly grown

in California. It should be tested out experimentally as a stock

for apricots to replace the susceptible one now being used.

The almond, from field observations, is one of our most sus-

ceptible stock and this is fully confirmed by the following inocu-

lation experiments: Fourteen different varieties of almond seed-

lings not summarized in the following tables were inoculated in

April of 1913 at the University Farm at Davis, California.

These in all cases showed a high percentage of infection. So far

the peaches and almonds have shown only slight resistance.

It will be noted that our most popular stocks as Myrobolan,

peach, apricot and almond are very susceptible, which only goes

to confirm field observations that the stock used for the stone

fruits are very susceptible to crown gall.

The work so far conducted shows that seedlings of the German

and Italian prunes might be promising stock for certain of the

stone fruits, probably those of the domestica type. However, no

definite recommendations can be given, as the work is now only

in its preliminary stages.

SHORTER ARTICLES AND DISCUSSION

EUROPEAN FOSSIL FISH-SCALES

In European Cretaceous deposits fish-scales have been found

at various times, and occasionally have been named and described

by paleontologists. Dr. A. S. Woodward, in his great ‘‘Cata-

logue of the Fossil Fishes,’’ has carefully and accurately listed

all the names so given, but has made little or no attempt to ex-

amine the records critically, assuming that they were valueless,

or nearly so. More recent work on fish-scales brings out the fact

that these materials are of great value for the understanding of

Mesozoic fish life, but unfortunately they have been described

with little knowledge of their significant characters. An im-

portant pioneer work was that of Geinitz,! describing scales from

the Turonian of Saxony. Geinitz realized that it was necessary

to make comparisons with scales of recent fishes, and gave a plate

of ‘‘Schuppen von lebenden Fischen,’’ but unfortunately chose

species which had little relationship, for the most part, with the

fossils studied. The three plates of fossil scales appear to have

been very carefully drawn, and from them it is possible to gather

a number of facts not brought out in the text. Cyclolepis agas-

sizi appears to be Salmonoid, agreeing quite well with the modern

Salmo. Aspidolepis steinlai is like the scales of living Stroma-

teide, as Poronotus. Osmeroides divaricatus evidently has

nothing to do with the genus to which it is assigned, but is of

characteristic Albulid type. Osmeroides lewesiensis (Mantell),

as determined by Geinitz, consists in the main of scales agreeing

with those of the remarkable living genus Pterothrissus. The

genus Cladocyclus presents some serious difficulties. The type

is a Brazilian species (C. gardneri Agassiz) from the Upper Cre-

taceous of the Province of Ceará. I am indebted to Dr. D. S

Jordan for material referred to this species, and it appears that

the large scales have extremely fine circuli, while those of the

lateral line possess branching canals of the same general type as

those of the living S. American genus Hydrolycus.? It does not

1*“Die Fossilen Fischschuppen aus dem Plinerkalke in Strehlen,’’ 1868.

2 These canals are in the apical, not the te field, as erroneously stated

by me in Annals Carnegie Museum, IX, p. 1

62 THE AMERICAN NATURALIST [Vou. LI

seem certain that this is the true Cladocyclus of Agassiz; it may

represent a new genus ancestral to the Neotropical Characoid

fishes. European ‘‘Cladocyclus”’ is in any event surely distinct

from the Brazilian. The C. strehlensis of Geinitz includes scales

approaching those of Potamalosa, but the species is founded in

the main on an entirely different type, which is evidently close

to the English C. lewesiensis. It is a question what generic name

should be used for the lewesiensis-strehlensis type, which must

be removed from Cladocyclus. It was formerly included in Hyp-

sodon Agassiz, but that generic name appears to belong properly

to the fishes usually called Portheus, the type being lewesiensis

Mantell — mantelli Newton. The name lewesiensis also belongs

strictly to the Portheus, and the English so-called Cladocyclus,

if distinct from the Geinitz species, seems to need a new name.

These matters will be taken up more fully elsewhere at a later

date. Beryx ornatus of Geinitz, properly called Hoplopteryx

lewestensis (Mantell), appears to be a primitive Berycoid type,

having scales such as might be expected in an ancestor of the

modern Berycide. Hemilampronites steinlai Geinitz consists of

scales differing little from the living Hyporhamphus. The scales

figured by Geinitz as those of Macropoma mantelli Agassiz? have

no resemblance to that species; from the fine transverse circuli,

basal radii, and apical teeth like those of Pomacanthus, they

appear to belong to some Teleost more or less related to the

Berycoids. Thus we find that although Geinitz knew little about

the affinities of his scales, they had excellent characters, remind-

ing us in certain cases of modern genera, and indicating the great

antiquity and constancy of peculiarities of scale structure. In

1878 Anton Fritsch* undertook to describe the fish-seales of the

Upper Cretaceous of Bohemia, and believed that he had a number

of the species of Geinitz. His Cladocyclus strehlensis and Cy-

clolepis agassizi are perhaps correct, but the others are evidently

different from the Geinitzian forms. His Macropoma speciosum

Reuss is a genuine species of that genus, with quite characteristic

seales. His Macropoma forte, on the other hand, appears to be

a Celacanthus. His Osmeroides lewesiensis has regular trans-

verse circuli between the radii, instead of the minute tubercles

(markings like the surface of a strawberry) of the Geinitz scales

3 Macropoma mantelli should be called Arm lewesiensis (Mantell),

based on the Amia(?) lewesiensis of Mani

4‘*Die Reptilien und Fische der ‘hated Kreideformation.’’

No. 601] SHORTER ARTICLES AND DISCUSSION 63

and of Pterothrissus. His O. divaricatus is wholly distinct from

the scale described by Geinitz under that name, and has not the

Albulid characters. The Beryx ornatus scales are printed up-

side down, and the artist has added ctenoid structures (small .

teeth) above, on what is really the basal margin. In 1874 T. C.

Winkler published a paper® in which he described two species

from the scales. His Osmeroides belgicus appears to be con-

generic with the Osmeroides lewesiensis as understood by Fritsch.

His Cycloides incisus, supposed new genus and species, of which

he says that he knows no fish, living or fossil, with such scales, is

apparently worthless. It may not be a fish-scale. In America

the fossil scales of Teleosts have received very little attention,

but a large collection accumulated by the U. S. Geological Survey

is now under review, and will undoubtedly yield much of value

for the understanding of Mesozoic fishes, and at the same time

throw light on the ancestry and relationships of modern families.

T. D. A. CocKERELL

UNIVERSITY OF COLORADO, BOULDER,

July 8, 191

5‘‘ Mémoire sur quelques restes du Poissons du systéme heersien,’’ Arch.

Mus. Teyler., IV.

THE

AMERICAN NATURALIST

VOL. LI. February, 1917 No. 602

THE SELECTION PROBLEM?

RAYMOND PEARL

Or all the supporters of the doctrine of natural selec-

tion as the chief factor in organic evolution, August

Weismann was preeminent. He stood shoulder to

shoulder with Wallace in his entire willingness to attempt .

the explanation by selection of any biological phenom-

enon whatsoever, and he far outstripped the latter in the

keenness and subtlety of his logical powers when an espe-

cially difficult bit of exegetic activity was called for.

Both, it hardly needs saying, left Darwin far behind in

the extent of their advocacy of the Allmacht of selection.

Certain it is that if any one could speak authoritatively,

and without suspicion of either hostility or doubt, about

the selection theory, Weismann could. For that reason

it seems desirable to take as the starting point of this dis-

cussion a statement made by that distinguished biologist

So lately as seven years ago. At the Darwin Centenary

meeting in Cambridge, Weismann, discussing the ade-

quacy of the selection theory to explain the initial steps

of evolutionary change, said:?

To this question even one who, like myself, has been for many years a

convinced adherent of the theory of selection, can only reply: “ We

must assume so, but we can not prove it in any case. It is not upon

1 Papers from the Biological Laboratory of the Maine Agricultural Ex-

periment Station No. 109. This paper constitutes the address of the retir-

ing President, read in abbreviated form at the dinner of the American So-

ciety of Naturalists in New York, December 29, 1916.

; 2**Darwin and Modern Science,’’ Cambridge, 1909, p. 25. The italics are

in the original.

66 THE AMERICAN NATURALIST [ Vou. LI

demonstrative evidence that we rely when we champion the doctrine of

selection as scientific truth; we base our argument on quite other

grounds.”

Even since 1909 a good deal of water has flowed under

all our bridges, and particularly under the evolutionary

ones. Among other changes in viewpoint there is evident

a marked disinclination in science nowadays to regard as

“scientific truth’? anything which is not based upon

demonstrative evidence. But it is also a fact, perhaps at

first thought to be regarded as curious, in view of the

opinion of Weismann which has been quoted, that there

are here with us to-day those who assert, with great zeal

and pertinacity, that in selection is to be found the chief

cause of evolutionary change. These things being so, it

has seemed that possibly it might be profitable to spend

a little time upon the selection problem, trying to deter-

mine whether the case is any better now than Weismann

conceived it to be seven years ago, from the viewpoint of

tangible objective evidence. It is to be hoped that it is,

for among working geneticists just now any theory

which has to depend for its sole support upon its ‘‘inter-

pretative value’’® is sure to receive scant attention.

So then what I shall try to do is to review briefly some

of the real evidence about the selection problem which

has been accumulating since biologists turned definitely

to. the experimental study of evolution, and definitely

away from the glorious, but on the whole unproductive,

attempt to solve its problems by @ priori reasoning.

From such a review it is to be hoped that we may get

some light as to the directions in which further research

and new evidence are most urgently needed.

I. NATURAL SELECTION

In considering the whole selection problem we may

well begin with an examination of the theory of natural

selection. The mere fact of natural selection, in the sense

solely and strictly of a process leading to the elimination

of some individuals and the survival of others, is no

3 Weismann, loc. cit., p. 50.

No. 602] THE SELECTION PROBLEM 67

longer questioned by any one who takes the trouble either

to think or to observe living things. It is a process which

goes on constantly and affects all organisms. In this

sense it is no more than the resultant of the observed

absence of individual, mundane immortality among living

things. The fact that individuals die implies that those

not yet dead are a selected lot, in at least one respect,

namely survival.

This mere fact of elimination and survival is, how-

ever, not in itself particularly illuminating. The first

question before us is whether such a process is capable

of bringing about evolutionary changes of a progressive

sort. Obviously it is capable of doing so, in theory at

least, if we add two assumptions, or better rules accord-

ing to which the Dance of Death is to be performed. The

first of these rules is that the individuals alive at any

time shall be different from those dead, in some other

respects than that of survival merely. In other words,

the elimination shall be selective. The second rule is

that the survivors shall transmit to their progeny those

differences which mark them off from the eliminated.

The theory that these two rules are always and every-

where in operation, taken together with the observed fact

that living creatures do die, is the Darwinian theory of

natural selection as a factor in organic evolution. If the

premise be granted that the game of survival is in fact

played by these rules, the conclusion is then logically

irresistible that evolutionary progress is bound to occur

in the direction of those differences which distinguish the

survivors.

Here many have been content to let the matter rest. In

the minds of an astonishingly large number of people,

which number includes some rather great names in the

world of science, it is precisely the same thing to show

that something logically must be so, as it is to show that

It is so. If the formal rules of logie are satisfied, truth

Seems to them to be thereby established. No further evi-

dence is demanded. As every one knows, this attitude

led practically to the intellectual bankruptcy of the whole

68 THE AMERICAN NATURALIST [ Vor. LI

evolution theory in the late nineties, from which it was

rescued only by the active movement towards an ob-

jective, experimental accumulation of facts about the sub-

ject. But the danger which lurks in formal logic is always

threatening the progress of science. In the field of sci-

ence in which we are interested the most recent conspicu-

ous example of it is found in the vicious attacks on Men-

delism, which upon analysis can be seen to have their only

basis in a formally logical, so-called ‘‘proof’’ that it can

not be true. The danger is so insidious, and takes such

diverse forms, that one feels justified in quoting a brief

statement made by Professor F. C. S. Schiller, which

might well, in sufficiently large type, be hung upon the

wall of every biological laboratory, as a constant reminder

that the foundations of scientific truth lie in experiment

and observation, not in logic. Schiller says:

The proof that any logic, which declines to consider the question of

the real truth of the reasonings it attempts to deal with, necessarily

condemns itself to utter formality is easily given, and very instructive.

It is a formal characteristic of every assertion that it claims truth, ab-

solutely and without reservation or suggestion of fallibility. Hence it

follows both if (a) the question of the actual value of this claim is ruled

out of order, and if (b) the assertion is accepted at its own estimation,

that the distinction between true and false must, in fact though not in

name, disappear from Logic. For all assertions will be held true be-

cause they formally claim truth; because none profess to be false, error

no longer exists—for Logie. Thus the logical form of an assertion

affords no means of deciding upon the real value of its claim to truth,

and hence any logic which restricts itself to the study of this form

inevitably accepts a truth-claim as the equivalent of real truth. It is

like a bank which does not distinguish between promises to pay and hard

cash.

Then clearly the question to which we want an answer

is not whether natural selection can cause evolutionary

changes, but rather whether it does cause such changes

in any significant degree or extent. In other words, we

shall prefer the ‘‘hard cash’’ of objective experimental

evidence to any logical ‘‘promise to pay,’’ however tight

and compulsive its reasoning. 2

4Schiller, F. C. S., ‘‘ Formal Logic. A Scientific and Social Problem.’’

London, 1912, pp. 6-7.

No. 602] THE SELECTION PROBLEM 69

The tale here is not a long one. Indeed it is surpris-

ingly brief, considering the mass of literature which the

theory of natural selection in its more formally logical

aspects has engendered. We have first the pioneer work

of Weldon® with Carcinus, in which a selective elimina-

tion of individuals different physically from the survivors

was first demonstrated numerically, the eliminating en-

vironmental factor being the silt in the water. This was

followed by a number of investigations of a more or less

similar character, notably those of Poulton and Sanders®

with Vanessa, and of di Cesnola” with Mantis, in which

different colored forms of these insects were exposed to

elimination by natural enemies, chiefly birds, with the

result that there was found to be some relation between

the chances of elimination and the degree to which the

insect matched its background. Bumpus® studied sur-

viving and eliminated English sparrows after a severe

winter storm. Crampton® measured the surviving and

eliminated pupe of Philosamia, the elimination having

been produced by wholly natural causes. Davenport,”

in a very small lot of chickens, found that those killed by

crows were colored differently from those eliminated.

Lutz!! found in Drosophila some differences in type be-

tween survivors and eliminated. Harrist? has shown that

among seedling beans abnormal types perished more fre-

quently than strictly normal types under the same field

conditions. The same author? has also made extended

5 Weldon, W. F. R., Proc. Roy. Soc., Vol. XLVII, pp. 360-379, 1894. Also

see Brit. Assoc. Rept., Bristol (1898), pp. 887-902, 1899.

ê Poulton and Sanders, Rept. Brit. Assoc. (Bristol), gid ni 1899,

7 di Cesnola, A. P., Biometrika, Vol. III, pp. 58-59,

8 Bumpus, H. C., Biological Lectures, Woods Hole, pae pp. 209-226,

Boston, 1899.

9 Crampton, H. E., Biometrika, Vol. III, pp. 113-130, 1904.

10 Davenport, C. B., Nature, Vol. LXXVIII, p. 101, 1908.

11 Lutz, F. E., Bulletin Amer. Mus. Nat. Hist., Vol. XXIV, pp. 605-624,

1915.

12 rg J. A., Science, N. S., Vol. XXXVI, pp. 713-715, 1912.

18 Harris, J. A., Science, N. 8., Vol. XXXII, pp. 519-528, 1910. Pop.

Sci. Honki, Vol. LXXVIII, pp- 521-538, 1912, and numerous other papers

in Biometrika, AMER. Nat. and elsewhere.

70 THE AMERICAN NATURALIST [Vou. LI

researches on the elimination of organs in a series of dif-

ferent plants.

The critical value of these different investigations is

not in every case equal. Some are distinctly fragmentary,

and in others the differences between eliminated and sur-

viving are so small as to be of extremely doubtful sig-

nificance. If one examines critically the actual biometric

constants in the more extended of these studies (e. g.,

Crampton’s and Bumpus’s as analyzed by Harrist) he

can not but be impressed with the doubtfulness of many

of the differences. However, if we take all these re-

searches at their face value, and give all the benefit of the

doubt to the weak, then they agree in indicating that the

survivors are of somewhat different type physically than

the eliminated.

But nearly as many investigations have been made

which show that, on the whole, the survivors are not

physically different from those naturally eliminated.

Again the studies of Weldon'® on Clausilia come first.

Closely related to these is di Cesnola’s'® work on Helix.

All three of these investigations agree in showing no sig-

nificant difference in physical type between the general

population before elimination and the selected survivors

from that population after elimination. There was in

Helix and in Clausilia laminata some reduction in vari-

ability, but even that failed in another species of Clau-

silia. Kellogg and Bell!" were not able to find any evi-

dence that survivors and eliminated were different in

respect of either type or variability under natural con-

ditions, in the case of bees, or of the lady-bird beetle Hip-

podamia. Pearl,’® in a much more extended series of ob-

servations than those of Davenport, found no relation

between the colors of chickens and their elimination by

14 Harris, J. A., AMER. NAT., Vol. XLV, pp. 314-318, 1911.

15 Weldon, W. F. R., Biometrika, Vol. I, pp. 109-124, 1901, and Ibid.,

Vol. IIT, pp. 290-307, 1904.

16 di Cesnola, A. P., Biometrika, Vol. V, pp. 387-399, 1907.

17 Kellogg, V., and Bell, R. G., Proc. Washington Acad. Sci., Vol. VI, pp.

203-332, 1904.

18 Pearl, R., AMER. NAT., Vol. XLV, pp. 107-117, 1911.

No. 602] THE SELECTION PROBLEM 71

natural enemies. This result, it may be said, has been

confirmed in subsequent years. Reighard,'® in one of the

most beautiful experimental studies of natural selection

which has ever been made, found that there was no rela-

tion between the colors of coral, reef fishes and their

elimination by natural enemies.

While the researches which have been mentioned do

not exhaust the literature, they are all for which time can

be spared now, and they are fairly representative of the

whole of the distinctly meager experimental and quanti-

tative evidence regarding selective elimination. On the

whole, the net result is not so clear-cut and outstanding

as could be wished. If a scientific person came here from

some other planet with an earnest desire to inform him-

self about selective elimination, of which he had not

before known anything, and read all the available real

evidence on the point, he would be sure to come to some

such conclusion as this: that in some cases natural elim-

ination is certainly in some degree selective, while in other

cases it certainly is not; and in the most favorable cases

of all the selection is apparently not very rigorous.

Grossly teratological abnormalities are eliminated. But

the smaller deviations from type, which in theory ought

to furnish the basis of selection, appear upon quantitative

study less generally and sharply determinative of sur-

vival than might reasonably have been expected theo-

retically. The case regarding this first element of the

theory of natural selection certainly seems far less strong,

under the critical eye of experiment and measurement,

than those of us who were nourished on Weismann,

Romanes, and their like, would have supposed possible

twenty years ago. Still the writer has no desire to be

controversial about the matter and if any one is disposed

to draw the opposite conclusion from the facts he is en-

tirely welcome to.

Let us now turn to the consideration of our second rule,

which must be fully enforced if natural selection is to be

an important factor in the causation of evolutionary

19 Reighard, J., Carnegie Institution, Publication 103, pp. 257-325, 1908.

tz THE AMERICAN NATURALIST [ Vou. LI

change. This, it will be recalled, was that the survivors

must produce offspring which bear characters like those

which had led to the survival. Or, to put the matter

crudely, the survivors must transmit their characters to

their offspring. In pre-Mendelian days this phase of the

subject was always neatly and summarily disposed of by

stating, as one of the facts on which the theory of natural

selection rested, that ‘‘variations are inherited’’ or ‘‘like

produces like.” Times have changed. We are a great

deal less certain about that particular brand of inheri-

tance which the theory of natural selection demands than

we were before any one had taken the trouble to make

experiments on heredity. The essential difficulty lies

here. The differences upon which natural selection di-

rectly operates are somatic differences, by hypothesis and

in fact. Every worker in genetics has learned since the

truly epoch-making researches of Johannsen”? to be ex-

tremely cautious in assuming a priori that any particular

somatic difference is so inherited.

The writer has lately been experimenting with a char-

acter which very well illustrates this point. A not infre-

quent variation of the single comb in poultry is the ap-

pearance, on one or both sides of the comb, of a small

excrescence, known technically as a side-sprig. Indi-

viduals exhibiting this variation have been selected for

breeding purposes. But, so far as the experiments have

yet gone, it does not appear that the offspring of such

animals are any more likely to exhibit the variation than

are the offspring of any random sample of single-combed

fowls. Now suppose, for a moment, that in a state of

nature the possession of a side-sprig on the comb gave a

bird a distinctly better chance for survival than did a

plain single comb. Those lacking the variation would

then by hypothesis tend to be eliminated, but there is not

the smallest indication that there would result any pro-

gressive evolution towards a side-sprigged race.

Now one might go on and review a great accumulation

20 Johannsen, W., ‘‘Ueber Erblichkeit in Populationen und in reinen

Linien.’’ Jena, 1903.

No. 602] THE SELECTION PROBLEM 73

of evidence from the work of de Vries,2! Dewar and

Finn,*? Bateson,?* Lloyd,?4 and many others, showing the

failure of the theory of natural selection to account satis-

factorily for various observed happenings in evolution.

It is not my purpose to do this. These facts are all

familiar, and indeed have become commonplaces of bio-

logical literature. We may, however, with some chance

of profit try to generalize all this evidence. If we do so,

the writer believes that the conclusion will be reached that

natural selection is no longer generally regarded as the

primary, or perhaps even a major, factor in evolution

because of three general groups of facts, each well estab-

lished by the common observation of many biologists.

The first of these large facts is that all organisms possess

in varying, but usually very large, degree the power of per-

sonal, immediate, individual, somatic adaptation to the en-

vironment. In consequence of this power of personal adap-

tation the survival expectation of anindividualis not gen-

erally and regularly a function of any static, single-valued

relation between its somatic structure, habits, or physi-

ology, on the one hand, and the impinging environmental

Stresses on the other hand. Yet such a relation is im-

plicitly assumed in that part of the theory of natural selec-

tion which affirms a selective elimination on the basis of

somatic characteristics. The second broad fact is that,

even when selective elimination on the basis of somatic

characteristics does occur, it does not follow generally

and regularly that the somatic differences on which the

selection acted will reappear in the progeny, or in short be

inherited, actual experience having abundantly demon-

strated that a very great many of such somatic differences

are not inherited. The third large fact is that observation

indicates that in many cases evolutionary changes have

come about by relatively large, discontinuous steps, the

21 de Vries, H., ‘‘The Mutation Theory.’’ Chicago.

22 Dewar, D., and’ Fi inn, F., ‘‘The Making of Species. ’’ London.

23 Bateson, W., ‘í Problenis of Genetics.’? New Haven, 1913.

24 Lloyd, R. E., , ‘‘The Growth of Groups in the Animal Kingdom. ”? Lon-

don, 1912,

74 THE AMERICAN NATURALIST [ Vou. LI

new form being not merely fully differentiated at its first

appearance, but also fully able to survive.

Natural selection is, from the point of view of modern

genetics, a somatic theory. It begins and ends in somatic

differences. Except under the most unusual and rare of

conditions natural selection can not possibly operate

directly upon germ-cells. It must, from the very nature

of the case, work only indirectly upon the germ through

the soma. Now it is a historical fact that just so long as

the study of heredity confined itself solely to the somatic

results of the process, substantially no advance in knowl-

edge was made. Only when it was clearly perceived that

heredity is primarily and fundamentally a problem in the

physiology of germ cells, and that the soma is, as some

one has said, only the mechanism which the fertilized egg

uses to produce another fertilized egg like itself, did we

begin to make progress, Can we suppose that these con-

siderations have no meaning or application in our at-

tempts to solve the larger problem of organic evolution?

If natural selection only could act directly upon germ

cells we should have a different story to tell. The writer

has lately been experimenting” with an agent which acts

with extraordinary precision and definiteness in a selec-

tive manner upon the germ cells, killing or inactivating

the weak, and leaving only the strong and resistant to

produce zygotes, and somata. This substance is alcohol.

In the case at least of the domestic fowl the evolutionary

effects produced by this substance are remarkable in their

magnitude and definiteness. It is not possible here to go

into details, but briefly it may be said that the first general

result of the continued administration of ethyl or methyl

alcohol, by the inhalation method, to the parents in poul-

try, is to diminish progressively the fertility. But the

smaller number of offspring formed by the surviving

germ cells, after selective elimination in the gonads has

occurred, are in every measurable respect distinctly and

markedly superior to the normal individuals of the races

25 Pearl, R.. Proc. Amer. Phil. Soc.. Vol. LV, pp. 243-258, 1916; Proc.

Nat. Acad. Sci., Vol. 2, pn. 380-384; Ibid., Vol. 2, pp. 675-683, 1916; Jour.

Exper. Zool., Vol. 22, 1917.

No. 602] THE SELECTION PROBLEM 76

from which they come. Here is real selection making

real evolutionary progress, because its point of applica-

tion is the germ and not the soma. That the same agent

may produce an evolutionary change in the opposite

direction in another organism, the guinea pig, as has been

shown by Stockard?® to be the case, seems to mean, from

the point of view of the present discussion, nothing more

than that the direction and amount of any evolutionary

change is, fundamentally, a function of two variables, the

organism and the environment. If the same environ-

mental stress produced the same evolutionary effect upon

all organisms, then it would follow that all organisms in

the same environment must necessarily be alike at the

end of the process, which is, of course, not the case.

II. THE EXPERIENCE or PRACTICAL BREEDERS

Let us at this point leave our discussion of natural

selection and turn to the other great aspect of the prob-

lem, artificial selection. Here we shall tread on surer

ground, first, because it is where the great bulk of the

experimental work on the selection problem has been con-

centrated, and second, because the considerable mass of

reliable historical material about the origin and improve-

ment of domestic animals and plants becomes available

as a source of pertinent and critical evidence on the prob-

lem. At the outstart it may be recalled that it was on the

Supposed results of artificial selection, as set forth in the

experience of practical breeders, that Darwin chiefly re-

lied for objective evidence in favor of natural selection.

In general this evidence has been accepted very un-

critically by followers of Darwin. This is not strange in

view of the fact that there have been, and are now, rela-

tively few trained biologists who know anything at first

hand about the practical breeding of animals for the show

ring, advanced registry test, or any other purpose which

involves necessarily the production of élite specimens

which shall rank measurably with the best of the breed.

26 Cf. Stockard, C. R., and Papanicolaou, G., AMER. Nart., Vol. 50, pp.

65-88, 144-177, 1916,

716 THE AMERICAN NATURALIST [ Vou. LI

This fact has led to some entirely unwarranted inclusions

in the technical literature of biology. Statements in the

agricultural press which were intended by their breeder-

authors merely as harmless generalities on a subject

about which they had not the slightest intention of being

specific, have been accorded, by the laboratory evolu-

tionist, the dignity and authority of detailed reports of

actual breeding operations, and cited as valuable evidence

on the problem of evolution.

This confusion has played particular havoc in discus-

sions of the selection problem because of the general and

usually quite irresponsible use of the term ‘‘selection’’

by practical breeders. In the literature of live stock

breeding the word ‘‘selection’’ has been, and is being

used to-day, to designate, upon occasion, every known

kind of breeding operation. To illustrate: a fancier who

bred a new variety of poultry started with a mongrel

male bird which happened to possess just the combination

of characters which he wanted in his new breed, as the

result of a previous series of indiscriminate crossings.

This male was crossed with a female of a well established

breed which possessed some of the desired characters.

The daughters from this mating were back-crossed to

their sire, the original male bird, and so in turn were his

granddaughters. The granddaughters’ progeny consti-

tuted the new breed, full blown and breeding tolerably

true. This was an entirely legitimate, and indeed usual,

way of making a new breed. But the point lies in the fact

that the breeder who did all this always refers publicly

to the series of matings which has just been described as

**this process of selection’’!

Since Darwin selection has been a word to conjure with

amongst the practical breeders. In most cases without

any comprehension whatever of the exact technical sense

in which the term was originally used breeders have taken

the word itself as a sort of fetish. Darwin?’ himself

speaks of artificial selection as ‘‘the accumulation in one

direction, during successive generations, of differences

27 Darwin, C., ‘‘ Origin of Species,’’ Chap. I, p. 26.

No. 602] THE SELECTION PROBLEM 77

absolutely inappreciable by an uneducated eye.” Men

in whose breeding operations selection in this sense

demonstrably plays no significant part whatever, attribute

to its magic power all improvement in their animals and

plants. This is harmless so long as one understands that

the ‘‘selection’’ is verbal and not biological. But unfor-

tunately it has not always been so understood. Conse-

quently we find the literature of evolution cluttered with

a lot of utterly preposterous statements about domestic

animals and plants, masquerading as valid evidence for

the selection doctrine.

So fixed in the minds of most biologists not acquainted

with agricultural matters at first hand is the idea that the

vast majority of improved varieties of plants and animals

owe their origin, or their improvement, or both, to cumu-

lative selection of slight differences, that it appears de-

sirable to review briefly a few of the actual facts. One

can not hope to do more than touch here and there in a

great body of evidence, but at least representative cases

may serve to indicate the general tenor of the whole.

We may consider first the cultivated grape, of which

there are over 1,300 recognized varieties grown in this

country. Hedrick?* and his assistants have made a very

careful and systematic study of the origin of these forms.

After discussing the early history of the vine in this coun-

try he says (p. 52):

We have found that the wild grapes of the country, valued but uncul-

tivated for two hundred years, became through mere transplanting from

the woods into the vineyards . . . one of our most important fruits.

Again in commenting upon the growth of the grape-

growing industry he says (p. 62):

The results achieved seem all the greater when one considers that

many of the best varieties now grown are the first, and searcely any are

further removed than the second generation from wild plants.

But we should not be content with these general state-

ments. Let us examine specifically the history of a well-

28 Hedrick, U, P., ‘The Grapes of New York.’ Albany, 1908.

78 THE AMERICAN NATURALIST [Vou. LI

known and very excellent ‘‘improved’’ variety, the Con-

cord. Of this grape Hedrick says (p. 219)

The Concord is known by all. The most widely grown of the grapes

of this continent, it also represents the dominant type of our native

species and with its offspring, purebred and crossbred, furnishes seventy-

five per cent. or more of the grapes of eastern America.

He speaks of ‘‘the preeminently meritorious character of

Concord which has enabled it to take first place in Amer-

ican viticulture.’’

Now for the origin and history of this paragon.

The seed of a wild grape was planted in the fall of 1843 by E. W.

Bull of Concord, Massachusetts, from which fruit was born in 1849.

The wild grape from which the seed came had been transplanted from

beside a field fence to the garden in which there was at least another

grape, the Catawba, and the wild vine was open to cross-pollination.

One of these seedlings was named Concord and the variety was exhibited

before the Massachusetts Horticultural Society in the fall of 1852. The

new grape was introduced in the spring of 1854 by Hovey & toe ie

of Boston. From the time of its introduction the growth of this

variety in popularity was phenomenal. In 1865 it was eae a prize

by the American Institute . . . as the best grape for cultivation.

But where in the history of this ‘‘ best’’ American grape

is the gradual accumulation of minute variations by selec-

tion? The story is of the same sort for all varieties of

grapes about whose origin anything is known; either they

were chance seedlings, or F, hybrids, or F, segregates,

grown under good conditions.

The same general situation obtains in regard to the

origin and improvement of other fruits besides the grape.

One need only mention various cases briefly to recall them

to mind. New and improved varieties of apples, plums,

cherries, strawberries, etc., have originated either as

chance seedlings, or as bud variations, or as hybrids. In

their production selection, in the sense of the accumula-

tion of minute favorable variations, has had no part.

In the case of many fruits the mere fact of domestica-

tion accounts for all the improvement over the wild type.

A striking example of this is found in the case of the most

recently domesticated wild plant, the blueberry. Mr. F

No. 602] THE SELECTION PROBLEM 79

V. Coville? succeeded in discovering some years ago the

two essentials for the successful cultivation or domestica- —

tion of the swamp blueberry (Vaccinium corymbosum).

These were found to be (1) an acid soil, and (2) a root

fungus that appears to supply the plant with nitrogen.

When these essentials are supplied, and the plant brought

under cultivation, a marked improvement in the size and

quality of the berries at once occurs. Further improve-

ment is being made by hybridization, and by seeking

superior natural variations to be used in such hybridiza-

tion and for asexual propagation. In his latest paper

Coville makes this statement, the significance of which

in the present connection will be noted.

Seedling plants, even from the largest berried wild parents, produce

small berries as often as large ones.

Selection, in the Darwinian sense, is playing no part in

the improvement of the blueberry, so far as we can learn

from the published records. The essential factors in the

improvement are better conditions, hybridization, and

the asexual propagation or superior natural variations.

Let us now turn to other sorts of plants. In 1910 my

colleague, Dr. Frank M. Surface, originated a variety of

oats, known as Maine 340, which is superior to any variety

which we have been able to find in the market and test.

It is now widely grown in Maine. For the conditions of

soil and climate in that state it is certainly to be regarded

as the most highly ‘‘improved’’ variety known. Its origin

and history are fully known, indeed are originally re-

corded in the archives of this laboratory.® All of the

thousands upon thousands of bushels of this Maine 340

oat which were grown this year are the lineal, unchanged

descendants of one particular oat plant which Dr. Surface

isolated in 1910. That original plant has simply been

multiplied, by seed, year after year without selection of

2° Coville, F, V., U. S. Dept. Agr. Bulletin 193, 1910; Circular 122, 1913;

Bulletin 334, 1915.

80 Cf. Surface, F. M., and Zinn, J., Me. Agr. Expt. Stat. Ann. Rept. for

1916, pp. 97-148. :

80 THE AMERICAN NATURALIST [Vou. LI

any sort or kind, after the first isolation of the plant

_ which originated the variety.

The commercial variety of oats which comes the nearest

under our conditions to equalling Maine 340 in yield and

other desirable qualities is one known as the Early Pearl.

The history of this variety has been given by Surface

and Barber,*! who got it from the originator, Mr. R. L.

Copeland. Mr. Copeland says:

The first seed was obtained from a bunch growing by the roadside

some twenty years ago, presumably from one seed. It was examined

and showed such merit that it was cut and preserved for seed. Although

the first seed was not secured by me personally, it soon after came into

my possession. The oat seemed to possess excellent qualities and as it

matured fairly early and had a pearly tint to the hull I gave it the

name of Early Pearl.

Since the beginning the oat has simply been grown by

Mr. Copeland unmixed with other sorts.

Here again that painstaking and laborious selection,

by which the practical breeder is supposed to make the

wonderfully improved and valuable varieties which we

have, is conspicuous by its absence. And one must not

for a moment suppose that this oat is not a wonderfully

superior one. Any oat which will yield, year in and year

out, good seasons and bad, not less than about 80 bushels

to the acre, and at the same time possess a whole series

of other desirable qualities, which are too technical to go

into here, is in the front rank of the products of the

breeder’s art. We find it to be surpassed only by some

of our own new varieties. It outranks all other com-

mercial varieties under our conditions.

Many other examples of the same sort of histories of

varietal origin and improvement might be given. But

de Vries®? has covered the ground thoroughly and we

need not stay longer over the plant side. The writer

wishes to make clear before leaving the subject the reason

for calling attention to these well-known matters. It is

to emphasize that the ‘‘experience of practical breeders’?

31 Surface, F. M., and Barber, C. W., Me. Agr. Expt. Stat. Ann. Rept.

for 1915, pp. 137-192.

82 de Vries, H., ‘‘Plant Breeding.’’ Chicago, 1907.

No. 602] THE SELECTION PROBLEM 81

shows that the principle of the gradual accumulation by

continued selection of minute somatic variations has had

no essential part in the origin or amelioration of cer-

tainly a great many of the best varieties of agricultural

plants which we have to-day. The essential factors which

have been involved in the production of our best fruits,

grains, vegetables, flowers, etc., have been (1) the im-

proved conditions of domestication, (2) mutations, lead-

ing at once to new and better forms, (3) hybridization,

which by new combinations of characters and as a result

of heterosis®* has led to amelioration, and (4) the puri-

fication of previously mixed races or varieties by selective

sorting. It is to the overwhelming importance of one or

a combination of these factors that the ‘‘experience of

breeders’’ points and not to Darwinian selection.

But what of the animal side? Here the true facts are

much more difficult to get at; in part for reasons which

have been developed earlier in this paper, and in part for

the reason that the making of new breeds of domestic

animals is no longer going on to any extent except in the

smaller sorts such as poultry. As has been pointed out

elsewhere,** this is primarily a result of the great devel-

opment of the system of pedigree registration, which

puts a ban on cross breeding in cattle, horses, ete.

_ So then let us take as our first example one from poul-

try breeding where unequivocal facts are available. In

his ‘‘Organic Evolution’? Metcalf% makes the following

statement:

The extent of the modification produced by artificial selection is very

_ great in many eases. Notice the common domestic chickens, in which

the different breeds differ from one another to such a degree that if

they occurred in nature the several kinds would be referred not only to

different species, but to different genera. Compare the slender “ game”

which most closely of all resembles the ancestral “jungle fowl,” with

the heavy “Brahma” or “ Cochin-china,” or with the ting tailed “ Jap-

anese” cocks, or with the little “bantam.”

_ 83 East, E. M., and Hayes, H. K., U. S. Dept. Agr., Bur. Plant Industry,

Bulletin 243, 1912,

34 Pearl, R., ‘€ Modes of Research in Genetics.’? New York, 1915.

se Metcalf, M. M., ‘‘Organie Evolution.’’ New York, 1904.

82 THE AMERICAN NATURALIST [Von. LI

All these forms, according to Metcalf’s idea, have been

produced by selection from the jungle fowl. For a num-

ber of years past the writer has been interested in col-

lecting evidence regarding the making of new races and

varieties of bantams, for the purpose of seeing what part

selection, in the Darwinian sense, probably plays in the

matter. The problem was given enhanced interest and

significance by the appearance of the important paper by

Punnett and Bailey, which showed that in respect of

body weight bantams are differentiated from large fowls

by at least three genetic factors, and that in a cross be-

tween a bantam breed (Seabright) and a larger breed

(Hamburg) the inheritance of body weight is typically

Mendelian. This latter result the writer had found to be

true, using different breeds from those employed by the

English workers, but had not worked out in detail the

exact mechanism of the inheritance. New varieties of

bantams are all the time being produced and exhibited at

poultry shows. Broadly speaking, it is nearly true that

for every different variety of large fowl a corresponding

bantam variety either has been produced or is sure to be

soon. In view of this great activity in the making of

new varieties it seemed that an excellent opportunity

was offered to find out how the expert bantam fancier

really turns the trick. So the writer has corresponded -

with bantam fanciers in all parts of the world and in this

way has accumulated a large amount of interesting ma-

terial.

One question was always asked, and always in the same

form. This was:

Do you know of any case in which a stable Tace, variety or breed of

bariams, which bred true indefinitely in respect to bantam size of body,

was originated or created solely by selection of small sized individuals

of a large race, variety, or breed of fowls, without any crossing in of

bantam blood? If so, please give a detailed account of the cireum-

stances. ;

36 Punnett, R. C., and Bailey, P. G., Jour. Genetics, Vol. IV, pp. 23-39,

1914.

No. 602] THE SELECTION PROBLEM 83

The answers to this question were negative in every

case except one. In that case the correspondent was

unable to cite any specific instances illustrating his con-

tention, but thought on general principles that it must be

so. In other words, his belief in the selection theory, like

that of Weismann, was based on wholly other grounds

than demonstrative evidence. The general tenor of the

answers to this question is well indicated by a statement

of Mr. J. F. Entwisle,*7 who is probably the greatest

authority on bantam breeds of poultry now living. He

stated that it was thought by some that

proper little bantams could be bred from large fowls without any

admixture of bantam blood. . . . If such ean be done, then our thirty-

odd years’ experience of bantam “manufacturing” counts for very

little. We’ have lived to see the manufacture of some forty varieties,

and none without crossing, so far.

If time permitted, the citation of the detailed history

of the making of several breeds of bantams would show

very clearly that Darwinian selection plays an extremely

minor and unimportant part in the process as it is actu-

ally performed. Large breeds of poultry show the same

thing. Two of our most important breeds, the Wyan-

dottes and the Orpingtons, are of comparatively recent

origin. The facts as to their origin are well known and

the essential biological factors concerned in both cases

are the same, namely, hybridization as a start, followed

by close inbreeding of desired segregating types. In

other cases new varieties of poultry have appeared as

sudden mutations by loss of factors. Such is the origin

of the White Plymouth Rock and the White Cornish, for

example.

III. SELECTION EXPERIMENTS

; We now come to the third class of evidence on the selec-

tion problem, namely, that afforded by controlled ad hoc

31 Entwisle, J. F., Poultry (London), Vol. 30, P 767, 1912.

38 Thé “we”? hate’ is editorial. Mr. Entwisle is speaking of his own per-

Sonal experience.

84 THE AMERICAN NATURALIST [ Vou. LI

experimentation. Here the facts are so recent and so

well known that a detailed review is unnecessary. I shall,

therefore, only attempt to deal with them, for the most

part, in a general way. Careful and critical selection ex-

periments may be said in general to have given opposite

results, according to whether the hereditary factors for

the character which formed the basis of the selection

were or were not positively known to be in a homozygous

condition in all the individuals of the race experimented

with. If the form used constituted a ‘‘pure line’’ in the

strict sense of Johannsen’s conception, so that every in-

dividual was surely known to be strictly homozygous for

some state or condition of the character selected, and

the mode of reproduction was such as automatically to

retain and continue this condition, then the results of con-

tinued selection have in most cases been wholly negative

so far as the production of any change in type is con-

cerned. This is shown by the work of the Svalof Sta-

tion®® with various cereals, of Johannsen*® with beans,

of Jennings*! with Paramecium, of Hanel*? with Hydra,

of Vilmorin? with wheat, of Ewing‘! with Aphis, of

Surface and Pearl** with oats, of Fruwirth*® with lentils,

peas, soy-beans and lupines, of Lashley‘? with Hydra, of

Agar* with Simocephalus, and of others.

39 Cf. de Vries, H., loc. cit. passim, and Newman, L. H., ‘‘ Plant Breed-

ing in Seandinavia.’’ Ottawa, 1912. :

40 Johannsen, W., ‘‘Ueber Erblichkeit in Populationen und in reinen

Linien.’’ Jena, 1902.

41 Jennings, H. S., Proc. Amer. Phil. Soc., Vol. 47, pp. 393-546, 1908;

and Amer. NAT., Vol. 46, pp. 487-491, 1912.

42 Hanel, E., Jenaische Zeitschr., Bd. 43, pp. 321-373, 1908.

43 Cf. Hagedoorn, A. L., and Hagedoorn, A. C., Zeitschr. ind. Abst. Ver.

Lehre., Bd. XI, pp. 145-183, 1914.

44 Ewing, H. E., Biol. Bul, Vol. 26, pp. 25-35, 1914; and Ibid., Vol. 27,

pp. 164-168; and Ibid., Vol. 31, pp. 53-112, 1916.

45 Surface, F, M., and Pearl, R., Me. Agr. Expt. Stat. Ann. Rept. for

1915, pp. 1-40.

46 Fruwirth, C., Zeitschr. f. Pflanzensiichtung, Bä. III, pp. 173-225, 1915.

47 Lashley, K. S., Jour. Exp. Zool., Vol. 19, pp. 157-210, 1915; and Ibid.,

tics 20, pp. "19-26, 1916.

gar, W. E., Phil. Trans. Roy. Soc., London, B, Vol. 205, pp. 421-489,

No. 602] THE SELECTION PROBLEM 85

So far as the writer is aware the only important ex-

ceptions to the general rule exemplified by the above-

cited researches are those obtained by Jennings“ in Dif-

flugia, and by his students, Middleton®® with Stylonychia,

and Stocking®! with abnormalities in Paramecium. The

facts in the case of these exceptions are beyond question.

Just what their correct interpretation is does not seem to

be so clear. Jennings himself (loc. cit., p. 529) has ex-

pressed some doubt as to the significance of Miss Stock-

ing’s results so far as concerns their relation to normal

reproduction. Morgan®? has suggested that Jennings’s

Diffiugia results may possibly be due to a sorting out of

genetic diversities in the germ plasm, which came about

from earlier conjugations, the material thus not repre-

senting a strictly homozygotic pure line. If this sugges-

tion should prove to be valid the Diflugia work would

fall at once into the same category as the cases of sorting

out of pure lines from a mixed population by selection,

with which the studies of Johannsen, de Vries and Jen-

nings himself have made us familiar.

There is another point in connection with this extremely

interesting and important investigation on Difflugia

which seems to the writer, in the light of his own experi-

ence in breeding, of really extraordinary significance.

One of the longest and most crucial selection experiments.

in the whole series was that for diverse numbers of spines

in Family No. 326. During the first six periods after

Selection was begun in this experiment (p. 488) ‘‘no

progress was made by selection.’’ Then the basis of

selection was changed. This change is described by Jen-

nings in the eee words (p. 489):

After this time selection was based to a considerable extent on past

performance. By this time many of the existent individuals had pro-

49 Jennings, H. S., Genetics, Vol. 1, pp. 407-534, 1916.

50 Middleton, A. R., Jour. Exp. Zool., Vol. 19, pp. 451-503, 1915.

51 Stocking, R., Jour. Exp. Zool., Vol. 19, pp. 387-449, 1915.

52 Morgan, T. H., ‘ʻA Critique of the Theory of Evolution.’’ Princeton,

1916,

86 THE AMERICAN NATURALIST [Vou. LI

duced several offspring. Where a parent of the low group had been

found to bring forth high progeny, that parent was removed. Simi-

larly, if a parent with a high number of spines is found to produce

offspring with low numbers, this parent was removed. Thus in the

low group we gradually tend to accumulate a set of individuals (1)

which in the past have produced progeny with low numbers of spines;

(2) whose ancestors for several generations back are individuals with

low numbers of spines. In the ligh group the reverse conditions are

fulfilled.

From the time this change in method was made until the

end of the experiment, selection produced a marked

effect, differentiating clearly high spine groups and low

spine groups.

The significance of this result seems to me to lie in the

fact that with the new method of selection described by

Jennings the ultimate basis of selection was changed

from the soma to the germ. Because after the change in

method what primarily determined the selection of any

particular individual for further reproduction was not

its own spine number, but instead its demonstrated ability

to produce offspring with a particular spine number (or

nearly that number). A low spine parent was allowed

to survive and reproduce not alone or primarily because

_ it had few spines but only when in addition it was surely

known to produce low spine progeny. This is indeed a

different basis than that which merely selects individuals

because of their somatic spine number and nothing else.

It abruptly and completely transfers the selection from

soma to germ. As has already been pointed out earlier

in this paper (p. 5), there can be no question about the

efficacy of selection which operates on a directly gametic

rather than a somatic basis. This idea of making the

basis of selection the ability to transmit to the progeny

the desired quality is one which the writer has for a good

many years strongly advocated as the only really useful

or hopeful method in the practical breeding of higher

animals. In his own work with poultry? it has been

crowned with the highest practical success. Beyond

53 Pearl, R., AMER. Nar., Vol. XLIX, pp. 306-317, 1915.

No. 602] THE SELECTION PROBLEM 87

doubt or question the reason for the success is because by

this method we select directly the kind of gametes we

want. In-ordinary Darwinian selection we select the

kind of somata we want, and trust blindly that a wise

providence has implanted in them the sort of gametes we

need in order to get further somata like those we selected.

And as in so many other troublesome affairs in this vale

of tears, too often we find in the outcome that our trust

has been misplaced!

It seems to me that whether Morgan’s suggestion re-

garding the highly interesting and important results with

Diflugia is true or not the fact dealt with in the pre-

ceding paragraph objectively paraHels exactly the phe-

nomena which one sees when he isolates pure lines

from a mixed population (e. g., in oats). He finds some

individuals which are somatically what he wants but

which fail to produce the sort of progeny he is looking

for. These he discards. Others produce progeny which

are like themselves. They transmit** their qualities and

hence are retained.

Having considered the results of experiments on selec-

tion in pure lines we may turn to similar experiments

with sexually reproducing organisms. Here the facts

are, in the main, no less clear, but they are, on the whole,

exactly opposite in their sense, at first sight at least. For

in most of the experiments of this sort selection has been

attended with an alteration of the type in the direction of

the selection. This has been the case in the writer’s*®

experiments on egg production, in the domestic fowl since

1908, in the work of Smith5* and others with maize in

54 Lest there should be any misunderstanding I may say that I am fully

aware that the old idea of heredity as a direct and material transmission of

personal qualities from generation to generation is wholly incorrect, out-of-

date, and pedagogically pernicious. I find it, however, extremely çonte-

nient, saving of breath and good white paper, and, with this explanation,

I hope permissible, to use ‘‘transmit’’ as a technical genetic term meaning

‘*to possess gametes of such sort as will produce in the progeny.’’

55 Pearl, R., AMER. Nat., Vol. XLIV, pp. 595-608, 1915.

56 Smith, L. H., Ill. Agr. Expt. Stat. Bul. 128, 1908.

88 THE AMERICAN NATURALIST [ Vou. LI

Illinois, in the work of Pearl and Surface®* with maize,

in MacDowell’s®* work on bristle number in Drosophila,

in the work of Zeleny and Mattoon”? with the bar eye of

Drosophila, in the experiments of Castle and Phillips®

with hooded rats, and in the work of some others. The

difficulty with all these experiments is not in the facts but

in their interpretation.

Before taking up this question of interpretation, how-

ever, it seems desirable to point out certain objective

features which the results of these experiments have in

common. The first is that they all occur (with the ex-

ception of the Jennings cases already discussed) in sexu-

ally reproducing organisms, not certainly known to be

homozygotie with respect to all the factors which may be

concerned in the production of the selected characters,

and subject to a mixing of germ plasms in each genera-

tion. The second is that when any result at all follows

selection in most if not all of the cases it comes quickly

(i. e., in a few generations), is relatively large in amount,

and either no further change follows further selection or

if it does occur it is again sudden and large in amount.

This was true in the work with high producing lines of

hens, of all work with maize by the ear-row method, and

of MacDowell’s with Drosophila, and also, as MacDowell’!

has so clearly demonstrated, in Castle’ S experiments with

rats. A third point which strikes one is that in many of

these successful cases of selection the basis of the selec-

tion has been fundamentally gametic, that of ‘progeny

performance,” rather than solely somatic. Individuals

are selected for further multiplication which have demon-

strated their ability to produce progeny bearing the de-

sired somatie qualities. This. was certainly the case in

57 Pearl, R., and Surface, F. M., Maine Agr. Expt. Stat. Ann. Rept. for

1910, pp. 249-307.

58 MacDowell, E. C., Jour. Exp. Zool., Vol. 19, 1915.

59 Zeleny, C., and Mattoon, E. W., Jour. Exp. Zool., Vol. XIX, pp. 515-

529, 1915.

60 Castle, W. E., and Phillips, J. C., Carnegie Institution, Publ. 195, 1914.

61 MacDowell, E. C., Amer. Nar., Vol. 50, pp. 719-742, 1916.

No. 602] THE SELECTION PROBLEM 89

the Illinois corn work, as Surface’? very clearly demon- |

strated. The writer? showed a number of years ago that

it was the basis of success in selecting poultry for egg

production. One strongly suspects it to be true in the

other cases, though because the importance of the point

has not been perceived, evidence in the published ac-

counts is lacking on which to make any positive statement.

What is the correct interpretation of these favorable

results? Two opposed opinions are held. Fortunately

the heat of the controversy has been intense enough to

produce some distillation and we at least have the issue

very clearly and sharply defined. On the one hand it is

held, because there has been an alteration of type in point

of time coincident with successive selections, that selec-

tion on the basis of personal somatic qualities only, as

such, in and of itself, has altered hereditary factors in the

germ plasm. This view makes selection a cause of genetic

variation,®* a total reversal of the position held by Dar-

win and most of his followers. The opposing view is that

selection can only be successful in altering the type when

hereditary determiners to produce the desired somatic

qualities are already present inthe germplasm. Selection,

on this view, has nothing whatever to do with the causa-

tion of the variation, and is wholly powerless and with-

out effect on the race unless either (a) the basis of the

selection is directly gametic, by means of progeny per-

formance test, or (b) the soniatically selected individuals

happen by good fortune to carry the necessary hereditary

determiners in their germ plasm.

The opposition here really goes very far back. It is

the world-old fight between heredity and environment,

nature and nurture, germ and soma. One side believes

first, that hereditary determiners or factors fluctuate reg-

e 62 Surface, F. M., IV° Conf. internat. de Génétique, Paris, 1911, pp. 221-

35.

63 Pearl, R., AMER. Nar., Vol. XLV, pp. 321-345, 1911.

64 Castle, W. E., Sci. Mo., Vol. 2, p. 91, 1916, and Castle, W. E., and Phil-

lips, J. C. , Onmnegle Inst. Publ. 195, p. 31.

90 THE AMERICAN NATURALIST [ Vou. LI

ularly and frequently, if not indeed usually, and in high

correlation with somatic characters; second, that mixing

of germ plasms in fertilization alters hereditary deter-

miners mutually and hence is, in and of itself, a cause of

genetic variations, and, therefore, third, that a purely ex-

ternal agent, the continued selection of personal somatic

qualities, will alter the germ plasm.*®

The other side believes first, that the germ plasm is

fundamental and remarkably conservative, basing this

belief on such observations®* on the one hand as those of

Walcott that pre-Cambrian annelids, snails, cr

and algæ were in many cases so iky forms living to- day

as to belong to the same genera, though a period of time

variously estimated at from 60 to 200 million years has

elapsed; and, on the other hand, those of Wheeler on ants

enclosed in amber two million years ago but morpholog-

ically identical with forms living to-day. It believes,

second, that when the germ plasm changes it does so as

a result either of wholly internal physiological causes,

or of very extraordinary environmental stresses acting

directly upon the germ cells; third, that mixing of germ

plasms, in and of itself, does not mutually alter hereditary

determiners, basing this belief on the regularity, con-

stancy and cleanness of typical Mendelian segregation;

and fourth, that selection only acts as a mechanical sorter

of existing diversities in the germ plasm and not as a

cause of alteration in it. .

The alternative views have been presented. In the

present state of knowledge nothing is to be gained by

mere assertions of opinion as to which more nearly repre-

sents the truth. But one may at least advance the view,

65 In his last paper MacDowell has justly emphasized the scientific futility

of defining and codifying the opponent’s position in a controversy, so that

one may the more neatly bowl him over. I am very sensible of the force of

this point, and therefore have been at great pains in the preceding sentence

to make only such statements as can be supported by verbatim quotations

from the literature. Since, however, it seems to me equally important to

the personal element out of scientific controversy, so far as may be,

I do not make the specific references.

66 Cited from Loeb, J., ‘‘ The Organism as a Whole.’’ New York, 1916.

No. 602] THE SELECTION PROBLEM 91

to which the whole of this paper has been leading, and

which one may hope will be heartily concurred in by both

sides in the selection controversy, that the great outstand-

ing need in research on the problem of evolution in gen-

eral, and of selection in particular, is more, and more

searching, investigations as to the causes of genetic (fac-

torial) variation. That both sides realize this need, and

are all the time bending more and more energies to its

selection, is indeed cause for congratulation and augurs

well for the future of that branch of biological science in

which America has taken a leading place.

MENDELIAN FACTOR DIFFERENCES VERSUS

REACTION SYSTEM CONTRASTS IN

HEREDITY. I

T. H. GOODSPEED anp R. E. CLAUSEN

The literature on species crosses shows clearly that all

gradations occur as regards fertility from complete steril-

ity to what is apparently complete fertility. Recombina-

tions may, therefore, in some cases, occur freely between

species that appear to be distinct. Lotsy (1913) in par-

ticular has shown this to be true for a number of species

crosses in Antirrhinum and doubtless such instances

might be multiplied considerably. But even in these cases

the behavior of the hybrid progeny in subsequent genera-

tions indicates that there is a possibility that some of the

recombinations do not form functional reaction systems

because of the discordant elements they possess. This is

shown in the entirely new characteristics which a certain

portion of the population may exhibit and in the peculiar

ratios which are sometimes obtained in segregation. Such

results only bear out more completely the conception that

for any recombination of elements to be completely func-

tional they must together form a harmonious reaction

system. Even Detlefsen’s (1915) results with the cavy

species cross which gave in F, sterile males and fertile

females may be brought into line with such a physiologi-

cal conception perhaps better than by trying to account

for it on the basis of any definite number of Mendelian

factors. At least in the cavy cross the attempt to account

for the results in this latter manner demonstrated that

the number of factors concerned must be relatively large,

and this is precisely what would be expected on the basis

of recombinations involving whole choromosomes or sec-

tions of chromosomes carrying with them, perhaps, many

discordant elements. If we recall the observation that

no crossing-over occurs in the sex heterozygote (Morgan

No.602] | MENDELIAN FACTOR DIFFERENCES 93

et al, l. c.), presumably the male in this case, then it would

be possible in the male cavy to secure only recombinations

involving whole chromosomes, or in other words involv-

ing the building up of reaction systems with a large num-

ber of interchanged factors. In the female, however,

these recombinations might include, in addition to those

resulting from redistribution of whole chromosomes,

cross-over gametes resulting from the exchange of sec-

tions of chromosomes. Such gametes might conceivably

contain fewer discordant elements or they might be dis-

tributed in such a way as to distrub the reaction system

thus formed less profoundly. Such data of course need

first to be reexamined from this viewpoint before any

definite conclusions can be reached, but the list of species

hybrids which Detlefsen gives which result in sterile

males and fertile females would seem to indicate that this

is a phenomenon connected in some way with the ob-

served lack of crossing-over in the sex-heterozygote

already demonstrated in the work with Drosophila and

the silkworm (Sturtevant, 1915). Until we know more

about the fundamental basis of crossing-over and the

factors affecting it, it is idle to speculate on such differ-

ences in behavior as are shown by males and females in

the species crosses mentioned.

The insistent way in which the species hybrids between

Tabacum and sylvestris point to the conception of the

Mendelian reaction systems as units in themselves is of

interest because of the broad and far reaching conse-

quences which follow the application of such anidea. For

if the nature of the progeny of these partially sterile

hybrids as grown through several generations points to

anything, it is that the abortive ovules and pollen grains

represent a selective elimination of certain types of re-

combinations. Obviously, then, the presence of any con-

siderable proportion of sterile ovules or pollen grains in

plant material may be a consequence of hybridity and

that of a rather profound type involving reaction systems

which are more or less specific in their nature and in part

incompatible with each other. The importance of this

94 THE AMERICAN NATURALIST [ Von. LI

fact has, perhaps, not been sufficiently emphasized in

work involving material which displays such partial ster-

ility. Obviously, however, it is impossible to regard

ratios obtained from such material as of any significance,

unless it be possible to demonstrate definitely the nature

of such gametes as fail to function. It is, therefore, not

strange that species hybrids as a class require a some-

what different sort of treatment from that applicable to

intervarietal crosses involving relatively few factor dif-

ferences.

In the extensive work which has been done with the

various species and forms of @nothera this influence of

partial sterility has undoubtedly played an important

part, but at the same time one which has not been clearly

defined. Jeffrey (1914) in particular has sought to es-

tablish the hybrid nature of O. Lamarckiana on the basis

of the high percentage of abortive pollen grains which are

found quite generally in the genus, and Heribert-Nilsson

(1912) has attempted to analyze the material from a Men-

delian standpoint. These attempts have not, however,

led to a consistent explanation of the results observed,

although they have established certain peculiar condi-

tions in Enothera which practically preclude the applica-

tion of a rigid Mendelian analysis to such a type of be-

havior. On the other hand, a critical examination of the

phenomena displayed by the various forms of Ginothera

clearly indicates that these belong to several distinct cate-

gories, and not to one as is very generally assumed in

discussions bearing on this subject. In this brief discus-

sion we propose to classify them roughly as follows: -

1. Strict factor mutations arising from unknown causes

but clearly referable to specific germinal changes in iso-

lated loci in the hereditary system. These display a

simple, consistent Mendelian behavior when tested with

the forms from which they arise. They usually show

relatively simple and definite character differences when

compared with the parent forms rather than complex dif-

ferences throughout.

2. Segregation phenomena of a complex type resulting

No. 602] MENDELIAN FACTOR DIFFERENCES 95

in the constant and continual production of a number of

distinct forms which display for the most part a compli-

cated behavior when tested with the parents from which

they arise and with other forms. Such forms are often

widely different from the parent forms in all or nearly

all of their characters.

3. Chromosome duplications resulting in duplication of

one or more or even all of the chromosomes to the ex-

tent of tetraploidy in some forms.

The first of these categories may be rigidly distin-

guished from the other two, both of which may be funda-

mentally expressions of some inherent condition in the

‘‘mutating’’ individual. The existence of this first type

of mutation can scarcely be denied in the face of the ex-

tensive evidence accumulated both on the plant and on

the animal side. In addition to this long series of past

observations, we have now the extensive work of Morgan

and his associates (l. c.) in which the origin of over a

hundred such factor mutations has occurred under obser-

vation in Drosophila cultures. These investigations indi-

cate clearly that such mutations are fundamentally de-

pendent upon actual changes in the germinal substance.

They are the loss-mutations of genetic literature, but with

the abandonment of the presence and absence hypothesis

such a classification, of course, loses its significance.

Practically always only one locus is involved in such a

change, and the new form displays a consistent alterna-

tive behavior when tested with the form from which it

arose. Such mutations are usually recessive, although a

few dominant ones have been secured. When obtained in

pure culture they show no tendency to revert to the parent

form, at least not more frequently than they tend to

change i in entirely different directions. They are rela-

tively rare, they do not recur in any definite considerable

ratio in any strain, and they are not clearly due to any

specific cause. In @nothera, rubricalyx appears clearly

to be a dominant mutation of this type (Gates, 1914).

There seems to be little occasion for confusing these strict

96 THE AMERICAN NATURALIST [ Vou. LI

factor mutations with the more complex type of behavior

included under the second and third categories. —

When the second category is considered we are met

with the task of harmonizing a large mass of rather con-

fusing data, and it is perhaps true that this can not be

done successfully at the present stage of our knowledge.

There are not lacking, however, as many others have

pointed out, a number of significant facts which are at

least as logically explainable on the basis of hybridity as

on assumptions of general germinal changes. If the re-

sults which have followed species crosses are to be ex-

tended to the type of behavior displayed by Lamarckiana,

then it is clear that the numerical ratio in which segrega-

tion occurs is of no particular significance except in so far -

as its constancy indicates that it is due to a specific be-

havior in gametogenesis. Lotsy (1912) in particular has

pointed out that in Antirrhinum species crosses, races

may be secured which behave very much like some forms

of Œnothera with respect to the segregation ratios ob-

tained. The significant facts with which we have to deal

are apparently, first that in @nothera these ‘‘mutations’’

affect the sum total of the characters of the individuals,

i. e., they are dependent on complex germinal differences

when compared with the parents, and second that these

‘‘mutations’’ continually recur within certain races in

fairly constant ratios. These are facts which are just as

simply explained on the basis of a complex type of segre-

gacion in which many of the systems formed contain dis-

cordant elements and therefore fail to develop as to refer

them to actual change in germinal substance. Moreover,

the former explanation harmonizes the results obtained

with the simpler category of strictly Mendelian phe-

nomena.

That this view of the @nothera situation has something

in its favor beyond the known general occurrence of par-

tial sterility in this genus is shown by some of the results

of hybridization between the various forms of Œnothera.

The frequent appearance of F, populations consisting of

distinct forms is usually taken to be an expression of

No. 602] MENDELIAN FACTOR DIFFERENCES 97

segregation in the gametic series of such forms. Beyond

this the Gnothera phenomena display a remarkably

orderly behavior, and, although complex in nature, such

orderliness points strongly to some kind of definite seg-

regation dependent upon the hereditary constitution of

the forms involved rather than upen any change in germi-

nal substance expressed in the gametic series. Lamarcki-

ana, for instance, produces constantly a small percentage

of nanella as well as a number of other forms. It is,

therefore, necessary to assume merely that nanella ga-

metes make up a small percentage of the gametic series in

Lamarckiana. When two nanella gametes meet, a nanella

individual is produced, and it breeds true, as might be ex-

pected. When, however, a nanella gamete meets a La-

marckiana gamete a Lamarckiana individual is produced,

which need not necessarily differ in its behavior with re-

spect to the production of nanella from other Lamarcki-

ana races, since practically all of the combinations in-

volving nanella elements would fail to develop, or in case

some few of these combinations did develop, they might

produce other characteristic forms unlike either Lamarckt-

ana or nanella. This conception is in part borne out by

the fact that nanella appears to differ from Lamarckt-

ana not only in stature, but also in other characters, as is

shown in hybridization phenomena involving this form.

From this standpoint also, the occurrence of nanella in

the progeny of a wide range of forms is perfectly intel-

ligible. When nanella, which apparently really breeds

true, is crossed back with Lamarckiana a small propor-

tion of the progeny is of the nanella type and the rest are

Lamarckiana. This proportion is apparently greater

than that normally obtained from selfed Lamarckiana,

and this is merely a consequence of the realization of the

gametic ratio of nanellas in the Lamarckiana series as a

phenotypic ratio. The true breeding of the forms thus

resulting, to the extent that they breed true, is a natural

consequence of the germinal constitution of such forms.

On the other hand, when rubrinervis, which never pro-

duces nanella as a ‘‘mutant’’ (Gates, 1915), is crossed

a: ieee

98 THE AMERICAN NATURALIST [ Von, LI

with nanella, nanella does not appear in F, and in F,

appears in a fairly definite ratio in the progeny of the

subrobusta forms thus produced (de Vries, 1913), whereas

the Lamarckiana forms produced breed true, after their

usual fashion. Obviously this behavior is simply a conse-

quence of the fact that rubrinervis does not produce a

-gametie series containing nanella, and, therefore, nanella

can not appear in F,. The impressively orderly behavior

throughout in these hybridization phenomena is an elo-

quent testimony of the existence of a casual agency of a

simpler nature than that called for under the hypothesis

of actual, germinal changes.

Those phenomena included in the third category and

dealing with chromosome duplication may be referred to

the same type of iregular behavior in gametogenesis as is

concerned in the production of the other ‘‘ mutants.’’

They are of interest most particularly from our stand-

point with regard to the structural relations which they

display i in comparison with the other forms. Thus there

is a series of lata forms dependent on the duplication of

one chromosome in Lamarckiana. They are not identical

within the series, but at least three or four are known

which differ from one another in a characteristic fashion.

This may well be dependent on the particular chro-

mosome pair which is concerned in the duplication as

Gates (1908) has suggested. According to the chromo-

some view of heredity this duplication has the effect of

altering the proportions of the various elements in the

reaction system, and naturally in a delicately balanced

system such alteration results in a change in the somato-

genic processes in a definite direction, the latter depend-

ent upon which particular elements are increased. Since

a whole chromosome with presumably a large set of fac-

tors is involved, it should follow that the entire set of

characters of the plant would be affected, as appears

actually to be the case. The important point in connec-

tion with these phenomena is the apparent consequence

that phenotypic changes may be dependent merely on an

alteration in the relative quantitative proportions of the

No.602] © MENDELIAN FACTOR DIFFERENCES 99

Mendelian units making up the reaction systems. Ap-

parently this will account satisfactorily for the orderly

resemblance of these chromosome ‘‘mutants’’ to each

other and to the forms from which they arise. Conceiv-

ably the great body of data on which the mutation theory

is based would, for the most part, find a simpler expla-

nation along the lines thus indicated.

SuMMARY

Summarizing briefly the content of this paper, the fol-

lowing facts have, on the experimental side, been pre-

sented with reference to a species hybrid:

1. N. sylvestris when crossed with various varieties of

N. Tabacum gives F, hybrids which are replicas on a

large scale of the particular Tabacum variety concerned

in the cross.

2. The F, hybrids of sylvestris and Tabacum produce

a small number of functional ovules which represent the

sylvestris and Tabacum extremes of a recombination

series, the great majority of the members of which fail to

function because of mutual incompatibility of the ele-

ments of the two systems. :

3. Back crosses with sylvestris give sylvestris and

aberrant forms, and of the two the sylvestris alone are

fertile and breed true. On the other hand, back crosses

with Tabacum produce apparently only Tabacum forms

of which some are completely fertile and continue to pro-

duce only Tabacum forms.

On the theoretical side the following conclusions have

been drawn and their application indicated:

1. As a consequence of modern Mendelian develop-

ments, the Mendelian factors may be considered as mak-

ing up a reaction system the elements of which exhibit

more or less specific relations to one another.

2. Strictly Mendelian results are to be expected only

when the contrast is between factor differences within a

common Mendelian reaction system as is ordinarily the

case in varietal hybrids.

100 THE AMERICAN NATURALIST [ Vou. LI

3. When distinct reaction systems are involved, as in

species crosses, the phenomena must be viewed in the

light of a contrast between systems rather than between

specific factor differences, and tke results obtained will

depend upon the degree of mutual compatibility displayed

between the specific elements of the two systems.

4, Sterility in such cases depends upon non-specific in-

compatibility displayed between the elements of the sys-

tems involved, and the degree of this sterility depends

upon the degree of such incompatibility rather than upon

a certain number of factors concerned in the expression of

such behavior.

5. The consequences of the application of such a con-

ception to the complex type of behavior in @nothera are

pointed out, and the suggestion is specifically made that

the type of behavior exhibited by Lamarckiana and its

segregants in hybridization may be referred to such com-

plex system interactions.

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1908. The Mechanism of Heredity. Science, N. $., 27: 89-99.

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Detlefsen, J. A.

1914. Genetic Studies on a Cavy Species Cross. Publ. Carnegie

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Johns Hopkins Univ. Circ., 1914,

Lotsy, J. P,

1912. Versuche über Artbastarde und Betrachtungen über die

Möglichkeit einer Evolution trotz Artbestiindigkeit. Z. Abst.

Vererbl., 8: 325-332.

1913. Hybrides entre ae d’Antirrhinum. IV. Conf. Inter.

Genetique, pp. 4

Miles, F. C.

1915. A Genetic and Cytological Study of Certain Types of Albin-

ism in Maize. Jour. Genetics, 4: 193-21

Morgan, T. H.

1914. Two Sex-Linked Lethal Factors in Drosophila and Their In-

fluence on the Sex Ratio. Journ. Exper. Zoology, 17: 81-122.

1915a. The Rôle of the Environment in the Realization of a Sex-

inked Mendelian Character in Drosophila. AMER. NAT.,

49: 385-429, 1915.

1915b. The Constitution of the Hereditary Material. Proc. Amer.

il. 3-153

Morgan, T. H., Sturtevant, A. H., Mallet, HJ. and Briages OB:

1915. The Mican of Mendelian Herviity:

Pearl, R.

1915. Modes of Research in Genetics.

Setchell, W.A.

1912. Studies in Nicotiana. I. Univ. Calif. Publ. Botany, 5: 1-86.

Sturtevant, A. H.

1915. No Crossing-over in the Female of the Silkworm Moth.

AMER. Nar. : 42-44.

de Vries, H.

1913. Gruppenweise Artbildung, p. 215.

Wilson, E. B,

1914. The Bearing of nage se Research on Heredity. Proc.

Roy. Soc. London, B88: 333-352.

SHORTER ARTICLES AND DISCUSSION

PIEBALD RATS AND MULTIPLE FACTORS

In the Naturauist for December, 1916, MacDowell has pub-

lished an extended criticism of experiments in the modification

of the hooded pattern of piebald rats by selection, in which my

colleagues and I have been engaged for some years. This is not

the first time that readers of the Narurauist have had their at-

tention called to these experiments by similar adverse criticism

and they are possibly quite weary of the subject. In so far as

MacDowell merely offers in new form arguments which have

already been presented by Muller and Pearl and answered by

me, I shall make no reply. But as regards two points which

may fairly be considered critical, one of which actually is so

designated by MacDowell, I desire to present some evidence

which I regard as conclusive but which MacDowell has not dis-

cussed, evidence possibly not accessible to many readers of this

journal. MacDowell’s criticism is based on the data presented

in Publication 195 of the Carnegie Institution (Castle and Phil-

lips, 1914), and in a brief paper in The Scientific Monthly

(1916). Many additional data are given in Publication 241 of

the Carnegie Institution, but this is not considered by Mac-

Dowell, although it was issued in September, 1916, as Paper No.

26 of the station with which he is connected, nearly two months

in advance of his own paper. Had he considered carefully the

evidence contained in this later publication, I am sure that he

would have modified his criticism materially.

In 1914 Phillips and I offered two alternative explanations of

the progressive changes observed under selection in the hooded

pattern. These were (a) variability of the unit-character (‘‘fac-

tor”) hooded, and (b) multiple modifying factors affecting

the hooded character. We found it difficult to decide between

these two interpretations on the basis of evidence then avail-

able. For this hesitancy we were promptly taken to task by

Muller, who championed the multiple factor interpretation now

adopted also by MacDowell. MacDowell elaborates in much de-

tail a dozen points which show compatibility between our ob-

servations and a multiple factor hypothesis, but without consid-

No. 602] SHORTER ARTICLES AND DISCUSSIONS 103

ering whether they are also compatible with the alternative

hypothesis of a single varying factor. Modification on crossing,

decreasing variability, regression, greater variability in F, than

in F,, effective return selection—these are all phenomena to be

expected equally on either hypothesis. To cite them is no argu-

ment for one hypothesis rather than the other. This point has

wholly escaped both Muller and MacDowell, who seem quite un-

able to conceive any but the single explanatory principle of mul-

tiple factors.

Putting aside these irrelevant arguments, there remain. two

points in MacDowell’s discussion which require further consid-

eration. They are the same two points which led us in 1914 to

hesitate between the alternative interpretations which we con-

sidered, but on which we now have fuller evidence.

But before we go into this new evidence one or two minor

points may be noted in which the accuracy of our generalizations

is questioned. MacDowell has gone over our 1914 publication

in great detail, devoting as many pages to its destructive criti-

cism as we to its original exposition, and recalculating the sta-

tistical coefficients. It is gratifying to know that he has de-

tected in these no serious errors, though his figures differ from

ours slightly in some cases. Whether his calculations are more

accurate than our twice-checked ones, I am unable to say with-

out detailed reexamination of the data. As these are public

property, the curious reader may satisfy himself on the point.

I do not consider it necessary to go into the matter anew since

the substantial correctness of our findings is not challenged.

MacDowell thinks that we did not sufficiently emphasize the

decreasing variability (standard deviation) and the decreasing

rate of divergence of the selected races, observed as the selec-

tion progressed. These to his mind imply that selection would

sooner or later cease to be effective. In this opinion I can not

concur, since in neither the plus nor the minus selection series

has the standard deviation decreased by half, although sixteen

Successive selections had been made and the hooded character had

been so modified as to be scarcely recognizable longer. Whether

one considers the decrease in variability large or small depends

principally upon how much importance he attaches to the values

found for the first two generations of the experiment, when the

numbers of individuals observed were still small and methods

of grading them had not yet been fully standardized. Mac-

104 THE AMERICAN NATURALIST [Vor. LI

Dowell emphasizes the high variability of these early generations,

- few in individuals, and attaches importance to the relatively

smaller variability of later generations. It seems to me fairer to

compare the first half of the series with the second half. Con-

cerning the point I have said (Publication 241, p. 172) :

The amount of the variation as measured by the standard deviation

is less in the last half of the experiment than in the first half. It is

also steadier, owing in part doubtless to the fact that the numbers are

larger, and in part to a more stable genetic character of the selected

races. But the genetic variability is plainly still large enough to per-

mit further racial modification and there is no indication that it will

cease until the hooded character has been completely selected out of

existence, producing at one extreme of the series all-black rats, and at

the other end of the series black-eyed white rats.

It should be noted that these conditions have already been

approximated in individual cases.

THE New EVIDENCE

1. The progeny of plus selected crossed with wild rats.

(Quoted without change from Publication 241, pp. 163-168.)

In 1914 Castle and Phillips published a report on breeding experi-

ments with hooded rats, in which it was shown that the hooded color-

pattern—itself a Mendelian recessive character in crosses with the

entirely colored (or “self ”) coat of wild rats—is subject to quantitative

variation, and that different quantitative conditions of the hooded

pattern are heritable. (Compare fig. 36, plate 7.) It was also shown

that by repeated selection of the more extreme variations in the hooded

pattern (either plus or minus) it is possible gradually to modify the

racial mean, mode and range as regards these fluctuations, without

eliminating further fluctuation or greatly reducing its amount. We

concluded that the unit-character, hooded color-pattern, is a quanti-

tatively varying one, but were at that time unable to decide whether the

observed variability was due simply and exclusively to variation in a

single Mendelian unit-factor or partly to independent and subsidiary

modifying Mendelian factors.

Since publication of the above I have been engaged in further experi-

ments designed to show which of the alternative explanations is the

correct one, and these are now sufficiently advanced to indicate definite

conclusions. Previous experiments had shown that when a race of

hooded rats, whose character has been modified by selection (either

plus or minus), is erossed with wild rats, the extracted hooded animals

obtained in F, as recessives show regression toward the mean condition

No. 602] SHORTER ARTICLES AND DISCUSSIONS 105

of the recessive race before selection began. This result suggested

that the regression observed might be due to removal by the cross of

modifying factors, which selection had accumulated in the hooded race.

If this view was correct, it was thought that further crossing of the

extracted hooded animals with the same wild race should result in

further regression, and that if this further regression was not observed

a different explanation must be sought for the regression already noted.

The entire experiment has accordingly been repeated from the be-

with the same result as regards regression in the first F, gen-

eration, but with no regression of the same sort in a second F, contain-

ing twice-extracted hooded animals. So far from observing further

regression as a result of the second cross with wild rats, we have unmis-

takable evidence that the movement of the mean, mode and range of

the hooded character has been in the reverse direction. So the hypothe-

sis of modifying factors to account for the regression and for the pro-

gressive changes observed under selection becomes untenable.

In repeating the experiment of crossing hooded rats of our selected

races with wild rats, great care has been taken to employ as parents

individuals of the greatest racial purity and to inbreed the offspring

brother with sister, thus precluding the possibility of introducing

modifying factors from other sources. In making the second set of

crosses, the extracted individual has, wherever possible, been crossed

with its own wild grandparent. In the few cases in which this was

impossible, wild animals of the same stock have been used. This stock

consisted of a colony of wild rats which invaded the basement of the

Bussey Institution apparently from a near-by stable. Owing to faulty

construction of the building they were able to breed in spots inaccessible

to us, and it took many months of continuous and persistent trapping

to secure their extermination. During this period we trap a hun-

dred or more of them, all typical Norway rats, colored all over, without

even the white spot occasionally seen on the chest of wild rats. Two

generations of rats from this wild stock have been reared in the labora-

tory, and all have this same self-colored condition.

The hooded animals used in the experiments to be reported on in

this connection consisted of 4 individuals of the plus selected series,

a male and 3 females, as follows:

TABLE 140

Individuai Grade.! Generation. |

9 Spig... +4} 10

48.. +4 10

600. . + 4} 12 |

| 969056... ; +4 12 |

1 See figure 35, plate 7 for significance of the grades.

106 THE AMERICAN NATURALIST [ Vou. LI

Each of these animals was mated with a single wild mate, and their

children were weaned directly into breeding cages containing a male

and two or three females (brother and sisters). In the case of two

matings, F, males of the same parentage were at the time lacking and

males froma different cross were used. The results of such matings are

tabulated by themselves and serve a useful purpose as controls. The F,

animals all closely resembled their wild parents, but many of them had

a white spot on the chest. They ranged from grade +5% to +6

(self).

The F, animals are classified in table 141, where it appears that 73

of them were hooded and 219 non-hooded (i. e., like F,), an exact 1:3

ratio. More than half of this F, generation consists of the grand-

TABLE 141

Table 141 shows the classification of extracted hooded first F, young ob-

tained from crossing hooded rats of the plus-selected series with wild rats.

Grade of hooded grandchildren. Total | Total | Means

- Hooded grandparents. hooded. |_ nOn- of

14| 12| 2 | 2}| 24| 22) 3 | 34| 34| 3ł| 4 hooded. | hooded.

9 5513, + 44, gen. 10....| 1/..| 3) 2} 1| 7| 8| 6! 5| 7| 1 41 107 | 3.05

d 6348, + 4, gen. 10..... .-|--| 1}..| 1} 2] 4) 3] 4) 6 I) 22 68 | 3.28

Q 6955, + 4, gen. 12..... Ros iar Rae rer E se e Ys |e Po ee 27 | 3.51

9 5513, + 44, an

6600; 48, gen. 13.056 b ech stots ead Bed des 3 D Sn

Q 5513, + 44, and

9 6955, + 4, gen. 12..:.. Pas Pree Fans Pay By bere aes Wes T 2 5 | 3.37

Teele eS 1)..| 4| 2| 2} oj14l11|12lt6| f 73 | 219 | 3.17

children of 95513, produced by breeding her children brother with

sister, those children all having been sired by the same wild rat. Her

grandchildren include 41 hooded and 107 non-hooded young. The

hooded young range in grade from +114 to +-4, their mean grade

ing + 3.05, a considerable on from the grade of the grand-

mother, which was 4.25.

Hooded rats of the same grade and generation as the grandmother,

when bred with each other, produced young of mean grade + 3.84.

(See table 10, Castle and Phillips.2) The mean of the extracted

hooded grandchildren in this case (being 3.05) shows a regression of

0.79 from that expected for the uncrossed hooded race. From the

extracted hooded grandchildren of 95513, produced as just described

by a cross with a wild male, 7 individuals, 2 males and 5 females, were

selected for a second cross with the wild race. They ranged in grade

2 Comparison should have been made with generation 11 offspring, whose

mean was 3.91 not 3.84. This would make the regression 0.86, instead

of 0.79.

No. 602] SHORTER ARTICLES AND DISCUSSIONS 107

TABLE 142

Table 142 shows the classification of extracted hooded second F, young

obtained from crossing first F, hooded rats (table 141) with wild rats. The

hooded grandparents were themselves grandchildren of 95513, + 44, gen-

eration 10, on the side of both parents.

Grade of hooded grandchildren. | Total | Total | Means

Hooded grandparents. | : i | hooded. |_ non- | of

23 | 2} | 2} | 3 | 34} | 3} | 34| 4 | | . | hooded.

i | | }

| |

“eS CA Se AR ae As Sp a, a) at Shah oe 8 | 3.37

g 9686, + 23 ir Peet oD | 28 | 3.40

F 9620, + 23....... H ieS ai arna aake 24 | 3.06

9 9729, + 23 vob bi) Oo 21-2110 22 62

ENM acin bist O1 OT Mtl) 71 at OO 1) Oe) Oa

2 Ore, E eee BC: ea ae Se ee 68 | 3.55

9 9621, +34... nia ny Ba Tae 1... tai B12: 18 42 | 3.70

Tome. oi yi" 3) 3 4 | 6|13|28|30|11| 98 | 296 | 3.47

from +2 to +314. (See table 142.) They produced several litters of

young of the same character as the first F, young, all being similar to

wild rats in appearance, except for the frequent occurrence of a white

spot on the belly. These second F, young were at weaning time mated,

brother with sister, in breeding-pens, precisely as had been done with the

first F,’s. They produced 394 second F, young, of which 98 were hooded

and 296 non-hooded, a perfect 1:3 ratio. The hooded young varied

in grade from + 2 to +4, as shown in table 142, the data there being

given for each family separately as well as for all combined in the totals.

One family was very like another as regards the character of the hooded

young, except that the higher-grade grandparents had grandchildren

of slightly higher grade. Thus the average of all the 98 hooded young

was + 3.47, but the average of those descended from the 3 grandparents

of lowest grade was less than this, while the average of those descended

from the 3 grandparents of highest grade was greater. This is just

what had been observed throughout the entire selection experiments.

(See Castle and Phillips.)

If we weight each of the grandparents in table 142 in proportion to

the number of its hooded grandchildren, then the mean grade of all the

grandparents is + 2.95. Since the mean grade of all the 41 first F,

hooded grandchildren, from which these 7 were chosen, was -+ 3.05, it

will be seen that these 7 are, so far as grade is concerned, fair repre-

sentatives of the 41, being in fact of slightly lower mean grade. It is

therefore all the more striking that their grandchildren, the second F,

hooded young (table 142), are of higher grade. They regress in an

Opposite direction to that taken by the first F, hooded young. Thus

the original hooded ancestor (25513) was of grade 4.25, The grade of

hooded young expected from such animals is 3.84. What she produced

108 THE AMERICAN NATURALIST [ Vou. LI

in F, following a cross with the wild male, was young of mean grade

3.05. Seven of these of mean grade 2.95 produced a second F, contain-

ing hooded young of mean grade 3.47. This is a reversed regression of

0.52 on the grade of their actual hooded grandparents, or of 0.42 on

the group from which their grandparents were chosen. Their mean lies

about midway? between that which would have been expected from

the original hooded female (5513) had no crossing with wild rats oc-

curred and that which was observed in the first

Obviously these facts do not harmonize with the assumption that

the regression observed in the first F, was due to loss of modifying fac-

tors accumulated during-the ten preceding generations of selection; for

no further loss occurs in the second F, On the other hand, a par-

tial recovery is made of what was lost in the first F, This suggests

the idea that that loss may have been due to physiological causes non-

genetic in character, such as produce increased size in racial crosses; for

among guinea-pigs (as among certain plants) it has been found that F,

has an increased size due to vigor produced by crossing and not due to

heredity at all. This increased size persists partially in F,, but for the

most part is not in evidence beyond F,. I would not suggest that the

present case is parallel with this, but it seems quite possible that similar

non-genetie agencies are concerned in the striking regression of the first

F, and the subsequent reversed regression in the second F,.

Whatever its correct explanation may be, the fact of the reversed re-

gression in a second F, is very clear, as other cases than those already

discussed will show.

A hooded rat of grade + 4 and generation 10, $6348, had by a wild

female several young of the character already described for the young

of 95513. These, mated brother with sister, produced a first F, (table

141) of 90 a 22 of which were hooded, 68 being non-hooded, again

a good 1:3 ratio. The hooded young ranged from + 2 to + 4 in grade,

their mean being 3.28. Of the 22 hooded individuals, 1 male and 7

females were mated with wild rats to obtain a second F,, and the

second F, animals were then mated brother with sister to obtain the

esired second F, The character of this is shown family by family in

table 143. It contained 497 individuals, of which 121 were hooded

and 376 non-hooded, a ratio of 1:3.1. The weighted mean of the 8

selected grandparents is 2.93, which is 0.35 below the mean of the 22

first F, hooded animals which they represent. The mean of the second

F, hooded young is 3.22, which indicates a reversed regression of 0.29

3In The Scientific Monthly (Jan. 1916) I have stated that a second

cross showed ‘‘a return to about what the selected race would have been

had no crossing at all occurred.’’ This is obviously inaccurate and should

be corrected. It rests on a comparison with the combined average of both

the older and the more recent experiments. [MacDowell devotes half a

page to demolishing the statement already corrected here.]

No.602] SHORTER ARTICLES AND DISCUSSIONS 109

on the grade of the grandparents, but shows no significant difference

from the mean of the grandparental group (3.28).

TABLE 143

Table 143 shows the classification of extracted hooded second F, young

“ obtained from crossing first F, hooded rats (table 141) with wild rats. The

hooded grandparents were themselves grandchildren of ¢ 6348, + 4, gen-

eration 10, on the side of both parents.

Grade of hooded grandchildren. “saan Total | Means

Hooded d ts. non] of

ae 12] 2 | 23 | 23 | 22 | 3 | 34] 33 | 33] 4 hooded. | hooded. | hooded

g 9639, + 2..... BS Lie St 6) ari G6 ll oe 400 e

Wie tE a ahal Linh Oh eal. 6 16 | 3.17

Q 9765, +3..... Sheds Yea ee Fic ake 1 10 | 3.50

OT aly OF OES el BA Ped Dok a ae A 7A 76 | 2.90

WW, PSG lt Pee 2h Sel: Bt 2 2-16 47 | 3.28

Q 9705, + 33 SED ice t ee el ee 74 | 3.48

F 9748, + 34 VIA WG Bi 9 40 | 3.36

Totale; onua. 2|10| 2| 2| 8|23| 8|35|24| 7| 121 | 376 | 3.22

All except one of the 8 families classified in table 143 show unmis-

takably the reversed regression. This exceptional family consists of

the grandchildren of 99747. They have a mean grade of 2.90, sub-

stantially the same as that of the entire group of grandparents, but con-

siderably lower than that of their own hooded grandmother. Appar-

ently she did not come up genetically to her oe e grade. This

the other grandparents of the group did. For those of lowest grade

(2, 234) produced lower-grade hooded pater than did the

grandparents of highest grade (314, 4), as was found to be the case also

in table 142

We may next trace the inheritance of the hooded character through

a third but smaller family produced by two successive crosses with wild

rats, the hooded character in this case being derived from ? 6995,

grade + 4, generation 12. The character of her first F, descendants is

shown in table 141. They consist of 5 hooded and 27 non-hooded

individuals. The mean grade of the hooded young is 3.51, but the

number of these young is too small to make this mean of much signifi-

cance. One of the hooded young (49660, + 334) was mated with a

wild female to secure a second F, generation and from this in due course

was produced the second F, generation (table 144). It consisted of 21

hooded and 44 non-hooded young. The hooded young showed the usual

ge (2 to 4). Their mean grade was 3.50, substantially identical

with that of the first F, animals, but 0.25 below that of the actual hooded

grandparent. This family history is less satisfactory than the two

already diseussed because of the smaller numbers which it includes. It

110 THE AMERICAN NATURALIST [Vou. LI

contains nothing contradictory to the sabi ame already given,

though reversed regression is not in this case in evidence.

TABLE 144

Table 144 shows the classification of extracted hooded second F, young

obtained from crossing first F, hooded rats with wild rats. The hooded

grandparent, $9660, + 33, was a grandson of 96955, + 4, generation 12,

on the side of both parents. The hooded grandparent 419711, + 34, was a

grandson, on the side of one parent, of 95513, + 44, generation 10, and on

the side of the other parent, of 9 6955, + 4, generation 12. (See table 141.)

Grade of hooded grandchildren. Total | Total | Means

Hooded grandparents. | naoded | non- of

2 | 2}|24]2ł}| 3 |34/3}|3f] 4 `| hooded.| hooded.

T O Vine. TERE OL Ce eee Gee See ge eke Weeder eae

oii, Far... rete Mt el 4 Sh Abe ie bere 33 3.28

Tou i 5s diss a tiet 1+ S 94 6} OPilt Ot o 97 27] AO

In two eases F, females could not be mated with brothers and so

mates were taken from other families. Thus “mixed F, matings”

were made between children of 5513 and 6600 and children of 5513 and

6955. (See table 141.) The former mating produced 3 hooded and 12

non-hooded “ first” F, young; the latter produced 2 hooded and 5 non-

hooded “ first” F, young. The grade of the hooded young produced

by these mixed matings was not different from that of brother-sister

matings, so far as the small numbers permit one to judge. One of

these mixed matings was carried into a second F, generation. The

first F, hooded & 9711, + 31⁄4, was mated with a wild female, and the

young were bred, brother with sister, producing 16 hooded and 33 non-

hooded young. (See table 144.) The mean grade of the 16 hooded

young was 3.28, substantially the same as that of the first F, hooded

grandparent. No additional regression through loss of modifiers (or

other agency) is here in evidence. The result is the same as that ob-

attention has been given to individual pedigrees, is particularly di-

rected to the foregoing case.

Having now discussed each family history separately, we may com-

bine all the second F, families in one table, in order to get a clearer

impression of the results as a whole. (See table 145.) The second F,

generation thus combined includes 256 hooded and 749 non-hooded

individuals, a ratio of 1: 2.9, an unmistakable mono-hybrid Mendelian

ratio. The mean grade of the hooded individuals is 3.34. The weighted

mean grade of their hooded grandparents was 3.02, which indicates a

reversed regression of 0.32 for the entire second F, group of hooded

animals.

No. 602] SHORTER ARTICLES AND DISCUSSIONS 111

TABLE 145

Table 145 is a combination of tables 142 to 144, in which the second F,

young are classified according to the grade of their first F, hooded grand-

parent. i

Gaat sehen | Grade of hooded grandchildren pukka Total Means

.toresenaoaeese (18 | 2 | 2 | 24 | 28| 3 | 3t| 38 st] 4 meg TE | nied

2 apep a}...1 akej 5}16| 6| ail 41 | 118 | 3.25

23 ee R ee We” a Aan Sa ets ADE eB 1 34 90 | 3.29

3 FERA E dd Od kame et eae LO PD 53 182 | 3.48

34 POT ee ad BIOS IO AS ee 59 151 | 3.22

34 coner Dip def Ode SEES ad 46 161 | 3.39

3ł TR EE A bin kee oO oe E 21 44 | 3.50

4 ae ole cata cer web ed i 2 3 3.87 |

3.02 2 | 12| 4) 6|15|32|27|72|65)21} 256 749 | 3.34

Classified according to the grade of the (first F,) grandparent, they

show a correlation between grade of grandparent and grade of grand-

child. The lower-grade grandparent has lower-grade hooded grand-

children, and the higher-grade grandparent has higher-grade hooded

grandchildren. This shows that the variation in grade is (in part at

least) genotypic. As the experiment yields no evidence that the varia-

tion in the hooded character is due to independent modifying factors,

there remains no alternative to the coneltision that the single genetic

Mendelian factor concerned fluctuates in genetic value. Fluctuation

accordingly is not exclusively phenotypic, as DeVries and Johannsen

have thought, but may be genetic also. Hence racial changes may be

effected through selection by the isolation of genetic fluctuations, as well

as by the isolation of mutations. Moreover, genetic fluctuation makes

tion attaining results which it would be quite hopeless to seek by any

other means.

. The progeny of ‘‘mutant’’ crossed with wild rats. (From

Piast. 241, p. 173.)

Castle and Phillips described, under the name of “ mutants,” 2 rats of

the plus-selection series of extremely high grade. They proved to be

eterozygotes between the average condition of the plus-selected race

at that time, about + 3.75, and a new condition, not previously known

in our hooded races, but resembling that seen in “ Irish” rats, which are

black all over except for a white spot on the belly and would be classed

on our grading scale as about +514. In later generations we secured

animals homozygous for the darker condition just deseribed (that of

Trish rats). The homozygous “ mutant” race proved to be very stable

in color pattern, varying only from 514 to 534, with a majority of ani-

mals graded 514. Attempts to alter the modal condition of the race

112 THE AMERICAN NATURALIST [Vor. LI

by selection have thus far proved futile because of our inability to in-

crease the race sufficiently to afford a basis for selection. Its inbred-

ness and its feebleness are perhaps causally related.

The suggestion was made that the change from our plus-selected

race, which had occurred in the mutant stock, might be due to some

supplementary modifying factor, not to a change in the hooded factor

itself.* If so, a cross with a race lacking the hooded factor or its

“ modifiers ” might serve to demonstrate their distinctness by separating

one from the other. A wild race seemed best suited for a test of this

hypothesis, since it would be free from suspicion on the possible ground

of harboring either the hooded pattern or its supposed modifier, which

had converted the hooded pattern into the mutant. It was to be ex-

pected, if the hypothesis were correct, that the mutant character was

hooded plus modifier; that then a cross with wild should produce in

F, hooded young (lacking the modifier) as well as mutants and selfs.

But if the mutant race had arisen through a change in the hooded factor

itself, then the cross should produce only mutants and selfs, without

hooded young in F, Crosses have now been made on a sufficient scale

to show beyond question the correctness of the latter alternative, which

is entirely in harmony also with the results described in the preceding

parts of this paper

Six homozygous “ mutant” females of grade + 51⁄2 were mated with

wild males of the same race described in Part I. They produced 46

young, all gray like wild rats and of grades as follows:

Exactly half of the 46 F, rats bore no white spot, i. e., were of grade

Seven more bore only a few white hairs (grade 57%). The re-

mainder were very similar to the mutant parent in grade.

Several matings were made of the F, rats, brother with sister, which

produced 212 F, young. About a quarter of these were black (non-

agouti), the rest being gray (agouti). Both sorts included about equal

numbers of individuals with and without white spots. No difference

was observed in this respect between the progeny of spotted and of

unspotted parents. Table 158 shows the F, young grouped family by

family according to grade. Three of the four families are descended

from a single mutant grandparent; the fourth family is descended

from two different mutant grandparents which were bred simultane-

4 This also is MacDowell’s view. He says, p. 734: ‘‘The newly discovered

factor acts independently of the other factors, is not modified by them, and

does not modify them. Being the one difference between the mutant and

the plus race at the time the mutant appeared, this factor affords a crucial

test for the interpretation of the modifications that result from crosses.’’

No. 602] SHORTER ARTICLES AND DISCUSSIONS 113

ously to the same wild male in the same cage. The 10 F, young of

this family may have been produced either by full brother and sister,

or by half-brother and half-sister; it is uncertain which, All other

F, young were produced by brother-sister matings.

TABLE 158

Table 158 shows the classification of the F, young obtained by crossing

homozygous ‘‘mutant’’ with wild rats. -

Grade of offspring.

Mutant grandparents. Sad a Totals.

5 | 64 | 53 | 53] 53] 6 :

2 0630, De ie oe ot | 81a2t 91 2} 2 46

ee E OE ee te ae 1} 2/22/29| r] 59 114

A A O E ed 333) 481 Bet 9 42

9 0630, + 54, or 0636, + 53............ 11 Scab es 10

OE ee ee ee 1| 6|49/50| 3 103] 212

It will be observed that the F, young (table 158) which are white-

spotted are in no case hooded. Their range of variation does not fall

beyond that of the uncrossed mutant race. It is certain, therefore,

that the “mutant” condition is not hooded plus an independent Mende-

lian modifier. It is a changed form of white-spotting, alternative to the

form of spotting found in the race from which it was derived (the plus-

Selection series, generation 10). It is, without much doubt, also alter-

native to the self condition of wild rats, though fluctuation in grade ob-

Secures the segregation, which may, very likely, be imperfect. This

serves to confirm the general conclusion that throughout the entire series

of experiments with the hooded pattern of rats we are dealing with

quantitative variations in one and the same genetic factor.

CONCLUSION

I have now presented the évidence which has led me to reject

the hypothesis formerly held tentatively that modifying factors

were largely concerned in changes produced in the hooded pat-

tern of rats under repeated selection. This evidence seems to

me to admit of only one consistent interpretation, that a single

variable genetic factor was concerned in the original hooded

race, that a changed condition of this same factor was produced

in the minus race, and another changed condition in the plus

race, and a third appeared in the mutant race. All are allelo-

morphs of each other, and of the non-hooded or self condition

found in wild rats, yet all tend to modify each other in crosses.

The character has a high degree of genetic stability, yet is sub-

114 THE AMERICAN NATURALIST [ Vou. LI

ject to continuous genetic fluctuation. I have been unable to

produce or to discover any race of spotted animals which is free

from genetic fluctuation, though I have made an extended search.

If MacDowell or any one else has discovered such a race, let it

be produced.

It does not, of course, follow that because white spotting in

rats is capable of indefinite modification through selection, there-

fore all heritable characters are equally capable of modification.

Physiological limitations no doubt often limit the modifiability of

characters. A sugar-beet can not be produced which is all sugar

or much over 25 per cent. sugar. There has to be retained a

plant mechanism for the production of sugar, a beet. Neither

is it to be expected that the thorax of Drosophila can be deco-

rated with an indefinite number of extra bristles. The bristles

have to be attached to something, and the thorax of Drosophila

is finite in size. It is not necessary to suppose that hypothetical

modifying factors have been used up simply because variation

ceases to progress in a particular direction. For no one, I sup-

pose, would contend that variation is equally easy in all direc-

tions and in all characters. De Vries has taught us the signifi-

cance of one-sided variation and we have become familiar with

recurrent types of variation which are encountered first in one

species and then in another. Such cases show that different

kinds of germplasm are similar in structure and likely to under-

go similar changes. But what happens to these spontaneous

variations ‘when once they have put in an appearance depends

on external agencies, man or other factors in the struggle for

existence. The modern study of evolution has indeed empha-

sized the importance of spontaneous internal changes in pro-

ducing variations, but we still have to reckon with selection, nat-

ural and artificial, in determining the survival of variations as

well as in controlling their magnitude and the direction of their

further variation.

W. E. CASTLE

BUSSEY INSTITUTION,

T HILLs, MASS.,

December 20, 1916

No. 602] SHORTER ARTICLES AND DISCUSSIONS 115

FIELD TESTS OF THEORIES CONCERNING DISTRIBU-

TIONAL CONTROL?

THE conditions of animal distribution and the causes of these

conditions are facts which concern intimately the problems of

the persistence and of the evolution of species. The present

writer believes that the field naturalist is in a position to con-

tribute in large measure toward the solution of these problems,

and it is the purpose of this paper to show how comparative

studies in the distribution of species may throw light not only

upon the nature of the environmental complex, but also on the

relative importance of its various component factors.

Some simple facts of distribution which are of common obser-

vation, and which were early recorded by the systematic zoolo-

gist, are: (1) that each animal occupies a definite area, that 1s,

has a habitat or range, which is distinctive enough to be included

among the characters of the species and described along with its

habits and the features of its bodily structure; (2) that some

Species (and even some of the higher systematic groups) range

widely, and cover great extents of country, while others are ex-

tremely local or restricted in their distribution; and (3) that,

notwithstanding considerable variation in this degree of distri-

butional restriction, many species (or higher groups) are found

nearly or entirely to coincide in range, so that sets of species, of

varying ranks, may be recognized distributionally, as constitut-

ing realms, zones, faunas, subfaunas, associations, etc.

Perhaps the most prominent delimiting factor, and the one

which has been emphasized through repetition in the early sys-

tematic writings, is the obvious one of physical barriers—repre-

sented by bodies of water in the case of the terrestrial species

and by land in that of the aquatic. The majority of animals

inhabiting islands and seas are specialized in such a manner as

to be hemmed in by the limits of their respective habitats. In-

dividuals overstepping the barrier in either case are subject to

prompt destruction. This obvious type of distributional control

has always been and will remain an important one for consid-

eration; but with the acquisition of detailed knowledge regard-

ing the distribution of animals on large continental areas,

naturalists have been led to propose many other factors which

1 Contribution from the Museum of Vertebrate Zoology of the University

of California

116 THE AMERICAN NATURALIST [ Vou. LI

have seemed to them to prevent the random and unrestricted

spreading of animals over the surface of the land. The fol-

lowing is a list of the factors which various writers have nomi-

nated as affecting the distribution of the higher vertebrate ani-

mals. This list is complete only to the extent that my own exam-

ination of the literature is so. Many of the items have been

found in dissertations upon bird migration, which is, of course,

but one phase of the general subject of distribution.

Vegetation.

Food supply, kind and quantity.

Rainfall.

Humidity of the air (relative or absolute).

Wetness or dryness of the soi

Barometric pressure, or altitude:

Atmospheric density.

Safety of breeding places.

Availability of temporary refuges.

Water (to land species).

Land (to aquatic species).

Nature and availability of cover, or shelter from enemies.

Nature of the ground (coarse or fine soil, or rock).

Insolation, or light intensity.

-Cloudiness.

Temperature: in general; mean annual; of winter; of period

of reproduction; of hottest part of year.

Interspecific pressure, or competition, or race antagonism.

Parasitism

individual, or racial, preferences.

It is at once plain that some of the items enumerated are ex-

tremely complex, and that the most superficial analysis will |

show some duplication among them. For example, the factor of

vegetation as influencing the distribution of different mammals

resolves itself principally into the elements of food-supply and

shelter, and, subordinately in most cases, into those of tempera-

ture, humidity, and nature of the soil. As some of the suggested

factors may really never function in any vital degree as sup-

posed, the total number of really critical factors is probably

smaller than the total of the items just listed. Time could not

here be taken to discuss the intrinsic nature of each elemental

factor, even if the writer were equipped to handle such a variety

No. 602] SHORTER ARTICLES AND DISCUSSIONS il?

of subjects; for such a discussion would in most instances lead

directly into physics and chemistry, and into a study of the

physiological processes of the animals affected by each of these

factors. I should, however, like to dispose at once of one of the

‘*factors’’ listed, and which I hear and see repeatedly cited as.

a cause of restriction in distribution—particularly in that of

birds.

Many people claim to see in the facts of distribution only the

operation of a preference on the part of each animal—by virtue

of which, if a heterogeneous lot of animals were introduced into

an area presenting diverse conditions, each species would choose

its ‘‘natural’’ surroundings and rapidly allocate itself in a nor-

mal way. I grant that such a choice would almost certainly be

made. In fact the hypothesis is being proved continually all

over the country in connection with the migration of birds.

Seores of species travel north in the spring to countries for a

preceding interval unoccupied; and while, roughly speaking,

they travel together, and arrive together, they segregate them-

selves, immediately on their arrival, and repair to separate sorts

of ground, each species by itself: the pipits to the prairie, the

water-thrushes to the streamside thicket, the black-poll war-

blers to the spruce forest, and so on. We have here an obvious

choice exercised in the selection of habitats. But does this

segregation of species by exercise of ‘‘individual preference’’ in

a uniform direction change the nature of the problem in any

fundamental way? Should we not here recognize merely a char-

acter in the cerebral equipment of each race, which, like every

external peculiarity in its structure, is in considerable measure

the result of protracted impress upon the organism from the

environmental complex of factors to which the race has been

subject through past time? There is no other additional factor

than those environmental ones (plus the intrinsic fixedness of

the species, within certain limits of plasticity, and the ‘‘evolu-

tionary momentum’’) to be called into account.

As to the mechanism of geographic limitation, the adjustments

to the various critical factors are inevitably forever in process,

though reduced to a minimum at times of slow environmental

change. The refined method of individual ‘‘preference’’ or

‘choice’? is superior to the wasteful process of wholesale de-

struction which would be experienced by individuals finding

themselves out of place as the result of a haphazard selection of

118 THE AMERICAN NATURALIST [ Vou. LI

locality. The frontier individuals, those on the margin of the

habitat of the species, may not prosper as greatly, or reproduce

as prolifically, as those in the metropolis of their species ; but they

certainly do not, as a rule, beat themselves to death individually

against their limiting barrier, of whatever nature it may be.

To resume the main topic of this discussion, I shall attempt to

show that it is possible from field observation to indicate in the

case of certain species, some, at least, of the factors which con-

trol their distribution ; and further that we who live in Califor-

nia have splendid opportunities to gather and examine data by

means of which the general laws of animal distribution can be

determined. An area within comparatively easy reach presents

a wide diversity in topographic and climatic features. Occupy-

ing this area is an abundant complement of the higher vertebrate

classes. Within the political limits of the state, systematists now

recognize the presence of 388 species of mammals, 543 of birds,

79 of reptiles and 37 of amphibians. We have plenty of ma-

terial to work with. I shall proceed to discuss a few selected

species about which we seem to have knowledge enough to war-

rant provisional inferences.

THE CASE OF THE OREGON JAY

The Oregon jay (Perisoreus obscurus), a close relative of the

Canada jay, or whisky-jack, occurs in California only in the

northern third of the state. Even there it is very local in its oc-

currence and absolutely non-migratory. On the Warner Moun-

tains, Modoe County, it ranges from the highest parts down to >

7,000 feet altitude. On Mount Shasta it ranges from near tim-

berline down to about 6,000 feet altitude. It is absent for a

long distance to the west, through the Trinity mountain mass,

but it recurs along the seacoast of Humboldt County, within fifteen -

miles of the ocean. And here is the curious point: along this

coast strip it does not range higher than 300 or 400 feet above

sea level, although there are mountains not far inland which rise

to an altitude of several thousand feet. Let us look into this

ease for the purpose of determining the factors responsible for

this interrupted range. ,

The Oregon jay, like most members of the crow family, is not

restricted in diet. It eats a great variety of both vegetable and

animal substances; its food varies in character according to

season and local conditions. -The supply of any particular kind

No. 602] SHORTER ARTICLES AND DISCUSSIONS 119

of food is not likely, therefore, to be a controlling factor in its

distribution.

he bird is a forest dweller. Its equipment as regards man-

ner of flight and course to take in case of attack by enemies is

adjusted to a forest habitat, and nowhere within the writer’s

knowledge does this jay extend its range beyond the limits of

woods of some sort. Although somewhat predaceous itself, it

has regular enemies among hawks and owls, for protection from

which it makes use of forest vegetation. This factor of forest

cover, then, must be counted as essential. But the range of the

bird is not continuous wherever forests extend.

In the interior of California it does not descend below a cer-

tain altitude. Now three other factors in its distribution are

quite obviously connected with that of altitude, namely, baro-

metric pressure, atmospheric density, and temperature. But

when we take into account the fact that the Oregon jay exists

at or close to sea level around Humboldt Bay, the first two fac-

tors, those of pressure, and air density, are instantly eliminated,

because of the obvious fact that the bird successfully maintains

itself in localities of widely differing altitude where these factors

are thus extremely diverse.

With reference to temperature, we know without recourse to

instrumentation that there is a decrease upwards at an average

rate of 3 to 4 degrees F. per thousand feet. If, then, the bird

is limited downwards at a critical point, the inference appar-

ently follows that temperature is the determining factor, and

this conelusion is inevitable if we consider only Mount Shasta

and the Warner Mountains. But the bird’s oceurrence at Hum-

boldt Bay complicates the problem. In order to reconcile these

facts of distribution we must look into the situation with refer-

ence to season. On doing so we discover that the home of the

Shasta and Warner jays is subject to severe winters with heavy

snow, very much colder than the winters at Humboldt Bay,

where the climate is equable and snow rarely falls. But the

summer temperature at Humboldt Bay is well known to be much

cooler than that of even somewhat higher regions in the interior,

up to an altitude of at least 4,000 or 5,000 feet, because of the

eastward moving air-currents, which are coolest where they first

leave the sea surface and warm up as they pass farther and far-

ther inland. We are therefore led directly to the final inference

that the summer temperature at sea level about Humboldt Bay

120 THE AMERICAN NATURALIST [ Von. LI

closely approximates the summer temperature at from 6,000 to

9,000 feet on Mount Shasta and above 7,000 feet on the Warner

Mountains. In these three areas, the air is cooler in summer

than in the interlying areas and thus better adapted to the finely

adjusted requirements of the Oregon jay. Summer tempera-

ture, between certain degrees, is one critical factor.

Three more factors present themselves for consideration in

connection with the Oregon jay, those of humidity, rainfall and

cloudiness. Humboldt Bay lies in the most humid and continu-

ously rainy section of California. Mount Shasta and the War-

ner Mountains are relatively arid, the latter most notably so.

It would appear, therefore, that humidity, rainfall and cloudi-

ness had little or nothing to do with cutting off the range of this

bird, though one or other of these factors may have been respon-

sible for the very slightly darker tone of color which distin-

guishes the coast jays (subspecies Perisoreus obscurus obscurus)

from those in the interior (P. o. griseus). But, however this

may be, it is clear that temperature must dominate greatly over

the three factors named in checking dissemination.

In summary, we may therefore dispose of the following fac-

tors as having little or no effect on the distribution of the Oregon

jay as a species: the nature or quantity of its food supply, at-

mospherie density and pressure, cloudiness, rainfall, humidity

of the air or soil, and winter temperature. This eliminates all

but the two factors: shelter of a sort provided by the forest

habitat, and temperature of the summer season.

THE CASE oF THE Cony

The cony or pika is a mammal represented in California by

four quite similar races (Ochotona taylori, O. schisticeps schistt-

ceps, O. s. muiri, and O. s. albatus) , which agree distributionally in

occupying a very restricted habitat along high mountain crests.

I know of no place in central California where conies range

below an altitude of about 8,000 feet, and they range upwards

to fully 12,000 feet in the vicinity of Mount Lyell. They thus

occupy an altitudinal belt between extremes 4,000 feet apart.

With regard to zones of vegetation conies live from considerably

below timberline to considerably above timberline. Exten

observation shows that their existence is in no way correlated

with that of trees or shrubs of any sort. Like their relatives, the

rabbits, they feed entirely on low vegetation, biennials mostly ;

No. 602] SHORTER ARTICLES AND DISCUSSIONS 121

but unlike most kinds of rabbits they are strictly dependent for

safety from enemies upon rocks, especially where these are

loosely piled as in talus slopes and so afford deep retreats within

their interstices. The whole equipment of a rabbit is clearly

adapted to foraging in the open, its keen hearing and eyesight

quickly warning it of the approach of enemies, and giving it

time to escape by means of its unusual running powers. But

the cony is equipped in a very different way, as it has relatively

small ears and eyes, and small hind legs. It is compelled to

forage close to or beneath cover. In fact in field observations it

is rarely seen on the move except momentarily, and then only

between or beneath angular granite blocks, where it grazes on

such little patches of vegetation as are within immediate reach.

Tt is clear from numerous observations that the cony is sharply

restricted in a large part of its range by the rock-pile habitat.

Even at favorable altitudes it is not found away from this

refuge. There are obviously, however, one or more additional

factors in its distribution. In many parts of the Sierras, talus

slopes occur from near the highest summits down to the foothills.

As examples of these, one may cite the vast earthquake taluses

of the Yosemite Valley proper, which occur almost continuously

down to and below the 4,000-foot contour. These taluses have

been searched diligently both by trapping and hunting, without

our naturalists finding a trace of conies below 8,000 feet. The

animals are easy to detect, by reason of their characteristic ery,

uttered at any time during the day, though more particularly in

the morning and the evening, and by the accumulations of their

feces, the pellets constituting which are, in size, shape and tex-

ture, unlike those of any other mammal. What is it, then, that

limits the conies downward on the western flank of the Sierras,

where their necessary rock habitat is continuous, and where food

of the right sort is also continuous? Let us try barometric pres-

sure, and atmospheric density, which may properly be consid-

ered together. These conditions change sensibly with altitude

and, if we take into account California alone, the facts would

Seem to entitle them to serious consideration as active delimitors

of the conies downward. But as we trace the range of the conies

far to the northward we are led to a different conclusion. The

altitudinal limits of their range is found to descend quite regu-

larly towards the north, until, in the case of one race, even sea

level is reached, at Bering Sea. Clearly, conies, generically, are

t22 THE AMERICAN NATURALIST [Vou. LI

thus proven not to be affected by atmospheric pressure, or by

atmospheric density, at least in as far as it is modified by alti-

tudes ùp to 12,000 feet. The same fact—depression of range

towards the north—discloses a third concomitant of altitude,

which is also a concomitant of latitude, namely, temperature,

and this is beyond doubt the determining factor. As the iso-

therms dip toward sea level to the northward so does the range

of the genus Ochotona. We have, therefore, by study of geo-

graphical distribution in this case established two important con-

trolling factors, namely (1) safety refuges of a sort provided by

talus slopes and glacial moraines; (2) temperature, at least

downward below the degree, correlated in the mountains of Cali-

fornia by a mean annual or summer computation or for a briefer

period at the time of reproduction, with an altitude of eight to

twelve thousand feet, according to latitude, slope exposure and

air currents.

It is not possible for one to say from the data in hand what

the direct controlling factors of the upward limits of the cony’s

range may be. Taluses extend up to the highest peaks, but there

is no growth of grass above about the 12,000-foot contour even on

‘the most favorable slopes. As the disappearance of the cony in

the higher altitudes is coincident with the disappearance of its

food, it appears as if failure of food alone were the delimitor

ere; but we have no way of showing that even if food did con-

tinue the cony would be restricted upward, as it certainly is

downward, by a change in temperature beyond some critical

point. The cause of its delimitation downward, however, re-

mains clear.

THE CASE OF THE Rosy FINCH

In the case of the bird called generically Leucosticte, or rosy

finch, we find a condition astonishingly similar to that of the

cony. In fact almost the entire preceding account could be

måde relevant here, by merely substituting the term rosy finch

for cony. The ranges, altitudinal and geographical, of the two

animals are almost identical. The only obvious differences ap-

pear in their ecologic relations, and consist in the lesser de-

pendence of the bird upon shelter and in the dissimilar nature

of its food. The rosy finch forages gregariously on the open

slopes, near timberline and above, though its nest is hidden

_ away in the clefts of rock ledges and taluses. It shuns the trees

No. 602] SHORTER ARTICLES AND DISCUSSIONS 123

and bushes even where it ranges well below timberline. It feeds

winter and summer upon seeds of dwarfed vegetation, including

those of grass and herbs of various sorts. As far as I can see,

its food and feeding habits are identical with those of such other

fringillids as goldfinches and siskins. Yet the leucosticte, by

the same tests as were used with the cony, is beyond any conten-

tion limited downward by an increase of temperature. We fin

the bird to possess various adaptive features in common with cer-

tain arctic finches, such as tufts of bristle-like feathers over the

nostrils to prevent fine snow from entering. These enable the

bird to spend the long winter on the cold wind-swept ridges, but

at the same time would hardly prevent the bird’s dropping to

warmer climes if the heat were not a strongly deterrent factor.

Cases of coincidence, as instanced by that of the cony and

leucosticte, among animals of widely different powers of locomo-

tion and ecologic position, are the rule, not the exception, and

impel the observer to belief in the efficacy of the controlling fac-

tor above mentioned.

THE CAsE OF THE Repwoop CHIPMUNK

The redwood chipmunk (Eutamias townsendi ochrogenys) is

an animal confined to a very narrow but exceedingly long dis-

tributional area extending south from the Oregon line as far as

Freestone, Sonoma County. Throughout this belt it is conspicu-

ously numerous, and is usually the only species of chipmunk

present, so that the limits of its range have been easy to mark

definitely along the several lines explored. This rodent, by

Various geographic tests similar to those I have recounted for

other birds and mammals, is clearly delimited away from the

- coast at the bounds ‘of the well-known fog-belt to which the red-

wood tree and numerous other plants as well as animals belong.

The chipmunk, however, depends in no way upon the redwood

or any other one plant species as far as I can see, but feeds

upon a great variety of seeds and fruits, like many of its con-

= geners elsewhere.

- That temperature is also a delimiting factor is shown in parts

of the range of the redwood chipmunk. But atmospheric humid-

ity or cloudiness or rainfall, factors which I have in this case

failed to dissociate, together constitute or include the chief

controls.

124 THE AMERICAN NATURALIST [Vou. LI

THE CASE OF THE BELTED KINGFISHER

It is to be observed that specialization for getting a particu-

lar kind of food invariably brings with it restriction of range to

the territory providing that kind of food. The northwestern

belted kingfisher (Ceryle alcyon caurina) is a good example of

this. In California we find this bird present at various times

of the year both along the seacoast and along various fish-support-

ing streams, from the Colorado River to the Klamath River and

up the mountain streams to at least as high an altitude as Yosem-

ite Valley. The kingfisher is seen during migration in many

places away from streams, but it tarries at such times only where

its natural diet can be procured, as, on occasion, at fish ponds in

city parks. There is a unique instance of a kingfisher observed

on the desert catching lizards, but exceptional occurrences of

this kind are of course not to be given consideration in making

generalizations.

It is observable further in regard to this species of kingfisher,

that it must have earth banks in which to excavate its breeding

tunnels. Lack of these along any stream, otherwise favorable,

prevents the bird from staying there through the season of re-

production. Furthermore, there is also obvious temperature re-

striction ; for, given a fish-producing stream, with banks appar-

ently well suited for excavation of nesting places, such as is the

Colorado River and its distributaries, and the summer tempera-

ture must be at least below that of southern California south of

the 35th parallel. That all such streams are well supplied with

kingfishers in winter, and are forsaken only during the hot sum-

mer, seems to show that a relatively cool temperature is for them

in some way or another essential to successful reproduction.

We find, then, in the case of the belted kingfisher, that the fac-

tors of a requisite kind of food, and a requisite kind of nesting

place, both having to do with the structural powers and limita-

tions of the bird, together with the factor of the temperature of

the summer season, are those that account for the distribution

of the species within the state of California, as we find it.

THE CASE OF THE MEADOWLARK

The western meadowlark (Sturnella neglecta) is a bird of

relatively omnivorous diet. Note that I say relatively, for the

word omnivorous unmodified would apply only to such an ani-

No. 602] SHORTER ARTICLES AND DISCUSSIONS 125

mal as would eat the sort of food that any animal eats, and this

is an obvious impossibility for the meadowlark when we con-

sider such uncommon articles of diet as wood and petroleum.

Compared with many other birds, the meadowlark does use as

food a very wide range of plant and animal objects. This food,

however, is restricted to a particular habitat source, namely to

the meadow. The bird’s entire equipment specializes it for

successful food-getting and for escape from enemies upon a

grassy plain or meadow. And it is a matter of common obser-

vation that its range is sharply delimited in most directions at

the margin of the meadow habitat, as where this is interrupted

by forest, brushland, marsh, rock surface or sand flat. This is

a conspicuous example of what we may call associational restric-

tion. But it is not the only way in which the meadowlark is

hemmed in. In this connection California again provides crit-

ical distributional evidence.

e find meadowlarks occupying practically every appropriate

meadow, large and small, from the Mexican line to the Oregon

line and from the shores of the Pacific to the Nevada line, ez-

cept above a certain level on the higher mountains. In travel-

ing up the west flank of the Sierras, and this I have now verified

along three sections, meadowlarks cease to be observed at ap-

proximately the 4,500-foot level, and this in spite of the fact that

above that altitude meadows are found which are to all appear-

ances ideal for meadowlark requirements. I need only refer to

such seemingly perfect summer habitats as Monache Meadows

and Tuolumne Meadows. And though, in the winter these

would be uninhabitable, so are other meadows (as those in the

Modoc region, for instance), which are in summer warm and at

that season abundantly inhabited by meadowlarks. By the elim-

ination then upon proper grounds of various factors from the

list, we have left only three possible factors in this upward de-

limitation, namely, decreased atmospheric pressure, decreased

air density and decreased temperature of the summer season.

Since meadowlarks exist at corresponding altitudes in the warmer

though elevated Great Basin region, and since it has been pos-

Sible to eliminate positively and in a similar way the first two

factors in the cases of many other birds and mammals, these fac-

tors are presumably sana pence on the meadowlark; and

there is left but one—tem

Within the state of APOE meadowlarks, without the

126 THE AMERICAN NATURALIST [Vou. LI

slightest detectable subspecific modification, thrive under both

the cloudy, humid conditions of the northwest coast belt and

under the relatively cloudless, arid conditions of Owens Valley.

Factors of humidity, of air and soil, cloudiness, and light in-

tensity, seem to avail nothing in checking their spread. With

such a degree of associational specialization as is exhibited by

these birds there is little chance of a serious competitive struggle

with other vertebrates, and no evidence of such has been ob-

served. As far as California is concerned, the meadowlark’s

range is thus only limited associationally and zonally, that is

by the extent of its particular meadow habitat and. by dimin-

ished summer temperature below some critical point.

The meadowlark well illustrates some further facts with re-

gard to distribution. In California it is unquestionably on the

increase as regards total population. This is due chiefly to the

great extension of habitable territory resulting from man’s oc-

-eupancy and cultivation of the land, bare plains, brushlands and

even woods being replaced by irrigated alfalfa and grain fields.

These the meadowlarks find suitable and invade because of their

expansive reproductivity, and soon populate to the fullest ex-

tent permitted by the minimum annual food supply. In other

words, associational barriers have moved, to the advantage of

this particular bird, though at the same time to the disadvan-

tage of endemic species of different predilections. I should esti-

mate that the total meadowlark population in the San Joaquin-

Sacramento basin is now fully three times what it was thirty

years ago.

Animal distribution is not fixed. It changes with the shifting

of the various sorts of barriers, and doubtless also as a result of

a gradual acquisition by the animals themselves of the power to

overstep barriers, as by becoming inured to greater or lesser de-

gree of temperature. The power of such accommodation, or in-

herent plasticity, evidently varies greatly among different ani-

mals; and at best its operation is very slow. Many species have

proved stubborn and have been exterminated, as the factor-lines,

or barriers, shifted. By the shifting of, say, two critical factor-

lines towards one another, the existence of a species may have

been cut off as by a pair of shears.

No. 602] SHORTER ARTICLES AND DISCUSSIONS 127

SUMMARY

In this paper I have enumerated various factors thought to

be concerned with the control of the distribution of vertebrate

animals. A number of birds and mammals have been cited to

show how we may use our more or less detailed knowledge of their

ranges so as to demonstrate the operation of one or several out

of the many possible factors as limiters to distribution. The

method employed is one of examination, comparison and elim-

ination, applied to all parts of the margin of animals’ ranges.

The range of any one animal must be examined at all points of

its periphery in order that all of the factors concerned may be

detected. One factor may constitute the barrier in one section

of the periphery of the range of a species, a totally different fac-

tor in another section.

The results of the geometric ratio of reproduction would

bring about areas of occupancy in the shape of perfect circles.

But we never find such symmetrical ranges. The very fact that

the outlines of the ranges of animals are extremely irregular is

significant of the critical nature or inexorableness of the factors

which delimit them. These factors have to do with the evolu-

tion, persistence and extermination of species.

Note that we always have to take into account, in attempting

to discern factors of limitation, the animal’s own inherent struc-

tural equipment. This prescribes restriction at once in certain

regards. Referring again to our list of suggested factors, we find

the long-emphasized ones of land to aquatic species and bodies

of water to terrestrial species really presenting an extreme mani-

festation of associational restriction. Food source, methods of

food-getting and safety refuges are involved.

It is to be noted further that the factors are various and that

the most important factor for one species may prove of little

effect with another species. Species do not react uniformly to

the same environment. It is undoubtedly always a combination

of factors which accounts for an animal’s geographic range in

all parts of the periphery of that range. It is most certainly

never one factor alone. No one will claim that temperature is

the only delimiting agent in controlling vertebrate distribution ;

nor could this claim be made for humidity alone, or for food

supply alone, or for safety of breeding-places alone.

Given a large continuous area, however, as upon the North

128 THE AMERICAN NATURALIST [ Von. LI

American continent, one single factor does happen to loom up

as being the most frequent delimiter of distribution, or even the

ultimately effective one, in greater or less degree, even though

other factors be effective also. This factor is temperature.

The cases cited illustrate the tenet that in some direction or an-

other, temperature beyond certain limits, up or down, cuts off

further dissemination. This is part of the basis of the life-zone

idea. But, as I have tried to bring out above, this fact is in no

way antagonistic to the claim that other factors, as of humidity,

food supply, and shelter, also figure critically, giving a basis

for recognizing faunal areas and associations. Finally, if our

discussion of the subject has been sound, it is evident that data

secured through field observation can be so employed as to bring

results essentially similar to, and as conclusive as, these secured

through laboratory experimentation.

JOSEPH GRINNELL

MUSEUM OF VERTEBRATE ZOOLOGY,

UNIVERSITY OF CALIFORNIA,

November 1; 1916

THE

AMERICAN NATURALIST

Vot. LI. March, 1917 No. 603

THE BEARING OF SOME GENERAL BIOLOGICAL

FACTS ON BUD-VARIATION?!

PROFESSOR E. M. EAST

Bussey INSTITUTION, HARVARD UNIVERSITY

I taxe it no one denies that in the Angiosperms vari-

ations may be produced in connection with reproduction

by means of buds and that these variations may be per-

petuated by the same method. Practically, as horticul-

turists and plant breeders, we care little about the occur-

rence of bud-variations elsewhere in the organic world.

Nevertheless, it may help in the orientation of our ideas

if we remember that budding is not a rare or unconven-

tional method of reproduction. In a generalized form,

the earliest method, it has persisted throughout the plant

kingdom from the most primitive to the highest and most

Specialized types. Sexual reproduction has not replaced

it, but has been added to it. Even in the animal kingdom,

though eliminated among the higher forms, it still exists.

as an occasional alternate method in three fourths of the

phyla. Such being the case, it would seem logically to

follow, that variation must have been within its possi-

bilities.

The cause, the frequency, the type, the constancy, the

mechanism, of these variations are more debatable, how-

ever, and on these questions many biological facts which

superficially seem unconnected, have a direct bearing. In

1 Read before the meeting of the Society for Horticultural Science, De-

cember 28, 1916.

129

130 THE AMERICAN NATURALIST [Vou. LI

fact, on certain phases circumstantial evidence is the only

evidence at hand.

The exact nature of the cause or causes of bud-variation

can hardly be discussed profitably. We may imagine

irregularities of cell division directed by combinations of

unknown factors, but to describe these factors in concrete

terms is at present impossible. At the same time, cause

can not be neglected entirely even at present, for cause in

a generalized sense is intimately connected with frequency

in that vigorous perennial the question of the inheritance

of acquired characters. The data on this subject are so

voluminous that each for himself must give them careful

conscientious consideration. Here no more can be done

than to point out some of the conclusions to which I, per-

sonally, have been driven, and their connection with the

subject in hand. These conclusions are:

1. Broad and varied circumstantial evidence indicates

unmistakably that the inheritance of acquired characters

has played an extremely important rôle in evolution.

2. Numerous experimental investigations designed to

test the possibility of such inheritance directly have either

failed utterly or have been open to serious destructive

criticism. Direct proof of the inheritance of acquired

characters is therefore lacking.

3. If conclusions 1 and 2 are to be harmonized, either

modifications are fully inherited so rarely that proof that

they do not belong to the general category of chance

changes in constitution of the germ-plasm is impossible,

or the imprint of the environment is so weak that ex-

tremely long periods of time—perhaps geological epochs

—are necessary for its manifestation. .

Diametrically opposed views on the inheritance of ac-

quired characters are held tenaciously and unequivocally

by equally eminent biologists. Those who concur with

the Lamarekian position are nearly always the students

of evolution who approach the subject from the historical

or the philosophical side and who rely almost entirely

on circumstantial evidence; those who adhere to the side

No. 603] BUD-V ARIATION 131

of Weismann are usually experimentalists whose evi-

dence is indeed direct, but often questionable, usually

capable of various interpretations, and always fragmen-

tary. I have been bold enough to grasp both horns of

the dilemma, and to plead that each is right from his point

of view. My confession of faith is, the environment has

been an immense factor in organic evolution, but its

effects are shown either so infrequently or after the elapse

of so great a time, that for the practical purposes of

plant breeding we can neglect it as we would neglect an

infinitesimal in a calculation. As Bergson, I think, said:

We have been trying to prove that the hour hand moves, in a second

of time.

A few words will make clear the general arguments in

favor of this position, although adequate support to the

thesis would require considerable time.

In the first place, it seems to me the possibility of the in-

heritance of acquirements must be admitted. Weismann’s

general contention that the chromatin of the germ-cells

is the actual hereditary substance, and that the germ-cells

themselves may be regarded as one-celled organisms re-

producing by fission and conjugating at certain times,

while the body must be considered simply an appendage

thrown off from and independent of the germ-cells, is not

supported merely by the embryological researches of

Boveri, Kahle and Hegner on two or three animal forms,

or by the ingenious ovarian transplantations made by

Castle and Phillips on guinea pigs, but by all of the recent

pedigree culture and cytological genetic work, botanical

as well as zoological. Nevertheless it has not been and

logically can not be proven that there is no way for en-

vironmental forces to produce germ-plasmic changes.

Memory is just as strange a phenomenon and Semon has

done biology a service by pointing out the analogy be-.

tween the mechanical requirements for memory and for

the inheritance of somatic modifications.

This possibility being admitted, one may well concede

the plausibility of the arguments of the numerous pale-

132 THE AMERICAN NATURALIST [Vou LI

ontologists, taxonomists and ecologists in favor of La-

marckian principles, in spite of the fact that their evi-

dence is circumstantial. They take a comprehensive view

of the actual conditions that exist among organisms,

which is impossible to the experimentalist. It will not do

simply to say that the manifest convergence of analogous

organs in all parts of the organic world, or the wonderful

adaptations of the social insects may be explained in some

other way. Of course there may be other explanations

for these phenomena; but until more satisfactory ex-

planations are forthcoming it is rightfully a custom in

science that the adequate interpretation at hand should

be accepted.

On the other hand it is equally wrong for the ardent

devotees of Lamarckism to clutch at every isolated case,

every inadequate and abortive experiment, when judicial

consideration shows not a single unassailable instance of

the inheritance of a somatic modification. Many of these

experiments have a direct bearing on bud-variation, and

I shall attempt to show where they lead us.

1. Inheritance of Mutilations.—The most radical La-

marckians of the present day only go so far as to sup-

pose that mutilations are inherited on very rare occa-

sions—and they are always zoologists. Ethnology has

furnished us with so many histories of mutilations of

ears, of lips, of feet, of reproductive organs, long con-

tinued in the folkways of a people, that new laboratory

experiments have been deserving of the ridicule they

have received. Botanists have seldom had any delusions

on the subject. Plants are so continually mutilated in

the buffetings they receive during life, with no resulf in

the next generation, that the non-inheritance of the effects

of such injuries is taken as a matter of course. Yet there

is occasionally one whose reason fails at the critical

moment, and who holds that cuttings from the chrys-

anthemum with the large flower resulting from the re-

moval of lateral branches, will produce larger flowers in

the next generation than will an untreated sister plant.

Tf not this, some equally indefensible doctrine.

No. 603] BUD-V ARIATION 133

2. Effects of Changed Food Supply.—This last ex-

ample was really one of changed food supply induced by

mutilation. Change of food supply by other methods has

been the basis of scores of experiments, particularly on

-insects. Many insects are so very whimsical about what

they eat that it seems possible their selective appetite

may be an inherited instinct impressed by the environ-

ment of countless generations. But the total result of all

experiments on them is merely to prove that a second

generation may be influenced in the start they get in life

by the nutrition of the mother. '

The same thing is true in plants. We fertilize a pop

corn to get a bumper crop of good plump healthy seeds,

but we don’t expect a dent corn as the next year’s result.

We very properly endeavor to give our potatoes a bal-

anced ration, in expectancy of a larger yield of well-

matured, healthy tubers, but we should not expect these

tubers to affect our next season’s supply other than by

their health. Similarly we take scions from well-lighted

parts of the tree where growth has been good. In such

twigs the graft union heals easily and properly, and a fit

channel for conveying nutrients is established. In doing

these things we are practising sanitation or preventive

medicine, as it were, a laudable proceeding. But the hor-

ticulturist who promises a different variety by such

means is illogical and misleading.

Yet we find Bailey so imbued with the idea of making

out a perfect case for Lamarckism that he lends the

weight of his authority to the following statement among

others :?

Whilst these ‘ ‘sports?’ are well known to horticulturists they are generally

considered to be rare, but nothing can be farther from the truth. As a

matter of fact, every branch of a tree is different from every other branch,

and when the difference is sufficient to attract attention, or to have com-

mercial value, it is propagated and called a ‘‘sport.’’

We may admit the differences between the branches of

a tree without cavil. What is more serious is the impli-

2 ‘í Survival of the Unlike,’’ p. 72.

134 THE AMERICAN NATURALIST (Vou. LI

cation to the reader that all variations have the same co-

efficients of heredity, that a bud-variation is simply a

wide fluctuation imposed by external conditions. If this

were true the whole organic world would be chaos. But

species and varieties do exist. They may be ‘‘judgments”’

in one sense, but in another they are concrete things. In

fact we learn this further on in this volume when it suits

Bailey’s purpose to have asexually propagated varieties

very constant. He says (p. 353):

At first thought this fact—that varieties may be self-sterile—looks

strange, but it is after all what we should expect, because any variety of

tree fruits, being propagated by buds, is really but a multiplication of one

original plant, and all the trees which spring from this original are ex-

pected to reproduce its characters.

3. The Effects of Disease.—The influence of disease is

in many ways like that of malnutrition, in that it is wholly

an effect on the physiological efficiency of the reproducing

cells. This fact is fairly clear when dealing with diseases

with outstanding symptoms. In many instances, how-

ever, diseases are not easily diagnosed. There may even

be no suspicion that disease is present. In such cases it

is rather hard to believe that selection is not accomplish- -

ing a positive and radical improvement. A good ex-

ample of this is the selection of potato tubers. No one

consciously selects a seed potato infected with blight. In-

dependent of the probability of reinfection, there is the

likelihood that the diseased tuber will not be able to pro-

duce a normal plant because of the effect the fungus has

had on its own cells. One doesn’t usually believe, how-

ever, that rejection of this tuber and selection of the

healthy sister is going to lead to the formation of a new

race. Yet numerous experiments on potatoes in which it

is shown that successive selections have raised the

average yield over that of the unselected tubers, are prob-

ably of just this type. The race is kept up by the re-

jection of diseased tubers, but there is no evidence what-

ever that it is improved. I am not going to argue that

desirable asexual variations may not occur during this

time, and be retained. I say only that any improvement

No. 603] BUD-V ARIATION 135

indicated by the raw data must be discounted by the

amount of deterioration shown by the unselected variety

under similar conditions. Such deterioration is very

common, and is due to disease, I believe, rather than to

any supposed disadvantage of asexual reproduction

per se.

This category of facts has been cited under the discus-

sion of the inheritance of acquired characters, because

such phenomena have perplexed other than botanists.

Belief in the transmission of disease, or the effects of dis-

ease, by sexual reproduction was current for many years.

It is only since the possibility of infection in the egg

itself was demonstrated for various diseases, that the

true state of affairs has been known.

Many other types of experiments designed to demon-

strate Lamarckism might be cited, but they have no direct

bearing on bud-variation except in so far as a positive

case would affect our general attitude on the frequency

of their occurrence. They are all similarly negative or

questionable, however, so that we must conclude with

Weismann that no case of inheritance of acquirements

has been proved beyond a reasonable doubt. In other

words we grant such a possibility but believe it to be so

rare or so gradual that practically it may be disregarded.

In reality one could hardly have expected any other

conclusion from the type of experiment by which the

question has been attacked. Generalized they are some-

thing like this. Species X having been grown under en-

vironment A for numerous generations is removed to en-

vironment B. An adaptive change occurs which persists

during several generations. Later the descendants of

the original plants are returned to environment A and

the change is reversed. When the reverse change occurs

more slowly than the original change, it is argued that

Lamarckian inheritance is shown. The logic used to draw

such a conclusion is indefensible, even if the difficulty of

correcting properly for changes due to normal heredity

is left out of consideration.

If acquired characters are inherited and the changes

136 THE AMERICAN NATURALIST [ Vou. LI

induced are reversible, the long period under environ-

ment A should have produced a deep impression on

species X. Change under environment B should be slow.

Reversal should be rapid, however, because of the slight

impression environment B must be supposed to have

made during the very few generations in which its influ-

ence was possible.

If acquired characters are not inherited, precisely the

same changes should occur, owing to somatic adaptation,

the only differences being that the total amount of change

in each case would be reached in the second generation

after the environment had acted during the earliest stages

of the life history.

If, on the other hand, the changes induced by environ-

ment B are not reversible, judgment must be based on

the percentage of individuals changed by B and not re-

changed by A. One can readily see how a just judgment

would be clouded by probable reversible somatic effects

in such cases. Instances of the inheritance of acquire-

ments, unless they were very frequent, which from our

general evidence is unthinkable, would be indistinguish-

able from ordinary chance variations. |

Such methods of attack on the subject being almost

predestined to failure from the inherent difficulties of

the problem, it would seem wiser to seek for a more hope-

ful methodology, and in the meantime to accept the only

conclusion justified by the data at hand; namely, the

inheritance of acquired characters is either so rare an

occurrence or so slow a process, that by plant-breeders

it may be assumed to be non-existent. One realizes of

course that the problem of sexual transmission of somatic

acquirements is not necessarily the same as that of asex-

ual transmission, but the experimental results have been

the same in both eases. Let us, admit, therefore, that.

one can not hope to obtain real improvement in asexually

propagated varieties merely by selecting buds from

plants or parts of plants which have developed under

especially favorable conditions.

This does not mean that radical environmental changes

No. 603] BUD-V ARIATION 137

may not be the direct cause of such a modification. Dr.

H. J. Webber once informed the writer that immediately

after the great Florida freeze of the early nineties bud-

variations in the citrus fruits of that region were greatly

increased. Such variations may have been induced by

the freezing, but they were not adaptive variations.

The conclusions reached thus far have not involved a

point of theory which practically is difficult to separate

from the one just discussed. It is this. If we disregard

adaptive variations, is there not still a reason for select-

ing fluctuations? Are there not internal factors which

so act that there is a narrow but appreciable variability

in an asexually produced population which may offer a

basis for selection? In other words, how constant is an

asexually propagated race?

We can make an effort to compute the frequency of

marked bud-variations. But have we any right to assume

that these represent the sum total of all bud-variations?

Are not bud-variations and perhaps all inherited vari-

ations like residual errors, the small ones frequent, the

large ones rare? This may be the case, but I should like

to emphasize the fact that we have no true criterion for

determining the size of a variation. A variation that ap-

pears large by visual criteria may be an extremely small

change in the constitution of the plant, and vice versa.

In view of this fact together with the practical consid-

eration that commercially valuable variations must be

measurable within a reasonable duration of time—say a

lifetime—it is by no means certain that we are going far

astray in calculating the frequency of bud-variations by

the so-called marked jumps or mutations.

Furthermore the range of the fluctuations of asexually

propagated varieties of most species is very small even

when broadened—as it always is—by the addition of the

effects of variable external conditions. It is not hard to

recognize a Winesap apple, a Clapp’s Favorite pear or a

Concord grape, even though these varieties have heen

srown extensively for a considerable number of years.

Certain local subvarieties of the pome fruits are said to

138 THE AMERICAN NATURALIST (Vou. LI

exist, but they are so extremely rare that one may admit

all cases of disputed origin and still have very little

asexual variation to account for.

I have never seen a published calculation of the fre-

quency of bud-variation, and presume it would be of little

value anyway, since the general evidence indicates a dif-

ferent frequency for different species and even for the

same species at different times. It may be mentioned,

however, that in personal examination of over 100,000

hills of potatoes belonging to several hundred varieties,

12 definite bud-variations have been seen, a frequency of

1 in 10,000; while just as careful a scrutiny of about

200,000 plants belonging to the genus Nicotiana has

brought to light but 1 case.

Probably a more practical and just as satisfactory an

estimate of the frequency of bud-variations in economic

plants is the record of varieties that have been produced

in this manner. Naturally such a record contributes little —

to theory because only a portion of the variations arising

are observed, and only a fraction of those observed are

propagated. Further, the origin of comparatively few

commercial varieties is known. Yet we may get some idea

of what to expect in the future, by noting what has oc-

curred in the past.

Data gathered in this manner will appear to give us

different values depending on how we approach the

matter. For example, in Cramer’s wonderful monograph

on bud-variation, the grape is cited as one of the species

that often varies in this manner. He cites some 25 or

more such varieties. Yet in the large list of American

grapes in Hedrick’s ‘‘Grapes of New York’’ only one

doubtful case of bud-origin is reported. When one re-

members that hundreds of varieties of grapes are grown

and millions of vines are examined each year, improve-

ment by this method seems rather hopeless. And ex-

amination of the list of present-day apples, pears, plums

and cherries, of the bush-fruits, or of potatoes—all groups

of considerable horticultural importance—is still more

disappointing. for I venture to say that the varieties of

No. 603] BUD-V ARIATION 139

these types in cultivation which have originated as bud-

variations can be counted on the fingers of one hand.

At the same time it would be wrong not to attribute

any importance to bud-variation as a plant breeding ad-

junct. Cramer lists several hundred chrysanthemums

and over a hundred roses as of bud-origin, as well as a

smaller number of varieties in species where bud-varia-

tion appears to be less prevalent. Further, Shamel is

said to have found bud-variation in the citrus-fruits to

be sufficiently common to be worthy of an extended inves-

tigation.

These species, heen with perhaps the banana and

the pineapple—the origin of whose varieties is little

known—are the outstanding examples of comparatively

frequent bud-variation, picked from our whole long list

of cultivated plants. The first two examples, moreover,

are species belonging to the domain of floriculture, where

rather superficial characters such as color are valuable.

In very few other species have bud-variations been re-

corded in sufficient numbers to justify us in employing

any other adjective than ‘‘rare’’ in describing them. And

of the sum total of these varieties only an extremely small

percentage are of such a nature that agriculture would

suffer a material loss if they were eliminated.

Perhaps these last statements appear to imply a very

limited type of bud-variations. This is not true. Bud-

variations are wholly comparable to seed-variations in

their nature, but they are handicapped because recom-

binations of variant characters are possible only in sexual

reproduction. N bud-variations in a species are simply

N variations, but N seed-variations may become 2" seed-

variations provided they are not linked together i in hered-

ity. An immense advantage thus accrues in favor of

seminal reproduction because by far the greater number

of commercially valuable characters are complex in their

heredity, i. e., they are represented in the germ-plasm by

several factors independently inherited.

Cramer divides bud-variations into the same classes

that de Vries has used for sexual mutations: progressive,

140 THE AMERICAN NATURALIST [Vou. LI

where new characters arise; retrogressive, where a char-

acter becomes latent or lost; and degressive, where latent

characters become active. In this important monograph

practically all recorded bud-variations to the date of pub-

lication, 1907, are discussed. Yet not a single case of

progressive variation is listed. They are all catalogued

as retrogressive or degressive. Their classification is

correct, however, only when a progressive variation is

defined as the addition of a character wholly unknown in

the previous history of the species.

As examples of what bud-variation does produce we

may well study Cramer’s painstaking work. There are

losses of thorns, hairs and other epidermal characters,

together with an occasional degressive change of the

same kind. There are changes in color in vegetative

parts. Green becomes red or ‘‘aurea’’ yellow, or a loss

of anthocyan occurs. Sometimes the changes are such

that the plants remain striped or otherwise variegated.

Flowers and fruits exhibit the same types of color varia-

tions in considerable numbers. They are mostly losses,

with the appearance of what in Mendelian terminology

is called hypostatic colors, but once in a great while

epistatic colors recur anew.

Monstrosities appear. Other parts of the flower take

on the appearance and form of petals or of sepals. Dou-

bling occurs in several different ways. Fasciations arise.

Changes in the character of the reproductive apparatus

are not uncommon, sometimes giving us seedless fruits.

Plants change their habit of growth. They become

dwarf. They retain juvenile characters. They become

laciniate, or develop the trait known as ‘‘weeping.’’

Thus we see that bud-variation is not limited in its

manifestations; and what is more important, we realize

that bud-variations are very comparable to seminal varia-

tions, there being hardly a type of change known in

sexually reproduced plants that has not been duplicated

asexually. What then is the difference, if any, between

true somatic changes and true germinal changes in con-

stitution? We can get clues which indicate a fairly satis-

No. 603] BUD-V ARIATION 141

factory solution of this problem from three different lines

of research, pedigree cultures, graft-hybrids and cell-

studies.

It is a noteworthy fact that the character of the progeny

produced sexually by bud-variations has been studied in

a comparatively few cases, and in most of these instances

self-pollinations were not made. Nevertheless Cramer

believes the following conclusions are justified:

1. In a vegetative Mendelization, of the progeny of a

branch with the positive character 75 per cent. have the

character and 25 per. cent. are without it, while the prog-

eny of a branch without the character all lack it.

2. In a vegetative ‘‘Zwischenrasse’’ by which he gen-

erally means a variegated race, of the progeny of each

type (original and variant), a part retain and a part lack

the character, the percentage being variable.

3. In a vegetative mutation, by which he means any

change not a ‘‘Zwischenrasse’’ and which did not appear

to him to be Mendelian in type, of the progeny of a branch

retaining the positive character, either all possessed it or

a part were with and a part without it, while the progeny

of a branch without the character were all of the same

type.

If we allow for some deviation due to cross-pollination,

I believe that Cramer’s records support this view, and

that modern genetic research suggests the interpretation.

In the first place, the ‘‘Zwischenrasse’’ are evidently

of the type studied principally by Correns and by Baur

in sexually reproducing races. They are due to chro-

matophore changes, and in many cases at least are not

the result of nuclear activity. This being true, one would

expect in neither asexual nor sexual reproduction the

same type of inheritance for variegated races that obtains

for other types of variation. Inheritance will parallel

cytoplasmic rather than nuclear distribution; an expecta-

tion apparently realized for both types of reproduction.

Omitting the ‘‘Zwischenrassen’’’ therefore, we have two

phenomena to explain, both of which are similar to cases

of inheritance in sexual reproduction where chromatin

142 THE AMERICAN NATURALIST [Vou. LI

distribution parallels the facts. In each instance the

negative variant—may we call it the recessive—breeds

true. In one case the positive variant breeds true, in the

other case it gives a simple Mendelian ratio.

The mechanism necessary for such phenomena is not

difficult to picture. Bud-variations are many times more

frequent in hybrids, that is, in plants heterozygous for

one or more characters, than they are in pure species.

This is the view of Cramer, this was the view of Masters,

the eminent English student of bud-variations and tera-

tological phenomena, this was the conclusion drawn by

the present writer in several articles published some

years ago. Such results would be obtained either when

the proper germinal change occurs in the chromosome

whose mate lacks a character for which the plant is hetero-

zygous; or, when there is a dichotomy in which the chro-

mosomes of such a pair are not halved but pass the

material basis necessary for the production of the posi-

tive character to one daughter cell and not to the other,

provided the daughter cell lacking the character gives

rise to a branch.

A bud-variation in a character for which the plant was

homozygous would be obtained only when simultaneous

like changes occur in both chromosomes of a homologous

pair, or when the material basis necessary for the pro-

duction of the positive character all passes to one daugh-

ter cell, as described above.

This hypothesis would account for the fact that hetero-

zygotes give rise to bud-variations more frequently than

homozygotes, since a germinal change seldom gives rise

to a new positive character, and a change in one chromo-

some of an identical pair tending toward the production

of a recessive, would not show in the latter case.

T am not certain that this hypothesis may not with

reason be applied to variations that are usually consid-

ered seminal. There is no particular ground for assum-

ing that such variations occur only at the maturation of

the germ-cells. We know that progressive variations of

whatever origin are extremely rare. Why then may not

No. 603] BUD-V ARIATION 143

most variations be produced in cell divisions previous to

the formation of the germ-cells? When recessive we

should not note them as bud-variations unless the plant

is heterozygous and the mutating cell gives rise to a

branch; when dominant we should only note them in the

latter eventuality. But if these mutating cells should

later give rise to germ-eells, the change would become

apparent in the progeny.

We have still one other hypothetical case to consider.

It is said that some bud-variations are not transmitted

by seed. I have not been able to trace an authentic case,

but such is the general belief, fathered, I think, by Dar-

win. The usual citation is the nectarine, which sometimes

is said to give nectarines but at other times gives only

peaches. Whether trichome characters only behave thus

I do not know. But if that be true, we can understand

why if we refer to Winkler’s work on the so-called graft-

hybrids.

Winkler found that the most interesting of these pecul-

lar phenomena are caused by the tissue of one species

growing around the tissue of the other. He therefore

gave them the euphonious name of periclinal chimeras.

Cytological examination showed that the epidermal tis-

sues only are from one race, the remaining tissues being

from the other. It is really a symbiosis and not a union.

Now as the germ-cells are formed wholly from subepi-

dermal and never from epidermal tissues, the seeds of

these plants always produced seedlings like the type

forming the inner cell-layers.

It seems probable that the production of the nectarine

may be analogous. If the change producing the nec-

tarine occurs after the epidermal tissue has been segre-

gated from other tissues, the cells which are ancestors

of the germ-cells should not be affected and the nectarine

seedlings would give peaches, If, on the other hand, the

change producing the nectarine, has occurred before any

such segregation, the progeny sexually produced should

in part be nectarines.

THE PROBABLE ERROR OF A MENDELIAN

CLASS FREQUENCY?

DR. RAYMOND PEARL

1. Wir the increasing volume of Mendelian experi-

mentation there is an ever-growing need for adequate

and clearly understood tests for the statistical significance

of differences between observed results and expectation.

A number of different methods of making such tests have

been proposed and used by different workers. For ex-

ample, early in the discussion of Mendelism, Weldon?

made use of the ordinary, and frequently inadequate, ex-

pression for the standard deviation of a sub-frequency

c= Vnpq. Johannsen? has also made much use of this

method. It has several defects. In the first place it as-

sumes the Gaussian distribution of the errors, an assump-

tion not often strictly warranted, as Pearson‘ has clearly

shown, and in many cases grossly in error. In the second

place it is not even approximately adequate under certain

extreme conditions (frequently realized in Mendelian

work) of class frequency. Harris® has proposed the x’

‘‘xoodness of fit’’ test for comparing observed and ex-

pected Mendelian distributions. There are several fea-

tures of this method which greatly limit it for such use.

Among these are (1) its failure to make correct allowance

for ‘‘tail’’ frequencies (it is just this class of very small

ecm which one most often wants to test in prac-

Papers from the ai Laboratory of the Maine Agricultural Ex-

sien Station No. 108. e author is greatly indebted to his assistant,

Mr. John Rice Miner, for Ki laborious arithmetic involved in Section 6 of

the paper

per.

2 Weldon, W. F. R., ‘‘ Mendel’s Laws of Alternative Inheritance in Peas,’’

pies bo Vol. I, pp. 228-265, 1902.

3 Johannsen, W., ‘‘Elemente der exakten Erblichkeitslehre,’’ Zweite Aus-

gabe, Jen 1913.

4 Pearson, K., ‘‘On the Influence of Past Experience on Future Expecta-

en ed ner Maj, verpnti 1907, pp. 365-378.

rris, J. A., ‘‘A Simple Test of the Goodness of Fit of Mendelian

hie? ? AMER. Nar, Vol. XLVI, pp. 741-745, 1912. Cf. also Pearson,

K., and Heron, D., ‘‘On Theories of Association,’’ Biometrika, Vol. IX, pp.

159-315, 1913.

144

No. 603] MENDELIAN CLASS FREQUENCY 145

tical Mendelian work), and (2) the fact that the test takes

into account only the magnitude of the error and not its

direction (i. e., whether in excess or defect) in any par-

ticular case. (3) It gives a result not particularly well

adapted to the actual needs of Mendelian research. The

x? test gives a measure of the goodness of fit of the

whole distribution, and only that. Now besides being in-

terested in that point the Mendelian worker quite as often

wants to know, in addition, something about the prob-

ability that particular classes observed are significantly

different from the expected. To that sort of knowledge

the x? test helps him not at all. It is an ‘‘all or none”

sort of method.®

2. It has seemed to the writer that it would be useful

to discuss methods of determining the true probable error

of each class frequency in Mendelian distributions as a

supplement to the x? test, and for use in cases where it is

not applicable. The fundamental theorems have all been

given by Pearson’ in a very important paper, which is

apparently almost entirely unknown to biologists. The

purpose of the present paper is first to show the appli-

cability of these theorems to the problem in hand, and

second to point out some matters regarding the practical

use of the method likely to be helpful to biologists with

but little mathematical training who may attempt to

use it.

3. In the paper referred to, Pearson, starting from

Bayes’ theorem, shows that the distribution of chances

of an event occurring in a particular way in a second

€I have earlier pointed out other objections to the x2 test in Mendelian

work, in particular its total failure to deal with cases where experiment

yields a small frequency on classes where the expectation is zero, and need

not further discuss them here. I have never thought it necessary to make

any rejoinder to Pearson’s Ne on bitter reply to my criticism,

nor do I yet. The x2 test leads to this absurdity: if I perform a Men-

delian experiment in which I get ni thousand million offspring agreeing

perfectly with expectation save for one lone individual (perhaps a mutation,

Perhaps a mistake in the record, or what not) which is of a sort not ex-

pected, then Pearson and the x2 test agree that the probability is infinitely

eet that the ten thousand million offspring do not follow Mendelian law!

earson, K., loc. cit.

146 THE AMERICAN NATURALIST [Vou. LI

sample from a population from which a first sample has

produced a certain value is given, not by the ordinates of

a normal curve of errors, as is commonly assumed in writ-

ings on the theory of probability, but by the successive

terms of a simple hypergeometrical series. In an earlier

paper the same author had solved the problem of the

momental properties of the hypergéometrical series.

Combining the two results he was able to derive the neces-

sary equations for the complete solution of the problem

of probable errors in sampling. We may proceed at once

to the exposition of these results, referring the reader for

the proofs to the papers of Pearson cited.

Let it be supposed that a first sample of n= p + q be

drawn from the population, p denoting the number of

times the event dealt with occurs in the v trials, and q

the number of times it fails.

Write

whence of course

p+q=1.

We then have for the chief constants of the error dis-

tribution for a second sample, of magnitude m, drawn

from the same population the following values:

ae H o eg é

Mean’ = mp + 749 — P) (i)

Mode = the integral ees of mp + p, (ii)

Standard Deviation = | m (z p +: wF 1-2)

x (a-pa) +g) ao

These values are entirely general, and independent of

the values of n, m, p and q. Under certain circumstances,

8 Pearson, K., ‘‘On Certain Properties of the Hypergeometrical Series,

and on a "Fitting of such Series to Observation Polygons on the Theory

of Chance,’’ Phil. Mag., Feb., 1899, pp. 236-246.

ə From origin at the lower range end, or r= 0.

No. 603] MENDELIAN CLASS FREQUENCY 147

as when n is very large as compared with m, and neither

p nor q are very small, (i) and (iii) are obviously capable

of being put in much simpler form and still giving a

sufficiently close approximation to the true result. For

Mendelian work, however, where frequently neither of

these conditions are even approximately realized, it will

in general be better to use the full expression as given

above.

The ordinates of the error distribution (the chances of

different occurrences) are given by the successive terms

of the hypergeometrical series

m p+1 , m(m—1) (p+1)(p+2)

cas -0147 ‘qtmt 2 UGA

ap ME 2) (p+1)(p+2)(p+3)

3 (q-+m)(q-+m—1)(q+m—2)

m(m—1)(m—2)(m—3)

j 4

x (p+1)(p+2)(p+3)(p+4)

(q-+m)(q+m—1)(q-+-m—2)(q+m—3)

(iv)

+etc. l,

where

T(q+m+1)0(n+2)

Co= G4 DT tm+2)"

(v)

As we shall presently see, the calculation of the terms

in (iv) becomes a tedious and laborious matter when the

number needed is at all considerable. Under such cir-

cumstances, and when in addition m and are even mod-

erately large, equation (iv) may be greatly simplified,

without significant loss of accuracy, by the use of Ster-

ling’s theorem (to the bracket) or by Forsyth’s approxi-

mation for such of the factorials as are not included in

the range of the Pearson!’ tables. Thus we have, by

Sterling’s theorem, apenas that r denotes any term

in the series, and writing s=m—rT,

10 ‘Tables for Statisticians and Biometrieians,”” ¢ edited by Karl Pear-

fon, Cambridge, 1914.

148 THE AMERICAN NATURALIST [Vou. LI

(P T | mrtg + s)etet8 ;

Using Forsyth’s approximation, which is extremely ac-

curate, one gets

Etri ientrar katoi N hes

pir | Esa) QH gm) +R) J *

The gamma terms in (v) will, of course, be caleulated

by some one of the well-known approximations (e. g.,

Sterling’s, Pearson’s, Forsyth’s) or by interpolation

from a table of factorials (Pearl'').

4. The proposal which I wish to make for the expres-

sion of a Mendelian result is that the expectation be

expressed as the quartile limits for each class frequency

in a second sample of the same size as the observed

sample. In using such an expression it must be clearly

understood that it does not measure the goodness of fit

of the distribution as a whole, because it takes no account

of correlations in errors. What it does give, in supple-

` ment to the x? test, is the limits of probability of each class

frequency, taken by itself.

The ordinary expression for a probable error (e. g.,

P. E. mean = + .67449(c/Vn)) gives the quartile limits

(i. e., the limits within which one half the frequency oc-

curs) on the assumption that the distribution is Gaussian,

since in such a distribution of unit area the quartile limits

are .6744898 . . . times the standard deviation on either

side of the mean. But in our persent work we are making

no assumption that the error distribution is Gaussian.

Consequently we must determine the quartiles directly

from the distribution. In cases where the number of

terms is not too great the ordinates may be calculated

from (iv) or (vi) and summed to find the quartile. In

many cases, however, this would be practically too tedious

CeCi

11 Pearl, R., ‘‘ Interpolation as a Means of Approximation to the Gamma

Function for High Values of n,’’ Science, N. S., Vol. XLI, pp. 506-507,

1915; ‘‘On the Degree of Exactness of the Gamma Function Necessary in

Curve Fitting,’’ Ibid., Vol. XLII, pp. 833-834, 1915.

No. 603] MENDELIAN CLASS FREQUENCY 149

an operation, and we may resort to an approximate

method. The simplest one is to take .67449¢ on either

side of the median, which is approximately determined

by remembering that the median lies between the mean

and the mode and approximately twice as far from the

-= mode as from the mean. The criterion of whether this —

method of fixing the quartile limits may be safely applied

will be found in the value of the skewness, Sk. In prac-

tical work this approximate method will give sufficiently

accurate results unless the skewness is very large, say

> 0.6. 7

We have by definition

Sk =

Q1&

(viii)

Hence having calculated the values of mean, mode and «

by (i), (ii) and (iii) we can readily obtain (viii), since

d= mean — mode.

We may now pass to the consideration of some numer-

ical examples, by means of which certain facts can be

better brought out than by further theoretical discussion.

5. As a first and simple example we may take some

data, recently published by F. L. Platt,!? on the results of

mating Blue Andalusian fowls. On account of the fre-

queney with which the Blue Andalusian case is cited as a

paradigm in Mendelism, coupled with the great dearth in

the literature of exact statistics of actual matings of this

breed of poultry, it seems especially worth while to dis-

cuss these statistics furnished by Mr. Platt, on the au-

thority of Mr. W. J. Coates, a breeder of Andalusians.

Table I gives the data, and in the last line, the Men-

delian expectation expressed in the form suggested in this

paper.

The occurrence of the ‘‘dark reds,’’ which Mr. Coates

informs us had a pattern like a Red Game, is a phenom-

enon not mentioned in textbook accounts of Mendelian in-

heritance in the Blue Andalusian. In the present con-

12 Platt, F. L., ‘‘ Western Notes and Comment,’’ Reliable Poultry Journal,

Vol. XXIII, p. 665, 1916.

150 THE AMERICAN NATURALIST [Vou. LI

TABLE I

SHOWING THE RESULT oF Martine BLUE X BLUE IN THE BLUE ANDALUSIAN

or POULTRY (Coarres’ DATA)

Oftspring

Mating

White Blue Black oo

W. O ERE EE E E EN EEES 4 10 3 1

MESS ESA REAM CANT BOs sg SANA EE 4 5 2 0

Cri 3 3 0 3

BP Di 0 12 1 0

fi OPRESL AER NEES DEL Meare ene CGM a PI kon TRS ee eo 3 3 1 0

SUA GDNGEVER Co. ce Cre Ot eet | 14 | 33 7 4

Total observed in Dre a white, (2) | me

blue, (3) pigmented not blue............ 14 | 33 11

-If the true ratio is 1 white : 2 fears 1 pig-

mented not it is an even chance,

considering each class by itself, that the

_ frequencies in a sample of this size

fall between. ie a ss SS 11.5 and | 25.8 and 11.6 and

17.8 32.9 17.8

nection, however, we can not pursue that point, but will

group together, as in the penultimate line of the table, the

blacks and reds as ‘‘pigmented, not blue,’’ and assume

that the three classes should occur in a 1:2:1 ratio. Do

the actual results bear out this assumption, having regard

to the errors of sampling?

Examining the last two lines of the table, it is clear that

each observed class, taken by itself, is by no means an im-

possible approximation to what would be demanded by a

1:2:1 ratio. The blues and the ‘‘pigmented not blues’’

fall outside the range for which the probability is 4 but

only slightly outside. It would be practically an even

bet, if Blue Andalusians really follow a law of 1:2:1

segregation when bred together, that any particular sam-

ple of 58 offspring would show in each particular class as

great a deviation as the present sample.’

Now we may consider in detail the mode of calculating

the figures in the last line of Table I.

13 Always on the assumption, of course, that it is legitimate to lump the

blacks. and reds together. There is room for scepticism on that point, but

we are here only concerned with the case as an illustration of method.

No. 603] MENDELIAN CLASS FREQUENCY 151

We have, by hypothesis, and from the statistics

E =D8.

A distribution of 58 in a 1:2:1 ratio is 14.5:29:14.5.

Assume a first sample of 58 to show exactly this distribu-

tion 14.5 :29:14.5, what will be the mean frequency of one

of the end classes, say white, expected in a second sample

of 58?

We have

ac A45

p= 5S. = 205,

g = .75,

whence, by (i),

Mean = 14.9833,

and, by (ii),

Mode = 14,

a=. .9833.

By the approximate method we get

Median = 14.656 approximately.

The standard deviation from (iii), is

o = 4.6364,

and, by (viii),

SR aye? A

Actual tests with curves of a degree of skewness no

greater than this show that the approximate method gives

the quartile limits with sufficient accuracy for practical

purposes. We have for the approximate quartile limits,

67449 X 4.6364 = 3.1272. This value, added to and sub-

tracted from the median 14.656, gives the results set down

in the last line of Table I.

Exactly the same procedure, with different numbers, is

followed in the case of the blue column.

6. Let us now consider a more completely worked out

illustration. Some time ago Mr. Alexander Weinstein, of

Columbia University, consulted the writer in regard to a

152 THE AMERICAN NATURALIST [Vou. LI

problem which had arisen in connection with his Men-

delian breeding experiments. A certain type of mating

gave the following class frequencies:

(2)

6363 + 579 + 3638 +- 1208 + 128 + 115

+ 350 + 6 = 12387 ... (a).

Another group of matings gave a total of 9,017 off-

spring, of which 30 fell in the v class, this being the only

class in regard to which a comparison is to be made. On

certain theoretical grounds the percentage frequency in

this æ class in the second sample would be expected to be

0.582 times the percentage frequency of this same class in

the first sample. The question is whether the actually ob-

served frequency of 30 in this second sample is such as

could reasonably be expected to occur if the theoretical

assumption actually were the fact.

It will be seen at once that, owing to the very small ab-

solute frequency of this x class in both samples, ordinary

probable error methods will be of no avail.

Approaching the problem by the method here proposed,

we have, as basic values for the computations,

n= 12387

m= 9017

pe 41d, ¢ = 12272

p = p/n = .009284

g=q/n = .990716.

Whence we have for the mean in the second sample of

9017 by (i)

Mean = 84.428137

and by (iii)

o = 12.020652.

By (ii) the mode—83, whence d—1.428137

and

1.428137

sk = 12.020652

= 0.118807.

No. 603] MENDELIAN CLASS FREQUENCY 153

Working directly from the moments of the hypergeo-

metrical series and, in effect, replacing that series with a

true curve, we find-

Mode = 83.222141,

d= 1.205996, and

Sk = 0.100327 F .008696.

TABLE II

Meio wiied THE SUCCESSIVE ORDINATES OF THE HYPERGEOMETRICAL SERIES

R THE SECOND SAMPLE

r G Sum r C, Sum r cx. . Sum

35| .000000 | .000000 | 73 | .022620 | .182838 | 111 | .003215 | .983125

36} .000001 | .000001 | 74 | .024355 | .207193 | 112 | .002740 | .9858

37 | .000001 | .000002 | 75 | .025996 | .233189 | 113 | .002325 | .988190

_ 88] .000002 | .000004 |. 76 | .027539 | .260728 | 114 |. .001964 | .990154

39 0 77 | .028943 | .289671 | 115 | .001651

40 | .000005 | .000012 | 78 319854 | 116 | .001382 | .993187

41 000020 | 79 | .031236 | .351090 | 117 | .001152

42| .000013 80 | .032085 | .383175 | 118

43 000053 | 81 | .032715 | .415890 | 119-| .000791 | .996087

44| .000031 82 | .03311 44 120 1 | .996738

eo 000130 033285 | .482291 | 121 | .00053. 99727

46| .000068 | .000198 033220 | .515511 | 122 | .000436 | .997707

47 297 | 85 54844 23 | .000354 | .998061

48 | .000142 86 | .032419.| .580859 | 124 | .000287 | .998348

49 000639 | 87 | .031706 | .612565 | 125 | .000231 | .998579

50| .000279 8 | 88 643370 | 126 | .000186 | .998765

51 001301 | 89 | .029738 | .673108 | 127 | .000149 | .998914

52| .000520 | .001821 | 90 | .028526 | .701634 | 128 | .000119

3 | .000696 | .002517 | 91 | .027193 | .72882 29 999127

t| .000919 | .003436 | 92 | .025763 | .754590 | 130 | .000075 | .999202

>| .001199 63 93 | .024262 | .778852 | 131 | .000059 | .999261

ìà | 001545 | .006180 2271 15 132 | .000046

57 | .001967 | .008147 | 95 | .021136 | .822699 | 133 | .000036.

58| .002476 96 | .019556 2255 | 134 999371

59| .003082 | .013705 | 97 | .017991 | .860246 | 135 | .000022

60| .003793 | .017498 | 98 16459 | .876705 | 136 | .000017 | .999410

61| .004617 99 | .014974 | .891679 | 137 | .000013 99423

62 .005561 | .027676 | 100 522 38 | .000010 | .999433

63 2 305 | 101 | .012195 | .917424 | 139 999441

64| .007821 | .042126 | 102 | .0 928341 | 140 | .000006 | .999447

65 051261 | 103 | .009722 | .938063 ! 141 | .000005 | .999452

66 | .010569 830 | 104 | .008614 | .946677 | 142 | .000004

67 | .012109 939 | 105 | .0075 .954270 | 143 | .000003 | .

68| .013743 | .087682 .006 144 | .000002 | .999461

69| .015455 | .103137 | 107 | .005813 | .966743 | 145 | .000001 | - 2

40} .017223 | .120360 | 108 | .005049 | .971792 | 146 | .000001 | .999463

71| .019025 | .139385 | 109 |. .976156 | 147 | .000001 | .999464

12| .020833 | .160218 | 110 | .003754 | .979910

The two sets of values are evidently sufficiently near

together to be used interchangeably for most practical

154 THE AMERICAN NATURALIST [Vou. LI

purposes, a sort of result which is familiar to any one

who has had any considerable experience with the method

of moments.

To return now to the series we find, using 10-place

logarithms in the intermediate computations and the

Forsyth approximation,

log Co = 72.8493814 — 100.

We have now to calculate the successive terms of the

series. If this were done for the whole range it would in-

volve a literally colossal amount of labor. Fortunately

this is not necessary. We need only take that part of the

range which includes appreciable frequencies. By a few

trials we find that this part of the range begins with

r= 36. In Table II are given the frequencies for the

several terms in the series between r— 36 and r—147 in-

clusive, the total area being taken as unity. To reduce

these frequencies to the actual numbers for the second

sample we have only to multiply in every case by 9017.

We have calculated C;, by (vii) and used the Forsyth Co.

From this table we easily deduce

Median = 83.5331,

Lower quartile = 75.6104 (ix)

Upper quartile —91.8218.

Now, remembering that if the same law holds for the

second Mendelian distribution as for the first we should

expect the x class in that distribution to be 0.582 times the

value of the same class in the first distribution, we have

Expected mean value of v class in

second distribution = 49.14

Expected modal value of x class in

second distribution = 48

Expected lower quartile value in

second distribution — 44.01

Expected upper quartile value in

second distribution — 53.44

No. 603] MENDELIAN CLASS FREQUENCY 1565.

The actual experimental value obtained was 30, which

is far below the lower quartile. From Table II we find,

remembering again that on a priori grounds the experi-

mental frequencies are reduced by the factor 0.582, that if

the two distributions were really samples of the same

population, obeying the same Mendelian laws, it would

be expected that the æ class would show a frequency as

low as or lower than 30, only 18 times in 10,000 trials of

samples of 9017. Or, in other words, the odds against

so low a value as 30 are about 556 to 1. These are about

the same odds as those associated with the occurrence of

a deviation 4.63 times the probable error (cf. Pearl and

Miner").

We may, therefore, conclude with great certainty that

the value of 30 is significantly smaller than would be ex-

pected to occur in the x class on the basis of chance (de-

viation due to random sampling) if the two distributions

were really samples of the same population.

Let us now go back and approach the problem de novo

by the approximate method suggested in section 4. We

ave

d—= mean — mode = 1.4281,

a ns = .4760,

‘84.4281 — .4760 =—83.9521—median (approx.),

12.0207 X .67449= 8.1078,

83.9521 — 8.1078 —75.8443— Lower quartile,

83.9521 + 8.1078 = 92.0599 = Upper quartile.

Comparing these values, in the obtaining of which all

the tremendously tedious and time-consuming arithmetic

involved in calculating Table II was avoided, with those

shown in (ix) makes it quite evident that for all practical

statistical purposes the approximate method would have

given sufficiently accurate results.

14 Pearl, R., and Miner, J. R., ‘‘A Table for Estimating the Probable

Significance of Statistical Constants,’’ Me. Agr. Expt. Stat. Ann. Rept. for

1914, pp. 85-88.

156 THE AMERICAN NATURALIST [Vou. LI

SuMMARY

In this paper is presented a method of calculating and

expressing the errors, due to random sampling, of a Men-

delian class frequency. The method consists essentially

in expressing each expected Mendelian frequency as the

probable quartile limits for that class frequency in a sup-

posed second sample of the same size as the observed

sample drawn from the same population. These quartile

limits are determined from the ordinates of a hypergeo-

metrical series. Various simplifications of method are

suggested and illustrated. The method is suggested as a

supplement to, not as a substitute for, the x? test for the

goodness of fit in Mendelian distributions.

OBSERVATIONS ON THE ECOLOGY OF THE

PROTOZOA

By LEON AUGUSTUS HAUSMAN

CORNELL UNIVERSITY

A great deal of excellent work has been done in census

taking among the Protozoa, and numerous catalogues of

species with descriptions and accompanying plates have

been issued for various states or portions thereof. This

present communication, however, is a slight contribution

toward census taking of a different sort, in that it aims to

set forth some facts regarding the different types of Pro-

tozoan habitats and the species usually associated with

each. It is well known that certain common forms, used

as type species in the laboratory (such as Ameba proteus

and Paramecium caudatum), can be found only in certain

fairly definite environments. The ecology of such forms

is well known, but the bionomics of the majority of the

Protozoa is still virtually a res ignota. The study of en-

vironmental units and Protozoan communities will con-

tribute to a more intimate knowledge of these elusive

forms.

Although little is definitely known concerning the ecol-

ogy of the Protozoa, yet I think that we are in position to

say that Protozoan inhabitants vary with their varying en-

vironments. A record of the inhabitants of a marsh pool

will not include the same species normally found in clear -

running streams, nor will cold waters yield the same forms

as warm. But we can go still farther, I think, and say that

the various portions of any given environmental unit,

even though they differ ever so slightly from one another,

will each have its own characteristic group of organisms.

The factors which are accountable for the variation in

Species or numbers of individuals of any species in such

instances ° may be hardly discoverable, but they are none

the less potent. Thus the entrance point of a tiny thread

158 THE AMERICAN NATURALIST [Von LI

of clear spring water in the midst of an impure pool may

furnish an abundance of Monas and Cercomonas, and

because of the presence of these, also the larger carniv-

orous forms such as Dileptus or Onychodromus. Or the

growth of myriads of bacteria at another point may induce

the increase in the numbers of Vorticelle, Amebe, or

Holophrye. A complete study of the multitudinous

minute variations in the environments of Protozoa, and

their complex relationships with the associated species is

still far away. But I believe that we are now ready to

undertake a preliminary survey of a number of typical en-

vironments and to ascertain what genera and species may

be normally expected to occur in each.

Of the many factors responsible for the localization of

species, the following are perhaps first in importance:

light, character of food, temperature of water, chemical

content of water, presence or absence of enemies.

Light exerts a powerful influence in determining the

distribution of species within a given body of water. Thus

one will find certain species in sunlit areas and certain

others in shaded ones. Not all of the Protozoa respond to

ordinary light stimuli, as has been shown experimentally

by Jennings. He has found that comparatively few of

the ciliate infusoria react to light stimuli. The flagellates,

on the other hand, show a definite reaction, congregating

in that region where the light is ordinarily strongest. The

reactions of Euglena viridis and Cryptomonas ovata are

the forms which have been most carefully studied in this

regard.

Jennings! further showed that Paramecia collect in

those regions of the water which contain a trace of any

weak acid, and this I have noted to be true of certain other

ciliates. This may be a dominant influence in localizing

forms in pools and streams in marshes where organic

acids are usually present. The presence of supernormal

amounts of oxygen, carbon dioxide, calcium carbonate,

iron, and other dissolved substances may also affect the

distribution of species.

1‘*Contributions to the Study of the Behavior of Lower Organisms,’’

H. S. Jennings, Washington, 1904.

No. 603] ECOLOGY OF THE PROTOZOA 159

Not only may the various stimuli arising from the dif-

ferent elements of the environment assort species into

communities, but the effects of these stimuli may not

always be the same. A given stimulus may at one time

produce a certain type of reaction, and at another time a

somewhat different type. This fact, also, experimentally

verified by Jennings, led him to suppose that something

analogous to, if not identical with true varying ‘‘ physio-

logical states’’ obtains in the Protozoan body. If this be

so then the problem of Protozoan ecology is still further

complicated, as far as any assignment of species to definite

fixed local environments is concerned.

For collecting Protozoa and water samples the writer

has found the following useful: a small silk plankton net

(with draw string bottom) about six inches in diameter

and ten inches deep; a glass or metal pipette, fully a foot

in length, operated by a compression bulb at one extrem-

ity, for sucking samples of light sediments from the bot-

toms of pools and streams; several small glass dipping

tubes; a large table spoon; a thermometer, and a plentiful

supply of variously sized water tight jars with screw

tops. With such an outfit as this the material described

in the following paper was secured. The samples were

examined immediately after being brought into the lab-

oratory, in order that the proportions of species might be

accurately recorded.

From each sample ten slides were searched. The sig-

EE of the terms few, numerous, rare, etc., is as fol-

ows:

Over ten individuals of one species per slide ....... abundant

Average of 6206s aroiu ke ben ee EC a numerous

Average Of 2-600 is ans sis se sa Vas eid several

Ave OF ME SEATS asan e ee Seen few

Average Ol Tell hin B o nc sv cies cnenices rare

The samples were taken from the uppermost layer of

silt on the bottoms of pools, streams, etc., the utmost care

being taken not to disturb the sediment below or to roil

the water. Upwards of fifty samples were secured repre-

senting five distinct environmental types. These five

types described are: `

160 THE AMERICAN NATURALIST [Vou. LI

No. 1. Characteristic marsh pools.

No. 2. Clear cold lakes and streams with no plant life.

No. 3. Clear springs and streams with plants abundant.

No. 4. Small, clear pools containing organic sediment

in decomposition and fed by pure, cold rills.

o. 5. Ditches and pools choked with alge, water warm.

All of the material was taken during the months of late

spring, summer, and early fall, while the aquatic vegeta-

tion, and the semiaquatics about the water margins, were

in vigorous growth.

ENVIRONMENTAL Tyrer No. I: Marsu Poors

Characteristic frog-inhabited marsh pools, containing

much decaying vegetable matter, supporting rank growths

of typical marsh plants about the margins, covered with

lily pads and filled with Ceratophyllum, Myriophyllum,

Sagittaria, duckweed, ete. Water warm, and emitting

characteristic swampy odor.

Predominant forms:

Ameba limaz, several Difflugia globulosa, numerous

Ameba proteus, several Euglypha alveolata, numerous

mæba radiosa, several Oikomonas sp., numerous

Arcella vulgaris, numerous Peridinium cinctum, abundant

Carchesium polypinum, numerous Stylonychia mytilus, numerous

Codonocladium umbellatum, numer- Stylonychia pustulata, numerous

ous ‘

Coleps hirtus, abundant Synura uvella, numerous

Coleps sp., abundant Trinema acinus, numerous

Difflugia acuminata, numerous Vorticella microstoma, numerous

Difflugia corona, numerous Vorticella nutans, numerou

Other forms present in less numbers (few or rare) :

Actinophrys sol Euplotes carinata

Arcella dentata Euplotes charon

Arcella discoides Halteria grandinella

Anisonema obliqua Heterophrys myriapoda

Astasia Be Holophrya sp.

Biomyza vagans Lacrymaria olor

Blephoriewa lateritia Lionotus wrzesmosky

Centropyxis aculeata Lionotus sp.

Colpoda sp. Loxophyllum

Cothurnia maratima Paramecium Saidia

Dactylosphærium radiosum Pleuronema sp.

Dinomonas voraz Prorodon griseus

No. 603] ECOLOGY OF THE PROTOZOA 161

Stentor ceruleus Urocentrum turbo

Trichodina pediculus (on Hydra Volvox globator

fusca) Vorticella sp.

Blepharisma lateritia (Fig. 1) is usually described as

showing pink or even reddish hues, and occurring rarely

colorless. My experience has been to find the greater num-

ber of individuals colorless and a very few showing even

a faint trace of pink. In reproducing the colors of Pro-

tozoa in plates there seems to be a tendency to represent

them more vividly than they occur in nature. It is inter-

esting to place a small chart of spectrum colors on the

table near the base of the microscope and compare them

with the hues of those species of Protozoa usually repre-

sented as brightly colored. It has been my experience to

find that the (depicted) decided colors of some of the Pro-

tozoa show themselves to be only the faintest tints.

Synura uvella (Fig. 2) is not entirely colonial in its

habit. I have found it sometimes singly, and often in

pairs. The normal number of individuals in a colony is

from 10 to 20. As many as 35 in one group have been re-

corded. The flagella are invisible unless iodine or some

good stain has been used.

The Coleps sp. (Fig. 3) which I found so frequently in

this one group of samples I have never found since. It

was appreciably smaller than Coleps hirtus (Fig. 4), being

about 30 microns in length, whereas hirtus is 50. Hirtus

is a species exhibiting a notable constancy in dimensions,

and this I found true also of all the numerous individuals

of Coleps sp. which I measured. No transitions in size

from one to the other could be found. Coleps sp. was not

the result of fission on the part of hirtus, for in all the

material my search revealed not a single individual un-

dergoing division. In appearance and activities the one

form was the exact counterpart of the other, with a soli-

tary exception: the movements of Coleps sp. were at all

times much more rapid than those of hirtus.

Lacrymaria olor (Fig. 5) described as a very variable

Species, is variable in size almost entirely. Its form is

quite constant, and offers a virtually certain criterion for

identification. :

162 THE AMERICAN NATURALIST [Vor. LI

Fig.2 Synura uvella

Fig.9 Cero fa ve se ae

Fig.10 Cercomonas termo,normal and. abnormal forms

No. 603] ECOLOGY OF THE PROTOZOA 163

PLATE II

Monas irregularis

Monas Dallingeri Monas fluida

Fig.11

Fig.l? Frontonia sp,2

Fig.18 Frontonia sp.l

164 THE AMERICAN NATURALIST (Vor LI

The body of Loxophyllum (Fig. 6) is surprisingly elas-

tic. For this reason the creature undergoes rapid varia-

tions in length. Even within the confinement of a viscous

gelatin solution which checks the motions of all of the

other ciliates its strength is such as to enable it to per-

form various evolutions over the slide. In staining it fre-

quently dies in a contorted and contracted condition.

Before staining, it should be narcotized with a weak ethyl

alcohol or killed with .01 per cent. osmic acid.

In Astasia (Fig. 7) the smaller secondary flagellum is

sometimes either unusually filamentous, and therefore in-

visible, or lacking altogether. In many individuals no

amount of manipulation of light directions and intensities

or stains will reveal the smaller flagellum.

Urocentrum turbo (Fig. 8) can always be recognized by

the frenzied and jerky rotation which accompanies its ex-

tremely rapid movement through the water. It usually

comes to rest either close beside or buried among masses

of alge or other convenient material. In this resting con-

dition it is liable to be overlooked. At such times its only

evidence of activity is a scarcely perceptible twitching.

This hiding in algal masses has all the appearance of being

a deliberate attempt at concealment. Suddenly without

\warning its crazied rotation through the water is begun

:again. When swimming with retarded velocity through a

‘gelatin solution, functional anterior and posterior por-

tions of the body are recognizable.

ENVIRONMENTAL Type No. II: CLEAR Cotp WATERS

ckInG PLANT GROWTHS

Sediment, composed of quartz and shale sands free from

„organic silt and supporting no plant life save a few Dia-

-toms, in clear, pure, cold lakes and streams; temperature

.of water, cir. 56°

Predominant forms:

. Astasia sp., abundant Nostolenus orbicularis, several

. Holophrya sp., numerous Nostolenus sp., several

iHolostichia vernalis, numerous

No. 603] ECOLOGY OF THE PROTOZOA 165

Other forms present in less numbers (few or rare) :

Cercomonas termo Euplotes sp.

Cercomonas crassicauda Lionotus sp.

Chlamydomonas sp. Paramecium bursaria

Colpidium sp. Stylonychia mytilus

The nucleus of Cercomonas crassicauda (Fig 9) is

located near the functional anterior end of the body, and

is not easily seen. The anterior flagellum is likewise diffi-

cult to distinguish, even upon staining, being exceedingly

filamentous. It seems to have little to do with locomotion,

and I believe that it is used principally as a sort of an-

tenna. The propulsion of the creature is apparently

accomplished by the lashings of the stout posterior fla-

gellum, no matter which end of the organism is directed

forward.

Cercomonas termo (Fig. 10), from 5 to 15 microns, is

extremely variable in shape in the adult form. Its com-

monest and therefore characteristic appearance is roughly

heart shaped, the flagellum arising from the broader ex-

~ tremity of the body. The young are not so variable, but

although constant in general form, confusingly resemble

the monads, in particular Monas irregularis. Their mi-

nuteness (.5 to 2 microns) makes them difficult to identify.

They should be stained with a very weak solution of iodine

or acetic methyl green, since the stronger stains, used for

the larger Protozoa, cause them to lose their character-

istic outline and to disintegrate in a short time.

ENVIRONMENTAL Type No. IIT: Crear Frowrne Water

WITH ÅBUNDANYT PLANT LIFE

Clear springs and streams supporting vigorous growths

of such alge as Spirogyra, Drapernaldia, etc., and water

cresses; bottoms covered with Diatoms (often chiefly

Meridion circulare), Desmids, and Oscillatoria. Tem-

perature of water, cir. 66° F.

Predominant forms:

Ameba proteus, abundant Chilomonas paramecium, abundant

Ameba proteus, flagellospores (%), Colpidium sp., several

abundant Colpoda inflata, several

Chilodon cucullus, abundant Difflugia constricta, numerous

166 THE AMERICAN NATURALIST [Vou. LI

Difflugia globulosa, numerous Monas irregularis, abundant

Diffiugia lobostoma, numerous Monas Dallingeri (?), abundant

Holophrya sp., several Nostolenus orbicularis, numerous

Holostichia vernalis, several Oxytrichia pellionella, cages

Monas fluida, abundant Prorodon teres, numerou

Other forms present in less numbers (few or a :

Arcella artocrea Euglena minima

Aspidisca costata Frontonia s

Astasia contorta Holophrya sp.

Cercomonas crassicauda Lionotus oa

Chilodon sp. Masti

Chlamydomonas sp. Giyimi pee

Colpidium striatum Oxytrichia bifaria

Dile Pe

Enchelys sp. Parameéci caudatum

Epiclintes radiosa Stylonyenta mytilus

Euglena viridis Stylonychia pustulata

The identification of the Monas species (Fig. 11) is very

difficult. Members of this genus resemble some of the

members of the genus Bodo. Because of the hyaline char-

acter of the body its outline is not easy to distinguish. I

have found that the most successful method of treatment

before identification is attempted, is staining with a strong

aqueous solution of iodine and potassium iodide. This

oth kills and stains. Examination must be made almost

immediately since the organisms begin to lose their char-

acteristic form in a short time. ,

Within the genus Holophrya have been provisionally

laced a number of forms very closely allied in general

characters. For a considerable number of these a separa-

tion into species has not yet been made.

The pseudopodia of the Mastigamceebe (Fig. 12) do not

invariably disappear with the appearance of the flagellum.

They often remain, though much diminished in size, and

even exhibit appreciable movement. Such movement,

however, does not appear to aid in locomotion.

Enchelys (Fig. 13) is very like Holophrya (Fig. 14)

and only under the most favorable conditions of staining

and lighting can the side opening buccal orifice be defi-

nitely located. The proboscis-like projection at the an-

terior extremity of the body is subject to considerable

modification, and can not be relied upon as a distinguish-

No. 603] ECOLOGY OF THE PROTOZOA 167

ing feature, but the position of the buccal cavity is virtu-

ally constant.

Euglena deses (Fig. 15) is recognizable by its enor-

mously elongated body, for the propulsion of which its

small flagellum seems inadequate. It frequently assumes

an almost ameeboid form, and not infrequently contracts

to such an extent as to become nearly globular. Being

variable in size, its form, when swimming by means of its

flagellum, offers the readiest means of identification.

One particular locality, given especial notice, deserves

detailed mention. This was a spring pool in a boggy up-

land meadow, almost hidden among large tufted clumps

of luxuriant sedge-like grasses. The depth of the pool

was about four inches, and its area about six square feet.

Although exposed to the rays of the sun during the greater

part of the day, yet the temperature of the water was kept

low by a constant trickle of cold water from seepage

springs in the glacial clays which underlay several acres

of the region. The iron content of the water was unusu-

ally high, though the pool was erystal clear. Of higher

aquatic plants there were none; Desmids were numerous;

Diatoms were sufficient in numbers to form a brown film

over the entire bottom. The pool contained seven large

black-nosed dace, and other adjacent pools harbored sev-

eral more. Snails, Limnea and Physa crawled every-

where. With the exception of half a dozen large Hydro-

philide there were no aquatic insects, and but very few

Entomostraca.

The ai forms were Monas fluida and irregu-

laris, occurring not alone in the bottom film but every-

where throughout the water and in great numbers. One

species of Holophrya and Cercomonas crassicauda (but

few individuals of each) completed the census of the

forms.

ExNnvmonmENTAL Type No. IV: Crear Smari Poots with

ABUNDANT DecomPosIiNG ORGANIC SEDIMENT

Small clear pools in depressions in rocks containing de-

caying leaf material and a small quantity of such algæ as

168 THE AMERICAN NATURALIST [Vou. LI

Spirogyra, Zygnemea, Mougeotia, ete., Desmids and Dia-

toms abundant. Water kept pure and cool by influx from

small rills or by seepage from adjacent stream. Tem-

perature of water, cir. 60°

Predominant forms:

Chilodon cucullus, numerou Holostichia — numerous

Chilomonas eee stunt Monas sp., abunda

Coleps hirtus, numero aramecium bursaria, numerous

Diffiugia globulosa, numerous Trachelocerca olor, numerous

Holophrya sp., numerous Vorticella asad severa

Other forms present in less numbers (few or rare) :

meba proteus Euglena viridis

Anisonema obliqua Euglypha alveolata

Arcella vulgaris Euplotes sp.

Aspidisca costata Frontonia sp.

Chilodon vorax H Siok dais papilio

Chlamydomonas sp. Loxophyllum sp.

Colpoda cucullus Nostolenus pie tens

Cyphoderia ampulla Oxytrichia bifaria

Dallasia frontinia Oxytrichia pellionella

Diffiugia acuminata Paramecium caudatum

Diffugia pyriformis Pleuronema sp

Dileptus gigas Prorodon armatus

Dileptus monilatus Stylonychia pustulata

Euglena deses Stylonychia putrina

Dileptus gigas (Fig. 16) is surely the king of beasts

among the ciliate Protozoa. It is entirely carnivorous and |

its appetite is apparently insatiable. The prey is stung

by the well developed trichocysts which Dileptus bears

upon its long ‘‘neck’’ and if too large to be swept into the

bugeal cavity by the cilia is forced in by the writhings of

‘neck.’? The creature varies greatly in size, but is

normally about 450 microns in length. Individuals have

been reported measuring 800 microns!

ENVIRONMENTAL Type No. V: Poots CHokep WITH ALG;

Water Warm

Ditches and pools choked with heavy, luxuriant masses

of alge (Spirogyra, Ulothrix, Zygnemea, etc.) and ex-

posed to the sun during the entire length of the day. Cy-

clops, Canthrocamptus, Gammarus, Daphnia, Cypris,

Simocephalus, etc., abundant. In lesser numbers: aquatic

No. 603] ECOLOGY OF THE PROTOZOA 169

insects (especially the Hydrophilide), Limnea, Physa,

Planorbis, etc. Temperature of water, cir. 70° F.

Predominant forms:

Cercomonas termo, abundant Monas irregularis, very abundant .

Chlamydomonas sp., numerous Peridinium cinctum, numerous

Diffiugia globulosa, numerous Synura uvella, numerou

Euglena viridis, very abundant Trepomonas = tty very yaad $n

Monas fluida, very abundant

Other forms present in less numbers (few or rare) :

Actinophrys sol Colpoda campyla

Arcella sae (?). Cyphoderia ampulla

Arcella mitrata Frontonia sp.

Arcella easa Vorticella nutans

The species which I identified as Arcella discoides (Fig.

17) was much smaller than usual. Although there is con-

siderable variation in size among the members of Arcella

and particularly among Arcella discoides and vulgaris,

yet I have never seen recorded individuals so small. The

average diameter of twenty-five individuals from one

sample was 70 microns.

The Frontonia species (Figs. 18 and 19) are very fully

equipped with trichocysts. When irritated with acetic

acid and then stained with iodine or methyl green they

show beautifully. For use in the laboratory in the demon-

stration of the trichocysts of the ciliata they offer the best

possible material. The species are not very common, how-

ever, and I know of no culture medium.

Trepomonas agilis (Fig. 20) varies greatly in size. Its

apparent variation in shape ean be explained, I think, by

the fact that it swims sometimes with one aspect of the

body presented to the observer and sometimes with an-

other. The curious irregularity of its body would there-

fore allow it to show a number of different outlines. Often

it swims in one position for a long period, and again it

twirls rapidly about going through the whole gamut of its

apparent changes of form in a few seconds.

In one typical roadside ditch overhung with grasses.and

weeds and literally filled to overflowing with rich masses

of Spirogyra I found an almost pure culture of Euglena

170 THE AMERICAN NATURALIST [Vor. LI

viridis. The only other forms present were but very few

Colpoda campyla and Cyphoderia ampulla.

Several samples were taken from leaves and grass

frozen together, lying beneath three inches of solidly com-

pacted. snow in a small oak grove not far from a ravine

through which flowed a perennial stream. This material

was allowed to stand in its own snow in a cotton-tamponed

jar until the snow had melted and the resulting water had

attained room temperature, cir. 72° F.

The Ameba proteus were more abundant than I had

ever seen them before except in artificial cultures. Not

infrequently as many as ten individuals could be counted

at once in the field of the 10 mm. objective. The other

predominant forms were:

Holostichia vernalis, abundant. Opalina ranarum, several

Monas irregularis, abundant. Paramæcium caudatum, several

Other forms present in less numbers (few or rare) :

Astasia lagenula j Paramæcium trichium

Oikomonas sp, Platyrichotus opisthobolus

CATALOGUE OF SPECIES NOTED WITH MEASUREMENTS IN

Microns

In each case length refers to the antero- Jito axis,

except with globular or subglobular forms when it refers

to the diameter of the body. All dimensions are given in

microns (= 1/1000 mm.).

It is interesting to recall, in connection with the sizes of

these organisms, that the diameter of the sl eh human

hair is 3 100 microns.

ae a Species Length

Tinea? AA sol ; : 60

Ameba LORS “C Vimax 50—60

Amæba ' proteus 125 (variable)

Amæba : _ radiosa 50-100 (variable)

Anisonema obliqua

Arcella artocrea ` 160

Arcella i dentata Ye OB,

Arcella discoides 115

Arcella | mitrata 100-150

Arcella ` vulgaris 55 (variable)

Aspidisca costata BD fess

No. 603]

contorta

lagenula

vagans

lateritia

polypinum

aculeata

crassicauda

termo

cucullus

vorax

sp.

paramæcium

sp.

umbellatum

hirtus

sp.

striatum

campyla

cucullus

inflata

maratima

pyriformis

igas

giga

monilatus

vorax

viridis .

alveolata

carinata

charon

grandinella

myriapoda

sp.

ECOLOGY OF THE PROTOZOA 171

30 (variable)

50 (variable)

170

60 (bell only)

125-150

25 (variable, body only)

150 |

100-300

150-250

20-50

90-120

250-350

450 (variable)

18 (variable)

50-200

30 (variable)

(variable)

172

Holostichia

Hyalosphenia

rymaria

Oxytrichia

Paramecium

acus

Platyrichotus

Pleuronema

Prorodon

Stentor

tylonychia

Stylonychia

Synura

Trachelocerca

vernalis

papilio

wrzesmosky

sp.

sp. (repetans?)

Dallingeri

fluida

irregularis

orbicularis

trichium

sp.

opisthobolus

sp.

pustulata

THE AMERICAN NATURALIST

and 5

100-400

100-300

80-150

50 (variable)

70-130

[Vou. LI

THE ROLE OF ISOLATION IN THE FORMATION

OF A NARROWLY LOCALIZED RACE OF

DEER-MICE (PEROMYSCUS).*

DR, F. B. SUMNER

SCRIPPS Institution, La JOLLA, CALIF.

No one who has critically examined large numbers of

specimens, belonging to such a widely distributed and

diversified genus as Peromyscus, can fail to be impressed

with two facts. First, the differences upon which the

so-called ‘‘subspecies’’ are based are real and obvious

ones. But, secondly, the actual subspecies which are

recognized and named are necessarily highly artificial

groups. On the one hand, each subspecies intergrades

with others to such an extent that the assignment of a

given specimen to one or the other group is often quite

arbitrary. And on the other hand, even these ‘‘sub-

species’’ themselves are far from being elementary. They

are composite groups, comprising, in many cases, a num-

ber—perhaps a great number—of distinguishable local

types. The word distinguishable is here used in a quali-

fied sense. It is likely that the distinctions would com-

monly be obvious just in proportion as the collections

were made at points which were remote from one another.

Indeed, it has been said by one who has monographed

this genus of mice’ that ‘‘classification becomes . . . like

dividing the spectrum and depends largely upon the

standards set, for, theoretically at least, the possibilities

of subdivision are unlimited (p. 17).’’

None the less, it is generally believed that where well-

marked physical or other barriers are interposed between

two groups of individuals, this continuous intergradation

*Read before Ecological Society of America, San Diego meeting, August,

1916,

1 Osgood, ‘‘ Revision of the Mice of the American Genus, to sua cual

North American Fauna, No. 28, Washington, 1909

173

174 THE AMERICAN NATURALIST [Vou. LI

of racial characters may be largely interrupted. It is the

object of this paper to discuss a ease of this sort which

I have had the opportunity of studying during the past

year.

The subspecies Peromyscus maniculatus rubidus, ac-

cording to Osgood,? who first described it, occupies a strip

of varying width on the ‘‘coast of California and Oregon

from San Francisco Bay to the mouth of the Columbia

River.’’ In discussing certain local variations shown by

this subspecies throughout its range, the same writer

states that ‘‘six specimens from the Outer Peninsula, near

Samoa, Humboldt Bay, are decidedly paler than others

from the neighboring redwoods. They evidently repre-

sent an incipient and very local subspecies, and well illus-

trate the plasticity of the group to which they belong.’’

Osgood further remarks that ‘‘a careful study of this

variation and the local conditions doubtless would prove

instructive’’ (p. 66).

During the latter part of May, 1916, I trapped on two

consecutive nights in the neighborhood from which Os-

good obtained his six ‘‘aberrant’’ specimens of rudibus.®

About one hundred live-traps were set on each occasion.

Twenty-eight specimens were taken, of which twenty-one

were later available for skinning and for careful meas-

urement. These last were all in either mature or adoles-

cent pelage, and were about evenly divided in respect to

sex.

The distinctness of this race from the rubidus of the

redwood forests on the mainland was evident from a

casual inspection of the living mice. A more careful com-

parison of freshly killed specimens from the two locali-

ties, and later of their prepared skins, justifies the fol-

lowing generalizations. These impressions were formed

independently by several other persons to whom I showed

‘he specimens, and were confirmed by more careful ex-

_ 2 Loe. cit., p. 65.

3 The trapping was done between one and two miles northwest of the

village of Samoa. Besides these Peromyscus, the only other animal caught

was a single specimen of Microtus.

No. 603] THE ROLE OF ISOLATION 175

amination and measurement. (1) The Samoa lot, as a

whole, were paler than the redwood lot; (2) the tails of

the former were shorter, and (3) the ears were longer.

To consider first the coat color, the mean difference be-

tween the two series of skins is evident at a glance. Like-

wise, it is plain that the palest Samoa specimen is paler

than the palest Eureka (redwood) specimen, and that the

darkest among the former is paler than the darkest

among the latter. It must be admitted, however, that the

two series overlap rather broadly,* the darker skins. of

the Samoa stock being as dark as or darker than the paler

ones of the Eureka stock.

An attempt to express the color of a mammal’s pelage

in terms of any set of ‘‘standard’’ colors is beset with

great difficulties. Instead of a uniformly tinted, plane

surface, we have to do with a mixture of variously colored

hairs, further diversified by minute shadows and reflec-

tions. I have, nevertheless, endeavored, in a rough way,

to ‘‘match’’ the colors of these two races with those of

Ridgeway’s ‘‘Color Standards and Color Nomencela-

ture.” In the Samoa race, the general tone of the lateral

regions of the body lies between the ‘‘tawny olive” and

‘‘Saccardo’s umber,” that of the dorsal darker stripe

being not far from ‘‘sepia.’? In the Eureka mice, the

lateral regions range from ‘‘Saccardo’s umber’’ to

‘‘sepia,’’ the dorsal stripe being of a depth somewhere

between ‘‘sepia’’ and black. These comparisons will ‘at

least enable the reader to judge of. the degree of differ-

ence between the two racs.®

As regards the tail, it was plain without measurement

that the average length of this member was greater in the

+I have at present for reference twenty-one skins of the Samoa lot and

thirty skins of wild adults from the redwoods. Ten of the latter indi-

viduals were trapped and skinned at about the same time as the former, so

that the factor of season may be disregarded.

5 Washington, 1912. Published by the author.

6 In my further studies of Peromyscus I plan to employ two revolving

color-wheels, on one of which the skin itself will be rotated, on the other

sectors of black, white and various primary colors. This apparatus is now

being tested by Mr. H. H. Collins and myself.

176 THE AMERICAN NATURALIST [Vou. LI

Eureka than in the Samoa race, though here again the

difference related to averages and did not hold for all

individual cases.

A comparison of the mean figures for absolute tail

length in two series of mice is not entirely justifiable, par-

ticularly if the two lots of individuals differ somewhat

in mean body size. But the relative tail lengths (ex-

pressed as percentages of body-length) may be fairly

compared, since there is good evidence that these ratios

remain nearly constant after the first few months of life.

The following table allows of a comparison between the

two races, in respect to this character:

Number of Mean Standard

Cases (Percentage) Deviation

Eureka (males) 83 104.39 + 0.387 | 4.95

Eureka (females) 53 103.60 + 0.54 | 5.85

sexes combined ) 21 97.48 +0.94 | 6.38

The differences between the Samoa lot ee com-

bined) and the Eureka males and females are 6.91 per

cent. and 6.12 per cent., respectively. These differences

are about seven and six times their probable errors, re-

spectively. Their significance may therefore be regarded

as fairly certain, despite the small numbers comprised

in the Samoa series.

As regards foot-length, the two races do not differ

significantly. But the ear, as already stated, is appre-

ciably longer in the Samoa mice, this difference being

perceptible, even without measurement. Here, as in the

ease of tail-length, a simple comparison of gross averages

for the two groups would be unjustifiable. But in the

present instance, the conversion of the absolute values

into percentages of body-length would be equally unjus-

tifiable, since the growth of the ear is not at all propor-

tionate to that of the body as a whole. We must there-

fore resort to the method of ‘‘size groups,’’ i. e., we must

divide each of our two lots of animals into small groups

comprising individuals of nearly equal size,

In the case at hand, we have fifteen groups, or othen

No. 603] THE ROLE OF ISOLATION 177

pairs of groups, within which a comparison of average

ear-length is possible. In twelve cases the mean figure is

greater for the Samoa mice, in two cases it is greater for

the Eureka mice, while in one case the two figures do not

differ appreciably. The probabilities against such a pre-

ponderance being due to chance are of course high. The

mean difference in ear-length between the two lots, com-

puted according to a method described by me in an earlier

paper,’ is 0.87 mm. Those who have made careful meas-

urements of mice will regard such a difference in the

length of this appendage as far from trivial.

Let me now say something as to the environmental con-

ditions under which these two races of rubidus live.

Those which I have designated as the ‘‘ Eureka”’ or ‘‘red-

wood’’ race were trapped by me during two different

years, within a distance of two miles from the southern

limits of the city of Eureka, California. The region is

one covered in large part by redwood forest, most of

which is of second growth, although there are some small

areas that have never been logged. The predominant tree

is the redwood (Sequoia sempervirens), but several other

conifers are common, the most abundant of these being

the Sitka spruce (Picea sitchensis), Douglas fir (Pseu-

dotsuga taxifolia), and lowland fir (Abies grandis). The

red alder (Alnus rubra), cascara (Rhamnus purshiana),

waxberry (Myrica californica), red elderberry (Sam-

bucus racemosa), and a willow (Salix hookeriana) appear

to be the chief non-coniferous trees of this district.6 The

“wild lilac’’ (Ceanothus thyrsiflorus) is likewise com-

mon in some of the more open areas, often reaching the

proportions of a small tree.

Except in recently cleared tracts, the region is one of

dense underbrush, the shrubbery and vines forming, in

fact, a veritable jungle which is frequently hard to pene-

T Journal of Experimental Zoology, Vol. 18, April, 1915, particularly, pp.

341 et seq. :

8 For the determination of many of the plants referred to in this paper I

am indebted to Professor H. M. Hall, of the University of California, and

to Mr. J. P. Tracy, of Eureka.

178 THE AMERICAN NATURALIST [Von LI

trate. Here we meet with the thimble-berry (Rubus par-

viflorus var. velutinus), the salmon-berry (Rubus spec-

tabilis var. menziesii), huckleberry (Vaccinium ovatum),

red bilberry (V. parvifolium), salal (Gaultheria shallon),

and in the more open areas the blackberry (Rubus viti-

folia): Two ferns (Aspidium munitum and Pteris aqui-

lina) are extremely abundant, the latter in particular

forming dense growths higher than a man’s head. Inthe .

op Lp Wy

“uy,

: p

% m

o Uy

y samog *, yy by, ~

Wie

go a ee Vi if 7 Ae ;

HUMBOLDT ae ie Eas YW, ce tte es

ma X Vi, a ns BS

ne )

Wy ie Hy Oss >

Fie. 1. Map of the vicinity of Humboldt Bay, California, kd upon J.

N. Lentell’s map of Humboldt County. The three principal trapping sta-

tions are designated by the letter T. Area occupied by redwood forests is

indicated by oblique shading.

more open areas a tall annual of the evening primrose

family (Epilobium angustifolium) constitutes an im-

portant element in the vegetation.

One coming from the more arid parts of California can

No. 603] THE ROLE OF ISOLATION 179

not fail to be impressed by the prevailing humidity of

both soil and atmosphere in this region. In the dense

shade of the great redwoods the ground is damp, even

during the summer months, and the fallen logs are coy-

ered with mosses and fungi.

When we cross Humboldt Bay to the narrow peninsulas

separating this body of water from the ocean (Fig. 1),

we enter a quite different environment. No redwoods are

found, the woods, where present, are open, and the ground

is prevailingly dry and sandy. In the wooded area, ex-

tending down the axis of the northern peninsula, the pre-

dominant tree is a small pine (Pinus contorta), though

the waxberry and willow (Salix hookeriana) are likewise

abundant, and small specimens of the Sitka spruce are

fairly common. Among the more frequent shrubs are

the huckleberry (V. ovatum), the twinberry (Lonicera

involucrata) and silk tassel bush (Garrya elliptica). The

ground is largely covered by two plants of trailing habit,

the bearberry (Arctostaphylos uva-ursi) and the beach

strawberry (Fragaria chilensis).

On its ocean side, the peninsula is bordered by a wide

strip of shifting sand. Here the process of dune forma-

tion may be witnessed to perfection, the dunes often

reaching a height of forty or fifty feet. In places the en-

croachments of the sand upon the hard-pressed vegeta-

tion are evidently rapid, solid ramparts of willows and

spruces being steadily engulfed by an advancing wall,

frequently as high as the trees themselves. Nevertheless,

even on the open sands of the dunes, certain trailing plants

maintain a precarious foothold. Among the commonest

of these are to be mentioned the yellow sand verbena

(Abronia latifolia), the beach strawberry (F. chilensis),

beach pea (Lathyrus littoralis), and two species of Fran-

seria (F. chamissonis and F. bipinnatifida), while the suc-

culent Mesembryanthemum aequilaterale is occasionally

met with.

Despite the nearness to the ocean and the high atmos-

pheric humidity, the peninsula region seems dry in com-

parison with the redwood forests. This is due in part to

180 THE AMERICAN NATURALIST [Vou. LI

the loose, sandy character of the soil—where, indeed, any

real soil exists—and to the comparative lack of shelter

from the prevailing westerly winds. Evaporation here is

doubtless more rapid than in the comparatively stagnant

air of the forests.

To my surprise, the footprints of mice and other small

mammals were abundant, even on the shifting sands, in

the areas of sparsest vegetation. Since these tracks, for

the most part, were effaced every day by the wind, the

animals must have been present in large numbers. In-

deed, it was in or close to the dune region that I trapped

most of the twenty-eight Peromyscus. It seems more

than possible, therefore, that the predominantly paler

shade of the mice dwelling here may be due to the same

causes which are operative in producing the yet paler

hues of many of the desert rodents. |

What the effective factors are can not yet be stated

with certainty in either case. Protective coloration is of

course an obvious explanation, but it is one of doubtful

applicability in the case of animals which are almost

wholly nocturnal in their habits. For this and other

reasons it seems more likely that the pale coloration of

these mice stands in some more direct relation to the

humidity of their immediate surroundings. That it is

not, however, a strictly ‘‘somatic’’ phenomenon, called

forth anew in each generation, I have already shown for

the desert race, P. m. sonoriensis.®

Whether or not the peculiar color of the pelage in the

Samoa race is likewise hereditary I have endeavored to

test experimentally. Seven living females and a number

of males were brought to La Jolla in June, 1916. Unfor-

tunately, it was not possible to obtain more than two

broods of young, comprising three individuals, one male

and two females. These animals were carefully examined

at the age of five months, in comparison with over forty

individuals, derived from the redwood stock, which were

9 AMERICAN Naruratist, Nov., 1915. I have since reared this race in

Berkeley as far as the third (in one instance the fourth) cage-born genera-

tion, without any certain modification in color.

No. 603] THE ROLE OF ISOLATION 181

mainly of the same age or older, and likewise reared

from birth at La Jolla. Not a single individual of the

latter stock was as pale as either of the two females of

Samoa parentage. The male of the Samoa race was,

however, of about the average shade of the redwood

descendants. As stated above, some of the wild parents,

trapped on the peninsula, were likewise as dark as many

of the redwood series.

No certain conclusions can, of course, be based upon

these three individuals. But the condition of the two

females certainly lends support to the belief that the

peculiar coat color of the Samoa race, however it was ac-

quired, has become fixed germinally.

Reference to the map shows that the northern penin-

sula of Humboldt Bay is largely isolated, so far as land-

living rodents are concerned. In addition to the ocean

and the bay, a marshy tract extends from the latter to

the Mad River, which, in turn, interposes a further barrier

on the north, and nearly converts the peninsula into an

island. Beyond the mouth of Mad River, this same type

of sand-dune formation extends uninterruptedly to the

mouth of Little River, about six miles to the north, where

it ends abruptly and the shore line becomes precipitous.

Now this northward extension of the sand-dune region

is not isolated by any physical barrier from the redwood

forest, which here comes near to the coast. It occurred

to me, therefore, to attempt the collection of Peromyscus

from a point somewhere within this region. The locality

chosen was close to the ocean, about two miles south of

Little River and four to five miles north of Mad River.

Here the conditions were found to be closely similar to

those on the exposed side of the northern peninsula of

Humboldt Bay. The dunes were on the whole lower, how-

ever, and some minor differences were noted in the flora.

The belt of shifting sand here ranges from five or six

hundred feet to perhaps a fourth of a mile, giving place

on the landward side to a narrow meadow or marshy

area, sueceeded by a high, steep, wooded ridge.

About ninety traps were set on two consecutive nights,

182 THE AMERICAN NATURALIST [Vot LI

yielding in all forty-eight Peromyscus, all belonging to

the subspecies rubidus. Many of these were still in

juvenile pelage and such individuals were kept and al-

lowed to mature in captivity.

A hasty comparison of the living Little River animals

(as I shall call them) with those from the Samoa and

Eureka trapping grounds made it plain that, in respect

to color, they belonged with the latter group rather than

the former. Careful comparisons of series of dead mice

and of skins were made later and the bodies were sub-

jected to the customary measurements. Owing to numer-

ous deaths, however, only twenty-eight individuals were

available for these purposes.

This more critical examination confirmed my earlier

‘belief that the Little River mice agreed pretty closely, in

average color, with the redwood stock, but that they dif-

fered widely from those taken on the peninsula. It

‘seemed probable, however, that the mean shade was

‘slightly lighter than that of the former animals, making

‘them, to this ‘extent, intermediate.

One conclusion then seemed plain. The peninsula race,

exposed to certain modifying conditions, was enabled to

differentiate from the mainland stock, owing to the almost

insuperable barriers to migration. The Little River

stock, exposed to practically the same conditions, have not

formed a distinguishable race, because the rate of dif-

ferentiation has been far exceeded by the rate of diffusion,

or intermingling with the great body of more typical

“rubidus,” dwelling in the redwood forests which extend

back from the coast. We might seem to have, therefore,

a particularly clear cut example of the effectiveness of

isolation in the formation of a local race.

Now, I am not yet prepared to admit that such con-

clusions would be groundless. But here, as so often hap-

pens, a further study of the data has shown that the prob-

lem is more complex than was at first suspected. It is

true that the mice of the more northern sand dunes have

not formed a distinct race as regards color. But it is

none the less certain that they differ from those of the

No. 603] THE ROLE OF ISOLATION 183

Eureka region in regard to both the length of the tail and

that of the ear. In respect to the former character, they

agree pretty closely with the Samoa race, the difference

from the redwood stock being statistically even more cer-

tain in this case. To still further complicate the situation,

we find that the ear, instead of being longer, is shorter

than that of the redwood mice by about half a millimeter,

and thus averages about one and one half millimeters

shorter than in the peninsula race. Here, too, the dif-

ferences are even more certain statistically than those

which distinguish the Eureka and Samoa series.

The numbers are small, of course, only twenty-eight

of the Little River mice having been available for meas-

urement. But as regards tail length, the difference be-

tween the averages is seven to nine!’ times its probable

error, so that the likelihood of its being due to random

sampling is very small.

Have we, then, here merely another example of incon-

clusive data, which might best have been left unpublished?

I do not think so. The mere existence of these local dif-

ferences in color and in the size of parts deserves careful

description, whatever interpretation we may place upon

them.

Moreover, I am disposed to a that the case of coat

color is not entirely comparable with that of the length

of the appendages. In another article’! I have given

reasons for thinking that some of the differences in the

former may have arisen in nature as more or less direct

effects of environmental conditions. On the other hand,

I have shown that such an explanation would be of very

difficult application as regards some of the measurable

differences in the parts of the body, even though the latter

are known to be readily influenced by various experi-

mental agencies.

Now the evidence at hand is sufficient to show that any

environmentally produced modifications of coat color are

10 Depending on whether the comparison is made with the Eureka males

or females, the sexes being combined in the case of the Little ot tet group.

11 AMERICAN NATURALIST, Nov., 1915.

184 THE AMERICAN NATURALIST [Vou. LI

at best rather gradual. Rubidus remains rubidus and

sonoriensis remains sonoriensis, after several generations

of captivity in changed climates. But even the first cage-

born generation of each of my subspecies is found to be

highly modified by confinement, in respect to the mean

length of: certain of the appendages. That this somatic

plasticity would be accompanied by a high degree of

germinal instability, as regards these parts, could not, of

course, be predicted in advance. But the frequent ap-

pearance of local differences of type renders it probable

that this is true. Whether or not these local peculiarities

are due in some indirect way to environmental factors,

or whether they are due to ‘‘spontaneous’’ mutation,

need not concern us here. The main point to bear in mind

is the probability that the pelage color is somewhat more

stable in these mice than are the bodily proportions,

despite the fact that it is the former, rather than the

latter, which gives the clearest evidence of a definite cor-

relation with known factors of the environment.

For the reason just stated, it is possible that the dif-

ferentiation of a new color race might require fairly

rigid isolation; whereas local differences in some of the

measurable parts might arise in the presence of no other

barrier than the naturally slow rate of diffusion of a non-

migratory animal. As was remarked earlier, we have

reason to suppose that representative collections from

an indefinite number of localities would reveal the exist-

ence of statistically certain differences between the mice

of many of these localities. In most cases, it would prob-

ably be unjustifiable to assign these series to distinct races,

or other definite taxonomic groups, since it is likely that —

perfect intergradation would be found between most of

them, and that the degree of difference would be largely

a function of the distance apart of their respective habi-

tats.

These last remarks are, of course, largely conjectural.

Part of the author’s present program consists in a care-

ful study of local differences of the sort here discussed.

No. 603] - THE ROLE OF ISOLATION 185

It is hoped that this will render possible more definite

answers to some of these difficult questions.

It seems to be held by certain zoologists that any dis-

cernible difference between two local types, if at all con-

stant, ought to be in some way recognized in the nomen-

clature. Indeed, I have been advised to name fhis modi-

fied race of rubidus from the northern peninsula of Hum-

boldt Bay. Such a practise, if carried out consistently,

would lead either to an endless multiplication of sub-

species, or else to the introduction of quadrinomial

names. Hither procedure would, I think, be deplorable.

The actual needs of the situation can commonly be met,

I believe, by stating the locality from which a given speci-

men or collection was taken. The bestowing of formal

names creates the false impression of a multitude of well-

defined entities which do not, in reality, exist. Moreover,

it is my firm conviction that nomenclature should have

for its object the recognition of resemblances as well as

the recognition of differences. The first of these func-

tions is all too frequently overlooked.

SHORTER ARTICLES AND DISCUSSION

THE MIGRATION OF FISHES

Unber the head of ‘‘The Migrations of Fish,’’ Professor Alex-

ander Meek has given a voluminous account of what is known of

the movements and the distribution of the various families of

fishes. The work is illustrated with drawings and photographs

of many species, showing not only their forms and their move-

ments, but often the stages of development and the structure of

fins and scales. Especially valuable is a series of maps showing

the geographical distribution of interesting groups. The word

migration is taken in its largest sense, including not merely move-

ments of individuals or of masses, but the larger problems of

distribution, extending often over geological periods.

It is plain that distribution is intimately related to migration and

migration to currents.

As the problems of fish conservation depend directly on the

facts of migration and distribution, especial attention is given to

the development and movements of food fishes: and naturally to

those of the North Atlantic.

After a general discussion of the continental and oceanic

changes which have taken place since Eocene times, these having

a direct bearing on modern conditions of fish-distribution, Pro-

fessor Meek takes up the various groups of fishes, beginning with

the lowest, treating of the habits, movements and distribution of

each group in turn.

The excellent account of the lampreys and hag-fishes shows a

certain omission. While the lampreys fasten themselves to other

river fishes, sturgeons, catfishes and the like, rasping great holes

with their teeth, the hag-fishes attack the throats of large sea-

fishes, entering the muscular system and almost destroying it

before the fish concerned finally dies. Around Monterey Bay,

various flounders and rock-fishes (Sebastichthys) are thus at-

tacked and drift about as living hulks while the hag-fish (Polisto-

trema) devours their muscular tissues

The interesting parallelism in habits and distribution of the

1*¢The Migrations of Fish,’’ by Alexander Meek, M.Sc., professor of

zoology, Armstrong College in the University of Durham, and director of

the Dove Marine Laboratory, Cullerecoats. Edward Arnold, London, Long-

mans, Green & Co., New York. Price $4.50.

186

No. 603] SHORTER ARTICLES AND DISCUSSION 187

sturgeon and the lamprey is noted by Professor Meek and in both

eases the facts now observed are of long standing. Both had ap-

parently ‘‘refuge-regions’’ during glacial times. We do not, how-

ever, see the reason for the suggestion that the green sturgeon of

California (now almost extinct) ‘‘may have been derived from

the Atlantic during the post-glacial disturbance.’’

The migrations and breeding habits of the herring are treated

with special fullness, proportionate to the economic value of the

species. For in the north, as Björnson informs us, wherever a

herring school touches the coast a town springs up, like drift-

wood on the beach.

In the account of the trout, very good as a whole, we may note

that the genus Salmo is represented by different forms, originally

derived from the Pacific coast, in the Great Basin of Utah, and

also in the headwaters of the Colorado, Rio Grande, Arkansas

and Platte, as well as the Columbia and Missouri. It is probable

that the freshwater irideus (Rainbow trout) and the sea-run

gairdneri (steelhead) are not really different, but both are quite

separate from the cutthroat trout (Salmo clarki, wrongly identi-

fied at first by American authors with the Kamchatkan Salmo

mykiss) from the Tahoe trout (Salmo henshawi) and from the

several local forms which have sprung from these or which have

preceded their advent. The last seems to be the case with the

silver trout of Lake Tahoe (Salmo regalis). The suggestion of

Professor Meek that the European salmon (Salmo salar) of the

Miocene was divided into a North Atlantic and a Mediterranean

form is interesting. The latter developed as a ‘‘trout’’ dividing

into sea trout (Salmo trutta) and burn (or brook) trout (Salmo

fario). But these two are as yet not really differentiated, corre-

sponding in a way to the rainbows and steelheads of the Pacific

coast. Professor Meek says:

There is thus good reason for believing that the sea trout and the

common trout may be the same, the one retaining the migratory habit

and the other confining itself to fresh water.

Our own experience with the species lends probability to this

view.

That ‘‘the salmon preceded the trouts’’ in time is also probable,

but the western species of trout must have been derived from the

trout of Europe and Asia.

The Pacific salmon must be older and more primitive than the

Atlantic salmon, for the six species differ from one another, more

than any trout or even the Atlantic salmon itself differs from

any other black-spotted trout whatever.

188 THE AMERICAN NATURALIST [Vou. LI

Professor Meek hardly does justice to the spawning habits of

the red or blueback salmon. It runs up rivers to varying dis-

tances—-from one mile to 1,500 miles (Lake Labarge on the

Yukon). But it never enters a stream which does not flow from

a lake and it spawns always in the small streams at the head of

the lake.

At Boca de Quadra in Alaska, the small stroni is barely. a mile

long. It comes from a clear like, perhaps five miles long. Into

this stream and lake the salmon crowd by the thousands. The

Yukon is not a good red salmon stream, because the nearest tribu-

tary lake, Labarge, is about 1,500 miles from the sea. Yet red

salmon enter the river and reach the lake. In streams without

lakes as the Skagway, red salmon are never seen. The King

salmon (Oncorhynchus tschawytscha) also runs for great dis-

tances, but it is absolutely indifferent to the presence of lakes.

It is probable that the red salmon spend their first winter in the

lake and some never leave it, remain landlocked and dwarf until

spawning time (usually four years).

One of the most difficult of problems is to understand the in-

stinct of the red salmon. Every individual of this and of each of

the other species of Pacific salmon (Oncorhynchus) dies after

spawning. How does the spawning fish, stupid in most regards,

know when it enters a river that there is a lake before it? How

does it come to avoid all lakeless tributaries as it goes up, finally

reaching the lake’s head and the brooks that feed it? And why

do the other salmon species totally lack this instinct? There are

other problems, yet unsettled, regarding the supposed homing

instincts of salmon. The majority (but not all) seem to return

to spawn to the parent stream which they left as fingerlings.

Why not all? And why any?

The recognition of the age of salmon and trout by the adjust-

ment of the rings on the scales, as recently worked out by Dr.

C. H. Gilbert and others, received full attention from Professor

Meek. The scales of the salmon are marked by concentric rings

of growth, and these are more widely separated in the summer,

the Peas time of the salmon when the individual grows most

rapi

Profit Meek devotes much space to the singular breeding

habits of the eel, which spawns in the.sea, entering rivers to feed.

But many individuals, in our Mississippi Valley never descend

to the sea. A very large eel, once taken by the present reviewer,

above the Cumberland Falls in Kentucky, 2,000 miles from the

No. 603] SHORTER ARTICLES AND DISCUSSION 189

sea, must either have never spawned or cast its spawn into the

river.

The larve of eels as well as of some other soft-rayed species

are quite pellucid, without pigment cells and with ‘‘a roomy

space between the skin and the muscles, distended by a watery

fluid.’’ Many of these larve, in their transformation to the con-

dition of young fishes become much reduced in size, though in-

creasing in weight, by the obliteration of these interspaces.

Professor Meek’s studies pass through the whole long series of

fish-families. For want of space, we may not follow them further

in these pages. We must give the work, as a whole, very high

praise as carefully, intelligently and scientifically done, and as

constituting a reference book of great value. The author has

well covered the range of the periodicals which treat of the dis-

tribution and habits of fishes. He seems, however, to have over-

looked the most extensive recent work of a similar range, ‘‘ Jor-

dan’s Guide to the Study of Fishes,’’ published in New York in

1905.

DAVID STARR JORDAN

NEW LIGHT ON BLENDING AND MENDELIAN

INHERITANCE

UnperR the above heading, Dr. Castle reviews a paper by Yuzo

Hoshino on the inheritance of the flowering time in peas., an

rice.

Since reading this review, Prof. Hoshino kindly sent us his

paper, and we have ourselves examined it with care to see

whether indeed it necessitates Dr. Castle’s rather sweeping con-

clusions, namely, that certain genes are themselves modified by

crossbreeding, one of the conclusions of Hoshino himself, and

that selection within a pure line, within a genotypically pure

population is effective.

It is well known that Dr. Castle counts among the few last

geneticians, who still believe that the genes themselves are modi-

fiable by selection. Hitherto in nearly all his writings on the

subject Dr. Castle claimed, that unit characters vary, and may

be modified by selection, a statement which can not very well be

opposed, given the loose way in which the obsolete term unit

character is usually applied. But it was clear, that Dr. Castle

really believed the genes themselves to be capable of variability

in potency, quality and value, and we think it of the utmost im-

portance that in the review under discussion he has stated the

190 THE AMERICAN NATURALIST [ Vou. LI

question in these words. Thus the issue between Dr. Castle on

one side, and Johannsen and us on the other narrows, and there

need be no more difficulty as to the exact meaning of the term

unit character. As to the effectiveness of selection in genotypi-

eally homogeneous material, all the evidence so far adduced

shows that selection in such material is absolutely ineffective.

It is evident that selection in a population is usually effective,

but this only shows that in ordinary populations, even in so-called

pure strains of animals, there is a good deal of genotypic varia-

tion, or in other words impurity.

The fact, for instance, that Dr. Castle’s selection in hooded

rats was effective, shows that his material was not originally

pure for all the genes. In all those instances where the guar-

antee for genotypic purity of the material was reasonably good,

selection has, until now, proved ineffective. We need only point

to the fifty years of selection in wheats by the de Vilmorin fam-

ily, and to the numerous selection-experiments with clones of

Paramecium by Jennings and others.

As to the so-called instances of the effectiveness of selection

on the genes themselves in alleged genotypically homogeneous

animal material, we repeat that the only way to show such an

effect in material which offers no sure proof of purity would be

to change a strain of severely inbred animals by selection to a

point removed from the range of the ordinary modification in

the material, continuing the inbreeding, and then, by contraselec-

tion, to bring the character under consideration back to its start-

ing-point. Since we wrote down this challenge to the believers

in the variability of genes, one such a series of selection-experi-

ments has been performed, namely, on flies, and in this series it

has been proved to be impossible to get the material back to its

original quality.

According to Dr. Castle, Hoshino’s Table 6 shows the effect of

selection within a pure line. In the cases taken from Hoshino’s

paper, in which the progeny of an early-flowering and a late-

flowering individual of the same ‘‘pure line’’ can be compared

(in the original table there is one more case in which the earliest

parent gives the latest progeny) there are more instances in

which an early parent gives an earlier progeny than a late

parent, than cases in which an earlier parent gives a later

progeny. But if we examine the figures more closely, we observe

that the mean deviation of offspring from parents in the case in

which the earlier parent gives the earlier progeny is 0.52 day,

No. 603] SHORTER ARTICLES AND DISCUSSION 191

whereas the mean deviation of offspring from parent in cases in

which the earlier parent gives the later progeny is larger, 0.65

day. The only conclusion from Hoshino’s Table 6 is the one he

makes himself, namely, that the variation is insignificant.

We are sure that no unbiased person would conclude from the

negative facts in the table in question that the variation in

these pure lines was genotypic, or that selection in these groups

has had an appreciable effect.

On page 332 Dr. Castle writes:

If I have correctly interpreted Hoshino’s observations, flowering time

in peas is clearly a Mendelian unit character, entirely devoid of domi-

nance, so that a strictly intermediate hybrid form is the commonest

end product of a single cross between early and late varieties.

Indeed, if Hoshino’s work on the inheritance of flowering-time

of peas were the only, or the first, or the most comprehensive of

its kind, we could see reasons for such a belief. But Hoshino

only crossed two varieties differing in time of flowering. But

in peas there do not exist only one late and one early variety, but

several thousands, each with its own time of flowering. It

would not be difficult to give a list of ten names of pea-varieties

of which in every preceding one all the plants would be in flower

before one of the next opened its first flower. Therefore crossing

experiments involving two varieties can never be sufficient basis

from which to conclude that flowering-time in peas is one thing

or the other.

Tschernack, in his well-known experiments with flowering-time

of peas (1911, Mendel’s Festchrift), cited by Hoshino, made

eight different variety-crosses. Whereas in Hoshino’s work the

two varieties crossed happened to be of such a constitution, that

in the resulting F, generation there did not occur plants which

commenced flowering at an earlier time than the earliest parent,

or at a later date than the latest parent, in Tschernack’s work

such cases were met with. In Tschernack’s experiment No. 81

(1906) there were in F, found plants flowering seven days

earlier than the early parent; in experiment No. 82 (1916) even

plants beginning flowering nine days earlier than the early

parent. In experiment No. 81 (1906) there were also found

plants starting to flower four days after the latest parent, and i

in experiment 38 (1902) there were plants, which did not begin

to flower before the late parent had been in flower for a week.

It is perfectly clear, that a sort of blending may be the result

of a difference between the parents in a number of genes, in-

fluencing the quality under observation in different directions.

192 THE AMERICAN NATURALIST (Vor. LI

On page 333 Dr. Castle writes:

In typical blending inheritance the determiners of contrasted parental

conditions apparently blend into a determiner of intermediate char-

acter, the gametes formed by an F, individual being practically as uni-

form in character as those of either parent. Blending is illustrated in

the inheritance of ordinary size-differences in birds and animals.

No one who knows the work of Punnett and Bailey (cited in

Hoshino’s paper) on chickens, in which they found not only in-

dividuals in F, as small as the smallest parent and as large as

the largest, but even individuals lighter than the lightest parent

and heavier than the heaviest, could maintain that ordinary size-

inheritance in birds is blending. The gametes formed by the

Hamburg X Sebright hybrids, or by our Leghorn fighting

bantam certainly were not as uniform as those of any of the four

parental strains!

We are perfectly in accord with Castle when he reasons that

if once we admit a contamination of genes and qualitative

changes in genes, we do not need to assume that flowering-time

in peas is influenced by two genes, in the cases studied by

Hoshino. In such a case the difference in one gene would suffice.

Indeed, we would go one step farther than Castle and declare,

that, on the assumption of qualitative changes in genes, we need

not assume a genotypic difference between the parent varieties

at all. Where we differ from Dr. Castle is in the fact that we

do not believe in qualitative variation of genes. Surely more

than ten genes must influence the beginning of flowering in the

pea, else there could not be so many varieties differing in the

time of flowering. All the genes which influence stature, shape

of flowering axis, color, must necessarily influence the onset of

flowering. And we need not look for coupling between color

factors and flowering-time factors, because the factors influencing

color influence the metabolism of the whole plant, and thus the

period at which it starts flowering.

If we compare Hoshino’s paper with Tschernack’s extensive

‘experiments on the subject, we find nothing in it, which would

e us assume contamination of genes by crossbreeding, or any

qualitative variability of genes.

A. C. HAGEDOORN,

A. L. HAGEDOORN

NAGASAKI,

December 19, 1916

THE

AMERICAN NATURALIST

Vou. LI. April, 1917 No. 604

THE SOURCES OF ANATOMICAL LITERATURE

PROFESSOR ROY L. MOODIE

DEPARTMENT OF ANATOMY, UNIVERSITY OF ILLINOIS, CHICAGO

Tue study of anatomical literature has not received the

attention that has been given the writings of men in other

lines of intellectual endeavor. When we compare, for

instance, our knowledge of the literature of anatomy, and

the men who have made this literature, with the work that

has been done on the history of poetry and the poets, or

fiction, or the history of nations, we see how greatly the

development of anatomical knowledge and literature has

been neglected. Locy! especially has shown us how this

field of study may be used as a field of research in early

human documents relating to anatomy. ‘The subject has

been further developed by Stieda, Holl,? Sudhoff,? Fors-

ter, McMurrich, Roth,* Téply? and others who have con-

tributed sundry studies along these lines. That there has

been no great amount of attention paid to the subject is

probably due to the fact that the subject matter of anat-

1 Journal of Morphology, Vol. 22, pp. 945-988, 1911.

2 Archiv fiir Anatomie und Physiologie, Anat. Abth., Jahrgang, 1905,

. 96.

3 Karl Sudhoff is editor of the Archiv fiir die Geschichte der Medizin, to

which he is an active contributor (especially to be noted are his original con-

tributions concerning medieval anatomical knowledge) and he is also the

editor of Pagel’s ‘‘Einfiihrung in die Geschichte der Medizin.’’

4 Archiv fiir Anatomie und Physiologie, Anat. Abth., 1904, pp. 372-384.

5 Medical Library and Historical Journal, Vol. 4, pp. 338-350, 1906.

— fiir Anatomie und Physiologie, Anat. Abth., 1905, p. 79; 1906,

T Anatomische Hefte, Bd. 25, Erste Abth., pp. 351-398, 1904.

193

194 THE. AMERICAN NATURALIST [ Vor. LI

omy has been and is of more interest than the form in

which it is presented.

There have been a number of classical studies in the

history of anatomy, the latest and best of which is that

by Toply.’ Other and earlier studies to be mentioned are

the productions of Lauth,® Haller,” Portal, LeClere

and Manget,!* Tarin,'** James Douglas,!? Goelickius and

many other early attempts at bringing together the re-

sults-of anatomical study.

More recently the work of Daremberg in France,

Carus,'* Wieger,’® Weindler,!® and Hopf? in Germany;

Osawa'® in Japan, Bardeen’® in America, and Chievitz?°

in Denmark are to be especially mentioned.

Besides the results contained in the above-mentioned

works there is much information to be gleaned’ from the

numerous histories of medicine and especially from the

8 Geschichte der Anatomie, in ‘‘Handbuch der Geschichte der Medizin,’’

begriindet von Th. Puschmann, — von Max Neuberger und

Julius Pagel, Bd. II, pp. 155-326, 1

9 Thomas Lauth, 1815, ‘‘ Histoire i Taalma’ Strassburg. Up to the

time of Thomas Bartholin, 1671

10 Albrecht von Haller, 17 74-177 7, ‘‘ Bibliotheca Anatomica, ’’ Tomes I-II.

11 Antoine Baron Portal, 1770-1773, ‘‘ Histoire de la anatomie et de la

chirurgie,’’ Paris, Tomes I-VI. ,

12 Daniel LeClere and Jacob Manget, ei ‘í Bibliotheca Anatomica. ’’

124 Pierre Tarin, 1753, ‘‘Dictionaire Anatomique.’’

120 James Douglas, 1715, ‘‘ Bibliographiw aiai specimen, seu cata-

logus omnium pene auctorum, qui rem anatomicum professo vel obiter

sah fi illustrarun

18 Ch. Paxdithare. 1870, ‘‘Histoire des sciences médicales comprenant

DEER la Sergei la médicine, la chirurgie et les doctrines de patho- ,

logie rale. 2t

14 J, ‘Victor oe 137%, ‘í Geschichte der Zoologie, tis auf Joh, Mueller

und Charl. Darwin.’

15 Friedrich lagi 1885, ‘‘ Geschichte der Medizin und ihrer Lehran-

stalten in Strassburg vom Jahre 1497 bis zum Jahre 1872.’’

16 Fritz Weindler, 1908, ‘‘Geschichte der gynaekologisch-anatomischen

Abbildung.’’

17 Ludwig Hopf, 1904, ‘‘Die Anfänge der Anatomie bei den alten Kul-

turvélkern.’’? Abhandl. zur Geschichte der Medizin, Heft IX, Breslau.

18 Gakutaro Osawa, 1895, ‘‘ Zur Geschichte der Anatomie in Japan.’’ Vor-

trag gehalten in der Naturforscher-Ges. zu Freiburg i.B. am 20, Nov. 1895.

A.A.B. 11, N. 16/17, pp. 489-504, 2 Abb.

19 Charles R. Bardeen, ragi Sineme in America,’’ Bulletin of the

University of Wisconsin, No.

20 I. H. Chievitz, 1904, epee historie,’’ Copenhagen.

No. 604] SOURCES OF ANATOMICAL LITERATURE 195

biographical dictionaries of Panckoucke,2* Gurlt und

Hirsch,?* Pagel,? and the various biographical encyclo-

pedias. . Much valuable biographical data of many biolo-

gists is to be found in the ‘‘ Nouveau Larousse Illustré,”’

as well as in other general encyclopedias.

Even a hasty survey of the geographical development

of anatomical literature will suffice to show that the con-

tinents of Europe and North America are the chief ones

to be considered. Asia, Africa, Australia and South

America each come in for some slight claim to attention,

as will be evident from the discussion of the geographical

distribution of anatomists given below.

It can not be said that all of the men considered in mak-

ing up the list referred to below have contributed new

ideas to anatomy. Many have not. None of the Romans

were men of original ideas, at least so far as a knowledge

of anatomy is concerned. Celsus is the only Roman

whose knowledge of anatomical subjects demands any

sort of respect and his knowledge, as given in the ‘‘De

Medicina,’’ is not acquired first hand although he is to be

greatly respected for producing a medical classic.

Stieda?** has shown, however, that the Romans were

not entirely devoid of anatomical knowledge, though this

knowledge was often erroneous. The ‘‘Donaria’’ de-

scribed and figured by Stieda are supposedly offerings to

the deity in connection with the suppliant’s plea for health.

The part offered, in the form of a model of a leg, foot,

breast, viscera or head, indicates the region in which the

suppliant suffered and from which distress he wished to

be relieved. The objects are of marble and bear the date

of about the first century B.c. They are, for the most

21C. L. F. Panckoucke, 1820, ‘‘Dictionaire des Sciences Médicales-Biog-

raphie Médicale,’’ 7 volumes.

22 <í Biographisches eea Martor agondn Aerzte aller Zeiten und

Völker, ”” 1884-88, 6 volum

23 a E Taikon hervorragender Aerzte des XIX. Jahrhun-

derts,’’ 190

230 ag Stieda, 1901, ‘‘Anatomisch-Archiiologische Studien,’’ II.

Anatomisches über alt-italische Weihgeschenke (Donaria), Anatomische

Hefte, Bd. XVI, pp. .1-84, Taf. I-IV.

196 THE AMERICAN NATURALIST [ Von. LI

part, crudely done and can not be taken as indicating any

attempt to illustrate anatomy. Often the internal parts

shown bear some resemblance to the human structures.

Occasionally the liver of a mammal is incorporated in the

same piece with the human heart and lungs. The viscera

are very crude and can not be taken as indicating any de-

gree of positive knowledge concerning the parts shown.

None of the Arabians produced original ideas or liter-

ature concerning anatomy. Abdollatif (1162-1231) is

the only one of the Arabians who departed in the slightest

degree from the writings of Galen and Hippocrates.

While in Egypt he was studying some human bones in a

cemetery when he ascertained that the jaw is formed of

one piece; that the sacrum, though sometimes composed

of several, is most generally of one. On the basis of these

observations he criticized the writings of Galen and thus

showed himself to be a man of original ideas.

Flores** in his ‘‘History of Medicine in Mexico’’ has

listed the following teachers of anatomy in the University

of Mexico: Febles, Benitez, Garcia, Cheyne, Peña, Garcia

Cabezon, Rendon, Escobedo, Villar, Jecker, M. Andrade,

Muñoz, Villagran, Duran, F. Ortega, Chacon, Montes de

Oca, Velasco, San Juan, and Cordero é Icaza, but, so far

as I have been able to ascertain, none 7 these men have

been productive.

There is no Egyptian literature of anatomy, and ap-

parently there was no definite knowledge of anatomical

structure. The practise of embalming had attained at

one period great perfection in Egypt and this may have

resulted in a certain degree of anatomical knowledge, but

it was so overclouded: by religious fanaticism and super-

stition that it amounted to little. Thus MceKay*** says:

“The Egyptians probably knew next to nothing about

anatomy, as their religion forbade dissection, and the em-

balmers probably learnt little. After the Paraschistes

24 Francisco A. Flores, 1888, ‘‘ Historia de la Medicina en Mexico desde la

epoca de los Indios hasta la Presente,’’ Tomo I-

24a W, J. S. McKay, 1901, ‘‘ The History of Ancient Gynaecology,’’ New

York, p. 6.

No. 604] SOURCES OF ANATOMICAL LITERATURE 197

had made the preliminary abdominal incision, the Tari-

cheutae were accustomed to pass their hands through

the incision into the body and remove the heart and

kidneys and digestive organs. If they were accustomed

to remove the uterus and ovaries, they must have gained

some knowledge of the organs, but we have no authority

for saying that the uterus was really removed. The

custom that the Egyptians followed, that of making

models of the parts?* that had been healed and then hang-

ing them in the temples, may have been useful for clin-

ical instruction.”’

Among the Hebrew peoples of ancient times sacrifices

(Genesis xv. 9-10) were common, and the appearance of

the viscera of the animals sacrificed were probably fa-

miliar. This may have resulted in a degree of anatom-

ical knowledge. There are, apparently, no definite state-

ments concerning anatomical matters in the Bible, the in-

formation there given being of a purely popular charac-

ter. In the Babylonian Talmud, however, there are a

number of references” to subjects of anatomical interest.

The number of bones in the skeleton is estimated at 248 or

252, and one of these, the bone Luz, which was supposed

to be situated somewhere between the base of the skull

and the coccyx, was regarded as the indestructible nucleus

from which the body is to be raised from the dead at the

resurrection.22 The Talmud also displays some knowl-

edge of the esophagus, larynx, trachea, and the mem-

branes of the brain. The pancreas and other internal

organs are briefly referred to.

Among the ancient peoples who thrived in and around

Mesopotamia there is, apparently, no anatomical liter-

ature. What little of anatomy may have been known was

acquired through religious observances, such as auguries

and sacrifices. Stieda? especially has studied the indi-

24b These were ‘‘Donaria’’ and the custom was doubtless derived from

the Romans.

25 Julius Preuss, ‘‘ Biblisch-Talmudische Medizin,’’ Berlin.

26 F, H. Garrison, N. Y. Med. Jour., 1910, Vol. 92, pp. 149-151.

27 Ludwig Stieda, Anatomische Hefte, Bd. 15, pp. 673-720, Taf. 57.

198 THE AMERICAN NATURALIST [ Von. LI

cations of anatomical knowledge among these ancient peo-

ples as this knowledge has been preserved in their sculp-

tures. It is a matter of great interest that he has inter-

preted a terra-cotta object from Babylon, to which an age

of from 2000-3000 s.c. may be assigned, as a model of a

sheep’s liver, supposedly used in connection with sooth-

saying or with sacrifices. This interpretation is sustained

by the description of two other similar objects of a later

date, one in alabaster from Piacenza, and a bronze liver

from Settina. One can recognize on the visceral surface

of these objects the processus papillaris, the processus

caudatus, and the vesica fellea; all of which are very

clearly represented. The lower surface of the object

from Babylon is divided into squares and studded with

inscriptions, supposedly of a prophetic nature.

In addition to these very definite anatomical models

many plastic representations exhibit some knowledge of

the superficial musculature of the extremities. The larger

subcutaneous veins, such as the cephalic, basilic, and

saphenous, are often clearly shown. From an anthro-

pological standpoint it is noteworthy that various racial

types are indicated in some of the representations of the

head, so that we can not say that these peoples were en-

tirely devoid of anatomical knowledge and we are forced

to admit their keen powers of observation.

Such anatomy as was taught to students in the medical

schools of China was highly erroneous and fantiful. Al-

though the study of medicine has a very ancient history

in China, as ancient as the history of its civilization, going

back to more than 3000 years B.c., anatomy was not studied

at all in any laboratory form. They taught, for instance,

that there are 365 bones in the human body; that the small

intestines were attached to the heart; that they were tra-

versed by the products of digestion; that the larynx opens

into the heart; the spinal cord into the testicles, that the

lung has eight lobes; the liver seven, that the kidneys, sus-

pended the vertebral column, have the form of an egg and

possess the subtle principle of generating the spermatic

No. 604] SOURCES OF ANATOMICAL LITERATURE 199

fluid, primarily elaborated by the brain, condensed in the

testes and from there conveyed to the spermatic duct.

Osteology was somewhat better known, although the

skull, pelvis, forearm and leg were regarded as being

formed of one bone each, or at times eight bones were

assigned to the head in the male and six in the female.

Something was known of the tendons and ligaments. The

spleen and heart were regarded as the organs of reason.

Ancient Chinese medical literature consists of a large

number of works, none of which are of any scientific im-

portance. There is no modern Chinese anatomical lit-

erature.

What little of anatomy was known in ancient India is

contained in the writings of Atreya, a physician who

wrote a good description of the bones of the human body,

and who is said to have taught in the Taxila University

during the sixth century B.c.; as well as in the writings of

the surgeon Susruta, of a somewhat later date. “As the

writings of these men have been interpreted by Charaka,

ancient Hast Indian anatomy regarded the body of man

as possessing seven skins, seven elements, 300 bones, 24

nerves, 3 fluids, 107 joints, or 68 movable joints and 142

immovable ones, 900 ligaments, 90 tendons, 40 principal

blood vessels with 700 branches, and 500 muscles. The

blood vessels and nerves®® radiated out from the um-

bilicus as a center. Nothing was known of the courses of

these structures within the body.

There is a later publication of about a.n. 800 entitled

**Amarakosha,’’ which discusses somewhat the nature of

the human body but there is no later treatise which might

be termed anatomical, and there is no modern East In-

dian anatomical literature.

While engaged in a biographical study of the men who

have contributed to the advancement of our knowledge of

vertebrate anatomy, the writer has been attracted by a

number of interesting facts relating to the sources of

anatomical literature, which, he believes, are not generally

28 Haeser, ‘‘ Lehrbuch der Geschichte der Medizin,’’ Bd. I, p. 18-20.

200 THE AMERICAN NATURALIST [Vou. LI

recognized. The following preliminary study is an at-

tempt to arrive at some conclusions as to the origin and

development of our modern anatomical literature. It is

presented here in anticipation of further studies along

these lines.

The names of the men included in the above-mentioned

study are of those anatomists, or contributors to ana-

tomical literature, who are no longer living, and who have

contributed in any way to the anatomy of the vertebrates,

whether by practical or theoretical studies. The men of

all countries and all times have been listed, so far as it

has been possible to ascertain them. Doubtless many

have been overlooked because their records are in rela-

tively obscure places.

The subjects represented in the present study are:

human anatomy, artistic anatomy, anthropology, com-

parative anatomy, embryology, histology, zoology, verte-

brate paleontology and subjects of general interest

which bear theoretically on the morphology and evolution

of the vertebrates, such as Mendel’s work at Briinn, and

the work of Darwin, Weismann, Charles Bonnet and

Lamarck. It may be contended that these subjects con-

stitute biology rather than anatomy, but biology is cer-

tainly the more inclusive term. We may, to be sure, speak

of the anatomy of the bacteria and in a sense the bac-

teriologist is an anatomist, but for my present purpose

the names of those men who have contributed to our

knowledge of the morphology of the vertebrates will suf-

fice. One of the guides, which has been useful in select-

ing the names suited for the list, is that of the anatomical

terminology. If there are anatomical structures (such,

for instance, as Hesselbach’s triangle) named for the

man, he is included, though this is by no means the only

guide. Those men whose writings are of a strictly taxo-

nomic nature are not included, unless important. theo-

retical results have arisen from such writings, such as has

been the case with the taxonomic work of Lamarck, Lin-

nus, Cuvier and others.

No.604] SOURCES OF ANATOMICAL LITERATURE 201

It is hoped later to make a comprehensive survey of

the development of anatomy. Over one thousand names

have been compiled, and will ultimately be studied. Eight

hundred of these have already been partially examined

and will shortly be published.

In the development of our anatomical literature there

has been involved a whole host of men in a number of dif-

ferent lines of activity, which it will be interesting to dis-

cuss. Many of the men included in the list were not

professional anatomists but since they contributed to the

advancement of anatomical knowledge we may regard

them as contributors and they are hence deserving of

consideration.

As would be expected, the following survey of the

anatomists indicates, in general, an intellectual develop-

ment in each country at the time when other conditions,

physical, social, religious and political, favored the growth

of mental work among the nation, although this statement

finds certain contradictions, as in the case of Michael Ser-

vetus, Abano, Fallopio, Malpighi, Vesalius, and many

more of the early students especially, whose work was ac-

complished under adverse conditions. The dates of the

majority of the anatomists who find a place in the present

study belong to a period when intellectual endeavor had

attained a firm place in each country. Among the Greeks

for instance, there is no one who attained eminence in

anatomy later than the third century a.D’. No modern

Greek anatomist is included in the list.

There are representative anatomists of twenty-seven

nationalities, though many of the countries are not widely

separated geographically. The following geographical

distribution indicates nothing previously unknown, but is

_ presented here simply as an interesting survey. ‘There

are doubtless many more men of all these nations who are

deserving of mention. The list contains 1 Japanese

(Mitsukuri, 1858-1909, an embryologist, who is here re-

garded as the only one of this nation who has occupied a

high place in anatomical work); possibly also the zoolo-

202 THE AMERICAN NATURALIST [ Von. LI

gist Nishikawa and the anatomist Taguchi should be

mentioned; 1 Armenian (Aleana Mosali, who in the thir-

teenth century wrote a treatise on the anatomy and dis-

eases of the eye, chiefly compiled from Arabian, Chaldean,

Jewish, Greek and other sources) ; 1 Hungarian, 1 Polish,

1 South American (Florentino Ameghino, 1854-1911, a

student of vertebrate paleontology, is the only represen-

tative of the large South American continent in the list.

Ameghino’s attainments in vertebrate paleontology en-

title him to a high place among the anatomists of the

world); 1 Turk (Schanzi Zadeh Mehemmed Ataullah, a

Turkish physician, who after completing his studies in

Italy, published, in 1820, a work on human anatomy, in

folio, illustrated with 56 copper plates); 2 East Indians

(Atreya, a physician, who was a teacher in the Taxila

University in the sixth century B.c. He wrote an osteol-

ogy, which was later edited by one of his students, Cha-

raka. Susruta, an East Indian surgeon also deserves

mention), 2 Bulgarians, 3 Flemish (of whom the greatest

was Vesalius), 4 Romans (none of them men of original-

ity), 5 Russians, 5 Belgians, 7 Irish, 7 Swedish, 7 Span-

ish, 7 Bohemians, 9 Arabians (Abdallatif, Albucasis, Avi-

cenna and others), 11 Scottish, 12 Danish, 16 Swiss, 17

Austrians, 22 Greek, 36 American, 40 Dutch, 77 English,

78 Italian, 127 French and 240 Germans, making a total of

seven hundred and thirty-six. The citizenship of many

of the men studied has been hard to determine on ac-

count of the migration of teachers from country to coun-

try, which in the seventeenth, eighteenth and nineteenth

centuries has been very common; but the above is a fair

representation of the proper distribution of the men who

have developed anatomy.

More than twenty-five professions are represented by

the men who have been given a place in the list. In at-

tempting to decide the position of a man in the following

scheme it is not always easy, on account of the varied in-

-erests of some of them, to place them properly. Should

Albrecht von Haller, for instance, be regarded as an anato-

No. 604] SOURCES OF ANATOMICAL LITERATURE 203

mist, philosopher, poet, physiologist, botanist, or as an ad-

ministrator, since he:attained some eminence in all of these

lines? Should Emanuel Swedenborg be classed as a

philosopher, anatomist, geologist, civil engineer or theo-

logian? In the present scheme Albrecht von Haller is

arbitrarily regarded as an anatomist, although a very

large share of his work was physiological. Swedenborg

is regarded as a philosopher, for as such he is usually

classed, although his anatomical writings were of a high

type. Descartes is likewise regarded as a philosopher,

although he might with justice be called a mathematician

or anatomist. The subdivisions of histology and embry-

ology are necessary since a few men specialized strictly

‘n these branches of anatomical work, and they are known

for their contributions to these subjects; such for in-

stance as Balfour’s noted studies in embryology and

Corti’s in histology.

The following list will show in a general way the numer-

ical distribution of the men in various professions: 1 jur-

ist, (Johannes Peyligk, who in 1499 published in Leipzig

his ‘‘Philosophie Naturalis,’’? which contains ten figures

of separate organs of the body), 1 statistician, (Francis

Galton), 1 beadle or exciseman (Leeuwenhoeck,”® who for

thirty-nine years worked as a subordinate customs officer

or beadle at a salary equal to $125 per year. In spite of

this meager income he contributed 375 papers to the Royal

Society of London and 17 to the Academy of Science in

Paris, besides making all of his microscopes), 1 pope (In-

nocent XII, who, working under the direction of Lancisi

(1654-1720), is said to have been one of the first to ob-

serve, under the microscope, the circulation of blood in

the capillaries); 1 prior, 1 journalist, 1 theologian (Cas-

par Bartholin, the founder of a professorial dynasty in

the University of Copenhagen whose members taught in

29 It should be noted that the following account is that of Sir Benjamin

Ward Richardson, ‘‘ Disciples of Ausculapius,’’ Vol. 1, p. 111. Garrison, how-

ever, says in his ‘‘Introduction to the History of Medicine,’’ p. 185, that

Leeuwenhoeck was ‘‘an inheritor of well-to-do brewers (and) led an easy-

going life.’’

204 THE AMERICAN NATURALIST [ Vor. LI

the university for one hundred and thirty-five years) ;

1 lawyer (Michel Alberti who contributed nearly 300

separate works on several phases of human knowledge) ;

1 bibliographer (Mangetus, ‘‘ Bibliotheca Anatomica’’),

1 clergyman (Wm. Buckland), 2 monks (of whom one

was Gregor Mendel and the other Michael Servetus, a

Spanish monk, the discoverer of the pulmonary circu-

lation, which he published in 1553, seventy-five years

before the appearance of Harvey’s great work on the

motion of the heart and the circulation of the blood);

3 physicists (Helmholtz and others), 5 poets (Mark

Akenside, who wrote his inaugural dissertation on the

fetus; Goethe, who is widely known for his papers in

comparative anatomy, and for his homology of the inter-

maxillary bone of men and mammals; Lucius Francois

Anderlini, a surgeon of Saint-Angelo, in the duchy of

Urbino, who published in 1739 a poetical work ‘‘The

Anatomist in Parnassus, or a Compendium of the Parts

of the Human Body arranged in Verse’’; Scipion Abeille,

a military ‘surgeon in Flanders who wrote, in 1689, a

poetical anatomy on the parts of the head and neck; Al-

brecht von Haller was a poet of note, and many other men,

interested in anatomical subjects, have been poetically in-

clined), 8 artists (Albrecht Dürer is well known for a

work on human proportions which is of value from an

anthropological standpoint; Michelangelo, working with

Realdo Colombo (1494-1559), became deeply versed in

human anatomy; Leonardo da Vinci, about 1510, com-

pleted a wonderful series of anatomical sketches, based

on his own dissections) ; 5 ophthalmologists, 5 anthropolo-

gists (Blumenbach (1752-1840) was the founder of this

science); 5 comparative anatomists, 6 embryologists, 7

pathologists, 9 histologists, 8 botanists, 14 paleontolo-

gists, 17 philosophers (Aristotle, Descartes, Swedenborg,

ete.), 24 physiologists, 52 zoologists, 69 surgeons, 175

physicians, and 255 professional anatomists who devoted

most of their attention to the teaching of anatomy.

It has not been possible to determine accurately the

No.604] SOURCES OF ANATOMICAL LITERATURE 205

profession of many of the men included in the list, and

for this reason many whose names are in the list are not

classified here. For instance, Petrus d’Abano, who pub-

lished in 1496 the first illustrations of the abdominal mus-

cles, was either a physician or a professional philosopher,

and probably the former, since Locy says the illustrations

seem to have been based on a dissection. And there is a

story concerning the large fees charged by Abano, which

indicates that his profession may have been medicine,

although his intellectual interests were chiefly philo-

sophical. Bartholomeus Anglicus was probably a physi-

cian.or a publisher. At any rate he published in 1485

one of the first printed illustrations (a wood cut) of any

anatomical interest. Many surgeons have contributed to

anatomy, and were really at the same time teachers of

anatomy, such as Nicolas Ivanovitch Pirogoff, who wrote

an enormous cross-section anatomy in five volumes, pub-

lished in 1852; notwithstanding which he is classed in the

list as a surgeon, since his anatomical teaching appears

to have been incidental to his surgery.

The social status of the men who have developed ana-

tomical knowledge has been difficult to determine because

of scant biographical data. There is sufficient, however,

to indicate that contributors to anatomical knowledge

have been recruited from a wide range of social condi-

tions. Some of them, and often the brightest, have lived

in poverty. Others have been representatives of a much

higher social class. It may safely be said that the study

of biological matters has attracted attention of no special

class, but that interest has been scattered. It may be said

that the great majority of men who have developed

anatomical knowledge have been men of moderate attain-

ments, belonging to an average rank in the social scale.

The above statements must be modified by the conditions

under which the men lived and the age in which they lived.

During the early centuries of the Christian Era living

conditions in general were not so wholesome® as they

have since become.

80 Hirsch, August, ‘‘Handbook of Geographical and Historical Pathol-

ogy,’’ 3 vols.

206 THE AMERICAN NATURALIST [ Von. LI

Precocity and productiveness have gone hand in hand

among the few anatomists who have exhibited these in-

teresting traits; yet it is only fair to state that pro-

ductivity has not been dependent on precocity. Such men

as Bichat, Balfour, Haller, Vesalius, Johannes Mueller,

Bernard Siegfried Albinus, Pollard, Sir Charles Bell,

are rather unusual examples of precocity.

It may be of interest to give a few detailed accounts of

some of these men. During the short period of seven

years, beginning his career at the age of twenty-three,

which Marie Francois Xavier Bichat (known as the father

of histology) devoted to his scientific studies, he came to

be recognized as one of the foremost biologists of all time.

He exhibited unusual talents for prolonged and intense

application to the pursuit of his favorite science. Be-

sides editing the surgical writings of his teacher, Pierre

Joseph Desault, in three volumes, he is himself the author `

of three separate works, any one of which would have

secured him fame. Bichat’s claim to recognition as a

great biologist lies in his division, in 1800, of the tissues

of the body into twenty-one non-microscopic varieties.

Francis Maitland Balfour ended his brief career at the

same age as did Bichat, thirty-one; but during the few

years he devoted to his favorite study of embryology he

laid a secure foundation for lasting fame. Especially in

his monograph on the development of the elasmobranch

fishes and in his comparative embryology, he exhibited a

broad grasp of the subject which has seldom been equalled

in the same field of learning.

Andreas Vesalius, the great Flemish anatomist, de-

scended from a family of learned physicians, began his

study of anatomy at the age of fourteen with Dubois in

Paris, and at the age of twenty-two was called to Padua

to give public demonstrations in anatomy. His large

work on human anatomy, ‘‘De corporis humani Fabrica,’’

which earned him the title of the founder of modern sys-

tematic anatomy, was published when he was thirty. Al-

though he lived for twenty years after its appearance he

No. 604] SOURCES OF ANATOMICAL LITERATURE 207

did little or nothing to develop anatomy save to issue suc-

cessive editions of his ‘‘Fabrica.’’ Three years before

his death there appeared from the press at Madrid his

edition of Fallopio’s anatomy.

Albrecht von Haller, Swiss anatomist, physiologist,

poet, botanist and administrator, deserves to be regarded

as the most precocious and one of the most productive of

all the men who have contributed to the advancement of

anatomy. At the early age of eight he is said to have

compiled a biographical index of over 2,000 eminent men

and women. This prodigious activity he continued for

the next sixty years, and it is stated that he conducted a

monthly scientific journal to which he himself contributed

12,000 articles on nearly every phase of human knowl-

edge. Nor were his contributions superficial, for Sir

William Turner says that his anatomical descriptions

and his beautiful and accurate figures were the most val-

uable which had appeared up to that time (1746-51). A

list of his medical writings alone fills eleven octavo

pages of closely printed type. Late in life he returned to

Berne from Göttingen, where from 1736-1753 he had held

the position as professor of anatomy, physiology, surgery

and botany, to engage in his native land in municipal ad-

ministration. :

Johannes Mueller, who, in the first half of the last cen-

tury, became famed as an anatomist, zoologist, and physi-

ologist, became, at the age of twenty-five, professor ex-

traordinary of physiology at the University of Bonn. He

began an early career of prodigious activity, which he

continued for thirty-three years.

Avicenna at the age of seventeen was regarded as an

excellent physician. At twenty-one he was the author of

several treatises. He was called ‘‘The Prince of Arabian

physicians’’ by his contemporaries. `

Bernhard Siegfried Albinus (1697-1770), for fifty

years a teacher at the University of Leyden, was called to

_ the University at the age of twenty-one, from Paris,

whither he had gone on the advice of his father, to study

208 THE AMERICAN NATURALIST [ Von. LI

medicine and especially anatomy with Winslow and Sénac.

He had hoped to spend some years in Paris, but after six

months, on the retirement of Rau from the professorship

of medicine, anatomy and surgery at Leyden, Albinus was

called, at the suggestion of Boerhaave, to take charge of

the anatomy. Shortly after reaching Holland the Uni-

versity of Leyden gave Albinus his doctorate of medicine

without either examination or thesis. His inaugural ad-

dress ‘‘Oratio inauguralis de anatome comparata’’ clearly

showed the master mind. At Leyden, Albinus gave a new

. direction to the study of anatomy which had lain dormant

since the appearance of Vesalius’s ‘‘De Corporis Humani

Fabrica” (1543). He brought to greater perfection

the art of anatomical illustrating, which had not pro-

gressed since Vesalius, and especially in his ‘‘ Historia

musculorum hominis, Leyden, 1734, in-4°’’, on which his

fame as an anatomist rests. This magnificent work was

twice reprinted and translated into French by Pierre

Tarin in 1753. Albinus published also other valuable

works and left a marked impression on his subject.

It would appear, from the above study, that the sources

of anatomical literature are to be found in the writings of

the men who have developed the subject in the various

countries mentioned. The literature of anatomy has

now attained sufficient dignity to warrant the prepara-

tion of a ‘‘Source Book,” which would be very useful.

Africa, aside from the Grecian incursion in the early cen-

turies of the Christian-era which resulted in the Alexan-

drian school, has produced no men of attainments in

anatomy. South America has one man to its credit.

Mexico and China have none. The literature of the rest

of the world has radiated out from those European coun-

tries which have fostered our modern civilization. The

outlook for an excellent type of anatomical literature in

the future is better than it has ever been and the student

who attempts to work in the field of the history of this

literature will find himself among interesting and de-

lightful surroundings.

THE CASE OF TRICHOMONAS!

DR. PHILIP HADLEY

THE great group of flagellated protozoa has, within the

past two decades, afforded a wealth of interest for those

concerned with pathogenic protozoology; and only in

slightly lesser degree for those concerned with taxonomic

problems involving these highly interesting microorgan-

isms. The field of trypanosome research has, in itself,

afforded much new data on morphology and on compli-

cated life histories; and has been the chief center of in-

terest for many years.

But there exists another group of the flagellated proto-

zoa, represented by some of the commonest forms encoun-

tered in the intestinal tract of man and the lower animals,

whose frequency of occurrence, simplicity of organiza-

tion and freedom from imputations of possessing patho-

genic powers, have enabled them to go their way, for the

most part unmolested by the protozoologist. If the proto-

zoan would escape the inquiring gaze of the researcher

he must be self-effacing; he must lead a quiet life of seclu-

sion, free from those public manifestations of unrest and

mob movement which are sure to bring him, sooner or

later, before the bar of investigation, whereupon his whole

life is laid bare.

Trichomonas was such a quiet law-abiding protozoan

before the trouble began, before he was detected in insti-

gating internal revolutions which bid fair to annihilate

the turkey-raising industry of the country. The cireum-

stantial evidence which has been brought forward against

him has served to reveal many aspects of the life history

of Trichomonas with which we were not previously ac-

quainted; to disclose his participation in activities for

which he was previously regarded as scarcely capable,

and to demonstrate the existence of certain family resem-

blances to some of his companions in mischief who have

long been recognized as trouble-makers in the cell or-

ganizations of many animals. j

1 Contribution No. 231 from the Agricultural Experiment Station of the

Rhode Island State College, Kingston.

210 THE AMERICAN NATURALIST [ Von. LI

Trichomonas is found living in the intestinal contents

of nearly all animals and has, since its discovery by Donné

in 1837, appeared under many different names. Itisa small

organism, built on an oval or pear-shaped plan, and meas-

uring in the adult trophozoite stage, about 10» in length

by 5 to 6» in breadth. The youngest free-swimming

stages are much smaller, about 5» in length; and some-

times trophozoites are encountered that measure 12 or

13». Although usually of an elongate oval or pear shape,

the morphology of the trophozoites is highly variable, and

triangular or crescentic forms are frequently encountered,

especially among the young. The anterior end is usually

blunt, while the posterior end is frequently drawn out into

a point.

If one adds to the salt solution in which these flagellates

are being examined a little albumen or glycerin, to lessen

the rapid swimming of the organism, some of the details

of structure can be made out. The body plasm shows a

greenish tint, and the nucleus, which is situated an-

teriorly, appears pinkish. In fresh preparations, one of

the most obvious features is the axostyle, a short bristle-

like structure which projects outward somewhere in the

posterior quarter of the body, and which is seen, upon

careful focusing, to extend into the body of the flagellate,

running anteriorly to terminate somewhere in the vicinity

of the nucleus (Figs. 1, 2). Inside the body the axostyle

appears homogeneous in structure and bandlike.

- Next to the axostyle, the most obvious feature is the

vibratory or undulatory membrane which extends like a

curved fin down the dorsal side of the flagellate body

(Fig. 1). It is shallow at the beginning and at the end,

but midway of its length it may have a depth of 2 to 3».

Over this membrane may be seen to travel at 3 to 4p in-

tervals, waves of motion from the anterior toward the

posterior end of the body. If one follows closely the.

„course of this membrane, it is found to have its origin in

a granule, or in a group of small granules, located in front

of the nucleus at the most anterior part of the animal,

and known as the blepharoplast-complex. The granules

No. 604] THE CASE OF TRICHOMONAS 211

are very small, measuring not more than 0.5 to 1.02, and

stain deeply with the chromatin stains. Their function is

at the present time only a matter of speculation. Tracing

the dorsal membrane posteriorly, it is found to extend to

the extreme end of the body, where it narrows and is con-

tinued in the form of a terminal flagellum (‘‘Schlepp-

geissel’’) which has a length ordinarily about dome to

that of the body.

_ From the anterior end of the flagellate extend cu

more flagella (Fig. 1). These may be even longer than

the body of the flagellate itself, and beat downward, as

indicated by the arrow in Fig. 1. It frequently appears

as if two of these three flagella were united in a common

stalk at their base, so that they beat together, while the

third flagellum beats independently. The origin of these

three flagella is difficult to make out, but in many cases

they appear to arise from one of the granules of the

blepharoplast-complex, and usually not from the granule-

which is the origin of the undulatory membrane.

The only other structures which can be seen well in

fresh preparations are the mouth or cytostome and

the food vacuole. The cytostome is a horn-shaped open-

ing which extends into the body on the ventral side, and

just behind the nucleus (Fig. 2). It may be bordered by

cilia. The beat of the anterior flagella isin such a direc-

tion that currents of fluid containing the bacteria which

serve as the chief food for the flagellates, are driven into

the mouth opening. Posterior to the nucleus, usually in

about the middle of the cell body lies an oval space, the

food vacuole (Fig. 2). It may sometimes be represented

by a group of smaller vacuoles which coalesce to form a

single cavity. In these vacuoles are usually present bac-

teria and cocci undergoing digestion. The structures

mentioned above can be seen well in unstained organisms,

but there are others which appear to advantage only upon

Staining. In preparations stained by the Heidenhain

iron-hematoxylin method (wet process) the most note-

worthy of the remaining structures is the chromatic line.

This is a heavily-staining band which extends like the are

212 THE AMERICAN NATURALIST [ Vou. LI

of a circle from the blepharoplast to the point where the

undulating membrane terminates. It thus follows closely,

in the body plasm, the trend of the membrane, and is re-

garded as representing a kind of supporting structure.

The chromatin line is heavier in its mid part and tapers

at each end. As will be pointed out later, when in the

process of spore formation, the trophozoites round off,

the chromatin line becomes bent into a hoop, so that its

extremities come very near to meeting (Fig. 4). .

Another structure which appears with distinctness in

stained preparations is the line of chromatic blocks (Figs.

3,4). These peculiar bodies appear as a single or double

row, or as a somewhat irregular line, of deeply staining

granules extending from the region of the blepharoplast

backward through the plasm to end somewhere in the

posterior quarter of the cell. The anterior portion is

likely to be thicker and sometimes may partially obscure

the nucleus. The curve followed by the line of blocks is

about parallel to that of the chromatic line and the two

are seldom far distant from one another.

It is interesting to observe in connection with all of

these struetures that, in their arrangement, they produce

in the flagellate organism a more or less perfect bilateral

symmetry. The normal swimming position of the tropho-

zoite is with the undulatory membrane above. Directly

below this extends the chromatic line and below the chro-

matic line is the ‘‘line of blocks.’? The cytostome is in

the midline and somewhat ventral. The blepharoplast is

in the midline except in some of the stages of division.

The food vacuoles occupy a variable position, but are usu-

ally grouped near the middle of the posterior body and

caudad of the chromatic line. Sometimes it appears as if

the line of blocks and the axostyle passed through the

food vacuoles. The axostyle projects from the cell body

in the midline although not necessarily at the most poste-

rior part of the body. This symmetry is easily seen when

the organisms are observed swimming freely in a favor-

able medium. Owing to the fact that the dorso-ventral

diameter is greater than the transverse diameter, most

214 THE AMERICAN NATURALIST [ Vou. LI

of the flagellates when stained on the slide present a

lateral aspect as shown in Fig. 2, since they fall over on to

their side in the drying out of the film.

But the appearance of the flagellate as described above

does not endure for very long, simply because the tropho-

zoite stage itself does not endure. The development of

the trophozoite marks the period of youth, and when the

organism has sufficiently fed on bacteria and cocci, and

obtained a sufficient amount of reserve food, it passes on

either into division or into a form of autogamous repro-

duction by which the flagellate population is increased at

a rapid rate.

In the case of division, the process seems to be for the

most part longitudinal. The first indication of it is to be

seen in the blepharoplast-complex and in the nucleus.

From each new blepharoplast there appears to grow out a

new chromatic line, extending more or less parallel to the

old line. From these new lines the new undulating mem-

branes appear to arise. The writer has not been able to

observe the division-stages of the flagella, although stages

have been seen in which new flagella are present in con-

nection with each new blepharoplast. Neither has it been

possible to follow the changes in the axostyle. As to the

chromatic blocks, these also seem to disappear and are

probably formed anew in the daughter cells.

But reproduction by division, though occurring com-

monly in the intestinal content, is probably not the chief

method of reproduction. At all times, though at some

times more markedly than at others, the flagellates enter

into a course of autogamous reproduction in which several

daughter cells are formed out of a single mother cell.

This interesting process can be followed in considerable

detail by means of suitably stained smear preparations.

The first step in this process is the ‘‘rounding-off’’ of

the previously elongate or crescentic trophozoite after it

has reached maturity. If the body-form was erescentic

there occurs a filling-out of the concave surface so that at

first a full oval shape is produced; later the organism be-

comes spherical. This rounding-off process, which is

No. 604] THE CASE OF TRICHOMONAS 215

usually accompanied by some increase in size, is marked

by important changes in the structures alluded to above.

These may be considered in some detail first with ref-

erence to the external features.

Perhaps the most noteworthy change, aside from the

assumption of a spherical shape, involves the chromatic

line. This gives the appearance of lengthening until it

forms a hoop almost completely encircling the organism

(Fig. 4). Itis common to see the ends of the line occupy-

ing positions less than 45 degrees apart as measured on

the circumference of the spherical flagellate. At the same

time the flagella have been lost and the undulatory mem-

brane has decreased in size, though it follows approxi-

mately that part of the circumference corresponding to

the chromatic line. Of course its functioning has been

proportionately reduced and although its undulatory mo-

tion may continue, this movement fails to cause progres-

sive movement of the flagellate, but brings about a slow

rotation of the organism in the same position. Occa-

sionally this movement may be assisted by a single an-,

terior flagellum or a remnant of one which remains after

the others have disappeared. In the final stage all trace

of the cytostome is lost, and in fresh preparations the or-

ganism appears as a ball of fairly homogeneous fluid, sur-

rounded by a granular cytoplasm containing the nucleus

(Fig. 5).

But more interesting are the changes that have been

occurring in the internal structures, as revealed by stained

preparations. The alterations in the food vacuole are

possibly the most significant. In the trophozoite stage

the vacuole was made up of one or more spaces represent-

ing probably not more than one eighth to one tenth of the

organism (Fig.2). As the rounding-off process proceeds,

the vacuole increases in size until it oceupies the greater

part of the ventral portion of the flagellate (Fig. 4). It

begins to crowd the cytoplasm against the dorsal wall,

and in this area lies the nucleus, which, as a result of

pressure, becomes somewhat flattened. At the same time

the ‘‘line of blocks’? and the axostyle, which gives the

216 THE AMERICAN NATURALIST [ Von. LI

appearance of passing through the food vacuole, begin to

degenerate and eventually both disappear. The chromatic

line endures for a longer period, however, and remnants

of it may be seen for some time after the ‘‘line of blocks,’’

axostyle and undulatory membrane have vanished. The

blepharoplast also can be detected as long as the remnants

of the chromatic line are visible (Figs. 6, 7). This in-

“crease in the size of the food vacuole seems to be due,

partly at least, to the taking-in of fluid, since while this

process is occurring the flagellate is increasing in size and

becoming more plastic in the constitution of its proto-

plasm.

The food vacuole has now increased in size to represent

the greater part of the flagellate cell and is surrounded by

a crescentic ring or layer of cytoplasm seemingly much

reduced in amount (Fig. 5). From this time on the most

important changes concern the nucleus. This is now flat-

tened or sometimes flask-shaped, and soon divides into

two equal portions which travel through the region of

cytoplasm to take positions at opposite sides of the ball

of reserve substance (food vacuole). Here each experi-

ences a further division resulting in the production of

four daughter nuclei (Figs. 7,8). These apparently may

divide again until either eight or sixteen daughter nuclei

are formed occupying positions about the periphery of

the cell. Frequently smaller portions of nuclear sub-

stance are to be seen in the cytoplasm following the first

nuclear division and it is probable that these represent

reduction bodies (Fig. 8), although the writer has not

observed them in the course of formation. About the

daughter nuclei there seems to gather by slow degrees a

layer of cytoplasm and eventually they break out of their .

peripheral ring of maternal cytoplasm to enter the ball of

reserve substance occupying the center of the cell (Fig.

10). This is gradually consumed by the young organisms

which slowly take on an elongated shape. During this

time the cyst wall which had formed about the mother cell

has been weakening and finally the young organisms

break out of the mother, cell and appear as the youngest

No. 604] THE CASE OF TRICHOMONAS 217

trophozoites measuring from 4 to 5» in length and about

3 in breadth, equipped with anterior flagella at least,

and possessing a relatively largé nucleus and minute

blepharoplast. The other organelles characteristic of the

mature trophozoites appear to develop by degrees as the

trophozoite increases in size.

These, then, are the two chief methods of reproduction.

Ordinarily the course is very simple, but from a study of

both fresh and stained material it is clear that several

complicating factors may enter. For instance there is

evidence that conjugation may occur, not only between

two individuals but perhaps between three or four. This

process is aided by the extrusion of a viscid membrane

by those organisms that have rounded-off. This naturally

helps to cause the individuals to adhere together. After

conjugation this viscid membrane appears to harden into

a protective cyst wall. Usually the size of the single cyst

is about 10 to 12, but in the ‘‘fused’’ or conjugated

forms the diameter may reach 20 to 30» as seen in fresh

preparations. It is also clear that the ‘‘double’’ and

‘*triple’’ cysts sometimes seen may represent a division

of the original cyst, whereupon each daughter cyst con-

tinues independently the production of daughter cells by

the usual method, described above.

Reproducing by the methods described above, Tricho-

monas ordinarily lives in the intestinal tract and causes

no recognizable injury to the host. It has never been re-

garded as other than a harmless commensal. Recent |

studies? have demonstrated, however, that, upon occasion,

this flagellate may depart from its usual mode of life, may

penetrate the tissues of its host and cause fatal lesions,

not only in the walls of the intestinal tract, but in the liver

as well. It is especially this.assumption of a pathogenic

rôle, this sudden adaptation to a new manner of life, to-

gether with the morphological changes that accompany it,

that constitute perhaps the most interesting phase of the

life of Trichomonas. First, how does it happen that the

flagellate gets started on its tissue-despoiling career?

2 Rhode Island Agricultural Experiment Station, Bul. 166, 1916.

218 THE AMERICAN NATURALIST [Vou. LI

What is the first stimulus that creates out of a commonly

law-abiding protozoan, an invader that has no equal

among protozoan forms in the rapidity and completeness

with which it carries on its ravages in the -intestinal

tissues?

This is a difficult question, and one which can not be

answered with any degree of finality at the present time.

The facts of the matter are these: The manifestation of

the disease, as it appears for instance in the so-called

blackhead of turkeys, is invariably preceded by a diarrheal

condition in which the flagellates appear in increasing

numbers as the course of the disease advances. Finally

they appear, not only in the liquid cecal content, but in

the very depths of the cecal tubules or crypts; and finally

in the tissues behind the epithelial wall. From this posi-

tion, by a process of autogamous reproduction, the in-

vasion of the mucosa, submucosa, muscularis mucose

and even the muscular layers, goes on rapidly; and even-

tually the whole cecal wall is crowded with the parasites.

Secondary bacterial infections may intervene and the re-

sults are almost invariably fatal. The question now

arises: Are these countless flagellates, present in the liquid

cecal contents at the beginning of the attack, the cause or

the result of the diarrheal condition? Clinical evidence,

which can not now be presented in detail, seems to indi-

cate that the latter circumstance is the actuality: that the

diarrhea is the primary condition and the increase in the

number of parasites the secondary. To explain the ‘first

cause’’ of the disease, then, one must explain the cause

of the diarrheal condition; and this, of course, is likely

to prove in itself, a complex problem, but seems to lead

back to certain circumstances related to the nature of the

food materials and their assimilation, lying outside the

province of the present paper.

For a long time it was not clear how, after their rapid

multiplication in the intestinal content, the parasites were

able to penetrate the epithelial wall and reach the sub-

epithelial tissues. Recent studies* have shown the rôle

3 Rhode Island Agricultural Experiment Station, Bul. 168, November,

1916.

No. 604] THE CASE OF TRICHOMONAS 219

played by the goblet or chalice cells of the crypts of

Lieberkiihn in this respect. Trichomonas, after congre-

gating in vast numbers in the fundi of the crypts, with a

consequent bulging of their walls forces its way into the

goblet cells. It is not deterred by the nucleus or the cell

wall at the basement end, but throws the former out of

place and breaks through the latter to assume a position

beneath the epithelium of the crypt. The wall having

been ruptured and an avenue created to the deeper tissues,

other flagellates follow by the same path until many are

present between the epithelium and the basement mem-

brane. But Trichomonas does not halt here. It is now

filled with the spirit of the invasion and quickly pushes

through the basement membrane into the loose connective

tissue of the mucosa. This tissue is speedily overrun by

the advancing hosts, the barrier of the muscularis mu-

cose is passed and the entire submucosa exposed to the

ravages of the parasite.

It is here that we recognize Trichomonas in a new rôle.

Having experienced its first taste of blood its whole nature

is changed; it becomes another animal, raging through

the tissues and impeded by no protective action that the

host organism is able to muster to the defense. Here then

we must recognize Trichomonas as a cell parasite, an or-

ganism that has the power to actively invade living cells

and to bring about their destruction. One may remark

that the type of cell invaded is highly specialized type,

and one that, by its nature, is more or less open to in-

vasion. But the fact remains that host cells are invaded,

and actively invaded; and in this circumstance we can

detect, in the behavior of Trichomonas, a foreshadowing

of those cell-invading activities regarded as character-

istic of the sporozoa.

But of course the host-organism must put up some de-

fense, and sometimes a very vigorous defense is offered,

chiefly by means of its batteries of endothelial and other

phagocytic cells. These come out in numbers to meet the

invaders and as a result many of the flagellates are en-

gulfed, either by single endothelial cells or in giant cells.

220 THE AMERICAN NATURALIST [ Vou. LI

But the curious part of this circumstance is that the en-

gulfing of the parasites seems to be of slight avail in re-

tarding the invasion; and, in many instances without ap-

preciable detrimental effect upon the parasites engulfed.

From observations on the staining reactions and on the

morphological features of the ingested parasites there is

good evidence that Trichomonas is not disintegrated by

the process; and much less killed outright. It shows a

marked resistance to the plasm of the endothelial cells,

within which it frequently appears that development may

proceed, and from which a new generation of flagellates

may break out to continue the course of infection. This

would imply that the parasites, once engulfed, are able

to make use of the plasm of the endothelial cell as food.

And some evidence actually seems to support the view

that the parasites fare better in the endothelial cells than

they do without. In any region of invaded tissue the ma-

jority of the organisms are present within the engulfing

cells. If these views should prove valid it must be ad-

mitted that a curious situation is produced: the parasites,

to survive, must be ingested by the defensive cells, while

these phagocytic agents in carrying out their normal de-

fensive function, are favoring the growth and activity of

the invaders. Of course the residence of Trichomonas

within the endothelial cells is purely a passive cell-para-

sitism, although the penetration of the goblet cells is an

act of active cell-parasitism. But when we regard both

together, the matter is of considerable interest in its bear-

ing upon the origin of the sporozoa, cell parasites most

exclusively. From such elementary invasive power and

from such primitive toleration of unfavorable host-cell

influences as we see in Trichomonas, it is easy to imagine

. how the most effective stages of sporozoan parasitism

may have evolved. It is a beginning of that marked

adaptability of form and of physiological organization

which lies at the base of all pure parasitism as it occurs

in the higher orders of the protozoa.

Another noteworthy feature in the life of Trichomonas,

and one which again serves to connect the organism with

No. 604] THE CASE OF TRICHOMONAS 221. -

the accepted type of sporozoan parasitism deals with the

manner of obtaining its food. It has already been pointed

out that when the trophozoites are developing in the in-

testinal contents they ingest large numbers of bacteria;

whether, at this time, osmosis plays any part in cell nutri-

tion is a question. When Trichomonas has entered the

deeper tissues, however, the situation is different, since

there are ordinarily few bacteria in these regions. Here

it seems that nutrition by osmosis must play an important

role in supporting the life of the rapidly multiplying or-

ganisms. It thus appears that Trichomonas is sufficiently

adaptive to new conditions of existence in the tissues to

substifute an osmotic method of nutrition for the in-

gestive. This nutrition by osmosis it will be at once

recognized is one of the characteristic features of the

sporozoa, and here again is to be seen a link connecting

these two protozoan types.

But there is another point of interest involved in this

change in the manner of nutrition when Trichomonas

enters upon its tissue despoiling career, and this concerns

the influence of the manner of nutrition upon some of the

morphological features of the parasites.

In regarding thé appearance of the flagellates pre-

ceding their invasion of the tissues, and after they have

gained a foothold in the submucosa, a marked difference

is to be observed. This has already been mentioned and

may be so great as to deceive one into the belief that the

parasites which are found in the intact crypts and which

penetrate the epithelial wall, are not identical in nature

with the organisms occurring in the deeper tissues. It is

this difference which has led some writers to believe that

we are dealing with two different protozoan forms. The

difference lies primarily in the following circumstance:

In the cecal content the flagellates are represented by two

forms, the motile trophozoite and the encysted organism.

In the case of the latter, one can usually observe clearly

the large ball of reserve-substance, and the relatively large

daughter nuclei. When developing in the tissues, on the

other hand, although the motile forms can be recognized

222 THE AMERICAN NATURALIST [ Vou. LI

without difficulty and although the sporulating forms,

characterized by the presence of the daughter nuclei, are

also observable, both of these are relatively uncommon,

and the stage which shows the well rounded ball of re-

serve-substance (‘‘Reservestoffsballen’’) is seldom met

with. How can these phenomena be explained?

The writer has introduced this point in connection with

the discussion of the methods of nutrition of the flagel-

lates, simply because it seems possible that the morpho-

logical differences alluded to above are conditioned by

the nature of the food supply. The writer has already

traced the changes which the food vacuole of Trichomonas

undergoes during the process of encystment. It was

shown that there is a direct transformation from the food

vacuole of the trophozoite, laden with bacteria and cocci,

to the ball of reserve-substance which eventually crowds

out the nucleus, chromatic line and line of blocks from the

inner part of the cell and may possibly absorb the axo-

style. Finally it comes to lie as a mass of varying size

with respect to the cell, in the center, or slightly to the

ventral side of the organism. Its staining qualities sug-

gest a glycogen-like substance, and its density appears to

vary with the stage of digestion of the food substances

which are to serve the young daughter cells.

As stated above, this well defined reserve-substance

mass is seldom observed, at least well developed, in the

flagellates located deep in the tissues where the evidence

favors a view of nutrition by osmosis. The question is

therefore raised: Can it not be that the marked difference

between the appearance of the flagellates in the tissues

and in the cecal content is dependent directly upon the

nature of the store of reserve food; and thus indirectly

upon the manner of nutrition. This view is in agreement

with the general observation that protozoa that subsist by

osmosis seldom manifest either food vacuoles or definitely

segregated bodies of reserve food substance.

In just what way the presence or absence of a ball of

-reserve-substance would explain all the differences ob-

served in the parasites in and out of the tissues it is diffi-

No. 604] THE CASE OF TRICHOMONAS 223

cult to say. That its absence would determine a more

homogeneous cytoplasm at all stages of growth is, of

course, obvious, but its effect upon the cell structures

such as chromatic line, blocks and axostyle, and upon the

relative size and distribution of the daughter nuclei is still

not clear. It can scarcely be wondered at, however, that

such a radical change in the manner of nutrition of a

parasite would be accompanied by alterations of some de-

velopmental significance.

Upon superficial observation it appears that, in a para-

sitism of this sort, when the organisms are driving ever

deeper into the tissues, one of the essential features of

complete parasitic activity is absent, namely, the ability

to escape from the tissues and to secure a position by

virtue of which the parasite can insure the possibility of

reaching other hosts. Without this possibility provided

for, no parasitism can be called complete. Although, in

the case before us, many of the parasites are so buried in

the tissues, a study of the trend of the infective process

as a whole has revealed a means by which the organisms

return to the cecal content after their invasive career has

ended. This is by spreading downward and inward

through the reticular tissue of the cores of the villi and

pushing the epithelium off of the villus tips. Behind the

epithelial wall at these points the parasites congregate

in vast numbers until finally the epithelium breaks and

liberates the flagellates into the cecal contents. That this

process of escape from the tissues takes place only over

certain areas of the intestinal wall is apparent; but the

fact that it occurs at all is sufficient evidence to indicate

that Trichomonas is not wholly lacking in this essential

element of successful parasitism.

And finally we find in the case of Trichomonas one

more lesson, and this is one for the etiologist, this being

of course any one who concerns himself seriously with

disease etiology. This important person, confronted with

a disease of unknown cause, busily sets about to discover

the germ; and having found the germ, he as busily en-

gages himself in ascertaining means and measures

224 THE AMERICAN NATURALIST [ Vou. LI

whereby the germ may be avoided by all susceptible folk.

We are warned to avoid the places where the germ lurks,

to boil our drinking water and to put cotton in our noses;

and of course this has been of immense value in prevent-

ing infection in the case of many communicable diseases.

But this conception of escaping the germ, a procedure

still by force of habit widely applied, unfortunately does

not work out successfully in all cases, simply because we

have at last found that the germ is not always escapable.

It may be right with us day and night; and whether we

succumb to an eventual invasion depends not upon our

side-stepping the organism, but upon our maintaining cer-

tain of the body defenses at the proper level of efficient

working. The case of Trichomonas in its proper host is

an instance. For twenty years (under other names) it has

been consistently avoided and wholesomely feared by in-

telligent turkey raisers. Five hundred regulations more

or less have been directed against it; and now we find that

it is always there and always will be there. To keep it in

an amicable state, to deter it from making destructive

excursions into the tissues, all that is required is to main-

tain a normal and hygienic condition of the intestinal

tract, whatever this may mean; this alone appears to be

sufficient. Thus, although no other intestinal protozoan

is able to exert, in a brief time, a greater destructive

activity than Trichomonas when properly aroused, still

we are far from justified in placing its name upon the

blacklist of unqualifiedly pathogenic types which are, by

both heredity and training, trouble-makers. On the other

hand we can not continue to place this flagellate in that

sainthood of parasites, the ‘‘ harmless commensals,’’ since,

upon occasion, it may be far from harmless. Trichomonas

must now be registered as a facultative parasite, which

offers a wealth of interesting subject-matter for research

covering several fields of biological study.

LINKAGE IN MAIZE: ALEURONE AND CHLORO-

PHYLL FACTORS!

E. W. LINDSTROM

CORNELL UNIVERSITY

Genetic linkages or correlations are beginning to con-

firm the modern chromosome conception of heredity. As

the Mendelian analysis of a species reaches a point where

the known genetic factors exceed the number of chromo-

some pairs, certain group relations between the factors

should become evident. Comparatively few genetic link-

ages have been observed in plants, however, probably be-

cause the number of Mendelian factors that have been

determined is relatively small compared with the number

of chromosomes in most species.

Physiological or morphological correlations, on the

other hand, are far more common. But in the present

state of knowledge they are not classified as genetic and

consequently can not be used as material for determining

the relationship between any series of heritable factors.

An intensive, Mendelian study of maize is gradually

revealing genetic correlations. Although more than thirty

definite Mendelian factors have now been determined in

this species, linkages are limited in number because of

the relatively large number of chromosomes (at least nine

pairs).

As early as 1906, Webber noted a general correlation

in maize between color in the aleurone layer and in the

stamens, glumes and silks. At that time, the genetic con-

stitution of color in the kernels and other parts of the

plant was unknown. Consequently the correlation was

not analyzed on a factorial basis.

In 1911, Emerson described an apparent linkage be-

tween color of cob, pericarp, husks, silks, and anthers in

1Given before the Botanical Society of America at the annual meeting

held in New York City, December 28, 1916. Paper No. 58. Department

of Plant Breeding, Cornell University, Ithaca, N. Y.

225

226 THE AMERICAN NATURALIST [ Von. LI

maize. Further evidence (unpublished), however, has led

Professor Emerson to prefer a simpler explanation for

this phenomenon than linkage.

Collins and Kempton (1911) and Collins (1912) have

reported a genetic correlation between aleurone color and

endosperm texture. In this case one of the pairs of

aleurone factors is apparently linked with one pair of

endosperm factors (horny and waxy). The data indicate

that there is a little less than twenty-five per cent. cross-

ing over.

In a later paper, Collins (1916) describes five character

pairs in maize that show apparent genetic correlation.

But since these characters exhibit ‘‘blending’’ inheritance

and have not been analyzed from any factorial stand-

point, it becomes impossible to use these correlations in

determining the group relations between the genetic fac-

tors concerned. Collins also notes a large number of

physiological correlations in this article.

LINKAGE BETWEEN ALEURONE AND CHLOROPHYLL FACTORS

A definite linkage has been found in maize between one

of the five pairs of aleurone factors (Aa, Cc, Rr, Pp, Ii)?

and one pair of chlorophyll factors of which there are at

least seven, as the writer has determined. Manifestly

this is not a physiological correlation, for it is difficult to

conceive of an anthocyanic pigment, limited to a single

layer of cells in the grain, being caused by the same

physiological factor that produces a plastid color, like

chlorophyll, so widely distributed in the plant. Breed-

ing evidence demonstrates that the correlation is genetic,

as will be seen later.

The aleurone factor ene is the R factor, which

together with C and A is needed to produce any color in

the aleurone cells of the corn grain (Emerson, 1917). To

determine linkages with any of the five aleurone factors,

it is obviously desirable to use material that is homo-

2 Reported in a paper given before the Botanical Society of America at

the annual meeting in New York City, December 28, 1916, by Professor R.

A. Emerson. The paper is now in manscript sing under the title, ‘‘A

Fifth Pair of Factors for Aleurone Color in Maize.

No. 604] LINKAGE IN MAIZE 227

zygous for as many of the non-linked factors as possible.

Fortunately, the plants used in this experiment were

homozygous for A, P and i, as will be shown later. This

left only C and R, giving either 3:1 or 9:7 ratios of

purple to colorless grains. The aleurone segregation on

the ear proved to be exceptionally distinct because the

factors A and P were homozygous.

The other factor involved in the linkage is concerned

with chlorophyll development in the mature plant. It is

one of at least seven factors necessary for the production

of full, normal green color in maize, and it has been termed

the G factor. Its allelomorph g produces a distinct yellow

or golden color in the leaves and stalk of the mature corn

plant. This color is comparable with that of the familiar

golden-leaved shrubs. It has been described and its in-

heritance discussed by Emerson (1912) and Miles (1915).

Suffice it to say that it is a simple recessive to normal

green.

During the summer of 1914, a green plant heterozygous

for R and G was pollinated by a golden plant that lacked

aleurone color. The cross can best be described by the

following factors:

GgRrCCAAPPw _, ggrrCcAAPPu

3472 (11) e A > ~

Proof for the correctness of these formule will be given

later.

_ A selfed ear of the female parent bore a 3:1 ratio

(271:88) of purple to colorless grains, showing that only

one aleurone factor was heterozygous. The male parent

was likewise selfed and showed no aleurone color. On the

ear of this cross there were 67 purple and 55 colorless

grains, approximating a 1:1 ratio.

The purple seeds on this ear were planted separately

from the colorless seeds. From the field counts of this

planting, which are given in Table I, it is seen that the

1:1:1:1 ratio of independent inheritance is noticeably

modified.

The observed numbers in the four classes give a ga-

228 THE AMERICAN NATURALIST [ Vou. LI

metic ratio of 3.9:1, or 20.4 per cent. of crossovers. It is

evident that the actual results agree very closely with the

theoretical expectancy on a 4:1 basis of linkage. Indeed,

the goodness of fit (Elderton, 1901 and Harris, 1912) is

so perfect that «?—.317, giving a very high value for P.

TABLE I $

SHOWING THE F, DISTRIBUTION FROM THE CROSS

GgRrCC _ggrrCe

3472 (11) ^` 3468 (10)'`

From Purple Seeds From Coiorless Seeds

| Green oe | Golden (Rg) | Green (rG) ‘cok Golden esd

WA WORE A a | pD T

Observed, corrected for aleurone ratio? 33, Lah S4 6517; 300

Theoretical, on a 4:1 gametic ratio.. 29.2 lo ee 7.3 29.2

From these results it may be said that, at gametogen-

esis, the factors of the female parent are so linked that

the gametes RG and rg are produced about four times as

often as the crossover gametes Rg and rG. Thus far, no

_ evidence is available for demonstrating the linkage of Rg

and rG (‘‘repulsion’’ between R and G

Additional evidence on the linkage was afforded when

the female parent of the cross and four other plants, in

which the R and G factors were heterozygous, were selfed.

Each of these plants bore ears with 3: 1 ratios in aleurone

color (total, 1052 purple: 339 colorless). The results ap-

pear in Table IT.

Obviously this F, distribution does not resemble a

9:3:3:1 ratio of independent inheritance. The agree-

ment between the actual results and the theoretical on a

4:1 gametic ratio, however, is close, P being .6733, which

is considered a good fit. It may be concluded, therefore,

that the factors in these five F, plants were so linked that

R and G occurred together in one chromosome, while r

and g were located in the homologous chromosome and

8 This correction is applied to equalize the proportion of the plants from

the purple and the colorless seeds. The proportion should be 1: 1 in this

ease, but variation in the percentage of germination or in the number of

purple and colorless seeds actually planted, often disturbs it. Such a cor-

rection is of course legitimate

No. 604] LINKAGE IN MAIZE 229

that crossing over occurred about twenty per cent. of the

time.

TABLE II

SHOWING THE F, DISTRIBUTION WHEN F, PLANTS HETEROZYGOUS FOR R AND

WERE SELFED

| From Purple Seeds F Colorless Seeds

Selfed Plants | i EET

| RG it? ee rG | rg

OHS A ONDE Bie PO Pong 12. | 9

3347 (2) parent of above | 3 3 8 | 6

3954 (1) heer wens. 0 gi toe

3954 (3) Bite ocho 2 3

3954 (11). E E hts hota Sat Be Oe | 8 | 3 2 6

Total..... | 106 10 26 41

Correction for E Peta Miota EY a 248 | | 28

Theoretical, 4:1 basis........... fice ae b A208 Gh 16 16.5- | -: 29.2

When plants that were heterozygous for G and for

‘both R and C were selfed, the ratio between the four

classes in the next generation appeared rather unusual.

This was found to be due to the influence of the 9:7 ratio

in aleurone color of each of the four plants that were

selfed (total, 477 purple: 387 colorless). The data from

such plants are arranged in Table III, which follows: _

TABLE III

SHowine F, DISTRIBUTION WHEN PLANTS HETEROZYGOUS FOR G, R AND C

WERE SELFED

From Purple Seeds From C Seeds

Plants Selfed

Green Golden Green Golden

noa hs a 32 3 il 4

3347 (3) 79 6 5l 31

3347 (4) 96 6 47 40

3477 (2) 38 nA 19 11

Total 245 18 128 86

Theoretical 4:1 basis 236 32 122 87

_ There is considerable deviation from the theoretical ex-

pectancy in this case and the value for P is small

(P= .0808). Nevertheless, these results, taken in con-

* The correction is applied because at planting time no attempt was made

~ plant three purple grains to one colorless grain.

230 THE AMERICAN NATURALIST [ Vou. LI

junction with those in Tables I and II, accord with the

idea of linkage between R and G on a 4:1 basis, especially

since they deviate so widely from the 27:9:21:7 ratio of

independent inheritance.

Another source of evidence on the genetic interrela-

tions of the R and G factors was noted in a back cross in

which the J factor for aleurone color was involved. No

aleurone tests have been made, but evidence from related

plants in pedigree cultures makes it seem reasonable that

the following factors are concerned:

GgRrecAAPPIi s 9gttCcAAPPu

021 (1) SHE 0)

In this case, the ears of both parents showed no aleurone

color. The ear from the cross gave a distinct segregation

of purple and of colorless grains (36 purple:195 color-

less), approximating the theoretical 1:7 ratio. Assuming

the factors as given above, this aleurone ratio is reason-

ably close to the expected proportion, the numbers being

relatively small. As a check upon this aleurone ratio, it

might be mentioned that six of the F, plans from purple

seed were selfed. Each one showed a 9:7 ratio of purple

‘to colorless grains on the ear (total, 1441 purple: 1088

colorless). Also three F, plants from colorless seed were

selfed and the ears showed no aleurone color.

The field counts of the plants from purple and from

colorless F, grains are classified in the following table:

TABLE IV

SHOWING THE F, DISTRIBUTION FROM THE CROSS

GgRrecAAPPIi _, ggrrCcA APPii

3021 (1) ~~ +3018 (10)

From Purple Seeds | From Colorless Seeds

| Green | Golden | Green | Golden

ao / |

Observed... | 12.0 3. | 22.0

Correctio n for kienrone ratio .. E 2." tl | 10.4 29.0

Theoretical, 4:1 ba | 4.5 fe Ft 18.0 21.4

Here again, while the value for P is relatively small

(P=.1171), it is noted that in general the observed re-

No. 604] LINKAGE IN MAIZE 231

sults correspond with the theoretical when a linkage on a

4:1 basis is assumed. Considering only the classes from

purple seeds (first two columns in Table IV), the agree-

ment is perfect. These classes are not disturbed by the

aleurone situation and consequently ought to show the

gametic ratio directly.

DETERMINATION OF THE ALEURONE FACTOR CONCERNED IN

THE LINKAGE

It has been shown from four independent sources that

the G factor is linked with one of the five aleurone factors,

which has been termed the R factor. It now becomes nec-

essary to prove that it really is the R factor that is in-

volved. From the aleurone ratios observed in this ex-

periment, às well as from evidence from related plants, it

is certain that the inhibiting factor J is lacking, with the

exception of the last cross described (Table IV). It is

also obvious that the P factor, which produces purple

color when C, R and A are present, must be homozygous

(PP) in both parents of the first cross since the color in

the colored grains is a deep purple with no trace of red.

This leaves only C, R and A to be considered.

In order to facilitate the presentation of the proof that

the R factor is the one concerned, Table V has been pre-

pared. In this table, the zygotic formule of the F, plants

of the first back cross (see Table I) are listed and the

plants that were tested are noted in the last column. The

factors are merely assumed as here given.

TABLE V

SHOWING THE ZYGOTIC FoRMUL2 OF THE F, PLANTS OF THE Cross 3472 (11)

X 3468 (10)

Parental Formule: GgRrCCAA X ggrrCcAA

Fı Zygotes F, Aleurone Color | F; Plant Type | Fi Pana aer mee a

GgRrCCAA ...... Purple | Green (1) (3) (11) (81) (33)

GgRrCeAA....... t A (34)

ggRrCCAA....... * Golden

geRrCeAA........ t t! (32)

GgrrCCAA........ Colorless Green 44

GgrrCcAA........ ciel sie a

ENE erbg Geen | fan) (22) (29) (48) (45)

232 THE AMERICAN NATURALIST [ Vou. LI

The fourth column shows the plant numbers of the F,

plants, which were self-fertilized. In addition, plants

(31), (82) and (34) were crossed with certain aleurone

testers of known constitution provided by Professor R.

A. Emerson.

All the grains on the ears of plants (21), (22), (29),

(43), (45) and (44) were colorless. The aleurone counts

on the ears from purple seed are arranegd in Table VI.

TABLE VI

SHOWING THE ALEURONE CouNTS ON SELFED Ears OF F, PLANTS FROM THE

Cross 3472 (11) X 3468 (10)

3:1 Ears 9:7 Ears

Ped. 3954 Plant No. —— ae

é Purple Colorless | Ped. 3954 Plant No. | Purple | Colorless

(1) 230 83 (32 we pee

68h ise. ss 303 | 88 (34) sae krmo

oe eee 248 80 | |

OE eee OR ay 180 45 | |

Se 224. | 79 | |

Potabeiassiyi 1,185 | 375 Totais | 238 | 228

Theoretical....... 1,17 390 |Theoretical....... 262 | 204

These ratios indicate that plants (1), (3), (11), (31) and

(33) are heterozygous for one aleurone factor only.

Plants (32) and (34) also contain that factor but appar-

~ ently they have in addition another aleurone factor, which

likewise is heterozygous because the aleurone ratios, al-

though they deviate somewhat from the 9:7 proportion,

can not be classified as 3:1 or 27:37 ratios.

Only tests with plants of known aleurone formule will

determine whether it is the C, R, or A factor that is linked

with G. Such tests have been made by using the aleurone

testers described by Emerson (1917). These aleurone

testers possess colorless grains in which all the aleurone

factors except P are homozygous. For example, the R

tester has the formula rrCC A Ait, the C tester the formula

RRecA Ati, and the A tester the formula RRCCaati. In

Table VII are presented the data involving the various

tests for the aleurone factors. Plants (31), (32) and

(34) possess all the three aleurone factors in question

No. 604] LINKAGE IN MAIZE 233

(R, C, and A), as can be seen from their records in Table

VI. Plant (41) is a golden type from colorless seed.

TABLE VII

SHOWING THE TESTS FOR THE PRESENCE OF ALEURONE FACTORS

Crosses with Aleurone Testers Aleurone Color of F; Grains

L A tester (RRCCaa) X 3954 (32) ............. 450 purple

2. C tester (RRccAA) X 3954 (32) F.. AR. rs T2 “z 69 colorless

3. E tester (rrCCAA) X 3954 (IZER ER TEKAN "

4. 3954 (34) X C tester (RRccAA) ......:...... B0Gar**a EAT VETS es

5. 3954 (31) X E tester (rrCCAA) -iiai p e ss BAG a

6. 3954 (41) (rrCcAA) X 3954 COIF ocijeni r : 101 e:

The data in Table VII prove several things, namely:

1. That the factors A, C and R must be present in all

the plants tested, because color was produced in some of

the F, grains of each cross.

2. That it is the R factor that is linked with G. This

is demonstrated in the fifth cross. Plant (31) was a green

plant from purple seed bearing an ear with a 3:1 aleurone

ratio, showing that it was heterozygous for the one aleu-

rone factor that isinvolvedin the linkage. Thetestclearly |

proves it to be the R factor, the aleurone ratio from the

fifth cross approximating the theoretical 1:1 proportion.

3. That the assumptions made in Table V as to the-

genotypic formulæ of the F, plants are correct. This

statement follows from a series of deductions. First, one

aleurone factor of the three concerned must be homo-

zygous (dominant) in all the plants, because the aleurone

ratios observed permit only two heterozygous factors at

the most (9:7 ratios). Since the C factor is heterozy-

gous in plants (32) and (34), and the R factor heterozy-

gous in plant (31), while Æ is homozygous in plant (32),

it is obvious that only the A factor could be homozygous

(dominant) in all the F, plants. Second, one of the re-

maining factors (C or R) must be homozygous (domi-

nant) in some plants and heterozygous in others to ac-

count for the 3:1 and the 9:7 ratios, respectively. The

second and fourth crosses in Table VII indicate that C is

heterozygous in plants (32) and (34), whereas the fifth

234 THE AMERICAN NATURALIST [ Vou. LI

cross, together with the 3:1 ratio of the selfed ear, shows

that C is homozygous in plant (31). Third, the remain-

ing factor, R, should occur only in a heterozygous or ina

homozygous recessive condition to account for the 1:1

aleurone ratio on the F, ear of the original back cross.

The fifth cross in Table VII proves that R is heterozygous

in plant (31), and the sixth cross shows that in plant (41)

this same factor is homozygous recessive.

From this series of interrelations it is seen that the

hypothesis is verified in all cases and that it is the R factor

for aleurone that is linked with G.

On THE QUESTION oF CROSSING OVER IN THE MALE AND

FEMALE

An interesting observation regarding the question of

crossing over in plants can be derived from some of the

data presented. It has been shown that crossing over

occurs in gametogenesis of the female (Table I). Does

it take place in the formation of the male gametes as well?

In certain animals, crossing over seems to be limited to

one sex. It occurs only in the female of Drosophila (Mor-

gan, 1915) and only in the male of the silkworm (Tanaka,

1914). Castle (1916) has noted that the phenomenon

occurs in both sexes of the rat. Among plants, the studies

with sweet peas and Primula indicate that crossing over

is not restricted to one sex. Perhaps it is to be expected

that, in the case of most plants, where the pistillate and

staminate parts are borne on the same individual, there

should be no difference in the genetic behavior of the two

reproductive systems in this respect. Nevertheless, it is

interesting to note the condition in the monecious corn

plant.

From the data in Table II, it is possible to demonstrate

that crossing over is found in both sexes of maize. In

order to do this, the observed frequencies can be com-

pared with the theoretical expectation when crossing over

occurs in both sexes and when it takes place only in the

female. Such a comparison is arranged in Table VIII,

which follows: `

No. 604] LINKAGE IN MAIZE 235

TABLE VIII

A COMPARISON OF THE RESULTS FROM TABLE II WITH THE THEORETICAL

EXPECTATION WHEN CROSSING OVER OCCURS IN BOTH SEXES

D WHEN IT OCCURS ONLY IN THE FEMALE

| | g

no | ty | E [Coen

| with Observed

Observed (from Webie try. 2 (125 112 |18 | 298 |

Theoretical, when crossing over oc- | |

curs in both sexes 120.8 | 16.5 | 16.5 | 29.2 | .6733

Theoretical, when crossing over oc- |

_ curs only i in the female 128;0| 9.0 |. 9.0. | 37.0 | .0067

Clearly; the first theoretical expectation fits the case

adequately, for with such a high value for P it is almost

certain that the deviations of the observed results from

the theoretical are due to errors of random sampling only.

Consequently one is justified in saying that crossing over

occurs in both male and female. This is especially true

when the fit in the second case is so poor. In fact, the

great difference between the two values for P makes it

seem reasonable that the intensity of the linkage is equal

in both male and female, although the high value for P

in the first case suggests that directly.

ÅDDITIONAL LINKAGES BETWEEN CHLOROPHYLL Factors

AND ALEURONE

Preliminary tests indicate that the same chlorophyll

factor, G, that is linked with R, is also concerned in a

linkage with one of the other chlorophyll factors termed

L. The latter has been found to be one of three factors,

two of which have already been described by Miles (1915),

involved in the production of chlorophyll in the seedling

stage of maize. —

Factors G and L seem to be linked although the data

from three back crosses, in which the numbers are small,

exhibit some variation in the percentage of crossing over.

Details of this linkage will appear in a later paper, deal-

ing with the inheritance of the three seedling chlorophyll

factors.

Apparently, then, the factor pairs Rr, Gg, and Ll con-

236 THE. AMERICAN NATURALIST [ Von. LI

stitute one factorial group in maize. It is to be expected

that Rr and Ll should bear a definite relationship to one

another. This has not yet been fully determined, although

there are some indications of such a linkage, for aleurone

color and chlorophyll development appear to_be genet-

ically related in different manner from that noted pre-

viously.

When purple seed of certain ears are planted sepa-

rately from the colorless ones, the former give a distinct

segregation of green and white seedlings, while the latter

give rise not only to the green and white, but also to a

constant proportion of yellow seedlings. The writer has

determined that these yellow seedlings depend upon a

definite genetic factor. Over two thousand seedlings have

now been grown and not one yellow seedling has resulted

from the purple grains. Discussion of this linkage will

also be reserved for the later paper, or until the aleurone

factor concerned has been identified. This may be the R

factor showing its theoretical relationship to the L factor.

- UMMARY

1. Linkage between the R aleurone factor and the G-

factor for chlorophyll development shows approximately

20 per cent. crossovers. ,

2, Crossing over takes place in both male and female

gametogenesis of the monecious maize plant.

3. Preliminary tests indicate that G is also linked with

L, a seedling, chlorophyll factor. Consequently the factor

pairs Rr, Gg and Ll constitute one factorial group in

maize.

To Professor R. A. Emerson, of Cornell University,

who so generously has shared his material for this inves-

tigation, the writer is deeply indebted and desires to ex-

press his sincere gratitude.

LITERATURE CITED

Castle, W. E.

1916. Further Studies of Piebald Rats and Selection, with Observa-

tions on Gametic Coupling. Part III of Carnegie Inst. Wash,

Pub. No. 241, pp. 175-180.

No. 604] ‘ LINKAGE IN MAIZE 237

Collins, G. N. & Kempton, J.

1911. Inheritance of aoe Endosperm in Hybrids of Chinese Maize.

In IV Conf. Internat. acaba Paris. Compt. Rend. et

Raps., 1911, pp. 347-357

Colin G. N.

1912. Gametie Coupling as a Cause of Correlations. AMER. NAT., 46:

569-590

Collins, G. N.

1916. gri Characters in Maize Predial Journ. Agr. Re-

rch, 6: 435-453, Plates 55-63.

Elderton, W.P

1901. Tables for Testing the Goodness of Fit of Theory and Observa-

tion. Biometrika, 1: 155-163.

Emerson, R. A.

1911. Genetic Correlation and Spurious Allelomorphism in Maize. In

Nebr. A xpt. Sta. 24th Ann. Rept., 1910, pp. 59-90.

1912. The Pilian of Certain Forms of Chlorophyl! Reduction in

aves. In Nebr. Agr. Expt. Sta. 25th Ann. Rept., pp.

89-105.

1917. A Fifth Pair of Factors for Aleurone Color in Maize. In

manuscrip

Harris, J. A.

1912. A Simple Test of the Goodness of Fit of Mendelian Ratios.

R MER. NAT., 46: 741-745.

Miles, F. C.

1915. A ATONE and Cytologie cal Study of Sear: Types of Albinism

3 . Genetics, 4: 193-214. Plate VII

ie T 3 Sturtevant, wer H., Muller, H. J., and pien Cc. B.

5. e Mechanism of Mendelian Heredity, pp. 1-262.

incites Hy

1914. Further she on the Reduplication in Silkworms. Journ. Col.

Agr. Tohoku Imp. Univ. Sapporo, 6 16.

Webber, H. J.

1906. Correlation of Characters in Sa Breeding. Amer, Breeders’

Assoc. Proc., 2: 73-83, Pl.

SHORTER ARTICLES AND DISCUSSION

THE APPLICATION OF CORRELATION FORMULA TO

THE PROBLEM OF VARIETAL DIFFERENCES IN

DISEASE RESISTANCE: DATA FROM THE

VERMONT EXPERIMENTS WITH

POTATOES

THE ultimate practical object of any study of disease resistance

in a series of varieties is the selection for future cultivation of

the few which are least susceptible. In practise a relatively large

series of varieties or strains is taken into cultivation for pre-

liminary study. The size of the cultures of the individual strains

must, on a given area, be inversely proportional to their number.

Since the individual cultures are necessarily small, it is impos-

sible to assert from the results of a single test that the observed

differences between the strains really represent varietal differ-

ences in disease resistance. They may be due merely to inade-

quately large cultures or to imperfectly controlled experimental

conditions. It is therefore necessary to repeat the experiment

another year or in a different locality in order to determine

whether the observed differences are really persistent, and so

characteristic of the strain, or whether they are due to transient

conditions only. The problem is then purely and simply one of

correlation. This is obviously true whether one chooses to avail

himself of the advantages of the statistical formule or not. If

the correlation between disease incidence in cultures of the series

of varieties grown in different years, or places, be zero, the vari-

eties show no permanent differentiation in disease resistance. If

the correlation has a significant positive value it indicates at once

that there are réally inherent varietal differences in disease re-

sistance. The numerical magnitude of the correlation indicates

something of the extent of this differentiation. If the correla-

tion be low, the prospect of isolating varieties sensibly more re-

sistant that the average will be slight. If the correlation be high,

it should be relatively easy to secure highly resistant strains.

Since the correlation method seems to have considerable value

in the analysis of data of this'kind, I have thought it might be of

service to geneticists and plant pathologists to illustrate it by the

constants which I have found it necessary to deduce for another

purpose from the published records of the series of experiments

on disease resistance in varieties of potatoes carried on during

1 Stuart, W., ‘‘Disease Resistance in Potatoes.’’ Bull. Vt. Agr. Exp. Sta.,

179, 1914.

238

No. 604] SHORTER ARTICLES AND DISCUSSIONS 239

the past several years at the Vermont Agricultural Experiment

Station,

In a recent bulletin Stuart? summarizes the data obtained dur-

ing five years’ observations on percentage infection by early

blight (Alternaria solani). In his Table I he gives the estimated

percentage infection in a series of varieties during the period.

Since during a portion of the experiment all the varieties were

not considered, I have calculated the correlations in two groups.

In one case N=149, in the other N=50. The smaller group

comprises only varieties also included in the larger. The corre-

lations, calculated by the usual product moment method? with-

out grouping, appear in the accompanying table.®

CORRELATION FOR VINE RESISTANCE TO EARLY BLIGHT IN Two YEARS

Years Compared Series of 149 Varieties Series of 50 Varieties

1905-1906 ...... + .055 + .055 — .056 + .095

1905-1907 ...... + .438 + .045 + .420 + .079

1905-1908 ...... — .021 + .095

1906-1907 i .... + .042 + .055 + .226 + .091

1906-1908 ...... + .323 + .085

1907-1908 ...... —— + .082 + .095

Only 2 of the 9 constants are negative; these are insignificant in

comparison with their probable errors. All the constants which

have substantial values and are materially larger than their prob-

able errors are positive in sign. The average of the two negative

constants is —.038, of the seven positive coefficients + .227, and

of all the (unweighted) values + .168. Thus there is clearly a

measurable differentiation of the varieties in respect to suscep-

tibility to Alternaria.

The values are, however, exceedingly variable, ranging as they

do from —.056 to + .438. The great variation in the actual

constants I am inclined to attribute to (a) the difficulty of esti-

mating the percentage of infection, (b) the unavoidable experi-

mental errors associated with relatively small cultures, and (c)

the wide variation in average percentage infection from year to

year. Both (a) and (b) are factors which tend to render the

actually recorded percentages somewhat erroneous as measures of

the real susceptibility of the variety, and tend in consequence to

dilute the strength of the correlation. With respect to the third

2 AMER. NAT., 44: 693-699, 1910.

3 The chief discrepancy between the results for the larger (N =149) and

the smaller (N = 50) series of varieties is to be seen in the interrelationship

for 1906 and 1907 where the two correlations are .042 + .055 and .226 + .091,

Here the disagreement is apparent rather than real. The difference is

-184 + .106, which can not be considered statistically trustworthy.

240 THE AMERICAN NATURALIST [ Von. LI

factor, (c), it is obvious that if there be only a very slight aver-

age percentage infection the test of disease resistance will not be

a very critical one, whereas the average percentage can not be very

high indeed unless conditions are so unfavorable that all varieties

are affected. The percentage infection of early blight varies enor-

-mously from year to year. Thus:

Percentage Infection

Year N = 149 N = 50

PD 5 eile lineal ah 3.3 2.4

PONG sce rials krai 85.0 83.2

ADDL Teorainn] 41.7 38.9

TOOG IE y yes — 10.8

With an incidence of 3 per cent. one year and of 85 per cent.

the following season one can, in view of the considerations men-

tioned above, hardly expect to obtain smooth values of the corre-

lation coefficient.

It is interesting to compare these results with those for other

maladies of the potato. In the same publication Stuart gives

the results of trials for resistance of tubers to scab. Unfortu-

nately the experiments of the second year, 1907, included only

20 of the 65 varieties from the first year. Calculations may be

based on the percentage of tubers which are free or nearly free

from scab. This is much lower the second year. ~

1906 1907

ORR oy Zee ck ee 64.21 f 28.20

ED l oe n 11.59 16.33

COPPEIBTION “soa ees 7 = 591 + .098

The probable error is high because of the fewness of the vari-

eties retained in the second year’s test, but the correlation is of

more than medium value and is relatively about 6 times as large

as its probable error. Thus susceptibility to seab is probably to

a very considerable extent a varietal character.

The results for tuber rot tests are not available for successive

years, but Stuart has given* the percentage of tuber rot in 89

varieties grown on sandy loam and on clay loam soil in 1905.

For these I find

Sandy Loam Clay Loam

MOAN noenee eens 8.68 39.76

Se TE EE 11.28 6.85

653 + .0:

4 Stuart, W., ‘‘Disease Resistance in Potatoes,’’ Bull. Vt, Agr. Exp. Sta.

122, Tables VI-VII, 1906.

5 The value of r given as .707 + .045 in Science, N. S., 38: 402-403, 1918,

is deduced from the 62 varieties for which laboratory cultures were avail-

able, and from modified percentages. The values agree within the limits of

their probable errors.

No. 604] SHORTER ARTICLES AND DISCUSSIONS 241

The correlation of these data, somewhat smoothed by Jones,’

with a series of determinations of the percentage growth of the

fungus on tubers in the laboratory has already been determined.’

For laboratory growth and loss on clay loam, r==.584 + .059.

For laboratory growth and loss on sandy loam, r= .594 + .055.

Taken as a whole these correlations indicate (a) that suscep-

tibility to both early and late blight and to scab differs greatly

from variety to variety, and (b) that, so far as the evidence goes,

the varieties differ more in resistance to tuber injury than to

foliage infection by early blight.

It is not at all necessary that the correlations be drawn be-

tween the amount of injury to the same organs of the plant or

by the same disease. In many instances the so-called cross cor-

relations yield valuable results.

For examplé Stuart® discusses the question of the relationship

between vine infection and tuber rot. The point may be sub-

jected to a statistical test by correlating between the maximum

percentage of foliage affected by late blight as given in his

Table V for potatoes grown on sandy loam soil in 1905 and per-

centage of rot as recorded in his Tables VI and VII. Unfortu-

nately, the percentages are available for the vines for sandy loam

soil only (Table V) while the figures for tuber rot are given for

both sandy loam and clay loam soil. Both correlations may be

worked out. I fin

For percentage Idia infection on sandy loam soil and per

cent. tuber rot on sandy loam soil

N=131, r—.316 + .053.

For percentage foliage infection on sandy loam soil and per

cent. tuber rot on clay loam soil

N= 80; re=.102 + 075.

In both cases the correlations are positive, and hence ii evi-

dence as they furnish indicates that the varieties which show

the greatest infection of the leaves actually are the worst to rot..

That the correlation between injury to the tops and tuber rot is

higher on the sandy loam soil is not at all surprising, since the

same individual plants—not merely the same varieties—are in-

6 Jones, L. R., N. J. Giddings and B. F. Lutman, ‘‘ Investigations of the

Potato Fungus Phytophthora infestans,’’ Bull. Vt. Agr. Exp. Sta., 168

74-81, 1912.

i Jones and collaborators, loc. cit., and the Reviewer, Science, N. By 38:

402-413, 1913.

8 Bull. Vermont Agr. Exp. Sta., 122, p. 116.

242 THE AMERICAN NATURALIST [Vou. LI

volved in the correlation. The problem is, however, a compli-

cated one and much more extensive data are needed for a com-

plete analysis.

A problem of very great biological interest as well as of prac-

tical importance is that of the specificity of disease resistance.

Concretely : Do varieties differ in their susceptibility to a specifie

disease only, or do they differ merely in susceptibility to disease

in general ?

A comprehensive and final answer will require far more data

than are available and more stringent statistical analysis than

ean be illustrated here. Some progress can be made by the

method of correlation as follows.

If susceptibility be purely specific there should be no correla-

tion between the incidence of disease x in year (or culture) p

and disease y in year (or culture) q, although there should be a

correlation between the incidence of disease x or disease y in

different years or cultures. If, on the other hand, differences in

disease resistances from variety to variety are determined solely

by general weakness or vigor of the stocks, one should expect the

correlations between the incidence of different diseases in dif-

ferent years or cultures to be (within the limits fixed by the

_ errors of measurement and the probable errors of random sam-

pling) as high as those between two series of determinations of

incidence of one and the same parasite.

Consider first the relationship between the percentage of

foliage injury by early blight in 1905, 1906, and 1907 and the

percentage of tuber rot in 1905. The correlations are:

Per Cent. Tuber Rot on Per Cent. Tuber Rot on

Sandy Loam, 1905 Clay Loam, 1905

Foliage Injury N= N = 89

Early Blight, 1905.... .167 + .057 .256 + .057

Early Blight, 1906.... .211 + .056 .249 + .067

Early Blight, 1907.... .291 + .054 440 + .058

Without exception the correlations are positive in sign. While

numerically low, the most of them taken individually may be

considered statistically significant in comparison with their prob-

able errors.

Thus it seems clear that the varieties with foliage most injured

by early blight are also most subject to tuber rot, just as has been

-shown to be the case in foliage and tuber infection by late blight.

For foliage infection by early blight in 1905, 1906, and 1907

and foliage injury by late blight in 1905 I find:

No.604] SHORTER ARTICLES AND DISCUSSIONS 243

Correlation, N = 131

Early Blight, 1905, and Late Blight, 1905.. — .066 + .059

Early Blight, 1906, and Late Blight, 1905. dg. 190 + .057

Early Blight, 1907, and Late Blight, 1905.. — .040 + .059

The results are not so consistent as those of the preceding

table. The two negative coefficients are insignificant in com-

parison with their probable errors, and the positive one is not

large, either absolutely or relatively. Possibly the laxness of

the correlation is in part due to the fact that the measurement

of both characters is subject to a large possible error.’

For freedom of the tubers from scab with the incidence of

other diseases every possible correlation has been determined.

The coefficients are shown in the accompanying table. Note that

in this case the correlation is between freedom from one disease

and occurrence of another disease. Hence a negative coefficient

has the same meaning as a positive one in the foregoing discus-

sions.

For PERCENTAGE OF TUBERS FREE OR NEARLY FREE FROM SCAB IN 1906 AND

907 AND INCIDENCE OF OTHER DISEASES

es Compared with Freedom fr cab Correlation 1906 Correlation 1970

Per Pen rot on Sandy Loam Soil, 1905 .. .. — .136 + .077 —.857 + .182

(N = 74) (N = 20)

Per Cent. rot on Clay Loam Soil, 1905 .... — .280 + .096 — .030 + .187

(N = 42) (N = 13)

Top Injury by Late Blight, 1905 ........ :+ .035 + .084 — .224 + .151

(N = 65) (N= 18)

Top Injury by Early Blight, 1905 ...... — 561+ .054 + .240 + .142

(N = 74) (N = 20)

Top Injury by Early Blight, 1906 ...... — .119 + .077 — .352 + .132

(N == 74) (N ==20)

Top Injury by Early Blight, 1907 ...... — .118 + .077 — .040 + .151

(N = 74) (N = 20)

Because of the small number of varieties involved and the

roughness of the measurements the correlations are low and

irregular. In ten cases the negative sign indicates that the

varieties which are most free from scab are also least susceptible

to attacks by other diseases. In neither of the two cases of posi-

tive correlation is the constant statistically significant in com-

parison with its probable error.

Thus altogether 23 of these cross correlations—that is correla-

tions between injury to different organs by the same disease, or

9 In one case, pe: the correlation is between foliage injury by two dif-

ferent organisms in the same year. What interrelationship is to be ex-

pected in such case requires further consideration.

244 THE AMERICAN NATURALIST [ Vou. LI

to the same organ by different diseases, or to different organs by

different diseases—have been worked out. Only 4 of these—

that is only about one ease out of six—are exceptions to the rule

that varieties which show more than the average amount of

injury by one disease will, on the whole, show more than the

_ average injury by another disease. No one of these exceptional

constants can be considered significant with regard to its prob-

able error. Several of the 19 which indicate the rule may be

looked upon as individually trustworthy. Thus notwithstanding

the large variations in numerical magnitude incident to small

series of data and rough measurement, the determinations taken

collectively certainly furnish highly convincing evidence that to

a considerable extent susceptibility to disease is general rather

than specific.

The fact that the series of correlation coefficients herd pre-

sented justify much more definite conclusions than those who

have considered the data without statistical analysis have drawn,

is sufficient indication of the usefulness of the biometric method

in the preliminary stage of disease-resistance experiments in

which large numbers of strains are being tested, and in which

the mass of data is highly confusing. The special cases illus-

trated by no means exhaust the possibilities of the biometric

formule now available. Had the data been more extensive, the

analysis might have been carried much farther.

Nothing that has been said in this paper in emphasis of the

statistical method must be taken to imply that the most careful

individual analysis is not desirable and essential. The two

methods are not mutually exclusive, but supplemental.

J. ARTHUR HARRIS

THE DIFFERENT MEANINGS OF THE TERM ‘‘FACTOR”’

AS AFFECTING CLEARNESS IN GENETIC

DISCUSSION?

IN the analysis of alternative (or segregating) heredity, we

find that certain potentialities, such as that of producing a cer-

tain color in some part of the soma, appear to be inherited inde-

pendently of certain other potentialities. We assume that the

germ-plasm carries various corresponding genes, factors, or deter-

miners, whose independence in gametogenesis determines the in-

dependence of the somatic characters. Cytological study leads

1 Paper No. 39, "n of California, Citrus Experiment Station,

Riverside, California

No. 604] SHORTER ARTICLES AND DISCUSSIONS 245

to some very probable conclusions as to the time and method of

segregation of these determiners; though it does not yet enable

us to identify with absolute certainty the actual physical unit of

segregation,. the cytological and genetic evidence indicates

strongly that such a unit exists.

In the current chromosome hypothesis, as developed especially

by Morgan and his collaborators (Morgan, Sturtevant, Muller,

and Bridges, 1915), the material unit of segregation is assumed

to be a part of achromosome. Breaks in two homologous chromo-

somes at meiosis, with consequent exchange of parts by the pair,

presumably occur at certain definite points only. How close these

points may be we can not say, but the general stability of Men-

delian characters indicates that the number of points is limited.

On these assumptions, the portion of a chromosome between two

adjacent points of possible breaking is the ultimate physical unit

of genetic segregation—essentially a locus as defined by Morgan

(1915, p. 419).?

It is now widely recognized that, in effect, a single real unit of

segregation may influence very diverse characters of the soma,

often in ways which can not be at all inferred one from another.

Very possibly one physical unit of segregation may affect, say,

fiower color and height in ways just as distinct physiologically

as may two distinct units of segregation, although transmission is

different in the two cases. In the latter case we say that two

genetic factors are concerned; are we compelled in the former

case to admit only one?

As a matter of fact, as will be evident on further considera-

tion, either course is possible, according to the definition of

factor accepted.

If by ‘‘factor’’ we mean a developmental potentiality, the de-

limitation of a particular factor is largely a matter of convenience

in analysis. On the other hand, if the term is used to designate

a supposed actual physical unit of segregation, a factor has a

definite objective extent.

The former view is that of the presence-and-absence terminol-

ogy, as it is generally understood at present. In this sense, a

factor is not an element of the germ-plasm; it is rather a prop-

erty or characteristic of the germ-plasm or of some element of the

germ-plasm. The characters of an organism, as Gates (1914,

2 Though Morgan, Sturtevant, Muller and Bridges (1915, p. 155) suggest

the possibility that the loci of linked factors may be so near together in a

chromosome ‘‘that they never (or very rarely) cross over.’’ The definition.

of locus is discussed below.

246 THE AMERICAN NATURALIST [ Vou. LI

p. 269) has remarked, are ‘‘attributes,’’ no more to be separated

from the organism than are the properties of a chemical com-

pound from that compound. The factors of the presence-and-

absence scheme, similarly, are inferred properties or attributes of

the germ-plasm, by whose behavior we explain the alternative

transmission of certain properties or attributes of the soma.

Obviously an organism is not composed of ‘‘characters’’—and

neither is its germ-plasm composed of ‘‘factors,’’ so long as the

factors are those of the presence-and-absence scheme. Such

factors are nothing but characters of the germ-plasm, and, like

the characters of the soma, they are more or less conventionalized

in description. We have no warrant for projecting these con-

ventionalized descriptions back into the actual germ-plasm, and

assuming the presence and absence there of strictly correspond-

ing material units of segregation.

The presence-and-absence scheme, when not encumbered with

non-essential hypotheses, is a strictly neutral instrument of genetic

analysis. If there is segregation in the formation of the germ-

cells, it is merely a matter of definition to state that a factor is

allelomorphic to its absence. That is, the assumption of segrega-

tion is the only assumption — by this scheme, which is the

logically simplest form of the ‘‘conceptual notation’’ (East,

1912) of genetics.

Very special emphasis must be placed on the fact that the

“absence”? is absence of a potentiality, without reference to the

presence or localization in the germ-plasm of any other poten-

tiality that may actually take its place. The allelomorphism of

the presence-and-absence notation is a logical opposition; when

it makes ‘‘A’’ and ‘‘no-A’’ allelomorphs, this involves no as-

sumption as to what may be physically opposed, in the chromo-

somes, to the physical basis of “A.”

If an ‘‘absence’’ a of a given factor A is always or commonly.

accompanied by an actual presence of a corresponding factor A’,

and we wish to represent this fact, it is provided for by the

terminology of linkage; we may use Aa’ and aA’, since the

presence-and-absence ‘scheme makes no assumptions as to the

structure of the germ-plasm. It is obviously simpler to write

simply A and A’, or A and a, for the two factors, and conveni-

ence may justify this practise; we should note, however, that in

thus abandoning the presence-and-absence terminology we intro-

duce a second assumption, that of actual factor-to-factor opposi-

tion or allelomorphism. This assumption is, of course, in view of

all the evidence, a highly probable one, and especially convenient

No. 604] SHORTER ARTICLES AND DISCUSSIONS 247

in cases of apparent multiple allelomorphism (Morgan, Muller

Sturtevant, and Bridges, 1915, chap. 7). In fact, this added as-

sumption probably permits a more direct and therefore prac-

tically simpler representation of the actual course of segregation.

Whether the corresponding factor-to-factor notations now used

for Drosophila (Castle, 1913; Morgan, Sturtevant, Muller, and

Bridges, 1915, p. 233) are everywhere adequate and convenient

is another question, as Emerson (1913) has shown.

Cases of multiple allelomorphism involve no special difficulty in

principle for the presence-and-absence scheme. They can of

course be represented only by linkage formule, in which the

‘*presence’’ of one factor of the set is linked with the absence of

the rest—but their very occurrence suggests that we might, as is

suggested above, correctly enough represent single factorial dif-

ferences in the same way. All this can affect only the conveni-

ence of the notation, and not at all its logical applicability.

If we adopt a factor-to-factor system of notation, it is natural

to conceive of the opposed ‘‘factors’’ not as mere potentialities,

but as physical units responsible for genetic potentialities. When

we have taken this viewpoint, we have begun to ‘use the word

factor in the second sense mentioned above; we are thinking of

assumed physical units of segregation, not merely of observed

peienticlitios of development. Moeaa (1915, p. 419), in dis-

cussing ‘‘presence and absence,’’ uses factor in this sense, as do

Morgan, Sturtevant, Muller, and Bridges (1915, pp. 220-222).

No doubt what has been said above is an old story to experi-

enced geneticists in general, in view of such discussions as those

of East (1912) and Morgan (1915). The distinction is so funda-\

mental, however, and the double use of the term factor so in-

creases the difficulties of the case, that consideration of the gen-

eral problem from the present terminological viewpoint seems

highly desirable. Perhaps greater precision in the use of several

terms could be attained.

Johannsen (1909, pp. 124-125), in defining the term Gen

(gene), makes it perfectly plain that he means the material

basis? or cause (the Anlage), of whatever sort, of a ‘‘unit char-

acter,’’ defining a unit character as one dependent on a special

kind of gene. He is evidently inclined to consider the gene as

the material unit of segregation, holding that the sum of the

genes constitutes the germ-plasm, and there is a widely prevalent

3 Or immaterial basis, if we must admit the theoretical possibility of the

existence of immaterial ‘‘entelechies’’ associated in some more or less mys-

tical way with the germ-plasm. ;

248 THE AMERICAN NATURALIST [ Vou. LI

tendency among geneticists to use gene, and its synonyms factor

and determiner, in this sense, which is the second of the two dis-

cussed above. Evidently gene is not properly used in the first

sense. A moment’s thought, however, will show the impractica-

bility of confining factor to that sense; the meaning of this term

shifts back and forth continually in common usage, and often

remains indefinite.

Further, when factor (or gene) is used in the second sense, we

consider it coextensive with locus (Morgan, 1915, pp. 419-20;

Goodspeed and Clausen, 1917, p. 32). A factor is a particular

state or condition of a locus. Let us, then, define locus as the

physical unit of segregation, almost certainly identified as a

genetically indivisible portion of a chromosome. Genetically in-

separable (‘‘completely linked’’) potentialities, then, belong to

the same locus, and hence to the same factor or gene; ‘‘completely

linked factors’’ are mainly‘ relegated to non-cytological discus-

sion, and especially to use with the presence-and-absence ter-

minology.

No doubt Mendelian analysis considers in any case, only some

of the most readily identifiable properties of the real units of

segregation concerned, and this fact seems to deserve a large

place in our genetic thinking. Especially is it important that

the two meanings of factor and its synonyms should be clearly

distinguished ; when these meanings are unconsciously inter-

changed and confused, vagueness and misunderstanding are sure

to result.

The student of genetics may read, for example (East, 1912),

If we forget ourselves and begin to speak of unit factors as particles,

only a confusion follows similar to that caused by Nägeli, Spencer, and

Weismann. Nothing is gained and even facts are obscured.

On the other hand, he will find the factors of Drosophila

located with mathematical exactness in diagrams of the chromo-

somes, and often apparently or explicitly considered as material

components of the chromosomes. In the interest of clear think-

ing, especially in the case of beginners and casual students in the

field of genetics, the explanation of this apparent contradiction

deserves very special emphasis.

As an example of the way in which this terminological con-

flict may cloud an argument when the essential facts are clear to

the writer, we may take the following case. Morgan (1913,

ra n temporarily complete linkage of genes must be excepted, as

in the usual case with the male of Drosophila. . The point is that the chromo-

some naa pai well consider, in any case, that potentialities s awaye asso-

ciated are manifestations of the same factor or gene.

No.604] SHORTER ARTICLES AND DISCUSSIONS 249

p. 10), in urging his substitute for the presence-and-absence

scheme, largely on grounds of convenience, agrees with East

(1912) as to the general usability of the latter scheme as a

‘‘system of nomenclature’’ without cytological implications. He

makes especially plain the undesirability of interpreting ‘‘ab-

Sence’’ as a physical absence in the germ-cell, or (1915, p. 419)

as “‘a hole in a chromosome.’’ In one respect, however, Morgan’s

discussion seems less clear than it might be, and this is in the use

of factor, in these articles, in a sense (the second here) which is

not that of the presence-and-absence scheme, with only vaguely

implied explanation of the distinction. It certainly is permissible

to speak of ‘‘the absence of a factor from the germ-plasm,”’

if we mean the kind of ‘‘factor’’ implied by the presence-and-

absence terminology.

We must make it as clear as possible that factor (1) sometimes

means a potentiality and (2) sometimes means a body, and that a

factor is assumed to be paired either (3) with its absence or (4)

with another (identical or different) factor. The combination of

(1) and (3), then, gives the presence-and-absence scheme, while

the combination of either (1) or (2) with (4) gives the scheme

used by Morgan (1913; see also Castle, 1913) and other students

of Drosophila. General objections to Mendelian analysis have

been based largely on confusion of (1) and (2), which often

leads to erroneous suppositions—for instance, that Mendelian

analysis in general, or the presence-and-absence method of Men-

delian analysis, requires the unnecessary and unwarranted as-

sumption involved im the combination of (2) and (3). Prob-

ably this confusion is also largely responsible for the persistence

of another often discredited notion, the idea that ‘‘Mendelians”’

suppose their factors to be individually the basis of somatie char-

acters, rather than simply necessary elements in an interacting

complex which produces the characters. i

SUMMARY

The term factor has, in genetic use, two distinct meanings,

which are continually interchanged or combined and often con-

fused. It is essential to clearness in genetic discussion that these

two meanings should be carefully distinguished. These mean-

ings may be indicated by the following formal definitions:

1. A genetic (Mendelian) factor is a property or characteristic

of the germ-plasm, more or less conveniently delimited for the

purpose of analysis of segregating heredity. :

2. A genetic (Mendelian) factor, or gene, is an actual material

250 THE AMERICAN NATURALIST [Vou. LI

unit of genetic segregation ; it is of unknown nature, but probably

consists of a genetically indivisible portion of a chromosome (a

locus) in a particular state.

The presence-and-absence scheme of factor notation properly

employs only the first of these meanings; the Morgan-Castle

scheme, on the other hand, may use either.

Howard B. Frost

CITRUS EXPERIMENT STATION,

RIVERSIDE, CALIF.

BIBLIOGRAPHY

Castle, hiran E. 1913. Simplification of Mendelian formulæ. Am. NAT.,

47: 170-182.

East, sansa M, 1912. The sagged Rp oie as a Description of

ee Facts. Am. NAT., 46: 5.

Emerson, py A. 1913. Simplified ea seta Formule. Am. NAT.,

47:

307

a R. hia 1915. The Mutation Factor in Pr "n Par-

icular Reference to Œnothera. 14 + 353 A ve Macm

Pe Thomas H., and Clausen, R. E. T: endelian rare Dif-

ferences versus diceateatenenbins ii in AAN Am. Nar., 51:

31-46, 92-101.

Johannsen, W. 1909, Elemente der exakten Erblichkeitslehre. 6 + 516 p.

n h

Morgan, Thomas H. "1913. Factors and Unit Characters in Mendelian He-

edity. Am. NAT., 47: 5-16

1915. The Bois of the Birra in the PE a s Sex-linked

Mendelian Character in Drosophila. Am. NAT : 385-4

a Thomas H., Sturtevant, A. H., Muller, H. i ne Pres, Calvin B.

The rekaan of Wondaiai ‘Heredity. 13 4+ 262 p. New

Te Henry Holt & Co.

THE SELECTION PROBLEM

Untess history fails to repeat itself, geneticists, whose atten-

tion is focused upon variation, sho sooner or later overem-

phasize its impoftance as a factor in shaping the organic complex.

There is, indeed, reason to believe that already a tendency for

some among them to do so is becoming apparent. Dr. Pearl’s*

recent paper under the title above affords an example in point.

In that communication its author fails to discriminate sharply

between two distinct phases of his subject. Whether selection

may affect the course of evolution is a matter entirely apart from

the possibility that it alters the germ plasm. Racial history

may possibly be modified, if the genetic composition of a mixed

population may be affected by selection based upon somatie dif-

1 Pearl, Raymond, 1917, ‘‘The Selection Problem,’’ THE AMERICAN NAT-

URALIST, Vol 51, pp. 65-91.

No.604] SHORTER ARTICLES AND DISCUSSIONS 251

ferences. But modification of the germ plasm by selection is

impossible, if that agency acts only as ‘‘a mechanical sorter of

existing diversities.’’

The present note is not concerned with the causes of variation.

It refers only to the first-mentioned phase of the selection prob-

lem. It accepts the statements in the quotation below as sub-

stantially correct, and attempts in brief compass to evaluate the

arguments by which Dr. Pearl supports his position regarding

them.

By transposition of a few phrases his ideas may be expressed

in his own words as follows:

The mere fact of elimination and survival . . . is capable, in theory

at least, of bringing about evolutionary pete of a progressive sort,

. if the elimination be selective, and the survivors transmit to their

progeny those differences that mark them off from the eliminated.

The theory that these two rules are always and everywhere in opera-

tion, taken together with the observed fact that living creatures do die,

is the Darwinian theory of Natural Selection as a factor in organie

evolution.

If, as is implied, Darwin gratuitously assumed the intolerable

burden involved in the use of the words, always and everywhere,

it is immaterial. It is not a vital issue whether the form in

which he expressed himself will bear literal interpretation, but

merely whether his idea is correct that natural selection effects

notable changes in the course of evolution. Hence it seems suffi-

cient to say, that if the ‘‘Dance of Death’’ is governed in gen-

eral, or even in part, by the joint action of the two principles

enunciated in the preceding paragraph, the changes described

there should follow as surely, although more slowly, than if the

conformity were complete.

It is stated by Dr. Pearl, as one of three broad facts on ac-

count of which natural selection is no longer regarded as a

primary, or perhaps even a major factor in evolution, that even

when selective elimination on the basis of somatie characters

does occur, it does not follow generally and regularly that the

somatic differences on which the selection acted will reappear in

the progeny, . . . actual experience having abundantly demon-

strated that a very great many of such somatic differences are

not inherited.

This may refer, first, to the fact that a single phenotype may

include members of different genotypes. Yet, even so, no strict

limitation is placed upon the possibility of changing the char-

acter of a mixed population by selection based upon somatic

qualities. If plus variants of an inferior strain seem superior to

252 THE AMERICAN NATURALIST [ Vou. LI

individuals of a higher order of genetic worth, this will have its

due effect in impeding progress; but since the essential point

is, that, collectively considered, members of different pure lines

do, in general, rather definitely reflect their different germinal

constitution, advance may undoubtedly be made. However, it is

unnecessary to labor the point, as it is not only admitted, but is

urged by geneticists themselves in explanation of such results, for

example, as those Castle and Phillips? obtained in selection ex-

periments with hooded rats.

Reference to the genetic behavior of such characters as side-

sprig of the comb in poultry may also be included in the quota-

tion above. If, in this case, emphasis is laid upon the fact

that selection might apparently be exercised indefinitely without

the least tendency toward evolution of a side-sprigged race, it

needs only be pointed out that the argument is directed against

the contention that selection is capable of modifying the germ

plasm. It has no bearing whatever upon the possibility of its

occurrence in nature, nor, aside from the point indicated, upon

its influence in evolution.

Upon the other hand it seems quite impossible that even if

characters of which side-sprig is representative were highly

useful, they should fundamentally modify the course of evolution

under selection, or place any notable obstacle in its way, for they

are not germinal variations and are as likely to occur in one line

of descent as another. Hence, other things being equal, it is quite

as probable that they should assure the survival of a subnormal

representative of a superior genotype, as that they should tide

over a superior representative of an inferior one; and the chance

would be no greater that the attribute in question should appear

in the offspring of one rather than in that of the other.

A second of the three general groups of facts to which refer-

ence has been made is summarized in the statement:

Observation indicates that in many cases evolutionary changes have

come about by relatively large, discontinuous steps, the new form being

not merely fully differentiated at its first appearance, but also fully

able to survive.

In another connection it is stated forcefully by Dr. Pearl that

if the game of survival is actually played by the quoted rules

he formulates (and no others are necessary) the conclusion is

logically irresistible that progress is bound to occur in the direc-

tion of those differences which distinguish the survivors. But

2 Castle, W. E., and Phillips, John C., 1914, Carnegie Institution of Wash-

ington, Publication 49. Castle, W. E., 1916, ‘Genetics and EES ” Har-

vard University Press, Cambridge, 8vo, pp. vi + 353.

No.604] SHORTER ARTICLES AND DISCUSSIONS 253

since obedience to his two rules is not in the least contingent

upon the magnitude of the variations upon which selection is

based, it must be admitted that the facts summarized above are

entirely irrelevant to the present discussion. They neither bear

upon the phenomena of inheritance, nor add anything to our

knowledge of selective elimination.

The third general fact cited in support of Dr. Pearl’s ries y

tion regarding the diminished esteem in which natural selection

is held as a factor in evolution is:

All organisms possess in varying, but usually in very large, degree

the power of personal, immediate, individual, somatic adaptation to the

environment.

It is affirmed in addition, that in consequence of this power of

personal adaptation the survival expectation of an individual is

not generally and regularly a function of any static, single-

valued relation between its somatic structure, habits or physiol-

ogy, on the one hand, and the impinging environmental stresses

on the other. Yet, it is asserted, such a relation is implicitly

assumed in that part of the theory of natural selection which

affirms a ‘selective elimination on the basis of somatie char-

acteristics.

The reply to these various statements is, that their substantial

truth may be admitted without the possibility that evolution is

affected by selective elimination being thereby in the least

diminished. The adaptive capability of any individual either

rests upon or lacks a germinal basis. In the former case there

is no obvious reason why it should not itself provide material

upon which selective elimination might be based, with consequent

change in the composition of the population. In the latter,

individual adaptability is as incapable of exercising influence

upon the course of evolution, as side-sprig should be, if it were a

useful character of the same order of importance.

If the accumulated results of genetic research provide no

more effective arguments than these, it must remain an open

question whether natural selection is not a primary factor, not

in the origin of species, but in the determination of the elements

composing the flora and fauna of the world at any period in its

history. In other words, one who wishes to force an abandon-

ment of that position must demonstrate that selective elimina-

tion does not occur upon such a scale that it may account for

the results ascribed to it.

For many legitimate reasons Dr. Pearl has not treated this

point at length in his article under discussion. But from

scanty evidence available he derives the following conclusion :

254 THE AMERICAN NATURALIST [ Von. LI

In some cases natural elimination is certainly in some degree selec-

tive, while in other cases it certainly is not, and in the most favorable

eases of all the selection is apparently not very rigorous. Gross terato-

logical abnormalities are eliminated. But the smaller deviations from

type, which in theory ought to furnish the basis of selection, appear

upon quantitative study less generally and sharply determinative of

survival than might have reasonably been expected theoretically.

It is perhaps worthy of note that ever since it appeared that

the larger, and rarer, discontinuous variations are in no danger

of being lost through swamping, it has been beside the mark to

ascribe especial theoretical significance to smaller deviations from

type. Attention may also be directed to the important admis-

sion that in some instances elimination is known to be selective.

It will then be in order to examine reports of researches upon

the basis of which it is confidently asserted that in other cases the

same is not true.

It happens that with five others one is cited which falls

squarely within my own field of investigation. This is Pro-

fessor Reighard’s* ‘‘Experimental Field Study of Warning

Coloration in Coral-reef Fishes,” which Dr. Pearl seems to

consider of particular significance for his own argument. But

since it has been my good fortune to study the same material in

the same place, more extensively and with better facilities, I feel

justified in saying that Reighard’s results will bear no such

interpretation as is here placed upon them. He proved that

gray snappers possess powers of discrimination and of memory

which would lead one to suppose that, if the bright colors of the

smaller reef fishes possess a warning significance, the snappers’

should be aware of it and avoid them. He did not prove beyond

possibility of doubt that they do attack such fishes freely, but

that is of no importance in the present connection; his con-

clusion that tropical fishes are not warningly colored with refer-

ence to their commonest enemies is perfectly sound. His ideas

regarding immunity coloration are, however, the only ones in

his paper which have the remotest bearing upon the matter of

selective elimination, and there is no reason to suppose that these

are more than logical deductions from incorrect premises.

Dr. Pearl’s* own report upon the natural elimination suffered

3 Reighard, Jacob, 1908, ‘‘ An Experimental Field-study of Warning Col-

oration in Coral-reef Fishes,’’ Carnegie Institution of Washington, Papers

from the Tortugas Laboratory, Vol. 2, pp. 257-325.

4Pearl, Raymond, 1911, ‘‘Data on the Relative Conspicuousness of

Barred and Self-colored Fowls,’’ THE AMERICAN NATURALIST, Vol. 45, pp.

107-117.

No.604] SHORTER ARTICLES AND DISCUSSIONS 255

by barred (Plymouth Rock) and black, or near-black, chickens

living under the same conditions is also mentioned. In this

paper photographs show the black fowls looming up against

natural backgrounds much more distinctly than do the barred.

This is accepted as ‘‘objective and unbiased evidence regarding

the relative conspicuousness of the two types of plumage

pattern.’’ It follows naturally, since the extensive record shows

little difference in the rate of elimination of the two sorts of

birds, that ‘‘the relative inconspicuousness of the barred color-

pattern afforded its possessors no great or striking protection

against elimination by natural enemies.’’ But photographs

serve as accurate measures of the conspicuousness of the fowls in

the eyes of color-blind enemies only. Therefore, if rats and pre-

daceous birds are not color-blind, and there is perfectly good

reason for supposing that creatures lower in organization than

either have color vision, it is not at all certain that the elimina-

tion in the two cases does not correspond fairly well with the

actual difference in conspicuousness of the two t ;

Kellogg and Bell’s® interesting ‘‘Studies of Variation in In-

sects’’ deals with 24 species. In 23 of them, including the lady-

beetle, Hippodamia, to which Dr. Pearl refers, the authors show

that there is much variation in individuals which have success-

fully run the gauntlet of natural selection. But since they

have no knowledge whatever of the variation in the original

populations, of which they have studied survivors only, these

their results show nothing regarding the extent, or even the oc-

currence, of selective elimination.

In the honey bee alone duplicate studies were made of the

variation of certain structures in individuals which were about

to hatch, and in others, apparently from the same hive, after

exposure to the vicissitudes of an active life. Among 200 drones

in the first group the veins of the fore wings in 11 were im-

perfectly developed, and as a result normal flight became difficult

or impossible. The variation in others of the first series seems

essentially the same as that observed in the 300 members of the

second, among which none of the defective individuals were

found. But if these facts prove anything, it seems to be that

selective elimination does occur when unfavorable variations

affect the normal functioning of an organ. Suggestion is en-

tirely lacking that the mechanical efficiency of the wing is im-

paired by the other variations noted, and it can scarcely be con-

5 Kellogg, V. L., and Bell, R. G., 1904, ‘‘ Studies of Variation in Insects,’’

Proc. Washington Acad. of Sciences, Vol. 6, pp. 203-332.

256 THE AMERICAN NATURALIST [ Vou. LI

sidered a pregnant fact, in the present connection at least, that

indifferent variations provide no basis for selective elimination.

In the same two series of bees the variation in the number of

hooks upon the costal margin of the hind wings was determined

without significant difference appearing in the two cases. In this

instance, since the hooks appear to operate to the insects’ ad-

vantage in binding the fore and hind wings of each side together,

it seems plausible enough at first glance, that the more hooks

there are the more efficiently their function will be discharged.

Upon second thought, however, a difficulty suggests itself. The

number of hooks varies from 19 to 29 in different individuals,

but even the smaller number may, for all that is known to the

contrary, perform perfectly the function ascribed to them. In

that event the others are superfluous and the advantage they

confer entirely fictitious. But waive the objection, and what

follows? Simply a conclusion which in its relation to the

present argument is already invalidated: Variations of the

magnitude indicated provide no ‘‘handle’’ for natural selection.

t is unnecessary to carry the examination of the evidence

farther. The three papers which have been reviewed are no

carefully selected for criticism, but are the last, and apparently

the most important, of six certified to be ‘‘fairly representa-

tive.’’ If, however, this characterization is correct, it is apparent

that the case against selective elimination is greatly exaggerated.

In conclusion, it appears that neither genetic research nor

studies upon elimination closely limit the possibility that selection

has played a very important part in evolution. In addition,

recent field-studies* demonstrate novel facts of common occur-

rence which must apparently be ascribed to the action of this

factor. Hence as was suggested in the beginning, Dr. Pearl

would seem to over emphasize the importance of variation, and

to attach too little significance to selective agencies in determin-

ing the course of racial history.

W. H. LONGLEY

GOUCHER COLLEGE,

BALTIMORE

e Longley, W. H., 1914, Report upon color of fishes of the Tortu

Reefs, Carnegie Inst. of Washington, Year Book No. 13, pp. 207-208; 1915,

t‘ Coloration of Tropical Reef Fishes,’’ Carnegie Inst. of Washington, Year

Book No. 14, pp. 208-209; 1916; ‘‘The Significance of the Colors of Trop-

ical Reef Fishes,’’ Carnegie Inst. of Washington, Year Book No. 15, pp.

209-212; 1916, ‘‘Observations upon Tropical Fishes and Inferences from

their Adaptive Coloration,’’ Proc. Nat. Acad. Sciences, Vol. 2, pp. 733-737.

THE

AMERICAN NATURALIST

Vor. LI. May, 1917 No. 605

STUDIES UPON THE BIOLOGICAL SIGNIFI-

CANCE OF ANIMAL COLORATION

Il. A Revisep Worxine Hyporuesis or MIMICRY

Dr. W. H. LONGLEY

GoucHER COLLEGE, AND DEPARTMENT OF MARINE BIOLOGY, CARNEGIE

INSTITUTION OF WASHINGTON

ALTHOUGH zoologists know that detailed resemblance

in outward appearance may occur between different

species of insects which are not closely related, they do

not agree in their interpretation of the facts they observe.

Present knowledge, indeed, justifies nothing more than

tentative explanations of mimicry ; but, in this matter, ob-

servations recently reported! limit one’s freedom of

choice, since they appear to bear directly upon the validity

of current hypotheses reviewed in the following pages.

The first attempt to interpret mimetic resemblance as a

result of natural selection was made by H. W. Bates,? who

writes:

What advantage the Heliconide possess to make them so flourish-

ing a group, and consequently the objects of so much mimetic resem-

blance, it is not easy to discover. . . . It is probable that they are un-

palatable to insect enemies. ... They have all a peculiar smell. I

never saw flocks of the slow flying Heliconide in the woods persecuted

by birds or dragon flies, to which they would have been an easy prey;

1 Longley, ‘‘The Colors and Color Changes of West Indian Reef-fishes,’’

Jour, Exp, Zool, 1917. It happens that the present paper will appear

slightly before that cited.

2 Trans. Linn. Soc. Lond., Vol. 23, p. 510.

258 THE AMERICAN NATURALIST [ Vou. LI

nor, when at rest on leaves, did they appear to be molested by lizards

or the predaceous flies of the family Asilidæ, which were very often

seen pouncing on butterflies of other families. If they owe their flour-

talidæ, whose scanty number of individuals reveals a less protected con-

dition, should be disguised in their dress, and thus share their immunity.

Bates himself points out the fact that ‘‘some of the

mutual resemblances of the Heliconidz seem not to be due

to the adaptation of the one to the other, but rather, as

they have a real affinity, . . . to the similar adaptation

of all to the same local, probably inorganic conditions.’’

Thus the application of his hypothesis was limited from

the beginning.

Fritz Miuller* showed how those instances of resem-

blance which his predecessor ascribed to the influence

of Lamarckian factors might be aligned with the Darwin-

ian hypothesis. In Meldola’s* translation of his original

paper his idea is expressed as follows:

What benefit can one species derive from resembling another, if each

is protected by “cag PUEA Obviously none at all, if insectivorous

birds, lizards, etc., have acquired by inheritance a knowledge of the

species which are ite) or distasteful to them—if an unconscious in-

telligence tells them what they can safely devour and what they must

avoid. But if each single bird has to learn this distinetion by ex-

perience, a certain number of distasteful butterflies must also fall vic-

tims to the inexperience of the young enemies. Now if two distasteful

species are sufficiently alike to be mistaken for one another, the ex-

perience acquired at the expense of one will likewise benefit the other;

both species together will only have to contribute the same number of

victims which each of them would have to furnish if they were different.

Recent years have been marked by a tendency upon

the part of some observers’ to extend the bounds of the

Miillerian associations, until in a given fauna a large pro-

portion of the insects which show the same color com-

bination are included in one bionomie group. Scores of

species have, indeed, been assigned to some, and it has

8 Kosmos, May, 1879, p. 100.

4 Proc. Ent. Soc. Lond., 1879, p. xxvii.

5 Marshall aed Poulton, ‘‘The Bionomies of South African Insects,’’

Trans. Ent. Soc. Lond., Vol, 41, pp. 287-584.

No. 605] ANIMAL COLORATION 259

been alleged that very many types from the same region

show the influence of one or another of the dominant

Miillerian aggregations. Miiller’s hypothesis, however,

has not attained preeminence solely by extension to newly

discovered cases of resemblance, but has prospered in

many instances at the direct expense of the Batesian con-

ception. Its changed fortune depends largely upon

Dixey’s® discovery of mimetic attraction, or reciprocal

mimicry.

This relation, which it is held exists between many in-

sects previously considered typical Batesian couples, sug-

gests that the observed resemblance involves mutual ad-

justment. But the idea that each species introduces into

its own pattern elements characterizing that of the other,

and thus contributes actively to the development of a

common type of coloration, is intelligible in terms of the

mimicry hypotheses, only if the superficial resemblance

so attained is mutually advantageous. Whatever justi-

fies change in the interpretation of fact lies here; for, if

it be assumed in the beginning that the likeness noted

must have arisen either through the action of Batesian or

Miillerian factors, it must be admitted that the notion of

mutual advantage seems more fitly associated with the

latter: two species, each of which enjoys marked immu-

nity, seem better able to force reciprocal concessions in

their achievement of resemblance, than they should, if

there were great disparity in their means of defence.

Perhaps the most obvious suggestion from Dixey’s .

research is not, after all, that a closer approximation to

truth may possibly be attained through reclassification of

mimetic resemblances, but that an intergrading series of

alleged Batesian and Miillerian mimics is perfectly con-

ceivable, in which no known test could possibly determine

the occurrence of a natural break. Hence there would

seem to be only historical reasons for maintaining the

two categories.

It is noteworthy that pthc hypothesis to which ref-

erence has been made was in its original form an attempt

6 Trans. Ent. Soc. Lond., 1894, pp. 249-334.

260 THE AMERICAN NATURALIST [Vou. LI

to explain the existence of conspicuous creatures. The

sole concern of each was the interpretation of resem-

blances, which were later commonly considered mere in-

cidents in the attainment and use of warning colors. This

shifting of emphasis from ‘‘likeness which is perfectly

staggering’ to conspicuousness, which failed to elicit a

single outspoken comment in the original papers of Bates

and Müller, is distinctly chargeable to Wallace, who ex-

tended his hypothesis of the functional conspicuousness of

bright colors, until it included the facts of mimicry.

Abbott H. Thayer® has proposed an explanation of the

resemblance between unrelated species of butterflies,

which is consistent with his thesis that the foremost func-

tion of animal coloration is concealment. This hypothesis

is Darwinian in principle, but in practise is directly op-

posed to current selectionist opinion. It is purely specu-

lative, and is stated as follows:

It is surely conceivable that in a certain region, one particular form

of flower-scenery representation may furnish such advantage to butter-

flies as to cause many widely separated species to become modified till

they wear a common aspect, and it is conceivable also that there would

be one common form of wing that would best lend itself to this scheme.

More recently Thayer’? adds that in the paper from

which the excerpt above is taken he ascribed more im-

portance to butterflies’ resemblance to flowers, as com-

pared to their rendering gf scenery, than he should at the |

later date; but this necessitates no modification of his

‘idea that mimicry is mere incidental resemblance between

species, which, through selection based upon the obliter-

ative effect of their coloration, conform ever more closely

to one ideal representation of their common background.

If ‘the Darwinian ranks are divided upon the question

of the prevalence of conspicuous types of coloration, sim-

ilar though less Moe dissension appears among their op-

7 Bates, l ¢., p.

t Dasiialen, p- pe pee: and Co., 1891.

9 Trans, Ent. Soc. Lond., Vol. 42, p. 557.

10 See Thayer, Gerald H., ee Coloration in the Animal King-

dom,’’ Appendix B, p. O51. Maemillan and Co., 1909.

No. 605] ANIMAL COLORATION 261

ponents. To Piepers,'! for example, specific coloration is

in large part a visible token of internal organization de-

termined from time immemorial, a result of orthoge-

netic evolution capable, however, of being accelerated or

retarded by external conditions. To Packard?? it repre-

sented a racial response of organism to environment, and

mimicry seemed an effect of exposure to conditions of the

same kind. But if evolutionary processes be largely be-

yond the control of external agents, and species spring

from species through internal reorganization, as one con-

figuration follows another in the kaleidoscope, one should

anticipate that many color combinations of exaggerated

conspicuousness might result. If, upon the other hand,

the development of color and pattern be determined by

animals’ environment, their coloration may well repeat

dominant notes from their surroundings. Hence it is not

surprising to find that Packard expresses hearty appre-

ciation of Thayer’s discoveries, and Piepers, despite his

anti-Darwinian attitude, might have much in common

with Wallace and Poulton. Thus the full series of con-

tradictions is rounded out, and the unsettled state of

opinion concerning mimicry, or indeed the whole matter

of animal coloration, is apparent, for the two qualities,

utility and conspicuousness, openly or tacitly affirmed or

denied, may be ascribed in every possible combination to

_ the color and pattern of a single organism.

It may apparently be stated safely without qualification

that the bright colors of tropical fishes as a class are cor-

related with the animals’ habits, and, in the case of all but

red, distinctly repeat tones characterizing their normal

environment. But, other things being equal, no one will

maintain that any system of external pigmentation could

be less conspicuous than one conforming to this principle.

Therefore, among these creatures at least, the occurrence

of bright colors in contrastive patterns is not inconsistent

with the idea that the forms that display them are as in-

conspicuous as may be under the conditions in which they

11‘ Mimikry, Selektion und Darwinismus.’’ Leiden, 1903.

12 Proc. Amer, Philos. Soc., Vol. 43, p. 421.

262 THE AMERICAN NATURALIST [ Von. LI

live. It is this fact that necessitates a review of hypoth-

eses of animal coloration that postulate conspicuous-

ness; for one cannot safely disregard the suggestion that

principles applicable to one group of animals may be

valid also in the case of others.

It is of interest to note that Chapman!* studied the

birds of Trinidad under favorable conditions and ob-

served that distinct types of coloration marked those of

different habits. The most brilliant species occupy the

most exposed positions in the treetops. More sedentary

forms inhabiting the body of the trees are largely green,

and brown predominates in the coloring of those that

climb upon the tree-trunks, frequent the undergrowth near

the forest border, or live upon the forest bottom.

These ecological records are a mere incident, a by-

product of their author’s activity. Through lack of de-

tail they possess no great intrinsic value, but are highly

significant in their present setting. Mention should also

be made of Potts’!* observation that shrimps living sym-

biotically with crinoids upon the Australian reefs repeat

= the colors of the forms with which they are associated.

That comparable facts regarding other groups of animals

are not available is immaterial. If the bright colors of

tropical birds, fishes and some crustacea repeat those of

the animals’ respective environments and minister to the

inconspicuousness of their possessors, it is of interest to

inquire what data and reasoning support the contention

that in insects similar combinations bear a different rela-

tion to the colors about them and discharge another func-

tion.

It appears first, from the statements of a number of

their more prominent advocates, that there are funda-

mental theoretical objections to the hypotheses of warn-

ing coloration and mimicry.

Poulton!® remarks that the acquisition of an unpleas-

ant taste or smell, together with a conspicuous appear-

13 Bull. Amer. Mus, Nat. Hist., Vol. 6, pp. 19-20,

14 Carn. Inst. Wash., Papers Dept. Mar. Biol., Vol. 9, pp. 71-96.

15 Proe. Zool. Soc. Lond., 1887, p. 192.

No. 605] ANIMAL COLORATION 263

ance, is so simple a form of protection, and yet ex hy-

pothesi so absolutely complete, that it seems remarkable

that more species have not availed themselves of this

mode of defence. He argues that if once their potential

vertebrate enemies were driven to eat any such insects in

spite of their unpleasant taste, they would almost cer-

tainly soon acquire a relish for what was previously dis-

agreeable, and the insects would be in great danger of ex-

termination, having in the meantime become conspicuous

by gaining warning colors. He concludes that if this

reasoning is correct, it is clear that this mode of defence

is not necessarily perfect, and that it depends for its ap-

parently complete success upon the existence of relatively

abundant palatable forms: in other words, its employment `

must be strictly limited.

Dixey! encounters the same difficulty in his consid-

eration of Batesian mimicry. He observes that in this

relation the advantage is all on the side of the edible

mimicking species, whose existence is, indeed, a source

of danger to the form mimicked, inasmuch as any ex-

perience gained by tasting the former would be used to

the detriment of the latter. From these considerations

he believes that such an association can exist only when

the numbers of the one species are insignificant in com-

parison with those of the other. Upon this point he is in

essential agreement with Wallace,” who states that mim-

icry has beén shown to be useful only to those species and

groups that are rare and probably dying out, and would

cease to have any effect should the proportionate abun-

dance of mimic and model be reversed.

Here, then, are two hypothetical types of association

whose persistence admittedly depends upon the main-

tenance of definite though undetermined ratios between

their components. Hence it devolves upon those who hold

that the assumed relations are real, to outline some sys-

tem by which the due proportion of protected and unpro-

16 Trans. Ent. Soc. Lond., 1897, pp. 317-332.

17 Westminster Review, Vol. 32, N. S., p. 35.

264 THE AMERICAN NATURALIST [Vou. LI

tected forms might be maintained through the sab a aba

of natural factors.

In an attempt to avoid this preliminary difficulty Poul-

ton declares that it has always been recognized that an

insect may be distasteful to one vertebrate enemy, but

palatable to another. He suggests a different counter-

balancing limit, which he admits would certainly in time

become identical with the other. He argues that a verte-

brate enemy may be forced by stress of hunger to eat an

unpalatable insect, by implication asserts that this adapt-

ability of potential enemies of forms tending to assume

warning colors would limit the number of species de-

veloping them, and considers the truth of his suggestion

confirmed by experimental tests.

It seems, however, that as long as warning coloration

confers any advantage, other species should move in the

same direction, for the same reasons that those did in

which it first appeared. The number of warningly col-

ored species should therefore increase until the situation

conceived by Poulton materialized. But in that event the

experimental proof that hungry animals are not so fas-

tidious as those that are well fed is insufficient to meet

the exigencies of the situation; for one has no reason to

believe that animals which might become adjusted to the

new condition would confine themselves to a diet of in-

sects whose warning coloration was recently acquired,

and would leave intact the vested interests of those that

first attained it. Indeed, if one is permitted to speculate,

it seems not wholly unreasonable to anticipate a swing

of the pendulum in the other direction, so that conspicuous

forms might face the possibility of almost complete ex-

tinction. This is suggested by the well-known fact that

interspecific adjustments are not rigid, and that a state

of approximate equilibrium is frequently modified* by

climatic or other factors, and restored only after a series

of more or less definite oscillations. Examples in point

are furnished by Howard’s'® observations upon ichneu-

18 ‘f New Nature Library,’’ Vol. 7, Pt. 1 (The Insect Book), p. 68. New

York, Doubleday, Page and Co.

No. 605] ANIMAL COLORATION 265

mon flies and their primary and secondary parasites, and

more particularly by those of Forbes!’ and Bryant”? upon

the feeding habits of birds.

In his paper, which has been cited above, Dixey was not

discussing the validity of the mimicry hypotheses and

has not attempted to explain what limits the numbers of a

mimic in proportion to those of its model. Wallace also

failed to elucidate the mystery, leaving his readers to find

the way out of their difficulty as they might best be able.

Search elsewhere for helpful suggestion in the matter

yields little of value. Poulton?! holds that ichneumon flies

are particular enemies of the larve of ‘‘protected’’ Lepi-

doptera, but this idea need not be taken very seriously at

present, for it is apparently based upon the observation

of a high proportion of parasitized individuals among

such forms rather than upon comparative statistics cover-

ing ‘‘unprotected’’ species as well. Even if it were true,

while it would bolster the warning color hypothesis, it

would aggravate the situation regarding Batesian mim-

icry. Therefore only one conclusion is possible: The

theoretical objections they themselves have raised are

not adequately met by spokesmen for the two hypotheses.

What observed facts support the contention that many

animals are made conspicuous and profit by the striking

combinations of color they display, should next be deter-

mined. :

In 1867 Wallace”? suggested before the Entomological

Society of London that, as a rule, brilliantly colored larve

are distasteful to birds, expressed his desire for infor-

mation and his gratification, if any who kept birds, par-

ticularly indigenous species, would make experiments

with different larve to ascertain which were eaten and

which rejected. Members of the society and others have

repeatedly acted upon his suggestion and commonly

19‘ The Regulative Action of Birds upon Insect Oseillation,’’ Jil. State

Lab. Nat, Hist., Bull. No. 6.

20¢«The Condor,”? Vol. 13, on p. 195-208.

21‘‘ The Colors of Animals,’’ p. 182. New York, D. Appleton and Co.,

1892. For additional data, see Trans. Ent. Soc. Lond., Vol. 41, p. 337.

22 Proc, Ent. Soc. Lond., 1867, pp. oo

266 THE AMERICAN NATURALIST [ Von. LI

- agree that the results of the experiments support his

hypothesis, whose application has meanwhile been greatly

extended. But the spirit in which the observed facts are

interpreted precludes all possibility of the main inference

drawn from them being seriously considered by any un-

prejudiced critic who examines the argument.

a dull-eolored insect be eaten, this is held by impli-

cation to lend strong support to the hypothesis of warn-

ing coloration; for palatable insects must be inconspic-

uous or be destroyed. If, upon the contrary, such an insect

be rejected, its distastefulness may be a useless character,

an accident of metabolism, or vestigial, or may be related

to functional distastefulness in preceding stages of the

life history; in any case ‘‘it must be remembered that an

unpleasant attribute must always appear in advance of

the warning coloring,’’?® so the result is not inconsistent

with Wallace’s suggestion. Again, if a bright-colored

insect be rejected, this accords with his contention; and

finally, if such a one be accepted, experimenters are prone

to agree with J. Jenner Weir? who writes:

But I am by no means inclined to attach undue importance to this

fact, because the birds, being in a state of confinement, might readily

be expected to eat insects, which in a state of nature, with a less lim-

- ited choice, they would reject.

It is unnecessary to review these experiments in detail

and to attempt to evaluate them, for this has already been

done thoroughly by McAtee,?° who shows their utter futil-

ity by comparing typical observations upon caged birds

with the facts revealed by analysis of the stomach con-

tents of wild specimens of the species experimented upon.

Regarding information from such sources as that last-

mentioned he writes:

Since this evidence is sufficient in itself and since experimental data

must be supported by it, why perform the experiments? The same

time spent in collecting trustworthy data regarding the natural food

23 Poulton, ‘‘The Colors of Animals,’’ p. 176

24 Trans. Ent. Soc. Lond., Vol. 7, Ser. 3, p. 22.

25 Proc. Acad. Nat. Sci. Phila., 1912, pp. 281-364.

No. 605] ANIMAL COLORATION 267

habits of animals would bring much greater returns, and the result

would be truth, not imaginative inferences from abnormal behavior.

Before concluding the discussion of this matter it

should be stated that even if it were proved that bright-

colored insects are distasteful, it might not be inferred

fairly that they are conspicuous, or that their coloration

has a specific warning (aposematic) function. Feeding

experiments under ideal conditions might determine the

presence or absence of distastefulness, and show to what

extent it is correlated with the display of color combina-

tions of a particular sort. But even a high degree of

` correlation between unpalatability and gaudy coloration

proves that the latter is conspicuous, no more than the

demonstration that an unknown substance has the ap-

proximate hardness of gold proves that it has the same

specific gravity; for brightness, or vividness of colora-

tion, and conspicuousness are incommensurable.

Except in Thayer’s contributions, confusion upon this

point has prevailed from the beginning, when Wallace

used interchangeably the expressions, ‘‘brilliantly colored

larve’’ and ‘‘caterpillars conspicuous by their lively

coloration.’’ But the assumption that some animals are

conspicuous, or, in other words, that while their habits

remain the same their average visibility might be greatly

diminished by another system of coloration than that

they possess, can neither be adequately defended nor re-

futed, until the results of such exhaustive studies of ani-

mals’ habits as have rarely been attempted are available.

The distribution of animals must be studied intensively,

for the division of the world into provinces and the sub-

division of these into their major components by gross

dissection is not a technique of sufficient refinement to

discover the essential relations between organism and en-

‘vironment,

Passing to another phase of the matter, the value of

recorded observations upon the conspicuousness of in-

sects may be shown very clearly.

Bates saw no Heliconide attacked by dragonflies or

268 ` THE AMERICAN NATURALIST [ Vou. LI

other predaceous insects which often pounced upon but-

terflies of other families. But Poulton? finds, to state it

mildly, that ‘‘there is good reason for believing that such

attacks are not rarely made, and that predaceous insects

are important enemies of aposematic butterflies.’? He

also writes?’ of the Batesian hypothesis:

This was not, as has been generally supposed, originated by Bates

during his years of observation in the Valley of the Amazon. It arose

in his mind after his return home, when he came to examine his collec-

tion and to reflect upon his experiences,

Under these circumstances the uncorroborated testimony

of this witness concerning matters which are not known

to have been carefully investigated in the Brazilian wil-

derness and are not determinable from the study of

preserved material is of little immediate consequence.

Among subjects regarding which his opinion can at pres-

ent he held only in slight esteem, and concerning which

he expressed himself in other communications than his

original paper upon mimicry, the inherent conspicu-

ousness of bright colors may be justly included.

e positive assertions in the following quotation

describing conditions observed by an entomologist in

British Guiana are also instructive; the same is true of

their author’s naive conclusion.

W. J. Kaye? writes:

The forest is dark and gloomy, and throughout the greater part of

the year excessively damp owing to a superabundant rainfall. The

character of the vegetation is always the same, as even in the dry

season the trees are never otherwise than a fresh green. It is not sur-

prising, therefore, that practically the whole of the Lepidoptera, except-

ing, of course, the several species of Morpho, present a very uniform,

somber tone of coloration. Even the very fine and brightly colored

Heliconius catharine, H. astydamia and H. egeria do not strike one in

their surroundings as being particularly gaudy, and one is bound largely

to admit the assertion of Abbott H. Thayer that many species we call

conspicuous are not really so in their natural surroundings. It must,

however, have been quite impossible for nature to have evolved such

26 Trans, Ent, Soc. Lond., Vol. 41, p. 328. See also Vol. 44, pp. 323-409.

27 ‘í Essays on Evolution,’’ p. 211. Oxford, Clarendon press, 1908.

28 Trans. Ent. Soc. Lond., Vol. 44, p. 412.

No. 605] ANIMAL COLORATION 269

minutely close resemblance in unrelated groups without the aid of

Miillerian mimicry.

It remains to state that among Lepidoptera different

species have their characteristic attitudes of rest, fre-

quent different places, fly at different levels, and are active

at different times in the day. Even the two sexes of some

species, and these are commonly dimorphic forms, do not

haunt the same stations. It is certainly a pregnant fact,

which we may accept since Wallace?® gives independent

testimony to the same effect, that Bates*® observed many,

apparently scores, of species, in which, as he says, the sun-

loving males flaunted their gaudy hues in open places,

while their respective females, soberly clad, frequented

the forest shades.

These facts and others that might be cited are indi-

cations of diversity of habit among insects comparable

with that which among fishes is correlated with the dis-

play of different types of inconspicuous coloration. They

suggest that in this group as well, external pigments are

distributed among species according to an intelligible

system other than that whose existence is commonly in-

ferred. But if this should eventually prove to be true, we

must have an explanation of mimicry without appeal to

the concept of warning colors.

Such a hypothesis has in fact been formulated by

Punnett,*! for in spite of his apparent belief in the con-

spicuousness of many species of butterflies it happens

that he lays no stress upon it in his consideration of the

origin of mimetic resemblance. His hypothesis, as he

fully recognizes, is at present little more than naked sug-

gestion. It is ingenious, is stated attractively in the cur-

rent idiom of genetics, and is effectively displayed against

a background of destructive criticism of its predecessors,

from which it differs in minimizing the influence of nat-

29 Trans. Ent. Soc. Lond., Vol. 2, Ser. 2, pp. 253-264,

30 ‘The Naturalist on the River Amazon,’’ p. 291. Reprinted, New

York, D. Appleton and Co.,

81 ‘í Mimiery in ce ae fe Cumbildgs; University Press, 1915,

270 THE AMERICAN NATURALIST [Vou. LI

ural selection. It proposes an entirely new explanation

of mimicry in the following terms:

If we assume that sudden and readily appreciable variations of the

nature of “sports” turn up from time to time, and if these variations

happen to resemble a form protected by distastefulness so closely that

the two ean be confused by an enemy which has learned to avoid the

latter, then there would appear to be good grounds for the mimicking

sport becoming established as the type form of the species. ... On

this view natural selection in the form of the discriminating enemy will

have played its part, but now with a difference. Instead of building

up a mimetic likeness bit by bit it will merely have conserved and ren-

dered numerically preponderant a likeness which had turned up quite

independently. . . . Why variations on the part of one species should

bear a strong Dihin to other, and often distantly related, species

is another question. . . . The occurrence of mimetic resemblances is the

hereditary factors of which the total number is by no means very great.

As many of the factors are common to various groups of butterflies, it

s to be expected that certain of the color patterns exhibited by one

group should be paralleled by certain of those found in another.

Upon examination these statements appear to embody

a formal explanation of the facts to which it is difficult

to take exception. Hence it must be admitted that this is

perhaps the goal toward which with regard to this prob-

lem naturalists have been working for more than half a

century. But while his hypothesis may be correct, its

author’s reasons for deeming it so seem quite insufficient.

The chief points of support on which it rests are the

following, which are not arranged in the order of im-

portance assigned to them:

1. The difficulty of finding the appropriate enemy

which shall exercise the discrimination postulated by cur-

rent hypotheses.

2. The alleged fact, mathematically demonstrated, that

reciprocal mimicry between two species can not be estab-

lished by selection of a long series of slight variations.

3. The theoretical difficulty of the initial variation in

cases other than that above, for it seems reasonable that

if the ancestral types from which mimic and model are

derived were in the beginning very unlike in appearance

No. 605] ANIMAL COLORATION 271

no slight departure from one in the direction of the other

could have selective value.

4. The non-appearance of intermediates when a form

which is assumed to have been derived from another by

selection of a series of heritable variations (mutations)

is crossed back with the original.

5. The apparent fact that the three females of the poly-

morphic oriental butterfly, Papilio polytes, occur in pro-

portions which are approximately the same now as fifty,

or possibly one hundred and fifty years ago, although it

may be demonstrated mathematically that if either of the

two mimetic forms possesses even a slight advantage

over that from which they are assumed to be descended,

this should have appeared in an altered ratio while they

continue to live and breed together under the same con-

ditions.

6. The fact that certain variations induced by differ-

ences in temperature or humidity are not directly in-

herited, since it is alleged that this limits the material

upon which selection might be supposed to operate.

Of these points the first three may be more conven-

iently considered later with other common objections to

current hypotheses of mimicry. The remaining three will

be next examined in order.

Punnett accepts Fryer’s®? conclusion that in P. polytes

the two supernumerary females which resemble P. aris-

tolochie and P. hector differ genetically from the third

female (which resembles the male) to the extent of one

and two Mendelian factors, respectively. He cites the

fact that there are forms of sweet peas, for example,

which are known to have arisen as sudden sports, and

behave in heredity as though they differed. from the nor-

mal by a single factor. Hence he infers from analogy,

first, that the two mimetic butterflies sprang from the

primitive type by one or two mutations, as the case may

, and, as a corollary, that resemblance to their models

was not attained by gradual shaping of their destinies

82 Phil. Trans. Roy. Soc. Lond., Vol. 204 B.

272 THE AMERICAN NATURALIST [ Von. LI

through the accumulation of lesser variations by natural

selection.

But Castle** still contends vigorously that a single ge-

netic character may undergo quantitative change under

selection, and if this be true the difference finally attained

by two forms differing only in one factor might follow

from the accumulation of an indefinite number of slight

variations. Still the complete abandonment of Castle’s

position would not save Punnett’s argument. For if re-

ported observations and inferences concerning Droso-

phila** are correct, a red-eyed strain has given rise to

white by mutation and this in turn to eosin, which being

crossed with the original red gave in the F, generation

offspring in the proportion of three red to one eosin.

It is quite immaterial whether one explains these rela-

tions upon the hypothesis of multiple allelomorphs, or,

as Punnett?ë prefers, upon the assumption of complete

coupling of factors. In the former case one must admit

that by breeding experiments the end product of a series

of mutations can not be indubitably distinguished from

one that results from a single modification of the affected

factor. In the latter, one thust grant that the occurrence

of the grandparental types in the offspring of hybrid par-

ents in the ratio of three to one is no proof that the grand-

parents themselves differed in respect to one character

alone, or that the difference between the two resulted from

changes occurring at one time in the germinal constitu-

tion of an ancestor of one of them. Hence, in so far as

this argument is concerned, there is in the case of P.

polytes, for example, no assured reason for supposing

that the aristolochia-like form did not attain its present

appearance by a series of steps, of which a number of the

later at least were preserved by virtue of the advantage

they conferred upon the individuals in which they ap-

peared.

33‘*Genetics and Eugenies,’’ p. 188. Cambridge, Harvard University

Press, 1916.

34 Morgan, Sturtevant, Müller and Bridges, ‘‘The Mechanism of Men-

delian Heredity,’’ p. 164. New York, Henry Holt and Co., 1915,

35 Jour. of Geneties, Vol. 5, pp. 37-50.

No. 605] ANIMAL COLORATION 273

Little need be said regarding the inference that the

constancy of the ratio in which the females of P. polytes

seem to have occurred for many years shows that natural

selection does not exist for this species in Ceylon, or

else that its force is so slight that in half a century, and

perhaps in a century and a half, it has produced no effect

appreciable to the method of examination employed.

This is valid only if it is true as postulated that the

various types of P. polytes constitute ‘‘a population liv-

ing and breeding together under the same conditions.”’

But it is gravely to be doubted that this indispensable

condition is fulfilled. We have some evidence: (that of

Bates and Wallace already cited) that butterflies which

differ in color differ in habit, and if it should appear that

the colors of butterflies in general are correlated with and

repeat those of their surroundings, Punnett’s fifth point

is forever invalid. For it will be impossible to establish

by observation the universal negative that is required,

which is, of course, that the three types of female do not

differ in any constant respect in their normal behavior.

Regarding the sixth point, which has reference chiefly

to the fact of seasonal dimorphism among butterflies, it

must first be affirmed that although the induced changes

differentiating the broods of the spring and summer, or

wet and dry seasons, are not directly inherited, the capa-

bility of responding definitely to the physical stimulus

of changed temperaturé or humidity is a heritable racial

trait. The seasonal variations in the coloration of but-

terflies may be analogous upon the whole with the instan-

taneous color changes of tropical fishes, which also occur

in response to external stimuli. The latter, however, fol-

low more quickly than the former upon appropriate stim-

ulation; they are reversible; and are known to be nor-

mally adaptive, since they reduce the conspicuousness of

the individuals in which they appear. It may eventually

prove to be a fact that instantaneous adaptive color ad-

justments, the phenomena of seasonal and sexual dimor-

28 Professor Gerould first called attention to this fact in THE AMER. NAT.,

Vol, 50 (1916), pp. 310-316.

274 THE AMERICAN NATURALIST (Von. LI

phism, and polymorphism all have the same biological

significance, i. e., that they represent different ways in

which the coloration of a species exercises its obliterative

function in a greater variety of circumstances than would

be possible if it were uniform. Upon this view of the

matter there would seem to be no reason why color vari-

ations of the seasonal sort should not provide material

for evolution by natural selection.

Before suggesting another possible explanation of the

fact of mimetie resemblance it seems desirable to state

more specifically why certain of those already mentioned

seem improbable.

Some color patterns are apparently limited to fishes

whose habits are similar. Others occur which have sur-

vived the introduction of marked structural changes and

are now the common property of whole families or groups

of families, whose manner of living varies decidedly from

species to species.. There is one such system of coloring

among grunts, groupers and snappers (Hemulide,

Epinepheline, and Lutianide), and Labrids and Scarids

share another. In each pattern modifications may be

_ noted which seem particularly appropriate under the local

conditions in which they appear. Individual elements

may lose all semblance of the original, and yet the nature

of the whole be not obscured. But these facts make one

skeptical regarding Thayer’s hypothesis, for if, in but-

terflies too, detail is less important than the appropriate

effect of the whole, the probability is remote that for dif-

ferent environments complex, ideal, protective or conceal-

ing patterns exist, whose slightest spot is so significant

that there is marked tendency for forms of different racial

endowment to attain them, if their habits are similar.

The same facts militate against such a conception as

Packard’s, that mimicry is a result of similar reaction to

the direct influence of one set of external conditions. For

coloration is characterized by such conservatism or in-

ertia, and the same elements of pattern appear in such a

variety of habitats, that the power of environmental in-

No. 605] ANIMAL COLORATION 275

fluence to induce uniformity of coloration seems dis-

credited.

If the possibility of the direct influence of local climatic

factors be excluded, Piepers’ hypothesis, that mimicry is

` largely due to species having independently attained the

same stage of development orthogenetically, leaves the

facts of geographical distribution of mimics and their

models enshrouded in mystery. That this is a very real

difficulty follows from Punnett’s statement,*7

Examples of close resemblance between butterflies which live in dif-

ferent parts of the world are relatively rare and serve to emphasize the

fact that the great bulk of these resemblance cases are associated in

pairs or little groups.

Finally, instances of mimicry are, after all, only selected

examples of resemblance, and it is desirable, if possible, to

formulate an explanation that will apply to all equally

well. But whether the likeness between them rises by

sporting or otherwise, it is not to be supposed that Phas-

mids and green leaves or dry twigs possess Mendelian

factors in common. Therefore it seems profitable to pro-

ceed for a little upon the assumption that mimicry is in

some cases at least a visible token of the fact that the

species manifesting it are linked by some bond other than

common descent, common habit, or exposure to the influ-

ence of a common environment. What this may be, does

not appear, unless through mutual resemblance advan-

tage accrues to some or all of the forms concerned.

Evidence compiled by Marshall®* shows that birds un-

doubtedly attack butterflies, but others deny that they

feed upon the insects freely enough to affect the evolu-

tion of their coloration, and more particularly the mimetic

resemblances between different species. Hence there

is plainly a question at issue concerning the sufficiency of

an assigned cause to produce a stated effect. Under the

circumstances any evidence tending to show that the fre-

~ quency of birds’ attacks has been underestimated, or that

87 L. €., p. 54. ;

3S Trans. Ent. Soc. Lond., 1909, pp. 329-383.

276 THE AMERICAN NATURALIST [ Von. LI

their influence may be supplemented by that of other

enemies is of the greatest interest.

In this connection Swynnerton’s*® observation that of

twenty small. bird excreta collected in the African forest no

less than eighteen contained scales and small wing frag- `

ments of Lepidoptera has suggestive value. But, for the

moment at least, it is more important that it appears that

mimicry might be initiated and advanced by indiscrim-

inate feeders, including lizards and insectivorous insects,

provided only that they possess color vision. For to

whatever extent such influence prevails it obviates the

necessity of appeal to the effects of discriminate feeding

by birds or other animals, and makes it possible to fore-

stall the criticism to which reference has been made above.

Therefore it is suggested as a tentative explanation of

mimicry, that it has commonly arisen as a result of bio-

nomic pressure applied first by discriminate or indis-

criminate feeders, which by elimination of unadapted

variants have forced their accustomed prey to assume

color combinations which most effectually conceal it in

its normal environment. In addition, for no demoystrated

reason, in a few of the many thousands of cases in which

colors adapted to the environment and habits of their

possessor have been evolved, patterns have appeared

which have been sufficiently like one another to deceive

enemies which exercise discrimination in their choice of

food. Beyond this point the evolution of resemblance

may have proceeded according to accepted formule, but

without conspicuousness being involved at any point in

the process. :

It is submitted that in our present state of ignorance

this construction may be placed upon observed facts

rationally and without exposure to the criticism that has

been directed against other attempted interpretations.

` However, the chief classes of facts to be explained and

the most serious objections registered against the Neo-

Darwinian hypotheses of mimicry will be presented, that

39 Ibis, 1912.

No. 605] ANIMAL COLORATION Zit

the reader may judge whether a passage between Scylla

and Charybdis may be made in safety.

Professor Poulton’s extensive studies have convinced

him that the evolution of mimetic resemblance has been

directed by natural selection, yet the evidence upon

which his conclusion rests may be taken over bodily and

supports the’ revised hypothesis as consistently as that

to whose service it was originally dedicated. There is

nothing anomalous in finding mimic and model living

under the same conditions, certain groups of insects show-

ing the same series of local color varieties, or such diver-

sity of coloration appearing in one group of butterflies

or moths as allies them outwardly with different ‘‘pro-

tected’’ genera. The same is true of the fact that insects

with every variety of larval experience as adults possess

the same type of coloration, that mimetic females are

more common than males, or that the common coloration

possessed by mimic and model is attained in the most

diverse fashion, that is, that cases of mimicry are typical

instances of analogy. Throughout the whole series of

observations the points of agreement and difference are

consistent, as far as is known, with the fundamental as-

sumption that color and habit are associated variables.

Passing to the negative side of the argument, we may

first consider the statement that it is impossible that re-

eiprocal mimicry should have been brought about by

natural selection of small variations. Punnett has this

idea from Marshall“ and uses it to emphasize the diffi-

culty of the initial variation even in cases where it might

seem that the theoretical advantage to be gained from

mutual resemblance by two species would simplify the

attainment of likeness. But Dixey,*? against whose posi-

tion the argument was originally directed, has exposed its

unsoundness by calling attention to a number of critical

40 See ‘‘ Natural Selection the Cause of Mimetic Resemblance and Common

Warning Colors’’ in ‘‘ Essays on Evolution,’’ 1908.

41 Trans. Ent. Soc. Lond., Vol. 45, pp. 93-142.

42 Trans. Ent. Soc. Lond., Vol. 45, pp. 559-583.

278 THE AMERICAN NATURALIST [ Von. LI

points which his opponent had failed to take into con-

sideration.

It may be added that Marshall’s reasoning rests upon

what is without much doubt a baseless assumption, for he

follows Müller in postulating that two species of distaste-

ful insects will lose the same absolute number of indi-

viduals through attacks of ignorant enemies which in the

beginning recognize neither of them. Asa matter of fact,

if two species differing in no respect except appear-

ance are represented in the same area by 100,000 and

5,000 individuals, respectively, as Marshall assumes, the

chances are 20:1 that any animal making an independent

test of the food resources of its environment would first

meet the more abundant form. Unless it learns its lesson

perfectly from a single experience, the chances are essen-

tially the same that it will kill another butterfly of the same

kind before it encounters one of the second distasteful sort.

But if most inexperienced enemies learn at the expense

of one species that some butterflies are not edible, it

is searcely to be supposed that they will undergo as

many unpleasant experiences before they retain an im-

pression of the disagreeable character of the other.

Hence Marshall’s criticism can not be considered at pres-

ent a valid objection.

Packard** believed that the concept of Miillerian mimi-

cry had been overextended. He thought that in ac-

cumulating so many examples of warning coloration in

their ‘‘Bionomics of South African Insects’? Marshall

and Poulton* in particular attempted to prove too much.

Why an association of some scores of species represent-

ing many orders of Mashonaland insects should be pivoted

upon the bitter-flavored beetle, Lycus, though some mem-

bers of the group seemed more amply protected from at-

tack by birds and lizards, was not clear. Yet one dares

not be dogmatic in such matters, for the wasp, Pompilus,

though more adequately equipped for defense than any

other member of the association, may have drifted toward

43 Proc. Amer. Philos, Soc., hig es p. 424,

44 Trans, Ent. Soe. Lond., Vol.

` No. 605] ANIMAL COLORATION 279

it at a comparatively late date, when the relatively slight

distastefulness of a large number of insects of one type

of coloration subtended a larger angle in the conscious-

ness of insectivorous animals than the greater unpal-

atability of any single form. However, the idea that what

has been considered mimicry is too common, and that in

general the most effectively protected types should be the

nuclei of the Miillerian combinations, is certainly not

wholly unreasonable. .

One of the chief reasons for believing in the existence

of warning colors, and particularly of common warning

colors, is the fact that some families of insects have slight

range of color and pattern compared with others.

Mayer*® found that ‘‘the 200 species of Papilio in South

America display 36 distinct colors, while the 450 species

of Danaoid Heliconide exhibit only 15,’’ and that ‘‘there is

-= no lack of individual variability among the species of the

latter, yet as a whole they vary but little from the two

great types of color-pattern represented by Melinea and

Ithomia.’’ To explain these facts he felt obliged to resort

to Miiller’s hypothesis, but if instead of thinking of Itho-

miine and Papilionide one considers Holocentride and

Labride, an alternative solution appears. The squirrel

fishes seem to be of red or reddish coloration the world

over, but their habits are equally invariable, while the

Labrids’ diversity of coloring is no greater than that pre-

vailing in the varied environments in which they live.

Such facts indicate the necessity of making detailed

studies of the coloration of tropical Lepidoptera and cor-

relating the facts discovered with the insects’ distribution

and behavior. When this is done there is reason to sup-

pose that combinations of the same colors will be found

upon animals of the same habit, which would have been

as they are in many species, if any or all the others which

display the same combinations had never existed. That is

to say, it is probable that much that has masqueraded

as Miillerian mimicry is nothing but the result of con-

45 Bull, Mus. Comp. Zool. Harv. Coll, Feb., 1897, p. 225.

280 THE AMERICAN NATURALIST [ Vou. LI

vergent evolution, which has been difficult to explain be-

cause of the deep-seated misconception that has prevailed

regarding the function of animal coloration.

Dewar and Finn** cite a number of instances of resem-

blance between mammals, and others between birds, whose

ranges coincide at no point. For the most part these

likenesses do not seem comparable with the clearest cases

of mimicry among insects in the degree of detailed re-

semblance they involve, and scarcely seem to rise above

the level of interesting coincidences. It is unquestionably

true, nevertheless, that such degree of likeness as may

spring up between two species whose bionomic association

is impossible on account of differences in geographical

distribution, may also arise between species of one region

without reference to the action of natural selection di-

rected toward the production of resemblance.

Lock* states that Syrphid flies, which closely mimic

small bees and wasps whose habits are similar to their

own, are surprisingly numerous in southern Japan, and

that their resemblance to bees is particularly noticeable,

though these are conspicuous by their absence. Hence

the question arises, how the flies can benefit by their re-

semblance to them: to which one must apparently answer,

that under the conditions stated, the bee-like disguise can,

as such, be of little value. But this query is overshadowed

in interest by another: If the Syrphids are unprotected

and driven by their enemies to assume the appearance of

defended forms, how do they survive in regions where

their disguise possesses no suggestion of unpalatability.

The idea is not to be entertained for a moment that

Lock would be at a loss for an answer. But if the concept

of warning coloration be abandoned, there is no reason

to suppose bees less perfectly adapted in color and form

than other animals to their respective modes of life. Bee-

like flies whose habits resemble those of bees should there-

46‘*The Making of Species,” pp. 242-245. London and New York,

J. Lane, 1909.

47 ‘í Recent Progress in the Study of Variation, Heredity. and Evolution,’’

p. 58. London, John Murray, 1907.

No. 605] ANIMAL COLORATION 281

fore be well able to exist beyond the range of models,

which they may have mimicked in other times and places,

if their particular type of coloration is as well suited to

the new environment as to the old.

An apparent inconsistency in the Batesian and Miiller-

ian hypotheses as at present interpreted has been fre-

quently noted by hostile critics, To Reighard‘’ it ap-

pears, for example, that if insectivorous vertebrates have

pushed the resemblance between mimics and their models

to the point of apparent identity, ordinary specifie dif-

ferences should suffice to warn them of the unpalatability

of prospective and familiar prey.

This objection. is so fairly met by the revised hypoth-

esis, and the ground for criticism so completely removed,

that further comment is unnecessary. But even when no

inconsistency is involved in the explanation of the facts,

some will doubtless consider the resemblance of the mimic

to its model, or of insects to other objects, hypertelic. It

is doubtful, however, whether hypertely embodies a real

difficulty. For just as two streams flowing down a tol-

erably smooth inclined plane of infinite length will even-

tually unite, if all deviations of one or both which exceed

a given magnitude are blocked when they tend to increase

the distance between them, so, if heritable variations in

the color and pattern of a given mimic are distributed ac-

cording to Quetelet’s law, for example, and only the ex-

treme forms most unlike the model be eliminated in suc-

cessive generations, closer and closer resemblance

between the two may appear and approach identity with-

out appeal to that over-refinement of vision whose ex-

istence among insects’ enemies is at least problematical.

It is a standing objection to the mimicry hypotheses,

and indeed to the explanation of any highly complex

adaptation by natural selection, that at every stage the

degree of resemblance attained must have been service-

able in order to assure its survival. It is understood,

however, that this objection is applicable only to stages

48 Carn. Inst. Wash., Papers from Tortugas Lab., Vol. 2, p. 315.

282 THE AMERICAN NATURALIST [ Vou. LI

following the first to which the selectionist ascribes de-

ceptive value. Resemblance resulting from undirected

variation, or existing for other reasons, is not subject to

this criticism.

Darwin recognized this fact and attempted to throw

upon another cause than natural selection a large part of

the burden of producing functional resemblance. His

idea may best be expressed in his own words:

The process of imitation probably never commenced between forms

widely dissimilar in color. But, starting with species already some-

what like each other, the closest resemblance, if beneficial, could readil

or coloring wholly unlike that of the other members of the family to

which it belonged. There is, however, some difficulty on this head, for

it is necessary to suppose in some cases that ancient members belonging

to several distinct groups, before they had diverged to the present ex-

tent, accidentally resembled a member of another and protected group

in sufficient degree to afford some slight protection, this having given

the basis for the subsequent acquisition of the most perfect resem-

blanee.*°

Weismann”? attempted to avoid the same difficulty in

another way. He makes no assumption that the original

difference betwen mimic and model was distinctly less

than that appearing at present between typical members

of their respective families, but magnifies the importance

of the first slight resemblance and subsequent positive

variations. He had been deceived repeatedly, at least for

the moment, by similarity in the flight of different species

_ whose colors were not the same, and held as a consequence

that mere variation in the manner of flight combined with

the habit of associating with the form mimicked might

have prepared the way for selection.

Wallace®! would have it that certain butterflies, having

49‘ Origin of Species,’’ Chap. XIV.

50‘¢The Evolution Theory,’’ Vol. 1, p. 93. London, Edward Arnold,

904,

51 ‘* Darwinism,’’ p. 243.

No. 605] ANIMAL COLORATION 283

become unpalatable through the possession of disagree-

able juices, developed distinguishing marks, whether in

color, form or mode of flight. He then plunges in medias

res with the assertion that ‘‘during the early stages of

this process, some of the Pieridæ, inhabiting the same dis-

trict, happened to be sufficiently like some of the Heli-

conide to be occasionally mistaken for them.’’ There-

after, as may be anticipated, evolution proceeded merrily,

and examples of Batesian mimicry were perfected in due

time.

Wallace’s pronouncement begs the whole question.

Weismann’s hypothesis is conceivably true, but lacks the

support necessary to carry conviction. Darwin’s idea,

finally, seems to be at variance with fact, since Poulton®?

infers from his own studies that the conclusion that

emerges most clearly is the entire independence of

zoological affinity exhibited by mimetic resemblance.

unnett also shows most clearly how impossible the

Darwinian suggestion is, but errs when he supposes that

it can not be true in many cases that model and mimic

were closely alike to start with. His demonstration may

be accepted that the development of mimetic resemblance

has not been commonly facilitated by preexisting like-

ness due to racial affinity, but he has wholly disregarded

the fact that the degree of likeness which it is necessary

to presuppose, if mimicry has been brought about by a

series of comparatively small variations, might occur for

other reasons.

May we not assume, for example, that the Pieride

and Heliconide are usually distinctly different in their

habits, and that the coloration of typical members of each

52 Proc. Linn. Soc. Lond., Vol. 26, p. 570.

53 This ean scarcely be considered a rash assumption, since Wallace

states (Trans. Ent. Soc. Lond., Vol. 2, Ser. 2) that the Pieride of the

Amazon valley generally are open-ground butterflies, two genera only, Lep-

talis and Terias, being true denizens of the forest. He also remarks that

most of the species of Heliconia prefer the forest shades, It is also of in-

terest to note that he comments upon the in ievousness of some species

at least of Ithomia, in which connection one should recall the observation of

W. J. Kaye already quoted.

284 THE AMERICAN NATURALIST [Von LI

group is a combination of hues well suited upon the aver-

age to render them inconspicuous in such places as they

commonly frequent. If this be so, the initial step toward

the production of new cases of mimicry might be any one

of many variations in mode of nutrition or reproduction,

which would lead repr tatives of the first family to

spend their lives after the manner of the second. Reason

has already been given for believing that convergence in

color would probably accompany or follow convergence in

habit. _

The new colors would undoubtedly appear in patterns

largely determined by and reflecting the Pierian ancestry.

Among fishes, as has been stated, a primitive color pat-

- tern peculiar to one or common to several closely related

families is sometimes readily recognizable, in which dis-

tinct elements are apparent, now definite, now diffuse,

mere stains of dyes that are not permanent. It is to be

expected no less in insects that the family patterns, like

finely wrought ornaments cast into the melting-pot, will

be reshapen and serve new purposes. But from the welter

of change and recombination which this involves may

come once in many times a new grouping of characters,

which suggests the pattern of another race. At this point

natural selection directed toward the production of a pro-

tective design painted in colors appropriate to the en-

vironment may yield to selection working in the direction

of resemblance. If so, a new pattern may be developed

in the same protective colors and coupled with such

change in the shape of the wings, or in other characters,

as confers the additional advantage of being mistaken for

a species which enjoys some measure of immunity.

Either in organization or development most animals -

give evidence of changes in habit much greater than the

initial one herein postulated. Yet admit that these may

occur, and what is already partly proved, that color is

correlated with habit throughout the animal kingdom, and

a theoretical difficulty that has engaged the attention of

adherents and opponents of the mimicry hypotheses van-

No. 605] ANIMAL COLORATION 285

ishes. No matter how wide the original gap between

mimic and model, it may be bridged; no matter what de-

gree of similarity between two forms may be necessary

before natural selection may become effective in heighten-

ing their resemblance, it may be attained without appeal

to chance that is wholly blind, for there appears to be an

automatic feature in the mechanism which has hitherto

escaped observation.

The ideas outlined in the preceding pages are neither a

pure product of reflection nor a compromise suggested by

an examination of the literature upon mimicry. They are

a normal outgrowth of studies which had no preconceived

relation to the problem of mimetic resemblance. They

constitute a working hypothesis, and as such are sub-

mitted to those biologists, particularly entomologists, who

may have opportunity to test them rigorously.

NUCLEUS AND CYTOPLASM AS VEHICLES OF

HEREDITY!

L. C DUNN

BUSSEY [INSTITUTION

Turre have been of late several attempts to effect a

compromise between theories of heredity through the

cytoplasm and theories which regard the chromosomes

as the vehicles of inherited characters. Conklin (’08)

was the first to suggest that egg, embryonic and general

phyletic characters of any stage of the organism were

determined in the egg cytoplasm while the determiners

in the chromosomes made their presence known only

through the specific or individual adult characters. Shull

(1916) has elaborated this suggestion, and has brought to

its support not only the older data on maternal inheritance,

matrocline hybrids and the facts of development which

relate to polarity, symmetry and organ-forming sub-

stances, but has added new evidence of his own from ex-

periments with rotifers. Most recently, Loeb, in his book

‘The Organism as a Whole,’’ has advanced a similar com-

promise theory, based on similar evidence.

Before examining in detail the experimental basis for

such a compromise, it is important that the terms to be

used be clearly and unmistakably defined. The first of

these is the word ‘‘determined.’’ That a character is de- _

termined in the germ cell means that the differential,

causal antecedents of that character are present in the

germ cell. It does not mean that the character itself is

present in the germ in any form, but rather that it is _

represented by substances or forces which not only stand

_for the character but in some way bring about its expres-

sion. : |

1A review made at the suggestion of Dr. H. W. Rand to whom grateful

acknowledgement is due.

: 286

No. 605] NUCLEUS AND CYTOPLASM 287

If this definition of ‘‘determined’’ is accepted, two

kinds of continuity in organisms are immediately differ-

entiated. The first sort may be called substantial con-

tinuity. It is the carrying over from one generation to

the next of autonomous organizations of protoplasm in a

manner analogous to the carrying of the bacilli of certain

diseases (e. g., syphilis) in the germ cell. Here the germ

cell is a passive vehicle. The character is present, not

determined; and its changes from fertilized egg to adult

are mere proliferations. If hereditary characters were

to be so viewed, and the view carried to its logical con-

clusion, the result would be something very like an ‘‘em-

boitement’’ theory, which facts of development have

proved to be untenable. Substantial continuity is hence

only a concomitant rather than a part or a method of

heredity.

The second type of continuity may be called ‘‘genetic”’

continuity, and characters which are genetically con-

tinuous are those which show a new coming into being

with every generation. They are developed anew, and

their resemblance to homologous characters in the pre-

ceding generation is due to their development not from

those characters but from homologous determinants.

Characters of this type are truly determined and all

hereditary characters are reducible to this type whether

they are exhibited in egg, sperm, embryo or adult.

It is now possible and desirable to define the expres-

sions ‘‘inheritance through the ecytoplasm’’ and ‘‘inher-

itance through the chromosomes.’’? The first properly

means that the locus of the determiners or representa-

tives of a character is the cytoplasm, and since it is the

egg alone which contains any significant amount of cyto-

plasm, the expression usually means the presence of these —

determiners in the egg cytoplasm. ‘‘Inheritance through

the chromosomes’’ means that the chromatic substance

of the nucleus is the locus of determiners, and since the

nuclear content of egg and sperm is equivalent this must

also mean an equal determinative share by egg and sperm

in heredity.

288 THE AMERICAN NATURALIST [Vou. LI

Are now both of these theories compatible with one

definition of ‘‘determined’’? Are they both possible and

both necessary?

Loeb has stated the problem and the ‘‘compromise’’ in

these words (1916, p. 245):

Question: “ Is the organism nothing but a mosaic of hereditary char-

acters determined essentially by definite elements in the chromosomes;

and if this be true what makes a harmonious whole TEREN out of

this mie a assortment? ”

Answ . . . the cytoplasm of the egg is the future embryo in the

rough, aad the factor of heredity in the sperm only act by impressing

the details on the rough block.”

Shull’s statement is as follows (p. 6):

The cytoplasm often (perhaps usually) determines the type of cleav-

age, the early course of development, and in large measure the larval

characters, while the adult characteristics are determined by the chromo-

somes

Conklin’s conclusions are (1915, p. 176):

There is no doubt that most of the differentiations of the egg cyto-

plasm have arisen during the ovarian history of the egg and as a result

of the interaction of nucleus and cytoplasm; but the fact remains that

at the time of fertilization, the hereditary potencies of the two germ

cells are not equal. All the early stages of development, including the

polarity, symmetry, type of cleavage, and the pattern or relative posi-

tion of future organs, being foreshadowed in the cytoplasm of the egg

cell while only the differentiations of later development are influenced

by the sperm. In short the egg cytoplasm fixes the general type of

development and the sperm and egg nuclei supply only the details. We

are vertebrates because our mothers were vertebrates and produced

eggs of the vertebrate pattern—but the color of our skin, eyes and hair

. were determined by the sperm as well as by the egg from which

we came,

The same author has reiterated and somewhat elaborated

the same views in an unpublished paper presented before

the National Academy of Science in November, 1916.!

1 Since the above was written Conklin’s paper (1917) has been published.

In its closing paragraphs he modifies materially the view which he had

earlier expressed, admitting that cytoplasmic differentiation of the egg-cell

probably arises under nuclear influence exerted equally by the egg and the

sperm nuclei of the previous generation, the view mainfained by the present

writer.

No. 605] NUCLEUS AND CYTOPLASM 289

The evidence and a criticism of parts of it follows:

1. SHULL’s EVIDENCE

(a) Cases of maternal inheritance. Under this head-

ing Shull places such experiments as those of Correns

(1909) on Mirabilis jalapa var. albomaculata. This plant

— the common four-o’clock—has variegated leaves, green

and white, the white being due to inhibited development

of green in the chromatophores. The amount of green

and white varies in different plants and furthermore

whole branches may be green while other whole branches

may be white. Flowers borne upon green branches, if

self-fertilized, give seed that produces only green off-

spring. Flowers from white branches, if selfed, give seed

that produces only whites, which die because they are

unable to carry on photosynthesis. Flowers on vari-

egated branches yield offspring some of which are green,

some variegated. Crosses among these green, white and

variegated plants reveal the fact that the offspring re-

semble invariably the female parent. White females pol-

linated by any green or variegated pollen yield only

whites which die. Green females pollinated by white or

variegated pollen yield only green descendants. The

paternal character never reappears in subsequent gen-

erations. :

Correns has assumed in explaining these remarkable

occurrences that a disease transmitted by the cytoplasm

of the ovule is the cause of the color differences, inasmuch

as the white color in either self condition or as mottling

on the green is a pathological condition. The chromo-

somes are assumed to be immune to this disease. If the

disease is caused by a germ (which is very likely) this

germ acts only on the chromatophores and may well be

passed through the egg like the germs of syphilis and

other diseases. If this is the case, true heredity is not

involved. The egg has simply acted as the passive bearer

of a foreign body. And if the disease is due to a defect

in the chromatophores, the case is not very different. The

290 THE AMERICAN NATURALIST [ Vou. LI

chromatophores, as Shull says, are probably ‘‘autonomous

bodies arising only from other autonomous bodies like

themselves.’’ On such a view they are simply structures

enclosed within the cytoplasm, having a continuity parallel

with but independent of the continuity of inherited char-

acters.

(b) Shull’s next evidence is drawn from experiments

resulting in so-called ‘‘matrocline hybrids,’’ which he de-

fines as ‘‘unequal reciprocal hybrids which resemble the

mother more than the father.’’ Under this head he cites

the well-known cases of species and genera crosses among

echinoderms. He says of the first generation from sea-

urchin 2 X starfish £ (Loeb, 1903), and from sea-urchin

2x crinoid ¢ (Godlewski, 1906) that the embryos were

purely maternal in character. In contrast to this, other

observers of species and genera crosses among echino-

derms (Morgan, Boveri, Baltzer and Herbst) have de-

scribed the F, embryos as intermediate between the

parents wherever there was normal union of maternal

and paternal chromatin. Shull emphasizes especially the

maternal character of embryos possessing no maternal

chromatin. These were produced by Godlewski, by fer-

tilizing enucleated fragments of sea-urchin eggs with

crinoid sperm. The larval stages were reported to have

been purely of the sea-urchin type. However, Boveri,

Bierens de Haans and Herbst have obtained results which

showed either the reverse condition, viz., paternal em-

bryonic characters, or else intermediate larve. Moreover

in the cross fertilization of giant sea-urchin eggs pos-

sessing twice the normal amounts of cytoplasm and chro-

matin, the larve inclined to the maternal side. That this

was not due to the doubled amount of cytoplasm was

demonstrated by Boveri, who fertilized nucleated half-

fragments of normal eggs with sperm of another species

and found no paternal inclination from the halved amount

of cytoplasm. That the phenomena are due rather to the

chromosomes is indicated by the same experimenter’s

work with dispermie fertilization. When more than one

No. 605] NUCLEUS AND CYTOPLASM 291

sperm enters the egg abnormal mitotic figures and ab-

normal chromatin dieteibntii are directly correlated

with abnormalities in the larvæ, although the egg cyto-

plasm remains constant. Baltzer’s fine work on species

crosses may also be cited as showing that Loeb’s and

Godlewski’s observations penetrated only part way toward

the truth.

As an example, only one of Baltzer’s crosses need be

cited. When eggs of Spherechinus were fertilized by

sperm of Strongylocentrotus, the mitotic figures and dis-

tribution of chromatin were normal and the larvæ were

intermediate, not maternal. From the reciprocal cross

‘‘matrocline hybrids’’ (most of them abnormal) did re-

sult, but their maternal resemblance was not due to cyto-

plasm. That it was due to irregularities in the chromatin

distribution was proved by Baltzer, who followed the his-

tory of the maternal and paternal chromosomes in the

hybrid embryos. He found that the majority of the

paternal chromosomes (15 out of 18) were inactive at

the first cleavage. They were extruded from the develop-

ing odsperm nucleus, and degenerated. The cells of the

hybrid had then 21 chromosomes, 18 maternal and 3 pater-

nal, and their maternal resemblance is easily explicable

on these grounds. It is not explicable on any other for

no abnormal conditions obtained in either cytoplasm or

the surrounding medium.

Herbst repeated the first of Baltzer’s crosses (Spher-

echinus 2 X Strongylocentrotus 3) but chemically induced

parthenogenetic development in the egg before the en-

trance of the sperm. Thus the ¢ pronucleus was behind

at the first division and failed to be incorporated into the

nucleus of one of the first daughter cells. One side of the

developing hybrid had, then, merely paternal chromo-

somes, while the other had both maternal and paternal,

and in striking sequence to this distribution were embryos

which had only paternal characters on one side, while

those of the other side were intermediate.

On the evidence thus far, Shull himself has not placed

292 THE AMERICAN NATURALIST [ Vou. LI

the maximum of emphasis, and the foregoing criticism

has been intended to indicate that its support of the cyto-

plasmic view has been and may continue to be so mini-

mized as to be non-existent. However, Shull does place

much emphasis on some carefully collected evidence of

his own. This does not, I believe, support his theory to

any greater extent than his quoted cases.

The evidence is briefly as follows: Shull crossed two

lines of rotifers which differed in two egg characters—

time of hatching of sexual eggs, and the proportions of

sexual egs which actually hatched. The eggs of line “A”

hatched on the average in 1-2 weeks, about 50 per cent.

emerging. Line ‘‘B’’ eggs took 5-6 weeks to hatch and

only 5 per cent. emerged. Line ‘‘A’’ females fertilized

by line ‘‘B’’ sperm laid eggs which hatched in 1-3 weeks,

50 per cent. emerging. The eggs thus resembled the

mother’s line in both respects. Line ‘‘B’’ females fer-

tilized by line ‘‘ A’’ sperm laid eggs, 30 per cent. of which

emerged in 4-5 weeks, resembling more the mother’s line

than the father’s. The reciprocal hybrids are thus very

unequal, says Shull, and since in crossing parents which

differ by Mendelian, chromosome-determined characters,

the resulting reciprocal hybrids are equal, the characters

under observation are non-Mendelian and determined in

the cytoplasm of the egg.

But it is to be objected that in reality these hybrid eggs

of the first generation are not hybrid in these characters

at all. The characters are egg characters and as such can

be exhibited only when the hybrid zygote produces its

eggs, not when the hybrid zygote is formed. The expres-

sion of the character is thus delayed until the hatching of

eggs laid by these F, zygotes. And Shull’s data shows

this to be the case.

But when new lines were obtained from these hybrid (F,) eggs, and

these lines produced sexual eggs of their own, the two reciprocal hybrid

lines were fully equal.

Now the usual occurrence is observed, viz., the reciprocal

hybrids are equal and the contributions to the character

No. 605] NUCLEUS AND CYTOPLASM 293

by g and 2? are proved to be also equal. Shull’s conten-

tion for the participation of the egg cytoplasm rests en-

tirely on the maternal character of the first egg-genera-

tion. These eggs were matured, since the mother was

homozygous in the characters, under the influence of the

like chromatic contributions of her parents; the hybrid

mother matured hers under the influence of the unlike

chromatic contributions of her parents and showed the

participation of her paternal chromosomes only in the

behavior of her eggs. The peculiarities of the case lie

not in that we are dealing with a cytoplasmically deter-

mined character, as Shull contends, but in (1) the fact

that the characters are exhibited only by females; (2) in

the fact that the characters are egg-characters, which

places segregation one generation farther away from the

original cross.

The case is quite analogous to the case of the inherit-

pace of red pericarp color in corn, which, although a

‘maternal character,” was shown to Mendelize by Lock

(706). It is also comparable to the egg-character ‘‘uni-

bivoltinism’’ in silk moths, which Castle (’10) proved

from Miss McCracken’s data to be a Mendelian character.

These cases will be discussed more fully in later para-

graphs.

Shull’s conclusion that cytoplasm determines egg and

larval characters is, I believe, unnecessary. It has been

shown that characters exhibited only by females and only

in the egg may be equally determined both in the egg and

in the sperm. The sperm contribution being predomi-

nantly chromatic, and the chromosomes being the ac-

cepted carriers of the determiners of other characters, it

is to be concluded that the determiners for the characters

investigated by Shull are also to be sought in the chromo-

somes.

Loeb, in his book (1916), has given considerable space

to this question, closely following the earlier treatment by

Conklin. His conclusion which has been stated and the

evidence on which it rests may be briefly criticized by the

294 THE AMERICAN NATURALIST (Von. Ll

addition of further evidence which warrants a changed

interpretation of certain facts.

Loeb first calls attention to the exclusively maternal

character of the early development of enucleated frag-

ments of eggs when fertilized by sperm of a different

species. Such evidence has already been treated above

(p. 5).

His second claim—that the rate of cell division and de-

velopment is determined only by the egg cytoplasm—

warrants further consideration. An egg from a line in

which segmentation of the egg takes place eight hours

after fertilization was fertilized by sperm from a line in

which segmentation begins in 30 minutes. The rate of

these cross-fertilized eggs was 8 hours, like the mother’s

line.

The careful and long continued work of Newman (714)

has, on the other hand, shown that the entrance of sperm

of a different species does materially alter the rate of de-

~ velopment.

In both reciprocal crosses between Fundulus heteroclitus and F.

majalis the rate of development of the hybrids was intermediate between

that of the two parent species. This was true of cleavage rate, rate of

germ-ring formation, ete.

In the cross F. heteroclitus X F. diaphanus ‘‘both recip-

rocal crosses have a higher rate than the pure bred strain,

Similarly, when we make reciprocal crosses between Cy-

pronodon and any species of Fundulus we find a marked

retardation in developmental rate in both crosses. .. .’’

It is of the greatest significance that in all three cases the

results of reciprocal crosses were equal. Either both

were intermediate, both were accelerated or both were

retarded regardless of which species was used as the egg-

parent. In the face of such evidence, a theory of exclusive

control of the egg over early development is untenable.

Newman’s fundulus hybrids, while demonstrating the

conclusion just stated, do not form critical evidence for

determining the action in heredity of such rate-characters

because only the F, generation is known. Another series

No. 605] NUCLEUS AND CYTOPLASM 295

of experiments on a hatching time character has, how-

ever, been carried through the F, generation and as an

illustration such a case may be cited in detail. It consists

of Miss MeCracken’s (1909) experiments with silk moths.

Castle later (1910) called attention to some facts in her

data which indicated that although a female-exhibited

character and confined to the egg in its expression, it

nevertheless gave evidence of Mendelizing in crosses.

Toyama (712) concluded that dominance was present, and

both of the latter investigators agreed that the males, al-

though unable to exhibit the character, gave evidence by

their genetic behavior of having an equal determinative

influence with the females. The data follows:

Silk moths lay one batch of eggs, always in the spring.

The eggs of some batches hatch out immediately, pro-

ducing another brood of larve and moths in that season.

The parents of such batches of eggs are hence known as

bivoltins. The eggs of other batches do not hatch for

twelve months, and since in this way there is but dne

brood or flight each season, the parents of such eggs are

known as univoltins. If a univoltin female is crossed

with a bivoltin male, the spring batch is laid as usual and

hatches in 12 months. This is just what would have oc-

curred if the mother had been fertilized by a male of her

own sort. When these eggs hatch, a hybrid brood emerges

which lay their egg batches immediately but the univoltin

character is again exhibited in that all of these eggs are

of the 12 months type. But, these eggs now differ among

themselves as is shown by the behavior of the zygotes

which emerge from them. Some of these females are

bivoltin, laying eggs which develop immediately, while

others are univoltin, laying eggs which hatch the follow-

ing spring. The expression of the paternal contribution

is delayed, but its activity in determining the time of

hatching is quite apparent.

The inheritance of red pericarp color in corn follows

exactly the same course as that outlined above, with red

dominant over white. The F, embryos must be raised

296 THE AMERICAN NATURALIST [Vou. LI

before the segregation of pericarp color among them can

be seen, for it is exhibited only in the seed coats. The

conclusions follow: (1) The egg and all its determinative

content is produced under the double influence of the

sperm and egg chromatin contributions which united to

form the producing zygote. (2) Hybridization experi-

ments with egg characters, to be critical, must be carried

as far the F, generation. (3) In all experiments which

I have seen reported, in which this condition obtained, the

influence of the sperm on the characters in question has

been observed.

Loeb’s evidence, however, introduces also crosses be-

tween Strongylocentrotus purpuratus and S. francis-

canus, and the statement is made that the development of

the hybrid up to the formation of the skeleton resembles

exclusively the development of the mother’s species. But

Loeb also finds that the cross-barring in the spicules of

purpuratus behaves as a dominant character in reciprocal

crosses. He assigns this character to a factor, which he

imagines to be a ferment or enzyme. This statement fol-

lows: ‘‘Since the pure purpuratus has two determiners

for the development of the cross-bars, and the hybrids

only one, the pure purpuratus should have twice the en-

zyme and develop twice as fast’’—and it did. He pro-

vides here not only evidence that avowed chromosome

characters do affect the rate of development, but even

furnishes an enzymatic mechanism by which they may do

it. And yet soon after the above quotation, we read:

We can therefore be tolerably sure that wherever we deal with a

hereditary factor which is determined by the egg alone, the cytoplasm

of the latter is partly or exclusively responsible for the result. We

have already mentioned that rate of segmentation is such a character.

The whole case of the supporters of any theory which

views the cytoplasm as determinative rests on either their

refusal to go back and inquire the source of this cyto-

plasm, or on their refusal to give due emphasis to the

source, even though they recognize it. Conklin recognizes

No. 605] NUCLEUS AND CYTOPLASM 297

the double influence which is exerted on the developing

egg better than any of the others who have adopted his

‘‘ecompromise theory.’’ He admits that ‘‘most of the dif-

ferentiations of the cytoplasm have arisen during the

ovarian history of the egg and as a result of the inter-

action of nucleus and cytoplasm.’’ He has demonstrated

better than any other one man how complex and definite

these differentiations in the egg cytoplasm are. All will

agree with him when he says that they ‘‘foreshadow”’ the

future organism. But ‘‘cytoplasmic organization, while

affording the immediate conditions of development, is

itself a result of the nature of the nuclear substance which

represents by its inherent composition the totality of

heritable potence.’’?’ These last are the words of E. B.

Wilson (1895, p. 25), although he has translated and

adapted them from an earlier paper by Driesch. They

represent the opinion of Wilson and of Driesch in full

accord. ‘‘The nuclear substance’? referred to was even

then known to contain equality of maternal and paternal

chromatin. j

Wilson himself had been able to demonstrate that the

structure of the cytoplasm in sea-urchin eggs was ac-

quired during ovarian life, and on the basis of this and of

a considerable body of similar evidence he was able to

conclude quite definitely:

That a preorganization of the cytoplasm can not be regarded as the

primary factor in heredity is conclusively proved by the old argument

based on inheritance from the father through the sperm nucleus.

The only link which is needed to make the chain com-

plete is some substantial body of evidence, demonstrating

the effect and the mechanism of action of the nucleus on

the cytoplasm. This, it must be admitted, has not been

entirely filled. Nägeli, to be sure, held a theory of a

dynamic effect of the nuclear idioplasm on the cytoplasm,

while Driesch contended that the mechanism was chem-

ical. The nucleus, in his opinion, exercised its governance

by means of ferments or enzymes.. There are facts in

298 THE AMERICAN NATURALIST [ Vou. LI

development which point to effects of the nucleus even on

the visible differentiation of the egg before fertilization.

In the sea-urchin, for instance, this differentiation is pre-

ceded by the absorption into the nucleus of part of the

fluid content of the cytoplasm, altering the chemical com-

position of the latter and greatly increasing the bulk of

the nucleus. The membrane of this enlarged nucleus then

dissolves and part of its contents by their color may be

traced to a clear cap of fluid which later gives rise to the

skeleton of the echinoderm. Such absorptions and ming-

lings probably play a large part in the reactions of

nucleus and cytoplasm, either at the successive disap-

pearances of the nuclear membrane during mitosis or

through that membrane.

Nucleus and cytoplasm may certainly be regarded as

forming a reaction system analogous to that which might

exist between a series of chemical substances (Jennings,

1914). The cytoplasm in turn is linked with the extra-

cellular milieu in a quite comparable way and forms the

intermediary between the nticleus and the exterior.

Evidence on this interaction is accumulating. As an

example I may quote the work of Cameron and Gladstone

on cells other than ovarian, and, to be sure, by the static,

histological method. But they have observed fine prep-

arations and have concluded that the cytoplasm is visibly

differentiated into two grades of endoplasm. The first is

next to the nucleus, is clear and refractive. This is the

nascent material of the cell and is the first visible stage

in the genesis of protoplasm. It is, they postulate, a

derivative of the nucleus itself, and to the nucleus is

ascribed the final elaboration of nutritive material which

has been ingested by the cytoplasm. This nascent endo-

plasm. they conceive to be the active material of the cell

grading into passivity toward the cell periphery, through

the maturer endoplasm and the ectoplasm.

Whatever relations may exist between the two, the fact

remains that the cytoplasm is necessary. Without it the

nucleus, deprived of its milieu, can not live, and develop-

No. 605] NUCLEUS AND CYTOPLASM 299

ment can not take place. The investigation of the finer

physiological reactions which take place between the

nucleus and cytoplasm is badly needed, and the restate-

ment of them in terms of physics and chemistry. Such

evidence as is available indicates that the importance of

the cytoplasm is, in the main, subordinate to that of the

nucleus.

The evidence from egg-characters, it might be noted in

conclusion, is one-sided. I have no doubt that if sperm-

characters were to be studied as intensively as egg-char-

acters have been (which has not been the case due to the

microscopic size of most sperms) the differential char-

acters in the sperm would be found to behave in heredity

like the differential characters of eggs, and would be de-

termined as largely by the egg nucleus as by the nucleus

of the sperm of the preceding generation.

CONCLUSIONS

Direct continuity of substances in the cytoplasm is not

a method of heredity. It simply provides for the autono-

mous proliferation of materials with no determinative

significance. No compromise, then, is possible between

the two views outlined as ‘‘eytoplasmic’’ and ‘‘chromo-

some’’ theories of heredity. The first is non determi-

native; the second is the primarily effective method of

heredity and of development. The working of the ef-

fective method is known for heredity, if heredity be prop-

erly only concerned with the way in which the hereditary

factors are distributed in the germ cells. For develop-

ment, its mechanism is but grossly known, but we have

learned enough of the determinative effect of the nucleus

and of the possibilities for interaction between cytoplasm

and nucleus to foster a suspicion that one day the gov-

ernance of the chromosomes over development will be ex-

plained in PERTE terms.

BIBLIOGRAPHY

Cameron and Gladstone. 1916. Journ. Anat. and Physiol., pp. 207-227.

Castle, W. E. 1910. Journ. Exp. Zool., Vol. 8, No. 2.

300 THE AMERICAN NATURALIST [Vou. LI

Conklin, E. G. 1908. Science, N. S., 27.

Conklin, E. G. 1915. Heredity sa Tao. Princeton Univ. Press.

Conklin, E.G. 1917. Proc. Nat. Acad. Sci., Vol. 3, No. 2.

Correns, C. 1909. Zeit. tn ae u. Vererb., 1 and 2.

Godlewski, E. 1906. Arch. Ent. ch., 20.

Lock, R. H. 1906. pose Roy. Bot. Gara, Peredeniya, 3.

Loeb, J. 1903. Univ. Cal. Pub. No.

Loeb, J. 1916. The eee as a Woot, nr N Y,

Newman, H. H. 1914 . Exp. shop

McCracken, I, 1909. ce urn. tas Zoo oe T ate 4,

hull, A. F. 1916. Ohio Journ. of or p DERA

Toyama, K. 1912. Biol. Centralbl., Vol. 32.

Wilson, E. B. 1896. Arch, Ent. Me oh: Vol. 3.

SHORTER ARTICLES AND DISCUSSION

MODIFYING FACTORS AND MULTIPLE ALLELO-

MORPHS IN RELATION TO THE RESULTS

OF SELECTION

In the prevailing controversy as to the effectiveness of selec-

tion, those who reject such effectiveness put forth multiple modi-

fying factors as the explanation of the results observed. The

given character (for example, the coat color in Castle’s hooded

rats) is held to depend on one main factor (determining the

presence or absence of the character) and upon numerous modi-

_ fying factors; the number of the latter present in a given case

determines the degree of expression of the character. Selective

breeding is then held to act, as it does with relation to all other

Mendelian factors, merely by making diverse combinations of

such factors. Many are gathered together in certain individuals,

few in others, and the degree of expression of the inherited char-

acter varies accordingly. :

Much evidence is presented that this is actually the mode of

operation in many cases where selection is effective. Thus are

explained the visible results of selection in Castle’s rats; thus

the unexpected fact that many of the mutations of Drosophila

have shown themselves (in aecordance with Castle’s prediction)

to be amenable to selection, although in other respects they be-

have like alterations of a single unit factor. This is indeed the

usual explanation for that effectiveness of selection which is

coming to light in so many eases; and in many of the cases it ap-

pears clear that the explanation is correct.

But in which direction does this explanation carry us? To

answer this question we must know what these multiple modi-

fying factors are. If they are mere examples of the statie con- -

dition of diversity observed among so many closely related or- _

ganisms, the answer falls in the negative direction, so far as

_ the effectiveness of selection in accumulating actual alterations

of hereditary characters is concerned. But if they should them-

selves turn out to be the actual alterations of hereditary consti-

tution that are accumulated by selection, then the answer con-

301

302 THE AMERICAN NATURALIST [Vou. LI

firms the effectiveness of selection and adds greatly to our

knowledge of how it is brought about. What are the facts?

For these we may turn to the organism of which the genetics

are best known; to the fruit fly Drosophila; and we may accept

the accounts presented by those most uncompromising opponents

of the effectiveness of selection, the investigators of Drosophila

in the Columbia laboratory. Their account we cannot suspect

of being colored to favor the selectionist point of view. We find

data as to certain known modifying factors in the recent im-

portant paper of Bridges (1916) on ‘‘Non-Disjunction of the

Chromosomes in Drosophila.’’ Bridges tells us that he has found

no less than seven diverse factors that modify the single primary

grade of eye color known as eosin. These seven factors are

located in parts of the chromosomal apparatus different from

the spot on which the presence or absence of eosin depends, and

each is inherited in Mendelian fashion. One of these factors

lightens the eosin color in a fly with eosin eyes, nearly or quite

turning eosin to white; this factor Bridges calls ‘‘whiting.’’ An-

other has the effect of lightening the eosin color a little less,

giving a sort of cream color; this is called ‘‘cream b.” A third

factor dilutes the eosin color not so much; it is called ‘‘cream

”? Tn addition to these, Bridges tells us that he has discovered

three other diluters of the eosin color; we will call them the

fourth, fifth and sixth diluters. And finally Bridges tells us

of another factor whose only effect is to make eosin darker; this

factor he calls ‘‘dark.’’ We get therefore the following list of

the modifying factors for eosin color:

1. Whiting

2. Cream b

3. Cream a

4. Fourth diluter

5. Fifth diluter

6. Sixth diluter

7. Dark

= We have then in Drosophila minutely differing conditions of

’ a single shade of color, brought about by seven modifying factors.

Concerning these, Bridges makes the following remark, which is

worthy of particular attention:

A remarkably close imitation of such a multiple factor case as that

of Castle’s hooded rats could be concocted with the chief gene eosin

No. 605] SHORTER ARTICLES AND DISCUSSION 303

for reduced color, and these six diluters which by themselves produce

no effect, but which carry the color of eosin through every dilution

stage from the dark yellowish pink of the eosin female to pure white

(Bridges, 1916, p. 149).

Thus we see that in Drosophila we could get the same sort of

graded results that Castle does with his rats, only in Drosophila

this is by multiple modifying factors, whereas Castle believes

that in the rat it is by actual alterations in the hereditary con-

stitution !

But what are these modifying factors? And here we come to

the astonishing point. These modifying factors are themselves

alterations in the hereditary constitution! Bridges leaves no

doubt upon this point. He lists and describes them specifically

as mutations; as actual changes in the hereditary constitution.

Now so far as I can see, the question involved in the selection

controversy is as to the occurrence of minute changes in the

hereditary constitution, and their accumulation by selection; so

that by selection various grades of a given external character

can be obtained. In Drosophila, according to Bridges, such

changes occur; changes which give, so far as our present imper-

fect knowledge goes, at least seven diverse grades of a single

tint (that is itself, as we shall note, only one grade in another

series of seven known grades). By means of these graded.

changes one could obtain, by the mutationist’s own statement,

the continuously graded visible results which selection actually

gives. Is not then the controversy as to the effectiveness of selec-

tion at an end?

As to just where the graded hereditary changes occur there

remain indeed certain differences of opinion; some selectionists,

like Castle, hold that the various grades of a given external char-

acter are due to diverse minute modifications of the same unit

character—of the same locus in the chromosome; while, as we

have seen, the modifying factors are due to changes in diverse

parts of the hereditary material. This matter of detail does not -

touch the main point, but it is of interest to ask what the work

of the mutationists gives us on this question. It is curious to

find that their studies of Drosophila furnish almost all that could

be asked by the radical selectionist as to the existence of a single

unit character in a series of numerous hereditary gradations.

The best instance here is again the color of the eye, which fur-

nished us also our example of modifying factors. The color

304. ~ THE AMERICAN NATURALIST [Vou. LI

eosin, of which the modifying factors give us seven grades, is

itself only one of another series of seven grades that .are due to

diverse alterations in the same unit factor—in the same chromo-

somal locus. As we know from the studies of Drosophila, this

locus is a certain region of the X-chromosome. When this locus

retains its normal condition the eye is red. Some years ago a

variation was observed by which the eye lost its red color, be-

coming white. Somewhat later another variation came, by which

the eye color became eosin. By the wonderfully ingenious

methods which the advanced state of knowledge of the genetics

of Drosophila has made possible, it was determined that the

mutations white and eosin are due to changes in a particular

part of a particular chromosome, and that indeed the two are

due to different conditions of a particular region of the X-chro-

mosome. In other words, they show different conditions of the

same unit. Moreover the normal red represents a third con-

dition of this same unit.

Later a fourth condition of this same unit was found, giving

a color which lies nearer the red, between the red and eosin; this

new color was called cherry. We have now four grades of this

single unit character.

And now, with the minute attention paid to the grades of eye

color, new grades begin to come fast. In the November number

m Genetics, Hyde (1916) adds two new grades, one called

‘blood, ”” near the extreme red end of the series; the other, called

‘‘tinged,”” near the extreme white end; in fact, from the de-

scriptions, it requires careful examination to distinguish these

two from red and white respectively. So we have now six grades

of this unit. And in the same number of the same journal, Safir

(1916) adds another intermediate grade, lying between tinged

and eosin; this he calls ‘‘ buff.’’

So, up to date we know from the mutationists’ own studies of

Drosophila that a single unit factor presents seven gradations of

color from white to red, each grade heritable in the usual Men-

delian manner. These grades or ‘‘multiple allelomorphs’’ as

they are called, are the following:

1. Red

2. Blood

3. Cherry

4. Eosin

No. 605] SHORTER ARTICLES AND DISCUSSION 305

5. Buff

6. Tinged

7. White

Three of these seven grades have been made known to us within

the last six months. It would not require a bold prophet to pre-

dict that as the years pass we shall come to know more of these

gradations, till all detectable differences of shade have been made

out and each shown to be inherited as a Mendelian unit. Con-

sidering that the work on Drosophila has been in progress but

eight or nine years, we have already remarkable progress toward

a demonstration that a single unit character may present as

many heritable grades as can be distinguished; that the grades

may give a pragmatically continuous series. This is precisely

the situation that the selectionist postulates.

Furthermore, as we have seen, besides this primary series of

seven grades, due to alterations of a single unit factor, there is

a secondary series containing seven more grades, all affecting

the central grade (eosin) of this primary series, but due to al-

terations of other parts of the germinal material. How much

more does the selectionist require?

This situation in Drosophila is not exceptional. To mention

one or two other examples, Castle and Wright (1916) find a

large series of such diverse conditions of a single factor (‘‘mul-

tiple allelomorphs’’) determining various shades of coat colors

in rodents. Emerson (1917) in his recent account of the extra-

ordinary condition of affairs in the genetics of pericarp colors

in corn, talks of ‘‘a series of not less than nine or ten multiple

allelomorphs,’’ which moreover leap back and forth from one

condition to another in bewildering fashion.

To sum up, it appears to me that the work in Mendelism, and

particularly the work on Drosophila, is supplying a complete

foundation for evolution through the accumulation by selection

of minute gradations. We have got far away from the old

notion that hereditary changes consist only in the dropping out

of complete units, or that they are bound to occur in large steps.

The ‘‘multiple allelomorphs”’ show that a single unit factor may

exist in a great number of grades; the ‘‘multiple modifying

factors” show that a visible character may be modified in the

finest gradations by alterations in diverse parts of the germinal

material. The objections raised by the mutationists to gradual

change through selection are breaking down as a result of the

thoroughness of the mutationists’ own studies.

306 THE AMERICAN NATURALIST [Vou. LI

The positive contribution of these matters to the selection

problem is to enable us to see the important rôle played by Men-

delism in the effectiveness of selection. Hereditary variations,

such as give rise to the multiple allelomorphs and multiple modi-

fying factors, occur in some organisms rather infrequently, as

measured by the time scale of human happenings. If there were

no interchange of factors among individuals and stocks, it would

take a long time to obtain in one individual all the six diluters

of the eosin color of the Drosophila eye; one arises in one in-

dividual, another in another. But by selective crossbreeding it

is possible to bring together into one stock all the modifiers that

have been produced in diverse stocks. Mendelism acts as a

tremendous accelerator to the effectiveness of selection.

PAPERS CITED

Bridges, C. S. 1916. Non- aen as Proof of the Chromosome Theory

of Heredity. Genetics, 1: 1-52, 107-1 63.

Castle, w. E., and Wri i S. 1916. Studies of Inheritance in Guine

Pigs EN Rats.. Publ. No. 241, RREN Institution of Washington,

192 pp. l

Emerson, R. A. 1917. Genetical Studies of Variegated Pericarp in Maize.

35.

Hyde, R. R. 1916. Two New pina ‘a Sex-linked Multiple (sex-

H aa oin System. Genetics, 1 580.

fir, S. B. 6. Buff, a New ew ATlelomorpl p White Eye Color in Dro-

sophila. ae 1: 584—

H. S. JENNINGS

THE JOHNS HOPKINS UNIVERSITY

A WING MUTATION IN PIOPHILA CASEI

In the early part of December, 1915, I began to breed the

‘‘cheese skipper’’ Piophila casei, in order to see if mutations

were to be found in this fly. The source of my stock was a small

piece of Italian cheese containing a dozen or so larve.t As these

were doubtless the offspring of one female, inbreeding has been

very close. Up to June 22, 1916, only one heritable mutation

had been found among the thousands of individuals bred; this

was the wing defect described below, which was first noted on

March 12, 1916.

1 This work was ee on at the ay Zoological Laboratory, Yale Uni-

versity, New Haven, Connecticut. It was in New Haven that I obtained the

cheese. Contribution No. 135, Zoological Laboratory, University of Texas.

No. 605] SHORTER ARTICLES AND DISCUSSION 307

The Defect—When viewed from the dorsal surface the defect

appeared as a blister of variable size on the proximal and

posterior part of the wing. From the ventral surface it appeared

as a pit. Occasionally a real blister filled with fluid was ob-

tained. The position of the defect was constant; when small it

lay in the posterior cell just below the discal cell. When large

it involved nearly the whole wing including the axillary, anal,

second basal, discal and posterior cells. Usually both wings were

affected alike, but here and there flies were found with one

wing normal and the other wing severely affected.

This factor is strikingly similar, both in its appearance and

the variability of its behavior, to the ‘‘balloon wings’’ found by

Morgan? in Drosophila and more recently fully described by

Marshall and Muller.* The flies carrying the defect, in my cul-

tures, were very frequently sterile, and in no case did their

fertility begin to approach that of normal stock.

In breeding, the character behaved as a mendelian recessive.

Normal crossed with balloon gave, in the F, generation, 196

normal and no affected individuals. (This included 4 matings.)

When brother and sister were mated, in the F, generation, 312

normal and 111 balloon offspring were obtained This is very

close to the expected 3:1 ratio, of a monohybrid cross. When

balloon flies were crossed, all individuals were affected (74 off-

spring obtained) but the character showed itself extremely vari-

able; in some cases the flies appeared normal until very closely

examined.

The defect was not sex-linked as is shown i the following

mating. A defective female was mated with a normal male of

normal stock. Of the 50 offspring resulting both males and

females were normal.

The variation in the appearance of the balloon flies suggested

either that the size of the blister was dependent upon some

unknown environmental factors, or else, was due to multiple

allelomorphs or multiple factors. A great number of matings

were made to gain light on this point, but due to the sterility

of the affected individuals, the evidence is not sufficient to allow

us to draw any conclusions. Two individuals both of whom were

severely affected were crossed. The 20 offspring resulting were

all severely affected. Two individuals, both of whom were only

2 In Morgan’s ‘‘A Critique of the Theory of Evolution.’’

3 Marshall and Muller, Jour. of Exp. Zool., Vol. 22, 1917.

308 THE AMERICAN NATURALIST [ Von. LI

slightly affected, were crossed. Of the 29 offspring resulting,

17 showed the defect in a severe form, and 12 showed only small

blisters. A female which had only one wing affected, was mated

to a male, one of whose wings was severely affected while the

other bore-a very small blister. Of the 45 offspring resulting,

27 bore the defect in a severe form on both wings and 18 showed

small blisters again on both wings.

Further experiments with this new character were under way

when the work was stopped by the mobilization of the Militia in

June. The work with these flies, however, is again being

resumed.

THEOPHILUS S. PAINTER

UNIVERSITY OF TEXAS

A CASE OF REGENERATION IN PANULIRUS ARGUS!

THE occurrence of regenerative processes in the crustacea has

been a matter of record for a number of years, but the instances

have been mostly confined to the regeneration of appendages and

portions of the nervous system. Observations on the regeneration

of portions of the exoskeleton of the trunk are far less numerous.

The present observations on the regeneration of a portion of the

rostrum of Panulirus argus, the common crayfish of the Bermuda

Islands, were made during the summer of 1916 at the Bermuda

Biological Station.

Panulirus argus when full grown is about 14 to 16 inches in

length. It lacks chelipeds, their place being taken by the ordi-

nary type of walking appendage. None of the walking append-

ages is provided with nippers, all being tipped with a single hook,

as, e. g., in the fourth pair of appendages of the crayfish Cam-

barus. The rostrum of Panulirus, instead of being a single

median projection, -consists of a pair of long (30-35 mm.),

sharply pointed spines, slightly compressed laterally, and grow-

ing out from the carapace just posterior and slightly dorsal to

the base of the eye-stalks.

The animal in question was a half-grown male, eight and one

half inches long. When caught, June 20, the left spine (com-

pare figure and explanation) of the rostrum was entirely miss-

ing. The carapace around the base was jagged and rough, as

though the break had been recent ; but a thin, soft membrane had

1 Contributions from the Bermuda Biological Station for Research, No. 58.

No. 605] SHORTER ARTICLES AND DISCUSSION 309

formed across the surface of the break. Five days later, June

25, the protecting membrane had hardened, so that it could not

be dented with the point of a scalpel. No further change could

be noted until after the molting, which occurred four days later,

June 29. The casting occurred at night, and the next morning

the new shell showed no signs of any wound. By one o’clock a

very slight hump appeared, and by ten o'clock at night a little

rudimentary spine 2 mm. in length had formed. The next morn-

ing another millimeter had been added to its length. Meantime

the normal spine had increased 1.5 mm. in length. No further

growth followed before the new shell had hardened.

Fie. 1. From a photograph of the left side of the head region of Panulirus

argus, showing (norm.) the normal, and (regn.) the regenerated rostral spine.

As the figure is reproduced from a r c print, the picture is reversed,

the right spine appearing like a left

Sixteen days later, July 15, another molt occurred. As before,

the old shell was cast at night and by the following morning the

regenerating spine had added 2 mm. to its length, being now 5

mm. long. By the next evening all growth had been stopped

by the hardening of the new shell, but the total length of the

spine was at this time 7 mm. The spine now showed a sharp

point and also a slight lateral compression like that of the normal

spine. At this casting the normal right spine added 1 mm. to its

length, showing that, while the whole animal was growing, the

310 THE AMERICAN NATURALIST (Vou. LI

regenerating part was increasing at a much faster rate than

other parts.

Thus in the period of twenty-seven days during which the ani-

mal was under observation, it had undergone two molts and had

regenerated a missing rostral spine of normal form, 7 mm. in

length, while the normal spine had added 2.5 mm. to its length

in the same period. These results show that the period between

molts for this animal under laboratory conditions is six-

teen days; that a rostral spine of normal form can be regen-

erated; and that the rate of this regeneration was nearly

three times the rate of normal growth of a similar spine during

the same period.

A. C. WALTON

HARVARD UNIVERSITY

NOTES AND LITERATURE

THE COAL MEASURES AMPHIBIA OF NORTH

AMERICA?

THE excellent monograph by Dr. Roy L. Moodie is a worthy

successor of the long series of works by Dawson and by Cope on

the air-breathing vertebrates of the Coal Period in North

America. The extremely varied amphibian fauna of the coal

swamps as described by Moodie contains representatives of no

less than 7 orders, 19 families, 46 genera and 88 species, the

animals ranging in size from the minute Humicrerpeton, less

than two inches long, to the great Leptophractus obsoletus,

which was as large as an adult Florida alligator. The wide dif-

ferentiation and high specialization of these amphibians shows

that the class even at that early epoch had evolved very far from

its first adaptive radiation, so that, as Dr. Moodie well observes,

the origin of land vertebrates from fishes must be looked for in a

much earlier time, perhaps the Silurian.

Carboniferous Amphibia are reported from various localities

in North America, but only four of these have yielded large or

important collections. From the South Joggins coal mines in

Nova Scotia Sir William Dawson secured most of the specimens

of Microsaurs described by him, many of the skeletons being

found in the rotten stumps of Sigillaria trees. This material is

preserved chiefly in the Museum at McGill University, Montreal.

From the Linton, Ohio, coal seams Newberry and his collectors

secured the great collections described by Cope and which are

now chiefly in the American Museum of Natural History. At

Mazon Creek, Illinois, the fossils are found in ironstone nodules

in a stratum of shale; the specimens have been described chiefly

by Newberry, Cope and Moodie and are scattered in various

museums. At Cannelton, Pennsylvania, the fossils occur in slates

and have been described by Moodie, the material being in the

National Museum.

On account of the fragmentary nature of most of the material

and the fact that generic and specific names have been based on

1 Carnegie Institution of Washington, Publication No. 238, 1916.

311

312 THE AMERICAN NATURALIST [Vou. LI

many different and non-comparable parts of these animals, the

author’s task was an exceedingly difficult one, and only those

who have occasion to study this work very closely can appreciate

either the magnitude of the undertaking or the thoroughness

with which it has been carried out.

Dr. Moodie’s monograph will NETE invite comparison with

the well-known works on the Permian Amphibia of Bohemia

and Saxony by Fritsch and by Credner. It must be admitted,

however, that many of the illustrations are inferior to those of

the works mentioned, partly on account of the difficulty of

showing the real character of these fragmentary specimens by

means of photographs.

The author’s method is so intensive that he has left even readers

who may have some first-hand knowledge of Paleozoic Amphibia

in need of many broader facts and comparisons which may rea-

sonably be expected to result from such a conscientiously exe-

cuted investigation ; it is the aim of this review in some measure

to supply this deficiency, in the hope that Dr. Moodie him-

self may be induced to write a general article covering more

fully the points here raised.

In the chapter on stratigraphic and geographic distribution

the author shows that the four chief Amphibia-bearing for-

mations in North America mentioned above are all in the Alle-

ghany or Lower Coal Measures and are thus much older than

those deposits (Salt Fork, Pitcairn) of the Upper Productive

Coal Measures at the top of the Pennsylvanian series, which have

collectively yielded Cricotus, PNE Heyope and other

genera characteristic of the Texas ‘‘Perm

The author does not discuss the piste seria of the Lower

Coal Measures fauna either with the ‘‘Permian’’ fauna of Texas

and other states, or with the Carboniferous and Permian faunas

of Ireland, Scotland, England, France, Saxony and Bohemia.

Even the Permian and Triassic amphibian faunas of South

Africa invite comparison with the varied Temnospondyli of the

Carboniferous and Permian of America and Europe.

The Lower Coal Measures fauna of America includes a long

series of branchiosaurs, microsaurs and primitive labyrintho-

donts (Spondylerpeton, Dendrepeton, Macrerpeton, Eoba-

phetes), and it is totally lacking in pelycosaurs, poliosaurs,

cotylosaurs, or any other reptiles except Eosauravus. The

Texas fauna, on the other hand, has only a single microsaur

(Crossotelos) and no branchiosaurs; its varied labyrinthodonts

No. 605] NOTES AND LITERATURE 313

(ineluding Cricotus, Eryops, Dissorophus and many others) are

all genera not found in the Lower Coal Measures, and it abounds

in reptiles of several orders and many families. Some of this

difference may be due to the fact that the Lower Coal Measures

fauna represents only the life of the coal swamps, while the

Texas fauna represents the life of the pools and streams of a

wide delta country (Case); but all authorities agree that the

former is much the older of the two.

The Lower Coal Measures fauna is far more similar to the Per-

mian fauna of Bohemia, which according to Fritsch’s classifica-

tion comprises a similar series of 13 families, 26 genera and 63

species, of branchiosaurs, microsaurs and temnospondyls. But

no genera are common to the two countries and many of the

‘*families’’ (as listed) are peculiar to one or the other. The

families peculiar to America are the Cocyctinide, Peleontide,

Tutidanide, Ptyoniide, Molgophiide, Sauropleuride, Amphiba-

mide, Ichthyeanthide, Stegopide, Macrepetide, while those

peculiar to Europe are the Apateonide, Limnerpetide, Micro-

brachide, Dolichosoma, Ophiderpeton, Melosauride and Arche-

gosauride. The families common to both continents are

Nyraniide,? Cricotidee (Diplovertebride), Anthracosauride,

Professor Case has directed attention* to the marked resem-

blance of two of the genera (Diplovertebron, Macromerion)

from the lowest Bohemian horizon (Nyran) to Cricotus of the

Upper Coal Measures of North America, as furnishing ewdence

that the Bohemian deposits are of Upper Carboniferous age.

Subsequent research may well show on the one hand that some

of the American ‘‘families’’ are more closely related to European

groups than is now recognized and on the other hand that some

of the ‘‘families’’ classed as common to both continents are

artificial or ill defined (Hylonomide?, Nyraniide?); yet even `

with our present imperfect knowledge it appears that the Lower

Coal Measures fauna of America and the ‘‘Permian’’ fauna of

Europe represent nearly identical life conditions and similar

2 Brachyderpeton of the English Coal Measures, as shown by Watson,

appears to be related to Diplocaulus.

3 The presence of this family in America is doubtful, and Dr. Moodie’s

reasons for assigning the genera Ichthyerpeton and Cercariomorphus to this

family are not stated and difficult to infer.

4 Science, Vol. 42 (Dee. 3, 1915), pp. 797-798.

314 THE AMERICAN NATURALIST [ Vou. LI

adaptations on the part of two divergent associations derived

from some older and common source, possibly of Mississippian

age and of wide distribution; and it further appears probable

that the American Lower Coal Measures fauna is somewhat the

older of the two.

The chapter on the morphology of the Coal Measures Am-

phibia contains a careful description of the characters of the

skull and other parts of the skeleton, but the author is extremely

chary of generalizations. He might have mentioned, for in-

stance, the interesting fact that the skull-pattern of these am-

phibians is a shifting mosaic, one in which several of the dermal

elements have different contacts and different positions in the

various families. In some microsaurs, for example, the post-

orbital grows backward and secures a broad contact with the

tabular; in others it retains its primitive position. The jugal

and lacrymal also differ widely in their form and contacts. The

nasals and adjacent elements are small and much crowded in

many branchiosaurs and microsaurs, long and wide in most

labyrinthodonts. Certain dermal elements are present in some

and absent in others, especially the intertemporal and the rare

interfrontal and internasal elements. The shape of the occiput

differs widely, sometimes truncate posteriorly, with the auditory

notch obsolete, sometimes angulate posteriorly, retaining the

primitively wide auditory notch. Very curious is the tendency

f the different families of microsaurs to develop ‘‘horns’’—

sharp backwardly projected apophyses in the occipital region—

growing sometimes from the tabular, sometimes from the squa-

mosal and sometimes from both at once. These remind one of

the backwardly directed processes from the ‘‘epiotic’’ and supra-

occipital in the skull of teleost fishes and perhaps they-may have

served for the attachment of longitudinal ligaments or muscles

in wriggling, aquatic types

All the differences in skull pattern may be regarded as minor

readjustments which were taking place after the more profound

transformation of a generalized pro-ganoid skull into the am-

phibian type, the greatest alteration including the loss of the

opereular bones so as to leave the gill chamber covered only by

membrane and the change of the preopereulars or cheek plates

into the squamosals. The author expresses the opinion that the

membrane bones may have originally been derived from scales

‘‘which later became consolidated into large bony scutes,” but

on histological grounds the reviewer regards it as far more prob-

No. 605] NOTES AND LITERATURE 315

able that in the ancestral fishes each membrane bone and each

scale grew from clusters of cosmine tubercles underlain by tracts

of vascular and stratified bony tissue, and that there never was

a time when the elements of the dermo-cranium were scale-like

in form (i. e., rhombic or polygonal), although the several tissues

involved were histologically identical in the body scales and in

the dermo-cranium.

On page 85 the author uses the name ‘‘squamosal’’ for the

clamant which he and most other authorities now designate as

‘‘supratemporal.”’?

In the description of the hyobranchial elements of Coocy Giants

(a genus doubtfully assigned to the Proteida), the reader looks

in vain for a comparison with the same elements in the Permian

‘‘Urodele’’ Lysorophus as described by Williston. It may be

noted, by the way, that the branchial arches in that genus are

extremely primitive and almost Polypterus-like in form and

arrangement, although doubtless homologous also with those of

the modern Amblystoma.

The author has given a very thorough study of the dermal

scales and scutes of the branchiosaurs, microsaurs and tem-

nospondyls. The ventral ‘‘seutelle,’? which appear to be

homologous with the abdominal ribs of reptiles, are formed, the

author holds, as ossifications in the connective-tissue septa or

myocomata of the ventral muscles, vestiges of these having been

found in modern urodeles. The highly differentiated charac-

teristics of this ventral armature affords many family and

generic characters; it is sometimes absent or reduced to needle-

like ossicles, sometimes highly developed, forming heavy median

` V’s and wide lateral shelves (Ctenerpeton). Some of the micro-

saurs had rounded, slightly imbricating fish-like body scales

with concentric markings which recall the similar armature of

certain Bohemian and Saxon types, such as Ricnodon and Dis-

cosaurus. Vestiges of such conditions may be represented in the

scales of modern excilians (as shown in the enlarged figures of

cæcilian scales by the Sarasin brothers

he reviewer ventures to doubt the correctness of Dr. Moodie’s

reconstruction of the shoulder-girdle of branchiosaurs and miero-

saurs, in the matter of the position of the seapula. Many of the

specimens figured by Fritsch and by Credner seem to indicate

that the concave border of the scapula was posterior in position,

as it is in Eryops and in modern urodeles, and that it did not

form the glenoid border as in Dr. Moodie’s reconstructions.

316 THE AMERICAN NATURALIST [ Von. LI

Dr. Moodie’s history of the classification of the Amphibia ap-

pears to the reviewer to be rather meager, since he simply lists

the classifications of his predecessors without giving any critical

discussion. It is surprising that in this chapter he did not men-

tion the work of Fritsch with which he must be extremely famil-

iar. Fritsch’s classification of the extinct Amphibia, although it

was adapted and extended from the classification proposed by the

British Association Committee in 1870, was, in the judgment of

the reviewer, a distinct contribution to the subject which cer-

tainly deserves notice in an historical review, especially since

Fritsch erected several new families and gave definitions of all

the European groups.

The author’s own classification is an interesting attempt to

divide the Amphibia of the Coal Measures into two major series

or subclasses, the first (Euamphibia) including all those which

may be related to modern types; the second comprising all the

wholly extinet groups (microsaurs, aistopods and labyrintho-

donts of all suborders). He derives most of the modern urodeles

(Caudata) from the branchiosaurs, for which he has given con-

siderable evidence; he follows Cope in provisionally deriving

the modern Proteida from the Coceytinide of the Coal Measures.

He regards the strange Diplocaulus, an amphibian with a head

like a colonial cocked hat, as a member of the Euamphibia, prob-

ably because its vertebre bear short, straight, double-headed ribs

which are attached to paired lateral apophyses springing from

the middle of the vertebre, after the fashion of those of branchio-

saurs and Caudata and quite unlike the hour-glass centra of

microsaurs, which bear long, slender ribs between the vertebre.

But Watson and Williston regard Diplocaulus and Brachyder-

peton as microsaurs, the last named genus showing in the ver-

tebre and in the skull how the Diplocaulus type may have been

derived from primitive microsaurian conditions. Indeed it may

well be argued that the branchiosaurs and urodeles (Caudata)

themselves, in spite of the retention of gills in the young, may

have been derived from primitive microsaurs, that is that the

vertebre and ribs of microsaurs are on the whole much more

primitive than those of branchiosaurs and Caudata.

The systematic relations and origin of the frogs and toads re-

main doubtful. Dr. Moodie gives an excellent discussion of the

resemblances of Pelion lyelli Wyman, from the Linton, Ohio,

Coal Measures, to the modern Anura but leaves the phylogenetic

problem open. Pelion is so little known that it may or not be

No. 605] NOTES AND LITERATURE 317

ancestral to the Anura, and the Jurassic Anura are so entirely

modernized that they do not bridge over the wide structural gap

between the Paleozoic Amphibia and the modern frogs and toads.

It seems to the reviewer, after repeated comparisons of the

—osteology of the Anura with that of many of the temnospondyls,

that some members of the latter group, in the brain-case, the

dermo-cranium and even in the vertebre and limbs retain many

characters which may reasonably be looked for in Paleozoic an-

. cestors of the frogs and toads; and that such forms as Brachyops,

Cacops and Dissorophus, although not directly ancestral, differ

from the Anura chiefly in the retention of many primitive am-

phibian characters. It may be that some of the short-headed

Triassic temnospondyls of South Africa will furnish the linking

forms; but at any rate it is interesting to note that the existing

frogs and toads retain a long series of characters in the skull

and skeleton which are seen in the Paleozoic temnospondyls, and

that they differ from the latter in such modernized characters as

the following: the wide fenestration of the occiput and palate,

the resulting slenderness of the skull bones, the loss of the dermo-

supraoccipitals, tabulars, ectopterygoids, pre- and post-frontals,

the completion of the auditory ring, the development of extreme

’ saltatorial adaptations in the skeleton, including the modifica-

tion of the vertebre from the rhachitomous into the notocentrous

and epichordal types, the development of a long continuous uro-

style coincident with the forward shifting of the sacrum and

lengthening of the ilium.

r. Moodie’s arrangement and sequence of the families of

microsaurs appear to the reviewer to be highly confusing.

would perhaps have been better, after beginning with the newt-

like types, to pass at once to the long-bodied Urocordylide and

the snake-like Molgophiide and Ptyoniidx, instead of interjecting

in the middle of the series the Stegopide, which appear to the

reviewer to be more nearly allied with the Temnospondyli, and

the Amphibamidx, which are heavy-limbed offshoots of the prim-

itive microsaurs. 7

The author’s ordinal and family definitions are extremely

full, but the reader will find so many characters that are com-

mon to several families and sometimes orders, that it is difficult

to cull out the most striking ones. This the reviewer has at-

tempted to do in the subjoined table in which he has also included

the principal European families of branchiosaurs and micro-

saurs. The families of microsaurs are arranged so far as pos-

318 THE AMERICAN NATURALIST [ Vou. Ll

sible in the general order of their specialization, proceeding from

the more primitive newt-like forms to the snake-like microsaurs

or Aistopoda.

` SYNOPSIS OF THE PRINCIPAL BRANCHIOSAURS AND MICROSAURS OF AMERICA

ND EUROP

A. Vertebræ oe i. e., having the notochord expanded in the

middle each vertebra; transverse process in dorsal region

large; ne short, RRS and heavy and borne on the trans-

verse processes, Sac near the middle of the vertebre. Skull

broad, obtusely rounded.

B. Auditory notch camer rather than lateral in arna

Bra osaurid

BB. Aae notch extended laterally, the squamosals ving A for-

MEO hae oe E EA eee Rane oi oa Ap

AA, Vertebre ris ae brig i. €., With the centra igi e yore con-

ted cylinders; ribs intercentral, typically long and curved.

B. Digits (when present) 4 in manus, 5 in pes; carpus and tarsus

artilaginous

C. Body newt-like.

D. Body covered with cycloid scales or sculptured. scutes.

mney longer than fore limbs.

E. Taan DOW s ee Hylonomide.

EE. Skull broa a

. Ribs short, slightly ago

nerpetide.5

F. Ribs thin, curved ...... Maroca hida:

DD. Body- Pao reduced or absent; neural and hæmal spines

caudal vertebræ often expanded.

E. eae scutelle absent, nes moderate in length,

skull without ‘‘horn

Tutidanide.

EE. Ventral scutelle weak or moderately i tail

long.

F. ‘‘Horns’’ on squamosals.

Diceratosaurus.

FF. ‘‘Horns’’ on tabulars. Goati

EEE. Ventral armature highly developed, consisting of

s, plates or stout bristles. Skull (so far as

known) without ‘‘horns.’’ Ribs broad and

heavy. Limbs well developed with claw-like

phalanges: 604.4566 8% Sauropleuride,

F. Skull very wide and obtuse; teeth heter-

OOONG. cs5 chaise Saurerpeton.

5 Permian of Europe.

ê Europe.

No. 605] NOTES AND LITERATURE 319

FF. Skull moderately oo teeth O

ropleu

FFF. Skull very large; teeth a cakes caus

apex and anterior cutting edge.

ie a

FFFF, Skull unknown; abdominal ribs very heavy

with poa shelf- tika pera rE

spines of vertebræ pectinate as in Urocor-

dylus, Tc ciekehis and Ptyo

gion Ee

CC. Body abn like (serpentine). Limbs much reduced or ab-

Re ea CREST eS Ta ee ( Aistopoda).

D. tect armature weak or absent.

E. Bi ee heavy and broad; neural tg hemal

short or absent ....Molgophiid

EE. mis s delicate, single- Seated neural ae wide

low spines. Skull n geet pointe sa

ichoso

EEE. ae well developed; neural set nat. ‘solace

audals expan soi scapes! skull lanceolate

isi long, slender . .Ptyoniide.

DD, Ventral armature consistin i ht he oat-shaped scu-

telle; ribs forked, two-headed; neural enya bo low

ae lower tra Hata process expanded i wide

plate in the anterior half of the vertebra. Stati thee

and hunker: than in Dolichosoma

Ophiderpeton.?

CCC. Body stout; oe well oo (but still with pyes

ginous carpus and us). Tail short, hea

rge. V miba ong.

D. No ‘‘horns’’ on squamosal, skin covered with rounded or

. hexagonal tuberculated seales. Ventral scutelle pres-

Ont lesa) ae oes Chae shes cae i i

DD. Squamosals produced into ‘‘horns.’’ Ventral scutellæ ap-

parently similar to those of Abaas

Eoserpeton tenuicorne.8

BB. Digits of manus unknown; pes with well ossified tarsus. (Limb

aper Erypos). Ventral scutellæ delicate. Centra amphice-

lou n broad and heavy ........... Ichthycanthide.

AAA. Vertebral centra discoidal.

B. TATE short, thick and ag apa Body covered

small cycloid scales ........... ‘í Nyranide’’( D 2

C. hEn MOWGIIEG ie igs ee ee a Ichthyerpeton bradleyi.

Cercariomorphus.

urope.

8 Placed by Dr. Moodie in the Urocordylide, but possibly related to Am-

phibamus.

9 The skull of Nyrania as figured by Fritsch (Vol. II, p. 34) appears to `

the reviewer to relate this genius with the ee but it is placed

provisionally by Dr. Moodie in the Microsau

320 THE AMERICAN NATURALIST [Von. LI

CC. Body Proteus BEE np eh. SOR i eee. Ichthyerpeton

squamosum.

. Vertebræ aac aioe deeply amphiceelous. .

ae Vertebrae nown. Skull of pretty sari ae ‘with separate

eee ee eis rymal and nasals large, orbits central rather

han anterior; squamosals produced into m divaricate

f O EE a NN S e ciple les Stegopide

(Stegons). 10

10 May be remotely related to the Temnospondyli (W. K. G.)

Wo. K. Grecory

AMERICAN MUSEUM OF

NATURAL HISTORY

THE

AMERICAN NATURALIST

Vout. LI. . June, 1917 No. 606

BIOLOGICAL ENIGMAS AND THE THEORY OF

ENZYME ACTION

DR. LEONARD THOMPSON TROLAND

HARVARD UNIVERSITY

Durine the past twenty years the sciences which deal

with inorganic physical phenomena have made astound-

ing progress in the logical synthesis of their facts and

theories.1 The beginnings of this synthetic tendency lie,

of course, in the middle part of the last century, in the

work of such men as Faraday, Maxwell, and Mendelejeff.

The discovery of radio-activity by Becquerel in 1896, and

the demonstration by Thomson of the electron, in the fol-

lowing year, let loose the pent-up forces of an intellectual

avalanche which swept scientific conservatism quite off its

feet, and seems to be carrying our thought with thrilling

rapidity towards a goal which metaphysical philosophers

have for ages regarded with wistful longing. This goal

is the comprehension of the physical universe in terms of

a few simple conceptions.

The lines of demarcation which once were so rigidly

drawn between the departments of physical science are

disappearing before our eyes. The discovery of radio-

activity, instead of adding a new science to the list, has

1D, F. Comstock and the present writer have attempted to give an ele-

mentary, but comprehensive presentation of the modern theory of matter in

their book, ‘‘The Nature of Matter and Electricity,’’ 1917.

321

322 THE AMERICAN NATURALIST [Vou. LI

brought us very close to a cancellation of all of the names

except one; the demonstration of the existence of par-

ticles of negative electricity smaller than any known

atom, instead of further complicating the facts of chem-

istry, has introduced a hundred simplifications. Mechan-

ics, chemistry, optics, and the sciences of heat, electricity

and magnetism are rapidly fusing into a single logical

system, the ultimate terms of which are minute particles

of positive and negative electricity, the ultimate laws

those of electro-dynamics, and the ultimate problems

those of the structures formed by these particles in space

and of the changes which these structures undergo in

time.

This startling progress in physics during the last two

decades has not been the product of unadulterate em-

pirical research. On the contrary, it has been made pos-

sible only by acts of daring speculation, which to certain

more orthodox scientists of an earlier period might have

seemed inexcusably foolhardy. However, their justifica-

tion has often come so quickly and in such unequivocal

terms, that methodological critics have been obliged to

remain modestly silent. To indulge in a definite and de-

tailed account of the structure and behavior of single

atoms of hydrogen—particles far beyond the visual range

of even the ultra-microscope—may seem no more a scien-

tific undertaking than the fabrication of a fairy-tale; and

yet when from this account there emerges by inevitable

logic a mathematical formula corresponding exactly with

the constitution of the complex spectrum of hydrogen,

our minds are opened to the possibility that the specula-

tion is pointing the way to a fundamental truth.2 This

impression becomes especially forcible when we consider

that the constitution of this same hydrogen spectrum had

for twenty-eight years defied the intellects of the best

scientists, and by some had been regarded as incapable

of explanation upon any simple hypothesis.

It is a fact of fundamental logical significance that the

2 The reference is to the theory of N. Bohr, published in the Philosoph-

ical Magazine, 1913, 26; 1, 476 and 857.

No. 606] BIOLOGICAL ENIGMAS 323

progress represented by the modern electro-molecular

conception of the physical universe has been achieved by

the utilization of a few general conceptions, such as those

of the electron and electrical action at a distance, These

conceptions, although general, i. e., universally applicable,

are nevertheless extremely definite. They are also as

tangible, or concrete, as it is possible to make them. It is

nearly as characteristic of the modern theory of matter

to eliminate abstractions as it is for it to gather up scat-

tered facts and theories to unite them into an integral

system. Although elements of abstraction still remain,

they are reduced to a minimum by the increasing tend-

ency to demand not only an algebraic symbol, but a visual

picture of the processes of nature.

e H

It is perhaps not surprising that the astonishing prog-

ress of general physics during recent times should thus

far have failed to exert any very notable influence upon

the science of biology. From the point of view of the

physicist, biological problems must be regarded as ques-

tions of special material structure, usually of a very in-

tricate character, and involving the arrangement and his-

tory of units of matter for the most part larger than those

upon which his attention is immediately concentrated.

The program of modern physics is to build up the theory

of all material structures by means of geometry and the

dynamics of electrical particles. The first problem,

logically, is that of the constitution of the atom, and as

the solution of this problem is still unfinished, too much

should not be expected of our knowledge of the config-

uration of particles and forces in higher aggregates of

matter.

However, a critic who sees current events in the light

of the history of science can hardly escape a twinge of

disappointment at the recrud in biological theory,

at the present time, of the doctrine of vitalism. The pres-

ent, of all periods in the history of thought, is an hour of

triumph of the monistic theory of nature, and yet now,

324 THE AMERICAN NATURALIST [Vou. LI

more frequently than during the nineteenth century, men

eminent in biology seem to quail before the complexity

and delicacy of the life process, and, while uttering

mechanistic truths about life, to offer them as sacrifices

to a spirit of vagueness and discouragement.*

It is my belief that this rejuvenation of mysticism and

Aristotelian teleology is due not so much to a natural ad-

miration on the part of biologists for obscure ways of

thinking, as to their neglect of modern physics and of the

methods of thought pursued in that science. It is the

purpose of this paper, which is intentionally polemical

in manner, to rebuke this tendency by commending to the

attention of biologists a general speculation concerning

the life process, which—although incapable of immediate

verification in all of its aspects—does answer the most

perplexing questions raised by vitalism, and at the same

time forms a perfectly distinct bond between biological

theory and the modern theory of matter.

It is not improbable that the future will look back upon

contemporary theoretical biology as a reactionary phase

in the history of the science. The great synthetic energy

of the Darwinian theory has been spent, has accomplished

its magnificent results, but has left many tattered ends,

by means of which a few of its enemies are attempting to

tear down the entire structure once more. Even the re-

markable discoveries which are classed under the name

Mendelism are sometimes turned against the mechanistic

conception of evolution. These discoveries, although

patently of fundamental importance for the theory of life-

processes, have as yet provided us with no new synthetic

instruments of thought, but instead have generated an

amazing and ever-growing list of abstract concepts. How-

ever, these concepts do furnish us with a means for the

analysis of species in terms of their genetic determination

and the recent studies of Morgant and Goldschmidt® in

8 Consider, for example, the contents of Haldane’s recent address on

0-632,

‘The New Physiology,’’ Science (1916), N. S., 44, 62

« Morgan, T. H., and others, ‘‘ The Sachantans of Mendelian Heredity,’’

1915,

5 See Goldschmidt, R., ‘‘Genetie Factors and Enzyme Reaction,’’ Science

No. 606] BIOLOGICAL ENIGMAS 325

this field are pointing the way to synthetic considerations

of far-reaching significance.

That biologists recognize the need of new light in the

theory of heredity and of evolution, is clearly shown by

the following quotations, from Bateson’s Silliman lec-

tures:

In Z ses OF the general attention devoted to the uae of varia-

knowledge of the chemistry and physics of living things which at pres-

ent is quite beyond our reach. It is however becoming probable that

if more knowledge of the chemical and physical structure of organisms

is to be attained, the clue will be found through genetics, and thus that

even in the uncodrdinated accumulation of facts of variation we are pro-

viding the means of analysis applicable not only to them, but to the

problems of normality also.

Again:

Somewhat as the philosophers of the seventeenth and eighteenth cen-

turies were awaiting both a chemical and a mechanical discovery which

should serve as a key to the problems of unorganized matter, so have

. biologists been awaiting two several clues. In Mendelian analysis we

have now, it is true, something comparable with the clue of chemistry,

but there is still little prospect of penetrating the obscurity which en-

velopes the mechanical aspect of our A ye morro

Again:

When with the thoughts suggested in the last chapter we contemplate

the problem of evolution at large, the hope at the present time of con-

structing even a mental picture of that process grows weak almost to

the point of vanishing. We are left wondering that so lately men in

general, whether scientifie or lay, were so easily satisfied. Our satis-

faction, as we now see, was chiefly founded on ignorance.’

It will be perceived that the demand made by Bateson

in these passages is not for new biological facts, but for

physico-chemical conceptions in terms of which a chaos

of biological facts, already at hand, can be explained, or

systematized. Moreover, the emphasis is laid entirely

upon the inability of the mind to conceive an explanation,

ee 43, 98-100, Also ‘‘Experimental Intersexuality and the Sex Prob-

>”? AMERICAN NaTuRALIST (1916), 50, 705-719.

ga ony W., ‘Problems of Geneties’’ (1913), 31, 32, and 97.

326 THE AMERICAN NATURALIST — [Vor. LI

or a synthesis of these facts, rather than upon the neces-

sity of detailed proof of some explanation which has al-

ready been offered. The contents of genetics would verify

the proper conceptions if the human mind were only

capable of suggesting them.

In another place,” Bateson says, with reference to the

mechanism of cell division:

It is, I fear, a problem rather for the physicist than for the biologist.

The sentiment may not be a popular one to utter before an assembly of

biologists, but looking at the truth impersonally, I suspect that when at

length minds of first rate analytical power are attracted to biological

problems, some advance will be made of the kind which we are awaiting.

As a matter of fact, in the school of the physical

chemists there has been in preparation, since the days of

Thomas Graham, a system of knowledge which, even in

its present unfinished form, has a most important and

direct bearing upon mooted biological problems. This

is the science of the colloidal state. The difficult abstrac-

tions and elaborate classificatory scheme, in terms of

which the theory is now stated, will tend to be cleared up

as our study of colloids comes definitely under the do-

minion of the general electro-molecular theory of matter.

Intimate contact with the latter has already been estab-

lished, indeed, through recent remarkable contributions

by Langmuir,’ dealing with the atomic constitution of

solids and liquids. It is to colloidal chemistry that we

must look for answers to the large majority of the fun-

damental problems of vital activity. These answers will

be slow in appearing, however, if we refuse to look. _

In fairness, it must of course be admitted that many

biologists are keenly alive to the importance of the theory

of matter, and especially of the theory of colloids, for the

advancement of their science. However, possibly because

the majority of these men are specialists in biochemistry,

there seems to be a lack of coherent applications of mod-

7 Loo. cit., 41.

8 Langmuir, I., ‘‘The Constitution and Fundamental Properties of Solids

and Liquids,’’ Journal of the American Chemical Society (1916), 38, 2221-

2295; and other forthcoming papers in the same journal and in the Phys-

ical Review.

No. 606] BIOLOGICAL ENIGMAS 327

ern physico-chemical ideas to the problems of evolution

and heredity, which make up the heart of the biological

mystery.

It has for some years been my conviction that the con-

ception of enzyme action, or of specific catalysis, provides

a definite, general solution for all of the fundamental bio-

logical enigmas: the mysteries of the origin of living

matter, of the source of variations, of the mechanism of

heredity and ontogeny, and of general organic regula-

tion.® In this conception I believe we can find a single,

synthetic answer to many, if not all, of the broad, out-

standing problems of theoretical biology. Itis an answer,

moreover, which links these great biological phenomena

directly with molecular physics, and perfects the unity

not alone of biology, but of the whole system of physical

science, by suggesting that what we call life is funda-

mentally a product of catalytic laws acting in colloidal

systems of matter throughout the long periods of geologic

time. This view implies no absurd attempt to reduce

every element of vital activity to enzyme action, but it

does involve a reference of all such activity to some en-

zyme action, however distantly removed from present

activity in time or space, as a necessary first cause. Ca-

talysis is essentially a determinative relationship, and

the enzyme theory of life, as a general biological hypoth-

_ esis, would claim that all intra-vital or ‘‘hereditary’’ de-

termination is, in the last analysis, catalytic.

The conception of enzyme action is, of course, one with

which all biologists, including students of genetics, are

extremely familiar.° Probably there is no student of

- morphogenesis who would not consider it absurd to deny

that enzymes play a very important rôle in individual

development. In a number of cases such participation

has been clearly demonstrated by experiment, and the

suggestion that the germ-cell contains ‘‘determiners’’ for

9See my two papers: ‘‘The Chemical Origin and Regulation of Life,’’

Monist (1914), 22, 92-134; and ‘‘The Enzyme Theory of Life,’’ Cleveland

Medical Journal (1916), 15, 377 ff.

10 On enzyme action in general, see Bayliss, W., ‘‘The Nature of Enzyme _

Action,’’ 1914.

328 THE AMERICAN NATURALIST [Von LI

the production of enzymes, which; in turn, regulate cer-

tain aspects of the development, is a common one.!

Several Mendelians have even hinted that the ‘‘ unit charac-

ters” themselves are enzymes,'* but so far as I am aware,

no worker in genetics, with the exception of Goldschmidt,

has regarded this conception as an important one. In-

deed, in the face of the nearly self-evident, they have

turned away to vitalism and despair.

Consider, for example, the Sii quotation from

Bateson.

We must not lose sight of the fact that though the factors: operate

by the production of enzymes, of bodies on which these enzymes can

act, and of intermediary substances necessary to complete the enzyme

action, yet these bodies themselves can scarcely be genetic factors, but

consequences of their existence. What are the factors themselves?

ence do they come? How do they become integral parts of the

organism? Whence, for example, came the power which is present in a

White Leghorn of destroying—probably reducing—-the pigment in its

feathers ?14

It is my contention in this and previous papers that

statements of this sort can hardly represent anything

less than intellectual blindness. On the supposition that

the actual Mendelian factors are enzymes, nearly all of

these general difficulties instantly vanish, and I am not

acquainted with any evidence which is inconsistent with

this supposition.

Up to very recent times, although a great number of

hypotheses to explain catalysis were in existence,’* no

11 See, for example, the following: Loeb, J., and Chamberlain, M. M., ‘‘ An

Attempt at a Be arr bice git Explanation of Certain Groups of Fluctuat-

ing Variations,’’ Journal of Painia Zoology (1915), 19, 559-568.

Moore, A. R., ‘‘On e delian Dominance,’’ Archiv für Entwicklungs-

em (1912), 34, 168-175. Riddle, O., ‘‘Our Kno f Melanin

r Formation and its Bearing on the Mendelian Description of Hered-

yay ? pesca Fyllelis (1908); 16, 316 ff.

12 See Bateson, ‘‘ Mendel’s Principles of Heredity,’’ 1909, 268.

13 The ests publication of experimental results of great importance in

Ep connection is promised by Goldschmidt. See above references.

14 Bateson, ‘‘ Problems of Geneties,’’ 86.

15 A comprehensive review of these theories and of the facts of catalysis

and fermentation is given by Mellor, J. W., ‘‘Chemical Statics and Dy-

namies,’’ 1914, 245-383. j

No. 606] BIOLOGICAL ENIGMAS 329

completely satisfactory general theory of the process

could be formulated. In this state of affairs, the use of

the conception as a general explanatory agent in biology,

could not be said to establish an unequivocal bond be-

tween biological regulation and the theory of matter. At

the present day, however, it is possible to frame a hy-

pothesis to account for catalytic action, which has general

applicability and at the same time rests directly upon the

ideas of modern molecular physics.

Ostwald defines a catalytic agent as ‘‘a substance which

changes the velocity of a reaction without itself being

changed by the process.’° In the older terminology of

the pioneer, Berzelius, it is ‘‘a substance which, merely

by its presence and not through its affinity, has the power

to render active affinities which are latent at ordinary

temperatures.’”7 According to Ostwald, catalytic power

is a universal property of matter, for he says:

There is probably no kind of chemical reaction which cannot be in-

fluenced catalytically, and there is no substance, element, or compound

which ean not act as a catalyzer.18

This being the case, it should often occur that a substance

will catalyze a reaction which generates further quan-

tities of the same substance, a process known as auto-

catalysis. Catalytic relationships may thus be classified

into the autocatalytic and the heterocatalytic. I shall at-

tempt to show that the former may be the more funda-

mental of the two relationships, and that reasons can be

adduced for regarding autocatalytie power as a necessary

property of every complex form of matter.

Perhaps the simplest illustration of a catalytic effect

of any sort is that of the production of crystallization in

a supersaturated solution of some substance by the intro-

duction of a small erystal of the same substance. This

of course has the form of an autocatalytic process. Al-

though effects of this kind are included in Ostwald’s

classification of varieties of catalysis,!® up to recent times

16 Mellor, loc, cit., 250.

17 Ibid., 246.

18 Ibid., 254.

19 Ibid., 255.

330 THE AMERICAN NATURALIST [Vou. LI

it might have been possible to raise a legitimate objection

to the illustration on the ground that the induced change

is not a chemical one. However, this objection is defi-

nitely disposed of by the recent work of the Braggs, and

others, on the constitution of crystals,2° which has shown

that the unit of structure in solid bodies is usually the

single atom, and not the molecule, since in crystals there

is, as a rule, no exclusive arrangement of the atoms into

molecular groups. The spacing of the atoms is such as

to make it clear, moreover, that the forces which hold the

total crystal system together are identical with those

which we regard as underlying chemical affinity. In other

words, in the crystal there is either no distinction between

inter-atomie and inter-molecular forces (i. e., between

‘ chemical affinity and cohesion), or else the entire crystal

must be considered to be a huge polymeric molecule.2! It

is therefore perfectly legitimate to treat the process of

crystallization as a chemical change, and to regard the

initiation of this process under the conditions above de-

seribed, as an example of autocatalysis, which may well

be typical.

Although the results of crystal analysis indicate that

no distinct molecules are to be found in the solid state,

this is not true of the dissolved, or of the gaseous state.

Moreover, on account of the fact that their component

particles are held in place by forces of electrical attrac-

tion and repulsion, all molecules must possess their own

fields of electrical force, and the field of any molecule

must have a spatial form which is characteristic of that

molecule. These field patterns will thus be different in

the molecules of substances which differ chemically, and

will be similar in molecules of the same or of an allied

chemical substance.?? The forces of cohesion in a crystal

may be thought of as resulting from the fusion of a large

number of these molecular fields into a continuous mosaic,

and in such manner that their several axes are parallel.

20 See Bragg, W. H., and W. L., ‘‘ X-Rays and Crystal Structure,’’ 1915,

21 Of. Langmuir, loc. cit., 2221-2222.

22 See Comstock and Troland, loc. cit., 86-89.

No. 606] BIOLOGICAL ENIGMAS 331

However, such fusion can not fail to have an influ-

ence upon both the form and the strength of the fields in

question, since it involves a redistribution of the atomic

forces. This will take the form of an opening out, or ex-

pansion, which will necessarily reduce the coherence of

the group of atoms originally forming the individual

molecule. The degree of this ‘‘opening’’ of the field

which occurs in crystallization must vary with the nature

of the molecule, and is probably smaller for organic sub-

stances than it is for the majority of inorganic com-

pounds.

= The mechanism of the autocatalytic process of crys-

tallization may be described somewhat as follows:

In a solution, or a gas, the molecules of the dissolved

substance move about at random among the molecules of

the solvent, and the orientation of the axes of their fields

is entirely haphazard. However, as soon as a crystal of

the solute is introduced, the field forces of the surface

layer of atoms attract the dissolved molecules and at the

same time tend to turn them on their axes so that, as they

condense, they will fall into the pattern of the ‘‘space lat-

tice” upon the plan of which the crystal is built.** As

this is the most stable position which they can assume,

they will tend to remain there and form a new surface

layer of the crystal, to act in turn upon further molecules

in the solution, until all of the surplus dissolved substance

has been deposited.

The primary force bringing the molecules to the erystal

face is of course not the surface field of attraction—

surface tension field—but their temperature motion—or

osmotic pressure. A similar force, of lower magnitude

in the case of a supersaturated solution, is constantly

disengaging molecules from the crystal and throwing

them back into the solution. The action apparently

ceases when the number of molecules deposited upon the

crystal surface in unit time becomes reduced—owing to

decreasing concentration—to an equality with the num-

ber leaving in the same interval.

23 Cf. ibid., 113.

332 THE AMERICAN NATURALIST [Von. LI

The essential feature of the above described mechanism

for the autocatalytie production of polymeric molecules

may be illustrated to the eye by means of a model con-

sisting of a board with a large number of small compass

needles mounted upon it. If these needles are freed from

the action of the terrestrial magnetic field and are then

shaken into a random orientation, they may remain in this

condition indefinitely. However, if a small number of

adjacent needles be turned by some outside force so as to

acquire a common direction, their combined magnetic

fields will cause other neighboring needles to swing into

line, so that the action must spread to all of the needles

on the board. The field of an ideal compass needle has a

simple bipolar pattern, and a symmetrical distribution of

forces. In the cases of specific atoms and molecules, how-

ever, this is probably seldom true. Nevertheless, the

general principles involved in their dynamic interaction

would remain the same as those for the case of the com-

pass needles.

It is clear that the explanation of autocatalysis above

given accounts immediately only for the synthesis of poly-

meric molecules from individual units which are all alike.

As a rule, chemical changes involve the interaction of dif-

ferent units, and it can easily be seen that the same gen-

eral mechanism will apply to the catalysis of reactions of

this sort as to that of simple crytallization. The prin-

ciples involved in the process have been made especially

clear in the recent articles of Langmuir.** Consider first

a solution containing two kinds of molecules which can be

deposited upon a erystal surface consisting of an orderly

arrangement of these two molecular groupings in mosaic.

or lattice form. The second species of molecules may be

considered, for example, to be those of the solvent, as in

the case of ‘‘ water of crystallization.’ There will be cer-

tain ‘‘elementary spaces’’—as Langmuir calls them—

upon the surface of the crystal, which will especially at-

tract and orient the water molecules, and adjacent ele- |

mentary spaces which will act in the same way upon the

24 Loc. cit., 2286-2292.

No. 606] BIOLOGICAL ENIGMAS 833

molecules of the solute. In this way the erystal or poly-

meric molecule will be built up out of two components by

the simultaneous and parallel action of two initially com-

_ bined species of molecular fields. This change is cat-

alyzed by the crystal, and is an autocatalytie process in-

volving the synthesis of two substances. It is clear that

any number of substances may be influenced in this way

by a similar, but more complex initial crystal form.

However, our explanation still remains somewhat spe-

cial in its application, as in the majority of cases the

products of catalysis do not adhere permanently to the

catalytic surface. The extension of the explanation to

cases of this sort is not difficult, since we have already

seen that, even in the case of crystallization, the heat

vibrations of the atoms are constantly throwing off molec-

ular groups from the surface of the solid. As pointed

out by Langmuir, the attraction between the surface and

two molecular groups which have a strong affinity for

each other may be less than the sum of the attractions of

the surface for each of the groups, when separate.2> This

is due to the ‘‘closing up’’ or contraction of the fields of

force of the groups as they come together. Hence com-

bined groups of this sort will be more easily detached

from the surface than will the uncombined groups, which

will tend to be held in place until their mates fall into the

right positions. The catalytic surface thus acts like an

orienting sieve which on account of its special structure

forces a chaotic crowd of individuals which come into con-

tact with it, to fall into a special configuration. Many

machines which accomplish exactly this effect are in use

in the industries.

Thus far we have dealt only with the mechanism of

autocatalysis. Heterocatalysis is probably to be regarded

as an extension of the process of autocatalysis. It is

obvious that exact similarity of the force patterns of the

catalyzing and catalyzed systems is not essential. In-

deed, the catalytic effect which is based upon direct simi-

larity of structure between the two systems should be

25 Ibid., 2257, 2264-2266.

334 THE AMERICAN NATURALIST [Von. LI

much weaker than that which accompanies certain types

of structural correspondence, such as that existing be-

tween a body and its mirror-image, or between a lock and

a key. Special structural relations of this sort probably

exist between stereochemical isomers, between acids and

bases, ete. It is easily conceivable that the patterns of

certain surfaces may be capable of distorting other special

configurations which come under their influence, so that

they fall into new equilibrium figures, without these

figures being of necessity identical with those of the

catalytic system. The general principles of the action,

however, remain the same.

Catalytic synthesis is a less common process in the

laboratory than is destructive catalysis, but the laws of

energy necessitate both effects, if either one is possible.

Consequently the mechanism which we have described

above must be an exactly reversible one, and must assist

in the decomposition of molecular complexes as much as

it aids in their synthesis. The deposition of the mole-

cules to be decomposed, upon the catalytic surface would

naturally follow the same principles as those stated for

simple polymerization. In this state of deposition the

. field forces of the crystal surface would inevitably have a

tendency to open up the field of the deposited molecule,

thus rendering it more unstable than before, in which con-

dition the temperature vibrations of the system could

break it up more easily than in the undeposited state. —

This weakening of the internal bonds of the molecule

in the field of the catalytic surface corresponds with the

weakening of forces of electrical attraction by increasing

the ‘‘dielectrie capacity’’ of the medium in which an elec-

trical system is contained. It is the same action which

permits water to dissociate neutral molecules into ions,?°

and is probably responsible for the high catalytic power

of water, in general. However, in detail, the process must

be a ‘‘personal’”’ affair between individual water mole-

cules and molecules of the dissolved substance, just as

in the case of the crystal surface, since the ionizing effect

26 Cf, Comstock and Troland, loc. cit., 139-140.

No. 606] BIOLOGICAL ENIGMAS 335

of water does not appear to depend merely upon the

chemical instability of the solute.

The increase in reaction velocity which characterizes

catalysis is to be attributed to three more or less sep-

arable influences exerted by the catalytic surface, (1) the

local increase in the concentrations of the reacting sub-

stances at the surface, (2) the impressment upon the

attached molecules, of a relative orientation which is

favorable to chemical union, or which in part constitutes

such union, and (3) the spreading and weakening of the

fields of force of the molecules, due to their interaction

with the surface fields. The first factor, alone, would be

of primary importance for the combination of free atoms

—a relatively rare process—while the last factor, alone,

would be responsible for the acceleration of simple de-

compositions. Reactions between two or more molecular

groups, whether synthetic or metathetic, should be influ-

enced by all three factors. Strutt” -has shown that in |

certain typical chemical reactions, only one out of many

millions of collisions between potentially reactable mole-

cules results in chemical interaction. The active collisions

probably coincide with the presence in the colliding sys-

tem of favorable relative orientati and states of tlie

molecular fields, which in the absence of a catalyzer de-

pend upon chance, but which in the presence of a catalyzer `

are encouraged by the nature of the catalytic surface.

It is of course not possible in a paper of this sort to

enter into the mathematics of the theory of catalysis which

is outlined above.?® Catalytic influence is obviously only

one among many factors which affect a chemical reaction.

Catalysis is possible only when the appropriate raw ma-

terials are provided, and when the energy relations of the

system are such as to make the reaction thermodynam-

ically conceivable. The heterocatalytic effect of a given

substance may far outweigh its autocatalytic effect either

27 Strutt, R. J., ‘‘ Molecular Statisties of Some Chemical Actions,’’ Pro-

ceedings of the Royal Society (1912), A, 87, 302-309.

28 Cf. Mellor, loc cit., 250-254, Also Bayliss, loc. cit., 49-71.

29 For a development of the mass action relationships involved, see Lang-

muir, loc. cit., 2287 ff.

336 THE AMERICAN NATURALIST (Von. LI

because the energy changes do not favor the-.latter, or be-

cause in a given system the raw material for the auto-

catalytic reaction is absent, while that for the hetero-

catalytic reaction is present in abundance.

However, the above considerations would lead us to be-

lieve that all substances should show some tendency to form

polymeric molecules or crystals. This appears to conflict

with the classical division of substances into erystalloids

and colloids, but this division, like all others, can not be

expected to stand unmodified by the modern analysis.

There is plenty of evidence from direct observation that

many colloidal particles are simply very small crystals.”

On the other hand, the molecules of polymeric substances

of high molecular weight, such as starch and certain pro-

teins, are probably of the same order of magnitude as

small colloidal particles. From the point of view of the

theory of matter, there is no fundamental difference be-

tween the general plan of a starch molecule and that of a

crystal of sugar, and it is highly probable that the dis-

tinction between colloids and ecrystalloids rests upon

purely quantitative relations, respecting the size of the

polymeric structures (crystals) produced under ordinary

conditions.

Large crystals are formed easily by simple substances

whose molecules have open fields of force or highly un-

saturated attractions. Small crystals are characteristic

of more complex substances, common among the com-

pounds of carbon, having relatively closed fields. Large

mosaics of such molecules become unwieldy and are easily

disrupted by the temperature vibrations. They are also

built up more slowly than are mosaics of molecules with

open fields. The distinction between these two classes of

molecules is of course merely quantitative; no type of

molecule has a completely closed field, and on the other

hand no substance is capable of forming indefinitely large

crystals in a finite length of time. The atomic structure

of the solid phase of a colloidal gel is probably analogous

30 See Ostwald, Wo., ‘‘A Handbook of Colloid-Chemistry,’’ English trans-

lation, 1915, 56-66.

No. 606] BIOLOGICAL ENIGMAS 337

to that of the mass of small crystals, compacted together,

which always results from the rapid crystallization of a

supersaturated solution of a substance like, e. g., sodium

thiosulphate.

It is evident, then, that the general theory of catalysis

which has been outlined is applicable to enzyme action,

which almost certainly depends upon the deposition, or

adsorption of the reacting substances upon the surfaces

of colloidal particles.*t Such adsorption, the molecular

mechanism of which has been made very clear by Lang-

muir,®* will tend to be specific, and the more specific the

more complex is the structure of the units making up the

mosaic of the surface. Molecules the field patterns of

which fit closely into the fields of the surface will tend to

displace others having a cruder correspondence. This

follows from either electro-dynamies or thermodynamics,

and obviously coincides with Fischer’s classical concep-

tion of the lock and key relation between enzyme and sub-

strate.**

It will be perceived that our theory of the catalytic

process is simply a refinement and extension of the clas-

sical theory of ‘‘intermediate compounds,’’ which has

been proven true in so many instances.** ‘‘ Adsorption

compounds,” which play the principal rôle in enzyme

action, do not differ dynamically from chemical com-

pounds in general, since the forces causing adsorption

are the same as those responsible for chemical union.

Conversely, catalytic action in which the catalyst is in a

molecular or unpolymerized state will not necessarily

differ in its mechanism from that characteristic of en-

zymes or of metallic surfaces.

The suggestion that the fundamental life-process of

growth is the expression of an autocatalytie chemical re-

31 See Bayliss, loc. cit., 104-123.

.32 Loc, cit., 2267-2278.

33 See Mellor, loc. cit., 363.

34 Cf., e. g., Kendall, J., and Booge, J. E., t‘ Studies on Catalysis. I. The

Addition Compounds of Esters with Grpiste Acids,’’ Journal of the Amer-

ican Chemical Society (1916), 38, 1712-1736.

338 THE AMERICAN NATURALIST [Von. LI

action has been made independently by a number of in-

vestigators.*> It will be perceived that on the basis of

the foregoing theory of autocatalysis, this suggestion

becomes closely allied to the familiar and ancient com-

parison of vital growth to the growth of a crystal. The

customary objection to this comparison, viz., that a erys-

tal grows by accretion whereas protoplasm increases by

intussusception, loses its force as soon as we regard liv-

ing matter as a complex mixture of substances suspended

by colloidal subdivision in water, since there is no evi-

dence that the individual colloidal particles do not grow

by accretion. On the contrary, it is almost inconceivable

that these bodies, which are the real chemical units of pro-

toplasm, should grow in any other way. The growth of

a system like a cell could be regarded as the resultant

effect of a very large number of component growths, each

governed by its specific autocatalytic mechanism. It has

been shown by T. B. Robertson** that growth curves, with

respect to the time, actually do coincide in general form

with the curve characteristic of an autocatalytic reaction.

A multitude of observations substantiate the belief that

the internal determination of cell-life rests primarily with

the nucleus,®? or with the chromatin substance of the cell,

when no well-defined nucleus is present. Even in the

highly organized cell, this substance can be seen to pos-

sess a mosaic structure, and it ean be shown that for a

given species this structure is sensibly constant,** so that

it is necessary to suppose that a reduplication of chromatin

units occurs with each cell-division. This process of re-

duplication is apparently made visible to us in mitosis.

35 See, for example, esis W, ‘t Ueber die zeitlichen Epe ane der

a Vorträge und Aufsätze über wicklungs-

E oe herausgegeben von W, Roux ( sor » Hoeft 5,

Leipzig.

36 Robertson, T. B., ‘On the Normal Rate of Growth of an Individual and

its Seppia Significance, ’” Archiv fiir sbi sir nae (1908), 25,

cael iy hi ep ee articles in the sa

n, E. B., ‘‘ The Cell in Develbinds wiy Inheritance,’’ second

54.

edition, uren l 1911), 30-31, 341

38 Cf. Boveri’s Individualitäts Hypothese and ‘‘law of proportional nuclear

growth. ”?

No. 606] BIOLOGICAL ENIGMAS 339

The simplest hypothesis to account for such reproduction

lies in the supposition that each unit can give rise to an-

other unit substantially identical with itself.

The Weismannian theory of the constitution of the

germ plasm,*® which is typical of the so-called ‘‘corpus-

cular theories’’ of the life-process or of heredity, also de-

mands the existence of vital elements, each possessing

the power of reproduction ad infinitum. The general

conceptions of this theory appear to find verification, first,

in the facts already mentioned, and second, in the discov-

eries of Mendelism. The recent work of Morgan and his

collaborators,#? moreover, reveals clearly the intimate

connection which exists between the corpuscular ‘‘unit

characters” of Mendelian heredity and the histological

units present in the chromosomes. Consequently, it

would seem to be a fairly safe generalization, or at least

an extremely probable hypothesis, which states that the

distinctive properties of cells, tissues, and species are

primarily determined by the nature of systems of colloidal

particles contained in cell-nuclei and, originally, in some

germ-cell nucleus.

However, in spite of the seeming strength of the evi-

dence, some biologists are of the opinion that such a view

as this must be rejected because it paralyzes thought.

Consider, for example, the following quotation from

Chid.“

It is scarcely necessary to call attention to the fact that these [cor-

puscular] theories do not help us in any way to solve any of the fun-

damental problems of biology; they merely serve to place these prob-

lems beyond the reach of scientific investigation. The hypothetical

units are themselves organisms with all the essential characteristics of

the organisms that we know; they possess a definite constitution, they

grow at the expense of nutritive material, they reproduce their kind.

In other words, the problems of development, growth, reproduction,

and inheritance exist for each of them, and the assumption of their

existence brings us not a step nearer the solution of any of these p

ems. These theories are nothing more nor less than translations of

the phenomena of life as we know them into terms of the activity of

39 Weismann, A., ‘‘The Germ Plasm,’’ English translation, 1893.

40 Loe. cit.

41 Child, C. M., ‘‘ Senescence and Rejuvenescence,’’ 1915, 11-12,

340 THE AMERICAN NATURALIST [Von. LI

raultitudes of invisible hypothetical organisms, and therefore contribute

nothing in the way of real advance. No valid evidence for the existence

of these units exists, but if their existence were to be demonstrated we

might well despair of gaining any actual knowledge of life.

We have in this passage a clear statement of the essen-

tiality of growth, as self-reduplication of specific sub-

stance, in the life-process. Consideration of Child’s re-

marks will show that.the difficulties which he raises are

almost completely dissolved as soon as we postulate for

the biological corpuscles the power of autocatalysis. In

the light of our previous discussion, it can not be claimed

that this is purely a verbal solution of the problem, as we

have advanced definite reasons for believing that auto-

catalytic activity is a property of all chemical substances

whatsoever, given the appropriate chemical’ environment.

Since the environment of the chromatin particles has been

made to order by evolution, the force of Child’s criticisms

would seem to be nil. Moreover, he certainly underesti-

mates the importance of the facts which point to an actual

corpuscular determination of vital functions.

In view of this, it would appear advisable to aecept the

Elementarorganismen'? as if they were clearly estab-

lished facts, and proceed to consider what further light

ean be thrown upon biological problems by the conception

of specifie catalysis.

It is well known that in many cases, at least, the nucleus

controls cell activity by liberating enzymes,** and the

mass activity of cells in the form of specific tissues has

been satisfactorily proven to depend, so far as it is di-

rectly chemical, upon the presence in these tissues’ of

specific enzymes. In the field of general adult metabolism

the determinative importance of catalysis would appear

to be no longer a matter of debate. Analogy would lead

us to believe that the same principle is of prime impor-

tance in the metabolism of development.

In laying emphasis upon the cardinal importance of the

riicke, Se Akademie der Wissenschaften, Wien,

42 See

PA, 44, (2), 381-4

43 See ‘Ment nu, G., * irs Chemistry of the ma g Rie 454 ff. Also,

Loeb, J., ‘‘ The Dynamics of Living Matter,” 1906,

No. 606] BIOLOGICAL ENIGMAS 341

enzyme for organic regulation we must of course recog-

nize that the exact effects produced by catalysis depend,

at all stages of development, upon the manner of its co-

operation with other physical principles, which may in-

volve the functioning of molar structures already pres-

ent. However, as we retrace the course of ontogeny and

of the evolution of any specific germ-cell, we should find

that the number and importance of such structures de-

crease, although the construction of any given tissue-

form always depends upon the action of specific enzymes

in conjunction with preéxisting tissue structures. It is

not to be doubted for an instant that important preéstab-

lished structures exist even in germ-cells, and enter into

the determination of their activity. It is therefore un-

fair to demand a catalytic explanation of such a complex

process as karyokinesis, which shall not take into con-

sideration the history or evolution of the cell.

The task of elucidating the exact mechanism by means

of which vital regulation is maintained, and especially of

showing how, in accordance with recognized principles |

of physics, a complex of specific, autocatalytic, colloidal

particles in the germ-cell can engineer the construction

of a vertebrate organism, is truly'so formidable that it is

unkind for the vitalist arbitrarily to deny us the use of

any of these recognized principles. For example, we

must be permitted to suppose that a large number of

variables can unite in the production of a single effect.

The greater part of the modern vitalistie worry over ‘‘or-

ganization” and vital ‘‘equilibrium’’** appears to depend

upon a tacit assumption, either that physical laws are not

reliable, or that it is impossible for a number of variables —

to control simultaneously a single process. Both of these

assumptions are self-evidently counter to the most funda- |

mental presuppositions of physical analysis. -

Although the fundamental life-property of the chro-

matin units is that of autocatalysis, it is necessary and

legitimate to suppose that the majority of them sustain

specific heterocatalytie relationships to reactions oc-

44 Consider, for example, Haldane, loc. cit.

342 THE AMERICAN NATURALIST [Vou. LI

curring in living matter. This is because nuclear ma-

terial makes up a relatively small percentage of proto-

plasm, and because the reactions governed by enzymes

are ordinarily heterocatalytic.

It is a remarkable fact that the chemistry of the cell-

nucleus has reached a stage of advancement superior to

that attained by the chemistry of the cytoplasm. It ap-

pears that the essential constituent of chromatin is a sub-

stance called nuclein, which is composed of a basic, pro-

tein factor and nucleic acid. The facts indicate that the

acid factor is the permanent and essential component of

the nucleus, and organic chemical analysis seems to prove

that only one kind of nucleic acid exists in animal tissues,

although a different variety is to be found in the cells of

plants.*® If, as now seems probable, the genetic enzymes

must be identified with the nucleic acids, we shall be

forced to suppose that these substances, although homo-

geneous—in animal or plant—from the point of view of

ordinary chemical analysis, are actually built up in the

living chromatin, into highly differentiated colloidal, and

colloidal-molar, structures. The apparent homogeneity

results from the fact that ordinary chemical analysis pro-

vides us only with the statistics of the fundamental

radicles which are involved.

To some minds, the idea that a portion of matter as

small as a germ-cell can contain sufficient catalytic sub-

stance to control the destinies of a complex organism,

seems hardly plausible. However, considering the slow-

ness of such processes as growth, it is clear that the quan-

tity of catalyzer required will usually be smaller than that

used in laboratory experiments; and it is a truism in

chemistry that radical alterations of reaction velocities

ean be caused by the presence of almost infinitesimal

amounts of catalytic material. From the nature of the

process, it is evident that only a few molecules of sub-

stance will be required to furnish the basis for an auto-

catalytic reaction which may eventually result in the pro-

45 See Jones, W., ‘‘ The Nucleic Acids,’’ 1914,

46 See Mellor, loc. cit., 248-249.

No. 606] BIOLOGICAL ENIGMAS 343

duction of any desired amount of this substance; and a

simple calculation shows that the chromatin of the human

zygote has sufficient volume to contain about one quad-

rillion (101°) molecules the size of that of oxygen.*7

In order that the enzymes of the germ-cell should be

able to determine the form of the mature organism, they

must have the power to govern (1) the physical and chem-

ical properties of specific tissue material, (2) the posi-

tion of specific tissues, (3) the size of these tissues and

(4) their form. Since the physical properties of any

piece of matter depend upon its chemical constitution,

and since any chemical change can be regulated by

catalysis, the mere presence of a specific catalyzer in a

favorable mixture is sufficient to determine the produc-

tion of matter of any possible variety, in any possible

amount. It is always necessary to assume that the his-

tory of an organic system is such as to have provided it

with the raw materials necessary to its activities. If this

is not the case, the system naturally perishes of ‘‘star-

vation.”

The most primitive form of cell-division involves noth-

ing more than reduplication, and this is the law of mul-

tiplication of the germ-plasm. Driescht8 argues that to

explain the reproduction of a nuclear ‘‘machine’’ which

determines development, we must postulate another ma-

chine to carry out the operation, and so on ad infinitum.

The nature of the autocatalytic process, however, shows

that this conclusion is in error, since pure autocatalysis

would tend to bring about an exact qualitative reproduc-

tion of any given plane or linear mosaic of specific units.

In a nutritive medium such a mesaic would tend to grow

in all of its parts by the deposition of similar substance.

Primitive nuclear division (as, e. g., in the Protista) may

depend solely upon the physical instability of colloidal

particles greater than a certain size, but it can hardly be

47 This calculation is based on the following assumptions: (1) that the

diameter of the germ-cell nucleus is .05 mm., and (2) that the molecules

fill only one-sixth of the total volume of the nucleus.

48 Driesch, H., ‘‘The Science and Philosophy of the Organism,’’ 1908, 2,

341.

344 THE AMERICAN NATURALIST [Vou. LI

doubted that the complex mechanism of mitosis rests

upon definite structural machinery, established by long

periods of evolution.

In order to account for the differentiation of cell-nature

which occurs in ontology, Weismann was led to assume

a thoroughgoing differential segregation of the biophores

of the original germ-cell in the course of embryological

development; in other words, he supposed that in this

process the rule of nuclear division is differentiation and

not reduplication. This assumption, although undoubt-

edly a partial truth, is neither necessary nor in harmony

with general biological probabilities, in the form in which

it was made by Weismann.*® Consequently the difficulties

into which it has led his general theory, can be regarded

as without important bearing upon the acceptability of

corpuscular hypotheses at large.

Since reduplicating division is the established rule

among unicellular organisms—which must have had a

long evolutionary history—we should expect this rule to

be conserved as far as possible in multicellular evolution.

According to the general law of recapitulation, this should

be especially true for the primary stages of ontogeny, for

which Driesch’s principle of the ‘‘equipotential system”’

appears often to hold. The blastula may well be simply

an undifferentiated mass of germ-cells, analogous to a

homogeneous colony of unicellular forms. Rudimentary

differentiation may be brought about and determined

by specific enzyme constitution, without differential par-

titionment of enzymes in segmentation, since the forces

acting upon any cell must depend upon its position in the

- mass, and the activation or inhibition of a given enzyme

may be conditioned by the presence of definite stimuli in

definite intensities. This being the case, any cell could

assume germinal characters if isolated from the total

mass.°°

49 Weismann’s theory, it must be recognized, assumes ‘‘doubling divi-

sion’’ for the early “ae of segmentation, a law which continues to hold

for the ‘‘ germ-tracks.’

50 Of. Hertwig, O., ‘Evolution or Epigenesis,’’ English translation, 1896.

No. 606] BIOLOGICAL ENIGMAS 345

However, the facts of ‘‘crossing over’’ observed in re-

cent studies on the relation between Mendelian charac-

ters and chromosome constitution®! show that the latter

is not inviolate, even in purely germinal segmentation.

Since the power possessed by cells to assume germinal

character, even to the limited degree of. being able to

regenerate a single organ or tissue, seems to vary in in-

verse proportion to the degree of specialization of the

cells, it is reasonable to suppose that Weismann’s prin-

ciple of differentiating division actually does operate in

the higher stages of development. However, at no stage

is it the only mechanism of differentiation, and it cer-

tainly is not the primitive means.

It is possible that cancer represents a return of tissue

cells to a germinal or semi-germinal stage, due to the

failure of a ‘‘stimulus of differentiation’’ to remain ef-

fective.

The control by the genetic enzymes of the position, size

and form of specific tissues must involve, first, a quanti-

tative regulation of the process of differentiation, which

can be effected by the establishment of definite relations

between the chemical constants of the catalytic reactions

and the conditions under which the course of development

necessarily places them; and, second, control of the planes

of segmentation of the cells. To attempt a specification

of the exact process by which this latter factor can be

governed by the chemical constitution of the cell-nucleus,

lies beyond the scope of the present paper, but it should

be pointed out that in the last analysis chemical constitu-

tion means nothing but a definite spatial arrangement of

electrical forces, so that there is nothing paradoxical in

the determination of ‘‘pure form’’ by chemical agents.

As is evident in the quotations made above from Bate-

son, the dominant problem in the modern discussion of

evolution is that of the origin of variations. ` It is the

failure of Neo-Darwinians to explain the appearance of

variations, and especially of new unit characters, which

has led such writers as Driesch, Korschinsky and Wolff

51 See Morgan, loc. cit.,

346 THE AMERICAN NATURALIST [Vón LI

to speak of the ‘‘episode of Darwinism’’ and of Das

Sterbelager des Darwinismus.®°2 The enzyme theory of

vital determination brings new life to the doctrine of evo-

lution by accidental variation and natural selection, first,

by showing that all fundamental variations should be dis-

continuous, or heterogenetic, as demanded by the muta-

tion theory of De Vries, and second by revealing the exact

mechanism of the production of these variations. The

discontinuity follows from the existence of qualitative

gaps between all specific chemical substances, such as

those making up the system of genetic enzymes. The

mechanism of production of variations is simply that of

the initial production of any new chemical individual, i. e.,

the fortuitous encounter of the appropriate molecules

with the right relative orientations and at the correct

speeds (vide supra). The ‘‘chance’’ nature of variation

thus is made to depend upon that ‘‘molecular chaos”’

which is so very familiar to all physicists, but the impli-

cations of which for biology have thus far been largely

neglected.

A moment’s thought will show that, on the basis of the

enzyme theory, variation should be additive, since an

autocatalytic individual, once established, will tend auto-

matically to maintain itself. The complete elimination of

such individuals will oceur only through the destruction

of the entire germinal mosaic of which they form a part,

an effect accomplished by natural selection unless the new

enzyme is in harmony with functions which preserve the

organism. It is very important to bear in mind that the

catalytic complex which is supposed to underlie organic

development and regulation has been determined in its

nature by excessively exhaustive practical tests and, as a

complex, by nothing else. It is therefore not surprising

that the practical delicacy of the regulation which it actu-

ally subserves should be very great.

In other papers, I have discussed somewhat in detail

the bearing of the enzyme theory upon the problem of the

origin of life. On the basis provided by this theory, the

52 See Kellogg, V. L., ‘‘ Darwinism To-day,’’ 1907.

No. 606] BIOLOGICAL ENIGMAS 347

origin of life can not be regarded as a catastrophic event;

life depends upon an organized complex of selected cat-

alytic material, and hence some life originates with each

new, successful mutation. Of course, if we trace the proc-

ess of the evolution of any given species back sufficiently

far, we must eventually come to the first mutation, which

would consist in the molecular production of an auto-

catalytic particle sustaining relations with its environ-

ment such as to make possible its continued growth and

reproduction. I have used the name protase to stand for

the ‘‘first enzyme’? of the archebiotic process, but there is

no particular reason for supposing that there was only

one enzyme to which this name could apply.

There is considerable evidence that free autocatalytic

enzymes exist in our biological universe even at the pres-

ent day. Such an hypothesis would serve to account for

the specific contagious diseases, such as measles, rabies,

and smallpox, which have been demonstrated to possess

‘‘filterable viruses.’ The so-called Chlamydozoa prob-

ably fall in this class.

That the Chlamydozoa consist of free chromatin ma-

terial is suggested by the late Professor Minchin, in his

admirable paper on the evolution of the cell,®* with the

main outlines of which the enzyme theory would entirely

agree. The single cell, and so-called simple protoplasm,

must be regarded as the products of a detailed process of

evolution, and hence can not form the ultimate explanatory

units in biology. Next to the free autocatalytic particle,

the simplest typical life-structure would consist of a single

particle of this sort surrounded by an envelope of semi-

liquid and chemically homogeneous substance with which

it sustains a heterocatalytic relationship. “The most

primitive substance of this kind might be called eoplasm,

to distinguish it from complex protoplasm, and the phys-

ical system made up of protase and eoplasm would repre-

sent a living cell in its most reduced form.

Minchin says, in the article referred to :**

53 Minchin, E. A., ‘The Evolution of the Cell,’? AMERICAN NATURALIST

(1916), 50, 5-39, 106-119.

54 Loc. cit., 35-36.

348 THE AMERICAN NATURALIST [Von. LI

The biochemist renders inestimable services in elucidating the chem-

ical mechanisms of living organisms but the problem of individuality

and specific behavior, as manifested by living things, is beyond the

scope of his science, at least at present. Such problems are essentially

of distinctive vital nature and their treatment can not be brought satis-

factorily into relation at the present time with the physico-chemical in-

teractions of the substances composing the living body.

in a certain historical epoch, and that in the future the chemist will be

able to correlate the individuality of living beings with their chemico-

physical properties, and so explain to us how living beings first came

into existence; how, that is to say, a combination of chemical substances,

each owing its characteristic properties to a definite molecular composi-

tion, can produce a living individual in which specific properties are

associated with matter in a state of flux.

It is my contention that the enzyme theory of life satis-

factorily meets these general requirements.

To arrive at a proper estimate of the importance of a

general theory such as the one discussed in the present

paper, necessitates considerable reflection. The path of

scientific progress is beset by the pitfalls of conservative

empiricism, on the one hand, and by those of radical spec-

ulation, on the other. ‘To the radicals the enzyme theory

presents an aspect of a priori self-evidence; to the con-

servatives it seems to be a vague generalization with no

particular or specific facts to support it, approximately

on the same plane as the statement that ‘‘life is motion,”

which Driesch says is about as useful as the proposition

that ‘‘Kant was a vertebrate.’’ Regarding the general

enzyme theory, the following opinion has been expressed

to me privately by an eminent zoologist.

The idea... is a perfectly familiar one. The trouble comes when

we attempt to make a specific application of this idea. to a concrete

problem, which is what science demands if a pure speculation is to

become a valuable working hypothesis. For instance, how an auto-

pratense molecule could produce the phenomena seen in the division of

chromosomes in the cell is by no means clear; nor is it clear why

pies molecules brought together during fertilization separate from each

other at the maturation division. It is these specifie questions that

must first be answered, I think, before we can make much advance, i in

No. 606] BIOLOGICAL ENIGMAS 349

regard to the nature of the phenomena. ... Of course, I realize that

general ideas are always important for the development of science,

only I think they should be advanced with caution and all attempts to

make them appear as specific explanations should be avoided.

_ There are a number of principles of scientific meth-

odology which have a bearing upon criticisms of this

sort. In the first place such a statement as that ‘‘life is

motion’’ would have value at a time when the connection

between these two ideas had not been noted, or had been

underemphasized to such an extent that eminent scien-

tists were bemoaning the inability of the human mind to

account for properties of life which the most superficial

examination would show to be identical with those of

motion. From my own point of view the proposition that

‘*life is determined by specific catalysis’’ appears to be

somewhat of the nature of a truism, indeed so much so

that even if we had no direct evidence for the existence

of enzyme action, we should be forced to invent the con-

ception to account for the most general properties of liv-

ing systems. It seems to me that this is exactly what a

considerable number of biologists actually have done, and

the only important error in their thinking lies in the ap-

plication to the concept of such names as ‘‘biophore,”’

‘‘determinant,’’ ‘‘unit character,” ‘‘formative factor,”

‘*Elementarorganism,’’ ‘‘élan vital, or ‘‘entelechy.’’

This error, however, is fatal to progress, as it multiplies

terminology and delays the synthesis of actual ideas which

is the goal of scientific endeavor.

Furthermore, it is not true that the establishment of a

general principle necessitates an examination of all of

the concrete details of specific systems. If this were so,

none of the fundamental laws of mechanics, such as the

first and second laws of energetics or Hamilton’s prin-

ciple, would possess- any rigidity, since they are derived

from a study of what may be called the ‘‘entrance and

exit’’ properties of mechanical systems, without reference

to their exact contents. It is to be admitted, of course,

that we can not rest content with this kind of knowledge, -

and that principles of this sort receive complete elucida-

350 THE AMERICAN NATURALIST > [Vou LI

tion only when the details of all systems are made clear,

but the security of the principles themselves is attected

searcely at all by this analysis.

I do not claim that the enzyme theory of life possesses

a general basis as adequate, for example, as that of the

principle of least action. I do claim, however, that this

is because the latter can be stated in terms of an exact

mathematical formula, whereas the enzyme theory has to

be given a qualitative description. The enzyme doctrine

is supported at the present time by a considerable number

of specific facts of cell chemistry, but it possesses a far

more substantial bulwark in the general facts of vital

function. Shall we deny that these facts are adequately

established, or that they are important, or that they merit

explanation? Shall we reject a definite physico-chemical

conception which at one stroke explains the majority of

the mass relationships of living matter, on the ground

that the details of some special life-processes have not yet

been described in terms of this conception? Or is it

preferable to preserve the inexplication of these same

generalities to furnish a basis for vitalism?

There are an indefinitely large number of ways in which

the principle of the conservation of energy can be exem-

plified in special pieces of machinery, and there are just

as many ways in which the principle of specific catalysis

can operate. Instead of holding the energy principle in

abeyance until we have seen how the action of a special

mechanical system can be explained in terms of it, we

usually assume it to be true, and shortly find the action

in question very easy to understand. This would seem to

be the only feasible method for employing any theoretical

proposition, even if it is merely a novel working hypoth-

esis. The trouble which arises in the attempt to apply the

enzyme theory to specific problems is a normal result of

the inertia of the human imagination, which does not im-

mediately outline a plan for a machine to accomplish a

definite purpose, even when it is provided with all of the

principles of mechanics. Surely, however, the plan can

never be developed if such principles are neglected.

MUTATION IN DIDINIUM NASUTUM

S. O. MAST

ZOOLOGICAL LABORATORY OF THE JOHNS HOPKINS UNIVERSITY

Tae origin of heritable variations or mutations consti-

tutes one of the most fundamental problems of biology.

It has long since been recognized that evolution depends

upon such variations, and they have consequently been

extensively studied by a considerable number of inves-

tigators, e. g., Darwin, DeVries, Batson, Kammerer,

Tower, Stockard, MacDougal, Jennings, Morgan, et al.

These studies have resulted in the accumulation of a mass

of facts of great importance, but the nature of the origin

of the variations in question is still shrouded in mystery.

In a series of experiments on the effect of conjugation

and encystment in Didinium, extending from April, 1910,

to May, 1914, there suddenly appeared, in the latter part

of July, 1912, a marked difference in the rate of fission in

the progeny of a single individual. This difference ap-

pears to have been permanent, as the results presented

herewith indicate. And it seems to show, in opposition to

the conclusions reached by a considerable number of in-

vestigators, that variations in organisms reproducing

asexually are at times heritable.

The difference in rate of fission mentioned was discov-

ered in a group of five pure lines, all of which had been

carried from the beginning of the experiment. These

lines all originated from the same individual, and before

the mutation occurred they had produced, without con-

jugating, an average of 721 generations; and without en-

eysting, 197 generations. Throughout this entire period

there was remarkably little difference in the rate of fission

in the five lines. The total number of fissions produced

by these lines during the 40 days.immediately preceding

the appearance of the mutation was respectively 164, 171,

351

352 THE AMERICAN NATURALIST [Von. LI

168, 166, and 168. Thus it is obvious that in the ancestors

of the mutants nothing in the nature of mutations in the

rate of fission had occurred for many generations. This

indicates that mutations do not ordinarily occur in asexual

reproduction.

During the period of 40 days mentioned above, ending

July 10, all of the lines were in excellent condition and

not a single individual died. On July 12, however, one

line died out and on the 14th three more died, leaving but

one line. For several days preceding the temperature

was very high. It was recorded twice daily and these

records show that it reached a maximum on July 9, when

it was 28.5° at 7:30 a.m. and 31° at 6 p.m. It was, how-

ever, high continuously from the 4th on, and during this

period reproduction was exceedingly rapid, as Table I

indicates. It was at the close of this period of rapid mul-

tiplication that the four lines mentioned above died out

and it is probable that this extraordinary environmental

condition had much to do with the nature of the variations

in the progeny of the remaining line, although similar

variations did not occur in four other groups of lines that

were running parallel with the one under consideration.

From the remaining line mentioned above five new lines

were started on July 15. For the first five days, the rate ©

of fission in these lines was nearly the same, the total

number per line being 26, 27, 28, 26 and 28, respectively.

During the next five days the difference became somewhat

greater, the total number of fissions per line being 21, 19,

18, 17 and 17, respectively. On the day following this

period, the line which had produced 19 fissions died out

and was replaced by a new line from the one which had

produced 21. There were thus two lines having more

rapidly, and three lines having less rapidly, dividing an-

cestors, all, however, originating from the same indi-

vidual. On October 14 the lines in both groups were in-

ereased to five and thus they were continued until the

close of the experiment, which extended through 315 days.

The individuals in all of the lines in each group repro-

No. 606] MUTATION IN DIDINIUM NASUTUM 353

TABLE I

THE RELATION BETWEEN THE FISSION-RATES OF Two STRAINS OR GROUPS OF

Lines ISOLATED FROM THE PROGENY OF A SINGLE DIDINIUM

June 1, 1912 to May 27, 1913

Each column under the brackets represents a line and each number in the

column the total number of fissions for five days; d indicates that the line

died out; c, that it eneysted; the brackets show the ancestry of the new lines

lines that died out are indicated in the table. Whenever a line died out

more than once in a five-day period, as sometimes happened, it is recorded

only once.

: Average Total No.

Fissions for Five-day

Periods

Pure Line with 553 + Generations without Conjugation

First Second

Group of Group of

Lines Lines

23; 23 22 21 22

14 15 14 15 15

17 18 18 af 17

18 19 18 18 21

20 21 21 21 20

23 22 22 21

21 22 21 21 23

28 31 32 31 29

Total 164 171 168 166 168

30 d d d d

26) 27 28 26 264

21 19 18 17 17 20 17

d 22 d d 22 22

i7| S 15 15 15 17} 15

20 15 16 16 20 154

d 26 20 22 21 26

24 24 a, 19 24 184

25 18 24 19 ri

20 21 13 18 15 204 15

c 19 15 16 15 19 54

26 | 20 21 21

25 24 19 19 20 244 19}

A bys ‘17 14 15 14 17 if

15 16 12 12 11 1 11

d 13 9 9 9 11 9

7 3 5 1

15 16 12 11 9 153 104

d 1 13 13 15 18 134

8 10 | 8 || 6 7 5

5643, 38 1-38 neS 9 9 12: 8%

354

THE AMERICAN NATURALIST

TABLE I (continued)

[Vou. LI

at wW

el 42

121-12

mH n

9i I0

9-10

10 | 10

9 9

10 | 10

10 d

10) 11

11 | e

41 | 12

d 13

d | 14

eer

15} 8

13 7-48

12-41

10i 10

41541

10; 10

10 -13

11 | 14

10: 10

7 8

91 138

7 | 12

10 14

8 | 12

ade 9

101 11

8 8

9 9

Average Total No.

Fissions for Five-day

Periods

Pure Line with 553 + Generations without Conjugation

Second

Group of Group of

Lines Lines

iis) eT % 8 ia Gen 74

BTR] 12 9 9 d 12 9

Coach Tee aes) pi iaee

13} 1S: | 18 d | 8 8 9 9 128 83

11 WFH 9 8 3l 8 7 11 8

tlw wl daj elot T| 8 9$ 6

10 d 11 7 5 6 6 d 10 6

EIO RATEN ENE

te ee oe ee ee ee ee 9} 4}

ss Smuspisaan hace.

1o Gi olib adl bl dl 8 9 51

a EEN A N ie tN,

a A e A a E 6}

dla ilo nr | Tor 9} 64

mMM | |

12} 11 | ie 81 ee | s| 8 | 104 8}

3i elisi eel T 8l a 8 eee 6

agnosis Eie o EAEE. peA Nieman;

12 | Ri eilel S å 11 64

d Bi n 9 6 9 8 8 12 8

440534. H 10 088 a0 18 16 14 102

H nHn HL B 9 19 10 14 94

1241S D 9 8 8 8 8 12 84

19: lei Mmi II 910 P isi 94

Fear a a a eee na

On i eC eT e g iv 7

dies SE | 2 8 8 8 8 t 1 7$

HiG 6 7i ja 10} 6

peu OnE

gin 4 10) eai g] e 7, g W 72

2 i) B 9u 8 8 8 114 84

dlld 10) o niii Bi . 98

fem Oh Ob ro diilad D

a -

GL Ol ey 4 n el Gg 8} 7

IZ: 12 d 10 8 9 9 9 114 9

Ca P

1B) 18 | in ae 8 8 9 8 114 . 88

12) 12 | I4 9 8 9 9 10 122 9

2 IEB 9 f 8 9 7 il 8

8 8 Ol 64-8 1 eB $ 83 6

A A

d Hinn 9 7; € 1.8 6 10} 7

Si elél g 27) oe 74 54

Pid id) 7j d | 13. 5. 8 7

No. 606] MUTATION IN DIDINIUM NASUTUM 355

TABLE I (concluded)

verage Total No.

aa for Five-day

Periods

Pure Line with 553 = Generations without Conjugation Spee SET TCT Te

Group of fanes of

} | tna. | pe seve Warne | |

9 9 1.38 7 7 | 6 6 ee ee. | 5 8 54

Drar aT ONC ete 7 12 8}

| Re arene. n AARNE aE GES

7 9 | 10 9 9 | 6 5 $ d | 7 84 5}

en,

16 | Ik | 13.1°14:| 14 d 10 % d | 9 133 82

| Pani ai eras wang

d eh eg 8 6 ee ee 5 4| 4 7 4

Se Pa eT ea Te Se Pa Te | 4 83 42

8 |} 71 i 9 8 ich & thd 9 73

——_—_

d 8 | 10 d | 10|| 6 d 8 5 | d 92 61

Total average generations per line in 315 days 838 + 634 +

Number of Hage died out | 30 33

es encys | 8 3

Number of aed miem gag ockurred before transfer was |

made | 0

duced at practically the same rate, but those in the former,

considerably more rapidly than those in the latter. Dur-

ing the 315 days each line in the one group produced ap-

proximately 838 generations, 2% per day, and each line in

the other group approximately 634 generations, 2 per day.

The averages for the five lines in each group for five-

day periods are presented in Table I and plotted in Fig. 1.

By referring to this table and the figure it will be seen

that the difference in rate of fission in the two groups

remained fairly constant throughout the entire 315 days,

and that in both groups the rate was high in July and

August, 1912, after which it decreased considerably and

then remained fairly constant.

The fluctuations in rate of fission were closely asso-

ciated with variations in temperature. This was true for

twenty-four-hour periods as well as for the five-day

periods given in the table. During July and August,

when the fission rate was high, the temperature was in

general much higher than it was during the rest of the

time, when the fission rate was relatively low. At the

[Vou. LI

THE AMERICAN NATURALIST

356

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No. 606] MUTATION IN DIDINIUM NASUTUM 357

close of the experiment, however, the rate of fission was

not as high as the temperature at this time would lead one

to expect. The didinia in both groups appeared to be in

poor condition. There were numerous very small in-

dividuals produced and an unusually large number of

monsters. Conjugation was prevalent, but it was almost

impossible to induce encystment. The death-rate was,

however, not abnormally high. Whether or not the lines

would have recovered from this depression if the ex-

periment had been continued, is a question which can not

be definitely answered.

Before the experiment was closed some cysts were se-

cured in both groups. These were kept in a damp cham-

ber as usual until the following year. Then they were put

into culture fluids of various sorts containing paramecia;

but only a few developed, all of which belonged to the

more rapidly dividing lines. From these, five new lines

were started and carried on for 40 days. During all this

time the condition of the individuals was much as it had

been immediately before encystment.

Throughout the entire experiment the didinia were cul-

tivated in rectangular watch-glasses having a depression

with a curved bottom. These dishes were piled one upon

the other and kept in a damp chamber. - All of the didinia

were fed with paramecia from the same cultures. At

each feeding an equal amount of solution was taken from

two of the most vigorous of four pint cultures which were

continuously kept in as flourishing conditions as possible

by adding fresh water and a little timothy hay from time

to time. The two equal quantities of solution were then

thoroughly mixed and two drops of this mixture contain-

ing numerous paramecia were put into each of as many

watch-glasses as there were didinia cultures. One drop

of solution containing one didinium was then taken from

each of the didinia cultures and added to’each of the

watch-glasses containing the paramecia. The remaining

didinia, after recording the number of generations pro-

duced, were destroyed or used in studying conjugation

358 THE AMERICAN NATURALIST [Vou. LI

and encystment. During the coldest weather it was suffi-

cient to transfer every other day, but during the warmest

weather it was found advantageous to transfer twice a

day. Nothing was sterilized in these experiments, but the

same pipet was used in all transfers and the watch-glasses

not in use were exposed to the air and allowed to dry.

Moreover, from time to time the didinia in each line in

either group were transferred directly to the watch-

glasses from which the didinia of the other group had

just been taken. In these dishes there always remained

considerable solution, in some instances a drop or more.

Furthermore, in a few cases didinia from the more rapidly

dividing lines were transferred directly without the addi-

tion of fresh food to dishes in which more slowly dividing

lines had died or from which all of the didinia had been

removed.

Such treatment had no appreciable effect on the relative

rate of fission in the two races. It is obviously evident,

therefore, that the difference in the rate observed was not

due to difference in the bacterial contents of the solution

if there really was any such difference, nor was it de-

pendent upon selection, natural or otherwise, for mem-

bers of the more rapidly dividing pairs were always trans-

ferred in all lines. And the number of lines lost by death

and encystment was essentially the same in both. In the

one 30 were lost by death and 8 by encystment, in the

other 33 by death and 3 by encystment. Assuming that

the weaker lines died out in every case, it is evident that

in this respect both races were subjected to practically the

same sort of selection. And since all of the cultures were

subjected to the same conditions otherwise, it is clear that

the difference in the rate of fission in the two races must

have been due to the constitution of the organisms.

We have consequently demonstrated that marked vari-

ations in the rate of fission may appear quite suddenly

in the progeny of a single individual without conjugation

or encystment, that some of these variations are heritable,

and that they can probably be produced by subjecting the

individuals to abnormally high temperature.

No. 606] MUTATION IN DIDINIUM NASUTUM 359

By referring to the table it will be seen that the mu-

tation investigated originated, as previously stated, at

the close of a period of extraordinarily high rate of fission

and immediately after a short period of very high death-

rate in which all but one of the lines died out. At the

beginning of this period and at the close of the preceding

period the individuals were very small and showed all

the characteristics in behavior common to individuals

about to conjugate. Whether or not anything in the

nature of a nuclear reorganization in preparation for con-

jugation occurred in these didinia is not known, but or-

dinarily such phenomena do not begin until some time

after union takes place in conjugating specimens. More-

over, the period between fissions was not long enough to

admit of much in the way of reorganization aside from

what ordinarily occurs during the process of fission.

Whether or not the ancestors of the mutants were actually

homozygous is not known. If they were not the mutation

may possibly have been due to a rearrangement of unit

characters represented in the chromosomes during fission

resulting in a change in dominance. However, if this did

actually take place it is not in accord with the results ob-

tained in very extensive investigations, all of which seem

to show that changes in dominance do not occur in asexual

reproduction. It is probable, therefore, that the mutation

was due to a direct effect of the environment on the physi-

ological processes in the organism and not to inherited

nuclear phenomena largely independent of the immediate

environment.

The mutation theory so ably championed by DeVries

has of late lost greatly in prestige, owing largely to the

contention that the plants (Gnothera) in which DeVries

discovered mutations were hybrids. If the conclusion

reached in this work proves to be correct it will strongly

support the theory in question. It will demonstrate that

marked variations may appear suddenly in organisms re-

producing asexually, that such variations may be heritable

and that they may have a decided evolutionary value.

360 THE AMERICAN NATURALIST [Vou. LI

This conclusion, though in opposition to a great bulk of

the experimental evidence gathered by some of the fore-

most biologists, Johannsen, Maupas, Morgan, Castle, Jen-

nings and many others, is supported by some of the re-

sults obtained by Barber (1907), Calkins and Gregory

(1913), Middleton (1915) and Jennings (1916).

SUMMARY

In a race of didinia originating from a single individual

there suddenly appeared a heritable variation in the rate

of fission. This variation occurred 721 generations after

conjugation and 197 generations after encystment.

Two strains were isolated from this race and kept

under observation for 315 days. During this time the

lines in one strain produced an average of 838 + gen-

erations (2% per day) and those of the other 634 + gen-

erations (2 per day).

THE METHOD OF EVOLUTION FROM THE VIEW-

POINT OF A GENETICIST"

A. FRANKLIN SHULL

UNIVERSITY OF MICHIGAN

A symposium upon the method of evolution, participated

in by students from widely different provinces, ean hardly

be expected to develop harmony of opinion. But to be

assigned a place in such a discussion as a representative

of one field of endeavor does not imply that the conclusion

one reaches will necessarily differ from that of his co-

symposiasts; for the question of the method of evolution

is a question of fact, and when the fact is discovered, it

will be recognized as completely by the paleontologist as

by the physiologist. And, in particular, to be assigned

the final place in the argument does not mean that the

doctrine preached will be, or even is, the last word on the

subject. In the present state of knowledge of biology the

most that can be expected of an address on this subject is

a statement of principles which should guide us in a

search for the facts. Beyond these principles there are

justifiable suspicions, and there may even be militant con-

jecture, but little else. `

The first fundamental prindiple for the guidance of one

who would find the method of evolution is a principle

common to all sciences which seek to explain the occur-

rences of a remote past. No agencies may be assumed

to have operated fifty million years ago of a different

order from those that operate to-day. If the phenomena

of the present afford a plausible, or even possible, expla-

nation of the past, there must be no appeal to other phe-

nomena, the like of which do not now exist. Just asa

geologist mentally constructs the rock strata a thousand

feet below the surface, and the glacial drift of regions

1 Concluding paper of a symposium on the method of evolution before the

zoölogical section of the Michigan Academy of Science, March 28, 1917.

361

362 -~ THE AMERICAN NATURALIST [Vou. LI

now temperate, on the basis of processes now going on in

certain parts of the earth; and just as the astronomer

creates the planetary systems in his mind by forces that

still govern, so the biologist must conceive evolution in

the past to have been the result of agencies that are still

causing change to-day. Whatever causes evolution now

may conceivably have caused it during the early history

of living things, and there are no circumstances which

compel one to devise other causes for past change.

Adherence to this principle automatically removes the .

first solution of the problem of the method of evolution

from the realm of the investigator who deals only with

past events or the results of past occurrences, and places

it in the hands of him who studies present-day. phe-

nomena. Conclusions based on statistics have repeatedly

shown how dangerous it is to argue from end results to

causes. The compiler who finds that among the poorer

classes of a population the ratio of male children to female

is higher than in the well-to-do classes, and coneludes that

deficient nutrition causes the high male-production, might

also have discovered, had his investigations borne upon

that point, that the poorer classes lived in houses pro-

tected with a cheaper grade of paint or even without this

protection. It would have been ridiculous to conclude

that cheap paint favored boys, but- that conclusion would

have been as nearly proven by the data collected as was

the more plausible conclusion involving nutrition. Causes

are not safely to be judged from results. In discovering

the method of evolution, the initiative is denied the paleon-

tologist, zoogeographer and the morphologist. No doc-

trine of scientific cloture is here advocated, however, for

the right of debate and even of veto is still theirs. The

experimentalist alone may propose, but his colleagues

employing the older forms of investigation may, and

doubtless will, dispose. The experimentalist accepts his

burden cheerfully. He knows that he may be unable to

create a correct theory, but he prefers dispensing with a

theory to adopting the wrong one.

No. 606] METHOD OF GENETICIST 363

If you grant that evolution in the past was caused by

the same agents as cause evolution to-day, to what phe-

nomena of living things will you apply this principle?

Evolution requires two things, namely, modification and

inheritance. Given these two things, the occurrence of a

new characteristic and the inheritance (or even only the

heritability) of the new characteristic, evolution has

occurred. It matters little now what becomes of the indi-

vidual or individuals possessing a new heritable char-

acter. They may even perish before they leave offspring,

yet evolution has occurred. What became of these

incipient races was the theme of the evolutionists of the

past half century, who devised many and fanciful theories

to account for their preservation or their destruction.

To-day we are concerned less with the fitness of the new

characteristic for the environment; we demand rather to

know how the new feature arose and why it was inherited.

Fortunately there is no fundamental disagreement with

regard to inheritance. Too much is known of the mechan-

ism of inheritance to allow of dispute. The chromosomes

have been saddled with the main responsibility. There

has never been any general attempt to refer inheritance

to the environment. No one has supposed that a goose

egg laid in the sand would produce a turtle. It is true,

the cytoplasm has a share in determining what shall

develop from an egg; so does oxygen, and so do other

components of the medium, as can be readily shown by

altering those components. What develops in the pres-

ence of this cytoplasm, and out of this cytoplasm, depends

specifically, however, upon the chromosomes. Disputes

regarding this fact have seldom been dragged into argu-

ments over the method of evolution.

With the primary requirement of evolution, the pro-

duction of new characters, matters have been otherwise.

The mode of origin of modifications has not shared the

good fortune of the mechanism of heredity. There is no

need to cite the hosts of opinions that have been held by

reputable scientists regarding the inception of evolu-

364 THE AMERICAN NATURALIST [Vou. LI

tionary change. They have ranged from those who would

make the living world of to-day wholly the product of the

environment, to those that deny any participation of

external factors in the course of evolution. Where in

this array of opinion is the probable truth? To answer

this question will be to express another opinion; but it

is possible to formulate an opinion which is based upon

principle, and which will therefore be more inviting than

mere conjecture.

With the aid of Sir Charles Lyell, who more than any

one else has taught us to seek the explanation of past

events in present processes, let us look about us for the

cause of diversity among individuals. We may ignore

differences which, from their fundamental nature, are not

permanent, that is, modifications which are not heritable;

for of such as these evolution is not made. Since inheri-

tance depends upon the continuity of material of the

chromosomes of the germ cells, changes in adult struc-

ture or function can only be permanent when they follow

a corresponding change in one or more chromosomes.

These chromosomal changes may conceivably arise from

within, or be impressed from without. Much of the mod-

ern investigation which has a bearing upon the method

of evolution is concerned with the question whether the

modifications of chromosomes are caused by internal or

external agencies.

Two of the most striking cases of the origin of new

heritable characteristics are those of the fruit fly Droso-

phila and the evening primrose (Enothera. Scores of

permanent changes in these organisms have appeared

within the last decade. These new features have appeared

in one individual among a hundred in the same bottle, or

among a thousand in the same field. Environmental dif-

ferences seem excluded in these cases. For, if one attrib-

utes these changes to invisible and unsuspected variations

of the environment in circumscribed regions in a bottle or

field, there is no need to appeal, as has usually been done,

to the grosser elements like climate and medium, and

No. 606] METHOD OF GENETICIST 365

evolution is once more made wholly speculative. Inas-

much as the very instability of protoplasm, which

accounts for the manifold metabolic processes that char-

acterize living things, makes not only possible but highly

probable alterations of the chromosomes which, in our

present state of knowledge, must be regarded as of

internal origin, the discovery of cases like those of the

fruit fly and the evening primrose, in. which environ-

mental agency is apparently inadmissible, should leave

no doubt that evolution can occur without reférence to-

specific elements of the outer world.

What the actual method of producing changes in the

chromosomes may be can only be conjectured. Morgan

and his students have abundantly demonstrated that the

continuous identity of chromosomes is, in at least one

animal, an invention based on appearances; that the

chromosomes of one individual are often not identical

with those of its parents. The crossing over which they

postulate is an even exchange of corresponding parts of

two chromosomes. How this exchange is brought about,

whether through the twisting of the chromosomes as the

students of Drosophila have assumed, or because of the

variability of the forces that hold the chromosomes

together, as Goldschmidt (1917) suggests, is immaterial.

If, occasionally, this exchange between the chromosomes

is not equal, an occurrence that is not inconceivable, a

chromosome might be produced unlike any that ever

existed. If the germ cell containing such a chromosome

were capable of producing a viable individual, to predict

the probable nature of such an organism would be idle

speculation.

Failure of the chromosomes to divide, and the passage

of one or more of them bodily to one end of the spindle,

would produce daughter cells with an unequal comple-

ment of hereditary material. Hyde (1916) has recently

reported a case in Drosophila which is probably of this

_ nature; the two X chromosomes appear to have remained

undivided, going to opposite daughter cells, resulting in

366 THE AMERICAN NATURALIST [Vou. LI

the production of right and left eyes of different sex-

linked colors. If, among the descendants of such unusual

cells, germ cells should be produced, a new type of organ-

ism should result from their development. Although

Babcock and Lloyd (1917) reject somatic segregation

because one supposed case of that phenomenon reported

from the Oregon Agricultural Experiment Station

proved, in their opinion, to be something else, there is still

some evidence, like that of Hyde’s, that such unequal

divisions’ do occur. If they occur in the line of the germ

‘cells, new modifications may thereby be produced in the

next generation.

Failure of the maternal and paternal chromosomes to

separate in the reduction division of maturation, a phe-

nomenon discovered in Drosophila by Bridges (1913) and

named by him non-disjunction, may also be the cause of

occasional evolutionary changes.

The foregoing chromosomal irregularities, which have

the appearance of being mechanical rather than chemical

. phenomena, are not, however, necessarily the instruments

with which permanent changes of organization are

wrought. Probably they are not the usual ones. They

have been mentioned first because there is evidence that

such changes are occurring now. Minute changes far

below the present limits of visibility are as conceivable,

and in my opinion quite as probable, as the grosser ones

named. In what these changes occur no one knows, for

no one knows the nature of the hereditary elements.

Suggestions involving enzymes and side chains have been

made. These are only conjectures, but they reveal a

belief that the phenomena of inheritance are chemical

phenomena. If we believe that heredity is dependent

upon chemical processes, there seems to me no escape

from the assumption that evolution is first of all a chem-

ical change. What the cause of these changes may be

is another question; but if changes in considerable frag-

ments of chromosomes, or even in whole chromosomes,

ean occur as a result of agencies within the organism, as

No. 606] METHOD OF GENETICIST 367

is plainly the case in Drosophila to-day, there is no reason

to deny that the invisible modifications of chromosomes,

if such oecur, are likewise of internal origin.

In suggesting possible sources of internal change result-.,

ing in evolution I am not blind to the fact that an ultimate

explanation of the method of evolution is not thereby

offered. The chemical processes which cause these phe-

nomena, while they are distinctly within the field of the

geneticist, are not within his knowledge. If there were

any prospect that an ultimate solution of the problem of

the causes of germinal changes could be offered at the

present time, invitation to participate in this discussion

should have been extended to a physiologist; for it is

from him that the eventual explanation of these internal

changes must come.

In this account of possible ways in which changes in

the chromosomes of germ cells arise, I have not forgotten

that it is conceivable that the changes are forced by

external agents. There are, indeed, biologists who regu-

larly attribute such changes to environment. The paleon-

tologists not infrequently seem to regard evolution as

ordinarily so caused. But with a few exceptions, those

who hold these views are not experimentalists. They are

not the biologists who are engaged in studying present

phenomena. They reason from results to cause. Out

of the conceivable causes they have picked on one which

has a chance of being the right one, but only a chance.

I venture to suggest that the theory of internal origin of

modifications will account for all paleontological, morpho-

logical, and geographical phenomena, and accord with all

evidence from those fields, quite as well as the environ-

mental theory.

Among the experimentalists, it is to be admitted, there

are a few who occasionally proclaim the discovery of a

modification produced by the environment and subse-

quently inherited. By one or two, not possessed of the

still small voice, these proclamations are made repeat-

edly. Sometimes the effect of the environment is admit-

368 THE AMERICAN NATURALIST [Vou. LI

tedly directly upon the germ cells, and the results are not

usually challenged. In other cases it is claimed to be

only upon the soma, which then modifies the germ cells.

These latter claims, however, meet with singular indif-

ference or even distrust on the part of other biologists.

Vulnerable places are too easily found, such as the lack

of adequate controls. Sometimes the environmental evo-

lutionist is charged with unwillingness or inability to

show his hand when pressed for further information.

Furthermore, it may seem strange that in a world of biol-

ogists, all anxious to solve the problem of the method of

evolution, and all so far as I am aware willing that that

method should be anything whatever, all of the important

supposed eases of permanent modification caused by

environment should be advanced by a handful of investi-

gators.

To conclude: We have affirmed our adherence to the

principle that evolution in past time is to be explained by

phenomena that occur to-day. No processes that do not

occur in living things now may be assumed to have

occurred in living things formerly, unless there is plain

evidence that events not explainable in terms of modern

metabolism once occurred. Applying this principle only

to the origin of modifications, not to their preservation,

we have shown that animals are evolving now through

agencies within themselves, independent of the environ-

ment. Whether environment also produces permanent

modifications is questionable, with the burden of proof

still resting upon those who hold that it does. All of the

known steps of evolution may be explained as originating

from within the animals’ organization. There is no neces-

sity of appealing to any other mode of origin, except,

perhaps, to satisfy a certain type of imagination. In

view of these considerations, it seems not illogical to me

to suspect that evolution, at least among all but the very

low animals and plants, is usually if not always initiated

by a chemical change, either directly or indirectly pro-

duced, in the chromosomes of the germ cells; that these

No. 606] METHOD OF GENETICIST 369

changes are inherited because they result from changes

in the chromosomes, and for no other reason; that such

changes are usually, if not always, independent of the

environment; that such changes produce unpredictable

changes in sdai structure or function; and that these

changes have no reference to the usefulness of the change

in the evironment in which the animal exists or in any

other environment.

If one desired to go beyond the first steps of evolution,

and discuss the factors that determine the course of evo-

lution by effecting the survival or destruction of such

new forms, it would not be difficult to maintain that sur-

vival is much less dependent upon fitness than is com-

monly supposed, and that natural selection probably

operates only to eliminate the most unfit. But such a

proposition necessarily involves much speculation, with

comparatively little information regarding present day

phenomena to serve as guide. I shall content myself,

therefore, with the above categorical statement of views

regarding the origin of permanent modifications, and

allow my colleagues to begin the sifting and testing opera-

tion which is theirs to perform.

LITERATURE CITED.

TUR E. B., and Lloyd, F. E.

: Somatic Segregation. Journal of Heredity, Vol. 8, No. 2, Feb-

ruary, pp. 82-89.

Bridges, C. B.

1913. Non-disjunction of the Sex Chromosomes of Drosophila. Jour-

nal of Experimental Zoology, Vol. 15, pp. 587-606.

Goldschmidt, R.

1917. Crossing over ohne Chiasmatypie. Genetics, Vol. 2, No. 1,

January, pp. 82-95.

Hyde, R. R.

1916. Two New Members of a Sex-linked Multiple (Sextuple) Allelo-

morph System. Genetics, Vol. 1, No. 6, November, pp.

535-580.

SHORTER ARTICLES AND DISCUSSION

AN INTRINSIC DIFFICULTY FOR THE VARIABLE

FORCE HYPOTHESIS OF CROSSING OVER

THE assumption of a ‘‘variable specific force,’’ made by Gold-

schmidt,* may seem to account for the frequency of the crossovers

occurring in a given simple case of linkage; but when this ex-

planation is extended to the results which such crossovers give

when bred, it creates a difficulty of the same type and magnitude

as the original problem of crossing over, for which, therefore, it

is not a satisfactory solution.

Briefly put, the explanation advanced by Goldschmidt as-

sumes that the genes are carried by the chromosomes, and that

each gene is incorporated in its characteristic locus by virtue of

a force residing in the chromosome and possessing properties

specifically related to the properties of the genes of that locus.

In the heterozygote Gg (see accompanying figure, line 1), the

two forces F, and F, residing in the homologous chromosomes C

and C’ possess not only a locus specificity but also an allelomorphic

specificity corresponding to the allelomorphs G and g. When the

chromosomes of the Gg heterozygote go into a resting stage, these

forces F, and F, relax, so that the genes G and g become freed.

When the chromosomes are reassembled preparatory to division

these forces again come into play with the result that gene G

is again incorporated into the chromosome in which F, resides,

while gene g is likewise reincorporated into the homologous

chromosome characterized by the presence of F,. In order that

crossing over may occur, the allelomorphie specificities of forces

F, and F, must, in the first place, be commensurable variables;

i. e., forces F, and F, must vary in that property which con-

stitutes their essential difference, and in such a manner that

when all the values of force F, are represented by a character-

istic frequency distribution and likewise all the values of F, are

represented by a second specifice distribution, these two distri-

butions will have a common base (see diagram, line 1). In the

second place, these two distributions must overlap on the common

base line so that a value chosen from the lower range of one may

1Dr. R. Goldschmidt, ‘‘Crossing over ohne Chiasmatypie?’’ Genetics, 2:

82-95,

370

No. 606] SHORTER ARTICLES AND DISCUSSION 871

be of the same magnitude as a value taken from the upper range

of the allelomorphic distribution, though the two forces thus

chosen are, of course, no more identical than are two of Johann-

sen’s beans which are of the same size but belong to different

pure lines. It is then assumed that in those cells in which the

values of F, and F, are equal, the chromosome carrying F,

should incorporate gene g as frequently as gene G, and in those

cells in which their normal order of magnitude is inverted, the

crossover incorporation should occur more frequently, depending

on the amount of inversion. Let us assume that in a given case

this overlap is of such a per cent. that one per cent. of the

gametes are crossovers (%1 of the diagram).

Now, in order to present the crux of the matter, let us proceed

with the analysis of the behavior of the crossovers produced in

the above experiment (see diagram, line 2). Let us mate a cross-

Heterozygote

heterozygote

New heterozygote

obtained from

two crossovers

Gametes of

heterozygote

372 THE AMERICAN NATURALIST [Vou. LI

over individual in which gene G is held incorporated by force

F, with the converse crossover individual in which gene g is

held incorporated by force F, (see diagram, line 3). As soon

as the ch1omosomes of the resulting heterozygote enter the proper

resting stage the forces F, and F, relax, freeing the genes G

and g. It must now be recalled that every value of force F, is

a member of a specific frequency distribution representing the

entire behavior of F,, and that any particular value of force F,

should give in succeeding generations the same result as every

other value of F,. Each value of F,, whether chosen from the

extreme upper range, the extreme lower range, or the mid-region,

should give rise among its descendent cells to a series of variates

which reproduce the original distribution F, and no other.

That is, the two distributions which describe the variates of F,

and of F, in the cells of the new heterozygote, being specific,

overlap in exactly the same fashion and to the same extent as did

the distributions of the forces F, and F, in the original hetero-

zygote (see diagram, line 3). Consequently, when the chromo-

somes are reassembled force F, will, as before, incorporate gene

G in 99 per cent. of cases and gene gœ in 1 per cent. of cases (see

diagram, line 4). But gene G entered the heterozygote as part

of the chromosome possessing force Fy, hence the 99 per cent. of

emerging offspring in which gene G is incorporated by the chro-

mosome bearing F, or gene g by the chromosome bearing F are

crossovers. As everyone acquainted with linkage knows, the

crossovers given by the heterozygote from the mating of two

crossovers are of the same frequency as in the original exper-

iment. The intensities of coupling and of repulsion are equal

and not complementary. Goldschmidt’s machine which at the

first revolution turned out a mere driblet of crossovers, should

overwhelm the operator with a deluge of crossovers at the next

turn of the crank. The whole explanation fails unless some added

agency be devised to take over the duty which the specifie allelo-

` morphic forces abandon after the occurrence of crossing over.

The original problem was to secure the replacement of gene

G in chromosome C by gene g, and at the same time the replace-

ment of gene g in chromosome C’ by gene G. Having assumed

the machinery of specific variable forces to accomplish this inter-

change, we find that the products of the interchange are not

stable, and furthermore they give a result the opposite of that

demanded by the well known facts of linkage. In order that

No. 606] SHORTER ARTICLES AND DISCUSSION 373

gene G should be stably related to its new position in chromo-

some C’ it must be held incorporated by force F, and not by

force F, as is the case. Added on to the original problem of the

interchange of the genes is now the second and equally imposing

problem of the interchange of the forces subsequent to the inter-

change of the genes. An actual bodily interchange of the forces

seems impossible in view of the assumptions we have had to make

as to their nature and action. The transformations would then

have to be accomplished by some transmutation in situ. It is

evident that no internal autonomous change short of a complete

and absolute mutation of force F¥ in chromosome C into F, and

simultaneously of F, in C’ into F, would suffice. But we have

no precedents for assuming such reciprocal mutations, and if we

had, we could have sidetracked this whole machinery by applying

this reciprocal transmutation idea to the genes and thereby

solved the first problem in such a way that the second could not

arise. Instead of localizing the cause of the reciprocal transfor-

mations of the forces in the forces themselves, one might transfer

it to the genes; i. e., one might endow the genes with the power

_ of causing reciprocal transformations of the forces rather than

empower the forces to transmutate of their own accord. While

this form of the transmutation idea carries something of an air

of plausibility, it can not be taken as more than an attempt at

formal escape from the difficulty—a lifting of one’s self by one’s

boot straps that makes more demand on credulity than, for ex-

ample, one would in assuming crossing over offhand as a specific

property of genes which needs, as support, only such formal ex-

planation. `

CALVIN B. BRIDGES

COLUMBIA UNIVERSITY

ON THE PROBABLE ERROR OF MENDELIAN CLASS

FREQUENCIES

Ax old friend of geneticists who dislike excessive calculation

has recently been attacked by Pearl,’ viz., the familiar formula,

¢==\/npq for the standard deviation of a Mendelian class fre-

quency. He proposes to substitute a more refined but much more

complicated method, originated by Pearson. In a Mendelian

illustration he obtains a result which differs by over 40 per cent.

1 Pearl, R., ‘‘The Probable Error of a Mendelian Class Frequency,’’

AMERICAN NATURALIST, Vol. LI, pp. 144-156, 1917.

374 THE AMERICAN NATURALIST [Vou. LI

from the usual. This seems to indicate that the old method is

wholly inadequate, but further examination shows that the differ-

ence is not due so much to method as to the fact that Pearl has

calculated something with a different significance from the usual

probable error. A cross of Mendelian heterozygotes (Blue Anda-

lusian fowls) gave three classes of young in the numbers

14:33:11. Expectation is 14.5:29:14.5. Pearl assumes that a

first sample of 58 has given exactly expectation and then cal.

culates the quartile deviations for each class in a second sample

of 58. The results are given as 3.13 for the heterozygous classes,

3.55 for the homozygotes which indicate an excellent fit of ob-

servation to expectation. By the usual method, if a first sample

of 58 had given exactly 14.5 black chicks and nothing were known

of any theoretical expectation, the probable error in a second

sample of 58 is measured by the probable error of differences.

The probable error of either sample as given by the formula

.6745\/npq is 2.22. The ee error of differences by the

usual formula .6745\/c,? + o, is 3.15. This does not differ ap-

preciably from Pearl’s quartile of 3.13. Neither of these

methods, however, gives what we really wish to know, the close-

ness of fit to Mendelian expectation. We have a theoretical ex- -

pectation which is not based merely on a particular sample of 58,

but which should hold with increasing accuracy the larger the

first sample taken. With an infinite first sample, the formula

given by Pearl reduces to the usual one, .6745\/npq giving a

quartile of 2.22. This is less lenient to the discrepancy between

expectation and observation than the first result, but the fit is

still not bad. In a second illustration which is given, we do

have two samples and no theoretical expectation suggested. The

usual method of comparing samples of different sizes would be

to find the standard deviation of differences on a percentage

basis. The percentage standard deviation for a sample of n

individuals is \/pq/n, for a sample of m individuals is \/p’q’/m

and for differences is V (pq/n) + (p’q'/m). The expected

standard deviation of a sample of m individuals is, however,

my (pq/n) + (pq/m) if p and q are based merely on the first

sample as in Pearl’s illustration. The formula given by Pearl

for the standard deviation rapidly approaches this form for large

values of m and n. Following are the results given by the long

method, by an approximation given by Pearl and by the usual

one just cited.

No. 606] SHORTER ARTICLES AND DISCUSSION 375

| Long Method | Approximate Method | Usual Method

| |

Median | 83.53 | 83.95 83,71

ower quartile 75.61 75.84 75.64

Upper quartile L TOLE a dooi OAO 91.79

The usual method gives substantially the same result as the

long one and a better result than the approximate method. From

the nature of experimental work, great refinement in statistical

treatment is often a waste of effort, and without questioning the

value of Dr. Pearl’s suggestion in cases in which the greatest

accuracy is warranted it appears that the simple formula is still

adequate for most practical purposes.

SEWALL WRIGHT

BUREAU OF ANIMAL INDUSTRY,

March 12, 1917

CHARACTERS INDICATIVE OF THE NUMBER OF

SOMATIC CHROMOSOMES PRESENT IN

(ENOTHERA MUTANTS AND

HYBRIDS

THE pollen grains of 28-chromosome @nothera Lamarckiana

igas de Vries were long ago shown (Lutz, ’09)* to be character-

istically 3 + -lobed (chiefly 4-), instead of 3-lobed, as in O. La-

marckiana and other diploid forms. Gates has since contributed

much to our knowledge of this subject. Recently Bartlett (’15)?,

in discussing the 3 + -lobed condition of the pollen of 28-chromo-

some O. stenomeres mut. gigas, stated that these 3 + -lobed grains

‘fare larger than the triangular grains of the type’’ (O. stenom-

eres). It may be added that the largest, best-appearing 3- of

tetraploid forms in general, is larger than the typical, best-ap-

pearing 3- of diploid, and the largest, best-appearing 3 -+ - of the

former, larger than the typical, occasional 3-+-- of the latter.

Smaller 3- and 3 + - grains are found in the pollen of both, but

they are rarely perfect-appearing, and it is doubtful whether

slightly imperfect-appearing grains are capable of functioning.

A careful examination of the adult characters of a form, together

1 Notes on the first generation hybrids of (@nothera lata X O. gigas,

Science, N. S., 29: 263-267. Gates (Pollen development in hybrids of

Ginothera lata X O. Lamarckiana, Bot. Gaz., XLIII, 81-115, Feb., a

had earlier observed 3 + -lobed grains in the pollen of a triploid form

2‘‘The Mutations of (nothera a . Amer. Jour. Bot., k 100-

-109.

376 THE AMERICAN NATURALIST [Vou LI

with a microscopical examination of the pollen of 10-15 buds

from different parts of the plant will enable one to estimate its

probable somatic chromosome number; this estimate becomes

more trustworthy when one considers also (using Lamarckiana

as the standard for comparison) the number of seeds produced

per fruit by selfed flowers, the percentage of seeds which germi-

nate, and the hereditary behavior of the plant.

All parts, or most parts, slender; pollen consisting of small, 3-lobed grains -

with an occasional 3 + -. Plant will probably be found to be dip-

loid, o r

A, PERL of pollen, 50 per cent. or more of the grains good-ap-

pearing. Abundance of seed secured from selfed oe germina-

ting about as for O. Lamarckiana when sown in soil; spring,

with the exception of a few mutants, Vig Westie the aN of

the parent. Plant will probably have 14 chrom

B. (a) Anthers barren as for Lamarckiana idia, or Oy Vanikie amounts

of pollen produced in different buds of same plant; entirely ab-

sent in some, present in small quantities or in moderate amounts in

‘others. In best buds, imperfect-appearing grains considerably in

excess of good-appearing; in others, greatly i in excess of them and

Lamarckiana flowers; lower eip capable of germinating,

when sown in soil, than is usual for Lamarckiana seeds. Plant will

probably have 15, possibly 14", or even 16, chromosomes,

Plants intermediate between O. Lamarckiana and Q. oe gig

stoutness of all parts; pollen absent, present in sm eaka or

in moderate amounts, much as for I B (a) and (b). Pollen contain-

ing a mixture of 3- and 3 + -lobed grains, the former exceeding

the latter in number. Largest grains larger than typical, best-ap-

pearin ins of diploid forms; relatively few of the grains good-

preng; even in best buds. Selfed flowers produce no seeds or very

when s are sown in soil, very small percentage germinate

Plant probably triploid, or approxima at 80; probably 21- pasas

selfed 14-chromosome plant, or of 14 x 28;

possibly 20 or 22 chromosomes. If paige by a selfed 15-chromo-

some form, or by 15x28, the chances of its having 22 are greatly

enhanced. és

III

All oa? stouter than for triploid forms; pollen grains characteristically

3 + -lobed, with relatively few 3-lobed (typical grain 4-). Larg-

est and best-appearing 3- and 3 + -lobed grains larger than typ-

No. 606] SHORTER ARTICLES AND DISCUSSION 377

ical, best-appearing 3- and occasional 3 + -lobed grains of diploid

forms; 40 per cent. or fewer, good-appearing. Moderate amount

of seed obtained from selfed flowers. Seeds large, germinate

quickly. Plant will probably have 28 chromosomes, particularly if

an offspring of a 14- or a 28-chromosome form, selfed, or of a 14 x 28

If the product of 15x28, it may have 28, 29, or even 30, chromo-

somes, I. Forms which are approximately, but not precisely, tetra-

ploid, may be wholly male-sterile.

These statements are not intended to imply that all diploid,

triploid and tetraploid forms have the characters enumerated

above, but merely that forms displaying certain pollen conditions

and vegetative characters will probably (by no means certainly)

have the number of chromosomes specified.

ANNE M. Lutz

LAFAYETTE, INDIANA

ON THE PERIODIC SHOREWARD MIGRATIONS OF

TROPICAL NUDIBRANCHS'

Many northern gastropods, including nudibranchs, are well

known to exhibit the habit of congregating in shallow water

along the shore at their time of breeding. This has been com-

monly interpreted as the result of migration from deeper water

at the approach of the egg-laying season. Certain species, at any

event, are from time to time found in great quantity at shore

stations which they do not frequent at other periods, and field

observations have apparently established beyond a doubt that

this inshore appearance is closely connected with mating and ovi- ©

position. The migration into shallow water, or other means

which accomplishes the shallow-water flocking in these cases,

may be regarded as a device which insures the concentration of

individuals within a relatively small area, thus tending to make

more certain the chances of pairing in a large number of in-

stances, as well as a method of determining favorable conditions

for larval development.

Collectors of nudibranchs who have worked in tropical waters

have also reported cases which at first sight seem to afford addi-

tional examples of the coincidence of the spawning period with

appearance in great numbers in the littoral zone (e. g., Cross-

land, quoted by Eliot, 1904, p. 87). While engaged in working

ong the shore during a period of some days or weeks, it is

1 Contributions from the Bermuda Biological Station for Research, No. 59.

378 THE AMERICAN NATURALIST [Von L-

noticed that a certain species of nudibranch, until then found

sparsely, if at all, suddenly begins to occur in abundance. It is

also observed that at this time these nudibranchs are depositing

eggs in the field, or that they pair readily and lay egg strings

when kept in aquaria. The inference which has been drawn in

such cases, namely, that the appearance in shoal water is in some

way intimately related to the mating process, seems legitimate

enough.

But I have observed at Bermuda certain facts regarding the

normal migrations of a member of the typically tropical genus

Chromodoris which, it seems to me, cast considerable doubt on

the theory that this species, C. zebra Heilprin, moves into shal-

low water for the purposes of mating and egg deposition. The

facts in this case, so far as they have been observed, are briefly

as follows:

It was necessary to obtain considerable numbers of C. zebra

for use in experimental work (Crozier, 1916, 1916”); conse-

quently collections were made at short intervals (every day

during some months) over the period from August, 1915, to

October, 1916. I had had occasion, also, to note the occurrence

of this species in the summers of 1913 and 1914. In June, and

during the early part of July, Chromodoris was found in great

abundance upon the ‘‘eel grass’’ in certain tidal ‘‘creeks’’

(Fairyland Creek, Millbrook Creek). Subsequently, in the last

two weeks of July and in August, they became very scarce in

such places, although a few could almost always be discovered

by careful searching. At other times of the year a supply of

the animals was obtained on hard, open bottoms in somewhat

deeper water (1 to 2 fathoms, at low tide), in places where, I

am certain, they would never have been seen during ordinary

shore collecting. Occasionally, however, as was noted particu-

larly in December, 1915, Chromodoris was abundant along the

rocky shores of smaller islands, ranging well up to low-water

level.

It seems clear enough that in Chromodoris zebra there un-

doubtedly does occur from time to time a movement of numbers

of individuals toward the shore. But there are several facts

which sharply contradict the view that this migration is con-

nected with reproduction. The nudibranchs pair in the lab-

oratory and lay strings of fertile eggs at all seasons of the year

(ef. also Smallwood, 1910), and not merely at the times when

No. 606] SHORTER ARTICLES AND DISCUSSION 379

they are abundant near low-water level. Moreover, I have ob-

tained the egg masses in dredgings at every season of the year;

hence we may regard the fact of egg laying at all seasons under

laboratory conditions as of significance in this connection. The

eggs, which are quite characteristic in appearance, and hence

easily identified, have been collected in depths of eight fathoms

and more. Large individuals of C. zebra are likewise not un-

-common at these depths; in fact, the first ones to be described

were dredged from ten fathoms in Harrington Sound (Heil-

prin, 1889, p. 187). A further point of considerable significance

is found in the fact that these nudibranchs, unlike Elysia and

certain other species, do not appear to deposit any egg masses

upon the ‘‘eel grass’’ on which the animals occur in such great

numbers throughout the early summer. The egg strings found

in the field are invariably attached to rocks, or to the shells of

Arca noe, the ‘‘mussel’’ with which the adults are frequently

associated. The gelatinous egg-ribbons (cf. Smallwood, 1910)

are quite large, measuring usually 120 to 150 mm. long by 15 to

17 mm. broad, and are much too heavy to be supported by a

blade of ‘‘eel grass,’’ as can readily be deterthined by trial. It

is only rarely that an egg mass has been obtained in shore col-

lecting.

The migration of C. zebra into shallow water cannot, then, be

directly connected with reproductive activities. Since, in the

laboratory at least, they deposit eggs usually within twenty-four

hours after pairing, it does not seem to me probable that these

nudibranchs pair to any great extent during the time which they

appear to spend in the tidal ‘‘creeks’’—no eggs, as stated,

having been collected from among the ‘‘eel grass,’’ nor were any

ever obtained on the muddy bottoms of these ‘‘ereeks.’’ Chro-

modoris seems to require a firm, hard substratum for the attach-

ment of its egg-ribbon. If individuals obtained in quite shallow

situations are kept singly in aquaria they sometimes deposit

after several days fragments of egg-jelly containing several

dozen unfertilized eggs, while they almost invariably pair readily

when given the opportunity. Nevertheless, it should be stated

that the nudibranchs usually do not occur singly, two or three

being commonly found within a space of several square meters

even when the total number of individuals in a given area is

small; and I am well aware that laboratory findings with re

to breeding habits are liable to be misleading. The established

380 THE AMERICAN NATURALIST [Vou. LI

fact of egg production throughout the year in deep water is,

however, good evidence that the periodic (or intermittent)

abundance of this nudibranch in shoal situations can have little

if any relation to oviposition.

It might at first be suspected that the periodic shoreward

movement represents the phylogenetic persistence of a well-

defined habit possessed by not distantly related northern species.

From this standpoint, reproductive functions in C. zebra might

be conceived of as having become dissociated from the habit of

migratory periodicity, since in warmer seas, where the seasonal

alteration in physical conditions is reduced to a minimum, it is

well known (ef., for example, Semper, 1881, p. 135) that many

forms have no specially restricted time for breeding. How-

ever attractive such a speculation may appear, it is eminently

more satisfactory to regard these periodic littoral appearances

of tropical nudibranchs as being controlled by definite physical

influences in each individual case. Such directing causes would

not necessarily be always the same for each periodic occurrence

of the animals in shallow water. Although shoreward migra-

tion and egg laying are closely connected in northern forms, it

is still probable that physical circumstances in the sea imme-

diately control the migrations even in this instance also.

I have purposely refrained until now from discussing certain

minor fluctuations in the littoral abundance of Chromodoris

which are, nevertheless, important in connection with the idea

that the supposed ‘‘migration’’ at certain times into very shallow

water is, after all, only the unrestricted expression of a tendency

to upward movement—negative geotropism. It has been men-

tioned that during the greater part of the year Chromodoris

was collected in 1 to 2 fathoms. But after storms of some

severity they were to be had only in much deeper water. The

nudibranchs undoubtedly move into deep, qufet places when the

surface is greatly disturbed. Just what their behavior is under

these circumstances can not be stated from direct observation,

for obvious reasons; and for several days, or even for a week

after a severe blow, the water in the sounds and bays remains

so roily that it is impossible to see the bottom. But I have fre-

quently observed individuals creeping up from deep water after

the sea has become quiet and transparent. As regards the bear-

ing of these facts upon the major flocking into the littoral zone,

which occurs in early summer, it is to be noted that the mere

No. 606] SHORTER ARTICLES AND DISCUSSION 381

continuance of quiet, still weather is not enough to determine the

abundance of Chromodoris in the tidal ‘‘creeks,’’ since they

disappear for the most part before the calm summer season is

half over. The occurrence of individuals in deep water, together

with field observations of specimens which were engaged in creep-

ing downward on the sloping sides of rocks and reefs, leads me

to doubt very much that any form of geotropic irritability exerts

a preponderant control over the normal behavior of these ani-

mals. My observations strongly suggest, however, that there

does occur to some extent (in appropriate places) a diurnal ver-

tical movement of Chromodoris, which is directly determined by

the positive phototropism of these nudibranchs.*

Specimens of the species known as Chromodoris roseapicta

Verrill (there is some doubt that it is really a Chromodoris)

have been found in littoral locations, only in the summer time,

but this type is not sufficiently abundant to make possible a test-

ing out of ideas concerning its migratory movements.

The point which I wish to emphasize most is the uncertain

nature of conclusions having reference to the normal behavior

of animals inhabiting the warmer seas on the basis of compari-

sons with superficial features of the movements of their rela-

tives in colder waters. In the case of Chromodoris zebra, it

seems to me definitely established that the periodic flocking of

individuals into very shallow water has no immediate connec-

tion with reproduction.

On Jan. 10th, 1917, I found that C. zebra was crowding in

great numbers into the entrance of Fairyland Creek. During

the next few days they became very abundant indeed, so that on

one occasion 230 of them were picked up in less than an hour’s

collecting. On Jan. 12 I began to find egg masses attached to

certain sponges, matted alge, mangrove roots, and sundry moor-

ing stakes in the ‘‘ereek.’’ I had not before found any in this

place, as stated above. The nudibranchs were observed in copu-

lation, and great numbers of egg-masses were found. The at-

tachment of the egg-masses was most frequently to some firm

object. Within the week Jan. 10-17 they began to disappear, and

after a fairly severe storm which came at that time very few were

obtainable in the ‘‘ereek.’’? This occurrence seems to form a good

2I am anticipating here the statement of certain facts regarding the re-

sponses of C. zebra which were established in this laboratory several years

ago by Dr. L. B. Arey (ef. also Crozier, 1916°).

382 THE AMERICAN NATURALIST [Vou. LI

instance of shoreward movement coupled with reproductive ac-

tivity, but the fact remains that the nudibranchs do breed

abundantly at other times and in much deeper water.

REFERENCES

Crozier, W. J.

1916*. Cell Penetration by Acids. Jour. Biol. Chem., Vol. 24, pp.

255-279

1916". Cell Penetration by Acids. III. Data on Some Additional

Acids. Ibid., Vol. 26, pp. 225-230.

1916. On the Immunity Coloration of Some Nudibranehs. Proc. Nat.

Acad. Sei., Vol. 2, pp. 672-675

Eliot, C.

1904. On Some Nudibranchs from East Africa and Zanzibar.

V. Proc. Zodl. Soc. Lond., 1904 (2), pp. 83-105, pl.

Heilprin, A

1889.

Part

The Bermuda Islands. Philad., vi+ 231 pp., 17 pl.

Semper, K.

1881. Animal Life as affected by the Natural Conditions of Existence.

Internat. Sci. Series, Vol. 30, xvi + 472 pp., New York.

Smallwood,

1910. Mitek: on the Hydroids and ae of Bermuda. Proc.

Zool. Soe. Lond., 1910 (1), pp. 137-

AGAR’s ISLAND, BERMUDA.

W. J. Crozier

NOTES AND LITERATURE

DEAN AND EASTMAN’S BIBLIOGRAPHY OF FISHES

In order that the production and diffusion of knowledge may

but be promoted, knowledge gained must be published in some

permanent form. But when the publications become numerous

and scattered throughout many journals, and in various lan-

guages, it becomes at length difficult, or even impossible, for any

human being to retain in mind all that others have discovered

and written. The literature must be organized in such a way

that the seeker after knowledge and the producer of knowledge

may be enabled to determine easily what has been published on

any particular subject. Hence the need for bibliographies and

bibliographies of bibliographies, for the Zoological Record, and

the International Catalogue of Science. Hence the justification,

the necessity, for Dean and Eastman’s Bibliography of Fishes.

Dean tells us in the preface that in this work there are listed

more than 40,000 titles. How small a number of these could any

man command were it not for some such collection!

One volume only of the work has yet appeared. This is a book

of 718 octavo pages of small print; and this is occupied simply

by the authors’ titles of papers alphabetically arranged. And

only those authors have been reached whose names begin with

the letters A-K. A second volume is to follow which is to include

the others. The time, the patience and the labor which the ac-

cumulation of such a list demands may be surmised by the reader

of the preface; it can only be realized by one who has tried his

hand at something of the kind himself.

As the work will then stand, the student of fishes can deter-

mine readily all the papers that any author, as Agassiz or Baird

for example, has written; or he can glance over all the 40,000

titles and pick out those which seem to have a bearing on his

subject. To obviate the latter necessity, a third volume is to

follow which is to be an index to the preceding volumes. In the

two volumes of authors’ titles each paper is followed by the year

of publication and a serial number, as ‘‘ Jordan, 1891, 4’’; and

in the index each paper is to be referred to briefly by the author’s

name, the year and the serial number. Economy of labor and

383

384 THE AMERICAN NATURALIST [Vou. LI

expense is thus effected. The index will certainly be classified in

such a way as to make it reasonably easy to arrive at the papers

desired. In estimating, therefore, the work that Dr. Dean and

his editor and assistants have done we must consider not only the

collection and preparation of the titles, but likewise the analysis

of these papers and the recording of the contents under their

proper heads.

There is a need for more yet to be done. The author tells us

' that the index does not include detailed references to species,

genera, or ever, in many cases, families of fishes. ‘‘This would

entail many years’ additional listing, but should unquestionably

next be done.’’ The busy student may want to know what has

been written on the Centrarchids, or the genus Lepisosteus, or

the rainbow trout; and he ought to find all of the papers re-

corded under each head. May the good men who have worked

on this Bibliography of Fishes retain their powers and live long

enough to accomplish the work.

However, it will be open to any one to go through those 40,000

books and papers and cull out the things bearing on the subject

he has chosen and to publish a little bibliography of his own.

The present writer has not undertaken to discover omissions

of papers or errors in quoting them. Certainly omissions and

errors occur, as in any human production ; but doubtless all pos-

sibla care has been taken to avoid them. Two omissions have

incidentally been brought to notice. The first of these is a paper

by Eigenmann on a fossil species of Sebastodes, in Zoe, Volume

I, 1890, page 17; although another paper cited ends with page

15. The other paper omitted is B. K. Emerson’s ‘‘Geology of

Old Hampshire County, Massachusetts,’’ in which there is a list

of the Triassic fishes found in the state mentioned. Dr. Dean

must have had a record of this paper.‘ A paper by E. W. Clay-

pole? is quoted from the American Geologist, Volume XXIX, p.

44; but the paper is not found as cited; nor elsewhere, so far as

the present writer knows.

Ouver P. Hay

1 Science, Vol. oe 1902, p. 701.

2 Claypole, 189

THE

AMERICAN NATURALIST

Vot. LI. July, 1917 No. 607

RATS AND EVOLUTION

A. C. HAGEDOORN, Mep.Arts, anp A. L. HAGEDOORN, Px.D.

In treating a large group of animals from the stand-

point of a systematical zoologist, it makes a very great

amount of difference whether one does the work in the

region inhabited by the animals, or somewhere else with

the aid of collections in a museum. A real systematist,

of the museum kind, does not come into touch with a

number of very real problems which present themselves

to field workers, and when he does, he has every induce-

ment to brush them aside with an authoritative gesture,

as he is not in a position to valuate their importance. He

takes for granted that two similar skins with similar

skulls which he receives from the same place, correspond

to a multitude of individuals, all with these same char-

acters; that they are a sample of a multitude of animals

all exactly alike, and when he finds that animals of such a

description have not hitherto been named, he can invent

a well-sounding name for the two skins, and publish

a description, and henceforth this description of the type

specimen and this species name are welded together. If

it so happens that an animal is never again collected

which corresponds to the published description, the

species becomes known as very rare.

There exist conventional rules, which, in the descrip-

tions of species in certain groups, ascribe more value to

certain characters than to others. In the systematic clas-

sification of rats, the points which are specially noted

385

386 THE AMERICAN NATURALIST [Vou. LI

in this connection are the shape of certain ridges on the

skull, pads on the soles of the hind feet, the relative length

of the tail, the length of molar complexes, and the length

of the ears.

It is significant to. observe, how every field worker

who occupies himself specially with rats has his own

opinion about the relative importance of these different

points for the systematic classification of the animals, and

discovers very soon that the work done in museums does

not materially help him in his quest.

In 1915 one of us was commissioned by the government

of the Netherlands to make a biological and zoological

study of the rat population of the Dutch East-Indian col-

onies, more especially of the island of Java, with the

ultimate object to find out what measures could be taken

to prevent the exceptionally serious damage to public

health and to agriculture caused by rats. Some pre-

liminary work on the subject had been done by medical

investigators and by a systematist working with pre-

served specimens in Holland. The systematic-zoological

work in Java was begun some years previously by Maj.

G. Ouwens, who is continuing the work after we were

obliged, for reasons of personal health, to leave the

tropics.

Very soon after arrival we discovered how very little

the work done in European museums was to help us out in

the field. We are not systematic zoologists, and our rea-

sons for accepting the task lay in the promise the material

gave of throwing light on the question of species (in

which it has not disappointed us). Therefore the only

group of animals with which we have at all deeply con-

cerned ourselves with systematics is the rat, and we

would not be prepared to maintain that for other groups

the ordinary museum-zoology has so little value in giving

a conception of the relationship between species in nature.

Still, the study of rats from a semi-economical point of

view has certain advantages over purely scientific col-

lecting, as the material studied is very plentiful, and an

No. 607] RATS AND EVOLUTION 387

extraordinarily great number of keen-eyed persons, public

health officials, anxious owners of coffee-plantations,

managers of sugar factories, native officials in rice-grow-

ing centers, are continually observing the animals, and are

more than willing to collect extraordinary large numbers

on request. Itis not uncommon for any one studying rats

to see several hundred animals brought together for him

to look over, and one of us has had the occasion to observe

a batch of ten thousand rats in one day within the grounds

of a sugar factory where between nine and twelve thou-

sand rats were killed daily for several years.

The study of rats has set several authors to speculate

as to the nature and the origin of species. Very prominent

amongst these is Lloyd (The growth of groups in the

animal kingdom). Our conclusions differ materially

from those of Lloyd, however. The reason for this dif-

ference, we venture to think, lies chiefly in the fact that

whereas Lloyd studied dead rats, and speculated upon the

origin of his animals, more especially of aberrant types,

we have been breeding rats for some six years, and have

witnessed the origin of aberrant types. The examples in

this paper will be found to be nearly all taken from rats.

When it is found in field work, that two species-names,

each given to a skin in a museum drawer, in reality corre-

spond to two real groups in nature, of which they are

representative, we may be dealing with one of two dif-

ferent possibilities. It may be that the variability within

the first group is not so great that individuals belonging

to it fall within the limits of variability of the second

group, or it may happen that two different skins in a

museum belong to one highly variable group of animals,

in which it is difficult to establish dividing lines. If, for

instance, two skins with different names in a museum

differ considerably in size, it may happen that even the

largest animals of the group to which the smallest skin

belongs are still very much smaller than the smallest

adult individuals of the group which corresponds to the

bigger skin. It may happen that two skins are consider-

388 THE AMERICAN NATURALIST [ Vou. LI

ably different in a preserved state in respect to some

salient character, whereas in nature this very character

may be found to be so variable even within a small,

- closely related family of animals, that it has no value

whatever for distinguishing two species. A case in point

is the presence or otherwise of flattened hairs, or spines

in the coat of rats. On the other hand, it may happen that

two species, if once they are dried and preserved in a

museum, present no, or, no appreciable, differences,

whereas in reality, these two species may be found to

differ very definitely biologically. As an illustration we

may cite the case of the field-rat and the tree-rat in Java.

The easiest way out of the difficulty is the one

taken by a great many zoologists, working through large

collections of animals in museums namely, to give a new

species-name to every animal which differs markedly

from other described species, and which as yet goes with-

out a name.

But if one wants to go deeper into the subject, if one

wants to know whether these species of the drawer have

their counterpart in as many species in the forest and

field, the task becomes more difficult and even hopeless for

a great many investigators. As soon as specialists. take

in hand some group or other, it is very soon obvious that

the task of finding out just how many species they are

dealing with and how they differ is very much more com-

plicated than it looked when studying the collections in a

museum, however well stocked. In treating rat material

from a zoological-systematical standpoint, a number of

problems confront the investigator from the very outset,

and he must try to find his own solutions. Every inves-

tigator treats the material in his own way, and where one

man makes fifty species, some other man will make two

species out of the same material. It is evident, that if the

term ‘‘species’?’ means anything at all, it must hypo-

thetically be possible to divide the material into a fixed

number of species, neither more nor less. The vague way

in which the term ‘‘species’’ is applied, must be chiefly

No. 607] RATS AND EVOLUTION 389

responsible for the unrestricted feeling of personal lib-

erty which systematists undoubtedly have about the way

in which they divide a number of dried animals into

-= species. It is for this reason that it here becomes neces-

sary first of all to give our definition of the term

‘species.

For numerous systematists, a ‘‘species’’ is the descrip-

tion of a skin and a skull deposited in a museum— the type-

- specimen—and to this species belong all the animals which

have just such a skin and skull. Some few botanists are

just now trying to reserve the term for a group of animals

or plants which have the same genotype, the same set of

inherited factors of development. As long as we concern

ourselves with autogamous plants, such a definition might

pass, we might, at least hypothetically, divide a popula-

tion of such plants into a number of species and a few

hybrid individuals.

Itis very obvious that this definition of ‘‘species’’ falls

short, as soon as we concern ourselves with animals, or

with allogamous plants. In such groups, according to |

this definition, there would be no species. Even the geno-

typically purest group of animals would in every instance

still be composed of two species, the males and the

females, for we now know that the sex difference is caused

by a difference in genotype! Therefore, such a definition

of the term although very concise and very short, is prac-

tically untenable.

When we say: Species are those groups of individuals,

which have a common genotype, and which are pure for

that genotype, we can most certainly concede to Lotsy that

species are not variable,? but if we do so, we limit the use

of the old word ‘‘species’’ to those groups of plants which

really are pure and therefore invariable, so that they can

not be changed by selection, natural or artificial.

-If we solemnly state that dogs have short twisted tails,

1 ‘í Mendelian Inheritance of Sex,’’ A. L. Hagedoorn, Archiv fiir Ent-

wicklungsmechanik, 1909.

. Lotsy, Handelingen van het Natuur en Geneeskundig Congres te

Delft, 1912.

390 THE AMERICAN NATURALIST [Von. LI

we are perfectly within our rights when we use the term

‘dog’ for bulldogs only. But such a statement brings

us no insight in the shape or the length and variability of —

the tail in the big group of animals which everybody, ex-

cepting breeders of bulldogs, knows under the name of

«d ogs.”?

We can say: ‘‘Carriages have small wire rubber-banded

wheels’’ and if so we are within our rights if we limit the .

term carriage to baby-carriages, but all such and similar

statements of wheat-growers, breeders of bulldogs and

manufacturers of baby-carriages, no matter how plausible

they may look to the people under consideration, have

this one thing in common, that they may not be general-

ized. Breeders of New Foundland dogs have as much

right to reserve the name dog for their animals, and to

say that dogs have long bushy tails, as the breeders of

bulldogs did, and if we permit the manufacturers of

gocarts to reserve the term ‘‘carriage’’ for their product,

and if we allow the breeders of autogamous plants to

limit the term species to species of wheat and barley and

peas, manufacturers of Pullman carriages certainly have

the right to state ‘‘Carriages are ninety-five feet long and

are entered by steps four feet from the ground”’ and the

breeders of sugarbeets or rye, and the zoologists will have

the right to state that species are variable.

When we want to make a definition of the term

‘species’? we must make it so that it fits rat-species as

well as wheat-species, and in such a way that the gene-

ticians as well as the systematicians can apply it to the

things they are wont to call by the name.

We know that all the different genes, all the different

inherited factors whose cooperation or non-cooperation

to the development of the most diverse organisms pro-

duces the hereditary differences among them, are each

in themselves invariable. We have called this invariabil-

ity of the genes Johannsen’s law.* Only in this way can

3A. L. Hagedoorn, ‘‘Wetten en Regels in Genetica en Eugenetica,’’

Handelingen van het Genootschap van Natuur, Genees-en Heelkunde, 1913.

No. 607] RATS AND EVOLUTION : 391

one explain that those groups of plants, which are so

constituted that they become automatically pure in a short

number of generation—the autogamous plants—con-

sist in the main of pure and invariable species, which can

not be changed by any amount of selection. Selection

within a group of plants which descends from one indi-

vidual, homozygous for all its genes by a continued auto-

fecundation, is ineffective. As we have the name ‘‘pure

line’’ for these groups of plants, there is no good reason

to limit the use of the term ‘‘species’’ to these groups

exclusively.

Liability to change by selection is synonymous with

genotypic variability, and this true variability is synony-

mous with impurity. Those species which do not exist

exclusively of individuals which are all mutually identical

in respect to all their genes, are variable and therefore

liable to change by selection. One single, genotypically

pure species as a rule can not give rise to new species.

There have become known a few cases® of real spon-

taneous genovariation, mutation, in which every known

cause for change in genotype was excluded (one of us has

noted three such instances in the mouse) ; but as in every

instance we have been concerned with a dropping out of

one gene we can practically leave them out of account

here. There exist pure species, but there certainly also

exist variable species, species which are certainly liable

to change by selection.

In evolution we are certainly concerned with two dif-

ferent sets of processes, on the one hand with the causes

of variability, and on the other hand with the processes

which limit variability.

Throughout this paper we will call total potential

variability the quantity of genes which not all the mem-

oorn and A. L. Hagedoorn, ‘‘ Studies on Variation and Se-

lection,’’ Zeitschr. fiir Induktive Abstammungs- und Vererbungslehre, 1914.

A. C. Hagedoorn and A. L. Hagedoorn, ‘‘ Can Selection improve the ity

of a Pure Strain of Plants?’’ Journal of the Board of Agriculture, 1914.

5A. L. Hagedoorn, ‘‘The Genetic Factors in the Development of the

fouse-mouse,’’ Zeitschrift fiir Induktive Abstammungs- und Vererbungs-

lehre, 1911.

392 ` THE AMERICAN NATURALIST (Von. LL

bers of a group have in common, or for which they are

not pure (homozygous), and the variability which this

impurity makes possible in the descendants.

At least ideally, we can express the potential variability

of a group of individuals in a number. There certainly

exist species with a total potential variability of zero;

these are, for instance, the pure lines of certain autogam-

ous plants, those species for which Lotsy would like to re-

serve the term species altogether.

We will now try, by the aid of this new term, total poten-

tial variability, to give such a definition of the word

‘t species” that it comprises everything which zoologists

and botanists, geneticians and systematists, have vaguely

meant by it. Our definition is as follows:

A species is a group of individuals which is so consti-

tuted genotypically and which is so situated, that it auto-

matically tends to restrict its total potential variability.

Every group of individuals which is closed to the ad-

mixture of individuals from without, such as the de-

seendants of an autogamous plant, the dogs or cattle in

an exclusive stud, a ‘‘Paarungsgenossenschaft’’ of ani-

mals or plants bound by a peculiar habitat, has the tend-

ency to become purer and purer automatically, and to

reduce its variability continually. Species originate,

given a certain variability of a group of individuals,

through all those agencies separately or in combination

which bring a group of individuals (not necessarily a

small group) into such conditions that the new group has

a tendency to become pure for its own genotype. We can

not say in general that species are produced by inbreed-

ing, or by isolation, or by a change of habitat, or by

colonization, or by selection exclusively. An individual

or a group must have a certain amount of potential vari-

ability to be able to produce a species, different from the

one to which it belongs.

We know now that the genes themselves are invariable.

There remain only very few authors who still believe in

the variability of the genes. It is therefore necessary to

No. 607] RATS AND EVOLUTION 393

find out the causes for genovariability. Real mutation,

as far as we know, exclusively consists of an occasional

loss of a gene without visible cause. Mutation therefore

can at the utmost heighten the potential variability by

one. De Vries’s conception of periods of mutation is at

present only of historical interest.

In our opinion, crossing, recombination of genes by

mating of individuals of unequal genotype, is to be re-

garded as the only real cause of variability. There is no

good reason to change the opinion of one of us, namely,

that there exist three different kinds of variability.®

A. Modification, the non-inheritable effect of the non-

genetic developmental factors.

B. Real inheritable variation caused by mutation, loss

of genes.

C. Real inheritable variation by recombination of

genes.

Lotsy has subscribed to our statement (loc. cit.) with the

exception that he denies the existence of loss-mutations.

We can no more say that species originate by crossing,

than, that they originate by isolation. New pure lines of

autogamous plants, the kind of species for which Lotsy

wants to reserve the term, can of course originate in the

descendance of one hybrid plant. There is no funda-

mental difference between evolution in these plants in a

state of cultivation and what it must be in nature. But

in allogamous organisms, we will only in exceptional cases

meet in nature the same course of evolution as in our

cages or experimental plots.

Even if crossing in the widest sense is the sole cause of

variabilty, we must not suppose that, as a rule, new species

come into being in the F, or F, generation from a cross.

If we make a hybrid between species, this hybrid indi-

vidual will have a total potential variability which is at

least as great as the number of genes which were not

common property of both the forms crossed. If we com-

oorn, ‘‘ Autokatalitical Substances the Determinants for

6A. L. H

the Inheritable Characters,’ Roux’ serie Vorträge und Aufsätze über Ent-

wicklungsmechanik, Leipzig, 1911.

394 THE AMERICAN NATURALIST [Von. LI

pose a group of nothing but such hybrid individuals we

will get an enormous amount of variability in succeeding

generations, and when the group gradually becomes more

and more pure for an own genotype this may be a com-

pletely new one. A species may have been produced with

totally new characters, possibly intermediary between the

parent species in some of them. The chance that hybrids

of allogamous organisms, even if they are viable and

perfectly fertile, will inter se produce a new species is

exceedingly small in nature. It is much more probable

that the process of species formation after crossing is as

follows:

There exists a species A, with a restricted potential

variability, a set of habits and mode of living all of its

own, adapted to a certain environment. As a general

rule, individuals of this species A mate exclusively with

members of their own species. Once in a while, small

groups may split themselves off from the multitude by

colonization, and each of these groups will have its own

potential variability, and each will gradually become pure

for its own genotype, and will be less variable than the

multitude.

In the same country there exists a species B, with a

slightly different genotype, a different potential variabil-

ity. Species B is somewhat differently built, somewhat

differently coated, compared with A, and therefore fits

into a somewhat different environment. As a rule, indi-

viduals of the two species do not come into touch. Let

us take as examples the grey-bellied Mus alexandrinum

which lives in houses and on roofs in northern Africa,

and the white-bellied Mus tectorum, which lives in trees

in the same countries. The same holds true for the house-

rat and the field-rat in Java, likewise for the house-rat

and the tree-rat.

Even if matings between the two species furnish hybrids

which are completely fertile, even in localities where two

species overlap and are plentiful, the occasional hybrids

will be far in the minority compared to individuals pro-

No. 607] RATS AND EVOLUTION 395

duced by matings between house-rats and house-rats or

tree-rats inter se. If the occasional hybrids grow up,

they will either become house-rats or tree-rats, biolog-

ically speaking. In the first case they will mate with in-

dividuals of the house-rat population, in the other case

with tree-rats. A new group, so situated that its potential

variability is bound to be reduced to produce a genotype

of its own or a new species, these, a few hybrid rats will

certainly not produce. A single mating of a house-rat

female with a tree-rat male may be the cause for a height-

ening of the potential variability of the house-rat popula-

tion into which the hybrids merge. Eventually this higher

potential variability will be reduced again. And re-

versely, an occasional mating of tree-rat females with-

house-rat males may be the cause for a greater potential

variability of the group of tree-rats to which the females

belong.

If it so happens that a few animals colonize out of such

a population at the time when the potential variability is

still higher than ordinarily, such a colony, which will

have a potential variability smaller than that of the mul-

titude, will have a chance of having a range of variability

differing from that of the multitude. Such a group may

become pure in respect to a somewhat longer tail, a some-

what darker belly or a somewhat greater size, as com-

pared to the population from which it ultimately was de-

rived.

Very good examples of such a process can easily be

found by observing the evolution of certain species of

dogs or poultry under domestication. For instance, the

species Airedale terrier has become variable, and there-

fore liable to the influence of selection in different direc-

tions, because of the fact that hybrids with Dobermann

pincher in Germany, and with the Gordon setter in Eng-

land, have been taken up into the species, the stud not

having been closed rigorously, such as the Sloughi stud,

or the Jersey cattle stud. But it must not be thought

that a new, improved species of Airedale terrier has been

396 THE AMERICAN NATURALIST [ Von. LI

bred from such hybrids inter se. The potential variabil-

ity of the collie was very small, a few years ago. Hybrids

with the Russian wolfdog have been taken up into the

species. For this reason the variability has been very

extensive during a number of years. And at present this

variability is reduced again, by selection. In the mean-

time the species has been changed as a whole, the fashion

having changed and having made much of the possi-

bilities afforded by the cross. The collie, which formerly

was an intelligent, affectionate dog, with a head shaped

like a fox; : inclined to be noisy, and to run after every-

thing ; with long straight, outstanding hair, and with color

ranging between black and tan, and sable, with a variable

-amount of white, has changed completely. The show

collie now is rather a treacherous and surly dog, with a

head shaped like that of a llama, silent and lazy, with hair

which inclines to be soft and wavy. The color is much

more variable and now includes white, slaty, creamy, and

generally fade tints.

In chickens, crossing is a common way of ‘‘improving’’

a species, and in all those instances we happen to know,

the hybrids were made by using an individual presenting

a character which it was thought desirable to fix into the

breed, or a certain degree of development of a character,

not reached by even the best individuals. Such an indi-

vidual used for crossing is sometimes a pure-bred animal

of another species, but much more often a mongrel of un-

known extraction, happening to be somewhat like the

breed to be improved, with the exception noted above.

It is the practice to breed the hybrids obtained from the

cross back to the species, and their offspring again,

always selecting those individuals which come nearest to

the general conformation of the species, but which have

the character to be fixed into the breed. For instance

one may want to breed blue Wyandottes. The breeder

will then take any blue fowl which happens to look some-

what like a Wyandotte, mate it into a strain of first-class

white or black Wyandottes, breed the hybrids back into

No. 607] RATS AND EVOLUTION 397

his species, selecting from among their blue offspring

those which are the most like a good exhibition Wyan-

dotte, and so on, for a number of generations. It is easy

to see that in such a case the general potential variability

of the whole group is very much increased. It diminishes

automatically again, because of the fact that in every

generation a few animals produce a great number of off-

spring. If ten young cockerells of a new species of fowl

were habitually derived from ten fathers, the progress

in the direction of purification, ‘‘fixing’’ the breed, would

be almost nothing. But as ten young males habitually

have only one or on the average less than one father, in

other words, as only a very small percentage of males

in every generation is used for breeding purposes, auto-

matic purification, automatic diminishing of the total

potential variability of the group, is very rapid. It is to

be noted that in the absence of selection, the group may

become pure for almost any conceivable genotype given

in the potential variability, the genotypic diversity of the

first animals. Therefore any character which has re-

ceived no or small attention from the breeder may turn

out to be different from what it was in the species to be

altered into a new breed. It is for this reason, very com-

mon to observe that a number of apparently closely re-

lated species in the common fowl, or in domestic pigeons,

differ, not only in the points which are obvious to every

observer, but in other minor points as well, points which

need not be in any way correlative to the obvious dif-

ferences. A few examples. The different species of Leg-

horn resemble each other very closely, differing to a

casual observer in color only. But the comb of black

Leghorns is noticeably larger than that in white and

brown Leghorns and the ears of the black species are

larger than in the brown and the white. The white Leg-

horn has a lesser tendency to become broody than the

buff. The hens lay more eggs than those of the buff or

the black breed. The plumage is generally looser and

longer in buff Leghorns than in blacks.

398 THE AMERICAN NATURALIST [ Von. LI

In the Wyandotte group of species, the texture of the

comb is very different in the blue kind from what it is in

the silver Wyandotte. The length of the tail feathers

differs very much in the different breeds. The white

Wyandotte lays dark brown eggs, the silver Wyandotte

lays salmon-colored eggs with minute white spots, the

black Wyandotte lays white eggs.

: It is very rare for new species in chickens and pigeons

to come up to the quality of old established ones, unless

the fashion or standard happens to change. The shape

and carriage of the tail, and the general shape of the body

are very much better in white Fantail pigeons than in the

newer black-tailed whites or white-tailed blacks. And the

shape of the new blue Wyandotte is not yet what it is in

the white and the silver.

We know of only a few instances of new dog or poultry

species being bred from hybrids inter se. In those cases

the breeders had no very definite object in view to start

with. This mode of origin of species under domestication

is certainly not the common one. Species of cultivated

animals are commonly being changed by a very notice-

able conscious selection. The variability necessary for

improvement is continually kept up, sometimes by de-

liberate, but mostly by a kind of unintentional crossing,

that is to say by admitting exceptionally fine offspring

produced by matings of hybrids back to the species, into

the registry. On the other hand, automatic purification,

automatic reduction of the heightened potential variabil-

ity, is the necessary outcome of the fact that only very

few and very exceptionally ‘‘good’’ males are used as

breeders.

Species of tame animals, especially fertile ones as

chickens, are easily kept apart so that excessive splitting

up into secondary species is possible and even the rule.

For instance, in those species in which a certain much

sought quality is influenced by the internal secretion of

the sex-glands, it is obviously impossible to make a pure

strain in which both males and females come up to one

No. 607] RATS AND EVOLUTION 399

standard. In silver Wyandottes, the standard calls for

white feathers, which are bordered by a line of black.

Now the males are very much lighter than the females,

so that in a pure species, in which the males are correctly

marked, the hens are too dark and in a strain in which the

hens are good, the males are too light. The only way out

of the difficulty has been the establishment of two dif-

ferent species, one which produces correct males and the

other which produces exhibition hens. This splitting up

of a species into two is very common in chickens. Such

pairs of two species are kept as far apart by careful

breeders as Wyandottes and Leghorns.

In the natural state, two species, even when hybrids

between them are perfectly fertile, and when the indi-

viduals exhibit no preference for mating with their kind,

may keep apart, if only each group is specially adapted

to an own environment, so that the bulk of the animals of

each species has no chance of mating with anything but

their kind.

Even if there is no sdaplation to an environment to

keep the multitude of the individuals of a species in their

place, two species may keep apart when only the animal’s

habits keep them from wandering very far. In such a

case the borderline, where outposts of both species mix,

will present a highly variable population of hybrids of

all grades, the variation becoming less and less the more

we look.for the animals in the exclusive territory of each

species. A case in point is, we think, the case of the two

woodpeckers cited by William Bateson.” When the spe-

cies differ in only one salient characteristic, the difference

between them being in the main due to the presence or

absence of only one gene, intermediates must be absent.

In such a case the two species may be present in more or

less extensive patches, separated from each other by

narrow strips of territory having a mixed population.

Such seems to be the case of the black and the hooded

crows in Europe. Here adaptation plays no rôle ap-

parently.

7 William Bateson, ¢<Problems of Geneties,’’ Cambridge.

400 THE AMERICAN NATURALIST [Von. LI

In one territory, two species can coexist only if for

some reason matings between individuals of different

species are impossible or at least less common than

matings between members of the same species, or when

the hybrids are sterile.

No matter where we find rats of the Rattus group there

are never more than one kind of tree-rat of this group, one

house-rat, and one field-rat simultaneously present in one

locality, the tree-rat living and foraging in trees, and

being exceptionally aggressive, the house-rat living in

houses, fearing water, and not afraid of man, the field-

rat living even far from cover, scarcely able to climb and

too timid to enter inhabited houses. In some regions

miniature rats, belonging to the same group, but too small

to mate with the bigger species as a rule, inhabit houses

and fields, it being very probable that these belong to two

species, a small field-rat and a small house-rat.

Such a set of three rat species, a tree-rat, a house-rat

and a field-rat, we not only find in Java, but also on Su-

matra, the Malay peninsula, British-India and Egypt.

It is our experience that rats of the Rattus group cross

with the utmost facility, and produce fertile hybrids. We

have come to the conclusion that the majority of house

rats remain pure for their own characteristics, even for

those which have no value whatever for the adaptation

of the species to its surroundings, not because no hybrids

are produced with tree-rats or with field-rats, or not be-

cause such hybrids when produced are sterile, but for the

simple reason that such hybrids are so far in the minority

that they disappear into the multitude of house-rats, and

that the heightening of the potential variability of the

house-rat multitude by such occasional crosses is only

local and very transitory. The same is true for the field-

rat multitude and the tree-rat population. Crossing pro-

duces for each of the three species a heightening of the

potential variability, and therefore it is possible that

more or less temporarily, there come into being small col-

onies of somewhat aberrant house-rats or field-rats, in

isolated places. r

No. 607] RATS AND EVOLUTION 401

In Solo and Djocjacarta in Java, the great tobacco-

growing companies erect enormously big sheds con-

structed of a very complicated scaffolding of heavy bam-

boo, with a thick thatched roof made of palm leaves.

Such sheds are erected in the midst of the fields, mostly

far from native villages. The native laborers leave food

about the structure, so that it very soon becomes inhabited

by rats. Now the rat population of these drying sheds is

always composed of house-rats; field-rats are too timid to

live permanently in places where human beings move

about so much. But as the sheds are built in isolated

places, they do not get their house-rat population as such

from neighboring houses. We are convinced that into the

composition of such rat populations, field-rats, and

hybrids between field-rats and house-rats enter to some

extent. This is the explanation of the fact, that very

often the rat population of such a shed is found to be

composed of an aberrant type of rats. If the population

of such a shed becomes very numerous and a native vil-

lage of some sort springs up in the immediate neighbor-

hood, the aberrant new type may have a swamping influ-

ence upon a minority of typical house-rats brought along

by the natives, so that the type may become locally com-

mon, and temporarily supersede the ordinary house-rat.

We remember Major Ouwens showing us great num-

bers of white-bellied house-rats, received from a tobacco-

growing firm in one of the big centers, Klaten.

When there exists in a certain locality an abundant pop-

ulation of rats of a certain species, immigration of a few

rats belonging to the same group but to a different species

will have no effect. And of course it will make no dif-

ference whether the multitude belongs to the common

species and the few immigrants to an aberrant new type,

or reversely, as in the case of the rats in the tobacco-

sheds.

Ships may occasionally bring rats to Java, Pras Eng-

lish India, or from Australia or Singapore, but the rat

fauna of Java will not be enriched by a new species, as

402 THE AMERICAN NATURALIST (Von. LI

‘the result of such an importation. At the utmost, the re-

sult will be, that the rat population of the warehouses in

the port of entry will become somewhat more variable. It

may happen that a single warehouse, empty of goods and

rats, will receive a small colony of imported rats with a

load of rice and rattan, but on the type of the rats of Java

such an occurrence will be of no importance.

A very different thing must happen, when rats from

ships come ashore in places where there is as yet no popu-

lation of rats of that same group, for instance, on newly

settled islands. There the imported rat population will

gradually become constant, but as often for an own, new

set of characters, as for those of one of the species, which

originally went into the composition of the ship’s popu-

lation. The rat population of the bigger ships very often

is a very peculiar one. It is not uncommon to find a very

homogeneous lot of rats on board a ship, for which no

corresponding type specimen can be found in any mu-

seum. In other instances the population of a ship may be

very heterogeneous indeed. The rat population of a ship

originates from rats which come aboard with cargo in

the most diverse places. By crossing of such animals, all

kinds of new types may arise. The rats on board a ship

live under very peculiar circumstances. As the animals

can not emigrate, their number is absolutely dependent

upon the kind of goods stowed in the ship. For a time the

circumstances may be so favorable for a multiplication

of the animals, that the ship is speedily overrun with rats.

Especially is this the ease when part of the load affords

good hiding places, such as rattan bundles, and if food is

abundant, as in a load of copra. On unloading part of

the cargo, a famine may result, from the effect of which

all the animals, excepting only a very few, may succumb.

The result of such a catastrophe, especially of a series

of catastrophes, alternating with periods of plenty, must

be, that the population, no matter how variable at one

time, must very quickly become pure for a genotype of

its own. The occurrence of rats on board of ships is so

No. 607] RATS AND EVOLUTION 403

common that it must be an exception when a ship trans-

ports a number of rats from one port to the other without

changing the type.

The rat population of a frequented port can not be

taken as typical for the country where the port happens

to be situated. It is always easy to find new types of rats

- for museum collections in cities having much shipping.

But it goes without saying, that such animals, with aber-

rant coat characters, aberrant tail length, aberrant type

of skull, perhaps, may not be called species without

further ado. It is very possible that at the present mo-

ment there exist in Sourabaya twelve still undescribed

types of rats, which exist nowhere else on Java. But it is

probable that after ten years, thirty-five generations,

those types will have all made place for an additional

dozen of completely different aberrant types.

Such new types have on Java, which is thickly infested

by rats, no chance as house-rats, no chance as field-rats,

no chance as tree-rats. <A little better is the chance which

species have, whose habits of life adapt them to a special

environment, where they have little or no competition to

fear, or at least only from species which have such a geno-

type, that they do not mate with the invading species.

Mus norvegicus does not mate with animals of the Rat-

tus group and therefore this species can, without being

annihilated, penetrate into a region which is already

settled by Rattus rats. We have tried to product hybrids

between Mus rattus and Mus norvegicus. We put eight

males and ten females of Mus rattus into a large cage, and

when we observed the animals mating, we took out the

females, and substituted an equal number of Mus norve-

gicus females. The males kept on copulating, but al-

though we saw numerous apparently normal matings

taking place, we never got a pregnant female. There is,

as we could observe, no real antagonism between Mus

rattus and Mus norvegicus. It is our experience that if

we put two Norvegicus rats who do not know each other

in a small cage together, there seldom is any serious fight-

404 THE AMERICAN NATURALIST [Vou. LI

ing. As a rule nothing happens in particular when we

introduce a Norvegicus to a Rattus rat. But if we put in

one cage two Rattus rats which are strangers to each

other, they almost always start a fight, and generally it is

a matter of life and death.

Mus norvegicus is a real water-rat, sewer-rat, field-rat,

and in some parts of Java, where the poor houses have

no floor, and where there are many covered sewers, as in

Solo and Sourabaya, it becomes a house-rat in a certain

sense. But it takes extreme negligence of the inhabitants

of a house to make it shelter this rat. It happens that in

houses where the bedstead is never moved from its place,

and where the space below it is used as a place to dump

the garbage, that this rat establishes itself there, exca-

vating numerous large burrows.

It is very remarkable that this rat, which is extremely

uniform all through its range in Europe, is very rare in

this island, where the geographical distribution shows it

to be a recent immigrant, which has come in by way of

the big rivers. The skull, the shape of the parietal ridges,

the relative size of the bulle, the relative size of the

molars, the relative position of the choane, characters

which are very constant in Europe, become very variable-

here. In size it varies very much, the biggest individuals

weighing nearly twice as much as the biggest European

animals. ‘The color, which hardly varies in Europe,

varies between very light gray agouti to a silvery blackish

dark gray, with dark belly there. It looks to us very

probable that this great variability may be the result of

crossbreeding between this species and species of Gu-

nomys or Bandicota. The variation of the species in Java

is certainly towards the characters of these rats, which

have a somewhat similar mode of life as Mus norvegicus.

As yet it has not been possible to make Bandicoots

breed in cages, although we have tried to make them do

so in very quiet concrete rooms. Whenever it will be

possible to breed these rats it will be very interesting to

observe whether Mus decumanus will mate with Bandi-

No. 607] RATS AND EVOLUTION 405

coots, and whether the hybrids are fertile. It seems cer-

tainly significant that almost nowhere is the ‘‘wirok’’

population composed of Norvegicus animals as well as

Bandicoots. From one locality the people will report and

send in gray ‘‘wiroks’’ (Norvegicus), from other locali-

ties they will send long-haired black ‘‘wiroks’’ (Bandi-

coots).

From the standpoint of a systematist, it may look as

if it were hardly more than a, question of education

whether a man is going to follow Hossack and bring all

the animals of the Rattus group to one single, variable

species, Mus rattus, and will look upon the differences

between the three main species of this group as unin-

teresting variations, because he finds all kinds of inter-

mediates in a museum, or whether he is to take the oppo-

site view with certain English museum people, and give a

new species name to every couple or trio of rats of a not

hitherto described species.

When we start with a drawerful of dried skins, it cer-

tainly is a matter of personal taste whether we will dis-

tribute the skins over three or ten or twenty smaller

drawers, each representing a species. Systematists may

quarrel about it, whether a difference in contour of a line

on a skull, or a different number of scales on the tail is or

is not sufficiently important to make a group deserve a

species name, or whether to call it a variety of some other

species.

As soon as we have to deal practically with a group of

animals like the rats of Java, and have to consider the

economic importance of tree-rats to plantations, of house-

rats in connection with infections, and of field-rats as re-

gards crops, the museum kind of systematics very often

proves insufficient, and we have to begin the work anew

in another way.

I remember that one day, among a batch of some ten or

eleven thousand rats caught on that day in a sugar plan-

tation, Ketangoengan, there were two with markedly

ruddy hue, two with very long tails, three house-rats

406 THE AMERICAN NATURALIST [Von. LI

(brought by the same boy), one tree-rat and several thou-

sand field-rats. If we suppose a man to prepare a batch

of these rats to send them to a zoological museum, this

museum would most certainly receive two reddish field-

rats, two long-tailed ones, three house-rats, one tree-rat

and three normal field-rats. It stands to reason that these

dead rats would become five species in the museum, and

to anybody looking through the drawer later on, these

five species must look equivalent.

By observing all kinds of rats with new characters in

the descendance of hybrids, we have become very skepti-

cal indeed in accepting as real existing species those rat

species which are represented by two or three skins in a

museum, such as, for instance, Mus Blanfordii, or Mus

Diardii.

It is possible that two real species, in the sense that

they are real constant types, which remain constant and

return to constancy after a cross which heightens their

potential variability, not infrequently intercross, the

hybrids always disappearing again into the multitude of

typical individuals of either species.

The finding of such hybrids has undoubtedly confused

the species question very much; on the one hand, several

hybrids or sets of hybrids of the first generation, as well

as ‘‘back crosses’? must have been described as species,

whereas, on the other hand, some naturalists, through the

observation of such intermediate individuals, linking the

types of the parental species must have come to the con-

clusion that they were dealing with only one varying

species.

We must never forget that, though certain systematists

may think that they can divide a chest of skins, according

to their taste or even after profound morphological or

biometrical studies, into two or six or sixty species, in

reality the boundaries between species in nature are far

from arbitrary. And species are really existing genuine

groups, with natural, permanent limits.

There do exist very peculiar groups of animals, poly-

No. 607] RATS AND EVOLUTION 407

morphic species. Whereas polymorphy in autogamous

plants really means the existence of a multitude of pure

lines, a great many closely related pure species of plants

which can easily be seen to originate through occasional

crossbreeding, polymorphic species in animals and wild-

flowering plants seems to be fundamentally different, in

that there is a continual crossbreeding going on without

the corresponding automatic purification which we see

everywhere. Such species as the ruff and some grouses

are always as variable as ever. The street-dog popula-

tion or the population of non-selected cats in any large

town will furnish examples of polymorphic animal spe-

cies.

Now one of the chief factors in the diminishing of the

total potential variability of a group is certainly the fact

that a given number of animals in one population are cer-

tainly not the descendants of a number of parents of the

same magnitude, but of a very much smaller number of

parents.

‘And it is easily conceived how the fact that every

female mates with several different males at each concep-

tion changes this disparity. This would partly account

for the continued existence of polymorphy in the ruff and

in the cats and dogs whose breeding is unrestricted, and

in the sugar beet.

As to the reality and the limitations, and differences of

species, the only way to reach a satisfactory conclusion

is breeding them. And the possibility of breeding rats

under scientific control is one of the reasons why so much

of the experimental probing into the species question is

connected with rats.

The Javanese house-rat has a uniformly dark belly,

dark feet and a long tail, and a certain ridge on the pari-

etalia which no other Javanese rat possesses. Once in a

while a rat is caught in a house or a loembong (rice store-

house) with a short tail, or a somewhat yellow tinge, or

with markings on the hind feet, or with a white beily. By

a study of these individuals only, it is impossible to find

408 THE AMERICAN NATURALIST [Von. LI

out whether the species house-rat is really so variable, or

whether we are dealing with a new species, or whether

they are hybrids having a field-rat or tree-rat father, or

descendants, backcrosses from such hybrids. The only

way to get light on these questions, which are not only of

interest for economics, but for genetics as well, is the

making of hybrids. It is very probable that in reality

there does not exist anything which corresponds to the

dozens of rat species which can be found in all the mu-

seum catalogues.

Zoologists and botanists often make short work of the

hybrid question, by. simply calling all intermediary indi-

viduals hybrids. In reality hybrids are very often inter-

mediary, especially when the parent species differ in a

great many genes. But very often hybrids show totally

new characters which would make them species in the eye

of several systematicians. `

We mated the small brown agouti house-rat of Java with

a large yellow, rather long-haired male, descending from

a complicated cross combining Mus rattus, Mus alexan-

drinus and Mus tectorum. The hybrids are dark grey,

with white belly and orange-ruddy sides, and very much

smaller even than house-rats of the same age. Rats like

these from a warehouse or from a ship, especially a litter

of similar ones as in our case, would certainly have ob-

tained a new species name in a museum. It is not impos-

sible that similar animals with a similar origin are

already present in a museum under a new name, as repre-

senting a rare species. As long as we had no proof that

a new alleged species of rats were not fairly constant

under cultivation, and produced a not too variable de-

scendance, we would not accept it as a good species. And

even so, we would require to know whether there were

anything in its habits of life, or in its relation to other

species, which warranted a belief that it would not be

swamped in a few generations. For the only thing which

distinguishes a species from a variety is the automatic

permanency of species as compared to the relative inse-

No. 607] RATS AND EVOLUTION 4.9

cure standing of varieties. If all the dwarf mice in a

given haystack have white tail tips, because of the fact

that the first two mice which happened to find the stack

when it was newly made had white tail tips, we can not.

say that we are dealing with a new species. We have a

white-tailed variety of the local species. But if we take

a dozen of these mice into our house and succeed in breed-

ing them in cages, we may say that now we have founded

a domestic species. This species will continue to exist

as long as men will keep dwarf mice in captivity (witness

the so-called Irish rats) and long after the stack is broken

up, and the few remaining white-tailed mice have been

taken up into the normal species. The difference between

species and varieties is not determined by the magnitude

of the departure from a given type, and it is not a genet-

ical difference. It is a difference in expected permanency.

Varieties can become species by migrating into new sur-

roundings, or by a change in surroundings.

It seems more than probable that a great many species

in museums are nothing but aberrant types which fall out-

side the normal variability of an existing species, and

have originated by crossing, one or more generations re-

moved.

As we have already said, the hai way to find out

whether individuals intermediate between existing species

have to be looked upon as hybrids, or descendants from

hybrids, or as variants of one of the species; is by pro-

ducing the hybrids and comparing them to the collected

material.

It is rather difficult to get rats of the Rattus group to

breed in captivity. As we did not succeed in the begin-

ning, we rented a small vaulted room in the ruins of a

castle in France, fitted it out with numerous old boxes and

baskets, faggots and straw, and turned two females loose

in it with one male. There we gave them enough food to

last them for a week so as to disturb them as little as pos-

sible.

Later on, in Bussum, Tollaiid; we succeeded in breed-

410 THE AMERICAN NATURALIST [Vou. LI

ing the rats in cubical houses of four feet in each direc-

tion, made of asbestos slates, and filled with rubbish for

the animals to hide in. In the beginning very many

animals refused to breed even in these cages, and as the

animals were crossbred from the very start, we believe

that a sort of very rigorous natural selection must have

been the reason for the fact that after a few generations,

every couple chosen could be relied upon to breed in as-

bestos cages, four feet deep and sixteen inches high and

wide. Thése cages were covered with small mesh netting

only on one half of the front, and they opened upon a sort

of corridor which was nearly completely dark, and could

be darkened entirely. In Java some of our rats even bred in

small tin cages of the size of kerosene tins. In Buiten-

zorg the Department of Agriculture has constructed a rat-

house from plans furnished by us, composed of a series

of concrete rooms, so made, that the animals can be ob-

served from a darkened corridor without knowing it, and

a series of masonry tanks with wire covers. This house

is used for a biological study of rats, and for experiments

in eross-breeding, to determine the status of doubtful

material.

It is not necessary to clean the cages very often, if only

they are well filled with dry straw and not overpopu-

lated. Disturbing the animals keeps them from breeding

freely. It happened that rats of this group bred in open

wire-netting cages, but in these cages the danger exists

that the mother can not make the nest sufficiently dark

and secluded to prevent disturbance by the male. It is

our experience, that a young female who has once neg-

lected or destroyed her litter, is almost certainly lost far

further work.

As a rule the females do not leave the nest for the

first two or three days, or as long as the young are cry-

ing. Afterwards, they cover the young in the evening,

bury the nest under earth, if they have it, to dig it up

again at the end of the night. When the young are three

days old, the mother permits young from an earlier litter

No. 607] RATS AND EVOLUTION 411

to return to the nest, but exclusively the females. Only

when the young open the eyes at fourteen to sixteen days,

the father is permitted to return into the nest. The young

males are kept out of the nest until the young are weaned.

To observe the habits of rats of this group, an endless

patience is required, as the animals, which are extremely

sensitive to hardly noticeable sounds and movements,

habitually are active only at night. If it is possible to

darken the room completely, it is possible to observe the

animals in the daytime by the light of a small lantern,

after rousing them. Weak artificial light seems to make

hardly any impression upon rats or mice.

We have seen wild rats, mating and foraging, to con-

tinue eating or playing, even when a small lamp was

waved to and fro under their very noses, whereas the

same animals would be disturbed by the falling of the

head of a match. A good plan is to feed caged rats only

once a day, at a set hour, to which they accustom them-

selves very rapidly, as in this way they can be counted

upon to be up and doing at a time when it is most con-

venient to observe them. Even wild-living rats and mice

accustom themselves to a fixed hour of feeding. A draw-

back of the system is that when the supply of food is not

more than abundant, delay in feeding of only two hours

may cause the death of recently weaned, sometimes even

of half-grown rats. The discouragement may be looked

upon as being partly the reason of this, for these rats are

extremely nervous animals. A shock, a sudden fright,

may cause them to lose consciousness for a long time, and

fright will often kill them outright.

To be able to observe rats of this group at our ease we

tried to tame some of them. Young Mus decumanus taken

at the time of weaning become tame, or rather stay tame

without more trouble. It is impossible to get them tame

by taking them at an age of six weeks to two months,

when they are wild and apt to bite. Full-grown animals

are easier to tame, even if wild caught.

To make Mus rattus tame, it is necessary to handle the

412 THE AMERICAN NATURALIST [Vou. LI

nest young before they are a week old, which is possible

only if the mother is tame enough to tolerate the dis-

turbance. In the first generations of our work we fre-

quently used tame Mus norvegicus females as foster

mothers. It is especially necessary to handle the young

from the very start at night, when they are very much

more active. Infinite patience is required for taming

these rats, for if once a young rat jumps from the hand,

which easily happens, as they are very nervous, it is im-

possible afterwards to induce it to remain on the hand.

It is possible to get the bigger species absolutely tame,

so that they will jump upon the owner’s hand when the

cage is opened, that they will come to the hand if it is

held out, will feed unconcernedly, will let themselves be

taken and restrained without resenting it, and that they »

will not let themselves be disturbed by onlookers even in

mating. It is curious to note that they do not seem to

know their trainer. A tame rat is tame in respect to all

humans. It seems as if taming a rat takes away a good

deal of its nervousness, as tame rats are very much `

quieter even-if among themselves, and will breed in

smaller cages, and grow fatter than wild ones.

Although we have had a good deal of experience in

_ taming nervous small animals we have never yet suc-

ceeded in taming the small house-rat, Mus concolor.

Even small blind nest young are so nervous that they

can not be induced to sit still in the hand without being

held. All we could do was to accustom the animals to

being restrained without resenting it.

There is a very great difference in the disposition of

different species of rats, even in one closely related group

such as the Rattus group. The field-rats, Javanese as well

as Egyptian, and from Sumatra, behave like Mus norve-

gicus, they are reckless, timid and impulsive. An escaped

field-rat can be caught in a moment, because it can be cal-

culated beforehand where the animal will run, namely,

along the walls, and thus it can be driven without any

trouble into a cage or catching net.

No. 607] RATS AND EVOLUTION 413

The house-rat, European as well as Javanese, is daring,

calculating and relatively little nervous, and on being

persecuted, looks out very well for possible hiding places,

in which the animal will remain immobile for hours. An-

escaped house-rat is very often found with the utmost dif-

ficulty. Their disposition makes them relatively easy to

tame.

The tree-rats, Egyptian as well as Javanese, try to es-

cape from a persecutor by climbing. They are excep-

tionally aggressive, we have certainly been bitten more

times by tree-rats than by all our other rats combined.

In our breeding experiments we used for all rats a card

catalogue. Every animal has its own card, on which are

noted its number, the numbers of its parents, eventual

outline drawings of its markings, and the numbers of the

animals it has been mated with, together with the num-

bers of its young born from these matings. In moving a

rat from one cage to the other its duplicate card was

moved with it to a receptacle attached to the cage. On

the card on file the cage number is noted in pencil. Ani-

mals which are dead get a distinctive mark, or their cards

are moved to the back of the file. With such cards it is

very easy to find out the ascendants and the descendants

of every given animal, and it is easy to arrange the card

on a big table in the form of a pedigree.

We started our experiments with Rattus rats, by taking

over some animals from Dr. Lewis Bonhote. From our

experiments, which we are about to describe, it became

clear, that crossing is not only the means of recombining

the characters of the species crossed, as many English

authors have it, but that absolutely new characters may

arise by it. This does not mean that new genes came into

being; the genes present were recombined in as far as the

total potential variability of the hybrids permitted. Only

new characters arose, which never showed themselves in

the species without crossing.

Dr. Bonhote in England crossed the Egyptian house-

rat, Mus alexandrinus, a gray agouti rat, with rather

414 THE AMERICAN NATURALIST [Vou. LI

short tail and dark belly, with the Egyptian tree-rat, Mus

tectorum, a fulvous-agouti smaller rat with a long tail

and white underparts, sharply demareated. The young

were all like tectorum. These animals, on being mated

inter se, gave some dark-bellied young, and from the

mating of two ‘‘tectorum’’ young he obtained, together

with some dark-bellied and white-bellied agoutis, a few

orange yellow rats. At this stage we took over his ani-

mals. Through the excessive zeal of the French custom-

officers, who feared that the animals might carry mala-

ria(!), they were returned from Dieppe to London, and

most of them died on the way, including all the yellow

ones. When finally the rats reached us in Verrieres, we

obtained only a few white-bellied animals.

White-bellied female no. 13 finally mated in the big

room with a black French Mus rattus male, after having

killed a great many males in cages. The hybrids were

black and had very long tails. We lost a good many in

transporting the animals from France to Holland.

One of the white-bellied agouti rats obtained, tree-

footed number 17, was mated to two black hybrid females,

24 and 25, and with tectorum female no. 19. From the

mating of 17 with 24 we obtained twenty young, of

which seven were blacks, seven white-bellied agouti

(like tectorum), five yellows and a few pearl gray.

Among the blacks one had a white tail tip, and one of

the white-bellied agoutis had also a white tip to the tail.

Three of the gray-bellied agoutis were waltzers. These

animals behave exactly like waltzing mice. They run

around in small circles with amazing rapidity, and they

are unable to climb. But whereas waltzing mice are less

viable than their normal litter brothers, the waltzing rats

are as vigorous as normals. And whereas waltzing mice

are congenitally deaf, our waltzing rats can hear per-

fectly normally.

From the mating of male 17 with female 25 we obtained

seventeen young, seven blacks, of which one waltzer and

one white-throated, seven white-bellied agouti, two gray-

No. 607] RATS AND EVOLUTION 415

bellied agouti, and one agouti with lemon-yellow belly.

As females 24 and 25 were litter sisters, with the same

parentage, we may be allowed, for the present discussion,

-= to add their young together. There were 37 young, of

which 14 were blacks and 17 agoutis (expected 15.5 and

15.5). Of the 37, five were yellow, one pearl gray, two

with white tail tip, one white-throated, four waltzers, and

one yellow-bellied, all of which are animals with totally

new characters.

We can easily explain the origin of the new characters

as follows. If both parent species possess a gene, which

by its presence or absence makes the difference between

anormal and a waltzer, or in other words, if to be normal

a rat’s germ must at least possess either Y or Z, the

hybrids, which are impure for Y as well as for Z, bass

inherited Y from one and Z from the other parent, will

produce one germ-cell in every four, from which both Y

and Z are lacking. Therefore such hybrids will produce,

when mated among themselves, fifteen normal young and

one waltzer in every sixteen. If we expect the same rea-

soning to hold good for a number of new recessive char-

acters, which are displayed by neither of the parents, so

that animals lacking W and X will be yellows, others,

lacking U and V, will have white-tipped tails, we should

in our case expect to find among our thirty-seven young,

two to three (2.312) with the new character in every case.

In reality we found yellow five, pearly gray one, white

tail tip two, white throat one, waltzers four, yellow belly

one, that is 2.33 on the average.

These numbers make it clear that we are not dealing

with a sort of period of mutation; it was easy to see that

the new types were already given in the ganotype of the

three species crossed.

Female no. 24 later was mated back to her son no. 95.

From this mating we obtained among a number of normal

rats, one chocolate and two pearl-gray young. Later we

obtained a cinnamon agouti rat, that is to say an animal

that probably stands genotypically in a relation to agouti,

416 THE AMERICAN NATURALIST [Von LI

as chocolate to black. It is to be remembered that in this

group black is dominant to agouti. In all we obtained six

wholly new characters from our matings, clearly as the

result of the absence of two genes in every instance.

Matings of white-bellied animals with gray-bellied

gave either only white-bellied or a minority of gray-

bellied in F,. Gray-bellied rats clearly have a gene less

than white-bellied. This is the same result which Morgan

obtained in his work with animals of this group. Black

was dominant over agouti and clearly there were two

kinds of blacks, with or without the gene which makes the

difference between white-bellied and gray-bellied agoutis.

We never obtained white-bellied black ones. But the

blacks with the gene under discussion had a much more

deeply black color, very often with a green or a violet

sheen. We obtained yellow-bellied yellows, and, just as

in the agouti series, white belly was dominant over yellow.

Male 28 and female 34, both white-bellied yellows, gave

three white-bellied and one yellow-bellied young. Our

chocolate and cinnamon rats died on the steamer bring-

ing them to Java. The character white tail tip proved to

be recessive. We obtained pearl-gray young and yellows

from matings between yellows and pearl grays, but yel-

lows never produced pearl grays. Two agouti animals

sometimes produced yellows, but never pearl gray.

These were only obtained when one parent was either

pearl gray or black. In other words, the factors which

produce the difference between black and agouti animals

are the same which make the difference between pearl

gray and yellow.

Our new rats, waltzers, and animals with new colors,

such as they are can not be called species. We can make

species out of them by continuing the breed. If we sell

a number of animals of one color to rat fanciers, and they

get sufficiently enthusiastic over them to provide classes

for them at pet-shows, we will be justified in calling such

a breed a domestic species.

We saw that in our experiments with rats no new

dominant characters originated, unless we want to call

No. 607] RATS AND EVOLUTION 417

the colored sheen on certain black ones by that name. In

every instance there appeared new recessive characters.

For every one of them we could see that crossing, re-

combination of genes, was the cause, not loss-mutation.

But it becomes ¢lear that it is very difficult to be sure that

apparent cases of loss-mutation are not due to recom-

bination, unless the number of young in the generation

in which the novelty appears is rather large. If we

mate a species A to a species B, and some yellow or

long-haired or albino animals are produced in F, we are

rather sure that recombination and not loss of genes

causes the novel form, even if the number of young is too

small to know whether the new character was found in

one animal among every four or among sixteen. But if

we mate two animals belonging to one single species, and

it happens that each possesses a gene which the other

lacks, the two genes having equal influence on the devel-

opment but of such a nature that animals lacking both

are albinos, or yellows, the production of a few animals

with new recessive character may easily be looked upon

as mutation. In such an instance, it will be found that

the two animals which produced the heterozygote who

gave the aberrant young would be found to be homo-

zygous in respect to the presence of ‘‘the’’ factor. For

if we mate an animal having YY to the new form yyzz,

all the young will be dark, and none albino. Conversely,

if we mate the ZZ parent to the albino, it will also be

found to be homozygous, all the young will be colored.

In other words, test mating will in certain instances be in-

sufficient proof for the occurrence of a loss-mutation.

In the days when we talked about ‘‘unit-characters’’

and the factors which ‘‘determined’’ unit characters, it

was commonly held that crossing in the widest sense,

mating of forms with diverse genotype could not count

for very much in evolution, as it could only recombine

existing characters and not create new ones. We have

since learned to look upon the genes as upon things

which help with other factors in the development to make

an organism develop, and we now know that the action

418 THE AMERICAN NATURALIST [ Von. LI

of genes upon what were called ‘‘unit-characters,’’ is a

very indirect one. We now know that new characters

may certainly come into being through recombination of

genes. Recombination may result in the origin of new

recessive characters, and this process may look very

much like loss-mutation. And crossing may result in the

origin of new dominant characters, color in chickens, in

rabbits, extra toes in chickens, and this process will look

very much like positive mutation, the creation of a gene

out of nothing. If we except Œnothera species, dividing

the organic world into animals, plants and Cinotheras,

for as long as no solution is found for the baffling delayed

and abnormal segregation in Œnothera hybrids, we may

sum up as follows:

Evolution is the result of a combination of all those

causes which heighten variability and which limit it.

The only cause for inheritable variability in multicellu-

lar organisms which can be of any account in evolution

is mating between individuals of unequal genotype, cross-

ing in the widest sense (Amphimixis).

All those causes which tend to reduce the potential

variability of a group of organisms tend to make vari-

eties or species of these groups. Such causes are iso-

lation, migration, adaptation, selection and especially the

fact that, either periodically or regularly, the number of

individuals of one generation is very much smaller than

that of the preceding one. This cause of purification of

the type, which we see in operation everywhere (think

of the numbers of house-flies a year in the last and

first generations), operates quite regardless of adapta-

tion or fitness. To this cause working upon variation

may be ascribed numerous characteristics for which we

can invent no earthly use, and for which nevertheless

species are pure.

Whereas species and varieties are realities, systematic

division of the organic world into groups of higher mag-

nitude is wholly arbitrary, and may without any doubt be

arranged to suit the capacity of museum cupboards.

DIFFERENTIATION BY SEGREGATION. AND

ENVIRONMENT IN THE DEVELOPING

ORGANISM’

DR. VERA DANCHAKOFF

Brovoeicau investigations in the twentieth century have

markedly strengthened the belief in the specificity of

different kinds of living matter. Paleontology.has shown

the existence of organisms which have retained their

specificity during millions of years: specific germplasma

has carried through ages specific characters. On the

other hand discoveries in the world of microorganisms

have shown, that even their simplest forms are character-

ized if not always by specific organization, at least by defi-

nite metabolism and other biological qualities which imply

a specificity of their constitution.

I shall not discuss the problem of genus specificity.

My subject is limited to the specificity of certain tissues

and cells found in the organism, the final development of

which results in the symbiosis of differently organized

| tissues. The problem whether the relations of these dif-

ferent tissues is definitely determined by their specificity,

or whether there exist in the organism plastic factors

which from a homogeneous cell material may mould dif-

ferently organized products is still unsettled. The solu-

tion of this problem would be greatly advanced, if the

results of experimental and descriptive histogenesis

received due consideration. Though the microscope can

indeed not distinguish between various colloidal solutions,

it might and does give data of definite biological sig-

nificance.

Different genera and species show under the micro-

scope a different structure of their building stones—the

1 From the Anatomical Laboratory of Columbia University. Read before

the Section of Biology, New York Academy of Sciences, April 9, 1917.

419

420 THE AMERICAN NATURALIST [Vou. LI

cells, and most conspicuously in their chromosome-

complexes. The specificity manifested by genus and

species, whether it is centered in specific proteins of the

cytoplasm or in specific molecules of the chromosomes,

forms one great chapter of the specificity problem, while

the specificity of different tissues and cells is another.

It is often stated that the different tissues and cells

of an individual of a given species, all have identical

chromosome-complexes. If the chromosomes are consid-

ered identical in all the cells of an individual, they can

not be regarded as responsible for the specificity of his

tissues. They can place no restriction upon a wide

range of permutability between the various cells in the

organism, can put no restraint upon unlimited regen-

eration or impede the perpetual proliferation of any type

of cells. The assumption of equality of chromosome-

complexes in different tissues and of their invariability

excludes them from the range of possible carriers of the

specificity of tissues and is usually associated with the

belief that the specificity of tissues is brought about by

segregation of cytoplasmic materials during develop-

ment. The possibility is also considered, that environ-

ment may act as differential factor.

Of these two latter factors the segregation of cyto-

plasmic materials in the early stage of development leads

to the formation of large cell groups (germ-layers,

anlages of organs), the differential characters of which

are believed to be determined by the presence of definite

cytoplasmic materials, transferred to them from the cyto-

plasm of the ovum. The differentiation brought about by

segregation is regarded as irreversible and though the

cells of the germ-layers show a great plasticity in their

response to different factors, there is a well-marked

limitation of their potencies, if compared with the first

blastomeres. It is believed, however, that the segrega-

tion does not affect the chromosomes and produces merely ~

a differential distribution of the cytoplasmic constituents

of the ovum among the resulting cell groups. It has been ~

No. 607] DIFFERENTIATION IN THE ORGANISM 421

recently shown that at least the embryonic mesenchymal

cells have an unlimited power of regeneration and there-

fore can be considered potentially immortal.

In passing I should like to point out that the uninter-

rupted synthesis of the chromatin during cell prolifera-

tion may be secondarily influenced by the differences in

the cytoplasm thus acquired. The assumption of invari-

ability on the part of the chromosome-complexes would

imply a further assumption of persistence in the cyto-

plasm at least of some unchanged metabolic processes

identical for all cells, to which the synthesis of identical

chromatin could be referred.

Differentiation by segregation is a fact proved experi-

mentally and many striking examples of segregation of

various cytoplasmic materials during cleavage are found

in Wilson’s and Conklin’s work. As result of segrega-

tion a number of cell groups appear. The groups are dif-

ferent, but the cells of each of them are similar. The

various cytoplasmic substances distributed to the cell

groups are specific, can not be built up by cells, which do

not contain them and influence the further development

of the cells in a definite manner.

These groups of cells proliferate and differentiate,

giving rise to a number of specific organs, tissues and

cells. Does a further segregation of definite substances

continue at the time of the final specialization of tissues,

are the cell potentialities gradually narrowed by further

differential distribution of cytoplasmic constituents, and

finally rendered univalent and irreversible? Leaving

aside the question as to how specific tissues arise from

_ specific anlages, Loeb in his last book, an important and

stimulating publication, adopts the view shared also by

Stockard, of the specificity of anlages in the organism.

The anlages are, in Loeb’s conception, ‘‘destined to give

rise to definite organs.” He considers ‘‘the formation

of the various organs of the body, as being due to the de-

velopment of specific cells in definite locations in the

organism, which will grow out into definite organs, no

422 THE AMERICAN NATURALIST [Von. LI

matter into which part of the organism they are trans-

planted.’’ This assumption may apply to a number of

developmental processes in the organism, but the state-

ment is only part of the truth. Years of study of the loose

mesenchyme and of the differential processes, observed

in this tissue, have yielded a few results, which most de-

cidedly do not harmonize with the generalization above

quoted.

The loose mesenchyme, which appears in the early

stages, is characterized by its ubiquity and by lack of

obvious special function, if its mere presence between

other organs has not to be considered as function. The

mesenchyme is a syncytium of similar cells, the structure

and most probably the metabolism of which is little if at

all changed, while the cells remain as constituent parts of

the syneytium. Influences of local origin which might

change the metabolism of some of the cells are inhibited

by continuous unimpeded flow and intermixture of sub-

stances in the undivided bodies of the cells.

Cells of the loose mesenchyme become isolated from the

syncytium in many parts of the organism. This process

of isolation is diffuse, in some parts of the organism it

affects merely a small number of cells, in others it is

displayed with great intensity. Seattered free cells or

large groups of them are formed. The cause of such

isolation? If it is not possible to formulate it in positive

terms, at least it can be stated, that it does not depend

upon predestination, centered in the syncytium itself,

since isolation of cells from a mesenchymal syncytium

ean be greatly intensified experimentally. Large groups

of free cells develop in the embryo after certain grafts

on its allantois in regions in which normally the cells

would retain their syncytial connections.

The free ameboid cells isolated from the mesenchymal

syneytium differ from the cells of their maternal basis in

many respects. Their metabolism is no longer controlled

and regulated by the metabolism of the whole colony of

mesenchymal tissue. Isolated they are very active, grow

No. 607] DIFFERENTIATION IN THE ORGANISM 423

intensely, frequently divide and their structure undergoes

rapidly a series of changes which are not always identical

and which transform them into various blood cells. Do

these various changes exclusively depend upon the

_ physicochemical constitution of the cells, in other words

are they predestined, will each of these cells grow into

a definite unit, no matter to what condition it is subjected?

Is the group of ameboid, morphologically similar cells

freed from the mesenchymal syncytium still formed by a

number of species cells, the characteristics of which con-

sist if not in a discernible structure, yet in an inherent

necessity to develop along definite lines?

A series of investigations, some of them my own, have

pointed to the group of the free ameboid cells as the

mother cells of various blood elements. In regions where

the isolation is merely occasional, scattered wandering

cells arise. In regions where the isolation of free cells is

intense, so-called anlages of hematopoietic organs de-

velop. The first stages of development of various hema-

topoietic organs were found to be much alike and the con-

tinuous differentiation of the various blood cells through-

out life was shown to have for its starting point a cell,

the structure of which is similar to that of the ameboid

cell, which arise from the mesenchyme.

Moreover, it was observed that there existed an invariable

association between the development of the mother cell into

a definite blood cell and definite environmental conditions,

viz., if left in the spaces amongst mesenchymal cells the free

ameboid cell develops into a granuloblast, especially in

the vicinity of thin walled vessels; if surrounded by endo-

thelial walls and subjected to intravascular conditions it

develops into an erythroblast. This association has been

established in the hematopoiesis of birds, reptiles, am-

phibia and certain fishes. The association between differ-

entiation of the stem cell and environment on account of

the regularity with which it was observed suggested to

me the idea, that it was more than mere coincidence, and

that possibly environment contained the differential fac-

424 THE AMERICAN NATURALIST [ Vou. LI

tors, which from a homogeneous cell material moulded

different products.

On the basis of descriptive histogenetic studies it

seemed plausible to admit that environment can modify

isolated cells; that the metabolic processes of the cells

are the resultant of their physico-chemical constitution

plus physico-chemical conditions of the environment (of

course hormons, enzymes and so forth are ineluded in the

environment) and do not depend exclusively upon their

physico-chemical constitution; that different substances

arise in the cell-body (hemoglobin, various specific gran-

ules) in polyvalent cells as result of changes, deter-

mined by differences in the environment. The exist-

- ence of cells endowed with various potencies has in conse-

quence been largely admitted. The specificity of the

various mature blood cells would thus be brought about

by factors extrinsic to the stem cells.

These conclusions are based on facts established by

descriptive histogenetic studies. Experimental proofs

are beginning to accumulate which soon will leave no

doubt of the validity of these conclusions. The existence

of polyvalent cells would be proved, if, for example,

hemoblasts subjected to various conditions would undergo

various differentiation. If stem cells from within the

vessels were transferred into the spaces between the

mesenchymal cells and here instead of developing into

erythroblasts, differentiated into granuloblasts (these

experiments are under way) the stem cells within the

vessels would be proved to be polyvalent. The same

applies to other blood cells. As recently shown, spleenic

follicles, the cells of which normally differentiate into

small lymphocytes, if grafted on the chick allantois’

resolve themselves into numerous hemoblasts, which

finally undergo a granuloblastic differentiation and give

typical granular leucocytes. Thus the results of the

histogenetic studies by experimental method entail the

recognition in the embryo and in the adult organism of

tissues and cells, which have not been fully differentiated

and remain polyvalent.

No. 607] DIFFERENTIATION IN THE ORGANISM 425

It is the polyvalent cells which are the source of the

wide range of regeneration encountered, particularly in

the lower animals. It is astonishing to see how readily

students of differentiation and specificity reconcile the

extensive regeneration observed in many organisms with

the belief in the specificity of the anlages of organs.

` Driesch has shown that gills excised from an Ascidian

can regenerate a whole animal with heart, intestine and

stolon. If in the particular case the anlages of the gills

and the gills themselves were built of specific cells, the

results of the experiment would be inconsistent. How

could heart, intestine and stolon regenerate from the gills

if the cells of the gills were not endowed with various

potencies; if specific, they would grow only into the same

tissue under all conditions. On what other basis could

the experiments of Child’s be explained, in which cells of

a definite segment in the Planaria will regenerate a head

or a tail, according to whether it formed the anterior or

the posterior part of the pieca.cut out from the worm?

The very fact that different specific structures may be

regenerated at the expense of one common source, as, for

example, heart and intestine from a gill or erythrocytes,

granulocytes and small lymphocytes from hemoblasts,

implies the polyvalency of their common source.

It is known, indeed, that environment can educe new

qualities in the organism, but they usually subsist only

while the specifie conditions are present, and are lost if

the organism is transferred to another environment.

Such changes are not specific. The changes revealed by

the freed mesenchymal cells, which result in the formation

of mature blood cells, would only then be called specific,

if they were retained by generations of their descendants

under different conditions. An indifferent hemoblast

within the vessels is soon transformed into an erythro-

blast, which shows in its cytoplasm the first traces of

hemoglobin. Is the erythroblast a definitively specifie cell,

univalent and no longer capable of heteroplastic differen-

tiation in new environment? New environmental condi-

426 THE AMERICAN NATURALIST [Vou. LI

tions for an erythroblast can be found in the organism

outside the vessels, where hemoblasts develop into

granuloblasts or small lymphocytes. If transplanted out-

side the vessels, the erythroblasts still developed further

into analogous cells, this would mean that the changes

which inside the vessels have transformed a polyvalent

hemoblast into an erythroblast are irreversible (at least

in the organism), that they have narrowed the potencies

of the erythroblast in comparison with its mother cell and

have rendered it specific, i. e. univalent and irreversible in

its metabolism. Positive results from such experiment, -

could they be attained, would be of great value; they

would prove that definite factors encountered in the nor-

mal organism outside of a cell call forth such changes as

would be transmitted by the cell to its daughter cells even

if the differential factors had no longer direct influence

upon them.

The arrangement of such experiments offers however

insuperable difficulties. _Hemoblasts or mesenchymal

cells can be transplanted, for there are stages in the

hematopoiesis of the yolk-sac, in which capillaries are

distended exclusively by hemoblasts and at this time

they can be transferred into the spaces between the

mesenchymal cells. It would be hardly possible to pick

out from within the vessels erythroblasts, in which hemo-

globin had already begun to develop, but which still were

capable of proliferation. Most fortunately the required

experiment has been carried out in a series of allantois

by nature herself.

The grafting on the allantois which I used in my recent

work is often accompanied by an extensive edema in the

mesenchyme, which also affected the endothelium of the

vessels. At the time of grafting (seventh to eighth day

of incubation) the vessels contain numerous young

erythroblasts, which after grafting become particularly

numerous. The loosening of the vaseular wall made it

possible for a number of erythroblasts to escape from

within the vessels. As a result of these conditions large

No. 607] DIFFERENTIATION IN THE ORGANISM 427

groups of cells appeared in the spaces between the mesen-

chymal cells, which already had begun their erythro-

blastic differentiation, while within the vessels. These

cells, now outside the vessels, proliferate and continue

their differentiation into erythroblasts, and their cyto-

plasm is gradually transformed into or substituted by

homogeneous hemoglobinic substance.

The changes undergone by a polyvalent hemoblast

within the vessels are thus no longer reversible outside

of them.. The differentiation determined by environ-

mental conditions has been rendered specific, i. e., uni-

valent and irreversible. The specificity of tissue and

cells can not therefore be the result alone of segregation

of different cytoplasmic materials during cleavage. The

process of segregation, of course, transfers different

materials to different cell groups, the presence of which

impedes their permutability, but these cell groups are still

polyvalent and may, under various conditions, undergo

various development.

The relations between these cell groups, the structures,

effected by them, the different products of their metabo-

lism, form the external factors of the environment which

gradually render the cells of a polyvalent group specific,

univalent and irreversible in their potencies. This speci- -

ficity is transmitted by mother cells to their daughter

cells irrespectively of the environmental conditions, to

which they are subjected.

A few words concerning the structural changes of the

cells during their definitive specialization. Differentia-

tion during cleavage is effected by transmission of differ-

ent cytoplasmic materials to different cell groups. What

kind of changes in the cell structure are induced by the

external factors of the environment? Compare the struc-

ture of the mature univalent blood cells with that of their

mother cells in the stage of a hemoblast. Cytoplasm,

structure of the resting nucleus, chromosome-complexes

during mitosis, as demonstrated by our microscopical

preparation, have undergone such fundamental changes,

428 THE AMERICAN NATURALIST [ Von. LI

as to have required thorough and detailed investigations

in order to establish their reciprocal relationship. The

size of the cells makes difficult a detailed study of the

changes in the chromosomes, and they require further

investigation, nevertheless the possibility of distinguish-

ing different types of chromosome-complexes in different

cells is not to be overlooked; it is easy to identify, for

example, in the thymus entodermal cells, hemoblasts and

small lymphocytes, during mitosis by their eh1

complexes. The assumption of invariability on the bee

of the chromosome-complexes in the somatic cells requires

some qualification. The chromosomes of a cell and the

eytoplasm together embody specificity. Changes in both

may transform the cell so completely as to deprive it of its

faculty of proliferation. Erythrocytes and leucocytes in

the blood cell series afford examples of such final modi-

fications which have been gradually determined at least in

part by the external factors of the environment.

A METHOD OF NUMBERING PLANTS IN

PEDIGREE CULTURES!

DR. HOWARD B. FROST

Instructor IN PLANT BREEDING, GrapuaTe SCHOOL OF TROPICAL

AGRICULTURE AND CITRUS EXPERIMENT STATION,

UNIVERSITY OF CALIFORNIA

Asout fifteen years ago, Dr. H. J. Webber (1906, p.

308) introduced into the plant-breeding work of the United

States Department of Agriculture a simple and convenient

method of pedigree numbering. This method has. three

essential features: (1) the use of an initial ‘‘series num-

ber’’ for each hereditary line or group of lines, the sets

of series for different crops being numbered separately ;

(2) the use of letters for particular parental combinations

in a hybrid series; (3) the use of numbers separated by

dashes to designate individuals of successive generations.

For example, with cotton, Series 1 might represent

selection for longer lint, within the variety Columbia;

1-1, 1-2, etc., would then designate the plants first selected

(P, generation), and 1-1-5 would designate a plant of the

second or F, generation.

Similarly, Series 2 might represent a cross between two

‘varieties (for example, Columbia 2 x Truitt g), and

Series 3 the reciprocal of this cross. Each combination

of ‘‘individuals’’ (plants, branches, or single flowers, as _

desired) within a hybrid series is represented by a letter,

as in 2A, 2D. The F, plants are then designated by num-

bers written after the letters, as in 2A1, 2D6, and the num- |

bers for later generations follow dashes exactly as in a

non-hybrid series (for example, 2A1-5). The use of

letters thus characterizes hybrid series.

This system of numbering, then, uses simple linear pedi-

1 Paper No, 40, University of California Graduate School z ake rag

Agriculture and Citrus Experiment Station. Riverside, Californ

429

430 THE AMERICAN NATURALIST [Vou. LI

grees for all cases, beginning a new pedigree whenever

two lines of descent are combined by crossing.? It is

adapted to self-fertile organisms, and its convenience and

usefulness obviously increase with the frequeney of

selfing. Pearl’s (1915) ‘‘system of recording types of

mating,’’ on the other hand, is especially adapted to diœ-

cious and self-sterile organisms, and in general its use-

fulness for recording or presenting data increases with

the frequency of crossing.

Several systems similar to Webber’s have been described

in recent genetical papers; these schemes usually differ

mainly in the method of indicating the ‘‘series’’ or ‘‘fam-

ilies.”’ In Jennings’ (1916, p. 415) system for asexual

reproduction with the animal Difflugia, for instance, each

‘*family’’ is a pure line descended from one selected indi-

vidual; each pedigree number, consequently, begins with

a simple number assigned to the P, individual. Here we

have the simplest possible form of pedigree numbering.

With the higher plants, however, we need some special

provision for cases of crossing, and also some method of

distinguishing asexually produced individuals from those

produced sexually.

Belling (1914, pp. 309-10),* for Stizolobium crosses,

uses for each series the initials of the common names of

the parent species (e. g., VL for velvet bean 2? X Lyon

bean ¢); this is practicable because the crosses involve

only a small number of named forms, themselves appear- .

ing practically constant. For the same reasons, the P,

plants, and usually the F, also, are not individually indi-

` cated in published pedigrees; VL3 is an F, plant, and

VL3~7 or VL-7 an F, plant. The obvious result of this

procedure is a gain in both clearness and brevity of pres-

entation.

Hayes and East (1915, p. 3) use for maize crosses a

scheme that resembles Belling’s in its direct indication of

the parentage of hybrids. ‘‘The various races were given

2 Except in cases where vicinism is undiscovered or ignored.

3 Or see Fla. Agr. Exp. Sta, Report for year 1913, 1914 or 1915.

No. 607] NUMBERING PLANTS IN PEDIGREE CULTURES 481

different numbers as No. 10 flour corn and No. 5 flint

corn.’’ Then the F, hybrids would be designated, for

example: (10 5)-1, (10x 5)-2, (5 10)-1, ete. If,

however, the individual P, plants are regularly indicated

in the series numbers, these numbers tend to become un-

wieldy, particularly if the P, plants themselves have some-

what lengthy pedigrees. In cases where this objection

does not apply, and where Belling’s method is inadequate,

Hayes and Hast’s scheme has some advantage in the im-

mediate significance of the series numbers of hybrids.

Of the systems described, Webber’s seems most gen-

erally applicable to work with the higher plants, though

the others may be somewhat more convenient in certain

cases. I wish to present several additions to that system,

designed in part to provide for somatic variation and

polyembryony.

First, capital letters may be used, as is often done, for

various special purposes. For instance, letters are some-

times added to distinguish particular types; Shull (1908,

p. 60), in describing his system of pedigree records, re-

stricts letters (aside from Roman numerals) to this use,

and Hayes and East (1915, p. 4) use them to designate

floury and flint-like types of maize kernel. When tem-

porary lot numbers are used, ‘‘L’’ prefixed to these num-

bers will distinguish them from any others. Again, Arabic

numerals preceded by ‘‘R’’ seem more convenient than

Roman numerals as used by Shull (1908, p. 60) to desig-

nate rows in field cultures—giving, for instance, R1, 3

(row 1, plant 3) for I, 3, and R28, 26 for XXVIII, 26. I

would suggest that capital letters, and capitals only, be

employed for such miscellaneous purposes.

Second, small letters may be used for the indication of

parts of individuals, whether the parts remain attached

or are separated in vegetative propagation. Then,

“«_5la” in a Citrus pedigree will indicate a particular

part of tree 51 in a certain generation of that series—

4 This is to replace a method of indicating parts of individuals by means

of fractions.

432 THE AMERICAN NATURALIST [Vou. LI

perhaps a part permanently marked, and noted in the

records, because of some somatic mutation. In the same

way, a small letter affixed to any individual designation of

a plant not in a pedigree culture, such as, for instance, the

number of a tree in a field experiment, may be used to

indicate a particular branch. <A small letter used alone

will indicate a ‘‘generation’’ of vegetative propagation;

for example, in the case mentioned above, ‘‘—5la—a’’ and

‘*_5la-b’’ would be trees budded from the mutant branch

tt a>

Third, small letters affixed to the series number may be

used to designate individuals of the first (or P,) gener-

ation of any series, whether hybrid or not. The definition

of individual would necessarily be determined and re-

corded for each type of work; where desired, the ‘‘indi-

vidual’’ may be a branch, or even a single bud or fruit.

Thus, in my work with Citrus, a letter is assigned to each

- self-pollinated branch giving seedlings. For example,

series 28 consists of descendants of selfed Valencia

orange; ‘‘28a,’’ then, indicates one bagged branch of

Valencia, ‘‘28b’’ another branch, ete. The F, progeny

will be 28a—11, 28a—12, 28b-32, ete.

For a hybrid series, on this plan, two letters are used

to designate the two parents, the letters being independent

of those used in the corresponding non-hybrid series. For

example, my Citrus series 27 represents Valencia orange

9 xX Imperial pomelo g, and ‘‘27aa’’ designates a cross

between two particular branches. 27aa—21, then, will be

an F; hybrid.

Similarly, in my work with Matthiola mutants, series

23 indicates the ‘cross Snowflake (‘‘normal’’) type Ẹ

X Slender type £. ‘‘23ea’’ designates the combination of

5 The complete pedigree numbers might be 28a—32—51a—a and 28a-32-5la—b

below

m gakk where the initial parents of a series are selected from larger

groups requiring designation of or the plants of these larger

groups may be given temporary numbers. For example, my Raphanus

series 14 began with plants from one lot of commercial seed of one variety,

numbered 14, 1; 14, 2; 14, 3; ete. In the next generation, 14, 3 became

14a, and 14, 16 became lb.

No. 607] NUMBERING PLANTS IN PEDIGREE CULTURES 433

two particular individual plants, not of two particular

branches as with Citrus.

Thus with Matthiola a series starts with the crossing,

in a given direction, of two apparently uniform seed-

reproduced types, while with Citrus a series starts with

the crossing of two clons. In another case it might be de-

sirable to ignore some evident genetic variation in fea-

tures not being studied, and to base the delimitation of

the series on genetic differences of seed-reproduced P,

individuals in some particular feature under consideration

(e. g., in color characters).

Fourth, in cases where polyembryony is to be expected

nine numbers (1 to 9), instead of one, may be given, so far

as needed, to the product of each seed. Thus, with the

Citrus cross mentioned above, the first seed will be as-

signed the numbers 27aa—11 to 27aa—19, the second seed

the numbers 27aa—21 to 27aa—29, ete.” The actual plants

from the first three seeds are therefore designated as

follows:

Seed No. 1 (2 plants), 27aa—11 and 27aa—12.

Seed No. 2 (2 plants), 27aa—21 and 27aa-22.

Seed No. 3 (1 plant), 27aa—31.

If, then, two trees are budded from tree 27aa-31, these

will be 27aa—31—a and 27aa—31-b.

It may be objected that this treatment of polyembryony

gives misleading numbers to plants from adventitious em-

bryos. It may, however, be impossible in many cases to

differentiate positively these asexually produced progeny

before maturity, if at all without progeny tests, and the

probable inapplicability of some of the numbers must be

kept in mind. Where, as with crosses of Citrus trifoliata

with Eucitrus species, the strictly maternal individuals

can be separated at an early stage, they can be discarded;

or, if such plants are to be kept, and their exact origin in-

dicated, letters may be used, thus:

43aa—11 (true hybrid).

43aa—la (for 43aa—12)) (plants from adventitious or

43aa—lb (for 43aa—13) asexually produced embryos).

7 The seeds themselves might be called 27aa—10, 27aa—20, ete.

434 THE AMERICAN NATURALIST (Vou. LI

By thus inserting letters in the hybrid number, to desig-

nate the second and third plants, we indicate the vegeta-

tive origin of these plants, and also their quasi-sib rela-

tion to the true hybrid.

Open pollination, or lack of protection of flowers in gen-

eral, can be indicated in the numbers, if this seems de-

sirable, by underscoring the proper letter or number,—

the use of two letters with the series number for hybrids

making it possible to do this with the pollen parent as well

as with the seed parent.

An incidental advantage over the original plan results

from the use of letters with the series number in the way

here indicated. This consists in the fact that the numbers

for hybrid and non-hybrid series are thus made sym-

metrical in relation to the number of generations involved.

As an illustration we may take the case of the Matthiola

cross mentioned above. This cross was made in 1914, and

the hybrid seeds were planted, together with seeds from

selfed parents of the same types, in 1915 and 1916. Corre-

sponding to the F, hybrids 23ea—1, etc., we have the F,

selfed progeny 19a-1, etc., from a Snowflake parent, and

25c-1, etc., from a Slender parent, while by the original

method these three numbers might be 23G1, 19-1-1, and

25-3-1.

As will readily be seen, this scheme is elastic; if the five

main features stated above are adopted, different workers

may add, modify, or omit various details, and still use

numbers intelligible to each other with little or no special

explanation. Further, the method of designating series

and initial individuals is essentially independent of the

other features suggested, so that any of the latter features

may be adopted without the former.

All the schemes so far discussed give cumulative num-

bers, which include the whole pedigree from the P, indi-

viduals down. Shull (1908, pp. 59-64) has described a

non-cumulative system, in which individuals have only

temporary numbers (in the field depending on row and

position in row) until selected as parents. Each parent

No. 607] NUMBERING PLANTS IN PEDIGREE CULTURES 435

is given the number of the notebook page on which its

progeny are to be described, preceded by two figures in-

dicating the year in which those progeny are grown; e. g.,

06230 is a parent whose progeny are grown in 1906 and

described on p. 230 of the 1906 notebook. Only parental

and grandparental numbers (e. g., 0557.230 for the case

just mentioned) are shown at the head of each notebook

page, but these numbers permit ready reconstruction of

pedigrees from the pages indicated. The labels. bear only

the parental number.

In Shull’s scheme, then, there is no cumulation beyond

the second generation, even in the numbers as written in

the notebook. The numbers would include 4 to 8 figures

(e. g., 083.7, or 05157.230) in the notebook and 3 to 5 fig-

ures (e. g., 097, or 06230) on labels. In the scheme here

suggested there is a continuous cumulation; a plant of the

second or F, generation is usually represented by 3 to 7

letters and figures (e. g., 5b-8, or 32ba—251), and after

from 2 to 4 more generations the numbers begin to be de-

cidedly unwieldy. The greater inconvenience and danger

of error in copying these larger numbers would seem,

however, to be largely offset by the growing familiarity

to the worker of the earlier part of a pedigree, and by the

identity of the temporary and permanent designations of

individuals. Further, the page-to-family feature would

be inconvenient in some cases, where several or many

actual pages are given to one progeny lot and so would

require the same number.

With a cumulative system, the simple device of using

temporary yearly lot numbers on individual labels will

obviate the necessity of writing a long pedigree number

for each plant. If the full number is written in the note-

book and on each lot label, together with the lot number

(e. g., L1 = 16aa—-6-3-44-18-3), and the latter alone on the

individual labels if these are used, much work can be

saved. In an extreme case, the parents belonging to a

given series which are included in a given culture can be

436 THE AMERICAN NATURALIST [ Vou. LI

arbitrarily made the initial (P,) individuals of a new

series.

The system here presented has been used for two or

three seasons’ work with the two types of hybridization

mentioned above, with Raphanus hybridization beginning

with highly heterozygous material, and with pure-line

breeding of the tepary bean (Phaseolus). It appears, so

far, to be adequate and generally satisfactory for all these

types of work. :

SUMMARY `

This paper describes a system of pedigree numbering

adapted to various types of genetical work with the higher

plants.

Other similar systems secure greater brevity or clear-

ness in certain cases, but are usually of less general ap-

plicability ; the main differences relate to the designation

of series and their initial individuals.

This system provides for polyembryony and somatic

variation, and permits of the addition of various other re-

finements in cases where they may be needed. The basic

scheme is perhaps as simple and convenient as is con-

sistent with use for all purposes without change in essen-

tial features.

In this and similar systems, the ibra are cumu-

lative; Shull’s non-cumulative system has both advan-

tages and disadvantages in comparison.

To summarize the most essential features of the pro-

posed method: (1) the series for a given plant (genus or

species) are numbered consecutively; (2) the initial ‘‘in-

dividuals,’’ as defined in the records, are denoted by small

letters affixed to the series numbers; (3) in each following

generation the individuals are numbered (if sexually pro-

duced) or lettered (if asexually produced), an affixed

letter indicating a particular part of an individual; (4)

reproduction or propagation is always indicated by a

No. 607] NUMBERING PLANTS IN PEDIGREE CULTURES 437

dash; (5) capital letters are employed for miscellaneous

special uses.

BIBLIOGRAPHY

Belling, John.

1914. The mode of inheritance of semisterility in the offspring =

certain hybrid plants. Zeitschr. f. indukt. Abstam.-

Ve i

Hayes, H. K., and East, Edward M

1915. Parther experiments on inheritance in maize. Conn, Agr. Exp.

Sta. Bull. 188: 1-31 1.

Jennings, Herbert S.

1916. eae Pg variation, and the results of selection in the uni-

parental reproduction of Difflugia corona. Genetics, 1: 407-

19 fig.

Pearl, Raymond.

1915. A system of Seem types of — in experimental breed-

ing operations. Science, n. s., 42: 383-386.

Shull, George H.

190 The pedigree culture: its aims and methods. Plant World, 11:

21-28, 55-64.

Webber, Herbert J.

1 Ferne ee ae in the Dene breeding work of the Depart

Agriculture. In: L, H. Bailey. Plant brooding.

re rt i p. MASAA New York

8 Of course, a period may be used, as is done by Jennings (1916) with

Difflugia, with a saving of space but possibly a greater liability to error in

copying.

SYNCHRONISM AND SYNCHRONIC RHYTHM IN

THE BEHAVIOR OF CERTAIN CREATURES

H. A. ALLARD

Wasuineton, D. C.

Ir is a matter of common experience to observe in-

stances of synchronous behavior and expression among

creatures. In such instances an entire group of creatures

may react simultaneously to the same external stimulus.

A flock of birds will arise from the ground and dash away

at the first signal of danger, or a school of fish will swerve

as a unit from a stick pushed toward them. In the same

way certain frogs in a pool may be started into a brief,

explosive chorus of simultaneous croaking by the notes of

a single individual. After a brief period during which

all have expressed themselves, silence ensues until the

next singing-reflex is unlocked by the croaking of another

individual. In New England I have heard the wood frog,

or so-called clucking frog (Rana sylvatica) give rise to

just such outbursts of simultaneous clucking, started

either by the frogs themselves or by my giving an imita-

tion of their notes during an interval of silence. This

habit of singing in concert is not unusual among certain

species of frogs, and is mentioned by D. D. Cunningham

(1903) in his excellent book, ‘‘Some Indian Friends. and

Acquaintances.” He says:

Such utterances recur several times in succession; a short pause fol-

lows and then the conversation begins again. The curious thing is that

all the performers seated in one patch of swamp should have such a

tendency to synchronous action that periods of total silence alternate

with those of general uproar. The phenomenon is parallel to that of

the synchronous mewn: that sometimes occurs so markedly in

groups of fireflies

In these scala synchronism is aiakohta at inter-

vals, but there is no regular rhythmic expression within

the group itself. Each frog croaks in its own way, until

a perfect babel of noise is produced.

Similar synchronous outbursts of sound also occur

among the musical insects. The tendency to respond to

the notes of their kind is very strong, and a single singer

438

No. 607] RHYTHM IN BEHAVIOR OF CREATURES 439

may be followed by thousands. Although the seventeen-

year cicada rarely sings at night, Hopkins’ noted a most

remarkable nocturnal concert which began with a single

singer. He says:

I was fortunate enough to hear the starting of one of these concerts

on a clear, moonlight night in June. One male in an apple tree near

the house suddenly called out as if disturbed or frightened. Hus

neighbors in the same tree were thus apparently awakened. One started

the familiar song note, which was at once taken up by numbers of other

males, and, like the waves from a pebble dropped into still water, the

music rapidly spread until it reached the edge of the thick woods,

where it was taken up by thousands of singers, and the concert was in

-as full blast as if it had been the previous day. This continued a few

minutes, until all had apparently taken part and the song had reached

its highest pitch, when it began to gradually subside, and in a short

time silence again prevailed.

In his book, ‘‘ Bolivia’’ (1914), Paul Walle (p. 268)

speaks of the sudden outbursts of noise in the tropical

wilderness as follows:

As the darkness grows deeper, the silence of the forest is broken

uproar lasts for a moment, and all relapses into a silence in which one

still hears, more or less sensibly, the murmur of a million insects.

In such instances where a group of creatures respond

simultaneously to the same initial stimulus, we have the

simplest case of synchronic behavior. I once witnessed

an instance of a similar synchronic behavior in the move-

ments of a colony of plant lice which thickly covered the

tip of a twig. While I was watching them, a tiny, para-

sitic wasp suddenly approached and hovered over the

colony preparatory to attacking them. The plant lice

became aware of its presence and in an instant the entire

colony raised the hind portion of their bodies simul-

taneously into the air at an angle of about 45° and began

waving their hind legs about. This behavior was prob-

ably more or less a protective response to the primary

stimulus afforded by the presence of the wasp. It is also

possible that the reaction, once started in a few individ-

1‘‘The Periodical Cicada,’’ by C. L. rage Bull. No. 14, Div. of En-

tomology, U. S. Dept. of Agr., 1898, p

440 THE AMERICAN NATURALIST [Vou. LI

uals, would tend to be transmitted to the entire colony by

the mere contact of their bodies.

The same sort of synchronous movement may sometimes

be noted in the reactions of the leaves and leaflets of the

sensitive plant (Mimosa pudica). A sudden shock may

cause every leaf of the plant to react synchronously.

Sometimes, when the stimulus is applied only to one or

two pairs of the basal leaflets, the closing of these and

their contact with those beneath them produce a pro-

gressive closing movement in all the pairs of leaflets

until the terminal ones are reached. In this instance we

have a progressive transmission of stimuli quite similar

to the transmission of certain automatic reactions which

sometimes take place in groups of insects, birds, or ani-

mals.

In other instances the reaction to a certain stimulus may

involve several similar, instinctive movements producing

the simplest form of synchronic rhythm. One interesting

instance of this sort of synchronous action has been ad-

duced by H. H. Newman, in Science, N. S., for January

12, 1917. Newman found that an enormous colony of

‘‘harvestmen,’’ of the genus Liobunum, resting beneath

an overhanging rock, when disturbed began a rhythmic

body movement, raising their bodies up and down at a

rate of about three times a second, for a brief period. If

the stimulus was set up in a few individuals of the colony,

the synchronous body movements spread rapidly over the

entire colony. After a time it was found that the reactions

became weaker and finally ceased. In this instance it ap-

pears that there was a secondary transmission of the

stimuli from individual to individual by means of their

closely interlocked legs. The writer has noted a similar

behavior among the individuals of certain caterpillars

which were arranged close together on a twig. These

caterpillars, when resting, had the habit of keeping the

anterior portion of their bodies raised in the air. If the

colony was disturbed, each individual began a synchronous

swinging of the free portion of the body from side to side,

violently, for a brief period. The primary stimulus could

affect all the caterpillars of a group, or a secondary trans-

No.607] RHYTHM IN BEHAVIOR OF CREATURES 441

mission could take place down the twig. Although the

swinging was not always in the same direction, a remark-

able degree of synchronic movement was brought about.

In those instances where the rhythmic expression of

each individual, when set up, continues for long periods

of time, as in the case of certain crickets, we have the de-

velopment of a more complex synchronic rhythm having

its origin in the instinctive habit of response, and prob-

ably also built up and maintained by the unconscious in-

fluences of the regular sounds of the crickets upon one

another.

I do not feel the slightest hesitancy in affirming that

certain crickets which have the intermittent habit of

chirping may build up and maintain a synchronic rhythm

under favorable conditions. I refer to the well-known

snowy tree cricket (Œ canthus niveus), whose synchronous

music has been noted and described by many well-known

observers and naturalists in this country. I have many

times heard the remarkable synchronous chirping of these

crickets in New England, and under exceptionally favor-

able conditions the synchronism has been so marked that

waves of solemn, rhythmical music have been produced

for long periods of time. This rhythmic music was

spoken of as a ‘‘slumbrous breathing’’ by Thoreau.

Hawthorne called it an ‘‘audible stillness” which, ‘‘if.

moonlight could be heard, it would sound like that.’ Bur-

roughs called it a ‘‘rhythmic beat.’’ McNeill has said of

the music of this cricket:

It is heard only at night and occasionally on cloudy days, but in the

latter case it is only an isolated song, and never the full chorus of the

night song produced by many wings whose vibrations, in exact unison

produce that characteristic “ rhythmic beat,” as Burroughs has happily

phrased it.

Dolbear, in the AMrertcan Naturauist for November, 1897,

refers to this cricket when he says: i

At night, when great numbers are chirping, the regularity is aston-

ishing, for one may hear all the crickets in a field chirping synchro-

nously, keeping time as if led by the wand of a conductor.

Although the facts may have been slightly overdrawn

when Dolbear stated that all the crickets in a field were |

442 THE AMERICAN NATURALIST [Vou. LI

chirping in unison, Shull was not justified in concluding

that the synchronism observed by Dolbear was merely an

illusion. If such were the case, it is surprising that so

many other excellent observers have also been misled by

the same illusion in reporting the music of the snowy tree

cricket. For many years I have made a very close study

of the stridulations of insects, yet I have noted this syn-

chronous chirping in but one other species of those

crickets which possess the intermittent habit of trilling.

One may frequently hear great numbers of the common

field cricket (Gryllus pennsylvanicus) chirping in the

fields, but these crickets never show the least tendency to

chirp in unison as do the snowy tree crickets. The jump-

ing tree cricket (Orocharis saltator) is also an intermit-

tent triller and may sometimes be heard chirping in great

numbers in certain copses, yet the ‘‘illusion”’ of syn-

chronous trilling one somehow never experiences. Like-

wise, there appears to be no tendency whatever for the

ground crickets, Miogryllus saussurei, Nemobius fas-

ciatus, or Nemobius ambitiosus, to chirp in unison. Many

other locusts and katydids, such as Conocephalus ensiger,

Conocephalus exiliscanornus, and the common katydid

(Cyrtophyllus perspicillatus) produce regular, intermit-

tent notes and stridulate in well-defined colonies, yet so

far as I have observed the individuals of a species never

show the least tendency to stridulate in unison.

In the south, however, I have heard the tiny tree ceils

(Cyrtoxipha columbiana) chirping in unison with re

markable precision, producing waves of shrill, rhythmic

sound, as in the case of the snowy tree cricket. In this in-

stance great numbers of these crickets were located in the

branches of a sarge evergreen holly tree. The shrill notes

of this little cricket are delivered with great regularity,

as are the low, solemn chirping notes of the snowy tree

cricket. This regularity in the delivery of the chivping

of these two crickets is especially striking when compared

with the musical efforts of other chirping crickets, such

as Ecanthus angustipennis, Orocharis saltator; or Gryllus

pennsylvanicus. This sustained regularity in the rate

of chirping of the snowy tree cricket has been noted by

No. 607] RHYTHM IN BEHAVIOR OF CREATURES 443

various observers. On the supposition that the rate of

chirping of these crickets is entirely a function of tem-

perature, it has even been considered that the crickets

may serve as an accurate thermometer. As temperature

indicators, however, the crickets can not always be relied

upon under all conditions, since wind, humidity, and elec-

trical conditions of the atmosphere preceding thunder-

storms, also appear to influence the activities of these in-

sects.

It is now a question as to whether these crickets per-

ceive the rhythm which is so pronounced in the regular

sequence of their chirpings. I believe they must, for it is

quite evident that they hear and respond to the peculiar

rhythmical ‘chirpings of their kind, which have become

the common language of the species. If they are able to

recognize the notes of their kind, it is reasonable to be-

lieve that the rhythmic character, as well as pitch, manner

of delivery, and even more subtle tonal differences enter

into the recognition.

The rhythmic chirping in unison which oftentimes be-

comes such a pronounced feature in the music of these

crickets takes place only in the evening and appears to

depend upon the nice adjustment of certain nocturnal

atmospheric relations—moonlight, temperature, humid-

ity, and stillness of the air. Early in the evening, per-

haps, a single cricket begins its stridulations which stimu-

late others to respond, and by degrees the great chirping

chorus is augmeiited. There may be no noticeable syn-

chronism in the chirping at first, but if conditions are

favorable, the crickets gradually build up a synchronic

rhythm until waves of solemn music are — by a

certain colony.

There seems to be a marked tendency for the indi-

viduals of each colony to adopt the rhythmic beat of their

particular colony, so that not infrequently a neighboring

colony may establish an antiphonal rhythm, with the re-

sult that waves of quavering sound swing backward and

forward between two neighboring colonies.

How is this synchronal chirping built up and main-

tained? It is probable that the instinctive habit of re-

444 THE AMERICAN NATURALIST [Vou. LI

sponse tends to bring the chirping of many individuals

into a regular synchronism, but I feel, also, that the

crickets are somehow unconsciously influenced by one an-

other in their chirpings so that they tend gradually to

build up a common synchronic rhythm as the night ad-

vances. Once a synchronic rhythm is established, I am

inclined to feel that it would be natural for those indi-

viduals which began chirping, at first asynchronously, to

chirp, sooner or later, in unison with their fellows.

From the tone of certain discussions which have taken

place in Science for the past several months, it is clearly

indicated that the synchronous flashing of fireflies as a

reality is somewhat doubted. There is no reason to con-

sider such synchronism ‘‘contrary to all natural laws,”

as Laurent as recently stated in Science for January 12,

1917. In the tropics it appears that great numbers of

fireflies frequently establish themselves in the crowns of

certain trees, and I am not at all ready to deny that under

certain conditions such colonies may not flash synchro-

nously, as reported by Cunningham (loc. cit.), Shelford,

and others. It is unfortunate that in most instances these

reports are accompanied by very meager details as to the

general behavior of the fireflies in these arboreal colonies.

Cuthbert Collingwood, however, in his book, ‘‘Rambles

of a Naturalist,’’ (1868), pp. 254-255, has given a very

careful account of his observations of the synchronous

flashing of fireflies, as follows: ‘‘ At Singapore, and also

at Labuan, the little luminous beetle commonly known as

the firefly (Lampyris Sp. Ign.) is common. When flying

singly it shines with an intermittent light which alternates

with darkness; but on fine evenings and in favorable (i. e.,

damp and swampy) locations, they present a very re-

markable appearance. Clustered in the foliage of the

trees, instead of keeping up an irregular twinkle, every

individual shines simultaneously at regular intervals, as

though by common impulse; so that their light pulsates,

as it were, and the tree is for one moment illuminated by

a hundred brilliant points and the next is in almost total

darkness. ‘The intervals have about the duration of a

second, and during the intermission only one or two re-

No.607] RHYTHM IN BEHAVIOR OF CREATURES 445

main illuminated. To all appearances they are not on the

wing at the time but settled upon the tree; for I was able

to recognize certain points of light which I especially no-

ticed, and which remained in the same situation with each

successive flash. When I disturbed them under such cir-

cumstances they flew about at random, each giving out a

more rapidly intermittent light. At Labuan, however, I

have frequently seen them shine with a steady light as

they flew along looking like little, flying stars of the

second, or even first, magnitude.’’ If there are periods

of repose or inactivity during which the insects cease

their flashing, it is easy to see how a part of the col-

ony or even all the insects could react simultaneously

to the same visual stimulus, such as the sudden flash-

ing of a single individual. If it is the habit of the in-

sects, before again becoming quiescent, to flash several

times in succession, following an appropriate stimulus, it

is very easy to see how distinct synchronous flashes of

light would now and then illuminate a portion of the tree,

or even the entire tree. Such synchronic rhythm in the

flashing of fireflies would be similar in every way to

those instinctive, automatic body movements observed by

Newman in the case of the ‘‘harvesters,’’ Liobunum—the

swinging of the pendulum, so to speak, two, three, or more

times, as the case may be, following the initial stimulus.

As Newman well suggests, it is possible that a transmis-

sion of stimuli could even build up and maintain for some

time a synchronous flashing in colonies of fireflies in a tree

or field. This flashing in unison would parallel the syn-

chronous trilling of the snowy tree crickets, and would

not necessarily violate known natural laws governing the

instinctive synchronic activities of various creatures.

By selecting two individuals which were evidently

chirping in unison, Shull? attempted to study the reality

of synchronous chirping in a colony of snowy tree crickets

by statistical methods. No greater statistical fallacy

2 Shull, A. F., ‘‘The Stridulation of the Snowy Tree-cricket (@canthus

niveus),’’ Canadian Entomologist, Vol. 39, 1907.

446 THE AMERICAN NATURALIST [Vou. LI

could be adduced, however, than to attempt to determine

the reality of synchronism in a colony of chirping tree-

crickets from statistical results obtained for only two

crickets of the colony. That synchronous chirping may

be a reality, it is not necessary that 100 per cent. of the

individuals of a colony chirp exactly in unison. A few

crickets chirping asynchronously would not necessarily

prove that a synchronism did not exist. As a matter of

fact, some individuals always chirp asynchronously, even

when the synchronic rhythm is most pronounced. Taking

any two crickets from such a colony, the results would

depend entirely upon which two crickets were chosen, and

either perfect synchronism or absolutte lack of synchro-

nism, would be established. X

It is obviously impossible to subject all the individuals

of a colony of chirping tree-crickets or a group of flashing

fireflies to statistical analysis. Because this is impossible,

however, one is not justified in concluding that judgment

based upon careful observation is of no value in deter-

mining the reality of synchronism. If one hundred men

were marching down a street and 75 were in step while 25

were not, judgment alone would establish the fact that a

- synchronic rhythm existed. This would be quite as true

for the chirping of tree-crickets or the flashing of fireflies.

As a matter of fact some of the most marvellous dis-

criminations depend upon niceties of judgment alone, and

no amount of statistical data would simplify the matter.

I can not yet agree with those who are inclined to be-

lieve that the snowy tree-crickets never chirp synchro-

nously, and that it is impossible for fireflies to flash syn-

chronously, especially certain tropical species of fireflies. I

will agree, however, that in practically all instances of

synchronic rhythm there seems to be no evidence of con-

scious, intentional imitation, but merely instinctive, reflex,

or automatic reactions to certain stimuli, similar in many

respects to the unconscious reactions of the leaves and

leaflets of the sensitive plant.

SHORTER ARTICLES AND DISCUSSION

SOLID MEDIA FOR REARING DROSOPHILA

BAUMBERGER and Glaser (1) recently described a method of

raising the banana fly on transparent solid media, thus enabling

the investigator to observe more accurately the rate of growth

and metamorphosis and the larval habits of this insect. The

medium was made as follows:

Five or six bananas were mashed up in 500 c.c. of water. This was

allowed to infuse on ice over night, after which the liquid was passed

through cheese cloth. Powdered agar-agar was then added in the pro-

portion of 144 gm. to 100 c.c. of the banana infusion. This was then

heated until the agar had dissolved. The liquid was then filtered

through a thin layer of absorbent cotton into test tubes. The tubes

were then plugged, sterilized and slanted in the eustomary manner.

As pointed out in the above article, one of us (2) had observed

that the bacterial growths which always develop on this medium

‘‘do not Reem to harm the larve’’ and the mold which sometimes

appears ‘‘is usually destroyed by the larve just as soon as they

hatch.’’ This question was further investigated and it was

found (2).that the prinicpal food of Drosophila is yeast and the

flies can not develop on banana which is kept free from micro-

organisms. Delcourt and Guyenot (3) had previously (un-

known to the author) published similar conclusions and Loeb

and Northrop (4) had confirmed them shortly before the author’s

report (2) was sent to press.

It is therefore very well known that the food of Drosophila is

yeast and the prime necessity of any medium for rearing this fly

must be either abundant food for yeasts to grow upon or the

presence of large numbers of yeast cells. If a medium is made

of sterile compressed yeast and agar-agar? it serves as a perfect

food for flies which have been freed from microorganisms; how-

ever, if living yeasts develop young larve are usually killed. As

1 Loeb and Northrop (4) raised a few flies on aseptic banana, but all

flies were sexually sterile. kniee (5) also succeeded | in raising a small

percentage of flies on steri

2 An excellent sichikiieiin ican eonsists of yeast cake moistened

with water.

447

448 THE AMERICAN NATURALIST [Vou. LI

adult flies usually carry living yeast cells upon them this medium

would be difficult to use for work in heredity. A nutrient

medium for yeast would best suit the needs of geneticists. Into

such a food the adults or pupæ would carry living yeast cells

which would ferment the sugars and produce odorous substances

which cause oviposition by the female fly. Larve on hatching

would spread the yeasts throughout the medium, thus increasing

growth and alcoholic fermentation which may prevent the de-

velopment of injurious microorganisms.

wo media might be suggested for this purpose, viz.: Fer-

mented banana agar and Pasteur’s nutrient agar. The former

may be prepared by adding two cakes of bread yeast separated

in 100 c.c. of water to one dozen mashed bananas, mixing thor-

oughly and allowing to ferment for twenty-four hours. This

material should be pressed through a sugar sack and the liquid

resulting thickened by heating with 1.5 gm. agar-agar per

100 c.c. and poured into slant culture tubes, plugged and

sterilized.

A perfect nutrient medium for yeast consists of 10 gm. am-

monium tartrate, 10 gm. ashes of yeast, 100 gm. rock candy,

1,000 gm. distilled water. This is called Pasteur’s culture fluid

and can be treated in the same manner as the above but should

be sterilized in an Arnold sterilizer for three successive days, as

it can not be heated to as high a temperature as the banana with-

out preventing jellation. Pasteur’s nutrient solution can be ap-

proximated by diluting molasses with three parts of water.

In the two media described above yeasts develop rapidly and

furnish abundant food for Drosophila larvæ and also produce

odors of fermentation which cause the female to oviposit readily.

A concentrated food for yeast such as banana flour would prob-

ably increase the value of the first medium as this substance is

now used for raising yeast in the brewing industry (6).

‘REFERENCES

1, Baumberger, J. P., and Glaser, R. W. Science, N. me XLV, pp. 21-22.

2. Baumberger, J. P. Proc. Nat. Ac. Sc., III, pp. 122-

3. Deleourt and Guyénot, Bull. Se. France et ay Pa 45, pp. 249-332.

4. Loeb, J., and Northrop, J. H. Jr. Biol. Chem., XXVII, pp. 309-312,

5. Guyénot, E. Compt. Rend. Soc. de Biol., 1913, LXV, pt. 1, p. 178.

6. Nagel, Z. Spiritusind., 35, p. 185

J. P. BAUMBERGER

Bussey INSTITUTION.

THE

AMERICAN NATURALIST

VoL. LI. August, 1917 No. 608

BIOCHARACTERS AS SEPARABLE UNITS OF

ORGANIC STRUCTURE

HENRY FAIRFIELD OSBORN

INTRODUCTION

As to the term ‘‘character,’’ in the commonly accepted

sense of zoology and botany, it has long been known that

different characters, large and small, exhibit different

rates of evolution and are in this sense ‘‘separable’’ or

‘‘independent,”” while in another sense it has long been

known that every character of an organism is correlated

or coordinated with every other character in function and

adaptation. Our general knowledge of character separa-

bility (for the want of a better English term) has been

more than confirmed by researches based upon the great

discovery of Mendel, namely, that many large as well as

minute characters which are closely associated or even

blended in the adult organism are very sharply separated

from each other in the germ plasm, in such a manner that

they may entirely appear or disappear in the crossing, or

hybridization of species, subspecies, varieties, races, no

less than of individuals. The theoretic separability in

heredity of the germinal ‘‘determiners’’ or ‘‘factors’’ of

characters is in full accord with the several aspects of

separability in evolution previously observed in paleon-

tology, embryology and individual development.

The purpose of this synopsis is to review and bring

together some of the noteworthy phenomena of character

separability as contrasted with those of interdependence,

cooperation, correlation and coordination.

449

450 THE AMERICAN NATURALIST [Vou. LI

It is probable that this principle of separability of

units of function and structure, which has been discovered

in so many processes of the organism, will prove to be a

universal principle. This principle is more or less a

necessary consequence of the unit-cellular structure of

the organism; if instead of being composed of cell units,

each possessing its peculiar heredity qualities, an organ-

ism were composed of fluid or solid masses of different

kinds, we can not imagine how it could split up into char-

acter units. Yet the cell is probably not the ultimate, or

least character unit, which is doubtless a chemicophysical

unit. This is extremely suggestive in connection with our

conceptions of the nature of the evolution process, for

the process more or less clearly resolves itself into three

problems, namely: (1) how do these character units arise;

(2) how are these character units coordinated into harmo-

nious action within the organism; (3) why do these char-

acter units independently evolve, progress or retrogress?

Since the word ‘‘character’’ is very vague, and since

the term ‘‘unit character’? has a special and limited

meaning in Mendelian heredity, I propose the new term

‘*hiocharacter’’ as a general designation of the character

unit in the organism.

1. Kryps or BIOCHARACTERS OBSERVED IN PALEONTOLOGY

Biocharacters are those characters, large and small,

which through the evidence afforded by ontogeny (t. e.,

zoology, embryology), phylogeny (7. e., paleontology), or

heredity (Mendelian inheritance )are found to be separable

from or independent of each other as units in the proc-

esses of heredity, of evolution, and of individual de-

velopment.

Paleontology gives evidence no less positive than em-

bryology and experimental heredity that each organism is

made up of a number of such separable characters, includ-

ing those known as the ‘‘unit characters’’ of Mendelian

heredity. In paleontology this separability in heredity

and evolution is found to apply to structural, or anatom-

ical, characters of three principal kinds, namely, I, II, ITI:

No. 608] BIOCHARACTERS AND ORGANIC STRUCTURE 451

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, divisibility, independ-

lity

The property of separab

ence of these biocharacters stands in contrast to that of

452 THE AMERICAN NATURALIST [Vou. LI

their interdependence and coordination of function in

the organism. As remarked above the discovery of this

property of separability of characters was gradually

prepared for in various branches of biology. First, in

comparative anatomy, through the observations of the

laws of independent degeneration, balance and progres-

sion of adjoining parts; second, through embryogeny and

ontogeny, in the observation of the hastened or retarded

development of adjoining parts; third, through heredity,

as, for example, in the mosaic inheritance of Galton;

fourth, through paleontology and phylogeny, in the law of

acceleration and retardation of Hyatt and, through the

observations of many other paleontologists, concluding

with the detailed observations of Osborn and Gregory.

But the property of separability first shone out clearly

and most brilliantly in the discoveries of Mendel in hered-

ity.

This property of structural separability and inde-

pendence of evolution is closely connected with separa-

bility or independence of function. Thus separability

may distinguish a great number of cells and tissues which

are united by a single function, or separability may dis-

tinguish a single cell, as, for example, the single giant cells

of the spinal cord of certain fishes and amphibians.

It is important, therefore, to realize that this property

of separability, the separability of biocharacters, is now

observable under six classes of evidence.

2. MODES or SEPARABILITY OF BIOCHARACTERS IN HEREDITY,

In GENESIS, IN Rate or EVOLUTION

I. Biocharacter heritage separability, unit or exclusive

inheritance.

1. Evidence of Galton, etc., as to mosaic inheri-

ance. ;

2. Character heritage separability, under the sepa-

rate ‘‘determiner” or ‘‘factor’’ hypothesis of

Mendel, Bateson, Morgan, etc., according to `

which each ‘‘biocharacter’’ of the soma may

spring from one or more ‘‘determiners’’ or

No. 608]

BIOCHARACTERS AND ORGANIC STRUCTURE 4538

‘‘oroups of determiners’’ in the germ. Many

characters are not entirely separable, but tend

to go in groups or to blend.

Character heritage blending, Castle, Osborn,

etc., as observed in color, size, proportion, ete.

II. Separability in genesis, biocharacter origin and evo-

lution.

. Origin through saltation, large heritable leaps

(saltus, a leap, syn. discontinuity, Bateson).

. Origin through minute heritable gradations

(gradus, a step), Darwin (minute heritable

variations), De Vries (mutations).

. Origin through continuity (continuatio, an un-

broken series; continuous describes that which

is absolutely without pause or break, in con-

trast to saltation—leaps, gradation = steps).

It has been shown (Osborn) that characters

continuous in origin may be separable or dis-

continuous in heredity, as in both the new

rectigradations and new proportion characters

of the hybrid of the horse and the ass.

Continuous rectigradations, Osborn, 1. e., ortho-

genetic or adaptive origin followed by adaptive

evolution in a single direction, a principle

probably corresponding with the Mutations-

richtung of Neumayr.

Homomorphic (Fiirbringer) rectigradations,

through independent origins, the independent

production of similar biocharacters in organ-

isms of similar ancestral affinity, the ‘‘poten-

tial homology” of Osborn, as distinguished

from the true homogeny, homology sensu

strictu, of direct descent of characters from

each other.

Mutations of Waagen, subspecific steps or grada-

tions in evolution of characters under the

mutationsrichtung, or trend of development i in

certain directions, of subspecific value, i. e.,

intergradations between species.

454 THE AMERICAN NATURALIST ~ [Voi LI

II. Separability in velocity, biocharacter motion (i. e.,

rate of transformation, or relative displace-

ment).

1. Ontogenetic acceleration, hastening of develop-

ment in ontogeny, resulting in certain biochar-

acters appearing at earlier and earlier stages

of development. Hyatt’s law.

. Ontogenetic retardation, slowing down of bio-

characters in ontogeny, resulting in certain

biocharacters appearing at later and later

stages of development. Hyatt’s law.

1 and, result in heterochrony (Gegenbaur).

Ontogenetic balance, resulting in biocharacters

appearing at the same stage as in the ances-

tral forms.

. Phylogenetic acceleration, appearance of certain

homomorphie biocharacters at earlier geologic

periods in some phyla than in others.

. Phylogenetic retardation, whereby some homo-

morphic biocharacters appear at later geologic

periods in some phyla than others.

. Phylogenetic balance.

jor)

IV. Separability in grouping, biocharacter cooperation

and coordination.

A biocharaecter may be closely linked with

others in group function or it may detach itself —

and connect with another group, e. g., color and

speed biocharacters in horses.

1. Biocharacter correlation into similar adaptive

character groups.

2. Biocharacter grouping through heredity, attrib-

utable to prolonged ancestral grouping.

3. Biocharacter compensation, the gain of one char-

acter at the expense of another. The law of

compensation of St. Hilaire.

4. Biocharacter sex linkage, the union of groups

of characters with the function of sex as family

or secondary sexual characters. :

No. 608] BIOCHARACTERS AND ORGANIC STRUCTURE 455

V. Separability in proportion characters. Character

proportion genesis, separability in the evolu-

tion and heritage of proportions.

1. Proportion genesis through fluctuation, theo-

retically through continued selection of plus

and minus variations in a given direction

in eases where such variations of proportion

are of adaptive significance, as in fluctuating

variations of length of neck in the giraffe.

2. Character proportion continuity in zoologic and

paleontologic series, the unbroken succession

in the evolution of changes of proportion, as in

brachycephaly and dolichocephaly in kindred

races of man.

3. Character proportion saltation, in E only,

sudden appearance of profound changes of

proportion, as in the Moùchamp breed of

sheep.

4. Chace proportion heritage separability.

Complete separation in heredity of certain

proportional characters, as in crosses between

dolichocephalic and brachycephalic types in

man.

5. Character proportion heritage blending, the

origin of blended, or intermediate, forms of

certain proportional characters in man and

horses.

6. Character proportion genesis, partly at least

through interaction of separably specific

harmones, chalones, internal messengers of

the thyroid and other internal secreting glands.

VI. Separability in orthogenesis, rectigradations, gene-

sis of new adaptive characters from infini-

tesimal beginnings.

1. Independent genesis of similar adaptive charac-

ters in different phyla giving rise to homo-

morphy.

456 THE AMERICAN NATURALIST [Vor LI

2. Evidence of hereditary predetermination or po-

tentiality of the genesis of similar new char-

acters in phyla derived from similar ancestors.

3. Continuous evolution of rectigradations m one

direction, Mutationsrichtung.

4, Mutations of Waagen, subspecific gradations of

character.

5. Complete separability of rectigradations im

heredity, as shown in the teeth of the hybrids

of the horse and ass, all rectigradations being

either present or absent but not blended.

3. SUMMARY

It appears from the foregoing classes of evidence that

biocharacters are separable in origin,’development, evo-

lution, and heredity. -First, biocharacters are separable

through their many different modes of origin from the

germ, either saltatory, gradational, or continuous. Sec-

ond, biocharacters have different rates of motion, or

velocity, in individual development (ontogeny), exhibit-

ing acceleration or retardation. Third, biocharacters

have different rates of evolution in different phyla

(phylogeny), again exhibiting acceleration or retardation

(phyla). Fourth, all the biocharacters of an organism

cooperate through various modes of grouping in func-

tional correlation, in compensation, in sex linkage. Fifth,

in the hard parts of the body while the biocharacters of

form and proportion may originate through continuity,

through saltation, or through minute gradations, all the

known evolution of proportion biocharacters is contin-

uous. Sixth, in the hard parts the biocharacters of recti-

gradations have only been observed to originate and de-

velop through continuity.

EVIDENCE OF MULTIPLE FACTORS IN MICE

AND RATS

C. C. LITTLE

HARVARD MEDICAL SCHOOL

Tae object of this paper is to record certain data on the

inheritance of two complex characters and analyze these

data together with those obtained in certain analogous

experiments by other investigators. This is done with a

view to ascertaining what they contribute to our knowl-

edge of the relative merits of the two more or less con-

tradictory hypotheses, multiple segregating factors or a

single fluctuating factor which are being advocated by

geneticists to explain certain cases of inheritance.

It will be useful at the outset to state in a somewhat

definite manner how the alternative hypotheses differ from

one another. MacDowell (1916) in a recent paper has

clearly and precisely defined the two views. From this

start the following statement may be made. The first

view supposes that variations of the germ plasm are in the

nature of fluctuations. The germ plasm is in a continuous

state of variation. The hereditary characters all vary

under observation and this is taken to mean that the fac-

tors in the germ plasm determining them also vary.

Fluctuation in the character is measured and used as a

means of detecting and recording a similar though not

identical variation in the germinal factor underlying and

determining the character under observation. To use a

concrete example. In a given species the individuals are

of various sizes, some larger, some smaller. Some of this

variation is considered as in part due to non-heritable

environmental influences. There is, however, a distinct

‘*inheritance’’ of size. This is considered the result of a

variable germinal factor which as Castle suggests may be

‘‘Perhaps some substance or ferment which varies in

457

458 © THE AMERICAN NATURALIST [Vou. LI

amount, larger amounts producing larger results’’ (1916,

p. 55). In crosses between animals possessing distinctly

different degrees of the size ‘‘factor’’ blending rather

than alternative inheritance is supposed to result. This

also holds in the case of crosses between races differing

only slightly in the degree of the size character. In such

cases says Castle ‘‘we do not find it easy to detect segre-

gation’’ (1916, p. 55).

The ‘‘second’’ view supposes that complex physiolog-

ical results such as the ‘‘size’’ of a certain animal depend

upon a complex of genetic factors. All these factors are

concerned in the growth and therefore the size of the

animal. The germinal determiners of these many factors

are considered to be units.? As such their behavior in

inheritance is definite, non-blending, and essentially Men-

delian in nature. The blending, fluctuating nature of the

character studied is supposed to be due to environmental

factors, to the large number of hereditary factors in-

volved, and to absence or incompleteness of dominance.

With this rather incomplete statement we may turn to

an examination of the experimental data.

I. THE INHERITANCE oF SPOTTING In MICE

Experiments on the inheritance of spotting in mice have

been carried on by the writer since 1909. As they pro-

gressed it became evident that spotting in mice offered

remarkable material for the investigation of the inheri-

tance of a variable character. Spotting as a character is

easily measurable and classifiable. It is not affected by

changes in the external environment. Variations in

1It is interesting to note in this connection, the quotation from Castle

given by MacDowell, 1916, page 741, describing the inheritance of minute

quantitative differences in intensity of yellow pigmentation in guinea-pigs.

The later work of Wright, 1915, also has a distinct bearing on this par-

ticular ease in that it shows four truly allel elomorphie grades of intensity of

pigmentation in guinea-pigs, Fluctuation occurs about these four variation

aim and Castle’s ‘‘complete series of intermediates’’ between red and

in guinea-pigs is broken into three distinct centers of variation

with overlapping range.

2 East, 1912, has made clear the fact that variation within the unit, under

i certain sondia must of course be supposed to be possible.

No. 608] MULTIPLE FACTORS IN MICE AND RATS . 459

degree of spotting are almost certain to be quickly recog-

nized.

In mice a so-called recessive ‘‘piebald’’ spotting has

long been known. In addition a distinctly different

hereditary type, commonly dominant, was recorded by

Miss Durham (1911), and was further investigated by the

writer who found it to be entirely independent in inheri-

tance from the ‘‘piebald’’ type. This ‘‘dominant’’ spot-

ting I have called the ‘‘black-eyed white’ type of spot-

ting. Further in 1914 a third type of spotting known as

‘‘blaze,”” consisting primarily of a white forehead spot,

was reported on by the writer. This type has since been

found to be independent of the other two in inheritance.

The existence of at least three genetically distinct types

of spotting in mice is therefore proven. It is not the

purpose of this paper to generalize from this fact, but-

to attempt to show that various grades of a single type

of spotting may be introduced into a cross and may re-

appear in the F, or back-cross generation, not rarely,

but in a considerable proportion of the animals obtained. `

This is a common breeding test of segregation as com-

pared with contamination and of alternative as compared

with blending inheritance.

The races of mice used offer for the most part extremely

homogeneous material. The experimental animals come

from closely inbred races which have undoubtedly reached

a degree of genetic homogeneity which would lead to defi-

nite results in breeding, and a clearer opportunity to

observe segregation if it existed. The degree of white

spotting in the races of piebald mice used is estimated

by recording the approximate per cent. of the dorsal sur-

face which is pigmented. This method is subject, as is any

system of arbitrary grades, to a certain amount of error,

It is, however, reasonably accurate and affords a fair

measure of the degree of pigmentation of any individual.

The first experiment to be recorded is a cross involving

an English piebald race descended from black-eyed

white mice (Little, 1915). These piebalds vary in the

extent of dorsal pigmentation from 20 to 96 per cent. It

460. THE AMERICAN NATURALIST (Vou. LI

will be seen from Table I that there are essentially two

modes to the variation curve, one of these occurring at

30 to 44 per cent., and the other at from 80 to 92 per çent.

Animals from this race were crossed with dilute brown

self mice, and with mice from a yellow and from a mixed

black-agouti and black race. The F, generation consisted

of solid colored young. When these F, self young were

erossed back with animals from the piebald race, a range

of variation was obtained which is shown in the second

line of Table I

TABLE I

PERCENTAGE OF DORSAL PIGMENTATION

alelelaigiaisieisiaisielelsisisielaisigigis

HAE ool Bl bl cl ul al ol bl el ul bl dl esl ot) Al bl ol

djs d| ASR A R S 8] HS) S$) 8) S e| S/F) Ke) | S S

lish stock. . —|—|—i— 2 | 2 |11127/18|26|18|.9 |14| 6 |10| 4 112| 2 |7 17 13 16/15) 1

Back-cross | TAR | Lia

pieb: 1} 1) 6|13} 6| 7]10! 2111) 2 | 6113/5 6101015

It will be seen that even though the total of the young

obtained is less than in the pure piebald race, its range

of variability is essentially the same and there are only

four animals among those raised from the pure piebald

race which fall outside of the range of variation of the

back-eross generation. There is, moreover, no evidence

of a single mode in the curve of the back-cross generation,

but the modal centers of the parent piebald race are each

represented by a large number of young in the back-cross

generation.

Another cross in which larger numbers have been

. recorded is one between Japanese spotted mice and two

races of self pigmented mice raised at the Bussey Institu-

tion. About two years before the self mice were crossed

with the Japanese, certain spotted mice of common ances-

try with them were separated off as a different stock.

The range of variation in the degree of spotting within

this last named race may be considered a fair indi-

eation of the probable appearance of the self animals

used if they had been spotted. It will be seen from

No. 608] MULTIPLE FACTORS IN MICE AND RATS 461

the first row of Table II that, in this race, animals

varying from 56 to 96 per cent. were obtained. There is

a tendency for a mode to be formed between 80 and 92

per cent. The Japanese race used is one which for sev-

eral years has beenclosely inbred and which holds remark-

ably true to type. Its range of variation is shown in the

second row of Table II. It will be seen that the animals

possess from 4 to 36 per cent. of the dorsal surface pig-

mented. A distinct mode is observed between 13 and 16

per cent.

TABLE II

PERCENTAGE OF DORSAL PIGMENTATION

ae lol «i | lxo] Eef aa

+o) 2/3] 84) 9 8/8) 9] 3] 8/8) 312 3/2/88) 3 5 3) e) 2

Jed SIS aR eS a s3S sees ssl ks 2 8's

Pe ra preie | | ———

Tame race... —— — 1} 1/1 6 105/131110 aa 9

Japanese ea EIRA | bo |

spotted... -|1 -8 |74|92/65 23| 7| 4) -2 — l

F: spotted i—i ——i 3} 2) 5 6| 4110/6] 5913 1u 5 6 4 ia 10 8 ra 18

Back-cross | orrie |

en. 1....}—/—| 3| 2) 4 4/14/14/14/16| 5 13| 8 |7 41 6 al} 2) il 2 sle

Back-eross | hetera | | aa |

spotted | ae Wt Ad | |

SHIN ihar ay telat obia aia | a aS

The F, generation obtained from crossing the Japanese

race with the self dilute brown or brown agouti animals

above referred to, consists of solid colored animals and

is therefore not to be recorded. The F, generation in

which 146 piebald animals have been recorded con-

tains mice ranging from 20 to 96 per cent. pigmented.

Among the 146 animals recorded, 20 or 13.6 per cent. fall

in grades characteristic of the Japanese grandparents.

94 or 63.6 per cent. are of grades found in spotted animals

of the other grandparental race, see Table II, line 3.

Two other generations of great interest have been tabu-

‘lated. The first of these, line 4, Table TI, is the result of

back crossing F, generation animals with animals of the

Japanese parent race. In this generation there is distinct

evidence of segregation. Fifty-five of the 131 animals

recorded fall within the limits of the Japanese grand-

408 . THE AMERICAN NATURALIST [Vor LI

parental race and 35 within the, variation limits of the

other grandparental spotted ancestor, and of these an

appreciable number occur at the upper limit of variabil-

ity, there being no evidence of a tapering of the curve

at this point. This fact would appear to be of marked

significance. When first generation back-cross animals

are bred inter se, a second back-cross generation is pro-

duced, which, though it includes only 38 animals, has given

extremely interesting results, see line 5, Table Il. There

are five animals which are distinctly Japanese segre-

gates, and of these three show a degree of pigmentation

which would make them easily mistaken for even the

extreme variants in the Japanese race. At the other

end of the curve it is interesting to note that six of the

thirteen young reproducing the condition of the non-

Japanese grandparental stock, fall into the two extreme

upper classes and may be considered as true segregates

rather than due to any chance occurrence of an abnormal

physiological condition.

A third cross involving spotted mice has been made.

This is between animals showing a small white forehead

1 2 3 3 4

Fic. 1 :

spot and a self race. The dilute brown self race used for

one parent is the same that has been already recorded

above in the second experiment with mice. The range of .

variation of white spotting in the blaze or forehead spot

race used, is recorded in line 1 of Table III. The grades

of spotting designated in Fig. 1, numbers 1 to 4, repre-

sent the increasing degrees of white spotting. The ani-

mals comprising this spotted race are all of them pure

No. 608] MULTIPLE FACTORS IN MICE AND RATS 463

wild mice descended from a few individuals captured at

Forest Hills, and at Wenham, Mass. The F, generation

obtained by crossing the ‘‘blaze’’ and dilute brown self

races is all self in character. The F, generation shows

a distribution of young recorded in line 2, Table III.

TABLE III

GRADE OF SPOTTING

Pure blaze animala ...........,:¢.90-7 | 21) \ fF eel 6 |

3 2

Me pioke animale... rt ok. ed. es Pete LBs 31 | | 3 1

F:, Fs, Fs blaze animals ........:...... 25 M36 | 24 (107) 25 | 5 (a ee

It will be seen that the extremes of variability in F, are

the same as in the pure inbred wild blaze race. F, Fy,

and F, animals raised without selection give a result

recorded in line 3 of Table I, and again show the same

limits of variation. It will be seen, therefore, that the

blaze character is segregated from the cross without

apparent modification, although the extremely minute

degrees of spotting which it includes are those which one

might expect would be modified or entirely swamped if

contamination between the gametes of the self and blaze

races occurred. This cross together with the cross be-

tween mutant and wild rats recorded by Castle to be con-

sidered later, give conclusive evidence that even a minute

quantitative character segregates after crossing and does

not afford grounds for the objection raised by Castle that

crosses between races differing slightly in size or like

fluctuating characters do not readily show segregation.

To sum up the results of spotting inheritance in mice,

it may be said that all the crosses made show a reappear-

ance of grandparental conditions in F,, back-cross, and

other advanced hybrid generations. The reappearance

of these grandparental types is frequent enough to lead

one to conclude that if segregation in a strictly Mendelian

sense is not taking place, that at least the outward appear-

ances of such a process are all of them present.

464 THE AMERICAN NATURALIST [Vou. LI

Il. THE INHERITANCE OF SPOTTING IN Rats

Castle’s work on the inheritance of fluctuations in the

hooded coat pattern of rats is well known to all geneti-

cists, and may now be considered in an attempt to examine

the bearing of spotting on the inheritance of fluctuating

characters in general. The hooded rats with which

-34

-1⁄4 O

In grades higher than +4 the whole dorsal surface is pigmented and the ven-

tral surface is becoming progressively more so.

FG. 2

Castle worked have been shown clearly by Doncaster,

Mudge, and others, as well as by Castle himself, to be

recessive to self or solid colored coat in inheritance. The

hooded pattern is, however, subject to wide fluctuation

producing a series of rats from those with the whole

dorsal surface and most of the ventral surface pigmented,

No. 608] MULTIPLE FACTORS IN MICE AND RATS 465

to rats in which only small spots around the eyes remain

pigmented. The following diagram will show roughly

the limits of variation and some of the intermediate types

as graded by Castle. Throughout the course of his selec-

tion experiments, Castle has at times crossed the plus

variants with the minus variants or else crossed selected

animals from the plus or minus series with wild or with

Irish rats. Both the last mentioned varieties are essen-

tially self pigmented animals and are dominant in inheri-

tance to the hooded pattern. The race with which Castle

started his selection experiments showed within the first

two generations of selection rats varying from grade

minus two to grade plus three and three quarters.

Castle and Phillips, 1914, have recorded the results of

two crosses between minus variants and plus variants.

The first of these crosses was between females of minus

two grade in the sixth selection generation and males of

plus three and one half. or three and three quarters

grades in the fifth selection generation. It is possible to

use the range of variation among the progeny of animals

of these grades within the selection generation from

which they are chosen to control the results of the cross.

In-Table IV? the first line represents the range of varia-

tion in the progeny of minus two animals of the sixth

selection generation. The second line represents the

range of variation in the progeny of plus three and one

half and three and three quarters animals of the fifth

selection generation. It will be seen that there is a space

of seven grades between the two limits of variation of

the parent races. The cross between these two types

produced in the F, generation a range of variation shown

in the third line of Table IV. It will be seen that for the

most part, the young fall in the seven classes between the

two parent races. In these seven classes will be found

sixty-eight or 73.1 per cent. of the ninety-three young.

Two or 2.27 per cent. of the young show grades of pig-

3 The references to tables and pages appearing in the first column of

Table IV, and ensuing tables, refer to Castle and Phillips, 1914.

[Vou. LI

THE AMERICAN NATURALIST

466

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No. 608] MULTIPLE FACTORS IN MICE AND RATS 467

mentation characteristic of the plus parent and twenty-

three or 24.75 per cent. of the young show grades char-

acteristic of the minus parent race. When the F, young

are bred inter se there is a marked increase in the per

cent. of young showing grades of pigmentation character-

istic of the grandparents. Ninety-three, or 30.5 per cent.,

of the 305 F, generation young fall in grades character-

istic of the minus grandparents. Fifty-two, or 17.0 per

cent., fall in grades characteristic of the plus grand-

parents. The remainder, or 52.5 per cent., fall in the

seven intermediate classes.

A second cross made between selected animals is shown

in Table V. Females of grade plus three and three

quarters of the tenth selection generation were crossed’

with a male of grade minus three and one quarter of the

tenth selection generation. As a control for the females

it is possible to use the progeny of grade three and three

quarter parents in the tenth and eleventh generations.

The reason for using two generations instead of one is in

order to increase the number of progeny available, since

the tenth generation alone shows such a small number of

young that they are not valuable as a significant breeding

test. The range of variation in the progeny of rats of this

grade is shown in the second line of Table V. As controls

for the minus parent, rats of grade minus two and three

quarters and two and seven eighths of the tenth selection

generation have been used. Although the total of the

young produced by them is very small (thirty-one), it

is, nevertheless, the only critical data available. The

range of variation of these young is shown in the first

line of the table. The F, generation resulting from the

cross of these two diverse selection types is shown in

the third line of Table V. The thirteen young comprising

this generation all fall in grades between the two parent

types. The F, generation shows a distinctly greater varia-

bility than the F, generation and includes four young of

grades characteristic of the plus grandparental race.

This cross is less conclusive than the previous cross, but

[ Vou. LI

THE AMERICAN NATURALIST

468

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No. 608] MULTIPLE FACTORS IN MICE AND RATS 469

does nevertheless show that 5.4 per cent. of the seventy-

three F, young reproduce the degree of spotting charac-

terizing one of the parental races.

The total number of animals observed, however, is con-

siderably smaller than in the previous experiment and

the results are therefore subject to greater error.

We may now consider several crosses made between

hooded and wild rats. The F, generation in such crosses

consists almost entirely of self pigmented animals. It is,

therefore, in a comparison of the range of variability

observed in the F, generation with that observed in the

pure hooded race from which the hooded grandparent was

taken, that we may expect to find evidence for or against

segregation. The first cross to be recorded is between a

female of grade — 1% in the 24 generation of the minus

selection series, and a wild male. As a control for this

female, the progeny of — 1? parents in the second and

third selection generations may be taken. It will be seen

that their progeny varies between grades — 2 and — }

(see line 1, Table VI), in a total of 90 animals. The F,

generation shows a range of variability between grades

— 14 and grade + 34. It is interesting to note, however,

that twenty-three or 37 per cent. of the sixty-two animals

observed fall within the range of variation of the hooded

grandparent. A comparison of grades — 14 and — 2 in

Fig. 2 will show how closely F, animals approach the

extreme condition of the hooded grandparental race.

In the second cross between hooded and wild rats,

females of minus two grade of the sixth generation of the

minus selection series were used. As controls for these

females the progeny of — 2 parents in the sixth generation

of the minus selection experiment may be used (see line

3, Table VI). The 969 young so obtained fall between

the grades — 24 and — 4. The forty-eight young show a

large range of variability from —1} to +23. Of the

forty-eight obtained, twelve, or 25 per cent., fall within

the range of variation of the progeny of the hooded grand-

parental generation.

470 THE AMERICAN NATURALIST [Von LI

The third cross was between wild males and females

of grade — 2 or 24 in the tenth generation of the minus

selection series. As a control for these animals it is pos-

sible to use the progeny of 24 parents in the tenth gen-

eration of the minus selection series (see line 5, Table

VI). The 474 young so obtained vary between grades

— 34 and — 1.

Among the ninety-one F, young obtained, eighteen, or

approximately 20 per cent., fall within the limits of vari-

ability of the hooded grandparents. The range of vari-

ability in the F, generation is considerable, being from

— 2 on one side to + 2 on the other.

Three crosses between animals of the plus selection

series and wild rats are recorded. In the first cross (see

lines 7 and 8, Table VI) females of grade plus three

of the third generation of the plus selection series

were used. The breeding capacity of these animals may

be fairly judged by considering the progeny obtained

from plus three parents in the third generation of the

plus selection experiment. The 143 young so obtained

range from grade + ł to + 33. Only twenty-one F, young

are recorded, varying between grades + 13 and + 34. It

is interesting to note that all of them fall within the range

of variation of the grandparental hooded race.

In the second cross females of grade + 31, fifth gen-

eration and females of grade + 34, sixth generation, were

crossed with wild males. The progeny obtained from

animals of similar grade and generation within the selec-

tion experiment can serve as controls. The 320 young so

obtained vary between grades + 14 and + 41. The thirty-

eight F, young obtained vary between grades +14 and

+ 3%, again, in every case, reduplicating the grand-

parental forms.

The third cross, which includes only small numbers and

is therefore of less relative value than the two previous

crosses, was between a female of + 44, tenth generation

and a wild male. The control animals gave twenty-five

young ranging from grades + 3} to +43. The F, gen-

No. 608] MULTIPLE FACTORS IN MICE AND RATS 471

eration, which consists of only sixteen animals, ranges

between the grades +2 and +33. Six of the sixteen

young fall within grades characteristic of the grand-

parental animals (lines 11 and 12, Table VI).

Crosses between hooded and Irish rats have given com-

parable results (Table VII). Rats of grades —14 gen-

eration 34 minus selection, were crossed with Irish rats.

As a control for the hooded animals the progeny of rats

of grade — 1} in the third and fourth selection generation

may be used. The total of the progeny so obtained is 112.

It will be noticed from Table VII, line 1, that they vary

between grades — 24 and +4. Only eight or 8.8 per cent.

of the F, generation vary outside of the grandparental

grades. The range of variability in this generation is be-

tween — 2 and + 14. The second cross is between females

of grade — 14, from the fifth selection generation of the

minus series and Irish males (lines 3 and 4, Table VII).

As a control for these the progeny of — 1% parents of a

similar generation may be used. The 143 progeny so ob-

tained fall within the grades — 2} and — $ inclusive. The

fifty-three F, young range between grades — 13 and +1.

Almost exactly 50 per cent. of them reproduced the grades

of the hooded grandparental types.

The third cross is between females of minus two grade

in generation 73 of the minus selection experiment and

Irish males. As a control, the progeny obtained from the

females of — 2 grade in the seventh and eighth selection

generations may be used. Such animals produced 2,013

young, ranging from — 23 to — 4. Sixty-six F, young

ranged from grades —2 to +2. Of these, 75.8 per cent.

reproduced the grades characteristic a the hooded grand-

parental race.

Two experiments are recorded Foie crosses of plus

selection animals with Irish males. In the first of these,

the females used were of grade + 2} in the second gen-

eration of the plus selection experiment. Animals of

similar grade and generation may act as controls, although

the number of young obtained from them is very small.

472 THE AMERICAN NATURALIST [Vou. LI

The eight young so obtained fall between grades + 14

and + 23. From this cross 239 F, young have been ob-

tained ranging from grades —1 to +34. 129 or 53.9

per cent. show grades characteristic of the hooded grand-

parent.

The remaining cross was between females of grade + 3,

third selection generation and Irish males. Controls ob-

tained by tabulating the progeny of animals of similar

grade and generation show in 143 young, a range between

grades + ? and + 3%. Only twenty-three F, young were

obtained, ranging between — 1 and + 24. Of these, six-

teen, or 69.5 per cent., reproduce the grades characterizing

the hooded grandparent.

One other striking cross is recorded by Castle in the

case of the rats. This is a cross between ‘‘mutant’’ rats

showing a particularly advanced degree of plus pigmen-

tation and pure wild rats. The range of variability of

the pure ‘‘mutant’’ race is according to Castle’s state-

ment (Castle and Wright, 1916, page 173) between grades

+54 and +53, see Table VIII. The 109 F, ‘‘mutant’’

young show a range of variation between the same grades.

According to Castle’s statement on page 174, ‘‘their range

of variation does not fall beyond that of the uncrossed

mutant race.’’ It would appear as though the evidence

of segregation in this case, even to an almost exact de-

gree, was clear. This case, together with that of the type

of spotting in mice known as ‘‘blaze’’ (Little, 1914) al-

ready discussed, appears to show that races differing

from each other in only a minute degree of a quantitative

character may show segregation clearly. ;

TABLE VIII

Generation eae rosg ojo ay we jorii

Pure mutants. ..........- | 2 | 4 | 28 | 17 | oa

To sum up the experiments with rats, it may be said

that while it can not be claimed that the evidence is final

in regard to the unit nature of the factors involved, they

No. 608] MULTIPLE FACTORS IN MICE AND RATS 473

offer distinct evidence of segregation. That is to say, the

combination of gametes formed by hybrid parents repro-

duce the same zygotic types as did combination of gametes

of the pure parent races.

The bearing of the results on the practical breeding of

farm animals seems clear. If a complicated and highly

variable character as the hooded pattern in rats may be

introduced in a cross with a non-hooded form and may be

recovered in a large proportion of the F, generation, we

may encourage crossing as a favorable method of pro-

ducing new and important breeds. This will be all the

more apparent if we agree with the selectionists who hold

that the character reappearing in F, will be at once amen-

able to selection and improvement in a desired direction.

Contamination of genes in breeding experiments which

are conducted on a large scale and are followed by rigid

selection, need not be considered as a factor of prime im-

portance.

ILI. PHYSIOLOGICAL Factors UNDERLYING GROWTH OF

IMPLANTED TISSUE

The study of the inheritance of spotting in mice and

rats has served to give a considerable amount of data more

or less directly comparable to that obtained in studies of

size inheritance; though presenting, as I shall try to show,

certain advantages in their freedom from environmental

and age influences and in their definiteness. :

We may now consider a very different line of werk,

which bears a most interesting relation to other studies of

the inheritance of complicated morphological and physio-

logical characters. The reaction of various closely inbred

strains of mice and their hybrids to implants of a single

tumor is definite, and characteristic. It is moreover un-

doubtedly hereditary as the work of many investigators:

has shown. |

Tyzzer and the writer (1916) have reported results ob-

tained in inoculating Japanese waltzing mice, closely in-

bred races of common mice and their hybrids, with an

474 THE AMERICAN NATURALIST [Vou. LI

epithelial tumor which originated in the Japanese waltz-

ing race. The parent animals all of them came from

races which, because of long continued inbreeding, may

be considered to have reached a degree of great genetic

homogeneity. It will be seen from the table (loc. cit., p.

403) that all the Japanese waltzing mice inoculated, 58

in number, grew the implanted tumor, while none of the

common mice showed continuous growth of the tumor.

This absolute difference between the parent races is

extremely interesting and offers ideal material for the

formation of intermediate conditions of susceptibility

in hybrid generations. They further offer a test of

the relative value of the hypotheses of multiple factor

and of blending inheritance. Sixty-two F, hybrids

obtained by crossing the Japanese with tame races were

inoculated. Of these, sixty-one grew tumors. The tumors

grew in most cases fully as rapidly if not more rapidly

than in the susceptible Japanese parent races. It is prob-

able that the one animal in this generation which failed to

grow the tumor is not a true exception, but that its be-

havior may be due to poor technique. The second genera-

tion hybrids have given an extremely interesting result.

Of the 183 inoculated, only three have shown continuous

growth of the tumor. This result is surprising in view

of the fact that susceptibility appeared to be a dominant

character in the F, generation. Only thirty-eight animals

of the F, generation were inoculated; none of them grew

the tumor. The striking difference between the F, and

the F, generations suggests at once, alternative rather

than blending inheritance. As we have suggested in our

previous paper, the most logical interpretation appears

to be that a certain physiological condition on which the

growth of the tumor depends, is produced in the animals

of the Japanese waltzing race. This condition is not

found in the tame mice used. The differences between the

races are hereditary, since succeeding generations of the

Japanese and tame mice behave like their parents. The

fact that susceptibility of the tumor occurs in both F, and

No. 608] MULTIPLE FACTORS IN MICE AND RATS 475

F, generation hybrids shows that the conditions on which

the growth of the tumor depends are reproduced in hybrids

of the two races. The behavior of the F, hybrid genera-

tion produced by reciprocal crosses indicates clearly that

even when only one of the parents is susceptible and comes

from the homogeneous Japanese race, its contribution to

its offspring is sufficiently powerful to produce sus-

ceptibility in that animal. In other words, we may say

that the hereditary factor or factors underlying suscep-

tibility are functional even when present in a ‘‘single

dose.’’ If there is a single general factor underlying

susceptibility we should expect that the F, generation

would show a large number of susceptible animals. This

is not the case. It is possible, however, to consider the

behavior of the F, generation as being largely due to

heterozygosis and not to true inheritance. To eliminate

this possibility a back-cross generation was made between

F, animals and pure Japanese. The sixty-three animals

comprising this generation all proved susceptible to the

tumor and in a majority of cases grew it as rapidly as did

the F, hybrids themselves. On the other hand, the F,

generation crossed with tame mice gave seventy-eight

young, all of which were non-susceptible.

In discussing the results, it was further suggested that

the explanation which best fitted the facts, indeed the only

explanation which fits all of the facts, is that susceptibility

depends for its manifestation upon the simultaneous pres-

ence of several factors in either the homozygous or the

heterozygous condition. The gametes of the Japanese

race possess all or nearly all of these in a homozygous

condition and therefore produce susceptible animals. The

F, hybrids possess all of these factors in a ‘‘single dose’’;

they having been contributed by the Japanese parent, and

are therefore susceptible. When, however, the F, animals

form gametes, these factors, if they are mendelizing and

not blending in nature, will be distributed at random in

the gametes. The result will be that the larger the num-

ber of factors involved, the rarer will be the inclusion of

476 THE AMERICAN NATURALIST [Vor LI

all of them within a single gamete formed by the F, ani-

mals. Since susceptibility in the F, generation will de-

pend upon the presence of all of the factors ordinarily

found in the Japanese race, it follows that the greater

the number of factors involved, the rarer will be the ap-

pearance of a susceptible animal in the F, generation. It

further follows that the susceptible animals of the F,

generation probably will not possess the factors in a

homozygous condition, as did the Japanese grandparents,

and therefore they will not, in most cases, breed true, as

did the Japanese grandparents, to the character of sus-

ceptibility.

For a more detailed discussion of these results from a

genetic point of view, the reader is referred to Tyzzer

and the writer’s earlier paper. It will suffice at the pres-

ent time to emphasize the fact that it is the inherent nature

of the tissue of the host animal that is being studied. The

tumor itself is as near a biologic constant as one can ob-

tain. Variation in its growth therefore means variation

in the attitude towards it, taken by the host tissue. This

attitude appears to be dependent upon a complex of dis-

tinct factors. If a change or substitution is made in any

one of the.members of this complex, a different reaction is

obtained. The behavior of the different factors in any

such complex is distinetly that of independent units in in-

heritance. The fact that the reactions of susceptibility

and non-susceptibility are dependent on multiple factors

seems established. If the tissue of the adult mouse may

be analyzed in this way, the conclusion is far reaching.

If the reaction of the tissue depends on its substance, and

its substance depends in turn on a certain hereditary com-

plex of factors, it is logical to suppose that the rate and

extent of development of the tissue as well as other proc-

esses of significance to the organism depend, in so far as

they are hereditary, on similar complexes of genetic fac-

tors. Environment undoubtedly influences certain char-

acters in their development far more than others, and in

this respect size appears to be one of the most susceptible.

No. 608] MULTIPLE FACTORS IN MICE AND RATS 477

On the other hand, rate and extent of growth is undoubt-

edly chiefiy dependent on the nature of the tissue involved,

and as we have seen there is every reason to believe that

this depends on the interactions of a complex of genetic

factors which are independent of each other in inheritance.

OTHER EXPERIMENTS WITH INOCULATED TUMORS IN MICE

Loeb and Fleisher (1912) have reported a series of

investigations on the hereditary factors underlying the

susceptibility of mice to a transplantable carcinoma. As

parent stocks they used three races of mice, one American

race, and two European. By breeding tests including

several generations the percentage of American mice to

show continued growth of the inoculated tumor was found

to be eighty-four, while those of the European races I and

II were twenty-three and three per cent., respectively.

The F, generation between American and European I

gave sixty-eight per cent. susceptible, F, from this same

cross gave thirty per cent. susceptible. When American

mice were crossed with European II an F, generation was

obtained in which one hundred per cent. of the animals

inoculated were susceptible. Only fourteen animals were

tested and the number is too small to establish this as an

accurate percentage for this generation. The F, genera-

tion of this cross gave twenty-six per cent. susceptible.

It is interesting to note that in the F, generation, where

sufficient numbers were obtained to afford critical evi-

dence, the percentage of susceptibility was intermediate

_between those of the parent races. There is a marked

decrease in degree of susceptibility in the F, generation.

The fact that some of the animals of the American parent

race failed to grow the tumors shows that this race is in all

probability not homogeneous, and the same is true of the

European races since animals within a single race fail to

react similarly to pieces of biologically similar tumor. If

such is the case, we should expect an intermediate result —

in the F, generation, just as we do when we cross two

races differing in size. The F, generation should also be

478 THE AMERICAN NATURALIST [Vou. LI

intermediate, though on the basis of blending inheritance

we should expect the percentage of positive animals to be

much closer to that observed in the F, generation than it

actually is.

On an hypothesis of multiple factors underlying sus-

ceptibility or immunity to the inoculated tumor the ex-

perimental results may well be explained. The F, gen-

erations of Loeb and Fleisher’s work give a result further

indicating the possible presence of multiple factors. If

a large number of F, animals mated inter se at random

are used to produce the F, generation the percentage of

susceptible animals in F, should be roughly approached

in the F, generation. 122 animals comprising the F,

generation show twenty-four per cent. susceptibility as -

compared with thirty per cent. in the F, generation of the

same cross. In the F, generation of the American times

European II cross, sixty-six animals have been inoculated

and have given only two per cent. of susceptibility. This

difference is possibly due to the fact that F, animals

forming gametes each closely resembling those of the

grandparent European race were unconsciously chosen

as parents for this generation.

The interesting part of Loeb’s work is the fact that the

relative homogeneity of the races of mice which he used

approximate closely the conditions in respect to sucepti-

bility and non-susceptibility which one ordinarily is deal-

ing with in size crosses as, for example, Castle’s work

and also MacDowell’s work with rabbits. In none of

these cases has there been excessively close inbreeding in

either parent race before crosses were made. There is, `

therefore, no definite complex of factors characterizing

the race. As a result the percentage of susceptible

animals varies and depends on the character of the par-

ticular animals used for breeding. The whole effect

produced is to obscure the true nature of the processes

involved. In respect to homogeneity the material at the

disposal of Tyzzer and the writer possessed a great ad-

vantage which became apparent in the definite results

produced.

No. 608] MULTIPLE FACTORS IN MICE AND RATS 479

Size inheritance studies have not been recently made

with mammals of known ancestry and of approximately

pure races. This fact greatly diminishes the value of the

results obtained even though they represent work of the

most painstaking sort. For this reason the writer started

last January a series of experiments on size inheritance

in pure races of rabbits. Polish rabbits are being used for

the small parent and Flemish giant rabbits for the large

parent. It is hoped by a careful study of variation within

the pure races to understand more clearly the method of

inheritance in the hybrid generations to be produced by

later experiments.

` To summarize the work with inoculable tumors, one

may say that it presents a type of inheritance not expli-

cable on an hypothesis of blending inheritance or of a

single variable gene. All the results may, on the other

hand, be satisfactorily explained by supposing that the

nature of the host tissue and its reaction to the implant

depend upon a complex of mendelizing factors.

CONCLUSION

The fact that three genetically distinct types of spot-

ting exist in mice; that segregation of the degree of spot-

ting occurs in both rats and mice; that segregation of

minute quantitative characters like the ‘‘blaze’’ spotting

in mice, and the pattern of the ‘‘mutant’’ rats occurs; and

finally that the composition and reaction of epithelial

tissue in mice depends upon a complex of mendelizing

factors, all indicate that in mammals the multiple factor

hypothesis is steadily being strengthened as a scientific

theory and a practical principle of great interest and im-

portance.

BIBLIOGRAPHY

Castle, W. E.

1909. Studies on inheritance in rabbits. Carnegie Inst. of Wash.,

Publ, No. 114.

Castle, W. E., and John C. Phillips.

1914. Piebald rats and selection. Carnegie Inst. of Wash., Publ. No. `

195.

480 THE AMERICAN NATURALIST [Vou. LI

Castle, W. E., and Sewall Wright.

1916. Studies of ee i in ee pigs and rats. Carnegie Inst.

Wash., Publ. No.

Doncaster, ti

1909. On the inheritance of coat color in rats. Proc. Camb. Phil. Soc.,

oe Ole Ae p. 215.

Durham, F. M.

1911. Further experiments on the inheritance of coat color in mice.

Jour. Genetics, Vol. 1, 9

East, E. M.

1912. The Mendelian notation as a description of physiological facts.

AM. Nart., 46: p. 633.

Little, C. C.

1914. Dominant and recessive spotting in mice. Am. Nar., Vol. 48,

4 .

Little, C. C.

1914. A ee Mendelian explanation of a type of eaii appar-

ntly non-Mendelian in nature. Science, n. s., Vol 904. .

Little, C. C.

1915. The inheritance of black-eyed white spotting in mice. AM.

Nat., Vol. ex bf 727-740.

Little, C. C., and E. E.

1916. Further experiment a studies on the inheritance of susceptibility

to ransplantable tumor, carcinoma w of the

Japanese waltzing mouse. Jour. of Med. Reisen, Vol. 33,

pp. 393—453.

Loeb, L., and M. S. Fleisher.

9. Untersuchungen über die Vererbung der das Tumor Wachstum

bestimmenden Faktoren. Centralb. f. Bakt, u. Parasit., Vol.

67, p. 135.

MacDowell, E. c. i .

1914. Size inheritance in rabbits. Carnegie Inst. of Wash., Publ.

No. 196.

MacDowell, E. C. -

1916. Piebald rats and multiple factors. Am. NAT., Vol. 50, p. 719.

Mudge, G. P.

1908a. On the hereditary transmission of certain coat characters in

rats. Proc. Roy. Soc., Series B, Vol. 80, p. 97.

Mudge, G. P. ;

1908b. Second paper, same title. Proc. Roy. Soc., Series B, Vol. 80,

p. 388.

Wright, Sewall.

1915. The albino oa of allelomorphs in guinea-pigs. Am. NAT.,

Vol. 49, p

THE INHERITANCE OF THE WEAK AWN IN

CERTAIN AVENA CROSSES’

H. H..LOVE AND A. C. FRASER

(In Tn with the Office of Cereal Investigations, U. S. Department

of Agriculture.)

To some time past, the writers have had under observa-

tion many different hybrid series of oats. Certain of

these offer an excellent opportunity for a study of the

inheritance of awns. This paper is a preliminary report

aiming to set forth ideas regarding the factor differences

between certain types of awns, as a basis for a further

study of the relation between awning and other charac-

ters of the oat grain. ;

Kinps or Awns

Practically all of the wild types of oats are character-

ized by a very strong awn. This awn is typically long,

stiff, and geniculate. The basal portion of the strong

awn is twisted in a clockwise fashion and either black or

dark brown in color. . Above the twist, the awn is prac- `

tically straight until it reaches the knee, at which point it

turns sharply and proceeds almost at right angles to its

former course and usually in a different plane. The first

step in the modification of this type of awn seems to be

the loss of geniculation, together with a reduction of the

stiffness. Then a further straightening of the awn occurs,

leaving it practically straight from the point of attach-

ment to the tip. Such a change is accompanied by a loss

of the dark color at the base of the awn. An awn of this

last type is usually spoken of as the weak awn. The weak

awn may vary greatly in length, thickness, and rigidity.

In some cases it becomes a mere hair-like appendage,

` 1Paper No. 62, Department of Plant Breeding, Cornell University,

Ithaca, N. Y.

481

482 THE AMERICAN NATURALIST [Vor. LI

Fig. 1. Showing gradations between the spikelet possessing two strong

awns, and the awnless spikelet. From left to right are shown: 2 strong awns;

1 strong and 1 weak awn; 1 strong awn; 2 weak awns; 1 weak awn; and the

awnless type. :

extending scarcely beyond the tip of the lemma and only

distinguishable by careful examination. As this awn

becomes weaker, it is produced nearer to the tip of the

kernel; that is, the rib of the lemma which forms the awn

adheres to the lemma for a greater distance before aris-

ing as an awn. Among the wild and cultivated types of

oats the awns are either characteristically strong, weak,

or lacking altogether. In hybrids of these, however, the

awns may present all gradations between the awnless and

the very strongly awned types. It is usually possible,

though, to classify the hybrids as having strong, interme-

diate, or weak awns. (See Figures I and IT.)

MetHops or Srupy

The parent plants and first-generation hybrids were

grown in the greenhouse, and the second and third gen-

eration hybrids were grown in the field. In the case of

the first-generation hybrids, all of the spikelets on all of

the plants could be studied. With the much larger Fs,

however, it was found impracticable to attempt to study

all of the spikelets on a plant. The study was limited,

No. 608] WEAK AWN IN AVENA CROSSES 483

Fic. 2. Showing apm in the weak-awn series, from a spikelet having two

awns down to the awnless type.

therefore, to one representative panicle from each plant.

The spikelets were picked from such a panicle, examined

for awns, and placed in a small seed envelope on which

was recorded the data as to total number of spikelets,

number with one awn, and number with two awns.

MATERIAL

The weak-awned varieties reported on here are the

Burt and a strain of the Red Texas. Attention was cen-

tered upon the variety Burt. The awnless type in all

cases was the cultivated variety Sixty-Day. For the

strong-awned oat, a strain of Avena fatua was used. All

forms had been grown in pure line culture previous to

crossing and were uniform within themselves,

Series 514al — Burt X Sixty-Day

(Weak Awn X Awnless)

A cross between the Burt and Sixty-Day gave an F,

which was almost awnless. A few plants had awns on

some of the spikelets, but the generation could be con-

sidered practically awnless.

484 THE AMERICAN NATURALIST [Vou. LI

The second generation plants showed all degrees of

awning, from the perfectly awnless condition to those

which were one hundred per cent. awned like the Burt

parent. These F, individuals were first grouped accord- -

ing to percentage of awned spikelets, with a class range

of ten per cent. (Table I.)

TABLE I

F, oF 514412

Per Cent. of Awning ft

0 110

1-10 29

11-20 23

21-30 25

31-40 18

41-50 18

51-60 14

61-70 8

71-80 12

81-90 5

91-99 12

00 66

The occurrence of plants having varying percentages

of awned spikelets and forming a more or less continuous

series between the parental types, at first suggested a

multiple factor condition for awning. A study of the

frequencies, however, showed that such an assumption

was incorrect. The frequencies of the zero and 100 per

cent. classes were too high to accord with an hypothesis

of this sort.

When the F, plants were grouped in the classes—awn-

less, partially awned, and fully awned, it was seen that

the data approached, in a general way, a ratio of 1:2:1.

(See Table II.) The ratio of the first two named classes

to the third was found to be 4.15:1, or, on a basis of four,

3.22: 78.

It remained for a study of the F, material, however, to

throw light upon the number of factors concerned in this

cross, and the relation of these factors to each other.

2 It was necessary to reduce the class range in the case of the 91-99 -=

in order to provide the 100 per cent. class. This, however, could have

effect on the conclusions drawn from this table,

No. 608] WEAK AWN IN AVENA CROSSES 485

TABLE II

F, or 51441

P is in sch an cess ee 6k 110 } 274

Partially swned CA ARAN 164

FANY AWE a ha. heal pn 66 66

340 340

Behavior of the Fully-awned F, Plants.—Seed of three

of the fully-awned F, plants was sown in pedigree culture

for an F,. The results obtained are shown in Table III.

TABLE III

F, FROM FULLY AWNED F, PLANTS—514A1

Pedigree % Awns in Fe | Awnless Partially Awned | Fully Awned

514a1-22 100 | 0 0 47

5l4al-88 | 100 0 0 36

5l4ai-05 | 100 0 0 | 20

| }

Total oe | 0 0 | g

From this data, it would appear that the fully-awned

type is the pure recessive. We have already seen that

this type has very little influence on the F, hybrid, and

that it appears in F, in only about 25 per cent. of the

individuals. Here we find the fully-awned plants breed-

ing true.

Behavior of the Partially-awned F, Plants.—Twelve

plants which showed some awning in the second genera-

tion were planted in pedigree rows for F, The per-

centage of awning in these plants varied from eleven to

eighty-seven. In spite of the wide difference as to per-

centage of awning, their behavior was strikingly similar.

With but one or two exceptions, the ratio of plants

not fully awned to those which were fully awned was

close to 3:1. A total of all these F, plants gave the

frequencies 419:118, or a ratio of 3.12:.88. In this case

the deviation is 2.4 times as great as the probable error,

but this can be accounted for by the somewhat wide devia-

tions occurring in cultures 106 and 194. With the excep-

tion of these pedigrees, the deviations from the expectancy

are not more than twice the probable error. It is of

486 THE AMERICAN NATURALIST [Vor. LI

interest to note that plants with a high percentage of

awned spikelets in F, did not tend to give a correspond-

ingly high number of awned plants in F;. Neither did

plants with a low percentage of awns in F, tend to pro-

duce more of the awnless or partially-awned types in Fs.

TABLE IV

F, FROM PARTIALLY AWNED F, PLANrs—514Al

Bia 65) 77 | 18 | 16") ee [eee Ep PY edo sa86 oe

-100} 24 | 36 | 17] 19 | 53 | 19 | 78 | 06 |.137| 44

106) 11 | 81 7 sf 38 | e PAB ior [trbt wos

-119; 20 | 17 R ae are nea 20 tee ae

-198|-s7 | 24 | 11 | 129 | 36| i oe [ete | 178 ie

iss} 32° fia | i5 5 | 28 5 | 33° | (39 | .203'| 1.92

-472| 15 |. 26 el ki B 8 | SN | -185,| 1.08

~194|14,|,.36 |: 19,}. 21 | ,55.| 1m | *33 | 33 | 144 | 2.20

saol 18 | 24} a2 {ar | deeh an pI .06 | .a7n | 35

sme æ p niw | 8 Jean a| OS | sis {aoe 9

-244, 60 | 13 | 17 7 1 30 CTT ae 192) 1.24

264. 81 | 23 Gj. 101m.) 10 | oo | ,.08 | 187 | 16

| 267 |. 152 | 118 | 419 | 118 | 222 | 42 | .05 | 2.40

Behavior of the Awnless F, Plants.—Eleven of the

awnless F, plants were selected for study in F,, and se

from them was sown in short pedigree rows. The be-

havior of these plants is shown in Table V. Five of these

awnless plants bred true to the awnless condition, giving

a total of 249 awnless plants in F,. The other six broke

up into awnless, partially-awned, and fully-awned plants.

In no case did the ratio of these types suggest a 1:2:1

ratio. When we group all of the plants which are not

one hundred per cent. awned, however, and compare them

No. 608] WEAK AWN IN AVENA CROSSES 487

with the fully-awned plants, we find that the separate

ratios closely approximate a 3:1 ratio. The ratio for all

six plants is 2.97:1.03, and its deviation is practically the

same as its probable error.

TABLE V

F, FROM AWNLESS F, PLANTS—514a1

| Aa Par- Not |

Pedigree | Awns Awnless| tially | Aon, | Fully | rey} Beto | p> | px. | DIP.E.

| in Awned Awned

5l4al— dila D 48 0 o |. 48 0

126 0 75 0 0 75 0

-185| D 31 0 0 31 0

-336| 0 32 0 o | 32 0

232) 0 63 0 o | 63 0

Total 249 249

3.24 |

514a1-339 0 34 0 8 | 34 8 76 | 24 | -180 | 1.33

-36 0 60s akaa T 66.1, g oy 14 .140 | 1.00

-176| 0 A E a a E aita 02 178

-221| 0 ite 8 7 | il 7 | 223 | 97 | 249! 1.08

1.27 |

Ma L Bir LBT 95 | e Fa as] 2.70

-291| 0 odes i u a a | 222 | 02-|.178) 4a

1.02 |

; : 2.97

To | o a | 67 | 198 | GY | 75, | 08 |072| 43

It is apparent from these data that the F, grouping used

here includes in the awnless class certain individuals

which are heterozygous for awning, and which really

belong with the partially-awned plants. According to

Nilsson-Ehle (1914) environmental conditions have an

effect upon the production of awns. It is quite possible

that the failure of these six plants to produce some awns

is due to undetermined environmental factors.

A comparison of the relative numbers of awnless and

partially-awned plants in Tables IV and V would seem to

indicate that awnless F, plants tend to give a higher per-

centage of awnless plants in F, than do the partially-

awned plants. This may be explained, however, by the

488 THE AMERICAN NATURALIST [Vou LI

fact that a high percentage of the awnless plants in the

second generation were yellow in color and consequently

many of them might well carry a factor which inhibits

awn formation. Data will later be presented to show a

definite linkage between the awn-inhibiting factor and the

factor for yellow color in the Sixty-Day.

Series 2501al — Burt X Sixty-Day

A second series of hybrids between Burt and Sixty-

Day behaved in a manner similar to series 514al. The F,

was nearly awnless in both the direct and reciprocal

crosses. The F, results are shown in Table VI.

TABLE VI

F, or 2501

Purcalty | way. | a | Paty | Ratio

Pedigree aie aaah kaii P Awat 34 D P.E.. | D/P.E.

2501b1 26 96 43 | 122 | 43 ns 04 |.0909| .44

250lar1 ‘| 17 61 23 | 78 | 28 yS 06 | .1134!| .53

2501ar2 4 32 17 | 86 | 47 mg 28 | 1604 | 1.75

2501ar3 1 11 4 12 4 Aa 00 | .2921 0.00

Total | 48 200 92 | 248 | 92 1e 08 |.0634 | 1.26

2501b1 = Burt X Sixty-Day. ;

250larl =Sixty-Day X Burt—selection of partially awned F, plants.

250lar2 —=Sixty-Day X Burt—selection of awnless F, plants.

250lar3 = Sixty-Day X Burt—unselected F,.

It will be seen from Table VI that the partially-awned

and awnless types of F, gave practically the same

behavior, each throwing about 25 per cent. of fully-awned

plants in F,.

Series 2401al — Red Texas X Sixty-Day

A cross between Red Texas (weakly awned) and Sixty-

Day gave an F, showing only 1.3 per cent. of awning.

The second generation of this cross has not yet been

grown.

No. 608] WEAK AWN IN AVENA CROSSES 489

Discussion of Results in Weak-awn X Awniess.—From

the data presented above, the following conclusions may

be drawn as to the inheritance of awns in crosses between

the weak-awned and the awnless types of oats.

The awnless type is almost completely dominant in the

first generation, only a few of the plants possessing awns

and those in small percentages. ;

The second generation gives awnless, partially-awned

and fully-awned plants in a ratio which approximates

1:2:1. The totals of data from second generation plants

of series 2,501 and 514 are reasonably close to this ratio:

| Awnless | Partially Awned Fully Awned

Série Sh0¥ i AU: 110 | 164 66

Maries: B14 erani i nere | 48 200 92

irinik. sen annoy | 158 | 364 158

tak a a 170 | 340 170

The behavior of the fully-awned plants shows that this

type is the pure recessive, for it breeds true in all cases

from the second generation.

All of the partially-awned F, plants proved to be

heterozygous, throwing in the third generation approxi-

mately three plants not fully awned to one fully-awned

plant.

The awnless plants of the second generation were

found to comprise both homozygous plants of the parental

type and heterozygous intermediates which later broke up

in the same manner as the partially-awned F, plants. It

might be expected that some of the awnless F, plants

would prove to be heterozygous, since awnless plants are

found commonly in the first generation.

From these results, it is apparent that we cannot cor-

rectly speak of the awnless oat as the dominant, type, nor

should we restrict the use of the term intermediates to

those plants which are partially awned.

It seems very probable that the difference between the

weak-awned and the awnless varieties of oats, at least in

the varieties studied, may be accounted for by the assump-

490 THE AMERICAN NATURALIST [Vou. LI

tion of a difference in one pair of genetic factors. It may

be that awnlessness is a definite character which is a true

allelomorph of the fully-awned condition. Some might

prefer, however, to consider awnlessness simply as the

absence of awning. In that case we must assume the

presence of an inhibitory factor to account for the partial

- dominance of the awnless Sixty-Day over the weak-awned

Burt. The data at hand seem to point to the presence of

an inhibitor to awning in the variety Sixty-Day. A pre-

ponderance of awnless yellows in F, and F, suggests a

linkage of this inhibitory factor with the factor for yellow

color in the Sixty-Day. (See Table VII.) Such a finding

would be in agreement with the results of Nilsson-Ehle

(1914). A very definite linkage of the inhibitory factor

with the factor for yellow color has already been observed

in a cross between A. fatua and A. sativa var. Sixty-Day.

This will be brought out in a later publication.

TABLE VII

SHOWING THE DISTRIBUTION OF REDS AND YELLOWS IN SERIES 514, WITH

PERCENTAGE OF AWNING AS RELATIVES

| 0 | 5 | 15. ir 25 |) 35 | Ane | 55 | 65 | 75 | 85 | 95 | 100

Reds i) 48°)| 120] 40. faBoler® fo 420 fob |, Sopi fy 74-88

Yaw 60 | 15 | 12 | 12 | 4] 10] 4] 2 | 2 /}01| 4 | 21

Certain other crosses with the Burt show that this

variety contains a factor for yellow which does not inhibit

awning. In the crosses Burt (red) X Swedish Select

(white), and Burt X Early Champion (white), the F, con-

tained a certain number of yellow-seeded plants, which in

turn gave some yellows in F;. All of these yellows were

fully awned. The existence of this yellow factor in the

variety Burt has complicated the study of the yellow of

the Sixty-Day in these crosses. The fact of the presence

of this yellow in the variety Burt should be kept in mind

when Table VII is examined.

It will be seen in Table VII, that the red grains are

nearly as numerous in the 100 per cent. class as in the

3 The classes are as follows: —0, 1-10, 11-20, ...., 91-99, -100.

No. 608] WEAK AWN IN AVENA CROSSES 491

awnless class, and that the other classes are represented

in practically equal numbers. In the case of the yellows,

however, there are about two and one half times as many

in the awnless class as in the fully-awned class. Fifty-

seven per cent. of the yellows have less than 20 per cent.

of awning, and seventy-three per cent. have less than 30

per cent. of awning. Many of the yellows in the 100 per

cent. class are doubtless due to the yellow factor con-

tained in the Burt parent. This factor does not inhibit

awning.

Strong Awn X Awnless.—The results of crosses be-

tween Avena fatua and the variety Sixty-Day (A. sativa)

agree closely with those obtained in the crosses between

the weak-awned and awnless types. (See Tables VIII

and IX.)

TABLE VIII

F, TOTAL or SERIES 2516 '

Partly | Fully

pateee | amni, | Zae | Zu, [nern Eug | Reo | o | ee, [oee

2516 | 169 | 377 | 201 | 546 | 201 | aa | 08 | 04 | 2.00

TABLE IX

F, or Heterozygous F, PLANTS

Pedigree ||, Awniom) | Fey | Fuly, [Not Futy| Fuy: |, Ratio | n, | pe | pje

687a1-15 | 61 im | 67") ish | e7. | Re) 06 | 07 E

EN aa 53 | 41 | 132 | 41 Toe k- 05. | 988 | 56

687a1-1 | 15 55. | 24 70 ih, Bg ane iaa AT

In a similar study on A. fatua X A. sativa var. Kherson,

Surface (1916) obtained results which agree closely with

those presented above. The F, plants were nearly inter-

mediate, although ‘‘The majority of F, spikelets show

no awn whatever’’ (p. 265). In the second generation

the following types appeared: . :

492 THE AMERICAN NATURALIST [Vou. LI

At first Surface assumed that the awnless plants were

homozygous and should, therefore, breed true. A test of

these plants, however, showed that a certain number were

heterozygous. Fifteen out of twenty broke up in the

third generation. This might be expected from the fact

that some of the heterozygous F, plants were awnless.

The failure of these plants to produce a few awns is attrib-

uted by Surface either to an undiscovered factor affecting

awning, or to an environmental influence. It seems quite

‘probable that the variety Kherson may carry a factor

inhibitory to awning, similar to the factor in the Sixty-

Day.*

OTHER CHARACTERS OF THE GRAIN

In connection with the above studies on awning, studies

were also made on the presence of basal hairs and the

type of articulation of the lower kernel of the spikelet.

A strong correlation was found to exist between the fully

awned condition and the Burt type (similar to that of

A, sterilis) of articulation, and also between the fully-

awned condition and the presence of medium-long basal

hairs such as are found on the Burt grains. When the

spikelets were all awnless, the union of the lower kernel

and its rachilla was generally of the type found in Avena

sativa and the basal hairs were either short or lacking.

It is interesting to note, in the crosses between the

weak-awned and awnless types, that in every case where

a panicle had two awns on a spikelet, all of the spikelets

on the panicle were awned. The irregular occurrence of

these two-awned spikelets, and the wide variability in

numbers on a panicle, makes it seem probable that there

is no definite factor for the two-awned condition. It

seems more likely that the occurrence of such spikelets is

due to environmental influences upon the factor for com-

plete awning. i

#In some logalities the names Kherson and Sixty-Day are used synony-

mously.

No. 608] WEAK AWN IN AVENA CROSSES 493

BIBLIOGRAPHY

Nilsson-Ehle, H.

14. Über einen als Hemmungsfaktor der Begrannung auftretenden

arbenfaktor beim Hafer. Zeitschr. ind, Abst. u. Vererb., 12:

Surface, F. M.

1916. apresa on Oat Breeding. III. On the Inheritance of Certain

e Characters in the Cross Avena fatua X A. sativa var.

PA Genetics, I: 252-286.

SHORTER ARTICLES AND DISCUSSION

NOTES ON THE FAUNA OF GREAT SALT LAKE

In the years during which the writer was zoologist at the Uni-

versity of Utah (1908-15) observations were made on the life of

the Great Salt Lake, when time could be spared from multitudi-

nous teaching duties. The animals of this brine lake earliest

reported, Artemia fertilis Verrill, and the larve of the small

Dipteron, Ephydra gracilis Packard, were naturally the first at-

traction, since they were abundant, commonly known to science,

and readily observable to any one looking for them. A second

species of Ephydra, E. hians Say, was reported by Aldrich in

1912.1. A Chironomus has been reported also, according to Tal-

mage,” but no reference to the authority is given and his own

statement is confusing, as he says he has ‘‘confirmed the pres-

ence of . . . the larve of one of the Tipulide, probably Chirono-

mus oceanicus Packard’’! He further states that ‘‘ The larvee

of the tipula may be taken anywhere near shore during the

warm months,’’ but the present writer is compelled to state

that neither larve, pupe or adults of either a Tipulid, or of a

Chironomus was ever observed by him in the Lake, nor are any

such reported by Aldrich, an authority on Diptera, in his reports

of collecting about Great Salt Lake. Other forms than

Ephydra might well occur in such a portion of the lake as the

great Bear River Bay, where the salt content of the water must

be much less, owing to a great influx of fresh water from the

Bear River, and to the fact that the bay is partially cut off from

the main lake by the causeway of the Southern Pacific Railway.

Aldrich, however, has certainly been on the Bear River Bay side

of the cut-off, as shown by Plate II, Fig. 8.1

In tentatively ‘‘ trying out ’’ to see what might be a profitable

line of study several dilutions were made in order to note the

1 Aldrich, J. M., ‘‘The Biology of Some Western Species of the Dip-

terous Genus Ephydra,’’ Jour. N. Y. Ent. Soc., XX, 77-99. In this are

photographs indicating the enormous numbers of Ephydra in the lake; also

first complete description of E. gracilis,

2 Talmage, J. E., 1900, ‘‘ The Great Salt Lake, Present and Past,’’ 67-68.

3 Aldrich, J. M., ‘‘Collecting Notes from the Great Basin and Adjoining

Territory (Dipt., Col.) ,’’ Ent. News, XXIV, 214-221,

494

No. 608] SHORTER ARTICLES AND DISCUSSION 495

effect, if any, on Artemia. The brine varied in density in the

lake at Saltair during the years of these observations, according

to season and rainfall, and besides the annual fluctuations gradu-

ally became less dense on account of a cyclical period of heavier

precipitation and consequent rise in level of the lake. In Oc-

tober, 1909, the density was 1.158, and in April, 1915, 1.136.

Dilutions were made by addition of distilled water as nearly as

was feasible to the following densities: 1.12, 1.10, 1.08, 1.06, 1.04,

1.02, 1.014 These dilutions were placed in small aquarium jars,

filled only 14 to 1% full, and covered to prevent entrance of dust,

and undue evaporation. It may be said at once that while

Schmankewitsch’s classic observations on Artemia were of course

in mind, it was not hoped to repeat them with the small amounts

of water used. However, some data obtained, though incom-

plete, seems worth recording, since the present writer can

scarcely hope ever to have further opportunity for pursuing

this line of investigation to the extent it deserves. It is sin-

cerely hoped that some one may be able to further investigate

the fauna normal to the unusual ecological conditions of brine

lakes.

Resistance of the adult Ar/emzas to sudden changes in the con-

centration of the salts, while greater than anticipated, only

` showed that they could not indefinitely survive too great a

change. Plunged into tap water, they appeared ‘‘heavy,’’ sink-

ing at once to the bottom, from which with most vigorous swim-

ming movements they were barely able to rise. Exact data as to

length of life in these solutions is not sufficient to offer, but in

general they survive a change to completely fresh water but a

few hours, and they do not survive for long periods in water in

which the amount of salts has been reduced to less than half the

normal. In stronger concentrations they survive for sufficiently

long periods that it seems likely they would live therein for a

normal life period if other conditions were favorable. ` Kellogg’

had opportunity in the case of A. franciscana Kellogg to note

differences in size, color and abundance of individuals which

had developed in waters of different densities, and it is interest-

ing to note that he found them largest in waters ranging from

1.11 to 1.13 in density. The latter figure is nearly the same as

4See article by Daines preceding this, with exact densities e one series.

Part of these observations were made in collaboration with Dain

5 Kellogg, V. L., ‘‘A New Artemia and its Life Conditions,” play N.

S., XXIV, pp. 5 594-596.

496 THE AMERICAN NATURALIST [Von. LI

that for Great Salt Lake water at the beginning of my observa-

tions, at which time the lake was in the rising period of its long

cycle of rise and fall, which rise continued at least up to 1915.

Some few years prior to 1909 the lake had been much lower and

the water at nearly the saturation point for NaCl. I believe

1.13 is somewhere near the mean density for Great Salt Lake.

Interesting facts were noted concerning eggs contained in

dilutions made in autumn (see annual cycle below). These

hatched in a few days or weeks, and they first hatched in the

most dilute water, next in the next more concentrated, and so

on up the seale of concentration in nearly regular order. The

conclusion naturally presents itself that the stimulus to develop-

ment lies in the reduction in amount of salts present, but later

it appeared (this point was not finally cleared up) that it lay

rather in a lack of oxygen resulting from insufficient aeration of

the water used. Young thus hatched never reached maturity.

Ephydra larve are even more abundant in the lake than Ar-

temias. They were found to be remarkably resistant to changes

in density of water, as well as to other changes in liquid environ-

ment. These larve will live at least for days in tap water, but

whether they could be brought to maturity in this or in very

dilute lake water was not determined. The fact that the puparia

drift up on shore in great ‘‘windrows’’ has already been noted —

by Aldrich, and in the Canadian Entomologist for 1891 (orig-

inal article not seen). The countless swarms of imagoes may

be seen by bathers resting on the surface of the water or flying

up at will, and it was found to be an easy matter to obtain the

eggs by imprisoning a number of these in a covered erystalliza-

tion dish with clean bottom, partly filled with brine, showing,

as suspected, that they drop the eggs freely into the water. AS

this was not done until near the close of my service in Utah, no

experiments were made with the eggs, but attempts to hatch the

eggs and rear the insects to the imago stage in dilute lake water

and in fresh water should be made. As instances of the resist-

ance of these larve may be mentioned the following: In more

than one case the larve were observed to live months in brine

which had evaporated to saturation, and beyond to the point of

containing a heavy deposit of erystals and of being completely

encrusted on top, and in one such case practically all of the

water had disappeared. Among the salt crystals in the little

remaining water the larve were somewhat inactive, but appeared.

to- be in good condition when water to about the normal amount

No.608] SHORTER ARTICLES AND DISCUSSION 497

was restored to the jar. Artemia is resistant to concentration,

but not to the same degree as Ephydra larve. Again, in an at-

tempt to kill larve without distortion some were placed in

Perenyi’s fluid and in this were capable of movement after more

than twenty-four hours. In Flemming’s fluid they live several

times as long as Artemia, but I have no record of the exact length

of time. I am able to verify with salah ia PERE s belief

that these larvæ do not rise to the surface for a

Most important of the incomplete Gaeta were those indi-

eating the presence of Protozoa as normal inhabitants of Great

Salt Lake. So far as I am aware, no Protozoa have been previ-

ously reported from brine lakes. Representatives of this group,

notably Amaebe, were first seen in the moderate dilutions after

some weeks in the laboratory, which proved to be in a sense cul-

tures. In March, 1910, several jars of a series, including one of

undiluted lake water, contained an abundance of these forms.

The specimens were of two or three varieties or species, by far

the most common being very like Ameba limax. I should not

have hesitated to call it that in a fresh-water culture. A class

of some 15 students was well supplied with Amebe for ‘labora-

tory work from one of these jars. Occasionally, in making micro-

scopic examinations of the cultures other Protozoa were met

with, but never in numbers. In fact only a single specimen at a

time was the rule. Specimens of Ciliata were seen, some closely

resembling a species of Uroleptus, while at least once a species

of Euglena was definitely noted. Chlamydomonas appeared

quite regularly and in great quantity in many of the cultures.*

I believe several species of Protozoa to be present normally in

the Great Salt Lake, but not generally very abundant, as many

of my efforts to secure them directly from the lake were failures.

However, some were certainly obtained directly from the more

or less decayed masses of organic débris which collect in enor-

mous quantity in the great stretches of shallow water along the

very flat shore, which masses consist mainly of the gelatinous

blue-green alga, Aphanothece packardii.* (This is the alga ‘‘of

the Nostoc group’’ mentioned by Aldrich.) In this material it

was expected there might be found Nematodes, as they are in so

many cases adapted to unusual environment, and so commonly

present in decaying substance, but none ever came under obser-

vation.

Perhaps a statement of the annual cycle of life of Artemia and

Ephydra may be of interest. For the latter it may be said that

498 THE AMERICAN NATURALIST [Vou. LI

larve and pupe are at all times of the year present in the lake,

though less abundant in winter. In the winter months there are

but few in the open water, but they are common in the débris

above mentioned. Dates for first appearance of adults were not

secured, though some appear as early as April; they become com-

mon by June, and in July and August are so exceedingly numer-

ous as to be a serious nuisance at times about Saltair pavilion,

wind conditions being apparently a determining factor in their

coming in swarms about the bathhouses. Ordinarily they keep

below the level of the floors, on the piles and on the water sur-

face. Whether any eggs survive the winter can not be stated.

There is no evidence of the pupe surviving on shore, where

thrown up by the waves. It seems likely that larve and pup

which remain submerged are the principal, if not the sole means

of surviving the winter period.

Adult Artemias, the females with fully developed egg sacs, are

very plentiful throughout the summer and fall into October. In

this month the temperature of the water falls from the summer

temperatures of between 25° and 30° C. (exact summer maxi-

mum unknown to writer) to as low as 15°-18° C. In November

with the temperature as low as 6° C. there may still be seen

some few adults. At a December temperature of 1° C. and

lower (doubtless goes lower at times for short periods) no adults

can be found, as a rule, though reported by Talmage. An abun-

dance of eggs can be secured in fall, winter and spring, especially

in the débris near shore. Possibly some may settle into the

smooth oolithic sand of the open lake bottom, but I have no evi-

dence that such is the case, and the eggs tend rather to float than

to sink. Young appear in April and May, abundantly in the

latter month. The earliest record secured for young was March

12 (1910), when a number of minute young were taken. The

temperature at that time was 9° ©. It will be noticed that Ar-

temia differs markedly in its long season of activity from its

fresh-water cousin, Branchipus, which is so soon gone from its

evanescent breeding pools. Correlated with this long active

period is the continued presence of abundant water and f

and an entire absence of enemies. Enemies play no part in keep-

ing down the numbers of Artemia, or of Ephydra in the larval

stage. In the midsummer bathing season both are present in

myriads in the open water, but so transparent are they that

the average bather, even the native Salt Laker, seldom notes

their presence.

No. 608] SHORTER ARTICLES AND DISCUSSION 499

The insect fauna of the lake shore presents material for a

study in itself, on which nothing has been published save the

material on Diptera by Aldrich, already cited. At the Univer-

sity of Utah I left the beginning of a collection of insects taken

in or on the waters of the lake, and I recall that a small Corisid

was several times seen and some specimens of it taken swimming

immersed in the brine near shore. The species appeared to be

the same as one common in fresh and slightly salt and sulphur

impregnated waters in the Salt Lake valley.

Probably correlated with the abundance of Ephydra adults as

food, may be mentioned a ‘‘plague of spiders’’ with which the

resort (Saltair) was troubled during one bathing season, about

910. Several cases of persons being bitten by spiders were re-

ported in one of the Salt Lake papers, though I can not vouch

for their authenticity. Certain it is that spiders of more than

one species were unusually numerous about the pavilion, as I

personally observed, and I learned later that the employees went

about with brooms every morning before the hour for opening

and destroyed as many as possible. The forest of piles and un-

derpinning beneath the structure, however, was an inexhaustible

reservoir from which the supply was constantly renewed. After

the close of the season, no other remedy having been found,

some employees were kept busy for weeks in boats beneath the

huge structure collecting and destroying the egg cocoons, and the

next season there was no serious trouble. Many bushels were

thus collected. The second autumn this task was again taken up,

and since that time no further plague of spiders has appeared,

but whether autumn cocoon collecting is still kept up I do not

ow. I have no doubt that the seemingly sudden appearance

of the great numbers of spiders was in reality but the time when,

owing to the availability of a great food supply and plenty of

space for spreading webs, they reached a high point in numbers,

the culmination of years of slow inerease.

Cuas. T. VORHIES

UNIVERSITY OF ARIZONA,

Tucson, ARIZONA

ON THE FLORA OF GREAT SALT LAKE

Very little investigation has been made of the plant life of

Great Salt Lake, either of a scientific nature or otherwise. So

far as the author of this paper knows, but one attempt has been

made in the past so scientifically classify the flora of the lake, and

500 THE AMERICAN NATURALIST (Von. LI

that attempt was interrupted before it had reached a successful

conclusion, so that no publication of the work was made.

Brief mention of what literature we have on this subject

seems not to be out of place here.

Professor Farlow (1879)! published a description of a blue-

green alga, Polycystis packardi.

Dr. A. Rothpletz (1892)? makes mention of the presence of

certain genera of blue-green alge, connecting them with the for-

mation of peculiar ooliths on shore. Dr. Rothpletz did his

work as a geologist, from a geological point of view. He made

no systematic study of the lake from a botanical standpoint.

The genera of alge he mentions—Gleothece and Gleocystis—we

have been unable to find in the part of the lake studied, and it

might be said, too, that the connection between these and the

ooliths has not been generally accepted, even by geologists.

H. F. Moore (1899)*, in reporting on the feasibility of intro-

ducing useful marine animals into the waters of the lake, makes

mention, briefly, of the presence of diatoms. As diatoms con-

stitute the chief food of the oyster, their presence was of con-

siderable importance in the investigation, and especially since

they are found in greatest abundance at the mouths of rivers

where the density of the water is more favorable for the develop-

ment of the oyster.

Talmage (1900)* speaks of the presence of at least three

species of alge—not naming them—and, besides these, he calls

attention to the presence of diatoms beds off from shore, as well

as living diatoms in the lake.

Tilden published in her distribution entitled ‘‘ American

Alge,’’ several species from Great Salt Lake. This distribution

has not been available, therefore, more definite mention of it can

not be made. They are as follows:

Aphanothece utahensis, no. 297,

Polycystis packardii, no. 298,

Dichothriz utahensis, no. 288,

Enteromorpha marginata, no. 266,

Enteromorpha tubulosa, no, 262,

Chara contraria, no. 255.

No other proof of the presence of abundant plant life in the

1 This paper was not available.

2 Rothpletz, = a, Centr., p.

3 Moore, H. F., ‘‘ The Feasibility of Introducing Useful Marine Animals

into the ae “of Great Salt Lake.

No. 608] SHORTER ARTICLES AND DISCUSSION 501

lake is needed than the presence of a fauna, abundant in indi-

viduals, if not in species. And no further demonstration of

the presence of this fauna is required than for one to visit the

lake and see, with his own eyes, the water literally teeming with

animal life.

The presence of plants is not so evident to the casual observer,

although, at certain times of the year, clumps of greenish ma-

terial, which must at least suggest a vegetable growth, are very

plentiful. Areas of a green scum on the surface of the water

in more or less protected places also give evidence, directly, of

the presence of plants.

The original purpose of this paper was to determine, if pos-

sible, the effect as to size of cells and rapidity of growth of dif-

ferent densities of Great Salt Lake water on a species of Chlamy-

domonas which is foûnd there. The problem, then, was to have

been purely a physiological one. During the course of investi-

gations along this line, however, other interesting things pre-

sented themselves, and a deviation was made from the first plan,

so that finally observations were extended to include every

species of plant found in the part of the lake investigated.

The observations made covered a small portion of the southern

end of the lake at what is known as Saltair Beach. This place

is easily accessible, and is at such a distance from any stream

entering the lake, that the density of the water there is not af-

fected to any degree.

The following plants are found PNAN i in the water at that

place:

A green alga, Chlamydomonas sp., which has been examined

by Dr. N. L. Gardner. Dr. Gardner believes it to be a new species

—he has not yet published a decription—near to Chlamydomonas

glæocystiformis Dill, and Chlamydomonas apiocystiformis ar-

tari. It has a rich green color, and occurs, during the warmer

weather, on the surface of the water in many more protected

places. It is found in less numbers in whatever decaying plant

or animal material may be present. The indications are that

this is one of the means the plant has of surviving the winter;

since such material brought into the laboratory in the very cold-

est weather has later developed a rich green growth of the alga.

A blue-green alga, determination of which has been made by

Professor W. A. Setchell. He says that it certainly is an

Aphanotheca, and is undoubtedly the same plant as the one

named Polycystis packardii by Farlow, and probably also the

502 THE AMERICAN NATURALIST [Vou LI

same as the one distributed by Miss Tilden from the Great Salt

Lake and named by her Aphanothece utahensis. On the au-

thority of Professor Setchell, we shall designate it Aphanothece

packardii.

The plant occurs in small masses, irregular in size, floating in

the water and piled up by the waves on shore. These masses

show a gradation in color from a deep blue-green, to light brown,

and some were colorless; this depending, no doubt, on the con-

ditions of the plants in the individual clumps, and not, as has

been suggested,* on a variety of species in the clumps. Micro-

scopic examination of this material shows the individual plants

in the mature condition, and also in various stages of division

by fission. Great numbers of the cells are held together by their

gelatinous secretions. The individual plants average about two

micra in diameter.

Microscopie examination of the lake Waie reveals at least two

species of diatoms. They probably belong to the genera Navi-

cula and Cymbella. These plants do not occur in sufficient num-

bers, in the denser water about Saltair, to be seen with the naked

eye.

The fact that putrefaction and decay are taking place in the

water, especially near to shore, where organic material is abun-

dant, shows conclusively that bacteria are present.

Here it may be well to suggest that at least some of the plants

distributed by Miss Tilden as Great Salt Lake plants, in all prob-

ability came from the fresher waters at and near the mouths of

rivers, or in the bays formed by the rivers at their place of en-

trance into the lake. As the present observations were confined

to the denser waters, even an indication of the plants referred

to—with the one exception noted—was not found.

For the physiological work, water was transferred from the

lake to the laboratory, in sufficient amount to make a number of

series of dilutions in glass aquaria. These series included solu-

tions of different density, varying in specific gravity from 1.0115

to 1.222, a saturated solution.

Masses—large in some series, but — in one—of Aphano-

thece packard were placed in these solutions, and, in every case,

enough Chlamydomonas was thus introduced to start a more or

less flourishing growth.

From time to time, measurements were made of the Chlamy-

domonas present in the solutions, and during the first few

4 Talmage, J. E., ‘‘ The Great Salt Lake—Present and Past,’’ p. 76. Salt

Lake City. :

No. 608] SHORTER ARTICLES AND DISCUSSION 503

months indications pointed very strongly to the fact that a re-

duction in size followed transplanting into less dense solutions.

A table below shows the results obtained with the first series.

No. 1 contains the water as obtained from the lake, analysis of

a sample of which (1910)° gives the following:

Constituents Grams per Liter % of Sample Taken | % of ‘Total Solids

ns solids 242.25 20.887 —

lorine 126.35 10.91 52.23

a dical 16.00 1.38 .65

Bait ite) bt Peers epee pein 5.18 0.45 14

Calcium 0.98 0.08 | .39

Sodium 85.10 7.25 34.68

Potassium | 8.82 0.76 .66

Rotak, of constituents........... 242.45 20.83 | 99.75

Salin kes. 213.32 18.39 88.09

Solutions 0 and 00 were allowed to become further concen-

trated by evaporation ih the laboratory. Nos. 2 to 8, inclusive,

were diluted with distilled water. The first measurements were

made some time after the series was started to allow the plants

to become accustomed to the new conditions, only, indeed, after

multiplication had begun. Blank spaces in the table indicate

that no motile zoospores were present at that time in the solu-

tion.

SERIES No. 1 STARTED OCTOBER 8

Measurements

o. Density | Dec. 15 | Jan. 13 | Feb. 14 |. Mar, 10 | Apr.16 | June 15 Average

Solution |. | |

00 1.222 11.76.7| | 15X10 |13.38.3

0 1.1825 | 13X7 ; | 1510 |13.7X7.8

1 1.1580 | 13x7.25| 12X .5|}136.5)12%5.4 |12xX6 112X 7/12.2Xx6.1

2 -1239 | 13X5 10X 5/112.

3 .1088 | 12X5 11x5 11.2x4.5 11X6 9x 5/10.8X5.1

4 .0822 | 12.5X5 12>¢6.5'11.255.5/10 5.5 11.45.6

5 1.0613 11x43 105.5 | 10X 5 10.3X4.9

6 1.0400 | 94.5 9x5 | 9Xx5.5 {105 9.255

T 1.0190 8.55 94.5 (8.5*4.5 8.75

8 -0115 ; 11x6.5 |10x5 |10X 6|10.3X5.8

This table seems to show a slight diminution in size as we pass

from the more dense to the less dense solutions, with the excep-

tion of the last and least dense of the solutions. It must be said

that it is very difficult in measuring Chlamydomonas zoospores

5 McFarlane, Wallace, ‘‘The Water of the Great Salt Lake.’’ (Read be-

fore the summer meeting (1910) of the Am, Chem. Soc. at San Francisco

by Professor W. C. Ebaugh.)

504 THE AMERICAN NATURALIST [ Vou. LI

to make definite comparisons as to size. The size of the indi-

vidual cells even in one solution varies so greatly that one can

only obtain an average of the size and then very roughly. The

measurements recorded in the table, and all others made, repre-

sent the average size of the larger cells in the solutions as far

as it was possible under the circumstances to measure them.

The results from the other series did not corroborate definitely

the results shown for the first series. Therefore, the only con-

clusion which can be drawn is, that so far as the present work

has shown, variations in density of the water of Great Salt Lake

cause no corresponding variations in size of Chlamydomonas

cells.

In every series but one, decided growth of the Chlamydomonas

began first in the dilutions about No. 5, and appeared then in

order up to No. 1, No. 0, and No. 00, and then down from No. 6

to No. 8. Sbiaeiae No. 4, No. 3, and No. 2, as a rule, showed a

greater abundance of the zoospores, judging from depth of the

green color given to the solutions by them. 7

The indication is, that water somewhat less dense than that

normally present in the lake at its present level is most favorable

to development of Chlamydomonas sp.

phanothece packardii does not grow well in the laboratory cul-

tures. It was interesting to note that they lost their blue-green

color and died in the weakest solutions first ; this condition follow-

ing regularly up the series to the most dense solutions. This species

gave us no further results. Whether this failure was due to

the weak solutions being particularly unfavorable to the alga,

or whether it merely indicates that this form is difficult to keep

under laboratory conditions, is not certain. The latter seems

the more likely conclusion.

The diatoms recovered from the dense waters, on being trans-

ferred to the weaker solutions in the laboratory, multiply read-

ily and actually thrive, giving large masses of the characteristic

brown growth. In every series, after about a month in the labo-

ratory, solutions No. 1 and No. 2 show a very few live forms

which soon die. In No. 3 a few persist; but in No. 4, No. 5, No.

6, and No. 7, they appear abundantly and continue to multiply

indefinitely. In No. 8 the live plants are again not very numer-

ous. These observations are in complete harmony with the state-

ments? that the diatoms are found in great abundance in the

shoaler, fresher waters near to the mouths of the rivers emptying

into the lake. They are reported to be especially numerous on

No. 608] SHORTER ARTICLES AND DISCUSSION 505

the alluvial fans at the mouths of both the Bear and the Jordan

rivers.®

The results seem to indicate that the diatoms obtained are true

Salt Lake forms, but have become adapted to less severe condi-

tions than prevail in the denser waters. That they are not fresh-

water forms which have accidentally found their way into the-

lake, is suggested by the fact that they do not thrive in the least

dense of the solutions of any of the series.

In every series, a cloudiness in the solution appeared as a re-

sult of bacterial growth, but the order of appearance in every

case was from the least dense solutions up to the most dense.

This cloudiness soon disappeared, to reappear at irregular in-

tervals. These facts led to an attempt to determine at least the

number of species of bacteria which may be found in the part of

the lake studied. So far as we can determine, no attention what-

ever has been given this phase of the question in the past.

Five distinct organisms, which have adapted themselves to

conditions there, were isolated in pure cultures. No detailed

study was made of them to determine their species, but enough

was done to leave no doubt as to their being at least separate

varieties, if one may judge from distinct differences in cultural

and morphological characteristics.

Water obtained from the lake under the strictest precautions,

was at first plated on phosphorescent, or salt agar, which con-

sists of 40 cc. of normal sodium hydroxide and 25 grams sodium

chloride, to 1,000 ce. of plain agar. Later samples of the water

were plated on gelatins containing different amounts of the

normal NaOH, and NaCl. Better results were obtained with

the salt agar than with the gelatin. Later, plain agar was used

with good results.

The number of bacteria per c.c. varies between 200 and 625,

counts having been made from a number of samples taken in the

coldest weather—water 33° F.—as well as in the warmer weather.

A very interesting fact developed; that of the five micro-

organisms isolated, three are decided chromogens, each produc-

ing abundant pigment. Of the five, one is a diplococeus, which

appears sometimes in tetrads and singly. It forms large white

colonies on the media used. The other four are bacilli. The

éne producing no pigment, forms delicate white colonies on the

solid media. Of the chromogens, one produces a lemon-yellow;

a second produces a bright orange; and the third produces a

violet pigment.

506 THE AMERICAN NATURALIST [Vou. LI

CONCLUSIONS

1. Variations in density of the water of Great Salt Lake, cause

no corresponding variations in the size of Chlamydomonas sp.

cells.

2. The indication is, that water somewhat less dense than that

normally present in the lake, at its present level, is most favor-

able to the development of Chlamydomonas sp.

3. The diatoms present in the lake multiply best in water

much less dense than the dense water at Saltair.

4. At least four species of alge are to be found in the part

of the lake investigated.

5. At least five varieties—possibly species—of bacteria have

adapted themselves to the severe conditions in the lake.

In conclusion, I wish to heartily thank Professor C. T. Vorhies

for the suggestions he has given me in the preparation of this

paper.

L. L. DANIELS

UNIVERSITY OF UTAH,

SALT LAKE CITY

NOTES AND LITERATURE

BIOMETRIC STUDIES ON THE SOMATIC AND dire i

PHYSIOLOGY OF THE SUGAR BEE

THE beet sugar industry, amounting to hundreds of millions of dol-

lars every year, is the direct result of scientific breeding.

A biologist is loath to demur at any statement which attaches

economic importance to scientific work of the kind in which he

is interested. The statement may be true. Certainly no one

can deny that far greater system and standardization of routine

has obtained in the beet sugar industry than in many other

branches of agriculture. But the trained scientific man who

conscientiously works through some thousands of pages of the

literature of sugar beet breeding and cultivation must hesitate

before regarding it as a triumph of scientific method. He will

rather, I think, feel that science has fallen woefully short of its

possibilities in dealing with many problems of great theoretical

interest and economic significance.

In no field of agricultural work is the failure of scientifie and

practical men to cooperate less excusable than in that of sugar-

beet breeding. In the routine operations of sugar-beet produc-

tion chemical data of a relatively satisfactory degree of trust-

worthiness are obtained for great numbers of individuals. It is

not unconservative to say that millions of individual weighings,

polarizations or analyses of various degrees of completeness

have been made. For two decades the biometric formule which

might have given meaning to some of these masses of data have

been available. Yet the problems which might have been solved

have remained unelucidated, to the material loss of both biology

and industry.

It seems worth while to illustrate the truth of these state-

ments by some of the advances in our knowledge of the genetic

and somatic physiology of the sugar beet which have been made

possible by the application of the biometric formule.

Consider first of all one of the simplest problems—that of the

relationship between the weight of the root and the sugar con-

tent of its juice. Notwithstanding considerable discussion this

508 THE AMERICAN NATURALIST [Vou LI

very simple problem was not definitely solved until 1913 when

actual correlations’ were available. Coefficients ranging from

— .224 to —.756 for the relationship between weight of root

and sugar content of juice in various short series of data were

found. The results were published only after failure in a con-

scientious and systematic effort to obtain from the agricultural

experiment stations really adequate series of data for detailed

biometric analysis.

Fortunately the conclusions have since been fully confirmed.

Pritchard,? in dealing with samples of 250 to 400 beets grown

at Fairfield, Washington, found constants ranging from — .2

to —.499. Working with larger samples (n==3.784) from

Brookings, S. D., he found r——.258, while Harris and

Hogensen,* who pad a sample of nearly 7,000 beetst from Utah

cultures, found r= — .288.

The splendid work of these investigators leaves no doubt that

the percentage sugar content decreases, and, as Harris and

Gortner indicated on their limited series of data, in a sensibly

linear manner, with increase in weight of root.

These studies, based as they are in some of these series, at

least, upon closely bred material, fully justify the criticisms of

the conclusions of Andrlik, Bartoš and Urban® by Hee and

` Gortner.®

Harris and Gortner have also found negative correlations

between weight of root and total solids and coefficient of purity.

hus the larger roots have a smaller quantity of total solids, a

lower percentage sugar content and a lower coefficient of purity.

1 Harris, J. Arthur, and R. A. Gortner, ‘‘On the Relationship between the

Weight of ‘the Sugar Beet and the Composition of its Juice,’’ Jour, Ind. an

‘Eng. Chem., 5, March, 1913.

2 Pritchard, P. J., ** R between Morphological ert and

the Saccharine Content of Sugar Beets,’’ Amer. Jour. Bot., 3: 361-376, 1916.

3 Harris, F. S., and J. - Hogensen, ‘‘Some Correlations in Sugar pas

Genetics, 1: 334-347, 191

4 Unfortunately the aes is not altogether trustworthy because the

largest and the smallest ma were excluded.

5 Andrlik, K., Cha wae N rban, ‘(Uber die Variabilität des

Gewichtes und des reret der PAAA ATETEA rzeln, und über die

AEE Beziehungen cage beiden Merkmale,’’ Zeitschr. f. Zucker-

industrie in Böhmen, 36: 193,

6 Harris, J. Arthur, and R. A bik ‘‘ Further Notes on the Relation-

ship between the Weight of the Sugar Beet and the Brg Ayr aps of its

Juice,” Biochem. Bull., 2: 524-529, 1913.

No. 608] NOTES AND LITERATURE 509

That large roots yield an actually larger amount of sugar is to

be expected, and Pritchard’s coefficient for the correlations be-

tween weight of root and total sugar content is high.

Such results are obviously of great practical significance.

Laying aside the possible desirability of modifying planting or

cultivation in such a manner as to influence root size, the ques-

tion of the selection of roots for sampling is one of real im-

portance.

Much of the early Acme tieas work on the sugar beet was devoted

to determining where the crop will give a yield per acre and a

sugar content and coefficient of purity satisfactory for economic

work. Roots were sent by farmers to the Agricultural Experi-

ment Stations, analyzed, and the results published in a great

series of bulletins. But since size and percentage of sugar are

correlated, and selection for size in the submitting of samples

was rarely guarded against, the great mass of figures have little

significance as measures of the merit of the cultures from which

the samples were drawn.

If physical characters of the root be associated with sugar

content or with purity of the juice, which is technically a highly

important factor, physical characters may serve as a guide to

selection.

Pritchard has devoted great care to the problem of the cor-

relation between a number of the morphological features of the

root and leaf and sugar content, and has determined the average

percentage of sugar and average sugar content in synthetic

types, i. e., those embodying the most desirable of the morpho-

logical characteristics. The results are of technical rather than

of general biological interest. The conceptions of a synthetic

type—a conception that has already been emphasized in a quite

different way by Raymond Pearl’—is well worth careful con-

` sideration by all those who have to do with breeding problems.

Both Pritchard’ and Harris and Hogensen have extended

their studies of the correlation of characters in the root to that

of the interrelationship of the characters of the root and those

of the fruiting shoots.

7 Pearl, R., and F. M. Surface, ‘‘Selection Index Numbers and their Use

in Heed, AMER. NAT., 43: 385-400, 1909. Also, R. Pearl, ‘‘ Further

Notes Regarding Selection Index Numbers,’’ AMER. NAT., 46: 302-307,

1912. :

8 Pritchard, F. J., ‘‘Some Recent Investigations in Sugar Beet Breed- `

ing,’’ Bot. Gaz., 62: 425-465, 1916.

510 THE AMERICAN NATURALIST [Vou. LI

They agree that there is no correlation between the sugar

content of a beet and the quantity of seed which is produced,

but Harris and Hogensen find a correlation of .308 + .013 for

the relationship between the weight of the seed beet planted and

the weight of seed produced, whereas Pritchard, from a number

of determinations, concludes that for beets of ordinary size such

as are grown for factory use the correlation between root weight,

percentage of sugar in roots and quantity of sugar in the seed

root on the one hand and the number of grams of seed produced

by the seed root is sensibly zero.

Harris and Hogensen find a correlation of about + .399 be-

tween height of plant and amount of seed produced, about

+ .277 between number of stems and weight of seed produced,

and about -+ .122 between number of leaves and weight of seed

produced.

Pritchard has shown that there is no correlation between the

amount of seed which a beet root yields and the sugar content

of its progeny. ‘‘The application of this fact to sugar breed-

ing,’’ says Pritchard, ‘‘is obvious, as extensive selection may be

made for freer seed production without danger of sugar de-

terioration. Moreover, it affords an opportunity to reverse the

order of selection by making the chief elimination in the seed

generation and thus greatly reduce the amount of chemical work

and increase the effectiveness of the working funds.’’

The physiological character time required for maturing seed

has received some attention by Harris and Hogensen, who find

a greater height and a higher production of seed in beets re-

quiring a longer period for maturity. The coefficients are, how-

ever, low, r—=+.175 + .016 for height and days required for

maturing seed and r= + .195+.016 for days required for

maturity and quantity. of seed produced. The correlation be-

tween the percentage of sugar in the mother beet and the

number of days required for maturing seed is negative,

r==— .129 + .014, i. e., the beets with higher sugar content

mature their seed more rapidly.

All these coefficients are very low. The experienced statis-

tician will be cautious in regarding them as significant, remem-

bering that when constants reach minimum values probable

errors can not be given their normal weight. Those who have

„had personal experience in the biological phases of such work

will realize its diffieulties, and allow the questions of the signifi-

eance of these correlations to remain open until more extensive

No. 608] NOTES AND LITERATURE 511

data are available. There are, furthermore, internal evidences

of serious heterogeneity in the materials upon which these con-

stants are based. Such irregularities as those seen in the fre-

quency distributions of number of days required for maturing

require See before coefficients based upon them can be

given much weight.

The result of Pritchard’s experiments which will arouse the

widest interest is the conclusion that with due regard to the

probable errors of random sampling, there is no correlation be-

tween the weight of the mother roots and the average weight,

the average percentage sugar content or the average total sugar

content of the progeny roots, that there is no correlation between

the percentage of sugar in the mother beets and the average

percentage of sugar in their progeny, between the actual amount

of sugar in the mother beets and the actual amount of sugar

in the progeny roots.

Thus in dealing with our long selected varieties of sugar

beets the author is faced to the conclusion:

Differences in the size and sugar content of individual beet roots

show no evidence of inheritance. They are fluctuations, therefore, and

apparently play no part in beet improvement.

The practical consequences of such a conclusion should be self

evident. One European firm is said to carry out 300,000

analyses annually in the selection of roots for seed production.

If the conclusion reached by Pritchard be of final significance,

it justifies the assertion that ‘‘the cost of analyzing mother beets

is an absolute waste of money.’’

Space precludes a discussion of the data given by Pritchard

on the average composition of progeny rows and on the influence

of environmental factors in observing genetic differences. From

this side his paper must be read, and will later be reviewed in

connection with one on the technical features of progeny tests.’

His studies show how small are the real genetic differences

which may appear, how deeply these differences may be buried

under those due to environmental factors, and how difficult in

consequence must be the attainment of real progress in the

further improvement of so highly selected an agricultural plant

as the sugar beet.

° Pritchard, F. T., ‘‘The Use of Checks and ce e Singhal in Ye

riety Tests,’’ Jour. Hadi Soc. Agron., 8: 65-81, 1916.

512 THE AMERICAN NATURALIST (Vou. LI

Pritchard is a mutationist rather than a selectionist.

The selection of choice roots by chemical and physical means has

probably played no part in sugar beet improvement except where an

occasional root has mutated and thus given rise to a superior physio-

logical species.

One does not need to agree with the form of Pritchard’s con-

clusion to recognize the great value of such studies as those

which he has carried out. Full knowledge of the difficulties

surrounding a task is one of the essentials to its accomplishment.

When all the variables that enter into the problem of sugar-

beet production and sugar-beet breeding are known in quanti-

tative terms, it will be possible for the practical man to decide

on the basis of the cost of labor and other economic considera-

tions what operations can be dispensed with and what other

changes in routine can be profitably made. Operations can then

be more properly designated scientific.

J. ARTHUR Harris

THE

AMERICAN NATURALIST

Vou. LI. September, 1917 No. 609

THE THEORY OF THE GENE.

PROFESSOR T. H. MORGAN

COLUMBIA UNIVERSITY

Ir is unfortunate that the method of analysis of the

problems of Mendelian heredity that has been adopted in

one form or another by those who work in this field, has

aroused a certain amount of antagonism on the part of

those whose work lies in other directions.

In the following pages I shall attempt to explain what

the genetic factor means to those who use it, and then try

to answer certain specifice criticisms of this form of

hypothesis, in a hope that a mutual understanding will

remove many of the objections that have been made to

this method of handling genetic problems.

The objections have taken various forms. It has been

said, for instance, that the factorial interpretation is not

physiological but only ‘‘static,’’? whereas all really scien-

tific explanations are ‘‘dynamic.’’ It has been said that

since the hypothesis does not deal with known chemical

substances, it has no future before it, that it is merely a

kind of symbolism. It has been said that it is not a real

scientific hypothesis for it merely restates its facts as

factors, and then by juggling with numbers pretends that

it has explained something. It has been said that the or-

ganism is a Whole and that to treat it as made up of little

pieces is to miss the entire problem of ‘‘Organization.’’

It has been seriously argued that Mendelian phenomena

are ‘‘unnatural,’’ and that they have nothing to do with

513

514 THE AMERICAN NATURALIST [ Vou. LI

the normal process of heredity in evolution as exhibited

by the bones of defunct mammals.’ It has been said that

the hypothesis rests on discontinuous variation of char-

acters, which does not exist. It is objected that the

hypothesis assumes that genetic factors are fixed and

stable in the same sense that atoms are stable, and that

even a slight familiarity with living things shows that no

such hard and fast lines exist in the organic world. These

and other things have been said about the attempts that

the students of Mendel’s law have made to work out their’

problems.

I think, however, that while a few of these charges may

appear to be serious, some of them rest on a misunder-

standing of what numerical treatment of any problem in

science means, and others are due to differences of def-

inition. But the most common misunderstanding arises,

I venture to think, from a confusion of the problem con-

cerned with the sorting out of the hereditary materials

(the genes) to the eggs and sperms, with the problems

concerning the subsequent action of these genes in the

development of the embryo.

What genes stand for can be most easily shown by

means of a few familiar illustrations. Mendel’s cross

with yellow and green peas (or any similar case in which

two characters are contrasted with each other as a pair)

will serve as an example. In the second generation from

such a cross the numerical results, viz., three yellow to

one green, find their explanation on the assumption that

the two original germ plasms (briefly the yellow and the

green) or some element or elements in them separate

cleanly in the germ cells of the hybrid of the first gen-

eration. This cross does not tell us whether the two

germ plasms separate as wholes—one from the other—

or whether only some part or parts behave in this way.

But the situation changes when two or more pairs of

contrasted characters are involved in the same cross.

1 This objection is not further considered here since it has been dealt

with elsewhere (‘‘ A Critique of the Theory of Evolution,’’ 1916, p. 84).

No. 609] THE THEORY OF THE GENE 515

For example, when peas that are both yellow and round

are crossed to peas that are both green and wrinkled,

there appear in the second (F,) generation not only the

original combinations, yellow round and green wrinkled,

but also the recombinations yellow wrinkled and green

round. Here also the numerical results, 9:3:3:1, can

be explained by two assumptions, viz., that, as before,

each pair of characters (or their representatives) are

separated in the germ cells of the hybrid (F,) and that

each pair ‘‘assorts’’ independently of the other pair. Ob-

viously, here, it can no longer be the wholes of the original

germ plasms that separate, for the two pairs of char-

acters behave independently of each other; but there must

be separate pairs of elements in the germ plasm that

assort independently of one another.

As a matter of fact it has been found that the many

pairs of characters that follow Mendel’s law are inde-

pendent of each other in inheritance. The only restriction

that this statement calls for is in the case of linked pairs

of characters of which I shall speak later.

The germ plasm must, therefore, be made up of inde-

pendent elements of some kind. It is these elements that

we call genetic factors or more briefly genes.

This evidence teaches us nothing further about the

nature of the postulated genes, or of their location in the

germ plasm. However, even if we postulated nothing

more about them than their independence of each other

and their distribution in the germ cells, we could still

handle the Mendelian results on a purely mathematical

-basis that would enable us to predict what new combina-

tions should give. This possibility alone would entirely

justify the hypothesis as a scientific procedure, whatever

carping critics may say to the contrary. In fact Mendel

himself did not carry his analysis beyond this point, for

he assumed only that definite paired elements that stand

in some way for the characters of the finished plant exist

in the germ plasm, and that the pairs assort independently

516 THE AMERICAN NATURALIST [ Von. LI

of each other at the time when the members of each pair

separate (segregate).

But between the year 1866, when Mendel published his

paper, and the present year, 1917—an interval of fifty-

one years—much water has run under the Mendelian mill.

In consequence we can now add certain further attributes

to the rather formal characterization of the gene as de-

ducible from Mendel’s law alone. But before I discuss

the evidence for these postulated attributes, I must pause

for a moment to call attention to a movement that was in

certain important respects a forerunner of our present

standpoint.

I refer to the views of Roux and of Weismann, both of

whom assumed that the germ plasm is made up of par-

ticles or determiners, as Bonnet, Spencer, Darwin and

others had done before them. Their argument was largely

speculative, and not of the same kind as the more recent

evidence derived from Mendelian analysis. Moreover in

all of Weismann’s earlier and best known writings his

idea of-the units in heredity was more involved than are

our present ideas. He thought that whole germ plasms

were the units that segregated, germ plasms that dif-

fered in one or many determiners, whereas the factorial

view that we follow since Mendelism came to the front

assumes that the units that segregate are themselves only

parts of a whole which is the sum total of all the units.

In his latest book, however, Weismann accepted the evi-

dence from Mendelism and modified his ideas accordingly.

We owe to Weismann the popularization of the view

hat the hereditary material is carried by the chromatin,

ut especially we owe to Weismann the development of

the idea that the sorting out of the hereditary materials

takes place at the time of the maturation process in the

gg and sperm.

On the other hand, it must be emphatically pointed out

that the earlier idea of Roux, adopted by Weismann, that

one of the hereditary complexes is sorted out during the

No. 609] THE THEORY OF THE GENE 517

cleavage process of the egg, is no longer acceptable; for

there is direct evidence to show that the whole hereditary

complex goes to every cell in the body. This conclusion

has the most. far- reaching consequences for our present

views as to how factors produce their effects in the de-

veloping organism, for it follows that the machinery

that separates the inherited material into its component

elements is not the same mechano-chemical process that

brings about differentiation in the embryo.

GENE AND CHARACTER

So far I have spoken of the genetic factor as a unit in

the germ plasm whose presence there is inferred from the

character itself. Why, it may be asked, is it not simpler

to deal with the characters themselves, as in fact Mendel

did, rather than introduce an imaginary entity, the gene.

There are several reasons why we need the conception

of gene. Let me illustrate by examples :—

1. The Manifold Effects of Each Gene

If we take almost any mutant race, such as white eyes.

in Drosophila, we find that the white eye is only one of

the characteristics that such a mutant race shows. In

the present case the solubility of the yellow pigment of

the body is also affected; the productivity of the indi-

vidual also; and the viability is lower than in the wild

fly. All of these peculiarities are found whenever the

white eye emerges from a cross, and are not separable

from the white eye condition. It follows that whatever

it is in the germ plasm that produces white eyes, it also

produces these other modifications as well, and modifies

not only such ‘‘superficial’’ things as color, but also such

‘*fundamental’’ things as productivity and viability.

Many examples of this manifold effect are known to stu-

dents of heredity.

It is perhaps not going too far to say that any change

in the germ plasm may produce many kinds of effects on

518 THE AMERICAN NATURALIST [ Vou. LI

the body. Clearly then the character that we choose to

follow in any case is only the most conspicuous or (for

us) the most convenient modification that is produced.

Since, however, these effects always go together and can

be explained by the assumption of a single unit difference

in the germ plasm, this particular element or gene in the

germ plasm is more significant than the character chosen

as an index for one only of the effects.

2. The Variability of the Character is not due to the

Corresponding Variability of the Gene

All characters are variable, but there is at present abun-

dant evidence to show that much of this variability is

due to the external conditions that the embryo encounters

during its development. Such differences as these are

not transmitted in kind—they remain only so long as the

environment that produces them remains. By inference

the gene itself is stable, although the character varies;

yet this point is very difficult to establish. The evidente

is becoming stronger nevertheless that the germ plasm

is relatively constant, while the character is variable. I

shall consider this evidence in another connection. Here

I wish merely to register some of the reasons why the

idea of the gene is useful.

3. Characters that are Indistinguishable may be the

Product of Different Genes

We find, in experience, that we can not safely infer

from the appearance of the character what gene is pro-

ducing it. There are at least three white races of fowls

produced by different genes. We can synthesize white-

eyed flies that are somatically indistinguishable from the

ordinary white-eyed race, yet they are the combined prod-

uct of several known genes. The purple eye color of

Drosophila is practically indistinguishable from the eye

colors maroon and garnet. In a word we are led again to

units in the germ plasm in our final analysis rather than

to the appearance of a character.

No. 609] THE THEORY OF THE GENE 519

4, Inference that Each Character is the Product of Many

Genes

We find that any one organ of the body (such as an eye,

leg, wing) may appear under many forms in different

mutant races as a result of changes of genes in the germ

plasm. It is a fair inference, I think, that the normal

units—the allelomorphs of the mutant genes—also affect

the same part. By way of illustration I may state that

we have found about 50 eye-color factors, 15 body-color

factors, and at least 10 factors for length of wing in

Drosophila. :

If then, as I have said, it is a fair inference that the

units in the wild fly that behave as Mendelian mates to

the mutant genes also‘affect the organ in question, it fol-

lows that many and perhaps a very large number of

genes are involved in the production of each organ of the

body. It might perhaps not be a very great exaggeration

to say that every gene in the germ plasm affects every

part of the body, or, in other words, that the whole germ

plasm is instrumental in producing each and every part

dy.

Such a statement may seem at first hearing to amount

almost to an abandonment of the particulate conception

of heredity. But in reality it is only a conclusion based

on fact. The essential point here is that even although

each of the organs of the body may be largely dependent

on the entire germ plasm for its development, yet this

germ plasm is made up of independent pairs of units.

5. Evidence that Genes have a Real Basis in the Germ

asm

In 1906 Bateson, Saunders and Punnett found that cer-

tain pairs of characters in sweet peas did not behave in-

dependently of each other, but tended to stay together,

or to keep apart, in succeeding generations according to

the way they entered the cross. Every year more cases

of linkage are found, so that there can be little doubt

520 THE AMERICAN NATURALIST [ Vor. Li

that this phenomenon is one of the fundamental attributes

of Mendelian inheritance

While the linkage relations of genes do not at present

have any immediate bearing on our conception of the

nature of genes, they havea very important bearing on the

problem of the localization of genes in the germ plasm.

The original evidence that Weismann accepted to show

that determiners are carried in the chromosomes, Viz., .

the evidence based on transmission through the proto-

plasm-free head of the spermatozoon, was made much

stronger from Boveri’s evidence derived from experi-

mental embryology.

The argument became still more convincing when the

facts of sex-linked inheritance and non-disjunction were

established. For, it was found that certain characters

have the same distribution as do the sex chromosomes,

and secondly by the actual cytological demonstration that

the rare exceptions to the rule are due to irregularities in

the distribution of the sex chromosomes.

_All of this evidence has played a rôle in persuading us

that the genes postulated for Mendelian inheritance have

a real basis and that they are located in the chromosomes.

Finally, in Drosophila, where there are four pairs of

chromosomes, there are also four great groups of linked

genes. This coincidence adds one more link to the chain

of evidence convincing a few of us that the gene in Men-

delian inheritance has a real existence.

CONSIDERATION OF CRITICISMS

I have tried to make clear how the genetic evidence has

necessitated the assumption of genes in heredity, and I

have pointed out what seem to me to be some of the at-

tributes that it has been desirable to add to the earlier

conception of the gene as our knowledge has increased.

Now that the ground is cleared, let me try to answer the

objections or criticisms which I mentioned at the start,

that have been advanced against this kind of hypothesis.

No. 609] THE THEORY OF THE GENE 521

(A) Assumption of Genetic Factors is Arbitrary

It hasbeen said that by assuming enough genetic factors

you can explain anything. This is true; and it is

the greatest danger of the factorial procedure. If, for

example, whenever one fails to account for a result he

introduces another factor to take care of what he can not

explain he is not proving anything except that he is in-

genious or only naive. To make good the introduction

of another gene in Mendelian work, its presence must be

established by the same kind of evidence as that on which

the existence of the original factors was established. For

example. Bridges found that after eosin eye color had

been crossed to a certain red-eyed stock, there appeared

in later generations a new class of eye color (Cream II)

that was far lighter than eosin. He isolated this new |

character and showed that the difference between it and

eosin was due to a specifie gene that in inheritance behaves

like other genes, although its action is not apparent on

the normal red eye, but is evident on the eye color eosin.

Here, then, through experimental tests, the actual demon-

stration was made that the change in color of the eosin

was due to another gene hidden in the normal stock.

(B) Stability of Genes versus Instability of Characters

It has been objected that it is unreasonable to assume

that genes are relatively stable. This objection is based

largely on the fact that characters are notoriously fluctu-

ating, and since characters form the basis of our numer-

jeal data from which the idea of the gene is derived, it is

supposed that genes too must be variable. This is by all

odds the most common criticism that has been brought

against the idea of genetic factors and the most difficult

one to disprove. There are five answers, however, to this

s . Pii 8

objection. ;

` In the first place it has been shown in a number of

instances that the variability of the character is due to

a mixed or composite population in which there are sey-

522 THE AMERICAN NATURALIST [ Vou. LI

-eral genotypes present. In other words, it was because

most material is itself not uniform that an exaggerated

idea arose concerning the nature of the variability of the

character.

In the second place, Johannsen’s experiments with

Princess beans have shown that when the material is

homogeneous in successive generations the variability

of the character is due to the environment and is not due

to changes in the genotype.

In the third place, any pure stock (and especially one

that has been made homozygous by inbreeding), so long

as it does not vary, is an argument for the stability of the

factorial basis. When changes occur in it as they are

pretty certain to do, the fact does not in itself prove

that the gene under observation has changed, for other

genes that affect the character may have mutated. Jen-

nings has recently said? that we maintain the constancy

of a given gene by assuming that other genes, rather than

the original gene itself, have changed. This would be of

course on our part a straight evasion of the issue. The

criticism would hold if the question involved were a purely

philosophical one, as Jennings might unintentionally lead

the reader to believe. Fortunately it is becoming more

and more possible to demonstrate that changes of this

latter kind do take place; for it is possible with suitable

material to show in such cases the exact ndture of the

change. Wherever it has been possible to do this it has

been found that a definite mutation in some gene has

taken place, or has been introduced into the culture

through crossing.

In the fourth place it has been found that more than

one mutant gene may be the mate (allelomorph) of the

same normal gene. Since no more than two of them may

exist at the same time in a given individual, and since

linkage experiments have shown in Drosophila that these

multiple allelomorphs have the same linkage relations to

all other genes (i. e., as we interpret the result, each such

2 Jour. Washington Acad. Science, VII, 1917.

No. 609] THE THEORY OF THE GENE 523

set of allelomorphs has the same locus in the same chromo-

some) this experimental evidence shows that several

allelomorphs of the same gene may exist. An interesting

relation in regard to these multiple allelomorphs is that

they affect chiefly the same part of the body in the

same general way. They may give a series of types that

is discontinuous, such as the quadruple mouse series:

yellow, gray white-belly, gray, black; or the more nearly

continuous septuple Drosophila series: red, blood, cherry,

eosin, buff, tinged, white. Whether such a series of

characters is large enough to appear continuous or not is

a matter of trivial importance in comparison with the es-

tablished fact that the genes behind such a series arose in

the same way as do other mutant genes, and after they

have appeared, are as constant as are other genes. There

is no experimental evidence to show that the multiple

mutant alleélomorphs are more likely to arise from each

other than they are from the normal allelomorph, and

even if this should be true for individual genes it is no

more than is true for other ‘‘normal’’ genes, some of

which mutate more readily than others. Emerson has

shown for corn that one allelomorph of a series is more

likely to mutate than others and we have shown for

Drosophila that certain normal genes, as the one that

mutates to produce vermilion eye color, are more likely

to mutate than are others.

When Jennings? tries to interpret this evidence of con-

tinuous series of allelomorphie characters as breaking

down all real distinction between mutation and continuous

variation, he leaves out of account certain very funda-

mental considerations. For example, De Vries himself

has always urged that mutations may be very small so

far as the character change is concerned; the Svalöf evi-

dence shows this in a very striking way, and Johann-

sen’s beans have been for several years a classic ease

illustrating how minute the characters depending on

3 Loc. cit. 7 :

524 THE AMERICAN NATURALIST [ Von. LI

genetic differences may be. It comes, therefore, some-

what as a surprise when Jennings states:

‘‘ Certain serious, difficulties appear in this view of the

matter; I shall mention merely two of them, for their

practical results. One is the very existence of the minutely

differing strains, which forms one of the.main founda-

tions of the genotype theory. How have these arisen?

Not by large steps, not by saltations, for the differences

between the strains go down to the very limits of de-

tectability. On the saltation theory, Jordan’s view that

these things were created separate at the beginning seems

the only solution.’’

It should be remembered too that it is possible to make

up just as continuous a series of characters with genes

belonging to different allelomorphie pairs (even when

they lie in different linked groups) as the continuous series

from multiple allelomorphs.

If there were any connections between the gradations

of character in allelomorphic series and the order in which

the characters appear, such a relation might appear to

furnish a support to the view that the assumed fluctuation

of factors is a sequential process, and that selection actu-

ally helps forward the direction in which mutation is

likely to take place, a view that Castle has at times ap-

parently espoused. As a matter of fact, there is no such

relation known—the known facts are exactly to the con-

trary; for the actual evidence from multiple allelomorphs |

shows that genes may mutate in all directions and also

that extreme mutations such as white eyes arise sine me

from red and not by graded steps

In the fifth place, the most recent work on Didbbiphita

has shown not only that every gene may act (and often

does act) as a differential for characters conditioned by

other genes, but also that there are genes whose most

visible effect is only on certain characters which may

therefore be said to be modified by the former. It would

be a great mistake to suppose that these modifying genes

are unique in any essential respect—the kinds of effects

No. 609] THE THEORY OF THE GENE 525

that they produce grade off into effects that the ordinary

genes produce. The chief interest in demonstrating (in-

stead of speculating about) such genes is that they go far

towards helping us to a clearer interpretation of certain

evidence that was heretofore obscure or misinterpreted.

Wherever the history of the origin of these genes is

known it has been found to be the same as for other genes

and their behavior in Mendelian inheritance is precisely

the same. Nevertheless, Jennings has, in the paper al-

ready referred to, left certain implications in regard to

them that, if not clearly understood, may throw the sub-

ject into worse confusion than before. He seems to imply

—perhaps he does not really intend to do more—that

since through such modifying genes a perfectly contin-

uous series of modifications of a character may exist,

all real distinction becomes lost between continuous and

discontinuous variation. Now as a matter of fact per-

fectly continuous characters, if due to overlapping of the

separate modifications, can be statistically handled, as

Johannsen has done for beans and as Jennings himself

has done for size differences in paramecium. Other ways

are also known by which the localization in the chromo-

somes of modifying factors can be studied by methods

that no student of Mendelian heredity can afford to re-

ject. All of this is familiar, of course, to Jennings. He .

means, however, to suggest that if the work on Drosophila

continues for another fifty years, so many modifiers may

be found that the characters will form a continuous series.

But suppose the mutants do become so numerous that it

is impossible to distinguish between any two by inspec-

tion., Are we then to reject all the body of evidence that

is fast accumulating that the modifying genes are ordi-_

nary Mendelian factors? It would be the height of ab-

surdity to throw overboard all this experimentally deter-

mined evidence as to the actual method of origin and

inheritance of these genes because a time may come when

members of a series have become so numerous that we

4 See ‘‘Mechanism of Mendelian Heredity,’’ pp. 192-4.

526 THE AMERICAN NATURALIST [ Vou. LI

will be too much bored to make the tests that will dis-

tinguish a given new member from some one or other of

the old ones. But Jennings may reply, suppose the selec-

tionist claims that his material is already in this finely

triturated condition! If, so, the answer is that by suitable

selection experiments an analysis may in many situations

still be made, and, secondly, the evidence, even from

Castle’s rats, is far from establishing that he is dealing

with such a sublimated process. On the contrary, there is

much in them to indicate that they may be capable of

being handled by rather simple Mendelian methods, as

MacDowell has shown.

As a matter of fact, when indistinguishable characters

are the product of one or another modifier, the identifica-

tion of the two genes involved, as independent, is per-

fectly easy and certain by means of linkage relations. If

a particular material is not sufficiently worked out to

make this test possible, is that a sufficient reason why we

should refuse to accept evidence where it can be obtained?

And if there are indistinguishable characters that are the

product of one or of another allelomorph, of course it can

not be determined which allelomorph produces the result;

but as, ex hypothesi, each allelomorph produces the same

indistinguishable result, a discussion of such a question

would be as profitable as the ancient one of the number of

angels that can stand on the point of a needle.

In conclusion then it may be said that by stable or

onstant genes we do not necessarily mean that the gene is

absolute in the sense that a molecule is absolute, for we |

\/ean not know this at present. We might mean by stable

Aai

| genes that even if there is a variability of the gene the

-variation takes place about a mode; and if in a given

individual the extreme of variation was caused by a corre-

_ sponding extreme in the variation of the gene, still the

experimental evidence shows that in the many cell-genera-

tions through which that individual’s germ cells pass to

produce the sperms or the eggs, the genic variation, if

there i is any, is still about the original mode and that no

No. 609] THE THEORY OF THE GENE 527

new mode has been established unless a mutation has

occurred. This latter interpretation is indeed in contra-

diction to the idea that the gene is a single molecule, for

molecules are not supposed to vary about a mode. A

present either interpretation is compatible with the evi-

dence, which does not discriminate between them.

At the time when Darwin wrote and for many years

afterward it was supposed that any new or unusual trait

of character would become obliterated by repeated cross-

ing with the normal or average individual of the species.

This was perhaps the most serious difficulty that Dar-

win’s theory of natural selection met with. It will be re-

called that in order to overcome it Darwin made a con-

cession that in principle amounted to an abandonment of

the origin of characters through natural selection of

chance variations. He admitted that only when a new

character appeared in a large number of individuals at

the same time was there an opportunity for its per-

petuation.

n sharp contrast to this earlier view, all the evidence

from Mendelian heredity goes to show that however often

ne EY ea

a new character, that rests on a genetic change in the

erm plasm, may have been kept out of sight by crossing

to dominant individuals, whenever the character emerges

from the cross, it shows at once that its gene has not been

contaminated by contact with other genes. This conclu-

-sion is an enormous gain for the theory of natural selec-

tion based on chance variation, and at the same time is an

equally strong argument to show that genes remain stable,

and are not infected or mixed in the presence of other

contrasting genes.” Let me illustrate by a case of my own.

5 Those who in their haste try to show that Darwin must have meant by

fluctuating variation small mutations, since he assumed such fluctuations to

inherited, might well ponder the difference between the two kinds of

variation cited above. If Darwin had realized the difference referred to,

he would not have had to make the damaging concession forced upon him

by his critie, a professor of engineering, Fleeming Jenkin, in the North

British Review (June, 1867).

eRe

528 THE AMERICAN NATURALIST [ Vou. LI

There is a mutant called ‘‘notch’’ (Fig. 1) character-

ized by a serration at the ends of the wings. The factor

that causes this is sex-linked, dominant in regard to the

Fic. 1. Notch female.

wing character but recessive in its lethal effect. A female

with notch wings carries the gene in one of her X-chromo-

somes and the normal allelomorph in the other X-chromo-

some. Half of her sons get the former and die, the other

half get the latter X-chromosome and live. As there are

no lethal bearing males, the females must in every gen-

eration be bred to normal males. For twenty generations

such matings have been made. Each time there have

come together in the same female one X-chromosome

carrying the gene for notch and its mate carrying the

normal allelomorph. Selection of those females that

No. 609] THE THEORY OF THE GENE 529

showed the least amount of notch, changed, after a few

generations, the outward character of the notch stock so

that at least half of those females that carry the notch

gene came to have normal wings. It might have seemed

that the gene itself had changed, possibly through con-

tamination with the normal gene, were such a thing pos-

sible. On the contrary, if these females with normal

wings are outcrossed to a male of any other stock, all the

daughters that carry the notch gene have the notch in the

original (atavistic) condition, showing that the gene still

acts in all its original strength. Moreover, suitable ex-

periments have shown that as a result of selection, a

modifying gene, already present in the original stock, has

been isolated. This gene modifies notch (although it

produces no visible effect on the normal wing) in such a

way that the notch is less likely to appear. The evidence

furnishes the twofold demonstration that the gene for

notch has not changed through contamination, and that

there is present a new and definite gene that does account

for the change.

(D) Methods of Inheritance that are not Mendelian

It has been claimed that Mendelian inheritance is only

one kind of inheritance and applies to only a limited

group of characters. It has even been implied that the

kind of characters involved in the process of evolution can

not be inherited in this way because, it is affirmed, evolu-

ee ee ee ee

tionary characters are not like Mendelian characters.

It is known that certain plastids, such as chloroplasts,

that lie in the protoplasm are transmitted as a rule only

through the egg protoplasm. There can be no doubt

that this sort of transmission takes place. In principle it

is not different from the transmission of certain kinds of

bacterial diseases like that of pebrine in the egg of the

silkworm moth. <Any inclusion in the cytoplasm capable

of increasing there by division would be mechanically

carried to all the new cells arising by division and there-

530 THE AMERICAN NATURALIST [ Vou. LI

fore into the egg cell also. Should the sperm cell strip

itself free of most of that part of the cytoplasm that con-

tained these inclusions, the spermatozoa alone of all the

cells in the body would be free from these cytoplasmic

materials, and in consequence would not transmit them.

So long as we recognize with what we are dealing here

it is largely a matter of personal choice whether we prefer

to include plastid transmission through the egg (or even

through the cytoplasm of the sperm in special cases)

under the term heredity.

The number of cases in which plastid inheritance is

known to occur is very limited,’ while Mendelian heredity

includes the vast majority of characters about whose in-

heritance we know something definite.

/ But it is a far cry from these cases of transmission of

plastids to the view that the cytoplasm transmits equally

with the chromosomes; or that the cytoplasm transmits

the fundamental attributes of the organism and that the

chromosomes transmit only the more superficial charac-

teristies—a view that Boveri discussed in detail in 1903,

land which was a favorite topicof his on several later

occasions. He changed entirely as the evidence came in

and finally abandoned the view in his last paper. (1914).

This is an old and familiar topic ‘with embryologists,

but since it has been recently revived, a brief statement

in regard to it may not be out of place. Fortunately this

view is no longer a matter of opinion but of experimentally

determined evidence.

In 1912, Toyama described some cases .in silkworm

moths of what is known as maternal inheritance—cases

in which certain characteristics that develop in the hybrid

embryo are like those of the maternal stock. He found

cases involving the color of the yolk, shape of the egg, and

the pigment (not present as such in the egg) that de-

velops after the serosa is formed. By breeding tests it

6If chondriosomes are ‘‘formative’’ materials as certain writers claim,

the type of plastid inheritance may include a larger group of characters

than we suppose at present

No. 609] THE THEORY OF THE GENE 531

was made clear that the cytoplasm transmits these char-

acteristics only because they have been impressed on the

cytoplasm by the chromosomes at some earlier stage in

the history of the egg cell. They are strictly Mendelian

(Fig. 2).

Pi oD by F R QR by 7D

K Ne

Eggs and embryo è }

Gene DR DR

tiii | |

z Eggs and embryo. ê ê

Genetic consti- DD DR RR DD DR RR

tuston of Po

individuals. | | | |

6 ® O @ _ ae

F3 Eggs D D R D D R

à 2 1 1 2 ł

Fic. 2. Maternal inheritance in the silk-worm moth according to Toyama.

It has also been suggested that the chromosomal, Men-

delian genes affect only trivial characters such as color,

while the more fundamental characters are carried in

the cytoplasm.” There. are in reality no grounds for as-

suming that some characters are more fundamental than

others; or that such hypothecated fundamental characters

have a different mode of inheritance. The old-fashioned

distinction between ordinal, class, family and generic

characters has long ‘Veer ed A as entirely artificial

and conventional while the so-called promorphological

characteristics such as shape of egg, type of cleavage,

axial relations are as variable as are other characteristics,

and some of them, such as shape of egg, location of micro-

pyle, etc., have been shown to fall under the Mendelian

formula. Take, for example, the following list of charac-

ters and try to decide whether they are fundamental

(generic) or only trivial; they are all Mendelian in some

cases at least:

Sterility, several types of which are recognized as Men-

delian ;

7 Boveri, 1903; Loeb, 1916.

532 THE AMERICAN NATURALIST [ Vou. LT

Sex, the inheritance of which is shown in many cases to

be associated with sex chromosomes;

‘‘Apterous,’’ loss of wings in certain stocks of Droso-

phila;

‘‘Hyeless,’’ partial or complete loss of eyes;

“Extra legs,’’ duplication of part or of entire legs which

in one race shows Mendelian sex-linked transmission;

Heliotropism, loss of positive response to light in one

stock of Drosophila.

Until there is forthcoming some direct evidence that the

cytoplasm apart from its contained plastids transmits

more fundamental characteristics than the chromosomes,

the claim that such a difference exists is not only entirely

speculative, but has been shown not to be true for a num-

_ ber of characters. No doubt the idea arose from the fact

that when the egg begins to develop it is the protoplasm

that exhibits most of the phenomena concerned with the

early development of the axial and bilateral relations, the

type of cleavage and the formation of the organs of the

embryo. But this kind of evidence shows no more than

that these characteristics are then present in the cyto-

plasm; it does not show whether they have come from the

chromosomes in the early history of the egg cell, or were,

as assumed, inherent properties of the cytoplasm as such.

In recent years, however, it has been possible in a few

cases, like those of Toyama, to get experimental evidence

` bearing on this point and it has shown beyond dispute

that such cytoplasmic types of behavior are impressed on

the cytoplasm by the chromatin in the same way presum-

ably as are all Mendelian characteristics.

No one has denied, so far as I know, that the cytoplasm

is essential for development. That it is transmitted

largely, if not entirely, through the cytoplasm of the egg

is too well recognized to debate, and that it may contain

substances that have never been a constituent part of the

nucleus and which may form the basis through which

material of nuclear origin may act must be freely granted

No. 609] THE THEORY OF THE GENE 533

as an important theoretical possibility. But it must not

be forgotten that the only characters that we know any-

thing about in genetics are under nuclear control with the

exception of plastids that can themselves multiply in the

cytoplasm.

There is a special case of inheritance that has been

called cytoplasmic that may equally well have a chro-

mosomal explanation. Goldschmidt finds that he can

account for certain of his results in gypsy moths by as-

eribing certain values to the cytoplasm. Thus he says

the two factors for femaleness (FF) are transmitted from

the mother to her daughters and the latter transmits

again to their daughters, ete. In other words, the factors

are carried only in the egg-producing line. Goldschmidt

concludes that the evidence proves that the ‘‘FF com-

plex is inherited . . . in the protoplasm of the female.’’

Now in moths in which the female is the heterogametic

sex, the Y chromosome (or the W chromosome to use a

different nomenclature) is transmitted only by the female

line and should this chromosome carry the factors in

question all the requirements of the experiment would be

fulfilled. There is no way of determining from this evi-

dence alone whether the case belongs to the plastid type

of inheritance, or is a case of W inheritance, except by

finding species in which the female normally lacks the

W sex chromosome, or by some anomalous condition has

lost it as in the 55 chromosome females that Doncaster

has found in the moth Abraxas.

There is still another rôle that the cytoplasm may play

in determining the nature of the next event to occur. In

Phylloxerans it has been shown that a whole sex chromo-

some is eliminated from the small eggs and in consequence

a male results from them. The presumption here is that

the effect is through the cytoplasm determining the dis-

tribution of the chromosomes, but it must be conceded

that the same environmental changes that affected the

cytoplasm may have had a simultaneous effect on one of

the sex chromosomes. In the case of certain generic

534 _THE AMERICAN NATURALIST [ Vou. LI

crosses in pigeons, Riddle, confirming Whitman’s dis-

covery, finds that when an enforced series of eggs are

laid, their chemical composition is changed and that they

produce at certain times a preponderance of males. Since

the female here is the heterozygotic sex (ZW) the results

are such as would follow a direct influence on the sex

chromosomes when the polar body is eliminated. Infor-

mation concerning sex-linked inheritance in these forced

offspring should settle the question.

To sum up, it may be said that ‘‘plastid’’ inheritance

is at present the only known method of transmission of

factors that does not come under Mendel’s laws. The

three principal kinds of Mendelian inheritance known at

present fall into the following groups:

1. Autosomal inheritance, where transmission is equally

to both sexes, or to all individuals of hermaphroditic

species.

2. Sex-linked inheritance, (a) where the distribution of

characters coincides with the distribution of the X

chromosomes in the Drosophila type, and of the Z

chromosomes in the Abraxas type; and (b) where the

distribution of characters coincides with the distribu-

tion of the Y chromosome (as illustrated by the fer-

tility of the male of Drosophila that depends on the

presence of the Y chromosome) or of the W chromo-

some in moths.

3. Inheritance due to unusual distributions of chromo-

somes, as seen (@) in doubling of their number (tetra-

ploidy); (b) in non-disjunction, as in the 15-chromo-

some type of @nothera and the XXY type of female

in Drosophila; (c) in irregularities of synapsis as

seen in species hybrids such as Pygera. This group

(3) is at present only provisional and will no doubt

be broken up at some future time into its different

parts.

The case of maternal inheritance, spoken of above (other

than Y or W linked or plastid inheritance), has been

No. 609] THE THEORY OF THE GENE, 535

shown to be only deferred Mendelian inheritance trace-

able to the chromatin of the nucleus in which the char-

acters shown by the egg or the embryo have already been

determined before fertilization by the chromatin of the

mother alone. In consequence the appearance of the

Mendelian ratio is deferred to a succeeding generation

(Fs).

(E) Action of Genes during Embryonic Development

versus their Distribution m Heredity

On several occasions I have urged the importance of

keeping apart, for the present at least, the questions con-

nected with the distribution of the genes in succeeding

generations from questions connected with the physio-

logical action of the genetic factors during development,

because the embryological data have too often been con-

fused in premature attempts to interpret the genetic data.

It has been urged that such a procedure limits the legiti-

mate field of heredity to a process no more intellectual

than that of a game of cards, for Mendelism becomes

nothing but shuffling and dealing out new hands to each

pepe generation. My plea is, I fear, based largely

on expediency, which may only too easily be interpreted

as narrow-mindedness; yet I hope to be amongst the first

to welcome any real contribution concerning the nature of

genes based on the chemical changes that take place

in the embryo where the products of the genes show their

effects. In fact I do not know of any other more direct

way in which we can ultimately hope to find out the nature

of the materials that we think of as genes in the germ

cells.

But experience has shown, I think, that only too often

the embryological data have been used to interpret the

transmission data to the detriment of both subjects; I

regret to see the inevitable difficulties that are natural, at

present, to the field of embryology thrust upon the other

subject, where the problem is comparatively simple; and

536

THE AMERICAN NATURALIST

[ Vox. LI

Fig, 3. Male, a, and female, b, Sebright.

No. 609] THE THEORY OF THE GENE 537

so far as it has progressed, understood. Do not under-

stand me to say that I think all the problems of heredity

have been solved, even with the acceptance of the chromo- .

somal mechanism as the agent of transmission.’ In fact,

I think that we are only at the beginning even of this

study, for the important work of McClung, Wenrich, Miss

Carothers and Robertson shows that there are probably

Fic. 4. Male, black-breasted game-bantam.

many surprises in store for us concerning modes of dis-

tribution of Mendelian factors. Moreover; the method by

which crossing over of allelomorphie factors takes place

is still in the speculative stage, so far as the cytological

evidence is concerned, as are also many questions as to

how the lineally arranged factors hold their order during

the resting stages of the nucleus and during the condensed

stages in the dividing chromosomes.

8 The statement that I made in my recent book on the ‘í Critique of the

Theory of Evolution,’’ that the traditional problem of heredity has been

solved, is not in contradiction with the above statement which concerns the

future problems of heredity.

538

THE AMERICAN NATURALIST

Fic. 5. F, male, a, and female, b, out of Sebright by Game,

[ Vou. LI

No. 609] THE THEORY OF THE GENE 539

It does not seem to me to lessen in any way the im-

portance of embryology to keep its problems for the pres-

ent separated from those of the method of transmission

of hereditary characters. It may well be that there are

more important discoveries to be made in future in the

field of embryology than in genetics, and that when the

subject of chemical embryology has arrived at its goal it

may be worth while to combine the two subjects into

a single one. I am also aware that to many persons the

interest in genetics is greatly increased when certain

stages can be demonstrated through which the genes bring

about their results. Far from being in opposition to such

interests, I can illustrate this very point by a case of my

own. The cock bird of the Sebright bantam is ‘‘hen-

feathered’’ (Fig. 3a), i. e., certain of the secondary sexual

characters are like those of the hen (Fig. 3b). This is

most noticeable in the short neck, back and saddle feathers

as well as in the absence of the long tail feathers. When

these birds are crossed to game bantams (a race in which

the male has the usual secondary sexual characters, Fig.

4), the F, cocks are hen-feathered (Fig. 5a). This is true

both when Sebright 3 is crossed to game 2 and when game

3 is crossed to Sebright 2. The latter cross shows that the

dominant character is carried by the female Sebright as

well as by the male.

When these F, birds are inbred, they produce in the

next generation (F,) both-cock-feathered and hen-feath-

ered males. There is complete segregation of the types

that went into the cross. Whether one or two genes for

hen-feathering are present is not entirely certain, but that

Mendelian segregation occurs there can be no doubt.

I was led to see what would happen when the hen-

feathered birds were castrated. Goodale had shown that

when the hen of normal breeds is spayed, she develops

the full male plumage, including the special feather re-

gions in which the Sebright is hen-feathered. At the

time of castration a few feathers were removed. The

new ones that came in showed at once that a great change

540 THE AMERICAN NATURALIST [ Vou. LI

had taken place both in the size, shape and color of the

new feathers (Fig. 6), which became like those of the

‘‘normal’’ male. Since the F, birds were heterozygous,

Fig. 6. Castrated F, male, originally like male in Fig. 5, a.

and the F, birds used might also have been heterozygous,

it became important to castrate the Sebright males. This

has been done and the same complete change takes place

in them, as the accompanying figures of the birds (Fig.

7) and of a few of their feathers (Figs. 8 and 9) show

very clearly.

Goodale’s evidence from the spayed hen makes prob-

able the view that the ovary of the hen produces some in-

ternal secretion that inhibits in her the full development

of her plumage which is potentially the same as that of

her male. After removal of the ovary the inhibition is

removed and when the hen moults she develops her full

possibilities of plumage. Similarly in the hen-feathered

male, some internal secretion must inhibit.the develop-

ment of certain of the secondary sexual characters.

owm ta a ants Ce eis o PHAPA eee. ia 2 ee ei AR N ;

542 THE AMERICAN NATURALIST [ Vou. LI

Here then we get an idea of one of the stages through

which the products of Mendelian genes for hen-feathering

produce their results. The presence of these genes within

Fig. 8. re from F, cock (like es in Fig. 5a) before a, b, c and after

EE eee astration ; a, a’ hackle, b, b’ saddle, c, ce’ wing

the male birds causes the testes to produce some substance

that carried into the body inhibits the full development

there of certain feathers. The presence of these genes in

the other cells of the body is without influence on the

plumage, except in the presence of the testes. The activ-

ity of the latter is such that a substance is produced there

that has an inhibitory effect.

In other words, we are fortunate enough in this case

No. 609] THE THEORY OF THE GENE 543

to be able to show a particular stage in the chain of events

by which the character of certain feathers is influenced.

I need not point out that there is not the slightest reason

to identify the substance produced in the testes with the

a al | b : b

Fig, 9. perri from Sebright cock (like Fig. 3a or Fig. Ta) before a, b, c and

afte , 0’, e’ castration; a, a’ hackle, b, b’ saddle, and c, c’ wing.

substance of the gene; the chemical composition of the

internal secretion may be entirely different from that of the

gene, the latter producing its result in conjunction with sub-

stances resulting from other genes. There is every reason

for supposing that the way in which the effects are pro-

duced here are the same as in all development when the

end result is the collective product of substances pro-

‘

544 THE AMERICAN NATURALIST [Kots LI

duced by the hereditary genes—a single gene difference

turning the scale in this way or in that. In this case we

have, I think, an excellent illustration of the difference

between the mechanism of inheritance and the chemical

effects of genetic factors on development. Highly inter-

esting and important as it undoubtedly would be to work

out these connections, yet the evidence is very explicit in

showing that the distribution of the materials of heredity

during the maturation process of the egg and sperm is

different in kind from their action through the cytoplasm

on the developing organism.

For purposes, then, of closer analysis, it seems desirable

in the present condition of genetics and embryology to

recognize that the mechanism of distribution of the hered-

itary units or genes is a process of an entirely different

kind from the effects that the genes produce through the

agency of the cytoplasm of the embryo. The activity of

the cytoplasm is, of course, bound up with the environ-

ment in which it takes place—a relation that is so intimate

that in most cases the constitution of the cytoplasm and

the nature of the environment in which it finds itself are

studied as two sides of the same problem. It is true that

the mechanism of Mendelian heredity may also be affected

by the environment, certainly by the external environ-

ment, as Plough has shown for heat; and also probably

by the cytoplasmic environment since Bridges has shown

that the process is somewhat different in young and old

flies. But there is no evidence that the relation of the

maturation process to the environment is in any way re-

lated to the reactions that go on between the cytoplasm of

the developing embryo and its environment, and it has

only led to confusion whenever an attempt has been made

to deduce from the nature of the embryonic reaction the

nature of the mechanism that distributes the genes in

heredity.

STUDIES ON INBREEDING. VII—SOME FUR-

THER CONSIDERATIONS REGARDNG THE

MEASUREMENT AND NUMERICAL EX-

PRESSION OF DEGREES OF KINSHIP?

DR. RAYMOND PEARL

1. In this series of studies certain concepts regarding

the quantitative aspect of inbreeding have been pre-

sented. These concepts have in part been rigorously

defined, and expressed in mathematical form. It is de-

sirable to repeat here and extend in certain directions,

the definition of two of the most fundamental of these

concepts.

I. Inbreeding is defined in these studies as the condi-

tion or state in which an organism has in fact fewer dif-

ferent ancestors than the maximum number possible.

The degree or amount of inbreeding (total) is measured

by a series of inbreeding coefficients, one for each ances-

tral generation, defined by the following equation:

gar i (i)

Pra

where Phr, denotes the maximum possible number of dif-

ferent individuals involved in the matings of the n+1

generation, qn the actual number of different individuals

involved in these matings, and Z» is the inbreeding

coefficient for the n + 1-th ancestral generation.

II. A state or condition of relationship or kinship be-

tween two organisms exists when these organisms have

one or more common ancestors. The degree, intensity or

closeness of the relationship is, in general, proportional

to the number of different ancestors which the two indi-

viduals have in common, out of the whole number they

might possibly have in common.

1 Papers from the aR Laboratory of the Maine Agricultural Ex-

periment Station. No.

545

546 THE AMERICAN NATURALIST [ Vou. LI

The degree or amount of relationship, in accordance

with the above definition, is numerically measured by

relationship coefficients, one for each ancestral genera-

tion. The coefficients are calculated in two slightly differ-

ent ways according to whether they are being evaluated

in connection with inbreeding coefficients, which will

usually be the case, or independently.

A. When calculated in connection with inbreeding

coefficients, a relationship coefficient is calculated, by

methods presently to be shown by example, in accordance

with the following equation:

Kn Ri (Pns Ag 5S usr) ets (sZn1'sPn rte dZ n_1"apn) (ii)

100- Pnn E

where the letters have the same significance as in (i)

with the additions that K denotes a relationship coeffi-

cient, a prefixed subscript s means that letters following

it refer to the pedigree of the sire only, and a prefixed

subscript d means that the letters following refer to the

pedigree of the dam only.

B. When calculated independently of inbreeding coeff-

cients, as, for example, to measure the relationship be-

tween two male animals, the relationship coefficient

becomes

100 a Pra f

where Pn — Yn; denotes the number of ancestors in the

n + 1-th generation (each individual and its ancestry being

counted once only) which occur, in the n + 1-th or some

earlier ancestral generation, in the pedigrees of both ani-

mals, or in other words which are common ancestors;

pn, denotes the total number of ancestors in the same

generation of both pedigrees taken together.

III. Inbreeding, defined in I, may exist in respect of

any individual, as a result of any one or a combination of

the following circumstances: (a) the sire of the individual

has fewer than the maximum possible number of different

ancestors, and no ancestors in common with the dam; (b)

K, ee Pru — Fnsi (iii)

No. 609] STUDIES ON INBREEDING 547

the dam of the individual has fewer than the maximum

possible number of different ancestors, and no ancestors

in common with the sire; or, (c) the sire and dam have a

certain number of common ancestors, and hence are, in

the common sense of the word, related to each other in

some degree.

IV. We may separate conceptually that portion of the

total inbreeding due to a or b or any combination of a and

b, from that portion of the total inbreeding due to c, and

define as due to relationship between the sire and dam

that amount or degree of inbreeding (in the sense of I)

which remains after the amount due to a or b (of III)

or any combination of a and b has been subtracted from

the total inbreeding.

A numerical expression of the portion of the inbreeding

in the nth generation due to relationship is obtained by a

partial inbreeding index of the following form:

KZu= DEn, (iv)

Expressed in words this means that we take as an index

of the part of the inbreeding due to relationship the per-

centage which one half of the relationship coefficient is of

the inbreeding coefficient, both referred of course to the

same ancestral generation.

2. The above paragraphs define a relationship coeffi-

cient much more rigorously and generally than was done

in my earlier paper on the subject,’ or in ‘‘Modes of Re-

search in Geneties.” Not only is this a gain in itself,

but also it makes possible a great simplification in the

actual work of calculating coefficients of relationship

from pedigrees. Extensive experience has shown that

the method of making these determinations given in my

earlier paper left much to be desired in the direction of

simplicity, ease of application, and even of accuracy in

case the pedigree dealt with was at all complicated in

2 Pearl, R., AMER, NAT., Vol. XLVIII, pp. 513-523, 1

1914,

3 Pearl, R., ‘‘ Modes of Research in Genetics,’’ New York, 1915 (Mae-

millan & D). Cf. pp. 101-156.

548 ; THE AMERICAN NATURALIST [ Vou, LI

_ respect of the distribution of its ancestral repetition. Out

of actual laboratory experience has been developed the

more simple and rigorous analysis of the matter pre-

sented in this paper.

3. It would appear that the briefest and simplest way

to make clear our concept of kinship measurements, its

use in the analysis of inbreeding, and its practical appli-

cation to pedigrees, is to carry out the work on some con-

crete examples, given by actual pedigrees showing a

rather high degree of inbreeding or relationship. This

we shall accordingly proceed at once to do, taking as our

first example the pedigree through five ancestral genera-

tions of the Jersey cow Letty’s Fancy Lady (241551).

The pedigree (for five ancestral generations) of this

cow is presented in Tables I and II. Table I gives the

pedigree of her sire, Rioter’s St. Lambert King (58644),

and Table II gives the pedigree of the dam of the cow,

Letty’s Fancy (160320). Tables I and II together, there-

fore, give the complete pedigree (to the extent already

indicated) of the cow herself. The reason for splitting

the pedigree into two parts in this way in its presentation

will be apparent as we proceed. The numbers preceding

the names of the animals are the registry numbers in the

Herd Books of the American Jersey Cattle Club.

In Tables I and II the symbols have the following sig-

nificance: A solid circle indicates a primary reappearance

of an ancestor, having reference to the pedigree of Letty’s

Fancy Lady as a whole, and an open circle indicates an

entailed reappearance consequent upon the primary re-

appearance denoted by the solid circle. A solid square

indicates a primary reappearance in the pedigree of the

sire of Letty’s Fancy Lady, considered by itself and with-

out reference to her dam’s pedigree; an open square de-

notes reappearance consequent upon those indicated by

the solid squares. Finally, a solid diamond indicates a

primary reappearance of an ancestor in the pedigree of

the dam of Letty’s Fancy Lady, considered by itself, while

the open diamonds denote the corresponding entailed re-

appearances.

No. 609]

STUDIES ON INBREEDING

549

TABLE I

PEDIGREE OF RIOTER’S St. LAMBERT KING (58644), SIRE or LETTY’s

Fancy Lapy (241551)

Ancestral Generation *

1 2 3 4 5

00 No. 15175 g No. 13656 dg No. 4 g

y iae Riotwrier Gt? e A of St. Lambert

Lambert No. 24990

King of St. | Ida of St. Lambert

> pe tambak. INg. 24001 9 No. E

— |

2 Allie of St. ou Saks Pogis 3d

E Lambert No. 512 9

H | Kathleen of St. Lambert

NM s |

s No. 28353 Q No. 2238 d'No. 1259 g

É i Stoke Pogis

= Stoke Pogis 3d

2 No. 3239 j Q

May Day Stoke Marjoram

wl Pogis No. 5109 2 No. 1066 F

Z 3 May Day of St. Lord Lisgar

Fip ARO? |. Ioia ọ

8| zZ Jerne

H| œ No. 15175 g'|No. 13656 F |No. 4558 3

a OO Ida's Ridter of OO Bachelor of St. Lambert

5 St. Lambert No

Lambert" INo. 24991 Q|No. 2

E o o Ate of St. OL aka Pogis 3d

g Lambert

No. 5 Q

4 ou Kathleen of St. Lambert

2 No. 43671 9 |No. 8388 d'|No. 6036 — g

Š à e George of St. Lambert

= Canada’s John Bull

= No. 12968 9

Allie of St. Lam- Nymph of St. Lambert

bert 2d

š ts No. 24991 Q|No. 2238

2 Fa es Alle of 8i on Stoke Pogis 3d

: : Lambert

o| 6

2 |Z ons

On: Taidan of St. Lambert.

4 Referred to the propositus, Letty’s Fancy Lady (241551).

550

THE AMERICAN NATURALIST

TABLE II

[ Vou. LI

PEDIGREE OF LETTY’S Fancy (160320), Dam or LETTY’S FANCY

Lapy (241551)

Ancestral Generations

1 2 3 4 5

F Bachelor of St: Oriont

Lambert -i -INo. 6638 9

į Exile of St. Charity of St. Lambert

2 Lambert No, 24991 Q No. 2338 B4

4 a Allie of Si tnia O Stoke Foead

2 bert No. 5122 9

a O Kathleen of St. Lambert

$ |No. 73475 Q No. 10481 g'|No. 6036 J

mn Diana’s Rioter

5 No. 6636

fan Letty Rioter

2 No. 48128 2 No. 10481 g

a è ẹ Diana’s Rioter

Dj + | Letty Coles 2d

ais No. 23351 Q

m A Letty Coles

|. |No. 17408 g |No. 8388 J No. 6036 F

2 3 }

8 ó Canade's6 aa O Sir George of St. Lambert

ia No. 12968 ` 9

O Nymph of St. Lambert

_ |St. Lambert Boy

No. 14880 9 No. 5248 g

8 le Lorne

$ Oakland’s Nora ~

2 No. 5123 g

w Pet of St. Lambert

2 :

3 |No. 124201 9 /No. 17408 d'No. 8388 J

A Boy No. 14880 o

tT]

8 B Lambert" iNo. 48128 Q No. 10481 F

N Age te

gis vis No. 23351 9

With these data in hand we may proceed to the evalua-

tion first of the total inbreeding. We have in Table III the

pedigree elimination table for this purpose, which lists

the primary reappearances indicated by solid circles.

` No. 609] STUDIES ON INBREEDING 551

TABLE III

PEDIGREE ELIMINATION TABLE FOR THE TOTAL INBREEDING OF

TY’s FANCY LADY

Ancestral Generation in which Primary

Name of Animal Primarily Reappearing

SS ae 3 4 5

King of St. Lambert. heh Ge Gee VOLG o= 1 2 4

Allie of St. Lambert. ooon] -— — -— 2 4

Canadivé Jobn Palkia ai — — === 1 2

St. Lambert ey veri. eeren oe — -= 1 2

ety Cols fa eee eee | — — — 1 2

Bachelor 3 A RISO es okies ual eo ak bred a == 1

Biako FUNG I E E a ss ne ]-|— 1

Sir George pbo st e a A ee eo S a — | — — — 1

Haas A O e ee a a ri | — si ei i 1

E ee oe | 6 1 7 | 18

Whence, by the usual method, using the tables of Pearl

and Miner,’ we have the following values:

TOTAL INBREEDING COEFFICIENTS FoR Letty’s Fancy LADY

Z,.=0, Z:=12.50, Z= 43.75, Z, = 56.25.

Let us next consider Table IV, which gives the pedigree

elimination for the pedigree of the sire, as given in Table

I, considered by itself, the primary reappearances listed

being those indicated by solid squares. It must be par-

ticularly noted that the primary reappearances listed*in

this table are referred to the ancestral generations of the

pedigree of Letty’s Fancy Lady, and not to the pedigree

of Rioter’s St. Lambert King, her sire, with whose pedi-

gree we are dealing.

TABLE IV

PEDIGREE ELIMINATION TABLE FOR RIOTER’S St. LAMBERT KING

Ancestral Generation® in which Primary

Name of Animal Primarily Reappearing ee Curt

1 2 3 4 5

King oF St. Lambert. 2 i id — — 1 2 4

Allie of St. Lambert. EE T Gar — — 1 2

Sipe Poo oa ee ee es — = -— a 1

ORME eS NCS Se ey OO oe OA 1 3 7

5 Pearl, R., and Miner, J. R., Maine Agr, Expt. Stat. Ann. Rept. for 1913,

pp. 191-202.

ê Referred to the pedigree of Letty’s Fancy Lady.

552 THE AMERICAN NATURALIST [Von LE -

In Table V exactly corresponding data are given for

the pedigree of Letty’s Fancy, the dam of Letty’s Fancy

Lady. The primary reappearances here are those indi-

cated by solid diamonds in Table IT. |

TABLE V

PEDIGREE ELIMINATION TABLE FOR LETTY’S FANCY

estral G tion® in which Primary

Name of Animal Primarily Reappearing ES

1 2 3 4 5

St. Lambert Boy.. Se MES Ghee Recep nee -— 1 2

Letty Coles 2d.. UO cata E Oe apap — | — — 1 2

Dikawa hota. o e se — | — — — 1

Wiha oN E he rer Otho 0 2 5

Combined Totals of Tables IV and V ....... 0 0 1 hr ep I2

Difference between combined bara and | |

totals of Table III (total inbreeding). Oe Boe | | 0 | 0 2 6

COEFFICIENTS

Pass

“sL Bos

Eae

7 £ 19 Z ‘

GENERATIONS $ È

Fic. 1. Diagram showing the inbreeding and relationship curves for Letty’s

Fancy Lady. Total inbreeding coefficients—solid line and circles; relationship

. The smooth

eding curves for continued brother x sister, parent x offspring, bay eee

and double cousin x cousin mating. These are inserted for compari

From the last line of Table V we deduce relationship

coefficients as follows:

No. 609] STUDIES ON INBREEDING 553

Ke, 2%: Rs 10x5 — 25.00,

eR ae re — 37.50

Expressed in words these coefficients mean that

Rioter’s St. Lambert King and Letty’s Lady are related

to the amount or degree of 25 per cent. in the third, and

37.5 per cent. in the fourth ancestral generation.

In Fig. 1 are shown the total inbreeding (solid line and

dots), the relationship (dashes and open circles), and the

partial inbreeding (dots and crosses) eurves for Letty’s

Fancy Lady.

Finally we have, from (iv), the ac coefficients of

partial inbreeding due to relationship.

ezna

w an ay

KZ, = 9A) — 28.57,

K Zam poe = 83.83,

We thus see that of the total inbreeding observed in the

third ancestral generation of Letty’s Fancy Lady, none is

due to relationship between her sire and dam; of that

observed in the fourth ancestral generation, 28.57 is due

to such relationship; and finally, of that observed in the

fifth ancestral generation, one third arises because of re-

lationship between sire and dam.

4, Let us next consider an example of measuring rela-

tionship independently, altogether apart from considera-

tion of inbreeding. We may take a very simple case af-

forded by the two milking shorthorn cows, Imp. Milk

554 THE AMERICAN NATURALIST [ Vou. LI

Maid 211032, and Imp. White Queen 545726. The pedi-

grees of these animals follow in Tables VI and VII. The

problem before us is to measure and express numerically

the degree of relationship or kinship between these two

animals.

TABLE VI

PEDIGREE OF Imp. MILK Marb (211032)

1 2 3

Ot se No. 409267 o'|No. 409193 a

x Inspector

wa as Morning Sun

> No. — Q

ao ? Bessie 44th

iA]

+ 2 INo. Q No. 40909 g

sy A Dainty Bean

aea ee ee Tulip 28th

z >i ulip

= ó No. Q

od Zi Tulip 23d

= | œ No. 433648 F |No. 80356 eH

a Arkin Beau

b Border Stamp

a E No. ——— [e]

4 White Sunshine

x re So

9 3 È No. — 2 |No. 425402 F

a o A Balmoral Pearl

È oy Lady Balmoral

} S BENS

Z Z Lady Benedict’s Farewell

We see that in these two pedigrees there is, in the first

ancestral generation, one ancestor (Ireby Signet) which

occurs in both. Hence we have

ida he — 50.00.

In the second generation there are three ancestors

(Morning Sun, Tulip 28th and Border Stamp), which

occur in both pedigrees, whence it follows that

100 (3

K,= wee) 75.00.

In the third generation there are six common ancestors

No. 609] STUDIES ON INBREEDING 555

TABLE VII `

PEDIGREE OF IMP. WHITE QUEEN (545726)

Ancestral Generation

| 1 | 2 3

Or boas No. 409267 g No. 409193 g

z | ‘ Inspector

a | Morning Sun

ponte Meee 2

| „20 Bessie 44th

| ae

bom Ne. Q No. 409093 g

el ek ae i] Dainty Bean

Bal) age se Tulip 28th

Ed 6 No. ———— Q

ge rA Tulip 23d

S| oO No. 433648 g No. 80356 g

i Arkin Beau

= z Border Stamp

= S No. ——— Q

& White Sunshine

3 11 @ a No Q No. 501767 F

ait Loa Levens Guardsman :

Sayre = Diamond Queen

SAPPY | No. ——— ọ

zZ | A | Landford Diamond

(all involved from the second ancestral generation) and

ence

K. == == 75.00.

100 (6)

So that we may say that Imp. Milk Maid and Imp.

White Queen are 50 per cent. related in the first ancestral

generation, and 75 per cent. in the second and third.

This case will illustrate the superiority of the present

exact numerical expression of relationship over the ordi-

nary verbal expression. These two cows are half sisters,

both having the same sire (this degree of relationship is

indicated numerically always by K, = 50). But they are

more closely related than two individuals which are only

half sisters, because they have also one grandsire (Border

Stamp) in common. Their total degree of relationship

is simply not expressible verbally, by any term of kinship

known to me in the English language. Yet by the method

556 THE AMERICAN NATURALIST [ Von. LI

here described it is exactly expressible in the form

K,=50, KiK 15.

5. It will be perceived that the form of relationship

coefficient here proposed leads to precisely the same

numerical results in simple pedigrees, with not too in-

volved inbreeding or kinship, as that given in my former

paper’ except for the fact that I have here changed the

subscript designation of the K’s to bring them into con-

formity with the total inbreeding coefficients. The earlier

form proposed for these coefficients would always give the

same numerical values as the present one if certain rather

complicated rules of application, which were not clearly

or rigorously set forth in the earlier paper, were to be

followed. But the present simplified form does away en-

tirely with the need for these complicated rules of pro-

cedure.

6. It is of interest to set forth in tabular form the

values of the relationship coefficients for the commonly

recognized degrees of kinship. This is done in Table

VIII, in which the different degrees of kinship are ar-

ranged in descending order of closeness, in general. In

some cases, as, for example, parent and offspring and

half brothers (or half sisters), groups of two or three

different sorts of kinship showing the same numerical

degree of relationship should be regarded as bracketed,

since there is no more reason for placing one of these

first than another. -

From this table a number of interesting points emerge.

We note that the absolute maximum of closeness of re-

lationship is that of brother and sister. The parent and

offspring relationship is one half as close. Uncle and

nephew (or niece), or single first cousins, are twice as

closely related as grandparent and offspring. Some of

these comparisons made obvious by the table may seem at

first thought to give unexpected results, but if one will

take the trouble to write down pedigrees for the stated

7 Pearl, R., AMER.: NAT., Vol. XLVIII, pp. 513-523, 1914.

No. 609] STUDIES ON INBREEDING 557

degree of kinship, he will see upon careful consideration

the reasonableness of the numerical result.

TABLE VIII

VALUES OF THE RELATIONSHIP COEFFICIENTS FOR VARIOUS DEGREES

F KINSHIP

Degree of Kinship | Kı | Kə Ky | K4

| Í

Í | |

Meee, “=a prore (or sister). . .-| 100 | 100 | 100; | 100

Par PR URA PBT TAE OER e O a Be

Half-brother anh half-brother (or half-sister)....... _ 50 | 50 | 50 50

PGubie first CONA. fc. co ie el ee | 0 100 | 100 | 100

Single first cousins. TE ae | 50 | 50 | 50

Uncle and nephew (or niece) apes Oi. 30) 804i 7 BO

Grandparent and off eg | 95 | 25 | 25

Quadruple second eousing..; -im cl. fea ae. [PO TO | 100 | 100

Double second Cousins. ss Sie ois ee 0 | 0 | 50 | 50

Single second cousins CVE SET Ee SRR ae 0 Qe 28 6

in once removed........... ee Do ae Oe

P ropositus and first cousin twice removed . a 5 Ol 0] 0 | 12.6

. 7. There are two points in the development of relation-

ship coefficients in this paper which may seem open to

criticism. The first is that according to the definitions

and formule of this paper, the degree of relationship be-

tween two individuals is not affected by the number of

times the same common ancestor occurs in the pedigree

of either of the two individuals. The fact that such an-

cestor occurs at least once in both pedigrees makes it a

common ancestor. If it occurred more times it would not

be a more common ancestor, because after all it would

still be, all the time, just the same identical individual,

made up of the same germ plasm. Put in another way, it

is community of ancestry of two individuals which makes

kinship. But the multiple appearance of the same indi-

vidual in two pedigrees does not make any more ancestors

common to the two related individuals than if this an-

cestor occurred only once in each pedigree. Consider an

individual A which is rather intensely inbred with refer-

ence to an ancestor X. Consider another individual B

which is also inbred to some extent with reference to the -

Same individual X. Because they have a common ancestor

X, A and B are related. But, according to the concep-

558 THE AMERICAN NATURALIST [ Vou. LI

tion on which the present method of measuring kinship is

based, the fact that A and B happen both to be inbred in

respect to X, does not make them any more closely related

to each other than if they were not so inbred. It may be

of interest in this connection to point out, not as adding

to the scientific exactitude of the position here taken, but

as indicating what the common sense of men who have

given thought to the subject of consanguinity has been,

that the position here adopted that in determining degree

of kinship a common ancestor counts but once as such,

appears to be exactly in agreement with the position of

both the canon law and the civil law on the same point.

The second point in regard to which criticism might

seem to be possible is the method of referring the in-

breeding or relationship to the ancestral generations. In

all of these Studies the inbreeding or relationship is re-

ferred to the generation of the more remote (from the

propositus) of the two appearances in a pedigree of a

repeated ancestor. The logic of this procedure, rather

than the reverse, is found in the circumstance that the

fact of inbreeding (or kinship) does not establish itself

until the more remote reappearance is reached. Thus it is

impossible to know that a mating is of uncle and niece

until the grandparental generation is reached.

Ancestral generation... Fi

ais the uncle of x, the common ancestors being b and c,

but this fact is not known until the second ancestral

generation is reached. The only logical method of rep-

resenting these facts exactly in a numerical way would

_ seem to be to say, in effect, that up to and including the

first ancestral generation of a and «x there is no evidence

that these individuals are at all related, and therefore

No. 609] STUDIES ON INBREEDING 559

K,=0. In the second ancestral generation, on the con-

trary, it appears that two ancestors, b and c, in the pedi-

gree of x are the same individuals as appeared in the first

ancestral generation of a. Therefore it now appears that

a and x are related to the extent of 50 per cent. by the

existence of community of ancestry in the second an-

cestral generation. It would seem only logical to attach

the numerical measure of relationship to the generation

in which it is first proved to exist. Again, this is precisely

the point of view regarding the matter which has been

taken by the canon law and Roman civil law.

These two points, which seem so obvious to the writer

as to be difficult to discuss, are taken up here because

correspondence has shown that they have been a source |

of difficulty with some who have undertaken the study of

inbreeding in domestic animals by the methods set forth

in these studies. It is hoped that the simpler and more

precise definitions of both inbreeding and relationship

constants given in this paper may help to clear up such

difficulties, which must arise, it would seem, from a lack -

of a thorough grasp of the characteristics of pedigrees.

SUMMARY

In this paper the basic concepts of inbreeding are re-

defined in a simple and rigorous manner, and on the basis

of these definitions a new and more accurate method of

measuring and expressing numerically the degree of kin-

ship between any two individuals whatsoever, whose pedi-

grees are known, is set forth and illustrated by examples.

A new constant, the partial inbreeding index, is de-

scribed. Its purpose is*to indicate numerically the part

of the total inbreeding exhibited in the pedigree of any

individual which is due to relationship between the sire

and the dam of that individual.

MULTIPLICATION. BY FISSION IN

HOLOTHURIANS!

DR. W. J. CROZIER

THERE is to be found in various text-books the state-

ment that certain pedate holothurians are capable of

spontaneous transverse division, each part so formed

producing a new individual (Lang, 1894, p. 1095; Morgan,

1901, p. 144). This opinion seems to be based, so far as

I can learn, upon the observations of Dalyell (1851, p.

74; Pl. XIV), although Morgan says that ‘‘more recent

observers have confirmed this discovery.” Chadwick

(1891), also, found small individuals of Cucumaria planci

to undergo self-division, and in one instance the posterior

portion so formed also divided. These are records of

division in holothurians which were being kept in small

aquaria, and there has been no evidence, so far as I am

aware, going to show that self-division of adult pedate

holothurians is a method of propagation among these

animals in their normal surroundings. Hence the possi- |

bility of non-sexual reproduction in this way is usually

stated with reserve (ef. Lang, 1894).

In other classes of echinoderms (aside from echinoids)

the expedient of reproduction by fission is of course not

unusual; but in ophiuroids and in such starfishes as

Linckia (Clark, 1913) and Coscinasterias (Crozier, 1914) ,?

we are dealing with the division or fragmentation of a

1 Contributions from the Bermuda Biologtcal Station for Research, No. 66.

2 I have been able to secure further evidence regarding the fragmentation

of Coscinasterias (Asterias) tenuispina (Lam.), which proves conclusively

that the rules previously deduced (Crozier, 1915a@) regarding this process

are indeed valid. This evidence will be published in connection with a de-

scription of experiments on the direction of progression in Coscinasterias.

The presence of great variation in ray-length, as well as of a variable num-

ber of madreporites, gives an opportunity to test out in this species the

validity of certain ideas concerning ‘‘ physiological polarization” in as-

teroids.

560

No. 609] MULTIPLICATION IN HOLOTHURIANS 561

many-armed creature relatively deficient in morpholog-

ical centralization; whereas in Cucumaria and in Holo-

thuria the body is compactly built, the animal much more

of a unified individual. Consequently the self-division of

these holothurians is not without interest, especially since

in these cases the plane of separation is anatomically per-

pendicular to that employed among the astroradiates, and

it is the purpose of this paper to present evidence which

proves that adult specimens of at least one species, Holo-

thuria surinamensis Ludw., do as a matter of fact divide

transversely into two parts under conditions which must

be regarded as normal. Since these divisions are not in-

frequent in large numbers of specimens, if not in a single

life-history, we must conclude that fission represents a

regular means of mutliplication in this species.

A few years ago I found (Crozier, 1915b) that about

10 per cent. of the examples of H. surinamensis which

were studied showed a condition of either the oral or of

the cloacal end which—on the basis of observed regen-

erations following experimental eutting—I interpreted

as representing regeneration, possibly as a consequence

of spontaneous self-division. Similar conditions have

been noted by others for some other species of holo-

thurians, e. g., by Benham (1912, p. 136) for Actinopyga

(Miilleria) parvula (Selenka), but they have usually been

referred to regeneration after injury by such bottom feed-

ing fishes as small sharks. Dr. H. L. Clark informs me

that he has found a corresponding state of affairs in some

Australasian holothurians, at least in regard to the oc-

currence in nature of specimens showing posterior re-

generation.

I subsequently obtained young individuals of H. cap-

tiva Ludw., about 6mm. in length, which were observed

to divide spontaneously in the laboratory (Crozier, 1914,

p. 18), precisely according to the procedure figured by

Dalyell (1851) and by Chadwick (1891). Only a single

adult H. captiva has been discovered, however, in which

there was evidence of normal regeneration; this indi-

562 THE AMERICAN NATURALIST [Vou. LI

vidual, which was 40mm. long, was obtained among a

group of 47 taken from under a large rock in April, 1916.%

The anterior end for a distance of 7 mm. from the tip was

light greenish yellow, with ten very feebly developed

tentacles; there was a sharp line of demarcation between

the light yellow surface and the dark olive green of the

rest of the body. If H. captiva undergoes division nor-

mally, it can only occur in very young stages.

With H. surinamensis, however, the case is quite dif-

ferent. In Table I there are summarized results of the

examination of several series of these animals collected ai

different times for this particular purpose. It will

noted that in these collections from 2.5 to 16.9 per su

(on the average about 11 per cent.) of the individuals

show a condition of either the oral or of the cloacal end

which is interpreted as representing regeneration. This

seems to be about the proportion of such instances which

is to be met with in general collecting, although numerical

records have been kept only in the cases cited. The

specimens represented in the tabulation were obtained

TABLE I

THE RELATIVE NUMBER OF CASES IN WHICH Holothuria surinamensis WAS

FOUND TO BE REGENERATING IN NATURE

bie Wo wi Regenerating zy

weit Oral Cloacal Total %

June, July, 1913. 200 z 13 20 10.0

July 30, 1916 ......... aa 39 0 1 1 2.5

n SO LIO... isser 84 6 5 ki 13.1

ve A! Bi GPR iio ee 70 6 2 9 12.8

Jan. 31, 1917.. „i 4 5 9 16.9

Totala E coleaki eee 446 23 27 50 11.2

Ratio of regenerating oral to cloacal wi: Iar:

from one locality, Fairyland Creek, where they notably

abound; but the species has been collected at many other

stations, where also the regenerating individuals are to

be found in approximately the same proportion. The

3 It is known that some holothurians tend to congregate together in con-

siderable numbers at their time of breeding. Graber considered this to

indicate the presence of a chemical sense (Delage et Hérouard, 1903).

No. 609] MULTIPLICATION IN HOLOTHURIANS 563

season of the year seems not to influence the occurrence

of regenerating specimens.

The criterion of regeneration in these cases consists in

the presence of an anterior or posterior terminal part of

the body characteristically different in appearance from

the normal buccal or cloacal end, the surface being clearly

marked off from that of the rest of the body. In typical

examples these regenerated ends of the animal are more

sharply pointed than is usual; they bear feebly developed

tentacles (at the anterior end), tube feet, and dorsal

papille, which are less reactive than those on animals

judged to be not regenerated; and these appendages are

very lightly pigmented (Fig. 1). These characteristics

a b

Fic. 1. Regeneration found occurring naturally. at atk ae sketches,

showing differences in pigmentation of a, cloacal end, b, oral end. Natural size.

undoubtedly become less prominent with time, the colora-

tion tending, however, to remain pale on the ventral sur-

face (trivium). The first pigment to appear is the green

fluorescent one (cf. Crozier, 1914, p. 9 and 1915b); the

dark brown substance develops more slowly, just-as in

the growth of the pest larval holothurians of this and re-

lated species. The spicules of the podia and skin seem

fewer than in corresponding non-regenerating parts, but

are of the usual sizes and shapes. The tentacles on re-

generating buccal ends are always fewer (9-15) than on

the normal individual (20).

564 THE AMERICAN NATURALIST [Vor. LI

That the oral and cloacal terminations just described

do in reality represent regeneration, has been verified by

observation of the course of regeneration in the labora-

tory after experimentally cutting the holothurians ün

various ways (cf. Crozier, 1915b). Certain specimens

also have been tabulated as ‘‘regenerating’’ when their

appearance (Fig. 2, c), backed up by dissection, suggested

that they had just completed division and had not yet

begun to regenerate. These specimens lacked either a

cloaca, or the stone ring and buceal structures, depending,

obviously, on their former relation’ to the complete indi-

vidual from which they were derived.

at the division area is also indicat

The evidence that the regeneration found occurring

under natural conditions results from the self-division of

adult holothurians, involves two considerations. The

first concerns (a) the relative size of the regenerating

animals, and (b) the relative frequency of anterior and

posterior ends noted as regenerating. The second has to

_do with direct observations of self-division.

No. 609] MULTIPLICATION IN HOLOTHURIANS 565

One hundred H. surinamensis collected in Fairyland

Creek ranged in length from 6 to 18 cm., with the mode at

14cm. The regenerating specimens ranged in length

from 4 to 9 cm., with the mode at 7em. While no numer-

ically exact argument can be based on these figures, since

the length of any one holothurian is variable, the fact does

stand out that the regenerating animals are about one

half the length of the non-regenerating ones. There is

also the significant fact that not a single instance has been

found in which both a (supposedly) new oral and new

cloacal end were present. If self-division has occurred,

then we should expect to find new oral and new cloacal

extremities in equal frequency; among the rather small

number of cases available, we find their ratio to be as

1:1.17, an agreement sufficiently close to favor belief in

self-division.

The evidence concerning the second point is even more

conclusive. I have seen, in all, nine cases in which a holo-

thurian (H. surinamensis), in the laboratory, divided

itself into two parts. The animals concerned seemed

healthy, and bore no visible signs of having been in any

way injured. In no case did the halves so formed redi-

vide, although in two cases the resulting portions lived

in the laboratory for a month (Aug. 3 to Sept. 5, 1916),

during which time, even in the absence of food, missing

structures were regenerated.

In one case the process of division occupied five days;

in another, twenty-four hours. Probably it is executed

more rapidly in the field. The details of the division were

not notably different from those described by Chadwick

(1891) for Cucumaria, except perhaps in one particular.

The intestine is not drawn out between the separated

halves, as found in Cucumaria and as I have observed

in the young of H. captiva. Division begins midway of

the length of the body with a deep insinking of the ‘‘dor-

sal” bivium. A powerful circular constriction, accom-

panied by some slight local disintegration of the integu-

ment, completes the separation (Fig. 2). During the

progress of division the animal is quiescent, although it

566 THE AMERICAN NATURALIST [ Vou. LI

may be adhering firmly by its tube feet to the vertical wall

of the aquarium. When the constriction and separation

of the skin- and muscle-layers is completed, a short length

of the intestine usually remains for a time connecting the

two pieces; it may rupture close to one of them, or may

disintegrate completely. The point to be noted is, that

the resultants of the division do not move apart, but re-

main quiescent.

Lastly, after considerable searching, I found in the

field one case in which division had evidently just been

completed. The halves were still joined by an exposed

portion of the gut

On the basis of all this evidence there is certainly reason

to believe that Holothuria surinamensis, in the adult state,

normally multiplies. its numbers by a process of binary

fission. The resulting organisms readily complete their

missing parts, but probably do not undergo a second divi-

sion until after the lapse of a considerable interval, if

they do at all.

It would be of some interest to determine the nature of

the sexual products in the animals which thus result from

ivision.

AGAR’S ISLAND,

BERMUDA

REFERENCES

Benham, [W. B.] 1912, Report on Sundry Invertebrates from oe Kermadec

Islands. Trans. N. Zeal. Inst., Wellington, Vol. 44, pp. 135-138.

Chadwick, H. C. 1891. No ae on Cucumaria planci. Trans. Liverp. Biol.

0C., pp. 81-82,

Clark, H. L. 1913. pean in Lacon. Zool. Anz., Bd. 42, pp. 156-159.

Crozier, W. J. 1914. The Orientation of a Holothurian by Light. Amer.

Jour. Physiol., Vol. 36, p 0.

1915a. On the Number of Rays in cool tenuispina Lamk. at Ber-

muda. AMER. NAT., Vol. 49, 36.

19156. The Sensory Reactions of Holothuria bE Ludwig.

ete., Vol, 1, London, 286 pp., 70 i

Delage, Y., et Hérouard, E. 1903. Les échinodermes. Traité de Zool.

concrète, T. 3, x + 495 pp., 565 figs., 53 pls.

Lang, A.. 1894. Lehrbuch der TENNA Anatomie der wirbellosen

Thiere. xiv + 1197 pp., 854 Fig. Jen

Morgan, T. H. 1901. Regeneration. Sets: Univ. Biol. Ser., VII,

xii + 316 pp., 66 figs.

SHORTER ARTICLES AND DISCUSSION

AN ATTEMPT TO MODIFY THE GERM PLASM OF

(ENOTHERA THROUGH THE GERMINATING SEED

WHEN a new character appears in a homozygous race or

species it may be either a mutation or an acquired character.

If a mutation it has been produced because the germ plasm has

in some way been affected and the succeeding generations may

be expected to show the same variation. If an acquired char-

acter it will be present for a single generation and is then lost

unless the cause that produced the somatic change also modified

the germ plasm in such a manner that it may develop the same

character, in succeeding generations. By ‘‘acquired characters’’

is meant any and all changes that are wrought in the soma of

the organism by the environment considered in its broadest

sense. It is the creed of modern biology that acquired characters

are not inherited unless the environmental influences also play

on the germ cells even while focused on the body tissues, pro-

ducing at the same time potential alterations in the former and

visible changes in the latter.

The causes of mutation are in dispute. It is fairly obvious,

however, that in the reported instances of mutation the varia-

tions arose as the result of changes in the germ plasm. A muta-

tion, therefore, has its origin from within and this origin has

no very evident connection in any way with external condi-

tions. If a case of an acquired character is shown to be in-

herited it is clear that the germ plasm of the organism must —

have been affected. The stimulus to change, therefore, in con-

trast with the cause of mutation, would have come from without.

While the end result—the alteration of the germinal constitu-

tion—is the same in both cases, the method or cause by which

it is brought about is different. From this point of view, the

relative value in evolution of mutation and of hereditary

acquired characters is open to various interpretations. I think

that in the case of mutations it may soon be possible to demon-

strate that some of the so-called examples of ‘‘mutations’’ are

due to or are associated with irregularities of karyokinesis. It is

not at all inconceivable that outside conditions producing ac-

568 THE AMERICAN NATURALIST [ Vou. LI

quired characters may at the same time effect chromosome struc-

ture and behavior in the germ plasm. The cause for unusual

activity on the part of the chromosomes in either case may, how-

ever, well be totally different. :

Interesting as are the effects of natural influences on the germ

plasm, of greatest importance is the problem whether or not

modifications may be produced and controlled artificially. The

fact that experimental research is tending to show the specificity

of certain chemicals for various organisms or parts of organisms

makes hopeful the outlook for finding a specific or many specifics

that will act upon the mechanism of heredity or different parts

of that mechanism. At present our investigations can only be

empirical, trying this or that method more or less blindly. Con-

siderable work in this field has already been done. Without

entering into a full discussion of the numerous investigations,

it may be said that alcohol, temperature, humidity, ether, zine

sulphate and radium have been used in attempts to alter the

germinal constitution. Changes indeed have been produced in

some cases but the effects have been generally physiological in

nature either interfering with development or influencing

color, length of hair, ete. In all cases where the offspring re-

sembles the altered parents the results have been readily inter-

preted on the assumption that eggs or embryos are influenced

at the same time as were the forms producing them. MacDougal

reports having produced changes in one of. the cnotheras

through ovarial injections. Although it may be possible that

he produced modifications, the plant he selected for experimenta-

tion was unfortunate since the natural variability of the ceno-

theras is in most cases great, and the gametic purity of his

material was not clearly demonstrated.

In many ways plants offer the most favorable material for

the study of experimental variation. Many parts of the plant

are adapted to experimentation. The pollen may be subjected

to treatment, the ovaries may be injected with chemicals or

otherwise handled, the seeds offer themselves to various manipu-

lations, many stages of growing plants are available for experi-

mentation, a variety of experiments may be conducted and,

if there are numerous branches, controls may be maintained on

the same plant.. Coupled with these advantages are possibilities

of cultivating pure lines for many generations. It would be

difficult indeed to find an animal about which all of the above

statements could be made.

No. 609] SHORTER ARTICLES AND DISCUSSION 569

Two methods of inducing germinal variation seem practical.

The first is the treatment of the germ cells. MacDougal’s

ovarial injections lie in this class. The other method is to attack

the buds or growing points of the stems. I do not at present

believe that exact results can be expected from ovarial injec-

tions since the ovules are generally so tightly packed that fluids

can not readily circulate and it is impossible to know the quan-

tity and the strength of the fluid that may reach the germ plasm.

The treatment of pollen may offer greater possibilities unless

unforeseen technical difficulties are encountered. By subject-

ing growing points to treatment the germ plasm may more

readily be affected and the complete chromatin equipment may be

placed under the influence of the materials used. If germinat-

ing seeds or seedlings are immersed in a given chemical solution

we may have reason to expect that the cells of the growing points

are probably in contact with the solution or some derivative of it.

If the chromosomes of a growing point can be influenced it is pos-

sible that the organs that are developed from this point may be

altered.

Two years ago, in connection with a program of study deal-

ing in general with problems of development, I had the oppor-

tunity of making some experiments on seeds and seedlings of

nothera biennis L. (the Dutch biennis) from a pedigreed line

which had been inbred for at least eight generations. Mno-

thera biennis L. is one of the most stable species so far studied

in this genus and its rare ‘‘mutations’’ are known from the

research of Professor DeVries. Consequently it seemed justi-

fiable to anticipate that any results obtained through experi-

mental treatment may readily be recognized. To Dr. Bradley

M. Davis I am indebted for suggesting (nothera biennis as a

favorable plant for study, for many ‘pedigreed seeds and for

the complete freedom of his garden. Without his aid in the

study of the plants and without his advice I should have made

little progress. In preliminary studies of this sort all the in-

investigator cah hope to accomplish is to determine certain solu-

tions which produce suggestive effects. The results of my

studies are here brought together in hope that they may be of

some help to other workers.

_ As has been pointed out, studies of this character must at

present be largely empirical. The problem is to find chemicals

that will modify the structure of the germ plasm or bring about

irregularities in the distribution of the chromosomes. Some of

570 THE AMERICAN NATURALIST [ Vou. LI

the chemicals used are those frequently employed in fixing fluids;

others were selected for various reasons.

As shown in the List of Experiments the seeds and seedlings

were soaked for varying lengths of time in the solutions. The

material was either thoroughly washed before being placed on

moist filter paper in petri dishes to complete germination or

it was placed on paper which had been moistened with the same

solution as that in which the material had been soaked. Since

the seeds of Gnothera biennis are about 96 per cent. viable,

seed sterility was not an important factor in the results of the

experiments. Dr. Davis’s large cultures under normal conditions

were used as controls. About one hundred seeds were used in

each experiment.

LIST oF EXPERIMENTS

Fluids Percentage beaa Prante pesbies sooo

BOOUG ME Ce Ae eee 0.125 | Seeds 4 days 25

0.125 Seedlings| 3 S

0.625 | Seeds 29 days 40

Butyee Held: oo eke oe eae ee Seeds 34 days 40

; 0.5 Seeds 34 days 0

1.0 Seedlings| 1 day

1.0 Seeds 5 days 0

Cherm hydrate... A FS 0.75 Seedlings) 5 days

0.75 Seeds 34 days 50

0.375 s 24 days 0

0.187 | Seeds 24 days 50

Chrotic tod. seauu A 0.03 Seedlings | 11 hours

° 0.015 | Seeds 4 days 65

0.015 s 3 days 60

0.015 | Seedlings 21 days

0.015 s ays 60

Ethyl sobol.. oia a a 5.0 Seedlings| 8 days

5.0 Seeds 27 days 0

1.0 Seeds 18 days 40

0.5 Seeds s 60

0.5 Seeds 24 days 80

0.25 Seeds 24 days |A few germi-

nations

Mothyi-aloghol i o. Aa aa 1.0 Seeds 18 days Normal ger-

mination

Amylie MOURO. 0 OSS a 1.0 Seeds 18 days 0

Butylic alobal. ieo eis. Gas 1.0 Seeds 18 days 0

Propylic MOOD. ana ea es 1.0 Seeds 18 days 0

mine sulphate, i 0 hie es 10.0 Seeds 18 days eas

5.0 Seeds 18 days (A few germi-

nations

Stryhn. a ssa es Seeds 10 days

Pot. bromide and iodide......... Seeds 10 days 0

POMC MN Ce or a as 4.0 Seeds 10 days 0

0.5 Seeds 14 days 19

No. 609] SHORTER ARTICLES AND DISCUSSION 571

RESULTS

In the acetic-acid solutions mold grew vigorously and possibly

interfered with the growing plants. The percentage of germina-

tion was low. In the young plants the cotyledons were rather

more pointed than normal, although this modification was not

marked. The leaves of young rosettes also appeared more nar-

row and pointed, but these peculiarities disappeared as the

plants matured.

All the seeds and seedlings treated with butyric acid died.

Chloral hydrate produced no effect other than retarding the

period of germination, reducing its percentage, and weakening

the plants.

Chromic acid produced by far the most interesting results.

In the various solutions used germination was prompt (about

the usual three to four day period) but the percentage was

materially lowered. The seedlings produced were vigorous in

appearance, although the root system was in most cases stunted.

There was a slight though not, I believe, significant modification

of the cotyledons which were somewhat less pointed than in the

type. Some of the seedlings were bright red and practically all

had a reddish or pinkish tinge. Growth after planting was

slow but all the plants finally developed normally.

Ethyl alcohol produced no modification of structure, although

I believe that it will be worth while to continue this line of ex-

perimentation. In all cases where seeds were allowed to soak in

ethyl alcohol the solution became thick and gelatinous from a

substance extracted from the seeds. The percentage of germina-

tion was much reduced.

Methyl alcohol retarded germination but the resulting plants

were fairly normal.

Amylic, butylic and propylie alcohols all inhibited germina-

tion in the strengths employed.

_ Germination was also inhibited by the solutions of zine

sulphate, strychnine, potassium bromide and iodide and by four

per cent. ferric alum.

In general it may be said that the treatment of seeds and seed-

lings in the experiments has resulted, as in the experiments of

others, in reducing the percentage of germination or in a general

weakening of the plants rather than in specifically modifying

the germinal constitution. The results from the experiments

with chromic acid and possibly with chloral hydrate and Sia

alcohol suggest the desirability of further studies. In futu

572 THE AMERICAN NATURALIST [ Von. LI

work the concentration of the agent and the length of treatment

should be studied in greater detail.

Rosert T. Hance

BOTANICAL AND ZOOLOGICAL LABORATORIES,

UNIVERSITY OF PENNSYLVANIA,

June, 1917

CONCERNING A MORPHOLOGICAL PREDICTION FROM

DISTRIBUTIONAL DATA AND ITS SUBSEQUENT

VERIFICATION? :

ALL species of the genus Salpa are notable for their two alter-

nating generations. One, known as the ‘‘solitary’’ generation,

produces offspring by budding and the buds, when fully mature,

constitute what is known as the ‘‘aggregate’’ generation, or, as I

shall call them, zooids. Each zooid produces, sexually, one of the

solitary generation, the embryo being nourished and carried

within the body of the zooid until after it has begun to form

zooids of the succeeding generation.

The relation between the two generations, however, is not

simple; and as there seems to be a widespread misconception re-

garding this relation, it is well to correct it.

One sees the statement in much of the literature that the sol-

itary generation is asexual, that the aggregate generation is

sexual (hermaphroditic), and that the developing embryo of the

solitary form is carried within the body of its mother. Such,

however, is not the ease; Brooks having clearly demonstrated

in his classical volume ‘‘The Genus Salpa,’’ that the solitary

form is, in the most literal sense, a female while the zooid it

produces by budding is a male. In brief, the curious sexual

relationships are as follows:

The solitary form, or female, produces immature males by

budding, within the body of each of which the mother tucks

away one fully developed and ripened egg together with its fol-

licle. Before fertilization the egg is suspended by means of a

fertilizing duct, which opens into the cloaca, into one of the blood

channels of the newly formed zooid. The spermatozoa which are

_ drawn into the pharynx of the zooid with the sea-water, are swept

past this opening by the contraction of the muscles in swimming,

and some of them enter, one of which penetrates to the egg and

_ fertilizes it. The embryo, at an early stage, pushes into the

1A paper read before the Western Society of Naturalists, Friday, April

6, 1917, at Stanford University.

No. 609] SHORTER ARTICLES AND DISCUSSION 573

cloaca, carrying its wall before it, thus becoming inclosed in an

epithelial capsule. This capsule is soon cast off and, in its place,

a placenta is formed which, communicating with the blood-

channels of the zooid, nourishes the growing embryo until birth.

While the embryo projects into the cloaca it is not, at first, ex-

posed to the water, but is enclosed by an epithelial capsule and,

after its disappearance, by an embryo sae resembling somewhat

the amnion of vertebrates. Later, but still while very young,

this sac is distended and finally broken by the growing embryo

and from then until birth, the embryo is directly exposed to the

water in the cloaca, being fastened to the zooid only by the pla-

centa and a narrow band of ectoderm which connects the neck

of the placenta to the walls of the cloaca. After the embryo has

reached maturity and made its escape into the water, the testis

matures and the zooid becomes a fully developed male. Vir-

tually, then, the mother salpa gives rise, by budding, to its sons;

and each son serves first as a depository for one of its mother’s

unfertilized eggs, then as a living incubator within which its

mother’s daughter is housed and reared, and lastly as a father.

Such is, in brief, the life-cycle of the Salpe.

In Salpa democratica, to which the distributional data to fol-

low relate, and which is the tiniest of all the Salpæ, the mech-

anism of budding is as follows: Within the body of the solitary

salpa, at its caudo-ventral extremity, lies a compact intestinal

tract called the nucleus. Closely associated with it is an organ,

‘‘the proliferous stolon,’’ which by segmenting distally gives

rise to the zooids. The zooids are budded off rapidly and no evi-

dence is at hand that the stolon ever exhausts its capacity to pro-

duce them. The zooids remain attached to each other and to the

stolon in the form of a chain and, as segmentation advances, they

become crowded and pushed along a spiral path encircling the

nucleus. The stolon undergoes more or less regular periods of

segmentation and rest so that the zooids are developed in sets or

blocks, all individuals in a single block being of approximately

the same size and in the same stage of development. Each block

contains from forty to sixty-five zooids, and as there are from

three to four blocks present when the distal end of the chain is

_ready to emerge from the test-cavity to the exterior, the stolon

carries in the neighborhood of two hundred zooids at one time.

In other species the chain remains intact and attached to the

stolon after, as well as before, the zooids are protruded into the

574 THE AMERICAN NATURALIST [ Vou. LI

water, but no evidence of this relative to S. democratica is re-

corded in the literature.

During June and July, 1908 and 1909, thirty surface-net hauls

were made in the vicinity of San Diego when the temperature of

the water was between 15°.9 and 18°.3 C., and forty-six when it

was between 18°.4 and 20°.8 C. Solitary forms were captured

in greater numbers per unit volume of water filtered from the

warmer water, and zooids from the colder water. But one or

more of both solitary forms and zooids were captured from a

larger per cent. of these unit volumes in the colder than in the

warmer water. This is better shown by the following table:

TABLE SHOWING SURFACE DISTRIBUTION OF S. democratica RELATIVE TO

M AND COLD WATER

Pancake te | No. of | _ Solitary Forms Zooids

See eer eee Ee eg Abund.! | Freq?

EOE en Be Fe wey o o wo oo

E 4-20.8..........| 46° | 160 | 73 t27 l 80

These data show that, while zooids occurred in greatest num-

bers in the places they frequented the most as would be expected,

solitary forms occurred in greatest numbers in the places they

frequented the least, or, to state it differently, they were found

most often where they occurred in smallest numbers. What

does this apparent paradox mean ?

Believing that these relations must have been consequent upon

a freak result of chance or random sampling, and discovering

that only 9 of the 30 cold-water hauls were made during the night

6 p.M.—6 A.M.) while 33 of the 46 warm-water hauls were made

at night, the day hauls and night hauls were separated, and the

data concerning each were retabulated with respect to the same

two groups of temperatures. The results are given in the table

on p: 575.

Be it noted that, although the magnitudes of the differences

vary, the directions of the differences are exactly the same as

revealed by the data in the above table, i. e., solitary forms are

most abundant and least frequent in the warmer water, while 7

zooids are most abundant and most frequent in the colder water.

= Still being in the position of an unbeliever, the data were re-

1 Abundance or number of individuals per unit volume of water filtered.

2 Frequency or per cent. of unit volumes containing at least one individual.

No. 609] SHORTER ARTICLES AND DISCUSSION 575

tabulated in every practicable manner: first, by eliminating all

hauls except those made between 6 and 10 a.M.; second, by elim-

inating all except those made between 10 a.m. and 2 P.m.; third,

by eliminating all except those made between 6 and 10 P.M.;

fourth, by eliminating all except those made during June, 1909,

and fifth, by eliminating all except those made between June 12

and 30, 1909, and within a distance of approximately half a mile

of each other. But, in every case without exception solitary

forms were most abundant and least frequent in the warmer

water, while zooids were most abundant and most frequent in the

colder water. Furthermore, the frequency of solitary forms was

found to be usually identical with that of zooids. Finally, the

probability of such an identical series of relations being due to

the effects of random sampling was computed, and the odds

against it were found to be more than 1,600 to 1. Obviously,

then, the apparent paradox has a significance. What is it?

DayLicHt HAULS (6 A.M.—6 P.M.)

| Solitary Forms Zooids

Hauls | j :

| Abund. | Freq. Abund. Freq.

Cold water E e T 710 96

Warm water $cc). Bb E 158 | 86

NigHtT HAULS (6 P.M.—6 A.M.) .

Cold water bee BS ikio Bits bead) 3.81

Warm water | 33 im. AB Lop

Let a solitary form be symbolized by a cork, a zooid by an iron

weight, warm water by the surface of the ocean, and cold water

by the bottom of the ocean. Flotation is then analogous to ac-

cumulation in warm water, and sinking to accumulation in cold

water. The problem may then be restated as follows:

Since corks float and iron weights sink, what is the relation

between them that necessitates taking some corks from the bottom

of the ocean whenever a number of iron weights are taken there-

from, and that necessitates taking some iron weights from the

surface whenever a number of corks are taken therefrom?

Stated in this symbolical language, it is obvious that the only

feasible answer is that at the time the corks and iron weights

-were removed from the ocean, they were tied together. Now, if,

576 THE AMERICAN NATURALIST [ Von. LI

by experiment, we find that one cork will barely float say six

iron weights, corks with more than this number attached would

sink, while those with less attached would float. Moreover, if

those corks with more than six weights attached usually outnum-

bered those with less, while occasionally those with less far out-

numbered those with more, then both corks and iron weights

would be so distributed with respect to surface and bottom that,

while corks in the long run would be obtained in greater num-

bers from the surface than from the bottom, at least one would

be obtained in a greater percentage of bottom than of surface

hauls. In other words corks would be most abundant and least

frequent on the surface, while iron weights would be most abun-

dant and most frequent on the bottom—the exact parallel of the

distribution of the two generations of S. democratica.

he conclusion, therefore, seems unescapable that the zooids,

after being pushed to the exterior on the proliferating stolon of

the solitary salpa, remain attached to each other and to the stolon

in the form of a protruding chain.

More positive proof being mandatory, each of the seventy-six

hauls were carefully examined but, although certain statistical

facts pointed toward ithe existence of protruding chains, no two

zooids were found attached together. But, being convinced

against my own prejudice, that such chains were encountered

and broken up during the processes of towing and washing the

net, hauls of brief duration were made, and in some of them

several fragments of chains were discovered. Comparison of the

size of these zooids with that of the largest ones found within the

test-cavity of the solitary salpa proves them to have remained

attached to their progenitor for a considerable period, probably

until at least one entire block of zooids had reached the exterior.

The distributional data carry many other significant implica-

tions which can not be discussed in this limited time. Suffice it

to say that a complete report is now nearly ready for the press

and will be published in the Zoological series of the University

of California under the title ‘‘Differentials in Behavior of the

Two Generations of Salpa democratica semeei to the Tem-

perature of the Sea.’’

Ertis L. MICHAEL

Scripps INSTITUTION FOR BIOLOGICAL RESEARCH,

La JOLLA, CALIF,

THE

AMERICAN NATURALIST

Vou. LI. October, 1917 No. 610

THE MUTATION THEORY AND THE SPECIES-

CONCEPT!

R. R. GATES

Iw the early days of natural history, when the concep-

tions of special creation held sway, it was supposed that

any one could determine species who was capable of ob-

serving the differences between existing forms. Linnæus

crystallized this sentiment into the dictum that there are

as Many species as were created in the beginning, imply-

ing that any one with sufficient powers of discrimination

could determine exactly how many species there were in

each group. But with the introduction of the theory of

evolution, species came to be viewed more and more as

dynamic entities, and questions of origin have entered

progressively into the species-concept. The latter has

grown continually more complex, and yet Darwin’s an-

ticipation that systematists would cease to discuss how

many Rubi there were in Britain or how many Crataegi

in North America, has not been realized.

On the contrary, with this increase in the complexity of

the conception of species, the extreme views as to what

constitutes a species have become more and more di-

vergent, until the ‘‘lumpers’’ and ‘‘splitters’’ among sys-

tematists usually differ radically in their interpretation

of the species in a given genus. This diversity of opinion

among systematists has been partly a direct result of our

increasing knowledge of the complexity of species, de-

1 Presented at the Pacific Coast meeting of the American Association for

the Advancement of Science at San Diego, August, 1916.

577

578 THE AMERICAN NATURALIST [ Vou. LI

rived from studies of variation and geographical dis-

tribution and from the experimental study of evolution.

aranana aaa aBa na

TAAL 2 a TE

HHH aunt s

kë CECH s

s ATRA T EATE

aan poo

For dam uae io Geography, History. Civica, Kecnomics, tc. Prepared by J. Peat Gonde. Published by The Calverstty of Chicago Prom, Clone Mitata

Fic. 1

Key to Map

1. Otus asio asio (Linn.) Ridgway (= floridanus).

2. Otus asio naevius (Gmel. ay.

3. mecallit (Cassin) Ridgway.

4 hasbroucki Ridgway.

5 aikeni (Brewster) Ridgway.

6 manwelliae (Rid

7 macfarlanet (Brewster) Ridgway.

8 kennicottii (Elliot) Ridgway.

9, brewsteri Ridgway.

10. bendirei (Brewster) Ridgway.

10a quercinus Grinnell.

13. (Brewster) Ridg.

14. Otus trichopsis (Wagler) Ridg.

15. Otus vinaceus (Brewster) Ridg.

If we look for a moment first at the complexities which

have been added to the original simple concept of species,

we find all grades and kinds of difference within the

races, ending finally in the differences between single in-

ividuals. Some of these conceptions as ordinarily used

are also related to geographical distribution. To. them

No. 610] MUTATION THEORY AND SPECIES-CONCEPT 579

must be added from experimental work the conceptions

of mutants, Mendelian units, phenotypes and genotypes,

and pure lines differing only in the position of their modal

condition and requiring statistical analysis for their

demonstration.

With such an array of apparently (though not really)

conflicting concepts before him, it is small wonder that

the systematist is inclined to cast them all aside and de-

scribe his species according to his own ideas of what they

are and how they have originated. Nevertheless, for him

as for the experimentalist the question What is a species?

is more or less colored, if not determined by the question

What is its origin? How didit appear? It might be said

that the systematist should pay no attention to origins at

all, merely describing what he sees: Some systematists

doubtless adopt this plan. But obviously, for an under-

standing of the characters and relationships of species

all possible facts and conceptions bearing on their origin

should be considered, and in this way systematics may

ultimately hope to become something more than a purely

descriptive science.

If we examine the ideas which form the background of

thought of the systematist in his work of constructing

species, we find almost invariably that they are based en-

tirely upon the Darwinian conception of natural selection

by the gradual accumulation of:slight individual differ-

ences. We are then concerned to ask, Is the systematist

justified in assuming that all specific and varietal differ-

ences have originated in one way? I can find no reason

in logic or philosophy why this should be the case; and

for ourselves, we believe there is no single method of

species formation, but we think the conclusion will ulti-

mately be reached that the methods of species formation

are multiform, though certain of them are doubtless more

widespread and important than others. Among the more

important factors in speciation which we wish to consider

here should therefore be mentioned (1) local adaptation

of races through natural selection or by direct response

580 THE AMERICAN NATURALIST [ Vou. LI

to environment, (2) mutations occurring more or less in-

dependently of the environment and not necessarily of

adaptive value, (3) orthogenesis, whatever that may im-

ply. These are by no means mutually exclusive, and we

can see no reason why all, and others as well which we

have not time to consider, should not have been at work

producing the result we call organic evolution.

It is not difficult to find, particularly among birds and

mammals, instances of specifie variation giving rise to

local geographic races which are apparently the result of

response on the part of the organism to local conditions.

Again, it is easy, particularly among plants, to find vari-

eties, species and even genera which have arisen appar-

ently through sudden mutations and without anything

in the nature of adaptational response. Finally, paleon-

tology teems with apparent cases of orthogenetic

phylogeny which are not at present clearly explainable

in -terms of natural selection or mutations. Before ex-

amining concrete cases which come under each of these

categories let us diverge for a moment to consider the

effect which natural selection as a theory has had upon

biological conceptions.

We see at once that the philosophical conception of con-

tinuity took an extraordinary hold on the minds of biol-

ogists. Largely as a result of the great influence of Dar-

win, towards the end of the nineteenth century continuity

in the origin of species became almost a fetish, and all

efforts were directed to showing how every character

whatsoever might have originated through the selection

of a series of gradually intergrading infinitesimal steps.

Yet it is more than doubtful if Darwin himself would

ever have been led into such an extreme position. Biolog-

ical philosophy has thus been ridden with the conception

that if a character could be shown to have arisen in a

gradual, piecemeal fashion its origin was thereby ex-

plained or accounted for, even though natural selection

could not be shown to have operated in its development.

On the other hand, the appearance of a character sud-

No. 610] MUTATION THEORY AND SPECIES-CONCEPT 581

denly, at one step, was considered practically equivalent

to its creation by a miracle, and the type of argument in-

volving this view is still not infrequently leveled against

the mutation theory.

But where lies the necessity for assuming that either

continuity or discontinuity is universal? Surely the

matter is one to be determined by direct observation, and

not by a priori argument. The continuity concept of

origins appears not to have influenced other sciences to

the extent it has biology. True, Lyell first introduced it

by developing the doctrine of uniformitarianism in geol-

ogy. Nevertheless the geologist has continued to deal

with large and relatively catastrophic effects occurring

at irregular intervals, such as landslides, floods, earth-

quakes and volcanic eruptions. The phenomena of ge-

ological history are then continuous only in a limited

sense.

Similarly, no chemist supposes it necessary to think

that, for example, carbon and silicon were gradually dif-

ferentiated from some previous substance which pos-

sessed certain qualities of both. On the contrary he sees

his atoms built of definite units, the electrons, combined

in various ways and numbers to give a variety of prod-

ucts, the elements, which are for the most part stable

from the first. Hence, while perhaps little can be gained

for the biologist by reasoning from analogy with other

sciences, yet we at least realize that concepts of discon-

tinuity are quite as widespread in science at large as are

those of continuity, and that the origin of a character is

not explained merely by breaking it up into infinitesimal

steps through which it may not have passed at all.

Let us consider now some concrete instances. And here

we shall select chiefly cases of discontinuity, since we are

considering especially the bearing of the mutation theory

on the conception of species. In examining species and

genera of plants and animals, we find very often, par-

ticularly in plants, characters which almost certainly had

a discontinuous origin. Perhaps the majority of generic

582 THE AMERICAN NATURALIST (Vou. LI

characters in higher plants have originated in this way.

Such morphological generic characters are found in num-

bers wherever one turns. They indicate a great variety

of marked changes, in addition to those involving altera-

tion in number of parts; they most often concern the

flower structure, on which generic differences usually de-

pend; and in many cases at least they can not reasonably

be supposed to be of any special value to the plant.

If we turn to the lily family and compare the well-

known North American genera, Smilacina and Maianthe-

mum, we find the following differences:

Smilacina Maianthemum

Perianth segments 6 Perianth segments 4

Stamens 6 Stamens 4

Ovary 3-celled Ovary 2-celled

Style short and thick Style about as long as the ovary

Stigma 3-grooved or 3-lobed Stigma 2-lobed or 2-cleft

Leaves oblong or lanceolate Leaves usually cordate at base

These generic differences are almost entirely in the

number of parts in the flower. Otherwise, in foliage and

habit Maianthemum might be considered a reduced boreal

subgenus of Smilacina. Can it be doubted that Maian-

themum originated from the ancestors of certain species

of Smilacina through a mutation, in which the flowers

changed suddenly from the hexamerous to the tetramerous

condition? All these changes in flower-parts would then

have occurred at one stroke. It can not well be imagined

that they passed through a series of gradual transition

stages which have since been lost. When one remembers

the almost universal occurrence of 3-parted flowers in

Monocotyledons, this change becomes all the more strik-

ing. The whole order Crucifere, among Dicotyledons,

must have originated in the same way, through a sudden

change from pentamery to tetramery.

If we examine the species of Maianthemum and their

varieties we find evidence that similar processes of dis-

continuous variation are going on at the present time.

The genus contains three species, M. canadense in Amer-

No. 610] MUTATION THEORY AND SPECIES-CONCEPT 583

ica, M. bifolium in Europe and M. dilatatum in western

America and northwestern Asia. M. canadense differs

from M. bifoliwm chiefly in leaf-shape and in being typi-

cally glabrous. The pubescence probably was lost at one

stroke, just as numerous glabrous varieties arise. An-

other step is sufficient to account for the alteration in

leaf-form, so that two steps are ample for the transition

from one species to the other. M. dilatatum resembles

M. bifolium except for its relatively gigantic size and the

fact that it is glabrous like M. canadense. Again two

definite steps are sufficient to account for its origin.

Turning now to the geographic variations of M. cana-

dense particularly as regards pubescence, a detailed study

shows that over the greater part of its extensive range it

is absolutely glabrous, but that pubescence has appeared

especially in two localized parts of its range. A heavily

hirsute variety interius Fernald, occurs in the Black Hills

of South Dakota, an exceedingly arid region on or near

the western extremity of the range of the species. This-

variety is apparently restricted in its distribution to the

arid portion of western South Dakota, and the most rea-

sonable interpretation appears to be that it has originated

here through a marked variation, and has thus enabled

the species to extend its range into this arid region.

Further east, chiefly in Minnesota and Wisconsin, a semi-

pubescent form occurs, and this may be the form from:

which the much more marked hirsute variety arose. The

evidence, when closely examined, favors then a discon-

tinuous rather than a continuous manner of origin of this

heavily pubescent condition. ‘The condition itself is

nevertheless an adaptation, enabling the plant to survive

in extreme conditions of aridi

The monotypic genus K nikada is related to Streptopus

in much the same way that Maianthemum is related to

Smilacina. It was originally described in the ‘‘Flora

‘Rossica’’ by Ledebour as Smilacina streptopoides from

eastern Siberia. His name indicates his idea of its rela-

tionships. Baker afterwards, from plants without flowers

584 _ THE AMERICAN NATURALIST [Vou. LI

collected in Oregon, described what has proved to be the

same form under the provisional name Streptopus brevi-

with Streptopus in foliage and in fruit and seed char-

acters, differs remarkably in its flowers. They are very

small, the perianth nearly rotate, dark purple; the sta-

mens altered; and in the absence of a style the discoid

stigma rests directly on the ovary. It is possible that

connecting forms between Kruhsea and Streptopus may

yet be found in Siberia, but at any rate the differences

between these two genera can not be reasonably sup-

posed to have arisen through natural selection. Kruhsea

appears to have originated through a few definite ger-

minal changes and to have since been momen by

heredity.

` Another pair of genera which is of inwth interest in

this connection is Platystemon and Platystigma, two Cali-

fornian genera of the Papaveracee. Both occur abun-

dantly as spring flowers, occupying similar habitats.

Their main differences are as follows:

ome: Platystigma

Stamens numero Stamens 6-12

Filaments eg ji flattened ilaments narrower, flattened or

Carpels 6-20, forming a compound filiform

ovary, which in fruit breaks up by Carpels 3, forming a 1-celled, 3-

constrictions into 1-seeded joints valved or terete ovary which in

fruit forms a 3-valved dehiscent

capsule

These genera are almost exactly alike in habit, foliage,

pubescence, color of flowers and general form of the sta-

mens. They differ chiefly in the pistils, and these differ-

ences only become conspicuous as the seed capsules

mature. Platystemon has acquired numerous carpels

which are connivent or coherent in a circle. In develop-

ing, the carpels separate and their free margins cohere

with each other. Each carpel then becomes torulose by

constrictions between the seeds. How shall we account

for the origin of such a condition except through a marked

No. 610] MUTATION THEORY AND SPECIES-CONCEPT 585

variation, which is perpetuated by heredity and not be-

cause the plant has any advantage or disadvantage in life

compared with Platystigma. Only one species of Plat-

ystemon (P. californicus Benth.) and two of Platystigma

have been generally recognized, although Greene? has

described some 50 species based on minor differences.

Another significant difference between Platystemon

and Platystigma is in the variations of the petals. In

Platystemon the number varies from 6 to 10 or more, and

all the petals of a flower or a plant vary together in color

from dark yellow through light yellow to white. In

Platystigma, on the other hand, the number of petals ap-

pears to be uniformly six, and the outer three vary in

color independently of the (alternate) inner three. Thus

in Platystigma lineare Benth. (which Greene calls Hes-

peromecon pulchellum) the outer petals may be dark yel-

low, or with a more or less extensive wedge-shaped dark

yellow mark at the tip, while the inner petals are light

- yellow or white.®

The peculiarity in the carpels of Platystemon acquires

added interest from the fact that, as Lindley pointed out,*

it is by no means unique, but contraction of the sides of

the carpels, forming a torulose structure, has occurred

equally and must have originated independently in Hype-

coum of the Papaveracex, in such genera as the radishes

among Crucifere, in Ornithopus among the Leguminose,

and in other families. We may look upon this condition

as apparently the result of parallel mutation in different

families, independent of utility; and countless other cases

of a similar kind occur among higher plants.

From the few instances I have cited, which could be

added to indefinitely, and from the abundant evidence of

marked variations which we have from experiment, the

2 Greene, E. L., 1903, ‘‘ Platystemon and its Allies,’’ Pittonia, 5: 139-194,

3 A figure of P. lineare in Bot. Reg., T. 1954 (1837), from the Russian

River, Cal., shows the petals alternately yellow and white.

Another interenting point, to which Mrs, K. Brandegee has directed my at-

tention, is the abundant occurrence of tiny plants bearing a single minute

flower, intermingled with the larger plants.

4 Bot. Reg., T. 1679 (1834).

586 THE AMERICAN NATURALIST (Vou. LI

conclusion seems clear that many marked morphological

characters in plants have arisen independently of func-

tion and without the aid of natural selection. This con-

clusion is all the more probable because form is so much

more loosely tied to function in plants than in animals.

In many plants it makes little or no difference what is the

shape of the leaf so far as its chlorophyllian function is

concerned, nor what is the shape of the anthers so long as

they produce pollen.

Another matter, which I have touched upon elsewhere,®

is the geographic relationships of the most closely related

species of plants. It appears that Jordan’s well-known

law that the most nearly related species occupy adjacent

areas, although widely applicable especially to the sub-

species of mammals and birds, is by no means so generally

true in regard to plants. But we shall come to this point

again.

Referring now to animals, the North American screech

owls afford an interesting case in which two kinds of

variability can be clearly contrasted as regards their geo-

graphic relationships. These two types of variations

are (1) those in which apparently continuous or nearly

continuous variations occur progressively over certain

geographical areas, with no two forms occupying the

same area, and (2) those in which two or more sharply

marked forms occupy the same area.

The accompanying map, compiled largely from Ridg-

way’s data, shows the distribution of the various sub-

5 Gates, R. R., 1916, ‘‘On Pairs of Species,’’ Bot. Gazette, 61: 177-212.

. 1.

6 Ridgway, Robert, 1914, ‘‘The Birds of North and Middle America,’’

Bull. U. S. Nat. Mus., No. 50, Part VI, pp. 882, pls. 36.

Ridgway says (p. 683): ‘‘In the main, geographic variations [in Otus]

are more or less marked and constant; but occasionally specimens oceur in

a given area which are with difficulty, if at all, distinguishable from the form

inhabiting another—sometimes distant—geographic area.’’ He further com-

ments on the fact that, while 0. choliba in South America is remarkably

uniform over a vast area, O. asio shows great change of coloration within

relatively short distances, indicating an organization sensitive to slight

changes in the physical environment.

No. 610] MUTATION THEORY AND SPECIES-CONCEPT 587

species of Otus Asio Stephens (formerly known as Meg-

ascops asio Kaup) over the North American continent.

While such a map is only approximately accurate, it

shows that in general only one subspecies occupies a given

geographic area.’ There are, however, certain excep-

tions. Thus in Central Colorado Otus asio aikeni and

Otus asio maxwellie both occur, the former finding here

its northern limit from Texas and Mexico, the latter the

southern limit of its range from Montana. It is stated,

however,’ that they occur in Colorado chiefly at different

altitudes, maxwellie up to 6,000 ft. and aikent from 5,000

to 9,000 ft. This is the reverse of what might be expected,

since aikeni is the more southern form. But Mr. Aiken

states? that at Colorado Springs maazwellie occurs only

in winter and aikeni only in summer, indicating a slight

migration. Again, gilmani and cineraceus—the latter

somewhat darker with coarser pencilings and averaging

slightly larger in size—both occur in southwestern Ari-

zona, but, according to Swarth,’® although both birds may

occasionally be taken in the same locality, this is only in

winter when cineraceus comes down from the higher alti-

tudes to the different life zone of the hot Lower Sonoran

valleys occupied by gilmani.

The differences between these various subspecies are

chiefly in density of coloration and in size! Thus Otus

asio nevius is larger than Otus asio asio and is also lighter

in coloration, with more white on the under parts. The

subspecies mccallai in Texas and northern Mexico is in-

termediate between these in size, but is paler than either

7It may be pointed out that there is sometimes discernible a tendency for

systematists to call a form a subspecies or a species according to whether or

not it is the only form in a given area, thus making the geographical rela-

tions of the form their criterion, rather than the degree of its distinctness.

8 Cooke, W. W., 1897, ‘‘The Birds of Colorado,’’ Bull. No. 37, Agric.

Expt. Sta., Fort Collins, Colo., p. 78.

9 Cooke, W. W., 1898, ‘“‘Further Notes on the Birds of Colorado,” Bull.

No. 44, Agric. Expt. Station, Fort Collins, Colo.

10 evar, H. S., 1916, ‘‘The Sahuaro Aak Owl as a Recognizable

Race,’’ Condor, 18: 163-165.

11 I am indebted to Dr. Grinnell for permission to examine series of speci-

mens in the Museum of Vertebrate Zoology of the University of California.

588 THE AMERICAN NATURALIST [ Von. LI

and more coarsely mottled. Hasbroucki, very limited in

known range (see map), is decidedly larger and darker

than mecallii, with much less buffy gray above and

broader transverse bars. Maawellie, another northern

form, is decidedly larger but paler than aikeni. It is the

palest of all in color, with more extensive pure white than

even nevius. West of maawellie, in Washington and

Oregon, is macfarlanei, which is larger and very much

darker, almost agreeing in coloration with bendirei of

California.

The Pacific coast forms comprise an interesting series

running down the coast, beginning with kennicotti, which

occurs from Sitka through British Columbia to the south-

ern border of Washington State. It is very large like

macfarlanei, but much darker, and browner rather than

gray. The remaining subspecies extending down the

coast region and into the desert become progressively

paler and smaller. Thus brewsteri in Oregon is smaller

and less brownish than kennicottii. In California occurs

bendirei which is lighter again and smaller. Grinnell*?

has segregated from bendirei in the more arid region of

southern California another form under the subspecific

name quercinus, considered to be paler dorsally and with

less or no ferruginous markings around the head. But I.

confess that this difference, if it exists as a constant dis-

tinction, is too fine for me to appreciate. On the contrary,

specimens of bendirei from Palo Alto appeared to me

somewhat lighter on the breast than a series from Pasa-

dena. Whether or not this very close form is distinguish-

able from bendirei, the next in the series are cineraceus,

gilmani and xantusi, becoming progressively lighter with

finer vermiculations, the two former in southern Arizona

and xantusi confined to the tip of the peninsula of Lower

California, smaller and with the toes less feathered.

- Thus the subspecies appear to be arranged progres-

sively in passing from one geographic area to another,

and there is little overlapping. But this conception of

12 Grinnell, 8 1915, ‘tA New Subspecies of Screech Owl from Califor-

nia,’’ Auk, 32:

No.610] MUTATION THEORY AND SPECIES-CONCEPT 589

gradual and progressive change can be overdone when it

is attempted to correlate the alterations observed with

climatic or other environmental features. Thus the pro-

gressive lightening in color from kennicottiu to xantusi,

first by lightening and restriction of the brown until it

practically all disappears and then by paling and diminu-

tion of the gray, is believed to be associated with the de-

creasing moisture in the northern part of the range and

the increasing aridity in the south. There are of course

many well-known cases of paler races of birds and mam-

mals occupying desert areas. Yet it is not clear that the

coastal region of Oregon, where the less dense brown

brewsteri occurs, is any less humid than the correspond-

ing part of Washington where kennicotti is found. Simi-

larly wantusi on the peninsula of Lower California can

not be supposed to exist in a drier habitat than gilmani or

cineraceus. Of course in none of these cases is it known

just what feature in the environment acts as the critical

factor nor how the race responds to it. The experimental

studies of Tower!® and others show that a race may re-

spond in the same way (i. e., by showing the same vari-

ations) to different environmental stimuli or in different

ways to the same stimulus. But studies of this character

are still too few to furnish a basis for interpreting these

reactions on the part of species of the higher animals.

The experiments being carried on by Sumner'+ with the

white-footed mouse, Peromyscus maniculatus may be ex-

pected to throw further light on this important question

of the origin of local subspecies.

Again, it is not certain that such races as kennicottiu,

brewsteri and bendirei form an absolutely graded series

with all intermediates. On the contrary there appears to

. be some evidence that although their boundaries are con-

tiguous there are definite though small steps from one to

13 Tower, W. L., 1906, ‘An Investigation of Evolution in Chrysomelid

Beetles of the Genes Leptinotarsa,’’ Carnegie Inst. Publ. 48, pp. 320, figs.

31, pls. 30.

14 Sumner, F. B., 1915, ‘‘Genetie Studies of Several Geographic Races of

California Deer-mice,’’ Am. NAT., 49: 688-701, with map.

590 THE AMERICAN NATURALIST (Vou. LI

the other. This may conceivably be explained through

the principle of invasion and reinvasion. Grinnell, * who

is doing so much towards a detailed knowledge of the

Pacific coast fauna, has considered this principle and also

the part played by barriers in the development of geo-

graphic subspecies or races, in connection with the discus-

sion of many specific cases of distribution in birds and

mammals. Walter P. Tayler,!® in a recent study of the

western beavers, concludes in agreement with others, that

migration, geographic isolation with adaptation to local

ecological niches, and final reinvasion of earlier-ocecupied

localities, will account for the origin and present distribu-

tion of geographic subspecies such as we have been con-

sidering. This explanation seems as likely as any other

at the present time, but it is beyond the purpose of the

present paper to discuss these aspects of speciation in

birds and mammals. The intention is rather to show that

the problems involved are entirely different from those

concerned with another type of variability to be men-

tioned ina moment. It may be pointed out, however, that

although the theory of reinvasion as developed involves

the conception of races isolated in certain geographic

areas becoming gradually modified through environ-

mental stress and fixed before the reinvasion takes place;

that there is at the present time no definite evidence that

fixation actually takes place gradually, in this way or in

any other way. If intermediates between the various

geographic subspecies do not occur, this may be because

definite though small steps in variation are taken from

one race to the other, which would do away with the

necessity for assuming a long period of isolation during

which the gradual development and fixation of the race

15 Grinnell, Joseph, 1914, ‘‘An Account of the Mammals and Birds of the

Lower Colorado Valley, with Especial Reference to the Distributional Prob-

lems Presented.’? Univ. Calif. Publ. Zool., 12: 51-294, 9 figs., pls, 3-13,

and other papers.

16 hide Walter P., 1916, ‘‘The Status of the Beavers of Western North

ca, with a Chusldpeaition of the Pasioni in Their Speciation,’’ Ma.

Calif. Publ. Zool., 12: 413-495,

No. 610] MUTATION THEORY AND SPECIES-CONCEPT 591

occurred. However, the process does appear to be

gradual at least in comparison with the other type of

variability, which is fundamentally different in its geo-

graphic relations.

The second type of variability in Otus asio to which I

have reference, consists in the occurrence of gray and

reddish or rufous phases of coloration in the same area

of distribution. Thus all the eastern subspecies, asio,

nevius, mecallii and hasbroucki, produce both gray and

red birds. These phases are sharply marked, and inter-

mediates rarely occur. Hasbrouck!" attempted an ex-

planation of this dichromatic condition, but some of his

conclusions were justly criticized by Allen.1s The gray

phase occurs more commonly in Florida and in the north-

ern part of the range of nevius,!® while the red phase oc-

curs commonly in the Central Atlantic states, perhaps

to the exclusion of the gray in some localities. The red

phase is unknown in the western forms of Otus asio.

Nevertheless grayish and rufescent phases of the small

O. flammeolus, which is found in the mountains of western

America from British Columbia to Mexico, occur in this

region. The red phase is found also in O. trichopsis

(see map). Similarly, brown and rufous phases are

found in O. choliba which extends over a large part of

South America, and also in the Central and South Amer-

ican species O. cassini, O. guatamale, O. barbarus and O.

vermiculatus.

Owls belonging to other genera also exhibit two phases.

For example Bubo virginianus (Asio magellanicus),” the

single species of Bubo occurring in all North and South

America, with many geographic varieties, shows dichro-

matism in various parts of its range. The same is ap-

parently true of various Old World owls.

17 Hasbrouck, E. M., 1893, ‘‘ Evolution and Dichromatism in the Genus

Megascops,’’ AMER. NAT., 27: 521-533, 638-649, 4 maps.

18 A (llen), J. A., 1893, Auk, 10: 347-351.

19 Oberholser, H. C., 1904, ‘‘A Revision of the American Great Horned

Owls,’? Proc. U. S. Nat. Mus., 27: 177-192.

20 The red phase is stated by Allen to be rare in Maine.

592 THE AMERICAN NATURALIST [Vou. LI

Dichromatism is then, both geographically and sys-

tematically, a widespread phenomenon in owls. The red

phase appears to be quite independent of geographic

locality in its origin. Hasbrouck attempted to show with

regard to Otus asio that the red phase had arisen gradu-

ally from the gray, which it was slowly supplanting in

certain areas. He believed that the grays inhabited

regions of greater humidity (Florida, northern range of

nevius) and the reds the drier interior, yet grays occur

in Florida and reds are found, though uncommonly, in

Maine. He also reported reds as occurring exclusively

in the relatively humid Mississippi valley. But, as Allen

pointed out, any such correlation with climatic or environ-

mental factors hopelessly breaks down because both types

are found indiscriminately over at least the greater part

of the eastern range. All writers agree that the two types

of plumage are independent of age, sex or season, and

that in many localities at least both occur together and

freely interbreed. Hasbrouck states, however, that gray

males far outnumber red males, while red females out-

number gray females 4:1. Confirmation of this point is

to be desired, as it suggests sex-linkage of the red con-

dition. It is further stated that on the continent of

Europe the red owls are said always to be females and

the grays males.

All young birds of Otus asio are gray in the down, the

red first appearing in the feathers. Observations go to

show that red birds mated with red may give (1) all red

offspring, (2) all gray, or (3) both red and gray. When

one parent is red and the other gray, the same three re-

sults may follow. Further, Hasbrouck claims that gray

gray gives always only gray young. This is probably

true, but since the result is based on observation of only

six matings of this kind in regions where reds occur, it is

much to be desired that further observations on this point

should be recorded.

The obvious hypothesis to explain ee facts is that

the red phase appeared as a mutation from the gray, and

No. 610] MUTATION THEORY AND SPECIES-CONCEPT 593

that it is inherited as a simple Mendelian dominant char-

acter. The results of the various matings between red

and gray would then be as stated above, according to

whether the red parent were homozygous or heterozygous,

but the offspring from red X red should seldom be all

gray, since this would be only a chance result when both

parents were heterozygous. It is not impossible, how-

ever, since the screech owls usually have only three or

four young in a nest, or sometimes only two.

Since the red phase occurs in various species as well as

subspecies it is not improbable that it has originated

through independent variations in different species. In

any case the geographic ranges of the red phases show

that, having appeared as variations, they are inherited

without any conspicuous advantage or disadvantage in

competition with the gray. The present frequency of the

reds in certain areas and their infrequency in others may

be merely an indication of the localities where the original

mutations took place, and from which as centers they

have gradually spread.

Although the western forms have no red phase, yet

Otus asio kennicottii exhibits in addition to its usual

tawny-brown phase a relatively rare gray phase. This

fact is indeed an argument favoring the assumption that

the brown phase of Kennicottii also arose at one step and

has since nearly supplanted the original gray form.

If now we compare the two types of variability that I

have described in Otus asio, we find them sharply con-

trasted in several respects: (1) the former is clearly re-

lated to geographical distribution, a single race occurring

in each locality: the latter has no such relation, but two

forms may occur interchangeably in the same place; (2)

the former is essentially continuous as a form of vari-

ation, the latter markedly discontinuous; (3) the former

appears to be related to environmental (climatic) con-

ditions, the latter apparently bears no such relation. As

regards their evolutionary significance, there can be little

doubt that the former or apparently continuous type of

594 THE AMERICAN NATURALIST [ Vou. LI

variations is more important in this case, for they appear

to have given rise to the geographic subspecies now recog-

nized, and, moreover, the specific differences in the genus

are merely an exaggeration or intensification of the kinds

of difference shown by these subspecies. It seems evi-

dent, then, that the differentiation which has gone on in

the evolution of the genus Otus is for the most part of the

kind exemplified by the small differences now existing be-

tween geographic races or subspecies occupying different

areas.

The same thing is true of many other birds and mam-

mals, but this condition is by no means universal even in

these groups of animals. On the contrary, it is not diffi-

cult to find instances in which the discontinuous type of

variation, independent of environment or function, has

been the main factor in speciation. I will merely mention

the case of the North American flickers, Colaptes auratus

and C. cafer, set forth by Bateson,” since the latter is a

Californian bird. These species differ remarkably in

their color markings, the most conspicuous differences

being (1) yellow or red quills, (2) a black or a red malar

strip in the males, (3) the presence or absence of a scarlet

nuchal crescent in males and females. C. auratus pos-

sesses the first of each pair of characters and C. cafer the

second. C. auratus extends from Alaska diagonally across

Canada and the United States to Texas and eastward to

the Atlantic, while C. cafer occurs in its pure form from

Oregon through Utah, California and Arizona into

Mexico. Each possesses 3 or 4 geographical subspecies.

Where the ranges of the species overlap over a large area

a mixed population of forms occurs which is usually in-

terpreted as a series of complex hybrids, but this will

bear further study. It is clear, however, as Bateson

points out, that the differences in range of the species

can not be associated with any constant environmental

difference in the habitats, and that the species can not

have differentiated from this mixed population of inter-

21 Bateson, W., 1913, ‘‘ Problems of Genetics,” Yale Univ. Press, p. 146.

No. 610] MUTATION THEORY AND SPECIES-CONCEPT 6595

mediate forms. However these species originated, they

can not be reasonably supposed to have developed through

gradual adaptation, but the color differences probably

play no more part in the economy of the species than is

the case with the red and gray phases of the screech owls.

Something in the germinal organization of Colaptes

doubtless determines the definiteness of its color patterns,

and it is probable that each element of the pattern was

changed by a marked step rather than through a series of

gradual stages. This view is strengthened by the fact

that a third species, C. chrysoides in Lower California, is

essentially a cafer with yellow instead of red quills.

Thus even in birds our second type of variation, non-

adaptational and not related to local conditions, is appar-

ently an important factor in speciation, although in

Colaptes too geographical races occur as well. In dis-

tribution also these species do not follow the rule for

geographic subspecies, for they overlap over large areas.

The fact that each species has its own geographic sub-

species shows that the origin of these species antedates

the development of their geographic varieties.

I have endeavored to show that in plant and animal

species there are two distinct types of variability, having

different geographical relations. The one is discon-

tinuous, independent of environmental or functional in-

fluence, and has given rise to many specific and generic

characters, notably in plants but also in higher animals.

The other is continuous and apparently represents the

results of the stress of the environment on the species in

its dispersal, leading to the gradual differentiation of

local races or subspecies whose peculiarities are ulti-

mately intensified and fixed. The latter type of specia-

tion is notably exemplified in birds and mammals, organ-

isms in which, unlike plants, the individuals can migrate

from place to place and so substitute for a stress result-

ing from overpopulation an environmental stress caused

by a new set of climatic or physiographic conditions.

FURTHER OBSERVATIONS ON THE EFFECTS

OF ALCOHOL ON WHITE MICE?

L. B. NICE

In a former paper (711) it was found that white mice

were not markedly affected when given alcohol in their

food. Since this paper appeared Stockard (’12, 713, 716)

has brought forth some striking and conclusive results

demonstrating that guinea pigs are very sensitive to

alcohol and decidedly injured by it. He administered the

alcohol to his animals through the lungs by placing them

in a tank containing alcohol at the bottom so that they had

to inhale the fumes. His work raised the question as to

whether similar results might be obtained with white mice

by using the same method. Therefore it was decided to

repeat my experiments, using the inhalation method.

For these experiments white mice eleven weeks old

were obtained. They were all from one strain inbred to

the fourth generation, two entirely distinct strains having

been united to form this strain.. They were divided into

four lines, viz., a control line, a double alcohol line, that is,

both males and females were subjected to alcohol, a female

alcohol line and a male alcohol line. There were three

cages in each line, each cage contained two females and

one male, thus making six females and three males in each

line. Two cages were made up of second generation al-

coholized mice; both males were from the male alcohol

line, two females from the same line and one female from

the female alcohol line. The same cages were used as in

my former experiments. They were made of 8-mesh wire

and were 6 inches wide, 6 inches deep and 12 inches long.

The mice were kept in a laboratory room heated by

steam. It was attempted to keep the room at a uniform

temperature, but fluctuations occurred.

1 From the Laboratory of Physiology in the University of Oklahoma.

or a review of the literature see Nice (’11 and 12). Also Stockard

(712, °13 and ’16),

596

No. 610] ALCOHOL AND WHITE MICE 597

All the animals were fed the same food, consisting of

wheat and kaffir corn with bread and milk once a day.

Every day except Sunday the double alcohol line, par-

ents and young, the males of the male alcohol line, the

females and young of the female alcohol line and the sec-

ond generation of alcohol mice with their young were

placed in a galvanized tank 26 inches long, 20 inches wide

and 14 inches deep. Alcohol had been poured on to cotton

which was placed under a wire mesh situated about 2

inches from the bottom of the tank, so the mice had to

breathe the fumes. The mice were kept in the tank each

day until they became intoxicated, as shown by their stag-

gering gait or inability to stand up. At the beginning of

the experiment the time necessary to intoxicate them was

about one hour. Later they would often be kept in the

tank for two hours. This shows that the mice acquired a

tolerance for alcohol. This tolerance was shown after they

had been treated about a month. To make sure that the

mice were being heavily alecoholized, a few times they

were left in the tank so long that they would not recover

from the effects for three or more hours, and in some

cases they did not recover from the intoxication, but died.

At the beginning of the experiment when the mice were

placed in the aleohol tank they would sneeze, their eyes

water and they would rush about in their cages, showing

great uneasiness. Later they ceased to be so much dis-

turbed, yet during the course of the experiment there was

no indication that the mice liked the aleohol fumes.

THE WEIGHT oF THE ADULT MICE

The adult mice were weighed at the beginning of the

experiment and once each month thereafter, to get an in-

dication as to their health. Since they were nearly the

same age and closely related, their average weights would

be expected to be about the same unless the alcohol treat-

ment had an injurious effect on them. By referring to

Table X, it will be seen that there is only a slight dif-

ference between the various lines. The average weight

598 THE AMERICAN NATURALIST [ Vou. LI

of the mice not treated with alcohol was 22.4 grams and

of those treated with alcohol 21.8 grams.

TABLE I

AVERAGE GAINS oF ADULT MICE

Those Not Given Alcohol

Average g Average

Line Sex No.of Mice| Gain in |No.ofMice| Gain in

Weighed | Gramsat4| Weighed | Grams at 7

Months Months

Control Male 3 4.6 3 4.9

Co ki. Female 6 4.3 6 9.3

Male alcohol Female 6 | 4.3 6 6.4

F le al Male 3 5.8

Average gain of all mice not given

alcoho! poas piue 15 7.2

TABLE II

AVERAGE GAINS OF ADULT MICE

Those Treated with Alcohol

Average Average

Line No. of Mice Gain in No. of Mice} Gain in

Sex Weighed Forks paa at Weighed Grams at

4 Months 7 Months

Double alcohol.................| Male 3 Hed 1 4.0

Double alcohol................. Female 8 4.8 2 4.2

Male alcohol wiiiis. a E Male 3 3.0 3 3.5

Female alcohol................! Female 4 3.5

Average pain of all mice given alcohol) 18 3.9 6 3.8

Tables I and II give the average gain of the different

lines for four months and for seven months. The mice

that did not receive alcohol gained more than those that

were treated; the former gaining 4.6 grams on an average

for four months and the latter 3.9 grams; in seven months

the untreated mice ening 7.2 grams and the alcoholized

3,8 grams. |

-Itis possible that dia Fasihi of the mice and the extra

exercise they took in the excitement of being alcoholized

might account in part for their growing less than the un-

treated mice. In the 1911 experiments the control mice

carried 7 months gained only 2 grams on an average while

the alcohol mice gained 6 grams; in the second generation

carried four months the controls gained 1 gram each and

No. 610] ALCOHOL AND WHITE MICE 599

15 ; pdi

Control line 31 mice

2 -m ao eee è , LSE alechol line 25 mice

-e 6 a comes § Femsle alcohol line 21 mice

w =n ass aw ane Double alcokol line 13 mice

| ;

-m = æ eee = æ Seconåd generation alcohol line ll stice

o 0 | 2 3 4 5 4

Fic. 1. Curve showing the growth of the mice. The abscissas — the

age of the mice in weeks and the ordinates their weights in gram:

600 THE AMERICAN NATURALIST [Vou. LI

the alcohol mice 2 grams. In that case the alcohol was

given in the food and water and apparently had a fat-

tening effect. None of those animals were handled except

for weighing them.

- Recorps oF THE Young oF HacH FEMALE

A record was kept of the young of each female. Many

of the young in each of the lines were eaten by their par-

ents, Tables III to VIII show the number of months each

female was carried; the number of litters each had; the

total number of young born, and the number that died ap-

parently from lack of vitality.

TABLE III

RECORD OF THE YOUNG OF EACH FEMALE CoNTROL LINE

Female No. of Mo. 3 No, of Young | No. of Young

ove ti * Born That Died

sheath

eO | ped ph poa eee Y jet

Total F;

TRANW AUR OS

o;joooooooeo

wej ORAS

ee oO

* Females G and H are second generation controls.

TABLE IV

MALE ALCOHOL LINE

Female ane | O ee | 7e on ate Taai

Aiai Canai 7 2 12 1

B 7 1 12 0

Chae 7 2 10 0

D ‘ 7 1 3 3

E 7 1 5 0

Mas | bi 3 24 0

eine | 7 o | a 4

No. 610] ALCOHOL AND WHITE MICE 601

TABLE V

FEMALE ALCOHOL LINE

No. of Mo. No. of Y No. ot Y

sven p Saio | OM Mie T That Dien

A 4 1 7 0

B 4 1 7 0

G 4 2 12 3

YS soa 4 2 15 1

E 2 0 0 0

F. 2 0 0 0

aa A A A O R 6 41 | 4

2:2 |

Note.—Females A, B, C, and D were killed by being left in the alcohol

tank too long. Females E and F were killed by accident.

TABLE VI

DOUBLE ALCOHOL LINE

Female ` pores i No. of Litters oig Haag na oer

4 4 | 1 5 0

B 4 | 1 7 0

a 9 | 0 0 0

D 9 | 3 20 0

p 4 | 2 15 z

F PE N 15 0

G 4 | i 5 1

T 4 | 1 6 2

Total ee a i. 73 5

2:9 | j

* These mice from A to F were left in the alcohol tank so long one day

that only C and D survived the experience. After this accident one more

cage, G and H, were made up from the original stock.

TABLE VII

SECOND GENERATION ALCOHOL LINE

Hoot. No. of

specs Mo. Observed | NO of Litters i aa Bom |. That pied”

A 23 1 6 1

B 24 1 10 0

g. 23 1 9 0

TOMS... SOLE 24 3 25 1

VIABILITY OF THE Youna

Table VIII shows the number of litters and the number

of young born in each line; also the number that died from

lack of vitality.

602 THE AMERICAN NATURALIST (Von. LI

TABLE VIII

RECORD OF THE YOUNG OF EACH LINE

Summary of Tables III to VII

Mice | Months | Litters | Young Died ‘ThatDied

ice cn |

Control | | 1 4 9} AT 0 0

aS 3 |

Male alcohol E. 7 10 | 66 4 6

Female alcohol.................... | 4 + 6 | 41 4 9.8

Double alcohol....,.............0+. | { 6 > ake! 13 we be

Second generation alcohol...... | 3 24 Se ce 1 4

As in my former experiments none of the control young

died of lack of vitality. The alcohol lines show a small

percentage of deaths—4 mice or six per cent. in the male

alcohol line, 5 mice or 6.8 per cent. in the double alcohol

line and 4 mice or 9.8 per cent. in the female alcohol line.

The second generation alcohol lines had 1 death or 4 per

cent. of all of their young. In the former experiments

(711) the fatalities were somewhat greater—9 young or

11.1 per cent. in the first generation of aleoholized mice

and 7 young or 12.5 per cent. in the second generation.

Stockard (716), with his guinea pigs, had a fatality of 43

per cent. in the male alcohol line, 52 per cent. in the female

alcohol line, 46 per cent. in the double alcohol line and 16

per cent. in the control line.

FECUNDITY

Table IX gives the average number of litters, average

number of young, and average number in a litter for one

female of the control line and one female of the male

alcohol lines for seven months; for one female of the

female alcohol line and double aleohol line for 4 months;

and for the second generation alcohol line for 24 months.

On account of the difference in the length of time the

different lines were carried, it is impossible to make a

direct comparison. However the greater fecundity of all

the alcohol lines over the control line is striking. Though

No. 610] ALCOHOL AND WHITE MICE 603

TABLE IX

FECUNDITY OF THE DIFFERENT LINES

Average of One Female of Each Line

tne | Months | Average in |Average No.|Average No.

Observed a Litter of Litters of Young

Control | 7 | 5.1] 1.3 6.5

ale alcoho Ei 6.6 1.66 11.0

Female alcohol pona 6.83 1.5 10.25

Double alcohol | 4 6.5 1.4 9.3

Second generation alcohol | 24 8.3 1.0 8.3

the control mice were carried longer than any line except

the male alcohol line, they have next to the lowest num-

ber of litters—the lowest being the second generation

alcohol line carried only one third as long as they. They

have the fewest young of all the lines and the smallest

litters. The male alcohol line can be compared directly

with the control line since they were both carried seven

months. They have somewhat larger litters, somewhat

greater average number of litters and nearly twice as

many young as the controls. It is not possible to compare

them directly with the lines that were only carried four

months, but since the averages of these lines are almost as

high as those of the male alcohol mice, it follows that the

male alcohol mice were not as fecund as the female alcohol

and double alcohol lines. The female alcohol mice show

the greatest fecundity of all the lines, while the double

alcohol and second generation of aleohol mice come next.

The three lines in which the females were alcoholized

were somewhat more fecund than the line in which the

males alone were alcoholized and decidedly more so than

that in which neither parent was aleoholized. These re-

sults confirm those obtained in my former work (711)

where the control mice carried 7 months had 2.2 litters or

13.3 young on an average and the alcohol mice had 2.8

litters and 16.1 young; the second generation of control

mice carried 4 months had 1.5 litters and 7.1 young,

while the corresponding alcohol line had 1.8 litters or 12.4

young. |

Why the mice had fewer young in these experiments

604 THE AMERICAN NATURALIST [ Vou. LI

than in the former is not clear. It may have been due in

part to the greater fluctuations of temperature in the

laboratory building used here. Whatever the reason, the

control mice in these experiments after the first few

months occupied themselves in growing fat instead of

having young.

Stockard’s results on guinea pigs are directly contrary

to these; his alcoholized animals had decidedly fewer

young than the control guinea pigs.

CoMPARISON OF THE GROWTH OF THE YOUNG IN THE

VARIOUS LINES

In comparing the weights in Table X and Curve I it

should be remembered that all of these young were al-

coholized except the male alcohol line and de course the

controls.

TABLE X

WEEKLY GROWTH OF THE YOUNG

3,/% r legis ie jas Fls 131%

Line BR) BA |Sa)og ney arian BE| BES tie

o 20/82 Bigsigeigeig 2o % v os

P eg (erifs\e6/g6lee RERE fa 88 | En

<"|< Ja |*8/< |< |< < |< |< EEE

'ontrols 22.6| 21.5| 31 | 1.4 2.3 3.8 49 6.6 8.7 10.2) 11.2) 11.6

Male alcohol 23.2) 24.8 25 | 1.2) 2.1 3.7, 4.8 7.4 9.3 11.1 13.1) 13.6

male 20.2) 21.4| 21 | 1.1| 2.5) 3.5| 3.8] 5.5) 7.7) 9.5) 10.3 14.3

Double EMRA EEPE 21.1| 23.7 13. 1.2) 2.6 3.5 5.9) 8.4 9.0) 10.9 11.3 18

Second generation alcohol... 13.5117 | 11/ 1.1) 2.4 3.8! 4.7' 6.4) 8.8' 11.5 14.5: 15.1

The weights of all the lines at birth and for the first

two weeks are quite similar. After that variations began.

The young of the double alcohol line surpassed all for four

and a half weeks, while the young of the female alcohol

line fell behind all the others at the beginning of the third

week and remained below up to the seventh week and at

the eighth week they were next to the highest. The young

of the control line, the male alcohol line and the second

generation of the alcohol line grew at about the same rate

up to the fifth week. At this time the weight of the male

alcohol line slightly surpassed all the others; then the

No. 610] ALCOHOL AND WHITE MICE 605 &

second generation of alcohol mice outgrew all and con-

tinued ahead until the end of the experiment. After the

sixth week there were rather wide variations and this con-

tinued as long as they were weighed. At the eighth week

the weights of the different lines stood in the following

order: second generation of alcohol mice 15.1 grams;

female alcohol mice 14.3 grams; male alcohol mice 13.6

grams; the double alcohol mice 13 grams; and the controls

11.6 grams. In my former experiments (711) the alcohol

young surpassed the controls in the rate of growth.

COMPARISON OF THE DIFFERENT LINES..

The control line had the fewest young of any of the

lines; they had no deaths from lack of vitality ; the growth

of their young was slower than that of any of the other

lines except the female alcohol line.

The male alcohol line was more fecund than the con-

trols, but less so than the other alcohol lines; their death

rate from lack of vitality was four mice or 6 per cent.; the

growth of their young was better than that of the controls

and female alcohol lines.

The female alcohol mice were the most fecund of all the

lines; their death rate was four mice or 9.8 per cent.;

their growth was even slower than the control mice until

the last week, when they made a large gain and outgrew

all but the second generation of alcohol mice.

The double alcohol mice were slightly less fecund than

the female alcohol line; five mice or 6.8 per cent. of their

young died; they grew a little faster than the controls.

For the second generation of alcohol mice, two males,

offspring of the male alcohol line, were mated with two

females, young of the same line and one female from the

female alcohol line. Thus one grandmother and all but

one of the grandfathers were alcoholized, the second gen-

eration were all alcoholized after they became adult and.

one from birth and their young also were alcoholized.

The fecundity of the second generation of aleohol mice

was high; they had one death from lack of vitality, or 4

« 606 THE AMERICAN NATURALIST [Vou. LI

per cent. of all their young, and their young grew the

fastest of all the lines.

It is a matter of regret that owing to an accident—

over-aleoholization one day—the second and third gen-

erations were not carried farther. However, as far as

they went, no injurious effect from alcohol is apparent in

fertility, nor vigor of growth, and but a small one in

viability.

From indications in our results it would seem to be

dangerous to draw far-reaching conclusions from data

obtained on a single species. Although this work was

not carried as long as it was planned, yet as it corrob-

orates my former experiments in practically every detail

it goes to prove that mice are to a degree resistant to

aleohol whether it is fed or inhaled by them. From re-

sults obtained in bacteriological laboratories it is well

known that mice are very resistant little animals, in com-

parison to sensitive animals like guinea pigs. Mice are

immune to the toxin of the tetanus bacillus. It seems

reasonable to expect that an animal which is immune to

such a virulent toxin might have a considerable degree of

resistance to the effects of alcohol.

SUMMARY

1. The white mice given alcohol by the inhalation

method gave much the same results as those that received

it in their food in my former experiments.

2. The fecundity of the alcohol mice was greater than

that of the control mice, as in my former study.

3. Six per cent. of the young of the male alcohol line,

6.8 per cent. of the double alcohol line, 9.8 per cent. of the

female alcohol line and 4 per cent. of the second gen-

eration alcohol line died from lowered vitality, while none

of the control young died. Similar results were obtained

in my former experiments, except that the alcohol line

had a higher death rate—11.1 per cent. in the first gen-

eration and 12.5 per cent. in the second generation.

4. The growth of the young of all the alcohol lines ex-

No. 610] ALCOHOL AND WHITE MICE 607

ceeded that of the controls, as in my former experiments.

The young of the second generation alcohol line outgrew

all the others.

5. There were no abortions, no still births and no mon-

sters obtained in these experiments, nor in the former.

BIBLIOGRAPHY

Nice, L. B

I9. e EAA Studies on the Effects of Alcohol, Nicotine, To-

bacco Smoke and Caffeine on White Mice. I. Effects on Re-

r 3, p. 133

pro

1912. Studies on the Effects of Alcohol, Nicotine and Caffeine on

ite Mice. II. Effects on Activity. Jour. Exp. Zool., Vol.

Stockard; C. R.

1912. An Experimental Study of Racial Degeneration in apeg

treated with Alcohol. Archiv. Internal Med., Vol. 10, p.

1913. The Effect on the Offspring of Intoxicating the Male he

and the pire Z the Defects to Subsequent Genera-

dá s. AT., Vol. 47, p. 641.

1914. A mA PA of Further onnon of Mammals treated with

i oc. Soc. Exp. Biol. and p

1916. A Further Analysis of the Hereditary Transmission of Degen-

i and Deformities by the Descendant of Alcoholized Mam-

Am. NAT., Vol. 50, p. 65.

LINKAGE IN LYCOPERSICUM

DONALD F. JONES

CONNECTICUT AGRICULTURAL EXPERIMENT STATION,

New Haven, Conn.

Tue known cases of linkage of hereditary factors in

plants are not as yet so numerous but that it seems de-

sirable to place on record all instances of this condition.

With that end in view I wish to call attention to some

scattered data obtained several years ago, before much

was known about linkage, and presented in publications

which are probably not widely circulated.

Part of the data to be considered resulted foauhs an in-

vestigation, started by Hedrick and Booth, shortly after

the beginning of the awakened interest in Mendelism,

which was designed to test the inheritance of Mendelian

characters in the garden tomato (Lycopersicum esculen-

tum Mill.). The results were published in the Proceed-

ings of the Society for Horticultural Science in 1907.

Two different crosses were studied. One cross was made

between two varieties which differed in one character

only, viz., standard and dwarf habit of vine. The other

cross was between two varieties which differed in three

characters, habit of vine, shape. of fruit and color of fruit.

It is this second cross which gives evidence that there is a

genetic linkage between the factors for habit of vine and

shape of fruit.

In this latter cross the varieties used are known under

the varietal names of Quarter Century and Yellow Pear.

The Quarter Century variety is described as having a

dwarf type of vine, red-colored fruit which is shaped like

that of the common garden varieties, i. e., more or less

spherical. The Yellow Pear variety has a standard or

spreading vine, fruit yellow in color and pear-shaped.

The first generation plants grown from this cross were

standard in habit of vine, with red-colored fruit which

differed in shape from either parent, being oval rather

608

No. 610] LINKAGE IN LYCOPERSICUM 609

than spherical, but not constricted like the pear-shaped

fruit. The second generation gave the two parental types

of fruit shape together with the heterozygous fruit shape

in approximately the ratio of 1:2:1. The actual numbers

obtained are as follows: 114 plants with fruit shaped like

the Quarter Century parent, 208 plants with fruit shaped

like that of the F, plants and 130 plants with pear-shaped

fruit. The F, shape of fruit was considered to be more

like that of the Quarter Century parent. Both types dif-

fered from the Yellow Pear shape by not having the con-

stricted neck. The non-constricted type is thus incom-

pletely dominant over the constricted.

The cross therefore received one dominant factor from

one parent (standard vine) and two from the other (red

and non-constricted fruit). Any linkage between the fac-

tors for vine habit and shape of fruit would in this cross

be a case of spurious allelomorphism or repulsion accord-

ing to the English designation of this condition.

The second generation segregated into 12 distinct cate-

gories according to the Mendelian expectancy for a tri-

hybrid where two factors show complete dominance and

one factor incomplete dominance. The actual results ob-

tained compared with the theoretical expectancies are

tabulated by Hedrick and Booth, and given here in Table I.

TABLE I

HEDRICK AND BootH’s Data SHOWING THE DISTRIBUTION OF THE F,

PLANTS FROM A CROSS IN WHICH THE PARENTS DIFFERED

IN THREE CHARACTERS

Plants Fo E

Standard vine, Fruit Quarter Century shape, red....... 48 63 9/16

yellow.....°16 213/16

Fruit Hybrid shape, re loch ins T 148 127 1/8

WOU. enc. 4s 42 3/8

Fruit Yellow Pear lat i Vinay ies 98 63 9/16

ou 29 213/16

Dwarf vine, Fruit Quarter Century shape, sie ja Gee 37 213/16

yellow ...... 13 71/16

Fruit Hybrid shape, vais a ea a ee ae 17 42 3/8

MCC cia eaves 3 141/8

Fruit Yellow Pear kerai ar E ta Sit 2 213/16

4 Parental combinations. Total..... 452 459

610 THE AMERICAN NATURALIST [ Vou. LI

From the results as given it can be seen that the plants

with the combinations of habit of vine and shape of fruit

obtained in F, which duplicated the parental combina-

tions, are more numerous than expected, whereas the two

new combinations, with respect to these two factors, are

less than expected. The writers observed these facts and

commented upon them as follows:

The percentage of plants which fall into each class are, however,

quite different from those of Mendel. This is of importance in that it

indicates the number of plants which it is necessary to grow in order to

get a plant with a certain combination of characters. Theoretically,

64 plants should have included all the combinations we secured; actu-

ally, with 452 plants there is one combination with only one representa-

tive. In place of one representative, there should have been seven.

Our results would indicate that it is necessary to raise seven times as

many tomatoes as are theoretically necessary in order to secure a desired

combination. There is apparently a method to this variation. The

tendency seems to be for the second generation hybrids to go back to the

same combinations of characters as the parents, rather than to form new

ones. Thus it will be seen that the tomato with Quarter Century fruit

on Yellow Pear vines is less than theoretical considerations alone would

indicate, while the number of tomatoes with Quarter Century fruit on

Quarter Century vines is more than theory would require; the same being

true for the yellow pear. Inertia seems to be a factor and the preserva-

tion of the status quo an object among tomatoes as among men (p. 23).

In the light of more recent investigations of factorial

linkage it is recognized at once that the above statement

fulfils the conditions of linkage between at least two of the

allelomorphic pairs concerned. Let us then examine the

data more closely to see if a clear case of linkage can be

made out.

. Since the deviations above and below the expectancies

are about the same in both the red-fruited and yellow-

fruited plants, it indicates that color of fruit is an inde-

pendent factor and that habit of vine and shape of fruit

are partially linked with frequent breaks in the linkage.

Combining the figures for yellow and red fruit and putting

the 452 plants into 6 categories instead of 12, the con-

densed results given in Table II are obtained.

1 The italics are mine.

No. 610] LINKAGE IN LYCOPERSICUM 611

TABLE II

DISTRIBUTION OF THE F, PLANTS WITH RESPECT TO THEIR HABIT OF VINE

AND SHAPE OF FRUIT

Categories Found Expected |F diE ted gomhinanone ot

Standard vine, sphericalfruit 64 84} New combination

F, fruit 188 1693 379| 339

Pear-shaped fruit 127 844 Parental combina-

tion

Dwarf vine, spherical fruit...... 50 | 28} Parental combina-

tion

F, fruit 20 56} 73| 113

Pear-shaped fruit........ 3 28} New combination

Total 452 | 452 452| 462

These figures bring out more clearly the fact that the

parental combinations are in excess while the new com-

binations are deficient when compared with the theoretical

expectations with independent assortment. Combining

the numbers of the three types of standard plants and the

three of dwarfs brings out another fact, viz.: that the

standards exceed the dwarfs far more than is to be ex-

pected. This result can not be accounted for on the basis

of linkage, because it makes no difference whether habit

of vine is or is not linked with any other factor; the ratio

of the total number of standards to the total number of

dwarfs should approach a ratio of 3:1, if the two char-

acters form a simple allelomorphie pair free from any

other complicating factors. The same deficiency of dwarfs

was noted by these investigators in the other cross re-

ported in both the F, generation and the F, generation -

from heterozygous F, plants. The numbers they ob-

tained were as follows:

Found _ Expected

Stone X Dwarf Aristocrat, F,: Standards ....2,289 2,176

! nEs Dwarfs s.ro. 61 25

Stone X Dwarf Aristocrat, F,: Standards ....1,086 1,026

Dwarfs. sssi. 382.

With regard to this Painia of dwarfs Hedrick and

Booth suggest that .

the smaller number may be due to a lesser vigor on the part of the

dwarf as compared with the standard plants, and an unconscious selec-

612 THE AMERICAN NATURALIST [Vor. LI

tion by the man pricking out the young plants from the seed boxes,

of the larger, that is, the standard plants. This point had been antici-

pated and the workmen cautioned to take the plants just as they came,

but it is against all of a gardener’s training to throw aside a good

vigorous plant and take one half the size. ;

However, in the F, plants given above, from F, segre-

gating plants, all the seeds which were planted and lived

were grown to maturity, so that the latter source of error,

of unequal sampling, was avoided. Still there was the

same deficiency of dwarfs.

Craig (1907), in the same publication, reports large

numbers of the same cross which also showed a deviation

in the second generation, of too many standard plants.

He does not state whether or not an attempt was made

to grow all the plants obtained from the seed pE

His figures are as follows:

Found Expected

Stone X Dwarf Aristocrat, F,: Standards ....2,499 2,367

Dwaris F068: 657 789

Stone X Dwarf Aristocrat, F,: Standards .... 154 155

Dwarfs ....... 52 51

Both Halsted (1905) and Price and Drinkard (1908)

give figures on the proportions of standard and dwarf

plants obtained in F, populations. I have tabulated their

data as follows:

Halsted’s Data (pp. 450-462)

Standards Dwarts

Dwarf Champion X Magnus, Py... is.. iss. 5 20

Dwarf Stone X Golden Queen, F, ................ 25 5

Dwarf Stone x Extra Early Tree, F, ..........:. 14 6

x Dwarf Champion, BP, ...........; 18 3

Total COUR. cc... seo pee dk 122 34

Prpa 6 fais 5 ook see Seeds Se ee ee yee nee 117 39

Price and Drinkard’s Data (Table XI, p. 40)

Standard Dwart |

Dwarf Champion X Red Currant ................. 21 3

Potato Leaf x Dwarf Champion ................+ 15 9

Total found ... ee) 12

Esrpocted ...... 55% 36 12

No. 610] LINKAGE IN LYCOPERSICUM 613

In these last two tabulations many of the crosses show

a deficiency of dwarfs, although the results as a whole

agree closely with expectations. However, the numbers

are too small to place much weight upon.

In connection with another investigation I have ob-

tained considerable data on the inheritance of this char-

acter, by simply growing the seedlings in flats from 6 to 8

weeks, and then counting the dwarfs and standards with-

out setting the plants in the field, as in all the previous

cases cited. It is not always possible to distinguish all of

the two types of plants, with certainty, at this stage espe-

cially, if the plants are crowded and there are many small

stunted plants. However, counting the plants at this time

removes the possibility of unequal sampling when only a

part of the seedlings are set in the field, and also the pos-

sibility of differential viability in the field. The distribu-

tions in 5 F, and 16 F, populations from heterozygous F,

plants gave the following results:

Standards |= Dwarfs

Dwarf Champion X Stone, 5 F, populations .... 1,103 437

Dwarf Champion Earliana, 1 F, population... 186 67

Dwarf Champion X Stone, 12 F, populations ... 1,707 730

Dwarf Champion X Earliana, 4 F, populations .. 571 149

COLNE COUN eker ho uy 6c eaan ay vee 3,567 1,383

TOROS C6. LEGO Uso e te sich ieee ee 3,713 1,237

Here the deviation from expectation is in the opposite

direction. There is an excess of dwarfs. It would seem

that too many of the small plants were classified as

dwarfs when they were really standards.. Two of the

above F, populations were grown longer than the others

in flats which were not so crowded, so that the errors in

classification, I believe, were more nearly overcome. The

following results were obtained:

Dwart Champion X Stone, F, .:........0052e00es 268 88

Dwarf Champion X Earliana, F; ...........++-++ 186 67

FORE SOURS Ae UE AE 454 155

614 THE AMERICAN NATURALIST [Vou. LI

From these data it seems justifiable to conclude that

dwarfness and standardness form a simple allelomorphic

pair, free from any genetically complicating factors.

I have gone to this length to demonstrate the normal

behavior of this character in order to be able to correct

Hedrick and Booth’s data according to the proportion

of dwarf and standard plants, which presumably. they

should have obtained if all the plants had been grown to

maturity, and if there had been equal viability. More-

over, whether or not the deficiency of dwarfs which they

obtained is due to unequal sampling, differential viability

or some unknown cause, there is no reason to suppose

that the cause, whatever it is, has anything to do with the

linkage between the factors for habit of vine and shape of

fruit. I have, therefore, in Table III increased the num-

TABLE III

CORRECTED DISTRIBUTION OF THE F, PLANTS WITH RESPECT TO THEIR

HABIT OF VINE AND SHAPE OF FRUIT—CHARACTERS

WHICH SHOW LINKAGE

ad Combinations of

y Characters

kei

For- Characters of F2 Plants PER

bad

A; Oo

284 New combinatio

AB.... Standard vine, oon ead Ese -m ce

95 Parental combination

Ab..... Standard vine, constricted fruit...... 7

aB.....|Dwa vine Danii. pre 70| 85121 95 Parental combination

sb... Dwarf vine, constricted fruit. ......... 3 28 ew combination

al ai ...'452 EEP SE,

ber of dwarfs to the number theoretically expected, keep-

ing the proportion of the two different kinds of dwarfs

the same with respect to shape of fruit. From Table II

it can be noted that 379 standards were obtained. The-

oretically the dwarfs should have been one third of this

number, or 126.3. There were actually only 73. This

number would have to be increased 1.73 times in order to

bring the number of dwarfs up to the expected number.

Combining both the standard and dwarf plants in two

classes each, those with and those without constricted

fruit, and multiplying these two classes of dwarf plants

No. 610] LINKAGE IN LYCOPERSICUM 615

by 1.73, the figures given in column 3 of Table III are ob-

tained. The figures in this column represent the number

of plants which presumably should have been obtained

in the four different categories, if the expected number of

dwarf plants had been obtained. .

These corrected numbers can then be compared with

the closest theoretical ratio where the gametes, instead

of being produced in the equal proportion of 1 AB:1 Ab:

1 aB:1 ab, were produced in unequal proportions (where

A and B represent the two dominant factors—standard

vine and non-constricted fruit). In this case if the

gametes were formed in the proportion of 1 AB:4 Ab:

4 aB:1 ab, the agreement between the corrected result

and the theoretical expectation is surprisingly close.

Corrected numbers ....... ron Be eos 262 9) 27 FSF :5

WOPPOCIed PALO... ore ics gute bole ae Poulos. 50.4: 25.4:° 24.2: 1

Theoretical TAGON ior VAS ocins cs awe SE 24 24 :1

(1: 4: 4: 1 gametie series)

Tt is seen that the data obtained by Hedrick and Booth

give a clear indication of linkage of the factor for stand-

ard vine with that for constricted fruit and dwarf vine

with non-constricted fruit. Frequent breaks in the linkage

occur to form the two new combinations. On the chromo-

some hypothesis the data show, in this case, that crossing

over occurs in 20 per cent. of the gametes formed.

TABLE IV

CORRECTED DISTRIBUTION OF THE F, PLANTS WITH RESPECT TO THEIR

IT OF VINE AND COLOR OF FruritT—CHARACTERS WHICH

Do not SHow LINKAGE

$ kzi 4

Bers Characters of Fe Plants ‘3 $ $3 4 TOE

mulæ a R S| #

i S oj A

‘AW..,.\Staridard vine, red hait 254 204 284 Sau otidan

Ab..... Standard vine, yellow fruit........... 85) 85 85) 95/Parental combination

aB.....| Dwarf vine, red fruit 6 85 97 95 Parental combination

ab: Dwarf vine, yellow fruit. 17, 28| 29| 31|New combination

Total 1505/505)

i | |

616 THE AMERICAN NATURALIST [Vou. LI

The data also show that there is no linkage between the

other two combinations of factors reported, viz., vine

habit and fruit color, and fruit color and fruit shape. Cor-

recting the number of dwarfs in the same way as in Table

TII the results for these two combinations of factors are

given in Tables IV and V.

TABLE V

CORRECTED? DISTRIBUTION OF THE F, PLANTS WITH RESPECT TO THEIR SHAPE

RUIT AND COLOR OF FRUIT—CHARACTERS WHICH

Do not SHow LINKAGE

Genetic p x] 3| E g

bs : 5 | Combinations of

oe Characters of Fz Plants ag 2j E ~+ A Chardenels

EA 8) al

AB....|Non-constricted, red fruit 250 254 (289 284| Parental combination

Ab...../Non-constricted, yellow fruit......... $ | 84| 95| New combination

aB..2..| Constricted, red fruit 00| 85101) 95 ‘New combination

SD. -srs Constricted, yellow fruit 30 28| 31| 31 Parental combination

| Total 459 452 R05 505!

| | EET

From these two tabulations it will be seen that the

agreement between expectation and observation, when the

number of dwarfs is increased to the number expected, is

reasonably close, and the deviation from the expected is

not such as to suggest linkage between any of these

factors.

Both Halsted, and Price and Drinkard, in the publica-

tions previously mentioned, give a large number of

crosses of tomatoes where the inheritance of many dif-

ferent characters are studied. Unfortunately, in most

cases the data are presented in such a way as to show the

inheritance of only one character pair at a time.

Halsted gives a dihybrid cross between two varieties

differing in habit of vine—standard (A) and dwarf (a),

and margin of leaf—serrate (B) and entire (b). The

2 Since habit of vine is not concerned in this cross it is, of course, un-

necessary to correct for the low number of dwarfs as in the two previous

tables. I have done so simply to show that it does not affect the goodness of

fit to any great extent.

No. 610] LINKAGE IN LYCOPERSICUM 617

cross was made in such a way that one dominant factor

entered from each parent. The numbers obtained

AB: Ab: aB:ab

OURO ree eee seks heb AN see ee cs Fhe 49:16: 13:7

Mipaeted.. ies 4,08 Fes ES. oh POT oA it 48:16: 16:5

do not indicate any linkage between these factors.

Price and Drinkard’s data indicate that there is no

linkage between shape of fruit and color of fruit in two

different crosses (agreeing with the data given in Table

V), none between foliage color and fruit color, and none

between foliage color and fruit shape. In these crosses

the numbers are too small to be sure of the conclusions

with regard to linkage. They give the results of a cross,

however, which shows complete linkage between green

foliage color and two-celled fruit, as opposed to yellow

foliage color and many-celled fruit. Only 24 F, plants

were grown, which were of two types only, duplicating

the parents.

These characters, foliage color and loculation of ovary,

can not be the expression of the same factor because many

varieties are known with these characters combined in the

other ways. In fact the majority of the common garden

varieties have green foliage and many-celled fruit.

Neither does it seem probable that these dissimilar char-

acters form a series of multiple allelomorphs as some

cases of complete linkage, for instance, cob and pericarp

colors in maize, are considered to be. Although the num-

ber of plants is small, as the writers state, it would seem

that among 24 plants at least one new combination would

appear if the factors were independent of each other.

Larger numbers of a similar cross, studied by back

crosses in the more favorable way, will probably show

these factors to be partially linked.

Crane (1915) reports a cross between varieties of toma-

toes differing in rather complex characters of inflores-

cence and fruit shape. He obtained figures which indicate

partial linkage in these characters, but states that ‘‘the

618 THE AMERICAN NATURALIST [ Vou. LI

‘numbers are not sufficiently large to form any conclusion

as to the intensity of the coupling, nor to establish the

existence of the same with certainty.’’

A number of clearly segregating characters are known

in the tomato. Halsted lists 7 alternative unit character

pairs, while Price and Drinkard give 13. However, from

their own statements in regard to the behavior of these

characters, and from my own rather limited experience

with tomatoes, the number of different character pairs

which they list should be reduced. For instance, only two

allelomorphic pairs are known for color of fruit, viz., red

and yellow flesh or endocarp, and yellow and colorless

fruit skin or epicarp, while Price and Drinkard give four,

and Halsted three, character pairs of fruit color. Different

combinations of skin colors and flesh colors give the dif-

ferent colored fruits. For example, colorless epicarp over

red endocarp gives pink-colored fruit.

TABLE VI

MENDELIAN CHARACTERS IN THE GARDEN TOMAT

(Revised from a lists given by Halsted and by Price nek Drinkard. )

Dominant | Recessive

Fruit hapt tA 1 Spherical (non-con- Pyriform (con-

tricted) stricted ) ....:-<ercesers

Fruit TEn ad e 2 | Roundish conic......... Roundish compressed..

Loculation of ovary....... 3 ilocular, Plurilocular.........-.-+

Endocarp color ............ 4 Yellow.......0.c0essseseeee

Epicarp color...... ......... 5 Yellow Colorléss ii.i Leeson.

uit surface . Smooth Pubescent.......-+-++++++°

Vine habit and leaf sur- ie tandard Bg, by E rE ty ae

ace Smoot as { Ragiss ioscan

Leaf margin.............00+ 8 cation (normal or Entire 1o potato” or

fine leat) 22s. 22622 coarse leaf )......-++++

Leaf type. 9 Pinan type... j arsa type...

Foliage color 10 T OOE E e Yellow... -reetis

Inflorescence type ®........| 11 Simple Compound. .....- -<1

It is somewhat uncertain as to the number of independ-

ent factors concerned in fruit shape. According to Crane

(loc. cit.) and Groth (1912 and 1915) there are a number

of factors and it is not always possible to distinguish be-

tween the various shapes. There is apparently a corre-

3 See Crane, 1915, p. 4

No. 610] LINKAGE IN LYCOPERSICUM ‘619

lation between the loculation of the ovary and some fruit

shapes, although not necessarily with the constricted type

of fruit. The foliage characters (Groth, 1911) are rather

complicated. Also the color of foliage and the color of

the epicarp of the fruit may be associated in the same

way that habit of vine and leaf surface are, i. e., the ex-

pressions of one factor. Dwarf plants always have a

more rugose foliage than standard plants. According to

Groth (1915, p. 17) dwarfness can not be associated with

pubescent fruit for some reason.

A list of the Mendelian genes, so far known in the

tomato, is given in Table VI.

The list is only tentative. A more detailed study of

these characters will probably necessitate further revi-

sion. Other character differences may be known and

should be added. There are, however, at least 10 plainly

segregating genes and probably more. The behavior of

6 of these with respect to their being linked or not linked

with each other, in all the 15 possible combinations,* is

known in the case of 7 of them and can be predicted for 5

others. These 15 combinations with respect to linkage

are summarized as follows:

CHARACTERS SHOWN TO BE LINKED FROM THE DATA OF HEDRICK AND BOOTH,

AND PRICE AND DRINKARD

Vine Habit, 7 with Fruit Shape, T

Foliage Color, : 10 with Loculation of Ovary, 3

CHARACTERS SHOWN NOT TO BE LINKED FROM THE DATA OF HEDRICK AND

BootH, HALSTED, AND PRICE AND KARD

Vine Habit, 7 with Endocarp Color, +

ine Habit, 7 with Leaf Margin, 8

Fruit Shape 1 with Endoearp Color, 4

Fruit Sha 1 with Foliage Color, 10

Endocarp Color, 4 with Foliage Color, 10

4 The possible number of combinations is obtained from the formula

n —

” where n? equals the total number of combinations, two at a time, be-

tween n different units but no factor can, of course, be paired with itself

and the remaining pairs are duplicated. —

620 THE AMERICAN NATURALIST [Vou LI

CHARACTERS WHICH CAN NOT BE LINKED (ON THE CHROMOSOME HYPOTHESIS

IF THE ABOVE CASES HOLD TRUE)

Endocarp Color, 4 with Loculation of Ovary, 3

Vine Habit, 7 with Loculation of Ovary, 3

Vine Habit, 7 with Foliage Color, 10

Fruit Shape, 1 with Leaf Margin, 8

Fruit Shape, 1 with Loculation of Ovary, 3

CHARACTERS WHICH MAY OR MAY NOT BE LINKED

Leaf Margin, 8 with Loculation of Ovary, 3

Leaf Margin, 8 with Endocarp Color, 4

Leaf Margin, 8 with Foliage Color, 10

Since not all the possible combinations of the 6 factors

have been tested, and 4 of the factors have not been tested

at all, either in combinations among themselves or with

any of the other 6 factors, the possibilities of linkage in

the tomato have only begun to be examined. It is note-

worthy that none of the 7 combinations which either do

or do not show linkage are at variance with the interpreta-

tion of linkage according to the chromosome hypothesis.

For instance, where one of two linked genes is unlinked

with a third, the other linked gene is also unlinked with

it. This is a necessity on the chromosome hypothesis.’

To fit the facts to the chromosome hypothesis it is only

necessary to assume that genes 1 and 7 are located in one

chromosome which we may call A; genes 3 and 10 must be

located in another chromosome, B; gene 4 must be located

in a third chromosome, C. Gene 8 can not be in A but

may be located in B, C or a fourth chromosome. With

these assumptions all the data so far obtained fall into

line and if these data are substantiated the other results

predicted must hold if the chromosome hypothesis is cor-

rect. It must be noted that many of the cases cited here

are not fully established on account of the small numbers,

and furthermore there is the possibility that what is taken

to be independent assortment may be crossing over of

about 50 per cent.

‘5 This may also be a necessity on the reduplication hypothesis or may even

be axiomatic and must hold for any and every hypothesis that might be put

forth to account for factorial coat a

No. 610] | LINKAGE IN LYCOPERSICUM 621

Since the chromosome number is comparatively low

(1m 12, Winkler, quoted after East, 1915) the tomato

is rather favorable plant material in which to study

linkage.

LITERATURE CITED

1. Craig, A. G.

1907. TE ’s Law Applied in Tomato Breeding. Proceedings of the

ety for Horticultural Science, 5: 24-27.

2. we e, M. B

1915. Heredity of Types of Inflorescence and Fruits in Tomato.

Journal of Genetics, 5: 1-11.

3. East, E. M.

1915. The Chromosome View of Heredity and Its Meaning to Plant

Breeders. AMER. NAT., 49: 457—494.

4. Groth, B. H. A.

1910. sp RE of Tomato Skins. New Jersey Agric. Exper. Sta. Bul.

228.

1911. ae is pian of Size, Shape and Number in Tomato Leaves.

and 2. New Jersey Agrie. Exper. Sta. Buls. 238

uns 9.

1912. The F, prak k of Size, Shape and Number in Tomato Fruits.

New Jersey Agric. Exper. Sta. Bul. 242.

1915. Some Results in Size Inheritance. New Jersey Agric. Exper.

Sta. Bul, 278.

5. Halsted, Byron D.

905. Report of the Botanist. New Jersey Agric. Expt. Station, pp.

423-525.

6. Hedrick, U. P., and eG rah O

1907. Mendelian Characters in Tomatoes. Proceedings of the Society

for snalin oe 5: 19-24.

7. Price, H. L., and Drinkard, Jr., A. W.

1908. Tuhetitands in Weihate Hybrids. Virginia Agric. Expt. Station,

Bul. 177.

GENETICS VERSUS PALEONTOLOGY

DR. WILLIAM K. GREGORY

American Museum or NATURAL History

ALTHOUGH the title of this article has a somewhat con-

troversial sound, its purposeis merely to discuss, in a per-

fectly frank and appreciative way, certain passages in the

recent works of two eminent geneticists, Professor Wil-

liam Bateson and Professor T. H. Morgan.

‘‘Naturally,’’ says Professor Bateson,’ in describing a

certain theoretical impasse as regards the method of evo-

lution, ‘‘we turn aside from generalities. It is no time to

discuss the origin of the Mollusea or of Dicotyledons

while we are not even sure how it came to pass that

Primula obconica has in twenty-five years produced its

abundant new forms almost under our eyes.’’

Taken in connection with other passages, this seems to

imply the belief that the present is no time to investigate

phylogenetic problems or to formulate any generalities

concerning the origin of systematic groups of organisms.

Until the facts of heredity are explained we should turn

aside from most of the major problems that engaged the

attention of the great comparative anatomists and pale-

ontologists of the nineteenth century. The origin of,

paired limbs, the origin of the vertebrates, the mutual re-

lations of the great phyla of invertebrates, and similar

phylogenetic problems in botany, all these and hundreds

more of the same category having been laid aside by the

majority of zoologists, are dead or moribund subjects

which a student of genetics had better leave in decent ob-

security. If Professor Bateson had said ‘‘I turn aside

from generalities. I have no time to discuss the origin of

the Mollusea or of Dicotyledons. I used to be interested

in such things, but now I would much rather study the

mutations of Primula obconica,’’ nobody could reasonably

object ; but when he says ‘‘we turn aside from generalities.

It is no time [for any one] to discuss the origin of the

1 Science, N. S., Vol. 40, 1914, p. 294.

622

No. 610] GENETICS VERSUS PALEONTOLOGY 623

Mollusca . . .,’’ ete., he is apparently mistaking a part

for the whole, and also confusing two fairly distinct lines

of investigation, genetics and phylogeny.

As long as museums and universities send out expe-

ditions to bring to light new forms of living and extinct

animals and new data illustrating the interrelations of

organisms and their environments, as long as anatomists

desire a broad comparative basis for human anatomy, as

long as even a few students feel a strong curiosity to learn

about the course of evolution and the relationships of

animals, the old problems of taxonomy, phylogeny and

evolution will gradually reassert themselves even in com-

petition with brilliant and highly fruitful laboratory

studies in cytology, genetics and physiological chemistry.

Very likely the fortunate few who gain some first-hand

knowledge in all these fields will realize that such prob-

lems as the origin of the Mollusea or the origin of the

Dicotyledons have as much vitality as the problem of the

origin of the earth or the problem of the phyletic rela-

tionship of man with the lower animals, `

The student of the evolution of the vertebrates may well

reserve judgment as to theories of evolution, and he must

even confess his inability to trace a detailed phylogenetic

succession except for short intervals; yet he is well as-

sured, from long experience with the paleontological

record and with the comparative anatomy of recent ani-

mals, that he can trace in a general way the history of

many groups and of many structures, and he should know

very definitely where the evidence is fairly complete and

where it is weak and lacking. In view of the wealth and de-

tailed character of the evidence (which is hardly known

except to a limited number of specialists) no competent

authority would doubt, for example, that all the races of

modern Equidæ, walking on the tips of their one:toed feet,

have been derived from three-toed Hipparion-like forms,

or that these in turn lead back to Eohippus-like forms of

the Eocene, with'four digits on each forefoot and three

on each hind foot; or'that during the Tertiary Period the

molar teeth of horses (in the broadest sense) changed

624 THE AMERICAN NATURALIST [ Von. LI

from low-crowned teeth of simple pattern into long-

crowned teeth of a complex pattern. And even in the

practical absence of paleontological evidence it is suff-

ciently established that the Cetacea, which are now of

pelagic habit and fish-like habitus, represent transformed

terrestrial or littoral quadrupeds, which at a remote epoch

were placental mammals of some sort. Nor can it be justly

doubted that birds are ‘‘glorified reptiles,’’ that bats are

volant derivatives of arboreal mammals, that teleosts

have been derived from ganoids. Detailed knowledge of

the evidence in hundreds of such cases leads the paleon-

tologist to say with considerable confidence: ‘‘this later

type of animal has probably been derived from that earlier

type; this structure has undergone such and such changes

during certain geological periods.’’

Professor Bateson is equally cold towards outworn

notions about adaptation. ‘‘Naturalists may still be

found,’’ he says,? ‘‘expounding teleological systems which

would have delighted Dr. Pangloss himself, but at the

present time few are misled. The student of genetics

knows that the time for the development of theory is not

yet. He would rather stick to the seed-pan and the in-

cubator.”’

Two very distinct ideas seem to be implied in this pas-

sage and the context, first the rejection of the supposed

principle of progressive adaptation in evolution, and sec-

ondly the idea that conclusions regarding evolution should

be limited to those in which control experiments can be

made.

As to the principle of progressive adaptation, it is an

indisputable fact that existing animals possess structures

which are highly efficient in the performance of certain

functions, e. g., the locomotive apparatus of the horse,

effective for progression over hard ground; its masti-

eatory apparatus, effective in the trituration of siliceous

vegetation. Paleontologists, after studying the phylo-

genetic history of such structures, must infer that pro-

gressive advance of structure has been influenced to a

2 Ibid., p. 293.

No. 610] GENETICS VERSUS PALEONTOLOGY 625

greater or lesser degree by environmental conditions. It

is certain that changes in the conditions of life are not

the sole causes of modification, it is highly probable that

the chromosomes are insensitive to most somatic reac-

tions to the environment; yet how can the student of the

Cetacea, who sees how thoroughly the ancestral quadru-

pedal heritage has been overlaid by the fish-like habitus,

doubt that in the end, and perhaps in some very indirect

way, the pelagic environment has conditioned the line of

evolution of the cetacean chromosomes, as it plainly has

conditioned the evolution of cetacean cytoplasm. And

when similar adaptations are produced among widely

separate stocks, it can scarcely be doubted that the similar

results are due to the similarity of the external conditions

as well as to the fundamental similarities of all cyto-

plasm and of all chromatin. Hence, without any com-

mitment as to the mode of evolution, paleontologists adopt

the principle of progressive and retrogressive adaptation

to environmental conditions as sufficiently demonstrated.

And most paleontologists would probably recognize that

the foot, for example, is just as much a part of the en-

vironment of the femur as is the medium upon which the

foot rests, in other words that evolution of a given struc-

ture is conditioned by its internal environment as much as

by external environment.

Yet such is the skepticism which sometimes results from

modern studies in genetics that I have known graduate

students who seriously doubted the reality and value of

the principle of progressive and retrogressive adapta-

tion, on the ground that, as natural selection and the in-

heritance of ‘‘acquired’’ characters had both been dis-

proved, there was no conceivable means whereby adapta-

tion could be brought about! But if these skeptics would

study for example the evolution of Triassic ganoids into

Cretaceous and modern teleosts, if they would consider in

detail the structural improvements in the locomotive ap-

paratus of teleosts, which involve the transformation of

seales into dermal rays, or of a heterocercal tail into a

homocereal tail, or if they would examine the evidence

626 THE AMERICAN NATURALIST [ Vou. LI

bearing upon the evolution of the paired limbs or upon

the evolution of the vertebrate skull, or of the carnassial

teeth of Carnivora, they would, I believe, be forced to ac-

cept the principle of the progressive efficiency of struc-

tures for special functions as at least a fruitful working

hypothesis.

A distrust of the word ‘‘adaptation,’’ which has been

in the bad company of the Lamarckian theory, is appar-

ently revealed in Professor T. H. Morgan’s ‘‘A Critique

of the Theory of Evolution’’ (1916). The author, how-

ever, apparently favors the idea of natural selection

operating upon ‘‘advantageous’’ or ‘‘beneficial muta-

tions’’ and eliminating the ‘Guiurions effects” of other

mutations. Of course if ‘‘adaptation’’ really implied an

acceptance of the Lamarckian theory it would be better

to use some such phrase as ‘‘progressive functional ad-

justment,’’ but the important point to bear in mind is that

nature has produced myriads of structures which have a

very definite functional adjustment with other structures,

in other parts of the body, or with parts of other bodies,

or with parts of the environment. And it is perfectly

plain from the evidence of comparative anatomy and

paleontology that functionally correlated parts have often

evolved together, and with definite reference to each

other, let the explanation of that fact be what it may.

Professor Morgan himself has fully recognized this fact

in his address? entitled ‘‘Chance or Purpose in the Origin

and Evolution of Adaptation.’’

The second idea which seems to be implied by Professor

Bateson, and which I have heard certain university stu-

dents express, is that phylogenetic ‘‘speculations’’ are un-

verifiable, because ‘‘control experiments’’ are not pos-

sible. By similar reasoning geological theories concern-

ing the history of the earth, archeological theories con-

cerning the history of peoples, and all historical studies

based upon internal or circumstantial evidence are equally

untrustworthy. The answer to such a theoretical objec-

tion, if it were definitely made, would be that nono s?

* Science, Vol. 31, 1910, pp. 201-210.

No. 610] GENETICS VERSUS PALEONTOLOGY 627

anatomy, geology, phylogeny, ete., are practical arts which

have to be learned by experience. Phylogenists must con-

stantly distinguish between primitive and specialized

characters, and if their experience, caution and judgment

be adequate they may be as successful as physicians are in

diagnosis. Of course physicians make mistakes and so

do phylogenists, but in the long run both succeed in sifting

the false from the true, even without the aid of direct ex-

perimentation. Nature herself often provides control ex-

periments, as when she forces animals of widely different

stocks into similar life habits, or when she takes a prim-

itive type of skull and dentition and molds them into a

wide variety of adaptive types, meanwhile preserving the

original pattern as a ‘‘control,’’ either in the form of a

‘‘living fossil,’’ persisting in a primitive environment, or

in the form of a real fossil found in Tertiary strata.

Professor Morgan makes a serious and important criti-

cism of the comparative anatomical and paleontological

doctrine that structures have been derived by progressive

continuous stages. He is evidently inclined to think that

structures have rather been derived through discontinuous

mutational stages. It would be easy, he shows, to arrange

a graded series of fruit flies belonging to distinct muta-

tions, having at the one extreme perfectly formed wings

and at the other extreme no wings at all. But this series

by no means represents the historical order of appearance

of these mutants, which are not genetically derived one

from the other, but have arisen independently. Again

(p. 13)

. .. it is easily possible beginning with the darkest eye color, sepia,

whieh is deep brown, to pick out a perfectly graded series [of races]

ending with pure white eyes. But such a serial arrangement would

give a totally false idea of the way the different types have arisen;

and any conclusion based on the existence of such a series might very

well be entirely erroneous, for the fact that such a series exists bears

no relation to the order in which its members have appeared.

‘*Suppose,’’ he continues, ‘‘that evolution ‘in the open’

had taken place in the same way, by means of discontin-

uous variation. What value then would the evidence [for

628 THE AMERICAN NATURALIST (Vou. LI

evolution] from comparative anatomy have in so far as

it is based on a continuous series of variants of any

organ?’’

. We may readily admit that if evolution in the open has

taken place through discontinuous variation, the supposed

evidence for evolution based on continuous series of va-

riants is valueless. But neither Professor Morgan nor

the present writer try to persuade students of the truth

of evolution upon the ground that supposedly continuous

series have been traced purporting to illustrate the evo-

lution of single structures. As he well intimates, the

strongest evidence for evolution is the fact that all the

widely diverse members of each group exhibit a common

heritage or ground-plan of homologous structures. When

that common ground-plan is recognized and when the

probable habits of the ancestral form are clearly per-

ceived a long step has been taken toward deciphering the

evolutionary history of the group; and it will often be

easy to decide what characters and habits have been lost

and what new ones have been acquired.

Whether we think evolution has taken place by means

of discontinuous variation or through regular progressive

and continuous series one of the chief aims of zoologists

is, or should be, to discover the facts concerning the

phyletic interrelationships of groups and the evolution of

their habits and structure. And often the chief earlier

and later stages might be recognized in spite of ‘‘discon-

tinuous variation.’’ For example, if one knew nothing

about the history of the mutant races of Drosophila it

would seem a safe inference that the apterous form had

been derived eventually from a winged type, because a

comprehensive study of Diptera in general would indicate

that wingless flies were degenerate and not primitive in

that respect. Similarly if the systematic relationships

and probable derivation of Drosophila were given due

consideration the races with imperfect eyes and those with

duplicated parts would naturally be regarded as degraded

or aberrant, rather than original or primary types; and

if many intermediate stages between ree and wingless

No. 610] GENETICS VERSUS PALEONTOLOGY 629

forms were found living at the same time in a restricted

area one might perhaps have suspected that these contem-

poraneous intermediate forms were parallel offshoots of

a normal parent stock rather than linear descendants one

of another.

It may well be true that, until it can be shown that evo-

lution ‘‘in the open’’ is continuous and not discontinuous,

all ‘‘laws’’ and ‘‘principles’’ which merely assume such

continuity are open to question. But there is considerable

evidence for the conclusion that many races of mammals

have evolved either quite continuously or by small suc-

cessive gradations. It is true that in some cases appar-

ently new and distinct forms also appear in successive

horizons, but these new forms may be immigrants from

other distribution centers‘—the little-modified descend-

ants of indigenous races being often found side by side

with their more progressive immigrant relatives.

The great collections of American Eocene and later

mammals which have been brought together by the sys-

tematic explorations of the American Museum of Natural

History are all exactly recorded as to level, so that ex-

cept in a few instances there can be no doubt whatever as

to the chronological sequence of the specimens. These

collections, numbering many thousands of specimens, are

being minutely studied by several investigators, who are

not trying to prove any theory of evolution, but are re-

cording and identifying specimens and analyzing their

observations, with such accuracy and judgment as they

may have gained from twenty years of experience in this

work.

The results of these studies, as bearing on the question

of continuity vs. discontinuity in evolution, are too ex-

tensive and complex to be summarized here, but a few

examples may serve to illustrate the kind of evidence

available and the conclusions which have been drawn in

typical instances.

Very often as we pass from lower to higher strata of

4 Matthew, W. D., ‘‘The Continuity of Development,’’ The Popular

Science Monthly, Nov., 1910, pp. 473-478.

630 THE AMERICAN NATURALIST [Von. LI

a given formation the successive species show a regular

increase in size and a progressive molarization of the

pattern of one or more of the premolar teeth. A typical

ease of this kind is recorded by Matthew*® in the genus

Cynodontomys, a small insectivorous mammal of the

Lower Eocene which is represented by three successive

species which do not overlap in time, but are separated

by small progressive differences in the premolars and

molars. Each species is represented by series of from.

ten to twenty specimens, from successive horizons of the

Bighorn and Wind River Basins in Wyoming. Another

instance of practically continuous evolution is furnished

by the Middle Eocene titanothere Paleosyops. Professor

Osborn and the present writer have observed that in this

genus the species named paludosus, major, leidyi and

robustus form a regular and nearly continuous series ex-

tending from the lower to the higher levels of the Bridger

Basin, in which the lower and upper premolars gradually

evolve toward the molar pattern. A fifth species, P. copet,

from the uppermost fossiliferous levels of the Bridger

Basin is considerably more advanced than any of its

predecessors, and is connected with them by intermediate

specimens from the nearby Washakie Basin of the same

age.

In other cases the material indicates that while some

phyla evolve at a nearly uniform rate others lag behind

at varying rates, the extreme cases furnishing the relicts

or ‘‘living fossils’’ which give so many useful hints as to

the primitive characters of a race.

Such an instance is furnished by the history of the

Eocene primates Pelycodus and Notharctus (Table I).

The oldest species, Pelycodus ralstoni, is of small size and

very primitive character. The latest species, Notharctus

crassus, is about twice as large and of very advanced

character. Many intermediate stages are known.

these P. relictus is an extremely conservative form which

has acquired only a few of the progressive characters

seen in its contemporaries.

5 Bull. Amer. Mus. Nat. Hist., Vol. XXXIV, 19, p. 470.

No. 610] GENETICS VERSUS PALEONTOLOGY 631

TABLE I

PROGRESSIVE hinian IN THE LENGTH OF THE LOWER MOLARS a IN

WER AND MIDDLE EOCENE LEMUROIDS OF THE FAMILY ADAPID

(SUBFAMILY NOTHARCTINÆ)

Data for “te Eocene species compiled from Matthew (Bull. Ame

Mus. Nat. Hist., Vol. XXXIV, 1915, p. 436. Data for Middle Eocene

species by ere and Gregory.

RIZONS pm* with two pin external cusps,

UPPER BRIDGER m! with large mesostyle, g w 7-98. 5

Bridger Basin, Wyo. || molars himdeaberenes. : adoros

P. re- N. for- an ne- ros- pug-

horer Tonm liotus mosus vape affinis Ae wanes tratus nar

a sane aar MAO 17D.» RB. o 28 Ct. AEG a 3B: 20.7

MIDDLE EOCENE

Lost CABIN

A . Notharctus nunienus N. venticolus

Aaa A Basin, 15.5 18-19.2

GRE P. tutus

3 (saa Kiin Puia N. M. :

& | Lysrre Polyeodus] frugivorus P. jarovii

3 Bighorn Basin, Wyo. ;

z ;

2i - ;

4 P. frugivorus P. jarovii

z 4 glare Aa ae

A Bighorn Basin, Wyo.| P trigonodus P. jarovii (rare)

= LOWER ape Bet

P. ralstoni

SAND CouLEE | Seales ge pm‘ with 1 external cusp

Clark’s Fork Basin, | 7° i apr hema jr without mesostyle, -

Wyo. > molars tritubercular.

* The upper levels of the Almagre of New Mexico are perhaps equivalent

to the Lysite. Granger, Bull. Amer. Mus. Nat. Hist., Vol. XXXIII,

1914, p. 207. ;

In certain cases the paleontological evidence is in-

decisive, as between the hypothesis. of successive muta-

tion in loco and the hypothesis of continuous evolution

in an unknown center of evolution followed by. discon-

tinuous immigration of later stages into the region under

observation. Such a case is described by Matthew® as

follows:

6 Bull, Amer. Mus. Nat. Hist., Vol. XXXIV, 1915, p. 316.

632 THE AMERICAN NATURALIST [Vou. LI

Osborn in 1902 pointed out the evolutionary progress observable in

the species of Hyopsodus from successive stages of the Lower and

Middle Eocene; this is in general confirmed and extended by the far

larger collections [comprising more than a thousand specimens] now

available and the somewhat wider geologic range of the genus; but it is

evident that not one but three or four phyla are present in each horizon;

the relations of the Lower Eocene species to those of the Middle Eocene

are not wholly clear, and the geological overlap of stages of each struc-

tural phylum suggests rather progressive displacement of older by

newer stages coming in from some other region, than gradual evolution

in loco. It might equally well be interpreted as the displacement of

older by newer “ mutants,” in the DeVriesian sense of the term.

However this may be, the Lower Eocene species are distinguished

from those of the Middle Eocene by the less molariform premolars, and

this is most noticeable in H. eis from fhe: lowest horizon, while

the Lost Cabin species [from the up of the Lower Eocene]

approach nearest to those of the Digar gi nii: Eocene].

Examples of this kind might be multiplied, tending to

show that the evolution of Tertiary mammals has often

been more or less continuoùs, or by small successive

changes, at least during the relatively brief geological

periods that are represented by a large series of speci-

mens from closely sequent levels of an uninterrupted

stratigraphic series. And although mutations may well

be a paleontological reality, there is little danger that ver-

tebrate paleontologists are likely to draw false inferences

regarding the history of structures and of races through

mistaking independent contemporaneous mutants for suc-

cessive stages, for the simple reason that their observa-

tions are based on long series of specimens which are ar-

ranged in their true chronological sequence, from ascend-

ing geological horizons covering the whole Tertiary

eriod.

In this connection I submit an accurate diagram (Fig.

1) by Mr. Granger, which is fairly representative of the

kind of evolution demonstrated among many, but not all,

known races of mammals during the Tertiary and Quater-

nary Periods, a period of time conservatively estimated at

4,000,000 years.

The character of the evidence tending to show that the

paleontologist is dealing with truly successive stages and

No. 610] GENETICS VERSUS PALEONTOLOGY 633

napia caballus Recent.

anes EGE oe pe

Pea complicatus Pleistocene.

-4

Hypohippus sp. Loup Fork.

_ Mesohippus sp. White River.

Epihippus uintensis Uinta.

Orohippus uintanus Bridger.

Eohippus venticolus Wind River.

Eohippus cristonensis Wasatch.

Frc. 1. ecurate outlines of lower upea aja of Equidæ. peda pank

point of mtg Pro apaidans e diameter i series, ranging ca eng hird

molar in the Wasatch species to the third oe in the modern hen After

W, pira een! gnati Mus. Nat. Hist., Vol. XXIV, Art. XV, si a ies.

1908.)

634 “ THE AMERICAN NATURALIST [ Vou. LI

not with an -arbitrarily selected series of mutants is

further illustrated in the following note by Dr. Matthew.

Of the hundreds of specimens examined no horse from the Lower

Eocene has ever been found which had any fully molariform premolars.

No horse out of the Middle Eocene has either more or less than one

molariform premolar in the lower jaw, on each side. Out of the Upper

Eocene all horses have two molariform premolars. In the Oligocene

all have three. All Oligocene and older horses have brachyodont molars

without cement. All Miocene horses are progressively hypsodont with

a progressive increase in the amount of cement. The milk teeth of

Miocene horses have almost no cement. Those of all Pliocene and later

horses are heavily cemented. At each successive stage of evolution the

cement appears at an earlier stage in the ontogeny of the tooth. These

are simply a few out of many progressive changes in the teeth, and

they are accompanied by equally clear progressive changes in the skull

and skeleton. Every one of these progressive stages is as exactly lim-

ited in time as the ones cited.

Geneticists who are examining the nature of the paleon-

tological evidence regarding modes of evolution would do

well to realize that only a small part of the available ma-

terial bearing on the subject is either exhibited or pub-

lished. The scientific staff of the American Museum of

Natural History would be very glad to exhibit to their col-

leagues the great wealth of accurate data, concerning the

chronological sequence of specimens, which has been gath-

ered during twenty years of close exploration; they would

also be pleased to place before them any of the extensive

series of specimens, sometimes amounting to several

thousands of individuals, which appear to throw light

upon the problem of continuity vs. discontinuity.

In conclusion, paleontologists can show that evolution-

ary changes have involved progressive and measurable

emphases or suppressions of earlier structures or of ear-

lier proportions (allometric evolution, Osborn); and

when the progressive emphases are manifested as focal

outgrowths they seem like ‘‘new’’ structures (rectigrada-

tions, Osborn). Paleontologists, however, are not in a

position to say which characters would be transmitted

according to the Mendelian ratio, nor can they prove what

were the cytological causes of the evolutionary changes

No. 610] GENETICS VERSUS PALEONTOLOGY 635

which they record or infer. In that direction lies oppor-

tunity for consultation with the men who study enzymes,

chromosomes, heredity and variation.

The Batesonian hypothesis that both the progressive

differential emphases or suppressions of organs, and the

focal outgrowth of new structures, have been due to a

secular, differential stopping down of inhibitory factors

inherent in the germ-cells seems to the present writer

quite consistent with the observed facts of evolutionary

change; but apparently no observations that the paleon-

tologist can make could furnish any critical tests of this

hypothesis; it therefore has for him a stimulative philo-

sophical value, but hardly constitutes a working hypothe-

sis for the discovery of new facts and principles in his

limited field.

The nature of later events being determined in part by

the nature of their precedent events, no matter how many

causal series may be interwoven in the final outcome, it

follows that paleontologists, like other historians, con-

tribute to a partial understanding of existing conditions

merely by arranging past events in their true chronolog-

ical sequence. The characteristics of existing Cetacea are

determined in part by the germinal and somatic charac-

teristics of their remote quadrupedal ancestors, as well

as by the conditions of the pelagic life into which they

somehow drifted; so too the characteristics of man, as a

bipedal, hiwanous. anthropoid Primate are determined in

part, as I believe, by the fact that the remote ancestors

of the man-greatape stock were arboreal, quadrumanous,

lemuroid Primates of the Lower Eocene.

For such reasons, I must continue to hold that ‘‘pro-

gressive adaptation’’ when cleared of all implications as

to the mode of evolution, stands for a historical and

verifiable process; that the time for developing phylo-

genetic conclusions and for revising comparative anat-

omy and classification is always now, as fast as the evi-

dence can be gathered and analyzed.

SHORTER ARTICLES AND DISCUSSION

STUDIES ON INBREEDING. VIII. A SINGLE NUMER-

ICAL MEASURE OF THE TOTAL AMOUNT OF

INBREEDING*

1. In the earlier numbers of these Studies, and particularly in

VII, methods have been given for measuring the amount or de-

gree of inbreeding exhibited in a particular pedigree by a series

of inbreeding coefficients, Zi, Za Za . . ., Zn, one for each àn-

cestral generation. The inbreeding for the whole pedigree is

indicated by an inbreeding curve, formed by plotting and con-

necting by a line the several coefficients.

2. From the earliest stages of this investigation the writer has

- been aware of the desirability of a single numerical measure, to

supplement or replace the inbreeding curve as a designation of

the total inbreeding exhibited. Such a designation has now been

found, which, it is believed, uniquely and rigorously meets the

requirements. It is the purpose of the present paper to describe

this new constant. Í

Consider Fig. 1. This gives, in the heavy line and solid circles,

the inbreeding curve for 9 ancestral generations of the Brown

Swiss bull, Saxton (2668). The values of the inbreeding co-

efficients are:

Z,.= 0, Z,=12.50, Z, = 26.95,

J. == 0; Z,=17.19, Ž, = 28.91, *

AE - B= 21.09, Z,= 29.30.

The smooth curve of Fig. 1 is the inbreeding curve for con-

tinued brother X sister mating. This represents the closest or

maximum degree of inbreeding possible in sexually reproducing

organisms.

It is clear from inspection of thin diagram, that Saxton is

much less intensely inbred in fact than he would be if in all his

ancestry the matings had been of brother sister out of brother

1 Papers from the Biological Laboratory of the Maine Agricultural Ex-

periment Station. No. 118.

2 Pearl, R., AMER. NAT., 1917, in press.

3 Cf. Pearl, R., these Studies, I. Amer. NAT., Vol. XLVII., p. 603, 1913.

No.610] SHORTER ARTICLES AND DISCUSSION 637

X sister, etc. This is evident, in the first place, because the or-

dinates of the Saxton curve, a c are nowhere as high as those of

the brother X sister curve, a b. But it would also be equally

clear that Saxton-was less inbred than the maximum possible

amount if the last ordinate at c, for example, had a value of 99.6,

as does the corresponding ordinate of the maximum curve.

COEFFICIENTS

aa ea

é é : 70 12 “4

GENERATIONS

Diagram showing the inbreeding curve of Saxton, a Brown Swiss

bull, in the heavy lines and solid circles. The smooth, light line curve is the

curve of maximum inbreeding (continued brother x sister breeding). For further

ciple nti: see text

Upon consideration it appears that the real measure of com-

parative amount or degree of inbreeding, considering the

gree as a whole, is given by the area included by the hates

inbreeding curve under discussion, as compared with the corre-

sponding area of the maximum (brother X sister) curve. Thus

in Fig. 1, Saxton is less inbred than the maximum possible

amount to an extent proportionate to the amount by which the

area T (a c d) is smaller than the area M (a b d). This con-

sideration gives us the desired method of uniquely expressing

the total amount or degree of inbreeding. It only remains to

consider practical methods of calculation. , :

3. Theoretically one should integrate the maximum (brother

X sister) curve, and the observed curve, and compare the areas

derived from such integrations. Practically this is not possible,

- because many observed curves of inbreeding can not be fitted by

638 THE AMERICAN NATURALIST [ Von. LI

any simple, readily integrable theoretical curves. We shall hence

be compelled in this case to make use of the expedient so fre-

quently employed in applied mathematical problems of all sorts,

namely, to take finite summation as a sufficiently close approx-

imation to integration. Doing so, we may take as the simple ex-

pression of total inbreeding, to and including the nth generation,

the following:

100° Fy.’ :

where 3 denotes summation of all values between the inclusive

limits indicated, and F z, is a constant having the value set forth

in Table I. Fz, is of course the total area of the maximum

brother X sister curve up to and including the n -+ 1-th genera-

tion. Since these successive values are constant they may be

tabled once for all.

TABLE I

VALUES OF F 7, THE wg soe AREAS OF THE MAXIMUM INBREEDING CURVE

Ancestral generation F. Ta

E Se oe a 4 50

e E Me gE 2 125

Be DA Vr 3 212.5

OAT ey TE P 4 306.25

Gare 5 403.125

Ree. see a 6 501.5625

AEF ay Saati, So a 7 600.78125

1 PSS iat LE E 8 700.390625

s LE EE ae N ie 9 800.19531254

EE. E Saray 10 900.09765625

ee eee eee. 11 1000.048828125

Oe oa ee ee ee 12 1100.0244140625

Pe Oy UO. s 13 1200.01220703125

1S BoE SARS 14 1300.006103515625

Bis 6 BAR oe = 15 -1400.0030517578125

In using the form of total inbreeding coefficients shown in (i)

there is one caution which must be carefully observed. This is

that only so many generations should be used as to include the

one in which the observed Z taken first reaches its highest value

for the pedigree under discussion, and not any beyond that one.

This will usually be for the earliest ancestral generation of the

pedigree, but not always. ,

#One would not, of course, use in practical calculation such excessive

numbers of decimals as are tabled from this point on

No. 610] SHORTER ARTICLES AND DISCUSSION 639

4. We may now consider some numerical illustrations. Let

us take first the bull Saxton, for which the several observed in-

breeding coefficients have already been given. We have

22 = 142.19

and hence, from Table I,

14219 ;

Zn = 800.1953 = 17.8.

Or we may say that Saxton is inbred in ten ancestral genera-

tions, taken together 17.8 per cent. of the maximum amount pos-

sible in those generations.

For comparison some other figures may be examined. Pearl

and Patterson’ have given mean values of the inbreeding co-

efficients for four groups of Jersey cattle: (a) Random sample

bulls, (b) register of merit bulls, (c) random sample cows, (d)

figures by the method here described. The results are given in

Table II.

TABLE II i

TOTAL INBREEDING COEFFICIENTS FOR JERSEY CATTLE. (PEARL AND PATTER-

son DATA)

_ Total Inbreeding Coefficients Zy,

units | Lower Limiting | Upper Limiti

venues r "alan sa Vaca

1. General population (pasaon sample) bulls| 25.39 30.48 27.94

2. Register of merit bul 24.52 29.17 31.85

3. General aserra ( wii sample) cows) 27.46 “oy 74 29.60

4. Register of merit c 20.72 27.08 23.90

From this table we see that American Jersey cattle, as judged

by random samples of the general population, are about 28 to 30

per cent. as closely inbred as the maximum possible amount,

taking account of the first eight ancestral generations as a whole.

It is not desirable to go further into the discussion of these

Jersey data, since the purpose of this note is simply an exposition

of method. This new method makes possible exact and unique

numerical comparison between pedigrees in respect of the degree

of inbreeding which they exhibit in the same i of ancestral

generations.

RAYMOND PEARL

5 Pearl, R., and Patterson, S. W., Proc. Nat. Acad. Sci., Vol. 2, p. 60,

1916.

THE

AMERICAN NATURALIST

Vou. LI. November, 1917 bi. No, G11

THE GENESIS OF THE ORGANIZATION OF THE.

INSECT EGG!

PROFESSOR ROBERT W. HEGNER

ZOOLOGICAL LABORATORY, UNIVERSITY OF MICHIGAN

I. THE COMPLEXITY oF ORGANIZATION OF THE Insect Eca

-~ 1. Introduction

THE morphological and experimental investigations of

the germ-cell cycle in insects which the writer has carried

on during the past ten years have resulted in the accumu-

lation of many data which indicate the complexity of or-

ganization of the eggs of these animals, and suggest

hypotheses regarding the nature and genesis of this or-

ganization. That the animal egg at the time develop-

ment begins does not consist of a homogeneous mass of

protoplasm, as the old theory of epigenesis required, but

is a highly organized cell containing various kinds of

protoplasm localized in definite regions has been proved

conclusively by numerous investigators working with the

eggs of many different species. The degree of organiza-

‘tion at the time of fertilization varies according to the

species of animal, but all embryologists admit that the

insect egg is one of the most highly organized of all.

The nature and genesis of the different kinds of proto-

. plasm in the insect egg is the principal problem discussed-

in the following pages. This problem is the logical suc-

cessor of those dealing with cell lineage and the organiza-

tion of the egg at the time development begins. The re-

1 Presented to the Johns Hopkins Scientific Association on October 9,

1917.

641

642 THE AMERICAN NATURALIST * [VoL UI

lations between this problem and the larger problem of

heredity and development are very close indeed. The

study of heredity is concerned not only with the adult

animal, but also with every stage in the development of

the adult since the fertilized egg, or embryo, or larva that

arises from it, is an individual just as is the fully devel-

oped animal. The organization of the fertilized egg is

the result of the processes of differentiation that take

place at each stage in the history of the egg and sperm

from the time the primordial germ cells are segregated

until the highly specialized gametes have become fully

formed. The period extending from-the formation of the

primordial germ cells to and through the growth period

of the gametes is one of the least known in the entire his-

tory of the individual. It is nevertheless a most im-

portant period, for during this time, at least in the insect

egg, the principal axes of the individual are established

and different kinds of cytoplasm are elaborated and lo-

ealized that are predetermined to form definite parts of

the embryo.

The stages in the germ-cell cycle in insects belonging to

different orders, families, genera or species are often

quite different, as is to be expected, hence the data on

which this paper is based were derived from the study of

a number of species. On this account it seems best to

give an abridged description of the germ-cell cycle in one

group and include, wherever necessary, data derived from

the study of other groups. The principal work has been

carried on with representatives of the orders Diptera,

Hymenoptera and Coleoptera, and of these, the order

Coleoptera has furnished the best material for experi-

mental purposes. We will select, therefore, the eggs of

certain chrysomelid beetles for deseriptive purposes.

2. The Structure of the Insect Egg at the Time of Depo-

sition’

At the time of deposition (Fig. 1) the beetle’s egg con-

sists largely of deutoplasm—a substance which is used

; 1 Hegner, 1909, Journ. Exp. Zool., Vol. 6.

No. 611] GENESIS OF ORGANIZATION OF INSECT EGG 648

up during the growth of the embryo.

This deutoplasm

is composed of vitelline spheres, which contain refringent

granules, the vitelline

bodies, and of oil glob-

ules. The deutoplasmic

bodies are embedded

in a viscid cytoplasmic

matrix which, however,

is very slight in amount

as compared with the

deutoplasmie material.

At the periphery of the

egg is a thin cortical

layer of cytoplasm

which is continuous with

the cytoplasm in which

the vitelline spheres lie.

A short distance back

of the anterior pole of

the egg is a thickening

of this cortical layer in

which the maturation

divisions of the oocyte

nucleus occur. The cy-

toplasm appears to be

homogeneous. except at

the posterior end, at

which place, in many

insects, inclusions have

been discovered which

appear to play a rôle in

the formation: of the

primordial germ cells.?

terior end.

= yolk. (From Hegner, 1909.)

proren, Lae

Fig, 1. Longitudinal section B ugh

an egg of Calligrapha bigsbyana four hours

` deposition. gcd = germ-cell deter-

ants. gn = germ-nuclei copulating. khb?

pepr layer of cytoplasm. p = pos-

om = vitelline bi, Yy

These inclusions in the w

somelid beetles take the form of a polar disc of granules

which I have called germ-cell, keimbahn, or germ-line

determinants.?

2 Hegner, 1909, Jou

Similar inclusions (Fig. 2) have been

Morph.,

Vol. 20.

3 Hegner, 1908, Biot, 2 Bull., Vol. 16.

4 Weisman, 18638, Zeit. f. wiss. Zool., Bd. 13; Metschnikoff, 1866, ibid.,

644 THE AMERICAN NATURALIST [Vou. LI

noted in Diptera,‘ in parasitic Hymenoptera,’ and in

Hymenopterous gall flies.6 There should also be men-

tioned in this connection minute bodies that have been

Cc Í

Fig. 2. Germ-line determinants in .the eggs of various animals. «a. Pole-

plasm (p Pl) at the posterior end of the egg of Miastor (Hegner, 1914). 0.

f. Ectosomen at end of the first cleavage spindle in the egg of Cyclops.

(Amma, 1911.)

discovered in the cytoplasm of the eggs of the carpenter

ant, Camponotus, and in those of various other insects.

Bd. 16; Ritter, 1890, ibid., Bd. 50; Noack, 1901, ibid., Bd. 70; Kahle,

1908, Zoologica, Bd. 21; Hasper, 1911, Zool. Jahrb., Bd. 31; Hegner,

1912, Science, Vol. 36; Wotan 1914, Journ. Morph., Vol.

5 Silvestri, 1906, Boll. Labor. Zool. E. Se. Agr. Portici, Vol. 1; Silvestri,

1908, ibid., Vol. 3; Silvestri, 1914, Anat. Anz., Ba. 47; Silvestri, 1915,

Boll. Labor. Zool. R. Se. Agr. Portici, Vol. 10; Silvestri, 1916, Rend. D. R.

Accad. D. Finit ci 25; Martin, 1914, Zeit. f. wiss. Zool, Bd. 110;

Hegner, 1914, Anat. Anz., Ba. 46; Hagas, 1915, Journ. Morph., Vol. 26.

6 Hegner, 1915, Journ. Morph., Vol.

eae, 1886, Festsch. nat med. Verein zu Heidelberg; Sule, 1906,

No. 611] GENESIS OF ORGANIZATION OF INSECT EGG 645

These have been considered symbiotic bacteria, but their

true nature remains yet to be definitely established.

3. Cleavage

The first cleavage nucleus of the beetle’s egg lies some-

what anterior of the center in a small island of cytoplasm

that is continuous with the cytoplasm that surrounds the

deutoplasmic bodies (Fig. 1, gn). During early cleavage

no cell walls are formed, but after each division the

daughter nuclei move a short distance apart and then

divide again. Successive divisions and migrations of the

cleavage nuclei (Fig. 3) finally result in the production of

= pole disc,

lastoderm stare. At the pésterior end are the primordial germ cells. (Heg-

ner, 1909, 1914

‘hundreds of nuclei, which come to lie just beneath the

cortical layer of cytoplasm, and are each surrounded by

an irregular mass of cytoplasm. The fusion of these

cytoplasmic masses with the cortical layer then takes

place, followed by the intervention of cell walls, thus form-

ing a blastoderm of a single layer of cells, each of which

contains a cleavage nucleus, part of the cytoplasm which

it brought to the periphery with it, and a portion of the

Stzber. bohm. Geselisch. Wiss. Prag.; Sule, 1910, ibid. ; Merceir, 1907, Arch.

Protistenk., Bd. 9; Pierantoni, 1910, Zool. Anz Ba; 36; Buchner, 1912,

Arch. Protistenk., Bd. 26; aigis, 1913, Bull. IU. St. Lab. Nat. Hist.,

Vol. 9; Hegner, 1915, Journ. Morph., Vol. 26

646 THE AMERICAN NATURALIST [Von. LI

cortical layer. Not all of the cleavage nuclei take part in

blastoderm formation, many of them remaining behind in

the yolk to aid in breaking down this substance.

4. The Origin of the Primordial Germ Cells

Blastoderm formation is interrupted at the posterior

end of certain chrysomelid beetles’ eggs by the segrega-

tion of the primordial germ cells (Fig. 4). Those cleav-

mordial germ cells entirely separated from the egg. (Hegner, 1909.)

age nuclei that encounter the granules of the pole-disc do

not produce blastoderm cells, but continue their migra-

tion and are finally cut off from the rest of the egg as

distinct cells. These are the primordial germ cells, of

which there are sixteen. Each of these cells contains a

portion of the cortical layer that includes pole-dise gran-

` No. 611] GENESIS OF ORGANIZATION OF INSECT EGG 647

ules, thus differing in content from the blastoderm cells.

- They differ also from blastoderm cells in size, being con-

siderably larger. This is probably due at first to the in-

clusion of the pole-dise granules, but later a greater dif-

ference in size is brought about by the failure of the germ

cells to divide as rapidly as do the blastoderm cells.

An early origin of the primordial germ cells in a simi-

lar manner has been described in a number of insects be-

sides Coleoptera, especially in the midge, Chironomus,’

where these cells are derived from one of the cleavage

nuclei at the four-cell stage; in the pedogenetic larva of

the fly, Miastor,? where one of the first eight cleavage

nuclei becomes the nucleus of the primordial germ cell, in

the fly, Calliphora,° and in parasitic Hymenoptera."

5. The Formation of the Ovaries

In chrysomelid beetles, Chironomus, Miastor and cer-

tain other species of insects, the primordial germ cells

undergo a multiplication period shortly after they are

formed. This is followed by a period during which they

become lodged within the embryo—either by the shifting

of the surrounding tissues or by migration or by both

these processes. At this time also they become separated

into two groups; in chrysomelid beetles each group ap-

pears to contain thirty-two germ cells; in Miastor each

consists of four germ cells. One group becomes located

on either side of the embryo and later gives rise to one

half of the germ glands. The sex of the individual can

be determined by the morphology of the germ glands be-

fore the young hatches.

The further history of the germ cells in female insects

is in general as follows. From each primitive ovary a

number of ovarian tubules arise each containing many

germ cells (oogonia) which have undergone a multiplica-

tion period. The oogonia pee cease dividing and the

8 Hasper, 1911, sap Jahrb., Bd.

® Kahle, 1908, p sae logica, Bd. 21; Hegner 1914, Journ. Morph., Vol. 25.

10 Noack, 1901, Zeit. f. wiss. Zool., Bd. 70.

11 Silvestri, l. c.

648 THE AMERICAN NATURALIST [Vou. LI

ultimate oogonia are ready to enter upon the growth

period. A period of differentiation may or may not in-

tervene, according to the species, during which nurse

cells are formed. When the oocytes have reached their

full size they separate from the ovarian tubule, pass down

‘the oviduct into the vagina and are deposited. Each egg

is surrounded by two membranes; a thin inner vitelline

membrane and a thicker, outer membrane, the chorion.

6. The Complexity of Organization of the Insect Egg.

(a) Comparison between Eggs of Insects and Those of

Other Animals.—Insect eggs differ greatly from those

usually employed for the study of egg organization, since

they are, as a rule, laid in the air and not in the water,

and because cleavage is of the superficial type, cell walls

being absent until a comparatively late cleavage stage. -

The eggs of chrysomelid beetles are particularly favor-

able for study, since they may be subjected to the most

violent experimental conditions without preventing their

development.'?

In insect eggs the character of the blastoderm cells

depends, as in holoblastic eggs, upon the kinds of proto-

plasm they contain, but all those phenomena connected

with the position of the cleavage spindle, which have been

so carefully studied in the eggs of mollusks, worms,

ascidians and other animals, can have no influence upon

the localization of different substances in various parts of

an insect egg, because in the latter the volume of the egg

is thousands of times greater than that of the cleavage

spindle. Furthermore in holoblastic eggs differentiated

substances are segregated in different cells during early

cleavage and are there isolated by cell walls, and to this

isolation is attributed in large part the progress of dif-

ferentiation; but in the insect egg the different kinds of

cytoplasm are in direct continuity until hundreds of cleav-

age nuclei are present, and are not separated by cell walls

until the blastoderm is fully formed.

12 Hegner, 1908, Biol. Bull., Vol. 16; 1909, Journ. Exp. Zool., Vol. 6;

1911, Biol. Bull., Vol. 2

No. 611] GENESIS OF ORGANIZATION OF INSECT EGG 649

(b) Results of Experiments with Gravity and Centrif-

ugal Force.—A chrysomelid beetle, such as Calligrapha

or Leptinotarsa, during the process of egg-laying clings

to the under side of a leaf and the end of the egg that

emerges first is glued to the leaf by a viscid secretion.

Then the egg is pushed back away from the abdomen and

another is laid'® (Fig. 5). In this way from four to

Fie. 5. Diagram showing a chrysomelid beetle, Calligrapha bdigsbyana,

clinging to the underside of a willow leaf and layin er eggs. The relation

between the orientation of the egg before and after deposition is indicated by the

letters. a= anterior. d= dorsal. = left. p = posterior. r= right

anterior ventral surface where a spot of India ink was placed as a guide for

orienting the eggs during experiments. (Hegner, 1909.)

eighty eggs are laid in one group within a period of about

an hour. These eggs hatch in approximately five days.

A few hours before they hatch the young can be seen dis-

tinctly through the semi-transparent egg shell. An exam-

ination of hundreds of eggs at this stage in their develop-

ment has established the fact that the posterior end of the

egg is attached to the leaf and the anterior end is free.

In every other respect the orientation of the young in

the egg corresponds to that of the egg as it lay within the

body of the mother before deposition; that is, the ends

and various surfaces of the egg are definitely determined

before deposition and correspond to the orientation of the

mother as indicated in the diagram (Fig. 5). This rigid

correspondence between the orientation of the egg and

that of the adult is known as the ‘‘law of orientation’?

which was first discovered by Hallez in 1886.

Since the eggs of these beetles are usually attached to

18 Hegner, 1909, Journ. Exp. Zool., Vol. 6. :

650 THE AMERICAN NATURALIST [Vou. LI

the underside of leaves, it was suggested that the orienta-

tion of the young might depend upon the force of gravity,

but eggs that were first marked with India ink and then

placed in every conceivable position with respect to grav-

ity proceeded to develop as though undisturbed.’* It

seemed from this, therefore, that the position of the young

must be predetermined in the undeveloped egg.

Several kinds of experiments were performed in order

to discover the complexity and fixity of this apparent

organization. First, the eggs were subjected to a force

greater than gravity by means

of a centrifugal machine. Hun-

dreds of eggs were revolved at

different rates of speed for vari-

ous lengths of time and in many

different positions. A description

of one experiment will serve to

illustrate the results obtained.’®

In this experiment freshly laid

eggs were placed in cavities in

a block of paraffin with the pos-

terior end toward the center of

rotation, and were revolved in a

hydraulic centrifuge for sixteen

hours. The heavier substances

were thrown to the outer end and

Side view of a

freshly laid egg of Calligrapha

multipunctata, which was cen-

trifuged for sixteen hours and

aken out and allowed to

the lighter protoplasm accumu-

lated at the inner end, where an

embryo developed (Fig. 6). It

is perfectly evident that the pro-

toplasm from the various parts

of the egg has, in its new posi-

tion, developed into the tissue

that it would have given rise to if

it had been left undisturbed. Normally the yolk would

_ be surrounded by the embryonic tissue and would be en-

14 Wheeler, 1889, Journ. Morph., Vol. 3; Hegner, 1909, Journ. Exp. Zool.,

Vol. 6. *

ee 15 Hegner, 1909, Journ. Exp. Zool., Vol. 6.

No. 611] GENESIS OF ORGANIZATION OF INSECT EGG 651

closed by the mid-intestine, but in this case a dwarf em-

bryo has developed without growing around the nutritive

material.

The effects of centrifugal force upon insect eggs are.

different from those produced upon the other types of

eggs that have been employed for such experiments. In

the eggs of worms,'® mollusks,” etc., apparently the ma-

terials that undergo stratification under the influence of

- centrifugal force have no influence upon the ‘‘ground sub-

stance” which is ‘‘the seat of polarity and pattern of

organization of the cell.’’ In the insect egg, the organ-

ized protoplasm is almost entirely limited to the cortical

layer and this layer may be shifted away from the

periphery by a sufficient force and may become massed at

the inner light end when an undeveloped egg is cen-

trifuged.

Since the cytoplasm develops in its new situation and

proceeds to build up an embryo as nearly normal as is

possible under the conditions imposed upon it, it is evi-

dent that the potencies of the cytoplasmic areas are pre-

determined at the time the egg is laid.

It was hoped by means of these experiments with cen-

trifugal force to throw the pole-dise granules and the

cytoplasm containing them into some other part of the

egg. If the germ cells arose from this material in its new

position the conclusion would have been convincing that

these substances were necessary for the formation of the

reproductive cells. Unfortunately, although the cortical

layer at the posterior end was shifted by the centrifugal

force, it was impossible to locate accurately the germ

cells in the embryos that developed from the eggs that

were thus operated upon.

zation.—During the course of my early studies of chry-

somelid eggs it occurred to me that the nuclei that result

from early cleavage might be definite in number and in

16 Lillie, F. R., 1906, Journ. Exp. Zool., Vol. 3.

17 Conklin, 1917, Journ. Exp. Zool., Vol. 22.

652 THE AMERICAN NATURALIST [Von. LI

distribution and that they might be qualitatively differ-

ent. If this were true, then nuclei of one sort might

always migrate into one part of the egg and might deter-

mine the nature of the tissue that developed there, and

nuclei of other sorts might likewise become located in

other predetermined parts of the egg. Careful studies of

the origin and migration of the cleavage nuclei'® have

led to the conclusion that the distribution of these nuclei

is adventitious and that they are all potentially alike— `

that is are totipotent—a view that is now held by most

embryologists regarding the relative importance of

nucleus and cytoplasm during cleavage. That the nuclei

may play a part in the differentiation of the cortical layer

of cytoplasm during the cleavage period is highly im-

probable, since definite cytoplasmic organization already

exists before cleavage begins. The factors brought into

the egg by the spermatozoon, however, have an oppor-

tunity at this time to modify the initial organization and

thus the early embryo may exhibit paternal characteris-

tics. Whether or not such an influence is exerted at this

time is not known.

The kind of tissue that develops from any part of the

egg, therefore, depends upon the kind of cytoplasm en-

countered by the nuclei.

(d) Complexity of Organization as Indicated by the

Development of Parts of Eggs.—More convincing evi-

dence of the presence of a complex and fixed organiza-

tion in the cytoplasm was derived from operations per-

formed upon eggs with a hot needle. Parts of the freshly

deposited eggs were killed by being touched with a hot

needle und these parts were thus prevented from taking

part in development. The living portions of the eggs

continued to develop and in every case produced those

parts of the embryo that they would have formed if the

egg had not been injured.!® This seems to prove that

every part of the egg cytoplasm is set aside for the pro-

` 18 Hegner, 1914, Journ. Morph., Vol. 25.

O Fegin, 1911, Biol. Bull., Vol. 20.

No. 611] GENESIS OF ORGANIZATION OF INSECT EGG 653

duction of a definite part of the embryo, and hence of the

larva and adult, and that the cytoplasm is therefore

highly organized at the time the egg is fertilized. After

such experiments there is no regeneration of substances.

As stated above, the cortical layer of cytoplasm is vis-

ibly alike throughout except at the posterior end, where it

has embedded in it the pole-disc granules. One of the

most interesting results of the operations performed with

the hot needle was obtained by killing the posterior por-

tion of the egg containing the pole-dise (Fig. 7). Eggs

Fic. 7. Diagrams showing the results of killing parts of the eggs of Lepti-

Teea oman ta with a hot needle. (Hegner, 1911.

ongitudinal section through an egg twenty-four hours old. The pos-

sia end _(k) was killed just after the egg was deposited (conditions as in

Fig.

. o germ cells were Oe uaa

tral view of an embryo three igi gs The posterior end (k) was

uta ae oe the egg was S denaii toi. N p ya: remained aliye gave rise

to the head va pean half of the thora

ew of a Sag five days ah: The aniditoe end (k) was killed in

the hinstoderm stage ir . 8, d). The part that remained alive produced the

te nUe f alte nd Cae tak of the thorax (t).

o Ven ral view of an egg three days old. Thé posterior end (k) was

ket when the embr Faih was two days old, The anterior Se continued to de-

pendence of the tissues is indicated by the minute end of the

Meee i pener riit normally after being a from the rest of

the embryo. The two parts of the egg underwent a revolution of ninety degrees

steep the twenty-four hours succeeding a ment.

= abdomen. bl= blastoderm. gcd = pole-disc. h = head. k= portion of

egg ini with hot needle. t= thorax. tf — tall fold. y= yolk. :

thus modified produced embryos without germ selli, prov-

ing that this cytoplasmic region is necessary for their

formation. The castration of the individual may also be

performed in a similar fashion after the germ cells have

been extruded from the egg (Fig. 3, d), and it is interest-

ing to note that sexless chicks have recently been pro-

654 THE AMERICAN NATURALIST [Vou. LI

duced in a similar fashion, by removing the region of the

embryo from which the germ cells arise.?°

The blastoderm is of course definitely organized, since

its cells contain organized cytoplasm, and by killing parts

of the eggs in the blastoderm and later stages results

were obtained similar to those produced when fresh eggs

were operated upon (Fig. 7, b, c, d).

7. Summary of Part I

Summarizing the data briefly given above, we may say:

1. Morphological and experimental studies have proved

that the eggs of animals are more or less highly organ-

ized at the time of fertilization.

2. We know almost nothing about the nature and gen-

esis of this organization.

3. Descriptions are given of the condition of the eggs

of certain chrysomelid beetles at the time of deposition,

of.the stages of cleavage and blastoderm formation, of

the origin of the germ cells, and of the principal stages

in the germ-cell cycle.

4. The eggs of certain chrysomelid beetles and of other

insects are definitely organized when deposited as indi-

cated by observations on normally developing eggs and .

by experiments with gravity.

5. This organization exists in the cytoplasm as indi-

cated by a morphological study of cleavage, by experi-

ments with gravity and centrifugal force, and by killing

with a hot needle parts of eggs in various stages of de-

velopment.

6. These observations and experiments prove also that

the nuclei up to the time of blastoderm formation are

totipotent.

II. THE Genesis or THE ORGANIZATION oF THE INsEcT Hee

1. Introduction.

I have decided to consider the organization of the egg

only in this discussion, since it contains everything neces-

: 20 Reagan, 1916, Abstracts 14 annual meeting Amer. Soe. Zool.

No. 611] GENESIS OF ORGANIZATION OF INSECT EGG 655

sary for the production of a complete organism. In many

species of insects and other animals, parthenogenesis is

a normal phenomenon and in many species whose eggs

must ordinarily be fertilized development may be ini-

tiated by artificial means.?™! Among these are the eggs

of the silkworm moth. It also seems certain that the

cytoplasmic regions of the insect egg have reached a high

state of morphological and physiological differentiation

before fertilization, judging from the results outlined in

Part I. of this paper. The cleavage nuclei may possibly

exert an influence upon the cortical layer of cytoplasm

before the blastoderm is formed, thereby enabling the

paternal contribution to the zygote to act, but besides be-

ing very improbable, such a phenomenon would, of course,

follow rather than precede the establishment of the ad-

vanced state of organization that exists in the undevel-

oped egg. |

2. Constitution of the Primordial Germ Cells

In certain beetles, flies and parasitic Hymenoptera, the

primordial germ cells are visibly different from the rest

of the embryonic cells that arise at about the same time.

This difference is primarily due to the inclusion within

them of visible substances that are located in the egg ma-

terial from which they originate. The eggs of these dif-

ferent insects are similar in certain respects and dif-

ferent in others. In every instance, however, this visible

substance, which forms the germ-line determinants, is

situated near the posterior end of the egg, and it is at this

point that the primordial germ cells are formed. The

origin of the germ-line determinants is not definitely

known in any insect, but their position in the egg and

their granular appearance are constant.

It has often been pointed out that the primordial germ

cells remain in a comparatively undifferentiated state

until the individual in which they lie has almost reached

maturity, and that they then undergo changes during

21 Loeb, 1913, ‘‘ Artificial Parthenogenesis and Fertilization,’’ Chicago.

6560- THE AMERICAN NATURALIST [Vou. LI

which they reach a high state of specialization. The dis-

covery of axial gradients of metabolism in the eggs of

certain animals in an anterior-posterior direction?? sug-

gests that this may also be true of insect eggs. If such

gradients exist in insect eggs and if the metabolic activity

decreases gradually from the anterior to the posterior

end, then the primordial germ cells, which arise at the

extreme posterior end, are actually the least active meta-

bolically of all the cells of the embryo. Their early sep-

aration from the egg would also tend to keep them in an

undifferentiated condition since they are on this account

less likely to be influenced by the rest of the embryo.

The primordial germ cells in these insect eggs are thus

visibly different because of the presence of germ-line de-

terminants and are probably physiologically different, at

least in part, because of their position at the posterior

end of the egg.

The contents of these cells are as follows (Fig. 4):

(1) part of the cortical layer of cytoplasm, (2) part of

the cytoplasm which surrounds the cleavage nuclei and

which is collected from among the yolk globules, (3) part

of the germ-line determinants, and (4) a nucleus with the

full amount of chromatin. The fourth item is mentioned

because in Miastor all of the nuclei that form somatic

cells undergo a diminution process, being similar in this

respect to Ascaris. This chromatin is in Miastor entirely

maternal since the eggs of this fly that have been studied,

develop parthenogenetically.

Nothing very definite has been discovered regarding

the arrangement of these substances in the germ. cells.

The nucleus lies near the center in all of them; the two

kinds of cytoplasm soon become indistinguishable; and

the germ-line determinants may, at first, be more or less

evenly distributed throughout the cytoplasm, as in chry-

somelid beetles and Miastor, or may be clumped in vari-

ous parts of the cell, as in Chironomus. In every case,

however, the germ-line determinants evidently become

22 Child, 1916, Biol. Bull, Vol. 30.

No. 611] GENESIS OF ORGANIZATION OF INSECT EGG 657

more or less evenly scattered since they cannot be distin-

guished in later stages in the germ-cell cycle.

3. Differential Divisions during the Formation of Nurse

Cells

There is no evidence of any definite localization of sub-

stances or physiological processes in the primordial germ

cells when formed, nor do these cells exhibit recognizable

polarity or symmetry of

any kind. As described

in preceding pages, they

multiply; migrate into or

are enveloped by the tis-

sues of the embryo; sepa-

rate into two groups from

which the ovaries on either

side of the body arise;

and then pass through an-

other period of multipli-

cation. This brings them

to the stage just preceding

the growth period. At

this time phenomena occur m.

in the ovaries of certain 4 youme De ae A a a

species of insects that ¢ompanying nurse cells (nc). gv= germ-

have a direct bearing upon inal vesicle. (Hegner, 1914.

our problem; these are concerned principally with the dif-

ferentiation of oocytes and nurse cells. In Miastor the

nurse cells are mesodermal in origin, and a group of nurse

cells and one oocyte become enclosed within a sheath of

epithelial cells (Fig. 8). As the oocyte increases in size

it elongates, and then for the first time in its history ex-

hibits recognizable polarity; the anterior end adjoining

the group of nurse cells. Polarity may, however, have

been present from the time the primordial germ cell was

first formed, corresponding to that of the parental egg.

The germinal vesicle soon becomes eccentric, but whether

or not this indicates that bilateral symmetry has also been

658 THE AMERICAN NATURALIST [Vou. LI

determined, as it does in certain other insects, is unknown.

It is thus certain that polarity exists soon after the be-

ginning of the growth period and that bilaterality is prob-

ably also established at an early stage.

The differentiation of oocytes and nurse cells in dy-

tiscid and gyrinid beetles is of peculiar interest, although

the early and later history of the germ cells in these in-

sects is not known. In the diving beetle, Dytiscus mar-

ginalis,?> a single oogonium gives rise to fifteen nurse

cells and one oocyte. The oocyte and its mother cell,

grandmother cell, and great-grandmother cell can be dis-

ere ox

Diagrams Boeman differential divisions ane the formation of

nurse sees in the errand _— igi? nigrior. Hegner and Russell, 1916.)

of an ovarian tubule showing two oocytes (0)

each accompanied d by seven nurse sol a j:

. Division of two-cell stage. An ultimate oogonium has divided forming

a iah cell (ne) and an oocyte grandmother cell (ogmc) containing the oocyte

determinant. 7 intercellul d.

grammatic ae of oocyte differentiation. The plain circles

Indicate nurse cells. = ultimate oogonium re the tie ds determinant

within its nucleus. Pome oocyte grandmother c o=

23 Giardina, 1901, Internat. Monatssch. f. Anat. u. Hai Bd. 18; Debai-

sieux, 1909, La Cellule, T. 25; Gunthert, 1910, Zool. Jahrb., Bd. 30.

No. 611] GENESIS OF ORGANIZATION OF INSECT EGG 659

tinguished from the nurse cells by the presence of a pe-

culiar ring of nuclear material within the cytoplasm and

by their larger size. The gyrinid beetle, Dineutes nigrior

(Fig. 9), resembles Dytiscus in general, but the ultimate

oogonium passes through one less division, thus giving

rise to one oocyte and only seven nurse cells.24 The im-

portant fact is that during these differential divisions, in

both cases, the nurse cells, which may be considered so-

matic since they are unable to reproduce, are deprived of

part of their nuclear material. Apparently they differ

from their sister cell, the oocyte, in this one respect, and

it is therefore the presence of this nuclear material that

makes it possible for the oocyte to develop into a new in-

dividual. This is one of the most striking cases of the

passage of large masses of nuclear material into the cyto-

plasm. No such differential divisions have been discov-

ered in chrysomelid beetles nor in the other insects where

the nurse cells arise from oogonia, but they may occur in

some way that has not been revealed by our methods of

research.

The writer has discussed this subject rather fully with

relation to the origin of nurse cells and oocytes in the

honeybee.” In this insect a single oogonium gives rise

to a rosette-like group of cells that are connected with

one another by strands—probably of a mitochondrial na-

ture—the remains of preceding mitotic divisions. There

is no visible difference among the cells in a rosette which

are hence apparently potentially alike. Nevertheless one

or several from each rosette enlarge to form oocytes

which are nourished by the rest acting as nurse cells.

“What determines the differentiation of certain cells into

oocytes is not known but the following hypotheses have

been expressed.

Three explanations have occurred to me: (1) There may be dif-

ferential changes during the mitotie divisions in rosette formation as in

Dytiscus resulting in one or more cells (oocytes) which differ in con-

24 Hegner and Russell, 1916, Proc. Nat. Acad. Sc., Vol. 2.

25 Hegner, 1915, Journ. Morph., Vol. 26.

660 THE AMERICAN NATURALIST [Vou. LI

tent from the others (nurse cells). No visible changes of this sort were

observed. (2) The polarity of the rosettes may influence the cells in

such a way that those near the center of the ovariole and closest to the

zone of differentiation tend to develop into oocytes. (3) Those cells of

the rosettes which reach the zone of differentiation first are stimulated

to become oocytes and by their growth and differentiation prevent the

other cells of the rosettes from, similar changes.

4. Constitution of the Oocyte at the Beginning of the

Growth Period

Very soon after the nurse cells are formed and the

oocytes begin to enlarge the main axis of the oocyte in all

AESA

‘ Bi

Fic. 10. The formation of oocytes in the honeybee. (Hegner, 1915.)

a. Part of an ovariole showing the rosettes (r) each resulting from the

division of a single oogonium.

b. Part of an oyariole in the zone of differentiation showing five oocytes (0),

many nurse cells: (n) and epithelial cells (e),

insects seems to be established. The germinal vesicle

at the same time changes its position from the center of

the cell to a point near the nurse-cell chamber at the an-

terior end as described above in Miastor (Fig. 8). At

what stage bilateral symmetry becomes fixed has not been

determined.

The oocytes of insects at the beginning of the growth

No. 611] GENESIS OF ORGANIZATION OF INSECT EGG 661

period differ from the other cells in the body in the fol-

lowing ways. (1) In all cases where germ-line determi-

nants occur the oocytes alone are provided with them and

with the cytoplasm in which they are embedded. (2) In

insects like Mzastor a full amount of chromatin is present

only in the oocytes. (3) In Dytiscus, Dineutes and prob-

ably other insects the oocytes contain nuclear material of

which the nurse cells are deprived, but this may be in-

terpreted simply as a means of inhibiting the reproduc-

tion of the latter and of changing them into nurse cells.

(4) The oocytes seem to have no influence upon the de-

velopment of the individual in which they lie, as indicated

by castration and transplantation experiments,” and are

in a comparatively undifferentiated condition when the

growth period begins.

26 Meisenheimer, 1912, Fest. 60 Geburtstage von Dr. J. W. Spengel III.;

Kopec, 1911, Arch. Daie. -mech., Bd. 33.

(To be continued)

INHERITANCE OF FERTILITY IN SOUTHDOWN

. . SHEEP?

EDWARD N. WENTWORTH

PROFESSOR OF ANIMAL BREEDING

AND

J. B. SWEET

ASSISTANT IN EXPERIMENTAL BREEDING, UNIVERSITY OF WISCONSIN

INTRODUCTION

Youatt (14)? says:

The disposition to twinning is undoubtedly hereditary:

“Ewes yearly by lambing rich masters do make:

e lambs of such twinners for breeders go take.”

Flockmasters of the last century have made selections

on this assumption, while the increased number at a

birth in the progeny of ewes born multiparously as com-

pared to the progeny of those born singly has been dem-

onstrated by several investigators. In general there has

been shown to be an increase in number produced at a

birth as the average birth values of the animals lambing

increase. Thus, Rietz and Roberts (13) present the fol-

lowing in Shropshires, the number at a birth being repre-

sented by the figures 1, 2, or 3:

Sire | Dam Offspring No. Cases

Ta e 1 1.3452 0.0059 3,059

PT 1 1.3946 0.0073 2,088

| ere ba 1.4171 + 0.0067 2,436

r 2 1.4548+ 0.0088 1,550

One parent a triplet 1.6076 + 0.030 158

Experimental investigations of the inheritance of twin-

ning in sheep have been attempted in few cases. Ains-

-~ 1Paper No. 5 from the Laboratory of Animal Technology, Kansas Ex-

periment Station.

2 Reference is made by number to literature cited at close of paper.

662

No. 611] FERTILITY IN SOUTHDOWN SHEEP 663

worth-Davis and Turner (1) reported a preliminary in-

vestigation on this subject, but their numbers are too

small and results too contradictory, as published, even to

be indicative of the method of inheritance. Arkell and

Jones (7) at the New Hampshire station also instituted

investigations along this line, but have published no re-

sults.

Due to the environmental and physiological factors in-

volved in multiple births, as well as to the economic im-

practicability of maintaining large flocks under rigid ex-

perimental conditions, there are at hand no considerable

masses of experimental data which yield evidence on this

point, nor are the probabilities great that such exper-

iments will ever be conducted on an adequate scale; hence

the bulk of evidence on the inheritance of fertility must

come from breeders’ flocks or from breed registry records.

Tue FERTILITY PROBLEM

High fertility obviously depends on three factors—the

number at a birth, the frequency of reproduction, and the

total number of successful gestations an animal may

undergo. Unfortunately flock book records give available

data on the first point only, although for specific cases

some evidence on the second point (barring abortions and

unregistered progeny) exists.

For breeding purposes the number of successful gesta-

tions is not a practical selective index, since the breeder

ean not afford to withhold progeny from breeding until

their dams or sires shall have completed their breeding

eycles. Frequency of reproduction or regularity of breed-

ing as termed by the breeder is a more practicable trait

for purposes of selection, but since barren reproductive

periods are so much more frequently due to pathological

or physiological causes than to genetic, most sheepmen

lay principal emphasis on the number of offspring at the

given birth.

There are two ways in which selection on this basis

may be applied. The ewe may be selected on the basis of

664 THE AMERICAN NATURALIST [ Von. LI

a particular lambing, or the basis of the best lambing she

shows. From a genetic standpoint the second criterion

would seem the better, but practical breeders would be

very likely to use the first. Unfortunately, records in

Southdowns on which a comparison can be based are few,

forty-three animals only being available. Table I pre-

sents the correlation of each individual record with the

average lambing record for each ewe, while Table II pre-

sents the correlation of the best record for each ewe with

her average. Nine of the ewes had four lambings to their

eredit, nine had three, while twenty-five had only two.

The inadequacy of these data is recognized, since there is

a false agreement between a single number and its average

with another as compared to its agreement with its average

with several numbers. Since, however, the material is

suggestive from a comparative standpoint, it is presented,

as the same actual error exists in each table:

; TABLE I

CORRELATION OF INDIVIDUAL LAMBING WITH AVERAGE LAMBING PER EWE

Average Lambing per Ewe

Individual 1 1.5 1.67 1.75 2 2.5 F

1 38 6 4 4 1 Oo. | 8

2 0 6 Cede CES 1 58

3 0 0 0 0 1 1 2

Total $% | 12 kelep feck as 2 fens:

The coefficient of correlation for this table is 0.81806

+ 0.02099.

TABLE II

CORRELATION OF BEST LAMBING RECORD WITH AVERAGE OF EACH EWE

Average Lambing of Ewe

High Record 1.00 1.50. | 167 1.75 | 2.00 2.50 | F

1 16 0 0 0 0 ö ow

2 0 4 4 4 13 0 | 25

3 0 Q 0 0 1 1 | 2

ead 16 4 4 t] H Ii u

The coefficient of correlation for Table IL was found to be

0.92354 + 0.01513.

No. 611] FERTILITY IN SOUTHDOWN SHEEP 665

‘While both records show a higher agreement with the

average than probably exists in actual selections, the fact

that the best record is more closely in agreement with the

average than a random record makes high production a

significant selection standard. The correlation between

random records and the best records is presented in

Table IIT

TABLE IMI

Best RECORD OF EWE

Individual Record 1 | 2 3 F

1 38 14 1 53

2 0 55 3 58

3.. 0 0 2 2

Total 38 | 69 6 113

The coefficient of correlation here is 0.6518 + 0.03665.

The relationship is not as great as between either of the

records and the average record, as shown in Tables I and

II. Since the correlation is not as high, and since an error

(false agreement with the average) is introduced into

each of the first two tables, it is well to determine whether

the difference between the first two correlation coefficients

is significant. Using the formula for the standard deviation

of the difference between the first two constants presented

by Pearl (10) : Error of (x — y)=V Ea? + E,? — 2 rey oe oy,

where E refers to the error, x to the larger constant,

y to the smaller, and rey to the correlation between

æ and y. The error of the difference between the cor-

relation coefficients of Tables I and II is 0.01598.

Since the difference is .10548, it is greater than three

times the probable error, hence it is justifiable to conclude

that the highest number at a birth is a better indication of

the average fertility of an animal than a random birth,

although on the basis of the figures presented the latter

relationship is high.

Youatt (14) reports in 1837 that one ewe out of five in

the average English flock produced twins, which would

give 120 per cent. of lambs as the Seas of English

flocks at that time.

666 THE AMERICAN NATURALIST [ Vou. LI

Mansell (12) reports 168 per cent. of lambs in 11,668

English Shropshires in 1896, while Humphrey and Klein-

heinz (6) from figures on the University of Wisconsin

flock made the following breed comparisons:

TABLE IV

Singles | Twins | Triplets

Breed im i AR il E E A Lor eet cng a

No. Per Cent. | No. Per Cent. | No. Per Cent.

Shropshire 42 Ve ESS eae E A 67.8 | 15 9.5

Dorset 10 33.3 | 20 66.7 | 0 0.0

* Southdown 27 PETOA IT 62.0 | 0 0.0

xfor 3 136 16 Tae i 3 13.6

tampshire 9 SLO | 20 69.0 | 0 0.0

hevi 9 31.0 20 69.0 0 0.0 s

Percentage of faha as given by Mansell is, of course,

only a rough indication of twin-bearers, since ewes having

triplet and quadruplet births may be aneluded:

Rietz and Roberts (13) show that 43 out of every 100

births in American Shropshires are multiple births, while

they have determined from Heape’s (5) statistics of

1895-96 that 64 out of every 100 births in English Shrop-

shires are multiple.

Plumb (12) found in 20,037 Shropshire births 59.2 per

cent. were singles, 39.2 per cent. twins, and 1.3 per cent.

triplets, all recorded in the American Shropshire Flock

Book, 1890 to 1899.

Heape (5), from a study of the birth records of 89,000

ewes in English flocks, presents the following data to

show the relative fertility of different breeds of sheep:

TABLE V

Per Cent. Lambs Per Cent. Twin Bearing

per Ewe

BUNGE oasis sss ceo te 141.77 52.22

BG PEE E Pn pas ag ol 124.05 31.38

Bouthdownh s.ro eevee 109.89 18.67

Hampshire s. css. tukso 114.69 24.09

Oxforda Down.. s ceros 119.16 35.02

Dorit Bom oa es i ee 123.63 37.55

PhropebyrG wie Ts es 136.79 46.84

Smee Oe eri es 111.10 29.09

No. 611] FERTILITY IN SOUTHDOWN SHEEP 667

The figures for the per cent. of lambs per ewe and the

per cent. of twin-bearing ewes do not in all cases check

each other, as records of certain ewes were available for

the one column but not for the other.

The writers tabulated birth frequencies in Shropshires,

Cotswolds and Dorsets with the following results:

TABLE VI

Singles | Twins | Triplets SSRN i

Breed r | | Í |

Shropshire............ 10,585 69.41 | 4,561; 29.91 102 .67 |2| .01

2,148 67.75 956 | 30.22 57 1.88 y 22

Cotswóld 5,528} 79.24 |1,431 | 20.53 | 16; .23

Dorsets seem to have an exceptionally high percentage

of triplets and quadruplets.

FACTORS AFFECTING FERTILITY

Heape (5) in a study of 122,673 breeding ewes, 413 Eng-

lish flocks, suggests five physiological factors that may

affect the hereditary expression of fertility. The most

important factor according to him is the physical condi-

tion of the ewe, which must be vigorous and healthy, espe-

cially at tupping (mating) time. The second most

important factor is the feeding of the ewe, especially

flushing previous to breeding, and careful diet during

gestation. The third factor in importance is the district;

he cited the fact that the Suffolk in its native country pro-

duced 60.46 per cent. of twins, while in Essex it produced

only 42.87 per cent. The fourth factor in importance he

found to be the age of the ewe; and the fifth, the season

of year at which mating occurred.

Carlyle and McConnel (3) at Wisconsin discuss time of

mating and age of ewe, factors similar to those mentioned

by Heape. In a study of twelve years of records of the

station flock at the University of Wisconsin they found

that ewes bred early in the season dropped a higher per-

centage of lambs than those dropped late in the season,

668 THE AMERICAN NATURALIST [Vou. LI

while ewes from three to six years of age seemed to be at

the optimum breeding period of their life. Humphrey

and Kleinheinz (6) found that two-year-old ewes pro-

duced 141 per cent. of lambs and six-year-olds, 191 per

cent. Possibly the writers do not understand the tables

presented by them, but their calculations on the basis of

the data there given would show the following averages at

each age:

TABLE VII

Age Average No. per Birth No. Cases

Corl seas ae wees 1.54 53

Bs a a es AT 1.56 52

4g. eee EOG Ee pO a | 52

TAE E E E 1.73 57

M E eae pe a a 1.92 24

EON aR ETRE R R 1.45 11

Bae CS tiie ay any oe a nes 1.00 2

BSS Pes ess aa 2,00 2

Pearl (9) made a biometric study of the fertility of a

long-lived ewe whose breeding record was as follows:

TABLE VIII

Lambs Lambs

April, 1806. oara oe aes a 1 ASLO cs ice town) SF ciee $ ree

BOOT see i ss ae l CRT ea a O se eas 2

SOUS i cei ss 2 od 0. Ue Os grips EE pe 2

Aprl 3, 1800 usoen Ae 3 1819 i.o a a Gee 2

Mar, 20, BIO anla 3 IBAN i cise ahi. saree hs 2

CORT Bey yes ea ns 6 3 ETA ee eee hee 1

Jee eters Gs oa 4 3 DORE csinosan e + 1

TOAD ce PU Le ete es 3 SORE CU eR eka fhe ee 0

WIA Beery es aa 3 ROLE neso > hie a A 0

TOIR ote. eee 2 Witel oan 36

Assuming that the ewe was about one year old when the

first lamb recorded was born, Pearl found that the mean

point of the ewe’s effective breeding life was 8.57 years,

that the median point was 8.17 years and that the modal

breeding point, or the point of maximum fertility per unit

of time, was at 7.34 years.

Taking into account the seventeen years in which some

young were born, the following constants regarding the

number of lambs per birth were found:

No. 611] FERTILITY IN SOUTHDOWN SHEEP 669

Mean number of lambs per birth, 2.12 lambs. f

Standard deviation in number of lambs per birth, 0.76.

Coefficient of variability in number of lambs per birth,

35.78 per cent.

Marshall (8) found after a study of the lambing sta-

tistics for various flocks of Scottish sheep for the years

1905, 1906, and 1907, that the percentage of lambs born

was, as a general rule, highest among sheep which had

been subjected to a process of artificial stimulation by

means of special diet at the approach of the breeding sea-

son. In some cases the number of lambs per ewes in the

‘*flushed’’ flocks was nearly 200 percent. Flocks which

were run upon special pasture upon the approach of the

tupping season generally produced a slightly larger per-

centage of lambs than those receiving no sort of special

feeding. Evvard (4) found among range ewes fed the

same ration that the fourteen heaviest gaining ewes at

time of breeding in his flock averaged 1.8 lambs; the four-

teen medium gainers, 1.59; and the fourteen lightest

gainers, 1.44.

RELATION OF MAMMÆ To FERTILITY

Alexander Graham Bell (2) conducted an experimental

investigation on the relation of the number of mamme to

fertility. An unusually high fertility among a flock of

native sheep in Beinn Breagh, Nova Scotia, led Bell to

examine the ewes in order to discover some distinguishing

mark of the twin-bearing ewe. He found a certain num-

ber of ewes with one to two supernumerary nipples in an

embryonic, functionless condition. Of these abnormally

nippled ewes, 43 per cent. had twin lambs, while of the

normally nippled ewes but 24 per cent. produced twins.

This apparent correlation between multinipples and in-

creased fertility led to an extended series of experiments

to ascertain whether by selective breeding, the super-

numerary nipples could be made functional, and whether

ewes with additional mammæ in a functional condition

were more fertile than ewes with the normal number of

nipples. ;

670 THE AMERICAN NATURALIST [ Von. LI

No ‘difficulty was experienced in obtaining ewes that

produced milk from six nipples. These multi-nippled

sheep, however, did not prove to be more fertile than

normally nippled sheep. In his 1912 paper (2) he states

that the indications are that the six-nippled stock will

ultimately prove to be twin bearers, as a rule, at ma-

turity.

METHOD OF OBTAINING DATA

The source of the data in the present study was the

American Southdown Record, the first twelve volumes

being used to obtain cases of triplets, and volumes nine

to twelve for twins and singles. The pedigree of each

animal was reported into the third generation, recording

the numbers of offspring at the birth of each animal.

Some records on triplets were also taken from the Amer- .

ican Shropshire Record, while Volume 25 was used to

determine the ratio of singles, twins and triplets, Vol-

umes 9-12 of the Southdown Flock Book for the same

purpose, Volumes 12, 13, and 14 of the Continental Dorset

Club Record, and Volumes 11 and 12 of the American

Cotswold Record. `

RELIABILITY or Frock Book Dara

Records of the number at a birth in sheep are probably

highly accurate for such material, since there is no ob-

servable tendency to discriminate in favor of, or against,

recording offspring of multiple births, except the indirect

one of lesser development in offspring from multiple

births. This would not affect the reliability of the figures

presented by the flockmaster, except perhaps to reduce

slightly the proportion of multiple births registered. It

may be safely assumed that the bulk‘of the records are

accurate, barring clerical error.

THE NUMBER AT A BIRTH as A Genetic INDEX

Due to the physiological causes limiting the full expres-

sion of the genetic fertility of an animal it is obvious that

animals recorded as singles may be potentially twin or

No. 611] FERTILITY IN SOUTHDOWN SHEEP 671

triplet bearers, or that ewes recorded as bearing twins

may be genetically triplet producers or better. Hence it

may be expected that not all single or twin bearers are

alike in zygotic make-up with reference to fertility or that

their breeding performance will fall into sufficiently well-

defined categories to permit a rigorous Mendelian group-

ing. The relation between a random lambing record and

the average record of ewes was shown earlier in this paper

to be high, hence a similar relation might be expected to

hold for true genetic fertility, were it measurable, and a

random record.

Tar Data INVOLVED

The Relative Influence of Sire and Dam.—Rietz and

Roberts (12) found a mathematically significant effect of

the sire on the number at birth as adjudged by the corre-

lation between offspring and sires, although they do not

find a similar relation between dams and maternal grand-

sires. While the authors have not secured correlation co-

efficients on this point, their averages may be so arranged

as to throw some light on the same point. Using pedi-

grees which were started from animals of single birth,

the following comparison between sires and dams is pos-

sible.

TABLE IX

RELATIVE INFLUENCE OF SIRE AND DAM ON BIRTH NUMBER, FROM PEDIGREES

or ANIMALS OF SINGLE BIRTH

1,872 1 1 -29 1,872 1 1 +29

925 1 2 .28 570 2 1 .25

14 1 3 .43 12 3 1 .50

5,570 2 1 .25 925 1 2 .28

2 2 .34 2 2 1.34

10 2 3 .20 6 3 2 Az

12 3 1 1.15 14 1 3 1.43

6 3 2 fet yi 10 2 3 1.20

Comparison of the records of single, twin and triplet

sires mated to single, twin and triplet ewes in the pre-

ceding table shows no particular influence of the birth

rank of the sire, a fact which is confirmed in Table X,

where the average performance of each is given.

672 THE AMERICAN NATURALIST [ Vou. LI

TABLE X

BREEDING PERFORMANCE OF THE MALES FROM PEDIGREES STARTED WITH

SINGLE BIRTHS

. Sires | Mean | Standard Deviation No. Casts

Pdi pcan ea: | 1.2864 .00593 4668 2,811

e aa ilies 1.2776 .01031 4553 886

CET ORR | 1.3888 .07750 4875 18

The difference between the breeding performance of

the singles and twins is 0.0088-+ 0.0119, which is, of

course, not sufficient to be significant. It indicates either

that the male has no influence on the number at a birth

(the most probable supposition) or that singles and twins

in the males are genetically similar. The difference be-

tween the breeding performance of the triplets and singles

is 0.1024 + .0777 and between the triplets and twins is

0.1112 + .07818, neither of which is significant.

For the ewes the result is not particularly different.

Table XI presents the result of this comparison.

TABLE XI

BREEDING Poroa OF THE FEMALES FROM PEDIGREES STARTED WITH

SINGLE BIRTHS

Dams | Mean | Standard Deviation | No. Cases

a ene 1.26365 = 0.00631 .4635 2,454

A clepetsc - 1,29345= 0.00893 ' .4658 1,23

Bornin 1.33333 + 0.06490 A714 24

The difference between the progeny of ewes born singly

and those born twins is .01349 + 0.1093; between singles

and triplets is .05338 + 0.06252; and hetwont twins and

triplets is .03989 + 0.0655.

TABLE XII

RELATIVE INFLUENCE OF SIRE AND DAM ON BIRTH NUMBER, FROM PEDIGREES

or ANIMALS OF TWIN BIRTH

9906) ee (4 1.51 2805 | 1 | 1 1.51

124 | i 2 1.55 ts |. 3 BT

21 1 3 1.86 19 3 1 1.68

687 |} 2%) 4 1.57 kieo oid 1.55

roe | 2 1.56 468. | 2 | 2 56

1 | 2 | 8 1.60 tA eps 1.43

G i 1.68 eves ORGS far 1.86

rts | Ss 1.43 “wie 3 1.60

No. 611] FERTILITY IN SOUTHDOWN SHEEP 673

Table XII shows the relative breeding performance of

the sires and dams in pedigrees started from twin births.

Treating the sires in pedigrees from twin births as in

Table X, Table XIII is produced.

TABLE XIII

BREEDING PERFORMANCE OF THE MALES PROM PEDIGREES STARTED WITH

Twin BIRTHS

Sires Mean Standard Deviation No. Cases

Wii RT EA | 1.5296 = .00543 .51659 4,120

oeei eai a | 1.5682 = .00724 .49704 A 165

e E NE | 1.6154 = .06435 . 48650 26

The difference between singles and twins as sires is

.0386 + .0091; between singles and triplets is .0858

+ .0645; and between twins and triplets is .0472 + .0647.

The difference between singles and twins is in this case

significant, being about 4.2 times the probable error.

Further consideration will be given this difference when

the ewes are discussed.

~ Treating the ewes in pedigrees from twin births as in

Table XI, Table XIV is produced.

TABLE XIV

BREEDING PERFORMANCE OF FEMALES FROM PEDIGREES STARTED WITH TWIN

BIRTHS

Dams Mean | Standard Deviation | No. Cases

e EP E -1.2529-+.00581 0.51075 3,511

r EERE BON Sage Ok 1.5551 =.00827 0.51583 1,769

Bsa aes 1.7742+.05065 0.41811 31

The difference between singles and triplets is 0.2513

+ .05098; between twins and triplets, 0.2191 + .05132;

and Faea singles and twins is 0.0322 + .01011. Ewes

from triplet births give significantly larger progenies

than ewes from single or twin births, while ewes from

‘twin births give significantly larger progenies than ewes

from single births, the last difference being 3.323 times .

the probable error. It is interesting to observe that both

674 THE AMERICAN NATURALIST [Von. LI

twin rams and twin ewes are significantly better breeders

than singles. Just why this result is obtained here in the

face of other contradictory data is difficult to understand.

In order to combine the results of the two types of pedi-

grees it was deemed advisable to utilize the ratio of

1:4.118 twins to singles discovered by examination of

volumes 9 to 12, respectively, in order to have the normal

relationship between twins and singles. This involved

dividing the numbers of individuals in the twin group or

multiplying those in the single group. In the first case

errors would be increased, due to the elimination of cer-

tain groups, while in the second case errors would be in-

creased due to the exaggeration of differences between the

random sample in the pedigrees begun from single births

and the normal distribution of such a population. It was

deemed best to use the second method, since it permitted

the retention of the small groups, hence the ratio 1:4.118

was multiplied by the ratio 3,715:5,311, the numbers of

individuals in the pedigrees from twin and single births,

respectively, which gave the multiplying factor 5.887 for

the pedigrees started from single births. Of course, this

result is only suggestive; but it was impractical to record

the additional 4,300 odd pedigrees necessary to get a true

random distribution. Treated this way, multiplying Table

V by 5.887 and adding to Table IX, Table XV is produced.

TABLE XV

No. Cases Sire Dam | Ave. No. Progeny| No. Cases Sire Dam lave. No. Progeny

18,82 | 1 1 1.33 13,826 | 1 1 133-

6,739 1 2 1.33 4,043 | 2 1 1.33

1,103 1 3 1.51 3 1 1.54

4,043 2 1 1.30 6,739 1 2 1.33

2,270 2 2 1.38 2,270 2 2 1.38

69 2 3 1.26 3 2 1.21

89 3 1 54 1,103 1 3 1.51

43 3 2 1,21 69 2 3 1.26

_ Treating the sires as in Tables VI and X, Table XVI is

produced.

No.611] FERTILITY IN SOUTHDOWN SHEEP 675

TABLE XVI

BREEDING PERFORMANCE OF THE MALES GIVEN IN TABLE XI

Sires | Mean . | Standard Deviation No. Cases

y ERPE TOE | 1.3340 = .00229 .48658 | -20,668

PATTE | 1.3308 = .00403 47677 | 6,382

Dats Baste E TEN 1.3318 = .2908 -49533 | 132

The difference between singles and twins is .0032

+ .0463; between singles and triplets, .0978 + .02916; and

between: twins and triplets, .1010 + .02936.

TABLE XVII

BREEDING PERFORMANCE OF FEMALES FROM TABLE XV

Dams Mean Standard Deviation No. Cases

E aa e a | 1.3274 + 0.00243 : 0.48261 17,958

yas ees A | 1.3444 = 0.00345 0.48713 9,052

ere EA / 1.4128 + 0.02533 0.49234 172

The difference between singles and twins is found to be

0.0170 + 0.00422; between singles and triplets, 0.0854

+ 0.02545; and between twins and triplets, 0.0684

+ 0.02556. Several of the differences in Tables XV and

XVI verge on significance, being at least three times the

probable error.

RELATIVE INFLUENCE OF MALE AND FEMALE IN

GRANDPARENTS

From the study of the relative influence of the sires

and dams on the progeny it would seem fruitless from

biometric grounds to look for transmission through one

sex more than the other. Yet logically it would seem that

the grandsire and grandam on the dam’s side would have

a more potent effect on the birth number from the dam

than would the paternal grandparents. Studies of this

sort are available from the pedigrees. Perhaps the first

concern is to determine the relation of the birth rank of

the grandparents to that of the progeny. Table XVIIT

presents this information.

676 THE AMERICAN NATURALIST [ Von. LI

TABLE XVIII

RELATION OF BIRTH FREQUENCIES IN GRANDPARENTS TO BIRTH FREQUENCIES

or P

ROGENY

Grandsire | Grandam > liros Ave. Progeny Sumun s No. Cases

l 1 1.6500= .00881 .5451 1740

į g 1.5 1.7041 .01488 6030 747

2 1 FO 1.7065=.01923 5717 402

2 2 2 1.7500+ .03328 5517 308

i 3 2 1.8095 = .08642 5871 21

3 J 2 2.0000= .07855 0000 6

z 3 2.5 1.6667 = .08297 .5634 21

3 2 25 1.7500 .14606 .4331

The difference between the average progeny from

grandparents 1 g X 19 and grandparents 2 § X19 is .0579

+ .02114. This is not three times the probable error,

therefore the difference is not significant. The differ-

ence between grandparents 1¢é X 19 and grandparents

1¢ 32 is .1609 + .08687. This also is less than three

times the probable error, hence is insignificant. In fact

none of the differences are significant.

To determine whether birth rank in males or females

among the maternal grandparents has effect on transmis-

sion, they were compared in the same manner as the sires

and dams were. The results for grandsires are:

TABLE XIX

RELATION OF BIRTH RANK OF GRANDSIRE TO BIRTH RANK OF PROGENY

Birth Rank of Grandsire| Ave. Progeny Standard Deviation) No. Cases

1 | 1.6675=.00760 5643 2,508

2 | 1.7209 .01442 5779 731

EE T TT | 1.9000 = .06399 3000. - 10

The difference between singles and twins is .0534

+ .0163; between twins and triplets is .1791 + .06559;

and between singles and triplets is .2125-+ .06444. The

difference between singles and triplets is 3.62 times the

probable error, while the difference between singles and

twins is 3.34 times its probable error.

. Treating the dams in the same manner as the sires

Table XX is produced:

No. 611] FERTILITY IN SOUTHDOWN SHEEP 677

TABLE XX

RELATION OF BIRTH RANK oF GRANDAM TO BIRTH RANK OF PROGENY

Birth Rank of Grandam| Average Progeny | Standard Deviation | th Olen.

1 | 1.6615=.00737 | .5064 | 2,148

2 | 1.7177=.01239 | .5979 1,059

3 1.7381 +.06034 ‘5798 | | 42

The difference between singles and twins is .0562

+ .01435; between singles and triplets i is .0766 + .06079;

and obre twins and triplets is .0204 + .06159. The

only significant difference is between singles and twins,

which is 3.88 times the probable error.

The probable errors involved seem to indicate little,

hence a comparison by correlation of the maternal grand-

sire and progeny, and maternal grandam and progeny

was instituted. Table XXI presents the correlation for

the maternal grandsire, Table XXII for the maternal

grandam.

TABLE XXI

CORRELATION OF MATERNAL GRANDSIRE AND PROGENY

Birth Rank Progeny

Birth Rank Grandsire f

1 2 3 4

1 54 1,435 118 1 2,508

2 251 431 49 731

3 9 1 10

f 1,205 1,875 168 1 3,249

TABLE XXII

CORRELATION OF MATERNAL GRANDAM AND PROGENY

Birth Rank Progeny

Birth Rank Grandsire pine d

1 2 3

1 811 1,254 82 2,148

y EEE TA 381 596 82 1,059

3 3 25 14

f. 1,195 1,875 178 3,249

The coefficient of correlation for Table XXT is .0496

+ .0118, while for Table XXII it is .0382 + .0118. The

difference between the correlations of maternal grandsire

678 THE AMERICAN NATURALIST [ Vou. LI

and grandam is .0114 + .0167, a difference insignificant,

hence one can not assume sex linkage.

EXAMINATION OF SHROPSHIRE DATA FROM THE MENDELIAN

STANDPOINT

A number of Shropshire pedigrees were tabulated which

were all started from triplet births. It had seemed from

inspection that triplets might be genetically different from

twins and singles, hence the pedigrees were tabulated to

discover such a difference if possible. If the maternal

grandparents affected the number at a birth from their

daughter, then it was possible that certain differences

might appear in the pedigrees indicating the genetic ef-

fects. The results follow.

TABLE XXIII

RELATION OF BIRTH RANK IN OFFSPRING TO BirTH RANK IN DAM WHEN

TH TERNAL GRANDPARENTS ARE SINGLES

Offspring

Dam 1 | 2 | 3 | 4 | Mean | Standard Deviation

AEN 17 16 | 17 0 2.00 0.824

ee 12 10 15 1 2.13 0.894

eS Q a l 0 3.00 0.000

TABLE XXIV

WHEN MATERNAL GRANDSIRE IS A SINGLE AND MATERNAL GRANDAM IS A

TWIN

Offspring

Dam | 1 | 2 3 _ Mean Standard Deviation

a ESITA ENE 15 9 15 2.00 0.873

AE TEOT 10 9 25 2.34 0.825

3.. 5 0 0 1.00 0.000

TABLE XXV

MATERNAL GRANDSIRE A TWIN, MATERNAL GRANDAM A SINGLE

3 Mean Standard Deviation

= aq QO

oom wN

13 ;

T 2.00 0.858

0 1.00 0.000

No. 611] FERTILITY IN SOUTHDOWN SHEEP

TABLE XXVI

MATERNAL GRANDPARENTS TWINS

Dam | 1 | 2 3 | Mean | Standard Deviation

by Ee 4 2 4 2.00 0.895

vae 9 9 9 2.00 0.817

desd tay 0 1 2 2.67 0.417

TABLE XXVII ;

MATERNAL GRANDSIRE A TRIPLET, MATERNAL GRANDAM A SINGLE

Offspring

Dam 1 | 2 | 3 | Mean | Standard Deviation

i E R E 0 0 0 0.00 000

Biiiecsverten 0 1 0 2.00 0.000

AES anger 0 0 0 0.00 0.000

TABLE XXVIII

MATERNAL GRANDSIRE A SINGLE, MATERNAL GRANDAM A TRIPLET

Offspring

Dam | 1 2 | 3 | Mean | Standard Deviation

Lio 0 0 | 0 0.00 0.000

ict deccs (ek 0 0 | 1 3.00 0.000

Lee mane 0 0 1 3.00 0.000

TABLE XXIX

MaTERNAL GRANDSIRE A TRIPLET, MATERNAL GRANDAM A TWIN

Offspring

Dam | 1 | 2 3 | Mean | Standard Deviation

a S 0 0 0 0.00 0.000

Dianna 1 0 0 1.00 0.000

SEE 0 0 i 0 0.00 0.000

TABLE XXX

MATERNAL GRANDSIRE A TWIN, MATERNAL GRANDAM A TRIPLET

Offspring

Dam | 1 | 2 | 3 Mean | Standard Deviation

ET tes 0 0 1 3.00 0.000

» Cee 0 1 1 2.50 0.500

Sass seeaesde 6. 0 0 0.00 0.000

680 THE AMERICAN NATURALIST [ Von. LI

Since all the pedigrees were started from triplets the

excess of triplets is so great as unduly to weight the

ratios. Inspection of the ratios does not reveal any par-

ticular difference in the progeny descended from a par-

ticular pair of grandparents, whether the dam is a single,

twin or triplet. Since also there seems to be no sex link-

age involved it seemed desirable to combine similar

matings from the standpoint of birth rank. The totals

produced are presented in Table XX XI.

TABLE XXXI

SUMMARY OF TABLES XXIII TO XXX witH RESPECT TO BIRTH RANK OF

MATERNAL GRANDPARENTS

No. Offspring

Birth Rank Maternal Grand- 1 2 3 4 Mean | Standard Deviation

parents

Both i ag single... 29 26 33 1 2.07 0.85851

One grand . seal AG 26 60 0 2.11 0.88983

Both grandpa coh twins...| 13 12 15 0 2.05 0.83516

One grandparent a pa 1 2 4 0 2.43 0.70855

Confirmation of the previous view that twins and singles

are genetically alike, while triplets differ from either,

seems to be found in Table XXXI. However, the differ-

ence between triplets and the mating where one grand-

parent is a twin is only 0.32+0.20. This is not three

times the probable error, but by consulting Pearl and

Miner’s (11) table it is found that the chances that the

difference is significant are about two and a half to one.

CONCLUSIONS-

1. In general sheep of a high birth rank tend to produce

offspring of a high birth rank.

2. On the basis of the few data presented, the high-

est record of a ewe appears to be a better selection stand-

ard for high fertility than a random record.

3. The frequency of multiple births in sheep varies with

the breed. ,

4. Physiological factors may exert a marked influence

No. 611] FERTILITY IN SOUTHDOWN SHEEP 681

on heredity, the most important factors being the vigor

of ewe, the feeding of ewe, the age of ewe, the season and

the region.

5. Apparently no relation exists between high fertility

and additional mamme.

. In pedigrees started from single births, the birth

rank of the sire does not affect the birth rank of the prog-

eny; in pedigrees started from twin births, the effect of

high birth rank of the sire is only slightly significant

(more than three times the probable error).

7. The effect of birth rank of ewe on the birth rank of

progeny is the same as that of the sire except in the case

of pedigrees started from twin births when it is slightly

greater.

8. No evidence for a sex linkage of fecundity factors

occurs in the pedigrees tabulated, as shown by a com-

parison of the relative influence of progeny of the mater-

nal grandam and the maternal grandsire.

9. Evidence from Shropshire triplet pedigrees suggests

that triplets are genetically different from twins and

singles, which two are probably genetically alike.

LITERATURE CITED

Ainsworth-Davis, J. R., and Turner, D.

1913. Fecundity of Sheep. In V Cong. Internat. Agr. Gand., Sec. 3,

question 4, p. 5

Bell, Serag Graham.

190 Seg apa Sheep of Beinn Breagh. In Science, N. 8.

9, p A

1912. Sheep Srecding Experiments. In Science, N. S., Vol. 36, pp.

Carlyle, W. E: ac McConnell, T. F.

1912. Some Observations on Sheep Breeding from the Experimenta-

tion Flock Records. In Wisconsin Sta. Bul., 95, p. 19.

Evvard, J. M.

1913. pien Data.

Heape, Walte

1899. peers Barrenness and Fertility in Sheep. In Journal of

Royal tip Soc. England, 3d series, Vol. 10, pp. 234-248.

Humphrey, Geo. C., and Kleinheinz, Frank.

1907. Darlia on Sheep Breeding from Records of the University

Flock. In 24th Annual Report, Agr. Exp. Sta., University of

Wisconsin, pp. 25-41.

682 THE AMERICAN NATURALIST [ Vou. LI

Jones, J. M.

1912. Sheep Breeding and Feeding Experiments. In- New Hamp-

shire Sta. Bul., 163, pp. 24-28.

Marshall, F.

1910. pijaiclogy of Reproduction. London, p. 598.

phe Raymond.

913. Note ah pan ve Relation of Age to Fecundity. In Science,

N. Vol. 37, pp. 226-228.

1917. The ‘Probable Error of a Difference and the Selection Problem.

In Genetics, Vol. 2, No. 1, p. 78

Pearl, Raymond, and Miner, John Rice.

1914. A Table for es ep Probable Significance of ree

i ants. In Papers m the Biological Lab. N

226. Maine Agr. Exp. “og p. 88.

abe Pep et

Hypes ma Breeds of Farm Animals. Boston, p. 391 (cites data

| of Mansell’s).

Rietz, H. L., and Riper, E.

1915

iii a Resemblance of Parents and Offspring with Respect to

Birth T for Registered Shropshire Sheep. In U. S.

t. ‘als Jour. Agr. Research, TA 4, No. 6, pp. 479-510.

Youatt, Wm

1837. EREN Their Breeds, Management and Diseases. London, p. 508.

LINKED QUANTITATIVE CHARACTERS IN

WHEAT CROSSES

DR. GEORGE F. FREEMAN

ARIZONA AGRICULTURAL EXPERIMENT STATION

Sıxnce wheat has but 8 chromosomes in the sexual cells

and since the parents in the macaroni bread wheat crosses

here discussed certainly differ in more than 8 visible char-

acters, it was thought likely that a genetic linkage of

some of these might be found. The following study is an

endeavor to discover whether or not there is such a link-

age between the shape of the head, 7. e., ratio of width of

head (measured parallel to the face of the head which

shows the sinuous furrow formed between the two rows

of spikelets) to the thickness (measured parallel to the

array of seeds in the spikelet) and the texture (trans-

lucency or opaqueness) of the grain. Of the two parents

here discussed No. 1, the macaroni wheat, had a much

flattened head and very hard translucent grains, whereas

the other parent, No. 35 (a bread wheat), had a nearly

square head with soft opaque grain.

The seed on the F, plants of this cross were all wrinkled

and intermediate in texture between the two parents, 7. e.,

they were dull, being neither translucent like the macaroni

parent nor opaque like those of the bread wheat parent.

In order to make a quantitative expression of hardness

the perfectly translucent grains of the macaroni parent

were called 100 per cent. hard, the seeds of the F, 50 per

cent. hard and those of the bread wheat parent were

called 0 per cent. hard. Since in the seeds of the F, and

F, plants every possible degree of intergradation oc-

-curred between the characters of the two parents and

since any form of classification adopted would be purely

arbitrary, it was decided to make it the most simple pos-

sible and place all of the variants into three groups by the

following means: a grain that was approximately as hard

683

[ Vou. LI

THE AMERICAN NATURALIST

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No. 611] LINKED CHARACTERS IN WHEAT CROSSES 685

as the macaroni parent was called 100 per cent. hard; a

grain as soft as the bread wheat parent was called 0 per

cent. hard; all grains intermediate between these were

called 50 per cent. hard. A plant which produced 60 per

cent. hard grains, 30 per cent. intermediate grains and 10

per cent. soft grains would therefore be classified as

follows:

.60 X 1.00 + .30 X .50 + .10 X 0—.75 = 75 per cent. hard.

Spotted grains (grains containing well-defined areas of

opaque starch in an otherwise translucent grain) such as

occur frequently in the macaroni wheat and also among

the hybrids were treated as intermediate grains. After

classifying the seeds of each plant in this manner all

those which were over 663 per cent. hard were termed

hard wheats, those from 334 to 66% per cent. hard were

classed as intermediate and all less than 334 per cent.

hard were classed as soft.

In 1914 the two parents (Nos. 1 and 35) and F, of this

cross were grown with the following results:

The ratio, W./T. of the F, plants of this cross, is thus

seen to be much nearer to the macaroni parent both in

average and distribution than it is to the bread wheat

parent. i

Table II shows this same study made for the F, plants,

grown in 1915.

_ A uniform correlation between the hardness of the

grain and the ratio of width to thickness of head is ap-

parent in Table II.

Table III gives the results of this same study for the

crop of 1916. There is again apparent a marked correla-

tion between the ratio of width to thickness of head and

the texture of the grain. It will be noticed that both in

1915 and 1916 the soft (0 per cent. hard) hybrids had a

higher average ratio W./T. than the sonora. It should,

however, be remarked that the hybrid softs were also

harder on the average than the pure number 35, but since

686 THE AMERICAN NATURALIST . [Von. LI

TABLE IV

DISTRIBUTION OF PLANTS WITH REGARD TO THEIR PERCENTAGE OF HARD

GRAINS AND THE RATIO OF WIDTH TO THICKNESS OF HEAD

Pure No. 1 in 1915 Pure No. 1 in 1916

Percentage of Hard Grains Percentage of Hard Grains

100| 95 | 90 | 85 | 80 | 75 70 | 65 60 | 55 | 50 |100 95 | 90| 85! 80 75| 70) 65) 60| 55| 50

96| 91 | 86 | 81 | 76 | 71 | 66 | 61 | 56 | 51 | 46] 96 91 | 86 81| 76 71| 66) 61| 56| 51| 46

244 |

240| 1 |

239 |

235

234

230

229

225 1

224

220 1

219

215

214

210 1 1 1

209

205

204

2001 111 Err ee 12

199

195

194

190| 1 1 { 2-a 1

189 >

185| 5 E AEA be Seer 2d

184

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No. 611] LINKED CHARACTERS IN WHEAT CROSSES

687

Pure No. 1 in 1915

Percentage of Hard Grains

100 | 95 | 90 | 85

96| 91| 86 | 81

80 | 75 | 70| es | 60 | 55

sa 61| 56 51

Pure No. 1 in 1916

Percentage of Hard Grains

100

95 |9085 30| 75| 70 65

91 |8681, |76)7 71| 66 61

60| 55

56 51

80 1

2/1]

they were opaque and graded insensibly into the condi-

tion of pure No. 35 it was considered impracticable to

make the arbitrary designation of degrees of hardness

any more complex than the three groups used. It should

be added, on the other hand, that a number of races were

secured which were as soft or softer than the type of No.

35 and a number of races which, to all appeafances, were

* fully as hard as pure No.1. The inheritance of hardness

will, however, be reserved for discussion in a later paper.

The question now arises as to whether this correlation

is genetic or physiological. Might it not be caused by the

simple fact that poorly filled (with starch) hard grains -

will give rise to a more flattened head, than will plump

(starchy, soft) grains by failing to fill up and distend the

688 THE AMERICAN NATURALIST [ Von. LI

glumes? This question can be answered by studying the

correlation between the flattening of head and hardness

of grain in a pure race. Since all of the No. 35 was soft,

this study could not be made for the soft wheat, but as

there were many plants of the pure macaroni which pro-

duced a greater or less proportion of soft grains, a com-

parison was possible. That the plants producing a large

proportion of hard grains on an average did not have

more flattened heads than those which produced a greater

proportion of soft grains is shown in Tables II and III

by comparing the ‘‘hard’’ with the ‘‘intermediate’’

groups of pure No. 1. This is perhaps better shown in

Table IV, where the distribution of the plants is made

with regard to their hardness per cent. and the ratio of

width to thickness of head. oo

It should be noted from Tables II and III that there

are numbers of individual plants with low ratios of width

to thickness of head, but with high percentages of hard

grains. It is difficult to see how this could occur if the

low ratio was due simply to the lack of plumpness of the

hard grain. .Moreover, races of hard macaroni wheats

occur which have approximately square heads, and there

are varieties of soft wheats (Little Club) with rather

strongly flattened heads. In 1916 there were a few cases

where hybrid races having low average ratios (W./T.)

also were rather high in average per cent. of hard grains.

All of the races in 1916 having ratios averaging as lew or

lower than 1.35 and average percentages of 60 or more

per cent. of hard grains are given in the following table:

It is thus seen that all of the races which on the average

violated the correlation in 1916 came from plants which ,

more or less markedly violated this same correlation in

1915. The cases given would indeed be hard to explain

on a basis of violation of physiological correlations but if

we are dealing with a genetic correlation, they may be

easily explained on the ‘‘cross over’’ theory as used by

Morgan for reversal of linkages in the characters of Dro-

sophila.

No. 611] LINKED CHARACTERS IN WHEAT CROSSES 689

TABLE V

INHERITANCE OF NON-CONFORMITY TO USUAL CORRELATION BETWEEN ater

ATIO W./T. oF HEAD AND AVERAGE PERCENTAGE OF HARD GRAIN

Parents in 1915 Offspring in 1916

w./T. Per Cent H. wW./T. Per Cent H.

132 93 98 1.34 88

169 1.10 50 1.24 73

219 1,20 50 1.35 ‘93

232 1,25 100 1.33 86

239 1.33 1,30 88

263 1.00 64 1.17 61

279 | 1.27 50 | 1.35 79

In+the opposite direction, 7. e., races which markedly

violated the correlation by abies very high ratios (1.50

or more) but with low percentages of hard grains did not

occur.

Again it may be objected that an explanation of this

correlation between shape of head and texture of grain

as a genetic linkage, is incorrect because the linkage is

not complete, 7. e., there is considerable regression. This

objection may be fully met by the observation that both

of the characters here concerned are quantitative and

hence subject to fluctuation around a mean. Moreover, it

` is almost certain that both characters are genetically com-

pound, i. e., each are the result of more than one factor,

recombinations of which may markedly vary the quanti-

tative visible expression of the characters. If, therefore,

but a single factor for grain texture be linked with one of

the factors concerned in the shaping of the head, there

will result a partial ae of these two characters

such as we find.

The data here presented, therefore, seems to indicate

that the two characters, hardness of grain and high ratio

of width to thickness of head, which entered this cross

together in the macaroni parent, tend to come out together

in the segregates of the F, and F generations, 7. e., that

there is a genetic linkage between one or more of the

factors controlling the grain texture and head shape in

the two varieties employed as parents.

ON REVERSIBLE TRANSFORMABILITY OF

ALLELOMORPHS

H. TERAO

THE IMPERIAL AGRICULTURAL EXPERIMENT STATION, TOKYO, JAPAN

In genetical studies of variegation in plants, the fact

has been observed occasionally that with a certain fre-

quency a dominant allelomorph occurs in the correspond-

ing recessive homozygote (De Vries,! Correns,? and

Emerson’). In this paper the author presents a new in-

stance of a similar phenomenon, which it is hoped may

throw additional light on the subject.

In certain pedigree cultures of the rice plant, Oryza

satwa L., there happened to occur in 1912 families con-

taining besides ordinary fertile plants a number of sterile

plants. These sterile plants were normal in their growth,

but showed a considerable barrenness at the ripening

season. Some of them yielded no seed whatsoever, others

bore a small number of normal seeds, and very few were

mosaic forms with higher fertility. These families, two

in number, each belonging to a different variety, were

derived from single plants of the former generation, and

were very uniform in other characters. From them the

experiment was started.

The rice plant, being a self-pollinated species, is con-

venient material for breeding experiments. Although

the experiments in this investigation were made largely

from open-pollinations, the results obtained were always

similar to those from experiments in which plants were

artificially protected against accidental natural crossing.

The observations of 1912 and 1913 are shown in sum-

marized form in Tables I and II, a and b, and point to the

following conclusions. Sterility behaves as a simple re-

1De Vries, H., ‘‘Die Mutationstheorie,’’ Bd. I, 1901, pp. 489-511;

‘Species and Varieties, their Origin by Mutation,’’ 1905, pp. 309-339.

2Correns, C., Berichte der Deutschen Botanischen Gesellschaft, Bd. 28,

1910, pp. 418—434.

3 Emerson, R. A., AMERICAN NaTuRALIST, Vol. 48, 1914, pp. 87-115;

Genetics, Vol. 2, 1917, pp. 1-35.

690

No. 611] - ALLELOMORPHS 691

cessive to fertility, and the seeds resulting from partial

fertility of sterile plants again give segregating families.

In Family A, which shows an exceedingly slight fertility

of sterile plants, the segregation ratio in the offspring

derived from fertile individuals is quite close to expecta-

tion, but in Family B which shows a considerably higher

grade of partial fertility of sterile plants, the progeny of

fertile individuals exhibit considerable deviations from

the expected segregation ratio.

3 TABLE I

THE SEGREGATING FAMILIES, A AND B, IN 1912

oe Sterile Plants

Fam. Total | Ratio per 4 Total | Fertile Spikelets

Fertile Sterile | No. of | Steriles % | No. of ene

Plants Plants Ind. | D R gg No. | 4

| !

ca. |

Aries 36 13 49 26.53 2.94 1.06 9,000 2 0.02

Ss sealers 105 25 130 19:23 | 3.23 0.77 |14,941| 434 | 2.90

TABLE II

THE FAMILIES DERIVED FROM FAMILIES A AND B

(a) The Progeny of the Fertile Plants

No. of Families f Ratio per3 ` Segregating Families

E Uni- wire eae Total

Families | Families vid

A. 10 22 32 0.94 2.06 | 1,068 346 414 | 24.46

B. 41 64 105 E17 1.83 | 4,874 | 1,301 te 21.06

(b) The Progeny of the Seeds on the Sterile Plants

ber

Aon. | Se | 2 | 0 | ee L

bE 24 401 115 516 | 22.29

These facts may be interpreted by the following hy-

pothesis. The dominant and the recessive types con-

cerned are assumed to be transformed by certain un-

known causes into the other allelomorph. The recessive

allelomorph which has made its appearance in Families

A and B is assumed to have originated in the preceding

692 THE AMERICAN NATURALIST _[Vou. LI

generation by the transformation of the dominant allelo-

morph. This recessive state of the hereditary substance,

however, has a tendency to revert into the original domi-

nant state. Such reversion is especially likely to occur in

vegetative cells, where each recessive allelomorph seems

to be able to revert independently. Consequently, in reces-

sive homozygotes the reversion generally will produce

heterozygotic cells, either one of the two recessive alle-

lomorphs being changed into the dominant. The hetero-

zygotic cells thus formed will give rise to partial fertility

in otherwise sterile plants. Again, the recessive allelo-

morph in heterozygotic cells may be subject to similar

reversion, and such reversion may occur both in the

heterozygotic cells of sterile plants and in normal hetero-

zygotes. Here, however, heterozygotic cells will be

transformed into dominant homozygotic cells without

visible effect on the plant concerned. The consequence

of this reversion in the next generation will be that the

proportion of the dominant segregates may exceed the

theoretically expected figure. Finally, it may be assumed

that between Families A and B there exists a difference

in the reverting tendency of the recessive allelomorph,

which necessarily will effect the differences in both the

intensity of partial fertility of sterile plants and the devi-

ations in the segregation ratio.

In Table ITI the segregating families derived from the

fertile plants of Family B are classified according to the

magnitudes of the deviations in terms of probable errors.

The true percentage for the recessive is assumed, in the

one case as 25 per cent. (the Mendelian ratio), and in the

other case as 21 per cent. (an arbitrary number). In

comparing the two different frequency distributions made

in this manner with the theoretical frequency distribu-

tion, it is observed that while the frequency distribution

of the deviations from 25 per cent. shows a considerable

discrepancy from the theoretical, the latter fits the fre-

quency distribution of the deviations from 21 per cent.

rather closely, the goodness of fit being P = 0.915. Con-

sequently, the ca. 4 per cent. deficiency of recessive segre-

No. 611] ALLELOMORPHS 693

gates is a normal expectation and not an experimental

error.

TABLE III

THE FREQUENCY DISTRIBUTION OF THE DEVIATIONS IN THE SEGREGATION

RATIOS IN THE GROUP OF 64 SEGREGATING FAMILIES DESCENDED

FROM FAMILY B OF THE YEAR 1912

Dev. /P.E. i —5 —4 —3 -2 —l 0 +i +2 +3 +4 +5 Total

I } | | | | + | | |

Experimental frequency (I). . iher 14; 17 15} | 2l

Experimental frequency HD: aS a il 10 64

Bx pecsation:.G. os ee ee pdt 10.3 16.0, ed ACECHAR

Note: In the apaina MERRTE (I) the true ai for re-

cessives is taken as 25 per cent., and in (II) as 21 per cent.

Such an aberrant segregation ratio seems to be a con-

stant tendency all through the generations descended from

Family B. This is shown in Table IV in which the ex-

periments in the years from 1912 to 1915 are summarized.

TABLE IV

THE ABERRANT SEGREGATION-RaTIOS OBTAINED IN THE Years 1912-1915

| i |

`- WE rie. vy 1 | Fertile 130) 105|. 25 | 19.23| 6.77} 2.55} 23

IMS “i 64 r 6,175| 4,874 | 1,301 | 21.06| 3.94 | 0.37 | 10.6

{b14 49h 40 “ 1,560] 1,207 | 353 | 22.63| 2.43 | 0.74 | 3.3

161g eT: 53 a 4,696] 3,732 | 964 | 20.52 |. 4.48 | 0.47| 9.5

Total....| 128 12,561| 9,918 2,643 | 21.04! 3.96 | 0.26 15.2

i a.: 24 | Sterile 516| 401 | 115 | 22.29! 2.71 | 1.21} 22

it. dk 34 ‘t 994| 779| 215 | 21.63| 3.37 |: 0.93 | 36

1018 23>: 19 a 684| 522| 162 23:68 | 1.32 iil 1.2

H Í

Tota.: d 7 2,194| 1,702 | 492 | 22.43| 2.57 | 0.62 | 4.1

Again, in regard to the intensity of partial fertility of

sterile plants, the descendants of Families A and B ex-

hibited respectively relations similar to those seen in 1912.

(Family A was not traced after 1913.) A count of fertile

spikelets on sterile plants descending from Family B was

made in 1914 on 281 plants bearing a total of 101,412

spikelets. In this count the number of fertile spikelets

was 3,857, corresponding to 3.78 per cent. of the total

number of spikelets. The latter figure may be regarded

_as the average fertility of sterile plants in the progeny

of Family B. :

694 THE AMERICAN NATURALIST [Vou. LI

The fertile spikelets of sterile plants are generally scat-

tered at random over the panicle, and each fertile spikelet

may be regarded as representing a separate case of re-

version; but in mosaic forms which show higher fertility

and are of rarer occurrence, the reversion may have

taken plaee in earlier stages of plant development, result-

ing in larger fertile sections. Consequently, when the

count of fertile spikelets is made with only the first type

of sterile plants, a more correct value for the frequency

of reversion may be obtained. The result of such a count

on 902 panicles containing 93,635 spikelets is 1,858 fertile

spikelets, i. e., 1.98 per cent. of the total number of

spikelets.

The mosaic forms appear in several different grades of

partial fertility. In a panicle either one or more branches

or even one half of the panicle can be highly or entirely

fertile, the remaining part being absolutely or nearly ab-

solutely sterile. Similarly, in a single plant some whole

panicles can be entirely or highly fertile while others are

of the ordinary grade of partial fertility. Furthermore,

similar mosaic conditions were also observed in single »

flowers of sterile spikelets. While all six anthers of a

sterile spikelet generally bear none or but few pollen

grains, occasionally flowers appear in which certain

anthers contain a considerable number of pollen grains

of normal appearance and others show the ordinary state

of sterility. Hence it may be assumed that the reversion

can take place at any stage of plant development.

The partial homozygosity of heterozygotes, correspond-

ing to the partial fertility of sterile plants, may be esti-

mated in the following way. Assuming that the possi-

bility of reversion at any stage of a plant’s life, similar

to that observed above, may also occur in heterozygotic

cells, then we may distinguish for convenience two differ-

ent types of reversions; there is the reversion which will

cause partial homozygosity within a single flower, and the

reversion which will produce an entirely homozygotic

spikelet or larger homozygotic sectant. Suppose then

that the latter reversion will give to the heterozygote

No. 611] ALLELOMORPHS 695

homozygotie (AA) spikelets in any part ‘‘x’’ of the total

number of spikelets which is taken as a unit, and again

that in the remaining (1 — x) part of the total number of

spikelets, the other type of reversion will occur, turning

some part ‘‘y”’ of the whole generative tissue taken as a

unit from the Aa state to the AA state. For simplicity,

however, we may substitute ‘‘x’’ for ‘‘y’’ in the above re-

lation, because it seems presumable that a similar prob-

ability of reversion may exist constantly all through the

plant life. Such a plant will have the following consti-

tution in regard to the generative tissue:

x(AA) + (1—x)[x(A‘A) + (1 — x) (Aa)].

As the result of self-pollination, the progeny of such a

parent plant will show the constitution:

x(AA) + (1 —x)[4(1+ x)?(AA) + $(1 — x?) (Aa)

+4(1 — x)?(aa)].

Applying arbitrary values to ‘‘x’’ in this formula, we

shall get numerical relations among segregates. In

Table V the results of such calculation are compared with

results obtained by the experiments in 1913-1915. Thus

we may find the average partial homozygosity of hetero-

zygotes around 4 to 6 per cent., the average partial fer-

tility of sterile plants being, as was already shown, ca.

4 per cent.

TABLE V :

CALCULATIONS ON DATA OF TABLE IV

; x % (AA+Aa) aa AA Aa

ag eee 77.88 % 22.12% || 38.74% | 61.53%

Sts See eae 78.57 21.43 39.69 60.31

Observation, No. of Inds...... 9,918 2,643 94 . 1135

Parodtitegh > e oo a 78.96 % 21.04% 41.05% | 58.95%

It has also been noticed that the sterility concerned is

associated with an abnormality represented by the be-

havior of chlorophyll at the ripening of seeds. While, at

the ripening season, the chlorophyll in the fertile sections

of the mosaic forms turns to yellow just as in ordinary

fertile plants, the chlorophyll in the sterile sections still

696 THE AMERICAN NATURALIST [Vou. LI

remains green. The fertile spikelets occurring in a small

number on the otherwise sterile panicle appear on rip-

ening as yellow spots scattered among green spikelets;

the plants with both sterile and fertile panicles appear in

the fall also as mosaic forms with green and yellow

leaves. This feature of the sterile plants is in direct

contrast to the behavior of the mosaic plants with the

variegated and the entirely green leaves studied by De

Vries and Correns.

The observations in the foregoing pages seem to paral-

lel those made by the authors cited at the beginning of

this paper. In the present investigation, however, there

was observed also the transformation of allelomorphs in

the opposite direction, that is, the transformation of the

dominant allelomorph into the recessive allelomorph,

something scarcely mentioned in the investigations re-

- ferred to above. The observations in this regard were in

brief as follows.

In the first place, the spontaneous occurrence of segre-

gating families was observed again among the descend-

ants of the families which had proved in the experiments

already described to be constantly fertile. This suggests,

just as did the occurrence in Family A and Family B in

1912, the probability of the AA cell changing into the Aa

cell.

In the second place, a constant tendency of the dom-

inant allelomorph to be transformed into the recessive

allelomorph. was observed in certain strains. In 1913,

special attention was paid to such segregating families in

which the excess of recessive segregates over the theo-

retical expectation was particularly high. Although, as

already noted, the variation among the segregating fam-

ilies in 1913 with regard to the deviations from the reces-

sive proportion might possibly have arisen from experi-

mental errors associated with a certain probability of alle-

lomorphic reversion from recessive to dominant, yet it

was deemed not impossible that the very considerable

excess of recessives exhibited by certain families might be

caused by other reasons. This point was seemingly de-

No. 611] ALLELOMORPHS 697

cided by the experiment made with Family B80 in 1913

(Table VI), since in this family there was noticed a con-

stant tendency toward the allelomorphic transformation

under consideration.

TABLE VI

THE SEGREGATION OF FAMILY B/80 AND Irs DESCENDANTS

> | No. of Parent. a | oni Sterile aaa of

se Families plants Brent Plants | Plants | Oye | Rocessives | 7 =

wa. 1 Fertile 991 69| 30| 30.30% | + 5.30% | 2.95%

1914.... 10 $ 1,020 Tal 293 28.73 + 3.73 0.9

1916... 5 4 435 309 126 28.89 + 3.89 | 1.40

1916:... 98 A 11,013) 7,832; 3,181 28.88 + 3.88 0.28

Total. . 114 Fertile gaa 8,937 | 3,630 28.89%-| + 3.89% |: 0.26%

| | ;

1914 (a). 161 | Sterile 199, 147| 52 |- 23.62% | — 1.38% | 2.04%

1914 (b). 131 Sterile 100 5 95|- 95. oo% | oe 00% 2.92%

aki 592 ie 548 32 516 94.1 1.25

1916....| 1202 | i 1,436) 99| 1,337| 93. ii E mar is | 0.77

Total. . 1923 | Sterile 2,084 136| 1,948| 93. 47% | | +68. 17% 0.64%

1 Derived from the family in 1913, i. e., Family B/80.

2 Derived from the group (d in aie?

3 Excluding the group (a) in

In Table VI there is beside the ca. 4 per cent. ex-

cess of recessives in the families derived from fertile

parents, a remarkable excess of recessives in the families

descended from the sterile parents in the group (b) in

1914. The sterile plant of this type could not be distin-

guished from those which, as was shown in Table IV,

gave segregating families with an excess of dominants in

the intensity of the partial fertility as well as in the be-

havior of chlorophyll at the ripening of the seeds. Con-

sequently, it may be presumed that although these two

types of sterile plants have the same genetical constitu-

tion originally, the dominant allelomorphs resulting from

the reversion of their recessive allelomorphs are of dif-

ferent stabilities in the dominant state; that is, in the first

type of sterile plants such dominant allelomorphs are

very easily re-transformed into the recessive state, while

in the second type the corresponding dominant allelo-

morphs tend to remain in the reverted condition.

698 THE AMERICAN NATURALIST [ Von. LI

Corresponding to the excess of recessive segregates, a

deficiency of dominant homozygotes among dominant seg-

gregates was also noticed. Among 153 families derived

from fertile plants in the experiment above mentioned, 40

families were uniformly fertile, the remaining 113 fami-

lies showing segregation. The former, therefore, is 26.14

per cent. of the total number of families, and shows

7.19 per cent deficiency from the theoretically expected

percentage, 33.33 per cent., the probable error being

+ 2.68 per cent.

In conclusion it may be stated that the allelomorphs

concerned in this investigation are probably subject to

reversible transformations, and that the probable fre-

quency of the allelomorphic transformation may be prac-

tically constant in a certain strain, and possibly may be

different in different strains. As to the conditions under

which such allelomorphic transformations take place,

nothing is yet certain except that these conditions are of

a hereditary nature. The manner in which different in-

tensities of allelomorphic transformations are inherited

will be the subject of further investigation.

A word may be added here regarding the conception

of dominance and recessiveness. Bateson’s theory of

‘‘presence and absence of factors’’ is sometimes under-

- stood in the sense that the dominant allelomorph is re-

garded as due to the real presence of an hereditary mate-

- rial unit which is absent in the recessive allelomorph.

Such a conception is not in full accordance with the idea

of the reversible transformability of allelomorphs as de-

seribed in this investigation. There is another possibility

of the nature of allelomorphs. The dominant and the re-

cessive allelomorphs may be supposed to represent two

alternative conditions or phases of a single hereditary

substance, somewhat resembling the chemical conception

of polymerization. Consequently, the interchangeability

between the dominant and recessive allelomorphs is not

improbable theoretically.

BUSSEY INSTITUTION,

August 26, 1917

NOTES AND LITERATURE

MUTATIONS IN DROSOPHILA BUSCKITI COQ.*

Two mutations in eye color have appeared in my cultures of

Drosophila busckvi. These mutations are of especial interest in

that, as far as the writer has been able to learn, they are the first

that have been recorded in this species. This is the eighth

species of Drosophila in which mutations have been recorded,

the other seven being ampelophila, repleta, confusa, tripunctata,

virilis, obscura, and similis.

The eye mutant which is brighter than normal has been ealled

‘*red’’ and the other which is darker than normal has been called

‘*ehocolate.’’ The normal eye of this species is darker than that

of Drosophila ampelophila. The mutant red corresponds very

closely to the normal eye color of ampelophila except that it is

slightly brighter. Ridgeway’s ‘‘scarlet’’ (Plate I, color num--

ber 5, Ridgeway’s Color Standards and Nomenclature, 1912)

corresponds most nearly to the eye color of this mutant. In

the red eye the central fleck shows as a small round point, while

in the normal busckii eye, it appears larger and less definite

in shape. The red eye darkens with age and closely approaches

the normal eye in color, but at its darkest stage it can be dis-

tinguished from the normal in that it is less translucent. The

chocolate eye is an opaque brown and presents none of the shiny

appearance of the normal eye. The central fleck is invisible in

newly emerged flies, but becomes more or less distinct as the fly

ages. With age the color approaches normal, but always remains

slightly darker. Flies over forty-eight hours old so nearly ap-

proach normal that they are difficult to distinguish. A newly

emerged chocolate corresponds most nearly to Ridgeway’s

‘*chestnut brown’’ (Plate XIV, color number 11, tone m}.

The mutation red eye was first observed in November, 1916,

and it seems probable that the original mutation occurred some-

what earlier and was overlooked as several red-eyed flies, both `

males and females, were obtained from this cross. The original]

stock had been collected about a month earlier in a tomato patch

No. 157.

699

700 THE AMERICAN NATURALIST [Vou. LI

near Bloomington, Indiana, and had been bred in the laboratory

for two generations.

The mutation chocolate eye was first observed in December,

1916, and here again the original mutation had probably been

overlooked as in the cross where the mutation was first ob-

served, several chocolate males and females appeared. The orig-

inal stock in which this mutation appeared had been bred in the

laboratory for three generations and was collected in the same

tomato patch where the original red eye stock was collected.

The stock in which the red eye appeared was collected on Sep-

tember 19, 1916, and the stock in which the chocolate eye ap-

peared was collected September 14 of the same year and these

stocks had been bred as two separate strains when the mutations

appeared.

Tue Genetic BEHAVIOR or Rep Eye

Some of the first observed red males were mated to virgin red

females and the offspring of this cross were all red flies. This

red stock has been kept going for several generations and has

‘given all typical reds. Both red males and red females were

crossed with normal wild flies and in F, of each cross nothing

but normal flies were found. Table I gives the results of the F,

of these crosses.

TABLE I

F, oF Rep X Witp Cross

Red 9X Wild g

' Culture Number Type of Mating | a aoan TOSE Eea

= Leia 9 a 9 Normal) Red

gaiu eased, 1 pair 317 | 322| 125| 119) 639| 244

og aparece pa aoa 305 | 313|. 109| 107| 618| 216

eee ERIE “ou 282| 100 557 | 198

ENAR TS “ou 326| 299 101) 625|: 1

a Mass 557| 552| 112|. 150|1,109| 262

pee SG i da 1,780.1 1,768 | 543 | 575 | 3,548 | 1,118

Red F X Wild 2

wo 340| 326| 101| 105| 666

e A mar 269| 293| 79| 88| 562| 167

pid hs PA “ou 231| 258}. 71 484

BM ars, “u 244} 250| 5 494| 145

rE a Mass 469| 466| 87| io0| 935| 187

POM anirai y a “ 228 4 1

Toth, inae. Be OE 1,818 | 1,816 | 487 555 | 3,634 | 1,042

Grand hii ice eis... 3,598 | 3,584 | 1,030 | 1,130 | 7,182 | 2,160

No. 611] NOTES AND LITERATURE ` 701

It can be readily seen that the red eye acts as a non-sex-linked

recessive character with the red class falling a little short.

Shortage of the mutational class frequently occurs. It seems to

make no difference whether the red male or red female is used in

the cross. In most cases when mass cultures were made, the ex-

pected 3 to 1 ratio was less nearly approximated. The ratio of

all the flies examined in the F, was 3.32 normals to 1 red.

THE GENETIC BEHAVIOR OF CHOCOLATE EYE

A pure stock of chocolate was obtained by mating some of the

first observed chocolate males to their virgin chocolate sisters.

This stock has bred true for several generations but since the

eye changes so rapidly to a color approximating normal, in

stocks where the flies are allowed to become more than twenty-

four hours old, all gradations between the typical chocolate and

normal will be found. The chocolate males and females were

bred to wild normals and the F, flies were all normal. The re-

sults of the F, of these crosses are shown in Table II.

TABLE II

F, OF CHOCOLATE X WILD Cross

Chocolate 9 X Wild g

Normal Chocolate Total | Total

y of Mati y Choc-

Culture Number ype ating 3 9 e 9 Normal inns

cy Seapine oe Gaver ies aS 1 pair 12 43 95 475 138

aoas Ub ae ree 154| 146|° 49 | 60

Oy ce cs “ou 223| 181| 57 | 109 | 404| 166

EE A: | Mass 529| 468| 67 | 136 | 997| 203

Total. ...; «. 1,169 | 1,007 | 216 | 400 | 2,176) 616

Chocolate &' X Wild Q

408 1 pair 257| 252| 58 509| 124

Boe Caer re 8 45 | 61

448i SO Ee 338 “ou 343| 312| 58 | 82 | 655| 140

P due “ou ad 67|.17 | 17 | 150). 34

rT oo Mass 812| 667| 78 | 161 |1,479| 239

ry meee ae s 426| 440| 106 | 133 | 866| 239

Ga a e E 2,159 | ?,980.| 362 | 520 |4,139| 882

Grand total, i .| 3,328 | 2,987 | 578 | 920 |6,315 | 1,498

Chocolate eye also acts as a non-sex-linked recessive character

with the chocolate class falling considerably below the expected

702 THE AMERICAN NATURALIST [Vou. LI

number. The number of chocolate males, especially, falls low.

The totals seem to indicate that this low number of chocolate

males in comparison to the number of normal males is partially

due to the fact that some of the chocolate males have been

called normal, for in practically all of the matings, the number

of normal males exceeds the number of normal females. This

is unusual, for the writer has examined large numbers of wild

Drosophila buscku and in a large majority of the cases the num-

ber of females has been equal to or greater than the number of

males. So it may be that the males approximate the normal

color more rapidly than the females and since the flies were ex-

amined only once a day, some of the chocolate males were mis-

taken for normals. Some counts were made, examining the flies

twice a day, to test this supposition and they indicated that

better ratios could be obtained in this manner. But since the

work was completed before this was realized, the difference to

be obtained by twice-a-day counts was not thought to be of

sufficient importance to require the repetition of the experi-

ments. Also in these matings, the relative number of chocolates

was lower where mass cultures were made. The ratio for all of

the F, flies examined was 4.21 normals to 1 chocolate.

THE GENETIC BEHAVIOR OF RED AND CHOCOLATE WHEN THEY ARE

MATED TOGETHER

Red males were crossed to chocolate females and red females

to chocolate males and in the F, of each cross nothing but normal

flies appeared. The results of the F, of these crosses are given

in Table ITI.

Here again the number of normal males is considerably above

the number of normal females. This could be explained as

before, that some of the chocolate males have been mistaken for

normals, thus increasing the normal class and decreasing the

chocolate class. Since the number in. the classes of red and

chocolate each fell low in their respective crosses to wild, we can

expect the number in these classes to be low in this cross. Ta-

king this fact into consideration, the ratio can be considered a

1:2:1 ratio and gives indication of linkage between the two

characters. No red-chocolate double recessives were found,

therefore the two mutations may be interpretated as being

-in the same chromosome.

No. 611] NOTES AND LITERATURE

TABLE III

F, oF Rep X CHOCOLATE CROSS

Red & X Chocolate 2

i Ch

ence E fart ee | Jing | a | 9 | eae Tae

£02 CI | 1 pair 237| 206) 95} 122 86 | 92| 443 217 | 178

ABR Spee f 149| 132} 70i- 56] 50l 48] 281] 126

452. i 21291 184| 78i 108} "73 83| '396| 186| 156

453 6 Hine o +8 207| 186 85} 70} 93| 393] 17

Tt ES e | te 246 | 238| 114| 129| 88 | 106| 484| 243| 194

a. | Mass 373| 360| 149| 153| 85 | 109| 733] 302} 194

Pee Riser V hemmed OY 1,306 | 592| 653| 458 | 531 2,730 1,245! 989

“Red 2 X Chocolate g

aBtaralati d lpair | 232| 178] 21|. 22). 41 72| 4 410 0, 4 113

AE ae oo 173| 163} 62] 68] 48 nd 336 | 130 107

450 SS eee 214] 178| 79] 66) 66 = 145| 126

MODE is. roi gmi 1 179| 93| 99| 50 a 192| 108

6 aS 243) 249! 94] 117| 90| 94 les f211| 184

yy eee Saran | Mass 370| 326| 121| 156| 90| 129! 696| 277| 219

Totale. oorh sacs nas r LABI] A70) 6281 385 | 472 |2,691| 998| 857

Grand E E .. esse + |2,842 [2,579 |1,062 |1,181| 843 (1,003 (5,421 |2,243 |1,846

Since mutations have occurred in eight species of Drosophila

it seems probable that mutations may be found in all the mem-

bers of this genus. As to the frequency of mutations, there may

be individual variation. The writer’s own experience would in-

dicate that mutations occur less frequently in busckti than in

ampelophila, for, during the same period in which the two

busckii mutations were found, a smaller number of ampelophila

were examined less critically and six mutations were found.

LITERATURE CITED

Metz, Chas. W.

1916. Mutations in Three Species of Drosophila. Genetics, I, 591-

Morgan, Sturtevant, Muller, aud Bridges.

1915. The see anism of Mendelian Heredity, pp. xiii + 262. New

York, Henry Holt and Co.

Don C. Warren

ALABAMA POLYTECHNIC INSTITUTE,

N, ALA.

704 THE AMERICAN NATURALIST [Vou. LI

SINGING MICE

In November, 1916, Mr. B. S. York, of Ann Arbor, brought

to me a “‘singing’’ house mouse that had been captured in his

home. This mouse had been heard by members of his family

for several weeks, especially late at night and early in the

morning. Arrangements were made to carry on breeding ex-

periments with it but it lived only two weeks.

Singing mice have been recorded in a number of publications

dating back many years. In 1912 Coburn! reported some work

he had done with a female singer captured in December, 1911.

This individual when mated with an ordinary mouse gave birth

to five litters (thirty-three young). None of these were singers

and no singers appeared in either the second or third genera-

tions. Two other singing mice were described by Coburn in

1913.2 One was caught in the home of an Italian family in

November, 1912, and the other was taken by a farmer in Mich-

igan in March, 1913. Both of these were females.

The Ann Arbor specimen that was brought to me also proved

on dissection to be a female. Her song was similar to that re-

ported by Coburn as follows:

The sound is best described as a rapid whole-toned trill involving the

tones c and d. .. . The quality of the tone resembled somewhat that

of a fife or flute, but each tone ended with a slight throaty click.

In every case the song could be heard at least 15 or 20 feet

away.

Many causes have been proposed for the presence of this

ability to sing such as pregnancy, a diseased condition of the

lungs or vocal cords, a parasitized liver, ete. There were no

embryos or young in the Ann Arbor specimen and Dr. George

R. LaRue was unable to find any parasites that could have in-

duced the singing. :

It has been suggested that since all of the singers captured

thus far have been females, this characteristic may be sex-linked

and due to some structural modification of the vocal apparatus.

R. W. HEGNER

UNIVERSITY or MICHIGAN

1 Coburn, C. A., Journ. Animal Behavior, Vol. 2, 1912, pp. 364-366.

2 Coburn C. A., Journ. Animal Behavior, Vol. 3, 1913, p. 388.

THE

AMERICAN NATURALIST

Vou. LI. December, 1917 No. 612

THE GENESIS OF THE ORGANIZATION OF THE

INSECT EGG. I

PROFESSOR ROBERT W. HEGNER,

ZOOLOGICAL LABORATORY, UNIVERSITY OF MICHIGAN

5. Interaction of Nucleoplasm and Cytoplasm

There are phenomena that occur during the growth

period that suggest how masses of cytoplasm that are

differentiated both morphologically and physiologically

may arise in the cortical layer of the insect egg. It has

been suggested that ‘‘most of the differentiations of the

egg cytoplasm have arisen during the ovarian history of

the egg and as a result of the interaction of nucleus and

cytoplasm; . . „°? and with this we fully agree, but our

problem is to determine the nature of this interaction and

in what ways it may take place.

During every mitosis there is a more or less thorough

mixing that involves the chromatin as well as other nuclear

constituents, since chromatin-diminution is a normal his-

tological process. Interchanges between nucleus and —

cytoplasm, therefore, occur during the two multiplication

periods that precede the formation of oocytes. Abun-

dant opportunity is thus offered for factors in the chromo.

somes to exert an influence upon the cell as a whole. A

similar and probably even greater discharge of chromatic

27 Conklin, 1916, ‘‘ Heredity and Environment,’’ New York.

705

706 THE AMERICAN NATURALIST [Von. LI

and other nuclear substances into the cytoplasm occurs

during the maturation divisions of the egg, but this period

may be neglected in this connection, since the organiza-

tion with which we are concerned is already established

before maturation takes place. Even when the nuclear

membrane is intact, substances undoubtedly pass in and

out of the nucleus much as they do through the cell mem-

brane, and as in the latter, the nuclear membrane may

change in permeability at different times, these changes

being due to chemical processes taking place within the

nucleus or in the cytoplasm. Such changes occur more

often during periods of cell activity than at other times

and thus we should expect pronounced interaction

throughout the growth period of the oocytes.

Besides gradual, and for the most part invisible, inter-

changes of this sort there may be actual transference of

visible masses of chromatin from the nucleus to the

cytoplasm. These chromatin granules that escape into

the cytoplasm have been called ‘‘chromidia’’ and are sup-

posed to play a part in cytoplasmic differentiation.

A peculiar process of interchange by means of sec-

ondary nuclei is exhibited by certain insects, especially

Hymenoptera.2® This process has been studied most

_ carefully in the carpenter ant, Componotus herculeanus

var. pennsylvanica (Fig. 11). At an early stage in the

growth of the oocyte small vesicles containing a few

granules of chromatin appear near the oocyte nuclei.

These ‘‘secondary nuclei’’ appear to arise as buds from

the primary nucleus, but no one has yet actually observed

their formation in this way. It has also been suggested

that they may be epithelial cells that have invaded the

oocyte, but this seems very improbable. The writer has

reached the conclusion that they consist of nuclear ma-

terials that have been given off into the cytoplasm and

have there become enclosed by membranes which give

them a nuclear-like appearance. As the oocyte increases

28 Blockmann, 1886, Festsch. nat.-med. Verein zu Heidelberg; Buchner,

1913, Biol. Centribl., Bd. 33; Hegner, 1915, Journ. Morph., Vol. 26.

No. 612] GENESIS OF ORGANIZATION OF INSECT EGG 707

in size the secondary nuclei increase in number until they

entirely surround the primary nucleus, forming several

layers. When the oocyte has nearly reached its full

growth they begin to migrate from the group near the

anterior end of the oocyte and become scattered through-

Vv)

J) a. aes

SL ARI AD. 2h

2.6

GG yes

= @5

O o % 009%.

Fie. 11. Secondary nuclei in the oocytes of the ne pte ant (a, b, c)

and the “Blynienopterous gall-fly, Rhodites ignota (d). (Hegn 1915.

a. Oocyte (o) shortly efter secondary nuclei (s) ating io appo =

nurse cells.

b. Older oocyte showing oocyte nucleus (0) ee by secondary nuclei

(s). pp tion between oocyte and n hamber.

. Part of a pHi eae oocyte inowtne follicular epithelium, yolk globules

(ack) ena secondary nuclei.

of an oocyte a Rhodites showing primary nucleus (large circle) and

ies aie (small circles).

out the egg, forming a rather oe layer a short dis-

tance beneath the periphery. The further history of

these bodies is not certain, but they undergo changes by

which they lose their identity, since they can not be found

in fully grown eggs. Their function is likewise prob-

lematical. They may take part in the formation of germ-

line determinants which probably occur in the eggs of

708 THE AMERICAN NATURALIST [Vou. LI

this ant;?° they may aid in changing the substances fur-

nished by the nurse cells into material available for the

embryo ;*° or they may have something to do with the for-

mation of yolk.*! It is also possible that they may con- `

trol differentiation in the peripheral layer of cytoplasm

and thus provide a method of nuclear control of the or-

ganization of the egg. The last hypothesis may be ob-

jected to on the grounds that the secondary nuclei appear

to be irregularly distributed and that they are known to

occur in only a few species of insects.

Another possible way in which the initial organization

of the insect egg may arise is through the activities of

mitochondria. The rather constant presence of these

bodies in the cytoplasm of almost all types of cells indi-

cates that they may be of considerable importance in the

process of differentiation. If they take part in the gen-

esis of egg organization they then may play the rôle

attributed to them by certain investigators of being the

cytoplasmic bearers of hereditary factors corresponding

in this respect to the nuclear bodies of similar function,

the chromosomes.

The most striking differentiation in the cytoplasm of

the insect egg is that which involves the germ-line deter-

minants. As stated above, we do not know for certain in

any case the origin of the peculiar cytoplasmic mass that

contains these determinants, but a number of hypotheses

have been suggested. In Miastor, for example, the fol-

lowing is offered to account for the appearance of the

‘‘pole-plasm’”’ in the fully developed oocyte.*”

It may be distinguished from the rest of the egg contents by its posi-

tion at the posterior end and because of its affinity for certain dyes. It

appears shortly before the maturation division is initiated, but no

transition stages have been discovered—it has been either present or

entirely absent in the preparations thus far studied. If we consider the

history of this substance from the formation of the primordial germ

29 Hegner, 1914, Journ. Morph., Vol. 26.

30 Marshall, 1907, Zeit. wiss. Zool., Bd. 86,

31 Loyez, 1908, C. R. Assoc. Anat., 10 Reunion, Marseille.

32 Hegner, 1914, ‘‘Germ-Cell Cycle in Animals,’’ New York.

No. 612] GENESIS OF ORGANIZATION OF INSECT EGG 709

cell to the growth period of the oocytes produced by this primordial

germ cell, we may conclude that at the time the multiplication perio

ends the pole-plasm has become equally distributed among the sixty-

four oogonia. Then ensues the growth period during which the pole-

plasm can not be distinguished. Later, however, just before matura-

tion, pole-plasm substance reappears which is equal in amount to that

contained in the primordial germ cell of the preceding generation or

to that contained in all of the sixty-four oogonia which descended from

that primordial germ cell. That is, the pole-plasm of the oocyte under

discussion has in some way increased until its mass is sixty-four times

as great as that of the oogonium before the growth period began. How

this increase has taken place can only be conjectured. The pole-plasm

in the oogonium may have produced new material of its own kind either

by the division of its constituent particles or by the influence of its

presence.

The influence of a specialized mass of cytoplasm upon

the chromatin is very well illustrated by the inhibition of

chromatin-diminution in Miastor and Ascaris. In Miastor

nuclear division is normal until at the four-cell stage one

nucleus reaches the pole-plasm at the posterior end (Fig.

12, a, IV.). During the succeeding mitosis this nucleus,

which is apparently under the control of the pole-plasm,

does not undergo chromatin-diminution, whereas the other

three do. One of the daughter nuclei resulting from the

division of this undiminished nucleus remains entirely

within the pole-plasm and is cut off from the rest of the

egg with this specialized mass of cytoplasm as the primor-

dial germ cell (Fig. 12, b). This nucleus always retains

the full amount of chromatin; but its sister nucleus, which `

remains in the egg and is thus separated from the direct

influence of the pole-plasm, undergoes diminution at the

next mitosis.

A similar segregation of specialized cytoplasm in the

primordial germ cells occurs also in certain other insects

and in copepods, but no diminution process has yet been

discovered in them. In Ascaris, where chromatin-diminu-

tion was first reported,** there is evidently a segregation

of germinal cytoplasm at each cleavage division up to the

sixteen-cell stage, when it is all confined in one cell, the

33 Boveri, 1887, Anat. Anz., Bd. 2.

710 THE AMERICAN NATURALIST [Vou. LI

primordial germ cell. This cytoplasm, which is not vis-

ibly different from the rest, as in Miastor, appears to in-

hibit diminution in every nucleus that comes within its

a, Longitudinal section through an egg of Miastor showing chro-

Pe alt ee ge uclei I. and III. but not in nucleus IV. which has come

under the influence of the pole-plasm (p Pl). Nucleus II. does not appear in this

section Mp = chromatin that is cast off into cytoplasm. ne= nurse cells.

pb= polat body. (Kahle, 1908.)

. Longitudinal sete E an egg of Miastor, norae nenn germ

cell (p.g.c.), nuclei undergoing chr Heng: ea (cMp), and the remains of

chromatin cast out into the hie (cR), c= cytoplasm inakit Oy nurse

cells above. (Hegner, 1914.)

immediate influence as indicated by experimental studies

on dispermic and centrifuged eggs.** In this respect it

resembles the pole-plasm of Miastor.

34 Boveri, 1910, Arch. Ent.-mech., Bd. 30; Boveri, 1910, Festschr. R.

Hertwig.,

No. 612] GENESIS OF ORGANIZATION OF INSECT EGG 11

6. Mendelian Factors and Cytoplasmic Organization

The central biological problem of the present time is

the method of evolution, and a knowledge of the mech-

anism of heredity has long been recognized as necessary

for its solution. The results derived from breeding ex-

periments with the fruit fly, Drosophila ampelophila, have

dominated the field of genetics for the past five years,

but although of very great interest and importance, their

evolutionary significance is not yet certain. To be of

primary value from this viewpoint it is necessary to

prove that new species may arise by means of Mendelian

characters (mutations) such as white eye, miniature wing,

club wing, ete. Since no one has ever been able to define

satisfactorily what a species really is and hence what

characters should be considered of specific value, this is a

difficult problem.

The definitions given by two of our foremost authori- `

ties, one a systematist and the other a geneticist, are as

follows: The systematist writes :*°

Forms of animals which present distinct assemblages of characters,

in form, color and arrangement of parts under natural conditions, which

are recognizable from descriptions and figures, should receive distinctive

names and be catalogued, provided, of course, that the assemblage of

characters includes all ontogenetic changes. If, in the examination of

abundant material from different natural environments, we find these

characters fairly constant, the forms may properly be called species;

if not, varieties or races,

The geneticist writes :°°

Species may thus be distinguished by peculiarities of form, of num-

ber, of geometrical arrangement, of chemical constitution and pro

erties, of sexual differentiation, of development and of many other prop-

erties. In any one or in several of these features together, species may

be found distinguished from other species.

The mutations that have appeared in Drosophila do

not become recognizable until a late stage in the life his-

tory of the individual, and are about the last characters

35 Williston, 1908, AMER. NAT., Vol. 42.

36 Bateson, 1913, ‘‘ Problems of Genetics.’’

712 THE AMERICAN NATURALIST [Vou. LI

to appear in the individual development. They for the

most part affect the size and shape of the wings, the size,

shape and color of the eyes, and the color of the body.

If a systematist were asked whether these new races of Drosophila

are comparable to wild species, he would not hesitate for a moment.

He would call them all one species. If he were asked why, he would

say, I think, “These races differ only in one or two striking points,

while in a hundred other respects they are identical even to the minutest

details.” He would add, that as large a group of wild species of flies

would show on the whole the reverse relations, viz., they would differ

in nearly every detail and be identical in only a few points.7

This point of view seems justified, since the foremost

dipterologist in this country, a man who has named over

one thousand species and genera, mostly of flies, says

regarding the results of certain experiments carried on

with Drosophila by one of his colleagues.**

But I think it is absolutely certain—and I speak as an entomologist

fairly familiar with flies—that it would be impossible to produce species

of his sports even though they were bred for a thousand years.*°

In talking over this species question with one who has

had considerable experience in systematic work* it be-

came clear that although as a rule only a few of the more

conspicuously contrasting characters are selected for de-

scriptive purposes, as a matter of fact the individuals of

different species are often different in practically every

morphological characteristic. One who is very familiar

with these species will realize these differences at once,

although many of them are of such a nature that they

can not be described so that any one else will recognize

them. There seems to be no difficulty, however, in finding

numerous describable contrasting characters in Droso-

phila, since at least fifty-nine are included in the descrip-

tions of two recently named species*! that were selected

87 Morgan, 1916, ‘‘Critique of the Theory of Evolution.’’

38 Dr, F. E. Lutz.

89 Williston, 1908, Par Ta Vol. 42.

40 Dr. Alexander G. Rut

41 Sturtevant, 1916, py "Ent. Soc. Amer., Vol. 9.

No. 612] GENESIS OF ORGANIZATION OF INSECT EGG 713

at random, D. superba and D. projectans, and these char-

acters relate to almost every part of the body. Many

other differences would probably also be found between

the physiological processes and general activities of the

adults and between the morphological and physiological

characteristics of the embryos, larve and pupx of the

two species if they were compared from these standpoints.

It has been shown that the factor for the character club

wing affects not only the character that gives this muta-

tion its name, but also other characters, for example the

presence or absence of a pair of spines on the sides of the

thorax, these being always absent when the factor for

club wing is present.42 It is possible that the combina-

tion of a number of such factors as that for club wing

would ultimately satisfy the requirements of systematic

entomologists and that new species could then be made up

in the laboratory. Such mutations might therefore be of

evolutionary value. If, however, these mutations fail to

furnish characters of specific rank, or characters that

may lead to the formation of new species, we must con-

clude that they are not of evolutionary significance, and

look elsewhere for the factors that are responsible for

specific characters and that may undergo changes which

lead to transmutation.

Factors of this sort may lie in the chromosomes or in

the cytoplasm, but they are probably the results of inter-

action between chromosomes and cytoplasm. As pointed

out above, interaction of this sort has abundant opportu-

nity to operate during the germ-cell cycle. The cytoplas-

mic differentiations resulting from the metabolic processes

that culminate in the formation of an egg ready to undergo

maturation are very striking in the case of insects, as in-

dicated by observations and experiments on the eggs of

chrysomelid beetles, and there seems to be no valid reason

why the eggs of these beetles are different in their type

and complexity of organization, both morphological and

physiological, from those of Drosophila; for while we do-

42 Morgan, Sturtevant, Muller, and Bridges, 1915, ‘‘ Mechanism of Men-

delian Heredity. ’’

714 THE AMERICAN NATURALIST ` [Von. LI

not know much about the growth of the egg and embryo-

logical development of this genus of flies, we do know that

these processes in certain other flies resemble those of

beetles.

If the Mendelian factors are located in the chromo-

somes, it is evident that they may exert an influence upon

the entire contents of the egg, (1) during the mitotic divi-

sions of the oogonia, (2) during the so-called resting

stages of the oogonia, and (3) during the growth of the

oocytes. It is also clear that all of the factors carried by

the chromosomes have an equal opportunity to interact

with the cytoplasm and not alone those that remain within

the egg after the elimination of chromosomes during

maturation. The adult, however, that develops from the

egg, whether fertilized or unfertilized, exhibits only those

detailed characteristics whose genetic factors are sup-

posed to be located in the chromosomes remaining in the

egg after maturation, or in those that are brought in by

the sperm. This seems to indicate that none of these

factors has any permanent influence upon the egg organi-

zation during the growth of the oocyte and until matura-

tion is completed.

It seems impossible to ignore the chromosomes or even

to locate the principal factors of heredity in any other

cell bodies. It may therefore be necessary to reconstruct

our ideas of chromosome architecture and thereby aban-

don the theory that these bodies consist of a linear series

of factorial determiners for certain ferments and of noth-

ing else. It may be possible to separate our hypothetical

factors into two groups, (1) those responsible for such

characteristics as the polarity, bilaterality and ‘‘pattern”’

of the egg, and (2) those that control mutations that ap-

pear at a late period in the life history like those that are

so abundant in Drosophila. Perhaps the latter may be

anchored to the chromosomes as has recently been sug-

gested ;*8 the main portion of the chromosomes might then

represent the foundation for the factors responsible for

the organization of the egg and the attached masses of

43 Goldschmidt, 1917, Genetics, Vol. 2.

No. 612] GENESIS OF ORGANIZATION OF INSECT EGG 1715

ferments might constitute the factors responsible for the

modification of embryonic, larval and adult characters—

factors such as have been employed for experimental

breeding purposes by most geneticists. According to this

hypothesis it would probably be necessary to consider

the main portions of each chromosome as sufficient for the

production of an entire organism. The fact that the

group of factors carried by any one chromosome in Dro-

sophila controls characters that are not restricted to any

definite part of the body gives weight to this assumption.

Most geneticists are accustomed to deal with adult char-

acters only, and on this account pay very little or no at-

tention to the eggs, embryos and larve of the species they

are experimenting with. But the eggs, embryos and

larve contain all the factors for these adult characters,

both those that are realized and those that are inhibited

either by internal or external causes, and they may ex:

hibit characters that make it possible to separate different

lines although the adults may be indistinguishable. Fur-

thermore, taxonomists have long recognized the value of

embryonic characters as an aid k determining species.

We should always be careful to distinguish between the

parts of the egg that are of hereditary significance and

those that are not. Thus the shell or chorion of the-silk-

worm egg has been discussed under the heading of ‘‘cyto-

plasmic inheritance,’’ whereas it is not a vital part of the

egg, but, being secreted by the epithelium of the ovarian

tube, is a well-defined characteristic of the adult female

and its coloration, which follows the laws of Mendelian in-

heritance,** is controlled by maternal factors.

Such fundamental characteristics as polarity, sym-

metry, and pattern, which are so clearly exhibited by the

eggs of insects and certain other animals, are much more

difficult to study than adult characters and are probably

not so easily modified. If any or all of them are carried

over from one generation to another in the cytoplasm we

have then a real instance of cytoplasmic inheritance.

Even if this is the case the chromosomes doubtless exert

44 Toyama, 1913, Journ. of Genetics, Vol. 2.

716 THE AMERICAN NATURALIST [Vou. LI

an influence upon the cytoplasm during the oogonial and

growth periods of the egg, and a study of the genesis of

cytoplasmic organization may lead to data that will help

us solve this difficult problem.

If the polarity of the oocyte when recognizable is not

inherited, i. e., if it is not transmitted to the primordial

germ cells by the egg, and retained by the oogonia, it

must arise de novo saat before or during the growth

period. One observer*® has found that in certain beetles

the position of the spindle remains, resulting from the

differential divisions that precede the formation of the

oocyte, indicates the polarity of the ultimate organism,

but he does not tell us how this ‘‘polarité predifferen-

tielle” is brought about. In all insects the end of the egg

directed toward the head of the mother becomes the an-

terior end of the offspring. This is also the pole of the

egg lying next to the nurse cells or that is closest to the

nurse-cell chamber. This relation between oocyte and

nurse-cells may be the determining factor in the polarity

of these eggs and, if so, would indicate that polarity here

is due to environment. How this relation could influence

the polarity may be explained by means of axial gradi-

ents of metabolism, such gradients in this case being

produced by greater external stimulation at the end near

the nurse-cell chamber where nutritive substances are

elaborated and added to the oocyte. By this theory of

metabolic gradients, differentiation along an antero-

posterior axis can be accounted for and further differen-

tiations of a morphological and physiological nature

would result from ‘‘chemical transportative correlation

between the different parts.’’*®

We should not lose sight of the fact, however, that these

hypothecated physiological activities require protoplasm

as a material basis and that their results depend upon the

character of this protoplasm. If polarity is established

at the stage suggested above, it follows a long series of

nucleo-cytoplasmic interactions which have no doubt re-

sulted in the differentiation and localization of numerous

45 Govaerts, 1913, Arch. Biol., Tome 28.

46 Child, 1916, Science, Vol. 43.

No. 612] GENESIS OF ORGANIZATION OF INSECT EGG 717

kinds of cytoplasm. The appearance of a definite polar-

ity might lead in some way to diffusion processes and the

circulation of secretions resulting in further specializa-

tions and localizations. One stage seems to initiate the

next stage in the series of processes that accompany the

visible changes in the growth and development of the egg,

and the character of these processes is of course due to

the specificity of the protoplasm.

That the cytoplasm may exert a controlling influence

upon the chromatin has been demonstrated in several in-

stances. For example, we know that the chromatin-

diminution processes during the early cleavage of both

Ascaris and Miastor are controlled by the cytoplasm and

that in these animals the germ-cell nuclei retain the full

amount of chromatin because of the germ-cell cytoplasm

they chance to encounter.

Probably the peculiar distribution of the chromosomes

at certain stages in the life histories of certain aphids,

phyloxerans, and Hymenoptera is also controlled by the

eytoplasm. In the aphid, Aphis saliceti, the first matura-

tion division is visibly differential both as regards the

chromosomes and the cytoplasm.“ The mitochondria

congregate at one end of the dividing spermatocyte; this

process is accompanied by a greater accumulation of

cytoplasm at this end so that cell division results in one

large cell containing all of the mitochondria and about

two thirds of the cytoplasm, and one functionless small

cell. The large cell also receives three chromosomes; the

small cell only two.

The peculiar maturation divisions in the males of the

honeybee*’ and hornet,*® during which one ultimate sper-

matogonium gives rise to only one spermatozoon instead

of the usual four, may also be the result of cytoplasmic

control. The cytoplasm may likewise be responsible for

_the passing of a sex chromosome into the polar body dur-

ing the maturation of the egg of certain aphids at the end

of the summer season.” Such eggs must be fertilized

` 47 Baehr, v, 1909, Arch. fiir Zellf., Bd. 3.

48 Meves, 1907, Arch. mikr. Anat., Bd. 70.

49 Meves and Duesberg, 1908, Arch. mikr. Anat., Bd. 71.

50 Morgan, 1909, Journ. Exp. Zool., Vol. 7 .

718 THE AMERICAN NATURALIST [Vou. LI

before they will develop, and always produce males.

Many other peculiarities in the behavior of chromosomes

that have been reported from time to time may also be

due to the influence of the environment (cytoplasm), and

there seems to be no reason why factors carried by the

chromosomes should not be affected by the cytoplasm as

well as are entire chromosomes.

By the interaction of Mendelian factors with the cyto-

plasm during the germ-cell cycle, it is even possible to

explain the fact that ‘‘crossing over” occurs in the

females of Drosophila, but not in the males.** In the

latter, the spermatocytes do not pass through a pro-

nounced growth period, and hence there is comparatively

little nucleo-cytoplasmic interaction, and since the cyto-

plasm carried by the sperm may be considered negligible,

the factors borne by its chromosomes are not interfered

with. In the female, however, there is ample opportunity

for such interaction during the growth period, and factors

at this time may be influenced by the cytoplasm or may

influence the cytoplasm in such a way as to cause an ir-

regular distribution of chromosomal factors.

To the writer the following conclusions seem justified.

The insect egg at the time of maturation is a mosaic of

differentiated cytoplasmic areas predetermined to de-

velop into definite parts of the embryo. This organiza-

tion has resulted from the interaction of nucleus and

cytoplasm during the germ-cell cycle. Such interaction *

is taking place at all times, but is visible only when such

processes as the protrusion of chromidia or chromatin-

diminution occur. The many cases of cytoplasmic con-

trol over chromatin behavior, and the apparent failure of

the factors for the characters commonly used by geneti-

cists to influence the egg organization, indicate the im-

portance of more careful studies of the genesis of this

organization. The importance of such studies is empha-.

sized by the possibility that they may help toward the

solution of the problem of the method of evolution.

51 Morgan, Sturtevant, Muller, and Bridges, 1915, ‘‘Mechanism of Men-

delian Heredity.’?

NEW FACTS AND VIEWS CONCERNING THE

OCCURRENCE OF A SEXUAL PROCESS IN

THE MYXOSPORIDIAN LIFE CYCLE.

DR. RHODA ERDMANN

OSBORN ZOOLOGICAL LABORATORY, YALE UNIVERSITY AND ROCKEFELLER

INSTITUTE FOR MEDICAL RESEARCH, DEPARTMENT OF

ANIMAL PATHOLOGY

Tar classic observations of Balbiani, Bütschli and

Thélohan on the myxosporidian development do not in-

clude the occurrence of a sexual process which compre-

hends the forming of a syncaryon in the life history of

this protozoan group. Doflein (1898 and 1901) suggested

two places in the life cycle of the myxosporidian where a

caryogamy might probably take place. In the next period

of investigations on myxosporidia the occurrence of this

sexual process was stated by various authors, but they

differ widely in the conception of the place in the life cycle

in which the copulation occurs. Mercier, Awerinzew,

1 For a clear understanding of the question under discussion, it is neces-

have a uniform nomenclature and to discard all terms which are

only of Haese value. Noyaux du sporoplasma, noyaux du germe,

noyaux sporoplasmiques, germnuclei, Amöboidkeimkerne were to be dis-

carded and gametonuclei, noyaux des gamétes, Gametenkerne were to be

sed. Instead of sporoplasma, sporoplasm or améboidkeim, only such ex-

ressions as gametes, gametes and Gameten are admissible. Identical and

adequate terms are capsulogenous cell, cellule en pS bar aut

Valve cells, cellules valvaires and Schalenzelle sho r those cells

which form the membrane of each single spore; cellule Venveoppe, envelope

cells, and Hiillzellen should be used rage those cells which form

brane of the fine ert In eases where only the nuclei of Pa cells

are present terms noyaux d’enveloppe, envelope nuclei, Hiillenzellen-

kerne agni $ substituted. If the cellular origin of the pansporoblast mem

brane is not ascertained, envelope, membrane d “envelop ppe or Hülle ma

be used. The terms Restkern, residual nucleus are eading. Somatic

residual nuclei or somatische Restkerne should be used, if the definition on

p. 679 holds true. Here a new name would be of great value eliminate

the wrong analogies created by Doflein (1898, p. 309). The term ‘‘ reduce-

tion aioe is only justified if the healers reduction of id cect

has been ascertained.

; 719

720 THE AMERICAN: NATURALIST [Vou. LI

Auerbach and Parisi try to show that a real syncaryon

formation takes place at the onset of spore formation.

Other authors, Keysselitz, Schroeder and Auerbach, be-

lieve that only a plasmogamy can be pointed out at the

beginning of spore formation, and that the union of the

nuclei is effected either in the fully developed spore or

in the young animal leaving the spore. The difference

between these last two conceptions is theoretically with-

out significance because the main part of copulation—the

union of the nuclei—takes place at the onset of the new

life cycle of the myxosporidian. Therefore it was of

the utmost importance for decisive proof of this fact

to find the copulation of the two gametonuclei inside

the fully developed spore or in the young myxosporidian.

Schroeder, 1909, observed the copulation of the two game-

tonuclei in the spore; Auerbach, 1907 and 1910, found

young animals of Myxidium bergense with one nucleus.

I was able to demonstrate young Chloromyxum leydigi

which were experimentally produced by placing the two-

nucleated spores on gall plates (Erdmann, 1911). Here,

after a treatment with intestinal secretions of the host

the young animals leave the spore. They are at first bi-

nucleate, later uninucleate. In my recent work, finished

in 1913, which did not appear until 1917 in consequence

of the war, I figured these young animals after fixation

and staining. Also, Davis, 1915, though with some re-

serve, presents young Spherospora dimorpha which have

left the spore and show the fusion of their two nuclei.

Later the separation of the syncaryon into its vegetative

and generative components takes place. Georgevitch,

1914, presents the development of the young animal in

Henneguya gigantea in—as it seems—changed pecu-

liar conditions. The spore is still inside of the cyst of the

big ‘‘tumor-forming’’ tissue-parasite. The binucleate

form becomes uninuclear and then the usual vegetative

multiplication of the nuclei begins, which leads up to a

renewed spore formation inside of the tumor cyst. In

Chloromyxum leydigi, a gall-bladder parasite, no such

No. 612] MYXOSPORIDIAN LIFE CYCLE 121

complicated process takes place. As the young uninucle-

ated forms develop we see an animal with three nuclei, all

of the same size. Later multiplication of these vegetative

nuclei and the formation of big syncytial masses occur.

The plasmatic bodies of these vegetative animals contain

two kinds of round corpuscles, ‘‘Reservekérper’’ and

‘‘Warbtrager.’’ In my publication in the Archw für Pro-

tistenkunde, 1917, I give proof that the ‘‘Reservekérper’’

consists mostly of glycogen and I point out that the gly-

cogenous contents are used up during spore formation.

The vegetative animal can multiply either by division or

by forming small vegetative gemmules (Erdmann, 1911).

The fact that inside the animal vegetative propagative

bodies can arise, was verified by Davis, 1915, pp. 354-355,

in Spherospora dimorpha.

Before the onset of spore formation a differentiation

in the syncytial masses of Chloromyxum leydigi begins.

We can distinguish parts in which the nuclei multiply and

other parts where only the vegetative nuclei are seen

widely scattered in the protoplasm. I called the first-

mentioned areas ‘‘islands’’ (Erdmann, 1911) because in

the living animal they rise above the surface of the vege-

tative plasmatic body. They are distinguished by their

pale color and in stained preparations by their large num-

ber of small nuclei. At first all the nuclei in these islands

are of the same size. Two nuclei with small cytoplasmic

bodies approach each other and each cell divides up into

a small and a big cell. The two small cells draw out in

length and surround the two big ones, in this manner

separating them from the other cells in the island. This

quadruple group, two big cells and two small ones, is the

starting point for the formation of the whole spore. The

two big cells are gametocytes. These two gametocytes

divide and form two gametes and two other cells which

after a further division give rise to four cells—these four

cells are the four capsulogenous cells. The whole spore

contains, therefore, eight cells—four capsulogenous cells,

two gametes and two cells which form the spore mem-

brane. (Fig. 1.)

722 THE AMERICAN NATURALIST [Vor. LI

I mentioned before that the glycogen which was found

in the vegetative body is used up in spore formation.

The membrane of the spore, the polar threads and the

darkly staining structureless lumps, which have been seen

by all authors inside the sporoblast, consist of glycogen

and stain as well by chromatin as by specific glycogen

stains. These lumps have been

0, 0. considered as ‘‘reduction nuclei’’

a o by various authors. They have

A2 also been called ‘‘Restkerne’’ or

‘‘residual nuclei.” It may be

emphasized for later discussion

that they are glycogenous and

0 0 not chromatic in Chloromyxum

On O On Op rris.

Our knowledge of the sexual

process in the myxosporidian life

0.0.0, 0... cycle since the investigations of

See one 5s Keysselitz, Schroeder, and others

le he or yrum tey:

digi: Az and Bz are the spore has been completed by recent

ar ee oe Eee authors: Georgevitch, 1914,

ut ire ag nn ar dena Davis, 1915 and Mavor, 1916.

: The best proof that no reduction

takes place in the spore is given by Georgevitch (1914)

and Davis (1915), who have been able to study the num-

ber of chromosomes in their specimens before and after

spore formation. Both authors agree that the number of

chromosomes is not changed before and after this phe-

nomenon. Davis figures six chromosomes in Spherospora

dimorpha and Georgevitch, investigating Henneguya

gigantea, finds eight. These two facts: first, that the

number of chromosomes is not changed in spore forma-

tion and, second, that the so-called “reduction nuclei”?

inside the spore are really glycogenous bodies which are

used up in forming the membrane of the spore, polar

threads, and spore membrane of Chloromyxum leydigi,

positively prove that the real reduction must occur at a

different place in the life cycle of Spherospora, Chloro-

No. 612] MYXOSPORIDIAN LIFE CYCLE 723

myxum, and Henneguya. The reduction consisting in the

transformation of a diploid nucleus into a haploid or of a

tetraploid one into a diploid can only occur at the begin-

ning of the new life cycle after or before the union of the

gametonuclei.

The further facts which Davis, 1915, presents in Sphe-

rospora dimorpha also tend to show that reduction

could only take place at the above outlined place. The

gametonuclei of this myxosporidian fuse together after

it leaves the spore and form by one subsequent division

two nuclei. One of these nuclei gives rise to all the

cells of the later sporogenous body. The other of these

two nuclei, distinguished by its size and structure, is

the vegetative nucleus of the animal, the somatic ‘‘Rest-

kern.” No other nuclei should be called ‘‘ Restkerne’’

except when they represent the nucleus or nuclei of the

vegetative myxosporidian body, which does not play a

part in spore formation. Such ‘‘Restkern’’ or ‘‘Rest-

TABLE I

oTilizelien

Occurrence of Envelope Saes Celis.

Bomatio Residual | Cells, Pan- They Ave

Author Species Nuclei in Sensu- sporoblast- Division

ta ranne a| Lotaria ot

| A R Loe Only Ti, OMmMOCrtee

Nuclei

1, Awerinzew.| Myzxidium sp. One — 2 for each

spore

2. ae aig Sere. None (p. 26) — of

Birisi spora dimorpha One, settee two — j

4. Awerhione. P, E Art drepa Two — ie

5. Mayor...i: Ceratomyxa acad Two — g

6. Erdmann...| Chloromyxum leydigi Many — +

Fa: Darit Spheerospora d ha, | Many — r

polysporous form

8. Auerbach...| Myxidium bergense, None = s

polysporous form

ene yaa

ch ha

sacred in

ono-,. di- an

| BdBiled delaby ec

orms only the

propogative

parts of the com-

lete animal

9. Parisi........, Sphaerospora cavdata | No facts men-| Two y

tioned

724 THE AMERICAN NATURALIST [Von LI

kerne,’’ the origin and fate of which agree with this defini-

tion, have been described by Awerinzew in Ceratomyxa

drepanopsette, and in Myxidium sp., by Davis in Sphero-

spora caudata, and by Mavor in Ceratomyxa acadiensis.

In the disporous form, Spherospora dimorpha, two

spores are found in the whole animal and the sporogenous

body finally contains twelve cells—half of this number

forms one spore (Fig. 2). These twelve cells are all

0,, 0;

“a2 ©B2

0. 0,2 Osr 0312

a2 B21

On 2 Alt2 0: 0.4 Gi. Mogae

2.. Spherospora dimorpha (disporous form): An As and Ba Bz are

the membrane-forming cells for each spore. Ay A12; Buz Bı are the two

etes in each spore. A,,, Ay; Bin Bin are the two capsulogenous cells in

each spore.

division products of the one nucleus, the sister nucleus

of which is the somatic ‘‘Restkern.’’ The cells which form

the spore membrane of each spore, lying independently

in the vegetative body, arise by a very late division. Chro-

matic lumps which could be considered as ‘‘reduction

nuclei’’ are lacking. It is easy to imagine why they are

absent. Spherospora dimorpha lives in the urinary blad-

der and has therefore a metabolism which may not afford

opportunity for an abundant glycogen formation. Also,

as mentioned before, no reduction of the chromosomes

takes place. These facts could be easily ascertained in

consequence of the large size of the cells and chromo-

somes. Awerinzew’s description of spore formation in

Ceratomyxa drepanopsette and Mavor’s of Ceratomyxa

acadiensis have many features in common, but Awerin-

No. 612] MYXOSPORIDIAN LIFE CYCLE 725

zew’s presentation differs from that of the other author

in one important point. The cells A and B in Fig. 2

are said to be in Ceratomyxa drepanopsette the prod-

ucts of a fusion of two cells. The reader has but to change

the lettering of A in AC and of B in BC to see that the

two*copule undergo changes identical with the two single

cells in Spherospora dimorpha. Except this one point

of difference—the beginning of spore formation—we note

that the late division of the membrane-forming cell, the

identical number of cells in each spore and the independ-

ence of each spore in the myxosporidian body characterize

both species of Ceratomyxa (Awerinzew and Mavor) and

Spherospora (Davis). It appears highly improbable that

in two different species of Ceratomyxide the basis of

spore formation should be a copula (Awerinzew) or an

univalent nucleus (Mavor).

Summarizing the known description of spore formation

of those myxosporidia, in which each spore is formed in-

dependently of the other in the somatic body, and where

no pansporoblast exists, we can demonstrate the following

uniform features in all investigated forms. 3

1. Six cells or nuclei are used for the formation of each

spore, when two polar capsules are present; eight, when

four polar capsules are present.

2. The cells which form the spore membrane have a

similar origin and are distinguished by the independence

in which these cells develop as compared with the other

constituents of the spore. Their mother cell is lying in a

resting stage till the division of the gametocyte is finished,

as described by Davis for Spherospora dimorpha, and by

Awerinzew for Ceratomyxa drepanopsette.

In Myzidium sp., where, according to the investiga-

tions of Awerinzew, either one, two or three spores are

lying independently in the myxosporidian body, there is

a very late division of the cell, the divisional products of

which form the spore membrane as recorded by this author

(Fig. 3). Here the one gametocyte divides into two

cells, one of which by a late division gives rise to the two-

726 THE AMERICAN NATURALIST [Vou. LI

spore membrane-forming cells, the other forms the two

capsulogenous cells and two gametes. We intentionally

avoid, in Fig. 3, calling

0, the two chromatin

ap lumps, which the author

himself (p: 202) ° has

4] called ‘‘iiberfliissiges

0. A12 Chromatin”? (degenerie-

o é rende Kerne), nuclei

Az. A22 and do not add them

6 0 0 as such in the diagram

Ati “M22 as Auerbach, 1912, p.

re the spore ibrao Feria colis 28, did when discussing

(valve cells). Am Ax are the gametes. Awerinzew’s investiga-

Anz and Ay: are the capsulogenous cells. ; S

ions. We consider

these chromatin lumps only as formations probably of

glycogenous nature and as being used during membrane

formation.

In Fig. 4 Auerbach’s conception (Type I) of how

the spore formation is effected in Myxidium bergense is

represented. Auerbach believes, as stated before, that

either a plasmogamy (Type I) or a real copulation (Type

Il) may be at the basis

of spore formation. We BI

will not discuss, for the 0,

present, how the bigger

and smaller cells which

are seen at the begin- 0. 0

ning of spore forma-

tion, arise. The latter an

“Bi2

divides once and the 0 0 0 0

two divisional products Am At A122

Mysidium bergense (Auer-

form the spore-mem- Fic, 4.

n bach Type I); By and By are the spore

brane-forming cells. The membrane-forming cells (valve cells). Anı

other cell divides twice "4 A are the two gametes. Aus and

ie Aim are the capsulogenous cells.

to give rise to two gam-

etes and two capsulogenous cells. The author does not

especially mention the order in which these cells divide,

No. 612] MYXOSPORIDIAN LIFE CYCLE 727

but nothing in his report contradicts the supposition that

in Myxidium sp. and in Myxidium bergense there is a

close analogy with Davis’s and Awerinzew’s observa-

tions. He also observes the elimination of chromatin and

‘‘eventuell Bildung von Restkernen”’ (p. 24). These are

not incorporated in Fig. 4 for the same reasons I pointed

out for Myxidium sp.

My observations in Chloromyxum leydigi show, further-

more, that the cells which form the valves of the spore do

not play a part in the development of the final contents of

the spore, but are here in this form (comp. Fig. 1) the

products of the first division of each gametocyte. In

the case of Chloromyxum leydigi two gametocytes form

by one division the two spore-membrane-forming cells;

in the three other species, Myxidium sp. (probably Myxid-

tum bergense), Ceratomyxa drepanopsette and Sphe-

rospora dimorpha, one gametocyte forms the one cell, the

division products of which are transformed into the valves

of the spore. But in all four species these cells have the

sole purpose of forming the spore membrane.

After surveying the Figs. 1, 2 and 3, and having com-

pared them, I have no doubt that the origin of the

spore-membrane-forming cells is identical in the so-called

monosporous and disporous forms. Advancing one step

farther and taking into consideration those forms in

which two gametocytes form the cells inside each spore

(Fig. 1) we notice that in dealing with the origin and

the position in the development of the spore, we have

to add nothing. The spore-membrane-forming cells are

distinguished by their early segregation from the game-

tocytes and their non-entering into the series of those

cells which are included in the spore. The only difference

is that these cells do not divide further; if they did, we

could easily construct the disporous type of Spherospora

dimorpha (Fig. 2). The same holds true for those

species which form two spores in one pansporoblast

(Fig. 4) and where two gametocytes are observed at

the basis of spore formation (Keysselitz, Schroeder).

728 THE AMERICAN NATURALIST [Vor. LI

If we conceive these two cells in question (A, and B,)

which form in Myxobolus pfeifferi (Keysselitz) the pan-

sporoblast membrane to divide once more and the last di-

vision inside the spore to be suppressed, we could have

the type of Spherospora dimorpha.

According to Keysselitz, in Myxobolus pfeifferi each

of the two gametocytes together with the small cell ap-

0... 0,. Opn 0,

qo oO. On 0.0, Oe Oa &.

O, Oraa OP ten

G. 5. General plan for polysporous disporoblastic forms. (Type

ses Ag and Bz are the envelope-forming cells (pansporoblast- a Peon

cells). An and A, and Bẹ» are the two gametes in each spore. The

products of “the fourth division form valve tells Ann, Aisi, iha Bing, and cap-

sulogenous cells Ajj, Aim Buw Biar

` proach each other and each divides up until six cells have

arisen. Thus we have in all cases 14 cells, two of which

have a different divisional capacity, for they stop dividing

and the big cells form all the other cells which at the end

compose the two spores. Their later fate is indicated in

Fig. 5 and, though this does not. concern us in this

discussion, we should like to emphasize the fact that two

gametes are always present in a certain stage of spore

development. We are convinced that the cells A, and B,

represent genetically in the pansporoblastic forms that

cell formation which in all monosporous, disporous and

polysporous species gives rise to the spore membrane

itself (Figs. 1 to 4). These cells or their nuclei were

observed by Keysselitz, Parisi, Lo Gindice, Auerbach

(Henneguya psorospermica), Georgevitch, and with cer-

No. 612] MYXOSPORIDIAN LIFE CYCLE 729

tain restrictions by Mercier and Schroeder. This cell

couple (A, and B,) should be called envelope cells or

envelope cells nuclei when they do not fulfill their des-

tin (Schroeder, probably Mercier). Even in those cases

in which a pansporoblast membrane had not been dis-

covered it might have been either overlooked or have

-been in evidence at the. beginning of pansporoblast

formation before the valves of each single spore had

been developed. Later these take up the function of the

Hiillzellen which make their retrogressive development

plausible. These Hiillzellenkerne are neither Restkerne,

nor reduction nuclei, nor somative residual nuclei. The

term for residual nuclei of somatic nature (see definition,

p. 679) has already been disposed of in monosporous and

disporous forms and must be used in the same way in

polysporous forms. In all forms which are polysporous

and have many singly developing spores, the whole vege-

tative body which is not used up in spore formation has

somatic ‘‘restkerne’’ or residual nuclei. As I pointed out

in Chloromyxum leydigi the vegetative animal may die

after spore formation together with the ‘‘restkerne.’’ In

this form the vegetative animal may prolong its life by

forming internal buds, if it has reached a considerable

size before and during spore formation. In all poly-

sporous forms with pansporoblast, i. e., the disporoblastic

forms, we have to be very careful when applying the name

of somatic residual nuclei. In those species which are not

tissue parasites and sometimes have cystlike formations

which are surrounded by gelatinous envelopes, we may

find somatic residual nuclei, because it seems improbable

that the whole vegetative body is used up for spore for-

mation. I believe this to be the case in Spheromyxum

sabrazesi and Spherospora caudata. Where no residual

vegetative nuclei were observed, the investigators may

not have studied the whole animal, but only the propa-

gative parts of it which have left the vegetative body

(Parisi, Fig. 3). Keeping this point in mind, later in-

vestigators may discover somatic residual nuclei in de-

730 THE AMERICAN NATURALIST [Vou. LI

generating stages analogous to those found in the mono-

sporous, disporous and the non-disporoblastic poly-

sporous forms, among the debris of the dying animals

inside the gall and urinary bladder, as I have shown in

Chloromyxum leydigi. In the so-called ‘‘tumor-forming’’

disporoblastic polysporous forms, no facts are known

- which show that somatic residual nuclei have been ob-.

served. The beginnings of cyst formation, however,

have never been studied, and it is only at this stage that

somatic residual nuclei may be seen, and not after the

eyst is crowded with sporoblasts and spores. But even

in the fully developed cysts there may be degenerating

somatic residual nuclei which have escaped observation.

The facts which Weissenberg found in Glugea anomala

and hertwigi—two Microsporidia—seem to support my

suggestion. But the Hiillzellen or Hiillzellenkerne of the

myxosporidia are never identical with somatic nuclei.

Their undisputed place in the development of the myxo-

sporidia will soon be clear.

Before we proceed further in discussing the formation

of the sporoblast membrane in those myxosporidian

species in which the spores are formed in pairs inside one

sporoblast, it may be recalled that several facts have been

ascertained concerning the fully discussed spore-mem-

brane formation in monosporous or disporous myxospo-

ridian species: (1) The copulation of two gametes occurs

during or after the two myxosporidia leave the spore.

(2) No reduction takes place from the beginning of spore

formation until the end, because the number of chromo-

somes remains the same (Davis and Georgevitch). (3)

The darkly staining masses of ‘‘restkerne,’’ ‘‘residual

nuclei,” ‘‘reduction nuclei’? have been shown to be gly-

cogenous and to be necessary for spore-membrane for-

mation. (4) Membrane-forming cells or nuclei are set

apart by different division intervals from the other cells

of the sporoblast.

Now from the above given summary of the latest facts

in monosporous or disporous forms, it is clear that they

No. 612] MYXOSPORIDIAN LIFE CYCLE 731

are strictly opposed to all the views which maintain that a

copulation or so-called syncaryon formation precedes

spore formation. But they are all in accord with the in-

vestigations of all authors who have shown that there is

no syncaryon formation, but merely a plasmogamy of

two cells, without any copulation, at the onset of spore

formation.

When I wrote the second part of my investigations on

Chloromyxum leydigi, 1913, I pointed out that the facts

which were presented by Auerbach, Mercier and Parisi,

as proofs of the occurrence of a synecaryon formation just

before the onset of spore formation, are not quite con-

vineing. Their figures can easily be arranged in such a

manner that the supposed synearyon formation represents

the division of gametocytes into a smaller cell, which in

most all other known cases forms the membrane of the

pansporoblast. (Compare Erdmann, 1917.) Itis not nec-

essary to repeat here the attempted revision and rear-

rangement of the figures of these authors. This same

holds true for the synearyon formation in Myxidium ber-

gense, Type II (Auerbach) and Ceratomyxa drepano-

psette (Awerinzew). We will take it for granted that our

views are correct as long as no new facts ascertained on

smears—not sections—compel us to change our opinion.

As mentioned above, all authors who have shown that

no synearyon formation occurs, but that a plasmogamy of

two cells without any nuclear fusion occurs at the onset of

spore formation, can agree with us that the sexual proc-

ess is going on at the beginning of the new life cycle.

Auerbach and Parisi do not convince us that the figures

which represent the so-called caryogamy can not be con-

sidered as the dividing of the gametocyte in the two cells.

In accordance with the facts and interpretations, Keys-

selitz, Schroeder, Lo Giudice, Erdmann, and Georgevitch

uphold the view that no merging of two cells or two cell

pairs takes place to form the couples of cells which are

later considerd as a quadruple group of the growing spore.

By comparing the series of figures of all those drawings

732 THE AMERICAN NATURALIST [Vou. LI

which are supposed to prove the merging of two cells,

they can, as said before, be interpreted as the division of

one cell into two. The larger of these cells, wrongly

called macrogametocyfe according to the cell fusion

theory, has divided and formed the cell wrongly called

microgametocyte.

This ‘‘microgametocyte’’ and its division products after

one division, or these ‘‘microgametocytes’’ in cases where

two gametocytes are observed at the onset of spore for-

mation (Keysselitz, Schroeder, and Erdmann) now form,

according to all known investigations, the pansporoblast

membrane. Just as we could point out in disporous

forms the uniformity of the origin of the spore-mem-

_ brane forming cells (Figs. 2, 3 and 4) so we can do the

same for the pansporoblast membrane and its nuclei in

the following forms: Myxobolus pfeifferi (Keysselitz),

Myxobolus ellipsoides (Lo Giudice), Spheromyxa sa-

brazesi (Schroeder), Spherospora caudata (Parisi), Hen-

neguya gigantea (Georgevitch), and Henneguya psoro-

spermica (Auerbach); all following Fig. 5, provided

we do not take into consideration the origin of the

cells A, A, and B and B,. Keysselitz and Schroeder’s

views, except one contradictory point, are exactly repre-

sented by Fig. 5, but there are differences mentioned

by the other authors. Still we make the generalization

that there is one and the same plan of spore formation in

the pansporoblastic myxosporidia though we know that

facts are reported which do not fit in with our view. We

hold the opinion that it is permissible to rearrange the

observed facts, because all interpretations have been

gained by piecing together and arranging facts according

to the theoretical viewpoint of the authors. No continued

observation of spore formation in the living animal has

been possible. Also we are allowed to add facts ascer-

tained in other species if the authors have only consid-

ered sections and not smears. Sections are misleading

because the whole quadruple group can not always be seen

~ on the same section and the origin of the small cell from

No. 612] MYXOSPORIDIAN LIFE CYCLE 733

the big cell can not be traced without doubt. Therefore,

most investigators have lately used smears to get a fuller

and more correct view of the origin of the different cells

from each other. It is astonishing how scanty the details

appear when one considers the formation of the quad-

ruple group in Auerbach’s, Lo Giudice’s, Parisi’s and

Georgevitch’s presentations. Mercier’s Figs. 19-27, Plate

1; Auerbach’s Figs. 8a-15, Plate 2; Lo Giudice’s Figs.

29-34, Plate 1; Parisi’s Figs. 13-18, Plate 16; and George-

vitch’s Figs. 32-35, Plate 1, do not show each single step

of this important process. Connecting stages are missing.

Therefore, one is allowed to interpret differently their

presented facts, as I have done in Fig. 5. In Table II

TABLE II

I II

Myxobolus pfeiffert Mercier. Spheromyxum sabrazesi Schroeder.

- Cell A (copula) forms all other 12 As B,

cells of the pansporoblast and the A, B,

two ‘‘ Hiillzellenkerne.’’ All cells divide up to form the 12

pansporoblastiec cells and the two

tt Hiillzellenkerne. ’’

Myzobolus ellipsoides Henneguya gigantea Henneguya psorospermica

Lo Guidice. Georgevitch. Auerbach (Type I).

A, An

A, Ay

Cells A, and A» do not form

any of the other 12 cells of

the pansporoblast.

we can study the different opinions from the authors’

point of view. Lo Giudice, Georgevitch, Auerbach, Keys-

selitz, and Schroeder are alike in interpreting that the

two cells which develop into the pansporoblastic mem-

brane or nuclei are separated very early from the other

cells. They never intermingle with those cells inside the

spore-membrane (except according to Schroeder). They

can not, therefore, be microgametocytes and in conse-

quence they have nothing whatsoever to do with a sexual

phenomenon. This adds strong support to our view that

734 THE AMERICAN NATURALIST [Vou. LI

the sexual process is at the beginning of the new life cycle.

I do not wish to veil the great discrepancy between the

conception of Mercier (Fig. 6) and the other authors

0 0.,

0., On 0. Ou

Omn Ore Ooa Oe Oon Oze On Ve

OPiMateA Ben” tat clad bane

6. Myzxobolus pfeifferi, Mercier: Oi, and Coe are We cellos d’en-

reloppe "oe = author, which represent the ja ii “ Restkerne ” or

tion nuclei” of other authors. The products of the fourth snvidie form, oe

each aes, the gametes, the valve cells and the capsulogenous cells.

mentioned. All cells are products of a copula; and there

is no setting apart of the g form-

ing cells or nuclei, though later they appear at the accus-

tomed places between the two spores (Plate I, Figs. 31,

32). I shall not risk an interpretation, but think a new

investigation on this same.subect might be very promising

and result in the desired uniformity. I think it highly

probable that in all pansporoblastic forms the spore de-

velopment follows the Keysselitz-Schroeder interpreta-

tion: that two gametocytes form the basis of the spore

formation. . But even if one believes that the quadruple

group is not formed by two but by one cell pair, the prin-

cipal point is not changed. It is indifferent for the the-

oretical interpretation whether a segregation of the sec-

ond cell pair from the first takes place, and both then form

the quadruple group, or whether two cell pairs approach

each other and form the quadruple group. The pedog-

amy is merely a closer one in the first case.

To summarize: In the observed myxosporidian species

No. 612] MYXOSPORIDIAN LIFE, CYCLE 735

with pansporoblast (exception, Mercier, Myxobolus pfeif-

feri), the first division products of the gametocyte or

gametocytes form the pansporoblastic membrane or, if

degenerated, its nuclei. This division is a heteropole di-

vision and forms highly chromatic small cells or nuclei

which never intermingle with the cells inside the pan-

sporoblastic membrane (exception, Schroeder).

On the basis of these facts, we need only state that the

heteropole division has no connection whatsoever with a

reduction division, as Keysselitz tentatively suggested.

This conspicuous division produces the Hiillzellen or

Hiillzellenkerne, and it may not be impossible that in the

case of Spheromyxa sabrazesi these small chromatin cells

do not intermingle with the others and divide up, though

the author mentions it on page 366. They originate, ac-

cording to Schroeder’s second interpretation, in the same

manner as most authors describe, but divide together with

the big cells until twelve cells are present in the pansporo-

blast; they then take their accustomed place inside the

sporoblast membrane and are easily recognizable. This

apparent exception merits further investigation.

We maintain our conclusion that the Hiillzellenkerne

or the Hiillzellen are identical with the spore membrane

forming cells of the non-disporoblastic polysporous forms.

They have the following features in common: they are the

first division products of the gametocytes; they do not

intermingle with the other cells inside the spore; they

form the envelope, in one case of the spore, in the other

of the pansporoblast. They are neither somatic residual

nuclei nor Restkerne nor reduction nuclei. They are

cells which have a tendency to degenerate in some disporo-

blastic forms when their functions are taken up at an

early period by the valve cells or spore-membrane-form-

ing cells.

It remains, as the last part of our discussion, to deal

fully with the significance of those darkly staining masses

which have been described as ‘‘Reductionskerne’’ or

‘*Restkerne’’ ‘‘inside the sporoblast.’’ In the following

table we give a short survey of the known facts.

736 THE AMERICAN NATURALIST [Vou. LI

A survey of Table III brings out clearly certain facts.

When darkly

Author

1. Awerinzew ..

2. Auerbach ...

4, Awerinzew ..

By ever. i543. e

6. Erdmann ....

Ty PRED bis ee K

9. Auerbach .

staining masses are observed inside the

TABLE III

Occurrence of Chromatic Bodies In -

side the Spore Interpreted as

Species uction

.Myzxiđdium spec. ........... Seldom distinct small nuclei,

generally ‘‘Zwei ziemlich

grosse Chromatinkiigel-

chen’’. (p. 201).

. Myxidium bergense ....... Diffusion of chromatin or

formation of two ‘‘rest-

kernartigen Gebilden’’

: (p. 20).

Spherospora dimorpha ,,..Formation of round chro-

matie bodies.

.Ceratomyxa drepanopsette.. Infiltration of chromatic

small hodies into the cyto-

plasm before the spore

membrane includes the

gametocytes after the sup-

posed copulation. Note

here the later Bigi

of spore membra

Ceratomyxa acadiensis .... Formation of coina chro-

10) which are later re-

. Chloromyxum leydigi ...... Poriation of several large,

i de

eeply staining bodie

ha disappear after a

ore membrane is formed.

.Spherospora caudata ..... ‘Formation of small, deeply

bodies before the

supposed copulation (Fig.

15).

Spherospora dimorpha,

polysporous form ....... No diffused infiltration of

chromatin observed, also

no formation of round

chromatic bodies.

..Myxidium bergense,

polysporous form ....... Formation of two ‘‘restkern

artigen Gebilden’’ or dif-

fusion of chromatin. |

No. 612] MYXOSPORIDIAN LIFE CYCLE 737

. Keysselitz ... Myxobolus pfeifferi ....... One to four round chro-

« Mercier ....%. Myxobolus pfeifferi ....... Diffusion of small chromatic

bodies into the cytoplasm

(Figs. 33, 34) after the

. 22, 2

. Lo Guidice ... Wyzobolus ellipsoides ..... Several round chromatic,

deeply staining bodies,

which are not observed

after Lae Anenii ae

: is formed (Figs. 42).

- Schroeder ...-§nhwromyxum sabrazesi ... Chromatic, deeply aan

brane is formed. (Comp.

Figs. 30, 32 with Figs. 33,

34.

. Auerbach .... Henneguya psorospermica ..

foul

To judge after Figs. 6 to

18, extrusion of a chro-

matic body in cytoplasm.

(Note, only sections to

fuel

. Georgevitch ..Henneguya gigantica ...... Four deeply staining chro-

matic bodies called by the

author degenerated nuclei.

spore, they disappear after the spore membrane is formed.

It is proved that in Chloromyxum leydigi they are of

glycogenous nature as well as the spore membrane itself

and the polar threads. In some cases their number is ir-

regular. These chromatic lumps may be products of

nuclear division, but the true chromosomes have not been

found. Those authors (Mercier, Awerinzew, Parisi) who

believe they have shown a synearyon forming, have also

observed an extrusion of chromatin immediately after the

union of the supposed micro- and macro-gametocyte. In

Mercier’s case a second diffusion of round bodies is shown

inside the spore which corresponds with the facts ob-

served in other species. Ceratomyxa drepanopsette

738 THE AMERICAN NATURALIST [Vou. LI

(Awerinzew) has only an extrusion of chromatin before

the synearyon formation, while in Myxobolus ellipsoides

(Parisi) it occurs immediately after this phenomenon.

These exceptions in the series, t. e., that inside the spore

no chromatin diffusion is observed, may be due in the case

of Parisi to a limited number of studied forms and in the

case of Awerinzew to the fact that the spore membrane

in Ceratomyxa is formed very late. Yet these exceptions

do not prevent the final statement that the darkly staining

chromatic masses in the spore are not reduction nuclei,

or restkernartige Gebilde, but play an important part in

the development of the spore membrane.

The whole trend of our critical review leads up to the

following conclusions:

1. Reduction in myxosporidia has thus far not been dis-

covered.

2. The so-called reduction nuclei inside the spore are

chromatic or glycogenous masses, which serve the spore-

membrane formation.

3. The so-called residual nuclei of the disporoblastic

forms can not be considered as identical with the somatic

residual nuclei of the mono-, di- or poly-sporous non-

disporoblastic forms. They are the functionless nuclei of

the envelope cells of the disporoblastic forms.

4. The envelope cells can by their origin only be com-

pared with those cells in the mono-, di- or polysporous

nondisporoblastic forms which later give rise to the valve

cells.

5. The somatic residual nuclei are well-defined in mono-,

di- or poly-sporous nondisporoblastic myxosporidia.

Their analogy has not thus far been discovered in disporo-

blastic polysporous forms.

LITERATURE

(For literature before 1910 compare Auerbach, M., ‘‘ Die Cnidosporidien,’’

Leipzig, 1910).

Anite M. 1912. Studien über die Myxosporidien der norwegischen

Seefische und ihre Verbreitung. Zool. Jahrb. Abt. f. Syst., Vol. 34,

pp. 1-50.

No. 612] MYXOSPORIDIAN LIFE CYCLE 739

Davis, H. S. 1916. The Structure and Development of a Myxosporidian

Parasite of the Squeteague, Cynoscion regalis. Journal of Morphology,

Vol. 27, pp. od 346.

Erdmann, Rh. 1911. Zur Lebensgeschichte von Chloromyxum leydigi,

einer mean aie we hrs aie 4 (Teil I). Arch. f. Protistenkunde,

Vol. 24, pp. 149-

Erdmann, Rh. sai ene a TE und a esa zur

ander ae ae (Teil II). Arch. f. Protistenkw ;

Geo enik, y 1908. Sur le cycle évolutif chez a SE oie C.

B. A Bo Ea T: pn p. 190.

ee a "1915. Etude du cycle évolutif chez les Myxosporidies.

rch d. Zool. exp. et gen., T. 54, pp —409

Lo ara P. 1911. Sullo Soe del Mynobolss ellipsoides Thel. Riv.

mens. Pesca Idrobiologia, Anno 6 (13).

Lo Giudice, P. 1912. Studi sui Cnidosporidi. Pavia, pp. 1-88.

Mavor, I. W. 1916. On the Life History of PP TEER acadiensis, a

New Species of Myxosporidia from the Eastern Coast of Canada.

Contrib. Zool. Lab. of the Museum of Compara. Zoology at Harvard

78.

Nemeczek, A. 1911. Beiträge zur Kenntnis der Myxo und Microsporidien

der Fische. Archiv. f. ieia Bd. 22, pp. 143-169.

Parisi, B. 1910. Spherospora caudata n. sp. Zool: Anzeiger, Bd. 36,

253-2

pp- :

Parisi, B. 1913. Sulla sphaerospora caudata. Atti della Societa Italiana

di Scienze Naturali, Vol. 51, pp. 1-11

* In consequence of the war I did not see my own reprint printed in the

Archiv für Protistenkunde so it is impossible to add volume and page

reference.

EVIDENCE FOR THE DEATH IN UTERO OF THE :

HOMOZYGOUS YELLOW MOUSE?

HEMAN L. IBSEN AND EMIL STEIGLEDER

Curnot (1905) and Castle and Little (1910) have pre-

sented conclusive evidence that yellow mice are always

heterozygous and hence cannot be made to breed true.

Their combined results show that when yellows are

mated together the proportion of yellows to non-yellows

in the offspring is almost exactly 2:1 instead of the usual

3:1 ratio resulting from the mating of heterozygotes.

Castle and Little seem justified on this account in assum-

ing that the homozygous yellows are not viable, especially

since the size of litter from the yellow X yellow mating

is markedly smaller than that obtained from yellow X

non-yellow or non-yellow X non-yellow matings.

Until quite recently no attempt had been made to de-

termine embryologically the actual fate of the homozy-

gous yellows. Since the present investigation was begun,

however, Kirkham (1917) has published a preliminary

statement of the results of such a study. His results,

presented only in abstract, show that of 69 embryos from

yellow X yellow parents, 26 or 37.8 per cent. were de-

generating. For ‘‘non-yellows’’ he used albinos.2 Of

1 Papers from the Department of Experimental Breeding, Wisconsin Agri-

cultural ee aad = No. 11. Published with the approval of the

Director of the 8

[The problem a ne fate of the homozygous yellow mouse was under-

taken at my suggestion during the summer of 1916 by Mr. Steigleder and

the experimental work on which the present paper is based was done en-

tirely by him. As he was, however, unable to complete the problem the

accumulated material and records were turned over to Dr. Ibsen, who has

checked all records with the preserved embryos and is alone responsible for

the tabulation, interpretation and presentation of the results—L. J. Cole.]

2 This selection of albinos for ‘‘non-yellows’’ was unfortunate, since

they apparently were not tested genetically, and hence may or may not

have carried the factor for yellow. From the fact that the proportion of

dead embryos was markedly different we may accept Kirkham’s assump-

ae 740

No. 612] DEATH IN UTERO OF MOUSE 741

the 84 embryos from albino parents, only 2, or 2.3 per

cent., were degenerating. This makes it seem quite prob-

able that the homozygous yellow zygote develops for a

time and then dies.

In our study no attempt has been made to investigate

the very early stages, as was done by Kirkham, but a

large number of embryos have been obtained from non-

suckling females pregnant from 13 to 19 days.* In all

688 embryos have been examined. These have been ob-

_ tained from (1) yellow females mated to yellow males,

(2) yellow females mated to non-yellow males (choco-

lates), (3) non-yellow females (chocolates) mated to yel-

low males, and (4) non-yellow females mated to non-

yellow males. In this last mating most of the parents

were self blacks.

During the investigation two distinct types of dead em-

bryos were encountered, (1) those in which development

had ceased shortly after implantation, corresponding to

those described by Kirkham, and (2) a few which seem

to have developed normally till about the thirteenth day

and then died, presumably because of overcrowding in

the uterus. These latter were characterized by their

dead, yellow appearance and smaller size as contrasted

with the living pink color and larger size of the normal

embryos. The first kind has been designated ‘‘dead em-

bryos A’’ in the tables, while the second kind is classed

as ‘‘dead embryos B.” We are primarily concerned with

‘‘dead embryos A,’’ and it is to be understood that ref-

erence is to this type unless specifically stated otherwise.*

Similarly, by ‘‘living embryos’? we mean those which

tion that they were really genetically non-yellows, though this brings the

argument dangerously close to reasoning in a cirele. In our work a number

of albinos were mated both to yellows and to non-yellows, but since the

genetic constitution of the albinos was not sufficiently established in most

ases, the embryos from these matings are not included in our tabulations.

3 The normal duration of gestation in the mouse is about 21 days, but it is

often less.

4 We are indebted to Dr. Alva Wilson for sectioning for us dead embryos

from each of the four types of matings. Microscopical examination of

these has verified our previous conclusions as to their character.

742 THE AMERICAN NATURALIST [ Vou. LI

were obviously alive when the mother was killed. As

the females were killed by chloroforming, all embryos

were usually dead by the time they were examined. The

following tables give the results obtained. Each of the

first four tables represents one of the four types of mat-

ings described above. In a few instances there has been

some uncertainty as to the exact stage of gestation at

which the embryos were removed, but in such eases this

has been determined approximately by means of weights

of the living embryos.

TABLE I

YELLOW 9X YELLOW ¢

r Average Size of Litter

Stage of Ges- No. of Livi: Dead Dead Percentage

tation Litters Dauro ae hes cas ae energy Living Total

Embryos | Embryos

13 days: 5 33 14 29.8 6.6 9.4

days: onii 6 50 9 15.3 8.3 9.8

15 days. oes: 4 26 10 1 27.0 6.5 9.3

Todays: ri 42 13 2 22.8 6.0 8.1

Beaks 5 25 4 13.8 5.0 5.8

18 days...... 5 27 13 32.5 5.4 8.0

IO:dayaic es: 1 4 100.0 4.0

‘SOtGh =. se 5 33 203 67 3 24.54 6.15 8.27

TABLE II

YELLOW Ọ X NON-YELLOW ¢

Average Size of Litter

Dead Dead Percentage

Stage of No. of Living

Gestation Litters Embryos agri T e arr Living Total

Embryos | Embryos

Saays. ENA 5 34 12 26.1 6.8 9.2

E a A 6 56 1 1.8 9.3 9.5

days. . 4 35 4 10.3 8.8 9.8

16 days. ..... 2 14 8 36.4 7.0 11.0

17 dave, 2. <. 3 25 1 3.8 8.3 8.7

1S days co 3 17 1 1 5.3 5.7 6.3

19days. sa; 1 10 10.0 10.0

Total ..... 24 | m 27 1 12.33 | 7.96 | 9.13

The data presented agree in the main with Kirkham’s,

but our percentage of dead embryos A, from the yellow

X yellow mating (Table I) is considerably less than his,

while our percentage from the non-yellow X non-yellow

No. 612] DEATH IN UTERO OF MOUSE 743

mating (Table IV) is somewhat higher. Theoretically,

if we assume that a certain proportion of embryos o

other gametic composition die from unknown causes in

mice of all colors and that all the homozygous yellows are

TABLE III

NON-YELLOW Ọ X YELLOW ¢

re | ? | Average Size of Litter

Stage of No. of Living Be se aan | Soret

Embryos | Embryos

tI dayo., 1 2 1 33.3 2.0 3.0

ee POT 1 6 6.0 6.0

PES EE PO 2 15 7.5 75

Ip dave. : is: 2 20 1 a d 4.5 10.0 11.0

17 days. 2 11 5. 5

IS dam.. iig 1 8 1 11.0 8.0 9.0

19 days......

Total cos, 9 62 3 1 4.55 6.89 To

TABLE IV

NON-YELLOW ? X NON-YELLOW ¢

| i TIENER Average Size of Litter

Stageof | No.of Living Dead Dead Dead

Gestation Litters | Embryos ur ver Emon Embryos | Living Total

A Embryos | Embryos

IS days. 0% 2. 3 22 3 12.0 7.3. 8.3

14 days...... 3 28 1 3.4 9.3 9.7

15 days. 2...

16diys. 3 Z 7.3 8.0

17 dat... 3 19 6.3 6.3

18 days...... 3 26 r: -10.3 8.7 9.7

19 dave. e 1 4 4.0 4.0

LO oe 16 121 7 2 5.38 7.56 8.13

represented as dead embryos, then the difference between

the percentages of dead embryos from the yellow X yel-

low mating and the non-yellow X non-yellow mating

should be approximately 25 per cent. In our results the

difference is 19.2 per cent., while in Kirkham’s it is 35.5

per cent. Neither of these is especially close to the ex-

pected percentage. If, however, his results and ours are

combined the difference is 23.0 per cent., which is close

to expectation.

If instead of comparing yellow X yellow with non-yel-

low X non-yellow only, all matings other than yellow

744 THE AMERICAN NATURALIST [ Vou. LI

X yellow are combined for this purpose, it is found that

the dead embryos in these combined matings constitute

8.9 per cent. of all embryos present. Subtracting this

from 24.5, the per cent. of dead embryos in the yellow

X yellow mating, the difference is only 15.6 per cent.

When all these results are combined with those of Kirk-

ham the difference is still only 19.4 per cent., which is con-

siderably lower than that obtained by using only the

classes considered by him. An attempt will be made

farther on to explain this deficiency.

Tables II and III, representing the reciprocal crosses

of yellow X non-yellow, show marked contrasts in sev-

eral respects. In the yellow ? x non-yellow & mating

(Table II) 12.3 per cent. of the embryos were dead, while

in the non-yellow Ẹ X yellow ¢ mating (Table III) the

percentage is only 4.5 per cent. For both matings the

percentage of dead embryos theoretically should be the

same as in the non-yellow X non-yellow mating (Table

IV), since in neither case is there the possibility of any

of the offspring being homozygous yellows. ‘The per-

centage in Table III is approximately the same as in

Table IV, but in Table IT it is much higher. It is well

known that yellow females tend to take on more fat than

females of other colors. There is a possibility that this

physiological difference may also in some way influence

the production of a greater number of dead embryos A.

This is offered merely as a suggestion, since there is no

direct evidence for or against it.

In discussing the stages of pregnancy in which the dead

embryos are to be found, Kirkham makes a statement

which does not accord with our observations. He says:

‘‘No degenerating embryos have been found in either

white [albino] or yellow mice pregnant more than sixteen

days.’’ He believes complete resorption of the degen-

erating embryos has taken place by the end of the six-

teenth day. Table V, which is a summary of all our four

types of matings, indicates that in our material there is

no marked decrease in the percentage of dead embryos

toward the end of pregnancy.

No. 612] DEATH IN UTERO OF MOUSE 745

TABLE V

RELATION OF DEAD EMBRYOS TO STAGE OF PREGNANCY FOR THE Four TYPES

OF MATINGS

Stage ot Gestation e ee TT a ot poet

E E E T ee 30 121 24.8

E e Va PE a A ees Ri 11 151 73

SO GSEs £55 hee he 14 91 15.4

1G GRUB io ee ee te 22 125 17.6

Le AGE crt i koe awn cng 5

(eS alk Raa ary AR arene 18 97 18.6

Moe n TE A SAO 4 18 22.2

His ee a | 104 688 15.12

As previously stated, Cuénot, and Castle and Little

noted that the average number per litter is less from yel-

low females mated to yellow males than from any other

type of mating. Our results, summarized in Table VI,

bear this out. Here it will be noted that the average num-

ber of living embryos is less for mating 1 than for any

TABLE VI

LITTER SIZE FOR THE DIFFERENT TYPES OF MATINGS

Average Number of Embryos per Litter

No. of i

ETUS E Nng Litters | Living Em- Dead Embryos

bryos A and B Total

1. Yellow 9 X yellow o'......4...:| 33 6.15 2.12 8.27

2. Yellow 9 X non-yellow co’....... 24 7.96 1.17 9.13

3. Yellow g -yellow F ....... 9 6.89 0.44 7.33

(2 and 3 combined)............. 33 7.67 0.97 8.64

4. Non-yellow 2 X non-yellow o.. 16 7.56 0.57 8.13

(2,3 pe 4 combined) .......... 49 7.36 0.84 8.47

of the other types of matings singly or combined. It is

evident that the average number of living embryos per

litter represents those which would in the regular course

of events have been born alive. In the yellow X yellow

mating the average is only 6.15,° while for the other mat-

ings combined it is 7.63. The average number when the

dead embryos are also included should be approximately

the same in both cases, and this proves to be true, being

8.27 for yellow X yellow and 8.47 for all other matings.

5 Two of the litters in this mating were made up entirely of dead em-

bryos A and ue es had no living embryos. So far as living embryos

are concerned their size would be 0, and they have been included as such

with the other litters produced by this mating.

746 THE AMERICAN NATURALIST [ Vou. LI

During 1916-17, the period at which the embryological

study was carried on, numerous living litters of mice

were born in the laboratory. Miss Sarah V. Jones, who

was also working with mice, has generously furnished

data from her own breeding experiments, and these have

been incorporated with ours. Some of the mice in her

experiments were black-and-tans, but as Dunn (1916)

has shown that these are a form of yellow and are also

always heterozygous, they have been classified as yellows.

Table VII shows the average size of litters for the various

types of matings.

TABLE VII

AVERAGE SIZE oF LITTERS Born Durine 1916-17

(Figures in parentheses indicate the number of litters.)

Type of Mating Average Number of Mice per Litter

At Time Color was

Type of Mating Recorded

iy Bellew OM yellow. g totes as 5.36 (140) 4. 55(121)

2. Yellow F X non-yellow du... ....s0%s 6.21(88) a §,63(71)

3. Yellow d X non-yellow F ............ 7.02 (50) 5.95(46)

(2 and Seombined} 25005 220008 6.51(138) 5.76(117)

4. Non-yellow ? X non-yellow ¢ ........ 6.88 (42) 5.49 (37)

(2, 3 and. 4 combined). .....6. 2. arau 6.59 (180) 5.69 (154)

It will be seen that there is a deficiency of litter size

from the yellow X yellow mating here as in the em-

bryological material. Theoretically the average size of

litter from yellow parents should be 75 per cent. of that

from any of the other matings. Both Cuénot, and Castle

and Little, however, have found it to be above 80 per

cent. Our results are in accord with these findings.®

Table VIII shows the percentages found by the various

investigators. In order to make them comparable with

the others our results as given in the table are for the

living litters only and do not include the data from the

embryological investigations.

6 Miss Durham (1911) found very little difference in average litter size

between the offspring from yellows X yellows and the offspring from mat-

ings where at least one of the parents was a non-yellow. She says: ‘‘Only

mice which lived long enough to have their colors determined are included

in these averages.’’ It seemed possible to us that she had not found any

No. 612] DEATH IN UTERO OF MOUSE 747

TABLE VIII

PROPORTIONATE SIZE OF LITTERS FROM YELLOW X YELLOW AND YELLOW

X NON-YELLOW MATINGS

(Figures in parentheses represent number of litters.)

Average Size of Litter atio of * Yello

Authority x Yellow” to‘ 'Yel-

x YellowX Yellow | Yellow xNon-yellow low XNon-yellow ”

Guia OO a aiana 3.38(50) | 3.74(50) 90.37 %

Castle and Little Sedo eS 4.71(277) 5.57(325) 63 %

bsen and Steigleder, 1917...... 5.36(140) 6.51(138) oe 33 %

The most striking fact brought out in this table is that

as the average size of the litters increases the ratio tends

to decrease and therefore to approach 75 per cent. It

would seem from this that if one could secure a race of

mice having a high enough average per litter the the-

oretical percentage could be obtained. Using Table VIII

as a basis for computation, such a race should average

approximately 10 young per litter in the non-yellow

x yellow mating and consequently about 7.5 per litter for

the yellow X yellow mating. It is not Prone that a

race of this sort exists.

Various theories have been advanced to explain this

unexpectedly large litter size in the yellow X yellow

mating. Two suggested by Castle and Little will be con-

sidered here. Both take as their starting-point that ‘‘the

perishing of a pure [homozygous] yellow zygote makes

possible the development of a certain number of other

fertilized eggs.’’ The explanation follows: ‘‘Two ways

may be suggested in which this might come about. First,

more eggs may normally be liberated at an ovulation than

there are young born subsequently. In that case, failure

of some eggs to become attached to the uterus may make

the chances greater that the remainder will become at-

difference because the size of litter had not been recorded at birth. Our

records have been gone over and the litter size found at the time the colors

were recorded. Some litters did not live long enough to be recorded in this

manner and hence could not be included. By referring to Table VII one

ean see that our results do not at all agree with Miss Durham’s. As a

matter of fact, in our material the percentage relation is lower than when

the litter size was computed at birth, being almost exactly 79 per cent.

when ‘‘ yellow x yellow’’ is compared with ‘‘non-yellow X yellow.’’

748 THE AMERICAN NATURALIST [ Von. LI

tached, or the perishing of some may make the chances

greater that the rest will successfully complete their de-

velopment. Or secondly, the production of a relatively

small number of young at one birth may lead indirectly

to more free ovulation subsequently, and so to the pro-

duction of a large litter at a second birth.’’

It will be seen in the first place that the above theories

are based on false premises. It was not known at the time

these theories were proposed that the homozygous yel-

low zygote does not perish in the sense of disintegrating

and finally di ing. It merely ceases to develop

after a certain stage has been reached, and then remains

more or less stationary till parturition. It might still

be maintained that since these undeveloped zygotes take

up very little room there would still be the possibility for

the ‘‘other’’ zygotes to develop. In that case the average

number of total embryos (including dead embryos A and

B) should be greater in the yellow X yellow mating than

in the non-yellow X yellow mating. Our data, presented

in Table VI, indicate that this is not the fact. The other

theory that ‘‘the production of a relatively small number

of young at one birth may lead indirectly to more free

ovulation subsequently, and so to the production of a

larger litter at a second birth’’ still remains a possibility

so far as our data are concerned.

There are several other possibilities which seem worthy

of consideration. Instead of looking for causes that tend

to increase the size of litters from yellows X yellows it

may be profitable to determine if possible causes that

may decrease the size of litters from the non-yellow

X yellow mating. The first and most obvious possibility

is that overcrowding in the uterus may have this effect

by causing the death of some of the embryos. However,

none of our results bear this out. In the first place there

are proportionately just as many dead embryos B (whose

death is probably caused by overcrowding) in the one type

of mating as in the other, and in the second place this

would mean that for our race of mice, having a high

average litter size, there should be a proportionately

No. 612] DEATH IN UTERO OF MOUSE 749

large death rate due to overcrowding, and this would

tend to increase the percentage relation between ‘‘yellow

x yellow’’ and the ‘‘non-yellow X yellow’’ instead of de-

creasing it, which actually is the case.

We know that dead embryos B do not materially de-

crease the litter size in the non-yellow X yellow mating,

but on the other hand we have clear evidence that dead

embryos A have a decided effect in this respect. The

only manner we could postulate in which this could affect

the litter-size percentage relation for the two contrasted

types of matings would be to assume that in the yellow

xX yellow mating dead embryos A are due almost entirely

to the fact of their being homozygous yellows, while in

the non-yellow X yellow mating separate agencies are at

work producing an appreciable number of deaths. If a

more careful examination of dead embryos A should re-

veal rather easily. distinguishable differences this ex-

planation could be tested.

There is still another explanation which so far as we

know has never been suggested, and which has more evi-

dence in its favor than any of the others proposed. When

yellows are mated to yellows it is to be expected that some

of the litters, especially if they are small, will consist en-

tirely of homozygous yellows. Since these do not com-

plete development, the entire litter will be composed of

dead embryos A and consequently there will be no living

embryos born at parturition. Such a litter will there-

fore be of 0 size. In our embryological investigation two .

litters consisting entirely of dead embryos A were found

in the yellow X yellow mating and none in the other types

of matings. Even with these two litters of 0 size in the

yellow X yellow mating the average size of litter as com-

pared to the litters of the non-yellow X yellow mating

was not sufficiently low to bring the percentage relation

down to 75 per cent. It is, however, 80.18 per cent., which

is appreciably lower than the percentage obtained from

litters of animals allowed to give birth to their young.

(See Table VIII.) In the latter case it would naturally

be impossible to detect the litters of 0 size. AS

750 THE AMERICAN NATURALIST [ Vou. LI

In our embryological study there were 33 litters in the

yellow X yellow mating. Of these, as previously stated,

two consisted entirely of dead embryos A. This means

that for 31 litters containing living embryos there were

two that did not, or 6.45 per cent. If we assume a like

35 T T T T T T T T T T T

30 w

25F eee UN Fi

í VAA

his “a g %7 Pi

2 20} kod X 7S 4

7 O y IY ETI N,

koma b , (A @ S ® N

5 oa Re

= 10k N Š Ya x <4

= X; N if N Pa

5 serii A * ‘ bee pe

eee Noes D

er See

efe i L L i fi fi l l L korbi

0 i g 3 8 9 10 il L

5 6 7

Size of litters

Fig. 1,

percentage of litters of 0 size with our 140 normally born

litters from ‘‘yellow X yellow” (Table VIII) the total

number of litters would be increased to 149 and their

average size would be 5.04 instead of 5.36. Taking 5.04

as a basis for comparison with 6.51, the average size of

litters from the non-yellow X yellow mating, we find that

the percentage relation is 77.42 per cent. This is reason-

ably close to 75 per cent., the expected percentage. In

this connection it may be well to call attention to a fact,

previously stated, that as the average litter size increases

the percentage relation tends to approach 75 per cent.

This is exactly what one should expect. For with in-

creased size of litter there would be fewer litters of 0 size,

and the averages as actually found would more arsed

represent the true averages.

Curves (Fig. 1) have been constructed oiin the

frequency of the litter sizes for certain of the types of

matings. The data upon which they are based may be

found’ in Table IX. A careful survey of these curves,

No. 612] ` DEATH IN UTERO OF MOUSE 751

however, does not seem to lead to any very definite con-

clusions as to the special fitness of any of the various

theories discussed in the preceding paragraphs. It will

be seen that in the yellow X yellow mating there are pro-

portionately more litters of small size and fewer of large

size than are to be found in the other matings. This is

what one should theoretically expect on all the theories.

TABLE IX

LITTERS Born Durine 1916-17, CLASSIFIED ACCORDING TO NUMBER OF

YOUNG IN LITTER

| Number of Litters |

No. in Litter

Yel. $ X Yel. 7 bree Ogee be ae N athe Y Non.-

T rae x 1

2 3 3 2

3 21 5 1 1

4 25 11 3 4

5 25 13 4 f

6 24 18 9 5

{T 25 11 6 12

8 10 10 12 3

9 3 il Bi 4

10 3 3 5 5

il 2 3 1

Total. 140 88 50 42

Summing up, we may say that all of our evidence tends

to confirm the conclusion of Castle and Little that in

mice homozygous yellow zygotes are produced in the

yellow X yellow mating, but that these zygotes fail to de-

velop normally after implantation in the uterus. Why

this should be so is not evident and our investigation has

not thrown any light on this point. Itis possible a careful

microscopical study of the embryos which die early might

reveal some abnormality of development which would

account for their failure to survive, but it is not probable

that it would be of such a simple nature as the analogous

cases of death of homozygous recessives lacking chlo-

rophyll in corn and some other plants. It seems more

probable that in mice there may be a ‘‘ lethal factor,’’

similar to those so well known in Drosophila, which is so

closely linked to the factor for yellow that they are prac-

752 THE AMERICAN NATURALIST [ Vou. LI

tically at the same locus and there is consequently no

crossing over.

According to the investigations of Little (1915) an en-

tirely similar condition obtains in regard to a dominant

white spotting factor (W) in mice, which, like yellow, ap-

pears never to occur in a homozygous condition. Whether

the homozygous individuals in this case also die at an

early stage and might be found as dead embryos has not

yet been determined. Little has, however, demonstrated

(1917) that the two factors are independent in heredity,

and that litters from yellows carrying W, mated inter se,

average only three per litter (10 litters), while similar

yellows mated to ww non-yellows have litters averaging

5 per litter (9 litters). Although the numbers are small

the percentage relation for the two matings, 60 per cent.,

is quite close to the theoretical expectation, 56.3 per cent.

LITERATURE CITED

Castle, W. E., and C. C.

1910. On a Modified pepe Ratio among Yellow Mice. Science,

N. S., Vol. 32, pp. 868-870.

- Cuénot, L. ;

1905. Les races pures et leurs combinaisons chez les souris. (4™°

note.) Arch. Zool. Expér. et Génér., 4° Series, Vol. 3, Notes

et Revue, pp. exxiii—cxxxii.

Cuénot, L.

1908. Sur quelques anomalies BARR des proportions Mendeliennes.

(6° Note.) Arch. Zool. r. et Génér., 4° Series, Vol. 9,

Notes et Revue, pp. vii-xv.

Dunn, L. C.

1916. The Genetic Behavior of Mice of the Color Varieties ‘‘ black-

and-tan’’ and ‘‘red.’’ AMER. Nar., Vol. 50, pp. 664-675.

Durham, F. M.

1911. Further Experiments on the Inheritance of Coat Colour in Mice.

Jour. Genetics, Vol. 1, pp. 159-178

Kirkham, W. B.

1917. Embryology of the Yellow Mouse. Proceedings of the Amer.

Zoologists, Abstracts. The Anatomical Record, Vol.

11, pp. 480-481,

Little, C. C.

1915. The Inheritance of Black-eyed White Spotting in Mice. AMER.

Nat., Vol. 49, pp. 727-740.

Little, C. ©.

1917. The Relation of Yellow Coat Color and Black-eyed White Spot-

Ang of Mice in Inheritance. Genetics, Vol, 2, pp. 433—444.

SHORTER ARTICLES AND DISCUSSION

ON THE FAUNA OF GREAT SALT LAKE

In a recent number of the AMERICAN NATURALIST! appeared a

paper entitled ‘‘ Notes on the Fauna of Great Salt Lake,’’ by Dr.

Chas. T. Vorhies. From observations made by the present

writer in the region at the mouth of Bear River, Utah, during

the summer and fall months from 1914 to 1916 inclusive, infor-

mation is available that supplements in part the data given by

Dr. Vorhies.

Bear River, the largest of the three main tributaries of Great

Salt Lake, breaks up into a series of channels at its mouth and

forms a great delta at the northern end of Bear River Bay. Im-

mediately below the mouth of the river the waters of the bay are

freshened by the incoming river water. Conditions here vary

greatly however from day to day, and at present heavy salt water

frequently comes up as far as Slaughter Island at the lower part

of the marsh area in the river delta. Below this point the sur-

face water coming from the river may be fresh while at a depth

of a few inches a stratum of brine may overlie the mud. On

calm days this overlapping proceeds for long distances. The

prevailing summer winds however are from the south and south-

west and these drive the salt water in toward the marsh nearly

every afternoon.

It is common belief that the Southern Pacific cut-off has served

as a dam to separate Bear River Bay from the main lake (cf.

Vorhies, p. 494). For a considerable distance this causeway is

made up of trestle work allowing free interchange of water from

either side. Although tests of the density of the water were not

made, the writer is certain that the difference in content of salts

between the water on the north and south sides of the cut-off is

slight while water sufficiently saline to enable the life characteris-

tic of the Lake to flourish is found at least twelve miles above

the cut-off and within four or five miles of the point at which

the main ae of Bear River opens into what is known as

South Ba

1 Vol. LI, No. 608, August, 1917, pp. 494-499.

753

754 THE AMERICAN NATURALIST [ Vou. LI

Brine shrimp, Artemia fertilis Verrill, occurred at this point in

enormous numbers and adults and larve of alkali flies, Ephydra

gracilis Packard and E. hians Say, were abundant. E. subopaca

Loew was less common. The brine shrimp were gathered in

great masses, and took advantage of the slightest depressions in

the mud as shelters against the ever-fluctuating currents.

Thousands frequently gathered in the lee of the boat during

periods of observation by the writer.

In May and June adult Ephydra were found on mud, laid bare

by water receding from the high spring levels, in which alkalis

were rising through surface evaporation. On these areas the

flies formed dense masses several feet square. The insects were

busily probing or kneading the mud with their proboscides so

that the surface was heavily pitted or stippled with small de-

pressions that were visible at a distance of several feet. The

greater part of these insects were Ephydra gracilis.

The statement made by Dr. Vorhies (p. 498) that ‘‘enemies

play no part in keeping down the numbers of Artemia, or of

Ephydra in the larval stage’ is not corroborated by observa-

tions of the present writer. After the first of September each

year shovelers, Spatula clypeata (Linneus), began to congregate

in the bay below the mouth of Bear River, and by October 1

thousands of these ducks were present. The birds lay in great

banks on the open water, and it was not unusual to see such

flocks that were at least two miles long and from one quarter to

one half a mile broad. The shovelers were feeding almost en-

tirely upon Artemia fertilis and larve and pupæ of Ephydra,

and were crammed with them constantly. Usually this species

of duck is not a good table bird but individuals shot here were

all exceedingly fat, and the writer found them excellent eating.

These ducks remained in fall until the fresh water bays were

covered with ice. Another species of duck, the lesser scaup,

Marila affinis (Eyton), came into this region from the north be-

tween October 2 and 12 each year, and by October 20, was abun-

ant. These lesser scaups also frequented the lower bay, and,

like the shovelers, fed to a large extent upon the brine shrimp

and the immature stages of the alkali flies. At dusk on October

14, 1914, flocks of these ducks were observed from Promontory

Point passing from Bear River Bay southwest past Fremont

Island in the open lake. As there is no fresh water feeding

ground in that direction it was assumed that they were going out

No. 612] SHORTER ARTICLES AND DISCUSSION 755

to feed at some favorable locality in the lake. Later in October

the other ducks were joined by American goldeneyes, Clangula

c. americana Bonaparte, while from observations it was certain

that the green-winged teal, Nettion carolinense (Gmelin), at

times fed upon this same food. The number of crustaceans and

fly larve destroyed by these birds must be enormous.

In addition to these ducks great flocks containing thousands of

Wilson’s phalaropes, Steganopus tricolor Vieillot, and northern

phalaropes, Lobipes lobatus (Linneus), are found on the salt

water during migrations, where these birds likewise feed upon

the brine shrimp and the fly larve and pupe. During October

and November flocks of eared grebes, Colymbus nigricollis cali-

fornicus (Heermann), were found on the lake along the cut-off

where their food must have been taken from the same supply as

none other suitable is found. It may be mentioned here that a

considerable number of shovelers and many thousand eared

grebes winter on Owen’s Lake in California, where saline condi-

tions are similar to those in Great Salt Lake, and where a simi-

lar fauna is found.

Avocets, Recurvirostra americana Gmelin, and black-necked

stilts, Himantopus mexicanus (Miiller), also fed upon Artemia

and Ephydra at the mouth of Bear River, and no doubt these

animals furnished food to other shore birds. Definite data on

this point is not at hand, however, as all of the shore bird

stomachs collected there have not yet been examined. It is

probable that the ring-billed gull, Larus delawarensis Ord, and

California gull, Larus californicus Lawrence, also take this same

food at times.

From the facts outlined above it will be seen that the toll

taken by birds from the brine shrimp and alkali fly larve and

pupex during the course of a season constitutes a mass of indi-

viduals almost beyond comprehension. The digestion of food

by the birds concerned is always a rapid process, and with soft-

bodied animals like the brine shrimp a considerable mass would

be consumed each day; and the same is true of the larve and

pupe of the alkali flies. The immense number of these creatures

in the waters of the lake must be attributed to the large number

of offspring produced rather than to an absence of enemies.

ALEXANDER WETMORE.

BIOLOGICAL SURVEY, WASHINGTON, D. C.

756 THE AMERICAN NATURALIST [ Vou. LI

FUSION OF ‘‘RHINOPHORES”’ IN CHROMODORIS!

THERE have been found during the present spring nine spec-

imens of the nudibranch Chromodoris zebra Heilprin which

form a series exhibiting an interesting gradation in the degree

of coalescence of the ‘‘rhinophores.’’ The animals were each

of average adult size, 10-12 em. in length. In none of these

cases was there any evidence that the structural variations had

resulted from injury. In the period over which these individ-

uals were obtained there were also collected about 1,000 normal

specimens of the same species. These figures give, however, no

precise idea of the relative frequency of ‘‘rhinophore’’ variation,

because a larger number of specimens had been collected in

previous years without any occurrence of these variations being

observed.

aa) (4) (2 | (a)

Fies. 1-6. Outlines of anterior ends of Chromodoris zebra Heilprin, show-

ing increasing degrees of fusion of the “rhinophores.” Fig. 5, frontal view;

the rest, dorsal aspects, g. la, the normal condition; Fig. 1b, variation in the

edges of the “rhinophoral’’ collars of three individuals

The bases of the two ‘‘rhinophores’’ of C. zebra are, as in

other Dorids, normally surrounded by well developed individual

cylindrical collars. The distal termination of a collar is usually

circular in outline, but occasionally pointed at one side (Fig.

1). In two specimens the ‘‘rhinophoral’’ collars were closely

approximated, after the fashion outlined in Fig. 2. Three spec-

imens were found in which the ‘‘rhinophoral’’ collars, and the

depressions into which the ‘‘rhinophores’’ are separately re-

tracted when stimulated, had completely fused (Fig. 3). In

~ 1Contributions from the Bermuda Biological Station for Research, No. 75.

No. 612] SHORTER ARTICLES AND DISCUSSION TST

these animals the two ‘‘rhinophores’’ themselves were separated

by their normal distance of about 1 em. The next step in ‘‘rhin-

ophore’’ fusion is illustrated in Fig. 4, one example having been

collected. In another specimen the ‘‘rhinophores’’ were found

to be closely united at the base (Fig. 5), while in the remaining

two specimens that exhibit fusion of the ‘‘rhinophores’’ (Fig.

6) the process of coalescence had been pushed much further, a

single stalk, giving rise at its free end to two short diverging

projections, representing the normal pair of ‘‘rhinophores.’’

‘rhinophore’’ of C. zebra is locally stimulated by

being touched, it is retracted within its pocket, the basal collar

usually contracting over it, while the companion ‘‘ rhinophore’’

on the other side of the animal is usually not contracted. In

other words, the ‘‘rhinophores’’ are, with reference to their re-

traction, subject to independent bilateral control. . The process

oe retracting the ‘‘rhinòphore’”’ consists of two phases—the

‘‘rhinophore’’ is itself contractile, and it is in addition pulled

down into its pocket by the action of muscles situated at its base.

With the fused ‘‘rhinophores,’’ even in such eases as that illus-

trated in Fig. 6, the independent bilateral control of the

organs is pre ved. If one tip be stimulated, that side of the

compound ‘‘rhinophore’’ is contracted, the other (unless the

stimulation be severe) remaining inert. Under slightly stronger

stimulation applied to one tip of a compound ‘‘rhinophore,’’ the

contraction of the organ itself is immediately followed by the

traction of muscles upon the same side of the base of the double

“‘rhinophore,’’ resulting in a bending of the whole structure

toward the point of excitation. .

The reactions of the abnormal specimens therefore support.

the view that these abnormal ‘‘rhinophores’’ have been pro-

duced by a process of fusion, probably rerniang from the orig-

inal close approximation of ‘‘rhinophoral’’ Anlagen. Two cases

have been available for experiment in which one of the normally

placed ‘‘rhinophores’’ possessed a divided tip; these divided-tip

‘‘rhinophores,’’ superficially not unlike the single median struc-

ture above described, gave no evidence of independent control

for the two tips, both parts contracting together when one tip

was irritated.

It would appear that the development of the collar surround-

ing the base of the ‘‘rhinophore’’ is directly dependent upon the

growth of the latter structure; in every case there was a close

758 THE AMERICAN NATURALIST [ Vou. LI

correspondence between the bulk of the - Fhinopbhoran:) and the

dimensions of the collar or collars.

W. J. CROZIER

AGAR’S ISLAND, BERMUDA

NOTE ON THE HABITAT OF GEONEMERTES

AGRICOLA!

THE terrestrial nemerteans include a small number of species,

all belonging, apparently, to one genus, but widely scattered

over the world. They occur conspicuously on islands, some of

which are well removed from any large mainland. The origin

of these land nemerteans is a matter of some interest, and sev-

eral suggestions have been made relative to the manner of their

evolution. One of these terrestrial nemerteans, Geonemertes

agricola (W.-S.), was found at Bermuda by v. Willemoes-Suhm

(1874). The anatomy of this species was subsequently de-

scribed in detail by Coe (1904), who gave some attention, also,

to the habits of the worm. These observers, as well as Verrill

(1902), agree that G. agricola is to be found ‘‘only along the

shores of mangrove swamps and on the adjacent hillsides’’ (Coe,

p. 566). Coe found it ‘‘not only above high-water mark but

also for some distance along a zone which is covered for a short

time each day with sea water,’’ but noted that the intertidal in-

dividuals were ‘‘as a rule smaller than those living in the soil

which is a little above the reach of the tide, but in earth which

is nearly saturated with salt water.’’

Standing bodies of fresh water are absent in Bermuda. Coe

consequently held that this particular species, at least, repre-

sents a land nemertean which has almost certainly been derived

directly from a marine ancestor, and not, as Montgomery (1895,

p. 483) had argued for the generality of land nemerteans, from

a fresh-water form.

During the past several years I have repeatedly encountered

G. agricola in a type of habitat which is significantly different

from that recorded for this nemertean by the observers just

quoted. In the neighborhood of every large or small mangrove

‘‘ereek’’ or swamp which I have examined, the worm has been

found, in relatively considerable quantities, well below low-water

mark even at spring tides. The species occurs in the localities

1 Contributions from the Bermuda Biological Station for Research, No. 76.

No.612] SHORTER ARTICLES AND DISCUSSION 759

listed by Coe, but is also common among the masses and sheets

of matted sea weeds (Laurentia, Valonia, Halimeda, and asso-

ciated plants) which cover the bottom of Fairyland Creek.

Specimens were also obtained from under rocks situated a few

feet beneath low-water level, in muddy bays bordered by man-

groves, such as Tucker’s Bay in Harrington Sound. The indi-

viduals collected in these places embraced white forms, some

with a tinge of pink, others decidedly pink (as in the ‘‘pale’’

form figured by Coe, 1904, Pl. 1). They were 30-60 mm. in

length, and some contained embryos.

In June and in July young Geonemertes were gotten among sea

weeds in Fairyland Creek; these were 6-12 mm. in length. They

were identified principally through the microscopic examination

of the stylets and other organs. The stylets and stylet basis in

these young specimens were of the juvenile type for this species,

as figured by Coe (1904, Pl. 25, Figs. 21, 24, 25). These young

specimens were in some cases pure white, in others tinged with

‘‘smoky brown.’’ I found no pinkish specimens less than 30

mm. in length.

The observations upon the specimens of this species inhabiting

salt water indicate, as Coe concluded from his study of the land-

living individuals, that liberation of the young occurs in June

and in July. My largest examples of G. agricola from the water

were obtained in the spring.

Large specimens of G. agricola are negatively phototropic, the

ocelli occupying the region of the body most sensitive toward

light. They orient away from the light with diagrammatic pre-

cision. This response leads to their being found, during the

day, under stones and about the roots of alge.

It is hardly possible to credit the view that G@. agricola has

extended the variety of its habitats during the brief time since

Coe’s studies were made (1903); it is therefore necessary to

believe that this species of nemertean is not only terrestrial in

the proper sense, but truly marine as well. There seems no

good ground upon which to distinguish and separate the indi-

viduals found respectively on land, in the intertidal zone, and

definitely in the sea water. The terrestrial ‘‘variety’’ may then

be regarded as having originated, perhaps not so very long ago,

from the form which is undoubtedly marine—unless one is pre-

pared to believe that, introduced as a terrestrial form, it has at

some time secondarily taken to the sea after a protracted evo-

760 THE AMERICAN NATURALIST [ Vou. LI

lution as a land animal. This case seems to have some resem-

blance to that of a grapsoid crab at Bermuda, Sesarma ricordi

M.-Edw., of which a terrestrial variety has been described by

Verrill (1908, p. 328). It is my impression that the larger

marine specimens of G. agricola are less hardy, more easily

caused to fragment by handling, than are those taken on land.

This may, however, be merely a physiological consequence of

differences in habitat, which could be exhibited within the life-

history of a single individual. I have not been able to keep the

salt water specimens alive after abruptly transferring them to

damp earth. The young individuals, however, are quite hardy,

and seem capable of enduring this treatment for several days at

least.

These observations add further, and possibly final, weight to

the argument that some, at least, of the land nemerteans have

proceeded directly from ancestors inhabiting salt water.

W. J. Crozier

AGAR’S ISLAND, BERMUDA

REFERENCES

Coe, W. R.

1904. The Anatomy and Development of the elena Nemertean

(Geonemertes agricola) of Bermuda. Proc. Bost. Soc. Nat

ist., Vol. 31, ka 531-570, pl. 23-25. se Poiainin

Biol. Sta., No. 4.)

gapti Te ti dr.

1895. T Derivation of the Freshwater and Land Nemerteans, and

d Questions. Jour. Morph., Vol. 11, pp. 479-484.

Verrill, A. E.

1902. The Bermuda Islands. (Repr. from Trans. Conn. Acad. Sci

Vol. 11, with changes.) New Haven, x + 548 pp., 38 pl., inde.

1908. Decapod Crustacea of Bermuda. I. Brachyura and Anomura.

eir Distribution, Variations and Habits. Trans. Conn.

Acad. Arts and Sci., Vol. 13, pp. 299-474, pl, 9-28.

Willemoes-Suhm, R. V

1 On a Taia Widhük found in the Bermudas. Ann. and Mag.

Nat. Hist., ser. 4, Vol. 13, pp. 409—411, pl. 17.

NOTES AND LITERATURE

SUNSPOTS, CLIMATIC FACTORS AND PLANT

ACTIVITIES

VARIATIONS in solar radiation, if of sufficient magnitude, should

be followed by variations in terrestrial climatic conditions. In

the absence of long series of determinations of the heat radiated

by the sun, meteorologists have turned to variation in the num-

ber of sunspots as a possible factor underlying variation in the

climatic factors. This involves the assumption that a period of

many sunspots differs from a period of few spots in heat and

light radiation.

If such climatic factors as heat and precipitation be closely re-

lated to the number of sunspots, the number of sunspots should

be a factor of importance in determining plant activities. In.

recent years attempts have been made to correlate growth, espe-

cially that recorded in the annual rings of trees, with number

of sunspots."

Since any attempt to relate growth phenomena to sunspot

number presupposes relationships between climate and sunspot

frequency, the botanist should be interested in the attempts of

the meteorologist to ascertain the relationship between solar and

terrestrial atmospheric phenomena. The purpose of this review

is to call attention to certain recent discussions of this subject.

For a review of earlier literature, the reader must refer to

Hann’s ‘‘Handbook of Climatology’’ and to the careful discus-

sion from the biological side in Chapter XIX of Huntington’s

‘‘ Climatic Factor.’’?

Heretofore, those who have discussed the interdependence of

terrestrial and solar phenomena have been content to plot curves

for the two phenomena and to determine the existence of relation-

ship between them by similar trends in the two curves.

The sources of error in such a method are very great. Fur-

thermore, it gives no quantitative measure of intensity of rela-

tionship. Such a measure can only be secured by means of some

correlation or contingency coefficient.

1 Douglas, A. E., ‘‘A Method of Estimating Rainfall by the Growth of

Trees.’’ In Puer Huntington’s ‘‘The Climatic Factor,’ pp. 101-121.

2 Huntington, E., ‘‘The Climatie Factor as Illustrated in Arid ame £

Pub. Carn. Tast. Wash., 192, 1914.

761

762 THE AMERICAN NATURALIST [ Von. LI

Walker, the director general of observatories for India, has

made a great advance in the investigation of the possible rela-

tionship between the number of sunspots and meteorological phe-

nomena by applying the modern methods of correlation to the

problem

I have tabulated his three series of correlations for a large

number of stations widely distributed over the earth, with the

results given in the accompanying table.

| Frequency of Correlations

Intensity of Correlation

Sunspots and Sunspots and Sunspots and

Rainfall Temperature Pressure

— .59 to — .53 — 2 —

— .52 to — .46 1 1 2

— .45 to — .39 5 6 2

— .38 to — .32 6 i 3

— .31 to — .25 9 10 8

— .24 to —.18 17 12 8

— .17 to —.11 15 15 8

— .10 to — .04 21 14 15

— .03 to + .03 27 16 11

+ .04 to + .10 13 A 8

+.11 to +.17 18 5 10

+.18 to + .24 9 4 8

+ .25 to + .31 T 1 6

+.32 to +. 6 — 2

+.39 to + .45 — — -—

+ .46 to + .52 1 — -—

Total number of stations. 151 97 91

Remembering that correlation is measured on a scale of — 1 to

-+ 1, this table shows at once that there is no uniformity for the

globe as a whole in the correlations between number of sunspots

and either of the climatic factors considered. Instead coeffi-

cients for some stations are positive while those for others are

` negative. Thus as far as the data available go, they indicate

that in some regions rainfall, temperature or barometric pres-

sure are higher in periods of larger numbers of sunspots, whereas

in other regions they are lower. The magnitude of the coeffi-

cients is generally low.* Over thirty per cent. of the constants

3 Walker, Gilbert T., ‘‘Correlation in Seasonal Variation of Weather,’’

IV-VI. Mem. Ind. Met. Dep., 21: 10-12, 17-118, 3 world maps, 1915.

4 These correlations are based on such small samples that for their full

interpretation the theory of the distribution of small correlations now being

developed by ‘‘Student,’’ Soper, Fisher, Young, Cave, Lee and Pearson must

be considered. Nothing brought out by the work of these writers, which

will be reviewed later, invalidates the general correctness of the conclusions

reached here.

No. 612] NOTES AND LITERATURE 763

lie between + .10 and —.10. The probable errors of the con-

stants are of about this magnitude.

The average values of the three sets of correlations are:

For sunspots and rainfall, 151 stations, r == — .0175

For sunspots and temperature, 97 stations, r = — .1360

For sunspots and pressure, 91 stations, r = — .0331

While these averages are exceedingly small, all are negative in

sign, indicating that for the globe as a whole lower rainfall, tem-

perature and barometric pressure are associated with greater

numbers of sunspots.

The same relationship is apparent if only the 76 stations for

which all three relationships have been caleulated be considered.

The averages are:

For sunspots and rainfall, r = — .0349

For sunspots and temperature, T= — .1534

For sunspots and pressure, T = — .0486

If in obtaining the average correlations the constants for the

several stations are weighted with the number of years for which

records are available the averages, indicated by the bars, are:

For sunspots and rainfall, 151 stations, r = — .0103

For sunspots and temperature, 97 stations, r = — .1243

For sunspots and pressure, 91 stations, r = — .0387

Thus, however calculated, the averages indicate generally

negative values of the correlation coefficient for all three rela-

tionships.

The same fact is brought out if the coefficients are classified

according to sign only. Thus:

Number of Sunspots Frequency of Posi- | Frequency of Zero | Frequency of Nega-

and: — tive Correlation Correlation tive Correlation

SOTA i cs ks ew 70 i 80

Pempermture 6506. bce wk 18 4 75

is Fae Daa ay en iar haan aa 38 3 50

For all three relationships the negative correlations are more

numerous than those which are positive in sign.

In a brief review it is quite impossible to give in detail the

meteorological considerations discussed in the original memoirs.

Furthermore, the most of these do not directly concern the botan-

ist. The conclusions of practical biological importance to be

drawn from Walker’s investigations seem to be the following:

764 THE AMERICAN NATURALIST [ Vou. LI

a. The relationship between the number of sunspots and the

annual record of terrestrial meteorological phenomena is very

slender indeed. It is so slight that at the present time it is im-

possible to assert on the basis of the data of any one station alone

that any relationship at all exists. Thus, as far as they go, these

data hold out very little hope to the biologist of being able to

correlate plant activities with sunspot number, unless light in-

tensity be the means of solar influence.

. For rainfall and barometric pressure the correlations are

aiaa low. They average practically zero, but are apparently

on the whole negative in sign.

c. The correlation between number of sunspots and terrestrial

temperature is the most consistent and substantial of the three.

The coefficients average about — .14. Thus years of larger num-

bers of sunspots are in the long run years of lower, not higher,

terrestrial temperature."

These results are directly opposed to the theories which seem

to have prevailed among many writers.

J. ARTHUR HARRIS

5 Possibly, as Walker suggests, superheating in equatorial regions may

raise the temperature in the upper air but lower that at ground level. The

temperatures in which the botanist is primarily interested are, however,

which may influence the film of vegetation which covers the globe.

INDEX

THE NAMES OF CONTRIBUTORS ARE PRINTED IN SMALL CAPITALS,

Alcohol and White Mice, L. B.

NIcE, 596

LLARD, a A., Troman and

Synchron e Rhythm

Allelomorphs, Multiple, pee Modi-

fying Factors in oats to 8

lection, H. S. JENNINGS, 301;

versible iesen omoabiity of, H.

ERAO, 690

Amphibia, a ge ap nba =

rth rica GRE

311

FR Ae Literature, Sources of,

Roy L. Moopts,

Awn, The Inheritance of the Weak,

in Ave S, H, Love

and A. C. FRASER, 481

BAUMBERGER, J. P., Solid Media

for rearing Drosophila, 447

Behavior, Synchronism and Syn-

chronic Rhythm in, H. A. ALLARD,

438

Biocharacters as Separable Units

of Organic Structure, HENRY

FAIRFIELD OSBORN, 449

e Facts and Bud-varia-

i E. M. East, 129; Signifi-

vst of Animal Coloration, W.

LONGLEY, 257; Enigmas and

the Theory of En e Action,

[LEONARD THOMPSON ‘TROLAND,

321

Biometrie Studies on the Somatic

and Genetic Physiology of the

Sugar Beet, J. ARTHUR HARRIS,

gir ag and Mendelian Inheri-

A.C. and A. L. Hae

Bripges, Catvin B., the Variable

Force Sy petheas of Crossing

Over, 370

Bud-variation, E. M. East, 129

CastLtE, W. E., Piebald Rats and

Multiple Factors, 102

Chromodoris, Fusion of Rhinophores

in, W. J. Crozier, sa

pe ee sa 3

Œnothera

ANNE M. Lutz, 375

present

Somatic, in

Mutants. and Hybrids, |

CLAUSEN, R. E. and T; H. G

SPEED, rilate Pause Diter

ences versus Reaction Ny

coi a in seat 31,

Cock ae A, snore

Foss ssil F Fish- PAE S, 61

oe Animal, W. H. LONGLEY,

Control, DIUNA, Field Tests

OSEPH GRINNELL, 115

Correlation p ierg al and the Prob-

f Varietal Differences in

Disease wee J. ARTHUR

Harr

Crosses, ‘heen, aE of the

ree a Lovs and

ree Wheat,

Linked _ Quantitative “Characters

GEO F, FREE 683

PE ina al the Variable Force

Hypothesis of, -CALVI B.

BripeEs, 370

Crown Gall, ng sages of Prunus

to, CLA apes TON O, SMI be

bay ZIER, ions of

IER, J. Migrat

Tropical pa 377; Mul-

Fission E olo-

Geonemertes agricola,

Daxc HAKOFF, VERA, Differentiation

in the Developing Organism, 419

Datnges, L. L., The Flora of Great

DAVENPORT, CHARLES B., The Per-

ity, Heredity and Work of

Otis

Whitm

Dean and Eastman’s "Bibliography

of Fishes, OLIVER P.

Deer-mice, The Réle of TAR aa in

the

Formation of a e of, F.

. SUMNER

Differentia tion n by Se tion and

Environment in the veloping

a , VERA DANCHAKOFF,

Dimidium neama, Mutation in, 8.

O. Mast, 351

Distributional Control, JOSEPH oe

NELL, Data, Erlis L.

oo Sh

765

766 THE

neal Mar Sere, Media for rear-

ing, J. P. BAUMBER

A Ksg relations in, Don

DUNN T m Nucleus and Cyto-

N, as Vehicles of Heredity,

286

EAST, E. M., The Bearing of B

ooN Facts on Bud- Satsnus,

eithin and Dean’s ak bo se

of Fishes, OLIVER P. Hay,

Ecology of the Protozoa, TAN

Egg, Insect, The Genesis of the Or-

ganization of the, Ropert W.

EGNER, 641, 705

— Action and Biological Enig-

mas, LEO HOMPSON TRO-

sae, 321

ERDMANN, RH Sexual Process

in the Paana ie Life Cycle,

719

Evolution, from the pini pari of a

Geneticist, A. FRANKLIN SHULL

361; and ’ Rats, A. °C. and A, K

GEDOORN, 385

‘Factor,’ ? The Different mer

of the, Howarp B. FROS

Factors, Multiple, and Pisbeld Pac,

W. E. Cas Modifying,

ENN

geval Inheritance of, in Sheep,

ARD N. WENTWORTH and J.

E. nan

Fish-seales, Fossil, European, T. D..

Fishes, The Migration of, Davin

ARR JORDAN, 1

Fossil Fish-seales, European, T. D.

i d H. H. Love, The

Tokat ianio of the Weak Awn in

Avena Crosses,

Paor GEORGE clea gree ak

titative Charac

Crosses, 683

i ag E Mendelian Class, RAY-

PEARL

e Different

tures, 429

Gates, R. R., The Mutation Theory

and the Species Concept, 577

Gene, The Theory of the, T. H.

Morean, 5 513

AMERICAN NATURALIST

[ Vou. LI

sa oe of the Daan of ond

Insect Egg, Ropert W. HEG

Genetics versus Paleontology, Wo.

EGOR

iaoea agricola, Habitat of,

We d.

ees

Germ Plasm of ’ Œnothera, ROBERT

T. HANCE, 567

GoopsPEED, T. H. and R. E. CLAU-

SEN, Mendelian Factor Piter-

sangen versus Reaction puer

in Heredity, 31,

Great Salt L Lake, Fauna pr CH

T. VORHIES, ” 494; Pr Tipton

WETMORE, 753; Flora of by L

DAINES; 499

REGORY, WM. K., The Coal Meas-

ures Amphibi a of North America,

311; Genetics versus Paleontol-

gy, 622

piisa wl JOSEPH, Field Tests of

Theo concerning Distribu-

Fratii Conival, 115

HADLEY, papisa The Case of Tri-

chomonas, 2

GEDOORN, A. A and A. L., Blend-

n Inheritance,

j 385

IS, J. ARTHUR, The Applica-

tion "of Correlation Formule to

ietal Differ-

ences in Disease

Biometric Studies on the Somatic

ic Physiology of the .

Sugar Beet, 507; Sunspots, Cli-

matic Factors and Plant Activi-

ties, 761

HAUSMANN, LEON a The

Ecology of the Protozoa, 15

Hay, OLIVER P., Dean and Tat

man’s Bibliography, of caine 383

NER, ROBERT W., The Genesis of

the Organization of the Insect

Egg, 641, 705; Singing Mice, 7

Heredity, Mendelian Factor Differ-

ences versus ion ne poor

rests in, Te

E. CLAUSEN, 92: Nodos

and Cy ee as Vehicles of, L.

Holothurians, ern falc by Fis-

in, W. J. Crozier, 560

T HEMAN I. and EMIL STEIG-

Death in Utero ae the Ho-

mony gous Yellow Mouse,

nbreedin De

grees

RAYMOND PEARL, 545;

Kinship,

A Single

No. 612]

Numerical Measure of the Total

Amount of, RAYMOND PEARL, 636

Inheritance, Mendelian, and Blend-

g, ; = DOORN,

189; of ae. Weak Aw H.

Love and A. C. Fra aiei "481; of

Fertility in os Epwarp N.

W: J. B. Sweet,

662

Isolation, The Rôle of, in the For-

mation of a Race of Deer-mice,

. B. SUMNER, 173

JENNINGS, H. 8S., Modifying Fac

tors and Multiple ‘Allelomorphs

and the Results of Select ibn, 301

JONES, DoNALD F., Linkage in Lyco-

on 60

RDAN, DAVID STARR, The Migra-

“Hoa of Fishes, 186

oe Degrees of, The Measure-

and Numerical, oe

of, ens PEARL,

LIN wage E. W., Linkage in

Maize

Linkage in wr bie i bate DONALD

F. JONES, 608

Linked ine eset ative Characters in

Whea osses, GEORGE F. FREE-

MAN, fasa.

Mice and Rats, 457

LONGLEY, W. H., The Selection

Problem, 250; The Biological

Significance of "Animal Coloration,

257

Love, H. H. and A. C. Fraser, The

Inheritance of the Weak Awn in

Cer Avena Crosses, 481

LUTZ, eye M., Characters Indic-

ative of the Num ber of Somatic

Chromosomes present in Ginothera

Mutants and Hybrids, 375

Mast, Ci >» asa ge in Didinium

Nas 851

Manan, Factor Differences versus

; SEW

Inheritance and

and A. L. HAGE-

RIG sa 373;

DOORN

Mice, and Rats, Multiple ~—. in,

cohol, L. B. Nice , 596; Presta

ROBERT EG „704

MICHAEL, ELL

s L., a apoE Pea

ical Prediction "tro

tional Data and its Verification, |

572

INDEX

767

et hiere s, DAVID STARR

6; of ee oe Nudi-

"ithe Theory of the

Morghclogian! Prediction from Dis-

tributional Data and its Verifica-

tion, ELLIS L. MICHAEL,

aw ee Factors and Piebald Rats

. CASTLE,

AINTER,

pt,

in Dros mene busckii ‘oe

. WARREN

Mutants and Hybrids, (¬hera,

Number of Somatic Chromosomes

present in, ANNE 375

NIc, L. B., ‘tase Effects of Alcohol

on White Mic , 59

Notes and Literate, 311, 383, 507,

Nucleus and Cytoplasm as Vehicles

’ Periodic ;

Shoreward Migrations, W. J.

CROZIER, 377

(Enothera, Mutants and Hybrids,

r of Somatic Chromosomes

present in, ANNE M. Lutz, 375;

An Attempt to modify the Germ

Plasm ntan ugh the Germinating

Seed, RoserT T. Hance, 567

Organism, Developing, Differentia-

tion by rai, a and Environ-

ment the, VERA DANCHAKOFF,

419

ot E of the Insect Egg, .

Genesis of the, Roperrt W. HEG-

641, 705

OSBOR? ; HENR Y FAIRFIELD, Biochar-

acters as obeak Units of Or-

ie §

44! H

PAINTER, THEOPHILUS S., A TA

Mutation of Piophila casei, 3 06

Paleontology versus Genetics, Wa.

K. GREGORY, 622

Panulirus argus, Regeneration in,

Eoi . WALTON, 308

RAYMOND, The Selection

Problem, 65; The Probable Er-

r of a Mendelian Class Fre-

noT, 144; Studies on aaea-

: The Measurement and Nu-

merical Exp.ession of Degrees of

Kinship, 545; A Single Numer-

ieal Measure of ot Total Amount

of Inbreeding, 6:

— “cultares, Howard B.

Potea u The Rôle of Isola-

tion in the Formation of a Race

of Deer-mice, F. B. SUMNER, 173

j i, A Wing Mutation

in, THEOPHILUS $S. PAINTER, 306

CLAYTON O. SMITH, 47

Quantitative Characters, Linked, in

Wheat Crosses, GEORGE F. FREE-

MAN, 683

_ ‘ow and ee Fac-

C 102; and

Evolution T C. and ryd L. HAGE-

, 385; and Mice, Multiple

wk O, Wai in Panulirus argus,

C, W. N,

Resistance of Prunus to Crown Gall,

CLAYTON °0. SMITH, 47

oe Problem, RAYMOND grr

sW“ He LONGLEY

Faetors

Southdown, Inheritance of

Seep, Sou in, Epwarp N. so ia

WORTH and J, >

THE AMERICAN NATURALIST

Ga i |

“102, 186, 238, 301, 370, tur aoa, | Whitman, Charles

(Von. LI

TEIGLEDER, EMIL and HEMAN

IBSEN,

ology of the, J. ARTHUR HARRIS

SUMNER, F. B., The Rôle of Iso-

pe in the Formation of a Nar-

Localize r-

icin (Peromyseus), 1

Sun Spots, Climatic Faa y

Plant Activities, J. ARTHUR

tility in Southd wn Sheep, 66:

Synchronism and nike so tiny thm

Behavior, H. A. ALLARD, 438

Terao, H., On Reversible Trans-

formability of Allelomorphs, 690

ger ene poe Pose ae of Al-

lelomorp

i The Cas Oie of, PHILIP

ADLEY, 209

TROLAND, LEONARD THOMPSON, Bi-

ological Enigmas and Enzyme

Action, 321

Vormis, CHas. T., The Fauna of

Great Salt Lake, 494

WALTON, A. o, Regeneration in

Panulirus 308

Warren, Don C., Mutations in Dro-

sophila busekii Coq, 699

WENTWORTH, Epwarp N. and J.

B. Inheritance of oe.

ai in Southdown wn Sheep,

ETMORE, ALEXANDER, Fauna a

Great Salt 753

les Otis, Personality,

Heredity and and Work ‘of, CHARLES

VENPORT,

Wing Mutation’ in in Piophila casei,

THEOPHILUS 8. PAINTER, 306

WRIGHT, Sewatt, The Probable

Error. of Mendelian Class Fre-

quencies, 3

n a ee ae