THE

AMERICAN NATURALIST

Vor. LVI. January-February No. 642

THE ORIGIN OF VARIATIONS

SYMPOSIUM AT THE THIRTY-NINTH ANNUAL MEETING OF THE

AMERICAN SOCIETY OF NATURALISTS, TORONTO,

DECEMBER 29, 1921

VARIATION IN UNIPARENTAL REPRODUCTION

PROFESSOR H. S. JENNINGS

THE JOHNS HOPKINS UNIVERSITY

Darwinism left the origin of variations the unsolved

problem. Give us inherited variations, it said, and we can

explain adaptation, by natural selection. But this was

the omission of 99 per cent., if not 100 per cent., of the

problem of evolution. Are we in better case to-day?

Has the experimental study of geneties given us some

solid knowledge of the origin, the causes, of variation?

Have we learned that the obvious differences observable

everywhere among individuals are the foundations of

evolution? Or that they are not? Are slight quantita-

tive fluetuations the material out of whieh evolution is

made? Have we discovered that extensive saltations are

the steps in evolution? Or that less extensive mutations,

qualitative or chemical changes, that may be minute or

large, are that by which evolution is constituted? Do we

know the origin of such saltations, mutations? Have we

found that the present constitution of the organism pre-

determines in some way the course of further change; or

that an élan vital is driving the organism to unfold in a

definite way, like a flower; that evolution is orthogenesis?

Do we comprehend the nature and causes of such a push

to unfold, and of the direetion in whieh it tends? Have

we found perhaps, as at least one investigator maintains,

6 THE AMERICAN NATURALIST [Vor. LVI

that it is mixing of stocks, hybridization, that is the origin

of organie diversity? Or do we know that the physieal

and chemical conditions of the environment produce

changes that are inherited and give us evolution? Or

finally, do several or all of these methods of action con-

cur?

Such are the questions, I take it, on which we hope for

light in the discussion this afternoon, and in the discus-

sion of orthogenesis before the American Society of Zo-

ologists, and of the species concept before the Botanical

Section of the American Association.

The lines of attack on the problem of variation are as

manifold as are the questions to be answered. The basic

idea in that attack whose results I shall try to summarize

is this: In the reproduction from two parents familiar to

us in higher animals and plants, there is a mixing of dif-

ferent stocks, a formation of great numbers of diverse

groups of the hereditary materials, with consequent pro-

duction of a great variety of diverse offspring from a

given pair of parents. This is the chief cause of the dif-

ferences everywhere observable among individuals: dif-

ferences formerly classed as variations and considered

the material of evolutionary change. But such kaleido-

scopic regrouping of materials, the units of which are not

changing, has no obvious relation with evolutionary vari-

ation; in the next generation a new grouping of the same -

material occurs, and so on indefinitely. If there likewise

occur progressive evolutionary changes, these are so lost,

so hidden, in the multitude of kaleidoseopie recombina-

tions that they ean not be distinguished; the literature

of evolution is filled with eonfusion due to this difficulty.

Therefore the idea suggests itself: Why not avoid at

once all this, by studving evolutionary ehanges in those

organisms where no mixing of stocks is oecurring; where

there is no kaleidoscopie regrouping of the hereditary

materials? "There are organisms that reproduce from

a single parent, with no shifting or recombination of the

germ plasm; in these, actual changes that persist from

No. 642] VARIATION IN REPRODUCTION 7

generation to generation, such as evolution requires,

should lie open before us, unconfused. We should see

evolution occurring, as we see water flowing.

This plain, simple and optimistic maxim has, I fear,

like many another such, not proved so illuminating as its

promise. But led by it, investigators set themselves at

the study of the passage of generations, with selection

and propagation of individuals showing diversities, in

these creatures where seemingly all lasting change from

parent to offspring must be evolutionary. Their hope

was to see evolution occurring. And what did they see?

I need not review the details; Johannsen, Barber, Hanel,

the present writer, Lashley, Agar, and others, followed

for long periods the passage of generations in many dif-

ferent organisms during uniparental reproduction.

Their report, after years of work, was astonishingly

simple and clear. As to the origin of hereditary varia-

tions, it resembled the famous chapter on the Snakes of

Ireland. It summed itself, in effect, in the succinct, suffi-

cient, exhaustive proposition that there is no inherited

variation; hence no origin of such variation. There is

nothing to find out about it, for it doesn’t occur. The in-

dividuals produced in uniparental reproduction may in-

deed differ, but these diversities are transitory effects of

environmental differences; they are not inherited. All

the descendants of a single individual are genetically and

hereditarily alike; they form in effect a set of identical’

twins. And from this it could be concluded that in bi-

parental reproduction all the observed diversities are

due to the kaleidoseopie regrouping of hereditary ma-

terials; nothing to evolutionary change.

Outeries—objurgations and aeeclamations— greeted

these propositions. Some reviled them for their mani-

fest absurdity, others acclaimed them for their obvious

truth and the clarification they wrought. Opponents

tried to disprove them by investigating the matter them-

selves; their evidence strengthened the propositions they

8 THE AMERICAN NATURALIST [Vor. LVI

had thought to overthrow; who came to scoff remained to

mourn.

Such was, in the gross, the upshot of the first phase of

the study of uniparental inheritance; of perhaps the first

ten years. But the matter could not rest here. This

work cleared the ground. It showed that 99 per cent. or

more of what had been ealled variation had nothing to do

with evolutionary change—a?' conclusion which Mende-

lian study was reaching independently. Now it remained

to aecept that faet, to take a new hold, to grapple with

the more diffieult question: Is there yet an infinitesimal

residuum of evolutionary change? If we select the most

favorable organisms, and study them in most minute de-

tail for suffieiently long series of generations, shall we

indeed find that there are no persistent variations what-

ever? Such is the work that has in this field occupied,

with redoubled intensity, the last ten years. What are

the results of this second phase of the work? |

Some of the workers devoted themselves to observa-

tional breeding work on the passage of many generations,

accompanied by selection; others attempted to modify

the inherited characters by physical and chemical agents.

In the observational search for persisting alterations,

with the attempt to accumulate their results by selection,

we find, first, that many of the organisms studied have

as yet defied all attempts to find any inherited variations.

Such is the report of Ewing on his extended work with

aphids ; such is the case with the fungi studied by Brierly

(1920). Such is the case with most of the strains of the

infusorian Paramecium, studied in detail for long periods

by many different observers. Only in certain deformed

strains, and possibly in one or two other instances, has

the occurrence of persisting variation been observed in

animals living under the usual conditions. Such is the

case with the great majority of the strains of the Clado-

cera studied with such extraordinary thoroughness for

long periods by Banta (1921); out of 16 strains to which

selection was applied for many generations, all but one

No. 642] VARIATION IN REPRODUCTION 9

gave on the whole negative results; they did not change.

Some of the investigators still insist that this is indeed

the outeome of all this work; that all eases seeming to

give other results are for one reason or another decep-

tive; that no hereditary variations occur; that evolution-

ary change has not been observed in this sort of repro-

duetion— and presumably therefore in no other sort.

Thus, for example, argue Brierly (1919), and, in effect,

Vietor Jollos (1921).

On the other hand, in some of the organisms studied,

visible changes persisting from generation to generation

of uniparental reproduction have been observed. Even

in the first period of this sort of work, extremely rare

** mutations ". were reported by Barber in his work on

baeteria, an apparent single one by Lashley in Hydra; a

** bud variation "" or two by Johannsen; and other iso-

lated cases occurred. In the second period of the work,

as a matter of observational faet, whatever the interpre-

tation, it is certain that in the lowest Rhizopoda: in Dif-

flugia, in Centropyxis, in Arcella; in the infusorian Stylo-

nychia, and in certain abnormal strains of Paramecium,

as studied in our laboratory at the Johns Hopkins Uni-

versity, there arise in uniparental reproduction, changes

affecting both physiological and structural characters;

changes that may be very slight, or of great extent; that

are passed on to later generations in uniparental repro-

duction. By selection and breeding of the changed indi-

viduals, stocks are isolated which differ persistently from

the stock with which the work of breeding began. In this

way might well arise the diverse biotypes found in nature

to occur within a species, in these organisms. Something

similar was found by Stout in the propagation of certain

plants by cuttings.

Again, among the 16 strains of Cladocera, subjected by

Banta to selection for a physiological characteristic, one,

and only one, showed persisting alterations, accumulated

by the selective process, so that from the single strain,

two continuously diverse strains were produced. Jollos

10 THE AMERICAN NATURALIST: [Vor.LVI

too has observed a few cases in which strains of Parame-

cium became differentiated in ways that could hardly be

considered the result of environmental action. Doubtless

some other cases might be collected. Here then we seem

to have what we were searching for; here at last is some-

thing solid; here by our presuppositions we have evolu-

tion evolving; we have seen it! But as with so many of

the seeming solid things of science—so these became

sicklied o'er with a pale cast of thought, of doubt, of

speculation. What, it is asked, is the cause, the funda-

mental nature, of these persistent changes? And are

they indeed of a sort to be considered steps in evolution?

And when we look closely, the observational and selec-

tional work has given us little information on these

points. In Arcella Hegner found that certain of the in-

herited structural changes are mere results of increase or

decrease in number of nuclei, brought about in a simple

manner. But most of the changes in the lower organisms

studied can not be accounted for in this way. The work

of Erdmann (1920) indicates that certain persistent

changes occur in Paramecium as a result of the periodic

nuclear reorganization called endomixis. These would

perhaps have only a significance similar to that of the

recombinations occurring in biparental inheritance. It

is a favorite speculative idea with opposing speculators

that most or all of the persisting changes we have men-

tioned arise through irregularities in nuclear division,

and hence are of little evolutionary significance, but this

is thus far a mere possibility, without solid base; as the

Germans say, it floats in the air. Another speculative

notion is that the changes lack permanence; that if fol-

lowed for a sufficiently great number of generations there

would be reversion to the original condition. Whether

this doubt can ever be resolved by observation ean not be

predieted; it depends perhaps on the number of genera-

tions demanded by the doubters.

In the attempts to modify inherited charaeters by

physical and chemical agents, more positive evidence as

No. 642] VARIATION IN REPRODUCTION 11

to the cause of variation has perhaps resulted. Can we

not, it is asked, by subjecting the hereditary material to

chemicals, to physical agents, alter it, as we can alter

practically everything else in nature? Of course we can;

it is easy. But when we alter it we usually kill it, or pre-

vent it from developing; our task is like that consumma-

tion devoutly to be wished, of killing the pathogenic bac-

teria in a man—which is easy—but it also kills the man!

Have we succeeded in so altering the germ plasm, without

killing it, that it now develops differently, and transmits

the diversity to its progeny?

It is easy by altering the chemical and physical condi-

tions to change tremendously the development and char-

acteristics of these creatures, and that without stopping

life and reproduction. But in the infinitely greater pro-

portion of cases such changes have no inherited effect;

so soon as these particular conditions are removed, the

progeny go back at once to the usual constitution. Such

has been the result of extensive experiments of my own in

modifying Paramecium with chemicals; and of Noyes in

modifying Rotifera. Startling transformations of form,

structure and function are readily produced and kept up

for generations, but disappear when the offspring are

reared under normal conditions. Once in our work the

task seemed accomplished. After many generations of

treatment with aleohol, Paramecium yielded monstros-

ities and deformities, analogous to those Stockard ob-

tained by the same method in guinea pigs, and these de-

formities were transmitted after removal from alcohol,

for generation after generation. This was stirring; all

the energy of the laboratory was devoted to following the

monstrous stock through long periods, leaving the formu-

lation of pedigrees till time permitted. But when this

could be done it appeared that all these abnormal indi-

viduals came from one single ancestor, out of the hun-

dreds with which the experiment began; the rest had all

returned at once to normal. We know that such heredi-

tarily abnormal stocks occur at times in Paramecium,

12 THE AMERICAN NATURALIST [Vor. LVI

produced in some frequency by an agency which takes

the matter at once out of the field with which I am dealing

—by the recombinations occurring at conjugation, at bi-

* parental reproduction. Our monstrous stock may have

come from such an individual, included by accident in the

experiment. Our spirit-stirring results faded into noth-

ingness—a type of what has so often happened in promis-

ing work in the inheritance of environmental effects, of

what will probably often happen again.

Other workers have been more successful. In ‘the bac-

teria, if we can accept the accounts given by many investi-

gators, and well summarized, for example, in Adami’s

** Medical Contributions to the Theory of Evolution,"

environmental conditions frequently alter, in an adaptive

way, the persisting characteristics of the stocks, differen-

tiating a single race into several. The difficulties of cer-

tainly working with unmixed strains is very great in these

minute creatures, a fact which leads many students of

experimental evolution to reject generalizations based on

these organisms. Further, the extraordinary work of

Lóhnis (1921), recently published by the National

Academy, tends, if substantiated, to so completely upset

all supposed knowledge of life history in the bacteria that

it will be best to omit these from consideration until the

air is cleared. For similar reasons, and from considera-

tions of space, I will not speak of the work on pathogenic

Protozoa.

Turning then to those larger organisms that are iso-

lated with as much ease as are guinea pigs, Middleton has

found that differences of vigor and of rate of reproduction

are produced by subjection of infusoria for long periods

to diverse temperatures, and are perpetuated, after

equalizing the temperatures, from generation to genera-

tion for long periods, and through the process of conju-

gation. At this meeting he has reported similar results

produced by subjection to diverse chemicals. How far

this is comparable to change of other characteristics than

reproductive vigor we do not know.

No. 642] VARIATION IN REPRODUCTION 13

Vietor Jollos (1921) has just published in this field

work which must make a deep impression on the study

of experimental evolution, work which gives us more posi-

tive results than have before been achieved. By experi-

mentation extending over years he has, by subjection for

long periods of time, altered the resistance of the infu-

sorian Paramecium to certain chemicals, and to heat.

After removal of the causative agent these physiological

changes are passed on from generation to generation of

uniparental reproduction, for longer or shorter periods.

Of extreme interest is the fact that longer subjection to

the altering agent causes longer persistence after the

agent is removed. . The induced changes lasted in some

eases for hundreds of generations, not yielding at the

periodic nuclear reorganizations known as endomixis.

But the acquired resistance in practically all cases finally

disappeared if the organisms were continued sufficiently

long in the normal conditions. Subjection to frequently

varied environment hastened the disappearance of the

persisting effect ; and it usually disappeared at once when

there occurred the profound reorganization accompany-

ing conjugation and biparental reproduction. But in

some cases, as in Middleton’s results, the acquired re-

sistance lasted through conjugation; even through several

cycles of conjugation. But in all cases in which it was

clear that he was dealing with resistance acquired

through subjection to chemical or physical agents, it

finally disappeared, after hundreds of generations, if the

organisms were kept sufficiently long in an environment

lacking the causative agent. Jollos is from this inclined

to draw the conclusion that the changes are not com-

parable to the (assumedly) permanent differences that .

separate genotypes or species, and hence that they do not

indicate a method by which such permanent differences

may arise.

. Here emerges an obvious logical difficulty involved in

all work on the production of inherited change through

environmental action. If we succeed in producing such

14 THE AMERICAN NATURALIST [Vor. LVI

change, it is clear that the character altered was not a

permanent one. And if after long re-subjection to the

original environment the induced change disappears, it

is equally clear that the new character was no more per-

manent than the original one. If we now assume that

there are other characters that are permanent, not alter-

able by environmental action, of course we can obtain no.

light on these by changing those characters that can be

changed. ‘To me it appears that we have no right to as-

sume, at the present stage in the game, that any such

absolutely permanent characters exist. If this be true,

then the production of changes persisting through many

generations of uniparental, and even of biparental, re-

production, with the further fact that the greater the

number of generations the altering agent has acted, the

greater the number of generations the change persists,

seems of the greatest interest. It perhaps would, if

action of the environmental agent continued sufficiently

long, lead to production of inherited characteristics that

are as permanent as any such characters are. It is cer-

tainly, as Jollos agrees, capable of producing such di-

versity of biotypes as we find within a species; and it

might perhaps, if the results of diverse agents are cumu-

lative, produce any of the inherited diversities found in

organisms. This is the most promising lead that we

have found in the study of uniparental production.

In sum, the study of variation in uniparental repro-

duction yields the following: The germinal or genotypic

constitution in most organisms is extremely stable; in

many stocks it changes not at all, so far as observation

goes. To alter it by physical or chemical agents is usu-

ally to kill it. In some of the lowest organisms—rhizo-

pods, bacteria, some infusoria—it changes with some-

what greater frequency, though still rarely. The nature

of the changes, and whether they may be permanent, or

must after many generations revert to the original condi-

1 The important observations and discussions of J ollos relating to changes

producible by environmental action at the time of conjugation do not fall

within the compass of a discussion of uniparental reproduction.

No. 642] VARIATION IN REPRODUCTION 15

tion, is in some dispute. In these same organisms, en-

vironmental agents may produce changes persisting

through many generations of uniparental reproduction

and even through biparental reproduction, the period of

persistence depending partly, on the number of genera-

tions through which the producing agent acted. This

suggests that inherited characters as permanent as any

that exist might in time be so produced. In spite of im-

portant differences of opinion among investigators, to the

reviewer the facts in uniparental reproduction seem to

point more toward the production of evolutionary change

by the action of the environment on the germ plasm than

by any of the other methods. In this respect it takes its

place in that modern revival of work on the inheritance

of acquired characters, of which we had so striking an

example this morning, in the account of the dizzy rats

and of the inheritance of their dizziness; though in the

study of uniparental reproduction nothing has appeared

that indicates a transfer of somatic characters to the

germ.

REFERENCES

(It has not seemed necessary to repeat here titles that are to be found

generally in the literature of this subject; e.g., in the writer's book, ‘‘ Life,

Death, Heredity and Evolution in Unieclulát- Organisms.’’ The following

are not found in that work.)

Banta, A. M,

1921. Selection in Cladocera on the Basis of a Physiological Character.

Carnegie Institution Publ. No. 305. 170 pp

Brierly, W. B.

1919. Some Concepts in Myeology—4An Attempt at a Synthesis, Trans.

British Mycol, Soc., 6, 204-235.

Brierly, W. B.

2 On a Form of Botrytis cinerea with Colourless Sclerotia. Phil.

Trans. Roy. Soc., Ser. B, 210, 88-114.

Erdmann, R.

1920. Endomixis and Size Variations in Pure Bred Lines of Parame-

cium aurelia. Arch. f. Entw.-mech., 46, 85-148.

Jollos, V.

1921. Experimentelle Protistenstudien. Arch. f. Protistenkunde, 43,

Lóhnis, F,

1921. gsm upon the Life Cyeles of the Bacteria. Part I. Mem.

Acad. Sci., 16, Second Memoir. 335 pp.

VARIATIONS IN DATURA DUE TO CHANGES IN

CHROMOSOME NUMBER -

DR. ALBERT FRANCIS BLAKESLEE

STATION FOR EXPERIMENTAL EvoLuTION, COLD SPRING

Hanson, L: I, N- Y.

Two forms with which we have recently carried on

breeding experiments, the garden flower Portulaca and

the jimson weed (Datura Stramonium), are strikingly

different in the types of variations which they show.

The Portulaca is procurable in a wide range of color va-

rieties, and is apparently subject to relatively frequent

mutations, both seminal and somatic, with sectorial and

periclinal chimeras a common phenomenon. Sufficient

breeding tests have been made to indicate that the varie-

ties of Portulaca are due in large measure at least to gene

mutations. In comparison with Portulaca, the jimson

weed is relatively stable so far as gene mutations are

concerned. Despite the large amount of breeding work

with this species, both before and since the rediscovery of

Mendel’s law, only the two allelomorphie pairs of char-

acters, purple vs. white flowers, and spiny vs. smooth cap-

sules, have been identified aside from the pair, tall vs.

short stature recently determined by the writer and

Avery (3

It is true that certain of our pure lines of Datura differ

slightly from others when grown in comparable pedi-

grees, but the fact remains that so far as sharply con-

trasting Mendelian characters are concerned, the jimson

weed is highly stable, while the Portulaca is highly mu-

table. Our knowledge of changes in chromosome number

in other forms is not sufficient to indicate if there is any

significance for the present discussion in the difference

just mentioned between Portulaca and Datura.

Our interest in Datura began about 1910 or 1911, when

the jimsons were used as demonstration Materi for

students in genetics. In 1915 we found our first mutant

which we called the Globe from the shape of its capsules.

í 16

No. 642] VARIATION IN DATURA 17

The capsules of normal plants are ovate and the edges of

the leaves somewhat toothed. Globe plants, on the con-

trary, have depressed capsules and broader leaves with a

more entire margin (cf. 3, figs. 7 and 9). Figure 1 shows

sro | | /6 SEIS ' - 16780 Ch

1. Young plants in 3-inch pots. The normal 2n za ra in the middle,

vin pis +1) Globe on the right, ut. e (2n + 2) Globe on the 1

young plants beginning to flower. In the center is a

normal and on the right a Globe. The leaves of the latter

are broader and more closely massed together. In the

plant on the left, the Globe characters are more strongly

developed. This plant represents an extreme type of the

Globe mutant, and has been called the Round-leaf Globe.

It is of considerable genetic interest and will be discussed

later. It was at first thought that the Globe might be a

tetraploid type like the Gigas GZnothera but a preliminary

cytological investigation showed that such was not the

ease.

A peeuliarity in the inheritanee of the Globe (1, table 3)

was found to be that the Globe complex is transmitted to

only about one fourth of its offspring when a Globe parent

is selfed; that about the same proportion of one fourth

Globes only appears in the offspring when the Globe

parent is erossed with pollen from a normal plant; and

that the mutant character is transmitted to only a slight

18 THE AMERICAN NATURALIST [Vor. LVI

extent or not at all through the pollen—to less than 2 per

cent. in a large series of crosses.

The next mutant found was Cocklebur (3, fig. 11)

named from the resemblanee of its fruits to those of the

cocklebur weed. The plant is weak and lopping and the

leaves narrow and twisted.

The Poinsettia mutant (3, fig. 14) was named from a

fancied resemblance of its long clustered leaves to the

hothouse plant of that name. The Poinsettia is of espe-

cial interest, since this mutant was found to give curious

ratios when heterozygous for color factors.

As our eyes became better trained, other mutants were

added to the list, largely through the keen discrimination

of Mr. Avery and Mr. Farnham, until we now have 12

main mutants with some varieties, all of which transmit

their mutant characters essentially in the same way in

which the Globe complex was found to be transmitted.

In addition we had a mutant which, unlike the 12 types

just mentioned, was found to breed true, and since it is

practically impossible to obtain crosses between it and

the normal form from which it arose, it was called ‘‘ New

Species "' (3, fig. 15). The capsules are somewhat spheri-

cal and the leaves broad, although in a race of the same

type later discovered the leaves are not greatly different

from the normals. Heterozygous plants of the ** N. S."

sometimes gave curious ratios in their offspring.

Such was the situation up to the spring of 1920, when

we were fortunate in securing the cooperation of Mr.

Belling in a study of the nuclear condition of our mutants.

On the basis of his work we are able to make the classi-

fieation of types shown in Fig. 2. In the individual fig-

ures—which of course are highly diagrammatie—the

chromosomal constitution of somatie cells is represented.

We have not attempted to represent the size differences

determined by Mr. Belling and pietured in our paper in

the morning session. A word of explanation of terms

is desirable. The terms diploid, triploid and tetraploid

are already current to indicate a balanced condition in

which each chromosomal] set (we can not say chromosomal

1To be published shortly in the AMERICAN NATURALIST.

No. 642] VARIATION IN DATURA 19

Balanced Types Unbalanced Types

Diploid’ Moditied Diploids

2 m Sy NS S

WE ANA ANZ

DASA TRA TRAN [| AA

SANTO [SANZISAVZISA SZ

es Simple Tris Simple TetraSomic Double Trisomic

Triploid Modified Triploids

4 M S

AN uL

VANI

(3n)

Tetraploid Modified Tetraploids

eO |Z SiG.

WMS [AS Au

NOE RO

Simple Pentasomic a Hexasomic

jene) 4ntr2)

Fic. 2, Diagrams illustrating the chromosomal types already found in Datura.

pairs when there are more than 2 in a set) has respec-

tively 2, 3, or 4 chromosomes. I have suggested (2) the

terms disome, to indicate a set of 2 chromosomes, trisome

a set of 3, and tetrasome a set of 4, ete., with the adjectives

disomie, trisomie, tetrasomie, ete. Such terms may be

found useful, but it seems impossible to devise a simple

terminology that will adequately describe even the chro-

mosomal irregularities at present known in Drosophila

and Datura. Accordingly, after considerable discussion

with Dr. Bridges, we have agreed upon a set of formule

which is illustrated in the diagram and which we shall

use in our present papers. A

20 THE AMERICAN NATURALIST [Vor. LVI

Of the balanced forms there are even-balanced or

stable, and odd-balanced or unstable types. In the even-

balanced diploid, which is the normal jimson weed, the

two chromosomes in each set go to opposite poles by the

ordinary process of disomic reduction, and the plants

breed true for chromosome number. Partly for the same

reason, the even-balanced tetraploid, which is our *' New

Species," breeds essentially true. The triploid, on the

other hand, is odd-balaneed and therefore unstable, since

in the trisomie disjunetion in each set two of the three

chromosomes go to the one pole and one to the other, the

process taking place at random. Through the operation

of chance, therefore, gametes of different chromosomal

number will be formed, and simple and double mutants

as well as diploids will occur in the offspring. The rela-

tion may be seen from the pollen of the three balanced

types under the same magnification (Fig. 3), where the

photograph at the left (a) shows a field of pollen from a

diploid; that at the right, (c) with larger grains, pollen

from a tetraploid; while that above (b) shows pollen from

a triploid. Pollen from a triploid is not only character-

ized by a large proportion of empty grains, but also by a

great diversity in the size of the grains brought about

by the differences in the number of ehromosomes which

they eontain. ;

The upper left-hand figure of the unbalanced types (Fig.

2) has one extra chromosome in the lower right-hand set,

indieated by the arrow, giving 1 trisome, and 11 disomes

in this nucleus, and its formula may be written (2n + 1).

Such a simple mutant is the Globe—simple because only

one set is affected. If another set has the extra chromo-

some—say the set on the right—instead of the one with

the arrow, this extra chromosome would cause the plant

to assume the characters of, say, the Cocklebur mutant.

It is obvious that since there are 12 sets in Datura and

each set may have an extra chromosome, there are 12 mu-

tants with the formula (2» +1) theoretically possibie.

Through the process of disjunetion in these 12 mutants,

half of the gametes should contain the extra chromosome,

No. 649] VARIATION IN DATURA 21

and half should not. Differential mortality, affecting

adversely zygotes with the extra chromosome, prevents

the expected equality of (2n) and (2n + 1) individuals in

the offspring from test erosses with diploids.

Fic. 3. Photomicrographs of pollen grains: (a) from a diploid Datura; (b)

from a triploid; (c) from a tetraploid. The magnification is indicated by the

seale, each division of which equals 0.10 mm.

The 12 mutants under discussion may best be repre-

sented in a single figure by their capsules. In Figure 4

we have capsules of the 12 simple trisomic mutants viewed

from the ovate side, each one of which represents the

addition of a single extra chromosome presumably in a

different set. There is the Globe with depressed capsules

and stocky spines; the large long-spined Poinsettia; the

narrow short-spined Cocklebur; the slender-spined Ilex;

22 THE AMERICAN NATURALIST [Vor. LVI

Pointe fa

Globe |

Md lated : : Super doef

a Glossy

Reduced I Baek ling

Fic. 4. Photographs of capsules of 12 mutants of Datura viewed from the

ovate side,

the Mutilated, usually mutilated with a dise: aged blotch;

the short-spined Sugarloaf; the shiny capsule of Glossy,

ete., with lastly the narrow, long-spined Wedge. I have

No. 642] VARIATION IN DATURA 23

provisionally called these mutants the 12 apostles. Cer-

tain of the 12 have varieties which may be called acolytes,

and perhaps some of these in the figure may be reduced

from the rank of apostles to that of acolytes when other

forms are discovered.

#66

Ba inset ts T fec Bodl %4

Uiiey Felled : Strawherey

Fic. 5. Capsules representing 3 pairs of mutants. Those in the lower row

are believed to represent varieties or ‘“‘ acolytes” of the ston rei types repre-

sented abov

In Figure 5, the mutants from which the capsules in the

lower row were taken have been provisionally classed as

acolytes of their respective apostles represented above.

The evidence is best in regard to the mutants Wiry and

Poinsettia which form the pair at the left in the figure.

They both contain a single extra chromosome of approxi-

mately the same size, and in both eases this extra chromo-

some is shown, by peculiar color ratios in their offspring,

to be in the set which carries the factors for purple and

white flower color. The fact that though perfectly dis-

tinet they are yet similar in appearance, and the fact that

one has not infrequently given rise to the other in our

24 THE AMERICAN NATURALIST [Vor.LVI

cultures, is a line of argument applicable not alone to the

pair Wiry and Poinsettia. It also leads us to consider

Rolled an acolyte of Sugarloaf, and Strawberry an aco-

lyte of Buckling. The possibility of acolytes being caused

by modifying Mendelian factors is being investigated.

I have said that the Poinsettia mutant gave curious

color ratios in its offspring (4 and 2, table 2). The evi-

dence seems conclusive that Poinsettia has its extra chro-

mosome in the set which carries the factors for purple and

white flower color. A heterozygous Poinsettia may have

one dose or two doses of the dominant purple flower color.

The offspring of Poinsettia (like those of the Globe), it will

be remembered, are part normals and part mutants. If

a Poinsettia parent is duplex for purple, its normal off-

spring show 8 purples to 1 white, while its Poinsettia

offspring are all purples. If the Poinsettia parent is

simplex for purple the ratio for the normal offspring is

5 purples to 4 whites, and for Poinsettia offspring is 7

purples to 2 whites. The back crosses are also distine-

tive. By similar.reasoning we believe the Cocklebur mu-

tant has its extra chromosome in the set which carries

genes for presence or absence of spines on the capsules. _

The evidence is especially good for Poinsettia, since the

color classes can be recognized in the seedpan. . Using a

Poinsettia which arose in a purple line from Washington,

D. C., we crossed it with a white line of similar appear-

ance also from Washington, and, without going outside of

these two lines, have synthesized Poinsettias of all the

possible combinations of color factors and have made

nearly all the possible combinations of crosses between

them. The results with the Washington lines are in ac-

cord with what would be expected from a random assort-

ment of 3 chromosomes in the set containing the purple-

white color factors. In a certain group of Poinsettias

simplex for purple in which the 2 chromosomes bearing

the white factor might have been brought in, so far as we

knew, either from the white Washington stock, or from a

distinct white line from Erfurt, Germany, the color ratios

in the offspring of some parents were according to calcu-

No. 642] VARIATION IN DATURA : 25

lation, but from other parents the whites were approxi-

mately 6 times as frequent as would be expeeted. Later

experiments seem to indieate: that we get the definite

excess in white offspring from simplex parents when both

the ** white ’’ chromosomes come from the German line;

that we get the Poinsettia ratios typieal of random as-

sortment when the two white chromosomes come from the

Washington whites ; and that we get both of the two types

of ratios from different individual F, parents when we

make up an F, Poinsettia containing both a Washington

white, and a German white chromosome. It is apparent

that the peculiarity must be attributed to the German

chromosomes. The question is receiving further experi-

mental investigation but our provisional hypothesis to

account for the difference in the ratios is that for some

reason in trisomie disjunction the German white chromo-

somes go to opposite poles rather than to the same pole

6 times as frequently as the laws of random assortment

would dictate.

Let us return to our diagrams in Fig. 2. Of the modi-

fied diploids we may have 2 extra chromosomes in a

single set forming a simple mutant of the formula

(2n-4-2). An example is the round-leaf Globe (fig. 1)

already mentioned.

If two different sets are affeeted each with a single

extra ehromosome we have a double mutant with the

formula (2n+1-+1). Of the 66 different double tri- —

somie mutants theoretically possible, we have a consider-

able number now under cultivation. As an example, the

double mutant Globe-Reduced is shown in Fig. 6. At the

top is a eapsule of a normal diploid with its chromosomal

diagram. At the left is a capsule of the Globe, and at the

right a eapsule of Redueed. "Their diagrams indieate that

the two mutants have different sets affected. "The plant

represented by the capsules below, from the appearance

of its leaves as well as from that of its fruit, is un-

doubtedly a double mutant with the two sets affected as

indieated in the diagram below. If the Globe-Reduced

behaves like other double mutants we have bred, its off-

26 THE AMERICAN NATURALIST [Vor. LVI

spring should contain normal diploids, both the Globe and

the Reduced mutants, as well as the Sanne ‘toe Globe-

Reduced, roughly in the proportion of 6: 2: 2:1

Peipioida (fig. 2) have been discussed in Tes morning's

session. Our prediction at last year's meeting has been

| TEN,

lode

Globe- Reduced

( dover i)

ł 1>

WG!

Trisomie

T nmm

hashes eet ha nettes

Sirs art Capsule of € diploid (25) Move: capsule of Reduced (2n +1 Rd)

aa ^ : bim of Glo (2n -1 Gl) at left; and capsule of double mutant

e-Reduced (2n +1 x Rd) below. Below peor capsule is given its ch

mosomal diagram, T poc

No. 642] VARIATION IN DATURA 2:

fulfilled and we have obtained, in the offspring of a tri-

ploid, practically the full range of (2n +1) mutants as

well as double mutants of the formula (25 + 12-1). No

modified triploids have as yet been identified, but even if

we found them we could not expect to be able to propa-

gate them by seed.

Heterozygous tetraploid plants. also show curious

ratios, according to whether there are 1, 2, or 3 doses of

the dominant factor. Duplex plants give a 35: 1 ratio

when selfed and the different types in the offspring segre-

gate in a characteristic fashion.

In the tetraploids we may have a single extra chromo-

some in one set making a simple (4n +1) mutant, or 2

chromosomes in a set making a simple (4n-+ 2) mutant.

We have two cases of a tetraploid with a deficiency in one

set, producing a (4n — 1) mutant.

Up to the present time, except for Gregory’s work on |

tetraploid Primulas (5) which was correctly interpreted

by Muller (6), Mendelian research has dealt almost ex-

elusively with disomic inheritance. Our work with the

jimsons and the recent investigations of Bridges on tri-

ploid Drosophilas offer an opportunity for the rather

novel study of trisomie, tetrasomie and pentasomie in-

heritanee. We do not believe, however, that the jimson

weed is peeuliar among plants in giving rise to chromo-

somal mutants.

The unbalancing effect of the extra chromosomes can

best be illustrated by extra chromosomes in the Globe set.

The (2n-+2) Globe has two extra chromosomes in the

Globe set and hence should show a greater divergence

from normal than the Globe with only one extra chromo-

some. Such is the case. The simple (2n +1) Globe (like

other mutants of this type) is less vigorous in growth

than normals. The (2n +2) Globe is still less vigorous

than the more common (2» 4- 1) Globe. From fig. 1 it will

be seen, further, that the Globe characters i in the (2n + 2)

Globe on the left, such as broadness of leaves, fatness of

bud, and density of foliage, are much further developed

28 THE AMERICAN NATURALIST [Vor. LVI

than in the (2n +1) Globe at the right, which has only

one extra chromosome.

Photographs of eapsules (Fig. 7) will further illustrate

the idea of unbalance. Unfortunately the (2n + 2) Globe

just mentioned fruits poorly and none of its capsules

were available when the fruits of the other types were

photographed. Later a photograph of a capsule was

made to the same scale, and inserted in the proper place

in the series. It will be evident that the Globe char-

acters of relative stockiness of spines and depression of

capsules are more marked in the (2n-+ 2) Globe where

there are 2 extra chromosomes in the Globe set than in

the (2n +1) Globe on the left where there is only one

extra chromosome in this particular set. Likewise in the

modified tetraploids the (plus 2) Globe on the right is

more Globe-like than the (plus 1) Globe beside it.

The degree of unbalanee of chromosomes in the nuclei

may be given a quantitative expression. Thus in the

(2n +1) Globe, the extra chromosome produces an excess

of one over the balanced 2n condition. The nucleus is

overbalanced by the active factors in a single Globe chro-

mosome. This unbalance may be said to be 1 over 2n.

In a similar way the (2n + 2) Globe with 2 extra chromo-

somes has an unbalance of 2 over 2n. Having in mind

these quantitative differences one would expect the

(4n +1) Globe with an unbalance of 1 over 4n to show

a less marked expression of the Globe charaeters than

the (2n +1) Globe with an unbalance of 1 over 2n, They

are, in faet, less readily recognized in recording our pedi-

grees. The relation of unbalance enabled us to prediet

the possibility of finding (4n +2) Globes with an unbal-

ance of 2 over 4» which one would expect to be as distinct

in appearance as (2n +1) Globes with an equivalent un-

balance of 1 over 2». The predietion has been fulfilled

and we are led to expect the appearance of Globes with 3,

and Globes with 4 extra chromosomes in the Globe set, if

tetraploid plants ean endure the extreme unbalanee of 4

over 4», the equivalent of 2 over 2n obtained in the

(2n + 2) Globe. :

No. 642] VARIATION IN DATURA 29

It must be emphasized that our quantitative expres-

sions of unbalance hold strictly only for the chromosomal

numbers in reference to a single set, and not necessarily

for the somatic characters conditioned by them, although

the nuclear unbalance seems to be reflected in the somatie

4ALS 4 MW

aes 2) <=

PA FA A n

vH SUG

an 4n

1 | sb Sour

(nie ai) (4n*1&() (4nt26)

Fia. Above, capsules with diagrams of a diploid (2n) and a tetraploid

(4n). Blov, capsules with diagrams of the different Globe mutants

appearance, at least in the Globe series just discussed.

In double mutants, moreover, somatic effects may be in-

tensified or largely neutralized by individual genes in the

two extra ehromosomes, and an easy expression of the

combined unbalance which they exert will therefore be

impossible.

The structural characters have been taken for illustra-

30 THE AMERICAN NATURALIST [Vor.LVI

tion from a particular part of a single mutant, the Globe.

A more detailed study of changes in external and internal

morphology brought about by the presence of specific

extra chromosomes in the several mutants is being under-

taken in eooperation with Dr. Sinnott. :

The unbalancing effect of an extra chromosome is

shown in the lessened vigor of mutant plants. Thus from

Globe parents as an example of (2n 4- 1) mutants, ordi-

narily only one quarter of the offspring to reach record-

able size are Globes, instead of the 50 per cent. expected.

Moreover, when the plants are crowded the proportion of

Globes surviving is considerably lessened.

We have been discussing the unbalance as affecting the

sporophytic generation. In the gametophyte, the un-

balance is doubled. Thus from (2x+1) Globe plants

with an unbalance of 1 over 2» the pollen grains with the

extra chromosome have an unbalance of 1 over ». This

extreme unbalanee hinders their funetioning and brings

it about that the Globe character is transmitted to only a

slight extent through the pollen (under 2 per cent. in a

considerable series of crosses). It is of interest in this

connection to note the results of selfing and erossing

Globes of the tetraploid series. The unbalance in a

(4n +1) Globe is 1 over 4n, while the unbalance in its pol-

len grains which carry the extra chromosome is 1 over 2n.

Due to this lessened unbalance in comparison with pollen

of (2n +1) Globes, the pollen of the (4» +1) Globe trans-

mits the Globe character to a higher percentage of its

progeny (14 per cent. in the single pedigree tested), and

partially for the same reason we have obtained higher

proportions of Globes in the offspring from selfing such

(4n +1) Globes (a total of about 60 per cent. in a single

experiment). A more specific study of the effect of ex-

tra chromosomes upon the gametophyte is being under-

taken in cooperation with Dr. Buchholz.

It will not be advisable at the present stage of our in-

vestigations to discuss the possible external and internal

factors which may induce the chromosomal aberrations

which form the basis of our common mutations in Datura.

No. 642] VARIATION IN DATURA 3l

A study of the effects of radium rays undertaken in co- `

operation with Dr. Gager has given results which, al-

though in an early stage of the experiment, appear sug-

gestive in this connection. Other stimuli are being tested

which appear to induce irregularities in the distribution

of chromosomes to the pollen grains. It will be a matter

of theoretical interest to be able to control experimentally

the production of chromosomal mutations. It might also

prove to be of considerable economie importance to be

able to produce at will the full range of chromosomal mu-

tants in any plants, especially in those which are propa-

gated by vegetative means.

To us, one of the most interesting features of the Da-

tura work is the possibility afforded of analyzing the in-

fluence of individual chromosomes upon both the mor-

phology and physiology of the plant without waiting for

gene mutations. Evidence is at hand which indicates

that every chromosome in Datura carries factors which

influence the expression of the so-called unit character

purple pigmentation. Our work so far we believe adds

evidence to the conclusion that the mature organism—

plant or animal—is not a structure like a child’s house of

blocks, made up of separate unit characters, nor is it de-

termined by separate and unrelated unit factors. It is

rather the resultant of a whole series of interacting and

more or less conflicting forces contained in the individual

chromosomes.

LITERATURE CITED

1. Blakeslee, A. F. 1921. ata Globe Mutant in the Jimson Weed.

Genetics, 6: 241—264, fi

. Blakeslee, A. F. 1921. ea of Mutations and Their Possible Signifi-

cance in Evolution. AMER, NAT., 55: 254-267

. Blakeslee, A. F., and B. T. Avery, Jr. 1919. Mutations in the Jimson

Weed. ‘Jour, Heredity. 10: 111-120, fig. 5-15.

. Blakeslee, A, F., John Belling and M. E. Farnham. 1920. Chromo-

vind Duplication i Mendelian Phenomena in Datura Mutants.

Science, N. S., 8-390.

: Gregory, R. P, SA On the pope s Tetraploid Plants in Primula

` Proc. Roya: Society, B 87: 484—492.

; Matas, = J. 1914. A New Mode x: ‘Segregation in Gregory’s Tetra-

ploid Primulas. AMER. NAT., 48: 508-512

ix)

we)

VARIATION DUE TO CHANGE IN THE

INDIVIDUAL GENE:

DR. H. J. MULLER

DrPARTMENT OF ZOOLOGY, UNIVERSITY OF TEXAS

I. Tue RELATION BETWEEN THE GENES AND THE CHAR-

ACTERS OF THE ÜRGANISM

Tue present paper will be concerned rather with prob-

lems, and the possible means of attacking them, than with

the details of cases and data. The opening up of these

new problems is due to the fundamental contribution

which genetics has made to cell physiology within the last

decade. This contribution, which has so far scarcely

been assimilated by the general physiologists themselves,

consists in the demonstration that, besides the ordinary

proteins, carbohydrates, lipoids, and extractives, of their

several types, there are present within the cell thousands

of distinct substances—the ‘‘ genes "; these genes exist

as ultramicroscopic particles; their influences neverthe-

less permeate the entire cell, and they play a fundamental

role in determining the nature of all cell substances, cell

structures, and cell activities. Through these cell effects,

in turn, the genes affect the entire organism.

It is not mere guesswork to say that the genes are

ultra-mieroscopie bodies. For the work on Drosophila

has not only proved that the genes are in the chromo-

somes, in definite positions, but it has shown that there

must be hundreds of such genes within each of the larger

chromosomes, although the length of these chromosomes

is not over a few mierons. If, then, we divide the size

of the chromosome by the minimum number of its genes,

we find that the latter are partieles too small to give a

visible image.

The chemieal doni Moe of the genes, and the for-

mule of their reactions, remain as yet quite unknown.

We do know, for example, that in certain cases a given

1 Contribution No. 156,

No. 642] VARIATION IN INDIVIDUAL GENE 33

pair of genes will determine the existence of a particular

enzyme (concerned in pigment production), that another

pair of genes will determine whether or not a certain

agglutinin shall exist in the blood, a third pair will deter-

mine whether homogentisie acid is secreted into the urine

(* alkaptonuria "), and so forth. But it would be

absurd, in the third case, to conclude that on this account

the gene itself consists of homogentisie acid, or any

related substance, and it would be similarly absurd, there-

fore, to regard cases of the former kind as giving any

evidence that the gene is an enzyme, or an agglutinin-like

body. The reactions whereby the genes produce their

ultimate effects are too complex for such inferences.

Each of these effects, which we call a ‘‘ character "' of

the organism, is the product of a highly complex, intri-

cate, and delicately balanced system of reactions, caused

by the interaction of countless genes, and every organic

structure and activity is therefore liable to become in-

creased, diminished, abolished, or altered in some other

way, when the balance of the reaction system is disturbed

by an alteration in the nature or the relative quantities

of any of the component genes of the system. To return

now to these genes themselves.

II. Tue PROBLEM or GENE MUTABILITY

The most distinctive characteristic of each of these

ultra-mieroseopie particles—that characteristic whereby

we identify it as a gene—is its property of self-propaga-

tion: the fact that, within the complicated environment

of the cell protoplasm, it reacts in such a way as to

convert some of the common surrounding material into

an end-product identical in kind with the original gene

itself. This action fulfills the chemist’s definition of

** autocatalysis ’’; it is what the physiologist would call

** growth °’; and when it passes through more than one

generation it becomes ‘‘ heredity.” It may be observed

that this reaction is in each instance a rather highly

localized one, since the new material is laid down by the

side of the original gene.

34 THE AMERICAN NATURALIST [Vou. LVI

The fact that the genes have this autocatalytic power

is in itself sufficiently striking, for they are undoubtedly

complex substances, and it is difficult to understand by

-what strange coincidence of chemistry a gene can happen

to have just that very special series of physico-chemical

effects upon its surroundings which produces—of all pos-

sible end-products—just this particular one, which is

identical with its own complex structure. But the most

remarkable feature of the situation is not this oft-noted

autocatalytic action in itself—it is the fact that, when the

structure of the gene becomes changed, through some

** chance variation,’’ the catalytic property of the gene

may * become correspondingly changed, in such a way as

to leave it still autocatalytie. In other words, the change

in gene structure—accidental though it was—has some-

how resulted in a change of exactly appropriate nature

in the catalytic reactions, so that the new reactions are

now accurately adapted to produce more material just

like that in the new changed gene itself. It is this para-

doxical phenomenon which is implied in the expression

‘* variation due to change in the individual gene,” or, as

it is often called, ** mutation."

What sort of strueture must the gene possess to permit

it to mutate in this way? Since, through change after

change in the gene, this same phenomenon persists, it is

evident that it must depend upon some general feature of

gene construction—common to all genes— which gives

each one a general autocatalytic power—a “carte

blanche ’’—to build material of whatever speeifie sort it

itself happens to be composed of. This general prineiple

of gene strueture might, on the one hand, mean nothing

more than the possession by each gene of some very

simple character, such as a particular radicle or ** side-

chain ’’—alike in them all—which enables each gene to

enter into combination with certain highly organized

materials in the outer protoplasm, in such a way as to

result in the formation, ** by ” the protoplasm, of more

material like this gene which is in combination with it. In

2 It is of course conceivable, and even unavoidable, that some types of

changes do d j i i

pianot : a estroy the gene’s autoeatalytie power, and thus result in its

No. 642] VARIATION IN INDIVIDUAL GENE 35

that case the gene itself would only initiate and guide the

direction of the reaction. On the other hand, the extreme

alternative to such a conception has been generally as-

sumed, perhaps gratuitously, in nearly all previous

theories concerning hereditary units; this postulates that

the chief feature of the autocatalytie mechanism resides

in the structure of the genes themselves, and that the

outer protoplasm does little more than provide the build-

ing material. In either case, the question as to what the

general principle of gene construction is, that permits

this phenomenon of mutable autocatalysis, is the. most

fundamental question of genetics.

The subject of gene variation is an important one,

however, not only on account of the apparent problem

that is thus inherent in it, but also because this same

peeuliar phenomenon that it involves lies at the root of

organic evolution, and hence of all the vital phenomena

which have resulted from evolution. It is commonly

sald that evolution rests upon two foundations—inher-

itanee and variation; but there is a subtle and important

error here. Inheritance by itself leads to no change, and

variation leads to no permanent change, unless the varia-

tions themselves are heritable. Thus it is not inheritance

and variation which bring about evolution, but the in-

heritance of variation, and this in turn is due to the

general principle of gene construction which causes the

persistence of autocatalysis despite the alteration in

structure of the gene itself. Given, now, any material

or colleetion of materials having this one unusual char-

acteristic, and evolution would automatically follow, for

this material would, after a time, through the accumula-

tion, competition and seleetive spreading of the self-

propagated variations, come to differ from ordinary in-

organic matter in innumerable respects, in addition to

the original difference in its mode of catalysis. There

would thus result a wide gap between this matter and

other matter, which would keep growing wider, with the

Increasing complexity, diversity and so-called ‘‘ adapta-

tion ” of the selected mutable material.

36 : THE AMERICAN NATURALIST [Vor.LV1

III. A POSSIBLE ATTACK THROUGH CHROMOSOME BEHAVIOR

In thus recognizing the nature and the importance of

the problem involved in gene mutability have we now

entered into a cul de sac, or is there some way of pro-

ceeding further so as to get at the physical basis of this

peculiar property of the gene? The problems of growth,

variation and related processes seemed difficult enough

to attack even when we thought of them as inherent in the

organism as a whole or the cell as a whole—how now

can we get at them when they have been driven back,

to some extent at least, within the limits of an invisible

particle? A gene can not effectively be ground in a

mortar, or distilled in a retort, and although the physico-

chemical investigation of other biological substances may

conceivably help us, by analogy, to understand its struc-

ture, there seems at present no method of approach along

this line. ;

There is, however, another possible method of approach

available: that is, to study the behavior of the chromo-

somes, as influenced by their contained genes, in their

various physical reactions of segregation, crossing. over,

division, synapsis, ete. This may at first sight seem very

remote from the problem of getting at the structural

principle that allows mutability in the gene, but I am in-

clined to think that such studies of synaptic attraction be-

tween chromosomes may be especially enlightening in this

connection, because the most remarkable thing we know

about genes—besides their mutable autocatalytic power—

is the highly specific attraction which like genes (or local

products formed by them) show for each other. As in

the case of the autocatalytic forces, so here the attractive

forces of the gene are somehow exactly adjusted so as

to react in relation to more material of the same com-

plicated kind. Moreover, when the gene mutates, the

forces become readjusted, so that they may now attract

material of the new kind; this shows that the attractive

or synaptic property of the gene, as well as its eatalytie

property, is not primarily dependent on its specific struc-

ture, but on some general principle of its make-up, that

No. 642] VARIATION IN INDIVIDUAL GENE 31

causes whatever specific structure it has to be auto-attrac-

tive (and autocatalytic).

This auto-attraction is evidently a strong force, exert-

ing an appreciable effect against the non-specific mutual

repulsions of the chromosomes, over measurable micro-

scopic distances much larger than in the case of the ordi-

nary forces of so-called cohesion, adhesion and adsorp-

tion known to physical science. In this sense, then, the

physicist has no parallel for this force. There seems,

however, to be no way of escaping the conclusion that in

the last analysis it must be of the same nature as these

other forces which cause inorganic substances to have

specific attractions for each other, according to their

chemical composition. These inorganic forces, according

to the newer physics, depend upon the arrangement and

mode of motion of the electrons constituting the molecules, -

which set up electro-magnetic fields of force of specific

patterns. To find the principle peculiar to the construc-

tion of the force-field pattern of genes would accordingly

be requisite for solving the problem of their tremendous

auto-attraction.

Now, according to Troland (1917), the growth of erys-

tals from a solution is due to an attraction between the

solid erystal and the molecules in solution caused by

the similarity of their force. field patterns, somewhat as

similarly shaped magnets might attract each other—

north to south poles—and Troland maintains that essen-

tially the same mechanism must operate in the auto-

catalysis of the hereditary particles. If he is right, each

different portion of the gene structure must—like a

erystal—attract to itself from the protoplasm materials

of a similar kind, thus moulding next to the original gene

another structure with similar parts, identically arranged,

which then become bound together to form another gene,

a replica of the first. This does not solve the question

of what the general principle of gene construction is,

which permits it to retain, like a crystal, these properties

of auto-attraetion,? but if the main point is correct, that

3It ean hardly be true, as Troland intimates, that all similar fields at-

traet each other more than they do dissimilar fields, otherwise all substances

would be autoeatalytie, and, in fact, no substances would be soluble. More-

38 THE AMERICAN NATURALIST [Vor. LVI

the autocatalysis is an expression of specific attractions

between portions of the gene and similar protoplasmic

building blocks (dependent on their force-field patterns),

it is evident that the very same forces which cause the

genes to grow should also cause like genes to attract each

other, but much more strongly, since here all the indi-

vidual attractive forces of the different parts of the gene

are summated. If the two phenomena are thus really

dependent on a common principle in the make-up of the

gene, progress made in the study of one of them should

help in the solution of the other.

Great opportunities are now open for the study of the

nature of the synaptic attraction, especially through the

discovery of various races having abnormal numbers of

_ chromosomes. ‘Here we have already the finding by

Belling, that where three like chromosomes are present,

the close union of any two tends to exclude their close

union with the third. This is very suggestive, because the

same thing is found in the cases of specific attractions

between inorganic particles, that are due to their force

field patterns. And through Bridges’ finding of triploid

Drosophila, the attraction phenomena can now be brought

down to a definitely genic basis, by the introduction of

specific genes—especially those known to influence chro-

mosome behavior—into one of the chromosomes of a

triad. The amount of influence of this gene on attraction

may then be tested quantitatively, by genetic determina-

tion of the frequencies of the various possible types of

Segregation. By extending such studies to include. the

effect of various conditions of the environment— such

as temperature, electrostatic stresses, ete.—in the pres-

ence of the different genetic situations, a considerable

field is opened up.

This suggested connection between chromosome behav-

ior and gene structure is as yet, however, only

sibility. It must not be forgotten that at present

over,

a pos-

Wwe can

if the parts of a molecule are in any kind of ** solid," three dimen-

sional formation, it would seem that those in the middle would scarcely have

opportunity to exert the moulding effect above mentioned. It therefore

appears that a ial manner of construction must be necessary, in order

that a complicated structure like a gene may exert such an effect,

No. 642] VARIATION IN INDIVIDUAL GENE 39

not be sure that the synaptic attraction is exerted by the

genes themselves rather than by local products of them,

and it is also problematieal whether the chief part of the

mechanism of autocatalysis resides within the genes

rather than in the ‘‘ protoplasm.’’ Meanwhile, the

method is worth following up, simply because it is one

of our few conceivable modes of approach to an all-im-

portant problem.

It may also be recalled in this connection that besides

the genes in the chromosomes there is at least one sim-

ilarly autoeatalytie material in the chloroplastids, which

likewise may become permanently changed, or else lost,

as has been shown by various studies on chlorophyll inher-

itance. Whether this plastid substance is similar to the

genes in the chromosomes we can not say, but of course

it can not be seen to show synaptic attraction, and could

not be studied by the method suggested above.*

IV. THE Arrack THROUGH STUDIES OF MUTATION

There is, however, another method of attack, in a sense

more direct, and not open to the above criticisms. That

is the method of investigating the individual gene, and

the structure that permits it to change, through a study

of the ehanges themselves that occur in it, as observed

by the test of breeding and development. It was through

the investigation of the changes in the chromosomes—

eaused by erossing over—that the structure of the chro-

mosomes was analyzed into their constituent genes in

line formation ; it was through study of molecular changes

that molecules were analyzed into atoms tied together in

definite ways, and it has been finally the rather recent

finding of changes in atoms and investigation of the

resulting pieces, that has led us to the present analysis

of atomie strueture into positive and negative electrons

having eharaeteristie arrangements. Similarly, to under- .

stand the properties and possibilities of the individual

gene, we must study the mutations as directly as possible,

and bring the results to bear upon our problem.

4It may be that there are still other elements in the cell which have the

nature of genes, but as no eritieal evidenee has ever been addueed for their

existence, it would be highly hazardous to postulate them.

40 THE AMERICAN NATURALIST [Vou LVI

(a) The Quality and Quantity of the Change

In spite of the fact that the drawing of inferences

concerning the gene is very much hindered, in this

method, on account of the remoteness of the gene-cause

from its character-effect, one salient point stands out

already. It is that the change is not always a mere loss

of material, because clear-cut reverse mutations have

been obtained in corn, Drosophila, Portulaca, and prob-

ably elsewhere. If the original mutation was a loss, the

reverse must be a gain. Secondly, the mutations in many

cases seem not to be quantitative at all, since the different

allelomorphs formed by mutations of one original gene

. often fail to form a single linear series. One case, in fact,

is known in which the allelomorphs even affect totally

different characters : this is the case of the truncate series,

in which I have found that different mutant genes at the

same locus may cause either a shortening of the wing, an

eruption on the thorax, a lethal effect, or any combina-

tion of two or three of these characters. In such a ease

we may be dealing either with changes of different types

occurring in the same material or with changes (possibly

quantitative changes, similar in type) occurring in dif-

ferent component parts of one gene. Owing to the uni-

versal applicability of the latter interpretation, even

where allelomorphs do not form a linear series, it can

not be categorically denied, in any individual ease, that

the changes may be merely quantitative changes of some

part of the gene. If all changes were thus quantitative,

even in this limited sense of a loss or gain of part of the

gene, our problem of why the changed gene still seems

to be autocatalytic would in the main disappear, but such

a situation is excluded a priori since in that case the

thousands of genes now existing could never have evolved.

Although a given gene may thus change in various

ways, it is important to note that there is a strong tend-

ency for any given gene to have its changes of a particular

kind, and to mutate in one direction rather than in

another. And although mutation certainly does not

always consist of loss, it often gives effects that might

be termed losses. In the case of the mutant genes for

No. 642] VARIATION IN INDIVIDUAL GENE 41

bent and eyeless in the fourth chromosome of Drosophila

it has even been proved, by Bridges, that the effects are

of exactly the same kind, although of lesser intensity, than

those produced by the entire loss of the chromosome in

which they lie, for flies having bent or eyeless in one

chromosome and lacking the homologous chromosome are

even more bent, or more eyeless, than those having a

homologous chromosome that also contains the gene in

question. The fact that mutations are usually recessive

might be taken as pointing in the same direction, since

it has been found in several cases that the loss of genes—

as evidenced by the absence of an entire chromosome of

one pair—tends to be much more nearly recessive than

dominant in its effect.

The effect of mutations in causing a loss in the char-

acters of the organism should, however, be sharply distin-

guished from the question of whether the gene has

undergone any loss. It is generally true that mutations

are much more apt to cause an apparent loss in character

than a gain, but the obvious explanation for that is, not

because the gene tends to lose something, but because

most characters require for proper development a nicely

adjusted train of processes, and so any change in the

genes—no matter whether loss, gain, substitution or rear-

rangement—is more likely to throw the developmental

mechanism out of gear, and give a ‘‘ weaker ” result,

than to. intensify it. For this reason, too, the most fre-

quent kind of mutation of all is the lethal, which leads

to the loss of the entire organism, but we do not conclude

from this that all the genes had been lost at the time of

the mutation. The explanation for this tendency for most

changes to be degenerative, and also for the fact that

certain other kinds of changes—like that from red to

pink eye in Drosophila—are more frequent than others—

such as red to brown or green eye—lies rather in develop-

mental mechanies than in geneties. It is because the

developmental processes are more unstable in one diree-

tion than another, and easier to push ‘‘ downhill ” than

up, and so any mutations that oceur—no matter what the

gene change is like—are more apt to have these effects

42 THE AMERICAN NATURALIST [Vor.LVI

than the other effects. If now selection is removed in

regard to any particular character, these character

changes which occur more readily must accumulate, giv-

ing apparent orthogenesis, disappearance of unused `

- organs, of unused physiological capabilities, and so forth.

As we shall see later, however, the changes are not so

frequent or numerous that they could ordinarily push

evolution in such a direction against selection and against

the immediate interests of the organism.

In regard to the magnitude of the somatic effect pro-

duced by the gene variation, the Drosophila results show

that there the smaller character changes occur oftener

than large ones. The reason for this is again probably

to be found in developmental mechanics, owing to the

fact that there are usually more genes slightly affecting a

given character than those playing an essential róle in

its formation. The evidence proves that there are still

more genes whose change does not affect the given char-

acter at all—no matter what this character may be, unless

it is life itself—and this raises the question as to how

many mutations are absolutely unnoticed, affecting no

character, or no detectable character, to any appreciable

extent at all. Certainly there must be many such muta-

tions, judging by the frequency with which *' modifying

factors ’’ arise, which produce an effect only in the

presence of a special genetic complex not ordinarily

present. ;

(b) The Localization of the Change

Certain evidence concerning the causation of mutations

has also been obtained by studying the relations of their

_ occurrence to one another. Hitherto it has nearly always

been found that only one mutation has occurred at a time,

restricted to a single gene in the cell. I must omit from

consideration here the two interesting cases of deficiency,

found by Bridges and by Mohr, in each of which it seems

certain that an entire region of a chromosome, with its

whole cargo of genes, changed or was lost, and also a

certain peculiar case, not yet cleared up, which has re-

cently been reported by Nilson-Ehle; these important

No. 642] VARIATION IN INDIVIDUAL GENE 43

cases stand alone. Aside from them, there are only two

instances in which two (or more) new mutant genes have

been proved to have been present in the same gamete.

Both of these are cases in Drosophila—reported by

Muller and Altenburg (1921)—in which a gamete con-

tained two new sex-linked lethals; two cases are not a

greater number than was to have been expected from a

random distribution of mutations, judging by the fre-

quency with which single mutant lethals were found in the

same experiments. Ordinarily, then, the event that

causes the mutation is specific, affecting just one par-

tieular kind of gene of all the thousands present in the

cell. That this specificity is due to a spatial limitation

rather than a chemical one is shown by the fact that when

the single gene changes the other one, of identical com-

position, located near by in the homologous chromosome

of the same cell, remains unaffected. This has been

proved by Emerson in corn, by Blakeslee in Portulaca, -

and I have shown there is strong evidence for it in Dro-

sophila. Hence these mutations are not caused by some

general pervasive influence, but are due to ‘‘ accidents ”’

occurring on a molecular scale. When the molecular or

atomic motions chance to take a particular form, to which

the gene is vulnerable, then the mutation occurs.

It will even be possible to determine whether the entire

gene changes at once, or whether the gene consists of

several molecules or particles, one of which may change

at atime. This point can be settled in organisms having

determinate cleavage, by studies of the distribution of the

mutant character in somatically mosaic mutants. If there

is a group of particles in the gene, then when one par-

ticle changes it will be distributed irregularly among the

descendant cells, owing to the random orientation of the

two halves of the chromosome on the mitotic spindles of

succeeding divisions, but if there is only one particle to

5 This depends on the assumption that if the gene does consist of several

particles, the halves of the chromosomes, at each division, receive a random

sample of these particles, That is almost a necessary assumption, since a

gene formed of particles each one of which was separately partitioned at

division would tend not to persist as such, for the occurrence of mutation in

one partiele after the other would in time differentiate the gene into a num-

ber of different genes consisting of one particle each.

44 THE AMERICAN NATURALIST — [Vor.LVI

change, its mutation must affect all.of the cells in a bloc,

that are descended from the mutant cell.

But the method that appears to have most scope and

promise is the experimental one of investigating the con-

ditions under which mutations occur. This requires

studies of mutation frequency under various methods of

handling the organisms. As yet, extremely little has been

done along this line. That is because, in the past, a muta-

tion was considered a windfall, and the expression ** mu-

tation frequency ’’ would have seemed a contradiction in

terms. To attempt to study it would have seemed as

absurd as to study the conditions affecting the distribu-

tion of dollar bills on the sidewalk. You were simply

fortunate if you found one. Not even controls, giving the

** normal ’’ rate of mutation—if indeed there is such a

thing—were attempted. ^ Of late, however, we may say

that certain very exceptional banking houses have been

found, in front of which the dollars fall more frequently—

in other words, specially mutable genes have been dis-

eovered, that are beginning to yield abundant data at

the hands of Nilsson-Ehle, Zeleny, Emerson, Anderson

and others. For some of these mutable genes the rate of

change is found to be so rapid that at the end of a few

decades half of the genes descended from those originally

present would have become changed. After these genes

have once mutated, however, their previous mutability no

longer holds. In addition to this ‘‘ banking house

method "' there are also methods, employed by Altenburg

and myself, for—as it were—automatieally sweeping up

wide areas of the streets and sifting the collections for the

valuables. By these special genetie methods of reaping

mutations we have recently shown that the ordinary

genes of Drosophila—unlike the mutable genes above—

would usually require at least a thousand years—prob-

€ Studies of ‘‘ mutation frequency '' had of course been made in the

CEnotheras, but as we now know that these were not studies of the rate of

gene change but of the frequencies of erossing over and of chromosome

aberrations they may be neglected for our present purposes

No. 642] VARIATION IN INDIVIDUAL GENE 45`

ably very much more—before half of them became

changed. This puts their stability about on a par with,

if not much higher than, that of atoms of radium—to use

a fairly familiar analogy. Since, even in these latter ex-

periments, many of the mutations probably occurred

within a relatively few rather highly mutable genes, it is

likely that most of the genes have a stability far higher

than this result suggests.

The above mutation rates are mere first gleanings—we

have yet to find how different conditions affect the occur-

. rence of mutations. There had so far been only the

negative findings that mutation is not confined to one

sex (Muller and Altenburg, 1919 ; Zeleny, 1921), or to any

one stage in the life cycle (Bridges, 1919; Muller, 1920;

Zeleny, 1921), Zeleny’s finding that bar-mutation is not

influenced by recency of origin of the gene (1921), and

the as yet inconclusive differences found by Altenburg

and myself for mutation rate at different temperatures

(1919), until at this year’s meeting of the botanists

Emerson announced the definite discovery of the influence

of a genetic factor in corn upon the mutation rate in its

allelomorph, and Anderson the finding of an influence

upon mutation in this same gene, caused by developmental

conditions—the mutations from white to red of the mu-

table gene studied occurring far more frequently in the

cells of the more mature ear than in those of the younger

ear. These two results at least tell us decisively that

mutation is not a sacred, inviolable, unapproachable

process: it may be altered. These are the first steps; the

way now lies open broad for exploration.

It is true that I have left out of account here the re-

ported findings by several investigators, of genetic vari-

ations caused by treatments with various toxic substances

and with certain other unusual conditions. In most of

these cases, however, the claim has not been made that

` actual gene changes have been caused: the results have

usually not been analyzed genetically and were in fact

not analyzable genetically; they could just as well be

interpreted to be due to abnormalities in the distribution

of genes—for instance, chromosome abnormalities like

46 THE AMERICAN NATURALIST . [Vor.LVI

those which Mavor has recently produced with X-rays—

as to be due to actual gene mutations. But even if they

were due to real genie differences, the possibility has in

most cases by no means been excluded (1) that these genic

differences were present in the stock to begin with, and

merely became sorted out unequally, through random

segregation; or (2) that other, invisible genie differences

were present which, after random sorting out, themselves

caused differenees in mutation rate between the different

lines. Certain recent results by Altenburg and myself

suggest that genie differences, affecting mutation rate,

may be not uncommon. To guard against either of these

possibilities it would have been necessary to test the

stocks out by a thorough course of inbreeding beforehand,

or else to have run at least half a dozen different pairs

of parallel lines of the control and treated series, and to

have obtained a definite difference in the same direction

between the two lines of each pair; otherwise it can be

proved by the theory of ** probable error ’’ that the dif-

ferences observed may have been a mere matter of ran-

dom sampling among genic differences originally present.

Accumulating large numbers of abnormal or inferior

individuals by selective propagation of one or two of the

treated lines—as has been done in some cases—adds noth-

ing to the significance of the results.

At best, however, these genetically unrefined methods

would be quite insensitive to mutations occurring at any-

thing like ordinary frequency, or to such differences in

mutation rate as have already been found in the analytical

experiments on mutation frequency. And it seems quite -

possible that larger differences than these will not easily

be hit upon, at least not in the early stages of our investi-

gations, in view of the evidence that mutation is ordi-

narily due to an accident on an ultramieroscopie scale,

rather than directly caused by influences pervading the

organism. For the present, then, it appears most prom-

ising to employ organisms in whieh the genetie composi-

tion ean be controlled and analyzed, and to use genetie

methods that are sensitive enough to disclose mutations

occurring in the control as well as in the treated individ-

No. 642] VARIATION IN INDIVIDUAL GENE 47

uals. In this way relatively slight variations in muta-

tion frequency, caused by the special treatments, can be

determined, and from the conditions found to alter the

mutation rate slightly we might finally work up to those

which affect it most markedly. The only methods now

meeting this requirement are those in which a ‘particular

mutable gene is followed, and those in which many

homozygous or else genetically controlled lines can be

run in parallel, either by parthenogenesis, self-fertiliza-

tion, balanced lethals or other special genetic means, and

later analyzed, through sexual reproduction, segrega-

tion and erossirig over.

V. OTHER POSSIBILITIES

We can not, however, set fixed limits to the possibilities

of research. We should not wish to deny that some new

and unusual method may at any time be found of directly

producing mutations. For example, the phenomena now

being worked out by Guyer may be a case in point. There

is a curious analogy between the reactions of immunity

and the phenomena of heredity, in apparently funda-

mental respects,’ and any results that seem to connect

the two are worth following to the limit.

Finally, there is a phenomenon related to immunity, of

still more striking nature, which must not be neglected by

geneticists. Thisis the d’Hérelle phenomenon. D'Hérelle

found in 1917 that the presence of dysentery bacilli in

the body caused the production there of a filterable sub-

stance, emitted in the stools, which had a lethal and in

fact dissolving action on the corresponding type of bac-

teria, if a drop of it were applied to a colony of the bac-

teria that were under cultivation. So far, there would

be nothing to distinguish this phenomenon from im-

7I refer here to the remarkable specificity with which a particular com-

plex antigen calls forth processes that construct for it an antibody that is

attracted to it and fits it ** like lock and key,’’ followed by further proc-

esses that cause more and more of the antibody to be reproduced. If the

antigen were a gene, which could be slightly altered by the cell to form the

antibody that neutralized it—as some enzymes can be slightly changed by

heating so that they counteract the previous active enzyme—and if this

antibody-gene then became implanted in the cell so as to keep on growing,

all the phenomena of immunity would be produced.

48 THE AMERICAN NATURALIST [Vor. LVI

munity. But he further found that when à drop of the

affected colony was applied to a second living colony, the `

second colony would be killed; a drop from the second

would kill a third colony, and so on indefinitely. In

other words, the substance, when applied to colonies of

bacteria, became multiplied or increased, and could be so

increased indefinitely ; it was self-propagable. It fulfills,

then, the definition of an autocatalytic substance, and

although it may really be of very different composition

and work by a totally different mechanism from the genes

in the chromosomes, it also fulfills our definition of a

gene But the resemblance goes further—it has been

found by Gratia that the substance may, through appro-

priate treatments on other bacteria, become changed (so

as to produce a somewhat different effect than before,

and attack different bacteria) and still retain its self-

` propagable nature.

That two distinct kinds of substances—the d'Hérelle

substances and the genes—should both possess this most

remarkable property of heritable variation or ‘‘ muta-

bility," each working by a totally different mechanism,

is quite conceivable, considering the complexity of proto-

plasm, yet it would seem a curious coincidence indeed. It

would open up the possibility of two totally different

kinds of life, working by different mechanisms. [ On the

other hand, if these d'Hérelle bodies were really genes,

fundamentally like our ehromosome genes, they would

give us an utterly new angle from which to attack-the

gene problem. They are filterable, to some extent isol-

able, ean be handled in test-tubes, and their properties,

as shown by their effects on the baeteria, ean then be

studied after treatment. It would be very rash to eall

these bodies genes, and yet at present we must confess

that there is no distinetion known between the genes and

them. Hence we can not categorically deny that perhaps

we may be able to grind genes in a mortar and cook them

in a beaker after all. Must we geneticists become bae-

8 D'Hérelle himself thought that the substance was a filterable virus para-

sitie on the bacterium, called forth by the host body. It has since been

found that various bactcria each cause the production of D’Hérelle sub-

stances which are to some extent specifie for the respective bacteria.

No. 642] VARIATION IN INDIVIDUAL GENE 49

teriologists, physiological chemists and physicists, simul-

taneously with being zoologists and botanists? Let us

hope so.

I have purposely tried to paint things in the rosiest

possible colors. Actually, the work on the individual

gene, and its mutation, is beset with tremendous difficulty.

Such progress in it as has been made has been by minute

steps and at the cost of infinite labor. Where results are

thus meager, all thinking becomes almost equivalent to

speculation. But we can not give up thinking on that

account, and thereby give up the intellectual incentive

to our work. In fact, a wide, unhampered treatment of

all possibilities is, in such cases, all the more imperative,

in order that we may direct these labors of ours where

they have most chance to count. We must provide eyes

for action.

"The real trouble comes when speculation masquerades

as empirical fact. For those who cry out most loudly

against ‘‘ theories ’’ and ‘‘ hypotheses ’’—whether these

latter be the chromosome theory, the factorial ‘‘ hypoth-

esis," the theory of crossing over, or any other—are

often the very ones most guilty of stating their results

in terms that make illegitimate implicit assumptions,

which they themselves are scarcely aware of simply

because they are opposed to dragging ‘‘ speculation "'

intothe open. Thus they may be finally led into the worst

blunders of all. Let us, then, frankly admit the uncer-

tainty of many of the possibilities we have dealt with, us-

ing them as a spur to the real work.

LITERATURE CITED

Blakeslee, A. F,

1920. A Dwarf Mutation in Portulaca showing Vegetative Reversions.

oura, Vol. 5, pp. 419-433.

Bridges, C. B.

1917. Deficiency. Genetics, Vol. 2, pp. 445—465.

Bridges, C, B.

1919. The Developmental Stages at which Mutations Oeeur in the Germ

Tract. Proc. Soc. Exp, Biol. and Med., Vol. 17, pp. 1-2.

Bridges, C, B.

1921. Genetical and Cytological Proof of Non-disjunetion-of the

50 THE AMERICAN NATURALIST [Vor. LVI

Fourth Chromosome of Drosophila me'anogaster. Proc. Nat.

Acad. Sci., Vol. 7, pp. 186-192.

D'Hérelle, F.

1917. Compt. rend. Acad., Vol, 165, p. 373.

1920. Compt. rend. Soc. Biol., Vol, ise pp. 52, 97, 247.

Emerson, R.

1911. The Inheritance of a Recurring Somatic Variation in Variegated

Ears of Maize. Amer. NAT., Vol. 48, pp. 87-115.

Gratia, A.

1921. Studies on the D'Hérelle Phenomenon. Jour, Ezp. Med., Vol.

34, pp. 115-126, à;

Mavor, J. W,

1921. On the Elimination of the X-chromosome from the egg of Dro-

sophila melanogaster by X-rays. Science, N. S., 54, pp. 277-

279,

Mohr, O. L.

1919. Charaeter Changes eaused by Mutation of an Entire Region of

a Chromosome in Drosophi'a. Genetics, Vol. 4, pp. 275-282.

Muller, H. J.

1920 Mine Changes in the White-eye Series of Drosophi'a and their

aring on the Manner of Occurrence 9t Mutation. Jour.

Rep . Zool., Vol. 31, pp. 443-473.

Muller, H. J., and E Altenburg.

1919. The Rate of Change of Hereditary Faetors in Drosophila.

Proc. Soc. Exp. Bio’. and Med., Vol, 17, pp. 10-14

Muller, H, J. and E. Altenburg.

1921. A Study of the Character and Mode of Origin of 18 Mutations

in the X-ehromosome of Drosophila. Anat, Rec., Vol. 20, p.

213.

Nilsson-Ehle, H,

1911. Ueber Fälle spontanen Wegfallens eines Hemmungsfaktors beim

a Zeit. f. Ind. Abst. u. Vererb., Vol. 5, pp. 1-37.

Nilsson-Ehle, H.

1920. — Allelomorphe und oo beim Weizen.

Hereditas, Vol. 1, pp. 277-312

Troland, L. T.

1917. Biological Enigmas and the Theory of Enzyme Action. AMER.

Nart., Vol. 51, pp. 321-350,

Wollstein, M.

1921. gone on the Phenomenon of D'Hérelle with Bacillus dysen-

tarie. Jour. Exp. Med., Vol. 34, pp. 467-477.

Zeleny, C.

_ 1920, The Direction and Frequency of Mutation in a Series of Multiple.

Allelomorphs. Anat, Rec., Vol. 20, p. 21

Zeleny, C.

1921. The Direction and Frequency of Mutation in the Bar-eye Series

of Mu ultiple Allelomorphs of Drosophi'a. Jour. Exp. Zool.,

Vol, 34, pp. 203-233.

THE ORIGIN OF VARIATIONS IN SEXUAL AND

| SEX-LIMITED CHARACTERS

DR. CALVIN B. BRIDGES

COLUMBIA UNIVERSITY

Ix dealing with sex and its determination, attention has

been most sharply foeused upon forms with separate

sexes and upon the visible differences between the chro-

mosome groups of the two sexes. The result has been

that the formulation of sex-determination has remained

in terms of chromosomes, while the modern unit of deter-

mination is the gene; and also the subject of sex has been

rather separated off from the main body of heredity. My

diseussion will be largely a process of resolving chromo-

somes into component genes, and showing that the con-

ception of the nature and action of genes as gained from

the study of non-sexual characters is valid in interpreting

sex phenomena.

The facts of mutation and of linkage have given us the

conception of a gene as a distinct chemical entity having

a definite location in a particular chromosome. Each

gene is essentially a factory, which is manufacturing a

characteristic set of chemical products that are delivered

to the common cytoplasm, and that produce development

through interaction with each other and with materials

from outside. But since the chemicals produced by the

different genes are different, some genes will have muck

effect upon one character and little effect upon another,

so that a relatively small proportion of the genes will be

actively concerned in producing any given character.

Some of these genes tend to make the character more pro-

nounced, and others tend to make it less pronounced, so

that the grade of development actually realized by each

particular character will be determined by the equilibrium -

between its modifying genes. The forms into which a

given character can be modified are in general quite di-

verse, but for the sake of simplicity we may call them all

plus or minus modifications. If the effectiveness of a

given plus or minus modifier is changed by mutation, the

grade of the character will shift correspondingly.

We can conceive of the evolution of the sexual

52 THE AMERICAN NATURALIST [Vou. LVI

characters of hermaphrodites in terms of successive

simple mutations in genes. But to interpret male `

and female forms with observed differences in number or

size of chromosomes and with sex-linked inheritaiee re-

quires comparison with mutations in which the unit of

change is a whole chromosome or section of chromosome

instead of a single gene. Such mutations can be under-

stood in terms of the action of component genes as fol-

lows. Linkage experiments show that the various kinds

of genes are distributed pretty much at random among

the various chromosomes and along each chromosome.

But since the number of genes with a given tendency is

relatively small, any particular small section of chromo-

some might not contain these genes in the same propor-

— tion as they exist in the entire complement, and still less

would the normal proportion of every kind be present.

The loss of a section of ehromosome (a eondition known

as deficiency) would ordinarily remove more minus than

plus modifiers (or vice-versa), and since in that case more

plus than minus modifiers would remain in action, the

grade of the corresponding character would be shifted in

a minus direction. This is the interpretation of the fact

that a deficiency may cause many character changes, the

complex of altered characters being inherited as a domi-

nant. When a whole chromosome is lost through non-

disjunction, the effects are similar to those in deficiency

for a section except that they are greater in degree.

The way in which genes act together in producing

a character, and the relation of the balance of plus and

minus modifiers to deficiency or to the absence of a chro-

mosome may perhaps be made clearer by an analogy.

Let us suppose that a man is an ardent stamp collector,

and has accumulated a lot of stamps. These stamps are

to represent genes, so their number may be put at 5,000 to

correspond roughly to the number of genes in Drosophila.

Among the Russian stamps, especially those of recent

issue, there is a very large number of reds, but also a fair

number of pinks, and even a few whites. These differ-

ences in tint correspond to the plus and minus modifiers

of a certain character, namely, the redness of Russian

stamps. Now the stamps of different tints are in some

definite ratio, whatever that ratio is, and we will call it the

No. 642] VARIATION IN SEX CHARACTERS 53

normal ratio or balance. This stamp collector carries

his collection around with him, and it fills two big, coat

pockets, a trousers pocket, and there are even a few in his

vest pocket. But unlike most collectors this one has

never taken the trouble to sort over more than a few of

his stamps. Meanwhile he strings them together pretty

much hit or miss. This stringing stamps together is

rather disapproved of by some other stamp collectors,

who think that is no way to treat stamps, and each of

whom has his own favorite method of arranging them.

Because of this hit or miss method of making the strings

of stamps the ratio among the different grades of redness

of Russian stamps is different in different parts of the

strings, and so if some other ardent collector should snip

off a piece of one of the strings and earry it away, the re-

mainder of the Russian stamps might have a eonsiderably

redder tone, while at the same time the Polish stamps

might become bluer. If a whole string were lost, then

many of the sets of stamps might have quite different

complexions. i

Now I have been recently studying the effects of the

loss of one of the ehromosomes of Drosophila, namely,

the small round fourth-chromosome, and the phenomena

offer striking parallels to those of dicecious sex, including

sex-linked inheritance and sex-limited characters. Indi-

viduals having only one fourth-chromosome show a

change in many characters, among which may be men-

tioned smaller size, smaller bristles, later hatching, poorer

viability, paler body-color, darker trident pattern, shorter

blunter wings, ete. Each of these differences corre-

sponds to a character for which the fourth-chromosome

was internally unbalanced, that is, for which the ratio of

plus to minus modifiers was different from that of the

whole group. For all of the characters in which there

was an internal preponderance of plus modifiers the

grade will be shifted in a minus direction by the loss of

the fourth-chromosome, for example, the shorter wings

and paler body-color. Likewise the characters that shift

in a plus direction, as the darker trident pattern and the

large eyes, are characters for which the fourth-chromo-

some possesses an excess of minus modifiers. In the

1 Proc. Nat’l Acad, of Sci., 7: 186-192.

54 THE AMERICAN NATURALIST [Vor.LVI

male of Drosophila there is only one X-chromosome,

though there is present a Y-chromosome that ean be dis-

regarded, since the evidence from non-disjunetion of the

X-chromosome shows that it has very little effect upon

sex or characters. These individuals with only one X-

Fic. 1. Wild-type (2n) female, with normal chromosome group.

chromosome likewise show a complex of characters that

are different from those shown by the individuals with the

normal two X-chromosomes. Among these characters

are gonads and genitalia of a type that we call male. The

haplo-X individual is also smaller, has smaller bristles,

is less viable, hatches later, and differs in other details

from the 2-X type that we call female. Each of these dif-

ferences likewise corresponds to a character for whieh

the balance of the genes in the X is different from that in

the’ group as a whole. The absence of one X leaves in

action an unbalanced set of genes which produces male

characters. The X-chromosome is a chromosome that is

internally unbalanced by an excess of genes that we may

eall female-producing.

No. 642] VARIATION IN SEX CHARACTERS 55

In an outeross of a haplo-IV individual to a normal,

the entire complex of characters is inherited as a simple

dominant and gives a 1:1 ratio, except that the haplo-

IV's are less viable. Likewise in outerosses of haplo-X

individuals the entire complex of male characters is in-

fic. 2. Haplo-IV (2n-1 IV) female, with chromosome group.

herited as a simple dominant and gives a 1 : 1 ratio except

that the haplo-X's are somewhat less viable.

When a haplo-IV individual is mated to a recessive

whose gene is in the fourth-chromosome, all the haplo-

fourth offspring show this recessive—a behavior that is

strictly parallel to sex-linked inheritance; for if a haplo-X

individual, that is, a male, is mated to a recessive whose

gene is in the X, all the haplo-X offspring show this re-

cessive.

The fourth-chromosome recessive characters present in

haplo-IV individuals from the cross of a haplo-fourth to

the recessive show a grade of development that is differ-

ent from their grade as homozygous characters in diplo-

IV's. This phenomenon is known as ‘‘ exaggeration,”’

and is interpreted as the effect of an unbalance within the

56 THE AMERICAN NATURALIST [Vor. LVI

normal fourth-chromosome. With respect to a character

that is exaggerated in a plus direction the fourth-chromo-

some has an unbalance in the minus direction. But since

the whole complement is in balance, this unbalance within

the fourth-chromosome is neutralized by a reciprocal un-

balance in the other chromosomes. So the removal of

one fourth-chromosome with its excess of minus modifiers

leaves the remainder of the genes with an excess of plus

modifiers, and these plus modifiers are free to work in

the same direction as the recessive gene that is present,

and thus to give an even greater effect than the homo-

zygous recesive. Corresponding to these exaggerated

fourth-chromosome characters there is a class of sex-

linked characters that are exaggerated in the absence of

one X-chromosome. These mutant characters show a

different grade of development in the male from that

which they show in the female. A good example is the

race called eosin, in which the male has a much paler eye-

color than the eosin female. These characters exagger-

ated by the absence of an X are called sex-limited. Some

of them, like eosin, are exaggerated in a plus direction,

corresponding to an excess of minus modifiers within the

X-chromosome, while others, such as bobbed, are exag-

gerated in a minus direction. Thus bobbed, which shows

searcely at all in the males, corresponds to an excess of

genes within the X tending to make bristles short, and two

X-chromosomes can outweigh the genes in the autosomes

that tend to make the bristles long, but one X is not

enough to do so.

When haploidy for the fourth-chromosome is combined

with mutants whose genes are outside the fourth-chromo-

some there is of course no effect corresponding to sex-

linkage, but there is ‘‘ exaggeration.” Thus, haploidy

for the fourth-chromosome exaggerates the third-chromo-

some mutant Hairless in a plus direction. This type

of exaggeration finds its parallel in the 20 or so sex-

limited mutations that are not sex-linked. These are

mutations whose differential genes are in the autosomes

and not in the X and which nevertheless show a different

grade of development in the male from that in the female.

In these cases also the modifiers of each character are of

different weights in the X from the general collection,

No. 642] VARIATION IN SEX CHARACTERS 57

and absence of one X leaves a surplus of genes that work

in the same or in the opposite direction from that of the

mutant in question.

Thus, by studying three kinds of effects, first, the

character complexes that result directly, secondly, the

exaggerations of the mutant characters whose genes are

in the same section or chromosome as that involved in the

loss, and thirdly the exaggerations of mutant characters

whose genes are in other regions, we can analyse roughly

the kinds and the signs of the genes that are in the region

in question.

Since sexual and sex-limited characters are shown to

rest on the same genetic basis, namely, a preponderance

within the X of the plus or the minus modifiers of those

characters, it may be questioned whether there js any real

difference between these two categories. If the race of

the mutant eosin were to become established in nature, a

systematist would certainly include this difference in

eye-color among his sexual differences. I am of the

opinion that there is no difference between these two cate-

gories except that we call those sexuał that are most

closely connected with reproduction.

There is one striking difference between haploidy for

X and haploidy for an autosome—namely, that the

changes connected with haploidy for autosomes are rela-

tively more numerous and extreme. Haploidy for the

second or third autosomes probably produces changes so

great as to be lethal, while haploidy for the very small ©

fourth-chromosome produces changes comparable in ex-

tent to all those of the male aside from the reproductive

organs. The proportion of sex-limited mutant charac-

ters is only about a tenth of the total, while X contains

about a quarter of the genes. Since the changes in char-

acter produced by absence of an X are relatively small,

the internal balance of the X must be relatively high.

For a high proportion of the characters of the animal, the

plus and minus modifiers in the X must be in about the

same ratio as in the group as a whole.

The comparison just made between the effects of hap-

loidy for an autosome and the effects normally present m

dicecious sex shows that they have similar genic bases—

namely, each is due to differences in the ratio between two

58 THE AMERICAN NATURALIST [Vor. LVI

aggregates of genes; and that the X produces its char-

acteristic effects because it contains a preponderance of

genes tending to produce the characters that we call fe-

male. This point of view receives even stronger and

more direct support from a study of cases in which the

f KY

Tre

vun mm f

Fic. 3. Triploid (3n) female, with chromosome group.

ratio of X-chromosome to autosomes has been changed,

and in which new sex relations are present. These new

types of chromosome combinations and of sex take their

origin in the occurrence of triploidy in Drosophila, for

which there is full genetical and cytological proof. The

first point is that individuals having three full sets of

chromosomes (3n) are females not to be distinguished

from normal females except for slight differences in size

and proportion that may well be due simply to the greater

2 Science, N. S., 54: 252-954.

No. 642] | VARIATION IN SEX CHARACTERS 59

amount of chromatin. The nearly complete identity be-

tween the triploid and diploid forms both as to sex and as

to non-sexual characters is a splendid evidence that these

characters owe their grade to the ratios among the genes,

for those ratios are identical in the 3n and 2n forms.

Among the offspring of triploid females are individuals

that are neither males nor females but are sex-interme-

diates, or rather, are mixtures of male and female char-

acters, very similar in type to the intersexes of Lyman-

iria? Genetical and cytological proof was obtained that

these intersexes in Drosophila possess two X-chromo-

somes and three sets of autosomes. The old formulation

of 2X equals 9 is at once seen to be inadequate, for here

we have individuals that have two X-chromosomes and

yet are not females. They are shifted out of the female

class by the presence of an extra set of autosomes, and

thereby the autosomes are proved to play a positive role

in the production of sex. Since the intersexes differ

from females by the assumption of certain male charac-

ters this effect of the autosomes is due to an internal pre-

ponderance of ‘‘ male-tendency "' genes.

We may now formulate the sex-relations as follows:

both sexes are due to the simultaneous action of two op-

posed sets of genes, one set tending to produce the char-

acters called female and the other to produce the char-

acters called male. These two sets of genes are not

equally effective, for in the complement as a whole the

female-tendency genes outweigh the male-tendency genes

and the diploid (or triploid) form is a female. When

the relative number of the female-tendency genes is low-

ered by the absence of one X, the male-tendency genes

outweigh the female and the result is the normal haplo-X

male. When the two sets of genes are acting in a ratio

between these two extremes, as is the case in the ratio of

2X: 3 sets autosomes, the result is a sex intermediate—

the intersex.

The intersexes as a class can always be easily distin-

guished from normal males and females by reason of

their large size, large coarse-textured eyes and by certain

other characters such as scalloped wing-margins. Some

- of these characters are probably non-sexual effects of the

3 R. Goldschmidt, Zeit. f. ind. Abst. u. Vererb., 23: 1-199.

60 . THE AMERICAN NATURALIST [Vor. LVI

triploidy for the autosomes, others are sex-limited.

Within the elass of intersexes there is a very wide range

of fluetuation, on the one hand to flies that are nearly fe-

male and on the other to flies that are entirely male in

appearance. In an intersex of a given grade the several

N '

Un. »

L Y

N à

4. Dorsal and ventral views of extreme Peces eel intersex. Ventral

view of mid-grade intersex. Chromosome group of intersex showing 2X and 3

sets autosomes.

characters do not all present the same intermediate step

between male and female, but, apparently just as in the

intersexes of Lymantria, some characters are completely

male, some completely female, while others are complex

mixtures of male and female parts. When the intersexes

are classified according to a system of grades, they are

seen to be a bimodal class consisting of more ‘‘ female-

type " and more ‘‘ male-type "' intersexes, both of which

fluctuate widely and overlap considerably.

The cytological investigation of the intersexes had

shown that there are four sub-types of intersexes that

differ in the presence or absence of a Y and in having

three or only two fourth-chromosomes. It is possible,

and there is some slight cytological and genetical evi-

dence in support, that the male- and female-types of

No. 642] VARIATION IN SEX CHARACTERS 61

intersexes correspond to the presence of three or of two

fourth-chromosomes respectively.

There is another connection in which the wide fluctua-

tions of the intersexes are interesting, namely, the aetion

(

H R f

D. I p 1 7/ m

NBS AA TUA

nma m my WE

Fic. 5. Dorsal and nai ipe of extreme female-type intersex. Two

chromosome groups, the left with two IV-chromosomes and a Y, the right

with two IV's but no Y

of environmental factors. The slight range of fluctua-

tion in such a character as miniature-wings in Drosophila

probably means that there is a critical balance or ratio

of plus to minus modifiers beyond which all balances

give miniature, at least until the overbalance proceeds so

far that a new critical ratio is passed and a new super-

miniature character is realized. The balance in minia-

ture is so far beyond the critical balance that only rarely

are the environmental factors strong enough to outweigh

this overbalance and thus cause fluctuation. In mutants

in which the overbalanee is slight there will be both wide

fluetuation due to environmental interference and a high

susceptibility to modification by other genes, as 1S no-

toriously the case with Beaded and with Truncate.

In normal males and females there are high overbal-

ances beyond the critical points, and consequently only

slight genetical or fluctuating variations. But in the in-

62 THE AMERICAN NATURALIST

[Vor. LVI

tersexes these two overbalances in opposite directions

cancel each other, and since the two sets of genes are now

of almost exaetly the same weight the point of balance is

between the two eritieal balances.

Accordingly the char-

Fic. 6. *''Superfemale" (2n+X), with two chromosome groups.

acters of the intersex fluctuate widely with slight environ-

mental differences, and fall into two modes corresponding

to the slight difference in balance between two and three

of the tiny fourth-chromosomes.

RELATION OF SEX TO CHROMOSOMES IN Drosophila me anogaster

X-chromo-

Sex somes

Buperiemale. 5s ei es 3

aage le Tt PEPEE E ee wee 3

Female

diio a OE pepe EN 2

—bDUDO Leve LS TERR EVEN 2

Intersex

HVE is Lu IRE CIR 2

Male.) eov our TEES 1

Buüpermalé >i iaooank a ae E Era oe 1

Sets Autosomes| Sex Index

B. 1.5

3 1

2 1

3(—IV) a 67+

3 .67

2 5

3 33

The phenomenon of intersexuality might be expected

to have a reciprocal phase—namely, supersexes.

If the

No. 642] © VARIATION IN SEX CHARACTERS 63

intersexes result from an intermediate ratio of X to auto-

somes because the X has a net female tendency, then it

might be expected that by increasing the ratio of X to

autosomes a superfemale would be produced, and con-

versely, a supermale by increasing the relative number of

rA DANS u

DANT,

tA n

Pig; i Supermale.” No cytological SAIS genetical tests show 1X

and 3 sets autosomes.

autosomes. Diploid individuals with an extra X-chromo- .

some (2n plus X) have now been identified among the

progeny of certain strains of high non-disjunction, among

the offspring of triploid females and elsewhere. These

flies resemble females but are very inviable and form a

distinet character type. They are sterile and sections of

the gonads show abnormal ovaries. These differences

all result from the unbalance within the X, and are there-

fore of the sexual-sex-limited category. That these dif-

ferences are not greater is partly due to the same high

internal balance of the X that we met with in analysing

males and intersexes, and is partly to be explained on the

ground that for many of the characters the overbalance

is not yet great enough to pass a second critical point.

Conversely, individuals with one X-chromosome and

an extra set of autosomes have been identified among the

offspring of triploid females. These are males distinctly

different from normal males and sterile.

If there were time, it would be interesting to supple-

ment and modify the view just presented by comparisons

with the rich materials elsewhere, and perhaps to specu-

late as to how this machinery was evolved, and how the

genes involved come to expression physiologically.

THE NATURE OF BUD VARIATIONS AS

INDICATED BY THEIR MODE

OF INHERITANCE'

PROFESSOR R. A. EMERSON

CoRNELL UNIVERSITY

Tue title limits this account to such bud variations as

have been studied critically with respect to their inheri-

tance in sexual reproduction. The further limitation of

time makes it necessary that I choose from among such

studies certain cases to serve as illustrations of the sev-

eral types of bud variation. I shall, therefore, attempt

no complete review of the researches bearing on the prob-

lem at hand.

A survey of published accounts of bud-variation studies

shows that as yet comparatively little is definitely known

of the real nature of these vegetative sports. It seems

not unlikely, however, that to point out some of the prob-

lems suggested by these studies and, where possible, to

note modes of attack may serve the purpose of this sym-

posium quite as well as a rehearsal of known facts and

their interpretation.

As here used, the term bud variation is synonymous

with vegetative as contrasted with seminal variation.

The term somatic variation may also be employed to the

same effect, provided it is not thereby intended to exclude

cases in which the germ tract as well as the soma is in-

volved. At the outset, however, there must be imposed

on any of these terms, for the purpose of this discussion

at least, the limitation that the variation involves a

change in the genetic constitution of the parts affected.

The expressions somatic mutation and somatic segre-

gation are specific terms and as such are not to be used

interchangeably with the more general terms somatic,

vegetative, or bud variations. Moreover, to speak of a

particular vegetative variation as a case of somatic muta-

1 Paper No. 94, Department of Plant Breeding, Cornell University, Ithaca,

New York.

No. 642] . NATURE OF BUD VARIATIONS 65

tion or of somatic segregation without basis from critical

inheritance or cytological studies is to prejudge the

nature of the observed modifieation.

FREQUENCY or Somatic VARIATIONS

Attempts have been made to estimate the relative fre-

quency of vegetative and seminal variations in plants, but

little definite information has been gained. The problem

is beset with grave diffieulties inherent in most attempts

to determine coefficients of mutability. The possibility

of overlooking even prominent variations until they have

once been noted, together with the readiness with which

they are found after one’s attention has been focused on

them, will hardly be questioned by anyone who has given

attention to the discovery of new variations in almost any

organism. One may attempt with some assurance an

estimation of the frequency of recurrence of a particular

mutation, for instance, whether it appears in vegetative

parts of individuals or in sexually produced progenies,

but it is a hazardous undertaking to estimate the fre-

quency of variations in general. Until some one can de-

vise a scheme for estimating the frequency of bud varia-

tions as Muller has done for determining mutation fre-

quencies in Drosophila, little progress can be looked for

other than through investigations of the somatic muta-

tion or segregation of specific genes.

The problem of the relative frequency of occurrence of

somatie and gametie variations meets the further diffi-

culty that it is often impossible to determine the ontoge-

netie stage at which particular variations have arisen—a

faet that has been noted for plants by various writers

(deVries, 1910; Emerson, 1913; East, 1917). Both

Bridges (1919) and Muller (1920) have discussed this

problem from the standpoint of studies of partieular mu-

tations in Drosophila. The prevalent opinion that varia-

tions arise in the gametes or at about the time of their

formation may have come in part from a belief that aber-

rant chromosome behavior is most likely to occur at the

time of the reduetion division. It seems likely, however,

that the situation has been confused by failure to realize

66 THE AMERICAN NATURALIST . [Vou.LVI

that recessive mutations—the most frequent kind—can

not be expressed in the individual in which they occur

except when the dominant allelomorph is simplex, while

such mutations may appear in a later generation of sexu-

ally produced progeny (East, 1917).

Somatic Mutation OF GENES

Several cases of vegetative variation in plants have

been studied with sufficient thoroughness to leave little

doubt that they are mutations in the strict sense, in-

volving the modification of particular genes. Most of

them are concerned with variegated color patterns of

flowers, leaves, or fruits, and they are more or less regu-

larly recurrent, a fact that makes them especially well

suited to quantitative studies, for it is obvious that a

quantitative study can be made only of variations that

occur. with considerable frequency. For the most part

also these somatic mutations are dominant to the type

from which they spring, appearing frequently in material

homozygous for their recessive allelomorphs, facts that

exclude the possibility of their being due to any sort of

somatic segregation of unlike genes. Blakeslee’s (1920)

case of a somatic variation in Portulaca is one of the few

examples not involving variegation. Other cases have

been reported by Baur (1918).

One of the earliest cases of somatic mutation was re-

ported by deVries in variegated flowers of Antirrhinum.

Though the work was done prior to the rediscovery of

Mendelism and not discussed from the standpoint of re-

cent genetic interpretation, there is little doubt, as I have

noted elsewhere (Emerson, 1913), that the results can

best be interpreted as due to a somatie gene mutation.

Correns's (1910) results with respect to the occurrence

and behavior in inheritance of green-leaved variations on

variegated-leaved Mirabilis and of self-colored flowers

on variegated flowered strains of the same species were

among the first to be subjected to critical genetic analysis.

The behavior in inheritanee of green branches of varie-

gated Mirabilis shows this vegetative variation to be a

simple dominant mutation affecting ordinarily only one

. of the duplex recessive allelomorphs. A mutated branch

No. 642] NATURE OF BUD VARIATIONS 67

is, therefore, as truly a heterozygote as if it had arisen

through hybridization of green and variegated strains.

Self-colored branches on variegated-flowered plants of

Mirabilis usually do not transmit the self-color character

to their seed progenies in greater percentages than do

variegated-flowered branches of the same plants. They

are thought by Correns to be fundamentally of the same

nature as the green branches of variegated-leaved plants,

their failure to transmit the self-color character being due

presumably to the accident that the mutation occurs in

epidermal cells from which no gametes arise. The fre-

quent occurrence of self-colored plants in seed progenies `

both of self-colored and of variegated flowers is consid-

ered evidence of their origin as vegetative rather than as

gametic mutations, their failure of expression in the

soma being thought due to their origin in sub-epidermal

cells in which these flower colors do not develop.

Studies of variations in variegated pericarp of maize

by myself (Emerson, 1914, 1917) and by Anderson,

Eyster, and Demeree;? involve practically the same results

as those so far reported in investigations of other species

and afford in addition quantitative data on certain as-

pects of the somatic-mutation problem not included in

other investigations. The genes for variegated pericarp

have been shown to belong to a comparatively large series

of multiple allelomorphs including those for colorlessness

(white seeds), self color of different intensities, and cer-

tain definite color patterns of both the pericarp of the

seeds and the glumes and pales of the cobs. Variegation

is known to be a simple recessive to self color and a domi-

nant to white.

Self-colored seeds whether occurring singly or in

groups in variegated ears produce progenies consisting

of approximately 50 per cent. self-colored ears, the other

50 per cent. being either all variegated or all white de-

pending on whether the parent was homozygous varie-

gated, V V, or heterozygous variegated, V W, from a pre-

vious cross with white. Seeds that are less than wholly

self colored throw a correspondingly smaller per cent. of

2 Unpublished data by W. H. Eyster and E. G. Anderson, and by E. G.

Anderson and M, Demeree,

68 THE AMERICAN NATURALIST . [Vor.LVI

self-colored ears. Self-colored seeds thus produced have,

so far as tested, proved to be heterozygous for self color,

behaving in later generations exactly as if produced by

crosses of self-colored with variegated or with white

races.

Certain cultures of self-colored maize produce a few

variegated seeds. Such seeds have been observed only

on ears that are heterozygous from previous crosses with

variegated strains, S V, or with white strains, S W, never

from ears that are homozygous for self color, S S. From

such variegated seeds, new variegated races have been

produeed.

These facts are regarded as indicating (1) that the oe-

currence of self-colored or partly self-colored seeds on va-

riegated ears is due to somatic mutations of the recessive

variegation gene to the dominant self-color allelomorph;

` (2) that only one of the two variegation genes of homo-

zygous variegated maize mutates at a given time; (3)

that it is always the variegation gene, never the white one,

of heterozygous material that mutates; (4) that the oe-

currence of variegated seeds on otherwise self-colored

ears is due to reverse mutations from the dominant self-

color gene to the recessive variegation allelomorph; and

(5) that only one of the duplex genes of self-color strains

so mutates at any one time, for otherwise there would re-

main no dominant self-color gene to prevent the expres-

sion of the mutation as variegated seeds in Hungop.

self-colored material.

Another type of somatie variation, quite distinet from

the self-color mutations discussed above and often termed

dark-erown variation, also occurs frequently in varie-

gated maize pericarp (Emerson, 1917). It is quite as

striking in appearanee as the self-color mutation, but is

not inherited, the progenies of the aberrant seeds being

in no way different from those of the normal seeds of the

same ears. Microscopic examination of dark-erown and

of self-color seeds indieates that in the former the epi-

dermis alone is colored while in the latter the epidermis

alone remains colorless. The conclusion seems war-

ranted, therefore, that the two types of variation are fun-

damentally the same, both being true gene mutations, and

No. 642] NATURE OF BUD VARIATIONS 69

that the non-inheritance of the dark-erown type is due to

the accident that it occurs in epidermal tissue outside the

germ traet.

Recent investigations of variegated maize by Eyster

and Anderson have established the fact that somatic mu-

tations affecting small areas occur much more frequently

than those affecting large areas. Since a mutation aris-

ing in a single cell late in development obviously could

not affect so large an area as one originating earlier, it

follows that mutations in variegated maize occur with

increasing frequency in the later stages of ontogeny. It

is true, as pointed out by Muller (1920), that given a con-

stant rate of mutation throughout all stages of ontogeny

and granting that one cell is as likely as another to mu-

tate, mutations should appear more frequently in the

later stages of development because of the fact that there

are then many more cells in which mutations may arise.

But Eyster and Anderson have found that the increase in

the frequency of occurrence of mutations during the

progress of development is accelerated far beyond ex-

pectation based on the increase in number of cells.

This behavior is strongly suggestive of a progressive

acceleration in the mutability of the variegation gene as

development proceeds. It is much too early to say

whether this progressive change, if such it be, is inherent

in the organization of the gene itself, as suggested by

Anderson and Demeree, or whether it is a response to

progressive changes in physiological and environmental

relations. Perhaps the assumption of an equal chance of

mutation as between any two cells is without sufficient

warrant. Possibly there is a time element to be taken

into account, as noted by Muller (1920). As cell division

becomes progressively retarded in the late growth stages,

may not each cell be exposed for an increasingly longer

period of time to the chance of mutation? Perhaps it

may be possible to test this assumption in favorable ma-

terial by a comparison of the frequency of mutation in

the very early slow-growth, the later rapid-growth, and

the final slow-growth periods of the life cycle; but the

relatively few cells present in the very early growth

period seems likely to place serious limitations on the

70 THE AMERICAN NATURALIST [Vou.LVI

practicability of such a test. An observation of possible

importance in connection with the question of a time ele-

ment in mutation and with the problem of environmental

and physiological influences is that made by Eyster and

Anderson concerning the greater frequency of the non-

heritable (epidermal) mutations than. of the heritable

(sub-epidermal) ones in variegated pericarp of maize.

I have recently obtained results bearing on another

phase of the somatie-mutation problem as related to

variegated maize pericarp, namely, the relative frequency

of mutation of homozygous, V V, and of heterozygous, V

W, material. It has been shown above that the W gene

for colorless (white) pericarp does not mutate, so far as

known, when paired either with itself, W W, with the va-*

riegation. gene, V W, or with the self-color gene, S W.

It will be recalled further that only one of the two homolo-

gous genes in homozygous variegated, V V, material mu-

tates at any one time. If it could be assumed that the

mutability of either allelomorph is uninfluenced by the

presence of the other, it should follow that somatic muta-

tions will occur with approximately twice the frequency

in homozygous, V V, as in heterozygous, V W, material.

But this expectation has not been realized. On the con-

trary, both heritable (self-color) and non-heritable (dark-

crown) mutations have appeared throughout all my cul-

tures with somewhat greater frequency in heterozygous

than in homozygous variegated ears. The difference has

been especially pronounced in very light variegated

strains, where mutations have appeared about two and

one half times as often in heterozygous as in homozygous

material. Even if mutations appeared with equal fre-

queney in heterozygous and in homozygous ears, the

simplex gene of the former must have a mutability of

about twice that of either of the,duplex genes of the

latter. In the very light variegated strains, therefore, a

simplex gene must have a mutability of about five times

that of a duplex gene.

What appears to be a similar result in Mirabilis has

been reported by Correns (1903, 1904). Crosses of a

supposedly pure white race with several self-colored pink

yellow, and pale yellow races resulted in every case in

No. 642] NATURE OF BUD VARIATIONS 71

plants with strongly red-striped flowers and with numer-

ous self red flowers or even whole branches of such

flowers. Intererosses of the pink and yellow races gave

only self-eolored progeny, from which fact it was con-

cluded that the white-flowered race carried a latent factor

for striping. It was later discovered that about three

per cent. of the flowers of the white race showed minute

flecks of red. It was evidently an extremely light, varie-

gated race, rarely if ever throwing somatic self-color

mutations when the variegation gene was duplex (homo-

zygous material) but producing such mutations with con-

siderable frequency when that gene was simplex (hetero-

zygous material). Correns concluded that red variega-

tion of Mirabilis flowers is a character that, with self-

fertilization or inbreeding, remains almost completely

latent, but which, through the entrance of foreign germ

plasms, is brought to full expression.

If the mutability of a gene can be increased through

the influence of some modifying factor or factors brought

into combination with it by crossing, as suggested by

Correns, it should be possible to discover crosses that

= would not produce the effects so far observed in Zea and

Mirabilis. While the problem deserves much more study

from this viewpoint, it seems unlikely that results with

maize can be explained on any such basis, unless the

postulated modifying factor is the allelomorph of the

variegation gene or some factor very closely linked with

it. It must be noted in this connection that the compari-

son in maize was made between homozygous and hetero-

zygous variegated ears of the same F, progenies grown

from self-pollinated F, heterozygotes—a circumstance

that would afford abundant opportunity for recombina-

tions of independently inherited modifying factors. That

the differences in mutability noted in maize may be due

to differences in the interaction of like as contrasted with

that of unlike allelomorphs, as suggested by Anderson

and Demeree, is a somewhat novel conception worth care-

ful consideration if means can be devised for subjecting

it to a.erucial test.

Before the topie of somatie mutation is dismissed, it

should be noted that the pups is not limited to

72 THE AMERICAN NATURALIST [Vor. LVI

plants. Among animals, Drosophila (Morgan and

Bridges, 1919) has furnished several examples of un-

doubted somatic mutation resulting in mosaic individuals

other than gynandromorphs.

SoMATIC SEGREGATION

Bud variations have probably been ascribed to somatic

segregation more frequently than to any one other cause.

Perhaps the opinion commonly held that bud variations

occur more frequently in hybrids than in other material

and the long known fact that seed-grown offspring of

hybrids exhibit segregation, is chiefly responsible for this

usage. It is, of course, possible that most vegetative

variations are of this nature, but the fact that the indi-

viduals in which they arise are frequently found to be

heterozygous for the genes concerned is no conclusive

evidence that segregation is involved. Mutations also,

as noted by several writers, are most likely to appear in

heterozygous material because most of them are recessive

and the unmutated dominant allelomorphs prevent their

expression in the individuals in which they originate if

the latter are homozygous.

Chromosome Elimination.—The best examples of so-

matic segregation that have been subjected to critical

genetic analysis are afforded by the work with Droso-

phila. lt has been shown by Morgan and Bridges (1919)

that, of the relatively numerous gynandromorphs which

have appeared in the course of investigations with Dro-

sophila, nearly all have resulted from the elimination of

the sex chromosome at some early cleavage division. If

a fertilized egg starts as a female, XX, and one X chro-

mosome is eliminated at an early segmentation that part

of the individual developing from the cell that receives

but.one X chromosome should be male, XO, while the re-

maining part should be female, XX.

The evidence in support of this view was obtained from

erosses the parents of which had different sex-linked and

different autosomal characters, that is, characters whose

genes are carried by the sex chromosomes and by the

autosomes, respectively. The male, as well as the female,

No. 642] NATURE OF BUD VARIATIONS 13

side of gynandromorphs appearing in such crosses ex-

hibited all the dominant autosomal characters whether

they eame from the maternal or the paternal parent.

When the mother had a recessive, mutant gene in one of

her autosomes and the father had its dominant, normal

allelomorph, the faet that the male side of gynandro-

morphs did not have the maternal, recessive autosomal

charaeter effeetively disposed of Boveri's hypothesis of

partial fertilization. On the other hand, when a recessive

autosomal gene entered from the father's side and its

dominant allelomorph from the mother's side, the fact

that the male side of the gynandromorphs did not show

the paternal, recessive character likewise eliminated

Morgan's earlier hypothesis of polyspermie fertilization.

It has been shown, further, from erosses, the parents of

whieh differed in sex-linked charaeters, that maternal

and paternal X ehromosomes are eliminated with about

equal frequency. i

In certain experiments with Drosophila, in which a de-

termination of the frequency of sex-chromosome elimi-

nation was undertaken, it was found that one gynandro-

morph appeared in about every 2,200 individuals. Since

only those individuals that start as females give the kind

of gynandromorphs observed in these tests, it was con-

cluded that one ease of chromosome elimination occurs

in about 1,100 individuals.

Of the evidenee from plant material there is the recent

account by Frost (1921) of the occurrence of a bud sport

in Matthiola in which presumably linked genes have

segregated out simultaneously in one or more branches.

While this ease will require further investigation before

the manner of its origin ean be positively established, it

seems probable that it belongs to the category of somatie

segregation by chromosome elimination or non-disjune-

tion.

Studies of mosaie endosperm of maize afford perhaps

the most definite evidence available in plants that certain

somatie variations are due to aberrant chromosome be-

havior such as non-disjunetion or elimination ( Emerson,

1921). The genetic evidence that I have been able to ob-

tain in support of this interpretation is of much the same

74 THE AMERICAN NATURALIST [Von LVI.

nature as that noted above for Drosophila gynandro-

morphs. In crosses in which recessive aleurone and

endosperm characters are contributed by the female

parent and their dominant allelomorphs by the male

parent, spots of the recessive (maternal) aleurone color

are underlaid by the recessive (maternal) type of endo-

sperm when the genes for these aleurone and endosperm

characters are genetically linked, that is, when they are

carried in the same chromosome. On the contrary, simi-

lar recessive (maternal) aleurone-color spots are always

underlaid by the dominant (paternal) type of endosperm

when the genes are not linked, that is, when they are

carried in non-homologous chromosomes. The fact that

linked genes separate out simultaneously while non-linked

ones do not do so supports the view that mosaic seeds are

the result of some chromosome aberration such as elimi-

nation or non-disjunetion, and renders untenable the

earlier hypotheses of incomplete fusion of endosperm

nuclei suggested by Correns and by Webber and also that

of gene mutation proposed by myself.

The work with aberrant maize endosperm has fur-

nished an opportunity to study the frequency of chromo-

some aberrations in a specialized tissue. The available

data show that when a single chromosome alone is con-

cerned, about one mosaic seed occurs in every 420 seeds.

If the other two homologous chromosomes of any one set

are involved as frequently and if any one of the ten trip-

loid chromosome sets is as likely to be involved as any

other one, one ease of aberrant ehromosome behavior

should occur in about every fourteen seeds. There 1s

some evidence, though not convineing as yet, that in dif-

ferent strains of maize chromosome aberrations may

occur with strikingly different frequencies. In one cul-

ture in which only a single chromosome could have been

involved in the origin of mosaic seeds, as many as twenty-

five such seeds have been observed on a single ear of ap-

proximately 500 seeds, or one for each 20 seeds. If this

behavior proves to be a constant one in this strain and if

the other 29 chromosomes behave in like manner, it

should furnish excellent material for cytological investi-

gation. Moreover, the possibility of the existenee of

No. 642] NATURE OF BUD VARIATIONS 75

strains of maize differing so widely in the frequency of

chromosome elimination or non-disjunction raises inter-

esting questions concerning the causes of such aberrations.

It would seem possible to determine by appropriate tests

something as to the relative influence of maternal and of

paternal contributions on the rate of chromosome elimi-

nation.

There are circumstances connected with these results

from Drosophila and Zea that may raise some doubt of

their general applicability to cases of bud variation. The

Drosophila evidence is limited almost exclusively to the

.sex chromosomes, though there is no positive evidence

that elimination may not occur among autosomes and re-

sult in non-viable individuals. The data from Zea re-

lates to endosperm alone, a specialized, nutritive, sterile,

triploid tissue. There is perhaps justification for a be-

lief that the sex chromosomes of animals and the triploid

chromosomes of the endosperm of angiosperms may be

subject to irregularities in behavior not commonly found

in other material. The only answer to such a contention

is (1) that gynandromorphs and endosperm mosaics are

the materials that have been critically studied and (2)

that there is, or should be, no presumption in favor of

vegetative segregation through chromosome elimination

or through other means as against vegetative mutation

or any other mechanism as a possible explanation of bud

variations that have not been subjected to cytological in-

vestigation or to critical genetic analysis.

Cytoplasmic Segregation.—Numerous cases of ap-

parent segregation of cytoplasmic elements have been

reported in plants. Of these, examples from Mirabilis,

Pelargonium, Primula, and Zea may be noted. All of

them involve visible effects on chlorophyll development

and all show non-Mendelian inheritance.

` Correns (1909a, b) working with a white-spotted-leaved

type of Mirabilis observed a very irregular distribution

- of the white and green areas, each varying from small

spots to whole branches. These white and green char-

aeters were found to be inherited through the mother

only. The situation with respect to Pelargonium, re-

w 4 THE AMERICAN NATURALIST [Vot.LVI

ported by Baur (1909), differs from that in Mirabilis in

that the spotting is transmitted through the pollen as

well as through the egg cells. Spotting appeared in F,

in crosses of white with green without respect to which

way the cross was made. As in Mirabilis, wholly white

and wholly green, as well as mosaic, branches were ob-

served.

Examples of maternally inherited chlorophyll variega- ~

tion have been investigated by Gregory (1915) in Primula,

and by Anderson? in Zea. The genetic behavior of these

materials is quite the same as that of Correns’s Mirabilis

variegation. The apparent difference in the cytological :

basis of their behavior, however, must not be overlooked.

Evidently these plants of Mirabilis, Pelargonium,

Primula, and Zea are sectorial chimeras. Their main

interest in connection with this discussion lies in the

fact that, starting with a single fertilized egg cell, certain

chlorophyll deficiencies are apparently separated out into

certain vegetative cells and handed on through definite

cell lines, while normal chlorophyll develops in other cell

lines, with the result that areas of varying extent have

one or the other of these characters. In what the

mechanism of this segregation consists—if segregation

it be—is not in all cases certainly known. It may even

be that some eases of variegated chlorophyll are to be re-

garded as recurrent variations arising de novo after the

manner of somatic mutations but effecting changes in the

cytoplasm, or some of its inclusions, rather than in the

chromosomes. Baur is inclined to the view that in mosaic

plants of Pelargonium deformed chloroplasts are respon-

sible for the chlorophyll deficiencies and that these are

segregated out by chance in cell division. This view is

supported by Gregory, who noted in the young leaves of

variegated plants of Primula the existence of normal and

chlorotic plastids in the same cells. Correns does not

commit himself to any particular element or inclusion of

cytoplasm as the seat of the cause of chlorophyll defi-

ciency. Randolph (1922), from cytological examination

of Anderson’s striped leaved maize, found that, in the

3 Unpublished data,

No. 642] NATURE OF BUD VARIATIONS ? 77

transition regions between the green and the pale-green

areas, the cells contain not only green and colorless plas-

tids, but all intermediate conditions as well. Since the

green and the white plastids are not two sharply differen-

tiated kinds, but are the end members of a continuous

series arising from minute primordia which, so far as ean

be seen, are of one kind, he regards any simple form of

segregation hypothesis as inadequate. It seems possible,

however, that these primordia may be functionally, even

though not morphologically, of two more or less distinct

classes.

Graft-hybrids and Other Chimeras.—' The well-known

graft-hybrids of Solanum reported by Winkler are of

interest from the standpoint of this discussion because of

the bud variations commonly exhibited by them. Sec-

torial chimeras, produced by adventitious buds arising

from the point of union of stock and scion of grafts of

tomato and nightshade, and having one side of the one

species and the other side of the other, have not infre-

quently later produced branches that were periclinal

chimeras having tissues of one species enclosed within an

envelope of the other. That these branches are really

periclinal chimeras has been established by chromosome

counts and by the fact that seedlings produced by them

are always of the species of the subepidermal tissue from

which gametes arise. These periclinal chimeras in turn

have been observed to produce branches wholly of one or

other of the parent species. The marked difference in

appearance between the sectorial and periclinal chimeras

and between the latter and either parent species places

this behavior clearly in the class of bud variation and,

since the production of branches of the parent species

from periclinal chimeras is the result of a separation of

genotypes that were closely united previously, the phe-

nomenon is perhaps rightly classed as a form of vegeta-

tive segregation. It is obvious, however, that the separa-

tion of tissues that are merely closely associated in the

graft hybrid is a fundamentally different type of segre-

gation from that by which the chromosomes or even the

° E

78 THE AMERICAN NATURALIST. [Vor.LVI

plastids or other cytoplasmic elements of a single cell are

dissociated.

The behavior of ‘‘ natural”? periclinal chimeras of

Pelargonium, noted by Baur (1909), and of Pelargonium

and several other forms, described by Bateson (1919), all

of which involve green and white regions of the plants

and some of whieh produce reverse periclinal chimeras,

is fundamentally the same as that of graft-hybrids. The

manner of origin of these natural chimeras is unknown,

but it is quite possible that they arose as somatic muta-

tions.

= The ease of Bouvardia also, as reported by Bateson

(1916), is presumably of quite the same order as the

examples noted above, though its behavior is strikingly

different in detail. Varieties of Bouvardia that are

maintained true to type by propagation from stem cut-

tings produce plants with very different flower form, size,

and color when propagated by root cuttings. While this

behavior is not to be taken as positive proof that these

varieties are natural periclinal chimeras, it is quite in

keeping with such an assumption. Since in normally

produced buds of the stem both the epidermis and the

deeper lying tissues are maintained through direct cell

lineage, while the roots produced by stem cuttings arise

from the plerome and break through the periblem and

dermatogen, forming these parts anew, sprouts that de-

velop from the roots must have the genotype of the stele

rather than that of the cortex or epidermis.

. From the results of critical investigations cited in

this account, it is evident that vegetative variations are

due to diverse causes. Some are certainly due to somatic

mutation of genes; others are as certainly due to chromo-

some aberrations; and still others have been somewhat

definitely shown to involve a vegetative segregation of

plastids or other cytoplasmic elements. There are many

problems relating to these several types of behavior that

are in great need of further critical study both genetic

and cytological. The results of future research will de-

' pend in large measure on the choice of favorable ma-

terial. Quantitative data are of the greatest importance

No. 642] NATURE OF BUD VARIATIONS 79

and from this standpoint no material gives more promise

of fruitful results than that involving variegation.

LITERATURE CITED

Bateson, W. Root-euttings, Chimeras and ‘‘ Sports.’’ Jour. Genetics, 6:

16.

Studies in Variegation. Jour. Genetics, 8: 93-98. 19.

Baur, Erwin. Das Wesen ugs die Erblichkeitsverhiiltnisse der ** Varietates

PRE ESY hort.’’ Von Pelargonium zonale. Zeitschr. indukt, Ab-

. Vererb., 1: 330-351. 09.

pae i von ette majus. Zeitschr. indukt. Abstamm.

Vererb., 19: 177—193.

sap ones A. F. A Dwarf Mutation in Portulaca Showing Vegetative Re-

ns. Genetics, 5: 418-4 920

Bridges, udi B. The Heine Stages at which Mutations Occur in

the Germ Tract. Proc. Soc. Exp. Biol. and Med., 17: 1-2. 1919.

Correns, C. Ueber Basta —M mit Mirabilis-Sippen. Ber.

: 594-608. 1903.

——— Zur Kenntnis der schei werd neuen TAN der Bastarde. Ber.

Deutsch. Bot. Gesellsch., 23:

—— Vererbungsversuche mit a ie ae und buntblattrigen =

pe ei Mirabilis Jalapa, Urtica pilulifera, und Lunaria annua

Zeitschr. indukt, ps Format Vererb., 1: 291-329. 1909a.

Zur Kenntnis der Rolle von Kern und drome bei der Vererbung.

Zeitschr. indukt, Abstamm. Fore, 2: 331-3 909b.

—— Der Übergang aus dem homozygotische is einen heterozygotischen

Zustand im selben Individuum bei buntblättrigen und gestreiftbluhen-

den Mirabilis-Sippen. Ber. Deutsch. Bot, Gesellsch., 28: 418—434. 1910.

. deVries, Hugo. The Mutation Theory (translation by J. B. Farmer and A.

D. Darbi 1910.

Emerson, R. A. The Possible Origin as Mutations i in Somatic Cells. AMER.

NAT., 47: 375-377. 1913.

The Inheritance of a Recurring Somatic Variation in Variegated Ears

of Maize. AMER. NAT., 48: 87—115. 1914

Genetical Studies of Variegated Pericarp in Maize. Genetics, 2:

curro drohen. fividence of Aberrant TaS Behavior in Maize Endo-

sperm. Amer. Jour. Bot., 8: 411-4 1921.

Frost, Howard B. An TTE e a Somatie ee involving

Two Linked Factors. AMER. Nat., 55: 461-464,

Gregory, R. P. On Variegation in Prima sinensis. e. Genetics, 4:

Pig" :

Morgan, T. H. and Bridges, C. B. The Origin of Gynandromorphs. Car-

negie Inst. Wash., Pub, 278: 1-122. 1919.

Muller, H. J. Further Changes in the White-eye Series of Drosophi'a and

their Bearing on the Manner of Occurrence of Mutation. Jour, Ezp.

Zool., 31: 443-473. 1920.

Randolph, LF E Oytological Study of Some Chlorophyll Types in Maize,

Bot. Gaz., 1992. (In press.)

SEROLOGICAL REACTIONS AS A PROBABLE

CAUSE OF VARIATIONS

PROFESSOR M. F. GUYER

UNIVERSITY OF WISCONSIN

WrirH an insight that has never been surpassed even

to this day Claude Bernard,' more than forty years ago,

remarked that ‘‘ Organic synthesis, generation, regenera-

tion, maintenanee, and healing of wounds, are different

aspects of an identical phenomenon," the phenomenon

alluded to being the constructive activity manifested in

ordinary nutritive processes. In a recent thoughtful

paper, R. S. Lillie? reiterates and expands this point of

view. That synthetic metabolism constitutes the very

essence of embryonic development and therefore of the

expression of heredity, scarcely admits of a doubt. To-

day it is a truism to say that the visible ‘‘ characters "'

we deal with in heredity are but the effects—by-products

as it were—of far-reaching metabolic reactions. And

since the metabolism of the actual living protoplasm cen-

ters, if not exclusively, at least principally, in the pro-

teins, the problems of metabolism, growth, reproduction

and heredity become largely the problem of why and

how a given kind of living protoplasm builds up proteins

of its own specific type.

The molecules of the ordinary native proteins are, as

is well known, huge polymeric structures of extremely

complex constitution. By appropriate chemical treat-

ment they may be broken down into successively smaller

and smaller units, each of which, however, still responds

to the ordinary qualitative tests for proteins. There

finally comes a point below which further reduction of

the molecule results in the loss of the distinctive protein

reaction, and the outcome is a series of ultimate char-

acteristic units, the amino-acids. Thus native proteins

seem to be built up of two different categories of units:

first, combinations of various amino-acids which consti-

tute the simplest protein blocks; and second, the combina-

tion of these into the much in molecules eharaeteristie

of the native proteins.

1**Tecons sur les phénomènes de la vie,” Vol. IL p. 514,

2 Biol. Bull., XXXIV, 2, 1918.

No. 642] SEROLOGICAL REACTIONS 81

In the process of digestion different proteins are broken

down into their amino-acid units and these are then re-

built into the tissue-proteins of the living organism, each

tissue selecting such amino-acids as are required to re-

construct its own peculiar complex. That is, the architec-

ture of the new proteins into which the individual building

units are regrouped is determined by the specific con-

stitution of the tissue-proteins themselves. In different

proteins the different amino-acids may exist in very dif-

ferent ratios, and certain of them necessary for the meta-

bolic repair of protoplasm may be lacking in some, such

as gelatin, but the amino-acids in any particular protein

are constant in nature and proportion and each probably

has a definite position in the molecule. While kinds and

proportions of amino-acid units determine in large meas-

ure the characteristics of individual proteins, it may well

be that configurational differences in molecules of the

same chemical composition are responsible for the specjfi-

cities of corresponding proteins in related species of

animals. One estimate, for instance, assigns to the serum-

albumin molecule alone the capability of having as many

as ten thousand million stereoisomers. One may perhaps

picture mentally, in a much simplified form, the simplest

protein molecule as a main chain or ring, of which the

representative links are amino-acid ‘‘ nuclei.” More-

over, to each such link

(e.g., in simplest form, dicere

a side-chain, differing in constitution in different cases, is

attached or is attachable by replacement of a hydrogen

atom.

It is, then, with such complex molecular configurations

that we have to do as a chemical basis for the phenomena

of life; and in them, as I have stated elsewhere,’ we have

** ample basis for that peculiar handing on of metabolic

energies already established which we term heredity.”

Although habitually when speaking of heredity we think

of the multifarious ** characters ”’ displayed by the adult .

organism as the things inherited, and strive to picture in

our minds how they are represented in the germ, it is

3 Amer, Nat., XLV, May, 1911.

82 THE AMERICAN NATURALIST [Vor. LVI

clear, in the light of modern geneties, embryology and

cytology, that what actually happens is a reduplieation

generation after generation of germinal protoplasm.

That is, the proteins already present in the germ-cell not

only determine what will be built up in growth, but also

the composition of that overgrowth which, as a detached

individual, eonstitutes the physieal basis of inheritance.

If the initial protoplasmic substance is chemically specific

then inevitably the anatomical and physiological com-

plexities which arise out of it must likewise be specific.

Before we can grapple with the problem of the possible

induction of changes in this fundamental mechanism

through influences emanating from the body, we must

consider some matters concerned with embryonic develop-

ment and the fundamental chemical nature of the somatic

cells.

As to how the constitution of the egg becomes trans-

formed into that of the adult, the most consistent and

reasonable hypothesis to date, in my opinion, is that

proposed by Child, based on axial or metabolic gradients.

A full exposition of his hypothesis must be sought in his

books, ‘‘ Individuality in Organisms "' and ‘‘ The Origin

and Development of the Nervous System from a Physio-

logical Viewpoint." I can sketch only such aspects of it

as pertain to my present subject. Starting with the

universally aecepted biological’ axiom that excitability

followed by some degree of transmissibility is a funda-

mental property of all living matter, Child believes, as I

understand him, that the establishment of polarity in the

fundamental organismie proteins of the germ-cell is the

beginning of development. 'The eggs of many species al-

ready show polarity (animal and vegetal pole) at the time

of ovulation; in other forms polarity is not established

until later. In the former case the polarity may have

been determined in earlier cell-generations by extrinsic

faetors or it may be due to the original position of the

ovum in the ovary with reference to the nutritive stream.

Yolk apparently accumulates in the region of least oxida-

. tion and thus marks the vegetal pole. In the second type

of egg, polarity, at first lacking, is soon established

beeause differential environmental exposure (difference

in oxygen supply, light, contaet, general surface exposure,

No. 642] SEROLOGICAL REACTIONS 83

or other external factor or factors) causes one region to

have the greatest metabolie aetivity. As does any stim-

ulated part with reference to a resting part (muscle,

nerve, ete.), this point of heightened activity sets the

pace, as it were, for the other parts. Thus an excitation

gradient is established which Child terms an avial gra-

dient. Since the excitation initiates transmission—

changes and thereby determines what shall happen at

successive levels along the path of transmission, the

region of highest excitation dominating and controlling

the rest, the axis in question may also be called a met-

abolic gradient. In this way a physiological unity is

established and maintained by bringing the different

regions within range of the gradient into definite physio-

logical relations.

Since the chief source of energy in protoplasm is oxida-

tion, and inasmuch as many different tests have shown

that the rate of oxidation gradually diminishes along the

gradient from the region of highest activity, Child infers

that differences in oxygen supply play a very important

part in the local metabolic differences which arise. In

any event, a differential axis of activity arises in the egg

as the result of differences in environmental conditions

(either before or after ovulation) and determines the

axiate pattern of the developing organism. In such a

complex system of chemical and physical activities, where

unquestionably many associated simultaneous reactions

and interactions are going on, different rates or condi-

tions of reaction in different regions must result in unlike

end-products. Thus, at different levels of a gradient

which was quantitative in origin, qualitative differences

arise. For once a gradient is established, any one of

several purely quantitative changes in the system, such

as increased oxidation which acts differentially on sub-

stances at a given point, changes in temperature, in water

content, or in colloidal state, or changes in the concen-

tration of the reacting substances, may alter certain com-

ponent factors of a given region more than it does the

- corresponding factors in other regions, with the result

that out of the same initial constituents the respective .

organ- or tissue-stuffs that characterize the organism are

gradually built up. For example, as Child points out,

84 THE AMERICAN NATURALIST [Vor. LVI

ïn a region of rapid oxidation certain substances might

be entirely oxidized as rapidly as they are formed, while

in a region of slower oxidation they might accumulate

as part of the structure.

Bilateral organisms follow a law of antero-posterior

development. Differential exposure having determined

which region shalllead and having thus set the rate of

activity of the successive regions, continuing differential

relations of the environment maintain the various levels

of the gradient, under the domination of the head-end, at

their respective rates of activity. While this is the

normal course of development, it may be greatly altered

by experimental methods; the original gradient, partic-

ularly in lower organisms, may be obliterated and a new

one engendered. The latter under certain conditions may

even be made to arise at right angles to the original axis.

Change of gradient may be readily observed, for example,

in the regulatory development of isolated pieces of many

planarians. Moreover, the remarkable capacity for self-

differentiation possessed by isolated parts taken at dif-

ferent levels of the body in such forms, shows that posi-

tional relations of the constituents of the regenerating

mass, rather than cellular specificity, determine what

structures shall arise in a given location.

Since many species, including representatives from all

the chief phyla of animals, show differential susceptibility

at some stage of their development, when subjected to

the action of various external agents such as alcohol,

anesthetics or potassium cyanide, these agents may be

used to bring about shifts of gradient, under-development

or over-development of certain parts, or a remodelling

of the organism or of various regions of it. Inasmuch

as any one of several agents may bring about the same

result, it is manifest, again, that quantitative external

conditions are the factors which initiate and thereby

determine the fundamental orientations and specializa-

tions of the parts of an organism.

As development progresses in the more complex organ-

isms, again through differential stimulation, secondary or

* symmetry ’’ gradients may also become established. `.

For example, each limb region of a vertebrate becomes

a subordinate system with its own internal correlations.

No. 649] SEROLOGICAL REACTIONS 85

In organisms with radial symmetry, special centers of

growth occur, and only at a certain distance from a given

center ean another arise.

After differences in protoplasmic constitution have

arisen at different levels of the gradient, a system of

chemical or transportative correlation probably begins

to operate, and out of it all finally comes the various sup-

portive and mechanieal tissues, vascular tissues, tissues

of excretion and secretion, nervous tissues, etc., which

constitute the underlying mechanisms of correlation and

integration in the finished organism.

The hypothesis says little of chromosomes, or of genes,

for its objective differs somewhat from that of the genet-

. jeist, but it in no wise denies the existence of such

entities. Child argues, however, that since each cell of the

body is a descendant of the original zygote and therefore

presumably possesses the full complement of chromo-

somes of that zygote, something other than the nuclear

pattern per se must be responsible for the fact that cells

become different in different parts of the body. And

this something, he would say, is the metabolic gradient

initiated by differential excitation, since the very estab-

lishment of such a gradient means the concomitant es-

tablishment of local differences along its path. As he

says, ** if all the cells are originally alike they cannot of

themselves become different.’? The specifice character of

the differentiation, the kind of organ or organism pro-

duced, he reiterates, is determined ‘‘ by the specific in-

herited constitution of the protoplasm.’’

So much for Child's hypothesis of axial or metabolic

gradients, in its bearings on embryogeny and differentia-

tion. Ihave reviewed it at some length because it shows

more clearly than any other theory of development with

which I am aequainted that there is no necessity for

believing that as cells become specialized they lose part of

their original constituents. Due to local conditions, strue-

tural modifications and special activities have appeared,

but these are changes rung on what is fundamentally the

same type of protoplasm in every cell, In higher organ-

isms, in some cells possibly irreversible changes have

oceurred—the cell may be incapable of dedifferentiation

—but nothing constitutional, call it gene or what you will,

86 THE AMERICAN NATURALIST [Vor. LVI

has necessarily been lost from the cell. The inheritance

complex of the germ is like goods in the piece; it is only

as development progresses that the garment becomes

specified ; but above all, be it remembered that the finished

garment is of the same fundamental constitution as the

goods in the piece.

It is a commonplace of experimental embryology and

experimental morphology, in faet, that the same initial

materials may yield very different end-products in dif-:

ferent environments. The phenomena of heteromor-

phosis, metaplasia, regeneration and regulation all attest

this. Blastomeres originally directed toward becoming

one part of an organism may be switched about to become

another part; tissues originally subserving one function

may be turned to other uses; ectodermal cells which by no

possible chance could have been predestined to form

erystalline lens will, nevertheless, form a lens similar to

that of the normal eye if stimulated by a transplanted

optic cup. Or, if the lens is removed from the eye of a

salamander, a new lens may develop from the edge of

the old iris, a part from which the lens never normally

develops in the embryo. In short, it is a well-established

fact in many organisms that cells occupied with the

specializations of one part of the individual still retain

the potentialities which would fit them to the functions

of some different part, and may, in fact, under exper-

imental conditions be made to redifferentiate into the

structures of another part. Such facts, together with

the exactitude of chromosome distribution in mitosis,

indieate clearly that many, possibly all, eells of an or-

ganism retain the hereditary tendencies that existed in

the original zygote. Because of limitations due to its

location in the organism, however, a given cell realizes

only a small proportion of its inherent possibilities. And

after all, this is no more remarkable than the fact that

the genes of recessive characters may slumber indefinitely

in germ and soma, generation after generation, until

conditions suitable for their expression as characters

occur.

But now, regarding heredity as in its simplest expres-

sion merely the passing on of metabolic activities already

established, and conceding that the distinctive structural

No. 642] 3 SEROLOGICAL REACTIONS 87

effects and functions which characterize the respective

tissues are probably the outcome of unequal activities

among the same kinds of fundamental protoplasmic con-

stituents in differing local environments, the question of

prime importanee to the student of evolution is how the

properties of these constituents have come to be changed

from what they were initially, how they may be altered

in the future—in short, the question of the nature and

origin of variations. For whatever we may believe about

the degree of preformation which exists to-day in the

mechanism of heredity, it is absurd to assume that in the

simpler primitive protoplasm from whieh modern forms

have evolved there could have been genes of the char-

acteristies of all the organisms now in existence. What-

ever individual development may be, we must assume that

racial evolution was epigenetie. While doubtless in a

sense man lived potentially in some primitive protozoan-

like creature, actual material antecedents of his existing

attributes were no more present in this ancestral ereature

than specific determiners for the oceans, continents and

topographieal features of the world to-day were present

in the original nebula which preceded our solar system.

The great central problem of evolution is just this very

one of how the determinative accumulations which exist

in germ-cells to-day have been incorporated step by step

into this erstwhile primitive protoplasm. Certain pos-

sibilities have. become realities and concomitantly as a

basis of this reality the old mechanism has in part been

altered, or a new mechanism has come into being which

persists as a part of the established constitution of the

germ-cell.

Before entering upon a diseussion of whether or not

any of the remarkable serological activities which have

come to light in recent years may be possible or probable

sources of germinal modifications, we must recall briefly

the general nature of immunologic reactions. As you

know, foreign proteins of either plant or animal origin

when injected directly or indirectly into the circulation

‘of an animal will engender antagonistic or neutralizing

substances to which the general name of antibodies is

applied. Thus the toxins of bacteria incite the production

of antitoxins; the bacteria themselves lead to the pro-

88 THE AMERICAN NATURALIST [Vor. LVI

duction of bacterial immobilizers or solvents termed

bacteriolysins, or sometimes to agglutinating substances

termed agglutinins which clump baeteria of the species

used in their production, if the two are brought together

in the blood-serum of the animal into which the bacteria

were originally introduced. Likewise a tissue of one kind

of animal injected into the circulation of another induces

the formation of antibodies of various kinds such as

precipitins which form a precipitate when the blood-serum

of the treated animal and an extract of the special tissue

used are brought together in vitro; or other antibodies

termed cytotoxins or cytolysins which possess a specific

toxic or solvent action for the kind of protein used in

their production. The alien substance employed to pro-

duce antibodies is commonly called the antigen. |

In this connection, the phenomenon of anaphylaxis

should perhaps also be mentioned. Anaphylaxis is a

name given by Richet to designate a highly supersensi-

tive state which, after a period of incubation, an animal

develops toward certain protein substances that were

practically harmless on first injection. Sometimes, par-

ticularly in guinea pigs, death results. The sensitizing

dose for the production of anaphylaxis may be very

small; one millionth eubie centimeter of horse-serum, for

example, has been known to render guinea pigs sensitive.

The reaction is specific; for instance, an animal sensitized

to sheep-serum, though reacting violently to this antigen,

displays little or no hypersusceptibility to other sera.

In the main all of the immunological reactions show a

considerable degree of specificity; the antibody will react

fully only with the particular kind of protein used as

antigen. The specificity is not absolute, however; a

.milder reaction may be obtained with homologous

proteins of related species, the extent of the reaction

being determined by the nearness of relationship of the

species to that from which the original antigen was ob-

tained. Similarly with bacteria, the reaction is in the

main specific, although so-called group-reactions may ap-

pear. The serum of an animal immunized against ty-

phoid, for example, may not only agglutinate Bacillus

typhosus but may also show this reaction in a less degree

with such related forms as the colon bacillus. Thus, ir-

No. 642] SEROLOGICAL REACTIONS 89

respective of whether the antigen consists of bacteria or

of other protein materials, there is a gradational spe-

cificity of reactions which apparently corresponds to tax-

onomie relationships.

An even more delicate biochemical measure of kinship

than the known immunological reactions has apparently

been established through the extensive researches of

Leo Loeb‘ and his associates on transplanted tissues. In

numerous of his papers Loeb has called attention to the

remarkable power of transplanted tissues to indicate dif-

ferent degrees of even close individual relationship, sueh

as the individual to itself, to a brother or sister, to a

parent, to a more distantly related individual of the same

species, or to an individual of a different species. Par-

ticularly the lymphocytes of the host serve as a delicate

indicator of such relationships.

Loeb assumes that a specific chemical group which he

designates as individuality-differential is common to all

the tissues of an individual and that in virtue of this

characteristic each creature differs from the others of the

same species. The individuality-differential of a trans-

plant (except in autotransplantation), since it is not

adapted to its new environment, assumes injurious prop-

erties, probably by engendering toxins. The relative -

strengths of these are determined by the degree of rela-

tionship that exists between the source of the transplant

and the host. In the circulating fluids of a given indi-

vidual, he believes that there are ‘‘ autosubstances "'

which exercise important regulative functions, such, for

example, as keeping the vascular supply of the various

tissues at an optimum, or holding in check lymphocytes

and invasive fibroblasts which when inadequately re-

strained, as in old age, become destructive agents. In

one place he speaks of their stimulating effects and he

regards them as responsible directly or indirectly for the

marked vascular reaction called forth by autotransplants.

In sexual reproduction, obviously two different ** indi-

viduality-differentials ’’ must combine to form the new

individuality-differentials of the offspring. These, Loeb

finds, are of varying degrees of intermediacy. This in-

termediacy is continued into the next generation. What

4 Amer. Nar., LIV, 1920.

90 THE AMERICAN NATURALIST [Vor. LVI

is of much interest from the standpoint of our quest of a

possible connection between reaction-products of the body

and alterations of the germ is the fact that he feels con-

strained to link up his serumal phenomena with the ehro-

mosomes. Thus, he says, ‘‘ The chemical individuality-

character of the chromosomes should lead to analogous

chemical differences consisting perhaps in the formation

of chemical side-chains attached to proteins; they should

be present primarily in cell-proteins and secondarily in

the proteins of the body-fluids. . . . These side-chains

must be identical in all the proteins of the same indi-

vidual and differ in the case of different individuals.’’

Another great group of influences which extend to the

furthermost reaches of the body and profoundly affect

the entire organism in development and in maturity—

those emanating from the various endocrine struetures—

I have barely time to mention. They must be kept in

mind, however, when we attempt to pieture the ebb and

flow of chemical influence which is indispensable to the

maintenance of general physiological equilibrium, inclu-

ding that of the gonads no less than of the other body

structures. ;

You may feel that in reviewing the nature of the protein

molecule, the behavior of the proteins of the cells in

morphogenesis, the gradational specificities of the im-

munological reactions, the relationships which exist be-

tween host and transplant, and in reminding you of the

intricate functions of the endocrines, I have wandered

far afield into irrelevant byways, but I hasten to assert

that these phenomena are not as unrelated as might ap-

pear at first sight; they are but different aspects of the

great salient fact of organismie unity, whether it be a

matter of chemical constitution, taxonomic relationship

or physiologic response.

And now I wish to raise the question of whether or

not in the light of the foregoing facts it is irrational to

believe that in all probability a thread of chemical iden-

tity persists between the chemical constituents of the

germ and the chemical substratum of the tissue-cells.

The nuclei of the various tissue-cells differ little in ap-

pearance from the nuclei of the germ-cells, and inasmuch

as the new germinal and somatic cells descend alike

No. 642] SEROLOGICAL REACTIONS 91

directly from a common source, presumably bearing in

their chromosomes samples of all the chromosomal com-

ponents of the original zygote, is it unreasonable to sup-

pose that if changes come to pass which can affect certain

constituents of tissue-cells, this influence, if borne in the

circulating fluids of the body, could also affect the ho-

mologous constituents of the germ-cells? Personally, I

think that such a hypothesis is not unr ble. But is

there even the least bit of evidence on this point? I

believe that there is. I feel that in the transmission

of eye-defects secured by Dr. E. A. Smith and myself in

fetal rabbits by means of serum immunized against rabbit

crystalline lens, we have a bona fide case of such parallel

influences. Since I have already presented the facts

before this Society and inasmuch as the details are avail-

able in printed form,’ I need not repeat them now. It is

sufficient to recall to you that we secured a fowl-serum

immunized against rabbit crystalline lens which when

injeeted into pregnant rabbits penetrated the placenta

and occasionally attacked the lens of the fetal young,

the outeome being marked eye-anomalies in such young.

Since, once produced, the defects were transmitted to

successive generations through both male and female

lines, we interpreted our results to mean that the immune

serum was not only specifically cytolytic for the newly

forming lens-tissue of the fetus, but that it also attacked

the representatives of such tissue—its genes, if you please

— in at least some of the germ-cells of the fetus. If true,

this must mean that there is some degree of constitutional

identity, probably protein homology, between the mature

substance of a tissue and its correlative in the germ. And

in view of the fact that, basically, inheritance is mainly

a question of the perpetuation of specific protein-com-

plexes, and development, the result of differential reac-

tions of these same fundamental constituents under dif-

fering conditions of environment, is this an unreasonable

inference? :

But does anything comparable to this occur in the

ordinarv course of animal existence? Do cytolysins or

kindred substances which can modify or destroy both

5 Jour. Exp. Zool., 31, 2, 1920, AMER. Nar., LV, 1921. Proc. Nat. Acad.

Sci., 6, 3, 1920.

92 THE AMERICAN NATURALIST [Vor.LVI

tissue-elements and their germinal correlatives ever occur

in animals without being introduced by man? Do animals

ever form such antibodies or other equally active sub-

stances against their own tissues? It is obvious, since

tissues persist intact under conditions of normal physio-

logical equilibrium, that they are not being subjected to:

such influences, or if they are, that they resist them. As

a matter of fact, Römer,’ using the complement-fixation

technique, found that the serum of adult human beings

may possess antibodies for their own lens proteins. It

seems reasonable to suppose that if the tissues of an

animal became injured or displaced in some way, or met-

abolically unbalanced, immunity reactions might be es-

tablished against them. We have some evidence that

such is the ease. During the late war, for example, it

was found that toxic reactions resembling anaphylactic

shock often followed extensive injuries of the soft tissues.

The matter can be tested experimentally. Because of

their distinctive nature and the ease with which they may

be isolated, I chose spermatozoa for such an experiment.’

I found that a rabbit will build antibodies against its own

spermatozoa when these are injected into its blood-

stream; also, that rabbits injected with rabbit sperma-

tozoa not only develop antibodies in their blood, but also

have their own spermatozoa greatly weakened, a condi-

tion shown in vitro by their lessened resistance to anti-

sera. This clearly shows that an animal can on occasion

build antibodies against its own tissues; and since anti-

bodies can apparently directly or indirectly affect germ-

cells, it seems reasonable to suppose that such influences,

especially if continued over a long period of time, might

be one source of germinal variations.

It is known from the experiments of Kuntz? and others

that the blocking off of the ductus deferens of one testis

may induce degeneration of the germinal epithelium, not

only of that testis, but of the other as well. Inasmuch

as the spermatozoa in the testis on the operated side

must die and be resorbed, is it not probable that in this

process spermatotoxins have been formed which have

then attacked the living germ-cells of the other testis?

Again, we are familiar with the fact that oculists fre-

6 Zinsser: ‘* Infection and Resistance.’’

7 Paper in press, Jour, Exp. Zool.

8 Anat. Rec., 17, 4, 1919.

No. 642] SEROLOGICAL REACTIONS 93

quently find it necessary to remove a severely injured

eye to prevent the ‘‘ sympathetic” degeneration of the

other eye. I am told by competent oculists that the ex-

tension of the degenerative influence involves more than

the atrophie effects which might result through direct

nerve connections. Does it not seem probable that here,

too, the disintegrative influence which comes to operate

on the uninjured eye is cytotoxic or cytolytic in nature?

And if it can operate on the tissues of the normal eye,

"why not on the corresponding protein constituents in the

germ, the prototypes of those which were originally in-

eited to form the ocular tissues?

It may be, it probably is true that there is sufficient dif-

ference between these factors of the germinal protoplasm

and those of the finished organ to render the former less

susceptible to such agents. It is not improbable that even

if some of the numerous germ-cells were affected many

others might not be. But any new organism which

sprang from such an affected germ would have its own

germ-cells similarly modified, since these would all be

derived from the same zygote. Even so, the defects

might not be manifested in offspring because of the prob-

ability of dominance by the corresponding factors from

their partner in fertilization. |

The only way to settle the matter, of course, is through

experiment. I know of no existing experimental evidence -

on this point. In my own laboratory, however, an in-

vestigator has an experiment in progress which I hope

will ultimately throw some light on the matter.

There are many bits of evidence to show that an or-

ganism may react against the tissues of other individuals

. of its own species. Thus Bradley and Sansum,’ employ-

ing anaphylactic reactions, found that guinea pigs in-

jected with various guinea-pig tissues such as heart,

liver, muscle, testicle, and kidney developed immunity

reactions. Moreover, certain changes in the blood of the

mother during pregnancy, apparently induced by cells or

cell-products set free from the newly-forming placenta,

seem to be of the nature of antibody formation. Then

again Turck'? has shown that products of the lung-tissue

of the eat, autolysed under sterile conditions in vitro, pro-

9 Jour, Biol. Chem., Vol. 18, 1914.

10 Med. Rec., 1919, 95, pp. 719-21.

94 THE AMERICAN NATURALIST [Vor.LVI

duced characteristic pulmonary lesions when injected into

other eats. Similarly autolysed lung-tissue of other

mammals had no effect on cats.

But, the question arises, in order to get parallel influ-

ences, in soma and germ, would there not have to be ab-

solute identity between the two sets of proteins con-

cerned? Before answering this question let us glance

for a minute at two types of specificity which are recog-

nized in serological reactions: namely, ‘‘ species-specifie-

ity" and ''organ-specifieity." What the serologist

means by species-specificity is the fact, shown through

precipitin reactions, that blood immunized against one

tissue of an alien species will react, although in a less

degree, with extracts of the other tissues of that species.

And that there may be a specificity of certain organ com-

plexes which is independent of species is shown by the

fact that an immune serum produced by using the crys-

talline lens of one species of animal yields a precipitin

which reacts more or less with the lens proteins of even

unrelated species. Similar results have been obtained

with proteins derived from the testis, and confirmatory

evidence of such organ-specificity has also been estab-

lished by means of anaphylactic reactions. Such facts

as these, together with those cited in the discussion of the

gradational reactions of various immune sera according

to the systematic relationships of animals, it seems to me,

answer our question affirmatively; there need not be ab-

solute identity between the proteins of the somatic cells

and their correlatives in the germ-cells for immune sera

engendered against the one to react also against the

other. I raise the issue because it might be urged that

such tissues of an organism as become so abnormal as to

excite the production of antibodies are no longer suffi-

ciently similar to the normal tissue-elements, and there-

fore to their germinal representatives, to make the anti-

bodies effective against either normal somatic or ger-

minal constituents.

It seems to me that all available facts indicate that the

constitution of an organism, whether germ or soma, is

not to be regarded as a congeries of cooperating, equi-

potent units, but rather as the outcome of interacting

systems which differ in their orders of organization; sys-

tems which in themselves possess more fundamental and

No. 642] SEROLOGICAL REACTIONS 95

more supplementary or fluctuating components ; chemical

groups which represent the more constant features of

organization coupled with subsidiary groups of more re-

stricted significance. That is, there seem to be series of

substances of like chemical constitution common to all

the cells of an organism, possibly to even various groups

of organisms, and superimposed upon these central or

foundational constituents, probably as parts of the same

molecules, are secondary systems, or possibly systems

within systems, which modify the main configurations in

various ways.

This conception certainly squares with the fact that

degrees of specificity paralleling the kinships of animals

may be shown by immune sera. It harmonizes with what

we know of the architecture of the native proteins as well

as with our whole scheme of natural biological taxonomy

in which we find certain fundamental stable features

representing a broad series of organisms, and less and

less inclusive characteristics which grade down to the

minor differences that separate species, varieties and in-

dividuals. Nor is it incompatible with what we know of

chromosomes and genes. The very fact that heritable

grades of a single gene in a given chromosome may occur

(e.g., in Drosophila) and that one of these variants may

in turn be modified gradationally by a series of secondary

factors located in other chromosomes suggests the type

of organization just discussed.

With the remarkable and abundant evidence of hand-

and-glove relationships between unit-characters and

chromosomes that has been accumulated in recent years

through the painstaking studies of workers on Droso-

phila, not to mention other. corroborative work, it seems

to me that there is no longer a reasonable doubt that the

differentials, whatever they may be, responsible for the

distinctiveness of the so-called unit-characters, reside in

the chromosomes. And while I have always believed” and

still believe that for the final outcome the cytoplasm 1s

just as necessary in its way, and must be just as char-

acteristic of the species as the chromosomes are, its dis-

tinetiveness must be of a fundamental organismie (prob-

ably chemical) type common to the species as a whole,

11 Bull. No. 2, Univ. of Cincinnati, Vol. III, Ser. II, 1902. Science,

June 28, 1907. fab Cincinnati Studies, Sept—Oct., 1909. AMER. NAT.,

XLV, 1911.

96 THE AMERICAN NATURALIST [Vor. LVI

since it ean be, in fact is, contributed in reproduction al-

most wholly by one parent, the female. It is apparently

a medium which responds specifically to the action of

the respective chromosomal incitants, whether these be of

maternal or paternal origin. All geneticists agree to-day;

I think, that any character of an adult can not be merely

the outeome of a unitary germinal antecedent; it is the

produet of many faetors. And ordinarily what we see as

a character-difference is. probably merely the outcome of

a factor-difference in one of the chromosomal cooperants.

In conclusion, let me say first of all that no one more

than myself realizes the inadequaey of my present argu-

ment as a complete or satisfying theory. The knowledge

in the fields on which it is based is as yet far too frag-

mentary to warrant anything but tentative conclusions.

But since various facts seem to me to point toward the

view that certain types of immunological reactions, no-

tably the cytolytic, engendered against various somatic

constituents may occasionally also affect chemically re-

lated substances in the germ, and inasmuch as many

other facts lend themselves to such an interpretation

without undue violence to scientific credulity, I have felt

justified in presenting the whole matter in the form of a

working hypothesis.

In the short time remaining I can not enter into the

important question of whether or not changes induced in

the blood-serum might be instrumental in leading to pro-

gressive rather than regressive evolution, and even had

I time for such a discussion, there are not sufficient data

available to support such a discussion affirmatively. I

should like merely to point out in closing that through

exercise we can initiate and promote growth in various

parts of the soma, we can induce hypertrophy, and in so

doing we are in some way leading the protein and other

constituents of the cells in question to make more of their

own kind of substance, in other words, to reproduce their

kind. We do not know what stimulates them to do so,

but, in part, it may well be something that is or can be

transported in the circulating fluids of the body; and if

so, then there exists the possibility that the correspond-

ing germinal representative of such a part, however

tenuous the thread of chemieal connection, might also be

modified in the direction of progressive germinal change.

THE

AMERICAN NATURALIST

Vor. LVI. March-April No. 643

ORTHOGENESIS

SYMPOSIUM ON ORTHOGENESIS BEFORE THE AMERICAN

SOCIETY OF ZOOLOGISTS, TORONTO, DECEMBER, 1921

ORTHOGENESIS FROM THE STANDPOINT OF

THE BIOCHEMIST

PROFESSOR L. J. HENDERSON

HARVARD UNIVERSITY

Ir does not seem likely that physical science should

have much to say about the theory of orthogenesis. In

the first place, it is hard to see what the term means if

one adopts a physico-chemical standpoint. In the second

place, organic evolution is more remarkable in its morpho-

logical aspects than in its chemical and physico-chemical

aspects.

The first point,may be dismissed with a few remarks.

Orthogenesis presumably means that evolution has taken

place in a straight line or in a very restricted path, and

that the straightness of the line depends, at least partly,

upon something which is internal to the organism,

though, of course, the process may be released by a stim-

ulus from the environment. The straightness of the proc-

ess must be largely a matter of definition. Physico-

ehemieally, it eould hardly mean more than that quanti-

tative ehanges have steadily the same sign over a con-

siderable period of time.

One might, perhaps, adopt such a view, if one could

believe, as has been often suggested, that variation is the

expression of a process which is approaching a condition

98 THE AMERICAN NATURALIST [Vorn LVI

of equilibrium, because then, so far as there is no unto-

` ward interference from without, it would be natural to

think that the eourse of the process must be in a certain

sense a straight one, with a negative acceleration. Taken

literally, such a consideration is, however, purely specu-

lative and for the present, I think, a sterile speculation.

Somewhat more clearly intelligible is a hypothesis

whieh arises from the study of hormones and their róle

in development. It appears to be quite possible that the

effect of increase or decrease in the amount of a single

chemical substance in a species might be a complex

change in its strueture, including modifieations of size, .

of the proportions of the different parts, of pigmenta-

tion, or of the other peculiarities which ordinarily arrest

the attention of students of evolution. This would be.

especially true if, instead of a change in the amount of a

hormone or other substance, it were a case of the forma-

tion of a new compound. Such changes, while directly

due to a single substance, might be greatly modified by

readjustments following the disturbances of the physio-

logical equilibria between the different parts of the body.

Compensatory readjustments of similar nature are, of

course, among the most familiar and interesting phenom-

ena in pathology. We are, accordingly, fully justified

in taking their possibility for granted.

It is, therefore, conceivable that evolutionary changes

should be occasionally progressive and apparently ortho-

genetic, although due to a simple physico-chemical modi-

fication. No doubt, if it were desirable, such considera-

tions might be developed into a clear and possibly useful

theory of orthogenesis, but I am not qualified to do so.

My object is only to insist that changes which from a

morphological standpoint are complex, continuous, and

progressive, may conceivably be due to a single, simple,

physico-chemical change.

Such reflections, vague though they may be, clearly

point to a conclusion which is, I feel sure, inevitable for

the physical scientist; morphological phenomena in them-

No. 643] ORTHOGENESIS 99

selves are not suffieient to establish the validity of any

theory of the mechanism of evolutionary variation.

More important than speeulating about such questions

is the fact that the underlying physico-chemical processes

in living organisms seem to have remained about the

same throughout the whole process of evolution. So far

as it is possible to form any opinion on the matter, this

conclusion is inevitable.

In considering the question of organic evolution it

should always be remembered that, with very trivial ex-

ceptions, the economy of life on the earth is now and prob-

ably always has been founded upon the synthesis of car-

bohydrates from water and carbonic acid with the ac-

companying fixation of energy, followed by the conver-

sion of carbohydrates into fats, proteins, and a great

variety of other related substances. Later there is an

oxidation of these substances back to water and carbon

dioxide, accompanied by the utilization of the energy in

various forms of organic activity. Correlated with this is

the fact that cells are made up of water, carbonic acid,

carbohydrates, fats, proteins, and certain other sub-

stances. They are enough alike in chemical composition

and in physico-chemical structure fully to justify the

concept of protoplasm as a fairly constant physico-chem-

ical apparatus throughout the organie world.

These familiar facts of chemical physiology and chem-

ieal morphology undoubtedly depend upon the properties

of the substances involved. Water and carbonic acid,

with which the process begins and ends, and which seem

to be everywhere the foundation of protoplasm, possess

in themselves such a large number of remarkable char-

acteristics and lead directly through the formation of

sugars to such a great variety of chemical substances and

chemical reactions, that it is hard to believe in the pos-

sibility of the existence on a large scale of any very dif-

ferent kinds of living organisms.

100 THE AMERICAN NATURALIST [Vor. LVI

This is a subject that I have elsewhere discussed at

length. Hence it will perhaps suffice briefly to recapitu-

late a few of the more striking facts. Because of its

peculiarities as a solvent, as an ionizing medium, etc.,

water makes possible the formation of an almost indef-

initely greater variety of physico-chemical systems than

does any other substance. On account of its high latent

heat of vaporization, its high specific heat, its high sur-

face tension, and the peculiarities of carbonic acid, such

systems often possess a very remarkable stability. The

elements hydrogen, carbon, and oxygen, of which water

and carbon dioxide are composed, seem to be unique in '

the number and variety of the substances which they can

form. In particular, the production of sugar from water

and earbon dioxide fixes a very great amount of energy

and leads directly to the greatest variety of chemical sub-

stances and reactions which are known to occur as the

result of one chemical process. Finally, water and ear-

bon dioxide are the two substances which are everywhere

available.

Anything so complex, so stable and yet so variable, so

widespread and so active as life can only occur when a

great variety of conditions are fulfilled. In other words,

the physico-chemical systems of the organism, in order

that life shall be capable of its evolution, must possess

altogether exceptional characteristics, which appear to

be quite impossible unless water and carbonic acid, and

compounds of the three elements, hydrogen, carbon, and

oxygen, and no doubt also of nitrogen, are at the basis of

them. These substances possess a set of properties each

one of which by itself and also in cooperation with the

others is necessary for the highest physico-chemical com-

plexity and variability. So far as we know, no other ele-

ments or compounds possess another set of properties

which permit similar physico-chemical complexity or

variability.

It is, I believe, for this reason that life has always op-

erated on the same basis.

No. 643] ORTHOGENESIS 101

Thus while the evolutionary process has certainly pro-

duced a large number of well-defined series of changes

when it is looked at from the morphologieal point of view,

it still remains very probable that such physico-chemical

changes as have occurred are not only of a secondary

nature, but that they are much less of the character of

serial modifieations. Indeed, one is tempted to say that

in a physico-chemical sense, the variations are distributed

in rather a random manner, without any particular indi-

cation of a general progressive tendency, such as we seem

obliged to think of in studying morphologieal variation.

No doubt the evolutionary proeess has, from time to

time, invented new chemieal substanees and greatly modi-

fied colloidal systems. In the total these changes are

very numerous and of the utmost importanee to the stu-

dent of evolution. But progressive change is more par-

tieularly a morphologieal phenomenon and it seems to be

almost self-evident that progressive morphological evolu-

tion should not be accompanied by the same degree of

continuous variation in straight lines in physico-chemical

properties. Such a parallelism would, I think, be well

nigh unaccountable. However that may be, there is no

evidence for it.

III

Another consideration which makes the theory of or- .

thogenesis seem very different to a physieal chemist from

what it must seem to a biologist, is the fact that chemistry

tends to deal with individual substances which either

exist or do not exist. The case of hemoglobin will illus-

trate this point. Hemoglobin is an individual substance

of very marked peculiarities. So far as known there are

no essential differences between the hemoglobins con-

tained in the bloods of different species. It is possible

that the known differences in crystal form depend upon

something more than trivial differences in the amino

acids which make up the molecule, but this seems unlikely.

In any case, it will do no harm to speak of hemoglobin as

102 THE AMERICAN NATURALIST [Vor.. LVI

a single chemieal individual in order to illustrate a par-

tieular point.

This substanee is the sole means of transporting more

than a small amount of dissolved oxygen in the blood of

those species which contain it. It is, therefore, apparent

that it may be thought about from the evolutionary point

of view, much as one thinks about an organ. I believe

that the success of Aristotle's system of classification

justifies this view. But while it is easy to think of the

gradual evolution of an organ as something which ean

not be regarded as appearing at any point in the evolu-

tionary process, being related by a process of continuous

differentiation to something which was certainly not the

same organ in an ancestral species, there is not the

slightest evidence for anything of the sort in the case of

hemoglobin, and it must seem to most chemists nothing

less than fantastie to assume such a continuous evolution

of a substance more and more closely approaching hemo-

globin. Moreover, it is almost as difficult to imagine such

a thing from the standpoint of a biologist, and it is cer-

tainly true that any given organism either does or does

not eontain a substance which is capable of de. a

loose chemical combination with oxygen.

But the difficulty in the case of hemoglobin is more

serious than this, for it has been found that hemoglobin,

like other organs, has more than one function. It has, in

fact, at least three; for it is the sole means of transporting

oxygen, almost the sole means of liberating carbonic acid

in the lung and absorbing it in the tissues, and the instru-

ment of the final delicate adjustment of the alkalinity of

the blood. The last two functions depend upon the same

property in the hemoglobin molecule, but this property is

a different one from that which enables hemoglobin to

combine with oxygen. We are, therefore, here confronted

with the task of imagining the origin of a chemical sub-

stance, quite different in its nature from any other known

substance, which possesses two chemical peculiarities,

and which, as a result of these two peculiarities, performs

three highly important functions.

No. 643] ORTHOGENESIS 103

Now it may be that originally hemoglobin possessed

only one of these peculiarities, so that its sole original

function was to carry oxygen. And accordingly one of

the most interesting questions of comparative physio-

logical chemistry concerns the respiratory function of the

blood. It would be a very important discovery to find a

kind of hemoglobin in which there is no specialized action

upon the transport of carbonic acid and upon the alkalin-

ity of the blood. But even if the earliest hemoglobin

were of such a nature, the first production of hemoglobin

would still seem to have been relatively an extremely dis-

continuous variation involving an unmistakable physio-

logical unit of great importance.

It is true, and should be noted in order to avoid con-

fusion, that there has been a later evolution of the proc-

ess of oxygen transport. This has been commented on

by Bareroft as a result of his own important researches.

It appears that variation in the electrolytes of the red

cells is aecompanied by remarkable variation in the af-

finity of their hemoglobin for oxygen, and that this is the

explanation of the differences in the so-called oxygen dis-

sociation curves of the bloods of different species of mam-

mals. Here, as Bareroft points out, there is no difficulty

in imagining a process of adaptation, for the fact of

chemical discontinuity is not involved. It is a question

of changing proportions of the different substances.

But in spite of the possibility of sueh phenomena, it

seems probable that there are, even in the human species

alone, a considerable number of important individual sub-

stances whose appearance in the course of organic evolu-

tion it is very difficult to imagine, except as a radical in-

novation.

Accordingly, it must be apparent that in the present

state of our knowledge, any theory which postulates con-

tinuity in evolution is very unsatisfactory to the chemist.

Moreover, in this case one seems to be confronted with

an appearnace of discontinuity which does not depend,

as is too often the case, upon a judgment of the magni-

tude of a difference.

104 THE AMERICAN NATURALIST [Vor. LVI

Of course, it is not difficult to imagine a sufficiently

close approach to continuity of evolution, and therefore,

to orthogenesis, in the case of simple proteins. But

here, very likely on account of our ignorance, there is no

indication of anything more than indefinite variation and

variability, accompanying variation in a definite direction

in the morphological characteristics of species.

On the whole, variation in the ultimate physico-chem-

ical nature of organisms seems to have been rather dis-

crete than continuous, not orthogenetie, but distributed

at random. Such a conclusion may possibly be illusory,

for our ignorance is greater than our knowledge. But

whatever the nature of the changes which it has under-

gone, the most striking thing about the physico-chemical

nature of protoplasm seems to be its uniformity through-

out nature.

Therefore, with due reservations because of the incom-

pleteness of bio-chemical knowledge, it seems reasonable

to suppose that apparent instances of orthogenesis may

sometimes depend upon a single important chemical

change in an organism, followed by slow and progressive

modifications leading up to a definitive morphological re-

sult. Such a process would be somewhat analogous to

the establishment of a condition of equilibrium.

ORTHOGENESIS IN BACTERIA

PROFESSOR CHAS. B. LIPMAN

UNIVERSITY OF CALIFORNIA

Ir is well to understand at the outset that bacteria, un-

like plants and animals, can not be studied from the

orthogenetie standpoint in the strict sense, owing to the

lack of a proper vantage point, or, perhaps more correctly

speaking, a basis from which one may start such a study.

In my opinion, all attemps at the establishment of sys-

tems of bacteria, and there have been many, have ended

in creating greater confusion than there was at the start.

Such frustration of well-intentioned programs was inevi-

table for at least three reasons, to wit: (1) Every bac-

teriologist used criteria of his own for the establishment

of new species. This is bound to lead to chaos. (2)

Nearly all bacteriologists used a morphological basis for

classification. Owing to the relative simplicity of form

of bacteria, this must inevitably result in erroneous dis-

criminations. (3) Nearly all bacteriologists in the past

and even to-day are laboring under the misconception that

bacteria are simpler forms of living organisms than they

really are. That this is incorrect has been shown by the

studies of Lohnis and Smith in 1916* and of Lóhnis alone

very recently.’

But assuming the foregoing to be true, it must follow

that it is impossible to trace the evolution of new species

. of bacteria in a definitely directed course. Not being cer-

tain what constitutes a forward or what a backward step

1 (a) ‘* Life Cycles of the Bacteria,’’ preliminary communication, Jour.

Agric. Res., Vol. 6, No. 18. (b) ** Life Cycles of the Bacteria,’’ paper read

at New Haven meeting of Soe. Amer. Baeteriologists, Dec. 27, 1916.

? ** Studies upon the Life Cycles of the Bacteria,’’ Part I, Review of the

Literature, 1838-1918, Nat. Acad. Sciences, Vol. XVI, Second Memoir.

105

106 THE AMERICAN NATURALIST [Vor. LVI

in bacterial development, it is obvious that we can not

apply as justifiably as we do in the case of the higher

organisms the criteria of definitely directed evolution.

To be sure, we have a number of instances of the estab-

lishment of permanent new characters in bacteria, yeasts,

and other fungi through the influence of a change in en-

vironment. Most of these are, however, induced through

changes in the medium under artificial conditions and

they do not necessarily indicate a change in the direction

of improvement of the organism or of greater complexity

in its organization which may in turn point to the evolu-

tion of a higher form from a lower one.

Despite the foregoing, it is probably well to examine

into certain facts with which we are familiar with regard

to microorganisms, and which may, perhaps, have a close

bearing upon what might be regarded as orthogenesis in

bacteria. The first fact to which I wish to refer is that .

of parasitism. There can probably be very little doubt

that parasitism on the part of bacterial cells is not an

original, but an acquired character, using the term ‘‘ac-

quired’’ in its literal, and not technical, sense. If that is

granted, it would also follow that the aequirement of such

a characteristic by a microorganism would mean the

gradual adaptation of a bacterial cell from one kind of a

medium to another. It would mean the gradual acquire-

ment of partiality on the part of a microorganism

towards certain chemical substances, certain tempera-

tures, or certain other conditions which obtain only in a

living host and not in an inanimate medium. The steps,

gradual or rapid, by which the aequirement of such pecul-

iar characteristics on the part of the microorganism

would occur in its change from a saprophyte to a para-

site would almost seem to imply evolution in a definite

direction. In a sense, therefore, we may regard para-

sitism in bacteria as an evidence of orthogenetie develop-

ment in such organism. It is, moreover, a case of evolu-

tion in a definite direction through the influences of en-

vironmental factors of the natural order and not those

No. 643] ORTHOGENESIS IN BACTERIA 107

which are produced artificially. In respect, therefore,

of causal factors in the evolution of bacteria, we have

parasitism exemplifying the antithesis, so to speak, of

changes which we induce in bacteria in our artificial

media, or by changes in the environment. These observa-

tions would seem to possess cogency, not only in the ease

of obligate parasitism, such as that characterizing the

organism of human tuberculosis, or of anthrax, or of the

fungus of wheat rust, but also that of what we may call

facultative parasitism in which the organism may have

adapted itself to life, both as a saprophyte and as a

parasite through the influence of certain chemical or physi-

cal-chemical agencies in its environment which have ren-

dered its protoplasm more highly adaptable than that of

the obligate parasite. We may, therefore, regard facul-

tative parasitism as an instance of orthogenetie evolu-

tion, just as we may so regard obligate parasitism. The

puzzling question whieh may, however, arise, from these

considerations is, which is the more advanced step in

orthogenesis in parasitic bacteria. Is the obligate para-

site the more advanced form, or is the facultative parasite

the more advanced form? While many would probably,

on first impulse, regard the former as the correct answer,

it does not necessarily follow that such is the case. Cer-

tainly in this regard, a great many more facts are needed

before any definite statements can be made.

Examples of other cases of orthogenetie evolution in

bacteria other than the case of parasitism, which I have

just discussed, may be multiplied ad libitum. But, owing

to limitations of time and space, it will suffice to mention

a few only.

The adaptation of bacteria to the physiological char-

acteristic of nitrogen fixation, such as is possessed by all

the Azotobacter species, and the Clostridium species and,

to a slight extent, by many other species, can scarcely

have been the result of anything else than a case of def-

initely directed evolution. This was probably accom-

plished through the influence of an environment in which

108 THE AMERICAN NATURALIST [Vorn LVI

it was impossible for the organisms existing therein to

live without aequiring a power of employing energy exist-

ent in carbonaceous material to fix atmospheric nitrogen

and make it available for their own life processes. The

next ease which may be cited is that of the lactic-acid

bacteria, which possess the power of transforming lactose

(or milk sugar) into lactic acid. These cells are not in

form or otherwise in function appreciably different from

any other bacteria with which we are acquainted. They

have, nevertheless, this specific and peculiar power to

which I have alluded. Is it likely that they have acquired

this power through any other influence than the influence

of environment which operated in a definite direction and

hence orthogenetically? The sulphur bacteria, or par-

ticularly those species of sulphur bacteria which have the

power of oxidizing sulphur to sulphuric acid, are another

ease in point. The nitrifying bacteria are still another

case in point. The iron oxidizing bacteria are still an-

other case, and so we might go on and mention very many

classes of bacteria, in each case of which there is a def-

inite, distinct, and strikingly peculiar functional power

which could not well have been developed without the

influence of some environmental factor or factors opera-

ting in a definite direction. It is not so easy on the mor-

phological side to give examples like those which I have

just cited from the point of view of function of the bac-

teria. The reason for that has already been touched on

above, namely, the simplicity of form and particularly

the slight variety in form which characterizes the bac-

teria. In fact, it is my conviction that it is best to ignore,

largely, morphological factors in bacteria when we study

the problem of bacterial evolution. My conviction arises

from a study of many and varied experiments which I

ean not discuss here.

Viewing our subject, then, from the standpoint that

orthogenesis in bacteria would be concerned with pro-

gressive changes in the organism, prineipally physio-

logical, due to its response to changes in environment, it

No. 643] ORTHOGENESIS IN BACTERIA 109

seems that we must admit that orthogenesis does exist

there. But if, on the other hand, progressive changes

like those in question must also be in the direction of pro-

ducing a more advanced form of organism, we are con-

fronted by a quandary resulting from a lack of an ae-

cepted definition for the term **advanced.?'

The argument that bacteria do not at all lend them-

` selves to appraisal as regards evolution by the standards

applying to the higher organisms is, perhaps, not sound

as shown again by the researches of Lóhnis, which I have

just cited. The objection to viewing bacteria in a man-

ner similar to the higher organisms because no sexual

reproduction is known among them is removed by Lohnis’

observations, which indicate that something akin to a real

conjugation of cells does occur in the bacteria. His stri-

king monograph in the Memoirs of the National Academy

should be read and studied by all those who seek new

light on the origin and nature of bacteria.

Another point of view which I believe may be intro-

duced into this discussion with some justification results

from a broad comparison of natural phenomena gener-

ally. In the inanimate world, we are confronted by the

evolution of substances in series in which the first mem-

ber of the series is simple and by small accretions be-

comes progressively more complex in the succeeding

members of the series until very complex materials are

finally built up. We are all well acquainted with the

seriation showing progressive complexity in the hydro-

carbons beginning with methane and going up; in the car-

bohydrates beginning with formaldehyde and going up;

in the proteins beginning perhaps with amino acids and

going up. Such examples of progressive seriation may

be multiplied ad libitum. Why, therefore, should it not

be possible that similar series should arise in the progres- .

sive evolution of bacteria through certain forces as yet

largely unknown which cause accretions of characters, so

to speak, to occur in bacteria through their being ren-

dered more complex and complicated by the influence of

110 THE AMERICAN NATURALIST [Vor. LVI

certain factors of the environment. It seems inconceiv-

able to me that the great diversity and complexity of

funetional nature in the baeteria eould have arisen other-

wise. Nevertheless, analogies between phenomena in

animate and inanimate nature must not be pushed too

far in the absence of the necessary facts for their sup-

port. While I believe them to be of great significance, I

do not desire to be dogmatie on the subject in the slightest

degree.

While all the foregoing as regards the evidence for

orthogenesis may be accepted as true, it does not follow

that the doetrine of orthogenesis is anything new or sig-

nificant or was so when it was first enunciated. It seems

to me to constitute merely one way of describing the

aetual eondition of progressive series in evolution, but

it seems to me that it explains nothing. In so far, how-

ever, as its advocates espouse the cause of those who be-

lieve in and give evidence for the inheritance of acquired

characteristics, the potency of environment in inducing

fundamental and permanent changes in the organism, and

the theory of mutation, they do contribute something sig-

nificant to the discussions and experiments which consti-

tute the amorphous symplasm, metaphorically speaking,

from which our knowledge of the well-defined and real

nature and origin of life may some day be expected to

emerge.

It is, perhaps, of particular importance now to con-

sider the bacteria as a class and their probable origin as

bearing on the question for which we are trying to find

an answer. There is a general disposition, and particu-

larly is it true that there has been in the past, on the

part of biologists and natural philosophers, so called, to

place the bacteria in point of origin among the most

primitive of living organisms. There is much inclination,

indeed, to regard them as the most primitive organisms.

While, superficially, this view seems attractive and cor-

rect, it loses much of its eogeney when one takes into

consideration the following situation: In all but a few

No. 643] ORTHOGENESIS IN BACTERIA 111

exceptional forms of bacteria, some of which I have

named above, the physiological characteristic is either

that of a saprophyte or of a parasite. It seems obvious

to me that neither a saprophytic nor a parasitic organism

can well be expected to originate in an environment

which is devoid of elaborated organic matter. Subject

to considerations which I shall diseuss later, we must,

therefore, accept one or two conclusions with regard to

the origin of bacteria in the seale of evolution of organ-

isms generally. Either they are the most primitive

forms of organisms which have lost their primitive

powers of living in purely inorganic media, or they are

a much more advanced form of life which came to be after

other organie forms had for some time been developing

on the earth's surface. The first possibility is merely

tantamount to saying that some cells of the most primi-

tive forms have gradually adapted themselves to either a

saprophytie or a parasitie existence and, therefore, is of

little assistance to us. The correctness of the second con-

clusion, however, would seem to depend on many little-

known factors. Still, it is the belief of many scholars.

Putting the matter in another way for greater clarity

and emphasis, I may state it as the opinion of several

plant physiologists who have speeulated upon this sub-

ject, that the primitive forms of living cells were prob-

ably those which could live in a purely inorganic medium.

Obviously, such cells must have been limited to the group

which we now eall the autotrophie organisms, and of the

autotrophic organisms, since the higher plants are cer-

tainly a very advanced form, we must have had some-

thing very much simpler, and the natural conclusion is

that such a simpler form of organism must have been

the single-celled green alga, or forms closely similar to

it. If we assume that such was the case, then it is not

diffieult to propose a scheme of evolution of the baeteria

which involves the gradual change of the unicellular

green alge into a variety of bacterial forms through the

influences of environmental faetors as I have already in-

112 THE AMERICAN NATURALIST [Vor. LVI

dicated. It is not at all inconceivable that a green algal

. cell may have adapted itself gradually to life within a

higher plant cell or within an animal cell, or to a sapro-

phytic existence in soil or other media devoid of light.

It may first have come there accidentally and then,

through the power to respond to such an environment

and to tolerate it, has gradually evolved new powers and

has lost some of its old powers. It is conceivable, there-

fore, that whether we regard parasites and saprophytes

among the bacteria as degraded forms or not, they

may be examples of evolution in a definite direction, pre-

sumably in this case in the direction of greater complex-

ity of function resulting from the urge of a constantly and

markedly changing and potent environment.

Since the foregoing observations on orthogenesis in

bacteria have led me to enunciate in another form a theory

accounting for the origin of bacterial forms which has

been discussed before, I feel constrained to go one step

farther into that subject in order that my own views may

not be misunderstood. While the idea of accounting for

the origin of the bacterial cell from the single-cell alga

seems attractive and appears to be in consonance with cer-

tain well-known facts, there are several troublesome

features about it. In the first place, it assumes the de-

velopment of so complicated and intricate a substance as

chlorophyll before any form of living substance was

evolved. While this may, of course, have been the case,

it seems doubtful, in view of what we must consider to

be the highly specialized nature of the green pigment of

plants. In the second place, we have seen that the strong

argument in favor of the theory of the single-celled alga

as the primordial cell, or rather against the theory that

bacteria may have been such primordial cells, lies in the

well-known fact that most bacteria require organic com-

pounds as energy for their life processes and that no

organic matter could have been available without the

activity of chlorophyllous organisms. This argument,

however, overlooks two points, viz., first, the existence of

No. 643] ORTHOGENESIS IN BACTERIA 113

autotrophic bacteria and, second, the possibility and even

probability that suffieient amounts of organie matter for

baeterial purposes may have been elaborated at the dawn

of life by chemical means, using the term ** chemical "'

in the broadest sense. It is, of course, well known that

the autotrophie bacteria, for example, the nitrifying bac-

teria, can live and build organie matter out of purely

inorganie substances, carbon being obtained from earbon

dioxide of the air, and in the absence of light and chloro-

phyll. But if this is so, why may it not be that of the

known forms of living cells, the autotrophie bacteria

were the first, since they are capable of living in a purely

inorganic medium, the ammonia which is necessary to

them being supplied from the small amounts resulting

from chemical reactions induced by electrical phenomena

in the atmosphere. As we have seen thus far, it may be

argued, with equal justice, that the activity of the nitri-

fying bacteria is a highly specialized one on the one

hand, and a very primitive one on the other.

But if, as just indicated, it should be argued that, after

all, the autotrophic bacteria are exceptions in the bac-

terial world and that most bacteria need elaborated or-

ganic matter and hence they could not have been the

primordial living cells, the second objection which I have

stated may be urged, namely, that organic matter may

have existed on the earth before living cells came into

being. Mature reflection will render it highly plausible

with the high temperatures, great electrical activity,

and probable intense radioactivity which existed on the

planet prior to the appearance of living cells, that un-

usual chemical activity inducing rapid and general com-

binations among the elements should have prevailed.

This, moreover, involves the assumption of the existence

of a degree of all these conditions which is requisite for

the synthesis, but not for the rapid destruction of the or-

ganic matter, which must also be conceded as probable.

Under such conditions, it is reasonable to suppose that

bacteria, on being evolved as the primordial cells, may

114 THE AMERICAN NATURALIST [Vor. LVI

have found the conditions requisite to their growth and

further development.

It seems, on careful deliberation, that strong arguments

may be brought forward for both the theory that single-

celled green alge and the theory that bacteria were the

primordial organisms, if we consider merely the argu-

ments which enter into the usual diseussions of the sub-

ject. But it appears to me that we must penetrate beyond

what is ordinarily called careful deliberation, if we would

see other possibilities for explaining the origin of living

matter. There is no logical reason for confining our

attention in these discussions to the single-celled alge

and the bacteria which we know. There are, in addition,

bacteria so small as to challenge and defy our ingenuity

for devising means for rendering them visible. What

may not further discoveries about their nature and re-

quirements for life unearth for us which may be of the

most vital significance to the solution of our problem? I

have tried in imagination to go beyond, far beyond, the

ultramieroseopie bacteria and have pictured to myself the

following condition for the origin of living matter: A

single molecule of organic matter, let us say, a polypeptid

or a proteid molecule produced by the force which I have

discussed, exerted as chemical energy, may, in floating

about in its aqueous medium on the earth’s surface, sud-

denly find itself in a field of radioactive ‘force or some

similar force which causes its atoms to orient themselves

in such fashion and to vibrate in such a manner as to

endow it with certain activities which we now regard as

attributes of life. Crude though this conception may be,

it constitutes a step, though perhaps a very bold one, into

the realm of possibilities for explaining the origin of the

first living cell, a subject which we must consider together

with all our theories of evolution if we do not wish to

remove the inspiration to progress by arriving at an

impasse in our theories and our hypotheses.

In conclusion, it is well to review briefly the discussion

which I have just presented in a very brief form. Out

No. 643] ORTHOGENESIS IN BACTERIA 115

of regard for your time and patienee, I have merely pre-

sented in outline each of the important considerations

which I deem of direct significance to the question at

issue. I have presented the diffieulties whieh lie in the

path of treating bacteria from the point of view of

orthogenesis, and yet have shown that they may be so

treated with certain justifiable assumptions as a basis.

Having thus treated them, however, I have shown that

whether the theory of orthogenesis holds for baeteria or

not, it can not be considered as explaining anything, but

merely as a mode of deseribing our observations. I have

gone into the more fascinating and what seems to me to

be the more useful diseussion of the origins of living

cells and the position of the bacteria with regard to such

primordial cells. I have mentioned the various hypoth-

eses which, in my opinion, may be considered to be the

most plausible in that connection, and have shown the

weaknesses and the strength of each. It has been my

purpose to give an unbiased presentation of my own

hypotheses and those of others without prejudiee to any

so that you might be enabled to diseuss them all and

arrive at your own conclusions. Without a thorough

review of the literature of bacterial physiology and mor-

phology, it is not easy to obtain a broad enough view of

the subject to do it justice and I would urge particularly

that those who are interested in it acquaint themselves

with the absorbing and inspiring literature of the subject

of mutation in microorganisms. I believe that it is full

of significance for biological progress and I wish that cir-

cumstances made it possible for me to present a brief

review of it for your consideration. As it is, I must

content myself with directing your attention to it and with

expressing the hope that my humble efforts in preparing

and presenting this paper will constitute a step forward

in our progress of thought and experimentation on prob-

lems in the evolution of living matter.

ORTHOGENESIS AND SEROLOGICAL

PHENOMENA

PROFESSOR M. F. GUYER

UurivERSITY OF WISCONSIN

As my diseussion progresses I fear that some of my

hearers may be reminded of the old joke about the mon-

goose. A stranger carrying an odd-looking box was asked

by a man whose curiosity got the better of his good man-

ners, what was in the box. The stranger replied that it

was a mongoose and went on to explain that his brother

was subject to delirium tremens, during the attacks of

which he believed that he was being strangled by snakes;

this mongoose was to catch the snakes. To the reminder

by the inquisitive man that these were imaginary snakes

he retorted, ** Yes, I know, but this is an imaginary mon-

goose."

Since some of our most competent investigators in the

fields of geneties and evolution are skeptieal apparently

about the whole question of orthogenesis, to them, at least,

I shall be making an imaginary attack upon a mythical

phenomenon. President Kofoid, however, seemed to think

that some of the recent work with immune sera done in

my laboratory, which strongly indieates the induction of

permanent germinal modifieations, might have possible

theoretieal implieations bearing on the question of ortho-

genesis, and I agreed to diseuss the subject, although

realizing at the outset that the net result would not be

a scientifie proof, but merely a suggestion which might

possibly be of some value as one of various working

hypotheses.

First as to orthogenesis itself; is there such a process?

Our answer must depend largely upon how we define

orthogenesis. It takes but a glance at the literature of

the subjeet to see that it has meant many different things

to many different people, ranging from a mystical inner

116

No. 643] SEROLOGICAL PHENOMENA 117

perfecting principle, to merely a general trend in devel-

opment due to the natural eonstitutional restrietions of

the germinal materials, or to the physical limitations

imposed by a narrow environment. In most modern

statements of the theory, the idea of continuous and pro-

gressive change in one or more characters, due according

to some to internal factors, according to others to external

eauses—evolution in a ‘‘ straight line "—seems to be

the central idea. To many, faced by the seeming im-

possibility of explaining by natural selection the origins

of new characters, it has been apparently merely a wel-

come general utility concept by which one may account

for the beginnings of new organs, or the development of

parts along definite lines, irrespective of utility.

For present purposes nothing is to be gained by a

review of the different theories of orthogenesis, all so

well summarized in Kellogg's ‘‘ Darwinism To-day,’’ and

I shall proceed merely on the assumption that, judging

from the statistical law of errors, certain variations are

apparently not fortuitous, since they tend to accumulate

in certain directions. It is customary to add that the

lines of development which result are independent of, and

in extreme cases may be opposed to, the operation of

natural selection. I see no reason, however, for believing

that if variations occur in definite directions of no use

to the organism, why they may not also occur just as

definitely in directions which lend themselves to the per-

fecting influences of natural selection. The difficulty in

determining this point lies in the fact that an evolution

based on the selection of even fortuitous variations must

in one sense be orthogenetic, that is, along definite lines,

so that there is no way in retrospect of telling whether

the underlying germinal variations were purely fortu-

itous, or whether they were biased toward an adaptive

outcome.

Of the various lines of evidence brought forward in

support of theories of orthogenesis, the ones which ap-

peal most convincingly to me are: (1) those based on

118 THE AMERICAN NATURALIST . [Vor. LVI

parallelisms in variation which appear in different

branches of the same large group of organisms; (2) those

argued from the premise that the very nature of the

chemical complexes which constitute the body of a living

organism necessarily limit changes to relatively few di-

rections; and (3) some of those instanced in the field of

paleontology.

As to examples of parallelisms in related forms, I am

most familiar with conditions to be seen in the color

patterns of the pheasants (Phasianine) and the guineas

(Numidine). Ina paper’ written some years ago I sum-

marized my observation on various features of the colora-

tion in a number of groups of genera and species in these

two subfamilies as follows:

. . there are certain basic tendencies for particular elements of

the coloration, such as the formation of eye-spots, barring, and the

like, to follow along definite paths of development. When arranged

with reference to one of these elements, such, for example, as bar-

ring, which is one of the most universal, instead of possessing dis-

tinct and unrelated markings, the different species in a given group

are seen to be standing merely at different levels in the develop-

ment of one, or at most a few, continuous progressions of the special

pattern in question. Since when so grouped the gradation in

pattern is as much in evidence between collateral kinsmen as be-

tween those of direct lineage, one can only conclude that the bias

toward a particular line of patterns is the product of fundamental

protoplasmic peculiarities implanted in the group as a whole.

Further on in the same paper it is shown that where

the pattern has become obscured it may be brought to ex-

pression again through hybridization. In the interesting

group known as the peacock pheasants (Polyplectron)

which by systematists is regarded as intermediate be-

tween the peafowls and the pheasants in the narrower

sense, the varying stages and types of ocellation to be

seen afford a good illustration of the point at issue. Quo-

ting again from this earlier study:

Again as regards ocelli or *eye-spots" in P. chalcurus, which

appears to be the most generalized species, one finds no ocellation.

The only hint of what is to be realized in the more specialized

1 Jour. Exp, Zool., VII, 4, 1909.

No. 643] SEROLOGICAL PHENOMENA 119

members of the group is found in a pronounced purplish and green-

ish “metallic” coloration present on certain feathers of the tail.

In the male of P. emphanes, while there are numerous green metallie

iridescent areas on the feathers of the upper wings and back, they

have not yet progressed to the condition of being definite ocelli,

although on the tail of this same individual there are two trans-

verse bands (the one on the retrices, the other on the upper tail

coverts) of ocelli. Still a step in advance, in the male of P. thibet-

anum, Gm. (P. alboocellatum Cuv.; type, Mus. d'hist. nat, Paris) '

the small feathers of the wings and the feathers of the inter-scapular

region bear distinct small purple ocelli ringed successively with

black, light brown, and white. The tail is also banded with ocelli.

In the male of P. germaini the wing-coverts and back bear numer-

ous green ocelli. The female of this species, as usual less advanced

phylogenetically than the male, has the ocelli of the body much less

distinctly marked

An idea frequently attached to the theory of ortho-

genesis, yet which I believe is in no wise a necessary

part of it, is that the various grades of a feature supposed

to show orthogenesis have arisen as a connected succes-

sion, the supposedly most advanced stage having emerged

from the stage next in order below it. That the individ-

uals of a large group which show some particular char-

acteristic expressed in different degree can be arranged in

a gradational series with reference to that characteristic

is obvious, but, as pointed out by various critics of the

theory, this does not prove that the various expressions

of the character in question arose thus sequentially.’ In

a recent study yet unpublished, made by Miss Sarah V.

Jones in the department of genetics at the University of

Wisconsin, on the genetical behavior of checks and bars in

inheritance in pigeons, for example, Miss Jones corrob-

orates the results obtained by Staples-Browne and by

Bonhote and Smalley which show that the two patterns

are independently inherited in Mendelian fashion with

checked-wing dominant to barred. She also found the

relation of uniform black to check to be one of simple

dominance, and furthermore, that certain grades of check-

ing are inherited independently. But she found no evi-

dence in support of the well-known view of Whitman that

120 THE AMERICAN NATURALIST [Vor. LVI

the various grades of checks form a series moving in one

direction, the ultimate outcome of which is the two-barred

and finally barless types. And Miss Jones points out

that it does not ‘‘ necessarily follow that because the

interaction of these several factors produces an apparent

epistatie series, the mutations producing the various

grades of checking should have occurred in any particular

order.’’

And here, to my mind, is the erux of the matter. In

order to have what may legitimately be termed orthogen-

esis, do the underlying mutations have to occur in any

particular order? Is not the very fact that, instead of

existing as a medley of wholly unrelated elements, certain

characteristics of organisms, such as color markings, can

frequently be arranged as parts of a definite pattern or

as stages in a general process—does not this in itself

indicate directional variation? When one sees in its

incipiency, as it were, in one species a character which

has attained to an advanced expression in a kindred

group, especially where there are intermediate expres-

sions of the same characteristic in other related species,

is not this indicative of a general trend in variation?

For instance, is not the tendency toward the formation

of ‘‘ eye-spots "' in the plumage of the pheasants hinted

at even in the greenish-black iridescence so often visible

in the tail feathers of the common rooster—is not this

tendency the expression of what in last analysis must be

a germinal bias? To be sure, this bias finds different

ranges of expression in different species: as eye-spots on

the wing-feathers in some species, on the body-feather:

in others. In one species they may occur as a single row

of ocelli, in another as two rows, across the tail. And

it is obvious that certain of these patterns have not been

derived directly from others, since they appear in what

are clearly collateral lines. Nevertheless, the tendency to

form ocellations is present in many if not all species of

this great group. We know nothing of the order in which

the mutations occurred which brought about any partic-

No. 643] SEROLOGICAL PHENOMENA 121

ular condition that at present exists in the group. Some

of them may have been small and sequentially related,

and it is not impossible that the extremes were thrown

in one line, while grades of less advanced type came into

expression in collateral lines. It is also clear that even

should certain grades have arisen as a progressive series

there is no reason, from the viewpoint of the mutation

theory, why any two partieular grades should not show

the characteristies of Mendelian unit-characters, irrespec-

tive of the order of their origin. The important point is

that in this group when mutations occur in certain col-

or pattern-controlling factors, whether great or small,

they tend toward the formation of eye-spots in some

degree.

While we know little of the chemistry of animal pig-

ments, the reactions involved in color-production in cer-

tain plants are better understood, since many of the pig-

ments have been extracted and analyzed. Along with the

understanding of strueture that has been gained in the

chemical studies of synthetic dye-stuffs, has come con-

siderable knowledge of the relation between color and

molecular structure. In many cases, for instance, as

Nietzki? has shown, where the pigments of most simple

construction are yellow, by increase of molecular weight

they change to red, next to violet, then to blue. A good

review of the theories of color in organic compounds,

given as an introduction to her own painstaking and

valuable chemical researches? on ‘‘ Pigments of Flower-

ing Plants,’’ will be found in a recent paper by Dr. Nellie

A. Wakeman. Most of the information about organic

pigments used in the present discussion has been obtained

from this source.

Upon reading such a piece of investigation together

with the accompanying discussion of related studies one

is impressed by the fact that a comparatively few proc-

esses underlie most pigmentary changes in plants. En-

zymes—hydrolases, reductases and oxidases—frequently

2 Trans. Wis. Acad., XIX, Part II, pp. 767-906, Madison, Wis.

122 THE AMERICAN NATURALIST [Vor. LVI

play an important part in the formation of pigments,

or in changes in pigments already formed. Shade of

color, for example, is evidently often merely a function

of oxidase content. With a graded increase of oxidase,

therefore, a plant might be put through a regular gamut

of color effects. In general, the mere addition of hy-

drogen to dye-stuffs reduces them to the corresponding

leuco base. Armstrong, in his quinone theory of color,

makes much of the quinones as the colored compounds

in dye-stuffs and maintains that the corresponding color-

less compounds are hydro-quinones. The structure and

size of the pigment molecule itself seems to be an impor- .

tant factor in color. Hydrocarbon radicals, for instance,

deepen the tint; the addition of hydrogen raises the tint.

In analyzing any particular case one has to take into ac-

count the original molecule, the position of any group

introduced and the number of groups introduced. It is

possible, for example, by the introduction of a tint-deep-

ening group to deepen the color, but by introducing two

or three more such groups to throw the absorption wholly

outside the visible spectrum and thus do away with the

color. From this it is clear that two compounds may be

closely related in constitution and yet one be colored, the

other colorless. As to why, physically, in both the aro-

matic and the aliphatic series, color is produced in certain

compounds and not in others, various investigators have

arrived at the conclusion that the cause of color is due

to ‘‘ the making and breaking of contact between atoms,

thus giving them marked activity,’’ a process known as

isorropesis, and Miss Wakeman goes on to explain:

This change of linkage which must accompany the transforma-

tion of one modification of the compound to the other is the source

of the oscillations producing the absorption bands. If these oscilla-

tions are synchronous with light waves of a high frequency they

give rise to absorption bands in the ultra violet and the compound

is colorless. If, however, they are less frequent, the absorption band

appears in the visible portion of the spectrum and this absorption

of colored rays results in the compound taking on complementary

color.

No. 643] SEROLOGICAL PHENOMENA 123

Among interesting facts that come to light in Miss

Wakeman's summarization may be mentioned the fol-

lowing: all organie pigment molecules are unsaturated ;

the quinone grouping is one of the best known of the

chromophorous groups; by far the largest number of

plant pigments are referable to hydrocarbons of satura.

tion C.H, .,, and C,Ha.,,; and finally, that it is the

relation of the ehromophorous groups to each other and

to the rest of the molecule, and not their mere presence

in the molecule, that postulates color in a substance.

I may seem to have dwelt unduly upon pigmentation in

plants but I have tried to go into the matter only suffi-

ciently to give a glimpse of some of the real conditions

which underlie some of the ‘‘ unit-characters ’’ we are

juggling about in genetics, and around which we are

attempting to frame hypotheses of evolution. Color, per-

haps more than any other one thing, has in recent years

been utilized for genetical observations. And when it is

known that in many cases color is merely a function

of the degree of oxidation of some fundamental com-

pound, or the introduction or subtraction of some hydro-

carbon radical, it does not tax the imagination to conceive

of how it is possible to have series of color ** characters ”’

that in the parlance of organic evolution represent ortho-

genetic series. As simple a matter as the relative degree

of oxygen supply, probably determined by the amount of

an oxidase present, may account for various stages of

color. It is manifest, moreover, that in a given group

there might easily be a tendency toward increase in oxi-

dase-production, which if present unequally in different

collateral lines might give us just the uneven condition,

with different species standing at different levels of ex-

pression of the trait in question, which exists in various

alleged cases of orthogenesis. It is obvious, furthermore,

that any higher state of development of the character in

a particular species need not have sprung from the next

lower stage, but may have had its immediate origin

from any level of the scale.

124 THE AMERICAN NATURALIST [Vor. LVI

Most of the constitutional changes which go on in the

living organism seem to center in the proteins of the

protoplasm. Metabolism is largely a question of the dis-

ruption and reconstruction of the various cell-proteins.

In the cell, moreover, the characteristic protein-complexes

themselves determine the nature of the synthesis that shall

go on. When synthetic activity is more than sufficient to

make good metabolic waste, growth results, and when such

increase becomes overgrowth and takes the form of a de-

tached individual, we pronounce it reproduction. Weare

then in position to talk about inheritance—the fact that a

new individual possesses the properties and, under similar

conditions, therefore, will express the activities and take

on the appearances of the earlier or parent form. Thus

the germ-cell is a reduplication of the zygote from which

it sprang, a detached bit of living matter made up largely

of certain characteristic protein-complexes. Even the

simplest protein is a huge molecule built up of a series

of different kinds of amino-acid ‘‘ nuclei ’’ which in differ-

ent proteins differ in numbers, kinds and arrangements.

Certain of them seem necessary to all proteins, others

are present in only some proteins. Each amino-acid, be-

sides being linked to its fellow, has a replaceable hydrogen

atom which may be exchanged for any one of several

radicals or ‘‘ side-chains." Furthermore, the ordinary

native proteins are secondarily compounded of a number

of the simpler blocks formed of linked amino-acids. The

unitary amino-acids which enter the blood as protein

digestion-produets are used as building units again, each

cell selecting the kind of units it requires for replace-

ments in its own proteins.

We have no reason to believe that the proteins of the

germ-cells have any mysterious powers associated with

them that are not shared by any or all of the somatic

cells. The modern view of embryogenesis and histo-

genesis no longer finds it necessary to picture troops of

pangenes departing from their home in the nucleus at

just the proper time to take possession of the cytoplasm

No. 643] SEROLOGICAL PHENOMENA 125

and turn the cell into a specifie tissue-cell. Each tissue-

cell probably retains all the essential properties of the

original fertilized ovum from which it has directly de-

scended. In many cases, among lower organisms, at least,

we know that somatie cells detached as buds or experimen-

tally ean through regulation and new growth reconstruct

themselves into complete organisms. That a particular

cell takes on the characteristics of a specific tissue seems

to be determined by the special environment in which the

cells happen to be placed in the organism.?

Exactly how much chemical difference there is between -

two unlike tissues or between the cells of a particular

tissue and the germ-cells is not known. As far as we

have any cytological evidence to the contrary the nuclei,

at least, of the tissue-cells are not essentially different

from the nuclei of the germ-cells. While the various tis-

sues differ very much in appearance, this is mainly the

result of the accumulations of intercellular products or

of cytoplasmic modifications. And many of the latter

may be largely changes in colloidal state rather than

fundamental changes in chemical composition. In any

event, the new condition is one which has sprung from a

cellular chemical constitution similar to that of the orig-

inal zygote. And if this is true, would not any internal

or external agent which could affect particular proteins

of the somatic cells be able also to influence the homol-

ogous elements in the germ-cells?

Inasmuch as I have already twice reported to this Soci-

ety on the work‘ of Dr. Smith and myself with fowl-serum

immunized to rabbit-lens. by means of which, through

injections into pregnant rabbits, we succeeded in obtain-

ing defective-eyed young, I shall not again relate the

details. The most interesting thing about the experiment

was the fact that the eye-defects were transmissible to

subsequent generations, and inasmuch as the condition

3 Cf. Child, ‘‘ Individuality in Organisms ’’; also ‘‘ Origin and Develop-

ment of the Nervous System.’’

4 Jour. Exp. Zool., 31, 2, 1920. Am. Nart., LV, 1921.

126 THE AMERICAN NATURALIST [Vor. LVI

could be passed down through the male line alone it is

evident that it is based on changes in the germ-cells.

In later experiments we obtained similarly defective

young by injeeting rabbit-lens into pregnant rabbits, al-

though we secured this result only after repeated trials

and in the young of but one female. Our belief is that

the eytolytie serum not only attacked the newly forming

fetal lens, but also its representatives in some of the germ-

cells of the fetus. "This implies, of course, that there is

a sufficient thread of chemical identity between the two

to render them both susceptible to the same specific in-

fluence. ;

For such serumal. effects to be of significance in evolu-

tion, however, the antibody or other factor operative on

a given tissue-protein would have to be one that could

arise directly in the organism itself. But since it is

known that animals will develop anaphylaxis against tis-

sues of their own species, and that a rabbit can be made

to build spermatotoxins against its own spermatozoa, it

is reasonable to suppose that if an animal’s own tissues

became displaced, injured or otherwise modified, they

might cause the production of antibodies. And these,

carried by the circulating fluids of the body into the

gonads, would have opportunity to influence suċh protein-

complexes there as were similar to those in the tissues

which served as antigens. Nor need the germinal and

somatic elements in question be identical in constitution,

for it is known that while an antibody against a particular

tissue shows its highest degree of specificity only against

that tissue, nevertheless, it will also react in some degree

with other tissues of the same individual. This phenom-

enon, termed species-specificity, clearly indicates that

there is a broad common basis of chemical identity under-

lying all the tissues of an organism. It is not unreason-

able, then, to believe that there is sufficient chemical iden-

tity between the proteins of tissue cells and the related

proteins of the germ for both to be influenced by the

same agents.

To construct a working hypothesis upon the possibilities

No. 643] SEROLOGICAL PHENOMENA 1A

before us we might suppose that as long as all tissues

are in normal physiological balance no antibody or similar

modifying agents are developed. The germ-cells, there-

fore, maintain the exaet constitution they derived from the

Zygote from which they descended. But with the occur-

rence of injury, undue stimulation or pronounced change

in any part of the body, serological changes would prob-

ably be produced in the blood-stream and the germ-cells

would then be exposed to possible modifying influences.

This would be more likely to happen, of course, if the ex-

posure continued through a long period of time. If the in-

fluence were disintegrative or poisonous as the eytolysins

or cytotoxins evidently are, then probably degenerative

changes would ensue. Such a hypothesis affords, perhaps,

a plausible explanation of such deteriorative evolutionary

processes as those seen in the formation of vestigial or-

gans. As a concrete illustration, purely hypothetical of

course, we may suppose that such a species as the mole

in gradually changing to a subterranean existence would

meet with frequent injuries to the eyes, and that, as a

result of the ensuing inflammatory and suppurative con-

ditions, resorptive influences would be set to work which

not only affected the proteins of the eye, but also the

related proteins of the germ. Once the degenerative proc-

ess got to going, it might for a time be based in each new

generation upon both the direct chronic irritation to the

eye and the parallel changes induced in the germ. Fi-

nally, we may suppose that the somatic influence would

cease when the eyes became of small size and the eyelids

remained permanently sealed, but that the conditions

induced in the germ would persist. If such atrophied

eyes continued to be resorbed more or less in each gen-

eration, however, variation toward still further reduction

might continue in the germ. Such a progressive degen-

eration might possibly be ranked as an instance of re-

gressive orthogenesis.

But what of the progressive aspects of evolution? Can

serological reactions be invoked here with any show of

reason? One great difficulty in dealing with progressive

128 THE AMERICAN NATURALIST . [Vor LVI |.

variation is that we know almost nothing about the chem-

ical and physical factors which underly growth, hyper-

trophy, hyperplasia, metaplasia, or other changes in

somatie tissues due to changed internal relations or to

unusual environmental stimuli. If. we only knew, for

instance, what happens in even as simple a case as when

epidermal cells develop into a callous in response to undue

pressure or friction, we might have a clue as to how, also,

constructive changes might occur in germ-cells; but we

have no such knowledge.

Certain types of tissue-overgrowth' in which there is

increase in the size of the tissue-elements (hypertrophy)

or in the number of such elements (hyperplasia) are

interesting in this connection. For example, increased

strain in bone leads to increased growth of bony tissue,

or excessive exercise leads to overdevelopment of certain

muscles. In such cases an increased demand on the nutri-

tive stream caused by unusual katabolism results in a

physiological hypertrophy. That is, an excessive syn-

thesis of certain types of proteins is set up. Does the

impetus to such extra synthesis extend also to the

related, though unstimulated, tissues? I know of no evi-

dence bearing directly on this point, although such phe-

nomena as compensatory overgrowth show that there are

influences at work outside the immediate tissue itself

which are instrumental in inducing the hypertrophy.

For example, if one of a pair of organs (lung, kidney,

testicle, thyroid) is lacking or is destroyed, the other en- -

larges in a short time to the size and functional capacity

of the pair combined. There is considerable evidence,

particularly in the field of pathology, to show that under

ordinary conditions the tissue-elements exert a sort of

balanced reciprocal restraint, but disturb this and the

whole system is more or less deranged until a new equilib-

rium is established. Since in compensatory adjust-

ments the compensating organ is generally not in direct

connection with the one which is missing or disturbed,

it seems probable that the agent which incites the hyper-

5 Cf. any General Pathology.

No. 643] SEROLOGICAL PHENOMENA 129

trophy is carried by the blood, although the possible influ-

ence of the nervous system must also be reckoned with

in higher animals. And if there is such a serum-borne

agent in the case of compensatory hypertrophy, may

there not also be one in that of the ordinary physiolog-

ical hypertrophy of the exercised muscle or stressed

bone? If so, we must keep our minds open to the pos-

sibility that it may also stimulate the germinal proto-

types of such proteins to additive functioning. For if

we had but a single side-chain in common between a pro-

tein of somatie tissue and a protein of the germ, any-

thing that could affeet one might well be expected to

affect the other.

Again, mechanieal stimuli, if not too severe, and vari-

ous irritative substanees in amounts sufficiently small not

to be destruetive or poisonous to the tissues, may stimu-

late cells to overgrowth. Very small amounts of arsenic

or phosphorus, for example, may thus affect the kidneys

and liver, and minute doses of phosphorus may cause in-

creased growth of bone. In such cases also it is probable

that serological changes are involved. This is almost

certainly true in eases of viearious overgrowth, where an

organ supposedly of related funetion takes over wholly

or in part the work of another tissue. An example of

this is seen in the enlargement of the pituitary gland

when the thyroid is atrophied or removed, or the com-

pensatory enlargement of the hemolymph glands and

bone-marrow following removal of the spleen. Still

further may be cited the phenomena of metaplasia, in

which, through modification of function and nutrition,

specialized tissues develop from cells which normally pro-

duce tissue of another order. It sometimes happens, for

example, that the choroid coat of a severely injured eye,

after the lapse of considerable period of time, will de-

velop a layer of true bone. In fact, metaplastic forma-

tion of bone is common in many tissues. Such facts

show that many, if not all, tissue-cells have the capacity

to form very different kinds of tissue in different en-

vironments, and suggest that they retain all the inheren-

130 THE AMERICAN NATURALIST [Vor. LVI

cies of the germ. They are what they are somatically :

because of the special restrictions or excitations of their

particular situation in the organism. But if these highly

specialized tissue-cells can be so stimulated as to form an

entirely different type of tissue, may not such stimulative

influences invade even the germ-cell with modifying ef-

fects?

Lastly, there are the endocrinal secretions to be reck-

oned with. Since they are at present popular subjects

of research and are constantly being alluded to and dis-

cussed in the biological literature of the day, I need not

review the field. It is evident that in them we have cir-

culating through the body a series of powerful substances

eapable of producing profound effects in any or all parts

of the body. Through them, apparently, various organs

effect reciprocal stimulations and the tissue-complexes of

the entire body are maintained in a state of general

physiological equilibrium. Both clinical and experi-

mental evidence reveals that hypertrophy or atrophy of

an endocrine gland may be followed by marked altera-

tions of structure or function in one or more regions of

the body. Thus the eretinism or the myxcedematous

condition which results from removal of the thyroid or

arrest in its function, or the symptoms resembling

exophthalmie goiter following hyperthyroidism are famil-

iar examples. The remarkable overgrowth of the bones

of the extremities and head known as acromegaly—mor-

bid giantism— associated with enlargement of the pitui-

tary body is another. Also the relations of the gonads to

the secondary sexual characters are well known, as is that

of the fetus to the normal hypertrophy of the mammary

glands in pregnancy.

Since hypertrophy or atrophy of an endocrine may pro-

duce deep-seated permanent changes in various tissues

of an organism, I would again point out the possibility

that the germinal homologues of the proteins of such

tissues, if such there be, might likewise be permanently

modified, and that if for some reason there came a con-

stant inherited increase or diminution of an endocrine

No. 643] SEROLOGICAL PHENOMENA 131

gland, or an environmental modification of it generation

after generation, we might have in its waxing or waning

output the exeitant necessary for germinal changes which

become outwardly expressed as a series of orthogenetie

changes. That this suggestion of endocrinal influence on

the germ is not so far fetehed as would appear at first

sight, is evident, I think, when we recall that certain of

the eonditions which ean be indueed in individuals by

experimental or pathological endocrinal upsets are known

to occur also as congenital defects which are inheritable.

For example, short-fingeredness (brachydactyly) may be

induced after birth by too much pituitary secretion, but

such a condition is also well known as a congenital defect

which is hereditary. In the latter case, is it more reason-

able to suppose that the short-fingeredness, could we

trace it back into the germ, is really represented by a

factor that has to do primarily with the finger or with a

factor directly concerned in some way with the pituitary

body? And did hypertrophy of the pituitary body origi-

nally induce the heritable type of brachydactyly? We do

not know, but the parallelism of the two conditions, it

seems to me is highly suggestive.

And let us glance for a minute at one of the well-

known studies on orthogenesis; that of Ruthven? on the

variations of seutellation in the garter snakes. In his

own words:

. it seems to me that the most tenable hypothesis of the evolu-

tion of the genus T'hamnophis is that it originated and became dif-

ferentiated into four main groups in northern Mexico. From this

region the groups radiated in all directions, but principally to the

northward, and wherever they entered different regions the changed

environmental conditions acted as an unfavorable stimulus which

retarded growth, and differentiated the groups into dwarfed forms.

And in another place he generalizes as follows:

(1) That the maximum scutellation and size in the genus Tham-

nophis occurs in the center of dispersal, and the forms that have

been produced in the history of its migration have been formed

principally by dwarfing and by a reduction in scutellation; (2)

that the variation in the number of scales in the different series is

6 Bull. 61, U. S, Nat. Mus., 1908.

132 THE AMERICAN NATURALIST [Vor. LVI

definite and not promiscuous, and is correlated in a remarkable

degree with changes in the environment.

Have we not here a condition strikingly like what we

should expeet to find if some factor or factors, external

or internal, were operating in such a way as to lessen the

output of some endoerinal secretion concerned in growth

or the determination of size? This is at least a possi-

bility worthy of consideration.

In elosing may I say that in what I have put before

you I do not pretend to have supplied the established

facts necessary for founding a scientific theory. The dis-

eussion is largely a series of suggestions, a mere work-

ing scheme which takes into aecount various phenomena

that appear to be related, and whieh in their present

states of disclosure seem to lend themselves to some such

interpretation as I have tried to give. It is presented

because, in my estimation, it suggests a line of thought

we may well entertain when we are wrestling with our

several problems of geneties, variation and evolution.

For if it can be clearly established that any one of the

serologieal influenees ean reach specifically from soma

to germ then it becomes a plausible hypothesis that many

of them do. If a changed or changing external or in-

ternal environment causes a long continued physiological

stress of certain parts, then as long as this stress is ac-

companied by changed conditions of the circulating fluids

of the body, so long also will the germ-cells be exposed

to these influences. If they are such as to induce varia-

tions in definite directions, orthogenesis must be the out-

come.

And if serological influences play an important part in

adaptive somatic changes, such as adaptive hyper-

trophies—or for that matter, adaptive atrophies—then

we have the way open to conceive of how adaptive ger-

minal changes may likewise be the outcome of these same

influences.

It is a noteworthy fact that in the geological past

whenever conditions suitable for new types of existence

occurred, new forms of life well adapted to the condi-

tions appeared. This has happened not only once, but

No. 643] SEROLOGICAL PHENOMENA 133

repeatedly. And since satisfactory adjustment to the

new conditions must mean not only one, but many favor-

able and interrelated variations, it seems almost incredible

that the adaptedness characteristic of the organisms in

question was attained merely through the operation of

natural selection generation after generation on as-

semblages of purely accidental mutations. Paleontolo-

gists tell us that times of marked evolutionary change

have coincided with periods of great geological change—

extremes of temperature, moisture or drought, or fairly

rapid fluctuation between such extremes. And while such

conditions would undoubtedly favor a maximal opera-

tion of natural selection, it is well to remember also that

the severe strains of somatic adjustment forced upon or-

ganisms existing at the time would doubtless result in a

maximal sweep of serological influences through the

sorely pressed body.

Although I have emphasized one side of the problem of

variation, I am not unmindful of the remarkable stability

of the germinal protoplasm as we see it expressed i in or-

ganisms to-day. It is obvious that not every minor or

temporary alteration in somatic mechanism is reflected

in the germ to any measurable extent. Since probably no

two living things of any kind are equally susceptible to

external influence, individual germ-cells doubtless vary

in susceptibility, possibly even the same germ-cell would

respond differently at different stages of maturity. It is

not unreasonable to believe, moreover, that only a few

out of many germ-cells might be sufficiently affected to

make a perceptible difference. I have already expressed

the opinion’ elsewhere that ‘‘no one to-day, qualified by

his knowledge of embryology and genetics to the right of

an opinion, would, I think, deny that the new organism

is in the main the expression of what was in the germ-

line, rather than of what it got directly from the body

." But we know that the germ does change from

irk "s time and it seems to my mind not illogical to sup-

pose that at least some of the changes are specifically re-

lated to changes in the soma.

7 Ax, Nart., LV, Mar.-Apr., 1921.

ORTHOGENESIS AS OBSERVED FROM PALE-

ONTOLOGICAL EVIDENCE BEGINNING IN

THE YEAR 1889!

DR. HENRY FAIRFIELD OSBORN

AMERICAN Museum or NATURAL History

1. THE OBIGIN oF SPECIES

Tur Origin of Species is now clearly understood in

the hard parts of invertebrates and of vertebrates, and

there is little to be added as to the modes of mechanical

evolution. No chances or experiments are tried by Na-

ture. The process is continuous, adaptive, mechanically

perfect in every Mutation of Waagen. As shown in

actual observations by all close students of vertebrate

and invertebrate morphology during the last fifty-two

years, and as summed up in the remarkable contribution

of D'Arey Wentworth Thompson (1917) on ‘‘Growth

and Form," animal mechanisms compete with each other

in close analogy to humanly made machines—automo-

biles, typewriters, aeroplanes. Consequently, while Na-

ture is constantly standardizing her machines through

individual competition and producing flocks of birds and

shoals of fishes which are so precisely alike that animals

of the same age, sex, environment and heredity show no

perceptible variation, she is also frequently substitut-

ing more perfect and more adaptable machines and dis-

carding older and less adaptable ones, exactly as man is

doing in the case of his automobiles, his typewriters, and

his aeroplanes. Thus the naturalist and the paleontolog-

1 Illustrated by twelve lantern slides exhibiting mutations of Ammonites,

of Spirifer, of Paludina; rectigradations of the grinding teeth of lemuroid

Primates; evolution of proportion from the rhynehocephalian type of Hat-

teria to the dinosaurs and birds of the genera Deinodon, Struthiomimus,

and Diatryma.

134

No. 643] ORTHOGENESIS 135

ist are alike impressed with the incessant action of Nat-

ural Seleetion on animal mechanisms and with the new

testimonials to this aspeet of Darwin's great principle.

When it comes to the origins either of new characters

or of new proportions quite different is the attitude of

observers of mechanical evolution; no evidence whatever

has been fortheoming from the same fifty-two years of

elose observation and research as to the causes of origin,

at the same time the modes of origin of all mechanical

characters are indubitably orthogenetie.

To further clarify the bearing of paleontology on

orthogenesis, I desire to point out that all visible me-

chanical evolution goes hand in hand with invisible physi-

cochemical evolution; and that there are steps in evo-

lution which are primarily physical, others which are

primarily chemical, others which are primarily mechani-

eal. Therefore the experimental botanist, zoologist, bio-

chemist, biophysicist, or geneticist, has the opportunity

to win immortal fame by discovering the causes of me-

chanical evolution.

Meanwhile the paleontologist enjoys the entirely

unique position of being the only competent observer of

the Origin of Species so far as specific characters are

recorded in the hard parts of animals and the relatively

few soft parts which are preserved in a fossil condition.

9. ORTHOGENETIC ORIGIN or NEw CHARACTERS

All agree that sound induction either as to the origin

of new characters or their transformation is an exceed-

ingly difficult matter. It has taken me thirty-three years

of uninterrupted observation in many groups of mam-

mals and reptiles to reach the conclusion that the origin

of new characters is invariably orthogenetic. ;

In 1889 I first observed (Osborn, 1889.46) that new

eusps originate on the grinding teeth of Eocene Pri-

mates, now recognized as lemuroids, in a definite and

adaptive manner from minute shadowy beginnings which

are mechanieally adjusted to similar minute shadowy

136 THE AMERICAN NATURALIST [Vor. LVI

beginnings of opposing eusps in the other jaw; whereby

there evolves a continuous reciprocal mechanism not dis-

similar to the reeiproeal serviees of the Yale key and the

Yale lock. The evolution of the key below proceeds with

the evolution of the lock above. ‘The process does not

go very far in the Primates, but in the purely herbivo-

rous ungulates, like the horse and the elephant, the re-

eiproeal grinding mechanism reaches a degree of com-

plexity to which the most intrieate lock and key devised

by man present but a feeble parallel. Every mechanical

deviee in the upper grinding teeth, adapted to the fine

comminution of grasses, is reversed in the lower grinding

teeth, on the principle of mechanical action and reaction;

nowhere in nature is reciproeal mechanieal co-adapta-

tion more perfectly evolved than in the upper and lower

grinding teeth of mammals.

Between 1889 (Osborn, 1890.47) and 1891 (Osborn,

1891.53) I made what I now believe to be an wnsound in-

duction from this evidence that this continuous mechani-

eal origin tended to support the Lamarekian theory of

the inheritance of adaptive reactions. I first termed the

orthogenetie process ‘‘definite variation’’; later I termed

it **progressively adaptive variation’’; by the year 1908

I realized that these new adaptively arising tooth ele-

ments were not variations in Darwin’s sense at all, and

I applied to them the distinctive term rectigradations

(Osborn, 1908.314). In the meantime I abandoned the

Lamarckian explanation and in 1895 (Osborn, 1895.97)

I started out upon a search for the unknown factors of

evolution, a search in which I am still busily occupied.

To return to the difficulty of making sound inductions

as to the origin of new characters in hard parts, in 1889

I opened a long correspondence with the leading expo-

nent of Darwinism in Great Britain, Edward B. Poulton,

who admitted the evidence but interpreted the facts in

the Darwinian way, namely, as the selection of mechani-

eal successes from non-observed mechanical failures. It

is a good thing to have a number of skeptical friends

No. 643] ORTHOGENESIS 137

about; it sharpens your powers of observation and

makes you much more eautious about your inductions.

My original observations on the Primates required cor-

roboration, and this I have sought through the observa-

tion of the origin of new charaeters in many other kinds

of mammals traced in their evolution over very long

periods of time, especially the horses, the rhinoceroses,

and recently the proboscideans, but most profoundly and

exhaustively the titanotheres, an extinet family remotely

related to the horses, which I have studied monographi-

cally for twenty-one years.

Even by trying to keep an absolutely open eye and

mind, entirely uninfluenced by any theory, or preconcep-

tion, or opinion, I have been unable to find a single ex-

ception among these many different kinds of mammals

to the observations made on the Primates in 1888 and

1889; not a single new organ is observed to arise for-

tuitously or indefinitely; it always arises gradually, con-

tinuously, and adaptively from its minute shadowy

beginnings. This continuous reciprocal, mechanical eo-

adaptation seems to be an established fact in evolution,

and is established most strongly where explanation or

search for causes seems to be most difficult.

I am not enthusiastic about the adoption of the term

orthogenesis, admirably significant as it is in its Greek

derivation, first, because Eimer connected it with La-

marck’s and Buffon’s principles of inheritance of ac-

quired modifications, and, second, because it does injus-

tice to the first great observer of direct adaptive origins

in nature, namely, the German paleontologist Wilhelm

Heinrich Waagen, whose observations in 1869 laid the

foundation of all subsequent work both among the in-

1 Osborn, H. F., ‘‘ The Titanotheres of Ancient Abbe cs Dakota, and

Nebraska. Life and Geography of the Central Rocky Mo ain Region in

Eocene and Oligocene Times. Evolution of the ri ig Th

Causes of Development and Extinction of Mammals,’’ U. S. Geol. Survey

Monograph No. 55. [Unpublished.] Completed for the Survey June 30,

1920. This monograph is the most complete and exhaustive analysis that

has thus far been made of the evolution of any family of organisms

138 THE AMERICAN NATURALIST [Vor. LVI

vertebrates and the vertebrates. To the best of my

knowledge he was the first naturalist to observe how

new species actually arise in nature. Compare Waagen’s

description (1869) of the genesis of new characters in

the shells of cephalopods (Ammonites subradiatus) with

those which Osborn (1889-1921) has observed in the

teeth:

‘Thus the species if considered as such may be con-

ceived and considered as a species, but in contrast with

earlier or later forms [1.e., ancestors or descendants] as

a mutation. Now as regards the value of these above-

defined conceptions, variety and mutation, on closer con-

sideration a quite decided difference in value becomes

apparent. The former conception [variety], in the high-

est degree variable, appears to be of small systematic

value; while the latter [mutation], although in minute

characters, 1s highly constant, always surely recogniz-

able; on which account far greater weight must be put

upon Mutations, they ought to be very precisely denoted

and held fast to with great persistence."

Twenty years later the German paleontologist Mel-

chior Neumayr observed this process of continuous de-

velopment, generation after generation, in a certain defi-

nite direction for which he proposed the term ''Muta-

tionsrichtung.’’ Thus the ‘‘mutation of Waagen"' arises

continuously through the inner working or tendency,

the ‘‘ Mutationsrichtung’’ of Neumayr.

It was not until 1894 that William B. Seott brought

Waagen's term ** Mutation" to the notice of vertebrate

paleontologists in this country, in antithesis to Dar-

win’s term Variation. Waagen's ‘‘Mutation’’ means

one thing, Darwin’s ‘‘Variation’’ means quite another,

as pointed out by Scott above. The term Mutation in

Waagen’s sense is now widely but not universally used

by paleontologists to designate intermediate gradations

of minor taxonomic rank which are observed in ascend-

ing or descending series of animals to connect the larger

stages of evolution which we call Species. As an ele-

No. 643] ORTHOGENESIS 139

mentary species a ‘‘Mutation’’ of Waagen is compa-

rable to a ‘‘Mutant’’ of De Vries in external appearance,

but not in mode of origin, because one arises through a

continuous '' Mutationsrichtung," while the other arises

through aecidental germinal saltation. To my mind the

continuous or discontinuous mode of origin either of a

‘‘mutation’’ or of a ‘‘mutant’’ is of small account as

compared with the fortuitous or orthogenetie nature of

the impulse in the germplasm which gives rise to it.”

So far as I know all observers of the hard parts of

extinct animals, whether vertebrate or invertebrate, con-

firm this classic observation of Waagen, and many in

this special field of observation also confirm the ‘‘ Muta-

tionsrichtung’’ of Neumayr. So far as I personally

have observed, this principle of ‘‘Mutationsrichtung”’

is especially dominant in the origins of charaeters; here

at least other interpretations are not applicable; there

is no question of Seleetion between two alternatives,

adaptive and inadaptive, because the inadaptive does

not occur, the whole process is adaptive and the differ-

‘ence between two organisms is the rapidity and direc-

tion with which the ‘‘Mutationsrichtung’’ is acting.

This is the same in the hard parts of the molluses Am-

monites, Paludina, and Planorbis, as it is in the mam-

mals Equus, Rhinoceros, and Elephas.

3. Tue Ortarn of New Proportions

In the evolution of proportions, that is, proportions

in the different parts of skeleton and skull as in Spheno-

don, Deinodon, Struthiomimus, Diatryma, it appears

probable that Selection may be constantly working on

all adaptive fluctuations of proportion in connection

with ontogenetic modifications in proportion which are

also adaptive, as in the classic case cited by both Dar-

win and Lamarck of the length of the neck of the giraffe.

2 TF, A, Bather in 1905 (Proc. Geol. Soc., Vol. 61, pp. Ixxii-Ixxiii) most

clearly elucidated Waagen's conception of the Formenreihe and of the Muta-

tion in Ammonites.

140 THE AMERICAN NATURALIST [Vor. LVI

It has been demonstrated experimentally that the limb

proportions in the brief life of a dog may be modified

from the cursorial to the saltatorial type by amputating

the fore limb. "This is a process of reciprocal Modifica-

tion and Selection which Osborn, Baldwin, and Morgan

term Organic or Coincident Selection. I have devoted

an immense amount of study to the causes of the evolu-

tion of proportion and have come to the conclusion that

orthogenesis in the evolution of proportion may be ap-

parent rather than real. In other words, whenever a

character assumes a survival or elimination value, it may

develop very rapidly through the selection of fluctua-

tions in the right direction and may result in apparent

but not real orthogenesis.

4, Summary AS TO ÜRTHOGENESIS

The visible ‘‘mutation of Waagen,’’ or ‘‘definite vari-

ation" or ‘‘rectigradation’’ of Osborn appears to de-

pend on the ‘‘Mutationsrichtung’’ in the germ-plasm.

The final question in my mind, as in yours, must be, if

such a ‘‘Mutationsrichtung’’ exists, is it the ‘‘internal

perfecting tendency,’’ is it the ''vitalism," is it the

‘creative evolution” which the majority of biologists

are so skeptical about?

I observe that it is not. I observe that while the ‘‘Mu-

tationsrichtung’’ is a real process, it differs from any

kind of internal perfecting M in the faet that it

which it ‘migrates. For example, the internal Sertost-

ing tendency to arboreal life does not manifest itself

when the animal seeks an aquatic life. Conversely,

aquatic adaptations are not constantly springing up

among arboreal mammals. Observations on fossil forms

have led to Dollo’s remarkable generalization regarding

*alternate adaptation," which renders any form of in-

ternal perfecting tendency in any predetermined direc-

tion inadmissible.

No. 643] ORTHOGENESIS 141

Summary of Observations.—In the hard parts of ani-

mals orthogenesis is observed both in the origin of new

adaptive characters and in the evolution of proportions.

(1) The induetion as to eause may be different in the

two eases. (2) In the origin of new adaptive characters

orthogenesis is attributable to definite germinal tend-

encies. (3) The origin of changes of proportion which

are subject to modification may be partly attributable

to Organie Seleetion. (4) There is positive disproof of

an internal perfecting tendency (Vitalism) in either the

origin of new characters or the origin of proportions.

(5) There are certain changes of length and breadth

proportion both in the shells of invertebrates and the

skulls of vertebrates which can not be explained by Or-

ganic. Selection. (6) There is very strong support in

fossil series for Selection incessantly acting on all char-

acters of survival or elimination value.

The above six principles are those which I have de-

rived from forty years of continuous observation; they

are actual modes of the mechanical evolution of new

species for which we have no theoretic explanation, un-

less it be that of Organic Selection in the single case

above noted.

Summary of Opinions.—I may add as a matter of

personal opinion and hypothesis three points: first, that

we are as remote from adequate explanation of the na-

ture and causes of mechanical evolution of the hard parts

of animals as we were when Aristotle first speculated

on this subject three hundred years B.c.; second, that the

chief outlook for experiment is in the domain of physics;

third, that the explanation, if ever it is to be found, is to

be along the lines of four systems of energy (— Tetra-

plasy, Tetrakinesis, Osborn) which surround the origin

and development of every charaeter in every organism;

fourth, I think it is possible that we may never fathom

all the causes of mechanical evolution or of the origin of

new mechanical characters, but shall have to remain con-

tent with observing the modes of mechanical evolution,

142 THE AMERICAN NATURALIST [Vor. LVI

just as embryologists and geneticists are observing the

modes of development, from the fertilized ovum to the

mature individual, without in the least understanding

either the eause or the nature of the process of develop-

ment which goes on under their eyes every day.

In conclusion, it is the great biological achievement

of the last half century that paleontologists have dis-

covered how new characters and new species originate.

It may be the achievement of the experimental biologists

during the next half century to explain why new char-

acters and new species originate.

HENRY FAIRFIELD OSBORN. BIBLIOGRAPHY ON SINGLE

CHARACTERS, MODES OF ORIGIN AND TRANSFORMATION,

ORGANIC SELECTION

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1912.372

1914.412

1915.416

1915.421

ORTHOGENESIS 143

Ti om une ge of Waagen and ‘‘Mutations’’ of De Vries or

[and] ctigradations'' of Osborn. Science, N.S., Vol.

Darwin's Theory o f Evolution by the Selection of Minor Salta-

tions. Amer. Naturalist, Vol Sind No. 542, pp. 76-82.

ird Continuous Origin of Certain Unit Characters as Observed

ya EISA Harvey Soc. Volume, Tth ser., Nov., pp.

[Abstr.] OUR NUM and Allometrons in Relation to the

Conception of the ‘‘Mutations of Waagen,’’ of Species,

D m Phyla. Bull. Geol. Soc. of Amer., Vol. 25, No

3, pp. 16.

Origin es i ngle Characters as Observed in Fossil and Living

Animals and Plants. Amer. Naturalist, Vol. XLIX, No. 580,

pp. 193-239.

The Origin of New Adaptive Characters. Nature, Vol. 96, No.

2402, pp. 284, 285.

THE EFFECTS OF ENVIRONMENT ON ANIMALS'

PROFESSOR A. S. PEARSE

UNIVERSITY OF WISCONSIN

As Henderson? has pointed out, the environment on the

surface of the earth is suited to, and largely responsible

for, the existence of living organisms. After an organism

comes into existenee, it strives to live in harmony with

its immediate environment. An organism is a ‘‘system

of aetivities'? which devotes its energies primarily to

three funetions: (1) eapturing energy for and releasing

energy from its own system, (2) protecting its system

from injury, and (3) producing other systems of activi-

ties similar to itself. If possible an organism reacts with

its environment in such a way that its system continues

to exist and carry on its three primary functions. It is

limited in its responses to a particular behavior pattern,

inherited from the system from which it came, but in

general it reaets in such a way toward its environment

that it selects by trial the optimum conditions for its own

existence. In other words, an organism generally re-

sponds in an adaptive way and selects the best environ-

ment that it ean. If the behavior patterns of certain sys-

tems, similar or dissimilar, are well suited to a particular

environment, such systems often are ‘‘successful.’’ They

may take possession of the environment, perhaps exter-

minating other systems, and, thus demonstrating their

**fitness,"' constitute what ecologists call a climax forma-

tion. Every organism in such a group must remain a sys-

tem of activities and must make continual physiologieal

adjustments to keep in harmony with the environment, or

it ean not continue to exist. Each organism assumes a

1 An address before the Geographical Society, University of Wisconsin,

January 11, 1922

Fr" The Order of Nature,’’ Cambridge, 1917.

3 This definition is not intended to exclude the possibility that an organism

may be more than matter and energy. It may contain an entelechy or some-

thing similar, but as yet there is no scientific proof that it does. The limita-

tion, and value, of science is that it must always deal with facts.

144

No. 643] EFFECTS OF ENVIRONMENT 145

partieular internal pattern that consists of a graded

series of metabolic activities which (de Child) is a direct

response to stimuli received from the environment.

In responding to environment plants and animals show

fundamental similarity. Many plants adjust themselves

to their surroundings by assuming the form that best

suits them to the particular space in which they happen

to take up a sessile life, and many animals secure a place

which is suited to their system of activities by moving

about until they find it. This difference between plants

and animals is largely due to the faet that the former

usually are able to subsist on inorganic foods, wuile the

latter require organic substances as a basis for their

metabolic activities. However, animals often respond to

the environment by assuming a particular growth form,

and plants have many motile systems of activities that

find favorable environments through active or passive

migrations. Being trained as a zoologist and knowing

little of the activities of plants, I gladly take the task as-

signed to me—‘‘to discuss the effects of environment on

animals’’—but I can not refrain from expressing my

opinion, that there is no essential distinction in this con-

nection between the two great kingdoms of life.

Animals are continually active and must continually re-

act with the environment. Alcock‘ said, ‘‘the three great

exigencies: to find something to eat, to avoid being one’s

self eaten, and to disseminate one’s species, give rise to a

perpetual struggle in which the fittest are successful."

The environment furnishes matter and energy to main-

tain the activities of each system and a considerable quan-

tity of both is neccessary. A silkworm during its short

life eats food amounting to 86,000 times its own weight at

the time of hatching. Animals take the most diverse mate-

ials from the environment and use them to build substance

or furnish energy. The clothes moth flourishes on a diet

of wool, which consists entirely of keratin. From this

almost pure, and to most animals wholly indigestible, pro-

*** A Naturalist in Indian Seas.’’ London, 1902.

146 THE AMERICAN NATURALIST [Vor. LVI

tein substance the moth makes carbohydrate, fat, and

water to supply the needs of its system. The bee moth

subsists on bee comb, which contains less than one per

cent. of protein and a large amount of rather insoluble

wax. Ants not only acquire food from the environment,

but give up what they have already swallowed to their

fellows, even when they are hungry themselves. In this

ease the ‘‘system’’ of the colony is more important than

that of the individual.

In order to keep their systems of activities intact, ani-

mals have adopted many means to escape dangers. There

are lurking enemies, physical changes, accidents, insidi-

ous parasites to be met or avoided continually. A walk-

ing-stick spends nine-tenths of its life in a ‘‘perfectly

quiescent’’ state, depending on being overlooked by

hungry enemies. A house fly escapes through endless

agility. A rotifer avoids drying up by secreting a cyst

about itself, and may remain dormant for years. Many

animals are able to change the usual rate of their meta-

bolic activities in response to changes in temperature and

pass cold periods in a hibernating state.

Animals, before all things, use the means they possess

in order to perpetuate their particular systems. New indi-

viduals must continually be started on new life cycles and

such reéreations involve reorganizations of systems,

changes in metabolism, and various responses by organ-

isms to the environment. Such qualities as odors, colors,

and songs may be very important for the survival of a

race. A male moth will migrate a mile or more to find a

mate—attracted by her odor. The daily routine of seek-

ing and escaping dangers is often neglected by animals

when the survival of their race is concerned. Greedy

penguins allow any youngster that comes to feed from

their crops. An adult bull seal takes no food from May

to August, but devotes all his energies to the defense of

his rookery. The male gaff-tops'l catfish takes the eggs

from his mate and carries them in his mouth for ninety

days—denying himself food in order that his offspring

No. 643] EFFECTS OF ENVIRONMENT 147

may survive. The little spider that spins a cocoon under

stones guards her treasure with watchful care and, if

she is compelled to leave her cocoon, spins a ground line

as she runs in order that she may return without delay.

A male spider dances, postures, and uses all his arts to

secure a mate. As soon as he has mated, Nature usually

sacrifices his life to his offspring—for his hard-earned

mate devours him if she can.

Thus it is wherever one considers animals. There is

adjustment, frequently of a very specialized type, to en-

vironment. The wonder of it all is the degree of adapta-

tion that animals show. In speaking of food relations

Semper® said, ‘‘there is scarcely a constituent of the

earth’s crust, whether on land or in water—not an animal

nor a plant, whether living, dead, or even in decomposi-

tion—which does not afford nourishment to some living

animal." The first more or less self-evident generaliza-

tion justified by this discussion may be stated as follows:

Animals are adapted to the environment.

That animals are adapted, probably noone disputes, but

there has been much controversy as to the means by

which they have become adapted. There appear to be

three effects that it is possible for the environment to

produce in animals: (1) a direct transformation or modi-

fication of the living system of activities, (2) the de-

struction of systems-unsuited to the environment and the

‘‘survival of the fittest," and (3) the migration of sys-

tems from unfavorable to favorable environments.

Animals are modified by external changes and may even

take on different forms to suit different environments.

Sponges and corals growing in deep water usually have

a branching form; the same species in shallow water form

flat, encrusting growths. The brine-shrimp, Artemia

salina, is a classical instance of an animal that has many

forms, and these are rather closely correlated with the

salinity of the water in which it lives. Sumner® and Shel-

5° Animal Life as Affected by the Natural Conditions of Existence,’’

N. Y., 1881.

6 Bull. U. S. Bureau of Fisheries, 1910,

148 THE AMERICAN NATURALIST [Vor. LVI

ford,’ working independently, have shown that very slight

structural differences that distinguish closely related

species of amphipods and tiger-beetles are correlated

with distinct habitat preferences. The structure and

physiology of animals are modified by environment—the

structures and activities of the systems are changed.

Different species may possess almost identical structures,

but show specificities of behavior in relation to environ-

ment.

Darwin made much of the struggle for existence among

animals, pointing out that many species hold their places

on the earth through wide dissemination and selective

survival. One who has seen the strangler trees gaining

a foothold in the tropical forest, the fiddler crabs fighting

to hold a favorable place on an ocean beach, or the oysters

in an overplanted area striving to survive, can not

doubt that there is such a struggle. More animals are

produced than can find a place to exist, and in general

those survive that are best suited to the environment that

is available.

Animals are not always obliged to adjust themselves

to the environment or struggle for a favorable place to

live init. They migrate from situations where their sys-

tems can not well carry on activities to some spot where

conditions are more propitious. In such migrations ani-

mals have very definite relations to the environment.

They are limited by their reaction pattern to certain

habitats; they must disperse from their ‘‘centers of

origin" through ‘‘highways,’’ and are prohibited from

migration into certain regions called ‘‘barriers.’’ Bar-

riers are areas where certain environmental factors vary

beyond the limit of toleration for a species. A ‘‘center

of origin” as usually understood by geographers, may be

the real place of origin of a species or it may merely rep-

resent the locality where the most environmental factors

are favorable. In general a uniform environment cover-

ing a wide range of territory permits the species suited .

to such an environment to have a wide geographic range.

7 Biol, Bull., 1911.

No. 643] EFFECTS OF ENVIRONMENT 149

Variable species usually have wider ranges than unvary-

ing, because they ean adapt themselves to more environ-

mental variations.

A second generalization is appropriate here: Animals

become adapted to environment by (1) transformation,

(2) selective survival from an overpopulated condition,

(3) migration from unfavorable to favorable situations.

It will be profitable now to examine two or three typical

associations in order to study animals in action with the

environment. If, in this connection, one thinks over the

great responses that animals have made to environment

in the past, he will probably conclude that the greatest

habitat change has been that from water to land. It

is generally supposed that life first appeared in

water. As a habitat, water has certain inherent advan-

tages—the chief of which is perhaps the slowness with

which temperatures change. It also has certain disad-

vantages, the most important of which are probably the

variability of its dissolved gases (the higher the tempera-

ture, the less gas can be held in solution) and its general

solving power, which makes it a transporting medium

for all sorts of substances, some of which are poisonous.

All animals require a more or less constant supply of

water and of oxygen for metabolic processes. When ani-

mals forsook the water for land habitats, they gave up

surety of water supply and conditions of reasonable

thermal stability. What did they get in return? Ap-

parently nothing but a stable gaseous condition for re-

spiratory needs. The danger of desiccation and the wide

variations of temperatures incident to land life were ap-

parently compensated for by this gaseous stability. Yet

the attractions of the water have at times led many ani-

mals, like the aquatic insects, that had become adjusted

to life on land to revert to aquatic habitats. In the past

races have doubtless many times become adapted by

transformation, selection or migration on account of the

advantages or disadvantages of one of two habits.

If one walks along a rocky shore, where the ocean

150 THE AMERICAN NATURALIST [Vor. LVI

waves and tides sweep, he may be surprised to find an

abundant fauna in the ** ’tween-tide " zone. The moving

water, teeming with mieroseopie organisms, brings an

abundance of food to those animals that are able to stand

the beating of the waves and the alternate submergence

and exposure due to the ebb and flow of the tides. A

roeky wall along the sea shore is no plaee for weaklings.

One minute the blistering sun bakes the exposed animals;

` the next, the rising tide has covered them with cold water.

The waves beat ceaselessly. The changing seasons bring

ice and torrid heat. How are the animals on these rocky

shores responding to the environment? Here one finds

a variety of hardy species which, though not closely re-

lated genetically, have many characteristics in common.

There are sponges, anemones, hydroid colonies, barnacles,

mussels, snails, small crustaceans, and a few scavenger

crabs. These animals for the most part obtain their food

by net fishing or by straining water through their bodies.

They are mostly attached firmly to the rocks, and thus

withstand the violent movements of the food-laden water.

The barnacles, sponges, and hydroids are grown fast; the

anemones and snails have sucking dises that enable them

to adhere firmly; the crustaceans have claws for attach-

ment and hard armor covering their bodies. Some of

these animals are small and can easily hide in crevices;

some of those of larger size, like crabs, are able to migrate

to other habitats during violent storms. If an animal is

attacked, it is advantageous for it to be able to receive

stimuli with facility from all directions of the compass,

and, as would be expected, many of the animals on rock

beaches are radially symmetrical. Radial symmetry has

marked advantages for sessile animals, but puts a

weighty limitation on psychic development. An animal

that is able to perceive stimuli equally well, through

equally efficient sets of sense organs that are symmetrical-

ly disposed about a central axis, is never able to develop

its power of paying attention to any considerable degree.

Its simple mind, if such an animal may be said to have

No. 643] EFFECTS OF ENVIRONMENT 151

a mind, must attend now to a stimulus received from one

side, now to that on another. Such vacillation is not con-

ducive to the development of higher types of mental life

through the delegation of psychic authority to one nerv-

ous center. The rocky ocean shores, then, put a pre-

mium on radial symmetry and thus as an environment

tend to foster psychically unprogressive animals. The

barnacles, that appear to have come from progressive,

bilaterally symmetrieal ancestors, have become degraded

with the taking on of the sessile life and radial symmetry

that suits them so well to wave-beaten shores. | :

The ebb and flow of ocean tides have a pronounced

effect on shore animals. "Those speeies that are not able

to survive alternating exposure to the desiccating effects

of air of varying temperatures and the activity of vio-

lently moving water of rather constant temperature ean

not exist on rocky shores. This fauna must be resistant,

and is so. An anemone can be kept out of water for a

week—until it looks like a dried raisin; or kept in a

tightly eorked bottle for ten days, and when replaced in

the ocean appear to be perfectly normal in an hour or

two. Such an animal will not readily succumb to the

exposure between tides or even to the stagnation likely

to oeeur in a beaeh pool that is eut off from the ocean

during a prolonged period of low water. The barnacles

and molluses on rocky shores are protected by heavy cal-

eareous shells. Flattely? has suggested that land animals

perhaps arose in the past on ocean beaches as a result of _

the resistance developed during exposure between tides.

As a whole the environment occurring on rock beaches

offers abundant food, but hard conditions for life. The

fauna is highly adapted to resist the two important en-

vironmental faetors —moving water and exposure to varı-

able conditions— and in this adaptation the fauna has in-

cidentally but of necessity become unprogressive and de-

votes most of its activities (1) to feeding rapidly when

the opportunity comes, (2) to resisting, (3) to resting.

* Science Progress, 1921.

152 THE AMERICAN NATURALIST [Yon LVI

One does not imagine such a fauna as developing, even

through countless ages, great appreciation of beauty, or

of any of the esthetic qualities of ‘‘higher’’ animals.

The adaptations here are to resist the unfavorable in the

evironment, and still live.

If a man walks in a tropieal forest, he is amazed at the

abundanee and variety of the life about him. He may see

a certain species of tree in one spot and not encounter

another like it for a mile. Meanwhile he has seen a hun-

dred other species of trees. What is the striking en-

vironmental faetor in this forest? It is life itself! "The

environment is favorable for so many systems of meta-:

bolie aetivity that hundreds of kinds of animals are

ready to live in it—if they can find a place. Is there a

struggle; is there adaptation? Nowhere on the earth are

these responses to environment more striking. Most of

the struggles to live in the forest are competitions with

other living systems that are trying to continue to exist.

And the adaptations are not often for resisting, for eat-

ing, for resting. Think of all the animals in the tropical

forest—is there one that is radially symmetrieal? Here

keen senses are at a premium. Life has always depended

upon seeing, hearing, feeling better than something else.

Lately it has come to depend upon thinking better than

something else. And the climax of adaptation in this

tropieal forest has been the greatest thinker of the ages.

A third generalization appears to be justified: Each

habitat, representing environment, limits the patterns of

the systems of activities that may persist from reactions

within it. The type of adaptation is set by the environ-

ment. `

Environment has a quality that any system of activi-

ties that attempts? to live in it must respond to. This is

its changefulness. The paleontologists say that environ-

ment punishes too much adaptation by ehanging. I think

it is proper to say that the chief cause assigned for the

9 The writer realizes that ** attempts ’’ may be pus A ger as teleologieal

—and rejoices in the sinfulness of it. If an organism does anything, it

strives to keep on existing. As far asit possesses means, it responds to what-

ever interferes with living

No. 643] EFFECTS OF ENVIRONMENT 153

dying out of extinct types of animals is ‘‘over-adapta-

tion,’’ or better ‘‘too much specialization." A system of

activities, as represented by an organism, can not depend

absolutely on another system of activities, as represented

by environment. The organism changes and the environ-

ment changes too. If the environment continues for a

time in a fairly stable condition, an animal may become

adapted to it to such a degree that, if the environment

then does change, the animal ean not respond enough to

continue to live. The wood frogs in the United States

breed when the water is at freezing temperatures ; frogs,

belonging to the same genus as the wood frog, that live in

Cuba die when the temperature falls below seven degrees.

These frogs are adapted to different environments and

those in Cuba will be in greater danger of extinetion if

there is a prolonged cold period.

There is a general tendeney among animals to find sue-

cess during conditions of stability. Certain arthropods

left the water and attained stable respiratory conditions

and freedom from water-soluble poisons by going on

land. Later, certain of these arthropods again gained a

thermally stable environment in the water and continued

to enjoy a stable gaseous environment by carrying air

into the water with them. When any raee of animals

attains a stable environment, it may become specialized

to it. We see a manifestation of the same type in the

psychology of man. It is ‘‘human nature” to desire

stability—to be free from care and worry; to know where

one stands.

On the other hand, continual change is a stimulus to

progressive response—in fact, one is tempted to say that

laek of change is injurious to living organisms and that

changes often stimulate living systems to renewed activ-

ity. Payne kept fruit flies continuously in the dark;

Calkins and Woodruff maintained protozoans on unvary-

ing culture media. All these investigators agreed that

lack of variation in the environment was injurious. This

raises a dilemma—on one hand animals tend to become

highly adapted (or specialized) when the environment is

154 THE AMERICAN NATURALIST [Vor. LVI

stable, and on the other hand a changing environment is

a stimulus to progressive changes in organisms. A few

animals have lived for ages in a stable environment.

Thompson cites the brachiopod, Ligula, as a ‘‘ supreme

instance of static racial inertia." However, most animals

must live in environments that change. How do these

respond?

It is a matter of common knowledge that animal sys-

tems of activities can become adapted to changes in the

environment, even when such changes constitute new

racial experiences. By taking increasing doses of certain

poisons at regular intervals animals develop enough im-

munity to be able to take daily a dose which in the begin-

ning would have been fatal. If a pigeon is fed nothing

but meat the lining of its stomach changes its character

and the bird’s metabolic activities become adapted to an

unusual diet. Many other instances of acclimatization .

to new conditions might be cited.

Every physiographer knows that earth environments

change by succession. Land forms erode and water forms

fill up with sediment. Physiographie succession brings

about a suecession of environments, or habitats. "These

are successively occupied by different groups of plants

and animals and there is thus an ecological succession,

which is a succession of species or groups of species.

Shelford has worked out excellent examples of ecological

succession in the streams and ponds along the shore of

Lake Michigan. Pioneer species of animals invade hab-

itats soon after they are formed, and as the habitats

change the pioneer species are succeeded by others that

are adapted to later stages in physiographie succession.

Ecologie succession is a succession of species; animals

do not change as the environment changes, but die or

migrate to more favorable localities. Animals do not

appear to have special means for adapting themselves to

such changes.

There are other types of succession, however, to which

animals show striking adaptation. The types are all

rhythmic (seasonal, monthly and daily) and depend pri-

No. 643] EFFECTS OF ENVIRONMENT 155

marily upon the motion of the earth and moon. As the

earth makes its annual journey around the sun, the ani-

mals of temperate and polar regions, and to a less extent

those in the tropics, are subjected to seasonal changes in

environment. These changes are related chiefly to tem-

perature, available moisture, and food. Animals gen-

erally respond to such environmental variations by

adjusting appropriate activities to favorable times. In

general winter is a season for resting; spring, for mating

and propagation; summer, for feeding and growth; and

autumn for fructification. Seasonal succession is a succes-

sion of stages in life cycles. The seasonal rhythm has a

short enough period to permit animals to become adapted

to it. Their systems of activities vary to fit the seasons.

Every one is familiar with the seasonal migrations ot

animals. The arctic tern travels from pole to pole, and

thus always lives in sunshine. Many animals do not

migrate, but pass the winter in a dormant condition. In

the tropics animals frequently estivate during the annual

dry season. Now many of these seasonal responses are

certainly due to stimuli received from the environment.

The little Daphnias, that live in fresh-water habitats the

world over, usually have long helmets in summer and

short helmets in winter, but long-helmeted forms can be

made to produce short-helmeted offspring in summer by

keeping them at low temperatures. In this instance the

effective stimulus appears to be thermal in nature. But

animals are adapted to seasonal succession beyond merely

responding as far as they are able to stimuli that come

with rhythmic changes without their bodies. The living

system apparently has arhythm of its own that is adapted

to the seasons. Smallwood” kept a female dogfish (Amia

calva Linneus) in an aquarium, practically without food,

for twenty months at rather constant temperature. Dur-

ing this time the fish twice took on its bright nuptial

coloration. Another instance of similar nature has come

to the notice of the writer. A tame spermophile, Citellus

tridecimlineatus (Mitehill), was kept in a steam-heated

10 Biol. Bull., 1916. |

156 THE AMERICAN NATURALIST [Vor. LVI

house for four years. In the autumn of the first year

it became very fat and stored a large quantity of food in

its burrow. About December 1, it went into its burrow,

closed the opening, and remained underground for 119

days. The following autumn the spermophile behaved in

a similar way but remained underground for only 28 days.

It did not hibernate during the two years following. This

animal had an established seasonal metabolic rhythm that

was correlated with seasonal environmental changes, but

the rhythm had a physiological basis for it persisted when

appropriate environmental stimuli were not present.

The rotation of the moon about the earth introduces

certain rhythmic variations into the earth environment to

which animals respond in adaptive ways. Such responses

are of course not due directly to the moon as such, but

to effects of the moon’s motion on matter belonging to the

earth. The famous Palolo worm and various other ma-

rine annelids come from their hiding places to spawn only

during certain phases of the moon. In these worms the

eggs do not ripen except when the moon is new or full; the

internal activities respond to outside changes, chiefly

referable to tidal variations, and a physiological rhythm

is established.

The earth rotates on its axis and thus the animals on

its surface are subjected to alternating light and dark.

Animals readily respond to this short-period rhythmical

change. Every one is familiar with nocturnal and diurnal

animals. They are adapted to rhythmical environmental

changes to such a degree that they may keep on respond-

ing periodically when the environment does not change.

Keeble and Gamble" have described an interesting shrimp

(Hippolyte varians) that has day and night color phases.

During the day this shrimp matches the background on

which it rests with a high degree of accuracy, assuming

quite a variety of colors and patterns. At night it turns

green, regardless of its background. When kept contin-

uously in light it undergoes rhythmic color changes at

about the time periods that correspond to day and night

11 Phil, Trans., London, 1904.

No. 643] EFFECTS OF ENVIRONMENT 157

for two days; and makes similar changes in the absence of

light for about a week. There is a physiological rhythm

that corresponds to periodic environmental changes.

A fourth generalization must again relate chiefly to

adaptation—Though animals possess considerable power

of adjustment to new or changed factors in their environ-

ment, they apparently do not usually become adapted as

species to physiographic changes, but are eliminated by

the variation of factors beyond their limit of toleration.

One species or group of species succeeds another during

physiographic succession. However, animals do respond

in an adaptive way to rhythmical daily, monthly and

seasonal successions. Some animals show adaptive re-

sponses to rhythmical environmental changes only once

during their life cycle. Salmon, for example, do not

migrate up rivers to spawn until they have reached a

certain age. Animals apparently become most special-

ized, or adapted to particular environments, when con-

ditions are most stable. Even the striking instances of

adaptations to rhythms show this tendency of adaptation

to attain stability—in this case a regularly changing sta-

bility.

Environmental changes have been important in their

effects on the evolution of animals. In this paper it has

been shown that living systems of activities are adapted

to the environment ; that they respond to the environment

by transformation, selective survival, or migration; that

each habitat limits the patterns of the systems that exist

within it; and, that, though adaptation to environment

may permit precise adjustment to rhythmical changes

extending over considerable periods, and though animals

generally become most specialized when conditions are

most stable, there is no evidence that living systems are

caused to change from one species to another by the

transformations of habitats due to physiographic suc-

cession. The pattern of evolution is set by environment,

but there is little or no evidence that changing envi-

ronment causes adaptive variations of such a degree

that new species are produced. Animals adapt them-

158 THE AMERICAN NATURALIST [Vor. LVI

selves to environment by changing their systems of ac-

tivities, but such responses are apparently limited in

extent to the inherent possibilities of variation already

within the system. Animals have great powers of adapta-

tion to environment, but are not fundamentlly changed

by it. Environment permits evolution and controls its

course, but does not appear to cause it. If variations fit

environment, they are adaptive; if they do not, systems

cease to exist. Environment does not appear to cause

variation. The living mechanism still holds the mystery

of variation within itself. Until there is conclusive evi-

dence, this one great remaining problem of evolution

ean not be solved. Yet, notwithstanding this lack of evi-

dence, there are still those who belive the environment

does cause evolution—though their only foundation for

such belief is what Bergson calls ‘‘ intuition.’’ Until

there is proof, science, if it would be scientific, must keep

in mind that these ‘‘ faithful " believers may be right,

and be content to wait, perhaps a hundred thousand years

—for evidence.

SUMMARY

l. Animals are systems of activities that are adapted

to environment.

2. Animals become adapted to the environment by

transformation, selective survival, migration.

3. Each habitat limits the patterns of systems of ac-

tivities that may result from reactions within it. The

type of adaptation is set by the environment.

4. Though animals possess considerable power of ad-

justment to changes in environment, there is no evidence

that they became adapted as species to slow changes due

to physiographic succession. They do respond to rhyth- |

mical daily, monthly, and seasonal changes in an adaptive

way. Animals appear to become most specialized, or

adapted to partieular environments, when eonditions are

most stable.

9. Environment permits and directs evolution, but does

not appear to cause it by forcing the acquirement of new

characters.

A SUMMARY OF THE FOOD HABITS OF NORTH

AMERICAN COLEOPTERA

HARRY B. WEISS

New JERSEY DEPARTMENT OF AGRICULTURE

Tug Coleoptera or beetles contain a very large number

of species and show a great diversity of habits. Most of

them are terrestrial and they live under almost all con-

ditions where insect life is possible. The economic status

of this group of insects is important. To the Coleoptera

belong some of our most pernicious agricultural pests

as, for example, the cotton boll weevil, which has caused

such ruin in the cotton belt, the Colorado potato beetle

with its familiar destructive activities and various other

species which attack forests and field crops with varying

degrees of intensity. However, many species of Coleop-

tera are engaged in useful activities and it is the purpose

of this paper to summarize briefly, and in a very general

way, the food habits of the families in this order. _

For the purpose of convenience in handling and for

the sake of simplicity, the families have been grouped

into a few important classes and the placing of each

family was based mainly on the predominating larval

activities of its members. In some families considerable

variation occurs in the food habits of the different spe-

cies. For instance, in the Scarabeide, some are destruc-

tive to green vegetation and others thrive on vegetable

decay. On the whole, however, their activities are

saprophytic and for this reason the entire family was

placed in the group Saprophaga. The Staphylinide were

placed in this group also, although this family contains

members which live in fungi, in animal and vegetable

decay, in the nests of ants and some which are predatory.

In quite a few of the families, the activities of the species

are practically identical.

159

TOO es THE AMERICAN NATURALIST [Vor. LVI

The classes into which the families are grouped are as

follows: Phytophaga, Saprophaga and Harpactophaga.

In addition to these three important ones, the species

attacking mammals and those whose family habits are

a 26 per cent

< 44 per cent

B 100 PER CENT

ca PLEET d `

B G

L^ 27 per cent

rA N n aS $ per cent

Diagram illustrating the comparative abundance ke the various types of

food-habits in the Coleopte

obscure have been grouped separately. In the Phytoph-

aga have been placed those species which feed upon

the higher plants. In the Saprophaga will be found

those forms which feed for the most part upon disor-

ganized tissue, vegetable and animal decay and such

No. 643] FOOD HABITS OF COLEOPTERA 161

species which remove or change the form of animal and

vegetable remains and aid in reducing such substances

into shape for assimilation by plants. While not strictly

belonging to this group, species feeding on low forms

of plants such as fungi and those living on dry vegetable

and animal matter have been included for the sake of

convenience and in order to avoid numerous subdivisions.

In other words, the term Saprophaga is used in a very

broad sense. poe

The Harpactophaga contains the predacious and car-

nivorous species, of which there are a great number, and

whose aetivities help to preserve a natural balance be-

tween certain groups. Many of them are general feeders,

appearing to be not partieular whether their prey is a

plant feeder or another predatory form. However, in

some families, such as the Coccinellide, there is a decided

specialization as to the prey, and such a group is very

often an important specific check to unusual increases in

the numbers of plant lice. The Coleoptera attacking

living mammals are few in number. The species in the

family Platypsyllide consists of a wingless beetle found

on beavers. In the Leptinide, the species have been found

in the nests of field mice and bumble-bees, but their exact

habits are somewhat obscure. It has been suggested that

the bumble-bee nest is the natural home and that the

field mice afford transportation from one nest to another.

The last group is made up of those families of which

little or nothing appears to be known concerning their

food habits. While this same lack of information is true

for a large number of individual species placed in the

other groups, yet enough is known of their general family

habits so that little risk is run in placing them as family

units. This, however, could not be done with any cer-

tainty in the case of the last class and they are presented

simply as a group difficult to classify from a food stand-

point.

The following tables show the name of each family, the

number of species in that family described up to and in-

162 THE AMERICAN NATURALIST [Vor. LVI

cluding 1918 and a brief statement indicating the more

important food habits. The information in the first two

columns was compiled from the recently issued ‘‘ Cata-

logue of the Coleoptera of America North of Mexico ”’

by C. W. Leng.

Family No. Species Habits

Lymexylide .......... Bore in hard wood.

Buprestide .......... 3 Wood borers in healthy and unhealthy trees.

erambycid® ......... 1,1123 Borers in dead, dying and healthy trees and

plants

somelide ,........ 974 Feeders on vegetable tissue.

MISES a eras 93 In men

TOMEI saech esan 6 ood.

MN Ie 1 Like Drait

Cureulionide ......... 1,839 Feeders e vegetable tissue,

Platypodide .......... Boring in

epi? bic u.s. 379 Borers in od healthy and sick trees.

SAPROPHAGA

ily No. Species Habits

Büphide aissi eunis? 137 Scavengers in dead animal and vegetable .

matter, in fungi.

Ones bidet ceci sarisi, 6 Same as above,

Orthoperide ......... 57 In decaying €—9À under bark, ete.

Staphylinide ........ 2,748 Varied, in ants’ nests, in fungi, in decaying

animal and PSEk matter, ete., preda-

tory.

Pselaphidsm .......... 355 Varied, in ants’ nests, under vegetable de-

cay, in wet moss, in rotten stumps, ete.

Clavigeride ......... 7 Same as above

Pude iser ET 83 In T vegetable matter, excrement,

fun ^

HIS olives 3 In uus decay.

Seaphidiide ......... 90 In rotten wood, fungi

Spheritide .......... 1 Same as Silp

zs cere 4 Under bark, in dry wood, iod be pm

Cidemeride ......... 49 In timber cast up by se

rdelide ...... v 142 Vows adults on flow mu larve in dead

ood, fungi, stems of live plants.

IAO soei 17 te mber.

Pyroehroldg ......... 11 Mts bark of tree stumps.

upende ons soe cd 39 In dead wood,

Cerophytide ......... 2 Probably like those of Elateride.

Cebrionide .......... 9 Probably like those of E aterida.

MEN iioii. 976 In decaying wood, in soil on roots of grasses,

PHYTOPHAGA

No. 643] FOOD HABITS OF COLEOPTERA 163

Melde oes. 57 In dead tree

Throscdade ciwon: 25 Like those of Elaterida.

Hide i oss 29 On roots of aquatics, in fungi.

Dermestidm .......... 129 In dried animal matter.

Ini ays ch 64 Varied, under bark, in granaries, in fungi,

predaceous,

Nitidulidae oe eek 132 Sap beetles, on flowers, predaeeous.

Rhizophagide ........ 14 Probably li M

Monotomide ........ 36 In ants’ nests, probably have no relations

with ants

Jrotyhdb os aka Gis 71 Mainly in füngl:

Cryptophagide ...... 135 In fungi and aaen zie vegetable matter.

Mycetophagide ...... 32 Under bark, in fungi.

Colydüdi- 605. cis: 84 In fungus covered wood,

LathrdHde |... 104 In fungi.

Mycetwide .......... 4 In fungi.

Endomychide ........ 34 In fungi.

Phalaeénde seleeni 117 Under bark, on flow

Aleéenhid ...ss 5.058 124 Larve in rotten ice adults on leaves,

flower

Tenebrionide ........ 1,139 In dry vegetable sae fungi.

Lagrüdb .. ics.. 17 Probably like

Melandryide ........ 81 In dry wood, nn.

Fin ilo 37 In dry onam and vegetable matter, wood,

drugs,

hobide ss 233 In dry ord matter.

aae spi eis 01 In d.

yetidi 215r 16 In dry wood.

sphindite s Verus 6 In fungi.

SB .. eee eta us 85 In fungi.

éatabaiijie E 996 Varied, in decaying vegetation, on roots of

plants, on green vegetation

bte sane REA ERA 30 In deeaying wood,

sald no ee eens 2 In decaying wood.

Pinkie umm 62 On dead wood, in fungi.

HARPACTOPHAGA

Family No. Species Habits

Cincindelide ........ 114 Predaceous.

RD eu Nes 2,165 Predaeeous.

Omophronide ........ 15 Predaceous.

Halplide ...... e 41 Aquatic, predaceous,

Dytissidte aee nnn 333 Aquatic, predaceous,

Mire oU cis ce esse 41 quatie, predaceous,

drophilide ........ 190 Predaceous.

Secydmenide ........ 174 Feeding on aeari, in ants’ nests.

Histor esee oe 384 Found in same situations as scavengers but

probably predaceous.

164 THE AMERICAN NATURALIST [Vor. LVI

byecide :.. cece ees 50 Carnivorous as larve.

Lampyride .......... 52 lLarve carnivorous, adults on flowers.

Phengodidm 2... vcs oes 23 Larve carnivorous, adults on flowers.

Cantharide ......... 155 Larve vun adults on vegetation.

BB i Se eae a 321 Predaceou ts flowers

Omni ie ids 181 Se Acces adults on flowers,

oe Can SUE T 38 Predaceous.

ephaloide .......... 8 Probably similar to those of —

mow sos eves 26 Larve in asitie in ants’ nests, on coc

roac

POM A es 227 Larve PPR adults on green vegeta-

tion.

Cuna so soari 85 Varied, under bark, predacious, in stored

roduets.

Coeeinellide ... í .... 862 Predaceous.

ANIMAL PARASITES

No. Species Habits

Piatypsyllide ea as 1 Animal para:

KOPRAD Sock ck ne es s,s 3 Probably uen on mammals.

Foop HABITS OBSCURE

Family No. Species Habits

Amphizoidme ......... 2 Aquatic.

Brathinidw .......;.. 3

Telegeuside ........ 1

Micromalthide ....... 1

Eurystethide ET se 3

Mi sais pes 54 Probably like those of Anthicide.

Anthieide ....... ^... 191 On surface of earth like ground beetles.

Plastoeeride ........ 19

hipieéeride isss 6 In wood,

Psephenide ......... 4 Semi-aquatic.

Dryopidibb viis P. 17 Aquatic.

Helle ci o 36 Aquatic.

Heteroceridm ..i..... 11 Semi- T

e Ory ser : 2 In wet plae

lodids$ os oe ss ves 32 Probably ae

treno ES I

Byrrsthide ess 97 Habits obseure, on ground beneath cover,

about grass roots.

Riysodidë oe ea 4

Derodontide ........ 5

Hs vee c cus 5

ORIGIN oo esses 1

Monommide SU EL es 6

No. 643] FOOD HABITS OF COLEOPTERA 165

SUMMARY

No. Species Per Cent. of Tota

Phytophaga o doses CER Yel 4,801 26

Baprophapa orse n a Nn eee 8,252 44

Harpactophaga cser osa S£ EXER 4,985 27

Animal parasites ...... 4 eek Res 4

Food habits obscure ;.......,. 7 e 501 3

18,543 100

About 26 per cent. of the species of Coleoptera are phy-

tophagous, most of this pereentage being made up of the

families Curculionide, Cerambycide and Chrysomelide.

Almost one half of the species of beetles, or 44 per cent.,

appears to be saprophagous for the most part and im this

group the families Staphylinide, Tenebrionide and

Scarabeide supply over half of the species. In the pre-

daceous group, consisting of 27 per eent. of the total, the

Carabide with its 2,165 species is the largest single con-

tributor. Thus almost three fourths of the species of

beetles in North America are apparently engaged in what

we call useful activities.

INDIRECT EVIDENCE FROM DUPLEX HYBRIDS

BEARING UPON THE NUMBER AND DIS-

TRIBUTION OF GROWTH FACTORS

IN THE CHROMOSOMES

DR. D. F. JONES

Connecticut AGRICULTURAL EXPERIMENT STATION, New Haven

Surricrent evidence has accumulated to indicate that

the main features of the chromosome theory of hereditary

transmission, as worked out for Drosophila, are appli-

cable.to plants. Peas, primula and maize have been the

best materials so far to demonstrate linkage of factors in

plants. Owing to the ease of culture, large number of

seeds produced and the great genetic variability the

maize plant is becoming very useful in this line of in-

vestigation. The agricultural importance of the plant

and the large number of people working with it have al-

ready made the list of Mendelian factors definitely de-

termined large and increasing rapidly. Due mainly to

the industry of Professor Emerson and his co-workers

at Cornell University, six linked groups are already

visible in rough outline, some of which have a goodly

number of factors fairly well located. It therefore seems

pertinent to consider some indirect evidence funished

by this plant having a bearing upon the chromosome

mechanism.

In working out the best means of utilizing inbred

strains of corn for the purpose of increasing production

it has been found to be advantageous to cross again two

different first generation hybrids each of which were the

result of combining two different self-fertilized families.

Altogether four homozygous types, each differing from

the other in many visible characters, are brought together

in this way in a progeny which has an.extremely complex

composition. Assuming that the inbred strains have been

reduced to complete homozygosity, the first generation

hybrid is uniform. Statistical measurements show this

166

No. 643] GROWTH IN CHROMOSOMES ` 167

to be so. Theoretically, all the plants are hereditarily

exactly alike. When such a hybrid with segregating

gametes is again crossed with a similar first generation

hybrid but having a different genetic construction, the

result is a mixed lot of plants in which practically every

individual differs in some degree germinally from every

other.

This statement holds for any numbers that it would be

possible to grow. Every inbred strain of maize, that has

so far been obtained by continued self-fertilization with

one progenitor in each generation, has differed in many

ways from every other inbred line, whether they came

originally from the same or different varieties. All the

inbred strains coming from different individuals at the

start show a noticeable increase in vigor when crossed

and a rapid reduction of growth and great increase in

variability in the immediately following generations when

again self-fertilized. It is therefore not at all improbable

that most of the self-fertilized strains differ from each

other by a large number of genes in every chromosome.

If such is the case, then the duplex combination will

have an extraordinary amount of genetic diversity. This

may be made clearer in the following illustration. If,

instead of being crossed, a hybrid was self-fertilized and

there was only one factor difference in each pair of

ehromosomes, over one million plants would have to be

grown in order to have an even chance of securing all

the possible combinations (assuming maize to have 10

chromosomes). But with more than one factor in each

chromosome the situation is far different. Two factors

in each chromosome having a linkage ratio of 10 per cent.

would necessitate 20?' individuals in the segregating

generations to obtain the same result. This is calculated -

from the formula [2(r 4- 1)"?]?* where r+ 1 is the link-

age ratio, in this ease 10 per cent., or 9+1, n is the

number of factors in each chromosome, and c is the num-

ber of chromosome pairs. This number of plants to be

grown would require an area roughly 57,346 million

times the total surface of the earth. But instead of being

168 THE AMERICAN NATURALIST [Vor. LVI

self-fertilized, the hybrids with their segregating gametes

are again erossed and certainly there are more than two

factor differences in most of the chromosomes having

varying degrees of linkage with each other. At present

almost nothing is known about the heredity which the

two first generation hybrids may have in common. But

all the four homozygous types when erossed singly in the

six possible combinations show about an equal amount of

heterosis. The double-erossed combination shows no re-

duction in vigor of growth, but on the other hand this

appreciably increased. This is due, however, in part to

a better start as the plants come from large, well-nour-

ished seeds grown on vigorous plants, whereas the first

cross is handicapped in this respect.

The doubly hybrid plants are theoretically more di-

verse than self-fertilized second generation progenies

coming from the same parents, but compared with the

first and second generations the double cross has features

of both. In respect to growth characters the plants are

a group of many different first generation hybrids. Very

little recombination can take place to allow recessive

weaknesses to appear. In fact any recombination that

does take place is probably out-balanced by an increase

in heterozygosity in other factors. A critical comparison

of such double hybrids with their parental first genera-

tion hybrids and with their second generation self-fertil-

ized sibs in respect to variability of different characters

ought to give some indication of the distribution in the

chromosomes of the hereditary factors affecting growth.

In those factors which are independent of the growth

of the plant the variability of the double cross should

approach or exceed that of self-fertilized second genera-

tion. In those characters which are directly dependent

upon the vigor of the plant the double cross should re-

semble more closely the first hybrid generation. Five

characters have been taken and measured in three

different but similar lots of plants. These are: number

of rows of grain on the ear (pistillate inflorescence) ;

nodes of plant, height of plant, length of ear; and pro-

No. 643] GROWTH IN CHROMOSOMES 169

duction of grain (weight of entire pistillate inflorescence

with mature seeds). A previous study of a large number

of first generation hybrids between inbred strains of

maize has shown that the average number of rows of

grain of the hybrids was inereased 5.29 per cent. above

the mean position of their parents; similarly nodes per

plant 6.45 per cent.; height of plant 27.44 per cent.;

length of ear 28.57 ; and total produetion of grain 180.00

per eent. The variability of these F, plants was slightly

decreased below the parental average in nearly every

ease in respect to these characters.

Rows of grain and nodes are therefore much less in-

flueneed by the vigor of the plant than are the other

characters, notably production of seeds, which is very

largely determined by the amount and rapidity of growth.

Assuming that the complementary aetion of dominant

favorable growth factors is responsible for the vigorous

growth of the hybrids, it would be expected that F, x F,

combination would not be as variable as the second gen-

eration resulting from self-fertilization in respect to

produetion of grain per plant, provided a large number

of essential growth factors were acting and that these

were distributed rather uniformly throughout the chro-

mosomes. On the other hand such characters as rows

of grain on the ear and nodes per plant being largely

independent of growth vigor, would not be expected to

show a reduction in variability when-compared with the

second self-fertilized generation.

The distribution and statistical constants for the sec-

ond generations grown from self-fertilized seed of the

parental hybrids have been compared to the reciprocal

erosses of the same parental hybrids in three different

sets of plants. In each ease the cross-fertilized seed,

which produced the F, X F, plants, and the self-fertilized

seed, from which the F, plants were grown, came from the

same ears. The two kinds of pollen were applied in a

mixture at one time and the seeds separated by their color

at maturity.

Without giving the extensive data upon which the

170 THE AMERICAN NATURALIST [Vor. LVI

figures are based, the averages of the coefficients of vari-

ability of the F, X F, and the F, families are brought

together in table 1. With these are given some figures

averaged from the F, parents. These are not from the

exact first generation parents of the progenies used to

TABLE I

A COMPARISON IN VARIABILITY OF SINGLE First GENERATION, DOUBLE

First GENERATION AND SECOND GENERATION HYBRIDS

Characters |

Rows of grain...... | 8.90 40- .98 | 12.76 .D2— .65 | 12.381 45- .82

Nodes of plant..... | 5.54 25- .73 5.88 .25- .27 6.20 26- .33

Height of roti d 708 .25-1.04 6.20 .25- .33 6.92 26- ,40

Length of ear...... |.- 13.83 ./2-1.66 | 13.23 .41- .75 | 16.90 .69-1.03

Weight of ndn SM | 24.13 |1.15-1.42 | 26.99 |1.19-1.44 | 32.68 /1.11-2.31

give the other results in Table I. They are similar but

were not grown in the same years. They can not be

compared as closely to the F, X F, and F, lots as these

can be compared with each other. The coefficients for

variability of the F, x F, and the F, plants, averaged

from three different combinations with a fairly large

number of plants in each grown from seed of which the

two contrasted kinds came from the same ears, are strictly

comparable. The greater growth of the double hybrids

as shown by the increase of the means makes comparison

of the coefficients of variability The

appearance of the plants in the field apports the statis-

tieal data, as it is the uniform produetion whieh makes

the hybrid plants so valuable for agricultural purposes.

There is a noticeable difference between the double cross

and the self-fertilized second generation in even size,

similar appearance and general excellence as the plants

are harvested in the field.

The figures show that the variability of the F, X F,

families is about the same as the F, families in rows of

grain and nodes per plant. In height of plant, length of

ear and weight of grain per plant, all characters which

No. 643] GROWTH IN CHROMOSOMES 171

are markedly influenced by the vigor of the plants, there

is a reduction in variability. Partieularly is this true

of length of ear and weight of grain, which are fairly

reliable measures of the plant's reproduetive ability,

whieh in annual plants sums up the organism's entire

energy. In other words the plants are uniformly vigor-

ous and are not dependent upon exceptional individuals

for their high average position. This is indirect evidence

that those hereditary factors which are concerned with

the growth of the plants are numerous and widely dis-

tributed throughout all or many of the chromosomes.

As a means of corn improvement it would be highly

desirable to bring together into a pure breeding homo-

zygous condition all those factors which cause the hybrid

plants to excel their parents. Such individuals should

be even more efficient in their growth processes than the

heterozygous combinations of the same factors because

the determiners responsible for hybrid vigor seldom show

complete dominance. The recombination of linked fac-

tors is a problem that demands the most careful attention

of the plant and animal breeder. It is the closely linked

factors which are the main concern. When the distance

between any two loci is fifty units or more, then all the

factors situated outside of these points are independent

of each other in transmission and it makes no difference

from the standpoint of recombination whether the factors

are in the same or different chromosomes. Therefore

the number and arrangement of the individual genes

themselves seem to be more important than the number

of chromosomes. Although as yet it is impossible to com-

pare the numbers of factors in different species, it

does not seem likely that the genus Rosa with 8 chromo-

some pairs is genetically less complex than Nicotiana

species with 24 pairs. Some crustacean species with

84 pairs of chromosomes are contrasted with various

mammals with 8 to 12. Even in the Arthropods alone the

haploid number ranges from 2 to 100. It seems profitless

to look for any significance in chromosome, numbers.

Leaving aside the matter of doubling of chromosomes any

172 THE AMERICAN NATURALIST [Vor. LVI

differences that there may be are probably qualitative

rather than quantitative. It is possible that there may be

very little difference in the amount of essential hereditary

material. But the word ‘‘ amount " must be considered

as equivalent portions. The visible size of the chro-

matin mass fluctuates greatly even at different stages of

growth in the same individual.

Although the cytological proof of the chromosome

theory is still so meager as to make speculation somewhat

useless, nevertheless, looking at the matter from the stand-

point of diffieulty of recombination the important consid-

eration is the number of fifty-unit lengths of chromo-

somes. However, the Morgan school unit of measure-

ment, the one per cent. of erossing over, is not a stable

unit, as they have shown that crossing over fluctuates

rather disconcertingly, due both to environmental and ger-

minal modifying factors. Detlefsen' finds the rate of cross-

ing over between certain loci to be very profoundly altered

by continued selection for high and low cross over stock.

So that for the present the terms proposed by Haldane*

of morgan and centimorgan as measures of chromosome

length do not have any precise applieation. At the same

time the rate of erossing over is the only measure avail-

able and ean not be given up until a better one is found.

The term morgan, referring to a one-hundred-unit length

of chromosome is convenient but does not have the bio-

logical significance that a fifty-unit length of chromosome

would have. Since every gene is independent in trans-

mission from all other loci in the same chromosome more

than fifty units distance from it, and has the usual Men-

delian relation with them as well as with all the factors in

the other chromosomes, the term mendel would perhaps

be useful, if the employment of such terms can be justified

at all. Applied in this way a mendel is a measure of

chromosome length equivalent to fifty per cent. of eross-

ing over.

It should be noted that a mendel is not comparable to a

1 Proceedings of the National Academy of Science, 6: 663—670, 1920.

2 Journal of Genetics, 8: 299-309, 1919.

No. 643] GROWTH IN CHROMOSOMES 173

single short chromosome fifty units long. It is not to be

thought of as a fixed portion of any chromosome. The

chromosomes are, or course, not to be considered as

marked off into fifty-unit lengths. But the result of re-

combination with a large number of factors is approxi-

mately the same as if such were the case. Because it

brings out the fact which has not always been fully

appreciated, that recombination within a chromosome

takes place as easily as between different chromosomes,

when the distance between the loci is sufficiently great,

the term mendel as a measure of chromosome length may

have some value.

In the primitive unicellular organisms it is conceivable

that the hereditary substances were not located in a

mechanisn as well regulated as in the higher organisms.

As specialization increased, the grouping of factors in

chromosomes has undoubtedly been of very great evolu-

tionary significance. The chromosome mechanism has

been subjected to natural selection as severely as any

external morphological feature and has developed co-

ordinately with sexual reproduction—the one to make

recombination possible, the other to make that process

orderly.

Although it is largely speculation it seems necessary

to believe that there is some functional relation between

the factors associated together in a chromosome or por-

tion of a chromosome. There is some evidence for this

in the quick and exact return of certain species hybrids

to one or the other parental type. Evidently only those

individuals resulting from gametes in which crossing over

has not occurred are able to live. So far the factors

which have been located seem to be placed at random

in the chromosomes, and it is impossible to make out any

significant relation among them. This in itself may be

an indication of an immense number of hereditary de-

terminers which play a part in the organism. For as

yet the function of only the relatively superficial factors

can be seen. The vitally important ones can not be dis-

pensed with and therefore can not be studied except as

the lethal factors show some effect in hybrid combination.

EXPERIMENTAL STUDIES ON THE DURA-

TION OF LIFE

II. HEREDITARY DIFFERENCES IN DURATION or LIFE IN

LINE-BRED STRAINS or DROSOPHILA +

PROFESSOR RAYMOND PEARL AND SYLVIA L. PARKER

INTRODUCTION

Ir was shown in the first paper in this series (27)? that

there was a marked difference in mean duration of life,

and in the form of the ls curve, between wild-type stocks

of Drosophila on the one hand and the synthetie quin-

tuple mutation stock on the other hand. It was further

made clear that, because of the technique used in the ex-

perimental work, there could be no doubt that the basis of

this difference must be hereditary and not environmental.

Furthermore, Hyde (11) and Pearl (6) have presented

evidence for the Mendelian inheritance of this character

duration of life.

Given it to be the fact, as the just cited work demon-

strates to be the case, that there are hereditary differ-

enees within the same species of Drosophila in respeet of

duration of life, the problem which next presents itself is

to determine whether within a particular strain of Droso-

phila hereditary differences exist, and if so what their

magnitude may be, their degree of permanence, ete. In

1 Papers from the Department of Biometry and Vital Statistics, School of

Hygiene and Public Health, The Johns Hopkins Uni , No. 48.

2 A word of explanation is necessary as to the ed of handling biblio-

graphie referenees in this series of papers. In the first paper a list of 26

references numbered eonseeutively from 1 was appended. It is proposed not

to duplieate referenees in any subsequent paper in the same series. nse-

quently the first new bibliographie eitation in the present paper is numbered

27. When any reference is made to titles already cited in the first paper in

the series, the numbers whieh they bear in the list appended to that paper

will be used. This practice will be adhered to in all subsequent papers in this

series of Studies.

174

No. 643] STUDIES ON THE DURATION OF LIFE 175

short one wishes immediately to get a kind of knowledge

for this organism and character similar to that which

Johannsen (28, 29) got for the size character of beans

from his pure-line work. The first, and in a sense pre-

liminary, investigations on this problem will be presented

in this paper. Later in the series we expect to publish

much more extended and penetrating evidence on the

same problem. Some, however, must be presented early

in the series in order to make the account of subsequent

experiments intelligible.

It is obvious that in the ease of an organism like Droso-

phila it is impossible to have a pure-line in the strict sense

of Johannsen. The most that one can do is to have inbred

lines, and the most intense degree of inbreeding possible

in the premises is by brother X sister mating. The gen-

eral plan of the experiments reported in this paper ean be

outlined as follows:

1. Mate a virgin brother and sister, chosen at random

each from the same one of the original 5 foundation .

stocks (cf. 27).

2. Repeat this for as many pairs as the facilities of the

laboratory make possible.

3. Test the progeny of each mated pair separately for -

duration of life, and form for each group of such progeny

a life table. |

4. Each such mated pair constitutes the beginning of a

line, in which at any time the processes noted under para-

graphs 1, 2, and 3 above could be repeated. In this paper

will be reported the results of one such repetition.

The general technique of the experimental work has

been fully described in the first paper of this series and

need not be repeated. It should merely be emphasized

again that the environmental conditions in respect of

food, housing, temperature (25° C.) and atmospheric con-

ditions were identical for all the flies in the experiments

here reported.

176 THE AMERICAN NATURALIST [Vor. LVI

Duration or LIFE IN DIFFERENT PROGENY Groups OUT OF

BROTHER X Sister MATINGS

The survivorship data (ls frequencies) for 7 progeny

groups each out of a mating of brother X sister are ex-

hibited in Table II. All distributions are put on the same

basis of 1,000 flies at emergence from the pupal stage.

The absolute numbers of flies involved in each experiment,

are given at the foot of each column. These numbers are

TABLE I

BROTHER X SISTER Matines. First TEST

Lines | Original Stock Date of Date

| (Described in (27)) Mating Emergence

108... | Old Falmouth April 8, 1920 April 19-May 3

IUE, s | ais " Apiil 7, 1920 April 17- Eemi :

s. | New Falmouth April 7, 1920 April 18- May

200 .—— | 3: i April 10, 1920 April tire E

300... | Sepia April 7, 1920 Apri! 17-May

301..... | cs April 6, 1920 Apul 17-May :

308... ss | e April 8, 1920 April 18- May 2

TABLE II

SURVIVORSHIP DISTRIBUTIONS OF PROGENY OF BROTHER X SISTER MATINGS.

BOTH SEXES TOGETHER

Numbers of Survivors up to Indicated Age in Lines No.

Age in

Days

100 101 201 202 300 301 | 303

1... 5 ud Lu Lt 1,000 | 1,000 | 1,000 | 1,000 | 1,000 | 1,000 | 1,000

ru eir eee 983 | 2993]|1,000| 689; 926; 870; 882

120 a eee 937 | 987 | 1,000 8| 727 64

IB. Oe a qa IK a ey 891 934 952, 492 809 02 702

Thee EE ie T ee 811 1 943 | 426 623 441 621

40... oM EU 743 875| 85 549 522

BO iro NUR ee 589 855 790 197 383 255 | 429

Loc D e eee tees 514]. 770] -6 1 2| 205; 311

481 is iaa oe et ae ae 406 | 599 5 148 148 130 | 261

o WD AN C NR ee AN 240 | 493 381 105 75 1

60. GE E E E eee TT 91 219 33 12 31 112

80. a R ton a A 29 99 133 | 16 6 12 56

TA 12 UTILI UNA RUE CU 6 29 10 | 0 2 0

TES hh dio as kia eee 0. IOl e i ES

Crus DM re ER Ww Wed os c ur

SU. VoU ce eee Kod sa | ^ie | 0 = = pur A rt

Abs. No. of flies..........-- | 175| 152| 105 | 61| 162| 161| 161

No. 643] STUDIES ON THE DURATION OF LIFE 177

smaller than is desirable, but these experiments represent

a relatively early stage of the work before the technique

of getting maximum progenies for life table work had

been perfected. Further it must be remembered that the

individuals in any eolumn are the progeny of only one

single pair of parents. The source of the lines together

with other pertinent data are shown in Table I.

1000

a OE o,

100

o Big

iO ET

ES has

Eve tow

E EE Y

EE IY au

d B iu

BAAS

Aah Lob cb ee ee p bob |

LB les 16 4 30 36 dB 4B SR cO 060 72 8 4 9

AGE IN DAYS

Fie. 1.

Survivorship (lx) graphs for lines 100, 101, 201, 202 and 301.

Five of these distributions are shown graphieally in

Fig. 1, and their biometrie constants are given in Table

TABLE III

FREQUENCY CONSTANTS FOR d; DISTRIBUTIONS. First TEST

i j rati i Deviati Coefficient of

e Mean — of Life "— Seton ion meant

3005.55 40.45 = .84 16.38 = .59 40.49 + 1.68

101... 50.02 + .85 15.51 = .60 $1.01 = 1.31

AZUL tae 47.40 + .99 .03 + $1.71 = 1.51

208 css | 22.04 = 1.57 18.18 = 1.11 82.49 = 7.74

300....| 3119 = .83 15.76 = .59 53 = 2.

S01... | 25.28 = .92 17.25 = .65 68.24 + 3.56

808.,... | 32.02 + 1.07 04 62.59 = 3.14

178 THE AMERICAN NATURALIST [Vor. LVI

HI. In calculating these constants, the absolute d; fre-

quencies, and not the per mille frequencies, were of course

used.

From these data it is at omce apparent that these

progeny groups show distinct, and in some cases decidedly

large, differences both in mean duration of life and in the

form of the mortality distributions. Lines 101 (Old Fal-

mouth stock) and 201 (New Falmouth stock) show the

longest mean duration of life, and they are sensibly iden-

tical in the form of the life curve, having regard to the

errors of random sampling. The difference in the means

for these two lines is 2.62 + 1.31 days, an obviously insig-

nificant difference, only 2 times its probable error. Simi-

larly these two lines do not significantly differ in absolute

or relative variability, the difference between the stand-

ard deviation being .48 + .92.

Line 100 (Old Falmouth stock) has a distinetly and sig-

nificantly lower mean duration of life than 101 or 201.

Comparing it with line 101 the difference in the means is

9.57 + 1.20 days or approximately 8 times its probable

error. The l- curve lies throughout its course below the

lines for 101 and 201. Line 100 is also relatively more

variable in duration of life than 101 and 201, but largely

because of the difference in the means.

The individuals in line 202 (New Falmouth stock) are

the shortest lived of any here dealt with, and the shortest-

lived wild-type strain we have as yet isolated. Its mean

duration of life is less than half that shown by lines 101

and 201 and only a little more than half that of line 100.

Line 202 shows the highest relative variability in duration

of life of any of the lines here discussed. It also has

the highest absolute variability with one exception (line

303).

Lines 300, 301 and 303 (Sepia stock) are all relatively

short-lived lines. 300 and 303 are substantially identi-

eal, while 301 has a lower mean approaching that of line

202. These sepia lines are also characterized by high

relative variability.

No. 643] STUDIES ON THE DURATION OF LIFE 179

RESULTS or [INBRED RE-TESTS ror Constancy

During the progress of the experiments described in

the preceding section the offspring flies (from original

brother X sister matings) in each of the lines, whose dura-

tion of life was being tested, were allowed to mate at

random in their bottles, and their progeny removed to

form stocks of the several lines. These stocks were al-

lowed to reproduce in stock bottles, all matings being

therefore random within the line, for a period of about 7

months (ef. Table IV). At the end of that time it was de-

cided to make a re-test of each line to see how it was then

behaving relative to duration of life. There was then

made, at dates indieated in Table IV, a random selection

from each line stock bottle from which a brother and

sister pair was bred, and these two individuals were

mated to get a set of progeny on which to carry out a sec-

ond set of life duration experiments. The necessary

facts as to line numbers and dates on this re-test are given

in Table IV.

TABLE IV

BROTHER X SISTER MATINGS. SECOND TEST

Line from which Number of Line Date of Date of

Second Selection of Po" of Vie uh Second Brother

of Brother and Second Brother Brother X X Sister

Sister Was Made X Sister Mating Sister Mating Mating

TOO ieee T 104 April 8, 1920 November 6, 1920

LOL Gea vv ORAN 107 April 7, 1920 October 14, 1920

201.1. va 3x 207 April 7, 1920 October 18, 1920

ZUR as 208 April 10, 1920 October 14, 1920

MO ee I 304 April 7, 1920 November 6, 1920

SUP CR aus eee 307 April 6, 1920 o , 1920

803,1: 4 bees oan ` 809 : April 6, 1920 October 14, 1920

The survivorship distributions of the progeny groups

of this second brother X sister mating are given in Table

V, and the biometrie eonstants ealeulated from the ob-

served d. distributions in Table VI. These tables are

for eomparison with Tables II and III above.

180 THE AMERICAN. NATURALIST [Vor. LVI

TABLE V

SURVIVORSHIP DISTRIBUTIONS OF PROGENY OF SECOND BROTHER X SISTER

Matines. BOTH SEXES TOGETHER

| Numbers of Survivors up to Indicated Age in Lines No.

Age in

Days

| 104 107 207 208 304 307 309

Eli... Oh oar s UR » WEE eS | 1,000 | 1,000 | 1,000 | 1,000 | 1,000 | 1,000 | 1,000

B ry S See eG dE EA | 997 | 1,000 973 833 | 1,000 862 | 1,000

PES Crise M vsus nacre gs 923 950 926 738 0 700 978

EN als Vereen Ce RI Es 871 926 819 643 870 623 911

SE Lu sU Usati iU alis 713 917 792 595 674 469 00

De OUT Au ea uu e FES | 629 901 785 478 392 489

AB. c OW VAN STI LEA ee 552 860 711 286 435 285 456

Bee Win TS. E DEN P S Vis 469 wae 644 167 261 177 267

SÉ ees eee et 395 686 530 0 152 92 89

CRM E veo seattle eee V E ae 595 3 — 109 4 67

| pete Set ee Gd er alee VOV S dr 178 488 255 0 23 44

SC ee eee Cea ip E 66 264 141 — — 8 0

WE. ERY aA) oer NIA UNE e 0 83 20 — — 8 —

COS EU pue E MCN E — 8 20 — — 8 —

BA RE FRHRR RE eA a dE — 0 T — — 0 —

DE ae M as — — 0 — — — —

Abs. No: of flies ......... 286 121 149 42 46 130 90

TABLE VI i

FREQUENCY CONSTANTS FOR d; DISTRIBUTIONS. SECOND INBRED TEST

Line Mean Duration of Life Standard Deviation Coefficient of

No. (Days) (Days) Variation

IOE .... 39.59 += .74 18.63 = .53 47.06 + 1.62

100155. 53.74 = 14.40 & .75 32.38 + 1.54

25230 45.34 = 1.10 19.97 + .78 4.04 2.03

208. 1. 25.65 = 1.53 14.68 = 1.08 57.23 = 5.42

304..... 32.09 + 1.43 14.43 = 1.01 44.97 = 3.75

807. iv. 25.22 = 16.70 = .70 66.22 = 3.79

S08. ei. 1 2.84 38.91 + 2.23

The purpose of this second test was, of course, to see to

what extent duration of life was holding constant in the

line. During the period between the first and second test

the stocks of the several lines had been subjected to vary-

ing environmental influences, in particular in relation to

temperature, the stock bottles having been kept at room

temperature, which varied rather extensively. Did the

lines after 7 months have the same characteristic life

curves that they exhibited on the first test? Allowing 12

No. 643] STUDIES ON THE DURATION OF LIFE 181

days from generation to generation in the case of flies re-

producing freely at random in stock bottles, the interval

elapsing between the first and second tests would cover

roughly almost 18 generations. "This is a long period

and affords abundant opportunity for change in the aver-

age genetic constitution of the population.

1000

W N e LS

ms.

va,

Bu a LC

~, -

- ->

me ee

oT TTT

LT TTT

SURVIVORS

TTT

Lp ee rs i E 4

Ir TE M a o 4 XP 4B 54 66 72

AGE IN DAYS

Fic. 2. Comparing the lx lines of the first and second inbred tests.

of lines 101, 100 and 301.

An examination of Tables V and VI and Fig. 2 shows at

once, in a general way, that the characteristic features of

the several lines in respect of duration of life did in fact

hold remarkably constant during this period. A more

precise comparison of the means is made in Table VII.

There can be no question of the substantial constancy

of these lines, over the period covered in the tests in re-

spect of duration of life. The le curves run well together

till the upper end of life is reached, where, because of the

small numbers involved, there is some irregularity. In no

ease is the difference between two comparable means, as

shown in Table VII, as much even as three times its prob-

182 THE AMERICAN NATURALIST [Vor. LVI

able error, nor is there any certainly significant change in

variability having regard to the probable errors of the

differences involved.

TABLE VII

DIFFERENCES IN MEAN DURATION OF LIFE BETWEEN THE FIRST AND SECOND

INBRED TESTS OF THE SEVERAL LINES

Corresponding Lines

(Mean of Second Test Difference of Means

inus Mean of First) (Day: P.E. Diff

£04-100 15244427542 Gg oe ca a CaN — .86 +1.12

IE FE IE A VE Re ARE T E Cer E es + 3.72 + 1.37 2.72

BUT EUIS. uA cd E ola Oe — 2.06 + 1.48 1.39

AUN MUSS Qu cceli RET eA Cn T ME + 3.61 + 2.19 1.65

BOO QU NS ons VENT CCP ERA LUE RO os + .90 + 1.65 54

E i S Sui a ci creek A CaS + 062+ 1.35 04

i a a IAS. E RC G HEC TEE + .98 + 1.40 70

Resuuts or Mass CULTURE Re-rests FOR Constancy

The point may well be made that in the re-tests of the

lines described in the preceding section an additional ele-

ment is introduced in the faet that the flies for the re-test

were the progeny of a second brother X sister mating.

What one wishes to know is: what degree of constancy

in duration of life is exhibited by the general stocks in

each line, mating purely at random, after the initial se-

lection and inbreeding? "We wish now to present some

data on this point. Table VIII gives the biometric con-

stants for this material. Mass culture re-tests have been

made on two of the original lines, 100 and 101. "These

mass culture re-tests were made in two ways as follows:

(a) From the stock bottles of the line to be tested a

large sample of progeny was taken at random each day

as the flies emerged from the pupal stage, and these

progeny flies were put in small bottles for a duration of

life experiment in the usual way deseribed in (27).

(b) From the stock bottles of a partieular line to be

tested a number of virgin flies (usually 8 to 10 of each

sex) were taken at random immediately upon emergence,

and mated as a group in a mating bottle. The progeny

from this sample was then removed, upon emergence, to

small bottles and a regular duration of life test carried

as described in (27).

183

No. 643] STUDIES ON THE DURATION OF LIFE

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184 THE AMERICAN NATURALIST [Vor. LVI

It is at once apparent that the mass re-tests on line 101

gave extremely satisfactory results as to constancy of

duration of life in the line, after intervals of approxi-

mately 5 and 11 months. The mean value for either the

A or the B test does not signifieantly differ, having regard

to its probable error, from the mean shown on the original

test at the start of the line. The mean of the A mass re-

test almost exactly agrees with that of the second inbred

test of the same line, as given in Table VI.

In the ease of line 100, the mass re-test after 54 months

approximately does not give such close agreement. The

mean is signifieantly lower, the difference being 6.6 times

its probable error. No explanation of this result is, as yet,

forthcoming, but it probably means no more than lack of

genetic purity in the line. It is, however, interesting to

note that the sense of the change is in the same direction

as that in which line 100 in general differs from line 101,

which we regard as our most typical wild-type line in re-

spect of duration of life. That is, line 100 is, as com-

pared with 101, a shorter-lived line. Its mass culture

re-test is still shorter lived. i

The variability in respect of duration of life, whether

measured in absolute or relative terms, is uniformly

higher and in two cases out of the three by a significant

amount in the mass culture than in the original inbred

tests. This is, of course, exactly what would be expected

on general genetice grounds. One brother X sister mating,

as has been shown by Pearl (30), Jennings (31) and

others, reduces the heterozygosis in the strain by only 50

per cent. It is interesting to note, in connection with the

explanation suggested above for the difference in the

means in the ease of line 100, that the variability in the

mass re-test on that line is very much bns than in the

original inbred test.

A mass re-test was carried out on two of the lines from

the second brother X sister matings. The results from

these experiments are presented in Table IX.

185

No. 643] STUDIES ON THE DURATION OF LIFE

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186 THE AMERICAN NATURALIST [Vor. LVI

The substantial constancy of line 101, in both mass and

inbred tests, is evident. In respect of variability the line

behaved somewhat like 303 diseussed below.

In line 303 again the constancy of the line in respect of

mean duration of life is as definite as could be expected.

Over periods of approximately 7 and 13 months, the mean

duration of life has not sensibly changed, having regard

to the probable error involved. The results respecting

variability are somewhat anomalous. Both the second

inbred and the mass re-test show variability of a dis-

tinetly lower order than was exhibited by the progeny of

the original brother X sister mating. It seems probable

that the original test by accident gave a variability re-

sult higher than was really characteristic of the line. But

the mass culture re-test exhibits a lower variability, not

- certainly significant, to be sure, than the first test on line

309. Of course it is to be expected that with continued

brother x sister mating the variability of mass cultures

from the line would come nearer and nearer to that of a

further inbred lot of progeny from the same line. Prob-

ably the results of Table IX are an expression of the

realization of such expectation, obscured by the fact that

the numbers are small and the errors of sampling conse-

quently relatively large.

Discussion AND SUMMARY

The data presented in this paper appear to demon-

strate, with comprehensiveness and accuracy, three broad

facts.

A. That there exist in a general population of Droso-

phila melanogaster (or its mutants) genetie differences

in respect of duration of life. |

B. That these genetic differences are capable of isola-

tion, by appropriate selection and inbreeding.

C. That within an even moderately inbred line, the gen-

etic differences in duration of life remain constant over

periods of at least 10 to 25 or more generations.

No. 643] STUDIES ON THE DURATION OF LIFE 187

These facts, based upon the determination experi-

mentally of the duration of life of 3,039 individual flies in

18 experiments, under constant environmental conditions,

place this character ‘‘ duration of life’’ in the category

of genetically definite and workable characters, and indi-

cate that it will just as well repay careful analytical study

as the characters more usually dealt with. Furthermore,

duration of life is a character of great general biological

significance.

LITERATURE CITED

27. Pearl, R. and Parker, S. L. Experimental Studies on the Duration of

lafe, L cater ype Discussion of the Duration of Life in Droso-

phila. AMERICAN NATURALIST, Vol. 55, pp. 481-509, 1921.

28. Johannsen, W. Ueber Erblichkeit in Populationen und in reinen Linien.

Jena (Fisher), 1903.

29. Johannsen, a Elemente der exakten Erblichkeitslehre, 3d Edit., 1913.

30. ge R. On the Results of Inbreeding Mendelian Population; & Correc-

and iie nsion of Previous Conclusions. AMERICAN NATURALIST,

31. Jennings, H. S. Formule for the Results of Inbreeding. AMERICAN

NATURALIST, Vol. 48, pp. 693-696, 1914

SHORTER ARTICLES AND DISCUSSIONS

NOTE ON A CASE OF HUMAN INBREEDING?

THrouGH the kindness of a friend the following pedigree is

presented. It is that of a family of English stock, which has

been in this country since the early eighteenth century, and

during that time has been one of the principal families of a

rural community.

ee 4i

4T: 3 4 r 4 ] F 8 OTHER CHILDREN

sT? dT? du

d | $ gT?

ENS IO OTHER CHILDREN

i Í zl

TUE ER REN dJ? 2 LMNG 90+ YEARS AG

f E tf 1

6 OTHER CHILDREN dT? 3 d

LIVING , NORMAL DIED TBG DIED TBC DiED TBC

ABOUT 20 YEARS 46 YEARS ^— 25 YEARS

QA dB gc

DIED INFLUENZA

IB YEARS

Fic. 1. Pedigree of an inbred family.

To quote from my eorrespondent's letter, ‘‘A was a fine

young girl. She had graduated from high school but did not

go to eollege as her mother had died in the summer and she

wished to take charge of the home. B is about 16 years old. A

splendid young man, bright and apparently healthy. He is in

school standing about average. C is 10 years old or thereabouts.

An exceptionally bright child and one that is very much alive

and full of spirit."

Assuming that the line of descent represented in the figure by

a broken line, indicating that the number of generations is not ©

known, includes the same number of generations as the other

. lines.the coefficients of inbreeding * for the children in the last

1 Papers from the Department of Biometry and Vital Statisties, School of

Hygiene and Public Health, Johns Hopkins University. No. 41.

2 Pearl, ‘f Studies on Inbreeding," I-VIII, AMERICAN NATURALIST,

1913-17.

188

No. 642]. SHORTER ARTICLES AND DISCUSSION 189

generation (viz, A, B, and C) are as follows:

Z, — 0, Z, =25,

Z. —25, Z, —3431,

Z = 25, 47, == 27.1,

ie. in five generations of ancestry the inbreeding is about a

quarter of the possible maximum.

There is no deleterious effect of inbreeding apparent in this

pedigree. The three children in the last generation, the most

inbred of any, show no signs of abnormality. In their father’s

fraternity, for which Z, —2Z,—2,—0; 2,—12.5; Zr,—4.1,

or in four generations of ancestry there is 4%; of the possible

maximum inbreeding, one of eight died of tuberculosis; the

other seven have attained adult age. In the mother’s fraternity,

for which Z2, — Z,-= 2%, ==0;; 2, 2=6.25:. 24, 29, two. out of

the three have died of tuberculosis. The least inbred, there-

fore, show the greatest susceptibility to tuberculosis. The num-

bers are, of course, too small to draw any certain inference, but

so far as they go, they accord best with the view that there

is no harmful effect of inbreeding per se.

Jonn Rice MINER

ON COLOR VARIATIONS IN CHITONS

` THE question was raised by Bateson (''Materials," 1894,

p. 307) as to whether variation occurring in serial parts whose

repetition is not strictly speaking of a metameric sort, would be

found to simultaneously affect each of the parts involved in sueh

a series. With this point in mind he examined a collection of

ehitons, the 8 shell plates of these animals providing an exeellent

opportunity for such observations. He found color variations

affecting all the plates of an individual to be of rather rare occur-

renee, but that plates 2, 4 and 7 seemed, on the other hand, to

exhibit a deeided tendeney to vary together (in several species of

Chiton).

Although the problem of metamerism, so far as it concerns

variation, has perhaps lost some of its original attractiveness, I

have thought it worth while to point out that in Chætopleura

several curious types of shell variation are apparent, involving

either simultaneous variation throughout the series or variation

in a single shell-valve alone, or both.

190 THE AMERICAN NATURALIST [Vor. LVI

The commonest type of color pattern, in Chetopieura apiculata,

is one which involves a double band of blackish or grayish pig-

ment running the length of valves 2 to 8, the bands joined on

2 and on 8 by continuous semicircular blotches (cf. Fig. 1, d).

In 3 out of 219 specimens, however, a central dark stripe,

clearly marked on valves 2 to 8 inclusive, accompanied a much

fainter double band extending to valve 1 (Fig. 1, b), and made

up of regular triangular grayish blotches on the posterior bor-

ders of valves 2 to 7. In one ease, a bright central band of white

Fic. 1. Chaetopleura apiculata (x 2).

was marked by a median grayish blotch on valves 3 to 7 (Fig.

1, a) ; a paler example of the same kind is shown in Fig. 1, e.

These are instances where variation from the more usual color

type clearly has taken place simultaneously in the whole series

of valve-plates, this condition being seen not only in the form of

the central stripe, but also in the shapes of the individual pig-

ment blotches comprised in the double band (ef. Fig. 1, a and b),

as well as in a few eases where three small but distinet pigment

flecks were noted on the lateral field of each plate.

In addition, however, two sorts of pattern variation occur

which are quite different from the foregoing. In three instances a

definite yellow or orange central bloteh appeared on valve 2, and

nowhere else (Fig. 1, e). And in five further instanees there was

found a marked blackish bloteh at either lateral margin of valve

No. 642] SHORTER ARTICLES AND DISCUSSION 191

4 (Fig. 1, d, e). In two further cases, this type of lateral marking

was continued in the form of less distinct marginal blotches on

valve 3. The marginal blotches on valve 4 may accompany an

otherwise ‘‘normal’’ pigment pattern (10 examples in 219 ex-

amined; Fig. 1, d), or may be present where there is evidence

of a tendency for the formation of a distinct axial stripe (five ex-

amples; Fig. 1, e). |

It is evident, then, that in Chitons eolor pattern variations

may oeeur in sueh a way as to affect single valves only (and, in

Chetopleura, specifically valve 2 or 4); and either quite inde-

pendently of this type of variation or accompanying it, may also

affect all valves in the series simultaneously. Such variations are

quite independent of age.

W. J. CROZIER

RUTGERS COLLEGE

FUGITIVE NET-VEINING IN THE CICADA

(HEMIPTERA)

TILLYARD has lately noted that, besides the chitinized veins

which serve for the support of the insect wing, there exist in

some eases at least fugitive blood-veins during the expansion of

the wing, which later collapse and more or less completely dis--

appear when the wing dries. In the Lepidoptera 1st A and the

base of M are veins of the same character, and possess trachese

like other longitudinal veins in that order. In every particular

except the absence of chitinization these appear to be true veins,

and in forms where the veins are provided with speeial series

of sete, as in Acrea, they are often similarly supplied.

In watehing a eieada expand, recently, I saw appear, as the

1 Proc. Linn. Soc., New S. Wales, 44, 621; 1919.

192 THE AMERICAN NATURALIST [Vor. LVI

expansion approached completion, a regular system of blood-

veins in the spaces between the permanent veins. These show

plainly only in the few minutes when the wing has become

partially transparent, but in the adult wing they produee a

characteristic waviness of the membrane, and a few of them may

be seen in a favorable light as faint white lines. The arrange-

ment is perfeetly definite: the narrow cells are filled by a series

of simple, evenly spaced, cross-veins, while in cells R, 1st M, and

M they form a double series of cells alternating with each other.

On the narrow margin beyond the ambient vein they are evenly

spaced, the regular longitudinal veins each ending opposite the

middle of a marginal cell. Toward the costa there are two veins

opposite each definitive cell, while opposite cells M, and M,

there are three, and opposite cell Cu, there appear to be four.

The margin of the hind wing is similar, but the dise of the wing

was not observed. In the large triangular anal cell (3d A,),

instead of cross-veins there is a series of closely spaced parallel

longitudinal veins, which remain visible in the dried wing.

It seems possible that these structures are the relic of a net-

veining such as occurs in the Neuroptera. The different arrange-

ment in the anal region is especially suggestive, as it would

correspond to the plaited portion of the wing in the Orthoptera,

where there exist numerous parallel longitudinal veins.

The figure is drawn from memory so far as the fugitive veins

are concerned, checked up by the few that could be traced in

the dry nne it ean be trusted only approximately.

WM. T. M. FonBEs

CORNELL UNIVERSITY,

ITHACA, NEW YORK

THE

AMERICAN NATURALIST

Vor. LVI. May-June, 1922 No. 644

IS THERE A TRANSFORMATION OF SEX IN

GS?

PROFESSOR W. W. SWINGLE

OSBORN ZOOLOGICAL LABORATORY, YALE UNIVERSITY

Tuis paper is a reply to the recent article of Dr. Emil

Witschi which appeared in a late issue of the NATURALIST

(Vol. LV, No. 641). Witschi is quite convinced that the

problem of sex development and differentiation in frogs

has been settled, and that nothing further remains to be

said. However, the writer feels that instead of being

solved, the time has come for a revision of the entire

question of sex development in Anurans, and that the

subject is ripe for a reinterpretation upon a more ra-

tional basis than that accorded to it heretofore.

The first portion of the paper will be devoted to a brief

exposition of the writer's interpretation of sex in frog

larve based upon data obtained from a study of the bull-

frog. The second part of the paper is a reply to certain

questions raised by Dr. Witschi.

In larval males of the bullfrog two gonads are formed,

just as there are two kidneys formed, a pro-testis or em-

bryonie sex gland destined to degenerate and disappear

in ontogenetic development and a definite or functional

testis which replaces it. The germinal elements of the

pro-testis arise in the entoderm and migrate into the

germ ridges early in embryonic life. The cells multiply

rapidly and together with the mesodermal elements of

the germ glands form paired ridges projecting into the

eclomie cavity. While the tadpole is very immature and

has yet a year of larval life before metamorphosing, the

193

194 THE AMERICAN NATURALIST [Vor. LVI

germ cells of the pro-testis undergo a precocious and

abortive sexual cycle culminating in degeneration and

resorption. Beautiful cysts of spermatocytes are formed,

but the first maturation division rarely proceeds past the

m -

$5.

VN x

X-

prs

Fic. 1. Transverse section pro-testis R. catesbeiana tadpole. Animal has

a year of larval es remaining. A, Spermatogonia Showing tse ipe polymor-

phism due to incomplete fusion ehromosomal vesicles; B, Final seil tia

gonad which develops as a core within pro-testis.

No. 644] TRANSFORMATION OF SEX 195

anaphase owing to fragmentation of the centrosome and

consequent formation of polyasters (Fig. 1). Sometimes

aberrant spermatids are formed by suppression of the

first and second maturation divisions and growth of axial

filaments from the centrosome. Practically all the germ

cells of the pro-testis degenerate and disappear while in

various stages of maturation—some undergo an oviform

type of degeneration, i.e., hypertrophy enormously and

take on the superficial characters of oocytes. The ovi-

form type of degeneration, however, is more character-

istic of the short larval-lived frogs than of R. catesbeiana,

for in many animals these large cells appear rarely and

in others not at all and this is an important point to keep

in mind. This type of degeneration will be discussed in

detail in a later paper; suffice to say it gives no clue to

the sex of a cell. (See Plates 1 and 2.)

Some cells of the pro-testis fail to take part in the

abortive sexual cycle persisting through the phase of ma-

turation and degenerate as spermatogonia. These ele-

ments migrate into the sex cords (Fig. 1, g) which have

formed meantime, and form a core of germinal tissue

extending through the center of the pro-testis. This core

of tissue plus the sex cords is the anlage of the definitive

testis and is quite distinct from the pro-testis, the cells

of which are maturating and degenerating, whereas the

cells of the forming functional gonad remain as primitive

spermatogonia. The definitive testis by rapid growth

completely supplants the pro-testis which usually disap-

pears some time before metamorphosis. The functional

gonad is generally fully formed at metamorphosis when

the larve are two years of age. Some tadpoles, but not

all, develop ripe spermatozoa in the gonad at metamor-

phosis due to a second sexual cycle of the germ cells of

the definitive gonad. (Swingle, '21, Jour. Exp. Zool.,

Vol. 32.)

In the frogs with short larval-life the same succession

of gonads oceurs, but in these forms the developmental

processes are greatly accelerated and the pro-testis ma-

196 THE AMERICAN NATURALIST [Vor. LVI

turation cycle is eut short by the cells early becoming

senescent and undergoing oviform degeneration t.e., hy-

pertrophy to such an extent as to superficially resemble

oocytes. This oviform degeneration occurs to an even

more marked degree in the progonad of the toad which

has a still shorter larval-life, e.g., in Bidder's organ. In

male anurans the entire pro-testis or larval gonad is the

homologue of the male organ of Bidder in Bufo.

The pro-testis of the short larval-lived frogs has been

misinterpreted as an ovary owing to the oviform-type of

degeneration characteristic of many of its senescent cells,

and hence tadpoles are said to develop first as females,

fifty per cent. later transforming into males. The normal

embryological process by which the definitive testis de-

velops as a central axis through the degenerating pro-

testis or larval Bidder’s organ, has been described by

Witschi as the transformation of female tadpoles into

males. In R. catesbeiana, where the larval life is pro-

longed over two years, the true nature of the pro-testis

is revealed, for relatively few of the cells are of the ovi-

form type and all transition stages between such cells

and normal spermatocytes occur. The evidence pre-

sented by this material will be published in due time, and

is too clean-cut to admit of any doubt that the entire

larval gonad of male anurans is simply an embryonic

male sex gland rudiment and not a temporary ovary.

Witschi’s Fig. 6 (this journal, Vol. LV), which he sup-

. poses is an ovary transforming into a testis is simply a

transition stage in the development of the definitive testis,

and degeneration of the pro-testis or Bidder's organ in

a short larval-lived frog. Compare his Fig. 6 with Fig.

1 of this paper and note how the true male character

of the cells of the pro-testis comes out in Rana catesbei-

ana tadpoles. |

When the facts are considered it is evident that th

transitory gonadie rudiment of male frog larve is an or-

gan of Bidder which degenerates and is replaced by the de-

finitive gonad. Any one who has studied the oviform-like

No. 644] TRANSFORMATION OF SEX 197

cells of the so-called sexually intermediate tadpoles and

compared them with the cells of Bidder's organ in male

toads, is at once struck by the remarkable similarity in

their origin, development, structure and fate in the two

groups. They are identical. The crux of the problem

is the nature of Bidder’s organ in male Bufonide and

of the oviform-like cells of the pro-testis. The advocates

of sex transformation have assumed that such cells are

undoubtedly female, but no proof has ever been advanced

that they are. Their ultimate fate is the same as that

of the first year spermatocytes in the bullfrog tadpole —

degeneration (see Plates 1 and 2). The sex-transforma-

tionists have been misled by the idea that everything

superficially resembling an oocyte is necessarily such, or

that any cell in tadpoles and first-year animals undergo-

ing the early growth stages, leptotene, pachytene, etc., is

to be regarded as female. These are fallacious criteria.

Enormously hypertrophied oocyte-like cells which have

passed through the early growth stages and entered the

** germinal vesicle ’’ period so characteristic of oocytes,

occur as normal features of the male sexual cycle of

certain animals, e.g., myriapods (Figs. 5-8). These

animals were at first regarded as hermaphrodites by

Blackman. (1905, Bull. Mus. Comp. Zool., Harvard, Vol.

XLVIII, no. 1) who found upon examination, however,

that these ‘‘ oocytes ’’ were in reality spermatocytes of

giant proportions, and developed into spermatozoa. The

writer has examined some of Professor Blackman's ma-

terial and the oocyte-like charaeter of the male sex-cells

is remarkable. In the material examined these cells prac-

tically fill the gonads. Firket, 1920, working on the chick

embryo, describes and figures spermatocytes undergoing

oviform degeneration, i.e., enlarging to such an extent

as to resemble oocytes. There are many other cases re-

ported in the literature. How does Witschi know that

the transitory oocyte-like cells he deseribes in the future

male tadpoles or so-called hermaphrodites, are female

cells and not senescent organ of Bidder cells occurring

198 THE AMERICAN NATURALIST [Vor. LVI

in the eourse of the abortive and degenerate sexual cycle

of an embryonie pro-testis?

The work of Witschi on the problem of sex in anurans

ean be summarized thus: He has described in great de-

tail and with admirable exactness the process of develop-

ment of the pro-testis or Bidder's organ in the short

larval-lived frogs, its degeneration and final replacement

by the definitive gonad. This process he calls transfor-

mation of females into males. The experimental investi-

gations of Witschi upon sex transformation by environ-

mental influences consists of this: By means of such

agents as heat or cold, etc., he has simply modified the

normal course of development of the pro-testis — Bid-

der’s organ, thereby accelerating or delaying the devel-

opment of the definitive testis. The experimental results

show that it is possible to modify the developmental rate

of the embryonic testis. Similar experiments carried out

with regard to other larval structures would unquestion-

ably give similar developmental modification. Cold hin-

ders metamorphosis and all the normal structural changes

metamorphosis implies. All of these environmental influ-

ences are interferences with the normal cycle of the go-

nads, by which the development of the definitive gonad

out of the pro-testis is accelerated, retarded, or possibly

prevented entirely. The following quotation from Wit-

schi '14, page 10, is significant in this connection:

Bei seinen Untersuchungen war es Hertwig aufgefallen, das unter

dem Einfluss verschiedener Aussenbedingungen sich nicht nur die

Geschlechtsziffern, sondern oft auch in ganz auffilliger Weise der

Rhythmus, in Welchem die Keimdriisen und manche andere Organe

sich anlegen und entwickeln.

It is probable, judging from certain experiments re-

ported, that the degree of development attained by the

larval gonadic rudiment, its position in relation to the

definitive gonads, its period of persistence, non-formation

in some forms, and such like, may vary in different frog

species and is determined by heritable factors. For ex-

ample, in Bufo, the structure persists throughout life in

No. 644] TRANSFORMATION OF SEX 199

males, disappears after two years in females, and is an-

terior to the funetional gonads. In frogs it forms the

outer husk of the germ gland enclosing the centrally de-

veloping functional testis and may or may not show the

oviform type of degeneration, e.g., R. catesbeiana.

If sex is so labile in tadpoles and young frogs, and

females so readily transform into males under environ-

mental stimuli, why is it that such sex reversals do not

occur in adult frogs after the degeneration of the pro-

testis and the formation of the definitive testis has oc-

curred? All investigators are agreed that the sex ratio

of adult frogs of all species reported is approximately

50-50. If environment (ever changing in the same lo-

cality, and never the same in different regions), plays

such an important sex transforming róle, why do male

tadpoles never transform into females — all investigators

agree that they do not. Why do only fifty per cent. of

the so-ealled larval females transform into males if they

were not zygotie males from the beginning, and why do

not all female frog larve transform into males instead

of only fifty per cent. if such transformation is possible?

Appeal eannot be made to Professor Hertwig's well-

known late fertilization experiments because in these ex-

periments the influence of the over-ripeness of the egg

upon the zygotie conditions determining sex are unknown.

Hormones! To date there is no positive evidence that

such secretions have ever aetually changed a female germ

cell into a functional male germ-cell.

Cases of hermaphroditism in adult frogs are thought

by some to furnish evidenee of a sex transformation in

frogs. However, true hermaphroditism in adult frogs is

as rare a phenomenon as it is in mammals when we con-

sider the few recorded cases, and the enormous number

of frogs annually dissected the world over. Crew (’21),

Journal of Genetics, Vol. II, no. 2, has summarized the

recorded cases of abnormal sexual organs in frogs and

states that there are forty cases. To this number should

be added a recent case described in the bullfrog, making

200 THE AMERICAN NATURALIST [Vor. LVI

forty-one. Among these forty-one cases, there are but

twenty-seven true hermaphrodites. Crew's cases, twenty-

one to thirty-three, inclusive, are not hermaphrodites,

nor is case thirty-eight, as none of the animals possess

ovotestes and some are entirely without gonads. True

hermaphroditism in frogs is a permanent and pathologi-

eal condition, probably due to a mix-up in the genetic

constitution of the individual, and is not to be confused

with the present problem which has to do with a normal

but transitory embryological process.

Much has been written about the marked ‘‘ sex poten-

cies ’’ of various portions of the gonads in so-called sex-

ually intermediate frogs, i.e., females transforming into

males. It is claimed that the outer rind of the gonad

exerts a profound female sex influence, while the inner

portion exerts a purely male influence. Germ-cells re-

maining in the outer husk (the main portion of the larval

gonad by the way) of the gland are female, those migra-

ting into the central part among the sex cords become

male. All such speculations are based upon misinter-

pretations. The outer portion or husk of the larval male

gonad is simply the pro-testis, the cells of which are un-

dergoing a precocious maturation cycle just as they do

in the organ of Bidder in Bufo, the inner portion or sex

cord region is where the definitive gonad begins develop-

ment and as it spreads and grows the embryonic male

gonad degenerates and disappears. It is in the region of

most marked *' female " tendencies that the writer finds

in the bullfrog entire cysts of unmistakable spermato-

cytes, and occasional spermatids (Fig. 1, e). In other

words, the pro-testis — what Witschi regards as an ovary

— can in the bullfrog, where its development is greatly

prolonged, give rise to practically mature male sex prod-

ucts. Recently, the writer made an observation of con-

siderable interest. In the degenerating Bidder's organ

(pro-testis) of a two-year-old male larva in which forma-

tion of the definitive testis had been delayed until meta-

morphosis and in which the oviform type of degeneration

No. 644] TRANSFORMATION OF SEX 201

was the most marked of any animal yet observed, several

cysts of unmistakable spermatocytes and spermatids were

observed. They arose from the maturating cells of what

Witschi regards as the female part of the gonad — in

reality the pro-testis, and were of the cell type charaeter-

istic of the adult frog. This observation shows two

things elearly: (1) That the direct descendants of the

male primordial germ cells (pro-testis elements) can pro-

duce practically mature. germ cells; (2) that the sper-

matocytes of the structure regarded by the writer as a

pro-testis are really male cells, and that the structure in

so-called sexually intermediate frogs and tadpoles is in

no sense to be regarded as female in character.

Another point is of interest here— the writer has

never observed direct testicular development in R. cates-

beiana, though it probably occurs in some strains; the

indirect method alone has been found, e.g., first a pro-

testis is formed which is later supplanted by the defin-

itive gonad. In the bullfrog, which has the longest

larval life of any anuran, the pro-testis persists longer

than in other forms, sometimes two years before giving

place to the definitive gonad. What the writer calls a

pro-testis of so-called sexually intermediate tadpoles is

according to Witschi a transitory ovary. If this is true

why is it that despite its persistence for such a long time,

relatively few oocyte-like cells are found in R. catesbet-

ana and in many individuals none, throughout a two-

year period, but instead the structure produces sperma-

tocytes and sometimes spermatids? Why is it, if this

structure is an ovary in the so-called females that later

transform into males, that the shorter the larval life of

male anurans, the more the pro-testis in its structure and

behavior resembles the Bidder’s organ characteristic of

male toads, due to rapid oviform degeneration of its

cells; the longer the larval life, e.g., Rana catesbeiana,

the more the germinal elements undergo a normal sexual

cycle characteristic of male cells? The answer is, because

in forms with extraordinary prolonged larval lives the

202 THE AMERICAN NATURALIST [Vor. LVI

true nature of the embryonic male gonad has sufficient

time to manifest itself before being supplanted by the

definitive gland.

We come now to a discussion of the nature of Ridder S

organ in Bufo, for this is the classical example of ovi-

form degeneration of racially senescent germ cells. Here-

tofore, this embryonic sex gland rudiment has been re-

garded as characteristic of toads, but such is not the

ease. In frogs the pro-testis or larval gonad is a Bid-

der’s organ, destined to be replaced by the definitive male

gonad developing within; in male toad larve on the other

hand, the functional gonad arises behind the pro-testis

or Bidder’s organ, consequently this structure persists

as a degenerate gonadie rudiment attached to the func-

tional gland.

According to the writer’s view, Bidder’ s organ in Bufo

is simply a vestigial larval gonad persisting throughout

life and has the same sex as the definitive gonad behind

it— male in males, female in females. It is just as

though the pro-nephros of tadpoles persisted as a non-

funetional and degenerate rudiment at the end of the

mesonephros. That many such larval and embryonic

rudiments do persist through adult life in various ani-

mals is a commonplace of embryology, and their per-

sistence in one species and total disappearance in another

related one, is also well known. Bidder’s organ in Bufo

then, is a persisting, in frogs a transitory, embryonic

sex gland rudiment, a relic of a phylogenetically earlier

sexual condition. The functional gonads are more re-

cently acquired structures (like the larval mesonephros)

superimposed upon the older degenerate glands. Briefly

stated, the evidence for the view that Bidder’s organ is

homologous to the pro-testis of frogs and that it is not

a rudimentary ovary except in female animals is as fol-

lows:

1. The cells of Bidder’s organ in Bufo are unquestion-

ably germ cells. The gland appears very early in em-

bryonic life (two weeks after hatching) and its cells far

No. 644] TRANSFORMATION OF SEX 203

outstrip in development the cells of the definitive gonads

located posteriorly.

2. The cells of Bidder's organ extremely early in de-

velopment undergo a precocious and abortive matura-

tion cycle and become senescent and degenerate oocyte-

like structures when the germinal elements of the func-

tional gonads have barely started to multiply to form

the definitive glands. This occurs in individuals of both

sexes.

3. The larval maturation cycle such as occurs in the

bullfrog, and in other anurans, throughout the entire

larval gonad is confined to Bidder’s organ in Bufo, and

the changes occurring in this structure do not affect the

normal developmental cycle of the definitive germ glands

behind.

4. The so-called transformation of female animals into

males, claimed by Witschi and others to be the normal

course of development in frogs, does not occur in toads.

Why? Because in Bufo, the definitive gonads are from

the beginning located posterior to Bidder’s organ, and

it is not necessary in order that they may develop that

this structure degenerate and disappear as is the case

in frogs where the definitive testis starts development

as a core within the pro-testis or Bidder’s organ, neces-

sitating its complete destruction.

ew have ever claimed that sex in toads is labile

and easily reversed by environmental influences. Why?

Because the sex of the definitive gonads is definitely fixed

and clear cut at an early stage of life. The separation

of Bidder’s organ and the gonads has precluded the

possibility of confusing the pro-gonad and the definitive

gonad. '

6. Bidder’s organ is merely a persisting embryonic

gonad whose cells have undergone oviform degeneration.

It is not a rudimentary ovary except in female animals.

This is indicated by its presence in both sexes in toads;

its presence in Spengel’s case of true hermaphroditism;

by the fact that neither in male or female of toads do

204 THE AMERICAN NATURALIST [Vor. LVI

its cells develop into true funetional eggs; and by its de-

generate structure from its inception in both sexes.

In a recent paper (Zoologischer Anzeiger, Dec., 1921)

Harms deseribes marked hypertrophy of Bidder's organ

following testis removal. He considers that castration

of males causes Bidder’s organ to develop into an ovary.

However, it should be noted that such operated animals

with hypertrophied Bidder’s organ (ovary according to

Harms) retain all their male secondary sex characters,

and their normal mating instincts and that these male

characters and instincts undergo a normal cyclical de-

velopment in such induced ''females." When Harms

removed both testes and Bidder’s organ the somatic sex

characters and instincts failed to develop, showing clearly

that Bidder’s organ in male toads acts like a testis in

maintaining the secondary sexual characters. This is

excellent evidence for the writer’s view that in male toads

Bidder’s organ is simply a persisting embryonic male sex

gland rudiment and not an ovary. If it is an ovary why

should it develop and maintain the secondary sex charac-

ters of the male in absence of the testis?

7. Recent investigators have inclined to the view that

this structure is a hermaphrodite gland, ?.e., in male

toads a rudimentary ovary, in females a rudimentary

testis. If this is true then the admission is made that

large, senescent, oocyte-like germ cells are not necessarily

female cells — the crucial point for which the writer is

contending.

8. Bidder's organ in Bufo corresponds to the larval

gonad of frogs which in these forms disappears in the

male and is replaced by the definitive testis. In the case

of female anurans so far as the writer is aware no one

has carried out a thorough investigation of the germ

cycle from larval to fully adult life to see whether or not

such a degeneration occurs in the female line. In mam-

mals and birds such degeneration of the female embry-

onic line of germ-cells is quite well established as the

work of Winiwarter, Firket and others shows.

No. 644] TRANSFORMATION OF SEX 205

The writer is of the opinion that it is only by adopting

the view advanced here regarding the homologous nature

of the larval male gonad of frogs, and Bidder’s organ

in Bufo, that the problem of sex differentiation in anu-

rans can be placed upon a rational basis. The theory

accords with the embryological facts, covers the experi-

mental finding of Witschi and others, accords with our

own cytological data in the bullfrog, accords with the

embryonic sexual conditions of other vertebrates, i.e.,

the degeneration of the embryonic line of germ cells in

birds and mammals, and lastly furnishes an explanation

of Bidder’s organ in Bufo.

The key to the puzzle of sex development in frogs is

simply this: every cell that superficially resembles an

oocyte is not necessarily a female cell especially when

occurring in an otherwise male individual, and that the

larval male gonad of anurans is an organ of Bidder —

a rudimentary embryonic sex gland with the same sex as

the definitive gonad arising out of it. Misinterpretation

of oviform hypertrophy and degeneration of racially

senescent sex cells has rendered chaotic the problem of

sex differentiation in anurans (see Plates 1 and 2).

Witschi regards the development of certain somatic

sex characters such as the Müllerian ducts as very

positive evidence for his theory of sex transformation.

e says:

In males which show a typical development of the testicles, no

Müllerian ducts of any significance are formed. On the other hand,

such animals as first develop ovaries and later undergo the trans-

formation of sex, also show regular oviducts; and these continue to

grow just up to the time when the transformation of sex begins.

This parallelism in the behavior of the Miillerian ducts and the

gonads furnishes definite proof that the “eggs” and “ ovocytes,”

described by the writer, are in fact really eggs and ovocytes and that

the transformation of sex is a well-established fact. After the trans-

formation of sex, when the ovocytes have disappeared, the Müllerian

ducts begin to shrink but they do not disappear completely, etc., ete.

The following data shows that in reality such so-called

parallelism in the behavior of the Miillerian ducts and

208 — THE AMERICAN NATURALIST [Vor. LVI

the gonads does not exist and that evidence based on such

parallelism is worthless.

In the normal males of adult Rana pipiens the Mül-

lerian duets are remarkable for their size and degree of

-= development. They arise as cellular cords in the peri-

toneum at the time of metamorphosis and only acquire

full development long after transformation when they

come to resemble to a striking degree the oviducts of

females (Fig. 2). In the larva of R. pipiens the so-called

2. Urogenital apparatus of adult Rana pipiens a the normal

sees of the Müllerian ducts (md) in males of this species

transformation of females into males (degeneration of the

pro-testis and formation of the definitive testis) occurs

very early in larval life, before the Müllerian duets ap-

pear, and in this species the ducts undergo practically

their entire development after the definitive testis has

formed. In other words, while subjected to the influence

of the fully formed testis and its ripening sex products

the duets undergo the most marked development known

in the males of any anuran species. Moreover, in Rana

catesbeiana, where if we accept Witschi’s interpretation

of femaleness, the so-called transformation of female in-

No. 644] TRANSFORMATION OF SEX 207

dividuals into males is a prolonged process requiring two

years, and where the future male larve are subjected to

the so-ealled female influence during the entire period,

the Müllerian duet does not appear. At metamorphosis

when the definitive testes are fully formed and sperma-

tozoa are beginning to appear the cellular cords repre-

senting the vestigial Miillerian ducts of the male form

but do not develop. If Witschi’s interpretation were

correct, one would certainly expect to find marked de-

velopment and hypertrophy of the Müllerian ducts in R.

catesbeiana because of their being so long exposed to

female influence. As a matter of fact, these structures

in the male bullfrog are less developed than in other

forms.

The same criticism applies to the so-called develop-

mental correlation of the Miillerian duct with the gonad

of the same side in cases of lateral hermaphroditism.

What Witschi terms lateral hermaphrodites are nothing

more than larve or young frogs which show the defini-

tive testis developing out of the pro-testis (larval male

Bidder’s organ) faster on one side than on the other.

(See Witschi, Am. Nar., page 533.) In the end such ani-

mals develop into definite males with testes symmetri-

cally formed. True lateral hermaphroditism in adult

frogs is an exceedingly rare phenomenon. In the wri-

ter’s material it is rare to find both definitive testes de-

veloping out of the pro-testes at the same rate, one gland

may be the finished gonad, the other the pro-testis un-

dergoing degeneration. Such larve are in no sense to

be regarded as lateral hermaphrodites. There is no de-

velopmental correlation of the Miillerian ducts with the

gonad of the same side in R. catesbeiana and R. pipiens,

because there are no ducts formed until after the defini-

tive testes are formed. Regarding the other somatic sex

characters such as seminal vesicles and thumb cushions,

it should be pointed out that the thumb pad in R. cates-

beiana is not formed until after metamorphosis when

Ev Tal Ww.

Cep MAS

MANT.

Post

SUM »

we Pee

D s

i ree

PLATE I

Fic. 3. So-called oocytes cecurring in the degenerating pro-testis of larval

bullfrogs. These cells according to

a's

the writer’s view are merely hypertrophied

iform erat

set of degeneraticn. At X

e giant sperma atocytes lopoda). The

ce i rm functional atezoa and make up the pocius part of the testes.

Note ie * germinal Tuto " condition of the nucleus

PLATE II

ad 6. a a of Scolcpen

"IG permatocytes of eias (Chilopoda). The resemblance

to oocytes m the germinal vesicle stage is remarkable. Sections of the testes

ook like

All photographs on Plates I and II made at a magnification d Er diameters,

No reduction. Figures 5-8 are from Professor Blackman’s mate

210 THE AMERICAN NATURALIST [Vor. LVI

the fully formed testes are present, and the seminal ves-

ieles are absent or rudimentary in the males of many

frog species, and exceedingly well developed in others.

In the few cases reported of true lateral hermaphro-

ditism in adult frogs there is not always a developmental

correlation of the Müllerian ducts with the gonad of the

same side. Crew (’21), (Journal of Genetics, Vol. II,

no. 2) has summarized the known cases of sexual ab-

normality in amphibians — see Figs. 7, 8, 9, 12, 14, and

16 of this paper, also the report of cases 21, 22, 23, 24,

and 39. These are exceptions to any rule of develop-

mental correlation. In several eases, Figs. 25 and 31,

the duets are quite as well developed in total absence of

ovarian tissue as when such is present in large amounts,

this, of course, being the normal condition in Rana pipi-

ens. Crew also gives a list of frog cases reported where

both gonads were entirely missing and yet the Müllerian

duets were well developed in such individuals.

. Because of these facts it is fair to conclude that the

appeal to the somatic sex characters completely fails as

proof of the transformation of female frogs into males.

In closing, it should be pointed out that Witschi has

made but one original investigation of sex in anurans

(Witschi "14, no. 1). His later papers on the subject con-

tain no new observations or experiments but are purely

speculative endeavors to interpret his early work in ac-

cordance with Mendelism (’14, no. 2), later (720, no. 3)

in accordance with internal secretions.

THE SEX-LINKED GROUP OF MUTANT CHAR-

ACTERS IN DROSOPHILA WILLISTONI

REBECCA C. LANCEFIELD AND CHARLES W. METZ

STATION ron EXPERIMENTAL Evotution, Corp Spring Harpor, N. Y.

INTRODUCTION

Tus present work was undertaken for the purpose of

comparing the genetical behavior of the fruit-fly Droso-

phila willistoni with that of Drosophila melanogaster and

other members of the genus. It deals with the 28 sex-

linked mutant characters thus far studied. The non-sex-

linked characters will be considered in another paper.

Drosophila willistoni Sturtevant (D. pallida Williston)!

is not unlike the well-known D. melanogaster in habits

and superficial appearance, but a detailed examination

reveals numerous features in which it differs from mela-

nogaster. Among these are the following: (1) absence

of sex combs in the male, (2) six instead of eight rows

of acrostichal hairs on the thorax, (3) smaller size and

more slender form, (4) vermilion instead of red eye color,

and (5) narrow instead of broad bands on the abdomen.

This species has been chosen for the present study be-

cause it is one of the species having the same general

type of ehromosome group as D. melanogaster. It will be

recalled that within the genus Drosophila at least eleven

different types of chromosome groups are represented

(Metz, 1916). The most common type is that called type

A (Fig. A, present paper), which is found in 13 of the

29 species studied. In these 13 species (which include

melanogaster and willistoni), the chromosome groups are

so much alike as to suggest that similar chromosomes

are homologous and earry homologous groups of genes

throughout. On the other hand, the species themselves do

not form a restricted taxonomie group, but seem to be

1 See Sturtevant, 19215, for description, ete.

ait

212 THE AMERICAN NATURALIST [Vor. LVI

scattered more or less at random through the genus —

which does not conform to such a view unless this type

of chromosome group be considered primitive and the

forerunner of several other types.

These eonsiderations indicated the need of a compara-

tive study of different species possessing this type of chro-

mosome group, in addition to the studies already being

made on species having different types of groups. Since

the species can not be hybridized (or have thus far refused

to hybridize — with one exception considered below), it is

necessary to make cytological and genetical studies of

them individually. This of course limits the comparison

to a very few species.

The -present paper supplements our previous one

(Lancefield and Metz, 1921) on the sex chromosome re-

lationships of willistoni and melanogaster, in which it

was shown by means of non-disjunctional flies that the

sex chromosomes are not strictly homologous in the two

species. In melanogaster the short, rod-like pair is the

sex chromosome pair (Bridges, 1916), whereas in willis-

toni we find that the rod-like pair is an autosome pair,

and that one of the large V-shaped pairs is the sex chro-

mosome pair. This relationship is shown in Figs. A

and B.

on i

A B

Fics. A and B. Diagrams of female chromosome groups of Droscphila me-

lanogaster and Drosophila willistoni 1espectively. The X-chromosomes are rep-

resented in solid black, the autcsomes in outline. In D. willistoni the small,

dot-like pair may be absent.

The genetical study considered here is for the purpose

of comparing the constitution of the sex chromosomes by

No. 644] MUTANT CHARACTERS IN DROSOPHILA 213

means of the sex-linked characters and their linkage re-

lations.

The stock of D. willistoni which we have used was

brought from Cuba in 1915, and was kept in the labora-

tory without being studied until 1919 when the present

work began.

In making the tests for linkage and in calculating cross-

over values, the usual procedure has been followed? We

have been concerned particularly with determining the

relative order of the genes and the approximate amount

of crossing over between them, but not with obtaining

exact crossover values. In consequence, the ‘‘ chromo-

some map °’ given here is to be considered as indicating

only the approximate location of the respective genes.

In presenting the data, the mutant types are described,

not in ehronologieal order, but in such a way as to follow

the serial order of the genes on the chromosome map.

All of the sex-linked characters are recessive. The data

on the origin of mutants are necessarily imperfect, and

in some cases are very meager, owing to the fact that

many of the mutants appeared in stock cultures, mass

cultures, ete., for which no complete records were taken.

In such cases the available data are given briefly under

the appropriate headings.

We are indebted to Mr. D. E. Lancefield for carrying

out some of the early experiments, and for finding the

mutants ‘‘rimmed’’ and ‘‘nicked.’’ Similarly, we are in-

debted to Miss Ruth Ferry for the mutant ‘‘ yellow ’’ and

for carrying out the experiments involving ‘‘ yellow.”

To Dr. A. H. Sturtevant we owe many valuable sugges-

tions regarding the comparison of mutant characters in

D. willistoni with those in D. melanogaster and D. simu-

lans. We are also indebted to the following persons for

making the accompanying drawings: Miss Ruth Lincks

— Figs. 1, 3, 7, 8; Mrs. D. B. Young — Figs. 2, 4, 5, 6, 17;

Miss E. M. Wallaee — Fig. 9, and Miss E. D. Mason —

Figs. 10 — 16.

2 This has been deseribed in earlier papers by Morgan and others, and

is to be found in eurrent books on geneties.

214 THE AMERICAN NATURALIST [Vor. LVI

DESCRIPTION AND ORIGIN? or MUTANT CHARACTERS

Stubby (sy)

Description.—Stubby is a bristle character, manifested

by all of the thoracic and head bristles (Fig. 2). These

are usually shortened, thickened, and somewhat curled,

and often are split or forked at the tip. The two pos-

terior scutellar bristles are frequently tightly twisted to-

gether and point anteriorly. The short, thick appearance

Lh d

Vs. j |

ih \

a E

‘Fig. 1.: Drosophila willistoni, “normal.”

of the bristles is never apparent in combination with

small-bristle, but the charaeter ean always be distin-

guished by the forking of the sternopleural bristles. Both

sexes are fertile. Stubby looks very much like forked in

anelanogaster.

|. Origin.—One stubby male was obtained from a pair

mating. No complete record of this culture was kept,

however, and it is not known whether others appeared

previously or not.

3 See Table I.

No. 644] MUTANT CHARACTERS IN DROSOPHILA 215

Orange (o)

Description.—The eyes are orange colored. In newly

hatched flies, the color is a pale lemon, which deepens

into orange as the fly matures and may become very

dark in old age. The color resembles garnet or coral of

D. melanogaster.

Fie. 2. Stubby, bristles.

Origin.—One male appeared among the offspring of

a mating of three normal females by an unrelated male.

The other offspring were all normal, but their number

was not recorded. Presumably, the mutation occurred in

one of the P, females and affected only one or a few germ

cells, although it is possible that this female was hetero-

zygous and produced a very small number of the flies in

the culture.

Small-bristle (sb)

Description.—All the bristles are more slender and

somewhat shorter than in normal flies. The character

is extreme when orange eye color is also present.

216 THE AMERICAN NATURALIST [Vor. LVI

Origin.—One small-bristle, forked male was obtained

from a mass eulture carrying rough and forked.

More than a year later, a seeond mutation to small-

bristle occurred in an entirely unrelated stock. In this

case the single small-bristle male found among the off-

spring of one pair was crossed to a female from a ho-

mozygous orange small-bristle stock and produced only

small-bristle flies.

Bent (bn)

Description.—The wings of bent flies are slightly spread

out, and are bent at the base so that they slope down

toward the body (Fig. 3). They are often slightly crum-

pled. The flies hatch as well as their normal sibs but do

not breed as readily.

Fic. 3. Bent, wings.

Origin.—Many bent males were found in a culture of

five orange females from stock mated to a single male of

different parentage. At least one of the females carried

bent, but the exact origin is uncertain. No bent flies were

ever observed in orange stock.

Forked (f)

Description.—In forked flies, all the bristles are wavy

with the ends sometimes forked. The females are sterile.

This character is similar to, but less extreme than, stub-

No. 644] MUTANT CHARACTERS IN DROSOPHILA 217

by. It recalls singed, of melanogaster although singed,

is slightly more extreme.

an ae

Fig. 4. Forked-2, bristles.

Origin.—Seven males were found in a stock bottle.

Since no forked females were obtained, it is possible that

this was the original appearance of the mutant and that

all of the forked flies were from one mother, heterozygous

for forked.

Forked-2 (fə)

Description.—This character is much more extreme

than its allelomorph, forked, or the similar mutant, stub-

by. The bristles are twisted and thickened with their

ends often split (Fig. 4). The twisting also affects prac-

tically all the hairs on the fly, including those on the inner

margin of the wing. The hairs on the antenne are forked.

Forked-2 resembles the melanogaster singed. The fe-

males are sterile.

Origin.—Several forked-2 males and one female ap-

peared in a stock bottle of small-bristle flies.

218 THE AMERICAN NATURALIST [Vor. LVI

Tiny (t)

Description.—Tiny-bristle flies usually have small an-

terior dorso-central bristles. Sometimes the two anterior

scutellar bristles are also small. Occasionally all the

bristles may be small, so that the individual may be in-

distinguishable from a true ‘‘ small-bristle’’ fly. The

character is rather variable and, in many cases, is very

hard to separate from normal. This difficulty was so

great that the stock was finally discarded.

Origin.—A single male was found on the last count of

the offspring from a pair mating. It is possible that

other tiny males were present among the previous off-

spring and escaped observation since the character is

very inconspicuous,

Square (sq)

Description.—The wings are about two thirds the nor-

mal length with the ends almost square instead of pointed

(Fig. 11). A characteristic slight wave extends through-

out the length of the wing. The females are sterile and

the viability of the males is rather poor.

The description of square suggests that of rudimentary

melanogaster but square is much less extreme than rudi-

mentary; the wing is not shortened so much and is not

eut off so squarely.

Origin.—Among the offspring from a pair mating

(rough female by orange rough stump male) several

square males were found, indicating that the mother was

probably heterozygous for square.

Reduced (re)

Description Reduced flies regularly lack the two an-

terior dorso-central bristles; occasionally, they also lack

one of the posterior dorso-centrals; and less frequently,

all four are absent. In combination with seute-2, how-

ever, the more extreme condition of reduced is frequently

found (Fig. 7). The reduced gene also affects the shape

No. 644] MUTANT CHARACTERS IN DROSOPHILA 219

of the abdomen, which is blunted, or apparently com-

pressed along the anterior-posterior axis. The abdominal

bands are slightly irregular.

Reduced flies, especially females, are hard to breed in

pairs, although those which do produce offspring seem

normally fertile. i

Origin.—Many males were found among the offspring

from a pair mating from orange stock. The mother of

the eulture was apparently heterozygous for the gene.

THE Scute ALLELOMORPHIC SERIES

1. Scute (sc)

Description.—The two anterior scutellar bristles are

usually lacking, although occasionally only one may be

gone. Rarely the combination of one anterior scutellar

bristle and one posterior one may be found. The remain-

ing bristles are normal in size. The character almost

always manifests itself in homozygous flies. Only one

exception to this has been detected up to the present time.

Origin.—Fifteen scute males and eleven normal males

` were obtained from a normal pair. The female offspring

were all normal (number not recorded). It is almost cer-

tain that the mother was heterozygous in this case, and

that the mutation occurred in a previous generation or

else very early in her own ontogeny.

2. Scute-2 (scz)

Description.—Seute-2, an allelomorph of scute and

seute-3, involves the same seutellar bristles as scute, but

varies toward a more extreme condition than this allelo-

morph. The two anterior scutellar bristles are always

missing, frequently one of the posterior scutellars is gone,

and oceasionally all four are lacking. The bristles on

the scutellum are fine and small. In a stock homozygous

for reduced and scute-2, both characters are more extreme

than either is alone (Fig. 7). Such flies often entirely

lack dorso-central and scutellar bristles, and lack one or

more orbital bristles.

220 THE AMERICAN NATURALIST [Vor. LVI

The compound seute seute-2 females are either some-

what intermediate between the two, or they may look en-

tirely like one or the other component. On the whole,

they are more apt to resemble scute-2 than scute.

Origin.—F rom a normal female mated to a scute male,

the following types of offspring were obtained: males — -

one half normal, one half seute-2; females — one half

normal, one half somewhat intermediate between scute

and seute-2. From this it was concluded that the parent

female was heterozygous for the new character and that

this character was allelomorphie to scute, a conclusion

subsequently verified by direct tests. Six sisters of this

female were also tested and none gave scute-2.

3. Scute-3 (sc)

Description.—Scute-3 is an allelomorph of seute and

seute-2. All four seutellar bristles, the two sterno-pleural

bristles, and a varying number of head bristles are ab-

sent. On the head, all three pairs of orbitals are usually.

missing, and occasionally some of the others are gone.

The compound females involving scute-3 and scute-2

are more apt to be like scute-3 than like seute-2, although `

in general they are intermediate. Such females could be

distinguished from the homozygous seute-2 females in all

the eases observed by the absence of at least one sterno-

pleural bristle and generally by the absence of all seutel-

lar bristles. Seute-3 males are sterile. |

Seute-3 strongly resembles the scute of melanogaster.

In both cases scutellar and head bristles are affected.

Two stocks of melanogaster scute kindly examined by

Dr. Sturtevant agree with scute-3 in lacking scutellar

bristles and orbitals, and in having small ocellar bristles.

They both possess post-orbitals, however, and one stock

occasionally shows the middle orbital present. The other

usually lacks the postverticals. :

Origin.—Scute-3 was first observed in the offspring of

an F, female from a cross of a seute female from stock by

two rough rimmed stump males. This female seemed to

No. 644] MUTANT CHARACTERS IN DROSOPHILA 221

be heterozygous for the new factor, and it was found

that the character was also present in males in sister

eultures which had been used for stocks.

Yellow (y)

Description.—In '* yellow ” flies the body, wings and

legs are deep yellow. The bristles and hairs are all yel-

lowish or bronze instead of black. In the latter respect

yellow differs from the yellow in Drosophila virilis which

has black or dark brown bristles and hairs.

Origin.—A single yellow male appeared in a bottle of

scute rough stump stock.

Yellow was found after the main part of this paper

was prepared for publication, and since the experiments

involving it have not added materially to the data given

in the tables they are omitted from the latter and are

given briefly here.

The original yellow seute rough stump male was mated

to normal females giving a normal F,. The latter, inbred

in pairs, gave 1354 normal daughters and the following

classes of sons: normal 488; yellow scute rough stump

466 (non-erossovers 954); yellow scute 25, rough stump

23 (single crossovers in region two 48); yellow scute

rough 49, stump 46 (single crossovers in region three 95) ;

yellow scute stump 3, rough 2 (double crossovers involv-

ing regions two and three, 5). In addition, two yellow

rough stump males and one yellow stump male were ob-

tained. Of the former, one proved to be genetically scute

when tested and hence should be in the non-crossover

class. The other gave no progeny, but presumably was

also a non-erossover. The third fly likewise failed to

breed, but since it lacked rough as well as seute it pre-

sumably represents a double crossover in regions one and

three. Itis this fact which leads to the tentative location

of yellow above rather than below seute on the map.*

4 This is supported by subsequent data.

222 THE AMERICAN NATURALIST [Vor. LVI

Peach (p)

Description.—Peach eye color is practically indistin-

guishable from orange eye color, although, as a rule, it

is a trifle darker than orange and does not have the range

of shades due to age which are observed in orange. In the

same culture, it is impossible to distinguish the two with

certainty. The double recessive of peach and orange is

probably indistinguishable from either eye color alone.

Homozygous peach rough flies have darker eye color than

orange rough flies, and are hard to separate from rough

alone. Peach eye color is similar to ruby and garnet of

melanogaster and to rubyoid and carmine of simulans.

Origin.—A. single male with peach eye color was found

in a double recessive forked stump stock.

Beaded (be)

Description.—Beaded refers to the condition of the

wings, which have the marginal hairs clumped in irregu-

lar patches, especially on the posterior half of the outer

margin. The wings are pointed at the ends due to a long

notch, extending from the tip of the third vein to about

Fie. 5. Normal, wing.

Fie. 6. Beaded, wing.

No. 644] MUTANT CHARACTERS IN DROSOPHILA 223

the region of the posterior eross-vein, and to the loss of

a section from the outside of the wing between the distal

ends of the second and third veins (compare Figs. 5 and

6). Beaded flies have poor viability, and the females are

sterile. Beaded is similar in appearance to the melano-

Fic. 7. Reduced scute-2 compound.

gaster cut, although the latter is slightly more extreme

than beaded. While cut, flies are vigorous and fertile,

some of the cut allelomorphs are not completely fertile

and have poor viability.®

Origin.—An out-crossed female, known to carry small-

bristle rough on one X-chromosome, and small-bristle

orange short-3 on the other, produced offspring in which

the small-bristle rough males were also beaded. This fe-

male was almost certainly heterozygous for the new gene.

Nine sisters were bred separately but no beaded flies ap-

peared in their offspring.

5 Unpublished data for which we wish to thank Drs. Mohr and Bridges.

224 THE AMERICAN NATURALIST [Vor. LVI

Rough (r)

Description.—Rough eye affeets mainly the surface of

the eye (Fig. 8). When the outer portion of the eye is

mounted and examined under the high-power microscope

it is seen that the ommatidia are irregular in shape and

size with uneven surfaces which are more convex than

the normal. The normal eye has regular hexagonal

faeets with a bristle at every alternate intersection of

the sides (See Carnegie Publ. 278, Plate 10, Fig. 3c for

the normal eye of D. melanogaster which has the same

arrangement). The bristles of rough eye are irregularly

distributed with groups collected in one place and no

- bristles at all in another. These bristles are about one

and a half times the length of the normal ones.

The roughened condition is similar to that found in

star eye of melanogaster (Carnegie Publ. 278, Text-fig-

ure 83). The eyes of willistoni rough are also somewhat

glossy in texture, and the wing veins are slightly heavier

than in the normal flies.

Origin.—Several rough males and females were found

in one of the bottles of a stock that had been kept in the

laboratory for approximately four years. It is probable

that the mutant gene had been present in the stock for

. some time. :

Triple (tr)

Description. — Triple causes four variable wing

changes, one or all of which may be present in either or

both wings (Fig. 10). (1) The second and third veins

may be fused for a short distance at their origin. (2)

The wings, slightly tilted up at the ends, are held away

from the body at an angle which varies up to about 90°.

(3) The third veins fail to reach the distal margin of the

wings by amounts which vary from almost nothing to

one third the length of the vein. This is particularly

evident in the females, where a large section may be

missing from the central part of the third vein. (4) An

extra cross-vein is present between the second and third

No. 644] MUTANT CHARACTERS IN DROSOPHILA 225

veins at a level about half way between the anterior and

posterior eross-veins. This vein, when not wholly formed

as a cross-vein, is often indicated by short pieces of dis-

connected vein.

The fusion of the second and third veins and the ex-

tension of at least one wing are constant characters as

far as observed. The latter forms the easiest basis of

distinguishing this mutant. The females are more ex-

treme than the males in all four of the changes involved.

Triple suggests the melanogaster mutant, bifid, by its

extended wings, fusion of the veins at the base of the

wing, and the shortening of one of the veins, although

the short vein is the fourth in bifid and the third in

triple and the third vein of bifid is thickened at the distal

extremity. !

Origin.—Triple was first noticed in the offspring of

a female out-crossed from wild stock. Half the males

were triple. On investigation it was found that several

bottles of wild stock contained similar males.

Triple males were found six months later in stump

stock. Crossed to the original triple stock, these males

produced triple female offspring in the F, generation.

The possibility of contamination of the stump stock can

be eliminated since the triple males found in the stock

were also stump, and there were no cultures containing

triple stump flies in the laboratory.

Tug DEFORMED ALLELOMORPHIC SERIES

1. Deformed (d)

Description.—Deformed, which involves many parts

of the body (Fig. 9), shows sexual dimorphism. In the

male the eye is about two thirds the normal size and very

rough; in the female the eye is normal in size and only

slightly roughened. In both sexes the bristles are ab-

normally long and irregularly bent. The thoracic hairs

are badly disarranged in both sexes, but the effect is

very much more exaggerated in the female than in the

226 f THE AMERICAN NATURALIST [Vor. LVI

male. In the former, the hairs are often clumped in a

compact mass on the anterior half of the thorax; while

in the male, the hairs are irregularly scattered over the

Fic, 8. Reugh (eye), rimmed (wing margin), stump (second wing vein)

compound.

whole area. The scutellum in the male (sometimes in

the female also) is blunt instead of pointed, posteriorly,

and the under portions of the thorax are consequently

visible. The wings are extended at an angle of about

45° to 90° in both sexes, and the veins are often faint,

short, and irregular, especially in the male.

These flies are rather feeble and breed poorly except

in mass culture, probably on account of the many physi-

eal defects present.

Origin.—Many males and females were found in a

stock culture of orange forked rough. Sister bottles

made up at the same time did not produce any deformed

flies.

No. 644] MUTANT CHARACTERS IN DROSOPHILA 227

2. Serrate (st)

Description.—Serrate is an allelomorph of deformed,

but involves only a part of the characters modified by

deformed. The changes in the eyes of the two sexes

are exactly the same as those caused by deformed. On

the other hand, the bristles and the shape of the scutel-

lum are almost normal and the thoracic hairs are only

slightly disarranged. The wings may occasionally be

held at an angle with the body, but the venation is prac-

tically normal. The only strikingly noticeable effect of

serrate is the change in the eyes.

Fic. 9. Deformed q.

The compound deformed-serrate females are inter-

mediate between the two allelomorphs but tend to re-

semble serrate more closely than deformed. Serrate flies

are more viable than deformed and breed more readily.

Origin.—A single male was found in an F, mass eul-

ture from a mating of two females by one male from

seute stock. No other serrate flies appeared in this cul-

ture or in a sister culture.

Rimmed (ri)

Description.—In rimmed flies, a heavy rim of marginal

hairs surrounds each wing and the wings curve down

228 THE AMERICAN NATURALIST [Vor. LVI

over the abdomen as if the margins were constricted

(Fig. 8). 'The depression between the seutellum and

thorax of normal flies is eradicated, leaving a smooth

surface at the junction. The thick marginal rim of hairs

is the most constant of the effects of rimmed, but the

other changes are usually apparent.

Origin.—Several males were found in wild type stock.

Pale (pa)

Description.—The post-vertical and all the thoracic

bristles are pale yellow. Occasionally, a few other head

bristles are also yellow. The bristles are thin, and the

entire fly is weak and small with the wings often not un-

folded. None of the original pale flies could be induced -

to breed. The heterozygous females produced a few

pale offspring, but the stock was soon lost.

Origin.—'The mother of the culture in which pale ap-

peared was heterozygous for seute rimmed on one X-

chromosome and for pale morula on the other. Five sis- —

ters of this female were bred, but no pale offspring were

obtained from any of them. It is impossible to tell

whether the mutation to pale occurred in the mother of

the eulture in which pale was found or whether it took

place in her mother.

Stump (s)

Description.—The distal portion of the second vein is

lacking, leaving only a stump at the base of the wing

(Fig. 12). This stump varies in length from one quar-

ter to two thirds that of the normal vein.

Origin.—Six stump males were obtained from a mass

culture in which the mothers were heterozygous for

forked and the fathers were normal. Four of the stump

males were also forked, the others were not.

THE SHORT ALLELOMORPHIC SERIES

1. Short (sh)

Description.—Typieally, all the veins of the wing

fail to reach the margin in short flies, although

No. 644] MUTANT CHARACTERS IN DROSOPHILA 229

sometimes the third vein is entire (Fig. 18).

The second vein is shorter than any of the others.

Ordinarily, the distance between the ends of the

veins and the margin is not great. The posterior

cross-vein is broken occasionally.

15 M 16

Fies. 10-16: Fig. 10, triple. Fig. 11, square. Fig. 12, stump. Fig. 13,

short ¢. Fig. 14, short-2 P Fig. 15, short-3 j. Fig. 16, nicked.

Origin.—Short was first observed in half the sons of

a single female indicating that the mother was hetero-

zygous for the short gene. This female carried orange

230 THE AMERICAN NATURALIST [Vor. LVI

rough on one X-ehromosome and stump on the other.

The mutation to short evidently affected a locus of the

orange rough ehromosome not far from the stump locus.

Several sister eultures were examined, but no short flies

were found.

2. Short-2 (sh,)

Description.—Short-2 -is the most extreme of the

series. In the females the second, fourth, and fifth veins

are very short, the fourth and fifth often-not reaching

as far as the posterior eross-vein. In eases in which they

extend beyond the éross-vein, this vein is broken. In the

males the fourth and fifth veins are about three quarters

the normal length, and the posterior cross-vein is broken

(Fig. 14). The males are indistinguishable from those

of short-3.

Origin.—A. single male was found in small- bristle

rough Stock:

Con 3. Short-3 (shay.

Description.—Short-3 is about the same in both sexes

(Fig. 15). The second vein is very short, and all the

others are about three quarters the normal length. The

posterior cross-vein is usually broken.

Females containing any two of these three allelomorphs

are intermediate between the two used, with perhaps a

closer resemblance to the more extreme member of the

pair.

Origin.—Several males were found in seute stock.

` Morula (m) s

Desoto —Morula involves a partial ut of

the eyes which is due to a consolidation of a group of

facets, especially in the central area of the eye, suggest-

ing the lozenge of melanogaster. The viability of this

stock is very poor, and the double recessives of morula

and any other mutant character rarely survive.

Origin.—At least five males were obtained from a mass |

culture of three pairs which carried rough. The classi-

No. 644] MUTANT CHARACTERS IN DROSOPHILA 231

fication of rough and morula was not accurate at its first

appearance. :

Nicked (nk)

Description.—Nieked is characterized by irregular

notches in one or both wings (Fig. 16). The indenta-

tions vary in size and location, but tend to show on the

posterior and inner portions of the wing. In certain

lines, the character shows regularly, while in certain

other lines it overlaps normal a great deal. Flies in

which nicked is combined with other mutant characters

have rather poor viability.

Origin.—Several individuals of both sexes were found

in a mass culture.

Rosette (ro).

Description.—In this mutant race, a large number of

characters are affected (Fig. 17). The eyes are slightly

roughened due to disarrangement of the facets; the

thoracic hairs are disarranged, looking as if they had

been brushed in the wrong direction; the bristles may

be bent; the distal tarsi of the legs may be twisted; and

the wings are generally held at an angle with the body,

and one or both may be small and circular. The rough

eyes and disarranged hairs are constant characters.

Rosette flies have very low viability and are hard to

breed, especially when other mutant characters are pres-

ent also.

Origin.—Four rosette rough males were obtained

among a large number of offspring from one morula

male by three rough females.

CONSTRUCTION or THE X-CHROMOSOME ‘‘Map’’

' With one or two exceptions the usual procedure? has

been followed in constructing the chromosome ‘‘map.’’

The order of the genes was determined by means of

erosses involving three or more loci (Tables III-VI), and

that order adopted which, in the consideration of any

three points, made the double crossover class the small-

? See footnote, p. 213.

232 THE AMERICAN NATURALIST [Vons LVI

est. In most cases the decision was confirmed by several

subsequent experiments made for other purposes. Tiny

and square have not been definitely located with refer-

ence to forked since they proved unsuitable characters

for use in linkage experiments. Similarly, the loci of

triple and deformed are known to be between rough and .

rimmed, but the relative positions of the two could not

be determined on account of the impossibility of using

the two characters together. Pale, morula, and rosette

are also only tentatively placed.

Fic. 17. Resette.

With the order of the genes established, the ‘‘dis-

tances,’’ or crossover values, between them were obtain-

ed by combining the data from all the experiments given

in Tables II-VI. Table VII gives the summary of all

data between any two loci in the ‘‘map’’ from those ex-

periments in which no intermediate genes were concerned.

This differs from the usual method of summarizing the

data in that it includes only experiments in which no

intermediate point was used.

No. 644] MUTANT CHARACTERS IN DROSOPHILA 233

As far as possible the po-

sitions of the genes on the

‘‘map’’ have been determined

by summation of the ‘‘dis-

tances’ between neighboring

loci taken in pairs, using

stubby arbitrarily as the zero

point. In several cases, how-

ever, the locus of a gene has

been assigned by reference

to some main well-established

point; notably, orange, forked,

seute, rough, or stump. In

Table VII, the starred data

are those on which the ‘‘map”’

is based. No correction for

data involving non-adjacent

loci has been made, since the

degree of numerical accuracy

does not warrant such a com-

putation in this ease. No cor-

rection has been made for

double crossing over in long

regions in which no mutant

loci are known.

Owing to the possible par-

allelism between the yellow

and seute in willistoni and

the yellow and scute in mela-

nogaster a second set of

readings has been given on

the ‘‘map’’ using the position

of yellow as the zero point and

plotting the others in opposite

(+ and —) directions from

this. Comparison with the

X-chromosome map of mela-

nogaster is thus facilitated.

+427] 84? rosette (ro)

+30 —L.72 nicked (nk)

+28? _ 1.70? morula (m)

+26 | 68 short etc. (sh)

418 —] 60 stump (e)

+142__| 56? -pale (pa)

ib um u

LES Ze a de wn v)

~ beaded (be)

LAS P (p)

=11? i31? square (eq).

-12 —f—30 forked etc» (f)

=14? |28? tiny (t)

-32 ——l]-10 bent (bn)

dT uus 9 enall-bristle (sb)

-5 0.7L. 1.3 orange (0)

2 —} O stubby (sy)

Fic. 18. Map showing linkage

relations of sex-linked genes in

Drosophila williston

234 |^ THE AMERICAN NATURALIST [Vor. LVI

Discussion

The previous work on the comparative genetical study

of different species of Drosophila has been concerned

largely with species having different types of chromo-

some groups. It has involved mainly the species

melanogaster, virilis, funebris, simulans and obscura.

Of these, only melanogaster and simulans have the

type of chromosome group with which we are

concerned here. The published data on the first four

of these species have recently been summarized by

Sturtevant (1920) and may be passed over briefly. The

data on obscura are in press and our references to them

are made with the kind permission of Mr. D. E. Lance-

field. A

In melanogaster, virilis, funebris and obscura, the evi-

dence suggests a tendency on the part of each species to

give mutants paralleling those in the others, although

the extent of this tendency ean not be ascertained ac-

curately because of the impossibility of proving the ho-

mology of similar characters. In the case of melano-

gaster and simulans the parallelism extends to nearly

all of the known simulans characters and certain homol-

ogies are established by means of hybridization (Sturte-

vant, ’20, *21a, 21b). To be sure, the two latter species

are almost identical and would be expected to give similar

genetical results; but it is of interest to note that there

is a close resemblance between the proven cases of par-

allel characters in these, and the apparent cases of par-

allel characters in the other species. This tends to in-

crease the probability of actual parallelism in the latter

where a series of linked characters is involved.

Upon comparing the mutant characters of willistoni

with those of the others it is evident that only a few

striking cases of resemblance are found. Of these the

most significant involve the characters yellow and scute.

Their morphological resemblances to the yellow and

scute in melanogaster have already been noted in the

No. 644] MUTANT CHARACTERS IN DROSOPHILA 235

descriptive section. But the evidence for their being

parallels is made particularly strong by the fact that

their genes are completely or almost completely linked

in both species. In melanogaster yellow and scute are -

located at the extreme end (zero point) of the chromo-

some map, while in willistoni they are approximately

in the middle.

A situation similar to this has already been found in

D. obscura (according to unpublished data of D. E.

Lancefield). Here the characters yellow and scute also

bear a close resemblanee to those in melanogaster and

are very closely linked. As in willistoni, the factors for

yellow and seute are near the middle of the chromosome

map. It will be recalled that obscura, like willistoni, has

a large V-shaped X-chromosome—although the other

chromosomes are different (Metz, 1916). In the two

species having. V-shaped X-ehromosomes, then, yellow

and scute are ‘‘located’’ near the middle of the chromo-

some map, while in melanogaster with its short, rod-like

X-chromosome, yellow and seute are at one end. As Lance-

field has pointed out in his discussion of obscura, this sug-

gests that one end of the rod-like X in the one ease cor-

responds. to the middle of the V-shaped X in the other.

And this suggests that the rod-like chromosome itself

may correspond to one arm of the V.

The only evidence in willistoni on the latter hypothesis

is that furnished by the characters forked and stubby.

These are possible parallels of the singed and forked in

melanogaster. They are similar in a general way in the

two species (see description above), and the serial order

of the genes is the same (Fig. 18), although the linkage

relations do not agree exactly.

In this connection it may ‘be recalled that **yellow,""

**singed" and ‘forked’? have also been found in Droso-

phila virilis (Metz, 1918, and unpublished data), and

may, likewise, be considered as possible parallels to those

in melanogaster. Virilis has a rod-like X-chromosome

resembling that of melanogaster, and the relative posi-

236 THE AMERICAN NATURALIST [Vor. LVI

tions of the three genes on the chromosome map re-

semble those in melanogaster. Yellow is about three

units from the end instead of at the end; singed is at

about 35 instead of 21 and forked is at about 58 instead

of 56.5.

The evidence is not sufficient to warrant the conclusion

that these are actually homologous series, but the fact

that such series exist suggests that by the present means

it may eventually be possible to obtain reliable data for a

comparison of the chromosomal make-up of the different

species.

Among the other characters in willistoni which show

some resemblance to characters in melanogaster or sim-

ulans the following may be noted as a matter of record,

although there is little indication of their being actual

parallels: orange and peach (which look alike) resemble

coral or ruby; beaded is similar to the cut allelomorphs

both morphologically and in respect to its sterile fe-

males and poorly viable males; triple suggests bifid, and

morula looks like lozenge. The small bristle of willistoni

may be comparable to the tiny bristle-2 of simulans.

The fact that the X-chromosomes in willistoni are mor-

phologically like the large autosomes and not like the

X-chromosomes of melanogaster suggests that we ought

to compare, not only the sex-linked groups of the two

species, but also the sex-linked group of willistoni with

the non-sex-linked groups of melanogaster. This has

been done, but without revealing any significant indica-

tion of parallelism.

In conclusion it may be noted that although the evi-

dence is not yet clear on the genetic relationship of the

sex chromosomes in melanogaster and willistoni, yet if

the above suggestion is correct, that the X-chromosome

of melanogaster corresponds to part of the X-chromo-

some in willistoni, then the resemblance ‘between the

chromosome groups of the two species is only super-

ficial. It may also be noted that the genetic ‘‘map’’ of

No. 644] MUTANT CHARACTERS IN DROSOPHILA 237

the X-chromosome of willistoni at present is only slightly

longer than the map of the melanogaster X-chromo-

some (84 as contrasted with 70 units), whereas the wil-

listoni X-chromosome itself appears to.be about twice the

length of that of melanogaster. This suggests that cross-

ing over is less frequent in willistoni than in melano-

gaster.

SUMMARY

1. Twenty-eight recessive sex-linked mutant charac-

ters in Drosophila willistoni are described and their

linkage relations considered.

2. In general, the genetic behavior of willistoni (as re-

gards crossing over, etc.) is similar to that of D. mela-

nogaster and the other species of Drosophila whose ge-

netic behavior is known.

3. There is a strong indication of parallelism between

the mutants yellow and scute in willistoni and yellow and

scute in melanogaster.

4. In both species these characters are completely or

very closely linked.

9. There is some indication of series between the

characters forked and stubby in willistoni and singed and

forked in melanogaster.

6. In melanogaster the genes for yellow and scute are

“located”? at one end of the chromosome map, and

singed and forked are 21 units and 56.5 units respec-

tively from this end. In willistoni yellow and scute are

near the middle of the map, and forked and stubby are

on one side at 12 units and 42 units respectively.

7. Since the X-chromosome of melanogaster is short

and rod-like, while that of willistoni is approximately

twice as long and is V-shaped, this relation of the chro-

mosome maps suggests that the melanogaster X-chromo-

some corresponds to one arm of the V-shaped X-chromo-

some of willistoni, with the locus of yellow correspond-

ing in the two cases. This agrees with the suggestion

made by Lancefield in the case of D. obscura in which the

X-chromosomes resemble those of willistoni.

238 THE AMERICAN NATURALIST [Vor. LVI

8. The comparative lengths of the X-chromosome

maps in melanogaster and willistoni suggests that there

is less crossing over in the latter than in the former.

TABLE I

ORIGIN OF MUTANTS

Ezplanation of ‘‘records’’: W indicates R. C, Lancefield records on

numbers 1-100 whieh fadiesin D. E. Laneefield; L indicates C. W.

R indicates ius Ferry.

Mutant Sym- First Record Parts Affected

bol Found

1. Stubby.......:.| sy | March, 1920, W 1128 |Bristles.

COCA ORAE. ois ve ok o April, 1919 L 37 Eye color.

Š July, 1919 | L 336

8. Small-bristle sb Uus: 1920 | W 1745 Bristes

4. Bent. :. s. bn | Nov., 1920 W 1687

D. Forked -> oc f March, 1919| L1 ed fertility of females.

6. Forked—2.....| f» March, 1920 | W 1177 |Bristles, hairs; fertility of

6 TINI Ursa t Jan., 1920 W 856 |Bristles.

8. Square.........| sq |Feb., 1920 | W965 |Wings; fertility of 9 9.

9. Reduced. ...... re | Oct., 1919 W 288 Usher abdomen.

10. Bonto i1 sd e May, 1919 L 231 Bri stles

11. Scute—2....... Sc? | Feb., 1920 WwW ristles

12. Seute—3....... sca | May, 1920 W 1346 Bristle; fertility of oo.

1d. Yellows; Sits Oct., 1921 R2 Color of body, wings, etc.

I4. Poeh. Se a. es p May, 1920 W 1384 |Eyec ilr

15. Beaded........ be | Nov., 1920 W 1964 "uer viability:

16, Rough... ... r March, 1919| L 9 Texture of eye.

: Dec., 1919

l6 TBI V I.e. tr May, 1920 | W 1498 HR i

18. Deformed...... d Nov., 1919 W 360 (Almost every part o of body.

19. Serrate........ t March, 1920 | W 1146 Texture and size of eyes.

20. Rimmed....... ri May, 1919 wi Wings and scutellum; vi-

ability.

21: Phe su. pa |Feb., 1920 980 |Bristles; viability

22. Hang; veces 8 June, 1919 L 254 ing vein.

28; Short. ies a sh Feb., 1920 W 1110 Wing veins.

24. Short—2.......| she | May, 1920 W 1440 | Wing veins

25. Short—3....... shs | March, 1920 W 1164 Wing veins.

206. Morul. o is m L411 Texture of eyes; viability.

27. Nioked. -i nk | June, 1919 Wil

28. Rosette........ ro | Nov., 1919 L 438 Almost every part of body.

In Tables II-VI parentheses indieate data omitted

from the regional summary on account of poor viability

of one class or else inability to classify one class. The

two eolumns under the respective headings represent

complementary classes, the one to the left that includ-

No. 644] MUTANT CHARACTERS IN DROSOPHILA 239

ing the normal allelomorph of the gene farthest to the

left. E.g., in Table II, experiment 3, under crossovers

in region 1 there are 48 normal bristle rough eye flies,

and 55 stubby bristle normal eye flies.

The plus sign (+) indicates wild-type or normal.

TABLE II

Two-PoINT CROSSES

| Crossovers in

Experi- | Re

ment Nature of Cross Non-crossovers | Total

Number |

| 1

Ned ea syr X + 73 | 48 55 247

x Rep qr pute osb X + 1,031 796 i 34 28 1,886

a obn X + 2 275 | 36 25 621

MU c Lo HUN xn 66 70 | 26 20 182

Bey MEI sc X ri 3 291 | 31 29 655

zi Wise ue e prx 131 7 224

Jue ONE psx + 1 111 | 20 21 252

SE. cil oes rri X + 127 H 1 202

a e. woe ae rxs 179.4470 20 98 398

407. Ga ee ssh X + 495 (560) | 37 (0) 532

Zi. vl. 126 (169) | 14 (0) 140

TABLE III

THREE-POINT CROSSES

Crossovers in Region

Experiment Nature of Non- Total

Number Cross crossovers

1 2 1,2

r lcu xs sy sb X bn 704 582 |28 29| 40 38 0 0| 1421

8: 2: 1. obn Xf» 35 6 16 sud 0 142

SG oc. fr Xre 943 238 |40 35] 12 25 |0 O: 593

BR III negli fs X sc 48 10 © u ui 9 146

os aD TRA Deae seri Xr 0. 180 120 .HT 3 30 0| 462

ss MONEE ay pede are sers X + 510 26 45 |4 2| 1130

vo IR o sxd obe. 994 |33 25 | 2b Apn 2 691

B vv. seri Xm 98 28 | 60 26/0 6| 625

NE V cT se s sh; X + 174 (146) (54) 55 | (8 19 3 (0| 251

[2 MEME A NU pr X be (20) 68 (0 | (1) 0 0i IU

7.7. E rrixtr 312 281 2 0 1 56 10 0| 601

TABLE IV

Four-POINT CROSSES

THE AMERICAN NATURALIST

[Vor. LVI

2E on- Crossovers in Region =

EE Nature of | cross- $

Ez overs E

a 1 2 3 h211;8]2,3 12,1

l.|spyr Xosb |321 325|9 4 |22 12244 2050 Ol 1/7 4/00 1,156

Tore Xfs 40. 5B0H5- 20|.3 13|15 19i 26 5| 3,00 187

Gof? xri 161 15070 88 {68 51| 10 218 102 412 1.0.1 618

l0.lorg Xt 48 -57180 27 115. 23 7. 15/5 13 3.|1 11.2 2-1; 240

12.lors X tr 37 56/40 50) 0 1 6. 710 08 2/0 0 01? 208

13.j0od X rri 1 19) 6 Lee 4 0 2/0 0,0 0/0 O00 48

15./f re sce r 11/54 3,9 4 | 43 260 01 00 000 781

21.|re se» X be r|(89) 268 1 (0)| 4 (0|(3 60 00 OlO 0 00| 279

22.scrs Xd 220 160/16 20] 8. 0| 14 19310 11 11i 0/00] 455

24.|scri Xrs |348 306 41 18518. 12 125 ae 13 210--0|]001] 779

27.scrs X nk |250 306/31 23 42 27| 28 10|l 43 9|1 19/00, 754

30.|sc ri X pa ym 10810 (22,7 (0)| ©) 70 00 (00 0|00]| 182

3l.scrim Xs |14 43|2 315112 ..61 12 13/2 21 010 0/00, 257

TABLE V

FIVE-POINT CROSSES

Be Crossovers in Region

£3 Nature of | Non- E

EE Cross cross- i

BZ 113] | 4 |L2531,4/532,43,4/1]| ©

[el

3,4

8 of ris| 64 5827 319 911 2 212 2/1 3/3 2/1 01 211 2/0 0| 239

16 rs 183 3 8 6 17 28000 12 110100 000 480

17...\fre se r Xro|232 222/41 271 121 14/190 75/0 00 0/6 210 01 02 111 0| 866

25...|sc ri Xr s nk 40 10 72011 0,27 6000 2,0 5/0 0/0 3/0 1410 1| 350

TABLE VI

SriX-POINT CROSSES

= Crossovers in Region

LET

o9 on-

LE Nature of | cross- F

Cross overs . TRI

a 2 3 4 5 11,2]1,3]11,4/11,5|2,4/2,5]3,4|3,5|4,5| 2, | 2,

ll.o są r sXsc ri| 92 60415019410 42 1.9 9332312160111/0120000102/331

14./f re scz rXp 8/180 152 16 18 11, 3 311 822 18/0 00 00 1/2 3/0 0/0 0 0 0/0 2/1 0 0 0 0 0,442

No. 644] MUTANT CHARACTERS IN DROSOPHILA 241

TABLE VII

SUMMARY OF ALL AVAILABLE DATA BETWEEN CONSECUTIVE LOCI

Cross-| Num- Cross-| Num- Cross-| Num-

Value | Flies Value | Flies í Value | Flies

8 E 13 Li t. 7 2 711 20.8 240 49 is oa

sy-sb...... 4.0 | 1,421 |sq-sc5. . ... 10.6 9891 [rt ll. 2.3 12,242

ge SER EE 41.7 re-sc$...... 0.95 | 2,848 [r-s9........ 11.1 | 3,444

o-sb$...... 3.5 | 3,042 ]re-r....... 6.2 593 |r-ro*....... 35

o-bB.. v. 10.2 FOU I To 23.0 187 [tr-ri$....... 0 601

aera 29.0 | 1,044 |seo—p®...... 1.8 PW ee 11.5 208

Oot. 8 30.4 240 |sce—be..... 1.4 79 REA rn B

m. bn 34.7 331 S. T. 6,988 Id-8........ 7.9 | 1,146

USC 44.5 256 |sc-d5. .....| 7.2 691 |ri-pa*......| 5.3 132

sb-bn* ,421 |sc-ri.. Tí 1,908 jri-s........ 7.5 | 1,956

sb- 40.0 | 1,156 [sc-s. ...... 21.9 397 Him... 14.7 625

bn-fi...... 19 142 |p-be* ..... i4 176 |pa-m. ..... 5.3 132

f-r 11.2 .| 3,349 Ip-r........ 5.0 654 |s-sh*.. ..... 7.9 923

TABOOS uu. 11.9 385 |p-s... 16.3 252 |s-m$....... 10.1 257

Te usd 21.2 618 |be-r....... 2.4 455 |s-nk*. ..... 11.5 | 1,100

I4. 1... 25.3 ISP... 0.5 809

LITERATURE CITED

Bridges, C

1916. ida as Proof of the Chromosome Theory of Here-

dity. Genetics, 1: 1-52, 107—163.

Bridges, C. B, and Morgan, T. H.

1919. The Second Chromosome Group of Mutant Characters. Car-

negie Inst. Wash. Publ. 278: 123—304

Lancefield, R. C. and Metz, C. W

1921. Proc. Nat. Acad. of 8c., August, 1921.

Metz, C. W.

1916. geen hien on the Diptera. III. Additional Types

of ge romosome Groups in the Drosophilidæ. AMER. NAT.,

50:

1918. The P RAS of Eight Sex-linked Characters in Drosophila

virilis, Genetics, 3: 107—134.

Morgan, T. H. and Bridges,

1916. Sex-linked Inherifance in Drosophila. Carnegie Inst. Wash.

Publ. 237: 1-87,

Sturtevant, A. H.

1920. Genetic Studies on Drosophila simulans. I. Introduction, Hy-

‘brids with Dr lano, Genetics 5: 00.

1921a. Genetic Studies on Drosophila inulat. II. Sex-linked

p nes. Genetics 6: 43-64,

1921b. The North American Species of the Genus Drosophila. Car-

negie Inst. Wash, Publ. 301, 150 pp., 3 pl., 49 text-figs.

$ These data were used in the construction of the chromosome ‘‘map.’’

INHERITANCE OF PLUMAGE COLOR IN CROSSES

OF BUFF AND COLUMBIAN FOWLS

DR. L. C. DUNN:

As. a part of a search for material suitable for use in

measuring the linkage strength of several sex-linked

characters in poultry, some preliminary experiments have

been undertaken on the inheritance of the Columbian plu-

mage pattern. The results of these experiments have

confirmed those of Sturtevant (1912) in establishing the

sex-linked nature of one of the genes involved in the pro-

duction of this pattern, and have demonstrated the rela-

tionship between it and the buff plumage coloration. The

inheritance and somatic effects of the chief factor in-

volved appear to be clear enough to make it useful in

genetic investigations on poultry. A short description of

the experimental results is therefore given here, to be

followed by a more detailed report when further evidence

is at hand. i

The Columbian pattern, sometimes known as the Er-

mine coloration, is characteristic of several standard

varieties of a number of breeds of poultry of which the

Light Brahma, the Columbian Plymouth Rock and the

Columbian Wyandotte are perhaps the most familiar.

Although subject to some variation the pattern consists

in general of a pure white surface color in all parts of the

plumage except in the hackles, wings, and tail feathers,

in which black is present either as a central stripe (hac-

kles); as a solid color covering somewhat more than half

the feather (primaries) or as a solid color covering the

whole feather (tail). In typical Columbian fowls the

undercolor or fluff at the base of the body feathers is

generally lead or slate, which is sometimes so pronounced

as to show through at the surface especially on the back.

1 Contributions in Poultry Genetics, Storrs Agr. Exp. Station.

242

No. 644] INHERITANCE OF PLUMAGE COLOR 243

This pattern is alike in both sexes except for the slightly

different appearance caused by structural differences in

the hackle and saddle feathers.

The down color of newly hatched Columbian chicks is

white or a yellowish white like the down characteristic

of the chicks of many white varieties of poultry, e.g.,

White Leghorns. Black or gray markings appear on

most Columbian chicks as a spot on the head, or as dor-

sal stripes on the head or back and in the developing

wing quills. This pattern varies in different individuals

from an entire absence of dark pigment to the presence

of rather heavy dark dorsal stripes. |

The color variety chosen for crossing with Columbian

was buff, since this offered a clear contrast in the absence

of white and the uniformity of coloration and because

the plumage color of both sexes is practically the same.

Moreover, buff is known to be recessive to many other

plumage colors and patterns and for this reason is less

likely to earry other factors which might complicate the

results. .

The first crosses were made between a Columbian male

extracted from the second generation of a cross between

Light Brahma and White Leghorn,? and purebred Buff

Orpington females.

Twenty-three chicks were hatched from these crosses.

Of these, twelve were predominantly white in the down,

and eleven were buff. Of the whites four were pure

white, five had a black streak or spot on the head and

saddle, and black pin feathers appearing in the wings,

and closely resembled purebred Light Brahma chicks in

color; one was smoky white and two were white with a

buff spot or streak on the head and neck. Of the buffs

eight were clear buff in color, one was a very light buff

2 The cross of Light Brahma by White Leghorn (quoted by permission

from unpublished data of Sinnott and Warner) when made reciprocally

produced white birds in F,, generally with some ticking with black and

occasional brassiness or tinging with buff. The White Leghorns used

were apparently pure for the dominant inhibitor of color (I) while the

Light Brahmas contained the recessive allelomorph of this gene (i).

244 THE AMERICAN NATURALIST [VoL. LVI

and two were buff with blaek down on heads and saddles

and with black feathers in the wings. All of the white

chicks developed adult plumage resembling the Colum-

bian pattern except that the black in the hackles, tail and

wings was a dingy gray, occurring as stippling on the

white ground rather than as a solid color. The buff chicks

which survived developed adult plumage in which the

hackles, tail and wing feathers were gray or black, while

the feathers over the rest of the body were buff. These

resembled mosaics of buff and Columbian in which the

Columbian pattern was imposed on a buff ground.’

In tabular form the results of this cross were as follows:

TABLE I

Columbian Male ^ Buff Female

Whi ta Buff

Down Colors 12 11

d X T

Adult Colors 6 6 8 6

The appearance of two kinds of offspring in equal num-

bers from this cross indicated that one parent was prob-

ably heterozygous in a factor causing the difference be-

tween white and buff. Later work showed this to be the

male. When a purebred Light Brahma male was mated

to purebred buff females (Orpingtons and Plymouth

Rocks) the thirty-seven offspring were without exception

white in the down and developed into white Columbians

as adults. The dominance of white over buff was prac-

tieally complete although one or two buff feathers were

noted on one hybrid and a slight buff tinge on another.

3' The resemblanee of these hybrids to deseriptions and illustrations of

early buff varieties (Tegetmeier, 1872) is quite striking. At present the

only buff variety characterized by a considerable amount of black in

hackles, wings and tail is the Buff Brahma, although this is not yet recog-

nized by poultrymen as a standard t

The coloration characteristic of the Rhode Island Red breed is essenti-

ally ermine or Columbian pattern with a red ground substituted for

the white of true Columbians. A very useful discussion of the relation-

ships between these patterns from the standpoint of a breeder and fancier

of long experience is given by Robinson (1921) see esp. pp. 55 and 56.

No. 644] INHERITANCE OF PLUMAGE COLOR 245

The offspring of the purebred Light Brahma male by buff

females were much whiter than the chicks from the first

male. Only one of the thirty-seven showed the dark head

spot characteristic of Light Brahma chicks and all were

of a clear dead white, lacking even the yellowish tinge

characteristic of most white chicks in the down.

adults these birds were very similar to the first lot. The

amount of black in hackles, tails and wings was about

intermediate between the amount present in the Colum-

bian parent and the absence of black in pure white birds.

The first generation hybrid chicks were crossed in two

ways. The F, Columbian females were backcrossed to

a purebred Buff Plymouth Rock male; the F, buffs were

bred inter-se. The results of these matings are presented

in Tables II and III.

TABLE II

RESULT OF CnossiNG F, COLUMBIAN FEMALES WITH PURE Burr MALE:

White Buff Total

Down Colors 36 38 74

Columbian Buff

9 3

Adult Colors 14 0 0 21 354

TABLE III

RESULT OF CROSSING E. BUFFS INTER-SE

Buff and White Buff Total

Down Colors 9 74 83

Columbian Buff

3 a. 2

Adult Colors 0 0 1T. J5 354

From the backcross of F, Columbian females with a

buff male equal numbers of buff and white chicks re-

sulted, a clear monohybrid segregation. Evidently one

factor determines the difference between white and buff,

and from the F, results it is clear that white is the domi-

nant allelomorph. This factor is however sex-linked, since

4The differences between the numbers of chicks and the numbers of

adults indicate the number of birds which died before definitive plumage

or secondary sex characters were developed.

246 THE AMERICAN NATURALIST [Vor. LVI

all sons of the F, Columbian females are white (Colum-

bian) while all the daughters are buff.

The mating of F, buffs inter-se produced only buff

chicks, indicating that buff is recessive and breeds true.

The nine chicks recorded as buff and white all had buff

heads or wings or both and those which lived developed

buff adult plumage. Genetieally they were probably ex-

tremely light buffs.

As regards only the difference between white and buff,

we may conclude that the Columbians contain a dominant

sex-linked gene for the inhibition or restriction of. buff

from the plumage. The first male was evidently hetero-

zygous for this factor; the second male was homozygous

for it; the Columbian females contained but one dose of

it, and this was located in the single sex chromosome;

while all the buffs lacked it entirely. This is evidently

the same gene (I) which Sturtevant (1912) found in Co-

lumbian Wyandottes, although its effects were somewhat

obseured by other factors in his crosses with Brown Leg-

horn.

The presence of this gene in some White Wyandottes

which I have studied strengthens the homology between

the gene with which Sturtevant was dealing and the gene

whieh is present in the Light Brahmas used in these ex-

periments. I have recently crossed two White Wyandotte

males with purebred Buff (Orpington) females. The

white males were known to be recessive white (cc), ?.e.,

they lacked the gene (C) for the development of color

in the plumage. The results of this ¢ross are shown in

the table following.

RESULT OF CROSSING WHITE WYANDOTTE MALES wiTH BUFF ORPINGTON

FEMALES

: White Buff Total

Down Colors 13 13 26

Columbian Buff

T d 3

Adult Colors 3 2 1 3 T 16

In addition to the types noted above three unclassified

No. 644] INHERITANCE OF PLUMAGE COLOR 247

chicks were born from one mating. These were chiefly

white in the down with black spots on the erown and neck

and black quills in the wings. They resembled very dark

Columbian chicks. These developed adult plumage dif-

ferent from the other chicks in this cross and could not

be classified either as Columbians or buffs. Additional

factors which have not been identified were probably

contributed by one of the White Wyandotte males and

further reference to these birds will therefore be post-

poned until more information is obtained. Omitting

these, the salient fact concerning this cross is the pro-

duction of only two classes of chicks, white (Columbian)

and buff in equal numbers. The White Wyandotte males

bred, therefore, like F, hybrids between Columbian and

buff and were undoubtedly heterozygous in the gene for

the restriction of buff. As adults the offspring of this

cross were indistinguishable in color from the offspring

of the heterozygous Light Brahma male first used in

crosses with buffs. The amount of black in the hackles

of these birds appeared to be somewhat greater than in

the offspring of the Light Brahma cross, but it was not

sufficient to serve as a distinguishing mark. White Wy-

andottes, therefore, may carry a gene for the restriction

of buff which is probably the same as the gene found in

Light Brahmas and Columbian Wyandottes.* It is not

demonstrable, of course, except in crosses of White Wy-

andottes with colored fowls which supply the dominant

gene C for the development of pigment.

In addition to these three instances of the occurrence

of a gene for restriction of buff there are numerous

other cases in the literature in which the difference be-

tween buff (or red) and white in certain parts of the

plumage is apparently due to the same gene or one with

similar effects. Davenport (1912) found a sex-linked dif-

5 Professor W. A. Lippincott has called my attention to this statement in

Robinson (1921), p. 42: ** The pattern (i.e., Columbian) was also produced

by erossing the Rhode Island Red (which has really the same pattern with

the blaek—on a red ground—redueed to a minimum) with a White Wyan-

dotte.’’

248 THE AMERICAN NATURALIST [Vor. LVI

ference between Dark Brahmas and Brown Leghorns,

the gene ‘‘ W’’ inhibiting the appearance of buff or red

in the hackles and saddles of Dark Brahmas. Jones

(1914) was probably dealing with a similar sex-linked

gene in his crosses between Silver and Golden Campines,

and Hagedoorn’s (1914) evidence indicates that the same

or a similar sex-linked gene differentiates Silver and

Golden Assendelvers. Punnett (1919) distinguishes a

sex-linked gene ‘‘S,’’ which in crosses of Silver and

Golden Campines inhibited the development of buff or

gold in the plumage, leaving certain portions of the

feather ‘‘ silver" or white. Most recently evidence pre-

sented by Haldane (1921) indicates that black and white

barring such as characterizes the Barred Plymouth Rock

variety is differentiated from black and buff (or red or

gold) barring by the same gene ** S" for the inhibition

of buff. This sex-linked gene ‘‘S,’’ Haldane found to

be linked, as was to be expected, with the sex-linked gene

B” (barring).

In each of these cases a dominant sex-linked gene was

found which restricted or inhibited the development of

buff (or red or gold) in certain parts of the plumage.

Although in the absence of data on erosses between the

varieties mentioned it is impossible to assert that the

restrietion of buff in the silver or white-patterned vari-

eties is in each ease due to the same gene, the presumptive

evidence in favor of such a view is strong. It appears

probable that Columbian and buff varieties of several

breeds (Leghorns, Plymouth Rocks, Wyandottes, etc.)

are differentiated by the presence in the Columbians of

a gene for the inhibition or restriction of buff pigment;

and in view of the history of the various color varieties

that this gene has been introduced into and now differ-

entiates Golden from Silver-laced Wyandottes, Golden

from Silver Spangled Hamburgs, gold pencilled (or part-

ridge) varieties from silver-pencilled ones and other

golden varieties from silver varieties which differ only

in the distinction between buff and white in the plumage.

No. 6444] INHERITANCE OF PLUMAGE COLOR 249

Data on the results of crosses involving these color vari-

eties are urgently needed, and the generalization offered

above is put forward as a temporary simplifieation in

lieu of but as an aid to more extensive research.

Tue BLACK COMPONENT OF THE COLUMBIAN PATTERN

When the experiments with buff and Columbian fowls

were begun it was supposed that at least two alternative

characters distinguished these varieties; viz., ground

color (white as opposed to buff) and pattern (black in

hackles, wing, and tail as opposed to self coloration).

The results of these experiments, a reexamination of the

parent types and a cursory review of poultry literature

indieate the error of this assumption.

1. Experimental.—The first generation of the cross

Columbian X Buff consisted of birds intermediate between

the parental types in the amount of black pigment pres-

ent. If four arbitrary grades (1-2-3-4) in the reduetion

of the amount of black in hackles, wing and tail are

made between typical Columbian and entire absence of

blaek (white or buff self) then the first generation is

found to consist of the following grades.

Columbian —1 —2 —3 —4 Self

0 8 10 2 0 0

If the buff parents are classified as self then the hy-

brids resemble the Columbian parent more closely. But

a careful examination of all the buff females used re-

vealed the presence in each of them of a small amount

of black pigment usually as broken patches or fine stipp-

ling in the tail and primary feathers, and occasional

traces in the hackles. The buffs, therefore, can not be

regarded as selfs and most of those used in these ex-

periments were assignable to grade-4. The amount of

6 It is the experience of farmers and poultrymen, as evidenced in poultry

literature, that buff fowls with no admixture of black pigment have been

rare. Black in wings and tail is being rigidly selected against and is

being gradually reduced in modern breeds.

250 THE AMERICAN NATURALIST [Vor. LVI

black in the F, fowls is only slightly above the mid point

between Columbian and grade-4.

An F, generation has not yet been raised from the

cross of typical Columbian X Buff,but some data are avail-

able on the F, generation from the cross of the hetero-

zygous Light Brahma which was first used in crosses

with buff. This male was lighter than typical Columbian,

about grade-1. His offspring were not graded but had

slightly less black than the offspring of the typieal Co-

lumbian male, averaging about grade-3. The amount

of black was similar in the Columbian and buff progeny.

When these F, buffs were bred inter-se the grades of the

F, adult fowls were as follows: '

Columbian —l —28 —3 —4 Self

0 7 13 10 rE 0

The variation in amount of black pigment was practi-

eally continuous, except that the Columbian parental

type was not recovered. No buffs were obtained which

were entirely free from black in tails or wings.

The F; Columbians were backcrossed with a pure Buff

Rock male which showed only faint traces of black stipp-

ling (mealiness) in the tail. The progeny of this cross

were of the following grades: )

Whites (Columbians) and buffs combined:

Columbian mi —2 —3 —4 Self

0 2 3 9 13 4

The amount of black in these fowls was obviously much

less than in the F, generation although the same grades

were represented. In four fowls (three buffs and one

white) no trace of black pigment could be detected.

It is obvious from these facts that as regards the black

component of the Columbian pattern, the Light Brahmas

and the buffs used differ only in amount. A blend oc-

curs in the first generation followed by segregation in the

second and backcross generation. It is probable, there-

No. 644] INHERITANCE OF PLUMAGE COLOR 251

fore, that the two types crossed differ from each other

by multiple factors affecting the amount of black pigment

produced. The number of these factors can not be esti-

mated because of the small numbers of animals involved

and because a second generation has been bred only from

an original eross in which the Columbian parent did not

have the amount of black normal to that variety. Fail-

ure to recover the typieal Columbian pattern in later

generations is probably due to the last named circum-

stance rather than the absence of segregation.

The two varieties probably do not differ by any single

factor determining the presence or absence of black pig-

ment, but only in the degree to which black is produced,

the degree probably being governed by accessory or modi-

fying factors. This fact attaches especial interest to the

appearance of several birds in the backcross generation

which show no trace of black pigment. Do these repre-

sent loss of a factor determining the ability to develop

any black pigment at all or are they segregates in which

factors limiting the exercise of the black-producing fune-

tion are at a maximum? Since they are few in number

and since variation in the amount of black grades im-

perceptibly into the self condition I am inclined to the

latter view. If this is true it should be possible to reduce

the amount of black in Columbian fowls by rigid selection

against it to such a point that birds might be produced

which were phenotypically white, but which as regards

restriction of buff would breed like Columbians.‘ Such

a character would be in effect a sex-linked self white and

the absence. of a sex-linked white in the many breeds

investigated points to the probability that none has been

produced in this way.

Much of the interest in the case presented here inheres

in the apparent simplicity of the results. The crossing

of Light Brahmas and Buff Orpingtons or Buff Plymouth

Rocks produces in the first, second and backcross gen-

erations only two easily distinguishable types, white (Co-

7 One such bird has appeared in the course of these experiments; see p. 244.

252 THE AMERICAN NATURALIST [Vor. LVI

lumbian) fowls and buffs—in which to be sure there is

some variation in the amount of black pigment present

in certain parts of the body, but apparently no epistatic

pattern factors are introduced from either side of the

cross to obscure the visible segregation of the main fac-

tors. Restriction of buff as found in Columbian fowls

is, therefore, a valuable sex-linked gene for use in meas-

uring linkage or in other Mendelian experiments with

poultry while buff appears to be the best color variety

to be used in studying the inheritance of unknown plu-

mage characters. The Brown Leghorn or game type plu-

mage pattern, although it resembles the supposed wild

type form, is in the writer's opinion less valuable than

buff because of the often evidenced? presence in the ge-

netie constitution of the Brown Leghorn of epistatie pat-

tern factors for extension of black pigment, stippling, ete.

The general results of the experiments reported have

been to confirm and extend the previously known facts

regarding the inheritance of the Columbian variation.

The genetic relationships of this pattern and the buff

coloration also throw some interesting light on the evo-

lution of these two color varieties. They differ, it has

been shown, only in one main gene which determines the

production or restriction of buff in the plumage. Both

are able to develop black pigment in certain parts of

the plumage, while they differ quantitatively in the de-

gree to which black may be produced. The former single

factor difference probably arose as a single mutation,

while the latter and less important difference is one which

could be brought about by selection of small variations

which had already arisen in a common parental stock.

The variation which produced the chief difference be-

tween these two color varieties, i.e., the restriction of

buff, undoubtedly took place at least 75 years ago and

probably in China, although there is no evidence that the

same variation has not occurred several times. The first

known Columbian breed was probably the Gray Shang-

8 Sturtevant, A. H. (1912); Lefevre, G. (1916).

No. 644] INHERITANCE OF PLUMAGE COLOR 253

hae, from which the Light Brahmas were derived. These

fowls were imported into the United States from China

in the decade before 1850? and into England shortly

afterward. At about the same period and often in the

same shipments were imported certain buff birds which

eventually became the foundation stock of the Buff Co-

chin breed from which practically all buff varieties of

the present day received their color. These two varieties

were practically identical in characters other than plu-

mage color’ and in the matter of plumage the chief dif-

ference was the difference in body feathers, being white

more or less stippled with gray in the Shanghaes and

buff similarly stippled with gray (mealiness) in the Buff

Cochins. In China, observers have regarded the buff as

the older color variety while the gray was noted as sep-

arate about 1840.1! "The Chinese apparently paid little

attention to color in breeding their fowls and the vari-

ation from buff to white (or the reverse) in the plumage

may have occurred many years or even centuries pre-

vious to this date.

The further differences between Columbian and Buff

breeds have taken place since their introduction from the

Orient, chiefly under the selective breeding of English

and American poultrymen. The buffs were at first char-

acterized by a great deal of variation in the shade of the

principal color—ranging from lemon to red; while the

wings, and tails, and tips or margins of the hackles va-

ried from solid black through stippling and blotching to

an absence of black in any one of these parts? All

subsequent selection has been against the black? and

the Ameriean Standard of Perfection now specifies ** buff

in all parts of the plumage." In the Shanghaes or Light

Brahmas on the other hand the object of the breeder

9 Weir, Johnson and Brown, ‘‘The Poultry Book,’’ N. Y., 1912, p. 528.

10 Tegetmeier, W. B., loc. cit., p. 63.

11 Weir, Johnson aid Brown, loc. cit., p. 528.

12 Weir, Johnson and Brown, loc. cit., p. 527; p. 630, p. 540. Tegetmeier,

loc. cit., "

18 With the exeeption of the selection for black in hackles, wing and

tail whieh was employed in developing the Buff Brahma variety.

254 THE AMERICAN NATURALIST [Vor. LVI

has been to preserve the black in the hackles, wings and

tails and to heighten the contrast with the white body

by selecting against grayness or mealiness in the body

feathers. Two principal processes were apparently in-

volved in the production of buff and Columbian vari-

eties; a discontinuous change or, mutation producing the

chief difference, and the accumulation by selection of

minor factors producing the minor changes. It is im-

possible to say whether the buff and Columbian varieties

which exist at the present time in the principal breeds

were derived from these original types by crossing or

whether the principal mutation and the minor changes

and selection have recurred in the different breeds. The

probabilities are in favor of the first alternative.

SuMMARY

1. The Columbian plumage coloration in domestic fowls.

is distinguished from buff coloration by the presence of

a gene S which determines the restriction or inhibition

of buff pigments from the feathers. This gene is sex-

linked, and dominant over its allelomorph s, which per-

mits the development of buff pigment.

2. Fowls with the Columbian coloration do not differ

from buff fowls in any single gene governing the develop-

ment of black pigment. Multiple genes appear to de-

termine the difference in the amount of black pigment

developed.

3. Columbian and buff fowls are genetically alike in

plumage pattern, that is, in the ability to develop black

pigment in the feathers of certain areas (hackle, wing

and tail feathers).

4. The buff coloration appears to have diverged from

the Columbian coloration, or the reverse, by a single gene

mutation affecting the development or inhibition of buff

pigment; and by the accumulation through artificial se-

lection of multiple genes for the development of black

pigment in the Columbian varieties of fowls, and by the

reverse selection in most buff varieties.

No. 644] INHERITANCE OF PLUMAGE COLOR 255

BIBLIOGRAPHY

Baur, E.

1914. Einfuhrung in der experimentelle Vererbungslehre— Berlin,

ea E. B.

1912. ag Exp. Zool. Vol. 13, pp. 1-18.

Hagedoorn, A

1909. utei by Davenport, 1912.

Hagedoorn, A

1914 E data quoted by Baur 1914, pp. 202-3,

Haldane, J. B. S.

1921. Science, N. S., LIV, p. 663.

1914. The Campine Club, 1914, Year Book. Quoted by Morgan.

1921. Utility Powtry Jour. Vol. VI, No. 4

Lefevre,

- 1916. Anat. Rec, XI, p. 499.

Morgan, T

1919. pee Inst. of Washington, Pub. No. 285.

Punnett, R. C.

1919. Mendelism, London, pp. 83-87.

Sturtevant, A. H.

1912. Jour. Exp. Zool., Vol. 12, pp. 499—518.

Robinson, J. H.

1921. Fundamentals n Poultry mim laee Poultry Journal

Pub. ney, Il en pp. (Contains fine ph

rh ‘end color plates o fst pe. feather patterns,

ete.)

Tegetmeier, W. B.

1872. The decani Book, London, p. 57.

Weir, Johnson and Bro

1912. The Poultry I Book, New York, pp. 527-528.

FURTHER NOTES ON THE PALEONTOLOGY OF

ARRESTED EVOLUTION

DR. RUDOLF RUEDEMANN

State Museum, ÁrBANY, N. Y.

Tue writer has in a former paper! endeavored to fol-

low up the eauses of persistence as seen from the side

of the paleontologist. Using as a basis the genera which

appear in Zittel-Eastman's Textbook of Paleontology

(1913) and defining as persistent all genera which pass

through more than two periods, the following data rela-

tive to number of persistent genera (4), total number

of genera cited (B), and percentage of persistent genera

A B C

Forsuabuerh.. 20.1. 1.525.705 8L 48 86 56

po TE E c uu do O 149 6

do e deu Ea a aN 46 294 15

aries e

POON g il a PISA 5 277 2

CVNKDERIERE. ee a 0 96 0

Pup ett] WEM ee a e 1 23 4

Diumuden -orea re ea eI 0 25 0

AStATONIGR ae es 5 43 11

BebinoHon o I ose s 19 191 10

ON CI CLIE Uc Tus 68 306 22

BracbioDodB.... e ee eva cvs 33 384 9

Mollusca:

Peleeypoda... vise rein 78 446 16

isst Bx A CNN REUS V E MEE 5 27

M SUES ee las E ees 126 420 30

Jiu ‘oad i ee ee 5 1 29

Pulsonifa. . 1 3 a ss 7 65 11

Are veu (a) punt 7 b cti 12 170 7

) Ammonoidea...... 0 455 0

cea

TUODA C UR D IUE M TE 131 4.5

a ert ike ea S 18 68 26.5

hive Cae he eee ee IS 4 20

Fei tri Linc Se I PUERILIS. 7 134 4.5

Arachnida... os a Ren 3 66 4.5

DHS OQ A ose eEE 16 168 9.5 (in

first edition)

1R. Ruedemann, ‘‘The Paleontology of Arrested Evolution.’’ Presi-

dential Address. Albany, 1916. New York State Museum Bull. 196, 1918,

pp. 107-138,

256

No. 644] ARRESTED EVOLUTION 204

Dipnoi, Teleostei, Reptilia each have one in the 1896

edition of Zittel-Eastman. The vertebrate volume had

not yet appeared of the second edition.

From an analysis of the percentages we drew the fol-

lowing inferences:

l. The lower classes tend in general to have more per-

sistent types than the higher.

|. 2. Within each order and class, again, the lower sub-

classes tend to furnish the greater percentage of per-

sistent forms.

3. Frequently the persistent genera form a primitive

central stock from which numerous shorter lived genera

branch off.

. 4. The stable conditions of the open ocean and deep

sea (as in the Foraminifera) and the subterranean con-

ditions favor persistence of types, the latter condition

including the burying and boring forms.

9. Sessile forms eontain more persistent types than

the vagile benthos.

6. Persistent types prevail in much greater number

among the marine forms than among the land and fresh-

water animals. Among the eontinental forms again the

limnal and fluviatile forms appear to be more persistent

than the terrestrial forms.

7. Most persistent types are small and inconspicuous

forms.

8. Many persistent genera show a slow development,

a distinct climacteric period and a long post-climacteric

period. Connected with this observation is the other

that persistent genera which slowly develop never pro-

duce many species during a single geologic period.

9. Minor factors of persistence are seen in (a) extreme

individual vitality (as in Lingula and Crania), (b) im-

mense broods (as in Ostrea and Limulus), (c) extreme

restrietion in the matter of food, as in the eaters of

carrion and refuse (Capulid:m, oyster, ete.).

The same criteria were found to hold, on the whole,

in regard to the persistent species and the higher groups

258 THE AMERICAN NATURALIST [Vor. LVI

(families and orders). In the latter case superior sets

of offensive arms and defensive armors, early developed,

appear to have helped to give stability to some, as in the

seorpions (pineers and poison glands), limulids (leathery

armor combined with burrowing habit and enormous

broods). Some, as the turtles, have successfully special-

ized for protection.

In trying to reduce the multiplicity of factors to a few

controlling agents, it was found '' that these are the fixa-

tion of the ‘ over-taken’ and post-climaeterie types, the

presence of stable physical conditions, and withdrawal in

various ways from the fields where the struggle for ex-

istence is fiercest. The stable physical conditions have

been found by many in the open ocean, by some in the

deeper littoral regions of the oceans, by others again in

subterranean fields, by some in the rivers and lakes of

continental regions that remained undisturbed by fold-

ing. Withdrawal from the struggle for existence with

other organisms has been accomplished by a variety of

means, as by isolation, burrowing life, small, inconspicu-

ous size, superior, often deadly, offensive and strong

defensive arms, through restriction to poor fare, great

power of endurance, ete.”

In an analysis of the biologic factors that have per-

mitted persistence, two entirely different groups of per-

sistent types must be distinguished: (1) The post-cli-

maeterie types; (2) the primitive central stocks. The

former rely on stable physical conditions and withdrawal

from the arena of the struggle for existence, as far as

possible; while the latter are frequently dominant in the

very seats of war. We have termed the first persistent

terminals, the others persistent radicles.

The persistent terminals were considered to have be-

come so fixed in all their characters as to make them

persistent partly by the factors of progressive fixation

and partly by the fact that they have in various ways

avoided the opposing factor of natural selection; their

conservation thus being in fact due in part to their ge-

No. 644] ARRESTED EVOLUTION 250

rontie condition and in part to the peacefulness of their

surroundings.

The persistent radieles, on the other hand, were thought

to owe their persistence to the fact that through their

primitive nature they are still adapted to a greater vari-

ety of conditions and that while there may be consider-

able variation, it is around a still unspecialized, primi-

tive form and thus diffieult of recognition.

Or, expressing the same difference in terms of the

four processes of heredity, ontogeny, environment and

selection, around which, according to Osborn, the life and

evolution of organisms continuously center, we found that

* the difference between the two groups of persistent

types, the relatively rigid terminals and the more vari-

able radicles, consists in the fact that in the former all

factors have become fixed and unresponsive to stimuli,

only the selection still slowly acting, while the latter are

so well adapted to a variety of conditions that no changes

readily originate through any of the processes of envi-

ronment, ontogeny and selection, which affect the whole

stock, while at the same time no changes in the germ

plasm are induced through hereditary tendencies."'

The following notes are written with the intention

partly to add certain new factors that appear to con-

tribute to the persistence of forms, and that had not been

taken into account in the first essay; and partly to enter

deeper into the analysis of the ultimate causes of per-

sistence made possible through more recent investiga-

tions into the nature of phylogenesis. ©

1. ADDITIONAL FACTORS or PERSISTENCE

The new factors here mentioned have all to do with

the methods of reproduetion whose influence had not

been recognized, in the first paper, in the percentage

table of persistent genera.

(a) Reproduction by Simple Division.—In the Proto-

zoa reproduction takes place by division without any

260 THE AMERICAN NATURALIST [Vor. LVI

loss, so that there is no distinction between parent and

offspring. There is no death and thus it is that Weis-

mann and others have spoken of the ** immortality of the

Protozoa." It is certainly significant, in this connection,

that among the Foraminifera 56 per cent. of the genera

were found to be persistent and many were found to

exhibit tremendous persistence, ranging from the Ordo-

vician, Silurian, Carboniferous and Triassic to recent

times, and that even species (see Ruedemann, op. cit.

p. 126) are known to extend from Silurian, Devonian,

Carboniferous and Triassic times to the present. These

forms the writer designated as actual ‘‘ immortal types ”’

in contrast to the theoretically immortal protozoans of

Weismann.

There occurs, however, among the protozoans besides

this asexual mode of reproduction a group of processes

that are clearly the primitive beginnings of fertilization.

In these forms of conjugation different stages may be dis-

tinguished, viz., the mere congregation of cells in groups

without visible exchange of plasms (cytotropy); the ex-

change of substance taking place only through osmotic

processes; further conjugation, where real fusion of

plasmas occurs but the cell-nuclei remain separate (plas-

togamy); and finally such modes of conjugation, where

also nuclear fusion of the conjugating cells takes place

(karyogamy); and here again, the pairing cells may be

either similar in size (isogamy), or even markedly dis-

similar in size (anisogamy).

It is, however, to be remembered that the usual re-

productive process among protozoans is simple fusion

of ordinary vegetative cells and conjugation as a rule

occurs at rare intervals in most forms, often only when

unfavorable conditions arise, or as Maupas’ experiments

indicate, the individuals in the course of numerous suc-

cessive asexual generations grow old.

(b) Reproduction by Budding.—This mode of asexual

reproduction differs from that of division originally in the

protozoans merely in the different sizes of the daughter-

No. 644] ARRESTED EVOLUTION 261

cells and the mother-cell, but develops into a complex pro-

cess in the multicellular forms. Distinct budding occurs

already in the protozoans as in Arcella, where a number

of small buds are constricted off all round. In sponges

it is developed to such a degree that no one can fail to

recognize the impossibility of drawing any rigid line be-

tween growth and asexual reproduction.? In the celen-

terates asexual reproduction runs riot, as Geddes and

Thompson state. It is, further, by far the prevailing

mode of reproduction among the stock-building bryozo-

ans; it also is common among marine worms, as with

the famous palolo-worm off the coast of Samoa, and fi-

nally it is also frequently found among the tunicates.

The primitive character of this mode of reproduction

ean not be doubted. It probably in all cases is an in-

herited character that persisted from the ancestral pro-

tozoans. It has by many zoologists been considered as

an acquired character among the tunicates, but Van

Name? has lately advanced good reasons for the conclu-

sion that it is also a primitive character among the as-

cidians inherited from their remotest ancestors and that

it is not a faculty that can be acquired secondarily.

Budding leads to the formation of colonies or stocks.

These as a rule are not favorable to a swimming or va-

grant mode of life, hence by far the majority of budding

forms are sessile, although there are a considerable num-

ber of exceptions in the swimming siphonophores, cteno-

phores, floating graptolites, and compound swimming

worms and ascidians. Since most of the colonial stocks

are sessile, budding has often been considered as having

been induced by a sessile mode of life and thus held to

be a function that could be acquired. Its absence among

the sessile cirripedes seems, however, to support Van

2 Geddes, Patrick, and Thompson, J. Arthur, ‘‘The Evolution of Sex,’’

London and New York, 1914, p. 205.

3 Van Name, Willard G., ‘‘Budding in Compound Aseidians and other

Invertebrates, and its bearing on the Question of the Early Ancestry of

the Vertebrates,’’ Bull. Amer. Mus. Nat. Hist., Vol, 44, art. 15, 1921, pp.

275—982.

262 THE AMERICAN NATURALIST [Vor. LVI

Name's contention that this function ean not be acquired

when once lost.

The faet that the sessile forms contain more persistent

types (corals have 15 per cent., bryozoans 22 per cent.)

than the vagile benthos would suggest that budding may

be a mode of asexual reproduction favorable to the per-

sistenee of types; and that it may be the cause of the

large percentage of persistent types among the sessile

forms. It must here, however, be considered that also

the sessile Cirripedia which lack the function of bud-

ding, have furnished 20 per cent. of persistent types;

and further that in all the classes here considered bud-

ding is associated with sexual reproduction, often, as in

many celenterates, in a regular alternation of genera-

tions. Moreover, the sexually reproducing brachiopods,

gastropods and pelecypods have furnished large percen-

tages of persistent types, a large number of which are

sessile forms.

While thus budding would not seem to be the control-

ling factor in the persistence of the sessile forms, it is,

nevertheless, true that budding may have a distinctly

retarding effect upon the evolution of such forms, prin-

cipally by the material decrease of the cases of sexual

reproduction. As in the ease of the corals, the number of

new stocks that originate from sexual reproduction and

finding a new lodging place, start new colonies, is very

small when compared with the number of asexually pro-

duced individuals on the stocks. There are therefore

many more generations of asexually than sexually pro-

duced individuals.

that possibly may have contributed to the persistence of

forms is hermaphroditism. Claus has pointed out that

hermaphroditism finds most abundant expression in slug-

gish and fixed animals. ‘‘ Among sponges, sea-anemones,

corals, Polyzoa, bivalves, etc., we find frequent illustra-

tion of the association of fixedness and hermaphroditism "'

(Geddes and Thompson, op. cit., p. 83). The origin of

No. 644] ARRESTED EVOLUTION 263

hermaphroditism is still a matter of dispute (see Geddes

and Thompson, pp. 83, 84) for while some, as Simon,

attribute it to a plethora of nutrition (as especially in

parasites), others are ‘‘ content to interpret it as an adap-

tation to ensure fertilization, for the possibilities of pair-

ing between separate sexes are certainly lessened if the

animals are sluggish, sedentary or parasitic." There is

likewise difference of opinion as to whether the stage

of hermaphroditism is the lower, and the condition of

distinct sexes has been derived from it (Gegenbaur),

or whether it is a secondary condition, derived from

primitive uni-sexuality as claimed by Pelseneer who con-

siders it grafted on the female sex in Mollusca, Crustacea

and Pisces (Geddes and Thompson, p. 84).

Considering its prevalence. among the lowest classes

with sexual reproduction, notably the sponges and corals,

and again among the Cirripedia, we believe that herma-

phroditism is in the former an inherited primitive char-

acter and in the latter an acquired one. At any rate,

since it is so frequently and distinctly associated with

sessility, as in the just mentioned Cirripedia, and in

many pelecypods (oyster) and with sluggishness in other

pelecypods and many gastropods, and since it is exactly

these same groups which contain numerous persistent

types, it seems probable that hermaphroditism is a fur-

ther reproductive condition contributory to persistence.

(d) Reproduction by Parthenogenesis.—Parthenogene-

sis is the mode of propagation in at least one typically

persistent genus, viz., Apus; but it has also become a

confirmed physiological habit in other archaic types of

crustaceans among the branchiopods, as notably in Ar-

temia, the brine-shrimp, in Branchipus, and in Limna-

dia; further in the equally primitive water-fleas (Daphnia

and Moina) and finally, among the ancient ostracods,

also in some species of the common Cypris.

Of the whole class of Branchiopoda, which through

paleontology, and notably through the recent amazing

264 THE AMERICAN NATURALIST [Vor. LVI

diseoveries of Waleott* in the Middle Cambrian of British

Columbia, are proven to reach back to the oldest fossili-

ferous beds (in Protocaris marshi Walcott to the Lower

Cambrian), Apus is the most remarkable and most often

cited form in paleontologie literature. The writer has

in a paper, now in press, shown that true Apus, identical

in form of carapace and ‘‘ shell glands has been found

in Permian beds of Oklahoma. It was before known from

the Triassie Buntsandstein of the Vogesian Mountains.

Its more than 70 pairs of gill-bearing feet and other-

primitive characters have made it the model of compar-

ison for Paleozoic crustaceans, especially the trilobites.

The Lower Cambrian Protocaris marshi is so closely

allied to Apus that it was termed Apus marshi by Ber-

nard. There is hence no doubt of the immense age of

this type.

Apus is now so parthenogenetical in its reproduction

that the males were not discovered until a hundred years

after the description of the first and best known species

(A. cancriformis Schäffer) ; and ** von Siebold repeatedly

investigated every member of a colony of Apus, once

over 5,000 in number, without finding a single male. At

other times he found one per cent. while in certain un-

known conditions (probably when food is scarce and life

generally unfavorable) the males may be developed in

crowds ’’ (Geddes and Thompson, p.189). Similar condi-

tions prevail in the brine-shrimp and the other branchio-

pods, cited above, as shown by Lereboullet and Nowikoff.

Parthenogenesis is associated with other strange habits

in the three branchiopods, Apus cancriformis, Limnadia

hermanni, and Branchipus stagnalis, which occur together

in Europe. These creatures occur only after very wet

seasons in puddles, road-ditches and other small pools,

where their eggs have lain for decades in the dry mud,

exposed to heat and frost. They develop with amazing

4 Walcott, Charles D., ‘‘ Middle Cambrian Branchiopoda, Malacostraca,

Trilobita, and Merostomata,’’ Smithsonian Miscellaneous Collections, Vol.

57, No. 6, 1912.

No. 644] ARRESTED EVOLUTION 265

rapidity, 4pus cancriformis reaching in two weeks a full

size up to five inches,? produce an enormous number of

eggs and die.

The origin of parthenogenesis in these forms as well

as in the rotifers and certain insects has been fully dis-

cussed by Geddes and Thompson, and they are certain

that it has originated as a degeneration from the ordi-

nary sexual process (ibid, p. 198) and is no direct

persistence of a primitive ideal state. "Their theory of

parthenogenesis is that the ova that develop partheno-

genetically ‘‘ are to be regarded as incompletely differenti-

ated female cells, which retain a measure of katabolic

(relatively male) products, and thus do not need fertil-

ization ’’ (they form only one polar body). ‘‘ Such a

successful balance between anabolism and katabolism is

indeed the ideal of all organic life. In parasitic fungi,

sexual reproduction disappears, and surrounding waste

products presumably help the purpose otherwise effected

by sexual organs, so peculiarities in the conditions of

parthenogenetic ova may explain the retention of the

normal balance which makes division possible without the

usual stimulus of fertilization. Abundant and at the same

time stimulating nutrition (Rolph), early differentiation

of the sex-cells (Simon), the general preponderance of

reproductive over vegetative constitution (Hensen), their

liberation before the anabolic bias has carried them too

far, are among these favoring conditions."

Parthenogenesis thus appears as a degenerative asex-

ual process arising from peculiar conditions, the most

important of which appears to be temporary over-nutri-

tion. As in the other asexual modes of propagation,

in division and budding, the inference suggests itself

readily that this suppression of fertilization must induce

persistence, for as Geddes and Thompson point out (ibid.,

p. 193) the establishment of parthenogenesis and the ab-

5See Bruno Weigand, ‘‘Mitteilung über das Auftreten der Limnadia

Hermanni Ad. Brgt. bei Strassburg im September 1912,’’ Mitt. der Philo-

mat. Gesellsch. in Elsass-Lothringen, Bd. 4, Heft. 5, Jahrgang 1912; 1913,

p. 730.

266 THE AMERICAN NATURALIST [Vor. LVI

sence of fertilization probably involves some diminution

in the frequeney and range of variability and thus the

establishment of parthenogenesis will be a handicap to

evolution.

In the case of Apus, and its other associated branchio-

pods as well, it is probable that the successful adaptation

to special conditions is a strong contributing factor in .

the establishment of persistence, as pointed out by the

writer in the former paper.. It is possible that Apus has

existed under these conditions from very early times.

Summing up the evidence on persistence of types from

the habits of reproduction, it seems that simple division,

budding, hermaphroditism and parthenogenesis have each

contributed to this persistence and in their way acted

as factors that arrested evolution, and that thus help to

explain the relatively large percentage of persistent types

in the protozoans, sponges, corals, molluscs and the just

mentioned branchiopods among the crustaceans.

While the facts thus seem to indicate that these modes

of reproduction, other than the normal process of fer-

tilization, were favorable to persistence in fossil types,

it is, in the present stage of our knowledge of the mean-

ing of fertilization, not so simple to recognize the under-

lying cause of their arresting influence on evolution.

The simplest explanation would obviously be to see

in fertilization the principal cause of variation, as such

authors as Treviranus, Brooks, Galton, Weismann and

Oscar Hertwig have done. Weismann has insisted that

the intermingling of two ‘‘ germ-plasms "' is an impor-

tant fountain of congenital variation. It ean be readily

seen that, under this view, the retarding effect of fission,

budding and parthenogenesis consists in the exclusion,

or restrietion to long intervals, of fertilization, thereby

redueing variability and the possible action of selection.

It is also plausible under this view that mutual fertiliza-

tion between hermaphroditie individuals tends toward

equalization of characters; and this tendency towards

equalization is still more increased by fertilization within

No. 644] ARRESTED EVOLUTION 267

the same colonial stock or neighboring colonial stocks of

plantations. The most important of the disadvantages

resulting from hermaphroditism would then be to reduce

the variability which is necessary to progress in the

struggle for existence.

While, however, the possibility is not denied that fer-

. tfilization may be a controlling factor in variation, as

stated, e.g., by William E. Kellieott in his ‘‘ Text-book

of General Embryology,’’ 1913, p. 216, it is also obvious,

according to the same author, that the evidence for this

view is still seanty and uncertain and, moreover, there :

are two exactly opposed views as to the nature of the

relation. While Hertwig maintains that the effect of

fertilization is to limit variation within a species, Weis-

mann asserts that the effect of syngamy or ‘‘ amphi-

mixis "' is to cause or promote variation.

Kellieott (op. cit., p. 214) states:

There is little direct factual evidence for or against these views,

either one of which can be maintained upon theoretieal grounds.

In a few cases it is known that the amount of variability is not

significantly different among sexually (gametically) or asexually

(parthenogenetically) produced individuals of the same species.

from the standpoint of more recent studies upon heredity and varia-

tion the evidence is chiefly either negative or opposed to the idea

that this relation constitutes an important element in the origin or

present function of fertilization. The present aspects of this reld-

tion between fertilization and variation merge in the larger question

of the relations with heredity.

While among the higher classes fertilization has be-

come a stimulus to reproduction and a means of heredity,

evidence from the lower groups tends to show that fer-

tilization in its results has undergone evolution like every

other organic function.

The view is widely accepted today (see Kellicott, p.

209) that among the Protozoa the processes of reproduc-

tion and fertilization are not fundamentally related, and

the primary significance of fertilization must be sought

in some other direction.

The observations made on protozoans have led to the

268 THE AMERICAN NATURALIST [Vor. LVI

rejuvenation hypothesis, chiefly represented by Biitschli,

Maupas and Richard Hertwig. ‘‘ It has been found that

protoplasmic activity tends gradually to diminish in in-

tensity, and that associated with this diminution are

certain morphologieal alterations in the structure and

composition of the cell ’’ (Kellieott, p. 209). These modi-

fications are known as senescence, the senescent condi-

tion of the cell eonsisting frequently in the relatively

large proportion of cytoplasm as compared with nuclear

substanee. Conjugation is assumed to restore the senes-

cent protoplasm to its original condition of vigor, bring-

ing about rejuvenation. It follows from this that pro-

toplasmie activity is cyclic and that periods of senescence

would lead to death unless fertilization should occur.

The real evidence for this cyclic character of the life

processes of the Protozoans has been furnished by the

observations of Maupas and Calkins on Paramecium.

But observations of Jennings have shown that in differ-

ent forms of Paramecium conjugation and rejuvenation

may occur at very different intervals, and Woodruff has

been able to prevent cyclic relations by substituting nor-

mal conditions for the artificial and more uniform ones

of the laboratory. ‘‘ By continually altering the char-

acter of the food, and by imitating in other ways the

naturally variable conditions of pond life, he has been

able to continue a single race of Paramecium for over

five years ” (quoting from Kellicott), during which peri-

od more than 3,000 generations were formed by simple

fission. It follows from these observations that proto-

plasmie aetivity among the Ciliata may not be cyclie in

character under certain conditions, and that when cyclic

periods of depression or senescence do occur, the proto-

plasm may be restored to a condition of normal vigor.

either by physieal or chemieal stimuli, or by fertilization

(Kellieott, p. 212).

Fertilization is in these cases a form of reaction that

takes place when external conditions become too uniform

to bring forth the normal vegetative activities, and that

No. 644] ARRESTED EVOLUTION 269

leads to an internal disturbanee, thereby correcting the

eonditions of uniformity.

Applying these conclusions to our case of the persis-

tent types it could be conceived that the reduction of fer-

tilization to rare intervals, or its entire suppression, in

the numerous persistent types that reproduce by fission,

budding, parthenogenesis or hermaphroditism, produces

a perpetual senescent condition that while not leading

to death as in the rapidly dividing and sensitive Para-

mecium, finds its expression in the rigidity of the forms,

recognizable in their lack of response to external stimuli

and of further evolution, i.e., in their persistence. Or in

other words, infrequency or entire lack of rejuvenation

through fertilization favors the persistent condition, at

least among those persistent terminals that do not live

under stable physical conditions. Those living under

stable conditions may require fertilization as a necessary

rejuvenating process counteracting progressive senes-

cence and final extinction through lack of external stimu-

li. It would then appear that these lower modes of re-

production and very stable external conditions could not

very well exist together.

However, as pointed out by Kellicott, there has been

an evolution both of the process and of the consequences

of fertilization, and the various possibilities as to the

significance of fertilization are not mutually exclusive.

It is therefore possible that the large percentage of per-

sistent types among forms with more or less suppressed

fertilization finds its explanation in some cases in the

resulting lack of variation, in others in the resulting

senescent and rigid condition of the race, and in still

others it may be sought in the process of heredity, con-

nected with fertilization. This last possibility will be

dealt with in the following chapter.

REDUCTION or Factors To FUNDAMENTAL CAUSES

The investigation of the various groups of persistent

types has indicated that there are a variety of factors

270 THE AMERICAN NATURALIST [Von LVI

involved in their produetion. Many of these were found

to be connected with the environment, others, acting

through variability, or its lack, with selection, and still

others with the processes of heredity and ontogeny.

While of these four fundamental processes of evolution,

viz., heredity, ontogeny, environment and selection, that

of selection may account for the cases of persistence

where variability has been reduced to a minimum, possi-

bly by the lower modes of propagation mentioned above,

and that of environment accounts for persistence in those

cases where the environment has become so stable as to

lack the aetual stimulus for further development, it is

obvious that still more important factors are involved

in heredity and ontogeny that make for persistence in

organisms, especially as it is seen in the post-climaeterie

forms, or persistent terminals. Both the conservative

proeess of heredity and the much less rigid one of on-

togeny appear to become more or less fixed and inacces-

sible to changes in persistent types.

None of these four processes gives any clue to the

actual mechanics of the factors that induce persistence.

In trying to trace the latter to its ultimate causes, it be-

comes, therefore, necessary to go beyond these processes,

and to appeal to the important conclusions that have

been obtained by modern experimentation and observa-

tion regarding the methods of inheritance and production

of new characters by means of the genes or character-

determiners of the heredity-chromatin.

Among these conclusions especially suggestive in regard

to our problem, are the views advanced by Diirken and

Salfeld.5 These authors have, one through an analysis

of all recent zoological experiments on evolutionary prob-

lems, the other through a corresponding analysis of the

evolution among the fossil ammonites, arrived at the view

that variability or the appearance of new characters, and

of new combinations of characters is produced in differ-

6 Dürken, B., and Salfeld, H., ‘‘Die Phylogenese. Fragestellungen zu

ihrer exakten Erforschung,’’ Berlin, Gebr. Borntrüger. 1921.

No. 644] ARRESTED EVOLUTION A

ent ways, by the genes; and not only through internal

faetors, as claimed by the Neo-Darwinian school, but

also through external ones as demanded by the Neo-La-

marckians. The genes, which are not only actual units,

or representatives of definite phenotypic characters, but

definitely delimited, material bodies, may not only pro-

duce new characters or character-combinations by a cor-

relative and a combinative mode of ontogenetic evolution,

or by loss of genes, as demonstrated by abundant experi-

ments, but undoubtedly there takes place also a new for-

mation of genes in evolution. This they hold to come

about in successive stages through long enduring ex-

ternal influence, which first acts upon the cytoplasm of

the cells and especially of the germ-cells. This cyto-

plasm in itself has been proven to have certain hereditary

possibilities (plasmogenous heredity). Under long per-

sistent external influence there form first preliminary

stages of genes in the cytoplasm which finally, when a

certain ‘‘threshold’’ (Schwelle) of continued strain is

passed, become true genes of the heredity-chromatin.

When this takes place, mutations appear abruptly (salto-

mutations).

This view, here altogether too briefly presented, would

explain the absence of evolution through salto-mutations `

in cases of persistence under continued stable exterior

conditions, and since the cytoplasm is known also to in-

fluence directly the heredity-chromatin, also the absence

of flucto-mutations or variations under stable conditions

through lack of external stimulation.

However, in the cases where no new genes are formed

by external influences, new characters could still appear

through loss of genes or correlative or combinative modes

of production of new genes from the old ones within the

germ-plasm. This, however, leads to a restrictive cone

of divergence (‘‘ Streuung’’) of the characters and

through ‘‘ self-differentiation’’ by a combinative mode

of gene-production to the excessive characters of many

terminal series (e.g., dinosaurians); and to the rigid

Zia THE AMERICAN NATURALIST [Vor. LVI

persistent terminal types, on the other hand, through the

gerontic rigidity of the remaining stock of genes. The

principal causes of the persistence of terminal forms

would then be the failure of production of new genes

arising from the cytoplasm, through external influences,

and the senescent rigidity of the remaining genes.

The persistent radicles, on the other hand, correspond

to the extreme development of what Salfeld terms ‘‘ Kon-

servativreihen.’’ There are series in which the salto-

mutations appear in very long intervals, while the nu-

merous side-branches (which furnish the index-fossils)

develop by rapid salto-mutations. These persistent radi-

cles are therefore able to undergo new periods of explosive

and climacteric development (‘‘ Virenz-perioden " of

Wedekind) and are thus still less absolutely persistent

than the persistent terminals. In these conservative

series, according to Salfeld, flucto-mutation is so prevalent

that sharply defined ‘‘ species,’’ or better mutants, can

not be separated, as notably in the phyla of Phylloceras

and Lytoceras which range, qualitatively unchanged in

their characters, through Jurassic and Cretaceous time.

They thus represent true persistent radieles. "This fact,

combined with the observation of the vitality, relative

primitive simplicity and adaptation to a variety of condi-

tions of persistent radicles, pointed out by the writer in

his former paper, suggests that the complex of genes is

able to remain relatively undisturbed through external

influences (only flucto-mutations appearing) in one part

of these groups which persist as radicles, while those parts

which become changed through the addition of genes by

way of the cytoplasm turn into the side-branches by salto-

mutation.

EXPERIMENTAL STUDIES ON THE DURATION

OF LIFE

III. Tue EFFECT or SUCCESSIVE ETHERIZATIONS ON THE

DURATION oF LIFE or DROSOPHILA !

PROFESSOR RAYMOND PEARL AND SYLVIA L. PARKER

PurRPosE AND PLAN oF EXPERIMENTS

In any experimental work of a genetic character on

Drosophila, it is often necessary to anesthetize the flies

which are to be used in an experiment for a sufficiently

long time so that they may be sexed and sorted into dif-

ferent groups for the purpose of making matings, etc.

It has been shown by Morgan (33) that this procedure

has no effect upon the causation of morphological mu-

tations, the inheritance of which he has studied (9). The

effect might, however, conceivably be quite different in

the case of a physiological character like duration of life.

Any one who has undergone a major surgical operation

feels that anesthetization is at least immediately a rather

profound physiological disturbance. Unfortunately, so

far as we are aware, no accurate determinations have ever

been made to show whether in man one or more anes-

thetizations changes the expectation of life. As a mat-

ter of fact, there are presumably no human data on the

point available in any such amount as would be necessary

for actuarial determinations, because in man anestheti-

zation is, generally speaking, only undertaken in connec-

tion with surgical operations of greater or less severity,

so that if we did have statistics of expectation of life of

persons who had been anesthetized, there would always

be involved the two factors of anesthetization and oper-

1 Papers from the Department of Biometry and Vital Statistics, School

of Hygiene and Public Health, Johns Hopkins University, No. 54. For

description of the method of numbering bibliographic citations see the

second paper in the series (32).

273

274 THE AMERICAN NATURALIST [Vor. LVI

ation. In Drosophila these two factors can be separated.

It has seemed important, in an early stage of our ex-

perimental work on the duration of life in this form, to

make a careful and extensive experimental test of the

question of whether anesthetization singly or repeated

changed in any way the expectation of life or form of

the life curve, so that if this factor does have any sig-

nificant influence, either favorable or unfavorable, due

allowance may be made for it. It is the purpose of this

paper to report the results of such a test.

The flies used in this experiment were flies of line 107

(generation 8 since January 14, 1921, line bred from a

single brother and sister mating for approximately 30

generations). The characteristics of this line relative to

duration of life have already been described (cf. Pearl

and Parker (32)). The 4,330 flies used emerged between

10 a.m. April 18, 1921, and 4 p.m. April 22, 1921, from

thirty-five mass cultures started in half-pint milk bottles

April 7, 1921. The regular procedure in these experi-

ments was to collect the flies from all 35 breeding bottles

in one empty bottle and then to count the flies through

a counting tube into 1-ounce vials, allowing 50 flies to

each vial? Ten vials were used for each series, except

the control series, which had 18. For two of the series

only two hours were allowed between successive empty-

ings of the mating bottles, to get flies at an average age

of one hour, assuming that they emerged uniformly over

the interval. - One series was etherized as soon as counted

out, and the other series kept as a special control group

to see if the handling when the flies were so young and

soft had any effect on the duration of life. For the rest

of the series the flies ` were allowed to emerge over a 24-

hour interval. - Each day’ s hatch was divided randomly

and as equally as possible among the | different series.

Sg It will be noted that the totals shown in Table I do not accord exaetly

with this statement. The discrepancies are due to the fact that a few flies

were lost in ehanging to fresh bottles in the eourse of the life duration de-

terminations made aceording to the technique deseribed in (27), and oc-

easionally a bottle was broken by accident and all its contained flies lost.

No. 644] THE DURATION OF LIFE 275

The counting tube referred to above is a device in-

vented in this laboratory which we find extremely useful

in a great deal of the experimental work. It was devised

and first used in connection with studies of the growth

of experimental populations of Drosophila (cf. Pearl

(7), and Pearl and Kelly (34)). Its construction is shown

in Fig.

a STS

em li p

E A. eT ae

1. Diagram showing Vise arty of Boab at sng: counting tube. The.

aperture at a is just large enough to allow one fly to pass through at a time.

The essential dimensions are as iem length over all 25 cm., diameter of

main tube 2 cm., diameter of funnel mouth 6 c

When it is desired to eount a definite number of flies

the small aperture a is temporarily plugged with a bit

of cotton wool, the plunger P is removed from the tube

and flies are shaken into the counting tube by inverting

the open bottle containing them over the funnel mouth

of the counting tube. Then the plunger is inserted and

gently moved forward to concentrate the flies in the

lower end of the counting tube. Then the counting tube

with enough cotton around it to close up the mouth of

the bottle is inserted into the bottle into which it is de-

sired to place the counted flies and the plug removed

from the aperture a. Then as the flies come out of the

tube, one by one, through the aperture a, they are counted

as they pass this point, with the aid of a tally register,

such as is used by doorkeepers at theaters, ete. The plun-

ger is gently moved forward as necessary to keep up an

even flow of flies through the mouth of the tube.

The ether dose used was constant for all the flies

throughout the experiment. The group to be etherized

was shaken into a clean half pint milk bottle; 5 c.c. of

ether was poured onto a piece of absorbent cotton fas-.

tened to the under side of a cork stopper; the bottle with

276 THE AMERICAN NATURALIST [Vor. LVI

the flies was stoppered tightly with the cork and left for

two minutes. Then the flies were turned out on a tile

and sexed and counted (since that operation corresponds

in extent of handling to what we need to do in making

up matings, éte.), then emptied into a vial with fresh

food, where they recovered from the ether in about half

an hour. For each successive group of flies a fresh bottle

and fresh cotton for the ether were of course used.

In all other, here unspecified, particulars the technique

used in these ether experiments was uniformly that de-

scribed in detail in the first paper of this series (27).

Seven series of experiments were conducted, differing

in respect of the number of times the flies were etherized,

and in their age at the time of etherization. The seven

series were as follows:

Etherized once when one hour of age.

Etherized once when twelve hours of age.

Etherized once when thirty-six hours of age.

Etherized once when three and a half days of age.

Etherized twice when seven, and fourteen days of age, respectively.

Etherized three times when seven, fourteen, and twenty-one days of

age, respectively.

Etherized four times when seven, fourteen, twenty-one and twenty-

eight days of age, respectively.

$ SSSAeh

Data

The l- lines for the several series of etherized flies and

the controls are given in Table I. These l» distributions

are calculated on the basis of 1,000 flies at emergence .

from the pupal stage, with the absolute number of flies

on which the distribution is based given at the bottom

of the column in each case.

The l» distributions for all etherized flies and for their

eontrols in the ether experiment, and for two tests of

the flies in line 101 and its continuation 107, are shown

graphically in Fig. 2. The data for the survivorship

lines in the two tests of line 107 are to be found in Pearl

and Parker (27).

No. 644] THE DURATION OF LIFE 277

TABLE I

SURVIVAL DISTRIBUTION OF ETHERIZED AND NON-ETHERIZED

DROSOPHILA CULTURES

| Etherized Series

Age | l | | Con- | Con-

in | | | | | All | Con- | trols | trols

Days A|/B|c|npn|z|£*| Gd | ma] usn Hare

| | | | ‘eed Old | Old

| | | | eriz

)-8 1,000 1,000 1,000, 1,000 1,000 1,000 1,000 1,000 1,000 1,000 1,000

7-12 988} 998| 988| 998 993| 990| 995| 993]

13-18 986 993| 978| 995| 984 995 988 980 987 976

19-24 984) 971 978 984! 971| 971! 964| 975| 974| 981| 970

25-30 970| 953| 966 957 918 910 949| 925 918 928

31-36 942|) 916| 912) 942 4| 910 857 918| 903 |

37-42 902| 880 926 901 879 810 880 843.

43-48 778| 792| 7 793| 763| 698, 771| 735| 753| 724

54 629| 634| 732| 725| 643| 598| 605| 652| 604| 701 550

55-60 453, 492| 625, 581| 465 4 476! 50 | 8

61-66 117| 95} 397| 301| 153| 249| 145| 183| 150| 138| 157

67-72 47} 34| 136| 116 9| 165 71

73-78 2 22, 65} 17| 27| 15| 19 13

0 0 0 | 0 0 0 0 0:

Absolute

number of

flies....] 428] 443 411) 432 445) 413) 420 2,992/ 1,338) 478 860»

It is at once evident, from an examination of the fig-

ures in Table I, and the diagram, that there was no con-

siderable difference in duration of life, or in the form

of the life curve, for the etherized flies taken as a class,

and the non-etherized groups. It is, however, desirable

to examine the results of the experiments in detail in

order to see whether there are detectable by biometrie

methods any small but still statistically signifieant dif-

ferences between the several groups. To this end, Table

II has been prepared, giving the usual biometrie constants

for the several series.

Comparing first the entire etherized group as a whole

with those which never had any ether at all in their lives,

it is seen that the mean duration of life (expectation of

life at emergence from pupa) is 1.82-+.30 days longer

in the former (etherized) than in the latter (normal)

group. The difference is thus slightly more than 6 times

278 THE AMERICAN NATURALIST [Vor. LVI

1000)

M \—_—07

ALL CONTROLS —>\ CN

. E. ALL ETHERIZEi ;

Joop

n c Ren

SGE

a s I

Cc "

sio bcd ck cbr PL

|) 4*7. H WM M AR 5 AI 44 5 67 73 79 8 9

DAYS O FLY LIFE

The 7, lines for all etherized and ccntrolled flies, plotted from the

Pik y^ ones 3

TABLE II

BIOMETRIC CONSTANTS FOR DURATION OF LIFE OF ETHERIZED AND

NorMAL DROSOPHILA

Num- |

Treatment ber Mean Standard | Coefficient

of (in days) | Deviation [n

Fli (in days) | Variation

cp V. ck PRIVAT C E EVA 2,992 |51.60 = .16 13.30 = .12125.77 = .24

All e Pepe ce Late Wd DEL ET CQ 1,338 |49.78 = .25/13.68 + .18/27.47 + .38

Etherized- V ON is zu 428 (50.82 + :38 11.76 æ .27'23.14

Etherized when 12 hours old......... 443 (50.20 = .39 12.25 + .28/24.41 = .59

Etherized when 36 hours old......... 411 |53.36 = 46 13.91 + .33/26.06 = .65

Etherized when 314 days old......... 43 a .36 = .28/22.68 = .55

Etherized when 7 and 14 days old 44 s .50 = .28/24.31 = .58

Etherized when 7, 14, and 21 days old. 413 .72 = .50|15.01 = .35|29.03 = .74

seer ot when 7, 14, 2L and 28 days

Pel. $20. CLE TE TERI ER MI 420 |49.26 + .47]14.42 + .34/29.26 + .74

Coe rols — out of mating bottles

i ag Oi ae A 478 |51.11 + .42/13.75 = .30|20.90 = .63

Controls Pw out of mating bottles

»whmi 12 bows 0D iiss oy Osa 860 |49.04 + .31/13.58 = .22/27.69 + .48

No. 644] THE DURATION OF LIFE 279

its probable error, and must therefore be regarded as

statistically significant. Absolutely, however, the differ-

ence is small. It is equivalent to only 3.7 per cent. in-

crease of the expectation of life of the controls. In va-

riability in respect of duration of life there is plainly

no significant difference between etherized and control

groups.

It is not entirely clear that the small difference be-

tween the etherized and control groups in mean duration

of life can be regarded as due to the influence of the

ether. An examination of the last two lines of Table II

shows that an entirely similar difference in the means

appears between the two control groups, which differ

only in respect of the time when they were taken from

the mating bottles, and without either having been ether-

ized. The difference in these two means amounts to

2.07 + .52 days, a statistically significant and absolutely

slightly larger difference than that between etherized

and control groups. Again there is no significant differ-

ence in variability in the two groups.

Altogether we shall be justified in concluding that there

is no evidence from these experiments that the occasional

etherization of Drosophila to the extent necessary in sex-

ing and making matings alters the expectation of life

by an amount large enough to introduce any sensible

source of error into experiments on the duration of life

in this form, except possibly where the most careful and

accurate actuarial determinations need to be made. Then

it will be well to have this possible source of error in mind

and to plan the experiments in such way as to check it.

Examining the results for the different etherized series

it is seen that the highest mean duration of life appears

in the group etherized once at 34 days of age, and next

to this stands the group etherized once at 14 days of

age. Both of these give relatively high mean values.

There also appears a definite, though not particularly

marked tendency for the variability in duration of life

to be greater in the groups which were etherized several

280 THE AMERICAN NATURALIST [Vor. LVI

times. No great importanee is probably to be attached

to these differences between the several groups, however,

though some of them appear significant statistically.

CONCLUSION

From the experiments herein described, involving the

determination of the total duration of life in 4,330 indi-

vidual flies, it may be safely concluded that no sensible

error will be introduced into duration of life experiments

on Drosophila as a result of completely anesthetizing the

flies with ether, at least up to as many as four times in

the course of their lives.

LITERATURE CITED

32. Pearl, ea and Parker, S. L. Experimental Studies on the Duration

of Life II. Hereditary Differences in Duration of Life of Line-

bred p een of Drosophila. AMERICAN NATURALIST, Vol. 56, pp.

174-187, 1922.

33. Morgen, T. H. The Failure of Ether to Produee Mutations in Dro-

sop AMERICAN NATURALIST, Vol. 48, pp. 70 , 1914.

34. ipis R. and K ae Y . C.. Forecasting the Growth of atis. The

Future Population of the World and its Problems. Harper's Mag.,

Vol. gv pp. 704—713, 1921.

SHORTER ARTICLES AND DISCUSSION

A TEACHING NOTE ON THE ARRANGEMENT OF THE

TUBE-FEET IN ASTERIAS

SEVERAL summers ago while direeting the laboratory work on

Echinodermata in the Invertebrate Course at Woods Hole, a

question was raised by one of the students as to the correctness

of the account which had been given of the arrangement of

the tube-feet in the common starfish, Asterias forbesi Desor.

An examination of the point in question revealed the occurrence

of a rather interesting irregularity which is here briefly re-

ported on. The source of the conditions here described is

entirely unknown, but inasmuch as this starfish is commonly

used as material for laboratory study, it occurred to me that

the facts themselves might be of interest to teachers of inverte-

brate zoology.

It will be recalled that in Asterias the tube-feet are arranged

in four longitudinal rows, two of which are on each side of the

radial eanal (the mid-ventral line of the arm). The tube-feet

in these rows of two are arranged in an alternate manner, nearer

or farther from the mid-line, thus allowing for the accommoda-

tion of more tube-feet in a given linear space. The tube-feet

are connected with the radial canal by short transverse canals,

which are thus longer or shorter according as they pass to tube-

feet in the inner or outer series. This arrangement of the tube-

feet can be clearly made out in properly dried specimens from

which the remnants of the tube-feet themselves are all removed.

Their position is clearly marked in such a preparation by the

perforations between each pair of ambulacral ossicles, and the

whole topography of the ambulacral groove is well demonstrated.

It is usually stated that? ‘‘Each pair of transverse canals con-

sists of a short canal on one side and a longer canal on the

opposite side of the radial canal. The short and long canals of

each side are alternating.’’ This arrangement of the tube-feet is

shown in a diagrammatic way in Fig. 1, in which the tube-feet

are represented as black ovals situated in the perforations be-

1 Quoted from Petrunkevitch, ‘‘ Morphology of Invertebrate Types," New

York, 1916, pages 177 and 178.

281

282 THE AMERICAN NATURALIST [Vor. LVI

tween adjacent ambulaeral ossicles. This, the common arrange-

ment, may be designated Type I. It will be noted that as one

runs along the arm the transverse canals of succeeding pairs

are long-short, short-long, and so on.

Figs. 1 AND 2

However, it appears from my experience in this laboratory

that some teachers give a different description of the arrange-

ment of the tube-feet. According to these teachers the length of

the transverse canals does not alternate in a single pair, but is

the same on both sides of the radial canal. This would lead to

an arrangement which is shown diagrammatically in Fig. 2.

According to this account as one runs along the arm the trans-

verse canals of succeeding pairs are long-long, short-short, and

so on. It seemed worth while from a teaching standpoint to de-

termine which of these descriptions is the correct one. For con-

venience, the arms of the starfish will be named in the conven-

tional manner a, b, c, d, e—a being the first arm to the right of

the madreporie plate (as seen from the aboral surface), the

others being named in a clock-wise direction around the dise.

In all, seventeen specimens of Asterias forbesi have been ex-

amined, some more completely than others. The first two or

three pairs of tube-feet at the very base of the arm are usually

rather crowded by the abrupt narrowing of the ambulacral

groove, so that it is rather difficult to say exactly to which type

No. 644] SHORTER ARTICLES AND DISCUSSION 283

of arrangement they belong. They seem usually to be more like

Type II than Type I. The groove widens rapidly, however, and

the four characteristic rows are quickly established. In the

majority of cases the arrangement is undoubtedly like Type I,

and this is obviously the source of the usual text-book description.

However, in at least nine specimens of the seventeen examined,

one or more arms have the Type II arrangement. This may

occur in any arm, but in my specimens is most frequent in arm

€ (five cases). Sometimes the Type II arrangement is estab-

lished from the very beginning of any regularity at the base of

the arm; in my specimens there were three (probably four) cases

of this kind in arm e and one in arm d. In such eases the Type

II arrangement may persist throughout the entire length of the

arm. More commonly, however, the Type I arrangement is first

established and after persisting for a longer or shorter distance

abruptly changes to Type II. The number of Type I pairs in

such cases seems usually to be small. The transformation is made

by a slight irregularity on one side such that two long or two

short transverse canals are adjacent—and thereafter the arrange-

ment is again entirely regular. Sometimes the region of change

is more irregular, but never strikingly so. In one case, in arm

a, the arrangement was first like Type I, soon changed to Type

II, and in the distal part of the arm changed back again to

Type I. In the seventeen specimens examined the Type II

arrangement has been found to occur (in some part of the arm) |

as follows:

BI ee ay ee Ck Rha CERES RR AE KA 3 eases

etl Sa UT AR bb Rael trices ine Mere OE oy 4 3 cases

SE ork rs Coe alc di WM Ra ed care PE 2 cases

CE ee AXE CERE EE Aedes CERTES l ease

Oe Te cw ee wy bd tcr EDU. C M Rd 5 eases

The number of arms with Type II arrangement in any one

individual varies eonsiderably, the results for my specimens

being as follows:

unn affócbod ui seu aeri ee ee 7 cases

$ ating affected) ..cluu dedo cut ia Raw ES 1 ease

B arma affected. ii. ecco vu stris duod exeo E 1 ease

In two cases, both arm a, Type II was found to occur in re-

generating arms, though near the base the Type I arrangement

284 THE AMERICAN NATURALIST [Vor. LVI

occurred. Whether the injury to the arm was the source of the

change is not apparent.

It will be seen, therefore, from the above account that both

deseriptions of the tube-feet arrangement are correct, but that

the one usually given in text-books (Type I) is by far the more

eommon; furthermore, that the one type may change to the

other with no apparent struetural reasons for the transforma-

tion. :

The faets here presented furnish, I believe, a complete explana-

tion of the differenee in the laboratory accounts as given by

different teachers.

Rosert H. BOWEN

MARINE BIOLOGICAL LABORATORY,

Woops Hore, Mass.

THE MICRO-FILTER FOR MINUTE FLAGELLATES

ITr is frequently desirable during the study of the minuter

protozoa, and espeeially of the small flagellates, to concentrate

the organisms. This the writer has been able to do in a very

simple and satisfaetory manner by means of the deviee shown

in Fig. 1, whieh may be ealled the miero-filter ; a name applied not

only beeause of its office, but also because of the minute piece

of filter-paper used.

The contrivance consists of a standard, either of wood or of

metal, which supports a burette tube, a minute circle of filter-

paper, and a vessel beneath. The water containing the protozoa

to be concentrated is introduced into the burette from above,

by means of a funnel, and the pinch cock (O) opened sufficiently

to allow the liquid to drop into the small funnel or circle of

filter-paper beneath (P). The filter is supported by means of

stout copper wire. The flow of water from the burette can be

nieely regulated by means of the pineh cock, which, to give the

best results, should be of the screw variety. The water drops

through a glass tube, drawn out into a fine point (T). It was

found eonvenient to have several of these tips of different diam-

ers.

Considerable experimentation is neeessary before the exaet

balanee between the flow of water from the burette and that

from the base of the filter-paper funnel ean be seeured. When

this balance is reached, the burette is filled and the water allowed

No. 644] SHORTER ARTICLES AND DISCUSSION 285

to filter into the vessel on the base of the stand. It is necessary,

at approximately fifteen-minute intervals, to thrust into the

burette, as far down as the shoulder, or point of taper (just

above the rubber tube on which the pinch cock rides), a straight

P Fic. 2. Pipette with flattened

tip for Scraping filter paper, to

rémove filtered organisms.

L tan: V

Fic. 1. The Micro-filter. Simple

gee: id pf the micro-filter, sup-

F), burette (B), clamp

eie seb putet (C), pinch cock (0).

capillary tip (7), filter paper (P), and

vessel for catching filtered water beneath.

eopper wire rod, holding in its lower end a bit of eotton. This

serves to stir up the material which it is desired shall be de-

posited upon the filter paper, to prevent it from settling and

adhering to the sides of the glass, on the slopes of the taper.

286 THE AMERICAN NATURALIST [Vor. LVI

When the entire amount of water has passed through the filter-

paper, the latter is removed, spread out, and immersed in a

bath of water, in a watch erystal. The water should just cover

the filter-paper.

The deviee shown in Fig. 2 is now brought into play. This

eonsists of a glass pipette, flattened and spread at its tip, and

serves admirably for gently scraping and sucking the surface of

the filter-paper, as it lies in the wateh erystal. This withdraws

into the pipette the organisms which have been filtered out.

These ean now be transferred to a glass slip and examined under

the microscope, or injected into culture media as inoculations.

The writer has found that, with practice, the possibilities of

the micro-filter may be extended to aid, in many ways, in the

study of the protozoa.

Leon A. HAUSMAN

CoRNELL UNIVERSITY

COMPLETE LINKAGE IN DROSOPHILA MELANO-

GASTER:

In 1917 a mating appeared in the cultures of the authors,

the flies from whieh showed no erossing over in the region

seute to forked of the sex chromosome, although the faetors

echinus, eut, vermilion and garnet, were between the extreme

points. This culture appeared spontaneously; selection played

no part in it. The stock from this culture has now passed

through not less than 80 generations and numbers over 3,000

matings. During this time no crossing over has appeared .

within the known length of the sex chromosome.

In experiments including the second chromosome points,

black and purple, it has been shown that no crossing over takes

place between these points when complete linkage exists for

the first chromosome. Likewise the third chromosome points,

dicheate and hairless, have shown complete linkage when the

points seute to forked in the first chromosome, and the points

black to Uren in the second chromosome show the same

phenome

The reine cause is genetic, behaving as a recessive. Its

1 Papers from the Biological Laboratory, Maine Agricultural Experiment

Station, No. 142.

No. 644] SHORTER ARTICLES AND DISCUSSION 287

position is in the region of dicheate hairless of the third chromo-

some. It may be noted that such recessive factors effecting

the mechanism of segregation show what might be ealled de-

layed Mendelian results for the F, flies must be tested for their

linkage relations before anything ean be said regarding the

stock.

Complete linkage has been reported in but one other ease.

Thus in 1912 Morgan showed that crossing over did not occur

in the second chromosome of the male of this same species,

melanogaster. This phenomenon has since been extended to

inelude the other ehromosomes. If it be eonsidered that eross-

ing over as originally diseovered for the female of this species

is the normal, then Sturtevant has shown not less than three

dominant factors to materially reduce the normal amount of a

crossing over in the second and third chromosomes. A further

incompletely analyzed case of the same investigator suggests

that a third chromosome dominant partly controls an increase

in erossing over in the second chromosome. Crossing over

variations have been shown by Bridges in his ‘‘deficiency’’

ease, ete. From this it appears that there are three kinds of

effects shown by the crossover mechanism. The first case, that

of Morgan, shows no crossing over in the male. No genetic

factors have as yet been shown to be responsible for this. The

second ease, that of Sturtevant, shows genetic dominant fae-

tors responsible for reducing crossing over in the female. The

third ease, given here, shows recessive genetic causes allowing

no crossing over in the female. It further shows these factors

capable of acting on chromosomes of which they are not a part.

Detlefesen and Roberts using the sex-linked factors, white

and miniature, present another kind of evidence. In a selec-

tion experiment they show crossing over to decline from the

normal amount (about 33 per cent.) to nearly zero per cent.,

no evidence being presented as to the causative agent, although

the suggestion is made that ''erossing over in the various

regions of the sex ehromosome (and the other chromosomes ?)

is prose eontrolled by multiple ineompletely dominant fae-

tors." From what has been indicated above it seemed more

probable that recessive factors, perhaps one, are responsible

for these linkage variations. Especially is this true of their

results in series A and At, for with delayed Mendelian segrega-

tion, recessive autosomal factors effecting crossing over in the

288 THE AMERICAN NATURALIST [Vor. LVI

sex ehromosome, mass mating in every other generation, and

eomplieations resulting from only being able to test the female,

it is to be expected that selection will progress slowly at first

and come suddenly to the climax of reduced crossing over.

Marie S. Gowen,

JOHN W. GowEN

ORONO, MAINE

THE

AMERICAN NATURALIST

Vor. LVI. July-August, 1922 No. 645

EXPERIMENTS WITH ALCOHOL AND WHITE

EDWIN CARLETON MacDOWELL

STATION FOR EXPERIMENTAL EvoLuTioN, Corp SPRING HARBOR,

Lona Istanp, N. Y.

Since the familiar paper by Elderton and Pearson

(710) upon the physique and ability of children from al-

eoholie parents, much discussion has taken place on the

relation of parental alcoholism to the condition of the

offspring. A small proportion of this has been based

upon experimental work with animals, as that of Stock-

ard (712 and 713), Stockard and Papanicolaou (’16 and

18), Nice (712 and ’13), Pearl (717), and Arlitt (719).

From such studies there should be no hope of obtaining

an immediate analysis of the human problem. In so far

as alcoholism in man is sociological, involving factors

of family life, environment and education, no study of

laboratory animals ean have significance. The way such

studies may have a bearing upon the human problem is

through the revelation of general biologieal reactions

that may in all the animals available for study, be found

so invariable that it becomes safe to conclude that they

appear in man as well How far the specific findings

herein reported for white rats may apply to different

animals is a matter for experiment and not conjecture.

But even were such a biologieal analysis secured, the

other phases of the human problem would not be solved.

From the data at hand are there any indications of

general biologieal reactions that may have significance

for all animals? Stockard and Papanicolaou, with gui-

nea pigs, found that aleoholization of parents gave un-

289

290 THE AMERICAN NATURALIST [Vor. LVI

favorable results in the offspring; Pearl reported gener-

ally favorable results in the offspring of treated fowl;

Arlitt reported unfavorable results from mild doses on

rats, while Nice, also with mild doses, found his test mice

slightly better in growth and fertility but less active, as

measured by the revolutions of the revolving cages in

which they were placed, than the controls. Earlier, Hod-

ges (703) had found the viability of puppies reduced by

the treatment of their parents; the treated dogs were

less active and more susceptible to distemper; Laitinen

(708) reported high rates of death at or soon after birth

of guinea pigs and rabbits from treated parents.

Accepting these general statements as correct, there

appears to be no obvious uniformity in the results ob-

tained by different investigators. But this lack of uni-

formity may be only apparent; it is possible that not all

the results as presented will be confirmed by subsequent

investigations since none of the experiments reported

have eseaped unfavorable eritieism from some stand-

point. Aleoholism has such a multiplicity of aspects that

it is a matter of great diffieulty to arrange experiments

concerning its effect on the offspring of treated animals

that will be beyond criticism. For technique satisfac-

tory to a physiologist may involve serious errors in the

eyes of a psychologist, while the experiments of both

may, to a geneticist, seem to have weak points. Until

aleohol studies meet the requirements of all erities no

final conclusions ean be reached. In problems involving

comparisons between experimental and control individu-

als the nature of the controls is no less important than

the comparison itself. However true this appears to be

for all experimental work, it is surprising to note that

the main adverse criticisms of the experimental studies

of the influenee of aleohol upon the offspring have been

aimed at the controls.

In spite of the general lack of uniformity in the results

as they stand, at least one criterion appears to show con-

sistency. This is the reproductive capacity of the treated

No. 645] ALCOHOL AND WHITE RATS 291

individuals. All the experiments appear to indicate an

immediate reduction in the number of offspring. The

uniformity of this result tends certainly to increase its

value as a general result; but even so, as long as the

controls are subject to criticism, the apparent consistency

may be due to the controls and not to the regularity of

the reactions to alcohol. For a single result can not at

the same time prove the reliability of the controls and

the results of aleohol treatment. It is hoped that the

controls employed in the following experiments will be

found to approach the ideal of satisfying all require-

ments.

METHODS

In 1914 an investigation was undertaken upon the in-

fluence of alcohol on the untreated descendants of white

rats with the primary object of studying the behavior,

or learning capacity, in different generations. In the

summer of 1917 war conditions necessitated repeated re-

ductions of the stocks until, by the end of the next year,

the material was completely lost. This calamitous ter-

mination of the work must be borne in mind, for, in spite

of the final nature of this report, the data come from

an investigation that was not completed.

Material and Breeding.—The rats employed belonged

to four strains; three of these strains originated respec-

tively from three pairs of rats in the Wistar Standard

Stock, the fourth strain had been bred in this laboratory

for three generations. All matings were between full

brothers and sisters. When 28 days old the litters used

to start these experiments were divided into two lots on

the basis of equal weight and equal numbers of each sex;

one of these lots was used as controls, the other was

treated. All matings were between the original treated

males and females or their descendants; or between the

original control males and females or their- descendants.

In each generation the control matings parallel those of

the descendants of the treated animals, so that each group

of test animals in each generation had its own particular

292 THE AMERICAN NATURALIST [Vor. LVI

group of controls. Since inbreeding was the rule, the

closest possible relationship for the tests and controls in

the successive generations was secured; they came from

a single pair of grandparents or great-grandparents, and

were thus raised at the same time, and after the same

number of generations of inbreeding.

= Treatment.—'The treatment of these rats was by means

of the inhalation method, now made familiar by the work

of Stockard and Pearl. The rats were placed in closed

tanks filled with aleohol vapor; these tanks have been de-

seribed in detail elsewhere (MacDowell and Vicari, ’21).

Beginning at weaning (28 days) the rats to be treated

were placed in the tanks for 30 minutes a day for 7 days.

After this the duration of the daily treatment was meas-

ured by the reactions of the animals; for the next 14

days the rats were left daily in the fumes until they were

obviously under their influence; subsequently the rats

were left each day until they were completely anesthe-

tized. This required from three to four hours for the

: older rats.

Criteria.—The term treated is used to indicate rats that

were placed in the alcohol fumes after birth. The fol-

lowing generations are herein reported: (1) the treated

rats, (2) the treated offspring, (3) the untreated off-

spring, (4) the untreated offspring of (3) (second un-

treated generation following one treated generation).

For these rats the following types of data are given:

the behavior in the maze, as measured by time per trial;

behavior in a multiple choice apparatus, measured by

the number of correet first choices; fertility, judged by

the size of the litters and the number of litters; body

weight, as judged by growth curves based on weekly

weighings.

Mazxr-BEnavion

Apparatus and Training.— The maze used in this study

was built according to the details given by Watson (714) ;

namely, a concentric arrangement of five alleys with door-

ways and blind alleys so arranged that the true path from

No. 645] ALCOHOL AND WHITE RATS 293

the outside to the center required a rat to turn alternately

to the left and the right at successive doorways. A rat's

training was started at the age of 56 days, after prelimi-

nary feeding in the center of the maze on each of the 7

preceding days. Three successive trials a day were given.

After the first and second trials the rat was removed

from the center as soon as it had tasted the food (bread

and milk) which was always found there; after the third

trial, it was allowed to eat for five minutes. This train-

ing was given for eight successive days. The observa-

tions were so automatic that there was practically no

possibility that the results were being influenced by an

unconscious bias on the part of the observer. In the

ease of the treated rats the aleohol was given each day

following the trials in the maze.

Results.—The average time per trial for each day of

the training of the different groups of rats is represented

in Fig. 1. The test rats, whether actually treated, or

the descendants of treated rats, are represented by the

broken lines, and their respective controls by the. solid

lines. The numbers of rats included in the different

curves, beginning at the left, are as follows: 55 treated

rats and 62 controls; 46 tests and 48 controls; 25 tests

and 25 controls; 8 tests and 20 controls. The broken

lines tend to lie above the solid lines. The tests tend to

give higher time averages than the controls, that is, the

tests took longer time to run a trial The inferiority

shown by the treated offspring from treated parents

(fourth pair of curves), and by the untreated offspring

from untreated parents and treated grandparents (third

pair of eurves) is of the same order of magnitude as

that shown by the treated animals themselves; untreated

offspring from treated parents show less inferiority than

their own untreated offspring. Considering the signifi-

cance of the differences between the tests and controls

for each day independently, the following results are

found: the differences between the tests and controls are

over three times their probable errors on five days in the

294 THE AMERICAN NATURALIST [Vor. LVI

first pair of eurves, on no day in the second pair, on four

days in the third pair and one day in the fourth pair.

All the significant differences favor the controls. How-

ever, more important than the significance of individual

MAZE

TIME PER TRIAL.

TREATED UNTREATED FROM UNTREATED FROM TREATED FROM

ENTS ED E

D PARENTS

SEC. PER AND TREATED ©

TRIAL GRANDPARENTS

PER SEC.PER

LAL `. TRIAL

SEC.PER

ae Ee Se a

Fic. 1. Comparisons of time averages in four groups of rats—those treated,

their treated and untreated children, and their untreated grandchildren. (Data

for the third set of curves taken from MacDowell and Vicari, '21, p. 233.)

Broken lines tests, solid lines controls.

differences as measured by the probable errors, is the

agreement in the direction of the differences on succes-

sive days. The fact that the differences on eight suc-

cessive days lie in the same direction probably has more

significance than that half of these taken separately may

be significant as judged by their probable errors. Con-

sidering the signs alone, in all the curves there are three

out of the 32 points of comparison showing the test av-

erages lower than the controls. One of these cases is

on the third day of training of the untreated rats from

treated parents, the other two cases are on the second and

third days of training of the treated rats from treated

parents. If chance alone is working, the probability of

No. 645] ALCOHOL AND WHITE RATS 295

eight days giving differences in the same direction is the

same as the probability of eight coins coming down all

heads; in the long run this will happen once in 256

tosses. The chances of seven out of eight, 1 to 32, of six

heads out of eight, 1 to 9. Carrying this comparison

further by considering all the generations together, the

chances of finding three cases favoring the tests out of

thirty-two are in the neighborhood of 1 to 860,000. From

all this it appears that the test rats are different, as a

group, from the controls. Apparently the only differ-

ence between the tests and controls that could explain

this result is the aleohol treatment given directly, or in

the ancestry of the test rats; this leads to the conclusion

that the difference in behavior is due to the alcohol

treatment.

BEHAVIOR IN THE MULTIPLE CHOICE APPARATUS

The difference in the behavior of the tests and controls

in the generation of the untreated offspring of treated

parents is further shown by the training on the multiple

choice apparatus. This is the only generation from which

sufficient data were gathered for the analysis of behavior

on this apparatus.

Apparatus and Training —The apparatus used in this

training consisted of a linear series of nine compart-

ments, with front and back doors operated at a distance

by the observer (see Yerkes, '21, for history and uses

of this apparatus). Different sets of front doors were

opened for the successive trials and the rat was given

its reward of food by raising the back door when it en-

tered the ‘‘ correct’? compartment. The ‘‘ correct ”’

compartment was the one at the extreme right or left

(according to the problem) of the series with open front

doors. In successive trials, therefore, the correct com-

partment was never the same one, and the solution of

the problem did not depend upon the repetition of a reg-

ular kinesthetic habit. The steps in the training were

these: at the age of 65 days the preliminary training

296 THE AMERICAN NATURALIST [Vor. LVI

was started; on the first two days the doors were all

left.open and food was exposed to view in every com-

partment; the rats in groups of five or so were left to

run at random in the apparatus. On the second two days

the front doors were all open as before, but the food was

concealed by covers fastened to the back doors, and when

a rat entered any compartment the food was revealed by

opening the back door; the rats were run singly on these

two days and given ten such feedings a day. On the

last two days of the preliminary training only the regular

series of doors were opened, but the rats were fed on

entering any compartment (20 trials).

Right-hand Problem.—In the first problem the rat was

fed only when it entered the right-hand compartment of

any set-up (those open in any trial); after wrong choices

the rat was confined in the compartment for half a min-

ute, and then, by raising the front door, was permitted

to make further choices (10 days, 100 trials); next, the

same problem was given with a different series of open

doors (2 days, 20 trials). Further training was given

in the form of a problem in which the correct door was

the open one at the left end of the open series, but the

results from this problem are so complicated that they

wil not be treated at this time. "The main reason for

this complication is the fact that at the end of the time

allotted for the mastery of the first problem the test and

control rats exhibited different degrees of perfection;

some had made considerable progress in learning, while

others had made very little advance. Accordingly, when

the reverse problem was given, those that had learned

the most were handicapped by the habit already ac-

quired, while those that had not formed the required

habit in the first problem were able to progress more

rapidly in learning the second problem.

Results.—From a study of the individual reaetion ten-

deneies as revealed in the last two days of the prelimi-

nary training before the problem was presented, and in

the regular training after the presentation of the prob-

No. 645] ALCOHOL AND WHITE RATS 297

lem necessitated the use of the trial and error method

of finding the correct compartment, it appeared that the

test rats continued the same tendencies in the regular

training that were initiated in the preliminary training,

but the controls, on the other hand, modified their re-

action’ tendencies as soon as the regular training was

started. This result is brought out by the curves in Fig.

MUL IHOLECHOGICE.

NUMBER OF CORRECT CHOICES

ESTIS CONTROLS

FROM TREATED PARENTS

J6 - 10 16L

de | A 14|

12 w aL

IOL IOL

8L sL

Stk. 6L

4l. 4L

ei. 2L

AEB | 1 L L L 1 l l 1 L 1 1 Sere | j

PRELIM |-2 3-4 56 78 9401H2 3-14 PRELIM |-2 34 56 78 9-10 IH2 314

DAYS IN TRAINING DAYS IN TRAINING

Fig. 2. Showing the pargar for rats from treated parents

liminary anā subsequent performance in the nerek choice apparatus. Aver-

age numbers of correct first serie are shown for each successive set of 20

trials. The rats have been classified into groups ng to t reliminary

records e fi the behavior of the tests in the limin

ary

trials is a fairly good index of their behavior in the regular training, but the

behavior of the controls in the preiiminary trials gives very little indication

of the later behavior.

298 THE AMERICAN NATURALIST [Vor. LVI

2. The test rats have been classified into seven groups

according to the number of right-end choices in the last

twenty trials of their preliminary training. The first

points of the lines given for the tests indicate the average

number of right-end choices made by the rats in each of

the groups in the preliminary training; the following

points give the average numbers of correct (right-end)

choices made by these same rats in successive sets of 20

trials in the regular training. Since the procedure in

the regular training is essentially different from that in

the preliminary trials, the lines connecting the first and

second points are drawn as arrows. The numbers at

the ends of the lines give the numbers of individuals

included in each group. The arrangement of the controls

follows the same plan. Whereas the curves for the tests

show a general parallelism, those for the controls are,

with the exception of the group of four rats whose

preliminary training gave between 12 and 14 right-end

choices, relatively independent of the preliminary records.

This matter can be brought out more clearly by a study

of the coefficients of correlation between the preliminary

record of each rat and the trials in the regular training.

When the correlation coefficients between the preliminary

records and the first 20 trials in regular training, and

between the preliminary and the second twenty trials in

regular training, ete., are calculated, the figures in Table

I are obtained. In every case the differences between

the coefficients of the tests and controls (fourth column

in Table I) show that the tests have higher correlations,

and in all but the correlation between the preliminary

trials and the last set of twenty trials in regular training,

the differences are statistically significant. These re-

sults indicate that there is a real difference between the

tests and controls in the way they react to the necessity

of using trial and error methods; this may be due to a

difference in responsiveness to changes in the situation.

‘The tests appear to be less responsive to the changed

procedure, since they continue the same general behavior

No. 645] ALCOHOL AND WHITE RATS 299

as in the preliminary training, whereas the controls mod-

ify their behavior as soon as the change is made in the

procedure.

TABLE I

CORRELATION COEFFICIENTS, SHOWING THE DEGREES OF SIMILARITY BETWEEN

THE NUMBER OF RIGHT-END CHOICES IN THE LaAsT 20 TRIALS OF

THE PRELIMINARY TRAINING AND THE CORRECT CHOICES IN

EACH SUCCESSIVE SET OF 20 TRIALS IN THE SUBSE-

QUENT TRAINING IN THE MULTIPLE CHOICE

PPARATUS.

Correlation Coefficients

Trials Correlated Difference D/P.E.

Tests | Controls

Preliminary by Ist 20 trials.. ..| .688+.039 .139 4.063 +.549 +.074 7.4

by2d “ “ ....| .628+.045) .072+.075 | +.556+.087 6.3

by 3d * “ ....| .692+.048 .339+.067 | +.253 +.082 el

by4th * *“ ....| .444+.060) .070+.075 +.374+.096 3.8

by 5th = “ ...| -432.061 .101+.074 | 4.331 27.095 3.4

by 6th * “ ....| .489+.057; .049 2-.075 +.440 2-.094 4.6

by7ih *. “ ....| .842+.061) .212+.072 -F.220 2-.094 2.3

All the coefficients are positive; the plus sign is used before the differ-

ences to indicate that the coefficients for the tests are higher than the

corresponding ones for the controls.

In view of the above, the direct comparison of the av-

erages of the tests and controls in regular training would

lead to error unless the average performance in the pre-

liminary training happened to be the same for both sets.

In the long run this would undoubtedly be the case, but,

as it happens, the averages for the tests and controls do

not agree in the preliminary training. However, it was

found that this difference depended upon the rats with

strong right- or left-hand tendencies, for if these (those

tests and controls with more than 12 or less than 3 right-

end choices in the preliminary training) be omitted, the

average of all the rest ‘of the rats was the same for the

tests and controls. Using the rats whose preliminary rec-

ords showed between 3 and 12 inclusive right-end choices,

the averages for the curves in Fig. 3 were obtained. Start-

ing with the same average tendency to enter the right-end

compartment in the preliminary training, the controls

300 THE AMERICAN NATURALIST . .[Vor. LVI

increase the number of correct first choices more rapidly

than do the tests, and as the difference between the av-

. erages increases it becomes statistically significant.

N9 OF

CORRECT

CHOICES

7 VESTS d Ln.

b CONTROLS

HAYA A EN v qu 5-6 7-8 9-6 ine ET

Average numbers of correct first choices in the multiple choice ap-

paratus, in the preliminary training and in the following pairs of days, when

rats are included which made from 3-12 correct first choices in

their preliminary training, i.e., eliminating rats with strong tendencies either to

choose or avoid the correct door, before regular training began. In this way the

preliminary averages of the tests and controls are brought together and it be-

comes possible to compare the averages in the regular training.

Granting that the controls are adequate, the data on

behavior indieate that a modifieation has been brought

about by the aleohol; the generation showing the least

absolute difference in maze-behavior is shown to be defi-

nitely modified when the tests are made on a multiple-

choice apparatus.

FERTILITY

Compared with the difficulty of measuring the behavior

tendencies of rats, the measure of fertility is very simple

and definite. However, the great amount of time required

by the behavior studies prevented the collection of many

of the available data on the purely physiological side.

As a result of this, instead of the long list of criteria

of fertility that have been given by other authors, it is

possible to give only two with any degree of accuracy

and completeness. "These are: the number of rats in a

litter, and the number of litters. A more detailed report

on the data leading to the following conclusions may be

found elsewhere (MacDowell, '22a).

No. 645] ALCOHOL AND WHITE RATS 301

Size of Litters—A general tendency for the litters of

the test rats to be smaller than the controls persists in

the summaries of all generations. The difference be-

tween the size of the litters from the original treated rats

and the litters from the controls is equal to 10.5 per cent.

of the size of the control litters. The treated offspring of

the treated rats produced litters that were 10.3 per cent.

smaller than the litters of their controls. It appears,

therefore, that the treatment of the parents’ of the litters

as well as the grandparents does not intensify the reduc-

tion in litter size found when only one generation was

treated. The untreated offspring from treated rats gave

litters that were 11.2 per cent. smaller than their controls,

and the untreated offspring from untreated parents and

treated grandparents gave litters that were 13.1 per cent.

smaller than the controls (see Fig. 4). These differences

in individual generations are based on too few cases to

be significant when compared with their probable errors,

but when the numbers are increased by taking all the gen-

erations together, the probable error is reduced so that

the difference attains statistical significance (3.6 times

its probable error). Litter size, then, gives a result not

unlike that given by the behavior data: the tests are

inferior in each generation, with no apparent relation to

the proximity of the alcohol or the number of generations

of treatment.

Number of Litters —Given equal time, the treated pairs

produced 0.72 litter per pair while the controls produced

2.07 litters per pair. This is a reduction of 64.8 + 3.3

per cent. in the number of litters, and as it is 19.2 times

its probable error, it is significant beyond all question.

The test litters were slower in appearing than the con-

trols. The treated rats from treated parents also gave

fewer litters than their controls, but instead of a greater

reduction than in the previous generation this second

treated generation produced relatively more litters. The

reduction was 35.4 + 6.9 per cent. of the controls. Com-

ing to the rats not directly treated, the untreated rats

302 THE AMERICAN NATURALIST [Vor. LVI

NUMBERS: OF RAIS PER LIITER

AVERAGES IN FOUR GENERATIONS

NUM

PER LITTER

TESTS TESTS TESTS TESTS

139

- 9 pum - 6

-10% t] 94 10 oZ ^

CONTROLS

TESTS * CONTROLS

8 TESTS

TESTS

FROM TREATEO RATS FROM FROM UNTREATED RATS FROM FROM TREATED RATS FROM FROM UNTREATED RATS

UNTREATED PARENTS TREATE ARENTS TREATED PARENTS FROM UNTREATED PARENTS

Fic. 4. Average litter size for the controls and tests baing the relation-

ships to the alcohol treatment indicated.

from treated parents gave 33.3 + 8.2 per cent. more lit-

ters than their controls, and the untreated rats from un-

treated parents and treated grandparents produced 55.6

+ 8.4 per cent. more litters than their controls (see Fig.

5). All of these differences are, without doubt, statisti-

eally significant.

Discussion.—Two generations of treatment made less

difference in number of litters than a single generation

of treatment, and two untreated generations following

No. 645] ALCOHOL AND WHITE RATS 303

WUMEER OF

LITTER

S CONTROLS

ac NUMBERS OF LITTERS

IN FOUR GENERATIONS

iets TESTS TESTS TESTS

— 35% + 335 +55%

TESTS

ITESTS

CONTROLS

20 TESTS

CONTROLS

TESTS CONTROLS

TREATED FROM TREATED FROM UNTREATED FROM UNTREATED FROM

pers erem Se a RA ERNE NTREATED PARENTS ANO

TD EDS TREATED GRANII/PARENTS

UNTREATED PARENT TREATED PARENTS

Fra. Relative numbers of litters produced in equal periods by the test

and control rats in different generations. Beginning at the left the test litters

irs: 44, 9, 19, 1; in each case

the con litters have been given

im Pus geh actual numbers of poti pore: involved were: 42, 12

the treatment produced more litters than the controls.

The number of litters is strongly reduced when the pa-

rents themselves are treated, but when the aleohol is more

remote, the reduetion vanishes and the untreated descend-

ants of the treated rats produce more litters than their

controls. To explain the reduction in the number of lit-

304 THE AMERICAN NATURALIST [Vor. LVI

ters in the presence of alcohol along purely physiological

lines would be a simple matter, but a genetie explanation

appears to be required when it comes to the inerease over

the eontrols given by untreated descendants of treated

animals. No general depression or stimulation will ac-

count for the continuation of small litters together with

the increase in number of litters in the generations not

given alcohol directly. It seems necessary to assume that

there are genetic factors influencing the number of litters;

aleohol prevents the reproduction of such females as carry

faetors working in the direction of lower reproductive ca-

paeity, so that the litters come alone from females carry-

ing higher litter-producing capacity; the next generation

will produce higher numbers of litters than the unselected

controls, for the controls still carry all grades of fertility,

while the tests lack the genetically lower grades. The

treated offspring of treated rats produced fewer litters

than their controls, but genetically they were superior,

as shown by untreated offspring giving more litters than

their controls; they were superior to the first generation,

for, instead of a 65 per cent. reduction, they gave only

a 39 per cent. reduction in the number of their litters.

Whereas the immediate presence of alcohol reduces the

number of litters, it acts to increase the number in the

next generation; therefore alcohol may produce two re-

sults upon a single character in two generations. This

could lead to much confusion were it not so easy to un-

derstand the first result as the cause of the second. -

This selective action of alcohol will account for the re-

sults from the number of litters, but will not account for

the uniform results given by litter size. If this is a -

correct statement of the situation, it indicates that the

number of litters is influenced by genetic factors that are

not identical with those influencing litter size. Although

such a distinction between genetic bases for the numbers

of litters and litter size has apparently not been made,

it is not difficult to conceive, for litter size is largely

dependent upon the number and constitution of the germ

No.645] . ALCOHOL AND WHITE RATS 305

cells liberated, while the somatie condition of the mother

plays a part in determining whether or not a litter will be

produced. The results from litter size agree strikingly,

qualitatively and even quantitatively with those of Stock-

ard and Papanicolaou from similar studies with guinea

pigs; the results from the number of litters agree with

Pearl’s on fowl in so far as they may be interpreted by

assuming a selective action of the aleohol working upon

existing genetie differences. In the fowl the aleohol ap-

pears to select between germ cells; in the rats it appears

to select between mothers of different physiological and

genetic grades.

WEIGHT

The data on weight (see MacDowell, ’22b) form an ex-

tensive series consisting of weekly weighings of practical-

ly all the rats raised in the various generations herein de-

seribed. Individual growth curves were plotted and from

these the weights at six ages were taken for statistical

study. This procedure was necessitated by the fact that

all the rats were weighed on the same day each week, so

that the rats were of different ages. The results are

based primarily upon the males (see Table II), since the

pregnancies of the females make their data less reliable.

However, when the data from the females with arbitrary

smoothing of the pregnancy peaks are summarized, the

results so obtained support those given by the males.

Each of the four strains shows that the treated rats grew

more slowly than the controls. This is an influence shown

. by the population as a whole, although there are some

individual treated males that remained as heavy as the

heaviest controls. The untreated offspring of the treated

rats tended to grow more rapidly than their controls.

This result is not so clear as the opposite result in the

preceding generation; the absolute differences are not so

large and the strains do not show this in equal measure.

Treated rats from treated parents barely differ at all

from their eontrols. Very little can be concluded from

the weights of the untreated offspring from untreated

THE AMERICAN NATURALIST [Vor. LVI

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II W'Id VL

No. 645] ALCOHOL AND WHITE RATS 307

parents and treated grandparents. Two of the three

strains represented in this generation show heavier aver-

ages for the tests and the third shows heavier averages

for the controls; when all the strains together are con-

sidered (as in Table II), the test averages are higher at

all ages.

This shows a marked similarity to the results from the

number of litters; just as the offspring of the treated

rats appear to be genetically superior to the controls in

the matter of litter production, so they are found to be

superior in the matter of weight, with the result that

when they themselves are treated, the immediate reducing

effect of the aleohol makes them about equal somatieally

to their controls, instead of growing markedly slower as

did their parents. This likeness in results leads to a

similar interpretation for the weight as for the number

of litters: the aleohol has aeted as a selective agent,

eliminating germinal material that included factors for

slower growth.

; Discusston

In view of the premature termination of these experi-

ments no discussion or interpretation can be justified

other than by its possible influence upon future work.

The data on behavior and litter size taken alone may,

if the controls are accepted as adequate, be considered

to lead to the general interpretation of a direct and defi-

nite modification of the germinal material brought about

by the aleohol treatment. On the other hand, the data

on the number of litters and weight, when taken alone,

agree in inviting the interpretation that the alcohol has

acted as a selective agent upon germinal differences that

were present in the germinal material of the original

animals. One tendeney pulls the race down, the other,

by sacrificing the fullest reproductive expression of the

treated individuals, tends to pull it up. The specific con-

ditions found then are end-results that depend upon the

interaction of different influences and do not measure di-

rectly the amount of influence exerted by the chemical.

308 THE AMERICAN NATURALIST [Vor. LVI

Obviously, the situation is complicated, and equally obvi-

ous is the impossibility of proving the individual effects

of two or more influences acting simultaneously. How-

ever, in this case the evidence favoring one supposition

(that of selective elimination of germinal material) is

very mueh more convincing than that favoring the sup-

position of germinal modifieation. So great, indeed, is

this difference that the evidence of direct modification

could easily be brushed aside and selective elimination

be effectively championed as the effect of the alcohol,

although even this involves two opposite results depend-

ing upon the proximity of the alcohol. But if a true

statement of the situation is desired, the conflicting evi-

dence must not be brushed aside.

If the germinal variability existing in the race is greater

than the variability caused by the direct action of the

alcohol upon the germinal material, the results actually

obtained would be expected; that is, the effects of selec-

tive elimination would appear more striking in the end

results. Since the reductions in litter size and in beha-

vior stand in spite of an apparently much stronger racial

improvement, these reductions give stronger support to

the supposition that germinal modification is a second

activity of the alcohol than is indicated by their magni-

tude.

The fact that so many different conclusions have been

reached by different investigators from experiments with

alcohol would in itself suggest very strongly that the ac-

tion of this chemical upon animals is not simple and di-

rect like the action of an acid upon a base, yet the general

attitude toward the problem seems to have been that

there should be a single answer, in one direction or the

other, and that as soon as an investigator devises the

perfect method, this answer will be disclosed. As long

as such an attitude persists the alcohol problem will

flounder about in the morass of futile and inconclusive

papers. The moment chemistry, and later, experimental

breeding, turned away from end results to the phenomena

No. 645] ALCOHOL AND WHITE RATS ^ 309

behind them (elements or factors), new epochs were

started in these sciences. The problem should not be to

judge how bad are the results of aleohol, but rather to

find through what channels aleohol may work. The final

results will differ in different eases according to differ-

ently combined influences of various sorts, just as the

same combination of chemieals will yield different results

under different conditions, and the same combination of

genetie factors will yield various somatie expressions; to

know the modus operandi of aleohol is fundamen

CONCLUSIONS

1. Beginning at the time of weaning, alcohol was ad-

ministered to white rats every day, in sufficient quan-

tities to cause complete anesthetization. This treatment

appears to account for the following differences between

the treated rats and their normal sibs:

The treated rats—(a) took more time running the maze.

(b) produced smaller litters.

(d) grew more slowly.

2. The treated offspring from the treated rats differed

from their controls in the following ways:

The treated offspring—(a) tended to take more time in running the maze,

(b) produced smaller litters.

.(e) produced somewhat fewer litters.

(d) grew at a very slightly lower rate.

3. The untreated offspring from the treated rats dif-

fered from their controls in the following ways:

The untreated offspring—(a) took a very little longer in running the maze.

(b) produced smaller litters.

(d) were heavier.

4. The untreated offspring in the second generation

from alcohol treatment differed from their controls in

the following ways:

310 THE AMERICAN NATURALIST [Vor. LVI

The seeond genération of untreated offspring—

(a) took more time in running the maze.

(b) — smaller ey

ced ers

(d) were kot baie

5. From these results it is concluded that the action of

alcohol is complicated; that it works in two or more dif-

ferent ways. The data on behavior and litter size suggest

that the alcohol may modify germinal material directly.

The data on the number of litters and growth indicate

that the direct effect of aleohol upon these characters is

in one direction and that its indirect effect is in the op-

posite direction; this may be interpreted by the assump-

tion of a selective róle played by the aleohol. It is urged

that the aleohol problem can be settled biologically only

when, instead of generalizing from the quality of specific

end results, we deal with the channels through which al-

cohol may work.

COLD SPRING HARBOR,

February, 1922.

LITERATURE CITED

Arlitt, A. H.

1919. T ara of Alcohol upon the Intelligent Behavior of the

Fior and its Progeny. Psychol Monog., Vol. 26, No.

bese eton

Elderton, E. x Reg Pear

1910. g et Study on the Influence of Parental Alcoholism. on

Physique and vig: of the Offspring. Eugenics Lab.

m No. 10. London

Hodge, C. F.

1903. T Influenee of Aleohol on Growth and Development. In

** Physiological nm of the Liquor Problem." New

York, pp. 359-3

Laitinen, T.

1908. Ueber die Einwirkung der kleinsten Alkoholmengen auf die

weiderstandfahigkeit des tierisehen Organismus mit besond-

erer Berueksiehtung auf die Nani miea] Zeitschr.

. Hygiene, Vol. 34, pp. 139—252.

MaeDowell, E. C.

1922a. as escis of Aleohol upon the Fertility of White Rats.

1922b. Pie ind the Growth of White Rats. Genetics, Vol. 7.

No. 645] ALCOHOL AND WHITE RATS 311

MacDowell, E. C. and Vicari, E. M.

1921. SEEN and the Behavior of White Rats. I. The Influ-

nce of Alcoholic Grandparents upon Maze-behavior. Journ.

Bap. Zool., Vol. 33, pp. 209-291,

Nice, L. B.

1912. Comparative Studies on the Effeets of Aleohol, Nieotine, To-

acco Smoke and Caffeine on White Mice. I. Effects on

Reproduction and Growth. Journ. Exp. Zool., Vol 12, pp.

133-152.

1913. Studies on the Effects of Alcohol, Nicotine and Caffeine on

hite Mice. II. Effects on PETET Journ. Exp. Zool.,

Vol. 14, pp. 123-151

Pearl, R.

1917. The Experimental Modification of Germ Cells. Parts I, II and

III. Journ. Exp. Zool., Vol. 22, pp. 125-186, and pp. 241-

310.

Stockard, C. R

1912. An B NUN Study of Racial Degeneration in Mammals

Treated with Alcohol. Arch. Internal Med., Vol. 10, pp. 369-

398.

1913. The Effect on the Offspring of Intoxieating the Male Parent

and the Transmission of the Defeets to Subsequent Genera-

AMER, xui dg 47,

Stockard, C. E and Papanieo N,

1916. Peas pee id the Hereditary Transmission of De-

gen gery and Deformities by the Descendants of Alcohol-

a mals, Amer. Nar., Vol 50, Part I, pp. 65-88,

AIL pp. 144-177.

1918. Arat prame on the Modification of the Germ Cells in Mam-

mals: e Effect of Alcohol on Treated Guinea-pigs and

their "isi ns Journ. Exp. Zool., Vol. 26, pp. 119-226.

Watson, J, B.

1914. A Circular Maze with Camera Lucida Attachment. Journ.

Animal Behav., Vol. 4, pp. 56-59

Yerkes, R. M,

1921. A New Method of Studying the Ideational Behavior of Men-

tally Defective and Deranged as Compared with Norma] In-

dividuals. Journ. Comp. Psychology, Vol. I, pp. 369-394.

EXPERIMENTAL STUDIES ON THE DURATION

OF LIFE. IV. DATA ON THE INFLUENCE

OF DENSITY OF POPULATION ON

DURATION OF LIFE IN

DROSOPHILA !:

PROFESSOR RAYMOND PEARL AND SYLVIA L. PARKER

Famy early in our experimental work on duration of

life in Drosophila it became apparent to us that the num-

ber of flies per bottle, or, since the bottles used are of

uniform size, the density of population, had some influ-

ence on the mean duration of life of the flies, when other

environmental conditions are constant. Such a relation-

ship might reasonably be expected a priori, from what

is known of the influence of this factor on human death

rates, commonly expressed as Farr’s Law (cf. Farr, W.

(35), Brownlee, J. (36, 37)), and on other biological func-

tions, such as growth (Semper, K. (38), Bilski, F. (39)),

resistance to poisons (Drzwina and Bohn (40)), rate of

reproduction (Pearl and Surface (41), Pearl and Parker

(42)), ete. As soon as it was recognized that this vari-

able, density of population, might influence our experi-

mental results with Drosophila, care was taken in setting

up experiments to make this a constant in each case. At

the same time the records of the earlier work were care-

fully re-examined to determine what part this variable

may have played in the results. Happily it was found

that in none of our work so far published upon the dura-

tion of life in Drosophila had density of population

varied enough to have any appreciable effect upon the

results or conclusions.

As was recently pointed out by Pearl and Parker (42),

however, ‘‘there can be no question that this whole

matter of influence of density of population, in all senses,

upon biological phenomena, deserves a great deal more

1 Papers from the Department of Biometry and Vital Statisties, School

of Hygiene and Publie Health, Johns Hopkins University, No. 63.

312

' No. 645] THE DURATION OF LIFE 313 -

investigation than it has had. The indications all are

that it is the most important and significant element in

the biological, as distinguished from the physical, en-

vironment of organisms.’’ In pursuance of this idea we

desire to present in this paper our accumulated statisti-

cal data on the influence of density of population upon

duration of life in Drosophila. This material is to be

regarded as preliminary rather than final. For reasons

which will appear as we proceed, we are inclined to with-

hold final conclusions as to the exaet form of the regres-

sion of duration of life upon density until we have com-

pleted an extensive ad hoc experimental investigation of

the problem. This experimental work is now in progress

and we hope to be able to report upon it in full in the

course of the next year. In the meantime we have an

impressive body of statistieal data gathered from the

eontrol groups of other experiments which it seems de-

sirable to diseuss now in a preliminary way.

The data of this study are derived from the normal

control groups of various experiments on duration of

life which we have carried out with Drosophila, accord-

ing to the technique described by Pearl and Parker (27).

All of the determinations of duration of life recorded in

the tables of this paper were made under constant condi-

tions of temperature (25° C.), food, ete., as described in

the paper referred to. We have divided the material

for the purposes of the present study into three groups

by stocks (cf. Pearl and Parker (27)), viz.: (a) wild

type flies, including our Old Falmouth, New Falmouth,

and Eagle Point stocks, (b) Sepia, and (c) Quintuple.

Throughout this paper density of population is taken

as the initial density (number of flies per bottle) in the

small bottles used in testing duration of life. Thus a

density of 22 means that 22 flies started in this particular

bottle. As time went on the number was diminished by

deaths until finally none was left. One of course might

use as the variable mean density over the whole life of a

314 THE AMERICAN NATURALIST [Vor. LVI

bottle, but a little thought will show that this would be

an erroneous procedure when one is dealing with dura-

tion of life as the second variable, because mean density

bears a direet and implieit functional relation to mean

duration of life of the flies in the bottle. We shall be on

a clearer footing to take initial density as the variable.

Since the cubical content of the bottles is constant

throughout, there is no necessity of reckoning density

per ee. The number of flies per bottle can be taken as

the measure of density, and a good deal of useless com-

putation saved.

We are indebted to Dr. John Rice Miner for aid in the

computations.

IIT

Table I presents the data for the correlation of dura-

tion of life with density of population for the wild type

flies. The material is in the usual form of a correlation

table.

An examination of this surface suggests at once that

the regression is probably non-linear. Owing to the

manner in which the material was obtained (by compila-

tion of the control series of a number of different experi-

ments) it results that the different arrays have rather

highly different total frequencies. The number of flies

per bottle was in no way artificially selected or prede-

termined in this material. Instead it was determined

solely by the aggregate fertility of the mating bottles

furnishing the material for each particular experiment.

As has been explained in the first of these Studies (Pearl

and Parker (27)), the routine procedure in our experi-

ments is to put into one bottle for duration of life test

all the flies emerging as imagoes at the same time (i.e.,

usually on the same day). It therefore would result that

if the hatch was particularly good on some day, there

might be as many as 90 flies in the duration of life bottle

initially. On the other hand, there might be only 2 flies,

because only that number emerged on that particular

day.

Even in spite of the differences in the frequencies of

THE DURATION OF LIFE 315

No. 645]

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316 THE AMERICAN NATURALIST [Vor. LVI

the several arrays, it still seems probable from mere in-

spection of the general surface that the regression is

non-linear. This idea is strengthened by examination

of the regression line itself, shown in Fig. |

“TITT

3 LARA PEN IN

/ "

: |

MEAN AGE AT DEATH IN DAYS

I |

x |

| |

s- 9 D H H 4 I9 339 AA 45 40 535 57.01 05 OD N T ai 8 89 98

NUMBER OF FLIES IN BOTTLE

Mean eto of life of Drosophila for different initial densities of

sd Wild s

It is seen from this diagram that, neglecting the great

dip of the line at density 55 which is consequent upon a

very small array with large probable error, the general

sweep of the curve indicates an optimum density (great-

est mean duration of life) in the general region of 35 to

45 flies per bottle, with a decline on either side of that

point, but falling lower on the side of high densities

than on that of low.

From this table we have the following constants:

r — — .0511 + .0068,

n= .2443 + .0064.

There can be no question that the regression is non-

linear. Blakeman’s (43) criterion has the following

value:

£— 0571 + .0031,

It must therefore be concluded that the eee is

significantly skew.

The correlation between duration of life and density

of population in the case of the Sepia stock is shown in

Table II.

THE DURATION OF LIFE 317

No. 645]

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318 THE AMERICAN NATURALIST [Vor. LVI

Here again there are a number of small arrays and

gaps towards the right-hand side of the table, due as be-

fore to the method by which the material was got.

The regression of duration of life upon density is

shown graphically in Fig. 2.

2 AN E3

x LI ON Was

E a wd. ies e

M 30 * e i

: \

M 20

5$. 9 1 IT. 0 M 29 Jd 37 4| 458 4D 313 537 WW n 6D "3 7 à 85

UMBER OF FLIES BOTTLE

Fic. 2. Mean pekea ls life of Drosophila for different initial densities of

population. Sepia s

It is apparent from T here as before that the

regression is not clearly linear, but rather indicates an

optimum density in the region of 35 to 45 flies per bottle,

with a diminished expectation of life at both lower and.

higher densities. The constants are

— — 132 +.014,

»- "283 -.013,

f= .0629 + .0066.

The criterion of linearity is nearly 10 times its prob-

able error, and we may therefore conclude for the Sepia

stock, as for the wild stocks, that statistically the regres-

sion of duration of life upon density of population is

significantly skew.

The data for the short-lived Quintuple stock are given

in Table III.

Owing to the faet that the Quintuple stock is charaeter-

ized by low fertility, as well as short duration of life,

No. 645]

THE DURATION OF LIFE : 319

TABLE III

CORRELATION SURFACE FOR THE VARIABLES (a) DURATION OF LIFE, AND (b)

INI STOCK

NITIAL DENSITY OF POPULATION. QUINTUPLE

Number of Flies in Bottle

Age at

CIS |S |13- 17 21-|25—/29— 33-|37—|41- 45- 49-153-| Total

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IQ ie ee 11 14 | 11| 42| A| dl TL. d bad al 57

+ vds 8:4 3031] 4165 8 ee ite es Sa Gite Bee i 44

Dp dul E Lo chbdgs|] 7| 8| B SL SU e ew. 35

ae nucon Oe Sere 2 SEE SY visos FoR a

"NUM gs nsa 6L. Bl 1 B IL baL. he45 | 1 15

AL d 219. —.] 3 (EU NEUES T E 8

EL oui. ve Yl «i A3 dododd4 located bled das oped | 1 9

46. acta IONS WIALGLGI3] dh dq Lob 11 10

48526. x 8i 3i XI Ne IU Borloo 8]

d oo oo s A bees [o uso pu ue Drei vii Va. dp e pompe e

Aet vous 173415 SESS ALENS SISSE SALE LAS RES 3

Total...... 139 | 261 | 230 202 | 74 |70 | 79 |29]. ..... Lob mb] iam

i " | i]

this table is less extensive in either direction than the

others.

Fig. 3.

det" Quan

MEAN AGE AT DEATH IN DAYS

(| 5 9 i3 M 2 £5 £9 33 37 Al 45 49 53 57

NUMBER OF FLIES IN BOTTLE

SS a of life of Drosophila for different initial densities of

stock.

320 THE AMERICAN NATURALIST [Vor. LVI

The observed regression line is shown in Fig. 3.

Here the regression appears at once to be substanti-

ally linear, and is proved to be by the analytieal con-

stants, which are as follows:

r= — 057 + .020,

y2 120 + .020,

Die IE 004.

The criterion ¢ is less than 3 times its probable error

and eannot be regarded as significant.

Putting all the data together, we have here indispu-

table evidence that the density of population is a signifi-

eant factor in influencing the duration of life (or death-

rate) in Drosophila. The correlation ratio » is certainly

significant in the case of all three stocks. Its lower value

in the case of the Quintuple stock is almost certainly due

to the fact that in the Quintuple experience there is not

a sufficiently extensive representation of densities. If

the other two tables were to be cut off at the density

array where the Quintuple is, they also would show a

much lower association between the two variables. So,

then, the general portion of Farr’s Law which affirms

that death-rate is some function of density of popula-

tion receives experimental confirmation in a widely dif-

ferent form of life.

When one comes, however, to the precise form dis-

covered by Farr (35) and confirmed by Brownlee (36,

37), the case is not so clear. We do not care to enter

upon any detailed discussion of the point now, because

we do not care to draw any conclusions as to the true

form of the skew regressions observed till we have some

additional experimental results in hand. Provisionally,

however, it may be said that the indications are that in

Drosophila something like the following relations hold:

(a) the lowest density is not the optimum; (b) the mean

duration of life tends to increase with increasing density

up to a certain point which is optimum; (c) after the

No. 645] THE DURATION OF LIFE 321

optimum region has been reached, increasing density is

associated with diminished duration of life, which pres-

ently falls below the lowest figure found with densities

below the optimum. These conclusions must for the

present be held as tentative.

In this paper data as to total duration of imaginal life

of 13,117 individuals of Drosophila are presented in re-

lation to the density of population. It is definitely shown

in the case of Wild, Sepia and Quintuple stocks that there

is a significant correlation between these variables. The

regression of duration of life upon density appears to be

significantly skew in the case of Wild and Sepia stocks.

The precise form of the regression and theoretical ques-

tions connected therewith are left for discussion in a

later paper upon the basis of more extensive material.

LITERATURE CITED

(The plan of numbering citations followed is explained in the second of

these Studies.)

35. Farr, W. Vital Statistics: A Memorial Volume of Selections from the

Repor rts and Writings of Wiliam Farr, M.D., D.C. po Vul. F.R.S.

Edit. by Noel A. Humphreys. London, 1885, xxiv + 5

36. Brownlee, J. Saag on the Biology of a Life-Table. na pei Stat.

Soc., Vol pp. 34-65, 1919. Discussion, pp. 66-77.

37. Id. Density d Death- Rate: Farr’s Law. Ibid., Vol 83, pp. 280-

38. sempe, rs “The Natural Conditions of Existence as they Affeet Crimi-

e. Fourth Edit., London, 1890

39. eria F. Über den Einfluss des Labani nsraumes auf das Wachstum

der amag rw s Arch., Bd. 188, pp. 254—272, 1921

40. Drzwina, and Bohn, G. Action nocive de lean sur les Sinters, en

Price PX la ENA de liquide. C. E. Soc. Biol. T. 84, pp. 917-

41. ~ 'R. ana Surface, F. M. A Biometrieal Study of Egg Production

n the Domestic Fowl. I. Variation in Annual Egg Production.

T. S. Dept. Agr. Bur. Anim, Ind. Bulletin 110, Part I, pp. 1-80,

1909.

42. Pearl, R. and Parker, S. L. On the Influence of Density of Population

upon t he Rate of woes cq in Drosophila, Proc. Nat. Acad.

Sci, Vol. 8, July, 1

43. Niles. J. On d. for Linearity of Regression in Frequency

Distributions. Biometrika, Vol. IV, pp. 332-350, 1905.

NOTES ON THE HYBRIDS BETWEEN THE

CANARY AND TWO AMERICAN

FINCHES

O. E. PLATH

MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE, Mass.

Peruars no animal has been so often crossed with other

species, and even genera, as the domesticated canary

(Serinus canarius). Darwin (1885, I, p. 311) speaks of

“nine or ten’’ such crosses, but many more have un-

doubtedly been made. The hybrids resulting from these

crosses are usually, if not always, infertile, and hence

are popularly known as ‘‘mules.’’ In almost all of these

crosses the domesticated canary serves as the female and

the wild finch as the male, but bird fanciers occasionally

succeed in making the reverse cross. The wild species

which is most commonly used for this ‘‘mule breeding"

is the European goldfinch, Carduelis carduelis Linnzeus.!

This fringillid is one of the handsomest finches in ex-

istenee, the plumage of the adults of both sexes being

made up of a beautiful combination of black, red, white,

yellow, and brown patches. The hybrids which result

when a yellow, or nearly yellow, eanary is erossed with

this fineh are chiefly interesting for two reasons: (1)

because they exhibit an apparently. endless chain of

variability in eoloration, and (2) beeause their plumage,

if dark, is conspicuously streaked, a character which is :

lacking (as far as external appearance is concerned) in

both the yellow canary and the European goldfinch.

Concerning the first of these two points valuable data

have been published by Bechstein (1795), Hünefeld

(1864), Blakston (1880?), Klatt (1901), Davenport

1 According to Chapman (1916, p. 383), this finch was introduced into

the United States at Hoboken, N. J. (in 1878), and Boston, and probably

still is a resident near both of these places. .

No. 645] HYBRIDS OF THE CANARY 323

(1908), and Galloway (1909). According to these au-

thors, the hybrids between the yellow eanary and the

European goldfineh may be: (a) completely dark, (b)

mottled (spotted), exhibiting an apparently endless

variation in color pattern, or (c) entirely white or yellow

(very rarely).?

The streaking in the dark plumage of canary-Euro-

pean goldfineh hybrids has been variously explained as:

(a) **derived from the original wild canary’’ (Darwin,

1885, IL, p. 15); (b) as reversion to the Serin finch,

Serinus hortulanus Koch (Klatt, 1901, p. 508) ; and (c)

as resulting from the latent streaking (visible in the

*green'' variety of the domesticated canary) factor of

the yellow canary, plus the color faetor of the European

goldfinch (Davenport, 1908, p. 20).

In 1914 the writer made several attempts to cross the

domesticated canary with some of our native American

finches, and some of the latter among themselves, since

such crosses, if made, seem to have never been recorded.

None of these experiments were successful. The work

was again taken up in the fall of 1918, and this second

attempt yielded several hybrids in 1919 and 1920. For

these latter experiments the writer had at his disposal

22 wild finches belonging to the following species: Ar-

kansas goldfinch (Astragalinus psaltria hesperophilus

Oberholser), willow goldfinch (Astragalinus tristis sali-

camans [Grinnell]), California linnet (Carpodacus

mexicanus frontalis [Say]), and California purple finch

(Carpodacus purpureus californicus Baird). Of these

22 wild finches, 5 were reared from eggs placed under

2 Galloway (1909, p. 4), who has probably reared more eanary-fineh hy-

brids than any other breeder, reports the following proportions of self-

eolored to variegated (mottled) individuals in the ease of canary-European

gold-fineh hybrids: (1) dark plumage (with no white or elear feathers), 172;

(2) slightly variegated (a few small white or elear spots in an otherwise

dark plumage), 74; (3) variegated (1/4 to 1/2 elear), 75; (4) lightly

bouton (1/2 clear to small ticks of dark in an otherwise clear plumage),

9; and (5) completely clear (total absence of dark feathers), 0.

3 A western sub-species of the American goldfinch doctis disini tristis

tristis Linneus), popularly known as the **wild canary.’

324 THE AMERICAN NATURALIST [Vor. LVI

canary females and the remaining 17 were trapped

shortly before the breeding season. It is chiefly due to

this second fact that the number of hybrids obtained

was not larger. All of the experiments were carried out

in separate breeding cages. The matings which yielded

results were the following:

TABLE I

i No.

Cross No. Year 9 sh of

Offspring

T Dor 1919 Yellow oniy x California linnet 3

P EE a Ee 1920 Yellow canary* x Willow goldfinch 5

E, PUDE 1920 Willow goldfinch X Arkansas goldfinch 4

The four hybrids resulting from cross No. 3 (willow

goldfinch 9 X Arkansas goldfinch d) died a few days

after hatching, and the female could not be induced to

breed for a second time. These hybrids differed from

ordinary newly-hatched finches and from the eight hy-

brids obtained from crosses No. 1 and No. 2 in having

exceedingly large abdomens, a condition which was prob-

ably due to the fact that a large quantity of yolk had not

been assimilated.

Cross No. 1 (yellow canary 2? X California linnet 4)

yielded three hybrids, one of which was accidentally

killed when nine days old. During the same summer

(1919) Mrs. L. V. Irelan of Berkeley, California, like-

wise sueceeded in rearing a brood (2 males and 2 fe-

males) of canary-California linnet hybrids? which the

writer was able to compare with his own.

Before going into detail regarding the coloration of

these canary-California linnet hybrids, it seems desir-

able to refer briefly to the plumage color of the paternal

species, the California linnet. Both sexes of this finch

are grayish-brown in color, but, when about three months

old, the male turns rose pink, orange red, or scarlet about

* The same female which was used in eross No. 1.

5In this case the mother was also completely yellow.

No. 645] HYBRIDS OF THE CANARY 325

the head, neck, breast and rump. These colors increase

in extent and brillianey with each molt. Males reared

and kept in captivity never develop anything but a yel-

lowish-buff color in these regions, and if a mature wild

male is confined, its red color, during the molt, likewise

becomes yellowish-buff. Both adults and young are con-

spieuously streaked, especially the latter.

The six* eanary-California linnet hybrids were all

completely dark (self-eolored) until the first molt (fall

1919), and closely resembled young California linnets,

but their plumage was less intensely dark than that of

thelatter. During the fall molt of 1919 all of the hybrids

became slightly ‘‘washed’’ (tinged) with yellow where

the California linnet d is red (or yellowish-buff). This

yellow tinge was more eonspieuous in the males than in

the females and became somewhat more pronounced

during the fall molt of 1920.

All six eanary-California linnet hybrids are streaked,

like the paternal and the ‘‘green’’ variety of the mater-

nal species. As regards size and shape, they differ very

little from the parents, both of which are similar in these

respects. Their notes are intermediate in timbre be-

tween those of the two parental species, the males hav-

ing a more powerful song than the canary.

In the spring of 1920 the writer paired two of these

eanary-California linnet hybrids. Both showed an ar-

dent desire to breed and the female exhibited consider-

able skill in nest building. The first egg was laid on May

6, and several days later a second (May 10). Both of

these eggs were only about half the size of canary or

California linnet eggs’ and were dark-blue in color, and

not speckled, while those of both parental species are

bluish-white and speckled. Both eggs were placed under

canary females, but proved to be infertile. The male

9 The hybrid which was accidentally killed was identical in coloration

with these six.

7 This corroborates similar observations by Bechstein (1795, IV, p. 469)

and Blakston (18807, p. 265), both of whom compare the eggs of canary-

fineh hybrids with peas.

326 THE AMERICAN NATURALIST [Vor. LVI

used in this experiment was also mated with a yellow

canary, but, despite much treading, all eggs were clear.

From cross No. 2 (yellow canary 9 X willow goldfinch

d) five? hybrids were obtained. A few years before, Dr.

H. C. Bryant of the California Fish and Game Commis-

sion also succeeded in rearing a canary-willow goldfineh

hybrid, concerning which he has been kind enough to

furnish the writer with complete information.

Before considering the plumage color of these canary-

willow goldfinch hybrids, it seems again desirable to

sketch briefly that of the wild finch. Both young and

adults of the willow goldfinch are chiefly olive-brown

and black in color, but the sexually mature male turns

eanary-yellow during the summer, with the exception of

the wings, tail and a small patch on the head, which re-

main blaek. Neither young nor adults show any streak-

ing.?

The three canary-willow goldfinch hybrids reared by

the writer are (January 6th, 1921) colored as follows:

No. 1, completely dark (self-colored); No. 2, likewise,

except for a few yellow feathers near the left eye; No.

3, dark, with a yellow band, about 5 mm. in width, run-

ning across the head; No. 4 (reared by Dr. Bryant),'?

dark, with some white feathers on the tail. All of the

hybrids reared by the writer are conspicuously streaked,

which, according to Dr. Bryant, was also true of hybrid

No. 4.

As regards size and shape, the writer’s canary-willow

goldfinch hybrids closely resemble the canary (this was

also true of hybrid No. 4), especially in shape of beak

. and length of tail, in which respects there is a consider-

able difference between the two parental species. As in

8 Two of these died shortly after hatching and hence furnished no re-

liable data as regards coloration,

9 This is also true of the remaining North American members of the

genus Astragalinus, the Arkansas and the Lawrence goldfinch (Astragalinus

„lawrencei Cassin), except that in the ease of the latter, the lower parts of

the young are indistinetly streaked (ef. Bailey, 1912, pp. 322, 323).

19 The eanary mother of this hybrid was also completely yellow.

No. 645] ` HYBRIDS OF THE CANARY 327

the ease of cross No. 1 (yellow canary 9 X California

linnet $4), the notes of the hybrids are intermediate in

timbre between those of the parents.

We now come to the question as to how these hybrids

compare with other canary-finch hybrids, and in how

far they conform with Mendel's laws of inheritance. It

will be noticed that in the case of the eanary-California

linnet hybrids, as in many mammalian crosses, dark

color is completely dominant over light color, but the

number of offspring (7) is too small to warrant the con-

clusion that this will always prove to be the case. On

the other hand, as regards the canary-willow goldfinch

hybrids, there is no complete dominance of one color,

the hybrids in this case showing a similar variability

to that of canary-European goldfinch hybrids.

Davenport (1908, p. 23) believes that the variability

in plumage color of canary-finch hybrids is entirely due

to the ‘‘mottling factor’’ of the yellow canary. He says

(p. 23):

It [the yellow canary] carries a mottling factor. Consequently

when the yellow canary is crossed with a pigmented canary or with a

finch the hybrids are mottled.

In support of this Spem he makes the following

statement:

That it is the yellow canary which contains the motie factor

and is the source of the variability of the hybrids is shown by the

fact that (1) hybrids with the green canary do not vary in this

fashion, and (2) hybrids between any two species of finches—of

which many are bred by fanciers—are “ cast in one mold.”

As regards the first of these two points, it may be said

that one should not expect canary-finch hybrids from a

‘‘oreen’’ (self-colored) canary to show yellow markings

as frequently as when a yellow canary is used. In regard

to the second point, Davenport (1908) seems to have

overlooked the fact that Blakston (1880?), on whose

authority this statement was probably based, states only

(p. 274) that all bullfinch-goldfinch ‘‘mules’’ are ‘‘cast

in one mould." In fact one of Blakston’s (1880?) re-

328 THE AMERICAN NATURALIST [Vor. LVI

marks clearly indicates that this is not true of the hy-

brids between all species of finches, for on the next page

(275) he makes the following statement concerning the

‘‘much more common”’ greenfinch-goldfinch hybrid:

It is not a very pretty bird, . . . partaking to a considerable extent

of its [the greenfinch’s] dull colour, though occasionally a more bril-

liant example than usual, having a good deal of the Goldfinch char-

acter about it, appears on the stage.

Davenport’s (1908) conclusion therefore does not seem

to be very well founded. i

Results published by Galloway (1909) since the ap-

pearanee of Davenport's (1908) paper seem to throw

some light on this question. As already stated, this

author (Galloway) obtained 172 dark (self-eolored) to

168 variegated (mottled) offspring from his canary-

European goldfineh (Carduelis carduelis) crosses. How-

ever, when he used the siskin (Carduelis spinus), a

closely related but darker species, he obtained nearly

three times as many (36 to 13) self-eolored as mottled

individuals, that is, almost a 3 to 1, instead of a 1 to 1

ratio. These results, supported by those set forth in

this paper, suggest that the frequency of mottling in

canary-finch hybrids is not solely due to the yellow

canary," but probably also depends on the coloration of

the wild finch.

LITERATURE CITED

Bailey, F. M

1902. Handbook of Birds of the Western United States. The River-

side Press, Cambridge.

Bechstein, J. M,

17 Gemeinniitzige Naturgeschichte Deutschlands nach allen drey

Reiehen. Vol. 4. Siegfried Lebrecht Crusius, Leipzig.

Blakston, W. A.

1880?. The Illustrated Book of Canaries and Cage-birds. Cassell,

London.

11 A similar problem exists in regard to the mottled seed-coat of the F,

of certain pigmented-white bean erosses. Shull (1907) suggested that it is

the white, and not the pigmented bean to which the mottling is due. How-

ever, Tschermak (1904, 1912) has shown that in some cases it is the pig-

mented bean which is the source of the mottling, a view which was later

aecepted by Shull (1908, pp. 437—439).

No. 645] HYBRIDS OF THE CANARY 329

Chapman, F. M.

1916. Handbook of the Birds of Eastern North Ameriea. D. Apple-

Co., New York and London

Darwin, C.

1885. The Variation of Animals and Plants Under Domestication. 2

Vols. John Murray, London,

cont DB

1908. Inheritance in Canaries. Carnegie Institute of Washington,

Publieation No, 95.

Galloway, A. R.

1909. prodi Breeding. A Partial Analysis of Records from 1891-

1909. Biometrika, Vol. 7, pp. 1-43, 5 figs.,

Hünefeld, H. V.

1864. Ueber Bastardzucht zwischen Stieglitz und Canarienweibchen.

Der Zo Garten, Vol. 5, pp. 139—144

Klatt G. T...

1901. Uber den Bastard von Stieglitz und Kanarienvogel Arch. f.

Entwicke'ungsmech. d. Organismen, Vol. 12, pp. 414—453 and

471—528, 1 pl

Shull, G. H

1907. otio dn Characters of a White Bean. Science, Vol. 25,

pp. 828—832.

1908. A New Mendelian Ratio and Several Types of Latency. AMER.

NATURALIST, Vol. 42, pp. 433—451.

Meer E. v

Weitere WD elaine an Erbsen, Levkojen und Bohnen.

Zeitschr. f. d. landw. Versuchswesen in Osterreich, Vol, 7, pp.

53 n (After Shull.

1912. ee e an Levkojen, Erbsen und Bohnen mit

Riicksi f die Faktorenlehre. Zeitschr. f. indukt. Abstam-

mungs- od Vererbungslehre, Vol. 7, pp. 81-234, 12 figs.

COEFFICIENTS OF INBREEDING AND

RELATIONSHIP

DR. SEWALL WRIGHT

Bureau or ANIMAL INDUSTRY, UNITED States DEPARTMENT

OF AGRICULTURE

Ix the breeding of domestie animals eonsanguineous

matings are frequently made. Occasionally matings are

made between very close relatives—sire and daughter,

brother and sister, ete.— but as a rule such close inbreed-

ing is avoided and there is instead an attempt to concen-

trate the blood of some noteworthy individual by what

is known as line breeding. No regular system of mating

such as might be followed with laboratory animals is

practicable as a rule.

The importanee of having a coefficient by means of

which the degree of inbreeding may be expressed has

been brought out by Pearl! in a number of papers pub-

lished between 1913 and 1917. His coefficient is based on

the smaller number of ancestors in each generation back

of an inbred individual, as compared with the maximum

possible number. A separate coefficient is obtained for

each generation by the formula

an+

Zn = 100 (1— 577^) —100 ü— gen)

where q»/2"* is the ratio of actual to maximum pos-

sible ancestors in the n + 1st generation. By finding the

ratio of a summation of these coefficients to a similar

summation for the maximum possible inbreeding in

higher animals, viz., brother-sister mating, he obtains a

single coefficient for the whole pedigree.

This coefficient has the defect, as Pearl himself pointed

1 AMERICAN NATURALIST, 1917, 51: 545—559; 51: 636-639.

No. 645] COEFFICIENTS OF INBREEDING 331

out, that it may come out the same for systems of breed-

ing which we know are radically different as far as the

effects of inbreeding are concerned. For example, in

the continuous mating of double first cousins, an indi-

vidual has two parents, four grandparents, four great

grandparents and four in every generation, back to the

beginning of the system. Exactly the same is true of

an individual produced by crossing different lines, in

each of which brother-sister mating has been followed.

Yet in the first the individual will be homozygous in all

factors if the system has been in progress sufficiently

long; in the second he wili be heterozygous in a maxi-

mum number of respects.

In order to overcome this objection Pearl has devised

a partial inbreeding index which is intended to express

the percentage of the inbreeding which is due to relation-

ship between the sire and dam, inbreeding being meas-

ured as above described. A coefficient of relationship

is used in this connection. These coefficients have been

discussed by Ellinger? who suggests certain alterations

and extensions by means of which the total inbreeding

coefficient, a total relationship coefficient and a total re-

lationship-inbreeding index for a given pedigree can be

compared on the same scale.

An inbreeding coefficient to be of most value should

measure as directly as possible the effects to be expected

on the average from the system of mating in the given

pedigree.

There are two classes of effects which are ascribed to

inbreeding: First, a decline in all elements of vigor, as

weight, fertility, vitality, etc., and second, an increase in

uniformity within the inbred stock, correlated with

which is an increase in prepotency in outside crosses.

Both of these kinds of effects have ample experimental

support as average (not necessarily unavoidable) conse-

quences of inbreeding. The best explanation of the de-

erease in vigor is dependent on the view that Mendelian

2 AMERICAN NATURALIST, 1920, 54: 540-545.

332 THE AMERICAN NATURALIST [Vor. LVI

factors unfavorable to vigor in any respect are more

frequently recessive than dominant, a situation which is

the logical consequence of the two propositions that

mutations are more likely to injure than improve the

complex adjustments within an organism and that injuri-

ous dominant mutations will be relatively promptly

weeded out, leaving the recessive ones to accumulate,

especially if they happen to be linked with favorable

dominant factors. On this view it may readily be shown

that the decrease in vigor on starting inbreeding in a

previously random-bred stock should be directly pro-

portional to the increase in the percentage of homozygo-

sis. Numerous experiments with plants and lower

animals are in harmony with this view. Extensive ex-

periments with guinea-pigs conducted by the Bureau of

Animal Industry are in close quantitative agreement.

As for the other effects of inbreeding, fixation of char-

acters and increased prepotency, these are of course in

direct proportion to the percentage of homozygosis.

Thus, if we can calculate the percentage of homozygosis

which would follow on the average from a given system

of mating, we can at once form the most natural coeffi-

cient of inbreeding. The writer? has recently pointed out

a method of calculating this percentage of homozygosis

which is applicable to the irregular systems of mating

found in actual pedigrees as well as to regular systems.

This method, it may be said, gives results widely different

from Pearl’s coefficient, in many cases even as regards

the relative degree of inbreeding of two animals.

Taking the typical case in which there are an equal

number of dominant and recessive genes (A and a) in

the population, the random-bred stock will be composed

of 25 per cent. 4A, 50 per cent. 4a and 25 per cent. aa.

Close inbreeding will tend to eonvert the proportions to

50 per cent. AA, 50 per cent. aa, a change from 50 per

cent. homozygosis to 100 per cent. homozygosis. Fora

natural coefficient of elc we want a seale which

3 Genetics, 1921, 6: 111-178.

No. 645] COEFFICIENTS OF INBREEDING 333

runs from 0 to 1, while the percentage of homozygosis

is running from 50 per cent. to 100 per cent. The for-

mula 2h—1, where h is the proportion of complete homo-

zygosis, gives the required value. This can also be

written 1—2p where p is the proportion of heterozygo-

sis. In the above-mentioned paper it was shown that

the coefficient of correlation between uniting egg and

sperm is expressed by this same formula, f — 1— 2p.

We can thus obtain the coefficient of inbreeding f» for a

given individual B, by the use of the methods there out-

lined.

The symbol r», for the coefficient of the correlation

between B and C, may be used as a coefficient of relation-

ship. It has the value 0 in the case of two random indi-

viduals, .50 for brothers in a random stock and ap-

proaches 1.00 for individuals belonging to a closely in-

bred subline of the general population.

In the general case in which dominants and recessives

are not equally numerous, the composition of the random-

bred stock is of the form a? 4A, 2zy Aa, y? aa. The per-

centage of homozygosis is here greater than 50 per cent.

The rate of increase, however, under a given system of

mating, is always exactly proportional to that in the

case of equality. The coefficient is thus of general ap-

plication.

If an individual is inbred, his sire and dam are con-

nected in the pedigree by lines of descent from a com-

mon ancestor or ancestors. The coefficient of inbreeding

is obtained by a summation of coefficients for every line

by which the parents are connected, each line tracing

back from the sire to a common ancestor and thence for-

ward to the dam, and passing through no individual

more than once. The same ancestor may of course be

involved in more than one line.

The path coefficient, for the path, sire (S) to offspring

(O), is given by the formula pos — àv (1+ fs)/(1 + fo),

where fs and f. are the coeficients of inbreeding for sire

394 THE AMERICAN NATURALIST [Vor. LVI

and offspring, respectively. The coefficient for the path,

dam to offspring, is similar.

In the ease of sire's sire (G) and individual, we have

Po.g = pos peo — 1 V (1 + fo)/ (1 + fo), and for any ances-

tor (A) we have for the coefficient pertaining to a given

line of descent p«« — (4)"V (1+ f.)/(1 + fo), where n is

the number of generations between them in this line.

The correlation between two individuals (rw) is ob-

tained by a summation of the coefficients for all connect-

ing paths.

Thus

1 n+" 1 š

T (3) N(1 4-5) + be)

where n and w are the number of generations in the

paths from A to B and from A to C, respectively.

. The formula for the correlation between uniting

gametes, which is also the required coefficient of inbreed-

ing, is

fo = rav (1 — fs) (1 -= fa),

where rsa is the correlation between sire and dam and fs

and fa are coefficients of inbreeding of sire and dam.

Substituting the value of rsa we obtain

fo — > (3)"""(1 + fa).

If the ancestor (A) is not inbred, the component for

the given path is simply (1)""" where n and w are the

number of generations from sire and dam respectively

to the ancestor in question. If the common ancestor is

inbred himself, his coefficient of inbreeding (fa) must

be worked out from his pedigree.

This formula gives the departure from the amount of

homozygosis under random mating toward complete

homozygosis. The percentage of homozygosis (assum-

ing 50 per cent. under random mating) is 4(1 + f.)

x 100.

335

COEFFICIENTS OF INBREEDING

No. 645]

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THE AMERICAN NATURALIST [Vor. LVI

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No. 645] COEFFICIENTS OF INBREEDING 337

By this means the inbreeding in an actual pedigree,

however irregular the system of mating, can be com-

pared accurately with that under any regular system of

mating.

As an illustration, take the pedigree of Roan Gauntlet,

a famous Shorthorn sire, bred by Amos Cruickshank.

This bull traces back in every line to a mating of Cham-

pion of England with a daughter or granddaughter of

Lord Raglan. For the present purpose we will assume

that these bulls were not at all inbred themselves and

not related to each other. Since the sire traces twice to

Champion of England and twice to Lord Raglan and the

dam once to each bull, there are in all four lines by which

the sire and dam are connected.

Common Ancestors

Individual of Sire $ n n! |)"

and Dam X (1 + ba)

Roan Gauntlet Champion of England

45,276 (35,284) CF OSB ea 2 1 .062500

2 .062500

Lord Raglan (13,244). . 0 3 3 -007812

3 .007813

.140625

The coefficient of inbreeding comes out 14.1 per cent.,

a rather low figure when compared to such systems as

brother-sister mating (one generation 25 per cent., two

generations 37.5 per cent., three generations 50 per cent.,

ten generations 88.6 per Se) or parent-offspring ma-

ting, (one generation 25 per cent., two generations 37.5

per cent. three generations 43.8 Eum cent., approaching

50 per cent. as a limit).

As an example of eloser inbreeding, take the pedigree

of Charles Collings’ bull, Comet. The sire was the bull

Favorite and the dam was from a mating of Favorite

with his own dam. As Favorite was himself inbred to

some extent, it is necessary to calculate first his own

coefficient of inbreeding.

338 THE AMERICAN NATURALIST [Vor. LVL

Common Ancestors :

Individual of Sire 5 n n (iu

and Dam x (1 + fa)

Favorite (252) mem id (2853)... S 0 1 1 .1250

Favorite (cow)........ 0 2 1 .0625

1875

Comet (115) sis (252). eb Leo 0 1 2969

PCIE (22 e 0 1 1 1250

ee Un dde 0 2 2 0312

Peet (COW) Oia. ch 0 3 2 .0156

| 4687

In the ease of Comet, Foljambe and Favorite (cow)

each appears twice in the pedigree of the sire and three

times in the pedigree of the dam. However, only those

pedigree paths which connect sire and dam and which do

not pass through the same animal twice are counted. The

, listing of Favorite (252) and Phoenix as common ances-

tors eliminates all but one path in each case as regards

Foljambe and Favorite cow. The remaining paths are

those due to the common descent of Bolingbroke, the

sire’s sire and Phenix as the dam’s dam from the above

two animals.

By tracing the pedigrees back to the beginning of the

herd book, the coefficients cf inbreeding are slightly in-

creased. This meant going back to the seventh genera-

tion for one common ancestor of the sire and dam of

Favorite. The coefficient in the case of Favorite be-

comes .192 instead of .188 and that of Comet .471 instead

of .469. Remote common ancestors in general have little

effect on the coefficient. It will be noticed that Comet

has a degree of inbreeding almost equal to three genera-

tions of brother-sister mating or an indefinite amount of

sire-daughter mating where the sire is not himself inbred.

THE ASSORTMENT OF CHROMOSOMES

IN TRIPLOID DATURAS

JOHN BELLING AND ALBERT F. BLAKESLEE

STATION FoR EXPERIMENTAL EvoLUTION, Corp SPRING ecc

Lone Istanp, New YORK

The present article is the one of a number of proposed

papers which will deal with the behavior of the chromo-

somes in the different classes of Datura mutants, the

correlation of the chromosomal differences with changes

in structural and other characters, and with the ratios

in which Mendelian allelomorphs are found in the off-

spring. The method mainly used in the microscopical

examination, and the general principles involved, are

given in two papers already in press for THE AMERICAN

NATURALIST,

Sizes of Chromosomes.—The diploid Datura Stra-

[A TO CA

Second metaphases of a normal Datura in a pollen-mother-cell.

h half sir constricted,

ration in

priate pressure so that the chromosomes were in optical contact with the cover-

339

340 THE AMERICAN NATURALIST [Vor. LVI

monium shows, in the metaphase of the second division

in the pollen-mother-cells (Fig. 1), two groups, each con-

sisting of 1 extra large chromosome, 4 large, 3 large me-

dium, and 2 small medium chromosomes, 1 small and 1 ex-

tra small chromosome. Thus the somatic formula is 2(L4-

C ry f Y

Ave TE ini i

Fic. 2. One second metaphase plate of a tetraploid Datura, in a pollen-

spi bgo

Late prophase of a normal Datura in a pollen-mother-cell. The

size Apea are especially distinct, for the smaller chromosomes have con-

densed earlier.

Fic. 4. Late prophase of a Visi Datura. The largest chromosome set

natin agg was f latest to conden

FiG rophase of a eae Datura. The largest chromosome set

is hook- [xdi ed. we late prophase or early metaphase trivalents often have

the form of a ring with a ha nale; whieh is indicated in only one trivalent in

Fig 4, and is not shown in Fig. 5.)

/.4]124- 3M 4-2m -- S 4- s). Tetraploid plants have arisen,

in rare cases, from these diploid Daturas (2). They

show (Fig. 2) twiee as many chromosomes in each of the

size classes, and have the somatic formula 4(L + 41 + 3M

--2m-FS--s). Ont of many crosses of tetraploid

No. 645] ASSORTMENT OF CHROM ES 341

Daturas by pollen from normals, 4 triploid plants have

resulted (3). Their somatic formula is shown to be 3(L+

4]--3M --2m + S +s). Similar results have been ob-

tained for triploid hyaeinths by de Mol (7).

Attraction of Homologous Chromosomes.—In the nor-

mal Daturas the late prophase or early metaphase of the

first division in the pollen-mother-eells shows 12 sets with

two united chromosomes (bivalents) in each (Fig. 3).

These bivalents can readily be arranged in the six size

classes. In the corresponding stage of the triploid

Daturas there are 12 sets of three united chromosomes

each, and these trivalents can be arranged according to

the size formula (Fig. 4). Sometimes two of the three

rod-shaped chromosomes are united together at both

ends, and the third is joined on at one end only, or the

three may form a hook (Fig. 5). Some trivalents were

seen by Osawa in triploid mulberries (8), and a group of

9 trivalents was also found in a triploid Canna (1). (The

complete group of 9 trivalents has also been seen in 4

other triploid Cannas.)

i : 4 È 2

" We se -

; $9 s» ug * E

/ E d $e... $ 8 [ 3 E

49 a $3 m

Ac P e

IB. ^ 06 e, 8$

Fic Second metaphases in a pollen-mother-cell of a triploid Datura.

The large and large medium chromosomes were not separable in this oT

Separation (Disjunction) of Chromosomes.—So far as

seen in Datura, two chromosomes usually pass to one

pole, and one chromosome to the other, from each triva-

lent, as is the case in triploid Cannas (1).

Assortment of Chromosomes.—From one triploid

342 THE AMERICAN NATURALIST [Vor.LVI

plant both groups of chromosomes were counted in each

of 84 pollen-mother-cells, which were in the second meta-

phases, and showed no detached chromosomes (Fig. 6).

The assortments are given in Table

TABLEI

ASSORTMENT OF CHROMOSOMES IN 84 POLLEN-MOTHER CELLS OF TRIPLOID

Datura, 19729(1)

Metaphase of Second Division

LD49 1.48 L BM il. 15 16 17 18

Assortment of Chromosomes | + | + + Bow aepo

24 | 23 | 22 1, |. 20 19 18

| 1 6 13 | 17 26 20

19.0

Nos. of double groups |

Calculated on duces orients- |

0.04 | 0.5

tion of trivalents.........

Early anaphase of the second divisio

Fic. 7.

pol Datura.

es had apparently

n in a pollen-mother-cell of a

a s

(The upper €——Ü plate was shifted upwa

tly been detached at the first

of the 3 extra large chrom

MCN and divided at the siecle division. Probably a tetrad with 2 micro-

cytes would have result

No. 645] ASSORTMENT OF CHROMOSOMES 343

It is evident that.the orientation of the trivalents in

the first metaphase must be nearly or quite a random

one, as was suggested in triploid CEnotheras (5, 6) and

mulberries (8), and as is the ease in triploid Cannas (1).

(Nearly similar results were also obtained from a total

of 58 single-metaphase plates from this triploid Datura.)

Detachment of Chromosomes.—' Three buds ‘yielded

62 pollen-mother-cells with both seeond-metaphase plates

countable, and among these there were six cells showing

that one chromosome had been detached at the first ana-

phase (Fig. 7), one cell showing detachment of two’

chromosomes, and one cell showing both one and two de-

tached chromosomes. Thus there were about 13 per cent.

of cases of detachment. These detached chromosomes

(8) form mieroeytes when the pollen-mother-cells con-

strict to form tetrads (Fig. 8). Table II shows the num-

3 ¢

Fic. 8. Tetrads, etc., of a triploid Datura. Above: (1) a normal tetrad;

(2) a tetrad with one microcyte; (3) a tetrad with 2 microcytes, Below: (1)

a tetrad with 4 microcytes; (2) two giant cells; (3) rare form with 6 not very

unequal cells.

bers of microcytes seen in nearly 3,500 tetrads from 3

triploid plants. The average is 13 per cent. of cases of

detachment, but the variation in different buds appears

too great to be due to chance alone. In 100 pollen-grains

there would be about 5 microcytes.

344 THE AMERICAN NATURALIST [Vor. LVI

Non-reduction.—In_ belated pollen-mother-cells the

chromosomes in the trivalents assume the four-lobed con-

dition of those in the adjoining cells which are in the

metaphase of the second division. The first nuelear divi-

TABLE II

DETACHMENT OF CHROMOSOMES. NON-REDUCTION

Pollen Tetrads of Triploid Plants. (Percentages)

Regular Double-sized

Microspores Microspores

| i | | Pa |

ied = — | | | |

Dunis 4 4 4/4 2 | 2 2 cent- |

| age of | Nos. o

| | | Ete. |Cases of. Tetads

No < Micro- | |

SETS 1 2 12L41—1Llt:11.4 tach-

Plant and Bud | | |

19729 (1) a..| 67.0 | 20.0 | 9.0 | 0.7 | 0.5 | 2.0 | 0.5 | 0.2 30.9 403

19729 (1) b..|91.5| 3.0} -5.3 | 0.2 | 8.5 436

19729 (1) c..| 90.3] 3.3 | 5.9 | 0.2 | 0.2 | 9.6 425

19729 (1) d.. 96.1 16] 09| — prs 1.4 | 2.5 433

20345 (1) a../ 83.8, 7.9| 8.1] 0.2 | | 16.2 444

20345 (1) b..| 97.8 | 0.5 | 0.7 | — | — | 0.7 | 0.2 13 412

20345 (1) c.. 98.0 0.8 —|—]|10! 1.1 400

20380 (1) -.. 65.5 | 19.0 | 14.6 | — | — | 0.6 | — | 0.4 34.0 542

Average..... 863| 7.0| 5,66|02/|0.1|0.7/0.1/0.1 0.03 | 13.0 Total

| | 3,495

Microcytes to 100 Percentage of double-sized

pollen-grains = 4.9 pollen-grains = 0.4

sion is entirely omitted, there is no reduction (8), and

two nuclei with 36 chromosomes each are formed at the

second division. The two cells which result are twice

the size of the average microspores, and can be seen in

the pollen as giant grains. Non-reduction may be greatly

increased by transient cold. It averaged 0.4 per cent.

in the tetrads. A hundred full pollen-grains were meas-

ured at random,from each of 8 flowers on 4 triploid

plants. The average was 0.5 per cent. of giant grains.

Chromosomes of Functional Egg-cells.—In one triploid

Datura, from three (or fewer) capsules pollinated by a

normal, there were produced 75 mature plants, 67 of

which had their chromosomes counted.

No. 645] ASSORTMENT OF CHROMOSOMES 345

TABLE III

CHROMOSOMES OF PROGENY OF TRIPLOID DATURA POLLINATED BY DIPLOID

Nos. and Assortment of Chro-

olo Soe ieee cia vue MO 12 13 14 - .13 24 18

+ + At se ts ate gas ES —

12 12 12 13 12 18

Nes? OF Plante: Vu 24 33 J0- er ee eee

Calculated on random as-

sortment for 4096 ovules. 1 12 66 oF pe Se HPS ee a sc

The number of normal progeny shown in Table III is

much beyond expectation (on the hypothesis that orienta-

tion of trivalents in the first division of the megaspore

mother-cell is random), even if we allow the excessive

total of over 4,000 ovules to 3 capsules. Detachment of

chromosomes in the megaspore-mother-cells to the max-

imum extent found in the pollen-mother-cells will only

partially account for this excess. Similar results were

obtained by van Overeem with triploid @nothera bien-

nis pollinated by the normal (9).

Triploid Inheritance.—The 75 progeny showed triploid

or trisomic (not disomic) inheritance (2) of two probably

independent pairs of genes, those for purple and white

flowers, and those for prickly and smooth capsules.

Distribution of Extra Chromosomes.—Among the 33

plants with one extra chromosome, cases were found

where this extra chromosome was extra large, large,

medium, small, or extra small. These plants showed 11

bivalents and 1 trivalent at the late prophase and early

first metaphase. Ten different forms were recognized by

external features among 30 of the 33 forms with an extra

chromosome. (Three plants have not yet been identified.)

Among these ten forms, 1 form (Globe) occurred 5

times, 3 forms (Buckling, Ilex, and Reduced) occurred 4

times, 2 forms (Glossy and Elongate) occurred 3 times,

3 forms (Rolled, Cocklebur, and Poinsettia) occurred

twice, and 1 form (Mieroearpic) occurred once. The ex-

pectations for each of 12 possible forms are presumably

equal, namely 2.5. The Datura plants with 2 extra

346 THE AMERICAN NATURALIST [Vor. LVI

chromosomes so far examined showed 10 bivalents and

2 trivalents at the first prophase.

Thus the random assortment of chromosomes in trip-

loid Daturas parallels the conclusions as to the random

assortment of genes in triploid (trisomic) inheritance,

and adds to the evidence for the chromosomal theory o

heredity given by the cytological and genetic work on

Drosophila (4) and other insects.

LITERATURE CITED

1. Belling, J. 1921. The Behavior of Homologous Chromosomes in a Trip-

loi nna. Proc. Nat. Acad. of Science, 7: 197—201.

2. Lieu A. F. 1921. Types of Mutations and their Possible Signifi-

ice in ToS AMER. NAT, pi 254-267

$. lenis, A. lling, and M. E. Yurnbán, 1920. Chromosomal

sahil yw Mendelian Phenomena in Datura Mutants. Science,

52: 388-390 -

4. Bridges, C. B. 1921. Triploid Intersexes in Drosophila melanogaster.

: 54

5. Gates, R. R. 1909. The Behavior of Chromosomes in (Enothera lata X

gigas. Bot. Gaz., 48: 179—199.

6. oni de: Tes 1911. Cytologische Untersuchungen einiger Bastarde von

a gigas. Ber. d. Deutsch. Bot. Ges., 29: 160—160.

7. de Ma oc i^ 1921. Over het voorkomen van heteroploide varieteiten

van H: gown: orientalis L, in de Hollandshe kulturen. Genetika, 3:

97-192,

8. Osawa, I. 1920. Cytological and Experimental Studies in Morus, with

S ference to Triploid Mutants. Bull. Imp. Sericult. Exp, Sta.

Japan, 1: 317—369.

Ð. van Overeem, C. 1921. Uber Formen mit abweichender Chromosomen-

zahl bei Œnothera. Beih, z. Bot. Centralbl., B. 38, Abt. 1, Heft 1, S.

73-113.

(ESTRUS AND FECUNDITY IN THE GUINEA PIG

DONALD B. TRESIDDER

DEPARTMENT OF ANATOMY, STANFORD MEDICAL SCHOOL

Tui study was undertaken at the suggestion of Pro-

fessor Meyer, primarily for determining the numerical

relation between the corpora lutea of pregnancy and im-

plantations in the guinea pig.

-Most of the animals used in this experiment were pur-

chased from dealers, for it was impossible, in the short

time at my disposal, to obtain young animals of uniform

age and with the exception of a few guinea pigs raised

in our laboratory, only approximate ages were known.

The guinea pigs were housed in a well-lighted, sunny,

heated room. Lantz, '13, reported that the optimum

temperature for the guinea pig is 65°. Draper, "20,

stated that they thrive best at temperatures between 50?

and 70? and found young animals extremely susceptible

to small changes in temperature; some of them dying

when the temperature was lowered permanently from 60?

to 58? F. However, I did not notice any marked differ-

ence in the behavior or condition of extremely young ani-

mals kept at a temperature of 50°. They showed every

sign of vigor and no animals were lost as a result of this

exposure. Indeed, I learned of guinea pigs kept in the

open in unheated pens, sheltered only from wind and

rain. These animals were said to thrive and to multiply

at the customary rate, but no records were kept. In my

own work I found that a few degrees above or below 50°

seemed to make no appreciable difference in the behavior

of the animals, and I hence am somewhat sceptical about

the marked susceptibility of the guinea pig to cold, so

often reported.

The animals were fed dry alfalfa and barley daily and

green vegetables about twice a week. Many writers have

reported that guinea pigs did not do well on dry feed,

but it was my experience that, if fed an abundance of

water, they throve on alfalfa and barley alone. Since

they are subject to intestinal disturbances, it is of con-

347

348 THE AMERICAN NATURALIST [Vor. LVI

siderable importance that they be fed with the greatest

regularity.

Several animals were lost during the course of the ex-

periments and in each case a necropsy was performed.

Illness, in several of the animals, extended over a period

of weeks. They lost steadily in weight, and tended to

assume a characteristically crouching attitude. The fur

became rough and tousled. Some of them chewed in-

eessantly, although some pain seemed to be associated

with the process. The full significance of this behavior

was made clear at the necropsy. Guinea pig No. 7, for

example, which succumbed after an illness of three weeks,

had an empty stomach, and the abdominal cavity was

absolutely devoid of fat. There were no macroscopic

signs of infection or disease. Examination of the teeth

revealed that the upper incisors were worn down almost

to the gums, with a more than corresponding increase in

the length of the lower incisors, making occlusion of the

molars impossible. The molars were loose and could

easily be picked from the jaw with an ordinary labora-

tory forceps. :

The body of guinea pig No. 12, which died with prac-

tically the same symptoms, showed extreme atrophy and

emaciation. Ascaroid parasites were found in the rectum.

The upper incisors were loose and worn and the short

stumps remaining could be be removed with the fingers.

The upper and lower incisors were separated by about 8

mm., due to the fact that the molars occluded first and pre-

vented the short, probably fractured incisors from meet-

ing. From the findings in these cases it would seem that

guinea pigs may die of starvation because of the presence

of worn or irregular teeth and consequent inability to

masticate food. It may perhaps be that the changes in

the teeth of these animals were due to senility, but fur-

ther observations are necessary to confirm this before a

definite answer can be given to the question.

In order to study daily stages in the pregnancy of guin-

ea pigs it became necessary to mate a large number of

animals and to know the exact time of copulation. Stock-

ard and Papanicolaou, 717, studied the estrous rhythm of

No. 645] FECUNDITY IN THE GUINEA PIG 349

the guinea pig by making microscopic examination of the

material found in the vagina. They found that ‘‘ Guinea

pigs kept in a state of domestication and under steady

environmental conditions possess a regular dicstrous cy-

cle, repeating itself in non-pregnant females about every

sixteen days throughout the entire year, with probably

small and insignifieant variations during the different

seasons. Each period of sexual activity lasts about 24

hours and is characterized by the presence of a definite

vaginal fluid which is not sufficiently abundant to be read-

ily detected on the vulva, but is easily observed by an

examination of the interior of the vagina." They added

that macroscopic signs of heat are unreliable.

In my work it was found impractical to determine the

existence of heat microscopically and the knowledge that

heat should recur about every fifteen days furnished a

starting point. . Each female was given a number and en-

tered on an individual record sheet giving the following

data:

Date and hour of attempted mating.

Result of attempted mating.

Each time the animal eame into heat the record showed:

Whether heat was recognizable by macroscopic examina-

tion.

Number of days since last heat.

Number of hours since the first successful coitus.

Number of hours that external signs of heat could be ob-

served by examination.

Matings were attempted daily, whether the animal was

supposed to be pregnant or not. The males were intro-

duced into the pens with the females regardless of whether

or not the latter were thought to be in heat, and they were

allowed to remain with the females from five to fifteen

minutes. It was easy to follow the dicestrous cycle of any

individual animal. A glance at the guinea pig’s record

each day showed the number of days since the last heat,

and, knowing that heat should return about the fifteenth

day, it was practically impossible for it to come and go

unnoticed unless it recurred altogether irregularly. We

350 THE AMERICAN NATURALIST [Vor. LVI

found that after some practise heat could be determined

rather accurately by inspection. A guinea pig in rut

will often assume the position of copulation when stroked

gently over the lumbar region. The vulva are swollen

and moist, and often a cheesy secretion is seen. The

latter is a positive sign of heat, but we found that some

guinea pigs refused to mate during the entire period in

which the secretion was present.

In young animals we found heat recurring every fifteen

or sixteen days with very little variation among indi-

viduals of the same age. Three striking exceptions in

which heat returned in twelve days will be reported later

in this paper. Papanicolaou and Stockard found that in

old multiparz the period may be lengthened to 18 days.

I also found that as the animals grow older they seem to

become more and more irregular in their rhythm. In

three very old animals I was unable to find any signs of

heat throughout an entire year, although I attempted to

mate them twice daily. Three other animals maintained

a cycle of 20 days, and in some cases we were unable to

demonstrate any regular estrous rhythm at all, either by

inspection or by the use of a male.

Subsequently (1920) these workers have reported that

‘* underfeeding with a diet of 20 grams of carrots per

day produces prolongation of the dicstrum, and at the

same time a congestion in the ovary and uterus and a de-

generation of developing Graafian follicles.” They con-

eluded that ** the extent of prolongation of the dicestrum

depends upon the stage at which an animal is underfed.

. . . Large follicles seem to require better nutrition than

a small primary follicle. . . . Thus a late underfeeding

has a more injurious effect than an early one, and post-

ponement of the next cestrus is correlated with a postpone-

ment of new ripe follicles in the ovary." Stockard and

Papanicolaou believe that the ovarian follicles are ex-

tremely sensitive to environmental conditions. They be-

lieve that extreme variations in the estrus cycle of cer-

tain animals may be accounted for, partially at least, by

differences in nutrition.

In the course of these observations the intervals be-

No. 645] FECUNDITY IN THE GUINEA PIG 351

tween attempted matings were shortened, with the idea

that heat might be recurring unnoticed, but mating never

oecurred at other intervals. It is doubtful whether any

definite rhythm is maintained by old guinea pigs, for pig

No. 9, which was observed to be in heat December 27,

was not in heat again until 49 days later. Animal No.

20 was in heat October 17 and heat did not return until

91 days later. In another instance heat returned after

118 days. However, since the age of these animals is not

known, it is impossible to be sure that these irregularities

are due to senility.

Bischoff, '44, stated that copulation in the guinea pig

occurs within 3 hours after parturition. In four cases in

which he prevented copulation heat returned after inter-

vals of 40, 50,51, and 51 days. Hensen, ’76, and Rein, ’83,

claimed that the most favorable time for copulation is

within one hour after parturition. I observed copulation

in 12 animals immediately after parturition. Matings

were attempted at one-hour intervals for six hours after-

ward. In four cases I was unable to mate the females at

this time. They were found in heat again 34, 36, 81, and

120 days later. The first two animals were about six

months old. The last two were very old, judging by their .

teeth. Two females mated 1 hour after parturition, 2

after 2 hours, 1 after 3 hours, 1 after 5 hours, and 2 after

6 hours. In three cases no pregnancy resulted and heat

returned in 31, 31 and 29 days.

Many writers have reported that females refuse the

male shortly after the first copulation. The inference is

that some nervous mechanism automatically terminates

heat soon after copulation. Instances have been reported

in which the female refused the male 20 minutes after the

first copulation. In observations extending over nearly a

year, however, three cases were observed in which the

female mated again eight hours after the first copulation.

In the majority of cases the female permitted copulation

three hours after the first mating. One animal mated 13

times in an interval of 8 hours. It seems that a female

accepts the male at any time during the first stage of heat

regardless of any previous intercourse, but apparently

302 THE AMERICAN NATURALIST [Vor. LVI

she permits matings somewhat reluctantly after this.’ In-

stead of assuming the position for copulation when ap-

proached by the male she often runs around the cage and

resists vigorously. Unless the male is very persistent

and active copulation will not occur. One female resisted

a second coitus for fifteen minutes by kicking, snapping,

ete., only to stop suddenly and take the position for copu-

lation. This behavior of the female may be due to pre-

vious mating or it may simply mean that the period of

heat is subsiding. I am inclined to the latter view, be-

eause we have eneountered many females among animals

which had not been previously mated, who resisted the

males vigorously for a time, only to yield in the end. The

time during which the females permitted copulation un-

hesitatingly was a relatively short one, but after this

phase had passed the animal might yet be mated if the

male was persistent.

Stockard and Papanicolaou, '17, are of the opinion that

among domestieated guinea pigs only a slight seasonal

variation exists in the occurrence of heat, but in the pres-

ent series of guinea pigs the fall months were the most

favorable for matings, as shown by the following table:

Month Number of Resulting Percentage

Matings Pregnancies

alo ilie ee MANI AO 23 21 91.3%

Octabum i P oro UY S 17 10 58.8

November... a a V LAS I 8 3 37.5

December oL. 11 4 36.3

JaDuAMY uL LL ee: 7 4 57.1

Febrtudz9 [105420228 eee coe 5 0 0.0

Mare; io eo LES 8 | 4 50.0

Apüho ui C d 12 | 5 41.6

MAS ess s xS a 9 5 55.5

PURO PA oU INL 6 5 83.3

The males seemed to be partly responsible for this wide

variation. During the winter months they were lethargie

and indifferent. When placed in a pen with a female

known to be in heat, the male often ignored her, eating

unconcernedly instead. In many instances several males

had to be placed with such a pig, in succession, before

a mating took place. This is in marked contrast to the

customary behavior, for when placed in a pen with two

No. 645] FECUNDITY IN THE GUINEA PIG 353

females, the male will often go directly to the female in

rut. Sometimes, however, he will mistakenly pursue the

one that is not in heat, although repelled by sharp bites

and other negations, only to wheel suddenly and mount

the receptive female. The pursuit of the wrong animal

may only serve to stimulate him, but in some instances it

was necessary to remove her before he would turn his at-

tentions to the one in rut. Puzzling sexual idiosynerasies

also were noted. Instances were observed, for example,

in which a male would not under any cireumstances mate

with a certain female which was in heat, although he was

persistent in the ease of others. On the other hand, some

females also were noticed to repulse a certain, male, al-

though accepting others.

It will be seen from Table I that 106 matings resulted

in 61 pregnancies, or 57.5 per cent. Draper, '20, reported

that only 40 per cent. of the animals bred by him became

pregnant. Since Stockard and Papanicolaou found 95.4

per cent. out of 88 pigs pregnant, considerable variation

would seem to exist. The large discrepancy between their

results and ours may be due to the fact that the latter

were working with uniformly young, selected animals or

that the males were left to remain with the females, in-

stead of being removed after several copulations.

In the many matings not followed by pregnancies, the

next estrous cycle was prolonged. This is shown by the

accompanying chart.

Guinea-pig Number “Heat returned after

Do Car ek we UNA MAR LIE LER E 30 days.

SE E E ve xe. Lh KA ERA E TA EY dex EE

LrgNtog ee uuu cre ET 28

OU ie M S a et eee 15

DU ouis E E S E E dta VERS 46

Be es ese E E 29

eee ees 30

E ee Rb. 31

dU diokeeko ves a ere ess Eee oe eet 12

SÉ cicer creas Gas ciel 15

Be ea se ee eR Tru E 29

DIAC. Vine ee UERE VEGAS ER ee eet eey 30

Bi ei cadi ee ee ae 15

354 THE AMERICAN NATURALIST [Vou LVI

As noticeable in the above chart, the lengthened dices-

trous periods are nearly exact multiples of 15, the nor-

mal period, thus showing that the cycle is definitely pe-

riodie as reported by Stockard and Papanicolaou, "17b.

Long, ’15, found that the cestrous cycle was prolonged by

inserting a glass rod in the vagina of the rat. He held

this prolongation to be due to a stimulation of the cervix

of the uterus. Although I stimulated the uterus of guinea

pigs by means of a warm glass rod in three cases only,

heat returned in 15, 15 and 16 days, and I regret that I was

not able to extend this series of experiments in order to

obtain more data on this interesting phenomenon revealed

by Long in the rat. However, from the above table, it

is clear that copulation definitely prolongs the next œs-

trous cycle in the majority of cases. This may be due

to direct stimulation of the cervix of the uterus, as ex-

plained by Long, or implantation may have occurred, fol-

lowed by abortion or by absorption of the young concep-

tuses, in cases in which the period was greatly prolonged.

Guinea pig No. 39 (see Table II) was mated two hours

after parturition, but no pregnancy followed. This ani-

mal was remated 12 days later, with resulting pregnaney.

This confirms a case reported by Rubasckhin, 705, in which

heat returned 10 days after parturition. Stockard and

Papanicolaou, in considering Rubasckhin’s report, re-

garded 10 or 12 days as too short a period to indicate the

return of heat. Nevertheless, in the ease reported here

heat was unmistakable, and this animal which was mated

12 days after parturition became pregnant. I observed

heat to return in 12 days also in two other pigs.

Young animals constantly in association with males

became pregnant at an earlier age than females isolated

from males. Of a litter containing 3 females and 1

male, two females were placed in separate cages a few

days after birth and the remaining male and female

were allowed to run together. At the age of 5 months,

the latter produced a litter. This indicates that the

mating of this pair occurred before the animals were

three months old. Yet no ill effects of this early mating

or of the inbreeding could be detected in the offspring.

No. 645] FECUNDITY IN THE GUINEA PIG 355

When the two sisters were two months old, males were

introduced into the pens twice daily, but no signs of heat

were observed, and no matings occurred until these fe-

males were five months old. Similar results were obtained

with two other litters. Since my work was done Mr.

Warnock, a fellow student, has observed two females to —

bear viable litters at the end of the third month. "This

implies mating at the early age of one month. The pa-

ternal male was several months older, however.

Tur CORPORA LUTEA or PREGNANCY

In order to study the correlation between corpora lutea

and implantations during the various stages of preg-

nancy, animals were mated and killed, from the seventh

day of gestation on, for each day up to and including the

fifteenth. From the fifteenth day to full term, animals

were killed every other day.

When the guinea pigs were killed, the ovaries and

uteri were removed and placed in formalin for twenty-

four hours and the number of embryos in each horn of

the uterus recorded. The ovary corresponding to the

horn of the uterus having the larger number of concep-

tuses was arbitrarily chosen for use in determining what

relation might exist between the number of conceptuses

and the number of corpora lutea. Thus guinea pig No.

10 had two conceptuses in the right horn and one in the

left. The right ovary was embedded and eut serially into

thick sections. The left ovary was cut 7 micra thick

for the study of changes in the corpora lutea during preg-

nancy.

In a study of 14 embryos, Draper, ’20, found 76 in the

left horn and 69 in the right, a ratio of 1 to 0.9. Of 98

embryos from 35 guinea pigs, I found 55 in the right horn

and 43 in the left, a ratio of 1 to 0.78. The average num-

ber of feetuses per pregnancy was three.

Table II shows that there is a marked agreement be-

tween the number of eorpora lutea in an ovary and the

number of implantations in the corresponding horn of

the uterus. Out of 34 ovaries examined, the number of

eorpora lutea was the same as the number of embryos

356 THE AMERICAN NATURALIST [Vor. LVI

in the eorresponding horn of the uterus in all save six

eases. In five of these six instances there was one em-

bryo-less in the horn of the uterus than there were

corpora lutea in the ovary. In the other case, the right

TABLE II

T : Embryos (Corpora Lutea

Guinea Duration of Remarks

Pig Pregnane

Right; Left | Right, Left

25838 150 hes 2 se 7 1 1 3 1 Well-formed but

p COO eM 8 0 3 1 3 no éxternal ine

dd. iuis 9 2 1 2 f of implantations.

nis NE MT 10 1 8 1 3

Bb ri 11 1 1 1 3 Well-marked evidence

PAPOEA 12 8 0 3 0 of resorption.

B vell 13 1 2 1 2

SN I IIO 14 g 1 3 1

2j lx ads 15 0 1 0 2

20:5... 1 x v 17 3 0 2 0

285. es 19 1 3 1 3

CA obi 21 2 1 2 1

Sd. cc rv 23 2 8 2 3

29 vuulou. 25 3 0 3 0

Zi 1 2T 2 0 2 0

NE ld i4 29 a 1 3 1

rp e ee qe 31 +2 1 3 1

Roo a 33 2 0 3 1

if 1 s 35 2 1 2 0

18.257. 2521 37 2 1 3 |

16250: 39 2 1 2

M Uae Se 41 1 2 1 2

PRO QE UM 43 i 2 1 2 :

12 311.5 5. 45 1 2 2 2 Conceptus on left side

bi ces 47 I 1 2 1 almost completely re-

wW ooa 49 2 1 2 1 sorbed.

9: 2: 0. 09 51 2 1 2 1

Son 53 1 2 1 2

Ti. 55 2 0 2 0

joa uo eS 57 1 1 2 1

be ae 59 1 2 2 2

L2 T QUIM 61 2 I 2

Siu SEVA 63 3 1 3

d lil eres Term 2 1 2 1

{ AG 23 0 0 2 OIA OL of areni but

Boi. 45 0 0 1 B | noimplantatio

nd. .

horn showed 3 embryos although only two corpora lutea

of pregnancy were present in the ovary. Hence, in this

ease, two embryos developed from a single ovum or a

single follicle contained two ova. In the instances where

there was one more corpus luteum than embryos it is

possible that another conceptus was present and became

No. 645] FECUNDITY IN THE GUINEA PIG 357

absorbed or that an ovum degenerated before implanta-

tion, or that it failed of fertilization.

As shown by Meyer, 717 and ’19, and Stockard and Pa-

panicolaou, 718, absorption is not uncommon in the uteri

in guinea pigs. In this series, three embryos which were

clear-cut cases of absorption were found upon examina-

tion of the uteri after their removal. In No. 12, which

was killed forty-five days after copulation, two normal

embryos were found in the left horn, but in the right horn

there was nothing but a small mass which had undergone

almost complete absorption.

According to Stockard and Papanicolaou, ’18, embryos

eight or ten days old may be detected by ‘‘ carefully feel-

ing the uterus through the body wall of the mother.”

They report a case as follows:

A normally developed embryo 19 mm. crown rump length is shown

in Fig. 6 and near it is seen an amorphous embryonic mass 2 mm.

in longest diameter which represents the other member of the litter.

. The entire mass of the smaller ovum in the uterus was about

that of a ten-day specimen, while the normal individual was a typi-

cal 20-day specimen. This case was detected by external examination

and was merely opened in order to use the embryos for illustrating

the phenomenon.

Although I used the method of Papanicolaou and Stock-

ard in palpating guinea pigs, in no instance was I able

to determine the number of embryos with certainty under

fifteen days. Because of this fact, I found it necessary to

sacrifice the animals in order to determine the number of

implantations before this period.

Guinea pig No. 35 and guinea pig No. 34 were killed

seven and eight days after conception, respectively, and

the uteri removed. Careful palpation of the removed

uteri failed to reveal the number of conceptuses. The

uteri were then opened, but in order to determine the

number of implantations present it was necessary to em-

bed them and make serial sections. From this I am led to

question the possibility of determining the number of em-

bryos in the uterus by palpation through the abdominal

wall on the eighth to tenth day of pregnancy. This skep-

ticism seems warranted, further, by the measurements of

358 THE AMERICAN NATURALIST [Vor. LVI

three ten-day conceptuses, 6.5 X 3 mm.; 6.8 X 4.5 mm.;

'6.5 X 4.5mm. respectively. Draper gave the estimated

length of an 11-day embryo measured under magnifica-

tion as 2 mm.

Stockard and Papanicolaou (1918) likewise reported

that a ‘‘ slightly cystic ovary ”’ has frequently been diag-

nosed by palpation through the abdominal wall of the

guinea pig. In my observations 23 out of 75 ovaries were

found to be cystic; but the largest cyst measured only

1.6 mm.X 1.68 mm. and not even this could by any chance

have been palpated through the abdominal wall. Hence,

it would seem that Stockard and Papanicolaou must have

been dealing with markedly large and unusual, rather

than with slightly, cystic ovaries.

From a study of a large series of gestations in the

domestic pig, Corner, ’21, concluded that internal migra-

tion of ova is relatively common. This small series of

pregnancies in the guinea pig furnishes very little evi-

dence upon this question, for such a possibility is sug-

^ gested only by No. 17, a pregnancy of 35 days in which

there were 2 corpora and 2 implantations on the right

side and no corpora but one implantation on the left side.

Since the total number of implantations in this case ex-

ceeds that of corpora, one must assume that one ovum

divided or that one follicle contained ova and that one

of the ova arising from the right then migrated to the

left cornu. However, since this pregnancy was so far

advanced, this assumption implies that a corpus luteum of

pregnancy in the guinea pig can not be wholly resorbed

in 35 days and that it never fails to form.

It is of special interest in this connection that a second

case of this kind has been observed in this laboratory by

Miss Clark. In this case there were two. corpora in the

left ovary and none in the right, with ore implantation

on each side. Since this pregnancy was only 17 days old,

the question of early resorption of the corpus luteum

probably can be excluded with considerable certainty but

that of failure of the corpus luteum to form, remains.

No. 645] FECUNDITY IN THE GUINEA PIG 359

REFERENCES

Bisehoff, H, L. W.

1844. Beweis der von der Begattung unabhängigen periodischen

Reifung und Loslósung der Eier der Süngethiere und des

Entwicklungsgeschichte des Meerschweinchen

Corner, George N.

2 Tate Migration of the Ovum. J. H, H. B., Vol, 32.

Draper,

1920. The Prenatal pav of the Guinea Pig, Anat. Rec., Vol. 18,

. 4, May, 1

Evans, H. M. id Long, J. a

1920. The Œstrus Cycle in the Rat (et seq.). Anat. Rec., Vol. 18.

Lantz, David.

——. The Raising of the Guinea Pig. U. S. Dept. of Agriculture,

armers’ Bulletin,

Long, J. A.

. 1919. The CEstrus Cycle in Rats. Proc. Am. Soc. Zool., Anat. Rec.,

Vol. 15, 1919.

Meyer, A. W.

1917.. Intrauterine Absorption of Ova. Anat. Rec., Vol. 12, 1917.

1919. Uterine, Tubal and Ovarian Lysis and Resorption of Con

ceptuses. Biol. Det, Vol. 36, April, 1919,

Rein, .

1883. Beitrage zur Kenntnis der Reifungsercheinungen und Befruch-

tungsvorgange am Saugetierei, Arch. f. Mikr. Anat., vol. 22.

Rubaschkin,

1905. Ober die Reifungs- und Befruchtungs- processe des Meersch-

weincheneies. Anat, Hfte., Abt. 1, Vol, 29, 1905

Stockard, C. R. and Papanicolaou, G N.

1917a. des sat re of a Typical CEstrus Cycle in the Guinea Pig,

h a Study of im poss nr and Physiologieal Changes.

Jour. Anat., , No. 2, Sept., 1917 (a).

19175. ^ "Bhythmical ro pe " MU ' in the Guita Pig. Science,

N. S., Vol. 46, pp. 42, 44, 1917 (b). "

Stockard, C. R. and Papani anieolao u, G. N.

1918. del BEE on the Modification of the enron in

Mam e Effect of Alcohol on Treated G a Pigs

their geri Tae Jour, Exp, Zool., Vol. XXVI p. 119,

ay,

1919. The Vaginal Closure agii. Copulation and the Vaginal

Plug in the Guinea Pig, Further Considerations of the

Œstrus Rhythm, Biol. Dull, Ye XXXVII, Oct., 1919,

Stockard, C. R. and Papanicolaou, G. N.

1920. Effect of oap on Ovulation and the CEstrous Rhythm

Guinea Pigs. Proc. Soc. Exper. Biology and Medicine,

XVII, iu.

Hensen,

iced " fBeobechtunges über die Befruchtung und Entwiekelung des

Kanin eerschweinch Zeit. f. Anat. u. Ent-

wick., Bd. I, 1876.

VARIATIONS IN THE NUMBER OF VERTEBRA

AND OTHER MERISTIC CHARACTERS OF

FISHES CORRELATED WITH THE TEMPERA-

TURE OF WATER DURING DEVELOPMENT

CARL L. HUBBS

Museum or ZooLocy, UwivERsITY OF MICHIGAN

Fon several years I have been studying the correla-

tions between altered environmental conditions and the

number of vertebre and other segmentally arranged

struetures in fishes. Johannes Sehmidt, of the Carls-

berg Laboratory in Copenhagen, has been carrying on a

series of intensive investigations (see bibliography) which

deal with the same problem, and which are for the greater

part rather closely paralleled by my own studies. Both

of us have obtained, independently, a rather large volume

of experimental and observational evidence indicating

that the meristie characters displayed by an individual

fish are determined not alone by heredity, but in part also

by the environmental conditions, particularly tempera-

ture, which prevail during some sensitive developmental

period.

The present study is one of those comprising the series

just mentioned. It deals with variations in the number of

vertebre, scale-rows and fin-rays within one year-class

and between two successive year-classes of the lake

** shiner," Notropis atherinoides (Cyprinide), and in

comparison between the corresponding year-classes of the

‘* blue-gill’’ sunfish, Lepomis incisor (Centrarchide).

These variations appear to be correlated with differences

in temperature prevailing eons the several develop-

mental periods involved.

The material of each species is probably a unit as re-

360

No. 645] VERTEBRJE OF FISHES E

gards ‘‘ race." It was all obtained in a lagoon in Jack-

son Park, Chieago, during the third week of December,

1919. At this time what seemed to be the entire fish

population of the lagoon was eongregated in an opening,

about five meters wide, in the ice-along shore. These

fishes showed symptoms of asphyxiation. They were so

abundant that at times, while they were gyrating about,

the mass of fishes below would foree the almost solid

upper layer a centimeter or two above the surface over

an area of perhaps a square meter. A water bucket was

filled with fishes, mostly Notropis atherinoides, by two or

three sweeps of a small hand-net. More than one thou-

bau

rj 19196

E 15 a t

Length to &audal Rn, mon.

Fic. 1. Frequency graph, indicating the year-classes of Notropis atherinoides.

sand of the young of that year (1919) of the Notropis

were saved after random selection, and preserved for

study with all older fish of the same species. All of the

sunfishes (Lepomis incisor) obtained at the same time

and place were preserved and studied. Of the two spe-

cies, the sunfishes belonged to a population practically

confined to the lagoon, while the minnows had moved into

the lagoon, late in the preceding autumn, from the more

open waters of Lake Michigan.

The specimens thus obtained were grouped into year-

classes. Age determinations were made by the usual

methods of counting the annuli (winter lines) on the

scales, and as a check the seasonal bands of the otoliths,

and furthermore by the preparation of a frequency graph

362 THE AMERICAN NATURALIST [Vor. LVI

from the length measurements of the entire material.

The young of the year (obtained in 1919) are referred to

as the 1919, class; those of the previous year as the 1919,

class, and so forth. The 1919, year-class of the Notropis

atherinoides is further divided into three subelasses, A,

B and C, named in the direct order of hatching, hence in

B-

lndivtdùsis

4 4 T (0 V 1 *

Fic. 2. Frequency graph illustrating the year-classes of Lepomis incisor.

the indirect order of size. The year-classes for both spe-

cies are indicated on the graphs forming Figs. 1 and 2.

The symbols on the curve for the 1919, class of each spe-

cies indicate the sex predominant among the representa-

tives of each size.

III

A series of water temperatures appear unavailable, but

in the case of such a shallow, nearly enclosed lagoon the

air temperatures of the region may safely be substituted.

Hence the Climatological Data (Illinois Division, 1918

and 1919) for Chicago were used in constructing Fig. 3;

the temperatures given for each week were obtained by

averaging the daily means.

On the temperature chart there’ are indicated the

periods of development for each of the two species as ob-

No. 645] VERTEBRÆ OF FISHES 363

served at the same locality in 1919. The data for Lepomis

incisor seem satisfactory (see Hubbs, 1919), but those for

Notropis atherinoides are less complete and more cir-

eumstantial. In the ease of the minnow, the develop-

mental period is divided into three periods (A, B and C)

corresponding with the three subclasses into which the

1919 year-class has been divided. Period A followed an

inshore spawning migration of the mature individuals,

coincident with the rapid rise in temperature during

March; period C preceded the withdrawal of the breeding

stock from the shore waters of the lake; the intervening

period is termed B.

The limited field observations on the spawning and

developmental period for Notropis atherinoides during

1919 are, fortunately, strongly confirmed by a study of

E Io18

Big e

: Tempe rature

Oo Jan. || Feb. | Mar. | Apr | May | Jupe | July | Aug

Io 15 20 25 30

‘WEEKS

Fic. 3. Air temperature at Chicago, 1918—1919.

the scales. The scales of the largest specimens taken in

December, namely those comprising subclass 1919,A, and

forming a distinct mode in the frequency graph (Fig. 1),

show a well marked nuclear area of weak concentrated

circuli indicative of retarded growth, followed by the

coarser, more regular circuli indicative of normal summer

growth. This initial period of retarded growth presum-

364 THE AMERICAN NATURALIST [Vor. LVI

ably eorresponds with the cold period in April (see Fig.

3). The scales of the medium-sized specimens (subclass

B) show on the average a narrower nuclear area suggest-

ing slackened growth. It is presumed that these individ-

uals passed through their early development toward the

end of this cold period. The scales of the smallest spec-

imens, those of subclass C, show no such nuclear area

of weak concentrated circuli. These fishes supposedly

developed during the warm weather of May.

The data on the developmental period of these two

species for the preceding breeding season (1918) are less

complete than those for 1919, yet not wholly lacking.

Lepomis incisor, at least, bred during the corresponding

weeks in both years (but in less abundance in 1918 than in

1919).

A comparison of the available observational data with

the temperature chart (Fig. 3) indieates that, on the

average, the developmental period for Notropis ather-

inoides was colder in 1919 than in 1918, whereas these

temperature relations were distinctly reversed in the case

of Lepomis incisor, and furthermore, that the tempera-

ture was distinctly higher at the beginning and toward the

close of the 1919 breeding season for the Notropis, than

during the middle of this period.

These differences in the developmental temperature ap-

pear to be correlated with variations in the number of

segments in the case of both fishes. Comparisons will

first be made between the two year groups of Notropis

atherinoides, then between the same year groups of

Lepomis incisor, and finally between the three subclasses

into which the 1919 brood of the Notropis has been di-

vided.

The vertebrz in the 1919, class of Notropis atherinoides

are sufficiently more numerous on the average than those

of the 1919, class to shift the modal number from 41 to

42, the average from 41.41 (+ 0.04)* to 41.74 (+ 0.015).

1 The probable error of the average.

No. 645] VERTEBRZ OF FISHES 365

SPECIMENS

9/9/92 3

E i ME

38 39. m T i 43 D?

VERTEBRAE!

FI Comparison of number of vertebre in successive year-classes of

Notropis atherinoides.

The portion of the vertebral column affeeted is the eaudal,

not the precaudal M plea division: the averages for

the precaudal vertebre are 22.82 (+ 0.02) for 1919, and

22.85 (+ 0.01) for 1919, for the caudal vertebrz, 18.60

(+ 0.035) for 1919,, and 18.87 (+ 0.01) for 1919,. Simi-

larly, the number of scales in the lateral line averages

higher in the 1919, lot : the modal numberis 40 rather than

39 as it is in 1919, class; the average number is 40.05

(+ 0.04) rather than 39.65 (+ 0.04). The modal number

SPECIMENS .

Fic. 5. Comparison of variati n number of branched and anal rays in

different year-classes of Notropis E ME

366 THE AMERICAN NATURALIST [Vor. LVI

of branched anal rays? is 10 in the 1919, series, 9 in the

1919, class; the averages are 9.52 (+ 0.05) for 1919, males,

FREQUENCY TABLE I

COMPARISON OF THE MERISTIC FEATURES OF THE 1918 AND 1919 BROODS OF

Notropis atherinoides

Character

Year-class Total Number of Vertebrze

: | : |

39 | ao | 4 | 42 | 4 | 44

i | — | a7 | s s | 13 |

1901905. 1. 1 4 356 539 | 137 | 12

! Number of Precaudal Vertebre

21 | 22 23 | 24 | 25

IBI. ae des 3 48 | 191: n —

101905... s 2 240 | 766 | 78 1

Wither ad 6 | 74 L-38 os

VG aie d 6 | 269 | 661 | 142 | 10

| | |

Number of Seales in Lateral Line

a | x | » | o | a | 2 | oo | ow | os

389.0 2 26 | 95 92 | 34 11 2 —|-—

1519... a) — | 22 | 90 | 104 | 66 | 21 9 2 1

| Number of Branched Anal Rays

EX 9 1 | 11 12

1002: asc, ka | foo k 233 | 99 |. 3

Mad.. FÉ 51.187 | 10 | —

19199 ....... 3 534 | 991 $6 | —

193109... 025. 4 72-1 H8 1.12 1

2 The last ray as usual was counted as double, i.e., as divided to the base.

esa the posterior half of this divided ray is again divided well

the base. In fact a complete transition can be traced between fins

pest a given number of rays with those having one more ray. It is highly

improbable, however, that this transition is suffieiently frequent as to permit

a serious modification of the average number of rays, through a personal

error in counting.

No. 645] VERTEBRZ OF FISHES 367

9.53 (+ 0.06) for 1919, females, and 9.69 (+ 0.03) for both

sexes of the 1919, class; in material collected in 1902 in

the same lagoon the average is still higher, 9.83 (+ 0.02).

The data on which these figures are based is given in Fre-

quency Table I. In all three characters, namely the num-

ber of vertebrz, of scales along the lateral line, and of

branched anal rays, the year-class developed in the cooler

season displays a significantly higher average.

A highly similar yet exactly reverse condition is dis-

played in the analysis of the counts on the Lepomis in-

cisor material. In this ease the total number of vertebrae,

and the number of caudal, but not precaudal, vertebre;

the number of dorsal spines, dorsal soft-rays, anal soft-

rays, and hence the total number of vertical fin-rays, all

E e

Opec Emens

+ eni

35 Se .5b 256 ST. ae 9

Total dorsa/ and ana/ rays

Fie Comparison of number of dorsal and anal fin rays in successive year-

classes ef Lepomis incisor.

average higher in the class born in 1918 than in that of

1919. But we noted above that the temperature relations

during the developmental periods of the two years were

likewise reversed. In both Notropis atherinoides and

368 THE AMERICAN NATURALIST —. [Vor.LVI

FREQUENCY TABLE II

COMPARISON OF THE NUMBER OF VERTEBRZ IN THE 1918 AND 1919 BRoops or

Lepomis incisor

Year-class | Character Average oe

Total Number of Vertebrze

28 | 29 | 30

INC el 95 | 9 29.10 0.02

2i. DR Nl Seen PUE >g 219 | 8 29.00 0.00

Number of Precaudal Vertebræ

11 | 12 | 13

gt UR ET aaa S 2 | 100 2 12.00 0.01

10106. 5s vs 2 | 230 2 12.00 0.00

Number of Caudal Vertebree

16 | 17 | 18

19106... 2002: 2 224 — 95 9 17.09 0.02

T0104... is ee Sud zi 219 8 17.00 0.01

4g0| 4 -

s 7

E E

E 26V

E E

x 5

: a

an ee i

#0} og a

Bo 3b HO | 6

Fic. 7. Illustrating seasonal variation in number of vertebrs in Notropis

atherinoides.

No. 645] VERTEBRJE OF FISHES 369

Lepomis incisor, therefore, a higher number of segments

was developed in the year class developed at the lower

temperature. The detailed data are given in Frequency

"Tables II and IIT.

Evidenee has already. been given indieating that the

1919 year-elass of Notropis atherimoides is divisible into

three subclasses, of which the middle (B) developed dur-

ing colder weather than either the first (A) or the last

(C). The data given in Frequency Table IV and in figure

6 demonstrate that this subelass B possesses a decidedly

higher number of vertebre than either of the other two.

The averages are as follows: for the 146 specimens of sub-

class A, 41.38 (+ 0.04); for the 845 comprising subclass

B, 41.84 (+0.02); for the 97 individuals of subclass C,

41.42 (4- 0.05).

FREQUENCY TABLE III

COMPARISON OF THE NUMBER OF FIN-RAYS IN THE 1918 AND 1919 Broops or

Lepomis incisor

Year-class Character | Average Li sos

Number of Dorsal Spines |

IX | x | XI XII |

JEDE ss i 79 22 v 10.21 0.03

IM s 2 74 11 1 10.125 0.03

Number of Dorsal Soft-rays

10 11 12 | 13

1915... els 1 37 63 — 11.61 0.03

JM. uu sss 3 51 32 2 11.375 0.04

Number of Anal Soft-rays

9 | 10 | 11 12

I9 a. — 2 80 19 Tia 0.03

In. ak: 1 12 70 5 10.90 0.03

Total Rays in Dorsal and Anal Fins

33 34 35 | 36 | 37 | 38 | 39

1915b....... — 2] 20] 68 | 18 1 — 35.96 0.05

1981087... ls i 12 | 34 | 33 6 | — 1 35.40 0.07

370 THE AMERICAN NATURALIST [Vor. LVI

FREQUENCY TABLE IV

VARIATION IN NUMBER OF VERTEBR2Z WITHIN ONE-YEAR CLASS OF

Notropis atherinoides -

Number of Vertebree

Sub- Size Average | Probable

class Group Error

; 39 40 41 42 43 44

1919s C.... 27 — — 1 =- — -— (41.00) —

28 — -= 1 1 1 — (42.00) 0.32

29 — — 5 2 — — (41.50) 0.29

30 — — 9 4 — — 1.31 0.09

31 — 1 5 3 — — 41.22 0.16

32 — 2 7 4 — 1 41.36 0.175

33 — 1 4 T 1 — 41.62 0.145

34 — 1 7 10 — — 41.50 0.095

35 — 1 13 7 1 —— 41.36 0.09

1919) B.... 36 — — 11 13 4 — 41.75 0.09

37 — 1 16 1 6 — 41.71 * 0.07

38 — 5 10 36 5 — 41.73 0.05

39 1 4 24 39 8 1 41.68 0.

40 — 3 44 Ww — 41.82 0.0.

Al — 2 24 46 16 2 41.91 0.055

42 — 1 21 67 18 3 42.01 0.04

43 — 3 24 41 1 41.87 0.06

44 — 1 18 43 14 1 41.95 0.

45 — 2 21 31 6 2 41.76 0.07

46 — — 13 23 10 — 41.93 0.07

47 — — 14 23 2 1 41.75 0.

48 — 1 16 16 7 — 41.72 0.08

19199 A.... 49 — 4 6 14 — — 41.42 0.10

50 — 3 14 |. 16 1 — 41.44 0.1

51 — 2 14 9 2 — 41.41 0.095

52 — 2 16 9 — — 41.26 0.075

53 ei 2 6 6 1 — 41.40 0.1

54 — — 7 2 — — 41.22 0.

55 — E 2 2 — — 41.20 0.225

56 — — |.1 2 — — (41.67) 0.18

57 — — — 1 — — (42.00) ee

"d 58 Aude ae MISES dé d ene MEER HSH

59 — — — — — — — —

60 = — 1 — — — (41.00) —

It has generally been taken for granted, as a basic as-

sumption, that such differenees as those here shown to

hold between two successive year-classes, and between

successive groups within a single year-class, are indie-

ative of racial distinetion. Obviously this assumption

ean not be maintained as wholly true. Moenkhaus (1895,

1898) indeed long ago demonstrated the occurrence of a

significant annual variation within one race of fishes (in

the ease of the darters Percina caprodes and Boleosoma

No. 645] JA VERTEBRAE OF FISHES 311

nigrum). Sehmidt (1921) has lately studied such annuat

fluetuations in great detail in Zoarces, and has induced

like changes by experimental control of temperature in

Lebistes (1919a, 19195) and Salmo (1921). I have ob-

tained similar experimental results for coregonine fishes

and for Esox lucius (data yet unpublished).

On the other hand it has been clearly demonstrated in

a number of cases that fine ‘‘racial’’ differences are in-

herited. Thus Schmidt (1917a, 19175, 1918, 1920, 1921?

has determined by his ‘‘offspring analyses" that a high

degree of positive correlation holds between the number

of segments and other features of the maternal parent

and the unborn embryos of Zoarces. Similar results

were obtained by Punnett (1904) for the viviparous

shark, Etmopterus [Spinax] niger. In Salmo, Schmidt

(1919c) has lately demonstrated that the finer differences

in the number of vertebre of both parents are inherited,

and in the viviparous teleost Lebistes reticulatus, the

same author has found (1919a, 19195) that minor varia-

tions in the parental number of dorsal fin-rays are in-

herited. In somewhat similar fashion Summer (1918,

ete.) has demonstrated that subspeeifie differences in

color and size in the mouse genus Peromyscus are in-

herited, even under changed enviromental conditions. A

considerable body of indirect observational evidence

might be brought forward, if needed, in confirmation of

the assumption that these fine racial differences are in-

herited.

Clearly the same sort of variations as are induced by

altered environmental conditions do characterize geneti-

cally distinct local races of fishes. Furthermore, these

two sets of correlations display certain striking simi-

larities or analogies, the significance of which the writer

is attempting to determine in the series of studies of

which the one here reported is a part.

LITERATURE CITED

ice Carl L

1919. The Nesting Habits of -Certain Sunfishes as Observed in a Park

Lagoon in Chicago. Aquatic Life, Vol. 4, pp. 143-144.

Sia THE AMERICAN NATURALIST [Vor. LVI

Moenkhaus, W. J.

1895. Variation of North American Fishes. n The Variation of

Etheostoma d Rafinesque in Turkey Lake and Tippe-

noe Lake. c. Indiana Acad. Kci., Yol. for 3805; pp. 278-

296.

1898. spectu for the Study of the Variation of Etheostoma ah Bex

e and Etheostoma nigrum Rafinesque in Turkey

e aas Lake. Ibid., Vol. for 1897, pp. 207-228.

Punnett, R. C.

1904. Merism and Sex in Spinax niger. Biometrika, Vol. 3, pp. 313-

362

puer Johs.

1917a. Racial Investigations. I. Zoarces viviparus L. and local races

of the same. Comptes-Rendus Trav. Lab. Carlsberg, Vol. 13,

pp. 279—397.

1917b. Racial Investigations. II. Constancy Investigations Continued,

Ibid., Vol. 14, No. 1, 19 pp.

1918. Racial Studies in Fishes. I. Statistical Investigations with

Zoarces viviparus L. Jour. Gen., Vol. 7, pp. 105-11

1919a. Racial Investigations. III. Investigations with Lebüstos reticu

latus (Peters) Regan. Comptes-Rendus Trav, Lab. codibiry,

Vol. 14, No. 5, 8 pp.

19195. Racial Stu diii in Fishes. II. Experimental Investigations with

Lebistes reticulatus (Peters) Regan. Jour. Gen., Vol. 8, pp.

147—153,

1919c. Racial Studies in Fishes. III. Diallel crossings with trout

arogi trutta L). Jour. Gen., Vol 9, pp. 61-67.

1920. Racial vestigations. V. Experim rimental Investigations with

Zour atk s L. Comptes-Rendus Trav. Lab. hatibele,

ol, 14, No. 9, 14 pp.

1921. iii Tovesligationg, VII. Annual Fluctuations of Racial

Characters in Zoarces viviparus L. Ibid., Vol. 14, No. 15,

4 a

Smith, Kirstin

1921. uid Investigations on Inheritanee in Zoarces viviparus L.

Ibid., Vol, 14, No. 11, 64 pp.

Sumner, F. B.

1918. Continuous and Discontinuous Variations and their Inheritance

in Peromyscus, IV. Heredity of the Racial Differences.

Amer. Nar., Vol. 52, pp. 290-301.

STUDIES ON FISH MIGRATION II. THE INFLU-

ENCE OF SALINITY ON THE DISPERSAL

OF FISHES*

DR. F. E. CHIDESTER,

West VinaGiNIA University, MonGaANTOWN, W. Va.

In connection with an extensive study of the factors

influencing fish migration, certain experiments were per-

formed during the summers of 1919 and 1920 to deter-

mine the effects of different salinities on the reactions of

fish under laboratory conditions. Besides testing the

animals with the salts of sea water, preliminary experi-

ments were made with changed temperature and stream

flow.

MATERIAL AND METHODS

The apparatus consisted of a two-tributary unit of a

river system so arranged that different solutions could

be introduced, affording the fish an opportunity to select

the more favorable one. Two almost parallel troughs

were so directed as to let the solutions flow down into

a long receiving trough that had adjustable outlets in

the middle.

. There was also an intake at the extreme end of the

large receiving trough so that if desired three intakes

could be used. When only the two converging troughs

were supplied with currents, a partition was placed

across the middle of the receiving trough so that the

water could flow laterally and eventually escape from

the pool by the regular outlet.

The two tributary troughs were each 10 feet long, 4

inches deep and 44 inches wide and the receiving trough

was 10 feet long, 8 inches deep and 82 inches wide. The

twin troughs were marked off in feet and conspicuously

1 Contribution from the Biological Laboratory of the U. S. Bureau of

Fisheries at Woods Hole, Mass.

373

374 THE AMERICAN NATURALIST [Vou. LVI

labeled at the proper points so that from a single ob-

servation post, record could be taken of the distances

traveled by fishes responding to the streams flowing down

the incline.

Streams were introduced after temporary storage in

two barrels located above the ends of the experimental

troughs. In some experiments the inflowing currents

came directly from the circulation pipes of the laboratory.

Experiments were performed with sea water, fresh

water and combinations of the two, followed by tests with

the individual salts of sea water in m/10 solutions. Tem-

perature and stream flow were varied and proved most

important adjuncts to the salts in affecting behavior.

In order to be quite certain that habit formation as a

factor was eliminated, it was customary to select a trough

used during the night for sea water inflow and introduce

a substance less attractive, for the first few experiments

with a group. As conditions of illumination were uni-

form and the troughs were so near each other, this proce-

dure probably reduced the error due to a habit factor.

The fish were males, selected for apparent vigor and

averaged about 12 centimeters in length. They were used

for a complete series of experiments in lots of ten, then

replaced by another ten of similar size. In the majority

of the experiments, the species used was Fundulus hete-

roclitus. Its habits throughout the year were already

known to the writer (1916, 1920). Loeb, Thomas and

others had already studied its susceptibility to toxie sub- -

stances. It is anadromous, highly resistant, yet furnishes

quick reactions. |

Fundulus majalis was used less frequently as it is not

so resistant to laboratory conditions and behaves differ-

ently with reference to tides. The observations of Mast

(1915) made it especially desirable to study the reactions

to currents and accordingly a series of eer Y was

made.

Clupea harengus dies quickly in ete Its re-

sponses are extremely delicate and it has been used quite

No. 645] FISH MIGRATION 915

successfully by Shelford, Powers and others in experi-

ments on temperature, acidity, alkalinity and salinity.

It proved too excitable for the experiments with which

the present work was concerned.

EXPERIMENTS

Fresh Water and Sea Water. (Temperature 20? C.)

With apertures # in. in diameter in two glass tubes

directing horizontal streams of fresh water and sea water

to a point six inches from the ends of the experimental

troughs, it was found that 10 fish responded during 25

trials in such a manner that 11.8 was the value for re-

sponses to fresh water and 44.6 was the value for the sea

water. These figures were obtained by multiplying the

number of fish responding by the feet traveled up the

trough towards the current, adding the total of 25 trials

and securing averages for control and experiment.

The fish responded readily to the flow of water and

since there was an admixture of fresh and salt water in

the lower ends of the troughs, they did not at first dis-

criminate the sea water before reaching a point 6 or 7

feet from the pool, that is 3 or 4 feet from the intake.

As their reactions to the currents became established,

however, they came in smaller numbers and finally be-

came aligned along the sea water current at a distance

of not more than a foot from the intake.

On changing the flow of fresh water to salt and vice

versa, it was noted that at first the fish came into the

trough formerly salt, and proceeded beyond the point

where they usually traveled in fresh water. This was in

part due to the habitual response and partly to the pres-

ence of some salts in the trough. On reaching the intake,

they rapidly returned to the pool, one or two pioneered

in each trough, then the whole group explored the salt

trough and finally came to a point near the salt water

intake.

376 THE AMERICAN NATURALIST [Vor. LVI

Reactions to Salts in Solution

A preliminary series of experiments was run with fish

immersed in m/10 solutions of the salts of sea water,

made up in fresh water. Results were obtained similar

to those recorded by Loeb, Thomas and others with fish

and corresponding ones known to the writer from experi-

ments with the larve of mosquitoes (1916).

By using the barrels above the experimental troughs

solutions of the salts individually and in combination

were introduced into the apparatus, with fresh water or

sea water run as the control current. At first tempera-

ture and stream pressure were kept constant. The tem-

perature averaged 20.5? C. and the pressure was suffi-

cient to send the eurrents horizontally to a distance of

six inches from the 2-in. glass tubes.

The reactions to individual salts as compared with

fresh water are shown in the table below, only the aver-

ages at the end of 25 trials with 10 fish being recorded.

RESPONSES OF FISH TO SALTS

MONO (dui as ee a ees 46 Control, 0

MUE seicesduecprssi MINE A E T 22.6 Control, 1

QUU cic ain os est E eevee vies 6 Control, 20

NUR I a ene career herp Ty 5.7 Control, 21.5

EA 8) GEERT eta E Opps FBLP Eis Va 2 Control, 15

It is quite evident that with temperature and stream

pressure the same, Fundulus heteroclitus will react quite

definitely to salts. It is attracted to the less toxic ones,

MgSO,, and NaCl, and is repelled by those that are most

toxic to it. |

Similar experiments with sea-water solutions and sea

water as the control eurrent brought out quite clearly

that for the species used, m/10 solutions of the more

toxie individual salts were not strong enough to repel

the fish. For example in the case of the most toxic, KCl,

the score for 25 trials with 10 fish was 43 for the control

sea water and 34 for the experimental current with KCl

in m/10 solution.

Likewise, combinations of the salts showed only too

No. 645] FISH MIGRATION 377

well the attractiveness of the mixed solutions. With an

m/10 solution of MgCl, plus MgSO, and fresh water as

control, the record was 11.2 for the control and 34.2 for

the mixture. Again, in the case of KCl plus NaCl in

m/10 solution, the score was 31 for the control and 17

for the mixture. With double sea water (specific gravity

1.050) and ordinary sea water at 20° C., it was found

that the fish were attracted at the ordinary pressure and

temperature, reacting to the stronger solution an average

of 19.3 and to the control sea water 17.8 times. Further

experiments should be run to determine the influence of

antagonistic action of the salts in pairs. Whether or

not the results will coincide with the results of permea-

bility experiments will probably depend somewhat on the

factor of temperature (Loeb and Wasteneys, 1912).

Influences other than Salts

The foregoing experiments indicate clearly that the

behavior of the fish under consideration is materially af-

fected by the salts with which they come in contact in

fresh water. However, the factors involved in the migra-

tion of fish are by no means thus explained. It is worthy

of note that the reactions of Fundulus heteroclitus to

toxic salts or even sewage are dependent on Papan

and stream pressure.

Temperature

Numerous experiments were tried with varying tem-

perature and it was found that a temperature greater

than 23? C. repelled the fish and eaused them to align

themselves along the current of fresh water at 20? C. in

preference to the slightly warmer sea water.

With a reduced temperature, even one degree less than

the control (19° C.), the fish were markedly attracted.

In fact it was possible to lure them into double sea water,

KCl or fresh water if these were presented at the proper

temperature. Further experiments and observations are

necessary for these and other species in order to deter-

mine the relation between gonad development, bodily

condition and the responses to temperature change.

378 THE AMERICAN NATURALIST [Vor. LVI

As pointed out by Gurley (1902), the minnows migrate

to warming water for the purpose of spawning, while the

cod and the salmon migrate to cooling water for the same

purpose. Chamberlain believes that the salmon come into

water warmer than the sea water (1906).

Field records for Fundulus heteroclitus secured by the

writer in eonneetion with another investigation (1916)

indicate the importance of temperature. The fish began

coming inland in the spring when the water was about

15° C. and continued to run in and out until the inland

pools had reached a temperature in August of about

24° C. Then for a period of over two weeks, they ceased

running. About September 1, when the temperature had

again lowered, they appeared again and continued to run

until the temperature ran down to 10° C.

Stream Pressure

When sea water was introduced through the 2-in. glass

tube with a force sending it horizontally to a distance of

6 inches, while fresh water was introduced through the

experimental tube into the adjoining trough with a force

sending it 12 inches from the end of the tube, there was

no difficulty in luring the fish away into the fresh water

and keeping them directed towards it.

Many experiments were made, toxic substances such as

KCl and double sea water also being introduced, but the

increased pressure always proved the powerful factor.

Chamberlain (1906), Prince (1920) and others have pre-

viously shown that in the case of the salmon, migration

into fresh water is delayed until the floods come down

into the bays and small streams. The arrival of a vol-

ume of rushing water furnishes the needed stimulus and

the fish proceed forthwith to obey their instinct to swim

against the current.

That fish can determine the presence of toxie sub-

stances in sea water or in fresh water is unquestionably

demonstrable. But we have much evidence that those

fish lying offshore and habitually migrating up a certain

No. 645] FISH MIGRATION 379

stream, will journey into polluted water, spawn in places

where the eggs can not develop and in many cases, die

in such water themselves.

Salmon are reputed to return to the lake-fed streams

where they were spawned and there is considerable evi-

dence that they are guided by temperature difference,

probably also by the current pressure, number of water-

falls, oxygen content and even by food. There is no ques-

tion (Meek, 1916), however, that salmon ascend streams

where no salmon could hitherto have spawn

The destruction of protecting forests, spoliation of

natural waterways and the utilization of streams by

manufacturers wishing to dispose of wastes are the fac-

tors which not only cause the death of fish embryos and

adults, but prevent the natural control of insect pests by

their destruction in the larval state.

SUMMARY

1. Fundulus heteroclitus is able to discriminate toxic

from non-toxie salts at a temperature and stream flow

the same as the control.

2. Variations in temperature or in stream flow pro-

foundly influence the reactions and are more powerful

factors in the behavior of the fish than presence or ab-

sence of salinity.

3. In the apparatus used, errors due to the notable re-

actions of fish to currents of water have been reduced

by presenting the control and experimental flows parallel

to each other.

BIBLIOGRAPHY

Calderwood, W. L.

1907. K Life of the Salmon. London, 1907.

Chamberlain, F. M.

1907. Some Observations on Salmon and Trout in Alaska. Report

and special papers for 1908. U. S. Bureau of Fisheries,

Document

Chidester, F.

1916. A Biological aoed of the More Important of the Fish Enemies

rsh Mosquitoes. Bull. N. J. Ag. Exp. Sta.

No. 300, pp. 134

380 THE AMERICAN NATURALIST [Vor. LVI

Chidester, F. E.

920. The Behavior of Fundulus heteroctitus on the "us Marshes

of New Jersey. Am. Nat. Vol. 54, pp. 551-55

Chidester, F. E.

1921. A Simple a EE E Studying the Factors Influencing Fish

oe Pro c. for Exp. Biol. and Med., Vol, 18, pp-

wit A

1902. Tue Habits of Fishes. Am, Jour. Psy., Vol. 13, pp. 408-425.

— di uo Wasten

On the vice of Fish (Fundulus) to Higher DEN

tures. Jour. Exp. Zool. Vol. 12, No. 4, pp. 543—557

Loeb, J.

1912. erp dues Aetion of Eleetrolytes and Permeability of the

Cell Membrane. Science, N. S., Vol, 36, No. 932, pp. 637-

639.

Lyon, E. P.

1904. On Rheotropism. I. Rheotropism in Fishes. Am. Jour. Phys-

4 9.

Lyon, E.

1909. p ithaca II. Rheotropism of Fish Blind in One Eye.

m. Jour. Physiol., Vol, 24, pp. 244—251.

Mast, S. O.

1915. The Behavior of Fundulus with Especial Reference to Over-

land Escape from Tide Pools and Locomotion on Land. Jour.

An. Beh., Vol. 5, pp. 341-350.

MeDonald, M.

1885. Report on the Pollution of the Potomae River by the Dis-

charge of Waste Produets from ied Manufacture, Bull.

1884, Vol. 5, U. S. Bureau of Fisher

Meek, A.

1916. The Migrations of Fish. London, 1916,

Prince, E. E.

1920. Why Do Salmon Ascend from the Sea? Trans. Am. Fish. Soc.,

Vol. 49, pp. 125-140.

Ringer, S.

1883. Concerning the Influenee of Saline Media on Fish. Jour.

ysiol., ba 5, p.

Shelford, V. E. and Powers, E. B.

1915. An Paia Study of the Movements of Herring and

Other Marine Fishes. Biol. Bull., Vol. 28, No. 5, pp. 315-

334.

Thomas, A.

1915. ciate of Certain Metallie Salts upon Fishes. Trans. Am.

Fish. Soe., March, 1915, pp. 120-124,

SHORTER ARTICLES AND DISCUSSION

NOTE ON ASSORTATIVE MATING IN MAN WITH

RESPECT TO HEAD SIZE AND HEAD FORM

ASSORTATIVE mating in man has been much discussed! but

has been little investigated by scientific methods.

For eharaeters sueh as age of husband and age of wife where

there is an obvious preferential mating we may have coef-

ficients of assortative mating as large as r= + .15. For stat-

ure, span and forearm Pearson has determined eoeffieients of

about + .20 for span and span, + .20 for forearm and forearm,

and + .28 for stature and stature in husbands and wives in his

English series. The cross correlations for these various charac-

ters are in general smaller. For bodily characters other than

stature the data are very few and are in general unsatisfaetory.

With characteristic caution Pearson long ago suggested? that

eoeffieients of assortative mating might be due to the husbands

and wives being drawn from the same local races. The im-

portance of this factor seems to be very small in his own ma-

terials.

This question must eontinually reeur whenever assortative

mating for physieal eharaeters is diseussed. It seems very de-

sirable, therefore, to obtain some measure of the correlation be-

tween husband and wife with respect to cephalic index, a char-

aeter whieh has been eonsidered of great importanee by an-

thropologists in differentiating the raees of Europe. For head

size and head form we have had, as far as we are aware, until

reeently only the data for forty-eight families of Eastern Euro-

pean (Russian) Jews living in New York City, for whieh Boas*

found assortative matings for cephalic index measured by

r—.15 + .10.

Recently Frets in a series of papers‘ has given data for head

1 The literature of the field has been reviewed up to 1912 by one of us:

Harris, J. Arthur, ‘‘ Assortative i of Man,’’ Popular Science Monthly,

80: 476-492, 19

5 Peation, E, “Data for the Problem of Evolution in Man. III.

the Magnitude of Certain Coefficients of Correlation of Man,’’ ete., Proc.

Roy. Soc., Vol. 66: 23-32, ;

3 Boas, F., ‘‘Heredity ir Head Form,’’ Amer. Anthrop. N. S., 5: 532.

1903,

4 Frets, G. P., ‘‘Heredity of Head Form in Man,’’ Genetica, 3: 193-400.

1921. This paper contains the original measurements. These have been

to some extent checked against his other papers.

381

382 THE AMERICAN NATURALIST [Vor. LVI

length, head breadth and cephalic index in a series of Dutch

families. He has himself calculated a coefficient of correlation

of .039 + .034 for the cephalic index of husband and wife in

389 families? We have felt it desirable to determine the cor-

relation for length and width of head, as well as that for index.

Because of a suggestion by Pearson (loc. cit.) that the cor-

relation apparently indieating assortative mating may be really

due in some eases to an association of fertility with homogamy,

we have thought it desirable to calculate all the coefficients of

correlation in two ways: (1) by using the actual number of

parents, and (2) by weighting the parents with the number of

offspring indicated in Frets’ tables.*

The correlation coefficients are as follows:

Length of husband’s head and length of wife’s head:

Parents only, r — 4- .0487 + .0377. r/Er — 1.29.

Parents weighted with their children,

r=+ .0616 + .0376. r/r == 1.63..

Breadth of husband’s head and wife’s head

Parents only, r =:+ .1197 + .0372. et 22.

Parents weighted with their MESE

= + .1184 + .0372. r/Er=3.18.

Index of husband’s head and index of ite? s head:

Parents only, r==-+ .0231 + .0377. r/Er=0.61.

Parents weighted with their US

— .0546 + .0376. r/Er = 1.44.

The constants are with one siens positive in sign. That

for the breadth of husband and breadth of wife may perhaps

be considered statistically significant in comparison with its

probable error. The others, particularly that for the cephalic

index, can not be so considered

The coefficients may, therefore, indicate a slight assortative

mating for the dimensions of the head. The coefficients, in

common with those for physical characters other than stature,

are relatively low. That the correlation for the cephalic index

is so low is a point of particular interest. If cephalic index be

a character of great importance in distinguishing races, and if

correlations which have been demonstrated between the physi-

5 Frets, G. P., ‘‘Erfelijkheid, correlatie en regressie,’’ Genetica, 3: 1-27.

1921.

9 We are able to abstract from Frets’ tables 319 pairs of parents in

whieh there were no indieations of typographieal errors when different

tables were checked against each other. These had a total of 1328 recorded

children. In ealeulating the probable errors of the coefficients we have

used the unweighted number of parents as N

No. 645] SHORTER ARTICLES AND DISCUSSION 383

eal characteristics of husband and wife be due primarily to the

tendency to marry within the same racial group, one might ex-

pect a large correlation for cephalic index. Instead we find

the lowest correlation of the three determined.

J. ARTHUR HARRIS,

ALBERT GOVAERTS

STATION FOR EXPERIMENTAL EVOLUTION,

COLD SPRING HARBOR, L,

A GYNANDROMORPH IN DROSOPHILA

MELANOGASTER +

In 1916 Hyde and Powell described a mosaic female with

one eye eosin and the other blood. They interpreted this case

in the light of Morgan’s suggestion of 1914 that ‘‘Gynandro-

morphs and mosaics may arise through a mitotie dislocation of

the sex ehromosomes." In other words they believed one X

chromosome earrying the gene for eosin went into the cells of

one eye and the other X chromosome earrying the gene for

blood went into the other eye. In 1919 Morgan and Bri

deseribed a large number of gynandromorphs. The hypothesis

of chromosomal elimination explains most of them, but a num-

ber of speeial eases are explained in other ways. One of their

special cases was a male with one eye eosin and the other eosin

vermilion. They explained this ease by assuming that the egg

had two nuclei, one of which after maturation had an eosin

vermilion X ehromosome and the other an eosin X ehromosome.

Further, they assumed each nucleus to have been fertilized by

a Y sperm. These hypotheses would explain the facts that the

individual was male throughout and that one eye was eosin

vermilion and the other eosin.

In our experiments a somewhat similar mosaie appeared.

The individual was made throughout, with one eye garnet and

one white. - The parentage was as follows: a garnet male was

mated to a yellow white female. An F, wild-type daughter

was mated to an F, yellow whife male. From this pair of

parents the mosaic arose. It was fertile and was bred to a

garnet female. In F, all males arid females were garnet. The

F, garnet males and females were inbred. In F, the females

were garnet but the males were garnet and white in approxi-

mately equal numbers (1,089 garnet to 1,026 white). This

demonstrates very clearly that the mosaie was genetieally a

1Zoologieal Laboratory Contribution No. 191. Indiana University.

384 THE AMERICAN NATURALIST [Vor. LVI

garnet white. Professor Morgan writes us that he would also

interpret this ease on the binucleated egg hypothesis. We see

clearly how the hypothesis may be applied and that the binu-

eleated eggs described by Doncaster may give indirect evidence

in its favor. Perhaps it is the best interpretation. We wish

to point out, however, that there are other possibilities although

they may have no direet or indireet morphologieal or experi-

mental evidence in their favor.

Let us assume the individual started as a rud male, the

single X chromosome carrying the genes for garnet and white.

Since the mosaic did not carry the gene for yellow, the garnet

white genes must have been brought together by a double cross-

ing over in the mother. The only assumption we need to make

is that during somatogenesis, the white end of one of the

daughter X chromosomes became in some way inactive or lost.

This would leave in one cell a whole X chromosome carrying

white and garnet; in the other an imperfect X chromosome

carrying garnet only. We know by test that white and garnet

in the same chromosome give an eye practically indistinguishable

from white. If one eye arose from the descendants of one of these

two cells and the other eye from the second cell, we could ae-

count for the difference in color. The only assumption we need

to make then is the loss or inaetivation of the white gene in

one of the early cleavage cells. On the binucleated egg hypoth-

esis we must assume, first, the presence of two nuclei within

the egg; secondly, that each nucleus is fertilized by a Y sperm;

and thirdly, that the sex cells of the male arose from the de-

seendants of only one of these nuclei, as all sperm were alike,

earrying garnet and white.

A second possibility is that of somatic mutation. If the white

gene in one of the cells should mutate to red, we would have a

cell whose X ehromosome earried the gene for garnet. If the

deseendants of this eell gave rise to one eye and the descendants

of the other cells to the seeond, we would have one eye garnet

and one garnet white, whieh is white. It is true that white eye

has never reverted to red in all the thousands which have been

bred. This fact renders this Suggestion improbable but not im-

possible.

F. PAYNE,

MARTHA DENNY*

ZOOLOGICAL LABORATORY,

NA UNIVERSITY

THE

AMERICAN NATURALIST

Vor. LVI. September— October, 1922 No. 646

EXPERIMENTAL STUDIES ON THE DURATION

F LIFE

V. Ow THE INFLUENCE or CERTAIN ENVIRONMENTAL

Factors on Duration or Lire IN DROSOPHILA !'

PROFESSOR RAYMOND PEARL AND SYLVIA L. PARKER

A. INFLUENCE OF VENTILATION ON DURATION OF LIFE

Tue standard method of handling Drosophila cultures,

as described by Pearl and Parker (27), includes the

plugging of the mouth of the bottle with absorbent

cotton to prevent the escape of the flies. The theory of

this practice, which is the custom in Morgan’s labora-

tory, presumably is that air will pass in and out through

the plug while the flies can not. No physicist or ventila-

tion engineer would, we believe, accept this theory.

Many years ago the senior author had occasion to make

some observations on the ventilation of curtain-front

poultry houses, and soon came to the conclusion that

curtains of one thickness only, of the very porous jute

bagging which is used for bran sacks, are practically

nearly as effective in preventing the natural unforced

circulation of air as a half-inch pine board would be.

We may be sure that the plug of cotton used in Droso-

phila bottles will be an even more certain preventative

of the natural unforced circulation of air. Theoretically

one may perhaps hold that there is more circulation of

air with a cotton plug than there would be with a cork

stopper, but the difference must be infinitesimal.

1 Papers from the Department of Biometry and Vital Statisties, School of

Hygiene and Public Health, J ohns Hopkins University, No, 67.

385

386 THE AMERICAN NATURALIST [Vor. LVI

In the systematie survey which we are making, at the

beginning of our experimental study of duration of life,

it seemed desirable to test the influence upon this char- |

acter of degree of natural ventilation of the bottles. It

is the purpose of this first section of this paper to pre-

sent the results of some experiments on this point.

Material and Methods

The experiments were carried out in two series. For

the first, wild type flies of our Old Falmouth stock

(Pearl and Parker (27)) belonging to Line 107, the dura-

tion of life constants of which have been given by Pearl

and Parker (32), were used. These flies were of the 25th

pedigreed generation. Eighteen mass matings of the

flies of this line were started for the present experiments

on March 13, 1922, and the flies to be used emerged

March 23-30, 1922.

For the second series short-lived flies of Quintuple

stock (Pearl and Parker (27)) were used, in the 27th

pedigreed generation. Twenty-five mass matings of

Quintuple line 405 were started April 10, 1922, and six

mass matings of mixed Quintuple stock were started

April 11, 1922. The flies for use in the experiment

emerged April 22-27, 1922.

The procedure in making up the experiments was as

follows: The flies were counted out each morning upon

emergence into our standard one ounce screw top shell

vials used in the determination of duration of life (Pearl

and Parker (27)). Fifty flies were put in each bottle.

The wild type flies were counted in through the counting

tube described in these Studies, III (Pearl and Parker

(44)). The Quintuple flies move through the tube so

slowly, however, that there is time for moisture to con-

dense and accumulate on the walls of the tube, killing

some of the flies by drowning, and injuring others. Con-

sequently the flies of this type were etherized and

counted into the bottles. It has been shown in these

Studies, IIT, that such etherization has no measurable

No. 646] THE DURATION OF LIFE 387

influenee on duration of life. Each day's flies were di-

vided equally between control and experimental groups.

Fertility in the Quintuple flies is so low that even with

the large number of matings the hatehes on some days

did not equal 100 flies. It thus resulted that there were

a few bottles of the Quintuples with fewer than 50 flies

to the bottle: 1 ease with 40 flies in control and 40 in the

experimental bottle, 1 with 37 flies in each bottle, and 1

with 23 flies in each bottle.

The control bottles were plugged with cotton in the

ordinary way. The experimental, ventilated bottles

were covered with one layer of silk bolting cloth of No.

48 mesh (48 meshes to the linear inch), this being the

largest mesh which could be used without any possibility

of a fly squeezing through the openings. The cloth was

held firmly and evenly in plaee by an aluminum serew

cap in the top of which a central hole a little more than

94 inch in diameter had been punched out. This is

practically the internal diameter of the shell vials which

we use.

Both control and ventilated bottles were carried in 25?

incubators, and all other procedure was that which has

been described by the authors (27) as standard in the

work of this laboratory on duration of life in Drosophila.

Results

The observed l- distributions (survivors out of 1,000

starting together) for the wild type Old Falmouth Line

107 are given in Table I, together with the absolute num-

bers of flies on which the distributions are based.

These distributions of Table I are shown graphically

in Fig. 1.

It is evident at once that the flies in the well-ventilated

bottles outlive those in the ill-ventilated. Their expecta-

tion of life is greater at every age. The magnitude and

significance of this difference can best be appreciated

from the constants of duration of life set forth in Table

388 THE AMERICAN NATURALIST [Vor. LVI

TABLE I

SURVIVORSHIP DISTRIBUTIONS (Iz) OF VENTILATED AND CONTROL FLIES

Old Falmouth, Line 107

Number of survivors up to indicated age.

Cc l

Age in days Ventila ontro

Be pes eee Pe he T C Cre 1,000 1,000

T CaL HIM AE D d siu nals s 986 984

AM ee Ces Cee ee ek ie qa 970 969

34 Oed as P eFra tau rcs uae 946 929

BB DP IIO EELVPDÜLE Cae EE CR 900 846

Blol.claideneWaesr5 cia Apis 804 730

CYESPOQs rast SEA MADE MEM C ED 697 615

di ehh es eked ers RÀ er rn 589 485

AM ioo LEUR aL soe ds d RD 480 397

DD Liao poe etc RR Sie AD CA 371 292

OL. Clu ULCUS S d E WEE TU. S Ee 278 195

OF ios wees ri Nod ee LEG 185 119

Y opu MUCH RU UE unge nca ie wes 103 44

vi ANEA EE se cee hs 12 2

BD E T ee ae ee T 0 0

Absolute number of flies ......... 946 931

TABLE II

FREQUENCY CONSTANTS OF dz DISTRIBUTIONS

Wild Type, Line 107

Standard Coefficient of

i Poup | Meah Deviation Variation

Con as ere te s | 43.66 + .39 17.63 + .28 40.38 + .73

Ventilated. 1.22 20 9.4 | 47.92 + .40 18.22 + .28 38.01 + .67

Differenoé. ... 2x a is | + 4.26 + .56 + .59 + .39 — 2.37 + .99

There is clearly a significant increase, amounting

roughly to 10 per cent., in the mean duration of life, or

expectation of life at emergence, in the flies in the venti-

lated as compared with the unventilated bottles, all

other conditions both genetic and environmental having

been the same in the two series.

That the increased amourt of fresh air is the cause of

the difference is evidenced by the behavior of the flies.

In the ventilated bottles the flies tended at all times to

congregate on the under side of the bolting cloth going

down to the bottom for food occasionally, but otherwise

exhibiting a strong preference for the region about the

No. 646] THE DURATION OF LIFE 389

mouth of the bottle, where the diffusion of air between

inside and outside was going on most rapidly. This be-

havior is in no way characteristic, in our experience, of

flies in the bottles stoppered with cotton. In those there

4000

SURVIVORS

jeep E NUN gy a NO ee

Fic. 1. Survivorship (Z,) lines for ventilated (solid line) and control (broken

line) flies,

is generally a fairly even distribution of flies throughout

the bottle, with such tendency towards concentration as

there is, in the direction of the bottom near the food

rather than the top.

In Table III are presented the survivorship distribu-

tions for the Quintuple flies. Because of their much

shorter life span, as shown in the life tables of the first

390 THE AMERICAN NATURALIST [Vor. LVI

one of the Studies (27), a shorter abscissal interval has

been used in the grouping. The figures for Quintuple

stock flies, and for an inbred Quintuple line (No. 405) -

are given separately.

TABLE III

SURVIVORSHIP DISTRIBUTIONS (Iz) OF VENTILATED AND CONTROL FLIES

uintuple Stock and Line 405

Number of Survivors up to Indicated Age in

Age in Days

Stock Stock Line 405 Line 405

Ventilated Control Ventilated Control

To eee AUTE. 1,000 1,000 1,000 1,000

Seed orn Cue AV 993 992 783 878

f Tenet ange oats aia 816 812 422 443

JO ace ens redi 218 368 62

IS Qv EE ERDSVONDES 81 158 18 36

18: 17 Oe RR 44 143 9 14

40 o ee DTE 29 113 9 5

Pee STR EA eis Pas 22 83 4 0

Di E ERE T ey a re week 22 60 4 —

DELI RA UE CR 22 30 0 —

SEEN Gi ec eno 22 23 — —

OR, iu E EE 15 23 — —

OF cm Ed 0 15 — =

FT RGR aaa uU ec S E — 15 — —

di. oS E S E E ek — 8 — —

AB uL odo s RE -— 8 — —

a I LIT — 8 -— —

DESI uta ERA aA mo 0 — —

Absolute number of files 136 133 209 221

The calculated constants from the de distributions are

given in Table IV.

TABLE IV

FREQUENCY CONSTANTS OF dz DISTRIBUTIONS

Quintuple Stock and Quintuple Line 405

Standard Coefficient of

Sort Group Mean Deviation Variation

Quintuple stock. .| Control....... 11.07 +.41 7.04 2-.29 63.58 +3.54

Ventilated ..... 9.34 +.26 4.57 +.19 48.92 +2.43

Difference

EEE DARET A EET TE — 1734.49 | —2.47 +.35 | —14.66 +4.29

eee GS |Control.......| 6.90+.18 | 200400! —42.09::1.57

Ventilated. 5... " 784.14 | 2.99210 | 44064171

Be RE LIAE ARS TA — 12+.19 | + 094.13 | + 1.97 +2.32

No. 646] THE DURATION OF LIFE 391

The situation here is evidently quite different from

what obtained with the wild type flies. The Quintuples

lived somewhat longer in the control bottles than in the

ventilated. In the ease of flies from stock, the difference

in the means amounts to 1.73 days, and is 3.5 times its

probable error. The numbers are, however, small, and

as an examination of Table III shows, the long survival

of 2 individuals in the control series after age 34 ac-

counts for a considerable part of the difference in the

means. With a larger experimental sample much of the

difference in the means would, we feel sure, disappear.

The influence of these same two individual flies is clearly

seen in the greatly inereased variability of the control

series over the ventilated in the stock groups.

In general we are of the opinion that in the case of

Quintuple flies the difference in ventilation represented

by a bolting cloth screen versus a cotton stopper has no

significant influence upon duration of life. The results

with extremely short-lived line 405, we regard as typical

of what one should expect with Quintuple flies in this

sort of an experiment.

The reason for the difference between wild type and

Quintuple flies in their response to ventilation is founded,

in our opinion, upon the normal differences in behavior

between the two types. In Quintuples the wings do not

function (the wing mutation in this stock is Vestigial).

The consequence is that these flies are much less active,

and generally appear to live on a lower metabolic plane,

than wild type flies. Their oxygen needs are presumably

smaller, and it would therefore be reasonable to expect

that they would not show the difference in duration of

life with increased ventilation that the wild type flies do.

In this connection, it should be noted that their actual

behavior in this experiment was in accordance with the

view here suggested. They showed no such definite tend-

ency to congregate at the top of the bottle under the

bolting cloth as the wild type flies did. Their distribu-

tion was about the same in ventilated as in the control

392 THE AMERICAN NATURALIST [Vor. LVI

bottles. Another consideration is that genetically Quin-

tuple carries factors for very short life. These genes

appear, in our experience with these flies, to be the over-

whelmingly important factors in determining their

length of life. No environmental factor, however favor-

able, makes much difference in their duration of life.

Summary

In experiments involving the determination of the

duration of life in 2,576 individual flies, it has been

found that in the case of Drosophila of wild type (i.e.,

carrying no mutations so far as known), an increase of

roughly 10 per cent. in the mean duration of life is

brought about by inereasing the ventilation of the cul-

ture bottles, by covering the mouth with one layer of

No. 48 mesh bolting cloth, as compared with the use of

cotton plug stoppers as is the usual practice in the cul-

ture of Drosophila in the laboratory. Owing, in our

opinion, to fundamental differences in behavior, no such

differenee appears in the ease of Quintuple flies.

B. Can THE Duration or LIFE BE INCREASED BY

EMBRYONIC JUICE?

If the theory of senescence and natural death which the

senior author has developed in his ‘‘Biology of Death’’

(1-7) is true, one consequence of it should be that it

might be possible to increase the duration of life, if by

appropriate means one could restore the normal func-

tional balance of the parts of the body after changes had

set in with advancing age. Might it not be possible, by

the use of X-rays for example, at the right stage of the

life curve, and in proper dosage, to destroy cells, or per-

haps even parts of tissues, which have got out of proper

functional balance, and thus pave the way to their re-

placement by regeneration with fresh, ‘‘young”’ cells or

tissues? In this way the life of the whole organism

might be prolonged. The work of Frisch and Starlinger

(45) with blood suggests that such a result might at least

No. 646] THE DURATION OF LIFE 393

be hoped for. In view of the known facts as to the po-

tential immortality of tissue cells in cultures in vitro, and

the apparent reason for the difference in the behavior of

the same cells in respect of duration of life when they are

in the multicellular body, all of which has been rather

fully discussed by Pearl in the ‘‘ Biology of Death’’ (loc.

cit.), it would seem that this is a line of experimenta-

tion well worth following. We have a number of experi-

ments along this line now in progress, particularly with

X-rays, which we expect later to report upon. Some of

the purely preliminary work has already been finished,

and we wish in this paper to report one piece of it.

The brilliant researches of Carrel and his coworker

Ebeling (cf. 46, 47) on the duration of life of cells in

eultures in vitro have brought to light the extraordi-

narily interesting and presumably important faet that

for the continued life of such cultures it is apparently

essential to have in the culture medium a small amount

of embryonic juice. In just what manner this functions

is not yet clear, but the necessity of its presence seems

well established.

It occurred to us in our preliminary work on prolonga-

tion of life in Drosophila, or as it is perhaps better to

put it, on changing the form of the l- line of the Droso-

phila life table, to see whether embryonie juice, applied

at a point on the ls curve after senescence had definitely

set in, would have any effect upon the subsequent course

of the curve, or in other words, upon the duration of life

of the organism as a whole, comparable to its effect upon

the life of cells in culture. The ideal way, of course, in

such an experiment would be to get the embryonic juice

to the tissues of the fly by a par-enteral route, but as no

practical method of doing this occurred to us, we decided

to feed it, and see if any results followed.

Material and Methods

The flies used in the experiment were all wild type, of

Old Falmouth stock, and belonged to Line 107, pedigree

394 THE AMERICAN NATURALIST [Vor. LVI

bred for 21 generations.. The individuals for the experi-

ment came from 20 mass matings of 3 pairs of parents

each from this line. The bottles were started December

16, 1921, and the flies used in the experiment emerged

December 28, 1921, to January 9, 1922.

The flies were eounted through the counting tube into

our standard shell-vials in groups of 50 each. Each

day's bottles were divided into three groups at the be-

ginning of the experiment, but all had the same regular

treatment until the flies in them were 30 days old. This

is a point where the le line is beginning distinctly to turn

downward. From that time on until the end of their life

one series of flies was given chicken juice in their food,

and one series the juiee and pulp of erushed Drosophila

larve. The chick embryos used were 14 days old. The

juiee was extraeted in a beef-juice extraetor, and added

to the regular food at the rate of approximately 2 c.c.

to 100 c.c. of food. With the Drosophila larve, the whole

pulp was used, and that too was added to the regular

food at the rate of approximately 2 c.c. to each 100 e.c.

of food. All the flies, experimental and control, were

transferred every day to fresh food, made up that day,

except on Sundays.

On Feb. 8 an accident happened to the incubator at the

source of our chicken supply, so that for 12 days no

chickens were obtainable.

In all particulars except those specified above, the

procedure in these experiments was the standard tech-

nique of this laboratory in duration of life work de-

seribed in (27).

Results

The survivorship distributions are given in Table V,

on the basis, A, of 1,000 starting at emergence, and, B,

of 1,000 starting at age 31 days, that is at the time when

the experimental feeding began.

2 We are greatly indebted to our colleagues, Dr. and Mrs. Warren H.

Lewis, for furnishing us with chicken material for this work.

No. 646]

THE DURATION OF LIFE

TABLE V

SURVIVORSHIP DISTRIBUTIONS (lz) OF GROUPS OF DROSOPHILA FED

In D

Old Falmouth Stock, Line 107

395

Number of Survivors up to Indicated Age in

Age in Days Controls Chicken Juice Larval Pulp

A B A B A B

Lo 0 eae 1,000 — 1,000 prm ,000 pes

Nu Ili I 975 — 970 — 970 —

tO epee OU 945 — 935 -— 930 —

18. 7 AA 884 — 873 — 858 —

ZR AR IYV RAV 797 -— 784 — 719 —

BEC. SI A An 616 1,000 648 1,000 591 1,000

ol QUSE na CE 491 796 456 703 464 785

4i) 1 1s 362 588 313 484 283 479

842 0n VL 286 465 246 380 210 356

DU CDU aaa 212 345 198 306 156 264

BL ere 156 253 152 234 116 196

eT S nus 120 197 110 170 82 140

Facti y 59 96 58 89 46 78

TE ull 21 34 24 38 28 48

Sh ovi ud ví ES 9 14 3 5

Bi. lloc vut 1 2 0 0 1 2

Wi Sd 1 2 — — 0 0

108 iis os 0 0 — — mx e

pepe number

EET 1,013 — 983 -— 994 —-

The biometric constants of duration of life calculated

from the dz distributions are given in Table VI.

TABLE VI

BIOMETRIC bere FOR DURATION OF LIFE IN DROSOPHILA ire DIFFER-

T CONDITIONS OF Foop.

A. From EMERGEN

B. From Acs 31 Days on

G Stand. Coefficient

Class Group Deviation

Gn days) | (in days) | Variation

Pes ees T E N i siio ccs 9.60 + 18.76 +.28 | 47.384 .85

Chiekon Jalo: ana: 38.66 +.40 | 18.61 +.28 | 48.12+ .89

Va E Eoi Y 36.74 +.39 18.01 2.27 03+

Bv. Ph ci os II .72 2-.40 14.66 +.28 aq 35 +1. ux

Chicken juice. ....... i. 512-.40 | 15.05+.27 96 +2.

a hare or E. 17.12+.39 14.03 +.28 * 982-1. e

396 THE AMERICAN NATURALIST [Vor. LVI

It is evident that there are no large differences in

mean duration of life between any of the groups. The

l- distributions and the constants are closely similar

throughout. This is true whether the whole life is taken,

or the expectation after age 31. "The exact nature of the

differences is shown in Table VII.

TABLE VII

DIFFERENCES IN MEANS OF TABLE VI

Class Difference Taken Value of | Diff./P.E. Diff

Difference or mue

X uc. Control — chicken juice. ............ .94 27.56 | 1.66

Control —larval pulp. .............. 2.86 +.55 5.15

Chicken juice —larval pulp. ......... 1.92 +.56 3.46

Bill Control —chicken juice............. 2.21 +.56 3.93

Control —larval pulp. .............. 2.60 +.56 4.67

Chicken juice —larval pulp. ......... .39+.56 .69

The control group had slightly the greatest duration

of life, both as a whole, and from the time of the begin-

ning of the special feeding on. The flies fed larval pulp

had the worst expectation of life, with those fed chicken

juiee in an intermediate position. None of the differ-

ences, however, is large. That some of them are signifi-

cant statistieally probably means no more than that the

changed food is not quite so favorable for the flies as the

normal, standard food. The numbers involved are large

relatively, and the probable errors eonsequently small.

We must then conclude that the administration of em-

bryonic juice in the manner, amount and time in the life

cycle, which defined its administration in these experi-

ments, does not bring about any prolongation of the life

of the whole organism, comparable to its effect in tissue

cultures in vitro. This does not necessarily mean that

under other eonditions of administration or dosage an

effect in this sense might not be produced. We believe,

however, that it is not probable that any prolongation

of life can be brought about by this method, for the rea-

son that in the first place the results of the present ex-

No. 646] THE DURATION OF LIFE 397

periment give no suggestion that with larger dosage any

such result would appear, and in the second place, be-

eause the experiments of Baeot and Harden (48) indi-

eate that as slight (or slighter) alterations of the food

of Drosophila as those of the present experiments may

produce marked effects in respect of viability.?

For some reason which we are unable to explain, the

-flies of Line 107 had, in all the series of this experiment,

a lower mean duration of life than this line has ever

shown before (cf. 32, 44, and section A of the present

paper). The values are extremely even and consistent

in this feeding experiment, but are about 10 days lower

than what previous work has indieated as the normal

duration of life in this line. "There has been no other

change in the line, in fertility or other characters. We

are inclined to believe that the low values in the present

experiments represent merely a temporary secular

change (? seasonal) in the duration of life characteristic

of the line.

Summary

In experiments involving the determination of the

duration of life in 2,990 individual flies, it was found that

there was no prolongation of the life of Drosophila pro-

duced by adding embryonic juice (either from the chick,

or from the larve of Drosophila itself) daily to the food,

to the amount of 2 per cent. of the total food material,

beginning with the 31st day of the flies’ life.

LITERATURE CITED

(The plan of numbering citations is explained in the second of these

Studies, AMER. NAT., Vol. 56, p. 174.)

44. Pearl, R. and Parker, S. L. Experimental Studies on the Duration of

Life, III. The Effect of Successive Etherizations on the Duration of

Life of Drosophila. AMER. NaT., Vol. 56, pp. 273-280, 1922.

45. Frisch, A. and Starlinger, W. Zur Frage der Protoplasma-aetivierung.

Zeitschr. f. d. ges. ezp. Med., Bd. 24, pp. 142-158, 1921.

3 It ought, however, to be pointed out that the experiments of Bacot and

Harden are extremely faulty from a technical standpoint. They evidently

know little of the practical husbandry of Drosophila. Their cultures were

incubated at 30? C. At this temperature one does not get anything remo otely

resembling normal physiological processes or duration of life, except after

many months of acclimatization.

308 THE AMERICAN NATURALIST [Vor. LVI

46. Carrel, A. and Ebeling, A. H. The Multiplication of Fibroblasts in vitro.

Jour. Exp. Med., Vol. 34, pp. 317-337, 1921.

47. Id. Heterogenie Serum, Age, and Multiplication of Fibroblasts. Ibid.,

Vol. 35, pp. 17-38, 1922.

48. Baeot, A. W. and Harden, A. Vitamin Requirements of Drosophila.

L Vitamines B and C. Biochem. Jour., Vol. 16, pp. 148-152, 1922.

VI. A Comparison or THE Laws or MORTALITY IN

DROSOPHILA AND IN Man

PROFESSOR RAYMOND PEARL

In the first of these Studies (27) there were presented

for the first time, so far as I am aware, complete life

tables for any other organism than man. Up to the pres-

ent time there have been presented in the published re-

sults of the work of this laboratory on Drosophila (27,

32, 44, 49, 50) exact determinations of the duration of

life in 24,329 individual flies. This is a statistically re-

spectable mass of material, and warrants some general

discussion.

In the first study a rough, purely graphical compari-

son of thé l- lines of the Drosophila and certain human

life tables was instituted. This comparison, rough as

is was, made apparent at once the fact that there was a

fundamental similarity in laws of mortality in these two

organisms.

It is my purpose in the present paper to make a more

exact comparison of the values of the life table functions

in the two eases. It will be seen that the similarity is

even closer than was supposed from the rough compari-

son, and that in faet we are dealing here with qualita-

tively identieal expressions of an obviously fundamental

biological law.

Upon what basis shall any life table function, say le,

of the Drosophila life table be compared with that of

man? The life span of one of these organisms is best

measured in days, while that of the other is measured in

No. 646] . THE DURATION OF LIFE 399

years. This fact, however, offers no insuperable diffi-

culty to the comparison. What is needed is to superim-

pose the two curves so that at least two biologically

equivalent points coincide. The best two points would

be the beginning and the end of the life span. But in

the ease of Drosophila our life tables start with the be-

ginning of imaginal life only. The larval and pupal

durations are omitted. In our preliminary comparison

(27) we took human age 15, as the point corresponding

biologically to the beginning of imaginal life in Droso-

phila.

I think we can get at this starting point more exactly

by putting the human and Drosophila l- curves together

as a starting point at the age for each organism where

the instantaneous death rate qz is a minimum. In the

‘case of Drosophila, I think we are safe in concluding, on

the basis of the work of Loeb and Northrop (14-17) as

well as frqm our own observations, that this point is at

or very near the beginning of imaginal life. We shall

accordingly take Drosophila age 1 day as this point.

Our life tables show that certainly after this time qz

never again has so low a value. Indeed the fundamental

law of mortality in Drosophila imagoes was stated in

(27) in this way (p. 492): *'the instantaneous death

rate inereases with age as a modified logarithmie fune-

tion of x."

The latest edition of Glover's (51) United States Life

Tables gives (p. 68) for white males in the original

registration states the following values for qz: for age

11-12 2.28, and for age 12-13, 2.29. We may, therefore,

with sufficient accuracy take exactly 12 years as the

minimum point, particularly as the l- figures we shall

have to use are tabled as of the beginning of the age

interval: `

For the other end of the life span we may conveniently

take the age at which there is left but one survivor out

of 1,000 starting at age 1 day for Drosophila and age

12 years for white males. This age for wild type Droso-

400 THE AMERICAN NATURALIST [Vor. LVI

phila is, to the nearest whole figure, 97 days. To de-

termine it for white males we have Table I, calculated

from Glover's Table 9

| TABLE I

SURVIVORSHIP OF WHITE MALES IN ORIGINAL REGISTRATION STATES ON THB

Basis oF 1,000 AT AGE 12

Number Number Number

Alive at Alive at Alive at

Age Beginning Age Beginning Age Beginning

of Age of Age of Age

Interval l, Interval /, Interval l;

12-18... 1,000 45-46 803 78-79 194

13—14..... 998 46-47 792 79-80 Iri

14—15..... 995 47—48 782 80-81 150

15-16..... 993 48-49 771 81-82 130

1 rg 990 49-50 760 82-83 110

IT-IB..- 987 50-51 749 83-84 93

18-19..... 83 51-52 737 84-8 TF

19-20..... 979 52-53 725 85-86 63

20-21..... 975 53-54 713 86-87 51

po Reo 5: 970 54-5 699 87-88 41

22-23.... 965 55-56 686 32

28—24..... 960 56-57 671 89-90 25

24-25..... 955 57-58 655 90-91 1

25-26..... 950 58-59 639 91-92 14

W- 944 59-60 622 92-93 10

27-28..... 939 1 604 — 7

28-29..... 934 61-62 585 94—95 5

29-30..... 928 62-63 566 95-96 4

30-31..... 922 63-64 54 96-97 2

81-32..... | 916 64-65 525 97-98 1.59

32-33..... | 910 65-66 504 98-99 1.01

BUREN 903 66-67 482 99-100 .63

34-35..... 896 67-68 459

35-306..... 889 8-6 436

36-37..... 881 69-70 412

37-38..... 873 70-71 38

38-39..... 865 71-72 364

39-40..... 857 72-73 340

40-41..... 849 73- 315

41-42..... 840 74-75 291

42-43.... 831 75-76 66

43-44..... 822 76-77 241

44-45..... 812 71-78 217

From this it appears that there is almost exactly one

survivor at 98 years. So then we have as biologically

equivalent life spans

97 days of Drosophila life as imago — 86 years

of human life. .

Whence it follows that

No. 646] THE DURATION OF LIFE 401

1 day of Drosophila life = .8866 year of human life

and

1 year of human life — 1.1279 days of Drosophila life.

We are now in position to make an exact comparison

between the life tables of the two organisms. This may

be done perhaps most instructively by setting up lz lines

for the two forms on the basis of age in centiles of the

life span, rather than days or years. That is to say, the

whole comparable life spans (as defined in this paper)

of 97 days in Drosophila and of 86 years for white males

will each be divided into 100 equal parts, and the survi-

vors at the attainment of the beginning of each centile

interval will then be computed.

This is done for wild-type (long-winged) Drosophila

males (Pearl and Parker (27) Life Table II) and male

whites in original Registration states in 1910 (Glover's

Table 9), in Table II. :

The two life curves of Table II are shown graphically

1n Fig. 1, plotted on an arithlog grid. We have, in Table

II and Fig. 1, for the first time, so far as I am aware, a

precise quantitative comparison of the life spans and one

of the mathematieal funetions of the mortality of two

different organisms.

It will be noted that:

1. The form of the l- distributions is fundamentally

the same in both of these organisms over the equivalent

life spans. Considering the extreme differences in

habits of life, structure, physiology, and environmental

stresses and strains in the two cases, this is a truly re-

markable result. It seems to me to mean that the fae-

tors which determine individual longevity, and differ-

ences in this character, are biologically deeply rooted,

at least as fundamental, apparently, as the faetors which

determine the specifieity in the morphogenesis of organ-

isms, and perhaps even more so. We are accustomed

loosely to think that the prime faetors in determining

402 THE AMERICAN NATURALIST [Vor. LVI

TABLE II

SURVIVORSHIP DISTRIBUTIONS (Iz) FOR EACH CENTILE OF THE COMPARABLE

SPANS OF (a) WILD TYPE DROSOPHILA MALES AND (b)

W EN IN THE ORIGINAL REGISTRATION

STATES IN 19

Centile |Numbers Alive at Beginning| Numbers Alive at Beginning

of Com- of Centile Age Interval Centile of of Centile Age Interval

parable Comparable

Life Life Span

Span Drosophila Man Drosophila Man

On il. 1,000 1,000 51-52 360 673

Te:M cen 991 998 52-53 344 659

2-8... 981 996 53-54 328 645

ge du. 972 994 54-55 312 631

4— 5..... 963 991 55-56 296 616

5- 0..... 54 989 56-57 280 601

6— 7. 945 986 57-58 265 585

7—- 8..... 935 983 58-59 250 568

8- 9..... 926 980 59-6 235 551

9-10..... 917 976 60-61 221 533

10-11. .;.. 972 61-62 207 515

H-a 898 968 62-63 193 496

2-13... 888 963 63-64 180 477

13-14..... 879 959 64-65 167 458

14-15.... 869 955 65-66 155 438

15-10... 859 950 6-67 143 418

16-17..... 946 67-68 132 397

17-18..... 941 68-69 121 377

18-19..... 828 936 69-70 111 356

19-20..... 818 932 70-71 102 335

20-21.... 807 927 71-72 314

2122..... 796 922 72-73 292

py ea, Saas 785 916 73-74 76 271

23-24..... 773 911 74-75

24-25..... 761 905 75-76 61 229

25-20..... 749 899 76-77 55 208

20-21;. 737 893 77-78 49 189

27-28..... 725 887 78-79 43 169

28-29..... 712 880 79-80 38 151

29-30..... 699 S74 80-81 34 133

0-31..... 867 81-82 30 117

31-82..... 672 ` 860 82-83 26 101

82-33.... 659 852 83 22

33-34.... 645 845 84-85 19 74

34-35..... 630 838 17 62

35-36..... 616 830 86-87 14 52

36-37..... 601 822 87-88 12 43

87-38..... 586 814 88-89 10 35

38-39..... 571 89-90 9 28

NUES 555 797 91 T 22

40-41..... 540 7 91-92 6 17

-42.... 524 719 -93 5 13

42-43..... 770 93-94 4 10

Vea 492 760 94-95 3.43 8

ES 475 750 95-96 2.80 6

45-40..... 459 740 7 2.97 4

SPA 443 730 97-98 1.84 3

47-48..... 426 720 98-99 1.47 2.11

48-49..... 410 709 99-100 1.18 1.37

49—50..... 697 100 .94 .87

50-51..... 377 685

SURVIVORS

No. 646]

THE DURATION OF LIFE

403

human longevity are such things as the infectious dis-

eases, exposure to unfavorable environment, ete.

But

Drosophila, which so far as is known has no infectious

diseases, and in general meets

a set of environmental

L000, m —

~~, ~

he “W

Q Z

D 2

MALAS N \

100 M V

XII

; \

O 4 8 2 6 20 24 28 32 36 40 44 48 52 56 60 64 68 72 76 80 84 68 92 96 00

AGE CENTILES

1. Comparing the survivorship Ss aoe. of Drosophila and man

Prec in both cases) over the equivalent life s

conditions wholly different, both qualitatively and quan-

titatively, from those which operate on man, shows

fundamentally the same form of distribution of degrees

of longevity

404 . THE AMERICAN NATURALIST [Vor. LVI

2. When compared exactly, on the basis of comparable

life spans, the human being has at every equivalent age

a higher relative expectation of life than does Droso-

phila, measured in terms of its own life span in each

ease. That this was the case for all but old age was

concluded from the rough graphical comparisons of the

first Study in this series. It is now seen that the same

is true over the whole of life. From this faet the con-

elusion appears warranted that while the laws of mor-

tality are fundamentally the same in kind for Drosophila

and for man, they differ somewhat quantitatively. There

is a temptation to conclude further that the quantitative

difference finds its cause,in man's own control and

amelioration of his environment though sanitation and

hygiene. Such a conclusion, however, seems to me not to

be strietly warranted, in the light of our present knowl-

edge. There is some suggestion that it is true, as was

pointed out in the first of these Studies, from the fact

that the progressive change of the human ls curve in

form during historical times has been in the direction

of moving from the form typical of Drosophila to that

now found for progressive, highly civilized groups of

men. But definitive conclusions on the point must await

further research.

3. The details of the quantitative differences in the

two curves are interesting. When the first 25 per cent.

of the equivalent life spans has been passed Drosophila

has lost almost exactly 25 per cent. of the individuals

starting life together, while man has lost but 10 per cent.

When 50 per cent. of the life spans has been completed

Drosophila has lost 72 per cent. of the individuals start-

ing together, while man has lost but 31.5 per cent. At

75 per cent. of the life span, Drosophila has lost 94 per

cent. of the individuals and man 77 per cent. From the

93d centile of the equivalent life spans on practically

to the end, man has more than twice as many survivors

out of a thousand starting together as does Drosophila.

Exactly similar results to those here presented are ob-

No. 646] THE DURATION OF LIFE 405

tained if one compares human and Drosophila life curves

for females. Since nothing new in principle is brought

out, it is not thought necessary to present the female

curves here.

In this paper it is shown that if we take as equivalent

life spans in Drosophila and man the period between (a)

the point in the life history of each organism where the

specific death-rate (qz) is a minimum, and (b) the point

where there is one survivor out of 1,000 starting at the

beginning as defined in (a), and then divide these equiva-

lent life spans into 100 portions (thus measuring age not

in absolute units but in centiles of the life span), the laws

of mortality are fundamentally the same in kind in the

two organisms. There is a quantitative difference ex-

pressible in the statement that at each centile age

throughout the life span the number of survivors, out of

the same original number starting together, is higher

in man than in Drosophila.

In a subsequent paper, I hope to take up in detail

the funetional relations (in a mathematieal sense) be-

tween the human and Drosophila equivalent le curves |

here presented.

LITERATURE CITED

(The plan of numbering citations is explained in the second of these

Studies, Amer, NaT., Vol. 56, 4.)

49. Pearl, R. and Parkir, S. L. Experimental Studies on the Duration of

IV. Data on the Influence of Density of Population on Dura-

tion of Life in Drosophila. AmER. NAT., Vol. 56, pp. 312-322, 1922.

50. Id. _Bapermental Studies on the Duration of Life. v. On the Influence

Certain Environmental Faetors on Duration of Life in Drosophila.

922.

Tii, Vol. 56, pp.

51. Glover, 3; W. United States Life Tables 1890, 1901, 1910, and 1901-

10. Washington (Bureau of the Census), 1921. Pp. 496, 4to.

THE SYSTEMATIC LOCATION OF GENES BY

MEANS OF CROSSOVER OBSERVATIONS

R. A. FISHER

RorHAMSTED EXPERIMENTAL STATION

INTRODUCTORY

. Ix the construction of a chromosome map, the dis-

tances between neighboring genes are equated to the per-

centage of crossovers which have been observed between

them. Owing to errors of random sampling, and some-

times to other disturbing causes, inconsistencies always

arise between the distances so determined. For example,

in the important data given by Lancefield and Metz for

the sex chromosome of Drosophila willistoni [1, p. 241]

we have the following values:

TABLE I

| Crossover Number of | Number of

stat

Percentage Observations Crossovers

Staite to Beaded. 606s. o Lee 279 | 4

Beaded to Hough... v y ea A 2.42 455 | 11

Pante to Roh. c oe | 7.09 6388 | 453

Within such a small range, double erossing over may

be ignored; yet it would be wrong to use such inconsist-

eneies as an argument against the linear arrangement of

the genes. For although the true erossover values may

be accurately additive, errors of random sampling will

certainly disturb the observed percentages. The practi-

eal problem is to assign to the distances between the

genes values which shall be as far as possible in accord

with the whole of the observations available. In other

words, we have to make use of as much as practicable,

ideally the whole, of the information supplied by the

data; giving due weight (i) to the greater accuracy of

the values obtained from the larger number of observa-

tions, (ii) to the greater accuracy of values obtained from

406 ‘

No. 646] THE SYSTEMATIC LOCATION OF GENES 407

closer pairs. In general, too, we shall have to consider

not three genes only, but a large number, lying sufficiently

close together for double crossing over to be ignored,

the percentage observed between

each pair of which gives indirect

information as to the position of

all the others. AE E Pines

In its general character the prob-

lem resembles those problems in- M. DEFORMED

volving errors of observation, where 8 L

a smaller number of unknowns are

determined from a larger number f ee

of inconsistent equations, and which 7 +

are usually solved by the method m mu

of least squares. The practical so- "

lution depends on the construction

of a number of ** normal equations ”’

for the unknowns, in which the in-

consistencies of the data are prop-

erly weighted and made to balance.

To make the sum of the squares of 4 L

the errors of the crossover percent-

ages a minimum would, however,

be wrong, and the method of least 3 Me Beapepd

squares is not directly applicable.

It has been shown that the whole of

the information supplied by the 2 F ~

data (2) is made use of by the E Peach

method of maximum likelihood,

and by a first approximation the

required normal equations may be .

construeted. o LB Scute

2. MATHEMATICAL THEORY

: —l—- REDUCED

In the above example, if we71 f

write p, and p: for the two adjacent

erossover ratios, the probability of

the aetual series of observations

408 THE AMERICAN NATURALIST [Vor. LVI

will be proportional to

pil — p)?5p4(1 — p: i(pi + p2)5(1 — pi — p2)995

and the likelihood of any given pair of values for p, and

p. will be proportional to the same quantity. In order:

to make this quantity a maximum for variations of pi

and p, we have the equations

4 275 453 i 5935 n

p 1—mp 2t» 1—m—7

453 5935 11 444

pts Lom "95 ^ im

These equations are exact, but for practical purposes

we need equations linear in p; and p;, and a first approxi-

mation is sufficient; if p differs little from z/(« + y) =

a/n, then

: 1 4 (GF Er lue a) te LP

So that we may rewrite Sees (1) in the practical

and approximate form

279: 6388?

ax2:5P7 t i x 2 (m t») = ae T 5935 '

6388 6388? | 455?

453 x 5935 P! + P9 ta x qi nt = 5035 | 444

For each percentage observation, therefore, we have

merely to calculate the two quantities »?/zy and n?/y;

then normal equations may be constructed in the form

aP F458, E iR.

ah +%.P,+:--=),

where a2 is the sum of the quantities »*/zy for which

both p; and p; are involved, a,, the corresponding sum for

all in which p, is involved, and b, the sum of the quanti-

ties n?’/y for which p; is involved.

3. Practica, EXAMPLE

In order to illustrate the practical application of this -

method to a complex ease, we will consider the location

of the 8 genes, from Reduced to Rimmed, in the middle

No. 646] THE SYSTEMATIC LOCATION OF GENES 409

of the sex chromosome of Drosophila willistoni. We have

here 7 intervals to determine, and fifteen crossover per-

centages are given [1]. Table II shows the data, and

the series of weighting quantities derived from them.

TABLE II

Per-

cent-| x n n?/y ni[zy Unknowns Involved

Reduced-Seute..... .95 | 27| 2,848 |2,875.26 gr 287 pı

Reduced-Rough....| 6.24 | 37| 593 | 632.46 0,136 pi, pz, ps, De

Seute-Peach....... 81 8|. 442| 450.15 aL 1

Scute-Beaded...... 1.4 279 ,742

Seute-Rough...... 7.09 | 453| 6,388 |6,875.58 | 96,956 p» Ps, Ds

Scute—Deformed 7.24 50 6 2 ,205 ps, ps, P4, Ds,

Seute-Rimmed.....| 9.91 | 189| 1,908 2,117.78 | 21,379| P2, ps, pa, Ds, De, D7

Peach-Beaded..... 1.70 3 6| 179.05 | 10,504 i

each-Rough...... 5.05 | 33| 654| 688.75 | 13,650) - ps, 74

Beaded-Rough..... 2.42| 11 455 | 466.27 | 19,287 pi

Rough-Triple...... 49 4| 809| 813.02 | 164,433 Ps

Rough-Deformed ..| 2.39 | 12 503 | 515.29 | 21,599 ps, pe

Rough-Rimmed....| 2.26 | 62| 2,742 |2,805.43 | 124,072 ps, pe, PT

Triple-Rimmed. 1.00 6| 601| 607.06 | 60,807 pe, P7

Def formed-Rimmed. 417| 2 48 50.09 1,202

From this table we write down the normal mice

313,423p + 10,136(p, + P, +P, 7.72

10 1136p, + 183,380p, “4 158 509p, -+ 138,766p, + 31,674p, + 31,6 lip,

21, 379p, = — 11,103.93

10,136p, + 158,509p, + 182,663p, + 152,416p, .- 31 enam, + 31,674p,

1,379p, = — 11,521.58

10,136, + 138,766p, + 152,416p, + 171,703p, + 31 srin, + 31,674p,

21,379p, = — 11,525.74

31,074 (p, + P, + p,) + 341,778p, + 177 345p, + 145,451p, = 6,996.42

31,674 (p, + p; +r, J+ 177,345p, + 238,152p, + 206,258p_ = 6,790.46

21,379 (p, he p, +4 p, ) +145 451p, 4 206,258p, + 217,460p — 5,580.36

Using a calculating machine, the work so far is rapid

and mechanical; the solution of the normal equations

may in this case be much simplified by observing the uni-

formity of some of the sets of coefficients, a type of uni-

formity which is probably characteristic of crossover

data. Thus by considering (p: +p: + pı) as a single

quantity, p, is immediately expressible in terms of it, and

by solving the last three equations we may do the same

for ps, p, and pz; substituting finally in equations (2, 3,

410 THE AMERICAN NATURALIST | Vou. LVÍ

4) we solve them for p», p, and p,, and obtain the values

shown in Table III.

The seven values obtained give mutually consistent

values for the crossover percentages between the fifteen

pairs tested, and are therefore suitable for the construc-

tion of chromosome map. If the conditions of Maximum

Likelihood had been exactly fulfilled they would agree

better than any other consistent series of values with

the percentages observed. As it is, it is only in the ab-

errant value of p; that the assumption that the observed

values are approximately correct breaks down, and it

is probable that such cases will ves occur when the data

are TORENT insufficient.

TABLE III

is : | Standard da

CM Observed oe d i

LC air Boso Preece. .90 pı .95 + .05 18 0

ced-Rough.......... 7.66 6.24 —1.4 1.09 1.70

Seats Paes wie Gree Gee) 1.67 ps 1.81 + .14 05

S WI. acci. 2.98 1.43 —1.53 1.02 2.31

Seute-Rough............. 6.76 7.09 + .33 1.18

te-Deformed.......... 8.40 7.24 —1.16 1.06 1.20

Scut SE S VIVIDE A. 8.97 9.91 + .94 65 2.09

Peach-Beaded............ 1.31 ps 1.70 — .39 86 2

Ph ROUGH: i sous 5.05 c .86 s

Beaded-Rough........... 3.78 pa 2.42 —1.36 .89 2.34

Rough-Triple... irere: ps 4 — .29 A8

Rough-Deformed......... 1.64 2.39 + .75 .57 133

Rough rs BARAT 2.21 2.26 —..05 .28 *- X

Triple-Rimmed.......... 1 1.00 -— .50 1.08

Deformed-Rimmed....... 57 pr 4.17 +3.60 1.09 10.91

i |

| | | x! = 25.34

Table III is arranged to compare the differences be-

tween the calculated and the observed percentages with

the standard errors due to sampling; except for p: all the

differences are less than twice their standard errors; thus

showing the general agreement between the data and the

theory of linear arrangement of the genes. The fit,

however, is not a close one, even if we omit pz; in the

present state of our knowledge this will not throw any

No.646] THE SYSTEMATIC LOCATION OF GENES 411

doubt on the scheme of linear arrangement, but will sug-

gest that the erossover ratios in this part of the chromo-

some were not constant in all the strains used to compile

the data.

In estimating the Goodness of Fit of data of this kind,

x? may be calculated by summing the values of d?/c?, as

in Table III Attention should, however, be called to

the faet that it has been recently shown (3) that in enter-

ing Elderton's Table we must put n’ equal to one more

than the number of degrees of freedom, remaining after

we have fitted our unknowns to the data. In the present

case we have found 7 unknowns from 15 equations, leav-

ing 8 degrees of freedom, so that w' should be 9, and

not 16.

In eonclusion it should be noted that to be available

for the use of this process the erossover data should be

stated in the form in which it is given by Lancefield and

Metz, in whieh the erossovers tabled between any two

genes do not include those experiments in whieh an inter-

mediate gene was under observation. The practice of

throwing together all the crossovers between two genes,

in order to improve the ratios between the more distant

points, causes the same crossover to appear repeatedly

in different entries. The data are no longer the product

of independent experiments, and must be re-summarized

before reduction.

REFERENCES

1. R. C, Lancefield and C. W. Metz. The Sex-linked Group of Mutant

aeters in Drosophila wilistoni. AMERICAN NaTURALIST, LVI,

pp. 211-241.

2. R. A. Fisher. On the Mathematieal Foundations of Theoretieal Statis-

ties. Phil. Trans, A, COXXII, pp. 309-368. ;

3. R. A. Fisher. On the Significance of x’ from Contingency Tables and

on the Caleulation of P. Journal of Royal Statistical Society,

LXXXV, pp. 87-94.

LINKAGE IN PEROMYSCUS

DR. F. B. SUMNER

Tue Scripps INSTITUTION For Bronoorcan RESEARCH, La JOLLA, CALIF.

Srupents of Mendelism are beginning to display the

same interest in possible homologies between the genetic

factors or ‘‘genes’’ of different species of animals or

plants which the morphologists of thirty years or more

ago did in homologies between organs. In considering

a given case of suspected homology between genes, two

criteria are, so far as I know, employed: (1) Resem-

blance between the developed characters which are at-

tributed to the action of supposedly homologous genes.

Mere similarity of appearance, however, is recognized

as an extremely fallible criterion of homology here as

in the case of comparative anatomy. (2) Agreement be-

tween the ‘‘cross-over’’ value shown by a pair of linked

factors in one species, as compared with the correspond-

ing value shown by supposedly homologous factors in

another species. If both of the two linked genes under

consideration are found to have much the same somatic

effects in the two species, and if, furthermore, the de-

gree of linkage is approximately the same in the two

cases, the argument is strong for a twofold homology.

Metz! and Sturtevant? have been investigating the

parallel mutations of several species of Drosophila, and

it is not unlikely that this genus will furnish the best

material for the study of genic homologies, just as it

has shown incomparable superiority for certain other

lines of genetic research.

For rodents, what appear to be parallel mutations have

been shown to occur among numerous species, even ones

1 Genetics, March, 1918.

2 Genetics, January, 1921.

412

No. 646] LINKAGE IN PEROMYSCUS 413

belonging to widely different families. In one case,

that of the mutation known as ‘‘ pink-eye,"" not only is

the visible modification elosely:similar in rats and mice,

but the linkage relations between this factor and that

for albinism are known to be of the same order of mag-

nitude in the two animals.*

Some years ago, Castle? described two similar muta-

tions in the Norway rat, which he termed ‘‘pink-eyed

yellow’’ and ‘‘red-eyed yellow,’’ respectively. These,

according to the published descriptions, differ chiefly in

the color of the eyes, the latter variety having darker

eyes than the former. These two mutations, and like-

wise true albinism, were all found to result from the

modification of distinct genetic factors. Any two of

them, when crossed, gave rise to the wild type in the

first hybrid generation. On the other hand, further

breeding tests led Castle to conclude that all three of

these factors were linked. When red-eyed and pink-eyed

rats were interbred, the cross-over percentage proved to

be about 18. When pink-eyed rats were crossed with

albinos, this value proved to be about 21. On the other

hand, the linkage between red-eye and albino proved to

be almost absolute. -One hundred and sixty F, albinos

and 57 F, red-eyed yellows, when mated with pure red-

eyes and albinos, respectively, yielded but a single off-

spring which was not of the wild type.

More recently Dunn? has tested the linkage between

this same red-eyed condition and albinism in the rat.

From his own data he computes a cross-over value of

1.8 per cent., but when his data are combined with those

. of Castle, this value falls to less than one per cent.

Castle and Dunn have likewise tested the degree of

linkage between ‘‘pink-eye’’ and albinism in the mouse

3 Dunn has eompiled these cases in a useful article in the Journal of

Mammalogy, August, 1921.

* According to Castle, the percentage of cross-overs is 21 for rats and 14

for mice. This may or may not be construed as evidence of ‘‘homology.’’

5 AMERICAN NATURALIST, February, 1914; Science, August 6, 1916 (with

Wright); Carnegie Institution Publications 241 and 288.

6 Genetics, May, 1920,

414 THE AMERICAN NATURALIST [Vor. LVI

(Mus musculus). The proportion of cross-overs was

found to be about 14 per cent.

Some five years ago I described a pale, red-eyed

mutant of Peromyscus,’ which originated among the off-

spring of three sibs in the F, generation of a cross be-

tween P. maniculatus rubidus and P. m. sonoriensis.

Since I have already described this ‘‘mutant’’ race

rather fully, and since it will again be discussed shortly

in a paper by Mr. H. H. Collins and myself, I need not

enter into a detailed account of it here. I have not seen

specimens of the ‘‘red-eyed yellow’’ rats described by

Castle, but I find little in the description of that race

which is at all at variance with my own ‘‘pallid’’ race

of Peromyscus. The latter has undergone a great re-

duction of the black pigment, while the yellow pigment

has been little if any affected. The eyes are commonly

dark red, rather than pink, though they present a con-

siderable degree of variability, ranging from a condi-

tion not much darker than the true pink of albinos to a

condition not much paler than the normal. There are,

however, no real intergrades between the pallid mice and

the wild type, and the behavior of this complex of char-

acters in crosses is that of a simple monohybrid reces-

sive. Furthermore, it is not an allelomorph of albinism,

since the wild type alone results from matings between

albinos and pallids.

I have recently carried out tests of the linkage rela-

tions between this factor and that for albinism. Thus

far, it has not been found practicable to devote any con-

siderable proportion of my time to this phase of the sub-

ject, and the numbers are accordingly inadequate for

any exact measurement of cross-over values. They are,

none the less, sufficient to show the existence of a high

degree of linkage between these factors. The number

T Genetics, May, 1917; AMERICAN NATURALIST, August-September, 1918.

This mutant was at first referred to as a ‘‘partial albino’’; later the non-

committal term ‘‘pallid’’ was applied to it.

8 The albinos used were all derived from a single brood belonging to the

subspecies Peromyscus maniculatus gambeli.

No. 646] LINKAGE IN PEROMYSCUS 415

of F, individuals derived from simple F, x F, matings

is too small to give a representative dihybrid ratio. The

really important tests have been made with ‘‘extracted”’

albinos and pallids of the F, generation.

Matings have been made (1) between ‘‘ extracted ’’ al-

binos and ‘‘pure’’ pallids (1.e., those known to be free

from the factor for albinism), (2) between extracted

pallids and pure albinos, and (3) between extracted pal-

lids and extracted albinos. There were likewise a num-

ber of matings in which the pedigrees were less simple.?

On the assumption of a wholly independent segregation

of these factors, our F, pallids (of simple pedigree)

should have a 2/3 chance of being heterozygous for al-

binism, while our F, albinos should have a 3/4 chance of

being either homozygous or heterozygous for pallid.?°

Eighteen F, mice were involved in these tests. The

total number of offspring derived from these was 135,

the number per parent ranging from 3 to 26. By no

means all of these parents, taken singly, have thus far

given birth to a sufficient number of young to prove their

genetic composition with any certainty. But the cumula-

tive testimony of all of these matings is overwhelming.

Not a single pallid mouse and only two albinos have ap-

peared among the 135 young which have thus far been

born. Had there been a normal proportion of ‘‘carriers’’:

among the parents, these matings should have yielded 37

albinos and 18 pallids, as the most probable ‘‘expected’’

numbers. That all of the offspring with two exceptions

(these being sibs) were of the wild type is evidence of a

high degree of linkage (in this case ‘‘repulsion’’) be-

tween the albino and the pallid factors.”

® Baek-erosses and heterozygous albinos figured in some of these pedi-

grees. In these cases the odds are different from those which hold for indi-

viduals derived from the simpler types of mating. They have, however,

been computed for every animal used. In about half of the ‘‘extracted’’

albinos, for example, there was only a 5/8 chance that the individual

carried the pallid factor.

10 It is a safe assumption that the double recessive form would be albino.

11 It might be supposed that the testimony of 18 parent mice, even if all

of these were shown conclusively to be lacking in ‘‘cross-over’’ gametes,

416 THE AMERICAN NATURALIST [Vor. LVI

From these considerations we may regard it as not

unlikely that my ‘‘pallid’’ race of Peromyscus has re-

sulted from the mutation of a genetic factor homologous

with that which has mutated in the case of Castle’s ‘‘red-

eyed yellow”’ rats.

This decisive result, as regards the existence of link-

age between the pallid and albino faetors in Peromyscus,

stands in contrast with the apparent absence of such

linkage in another eross between mutant strains of these

mice. Albinos were mated with mice belonging to a

strain which I have elsewhere referred to rather inap-

propriately as 'yellows.''!? The latter vary from clay

color to a distinctly reddish hue, according to the strain,

and are characterized primarily by a marked increase in

the length of the ‘‘agouti’’ cross-band and by a decrease

in the proportionate number of all-black (unbanded)

hairs in the pelage. Where present, however, the black

pigment is of full intensity. This applies to the basal

zone of the body hairs, both dorsal and ventral, to the

black hairs of the dorsal tail stripe, as well as to the

eyes, ears and soles of the feet.

Matings between albinos and ‘‘yellows’’ have resulted

exclusively in F, mice of the wild type (dark). An F,

generation of 83 was obtained, consisting of 52 dark

individuals, 13 yellows and 18 albinos. On the assump-

tion of purely random assortment of gametes, the ‘‘ex-

pected” numbers are 44, 15 and 20, respectively. ‘The

observed numbers are doubtless within the range of ‘‘ac-

eidental" variability. In any case they give no evidence

would not be sufficient to prove the existence of linkage. It should be

repeated, however, that we are not here dealing with cases in which there

would be merely an equal chance of combining the two mutant factors in

the same individual, The odds in favor of this (linkage aside) may

stated above, be as high as 2 to 1, or even 3 to 1. Thus, the likelihood of

obtaining, pi opr alone, 17 non-cross-over cases out of 18 becomes

vanishingly

12 Genetics, ae 1917; AMERICAN NATURALIST, Augast -Hepteuber, 1918.

A more complete account of these mice, dealing with two subvarieties dif-

fering somewhat in color, is included in a forthcoming paper by Mr. H. H.

Collins and myself,

No. 646] LINKAGE IN PEROMYSCUS 417

of linkage, the occurrence of which would have reduced

the proportionate number of dark individuals, instead

of increasing it.

The number of F, albinos and yellows which have

been thus far tested is very small, but it is of interest

that the proportion of recombinations is even greater

than would be expected from random assortment. In-

clusion of these meager results in the present report

seems justified by the probability that we shall not soon

rear any considerable number of hybrids between the

yellow and albino varieties.

Seven extracted albinos have been mated with pure

yellows. Three of these have given only yellow offspring,

the numbers being 9, 13 and 21, respectively. Thus, three

of these seven albinos are, in all probability, double re-

eessives (ccyy). (One in four should be double reces-

Sives, according to chance.) Three other albinos have

given mixed offspring. They are evidently of the for-

mula ccY y. The remaining one appears to have the for-

mula ccY Y, as judged by the produetion of 15 dark young.

Two extracted yellow females mated with a (sup-

posedly) pure albino male gave birth to 4 albinos and 4

dark.'* No albinos would be expected here if linkage

were complete, while only one third should be albinos

in the total absence of linkage. Thus the number of re-

combinations is again too high, even on the assumption

of no linkage.

These numbers are, of course, very small. But even

here such proportions would have been quite improbable

had any marked degree of linkage existed—such, for ex-

ample, as has been found to exist between the pallid and

albino factors.

13It is only fair to add that 4 yellows likewise resulted from these ma-

tings. This was doubtless due to the fact, unsuspected at the time, that

the albino male carried the ‘‘yellow’’ factor, one of his two great-grand-

parents having been heterozygous for yellow.

THE SOUND-TRANSMITTING APPARATUS OF

SALAMANDERS AND THE PHYLOGENY

OF THE CAUDATA

E. R. DUNN

SMITH COLLEGE

ResEARCHES by Kingsbury and Reed, extending through

a number of years, have shown that the sound-trans-

mitting apparatus of salamanders consists of two ele-

ments. These are the columella and the operculum.

In the most recent paper on this subject, Reed (1920)

gives a résumé of all the previous work, an extensive ac-

count of the state of affairs in the Plethodontide, a brief

account of the conditions in other forms, and the findings

are presented in the form of a family tree.

The purpose of the present article is to add an aecount

of the condition of the apparatus in two forms not seen

by Reed, to question the condition described by Kings-

bury and Reed for Dicamptodom ensatus (Ambystoma

tenebrosum Auct.), to suggest a somewhat different inter-

pretation of the faets observed by them, and to propose

a somewhat different phylogeny, which seems to agree

quite as well with the otic apparatus and far better with

other anatomical features.

Kingsbury and Reed (1909) were unable to examine

any of the Asiatic forms related to Hynobius. These

forms, as Cope pointed out long ago, are rather different

from the Ambystomide, with which they have usually

been associated, and should in fact form a family Hy-

nobide.

I have recently been able to examine large series of

Hynobius leechii from Korea. This animal shows a con-

dition of the otic apparatus different from any seen by

Kingsbury and Reed, and a condition which I am com-

pelled to consider primitive. Both columella and oper-

418

No. 646] THE PHYLOGENY OF THE CAUDATA 419

culum are present as free and distinct elements. Both

are readily movable. There is a m. opercularis.

I have not been able to examine skulls of Onychodac-

tylus, or of Ranodon. Okajima’s (1908) figures of Ony-

chodactylus show only one element which is in appear-

ance much like that of Cryptobranchus. This is very

different from the appearance of the apparatus of Hyno-

bius. It is evident that either fusion of operculum and

columella has taken place or that the operculum has not

developed. Onychodactylus is partly aquatic, a moun-

tain brook animal. Cryptobranchus, which, as I shall

show later, is a derivative of the Hynobiide, has failed

to develop the operculum. Probably the same is true

of Onychodactylus and of Ranodon as well, although for

the latter Wiedersheim’s (1877) figure is all we have.

Still, as Kingsbury and Reed (1909) say, his Fig. 67

‘‘suggests a condition such as is found in Cryptobran-

chus.”’ i:

Rhyacotriton olympicus was not examined by Kings-

bury or by Reed. This animal (Dunn, 1920) possesses

both columella and operculum. The columella is free from

the periotic and is readily movable. The operculum is

little developed. The animal is in part aquatic, a moun-

tain brook species.

Dicamptodon ensatus was examined by Kingsbury and

Reed (1909), and while my dissection of an adult showed

the state of affairs which they describe, I can not follow

them in calling it ‘‘much like that in the adult Amby-

stoma.” In adult Ambystoma the columella is solidly

fused to the periotic. A bony operculum nearly fills the

opening of the fenestra, and is attached by a membrane

around its circumference. In Dicamptodon, on the other

hand, about half of the fenestra is filled by the plate of

the columella, and the remainder by cartilage. The car-

tilage extends around the plate of the columella. There

is nothing that could be called a definite operculum. If

the cartilage is called the operculum, then the columella

. and operculum are fused and the operculum is fused to

420 THE AMERICAN NATURALIST [Vor. LVI

the ear capsule by nearly its whole border. It seems to

me that in this ease the columella is at least more free

than in Ambystoma, and the operculum less developed.

This would be in line with what is known of the habits

of Dicamptodon. It is a much more aquatic animal than

is Ambystoma.

In the Caudate sound-transmitting apparatus, taking

Reed (1920) as a basis, there are the following sets of

conditions:

I. Both columella and operculum present. Both fre

Hynobius, coa ue

II. Opereulum not developed. Columella free.

ptobranchus.

Sil See dl Ranodon

Onychodactylus goes t

III. Operculum developed, free. Columella fused to periotis, stylus present.

alamandra, ystoma.

IV. Opereulum developed, free. Columella fused to periotie. Stylus absent.

Triturus, Pachytriton, P:eurode'es 1,

Ty ototriton 1.

V. Operculum developed, free. Columella ?,

Siren, Batrachoseps.

VI. Both columella and opereulum present, fused together, free from

periotie.

Necturus.

— columella and operculum vitu Fused together. Opereulum

ed by narrow fusion to per

par e Plethodontide

(exe. Batrachoseps).

Inasmuch as II is a condition found also in larvæ, there

is no reason to suppose that the animals in which this

condition occurs form a natural group.

Condition V has been commented upon by Reed (1920),

and I am fully in accord with his ideas in this connection.

Siren and Batrachoseps are certainly not related. Both

are extremely specialized. Batrachoseps has certainly

passed through stage VII. Siren has certainly passed

through an ancestral period of terrestrial life, yet its

other peculiarities are such that it is dangerous to state

that its relationships are with the forms in stage IV.

he forms which show condition VI and condition VII

No. 646] THE PHYLOGENY OF THE CAUDATA 421

form what Reed (1920) calls Legion II, as distinct from

the forms which show conditions I-V (exe. Batracho-

seps), which Reed calls Legion I.

But the sound-transmitting apparatus of Necturus

agrees with that of Amphiuma and the Plethodontide

only in having the columella and operculum fused.

There is no reason to suppose that such a fusion may

not have occurred twice, especially as the details of the

fusion in Necturus differ somewhat from the manner in

which the fusion occurs in Amphiuma and the Pletho-

dontide. In Necturus the columella forms a goodly part

of the plate-like portion of the apparatus. In the forms

of condition VII, the plate-like portion is almost entirely

composed of the operculum, and the columella is repre-

sented by the stylus. In this case the evidence of the

ear bones is non-eommittal. Considered apart from all

other features of the anatomy condition VII might

equally well be derived from condition VI or both inde-

pendently from condition I. But, as we shall see, evi-

dence from other features of the anatomy precludes our

regarding Necturus as intervening between the Pletho-

dontide and the other Mutabilian forms.

It is extremely interesting to note that Reed has found

almost exactly the same state of affairs in Amphiuma and

in the Plethodontide. The exact relationships of Am-

phiuma have long been in dispute, and while I prefer to

be eonservative about the position of the animal, I

think it extremely likely that further evidence will show

that it is closer to the Plethodontide than it was placed in

the older classifications.

Any classification should be based upon all available

characters, so that possible parallelisms will not lead to

wrong conclusions. In the present instance we are deal-

ing with a stock neither absolutely terrestrial nor abso-

lutely aquatic. From this stock there have been several

branches which have become more aquatic and several

which have become more terrestrial. Excellent examples

of this are the numerous incursions into a mountain

422 THE AMERICAN NATURALIST [Vor. LVI

brook habitat, with the penalty of loss or reduction of

lungs. The list is extensive, Onychodactylus, Rhyaco-

triton, four species of Triturus, Salamandrina, Chio-

glossa, all the stock of the Plethodontide, an assemblage

representing four families. The sound-transmitting ap-

paratus is admittedly correlated with the mode of life.

Therefore as a character in determining relationships it

must be used with extreme caution.

The following outline classification of salamanders

does not counter any of the facts concerning the otic

apparatus, and is based on many characters.

As regards the Plethodontide and the Hynobiide, re-

visions of both are nearly completed, based on the exam-

ination of some 8,000 specimens of the first family and

1,000 of the second.

The Sirenide are the most isolated group. Searcely

a character can be found to ally them with one or an-

other of the main stocks. The pelvis is gone, the skull

is that of a very specialized larva, the hyoids are those

of almost any larva, the tail vertebre are very different

from those of any other salamander, inasmuch as there

is no hemal arch. There are flat plates on each side

which do not meet in the mid-ventral line. There is no

prearticular.

The Proteide are only slightly less isolated. The

pelvis differs in having an anterior median projection and

no ypsiloid apparatus. The skull is larval. The bran-

chial arches are reduced from the primitive larval quota.

The prearticular is absent.

The Amphiumide also have modified larval branchial

arches, and the pelvic girdle lacks the ypsiloid appa-

ratus. But Amphiuma has an adult skull which resembles

remotely that of the Salamandride. The otic apparatus

is that of the Plethodontide. There is no prearticular

bone. It is quite possible that this genus is descended

from primitive Salamandrids.

The others have directly comparable skulls, branchial

arches, and pelves, and in dealing with their relationships

we are on much firmer ground.

No. 646] THE PHYLOGENY OF THE CAUDATA 423

Several characters divide them into two series, which

should, I think, rank as superfamilies.

1. Prearticular bone. Present in Cryptobranchide and

Hynobide, and absent in Ambystomide, Salaman-

dride and Plethodontide.

Second epibranchial. Present in Cryptobranchide

and Hynobiide, and absent in Ambystomide, Sal-

amandride, and Plethodontide.

First ceratobranchial and first epibranchial fused into

a single cartilaginous rod in Cryptobranchide and

in Hynobide. Separate elements in Ambysto-

' mide, Salamandride (exe. Salamandra, where all

parts fuse), and Plethodontide.

Nasals meeting in median line and premaxille without

nasal process in Cryptobranchide and Hynobide.

Nasals separated by nasal spines of premaxille in

Ambystomide, Salamandride, and Plethodontide

(exe. Pseudotriton, where nasals overlap premaxil-

lary spines).

Pubotibialis muscle fused with puboischiotibialis in

Cryptobranchide. The two muscles are separate

in all other salamanders (Noble, 1922). I have

ascertained that the two are fused in Hynobius

and in Onychodactylus.

Larve of Ambystomide, Salamandride, and Pletho-

dontide have the first ceratobranchials fused with

the second basibranchial (Smith, 1920). This fu-

sion does not occur in larve of he ant

or of Hynobide.

les

Within the superfamily Salamandroidea the Ambysto-

mide and the Salamandride are about parallel. The

long posterior process of the prevomer distinguishes the

Salamandride, and as the parasphenoid tooth patches of

Plethodontide are the morphological equivalent of this

process (Wilder, 1920) it is probable that some primi-

tive Salamandrid (having the two otie elements free)

gave rise to the much degenerate Plethodontide. The

424 THE AMERICAN NATURALIST [Vor. LVI

mountain brook habitat of the ancestral Plethodontid

(Wilder and Dunn, 1920) accounts perfectly for the re-

tention of the columella through adult life as a working

part of the sound-transmitting apparatus.

"The Cryptobranchoidea contains two families. Of

these the Hynobiide is the more primitive. The Crypto-

branchide differ in lacking the lachrymal bone, in the

larval position of the vomerine teeth, and in the much

depressed form of the body and head, the last two evi-

dently adaptations for aquatie and bottom-living habits.

Besides the characters mentioned in the list as aligning

the Cryptobranchide with the Hynobiide, several minor

points also show this relationship. Both Ranodon and

Hynobius frequently have a lateral fold between the in-

sertions of the legs. This is very prominent in both

Cryptobranchus and in Megalobatrachus, and is not

found elsewhere. Onychodactylus larve have a marked

fold on the posterior side of the limbs. This is seen else-

where only in Cryptobranchus and in Megalobatrachus.

Inasmuch as the characters differentiating the two gen-

era of Cryptobranchide have not been clearly understood

in the past they are here stated.

Megalobatrachus, Two persistent branchial arches:

Frontal not entering naris:

Branchial clefts closed in adult.

Cryptobranchus, Three persistent branchial arches:

rontal entering naris:

Branchial clefts open in adult.

In all three of these characters the American genus

shows greater adaptation to aquatic life. The European

fossils of this family appeal to Megalobatrachus in the

one skull character which separates the two genera.

Neither in Andrias schuchzeri nor in A. tschudii does

the frontal enter the naris.

It is also interesting to note that Megalobatrachus

shows no ‘‘Derotreme’’ characters whatever, although

in the older classifications it was included in the Dero-

iremata.

No. 646] THE PHYLOGENY OF THE CAUDATA 425

The extreme antiquity of the Caudata can be readily

seen when an end form, a river adaptation, is found in

Oligocene times.

This of course puts the origin of the main stocks back

at least to the end of the Mesozoic, a conclusion to which

the distribution also forces us.

The primitive characters appear in widely scattered

and rather unrelated forms. "The free prearticular has

already been mentioned. A free lachrymal is found in

Hynobiide and in an Ambystomid, Rhyacotriton. A

postfronto-squamosal arch is found in one group of the

Salamandride. A T-shaped parasphenoid 1 is found in an

Ambystomid (Dicamptodon) and in a Salamandrid

(Tylototriton). Long maxille are found in the two

forms just mentioned and in another Salamandrid,

Pachytriton. Posteriorly projecting prevomers are

found in Amphiuma, in all Salamandride, in some Hy-

nobiide (Hynobius, Pachypalaminus), and to a less ex-

tent in Dicamptodon.

All these are theoretically primitive skull characters

of amphibians. Their appearance separately in diverse

forms is sufficient indication that the three families

Hynobiide, Salamandride, and Ambystomide, while con-

taining all the more primitive forms of the order, stand

in no direct genetic relationship to each other, but must

be derived from a more or less remote common stock

which combined the otic apparatus, lachrymal, and pre-

articular of Hynobius with the long maxilla, T-shaped

parasphenoid, and postfronto-squamosal arch of Tylo-

totriton.

The evidence of Paleontology, as far as it goes, sup-

ports this view. I intend in a later paper to assemble the

meager facts regarding fossil salamanders. These facts,

it may be here stated, lend no support to the prevalent

view that the Proteida are an old, a primitive, or an an-

cestral group.

The following outline classification indicates the size

and position of the modern groups. The genera and

426 THE AMERICAN NATURALIST [Vor. LVI

species of the Salamandride are probably not wholly ac-

eurate. Future work will perhaps indieate the affinities

of Amphiuma, the Proteide, and the Sirenide.

Of the larger families, the Hynobiide are entirely

Asiatic, the Salamandride are Eurasiatie with four

American species, the Plethodontide are American with

two species in Europe and four in South America, and

the Ambystomide are American with one Asiatic species.

As the Northern land masses have been connected with

each other during Tertiary times this distribution is

not extraordinary, although close resemblance between

widely separated species is eloquent testimony as to the

antiquity of some of the ‘‘modern’’ forms.

Twenty-two of the recognized genera and 105 of the

species are restricted to North America, 13 genera and

96 species are Eurasiatie, while three genera are found

both in North Ameriea and in some parts of the Old

World.

Mutabilia

Salamandroidea

l. Ambystomide .......... 3 genera, 16 species

Dicamptodon 2, Rhyacotriton 1,

Ambystoma 13

2. Salamandride .......... 7 genera, 37 species.

Salamandra 5, Chiog!ossa 1,

Ty ototriton 2, Pachytriton $

P eurodeles 3, Triturus 24,

; ; , Salamandrina 1.

9. Plethodontide ber ds +16 genera, 83 species

Desmognathus 7, Leurognathus 1,

on 11, E

dipus Bai ina

Amphiumoidea (Relationships uncertain, possibly should stand as @

amily under Salamandroidea)

4. Amphiumide

ie cks .... 1 genus, 2 species,

Amphiuma 2.

No. 646] THE PHYLOGENY OF THE CAUDATA 427

Cryptobranchoidea

B. Hye iecore 5 genera, 20 speei

Hynobius 15, Po kes duces $.

ee 2, Ranodon 1,

Batrachuperu s1.

6. Cryptobranchidæ ........ 2 gen

, 2 species.

RSR A " Cryptobranchus 1.

Proteida d uncertain)

ee eat are Be ...2 genera, 3 species.

Necturus 2, Proteus 1.

Lissa Lis EC E 2 kaei 2 speci

nl, PESEE 1.

Total number of genera 38, ty species 165.

LITERATURE CITED

Dunn, E. R. 1920. Notes on Two Pacific Coast Ambystomide. Proc. New

Eng and Zool. Club, VII, pp. 55-59.

Kingsbury, B. F., and Reed, H. D. ea The Columella Auris in Am-

phibia. dien Ri. XX, pp. 549

Noble, G. K. 1922. The Phylogeny of e ‘Balientia, Part I. The Oste

ology and the de Museulature, their Amie on Classifieation and

Phylogeny. Bull. . Mus. Nat. Hist., XLVI, pp. 1-87.

Okajima, K. 1908. wen Osteologie ei Onychodacty'us japonicus.

Zeitschr, wiss. Zool., XCI, 3, pp. 351-

ed, H. D. 1920, The Morphology of the Sound -transmitting Apparatus in

Caudate Amphibia and its Phylogenetic Significance. Jour, Morph.,

5-375.

Smith, L. 1920. The Hyobranchial Apparatus of Spelerpes bislineatus.

Jour. Morph., XXXIII, pp. 527-5

Wiedersheim, R. 1877. Der Kopfskelet der Urodelen. Morph. Jahrb.,

» pp. 35 .

Wilder, I. W. 1920. The Urodele Vomer. Anat. Record, XVII, p. 349.

Wilder, I. W., and Dunn, E. R. 1920. The Correlation of Lunglessness in

Salamanders with a Mountain Brook Habitat. Copeia, 84, pp. 63-68

AGENCIES WHICH GOVERN THE DISTRIBU-

TION OF LIFE

A. BRAZIER HOWELL

PASADENA, CALIF.

Tue problems presented by the distribution of plants

and animals is a fertile field for investigation. "These

problems are essentially ecological in character, for

often, perhaps always, the range of a species or genus

is dependent upon a number of diverse environmental

faetors, some of which are readily apparent, while others

are obscure; but always they merit careful study.

In investigating and mapping the ranges of living

organisms and in following the evolutional tendencies of

species in so far as we are able, environment and its in-

fluences are of the greatest moment, especially from an

ecological standpoint. Botanical subjects may usually

be allocated in relation to their surroundings with con-

siderably greater ease than can active forms of life, for

the former are acted upon only by the agencies to be

found in one spot, while the latter may experience not

only all the influences operative over several square

miles, more or less, of diversified territory, but, in the

case of a migratory bird or mammal, will be subject dur-

ing a part of the year to environmental factors of which

we may know nothing. Whether a species is common or

rare in a certain area depends upon its rate of reproduc-

tion, which is usually entirely adequate unless new and

disturbing influences have been introduced; upon the

number of favorable or unfavorable conditions which it

encounters, the amount of competition with which it has

to contend, and its phylogenetic characters, as to whether

it be of a plastic type or one which is senescent and over-

specialized: all of which may be summed up in the phrase

‘adaptability to its habitat.’’

428

No. 646] THE DISTRIBUTION OF LIFE 429

In any one realm, or larger region of the earth’s sur-

face, there are various climatic divisions, the chief of

which have been named zones, and these stretch across

the continent following isotherms, or mean temperature

bands, usually, for our purpose, based upon the average

amount of heat present during the three chief reproduc-

tive months. Zones are divisible into faunal districts,

whose bounds are limited by conditions of humidity, pre-

cipitation and a few other causes that may be operative

over considerable areas. These are further divisible into

associations, an almost limitless number of which may

be recognized. Thus, we have littoral, riparian or

stream bank, palustral or marshy associations, the latter

being capable of still narrower subdivision into tule,

arrow-head or salt grass associations, and so on with-

out end.

Associations are sometimes but little considered in

parts of the country where climatic conditions are uni-

form over a wide extent of territory; but in the moun-

tainous parts of the west, where practically every pos-

sible local environment from the hottest, most arid des-

erts, to arctic-alpine conditions may be encountered

within a few miles, the importance of their recognition

can hardly be overestimated.

In considering the agencies governing the range of

a form, the question of temperature is undoubtedly of

chief importance as a usual thing, but in some cases

physical barriers should be given greater weight, for it

need hardly be indicated that it is such directly—and

temperature only indirectly if at all—that keep many

forms of life from greatly increasing their ranges. In

studying such barriers, manner of dispersal may be of

much importance. In the case of plants more than of

vertebrates (with few exceptions), human agency must

now be taken into account, for the activities of man, both

intentional and unintentional, are responsible in greater

degree for the widespread dissemination of seeds and

insects over vast stretches of the earth’s surface than

430 THE AMERICAN NATURALIST [Vor. LVI

any other cause. Natural manner of dispersal must also

be earefully serutinized as a preliminary step, for what

will prove a barrier to the extension of the range of a

plant with what I may term unadorned seeds may be

inoperative in the ease. of seeds adapted to dispersal by

the wind, and again, those whose covering is fitted for

adhesion to the coats of mammals will often be still more

widely seattered.

In the ease of an animal, the first thing to be considered

is the life-type to which it belongs, the chief divisions of

which are aquatic, fossorial, terrestrial, arboreal and

volant types, which are limited in varying degrees by

physical barriers. To an aquatic form, land masses are

insuperable obstacles, while to many terrestrial species,

especially such as live in very arid regions and are

totally independent of water, even a large river may

prove a delimiting agent. A strip of rocky country or

. an extent of arid plain will prevent the spread of such a

fossorial mammal as the mole. Arboreal forms are

checked by large, treeless areas, and animals which are

adapted to a life on the plains will usually shun the for-

ests. Volant types are the most independent of physical

barriers of all, and to some even wide stretches of ocean

are no obstacle, as in the ease of the Pacifice Golden

Plover (Charadrius dominicus fulvus), in its annual

migrations between Alaska and the Hawaiian Islands.

While eoneeding that temperature is the most impor-

tant faetor in the distribution of life, the writer is of the

opinion that not enough importance has been credited to

other agencies. Dr. C. H. Merriam was, I believe, the

first to formulate the theory that the northward range

of a species is governed by the mean amount of heat

present during the season of reproduetion, while the

southward range of northern forms is restricted by the

mean temperature during the very hottest portion of the

year. Isotherms have been determined and our conti-

nent plotted and mapped into zones, called Arctic, Hud-

sonian, Canadian, Transition, Upper Sonoran, Lower

No. 646] THE DISTRIBUTION OF LIFE 431

Sonoran and Tropical, some of which are known by

other terms in the eastern part of the country. Roughly,

the position of an isotherm, as well as the temperature

of a region at other times of the year, depends upon

latitude, altitude and distance from the sea. Hence it is

that the winter temperature of parts of Montana at a

considerable altitude and far from the sea reaches a

lower figure than has been recorded on the coasts of the

Arctic Ocean. The coldest temperature ever known upon

the face of the earth—minus 92 degrees F. in the in-

terior of Siberia—is much lower than has ever been

found by any of the ‘‘farthest north’’ expeditions.

We may safely infer that the degree of winter cold,

below a certain point, is largely immaterial, for it makes

no difference to a tree whether the thermometer is ten

or sixty degrees below zero, nor to the lesser vegetation

and many rodents safely protected by a deep blanket of

snow. Even to the few species of birds which habitually

spend the winter in high latitudes, very low tempera-

tures are seldom disastrous, but rather is it due, when

numbers perish, to a failure of the food supply during

sieet storms or long blizzards. Neither birds nor mam-

mals migrate so much because of cold as because their

usual foods are not to be obtained in adequate amounts

during the winter.

Certain forms of life may have to contend, in rela-

tively low latitudes and altitudes, with conditions which

approximate those to be found much farther north. W.

T. Shaw has but just brought to our attention the fact

that in eastern Washingtor, where Upper Sonoran con-

ditions are the rule, estivation and hibernation of the

Townsend Ground Squirrel (Citellus townsendi) are so

long continued that this animal enjoys but four months

of activity during the year. The squirrels emerge as

soon as the first growth starts in the spring, but retire

to their burrows for the long sleep when the arid condi-

tions of early summer cause a desiccation of their food

supply. To a torpid animal in its nest below ground it

432 THE AMERICAN NATURALIST ' [Vor. LVI

makes no difference whether it is summer or winter

above, and so these squirrels seem to lead an existence

closely similar to that of their near kin at the Aretie

Circle, but with the probable difference that the northern

forms experience an actually greater number of hours

of daylight throughout the long aretie summer months.

In the plains section of the interior, zonal divisions

are acted upon by comparatively few modifying agencies,

and their boundaries are rather regular and easily de-

fined, but in parts of the three Pacifie Coast states, whose

shores are bathed by warm ocean currents, and where

the topography is decidedly irregular, the problem of

zonal definition is often extremely complicated. In the

eoast region of northern California, for instance, there

is but slight daily and seasonal change of temperature,

and a number of Boreal forms are able to occur there

beeause the summers are cool enough for them, while

certain Sonoran species are also able to exist because the

mean temperature of the breeding season is high enough

for their needs. The result is a confusion of zonal in-

dices that is extremely puzzling at first glance.

To these three widely-recognized zonal factors, when

operative in certain regions, should undoubtedly be added

character of the coastal sea currents—whether warm or

cold—and direction of the prevailing winds.

Faunal conditions depend largely upon humidity as

well as upon all zonal factors. The chief cause of a hu-

mid climate is, of course, ample precipitation, either

rather evenly distributed throughout the year, or else

supplemented during the drier season by heavy fogs

and dense forests to retard evaporation, while a cool

climate is often helpful. Precipitation may be largely

dependent upon the position of adjacent mountain masses

with respect to the prevailing winds, for, as is well

known, moisture-laden air is cooled upon contact with

an elevated land mass, and precipitation results; but

little moisture will then be left in the clouds for rain in

the trans-montanic sections. This fact is beautifully

No. 646] THE DISTRIBUTION OF LIFE 433 .

shown by the humid and heavily forested coast and

mountain areas of northwestern Washington, in eontrast

to the bare, arid plains east of the Cascade range.

Associational temperature is induced by many causes,

and although limited in extent it profoundly influences

local zonal boundaries. Even associational factors other

than temperature may raise barriers to distribution that

are insurmountable to many organisms.

Insolation, or the relative amounts of sun and shade

received by a species in its habitat, is sometimes of

paramount importance. This may be influenced by

cloudiness, by the amount and density of surrounding

vegetation or by the character of the topographical en-

vironment. In illustrating this point, we may mention

as extremes the bottom of a'deep, narrow, forested gulch,

and the top of a warm, bare ridge; the face of a steep

north slope, and one facing south. A gully on a north

slope may be so situated as never to receive the rays of

the sun, while at a certain optimum angle one facing

towards the south will receive forty per cent. more solar

heat than will a level surface. Hence, zonal boundaries

upon the two slope aspects will be found to oceur at very

different altitudes. Soil conditions are of great impor-

tance in influencing the temperature immediately above

its surface, and its character helps to control both the

amount of evaporation and the degree of moisture which

it is capable of retaining. A light-colored soil is con-

siderably cooler, other things being equal, than a dark,

rocky one, which will absorb and retain more heat. The

importanee of the ehemieal eomposition as well as the

mechanical condition, with amount of humus, acid or

alkali, in the soil need be no more than mentioned.

The temperature of the soil and the atmosphere above

it is often greatly influenced by near-by cold mountain

streams, and in places zonal boundaries may be de-

pressed one or two thousand feet in altitude by this

ageney. Large snowbanks and glaciers have a similar.

effect, though usually less pronounced or, rather, more

434 THE AMERICAN NATURALIST [Vor. LVI

locally restricted. A forest fire or avalanche, by de-

stroying ground shade with the consequent raising of

the soil temperature, will usually cause an area to grow

up to plants and trees of the zone immediately below, to

be gradually restored, in future years, to its original

zonal status. Base level has its effect, for the foot of a

mountain mass rising from a plain five thousand feet in

altitude will have lower zonal tendencies than will the

five thousand foot level of a mountaix rising from a plain

with an elevation of but one thousand feet, because the

higher plain accumulates more heat. Similarly, a large

mountain mass is less influenced by the conditions which

surround it than is an isolated peak. A steep slope will

carry a certain zone to a greater height than will a

gentle one, because the former will receive, during the

day, more of the warm air arising from the lowlands,

and the cold air which descends during the night will

flow off more rapidly. However, this rule is often nulli-

fied by the steep slope being so situated that it receives

less sunlight than the more gentle gradient. These

points are finely illustrated on most of the mountains of

the southwest. Plants and trees of the Transition Zone

often flourish on the bottom of a north-facing canyon,

while the Sonoran sagebrush extends a couple of thou-

sand feet higher upon the steep slopes with southern ex-

posures.

Protective eover is important to most of the more re-

tiring forms of active life, and to such it is not only

necessary as a sereen during their daily foragings, but

they must have holes into which they may dart at the

approach of danger and safe retreats in which to rear

their young. To very few vertebrates is the actual char-

acter of the soil of great moment, but there are excep-

tions, as instanced by the large kangaroo rat, Dipodomys

deserti, the front feet of which are so weak that it seems

able to burrow only in deposits of æolian or other loose

sand, and it is useless to expect to find this species in

hard soil. Needless to say, character of food, both gen-

No. 646] THE DISTRIBUTION OF LIFE 435

eral and specific, is a powerful determining factor of dis-

tribution, and with this should be elassed not only the

manner of feeding but the methods employed in secur-

ing sustenance. The search for a favorite food item will

even, in time, indirectly change a mammal from a ter-

restrial to an arboreal type, as it evidently has the tree

mouse, Phenacomys longicaudus, of the coasts of Oregon

and northern California, which, so far as known, feeds

exclusively upon the needles of coniferous trees.

The question of enemies, it seems to me, should be

given much more weight in distributional problems than

it usually receives. This factor may be divided into ac-

tive and passive enemies. By the latter term is meant

competitive forms, as the more robust growth that chokes

out a tender seedling, or an organism which, being more

adaptable to a variety of conditions, forges ahead of less

plastic forms whose habits are competitive. It is the

opinion of the writer that such competition constitutes

the real remorseless struggle for existence which most

species are obliged to carry on in order to survive, rather

than their efforts to elude their active enemies. Al-

though these passive enemies are not spectacular and

are apparent only after scrutiny by an understanding

person, they are, nevertheless, always present and opera-

tive.

Active enemies may be divided into irritating and ex-

terminating types, and in certain sections the former

may constitute a formidable barrier to dispersal. Few

of the larger parasites directly cause death, but the pres-

ence of great quantities of aphis, scales, ticks or intesti-

nal worms upon their respective hosts may so handicap

a species that it is forced to the wall by the competition

of more favored forms. Unusual numbers of horse flies

in a mountainous section may so harass stock that they

utterly refuse to dwell in such regions.

Exterminating agencies may consist of directly pre-

daceous organisms, such as carnivores which consume

the flesh of their victims, or rodents whose presence in

436 THE AMERICAN NATURALIST [Vor. LVI

great numbers seriously interferes with the propagation

of certain plants. The overstocking of a range with

cattle or the presenee of a vast colony of prairie dogs

may actually extirpate certain grasses in those districts,

and hordes of some rodents will prevent reforestation

in spots because all tree seeds are eaten as fast as pro-

duced. Poisonous plants work great havoe among range

stock at times, and although the amount of such devasta-

tion among wild forms has seldom or never been investi-

gated, it is doubtless an appreciable factor. In some

regions, bacteria and disease, including the smaller para-

sites, play a most important role. The tse-tse fly in por-

tions of Africa has rendered it utterly impossible for

certain herbivorous mammals to be kept in the infested

districts; the Stegomyia mosquito that is instrumental

in the spread of yellow fever probably caused the Mayan

survivors of this dread disease to abandon the ancient

civilization of Yucatan, which was at one time so densely

populated, and many ailments, comparatively harmless

to white men, who have developed a degree of immunity

to them, are largely responsible for the decrease in the

numbers within recent years of the more savage peoples.

From time to time either totally new bacterial diseases

appear or else old ones suddenly aequire new virulence,

and throughout the ages, such have undoubtedly killed

off certain species from faunal divisions; and it is: not

at all improbable that during the course of bacterial evo-

lution whole genera, or even families, have been extermi-

nated by this agency.

It seems advisable to append to the ek paper a

chart, or key, to the factors chiefly responsible for the

distribution and restriction of the ranges of living forms,

but this is submitted with considerable hesitancy: Most

of the factors mentioned are so interdependent upon

others that it is merely a matter of personal opinion as

to which heading they should be placed under. For in-

stance, it is impossible to decide whether the effect of a

cold mountain stream should better be listed under zonal

No. 646] THE DISTRIBUTION OF LIFE 437

or associational conditions, for it is operative in both

connections. It should be understood, therefore, that

the arrangement is only tentative, and that the list has

been made to eonform to the viewpoint of a vertebrate

zoologist.

FACTORS TO BE CONSIDERED IN THE DISPERSAL OF LIFE

Life Types:

Active Forms.

olant.

Sedentary Form

Character r ot Habita

an dn seeding or reproducing.

Direct Physical tan

Oceans, Et a ee land forms).

s, mountains, ete. Me aquatie forms).

oss plains, deserts,

Protective cover.

Regulation by Temperature:

Zonal

Latitude. Mean is io during

Altitude. reproduetion,

Proximity to sea. Mean maximum.

cean currents. Mean minimum,

Prevailing winds. Delimiting temperatures

(as frost to tender

species

unal.

Humidity.

cua ptr

eation of near mountain masses, if any.

"fuccum of near bodies of water, if any.

Associational.

ree of insolation.

Effects of fires and avalanches.

Presence of cold streams or glaciers,

Topographical situation.

Slope a i

Slo

Base level.

Soil.

Chemical and mechanical character.

438 THE AMERICAN NATURALIST [Vor. LVI

Moisture.

General and specific character.

d habits.

Enem

Paiaive (competitive forms).

Active.

Directly predaceous.

Poisonous foods

Bacteria, protozoa, ete.

LITERATURE

Allen, J. A.

1892. The oe Distribution of North American Mammals.

Bw r. Mus. Nat. Hist., IV, No. 1, Art. 14; 199

Clements, F. E.

1916. Plant Suecession. Carnegie Inst. Wash., Pub. 242.

1920. Plant Indicators. Carnegie Inst. Wash., Pub. 290.

Grinnell,

1914. Barriers to Distribution as Regards Birds and Mammals. AMER.

Nat. 8

1917. visent ‘Meats of Theories Romig Distributional Control.

. Nat., Vol. 51, p.

Hall, H. M. t: de nnell, J.

1919. Life-Zone fndicstón in California. Proc. Ca if. Acad. Sci., 4th

Ser., IX; 37.

Merriam, C.

1890. Results fi a ngage Survey of the San Francisco Mountain

d of the Little "TT Arizona. U. S.

Dept. grem ` SOR Amer. Fauna, N

1892. The Geographical Distribution of Life in "North America with

Special Reference to the Mammalia. Proc. Biol. Soc. Wash.,

MH:

1898. Life Meg and Crop Zones of the United States. U. S. Dept.

. Bull. No. 10.

1899. Pun ‘of a Biological Survey of Mount Shasta, California.

U. S. De ept. Agric., North Amer. Fauna, No. 16.

Shaw, W. T.

1921. Moisture and Altitude as Factors in Determining the Seasonal

Aetivities of the Townsend Ground Squirrel in Washington.

Ecology, II; 189.

THE TAPEWORM INFECTION IN WASHINGTON

TROUT AND ITS RELATED BIOLOGICAL

PROBLEMS

PROFESSOR NATHAN FASTEN

OREGON AGRICULTURAL COLLEGE, CORVALLIS, OREGON

Ix the whole realm of nature man is the only creature

whose ailments have seriously occupied the attention of

experts. Leta disease break out amongst the human fam-

ily in some corner of the globe and almost immediately the

affliction becomes the target for the trained minds of our

ablest pathologists. Not so, however, with the maladies

of the lower forms. Man’s only interest in them has

been one of selfish exploitation, and he has done little to

encourage investigations along any other lines except

those which bring him immediate monetary returns. It

is, therefore, not at all surprising that we possess such

meager and fragmentary knowledge concerning disease

amongst the lower animals. |

It is almost superfluous to say that this attitude must

. change if we are to intelligently conserve the lower crea-

tures as natural resources. In the last few years we have

been hearing a great deal about the conservation of nat-

ural resources, and yet very few of us realize the full

meaning of conservation. To my mind real conservation

implies a thoroughgoing knowledge of the objects to be

conserved, coupled with an intelligent application of the

factors controlling their preservation. We must possess

more knowledge concerning the diseases of the lower

animals because it is of prime importance in all conserva-

tion programs, in that it may be helpful in preventing

great losses of animals which are beneficial to man.

In the state of Washington, as well as in the other

states of the Pacific coast, fish afford a natural resource

of tremendous importance to the welfare of a large pro-

K 439

440 . THE AMERICAN NATURALIST [Vor. LVI

portion of the eitizens, and yet eomparatively little is

known regarding the diseases which affect these aquatic

animals. We become alarmed when the fish begin to diein

great numbers, and only then are we in any manner con-

cerned with finding out what ails them.

During the summer of 1919 it was my good fortune to

be chosen by the Washington State Fish Commission as

a special investigator for the purpose of studying the

parasites of the fish in some of the fresh-water lakes and

streams of the state of Washington. Prior to undertak-

ing these investigations reports had been coming in to

the fish commissioner's office that the fish were dying in

the mountain lakes and streams of Kittitas county and,

therefore, it seemed advisable to spend most of my time

in this region studying the nature and extent of the

disease. Itis with this epidemie in partieular that I wish

to deal in the present paper. Incidentally, I desire to

point out some of the interesting biological problems

with which the question is intimately linked up.

On arriving in Kittitas county the writer found that the

people, especially the sportsmen, were very much dis-

turbed about the mortality of their lake trout, for they

depended upon these fish to yield them spawn for their

county hatcheries. They were particularly distressed

about the dying of the trout in Cooper lake, and therefore

this lake was the first one which I visited. |

Cooper lake is situated in the heart of the Cascade

mountains about thirty miles outside of Roslyn. Fig-

ures 1-3 show various views of the lake. It is a clear

body of water, filled with cut-throat trout. The county

game commissioners closed the lake some six years ago

in order to obtain a plentiful supply of fish for breeding

purposes, and as a result of this the trout have multiplied

very rapidly within its waters. For the first few years

the results obtained were excellent, but within the last

two years the fish commenced to die at an alarming rate,

so that all spawning operations had to be abandoned.

An examination of the cut-throat trout of this lake

No. 646] TAPEWORM INFECTION 441

showed them to be heavily parasitized with larval tape-

worms which attack the abdominal eavity. From all ap-

pearances these larve somewhat resemble those described

by Professor Linton in 1889 for the trout of Yellowstone

National Park, and, undoubtedly, belong to the genus

Dibothrium or Diphyllobothrium, but are probably of a

General view of Cooper

: lake.

Fig. 2. d a d Goaper lake show =~. racks, a favorite place for

the blue her

Fic. 3. (— -n of Cooper iake ar shore affording an ideal

sting place for fish- aceti birds.

442 THE AMERICAN NATURALIST [Vor. LVI

Fig. 4. Tapeworm larva in cyst, x 20.

Fic. 5. Numerous free-boring and encysted tapeworm larve, X B.

Fic. 6. oe Pepe of acaso larva, x 2í

FIG. Head end of tapeworm larva, x 65

different species from Dibothrium cordiceps Leidy, the

ones discussed by Linton. According to Professor A. R.

Cooper, of the University of Illinois College of Medicine,

to whom specimens of the tapeworm larvæ were sent for

identification, *' the placing of these larvæ specifically is

a matter of the working out of the life histories of the

species in question.’’

The larval tapeworms under consideration may be en-

No. 646] TAPEWORM INFECTION 443

eysted (Figs. 4 and 5) along the walls of the digestive

traet, particularly on the stomach, or they may be found

burrowing freely amongst the visceral struetures, or

within the surrounding muscular walls. In appearance

they are translucent, whitish or yellowish-white organ-

isms which may vary from a few millimeters to about

twenty millimeters in length. They are long, slender and

worm-like in character (Figs. 5 and 6). At the anterior

end is the head (Fig. 7), which possesses two lateral slits.

This head end is constantly changing its shape in the liv-

ing specimens, becoming slender and spear-like at one time

and stouter and knob-like at another time. The body

proper of the larva may undergo periodie contractions

and extensions. Covering its entire outer surface are

stiff, bristle-like structures which, at first glance, seem to

resemble cilia, but which do not possess any independent

motion. Posteriorly the body tapers off into a blunt

rounded margin (Fig. 6).

The damage done to the fish by these larval —

is considerable. In the first place, the fish lose their

healthy appearanee, becoming much thinner and paler in

hue. The parasitic larve undoubtedly produce injurious

toxins which interfere with the proper functions of the

host. Then, again, the burrowing habits of these para-

sites injure the tissues of the fish, causing them to become

mushy. And finally, secondary infections of a serious

sort may develop within the injured portions. As.a re-

sult of all this damage great numbers of the fish die.

The life history of these larval tapeworms is extremely

interesting. "Those who are familiar with tapeworm in-

feetion know that ordinarily two organisms are necessary

for the eompletion of the life history. The adult tape-

worm lives in one animal ealled the primary host, where-

as the larval tapeworm dwells in another animal called

the secondary host. The primary host becomes parasi-

tized by eating the infected portions of the secondary host.

In the case of the tapeworm under consideration it is

quite obvious that the trout acts as the secondary host.

444 THE AMERICAN NATURALIST [ Vou. LVI

The primary host, however, is not definitely known.

Professor Linton found that in the case of the infection

of the trout of Yellowstone Park the white pelican acted

as the primary host, and, in the light of this finding, it

is quite probable that some similar fish-eating bird is the

primary host of the larval tapeworm under discussion.

While at Cooper lake a canvass was made of the com-

mon fish-eating birds which visit, the lake, and it was

found that the blue heron is the most frequent visitor.

Since no pelicans are known to come to the lake, I rather

strongly suspect that the blue heron acts as the primary

host for the larval tapeworms of the trout. If this should

prove to be the case then the life history, in all prob-

ability, would be as follows: The adult Diphyllobothrium

tapeworm develops in the intestinal tract of the blue

heron, and when the segments become mature they are

periodically passed out with the feces. These mature

segments contain large numbers of developing embryos

and if they are deposited in a stream or lake the embryos

are swallowed by the fish, in which they develop into the

larval tapeworms already described. When a blue heron

captures one of these infected fish, the larve attach them-

selves to the bird’s intestinal wall and shortly develop

into adults capable of carrying on the life cycle.

My visit to Cooper lake convinced me that it was pure

folly to entirely elose down a lake for more than a year

or two. In the first place, closing down a lake makes

for a rapid inerease of fish so that the available food

supply soon becomes inadequate for maintaining all of

them, with the result that a fierce struggle for existence

ensues, in whieh many of the weaker, but nevertheless

desirable, fish are killed off. Even those which survive

in the struggle appear to be starved. Secondly, when a

lake is closed its shores afford an ideal, undisturbed nest-

ing place for such fish-destroying birds as the blue heron,

kingfisher and the like. These birds not only destroy

. large numbers of fish, but they may be the means of dis-

seminating parasitic infections. And lastly, in the light

No. 646] TAPEWORM INFECTION 445

of the experience in other states, it is a useless waste of

money to depend on the fish in a large natural body of

water for spawn, because it is very difficult to control the

factors which insure success.

Two other mountain lakes were next visited: Lost lake

on Roaring creek, near Keechelus, and Fish lake.

Lost lake is stocked with eastern brook and cut-throat

trout, with the former predominating in much larger

numbers. The lake has been closed for several years

and was utilized by the county game commissioners as

a place for obtaining eastern brook-trout spawn. From

this lake seventy-six brook-trout and two cut-throat trout

were examined, and with the exception of two brook-trout

all the fish were found to be clean and healthy. The two

exceptions mentioned were each parasitized with a single

larval tapeworm cyst.

The situation at Lost lake seemed very striking as well

as significant, and it suggested the possibility that per-

haps the brook-trout are more resistant and immune to

the parasitism of the tapeworm larve. At any rate, this

is worth while testing out much more thoroughly.

One other point which the trip to Lost lake strength-

ened was in regard to what has already been said con-

cerning the food supply of a closed lake. The fish in this

lake, although they were nearly all healthy, were never-

theless very thin. The most prominent parts of them

were their heads. In two cases the fish were so hungry

that they captured field mice which probably attempted

to swim across the lake. These were found partially di-

gested within the stomachs of the fish.

At Fish lake one hundred and nine trout were caught,

mainly of the cut-throat species, and' a careful examina-

tion revealed the fact that they were all healthy and clean.

There wasn’t a single indication of tapeworm infection.

Fish lake was an open body of water and this probably

accounts for the healthy state of the fish. When sports-

men can get into a stream they are a source of disturb-

ance to the blue heron and other fish-eating birds, and.

446 THE AMERICAN NATURALIST [Vor. LVI

therefore, these birds are prevented from nesting along

the shores, thereby protecting the stream from becoming

infected with the tapeworm disease.

At the termination of the investigations in Kittitas

county, the writer made the following specifie recom-

mendations to the county game commissioners:

l. Not to close lakes for more than a short time, say a

year or two, and only for the purpose of conserv-

ing the fish. When a lake is closed for many years

the normal multiplication of fish is such.that the

food supply within the lake is greatly diminished,

resulting in a starvation process. Furthermore,

unless adequate watch is maintained, the heron

and other fish-destroying birds will live along the

shores of these closed lakes and serve as a con-

stant source of infection for the fish.

2. Not to depend on the closed lakes for spawn, but in-

stead to develop a hatchery or a series of hatch-

eries with numerous outdoor ponds where they can

place many of the healthy trout from Lost and

Fish lakes, which will give them a constant supply

of healthy spawn. They will not only save money

by such a projeet, but their efforts will not be

wasted.

After the completion of the above studies the writer ex-

amined fish from various places in King county, in which

he has found the same larval tapeworm infection. Num-

erous cut-throat trout of Klause lake near Snoqualmie

falls were examined and found to be heavily parasitized.

Also, the silver salmon and the so-called red fish or silver

trout (which are nothing more than land-locked sockeye

salmon) were found to be heavily infected with the same

parasites. The striking thing about the parasitism of

these last-named fish was that they were more heavily

parasitized than any of the fish previously examined in

which the tapeworm larvae were found to dwell.

No. 646] TAPEWORM INFECTION 447

The observations recorded in the present paper make

it obvious that a good many of our fish and game eultural

practices are utterly wasted because we are ignorant of

those factors which ought to insure success. What is ur-

gently needed in the state of Washington as well as in

the neighboring states of the Northwest is a series of

** Biological Surveys ’’ for the purpose of studying and

mapping out the various ecological factors of the regions

in which fish or game are to be planted. We ought to

know a good deal about such faetors as available food

supply, oxygen content, temperature variations, pred-

atory and parasitic organisms, etc., of a place before any

kind of animals or plants are introduced into it. Know-

ing these eonditions we ean then intelligently fit each

organism into that partieular environment where it will

thrive best. But without this knowledge we are simply

groping in the dark and are powerless to do any real

good.

MIGRATIONS AND AFFINITIES OF THE

FOSSIL PROBOSCIDEANS OF EU-

RASIA, NORTH AND SOUTH

AMERICA, AND AFRICA.

(SIXTH CONTRIBUTION ON THE EVOLUTION OF THE

PROBOSCIDEA )

DR. HENRY F. OSBORN

AMERICAN Museum or NATURAL History

Dr. Hrxosutcutro Matsumoto, of the Tóhoku Imperial

University, Sendai, Japan, has recently been studying

the Fayüm collections of primitive proboscideans and

hyracoids in The American Museum of Natural History,

followed by a visit to the British Museum where he has

been making comparisons with the types of these mam-

mals, described by Dr. C. W. Andrews in his series of

papers beginning in 1901. In 1918 Doctor Matsumoto!

published a series of five papers on the elephants, turtles,

sirenians, cervids, and bisons of Japan compared with

those of India. He pointed out that the Japanese archi-

pelago was an integral part of the continent from the be-

ginning of the Miocene to the middle of the Pleistocene,

and that the period of separation seems to have dated

from the recent Pleistocene. Consequently its relations

with the animal life of southern China and with the more

distant peninsula of India are very close.

The ancient Japanese proboscideans are chiefly of

three kinds, of which the most numerous are the forest-

living stegodonts, closely related in their specific phases

to the stegodonts of China, such as the species Stegodon

sinensis. There also occurs in the early Pleistocene the

11. **On a New Archetypal Fossil Elephant from Mt. Tomuro, Kaga.’’

2. '*On a New Fossil Trionyx from Hokkaido." 3. “A Contribution to

the Morphology, Paleobiology and Systematic of PE m A COR

a New Archetypal Fossil Cervid from the Prov. of Mino. 5. **On Some

Fossil Bisontines of Eastern Asia.’’ Sei. Rep. Tóhoku Imp. Univ., See.

Ser. (Geology), Vol. III, No. 2,

448

No. 646] THE FOSSIL PROBOSCIDEANS 449

great Loxodon antiquus namadicus, the straight-tusked

elephant, which ranged all over southern Eurasia and

probably arose originally in the African continent.

In the early formations, such as the Middle Pliocene

of Tomuro, Kaga, we meet the Elephas aurore, regarded

by the author as an intermediate type between the stego-

donts of the Upper Pliocene of India and Elephas plani-

frons, which in turn is related to the true mammoths

(Elephas primigenius) and wandered all over southern

Europe in Upper Pliocene time, namely, Bessarabia,

. Austria, and southern France. In still earlier deposits,

such as the Upper Miocene of Kuji, occurs a mammal

whieh the author refers to Stegodon latidens, an ances-

tral stegodont of Burma, India. In the Lower Miocene

of the Provinee of Mino occurs a form very similar to

the Trilophodon angustidens of the Middle Miocene of

France, ancestral to all the long-jawed proboseideans.

The Stegodon itself is peculiar to India, China, Japan,

and the larger islands of the Malayan archipelago, such

as Sumatra, Java, and Borneo. The author notes that

there is a marked difference between the sexes, so that

the stegodonts of each geologic period seem to have re-

ceived two specific names, one applied to the female, the

other to the male form. Among these couples are S.

Cliftii-bombifrons, dating from the Upper Pliocene and

from the Lower Pliocene of India; S. ganesa-insignis,

dating from the Upper Pliocene sd from the Postplio-

cene of the same area; S. sinensis-orientalis, dating from

the same strata of China and Japan; S. airawana-tri-

gonocephalus from the Postpliocene of Java. This sex

dimorphism is very marked, especially in the great dis-

parity of size of the upper tusks, which are much smaller

and more slender in females than in males. This tusk

structure in turn affects the entire form of the head.

The Bison occidentalis of Japan seems to spring from

the B. sivalensis of the Upper Pliocene of India. It is

similar in faet to the bison found in the ancient Pleisto-

cene of Kansas, in the basin of the Ohio River, in Alaska,

450 THE AMERICAN NATURALIST [Vor. LVI

and in the region of the Yenisei River in Siberia. Ac-

cording to the author, in the Transbaikal region the

same species oecurs in association with the giant woolly

rhinoceros (Diceros antiquitatis), with the hairy mam-

moth (Elephas primigenius), and with the heavy-horned

bison (Bison crassicornis).

Quite a different order of distribution has the remark-

able Desmostylus, a sirenian or sea cow peculiar to the

coasts of the Pacifie Ocean, first deseribed from the Cali-

fornia coast many years ago by Professor Marsh and

more recently recorded from Japan. The Japanese

species is much more specialized and of larger size than

the forms occurring on the Oregon and California coasts,

which points to a general migration from east to west,

that is, from the Orient to the Pacific coast of North

America.

From this series of papers we are able to draw up the

following table showing the principal distribution of the

species of mammals in the descending order of the de-

posits in Japan:

Postpliocene of Shózu-shima (Sanuki): Stegodon sinen-

sis, S. orientalis, Loxodon antiquus namadicus, Bi-

son occidentalis, Cervus (Sika) ef. nippon.

Upper Pliocene of Ikadachi-mura (Omi): Stegodon si-

nensis, S. orientalis, Buffelus sp.

Middle Pliocene of Tomuro (Kaga): Elephas aurore.

Upper Miocene of Kuji (Hitachi) : Stegodon cf. latidens.

Middle Miocene of the Provinces of Teshio, ete.: Des-

mostylus japonicus.

Lower Miocene of the Province of Mino: Trilophodon

cf. angustidens, Teleoceras sp., Amphitragulus mino-

énsis.

The present researches of Doctor Matsumoto on the

rich Fayüm collections of the American and British

Museums have enabled him to draw an important dis-

tinction in northern Africa between the true forest-liv-

ing mastodons, which appear to be directly descended

No. 646] THE FOSSIL PROBOSCIDEANS 451

from the genus Paleomastodon of the Fayüm, and the

long-jawed mastodons, which appear to be directly de-

scended from Phiomia of the Fayüm. This interesting

diseovery, whieh was partly anticipated in Doctor An-

drews's own papers, enables us to trace the American

mastodon far back into Upper Eocene times of northern

Egypt.

In this connection may be mentioned also a series of

five papers? by the present reviewer on the ‘‘ Evolution,

Phylogeny, and Classification of the Proboscidea’’ which

have appeared successively since 1918. The writer is

attempting to give an iconographic revision of the en-

tire group of proboseideans, including the progenitors

of Africa and Eurasia and the highly developed descend-

ants of North and South America, which together make

up the most remarkable family history of which we have

record.

In 1900 Osborn predicted that the source of the mam-

malian order of the Proboscidea would probably be dis-

covered in Africa. In 1901 Beadnell and Andrews re-

vealed, through the Geologieal Survey of Egypt, the rich

fauna of the Fayüm, southwest of Cairo, in which were

found the remains of three proboscidean genera, named

by Andrews Maritherium, Paleomastodon, Phiomia, and

confirmed by subsequent exploration and research to be

the oldest proboseideans thus far known. Animals simi-

lar to Meritherium and Phiomia have since been re-

ported by Pilgrim in southern Asia. These animals are

? The first paper in this series is entitled ** A Long-jawed Mastodon Skele-

ton from South Dakota and Phylogeny of the Proboscidea,’’ Bull. Geol, Soc.

Amer., XXIX, March, 1918; the second paper, ** Evolution, a and

Chimifontion of the Probóseldes, '" Amer. Mus. Novitates No, 1, January

31, 1921 (Osborn, 1921. “m the third paper, ‘í First Appearance p the

"ror Mastodon in Ameriea," Amer. Mus. Novitates No, 10, June 15, 1921;

the fourth r appears in the Bulletin of the Geological Society of

America, under the title ** Evolution, Phylogeny, and Classification of the

PAPIERA in ; the fifth paper, ‘‘ Adaptive Radiation and Classification

of the Proboscidea,’’ was read before the National Academy of Sciences,

April 26, 1921. The present is the auk paper. The Ieonographie Type

Revision will form one of the Memoirs of the Ameriean Museum of Natural

istory.

[Vor. LVI

THE AMERICAN NATURALIST

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No. 646] THE FOSSIL PROBOSCIDEANS 453

now found to belong respectively to three distinct lines

of the Proboscidea, namely, the meritheres, the true

mastodonts, the long-jawed bunomastodonts, as indicated

in black on the accompanying diagram. They point,

however, to a long antecedent origin and radiation. This

is part of the evidence for an ancient adaptive radia-

tion proeess by which it now appears that the probos-

cideans, like other hoofed mammals, were broken up into

several great primary stocks way back in Eocene times,

namely:

An amphibious stock, adapted to rivers and swamps, of

limited migration (= Meritherium, Dinotherium).

A mastodont stock, adapted to forests and savannas, of

wide migration (= mastodonts, trilophodonts).

A stegodon-elephant stock, adapted to southern forests,

to grassy plains, to savannas and steppes, of wide

migration (— Stegodon, Loxodon, Elephas).

These primary stocks gave off from two to six

branches each, so that the Proboscidea as a whole are

not two branched (i.e., mastodonts and elephants), as

formerly supposed, but many branched or polyphyletic.

The forest and savanna browsers and the grazers of the

plains and steppes were the long distance travelers and

from an Afriean or Asiatie center in Eocene times they

reached in the Middle and Upper Miocene all the conti-

nents of the world except Australia, while the amphibi-

ous forms remained in Afriea and southern Eurasia.

Certain of these branches, like the true mastodons, are

of very great geologie antiquity. Intelligent, independ-

ent, well defended, resourceful, adaptive, we find eleven

very distinct branches of proboscideans persisting into

Upper Pliocene times, five of the least hardy of which

became extinct during the colder conditions of the Lower

Pleistocene. The known lines of evolution are shaded

on the accompanying diagram; the unknown are left in

white. The theoretic adaptive radiation may be ex-

pressed in a formal classification as follows:

454 THE AMERICAN NATURALIST [Vor. LVI

Amphibious and swamp-living stock

I. MCERITHERIOIDEA (M«eritheres)

1. Moeritheriinij amphibious or swamp-living forms

own in the Upper Oligocene of Africa.

IL. DINOTHERIOIDEA (Dinotheres)

2. Dinotheriini,* large amphibious forms frequenting the

4 Ibid.

rivers of southern Eurasia throughout the

Miocene to the close of the Pliocene.

Forest and savanna grazers

III. MASTODONTOIDEA (Mastodonts and Bunomasto-

nts)

MasToDoNTIDAE or “ true mastodonts,” including the sub-

families

3. Mastodontine, springing from Palwomastodon of

the Oligocene of North Africa, and terminat-

ing with Mastodon americanus of the Pleisto-

cene forests of North America; grinders

lophodont, lacking trefoils.

4. Serridentine,® first known in the Middle Miocene

of France and Switzerland, spreading over

into India and North America; lacking the

trefoils.

BUNOMASTODONTIDÆ, the bunomastodonts, springing from

orms similar to the Phiomia of North Africa

and separating into four main divisions:

6. Longirostrine, typical long-jawed bunomasto-

donts arising in North Africa (Phiomia),

spreading all over southern Europe, Asia, and

North America

5. Notorostrins, a special branch entering the An-

dean region of South America and spreading

over the South American continent, distin-

- guished by the loss of ios lower tusks and the

abbreviation of the ja

T. pcr imn beaked AERE EE known

in the southern United States and north-

ern Mexico, with powerful downturned upper

and lower tusks.

8. Lon ui short-jawed bunomastodonts, which

tate both the true mastodonts and the

emend in the abbreviation of the lower

jaw and the early loss of the inferior tusks.

3 Herluf Winge, 1906, p. 172,

5It is a question whether this subfamily is nearest the Mastodontide,

with whieh its members are generally plaeed by European paleontologists.

No. 646] THE FOSSIL PROBOSCIDEANS 455

These animals wandered all over Europe,

Asia, and western North America.

IV. ELEPHANTOIDEA (the Elephant stock)

. Stegodontins, the original members of which were

doubtless ancestral to all the higher elephants,

persist as an independent branch into the Lower

Pleistocene of eastern Asia.

10. Loxodontine, embracing the great African division

of the elephants beginning with varieties of the

Loxodon antiquus of the Upper Pliocene, which

wandered all over southern Eurasia and radiated

widely over Africa.

11. Mammontine, including (a) the Southern Mam-

moths (Elephas planifrons of India and FE.

meridionalis of Europe), from which is derived

E. imperator of North America, and (5) the

Northern Mammoths, which probably include Æ.

columbi and the widespread E. primigenius of

the northern steppes; (?) tetradactyl pes.

12. Elephantine, the true elephants (E. indicus of

India), which do not appear until the Upper

Pleistocene; pentadactyl pes.

This twelve-fold branching of the proboscideans is

similar to the adaptive radiation which the author has

traced in the evolution of the horses, of the rhinoceroses,

and of the titanotheres, carrying the fundamental lines

of separation back to the Middle Miocene as the most

recent date, and to the Middle or Lower Eocene as the

most remote date. It will be observed from the diagram

(Fig. 1) that the shaded areas represent those probos-

eidean phyla of which remains have been discovered.

The large unshaded area includes the entire Oligocene,

Miocene, and Lower and Middle Pliocene history of the

Elephantide which is still unknown but which is likely `

to be revealed at any time by discoveries both in Africa

and in central Asia. A very striking fact is that the

early member of the Elephantoide, the Elephas plani-

frons of the Upper Pliocene of India and the apparent

ancestor of the mammoths, is now antedated in geologic

time and in its transitional structure by the Elephas

aurore (i.e., of the rising sun region) of Japan.

BOOKS AND LITERATURE

The Conservation of the Wild Life of Canada. By Dr. C. GORDON

Hewirt, late Dominion Entomologist and Consulting Zoologist.

York: Charles Seribner's Sons, 344 pp., illustrated.

vd book was in manuseript before the untimely death of

Doetor Hewitt, February, 1920, and has been prepared for

publieation by his wife. Mrs. Hewitt has also written a beautiful

prefaee whieh ean perhaps be fully appreciated only by those

who had the rare good fortune to eount Hewitt as a personal

friend.

To get the proper perspeetive on this book, one should know

that Doetor Hewitt was a zoologist of broad training. Previous

to coming to Canada he had worked not only on insects but also

on several problems on birds and their control of insect pests.

The reeord of his work as Dominion Entomologist from 1909

until his death is a brilliant one. Throughout this period he was

frequently consulted regarding various zoological problems which

eame before the Advisory Board on Wild Life Protection and in

1916 he was appointed Dominion Consulting Zoologist which

broadened his official interest. The work recorded in the book

under discussion was done chiefly during the last four years of

his life. For so busy a man to undertake a task of this size and to

cover the field so well in so short a time is an enviable accomplish-

ment.

The reading of this book is like a trip to the North Woods, but

with a scientist as companion rather than a record-breaking

hunter of big game. Although the title might properly include

fur-bearing animals and other natural groups, the discussion is

chiefly limited to the larger wild mammals and birds of Canada.

The information regarding the present distribution and abun-

dance of the several species is accumulated from many sources

and constitutes a valuable inventory of the remaining but di-

minishing resources of the Dominion. As might be expected of

one who understands the dangers of promiscuous and ignorant

hunting and who appreciates wild life, the dangers and economic

loss of unrestricted shooting are constantly set forth, and the re-

sults of inadequately controlled slaughter in the United States

456

No. 646] BOOKS AND LITERATURE 457

are used as an ignoble example. It is not too late in Canada to

profit by mistakes south of the boundary, and Doetor Hewitt's

book should serve as a timely warning.

Considerable progress has already been made in establishing

government and private reserves in Canada and the record of

this movement as given in this book is one of the most valuable

features of the work. The author took a lively interest in this

movement, and in efforts to conserve the wild life of the Domin-

ion he did everything possible, from revising the game laws of

the Northwest Territories to the instruction of Boy Scouts in bird

protection. Previous to his work the game laws of the Northwest

Territories had not been revised for many years, and he succeeded

in the diffieult task of getting through a revision that is a great

improvement over the former regulations. His successful effort

to bring about the Migratory Birds Treaty between the United

States and Canada was an accomplishment of high order. There

were, of course, other earnest men on both sides of the boundary

who assisted in this work, but to the author of this book fell

some of the most aggravating and ability-testing tasks. If the

full history of this effort is sometime written, Doctor Hewitt’s

part will appear as a large one.

The discussion of the periodic fluctuations of Canadian fur-

bearing animals in Chapter IX is perhaps the best example of

scientific method in the book. These fluctuations have long at-

tracted the attention of scientific and commercial men and they

are here diseussed from abundant data and from a biologieal

point of view.

This posthumous book is an additional monument to the seien-

tifie skill and personal abilities of the author. It should serve as

a valuable warning to Canadians and will be of value to readers

everywhere in giving a summary of the resources of the Domin-

ion in one of its most interesting and economically valuable

assets. Beeause of the wide interest in big game it should attraet

temporarily or permanently to Canada those who retain a whole-

some love for the outdoors.

E. F. PHILLIPS

SHORTER ARTICLES AND DISCUSSION

THE PROBABILITY ESTABLISHED BY A CULTURE OF

GIVEN n THAT A MATING e Sages OF

RODUCING ONLY DOM NT

INDIVIDUALS

To distinguish individuals heterozygous from those homozygous

for a given dominant factor is a matter of mere inspection when

the simplex condition is somatically distinct from the duplex

condition, as is the case with the mottling factor in the Adzuki

Bean. Generally, however, the degree of dominance is such

that a breeding test must be resorted to in order to distinguish

these two types. A homozygous dominant will breed true for the

character whether selfed or back-crossed to the recessive, whereas

a heterozygous individual will give 3 : 1 and 1 : 1 ratios respec-

tively when similarly treated. The common breeding practice

is to eonsider the parent homozygous when, if selfed or back-

erossed, it fails to produce any recessive individuals in a reason-

ably large number of offspring.

Just what is to be considered an adequately large number of

offspring has in the past been determined by the personal judg-

ment of the individual investigator, and the diffieulty of obtain-

ing offspring in large numbers. There has been no general

agreement based on mathematical considerations, probably be-

cause large numbers of offspring have not been found necessary

in order to distinguish a homozygous dominant from a heterozy-

gous parent producing such ratios as 3 : 1 and 1 : 1. The need

of a statistieal eriterion of what is an adequately large number

of offspring was realized when it beeame neeessary in tetraploid

races of the Jimson Weed (Datura Stramonium) to distinguish

between matings which should produce only dominant purple

offspring and those which should produce a 35 : 1 ratio of purples

to whites. In distributions which are so asymmetrical as those

given by sampling from the 35 : 1 ratio, we are hardly justified

in using the ordinary theory of probable errors. Special tables

have, therefore, been computed for use in work under way at

the Station for Experimental Evolution. Since other investiga-

tors will probably meet with the need for similar criteria, it

seems worth while to give tables showing the number of offspring

1 Jour. Hered., 8, 125-131, Fig. 10, 1917.

458

No. 646] SHORTER ARTICLES AND DISCUSSION 459

which should be considered in order to distinguish matings which

should give_all dominant individuals from those which may pro-

duce recessives,

The theory is of course quite simple. It is assumed that the

expected ratio of dominant to recessive is known, and is p : q,

where p+q=—1. The distribution of the chances of obtaining

dominant and recessive individuals in the frequencies n : 0,

(n—1l) : 1, (n—2) : 2, ete., when n individuals are grown is

(p+ q)”. To ascertain the probability of securing all dominant

individuals in a eulture whieh should show a definite ratio of

dominant to recessive offspring we have merely to table p" against

n. Ifthis value is very small, it is reasonable to assume that in

practice a culture of n individuals all of the dominant type

represents a parent or parents eapable of produeing only off-

spring of the dominant type. Thus, for example, if seeds which

should produce dominant and recessive individuals in a 5 : 1

ratio were sown, a culture of 35 all dominant individuals should

be obtained only 17 times in 10,000. Hence, if a sowing is made

to distinguish between a mating eapable of producing only domi-

nants and one which should give recessives in a 5 : 1 ratio, and

there results a eulture of 35 individuals all of the dominant type,

it is altogether reasonable to assume that the mating in question

is ineapable of produeing recessives.

Tables have been formed to inelude the 3 : 1 and 1 : 1 ratios

familiar in ordinary disomie inheritanee, the 2 : 1 and 8 : 1

ratios found in trisomie inheritanee in the mutant Poinsettia,

and the 5 : 1, 11 : 1, and 35 : 1 ratios found in tetraploids in

Datura. Some of these ratios are suggested by published data

on @nothera Lamarckiana and Primula sinensis, and will prob-

ably be found ultimately by those studying other forms.

The tables enable one to deeide how large a culture is neces-

sary on a probability basis. If it is felt that only 1 chance in

1,000 of the mating being capable of producing a recessive is

sufficient evidence that the culture represents only dominants,

then, to distinguish a mating which ean produce only dominants

from one which should give a 1 : 1 ratio, a culture of at least 10

individuals is necessary. If the 3 : 1 ratio is the one in question,

then 24 individuals are necessary ; while if a 35 : 1 ratio is con-

sidered, 244 individuals are required. In other words, cultures of

10, 24 and 244 individuals are of equal value in distinguishing

matings which should produce only dominants from those which

460

THE AMERICAN NATURALIST

[Vor. LVI

should give, respeetively, 1 : 1, 3 : 1, and 35 : 1 ratios of domi-

nants to recessives.

A. F. BLAKESLEE,

JOHN BELLING,

J. ARTHUR Harris.

TABLE I

VALUES OF p” FOR 1: 1, 2 : 1, 8 : 1, AND 5 : 1 RATIOS

N is 2:1 SI 5:1 N 3:1 5:1

I. .5000 6667 .7500 8333 19 .0042 0313

Bes -2500 .5625 .6944 20 .0032 0261

dus .1250 .2963 .4219 .5787 21 .0024 0217

4... .0625 .1975 .3164 .4823 22 .0018 0181

D. .0313 .1317 2373 .4019 23 .0013 0151

6.3. .0156 .0878 1780 .3349 24 .0010 0126

T. .0078 .0585 .1335 .2791 25 0105

$2. .0039 .0390 .1001 .2326 26 — .0087

9. .0020 .0260 . .0751 .1938 27 — .0073

10... 0010 .0173 .0563 .1615 28 — .0061

IL. — .0116 .0422 .1346 29 — .0051

12.5 — .0077 .0317 .1122 30 — .0042

ge — .0051 .0238 .0935 31 — .0035

14... — .0034 0178 .0779 32 — .0029

IB. — .0023 .0134 .0649 33 — .0024

16.. — .0015 .0100 .0541 34 — .0020

An — .0010 .0075 .0451 35 — .0017

18.. — — .0056 .0376 36 — .0014

TABLE II

VALUES OF p^ FOR 8 : 1 RATIO

N 0 1 2 3 4 5 | 6 7 8 9

Li .3079 | .2737 | .2433 | .2163 | .1922 .1709 | .1519 | .1350 | .1200 06

Be. E 4 .0843 | .0749 | . .0592 | .0526 | .0468 | .0416 | .0370 | .0329

a. .0292 | .0260 | .0231 | .0205 | .0182 0162 | .0144 | .0128 | .0114 | .0101

(eee z .0080 | .0071 -0056 | .0050 | .0044 | .0039 | .0035 | .0031

D o .0028 | .0025 | .0022 | .0019 | .0017 0015 .0014 | .0012 | .0011 | .0010

TABLE III

VALUES OF p? FOR ll : 1 Ratio

N 0 1 | 2 3 E 5 6 7 8 9

T5. .4189 | .3840 | .3520 | .3227 711 | .2485 | .2278 | .2088 | .1914

2. .1755 | .1 .1475 | .1352 | .1239 | .1136 | .1041 | .0954 | .0875 | .0802

See -0735 | .0674 | .0618 | .0566 | .0519 | .0476 6 | .04 .0366 36

a. .0308 0282. .0259 | .0237 | .0217 | .0199 | .0183 | .0167 | .0154 | .0141

&... .0129 | .0118 | .0108 | .0099 | . 0083 | .0077 | .0070 | . 0059

A. .0054 | . .0045 | .0042 |. i .0032 | .0029 | .0027 | .0025

[ens .0023 | .0021 | .0019 | .0017 | .0016 | .0015 | .0013 | .0012 | .0011 | .0010

No. 646] SHORTER ARTICLES AND DISCUSSION 461

TABLE IV

VALUES OF pn FOR 35 : 1 RATIO

| | |

N 0 1 2 | 3 4 | b LR 1i Ri 9

CUR 4295 | .4176 | .4060 | .3947 | .3837 | .3731 | 3627 .3526 | .3428 | .3333

4.... .| -3241| .815 .2978 | .2895 | 2815 | | -2737 | .2661 | .2587 | .2515

5.....| -2445 | .2377 | .2311 | .2247 | .2184 | .2124 | .2065 | .2007 | .1952 | .1897

6.....| .1844 | .1793 | .1744 | .1695 E 1558 | .1515 | .1473 | .1432

NI. 1392 | .1353 | .1316 | .1279 | .1244 | .1209 | .1175 1143 | 1111 | .1080

8 1050 | .1021 | .0993 | .0965 |.0938 | 0912 0887 | .0862 | .0838 | .0815

9. 0792 | .0770 | .0749 | .0728 | .0708 | .0688 | .0669 | .0651 | .0632 | .0615

HE. 0598 | .0581 | .056 9 | .0534 | .0519 | .0505 | .0491 | .0477 | .04

11 0451 | .0439 | .0426 | .0414 | .0403 | .0392 | .0381 | .0370 | .0360 | .0350

id ou 0340 | .0331 | .0322 | .0313 | .0304 | .0296 | .0287 | .0279 | .0272 | .0264

13 0257 | .0250 0243 | 0236 |.0229 | .0223 | .0217 | .0211 | .0205 | .0199

hb 0194 | .0188 | .0183 | .0178 | .0173 | .0168 | .01 159 | .0155 |

15 0146 | .0142 | .0138 | .0134 | .0131 | .0127 | .0123 | .0120 | .0117 | .0113

Hu 0110| .0107 | .0104 | .0101 | .0098 | .0096 | .0093 | .0091 | .0088

M 0079 | .0076 .0074 | .0072 | .0070 | .0068 | 0065

Hn 0063 | .0061 | .0059 | .0058 | .0056 | .0055 | .0053 | .0052 | .0050 | .0049

15 55. 7 | .0046 | .0045 | .0044 | .0042 | .0041 | .0040 | -0038 | .0037

20 0036 | .0035 | .0034 | .0033 | .0032 | .0031 | .0030 | .0029 | .0029 | .0028

Me oo 0027 | .0026 | .0025 | .0025 | .0024 | | .0023 | .0022 | .0021 | -0021

22.....| .0020 | .0020 | .0019 | .0019 | .0018 | .0018 | .0017 | .0017 | .0016 | .0016

233 .0015 | .0015 | .0015 | .0014 | .0014 | .0013 | .0013 | .0013 | .0012 | .0012

24.....| .0012 | .0011 | .0011 | .0011 | .0010 | .0010 | .0010 | .0010 | .0009 | .0009

LINKAGE BETWEEN BRACHYSM AND ADHERENCE

MAIZE

ADHERENCE first appeared in the seeond generation of a

braehytie x Boone Co. White hybrid and seemed to be linked

closely with normal stature) Subsequent progenies indicated

that there was no very close linkage between these characters

and possibly none at all? "The relationship of these two inter-

esting eharaeters has been tested now in more detail and it

seems certain that their genes are located on the same chromo-

some.

A cross was made between a non-adherent brsehyiie plant

and an adherent plant of normal stature, both plants being

segregates in the F, of the braehytie-Boone hybrid. The first

generation segregated with respect to the brachytic culms, ap-

proximately half the plants being of normal stature, but none

exhibited a tendency toward adherence. From the behavior of

the F, plants it is apparent that the adherent parent of the

cross was heterozygous with respect to the brachytie character.

1 Kempton, J. H., ‘‘A Braehytie Variation in Maize,’’ U. S. Dept. of

Agri. Bull. 925, Feb., 1921.

2Kempton, J. H., ‘‘Heritable Characters in Maize V. Adherence,’’

Journal of Séredüly, Vol. XI, No. 7, Sept.-Oct., 1920.

462 THE AMERICAN NATURALIST [Vor. LVI

Three F, plants of normal stature were self-pollinated and

three were baek-erossed on the double reeessive (adherent-

braehytie). The six ears were planted separately at Arlington,

Virginia, but the resulting F, populations were not as large as

eould be desired.

The eombined self-pollinated progenies gave the following

distribution:

No. Plants | Per Cent.

QUNM

Nor. | Br. Ad. | Br.-Ad. | Br. | A | Crossover | Q.

| |

217 | 91 | 8 | 4 | 23.9 | | F 22.2 + 3.4 | 798 + .06

and the plants of the combined back-crossed progenies are dis-

tributed as follows:

Nor. | Be, | Ad. | Brad. | Br. | Ad. | Crossover

86 | 188 | 178 | fas | 49.5 | 47.6 | 30.0 + 1.35

These distributions clearly indicate that crossing over between

these two factors occurred in from 20 to 30 per cent. of the

gametes.

Additional evidence of linkage between these characters is

afforded by the second generation of a cross between an ad-

herent plant of normal stature and a ramose-braehytie plant.

The F, of this cross was normal with respect to all three char-

acters, and they all reappeared in the progenies of the second

generation. Five F, plants were self-pollinated and the result-

ing ears planted separately. Unfortunately in most of the F,

progenies there is a deficiency of adherent plants and for the

combined progenies the departure below the expected 25 per

cent. is 7.8 + .87, a deviation too large to be ascribed to chance.

Whether this deficiency represents seedling mortality is not

known, but at the time the plants were classified many of the

progenies contained late plants strikingly smaller and weaker

than their mature sisters. Some of these plants consisted of a

small cluster of grasslike leaves with inflorescences hardly de-

veloped beyond the embryonic stage. Such plants could not be

classified with respect to adherence, though in many cases it

was possible to determine satisfactorily whether they were ra-

mose or brachytic. With respect to these last two characters

No. 646] SHORTER ARTICLES AND DISCUSSION 463

the small late plants approximated the familiar 9-3-3-1 group-

ing. If the assumption is made that all these late plants were

adherent, the percentage of adherent plants in most of the prog-

enies would then approximate the expeeted. For the present

analysis of the relationship of brachytie and adherent, the low

pereentage of adherent plants is not important, sinee the per-

eentage of erossovers ean be determined from the ratio of

normal to braehytie plants or by the use of Yule's Coeffieient

of Association.’

Combining the five progenies the distribution of plants is as

follows:

NUMBER OF PLANTS

| | |

| Ad.-Ra. | Small

Nor. | Ad. | Hw | Be, |} Ad. Ra, Ad.-Br. | Ra.-Br. | e d Pants

361 | 135 | 117 | 193 | 18 po. qu $ i a

PER CENT.

Ad. m and Small Plants Ra. | Br.

17.8 + .87 | 23.2 + .92 | 21.9 + .94 | 27.9 + 1.0

PER CENT. OF CROSSOVERS

hate. Ad.-Br. Ra.-Br.

Q. | % Q. | om Q. | %

37 + .06 | 38.5 £1.8 | .886 + .03 | 16.8 +19 | .05 +.06 | 49.9 + 0.4

. It is seen that the progenies of this hybrid indieate about 17

per eent. of erossing over while the three self-pollinated prog-

enies of the other hybrid, involving brachytie and adherent,

indicate 22 per cent. and the back crosses 30 per cent. It

seems inadvisable to combine the self-pollinated progenies from

the two hybrids to arrive at a single figure for the percentage

of crossovers since the degree of crossing over between two fac-

tors often varies greatly in different progenies. It seems certain

from these two hybrids that these two characters are located

in the same chromosome separated by a distance varying from

18 to 30 units, thus making a linkage series of brachytic, adher-

ent and pericarp color.

3 Yule, G. Udney, **On the Association of Attributes in Statisties,’’ Phil.

Trans. Roy. Soc., London, S. A., Vol. 94, pp. 257-319, 1900.

464 THE AMERICAN NATURALIST [Vor. LVI

The progenies of the braehytie-adherent-ramose hybrid fur-

nish evidence that the ramose character may belong to the same

linkage series, though the linkage is rather loose.

Although the tassels of ramose plants are much larger than

those of normal plants and it seemed not unreasonable to ex-

pect adherent-ramose tassels to present a large thickened mass,

nothing of the sort was found and the ramose-adherent plants

could be separated from the normal-adherent plants only by

examining the ears.

White and colored seeds were planted separately, but the

percentage of the three characters are essentially alike, as is

shown by the following figures indieating that all three are in-

dependent of one of the aleurone faetors:

95 Adherent 95 Ramose 95 Brachytic

White seeds planted ....... 16.4 + 1.65 24.3 + 1.92 31.5 + 2.04

Colored seeds planted...... 18.3 + 1.00 21.1 + 1.07 27.9 + 1.17

Dione. e r 1.9 + 1.93 3.2 + 2.2 3.6 + 2.34

J. H. KEMPTON

BUREAU OF PLANT INDUSTRY,

U. S. DEPARTMENT OF AGRICULTURE

A GENE FOR THE EXTENSION OF BLACK

PIGMENT IN DOMESTIC FOWLS!

Tue results of recent experiments on the inheritance of

plumage colors in fowls indicate that varieties in which black

pigment extends to all or nearly all of the plumage (e.g., self

black) differ by one dominant autosomal gene from varieties in

which black pigment is restricted to the hackle, flight and tail

feathers (e.g., Columbian and buff varieties). This gene has

been called ‘‘extension of melanie pigment’’ and has been as-

signed the symbol E",

The evidence is derived from reciprocal crosses between Black

Orpington and Columbian pattern (Light Brahma) fowls.

Whichever way the cross is made the F, chicks are all black

in the down. As adults, the males from the reciprocal crosses

are alike. They are black with white-bordered hackles and

saddle feathers; white-bordered and splashed or stippled wing

coverts and narrow white borders on the upper breast feathers.

They resemble fairly typical Dark Brahma or Duckwing males.

1 Contributions in Poultry Geneties, Storrs Agr. Experiment Station.

No. 646] SHORTER ARTICLES AND DISCUSSION 465

The females from the reciprocal crosses are unlike in adult

plumage. From the cross of Black male by Columbian female,

the daughters are self black. From the cross of Columbian

male by Black female, the daughters are black with white bor-

ders on the feathers of head, hackle, and upper breast. They

resemble the pattern known as Birchen

When backerossed with Columbian tole the F, males have

produced black, Columbian and buff chicks in the ratio of 4:

3: 1; or approximately equal numbers of chicks with extended

and restricted black pigment. When crossed with buff females

the same F, males have produced chicks in approximately the

ratio 2 black: 1 Columbian: 1 buff; again showing equality be-

tween the extended and restricted Gasses. The F, black fe-

males crossed with buff males have produced equal numbers of

black and buff chicks, while the F, Birchen females have pro-

duced, when crossed with buff males, black, Columbian and buff

chicks in a ratio approximating 2: 1: 1. The ratios as quoted

above have all been obtained and will be reported in full when

the adult classifications have been completed. All of these

erosses represent matings of fowls heterozygous in extension

(E"e") with fowls recessive in extension (e"e"). The expecta-

tion is equal numbers of black (extended) and non-black (re-

stricted) chicks. The experimental numbers at present are 99

black (E"): 98 non-black (Columbian or buff e"), A clear

monohybrid segregation is evident between extension (E") and

restriction (e") of black pigment.

The above results are all explained on the following hypothe-

ses:

l. The black fowls have the dominant allelomorph of an auto-

somal gene (E") which determines the extension of black pig-

ment to all parts of the plumage. The reeessive allelomorph

(e") of this gene is present in the Columbian and buff fowls.

2. The black fowls contain the recessive allelomorph of the

dominant sex-linked gene S (silver). This dominant gene in-

hibits the produetion of buff ground eolor and eauses the pro-

duetion of silver or white ground eolor;"? it is known to be

present in Columbian fowls, while the recessive allelomorph

characterizes the buffs. As regards these two genes the blacks

used in these experiments have proved to be E"E"ss in composi-

tion, the Columbians e"e"SS (male) or e"e"S-(female), and the

1 Sturtevant, A. H., 1912, Jour. Ezp. Zool., 12: 499—518,

2 Dunn, L. C., 1922, Amer. NaT., 56: 242-255.

466 THE AMERICAN NATURALIST [Vor. LVI

buffs e"e"ss, Blacks are therefore genetically buffs with an

epistatie gene for the complete extension of black pigment.

3. Extension of black is incompletely epistatie over silver so

that in fowls of the genotype E"e"Ss (male) or E"e"S-(fe-

male) silver appears in certain parts of the plumage, produ-

eing a pattern like that of the Dark Brahma.

Collateral evidence indicates that the gene for extension of

black pigment (or one with similar effeets) is present in Barred

Plymouth Rocks and White Plymouth Rocks (as a eryptomere) ;

and that it is absent in Columbian and buff varieties and in

Rhode Island Reds.

Hurst? was probably dealing with the same gene in his erosses

between Black Hamburgs and Buff Cochins, since F, from this

cross consisted of all black chicks, while in F, black and buff

chicks occurred in the proportions of 88 black: 31 buff. In in-

terpreting the results of this eross Morgan* states that either

= or two pairs of factors may be involved; which is right

**eould only be determined by an F, ratio." Yet the F, ratio

is given by Hurst (p. 138) and is surely a sufficiently close ap-

proach to a monohybrid ratio. The ratios obtained in our ex-

periments agree throughout with a mono-factorial interpreta-

tion.

It is believed that this gene will be found to characterize

many color varieties of fowls in which black, either as a self

color or as a component of a pattern extends to all or nearly all

of the plumage. Concerning its origin no direct evidence can

be offered at present. Its occurrence as a discrete unit indicates,

however, that its origin was discontinuous and that black varie-

ties probably had their genesis in mutation rather than in selee-

tion of particolored types toward black.

L. C. DuNN

THE EFFECTS OF SO-CALLED CONJUGATION IN

SHELLED RHIZOPODS :

THE phenomenon of conjugation in the Protozoa is regarded

as the forerunner of sexual reproduction in the higher animals,

3 Hurst, C. C., 1905, Reports to the Evo. Comm., II, pp. 138-39.

. * Morgan, T. H., 1919, Publ. Carnegie Inst. No. 285, p. 24.

The experimental work on this problem was carried on in the Zoological

Laboratory of the Johns Hopkins University. I wish to thank Dr. H. S.

Jennings, of that institution, for suggesting the problem and for his aid

in pursuing the investigations.

No. 646] SHORTER ARTICLES AND DISCUSSION 467

in which there is a union of a sperm and an egg. This latter

proeess is fundamental in the life of at least all the higher

Metazoa. By this union the race is perpetuated and hereditary

characters are intermingled. It would seem that studies of a

similar process in the unicellular forms might throw light upon

the basic relations of the sexual preron to the life of proto-

plasm.

Various investigators have shown that conjugation is a rela-

tively common occurrence among the more complex Protozoa,

such as the Paramecium, and that hereditary characters are

intermingled in this way. During conjugation two Paramecia

fuse by their oral surfaces and there is an interchange of nu-

clear material between the individuals. The latter then sepa-

rate and reproduction by division occurs. The races resulting

from such divisions show the effects of modifications due to

hereditary characters coming from both the conjugating indi-

viduals.

In the ease of the more primitive Protozoa, the Ameba and

other Rhizopods, not a great deal is known. It has been ob-

served that sometimes two individuals unite, but it is uncertain

whether or not true conjugation occurs with interchange of

nuelear material and subsequent modification of the offspring.

If sueh proves to be the ease, we shall have shown that the phe-

nomena of sex are found in the very lowest animals, and are of

general fundamental importance in the life process.

The present investigation was undertaken in the effort to

throw some light on this question. An attempt was made to

test the matter by indueing eonjugation between various indi-

vidual Rhizopods and noting if any inherited differenees arose

from these unions. (A eytologieal study of the behavior of

the nuelei of sueh individuals must be made before the evidence

ean be fully weighed.) A shelled Rhizopod, Difflugia corona,

was used, since the shell exhibits marked characteristics which

vary among the different races of the species. The ordinary

shellless Amceba presents so few characters of a permanent na-

ture that it is unsuited for a study such as this. The Dif-

flugia is an Amoba which builds from microscopic sand grains

a shell shaped much like an old-fashioned soap kettle with the

legs represented by spines projecting from the rounded aboral

surface. The animal lives inside this shell and thrusts its

pseudopodia from the oral opening. It reproduces by division,

as other Protozoa, half the body being extruded from the oral

468 THE AMERICAN NATURALIST [Vor. LVI

opening of the shell and a new shell being formed over the ex-

posed part of the body, the two shells, old and new, lying mouth

to mouth. The body then divides and the new individual

moves away to lead a separate existence.

At times two Difflugias have been observed attached mouth

to mouth and have been thought to be conjugating. When di-

viding the new shell is much lighter in eolor than the old and

in the eases supposed to be eonjugating both shells were of the

same shade, that is both dark, so that the phenomenon did not

seem to be that of division. It was this attachment or so-called

conjugation which I endeavored to investigate.

It was found by Dr. Jennings (not published as far as I am

aware) that two Difflugias eould sometimes be made to attach

themselves together by keeping them in a drop of distilled

water for a few hours. At his suggestion, I used this method,

endeavoring to hasten the proeess somewhat by pushing the

individuals together by means of a fine glass rod. In several

cases, the members of the pair became quite firmly united and

remained so for some time. "These pairs I then put into a drop

of culture medium: in the concavity of a hollow ground slide.

In some eases such individuals never separated but died. In

several instanees they did separate and lived and began to re-

produee by division.

Briefly, my procedure then was this. The number of spines

varies in different races of Difflugia, sometimes averaging 2 or

3, sometimes as high as 5 or 6. The size of the shell also varies.

I used the diameter across the widest part of the shell. I se-

lected, for example, a small individual with a few spines and

kept it under observation on a hollow ground slide in culture me-

dium until it had produced an offspring by division. (The eul-

ture medium consisted of tap water containing the microscopic

débris washed from the leaves of Elodea.) I then isolated the

offspring and allowed it to produce a race, keeping each indi-

vidual separate on a slide, and measuring and counting the

number of spines of each. The original Difflugia I tried to

mate, so to speak, with a large Difflugia with many spines,

which had previously produced an offspring which I had iso-

lated and allowed to found a race. If the large and small Dif-

flugias became attached, supposedly conjugating, and were suc-

cessfully separated, I then isolated each one on a slide and al-

lowed each to start a line of progeny. I then had 4 lines

going, one from each Difflugia before conjugation and one from

No. 646] SHORTER ARTICLES AND DISCUSSION 469

each after conjugation with the other. The following diagrams

may serve to make my meaning clear.

20. 55 lsp ¥9P ` osR sp

Biro SP SP Fag ad

: D. 3 70 D.38 O26 D?

RO 3 D O-O ‘ D.33

p^ v ^^

qd `q d »

a bi £ d € f| s h

Fb 107| 104 79). 1/2 102| 196 2 :

€ ox

: yt 222] 36} 366 30| 298] 363) 32

Ave.No.. i ;

Sp. 277] 239] "^ #28 253) ajas 4 293| wr] vo

Diagrams illustrating the manipulation of Difflugia in the experiments

with so-ealled conjugation and the results attained in three cases

cles at the top cf each diagram represent the individual Difflugias which became

attached to each other, D., diameter- Sp., spines. ind., individuals. Ave.,

average

In each figure the circles at the top represent the Difflugia

which were paired. For example, in A an individual with a

diameter of 29 units founded a line a and then was paired with

a Difflugia with 4 spines with a diameter of 33. This had previ-

ously started line d. After the separation of the Difflugias,

they founded lines b and c respectively. The dotted cross lines

represent the influence which might be expected to come from

the other member of the pair if there were actual conjugation.

Line a was carried on until 103 individuals were produced, the

average number of spines being 2.79 and the diameter 29.6

units. Line b, started after the attachment of the progenitor

: to the other Difflugia, was carried for 107 individuals, with an

average of 2.85 spines and a diameter of 29.2. The diagrams

show the results gained from earrying out the lines in the other

experiments. Unfortunately line i died before producing any

individuals and line h produced only 7 before dying out.

By eomparing the four lines in each experiment with each

other, evidence may be gained relative to whether or not, dur-

ing the supposed conjugation, the Difflugias exerted an effect

upon each other suffieient to cause modifieation of the diameter

and number of spines of the offspring in the direetion of the

line started by each before the attachment. That is, for ex-

ample, line b should be more like line d than is line a, and line

c should be more like a than is line d, and so on throughout

the experiments.

470 THE AMERICAN NATURALIST [Vor. LVI

A study of the data set forth in the diagrams will show that

there is praetieally no modifieation of any line springing from

a Difflugia, after the supposed eonjugation, in the direetion of

the characters of the line founded by the other member of the

pair before the union. Any slight changes seeming to show

such modification are offset by just as marked variations away

from that line. Comparing line g with h, it would seem that

there is a marked modifieation of g in the direetion of line e.

It must be noted, however, that line h consists of only 7 indi-

viduals, so that the average is untrustworthy. In no other ease

is there any signifieant leaning toward the other line, although

there are very slight tendeneies in that way in the spine num-

bers in experiment A. Line a has 2.79 spines, b 2.85, c 4.05

and d 4.22. On the other hand, in experiment B the spine num-

ber in line e is 3.58 and in f only 2.12, to be compared with 4

inline A. It would be expected that line f would show a greater

number of spines than line e. In experiment C line k shows a

slight increase in spine number instead of the expected de-

crease. In general there are no apparent modifications of the

offspring as the result of the pairing.

The experiments are open, of course, to the criticism that

the attachment between the Difflugias was brought about by

keeping the individuals in distilled water to bring them to the

state of partial starvation whieh seems usually to be the fore-

runner of eonjugation in the Protozoa. It is possible that under

these somewhat unnatural eonditions, the preliminary steps

incident to conjugation would be inaugurated but that the

proeess would stop before eompletion. In answer to this, I ean

only state that the Difflugias remained attached from 12 to 24

hours, thus allowing suffieient time for nuelear changes to have

oeeurred. They became separated only when placed in eultures

eontaining food.

o summarize then, as far as it is safe to base conclusions

on the results of this limited number of experiments, it seems

that the offspring of the Difflugias were not influenced by the

attaehment or so-ealled eonjugation of the parents. From this

fact it appears probable that this phenomenon of attachment

sometimes observed in the shelled Rhizopods is not a true con-

jugation and that there is no interehange of nuclear material

between the individuals taking part in it.

E. P. CHURCHILL, JR.

UNIVERSITY OF SOUTH DAKOTA

No. 646] SHORTER ARTICLES AND DISCUSSION 471

ON chi oe SEXUALLY MATURE PLATYNEREIS

EGALOPS FROM EGGS

THE literature affords so few cases of marine animals reared

under laboratory conditions that the writer ventures to com-

munieate his successful attempts to carry through to sexual

maturity the nereid, Platynereis megalops, from eggs laid in the

laboratory. This work had its origin in a suggestion made by

Dr. F. R. Lillie in 1911 that the capacity for cross fertilization

between Nereis limbata and Platynereis megalops be tested. At

that time, however, since we knew so little of the life history of

these forms, we felt that it was necessary to get all data possible

on each life history in order to have a standard of comparison

for the life history of the hybrids. So far all efforts to cross these

nereids have failed. The difference in the breeding habits of

Nereis and Platynereis is so striking that this alone might ac-

count for the failure of cross fertilization. Nereis sheds eggs into

the sea-water where fertilization takes place; Platynereis lays in-

seminated eggs soon after copulation. However, this very differ-

ence is calculated to enhance the interest attaching to the cross

fertilization. It might be possible to study the inheritance of the

egg-laying reactions. In addition, early observations revealed

that the young Platynereis megalops closely resemble Nereis

dumerilii. Since, as is well known, Nereis dumerilii has a com-

plex life history, we felt that the life history of Platynereis

might well repay study for its own sake.

PLATYNEREIS MEGALOPS REARED UNDER LABORATORY CONDITIONS

TO SEXUAL MATURITY

The writer has found that it is possible to rear Platynereis

megalops to sexual maturity under laboratory eonditions. This

was first accomplished in 1913-1914, repeated in 1920-1921, and

again in 1921-1922. The results may be briefly recounted.

Methods

Males and females eaught with a hand net in the evenings of

the July and the August full moon are kept in separate dishes.

In the laboratory as shortly after capture as possible a male and

472 THE AMERICAN NATURALIST [Vou. LVI

a female are placed in a finger bowl of clean sea-water. After

copulation and egg-laying the animals are removed from the

finger bowl. After the jelly has been extruded by the eggs, the

supernatant sea-water is poured off, leaving the eggs in the mat

of jelly stuck to bottom of the bowl. At first cleavage, which is

invariably one hundred per cent., the jelly-mass is gently broken

up and the eggs equally distributed among seven to ten finger

bowls of elean sea-water. Early the next morning the sea-water

is changed. At this time all eggs that possess fewer or more

than four oil drops, one in each maeromere, are discarded. Only

those larve that possess four oil drops evenly distributed among

the four macromeres give rise to normal swimming larve. As

the trochophores rise to the surface in each dish they are

pipetted off. Trochophores that fail to swim at the surface in

twenty-four hours laek the viability of those that rise earlier.

The young larve are kept in subdued light a few in each dish

because they tend to aggregate in such dense masses that many

. die off. This tendency to collect in one spot makes it easy to

change the water and thus avoid too great rise in temperature,

which is fatal to the animals. The larve will reach the stage of

three swimming segments without the addition of food.

en the segments appear, the larve must now be baid

very carefully in order that food may be given at the proper

time. The criterion for the initial feeding is the complete dis-

appearance of the oil drops from the entoderm cells.

In the eggs of both Nereis and Platynereis there is at the time

of fertilization a girdle of some eighteen to twenty-two oil drops

in the equatorial zone. These oil drops in the maturation stages

following insemination move to the vegetative pole. During

cleavage the number of oil drops is reduced to four large glob-

ules which normally are distributed to the cells of the gut. Be-

ginning with the third or fourth day after laying, the oil in the

gut cells of the larvæ begins to form an emulsion of smaller and

smaller drops. It is thus possible to follow the history of the oil

drops very fully in these ereatures that make veritable living

test tubes in a fat-digestion experiment. If food is given the

worms before the oil has been completely-used, they are killed in

large numbers. On the other hand, food must not be withheld

too long after the disappearanee of the oil. The first feeding

consists of ten c.c. of a diatom culture known by previous ex-

amination under the microscope to be free of metazoa or larve,

No. 646] SHORTER ARTICLES AND DISCUSSION 473

strained through three thicknesses of bolting silk of very fine

mesh. As the larve add segments more food is given. When the

larve build their tubes both food and mud are added until the

bottom of the dish is well covered. The method of preparing the

diatom culture may now be considered.

In 1911 I procured food according to the method deseribed by

Hempelmann in his study of the life history of Nereis dumerilii

at Naples. This method consists prineipally in seraping the:

growths from the live tables. The bottom and sides of aquaria

under running sea-water frequently show a felt-like growth of

diatoms and protozoa. Serapings from such aquaria suspended

in sea-water will give food suffieient to keep a few young worms

of both Nereis limbata and Platynereis. The method does not

allow the rearing of any large number of worms. Similarly, at-

tempts at a pure eulture of diatoms gave poor results.

In 1913 through the kindness of Dr. Caswell Grave I procured

a remarkably fine eulture of diatoms from Beaufort, N.C. With

this, the first sexually mature worms were obtained. But obvi-

- ously, Platynereis at Woods Hole must live on food got in Woods

Hole waters. I, therefore, made various attempts to get an ade-

quate diatom culture from the immediate vicinity. The success-

ful method follows.

At the beginning of the season mud is taken from Eel Pond,

near-by flats, or scraped from eel grass, together with animal and

plant life. This is placed in jars with the addition of an equal

volume of sea-water. The jars are then covered with glass plates

and set aside in subdued light. In a day or so all metazoa—

worms, crustacea, ascidians, ete.—are dead. After a period of

putrefaction, the culture purifies itself and a rich growth of

diatoms begins.

For young worms a suspension of diatoms strained through

several thicknesses of bolting silk is used. The diatoms for this

purpose are previously examined under the microscope, one e.c.

at a time; usually no metazoa are found. The suspension is then

made up in filtered sea-water. As the larve increase in size and

vigor food is added in greater quantities.

A brief summary of the three cultures of Platynereis megalops

reared to sexual maturity may now be given.

The Larval Cultures

The 1911 and 1912 larve were not kept after September first.

The 1913 Culture.—During August, 1913, from eggs laid in

474 THE AMERICAN NATURALIST [Vor. LVI

the laboratory by twenty females over 100,000 larve were reared.

On the eve of my departure from Woods Hole the larve were

all carefully removed from their tubes and placed in half-gallon

Mason jars. Each jar contained 500 ¢.c. of the rich Beaufort

diatom culture and sea-water to within ten centimeters of the

top. The jars were then tightly covered and set aside. After

the worms had had time to build new tubes, the jars were shipped

-to Washington, D. C. The worms at this time averaged about 10

mm. in length. Early in June, 1914, these worms were shipped

from Washington to Woods Hole. Relatively few survived the

journey. The largest worms (females), brought carefully in a

hand bag, died before the journey was half made. Since during

the winter hundreds of these worms had been killed periodically

for future study, the number left from the 1913 culture had been

greatly reduced. Some animals of this culture were carried

through the summer of 1914. They never reached sexual matu-

rity. They were taken back to Washington at the end of 1914.

In 1915 they were brought back to Woods Hole and returned to

Washington that fall. During this period they still showed no

change. .

In Washington the animals were kept in the clamped jars with-

out any change of water or additions of distilled water. One

culture was kept in a battery jar covered with a glass plate. Nor

was any addition ever made to this culture. The jars were kept

at room temperature in subdued light. To avoid contamination

worms removed for study were from the culture in the battery

jar only. After observing the worm I never replaced it, but

killed it for in toto mount or sectioning.

In 1917 several very fine cultures of worms were started, but

they died in transit to Washington. In 1918 and 1919 no worms

were reared.

The 1920 Culture—In August, 1920, very beautiful cultures

of about 50,000 larve were started: unfortunately, the majority

of these died very suddenly late in August. About a thousand

worms survived. These were distributed among twelve dishes

with food and left over winter in the heated laboratory at Woods

Hole. The dishes were left covered with glass plates exposed to

north light. No.change was made in the water or any additional

food given during the period September 1, 1920, to June 1, 1921.

On May 17, 1921, about 200 worms of different sizes were found

in the dishes. Of these some were preserved from time to time.

No. 646] SHORTER ARTICLES AND DISCUSSION 475

The history of the others shows that the first female with ripe

eggs appeared June 5. She was discovered slowly crawling

around the dish near the surface of the water. In color and in

form this animal resembled the females collected during the

breeding season. In size she was rather below the average and

somewhat more sluggish. The eggs in size, color and form were

identical with the eggs got from animals captured during the

breeding season. Subsequently, mature females were found at

intervals through the summer. No males appeared until late in

June. Eventually, thirty-two females and twelve males fully

mature were got from this 1920 culture.

Males got from the sea copulate with females reared in the

laboratory ; such females lay normal eggs that give rise to larve

of a high degree of viability. Males reared in the laboratory

copulate with females taken from the sea. The eggs are perfectly

normal. On only one occasion did I find a male and female from

this 1920 culture sexually mature at the same time. They copu-

lated in normal fashion. The eggs laid were normal in every

respect and gave rise to larve that I kept for two weeks before

discarding. These larvæ could not be distinguished from larve

resulting from eggs laid by animals taken from the sea.

The 1921 Culture.—At this writing only two mature animals

(females) have appeared—one May 1 and one May 6, 1922."

The Rate of Growth

Some idea of the rate of growth in these worms may be ob-

tained from data collected from the 1913 culture. This was the

only culture on which I had the opportunity to make continuous

observations.

Life History

Observations so far made on eultures of Platynereis megalops

reared in the laboratory from eggs laid by animals taken from

the sea do not reveal any indication of a sexually mature inter-

mediate form. So far, all eggs obtained appear to be identical

with those got from animals in nature. This would seem to sug-

gest that the life history of Platynereis is simple—without the

complexity of form and sexual condition found in Nereis dumer-

ilii, which Platynereis so closely resembles. It must be clearly

1 Since the above was written, 23 animals have reached maturity—17

females and 5 males. One reason for this sex ratio is that the males

have difficulty in getting out of their tubes; their mortality is therefore

high.

476 THE AMERICAN NATURALIST [Vor. LVI

stated, however, that on this point the observations so far made

. are not eonelusive. In order to determine fully that the eggs laid

by worms in the cultures in the laboratory are from the same

worms started in the eulture and not from an intermediate form

and are the only eggs laid, it would be necessary to make continu-

ous observations on isolated worms. So far it has not been

feasible to do this, since it would mean praetieally eontinuous

residence at Woods Hole through the winter.

TABLE I

RATE OF GROWTH OF PLATYNEREIS MEGALOPS FROM EcGGs LAID ON THE

VENING OF JuLY: 21, 1913

Segmen

ate pelo Mode Length in Mm.

July 28-1913 4 co eser Vs 3

July 29. 2 surdis (Nodo detit 4 to 5

July 280. tenet as oy wins d s 5

July Sb 075. ay ren hen ERR oe 6

Aarons Io | 75 V re 10

Aupub 0 eae ades 16 2

Anpust 8 505. ey ee as 22 4

Amt 48 o aa ay wale 26 5

PROGRES oe eee 24 T a 7

| Wo AG INIS ULT E RM 14

Oet 305. 46v VPE Cees 18

Nov. dU c CLAVES OC US 20

Dee. Ac Sieg ks Cie P B 25

Jan, 10, 1814... s ers 30

Feb. B OO oie a 33

NAMES 1o eat gan tee 40-45

April E-E 0 Nata eee ees 40-50

May 8 — Sa E ee ees 50-60

May NR o IR Mh ee er aes 40-50

On the other hand, it is just barely possible that in a state of

nature the life history is more complex than in the laboratory

cultures. Under operation of changes in such factors as density

of the sea-water, food, and temperature, the life history of the

. worms may be modified. That this possibility deserves some con-

‘sideration we may conclude from the sex ratio, if such meagre

data will allow. In the laboratory eultures females appeared first

in all three years and they outnumber the males. In nature

just the reverse is true.

Whatever our conclusions as to the interpretation of these ob-

servations, it seems to the writer that the life history of this

interesting nereid is worthy of further study.

No.646] SHORTER ARTICLES AND DISCUSSION 477

A Comparison with Other Forms

The method used for rearing sexually mature Platynereis from |

- the fertilized egg has been used to rear other worms through to

the adult stage: namely, Pectinaria gouldii, Diopatra, Nereis

limbata, and Chetopterus. In all cases the worms were reared

from eggs cut out of the females and inseminated in sea-water.

In no ease were the worms kept beyond September 15 (from one

to three months). Though it is usually stated that artificial in-

semination of Diopatra eggs is not possible, every attempt made

by the writer in 1911, 1912, 1913, 1914 and 1915 was successful.

There is one danger to avoid with these eggs—initiation of de-

velopment by mechanical shock. The worms reared from Di-

opatra eggs are if anything more hardy than those of Platy-

nereis. In 1913 I reared Diopatra in a watch glass to a length of

four centimeters.

Pectinaria gouldii are likewise readily reared from eggs in-

seminated in the laboratory. These eggs are extremely beautiful,

small, and almost wholly transparent. They are easy to handle.

I have found them the best eggs in my experience for study

under.high power (oil immersion lenses).

The specimens used were from the Eel Pond and are normally

smaller than Pectinaria found outside of Eel Pond. They are

infested with a distome and an interesting eiliate; the latter I did

not find in the larger speeimens (1911). This, if it be generally

true, together with the size of the Eel Pond specimens makes an

interesting ease from the point of view of ecology.

Among the shed spermatozoa of Pectinaria are many in bundles

that break up after a short time in the sea-water. In addition

to these one ean always get bundles of spermatoeytes, immature

sperm, ete., by puncturing the body wall. It is a very excellent

form to use for the study of eytoplasmie inelusions: it is pos-

sible to get the whole history of the sperm on one slide.

My objeet in studying these ova was to try to learn if size,

opacity, and yolk influence the ease with which the animals ean

be reared under laboratory eonditions. I found no correlation.

Thus, the egg of Platynereis is almost transparent; it measures

180-200 u. Nereis egg has more color and measures about 100 y.

The Nereis egg is the hardest of all to earry through. The egg

of Pectinaria is small and almost wholly transparent. It is

readily reared. The Chetopterus egg has more color than that

of Nereis and is smaller. It is easier to rear than the egg of

Pectinaria. The Diopatra egg is wholly opaque; it is the largest

478 THE AMERICAN NATURALIST [Vor. LVI

of the five eggs and perhaps the easiest to rear. The eggs may be

arranged according to size, depth of color and ease with which

they may be reared as follows:

Size Depth of Color Ease of Rearing

Diopatra Diopatra Diopatra

P'atynereis Chetopterus P d

Nereis Nereis Chetop

Chetopterus P atynereis sae ahaa

Pectinaria ectinaria Nereis

As in the ease of Platynereis the essential point in rearing

these annelids is to give them food at just the right time in the

larval stage. This time varies somewhat with each form. Briefly,

food must not be given before the yolk and oil are wholly used

up. One needs but to watch the larve, note the disappearance of

the oil from the gut, and then add diatoms.

E. E. Just

HOWARD UNIVERSITY

. REFERENCES

Hempelmann, F.

'll. Zur Naturgeschichte von Nereis dumerilii Aud. et Edw. Zoologica,

ns 25, Lief 1 (Heft 62).

Just, E.

14, a ae of Platynereis megalops at Woods Hole, Mass.

Biol. Bull.

Lillie, F. R. and das A E.

'13. Breeding Habits of the Heteronereis Form of Nereis limbata at

Woods Hole, Mass. Biol. Bull.,

AN OBSERVATION ON THE ‘“‘CLUSTER-FORMATION”

OF THE SPERMS OF CHITON +

WHILE engaged with an inquiry into the natural history of

the chitons, in 1918,? I several times made an observation which

may have a bearing on the significance of sperm-clusters, and on

the mechanism of their formation. The matter could not at

the time be adequately investigated, but since I shall not soon

be in a position to examine it further my observations are here

related for what they may be worth. The species concerned is

Chiton tuberculatus Linn., an intertidal form quite abundant at

Bermuda. It i is PAHPIREN to note, first, certain features of the

breeding process, which seems to me to have heretofore been

1 Contributions from the Bermuda Biologieal Station for Research. No.

119.

2 The corrected proof and manuscript of this artiele were returned to

the publisher Aug. 18, 1920; but the corrected article was accidentally

taken out of type in the office of the printers. The author has now re-

written the paper. E. L. M.

No. 646] SHORTER ARTICLES AND DISCUSSION 479

somewhat misunderstood. In another connection I shall de-

seribe several aspects of the reproductive activities of these ani-

mals, the present remarks having to do merely with the act of

feeundation.

. Although it has commonly been held that the liberation of

eggs by a female chiton is due to the reception of spermatic

fluid diffusing into her respiratory water-currents from a near-

by male, the proeess of fertilization would appear in faet to be

initiated in a quite different manner. Stated briefly, the pres-

enee of one or more neighboring females serves in some way to

aetivate the diseharge of sperm by the males, the spermatie

substances secondarily inducing the liberation of eggs. Nor-

mally this occurs only at those periods when the flow of the

tide begins just before sunrise, the shedding of the genital

products commencing as the chitons become covered by the sea.

The discharge of sperm can, however, be induced artificially at

certain times, in the laboratory, even a month or more before

the eggs are matured. A method which several times yielded

this result consisted in keeping some male chitons in a damp,

darkened vessel for about 14 hours, then covering them with

sea water and admitting light. It should be noted here that

C. tuberculatus is an animal nicely fitted for observations of

this kind, because the differential pinkish tint of the soft tissues

of the females permits the quick and accurate identification of

sex.*

In May, a month before ripe eggs are seen, it was noticed

that when sperm diffusing from a male, in a glass dish, was

taken up between the etenidia of a female, it issued from the

posterior ends of the etenidial channels in an altered state, for

the sperm-stream was then seen to eontain numerous aggluti-

nated masses of active sperms, which persisted in sea water for

at least half an hour.

During natural feeundation, however, no sperm-balls are

formed. The thick glutinous stream of spermatozoa passes

under the girdle of a female, is somewhat diluted with sea water

3 That the discharge of sperm is under nervous control is indicated by the

behavior of male Chetopleura following strychninization (cf. Crozier, 1920,

Jour, Gen. Physiol., Vol. 2, pp. 627-634)

4 See Crozier, W. J., 1920, ‘‘Sex-correlated Coloration in Chiton,"" AMER.

Nart., Vol. 54, pp. 84-88. Tidal, or rather lunar, periodicity in the libera-

tion of gametes has been observed also in Chetopleura; I was able to note a

probable lunar periodieity in this genus, in 1919, at Woods Hole, and

the point is dealt with at length in a recent paper by Grave, B. H., 1922.

Biol, Bull., Vol. 42, pp. 234-256.

480 THE AMERICAN NATURALIST [ Vor. LVI

by the traetive eurrent, and emerges posteriorly in eompany

with numerous large greenish eggs, about whieh, under the

mieroseope, it ean be seen that many sperms are gathered. But

no real ‘‘eluster-formation’’ takes place.

The body juiees of the ripe female, whether or not diluted

with.sea water, do not eause agglutination of sperm suspen-

sions. But ovarian extraets from (mature) eggs in sea water

do induce decided and apparently typical agglutination. So

far as I know, sperm-agglutination by ovarian extracts has not

previously been seen in molluscs.” Sea water into which ripe

eggs have been shaken from an ovary and the whole allowed to

stand for half an hour has a similar agglutinative effect.

Coneerning the signifieanee of the cluster formation, then,

these two points seem significant: (1) the absence of such a

process in normal feeundation, and (2) its conspicuous occur-

rence when sperm, before the real onset of the breeding season,

has passed through the etenidial channels of males or immature

females. It could not be discovered whether or not the mature

female in a non-spawning interval would cause this cluster pro-

duction, because at such times the consistent response of a fe-

male to an impinging current of sperms was to depress the

girdle to the substratum, thus cutting off the water current

carrying sperms, and, by reducing the volume of the etenidial

channel, violently to expel from below the sperms already ad-

mitted.

These observations do not, of course, merit analysis of the

rôle of egg-substances in fertilization of chiton, but do serve

to point the contention that mere evidence of sperm agglutina-

tion (cluster formation) may well have no bearing on such anal-

ysis. It is possible that the sperms set free at a period before

the natural ripening of eggs are in some degree immature, their

surface perhaps more sticky, or liable to be made so by slight

external changes experienced in passing between the gill fila-

ments of another individual.

W. J. CROZIER

ZOOLOGICAL LABORATORY,

UTGERS COLLEGE

5 Loeb, J., 1916, ** The Organism as a Whole," x + 379 pp., New York.

Woodward, A. E., 1918, ‘* Studies on the Physiological Significance of

Certain Precipitates from the Egg mcm of Arbacia and Asterias,’’

Jour. Ezper. Zool., Vol. 26, pp. 459-5

Just, E. E., 1919, ** The teen. Renetion 1 in Echinarachnius parma,’’

II, Biol. Bull. Vol. 36, pp. 11-38.

THE

AMERICAN NATURALIST

Vor. LVI. .. JNovember- December, 1922 No. 647

THE PROGRESSION OF LIFE IN THE SEA!

DR. E. J. ALLEN, F.R.S.

THE method we usually follow in the ordinary course

of zoologieal work is to make first, with the unaided eye,

a general examination of the animal that interests us,

and then study in detail its separate parts with a simple

lens, with a low power of the microscope, with gradually

inereasing powers, until, finally, minute portions are ex-

amined with the highest oil-immersion lens. The suc-

cessful research worker is generally one who, whilst car-

rying to the utmost limit he ean achieve his search into

detail, maintains as by instinet a true sense of proportion

and holds firmly to the idea of the organism as a whole.

In diseussing the living organisms of the sea I shall

try to follow a similar plan, thinking of the life of the

sea as a whole, built up of individual plants and animals,

each in intimate relation with its surroundings, and all

interdependent among themselves. But even this is not

enough, for we must take still a wider view and keep in

mind not only the life of the waters, but that also of the

land and of the air, for both, as we shall see, have a bear-

ing on our theme. Deep oceans, coastal waters, shallow

seas, rivers and lakes, continents and islands, all play

their part in one scheme of organic life—life which had,

it seems, one origin, and, notwithstanding migrations and

transmigrations from water to land, from land to air, and

from land and air back again to the water, remains one

closely interrelated whole.

1 Address of the President of the Section of Zoology of the British As-

sociation for the Advancement of Science, Hull, September, 1922.

481

482 THE AMERICAN NATURALIST [Vor. LVI

Both Brandt* and Gran* have recently emphasized the

faet that it is in the coastal waters and shallow seas,

which receive much drainage from the land, that plant

and animal life are most abundant, the more open oceans

far from land being relatively barren; as Schütt puts it,

the pure blue of the oceans is the desert color of the seas.

This increased production in the coastal waters is due

principally to the presence of nitrogen compounds and

compounds of phosphorus derived from terrestrial life.

From forest, moor and fen, wherever water trickles, the

life of the land sends its infinitesimal quota of these es-

sential foodstuffs to fertilize the sea.

When, however, we go back to the beginning of things,

we shall probably be right if we say that any influence of

terrestrial life upon life in the sea must be left out of

account. Different views are still held as to where life in

the world had its origin, but no one questions that it

began in close connection with water. That it began in

the sea, where the necessary elements were present in

appropriate concentrations and in an ionized state, is an

idea which appeals to many with increasing force the

more closely it is examined. This view has been devel-

oped recently by Church * in his memoir on ** The Building

of an Autotrophie Flagellate,’’ in which he boldly at-

tempts to trace the progression from the inorganic ele-

ments present in sea-water to the unicellular flagellate

in the plankton phase, floating freely in the water. The

autotrophic flagellate, manufacturing its own food, he

regards as the starting-point from which all other organ-

isms, both plants and animals, have sprung. To under-

stand the first step i in this progression, the passage from

the dead inorganic to the living organic remains, as it

has always been, one of the great goals of science, not of

biological siendo alone, but of all science. Recent re-

search has, I think, thrown much light on the fundamental

problems involved. In a paper published last year, Baly,

2 Wissensch. Meeresunters. Kiel, 18, 1916-20, p. 187.

3 Bull. Planktonique. Cons. Internat., 1912 (1915).

* Biological Memoirs I. Oxford, 1919.

No. 647] PROGRESSION OF LIFE IN THE SEA 483

Heilbron, and Barker,’ extending and correcting previous

work by Benjamin Moore and Webster,’ have shown that

light of very short wave-length (A= 200 me), obtained

from a mercury-vapor lamp, acting upon water and ear-

bon dioxide alone, is capable of producing formaldehyde,

with liberation of free oxygen. Light of a somewhat

longer wave-length (A= 290,44) causes the molecules of

formaldehyde to unite or polymerize to form simple

sugars, six molecules of formaldehyde, for example, uni-

ting to form hexose. The arresting fact brought out in

these researches is that the reactions take place, under

the influence of light of appropriate wave-lengths, with-

out the help of any catalyst, either organic or inorganic.

Where a source of light is used which furnishes rays of

many wave-lengths, the simple reaction of the formation

of formaldehyde is masked by the immediate condensa-

tion of the formaldehyde to sugar, but this formation of

sugar can be prevented by adding to the solution a sub-

stance which absorbs the longer wave-lengths, so that

only the short ones which produce formaldehyde are able

to act.

When the formation of sugars is postulated, the intro-

duction of nitrogen into the organic molecule offers little

theoretical difficulty ; for not only has Moore‘ shown that

nitrates are converted into the more chemically active

nitrites under the influence of light of short wave-length,

but he maintains that marine alge, as well as other green

plants, can under the same influence assimilate free nitro-

gen from the air. Baly® also has succeeded in bringing

about the union of nitrites with active formaldehyde in

ordinary test-tubes by subjecting the mixture to the light

of a quartz-mercury lamp.

It will be admitted that these three reactions: (1) the

5 Journ. Chem. Soc., London, Vols. 119 and 120, 1921, p. 1025. Nature,

Vol. 109, 1922, p. 344.

6 Proc. Roy. Soc. B., Vol. 87, p. 163 (1913), p. 556 (1914); Vol. 90, p.

168 (1918). |

* Proc. Roy. Soc. B., Vol. 90, p. 158 (1918); Vol. 92, p. 51 (1921).

8 Baly, Heilbron and Hudson, Journ. Chem. Soc., London, Vols. 121 and

122, 1922, p. 1078.

484 THE AMERICAN NATURALIST [Vor. LVI

formation of formaldehyde, H.CO.H, from carbonic acid,

OH.CO.OH, with liberation of free oxygen, or, to put it

more simply, the direct union of the carbon atom of CO,

with a hydrogen atom of H-O; (2) the formation of

sugars from formaldehyde, and (3) the formation from

nitrites and formaldehyde of nitrogenous organic sub-

stances, are the most fundamental and characteristic re-

actions of organic life. It is true that light of such short

wave-lengths (A= 200 »») as were required in Baly's ex-

periments to synthesize formaldehyde does not occur in

sunlight as it reaches the earth to-day; but, as we shall

see later, the same author has shown that, in the presence

of certain substances known as photocatalysts, the reac-

tion can be brought about by ordinary visible light; and

from Moore and Webster’s work it appears that colloidal

hydroxides of uranium and of iron are suitable photo-

catalysts for the purpose.

If these results of the pure chemist are justified, they

go far towards bridging the gap which has separated the

inorganic from the organic, and make it not too presump-

tuous to hazard the old guess that even to-day it is possible

that organic matter may be produced in the sea and other

natural waters without the intervention of living organ-

isms. We may note here, too, that if we take account of

only the most accurate and adequately careful work, the

actual experimental evidence at the present time requires

the presence of a certain amount of organie matter in the

culture medium or environment before the healthy growth

of even the simplest vegetable organism can take place.

This was illustrated in some experiments made by myself

some years ago when attempting to grow a marine diatom,

Thalassiosira gravida, in artificial sea-water made up

from the purest chemicals obtainable dissolved in twice-

distilled water. Even after nutritive salts, in the form

of nitrates and phosphates, had been added, little or no

growth of the diatom occurred. But if as little as 1 per

cent. of natural sea-water were added, excellent cultures

resulted, in which the growth was as healthy and vigor-

ous as I was able to obtain when natural sea-water was

No. 047] PROGRESSION OF LIFE IN THE SEA 485

used entirely as the basis of the culture medium. There

was clearly some substance essential to healthy growth

contained in the 1 per cent. of natural sea-water, and from

further experiments it became praetieally certain that it

was an organic substance. When, for instance, the nat-

ural sea-water was evaporated to dryness,.the residue

slightly heated and redissolved in distilled water, 1 per

cent. of this solution added to the artificial culture me-

dium was as potent in producing growth of the diatom

as the original natural sea-water had been. When, on

the other hand, the residue after evaporation was well

roasted at a dull red heat and redissolved in distilled

water, the addition of this solution to the artificial culture

medium produced no effect and growth did not take place.

Growth could also be stimulated by boiling a small frag-

ment of green seaweed (Ulva) in the artificial culture

medium, the weed being removed before inoculation with

the diatom. All this points to the necessity for the pres-

ence of some kind of organic matter in the solution before

growth can take place. One must not dogmatize, how-

ever, for there are many pitfalls in the experimental

work and the necessary degree of accuracy is difficult to

attain. My own experience of these difficulties culmi-

nated when I discovered, covering the bottom of my stock

bottle of distilled water—water which had been carefully

redistilled from bichromate of potash and sulphuric acid

in all-glass apparatus—a healthy growth of mold.

Let us then assume that we are allowed to postulate 1n

primitive sea-water or other natural water organic com-

pounds formed by the energy of light vibrations from

ions present in the water, and see how we may proceed

to picture the building up of elementary organisms.

Without doubt the evolutionary step is a long and elab-

orate one, for even the simplest living organism is al-

ready highly complex both in structure and in function.

As the molecules grew more complex by the progressive

linkage of the carbon atoms of newly formed carbohydrate

and nitrogenous groups, we must suppose that the or-

ganic substance, for purely physical reasons, assumed

486 THE AMERICAN NATURALIST [Vor. LVI

the colloidal state, and at the same time its surface-ten-

sion became somewhat different from that of the sur-

rounding water. With the assumption of the colloidal

state, the electric charges on the colloidal particles would

produce the effect of adsorption and fresh ions would be

attracted from the surrounding medium, producing a kind

of growth entirely physical in character. We thus ar-

rive at the conception of a mass of colloidal plasma dif-

fering in surface-tension from the water and increasing

in size by two processes, the one chemical, due to linkage

of carbon atoms; the other physical, brought about by

the adsorption of ions by the colloidal particles.

The difference of surface-tension would tend to make

the surface a minimum and the shape of the mass spher-

ical. On the other hand, maximum growth would demand

maximum exchange with the surrounding medium, and

hence maximum surface. From the antagonism of these

two factors, surface-tension and growth, there would fol-

low, firstly, the breaking up of the mass into minute par-

ticles upon the slightest agitation, and, secondly, changes

of form wherever growth involved local alterations of

surface-tension, which changes of form would represent

the first indication of the property of contractility.

So far we have considered only the process of the

building up of the elementary plasmic particles, the

anabolic: process. Church, whose memoir already re-

ferred to I am now closely following, points out that

these anabolic operations must from the beginning have

been subject to the alternations of day and night, for dur-

ing the night the supply of external energy is removed.

** If during the night,’’ he asks, ‘‘ the machine runs down,

to what extent may it be possible so to delay the onset of

molecular finality that some reaction may continue, at a

lower rate, until the succeeding day?" And his answer

is: ** The successful solution of this problem is defined

physiologically by the introduction of the conception

‘katabolism,’ 'as implying that energy derived from the

‘breaking down’ of the plasma itself... may be re-

garded as a ‘ secondary engine,’ functional in the absence

No. 647] PROGRESSION OF LIFE IN THE SEA 487

of light, and evolved as a last resort in failing plasma."

Katabolism persists as the ultimate mechanism in the

physiology of animal as contrasted with plant life, but if

the suggestion just quoted is sound, it originated, as the

first ** adaptation " of the organism, to meet the factor

of recurring night and day. That the problem was suc-

cessfully solved we know, but as to the mechanism of its

solution we have no key. It is at this point again, to use

Church’s words, that the ** plasma, previously within the

eonnotation of chemieal proteid matter, becomes an auto-

trophie, inereasingly self-regulated, and so far individu-

alized entity, to which the term ‘ life’ is applied."

The elementary plasma is thus now fairly launched as

an individual living organism, and the great fundamental

problems of biology —memory, heredity, variation, adap-

tation—face us at each step of our further progress. We

see in broad outline the conditions the advaneing organ-

ism had to meet, we see the means by which those condi-

tions were in faet met, we know that only those individuals

survived which were able to meet them. Further than

this we, the biologists of to-day, have not advanced. The

younger generation will pursue the quest, and, with pa-

tient effort, much that now lies hidden will grow clear.

The differentiation of the growing particles of plasma

into definite layers, which followed, seems natural; first

the external layer, in molecular contact with the sur-

rounding water, from which it receives substances from

outside in the form of ions, and to which it itself gives

off ions; beneath this the autotrophic layer to which light

penetrates, and in which, under the influence of the light,

new organic substance is built up; in the center a layer

to which light no longer penetrates. This central region,

the nucleus, depends entirely on the peripheral layers for

its own nutrition, and becomes itself concerned only with

katabolie processes, those processes of the organism

whieh depend upon the breaking down, and not the build-

ing up, of organie substance.

At an early stage in the development of the individual

organism the spherieal shape, which the organie plasma

488 THE AMERICAN NATURALIST [Von. LVI

was compelled to assume under the influence of surface-

tension, underwent an important modifieation, the effect

of which has impressed itself upon all later develop-

ments. A spherical organism floating in the water and

growing under the direct influence of light would ob-

viously grow more rapidly on the upper side, where the

light first strikes it, than it would on the lower side away

from the light. There followed, therefore, an elongation

of the sphere in the vertieal direction, and the definite

establishment of an anterior end, the upper end which

lay towards the light and at which the most vigorous

growth took place. In this way there was established a

definite polarity, which has persisted in all higher organ-

isms, a distinetion between an anterior and a posterior

end. With the concentration of organic substance which

took the form of nucleus and reserve food supply, the

specifie gravity of the plasma would become greater than

that of the surrounding water and the organism would

tend to sink. The necessity, therefore, arose for some

means of keeping it near the surface, that it might con-

tinue to grow under the influence of light. The response

to this need, however it was attained, came in the de-

velopment of an anterior flagellum. This we may regard

as an elongation in the direction of the light of a contrac-

tile portion of the external layer, moving rhythmieally,

which by its movement counteracted the action of gravity,

and acting as a tractor drew the primitive flagellate up-

wards towards the surface layers, into a position where

further growth was possible. That this speculation of

Church’s represents what was actually accomplished,

‘even though it does not make clear the means by which

it was brought about, is shown by the interesting re-

searches of Wager?’ on the rise and fall of the more highly

organized flagellate Euglena. Euglena is a somewhat

pear-shaped flagellate, the tapering end being anterior

and provided with a single flagellum, which acts as a

tractor drawing the organism towards the light. The

9 Phi!. Trans. Roy. Soc., Vol. 201, 1911; and Science Progress, Vol. vi.

October, 1911, p. 298.

No. 647] PROGRESSION OF LIFE IN THE SEA 489

posterior end carries the nucleus and most of the chloro-

phyll and food reserves. The whole organism has a

specific gravity of 1.016, being slightly heavier than the

fresh water in which it lives. When dead, or when the

flagellum is not moving, it takes up, under the action of

gravity alone, a vertical position in the water, with the

pointed anterior end uppermost, and the heavier, rounded,

posterior end below, and sinks gradually to the bottom.

In a very crowded culture a curious phenomenon is

seen, because the organisms tend to aggregate into clus-

ters beneath the surface film, and when they are crowded

together in these clusters the flagella cease to work. This

makes the whole cluster sink to the bottom under the

action of gravity. When the bottom is reached the in-

dividuals are spread out by the action of the downward

current, and, when they are sufficiently widely apart, the

flagella again begin to move, carrying the organisms in

a more diffuse stream once more to the surface. The

whole culture vessel becomes filled with a series of ver-

tical lines of closely aggregated falling organisms, sur-

rounded by a broad cylinder of disseminated swimming

ones, rising to the surface by the action of their flagella.

If the conditions are kept uniform, such a circulation of

Euglenas, falling to the bottom by gravity when the fla-

gella are stopped and returning to the surface under

their own power, will continue for days.

The flagellum in this species, therefore, retains its

most primitive function of drawing the organism to the

light in the surface layer. With the establishment of the

flagellum an organ is produced which shows remarkable

persistence in both the animal and vegetable kingdoms,

and from the existence of the flagellated spermatozoon in

the higher vertebrates, in accordance with Haeckel’s bio-

genetic law that the individual in its development repeats

or recapitulates the history of the race, we conclude that

they also in their earliest history passed through a plank-

ton flagellate phase.

Exactly at what stage in the history of the autotrophic

flagellate the first formation of chlorophyll and its allied

490 THE AMERICAN NATURALIST [Vor. LVI

pigments took place we have no means of determining,

but it may have been before even the flagellum itself had

begun. This advance and the subsequent concentration

of the pigments into definite chromatophores or chloro-

plasts doubtless immensely increased the efficiency of the

organism in producing the food which was necessary to

it. The recent work of Baly and his collaborators be-

comes here again of the first importance, and though the

subject of the part played by chlorophyll in photosyn-

thesis belongs rather to botany and chemistry than to

zoology, I may perhaps for the sake of completeness be

allowed to refer to it very briefly. . I have already said

that Baly brought about the synthesis of formaldehyde

from CO, and H.O under the influence of rays of very

short wave-length (A= 200) from a mereury-vapor

lamp. He was also able to show that when certain col-

ored substances were added to the solution of carbon

dioxide in water the same reaction took place under the

influence of ordinary visible light. His explanation of

this process is that the colored substance known as the

photocatalyst absorbs the light rays and then itself radi-

ates, at a lower infra-red frequency corresponding to its

own molecular frequency, the energy it has absorbed. At

this lower frequency the energy thus radiated is able to

activate the carbonic acid, so that the reaction leading

to the formation of formaldehyde can and does take

place. In the living plant this synthesized formaldehyde

probably at once polymerizes to form sugars.

Malachite green and methyl orange, as well as other

organic compounds, were found to act as photocatalysts

capable of synthesizing formaldehyde, and Moore and

Webster’s work had previously shown that inorganic

substances, such as colloidal uranium oxide and colloidal

ferric oxide, can do the same. Chlorophyll in living

plants may with some confidence be assumed to operate

in a similar way, though no doubt the series of events is

more complex, since the green pigment itself is not a

single pigment, and others, such as earotin and xantho-

phyll, are also concerned.

No. 647] PROGRESSION OF LIFE IN THE SEA 491

We have tried to pieture the gradual building up from

elements occurring in sea-water of a chlorophyll-bearing

flagellate, capable of manufacturing its own nourishment

and able to multiply indefinitely by the simple process of

dividing in two. If we assume only one division during

each night as a result of the day’s work in accumulating

food material, such an organism would be able in a com-

paratively short space of time to occupy all the natural

waters of the world. But here we are met by a difficulty

which is not easily overcome. Chlorophyll, the photo-

catalyst, the most essential factor in the building up of

the new organic matter, is itself a highly complex organic

substance, and in any satisfactory theory its original for-

mation and its constant increase in quantity must be

accounted for. Lankester?? has maintained that chloro-

phyll must have originated at a somewhat late stage in

the development of organie life, and has suggested that

earlier organisms may have nourished themselves like ani-

mals on organie matter already existing in a non-living

state. An alternative hypothesis, which in view of the

recent work seems more attractive, is to suppose that the

earlier organisms were either activated by some simpler

photocatalyst, or that they received the necessary energy

at suitable frequency directly from some outside source.

It must not be forgotten, also, that at the time these

developments were taking place the conditions of the en-

vironment would in many ways have been different from

those now existing in the sea. One suggestion of special

interest that has been made” is that the concentration of

carbon dioxide in the atmosphere, and hence also in nat-

ural waters, was very much greater than it is to-day.

Free oxygen, indeed, may have been entirely absent, and

all the free oxygen now present in the air may owe its

existence to the subsequent splitting up of carbon diox-

ide by the action of plant life. With such possibilities

of differenees in the conditions in this and in so many

10** Treatise on Zoology,'' Part I, Introduction. London, 1909.

11See Carl Snyder, ‘‘Life without Oxygen,’’ Science Progress, Vol. vi,

1912, p. 107:

492 THE AMERICAN NATURALIST [Vorn LVI

other directions, may we not be well satisfied if, for the

time, we can say that the formation of carbohydrates and

proteids has been brought within the category of ordi-

nary chemical operations, which can occur without the

previous existence of living substance?

To return once more, however, to the free-swimming,

autotrophic flagellate. In the early stages of its history

the loss caused by sinking, and so getting below the in-

fluence of light and the possibility of further growth, must

have been enormous. We may conceive a constant rain

of dead and dying organisms falling into the darker re-

gions of the sea, and thus a new field would be offered

for the development of any slight advantages which par-

ticular individuals might possess. Under such conditions

we may suppose that the holozoie or animal mode of nu-

trition first began in the absorption of one individual by

another one, with which it had chanced to come into con-

tact. If the one individual were more vigorous and the

other moribund, we should designate the process ** feed-

ing,’’ and the additional energy obtained from the food

might well cause the individual to survive. If the two

individuals which coalesced were both sinking from loss

of vigor, the combined energy of the two might make pos-

sible a return to the upper water layers, where under the

influence of light growth and multiplication would pro-

ceed, and we should, I suppose, designate the coalescence

** conjugation,’’ or sexual fusion.

Other individuals, again, sinking in shallow water,

would stick to solid objects on the sea-floor, whilst the

flagellum continued to vibrate. The current produced by

the flagellum under these conditions would draw towards

the organism dead and disintegrating remains of its fel-

lows, and again we should have ingestion and animal

nutrition. At this stage we witness the definite passage

from plant to animal life. A further stage is seen when

a cup-like depression to receive the incoming particles of

food is formed at the base of the flagellum, to be followed

still later by a definite mouth.

Any roughening of the external surface of the swim-

No. 647] PROGRESSION OF LIFE IN THE SEA 493

ming flagellate, such as we so often find brought about by

the deposition of ealeareous plates or silicious spicules

or the produetion of ridges or furrows, would tend to

slow down its speed of travel, from increased friction

with the surrounding water. This would have a similar

effect to actual fixation in drawing floating particles by

the action of the flagellum, and also lead to animal nutri-

tion. Still another development would oecur when the

fallen flagellate began to creep along the sea-floor by

contractile movements of the plasmic surface, losing its

flagellum, and adopting the mode of life of an ameba.

That amoba and its allies, the Rhizopods, are descended

from a flagellate ancestor is a view suggested by Lan-

kester'* in 1909, which was adopted by Doflein,? and is

now strongly advocated by Pascher™ as a result of much

new research.

The transformation from the plant to the animal mode

of feeding we can see in action by studying actual organ-

isms which exist to-day. In the course of my work al-

ready referred to on the culture of plankton organisms

there has on several occasions flourished in the flasks a

small flagellate belonging to the group of Chrysomonads,

which was first described by Wysotzky under the name of

Pedinella hexacostata, and to which I drew the attention

of Section D at the Cardiff Meeting in 1920. The general

form of Pedinella resembles that of the common Vorti-

cella, but its size is much smaller. The body, which is

only about 5» in diameter, is shaped like the bowl of a

wine glass, and from the base of the bowl, which is the

posterior end, a short, stiff stalk extends. From the

center of the anterior surface there arises a single long

flagellum, surrounded at a little distance by a circle of

short, stiff, protoplasmic hairs. Arranged in an equa-

torial ring just inside the body are six or eight brownish-

green chromatophores or chloroplasts. In a healthy eul-

1? Lankester, ‘‘ Treatise on Zoology,’’ Part I, London, 1909, p. xxii.

13 Doflein, ‘‘ Protozoenkunde,’’ 1916.

14Pascher, Archiv f. Protistenkunde, Ba. 36, 1916, p. 81, and Bd. 38,

1917, p. 1.

494 THE AMERICAN NATURALIST [Vor. LVI

ture Pedinella swims about freely by means of a spiral

movement of the flagellum, which functions as a tractor,

the stalk trailing behind. The chromatophores are large,

brightly colored and well developed, and the organism

is obviously nourishing itself after the manner of a plant,

like any other Chrysomonad. But from time to time a

Pedinella will suddenly fix itself by the point of the trail-

ing stalk. The immediate effect of this fixing is that a

eurrent of water, produced by the still vibrating flagel-

lum, streams towards the anterior surface of the body,

and small particles in the water, such as bacteria, become

caught up on the anterior surface, the ring of fine stiff hairs

surrounding the base of the flagellum being doubtless of

great assistance in the capture of this food. One can

clearly see bacteria and small fragments of similar size

engulfed by the protoplasm of the anterior face of the

Pedinella and taken into the body. The organism is now

feeding as an animal. In some of the cultures in which

bacteria were very plentiful nearly all the Pedinella re-

mained fixed and fed in the animal way, and when this

was so the chromatophores had almost disappeared,

though they could still be seen as minute dark dots. We

can, as it were, in this one organism see the transition

from plant to animal brought about by the simple process

of the freely swimming form becoming fixed.

In the group of Dinoflagellates, also—the group to

which the naked and armored peridinians belong—the

same transition from plant to animal nutrition ean be

well followed by studying different members of the group.

In heavily armored forms, with a rich supply of chro-

matophores, nutrition is chiefly plant-like or holophytie.

In those with fewer ehromatophores there is, on the other

hand, often distinct evidence of the ingestion of other

organisms, and nutrition becomes partly animal.like.

Amongst the naked Dinoflagellates such holozoie nutri-

tion is very much developed, and in many species has

entirely superseded the earlier method of carbonic acid

assimilation.

It is really surprising how many structural features

No. 647] PROGRESSION OF LIFE IN THE SEA 495 .

found in higher groups of animals make their first ap-

pearance in these naked Dinoflagellates in conjunction

with this change of nutrition, and we seem to be led directly

to the metazoa, especially to the Coelenterata. In Poly-

krikos there are well-developed stinging cells or nema-

toeysts, as elaborately formed as those of Hydra or the

anemones. In Pouchetia and Erythropsis well-developed

ocelli are found, consisting of a refractive, hyaline, some-

times spherieal lens, surrounded by an inner core of red

pigment and an outer layer of black; the whole structure

is comparable to the ocelli around the bell of a medusa.

In Noctiluca and in the allied genus Pavillardia a mobile

tentacle, which is doubtless used for the capture of food,

is developed. Division of the nucleus, with the formation

of large, distinet chromosomes, has also been described

in several of these Dinoflagellates. With the tendency

of the cells in certain species to hold together after divi-

sion and form definite chains, we seem to approach still

nearer to the metazoa, until, finally, in Polykrikos we

reach an organism which may well have given rise to a

simple pelagic eclenterate. It is difficult to resist the

suggestion put forward by Kofoid* in his recent mono-

graph, that if to Polykrikos, with its continuous longitu-

dinal groove which serves it as a mouth, its multicellular

and multinucleate body and its nematocysts, we could add

the tentacle of Noctiluca, and perhaps also the ocellus of

Erythropsis, ** we should have an organism whose ‘struc-

ture would appear prophetic of the Coelenterata and one

whose affinities to that phylum and to the Dinoflagellata

would be patent." Or it may be that the older view is

the correct one here, and that the first cclenterate came

from a spherical colony of simple holozoic flagellates, ar-

ranged something on the plan of Volvoz, in which the

posterior cells of the swimming colony, in whose wake

food particles would collect, had become more speeialized

for nutrition than the rest.

Before proceeding, however, to consider the further

15 Kofoid and Swezy, ''The Free-living Unarmored oe M

Mem. Univ. California,

496 THE AMERICAN NATURALIST [Vor. LVI

progress of animal life, we must pause for a moment to

ask in what direction plant life in the sea developed,

from which the inereasing animal life derived its nourish-

ment. Here the striking fact is the lack of progress in

the free, floating, plankton phase. The plant life of the

plankton has never proceeded beyond the unicellular

stage, for the plankton diatoms, which with the peri-

dinians form the great, fundamental vegetable food sup-

ply of the sea, are only autotrophic flagellates which have

lost their flagella, having acquired other means of flota-

tion to keep them in the sunlit region of the upper water

layers. Deriving their food, as these plants do, directly

from molecules in the sea-water, the factor which is for

them of supreme importance is the exposure of maximum

surface directly to the water. Hence the minute unicel-

lular form has been the only one to survive as phytoplank-

ton. The marine region in which plant life has succeeded

in making some progress is the narrow belt along the

shores, where a fixed life is possible, but this belt, limited

by the amount of light which penetrates, extends only to

a depth of about 15 fathoms. The available area is

further restricted to rocky and hard bottoms, and is

therefore nowhere great. This is the wave-lashed region

of the brown and red seaweeds. In the brown seaweeds

a history ean still be traced, from the fixture of an auto-

trophie flagellate to the building up, by laying cell on

cell, of the essential structures which afterwards, on trans-

migration to the land, reached their climax in the forest

tree.

But if the flagellate thus rose and gave origin to the

flora of the land, it also degenerated, for it adopted a

parasitie habit, living in and direetly absorbing already

formed organic matter. In this way the bacteria arose,

whose activities in so many directions influence the life

of to-day. This view exceeds in probability, I think, the

suggestion often put forward,” that it is to the simpler

bacteria we must look for the first beginnings of life.

16 Church, Botanical Memoirs, No. 3. Oxford, 1919.

17 Osborn, ‘‘The Origin and Evolution of Life," 1918. Waksman and

Joffe, **Miero-organisms concerned in the Oxidation of Sulphur in the

No. 647] PROGRESSION OF LIFE IN THE SEA 497

After this digression on the botanieal side we must

return to the primitive eclenterate and see on what lines

evolution proceeded in the animal world. As a purely

plankton organism, swimming freely in the water, the

progress of the ecdlenterate was not great, and reached,

as far as we know, no further than the modern Cteno-

phore. The Ctenophore seems to represent the culmi-

nating point of the primary progression of pelagie ani-

mals, which derived directly from the autotrophic

flagellate. Further evolution was associated with an

abandonment by a eolenterate-like animal of the pelagic

habit, and the establishment of a connection with the

sea bottom, either by fixing to it, by burrowing in it, or

by creeping or running over it. At a later stage many

of the animals which had become adapted to these modes

of life developed new powers of swimming, and thus gave

rise to the varied pelagic life which we find in the sea

to-day; but this must be regarded as secondary, the pri-

mary pelagic life, so far as adult animals were concerned,

having ended with the evolution of the Ctenophore.'*

Sueh is the teaching of embryology, the history of the

race being conjectured from the development of the in-

dividual. In group after group of the animal kingdom,

when the details of its embryology become known, the

indications are the same—first the active spermatozoon,

reminiscent of the plankton flagellate, then the pelagic

larval stage, recalling the celenterate, and then a bottom-

living phase.

The primitive, free-swimming celenterate, adopting a

fixed habit and becoming attached mouth upwards to

solid rock or stone, gave rise to hydroids, anemones and

Soil,’’ Journal of Bacteriology, VII, 2, March, 1922. The authors claim

that Thiobacillus thiooxidans will grow in solutions containing no organic

matter. In view of the minute traces of organic matter that suffice for

the growth of bacteria and molds, care must be taken, however, in draw-

ing conclusions from experiments made in flasks or tubes closed in the

ordinary way with cotton-wool plugs and subsequently sterilized in flowing

steam.

18 There is perhaps a possibility that further knowledge of the embry-

ology of Sagitta and its allies might make it necessary to modify this

suggestion. :

498 THE AMERICAN NATURALIST [Vor. LVI

corals, typical inhabitants of the coastal waters, for the

sands and muds at greater depths offered few points of

attachment suffieiently stable.

A Volvox-like colony of simple holozoie flagellates, ac-

cording to MacBride,” commenced to feed upon micro-

scopic organisms lying on the sea bottom, and under these

circumstances only the cells of the lower half of the

colony would be effective feeders. The upper cells, there-

fore, lost their flagella and became merely a protective

layer, which finally grew downwards outside the others

and fixed the colony to the ground. In this way a sponge

was formed. The collar cell, so typical of the group, had

been developed already by the flagellates, its first incep-

tion being perhaps a circle of protoplasmic hairs such as

we find in Pedinella. But this adoption of a fixed habit,

as it were mouth downwards, did not lead very far, and

though there has been much elaboration within the group

itself, the sponges have remained an isolated phylum,

unable to develop into higher forms.

It is in a Ctenophore-like ancestor that we find the line

of development to higher animal groups, and this an-

cestor must have been at one time widely distributed in

the seas. Its immediate descendants are familiar to

every zoological student in the well-known series of pe-

lagie larval forms. Müller's larva, taking to the bottom,

and in its hunt for food gliding over hard surfaces with

its eilia, led to the flatworms; the Pilidium, developing a

thread-like body and creeping into cracks and crevices

to transfix its prey, gave rise to the nemertines. A Tro-

chophore, burrowing in soft mud and sand, developed a

segmented body which gave it later the power of running

on these soft surfaces, and became an annelid worm. An-

other Trochophore, developing a broad, muscular foot,

crept on the sand, and afterwards buried itself beneath

it as a lamellibranchiate molluse, or migrated on to

harder surfaces as the gastropod and its allies. Pluteus,

Bipinnaria, Auricularia, first fixing, as the crinoids still

do, and developing a radial symmetry, afterwards broke

free and wandered on the bottom as sea-urchin, star-fish

19'fTextbooks of Embryology. Invertebrata." London, 1914.

No. 647] PROGRESSION OF LIFE IN THE SEA 499

and cucumarian. Tornaria developed into Balanoglos-

sus, whose structure hints to us that the ascidians and

vertebrates came from a similar stock. All the phyla

thus represented derive directly from the free-swimming

Ctenophore-like ancestor, and only one considerable

group, the Arthropods, remains unaccounted for. The

evolutionary history of an Arthropod is, however, not in

doubt. Its marine representatives, the Trilobites and

Crustacea, came directly from annelids, which, after their

desertion of a pelagic life to burrow in the sea-floor and

run along its surface, again took to swimming, and not

only stocked the whole mass of the water with a rich and

varied life of Copepods, Cladocera and Schizopods, but

gave rise to Amphipods, Isopods, and Decapods, groups

equally at home when roaming on the bottom or swim-

ming above it.

Another important addition to the pelagic fauna we

should also notice here. From the molluses, creeping on

solid surfaces, sprang a group of swimmers, the Cephalo-

pods, which have grown to sizes almost unequaled

amongst the animals of the sea.

All these invertebrate phyla had become established

and most of them had reached a high degree of develop-

ment in the seas of Cambrian times. Amongst animals

then living there are many which have survived with little

change of form until to-day. One is almost tempted to

suggest that the life which the sea itself could produce

was then reaching its summit and becoming stabilized.

Since Cambrian times geologists tell us some thirty mil-

lion years” have passed, a stretch of time which it is

really difficult for our imaginations to picture. During

that time a change of immense moment has happened to

the life of the sea; but if we read the signs aright, that

change had its origin rather in an invasion from without

than in an evolution from within. Whence came that

tribe of fishes which now dominates the fauna of the

sea? It would be rash to say that we can give any but a

speculative reply to the question, but the probable an-

swer seems to be that fishes were first evolved not to meet

20 Osborn, ‘‘ Origin and Evolution of Life,’’ 1918, p. 153.

500 THE AMERICAN NATURALIST [Vor. LVI

eonditions found in the sea, but to battle with the swift

eurrents of rivers, where fishes almost alone of moving

animals can to this day maintain themselves and avoid

being swept helplessly away." It was in response to

these conditions that elongate, soft-bodied creatures,

which had penetrated to the river mouth, developed the

slender, stream-lined shape, the rigid yet flexible muscu-

lar body, the special provision for the supply of oxygen

to the blood to maintain an abundant stock of energy,

and all those minute perfections for effective swimming

that a fish’s body shows. The fact that many sea-fishes

still return to the rivers, especially for spawning, sup-

ports this view, and it is in accordance with Traquair's

classical discoveries of the early fishes of the Scottish

Old Red Sandstone, which were for the most part fresh-

and brackish-water kinds.

Having developed, under the fierce conditions of the

river, their speed and strength as swimmers, the fishes

returned to the sea, where their new-found powers en-

abled them to roam over wide areas in search of food,

and gave them such an advantage in attack and defense

that they became the predominant inhabitants of all the

coastal waters, and as such they remain to-day.

The other great migration of the fishes, also, the migra-

tion from the water to the land, giving rise to amphibians,

reptiles, birds and mammals, must not be left out of ac-

count. The whales, seals and sea-birds, which after de-

veloping on land returned again to the waters and became

readapted for life in them, are features which can not be

neglected. |

And so we are brought to the pieture of life in the sea

as we find it to-day. "The primary produetion of organie

substance by the utilization of the energy of sunlight in the

bodies of minute unicellular plants, floating freely in the

water, remains, as it was in the earliest times, the feature

of fundamental importance. The conditions which control

this production are now, many of them, known. Those

of chief importance are (1) the amount of light which

21 Chamberlin, quoted in Lull, ‘‘Organie Evolution," New York, 1917,

p. 462.

No. 647] PROGRESSION OF LIFE IN THE SEA 501

enters the water, an amount which varies with the length

of the day, the altitude of the sun, and the clearness of

the air and of the water; (2) the presence in adequate

quantity of mineral food substances, especially nitrates

and phosphates; and (3) a temperature favorable to the

growth of the species which are present in the water at

the time. Experiments with cultures of diatoms have

shown clearly that if the food-salts required are present,

and the conditions as to light and temperature are satis-

factory, other factors, such as the salinity of the water

and the proportions of its constituent salts, can be varied

within very wide limits without checking growth. The

increased abundance of plankton, especially of diatom

and peridinian plankton, in coastal waters and in shallow

seas largely surrounded ‘by land, such as the North Sea,

is due to the supply of nutrient salts washed directly

from the land by rain or brought down by rivers. An

exceptional abundance of plankton in particular locali-

ties, which produces an exceptional abundance of all ani-

mal life, is also often found where there is an upwelling

of water from the bottom layers of the sea. These condi-

tions are met with where a strong current strikes a sub-

merged bank, or where two currents meet. Food-salts

which had accumulated in the depths, where they could

not be used owing to lack of light, are brought by the

upwelling water to the surface and become available for

plant growth. The remarkable richness of fish life in

such places as the banks of Newfoundland and the Agul-

has Banks off the South African coast, each of which is

the meeting-place of two great currents, is to be explained

in this way.

Our detailed knowledge of the steps in the food-chain

from the diatom and peridinian to the fish is increasing

rapidly. The Copepod eats the diatom, but not every

Copepod eats every diatom; they make their choice. The

young fish eats the Copepod, but again there is selection

. of kind. Even adult fishes like herring and mackerel,

which were formerly supposed to swim with open mouth,

straining out of the water whatever came in their way,

are now thought largely to select their food.”

22 Bullen, Journ. Mar. Biol. Assoc., 9, 1912, p. 394.

502 THE AMERICAN NATURALIST [Vor LVI

A result of extraordinary interest in connection with

the food-chain has recently been brought to light by two

sets of investigators working independently. In seeking

to explain certain features which he had found in connec-

tion with the growth of the cod, Hjort” undertook a

study of the distribution in marine organisms of the

growth stimulant known as vitamin. Fat-soluble vitamin

was already known to be present in large quantities in

eod-liver oil, and is what probably gives the oil its medic-

inal value. Hjort was able to trace the vitamin, by

means of feeding experiments on rats, in the ripe ovaries

of the eod, in shrimps and prawns, which resemble the

animals on which the cod feeds, and in diatom plankton

and green alge. Jameson, Drummond and Coward*

cultivated the diatom Nitzschia closteriwm, and by a simi-

lar method to that used by Hjort showed that it was

extraordinarily potent as a source of fat-soluble vitamin.

We thus conclude that this substance, so essential to

healthy animal growth, is produced in large quantities

by plankton diatoms, and passed on unchanged to the fish

through the crustaceans which feed on the diatoms. In

the fish the vitamin is first stored in the liver, and with

the ripening of the ovary passes into the egg, to be used

to stimulate the growth of the next generation. Again

we see the fundamental importance of the food-producing

activities of the lowest plant life.

Attention has already been drawn to the suggestion that

fishes developed their remarkable swimming powers in

rivers, in response to a need to overcome the currents,

and that they afterwards returned to the sea, where they

preyed upon a well-developed and highly complex inverte-

brate fauna already fully established there. Their speed

enabled them to conquer their more sluggish predecessors,

whilst they themselves were little open to attack. With

the exception of the larger cephalopods, which are of

comparatively recent origin, and were probably evolved

after the arrival of the fishes, there are few, if any, in-

vertebrates which capture adult fishes as part of their

23 Proc. Roy. Soc., May 4, 1922.

24 Biochemical Journal, 1922.

No. 647] PROGRESSION OF LIFE IN THE SEA 503

normal food. Destructive enemies appeared later in the

form of whales and seals and sea-birds, which had devel-

oped on the land and in the air.

And now in these last days a new attack is made on the

fishes of the sea, for man has entered into the struggle.

He came first with a spear in his hand; then, sitting on a

rock, he dangled a baited hook, a hook perhaps made

from a twig of thorn bush, such as is used to this day in

villages on our own east coast. Afterwards, greatly dar-

ing, he sat astride a log, with his legs paddled further

from the shore, and got more fish.. He made nets and

surrounded the shoals. Were there time we might trace

step by step the evolution of the art of fishing and of the

art of seamanship, for the two were bound up together

till the day when the trawlers and drifters kept the seas

for the battle fleet.

There can be little doubt that in European seas the at-

tack on the fishes in the narrow strip of coastal water

where they congregate has become serious. A consider-

able proportion of the fish population is removed each

year, and human activity contributes little or nothing to

compensate the loss. We have not, however, to fear the

practical extinction of any species of fish, the kind of

extinction that has taken place with seals and whales.

Fishing is subject to many natural limitations, and when

fishing is suspended recovery will be rapid. There is evi-

dence that such recovery took place in the North Sea

when fishing was restricted by the War, though the in-

crease which was noted is perhaps not certainly outside

the range of natural fluctuations. Until the natural fluc-

tuations in fish population are adequately understood,

their limits determined, and the eauses which give rise

to them discovered, a reliable verdict as to the effect of

fishing is diffieult to obtain.

If such problems as these are to be solved, the investi-

gation of the sea must proceed on broadly conceived lines,

and a eomprehensive knowledge must be built up, not

only of the natural history of the fishes, but also of the

many and varied conditions which influence their lives.

The life of the sea must be studied as a whole.

FAMILY RESEMBLANCES AMONG AMERICAN

MEN OF SCIENCE

DR. DEAN R. BRIMHALL

SECRETARY OF THE PSYCHOLOGICAL CORPORATION

Tue fascinating problems that concern the causes of

individual and group differences among human beings

are still with us. Since Galton set out to prove that ‘‘a

man’s natural abilities are derived by inheritance under

exactly the same limitations as are the form and physical

features of the whole organic world ”’ the biological sci-

ences have made many and notable contributions to the

fund of knowledge concerning the derivation ‘‘ of the

form and physical features of the organic world.’’ But

the influences by which individual and group differences

come about, particularly differences in intellectual per-

formance, seem to have been singularly neglected.

The problem has been avoided partly because of the

nature of the material. Human beings are not only com-

plicated in organic construction, but they are mongrel in

breed, the period between generations is long and direct

experimentation impossible. Few scientific problems are

more likely to be disturbed by the bias of the experi-

menter. The American millionaire or European aristo-

erat explains differences in the wealth gathering or

keeping performance of human beings in terms of innafe

ability. To the socialist the expression ‘‘ royal minds ”’

has little basis in fact. Laws, taboos, economic and social

conditions are thought to be the proper explanations of

differences in human behavior. So deeply do the facts

concern the fundamental concepts about the organization

of society that debate with its anecdotal method should

be supplanted by objective method of the best sort avail-

able.

The method of approach used in this study is statisti-

eal. The investigation represents an attempt to deter-

mine some of the differenees or resemblances, the causes

No. 647] FAMILY RESEMBLANCES 505

of which have been so often the subject of debate and

argument. It is necessary to determine what resem-

blances or differences exist before causes can be explained.

This is a study of family resemblances in intellectual per-

formance, particularly in the field of science.

By limiting the problem to the measurement of resem-

blances the advice of a gifted and successful worker in

this field is followed. He writes:

It is impossible at present to estimate with security the relative

shares of original nature, due to sex, race, ancestry and accidental

variation, and of the environment, physical and social, in causing the

differences found in men. e can only learn the facts, ai

them with as little bias as possible, and try to secure more

By this same limitation it is hoped that a serious and

common error will be entirely avoided, namely, the fail-

ure to realize the twofold nature of the problem of in-

heritance as ordinarily discussed. The following analy-

sis is so clear and the need of it so general that it is given

at length.

Most sociological writers and some biologists are confused in their

use of the concept of heredity. When there is discussion of the rela-

tive influence on performance of heredity and environment, by hered-

ity there is sometimes understood the original constitution of the

individual and sometimes his resemblance to parents and other rela-

ives. It is conceivable that the original constitution of son and

father might be exactly the same and yet the individual be so plastic

to environment that under different conditions there would be but

slight similarity between their performances. It is also conceivable

that there might be no similarity between the original constitution

of son and father, and yet the performance of each be determined by

his original constitution almost without influence from environment.

Under which of these extreme hypotheses would the current sociologist

call heredity strong or weak? The word heredity should be reserved

for resemblance due to a common germ plasm and some other word

found for the constitution of the fertilized ovum or zygote; perhaps

the best that can be done is to use this uncouth word. We can then

discriminate between the two distinct questions: What is the resem-

blance between the zygotes of two brothers? How far does the zygote

of an individual determine his performance as an adult? 2

1 Thorndike, ‘‘ Educational Psychology,’’ Vol. III, p. 310.

2 J. McKeen Cattell, ‘‘ Families of American Men of Science,’’ Pop. Sci-

ence Monthly, May, 191 15.

506 THE AMERICAN NATURALIST [Vor. LVI

It must not be inferred that this study is an attempt

to determine ‘‘ how far the zygote of an individual de-

termines his performance ’’ or ‘‘ what is the resemblance

between the zygotes of two brothers." It is primarily

a statistical measurement of resemblance in performance

with particular reference to performance in science.

With the results of these measurements at hand, some-

thing about the resemblances of the zygotes of near rela-

tives and about how far the zygote of an individual de-

termines his performance may be estimated.

By resemblance is meant, not identity, but degree of

similarity. Galton, with the idea of particulate inherit-

ance in mind, early insisted on measuring resemblances

as deviations from an average. He justly claims to have

been the first to ‘‘ introduce the law of deviations from

the average into the discussions on heredity."? Almost

forty years later he is found insisting that ‘‘ proba-

bility is the foundation of eugenics.’’* It is here that the

statistical method avoids the pitfalls of proof by anec-

dote. Given a group, selected for some particular sort

of performance, the number in any particular degree of

relationship showing similar performance may be de-

termined and compared with a similar group of the gen-

erality. This is the method used in this study.

The group studied consists of approximately 1,000

American men of science and their families. The wives

and the near relatives of the wives of the men of science

are included in the data, and the results of the compari-

sons offer perhaps the most unique contribution of the

investigation. The statistical data include only relatives

of a degree no more remote than first cousin. These rela-

tives are: brothers and sisters, sons and daughters,

fathers and mothers, nieces and nephews, uncles and

aunts, grandparents and first cousins.

It may be well here to anticipate a criticism of the use

of the term resemblance. Since the group of men of sct-

ence is made up of persons of known distinction one since

3 ‘f Hereditary Genius,’’ Preface, 1869.

4 Spencer lecture, 1907.

No. 647] FAMILY RESEMBLANCES 507

resemblance of near relatives is measured in terms of the

number of the latter who become distinguished, it is as-

sumed that distinction in any intellectual performance is

evidence of resemblance. Thus, a psychologist whose

cousin is a psychologist may be said without much fear

of contradiction to resemble that relative, but does he

really resemble his brother, who is a well-known judge?

Does he resemble his distinguished father, a former presi-

dent of the University of Michigan, a gifted adminis-

strator?® Apparently, that has been assumed. The fact

is, they do resemble each other in so far as they vary in

the same direction from the average person in the direc-

tion of performance.

The selection of the group of scientific men used has

become a classic in individual psychology and need not

be related in detail here. Briefly, it may be said, the

Workers in science were grouped in twelve general divi-

sions as follows: Anatomy, anthropology, botany, chem-

istry, geology, mathematies, pathology, physies, physiol-

ogy, psychology and zoology. The workers in each

Science were arranged in an order of merit by ten leading

men in each of those sciences. The average position as-

signed each man, together with the probable error, was

computed. Thus each man's position with the reliabil-

ity of the figure describing his position was determined,

and a thousand of the leading men of science were selected

as a group for study. Two selections were made, the

first in 1903, the second in 1910. The lists varied some-

what in composition due to deaths, changes of position

within the group, removal to a foreign country and the

like." The positions attained were not published, that

5 Since the above was written the psychologist, James Rowland Angell,

has become a member of the National Academy of Sciences and the presi

dent of Yale University. The question banman less pertinent but the

case more dramatic.

6J. McKeen Cattell, ‘‘ American Men of Seience,’’ appendix, second

edition, 1910.

A third selection has now been made and will furnish material for a

continuation of this study. See ‘‘ American Men of Science,’’ third edi-

tion, J. McKeen Cattell and Dean R. Brimhall, 1921.

508 THE AMERICAN NATURALIST [Vou. LVI

.information being confidential, but the names of those

achieving a position in either selection were marked with

an asterisk in the handbook in which they were published.

They are referred to in this study as the starred group.

The members of the starred group were asked to re-

port among other data the names of relatives as follows:

Relatives who have done scientific work with ‘designation of relation-

ship and direction of work.

Relatives (with designation of relationship and direction of work)

sufficient to warrant inclusion in a book such as “ Who’s Who,”

say among the first twenty thousand of a hundred million popula-

tion.

Relatives (with designation of relationship and direction of work)

who have done scientific work or work of distinction in other

directions

Polas Cattell, to whom sole credit is due for gath-

ering the original d writes concerning requests and

replies:

Of one thousand one hundred and fifty-four scientific men from

whom information in regard to their families was requested 1,036

replied and 118 did not. Of the replies 16 were blank, sometimes ac-

companied by the explanation that the information was not readily

attainable or the like, 7 were to the effect that the information would

be sent later or the like, 13 were received too late, 25 were very im-

perfect, 975 were usable and in most cases complete. This is an

unusually full reply to a questionnaire. For example, in answer to

an inquiry in regard to noteworthy relatives addressed to 467 fellows

of the Royal Society, Sir Francis Galton received 207 useful replies,

and the completely available returns “scarcely exceeded 100

Following a thorough investigation of that vet of the

data concerning relatives, in an attempt to supplement

and correct them by the use of biographical and genea-

logical handbooks, the writer sent 186 letters to as many

of the men of science, with a report of what had been

found in the way of additional information, and asked

for corrections and additions. Second and third requests

were sometimes sent and in some cases a personal visit

to the man of science or near relative was made. As a

result the number of usable replies for this sue proved

to be 956.

8 ‘Families of American Men of Science," Popular Science Monthly,

May, 1915.

No. 647] - FAMILY RESEMBLANCES 509

Of these 956 records 22 were incomplete in the case of .

relatives more remote than parents, children, brothers

and sisters. Twenty-three were incomplete in kinships

more remote than those mentioned. Fully half of the

replies of those found to have distinguished relatives

were originally incomplete either in names or designation

of relationship of names or both. The brother relation-

ship, where it would be supposed complete information

would be available, had 84 eases in the original data.

This number was raised to nearly 150 through consulta-

tion of the handbooks mentioned below. Not more than

25 of those added were found to have first biographical

mention at a date later than that of the request for in-

formation.

It is unlikely that the ten per cent. who failed to reply

.did so beeause of lack of relatives to report; it is un-

likely, beeause that information was a relatively small

part of the total requested. Two hundred and fifty-six,

or about one fourth of the number replying, were found

to have relatives of distinetion or relatives who were

scientific men; since the other three fourths replied,

though they had no relatives to report, it seems reasonable

that those who did not reply did not represent a select

group. This is further shown to be the case in the num-

ber of cross relationships between the two groups. There

are found to be brother and cousin relationships that were

reported by some of those replying that would have been

reported if the others had replied.

The objective criterion used is biographical inclusion

in one or more of the three following handbooks: ** Amer-

ican Men of Science," ‘‘ Who's Who in America,’’ ** Ap-

pleton’s Cyclopedia of American Biography." Both

editions of ‘‘ American Men of Science,’’ that is, the edi-

tions of 1903 and 1910, were consulted, and biographies

found in either were counted. Those found in the orig-

inal edition of ** Appleton's Cyclopedia,’’ published in

1887-88, together with the appendix of 1900 and all ten

volumes of ** Who's Who in America," covering the pe-

510 THE AMERICAN NATURALIST [Vor. LVI

riod from 1910. to 1918, were also included. The first

edition of ‘‘ American Men of Science’’ contains more

than 4,000 men of science, of entire North America, the

second edition about 5,500 names. *' Appleton's Cyclo-

pedia of American Biography (1887-88)"' contains

‘above 15,000 prominent native and adopted citizens of

the United States, including living persons, from the earli-

est settlement of the country." In the appendix of

1899-00 ‘‘ will be: found nearly 2,000 notices of Ameri-

cans who won renown in the war with Spain . . . and of

persons of the New World who have become prominent

in the peaceful activities of life during the decade,’’ be-

tween the appearance of the two publications.. The ten

volumes of ‘‘ Who’s Who in America’’ contain 36,915

biographical sketches. The first volume contains 8,602

biographies, while Volume 10 has 22,968. It is evident

that the three publications have varying standards of

selection, and it becomes necessary to get some statement

of the degree of fineness of selection represented by each.

If the reader doubts the validity of any one of the three

measures he may disregard those found in that handbook

because the lists of names and tables are arranged to that

end. That there are biographies of persons included

that are out of place is likely and that omissions of others

quite deserving occur is also likely, but inclusion repre-

sents unusual performance that is a reality.

There is given below the biographical account of one

of the persons in the study as it is given in the three dif-

ferent handbooks. Besides adding reality to the data in

the lists it will afford a comparison of the characteristic

methods employed by the editors of the different publi-

cations. The accounts give some idea of the interesting

and voluminous records that would be necessary if no

more than a brief history of each individual were given.

The histories of the men of science and their relatives,

if abbreviated in the most careful manner, would make a

fair-sized volume. One need only imagine the size of the

volume necessary to give an account of the unusual per-

No. 647] ` FAMILY RESEMBLANCES 511

formance of an equal number of people taken at random

to see the difference.

BIOGRAPHICAL Account or EDWARD CHARLES PICKERING, AMERICAN

MEN or SCIENCE, 0

Piekering, Prof. Edward C(harles), Harvard College Observatory,

Cambridge, Mass. * Astronomy, Astrophysics. Boston, Mass, July

19, 46. B.S, Harvard, 65, A.M, 80, LL.D, 03; California, 86; Michi-

gan, 87; Sc.D, Victoria (England), 00; LL.D, Chicago, 01; Ph.D,

Heidelberg, 03; LL.D, Pennsylvania, 06. Instr. math, Lawrence

Sci. Sch, Harvard, 65-67; prof. physics, Mass. Inst. Tech, 67-77;

astron. and director, Harvard Col. Observatory, T7- Bruce Gold

Medal, Pacific Astron. Soc; Rumford, Draper, Bruce, two Royal

Astron. Soc. and other medals. Nat. Acad; F.A.A. (v. pres, 77);

Astron. and Astrophys. Soc. (pres, 06-08); Philos. Soc. (v. pres,

09) ; fel. Am. Acad; Wash. Acad; hon. mem. N. Y. Acad; cor. mem.

Berlin Acad; Soe: astron. de France; Inst. de France; Royal Soe.

‘Upsala; Soc. Lynceorum Nova; St. Petersburgh Imp. Acad; Socie-

ties of Cherbourg, Palermo, etc. Stellar photometry and spectros-

copy.

ACCOUNT GIVEN IN WHo's Wuo 1n AMERICA, Vor. 6, 1910-11

Pickering, Edward Charles, astronomer; . b.. Boston, July 19, 1846.

s. Edward and Charlotte (Hammond) P; brother of William Henry

P. (q.v.) ; ed. Boston Latin School; S.B, Lawrence Scientific Sch.

(Harvard), 1865 (hon. A.M., 1880; LL.D., univs. of Cal, 1886,

Mich., 1887, Chicago, 1901, Harvard, 1903, Pa., 1906; Ph.D., Heidel-

berg, 1903; D.Se., Victoria U., Eng., 1900; m. Lizzie Wadsworth,

d. Jared Sparks, Mar. 9, 1874. Instr. mathematics, Lawrence Scien-

tifie Sch., 1865—7; Thayer prof. physies, Mass. Inst. Tech., 1867-76;

prof. astronomy and dir. Harvard Coll. Obs. since 1876. Estab-

lished 1st physical lab. in U. S.; under his direction, invested capi-

tal and income of the observatory has increased fourfold. Study

of light and spectra of the stars have been spl. features of his work;

devised meridian photometer and made 1,400,000 measures of the

light of the stars with it. By establishing an auxiliary sta. in

Arequipa, Peru, Southern stars are also observed, extending the

work from pole to pole, in which 200,000 photographs are included.

Accompanied Nautical Almanac expdn. to observe total eclipse of

sun, Aug. 7, 1869; mem. U. S. Coast Survey expdn. to Xeres, Spain,

Dee. 22, 1870. Awarded Henry Draper medal for work on astron.

physies; gold medals, Rumford, 1891, Bruce, 1908, Royal Astron.

Soc., 1886, 1901. Mem. Nat. Acad. Sciences; hon. mem. of Socs.

at Mexico, Cherbourg, Liverpool, Toronto, Upsala and Lund; mem.

Royal Astron. Soc., Royal Instn. Acaad. dei Lincei, Royal Prussian,

and Royal Irish socs., Royal Soc. of London, Institute de France,

Imperial Acad., St. Petersburg; pres. Astron. and Astrophys. Soc.

512 THE AMERICAN NATURALIST | [Vor. LVI

America, 1906-9; fellow Am. Acad. Arts and Sciences; founder and

1st pres. Appalachian Mountain Club; mem. Century Assn. New

York. Author: Elements of Physical Manipulation, and 60 volumes

of annals and other publieations of Harvard Coll. Observatory.

Address: Harvard Observatory, Cambridge, Mass.

ACCOUNT GIVEN IN APPLETON'S CYCLOPEDIA OF AMERICAN

BIOGRAPHY,

Pickering, Edward Charles, astronomer, b. in Boston, Mass., 19

July, 1846, was graduated in civil engineering course at the Law-

rence scientific school of Harvard in 1865. During the following year

he was called to the Massachusetts institute of technology as assistant

director of physics, of which branch he held the full professorship

from 1868 till 1877. Prof. Pickering devised plans for the physical

laboratory of the institution, and introduced the experimental method

of teaching physics at a time when that mode of instruction had not

been adopted elsewhere. His scientific work of these years consisted

largely of researches in physics, notably investigations on the polari-

zation of light and the laws of its reflection and dispersion. He also

described a new form of spectrum telescope, and invented in 1870 a

telephone receiver, which he publicly ‘exhibited. He observed the

total eclipse of the sun on 7 Aug., 1869, with the party that was sent

out by the Nautical almanac office, at Mt. Pleasant, Iowa, and was a

member of the U. S. coast survey expedition to Xeres, Spain, to

observe that of 22 Dec., 1870, having, on that occasion, charge of

the polariscope. In 1876 he was appointed professor of astronomy

and geodesy, and director of the observatory at Harvard, and under

his management this observatory has become one of the foremost in

the United States. More than twenty assistants now take part in

investigations under his direction and the invested funds of the

observatory have inereased from $176,000 to $654,000 during his

administration. His principal work since he accepted this appoint-

ment has been the determination of the relative brightness of the

stars, which is accomplished by the means of a meridian photometer,

an instrument specially devised for this purpose, and he has prepared

a catalog giving the brightness of over 4,000 stars. Since 1878 he

has also made photometer measurements of Jupiter’s satellites while

they are undergoing eclipse, and of the satellites of Mars and other

plication of photography to astronomy, as a Henry Draper memorial,

and the study of the spectra of the stars has been undertaken on a

scale that was never before attempted. A fund of $250,000, left w

Uriah A. Boyden (q.v.) to the observatory, has been utilized for the

special study of the advantages of very elevated observing stations.

Prof. Pickering has also devoted attention to such objects as moun-

tain surveying, the height and velocity of clouds, papers on which he

No. 647] FAMILY RESEMBLANCES 513

has contributed to the Appalachian Club, of which he was president in

1877, and again in 1882. He is an associate of the Royal astronomical

society of London, from which in 1886 he received its gold medal for

photometrie researches, and besides membership in other scientific

societies in the United States and Europe he was elected in 1873 to

the National academy of sciences, by which body he was further

honored in 1887 with the award of the Henry Draper medal for his

work on astronomical physics. In 1876 he was elected a vice-presi-

dent of the American association for the advancement of science, and

presented his retiring address before the section of mathematics and

physics at the Nashville meeting. In addition to his many papers

which number about 100, he prepared “ Reports on the Department of

Physies," for the Massachusetts institute of technology, and the “ An-

nual Reports of the Director of the Astronomical Observatory," like-

wise editing the “ Annals of the Astronomical Observatory of Harvard

College." He has also edited with notes * The Theory of Color in

Relation to Art and Art Industry," by Dr. William von Bezold (Bos-

ton, 1876), and he is the author of * Elements of Physieal Manipula-

tion" (2 parts, Boston, 1873-6).

The raw material of the investigation is found below

in the lists of men of science and their relatives. Sta-

tistieal treatment of these data will follow. "They are

arranged so that any competent observer can test their

validity. While great effort has been made to have the

details reliable, it is possible that mistakes may be found

in the designation of relationship, but it is thought that

such mistakes are few if any.

Tue MEN or SCIENCE AND THEIR NEAR RELATIVES

OF DISTINCTION

The names of the men of science and their near rela-

tives of distinction are given at the left of the page. The

name of the man of science comes first and is followed by

a short dash. The names of the relatives follow and are

preceded by the letter or letters which tell the relation-

ship. The first name, for example, is Allis, Edward

Phelps; he has a cousin (FSiS, a father's sister's son),

Callahan, Henry White, whose work is in edueation. The

biography of this relative is found in ** Who's Who in

Ameriea." When the name of a relative is printed in

small capitals it shows that the person is known for work

514 THE AMERICAN NATURALIST [Vor. LVI

in science. The direction of the performance of the rela-

tives is given at the right of the name. The handbook

or books containing his biographical account are shown

by the abbreviations at the right. These abbreviations

are to be understood as follows: A.M.S, American Men

of Science (if preceded by an asterisk the person is in

the starred group of men of science); W.W, Who’s Who

in America; A.C, Appleton’s Cyclopedia of American

Biography. |

Any degree of relationship can be conveniently and ac-

eurately deseribed by one, or a combination of two or

more, of the following seven letters: S for son, D for

daughter, B for brother, Si for sister, F for father, M for

mother. Thus, paternal grandfather can be written as

FF, meaning father's father, maternal grandfather, MF,

meaning mother's father, FBS meaning first cousin or

father's brother’s son, etc. These symbols precede the

name and show the kinship of the person to the man of

Science.

The men of science are arranged according to the sci-

ence in which they were recorded as obtaining a place in

the starred group. The groups are arranged alphabeti-

eally, beginning with the anatomists and closing with the

zoologists.

penc fet ge P ists nr qus A eren ud

and near relatives i

of distinction sadeqene pt aP

of relatives

Anatomists

Allis, Edward Phelps— :

FSiS Callahan, Henry White Education W.W.

Bardeen, Charles Russell—

Bardeen, Charles William Education Ww

— Robert Russe

Bensley, Beijaitk Arthur Zoology A.M.S.

TER Thomas—

WARREN, JONATHAN MASON Surgery A.C.

XY WARREN, JOHN COLLINS Surgery A.C.

MBS WARREN, JOHN COLLINS Surgery *A.M.S; W.W:

* AC

FBS Dwight, Wilder Warfare A.C.

FBS Dwight, William Warfare W.W.

No. 647] FAMILY RESEMBLANCES

Greenman, Milton Jay—

FBS GREENMAN, JESSE MORE "e

Meyer, Arthur Will

B Meyer, Balthasar Henry Polit. econ,

Spitzka, pate Anthony—

F TZKA, Epwarp A, Neurology

Anthropologists

Dorsey, George Amos—

Dorsey, CLARENCE W. Soil physies

B DORSEY, HERBERT GROVE Physics

Farrand, Livingston—

Farrand, Max History

B Farrand, Wilson Edueation

Hough, Walter—

FBS Hoven, THEODORE Physiology

Astronomers

Doolittle, Charles Leander—

DOOLITTLE, Eric Astronomy

Doolittle, Erie—

DOOLITTLE, CHARLES L. Astronomy

Frost, Edwin Brant—

B Frost, GILMAN DuBois Anatomy

Lowell, Pereival—

Lowell, Abbott Lawrence Education

Si Lowell, Amy Poetry

MF Lawrence, Abbot Diplomaey

FSiD Paid Ella Lowell Lyman Edueation

MSiS R , ABBOTT LAWRENCE Physies

MSiS otek, Asme Arehitecture

Pickering. Edward Charles—

B PICKERING, WILLIAM H. Astronomy

FB ER CHARLES Ethnol; Bot.

Pickering, William Henry—

B PICKERING, EDWARD C. ronomy

FB PICKERING, CHARLES Ethnol; Bot.

Pritchett, Henry Smith—

F Pritchett, Car Waller Ministry; Educ.

515

*A.M.S; W.W.

W.W.

A.M.S; A.C.

WAW,

A.M.S.

W.W.

*A.M.8; W.W.

*A.M.S; W.W;

A.C.

* A.M.S.

A.C.

W.W.

516 THE AMERICAN NATURALIST [Vor. LVI

Searle, Arthur— Astron; Religion A.M.S; W.W;

B SEARLE, GEORGE MARY A.

Stone, Ormond— Journ; Finance

B Stone, Melville Elijah W.W AC,

Wright, William Hammond—

Wright, Johanna Maynard Organization W.W.

Botanists

Beal, William James—

MSiS STEERS, JOSEPH BEAL Zoology A.M.S; W.W.

Bessey, Ernst Athern—

F BESSEY, CHARLES EDWIN . Botany ; *A.M.S; WW.

Bessey, Charles Edwin—

S BESSEY, ERNST ATHERN Botany *A.M.S; WW,

Blakeslee, Hoe Franei

B Blakeslee, assent Hubbard History W.W.

Blakeslee, Franeis Durbin Ministry W.W.

Bray, Wil'iam—

MBS or FSiS Foster, LUTHER Botany W.W.

Campbell, aii xiu ms

B CAM ARD DEM. Chemistry *A.M.S; W.W.

B wii Mus Munroe Law W.W

F Campbell, James V. Law A.C.

Coker, William Chamber

Coker, James Lide Manufacturing W.W.

FBS COKER, ROBERT IRWIN Zoology A.M.S; W.W.

Coulter, John Merle—

B COULTER, STANLEY Botany *A.M.8; WW.

S COULTER, JOHN GAYLORD Botany A.M.S.

FBS Counter, SAMUEL Monps Botany A.M.S.

Coulter, Stanley—

B ULTER, JOHN MERLE Botany . *A.M.S; W.W;

A.C.

BS COULTER, JOHN GAYLORD Botany A.M.S.

FBS CouLTER, SAMUEL MoNDs Botany A.M.S.

Coville, Fred Vernon—

B COVILLE, LUZERNE Medicine oe v m.

Davis, Bradley Moore—

FSiS Woop, RoBERT WILLIAMS Physics "AMB: W.W.

No. 641]

Duggar, Benjamin Minge—

B DUGGAR, JOHN FREDERIC

Earle, Franklin Sumne

i orne, Mig n Earle

F EARLE, PARKER

Fernald, Merritt Lyndon—

B FERNALD, ROBERT H.

F FERNALD, MERRITT C.

Greenman, Jesse More—

REENMAN, MILTON JAY

Halstead, pides David—

SiS RCHILD, DAVID G.

SiS pma Edwin Milton

Kearney, Thomas H.—

i MB Miner, Charles Wright

` Maebride, Thomas Huston—

FSiS Sterrett, James M.

Mec Gifford—

ine

FAMILY RESEMBLANCES

Agronomy

Fietion

Horticulture

Mech. eng.

Edue; Physics;

Math

Anatomy

Botany

Education

Warfare

Ministry; Hist.

hot, Amos Law; Politics

* Pinehot, James W. Trade

MF Eno, Amos R. Finance f

Pound, Roscoe—

Si Pound, Louise Philology

Robinson, Benjamin Lincoln—

obin ecd James H. History

Shull, George Har

B SHULL, eae ALBERT Zoology

B Scholl, John W Literature

i Chemists

Acheson, Edward Goodrich—

FB eson, Marcus Wilson Law

FBS Acheson, Alexander M Civil Eng.

FBS Acheson, Alexander W. Med; Politics

FBS Acheson, Ernest Francis Journal;

olities

FBS Acheson, Marcus W. Jr. Law

FSiS Brownson, Marcus A, Ministry

FSiD Brownson, Mary Wilson Literature;

Math

pady Wilder Dwight—

Bancroft, George

History

517

AMS; W.W.

W.W.

A.C.

A.M.S; W.W.

*A.M.S; W.W.

W.W

W.W.

518 THE AMERICAN NATURALIST [Vou. LVI

Blair, Andrew Alexander—

F Blair, Francis Preston Warfare; Polities A.C.

FF Blair, Francis Preston Journal; Polities A.C.

Burgess, Charles Frederick—

Burgess, George H. Railway Eng. W.W.

Campbell, Edward DeMille—

B CAMPBELL, DovGLAs H. Botany "AMS: WW.

B Campbell, Henry Munroe Law W.W.

F Campbell, James V. Law A.C.

Chatard, Thomas Marean—

B Chatard, Franeis Silas Edue; Ministry; W.W; A.C,

FB Chatard, Frederick Warfare A.C.

Crafts, James Mason—

` Mason, Jeremiah Law AC.

Dabney, Charles Willia

F Dabney, ober: Lewis Educ; Ministry A.C.

Doremus, Charles Avery— :

F DongEMUS, ROBERT O. Chemistry A.M.8; W.W;

FM Doremus, S. P. (Haines) Philanthropy A.C.

iege ie Franeis Perry— :

Keener, John C, Ministry : WW; AC.

Franklin, Edward Curtis—

B FRANKLIN, WILLIAM f. Physies *A.M.S; W.W.

Freer, Paul Casper—

B Freer, espa W. Art (Painting) W.W.

B Prem, OTTO Tie Laryngology W.W.

are Eugene Woldemar—

ARD, JULIUS Math; Geodesy A.C.

HILGARD, THEODORE C. Biology A.C,

F HILGARD, THEODORE E. Law A.C.

SiS Tirrman, OTTO HILGARD Geodesy A.M.S; W.W.

Jackson, Charles Loring—

FSi Lowell, Anna C. J. Education A.C.

FF Jackson, Patrick Tracy Manufacturing A.C.

i tles

FSiS CABOT, ARTHUR Tracy Surgery .

MBS Loring, William Caleb Law W.W.

FSiS Lowell, C. R. Warfare A.C.

Lewis, Gilbert Newton—

FB wis, Homer Pierce . Education W.W.

No. 641]

Lloyd, John Uri—

B LLOYD, Curtis GATES

Loeb, Morris—

Loeb, James

More, Riehard Bishop—

F Moore, William Thomas

MF Bishop, Richard Moore

Morely, Edward Willia

B Moreley, John Sidós

ae Charles Edward—

BS Munroe, James Phinney

ne Musrot, Kirk

Norris, James Flaek—

B Norris, RICHARD C.

Norton, Thomas Herber

MB HORSFORD, "uu NORTON

MF Horsford, Jerediah

MBD HORSFORD, CORNELIA

FBS Norton, LEWIS MILLS

Noyes, -William Albert—

i Davidson, Hanna M. N.

Orndorf, William Ridgely—

MF Ridgely, James Lot

Osborne, Thomas Burr—

MB BLAKE, ELI WHITNEY

MF Blake, Eli Whitney

Palmer, Chase—

FSiS Harris, George

MBS Chase, George

Pellew, Charles Ernest—

F Pellew, ey Edward

MB Jay

MF J M, iene

MBS Jay, William

Pond, George Gilbert—

iB OND, FRANCIS JONES

Reese, Charles Lee— ic

Reese, Frederick Focke

Riehards, Theodore William—

B RICHARDS, HERBERT M.

F Richards, William Trost

FAMILY RESEMBLANCES

Botany

Finance; Archeol,

Ministry; Editing

ae H

Polities; Trade

Ministry; Edue.

Mfg; Writing

Fietion; Journal

Surgery

Chemistry

Are

Chemistry

Edueation; Lit.

Law

Chem; Physies

Invention; Mfg.

Ministry; Lit.

Edue; Law

Philanthropy

Diplomacy

Law

Chemistry

Ministry

Botany ;

Art (Painting)

519

W.W.

WW,

WW.

W.W.

*A.M.S; W.W.

W.W; A.C.

520

Sadtler, Samuel Phili

F dtler, Benjamin

MB Sehmucker, B. Melanehton

MB Schmucker, Samuel M

MB Schmucker, Samuel D.

MF Sehmucker, Samuel S.

MBS ScHMUCKER, SAMUEL C.

Sanger, Charles Robert—

Sanger, George P.

Saunders, inis Perey

B SAUNDERS, ice. E.

B SAUNDERS a Ai

B Savausas, WILLIAM

F SAUNDERS, duin

Sherman, Henry Clapp—

B SHERMAN, FRANKLIN, JR.,

FBS Sherman, Frank D.

Shimer, Porter William—

F HIMER, HERVEY W.

Smith, Edgar Fahs—

SMITH, ALLEN JOHN

Stieglitz, Julius Osear—

Stieglitz, Alfred

Stillman, John Maxon—

STILLMAN, STANLEY

FB Stillman, Thomas Bliss

FB Stillman, William James

FBS STILLMAN, THOMAS B

Stillman, Thomas Blis

FB Stillman, TRAMA Bliss

Stillman, William James

FBS STILLMAN, JOHN Maxon

FBS STILLMAN, STANLEY

Tuckerman, Alfred—

MB Gibbs, George

MB GisBs, OLIVER Wo.corr

FF Tuckerman, Joseph

MF GIBBS, Gro E

FSiS Broke, GEORGE F.

VanSlyke, Lucius Lincoln—

S ANSLYKE, DoNALD D.

THE AMERICAN NATURALIST

[Vor. LVI

Ministry A.C

Ministry A.C.

Writing A.C.

Law W.W.

Educ; Theol. A.C.

Botany A.M.S; W.W

Law A.C

Chemistry A.M.S.

ee * A.M.S; W.W

Ornith; B A.M.S.

naire A.M.S

Entomology M.S.

Architect; Poetry W.W.

Geology A.M.8; W.W.

Pathology A.M.S; W.W.

Photog; Chem. W.W.

Surgery W.W.

Manufacturing A.C.

History; Journal W.W; A.C.

Chemistry *A.M.S; W.W.

Manufacturing A.C.

History; Journal W.W; A.C.

Chemistry *A.M.8; W.W:

Surgery Ww

History W.W.

Warfare A.C.

Antiquarianism A.C

Chemistry *A.M.8; W.W;

: A.C.

Ministry A.C

Geology A.C.

Geology *A.M.S; W.W

Chemistry A.M.S.

No. 647]

Venable, Francis Preston—

FAMILY RESEMBLANCES

F VENABLE, CHARLES S. Astronomy

MF McDowell, James iti

Waller, Elwyn—

B Waller, Frank Architecture

Geologists

Ashley, George Hall—

B Ashley, Roscoe Lewis

Becker, George Ferdinand—

MSiS Tuckerman, Bayard

Brooks, Alfred Hulse—

Brooks, THOMAS B.

Si Paige, Gaspard B.

Chamberlin, Thomas Corwin—

S CHAMBERLIN, ROLLIN T.

Clarke, John Mas

B Clarke, ond Mason

Dana, Edward Salisbury—

Dana, JAMES DWIGHT

MB SILLIMAN, BENJAMIN JR.

MF SILLIMAN, BENJAMIN

Davis, William Morris—

Mott, James

MM Mott, Lucretia

Farrington, Oliver Cummin

B a

ngs—

ington, ` Wallace R

B Tüsxmeron,

Regents Grove Kar

Gilbert, e: Sheldon

Grant, Ulysses Sherman—

F Grant, Lewis Addison

Hague, Arnold—

B HAGUE, JAMES DUNCAN

F Hague, William

Harris, Gilbert Dennison—

HARRIS, ROLLIN ARTHUR

Epwarp H.

History; Econ. .

Ministry

Chemistry

Biography;

Hist

eology

Fiction

Geology

Ministry

Geology

Chemistry

Chem; Geol.

Philanthropy

Min

inistry

(Quaker)

Journalism ;

Chemistry

Art

Law; Warfare

Geology

Ministry

Geodesy

521

W.W; A.C.

A.C.

W.W; A.C.

*A MS; W.W.

522

Hayes, Charles Willard—

UM LLEN

Hitcheock, staples Henry—

F TCHCOCK, EDWARD

B adu EDWARD

BS HITCHCOCK,

Irving, John Duer—

F Irvine, ROLAND DUER

Jaggar, Thomas Augustus, Jr.—

F Jaggar, Thomas A

Keith, Arthur—

MSiS GALE, Hoyr STODDARD

Mathews, a, Bennett—

B Mathews, Shailer

Merriam, John Campbell—

B Merriam, Charles E.

Merrill, Te Perkins—

B RILL, Lucius H.

Penrose, Richard Alex. Fullerton—

B Penrose, Boies

B PENROSE, CHARLES B.

B Penrose, Speneer

F PENROSE, RICHARD A. F,

.FB Penrose, Clement B.

FF Penrose, Glasi B.

FBS Penrose, Stephen B. L.

Pumpelly, Raphael—

D Smyth, Margarette P.

M Pumpelly, Mary Weller

Rice, William North—

S ICE, EDWARD LORANUS

€ yya aa

, HUGH LENN

io Hole punte Fins

MF Hodge, Charles

Smith, James Perrin—

B Smith, Charles Forster

Stevenson, John Jam

MB Wil

MBS Willson, David Burt

EDWARD, JR.

THE AMERICAN NATURALIST

Mathematies

Geol; Edue.

Hygiene

Geology

Ministry

Bel

Edue; Theol.

Polities; Hist.

Chemistry

Polities ; Law

Law

Edue; Philos.

Art (Painting)

Poetry

Theology

Philology

Philol; Theol,

Philol; Theol.

[Von. LVI

W.W; A.C.

W.W.

A.M.S; W.W.

W.W; A.C,

No. 647] FAMILY RESEMBLANCES

Taylor, Frank Bensley—

F Stewart, Robert

Vaughn, Thomas Wayland—

FBS "Vaughn, Horaee Worth

Weed, brun Harvey—

Weed, Samuel Riehards

Weller, Stewart—

Tarran, J. T.

White, David—

MSiS Kent, Charles Foster

Willis, Bailey—

Willis, Nathaniel P. i Poetry

FB Willis, Richard Storrs Music

Winchell, Alexander Newton—

B WINCHELL, Horace V. Geology

F WINCHELL, NEWTON H. Geol; Archeol.

FB CHELL, ALEXANDER Geology

FB Mise Bando R. Edue;

Journalism

Winchell, Newton Horace—

B -.WINCHELL, ALEXAND Geology

B Winchell, Samuel R, uc;

J ournaliam

S WiNCHELL, ALEX."N. Geology

S WINCHELL, HoRACE V. Geology

FBS Winchell, Benj. La Fon Ry. Management

FB Winchell, James M Ministry

Wright, id pies Daneel

B WRIGHT, CHARLES WILL Geology

Mathematicians

Birkoff, George David—

MB Droppers, Garrett Polit. Econ.

Coolidge, Julian Low

B Co Wie eae ibald C. History

B Coo. , John Gardiner Diplomacy

B Coalides: J. Randolph Jr. Architecture

FB Coolidge, Jeffe Diplomaey

FBS Coolidge, T. Jefferson Jr. Finance

Fine, Henry Burchard—

FF Fine, John Polities; Law

Polities; Law

Finanee; Lit.

Law

Hist; Archeol.

523

524 THE AMERICAN NATURALIST (Vor. LVI

Franklin, Fabian—

Heilprin, Michael History; A.C,

Sociol.

MF Heilprin, Phineas M. Semities x.

MBS HEILPRIN, ANGELO Geology FANS Wows

: A.C,

MBS Heilprin,. Louis Philology : W.W; A.C.

Halsted, George Bruce— :

F Halsted, Oliver Spencer Politics A.C.

FF Halsted, Oliver Spencer Philology A.C.

Johnson, William Woolsey— ent

B Johnson, cae Fred. Philology; Math. W.W.

McClintock, Emory—

McClintock, John Educ; Ministry A.C.

T Eliakim Hastings—

Moore, David Hastings Educ; Ministry W.W.

Pierce, Charles Santiago Sanders—

eirce, Herbert H. D. Diplomaey W.W.

B PEIRCE, JAMES MILLS Math; Edue. 1MB: WOW,

; A.C

F PEIRCE, BENJAMIN Mathematies A.C,

-FB PEIRCE, CHARLES HENRY Chem; Med. A.C.

FF Peiree, Benjamin Lines A.C.

(Harvard)

MF Mills, Elijah Hunt Polities A.C.

Roe, Edward Drake Jr—

FB oe, Franeis Asbury Warfare W.W; A.C.

Slichter, Charles Summer—

BS SLICHTER, WALTER I, Elee. Eng. A.M.8; W.W.

Van Vleek, Edward Burr—

VAN VLECK, JoHN M. Astron; Math. A.M.8; W.W;

A.C.

Veblen, Oswald—

F VEBLEN, ANDREW A. Math; Physies A.M.S; W.W.

FB Veblen, Thorstein B. Economics W.W

Wilson, Edwin Bidwell—

Wilson, Frank E, Polities; Law W.W.

Pathologists

Biggs, Herman Miehael— :

FBS Bices, GEORGE PATTEN Pathology A.M.S,

Blumer, George—

LUMER, GEORGE ALDER Neurol; Med WVW.

No. 647]

Cabot, "ise Clarke—

FBS

FBS cues GODFREY L.

Christian, Henry Asbur

FBS Christian, dhyo L.

pnus pond Williams—

Cus Y

SiS CREHORE, WILLIAM

Dana, Charles Loomis—

Dana, John Cotton

Dock, George—

Si Dock, Lavina L.

Ernst, Harold Clarence—

rnest, George um

B ERNST, OSWALD

MF OTIS, GEORGE ALEX.

Flexner, Simon—

Flexner, Abraham

Hurd, Henry a

jB Hur

Loeb, Leo—

pup teur William George—

MacCAL

` MACCALLUM, GEORGE A

Mitchell, Silas Weir—

S M

Musser, John Herr—

MBS or FSiS Herr, Edwin M.

Park, i Halloek—

Hallock, William S.

MSiS Johnson, William H.

Putnam, James J.—

Jackson, James

LOEB, JACQUES

ITCHELL, JOHN K.

S Mitehell, Langdon E.

MrTCH JOHN K

FAMILY RESEMBLANCES

Med; Surg.

Chemistry

Polities; Lit;

Geology

Law

Physies; Eng.

Mech. Eng.

Library

Medieine

Law

Astron; War;

Eng.

Surgery

Edueation

Psychiatry

Zoology

Anatomy

Ornith; Med.

Neurology

Playwriting

Chem; Med

Elec. Eng.

Editing;

Ministry

Ministry ;

Philos,

Clin, Med.

525

W.W.

*A.M.8; W.W.

*A.M.S; WW.

W.W.

AMS; W.W.

A.C.

W.W.

526

Ravenel, Mazyek Porcher—

FBS RAvENEL, HENRY W.

MBS PorcHer, FRANCIS P.

Thayer, William Sydney— :

B pach Ezra Ripley

F Thayer, James Bradley

MSiS titus Edward

Warren, John Collins—

F WARREN, JONATHAN M.

FF WARREN, JOHN suai

FSiS Dwicut, THOM

Williams, Herbert Upha

Si Williams, iis, _ Sprague

FSiS Sprague, Carle

Welch, William Henr

THE AMERICAN NATURALIST

Botany

Botany; Chem.

Law

Art (Painting)

Surg; Med.

Surgery

Anatomy

Sociolo

Finance; Art

FSiS Cowles, John Guiteau Finanee

MBS Collin, Frederick Welch

MBS Collin, Charles Avery Law

Physicists

E Cleveland—

" ABBE, CLEVELAND, JR.

S ABBE, M

FSiS Smith, Guilford

Abbot, Charles Greeley—

FBS Abbot, Henry Larcom

FBS Abbot, Edwin Hale

Bauer, Louis Agricola—

B Baver, WILLIAM C.

Bell, Alexander Graham—

F EX, MELVILLE

Bell, Louis—

F Bell, Louis

FB Bell James

FB ELL, JOHN

FB BELL, LUTHER V

FB Bell, Samuel Dana

MB Bouton, John Bell

MF ues Nathaniel

FF Bell, uel

FBS Bell, Peas Newell

Surg; Physics

Meteorol; Geog.

siol.

urg;

inanee;

Philanth.

Eng; Warfare

Finance; Law

Elec. Eng.

Physiology

Warfare; Chem.

Polities; Law

Editing; Med

Medicine

Polities; Law

A.C.

WW.

[Vor. LVI

No. 647]

Buckingham, Edgar—

FF Buckingham, Joseph T.

Crehore, Albert Cushing—

B CREHORE, WILLIAM W.

MSiS Cusuine, Harvey W

MSiS Cusuine, HENRY PLATT

MSiS Cushing, William E.

gne Harvey Nathaniel—

AVIS, NATHANIEL F.

Duane, William—

B Duane, Russel

FF Duane, William

Franklin, William Suddards—

B FRANKLIN, EDWARD C.

Hering, Carl—

B HERING, RUDOLPH

Humphreys, William Jackson—

FB Humphreys, Milton W.

Ives, Frederick Eugene—

S Ives, HERBERT EUGENE

Jackson, Dugald Caleb—

B JACKSON, JOHN PRICE

B Jackson, William B.

FSiS Cravath, Paul Drennan

Kent, Norton Adams—

B Kent, William

Kimball, Arthur Lalann

MBS Fisher, Samuel S., Jr.

Kinsley, Carl—

F Kinsley, William W.

Lyman, Theodore—

F LYMAN, THEODORE

FF Lyman, Theodore

Magie, William Franeis—

F Magie, William Jay

Mann, Charles Reborg—

F arles H.

FSi Miller, Harriet Mann

FAMILY RESEMBLANCES

Editing;

Publish.

Bridge Eng.

Pathology

Geology

Mathematics

Law

Publishing

Chemistry

Hydraulic Eng.

Philology

Physics

Elec. Eng.

Engineering

Law ;

Philanthropy

Finance

inistry ;

M Educ.

Politics;

Law

Math; Theology

Zoology

Philanthropy

Polities; Law

Inventing;

Editing;

„Ministry

Ornith; Writing

527

A.M.S; W.W.

W.W.

A.C.

*A.M.8; W.W.

AMS.

W.W; AC.

W.W.

A.C.

W.W.

528

Mendenhall, Thomas Corwin—

MENDENHALL, C. E.

Mendenhall, Charles Elwood—

MENDENHALL, T. C

More, Lewis Trenchard—

B More, Enoch Anson, Jr.

B More, Paul Elmer

MF Elmer, Lueius Q. C.

Northrup, Edwin Fite

B Northrup, Eos J ris

F Northru sa nsel J

FB NongTH e. pi

MB Fiteh, nie us

Parson, William Barclay—

B Parsons, Harry DEB.

Roteh, Abbott Lawrence—

B teh, hur

_MF Lawrence, Hei

FBS Rorcu s M.

MSiS Lowell, cum posce

MSiS LOWELL, PERCIVAL

MSiD Lowell, Amy

Saunders, Frederick Albert—

B SAUNDERS, ARTHUR P.

B SAUNDERS, CHARLES E.

B SAUNDERS, WILLIAM E.

F SAUNDERS, WILLIAM

Stevens, Moss usps

, JOHN

MB one JOSEPH

MF LECONTE, LEWIS

MBS LECONTE, JosEePH N.

Stewart, Osear Milton—

STEWART, GEORGE W.

Stewart, George Walter—

STEWART, Oscar M.

Trowbridge, Charles Christopher—

Trowbridge, S. B. P.

F TROWBRIDGE, W. P.

THE AMERICAN NATURALIST

Physics

Fiction

oetry;

Editing

Polities ;

Law

Pathology

Editing; Edue.

Mech. Eng.

Architeeture

Diplomaey

Pediatries

Edue.

Astronomy

Poetry

Chemistry

otany

Horticulture

Physies

Geology

Botany

Mech. Eng.

Physies

Architecture

Engineering

Law

*A.M.S; W.W.

*A M.S; W.W;

E eH

W.W.

A.C.

.W.

W.W; A.C

A.M.8; W.W

WwW.

A.M.8; W.W

A.C

AC.

"ANB. W.W

*A.M.S; WW

A.C.

W.W.

*A.M.8; W.W

A.M.S

A.M.S,

A.C.

W.W; AC

A.M.S; W.W

*A.M.S; W.W

"AMB; W.W.

W.W.

A.C.

[Vor. LVI

No. 647] FAMILY RESEMBLANCES 529

Very, Frank tiens

FB ery, Jones Lit; Ministry A.C,

FSi Very, sn Louisa A. Literature W.W: AC.

Wead, Charles Dasson—

MB Kasson, John Adams Polities WW; A.C.

Whitman, Frank P

MSiS Taylor, piget Monroe Edue; Ethies W.W; AC.

MSiD Bissell, Mary Taylor Medieine W.W.

Wood, Robert Williams—

MBS Davis, BRADLEY Moore Botany *A.M.S; W.W

Wurts, Alexander Jay—

B Wurts, John W.W

MF Jay, JOHN CLARKSON Medieine A.C

Pen John—

ZELENY, ANTHONY Physics *A.M.8; W.W:

: ZELENY, CHARLES Zoology *A.MB; W.W.

Zeleny, Anthony—

B ZELENY, CHARLES Zoology *A.M.S; W.W.

B ZELENY, JOHN Physies *A.M.S; W.W.

Physiologists

Curtis, John wore

Curtis, Edward Medicine W.W; A.C

B Curtis, sans Bridgham Warfare; Eng. .C.

3B ien xam i William Lit; nblis shing W.W.

B , Constan Art (Painting) W.

BD du MU Music W.

Dawson, Perey Millard—

F Dawson, Samuel quede"

FSiS Apams, FRANK Daw

Hare, Hobart Amory—

F Hare, William Hobart

FF Hare, George Enlen

MF Howe, Mark A. DeWolfe

MBS Howe, Mark A. DeWolfe

Henderson, Yandell—

MB YANDELL, DaviD WENDEL

MF YANDELL, LUNSFORD

Hough, Theodore—

FBS Hoven, WALTER

Hist; Publishing A.C,

Geology A.M

Ministry A.C,

Ministry. AG. .

Ministry W.W; A.C.

Editing W.:

Surgery A.C,

Geology; Med, A.C,

Anthropology *A.M.8; W.W.

530 THE AMERICAN NATURALIST [vor LVI

Lee, - Schiller—

LEE, LESLIE ALEXANDER re Geo *A.M.8; W.W.

3 Lee, John Clarence dici W;W

F Lee, John Stebbins dee Ministry W. W.

pea panera

Lusk, WILLIAM T. Physiol; Med. A.C,

de nds. inb HM. Finanee; AC.

Polities

Sewall, Henry—

F SEWELL, THOMAS Medicine — ALC.

Psychologists

Angell, James Rowland—

B Angell, Alexis Caswell Law W.W.

F Angell, James Burrill Educ; W.W; AC.

; Diplomacy

MF CASWELL, ALEXIS Astron; Educ. A.C.

FBS ANGELL, FRANK Psychology *A.M.S; W.W.

Angell, Frank—

FB Angell, James Burrill Educ; W.W; AC.

FBS Angell, morte Caswell W.W.

ANGELL, JAMES R. Psychology *A.M.S; WW.

Bently, Madison— ` ; ;

Bentiy, Charles E. Ministry W.W; A.C.

sie William Lowe—

Bryan, Enoch Albert Edueation W.W.

Cattell, ~ a a

B NRY WARE Pathology A.M.S; W.W.

F pa nee wii Educ; Ministry A.C.

FB Ca ttell, Merce ` Finance; A.C.

Polities

FBS Cattell, Edward James Econ; Geog; WW.

Lit. .

FBS Cattell, William A. Engineering W.W.

Delabarre, Edmund Burke—

: Delabarre, Frank Alex. Med; Dentistry W.W.

Dewey, John—

B Dewey, Davis Rich Econ; Statisties W.W.

Hall, Granville Stanley—

MBS Brats, EpwArp ALDEN Meteorology WW:

No. 647] FAMILY RESEMBLANCES

Jastrow, Joseph—

B Jastrow, Morris Theol; Sociol.

F Jastrow, Mareus Philology

Patrick, George Thomas White—

Patrick, Mary Mills Edue; Writing

sages Edmund Clark—

SiS SHINN, CHARLES H. Botany

xb SHINN, MrinicENT W. Psychology

Stratton, George Maleolm—

B Stratton, Frederick S. Law

Strong, Charles Augustus—

F Strong, Augustus H. Educ; Theology

Thorndike, Edward L

B Thorndike, one H. Philology

Wells, Frederie Lyman—

Wells, Benjamin Willis Language; Econ.

Woodworth, Robert aani

4B Woodworth

, Frank G. Educ; Ministry

MB Sessions, nus. R. Polities; Agrie.

Zoologists

Andrews, genes Allen—

B DREWS, HORACE Civil Eng.

FF Tct Ethan Allen Lexieography

Bruce, Charles Thomas—

Armstrong, William Musical

Criticism

18i Benough, Elisa A. Fiction

Clark, Hubert Lyman—

F CLARK, WILLIAM 8. Chemistry

MF Richards, Willia Education

MBS WILLISTON, pinnis L. Mech. Eng.

MBS Williston, Samuel :

Crampton, Henry Edward—

MB Miller, Charles Henry Art (Painting)

Dahlgren, Ulrie—

FB Dahlgren, Ulric arfare

FF DAHLGREN, JOHN A. Math; Warfare

Dall Wiliam Heal

Dall, and Henry A. Minist

Dall, Caroline Wells H. Leeturing; Lit.

531

W.W.

AMS; W.W.

W.W.

W.W; A.C.

W.W.

WW;

532 THE AMERICAN NATURALIST . [Vor. LVI

M Ree Charles Benediet—

Davenport, William E. Sociol; Ministry W.W.

us Davenport, Frances G. History W.W.

Drew, Gilman Arthur—

Drew, William Lineoln Law W.W.

Forbes, eas Alfred—

S RBES, ERNEST B. Entomology WW.

BS ise RosERT H. Soil Chemistry A.M.S; W.W.

Gage, Simeon Henry—

Si GAGE, MARY Sanitation W.W.

Gerould, John Hir

Gerould, gore Hall Philology W.W.

B Gerould, James Library - W.W.

Glaser, Otto Charles—

F GLASER, CHARLES : Chemistry A.M.S.

Grave, Caswell—

RAVE, BENJAMIN H. Zoology , AMS,

Gulick, John Thomas—

S GULICK, ADDISON Zoology A.M.S.

F Gulick, Peter Johnson Ministry A.C.

BS GULICK, LUTHER H. Physiol; Edue A.M.8; W.W

BS Gulick, Sidney Lewis Ministry ; .W.

Writing

BD Jewetts, Frances Gulick Hygiene W.W.

FBS Gulick, Charles Burton Philology W.W.

Hargitt, Charles Wesley—

S HanarTT, GEORGE T. Geology | A.M.S.

Herrick, Charles Judson— ; ;

B HERRICK, CLARENCE L. Neurology A.M.S,

Howard, Leland Ossian—

MSiS Stimson, Henry lewis Polities ; W.W.

Warfare

MSiD Keith, Dora Wheeler Portrait W.W.

Painting

Jayne, Horaee—

B Jayne, Henry La Barre Law W.W.

F JAYNE, DAVID Medieine; A.C,

Pharmacy

Lefevre, George—

B Lefevre, Albert Philosophy W.W.

B Lefevre, Arthur Edueation W.W.

No. 647]

Lillie, Frank Rattray—

B LILLIE, RALPH STAYNER

Lillie, Ralph Stayner—

B LILLIE, FRANK R.

Loeb, Jacques—

B OEB, LEO

Mayer, Alfred Goldborough—

F MAYER, ALFRED M,

FB Mayer, Franeis B,

Merriam, Clinton Hart—

Si BAILEY, FLORENCE M.

FB Merriam, Augustus C.

—€— Maynard Mayo—

etealf, Irving Wight

B METCALF, WiLMOT V.

FBS Metcalf, Wilder S.

Montgomery, Thomas Harrison—

B Montg A.

omery, James

MB Morton, James St. Clair

B MonTON, THOM

MF Morron, SAMUEL G.

Moore, John Perey—

B Mover, HENRY FRANK

Newman, Horatio Haekett—

Newman, Albert Henry

Nutting, Charles Cleveland—

MB Hunt, Henry

MB Hunt, Lewis Cass

Osborn, Henry Fairfield—

Osborn, William Church

MF Sturges, Jonathan

Peckham, George Williams—

Peckham, R. Wheeler

FBS Peckham, R. Wheeler, Jr.

FBS Peckham, Wheeler H

Rice, Edward Loranus—

F Rice, WILLIAM NORTH

FAMILY RESEMBLANCES

Zoology

Pathology

Physies

Art

Ornitholo

Archeol;

ogy

Finance;

Ministry

Theol; History

Ethnol; Path;

Zoology

History; Theol.

Warfare

Law; Polities

Trade

Philol.

533

* A.M.S.

*A MS; W.W.

*AMS; W.W.

AMS; W.W.

W.W.

534 THE AMERICAN NATURALIST [Vou. LVI

gaa si Robert Wilso

Shufeldt, a W. Warfare A.C.

Stone, Witmer—

Stone, Frederiek D. History; A.C.

Library

True, Frederick William—

B TRUE, ALFRED CHARLES Educ; A.M.8; W.W.

Agriculture

F True, Charles Kitredge Ministry

Verrill, Addison Emery—

VERRILL, ALPHEUS H. Zoology A.M.S; W.W.

Ward, cag Baldw

F WARD, Bisnis H. Bot; Microscopy A.M.S; W.W;

A.C,

FSi Ward, Anna Lydia Ethnol; WW} AC.

Lexicog.

Weed, Clarence Moores—

Weep, Howarp Evarts Entomology A.M.S.

Zeleny, Charles—

ZELENY, ANTHONY Physics *A.MS; W.W.

B ZELENY, JOHN Physies "AMS: W.W.

RELATIVES OF THE WIVES OF MEN OF SCIENCE

The same general plan used in the listing of the men of science and

their distinguished relatives is followed below.

Anatomists

Donaldson, "um uu Herbert—

F , Calve Arehiteeture A.C.

MB Me Mun. ld Architecture AC.

Anthropologists

McGee, Mrs. W. J.—

F NEWCOMB, SIMON Astronomy "AMB; W.W:

: AC,

MB Hassler, Ferdinand A. Med; Literature W.W.

Astronomers

Doolittle, Mrs. Charles Leander—

B Wolle, Fred Music W.W.,

S DOOLITTLE, ERIC Astronomy *A.M.S; WW.

F WOLLE, FRANCIS Botany A.C.

No. 647] FAMILY RESEMBLANCES

Frost, Mrs. Edwin Brant—

Hazard, Marshal Editing

Holden, Mrs. Edward Singleton—

B CHAUVENET, REGIS Mining Eng.

B CHAUVENET, WILLIAM M. Chemistry

F CHAUVENET, WILLIAM Mathematics

Loud, Mrs. Frank Herbert— j

ILEY, WALTER H. Mining Eng.

Mitehell, Mrs. Samuel Alfred—

F DuMBLE, Epwin T. Geology

Pickering, Mrs. Edward Charles—

r park

rks, History; Educ.

MF Silsbee, Nathaniel Polities

Pritehett, Mrs. Henry Smith— À

FB McAlister, Ju im Warfare

FF McAllister, Nath. Hall Law

FBS McAllister, Ward _ Jurisprudence

ye gos William Hammond—

eib, Samuel aw;

Hortieulture

Botanists

Atkinson, Mrs. George Franeis—

Kerr, W. C Geology

Bessey, Mrs. Charles E.—

S Bessey, ERNST A. Botany

Clements, Mrs. Frederie Edward—

Si Sehwartz, Julia Literature

Coulter, Mrs. John Merle—

S COULTER, JOHN G. Botany

Coulter, Mrs. Stanley—

id Roswell iban Ministry

FB Post, Truma Ministry

fox, Mrs. William Gilson—

Si Horsford, Cornelia Areheology

F HonsroRp, EBEN N. Chemistry

M Horsford, Mary L. H. Poetry

FF Horsford, Jedediah . Warfare;

Polities

Ganong, Mrs. William Francis—

B arman, Bliss Poetry; Editing

535

A.M.S; W.W.

*A.M.S; W.W.

W.W.

A.M.S.

W.W.

536 THE AMERICAN NATURALIST [Vor. LVI

Greenman, Mrs. Jesse More—

MSiS Hartranft, John F. Polities A.C.

Pinchot, Mrs. Gifford—

F Bryce, Lloyd 8. Editing; W.W.

Polities

MF Cooper, Edward Finanee; Ww.

Polities

Ramaley, Mrs. Franei

JACKSON, Runs Ophthalmology W.W.

T 2 Joseph Nelson— :

Sims, Charles R. Ministry; Edue. A.C.

Stone, Mrs, George Edward—

F CLARK, HENRY JAMES Botany - A.C.

Wilson, Mrs. William Posell—

FF Williams, Charles K. Polities A.C.

Chemists

Bigelow, Mrs, Samuel Lawrenee—

Harrison, Joseph Railroad A.C,

Building

Burgess, Mrs. Charles Frederick—

B Jackson, Charles F. Literature W.W.

Cushman, Mrs. Allerton Seward—

B Hoppin, Joseph Clark Archeology ; W.W.

Art

FB Hoppin, Augustus Art; Literature A.C.

FB oppin, Thomas Ast: Seulptoring A.C.

FB Hoppin, William Jones Stage; Editing A.C.

Franklin, Mrs. Edward Curtis—

B Seott, Charles Fred. Polities W.W.

Gies, age William John—

Tressler, David Education AC,

es Tressler, Victor Edueation W.W.

Kahlenberg, Mrs. Louis— ;

B EALD, FRED. DeForest Botany "AMS; WVW.

Long, Mrs. John Harper—

FB Stoneman, George Warfare AC.

Marshall, Mrs. John—

F Ww

ORMLEY, T. G. A.C.

No. 647] FAMILY RESEMBLANCES

Mine. Mrs. Charles Edward—

F BARKER, GEORGE FRED.

Osborne, Mrs. Thomas Burr—

JOHNSON, SAMUEL WM,

Palmer, Mrs. Chase—

F Edwards, Howard

FBD Edwards, Louise

Pellew, Mrs. Charles Ernest—

CHANDLER, CHARLES F.

FB CHANDLER, WILLIAM H.

Richards, sare Theodore

F Thayer, edi Heny

Sanger, Mrs. Charles Robert—

F Davis, And

FB Davis, Hasbrook

FB Davis, Hora

FB Davis, John C. B

FF Davis, John

a 0

FBS Davis, John

Saunders, Mrs. Arthur Perey—

Es s Brownell, Silas B.

Shimer, Mrs, Porter William—

B Sandt, George W.

Talbot, Mrs. Henry Paul—

FSiS Baker, Newton D.

Tassin, Mrs. Wirt—

F Moran, Thomas

M Moran, Mary Nimo

FB Moran, Edward

Peter

. FBS Moran, John Leon

FBS Moran, Edward Perey

FBD Moran, Annette

Van Slyke, Mrs. Lucius L.—

8 Van SLYKE, DONALD D.

Physies

Chemistry

due; i

Linguisties

Literature

Chemistry

Theology

Numismaties

are

Manufaeturing

Diplomaey

Polities

Law; Diplomaey

Law

Ministry;

Editing

Law; Diplomaey

Art; Exploration

*A.M.8; W.W;

A.C.

*A.MS; W.W;

A.C

W.W.

W.W

"AMS: WW:

A.C.

AMS; WW.:

.C.

W.W; A.C

A.C

A.C.

A.C,

‘AC

A.C,

W.W

W.W.

WW: AC

A.C.

A.C,

Ww AU

W.W; AC

WwW

A.M.S.

538 THE AMERICAN NATURALIST [Vor. LVI

Venable, pm Francis Preston—

anning, Jam Jurisprudenee W.W.

FB NAE iones C. Jurisprudenee A.C.

Wiechman, Mrs. Ferdinand G.—

B Damrosch, Frank Musie W.W; A.C.

B Damrosch, Walter Musie W.W; A.C.

F Damroseh, Leopold Musie AJ

F Mrs. Harvey Washington—

Kelton, John C. Warfare; A.C,

Sociol.

Geo ogists

Brooks, Mrs. Alfred Hulse—

F BAKER, FRANK Anatomy *A.M.B; WW.

Chamberlin, Mrs. T. C

S CHAMBERLIN, R. T. Geology A.M.8; W.W.

Cross, Mrs. Whitman—

FBS Places Naas L Exploration; A.C.

Eng.

Eastman, 2» Charles—

F ‘LARK, ALVAN G. Astronomy A.C.

FF CLARK, ALVAN Astronomy A.C.

Gannet, Mrs. Henry—

FSiS Gerdon, Seth C. Surgery W.W.

MSiS Howe, Lucien Ophthalmology W.W.

Grant, Mrs. Ulysses Sherman—

B WINCHELL, ALEX. N. Geology * A.M.8; WW.

B WINCHELL, Horace V. Geology A.M.8; W.W.

F WiwcHELL, NEWTON H. Geology *A.M.8; W.W;

A.C.

FB WINCHELL, ALEXANDER Geology AC,

FB Winchell, Samuel R. Edue; Lit. W.W.

.Harris, Mrs. Gilbert Dennison—

B Stoneman, George Warfare A.C.

Hitchcock, Mrs. Charles Henry—

F Ba

arrows, E. P. Linguisties A.C.

Hobbs, Mrs. William Herbert—

S Kimball, Alonzo Art W.W.

FSiS Banister, HENRY Geol; Med. A.M.S.

Mathews, Mrs. Edward Bennett—

B WHITMAN, FRANK P. Physies *A.M.S; WW.

No. 647] FAMILY RESEMBLANCES 539

Pirsson, Mrs. Louis Valentine—

F B

RUSH, GEORGE JARVIS Mineralogy *A.M.8; W.W;

A.C.

oe Mrs. Raphael—

Smyth, Margarita P. Art W.W.

vt Hill Edward B. Musie W.W.

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No. 647]

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(To be continued)

AUTOPHORIC TRANSPLANTATION, ITS THEORY

AND PRACTISE

PROFESSOR HANS PRZIBRAM

BIOLOGISCHE VERSUCHSANSTALT DER AKADEMIE DER

WISSENSCHAFTEN, VIENNA

Ir a machine breaks down, the mechanical engineer has

four ways of repairing it. He may discard the broken

parts and reconstruct the whole on a smaller scale; he

may fabricate the missing part and fit it into its right

place again; he could also take a piece from another

machine of more or less similar type, as long as an ex-

change is made possible by the material of the parts,

soldering the broken pieces together or fixing them by

screws, wires, etc.; or lastly he may simply exchange

the broken part for a whole one, first taking the former

out of the broken machine at the points where it was

joined, and refitting the new part, taken in like manner

out of a similar machine by the same means, in the place

of the first. An organism is often just as badly in want

of repair as a machine of human fabric. In comparing

the two I do not wish to enter here into the controversy

of Mechanism versus Vitalism. No vitalist will deny

that the body of an animal, let us say of vertebrate or

arthropod type, is built up of various contrivances the

physicist calls machines, and that its functions are best

described in physical and chemical terms. It is not the

machinery of organized forms that he would throw doubt

on, but the mechanical or chemical nature of its driver.

Now, when living machinery is broken or maimed, there

are the same four possibilities of repair stated above.

The organism may shed such parts as are now super-

fluous for its reduced size and reconstruct itself on the

basis of a proportionately diminished form, as in small

pieces of planarians, a process called *' Morphallaxis,’’

by T. H. Morgan. Secondly, a missing part may be

548

No. 641] AUTOPHORIC TRANSPLANTATION 549

manufactured anew by the remaining body of the ani-

mal, such ‘‘ Regeneration ’’ not being uncommon even in

whole extremities of amphibians and crayfish. But, un-

fortunately, in the warm-blooded vertebrates this faculty

is very limited, not extending much beyond the repair of

small pieces of tissue, and never including a whole organ

or appendage. It has therefore long been customary in

human medicine to try to replace lost parts by ‘‘ trans-

plantation ’’ of cornea, skin, muscle, bone, or even nerve

and blood vessel. Without regard to the composition of

the injured part, small pieces or larger portions have

been taken from the same or from another individual,

and again without special orientation have been grafted

upon the wound. All sorts of fastenings have been tried,

bandages, plaster, wires, ligatures, but mostly with poor

results. The same methods and many others have been

applied in experimental zoology, but only when embry-

onic stages which had not functioned before the operation

were used have good results been achieved. Neverthe-

less it has been demonstrated by A. Carrel that even

whole limbs and kidneys may be again healed back in

mammals and in the ease of the latter again become func-

tionally active. But the tedious method of sewing every

sinew, blood vessel and nerve together seems to have pre-

vented till now the general application of this discovery.

Carrel’s method, as also that of other surgeons, must be

compared to the third method of the engineer, when he

is soldering or fixing a broken piece on to another, trying

to repair the machine without taking it to pieces. Now

it is generally simpler to take out the injured piece of

a machine, by unscrewing or unsoldering or even by

striking it out of the whole by sheer force, so that its

connections give way at the points of least resistance,

and to replace it by a new one of exactly the same form,

than to try and fix the broken parts together again at

the point of breakage. Is there a possibility of applying

this fourth method of the engineer to the organism? One

will, perhaps, at first be inclined to doubt this proposi-

550 THE AMERICAN NATURALIST [Vor. LVI

tion. The vitalist will now come forward and claim that

the organism is not constituted by parts simply fastened

together at certain points, that its unity is the cause of

its function; the mechanist will be inclined to doubt the

possibility of whole organs regaining their function

by ‘‘ exchange " in animals without high regenerating

power, for he has been trained to believe in the destruc-

tion of function by the severing of the nerve.

Let us turn to facts. Certain animals, widely distrib-

uted through the animal kingdom, practise the faculty of

shedding appendages or other parts of their body at cer-

tain preformed breaking points. This ‘‘autotomy’’ is

also observed in the Crinoid, Antedon rosaceus. Work-

ing at the Naples Station in 1900 on the regeneration of

‘these Crinoids I wanted to find out if the color in regen-

erating arms would be influenced by the color of the vis-

ceral mass. Now Antedon shows a great variety of very

distinct shades, such as bright yellow, carmine red and

chocolate brown. The visceral mass, easily shed by the

animal, was transplanted in proper orientation to a speci-

men of different color, also void of its viscera. It was

immediately accepted by the new owner and clutched

tightly to the calyx, as is the usual thing with the normal

animal. The connections between the new visceral sac

and the body were soon restored, the exchange succeeding

in every ease. Mouth and anus, both situated on the sur-

face of the visceral sae, became functional again. It is

clear that here there is a case of the fourth method of the.

engineer, namely the replacement of a missing part by a

new one of exactly the same form fixed in at the same

connecting points as before. One difference is apparent:

in the machine there will be little if any activity on the

part of the receiver or the new part, whilst in the Crinoid

the newly fixed parts are reunited by internal forces. If

we want to understand the ‘‘ exchange "' followed by func-

tion, it is therefore necessary to know the nature of these

forces. Is it possible to account for them on the ground

of our present knowledge of living matter? Can we con-

No. 641] AUTOPHORIC TRANSPLANTATION 551

ceive the organism as an engineer mending his own body?

When the visceral mass of Antedon is not replaced, a new

sac is regenerated by the creature. As in all cases of

regeneration known to me, it is nothing else than an ac-

celeration of growth going on normally at slower rate,

but in the same direction and sense. From this theoreti-

eal standpoint, which has been proved to be correct over-

and over again, we can be satisfied that there are growing

forces in the Antedon sufficient to ensure the attachment

of the new visceral sac.

We have heard that in higher animals regeneration is

not as ready to supply lost parts, and as soon as growth

ceases, for instance in the imago of insects, the faculty

of restoring missing limbs is lost. But a certain degree

of repair has been noticed and experimentally tested even

here, for instance the closing of holes pricked in the in-

tegument of beetles, and even the resprouting of torn-

out wings as mere skin duplicatures. In vertebrates a

good deal of physiological regeneration is always going

on in the tissues, and transplanted pieces of living tissue

often become attached in a short time by connective tissue

and blood vessels growing over and into them. Will ex-

change of organs lead under certain conditions to their

functional restoration also in such animals as these?

The first condition must be the possibility of removing

the part to be replaced always in the same place and man-

ner, so as to be sure that it will comprise just the same

material and fit in again in the corresponding place of

the new host. Planes of preformed breakage would an-

swer best to this condition, but they are generally pre-

cluded by the second condition that must be fulfilled,

namely retention of the implanted organ by the own forces

of the recipient. Such forces may be divided into three

groups: first, the natural friction of a mass pressed into

a socket, also aided by atmospheric pressure; secondly,

the active aid of muscle and nerve clutching the im-

planted organ and preventing it from falling out of its

place; thirdly, the clotting of the body fluids, gluing, as

552 THE AMERICAN NATURALIST [Vor. LVI

it were, the graft to the stock. During the last two years

my pupils and myself have tried to extend this method,

which I now call ** autophorie ” or self-retaining trans-

plantation, to other cases than the visceral sac of Ante-

don, and we have found that under these conditions func-

tion can be restored in a degree unknown till now, at

least in developed animals.

The eye of vertebrates may be described as a ball-

shaped camera movable by three pairs of levers in all

directions of space, connected with its supply of chemi-

cals by the blood vessels and in communication with its

operator, the brain, by the optic nerve. If these fixing

strings are severed, there is scarcely any attachment to

the surroundings save some connecting tissue of unspe-

cialized sort. The ‘‘ camera "' itself will not be injured,

if the whole eyeball be taken out of the orbit, and there

is scarcely a possibility of altering the points of sever-

ance if the enucleation be made quickly and with decision.

If the eye is restored to its orbit, it will therefore be

possible for all the above-mentioned connections to join

again. This was observed as long ago as 1906 by Rug-

gero Pardo in Triton, who made experiments on the neces-

sity of the presence of the optic nerve for the regenerative

process in the eye of this amphibian. Unintentionally

he had excised the eyeball with the nerve and was much

astonished at its reattachment to the orbit. But will eye-

sight be restored with this reattachment? Pardo was not

able to convince himself of this fact, although on histo-

logical examination he found the optic nerve regenerated.

I have suspected for some time that the vertebrate eye

might furnish good material for the restoration of fune-

tion by autophorie transplantation, as it will in many

forms be retained in the orbit by friction and atmos-

pherie pressure alone, aided also in some cases by the

eyelids elosing over the eyeball, and by its great surface

securing wide contact with the blood issuing into the

orbit after extirpation. My own first experiments to

realize this expectation in new-born rats failed.

No. 647] AUTOPHORIC TRANSPLANTATION 553

In the new-born rat, as in many mammals, the eyes are

tightly closed and the lids connected by tissue. This

seemed to afford favorable conditions for the exchange

of eyes, as they would be kept in place by the tight closure

of the eyelids. Having severed the lids, I interchanged

the eyes and, as expected, the eyelids shut again tightly

and kept the eyeballs in place. But when the eyelids

opened again at the normal time, the eyes had grown on,

although they were not functional, and totally disap-

peared in time. Disappointed at this failure, the experi-

ments were discontinued. It is now pretty certain that

this poor result was due to the unfavorable conditions

obtaining in very young mammals, for we are now able

to demonstrate the correctness of my original supposi-

tion. Theodor Koppányi, a young Hungarian student,

working under my direction in the ‘‘ Biologische Ver-

suchsanstalt ’? in Vienna, has succeeded in making the

autophorie transplantation of the eye in a variety of

species, extending from fish to mammal. The work of

Pardo on Triton was confirmed, and older rats yielded

excellent results. It seems that in the young stages of

rats there were difficulties in the way of the eye obtaining

a sufficient supply of blood, since also in Koppanyi’s ex-

periments it was far easier to get the eyes to become

reattached and functional in older specimens.

Indeed, it is probable that the pressure of the eyelids

exerted on the replaced eyeball in the new-born rats is a

hindrance. Grown rats do not close the eyelids tightly

upon the eyeballs, so that it is even advisable to pin the

lids or sew them together for a day or two, lest the ani-

mal whisk out the implanted eyes or seratch at them be-

fore they are attached sufficiently firmly to withstand such

treatment.

We have been able to show that these replanted eyes

are funetional, all possible tests yielding positive results

and being in striking contrast to those in blinded ani-

mals. Microscopical examination of sections through

1For details of these experiments I must refer to our previous short

. 554 THE AMERICAN NATURALIST [Vor. LVI

replanted eyes, which had again regained their function,

has been made by Professor Walter Kolmer, of the Physi-

ologieal Institute, University of Vienna, and the re-in-

growth of the severed optic nerve-fibers into the optic

thalamus is beyond doubt. Professor Kolmer, as all

other authorities, to whom the animals with functioning

replanted eyes were shown, stated that they would

scarcely have believed the fact, without having them-

selves seen and tested it. Some oculists even refused to

believe what they saw, taking refuge in far-fetched ex-

planations for the absolutely normal behavior of the rats

and for the connection of retina and brain in anatomical

and microscopical preparations. But is the restoration

of function in the vertebrate eye really in contradiction

to the facts known to us concerning the regeneration in

this animal type? If we resort to our theory of regen-

eration as accelerated growth, moving on the same lines

as normal differentiation, and waning with higher spe-

cialization, it is necessary to inquire into the normal de-

velopment of the eye and optic nerve, before answering

this question. The vertebrate eye grows from multiple

origins, the nervous elements being derived from a fold

of the central nervous system (brain). It is generally

believed that the nerves of the brain grow in centrifugal

direction and are incapable of regeneration, as one does

not observe regeneration-cones at the peripheral end of

sectioned central nerves as a rule. Ramón y Cajal, on the

other hand, thinks that this inability to regenerate is

only a consequence of secondary difficulties, regeneration

at least commencing when the right nurture is given:

this may be accomplished by inserting degenerating

nerve-pieces into the pathway of the sectioned nerve. At

any rate there would be but little chance of quick and suf-

ficient regeneration, if the eye depended on the nerve

growing into it from the brain. Fortunately, as is well

known, the fibers of the optie nerve in ontogeny grow

communications in the Akademischer Anzeiger, Wien; they will be followed

by publieation in extenso in the Archiv für Entwicklungsmechanik, 1922.

No. 647] AUTOPHORIC TRANSPLANTATION 555

centripetally from the retina towards the thalamus op-

ticus. In regeneration this same process need only be

repeated. Edward Uhlenhuth, while working at our

** Biologische Versuchsanstalt,” proved in 1912 that the

optic nerve of salamander eyes implanted on the back

of the same species grows centripetally towards the spinal

cord and even in several instances united with the next

spinal ganglion. These transplanted eyes were of course

devoid of function, as the nerve had not reached its

proper center, but it was of greatest interest to note that

the eye, although severed and removed from its natural

connection, had totally regenerated after a short period

of partial degeneration. Bearing these two points in

view, the centripetal growth in ontogeny and the same

process in transplanted eyes, we see our theoretical de-

mands for the reattachment of replanted eyes fulfilled:

the nerve fibers will grow backwards through the orbit,

continuing on their usual path and probably finding good

conditions there in the degenerating central stump. The

usual assumption that function of a sensitive organ can

not be restored after severing the nerve is based on false

presumptions, especially the idea that the proper central

nerve center is responsible for regeneration. We have

in several instances proved that it is not necessary for a

body part to be connected with its normal nervous center

for regeneration to set in and proceed till completion. I

may call attention to Oskar Kurz’s transplantations of

knees taken from developed tritons and placed on the

side of the same animal. Out of this bit of leg all distal

parts were regenerated, tibia, fibula, foot and toes, al-

though connection of the nerve-stump remaining in the

graft with the normal nervous center in the lumbar region

can not have taken place. It is quite another question,

how far the presence of nerve is necessary for restoration

of normal form; a question often confounded with the

inability of reestablishing function after severing of

nerves. I will not enter into these problems here, as they

are being investigated by several of my fellow-workers

556 THE AMERICAN NATURALIST [Vor. LVI

and definite statements can not yet be made. The foun-

dation for the statement that eyes severed from their

connection with the brain are not able to regain sight

seems to lie in the fact that the optic nerve in mammals,

when the eyes are left movable by their proper muscles,

can not find its way to a connection with any nerve center,

and then degenerates with the other parts of the eye. It

seems that the regenerating ends of the optic nerve fibers

coming from the retina are carried to and fro by each

rolling of the eye and thus fail to connect with the central

stump of the nerve. In contrast to this sheering of the

fibers in eyes left attached to the orbit after severing of

the nerve, the nerve fibers in autophorie replantation

reach their goal before the muscles have grown together

and become movable again. It must be emphasized that

our method involves no injury to the nerve besides a clean

cut, and also that Boeke in Amsterdam has been able to

obtain results in nerve regeneration far exceeding those

of previous experimenters by avoiding suturing or other-

wise ill-treating the nerves.

A second opportunity for autophoric replantation is

afforded in the vertebrate eye by the lens. It is well

known that this part of the eye is derived ontogenetically

from an invagination pinching off from the outer layer

of ectoderm. The lens of cold-blooded vertebrates, espe-

cially urodeles, is capable of regeneration and is easily

extracted as a whole, and when it is replanted again into

its former place, it fits well into the lens-sac. At my sug-

gestion Berthold Wiesner has applied the method of

autophorie replantation to the lens of fish and amphibia;

the results show that replanted lenses can clear up again

and restore normal eyesight to their bearer. In mam-

mals analogous experiments have not yet succeeded,

perhaps because in the rat, the only available mammals

for the present, conditions are unfavorable in respect to

the relative size of lens, cornea and eyeball. In other

forms, as in man, where the lens relative to the size of

the eye is much smaller, replantation should succeed, as

No. 647] AUTOPHORIC TRANSPLANTATION 557

the retraction often practised by the oculist is easy, and

even regeneration of the lens has been occasionally re-

corded (see Literature, Przibram, Regeneration, 1909).

Unlike the eye of vertebrates, arthropod eyes are not

suitable for our method of transplantation. They usu-

ally protrude much too far from their socket to be kept

in place after their replantation solely by the friction or

other forces exerted by the host. A discovery of Walter

Finkler has nevertheless put us in position to avail our-

selves of the autophorie method for furnishing insects

with a new pair of eyes. This young student, having had

the opportunity of seeing the results in vertebrates, sev-

ered the head of several types of hexapodes from the

thorax and, replanting it on its own body or on that of

another decapitated individual, observed its retention by

the friction and blood clot. There can be no doubt that

also in these cases function is restored, all reactions of

the normal animal reappearing after,a few days or weeks,

and the tissues joining quickly. Finkler has worked on

the larval, pupal and imaginal state. Perhaps the most

astonishing fact is the ready response of the imago to

such operations in spite of its lack of regenerative power.

But also in this case, as in the higher vertebrates, we shall

have to take into account that in our experiments no other

processes of reparation are called into play than those

of slow physiological regeneration, which still persist in

adult organisms. At any rate, in all the tissues of adult

insects severed connections are quickly restored, when the

organs are left in place, as Finkler could prove. His

experiments on autophorie transplantation in insects will

be.extended to appendages, whilst P. Weiss, Koppányi,

Finkler and Wiesner are also occupied with autophorie

replantation in parts of the vertebrate body other than

the eyes.

SUMMARY

1. Well-defined parts of the animal body that may be

easily detached at the same connecting points can be re-

placed by similar new organs under following conditions:

558 THE AMERICAN NATURALIST [VoueLVi .

(a) equal size and orientation; (b) simple exchange with-

out exertion of pressure or additional injury to the nerve

beyond a clean eut; (c) prevention of loss by the natural

means of the animal itself (friction, clasp, blood clot).

2. By this method of ‘‘ autophoric’’ or *' self-retain-

ing "' transplantation, the graft taken from an adult in-

dividual and replanted into another may be restored to

function, even the nerves of the head reuniting, and the

bearer being repaired in every respect.

3. These achievements are in accord with the theory

stating regeneration to be nothing else than the accelera-

tion of physiological processes going on all the time in

the body of organisms, for it can be demonstrated that

the reattachment proceeds in the same sense as the first

growth of the nerve. They contradict, however, the gen-

eral assumption that the maintenance and functional re-

generation of organs are dependent on their uninter-

rupted connection with their special nervous center.

4. Till now we have been able to obtain autophorie

‘replantation with restoration of function in the visceral

sae of Antedon (Echinoderms— Preibram, 1901), in the

eyes of fish, amphibia and mammals (Vertebrates— K op-

pányi, 1921), in the lens of the two former classes ( Wies-

ner, 1921), in the heads of insects, walking sticks, water

bugs, water beetles (Insects—Finkler, 1921) and in other

cases not yet ready for publication.

5. Experimenís with larval stages of amphibia and in-

sects as compared with the imaginal state of the same

species show that there is no radical difference as to the

restoration of function after excision and replantation of

a part, in mammals (rats) grown-up specimens even

seeming to be more favorable for autophoric replanta-

tion.

LIST OF REFERENCES

Boeke. Studien zur Nervenregeneration, I. Verhandl. Kon. Akad. van

etensch. te Amsterdam, 2. Sekt. Deel XVIII, 1916; II. XIX, 1917.

Cajal, Ramón y. Studies sobre la Degeneraeión y Regeneracién del

sistema nervioso. Madrid, Hijos de Nicolás. moya, I, 1918, II, 1914.

Finkler, W. Kopftransplantation bei Insecten, I. Funktionsfühigkeit

No. 641] AUTOPHORIC TRANSPLANTATION 559

replantierter Köpfe. Akademischer Anzeiger, Wien, No. 18, 1921. II.

Austausch von ee ee zwischen Männchen und Weibchen,

Ak, Anz. , 192 uss des replantierten Kopfes auf das

Farbkleid pends Sr aad kademischer : Anzeiger, Wien, 1922.

Jelinck, A. Die —X ani von Augen VII. Drwecrvitsnehe an Ratten.

prom Anzeiger, Wien, 1922.

pii. W. Die Divides von Augen V. ub aeger cur

n transplantierten Augen. Akademischer Anz , Wie

Eo. Th. Die Re plats tiis von Augen, II, Makjariett dui Tub

tionsprüfung bei verschiedenen Wirbelttierklassen. Akademischer An-

zeiger, Wien, Nos. 7-8, 1921. III. Die ae ee rot id pen jg

Süugeraugen. Akadem licher Anzeiger, Wien IV. Ueber

das Waehstum der replantierten Jupo. y poy Wie No. 18,

1921. VI. Wechsel des Augen- und Kórperfarbe bei Anamniern, Akad.

Anz., Wien, 1922. "VIII. Hetero- und Dysplastik. Akademischer An-

zeiger, iia uem

Kurz, O. Uebe Regeneration ganzer Extremitäten aus transplantierten

Ex Elo en vollentwiekelter Tiere. Zentralblatt für Physiol-

ogie, gp No. 12, 1908.

Pardo, R. Enucleazione ed innesto del bulbo oculare nei tritoni. Rendi-

nli Accademia Lincei (5), XV, 2. Sem., 744, 1906.

pomis H. Experimentelle singe über Regeneration. Archiv fiir Ent-

icklungsmechanik, XI, , 1901. Experimentalzoologie 2. Regen-

Sen Leipzig & Wien, F. nitida, 1909. Methodik der Experi-

mentalzoologie. Abderhaldens Handbuch der biologischen Arbeits-

methoden (S. 41), 1921. Die Replantation von Augen, Die

autophore Methode. Akademischer Anzeiger, Wien, Nr. T n 8, 1921.

pna m Die Transplantation des Amphibienauges, I. hiv für

ungsmechanik, XXXIII, 732, 1912. II. Archiv de e wick-

lun Mb 839 XXXVI, 211, 1913.

Wiesner, B. Replantation der Linse, I. Fische d Amphibien. Akad,

Anzeiger, Wien, 1921

SPONTANEOUS METAMORPHOSIS OF THE

AMERICAN AXOLOTL

PROFESSOR W. W. SWINGLE

OSBORN ZOOLOGICAL LABORATORY, YALE UNIVERSITY

Tar following experiments on axolotl neoteny and meta-

morphosis are published, not because of the conclusive

nature of the results obtained, but the reverse—because

of their inconclusiveness. A record of the work seems

warranted in order that other investigators of this prob-

lem may be spared considerable expense, time and effort

due to unsuitability of the material for experimentation.

The latter part of April, 1922, one hundred and nine

axolotl larvæ of Amblystoma tigrinum were received

from Albuquerque, New Mexico. These animals were

obtained through the courtesy of Mr. J. N. Gladding.

They varied in length from four inches to fourteen

inches, though the average total length was about seven

inches. One animal measured fourteen inches from

snout to tail tip, another measured eleven inches. They

were the largest individuals of the lot. The animals were

in excellent condition on arrival and none showed any

indications of metamorphosis.

EXPERIMENT 1. Avrtopuastic THYROID TRANSPLANTATION

May 5, 1922, the thyroids of seven axolotls, seven inches

in length, were removed under chloretone anesthesia and

each gland transplanted intraperitoneally into the same

individual from which it was taken. The idea was that

the acquisition of a new blood and nerve supply by the

gland in its new environment might permit the release

of the accumulated secretion and so metamorphose the

animal. It was shown by the writer (21) that the thy-

roid glands of axolotls are highly active metamorphosis-

inducing agents providing the hormone escapes into the

560

No. 647] METAMORPHOSIS OF AMERICAN AXOLOTL 561

blood stream. In these forms there appears to be some

inhibition of the secretory (excretory) functions of the

thyroid, and the hormone is retained within the gland

vesicles,

The experimental animals and their controls were kept

in large aquaria with plenty of water and food. One

of the grafted animals had metamorphosed by June

27. Three others transformed by July 1; a fifth animal

died without transforming July 6. The two remaining

axolotls had not metamorphosed by September 1. Dur-

ing the interval between May 21 and September 1, all of

the controls spontaneously transformed. The experi-

ment is, of course, without significance because of the

unstable nature of the control material. It is highly

probable that the operated animals would have meta-

morphosed just about as rapidly if the thyroid had been

left in its normal position.

EXPERIMENT 2. Homopuastic THYROID TRANSPLANTATION

Five seven-inch axolotls were engrafted intraperitone-

ally with the thyroid gland of other animals of similar

size and appropriately controlled by at transplanted

with pieces of muscle tissue.

The transplants were made May 2, 1922. One animal

had transformed by June 3, a second by June 6, a third

June 11. Two animals remained as larve and were re-

engrafted June 11 with axolotl thyroids, and metamor-

phosed by July 3. In the meantime the controls also

transformed. A large series of transplantation experi-

ments were performed, using various endocrine glands,’

but in every case except two experiments the controls

metamorphosed along with the operated individuals.

Heteropiastic THYROID TRANSPLANTATION

Four eight-inch axolotls were engrafted intraperitone-

ally with the glandular tissue of adult Necturus macula-

tus. Each axolotl received the entire thyroid of a single

562 THE AMERICAN NATURALIST . [Vor. LVI

Necturus. The experiment was performed May 15. By

June 11 all of the engrafted animals had transformed but

none of the controls for this particular group, though nor-

mal, untreated animals used as checks for other experi- |

ments were metamorphosing during this interval.

Despite the unstable nature of the control material

used, this experiment seems fairly sound and indieates

that Necturus thyroids when injected in sufficient quan-

tity will metamorphose axolotl. To be absolutely reliable

this experiment should have been performed upon thy-

roidectomized forms, but unfortunately the unsuitable

nature of the controls was not known until too late.

THYROID FEEDING EXPERIMENTS

Five six-inch axolotls were fed desiccated thyroid tis-

sue (Parke, Davis and Company), containing 0.21 per

cent. iodine by weight. The feeding was done by means

of a pipette May 18. Two animals had transformed by

May 27, and all by June 10. None of the controls meta-

morphosed during this interval but all transformed by

July 25. The experiment seems trustworthy, especially

in view of similar results obtained by other investigators

on animals of the European strain.

HETEROPLASTIC PITUITARY TRANSPLANTATION

Five axolotls varying in length from four to seven

inches were each grafted with two whole pituitary glands

of adult Rana clamata frogs. The grafts were made May

.5. June 3 one animal metamorphosed; June 7 a second

transformed. June 10 the three remaining animals were

reengrafted with frog pituitaries. All metamorphosed

by June 25.

During the interval between May 5 and June 25 only

two of the controls for this particular group transformed,

but it must be remembered that control animals of other

cultures were metamorphosing. The experiment is re-

corded for what it is worth, but the writer believes that

No. 647] METAMORPHOSIS OF AMERICAN AXOLOTL 563

injection of fresh pituitary substance does induce axo-

lotl metamorphosis possibly by serving to release the

thyroid hormone. This experiment should be tried on

the Mexiean strain of axolotl which apparently rarely

spontaneously metamorphoses and hence can be safely

controlled.

THYROIDECTOMY AND METAMORPHOSIS

Eight axolotls varying from seven to fourteen inches

were thyroidectomized and at the present writing, Sep-

tember 1, are still larve and show no indications of

transforming. Out of the original one hundred and nine

animals received from New Mexico these eight are the

only ones that have not metamorphosed. It is a fairly

safe assumption that these axolotls will remain perma-

nently as larva now that the thyroid gland is lacking.

The thyroids of several animals were removed after

the onset of metamorphosis, i.e., after the tail fin and gills

were undergoing reduction, but in all cases the removal

of the thyroid failed to prevent the completion of meta-

morphosis.

Discussion

The conclusion to be drawn from these experiments is

that the New Mexican strain of axolotl is entirely too

unstable to work with on any problem involving the

methods of feeding, injection or transplantation, where

the results require a lapse of several weeks to obtain.

The animals can not be controlled when the thyroid ap-

paratus is left intaet. It is evident that conclusive ex-

periments of the above kinds on the New Mexiean strain

of axolotl (where the animals themselves are used as

1 The thyroidectomized animals were kept for five months and then in-

jected with iodotyrosine and iodoserumglobulin. Metamorphosis resulted

within a period of twenty days following injections of either substance.

metamorphosed by injection of iodoserumglobulin. Injections of tyrosin

dibromtyrosin and globulin had no effect upon metamorphosis. Uhlenhuth’s

conclusion that only thyroid iodine (iodine which has undergone transforma-

tion within the thyroid gland) is tena in metamorphosing urodele

larve is invalid.

564 THE AMERICAN NATURALIST [Vor. LVI

experimental material) ean only be obtained by using

thyroideetomized animals.

Professor Henry Laurens, of the Department of Physi-

ology, informs me that several years ago he had a similar

experience with axolotls from New Mexico. He received

a shipment of several dozen in the spring, but was unable

to prevent them from transforming shortly after arrival

in New Haven. Only one animal of the lot failed to

metamorphose and was kept two years in the laboratory,

attaining a length of 14.25 inches. "This individual was

used by the writer for thyroid transplantation work.

The marked tendency of the New Mexican and other

American axolotls to metamorphose spontaneously when

moved from one locality to another prevents their being

used for aquarium purposes. It is an odd fact that prac-

tically the only axolotls used as aquarium material in the

United States are those that have been shipped from

Europe. :

The European strain seems to differ from the New

Mexiean form in regard to spontaneous metamorphosis,

because these animals are handled by practically all

aquarium dealers in Germany and ean be obtained for

a few cents apiece. Apparently they rarely spontane-

ously transform according to Jensen (’20), who has

worked extensively with this strain. The curious thing

about the New Mexican strain is that in their native

habitat they too may remain for considerable periods as

larva, yet when shipped from New Mexico to New Haven

promptly metamorphose regardless of size or age. One

large animal of this strain obtained by Professor Lau-

rens failed to transform and was kept in the laboratory

for two years; at the end of this time it showed no indica-

tions of metamorphosis and was killed for thyroid trans- -

plantation work.

According to Gadow (708) the strain of axolotls estab-

lished in Europe came originally from the vicinity of

Mexico City. The first axolotls were brought to France

by Marshal Forey in 1863, and the present strain is de-

No. 647] METAMORPHOSIS OF AMERICAN AXOLOTL 565

scended from these animals. Gadow also states that the

axolotls of Lake Xochimileo have never been known to

metamorphose in their native habitat. However, several

of the descendants of the animals taken to Europe did

metamorphose, so that spontaneous transformation in

the Mexican strain does sometimes occur, though rarely.

In an earlier paper (722) the writer showed that the

thyroid mechanism of axolotls is filled with physiologi-

eally aetive hormone capable of inducing metamorphosis

but that the secretion is apparently not liberated into the

blood stream, hence the retention of the larval characters

despite the possession of a large well-formed gland. The

thyroid of a fourteen-inch axolotl several years of age

was extirpated and eut into small pieces, each piece then

transplanted into an immature Anuran larva. The single

axolotl thyroid promptly metamorphosed five such tad-

poles within fourteen days, whereas left intact within the

axolotl's body it was quite ineapable of inducing trans-

formation.

This same experiment was repeated upon thyroidecto-

mized and hypophysectomized Rana sylvatica tadpoles

with similar results. Small pieces of axolotl thyroid

when engrafted into thyroidless and pituitaryless larve

promptly induce metamorphosis within ten or twelve

days.

It is quite clear from these experiments that axolotl

neoteny is due to retention of the thyroid hormone within

the gland vesicles. Under normal conditions and in its

native habitat, the releasing mechanism apparently fails

to act, but when the animals are shipped from one place

to another and subjected to new environmental conditions

metamorphosis promptly ensues. In the New Mexican

strain slight stimulation is sufficient to initiate meta-

morphosis, but in the European and Mexican forms very

powerful stimulation is needed to overcome the thyroid

inhibition and release the secretion. In the European

strain the following agents have been used successfully

for inducing metamorphosis: thyroid feeding (Laufber-

566 THE AMERICAN NATURALIST [Vor. LVI

ger 713), salicylic acid injections (Kaufman 718), iodine

and iodoform injections (Hrischler ’18-’19), organic io-

dine feeding —iodothyrosine, also injections of iodocasein,

iodoserumglobulin and iodoserumalbumin (Jensen ’21) ;

and of course Marie von Chauvin’s experiments are well

known.

It is evident that the peculiar thyroid inhibition caus-

ing neoteny in axolotl is due to genetic factors and that

the condition is hereditarily transmitted. It is interest-

ing to note that in axolotl we have one of the best ex-

amples of hereditary transmission of an endocrine defect

known. Attempts to explain neoteny by assuming that

environmental agencies such as cold, altitude and the like

are the chief causative factors are too crude to be seri-

ously considered and for this reason—the aquarium deal-

ers of Europe breed their animals as larve and the young

grow up as axolotls, the matter of cold or altitude not en-

tering into the question. As was previously mentioned,

the European strain arose from a few animals taken to

France in 1863.

Then, too, both Professor Laurens and myself received

our animals from Albuquerque, New Mexico, where they

breed. The animals were old when captured. The tem-

perature of the pools in the vicinity of the city can not

be very low even in winter—not nearly so cold as those

of the middle western states, northern New York, Ohio,

or Wisconsin—and axolotls have never been reported as

oecurring in these states so far as the writer is aware.

The Amblystoma tigrinum resulting from the meta-

morphosis of the axolotls during my experiments were

placed in certain pools in the vicinity of New Haven

where other species of Amblystoma are known to breed.

The animals are full grown and should breed next spring

(1923). By following the life history of the larve it is

hoped that some new light may be shed upon the obseure

and much debated problem of the relation of neoteny to

environment.

No. 647] METAMORPHOSIS OF AMERICAN AXOLOTL 567

LITERATURE CITED

Chauvin, ai 1875. ber die Verwandlung des mexikanischen

S e rai Zeitschr. f. wissensch. Zool., Bd. 25, Suppl.,

olot

und ies 27, 1876.

Gadow, H. 1908. Through Southern Mexico. Charles Scribner’s Sons,

ve k.

ame G. 1918-19. Sur la metamorphose didit: chez l'axolotle à

e d'iode et des expérience apparentées. Extrait de Ko wl.

A 3 Soc. Polonaise d. Naturalistes à Leopol. (Cited by Kopee, Biol.

ull., Vol. XLII, No. 6, 1922.

Jensen, C. O. 1921. Métamorphose provoquée par l'injeetion de prépara-

tons deca et de thyroxine a des Axolotls ayant subi la

eité

d'animaux t Vid hake ompt. rend. soc. de bio!., 85,

Kaufman, L. Researches on the emu Metamorphosis of

Axolotls. Bull. de VAc C. a

Laufberger, V. 1913. O SEDAN apnd mt Mdh krmenim zlazou

stitnou. cep ber Lysty. (Cited by Adler, L., 716, Arch. f. d. ges.

Physiol., bg

Shufeldt, R. id Mexican Axolot] and its Susceptibility to Trans-

sient > satin Vol. 6.

Swingle, W. W. 1921. A. ees me the Thyroid Glands of

Necturus and Azolotl. Anat. Record, 1 IND. 4. De 100.. 1922.

B. Thyroid Glands of -the cni ipei Amphibians, Anat.

Record, Vol. 23, No. 1, page 106. 1922, C. Experiments on the Meta-

morphosis of Neotenous Amphibians. Jcur. Exp. Zool., 1922, Vol. 36.

SHORTER ARTICLES AND DISCUSSION

MORE EYELESS CLADOCERA

Just before a note appeared in Science (Vol. 53, pp. 462-

463, May 13, 1921) concerning an eyeless cladoceran individual

(a Simocephalus exspinosus), two additional eyeless daphnids

occurred in another species of the experimental stock at the

Station for Experimental Evolution. These were among off-

spring of some Moina rectirostris which were being subjected

to crowding in a sex-control experiment (10 mothers in each 130

e.c. wide-mouthed bottle containing about 75 c.c. of culture

medium). While these two eyeless young were released on sue-

eessive days and possibly in separate bottles, they were in bottles

whieh belonged to the same series and received the same treat-

ment.

The precise identity of the mother of neither eyeless young

could be determined (since there were 10 mothers producing

parthenogenetic young in each bottle), but it is certain that

the mothers were normal-eyed and were sisters, or came from

mothers which were sisters. All of the mothers’ collaterals,

which were examined, approximately 250, had normal eyes.

302 other young, produced by the 10 mothers in the bottle in

which the second of these eyeless appeared, were normal. In

all about 5,953 young were microscopically examined—a few

of which were presumably sisters of the eyeless individuals and

the others of which were young from sisters of the mothers of

the eyeless individuals. All were normal-eyed.

One of these eyeless individuals produced 5 broods, contain-

ing in all 66 young, all normals. The other produced 4 broods,

containing 38 individuals, all normals. 841 offspring of daugh-

ters of the one eyeless, and 412 offspring of daughters of the

other eyeless were found to have normal eyes. All examined

among the collaterals of the eyeless individuals, 5,953 in all,

and 1,357 direct first and second generation descendants of

the eyeless mothers themselves—a total of 7,310—were normal.

Hence despite the fact that there were two eyeless individuals

produced by sisters (or by individuals whose mothers were

sisters), while among many thousands of Cladocera previously

seen under the microscope only a single similar individual had

568

No. 647] SHORTER ARTICLES AND DISCUSSION 569

been found, eyelessness in these individuals was clearly not in-

herited. The lack of inheritance in these Moina rectirostris

would have been anticipated if due regard had earlier been

given to a peculiar feature of the head of these eyeless indi-

viduals. This will be discussed in a later paragraph.

The next occurrence of eyeless Cladocera was in February,

1922, when seven eyeless Moina macrocopa were found among

147 young of the third brood from 10 mothers in a crowded

bottle. The culture water in this bottle seemed rather cloudy,

an appearance known frequently to be associated with unfavor-

able conditions which sometimes result in death to part or all of

the Cladocera in such a bottle.' In the present ease in addition

to one eyeless male and 6 eyeless females among the 67 females

and 80 males in the bottle, there were other abnormals—6 or 8

with abnormal eyes (pigment reduced or eye not completely

formed) and perhaps an equal number with abnormal antenne

(certain segments missing, aborted or fused with others) and

one male with an abnormal eye and an abnormal antennule.

Some of the eyeless individuals and some with abnormal eyes

had abnormal antenne also. Others showed abnormality in only

one feature. Sinee these abnormals appeared in a erowded bottle

(10 mothers) it is impossible to know, but they probably did

not come from a single mother. Among the next brood of

young from the same mothers were a few with abnormal an-

tenne and slightly abnormal eyes. Subsequent young were

normal.

Early attention to an interesting feature of the heads of these

eyeless individuals removed any temptation to anticipate in-

heritanee of eyelessness in these cases; and, as expected, all the

numerous young examined from tha eyeless individuals (and

from the other abnormals as well) were normal. Since in these

eases eyelessness was not hereditary some developmental aeci-

dent would seem probably responsible for its oeeurrenee. In-

deed, it seems fairly evident, in view of the occurrence of other

abnormalities in the same and other similar eulture bottles,

that these abnormalities were related to some unfavorable fac-

1In other cases such conditions hey the culture medium were associated

with pigmentless eyes in some of the newly released young. However, the

pigment develops to its full nea in from one to five days after the

young animals are released from the mother’s brood chamber. Newly

released young from the formerly pigmentless-eyed individuals have nor-

mally pigmented eyes from the first.

570 THE AMERICAN NATURALIST [Vor LVI

tor or factors in the environment, although nothing definite is

known as to what these factors were.

A peculiar structural feature of the heads of the young eye-

less individuals suggested the possible manner in which eyeless-

ness came about in these cases. When young, the seven eyeless

Moina macrocopa had on the anterior head margin a small

nodule or excrescence which, though not so conspicuous at later

stages, yet in most cases persisted through several moults. In

each of these eyeless individuals the optic ganglion was reduced

or lacking, and the margin of the head was readjusted to com-

pensate for the reduced and missing organs. Substantially the

same structural conditions were found with the two eyeless

Moina rectirostris, absence or reduction of optie ganglia, the

shortening of the head margin and the occurrence of a small

bit of apparently necrotic material attached to the front of the

head.’

It seems possible that this apparent exudate on the heads of

the eyeless individuals really represented an aborted or necrotic

portion of the embryo which included the primordium of the

missing parts.?

The fourth occurrence of eyeless Cladocera (the eleventh eye-

less individual seen) was June 26 in a crowded bottle of Moina

macrocopa. In addition to the lack of eye and of optie ganglion,

the brain proper was reduced in size. This animal was not ex-

amined until mature and an excrescence on the head, if present

in the young animal, had by that time disappeared. This indi-

vidual swam in small circles, although its swimming organs ap-

peared entirely normal. It died after producing two broods

(10 females and 12 males) of normal young.

The occurrences of eyeless Cladocera have included three

species, eleven individuals and four different time periods. The

last three occurrences, and probably the first one, were in

erowded bottles, suggesting environmental factors as causative

2 That this material was intimately associated with the head structures

and really a part of the animal is attested by the fact that it persisted

through eedysis, whereas any material merely esie to the external

surfaee of the exoskeleton would be eliminated by eedys

3 A somewhat similar appearance in larve arising om pE eggs

of Ambystoma punctatum was presumably correlated with failure of

development of the anterior part of the head. (Banta, A. M., and Gortner,

A., ‘‘Aceessory Appendages and Other Abnormalities Produced in

Amphibian Larve through the Action of Centrifugal Force,’’ Jour. Exp.

Zool., 18: 433-446, pls. 1-3. 1915.)

No. 647] SHORTER ARTICLES AND DISCUSSION 571

agents. Those which lived to produce young gave rise exclu-

sively to normal young, indicating that genetic changes were

not responsible for the abnormal heads. However, in view of

the known inheritance of eyelessness in cave arthropods and

vertebrates and in Drosophila melanogaster, it seems of interest

to examine each case of profound eye modification in erusta-

eeans and elsewhere to gain information on the origin and in-

heritanee of any possible mutation of this character.*

ARTHUR M. Banta

. A. Brown

STATION FOR EXPERIMENTAL EVOLUTION

COLD SPRING HARBOR, L, I.

CROSSING-OVER INVOLVING THREE SEX-LINKED

GENES IN CHICKENS

IN the course of the last year several crosses of chickens

earried out at the genetics station at Anikovo (near Moscow)

have made it possible to observe erossing-over in this form. The

genes ‘‘suke,’’ ‘‘tuge’’ and ‘‘trage’’ were studied. The first,

suke, retards the development of feathering in the chicks, so that

at the age of 1 to 1.5 months they have very small tails. The

development of the wings, too, is very slow. The genes trage

and tuge together eause the well-known Plymouth Rock mark-

ings, trage eausing the erossbarring, and tuge (not very visible

in Plymouth Rocks, where it causes the contrasts in the mark-

ings) is the same gene as silver coloring, which was first re-

ported by Hagedoorn in the Assendelver chickens. Later

(1912) Davenport observed it in the cross of Dark Brahma X

Brown Leghorn, where, however, on account of the absence of

several other genes, tuge has very little expression—only as a

whitish edge on the feathers.

The genes suke, tuge and trage are all present together in the

Plymouth Rceks. The Russian Orloff chickens have none of

these genes, a condition which may be expressed as asuke-atuge-

atrage. All these genes are sex-linked, and therefore are trans-

mitted with complete linkage from mother to son. The cross

4Since this manuscript went to the printer two more eyeless Moina

macrocopa were found in a crowded bottle. These two with the last one

mentioned above were the only eyeless occurring among approximateiy

33,000 individuals microscopically examined (in sex-control experiments)

during three months. The facts, that of these three two occurred in the

same bottle and that the character is not inherited, again indicate clearly

enough that external, not internal, factors are responsible.

572 THE AMERICAN NATURALIST [VoL. LVI

Orloff male Plymouth Rock female gives cocks closely re-

sembling the true Plymouth Rock, that is, erossbarred with slow

feathering development. All the hens, however, are black (since

in the Plymouth Rock there is also a gene for melanism, ‘‘tifa,’’

which is not sex-linked), and they develop feathers quickly.

d: asuke atuge atrage atife X 9: suke tuge trage tifa

F, d: suke tuge trage tifa 9: asuke atuge attage tifa

In F, the coupling between suke, tuge and trage becomes

broken, and different new combinations are to be observed in

rather large numbers. More often the forms asuke-tuge-trage

are obtained, colored like Plymouth Rock, but with quick de-

velopment of feathering (among these there are also cocks), and

conversely suke-atuge-atrage, with slow feathering, but black

(when tifa is present). In one ease a suke-tuge-atrage chick

appeared, with slow feathering and silvery, but not crossbarred.

In the light of the Morgan theory these facts can be explained

by regarding the genes suke, tuge and trage as being in a sex

chromosome which cannot give crossing-over in the heterozygous

sex (female). But when the same chromosome is transmitted

to the F, male, it undergoes crossing-over with its partner, which

occurs most often in the space between suke on the one side and

tuge-trage on the other. Crossing-over between suke-tuge on

the one side and trage on the other oceurs less often, wherefore

the arrangement of the genes in the F, may be represented as

follows:

trage

However, the counts of chicks which have so far been obtained

in F, are not yet large enough to ascertain definitely the order

of the genes, and therefore still less the exact distances,

S. SEREBROVSKY

INSTITUTE OF — Brioroav,

41 SrvTSEV VRAZ

Moscow, pps 21, 1922

[Crossing-over between ''suke"' (barring) and ‘‘tuge’’ (sil-

very) has also been announeed by Goodale (1917) and by Hal-

dane (1921), in the papers listed below, which were not available

to the above author. i:

Goodale, H. D. 1917. Crossing-over in the Sex Chromosome of the Male

Fowl Science, N. S., Vol. 46, p. 213.

Haldane, J. B. S. 1921. Linkage in Poultry. Science, N. S., Vol. 54,

p. 663.

Note of Transmitter, H. J. Muller.]

No. 647] SHORTER ARTICLES AND DISCUSSION 573

A FOURTH ALLELOMORPH IN THE ALBINO SERIES

IN MICE?

In recording the occurrence of a new mutant gene in the

house mouse, allelomorphie to color and albinism, Detlefsen

(721)? described a very dilute, wild form in which the hair

showed traces of a light brownish tinge with a suggestion of

sootiness, and the eyes were somewhat less heavily pigmented

than in the wild type. This general form of pigment reduc-

tion is also eharaeteristie of other eolor allelomorphs; for in

the ease of the ruby-eyed rat, the ruby-eyed guinea-pig and the

chinchilla rabbit (Castle 721), the yellow pigment is very

greatly reduced or even obliterated, while the darker pigments

(black or brown) are at least slightly modified. The mutant

mouse, however, showed a far greater pigment reduetion than

either the rat, guinea-pig or rabbit mutants. Breeding tests

demonstrated that this dilute mouse mutant was a color-albino

allelomorph, and in this respeet resembled the ruby-eyed rat

and guinea pig genetically (the chinchilla rabbit had not been

recorded at that time), but Dr. Detlefsen pointed out that ‘‘it

is hardly safe to insist that these mutations are identical. . . . :

We are also unable to prove that they are different, for the

genes may be identieal but simply give different somatie ef-

feets, sinee the residual inheritanee ean not be the same." He

also suggested that the diseovery of a new dilute type of mouse

(whieh he was seeking at that time), more like the rat or

guinea pig in its somatie appearanees as well as in its genetie

behavior, would give us more assurance that his extreme dilute

mouse mutant was not the homolog of the ruby-eyed rat or

guinea pig. Unusual as it may seem, I had discovered exactly

such a new dilute mutant mouse in January, 1919. By com-

paring it with Dr. Detlefsen's set of rodent skins and by test-

ing it in appropriate matings, I reeognized its genetie signifi-

eanee just before his paper appeared in print.

The diseovery of this new mutant mouse enables us to say at

onee that the extreme dilute mutant was not the homolog of

the ruby-eyed rat or guinea pig or the chinchilla rabbit, and

supports Dr. Detlefsen's position in hesitating to homologize

1 Paper No. 22 from the Genetics Laboratory, College of Agriculture,

University of Illinois

2 Detlefsen, J. A., 1921, AMER. Nat., Vol. 55, p. 469.

3 Castle, W. E., 1921, Science, N. S., Vol. LIII, p. 387.

574 THE AMERICAN NATURALIST [Vou. LVI

his mutant with these forms. Dr. Detlefsen’s form is evidently

lower in the scale running from color to complete albinism in

very much the same way that the Himalayan form is nearer to

the albino than is the chinchilla rabbit

The new mutant was procured from a fancier who had been

breeding it for some time. It resembles the ruby-eyed guinea

pig, ruby-eyed rat and the ruby-eyed or chinchilla’ rabbit

(Castle ’21)* in the degree of pigment reduction in the hair,

but the eyes are apparently darker than those of the rat and

guinea pig. I have not had an opportunity to examine the

eyes of the chinchilla rabbit. It forms one of a series of quad-

ruple color allelomorphs in the mouse and may be designated

as c”. In a scale of dominance, the four forms probably fall

into the following order: ordinary intense or wild eolor, C;

dilute, c" (described in this paper); extreme dilute, c^ (de-

scribed by Detlefsen ('21);* end complete albinism, c, Wild

eolor (C) is eompletely dominant to the other allelomorphs, but

c” and c? are incompletely dominant to albinism. The cross

between c" and c^ has not yet been made, but the heterozygote

(c"c^) will probably be found to give an intermediate shade.

The black agouti type of the homozygous mutant (AABBc'c")

possesses black pigment which is reduced to a/very dark dull

slate-color, while yellow is greatly reduced and appears about

intermediate between white and the normal yellow of the wild

type. In the non-agouti type of the homozygous mutant

(aaBBe'c"), which ean be distinguished readily from the agouti

form, the black pigment is also reduced to a very dark dull

slate-eolor, but perhaps darker than in the agouti type.

en the blaek agouti type of the mutant is heterozygous

for albinism (AABBe'c), black pigment is reduced to a brown-

ish shade and yellow is practically reduced to white. In the

non-agouti type of the heterozygous mutant (aaBBc'c), black

is reduced to a dull brown, a little lighter than the ordinary

fancier’s chocolate type. The heterozygous mutants, mated

interse, produce the rae ea ns type, the heterozygous type

and albinos in the ratio of 1: 2: 1.

I have not yet identified the mutant without black pigment

that is in the cinnamon or brown class.

H. W. FELDMAN

4 Loc. cit.

5 Loc. cit.

INDEX

NAMES OF CONTRIBUTORS ARE PRINTED IN SMALL CAPITALS

Alcohol and White — EDWIN

CARLETON MACDOWELL, 289.

ALLEN, E. J., Frera of Life

in the Sea , 481.

Asterias, Tube- feet in, RoBERT H.

BowEN

Axolotl, Spontaneous Metamorpho-

sis of; . SWINGLE, 560.

BAN ARTH M., ‘and L.' A

indie ade vx es 568.

BELLING, JOHN, ALBERT F.

BLAKESLEE, Chromosomes in Trip-

loid Daturas, 339; A. F. BLAKES-

LEE and J. RTHUR HARRIS, Dom-

inant ee 458

LBERT FRANCIS, ve

B., Sexual and

Sex- init. Characters, tur

P MHALL, R5 mily R-

mblanees can bibe Men

of eg ce, 504.

Brow L. A. and ARTH M.

Bats, Eyeless Cladocera, "568.

CHIDESTER, F. E., Fish Migration,

373.

Chiton, Color Variations

* (luster -formation

J. Crozier, 478.

in, adi

of Sperm

i Growth Factors i

d ae ewe Sar

CHUR JR. ; URNA OR

in n Shelled Tot d

Cicada, Fugitive Net- seng in, W.

ToM. » 191.

Coleoptera Food Habits of, Harry

B. Weiss, 159.

CROZIER, W. J., Color Variati ns in

Chitons 189; * * Cluster-forma-

tion? of Sperms of Chiton, 478.

Datura, Variations in, ALBERT FRAN-

cis BL*KESLEE, 16; Chromosomes

in Triploid, Jonn BELLING and

Y: PAYNE

Gynandromorph in Trosi

Melanogaster, 383.

Dominant eit gee = Tus BLAKES-

LEE, and J.

ARTHUR Pise 7 458.

Drosophila, ag aset Complete

Linkage in, MARIE S. and Jo

Willistoni,

LANCEFIELD and

x I

HARLES W.

Salamand^rs

‘Phylogeny P eae 418.

Du rose: of Buff rnd

tin Fowls, 242; Black Pig-

ment in Domestice Fowls, 464,

and

Emerson, R. A., Bud Variations, 64,

Environment, Effect of on Animals,

144.

Bae, Paleontology of Arrested,

F RUEDEMANN, 256.

Family Resemblanees among Ameri-

ean Men of Seienee, DEAN

FASTEN, NATHAN, Tareworm In'ce- .

ourth All lo-

MM ‘in Albino Boden in Mice,

573

Fishes, Variati

HUBBS s, 360; geo hs us TY. E

CHIDESTER, 373.

FISHER, A., Genes, è

FORB . T. M., Fugitive Net-

vei Cicada, 191.

MN Crosses m ies and Colum-

Puit in Domani L. C. Du

Frogs, Transformation of Sex in,

W. W. SwINGLE, 193.

Genes, are. Bo: LR 32;

Loeat n of, R. A. Fis 406;

Cro eb over involving Three Sex

linked, in Chickens, S. SERE-

BROVSKY, :

GOVAERTS, ALBERT,

and J. ARTHUR

a Assortive ‘Mating in Man,

cers Mar S. and Joun W.,

raiik ge mag 286.

Guyer, M. F., Serological Reactions

80; Or rthogenesis of Sero logieal

Phenomena, 116

Harris, J. ARTHUR, and ALBERT

GOVAERTS, jere i Mating in

Man 381; A. F. BLAKESLEE and

JOHN BELLING, Dominant Individ-

uals, 458,

575

576

HAUSMAN, LEON A., Miero-filter for

enn Flagellates, 284.

HENDE <da Or A from

crees of Biochemi

HOWELL, A. BRAZIER, Distribution of

Life, 428.

CARL L., Variations in

, 360.

between Canary

O. E. PLATH, 322.

Hybrids.

Finches,

and

Human, Jom

188; and Redi.

pane. WRIGHT, 330.

rec c

JENNINGS, H. S., Variation in Uni-

par ental Reproduetio n,

jii D. F., Growth "Factors in

Chromosomes, 166.

Just, E. E. Rearing pru

Megalops from Eggs, 4

MPTON, J. H., Braehysm and Ad-

Trone in Maize, 461.

LANCEFIELD,

CHARLES

Willistoni, š

Li erai of, RAYMOND PEARL

REBEC

CA. C., and

Metz, Drosophila

, Orthogenesis

in Baeteria, 105.

MACDOWELL, EDWIN Serres Al-

cohol and "White R 289.

aize, Brachysm seg ys esia in,

J. H. Ke EMPTON, 461.

Man, Assortative Mating in, J.

ARTHUR HaRRIS and ALBERT Go-

.„ and REBECCA C.

LANCEFIELD, Drosophila Willistoni,

11.

Miee, Fourth Sg ag ao in Albino

S in, . FELDMAN, 573.

ULLER, H. J., Individual Gene, 32.

Oriire (Symposium): from

poin

Stand t of Biochemist, L. J.

ERSON, : acteria,

CHARLES , 105; and

Serologieal Phenomena,

G 11 rv

Guyer, 116; as Observed

Paleontological Evidence, H,

OSBORN,

OSBORN, H. F., Ort rthogenesis, 136;

Fossil Proboscideans, 448,

PAYNE, F. liboessetung d me in Droso-

phila a Melanogaster,

THE AMERICAN NATURALIST

[Vor. LVI

Print, RAYMOND, and SYLVIA L.

n of Life, 174,

RKER, Duratio

273, 312, 385.

uA olet A. Effeets of Environ-

n Animals, 144.

Peromyscus, Linkage in, F. B. SUM-

412.

Pini E OR. e on Conser-

vation of Wild Life, 456.

Hybrids between Ca-

TAS

ary and Finches,

Platvnerele Megalops, d arbe from

Eggs, E. E. Just, 471.

Proboscideans, Mipsiticans and Affin-

ities of Fossil, Henry F. OSBORN,

448.

PRZIBRAM, Hans, Autophorie Trans-

plantation, 5 548,

DE Aleohol and heise EDWIN

MACDOWELL, 289.

Rhizopods Conj jugation = Shelled,

gee

of Arrested Evolution, 256.

Rotamandpr go Sarney of Cau-

dat

5 r^ gp se ing-over in-

ais three box inked Genes in

‘Chick

Pis we war. E M. F. GUYER,

Sexual and Sex- ie Characters,

CALVIN

Sumner, F. B., Pn in Peromys-

SWINGLE, W. W. Transformation of

Sex in Frogs, 193 ee

Metamo m sis of dan n Ax-

* olotl, 560

ic vejet a in Washington

Trout, STEN,

Tran ansplantation, | Autophorie, Hans

PRZIB

TRE soi agg Estrus and

Feeundi a x CORE Pig, 347.

Variations, Origin of (Symposium):

in Uni nipar rental Reproduction, H.

s. ehe 5; in Datura, due -

romosome ees

‘Atanas Paano BLAKES 16;

` due to Change in Individual ld

H. J. MULLER, in Sexual an

Sex linked i Char: ters, CALVIN B.

Brinegs, 51; Natin of Bud Vari-

ne d as Indicated by ps He

of Inheri EM

64; Serol logical Reactions ye j4

Probable Cause, M, F. GUYER, 80.

s, Harry B. Food Habits of

V Coleapter, 159.

WRIGHT, SEWALL, Inbreeding and Re-

laticaadity, 330.