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THE

AMERICAN NATURALIST

Vou. ALIX January, 1915 No. 577

. SOME FUNDAMENTAL a aaaa

OBJECTIONS TO THE MUTATION

THEORY OF DE VRIES

PROFESSOR EDWARD C. JEFFREY

HARVARD UNIVERSITY

Tuer hypothesis of the saltatory origin of species has

received a new impetus from the investigations of De

Vries,* published in his ‘‘Mutationstheorie’’ and subse-

1To an address delivered in Brussels before the outbreak of the war and

published in Science (Vol. 40, No. 1020, July 17th. ), Professor de Vries

appends a criticism of the eitri ‘rolinliney article on mutation, likewise

published in Science (Vol 39, No. 1005, April 3d.). The gist of his objection

to the writer’s tae that Œnothera and other members of the Ona

are in a position of hybrid contamination, as evidenced by the frequent

rility or en sterility of their pollen, is the contention that polle

sterility and gametic sterility in general is not sufficient evidence of hybrid

contamination. To this statement two replies may be made. In the first

Place prominent geneticists for many years have recognized pollen sterility

as important evidence of edema Secondly investigations, which have

now become very extensive, on the iosperms as a whole, show very inter-

esting conditions in many natural Faaite While the monotypie species

and those which are isolated geographically or phenologically (that is by a

time of flowering later or earlier than that of the mass of species belongin

to the genus) have invariably good pollen, those species, which me in

their geographical range and in their times of flowering in many ¢

characterized by abortion of the reproductive cells. In other words speia

infertility is only found where the possibility of crossing is present. This

PT has been illustrated in the body of the present article by reference

the Rosaceæ. ing a further illustration from the large family

Barne Ranunculus acris and R. repens, which overlap both in range

and time of flowering have pollen, which is ithe largely imperfect, particu-

larly in the first mentioned species. R. rhomboideus on the other hand,

flowering in the very early spring has perfect pollen development. _

6 THE AMERICAN NATURALIST [Vor. XLIX

quent works. The chief foundation for his views, in re-

gard to the instantaneous origin of species, is furnished

by the conduct of Enothera lamarckiana in cultures. It

has been somewhat generally recognized that O. lamarck-

iana, and more recently, other species of the genus as well,

constitute crucial evidence in regard to the validity of the

mutation hypothesis on the botanical side. A great many

investigations on the genetics and cytology of O. lamarck-

iana and other species, as well as crosses between species

and ‘‘mutants’’ of Enothera, have been carried on during

the past decade by De Vries, and his followers and oppo-

nents. As a result a huge and highly technical literature

has grown up. @Œnothera is obviously regarded, on the

botanical side at any rate, as the touchstone of the muta-

tion hypothesis as formulated by De Vries. Obviously

if this genus does not stand the test of critical investiga-

tion, the mutation hypothesis, so far as its validity de-

pends upon De Vries’s chosen illustration, is discredited.

Since @nothera and by obvious implication the Ona-

grace, to which it belongs, have become authority for

the mutation hypothesis, in its latest revival, they must

like Cæsar’s wife be beyond suspicion. Like Cæsar,

(Enothera has become a name of authority and its family

affairs accordingly, should be beyond suspicion, when sub-

jected to the most searching investigation. It is appar-

ently just in this direction that the weak spot of the muta-

tion hypothesis lies. Too much attention has apparently

been given to ringing the changes on the so-called mutants

of Gnothera and not enough to the investigation of

the general morphological situation in the Onagracee, to

which this much-discussed genus belongs.

Unusual variability in plants is ordinarily regarded as

prima facie evidence of hybridism and the suggestion has

in fact frequently been made by professional geneticists

(e. g., Bateson, Davis, East, Gates and others) that

(nothera lamarckiana is a hybrid. It is perhaps of inter-

est in this connection to recall that one of the commonest

expedients adopted by the practical breeder, for breaking

No. 577] MUTATION THEORY OF DE VRIES 7

up the continuity of the germ plasm, is hybridization.

Apposite in this connection is the wholesale hybridizing

practised by Burbank, for the purpose of bringing about

the necessary genetic plasticity in his cultures and thus

obtaining by resultant mutation or variation, new and

desirable varieties of useful plants. The morphological

peculiarities of hybrids have been clearly recognized for

nearly a hundred years. They are for example clearly

set down in Gaertner’s rare and classic prize essay, en-

titled ‘‘ Versuche und Beobacthungen ueber die Bastarder-

zeugung im Pflanzenreich’’ (Stuttgart, 1849). Curiously

enough these important criteria have been largely ignored

by the adherents of the mutation hypothesis of De Vries.

A very important and generally observed difference be-

tween hybrids and genetically pure species, is the very

easily detected one of pollen sterility, partial or complete.

Of course when the hybridizing forms show a considerable

degree of compatibility, this character may be inconspicu-

ous or even absent. Further even in cases where it is

originally present, it may be subsequently largely elimi-

nated by selection. De Vries himself has noted that about

one third of the pollen of O. lamarckiana is abortive. The

English geneticist Bateson was struck with this peculiarity

of the species, so much discussed in recent years, in rela-

tion to its variable offspring in cultures and promptly and

first called attention to the obvious significance of this

feature, suggesting that O. lamarckiana was a hybrid and

that its remarkable conduct was the result of hybridiza-

tion. This objection has in reality never been met. It is

the purpose of the present article to show on grounds

commonly accepted by geneticists and morphologists, that

not only is genus Œnothera in general characterized by

genetically impure or hybrid species, but that the condition

of genetical impurity is extremely common in the nma

graceæ as a whole.

It will be convenient to begin with the examination of

our common and very variable garden Fuchsias, which

belong to the family Onagraceæ. The common Fuchsia,

8 THE AMERICAN NATURALIST [ Vou. XLIX

sometimes known to gardeners as Fuchsia speciosa, is

recognized as a hybrid derivative of Fuchsia magellanica,

a native of southern South America. Fig. 1 illustrates

bic. 1

photomicrographically, the condition of the pollen in one

of the garden varieties of Fuchsia. The sound pollen

grains appear as dark bodies with two or more germina-

tion pores projecting from their surfaces. The dark color

of the grains is due to the deeply staining character of

their protoplasmic contents. More than a third of the

pollen present in the anther cavity is abortive and is

represented in the photograph by shrivelled light-colored

objects, which are in fact empty and collapsed pollen

grains. In other varieties of the garden Fuchsia, the

grains may either be entirely abortive and empty (as is

the case for example in the so-called mutant of Ginothera

lamarckiana, known as O. lata) or they may all be more or

less well developed so far as their protoplasmic contents

are concerned, but extremely varying in size. In the pres-

ent description, perfection or imperfection of pollen is

judged only from the morphological aspect, because this

is the significant point of view from the standpoint of the

No. 577] MUTATION THEORY OF DE VRIES 9

detection of hybridization. Physiological sterility is fre-

quently due to entirely different causes than genetical lack

of harmony, as for example in the horseradish “or the

potato (Solanum). In the former it has been found pos-

sible to bring about the formation of fertile seed by simply

girdling the top of the subterranean storage region of the

plant, so as to prevent the undue descent of assimilates.

The common white lily, Lilium candidum, presents a

similar condition, for here the setting of seed takes place

only when the leafy flowering axis is severed from its

bulb and kept in water. So far as I am aware, there have

been no experiments as to the result of severing the con-

tinuity of the phloem (girdling), in relation to the restora-

tion of seed production in the potato. The common yellow

day lily (Hemerocallis) possibly presents a case similar

to that of Lilium candidum, for it does not ordinarily set

seed, although in all the examples I have examined the

pollen was morphologically perfect. I have not yet been

able to secure flowers of any pure species of Fuchsia, a

genus which flourishes mostly in the remoter parts of

South America and in the New Zealand islands. The

cultivation of Fuchsias, although once very popular, has

now gone out of vogue and it is consequently difficult to

secure specimens of the species. As has been pointed out

the commonly cultivated Fuchsias are of hybrid origin.

We may now turn our attention to a very puzzling genus

of the Onagracex, namely Epilobium. This genus has

been a great riddle.to systematists and the determination

- of species has been extremely difficult on account of their

extreme variability. In European systematic works, this

high degree of variability is recognized clearly to be

largely due to hybridization and in such a standard work

as the ‘‘Naturliche Pflanzenfamilien’’ of Engler and

Prantl, the statement is definitely made that the various

species of Epilobium frequently and commonly hybridize

with one another in nature. Let us consider in this con-

nection the northern hemisphere cosmopolitan species,

known as Epilobium angustifolium, the willow herb or

10 THE AMERICAN NATURALIST [Vou. XLIX

fire weed, which by contrast to many of the other Epilo-

biums, is so constant and distinct that it is frequently

referred to a separate genus, Chamenerion. This species

shows its most marked distinction from other species of

Epilobium (Epilobium proper) in the fact that its pollen

grains are separate and not in tetrads, as is the case in

other common species. Fig. 2 reproduces photograph-

ically a transverse section of a mature flower bud of

E. (Chamenerion) angustifolium. On the outside are

seen the floral envelopes, two in number, composed, as is

the rule in the Onagracex, of four parts each. Within lie

four stamens represented by their anther sacks and inter-

nal to these are four stigmas representing the carpellary

or ovarial portion of the flower. The photograph is on a

sufficient scale of magnification to show the pollen grains

in the loculaments or cavities of the anthers. Obviously

the pollen is very uniform and perfect in its development.

Fig. 3, likewise photographic, illustrates the organization

of the pollen as viewed with a much higher magnification

of the microscope. Although some of the grains are only

No. 577] MUTATION THEORY OF DE VRIES 11

partially included in the plane of section, it is quite clear,

that like those of Fuchsia, figured above, they have pro-

jecting germination pores, but unlike the Fuchsia of our

illustration, all the pollen grains of Epilobium (Chame-

nerion) angustifolium are perfectly developed. I have

examined the pollen of the species under discussion from

widely separate geographical regions and under different

conditions of growth and season, with the uniform result,

E n As p 7

a AR “en pa

Fie. 3

that the pollen is perfect and invariable in any important

respect. E. angustifolium is a species which apparently

is not known to hybridize with other species and indeed it

is not easy to see how it could cross with those having

their pollen grains in tetrads. The perfection of the

pollen in view of this condition appears particularly sig-

nificant. The failure of E. angustifolium to hybridize in

- nature with other species of the genus is doubtless due to

the fact that it is morphologically very distinct from these

and would in all probability produce, if artificially crossed,

only sterile hybrids.

We may now turn by way of comparison to a species

of Epilobium of the ordinary type. Fig. 4 illustrates

12 THE AMERICAN NATURALIST [ Vou. XLIX

photographically the floral organization of Epilobium

hirsutum, as seen in transverse section of the bud just

about to open. The illustration shows the floral envelopes

and the stamens, together with the pistillary portion of the

flower, the latter being somewhat displaced in the figure

and cut through the region of the style. The long hairs

] teristic of the calyx of this species have been

trimmed off, for the purpose of facilitating photo-

mechanical reproduction. As in the two illustrations

above, the anther sacks are the most significant feature.

Even with the low magnification employed for the purpose

of illustrating the whole flower, the pollen grains in the

loculaments of the anthers are easily discernible and pre-

sent a striking contrast to those of E. angustifolium, in the

respect that they are in groups of tetrads. Some of the

groups are partially or wholly made up of individual

grains without protoplasmic contents, which are smaller

in size than the normal grains. Fig. 5 shows one of the

anthers much more highly magnified. The anther walls,

cavities and the pollen grains are now clearly distinguish-

No. 577] MUTATION THEORY OF DE VRIES 13

able. Some of the grains are full size and present dark

contents. Others are considerably smaller and are devoid

of protoplasm. The latter are abortive or sterile grains.

We have in fact before us a hybrid derivative of E. hir-

sutum, commonly found near ballast in New England and

not unfrequently cultivated in gardens. Other species of

Epilobium in the stricter sense of the generic appellation,

show similarly abortive pollen development and the con-

clusion reached by old world systematists on the external

Fie. 5

characters, that hybridization is common among the spe-

cies of Epilobium proper, is entirely confirmed by the

study of the pollen. It need hardly be emphasized in this

connection, that imperfect pollen development has been

recognized for nearly a century by scientific plant breed-

ers, as a criterion of hybrids.

The genus Œnothera may now be profitably considered.

Fig. 6 presents a magnified view of a transverse section of

a mature flower bud of one of the commonest of eastern

species of (nothera, namely Œnothera biennis. The

floral envelopes are more voluminous than in the two

genera illustrated above. Within are the stamens and in

the center of the figure the style appears as a large

rounded structure. Even with the low magnification em-

ployed, it is easy to discern that the contents of the anther

sacks present a very different appearance from those of

14 THE AMERICAN NATURALIST [ Von. XLIX

Epilobium angustifolium. Many of the grains of pollen

are light colored and devoid of the protoplasm which

gives a dark appearance to the sound grains. Fig. 7 illus-

r ia PERRE 2

Pere

Passio =D.

Fig. G

trates a single stamen under a high degree of magnifica-

tion. The characteristic layers of the wall of the anther

sack, described comparatively and in detail in the classic

memoir of Chatin, can readily be distinguished. Within

lie the pollen grains. Clearly only a few of these are fully

developed and possess normal protoplasmic contents.

The greater number are shrivelled and empty. Judged

from the generally accepted canon of the abnormalities of

hybrids, O. biennis is of hybrid origin. This view of its

nature is in harmony with its wide degree of inconstancy

throughout its very extended range. This feature is

doubtless responsible for the fact that the genus Œnothera

is at the present time undergoing considerable elaboration,

on the part of systematists. I have satisfied myself that

the pollen peculiarities of O. biennis are uniformly pres-

ent in specimens collected hundreds of miles apart, from

the Province of Ontario, the shores of the Gulf of St.

No.577] MUTATION THEORY OF DE VRIES 16

Lawrence and the New England States. I have further

examined a large number of species of Œnothera from

various parts of the continent and in every instance have

found a greater or smaller amount of abortive pollen as a

characteristic feature of the anther contents. De Vries

in his ‘‘Mutationstheorie’’ describes the abortive condi-

tion of about one third of the grains in O. lamarckiana:

This feature has been seized upon with insight by Bate-

son, as indicating the hybrid origin of O. lamarckiana. It

is extremely curious that its significance should have

Fig. T

escaped De Vries and his numerous disciples on this con-

tinent. Not only is O. lamarckiana itself characterized by

a large proportion of abortive pollen but its so-called

mutants are similarly characterized. In the feebler ‘‘ele-

mentary species’? the pollen is often almost entirely

abortive (O. nanella) and this is also generally the situa-

tion in O. lata. It should be further noted in this connec-

tion that if O. lamarckiana is of hybrid origin, the: same

statement must hold of the other species of @nothera,

since like this much-disputed one, they are similarly char-

acterized, so far as they have been studied, by two corre-

lated features, namely more or less abortive pollen and the

peculiarity of throwing so-called mutants or ‘‘elementary

species’’ in cultures. As a consequence of this condition,

16 THE AMERICAN NATURALIST [Vou. XLIX

it becomes more or less a superfluity to study any partic-

ular species of Œnothera from the genetical and morpho-

logical standpoint, since it is the genus as a whole which

manifests the peculiar features, which have brought it so

much into the foreground of biological controversy during

the past decade. This is on the whole a satisfactory situa-

tion as it enables us to cut the perplexing gordian knot

involving the controverted origin of O. lamarckiana.

The mutation hypothesis of De Vries accordingly turns

not upon the finding of new herbarium specimens which

may throw light upon the origin of a particular species

but upon the much larger question of the genetical status

of the genus Ginothera as a whole. This question can be

settled only by consideration of the Onagracee as a whole

and of other families of the Angiosperms, which present

similar reproductive peculiarities. _

Before proceeding however to the discussion of the

facts recorded above in their relation to the mutation

hypothesis of De Vries, based on the conduct of O. lamarck-

iana in cultures, it will be necessary to make some brief

_ reference to other studies carried on in the laboratories of

plant morphology of Harvard University, which will be

published elsewhere, either at the present time or at a

later period. Obviously of great importance in the pres-

ent connection is a comparison of the conditions of spo-

rogeny found among the lower plants, the Bryophyta, the

Pteridophyta and Gymnosperms, which are not character-

ized by enormous multiplication of species, with the

sporogenic features of the Angiosperms in which the

multiplication of species has run riot. Further compari-

son of liverworts, belonging to the Marchantiales, Antho-

sperms, manifesting similar sporogenic and specific pecu-

liarities, is both pertinent and necessary, in the present

connection.

It will be convenient to deal first summarily with the

sporogenic conditions found in the lower forms of the

Embryophyta from the Bryophyta to the Gymnosperms.

In the present connection a considerable number of spe-

No. 577] MUTATION THEORY OF DE VRIES 17

cies of liverworts, belonging to the Marchantiales, Antho-

cerotales and Jungermanniales, both acrogynous and

anacrogynous have been examined with the general result

that the only sterile cells present in the capsule cavities

were the elaters. Infertile spores and hybridism both were

conspicuous by their absence in the forms studied. The

same statement mutatis mutandis holds for the true

mosses. Some indication of spore abortion was detected

in the extremely variable genus Sphagnum. It would

seem that natural hybrids exist to some extent in this

genus. Among the Pteridophyta both the Lycopsida and

Pteropsida were studied. None of the numerous Lycopsid

forms investigated showed signs of spore abortion or

hybridism. Among the Pteropsida, the only well-known

hybrids are found among what is probably the highest

family, the Polypodiacew. There is a considerable litera-

ture upon hybrid ferns, in which references to spore abor-

tion as an accompanying feature are common. No evi-

dence of hybridism in the form of abortive spores was

found in examples of the Marattiacee, Ophioglossacex,

Osmundacee, Gleicheniacex, etc., were found, although a’

large amount of material was examined. Among the

Gymnosperms, the Cycadales, Ginkgoales, Coniferales

and Gnetales were examined. The Coniferales yielded

only a single species of Abies, which showed evidence by

the presence of abortive pollen grains of hybrid origin.

The genus Pinus is very old and its species accordingly

very distinct. Not the slightest evidence of hybridization

was found here or in other numerous and widely distrib-

uted species of conifers, other than Abies mentioned

above. This does not of course preclude the discovery of

such conditions later. The writer has had the opportunity

of examining the spores of a number of fossil forms from

the Paleozoic and Mesozoic, still contained within the

sporangia, and in no case were abortive spores recognized.

The general conclusion can be drawn from the forms just

considered that hybridism is rare among them and that

18 THE AMERICAN NATURALIST [Vor. XLIX

where it occurs it is accompanied by the phenomenon of

spore abortion.

If we turn to the Angiosperms with their nearly one

hundred and fifty thousand recognized species, we find

that hybridism is very commonly recognized. It would

take us much too far to discuss the situation here at any

length. The consideration of a single important family

must suffice. The one chosen, as being of particular sig-

nificance in the present connection, is the Rosacee. We

have had a recognition for many years past on the part of

systematic botanists in this country and in Europe that

hybridism is extremely common as a natural condition in

certain genera of the Rosaceæ. The inference in such

cases is generally based on the blended character of the

hybrids themselves, which show to a large extent a com-

bination of the characters of their parent species. Pro-

fessor Brainerd has recently made some very interesting

investigations in this direction in the case of American rep-

resentatives of the Rosaceæ. The recognized hybrid forms

in the Rosaceæ are usually characterized by a considerable

degree of pollen sterility, unless the parents happen to be

species not very remote in relationship. In addition to

the recognized hybrids of the rosaceous species, the work

carried on in the Harvard laboratories has revealed a

large number of hidden hybrids or erypthybrids, which

are quite constant in their characters and are recognized

by systematists as good species, but differ from normal

species in the fact that their reproductive cells are to a

greater or less degree abortive. Species of this kind are

extremely common among those rosaceous genera, which

have become of economic importance, such as Rubus,

Rosa, Pyrus, Malus, Sorbus, Crategus, ete. Taking Rosa

as an illustration, in addition to numerous recognized

hybrids, there are many types recognized as good species,

e. g., Rosa blanda, in which the pollen is normally largely

abortive, in still other species, frequently those which are

isolated geographically, the pollen is quite sound, ʻe. g.,

Rosa rugosa of Japan. The latter type of species must be

No. 577] MUTATION THEORY OF DE VRIES 19

regarded as a species in the strict sense, while those of

the type of Rosa blanda, in which abortive pollen similar

to that characteristic of forms clearly recognized as hy-

brids, is present, are hidden hybrids. It follows that in

Rosa (or practically any of the other rosaceous genera

cited above), there are three types of individuals, namely

good species, hidden hybrids and open hybrids. The

middle condition is extremely common among the Angio-

sperms and is of the greatest importance in connection

with clear views in regard to the origin of species. Obvi-

ously constant or relatively constant hybrids can not rank

with pure species, such as are characteristic for example

of the Gymnosperms, in discussions in regard to the

origin of species by mutation or otherwise. The conduct

of such forms is conditioned to a greater or less extent by

their mixed blood. We may appropriately designate obvi-

ous hybrids as phenhybrids and those hybrids which are

recognizable as such by their internal morphological char-

acters as crypthybrids. Crypthybrids will probably when

studied more extensively in cultures by the geneticist, give

evidence of their hybrid origin in cultures. There can

be no doubt that many of the recognized species of the

Angiosperms are in reality erypthybrids. The enormous

multiplication of species in this great group of plants is

in all probability largely related to hybrid crossing. It

is of the utmost importance however to keep clearly in

mind that such hybrid species or erypthybrids are not at

all in the position of true species from the evolutionary

standpoint and that conclusions derived from their study

can not be applied without large reserves, to the question

of the origin of species in the strict sense. The species of

Pinus, so far as we have any evidence, since the main

types are known to have existed well back into the Meso-

zoic, in all probability illustrate the origin of species some-

what along the lines of the Darwinian hypothesis. On the

other hand the species of Rosa present obviously an

entirely different problem in evolution and the necessity

of making distinctions if we are to reach any definite bio-

20 THE AMERICAN NATURALIST [Vou XLIX

logical goal is very clear. A great deal of the pessimism

which at the present time is sending too many biologists

after strange gods in other scientific shrines is doubtless

to be traced to the failure to make this distinction. It may

not be possible to make the distinction in all cases even

among the higher plants; but it certainly will be necessary

to realize its significance. Probably plants will in regard

to this possibility enjoy in this respect, as in so many

others, an advantage over animals in the studies of the

experimental evolutionist.

.We may now consider with advantage the status of the

species of the genus @Œnothera. The pollen sterility

which characterized them all to a greater or less degree

is indisputable evidence of their probable hybrid origin.

The general situation in regard to the criteria of hybrid-

ism in plants has been recognized for nearly a hundred

years. It has been made clear by Bateson in regard to

(Enothera lamarckiana. The observations chronicled

here appear to make it obvious that all the species of

(nothera are in the same boat genetically, that is that

they are all of hybrid origin. They likewise probably will

all be found to ‘‘mutate’’ just as O. lamarckiana, O. bien-

nis, etc., are already known to do. It may appear later

that there are certain species which have escaped, through

geographical isolation or other causes, the mingling of

blood, which is certainly characteristic of the Ginotheras

of the Eastern United States. So far as we know them

at present, the species of @nothera are obviously in the

same position as such species as Rosa blanda, that is they

are crypthybrids. Doubtless the peculiarities of O. la-

marckiana, O. biennis, etc., can be more clearly explained

in the present condition of our knowledge as the result of

hybrid origin than in any other way. It follows that the

doctrine of mutation so far as it depends for its support

upon the @notheras is in a discredited condition, as an

explanation, in any proper sense of the term, of the

origin of species.

No. 577] MUTATION THEORY OF DE VRIES 21

CONCLUSIONS

1. The Onagraceæ are largely characterized by hybrid

contamination in nature,

2. This statement holds with particular force for

(nothera lamarckiana and other species of the genus

(nothera, which have served as the most important basis

of the mutation hypothesis of De Vries.

3. Constant hybrids or erypthybrids are of very com-

mon occurrence among the Angiosperms and have been

illustrated in the present article by reference to the gene-

tical conditions occurring in certain Rosacee.

4. The species of Œnothera are to a large extent, if not

wholly, erypthybrids.

5. The objection raised by Bateson to the genetical

purity of @nothera lamarckiana is confirmed and is ex-

tended to the Onagracee in a general way, as well as to

other species of @nothera.

6. Hybridism is the best explanation yet put forward of

the peculiar conduct of @nothera lamarckiana, as well as

other species of the genus in cultures.

7. The mutation hypothesis of De Vries, so far as it is

supported by the case of (nothera lamarckiana, is

invalidated.

Ics. 1 AND 2 at Tor; Fics. 3 AND 4 IN THE MIDDLE; Fics. 5 AND 6 AT

1-4

~4, in terms of hia all the rabbits described in these experiments have been

classified. Fig. Rabbit 4214, Fat of the Serles I Young. Fig. 6, Rabbit

40A, Father of the Series II Youn

THE ENGLISH RABBIT AND THE QUESTION OF

MENDELIAN UNIT-CHARACTER CONSTANCY

W. E. CASTLE AND PHILIP B. HADLEY +

Wuatever the theoretical importance of Mendel’s law,

its practical utility depends largely upon the purity of

the gametes. If Mendelian unit-characters can through

hybridization be recombined in desirable ways without

essential modification during the process, Mendel’s law

is evidently a distinct acquisition to the practical breeder.

` Nevertheless, if crossing is likely to produce considerable

changes in the characters which it is desired to combine

in a new race, it is evident that Mendelian crosses must

be used judiciously and with caution by the practical

breeder.

Considerations such as these have led the senior author

for several years to concentrate his studies of genetic

problems upon the question of gametic purity. As a

crucial experiment he conceived the plan of deriving an

entire race of animals, not from a single pair of ancestors,

but from a single gamete, so far as concerns a particular

unit-character. It was thought that in a race so derived,

if the principle of gametic purity holds, there should be

no variation whatever in the particular unit-character

concerned.

Color patterns of mammals seemed especially well

adapted for such studies, since they are early differen-

tiated and clearly Mendelize in crosses. The so-called

“English” piebald rabbit presents an especially fine

example of such a color pattern. The figures give a

good idea of this striking pattern in which white and

colored areas are interspersed much as in the ‘‘coach-

1 Joint publication of the Laboratory of Genetics of the Bussey Insti-

tution, Harvard University, and of the Agricultural Experiment Station

of the Rhode Island State College (Contribution 211).

24 THE AMERICAN NATURALIST [Vou. XLIX

dog.” It would be a distinct gain to breeders if they

could reduce the variation in details of the English pat-

tern so that ‘‘prize-winners’’ could be bred without the

production of so many ‘‘wasters,’’ which depart in essen-

tial points from the standard pattern adopted for the |

breed. This was an additional reason for undertaking

work with the English rabbit.

The first standard-bred English rabbits which the

senior author had under observation, when mated inter se,

produced young of three sorts. About half the young

were fairly good ‘‘standard’’ English extensively marked

with colored spots (see Fig. 3). About one fourth were

much whiter than the standard demands, their spots being

fewer and smaller (see Fig. 1). And the remaining

fourth were without spots, that is, were self colored.

This last class was found to be recessive and not to pro-

duce English offspring, if mated inter se.

The whiter-than-standard English proved to be homo-

zygous for the pattern, the ‘‘standard’’ English being

heterozygous and breeding like their parents.

From these observations it was clear (1) that the Eng-

lish pattern is a Mendelian dominant and. (2) that the

breeding of English rabbits resembles that of blue

Andalusian fowls. For the standard-bred animal is a

heterozygote in the production of which there is bound

to be a constant production of ‘‘wasters’’ unless either

the standard is changed or the homozygote can be changed

to conform with the standard, producing an animal with

more color. In the latter case homozygotes could be

bred with each other and wasters eliminated. The ques-

tion whether the pattern can be changed becomes there-

fore one of practical as well as theoretical interest.

In making crosses of English with other breeds of

rabbits, there was found to be considerable variation '

among the heterozygous English produced, some being

much whiter than others, i. e., having less extensive

colored spots. Plus (dark) and minus (light) selections

were made to see to what extent the pattern was capable

No. 577] UNIT-CHARACTER CONSTANCY 25

of modification. These selection experiments are still in

progress, but will be reported upon at another time.

The single-gamete experiment, with which this report

will deal, was placed in the hands of the junior author,

who has carried it out at the Rhode Island Agricultural

Experiment Station.

As foundation stock for the experiment a single hetero-

zygous English rabbit of standard character (grade 2,

Fig. 5) was selected. To mate with him, it was desired

to obtain a distinct breed of rabbits, free from the Eng-

lish pattern, and as pure (uniform) in all respects as

possible. For this purpose the ‘‘Belgian hare’’ was.

chosen. A buck and two does obtained from Mr. G. W.

Felton, Cliftondale, Mass., were found to breed very true.

From them was bred a stock of does very uniform in

character, twelve of which, together with one of the par-

ents (24), were mated with the selected English buck

which we may henceforth call by his record number §214.

The young thus produced will be called ‘‘Series I’’ off-

spring. About half of them were self (non-English), the

remainder (187 in number) were English.? The latter,

although all undoubtedly heterozygous, varied in white-

ness from grade 1 to grade 4 (Figs. 1-4), the modal or

commonest condition being about the same as that of the

: father (grade 2). The distribution of the young in rela-

tion to our grades is shown in Table I. Statistical treat-

ment of the table gives the average grade of the young as

2.43, that is somewhat darker than the father. Inspec-

tion of the table shows that more than half of the young

are darker than the father, which supports in a general

way the statistical average grade. If we consider sepa-

rately the average grade of the young produced by each

2 The total number of young obtained from 421A, when mated with Bel-

gian hare does, has been to the time of writing 436. The English young

now number 210, the non-English (self) number 226. For Series II mat-

ings presently to be described the corresponding numbers of young are:

English, 219, non-English 196, total 415. For Series I and II combined

the numbers are: English 429, non-English 422, total 851. This is un-

mistakably a 1: 1 Mendelian ratio. -

= 26 THE AMERICAN NATURALIST [Vou. XLIX

mother, we find that it ranges from 2.15 in the case of

?18F, which had 5 English young, to 2.79 in the case of

916D, which had 14 English young. The average number

of English young to a mother is 14.4.

After this series of matings had been completed, a

second series was begun in which the same 13 females

were mated with one of the darkest bucks produced in the

Series I matings (a son of 2916H#). The selected buck was

340A (Fig. 6), grade 3.75, considerably darker than his

father (Fig. 5). This series of matings produced 189

English young, together with a like number of self (non-

English) young. The grade distribution of the English

young is shown in Table I, Series II. All of the 13

mothers except one (9916F) produced darker offspring in

the Series II than in the Series I matings. The lowest

average grade was shown by the young of 917G, viz., 2.44.

For Series I matings the lowest average was 2.15. The

highest average grade in the Series II matings was given

by the young of ?162#, viz., 3.50. For Series I matings

the highest average was 2.78. Consequently, both maxi-

mum and minimum averages were higher in the Series IT

than in the Series I matings. The grand average of all

the 189 Series II offspring was 2.92 as compared with 2.43,

the average grade of the Series I young. Their modal

grade is 3.25. The modal grade for Series I was 2.00.

Since the mothers were identical in both series, the differ-

ence in the young can be attributed only to the difference

in the fathers. The male used in the Series II matings

differed genetically as well as somatically from his father,

who sired the Series I young. Not only was he darker,

but he also produced darker English young. Yet the

father contained only a single dose (one gamete) of Eng-

lish pattern and the son derived his English pattern ex-

clusively from this same source. Hence the English

unit-character had changed quantitatively in transmission

from father to son. This seems to us conclusive evidence

against the idea of unit-character constancy, or ‘‘gametic

purity.’’ If unit-characters are not constant, selection

No. 577] UNIT-CHARACTER CONSTANCY 27

reacquires much of the importance which it was regarded

as possessing in Darwin’s scheme of evolution, an impor-

tance which many have recently denied to it.

TABLE I

SHOWING THE DISTRIBUTION OF GRADES OF OFFSPRING IN THE First AND

SECOND SERIES OF MATINGS FOR EACH INDIVIDUAL MOTHER

| Grades of Young Totals | yess

Mother Series! > | | PEA, 5 = | age

ewes R E EOR E E 5 4.00 Ser. I Ser.II

iča Di EEK Oo Ro ihe aed a 2S Lk ERR ga ear 2.30

II | Sie Ses Bee oh hae ee ee 21 | 3.03

MB rc a a Be a eT eo 1 Fi Seen 2.39

Bas ed a ie ES a hs as 12 | 2.67

16D | I epee 2] 5].../...] 1) 2) 8) 1 ita 2.79

U ikea e e a E Bno.: 12 | 3.19

IOR A Tee akat GR barle A cle i ea 2.29

of: Spgs PA ees ess TER Gi Nae Sey BR oper 5 | 3.50

16F | I |1 Caeo ads bA OE Bares WES 2.62

II | Ee Bae St 2 Se wie i gd Roe aes a 11 2.48

16651 Bed r E Be Bet ah. Wi 2.35

II et ak eA be e p 13 3.06

16H | I dio ee 81 1) Ss) Bt 2 Bt a 8 1 2.76

II rq eeeGn 2 oy Cane kes ge HOM Eini 20 | 3.06

yd ag ke Le a Otay See) 2 2 PD ot BS ig SRR 2 2.36

II 9) 87 G Sy Se a be: 27 | 2.97

17G i í POT Ot 81 St. Sik St aer AE 2.27

be pie ecm ip a ee 2 a oe Et ee ee We et ke ge Been 9 | 2.44

isp | I Pitot aseen TI Rie Iio 2.58

II ie Re ee Sie Bie 8 Sr. ee Da 16 | 2.91

sf | I ao Po e oes clos eee OP a eee OK: 2.15

II ree ie Se Ge ee ae) Oe Oe ie e 16 | 2.97

18H | I Blac are Bi ie al 10 a. 2.43

H Pete ey Bieta ice e aoe 19 | 2.87

RA ay De ee ee OT Bt 2d ors ie chs O Recess | 2.22

II UALS i gan ter es ey a Bfe 8 | 2.78

Totals] I | 1 | 5 |10|18|33/31/24/16/18/11/13| 6| 1 | Tg | 2.43

II 1 5117 13/10912% 18 | 37/27/14} 7 |..... 189 | 2.92

The question whether an imaginary ‘‘unit-factor’’ for

English pattern has or has not changed in correlation

with the visibly changed English unit-character is not

here discussed. We recognize that it has an academic

interest, which, however, scarcely affects the practical

question whether the visible Mendelizing characters of

animals are subject to change through crossing or through

selection or both.

™

CONTRIBUTIONS FROM THE ZOOLOGICAL LABORATORY

OF THE MUSEUM OF COMPARATIVE ZOOLOGY AT

HARVARD COLLEGE, NO. 256.

ON THE NUMBER OF RAYS IN ASTERIAS

TENUISPINA LAMK. AT BERMUDA!

BY W. J. CROZIER

HARVARD UNIVERSITY

I. It was suggested by Clark (1901) that the average

number of rays borne by Asterias tenuispina was different

for separate localities in Bermuda. He examined forty

specimens of this species—eleven from Coney Island and

twenty-nine from Harrington Sound; in the first set the

average number of rays was 5.91 (I find the mode to be 6),

in the second set 6.93 (with a mode of 7). If this condi-

tion really obtains, it would be an exceedingly interesting

matter to determine the factors responsible for this sort

of difference. I have therefore examined a number of

Asterias (312 in all) from several localities in the Bermu-

das, namely: Agar’s Island, Spanish Point, Hawkins

Island, Ely’s Harbor, Hungry Bay, Harrington Sound

and Coney Island; the first four are situated on the

periphery of Great Sound, the others at widely removed

` points on the north and south shores. For the identifica-

tion of these places, references may be made to the maps

published by Mark (1905).

These observations were made at the Bermuda Biolog-

ical Station, mostly during the summer of 1914.

II. The first lot of starfishes was collected in the imme-

diate vicinity of Agar’s Island in 1913. The number of

rays varied from 2 to 9; the frequency distribution is

given in Fig. 1. The modal number of rays is clearly 7.

In 1914 a collection of Asterias from this place gave the

ray frequency distribution shown in Fig. 2, where the

modal number of rays is again 7. Collections, during

1914, at the other stations named gave the following ray

frequency counts:

1 Contributions from the Bermuda Biological Station for Research, No. 35.

No. 577] NUMBER OF RAYS IN ASTERIAS ° 29

Station and Year Pheer, By aol See Figure

Agar’s Isl., 1913 43 7 1

Agar’s s Isl., 1914... 62 7 2

Spanish Point, 1914 33 7 3

w sl., 1914 39 7 4

y's Harbor, 1914 36 7 5

Hungry Bay, 41 7 6

Coney Island, 1914... eien oes 20 7 1

Harrington od 1914 38 7 8

The modal number of rays is in each case 7. This is

true for the same locality in two successive years, for

near-by localities and for places widely enough separated

ole queney

Island - I914.

to yield oiii data relative to the suggestion which

prompted this inquiry. For the total population ex-

amined the ray frequency distribution, which of course

gives a mode of 7 rays, is plotted in Fig. 3. It is to be

noted further that according to Ludwig (1897, p. 345) the

most common number of rays in A. tenuispina from the

Mediterranean is also 7.

III. It has been observed by every one who has studied

A, tenwispina that in most of the individuals the rays oc-

cur in two groups, those of one group being longer than

those in the other, though within each group the rays are

of about the same length. This condition is evident in

259 (83.6 per m of my specimens. There is ee a

30 THE AMERICAN NATURALIST [Vou XLIX

agreement (cf. Ludwig, 1897, and Ritter and Crocker,

1900), that in some cases, if not in all, ‘‘this disparity in

size is due to the regeneration of halves of automatically

bisected animals.” My observations fully confirm this.

I have witnessed, as did Ludwig, several cases of spon-

Fre quency

taneous self-division in the laboratory. The casting off

of one or more rays may at any time be induced by holding

or injuring one or several rays, or by the stimulation of a

ray with dilute acid applied with a pipette. The autotomy

of a single ray takes place very much as described by

King (1898) for Asterias vulgaris ; the existence of a

ss Jo in the region of the ae ae

No. 577] NUMBER OF RAYS IN ASTERIAS 31

ossicle is shown by the fact that even in preserved ma-

terial the rays part very easily in that region.

The relative abundance of cases in which there are evi-

dent two groups of rays of different length indicates that,

as in Linckia (Clark, 1913), autotomous division is a

normal method of asexual reproduction.

FIG. I

istribution ofray Ser ok a bey

H individuals with all fe

Jor nearly equał len gts BSE

Distribvtion of rey frequencies*

in the total population. i

Relatien of long to shert

IV. The numerical relations of the old rays to the re-

generating ones, and the topographical arrangement of

the latter, yield evidence relative to certain questions in

the physiology of regeneration.

(a) It is to be observed that the regeneration in ques-

tion has taken place apart from experimental control;

therefore information as to the number of rays usually

present just before Asterias undergoes self-division must

deduced from the data at hand. The modal-ray fre-

quency for specimens with rays of very nearly equal —

length is 7 (Fig. 10), but it is a question whether this ap-

pearance of equality in ray length may not be due to a — .

32 THE AMERICAN NATURALIST [Vou XLIX

variety of conditions, especially the rapid growth of re-

generated rays. The regenerating rays of Linckia (Clark,

1913; Monks, 1904) and the newly formed rays of multi-

radiate types (Ritter and Crocker, 1900) grow more rap-

idly than the old ones and soon reach the dimensions of

the latter; this is also indicated in my series. But the cor-

relation of the number of long with the number of short

rays (using only those cases in which the two groups were

clearly distinct) makes it evident (Fig. 11) that the condi-

tion in which there are 3 or 4 long rays and 4 short ones is

by far the most common; and further, that the cases in

which there are either 3 or 4 long rays are almost equally

abundant. It seems not unlikely, then, that A. tenuispina

usually has 7 rays before it divides, and that it divides

into two parts having, respectively, 3 and 4 rays, the divi-

sion-surface then giving rise, in the greater number of

cases, to 4 new rays, but sometimes to 5, 3 or even 2.

If all the individuals observed had undergone autotomy

and regeneration according to this scheme, then those

with 7 and those with 8 rays would be expected to occur

in equal abundance; 8 is next in frequency to 7, but the

latter preponderates because some starfishes have prob-

ably not autotomized at all, and because all the animals

which have divided do not adhere to this paradigm (see

Fig. 11). Yet, in the majority of cases, 4 rays are regen-

erated whether there are 2, 3 or 4 long (old) rays in

evidence.

It would seem that self-division may occur at any time

in the life history of A. tenuispina, or at least in animals

of all sizes, though it is my impression, gained from hand-

ling many live individuals, that the smaller (younger ?)

ones autotomize more readily than larger ones. Those

showing two distinct ray groups ranged in longer ray

length from 11 mm. to 65 mm. There is no evidence that

autotomous divisions follow one another rapidly, or in-

deed that they occur more than once in any given indi-

vidual.

One case was observed in which there was one long ray

only, and 6 shorter ones. This may mean that a single

ray can regenerate the whole body, as suggested by v.

No. 577] NUMBER OF RAYS IN ASTERIAS 33

Martens (1866, quoted by King, 1898) for this species.

I have not been able to substantiate this idea by laboratory

experiments, for, in my tests, single isolated rays did not

live more than a few weeks.

(b) Newly forming rays have a tendency to appear in

symmetrically disposed pairs (see Fig. 12), which gives to

Se FIG, 12.

Ase Wat

DIAGRAMATIC REPRESENTATION OF THE RAYS OF Four ASTERIAS, SHOWING TEND-

Y OF RAYS TO APPEAR IN Parrs. Measured from the mouth along

the ventral side.

X e X

FIG,.13.

RB Raia THE RELATIONS OF New Rays.

many individuals a strikingly bilateral aspect. This is

accentuated by their behavior, for, in the absence of

directive stimuli, they commonly move with the longest

rays in advance. In moving away from the light, the loco-

motor movement of the group of longer rays also tends,

in many cases, to produce a spurious ‘‘orientation.’’

When placed oral side up, the larger rays exert a de-

termining influence on the direction and manner of right-

ing. These effects are due to the greater pedicel and

muscle development of the longer, thicker, rays.

e formation of two rays at a radial cut on the disc

was found by King (1900) in Asterias vulgaris.

V. I have suggested, above, that Asterias with 7 sub-

equal rays have probably arrived at that condition by

different routes. One method of ray multiplication ap-

pears to be the spontaneous addition of new rays at any

point on the disc. Twelve starfish were found which

showed but one ray markedly shorter than the others.

34 THE AMERICAN NATURALIST [Von. XLIX

Of these, 4 had 5 long rays, 4 had 6, 2 had 7, 1 had 3 and

1 had 4 (see Fig. 11). The addition of new rays during

adult life is, so far as known, unusual among starfish, ex-

cepting in the multiradiate forms (cf. Ritter and Crocker,

1900; Clark, 1907; M’Intosh, 1907). The twelve cases

found in A. tenuispina may mean merely that a single ray

has been cast off and is being regenerated, for there is

found about the same percentage of naturally occurring

regenerating examples of A. vulgaris (King, 1898; 1900).

Yet I am inclined to interpret this condition as indicating

the way in which the modal hepta-radiate form is derived

from the fundamental penta-radiate one, or from a hexa-

radiate plan, if the young of A. tenuispina be like the post-

larve of Pycnopodia (Ritter and Crocker, 1900) previous

to self-division.* The three smallest Asterias seen had

6 rays. These were subequal and 8+ mm. long. Other

specimens, slightly larger, had either 7 or 8 rays.

Cases such as those illustrated in Fig. 13 may further

prove that addition of new rays occurs independently of

the reformation of rays subséquent to self-division. :

VI. The number of madreporites in A. tenuispina is

also variable, as noted by Ludwig (1897, p. 358) and

others. The number of madreporic bodies is certainly not

correlated with the size of the starfish. One of the small-

est ones seen had 8 rays and 5 madreporites, its mean ray

length being 10 mm.; while the largest animal collected

had 5 rays, with a mean ray length of 70 mm., and but one

madreporite. The table in Fig. 14, which includes all

cases in which the madreporites were counted, shows that,

while the distribution of these bodies is irregular, their

number is to some extent correlated with the number of

rays. Ludwig gave it as his opinion that there was no

correlation of this sort. The relation stands out more

clearly if only those individuals having equal rays (and

therefore presumably ‘‘full grown’’) are included (Fig.

15). Unfortunately, the number of animals is small.

Multiple madreporites were noted in 5 out of 101 ex-

3 According to Clark’s (1907) studies, the young Heliaster has five rays

only; his results throw considerable doubt upon the correctness of the

conclusions of Ritter and Crocker.

No. 577] NUMBER OF RAYS IN ASTERIAS 35

amples. Three of these showed a condition which might

have arisen either by the fusion of two plates or by the

division of a single one. The other two cases were simi-

lar, but of trefoil form. Dissection showed, in each in-

stance, that a single stone canal was present. Therefore

these multiple plates had probably arisen by the division

of an originally single one. (For a similar condition in

A. vulgaris, see Davenport [1901].) Only one multiple

madreporite was found in any one individual.

SUMMARY

1. The modal number of rays in Asterias tenuispina

is 7. The range in ray number is from 2 to 9.

2. The 7-ray condition is uniformly the most frequent,

even in widely separated localities.

3. The modal ray number is the same for animals with

subequal rays as for those with a group of regenerating

rays, 43 |

4. The evidence indicates that, most commonly, A.

36 THE AMERICAN NATURALIST [ Von. XLIX

tenuispina has 7 rays before it undergoes autotomy, that

it divides into 3-ray and 4-ray portions, and that each of

these parts regenerates 4 rays.

5. Regenerating rays tend to appear in bilaterally dis-

posed pairs, as regards size.

6. There is no evidence that self-division occurs often

in the life of individuals, though possibly it does.

7. New rays may be added at any point on the disc.

8. The number of madreporites varies from 1 to 5, and

is to some extent correlated with the number of rays; it is

not correlated with the size of the animal.

9. Double or triple madreporites occur in about 5 per

cent. of the individuals.

REFERENCES

Clark, H. L. 1901. Bermudan Echinoderms. A Report on Observations

and Collections Made in 1899. Proc, Boston Soc. Nat. Hist.,

Vol. 29, No. 16, pp. 339-3.

1907. gs kojen of the Genus Hetioster. Bull. Mus, Comp. Zodl.,

1, pp. 23-76, 8 pls.

1913. cate in Linckia. Zool. Anz., Bd, 42, No. 4, pp. 156-159.

Davenport, G. C. 1901. Variation in the Madreporic Body and Stone

Canal of Asterias vulgaris. Science, N. S., Vol. 13, pp. 374-

375

King, Helen D. 1898. Regeneration in Asterias vulgaris. Arch. f. Entw.-

mech., Bd. 7, Heft 2-3, pp. 351-

1900. Further Studies on Regeneration in . ateriat vulgaris. Arch.

f. Entw.-mech., Bd. 9, Heft 4, pp. 737.

Ludwig, H. 1897. Die Saciigins des Mittelmeeres. Fauna u. Flora d.

Golfes v. Neapel, Monogr. 24 x + 491 p., 12 Fig. and 12 Taf.

M’Intosh, D. C. 1907. Meristic Variation in the Common Sun-Star (So-

laster papposus). - Proc. Roy. Phys. Soc. Edinburgh, Vol. 17,

pp. 75-78.

Mark, E. L. 1905. The Bermuda Islands and the Bermuda Biological

Station for Research. Proc. Amer. Assoc. Adv. Sci., Vol. 54,

pp. 471-501, 16

Martens, E.von. : 1866. ela ostasiatische Echinodermen. Arch. f.

Naturg., Jahrg. 32, Bd. 1, pp. 57-88.

Monks, Sarah P. 1904. Variability and Autotomy of Phataria1 [Linckia].

Proc. Phila. Acad. Nat. Sci., Vol. 56, pp. 596-600.

Ritter, W. E., and Crocker, G. R: 1900. Multiplication of Rays and Bi-

Jateral Symmetry in the 20-rayed Star-fish, Pyonopodia heli-

anthoides (Stimpson). (Papers from the Harriman Alaska

Expedition, III.) Proc. Wash. Acad. Sci., ‘Vol. 2, pp. 247-274,

pl. 13, 14.

_ 1‘*Phataria’’ is an error, as pointed out by Clark (1913).

SHORTER ARTICLES AND DISCUSSION

MR. MULLER ON THE CONSTANCY OF MENDELIAN

FACTORS

In discussing the selection experiments of Phillips and myself

with hooded rats,1 Mr. Muller? accepts the explanation of ‘‘ modi-

fying factors ’’ which we offered to account for certain peculiar

results obtained, but rejects the idea which we also suggested,

that the chief genetic factor concerned may be undergoing quan-

titative variation. He rejects it on the ground that this ex-

planation is not ‘‘ in harmony with the results of Johannsen and

other investigators.’’ The work of Johannsen with seed-size in

beans and the work of others with Drosophila is cited in support

of this statement.

It is difficult to understand how the experiments of Johannsen

have any direct bearing on the case since no single Mendelizing

unit-factor was demonstrated in that connection; but in the

hooded pattern of rats a Mendelizing unit-factor is unmistakably

present and it is the quantitative variation of this which is under

discussion, not the presence of many or few additional factors,

concerning which Muller adopts our explanation. Appeal to the

work of Johannsen with bean-size to show that our conclusions

concerning color pattern in rats are incorrect is illogical because

the cases are not parallel. The citation by Muller of the work

on rabbit-size by MacDowell and myself? is equally non-germane,

because no demonstrable Mendelizing unit-factor is involved in

that case either. He might with propriety cite the bean work as

bearing on the interpretation of the inheritance of body size in

animals, or vice versa, since both involve blending inheritance.

But. neither of these cases has any direct bearing on the question

of unit-character constancy, since in neither case has a unit-

character, either constant or inconstant, been shown to exist.

The citation of work with Drosophila is more to the point, since

the ‘‘ mutations’’ of Drosophila Mendelize. But is it certain

that they do not vary? Muller admits that they do occasionally

vary, stating that ‘‘ in one case (possibly in two or three cases)

1 Castle and Phillips, ‘‘Piebald Rats and Selection,’’ Publ. No. 195, Car-

negie Institution of Washington.

2 AMER. NAT., Vol. 48, p. 567.

8 Publ. No. 196, Carnegie Institution of Washington.

38 THE AMERICAN NATURALIST [ Von. XLIX

a locus has mutated three times, each time in a different way.’’

He does not think that smaller changes than these have occurred,

since ‘‘ much smaller could easily have been detected.’’ From this

statement I infer that the opinion rests on casual inspection

rather than measurement, for which reason I do not attach much

importance to it. The hooded pattern of rats was not supposed

to vary quantitatively until its quantitative study was under-

taken. Two types of hooded rats were recognized, one more ex-

tensively pigmented than the other, and these were supposed to

be discontinuous like the several ‘‘ mutations of a locus’’ in

Drosophila. Quantitative study has completely dispelled this

idea as regards the hooded pattern of rats, and I have no doubt

the same would be true of Drosophila. How easy it is to be sure

of a thing which has not yet been investigated, so sure that in-

vestigation of it is considered a waste of time. Muller is con-

fident that such variation as occurs in Drosophila ‘‘ can not even

remotely be compared to fluctuating variability,’? and he gen-

eralizes thus:

“Tn no known case do the variations of a gene among, let us say,

several thousand immediate descendants of the individual possessing it,

form a probability curve.”

The use of the word ‘‘ gene ’’ in this sweeping statement safe-

guards the author, since no one, so far as I know, claims ever to

have seen a ‘‘ gene’’ or to have measured it. How could the

‘* variations of a gene’’ be expected to ‘‘ form a probability

eurve’’ if the gene is not measurable? But if the author will

allow the substitution of visible character for ‘‘ gene’’ in his

challenge, I will gladly accept it and I will add this generalization

for his consideration—No one has by actual observation and

measurement shown the existence of any visible character in any

animal which is not quantitatively variable.

As regards the mutations of Drosophila which Muller is con-

fident (apparently without having studied the matter himself)

do not vary so as to form a probability curve, I had sufficient

curiosity some months ago to suggest a quantitative study by one

of my pupils, Mr. D. H. Wenrich. Mr. Wenrich:studied the

wing-length of flies from a culture kindly supplied me by Pro-

fessor Morgan under the name “‘ vestigial.” In advance of a

more detailed publication, Mr. Wenrich kindly permits me to

state the following facts. The wing length measured in ocular

micrometer units was found to vary as follows:

No.577] SHORTER ARTICLES AND DISCUSSION 39

eee 25-29 30-34 35-39 40-44 45-49

Tensy Seay ee rs 6 34 67 43 3

Dep nhl R E E N Sawa S 50-54 55-59 60-64 65-69

Hume OS honey eae 1 1 0 1

The wing-length manifestly varies so as to form a pretty good

probability curve; what the ‘‘ gene’’ is doing, I do not under-

take to say.

It is, of course, conceivable that the variation here observed in

actual wing length might be due to variation in general body

size, larger flies having longer wings. To determine this point

measurements of tibia-length were made on the same flies, and

in the case of each individual the ratio was computed between

wing-length and tibia-length. These ratios are distributed as

follows: :

HAVIOR ssi. .70—.79 .80-.89 .90-99 1.00-1.09 eta 1.20-1.29

Frequencies 2 7 26 49 23

e SVU wks saute 1.30-1.39 1.40-1.49 1.50-1.59 1. wa 69 1.70-1.79

Frequencies ........ 7 3 0 0 2

It is evident that there is no constant relation between wing-

length and tibia-length, and so between wing-length and general

size, with which tibia-length is closely correlated. "App we ob-

tain a good probability curve. Does the ‘‘ gene’’ vary or are

we dealing also with additional modifying ‘‘ genes’’? We are

confronted here with the same problem as in the case of the rats.

But it is possible to assume that the considerable variation

shown by vestigial wings in Drosophila is purely somatic, ‘‘ phe-

notypic,’’ not due to genetic causes, and so would not show any

effects if subjected to selection. So it was thought in the case of

the plus and minus variations in the hooded pattern of rats,

before the experiment was made, but experiment has shown, even

to Mr. Muller’s satisfaction, that the variations are in part due

to genetic causes and that selection slowly and surely changes

the range of variability. Is it safe to assume the contrary for

Drosophila in the absence of all experiment?

Mr. Wenrich has also studied the wing-length of ‘‘ extracted ”’

vestigial flies obtained in the second generation from a cross

between pure vestigials and normal flies, and he finds that the

variability is regularly increased as compared with that of the

uncrossed vestigial race. This again is parallel with what occurs

when hooded rats are crossed with wild or with Irish rats, and

indicates that similar causes are at work in the two cases. Such

40 THE AMERICAN NATURALIST [Vou. XLIX

cases present to the genotype theory the following dilemma.

Hither one gene is concerned in the case or many genes. If one

only is concerned, it is variable. If many genes are concerned,

they are so numerous (whether or not constant) that they present

to the observer of the visible character affected a continuous

variation series, one capable of indefinite displacement up or

down the quantitative scale. The supposed distinction between

continuous and discontinuous variation then vanishes. Selec-

tion in that case meets with no “‘ fixed limit ” beyond which it

cannot go.

Mr. Muiler is seriously disturbed (p. 573) because we are will-

ing to consider it possible that the ‘‘ factor for hooded ”’ may be

contaminated by ‘‘ its allelomorph (the factor for self) ’’ while

associated with it in the zygote represented by the F; rats. (The

evidence of modification is unmistakable, however one at-

tempts to explain it.) He says this is ‘‘ violating one of the most

fundamental principles of genetics—the ‘non-mixing of factors—

_in order to support a violation of another fundamental prin-

ciple—the constancy of factors.” Now, when, I should like to

inquire, did these principles become ‘‘ fundamental ”?; by whom

were they established and on what evidence do they rest? I

should suppose that Bateson, president of the British Association,

might be considered fairly well posted on the ‘‘ principles of

genetics,’’ but neither in his earliest papers nor in his latest do

we find any mention of these sacred principles. In his recent

presidential address* he frankly states his belief that segregation

is often imperfect and that ‘‘ fractionation ” of factors fre-

quently occurs as a result of crossing.

We shall look in vain, I think, for those ‘‘ principles ’’ outside

of the ‘‘Exakten Erblichkeitslehre’’ (or its imitations), and when

we inquire as to the experimental basis of the principles in ques-

tion we are met with the satisfied reply, ‘‘Johannsen’s beans.’

What a slender basis and what and absurd one from which to

derive the ‘‘ fundamental principle ’’ that Mendelian factors are

constant! Yet to date this case, which admittedly involves no

clear Mendelian factor, is the only evidence worth mentioning in

favor of the constancy of Mendelian factors! Do biologists take

themselves seriously when they reason thus? Certainly no one

else will long take them seriously.

Finally, I may be permitted to correct two misapprehensions

4 Science, August 28, 1914,

No.577] SHORTER ARTICLES AND DISCUSSION 41

into which Muller in common with the Hagedoorns® has fallen,

viz., (1) that individual pedigrees were not recorded in the

course of our selection experiments and (2) that no considerable

amount of inbreeding occurred in our work.

It has been our invariable practise, upon recording the birth of

an animal and its grade, to record on the same line of the ledger

the record number of its mother and father. This enables one in

any particular case to trace back the pedigree to the very begin-

ning of our experiments. We have spent much time writing out

and studying individual pedigrees, but without discovering any

evidence of pure or prepotent lines or individuals, except in a

single case, that of our ‘‘mutant ’’ series, the origin and complete

history of which we have described in detail. The pedigrees,

however, of our rats are on record available for study at any

time; their full publication would be a quite impossible under-

takin

That extensive and intensive inbreeding has occurred in our

experiments will be obvious when I state that all our animals

were descended from a very small initial stock, less than a

dozen individuals, that from the beginning we have made the

most extreme selections possible, mating like with like, never hesi-

tating to mate brother with sister, and putting aside for strict

brother-sister matings any litter of young which seemed espe-

cially promising. I may say that in no single case (except that

of the ‘‘ mutant ”’ series) have these ‘‘ special’’ pens given us

advancement obviously greater or less than that of the general

selection series of which they formed a part. Nevertheless, we

are still continuing to follow them up and will later publish a

detailed account of them. Finally I would call attention to pp.

20 and 21 with Tables 48—49 of our full publication, in which

` are described the hooded offspring of a single selected hooded

and a single wild rat. The hooded and the wild rat produced

several young resembling the latter, that is, not hooded; these `

were mated inter se, brother with sister. Among the grand-

children (F,) occurred the usual 25 per cent. of recessives,

hooded. Two males were selected from these and mated with

females of as nearly the same grade as were available. This

process was repeated through seven generations in succession.

Seven times animals of like grade were mated together, brother

5 Zeit. f. ind. Abst. u. Vererbungslehre, 11, p. 145. See also my reply in

the same journal, 12, p.

42 THE AMERICAN NATURALIST [Vou. XLIX

with sister when possible, less often brother with half-sister,

rarely cousin with cousin. In this way were obtained 804 young

from rigidly selected, closely inbred descendants of a single pair

of rats, the series extending into generation F,. We have shown

(l. c., p. 21) that the progress of selection within this inbred

family follows a remarkably close parallel, generation by gen-

eration, to the progress of selection in our plus series as a whole.

Muller’s anticipation that a different result would follow close

inbreeding is not justified by our observations.

In discussing this experiment (p. 21) we have italicized the

statement that (so far as the hooded character is concerned) the

entire series is derived from a single hooded individual! When

the Hagedoorns made the statement that our stock had not been

sufficiently inbred, they had apparently not seen our full pub-

lication and so had no means of knowing to what extent it had

been inbred, but Muller, with our full publication before him,

apparently repeats the statement without taking the trouble to

verify it.

. W. E. CASTLE

BUSSEY INSTITUTION,

October 23, 1914

NO CROSSING OVER IN THE FEMALE OF THE

SILKWORM MOTH

IN a recent review’ of a paper by Y. Tanaka? on linkage in the

silkworm moth, I pointed out that some of his data suggested

that crossing over was occurring in only one sex. While the data

were not sufficient to establish this conclusion, there was at this

time another paper by the same author*® which I had not seen.

In this paper are presented data which clear up the matter.

Tanaka has now made back-cross tests of both sexes. That

crossing over does occur in the males was shown by the mating

sysy 2 X SYsy 3 which gave a total of 865 cross-overs among

2,907 offspring. The cross sysy 2 X SysY g gave 151/488 as the

proportion of cross-overs. But when females were tested,

SYsy 2 X sysy ¢ gave no cross-overs in 1,183 offspring. Tanaka

refers to another paper, apparently in press, in which he has

shown the same relations (i. e., crossing over in males, none in

1 AMER. NAT., XLVIII, 1914.

2 Jour. Coll. Agr. Tohoku Imp. Univ. Sapporo, V, 1913.

8 Jour. Coll. Agr. Tohoku Imp. Univ. Sapporo, VI, 1914.

No. 577] SHORTER ARTICLES AND DISCUSSION 43

females) for the combinations NynY and MYmy. As stated in

my former review, there was in the earlier paper a record of the

mating sysy 2 < SysY 4, giving no cross-overs in 128 offspring.

Tanaka now says, referring to this case: ‘‘ Whether there may

exist, in certain occasion, a complete reduplication [linkage] in

male, or whether the above result is due to any mistake by which

sex-signs have been reversed, is at present uncertain. No similar

case has as yet been found in other families.”’

The evidence seems to make it highly probable that crossing

over in the silkworm moth occurs only in the male; a surprising

result when we remember that in Drosophila it occurs only in the

female. One is immediately reminded that in Drosophila the

male is heterozygous for the sex-differentiator, while in Abrazas

and probably all moths the female is the heterozygous sex. These

facts are highly suggestive, and lead one to wonder what will be

found with regard to crossing over in the two sexes in birds and

mammals, where similar differences in sex-determination occur.

Another point worth noting in this connection is that in the

hermaphroditic sweet pea and Primula crossing over occurs in

the formation both of pollen and of ovules.

Tanaka reports two cases of aberrant results which, as he says,

-may be explained as due to mutation (‘‘dropping out’’) of S in

one case, and of both S and Y in the other. He adds that such

an assumption is premature. To the writer it seems more prob-

able that the females involved were not virgin. The results are

easily explained on the assumption that they had paired with

brothers before isolation, since brothers of the necessary composi-

tion are shown by the pedigrees to have been present in each case.

Another interesting point brought out by Tanaka’s more re-

cent paper is the relation between the larval patterns known as

striped, moricaud, normal, and plain. In my earlier review I

followed Tanaka in treating these patterns as affected by three

pairs of genes: S (striped) and s, M (moricaud) and m, and

N (normal) and n, plain being the triple recessive. The same

scheme has been followed in the early part of this paper. On

this assumption, as Tanaka points out, it is necessary to suppose

that complete linkage occurs between these three pairs of genes.

The evidence need not be gone over in detail here, but there are

over 10,000 larve recorded from various tests of this relation,

without a single cross-over among them. Although Tanaka does

not mention the point, this at once brings up the possibility that

44 THE AMERICAN NATURALIST [Vor. XLIX

we may be dealing with a system of multiple allelomorphs, No

two of the types when mated together give a third in F,; and,

unless one or both carry a recessive in heterozygous form, any

two types give a 3:1 ratio in F,, or 1:1 on back-crossing to a

recessive. The four patterns involved seem, from the descrip-

tions, to fall roughly into a series in the order striped, moricaud,

normal, and plain, That is to say, the second two are rather

intermediate in appearance between striped and plain. Al-

though I believe any arguments as to the nature of genes which

are based on the appearance of characters are open to very seri-

ous objections, it must still be admitted that the different char-

acters involved in a case of multiple allelomorphism are gener-

ally of the same sort.*

On the chromosome view, if the genes just discussed are allelo-

morphs they occupy identical loci in homologous chromosomes.

If they are not allelomorphic but closely linked, they occupy

different but closely opposed loci in homologous chromosomes.

In either case, any combination of them should give approxi-

mately the same linkage to the Y-y pair of genes, which occupy

a locus in the same chromosome, but some distance away. The

linkage of the striped-normal, striped-plain, and moricaud-plain

combinations with the Y—y locus appear from Tanaka’s data to

be in fact about the same, though the data on the first (striped-

normal) are the only ones sufficiently large to be very significant.

A. H. STURTEVANT

COLUMBIA UNIVERSITY,

October, 1914

THE INFLUENCE OF POSITION IN THE POD UPON

THE WEIGHT OF THE BEAN SEED

IN a note on the pure line problem Belling’ has emphasized the

significance of position in the pod as a factor in determining the

weight of the bean seed. Since this point in his paper seems to

have attracted some attention among those interested in genetics,

it may not be out of place to call attention to a series of quanti-

tative determinations of the intensity of the relationship? and to

illustrate the results secured.

If one numbers the successive ovules of the pod from 1 up,

4I have discussed this aspect of the matter briefly in another paper

(Amer. Nar., XLVII, 1913, p. 237)

1 Belling, J., ‘‘Selection in Pure Lines,’’ Amer. Breed. Mag., 3: 311-312,

912.

2 Harris, J. Arthur, ‘‘A Quantitative Study of the Factors Influencing the

No.577] SHORTER ARTICLES AND DISCUSSION 45

he may regard the numbers as measures (in units of intervals

between adjacent ovules) of the distance of ovules from the

Scale of Mean Weight.

LOTTIE TTT TTT TT TTT TTT Tr

oe p ces Bes eo pe

+ A it

sss

Alad

4 OVULES 5 OVULES 6 OVULES 7 OVULES

FIG. 1.

Position in Pod.

proximal end of the pod, and may then express in terms of corre-

lation the prenan i between the T of the seed and its

position in the p

Scale of Mean Weight.

O Ly Oh

ee S

X ÍI a

ANE X

Position in Pod.

Ea |

4 OVULES | 5 OVULES | 6 OVULES | 7 OVULES 8 OVULES

Fia. 2.

In doing this, the pods should of course be sorted into classes

according to the number of ovules which they produce and the

relationship computed for each group of pods separately, for

there is no reason for believing that the fourth in a pod with 4

ovules is comparable with the fourth seed in a pod with six. This

Weight of the Bean Seed. I. Intra-Ovarial Correlations,’’ Beih. Bot. Cen-

tralbl. Abt., I, 31: 1-12, Pl, 1-4, 1913,

46 THE AMERICAN NATURALIST — [Vou. XLIX

has now been done for twenty series of pods, drawn from five

cultures belonging to three distinct varieties (Navy, Golden Wax

and Burpee’s Stringless) and embracing altogether about 23,000

individually weighed seeds. In every one of these cases a positive

correlation has been found, i.e., the weight of the seed increases

as its distance from the base of the pod becomes greater. The

intensity of this interdependence is, however, not very great, at

least in the varieties so far studied. The correlations range from

014 + .046 to .238 + .068, with an average value of about .132,

or about 13 per cent. of perfect correlation.

The rate of change has been expressed by the slope of a straight

line for four different classes of pods studied for a culture of

Navy beans made at Sharpsburg, Ohio, in 1907 (Diagram 1°) and

for five classes from a culture of Burpee’s Stringless beans grown

at the Missouri Botanical Garden in the same year.

In the first of these, the

? Navy series, it appears that

P- ANS | | the observed mean weights at

PA ASAS ae first increase rather rapidly,

E A ei Se | then the rate of increase falls

HEDE SNS | off and finally the seeds near- -

TA _ est the tip (distal or ‘‘blos-

ef’ af Pais - som” end of the pod) become

Ai aot ‘aoe somewhat lighter than those

a fe E a little lower down. Here a

ei a Ao curve would fit the observed

R: E ee means better than a straight

AA ies line. In the Burpee’s String-

rA r Se oe less culture (Fig. 2) however,

i7 12 FA aaa the change in seed weight can

oe Sten maa k < for all practical purposes be

| ify represented by a straight line

ify on ES as well as by any curve.

ita The percentage of ovules

Jil which develop into seeds also

he Ba Tome increases from the base to-

ig es = ward the stigmatic end of the

Ke pod. In small pods the rate

Fic. 3. of increase may be fairly

regular, but in larger pods

s Ta the diagram for this series published in the original paper there is a

slip in the representation of the slope of the line for pods with 4 ovules.

No.577] SHORTER ARTICLES AND DISCUSSION 47

it falls off toward the stigmatic end, where the fecundity

may be even lower than it is a little farther down in

the pod. This is admirably shown in Diagram 3, in which GG

stands for a series of Burpee’s Stringless grown at the Missouri

Botanical Garden, NH for a series of Navy beans grown at

Sharpsburg, Ohio, and LL for a series of Golden Wax beans

grown at Lawrence, Kansas. All were grown in 1907. Here the

percentage of development of ovules at different positions in the

pod is shown for the different classes of pods by the scales to the

left of the figures. The reader may ascertain the class of pods

represented by any particular curve by noting the number of

circles representing percentage development in the various posi-

tions. These correspond to the number of ovules per pod. In the

diagrams the positions (abscisse) from left to right represent the

positions from the base to the tip of the pod.

J. ARTHUR Harris

ANOTHER GENE IN THE FOURTH CHROMOSOME OF

DROSOPHILA

UNTIL the appearance of bent wings, only three groups of

linked genes had been found.in Drosophila amelophila, although

four pairs of chromosomes had been identified in the diploid

group. Since the character bent wings, worked out by Mr. H. J.

Muller, was found to be unassociated with any of the three

groups, the gene producing this character was said to be located

in the fourth chromosome.

Recently a new character, designated as eyeless, appeared.

Flies having this character either lacked eye pigment and om-

matidia or had one or both eyes reduced in size. All of the pure

stock showed some loss of eye structures. Eyeless is recessive to

the normal eye. In order to determine the linkage, eyeless males

were crossed in turn to females of the stocks at Columbia Uni-

versity. These stocks representing the three groups were (1)

miniature wings, (2) black body and vestigial wings, and (3)

spread wings. The genes producing these characters are in the

first, second and third chromosomes, respectively. The F, from

all three crosses had normal eyes. They were inbred in each

case and gave the following..

The equation should be w==9.987 + .021 p. The line as it appears here is

_ correctly drawn.

48 THE AMERICAN NATURALIST [Vou. XLIX

Cross 1. Miniature 9 by Eyeless g

F; Normal Long Normal Miniature Eyeless Long Eyeless Miniature

1142 0 245 193

Since the eyeless flies were females as well as males, the character

eyeless is shown not to be a sex-linked character; for, if it were,

it would be inherited only by the grandsons of the eyeless male.

Since the eyeless flies are not nearly as viable as the wild stock,

the eyeless classes fall below the expectation.

Cross 2. Black Vestigial 2 by Eyeless g

F.» Normal Long Normal Vestigial Eyeless Long LEyeless Vestigial

1303 417 $ 278 97

The same count, when grouped according to the body color, was

as follows:

F, Normal Gray Normal Black Eyeless Grey Eyeless Black

1289 431 - 293 82

Cross 3. Spread ? by Eyeless ¢

F.. Normal not Spread Normal Spread Eyeless not Spread Eyeless Spread

1349 373 300 76

Allowing for the decreased viability of eyeless, both of the pre-

ceding crosses may be regarded as 9:3:3:1 ratios. Hence they

show that there is no linkage of eyeless with the characters whose

genes are in the second and third chromosomes.

Eyeless females were then crossed to bent-winged males (Cross

4). No bent eyeless flies were produced in the F,. As the count

was small, the F, bent flies were crossed to the F, eyeless, and

then the F, normal, which had the same germinal constitution as

the F,, were inbred to give F,, which should give the same re-

sults as the F..

Cross 4. Bent g by Eyeless ?

Normal not Bent Normal Bent- Eyeless not Bent Eyeless Bent

596 193 195 0

F. 741 172 131 0

Total 1337 365 326 0

Since an approximate 2:1:1:0 ratio, instead of a 9:3:3:1

ratio, was realized, the conclusion that eyeless and bent belong

No.577] SHORTER ARTICLES AND DISCUSSION 49

to the same group and in this sense may be said to be in the

same chromosome pair is evident. Until a bent eyeless fly—a

cross over—is obtained, the amount of crossing over between

these two characters in the fourth chromosome can not be directly

determined.

MILDRED A. HOGE

AN ABNORMAL HEN’S EGG

In a frequently quoted paper, Parker (’06) has classified

double eggs on the basis of the factors supposedly concerned in

their formation. Considering the ovarian and oviducal factors as

independent, Parker says: `

As a result of these two factors, three classes of double eggs can be

distinguished; first, those whose yolks have come from an abnormal

ovary but have passed through a normal oviduct; secondly, those whose

yolks have come from a normal ovary but have passed through an ab-

normal oviduct; and finally those produced by an ovary and oviduct

both of which have been abnormal in their action.

Fig. 1. PHOTOGRAPH OF THE SPECIMEN X 1.

Cases of ovum in ovo have been attributed by Parker and

others to antiperistalsis. Patterson (’11) mentions a case of an

inclosed double egg in which there were two distinct peristaltic

actions. Féré (’98) has called attention to the fact that hens fre-

quently lay several double eggs in succession. Féré claims that

he succeeded in producing double eggs in a hen which normally

laid single eggs, by drugging her with atropine sulphate. Glaser

(713) has described the ovary of a hen which habitually laid

double eggs and coneludes that fusion of the follicles is the expla-

nation of some double eggs.

50 THE AMERICAN NATURALIST [Vou. XLIX

The case which I wish to record is very similar to that figured

by Hargitt (’12) and termed by him a ‘‘gourd-shaped’’ egg. Un-

fortunately, the egg which Professor Hargitt studied was not

preserved carefully and on account of evaporation, the condition

was such that he could not be certain of the presence of yolk in

the smaller end. He assumed that the egg was comprised of

Fig. 2. DIAGRAMMATIC MESIAL VIEW OF THE ABNORMAL EGG, SHOWING THB

ELATION OF THE YOLK TO THE ALBUMEN,

about normal parts in the larger end, and that the smaller con-

sisted of only albumen, ‘‘its yellowish tint having resulted from

the evaporating process which had taken place.”’

The egg shown (Fig. 1) was presented to Professor Julius Nel-

son, of Rutgers College, several years ago and was carefully pre-

served in a jar of alcohol. The result was that although the ac-

tion of the alcohol had partially decolorized the yolk, it was pos-

sible to trace it throughout the entire extent with no difficulty.

As can be readily seen from the photograph, that part of the egg

which might be termed the ‘‘neck’’ presented a much roughened

appearance from the excessive accretion of lime. A nodule of

lime at the smaller end of the shell would seem to indicate that

the last deposit of the shell glands was there received.

For convenience in examination of the irregular shaped egg, it

was separated at the circling line seen in Fig. 1, and then the two

parts were halved with a sharp scalpel, after the penetration of

the shell by means of scissors.

When the first separation was made at the line indicated, one

could readily discern the presence of a constricted yolk sur-

rounded by apparently normal albumen. Examination of the

halved portions showed that the yolk extended from the larger

end through the constricted region to occupy a position approxi-

mately normal in the smaller end. It seems possible that this

particular abnormality may have been caused by a constricted

No.577] SHORTER ARTICLES AND DISCUSSION 51

oviduct rather than from the fusion of two eggs during ap-

position, induced by anti-peristalsis.?

F. E. CHIDESTER

RUTGERS COLLEGE.

LITERATURE CITED

Féré, C.

’98. Deuxième note sur le devellopment et sur la position de 1’embryon

de poulet dans les oeufs a deux jaunes. C. R. de Soc. de Biol.,

1898, p. 922.

Glaser, O.

713. a the Origin of Double Yolked Eggs. Biol. Bull., Vol. 24, pp. 175-

186.

Hargitt, C. W.

99. Some Interesting Egg Monstrosities. Zool. Bull., Vol. 2, pp.

225-229.

712. Double Eggs. AM. NAT., Vol. 46, pp. 556-560.

Parker, G. H.

706. Double Hen’s Eggs. Am. Nart., Vol. 40, pp. 13-25.

Patterson, J.

TLA Double Hen’s Egg. Am. Nart., Vol. 45, pp. 54-59.

1Since the above was written, but before the proof came to hand, an

authoritative paper has been published (Maynie R. Curtis, Studies on the

Physiology of err kaeee in the Domestic Fowl, Vi. Double- and Triple-

Yolked Eggs. Biol. Bull. Vol. 26, pp. 55-83.) in which no mention has been

made of the possibility of incomplete separation of both yolk and albumen

of a single egg. Evidence of such separation is not wanting in other verte-

brates, however scant it may be in the fowl.

SCIENTIFIC LITERATURE

GENETIC DEFINITIONS IN THE NEW STANDARD

DICTIONARY

THE widely advertised aim of the Funk & Wagnalls Company

to include in their ‘‘New Standard Dictionary of the English

Language ’’ all of the new additions to scientific terminology natu-

rally invites the specialist in each branch of science to examine

the definitions of the new words in his own field. Professor

Miller’ has called attention to the fact that the mathematical

definitions are not reliable. The same criticism must be made

regarding the definitions of many terms now familiar in the liter-

ature of genetics. For some of the errors in these definitions the

editorial staff can not be blamed, because the errors were passing

current among genetic writers themselves, at a time when further

changes in the dictionary probably became impossible; other

errors are less easily explained. While such a monumental work

as the Standard Dictionary tends to fix the usage of language,

the shortcomings of the genetic definitions may not be expected to

seriously affect the terminology actually used by the specialists

in this field; but for those who are engaged in other scientific

fields, who hive only a casual interest in genetics, and who must,

therefore, depend upon the dictionary for the meaning of any

genetic terms they may happen to meet, the erroneous definitions

are unfortunate. While very few of the genetic definitions are

free from defects, either of omission or of commission, only those

which seem most obviously defective will be considered here. In

the following list of words the definition of the New Standard

Dictionary is stated first, and then follows, in italic type, a defi-

nition which I believe will meet with the approval of most

geneticists.

Acquired. Transmitted by inheritance to subsequent generations ; as,

acquired characters.

Acquired character. A modification of bodily structure or habit which is

impressed on the organism in the course of individual life.

Both of these definitions occur in the New Standard Dictionary,

the first under ‘‘acquired,’’ the second under ‘‘character.’’ Al-

though ‘‘impressed on’’ may not be the best figure of speech to use

in this connection, the second definition represents fairly well the

correct usage of this phrase. It is difficult to understand east

1 Science, N. S., 38: 772, November 28, 1913.

No. 577] NOTES AND LITERATURE 53

essentially the same definition should not have been given at

both places.

Allelomorph. ‘‘In Mendelian inheritance a pair of contrasted ariaa

which become segregated in the formation of reproductive cells.’

elomorph. One of a pair o contrasted characters which are alternative

to each other in Mendelian inheritan Often used with doubtful pro-

priety as a synonym for gene, factor or r aiia

The defects in the dictionary definition in this case are two:

(a) The definition is plural, while ‘‘ allelomorph ’’ is singular;

the ‘‘allelomorph’’ is not a pair of characters, but a single char-

acter. (b) No segregation of allelomorphs takes place in the

formation of asexual reproductive cells.

elomorphism. ‘‘The presence of ae pairs of characters. ’’

Allelomorphism. A relation between two characters, suc t the de-

terminers et both do not enter the same juin. but are separated into

mer gamet

terna See inheritance. ‘‘The transmission to alternating generations

of descendants of the characteristics of either parent, as that of the father

to the odd, and of the mother to the ois generations. ’’?

Alternative inheritance. A distribution of contrasting parental or an-

cestral characters among offspring or descendants, such that the individuals

exhibit one or other of the characters in question, combinations or blends of

these characters being absent or exceptional.

Biotype. ‘‘In Mendelian inheritance a race or strain that breeds true or

almost true; a term introduced by Johannsen.’’

Biotype. A group cf individuals all of which have the same genotype.

The word ‘‘biotype’’ was introduced into English by Dr.

Johannsen? in 1906 with the definition ‘‘one single ‘sort’ of

organisms.’’ It is a term of general applicability and not limited

to Mendelian races, as stated in the New Standard Dictionary.

Although homozygous biotypes generally do breed true, this is not

an essential feature and therefore should not be included in the

definition. Ever-sporting varieties are now well known which do

not breed true, but which, so far as present evidence goes, do

constitute single homozygous biotypes. Heterozygous biotypes

genen do not breed true.

Clon. ‘‘A plant-group the members of eja have been grown from an

original stock, but which do not come true from seed.

yore _A group of individuals produced Wok a single original individual

by some process of asexual reproduction, such as division, budding, slipping,

grep, parthenogenesis (when unaccompanied by a reduction of the

hromosomes),

There are me defects in the dictionary definition of this

word, even if restricted to a plant-group in accord with the

original meaning given to it by Webber, who introduced the word.

2 Report of the third International Conference of Geneties, p. 98.

54 THE AMERICAN NATURALIST [Vou. XLIX

The defects consist, first, in the ambiguity of the word **stock,’’

because we may grow plants ‘‘from an original stock’’ of seeds,

quite as well as from cuttings, while a clone is derived from a

single individual; second, the statement that clones do not come

true from seed is incorrect, for a clone formed by cuttings, ete.,

from a homozygous individual does ‘‘breed true,’’ å. e., it pro-

duces seedling offspring of its own type. The word is now

being generally applied to animals as well as to plants.

Coupling. (‘‘ Genetic coupling’’ is not defined in the dictionary.) Such

over. (Not given a genetic definition in the dictionary.) A sepa-

ration into different gametes, of determiners that are usually coupled, and

the association of determiners in the same gamete, which are generally alleto-

morphic.

Cryptomere. ‘‘A plant a which may exist in the germ-cells with-

out making its presence visible

mere. A factor or gene whose presence can not be inferred from

an inspection of the individual, but whose existence can be demonstrated by

means of suitable crosses.

The chief defect in the dictionary definition is the restriction

of this term to plant characters. ‘‘Cryptomere’’ is a general

genetic term which may be applied as well to animals as to plants.

Determiner. ‘‘The same as determinant 3.’

Determiner. An element or condition in a germ-cell which is essential to

the development of a particular feature, quality or manner of reaction of the

organism which arises from that germ-cell; a gene or factor.

The word ‘‘determiner,’’ as used in recent years, is not the

equivalent of ‘‘determinant 3,’’ which latter is correctly defined

in the dictionary in terms of Weismann’s complicated hypothesis.

“*Determiner,’’ ‘‘factor’’ and ‘‘gene’’ are now quite generally

used interchangeably without implication as to their fundamental

nature, ites i in the generic sense, as ‘‘that which determines.”’

Dominance. ‘‘In the cross-bred offspring of parents with marked mu-

tually antagonistic characteristics, the exhibition by such peste or its

descendants of one of these characteristics to the exclusion of the eh

Dominance. In Mendelian hybrids the capacity of a aada which is

derived from only one of the two generating gametes to develop to`an extent

nearly or quite equal to that exhibited by an individual which. has derived

the same character from both of the generating gametes. In the absence

of dominance the given character of the hybrid usually presents a ‘‘blend’’

or intermediate conldition between the two parents, but may present new

features not found in either parent.

There are several defects in the dictionary definition. In the

first place, the parents used in a given cross may not themselves.

No. 577] NOTES. AND LITERATURE 55

be homozygous, in which case some of their offspring will resemble

one parent and some the other; in such a case, according to the

dictionary, both of the contrasted characters would exhibit domi-

nance. The phrase ‘‘or its descendants’? would make it pos-

sible, in any case, to include both recessives and dominants, since

among the descendants of such cross-bred individuals there will

also be recessive individuals which ‘‘exhibit one of the character-

istics to the exclusion of the other.’’

Dominant. ‘‘(1) A marked parental character exhibited by a cross-bred

organism and its descendants. (2) The parent, cross-bred organism, or

descendant exhibiting such character. Parental characters latent in a cross-

bred organism, but actively evidenced by its dengensanie; are called reces-

sives, as are the descendants which exhibit them

Domin: (1) A character which exhibits Joi inance, i. e., that one of

two contrasted parental characters which appears in the individuals af the

first hybrid PEHE to the exclusion of the alternative, ‘‘recessive,’’ char-

ter. (2) individual possessing a dominant character, in contrast to

those ads which lack that character, which are called ‘‘ recessives,’’

An ‘‘extracted dominant,’’ as defined in the dictionary, is not

distinguishable from the pure homozygous dominant used in the

cross from which the dominant in question was ‘‘extracted,’’ as

no mention is made of the essential historical fact that it is of

hybrid origin and that its parent or other known ancestor did not

breed true to the same dominant character.

Factors. ‘‘ Latent rks unite which upon crossing give rise to

the new characters found in the h

Factor. An independently gubarstabts element of the genotype whose

pre. e makes possible any specific reaction or the development of any par-

ia unit-character of the organism which possesses that genotype; a gene

or determiner.

The limitation of the term ‘‘factor’’ to those cases in which new

characters appear in hybrids, is not in accord with present usage.

All the various characters of organisms are to an important degree

dependent upon the existence of genotypic factors, regardless of

the behavior of these organisms in crosses.

“¿<A minute hypothetical particle supposed to be the bearer of he-

reditary qualities.’’

n element of the genotype; a genetic factor; a determiner.

The treatment of this word in the dictionary is particularly

mischievous. When I introduced the word ‘‘gene’’ to English-

reading students, I said:* ‘‘This word is proposed by Dr.

Johannsen .. . to denote an internal something or condition

upon whose presence an elementary morphological or physio-

logical characteristic depends. The word ‘gene’ has the advan-

8 Am. Nat., 43, p. 414, 1909.

56 THE AMERICAN NATURALIST [ Vou. XLIX

tage that it does not assume by its form or derivation any hypoth-

esis as to the ultimate character, origin or behavior of the deter-

mining factor.’’ In adopting the word ‘‘Gen’’ in the German,

Johannsen said :* ‘‘Das Wort Gen ist völlig frei von jeder Hy-

pothese ; es driickt nur die sichergestellte Tatsache aus, dass jeden-

falls viele Eigenschaften des Organismus durch in den Gameten

vorkommende besondere, trennbare und somit selbständige

‘Zustände,’ ‘Grundlagen,’ ‘Anlagen’—kurz, was wir eben Gene

nennen datn- beun sind. .. . die Gene sehr vieler Eigen-

schaften glatt trennbar sind, während andere nicht oder nicht

glatt sich trennen. Dies alles erinnert an das Verhalten chemi-

scher Körper. Damit ist aber noch gar nicht gesagt, dass die Gene

selbst chemische Gebilde oder Zustände seien—darüber wissen

wir vorläufig noch gar nichts.’’ How different is all this from ‘‘a

minute hypothetical particle’’! It is obviously improper, there-

fore, to define a gene as a ‘‘minute particle.’’ Neither is it correct

to say that it is ‘‘supposed to be the bearer of hereditary qual-

ities.” It is only the something of unascertained nature, which

must lie at the foundation of any elementary hereditary quality.

The spelling ‘‘gene’’ is not even mentioned in the dictionary as a

variant, yet this was the original spelling and is now in practic-

ally universal use among geneticists, while no one uses ‘‘gen.’’

‘t A race of organisms different from another in its hereditary

qualities; contrasted with phenotype.’’

Genotype. The fundamental hereditary constitution or sum of all the

genes of an organism,

The unfortunate definition of ‘‘genotype’’ given in the dic-

tionary was current in America at the time when the dictionary

forms were probably closed, so that the editors are not in any way

to blame for the totally erroneous definition. The definition given

by the dictionary for ‘‘genotype’’ fits fairly well the word

**biotype.’’

Heredity. ‘‘The oo manifested by an organism to develop in the

likeness of a progenitor.

Here The distribution of genotypic elements of ancestors among

the descendants; the resemblance of an organism to its parents and other

ancestors with respect to genotypic constitution.

The results of modern experimental work on heredity show that

the definition given by the dictionary is entirely too restricted.

Heredity must be so defined that it may apply to characters mas

were never exhibited by any ancestor.

Heterozygosity. ‘‘In Mendelian inheritance, the state or condition due

to an organism having developed from a heterozygote.’’

4‘*Elemente der exakten Erblichkeitslehre,’’ 1. Aufl., 1909, pp. 124-125.

No. 577] NOTES AND LITERATURE 57

Heterozygosity. The condition of an organism due to the fact that it is

a heterozygote; the state of being heterozygous; the eet, to which an

individual is heterozygous.

Heterozygote. ‘‘A Mendelian hybrid resulting from the fusion of two

gametes that bear different allelomorphs of the same character =s which

in consequence does not breed true; contrasted with homozygote.

Hete A zygotic individual in which any given genetic factor

has been derwed from only one of the two generating gametes. Both eggs

and sperms produced by such an individual are typically of two kinds, half

of them containing the gene in question, the rest lacking this gene; conse-

quently the effspring of heterozygotes usually consist of a mixture of indi-

ee some of which possess the corresponding character while others

lack

etic ‘t Development em a zygote originating from a union

of two gametes of the same kind,’

zygosis, sis state of oh homozygous; the extent to which an

Homozygote. iy sels formed by the conjugation of two gametes of

the same stock; any animal or plant that receives and retains the dominant

or recessive characters of both its parents, and is therefore said to be true

to type, and breeds true to t

Homozygote. An individual in which any given genetic factor is doubly

present, due usually to the fact that the two gametes which gave rise to this

individual were alike with respect to the determiner, in question. Such an

individual, having been formed by the union of like gametes, in turn

generally produces gametes of only one kind with respect to the given

character, thus giving rise to offspring which are, “ this Com like

the parents; in other words, NaDa usually ‘‘breed true.’’ A

**nositive’’ homozygote with respect to any character contains a pair

determiners for that character, while a ‘‘negative’’ homozygote lacks this

pair of determiners.

‘‘Two gametes of the same stock’’ is ambiguous because of the

indefiniteness of the word ‘‘stock.’’ Many homozygotes receive

some dominant and some recessive characteristics of the two par-

ents; and what can be intended by the statement that a plant or

animal which receives certain characteristics also ‘‘retains’’

them? How could it do otherwise?

Hypostasis. (Not given a esis definition in the dictionary.) That

relation of a gene in which i ion fails to appear because of the

gee or Dans effect of ‘witli gene; contrasted with ‘‘ epistasis.’’

The corresponding adjective ‘‘hypostatic’’ is smo not given a

genetic “definition in the dictionary.

Mendelize. ‘‘To cause to follow Mendel’s law of inheritance.’’

Mendelize. To follow Mendel’s law of inheritance.

The word is rightly indicated in the dictionary, as an intran-

sitive verb; it is manifestly incorrect to define it by the use of a

transitive ark

58 THE AMERICAN NATURALIST [Vou, XLIX

Mutant. ‘‘That which admits of or undergoes mutation or change;

specifically, an individual or a species which shows significant changes in

form or character in a single generation.’’

Mutant. An individual possessing a genotypic character differing bg

that of its parent or those of its parents, and not derived from them

normal process of segregation.

The expression ‘‘significant changes’’ is ambiguous, since every

change is significant of something.

Mutate. ‘‘To ‘sport.’ ’’

Mutate. To undergo a change in genotypic character independently of

normal segregation,

The word ‘‘sport’’ which is used in the dictionary definition of

‘‘mutate’’ is defined thus: ‘‘To vary suddenly or spontaneously

from the normal type; said of an animal or plant or of one of its

parts.’’ It is well known that many such sudden and spontaneous

variations from the normal type are not due to mutations. The

word ‘‘mutation’’ is defined in the dictionary as ‘‘a permanent

transmissible variation in organisms, as distinct from fluctuation.”’

This definition is good as far as it goes, but should expressly ex-

clude transmissible variations which are due to normal segrega-

tion and recombination of determiners.

Phenotype. ‘‘A type or strain of organisms distinguishable from others

by some character or characters, whether their observable differences from

other organisms be due to their inherent hereditary differences or to the

direct action of the environment upon them: contrasted with genotype.’’

Pheno e ee type of an individual or group of individ-

uals, i. e, the sum of the externally obvious characteristics which an indi-

vidual possesses, or which a group of individuals possesses in common; con-

trasted with genotype.

‘‘Phenotype’’ and ‘‘genotype’’ are both abstractions; the qual-

ities which distinguish the phenotype are always capable of direct

observation, while those of the genotype can only be inferred from

the results of genetic experiments.

e and absence hypothesis, ‘‘in the Mendelian doctrine of in-

heritance, the theory that an allelomorphic pair of characters in every zygote

has two contrasted factors or determinants, one representing the por

character of the generated organism and the other denoting its absence.’

Presence and absence hypothesis. The hypothesis that any simple Men-

delian difference between two individuals, results solely from the presence

of a factor in the genotype of the one individual, which is absent from that

of the other. Presence and absence of unit-differences as a convenient

method of describing the results of genetic experiments should be carefully

distinguished from the presence and absence hypothesis. The method is-

purely objective and entirely free from hypothetical implications.

It will be noted that the dictionary definition of this phrase is

directly opposite in significance to the one here set forth.

No. 577] NOTES AND LITERATURE ` 59

Pure line (Not included in the dictionary.) A group of individuals

derived solely by one or more self-fertilizations from a common homozygous

ancestor. Sometimes erroneously applied to groups of individuals believed

to be genotypically homogeneous (a homozygous biotype or a clone) without

regard to their method of reproduction.

pulsion. (Not given a genetic definition in the dictionary.) Such a

relation between two genetic factors that both are not, as a rule, included

in the same gamete, referring especially to cases in which the factors in

question give rise to enon different characteristics; also called

‘‘spurious allelomorphism. '

Sex-limited inheritance. (Not defined in the dictionary.) The associa-

tion of the determiner for any unit-character, with a sex-determiner, in such

a manner that the two determiners are either generally included in the same

gamete, or that they are generally included in different gametes, This

method of inheritance is also called ‘‘seu-linked’’ inheritance by Prater

£ rgan and his students.

Segregate. ‘‘To become separated from the rest; specif., of Mendelian

cia’ = separate, by a numerical law, into dominants, hybrids and re-

cessives

Segre: wa ate. With reference to Mendelian unit-characters, to become sep-

arated through the independent distribution of the genetic factors before or

at the time of the formation of the gametes

The dictionary definition goes too far; the formation of domi-

nants, hybrids and recessives depends not alone upon the fact that

the factors segregate, but that the segregated factors recombine,

The word ‘‘segregation’’ receives a fairly satisfactory definition.

Unit-character. (Not included in the dictionary.) In Mendelian in-

heritance a character or alternative difference of any kind, which is either

present or absent, as a whole, in each individual, and which is capable of

becoming associated in new combinations with other unit-characters.

I have made no systematic study of the definitions of technical

terms in other related fields, but have noted incidentally that

there is no recognition in the New Standard Dictionary of the

generally familiar usage of the words ‘‘meristic’’ and ‘‘sub-

stantive’’ as applied to types of variation.

G. H. SHULL

PROFESSOR DE VRIES ON THE PROBABLE ORIGIN OF

ŒNOTHERA LAMARCKIANA

IN a recent paper Professor Hugo De Vries' has given us the

results of a second examination in 1913 of material from the

herbarium of Lamarck, and of other sheets of @nothera in the

collections of the Muséum d’Histoire Naturelle in Paris.

1De Vries, Hugo, ‘‘ The Probable Origin of Gnothera Lamarckiana Ser.,

Bot. Gaz., Vol. LVII, p. 345, 1914.

60 THE AMERICAN NATURALIST [Vor. XLIX

is a very important contribution for there have been some changes

in the mounting of important specimens in the herbarium of

Lamarck since the first studies by De Vries in 1895 and it was

not clear what material formed the subject of his discussion in

* Die Mutationstheorie.’’ As the result of this second examina-

tion (1913) there can be no misunderstanding of De Vries’s

conclusion as to what represents the type of Œnothera Lamarck-

iana Seringe, and we have also very positive opinions on the

identity of other interesting material in the collections at Paris.

Thanks to his descriptions and photographs of these sheets further

confusion will be impossible and botanists may now make for

themselves the observations that will in the end determine their

judgment of the soundness of Professor De Vries’s views and of

the value of the exceptions that may be taken to them.

I shall not at this time discuss in detail the queries which pre-

sented themselves on my reading of De Vries’s paper. The most

important of the points probably rest on facts that should be

shown by the material, but which have not been published in the

account of De Vries. I expected to have the data in question this

autumn but the European disturbances have necessarily upset

my plans and it may be very many months before I can take up

the matter. `

However, I will briefly say that De Vries’s identification of

the sheets under consideration are to me not convincing chiefly

for the following reasons. His account gives no description of

the pubescence of the sepals, stems, or capsules when present.

Yet pubescence is a character of great importance in the descrip-

tion of many species of @nothera. To illustrate the point, all

races of O. grandiflora Solander that I know have sepals and

capsules almost glabrous or very sparsely pilose and puberulent.

Lamarckiana on the contrary presents sepals and capsules with

a very heavy puberulent and pilose pubescence. Should any of

the specimens at Paris which De Vries has identified with the

Lamarckiana of his cultures present sepals or capsules lacking

the heavy pubescence of this plant the fact to me would be very

strong evidence that his identification was incorrect.

There are two sheets under consideration as standing for the

type of G@nothera Lamarckiana Seringe. De Vries regards one

as unequivocally representing the type specimen. I have for

various reasons placed the greater emphasis upon the other.

Both specimens as shown in photographs appear to have essen-

tially the same features as to their general morphology. Miss

No. 577] NOTES AND LITERATURE 61

Eastwood and M. Gagnepain who compared the two specimens

reported to me that they were very similar. Both were undoubt-

edly known to Lamarck since the two sheets bear his hand-

writing, and it is quite possible that Lamarck based his descrip-

tion on both specimens,

The general morphology of these specimens presents several

features that are not those of the Lamarckiana of De Vries’s

cultures. Chief among these are (1) the approximate branches,

(2) the foliage of narrower and more distinctly petioled leaves,

(3) the inflorescence more open and with narrower bracts, (4)

the buds more slender and tapering, and apparently with more

attenuated sepal tips, (5) the long delicate hypanthium. In

these features the specimens are closer to O. grandiflora than to

Lamarckiana. Such morphological characters, it is true, might

vary somewhat under different conditions of growth and with

the time of collection whether early or late in the season. The

pubescence should give us the stronger evidence of relationship

since pubescence would be little if at all affected by growth con-

ditions or by season. Of the pubescence on one of these speci-

mens I have Gagnepain’s statement that it is close to that of

grandiflora, but it is only fair to say that no @nothera specialist

has reported upon such a comparison as is desired.

Lamarck’s description of the capsules of his plant as short and

glabrous is a point of great importance. The capsules of De

Vries’s Lamarckiana are certainly not glabrous but they are

short. In my contention that Lamarck’s plant was a form of

O. grandiflora Solander I was at first forced to assume that

Lamarck must have described immature or partially pollinated

capsules. I have, however, this summer grown cenotheras from

Mississippi which have the rosettes, habit, foliage, inflorescence,

and flowers of grandiflora, but which developed glabrous short

capsules essentially of the same relative proportions as those of

Lamarckiana. It is immaterial what is the origin or genetic

history of these plants; systematically speaking they represent

short-capsuled forms of O. grandiflora. Thus we now know of

grandiflora-like types which even as to their capsules agree with

the description of Lamarck. De Vries does not seem to be dis-

turbed by the fact that the material of his cultures presents

capsules with a heavy puberulent and pilose pubescence while

Lamarck’s description specifies a capsule ‘‘glabre.’’

In summary I must say that my opinion remains auhani

with respect to the affinities of the plant deseribed by Lamarck,

62 THE AMERICAN NATURALIST | [Vou. XLIX

@nothera Lamarckiana Seringe. Whichever of the two speci-

mens considered above represents the type, or if both were con-

cerned in the description, the evidence is to me very strong that

Lamarck dealt with forms of O. grandiflora Solander. I can see

no proof or even reasonable evidence that the Lamarckiana of

De Vries’s cultures agrees with either of the specimens from

Lamarck’s herbarium. A final judgment, however, should not

be made until we have before us details respecting the pubescence

of the specimens known to Lamarck.

De Vries is very positive that two other sheets in the collec-

tions at Paris present specimens agreeing with his Lamarckiana.

The first of these (De Vries, Plate XVIII) is from the her-

barium of Abbé Pourret and shows material which seems to me

to offer very much the same difficulties to an identification with

De Vries’s Lamarckiana as do the specimens of Lamarck. The

foliage of lanceolate leaves clearly petioled, the slender tapering

buds, the long delicate hypanthium; these are not characters

representative of the plants from the cultures of De Vries. They

are characters of O. grandiflora Solander and should the pubes-

cence prove to be similar to this species I should not hesitate to

place these specimens of Abbé Pourret among the forms of

grandiflora. Until we know the facts of the pubescence, further

discussion is unwise, but it does not seem to me that De Vries’s

identification rests on good evidence.

The remaining sheet at Paris which De Vries (Plate XIX)

identifies with his Lamarckiana is a plant from the herbarium

of André Michaux. De Vries on historie grounds naturally

attaches importance to this sheet for if it could be established

as in agreement with his plants the fact would bear directly on

the problem of the origin of O. Lamarckiana. The flowers are

large and the buds rather stout as we find them in our cultivated

Lamarckiana, but the sepal tips are longer and the bracts much

narrower than in Lamarckiana. The most striking characters

of this specimen as shown in the photograph are the narrow

lanceolate leaves and the extraordinary length of their petioles.

That such a plant could be related to De Vries’s Lamarckiana

which has ovate-lanceolate leaves, sessile or almost sessile, seems

to me well nigh impossible. Of the pubescence De Vries tells

us nothing, yet the numerous buds on the specimen should make

it easy to determine this character and it may become a crucial

point in judging the possible or impossible relationships of the

plant.

No. 577] NOTES AND LITERATURE 63

In the discussion which must develop from the conclusions of

De Vries he has taken by far the more difficult position since he

attempts an identification of herbarium material with a type

very accurately known to us through widely cultivated living

forms. My argument is presented primarily against his identi-

fications. It is not in any degree necessary to my argument that

I should assign the sheets under consideration to definite species.

Whether this can be done for any of them time will tell and I

must repeat that as evidence the character of the pubescence

may prove of the greatest value. I am working on the hypothesis

that the specimens of Lamarck and that of Abbé Pourret are

forms of O. grandiflora Solander. As for the specimen of André

Michaux, so many remarkable forms of @nothera are coming

into the experimental garden from the southern and western

United States that I am quite unwilling to express at present

even a guess as to its affinities.

De Vries has welcomed my suggestion that the source of the

cultures of Carter and Company may have been not Texas, as

they state, but England. This possibility seems to me to offer

an important line of investigation of early British records and

collections, but at present the suggestion appears to me nothing

more than a working hypothesis, although well worthy of atten-

tion. Texas and the West have some wonderful large-flowered

cenotheras and Carter and Company may have obtained from

such sources a plant which later hybridizing with other forms

produced the Lamarckiana of our present cultures. That there

are American western species which will hybridize with Euro-

pean biennis and produce a synthetic Lamarckiana is I believe

established by my present studies with Œnothera franciscana

Bartlett.

In recent papers I have reported that first generation hybrids

of O. franciscana pollinated by the Dutch biennis have the

essential taxonomic characters of the small-flowered forms of

O. Lamarckiana. They differ from Lamarckiana in relatively

small plus or minus expressions of these characters. It was to be

expected that large F, generations would give a wide range of

variation or segregation of characters and that forms would

appear much closer to Lamarckiana than the parent F, plants.

This proved to be the case in F, cultures of last summer (1914)

totaling about 1,600 plants. Among these I obtained a number |

of individuals which were so close to the large-flowered Lamarck-

iana that flowering shoots could scarcely be distinguished as to

64 THE AMERICAN NATURALIST [Vor. XLIX

pubescence, foliage, inflorescence, buds, flowers, and capsules.

The rosettes were also Lamarckiana-like. Only in habit was it

somewhat difficult to match the symmetry of Lamarckiana.

That further selection in later generations is likely still to fur-

ther improve on the results of this synthesis seems altogether

probable. These studies will shortly be described in full.

I am well aware that a synthesis of a Lamarckiana-like hybrid

even should it throw in successive generations a series of marked

variants (mutants) will not be considered by De Vries and his

disciples as casting doubt on the validity of the ‘‘mutation’’ of

Lamarckiana. They will say that in this case the hybrid took its

mutating habit from one or both of the parents. Since in my

cross one of the parents is the Dutch biennis which Stomps has

shown can produce nanella, semi-gigas and sulfurea mutants, it

will be claimed that any behavior of my hybrids similar to

mutation will be due not to the mixing of diverse germ plasms,

i. e. to crossing, but will be merely a further expression of

mutating habits inherent in the germ plasm of at least biennis

if not also of franciscana.

This phase of the discussion may rest until we know the future

behavior of my hybrids and the possibilities of the Dutch biennis

-as a form capable of mutation. It is to be expected that Stomps

will carry out his very important studies on a scale that will

virtually exhaust the mutative possibilities of this species. Such

a study on a close-pollinated species of Œnothera so well known

-as the Dutch biennis will give, it seems to me, the safest data

that has yet been published by students of mutation among the

Gnotheras. It becomes a matter of great interest to know the

range of variants that such a type can produce. Similar studies

= among some of the wild American species should also be made.

The open-pollinated assemblage of forms to which Lamarckiana

belongs must always be open to suspicion of hybridization more

or less remote in time or distant in relationship. Only prolonged

experiment can establish an open-pollinated @nothera as free

from the taint of crossing.

It is, I trust, clear that one may believe very strongly that

nothera Lamarckiana is not safe material on which to base

experiments designed to test the mutation theory and yet remain

rebaptive to evidence that may come from other sources.

BRADLEY Moore Davis

UNIVERSITY OF PENNSYLVANIA,

_ October, 1914 .

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THE

AMERICAN NATURALIST

VoL. XLIX February, 1915 No. 578

CYCLES AND RHYTHMS AND THE PROBLEM

OF “IMMORTALITY”? IN PARAMECIUM

PROFESSOR GARY N. CALKINS

CoLUMBIA UNIVERSITY

Tue recent brilliant work of Woodruff and Erdmann

has thrown a flash of light upon the old question of age

and death in protozoa and upon the problem of the sig-

nificance of conjugation. The long, successful cultivation

of Paramecium aurelia by Woodruff led Jennings to say:

The work of Woodruff demonstrates that the very limited periods

within which Maupas and Calkins observed degeneration has no signifi-

cance for the question as to whether degeneration is an inevitable

result of continued reproduction without conjugation. In other words,

it annihilates all the positive evidence for such degeneration, drawn

from work on the infusoria. It justifies the statement that the evidence

is in favor of the power of these organisms to live indefinitely, if they

are kept under’ healthful conditions. It shows that Weismann was

correct in what he meant by speaking of the potential immortality of

these organisms.

The same work of Woodruff led Minot to say in the

course of his German lectures:

Quite conclusive as to the absence of senescence are the experiments

of L. L. Woodruff, who has maintained a — race of Para-

mecium for five years without conjugation.?

Woodruff also makes the statement in different publica-

tions that the cells of his pedigreed race of Paramecium

1‘*Age, Death and Conjugation in the Light of Work on Lower Organ-

isms,’’ Pop, Sci. Mo., June, 1912, p. 568.

2 ‘í Modern Preble of Biology,’ 2018, p. 62.

66 THE AMERICAN NATURALIST [Vou. XLIX

aurelia possess the potentiality to perpetuate themselves

indefinitely by division under proper environmental con-

ditions. In short, his results have given almost the only

experimental evidence in support of the view, advocated

by Weismann, that protozoa are potentially immortal.

The importance of this generalization and the deduc-

tions from it are self evident, and it is unfortunate that

so many should have advanced it before the life history

of Paramecium aurelia was fully known. Woodruff is to

be congratulated, however, in that he, with Miss Erdmann,

has now worked out stages in the life history of this or-

ganism which go far in clearing up the discrepancy be-

tween his results and those obtained by Maupas and his

followers.

Woodruff has carried on his pedigreed race of Para-

mecium aurelia for more than seven years with a fairly

uniform division rate, subject, however, to occasional and

periodic fluctuations which he calls rhythms. These cor-

respond roughly to what I have termed cycles which end

in depression periods and, unless stimulated, by death;

in rhythms, however, Woodruff maintains, there is no evi-

dence of depression.* Recently Woodruff finds from a care-

ful study of material fixed during the low periods of his

division rate rhythms that there takes place a complete

nuclear reorganization, after which the organisms continue

to live with renewed vitality as shown by the ascending

division rate. This process consists in the disintegration

and probable absorption in the cytoplasm of the old macro-

nucleus, one or more divisions each of the old micronuclei,

degeneration of some of the products of these divisions,

and the ultimate reformation of functional macronuclei

and micronuclei from others. These are, in essence, the

important new facts which cytological study has revealed

in the life history of Paramecium aurelia, and some evi-

-83I would like to suggest to Professor Woodruff that he work out the

death rate, the data for which he can undoubtedly obtain from his records.

I venture to predict he will find that the death rate rises with the decline of

the division rate and during the low sweep of the rhythms.

No. 578] CYCLES AND RHYTHMS 67

dence is further adduced to i that similar processes

occur in Paramecium caudatum.

While there is little to criticize in regard to the facts as

described for this. remarkable process, there is room for

difference of opinion in regard to the conclusions which

Woodruff and Erdmann draw from them. In addition

to what Hertwig has already written about this work, I

would call attention particularly to their conclusions con-

cerning endomixis, parthenogenesis, conjugating and non-

conjugating lines, Gi life cycle, and the potential immor-

tality of Paramecium.

In regard to endomixis the authors state:

Since the process results in the dissemination of the material from the

old macronucleus and the so-called reduction micronuclei in the cell, it

tion of the cell. This involves a more profound intermingling of

nuclear and cytoplasmic substances than is possible during the typical

vegetative life of the cell. Since this intermingling occurs within a -

` cell we term this reorganization process endomixis. Endomixis is fol-

lowed by a slight acceleration of cell phenomena and a new rhythm is

initiated.*

Further on they add:

We would therefore put emphasis on molecular re eae as the

result common both to endomixis and to conjugation

Nearly forty years ago Engelmann Se conju-

gation in much the same way as a process of reorganiza-

tion of the cell:

. die Conjugation der Infusorien leitet nicht zu einer Fortpflanzung

durch ‘Eier, ‘Embryonalkugeln’ oder irgend welche andere Keime,

sondern zu einem eigenthiimlichen Entwickelungsprocess der conjugirten

Individuen, den man als Reorganization bezeichnen kann.®

In several places in the same publication Engelmann

speaks of physical and chemical changes as accompanying

t Woodruff and Erdmann, ‘‘A Normal Periodice Reorganization Process

without Cell Fusion in Paramecium,’’ Jour. Exp, Zool., Vol. 17, No. 4,

1914, p. 491. The italics are in the original.

5 Ibid, p. 491.

6‘‘Ueber Entwickelung und Fortflanzung ‘von Infusorien,’’ Morph.

Jahrb., 1, 1876, p. 628.

68 THE AMERICAN NATURALIST [Vou. XLIX

conjugation. A similar interpretation was given by

Calkins:

. it is now a well-known fact that in this process of reorganization

the old macronucleus fragments and ultimately disappears in the cyto-

plasm. This disappearance must give rise to a great increase in the

nucleo-protein content of the cell, therefore to a new chemical composi-

tion of the cell as a whole. We have recently shown that, under cer-

tain conditions, nucleo-proteins (especially the purines) have a mark-

edly stimulating effect on the rate of cell division.’

Now such intermingling is no more characteristic of this

process of asexual reorganization than it is of the reor-

ganization following conjugation. In both cases, as

Woodruff and Erdmann show, reorganization is effected

by the physical and chemical change of the old macro-

nucleus and portions of the old micronucleus or micro-

nuclei. The sole difference in these processes of reor-

ganization is not to be found in the molecular rear-

rangement of the cell, but, as Woodruff and Erdmann

state, in the presence after conjugation of a syncaryon

and the nuclei derived from it. This difference, how-

ever, does not amount to much in closely related pairs

in conjugation. Several observers have shown that

closely related individuals, even sister cells, of Para-

mecium may conjugate, and I have followed out through

360 generations the history of such an endogamous ex-

conjugant from a pair which came from the same ances-

tral cell not more than ten days prior to conjugation.

There can not be a great difference in the syncaryon re-

sulting from such a union, over the functional micronu-

cleus had it undergone asexual endomixis. In other

words, the excellent term endomixis does not indicate

phenomena peculiar to asexual reorganization in Para-

mecium, but applies equally well to the process of reor-

ganization following conjugation. The terms asexual en-

domixis and sexual endomixis may serve to distinguish

the process of intermingling during parthenogenesis and

after conjugation, respectively.

7<*The perp conic: Conjugation of Blepharisma wnavtans Jour.

Morph. Vol. 23, 1912, p. 685.

No. 578] CYCLES AND RHYTHMS 69

Woodruff and Erdmann limit the application of the

term endomixis to the process of reorganization without

conjugation:

We therefore have employed a new term “ endomixis” for the re-

organization process in Paramecium, in preference to parthenogenesis

which Hertwig applied when he incidentally noted some isolated stages

of the nuclear phenomena which we have elucidated.®

A new name can not alter the significance of a process or

phenomenon. Parthenogenesis, in its broad sense, is the

development of an individual from an egg without fertili-

zation. In the same sense that a Paramecium ex-conju-

gant develops into a new individual, so does a Parame-

cium after this process termed endomixis. Woodruff and

Erdmann say:

In parthenogenesis there is à chromatin reduction which occurs and

is compensated for either in the egg itself or in some later period of the

life cycle of the race.®

The authors are not very happy in selecting this feature

as distinguishing parthenogenesis from asexual endo-

mixis, for in most cases of recognized parthenogenesis

in metazoa chromatin reduction plays no part; for exam-

ple, the majority of parthenogenetic’eggs give off only

one polar body, thus retaining in the egg the diploid num-

ber of chromosomes; others, notably the aphids and phyl-

loxerans, do not undergo synapsis or chromatin reduction ;

some others it is true, give off both polar bodies and develop

with the haploid number of chromosomes as is the case

in bees (males), and in artificial parthenogenesis. As to

the significance of parthenogenesis neither polar body

formation nor chromosome reduction furnishes the key,

for in many cases the eggs are predestined to partheno-

genetic development long before the polar body nuclei

are formed.

In regard to the reducing divisions of the chromosomes

in Paramecium we know very little. Evidence has been

adduced to indicate that the chromosomes are divided

8 Ibid., p. 493.

9 Ibid., p. 492.

70 THE AMERICAN NATURALIST [Vou. XLIX

longitudinally in both the first and the second divisions

of the maturation process. The significance of the third

division is as obscure in Paramecium as maturation is in

some metazoan hermaphrodites.

In parthenogenesis, finally, we are dealing with a bio-

logical phenomenon, not with an interpretation of par-

thenogenesis by Winkler or Strasburger or any other

individual, and to interpret this highly significant phe-

nomenon in Paramecium solely in the light of such defi-

nitions, as Woodruff and Erdmann do (p. 493), does not

carry conviction, nor does it conceal the real significance

of the phenomenon. Asexual endomixis in Paramecium

is parthenogenesis and nothing else, as Hertwig origi-

nally maintained in connection with these same phenom-

ena. Nor, except for the protozoa, is it a ‘‘new type of

parthenogenesis’’ for, if we accept conjugation as equiva-

lent to fertilization, its analogue is shown by the majority

of parthenogenetic eggs.

In regard to conjugating and non-conjugating races of

Paramecium, Woodruff and Erdmann state: |

Thus it is proved that both the reorganization process and conjuga-

tion are potentialities of the same race—and therefore there is no evi-

dence for the view of Calkins (713) that conjugating and non-conjugat-

ing races of Paramecium exist, or that “apparently some paramecia

are potential germ cells, others are not.”1°

This is rather a sweeping generalization to. draw from one

pedigreed line in which conjugating animals appeared

only after six years in culture. If every Paramecium is

a potential germ cell, why was it that no pairs of conju-

gating aurelia were found during these six years? Or,

in Calkins and Gregory’s observations on the first 32

cells and the pure lines arising from them, all from a

single ex-conjugant, why was it that all lines from one

quadrant gave epidemics of conjugation whenever the test

was made during a period of six months, while all other

lines from the remaining three quadrants failed to give

a single pair when tested under identical conditions?

10 Ibid., p. 490. Italies in the original.

No. 578] CYCLES AND RHYTHMS 71

Woodruff and Erdmann maintain that ‘‘under just

the proper conditions’’ conjugation will occur; this, of

course, can not be denied, but the fact that under the

same conditions some lines will conjugate while otherg

will not shows a physiological difference between them

which can not be gainsaid. I have no paternal jealousy

whatsoever in regard to the terms ‘‘conjugating lines’’

and ‘‘non-conjugating lines,” and am entirely willing to

accept in their place any terms which indicate the physio-

logical difference that I wished to express. I know of

no terms that express the conditions adequately. Substi-

tute for them, if more suitable, such expressions as

‘‘always ready to conjugate’’ and ‘‘rarely ready to con-

jugate.’’ Our observations on the 32 lines certainly jus-

_ tify the statement that some lines in regard to conjuga-

tion, were always ready, while others were rarely ready.

Woodruff and Erdmann have paid no attention to the

physiological conditions which the (perhaps unfortunate)

expressions ‘‘conjugating lines’’ and ‘‘non-conjugating

lines’’ were meant to express. It is true that after ten

months all but four of the so-called non-conjugating lines

each furnished a few pairs of conjugating individuals,

just as Woodruff’s line did after six years, facts which

show that the terms ‘‘conjugating lines’ and ‘‘non-

conjugating lines’’ as applied to races of Paramecium, if

used at all, should be used only in respect to relative in-

tensity of conjugating power. In this sense Woodruff’s

race is a non-conjugating race. We have found, further-

more, that conjugating lines have a lower vitality as

measured by the division rate, and a much higher death

rate, than do non-conjugating lines, all but four of the

eight lines from the conjugating quadrant dying out

within three months as against four of the twenty-four

lines of the non-conjugating quadrants, while at the end

of twenty months only one conjugating line was alive and

sixteen non-conjugating lines, a mortality of 87.5 per cent.

for the former and 33.3 per cent. for the latter. In Para-

mecium it is conceivable that lines with a high conjugating

72 THE AMERICAN NATURALIST [Vou. XLIX

power have a less well developed power of asexual endo-

mixis than do lines that are relatively sterile, and this,

correlated with their reduced vitality, if conjugation were

prevented, would account for the death of all pedigreed

races prior to Woodruff’s, which, as Woodruff and Erd-

: mann now show, has a high power of asexual endomixis.

We are still justified, I believe, in maintaining the state-

ment—modified now by their description of asexual reor-

ganization—as quoted by Woodruff and Erdmann:

Woodruff’s Paramecium aurelia is evidently a Paramecium Methuse-

lah belonging to a non-conjugating line the life history of which is not

known in any ease.11

‘It is clear that the cycle emphasized by Maupas, Calkins and others

is merely a phantom which has continually receded as each successive

investigator has approached the problem with improved culture methods

until it has vanished with Woodruff’s race of (so far) 4,500 generations.

What remains then is the rhythm and in the light of the present study,

which demonstrates the underlying cytological phenomena of which it

is an outward physiological expression, the whole problem takes on a

new aspect. The cell automatically reorganizes itself periodically by a

process which, in its main features, simulates conjugation—but without

a contribution of nuclear material from another cell. Therefore it is

evident (as has been shown by this culture) that the formation of a

synearyon, whose components are derived from two cells, is not nec-

essary for the continued life of the cell—it has an internal regulating

phenomenon which is oF adequate to keep it indefinitely in a per-

fectly normal condition.??

Here we are brought up sharply to face the question

which every student of pedigreed infusoria since Maupas

has tried to solve. Woodruff and Erdmann conclude

from their observations that old age and natural death

do not occur in Paramecium and that the so-called ‘‘cycle’’

is non-existent. I would draw from their observations

exactly the opposite conclusions, viz., that the one appar-

ent exception among pedigreed races, to the rule of de-

pression and natural death in the absence of conjugation

or its equivalent, is now removed, and that Woodruff’s

culture is no more than a long series of cycles.

11 Ibid., p. 429.

12 Woodruff and Erdmann, p. 489.

No. 578] CYCLES AND RHYTHMS 73

We understand by a ‘‘cycle,’’ in the sense with which

the term was first employed by Calkins, a more or less

periodic alternation of high and low vitality as measured

y the division rate. The lowering division rate indi-

cates the approach of a period of depression which was

interpreted as the equivalent of old age in metazoa, since

it indicates a weakening in the chain of vital activities and

ends in death unless conjugation or its equivalent is

permitted. No one since Maupas, so far as I am aware,

has attempted to limit a cycle in terms of definite numbers

of generations or definite lengths of time. In 1904 I

stated:

The well-marked cycles, therefore, with periods of depression which

demanded stimulation of a decided character, were apparently of six

months duration, while intermediate cycles of less importance were about

three months long. . . . During the first three cycles the number of

generations was nearly the same (200, 198, and 193, respectively), the

last, on the other hand, was much less, the individuals dividing only

126 times.18

The period of six months, more or less, or 200 + genera-

tions were not regarded as measures of the cycle, and it

was understood at that time that conjugation or its equiva-

lent always inaugurates a new cycle. Woodruff in 1905

introduced the term ‘‘rhythm’’ to designate the lesser

periodic fluctuations which I had called ‘‘intermediate

eycles.’’ Since the entire substance of the much-discussed

problem of immortality in infusoria is bound up with this

question of the cycle, it is necessary to analyze the so-

called rhythms of Woodruff to see how they agree with or

differ from the so-called cycles. In Paramecium the

cycle consists of the history of a bit of protoplasm in an

ex-conjugant and its progeny from which conjugation or

its equivalent is excluded, until natural death of the en-

tire race ensues. If conjugation or its equivalent occurs

the old cycle is abandoned and a new one is started, and

there must be as many new cycles as there are times when

conjugation or its equivalent takes place. It is imma-

18 ‘Studies on the Life History of the Protozoa,’’? IV. Jour. Exp. Zool.,

Vol. I, 1904, p. 424,

74 THE AMERICAN NATURALIST [Vor. XLIX

terial, furthermore, whether such conjugation occurs be-

tween individuals of the same race, or between individuals

of diverse ancestry, the effect is the same in putting off

ultimate weakness and death. With repeated conjuga-

tions in such a race the ultimate death may be postponed

indefinitely, and this was the argument on which Weis-

mann’s revised theory of potential immortality was based.

Now it is exactly the same with Woodruff’s rhythms.

He finds in his long culture repeated instances of ascend-

ing and descending division rates in fairly regular alter-

nate succession. The descending division rate is stopped

by an ‘‘internal regulatory phenomenon, endomixis.’’’*

Woodruff and Erdmann, while showing that endomixis

is different from conjugation in the absence of a syn-

caryon, apparently accept it as equivalent to conjugation

in connection with vitality of the protoplasm:

Endomixis and conjugation may occur simultaneously in different

animals of the same culture, thus strongly suggesting that the same gen-

eral conditions lead to both phenomena—one animal meeting the con-

ditions one way and another by the other, and that both phenomena

fill essentially the same place in the economy of life of Paramecium

awrelia.®

Again they say:

Endomixis does initiate a new rhythm in the life history of Para-

mecium, i. e., a period of increased metabolic activity and therefore of

reproductive activity, and since its fundamental morphological features

are almost identical with those preliminary to the formation of the

stationary and migratory micronuclei in conjugation, it lends strong

support to the view that the dynamic aspect of conjugation is not

absent.1®

Throughout the long period of seven years the Para-

megin aureha Pope without conjugation: ‘‘has

, undoubtedly on the aver-

age once each meea (ibid., p. 495). Hertwig has

already shown, as I do above, that asexual endomixis is

parthenogenesis, and if, in connection with the problem

of vitality, this is equivalent to conjugation, then we are

14 Ibid., p. 497.

15 Ibid., p. 492; the italies at the end are mine.

16 Tbid., p. 496.

No. 578] CYCLES AND RHYTHMS 75

justified in saying that throughout the seven years Wood-

ruff’s Paramecium has undergone the equivalent of con-

jugation on the average once each month, and if it is

equivalent to conjugation, then his long culture of more

than 4500 generations has no bearing on the question of

old age and natural death in Paramecium.

Nothing in this work of Woodruff and Erdmann seems

more clearly and forcibly demonstrated than that the cycle,

this ‘‘phantom’’ of many investigators, resolves itself

into a demonstrated fact, and that Woodruff’s ‘‘rhythm’’

and Calkins’s ‘‘eycle’’ are but different names for the same

phenomenon. If natural death is a necessary end to jus-

tify our use of the term ‘‘cycle,’’ we may ask the perti-

nent question: What happened to those individuals which

did not undergo asexual endomixis in Woodruff’s long

culture? If they died, does not this fact indicate the end

of a cycle? If they underwent parthenogenesis, the

equivalent of conjugation, does not this fact indicate the

beginnings of new cycles? If they continued to live with-

out reorganization, evidence for which has never been

given by Woodruff, then there would be some justification

for our authors’ conclusion. To argue that it is the same

race which continues after asexual endomixis is to use

the same argument that Weismann used unsuccessfully,

viz., that an ex-conjugant is the same old individual since

no corpse has been formed and therefore the infusoria

are immortal.

The frequent statement made by Woodruff that his

long culture sustains the view that old age and need of

conjugation are not necessary attributes of living matter

are contradicted by these later results. For example, he

states in 1913:

Diese Untersuchung hat uns gezeigt, dass, unter günstigen äusseren

Umständen, das Protoplasma der zuerst isolierten Zelle mindestens die

Potenz hatte, ähnliche Zellen bis zu einer Zahl von 2%*4° und eine

Masse Protoplasma von mehr als 10*°°° mal der Masse des Erdballes

zu erzeugen. Dieses Resultat, glaube ich, bestätigt unzweifelhaft die

Annahme, dass das Protoplasma einer einzigen Zelle unter günstigen

76 THE AMERICAN NATURALIST [Vou. XLIX

äusseren Umständen ohne Hilfe von Konjugation oder einer künstlichen

Reizung imstande ist, sich unbegrenzt fortzupflanzen und zeigt ferner in

klarer Weise, dass das Altern und das Befruchtungsbediirfnis nicht

Grundeigenschaften der lebendigen Substanz sind.17

I am entirely in sympathy with Hertwig when he says,

in connection with this citation:

Nach meiner Ansicht sind die Resultate, zu denen in den unseren

Auseinandersetzungen zum Ausgangspunkt dienenden Artikel Wood-

ruff gemeinsam mit Rhoda Erdmann gelangt ist, mit den hier zitierten

Sätzen unvereinbar.1§

The discovery of parthenogenesis in the life cycle of

Paramecium aurelia by Woodruff and Erdmann clears up

the obscurity which has involved all theoretical discus-

sions following pedigreed culture work with infusoria,

and we now see with much clearer vision the probability,

first, that conjugation or its equivalent has primarily the

result, as originally interpreted by Biitschli, of offsetting

and overcoming the progressive weakening of vitality in

infusoria; second, that more or less definite cycles of

vigor and depression, ending in natural death unless con-

jugation or its equivalent supervenes, are characteristic

of all pedigreed races of infusoria; third, that physical

‘‘immortality’’ is true of Paramecium and other ciliates

only in the same sense that it is true of metazoa; fourth

and last, that Paramecium protoplasm is subject to the

same laws of physiological usury that apply to metazoa,

and undergoes phenomena which, in metazoa, we call old

age, and which, as in metazoa, ends in natural death un-

less conjugation, or its equivalent parthenogenesis, saves

e race.

CoLUMBIA UNIVERSITY

17 Dreitausend und dreihundert Generationen von Paramecium u. s. W.,’

Biol. Centr., Vol. 33, No. 1, 1913, p. 35.

18 ‘‘ Ueber Piithansgencels der Infusorien,’’ ete., Biol. Centr., Vol. 34,

No. 9, 1914, p. 577.

THE PHENOMENON OF SELF-STERILITY!

PROFESSOR E. M. EAST

BUSSEY INSTITUTION, HARVARD UNIVERSITY

In both animals and plants in which the two sexes have

been combined in the same individual, cases have been

found where self-fertilization is practically impossible.

This gametic incompatibility has been called self-sterility,

although the term is hardly proper as applied to normal

functional gametes that may fuse with their complements

in the regular manner, provided each member of a pair

has been matured in a separate individual.

In plants the phenomenon has been known since the

middle of the nineteenth century, in animals a correspond-

ing discovery was made in 1896 by Castle, the species

being one of the Ascidians, Ciona intestinalis. During

the eighteen years that have passed since Castle’s dis-

covery, Ciona has been studied on a large scale by Morgan

(1905), Adkins (Morgan, 1913), and Fuchs (1914). The

botanists, however, have lagged somewhat behind; for, in

spite of having been acquainted with self-sterility in

plants for over half a century, and having found over

thirty species where a greater or less degree of self-

sterility occurs from which to select material, very few

thorough investigations into the physiology of the subject

have appeared.

The main facts regarding fertilization in Ciona intesti-

nalis are about as follows:

1. Under uniform suitable conditions, individuals vary

in degree of self-sterility, it being exceptional to find an

animal that is perfectly self-sterile.

2. Self-fertility has never equaled cross-fertility, though

the possibility remains that some animals may be self-

ad by title at the thirty-second ya of the American Society of

Aae December 31, 191 bh:

78 THE AMERICAN NATURALIST [Vou. XLIX

fertilized as easily as they may be crossed with certain

particular individuals.

3. The ease with which the ova of any animal ‘‘A’’ may

be fertilized by the sperm of other individuals may vary.

Morgan (1913) concluded from his own work and that

of Adkins that there were wide differences in the compati-

bility of ova to different sperm. Fuchs (1914) maintained

that 100 per cent. of segmenting eggs can be obtained in

every cross if the ova are normal and a sufficiently con-

centrated sperm suspension is used. It is possible that

Fuchs is correct and that varying concentrations of sperm

suspension were the cause of Morgan’s and Adkins’s re-

sults, yet the possibility of differences in this regard in-

herent in the individual is not to be overlooked. It will

be seen later that I regard the matter as of great impor-

tance to the general subject.

4, A chemical basis for self-sterility is shown in Fuch’s

experiments by (a) the decrease in ease of cross-fertiliza-

tion after contact of ova with sperm from the same ani-

mal, and by (b) the difference in ease of self-fertilization

after various artificial changes in the chemical equilibrium

of the medium surrounding the ova.

From the botanical side various studies on the physiol-

ogy of self-sterility have appeared since such investiga-

tions were initiated by Hildebrand in 1866. At this time

itis necessary for us to consider only those of Jost (1907),

Correns (1912), and Compton (1913).

Jost was able to show that in self-sterile plants tubes

formed from their own pollen were so limited in their

development that fertilization did not occur, although the

necessary length of pollen tube was easily developed after

a cross-fertilization. He saw as the cause of these phe-

nomena the presence of ‘‘ individueller Stoffe.’’ Pollen

was indifferent to ‘‘Individualstoff’’ of the same plant,

but was stimulated by that of other plants.

Correns (1912), working with one of the bitter cresses,

Cardamine pratensis, obtained results to which he gave a

simpler interpretation. Starting with two plants, B and

No. 578] SELF-STERILITY 79

G, he crossed them reciprocally and tested 60 of the off-

spring by pollinating from the parents, on the parents,

and inter se. The back crosses of (BX G) or (GX B)

with B and with G apparently indicated four classes about

equal in size with reference to gametic compatibility:

(1) plants fertile with both B and G; (2) plants fertile

with B but not with G; (3) plants fertile with G but not

with B; (4) plants fertile with neither B nor G.

To these facts Correns gave a Mendelian interpretation

by assuming the existence of two factors each of which in-

hibits the growth of pollen tubes from like gametes. Rep-

resenting these factors by the letters B and G, it is clear

that types BB and GG could never be formed. The orig-

inal plants were supposed to be of classes Bb and Gg, re-

spectively. When crossed there resulted the four types

BG, Bg, bG and bg. Plants of types BG, Bg, and bG

should be self-sterile, while plants of the type bg should be

self-fertile. Plants BG should be fertile with plants bg,

plants Bg should be fertile with bG and bg, and plants bG

should be fertile with Bg and bg. As a matter of fact

Correns’s results were not clearly in accord with the

theory. Plants of the type bg were not self-fertile, and

the other classes of matings showed many discrepancies.

It is only fair to say, however, that the author recognized

some of these difficulties, but believed them to be due to

other inhibitors.

In a part of Compton’s (1913) work, a still simpler

interpretation of. self-sterility is offered, at least for a

particular case, that of Reseda odorata. Darwin’s origi-

nal discovery that both self-sterile and self-fertile races

of this plant exist was confirmed and the following results

obtained in crossing experiments. Self-sterile plants

crossed either with self-sterile or with self-fertile plants

gave only self-sterile offspring. Certain self-fertile

plants, however, gave only self-sterile offspring when self-

pollinated. Other self-fertile plants gave ratios of 3 self-

fertile to 1 self-fertile offspring when self-pollinated, and

ratios of 1:1 when crossed with pollen from self-sterile

80 THE AMERICAN NATURALIST [Vow XLIX

plants. For these reasons he regards self-fertility as a

simple Mendelian dominant to self-sterility in the case

studied. I believe Compton would draw no such sharp

line about self-sterility in general. In fact, he follows

Jost in suggesting the presence of a diffusible substance

in the tissues of the style and stigma which retards or

promotes pollen tube growth after self-pollination or

cross-pollination in some manner analogous to the mech-

anism that promotes animal immunity or susceptibility

after infection.

The only alternative general hypothesis has been pro-

posed by Morgan, and this can be discussed more advan-

tageously after the presentation of my own work, of which

only an abstract will be given at this time.

In 1909 I made a cross between a small red-flowered

Nicotiana, Nicotiana forgetiana (Hort.) Sand. and the

large white-flowered Nicotiana of the garden Nicotiana

alata Lk. and Otto. var. grandiflora Comes. All of the

plants of the F, generation appeared to be self-sterile.

Tests of Nicotiana forgetiana? have shown these plants

also to be self-sterile, but both self-fertile and self-sterile

plants of the other parent have been found. From data

gathered later, there seems to be no doubt that a self-

sterile plant of Nicotiana alata grandiflora was used in

the actual cross. This conclusion seems reasonable in

view of the fact that of over 500 plants of the F,, Fa F;

and F, generations tested, not a _— self-fertile plant

was found.

The plants of the F, generation were all vigorous and

healthy, and in spite of the fact that they resulted from a

species cross which Jeffrey claims always produces large

amounts of abnormal pollen, a large number of examina-

tions of pollen from different individuals showed from 90

2I thought originally that both of these species (East, 1913) were self-

fertile. Seed had been obtained from a carefully bagged inflorescence of

each species in 1909. Either the plant of N. forgetiana which gave this

seed was self-fertile—something that I have never been able to find since

that time—or there was an error in manipulation. At any rate, the plants

resulting from this seed were all self-sterile

No. 578] SELF-STERILITY 81

to 100 per cent. of morphologically perfect pollen grains,

a condition about the same as was found in the pure spe-

cies. To this statement there is one exception. A single

plant was found with only about 2 per cent. of good sound

pollen.

Several experiments were made in which crossing and

selfing was done on a large scale, using plants of the F,,

F, and F, generations which had segregated markedly in

size and were of at least 8 different shades of color. In

one of these experiments 20 plants of the F, generation

coming from 2 crosses of F, plants were used. It was

planned to make all possible combinations of these plants,

400 in all. This task proved overburdensome, however,

and in addition to the self-pollinations but 131 inter-

crosses were made with the following results.

1. Each plant was absolutely self-sterile.

2. Leaving out of consideration the plant with shrunken

imperfect pollen only two crosses failed. This failure of

1.5 per cent. of the crosses may have been due to im-

proper conditions at the time of the attempts, but as a

number of trials were made the possibility remains that

there is a small percentage of true cross-sterility.

3. Of the 129 successful inter-crosses, 4 produced cap-

sules with less than 50 per cent. of the ovules fertilized.

The remaining crosses produced full capsules. It is

barely possible that this result shows a slight variability

in ease of cross-fertilization, but I am more inclined to

believe that these 4 cases where a low percentage of fer-

tilized ovules were obtained were accidental.

Other crossing experiments of the same kind have cor-

roborated these results. Out of 120 inter-crosses, only 3

failed.

Later, something over 100 inter-crosses were made be-

tween 12 plants of an F, population resulting from cross-

ing two sister F, plants. Six of the attempts at cross-

fertilization—3 to 8 trials per plant being made—were

failures. These plants as well as others tested were com-

82 THE AMERICAN NATURALIST [Vou. XLIX

pletely self-sterile, and apparently there was cross-steril-

ity in about 6 per cent. of the possible combinations.

In the F, generation, 10 plants resulting from crossing

two sisters of the F, generation were selected for experi-

ment. Unfortunately, I was able to make only 58 inter-

crosses, 5 of which, almost 10 per cent., failed.

Back crosses have furnished another line of experiment,

though they have not been carried on as systematically as

were those of Correns. Nearly 85 back-crosses using

plants from the progeny of four combinations which: in-

cluded four individuals as parents, have been made. The

plants themselves all proved self-sterile, and in addition

5 of the back crosses failed.

When these experiments were begun I expected to find

that the facts would accord with a simple dihybrid Men-

delian formula similar to that which Correns later pro-

posed as an interpretation of his results, yet only by con-

siderable stretching and a vivid imagination will Cor-

rens’s data fit such an hypothesis, and my own data do

not fit at all. No self-fertile plants have been produced

by any combination, and cross-sterility is a possibility in

only from 1.5 to 10 per cent. of the combinations. Fur-

thermore, Correns’s idea of inhibitors appears unlikely

from some other data I have gathered with the help of

Mr. J. B. Park. Ten plants were involved in this experi-

ment. Pairs of plants were provided to furnish series

of selfed and crossed flowers. The pistils of these flowers

were fixed at regular periods after pollination, stained,

sectioned, and the pollen tubes examined. Fertilization

not later than the fourth day marked the end point of the

crossed series, the dropping of the flowers between the

eighth and the eleventh day ended the selfed series. As

the flowers on each plant had about the same length pistils,

curves of pollen tube development for both crossing and

selfing could be constructed. The pollen grains germi-

nated perfectly on stigmas from the same plant, from

1,200 to 2,000 tubes having been counted in sections of

single pistils. The difference between the development

No. 578] SELF-STERILITY 83

of the tubes in the selfed and the crossed styles is wholly

one of rate of growth. The tubes in the selfed pistils de-

velop steadily at a rate of about 3 millimeters per twenty-

four hours. There is even a slight acceleration of this

rate as the tubes progress. If the flowers were of an

everlasting nature one could hardly doubt but that the

_ tubes would ultimately reach the ovules, though this would

not necessarily mean that fertilization must occur. Since

the maximum life of the flower is about 11 days, however,

the tubes never traverse over one half of the distance to

the ovary. On the other hand, the tubes in the crossed

pistils, though starting to grow at the same rate as the

others, pass down the style faster and faster, until they

reach the ovary in four days or less.

From these facts it seems reasonable to conclude that

the secretions in the style offer a stimulus to pollen tubes

from other plants rather than an impediment to the de-

velopment of tubes from the same plant.

The whole question, therefore, becomes a mathematical

one, that of satisfying conditions whereby no stimulus is

offered to pollen tubes from the same plant, but a positive

stimulus is offered to tubes from nearly every other plant.

Morgan has given an answer to this question in a gen-

eral way. If I understand his position correctly, my own

conclusions are not very different from his, but are some-

what more definite. Morgan (1913) states that the re-

sults of Adkins and himself on Ciona intestinalis can best —

be understood by the following hypothesis:

The failure to self-fertilize, which is the main problem, would seem

to be due to the similarity in the hereditary factors carried by the eggs

and sperm; but in the sperm, at least, reduction division has taken

Place prior to fertilization, and therefore unless each animal was

homozygous (which from the nature of the case cannot be assumed

possible) the failure to fertilize can not be due to homozygosity. But

both sperm and eggs have developed under the influence of the total or

duplex number of hereditary factors; hence they are alike, i. e., their pro-

toplasmie substance has been under the same influences. In this sense,

the case is like that of stock that has long been inbred, and has come

to have nearly the same hereditary eee If this similarity decreases

84 THE AMERICAN NATURALIST [Vov. XLIX

the chances of combination between sperm and eggs we can interpret

the results.

I make this quotation to show Morgan’s viewpoint. It is

for him to say whether the following conclusions are ex-

tensions of his own or not.

The tolerably constant rate of growth of pollen tubes in

the pistils of selfed flowers, compared with the great ac-

celeration of growth of the tubes from the pollen of other

plants as they penetrate nearer and nearer to the ovary,

undoubtedly shows the presence of stimulants of great

specificity akin to the ‘‘Individualstoffe’’ of Jost. We

are wholly ignorant of the nature of these stimulants, but

I am inclined towards a hypothesis differing somewhat

from his. Experiments by several botanists, which I

have been able partially to corroborate, point to a single

sugar, probably of the hexose group, as the direct stimu-

lant. The specific ‘‘Individualstoffe’’ I believe to reside

in the pollen grains and to be in the nature of enzymes of

slightly different character, all of which, except the one

produced by the plant itself for the use of its own pollen

or by other plants of identical germinal constitutions,

can call forth secretion of the sugar that gives the direct

stimulus. At least this idea links together logically the

fact of the single direct stimulus and the need of ‘‘Indi-

vidualstoffe’’ to account for the results of the crossing and

selfing experiments. But whether or not this be the cor-

= rect physiological inference, the crossing and selfing ex-

periments call for a hypothesis that will account for no

stimulation being offered the tubes from the plant’s own

pollen, while at the same time great stimulation is given

the tubes from the pollen of nearly every other plant.

This is a straight mathematical problem, and it is

hardly necessary to say that it is insoluble by a strict

Mendelian notation such as Correns sought to give. This

is obvious to any one familiar with the basic mathematics

of Mendelism. On the other hand, a near Mendelian in-

terpretation satisfies every fact.

Let us assume that different hereditary complexes stim

No. 578] SELF-STERILITY 85

ulate pollen tube growth and in all likelihood promote fer-

tilization, and that like hereditary complexes are without

such effect. One may then imagine any degree of hetero-

zygosis in a mother plant and therefore any degree of

dissimilarity between the gametes it produces, without

there being the possibility of a single gamete having any-

thing in its constitution not possessed by the somatic tis-

sues of the mother plant. From. the chromosome stand-

point of heredity the cells of the mother plant are duplex

in their organization; they contain N pairs. The cells

of the gametes contain N chromosomes, one coming from

each pair of the mother cell; but they are all parts of the

mother cell and contain nothing that that cell did not con-

tain. These gametic cells can not reach the ovaries of

flowers on the same plant because they can not provoke

the secretion of the direct stimulant from the somatic cells

of that plant.

All gametes having in their hereditary constitution

something different from that of the cells of a mother

plant, however, can provoke the proper secretion to stim-

ulate pollen tube growth, reach the ovary before the flower

wilts and produce seeds. Such differences would be very

numerous in a self-sterile species where cross-fertilization

must take place; nevertheless like hereditary complexes:

in different plants should be found, and this should ac-

count for the small percentage of cross-sterility actually

obtained. It must be granted that this hypothesis satis-

fies the facts, but that is not all. It is admittedly a per-

fectly formal interpretation, but from a mathematical

standpoint,—granting the generality of Mendelian inheri-

tance,—it is the only hypothesis possible that can satisfy

the facts.

Let us now look into a few of the ramifications of the

subject. Examinations of the pistils that have been sec-

tioned after cross-pollination show a considerable varia-

tion in the rate of growth of individual pollen tubes,

though our curves of growth have been made by taking

the average rate of elongation. Is this variation a result

86 THE AMERICAN NATURALIST [Vou XLIX

of chance altogether or must we assume a differential rate

of growth increasing directly with the constitutional dif-

ferences existing between the somatic cells and the vari-

ous gametes? If we assume that any constitutional dif-

ference between the two calls forth the secretion of the

direct stimulus to growth, chance fertilization by gametes

of every type different from that of the mother plant will

ensue; if there is a differential rate, selective fertilization

will occur. This question can not be decided definitely at

present, but two different lines of evidence point toward

chance fertilization.

1. Flowers from a single plant pollinated by different

males show no decided difference in rate of fertilization.

2. Color differences are transmitted in expected ratios.

Further, it will be recalled that beginning with the F,

generation, sister plants crossed together have given us

our F, and F, populations, and that these F, and F, popu-

lations apparently have given a constantly increasing per-

centage of cross-sterility. This is what should be ex-

pected under the theory that a small difference in germ

plasm constitution is as active as a great difference in

causing the active stimulation to pollen tube growth. -

Breeding sister plants together in succeeding generations

causes an automatic increase of homozygosity as is well

known. This being a fact, cross-sterility should increase.

Such an increase in cross-sterility has been observed in

the F, and the F, generations, but it would not be wise to

maintain dogmatically that it is significant.

There are various questions, including the important

one of the origin of self-sterility, that can not be discussed

at this time. In conclusion, therefore, let us turn once

more to the phenomenon of self-sterility in Ciona intes-

tinalis. It seems to me that the hypothesis outlined above

has few, if any, drawbacks when applied to self-sterility

in plants. The question there, as far as we have gone, is

one of pollen tube growth, and the theory that the secre-

tion of the direct stimulant can be called forth only by a

gamete that differs in its constitution from the somatic

No. 578] SELF-STERILITY er. «|

cells between which the pollen tube passes, is logical. If

the same theory is to be extended to animals, however, it

follows that the external portions of the membranes of

the animal egg that have been shown by the wonderful in-

vestigations of Loeb and of Lillie to have such important

functions, must be functionally zygotic in character. I

am aware that this suggestion may be considered pretty

radical, but it certainly should be given consideration.

I do not like to draw an analogy between the animal egg

and a pollen grain, but it may be mentioned that in these

structures—surely comparable to the animal egg in the

fineness of their membranes and walls—both color and

shape are inherited as if they were zygotic in nature.

December 5, 1914.

LITERATURE CITED.

Castle, W. E. The Early Embryology of Ciona intestinalis Flemming (L.).

Bull. Mus. Comp. Zool., Harvard University 27, 201-280. 1896.

Compton, R. H. Phenomena and Problems of Self-sterility. New Phytolo-

gist, 12, 197-206. 1913.

Correns, ©. Selbststerilitiit und Individalstoffe. Peéstechr. d. mat.-nat.

Gesell. zur 84. Versamml, deutsch. Naturforscher u. Arzte, 1912.

Miinster i, W., pp. 1-32.

East, E. M. Inheritance of Flower Size in Crosses between Species of

Nicotiana. Bot. Gaz., 55, 177-188. :

Fuchs, H. M. On the Conditions of Self-fertilization in Ciona. Archiv.

f. Entwickl. d. Org., 40, 157-204.

pee i Action of ter Somat a on the Fertilizing Power of Sperm.

52. 1914.

~fruchtung von Corydalis cava. .

Jost, L. Zur Physiologie des Pollens. Ber. i deut. bot. Gesell., 23, 504-

515. 1905.

—— Ueber die PAET einiger Blüten. Bot. Zig., Heft V and VL

1907.

Morgan, T. H. Some Further Experiments on Self-fertilization in Ciona.

Biol. Bull., 8, Stags 1905.

SETIN Heredity ù d Sex. New York. Columbia Univ. Press, pp. ix + 1-

282. 1913 rek cited 217).

THE BLACK-AND-TAN RABBIT AND THE SIG-

NIFICANCE OF MULTIPLE ALLELOMORPHS

W. E. CASTLE AND H. D. FISH

Bussey Institution, Forrest Hiuus, Mass.

Ir is well known that the European rabbit has under-

gone great variation, and now exists in a large number of

domesticated varieties. Darwin and most other natural-

ists speak of this as ‘‘variation under domestication,’’

implying that domestication has caused the variation.

Modern genetic research, however, indicates that domesti-

cation has occasioned the preservation rather than the

origin of the fundamental variations involved. But to

what extent man through selection is able to modify the

fundamental variations which nature occasionally pro-

duces as sports is still an open question. Evidence is

nevertheless accumulating that certain of these funda-

mental variations may occur in two or more alternative

forms, and the question then arises (1) whether these al-

ternative forms have arisen independently by distinct acts

of mutation, or (2) whether one has arisen from another

by a process of secondary mutation, or (3) whether one

may not have been transmuted into another by a more or

less gradual process. Toward the testing of these sev-

eral hypotheses much genetic research is now being di-

rected. The first step to be taken is evidently to ascertain

in how many alternative forms the same fundamental

variation may occur and how these forms are inter-

related. A further step will be the attempt to produce

new alternative forms at will. It is our purpose, in this

paper, to discuss a newly discovered alternative form

(allelomorph) of the gray, or agouti, type of coat found

in wild rabbits. It occurs in the variety known as black-

and-tan.

This variety appears to have arisen from the wild gray,

or agouti, type without the loss of any known genetic fac-

tor, but by a modification in one. Simple loss of genetic

factors is believed by most students of genetics to have

No. 578] MULTIPLE ALLELOMORPHS 89

given rise to black, chocolate and albino varieties of rab-

bits and other rodents, but a hypothesis of this sort will

not fit the present case. No factorial loss can be detected,

but only a change in that genetic factor which has been

called the agouti or gray factor. Under the influence of

this factor, what would otherwise be a black variety be-

comes gray, and what would otherwise be sooty yellow

(‘‘tortoise’’ of the fanciers) becomes clear yellow (‘‘fawn’’

of the fanciers). This same factor converts chocolate

into cinnamon (Punnett, 1912). In every way, accord-

ingly, its influence on the coloration of rabbits is similar

to that of the agouti factor in guinea-pigs and mice.

But in mice Cuénot (1909) showed that the agouti factor

may assume three distinct forms allelomorphic to each

other, the effects of which are seen respectively in gray,

light-bellied gray, and in yellow mice. Entire absence of

agouti marking from the fur (non-agouti) forms a fourth

allelomorph in the series.

In guinea-pigs the agouti factor assumes two alterna-

tive conditions, the effects of which are seen in ordinary

(light-bellied) agoutis and in agoutis with ‘‘ticked’’ bel-

lies, respectively (Detlefsen, 1914). These two conditions

correspond closely in appearance and in order of domi-

nance to the light-bellied gray and the ordinary gray of

mice, the former being dominant in both cases. Non-

agouti is an allelomorph to both, as in mice.

The peculiarity of the agouti seen in black-and-tan rab-

bits is that it produces less extensive ticking of the fur

than does ordinary agouti. In a typical black-and-tan

rabbit the light-colored (yellowish) bands on the hairs,

which constitute the ‘‘ticking,’’ occur only sparingly on

the sides of the body, and not at all on the back or the

head. But the under side of the body, including the

throat and under surface of the tail, are light (yellowish

or whitish) and the back of the neck and inside of the ears

bear reddish or yellowish pigment, as in gray rabbits.

The typical black-and-tan rabbit of the fanciers has very

intense pigmentation which deepens the shade of the

“tan” (yellow) found on belly, sides, ete. But this inten-

90 THE AMERICAN NATURALIST [Vou. XLIX

sity is inherited independently of the agouti factor as

crosses with dilute colored varieties of rabbit show. For

a cross between black-and-tan and blue produces in F,

(1) blue-and-tans as well as (2) black-and-tans, (3) blacks,

and (4) blues. This result is strictly parallel with that

obtained by crossing intense gray rabbits with blue ones.

In that case there are produced (1) blue gray, (2) intense

gray, (3) black, and (4) blue young in F,. It is evident

that in each case a dihybrid cross is made and that the end

products are the same in the two series except for the dif-

ference in the agouti marking of varieties (1) and (2).

The natural conclusion is that. black-and-tan contains an

alternative form of agouti to that found in gray rabbits.

If so, it should be capable everywhere of substitution for

gray, wherever the latter occurs throughout the entire

series of color varieties, and indeed this appears to be the

case.

That the black-and-tan factor, like the ordinary agouti

factor, is independent of the extension-restriction pair of

allelomorphs is shown by a cross of black-and-tan with

sooty yellow (i. e., non-agouti yellow or ‘‘tortoise’’).

F, contains (1) black-and-tan, (2) black, (3) yellow

(‘‘fawn’’), and (4) sooty yellow (‘‘tortoise’’) young.

The first two are varieties with extended pigmentation,

and the second two are varieties with restricted pigmen-

tation; further, varieties (1) and (3) contain modified

agouti, but varieties (2) and (4) do not.

If a gray rabbit had been used, instead of a black-and-

tan, in making the cross just described, three of the four

varieties obtained in F, would have been indistinguish-

able from those enumerated, and the fourth one would

merely have been gray instead of black-and-tan. This

supports the view that black-and-tan is merely an alterna-

tive form of gray.

Further, we have evidence to show that the black-and-

tan form of agouti, like the agouti of gray rabbits, is inde-

pendent of the genetic factors which respectively produce

Dutch pattern, English pattern, and angora coat, since we

have been able to coe aa individuals in which black-and-

No. 578] MULTIPLE ALLELOMORPHS 91

tan was associated with each one of these Mendelizing

characters, as well as others in which it was not associated

with them. Finally Haecker (1912) has shown that black-

and-tan, like the ordinary form of agouti, is independent

of albinism, since when black-and-tans are crossed with

Himalayan albinos, not only these two varieties are ob-

tained in the F, generation, but also blacks. The propor-

tions in which these three varieties were obtained by

Haecker approximate the modified dihybrid ratio, 9 black-

and-tan: 3 black: 4 Himalayan. One of the two Men-

delian pairs concerned is color vs. albinism; the other and

independent one, black-and-tan vs. black.

It is known that if a gray rabbit is used, instead of a

black-and-tan one, in a cross with Himalayan albinos, the

same 9:3:4 ratio is obtained in F,, of grays, blacks, and

albinos, respectively. The observed results differ, in the

two cases, only in the substitution of gray for black-and-

tan, which is further evidence that it is only another form

of the same genetic factor.

Notwithstanding all this consistent and converging evi-

dence, it is possible that the modified form of agouti seen

in black-and-tan is not due to a changed agouti factor

itself, but to the modifying action of a factor associated

with it which partially inhibits its action. Here we must

consider two subordinate possibilities: (a) that the sup-

posed modifier is wholly independent of the agouti factor,

and (b) that it is coupled with the agouti factor. The

first possibility is readily disproved; the second one is not

so easily disposed of.

(a) If black-and-tan were due to the action of an inde-

pendent modifying factor associated with agouti, a cross

of black-and-tan with ordinary black should permit the

separation of agouti from its supposed modifier in a con-

siderable part of the F, gametes and F, zygotes, so that

we should expect F, to contain gray animals as well as

blacks and black-and-tans. But experiments started sev-

eral years ago at the Bussey Institution show that when

black is crossed with black-and-tan no gray offspring are

_ obtained either in F, or in F,, but a black-and-tans in

92 THE AMERICAN NATURALIST [Vow XLIX

F,, and black-and-tans and blacks in F,. This result

shows that black-and-tan is a simple dominant over black.

To establish the allelomorphism of black-and-tan with

gray the following experiments may be cited. A black-

and-tan rabbit heterozygous for black was crossed with

a pure-bred Belgian hare, which variety possesses the

genetic color factors of wild rabbits, including the ordi-

nary agouti factor. All the F, young were gray, closely

resembling Belgian hares, but proved to be genetically

of two types. For, when mated with black rabbits, some

of them produced gray young and black young, while

others (even when mated, as in some cases, with the same

black animals) produced gray young and black-and-tan

young. This result was quite what was to be expected if

_ gray, black-and-tan and black are mutually allelomorphic

conditions. On no other hypothesis which we can sug-

gest was it to be expected. For the black-and-tan parent

in the cross was known to be heterozygous for black. It

accordingly should form two sorts of gametes, black and

black-and-tan respectively, provided that these conditions

are allelomorphic to each other. The Belgian hare parent

was known to transmit gray in all its gametes. The com-

binations expected from the crdss are therefore of two

types, viz.: (1) gray combined with black, and (2) gray

combined with black-and-tan. It is well known that gray

and black are allelomorphs of each other, the former being

dominant. Zygotes of type (1), therefore, should pro-

duce gametes of two sorts, gray and black; and when

back-erossed with black should produce equal numbers of

gray young and black ones but no black-and-tan young.

We have tested 12 F, gray young from this cross (6 males

and 6 females) which are evidently of type (1). Mated

with black animals, they have produced 69 gray young,

and 65 black ones, but no black-and-tans. ©

-On the other hand 8 F, gray rabbits from the cross

under discussion have proved to be of type (2), producing

gray young and black-and-tan young but no black ones.

Together they have produced 44 gray and 51 black-and-

tan young, besides 14 other young (two litters) which

No. 578] MULTIPLE ALLELOMORPHS 93

were certainly not blacks, since they had light bellies,

but which died before attaining the age at which gray

can be distinguished from black-and-tan. It is certain

that among the 109 young produced by the 8 animals of

type (2) not a single one was black.

But if black-and-tan is not an actual allelomorph of

gray, black young as well as black-and-tans should have

been produced in the foregoing case. For if black-and-

tan is not allelomorphic with gray, or is due to an inde-

pendent inhibitor of gray, then an F, gray should produce

gametes of four sorts, rather than as indicated of two

sorts; t. e., gametes should arise which transmit both gray

and black-and-tan, and others which transmit neither gray

nor black-and-tan. The former sort possibly might not

be capable of immediate detection in the back-cross with

black, but the latter should be readily discovered since

they would necessarily produce black young (neither gray

nor black-and-tan). The total absence of black young

from the litters produced by type (2) matings therefore

indicates strongly that gray and black-and-tan are allelo-

morphs of each other.

(b) An alternative view, however, deserves. considera-

tion. If gray and black-and-tan are not actual allelo-

morphs, it is conceivable that they may each be closely

‘‘coupled’’ with a common structure in the germ cells and

so behave as allelomorphs under ordinary circumstances,

though not being such in reality. Or, what would give

the same practical result, gray and black-and-tan might

be supposed to contain the same agouti factor, but this

might be considered in one as closely coupled with a modi-

fying factor which made its action different. Neither

form of this hypothesis is capable of proof or disproof,

for which reason alone the hypothesis is unimportant, but

its probability grows less the larger the number of records

obtained which show no breaking of the supposed coup-

ling. Our cases are not as yet numerous enough to throw

much light on this question, but so many cases have

already been discovered in which characters assume three

or more mutually allelomorphic conditions and in which —

94 THE AMERICAN NATURALIST [Vou. XLIX

no evidence of coupled modifiers has yet been discovered,

that the existence of such assumed modifiers seems at

present doubtful.

Besides the triple or quadruple series of agouti allelo-

morphs now known for mice, guinea-pigs and rabbits, at

least three other Mendelian factors concerned in the pig-

mentation of rodents vary discontinuously in this way.

1. Castle (1905) and Punnett (1912) have shown that

the Himalayan rabbit possesses a form of albinism allelo-

morphic with that of ordinary albino rabbits, and that

both are allelomorphic to ordinary pigmentation. Guinea-

pigs show an even more extended series of albino allelo-

morphs (Castle, 1914, Wright, unpublished data).

2. Punnett (1912) has discovered in rabbits an alterna-

tive form of the ‘‘extension’’ factor, one in the presence

of which the agouti factor produces a less amount of tick-

ing than normally. He describes it as a darkened exten-

sion, č. e., as ordinary extension modified by a coupled

darkening factor. This is of course only an alternative

form of statement to saying that extension occurs in two

forms, for he discovered no cases in which the hypothet-

ical coupling was broken. The three allelomorphs in the

ease of Punnett’s rabbits were accordingly: 1, ordinary

extension; 2, darkened extension, and 3, restriction.

3. In still another Mendelian factor affecting the pig-

mentation of rodents discontinuous variation occurs at-

tended almost certainly by the formation of a series of

allelomorphs. Cuénot (1904) stated that white-spotting

in mice occurs in a graded series of conditions as regards

the amount or extent of the white areas. He found that

widely separated stages in the series Mendelize on cross-

ing, 7. e., that the segregates fluctuate about modal con-

ditions corresponding roughly with the conditions of

spotting found in the respective parents crossed, and he

concluded the number of allelomorphs which it would be

possible to find in the series to be indefinitely great. Sub-

sequent studies of the subject made by Little (1914) in

mice, and by Castle and Phillips (1914) in rats, have not

served to simplify the matter, and yet they confirm Cué-

No. 578] MULTIPLE ALLELOMORPHS 95

not’s general idea that a series of mutually allelomorphic

conditions of spotting exists. Unquestionably in rats,

‘*hooded’’ and ‘‘Trish’’ are such modal conditions of

spotting, allelomorphic with each other and with the un-

spotted or self condition (Doncaster, 1905; MacCurdy

and Castle, 1907; Castle and Phillips, 1914). The last-

named authors find that independent factorial modifiers

probably affect the extent of the spotting and yet .that,

aside from such modifiers, the spotting factor proper may

assume relatively stable allelomorphic conditions which

Mendelize when crosses are made between stages suffi-

ciently distinct. The point of especial interest in allelo-

morphic conditions of spotting is that they are not per-

fectly stable, but are capable of gradual and apparently

indefinite modification through the selection of fluctua-

tions either plus or minus. It would be premature to

conclude that similar fluctuations (though perhaps less

conspicuous ones) do not occur about the modal condi-

tions of other genetic factors which show allelomorphic

variation. The black-and-tan form of agouti certainly

fluctuates in the amount of ticking found on the sides of

the body and the head; doubtless some of this fluctuation

may be due to factors genetically distinct from the chief

allelomorphic factor concerned, but there is at present no

sufficient ground for supposing the chief factor itself to

be incapable of fluctuation. Indeed, it seems highly prob-

able, in the light of evidence already obtained, that the

present modal condition of the black-and-tan character is

one which has been attained only as a result of persistent

selection, and that.reversed selection will carry it back

appreciably nearer to the modal condition seen in gray

rabbits. Accordingly, it appears doubtful whether allelo-

morphs are themselves perfectly and permanently stable.

Moreover, the rapid increase of recognized allelomorphs

makes us wonder whether their number is limited and defi-

nite. Black-and-tan represents, on the whole, an inter-

mediate condition between black and gray. Is it not con-

ceivable that intermediates may yet be discovered be-

96 THE AMERICAN NATURALIST [Vou XLIX

tween black-and-tan and black, or between black-and-tan

and gray, or even that black-and-tan itself might be dis-

placed to such an intermediate condition by selection of

its fluctuations? Here are fruitful fields of inquiry to be

cultivated before we conclude with the exponents of ‘‘ex-

act’’ heredity that selection of fluctuations is useless and

that only mutations count in evolution.

December 26, 1914.

PAPERS CITED

Castle, W. E.

1905. Heredity of Coat Characters in Guinea-pigs and Rabbits. Publ.

No. 23, Carnegie Institution of Washington

1914, ere New Varieties of Rats and Gatnpa-piga and their Rela-

tions to Problems of Color Inheritance. AMER. NAT., 48, pp.

65-73.

Castle, W. E., and J. C. Phillips.

1914. Pi ebald Rats and Selection. Publ. No. 195, Carnegie Institu-

tion of Washington

Cuénot, L

1904. L’hérédité de la pigmentation, chez les souris (3me Note).

. de Zool. Exper. et gen., Notes et Rev., p. xlv.

1909. Recherches sur l’hybridation. Proe. Seventh Internal, Zool.

Congress, pp. 45-56. (Prize essay submitted to the Congress,

August 1907.)

Detlefsen, J. A.

1914. Publ. No. 205, Carnegie Institution of Washington.

Doncaster, L.

1905. On the Inheritance of Coat-color in Rats. Proe. Camb. Phil.

Soc., 13, p. 215

Haecker, V.

1912. Ueber Kreuzungsversuche mit Himalaya und Black-and-Tan

aninchen. Mitt. d. Naturf. Gesell. zu. Halle, 2 Bd., 1912,

pp. 1-4

Little, C. C.

1914. ‘*Dominant’’ and ‘‘ Recessive’? Spotting in Mice. AMER. NAT.,

48, pp. 74-82.

MacCurdy, H., and W. E. Castle

1907. Selection and Cross-breeding in Relation to the Inheritance of

oat-pigments and Coat-patterns in Rats and Guinea-pigs.

Publ. No. 70, Carnegie Institution of Washington.

Punnett, R. C. ‘

1912. Inheritance of Coat-color in Rabbits. Journ. of Genetics, 2,

DATA ON A PECULIAR MENDELIAN RATIO IN

DROSOPHILA AMPELOPHILA

JOSEPH LIFF? .

A Mutant with pink eyes was found by Professor T. H.

Morgan in the summer of 1910, in one of his culture

bottles which contained wild, red-eyed Drosophila. He

described it as follows :?

‘‘The pink eye is more translucent than the red eye, but

of about the same general tone. It lacks the dark fleck

seen in the red and vermilion eye when the eye is exam-

ined with a lens. This black fleck changes its position as

the lens travels over the eye. The pink eye, P, is witha

little experience easily distinguished from the other colors,

especially in newly hatched flies. When the fly gets old

the eye turns to a brown color very characteristic of this

type of eye.’’

Pink was found to be recessive to red. The Mendelian

expectation in the F,, viz., three red to one pink, gave the

following (Morgan, 1911):

TABLE I

5 pi Fe Proportion of

1 Red | Pink Red: Pink

Red tk Ki ee | 3,063 | 169 18:1

Tek Oo xed n Sioa LAS 237 5:1

The expectation in either case was 3:1, but the num-

bers realized were’ 18:1 and 5:1.

In the spring of 1912 I repeated this experiment under

the direction of Professor Morgan in order to find

whether or not the above ratio would persist. The results

have already been published (Morgan, 1912), but a brief

summary is here reproduced for reference:

1 From the Zoological Laboratory of Columbia University.

2 Jour, Exp. Zoology, Vol. 11, No. 4, November, 1911.

98 Drar AMERICAN NATURALIST [Vou. XLIX

TABLE II

Red 9 X Pink g — in F2 Pink X pg Red o> in Fə

| | | |

Pee A ae eect a... 541 | 124 bast

B.....| 140 | 34 | 4.1:1 Bi 190 1 68 | Bed

C....] 375 | wW | 5.3: 1 PE 582 | 136 | -43:1

The above are records of mass cultures. When pairs

were used, the fluctuations in ratio were much more

marked. The records of 40 pairs gave an almost un-

broken series running from 1.8:1 up to 6:1. In seven

cases out of the 40 (18 per cent.) the pink flies exceeded

the expectation; 3 pairs (7.5 per cent.) gave a 3:1 ratio,

while in the remaining 30 pairs (75 per cent.) the pink

fell behind. The total number produced by these 40 pairs

was 4,056, of which 891 were pink—an average ratio of

3.98: 1, about the same as that shown in Table IT

In a second experiment the F, hybrids were back-

crossed to the pink. The expectation was 1:1. But the

records of 15 bottles of mass culture showed fluctuations

running from 1:1 up to 2.3:1. The total number counted

in these back crosses was 5,527, of which 2,391 were pink,

giving an average ratio of 2.31:1. The pink flies fell

behind again, and in about the same proportion as in the

normal cross.®

These remarkable fluctuations were observed at the

time the experiments were in progress, and it was sug-

gested that some environmental condition was responsible

for the results by either accelerating or retarding‘ the

development of the one or of the other variety. The fact

that all these experiments were performed at the same

time, and the bottles kept side by side in a room in which

a nearly constant temperature was maintained through-

out the winter, precludes the chance of a factor outside

the culture bottles operating here. Attention was there-

8 For a detailed account of these experiments see Morgan, 1912.

4It should be noted here that owing to the danger of overlapping of

generations, the bottles were discarded on the tenth day (counting from the

day the first F, emerged) regardless of the number of unhatched pupe

No. 578] DROSOPHILA AMPELOPHILA 99

fore directed to the condition of the food inside the bottles,

An examination seemed to indicate that those in which the

food was dry yielded the higher pink ratios. To test this,

two of the bottles in which conditions were normal, and

in which the F, had just begun to emerge, were made

‘‘wet’’ by the addition of a considerable amount of banana

juice. But they still showed a similar tendency to yield

a relatively higher proportion of pink.

To ascertain more definitely whether or not moisture

or dryness affected in any way the development of these

flies, a special experiment was arranged in which some

flies were bred in ‘‘dry’’ bottles, and some in ‘‘wet’’

bottles. In the first case, the banana was thoroughly

dried by means of filter paper which was discarded after

it had absorbed all the available moisture, and the banana

wrapped in fresh paper; in the second, banana juice was

added every second or third day, so that there was

throughout the experiment an abundant amount of wet

food in the bottles. The effect of this treatment is shown

in Tables III and IV:

. TABLE III

RECORD oF F, or A Cross RED BY PINK IN WHICH THE FLIES DEVELOPED IN

BOTTLES IN WHICH THE Foop was ‘‘Dry’’

Pink 9 x Red # Red 9 X Pink 7

Er: | Í j

Red Pink | P $ Red Piok | P ti

Bottle roportion Bottle | ote pee on

y ayle | Red: Pink | a | ole | Red : Pink

A....| o] 86| 25|18| 42:1 |a....| 91/109] 28| 32] 33:1

Boiss 73| 78| 20 4 s:r fig 76) 05] | 35) 26:1

Cau 182|164| 39 | 44| 43:1 |e..... 42| 14 | 15 | 3.0:1

D -Iola ptei S- he ‘| yet 117| 55 |46 | 2.7:1

TABLE IV

RECORD oF F, oP a Cross RED BY PINK IN WHICH THE FLIES DEVELOPED IN

BOTTLES IN WHICH THE Foop Was ‘‘WET’’ FROM THE BEGINNING

Pink 9 x Red # Red 9 X Pink ð

Red Pink Red | Pink |

Bottle |-——— ee Lae | eee pe hy

e|e|ele ; gia el?

A.. -dorioa w) 28:1 |a....|82|89|17/17| 50:1

B.. J2 964-46) aed Bold [b -Jiel 8 | 8 6| 20:1

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[Vou. XLIX

THE AMERICAN NATURALIST

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No. 578] DROSOPHILA AMPELOPHILA 101

It is evident that neither dryness nor moisture has any

effect in rendering more favorable the conditions needed

for the emergence of either the red or the pink variety.

The results show that under unfavorable conditions, large

numbers of larve and pupe fail to develop, since the total

yield of each and every bottle is far below the normal

output; and those which do emerge are but chance sur-

vivals.

It was suggested that the reason the pink flies fell be-

hind the expected ratio, was the fact that the mutant

was weaker than the wild stock and therefore less likely

to come through the. larval and pupal stages. If this

were the case, they should always fall behind. In many

cases, however, they actually exceeded the expectation.

Furthermore, they always seemed to be just as vigorous,

and to live as long as the wild fly.

The hypothesis which was formed at this stage, and

which determined to a large extent the experiments which

followed was, that another factor not related to eye-color

was at work. Such a factor, if one is assumed to be pres-

ent, by its independent action might be responsible for

the disturbance in ratio. It might, moreover, be present

in the wild stock which originally gave rise to the pink,

since the wild fly is similarly, though less frequently,

affected. It is with the search for such factors that the

subsequent experiments will chiefly deal.

Before presenting the data, it will be well to point out

some of the possible sources of error which were to a

great extent eliminated.

I. The method usually employed in these experiments

is as follows: The flies, which are to be cross-bred, are

taken out of the culture bottles as soon as they hatch and

before they have time to mate. They are then put into

a clean, sterilized bottle in mass cultures of about five or

more pairs. There they remain till their offspring (F,)

are ready to emerge: 9-10 days in summer and 11-12 or

13 days in winter when the temperature is low. The F,

flies are placed in fresh bottles for a similar length of

102 THE AMERICAN NATURALIST [Vou. XLIX

time, and then removed. During the succeeding ten days

the F, are counted each day as they hatch. The bottle is

then discarded for fear of overlapping of generations;

for, the F, might mate and deposit eggs before removal.

It has, however, been observed that each time a bottle

is discarded a considerable number of pupe and even

larve remain behind. This being the case, it is possible

that the ratio we get does not always represent what

actually happens. In order to count the total output, it

was decided to transfer the flies to a second bottle on the

fifth day. All eggs deposited, during the five days that

the parent remained there, would thus have at least fifteen

days to develop. ‘It was hoped that, in this way, a more

representative ratio would be obtained.

II. It was shown (Tables III and IV) that large num-

bers of larvee fail to develop when a bottle becomes too

‘“dry’’ or too ‘‘wet.’’? Considerable care was taken to

avoid either of these conditions. If a bottle showed a

tendency to dry up, fresh food was immediately added;

when it was too wet, the moisture was absorbed by filter

paper.

III. The yield of a mass-culture bottle is always rela-

tively small as compared with that of the same number of

flies mated in pairs. This would indicate probably greater

mortality due to overcrowding. For this reason only

pairs were used in the later experiments.

In the first of these experiments pure stocks, both pink

and red, were used; for it was believed that if differences

existed other than the red-pink distribution, between the

two varieties, they would be more emphasized if hybridi-

zation had not been effected. The chief purpose, how-

ever, was to become familiar with the modes of behavior

of the races. The experiment follows:

A number of flies, both pink and red, were isolated

within one to six hours after hatching and the sexes kept

apart for 3-4 days, after which time they were mated,

red to red, pink to pink. Immediately after mating, which

took place within five minutes to two hours, the males

No. 578] DROSOPHILA AMPELOPHILA 103

were removed. One red and one pink of these females

were put into each of seven bottles. In this way the same

environmental conditions were secured for the eggs of

both. Five days later they were allowed to mate again

(not by the same males) and placed in a second set of

bottles. The same two females that were together in the

first set were also together in the second. There they

remained five more days. Counts of the flies that hatched

were made from day to day, and the bottles were emptied

as long as they continued to yield. The results are given

in Table V.

The records of these flies show several interesting and

suggestive facts. It will be noted, in the first place, that

the length of larval life varies through wide limits. Eacli

bottle contained eggs which were deposited during a

period of no more than five days. The hatching periods,

however, extended through eleven days in the first set of

bottles (April 25-May 6) and twelve days in the second

set (April 30-May 12). The flies which emerged first

consumed but ten days for development; those which

emerged last took at least sixteen days. This phenom-

enon was more marked where the number produced was

larger, suggesting that crowding may retard the devel-

opment of some individuals.

Of equal interest is the fact that the pink flies invariably

began to hatch from 24 to 48 hours later than the red. This

was true in the second set of bottles as well as in the first,

which proves that it was not due to late maturity of the

parents, for, at the time of transfer, they were in the

midst of their productive period.

Another point of interest is to be found in the fact that

the pink stock was, on the whole, less fertile than the red.

In the two bottles n and ‘g’ where the productivity of the

two was about equal the red, like the pink, were also low-

producers. This is significant, and will be referred to

later.

In order to test the above-mentioned facts, the follow-

ing periment: was performed. F, hybrids were mated

104 THE AMERICAN NATURALIST [Vou. XLIX

in pairs, and transferred during a period of twenty days

(May 16—June 4) 13 times, remaining in each bottle from

one to two days. Care was taken to count every fly of the

F, that hatched. The result follows:

ABLE VI

RECORD OF F, FLIES WHICH HATCHED FROM EGGS DEPOSITED DURING A

PERIOD OF 20 Days; DURING WHICH TIME THE PARENTS WERE

TRANSFERRED THIRTEEN TIMES

Pink 9 X Red g — in F2 Red ọ X Pink ð > in F?

ree Red Pink Proportion ae Red Pink *| 5. ortion

9 S 9 g Red; Pin 9 E g 3 Red : Pin

A. 235 | 209 95 2.3 :1 a 134 | 118 | 42 | 37 3.231

Bosch 220 | 213 | 84 | 75 WL A | b 105 | 108 | 67 | 64 16:1

Cas 162 | 168 | 65 | 58 rA aes | Cee 189 | 153 | 52 | 53 3.2:1

D....|202|119| 14 | 19 O72 5 ds 58| 11 8 6.5 :1

Here we have a group in which the pink ran sometimes

relatively ahead of the red. But the other extreme is also:

represented in pairs D and d. The numbers obtained are

in each case large enough to be significant.

This experiment was repeated on a larger scale in the

fall of 1912. Ten pairs were used for. each of these

crosses and they were continually transferred as long

as they lived. The records follow:

TABLE VII

F, RECORD FROM RED-EYED FLIES CROSSED TO PINK-EYED FLIES MATED IN

PAIRS. SHOWING THE TOTAL OUTPUT OF EACH F, PAIR

DURING ITS LIFETIME

PINK 9 X RED f > IN F,

DSe a reier e PoR Total | Total mye Lh tag Proportion

1 u

A..| 45 27 |604578| 89| 81| 1,282 | 170 1,452 7.5:1

Bist 8# 15 169145) 30| 41| 314| 71 385 44:1

Cin ME 22 |320/305/116| 94| 625 | 210 | - 835 3.0 :1

Di Of 32 |658 681/203 221| 1,339 | 424 1,763 3.2:1

E.. 16 {218 218) 79 436 | 152 2.9 :1

ri p 28 |476435/153|144| 911 | 297 1,208 3.0 :1

a. m 17 [259248 83) 89] 507 | 172 679 |29+:1

E T 22 392,396 152/125] 788| 277 f 28+: 1

I G 32 [864805 258'281| 1,669 | 539 2,208 3.1:1

Juj 8 19 |357 358130124) 715 | 254 969 2.831

5 Lived only eight days. i i

6 The length of time a fly liveđ should not be taken as a criterion for

measuring its vigor. In most cases death is accidental.

No. 578] DROSOPHILA AMPELOPHILA 105

TABLE VIII

F, RECORD FROM RED-EYED FLIES CROSSED TO PINK-EYED FLIES MATED IN

PAIRS. SHOWING THE TOTAL OUTPUT oF EACH F, PAR

DURING ITS LIFETIME

RED 9 X PINK fd > IN F,

No.of | Red | |

Py A FHE | Total | Total Total No. Proportion

E rR Days Each Mee DR e| Be | eja] Hed | Pink | Produced (Red; Pink

ps | 28 20 30 2041 p 660 | 236 896 | 28%)

b. Si 13 11 1631 70, 58| 49| 333| 107 440 S45)

c. 7 5 74 90; 22| 28) 164 50 214 | 3a: i

a... 14 12 213/195) 58} 57| 408) 115 523 3.5+:1

é: 22 15 101 106) 33| 26; 207 59 266 g0: i

ie 21 16 215266 95| 78) 481| 173 654 2.8: 1

g. 37 24 erami 13,139 646 | 252 898 260:1

X 45 2 (433 444/179 169| $877 | 348 1,225 | 2.2+:1

i. 43 26 1546 533187 185) 1,079 | 372 1,451 2.0.21

L > 30 21 298 306 90| 83, 604 173 777 | Bs Fs ae |

A comparison of Tables VI, VII and VIII suggests the

possible presence of high and low pink-producing

‘*strains’’ in these stocks. To test this, some of the off-

spring of pair A (Table VII) in which the ratio was 7.5

of red to 1 of pink, were inbred for the F, in order to see

if the same ratio would persist. As there were among the

red both homozygous and heterozygous forms, they were

each mated to their pink sisters or brothers. This com-

bination would give with the former all red (since red is

. dominant) and with the latter a ratio of 1:1.

Pair F (Table VII) in which the ratio was ideal, 3:1,

was chosen for the control, and treated in like manner.

In this as in the preceding experiment the flies were

mated in pairs and transferred to fresh bottles every

second or third day. A peculiar thing happened. Out of

25 pairs taken from ‘‘A’”’ only two gave offspring; the

remaining 23 pairs were apparently sterile. It could not

have been due to bad banana or any other unfavorable

condition, for the flies had already been transferred five

times and no pupæ were found in any of the other bottles.

Furthermore, the 16 pairs of the control which ran paral-

lel to them, and were fed with the same food, did well.

106 THE AMERICAN NATURALIST [Vow XLIX

To find out whether these flies were actually sterile,

each of the 14 remaining pairs—9 having meanwhile

died—were separated and every individual mated to wild

red-eyed stock. The sterility of the pink flies, both male

and female, was found to be absolute, while all red of

both sexes were fertile.

As an additional test, some of the offspring of the last

cross were inbred en masse in order to extract the pink

flies which they would produce, since some of them were

heterozygous for eye color.

A small number of pink flies were obtained and mated

to their red brother and sisters: each pink female was

put in a bottle with 3 or 4 red males, and each pink male

with 3 or 4 red females. Out of 19 individuals thus tested,

only three were found to be fertile; the remaining 16 were

sterile.

These facts seem to indicate that some factor or group

of factors which make for sterility were present in the

‘*pink’’-containing gamete. The results are the more

significant since the hybrid fly, in which this condition

prevailed, produced a very low pink ratio. Of the control

in which 10 pairs were found to be heterozygous for eye-

color with an expectation of 1:1, the following results

were obtained:

TABLE IX

RECORD OF THE OFFSPRING OF F, FLIES OF A Cross oF PINK 9 By RED ĝ IN

WHICH A Ratio Was 3:1, as EXPECTED. (See pair F of Table VIII)

Red Heterozygous 2 by (Brother) Pink g

Red Pink Total No. i

Pair [Faek Liv Rod | Pink | Produced | Ror Pine

9 g 9 a ch

1 50 352 348 236 244 700 480 1,180 Leet

2 27 150 130 170 161 280 231 511 E21

3 18 51 85 59 50 136 109 245 12+:1

4 29 251 245 240 258 496 498 994 10:3

5 10 147 132 133 112 279 245 524 gS Fa |

The reciprocal cross gave the following:

No. 578] DROSOPHILA AMPELOPHILA 107

Pink Heterozygous Q by (Brother) Red ¢

| Red Pink |

._ |No. of Days! : Total | Total Pro —

Pair g | Produce

Each Lived Pe o 9 3 ed Pink by Eac Re

I 20 82 8 69 9 171 128 299 13+:1

| 123 124 94 107 247 201 448 L2: i

III 32 | 223 240 213 247 463 460 920 sR i aah S

IV 29 | 215 176 184 163 391 347 738 | Fs Gee |

y 40 216 178 101 136 394 237 631 | i he aoe |

It will be seen that all the red flies of the last cross were

heterozygous, and should give, on further inbreeding, a

ratio of 3:1. Four pairs out of five (one being sterile),

taken from Pair III of Table IX, gave the following:

TABLE X

RED 9 X Rep ¢ or Pair III, TABLE IX

No. of Red Pink Total No,

Pair Days Each ——— Total | Total | produced | Pro rtion

Dea g E 9 gi | Rel i, Pink | FIMA | : Pink

a 40 312 | 348 43 45 | 660 88 748 Cf BE

b 23 282 | 316 80 103 | 598 183 781 8.321

c 40 194 | 214 60 70 | 408 130 538 | 3.1:1

d 14 175 | 163 47 59 | 338 | 106 444 | 32:1

Pair ‘‘a’’ above gave the same result as pair “A”

(Table VII)—the ratio in each case being 7.5: 1. The off-

spring of the latter were found to contain a high percent-

age of sterile pink flies, owing to which the attempt then

made to test that ratio failed. It was therefore decided

to repeat the same experiment with the offspring of this

‘a’ pair. As in the former case, the heterozygous red

flies were picked out by crossing them to their pink

brothers and sisters. The expectation was again 1:1.

The records follow.

TABLE XI

REcorpD oF E1eut Pas, HETEROZYGOUS RED X TO ngs TAKEN FROM THE

OFFSPRING OF Pair ‘‘a,’’ TABLE

Pink 9 x Heterozygous Red $

shag — Pink Total | Total San No. | Proportion

Days Each roduced Poe

e iivet | ol @ | 6 Lo | Bet| Fmt |, by Meck | Bod t Fisk

r 27 179 176 79 88 | 355 | 167 522 21+:1

A. 12 155 153 83 66 | 308 | 149 457 204+ :1

g... 28 163 | 205 | 126 | 159 | 368 | 285 653 1.3 ii

Di s 243 | 222 | 206 | 219 | 465 | 425 | 890 | r1:1

108 THE AMERICAN NATURALIST [Vou. XLIX

The reciprocal cross gave:

Red Heterozygous 2 X Pink g

| i |

No, of Red Pink | Total No .|

n Total | Total | Proportion

eine g FOO eae ` FEF a | Red | Pink | b tucht | Red: Pink

a 28 282 236 210 260 518 470 988 | be Nees |

b 28 296 290 5 5 586 10 596 | 59.0: 1

e 12 144 158 136 152 302 288 590 1.0+:ł

d 25 Ta 113 63 98 185 161 346 }11i+:1

The pair with which we started (F, Table VII) gave

the ideal 3:1 ratio; but in each of the three generations

which were bred from its offspring (Tables IX, X, XI)

there appeared again the same fluctuations which were

observed in the preceding experiments, and with even

more striking emphasis. Among the offspring of the

same pair are found some that give a 3:1 ratio and some

that give a 7.5:1; in a second pair we have some giving

1:1, and one giving 59:1. The latter especially suggests:

the presence of a factor that actually inhibits the devel-

opment of the pink flies, and, moreover, that it is being

segregated in a mixed stock.

If the presence of such factor is assumed, we should be

able by inbreeding to select stocks in which it is present

and in which it is absent. For this reason the experi-

ment recorded above (Table V) was here repeated with

some modifications. It will be rémembered that in the

former, a fertilized red female and a fertilized pink male

were placed in each bottle and their offspring, the F,,

counted. In the following experiment, in order to secure

segregation, the F, were counted. Four virgin pairs, two

red and two pink, were taken out of the culture bottles and

mated separately. . Of the F, of each of the four, six pairs

were taken out, 24 pairs in all, and bred for the F,

Unlike the first experiment, the males in this case were

allowed to remain with the females throughout the ex-

periment. This insured sufficient sperms for the eggs.

Every second day the food was removed, together with the

No. 578] DROSOPHILA AMPELOPHILA 109

eggs deposited upon it, and fresh banana supplied. Each

two batches of eggs—one deposited by a red female, one

by a pink female—were placed together in one bottle so

that they might develop side by side and under the same

environmental conditions. The result of this experiment

is shown in Table XII.

TABLE XII

F, oF Two PINK Pairs A, B, AND Two RED PAIRS a, b, SHOWING SEGREGA-

TION OF PRODUCTIVITY. Eces or Al-al, BI-bI, ETC., WERE

DEVELOPED IN THE SAME BOTTLE

Pink Red

No, of No. of |

Days Total | Ave. F; Days | | pe | E

gong ym 7 s E Das er ieee’ ks duced | Day

AI | 44 |450 a0 896 | 20.40 aI | 20 233219 452 | 22.60

~ |All 169/224; 393 | 16.36 | 5 H o o S MO

„|I| 28 | 61) 67| 128 | 457| |a] 25 |63| 64) 127 sao

S| AIV| 30 |221|233 15.13 a aIV | 31 (272232) 504 | 1

MAV | 36 /331\345| 676 | 18.77 aV | 30 (179/171 350 “1166

AVI} 21 | 37) 33) 70 | 3.33 aVI | 22 152/138 390 | 17.73

BI | 29 {199/217 416 | 14.34 bI | 44 122104 226 | 5.10

m |B | 24 93| 1 7.75 |_,| bI | 28 |103| 77) 180

Bl} 35 | 31 a7 78 | 28g b TII | 302256 558 | 12.70

2@|BIV| 30 |15|13| 28 | 093| &|bIV | 35 | 22/34 56

MTBN | 283 |11 10 21 | 0.75 bV | 302298 595 1920

BVI! 18 8 1.00 BVI | 44 154139 293

—— |

Segregation with respect to productivity is here evi-

dent. Whether the low fertility? seen in so large a pro-

portion of these flies was due to an actually low egg-

production, or whether it was due to something which

prohibited development or to some defect in the germ

cell owing to which fertilization could not be effected, is

not known. That one of the latter possibilities is likely

to be realized here can be inferred from the work of Dr.

R. R. Hyde in this laboratory. He counted the eggs of

hundreds of individuals, and compared them with the

number of flies which emerged from them. According to

T The term ‘‘fertility’’ is used here, as defined by Hyde, to indicate the

number of eggs that complete development and give rise to ma

(See Hyde, Jour. Exp. Zcol., August, 1914, p. 185.)

110 THE AMERICAN NATURALIST [Vou. XLIX

his observations, only about 75 per cent. of the eggs of the

wild fly ever reach maturity, and in some of the muta-

tions no more than 25 per cent. of the eggs develop.

Another point of interest brought out in the last experi-

ment is the fact that the wild, red-eyed fly behaves in

exactly the same manner as the mutant pink fly. This

may be the reason for the observed shifting of the ratio

sometimes in favor of the one variety, sometimes in favor

of the other. It shows furthermore that it was not the

pink as such that caused the disturbance. The red also

might be similarly disturbed and perhaps by the same

agent or by another agent that affected the productivity

in the same way.

If the abnormally low number produced by some of the

pairs of Table XII be due to the inability of a large num-

ber of their eggs to develop, and if we assume this char-

acter to be transmissible, it must reappear in the F, of a

cross in which one of the parents possessed this factor,

i. e., a large number of individuals, one quarter of the

output, should fail to develop. This would be in accord-

ance with Mendelian principles. A number of crosses

were therefore made in various combinations with the

individuals taken from Table XII. The results follow:

TABLE XIII

F, or 16 PAIRS oF A Cross RED BY PINK IN WHICH THE PARENTS CAME

FROM AT, aI, TABLE XII, THE AVERAGE DAILY PRODUCTIVITY OF

WHIcH WAS 22 AND 20, RESPECTIVELY

A. Pink Q (Productivity 20 Per Day) X Red g (Prod. 22 Per Day)

No. of Days Red Pink Total | Total | Total No. | proportion

ch à

Pair = ‘ P ý r Red | Pink p Red : Pink

1 17 301 110 04 595 214 2.00e2 1

2 32 4 457 60 | 147 941 1,248 | 301:1

3 32 570 181 189 | 1,074 370 1,444 2.90: 1

4 32 559 548 20. „l 405 1,512 PATA a i

5 8 125 126 251 5 326 8,89: 1

6 18 261 243 98 89 504 187 691 27071

7 21 391 | 449 | 155 | 142 | 840| 297| 1,137 | 2.86:1

8 32 673 700 203 | 236 | 1,373 439 1,812 3.10: 1

Total number produced by 8 pairs....... 6,685 | 2,294 | 8,979

Average proportion, 2.91 : 1

No. 578] DROSOPHILA AMPELOPHILA 111

B. Red Q (Productivity 22 Per Day) X Pink g (Prod. 20 Per Day)

Red | Pink

| | |

i No.of. odes vines 2 Total | Total | Total No. | proportion

I 30 415 | 395 | 135 | 127 | 810] 252| 1,062 | 3.21:1

II 14 132 121 41 73 253 | 114 207 4 2.22: 1

III 24 317 337 97 94 654 191 | 845 | 3.42:1

Vv 30 484 | 378 | 119 20 | 862) 239) 1,101 | 3.60:1

24 392 418 96 140 810 | 2 1,046 | 3.42:1

y 30 656 592 198 20 248 | | 646 | 3.14:1

VII 30 566 647 182 09 | 1,213 391 | 1,504 | 2.10: I

VIII 24 438 451 132 153 889 1286] 1,174 | 3.10:1_

Total produced by 8 pairs................. | 6,739 | 2,106 | 8,845 |

Average proportion, 3.24 : 1

If the proportion of red to pink, realized in the F,,

depends upon the relative fertility of the two parents

which form the cross, we should get in this case, where

the parents were supposedly equally fertile, the ideal 3:1

ratio. The records, however, show considerable fluctua-

tions. Nevertheless, these results are perfectly in accord

with our hypothesis. Looking back to Table XII, which

furnished the parents of this cross, the explanation is

obvious. The averages per day for AI—AVI were 20, 16,

4, 15, 18 and 3, respectively. Similarly, al-aVI gave 22,

0.7, 5, 10, 16, 11 and 17, respectively. It is therefore

reasonable to assume that among the offspring of AI

(productivity 20) and al (productivity 22) individuals

should be found which would repeat the series. Fluctua-

tion is, therefore, to be expected. The average of many

such pairs, however, should be 3:1. The proportion ob-

tained was 2.91:1 in one case; 3.24:1 in the other, or a

general average of 3.08: 1.

It should also be noted here that in this as well as in

the subsequent experiments, wherever eight pairs are

recorded, they are not the offspring of one, but of two

distinct crossings of one pair each which were made at

the same time; that pairs 1-4, 5-8; I-IV, V-VIII, respec-

tively, were brothers and sisters. More than one line is

thus represented in each case. With these facts in mind,

we may pass on to the remaining experiments,

112 THE AMERICAN NATURALIST [Vow XLIX

TABLE XIV

F, of 12 PAIRS OF a Cross RED BY PINK IN WHICH THE PARENTS WERE AI

AND bII (TABLE XII) THE AVERAGE DAILY PRODUCTIVITY OF

WHIcH WAS 20 AND 6, RESPECTIVELY

A, Pink 2 (Productwity 20 Per Day) X Red g (Productivity 6)

No. of Da Red Pink Total No,

Pair | Each Was. Total | Total | Produeed | Proportion

ie ee ci eae

1 32 355 331 117 95 686 212 898 Sze f1

2 28 340 373 126 132 713 258 971 2.761

3 19 330 288 120 124 618 244 862 2.52: 1

4 32 544 562 188 188 | 1,106 376 1,482 2.94 :1

5 23 574 578 203 214° | 1,152 417 1,569 Trd o e D

6 14 196 194 66 59 390 125 515 3.12: 1

7 32 648 603 222 246 | 1,251 468 1,719 2.6754

8 32 429 374 141 144 803 285 1,088 ASL Sy

Total number produced by 8 pairs.......-. | 6,719 | 2,385 | 9,104

Average proportion, 2.84 : 1

B. Red 2 (Productivity 6 Per Day) X Pink g (Productivity 20)

Pair | Each W | : Produced N

sir yg we d as 9 3 9 | Red | Pink fey wie Red ; Pink

I 28 488 482 176 IF 970 | 353 1,323 2.74: 1

II 6 83 78 21 30 161 51 212 3.15 <1

HE 28 463 465 164 153, 928 | 317 1,245 2.93: 1

IV 21 375 383 114 116 758 | 230 988 8.20 ri

Total number produced by 4 years....... 2,817 | 951 3,768

Average proportion, 2.96 : 1

In most of these pairs the pink slightly exceeded the

3:1 expectation. In the few in which they fell behind,

the red (if we assume fertility to be the cause) might have

been of a higher fertility than the pink, as has been

explained. As a group, however, they give a proportion

somewhat below 3:1. _

In the next cross, the red fly was the more fertile. The

results are given in the following table:

No. 578] DROSOPHILA AMPELOPHILA 113

TABLE XV

F, of A Cross RED BY PINK IN WHICH THE RARENTS WERE BIV AND al

(TABLE XII) THE AVERAGE DAILY PRODUCTIVITY OF WHICH

AND 22, RESPECTIVELY

A. Pink 9 (Productivity 1 Per Day) X Red g (Productivity 22)

of Red | Pink Total | Total

Pair | D. 'E h ; a ota zo a Si Proportion

Days OB vod 9 | P | 9 p Red | Pink ts 0 iue È : Pink

1 22 398 | 405 | 120 | 105 225 | 1,028 | 3.52 :1

2 28 512 | 477 | 107 | 125 | 989| 282] 1,221 | 4.26:1

3 22 420 | 389 | 104 | 135 | 809| 239| 1,048 | 3.34:1

4 18 340 | 06 192 3.33 :1

5 19 420 | 428 | 129 | 134 | 852] 262] 1,115 | 3.24:1

6 19 372 | 396 | 100 04 | 768 72 | 3.76:1

7 17 198 | 220 | 418| 141| 559 | 3.00:1

8 174 | 212 62 62 | 386 510 | 3.10:1

Total number produced by 8 pairs......... 5,665 | 1,620 | 7,285

Average proportion, 3.50 : 1

B. Red Q (Productivity 22 Per Day) X Pink 3 (Productivity 1)

No. of Days Red Pink | Total | Total | Total No. | proportion

Pair eo Was Produced

red 9 a g e Red Pink by Eact : Pink

I 31 264 | 262 | 101 | 87 | 526| 188| 714 | 2.80:1

II 27 353 | 350 703| 165 4.26: 1

Ill 31 430 | 403 112 1,042 1

IV 31 420 | 111 | 128 9| 1,086 | 3.54:1

vV 28 471 | 122 | 147 | 957| 269 3.60 : 1

VI 573 | 568 39 | 154 | 1,1 1,434 | 3.90:1

VII 28 116 | 127 |1,010| 243| 1,253 | 4.15:1

VII 24 | 502 | 501 | 134`| 140 |1,003| 274| 1,277

Total produced by 8 paits.........-,., 20%- 7,020 | 1,880 8,900

Average proportion, 3.73 : 1

Of the 16 pairs of this cross only one gave less than 3: 1.

the remaining 15, the proportion was, in each case,

considerably higher than 3:1. It will be noted that of

all 16 pairs that one was the least fertile. This would

indicate, on the hypothesis suggested, that the gamete

containing the ‘‘red’’ factor did not have relatively as

high a potential of tortility as did the parent which pro-

duced it.

A comparison of Tables XIV and XV shows that we

have two distinct groups: one in which the extracted pink

exceed the expectation, and one in which they fall behind

114 THE AMERICAN NATURALIST [VoL. XLIX

the expectation. Yet the method employed in each case

was the same; the history of each is the same. The only

difference is to be found in the fact that in the one case

the pink came from a more fertile parent; in the other,

the red.

The offspring of pairs ‘‘7’’ (Table XIV) and ‘‘2’’

(Table XV) in which the ratios were 2.67: 1 and 4.26: 1,

respectively, were inbred for the F,. Fifteen pairs were

taken from each, but as there were among the red both

homozygous and heterozygous flies, only eight gave pink

in each case. The results follow:

TABLE XVI

RECORD OF 8 PAIRS HETEROZYGOUS RED-EYED F, OF PAIR ‘‘7’’? (TABLE XIV)

IN WHICH THE Ratio Was 2.67: 1

Red Pink Total No.

No. of Total | Total | produced b Proportion

Pair ae a 2 z | Red | Pink Each | Red: Pink

1 14 270 279 80 78 158 707 3.47 :1

2 14 159 167 58 42 326 1 426 3.26: 1

3 14 7 2 1 12 99g: 1

4 14 135 143 46 49 278 95 373 2.93 : 1

5 14 1 157 49 50 340 99 439 3.23: 1

6 14 172 54 45 42 326 87 413 3.74 :1

7 1 142 137 43 49 279 92 371 3.00: 1

8 14 12 16 103 28 131 2:67 : 1

TABLE XVII

RECORD OF 8 PAIRS HETEROZYGOUS RED-EYED F, OF PAIR ‘‘2’’ (TABLE XV)

IN WHICH THE RATIO OF RED TO PINK Was 4.26: 1

Red Pink Total No.

pais | Be Teta | Tote | rete | apron

Q g Q a

1 14 295 308 100 603 197 800 3.06 :1

2 14 392 326 97 105 718 2 920 55:1

3 14 281 95 9 181 750 3.14: 1

4 14 110 32 214 279 3.31: 1

5 14 167 170 70 59 337 129 4 1

6 14 314 277 82 86 591 168 759 3.52: 1

ri 14 160 32 41 329 7 402 50

8 14 133 146 49 Al 90 369 3.10: 1

These results are inital, in that they show that the

original ratios, which their parents gave, were lost.

No. 578] DROSOPHILA AMPELOPHILA 115

The fact that it has been found possible by proper

manipulation to get a group in which the ratio fluctuated

in one direction only, even if it was not as marked as was

hoped it would be, indicates that the disturbance is due to

an internal, and not to an external, cause. This was

further emphasized by the distinct tendency for segrega-

tion, as was to be expected if there were some hetero-

zygous individuals. It was also suggested in another

way. No matter how short-lived or how long-lived a pair

was; whether it was transferred once, twice, or even

twenty times, the ratio of red to pink did not vary

throughout its life when the yields of the several bottles

were compared with one another.

TABLE XVIII TABLE XIX

F, or Four Pars (A, B, C AND F, or Pams A, B, C anD D or

D) Rep? X PINK ĝ IN WHICH TABLE XVIII

THE MALES WERE CROSSED Expectation 3: 1

EACH TO SEVERAL oF His

OWN DAUGHTERS

Expectation 1:1

Pi F,of No.of | Total | Total | Proportio

> $ 7 Tea Pak ko oon Phir Pair Red Pink Red: Pink

1 45 | 2.15:1 8.) G 3ni

2 105 71 | 146:1 A 2 158 | 55 | 3.00:1

ax 3 231 161 | 1.43:1 96 21 | 4.60:1

4 171 | 123 40:1

5 Sit ti 1.10 :1

1 110 80 | 1.38:1 1 140 | 43 | 3.27:1

2 263 | 251 | 1.00:1 B 2 215 | 72 | 3.00:1

BX 3 242 | 198 | 128:1 3 | 1% | 7 | 109:1

4 183 | 143 | 1.28:1

5 231 | i89 | 122:1

6 162 |: 102 | 1.62:1

1 %1 | 113 78:1 1 50 | 21 2.38: 1

2 257 | 116 | 2.22:1 c 2 125 | 43 | 290:1

“Cx 3 255 1. 1 3 122 | 49 | 2.49:1

4 206 | 153 | 1. 1 4 07 | 288:1

5 943 | 107: | 1.28:1

6 125 1.27:1

5 —

179 1.30 :1 26 | 6 | 433:1

DX 2 | 997: | 191 |-220:1 D 2 112 | 34 p ago:

107 44: 3 194 | 74 | 2.62:1

116 THE AMERICAN NATURALIST [Vou. XLIX

The proportion of red to pink was found to bear a

direct relation to the relative ‘‘fertility’’ of the parents

which produced the hybrid. This suggests a causal rela-

tion between the two.

In dealing with ‘‘fertility’’ the difficulty that one en-

counters is, that the offspring of any pair may, with

respect to this character, differ from either parent, and

also differ amongst themselves, forming a graded series

running from the most to the least fertile. An individual

taken from such a population is an indefinite quantity and

will often defeat the purpose of the experiment. In order

to simplify this as far as possible, the following experi-

ment was planned:

Four red-eyed, virgin females were each mated to a

pink male. Each male was again crossed to several of his

own daughters. The records are given in Table XVIII.

As a control a number of F, pairs were bred in each case.

The records are given in Table XIX.

A graphic representation of all pairs recorded in

Tables VI-XIX, except for the several very unusual

ratios, is given in Figs. 1 and 2.

—

‘ l

UES |

3.0:1

Ee,

| 35:1

4.6:1

oc hind B

3 3

oi +

Fig.1

m Leil

Fig. 1 contains 99 pairs in each of which the expected

ratio was 3:1, with a total population of 82,607. They

are distributed as follows:

No. 578] DROSOPHILA AMPELOPHILA 117

No. of Ratios of

Pairs Red : Pink

: eee

Rn Se ee eee

pæd

Total..

1.0:1

Fig.2

Fig. 2 contains 37 pairs of back-crosses; expected ratio

1:1; total population 17,008. They are distributed as

follows: :

118 THE AMERICAN NATURALIST [Vou. XLIX

No. of Ratios of

Pairs Red : Pink®

LOSI

gave 1.1:

gave 1.2:

gave 1.3:

gave 1.4:

gave 1.5:

[e]

D H Om wM a OON O

($)

pi pa pn d ped pad, had pad d pd. l pat

Total. .37

To these should be added:

1 pair which gave 9.7: 1, Table V

1 pair which gave 6.5: 1, Table VI

1 pair which gave 7.5: 1, Table VII

1 pair which gave 7.5: 1, Table X

1 pair which gave 59.0: 1, Table XI

Except for the several detached pairs at the extreme

limits, Fig. 1 shows a normal curve. A disturbance of

0.5 in either direction (less than 10 per cent.) is quite

within the limits of experimental accuracy. The larger

disturbances, ratios of 6 or 7:1, and also the first results

reported by Morgan (711 and ’12) are yet to be explained.

These are too large to be attributed to experimental error.

The data presented in the foregoing pages show that

there has been a marked improvement in the ratio of pink

to red since 1911. In one ease only (1913) was the dis-

turbance greater than those of Morgan (59:1). The

remaining very marked disturbances were between 6 and

10:1. And these appeared so infrequently that in mass-

cultures their presence would hardly have been felt.

A corresponding improvement has also been observed

in the fertility of the pink-eyed race between 1912 and

1913. This is seen on comparing Tables V and XII. In

the first, the fertility of the pink was much lower than

that of the red; in the second (about one year later), it

was as high.

Hyde (’14) showed that in some races of Drosophila

8 None gave a ratio of less than one red to one pink.

No. 578] DROSOPHILA AMPELOPHILA 119

ampelophila, the number of eggs failing to reach matu-

rity is between 25 per cent. and 75 per cent. of the total

output; and concluded that this peculiarity probably be-

haves as a Mendelian recessive factor. More recently,

Morgan (’14) describes recessive lethal factors in Droso-

phila, which he defines, ‘‘as any factor that brings about

the death of the individual in which it occurs, provided

that its effect is not counteracted by the action of its

normal allelomorph.’’

In the light of this evidence, the following conclusions

suggest themselves: ie

1. The original pink-eye mutant was heterozygous for

some non-sex-linked factor which, in the homozygous state,

acts like Morgan’s lethal. This factor was, in the course

of time, to a large extent eliminated, as is to be expected

if the individuals homozygous for it are more likely to

die. The chance of such homozygous forms appearing

again, has thereby been much reduced. This is borne

out by, and also explains, the improvement in the pink

race.

2. A similar recessive, though not necessarily the same

factor, might also be present in some individuals of the

wild, red-eyed stock. Hyde’s work mentioned above

gives weight to this assumption—which is not at all an

unreasonable assumption in a species as unstable as this,

judging by the vast number of mutations reported. For

this reason, the red sometimes fall behind the expected

ratio. 7

3. The mode of action of these lethals shows that they

are linked to the ‘‘pink’’ factor or to its normal ‘‘red’’

allelomorph. This will be clear from the following

analysis:

Of the flies recorded in Fig. 2, one parent was RP (with

gametes R and P); the other was PP (with gametes P

and P). The zygotes resulting from these gametes almost

invariably give fewer PP’s than RP’s. In other words,

the homozygous forms run behind the heterozygous forms.

The relation between these two classes may also be sup-

posed to hold in the F, cross (Fig. 1). Here, however,

the reds (RR and RP) run relatively less often ahead of

120 THE AMERICAN NATURALIST [Vow. XLIX

PP. This must be due to a deficiency in the homozygous

RR flies. In other words, the results taken all together

(Figs. 1 and 2) show that the disturbance is brought

about by factors (in the third chromosome) which in the

homozygous state act as lethals or perhaps as semi-

lethals. Random introduction of one or two or no lethals

may be assumed, as follows:

(A) If the lethal is introduced by the ‘‘pink-bearing”’

tna the homozygous pink will be depressed in

the

on ‘Te introduced by the ‘‘red-bearing’’ chromosome,

the homozygous red will be depressed in the F,.

troduced at the same time, one by the red and one by the

pink, all classes will be equally depressed,’ and the re-

sults as far as concerns the F, ratio will be the same as if

there were no lethals present, i. e., the 3:1 ratio will be

realized.

(D) If two lethals that are different are introduced

at the same time, one by the red and one by the pink, both

the homozygous classes (RR and PP) will be depressed,

but not the RP. There would be somewhat fewer pinks

than expected in the F,.

I wish to acknowledge my indebtedness to Professor

T. H. Morgan, whose kind attention and suggestions both

throughout the foregoing experiments and in the prep-

aration of the present report, were invaluable. I also

wish to express my appreciation to Mr. H. J. Muller to

whom I owe some suggestions concerning the ph pb

tion of the results.

“LITERATURE CITED

Hyde, R. R. Fertility and Sterility in Drosophila ampelophila. Jour.

. Zool., Vol. 17, No. 2, August, 1914,

Morgan, T. H. An Attempt to Analyze the Constitution of the Chromo-

somes on the Basis of Sex-Limited Inheritance in Drosophila. Jour.

Exp. Zool., Vol. 11, No. 4. .

Two Sex-Linked Lethal Factors in Drosophila and their Influence on the

Sex-Ratio. Jour. Exp. Zool., Vol. 17, No. 1, July, 1914.

9 ‘í Crossing-over”’ is ignored as the character of the results is not changed

thereby.

SHORTER ARTICLES AND DISCUSSION

SELECTION, SUGAR-BEETS AND THRIPS

A DISCOVERY of great importance to students of genetics has

recently been made by one of the plant-breeders' of the U. S.

Department of Agriculture, viz., that beets are regularly cross-

pollinated and that an important agent in the process is a minute

inconspicuous insect, so small that it readily passes ‘‘through the

meshes of fine silk chiffon.’’

To understand fully the theoretical importance of this dis-

covery one need only recall the large attention given to the

sugar-beet in recent adverse criticisms of the selection-theory.

De Vries in his ‘‘Mutationstheorie,’’ p. 72, cites the case of the

sugar-beet as showing the most systematic, refined and elaborate

selection known for any cultivated plant, and yet as being with-

out any permanent effect in raising the sugar content of the beet.

For, although the average sugar content of the beet has by syste-

matic selection been practically doubled in the last 60 years,

De Vries holds the improved racial condition to be unstable and

thinks that the improved race would within a few generations

revert to its old level of sugar-content if the selection were dis-

continued. His reason for thinking so is the familiar fact that

the offspring of the best selected beets are on the average not

quite so good as their selected mother-beets, but show a tendency

to regress downward toward the old level of sugar content. It

should be pointed out, however, that in reality regression is not

toward the original average of 7 or 8 per cent. sugar-content, but

toward an average twice as high as this. For De Vries’s varia-

tion polygon (l. c., Fig. 22) for the sugar content of 40,000 beets

shows a nearly kyara probability curve about a mode at

15.5 per cent. It is to be supposed therefore that regression

would occur toward this condition from both the upper and the

lower halves of the frequency polygon, rather than toward the

old average condition of 7-8 per cent., which, according to the

data of DeVries, is now rarely if ever seen in the improved race.

To have doubled the average sugar-content of the beet is cer-

tainly something of an achievement for selection; the form of

1 Shaw, Harry B., ‘‘Thrips as Pollinators of Beet Flowers,’’ Bull. No.

104, U. S. Dept. Agr., July 10, 1914.

121

122 THE AMERICAN NATURALIST [Vou. XLIX

the variation polygon indicates that the change is permanent, so

far as ordinary racial characters have permanency.

But why, it may be asked, has selection not achieved more in

this case? Why should the descendants of, say, a 25 per cent. beet

not score better than this? There are probably several reasons

why. (1) Physiological reasons probably offer obstacles. A beet

can not be formed which is all sugar. There has to be present

in the beet a machinery for manufacturing the sugar. Perhaps

25 per cent. is an impossibly high average for a race of beets.

(2) Perhaps the exceptional 25-per-cent. beet owes its extra

sweetness in part to environmental causes which are not per-

manent. In that case the extra sweetness is ‘‘ somatic rather

than germinal,’’ as we should say in the case of an animal.

(3) Finally the discovery that beets are never self-fertilized,

but in every generation are cross fertilized, explains why im-

provement of the beet through selection is so slow and tedious a

process. What progress could the animal breeder expect to make

if he were able to select only the dams, but never the sires, for his

flocks? This is the condition which confronts the plant breeder

in attempting to improve the sugar beet. The animal breeder

is often chided with the small numbers which his experiments

yield as compared with the enormous numbers which an ex-

periment with plants may produce, but the animal breeder has

at least this satisfaction that when the animals are securely

penned there need be no uncertainty about pedigrees.

The careful observations of Shaw show that thrips, so common

in the blossoms of plants and yet so minute as easily to escape

notice and to penetrate within silk nets and under paper bags,

may be a cause of unsuspected cross-pollination and unaccount-

able ‘‘ mutation ’’ in the breeding of cereals and other plants.

W. E. CASTLE

BUSSEY INSTITUTION,

October 24, 1914

A NOTE ON MULTIPLE ALLELOMORPHS IN MICE

Proressor T. H. Morean has recently published in this jour-

nal the results of some of his experiments on color inheritance in

mice. In this paper he offers material which he considers ‘‘evi-

dence establishing”’ a series of multiple allelomorphs. His series

consist at present of four forms, ‘‘yellow, gray white-belly, gray

No. 578] SHORTER ARTICLES AND DISCUSSION 123

gray-belly and black.’’ The essential point of his conclusion is

that no more than two of these conditions can be transmitted by

any one animal.

The fact that Cuénot in his series of classic papers on color

inheritance in mice (1902-1911) recognizes these same four types

as forming a group of allelomorphs is not mentioned by Morgan,

whose paper, without knowledge of Cuénot’s work, might well be

taken to contain ‘‘the evidence establishing this series of allelo-

morphs’’ as he himself considers that it does. Since Morgan

appears to have overlooked Cuénot’s work with these forms, it

may be interesting to give a brief statement of Cuénot’s results.

As early as 1903 Cuénot recognized that albinos, potentially

yellows, when crossed with black gave besides yellow offspring

either black or agouti young, but not both. This is, of course,

evidence that yellow, agouti and black are all allelomorphic to

one another. In 1904 he gives formule (p. 46) showing that he

considers this to be the case. At the same time he gives the.

ratios produced by crossing an albino potentially a heterozygous

gray (agouti) with a yellow carrying black, but no agouti, and

albinism. For present purposes the albinism in the cross is

negligible. Cuénot recognized that the ratio expected from this

cross was 2 yellow, 1 black and d agouti (gray). He obtained

34 yellow, 20 black and 16 agouti; the calculated numbers being

38:19:19. Sturtevant (1912) in discussing the allelomorphism

or coupling of black, agouti and yellow in mice has also over-

looked Cuénot’s results, for in mentioning the cross of a hetero-

zygous agouti with a yellow carrying black, he states “‘appar-

ently Morgan is the only one who has reported such a cross. He

obtained 4 yellows, 5 agoutis and 1 black.’’

To return to Cuénot’s work; in 1907 he made a report on the

hereditary behavior of the white bellied agouti variety (gris à

ventre blanc) which he considers allelomorphic to yellow, agouti

and black. On page 10 in speaking of determinants he says:

“Il y en a le même nombre dans les races unicolores et dans la

race grise; ces races diffèrent, non pas par la quantité de leurs

déterminants mais par la qualité.’’ This is essentially the idea

underlying multiple allelomorphism. Later in the same paper

he says of G, the agouti determinant ‘‘. . . il présent un grand

nombre de mutations: G’, N et J.” (@' = white bellied gray;

N =black and J=yellow.) On page 13 he tabulates the vari-

eties, in order of their dominance, yellow, white-bellied agouti,

124 THE AMERICAN NATURALIST [Vou. XLIX

agouti and black. Morgan reached the same order of dominance

in 1911 and has récently (1914) recorded them, beginning with

black, as follows:

b= black,

BS&=eray gray-belly,

BY = gray white-belly,

BY = yellow.

In 1908 Morgan published certain facts concerning the inher-

itance of the white-bellied gray pattern. Cuénot at once (1908)

publicly called Morgan’s attention to the similarity of their

material and added facts which showed that he had already

investigated the inheritance of this same pattern in 1907.

Morgan later acknowledged its similarity.

In 1911 Cuénot states plainly (p. 47) : ‘‘Les souris jaunes sont

characterisées par un déterminant J, allélomorphe a G, G’ et N,

at qui les domine tous dans les croisements... il n’y à que les

` zygotes renfermant J dominant un autre déterminant allélo-

morphe (G, G’ ou N) qui peuvent évolouer.’’

Morgan’s 1914 paper adds several detailed matings and records

the testing of yellows of both sexes. However, in most respects,

his work corroborates the pioneer experiments of Cuénot and does

so in such detail that he falls into the same error as did Cuénot

in considering ‘‘black’’ as a necessary member of the allelo-

morphie series. This is obviously incorrect for the whole series

of allelomorphs exists equally well in forms utterly lacking the

ability to produce black pigment as some of Morgan’s experi-

ments showed. The true series of allelomorphs is yellow, white

bellied agouti, gray-bellied agouti and non agouti (not black).

BUSSEY INSTITUTION,

October 19, 1914

LITERATURE CITED

Cuénot, L.

1902. La loi de Mendel et 1’héredité de la pigmentation chez les souris.

Arch. Zool. Exp. et Gén. (3), Vol. 10, Notes et revue, p. xxvii

1903. 2me note. Arch. Zool, Rap. et Gén. (4), Vol. 1, Notes et revue,

p. xxxiii.

1904. 3me note. Ibid., Notes et revue (4), Vol. 2, pp. xlx-lvi.

(1905. 4me note. Ibid., Notes et revue (4), Vol. 3, pp. exxiii—cxxxii.

1907. 5me note. Ibid., Notes et revue (4), Vol. 5, p. 1.

1908. 6me note. Sur quelque anomalies apparentes de proportions

incised Ibid. (4), Vol. 6, Notes et revue, pp. vii—xv.

No. 578] SHORTER ARTICLES AND DISCUSSION 125

1911. 7me note. Les déterminants de la couleur chez les souris, étude

comparative. Ibid., Notes et revue (4), Vol. 8, pp. xl-Ivi.

Morgan, T. H.

1908. Some Experiments in Heredity in Mice. Sei, N. S., Vol. 27,

p. 493.

1911. The Influence of Heredity and of Environment in Determining

the Coat Color in Mice. Annals N. Y. Acad. of Sct., Vol. 21,

pp. 87-117.

1914. Multiple Allelomorphs in Mice. Am. Nat., Vol. 48, pp. 449—458.

Sturtevant, A. H

912. Is There Association Between the Yellow and Agouti Factors in

Mice? AM. Nat., Vol. 46, pp. 368-371,

ON THE TIME OF SEGREGATION OF GENETIC

FACTORS IN PLANTS

In @nothera lamarckiana, Geerts (3) has observed that two mi-

crospores of each tetrad abort. From the results of reciprocal

crosses, De Vries (9) concluded that there was a segregation of

genetic factors between the aborted and unaborted pollen-grains.

In my crosses of Stizolobium species (2), half of the pollen-grains

abort in a random manner in the anthers of the F, hybrids; and

I can only explain the results of the breeding work on the hypoth-

esis that there is a segregation between the four microspores of

each tetrad. Hence I conclude that the segregation does not take

place before the cell-divisions which form the pollen-mother-cells,

but takes place in the divisions which form the microspores. In

other words, segregation occurs here, not among the cells of the

diploid generation, but at the moment of formation of the indi-

viduals of the haploid generation.

In the ovules of Stizolobium crosses I have shown that there

is a random segregation of aborted and normal embryo-saes; and

this agrees with the observations of Geerts on the functional mega-

sporesof O.lamarckiana. If somatic segregation occurred, there

would be a segregation of whole ovaries or parts of ovaries with

ovules all aborted or all normal, causing a distribution which

would differ markedly from the binomial distribution demanded

by a random segregation according to the law of chance. I have

shown that with lots of ovules each, the distribution of the

aborted and normal ovules corresponds to the binomial (1 + 1)”.

Hence segregation can not have taken place before the formation

of the nucellus of the ovule.

In many species and varieties of Citrus, as Strasburger (7)

. 125

126 THE AMERICAN NATURALIST [Vou. XLIX

and Osawa (4) have proved (and as I can confirm), embryos

are formed from the tissue of the nucellus adjacent to the em-

bryo-sac. I have also shown (1), as Strasburger suspected, that

a similar mode of formation prevails in certain varieties of Man-

gifera indica. In F, hybrids between certain Citrus species (8),

these adventive embryos do not show segregation; and the ad-

ventive embryos of a mango variety give plants nearly constant

to that variety. Hence segregation had not taken place when

the cells surrounding the megaspore-mother-cell were formed.*

The same conclusion follows on the work of Ostenfeld (5) and

Rosenberg (6) with certain Hieracia.

JOHN BELLING

FLORIDA AGRICULTURAL EXPERIMENT STATION

REFERENCES

1. Belling, J. Report of Florida Agricultural Experiment Station for 1908.

Pp. ex—cexxv, Plates VII-X, 1909.

- Belling, J. The Mode of Inheritance of Semi-sterility in Certain Hybrid

P Eie Zeitschrift für induktive Abstammungs- und Vererbungslehre,

Bd. XII, S. 303-342, 1914.

3. Beiträge zur Kenntnis der Cytologie und der partiellen

Sterilität von Gnothera Lamarckiana. Récueil des Trav. Bot. Néerl.,

Vol. 5, pp. 93 ff., 1909.

4. Osawa, I. Gridlogies! and Experimental Studies in Citrus. Jour. Coll.

Agr. Imp. Univ, eed Vol. 4, No. 2, pp. 83-116, 1912.

. Ostenfeld, C. H. Further Studies on the Apogamy and Hybridization

of the Hieracia. piesa ind. Abst. u. Vererbungslehre, Bd. III, S.

241-285, 1910.

- Rosenberg, O. Cytological Studies on the Apogamy in Hieracium. Bot.

Tidskrift, Vol. 28, 1907.

7. Strasburger, E. Veber Polyembryonie. Jenaische Zeitschr. f. Naturwiss.,

Ba. 12, S. 647, 1878.

Swingle, W. T. New Types of Citrus Fruits. Proc. Florida State

Hortieultural Soe. for 1910, pp. 36-42. Plates I-VIII, 1910.

9. De Vries, H. Gruppenweise Artbildung, 1913.

1 Somatic segregation is not the only available hypothesis in the eases of

the double Matthiola and Petunia. For the double stock may have one half

or less of its pollen-grains ineffective for fertilization (compare Correns on

the pollination of Mirabilis jalapa, in Ber. Deutsch. Bot. Ges., Bd. 18, S.

422-435); and in the ev doubleness may be incompletely dominant, as

in the greenhouse earnatio

NOTES AND LITERATURE

REPULSION IN WHEAT?

THE evidence was furnished by the (F,) of the cross: Smooth

Black X Rough White. ‘‘Smooth Black” is a wheat obtained

from the (F,) of the Rivet X Fife cross and it breeds quite true.

Its glumes are absolutely glabrous and of a burnished black color.

“Rough White’’ is the well-known Essex Rough Chaff Wheat.

The glumes are very hairy and of the ordinary white color. The

(F,) sorted into the following classes:

Rough Rough Smooth Smooth

Black White Black White

120 43 47 3

The expectation for the 1:3:3:1 repulsion is:

109.8 49.9 49.3 3.3

‘“‘Blackness’’ is probably not a simple character for in the (F,)

various degrees of it occur—the patches of it on the glumes being

of various sizes and intensities of color. There is evidence that

it is closely connected with the ‘‘gray’’ color of Rivet glumes.

F. L. ENGLEDOw

THE DETERMINATION OF THE BEST VALUE OF THE

COUPLING-RATIO FROM A GIVEN SET OF DATA!

Mr. G. N. Couns has suggested in this journal? a general

method for determining the value to assign to the coupling-ratio —

for a given set of data. He has worked out the value of a coeffi-

cient of association for the whole series of possible integral ratios

1:1:1:1, 2:1:1:2, etc., and then used the observed value of the

same coefficient to decide which ratio gives the best agreement

with the facts. The method is very simple, but does not lead to

the value which is the most advantageous in a certain sense. If

F,, F,, F,, F,, are the set of theoretical frequencies for a given

value of the ratio and if F,’, F, F,’, F,’, are the observed fre-

1‘*A Case of Repulsion in Wheat,’’ by F. L. Engledow, St. John’s Col-

lege, Cambridge (Proc. Camb. Phil. Soe., Vol. 18).

1F, L. Engledow and G. Udny Yule (Prog. Cambridge Phil. Soc., XVII,

6).

127

128 THE AMERICAN NATURALIST [Vou. XLIX

quencies, and if x =X (F' — F )?/F, then the probability p that

in random sampling deviations of equal or greater improba-

bility will arise is a function of x? which decreases continu-

ally as x? increases. The best value of the ratio will then be

that value which makes p a maximum or x? a minimum. The

problem taken in the note is to determine this value. Un-

fortunately the solution is not a simple one, depending on an |

equation of the fourth degree. A few cases are, however, taken

as illustrations and the question of probable error is discussed.

The recognized fact that, especially when the coupling-ratio is

high, its value may receive considerable alteration without

greatly altering the closeness of agreement between theory and

fact, receives additional emphasis from some of the results given

and makes it clear that considerable caution must be used before

attaching importance to the precise values of high ratios.

F. L. E ann G. U. Y.

2 AM. Nat., XLVI. i

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THE

AMERICAN NATURALIST

VoL. XLIX March, 1915 No. 579

MUTATION EN MASSE

HARLEY HARRIS BARTLETT *

Dure the writer’s experiments with @nothera two

different species have been discovered of which certain

strains give rise by mutation to large numbers of dwarfs.

In both cases the dwarfs occur in far greater numbers

than experience would lead one to expect, even in the most

actively mutant strain. Similar, although not exactly

parallel, phenomena have been observed by both de Vries

and Davis in certain hybrid @notheras, but not, as far as

the writer knows, in any unhybridized species. Since the

cultures have now been continued long enough so that

there can be no doubt as to the accuracy of the observa-

tions, the least complicated of the two cases is here placed

on record. It concerns @nothera Reynoldsii sp.nov. (A

technical diagnosis of this species will be published else-

where.) The seeds from which the cultivated strain arose

were collected at Knoxville, Tennessee, in the fall of 1910,

by Dr. E. S. Reynolds, then connected with the botanical

department of the University of Tennessee.

Fig. 1 is a diagram showing the size and relationship

of the cultures of @nothera Reynoldsii which have thus

far been grown. No diversity was found in the small

F, and F, cultures, of only ten and five plants, respec-

tively, which were grown in 1911 and 1912. The F,

generation of twenty-six plants, grown in 1913, exhibited

‘1 From the Bureau of Plant Industry, U. S. Department of Agriculture,

Offce of Plant Physiological and Fermentation Investigations. Published

by the permission of the Secretary of Agriculture.

129

130 THE AMERICAN NATURALIST [ Vou. XLIX

a most unexpected segregation into three marked types,

forma typica, reproducing the parental form, and two

dwarf types, mut. semialta and mut. debilis, so named

because of their resemblance to the two classes of dwarfs

which de Vries? obtained from Œ. nanella X Œ. biennis.

Mut. semialta is about half as tall as f. typica and has a

LHO

MLD

E; IROI WILD SEED

491, lO PLANTS

ALL F TxPICA

L ARONI NO. 89, E IVCA aiie 0.05, F

A PA 105 PLANTS kh PLANT:

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LITUTATTON

SF rman 89-3, F TIPICA A

1973,

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29 EIVA | 2 rer semua | 18 UT CERES

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4g PROT 89-3 9-3743, £F EKPA i

og 1914, 28 PLANTS iy ea aoe EE [VOT SLUTS Fy PROM 89-93-25, UT. DEBILIS

sr LUF, AP PLANTS

gram showing the size and relationship of the cultures of @no-

Wet oe 1911-1914,

very dense and showy inflorescence in which the fruits

and flowers are very little smaller than in the parent

form. The leaves, however, are decidedly reduced. Mut.

debilis is more variable in size than mut. semialta, but

averages about half as high as the latter. Its fruits and

flowers are somewhat reduced, but by no means propor-

tionately to the size of the plant. The leaves, on the

contrary, are much more reduced than those of mut.

semialta. The inflorescence is not as dense, but often

longer.

The unlooked-for occurrence of these types in the F;

of 1913 led to the duplication in 1914 of both the F, and

F, generations from seeds which had been left over from

former years. In 100 additional F, plants of the mutant

2‘‘Gruppenweise Artbildung,’? pp. 241-244.

No. 579] MUTATION EN MASSE 131

strain there were 99 plants of f. typica and one mutation

of a quite different type from either mut. semialta or

mut. debilis. The original F, culture had consisted of

26 plants, including two of f. typica, 16 of mut. semialta

Fig. 2. A random sample ae six plants from the Fs culture of 1913. No. 4

is f. typica; the rest are all mut. semialta.

and eight of mut. debilis. In the supplementary culture

of 53 sister-plants, grown in 1914, there were 27 plants

of f. typica, 16 of mut. semialta and ten of mut. debilis.

132 THE AMERICAN NATURALIST [Von XLIX

Fic. 3. Adjacent plants of mut. ogc se the left No. 89-3-25, chosen as

parent of one of the F, progenies) and mut. semialta (on the right; No, 89-3-24,

chosen as parent of st of the F, pando dich The small labels on the plants

are 10 cm. long. (Reduction same as in Fig. 4.)

There can therefore be no doubt that the F, was an essen-

tially uniform generation and that the F, was the first

generation to throw the two dwarf types, except perhaps

as rare mutations, which were not detected on account

of the small size of the cultures. In this connection it

may be remarked that the mutations of Gnothera Rey-

noldsii can not be detected in very young cultures with

any degree of precision. Up to the time the rosettes are

set out in the garden, after they have been started in the

greenhouse in pots, they show no consistent differences

among themselves. It happens that six seedlings of the

1913 F, were photographed before any diversity what-

ever had been detected in the culture. They must there-

fore be considered a random sample from the 26 plants.

All turned out to be mut. semialta except one, which was

f. typica. The photograph is reproduced as Fig. 2.

At maturity the contrast between the classes is very

No. 579] MUTATION EN MASSE 133

striking, and leaves no room for doubt as to the proper

classification of any individual. Fig. 3 shows adjacent

plants of mut. debilis and mut. semialta; Fig. 4 mut.

debilis and f. typica. Figs. 5, 6 and 7 show branches of

the three forms, on the same scale of reduction.

The F, generation, grown in 1914, consisted of the

progenies of two plants of each of the three types. The

two externally identical parent plants of f. typica (there

ae |

Adjacent plants of mut. debilis (in front) and f. typica (behind ;

IG. 4. j

No. 89-3-13, chosen as parent of one of the F, progenies

). The small labels on

the plants are 10 em. long. (Reduction same as in Fig. 3.

134 THE AMERICAN NATURALIST [ Von. XLIX

were only two in the F, of 1913) proved to be of very

different genetic constitution. The progeny of one, num-

bering 100 plants, were all strictly like the parent, show-

ing not the slightest deviation from f. typica. The other

progeny, however, repeated the diversity of the F, gen-

eration, containing five plants of f. typica, 13 of mut.

semialta and five of mut. debilis in a culture of 24 plants.

This progeny, also, included one plant of a third dwarf

5. Mnothera Reynoldsii f. typica. Branch from F, plant No. 89-38-18,

chosen as parent of one of the F, cultures. The entire plant is shown in Fig. 4.

mutation, which will be referred to below as mut. bilonga.

The two F, plants of mut. semialta which were used as

parents gave very similar progenies, consisting of mut.

semialia and mut. debilis. In one case the numbers were

41 of mut. semialta and five of mut. debilis in a total of

46; in the other case, 83 of semialta and four of mut.

debilis in a total of 87.

No. 579] MUTATION EN MASSE 135

The two progenies from mut. debilis parents, contain-

ing 85 and 43 plants, respectively, were all mut. debilis

like the parents, except that each progeny contained one

individual of mut. bilonga. Before discussing the latter

mutation it may be well to capitulate.

1. The individuals of f. typica are of two kinds, (a)

those which do not throw dwarfs, and (b) those which

throw from 60 per cent. to 80 per cent. of dwarfs.

Fic, 6. Mut. semialta. Branches of Fs plant No. 89-3-23.

2. The dwarfs are of two kinds, one of which, mut.

semialta, is intermediate between f. typica and the ex-

treme dwarf, mut. debilis.

3. Mut. semialta reproduces itself in the greater part

of its progeny, but throws a small number (seemingly

about 7 per cent.) of mut. debilis.

4. Mut. debilis does not throw either f. typica or £

semialta. It comes true, except for the fact that it rarely

throws mut. bilonga. .

Mut. bilonga is by far the most interesting of the vari-

ants of Gnothera Reynoldsii. Tt has occurred once as a

136 THE AMERICAN NATURALIST [ Von. XLIX

primary mutation from f. typica, and twice as a secondary

mutation from mut. debilis. Although mut. debilis seems

to be an extreme recessive, derived from f. typica either

by the simultaneous or by the successive loss of two

factors for height, it throws mut. bilonga, which shows

a return to the stature of mut. semialta. In fact, mut.

bilonga would be identical with mut. semialta if it were

not for the difference in the length of the fruits. It has

already been stated that in both mut. semialta and mut.

debilis the fruits are by no means as reduced in size as

the foliage and stems. It seems almost as though the

IIG. 7. Mut. debilis. Branches of Fs plant No. 89-3-12. The entire plant is

shown in Fig. 4.

process of mutation, which results in the formation of

either of these dwarfs, does not involve the factors deter-

mining fruit size. In other words, the slight reduction in

size seems not to be due to a modification of the hereditary

qualities of the plant, but rather to diminished nutrition.

If this explanation is the true one, the fruits of mut.

No. 579] MUTATION EN MASSE 137

# eet

shown in Figs. 4

debilis are small for the same reason that the late autumn

fruits on weak lateral branches of f. typica are smat.

When, by mutation to mut. bilonga, mut. debilis reassumes

the stature and foliage size of mut. semialta, there 1s a

modification of the characters which determine the length

of the fruit. Not only is the stature doubled, and the

length of the leaves doubled, but the length of the fruit

is also doubled. Mut. bilonga is to all outward appear-

ance the same as mut. semialta, except that the fruits are

twice as long. Thus, we have the anomalous situation

that mut. bilonga, a dwarf type, is characterized by the

138 THE AMERICAN NATURALIST [Vou. XLIX

Branches of mut. debilis (left; No. 89-3-21-1) and mut. bilonga

(right; No. 89-3-21-85) ee ce ng in both foliage and fruits. The

two forms were sisters in the progeny of one of the original examples of mut.

debilis which appeared in the Pe of 1913.

longest fruits in the subgenus Onagra. Txeptionai fruits

are 70 mm. long; the average length of six hand-pollinated

_ fruits was 62 mm. By way of comparison, it may be

stated that the length of the average fruit of f. typica is

about 33 mm., and that the longest is 38 mm. None of

the immediate allies of @nothera biennis have longer

fruits than those of O. Reynoldsii f. typica, although

there are allies of O. muricata in which the fruits average

as long or longer. There is no species, however, in which

the fruit length of mut. bilonga is even approached. Here

we have an apparent case of progressive mutation, which

will be tested out as soon as possible. Mut. bilonga has

not thus far been carried into a second generation. Both

it and the two other dwarfs are completely self-fertile,

No. 579] MUTATION EN MASSE 139

and furnish an abundance of good seed. It is planned to

make a biometrical study of fruit length next year, when

the second generation of mut. bilonga will be available.

In Fig. 8 the two branches on the left are mut. semialta;

the two on the right mut. bilonga. The plants which fur-

nished the material belonged to an F, culture from f.

typica, containing five plants of f. typica, 13 of mut.

semtalta, five of mut. debilis and one of mut. bilonga.

In Fig. 9, on the contrary, the contrast is between sister-

plants of mut. debilis and mut. bilonga in the progeny of

mut. debilis. A comparison of the figures will show the

identity of mut. bilonga from the two sources.

The phenomenon presented by @nothera Reynoldsii,

called mutation en masse for want of a better name, seems

of sufficient interest to justify this preliminary paper.

The fact that it appears in one of the short-styled, self-

pollinating species makes it of especial interest. An ex-

planation can hardly be attempted until the interrelation-

ships of the various derivations have been worked out by

a series of crosses. Nevertheless, it seems clear that

mutation en masse bears a certain degree of resemblance

to Mendelian segregation. The fundamental mutation

which causes the diversity possibly occurs in only one of

the two gametes in a generation preceding the one in

which diversity becomes manifest. It is masked by the

dominance of the parental characters transmitted through

the other gamete. Segregation then occurs in the follow-

ing generation. No explanation suggests itself for the

enormous surplus of dwarfs in the progenies exhibiting

diversity, unless perhaps it is that the results are com-

` plicated by selective germination or selective mortality.

At any rate, the ratios thus far obtained do not conform

to any Mendelian expectation. Larger cultures, to be

grown next year, may prove more enlightening.

To the mutationist, the most interesting problem pre-

sented by Gnothera Reynoldsii is the origin of mut.

bilonga from mut. debilis, involving, as now seems prob-

able, the omin of a new character.

THE ALBINO SERIES OF ALLELOMORPHS IN

GUINEA-PIGS

SEWALL WRIGHT

BUSSEY INSTITUTION

Aupinism is one of the most familiar color conditions

found in mammals. In all cases it has proved to be a

simple Mendelian recessive to the pigmented condition.

This was demonstrated for guinea-pigs by Castle and

Allen in 1903. In the present paper evidence will be pre-

sented showing that in guinea-pigs there are two grades

of pigmentation, intermediate between full intensity and

albinism, which form with these a series of four allelo-

morphs with dominance in the order of increasing pig-

mentation.

The most highly pigmented condition is also the most

familiar. To this condition, which we may call intensity,

belong those types of guinea-pigs which show in the fur

intense black pigmentation or the intense orange-yellow

known as ‘‘red,’’ or both. Examples are the blacks, the

reds, the golden agoutis and the black-and-red tortoise-

shells of the fanciers. All of these have black eyes.

The second condition in intensity and order of domi-

nance contains color varieties which have long been

known. In these black is reduced to a sepia-brown color

much like human brown hair, known very inappropriately

as ‘‘blue.’’ Red is reduced to yellow or cream. The

eye color remains black. Thus we have blues, creams,

silver agoutis and blue-and-cream tortoise-shells in place

of the four types mentioned as of the intense condition.

That these four so-called dilute types, as well as others-

not mentioned, differ from the intense types by the same

factor or factors has long been known. It is shown by

the fact that one can start with any of these and by crosses

with the appropriate intense variety produce any other

140 ;

No. 579] ALBINO SERIES OF ALLELOMORPHS 141

dilute variety in the second generation at latest. The

writer has done this for all of the types mentioned by

starting with the cream variety.

The third condition is not so familiar as the others. It

has appeared at the Bussey Institution only in the de-

scendants of three guinea-pigs brought from Peru by Pro-

fessor Castle in 1911. Among these black is reduced to

sepia (or ‘‘blue’’), indistinguishable from the ‘‘blue’’ of

the dilutes. Red is reduced to white. Nota trace of yel-

low pigment has been found in guinea-pigs with this al-

lelomorph. One of the most striking features of this

condition is the glowing red color of the eyes, easily dis-

tinguishable from the black eyes of the intense and dilute

guinea-pigs as well as from the pink eyes of the albinos.

There is a deficiency of pigment in both retina and iris.

Because of this feature this condition will be known as

red-eye. It was announced as an allelomorph of albinism

by Castle (1914). Permission has very kindly been given

the writer to present in this paper data on the red-eye

condition, in the work on which he has been associated.

With the red-eye factor, the blacks, reds, golden agoutis

and black-and-red tortoise-shells become red-eyed blues,

red-eyed whites, red-eyed silver agoutis and red-eyed blue-

and-white tortoise-shells, respectively. These four varie-

ties have all been obtained by crossing one of them, the

red-eyed silver agouti, with various stock guinea-pigs

and extracting the different combinations in F,. The

red-eyed white is an interesting variety thus derived.

Red-eyed whites have been tested by crosses with reds and

= creams and have been shown conclusively to be the red-

eyed representative of these varieties, such crosses having

given 9 reds, 3 creams, 6 red-eyed whites and 6 albinos

only. This red-eyed white demonstrates most forcibly

the complete inhibition of yellow in the presence of the

red-eye factor.

In the albino condition black disappears from the coat

except in patches on the nose, ears and feet, and occa-

sionally some sootiness on the back. In this connection

it is interesting to note that nose, ears and feet are gener-

142 THE AMERICAN NATURALIST [ Vou. XLIX

ally the most highly pigmented regions in the dilute and

red-eye conditions. In the albinos, yellow disappears en-

tirely, just as in the red-eyes. The eyes are pink, due

to the loss of all pigment from the iris and retina. The

blacks and golden agoutis are replaced by sooty albinos;

the reds, by clear albinos; and the black-and-red tortoise-

shells, by albinos in which nose, feet and ears are sooty

or white, depending on the location of the spots.

The effects of the four allelomorphs on the appearance

of eye and fur may be tabulated as follows:

Effects of On Eye Color On Black Fur | On Yellow Fur

Intensity Black Black | Red

iluti Black Sepia | Cream

Red-eye Red Sepia _ White

binism White White

(sepia points)

It should be added that dilution of pigmentation may be

produced by other factors than members of the albino

series of allelomorphs. In the foregoing discussion such

factors have been assumed to be absent. It may be said,

however, that by starting with variations which owe their

dilutions to factors which are independent of the albino

series, doubly dilute varieties have been produced on in-

troducing the dilution or red-eye allelomorphs of albi-

nism. The effects of dilution, red-eye and albinism on

brown pigment are parallel in all cases to their effects on

black.

It should be said that the sepia (or ‘‘blue’’) due to the

dilution factor, or to the red-eye factor, varies through a

wide range which intergrades with black. Thus Castle .

(1905) and Sollas (1909) recognized that both intense and

dilute forms of pigmentation occur commonly in guinea-

pigs, but did not suggest any factorial explanation be-

cause of this intergrading. The inheritance of these fluc-

tuations is at present under investigation.

If intensity, dilution, red-eye and albinism are allelo-

morphs, gametes should always carry one, but only one,

of the four. Zygotes must always have two representa-

No.579] ALBINO SERIES OF ALLELOMORPHS 143

tives from the series, never more or less, which two may,

of course, be alike. Thus with dominance in the order of

increasing pigmentation intense guinea-pigs should be

- homozygous, or else carry recessive dilution, recessive

` red-eye or recessive albinism, but never more than one of

these; dilute guinea-pigs should be homozygous, or carry

recessive red-eye or recessive albinism, but never both;

red-eyes should be either homozygous or carry recessive

albinism; and finally albinos should always be homozy-

gous and never have the power of transmitting intensity,

dilution, or red-eye to their descendants. All of these

types have been obtained and tested with results in har-

mony with expectation. In this paper only a few of the

most critical crosses will be given, reserving a more de-

tailed discussion for a later paper.

Red-eye, as mentioned before, has occurred only in the

descendants of certain pigs brought from Peru. No al-

binos appeared in the pure stock. In the pure races, red-

eye behaved as a simple recessive. Thus intense by in-

tense gave 63 intense and 19 red-eye young, while red-eye

by red-eye gave only red-eyes, 28 in number.

As red-eyes had never appeared in our stock guinea-

pigs, it was natural to expect that any stock pig crossed

with red-eye, an apparently recessive condition, would

give only intense young. As a matter of fact, however,

numerous red-eye young appeared in F,. The next ques-

tion was whether one kind of stock differed from another

in its power of bringing about this apparent reversal of

dominance. A study of the records soon showed that

albinism had something to do with the matter, as the fol-

lowing tabulation indicates:

Intense Red-eye Albino

Red-eye X intense ...........- 48 22 20

Modave < Alino... cs cis 0 80 32

The difference in result of the two sorts of matings is

obviously significant. With an intense parent there were

more than 50 per cent. intense young and comparatively

few red-eye young. With an albino parent there were no

144 THE AMERICAN NATURALIST [Vou. XLIX

intense but numerous red-eye young. The intense ani-

mals and the albinos used were of the same stock and

hence could differ consistently only as regards albinism.

Clearly red-eye is not inherited independently of albinism.

That the apparent reversal of dominance is not due

merely to the presence of recessive albinism is shown by

the fact that F, red-eyes crossed inter se produced 89 red-

eyes, 36 albinos, but no intense young. Among these F,

red-eyes, some were demonstrated to be free from re-

cessive albinism. This complete inability of albinos to

transmit the intense allelomorph of red-eye in crosses

with the latter can only be interpreted in one way, aside

from linkage hypotheses. The intense allelomorph of

red-eye must also be an allelomorph of albinism. Thus

red-eye must either be an allelomorph of albinism or be

albinism itself, genetically, plus a modifying factor. The

latter rather improbable hypothesis has been definitely

eliminated. The pure South American stock under this

hypothesis must be homozygous for all such modifying

factors, since no albinos have appeared among them. The

hypothetical modifying factor must be a dominant unit

factor to account for the results given for F, and F,.

Some pure South American intense animals were crossed

with stock albinos. They produced F, intense young,

which must (under the hypothesis) be heterozygous for

albinism and for the modifying factor. These F, in-

tense young were back-crossed with stock albinos. There

should be both red-eyes and albinos among the young,

25 per cent. of each, if red-eye is albinism associated with

a modifier. But no red-eyes actually appeared. There

were 14 intense and 25 albinos. The chance that no red-

eyes would appear in 39 young is (3/4), or .000,001.

Thus the hypothesis that red-eye is albinism plus a modi-

fier may be dismissed.

On the view that red-eye is a dominant allelomorph of

albinism, the results above are easily explained. Red-

eye by albino or by red-eye should give only red-eyes and

albinos. The F, intense, which must carry recessive al-

No. 579] ALBINO SERIES OF ALLELOMORPHS 145

binism because of the stock albino parent, should not be

able to transmit red-eye. As for hypotheses of linkage,

it need only be said that no results have been obtained

which require them. The critical crosses have all been

made reciprocally as regards sex.

The fact that dilutes are more or less intermediate be-

tween intense and red-eye varieties suggested the fol-

lowing experiments which were designed to demon-

strate at once whether there was any relation in inheri-

tance between albinism and dilution. Dilutes were crossed

with albinos from certain stocks which for years had given

only intense and albino young, but no dilutes. Second,

intense pigs from these same stocks, which had given only

intense and albino young, were crossed with albinos from

dilute stock. If intensity and dilution form a pair of

allelomorphs which segregate independently of the pair,

color and albinism (as is the case in mice and rabbits),

these two crosses must give identical results. In each

case color is introduced by one parent, albinism by the

other; the intensity of certain stocks by one parent, the

dilution of certain stocks by the other parent. In fact

identical results should be obtained regardless of

whether dilution is due to a unit factor or multiple fac-

tors, or even whether its inheritance is Mendelian or not,

povided only that it is inherited ind i yofalbinism.

As it happened, these two crosses gave strikingly differ-

ent results. The first cross, viz., dilute by albino from

intense stock, gave only dilutes, 37 in number, aside from

albinos. The second cross, intense from intense stock

by albino from dilute stock, gave only intense young, 49

in number, aside from albinos. These different results

can only be explained by assuming that a member of the

albino series of allelomorphs, recessive to intensity, is

essential to dilute animals. Thus genetically, dilution

may be albinism plus a modifying factor, or it may be

red-eye plus a modifying factor, or it may be a new allelo-

morph. The last has proved to be the case. A large

number of intense animals, at least half of which under

146 THE AMERICAN NATURALIST [ Vou. XLIX

the first hypothesis would be expected to be heterozygous

both for albinism and the modifying factor, have been

crossed with albinos. None of them have given both

albinos and dilutes. It is of course expected under the

hypothesis of allelomorphism that no intense animal

should transmit both albinism and dilution. The view

that dilution is red-eye plus a modifying factor has also

been eliminated. Red-eye has never appeared in our

stock guinea-pigs, which must therefore be pure for any

modifying factor which might changea red-eye to a dilute.

But red-eyes of any generation crossed with stock albinos

have never given dilutes in 105 young. Therefore dilu-

tion can not be red-eye plus a modifying factor. The only

remaining hypothesis is that dilution is an allelomorph of

red-eye and albinism. It is dominant to both since dilute

by dilute has often given red-eyes and albinos, while the

latter varieties crossed inter se have never given dilutes.

Thus we have four allelomorphs corresponding to four

grades of pigmentation. The existence of such series has

a bearing on the nature of unit factors. The results could

be explained by perfect coupling, but such an explanation

seems highly arbitrary where the characters fall into a

natural physiological series. The series seems to suggest

that we have four variations in some one entity. Fur-

thermore, while we have only four such variations at the

Bussey Institution, it may well be that others exist else-

where, forming perhaps a continuous series. Such varia-

tions in this factor probably do not occur frequently.

When they do occur they probably take place by distinct

steps. The rather frequent occurrence of albinos in wild

species, without intermediates, indicates that variation

from one extreme to the other in the condition of the

factor may take place.

A point which has a bearing on the physiology of pig-

ment is the fact that members of the albino series of allelo-

morphs do not cause diminution in quantity of pigment,

merely as pigment, but affect yellow pigment differently

from black. This is seen most clearly in the red-eyes, in

No.579] ALBINO SERIES OF ALLELOMORPHS 147

which yellow is completely inhibited, while black is only

slightly affected.

Finally the question is raised whether anything similar

to this can be found among other mammals. Albinos are

found in many mammals as well as in lower animals. Asto

multiple allelomorphs, the case of the Himalayan rabbit

is well known and compares well with the guinea-pig

series. The Himalayan rabbit with its pink eyes and

white fur with dark patches on nose, ears and feet is com-

parable to the guinea-pig albino. The complete albino

rabbit recessive to the Himalayan is lower in the series

than anything known in guinea-pigs. The dilution of the

blue rabbit as well as that of the blue mouse and maltese

cat is of a different type from the guinea-pig dilution.

As Miss Sollas has shown, the pigment is clumped in-

stead of uniformly decreased in quantity. The effect is

slate-blue instead of sepia-brown. Mr. H. D. Fish has

made crosses (unpublished data, to which I refer with his

permission) which show as expected that rabbit dilution

is inherited wholly independently of albinism.

In man, we have albinos which are probably comparable

to guinea-pig and rabbit albinos. A study of the enor-

mous collection of data in the Monograph of Pearson, Net-

tleship and Usher convinces one that albinism in man is

recessive. But as Pearson points out, there are many

grades of albinism and each grade tends to maintain its

identity in inheritance. Among negroes there are albinos

with blue irises, red pupils, white skin and nearly white

hair. There are also darker grades, as with brown skin,

eyes and hair. There is no sharp line anywhere between

the complete albinos and the so-called xanthous types.

In the white races albinos pass into the extreme blonds in

a continuous series. In fact, study of records convinces

one that in some cases the same factor may produce well-

marked albinism, with red eyes, nystagmus and photo-

phobia in one member of a family, but merely extreme

blondism in another. It is worthy of note that human

light hair resembles closely the sepia of dilute guinea-

148 THE AMERICAN NATURALIST [ Vou. XLIX

pigs, and not at all the slate blue of dilute rabbits, mice

and cats. Thus, while I have not been able to find any

critical evidence, the suggestion seems worth making that

a series of allelomorphs of albinism may be in part re-

sponsible for differences in intensity of human pigmen-

tation.

Summing up: the results in guinea-pigs and rabbits sug-

gest that there is a hereditary factor in mammals, which

may exist with stability at different stages of divergence

from the normal; that divergence from the normal in the

factor tends to produce in the animal a corresponding re-

duction in the quantity of melanin pigment throughout

the body, conspicuously in fur, skin and eyes, of which re-

duction the limit is complete albinism; that in this reduc-

tion the qualitative differentiation of the pigment is a

factor, in that yellow pigment is affected more strongly

than black and its threshold of complete inhibition is

reached with less divergence of the factor; that in the re-

duction the location of the pigment is a factor, in that there

is less tendency toward reduction at the extremities—feet,

ears and nose—than elsewhere in skin and fur; that,

finally, any stage of divergence is dominant to any stage

‘more remote from the normal.

In conclusion, I wish to thank Professor Castle for the

opportunity to carry on this work and for numerous

suggestions during its progress.

December 24, 1914

LITERATURE CITED.

Castle, W. E. 1905. Heredity of Coat Characters in Guinea-Pigs and

Rabbits. Carnegie Institution of Washington. Publication

No. 23.

1914. Some New Varieties of Rats and Guinea-Pigs and their Rela-

tion to Problems of Color Inheritance. AMER, NAT., Vol. 48,

p. 65.

Castle, W. E. and G. M. Allen. 1903. The Heredity of Albinism. Proc.

Am. Ac. Arts and Sci., Vol. 38, No. 21, p. 603.

Pearson, K., E. Nettleship, and C. H. Usher. 1913. A Monograph on

Albinism in Man. Parts I and IV. Dulau & Co., London.

Sollas, I. B. J. 1909. Inheritance of Color and of Supernumerary Mam-

mae in Guinea-Pigs, with a Note on the Occurrence of a

Dwarf Form. Reports to the Evol. Com. of the Roy. Soc.,

No. 5.

PROGRESSIVE EVOLUTION AND THE ORIGIN

OF SPECIES?

PROFESSOR ARTHUR DENDY

THE opening years of the present century have wit-

nessed a remarkable development of biology as an ex-

perimental science, a development which, however full

of promise it may be for the future, for the time being

appears to have resulted in a widespread disturbance

of ideas which have themselves only recently succeeded

in gaining general acceptance. The theory of organic

evolution, plainly enough enunciated at the close of the

eighteenth and the beginning of the nineteenth century

by Buffon, Lamarck, and Erasmus Darwin, remained un-

convincing to the great majority of thinking men until

the genius of Charles Darwin ‘not only brought together

and presented the evidence in such a manner that it could

no longer be ignored, but elaborated a logical explana-

tion of the way in which organic evolution might be sup-

posed to have taken place. Thanks to his labors and

those of Alfred Russel Wallace, supported by the power-

ful influence of such men as Huxley and Hooker, the

theory was placed upon a firm foundation, in a position

which can never again be assailed with any prospect of

success.

This statement is, I believe, entirely justified with re-

gard to the theory of organic evolution itself, but the

case is very different when we come to investigate the

position of the various subsidiary theories which have

been put forward from time to time with regard to what

may perhaps be termed the modus operandi, the means

by which organic evolution has been effected. It is in

this field that controversy rages more keenly than ever

before. Lamarck told us that evolution was due to the

1 Address of the president of the section of zoology, British Association

for the Advancement of Science, Australia, 1914.

149

Do THE AMERICAN NATURALIST [VoL. XLIX

accumulated results of individual effort in response to a

changing environment, and also to the direct action of

the environment upon the organism. Darwin and Wal-

lace taught us that species originated by the natural se-

lection of favorable variations, and under the influence

of Weismann’s doctrine of the non-inheritance of ac-

quired characters the theory of natural selection is in

danger of becoming crystallized into an inflexible dogma.

In recent years de Vries has told us that species arise

by sudden mutations, and not by slow successive changes,

while one of the most extreme exponents of ‘‘Mendel-

ism,’’ Professor Lotsy, lately informed us that all species

arise by crossing, and seriously suggested that the ver-

tebrate type arose by the crossing of two invertebrates!

This curious and many-sided divergence of opinion

amongst expert biologists is undoubtedly largely due to

the introduction of experimental methods into biological

science. Such methods have proved very fruitful in

results which at first sight seem to be mutually contra-

dictory, and each group of workers has built up its own

theory mainly on the basis of observations in its own

restricted field.

Professor Bateson has said in his recently published

‘‘ Problems of Genetics’’:

When ... we contemplate the problem of evolution at large the

hope at the present time of constructing even a mental picture of that

process grows weak almost to the point of vanishing. We are left

wondering that so lately men in general, whether scientific or lay, were

so easily satisfied. Our satisfaction, as we now see, was chiefly founded

on ignorance.”

In view of this striking pronouncement on the part

of one who has devoted his life with signal success to

the experimental investigation of evolutionary problems,

the remarks which I propose to lay before you for your

consideration to-day may well appear rash and ill-ad-

vised. I cannot believe, however, that the position is

really quite so black as it is painted. We must perforce

admit that the divers theories with regard to the work-

2** Problems of Genetic,’’ p. 97.

No. 579] PROGRESSIVE EVOLUTION 151

ing of organic evolution cannot all be correct in all their

details, but it may be that each contains its own elements

of truth, and that if these elements can but be recognized

and sorted out, they may perhaps be recombined in such

a form as to afford at any rate a plausible working

hypothesis. We must bear in mind from the outset that

in dealing with such a complex problem many factors

have to be taken into account, and that widely different

views on the question may be merely one-sided and not

necessarily mutually exclusive.

I take it there are three principal facts, or groups of

facts, that have to be accounted for by any theory

of organic evolution:

1. The fact that, on the whole, evolution has taken

_ place in a progressive manner along definite and di-

vergent lines.

2. The fact that individual animals and plants are

more or less precisely adapted in their organization and

in their behavior to the conditions under which they have

to live.

3. The fact that evolution has resulted in the existence

on the earth to-day of a vast number of more or less

well-defined groups of animals and plants which we call

species.

The first of these facts appears to me to be the most

fundamental, and at the same time the one to which

least attention is usually paid. The great question, after

all, is, Why do organisms progress at all instead of re-

maining stationary from generation to generation? To

answer this question it is not necessary to go back to

the beginning and consider the case of the first terres-

trial organisms, whatever they may have been, nor are

we obliged to take as illustrations the lowest organisms

known to us as existing at the present day. We may

consider the problem at any stage of evolution, for at

each stage progress is, or may be, still taking place.

We may even begin by considering what is usually re-

garded as the highest stage of all, man himself; and

indeed this seems the most natural thing to do, for we

152 THE AMERICAN NATURALIST [Vov. XLIX

certainly know more about the conditions of progress in

man than in any other organism. I refer, of course, at

the moment, not to progress in bodily organization, but

to progress in the ordinary sense of the word, the prog-

ress, say, of a family which rises in the course of a few

generations from a position of obscure poverty to one

of wealth and influence. You may perhaps say that such

a case has no bearing upon the problem of organic evo-

lution in a state of nature, and that we ought to confine

our attention to the evolution of bodily structure and

function. If so, I must reply that you have no right

to limit the meaning of the term evolution in this man-

ner; the contrast between man and nature is purely ar-

bitrary; man is himself a living organism, and all the

improvements that he effects in his own condition are

part of the progress of evolution in his particular case.

At any rate I must ask you to accept this case as our

first illustration of a principle that may be applied to

organisms in general.

If we inquire into the cause of the progress of our

human family I think there can be only one answer—

it is due to the accumulation of capital, or, as I should

prefer to put it, to the accumulation of potential energy,

- either in the form of material wealth or of education.

` What one generation saves is available: for the next,

and thus each succeeding generation gets a better start

in life, and is able to rise a little higher than the pre-

ceding one.

Every biologist knows, of course, that there are many

analogous cases amongst the lower animals, and also

amongst plants. The accumulation of food-yolk in the

egg has undoubtedly been one of the chief factors in the

progressive evolution of animals, although it has been

replaced in the highest forms by a more effective method

of supplying potential energy to the developing off-

spring. It may indeed be laid down as a general law

that each generation, whether of animals or of plants,

accumulates more energy than it requires for its own

maintenance, and uses the surplus to give the next gen-

No. 579] PROGRESSIVE EVOLUTION 153

eration a start in life. There is every reason to believe

that this has been a progressive process throughout the

whole course of evolution, for the higher the degree or

organization the more perfect do we find the arrange-

ments for securing the welfare of the offspring.

We cannot, of course, trace this process back to its

commencement, because we know nothing of the nature

of the earliest living things, but we may pause for a

moment to inquire whether any phenomena occur

amongst simple unicellular organisms that throw any

light upon the subject. What we want to know is—How

did the habit of accumulating surplus energy and hand-

ing it on to the next generation first arise?

Students of Professor H. S. Jennings’s admirable

work on the ‘‘Behavior of the Lower Organisms’’ will

remember that his experiments have led him to the con-

clusion that certain Protozoa, such as Stentor, are able

to learn by experience how to make prompt and effective

responses to certain stimuli; that after they have been

stimulated in the same way a number of times they make

the appropriate response at once without having to go

through the whole process of trial and error by which it

was first attained. In other words, they are able by

practise to perform a given action with less expenditure

of energy. Some modification of the protoplasm must

take place which renders the performance of an act the

easier the oftener it has been repeated. The same is,

of course, true in the case of the higher animals, and we

express the fact most simply by saying that the animal

establishes habits. From the mechanistic point of view

we might say that the use of the machine renders it more

perfect and better adapted for its purpose. In the

present state of our knowledge I think we cannot go be-

yond this, but must content ourselves with recognizing

the power of profiting by experience as a fundamental

property of living protoplasm.

It appears to me that this power of profiting by ex-

perience lies at the root of our problem, and that in it

154 THE AMERICAN NATURALIST [ Vou. XLIX

we find a chief cause of progressive evolution. Jennings

speaks of the principle involved here as the ‘‘ Law of the

readier resolution of physiological states after repeti-

tion,’’ and, similarly, I think we must recognize a ‘‘Law

of the accumulation of surplus energy’’ as resulting

therefrom. Let us look at the case of the accumulation

of food-yolk by the egg-cell a little more closely from

this point of view. Every cell takes in a certain amount

of potential energy in the form of food for its own use.

If it leads an active life either as an independent or-

ganism or as a constituent part of an organism, it may

expend by far the greater part, possibly even the whole,

of that energy upon its own requirements, but usually

something is left over to be handed down to its imme-

diate descendants. If, on the other hand, the cell ex-

hibits very little activity and expends very little energy,

while placed in an environment in which food is abun-

dant, it will tend to accumulate surplus energy in excess

of its own needs. Such is the case with the egg-cells

of the multicellular animals and plants. Moreover, the

oftener the process of absorbing food-material is re-

peated the easier does it become; in fact, the egg-cell es-

tablishes a habit of storing up reserve material or food-

. yolk. Inasmuch as it is a blastogenic character, there

can be no objection to the supposition that this habit

will be inherited by future generations of egg-cells. In-

deed we are obliged to assume that this will be the case,

for we know that the protoplasm of each succeeding gen-

eration of egg-cells is directly continuous with that of

the preceding generation. We thus get at any rate a

possibility of the progressive accumulation of potential

energy in the germ-cells of successive generations of

multicellular organisms, and, of course, the same argu-

ment holds good with regard to successive generations

of Protista.

It would seem that progressive evolution must follow

as a necessary result of the law of the accumulation of

surplus energy in all cases where there is nothing to

No. 579] PROGRESSIVE EVOLUTION 155

counteract that law, for each generation gets a better

start than its predecessor, and is able to carry on

a little further its struggle for existence with the en-

vironment. It may be said that this argument proves

too mueh, that if it were correct all organisms would by

this time have attained to a high degree of organization,

and that at any rate we should not expect to find such

simple organisms as bacteria and Amebe still surviving.

This objection, which, of course, applies equally to other

theories of organic evolution, falls to the ground when

we consider that there must be many factors of which we

know nothing which may prevent the establishment of

progressive habits and render impossible the accumula-

tion of surplus energy. Many of the lower organisms,

like many human beings, appear to have an inherent in-

eapacity for progress, though it may be quite impossible

for us to say to what that incapacity is due.

It will be observed that in the foregoing remarks I

have concentrated attention upon the storing up of re-

serve material by the egg-cells, and in so doing have

avoided the troublesome question of the inheritance of

so-called acquired characters. I do not wish it to be

supposed, however, that I regard this as the only direc-

tion in which the law of the accumulation of surplus

energy can manifest itself, for I believe that the accu-

mulation of surplus energy by the body may be quite as

important as a factor in progressive evolution as the

corresponding process in the germ-cells themselves.

The parents, in the case of the higher animals, may sup-

ply surplus energy, in the form of nutriment or other-

wise, to the offspring at all stages of its development,

and the more capital the young animal receives the better

will be its chances in life, and the better those of its own

offspring.

In all these processes, no doubt, natural selection plays

an important part, but, in dealing with the accumulation

of food material by the egg-cells, one of my objects has

been to show that progressive evolution would take place

156 THE AMERICAN NATURALIST _[Vou. XLIX

even if there were no such thing as natural selection, that

the slow successive variations in this case are not chance

variations, but due to a fundamental property of living

protoplasm and necessarily cumulative.

Moreover, the accumulation of surplus energy in the

form of food-yolk is only one of many habits which the

protoplasm of the germ-cells may acquire in a cumu-

lative manner. It may learn by practise to respond with

increased promptitude and precision to other stimuli

besides that of the presence of nutrient material in its

environment. It may learn to secrete a protective mem-

brane, to respond in a particular manner to the presence

of a germ-cell of the opposite sex, and to divide in a

particular manner after fertilization has taken place.

Having thus endeavored to account for the fact that

progressive evolution actually occurs by attributing it

primarily to the power possessed by living protoplasm

of learning by experience and thus establishing habits

by which it is able to respond more quickly to environ-

mental stimuli, we have next to inquire what it is that

determines the definite lines along which progress mani-

fests itself.

Let us select one of these lines and investigate it as

fully as the time at our disposal will permit, with the

view of seeing whether it is possible to formulate a

reasonable hypothesis as to how evolution may have

taken place. Let us take the line which we believe has

led up to the evolution of air-breathing vertebrates.

‘The only direct evidence at our disposal in such a case is,

of course, the evidence of paleontology, but I am going

to ask you to allow me to set this evidence, which, as you

know, is of an extremely fragmentary character, aside,

and base my remarks upon the ontogenetic evidence,

which, although indirect, will, I think, be found sufficient

for our purpose. One reason for concentrating our at-

tention upon this aspect of the problem is that I wish

to show that the recapitulation of phylogenetic history

in individual development is a logical necessity if evolu-

tion has really taken place.

No. 579] PROGRESSIVE EVOLUTION 157

We may legitimately take the nucleated Protozoon

cell as our starting point,.for, whatever may have been

the course of evolution that led up to the cell, there can

be no question that all the higher organisms actually

start life in this condition.

We suppose, then, that our ancestral Protozoon ac-

quired the habit of taking in food material in excess of

its own requirements, and of dividing into two parts

whenever it reached a certain maximum size. Here

again we must, for the sake of simplicity, ignore the

facts that even a Protozoon is by no means a simple

organism, and that its division, usually at any rate, is a

very complicated process. Each of the daughter-cells

presently separates from its sister-cell and goes its own

way as a complete individual, still a Protozoon. It

Seems not improbable that the separation may be due

to the renewed stimulus of hunger, impelling each cell

to wander actively in search of food. In some cases,

however, the daughter-cells remain together and form a

colony, and probably this habit has been rendered pos-

sible by a sufficient accumulation of surplus energy in

the form of food-yolk on the part of the parent render-

ing it unnecessary for the daughter-cells to separate in

search of food at such an early date. One of the forms

of colony met with amongst existing Protozoa is the

hollow sphere, as we see it, for example, in Spherozoum

and Volvox, and it is highly probable that the assump-

tion of this form is due largely, if not entirely, to what

are commonly called mathematical causes, though we

are not in a position to say exactly what these causes

may be. The widespread occurrence of the blastosphere

or blastula stage in ontogeny is a sufficiently clear indi-

cation that the hollow, spherical Protozoon colony

formed a stage in the evolution of the higher animals.

By the time our ancestral organism has reached this

stage, and possibly even before, a new complication has

arisen. The cells of which the colony is composed no

longer remain all alike, but become differentiated, pri-

158 THE AMERICAN NATURALIST [ Von. XLIX

marily into two groups, which we distinguish as somatic-

cells and germ-cells respectively.

From this point onwards evolution ceases to be a

really continuous process, but is broken up into a series

of ontogenies, at the close of each of which the organism

has to go back and make a fresh start in the unicellular

condition, for the somatic cells sooner or later become

exhausted in their conflict with the environment and

perish, leaving the germ-cells behind to take up the run-

ning. That the germ-cells do not share the fate of the

somatic cells must be attributed to the fact that they take

no part in the struggle for existence to which the body

is exposed. They simply multiply and absorb nutriment

under the protection of the body, and therefore retain

their potential energy unimpaired. They are in actual

fact, as is so often said, equivalent to so many protozoa,

and, like the protozoa, are endowed with a potential

immortality.

We know that, if placed eee suitable conditions, or

in other words, if exposed to the proper environmental

stimuli, these germ-cells will give rise to new organisms,

like that in the body of which they were formerly en-

closed. One of the necessary conditions is, with rare

exceptions, the union of the germ-cells in pairs to form

zygotes or fertilized ova; but I propose, in the first in-

stance, for the sake of simplicity, to leave out of account

the existence of the sexual process and the results that

follow therefrom, postponing the consideration of these

to a later stage of our inquiry. I wish, moreover, to

make it quite clear that organic evolution must have

taken place if no such event as amphimixis had ever

occurred.

What, then, may the germ-cells be expected to do?

How are they going to begin their development? In

endeavoring to answer this question we must remember

that the behavior of an organism at any moment de-

pends upon two sets of factors—the nature of its own

constitution on one hand, and the nature of its environ-

No. 579] PROGRESSIVE EVOLUTION 159

ment on the other. If these factors are identical for

any two individual organisms, then the behavior of these

two individuals must be the same. If the germ-cells of

any generation are identical with those of the preceding

generation, and if they develop under identical condi-

tions, then the soma of the one generation must also be

identical with that of the other. Inasmuch as they are

parts of the same continuous germ-plasm—leaving out

of account the complications introduced by amphimixis

—we may assume that the germ-cells of the two genera-

tions are indeed identical in nearly every respect; but

there will be a slight difference, due to the fact that those

of the later generation will have inherited a rather larger

supply of initial energy and a slightly greater facility

for responding to stimuli of various kinds, for the

gradual accumulation of these properties will have gone

a stage further. The environment also will „be very

nearly identical in the two cases, for we know from ex-

periment that if it were not the organism could not de-

velop at all.

Throughout the whole course of its ontogeny the or-

ganism must repeat with approximate accuracy the

stages passed through by its ancestors, because at every

stage there will be an almost identical organism exposed

to almost identical stimuli. We may, however, expect

an acceleration of development and a slight additional

progress at the end of ontogeny as the result of the

operation of the law of the accumulation of surplus

energy and of the slightly increased facility in respond-

ing to stimuli. The additional progress, of course, will

probably be so slight that from one generation to the

next we should be quite unable to detect it, and doubtless

there will be frequent backslidings due to various causes.

We can thus formulate a perfectly reasonable explana-

tion of how it is that the egg first undergoes segmenta-

tion and then gives rise to a blastula resembling a hol-

3 This is, of course, a familiar idea. Compare Driesch, ‘‘ Gifford Lec-

tures,’’ 1907, p. 214.

160 THE AMERICAN NATURALIST [ Vou. XLIX

low protozoon colony; it does so simply because at every

stage it must do what its ancestors did under like condi-

tions. We can also see that progressive evolution must

follow from the gradual accumulation of additions at

the end of each ontogeny, these additions being rendered

possible by the better start which each individual gets

at the commencement of its career.

Let us now glance for a moment at the next stage in

phylogeny, the conversion of the hollow spherical proto-

zoon colony into the cclenterate type of organization,

represented in ontogeny by the process of gastrulation.

Here again it is probable that this process is explicable

to a large extent upon mechanical principles. Accord-

ing to Rhumbler,* the migration of endoderm cells into

the interior of the blastula is partly due to chemotaxis

and partly to changes of surface tension, which decreases

on the inner side of the vegetative cells owing to chem-

ical changes set up in the blastoceel fluid.

We may, at this point, profitably ask the question, Is

the endoderm thus formed an inherited feature of the

organism? The material of which it is composed is, of

course, derived from the egg-cell continuously by re-

peated cell-division, but the way in which that material

is used by the organism depends upon the environment,

and we know from experiment that modifications of the

environment actually do produce corresponding modifi-

cations in the arrangement of the material. We know,

for example, that the addition of salts of lithium to the

water in which certain embryos are developing causes

the endoderm to be protruded instead of invaginated,

so that we get a kind of inside-out gastrula, the well-

known lithium larva.

It appears, then, than an organism really inherits from

its parents two things: (1) a certain amount of proto-

plasm loaded with potential energy, with which to begin

operations, and (2) an appropriate environment. Ob-

4 Quoted by Przibram, ‘‘ Experimental Zoology,’’ English Trans., Part

I, p. 47.

No. 579] PROGRESSIVE EVOLUTION 161

viously the one is useless without the other. An egg

can not develop unless it is provided with the proper en-

vironment at every stage. Therefore, when we say that

an organism inherits a particular character from its

parents, all we mean is that it inherits the power to pro-

duce that character under the influence of certain en-

vironmental stimuli.© The inheritance of the environ-

ment is of at least as much importance as the inheritance

of the material of which the organism is composed. The

latter, indeed, is only inherited to a very small extent,

for the amount of material in the egg-cell may be almost

infinitesimal in comparison with the amount present in

the adult, nearly the whole of which is captured from

the environment and assimilated during ontogeny.

From this point of view the distinction between soma-

togenic and blastogenic characters really disappears, for

all the characters of the adult organism are acquired

afresh in each generation as a result ‘of response. to en-

vironmental stimuli during development. This is clearly

indicated by the fact that you cannot change the stimuli

without changing the result.

Time forbids us to discuss the phylogenetic stages

through which the ecelenterate passed into the cœælomate

type, the cœlomate into the chordate, and the chordate

into the primitive vertebrate. We must admit that as

yet we know nothing of the particular causes that de-

termined the actual course of evolution at each succes-

sive stage. What we do know, however, about the in-

fluence of the environment, both upon the developing

embryo and upon the adult, is sufficient to justify us in

believing that every successive modification must have

been due to a response on the part of the organism to

some environmental change. Even if the external con-

ditions remained practically identical throughout long

periods of time, we must remember that the internal

conditions would be different in each generation, because

5 Compare Dr. Archdall Reid’s suggestive essay on ‘‘ Biological Terms as

(Bedrock, January, 1914).

162 THE AMERICAN NATURALIST [ Vor. XLIX

each generation starts with a slightly increased capital

and carries on its development a little further under in-

ternal conditions modified accordingly.

At this point it may be asked, Is the response to en-

vironmental stimuli a purely mechanical one, and, if so,

how can we account for the fact that at every stage in

its evolution the organism is adapted to its environment?

We shall have to return to this question later on, but it

may be useful to point out once more that there is good

reason to believe—especially from the experimental

work of Jennings—that the response of even a unicellu-

lar organism to stimuli is to a large extent purposive;

that the organism learns by experience, by a kind of

process of trial and error, how to make the response most

favorable to itself under any given change of conditions;

in other words, that the organism selects those modes

of response that are most conducive to its own well-

being. Under the term response to stimuli we must, of

course, include those responses of the living protoplasm

which result in modifications of bodily structure, and

hence the evolution of bodily structure will, on the whole,

be of an adaptive character and will follow definite lines.

There is good reason for believing, however, that many

minor modifications in structure may arise and persist,

incidentally as it were, that have no seen as adap-

tations.

One of the most remarkable and distinctive features

of the lower vertebrates is the presence of gill-slits as

accessory organs of ‘respiration. These gill-slits are

clearly an adaptation to aquatic life. When the ances-

tors of the higher vertebrates left the water and took to

life on land the gills disappeared and were replaced by

lungs, adapted for air-breathing. The change must, of

course, have been an extremely gradual one, and we get

a very clear indication of how it took place in the sur-

viving dipnoids, which have remained in this respect in

an intermediate condition between the fishes and the

amphibia, possessing and using both gills and lungs.

No. 579] PROGRESSIVE EVOLUTION 163

We also know that even the most highly specialized

air-breathing vertebrates, which never live in water and

never require gills or gill-slits at all, nevertheless pos-

sess very distinct gill-slits during a certain period of

their development. This is one of the most familiar il-

lustrations of the law of recapitulation, and my only

excuse for bringing it forward now is that I wish, before

going further, to consider a difficulty—perhaps more ap-

parent than real—that arises in connection with such

cases.

It might be argued that if gill-slits arose in response

to the stimuli of aquatic life, and if these stimuli are no

longer operative in the case of air-breathing vertebrates,

then gill-slits ought not to be developed at any stage of

their existence. This argument is, I think, fully met by

the following considerations.

At any given moment of ontogenetic development the

condition of any organ is merely the last term of a series

of morphogenetic stages, while its environment at the

same moment—which, of course, includes its relation to

all the other organs of the body—is likewise merely the

last term of a series of environmental stages. We have

thus two parallel series of events to take into considera-

tion in endeavoring to account for the condition of any

part of an organism—or of the organism as a whole—at

any period of its existence:

E, E, E, ... En environmental stages,

M,M.,M, ... Mn morphogenetic stages.

Ontogeny is absolutely conditioned by the proper cor-

relation of the stages of these two series at every point,

and hence it is that any sudden change of environment

is usually attended by disastrous consequences. Thus,

after the fish-like ancestors of air-breathing vertebrates

had left the water and become amphibians, they doubt-

less still had to go back to the water to lay their eggs,

in order that the eggs might have the proper conditions

for their development.

164 THE AMERICAN NATURALIST [Von XLIX

Obviously the environment can only be altered with

extreme slowness, and one of the first duties of the

parent is to provide for the developing offspring con-

ditions as nearly as possible identical with those under

which its own development took place. It is, however,

inevitable that, as phylogenetic evolution progresses,

the conditions under which the young organism develops

should change. In the first place, the mere tendency to

acceleration of development, to which we have already

referred, must.tend to dislocate the correlation between

the ontogenetic series and the environmental series.

Something of this kind seems to have taken place in the

life-cycle of many hydrozoa, resulting in the suppression

of the free medusoid generation and the gradual degen-

eration of the gonophore. But it is probably in most

cases change in the environment of the adult that is re-

sponsible for such dislocation.

To return to the case of the amphibians. At the

present day some amphibians, such as the newts and

frogs, still lay their eggs in water, while the closely re-

lated salamanders retain them in the oviducts until they

have developed into highly organized aquatic larve, or

even what is practically the adult condition. Kammerer

has shown that the period at which the young are born

can be varied by changing the environment of the parent.

In the absence of water the normally aquatic larve of

the spotted salamander may be retained in the oviduct

until they have lost their gills, and they are then born

in the fully-developed condition, while, conversely, the

alpine salamander, of which the young are normally born

in the fully-developed state, without gills, may be made

to deposit them prematurely in water in the larval, gill-

bearing condition. :

There can be no doubt that the ancestral amphibians

laid their eggs in water in a completely undeveloped con-

dition. The habit of retaining them in the body during

their development must have arisen very gradually in

the phylogenetic history of the salamanders, the period

No. 579] PROGRESSIVE EVOLUTION 165

for which the young were retained growing gradually

longer and longer. It is obvious that this change of

habit involves a corresponding change in the environ-

mental conditions under which the young develop, and

in cases in which the young are not born until they have

reached practically the adult condition this change di-

rectly affects practically the whole ontogeny. We may

say that the series

E, E, E ... En has become

Bi Big Mie css duns

and as the change of environment must produce its ef-

fect upon the developing organism the series

M, M, M; ...° Mn will have become

Ag. Pe Cade Fe

We must remember that throughout the whole course

of phylogenetic evolution this series is constantly length-

ening, so that what was the adult condition at one time

becomes an embryonic stage in future generations, and

the series thus represents not only the ontogeny, but

also, though in a more or less imperfect manner, the

phylogeny of the organism.

The character of each stage in ontogeny must depend

upon (1) the morphological and physiological constitu-

tion of the preceding stage, and (2) the nature of the

environment in which development is taking place. We

can not, however, distinguish sharply between those two

sets of factors, for, in a certain sense, the environment

gradually becomes incorporated in the organism itself

as development proceeds, each part contributing to the

environment of all the remainder, and the influence of

this internal portion of the environment ever becoming

more and more important.

The whole process of evolution depends upon changes

of environment taking place so gradually that the neces-

sary self-adjustment of the organism at every stage is

possible. In the case of our amphibia the eggs could

166 THE AMERICAN NATURALIST [ Von. XLIX

possibly undergo the first stages of development, the

preliminary segmentation, within the oviduct of the

parent just as well as in the water, for in both cases

they would be enclosed in their envelopes, and the

morphological differences between the early stages in

the two cases might be expected to be quite insignificant.

But it must be the same at each term of the series, for

each term is built upon the foundation of the preceding

one, and the whole process takes place by slow and im-

perceptible degrees.

It is true that by the time we reach the formation of

the vestigial gill-slits in the embryo of one of the higher

vertebrates the environmental conditions are very dif-

ferent from those under which gill-slits were developed

in their aquatic ancestors. But what then? Are not

the gill-slits also very different? The changed environ-

ment has had its effect. The gills themselves are never

developed, and the gill-slits never become functional;

moreover, they disappear completely at later stages of

development, when the conditions of life become still

more different and their presence would be actually det-

rimental to their possessor. The embryo with the ves-

tigial gill-slits is, as a whole, perfectly well adapted to

its environment, though the gill-slits themselves have

ceased to be adaptive characters. They still appear be-

cause the environmental conditions, and especially the

internal conditions, which have now become far more

important than the external ones, are still such as to

cause them to do so.

I think the chief difficulty in forming a mental picture

of the manner in which evolution has taken place, and

especially in accounting for the phenomenon of recapitu-

lation in ontogeny, which is merely another aspect of

the same problem, arises from attempting to take in too

much at once. There is no difficulty in understanding

how any particular stage is related to the corresponding

stage in the previous generation, and the whole series of

stages, whether looked at from the ontogenetic or from

No. 579] PROGRESSIVE EVOLUTION 167

the phylogenetic point of view, can be nothing else but

the sum of its successive terms.

It will be convenient, before going further, to sum up

the results at which we have so far arrived from the

point of view of the theory of heredity. We have as yet

seen no reason to distinguish between somatogenic and

blastogenic characters. All the characters of the adult

animal are acquired during ontogeny as the result of

the reaction of the organism to environmental stimuli,

both internal and ‘external. All that the organism ac-

tually inherits is a certain amount of protoplasm—en-

dowed with a certain amount of energy—and a certain

sequence of environmental conditions. In so far as

these are identical in any two successive generations the

final result must be identical also, the child must re-

semble the parent; in so far as they are different the

child will differ from the parent, but the differences in

environment can not be very great without preventing

development altogether.

So far, it is clear, there has been no need to think of

the germ-cells as the bearers of material factors or de-

terminants that are responsible for the appearance of

particular characters in the adult organism; nor yet to

suppose that they are, to use the phraseology of the

mnemic theory of heredity, charged with the memories

of past generations. They have been regarded as simple

protoplasmic units, and the entire ontogeny has appeared

as the necessary result of the reaction between the or-

ganism and its environment at each successive stage of

development. This can not, however, be a complete ex-

planation of ontogeny, for if it were we should expect all

eggs, when allowed to develop under the same conditions

from start to finish, to give rise to the same adult form,

and this we know is not the case. We know also, from

observation and experiment, that the egg is in reality by

no means a simple thing but an extremely complex one,

and that different parts of the egg may be definitely cor-

related with corresponding parts of the adult body. It

168 THE AMERICAN NATURALIST [ Vou. XLIX

has been demonstrated in certain cases that the egg con-

tains special organ-forming substances definitely located

in the cytoplasm, and that if these are removed definite

parts of the organism into which the egg develops will

be missing. We know, also, that the nucleus of the germ-

cell of either sex contains—at any rate, at certain

periods—a number of perfectly well-defined bodies, the

chromosomes, and these also have been definitely cor-

related in certain cases with special features of the adult

organization.

Before we can hope to complete our mental picture of

the manner in which organic evolution has taken place,

if only in outline, it is evident that we must be able to

account for the great complexity of structure which the

germ-cells themselves have managed to acquire, and also

to form some idea of the effect. of this complication upon

the development of both the individual and the race.

We must consider the origin of cytoplasmic and nuclear

complications of the egg separately, for they appear to

be due fundamentally to two totally distinct sets of fac-

tors. In the first place we have to remember that during

oogenesis the egg-cell grows to a relatively large size

by absorbing nutrient material from the body in which

it is enclosed. It is this nutrient material that is used

for building up the deutoplasm or food-yolk. There is

good reason for believing that the character of this

nutrient material will change, during the course of evo-

lution, pari passu with the changing character of the or-

ganism by which it is supplied. Doubtless the changeis of a

chemical nature, for we know from precipitin experiments

that the body fluids of closely allied species, or even of

the two sexes of the same species, do exhibit distinctly

recognizable differences in chemical composition. It

also appears highly probable, if not certain, from such

experiments as those of Agar upon Simocephalus, that

substances taken in with the food, which bring about

conspicuous modifications of bodily structure, may at

the same time be absorbed and stored up by the egg-cells

No. 579] PROGRESSIVE EVOLUTION 169

so as to bring about corresponding changes in the adults

into which the eggs develop.

There seems therefore to be no great difficulty in com-

prehending, at any rate in a general way, how the egg

may become the repository of definite chemical sub-

stances, organ-forming substances if we like to call them

so, possibly to be classed with the hormones and en-

zymes, which will influence the development in a particu-

lar manner as soon as the appropriate conditions arise.

Unfortunately, time will not allow of our following up |

this line of thought on the present occasion, but we may

notice, before passing on, that with the accumulation of

organ-forming substances in the egg we have introduced

the possibility of changes in bodily structure, to what-

ever cause they may be due, being represented by cor-

related modifications in the germ-cells, and this is doubt-

less one of the reasons why the germ-cells of different

animals are not all alike with regard to their potentiali-

ties of development.®

We now come to the question of how the nucleus of the

germ-cell acquired its great complexity of structure. f

We are not concerned here with the origin of the dif-

ferentiation into nucleus and cytoplasm and the respec-

tive parts played by the two in the life of the cell. The

problem which we have to consider is the complication

introduced by the sexual process, by the periodically re-

curring union of the germ-cells in pairs, or, as Weis-

mann has termed it, amphimixis. This is well known

to be essentially a nuclear phenomenon, in which the so-

called chromatin substance is especially concerned, and

it is a phenomenon which must have made its appear-

ance at a very early stage of evolution, for it is exhibited

in essentially the same manner alike in the higher plants

and animals and in unicellular organisms.

Let us suppose, for the sake of argument, that when

amphimixis first took place the chromatin of each germ-

6 Compare Cunningham’s ‘‘ Hormone Theory of Heredity ’’ (Archiv für

Entwicklungsmechanik der Organismen, Bd. XXVI, Heft 3).

170 THE AMERICAN NATURALIST [Vou. XLIX

cell was homogeneous, but that it differed slightly in dif-

ferent germ cells of the same species as a result of ex-

posure to slightly different conditions during its past

history. What would be likely to happen when two dif-

ferent samples of chromatin came together in the zygote?

The result would surely depend upon the interaction of

the complex colloidal multimolecules of which the chro-

atin is composed. Various possibilities would arise.

(1) The two samples might differ in such a way as to

act as poisons to one another, disturbing each other’s

molecular equilibrium to such an extent that neither

could survive. This is possibly what happens when an

ovum is fertilized by a spermatozoon of a distinct

species, though there are, of course, exceptions. (2)

They might be so alike as to be able to amalgamate

more or less completely, so that there would simply be

an increase of chromatin of possibly more or less modi-

fied constitution. (3) They might continue to exist side

by side, each maintaining its own individual character.

In the third case the union of the two different samples

would give rise to a mass of chromatin of twofold na-

ture, and repetition of the process from generation to

generation would, as Weismann has shown, result in

ever-increasing heterogeneity, until the chromatin came

to consist of a great number of different concrete par-

ticles, each of which might conceivably differ from all

the others. But when two heterogeneous masses of

chromatin meet in the zygote there may be all sorts of

mutual attractions and repulsions between the different

colloidal multimolecules, for all three of our supposed

cases may arise simultaneously, and thus the results may

become extremely complicated.

The chromatin of the germ-cells in all existing or-

ganisms is undoubtedly heterogeneous, and this hetero-

geneity may be to some extent visibly expressed in its

arrangement in more or less multiform chr omes

during mitosis. We may provisionally accept Weis- —

mann’s view that these chromosomes are themselves

No. 579] PROGRESSIVE EVOLUTION : 171

heterogeneous, being composed of chromomeres or ids,

which in their turn are composed of determinants.

All this complexity of structure may be attributed to

the effects of oft-repeated amphimixis, a view which is

supported in the most striking manner by the fact that

the nucleus in all ordinary somatic cells (in animals and

in the diploid generation of plants) has a double set of

chromosomes, one derived from the male and the. other

from the female parent, and by the well-known phe-

nomenon of chromatin reduction which always precedes

amphimixis.

When we approach the problem of heredity from the

experimental side we get very strong evidence of the

existence in the germ-plasm of definite material sub-

stances associated with the inheritance of special char-

acters. Mendelian workers generally speak of these

substances as factors, but the conception of factors is

evidently closely akin to that of Weismann’s hypothetical

determinants. The cytological evidence fits in very well

with the view that the factors in question may be definite

material particles and it is quite possible that such par-

ticles may have a specific chemical constitution to which

their effects upon the developing organism are due.

From our point of view the interesting thing is the

possibility that arises through the sexual process of the

permutation and combination of different factors de-

rived from different lines of descent. A germ-cell may

receive additions to its collection of factors or be subject

to subtractions therefrom, and in either case the result-

ing organism may be more or less conspicuously

modified.

By applying the method of experimental hybridization

a most fruitful and apparently inexhaustible field of re-

search has been opened up in this direction, in the de-

velopment of which no one has taken a more active part

than the present President of the British Association.

There can not be the slightest doubt that a vast number

of characters are inherited in what is called the Mende-

172 ` THE AMERICAN NATURALIST [ Vou. XLIX

jan manner, and, as they are capable of being separately

inherited and interchanged with others by hybridization,

we are justified in believing that they are separately

represented in the germ-cells by special factors. Im-

portant as this result is, I believe that at the present

time there exists a distinct danger of exaggerating its

significance. The fact that many new and apparently

permanent combinations of characters may arise through

hybridization, and that the organisms thus produced

have all the attributes of what we call distinct species,

does not justify us in accepting the grotesque view—as it

appears to me—that all species have arisen by crossing,

or even the view that the organism is entirely built up

of separately transmissible ‘‘unit characters.’’

Bateson tells us that

Baur has for example crossed species so unlike as Antirrhinum majus

and molle, forms differing from each other in almost every feature

of organization,

Surely the latter part of this statement can not be

correct, for after all Antirrhinum majus and molle are

both snapdragons, and exhibit all the essential charac-

ters of snapdragons.

I think it is a most significant fact that the only char-

acters which appear to be inherited in Mendelian fashion

are comparatively trivial features of the organism which

must have arisen during the last stages of phylogeny.

This is necessarily the case, for any two organisms suffi-

ciently nearly related to be capable of crossing are iden-

tical as regards the vast majority of their characters.

It is only those few points in which they differ that re-

main to be experimented on. Moreover, the characters

in question appear to be all non-adaptive, having no ob-

vious relation to the environment and no particular value

in the struggle for existence. They are clearly what

Weismann calls blastogenic characters, originating in

the germ-plasm, and are probably identical with the mu-

tations of de Vries. These latter are apparently chro-

No. 579] PROGRESSIVE EVOLUTION 173

matin-determined characters, for, as Dr. Gates has re-

cently shown in the case of nothera, mutation may

result from abnormal distribution of the chromosomes in

the reduction division."

We have next to inquire whether or not the Mendelian

results are really in any way inconsistent with the gen-

eral theory of evolution outlined in the earlier part of

this address. Here we are obviously face to face with

the old dispute between epigenesis and preformation.

The theory of ontogeny which I first put forward is

clearly epigenetic in character, while the theory of unit

gis aeaie represented in the germ-cells by separate

‘“factors,’’ is scarcely less clearly a theory of preforma-

tion, and of course the conception of definite organ-form-

ing substances in the cytoplasm falls under the same

category. The point which I now wish to emphasize is

that the ideas of epigenesis and preformation are not

not inconsistent with one another, and that, as a matter

of fact, ontogenetic development is of a dual nature, an

epigenesis modified by what is essentially preformation.

We have already dealt briefly with the question of

organ-forming substances in the cytoplasm, and it must,

I think, be clear that the existence of these is in no way

incompatible with a fundamental epigenesis. We shall

find directly that the same is true of Mendelian ‘‘fac-

tors’? or Weismannian ‘‘determinants.’’

We have seen that it is possible to conceive of even

a complex organism as inheriting nothing from its parent

but a minute speck of protoplasm, endowed with poten-

tial energy, and a sequence of suitable environments,

the interaction between the two bringing about a similar

result in each suceeding generation, with a slow progres-

sive evolution due to the operation of the law of accu-

mulation of surplus energy. If any of the conditions of

development are changed the result, as manifested in

the organization of the adult, must undergo a corre-

sponding modification. Suppose that the chromatin sub-

7 Quarterly Journal of Microscopical Science, Vol. LIX, p. 557.

174 THE AMERICAN NATURALIST [ Von. XLIX

stance of the zygote is partially modified in molecular

constitution, perhaps by the direct action of the environ-

ment, as appears to happen in the case of Tower’s ex-

periments on mutation in the potato beetle, or by the in-

troduction of a different sample of chromatin from an-

other individual by hybridization. What is the germ-

plasm now going to do? When and how may the

changes that have taken place in its constitution be ex-

pected to manifest themselves in the developing or-

-ganism? !

Let us consider what would be likely to happen in the

first stages of ontogeny. If the germ-plasm had re-

mained unaltered the zygote would have divided into

blastomeres under the stimuli of the same conditions,

both internal and external, as those under which the

corresponding divisions took place in preceding genera-

tions. Is the presence of a number of new colloidal mul-

timolecules in the germ-plasm going to prevent this?

The answer to this question probably depends partly

upon the proportion that the new multimolecules bear

to the whole mass, and partly upon the nature of the

modification that has taken place. If the existence of

the new multimolecules is incompatible with the proper

functional activity of the germ-plasm as a whole there

is an end of the matter. The organism does not. de-

velop. If it is not incompatible we must suppose that

the zygote begins its development as before, but that

sooner or later the modification of the germ-plasm will

manifest itself in the developing organism, in the first

instance as a mutation. In cases of hybridization we

may get a mixture in varying degrees of the distinguish-

ing characters of the two parent forms, or we may get

complete dominance of one form over the other in the

hybrid generation, or we may even get some new form,

the result depending on the mutual reactions of the dif-

ferent constituents of the germ-plasm.

The organism into which any zygote develops must be

No. 579] PROGRESSIVE EVOLUTION 175

a composite body deriving its blastogenic characters

from different sources; but this cannot affect its funda-

mental structure, for the two parents must have been

alike in all essential respects or they could not have in-

terbred, and any important differences in the germ-

plasm must be confined to the ‘‘factors’’ for the differen-

tiating characters. The fundamental structure still de-

velops epigenetically on the basis of an essentially simi-

lar germ-plasm and under essentially similar conditions

as in the case of each of the two parents, and there is no

reason to suppose that special ‘‘factors’’ have anything

to do with it.

We thus see how new unit characters may be added

by mutation and interchanged by hybridization while the

fundamental constitution of the organism remains the

same and the epigenetic course of development is not

seriously affected. All characters that arise in this way

must be regarded, from the point of view of the or-

ganism, as chance characters due to chance modifications

of the germ-plasm, and they appear to have compara-

tively little influence upon the course of evolution.

One of the most remarkable features of organic evo-

lution is that it results in the adaptation of the organism

to its environment, and for this adaptation mutation and

hybridization utterly fail to account. Of course the ar-

gument of natural selection is called in to get over this

difficulty. Those organisms which happen to exhibit

favorable mutations will survive and hand on their ad-

vantages to the next generation, and so on. It has fre-

quently been pointed out that this is not sufficient. Mu-

tations occur in all directions, and the chances of a favor-

able one arising are extremely remote. Something more

is wanted, and this something, it appears to me, is to be

found in the direct response of the organism to environ-

mental stimuli at all stages of development, whereby in-

dividual adaptation is secured, and this individual adap-

tation must arise again and again in each succeeding

176 THE AMERICAN NATURALIST — [Vou. XLIX

generation. Moreover, the adaptation must, as I pointed

out before, tend to be progressive, for each successive

generation builds upon a foundation of accumulated ex-

perience and has a better start than its predecessors.

Of course natural selection plays its part, as it must

in all cases, even in the organic world, and I believe

that in many cases—as, for example, in protective re-

semblance and mimicry—that part has been an extremely

important one. But much more important than natural

selection appears to me what Baldwin® has termed

‘‘ Functional Selection,” selection by the organism itself,

out of a number of possible reactions, of just those that

are required to meet any emergency. As Baldwin puts

it, ‘‘It is the organism which secures from all its over-

produced movements those which are adaptive and bene-

ficial.’ Natural selection is here replaced by intelligent

selection, for I think we must agree with Jennings® that

we can not make a distinction between the higher and

the lower organisms in this respect, and that all purposive

reactions, or adjustments, are essentially intelligent.

Surely that much-abused philosopher, Lamarck, was

not far from the truth when he said, ‘‘The production

of a new organ in an animal body results from a new

requirement which continues to make itself felt, and

from a new movement which this requirement begets

` and maintains.’ Is not this merely another way of

saying that the individual makes adaptive responses to

environmental stimuli? Where so many people fall foul

of Lamarck is with regard to his belief in the inheri-

tance of acquired characters. But in speaking of ac-

quired characters Lamarck did not refer to such modifi-

cations as mutilations; he was obviously talking of the

gradual self-adjustment of the organism to its environ-

ment,

8** Development and Evolution °’? (New York, 1902), p. 87.

9‘* Behavior of the Lower Organisms °? (New York, 1906), pp. 334, 335.

10‘* Histoire naturelle des Animaux sans Vertébres,’’ Tom. I, 1815, P.

185.

No. 579] PROGRESSIVE EVOLUTION 177

We are told, of course, that such adjustments will only

be preserved so long as the environmental stimuli by

which they were originally called for continue to exer-

cise their influence. Those who raise this objection are

apt to forget that this is exactly what happens in evolu-

tion, and that the sine qua non of development is the

proper maintenance of the appropriate environment,

both internal and external. Natural selection sees to it

that the proper conditions are maintained within very

narrow limits.

A great deal of the confusion that has arisen with re-

gard to the question of the inheritance of acquired char-

acters is undoubtedly due to the quite unjustifiable limi-

tation of the idea of ‘‘inheritance’’ to which we have ac-

customed ourselves. The inheritance of the environ-

ment is, as I have already said, just as important as the

inheritance of the material foundation of the body, and

whether or not a newly acquired character will be in-

herited must depend, usually at any rate, upon whether

or not the conditions under which it arose are inherited.

It is the fashion nowadays to attach very little impor-

ance to somatogenic characters in discussing the problem

of evolution. The whole fundamental structure of the

body must, however, according to the epigenetic view,

be due to the gradual accumulation of characters that

arise as the result of the reactions of the organism to its

environment, and are therefore somatogenic, at any rate

in the first instance, though there is reason to believe

that some of them may find expression in the germ-cells

in the formation of organ-forming substances, and pos-

sibly in other ways. Blastogenic characters which ac-

tually originate in the germ-cells appear to be of quite

Secondary importance.

We still have to consider the question, How is it that

organic evolution has led to the formation of those more

or less well-marked groups of organisms which we call

species? We have to note in the first place that there

178 THE AMERICAN NATURALIST [Vou. XLIX

is no unanimity of opinion amongst biologists as to what

a species is. Lamarck insisted that nature recognizes

no such things as species, and a great many people at

the present day are, I think, still of the same opinion.

In practise, however, every naturalist knows that there

are natural groups to which the vast majority of indi-

viduals can be assigned without any serious difficulty.

Charles Darwin maintained that such groups arose,

under the influence of natural selection, through gradual

divergent evolution and the extinction of intermediate

forms. To-day we are told by de Vries that species

originate as mutations which propagate themselves with-

out alteration for a longer or shorter period, and by

Lotsy that species originate by crossing of more or less

distinct forms, though this latter theory leaves quite un-

solved the problem of where the original forms that

crossed with one another came from.

I think a little reflection will convince us that the origin

of species is a different problem from that of the cause

of progressive evolution. We can scarcely doubt, how-

ever, that Darwin was right in attributing prime im-

portance to divergent evolution and the disappearance

of connecting links. It is obvious that this process must

give rise to more or less sharply separated groups of in-

dividuals to which the term species may be applied, and

that the differences between these species must be at-

tributed ultimately to differences in the response of the

organism to differing conditions of the environment. It

may be urged that inasmuch as different species are

often found living side by side under identical conditions

the differences between them can not have arisen in this

way, but we may be quite certain that if we knew enough

of their past history we should find that their ancestors

had not always lived under identical conditions.

The case of flightless birds on oceanic islands is par-

ticularly instructive in this connection. The only satis-

factory way of explaining the existence of such birds is

No. 579] PROGRESSIVE EVOLUTION 179

by supposing that their ancestors had well-developed

wings, by the aid of which they made their way to the

islands from some continental area. The conditions of

the new environment led to the gradual disuse and con-

sequent degeneration of the wings until they either be-

came useless for flight or, in the case of the moas, com-

pletely disappeared. It would be absurd to maintain

that any of the existing flightless birds are specifically

identical with the ancestral flying forms from which

they are descended, and it would, it appears to me, be

equally absurd to suppose that the flightless species arose

by mutation or by crossing, the same result being pro-

duced over and over again on different islands and in

different groups of birds. This is clearly a case where

the environment has determined the direction of evo-

lution.

In such cases there is not the slightest ground for be- .

lieving that crossing has had anything whatever to do

with the origin of the different groups to which the term

species is applied; indeed, the study of island faunas in

general indicates very clearly that the prevention of

crossing, by isolation, has been one of the chief factors

in the divergence of lines of descent and the consequent

multiplication of species, and Romanes clearly showed

that even within the same geographical area an identical

result may be produced by mutual sterility, which is the

cause, rather than the result, of specific distinction.

Species, then, may clearly arise by divergent evolu-

tion under changing conditions of the environment, and

may become separated from one another by the extinc-

tion of intermediate forms. The environmental stimuli

(including, of course, the body as part of its own en-

vironment) may, however, act in two different ways:

(1) Upon the body itself, at any stage of its development,

tending to cause adaptation by individual selection of the

most appropriate response; and (2) upon the germ-

plasm, causing mutations or sudden changes, sports, in

180 THE AMERICAN NATURALIST [ Von. XLIX

fact, which appear to have no direct relation whatever

to the well-being of the organism in which they appear,

but to be purely accidental. Such mutations are, of

course, inherited, and, inasmuch as the great majority of

specific characters appear to have no adaptive signifi-

cance, it seems likely that mutation has had a great deal

to do with the origin of species, though it may have had

very little to do with progressive evolution.

Similarly with regard to hybridization, we know that

vast numbers of distinct forms, that breed true, may be

produced in this way, but they are simply due to recom-

binations of mutational characters in the process of am-

phimixis, and have very little bearing upon the problem

of evolution. If we like to call the new groups of indi-

viduals that originate thus ‘‘species,’’ well and good, but

it only means that we give that name, as a matter of

convenience, to any group of closely related individuals

which are distinguished by recognizable characters from

the individuals of all other groups, and which hand on

those characters to their descendants so long as the con-

ditions remain the same. This, perhaps, is what we

should do, and just as we have learned to regard indi-

viduals as the temporary offspring of a continuous

stream of germ-plasm, so we must regard species as the

somewhat more permanent but nevertheless temporary

offshoots of a continuous line of progressive evolution.

Individuals are to species what the germ-plasm is to in-

dividuals. One species does not arise from another

species, but from certain individuals in that species,

and when all the individuals become so specialized as to

lose their power of adaptation, then changes in the en-

vironment may result in the extinction of that line of

descent.

It is scarcely necessary to point out that no explana-

tion that we are able to give regarding the causes of

either phylogenetic or ontogenetic evolution can be com-

plete and exhaustive. Science can never hope to get to

No. 579] PROGRESSIVE EVOLUTION 181

the bottom of things in any department of knowledge;

there is always something remaining beyond our reach.

If we are asked why an organism chooses the most ap-

propriate response to any particular stimulus, we may

suggest that this is the response that relieves it from

further stimulation, but we cannot say how it learns to

choose that response at once in preference to all others.

If we are asked to account for some particular muta-

tion, we may say that it is due to some modification in

the constitution or distribution of the chromosomes in

the germ-cells, but even if we knew exactly what that

modification was, and could express it in chemical terms,

we could not really say why it produces its particular

result and no other, any more than the chemist can say

why the combination of two gases that he calls oxygen

and hydrogen gives rise to a liquid that he calls water.

There is one group of ontogenetic phenomena in par-

ticular that seems to defy all attempts at mechanistic

interpretation. I refer to the phenomena of restitution,

the power which an organism possesses of restoring

the normal condition of the body after it has been vio-

lently disturbed by some external agent. The fact that

a newt is able to regenerate its limbs over and over

again after they have been removed, or that an echino-

derm blastula may be cut in half and each half give rise

to a perfect larva, is one of the most surprising things

in the domain of biological science. We can not, at

present, at any rate, give any satisfactory mechanistic

explanation of these facts, and to attribute them to the

action of some hypothetical entelechy, after the manner

of Professor Hans Driesch, is simply an admission of

our inability to do so. We can only say that in the

course of its evolution each organism acquires an indi-

viduality or wholeness of its own, and that one of the

fundamental properties of living organisms is to main-

tain that individuality. They are able to do this in a

variety of ways, and can sometimes even replace a lost

182 THE AMERICAN NATURALIST [ Vou. XLIX

organ out of material quite different from that from

which the organ in question is normally developed, as

in the case of the regeneration of the lens of the eye

from the iris in the newt. That there must be some

mechanism involved in such cases is, of course, self-evi-

dent, and we know that that mechanism may sometimes

go wrong and produce monstrous and unworkable re-

sults; but it is, I think, equally evident that the organism

must possess some power of directing the course of

events, so as generally to secure the appropriate result;

and it is just this power of directing chemical and phys-

ical processes, and thus employing them in its own inter-

ests, that distinguishes a living organism from an inani-

mate object.

In conclusion I ought, perhaps, to apologize for the

somewhat dogmatic tone of my remarks. I must ask

you to believe, however, that this does not arise from

any desire on my part to dogmatize, but merely from the

necessity of compressing what I wished to say into a

totally inadequate space. Many years of patient work

are still needed before we can hope to solve, even ap-

proximately, the problem of organic evolution, but it

seemed to me permissible, on the present occasion, to

indulge in a general survey of the situation, and see how

far it might be possible to reconcile conflicting views

and bring together a number of ideas derived from many

sources in one consistent theory.

SHORTER ARTICLES AND DISCUSSION

THE ORIGIN. OF A NEW EYE-COLOR IN DROSOPHILA

REPLETA AND ITS BEHAVIOR IN HEREDITY

‘

In September, 1913, a new eye-color ‘‘scarlet,’’ appeared in

one of my cultures of Drosophila repleta Wollaston. The new

eye color is a bright scarlet when first hatched and darkens but

little with age. The eyes of the wild flies, on the other hand, are

a deep mahogany which darken soon after hatching until they are

almost black. This last statement is true of the stocks I have

found in New York City, Woods Hole, Mass., North Manchester,

Ind., Brazil, Ind., and Terre Haute, Indiana. The eye-color of

the newly emerged mutant corresponds to the color chart in

Ridgeway’s Color Guide, Plate VII, No. 11 (Boston, 1886). The

large scarlet eye in contrast to the dark body of the fly makes

the new repleta an object of great beauty as contrasted with the

wild species.

The new fly in all probability came from heterozygous stock, as

is shown by the following facts. The original stock was obtained

by exposing a fruit jar with banana in a fruit store in North

Manchester, Indiana, September 10, 1913. From this bottle!

there hatched 777 92 and 206 ¢¢ of Drosophila ampelophila.

On November 5 appeared repletas. November 15, I found one

scarlet female among 35 repletas. November 16, one scarlet

male among 20 flies. November 17, one scarlet female among

25 flies. Some of the virgin flies were isolated and four scarlets

appeared on January 24. My assistant, Mr. Powell, also isolated

some of the original stock and later found three scarlets. This

would seem to show that the stock had mutated some time before

‘being taken into captivity. During September, 1915, I set a

great many traps in the region where the above stock was taken,

1I should call attention to the aberrant sex ratio found here in Droso-

phila ampelophila. Culture from this stock later gave 491 99 and 45 gg.

I have data on the sex-ratio in this species for over three years and in

many different stocks. With this exception I have found it approaching

equality. I mated 25 pairs of virgin flies from this stock with the expecta-

tion of finding a sex-linked lethal but in each of the twenty-five bottles the

sex-ratio was practically one of equality. The subsequent history of the

stock was not followed, owing to an accident.

183

184 THE AMERICAN NATURALIST [ Vou. XLIX

with the hope of finding whether or not scarlet was common in

this region. I have bred many of the stocks since that time, but

so far no scarlets have appeared.?

BEHAVIOR OF SCARLET IN HEREDITY

One of the original virgin scarlet females was mated to a

scarlet male. The union was fruitful and a pure scarlet race

was produced which has bred true since that time. The sexes are

easily distinguished, the life cycle is about thirty days, and after

long experience I have found it comparatively easy to breed

this fly in captivity.

Scarlet was crossed to a wild stock which had been taken about

four months previously in Terre Haute. This stock bred true

to black eyes. The flies were studied in mass culture and virgin

flies were used in crossing (the sexes were separated every 18

hours). The offspring, which had eyes like the wild stock, were

mated in mass culture for the F, generation. The apse

tables give the results from the crosses.

TABLE I

SHOWING THE RESULT IN THE F, GENERATION OF CROSSING SCARLET

ox Wop g

N Scarlet | Scarlet Black Black Total Total Total Total

-~ Cea 29 ad 99 ad 99 Scarlet | Black

1 57 64 139 159 196 223 121 298

2 42 27 126 85 168 112 69 211

3 73 31 148 132 221 163 104

4 61 61 210 166 271 122 376

5 72 73 263 193 266 145

6 ss RE ai nee _ — 175 530

7 pts coe sis ase le —_ 52 182

Total, 305 256 886 735 1,191 991 788 2,333

These tables bring out the fact that the new eye color is a

simple Mendelian recessive character since it approximates the

2 It is only fair to state that I had made earlier attempts to find muta-

tions in this species. In the fall of 1911 a female of D. repleta was taken

in the Zoological laboratory at Columbia University and from this a stock

was obtained which was kept going on well-ripened bananas with more or

less difficulty for more than a year. It was comparatively easy to keep the

colony going in the same bottle by adding food from time to time but

difficulty was experienced in founding new colonies. During the period of

observation I examined many hundreds of repletas without finding a single

mutation. ms ;

No.579] SHORTER ARTICLES AND DISCUSSION 185

TABLE II

SHOWING THE RESULT IN THE F, GENERATION OF CROSSING SCARLET

XxX WILD 2

N Scarlet Scarlet Black Black Total Total Total | Total

2 ad 29 ley ge PF ge Scarlet | Black

8 34 37 111 118 145 155 71 | 229

9 31 56 134 165 165 221 87 299

10 38 46 121 137 159 183 | 258

11 ai aon are S 102 300

12 69 91 216 257 285 348 160 473

13 22 19 39 61 61 80 41 141

14 — — — — — — 80 264

15 oe bas wad ee 25 — 74 230

Totall 194 | 249 | 621 | 738 | 815 987 | 699 | 2,194

expected ratio of three to one. There appeared in the F, gen-

eration from the scarlet male a total of 699 scarlets and 2,194

blacks,—a ratio of 3.14 black to one scarlet. From the scarlet

female there appeared in the F, generation 788 scarlets and

2,333 blacks,—a ratio of 2.96 black to one scarlet. It is to be

noted that the sex ratio is practically one of equality.

Roscoe R. HYDE

A WING MUTATION IN A NEW SPECIES OF

DROSOPHILA

A NEW wing mutation which appeared in my cultures of

Drosophila confusa Auct. (not Staeg.) is characterized by the

fact that the wings curve upward at an angle of about 45 degrees

from the region of the tip of the abdomen. The new wing re-

sembles somewhat the shape of a petal of the rose and is easily

distinguished from the wild species since the wings of the wild

fly project horizontally over and beyond the abdomen, as is

characteristic of the diptera. I shall refer to the new fly as

: jaunty C.2

The wild stock from which jaunty C arose was taken in an

orchard on the Coss farm about seven miles south of North

Manchester, Indiana, in September, 1913. The original stock

was bred in a glass vial to which fresh banana was added from

time to time. Several stock bottles were made up from this

1 The wing is like that of jaunty in D. ampelophila and is here designated

jaunty C( = confusa) to call attention to this resemblance.

186 THE AMERICAN NATURALIST [Vou. XLIX

bottle. All the offspring were examined with a hand lens but no

unusual forms appeared until the fourth or fifth generation when

jaunty C was discovered. Subsequently three or four similar

mutants were found in the cultures, which would seem to indi-

cate that they arose from heterozygous stock. Pure stock was

obtained by crossing to the wild flies and ‘‘extracting.”’

When jaunty C is crossed to the wild type all of the flies of the

F, generation have long wings. No exact record was kept but

this statement is true of several hundred that were observed.

The sex ratio was practically one of equality. In the F, genera-

tion jaunty C reappeared, as shown in the following tables.

F, GENERATION FROM JAUNTY C Jf F, GENERATION FROM JAUNTY C 9

TABLE I . TABLE II

No. Jaunty C Long No. Jaunty C Long

1 40 176 3 37 124

2 38 150 4 24 145

5 66 308

Totalc?. 78 326 127 577

Among the grandchildren from the jaunty C male the ratio is

one jaunty C to 4.18 long, while among the grandchildren of the

reciprocal cross the ratio is one jaunty C to 4.54 long. The

sex ratios were near equality.

These ratios do not conform very closely to Mendelian ex-

pectations, but I have found this species very hard to breed, and

since the flies were bred in mass cultures it may be that jaunty C

was repped affected by crowding of the larve.

to carry out more elaborate experiments during

the summer of 1914 and had about twenty bottles of the new

stock in pure culture and also some wild stocks, when the flies

commenced to die during the hot days in the latter part of May

and June. Finally the last individual disappeared despite all

the care that I could exercise, and no larve were left in the

bottles to take their place. As the June temperature increased

other stocks failed to reproduce and died out. That the warm

weather was in all probability responsible is shown by the results

which were obtained by placing the stocks in a refrigerator. All

those stocks placed in the refrigerator remained very active and

continued to reproduce while all the stocks left on the outside

died out with the exception of the wild stocks of D. ampelophila.

No.579] SHORTER ARTICLES AND DISCUSSION 187

But even ampelophila does not thrive when the temperature

reaches 100°.

During September, 1914, I took several wild stocks of confusa

from the same region, and have examined many of the offspring

with the hopes of again finding this form but so far no unusual

forms have appeared.

Roscoe R. HYDE

MUTATIONS IN TWO SPECIES OF DROSOPHILA

In our cultures of Drosophila, mutations have appeared re-

cently in two species other than Drosophila ampelophila. Both

mutants are characterized by abnormalities in wing venation.

One of them has irregular extra veins in the axillary cell, and

hence may be called axillary. The other is distinguished most

clearly by the fusion of the distal end of the second vein to the

costa, producing a double vein for a considerable distance, for

which reason it is called confluent. In each of these cases other

abnormal characters are associated with those mentioned, but

they are relatively inconspicuous.

The mutant called axillary arose in normal stock of D. tri-

punctata Loew, which has been bred in the laboratory for about

six generations. This stock was kept in milk bottles and fed

on banana, but received no artificial treatment except anesthesia

with ether once per generation. Axillary behaves as a simple

Mendelian recessive when crossed with normal, and breeds true

in pure cultures.

The mutant called confluent appeared in a culture of an un-

described species of Drosophila, referred to as ‘‘species B” by

one of us in a paper describing its chromosomes.’ Confluent is

a dominant character (i. e., it appears in the heterozygous fly),

and so far as we have been able to ascertain it never occurs in

the homozygous condition. At least no flies homozygous for it

have as yet been found, although numerous matings have been

made which should have produced them. The original fly show-

ing the confluent character (a male) appeared in a stock culture,

all of his brothers and sisters being normal. He was hetero-

zygous, as shown by matings with normal females, which gave

15 normal and 13 confluent offspring. Seven of the latter, bred

1¢Chromosome Studies in the Diptera,’’ I, Jour. Exp. Zool, XVII. p.

45, 1914.

188 THE AMERICAN NATURALIST [ Von. XLIX

to normals in pairs, gave 778 normals and 691 confluents, show-

ing that they too were heterozygous.? The remaining six were

bred together in pairs and gave 261 normal and 431. confluent

progeny, or a ratio of approximately 1:2 instead of the expected

1:3. According to expectation one third of the 431 confluent

offspring in this generation should be homozygous, and random

matings in pairs (confluent by confluent), should give in five

cases out of nine only confluent progeny. Sixteen such matings

have been made, none of which gave this result; instead each gave

approximately one normal to two confluent, just as did the F,

heterozygotes. Normal brothers and sisters of confluent in both

generations bred en masse gave only normals, showing that none

of them was heterozygous for confluent. From these data we

conclude that the homozygous confluent flies are not viable, and

that the 1:2 ratio is due to the total absence of this class. To

our knowledge such a condition as this has been previously re-

corded in only three cases: the ‘‘aurea’’ Antirrhinum of Baur,

the yellow mouse of Cuenot, Castle, ete., and the dwarf wheat of

Vilmorin. Baur’s case differs somewhat from the others and

from ours in that the homozygous mutant class appears, but

soon dies (due to the absence of chlorophyll).

With regard to the origin of mutations the present cases are

instructive in showing that they may appear without the use

of artificial chemical or physical agents, and without hybridiza-

tion. No radium, X-rays or any chemicals whatever have been

applied to these cultures, except ether, and that only for anes-

thesia of the adult flies in each generation. The stock of D.

tripunctata from which axillary arose was obtained wild, and

had been inbred for six or seven generations; that of the other

species, from which confluent arose, is all descended from one

pair of wild flies, almost certainly brother and sister, and had —

been inbred for about twelve generations when the mutant ap-

peared. In neither case had flies from two localities been crossed ;

both stocks were pure and inbred. The only agent that could

possibly fall under suspicion as a causative one, then, is ether,

but this was used uniformly throughout the experiments, and

since only two mutations appeared among many thousands 0

flies, there is no reason for attributing them to the specific

-~ 2The offspring per pair were respectively: 242 : 194, 93 : 73, 97 : 106,

42 : 47, 133 : 125, 76 : 65, 110: 94.

No.579] SHORTER ARTICLES AND DISCUSSION 189

effect of ether ;? a conclusion made even more certain by the fact

that other species were bred during the same time, under iden- -

tical conditions, and with the same treatment, but without the

production of mutations. There is every reason to believe,

therefore, that the cause of the mutation in each case was piiely

fortuitous.

One of the aims of our work on the Drosophilas is to apply

the chromosome hypothesis to species having chromosomes dif-

ferent from those of D. ampelophila. The experimental work of

Morgan and others on D. ampelophila has pointed directly to the

conclusion that the four groups of linked factors which they have

studied are located, respectively, in the four pairs of chromo-

somes of this species. One of us has recently shown in the paper

above cited that several other species of Drosophila have chromo-

some groups differing from that of ampelophila in the number

and relative sizes of the chromosomes. Of the two species con-

sidered in the present paper, one, ‘‘species B,’’ has six pairs of

chromosomes, and should therefore, on the chromosome

hypothesis, give six series of linked characters. The other, D.

tripunctata, has four pairs of chromosomes, but of a type

essentially different from that of ampelophila, and consequently

should also give essentially different linkage series.

It is significant that both of the mutations which we have

found (axillary and confluent), are represented by similar muta-

tions in D. ampelophila. Judging from these it is not too much

to expect that among other mutations which may subsequently

arise in our species, some will likewise correspond to some of

those in ampelophila, and that upon this basis it may be possible

to homologize linkage groups, and thus more definitely homolo-

gize chromosomes in different species.

C. W. Merz anv B. S. Merz

CARNEGIE INSTITUTION,

STATION FOR EXPERIMENTAL EVOLUTION

A SEX-LINKED CHARACTER IN DROSOPHILA

REPLETA

` Drosophila repleta Wollaston (D. punctulata Loew) is a

cosmopolitan species, though only recently introduced into the

3 Professor grae 1c arrived at the same conclusion with regard to

the appearance of m in Drosophila ampelophila, Cf, AMER, NAT.,

1914, ‘‘The Failure of F his to Produce Mutations in Drosophila. ”?

190 THE AMERICAN NATURALIST [Vou. XLIX

greater part of this country. The color of the thorax (dorsal

side), in most specimens, is light gray, each hair having a dark

blackish brown spot at its, base. These spots are somewhat

irregular, and coalesce in certain regions,

In October, 1914, I collected a number of specimens of D.

repleta in the zoological laboratory at Columbia University.

About one sixth of these had a lighter color on the thorax than

that found in normal flies. The dark spots, while of about the

same number and color as usual, were much smaller and only

coalesced in a few small regions. Several females of both kinds

were isolated and their offspring observed. These females were,

in each case, mated with males of their own kind: but they were

of unknown age when captured, and several of them had prob-

ably already mated with other males. In the tables given here

‘*dark’’ refers to the normal type; ‘‘light,’’ to the new character.

TABLE I

WILD FEMALES

Offspring

Culture Mother

Dark 9 Dark g Light 9 Light #

PA Light 5 0 91 86

Q Light 12 0 50 53

ig Dark 62 76 0

U Dark 71 52 11 41

y Dark 96 50 0 41

wW Dark 36 30 0 0

X Dark 32 47 0 0

Light offspring from J and from Q, when mated together,

gave 166 lights in the next generation—no darks. Darks from

T, mated together, gave 180 darks—no lights.

On the basis of these results it is probable that the light char-

acter is a sex-linked recessive. The two light females, J and Q,

had paired with dark males before being captured, since they pro-

duced a total of 17 dark offspring: but these darks were all

females, showing either that the male-producing sperm of the

father carried no dark factor (i. e., that the factor is sex-linked),

or that the light character is dominant in the males and recessive

in the females,

Female V, since she produced light sons but no light daughters,

must, on either of the above views, have been mated only by a

dark male, and she must have been heterozygous for the light

No.579] SHORTER ARTICLES AND DISCUSSION 191

character. Female U must have had the same constitution, but

had probably mated with both kinds of males.

The crucial test between the two views was furnished by

mating a dark female from culture T to a light male from J.

The result was 25 dark females and 26 dark males. This is the

expectation if the character is sex-linked; but if light is recessive

in the females and dominant in the males, the mating should

have given only dark females and light males. The light char-

acter is, therefore, sex-linked and recessive.

A further test was made by mating heterozygous females (one

from Q and one from U) by their light brothers. Table II

shows that the result approximates to the expected 1:1:1:1

ratio.

TABLE II

Culture Dark 9 Dark of Light 9 Light #7

Q2 12 12 19 15

U1 15 17 17 13

27 29 36 28

In all the cultures it has been observed that the heterozygous

females average a little lighter in color than do the homozygous

darks. This difference, however, is not sufficient to allow an

accurate separation of the two classes. Dark males are of the

same color as the homozygous dark females.

In October, 1914, I received some banana collected by Mr. B.

Schwartz at Fayetteville, Ark. From it there hatched one

repleta male, which was of the light type. Bred to light females

from culture J, this male produced 133 offspring, all of which

were light.

An examination of the pinned material in my own collection

and that of the American Museum of Natural History has shown

the existence of a number of specimens which seem to belong to

the light type. The following table shows the distribution of the

specimens examined. Those marked ‘‘not workable,’’ are not

in good enough condition to be classified with certainty.

The table shows the light form to oceur in New York, Alabama,

Arkansas, California, and Cuba. The Cuban record is of in-

terest because the date, 1904, is the earliest of the seven cases.

192 THE AMERICAN NATURALIST [ Von. XLIX

TABLE III

Locality Date Dark Light Not Workable

Woods Hole, Mass........ June, 1913 3 0

New: York; N: Ya cctv: Feb., 1913 2 1

eee June, 1913 3 1

fe eeu EA ct., 19 83% 17%

Washington, D. C........ ct., 1912 3 0

N. Manchester, Ind....... Sept., 1913 2 0

LIRGLOBR, Fk. cs ap oe ees Mar., 1914 1 0

Gene. Als o Oi ewe ie June, 1914 3 1

Pavestevilie, FP Oct., 1914 0 1

Claremont, Calif......... May, 1914 4 0

ewport, Califs,:. 6.0062: Sept., 1913 2 6 1

Berkeley, Calif........... 191 2 0

ear ana, Cuba...... Nov., 1904 3 3 3

Guantanamo, Cuba....... Dec., 1913 5 0 1

u, Dominica........ June, 1911 5 0 1

At that time D. repleta seems to have been rather rare in the

United States.

A. H. STURTEVANT

COLUMBIA UNIVERSITY,

January 1915

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AMERICAN NATURALIST

Vor. XLIX April, 1915 No. 580

ORIGIN OF SINGLE CHARACTERS AS OBSERVED

IN FOSSIL AND LIVING ANIMALS

AND PLANTS!

HENRY FAIRFIELD OSBORN

COLUMBIA UNIVERSITY

AMERICAN Museum or NATURAL HISTORY

In the last thirty years two biologies have been develop-

ing. The first is the biology of the garden, the seed pan,

the incubator, and the breeding pen. The second is the biol-

ogy of the field zoologist, of the field botanist, of the pale-

ontologist. Inasmuch as one regards unnatural processes

and the other regards natural processes it is small wonder

that these biologies have become as far apart as two re-

ligions and have developed their sects and their dog-

matists. Yet the actual facts assembled in these two

biologies as distinguished from the opinions based there-

upon can not be in the least discordant, for certainly

there is only one system of law operating in the living

world and there can be only one ultimate and final biology.

In my Harvey lecture of 1912? the search for some unity

between the observations in these two great fields of `

natural and experimental research met with some failure

1 Presidential address before The Paleontological Society of America,

delivered in the Academy of Natural Sciences of Philadelphia, Wednesday,

December 31, 1914.

2 The present address, as a comparison of zoological, paleontological, and

experimental results, is a sequel to the author’s Harvey Lecture of 1912,

entitled ‘‘The Continuous Origin of Certain Unit Characters as Observed

by a Paleontologist.’’ Harvey Soc. Vol, 7th ser., Nov., 1912, pp. 153-204.

It employs in part the same materials and illustrations.

193

194 THE AMERICAN NATURALIST [Vou. XLIX

and some success, and in the present address I am push-

ing inquiry along the same line, choosing the ‘‘single

character’’ as the point of investigation and comparison.

THE ORIGIN oF CHARACTERS

The old and ever vague problem of the origin of species

is being resolved into the newer and more definite prob-

lem of the origin of characters; in the dim future when

we know how and why new characters originate, and how

and why they transform and disappear, the problem of

natural and experimental research met with some failure

and some success, and in the present address I am push-

ing inquiry along the same line, choosing the ‘‘single

character’’ as the point of investigation and comparison.

THe ORIGIN OF CHARACTERS

The old and ever vague problem of the origin of species

is being resolved into the newer and more definite prob-

lem of the origin of characters; in the dim future when

we know how and why new characters originate, and how

and why they transform and disappear, the problem of

„Species will have long been solved and well-nigh for-

gotten. This is because a species is an assemblage or

colony of similar individuals, each individual is composed

of a vast number of somewhat similar new or old charac-

ters, each character has its independent and separate

history, each character is in a certain stage of evolution,

each character is correlated with the other characters of

the individual.

Thus in a sense the species, the subspecies, the variety,

even the individual is not a zoological unit, whereas the

‘‘character’’ when narrowed down to the last point of

divisibility seems to be a unit both among plants and ani-

mals, and a very stable one, with certain distinctive

powers, properties, and qualities of its own. We have

been approaching this new conception from many dif-

ferent lines of observation among fossil and living ani-

mals and plants, and a preliminary survey of results is _

opportune.

No. 580] ORIGIN OF SINGLE CHARACTERS 195

My chief purpose in this address is to show what one

of these ‘‘single’’ or ‘‘least characters’’? is and what pe-

culiar powers and properties it possesses which distin-

guish it from other ‘‘least characters’’ and give it a cer-

tain individuality and separateness.

If you read your Lamarck, your Darwin, your Cope

afresh with this general conception in mind you will find

that throughout biological literature the problem of

species has always been an incidental one, a sort of

by-problem and relic of the very ancient controversy as

to whether species were created suddenly or evolved

gradually. The real problem has always been, that of

the origin and development of characters. Since the

‘‘Origin of Species’? appeared the terms variation and

variability have always referred to single characters; if

a species is said to be variable we mean that a acne.

able number of the single characters or groups of char-

acters of which it is composed are variable. In botany the

long overlooked discovery of Gregor Mendel in 1865 had

as its most essential feature the separability of characters.

in heredity. In paleontology as long ago as 1869 Waagen

sharply focused our attention on single phyletic charac-

ters as of far greater significance and importance than

the matter of local races, varieties, and subspecies. The

modern observers in experimental zoology and heredity

are far less concerned with ‘‘species’’ than with the sep-

arate characters of which the individuals within a species

are composed :

Some naturalists incline to regard the ‘‘character’’ as

observable only by certain methods of their own, but it is

obvious that since all hereditary ‘‘characters’’ are germi-

nal there can be no royal or exclusive road by which we

may observe their origin and transformation, for the ger-

minal and somatic laws controlling the characters of

83 T. H. Morgan has pointed out that the term ‘‘unit character’’ was im-

properly used in my Harvey address. ‘‘Unit character’’ is a germinal

rather than a bodily term. I am treating here of single bodily or mew

characters which may be represented by one or more ‘‘unit characters’? i

Tm. i

196 THE AMERICAN NATURALIST [ Vou. XLIX

the bean,* the fly, the molluse,® the titanothere,” and

man’ are doubtless identical.

Accordingly my second purpose in this address is to show

that there is a certain harmony in the results obtained in

widely different fields of research although some of these

results may appear at first to be entirely unrelated and

even discordant.

In this attempt to discover an underlying harmony let

us first glance at the ‘‘character’’ conception in the older

natural sciences of animals and plants. CHARACTER is

the most frequently used term in the vocabulary of zool-

ogy and botany. It occurs far more often than any other

word. It has been used millions of times in systematic

definition since Linneus. Yet I do not know of any

attempt to clearly define or analyze the meaning of the

word character in its biologic sense while hundreds of

attempts have been made to define the word species.

Here again the greater is involved in the less and when-

ever we shall succeed in clearly defining ‘‘character’’ the

definition of species will follow as an incidental result.

The derivation of the word is from the Greek yapaxryp

properly an instrument for marking or graving; as ap-

plied to a person, an engraver; as commonly used, any

mark engraved or impressed, the impress or stamp on

coins and seals. It passes into the word characteristic,

which means a distinguishing feature.

The use of the word is not only universal among sys-

- tematists and experimentalists of our day, but it has be-

come one of the most elastic words in our language; the

“character”? may be as comprehensive as the general

habit of an entire organism, as where we speak of the

lethargic character of the sloth, or as restricted as a single

minute cuspule on a fossil tooth, or the barely visible

outgrowth on the surface of a fossil shell. The speed of

the race horse is a character, its tractability or viciousness

are characters, the position of the horse’s tail in running

4 Johannsen, 7 Osborn.

5 Morgan. 8 Galton.

6 Waagen, Neumayr, Hyatt, Jackson.

No. 580] ORIGIN OF SINGLE CHARACTERS 197

is a character, the color of the horse’s hair is a character,

the most minute cellular structure of the tissue of the

hoof is a character.

There is an underlying reason why this very elastic

use of the term is absolutely scientific: it is, that every

one of the above diverse applications of the term to animal

or plant life refers to some structure or some quality

which is heritable; heredity is the unifying principle.

The word is again elastic and often confusing in being

used both for germinal characters which are always herit-

able and for bodily modifications of character acquired

through habit or environment which may not be heritable.

When we speak of characters which are not known to be

hereditary we should qualify them as acquired, as modi-

fied, as due to nurture, to habit or ontogeny, to environ-

ment, as somatic rather than as germinal. Thus it is per-

fectly proper to speak of ‘‘ ontogenetic species’’ as Jordan

does, species the bodily characters of which are due to

certain habits; or of ‘‘environmental species’’ the bodily

characters of which are due to peculiarities of environ-

ment. While such modifications by habit and by en-

vironment make up a considerable part of the characters

which distinguish geographic species, subspecies and

races, it is not the origin and the transformation of these

characters which we are now considering, for that prob-

lem is comparatively simple, but rather of those under-

lying germinal and heritable characters the origin and

transformation of which is absolutely an impenetrable

mystery at the present time.

How do we know through zoology, botany, and paleon-

tology as well as through experiment that ‘‘characters’’

are real units of structure with some individual and dis-

tinct qualities and properties of their own which separate

them from all their fellows and at the same time with

certain properties of correlation which unite them with

all their fellows? i

First, we may observe in these living and extinct forms

evidences of two such antithetic principles, a principle

198 THE AMERICAN NATURALIST (Vou. XLIX

of hereditary separability whereby the body is a colony,

a mosaic of single individual and separable characters,

which is combined with a principle of hereditary correla-

tion whereby the body is a complex of minutely related

and interacting units so that functionally and structur-

ally many of these units are linked with others. Neither

principle is simple; on the contrary, both principles are

extraordinarily complex and go back to the very begin-

ning of things. Comparing more closely the observa-

tions on fossil vertebrates and invertebrates, we develop

laws of separability as well as laws of correlation, and

note that certain of these laws are far more clearly per-

‘ceived in some fields of observation than in others.

The biologic value of the field to which our Paleonto-

logical Society is especially devoted lies in the revelation

of certain of these laws and causes of the separability of

characters which are not revealed at all to the zoologist

or to the experimentalist. The paleontologist is in a

position to understand why certain characters fall apart

and become separable in cross breeding, the cause being

connected with their origin and antecedent history.

Of far broader biologic significance is the fact that all

principles which may be discovered through paleontology —

regarding the ‘‘origin of characters’’ in the hard parts,

govern alike characters of the soft parts as well as of

other structures and functions. For there can not be

one principle governing the ‘‘characters’’ of bones, an-

other those of the muscles, another those of nerves; one

principle for structures, another for functions. But

while these principles are unlimited, our comparisons

with zoology, for example, are limited to the origins of

characters which may be observed both in living and

fossil forms, namely, in the skeleton and in the teeth;

and at the outset a convenient and readily understood

distinction may be made between the origins of numerical

and of proportional characters, as follows:

No. 580] ORIGIN OF SINGLE CHARACTERS 199

Numerical Proportional

Presence and absence characters, Changes of form in the length,

e. g., numbers of teeth, of cusps breadth and height of parts.

on the teeth, of vertebra, of Quantitative changes in the hard

toes, of pads on the feet, of parts. Such characters as may

mamme. Meristic or segmental partly be expressed in indices

characters, such as may be and ratios.

partly expressed in formule.

Proportional characters may through prolonged reduc-

tion lead into numerical characters. Thus the reduction

in length of one of the toes may precede the loss of the

toe, which is a numerical change. Yet we shall see that

somewhat different principles prevail in the origins of

certain numerical characters as contrasted with the

origins of proportional characters.

1. Use of Numerical and Proportional ‘‘Characters’’ in

Classification of Mammals

In our attempt to analyze ‘‘characters’’ as they are re-

vealed to the systematic and field zoologist let us take as

two examples, first, ‘‘ The Catalogue of the Mammals of

Western Europe” by Gerrit S. Miller,’ and, second, the

‘Revision of the Mice of the genus Peromyscus,” by

Wilfred H. Osgood. It is of the utmost importance that

mammalogists, whether working among living or fossil

forms, should use similar methods of description and defi-

nition of characters, and we especially welcome in the

monumental work of Miller the fact that the definitions

and the keys are chiefly upon the hard parts which are

also available to the paleontologist. We select as typical

his treatment of the Order Carnivora and of the Family

and Genera of the wolves and foxes, which he distin-

guishes by the following enumeration of characters:

Miller’s Our Analysis of _ Kinds of

Charac

Diagnoses and Definitions

ORDER Carnivora. Characters. Chief habits, oie adaptations

—Terrestrial (rarely aquatic or of the teeth and limbs; chief char-

9 Miller, Gerrit S., ‘‘Catalogue of the Mammals of Western nhs

(Europe exclusive of Russia) in the Collection of the British Museum

London, 1912, 1019 pp.

200

semi-aquatic), non-volant, placen-

tal mammals with rather high de-

velopment of brain. The cerebral

hemispheres with distinct convolu-

unguiculate, never

tion of a modified tubereulo-sec-

torial type, the posterior upper

premolar and anterior lower molar

usually developed as special car-

nassial or flesh-eutting teeth

amily CANID#. Characters.—

Larger cheek-teeth of a combined

trenchant and crushing type, the

last upper premolar and first lower

molar strongly differentiated as

carnassials, the former 3-rooted,

its inner lobe in front of middle

of crown, its position, somewhat

posterior to level of anteorbital

foramen, at point of greatest me-

chanical efficiency; auditory bulla

moderately or considerably in-

flated, without septum; form

rather light, the legs long; size

moderate; feet digitigrade; toes,

5-4 or ;

Genus Canis. Characters.—

Skull heavy and deep (depth of

brain-ease more than one-third

condylobasal length); interorbital

region thickened and elevated, the

frontal sinuses rather large, the

postorbital processes thick, convex

above, their edges rounded off;

dorsal profile of forehead rising

rather abruptly and noticeably

above level of rostrum; dental for-

;

j 83 1-1 4-4 2-2

Sa Sa Pa ae

teeth heavy and large, the length

of carnassial and upper molars

together contained about 214 times

THE AMERICAN NATURALIST

[Vou. XLIX

acters of the brain. Inherited

from “ least characters ” which ac-

cumulated and evolved in Mesozoie

and early Tertiary time.

Characters of proportion and

changes of form; characters of

funetion or adaptation; presence

or absence of certain numerical

characters. i

the ancestors of the

verged as terrestrial and cursorial

Carnivora from other Carnivora.

Chiefly characters of propor-

tion; also numerical characters of

the teeth. Characters clearly mani-

fested in lower and middle Eocene

time and taking on their modern

aspect in early Oligocene time.

No. 580]

in palatal length; canines robust

scarcely beyond middle of mandi-

bular ramus when jaws are closed

(Fig. 65

[Species] CANIS LUPUS. Diag-

nosis.—Condylobasal £

225 mm.) ; cheek-teeth larger than

in the largest races of domestic

ORIGIN OF SINGLE CHARACTERS

201

Chiefly characters of propor-

tion; certain minor numerical

characters. Characters distinguish-

ing Canis lupus from Vulpes, first

apparent in Miocene and E hosie

dogs, the upper carnassial 25 to time.

27 mm. in length, but structure

not peculiar, the upper molars

with narrow, inconspicuous cingu-

lum on outer side (Fig. 61).

[Subspecies] CANIS LUPUS LU-

PUS. Characters.—Size maximum

for the species; general colour not

markedly tawny; white of throat

not extending to cheeks. The few

skulls examined agree with Asiat-

ic specimens in having the outer

cusps of m! moderately large, the

paracone with transverse diameter

of base about equal to width of

large flattened portion of crown.

Size characters ; color charac-

veloped in early Pleistocene time,

perhaps 500,000 years ago.

In the ascending order of Miller’s definitions we note

that ‘‘subspeciesare mainly distinguished hy characters of

proportion and of form and by the degrees and intensities

of color, but rarely if ever by numerical characters. ‘‘Spe-

cies’’ are mainly distinguished by the proportions of the

various hard parts and to a less extent by the presence

and absence of minor ‘‘numerical ’’ characters. ‘‘Genera’’

are distinguished by the proportions, by the presence or

absence of several numerical characters, also by fune-

tional characters such as dental succession. ‘‘Families’’

are distinguished by changes of proportion and of form,

by many numerical characters, such as the presence or

absence of certain parts, by structural adaptations in the

teeth and feet. ‘‘Orders’’ are distinguished by the funda-

202 THE AMERICAN NATURALIST [ Vou. XLIX

mental and very ancient chief habits, chief adaptations in

the hard parts, chief brain features.

Thus we see that two kinds of characters are employed

by Miller throughout, namely: first, characters of pro-

portion of form and of degree; second, numerical or

Fic. 1, Skulls and cheek teeth of the wolf (Lupus), arctic fox (Alopex), and

red fox (Vulpes), illustrating the differences in proportional characters of the

skulls and teeth and the resemblances in the numerical characters, or rectigra-

dations (R).

presence and absence characters. We are struck by the

fact that changes in proportion embrace by far the larger

part, perhaps nine tenths, of the ‘‘characters’’ enumer-

ated by Miller in his systematic descriptions; this is þe-

cause change of proportion is the chief and most universal

phenomenon in the adaptation of mammals to different

habits and habitats. Numerical change is hardly less im-

portant, but is less universal and less frequent.

Similar weight upon the value of characters of propor-

tion is seen in the contrast between Miller’s definitions of

the three genera of dogs, namely: Canis, Alopex, and

Vulpes. Here again the vast majority are characters of

proportion and of form.

No. 580]

I. Genus CANIS

Characters. — Skull

heavy and deep (depth

of brain-case more than

one-third ™ condylobasal

length) ; interorbital re-

gion thickened and ele-

vated, the frontal si-

nuses rather large, the

postorbital processes

ick, convex above,

their edges rounded off;

above level of rostrum;

dental formula:

gk 1 4-4

3-37 So m 4-4’

teeth heavy and large,

the length of earnas-

sial and upper mo-

lars together contained

about 2% times in pal-

atal length; canines ro-

bust and not specially

elongated, the point of

upper tooth extending

scarcely beyond middle

of mandibular ramus

when jaws are closed

(Fig. 65).

The fact that changes of proportion

ORIGIN OF SINGLE CHARACTERS

II. Genus ALOPEX

Characters. — Skull

intermediate in general

form between that of

Canis and Vulpes; oecip-

ital depth about one-

third eondylobasal

length; interorbital re-

gion more elevated than

in Vulpes owing to

greater inflation of the

frontal sinuses; postor-

bital processes thin, flat

or slightly concave

above, with bead-like,

overhanging edges; dor-

sal profile of forehead

rising abruptly above

rostrum as in Canis;

teeth moderately heavy

and large, the length of

earnassial and upper

molars together con-

tained about 234 times

in palatal length; ca-

nines and incisors inter-

mediate between those

of Canis and Vulpes

(see Fig. 65); external

form fox-like, but ear

short and rounded, not

conspicuously overtop-

the

surrounding ga

fur.

203

III. Genus VULPES

Characters. — Skull

slender and low

(depth of brain-case

less than one third

a ee A

interorbital regio

nearly flat, the Sotal

sinuses scarcely in-

flated, the postorbi-

tal processes thin,

slightly concave

above, their edges

overhanging and

bead-like; dorsal pro-

file of forehead ris-

ing very slightly and

gradually above level

of rostrum; dental

formula as in Canis;

teeth relatively light

and small, the length

of upper carnassial

and molars together

contained about 234

to 3 times in palatal

teeth somewhat more

trenchant than

Canis, the canines

slender an e

ed, point

margin of mandibu-

lar ramus when jaws

are closed (Fig. 65).

include the most

frequent characters while numerical changes include the

least frequent characters is again very strikingly brought

out in Miller’s remarks on the origin of the domestic

dogs from the wolf (Canis lupus):

204 THE AMERICAN NATURALIST [ Von. XLIX

The only known characters by which the skull of Canis lupus can

be distinguished from that of the larger domestic dogs is the greater

average general size and the relatively larger teeth. In a dog’s skull

with condylobasal length of 230 mm. the length of upper and lower

carnassials is, respectively, 21.6 and 25.0 mm. In ten skulls with con-

dylobasal length of more than 200 mm. the average and extremes for

these teeth are: upper, 20.5 (19-22); lower, 24.0 (22.8-26.0). In all

the dog skulls which I have examined, representing such different

breeds as the pug, fox-terrier, bloodhound, mastiff, ancient Egyptian,

ancient Peruvian, Eskimo (Greenland and Alaska) and American In-

dian, the teeth are strictly of the wolf type, never showing any ap-

proach to that of the jackal (Fig. 62).

This indicates that the profound differences of osteolog-

ical character which separate the larger breeds of domes-

tic dogs are chiefly in the proportions.

No numerical, or presence and absence characters are

used in Miller’s definition of the wolf, arctic fox, and red

fox although a number of minor numerical characters are

clearly described and figured in his text, especially the

cuspules on the incisor and premolar teeth, as shown in

Fig. 1. These numerical cusp characters would have re-

ceived more attention from a paleontologist partly be-

cause of the paucity of material which comes into his

hands, partly because he is in a position to observe the de-

velopment of these cuspules.

This contrast between proportional and numerical char-

acters brings out a fundamental law in the evolution of

the hard parts of mammals which is of great importance.

First, characters of form and proportion, without numer-

ical change, are constantly originating as a universal prin-

ciple and forming the chief distinctions between divisions

from the high rank of orders down to those of subspecies,

races, and even individuals. Second, numerical loss or

fusion of old characters of teeth, digits, or vertebre is

next in frequency, the loss always following diminution

in form and proportion. Third, numerical gain of new

characters is the least frequent process; it is relatively

rare in the endoskeleton, that is, in added teeth, added

vertebre and other segmental parts, added cranial bones,

added phalanges; it is more frequent in added cusps on

No. 580] ORIGIN OF SINGLE CHARACTERS 205

the teeth or added horns and appendages of the skull; it

is still more frequent in added exoskeletal characters, such

as dermal ossicles and armatures.

The contrast between the wolf (Canis lupus), the arctic

GEOGRAPHIC DISTRIBUTION

AT PRESENT TIME

True Fox Arctic Fox Species or Worf

Zoological VuLpes ALopex ANIS

Observation LUPUS l }

7 —..o

+ ©

ose

oo g 285

joS2

= o> |

ay <5

Se aoe dt E

ee ee

l i PESTER |

<— GEOGRAPHIC DISTRIBUTION ——>

IN PAST TIM

Lines and dots represent the pyle also the pot and existing

distribution of. geograp ic (onto netic and environmental)

sub- species, races, and intergrades A= ancestral type

zontal lines).

fox (Alopex lagopus), and the red fox (Vulpes vulpes)

may, moreover, be adduced for four purposes: first, to

direct attention to the nature of the numerical characters

which separate these three genera; second, to direct at-

tention to the fact that these numerical characters are

very inconspicuous and unimportant in contrast with

characters of proportion; third; to illustrate the extremely

slow development in time of new numerical characters;

fourth, to illustrate the difference between paleontological

and zoological observation, a difference which is graphic-

ally represented in the diagram (Fig. 2y.

As to time Vulpes has been separated from Canis for an

206 THE AMERICAN NATURALIST [Vou. XLIX

enormous period.’ It is clearly distinguishable in the

European Pliocene where three species of canids are

referred to the genus Vulpes by Schlosser and others.

Again, in the Upper Pliocene of India there occurs a spe-

cies of fox as well as in the Pliocene of Chine. In North

America the fox is first recorded from the Pleistocene

definitely, although an Upper Miocene species (Canis

vafer Leidy) is regarded by some as the forerunner of

Vulpes and by others as a pro-Vulpes genus. It is there-

fore probable that the phylum of the fox diverged from

that of the wolf as early as Miocene times, perhaps a

million years ago, although the generic distinctions of

proportion-characters were not fully acquired until Plio-

cene times. The ancient geologic separation of Canis and

` Vulpes is further indicated by the fact that they do not

interbreed. The marked divergence in proportions—the

fox small, slender, narrow-headed, a small-mammal and

bird catcher, the wolf: relatively large, massive, broad-

headed, a large-mammal catcher—is accompanied by the

gain or loss of several relatively obscure numerical char-

acters, such as the cuspules on the incisors and premolars

(Fig. 1. r,r, r), which are strong in the wolf, intermediate

in the arctic fox, and absent in the red fox. It would

appear that the wolf had developed these numerical cusp

characters more rapidly than its congeners. In a fossil

series the development of such cusp characters may be

followed stage by stage.

2. Observations by a Field Zoologist on the Modes of

Origin of Numerical and Proportional Characters

The special features of the field work developed under

C. Hart Merriam’s direction in the U. S. Biological Sur-

vey are: (1) the vast quantity of comparative material

brought under examination, (2) the exact geographic, cli-

matic and environmental records, (3) the assemblage o

numerous intergradations between species and sub-spe-

cies, (4) the precision of the measurements and observa-

10 I am indebted to the authority of Dr. W. D. Matthew for these remarks.

No. 580] ORIGIN OF SINGLE CHARACTERS 207

tions, but above all (5) that the facts are recorded entirely

without the influence of any biological theory, the mind

of the observer being absolutely fresh and unprejudiced.

The observations published in 1909 by Wilfred H. Os-

good on the mice of the genus Peromyscus therefore

constitute a notable and wholly unbiased research on

bodily ‘‘characters’’ as they appear to a zoologist col-

lecting and observing in the field, but examining and re-

viewing his material in the museum. The following ab-

stract is mainly in the author’s own language and has been

verified by him, although the order of treatment is rear-

ranged entirely and italics are added for emphasis in its

bearing upon the modes of origin of single characters in

living mammals.

As recorded there have been examined more than 27,000 specimens

of the American rodent genus Peromyscus (Gloger, 1841), ineluding

the so-called wood mice, deer mice, vesper mice, or white-footed mice,

having a total range from the Mexican province of Oaxaca on the

south to the Yukon, Alaska, on the north, and from Labrador to

Florida on the east to Alaska and southern California on the west.

The “genus” Peromyscus is for convenience divided into five “ sub-

genera,” which are distinguished mainly by the presence or ie

of three numerical characters, namely, tubercles on the soles of the

feet five or six, presence or absence of accessory tubercles on the first

and second molar teeth, presence. or absence of two or three pairs of

mammæ. The remaining subgenerie characters lie in differences of

proportion and in color relations. The “subgenera,” which are usually

defined by a combination of characters, may merely represent opposite

ends of an almost continuous series (e. g., oe E

Megadontomys). Intergradation is- observed also ‘cert. of the

numerical characters, as in the six to vestigial we. lake peo

of the P. maniculatus group.

The species of Peromyscus maniculatus (Wagner), alone including

forty-four subspecies, ranges from Vera Cruz to Labrador and has a

wider distribution and a larger number of intergrading forms than

any similar group of mammals known. From the typical P. manicu-

latus development may be traced step by step absolutely without

break through all the numerous subspecies.

Perfect integradation, in proportion and color intensity and dis-

tribution characters, is observed between the related forms e sub-

11 Osgood, Wilfred H., ‘‘Revision of the Mice of the American Genus

Peromyscus,’’ U. 8. Sask: t. of Agric., Bureau of Biol. Surv. No. Amer.

Fauna, No. 28. Apr. 17, 1909, 285 pp.

208 THE- AMERICAN NATURALIST [Vou. XLIX

rey

SUBSPEC IESO OF mowed YSCUS

es Bae MCPS m 1

petari

by coolidgel ie

a z paes

A S —* 6 Jj

3 zi sonoriensis “ 7 y ie |

ee rufinus ag We

rubidus ee qi

g * nebrascens. 10 AR

nubiterrae t A

Penre bairdi wi) Å i

3 i 1s j mY j

2 S artemisiae “14 &

= gracilis "Is

2 = -g

s3 oreas “7 Aint

hy! “18

nf maniculatus “ 19

re macrorhinus “

bes me: hylacus ea

pecies are represented by continuous or

omplete intergradation or continuity be-

ted a r. eniai shading. Where there is no

spys uity which, as indicated in the diagram

t , is not real; this dia shows the various con-

tinuous chains of s subspecies kúk intergradations the terminal members of which

appear to be disconti

species”) of the many different faunal areas. Hundreds and even

thousands of specimens are intergrades almost equally resembling two

or more adjacent forms. Many specimens fall so near an imaginary

line between two or more “ ERS ” that it is practically a

No. 580] ORIGIN OF SINGLE CHARACTERS 2C9

to classify them other than as intergrades. Particularly difficult cases

are those in which the intergrades approximate the color of one “ sub-

species ” and the cranial characters of another, thus reducing the ques-

tion of definition to one of the relative importance of characters.

Classification becomes like the division of a spectrum and depends

largely upon the standards set, for theoretically at least the possibili-

ties of subdivisions are unlimite

Some of the principles of variation [and perhaps of hybridization,

H. F. O.] are as follows:

(1) Fortuitous individual variation is greatest in specimens from

localities lying just between the ranges of two well-established forms.

Where two genuine “subspecies” inhabit the same area and

maintain themselves distinct, each may in certain cases be traced by

a definite geographic route through every degree of intergradation to

one parent form. For example, P. arcticus lives side by side with P.

algidus in the upper Yukon, but both intergrade toward the south

with P. oreas (see Fig. 3). If from sudden or gradual natural

causes these intergrades between P. arcticus, P. oreas, and P. algidus

were to become extinct three entirely separate and distinct subspecies

would apparently be created.

(3) Sexual variation in proportional characters is so ‘slight as to

be practically unmeasurable.

4) The “species” are fairly well characterized in eranial propor-

tions, but the cranial proportions in “ subspecies” are seldom constant

throughout a series although they often afford average proportional

characters of considerable value. For example, among “ species” that

are normally brachycephalie a greater or less tendency to dolicho-

cephaly is sometimes found, and vice versa. The teeth vary chiefly in

‘proportions but seldom to great extent. Some subspecies are

dichromatie.

(5) In color there is a range of seasonal, polychromatie, and local

or geographic variation. A complete intergradation between two color

extremes may often be found in localities lying just between the ranges

of two well-established forms. Color intensities are often extremely

local and doubtless are produced immediately upon contact with cer-

tain environments. Thus if the range of a given subspecies includes

a few square miles of lava beds, specimens from that area show ap-

preciably darker color than the normal members of the subspecies oc-

cupying the surrounding region. Again, specimens from the bottom

of a dark, wooded cañon may be noticeably darker than those inhabit-

ing an open hillside only a few hundred yards away. One can hardly

avoid the suspicion, observes Osgood, that if the progeny of paler

individuals were transferred at an early age to the habitat of the darker

ones they would quite regardless of heredity develop darker color.

Such local “ geographie variations” are so great that most of the

species have developed- gece apie a by means of which

210 THE AMERICAN NATURALIST [Vowu. XLIX

they have been subdivided into -numerous “ geographic races” and

“subspecies.” Thus P. maniculatus, which ranges from the Arctic

Cirele to the Isthmus of Tehuantepec, remains constant only where

the environment is identical, hence it is represented by definable

subspecies” in almost every faunal area which it enters (see Fig. 3).

These observations of Osgood may be compared with

the taxonomic results of Miller on the one hand and with

the observations of paleontologists on the other:

First: we note that in the ‘‘species’’ of the subgenus

Peromyscus and in the ‘‘subspecies’’ of Peromyscus man-

iculatus among the vast number of characters enumer-

ated there is not a single distinction recorded in numerical

or presence and absence characters; every single charac-

ter recorded is either in the proportions of the skull, ears,

feet, and tail, or in the intensities and distribution of the

color areas—all characters of degree. The field and

museum work of Osgood thus independently accords with

the taxonomic work. of Miller, namely, ‘‘proportional

characters’’ are universal and abundant, ‘‘numerical

characters’’ are less frequent and of a higher or different

taxonomic order because much more gradual in evolution.

Second: the evidence for continuity in the origin of pro-

portional characters is absolute.

Third: in a broad way continuity is also the mode of

origin of the so-called numerical characters for it is posi-

tively observed except in the case of the mamma, and

there is no apparent reason, remarks Osgood, why the

mamme also may not have developed in the same way as

the more trivial characters. In other words, there is

almost complete continuity between groups which many

taxonomists would regard as different ‘‘genera.’’ The

numerical differences in the plantar tubercles on the soles

of the feet have not been sufficiently studied, but it is clear

that the change from 5 to 6, or vice versa, has come through

the gradual. reduction or growth of one tubercle and not

through any sudden change. Most interesting also is the

fact that the 5-tubercled Peromyscus shows decided simi-

larity to the genus Onychomys, which is 4-tubercled and

-closely allied to a

No. 580] ORIGIN OF SINGLE CHARACTERS 211

Fourth: while the numerical characters are solely ger-

minal, it is difficult or impossible to distinguish both in re-

spect to color intensities and to proportions, what is ger-

minal, permanent and hereditary from what is somatic or

due to environmental and ontogenetic influences.

These four chief conclusions drawn from the observa-

tions of Osgood may now be compared with those inde-

pendently obtained by paleontologists. i

3. Likeness and Unlikeness Between Paleontologic and

Zoologic Observation

The mammalian paleontologist observes exactly the

same kinds and degrees of characters as the zoologist,

namely, very numerous changes of proportion and form,

and relatively infrequent numerical changes. In both

respects, however, the paleontologist has the very great

advantage of observing the extremes and also many of the

intermediate stages.

The chief distinction between these observers is that

as the zoologist sees characters they are stationary, he

can only infer their separability in movement through his

inferences from the comparison of forms like Canis, Alo-

pex, and Vulpes, while the paleontologist observes several

new evolution properties in these same ‘‘characters,”’

namely their actual movement and their relative rate of

movement in various lines of descent, as well as their

origin and subsequent progression or retrogression, in

brief, their phyletic history. Thus the paleontologist is

in a position to observe more of the evolution properties

in characters of exactly the same kind. Whereas in a

series of living forms each character appears to the zool-

ogist-observer as dead or static, in a fossil series each

character appears to the paleontologist-observer as living

or dynamic, the life being displayed in what may be called

its two movements in a phyletic series. ;

The first property of the ontogenetic movement of char-

acters in fossils constituted the life work of our great

observer Alpheus Hyatt, who proposed the significant and

easily recalled terms acceleration and retardation for the

212 THE AMERICAN NATURALIST (Vor XLIX

two directions of movement seen in ontogeny and phy-

logeny. Accelerated characters are those which hurry

forward and appear in successive generations at earlier

and earlier stages in the development of the individual;

while retarded characters are those which hold back or

slow down and appear in later and still later stages in

the development of the individual of succeeding gener-

ations. We know that such ontogenetic movement is

shown both in embryonic and phylogenic development of

the individual; it causes characters to appear in ontogeny

out of the order in which they arise in phylogeny; it gives

rise to the heterochrony of Gegenbaur; its rate is meas-

ured by comparing one character with all the other char-

acters of an individual.

Psi

5 Eotitanops

~ Pa

a A d

`, 4

“Ny F

Fic. 4. Evolution = jane different proportional “ion a (B, C) from

stors (A) having similar proportio

Quite distinct is what we may call the phyletic move-

ment of a character; its rate is measured by comparing a

character in individuals of one phylum with the same

character in individuals of other phyla. It is illustrated

in the comparison of the secondary cusps of the incisor

and premolar teeth in Canis, Alopex and Vulpes; in each

phylum the same cusp has its distinctive rate of evolution

and thus may appear early in geologic time or late in

geologic time. Thus comparison of the phyletic move-

ment of the same ‘‘character’’ in various lines of descent,

No. 580] ORIGIN OF SINGLE CHARACTERS 213

which is a matter of phylogeny, is quite different from

comparison of the relative movement of a number of

different characters in single lines of descent, which is

the basis of Hyatt’s law.

To illustrate the distinction between ontogenetic and

phyletic movement: a rudiment of a horn may appear

upon the skull in one phylum of titanotheres during the

period of deposit of the base of the Bridger beds (Fig. 5),

which are 1,500 feet in thickness, and in another phylum

(Fig. 5) at the summit of these beds, many thousands

of years later; this is its relative phyletic movement.

Second, after the same horn-character has appeared long

subsequent to the birth of the individuals, in both phyla

it begins to be thrust forward in the ontogeny of individ-

uals, so that in Lower Oligocene time it begins to appear

long before birth; this is its acceleration or ontogenetic

movement,

Paleontology has also revealed the marked distinction

in the mode of origin of the two kinds of characters ob-

served in zoology, namely, between the almost universal

changes of proportion and the comparatively rare new

‘‘numerical characters. ’’!?

To the former I have applied the term allometrons, >

which signifies that differences of measurement express

all changes of proportion. From these differences indices

and ratios may be calculated. Such differences arising in

the head and in the feet are indicated in the familiar

terms dolichocephaly, brachycephaly, dolichopody, brachy-

pody, and many other convenient combinations of Greek

terms. That these changes of proportion become distinct

hereditary ‘‘characters’’ is proved in certain hybrids of

Mammals where they appear to be partly or completely

separable. Thus the cross of human broad-heads with

long-heads does not produce a blend between the two but

produces, for some generations at least, either pure doli-

12 Osborn, H. F., ‘‘Coincident Evolution Through Rectigradations (Third

Paper),’’ Science, N. S., Vol. XXVII, No. 697, May 8, 1908, pp. 749-752

(p. 752).

18 ‘í Biological Conclusions Drawn from the Study of the Titanotheres,’’

Science, N. S., No. 856, May 26, 1911, pp. 825-828 (p. 826).

214 THE AMERICAN NATURALIST [Vou. XLIX

chocephals or pure brachycephals. Characters of pro-

portion are thus ‘‘single characters’’ in the hereditary

sense.

In the comparison, for example, of certain broad-heads

with other broad-heads such characters are termed

analogous because due to similarity of structure arising

from similarity of function. Thus brachypody (abbrevia-

tion of the digits) is analogous in the rhinoceroses and

the titanotheres. The broadening of the shell of one mol-

luse is analogous to the broadening of the shell of another

molluse. The broadening is none the less the heritable

characteristic of the skull or of the shell.

Quite different are certain of the new numerical charac-

ters to which I have applied the term rectigradations,

such as new cuspules on the teeth and new rudiments of

horns, for these give rise to characters which are regarded

as homologous although not directly descended from each

other. Thus the horns in all the titanotheres are consid-

ered homologous, although they arise independently at

different times in different phyla. The larger number

of cusps in the teeth of mammals are termed homologous,

although they also have arisen quite independently of

each other. Itis obvious that unless all similar new char-

acters have originated in the offspring of a single pair,

which we know is not the case, that the vast majority of

similar new numerical characters both in vertebrates and

invertebrates are related through similarity of ancestry,

through the similarity of the tissues from which they

arise, and through the similarity of their relations, form-

ing a special kind of homology which Firbringer has

termed homomorphy.

While different in these respects of analogy and

homology there are many properties which allometrons

and rectigradations as heritable characters have in com-

mon, such as the laws of growth, correlation with sex,

mechanical correlation, differential ontogenetic move-

ment, differential phyletic movement, or differential rates

of evolution, continuity of origin, increasing intensity of

No. 580] ORIGIN OF SINGLE CHARACTERS 215

“ihe v

atA mest

vs ý

ah mcesd

asd Il

vy i

Palæosyops >

P: d

‘Op l 5 I

Eotitanops J

$ I

A B D

A cti igradatio Allom

lew characters, ailt but ; New piperis iirin

si alee tly arising of S26 P hylum. Different

every phy sy Lerma Le all other phy la

Fig. 5. hiaai origin and evolution of similar numerical charac-

ters (A, P Garh of ns roportional characters. (0, D) all arising in

pendently ig same ancestors. Each of the five phyla (I-V)

exhibits Mati praes a (pad, mes, H) and dissimilar proportions both

in ">e. skulls and metapodials.

216 THE AMERICAN NATURALIST [Vou. XLIX

development in successive generations. For example,

rectigradation like the hypocone may become more dis-

tinct, a change of proportion like brachyecephaly may be-

come more pronounced in successive generations. Yet

there are a number of additional contrasts between the

proportional and certain numerical characters, a few of

which may be enumerated:

Proportional characters = Allo-

etrons

Allometrons give rise to analo-

gies, never to homologies; they

are quantitative and intensive and

not numerical; _ closely related

forms give rise to different al-

lometrons even within SAP ;

they may be induced experim

tally in pe ae they pena

afford indices and ratios; even spe-

cific affinity may not predispose to

the same allometrons; Sue

—both harmonic and rmonie

—frequently accompany eas

of environment; they give rise

both to convergence and to di-

Orthogenie numerical characters =

Rectigradations

Rectigradations give rise to

homologies, strictly speaking ho-

momorphie structures; they are

neomorphs, new outgrowths, nu-

merically new characters; similar

rectigradations may

parallelism or convergence be-

tween the members of related

phyla; they are comparatively in-

frequent phenomena; they are not

known to be produced experimen-

tally in ontogeny; they arise from

vergence. minute beginnings at different

points in the tissues; they adopt

the characters of proportion in

surrounding parts; no true recti-

merous the similar rectigradations.

4. Differences of Opinion as to the Origin of New

Numerical and Proportional Characters

In my opinion, which is not shared by all my co-workers,

rectigradations and allometrons are qualitatively differ-

ent characters and are attributable to different combina-

tions of causes. For example, the additional cuspules on

the teeth of Canis, Alopex and Vulpes are typical recti-

gradations; they are ‘‘characters’’ qualitatively different

from the dolichocephaly of Vulpes or the relative brachy-

No. 580] ORIGIN OF SINGLE CHARACTERS 217

cephaly of Canis. This opinion was formed in 1905 and

has in my mind been established by further research.

It is, moreover, my theoretical view that rectigrada-

tions arise from some kind of germinal predisposition or

perinad or potential homology. While the‘‘homology’’

r ‘‘homomorphy’’ uniting these new characters seem

2 be due to some internal hereditary kinship between the

descendants of similar ancestors, their appearance is not

Fic. 6. Distinction between sport or mutational characters (s), which have

no significance in the evolution of the teeth, and rectigradations (r), which

are very important.

spontaneous, but is invoked in some way connected with

similar bodily and environmental reactions which also we

do not at all comprehend. For certainly there is no evi-

dence that such ‘‘homologues’’ or ‘‘homomorphs’’ arise

from similar internal perfecting tendencies or teleologic

causes which operate independently of the reactions of en-

vironment and habit.

The fact that certain rectigradations appear to corre-

spond with antecedent mechanical reactions in certain

cases, such as in the cuspules of the teeth, has led to the

opinion of Cope that these bodily mechanical reactions are

causative, but this opinion is completely offset by the fact

218 THE AMERICAN NATURALIST [Vou. XLIX

that many rectigradations occur in both vertebrates and

invertebrates which are not preceded by mechanical reac-

tions in the bodily tissues, the ornamental characteristics

of the shells of molluses, for example.

In brief, the mechanical reaction hypothesis of Lamarck

and Cope fails both as to the origin of certain new recti-

gradations and of certain new allometrons. For example,

the extremely elongated limbs of certain young quad-

rupeds, such as young horses and young guanocos, are

proportional characters which are certainly not due to the

inheritance of mechanical reactions in the adults because

they are entirely different from the adult proportions.

For these various reasons I have reached the opinion

that, whatever the respective causes of rectigradations

and allometrons may be, they are different; that is, the

occasional origin of new numerical characters and the

.constant changes of proportion which are going on in all

organisms are due to a different series of direct causes.

This divergence into matters of opinion is, however,

parenthetical. Let us now return to the observation of

facts which throw light upon the properties and qualities

of these least characters.

5. Observed Differences in the Origin and Inheritance of

Proportional and Numerical Characters

Origin. Thefundamental distinction between the origin

of rectigradations and of allometrons is well illustrated

in the six phyla, I-V, of Eocene titanotheres (Fig. 5).

It is seen that similar horn rudiments and similar cusp

rudiments arise independently at different geologic times

in every phylum, giving rise to a great number of new

homomorphie characters. On the other hand, each phylum

has its peculiar and distinctive allometrons both in the

bones of the skull and of the feet. These changes of pro-

portion are so universal and so profound that by a vast

system of comparative measurements it has been ascer-

tained that every bone of the skull, of the limbs and of

the feet has its differential rate of increase and decrease.

Since these characters of form and proportion are real

No. 580] ORIGIN OF SINGLE CHARACTERS 219

characters and since they affect every bone in the skele-

ton we discover that characters of taxonomic import may

be found in every one of the small bones of the wrist and

ankle joints, which while less readily measurable are of

exactly the same kind of value in classification as the more

conspicuous changes of proportion in the skull and in the

KIANG

<5 :

MERYCHIPPUS MULE ZEBRA

gypave

ORSE

Fig. 7. The pli eee (5) a ee pepanen in the grinding teeth

of different members of the family of horses. Present in the Miocene Mery-

chippus, in the jaren he kiang, zebra, owdi horse, common horse; absent

in the ass and the mule.

feet which Miller has used throughout in his definitions

of the Carnivora. In other words a ‘‘species’’ may as

consistently be defined by the proportion-characters of

one of its carpal bones as of one of its cranial bones;

such a definition would be strange and inconvenient, but

it would be quite as scientific.

The rectigradations are also used in systematic defini-

tion only as soon as they become sufficiently large and con-

spicuous to be computed numerically. Looking up the

ancient definitions of the Eocene horses by Marsh and

220 THE AMERICAN NATURALIST [Vou. XLIX

Cope we note in every instance that as soon as a cusp

passes beyond the rudimentary stage it is apt to be ob-

served and used in definition.

So far as we know both rectigradations and allometrons

arise continuously, definitely or determinately, and so

far as we have observed they arise adaptively or in an

adaptive direction from the very beginning.

Inheritance. The germinal separability of the ‘‘least-

characters’’ known as rectigradations is well illustrated

in the case of the ‘‘ pli caballin,’’ a delicate fold of enamel

A = Thag

E.frateynus E Aelius

m pt

E. sepli at E: complicatus

i pe

~-5

E.lauwrentous

KSN

E. paci icus

E.niobravensis pt

7 a ~--5

pee heed "> eee E. giganteus

Fie. 8. The pli caballin (5) more or less distinctly developed in the superior

grinding teeth of twelve species of the Pleistocene horses of North America. it

is observed that these grinding teeth differ profoundly in the proportions of all

their parts. The pli caballin (5) is worn off in the aged grinding tooth.

which the French systematic writers a century ago selected

as a specific ‘‘character’’ by which the horse (E. cabal-

lus) could invariably be distinguished from the ass (L.

asinus). They little knew how very ancient and. stable

this minute character is. We see it strongly developed in

the Miocene Merychippus. We do not know whether it

No. 580] ORIGIN OF SINGLE CHARACTERS 221

developed gradually or suddenly within the highly varied

horses of this genus. It appears (Fig. 5) more or less

fully developed in all of the many known species of Pleis-

tocene horses of America as described by Leidy, Gidley

and Hay. It lies near the surface of the crown, and in

much-worn teeth it disappears because the fold is seldom

continued down into the lower half of the crown. It is

entirely absent in the grinding teeth of the domesticated

ass (E. asinus), yet it is present in the kiang (E. kiang).

The complete germinal separability of the ‘‘ pli cabal-

lin’’ as a hereditary character is demonstrated by its

absence in the grinders of the mule, the cross between

E. caballus Ẹ and E. asinus g; these grinders of the mule

hybrid also prove that rectigradations are distinct from

allometrons, because the rectigradations of the maternal

horse molar are not inherited in the hybrid while the

allometrons are inherited, namely, the elongated propor-

tions of the maternal horse molar. I am preparing to

investigate the grinding teeth of the hinny, the cross

between the male horse and the female ass, to ascertain

whether the same contrast in heredity prevails here. I

suspect not because the hinny appears to have the shorter

head of the ass rather than the very long horse-like head

of the mule.

The germinal separability of allometrons or propor-

tional characters of mammals is also observed, but it

appears to be less complete than that of rectigradations.

This is demonstrated not only in the grinding teeth but

in the skull of the mule hybrid, in which the majority of

the head proportions present the same indices as in the

horse, while the minority of the head proportions present

a blend between the indices of the horse and ass. Again

in Homo sapiens the allometrons are in the first genera-

tion completely separated; in intermarriage of dolicho-

cephalic and brachycephalic individuals the children

do not form a blend of their parents but inherit either

the pure dolichocephalic or pure brachycephalic head

form. Prolonged interbreeding and intermixture þe-

tween long-headed and broad-headed human races ap-

222 THE AMERICAN NATURALIST [Von XLIX

pears to break down these separable allometrons and ul-

timately results in blending. This may be partly due to

the fact that changes of cranial proportion occur not only

within the species, but within the races and sub-races of

Homo sapiens, as witnessed in the mongoloid Indiam

races of North and South America. In other words, the

allometrons in man are of more recent origin than in the

horse and ass, which probably separated from each other

as far back as the Lower Miocene. Further experiments

and observations are greatly needed as to the separable-

ness or blending of allometrons in hybrids.

As to the rapidity of evolution of proportional and

numerical characters it appears that in certain lines al-

lometrons may evolve more rapidly than rectigradations.

This is seen in the titanotheres (Figs. 4, 5, 10), in which

changes of proportion develop very rapidly, while the

rectigradations on the grinding teeth and the rudiments

of horns develop very slowly. On the other hand, in the

contemporary Eocene horses the rectigradations seen in

the addition of cusps develop very much more rapidly

than the changes of proportion in the skull. This con-

trast between horses and titanotheres, however, confirms

the universal law that every ‘‘character’’ has its differen-

tial phyletic movement as well as its differential onto-

genetic movement.

That these movements are not identical is further

shown by a familiar illustration. The median toes of

the feet of the desert-living Hipparion have a much more

rapid phyletic movement than the median toes in the

forest-living Hypohippus, yet we may be sure that the

limbs of the newly born foals of Hipparion and of

Hypohippus were alike relatively elongated to enable

these foals to accompany the mares in flight, this adapta-

tion being secured through ontogenetic movement, or ac-

celeration.

These differentials in the velocity of characters in their

phyletic and in ontogenetic movements may afford one

of several reasons why allometrons, or proportional

Sharhehirs are separable in hybrids, why some ‘‘unit

No. 580] ORIGIN OF SINGLE CHARACTERS 223

characters’’ are dominant and others recessive. This

raises the general problem of the various causes of sep-

arability of characters in the body and in the germ.

First, it will appear that continuity or discontinuity of

origin has little to do with separability in the germ.

6. Waagen’s Observations on the Continuous and Ortho-

genic Origin of New Characters

The first paleontologist to point out the separate origin

and phyletic movement of single new numerical charac-

ters as distinguished from contemporary proportional

changes was Waagen in his observations on Ammonites

subradiatus, published in 1869 (p. 23). His two great

PEIEE announced as follows:

I. [The Variety.] The characters observed in space by botanists

and zoologists to a “local varieties,” “ geographic varieties,”

“varieties in space” are of variable value and of small systematic

importance. They appear to be temporary. They do not reappear in

the next higher geologic stratum. For these characters the long-used

name “ variety ” will suffice.

II. [The Mutation.] In contrast to the variety I venture to pro-

pose a new term, “mutation,” for the early and later phases (formen)

of a species observed in time. These mutations are characters which

are highly constant, although minute they surely are recognizable

again, on which account far greater weight must be put on mutations.

They ought to be very precisely pointed out, for mutation characters

even when displayed in the most minute features are certain to re-

show a somewhat different appearance. Ordinarily the gradations

between the mutations are the more minute as the stratum from whieh

specimens come are the more closely connected.

An ascending series of mutations in successive geologic

horizons taken together constitute Waagen’s Collectivart,

‘which is equivalent to the Formenreihe of Beyrich; it is

also equivalent to the phylum of more modern termi-

nology. Each mutation stage includes a number of geo-

graphic ‘‘varieties.’’ In any given geologic stratum a

14 Waagen, W., ‘‘Die Formenreihe des Ammonites subradiatus. Versuch

einer Palkonitologivehsn Monographie,’’ Geognostisch-Paldontologische pei

padi a II, Heft II, Nov. 1869, pp. 179-256 ae pp. 1-78),

224 THE AMERICAN NATURALIST [Vou. XLIX

‘‘mutation of Waagen’’ would appear as a Linnean

‘<species’’ when compared by an observer with contem-

porary mutations in other phyla; that is, each phylum

may be separated from contemporaneous phyla by valid

Linnean characters.

The essence of Waagen’s discovery is that when we

observe the origin and evolution of single characters in

time we are able to detect the incipience of new charac-

ters and the profound hereditary phyletic movements

Fic. 9. “ Mutations of Waagen ” seen in Spirifer mucronatus. On horizonta

gees are the geographic “ varieties ” differing in proportions. ta vertical lines

are the successive “mutations ” differing in proportional and numerical char

acters. After Grabau.

which can not be observed by the zoologist at all. We

are able, moreover, to distinguish the minute and even

inconspicuous characters, which are evolving in definite’

directions and accumulating in successive generations,

from the indefinite and transitory characters of the geo-

graphic ‘‘variety.’? The underlying cause of this dis-

tinction in the light of our present knowledge is that mu-

tations denote germinal or phyletic evolution while vari-

eties may simply denote the bodily fluctuations caused by

No. 580] ORIGIN OF SINGLE CHARACTERS 225

habit and environment. This phyletic movement was

termed Mutationsrichtung by Neumayr.

The significance of the term mutation as defined by

Waagen is to be found only in his original definition;

it has been used in many different senses before and

since.!ë It is a taxonomic term for each of the minute

subdivisions of a specific phylum which may be defined

by certain degrees of advance in ‘‘mutation-characters”’

evolving continuously in definite directions. The verte-

brate paleontologist Depéret in 1907 pointed out that the

Waagen ‘‘mutation-characters’’ have this special charac-

teristic, they are always produced in the same direction

without oscillations or retarded steps. The lacune are

so infrequent as not to interrupt the general view of the

continuity. Each of the closely linked terms of any

series may be designated as ‘‘ascending mutations’’ in

rising strata. It becomes possible to recognize the in-

tensity of the action of time.

The mutations of Waagen demonstrate five very im-

portant principles in tlie evolution of certain ‘‘least char-

acters’’ as follows: (1) origin from inconspicuous begin-

nings; (2) continuity rather than discontinuity; (3) defi-

nite direction or Mutationsrichtung rather than indefinite

or variable evolution; -(4) a definite rate of phyletic

movement.

These principles appear to involve a hereditary or

germinal basis, a Mutationsrichtung, such as also appears

to underlie Osborn’s rectigradations.

The two kinds of characters observed by Waagen’? are

also exactly similar to those observed by field zoologists

and by vertebrate paleontologists, namely:

The mutation of Waagen is a stage of advance in the development

either of numerical or of proportional characters, definable when one or

more of these minute and originally unimportant characters become

visible and measurable. r

15 Scott, W. B., ‘‘On Variations and Mutations,’’ The Amer. Journ. of

Science, 3d Ser., Vol. XLVIII (Whole No. CXLVIII), Nos. 283-288, July-

Dec., 1894, pp. 355-374. In this paon wore continuous ‘‘ mutation’’ is

dietiniguighad from indefinite ‘‘ variation

16 Waagen, op. cit.

226 THE AMERICAN NATURALIST [VoL. XLIX

It has now been made clear why these stages are recog-

nizable and definable by the paleontologist and not by the

botanist, zoologist or experimentalist.

To sum up the observations of zoologists and pale-

ontologists with regard to the single property of the

movement of characters in progressive organisms the

following principles are observed:

All characters are in simultaneous movement; such

movements are differential, each character has its own

rate; some movements are ontogenic or with a velocity-

relation to other characters in the same individual; others

are phyletic or with a velocity-relation to similar charac-

ters in other species and genera; ‘‘least-character”’

movements are continuously progressive or retrogres-

sive; certain least-characters are stationary; ‘‘least-char-

acter’? movements may develop or manifest a certain

direction or trend, the Mutationsrichtung, and thus may

be cumulative to an extreme; all character movements

which are cumulative in successive generations have a

germinal or hereditary basis. Thus differential move-

ment is one of the most distinctive and important proper-

ties of the ‘‘character.’’

This principle of continuous germinal change which

appears to underlie the continuous development of visible

bodily characters may prove to be in harmony with

rather than in opposition to the law through which some

characters appear suddenly, or by saltation. As I

pointed out many years ago, there may be an apparent

but not a real eontrast between the ‘‘mutations of

Waagen” and the ‘‘mutations of De Vries.” If the

former rise through continuous germinal changes and

the latter rise through discontinuous germinal changes

the common element in both may be the Mutationsricht-

ung, or trend of development. In Waagen’s law this

trend of development appears to express itself in a con-

tinuous change of visible somatic development. of charac-

ters. In De Vries’s observations the change is believed

to be discontinuous, suddenly constituting the ‘‘mutant’’

No. 580] ORIGIN OF SINGLE CHARACTERS 227

or ‘‘elementary species’? which is a subspecific stage

comparable to the ‘‘mutation’’ of Waagen. l

T. De Vries’s Observations on the Discontinuous and

Indefinite Origin of Characters

The sudden origin of ‘‘characters,’’ new, germinal,

saltatory, in every direction but of sufficient value to

come under the influence of selection—these are the es-

sential features of the famous mutation hypothesis of

De Vries. While I do not accept this hypothesis as a

demonstrated natural principle like that of Waagen, the

opinions of its distinguished author may be clearly set

forth as compared with the observations of Waagen

which have been repeatedly confirmed and verified:

(1) De Vries’s ‘‘mutants’’ differ from the ‘‘muta-

tions’’ of Waagen in appearing as fully formed ‘‘charac-

ters’’ and attracting our immediate attention and obser-

vation, instead of passing through a long series of initial

and rudimentary stages in which they are barely dis-

cernible. (2) The ‘‘mutation-characters’’ observed by

De Vries differ from Waagen’s mutation-characters in

lacking any definite or determinate direction; on the con-

trary, it is of their essence that they appear in any or

-all directions. (3) They agree, however, with the ‘‘mu-

tation-characters’’ of Waagen and with the rectigrada-

tion-characters of Osborn in the fact that similar muta-

tions may arise independently at various times in

branches of the same stock, thus giving rise to homo-

morphic characters. (4) Let us note that the new sys-

tematic unit of De Vries, the ‘‘mutant”’ or ‘‘elementary

species,’’ is a space or geographic phenomenon; it may

be contemporary with many other mutants of a single

Linnean species. (5) The ‘‘mutation-character’’ of De

Vries is not a demonstrated equivalent to the ‘‘mutation-

character” of Waagen, which is a time or geologic phe-

nomenon character, observable only in a long series of

generations from the same ancestor.

Now as to the present state of evidence for the saltation

228 THE AMERICAN NATURALIST (VoL. XLIX

hypothesis of De Vries, let us be on our guard between

fact and opinion, between natural and unnatural phe-

nomena. That the saltation of characters occurs very

frequently in plants and in animals under artificial con--

ditions there can be no doubt; yet the mass of existing

evidence is from artificial rather than from natural

sources.

The recent opinion of Bateson,’* who by his advocacy

of discontinuity in the origin of all specific characters

would be predisposed to favor the saltation theory held

by De Vries, is partly negative.

The evidence for the appearance of mutations of higher order,

by which new species characterized by several distinct features are

ereated, is far less strong, and after the best study of records which I

have been able to make I find myself unconvinced. ... In so far as

mutations may consist in meristie [i. e. numerical]1* changes of many

kinds and in the loss of [germinal]?® factors it is unnecessary to

repeat that we have obtained evidence of their frequent occurrence.

Negative conclusions have also been reached by various

botanists, as, for example, Jeffrey :1°

1. The or amen are largely characterized by hybrid contamina-

tion in natur

2. This atest holds with particular force for Gnothera lamarck-

iana and other species of the genus @nothera, which have served as

the most important basis of the mutation hypothesis of De Vries.

7. The mutation hypothesis of De Vries, so far as it is supported

by the case of Œnothera lamarckiana, is invalidate

I do not know of a single instance where a field observer

in mammalogy or in paleontology. has recorded a new

saltation character which is known to be of any signifi-

cance in the evolution of the race. On the other hand,

certain field observers of birds (Beebe) and of molluscs

(Crampton) are of the opinion that they have discov-

ered proofs that certain characters arise by saltation

17 Bateson, William, í Problems of Geneties.’’ Oxford University Press,

1913, 250 pp.

18 These [] are insertions in Bateson’s text by the present author.

19 Jeffrey, Edw. C., ‘‘Some Fundamental Morphological Objections to

the Mutation Theory of De Vries,” Tue AMER. Naturalist, Vol. XLIX,

No. 577, Jan., 1915, pp. 5-21.

No. 580] ORIGIN OF SINGLE CHARACTERS 229

in a state of nature. The vast majority of observa-

tions on the evolution of mammals either in the field

(e. g., Osgood) or among fossil series, where the in-

tergradations have not been destroyed, points to con-

tinuity in the origin of changes of proportion. The evi-

dence as to this continuity both in proportional and in cer-

tain numerical characters in fossil vertebrates and in-

vertebrates is overwhelming. Saltation is, however, theo-

retically probable in certain numerical and meristic char-

acters, such as supernumerary teeth and vertebre.

8. The Separability of Characters in the Body

Apart from the question of the origin of new charac-

ters by saltation, the observations of De Vries and his

followers furnish additional evidence of the separability

of characters both in the body and in the germ. This

law of separability in its human aspect was well ex-

pressed by Galton in 1889.2?

. We seem to inherit bit by bit, this element from one progenitor, that

from another, under conditions that will be more pate expressed as we

proceed, while the several bits are themselves liable me small change

during the process of transmission. Inheritance may enon be described

as largely if not wholly ‘‘particulate,’’? and as such it will be treated in

these pages. Though this word is good English and accurately expresses

its own meaning, the application now made of it will be better understood

through an illustration. Thus, many of the modern buildings in Italy are

historically known to have been built out of the pillaged structures of older

days. Here we may observe a column or a lintel serving the same purpose

for a second time, and perhaps bearing an inscription that testifies to its

origin, while as to the other stones, though the mason may have chipped

them here and there, and Pape their shapes a little, few, if any, came

direct from the quarry. This simile gives a rude pi gh true idea of the

exact meaning of Particulate idle! sae namely, that each piece of the

new structure is derived from a corresponding piece of some older one, as

a lintel was derived from a lintel, a column from a column, a piece of wall

from a piece of wall

I will pursue this rough simile just one step further, which is as much as

it will bear. Suppose we were building a house with second-hand materials

carted from a dealer’s yard, we should often find considerable portions of

the same old houses to be still grouped together. Materials derived from

various structures might have been moved and much shuffled together in the

20 Galton, Francis, ‘‘ Natural Inheritance.’’ 8vo. The Macmillan Com-

pany, 1889.

230 THE AMERICAN NATURALIST [VoL. XLIX

yard, yet pieces from the same source would frequently remain in juxta-

position and it may be entangled. They would lie side by side ready to be

carted away at the same time and to be re-erected together anew. So in the

process of transmission by inheritance, elements derived from the same

ancestor are apt to appear in large groups, just as if they had clung

weet in the pre-embryonic stage, as perhaps they did. They form what

is well expressed by the word ‘‘traits,’’ traits of feature and character—

that is to say, continuous features and not isolated points.

The observations which we have been comparing on

the origin of new characters in vertebrates, inverte-

brates and plants certainly afford some insight into the

laws of germinal change wherever we can distinguish

between the true germinal expression of a character and

its visible modification by ontogeny or environment.

Recurring to the antithesis between the separability and

the correlation of characters we may again sum up some

of the many properties and qualities of single characters:

Laws of Fo Laws of Correlation

ndent germinal o Hereditary connection with the

ndepen

characters, either paei or

discontinuous; independent devel-

opment of similar new characters

in near or remotely related de-

scendants of the same ancestors;

development of dissimilar changes

of proportion in descendants of

nearly related ancestors; develop-

nape of similar “ rectigradations,”

“mutations of Waagen,” and

“mutations of De Vries” at dif-

ferent times in descendants of the

same ancestors; separate rate of

evolution in ontogenetic movement

and in phyletic movement; each

character with its own origin, in-

dividuality, and rate of movement,

origin of similar characters in

other lines of descent; strong sex

correlation in the size and pro-

portions of all characters; mechan-

ical correlation both in the al-

rons and rectigradations;

compensation correlations when

one character is developed by the

sacrifice of another; proportional

—

all the new characters and changes

of proportion share the general

form; a utility or selection cor- '

relation where one character is

adaptive, defensive and offensive

correlation where groups of char-

acters evolve to serve'similar pur-

poses.

At the present time we appear to understand the laws

of separability somewhat better than the laws of corre-

lation, for the latter are enveloped in the deepest mys-

tery. We have not even alluded to the chemico-physical

No. 580] ORIGIN OF SINGLE CHARACTERS 231

correlations, by means of the hormones, which are observ-

able in the field of physiology and medicine. Mechanical

correlation, as where an incipient rectigradation in an

upper tooth corresponds precisely with an incipient recti-

gradation in a lower tooth so that the upper and lower

teeth evolve. throughout in perfect mechanical harmony

by the addition of character after character, affords one

of the most vivid instances of our total ignorance of the

causes underlying the origin of new characters.

9. The Separability of ‘‘Characters’’ in the Germ

The pioneer discoverer of the separability of ‘‘charac-

ters’’ in the germ was Gregor Mendel, who in 1865 exam-

ined seven pairs of alternating characters in hybrids of

two varieties of the common pea (Pisum sativum). The

outstanding feature of this great discovery is that the

separability of the ‘‘determiners’’ of characters in the

germ is far more sharply defined than the separability

of the corresponding somatic ‘‘characters’’ in the visible

body; as regards the ‘‘determiners’’ of many characters

it is sharp and absolute.

A second feature of Mendel’s discovery is of special

significance in our present review of proportional and

numerical characters in the hard parts of vertebrates

beeause the alternative characters which Mendel experi-

mented with were of both the proportional and the nu-

merical kind.. For example, Mendel’s proportional char-

acters of ‘‘tallness’’ and ‘‘dwarfness’’ in the pea stalk

may not improperly be regarded as analogous with the

alternative characters of dolichocephaly and _ brachy-

cephaly of the skullofthe¢mammal. Again, Mendel’s form

-of the pea-seed, whether round or wrinkled, may not im-

properly be compared respectively with the folded or

smooth condition of the enamel in the molar teeth of the

ass and of the horse, which we observe is alternative in

heredity. On the other hand, Mendel’s definite color

characters, such as his flower color, whether purple, red

or white, or his seed color, whether yellow or green, have

been definitely compared by experiment and found to

232 THE AMERICAN NATURALIST (Vor. XLIX

correspond in heredity with the coat colors of mammals.

A third great feature of Mendel’s discovery is that in

such alternative pairs of characters as tallness and

dwarfness one may be dominant and the other recessive,

following in successive generations the well-established

Mendelian law.

It remains to be observed whether any of the propor-

tional characters of mammals follow this law.

It remains to be observed, also, whether rectigrada-

tonil characters like the ‘‘ pli baballin’” in the grinding

teeth of the horse exhibit in heredity the Mendelian laws

of dominance and recession. This could only be ascer-

tained among mammals by observations on hybrids in

such a family as the Bovide, which are fertile inter se,”

or on similar characters in the hybrids between wild

natural breeds.

The discovery through experiment by zoologists and `

botanists that many saltation characters, such as sports

and abnormalities, follow the Mendelian law of domi-

nance and recession has led to the entirely unwarrant-

able assumption that only characters which are discon-

tinuous, or of sudden origin, are sharply separable in

heredity. This we have seen to be not in accord with

the facts, for the principle of separability is quite as

sharply defined in certain characters which have evolved

slowly and continuously as in those which have evolved

suddenly.

The psem significance of recent Mandelo discov-

21 Bartle D ‘Wild en in Captivity.’’ 8vo. Chapman and

Hall, Ld. tee 1899, p. 219. ‘‘The two species of camel (Camelus

dromedarius and C. bactrianus) will breed together; the llama (Auchenia

glama) will breed with the alpaca (A. pacos), and the offspring are fertile.

Several species of deer, when crossed, produce fertile hybrids: for instance,

the Barbary deer (Cervus barbarus) with the red deer (C. elaphus), the

Mexican (C. mexicanus) with the Virginian deer (C. virginianus). Several

others are also recorded upon good authority. Several instances of hybrids

among the carnivora are well authenticated. The lion (Felis leo) has bred

with the tiger (F. tigris), the leopard (F. leopardus) with the jaguar (F.

geet = wild cat (F. catus) with the domestic cat (F. domestica).’’

‘‘ Wild Beasts in the ‘Zoo.’ ’? 8vo. Chapman and Hall, Ld. London,

1900, er 71-72. ‘‘Hybrid Bovine Animals. . . . In the first place, the bull

No. 580] ORIGIN OF SINGLE CHARACTERS 233

eries to the zoologist and paleontologist is that what

we zoologists describe as a ‘‘single character,’’ the horn

of a sheep or of a titanothere, for example, is probably

the expression of a very large number of germinal ‘‘de-

terminers’’ all of which are necessary in the germ to

produce the horn. If only one of these ‘‘determiners’’

should change the character of the horn would change,

or the horns might be lost altogether. Thus the germi-

nal correlation of ‘‘determiners’’ to produce what ap-

pears as a single character to the zoologist and paleon-

tologist is visibly represented in the bodily correlation

of the horn with a very elaborate offensive and defensive

mechanism including all the bony and muscular charac-

ters necessary to operate the horn effectively, as well as

the psychic desires and impulses to use the horn. We

thus have a vast array of internal and external, of struc-

tural and functional correlations with this single charac-

ter, the horn.

10. Conception of the ‘‘ Least Character”?

In the beginning of this address I noted that no one

has ever undertaken to define the ‘‘character.’’

It is very difficult if not impossible to define one of

these least characters as observed in living and fossil

series even when reinforced by the experimental evi-

dence of heredity. A definition may be essayed through

Zebu (Bos indicus) was introduced to the cow Gayal (Bibos frontalis), and

a female hybrid was born October 29, 1868 (A of pedigree).

(A) produced her first calf June 17, 1872, a second one October 16, 1873,

a third one January 5, 1875, a fourth March 11, 1876, a fifth November 2,

1878; these five calves were the produce of this female hybrid Gayal with

the Zebu bull. She was now introduced to the male American Bison pipt

earar and on May 21, 1881, she produced a fone. No. 2 (B

pedigree), ?

‘‘It will be seen that this animal (B) is the product not only of the

intermixture of three well-marked species, but, according to our present

definition, of three distinct genera.

‘‘ This remarkable animal, the result of the triple alliance, was last year

introduced to the bull Bison, and on March 12, 1884, she produced a female

(C of pedigree). This last individual, now eleven weeks old, is undistin-

guishable from a pure-bred Bison of the same age.’’

2AT: ee THE AMERICAN NATURALIST [Vou. XLIX

an enumeration of the known properties of a ‘‘least

character.”’ :

` As distinguished from a group of characters the prop-

erties of a ‘‘character’’ are its separability, its inde-

pendence, its individuality, its own rate of movement

ontogenetic and phyletic, its differentiation by these

properties from other least characters. Its separability

in heredity is shown where it can be hybridized.

From the structural or anatomic standpoint a least

character is a group of cells and tissues constituting a

diminutive organ or part of an organ subserving a dis-

tinct though subsidiary function. For example, the ‘‘pli

caballin’’ in the enamel of the horse’s tooth or the rudi-

mentary cuspule may be cited as least characters, for

each is composed of a vast number of cells and more than

one tissue, but seems to have the property of rising or

falling and behaving like a unit. -

11. “Least Characters” in Classification and Systematic

Work

This ‘‘least-character’’ conception is of great value to

the zoologist and botanist in systematic work, this con-

ception of an individual as a colony of ‘‘characters’’ each

with its principles of independence and its principles of

correlation, germinal in origin but subject to somatic

modification by environment and habit.

First, among these single characters are those ob-

served by Waagen which accumulate until they build up

into one of his ‘‘mutations.’’ One or more such single

characters compose the ‘‘mutants’’ of De Vries.

Second, the old but oft-confusing term ‘‘races’’ be-

comes clear; we may now understand the significance of

the races of the horse, for example, the Arab, the Forest,

the Steppe horse. These races are all fertile inter se

and thus have never been defined as species although fer-

tility and non-fertility are no more important in the dis-

tinction of species than any other ‘‘character.’’ The

characters which distinguish races are, nevertheless, often

of specific value; they are either proportional or numer-

No. 580] ORIGIN OF SINGLE CHARACTERS 235

ical, because in the production of these modern races

the pure ancestral forms had in their natural state

evolved a very large number of allometrons as well as

rectigradations and other numerical characters which

have to a slight degree blended in intercourse and to

a larger degree have maintained their purity and dis-

tinctness. Thus you will observe among the modern

races of horses the most incongruous mixtures; an old

eart horse with the head and quarters of the Forest

type will gallop across a field and raise the bones of the

tail perfectly erect exactly like a pure bred Arab.

Similarly a ‘‘species’’ is a mosaic of an infinite num-

ber of least characters in a state of movement only a few

of which may be so definite and measurable as to be

employed in systematic definition.

12. Theoretical Conclusions as to ‘‘Characters’’ and

the ‘‘Organism’”’

These least characters when assembled in an organism

and dominated by the principles of separability and cor-

relation present to our fancy the picture of a vast regi-

ment of soldiers walking in single line; each soldier pos-

sesses his own individuality and separableness from his

comrades, each advances or lags behind according to his

individual velocity, but each subserves the general pur-

poses of the entire regimental line through the uniting

force of training and the unseen spirit of the regiment,

which represents the law of correlation.

It appears that we paleontologists have already learned

much and that we have still far more to learn by the clos-

est observation of ‘‘characters’’ in a state of natural evo-

lution. We are on somewhat safer ground than the ob-

server of the unnatural or hotbed evolution of characters

in the artificial breeds, hybrids of animals and plants

under domestication. The contrast between the excess-

ively slow natural evolution during the past million years

of the wolf, the arctic fox and the red fox, and the feverish

unnatural evolution of the domestic breeds of dogs dur-

236 THE AMERICAN NATURALIST [Vou. XLIX

ing the last ten or twelve thousand years is extremely

significant.

If the student of genetics abandons the natural and the

Illustrating the Continuity Theory

The young

Titanotheres

of every

stage in-

herit ther

Characters,

new ana Fa ower OTR

e Brontothérium

from the 12

Corm Calls an HL Titanotheres

weer d Riv oe Eoc)

of the wie rinses a

Germ

parent cell

Titanotheres. B /

The body 2G

of the

Titanothere Ge .

tS an af Y J a

offshoot 1*Gen Lower Eocene

eee Germ, Eotitanops

Celty ate |

its parent Comtenserty

Germ Plasm

(Heredity)

1c. 10. Evolution by the constant addition of koe illustrated in the

descent of Brontotherium (B) from Eotitanops (A). The nimals are repre-

sented to the same scale. They flnstrate the constant haaie on of new char-

acters in every part of the organism. Evolution in this family of quadrupeds is

almost entirely by the addition of characters. Comparatively few characters

degenerate or disappear.

normal for the unnatural and the abnormal and sticks

solely to his seed pan and his incubator he is in danger

of observing modes of origin and behavior of characters

No. 580] ORIGIN OF SINGLE CHARACTERS 237

which never have and never will occur in Nature. He

may, moreover, never observe at all certain modes of

origin and behavior as well as certain properties and

qualities of characters which are of the most fundamental

importance in relation to his particular field of heredity

and hybridizing.

While twenty years of observation of the normal and

the natural aspects of nature have brought the zoologist

and paleontologist somewhat nearer to a conception of the

modes of evolution, twenty years of continuous observa-

tion of the abnormal and unnatural have landed one of

the leading experimentalists, William Bateson, in the

state of skepticism and agnosticism expressed in his recent

work (p. 248, italics our own) :??

The many converging lines of evidence point so clearly to the central

fact of the origin of the forms of life by an evolutionary process

that we are compelled to accept this deduction, but as to almost all

the essential features, whether of cause or mode, by which specific

diversity has become what we perceive it to be, we have to confess an

ignorance nearly total. The transformation of masses of population

by imperceptible steps guided by selection, is, as most of us now see,

so inapplicable to the facts, whether of variation or of specificity,

that we can only marvel both at the want of penetration displayed by

the advocates of such a proposition, and at the forensic skill by which

it was made to appear acceptable even for a time.

If the principle of the continuous and independent

movement of each member of a vast colony of single

characters is firmly established, as it appears to be

through vertebrate and invertebrate paleontology, we

must abandon entirely one tradition left by the master

mind of Darwin which has permeated the work of all the

original Darwinians and Neo-Darwinians, and which is

equally strong in the mind of De Vries. Bateson has re-

cently maintained this tradition of the origin of ‘‘species”’

from fortuitous saltatory characters in the following lan-

guage.?3

22 Bateson, William, ‘‘ Problems of Genetics.’’ 8vo. Oxford University

Press, 1913, 250 pp.

23 Op, cit., p. 248. Italics our own.

238 THE AMERICAN NATURALIST [Vou. XLIX

In place of this doctrine we have little teaching of a positive kind

to offer. We have direct perception that new forms of life may arise

sporadically, and that they differ from their progenitors quite suffi-

ciently to pass for species. By the success and maintenance of such

sporadically arising forms, moreover, there is no reasonable doubt that

innumerable strains, whether in isolation or in community with their

co-derivatives, have as a fact arisen, which now pass in the lists of

systematists as species.

Broadly stated, this tradition is that evolution mani-

fests itself suddenly in one character or group of char

acters; that either through individual variation such a

character or group of characters is preserved and accu-

mulated by selection, or, through saltation that such a

character or group of characters suddenly arises and is

imperishably fixed in the race by selection.

This is the essential feature of the Darwinian concep-

tion of evolution, namely, that an organism advances now

here, now there. Such a conception is one which would

naturally be fosterd by observers of single living plants `

or animals living under unnatural conditions, or by ex-

perimentalists who observe a brief contemporary chain

of organisms.

The observation of ‘‘characters’’ in phyla or groups of

organisms advancing on a grand scale in space or in time

shows that this Darwinian tradition is so partial and inad-

equate as to be practically false. It has been observed

that every organism consists of an almost infinite number

of characters, it has also been observed that the evolu-

tion of some of these characters may be so conspicuous as

for a time to attract the attention of the observer or as

to constitute the chief magnet for the power of selection.

It has not been observed that the entire organism waits

on any one of these characters. On the contrary, in all

progressive organisms in which a very large number of

characters are simultaneously observed it proves that

every character in every part of the body is in a contin-

uous state of movement. This is the actual result of

observation and measurement.

As regards natural selection in relation to the “oe of

No. 580] ORIGIN OF SINGLE CHARACTERS 239

characters we know nothing, we stand by the theoretic

opinion that: Selection is operating always upon the sum

of all the movements, actions and reactions of characters

known as the Orcanism and upon all single characters

of survival or elimination value.

Very recent is Bateson’s enunciation** of the novel

hypothesis that we may have to forego the theory of

addition of germinal factors or determiners and substitute

a theory of variation by loss of ‘‘factors’’:

- Paleontology affords only indirect evidence as to ger-

minal ‘‘factors’’ but it offers the most positive testimony

both as to evolution largely by the loss of characters, as in

the case of the family of horses, and evolution largely by

the addition of characters, as in the family of titanotheres -

displayed in Fig. 10. It is the constant addition of new

somatic characters in the evolution of members of the

latter family which forms the background of the present

address. Whether the incessant and most impressive ad-

dition of the new somatic characters which transform Eoti-

tanops into Brontotherium are the visible result of a sub-

traction of germinal ‘‘factors’’? may be a subject for

metaphysical discussion, but is certainly without the

bounds of all natural evidence. A natural view is that the

invisible germ is being continuously enriched with the vis-

ible body by processes of which we can form no concep-

tion whatever.

24 Bateson, Wm., ‘‘ Heredity.’’ Inaugural Address of President to The

Australian Meatiag of the British Association. Nature, Vol. 93, No. 2338,

Aug. 20, 1914, pp. 635-642. (Italies our own.) ‘ʻI feel no reasonable

doubt that though we may have to forego a claim to variations b

of factors, yet variation both by loss of factors and by fractionation of

factors is a genuine phenomenon of contemporary nature. If, then, we

have to dispense, as seems likely, with any addition from without we must

begin seriously to consider whether the course of evolution can at all reason-

ably be represented as an unpacking of an original complex which contained

within itself the whole range of diversity which living things present. I do

not suggest that we should come to a judgment as to what is or is not

probable in these respects’’ (p. 640).

THE INFERTILITY OF RUDIMENTARY WINGED

FEMALES OF DROSOPHILA AMPELOPHILA

PROFESSOR T. H. MORGAN

COLUMBIA UNIVERSITY

Wane the infertility of the females of the mutant stock

of Drosophila called rudimentary, was apparent from the

beginning, the cause of the infertility was uncertain. Many

rudimentary females bred to males of their own kind gave

no offspring. The males with rudimentary wings, on the

other hand, were perfectly fertile with wild females and

with females of other stocks. The results might seem to

show that sperm bearing the factor for rudimentary could

not fertilize the eggs carrying the same factor. But that

this was not the entire explanation was evident: for, he-

terozygous females fertilized by rudimentary males gave

rudimentary females and males as well as long winged

flies. In the heterozygous females, however, the egg, up

to its maturity, has developed under the influence of the

normal allelomorph of rudimentary, as well as of the rudi-

mentary factor. I suggested,' therefore, that, due to this

difference during the ripening period, the rudimentary

bearing egg of the heterozygote could be fertilized by the

rudimentary sperm, although the egg of the rudimentary

female itself could not sueceed in this combination, but I

have never felt satisfied with this tentative explanation;

for, there were other possibilities, not sufficiently studied,

that might affect the result. For instance, it was not

actually observed that the rudimentary males copulate

successfully with females of their own kind, although it

was known that they could mate with any other females.

This question had first to be settled by direct observation.

Rudimentary winged females were isolated for three

1 Morgan, Zeit. f. indukt. Abs. und Vererb., VII, 1912.

240

No. 580] INFERTILITY OF DROSOPHILA 241

days after hatching, and. then each was mated to a rudi-

mentary winged male that had similarly been isolated.

In about twenty minutes, on an average, mating occurred

in an entirely normal manner. The females that had

mated were kept each in a separate bottle and given the

best food. Examination showed that hardly one of the

females had laid eggs; but in the rare cases where a

few eggs were observed, some flies developed. In the first

experiment seventeen females were seen to mate, and were

then kept alone, or with their mates. One female pro-

duced one rudimentary winged son; another gave one

rudimentary winged daughter and one such son. These

three flies were the total output of seventeen females.

The next point was to determine whether these seven-

teen females were infertile only with their own kind of

males. Each was again paired, this time to a male with

bar eyes. The character bar eye is dominant. If sperm

of these males should be successful, the female offspring

from this cross would have bar eyes, and could be distin-

guished from any others that might come from the first

‘mating. One female gave one bar daughter; another fe-

male also had one bar daughter. ` These results show that

the rudimentary females were no more successful with bar

males than with their own kind.

In a second experiment eleven rudimentary-winged fe-

males were tested with rudimentary males. One gave one

rudimentary daughter and one rudimentary son, but also

two long-winged daughters. Since I had not taken the

Same care here (using twenty-four-hour flies) as before to

be certain that the females were virgin, these two long-

winged daughters are supposedly due to fertilization be-

fore isolation, since long-winged males were hatching at

the time in the parent stock. I tested this supposition by

mating the two females to a rudimentary male, and ob-

tained the following kinds of offspring:

Long ? Long ¢ Rudimentary 9? Rudimentary ¢

56 64 15 23

242 THE AMERICAN NATURALIST [ Vou. XLIX

Evidently then the rudimentary females had been fertil-

ized by a long-winged brother before isolation, as well as

by the rudimentary male later. No offspring were pro-

duced by a third mating, to bar males.

A third and similar experiment was made. Of twelve

females, none gave any rudimentary offspring, two gave

three bar daughters apiece, but no rudimentary sons.

In a fourth experiment thirteen rudimentary-winged

females were isolated from stock. They were not neces-

sarily virgins. One gave a rudimentary-winged son; an-

other gave two rudimentary daughters and six such sons.

If only a single pair of flies is present in a culture and

few or no larve are produced, the banana generally decays

instead of fermenting. It might happen under these con-

ditions that the few larve from rudimentary females

might fail to develop, and the rudimentary sons might

also suffer, even when some of their long-winged sisters

(the father being a normal male) succeed in developing.

To make conditions favorable in this respect I proceeded

as follows: A red-eyed rudimentary female was kept at

first with a red-eyed rudimentary male for three or four

days. Then a few old white bar females and males were

added and fresh food given. The presence of these flies

and their progeny would serve to keep the food in good

condition. Moreover if the rudimentary female had been

fertilized by the rudimentary male she would produce ru-

dimentary daughters and sons. If she were subsequently

fertilized by the white bar males she would also give red

(heretozygous) barred daughters, but these could not be

distinguished from the daughters that the white-bar fe-

male would give were she fertilized by the red rudimentary

males. Nevertheless all of the sons of a rudimentary fe-

male would be rudimentary round-eyed males, regardless

as to which male was their father, and their presence

would show to what extent the rudimentary females were

fertile. The experiment was varied and simplified by

removing the rudimentary males, when the white bar

males and females were added.

No. 580] INFERTILITY OF DROSOPHILA 243

One hundred and two rudimentary females were tested

in these ways. In only three cases were rudimentary

males produced. One female produced two; one female

produced four, and another female produced one male.

It is evident, therefore, that the scarcity of rudimentary

sons can not, in general, be ascribed entirely to the condi-

tions of the food.

As pointed out above, red bar daughters might appear

in the foregoing tests and such females might have either

of the two parentages specified. Most of the females of

this kind would be expected to come from white bar fe-

males by rudimentary males, since the converse case would

rarely be realized. Seven females, that appeared, were

tested by breeding to white bar males and gave the results

in the first of the two following tables. Four others were

tested by breeding to rudimentary males with the result

shown in Table Ia. The results confirm the expectation

TABLE I

F., Rep, Lone Bar (HETEROZYGOUS) 9 BY WHITE Bar ĝ

Red White Red White Red | White| Red | Whit ed | White

Long Long Rud. Long Long Rud. | Rud. | Long | Long | Rud.

Bar Round Bar Bar Round | Bar | Round | Round Bar

; g g F a Sor g

55 44 13 24 21 t

30 30 3 14 ) 2

6 61 s 27 10 5 2

85 71 17 34 28 19

48 53 15 27 21 17

37 39 5 25 13 9

12 10 1 5 5 0 ] 1

342 304 57 156 113 59 1 2 1

TABLE I®*

F., Rep, Lone BAR (HETEROZYGOUS) 9 BY RUDIMENATRY ¢

Red | Red | Red | Red | White| Red | White| Red | White, Red | White

Long | Rud. | Long | Rud. | Long | Long | Rud. | Rud. | Long Long | Rud.

Bar | Round! Round Round| Bar Bar | Round! Bar | Round Round, Bar

8 9 9 f a E ot: dae e cde

22 15 14 13 14 6 1

37 13 1 17 26 16 9

65 10 9 26 25 24

56 25 25 12 14 12 a ea

180 63 1 65 77 6 51 1

244 THE AMERICAN NATURALIST’ [Vou. XLIX

in regard to the character of these females. Three pairs

of factors are involved which should give the following

classes of males:

Non-cross-overs Single Cross-overs Double Cross-overs

Red, rud., round. Red, long, bar. Red, long, round.

White, long, bar. White, rud., round. White, rud., bar.

Red, rud., bar.

White, long, round.

It will be observed that the rudimentary males run far

behind their schedules, due beyond doubt to their poor

viability.

White

Red ong Round

Fig. 1.

Double crossing-over took place four times in the ex-

periment. If the two X chromosomes that carry respec-

tively the factors for red rudimentary round and white

long bar are represented as twisted once around each

other, as in text-fig. 1, a, the result of fusion and recom-

bination at the crossing points would give the two chromo-

somes shown in 1, b. One chromosome now carries the

factors for red, long, round, and the other the factors for

white, rudimentary, bar. As the tables show there are

No. 580] INFERTILITY OF DROSOPHILA 245

four males that fall into these two classes. There is one

female in the second table, that is red, long, round. She

must have resulted from a cross-over gamete, a long,

round egg being fertilized by a female producing sperm

of the rudimentary male.

Still another experiment like the last one was made, but

vermilion-eyed flies instead of bar-eyed flies were added.

The virgin rudimentary females that were used were not

allowed to mate first (as before) with rudimentary males,

in order to meet a possible objection to the preceding ex-

periment, namely that the spermatheca, if first filled with

sperm from the rudimentary males, might be incapable of

filling again with sperm when another male of a different

stock is added. The vermilion (long-winged males) would

give, with their own females, flies with vermilion eyes,

while the vermilion males that mated with the rudimen-

tary females should give red-eyed, long-winged females

and rudimentary red-eyed males. In the following table

the number of rudimentary females tested in each culture

is given in the top line; in the second, central, line the

number of red, long offspring given by the flies in the

square above; and in the lowest line a record of the num-

ber of vermilion offspring given by the flies in the culture

under observation. |

T Í 1 |

Number of rudimentary — | | |

2 tested Lory Uy o To oe 8 156 4 | 4

| | | bee

Fia] | | 159)

Red long daughters... | 7| H | taa

Vermilion @ and 9..... 118463 76 119 105 3 8 654/179 0) 1 167 7 46

Out of a total of ge ay rudimentary females

only nine red-eyed daughters were produced (if we ex-

clude one culture in which five red long females and three

red-eyed males appeared which must be due toerror or to

contamination). Of the nine offspring seven came from

one culture, and possibly from one female in that culture

that laid an exceptionally high number of eggs. The

complete absence of rudimentary males may be explained

246 THE AMERICAN NATURALIST [Vou. XLIX

as a result of competition, for, as Morgan and Tice have

shown, such males tend to disappear if too many other

larvee are present.

Lastly sixty-eight more rudimentary females from stock

were tested with bar males. They gave twenty-four long

bar (heterozygous) females, two rudimentary round males

and one mosaic that will be described below. In one bottle

there had been twenty-seven rudimentary females and an

examination of their food showed over forty eggs present.

Since the eggs are not easily found I estimate that prob-

ably a hundred eggs were present. Out of these eggs

sixteen females and one male developed (included in the

total given above). It appears then that many of the

eggs laid by the rudimentary females do not develop.

‘The condition of the ovaries of the eight surviving rudi-

mentary females showed that seven were full sized and

contained mature eggs. The mosaic that appeared in one

of the last crosses (Fig. 2) is interesting in several ways.

Genetically it is a female, externally it is a male in ap-

pearance, in reality it is a male in part and a female in

part although the egg must have been fertilized by a

female-producing sperm. On the right side of the body

the eye is heterozygous for bar, there is no sex comb on

the fore leg, the spines on the thorax are long, and the

wing is large. On the left side the eye is pure bar, there

is a sex comb on the foreleg, the spines on the thorax

are short, and the wing is small. The difference in size

of the two wings, and of the spines, is a characteristic

difference between the male and female, connected with a

difference in body size. The abdomen is pigmented above

as in the male, and below there is a normal penis.

Despite the apparently normal male copulatory organs,

the mosaic, when placed with mature, unmated females,

paid not the slightest attention to them, although it was

quite active. Of course its organs of perception were

female on one side of the anterior end, although male on

the other side. What physiological complex this might

give, is, of course, problematical. The mosaic died by

No. 580] INFERTILITY OF DROSOPHILA 247

becoming stuck to the glass before its behavior towards

males could be studied.

There are two ways in which this mosaic can be ac-

Fic. 2.

counted for. If an egg of the round-eyed, rudimentary

female was fertilized by a female producing spermato-

zoon of the bar-eyed, long-winged male the result should

248 THE AMERICAN NATURALIST [Vou. XLIX

be a bar (heterozygous) eyed, long-winged female, since

these are the dominants. If, then, after fertilization, dis-

location of the X chromosomes occurred at some early

division, so that while the X carrying the factor for

bar and long divided normally (each daughter nucleus

getting its proper half), the other X chromosome carry-

ing the factors for round eye and long wings failing to

divide (or else one half failed to go to one daughter

nucleus) the characteristics of the mosaic can be ac-

counted for. On the male side, the left, there would be one

X chromosome in each cell, that carries the factors for

bar eye and long wings. ‘The size of the wing and of the

spines, and the presence of the sex comb are a consequence

of the ‘‘maleness,’’ resulting from the presence of only

one X. On the female side, the right, there would, be two

X chromosomes in all of the cells, hence the heterozygous

nature of the bar eye. The length of the wing (the female

being larger than the male) and the absence of the sex

comb are a consequence of the ‘‘femaleness,’’ due to the

two X combination. The fact that the posterior end of

the abdomen is purely male is owing to this region coming

from the male contingent of nuclei, that must have over-

. lapped to the right side in this region.

The other explanation of the mosaic is that two female

producing nuclei entered, one alone giving rise to the

male side, the other one uniting with the egg nucleus giving

rise to the female side. Boveri’s explanation of gynan-

dromorphs will not apply to this case. There is no way

to decide between the first two hypotheses, but, as I

have shown elsewhere,? the hypothesis of chromosomal —

dislocation will cover all cases of gynandromorphs in

Drosophila, while that of double fertilization will not ap-

ply to one ease that gives, for itself at least, a crucial test

of the alternative hypotheses. The hypothesis of chro-

mosomal dislocation is, therefore, to be generally pre-

ferred, unless in some special case it can be shown that

2 ‘í Mosaics and Gynandromorphs in Drosophila,’? Proc. Soe. Exp. Biol.

and Med., XI, 1914.

No. 580] INFERTILITY OF DROSOPHILA 249

double fertilization has actually brought about the par-

ticular results that that case shows.

Incidentally this sex mosaic (gynandromorph) and others

of its kind confirm the conclusions drawn from grafting

experiments in insects, namely, those in which the testes

were grafted into the female and the ovary into the male

without influence on the secondary sexual characters that

developed later. These characters in the insects must be

determined by the chromosomal composition of the cells,

and not be affected by the sex ‘‘glands’’ as such. In

contrast to this situation in the insects we find in birds

that the sex ‘‘glands’’ of the female play an important

role in the suppressing in the female of some of the sec-

ondary sexual characters—characters that appear only in

the males or.in castrated females. Gynandromorphs are

exceedingly rare in birds, but there are a few well-authen-

ticated cases. It is difficult to explain their occurrence

under the conditions named above. It is just possible, how-

ever, that their occurrence may be accounted for in the fol-

lowing way. -If a mosaic condition of the chromosomal

complex shouldarise the secondary sexual characters would

still all be like those of the female, owing to the presence

of the ovarian secretion, but, if, in such a case, the ovary

should become infected, or degenerate through senile

changes, the true male parts might sooner develop the

characteristics of the male than do the true female parts,

i. e., those parts of the body that have the female sex com-

plex. This suggestion has no value unless it may lead

some one to examine the condition of the ovary, when such

a Sex mosaic again appears.

An examination of the ovaries of many rudimentary

females was made. In the majority of cases the ovaries

become nearly as large as those in the normal female, and

while they may contain full-sized eggs most of the eggs

remain immature. Examination of the food shows that

very few eggs are laid; in fact, most females lay no eggs.

Of those laid some at least hatch. From these observa-

tions, and from the experiments, it seems clear that the

250 THE AMERICAN NATURALIST [Vou XLIX

infertility of the rudimentary females is due, largely at

any rate, to their retention of their eggs, even after copu-

lation; and since in a few cases rudimentary females and

males bred together have produced daughters as well as

sons, the hypothesis of prematuration that I suggested in

1912 is not the correct explanation of the sterility of the

females of the rudimentary winged stock mated to rudi-

mentary males. Moreover, since many of the females

tested, especially in the later experiments, were F,’s ex-

tracted through other fertile stocks, the sterility can not

be supposed to be due to any additional peculiarity that

has appeared in the rudimentary stock, but must be one of

the attributes of the factor for rudimentary itself.

NOTES AND LITERATURE

DIPTERA FROM THE SEYCHELLES.—An important work has just

come to hand* in which Mr. ©. G. Lamb describes the muscoid

flies of several groups, collected in 1905 in the Seychelles and

other islands of the Indian Ocean by the expedition under the

leadership of Mr. J. Stanley Gardiner. Considering the remote-

ness of the regions explored, and the total lack of general inter-

est in the taxonomy of these small Diptera, one would not at first

see any reason for calling special attention to this paper. When,

however, we think of the wonderful results attained by Morgan

and those working with him through the intensive study of

Drosophila, Mr. Lamb’s work, dealing in part with this very

group, gains new significance and suggests many strains of

thought. Some years ago, after looking at a number of the strange

Drosophila mutants in Professor Morgan’s laboratory, I raised

the obvious question: ‘‘How do you know that all this has any-

thing to do with the evolution of species?’’, and Professor Mor-

gan replied that he did not know it. The real answer to my

question must be found by investigating the allied species, to see

whether they do in fact differ in ways at all paralleled by Mor-

gan’s mutants, or likely to have arisen in similar fashion. The

important cytological paper by Metz, just published, represents

one way of attacking this problem; the taxonomic results of

Lamb, based on twenty species, afford us another.

At the outset, we are struck by the fact that the Seychelles

Drosophila species have been modified in a great variety of dif-

ferent ways, in several cases so remarkably that Lamb hesitates

whether to base new generic or subgeneric names upon them.

There is nothing like orthogenesis, apparently. Here is a list of

some of the more noticeable modifications:

1. Costa extending to third vein.

2. Remarkably constricted waist and sian wings. (Compare

Morgan’s short winged forms

3. A remarkable slit on the eet the end provided with spines

and bristles.

4. Remarkable transverse or oblique eyes.

5. Remarkable spines on front tarsus.

1 Trans. Linnean Sec. London, Zoology, Vol. XVI, Part 4, July, 1914.

251

252 THE AMERICAN NATURALIST [Voin XLIX

6. Curious curled hairs on front legs.

T. Marmorated thorax.

8. Entirely black, except brownish antennæ and lighter face.

All the species are new except two, one of these being the D.

ampelophila of Morgan’s experiments, the prior name for which

is D. melanogaster Meigen. One of the new species, D. similis, is

based on males differing from D. melanogaster in lacking the

large combs on the front legs, having instead only minute combs

which require a high magnification to be seen. In other respects

the flies are almost exactly as in melanogaster, and in the female

sex it is practically impossible to distinguish between the species.

There are in addition five females resembling melanogaster and

similis, but differing in a detail of the venation. May we not

suppose that D. melanogaster was introduced into the Seychelles

by man and that D. similis and the females (left unnamed)

with peculiar venation have arisen from it e mutation since

that time? T. D. A. COCKERELL

STERILITY IN A SPECIES CROSS

PROFESSOR J. A. DETLEFSEN, of the University of Illinois, has

recently published an interesting paper entitled ‘‘Genetie Stud-

ies on a Cavy Species Cross.’?! Several wild cavies from Brazil

(Cavia rufescens) were crossed with domestic guinea-pigs (C.

porcellus) and a study of the hybrid offspring was continued

for seven generations. The experiments were begun in 1903 by

Professor Castle who turned them over in 1909 to Professor

Detlefsen. They were carried on at Harvard and at the Bussey

Institution. The paper is divided into three parts; the first two

treat respectively of the genetics of color and coat factors, and

growth and morphological characters; the third and most im-

portant deals with a study of the sterility of hybrids.

Cavia rufescens differs from the guinea-pig in several charac-

ters. In size it is about half as large as the guinea-pig. It has

an agouti (gray) coat, but the animal has a darker appearance

than tame agouti guinea-pigs, owing to the yellow bands in the

ticked hair being much reduced. The belly of the wild species

varies from a light yellow to a slightly ticked condition. In

agouti guinea-pigs the belly hair is usually yellow with a dark

base, but never ticked.

Of the wild stock, only males were used in crossing, on account

of the difference in size. All F, males from such crosses were

1 Carnegie Inst. Publication No. 205, 1914.

No. 580] NOTES AND LITERATURE 253

found to be sterile but the F, females were fertile, and the line

was continued only by crossing these females with guinea-pig

males, Thus with each succeeding generation there was a reduc-

tion in the amount of wild blood and the author refers to his

hybrids as one half wild, or F,, one fourth wild or F,, ete.

As to the inheritance of coat color, the tame agouti coat is

dominant over the wild agouti. These two types segregate and

are allelomorphie to each other. Each is also allelomorphie to

its absence. Detlefsen finds that there is a constant relation be-

tween back color and belly color, but this condition is not due to

separate factors because they can not be transmitted independ-

ently. The two types of tame and wild agouti, he thinks, are

perhaps comparable with the types of gray mice described by

Cuénot and Morgan, viz., gray-bellied and light- (or white-)

bellied agouti. In crosses with non-agouti, the wild agouti type

is dominant over black and over red, as in domestic guinea-pigs.

After back-crossing the wild agouti colored hybrids with non-

agouti for several generations, it is found that the agouti factor

is modified, producing a darker coat, in some cases almost black,

the ticking being faintly seen only on the belly. Roughness of

coat is imperfectly dominant over smooth coat. In later genera-

tions it regains its dominance.

In respect to growth and vigor, the F, hybrids were heavier at

all ages than the guinea-pig parents, and were more vigorous

than either parent. These F, individuals were crossed with

guinea-pigs and gave young which were smaller than the F, ani-

mals in every way, and in size resembled the guinea-pig parent.

The variability of the wild stock in weight and vigor is unknown,

but guinea-pigs are remarkably uniform in both respects. In

morphological characters, the M-shaped nasal-frontal suture of

the wild species is dominant over the truncated nasal suture of,

the domestic form. -The truncated suture reappears in the sec-

ond generation but does not breed true. As to skull shape, the

wild has a pointed head and the tame species a round one. In

F, a blending oceurs, and in later generations the wild pointed

head disappears. In the wild cavy a narrow indenture is pres-

ent on the outer surface of the last upper molar—a character

held to be of much importance by systematists. In F, this in-

denture showed to a slight degree, and in subsequent genera-

tions was lost.

The section of the paper dealing with sterility is of great in-

terest. No previous investigations on sterility in animals have

254 THE AMERICAN NATURALIST [Vou. XLIX

been made on such a scale as the experiments reported by Det-

lefsen. The causes of sterility are very obscure and but little

understood. A change of environment and consequent lack of

exercise or difference of diet may be a contributing cause of ster-

ility in birds and wild animals in captivity, but none of these

influences were operative in Detlefsen’s experiments, because the

wild cavies from Brazil bred inter se under laboratory condi-

tions. Sterility is frequent in hybrids of species not closely re-

lated, and it is an axiom among biologists that crosses between

different species or genera produce sterile hybrids in one or

both sexes. As stated above, all F, hybrid males from a cross

between a wild cavy male and a guinea-pig female were sterile.

However, the F, females were fertile and were crossed back to

guinea-pig males. These likewise gave in F, sterile males and

fertile females. Repeated back crosses of fertile females with

guinea-pig males produced fertile males in increasing numbers

with each generation.

In order to test the fertility of the hybrid iia two methods

were used: (a) breeding tests; (b) microscopic examination of

spermatozoa obtained by transecting several tubules from the

epididymis on one side of the animal. Such an individual could

be bred subsequently. In all, 483 males were tested by one or

both methods; 50 by breeding alone; 331 by microscopie exami-

nation alone; and 102 by both methods. The following table,

giving the results of combined microscopic and breeding tests,

indicates the value of microscopic examinations in determining

the fertility of males:

; | Breeding Test

Microscopic Test No. |

| Sterile Fertile

* Without spermatozoa............... 23 23

With immotile sperm. 22 6 oo -isi 11 11

With few motile sperm. ............. 10 9 1

With many motile sperm............ 58 14 44

ee SES agen. Gear

It will be noted that of the 58 males with many motile sperma-

tozoa, 14 proved to be sterile upon breeding. Among these

males, Detlefsen attributes the sterility of 9 to external causes,

without specifying them, but he can assign no reason for the im-

potency of the remaining 5. He therefore concludes that

the number and motility of the sperm are not the only essentials for a

real fertility, inasmuch as real fertility in the last analysis may mean

No. 580] NOTES AND LITERATURE 255

the capacity to fertilize eggs and sire young. There are further reasons

for concluding that the motile sperm of the hybrid males may be physio-

logically different from those of the normal guinea-pig, for it often re-

quired much more time to obtain young from the hybrid males and the

litters were unexpectedly small.

It may be added that sterility was not due to the absence of sec-

ondary sexual characters, for all the males were normal in this

respect.

The percentage of fertile males in each generation from the

back crosses above described, was as follows:

F, F, F; F, 5 F, F, -

1/2 Wild 1/4 Wild 1/8 Wild 1/16 Wild 1/32 Wild- 1/64 Wild 1/128 Wild

14,29 33.32 60.67 69.39

In the generations having the more dilute wild blood the percent-

age of fertile males increased. The author holds that some dis-

turbance occurred in the gametogenesis of the males, subsequent

to hybridization. The females were normal, but they transmitted

this disturbing element to their sons. However, by back-cross-

ing with guinea-pigs this peculiar quality was segregated out.

It is evident that if the heredity of fertility and sterility in this

case is Mendelian, it is due not to one or two allelomorphic pairs

of factors, but to multiple factors. A table is given of the per-

centages of ultimate recessives expected in back crosses on the

basis of various numbers of factors involved. The series for 8

factors, given below, approaches most nearly the percentage of

fertile males obtained (see above) :

F F

1 i i oA F: P, F; 6 F.

0.0 0.39 10.1 34.36 59.67 77.58

88.16

The application is somewhat misleading, as the author states,

since the probable errors are not given. In each generation the ©

probable error would have to be calculated on the supposition

that the females of the preceding generation were normally dis-

. tributed, otherwise one would have to take into account the error

of all the preceding generations. It is improbable that the fe-

males of any generation, except F,, were normally distributed.

He concludes that fertility acts as a very complex recessive

character, the results being in accord with the expectations if a

number of dominant factors for sterility were present. After

these dominant factors were eliminated, there would be produced

a fertile recessive type.

Byron B. Horton

256 THE AMERICAN NATURALIST [Vou. XLIX

FLOWER PIGMENTS

RECENT researches by Wheldale and Bassett! have shown that

there are four flower pigments, i. e., ivory, yellow, red and

magenta, in Antirrhinum majus, and that these, in various com-

binations and in different states of concentration and dilution,

are responsible for all the color varieties. The ivory and yellow

pigments have been identified with apigenin and luteolin respec-

tively, i. e., members of the class of soluble yellow plant pigments

containing carbon, hydrogen and oxygen; the red and magenta

pigments are anthocyanins. The yellow, red and magenta pig-

ments occur only in the epidermis of the corolla, but ivory is

present in the inner tissues. The pigments are present in the

plant as glucosides, that is combined with sugar. For prepara-

tion, the flowers are boiled with water, the pigments precipitated

as insoluble lead salts from the filtered solution by adding lead

acetate. The lead salts are filtered off and decomposed with di-

lute sulphuric acid which forms insoluble lead sulphate and sets

free the pigment again in dilute acid solution. These solutions

are then boiled for several hours, whereby the sugar is split off

from the glucoside and the free pigment, which is less soluble,

separates out and is filtered off. The anthocyanins are separated

from the yellow (flavone) pigments by extracting the latter with

ether in which the anthocyanins are insoluble. The red and

magenta pigments have been purified and analyzed and shown to

contain carbon, hydrogen and oxygen only but a higher percent-

age of oxygen than the flavones. Determination of the molec-

ular weights of the anthocyanins also indicates that their

molecules are larger than those of the flavone pigments. Hence

if the anthocyanins are derived from the flavones, it seems likely

that the process is one of oxidation accompanied by condensation

of two or more flavone molecules or the union of flavone mole-

cules with other allied compounds in the plant. It is possible that

the factors for red and magenta color will come to be expressed in

terms of chemical substances which condense with the flavones to

from the larger molecules of the anthocyanins.

M. W.

1 Wheldale, M., ‘‘The Flower Pigments of Antirrhinum majus. 1. Method

of Preparation,’’ Biochem. Jour., 1913, 7, 87. Wheldale, M., and Bassett,

H. Ll., ‘‘The Flower Pigments of Antirrhinum majus. 2. The Pale Yellow

ór Ivory Pigment,’’ Biochem. Jour., 1913, 7, 441; ‘‘The Chemical Interpre-

tation of Some Mendelian Factors for Piwutesten? Proc. Roy, Soe., 1914,

B, 87, 300; ‘‘The Flower Pigments of Antirrhinum majus. 3. The Red and

_ Magenta Pigments,’’ Biochem. Jour., 1914, 8, 204.

VOL. XLIX, NO, 58 MAY, 1915

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THE

AMERICAN NATURALIST

Vou. XLIX May, 1915 No. 581

ON THE NATURE OF THE CONDITIONS WHICH

DETERMINE OR PREVENT THE ENTRANCE

OF THE SPERMATOZOON INTO THE EGG

JACQUES LOEB

Tue ROCKEFELLER INSTITUTE ror MEDICAL RESEARCH, New YORK

Tae well-known fact that a spermatozoon can no longer

enter an egg after it is once fertilized raises the question

whether this is due to the changes necessarily connected

with development; or whether development of an egg can

take place without the existence of such a block. We are

in possession of facts speaking in favor of the second

view. Thus the writer has shown that if the eggs of

Strongylocentrotus purpuratus or Arbacia are induced to

develop by the methods of artificial parthenogenesis a

spermatozoon can enter the egg or an individual blasto-

mere of a segmenting egg, while the latter is in the full

process of development. This leaves no doubt that the

block caused by the entrance of a hale into an

egg for the entrance of further spermatozoa must be due

to a change not necessarily identical with that inducing

the development of the egg. \

A second group of observations made by the author

deals with the phenomena of specificity and these prove

that the block which an egg offers to heterogeneous spe

is rapidly reversible and confined to the surface of the e

or the spermatozoon or both. In the case of the egg o

purpuratus and sperm of Asterias (and many similar in- \

257 `

258 THE AMERICAN NATURALIST [ Vou. XLIX

stances) the specific block can be overcome if we slightly

increase the alkalinity of the sea water. The spermato-

zoon can only enter the foreign egg while both sperm and

egg are in the hyperalkaline sea water, whereas if the egg

and sperm are treated separately with hyperalkaline so-

lution (no matter how long) and put together in a suffi-

ciently large quantity of normal sea water no egg can be

fertilized’ while fertilization will take place as soon as

the hyperalkalinity is restored. This shows that the

change (brought about by the hyperalkaline sea water)

which makes the fertilization possible is rapidly reversible,

as we should expect it to be if it consisted merely in a

physical change at the surface of the egg. To this series

of facts, others might be added which point in the same

direction. In this paper we intend to discuss a little

more fully the various conditions which block or favor

the entrance of a spermatozoon into an egg, in order to

form an idea of the nature of the forces which control

these phenomena.

1. When the unfertilized eggs of S. purpuratus are

treated for two hours with hypertonic sea water (50 c.c.

sea water +8 c.c. 24 m NaCl or Ringer solution) the

eggs of certain females will develop into blastulæ, gas-

trulæ and plutei, while the eggs of other females can not

be caused to develop in this way. These individual dif-

ferences coincide possibly with those observed by the

writer in regard to spontaneous membrane formation in

the eggs of different females? and it is possible that only

the eggs of such females of purpuratus can be induced to

form larvæ through a mere treatment with hypertonic sea

water in which the latter can induce the cortical changes

underlying the membrane formation. Whatever the na-

ture of the individual difference may be, purpuratus eggs

1 The large quantity of sea water is necessary so that the hyperalkaline

sea water at the surface of the egg and sperm can diffuse away before both

gametes ger in contact.

2 Loeb, Arch. f. Entweklngsmech., XXXVI, 626, 1913; ‘‘ Artificial Par-

thenogenesis and Fertilization,’’ Chicago, 1913, p. 219.

No. 581] ENTRANCE OF THE SPERMATOZOON 259

which have been induced to develop into larve by a hyper-

tonic solution can be fertilized with sperm while they are

in the process of segmentation. When such eggs are in

the two-, four-, eight-, or sixteen-cell (and possibly also

later) stages the sperm can enter into one or more blasto-

meres of such an egg and this entrance betrays itself by

a distinct and clear membrane formation around each

blastomere.? While the segmenting eggs which were not

fertilized with sperm develop into larvæ, those into which

Sperm enters perish very rapidly. This simple and

rather striking experiment which can easily be performed

in the eggs of Strongylocentrotus, where the membrane

formation around a single blastomere can be clearly recog-

nized, shows that the process of development in a fer-

tilized egg in itself can not be responsible for the block

caused by fertilization. It looks as if the entrance of a

spermatozoon into the mature egg, independently of the

developmental changes it induces in the egg, causes some

physical or physico-chemical change (of the surface of

the egg?) which renders the subsequent entrance of a

Spermatozoon impossible.

2. With the eggs of most females of purpuratus the

treatment with a hypertonic solution does not lead to a

development into larve, but only to the first segmentation

Stages in a limited number of eggs (provided that the

eggs have been exposed to the solution the proper period

of time). Such blastomeres afterwards go into a resting

Stage. If one waits long enough, until there is no doubt

left that the blastomeres have reached a resting condition

and will divide no further, and if one then adds sperm,

the individual blastomeres can again be fertilized, which

is indicated by a membrane formation around each indi-

vidual blastomere and the sul t of such

blastomeres into swimming larve. The fact that each

individual blastomere in this ease is fertilized independ-

3 Loeb, ‘‘ Artificial Parthenogenesis and Fertilization,’’ p. 240; Arch. f.

Bniwekingamech, XXIII, 479, 1907. aS

4Loeb, Arch. f. Entweklngsmech., XXIII, 479, 1907; ‘‘ Artificial Par-

Decree and Fertilization,’’ p. 237.

260 THE AMERICAN NATURALIST [Vou. XLIX

ently of its neighbors suggests that there is no protoplas-

mic connection between the neighboring blastomeres;

otherwise the entrance of a spermatozoon into one should

cause its neighbors also to form a fertilization membrane,

which does not happen.

All these facts show that the changes underlying devel-

opment do not necessarily prevent the entrance of a sper-

matozoon into an egg fertilized by sperm.

3. Development can be initiated in an unfertilized egg

by causing a membrane formation by a fatty acid. Eggs

after such an artificial membrane formation perish as a

rule rapidly at room temperature (if no second treatment

is given them) but they may segment if kept at a low tem-

perature. The eggs are usually put after treatment with

the butyric acid into normal sea water in which they form

a membrane. This membrane is different in the eggs of

different species of sea urchins. In the egg of S. pur-

puratus the membrane is tough and entirely impermeable

to the spermatozoon. When we add sperm to such eggs

with a butyric acid membrane they behave exactly as if no

sperm had been added, they all perish rapidly (at room

temperature). The question arose, if a spermatozoon

could still enter the egg of purpuratus after membrane

formation, provided the membrane could be destroyed.

This can be done in a certain percentage of the eggs of

purpuratus by shaking them after artificial membrane

formation; the number of eggs whose membrane is torn

varies in different experiments owing probably to dif-

ferences in the thickness and toughness of the membrane.

Even if the membrane is torn the edges may come close

together again so that the opening often is closed

again and no spermatozoon can go through. Kupelwieser

and the writer performed this experiment on the eggs of

purpuratus and it was found that such eggs with torn

membranes were fertilized upon the addition of sperm

and developed normally; while the eggs whose mem-

branes were intact all perished.®

5 Loeb, ‘‘ Artificial Parthenogenesis and Fertilization,’ p. 234.

No.581] ENTRANCE OF THE SPERMATOZOON 261

The writer repeated this experiment last winter with

the same result. He found that eggs with torn mem-

branes when subsequently fertilized with sperm did not

form any new membranes as he had stated before. It is

possible that he mistook at that time the new hyaline

membrane which forms around the egg after membrane

formation and fertilization for a new fertilization mem-

brane.

It is not necessary that these eggs be fertilized im-

mediately after the artificial membrane formation, the ex-

periment succeeds also after some time (one hour or

more) ; only with this difference that the eggs perish very

rapidly after the membrane formation if they receive no

second treatment. In order to avoid this difficulty the

writer last winter proceeded as follows: Artificial mem-

brane formation was produced in the eggs of a purpuratus

and all eggs had formed perfect membranes. One con-

trol was kept and the rest were shaken. These were di-

vided into three lots, one served as a control; the eggs of

the latter all perished as fast as the eggs of the first control

(which were not shaken). The second lot were fertilized

after about one half hour after membrane formation.

Twenty per cent. of these eggs developed into normal

larve, the rest perished. The percentage of developing

eggs corresponded roughly with the percentage of eggs

whose membrane was torn. The third lot of the shaken

eggs was put overnight into 50 c.c. sea water +7 drops

of 1/10 per cent. KCN, to prevent the disintegration of

these eggs. The next morning (sixteen hours after the

membrane formation) the eggs of Lot 3 were transferred

into normal sea water and divided into two lots, one was

fertilized with sperm, the other was kept as a control.

About twenty per cent. of the eggs which were fertilized

began to segment, but many in an abnormal way and

none developed into larve. Of the second lot to which

no sperm was added also a few began to segment. As

the writer has shown in former experiments, the eggs of

Strongylocentrotus can be caused to develop after artifi-

262 THE AMERICAN NATURALIST (Vou. XLIX

cial membrane formation if they are either treated for a

short time with a hypertonic solution or if for a longer

period the oxidations are suppressed in them by lack of

oxygen or the addition of cyanide. There is therefore no

doubt that the eggs of purpuratus in which the artificial

membrane formation has been induced by butyric acid

ean be fertilized subsequently with sperm.

4. The treatment of the eggs of Arbacia with butyric

acid leads to the formation of a membrane which varies

considerably in the eggs of the same female. Some eggs

have a thin membrane which is permeable to the sper-

matozoon, others have a tough fertilization membrane

which is as impervious to the spermatozoon as the regular

fertilization membrane. The percentage of the eggs with

membranes permeable for sperm varies very much in dif-

ferent experiments, according to the material and accord-

ing to the external conditions. If this is kept in mind it

is easily understood that the number of Arbacia eggs

which can be fertilized after they have been treated with

butyric acid differs in different experiments. Since the

membrane called forth by butyric acid is not always

plainly visible, it is a prerequisite that always one set of

such eggs should be set aside as controls to ascertain

whether or not all the eggs disintegrate rapidly (if no

second treatment is given to them). Only if they all dis-

integrate rapidly have we any guarantee that in all of

them the membrane formation has been effective. The

former experiments of the writer show that such eggs

can be fertilized by sperm; in fact they show that while

the unfertilized eggs disintegrate rapidly after the in-

ducement of the membrane formation with butyric acid,

the subsequent fertilization of such eggs by sperm saves

their lives and makes them develop.®

1. It is a well-known fact that most eggs can only be

fertilized by sperm of their own or a closely related

species. The writer thought that in order to obtain light

€ Loeb, Arch. f. Entweklngsmech., XXXVIII, 416, 1914.

No. 581] ENTRANCE OF THE SPERMATOZOON 263

on the nature of the block to the entrance of hetero-

geneous sperm it was necessary first to find the means by

which this block could be overcome. He succeeded in

showing that the egg of the sea urchin S. purpuratus can

be fertilized by the sperm of starfish, brittle stars, and

holothurians in sea water (or other balanced solutions)

if their alkalinity was a trifle higher than that of ordinary

sea water (e. g., in a solution of 50 c.c. sea water + 0.6 c.c.

N/10 NaOH). Godlewski’ succeeded by the same

method in the fertilization of the egg of the sea urchin

with the sperm of crinoids

The most important fact found out in this connection

was the following, namely, that the fertilization of the

egg of purpuratus by the sperm of Asterias only takes

place while both eggs and sperm are in this hyperalkaline

solution. If eggs and sperm are put into these solutions

separately and if then from time to time sperm and eggs

so treated are transferred into normal sea water, as a

rule not a single egg is fertilized; while with the same

material when eggs and sperm are together in the hyper-

alkaline solution as many as 100 per cent. of the eggs may

be fertilized. The effect of the alkali is, therefore, rap-

idly reversible; the eggs when put from the hyperal-

kaline sea water free from sperm into the normal sea

water containing very motile sperm of Asterias can not

be fertilized; when put back into hyperalkaline sea water

containing Asterias sperm they will be fertilized rapidly.

This rapid reversibility of the effect of the NaOH in-

dicates that it must be confined to the surface of the egg

and the spermatozoon or both; and this is corroborated

by the fact that the NaOH does not enter the cells. One

of the forces which determine the entrance of the sper-

matozoon into the egg may be surface tension and the

phenomenon of the entrance may be comparable or pos-

sibly identical with the phenomenon of phagocytosis.

Godlewski mentioned that he occasionally observed a

7 Loeb, Pfliiger’s Arch, IC, 323, 1903; CIV, 325, 1904; Arch. f.

Entweklngsmech., XL, 310, 1914; Science, N. S., XL, 316, 1914.

8 Godlewski, Arch. f. Entwekingsmech., XX, 579, 1906.

264 THE AMERICAN NATURALIST [Von. XLIX

fertilization of the egg of the sea urchin with the sperm

of a crinoid in normal sea water after both had been

treated with hyperalkaline sea water separately. This

observation is correct but finds its explanation in the as-

sumption that in such cases the hyperalkaline sea water

had not had time to diffuse from the jelly of the egg or

from the surface of the egg protoplasm by the time the

‘spermatozoon came in contact with it. In order to test

this view the writer treated the eggs of purpwratus with

a hyperalkaline solution of greater than the optimal con-

centration while the sperm was treated separately with

the optimal concentration (50 c.c. sea water + 0.6 c.c.

N/10 NaOH) and then both were mixed in a little sea

water in a watch glass. In such a case a large number

of eggs were fertilized, but while the fertilization occurred

nominally in normal sea water it really occurred in a

layer of hyperalkaline sea water surrounding the proto-

plasm of the egg.

The conclusion from these experiments is that the block

to the entrance of the spermatozoon of Asterias into the

egg of purpuratus is of a rapidly reversible character,

consisting in some alteration of a physical property of

the surface. On this assumption the factor of specificity

consists of an agency which affects these properties of

the surface of the egg in the same sense as the increase in

the concentration of the alkali. It should be added that

the writer observed also that an increase of the concentra-

tion of Ca in the sea water acts in the same sense as an

increase in the alkalinity; and that if the concentration

of Ca is increased the increase of NaOH may be less than

is necessary otherwise.

2. If the idea was correct that the factor of specificity

contained in the spermatozoon affected only the forces

acting at the surface of the egg; and that the lack of this

factor could be replaced by a rise in the alkalinity of the

sea water, it was to be expected that the reverse should

also be possible: namely, that a change in alkalinity or

the constitution of the surrounding medium should pro-

No. 581] ENTRANCE OF THE SPERMATOZOON 265

duce a reversible block to the spermatozoa of the same

species. That means, it should be possible to find solu-

tions in which the egg does not suffer for a long time, in

which the sperm lives for a long time, and in which the

sperm of the same species is intensely active and attacks

the egg with the greatest eagerness and yet is not able to

enter; while if the medium is but slightly changed the

sperm enters the egg at once. The writer carried out

such experiments a year ago in Pacific Grove and last

summer in Woods Hole and found this to be true.®

For the purpose of these experiments the ovaries and

testes of the sea urchins were not put into sea water but

into a pure m/2 NaCl solution (after several washings in

such a solution) and kept in such a solution. Several

drops of sperm and one drop of eggs were in one experi-

ment put into 2.5 c.c. of a neutral mixture of m/2 NaCl

and 3/8 m MgCl, in the proportion in which these two

salts exist in the sea water. In such a neutral solution

no egg of Arbacia or of purpuratus is fertilized no matter

how long they remain in the solution, although the sperm

is very active. If the eggs and sperm are transferred

into the same solution which contains in addition 1 drop

of a N/100 solution of NaOH (or NH,, or benzylamine,

or butylamine) or 8 drops of m/100 NaHCO,, most and

often practically all the eggs at once form fertilization

membranes and begin to segment at the proper time.

The same result can be obtained if the eggs are trans-

ferred into a neutral mixture of NaCl + MgCl, + CaCl,

(in the proportion in which these salts exist in the sea

water) or into a neutral mixture of NaCl -+ MgCl, +

CaCl, + KCl. In such a neutral mixture the eggs form

fertilization membranes and begin to segment.

The eggs will not be fertilized if transferred into a

neutral solution of NaCl or of NaCl + KCl.

It is, therefore, obvious that if we diminish the alkalin-

ity of the solution surrounding the egg and if we deprive

this solution of CaCl, we establish the same reversible

® Loeb, Science, N. S., XL, 316, 1914.

266 THE AMERICAN NATURALIST [ Von. XLIX

block to the entrance of the spermatozoon of Arbacia into

the egg of the same species as exists for the entrance of

the sperm of starfish into the egg of purpuratus in normal

sea water.

Another form of the experiment may be mentioned.

When we put sperm and eggs of Arbacia (which had been

washed in an m/2 NaCl solution) into a neutral mixture

of NaCl+ KCl no egg can be fertilized although the

sperm may be so active and concentrated that the eggs

roll around in the solution and the chorion (the jelly sur-

rounding the egg) may be filled with spermatozoa. In <

one experiment the eggs and sperm of Arbacia were kept

overnight in watch glasses containing 2.5 c.c. of this mix-

ture of neutral NaCl + KCl. The next morning all the

eggs were intact and not a single one was fertilized. At

that time 20 drops of sea water were added to the mixture

and instantly fertilization membranes were formed and

practically all the eggs segmented.’

It can be shown that in this experiment the sea water

added two important substances, Ca and NaOH. If

NaOH alone is added to the mixture of NaCl + KCl, as a

rule no egg is fertilized or only a few; if CaCl, is added

to a neutral mixture of NaCl+ KCl a number of eggs

are fertilized. If both CaCl, and NaOH are added in the

proper proportion as a rule all the eggs are fertilized.

It is perhaps important to call attention to the fact

that if eggs of Arbacia are fertilized in sea water and if

after repeated washings in a mixture of NaCl + KCl or

of NaCl+ MgCl, they are put into these solutions they

will segment repeatedly in these solutions, thus showing

that the eggs were really not fertilized in these two so-

lutions in the above-mentioned experiments.

The striking fact is again that the block created by the

ves This experiment was carried out with different concentrations of sperm

and it was found that only in the dishes where the concentration of sperm

was sufficiently high were all the eggs fertilized upon the addition of sea

water. This is perfectly natural as the majority of spermatozoa die grad-

ually (as do also the eggs) and hence enough spermatozoa will only be alive

the next day if the concentration of sperm was not too low.

No. 581] ENTRANCE OF THE SPERMATOZOON 267

lack of CaCl, or NaOH or both to the entrance of the

spermatozoon is removed immediately after these sub-

stances are added. The block must be due merely to a

change in the physical condition of the surface (which

may be based on a rapidly reversible chemical reaction).

In these experiments the NaCl can not be replaced by

isotonic sugar solutions. The same fact was found by

the writer to be true for heterogeneous hybridization.

It is of importance to call attention to the fact that

the abolition of the block in the case of heterogeneous

hybridization depends upon the same substances, CaCl,

and NaOH (or some other alkali), which make normal

fertilization possible. The influence of electrolytes on

the fertilization of the egg of purpuratus by the sperm of

Asterias is parallel to the influence of the same electro-

lytes on the fertilization of the same egg by the sperm of

purpuratus; only the concentrations differ, and always

in the same sense. The forces at work are, therefore,

apparently the same in both cases; but we can only ex-

press surmises as to their nature. The rôle of salts as

well as the rapid reversibility indicate that they are

forces situated at the surface of the egg and the sperma-

tozoon or both. In the first place we may think of sur-

face tension conditions and in this respect it is possible

that the entrance of the spermatozoon into the egg may

be determined by such forces in a way similar to the

process of phagocytosis. In the second place it may be

that previous to the action of surface tension forces an

alteration in the degree of fluidity of the egg surface may

be required (e. g., that physical change which finds its

expression in the formation of the fertilization cone).

Thirdly, it may be possible that before the surface ten-

sion forces can act the spermatozoon must agglutinate

with the egg surface and that this agglutination is de-

termined by certain specific substances or by certain salts

(CaCl, and NaOH) or by both.

Brief mention should be made of the block discovered

by Godlewski’! to the entrance of a spermatozoon into

268 THE AMERICAN NATURALIST — [Vou. XLIX

the egg if the sperm of the same species is mixed with the

sperm or the blood of a species widely apart. If, for

instance, the sperm of a sea urchin is mixed with the ~

sperm of certain annelids (Chetopterus) or molluses and

if after some time the eggs of the same sea urchin are

added to the mixture of the two kinds of sperm no egg is

fertilized. If the solution is, however, subsequently

diluted with sea water or if the egg that was in this

mixture is washed in sea water, the same sperm mixture

in which the egg previously remained unfertilized will

now fertilize the egg. From these and similar observa-

tions Herlant!? draws the conclusion that the block

existed at the surface of the egg, inasmuch as a reaction

product of the two types of sperm is formed after some

time which alters the surface of the egg and thereby pre-

vents the sperm from entering. This view is not only

supported by all the experiments but also by the observa-

tion of the writer that foreign sperm or blood is able to

cause after some time a real agglutination if mixed with

the sperm of a sea urchin or a starfish.12 We can imagine

that the precipitate forms a film around the egg and

acts as a block which can be removed mechanically by

washing.

It is not impossible that the block which exists in the

fertilized egg is due also to an alteration of the physical

character of the surface of the egg which in this case is,

however, induced from within the egg by changes caused

by the entrance of the spermatozoon, which, however, are

not necessarily identical with those causing development

as was shown by the facts in the second chapter.

EY.

We will now turn to the question whether the motility

of the spermatozoon plays no other rôle than to bring the

spermatozoon so close to the surface of the egg that sur-

face tension phenomena can engulf the spermatozoon

into the egg. It is easy to show that if the spermatozoa

11 Godlewski, Arch. f. Entweklngsmech., XX XIII, 196, 1911.

12 Herlant, Anat. Anzeiger, XLII, 563, 1912.

“hes Loeb, Jour, Exper. Zool., XVII, 123, 1914.

No.581] ENTRANCE OF THE SPERMATOZOON 269

of purpuratus are immobilized by NaCN no egg of the

same species can be fertilized, no matter how concen-

trated the sperm; while the same sperm when it revives

from the effect of NaCN fertilizes the same eggs at

once. This meets with the possible objection that the

motility of the sperm might be only necessary to allow

the latter to penetrate the jelly surrounding the egg

protoplasm. In order to test this objection the writer

freed the eggs of purpuratus from this jelly by treating

them for two minutes in a mixture of 50 c.c. sea water

+ 3 c.c. N/10 HCl in which all the jelly is dissolved. The

eggs were washed afterwards in sea water and it was

found that if sperm was added practically all were fertil-

ized. The writer put such eggs with sperm which was

immobilized by NaCN. The eggs and the sperm were

squirted together with a pipette in order to bring about a

close contact. No matter how concentrated the sperm

was, not a single egg was ever fertilized. As soon as

the spermatozoa recovered and showed only a slight

degree of motility fertilization became possible. This

leaves no doubt that the motility of the sperm is one

of the forces required to bring the spermatozoon into

the egg.

That motility is not the only force was already indi-

cated by the previous chapter which made it clear that

even if the sperm is active it can not enter the egg unless

certain physical conditions at the phase boundaries of

egg, spermatozoon and surrounding solution were right.

In order to leave no doubt about this fact the following

experiments may be quoted. If we put NaCl sperm**

of purpuratus or of Arbacia into a neutral mixture of

NaCl + KCl containing eggs of the same species the —

sperm will sooner or later become very active. Yet not

a single egg is fertilized. If we make the solution

slightly alkaline the sperm becomes at once extremely

active yet with a few exceptions no egg is fertilized; while

much less active sperm will fertilize all the eggs if CaCl,

is added. The second fact is this: that the most active

14 Sperm from testicles washed in m/2 NaCl and kept in such a solution.

270 THE AMERICAN NATURALIST [Vou. XLIX

sperm of Asterias will not fertilize the eggs of purpu-

ratus in sea water while it will do so in hyperalkaline sea

water (50 c.c. sea water + 0.6 c.c. N/10 NaOH).

We, therefore, arrive at the conclusion that aside from

the physical conditions at the surface of the egg and the

spermatozoon the impact of the spermatozoon against

the egg is a prerequisite for the process of fertilization.

von Dungern was, as far as the writer is aware, the

first to call attention to the fact that the egg itself causes

resting spermatozoa to become active,'® but curiously

enough he tried to show that only foreign sperm is

‘¢ stimulated ’’ in this way by the egg (which is, as F. Lillie

pointed out, not correct) and v. Dungern tried to explain

on this basis why it was not possible to fertilize the egg

of the sea urchin with the sperm of the starfish which

had at that time not yet been accomplished.

von Dungern noticed that the egg of the sea urchin

‘‘stimulates’’ the spermatozoon of starfish to greater

action and he concluded that since ‘‘stimulation’’ accord-

ing to Jennings causes ‘‘motor reaction’’ whereby the

direction of the motile organism is changed this very

stimulating influence of the egg of the sea urchin upon

the spermatozoon of the starfish prohibited the latter

from getting into the egg. On the basis of the same idea

von Dungern was consistently led to the further con-

clusion that the egg exercised no ‘‘stimulating’’ influence

upon spermatozoa of its own species and that thereby the

spermatozoon of the same species was enabled to get

into the egg. A year after the appearance of von

Dungern’s paper the writer succeeded in accomplishing

the hybridization of the sea urchin egg with starfish

sperm by a method which contradicted von Dungern’s

theory, namely, by increasing the alkalinity of the sea

water whereby the spermatozoon is ‘‘stimulated’’ to still

greater activity; and on the other hand it is a common

experience that a sea urchin spermatozoon becomes more

active when it comes near an egg of its own species.

The writer was anxious to compare the activating

15 v: Dungern, Ztsch. f. allg. Physiol., I, 34, 1902.

No. 581] ENTRANCE OF THE SPERMATOZOON 271

action of eggs of the same and various foreign species

upon spermatozoa. Since the spermatozoa of the sea

urchins are usually very active in pure sea water (i. e.,

sea water free from egg substance) it was necessary to

find a solution in which these spermatozoa will keep alive

for a number of days without showing any motility.

Such a solution was found in a neutral m/2 NaCl solution

and this led to the method of putting ovaries and testes

directly into such solutions instead of into sea water.1®

The ovaries and testes were first washed repeatedly in

these solutions to free them from the blood or its salts,

and then one drop of eggs and one or more drops of the

sperm suspension were mixed in a watch glass containing

5 c.c. m/2 NaCl (free from egg contents). In one experi-

ment the sperm and eggs of two sea urchins, purpuratus

and franciscanus, and two starfish, Asterias ochracea

and Asterina (at Pacific Grove), were used. None of

the four forms of spermatozoa showed any motility in a

pure NaCl solution (without egg contents). In sea

water (free from egg contents) the spermatozoa of the

two forms of sea urchins were very active, those of the

starfish were immobile. The starfish eggs were imma-

ture and did not mature during the experiment (those of

Asterias were out of season and very small); the sea

urchin eggs were mature. The result is indicated in the

following table.

That there exists no strict specificity is obvious by the

fact that the immature eggs of Asterina activate the

sperm of the sea urchin franciscanus as powerfully as is

done by the mature eggs of the sea urchin purpuratus

and franciscanus. But the spermatozoa of the two

species of starfish show a marked specificity inasmuch as

they are activated strongly only by the (immature) eggs

of their own species and only to a slight degree by the

16 The writer had found previously that the unfertilized eggs of purpuratus

are killed more rapidly in sea water than in a neutral m/2 NaCl solution,

probably on account of the greater alkalinity of the former. The same may

be true for the sperm of this species, athough this has not.yet been tested.

The unfertilized egg of Arbacia is more sensitive to a pure NaCl solution

than that of purpuratus.

272 THE AMERICAN NATURALIST (Vou. XLIX

TABLE I

SPECIFICITY OF ACTIVATION OF SPERM BY EaGes

| Asterias d | Asterina € . | Franciscanus g| Wirpa

Asterias 9 (immature). . | | No Moderately iraa effect

very motile. | activation. active. | medi-

ate eae

egg.

Asterina 2 (immature). Not motile. elie activ- Violent activ- Sticke effect

| ity. | ity. | en near

| |

Franciscanus 9 (mature) Slightly | No motility. Immediately Immediately

motile. | active otile.

Purpuratus 9 (mature). Slightly tien effect Immediately Inm petane

motile afterin immediate

some time. bonte ct wit

eggs of the sea urchin purpuratus. In judging these

results the reader must keep in mind first that all these

experiments are made in a NaCl solution, and second,

that it requires a stronger influence to activate the

spermatozoa of the starfish which are at first not motile

in sea water (free from egg contents) than the sea urchin

spermatozoa which are from the very first very active

in such sea water and which may therefore be considered

as being at the threshold of activity in the pure NaCl

solution.

If instead of the eggs themselves the supernatant NaCl

solution from eggs is added to the sperm it is found that

it requires a very much greater concentration of the

supernatant NaCl solution from Asterias eggs to arouse

the purpuratus sperm in NaCl into activity than if the

supernatant NaCl solution from purpuratus or from

franciscanus eggs is used.

he question now arises whether the relative influence

of the egg on the motility of the sperm bears any relation

to the power of the latter to enter the egg; or in other

words if we can foretell which forms will hybridize by

observing the relative activating effect of the eggs upon

the spermatozoa. This does not appear to be the case

on the basis of our present limited experience, since the

activating effect of the franciscanus egg upon the sperm

of Asterias is just as great if not greater than that of

: purpuratus eggs and yet Asterias sperm can enter the

No.581] ENTRANCE OF THE SPERMATOZOON 273

latter and not the former. Even if we intensify the

activity of the spermatozoon of Asterias by putting it in

hyperalkaline sea water it will not enter the egg of

franciscanus.

If we mix eggs of franciscanus and purpuratus in sea

water and add the sperm of purpuratus the eggs of

purpuratus will be fertilized more quickly than the eggs

of franciscanus; and the reverse is true if the sperm of

franciscanus is added to a mixture of both eggs in sea

water. The writer is not quite certain that this differ-

ence is accompanied by a corresponding difference in the

influence of these eggs upon the motility of their sperma-

tozoa. It is certain, however, that the addition of egg

sea water from Asterias does not help the fertilization of

purpuratus eggs by Asterias sperm, although the egg sea

water from Asterias increases the activity of Asterias

sperm.

The writer is, however, of the opinion that this activat-

ing effect of the egg upon the spermatozoon is of the

greatest importance for fertilization in nature and that

the degree of specificity which exists (although it is far

from absolute) is a means of preventing hybridization.

The writer is under the impression that the eggs which

are naturally fertilized in water are fertilized almost

instantly after they are shed. Thus it is stated at

hatcheries that the egg of the salmon loses its power of

being fertilized in a few minutes and in the case of

Fundulus the egg loses this power also very rapidly.

The ripe egg of starfish dies rapidly if not fertilized. On

the other hand, the writer has often been struck with the

fact that the sperm of most marine forms when put into

sea water is at first practically not motile. When the

eggs have a specific gravity considerably greater than

the water (as is the case for Fundulus) the eggs will sink

very rapidly while the sperm remains suspended for

some time. Now we have mentioned that if the abso-

lutely inactive sperm of Asterias or Asterina comes in

contact with eggs of its own species (even if they are

immature) it is at once aroused into violent activity. If

274 THE AMERICAN NATURALIST [ Vou. XLIX

the same were true for the egg of Fundulus fertilization

could take place probably before the egg reaches the

bottom of the water. If by chance a teleost of a different

species would shed its sperm in the immediate neighbor-

hood and some of it could reach the egg of Fundulus

while it is falling the foreign sperm could probably not

be aroused as quickly by the egg of Fundulus as the

sperm of the Fundulus male and hence no hybridization

would occur. In fish we can see that the male and female

shed their sexual cells simultaneously so that they come

at once in contact. The writer is inclined to believe that

something similar occurs also in Echinoderms. He had

last year a chance to verify once more an observation he

had made for a number of years and which he had already

mentioned in a previous publication.” The sea urchins

at Pacific Grove are found in large numbers on rocks in

certain coves near the shore. Up to a certain day in

March every female of purpuratus was full of eggs. On

the next day the surface of the sea in this region showed

the usual indication of the spawning of large masses of

animals: namely the enormous foam formation in the

little coves although the sea was only moderately agi-

tated. This foam formation is due to an increase of

organic substances which lower the surface tension of

the sea water and make the foam more durable. The

writer realized that this might mean the end of material

for some time to come and indeed not a single female of

purpuratus of hundreds opened on that day had eggs.

The condition was the same for all the sea urchins col-

lected for two miles along the shore. During the next

week immature eggs began to appear again in the sea

urchins and in about ten days ripe eggs were again found.

This indicates that in this region the males and females

shed their eggs and sperm simultaneously. It is not im-

possible that among sea urchins which are found in

colonies on the rocks the shedding of the sexual products

of one or several individuals acts as an incentive for the

whole colony. Since the eggs fall in this case also much

17 Loeb, ‘‘The Mechanistic Conception of Life,’’ Chicago, 1912, p. 196.

No.581] ENTRANCE OF THE SPERMATOZOON 275

more rapidly to the bottom than the spermatozoa it is

also very probable that the eggs are fertilized before they

reach the bottom of the sea. We can understand under

these circumstances that the specificity which exists in

the activating effect of the egg upon the sperm is one of

the safeguards against hybridization for eggs that are

fertilized in the water, inasmuch as this specificity acti-

vates the sperm of the same species much more quickly

than that of a foreign species. Other safeguards are the

phase-boundary conditions which we discussed in the

previous chapter.

If we assume that the spermatozoon bores itself into

the egg by the energy of the vibrations of its flagellum it

is easy to understand the importance of its motility for

this process. It is, however, equally possible that a cer-

tain energy of vibration is needed to make the spermato-

zoon stick to the surface of the egg and that afterwards

forces of a different character bring the spermatozoon

into the egg. The fact that under normal conditions a

very slight degree of motility on the part of the sper-

matozoon allows it to enter the egg seems to favor such a

view.

von Dungern had already discussed the possible rôle

of phenomena of sperm agglutination in fertilization as a

protective agency. F. Lillie discovered the transitory ag-

glutination of sperm induced by a substance from eggs of

the same species.’8 When the sperm of the sea urchin

Arbacia is mixed with the supernatant sea water from

eggs of the same species a cluster formation occurs which

may last a number of minutes and which is essentially a

transitory agglutination. In Arbacia the agglutination

is very striking, in purpuratus the phenomena of agglu-

tination are not lacking but the writer was under the im-

pression that other phenomena of the type of tropisms

might enter. But he was not very certain on this point

ana ph that question open for further discussion. The

. Lillie, Science, N. S., XXXVIII, 524, 1913; Jour. Exper. Zool.,

Sop 523, 1914.

276 THE AMERICAN NATURALIST [ Von. XLIX

writer is, however, under the impression that no proof

for the existence of a positive chemotropism of the sea '

urchin sperm for the eggs of the same species has thus

far been given.

The writer observed that this phenomenon of sperm

agglutination depends on the motility of the sperm:’®

It only appears when the sperm is extremely motile and

it lasts only a number of minutes, often only a fraction

of a minute as Lillie had found. The writer observed

that the duration of the clusters depended to some extent

on the alkalinity of the solution. The more alkaline the

latter the more rapidly the cluster scatters. The pres-

ence of a salt with a bivalent metal, especially Ca, seems

necessary for the cluster formation. Sr and Ba act like

Ca and so does Mg but in the latter case a slightly higher

concentration is needed. The more Ca is added the more

powerful the agglutination becomes. These facts sug-

gest the following origin of the agglutination. From the

jelly surrounding the eggs a certain substance is dissolved

in the sea water which reacts chemically with a certain

substance at the surface of the spermatozoon. If this

reaction takes place in the presence of one of the salts

of a bivalent metal, especially Ca, a sticky precipitate is

formed on the surface of the spermatozoa, which is slowly

soluble in the solution; and the more rapidly the more al-

kaline the solution. If the spermatozoa are very active

the impact with which they strike each other may lead to

their sticking together and this agglutination will last

until the precipitate is dissolved again.”

The writer mentions this fact here because it might give

us a clue to the rôle of the motility of the spermatozoon

for its entrance into the egg. One can imagine that the

spermatozoon must stick to the surface of the egg in or-

der to be taken into it and this sticking may not come

about unless the spermatozoon strikes the surface of the

19 Loeb, Jour. Exper. Zool., XVII, 123, 1914.

20 Lillie measures the degree of agglutination by its duration; if our as-

sumption is correct he really measures the time required for the solution of

_ the sticky precipitate on the surface of the spermatozoon by the sea water.

No. 581] ENTRANCE OF THE SPERMATOZOON 277

egg with a certain velocity. This is, however, merely a

suggestion. The really serious difficulty of such an as-

sumption lies in the fact that the specific and transitory

cluster formation or agglutination of the spermatozoa is

not a general phenomenon. It may even turn out to be

confined to sea urchins and certain annelids. It is prob-

ably lacking in all cases of hybridization. Yet this would

not necessarily speak against the possibility of an ag-

glutination of the spermatozoon to the egg as a prerequi-

site of fertilization.

This latter idea receives some support in the writer’s

experiments on heterogeneous hybridization. He was

able to show that both NaOH as well as CaCl,, which

render possible the fertilization of the eggs of certain sea

urchins through the sperm of starfish, also favor the ag-

glutination of that sperm to the chorion of the egg. This

leads to the peculiar phenomenon of mere membrane for-

mation in the egg by the living spermatozoon without the

entrance of the latter into the egg.*!

Lillie seems to take it for granted that the substance of

the egg which causes sperm agglutination is identical

with the substance which stimulates the spermatozoa into

greater activity. If this were correct the conditions for

the two phenomena should be identical, which is however

far from being the case.

The writer showed that if we deprive the eggs of pur-

puratus of the jelly which surrounds them and if we wash

them afterwards a few times in sea water to deprive them

of the last vestiges of jelly substance which may still ad-

here to them they have lost completely and permanently

the power of forming clusters with the sperm of their

own species. Such eggs were washed four times in m/2

NaCl and when a drop of the supernatant NaCl solution

was added to NaCl sperm of purpuratus which was not

motile it activated the sperm very powerfully.

The writer had found that the egg sea water of S. fran-

21 Loeb, Arch. f. Entweklngsmech., XL, 310, 1914.

278 THE AMERICAN NATURALIST [ Von. XLIX

ciscanus does not give a trace of agglutination with the

sperm of purpuratus but if the experiment is made in

m/2 NaCl solutions it can be shown that the franciscanus

egg NaCl solution activates the NaCl sperm of pur-

puratus in an m/2 NaCl solution very strikingly.

The immature eggs of Asterias ochracea activate the

otherwise non-motile sperm of the same species, but the

eggs of this starfish do not give any agglutination reac-

tion with their own sperm and Lillie found the same for

the starfish in Woods Hole. It might be said that all this

only proves that the activating effect requires a smaller

concentration than the agglutinating effect, but may yet

be caused by the same substance. This objection is, how-

ever, not tenable in the following case.

Purpuratus sperm washed in m/2 NaCl is as a rule

more active in a mixture of NaCl + KCl than in a mixture

of NaCl + CaCl, (if both solutions are free from egg con-

tents); yet in the latter solution the agglutination reac-

tion upon the addition of egg-NaCl is very strong while

in the former it is lacking (unless the sperm or testicles

or ovaries give off some CaCl, to the surrounding solu-

tion). Again it might be argued that the activation of

the spermatozoon might be induced by the same sub-

stance as the agglutination, but that the agglutinating sub-

stance in both cases reacted with different constituents

of the spermatozoon. While this may be admitted, it

must also be conceded that with the facts which we have

at our disposal at present we can not be certain that the

aggultinating and activating substances are identical.

VII

Lillie?? not only takes the identity of the two substances

for granted but he assumes that without the agglutinating

substance in the egg (to which he gives the somewhat

prejudicial name ‘‘fertilizin’’) no fertilization is possible.

Fertilization in his opinion consists in the combination

of the spermatozoon with a molecule of or in

22 Loe. cit.

No.581] ENTRANCE OF THE SPERMATOZOON 279

the egg, whereby the fertilizin molecule undergoes a

change in the other end and this change causes the egg to

develop. The fertilizin is thus an ‘‘amboceptor”’ in the

sense of Ehrlich’s side-chain theory.

The side-chain theory was invented by Ehrlich for an

altogether different purpose. Bordet had found that for

certain phenomena of immunity two substances’ were

needed (which Ehrlich named amboceptor and comple-

ment, respectively). Ehrlich assumed that they were

bound chemically by the antigen (the substance against

which the organism was immunized) but found that while

the antigen (4) was able to bind B (the amboceptor) in

the absence of C, it was not able to bind the complement

C in the absence of B. From this Ehrlich concluded that

of the two possible modes of linkage between the three

bodies 44 a and A—B—C the latter was the one which

really occurred. Since in this case C is not directly

linked with A but through the intermediation of B he

called B the ‘‘ amboceptor ’’ and the scheme of linkage a

** side-chain °’ linkage.

Lillie applies this theory (which covers the two possible

modes of linkage of two chemical compounds to a third

one) to the entrance of the spermatozoon into the egg, by

calling the egg an antigen A and the spermatozoon a com-

plement C and assuming the existence of a hypothetical

amboceptor B in the form of the substance that causes

agglutination, the ‘‘ fertilizin.’’ Even if we are willing

to overlook the fact that the egg and the spermatozoon

are cells and not simple organic compounds and if we are

willing to overlook the further fact that the assumption

of an amboceptor as a connecting link between the two

is arbitrary we can not overlook the fact that the sperma-

tozoon does not combine chemically with the egg but that

it actually enters into the egg and attaches itself to the

egg nucleus. It seems then futile to discuss whether the

Spermatozoon combines with the egg in side-chain fashion

(namely, Egg—Fertilizin—Spermatozoon) or in direct

280 THE AMERICAN NATURALIST [ Vou. XLIX

fashion, namely,

/ Fertilizin

\Spermatozoon

since the engulfing of the spermatozoon into the egg is a

physical process which bears no relation to either possi-

bility.

It has been stated that the ‘‘ fertilizin theory ’’ explains

also the phenomena of artificial parthenogenesis just as

well as any other theory. In a recent book on artificial

parthenogenesis the writer has given the results of a

large number of experiments and he has tried to explain

some of them; the reader would, however, vainly look

for a ‘‘theory”’ of artificial parthenogenesis. A theory

in a scientific sense consists in the presentation in

mathematical or numerical form of a phenomenon as

the function of its variables. The writer has tried to pre-

pare the ground for such a treatment of the phenomena

of fertilization and of the first development of the egg by

working out those variables which permit a quantitative

treatment, but even if the exploration had been advanced

further than it actually has been, it would not be possible

to ever expect that a single theory could cover all the

phenomena of fertilization and development, since under

these two headings so many physically and chemically

different processes are included (of which one follows the |

other) that they can not be covered by one theory. It is

true the writer had in former publications océasionally

used the term ‘‘ lysin theory of fertilization ’’ but only to

express the fact that cytolytic agencies induce membrane

formation and that the membrane formation induced by a

spermatozoon might also be due to a cytolytic agency con-

tained in the spermatozoon; but he has dropped this term

in his recent book on the subject.

While the writer does not desire to enter into a further

discussion of the side-chain theory of fertilization he

wishes to point out that it rests on the claim that that

substance which causes sperm agglutination is contained

Egg

No. 581] ENTRANCE OF THE SPERMATOZOON 281

in the unfertilized egg and that the egg can only be fer-

tilized as long as this ‘‘ fertilizin ’’ is present in the egg.

It is obvious that such an assumption demands for its

proof that in all cases in which an egg can be fertilized it

must contain the agglutinating substance. There is only

one test for the presence of this substance, namely the

cluster formation of the sperm in the presence of egg sea

water. This proof can not be furnished since, as the

writer had shown in a former paper, the reaction is lack-

ing in many cases of hybridization; it is also lacking in

the case of the starfish.” It is not impossible that if the

theory is tested further it will be found lacking in a con-

siderable number of cases. To this objection Lillie re-

plies that it is not necessary that the eggs should actually

give the agglutinin reaction, it is sufficient that the ag-

glutinating substance is contained in the egg. But how

can we tell that it is contained in an egg which fails to

give the agglutination reaction as long as this reaction is

the only reliable test for the presence of the agglutinating

substance in the egg? Rigorously speaking, even if all

eggs of every species gave the agglutinin reaction it would

still be necessary to furnish a direct proof that the ag-

glutinin has anything to do with fertilization and develop-

ment.

It may be possible that Lillie considers such a proof

to be contained in the following statement.

I adopted then the working hypothesis that this substance?* is neces-

sary for fertilization and there followed immediately three corollaries,

iz.: (1) if it were possible to extract this substance from eggs they

would no longer be eapable of fertilization; (2) fertilized eggs are inca-

pable of uniting again with spermatozoa, hence if the hypothesis is

correct they could no longer contain free fertilizin; (3) eggs in which

membranes have been formed by methods of artificial parthenogenesis

become incapable of fertilization; such eggs must also therefore be de-

void of free fertilizin after they have reached the non-fertilizable con-

dition if the eta: is correct. These consequences were actually

found to be true.?

23 Lillie, Biol, Bull., XXVIII, 18, 1915.

24 The ‘‘ fertilizin.’’

25 Lillie, Jour. of Bio, Zool., XVI, 523, 1914.

282 THE AMERICAN NATURALIST [Vov. XLIX

Of these three ‘‘ corollaries ’’ the first one is the most

important, since it claims that the power of the eggs of

being fertilized varies with their contents of fertilizin.

The proof consisted in this: that eggs were washed a

number of times during three consecutive days and after

two days the percentage of eggs that could be fertilized

were diminished to about one third.

There is thus the anticipated decrease in the percentage of fertilizations.

It is a well known fact that the unfertilized eggs of the

sea urchin (in fact of all marine animals) perish when

they lie for some time in sea water and one of the main

causes of this phenomenon is also known, namely oxida-

tions. If the oxidations are inhibited through the removal

of oxygen or the addition of KCN the life of the eggs can

be prolonged.’ In the mature starfish egg this death

which is accelerated by the temperature (and has the high

temperature coefficient of many life phenomena) takes

place in a few hours,” while it begins a little later in the

egg of the sea urchin. After the artificial membrane for-

mation it takes place very rapidly also in the sea urchin

egg (coincident with the enormous increase in the rate of

oxidations caused by the artificial membrane formation)

and in this case the death of the egg can also be retarded

by the withdrawal of oxygen or the addition of eyanide.*$

In view of these facts the objection can not be avoided .

that in Lillie’s experiment the number of eggs which could

be fertilized fell off after two days to one third not on

aecount of the loss of ‘‘ fertilizin’’ but because of the

fact that two thirds of the eggs were dead by that time.

That this assumption is well grounded is testified by

Lillie’s own remarks:

Concomitantly, with these effects of the series of washings the devel-

opmental energy becomes greatly reduced. This was very obvious from

the second fertilization.2® On August 24 (48 hours after fertilization)

a large quantity of living material was contained in the second A fertili-

26 Loeb and Lewis, Am. Jour. Physiol., VI, 305, 1902.

27 Loeb, Biol. Bull., III, 295, 1902. _

28 Loeb, ‘‘ Artificial Parthenogenesis and Fertilization.’’

29 Which occurred on the second day.

No. 581] ENTRANCE OF THE SPERMATOZOON 283

zation but none had even approximately pluteus:structure. The most

common form was a stereoblastula. In the second B fertilization there

were a few abnormal prismatic plutei, while the majority were gastrulae.

The third fertilization resulted in extremely abnormal ciliated types.

The fourth and fifth did not proceed beyond abnormal cleavage stages.

From this and similar experiments Lillie draws the fol-

lowing conclusion:

The eggs have evidently lost something which affects their power of

fertilization. Table 3 shows the measure of loss of the sperm agglu-

tinating substance and justifies the general conclusion that this is a

factor in the result. The loss of other substances may also combine in

the decrease of fertilizing power, but of this we know nothing definite.

As a matter of fact, fertilizing power is gradually lost with decrease of

fertilizin content of the egg.

It seems to the writer that in these experiments the

power of being fertilized was gradually lost by the death

of the eggs. And an additional justification of this criti-

cism is given by the following fact, that if we deprive

fresh eggs of purpuratus permanently of their power of

giving off ‘‘ fertilizin ’’ their power of being fertilized is

not only not lost but is entirely unaltered. The writer

has shown that if the eggs of purpuratus are treated for

two or three minutes with a mixture of 50 c.c. of sea water

+3 c.c. of HCl (whereby the jelly surrounding the egg

is dissolved) and if the eggs are washed they give no

trace of a fertilizin reaction but 100 per cent. of the eggs

can be fertilized.* ;

It might be argued that the supernatant sea water from

these eggs had not lost all power of causing agglutination

of the sperm. This the writer must deny but for argu-

ments’ sake he will admit that a trace near the ‘‘ psycho-

logical limit ’’ might have been overlooked where a ‘‘ fer-

tilizin ” partisan might have declared that he still could

perceive a faint indication of a ‘‘ fertilizin ” reaction.

In that case only a few eggs should have been fertilized—

the fertilizin theory rests on this assumption; in reality,

however, practically one hundred per cent. were fertilized

in every case (provided the eggs had not been lying in the

see water too long, i. e., more than a day or two).

30 Loeb, Jour. Exper. Zool., XVII, 123, 1914.

284 THE AMERICAN NATURALIST — [Vou. XLIX

To this Lillie replies that perhaps the sperm of pur-

puratus is not so delicate an indicator for agglutinin as

the sperm of Arbacia—but as long as the agglutination

reaction is the only test for the presence of fertilizin in

the egg, such an answer begs the question.

From the fact that the power of agglutinating the sperm

is lost if the egg of purpuratus is deprived of its jelly by

acid treatment the writer drew the conclusion that in this

egg the ‘‘ fertilizin’’ does not come from the unfertilized

egg but only from its jelly and that this was contrary to

Lillie’s assumption. To this Lillie?! replied by pointing

out that the immature eggs of Arbacia do not give the ag-

glutination reaction while the mature Arbacia egg gives

the reaction very powerfully, and that we must conclude

from this that the ‘‘ fertilizin’’ contained in the jelly

comes from the egg and is given off during the period of

the maturation divisions (the latter statement, however,

is after all only an assumption though a probable one).

But this does not meet the question at issue, namely that

in the egg of purpuratus at the time of maturity the fer-

tilizin which is given off is contained exclusively in the

jelly and not in the egg, as it should be if the presence

of fertilizin in the egg were a prerequisite for its ability

of being fertilized. It is true that if we repeat this ex-

periment in the egg of Arbacia we find that after the re-

moval of the jelly by HCl a trace of the agglutinating sub-

stance may still be given off by the egg, although little in

comparison with that given off by the jelly. But this

does not alter the facts as they are found in the egg of

purpuratus.

As far as the two other proofs of Lillie are concerned,

we have already touched upon them in the previous parts

of this paper. The fact that the fertilized eggs of Ar-

bacia (and of purpuratus) cease to give the agglutinin

reaction is due to the loss of the jelly on the part of the

fertilized egg to which in Arbacia should be added the

fact that some of the material of the cortical layer is given —

31 Lillie, Biol. Bull, XXVIII, 18, 1915,

No. 581] ENTRANCE OF THE SPERMATOZOON 285

off during the process of membrane formation. The

writer has pointed out in former papers that the cortical

layer of the egg which undergoes liquefaction in the

process of membrane formation behaves towards reagents

very much like the jelly which surrounds the egg.*? But

since in the egg of purpuratus the loss of this agglutina-

ting power on the part of the egg is not necessarily accom-

panied by the loss of the power of being fertilized—e. g.,

in the HCl experiment—we are inclined to believe that

there must be another reason that an egg fertilized by

sperm can not be fertilized a second time.

As far as the statement is concerned that the egg can

no longer be fertilized after artificial membrane forma-

tion by butyric acid the writer can not admit the correct-

ness of this statement (see Chapter III). In the eggs in

which artificial membrane formation has been called forth

by butyric acid the main if not the only block to a subse-

quent fertilization is the membrane itself.

This can be proved by a very simple experiment. If

we call forth the membrane formation in the egg of

purpuratus in a neutral or faintly alkaline solution of m/2

(NaCl + KCI + CaCl.) (instead of in sea water) a very

thin membrane is formed, which is easily torn and offers

no resistance to the spermatozoon. All the eggs treated

in this way can be fertilized by sperm. The agglutinin

reaction of such eggs is, however, permanently lost.

The facts thus far known seem to force us to the conclu-

sion that no adequate proof has been offered thus far for

the connection between the power of an egg of being fertil-

ized by sperm and its power of causing a cluster formation

of the sperm. The writer has pointed out in a previous

paper that it is difficult to see why there should exist

such a relation, since sperm agglutination can only in-

. hibit the entrance of the spermatozoon into the egg.

82 ‘í Artificial Parthenogenesis and Fertilization,’ Chicago, 1913, pp.

210-14, University of California publication, Physiology, Vol. 3, p. 1, 1905.

GERM CELLS AND SOMATIC CELLS?

LEO LOEB

Resvtts obtained in the field of experimental pathology

and especially in cancer research have an important bear-

ing on certain problems of general biology. In the follow-

ing I wish to consider connectedly some of these facts

from this point of view.

I. A sharp distinction between germ cells and somatic

cells has become clearly established, especially through

the writings of Nussbaum and Weismann. More recent

results which demonstrated that the differentiation of

germ cells from the somatic cells at a very early stage

of embryonic development and their non-participation in

the formation of somatic tissues exists in various species,

tended to emphasize this sharp distinction between

somatic and germ cells.

Weismann? especially insisted on the radical difference

between germ cells and somatic cells, inasmuch as he

attributed potential immortality to the former and only a

temporary existence to the latter. And Weismann re-

gards this difference as essentially founded in the struc-

ture of both kinds of cells and fundamentally connected

with the functioning of the somatic cells; this difference

was obtained through selective processes as an adaptation

in the struggle for existence. He does not regard the

death of somatic cells as an accidental occurrence due to

unfavorable conditions which it might be in our power to

change, but as an inherent characteristic of somatic cells.

He mentions, though casually, that the life of the cock’s

comb might be prolonged by grafting it on another fowl—

but only to dismiss this idea as having no important theo-

1 From the Department of Pathology, Barnard Free Skin and Cancer Hos-

pital, St. Louis.

2A,

Weismann, ‘‘ Ueber Leben und Tod,’’ Jena, 1884; ‘‘ Ueber die Verer-

bung,’’ Jena, 1883

286

No. 581] GERM CELLS AND SOMATIC CELLS 287

retical bearing. R. Hertwig? also regards the death of the

somatic cells as unavoidably determined by their organi-

zation which precludes necessary readjustments.

Minot? likewise held the life of somatic cells to be

limited in duration and he ascribed this limitation to

changes in cell structure, leading to a differentiation of

the cytoplasm during the process of life; a change which

he designated as cytomorphosis.

Within the last 14 years certain facts have been estab-

lished which are contrary to this conception of a radical

difference between germ and somatic cells as far as their

potential immortality is concerned. Experimental inves-

tigations in tumor growth have furnished these facts.

Before we state these results we have first to consider,

how far tumor cells can be regarded as somatic cells. We

consider here malignant tumors (cancers). They origi-

nate at various parts of the body, often under the influ-

ence of long-continued irritation. In many cases we can,

if we obtain sufficiently early tumors, trace the trans-

formation of the normal into the abnormally proliferating

(tumor) tissue. This has been, as was to be expected,

especially observed in the case of superficial cancers,

where early stages of tumors are most likely to be en-

countered, for instance, in cancers of the skin, of certain

mucous membranes, but also occasionally in internal can-

cers as in those of the stomach. In such cases the cancer

cells are undoubtedly the offspring of ordinary somatic

cells. There are, however, tumors, so-called teratomata,

which in all probability take their origin in the germ

glands and other parts of the body from parthenogenet-

ically developing ova. But while these latter tumors do

not originate from somatic, but from germ cells, the tumor

cells themselves are no longer germ cells, but somatic cells

in the same sense as the ordinary tissue constituents

which also are derived from germ cells. We can therefore

3 R. Hertwig, Biol. Centralblatt, Bd. XXXIV, No. 9, 1914.

+C. S. Minot, ‘‘The Problem of Age, Growth and Death,’’ New York,

1908,

288 THE AMERICAN NATURALIST [Vou. XLIX

without doubt regard tumor cells as a kind of somatic

cells.

One of the most characteristic properties of cancer cells

is their ability to grow after transplantation into other

animals of the same species. This applies not to all, but toa

certain number of spontaneous cancers; the majority of

spontaneous tumors are not transplantable into other in-

dividuals of the same species. They grow, however,

usually after transplantation into the same individual in

which they originated. There does not exist as far as

their origin is concerned any essential difference between

these two kinds of cancers—those transplantable and not

transplantable into other individuals. The cancers used

in experimental tumor investigation take their origin

from somatic cells; but it appears some are less sensitive

to the difference in the chemical composition of the body

fluids which exists between different individuals of the

same species than others, and those less sensitive can be

transplanted, while others can not.

In those tumors which are transplantable, relatively

few tumor cells give after inoculation into other animals

origin to the new tumors, and the tumor cells after the

first transplantation not rarely multiply with greater

vigor than they did in the original animal, an effect caused,

as I could show, through the stimulating influence of the

cutting and otherwise manipulating the tumor cells. In

each animal therefore there are produced many successive

generations of tumor cells, and after transplantation into

another individual each surviving cancer cell produces

again new generations. Consecutive transplantations into

many individuals have been carried out with the same

tumor. The potential proliferative power of the cancer

cells is therefore enormous. It is, however, not so much

the intensity of the proliferative power of the tumor

cells which we wish to consider as the potential duration

of their life. It has been shown that epithelial, as well as

connective tissue tumors can be transplanted through

many generations and can survive for a long time the

animal in which the tumor originated. Thus I was able

No. 581] GERM CELLS AND SOMATIC CELLS 289

to transplant the connective tissue cells of a rat sarcoma

through forty successive generations of animals, and it

was merely the result of accidental bacterial infection

due to the unfavorable conditions under which the work

had to be carried out which caused the ultimate death of

the propagated cells.

An epithelial tumor found by Jensen in a mouse has

been propagated in various laboratories through a period

of almost fifteen years, and another epithelial tumor of

the mouse we have been propagating in mice for a period

of seven or eight years, without any sign of diminishing

vitality in the propagated cells being noticeable.

In all these transplantations of tumor cells, be they of

connective tissue or epithelial origin, it could be shown

that the peripheral cells remain alive and from these sur-

viving cells the cell growth starts. These observations

suggested to me in 1901 the conclusion that tumor cells

may have a potential immortality in a similar manner as

germ cells,® and inasmuch as tumor cells are only modified

somatic cells, I furthermore concluded that the same

statement holds good in the case of somatic cells.” Fur-

ther experiences in the field of experimental tumor inves-

tigation during the following years confirmed this conclu-

sion and permitted its enunciation with greater definitive-

ness. The potential immortality of the somatic cells of

course can only be made probable, it can never be defi-

nitely proved, inasmuch as our experience merely deals

with finite periods. But the same restriction holds good

in the case of the germ cells in which the potential immor-

tality is likewise merely a strong probability and not a

definitely proven fact.

Weismann believed that protozoa are in the same sense

potentially immortal as germ cells, in contradistinction to

somatic cells which do not possess potential immortality.

Some facts were, however, discovered which, according to

5**On the Transplantation of Tumors,’’ Jour. Medical Research, Vol. VI,

No. 1, 1901, p. 28; Virchow’s Archiv, Bd. 167, 1902, p. 175.

6‘‘Tumor Growth and Tissue Growth,’’ Am, Philosophical Society,

XLVII, 1908, and at other places.

290 THE AMERICAN NATURALIST [Von. XLIX

the interpretation given them, seemed to contradict

Weismann’s conception. Thus Maupas found that vari-

ous kinds of infusoria did not propagate by fission indefi-

nitely, but that a sexual process, conjugation, was neces-

sary at certain times, and Calkins showed that there were

regular periods of depression, and while a spontaneous

recuperation from the effects of certain depressions could

take place and in still other cases artificial stimulation

would aid the animals in overcoming the critical periods,

at other times depressions proved fatal without an inter-

vening conjugation. Woodruff, however, by choosing

conditions of environment more in accordance with the

conditions found in nature, could keep a strain of Par-

amecium apparently indefinitely alive without any inter-

vening periods of copulation being required. This seemed

to point to a potential immortality of protozoa in the

sense of Weismann. Recently, however, Woodruff and

Erdmann‘ found that the recovery from depression which

takes place is accomplished through nuclear changes com-

parable to, but not identical with, those observed during

copulation. This seems in some respects to agree with

R. Hertwig’s previously enunciated theory according to

which depressions and senility in cells are due to a dis-

proportion between the nuclear and cytoplasmic material,

and that recovery from such unfavorable conditions de-

pends upon the reorganization of the nucleus, essentially

consisting in a diminution of the mass of the latter. Inas-

much as in metazoa—he concluded, further—such a rear-

rangement between nuclear and cytoplasmic masses can

only take place in the case of germ cells, but not somatic

cells, only germ cells are immortal, while somatic cells

are necessarily mortal. While Weismann regarded the

unavoidable mortality of the somatic cells as a secondary

acquisition, the result of a process of selection, the death

of somatic cells being of advantage to the propagation of

the race, Richard Hertwig’ regards the death of somatic

cells as inherent in their structure, which precludes the

7 Biol, Centralblatt, Bd. 34, August, 1914, p. 484.

8 Biol. Centralblatt, Bd, XXXIV, 1914, No. 9.

No. 581] GERM CELLS AND SOMATIC CELLS 291

possibility of nuclear reorganization of the cell necessary

for continued life. In a somewhat related way, Minot

considers, as mentioned above, the death of somatic cells

as inevitable and as the result of cytomorphosis, which

means the relative increase in size and differentiation of

somatic cells during life. In this connection it is inter-

esting to note that while R. Hertwig considers (in pro-

tozoa primarily, but secondarily also in other cells) an in-

crease in the size of the nucleus—the result of the activity

of the cells—as the cause of functional disturbances lead-

ing to senility, Minot on the other hand connects senility

with a relative decrease in the size of the nucleus and an

increase in the mass of the cytoplasm. Now as far as the

protozoa are concerned, the controversy does not seem to

concern so much the potential immortality of these organ-

isms as the problem as to whether the individual pro-

tozoon corresponds to a germ cell or to a somatic cell of a

metazoon, or whether it partakes of the character of both.

There can be little doubt that individual protozoa possess

potential immortality, a conclusion which would not be

invalidated through a loss of certain parts of the pro-

tozoon body at certain periods of its life cycle.

We may therefore conclude that all three kinds of cells,

protozoa, germ cells, as well as certain somatic cells of

metazoa, possess a potential immortality.

Tumor cells are somatic cells in which such secondary

changes leading to a cessation of proliferation as take

place under certain conditions in all the individual cells in

some kinds of somatic tissues, are affecting only a certain

number of cells. In the case of some somatic cells, as, for

instance, those of the epidermis, it is evident that the

secondary changes in structure and metabolism, which

lead to a cessation of proliferative power, are due to un-

favorable conditions of blood-supply. What Minot calls

eytomorphosis can therefore in this case be referred not

to necessary transformations inherent in the cells, but to

unfavorable environmental conditions into which the

cells are placed as a result of their multiplication. Such

secondary degenerative changes take place also in tumor

292 THE AMERICAN NATURALIST [Vou. XLIX

cells under similar defective conditions of blood-supply.

Here also degenerative changes entail a cessation of pro-

liferation in a similar manner as in ordinary tissue cells.

While farther away from the blood-vessels the tumor cells

degenerate and die, near the blood-vessels they continue

to live and to multiply.

While from a theoretical point of view, therefore, the

question as to the potential immortality of somatic cells

has through the experiments on tumor cells been answered

in a decisive manner, it was nevertheless of interest to

extend these investigations to ordinary tissues. Such

investigations we undertook in the course of the last

eight years, and while certain obstacles were encountered,

which prevented the continued life of ordinary tissues, the

results were of interest in giving an insight into some of

the conditions which determine the growth, life and death

of somatic cells. These investigations have shown that if

tissues are transplanted into another individual of the

same species, under the influence of the constitution of

the body fluids, which differs in different individuals of

the same species, the metabolism in the transplanted

tissues is interfered with as shown, for instance, in patho-

logical differences in pigmentation seen in black skin of

the guinea-pig after transplantation into other animals of

the same species. After transplantation of pigmented

skin into the same individual in which it originated, such

pathological changes do not occur. As I have previously

pointed out, a certain adaptation exists between the

tissues and body fluids in animals of the same species, and

even between the tissues and body fluids of the same indi-

vidual. Thus it comes about that the interaction of tis-

sues and body fluids of the same species leads to different

and less toxie products than those produced through the

interaction of the body fluids of one with the tissues of

another species. Even the interaction of tissues of one

animal with the body fluids of another animal of the same

species leads to more toxic products than the interaction

of body fluids and tissues of the same individual. In the

latter case toxic products, interfering with the life of

No. 581] GERM CELLS AND SOMATIC CELLS 293

normal tissues, are not produced, while in the former cases

such products acting directly or indirectly are formed.

As an illustration of such a specific relationship between

body fiuids and tissues, I cited the specifically adapted

effect which tissue coagulins exert on the constituents of

blood plasma.’

Now as the result of these differences in metabolism

induced through the differently constituted body fluids the

lymphocytes begin to invade the transplanted tissues, and

the invading connective tissue does not preserve, as it

does after auto-transplantation, its young and cellular

state, but produces fibrous bands which contract around

the parenchyma after homoiotransplantation, and thus

exert pressure. Both connective tissue and lymphocytes

destroy thus the homoiotransplanted tissue, while they

usually spare the autotransplanted tissue the metabolism

of which is normal. In the case of certain tissues, as, for

instance, kidney, however, even after autotransplantation

into the subcutaneous tissue the metabolism of the trans-

planted cells becomes abnormal under the abnormal con-

ditions under which they now live, and here the lympho-

cytes and connective tissue destroy, therefore, even the

autotransplanted tissue, although at a later date than the

homoiotransplanted kidney tissue.

The fitness of a tissue in an individual determining its

power to live or to grow depends, therefore, on two factors:

(1) on the specific adaptation existing between tissues and

body fluids, and (2) on the way in which various sub-

stances are carried to the tissue. A perfect nutrition im-

plies the carrying of the food substances to the tissues in

the normal way through blood-vessels. It is probable that

on the intact relations between capillary endothelium and

parenchyma cells depends such a sifting of various food

substances and waste products as is best suited to the

normal metabolism of the cells. If, as in the case of the

kidney tissue, this mechanism is disturbed, abnormal sub-

stances are produced notwithstanding the specific adapta-

tion existing in this case between tissue cells and body

? ‘“‘Immunity and Adaptation,’’ Biol. Bulletin, Vol. IX, 1905, p. 141.

294 THE AMERICAN NATURALIST (Von. XLIX

fluids after auto-transplantation. And it seems that a

perfect fulfilment of the second requirement might even

be able to overcome a deficiency in the first condition, the

specific adaptation between tissues and body fluids. This

seems at least to be the case, whenever a kidney is suc-

cessfully transplanted into another individual of the same

species and lives here for a long period of time.

A peculiar resistance to foreign body fluids is appar-

ently shown by the germ cells. They represent in reality

individuals residing in a host organism of the same spe-

cies. In this case the host organism is nearly related to

but not identical with the individuality of the germ cells.

In some respects we have, therefore, here a condition com-

parable to one existing after homoiotransplantation of

tissues. And still the germ cells do not show any signs of

injury. There is, therefore, in germ cells as yet lacking

that substance which has a specific affinity to certain parts

of the body fluids, or through their situation the germ

cells are somehow protected against the injurious influ-

ence of these substances.

Thus it comes about that through transplantation into

other individuals of the same species the potential im-

mortality of the ordinary tissues can not be demonstrated.

This applies to the tissues investigated so far.’ How-

ever, it is quite possible that we may yet find that in the

case of certain tissues the life may be permanent even

after homoiotransplantation. It was furthermore think-

able that through serial transplantation, retransplanting

the tissue at an early date before the lymphocytes and con-

nective tissue had had a chance to seriously injure it,

better success could be obtained. In the case of the skin

I have undertaken such serial transplantations some years

ago; our investigations have, however, in this case shown

that it was not possible to retransplant this particular

10 Leo Loeb u. W. A. F. Addison, Arch. f. Entwicklungsmechanik, Bd.

XXVII, 1909, p. 73; Bd. XXXII, 1911, p. 44. Max W. Myer, Bd.

XXXVIII, p. 1, 1913. Llewellyn Sale, Bd. XXXVII, 1913, p. 248, M'G.

Seelig, Bd. XXXVII, 1913, p. 259. Cora Hesselberg, Journ. Experimental

Medicine, Vol. XXI, 1915, p. 164.

No. 581] GERM CELLS AND SOMATIC CELLS 295

tissue indefinitely ;'! these experiments ought to be ex-

tended; especially might it be of interest to use the direct

descendants as hosts for the tissues of the parent. It is to

be expected that the quality of the parents which makes

the body fluids suitable for their own tissues might make

them likewise suitable for certain of their offspring. Such

experiments I began some time ago and I expect to

continue them if opportunity should present itself.

The growing of tissues in culture media, which excludes

attack on the cells by connective tissue and lymphocytes,

may also serve the same purpose and quite recently has

been used through a larger number of generations. But,

as stated above, we have in these experiments merely to

deal with an attempt to confirm the potential immortality

of the somatic cells which had in principle been estab-

lished through previous investigations on the life of tumor

cells.

While thus various kinds of tissues of an organism have

the potentiality of an immortal life, separated from the

organisms to which they belonged, the organism as a

whole invariably dies and with it its component tissues.

This is evidently due to the interdependence of various

parts of an organism and to the death of certain sensitive

cells, especially the ganglia cells of the central nervous

system. We might therefore be inclined to conclude that

these ganglia cells do not possess the potentiality of im-

mortal life. But even in the case of the ganglia cells,

which are of such significance for the life of the organism

as a whole, we can at present not deny the possibility that

they also may have the potentiality of immortality and

that they merely succumb under the influences of certain

injurious conditions arising in the organism. On the

other hand, fully developed ganglia cells have apparently

lost the power to multiply; they are furthermore sensi-

tive to certain insults to which other tissues show resist-

ance. Thus the unfavorable condition prevailing during

the process of transplantation into another organism and

directly afterwards seems to be sufficient to cause the death

11 Leo Loeb, Archiv, f. Entwicklgsmch., Bd. XXIV, 1907, p. 638.

296 THE AMERICAN NATURALIST [ Vou. XLIX

of certain ganglia cells when other tissues would survive.

But neither of these facts prove that under favorable con-

ditions very much differentiated cells, like ganglia cells,

might not have the power to live indefinitely, although they

have lost the power to multiply. Sensitized connective

tissue cells of the uterus may after transplantation into

the same or another individual in which corpus luteum

substance is circulating grow very energetically and pro-

duce placentomata, while after transplantation of fully

developed deciducomata no further growth can be ob-

tained and all or almost all the cells die. Here also the

fully ‘‘differentiated’’ cells have lost the power to multi-

ply and at the same time they have apparently become

more sensitive to the effect of injurious influences than

young and yet undifferentiated predecidual cells of the

uterine mucosa.

But here we can observe that some strands of fully

differentiated placentoma tissue may survive even under

those unfavorable conditions—without, however, resuming

growth or returning to the undifferentiated condition—

namely, such strands of tissue as are situated under the

best environmental conditions, in close proximity to the

host tissue, at places most accessible to the foodstuffs or

oxygen supplied by the circulating blood or by the peri-

toneal fluid. This suggests that even much differentiated

cells which have lost their power to propagate may still

have the power to live, when kept under favorable condi-

tions, and that their death is the result of unfavorable

environmental influences. Thus we must at least admit at

the present time the possibility that also the ganglia cells,

while they do no longer multiply, may still possess a

potential immortality; that cellular differentiation pre-

eludes the latter possibility has as yet not been demon-

strated. We must therefore sharply distinguish between

the power of cells to grow and their power to live; while

the former seems to be destroyed through differentiation

—at least in some cases—the latter may still exist. In

the case of other tissue cells we have it to a certain

extent in our power through experimental conditions

No. 581] GERM CELLS AND SOMATIC CELLS 297

to prevent those changes which lead to differentiation

and death; thus in the case of tumor cells through con-

stant transfer into a new host we can enormously in-

crease the number of as yet less differentiated cells

on which the propagation depends by causing an in-

tense multiplication of these tumor cells, many of which,

if left in the same organism, would have undergone sec-

ondary degenerative changes. Through experimental

means, viz., through the transplantation into different

kinds of hosts the relative preponderance of propagation

and differentiation of tumor cells can be varied. We fur-

thermore know that through ‘‘chemical’’ sensitization

combined with mechanical stimulation, the same effect can

be produced, at least temporarily, in the connective tissue

cells of the uterine mucosa. Under those conditions a

large number of cells are induced to propagate and re-

main young while their offspring gradually change into

fully differentiated cells. If we grant the possibility that

differentiation of such cells as ganglia cells, while it en-

tails loss of the power to propagate and greater sensitive-

ness to insults, does not necessarily mean the necessity to

die, then the problem of prolongation of life would to a

great extent depend upon the possibility of preventing

injurious influences which at present disturb the function

of ganglia cells from attacking these cells and causing

their death.

II. The germ cells are potentially immortal, but this

potential immortality can only be realized, if at certain

periods certain changes take place within the cells, which

concern especially the nucleus, phenomena consisting in

maturation, followed by fertilization or parthenogenetic

development. In a similar manner the observations of

Woodruff and Erdmann suggest that at the time of de-

pressions in the life of the protozoa, possibly similar nu-

clear phenomena take place at least in certain cases. We

have seen that in the case of somatic cells there are also

indications of the existence of potential immortality. The

question may therefore be raised, whether similar periodic

rearrangements of the nucleus, as in the case of the germ

298 THE AMERICAN NATURALIST [ Vou. XLIX

cells and protozoa, may not also take place in the case of

the somatic, especially of tumor cells. Without consider-

ing any connection with the problem of the immortality of

the somatic cells, Bashford, Murray and Bowen"? stated

on an empirical basis that in charting the number of suc-

cessful inoculations of a mouse carcinoma in mice, in

different generations and in different strains of the same

generation, they noticed definite rhythmic variations in

the number of successful inoculations, a maximum of suc-

cessful inoculations in one generation being followed by

a minimum in the succeeding generation. However, they

also state that parallel strains of the same tumor did not

show maxima or minima at the same time. Bashford,

Murray and Bowen, in order to explain these observations,

assumed that different parts of the same tumor show

different degrees of gsowth energy at the same time; this

would imply that such areas differing in growth energy

at the same period are separated through transplanta-

tion; so that in one generation mainly energetically grow-

ing pieces are used for transplantation in the succeeding

weakly growing pieces almost altogether, an assumption

which does not appear very probable.

Calkins! held that there occur in succeeding genera-

tions not so much rhythmic variations in the number of

successful transplantations as in the growth energy of

the tumors. He compared these rhythmic variations with

the rhythms observed by him in the case of Paramecium.

However, such rhythms were not noticeable in the mouse

carcinoma which we have propagated for a number of

years in our laboratory, as has been shown by Moyer S.

Fleisher.‘* He furthermore shows that even in the case

of those tumors, on the study of which Bashford and his

collaborators and Calkins base their conclusion, it is very

probable that the variations which these authors ob-

served do not represent definite rhythms, but are, as far

12 Bashford, Murray and Bowen, Zeitsch. f. Krebsforschung, 1907, Bd. 5,

Heft 3.

18 Calkins, Jour. Exper. Med., 1908, X,

14 Moyer S, Fleischer, Zeitschrift f. So Se ae Bd. 14, Heft 1, 1914.

No. 581] GERM CELLS AND SOMATIC CELLS 299

as their conclusions are not based on methods of deter-

mining the growth energy of tumors, not suitable for this

purpose, in all probability merely the expression of the

existence of a number of uncontrolled variable factors.

Such factors are numerous and they may explain certain

variations observed in growth energy and number of takes

in transplantations undertaken at different times or in

different mice. There exists, therefore, at the present time

no evidence making even probable the existence of

rhythms of growth and vitality in somatic cells com-

parable to those found in protozoa; neither have thus

far been found in somatic cells indications of nuclear

changes similar to those periodically occurring in germ

cells and probably also in some protozoa and apparently

bearing some relation to variations in growth and vitality

in these cells. At present we must therefore reckon at

least with the possibility that the immortality in somatic

cells is not connected with rhythms in vitality and in nu-

clear changes of such a character as observed in the other

two kinds of potentially immortal cells.

II. External factors acting on an organism may exert

an influence on its germ cells and here produce certain

changes which may be transmitted to the following gen-

erations, and thus through a number of generations the

offspring may show deviations from the type, although

the character of the lesions appearing in different gener-

ations may not be identical. This has been observed as

a result of the action of poisons such as lead and alcohol.

Especially the extensive investigations of Stockard on the

action of aleohol in guinea pigs demonstrate conclusively

that defects appear through several generations. In the

case of these injuries transferred to the offspring, it is

doubtful whether and to what extent these inheritable

defects are characteristic for a certain poison, or whether

we have to deal with traumatisms which might be caused

in a similar manner by many poisons or even by injurious

physical agencies. There is some evidence tending to

show that most diverse chemicals may influence embryonic

development in a similar manner, that they may produce

300 THE AMERICAN NATURALIST [Von. XLIX

identical defects in the developing organisms. It seems

to be otherwise in the case of certain external conditions

which produce first changes in some somatic cells which

on their part apparently induce such secondary changes

in the germ cells that in the offspring, not exposed to the

external conditions that affected the parents, again

changes appear in some somatic cells similar to those

produced in the parents through the external conditions.

Such results were published by Kammerer. In the latter

ease the changes produced and transmitted to the off-

spring showed evidently a characteristic specific relation-

ship to definite external conditions. Such a specific rela-

tionship is, as far as we can judge at present, lacking in

the case of defects or deficiencies produced through the

action of poisons.

I wish to report briefly on a change which my collab-

orators Moyer S. Fleisher, Miguel Vera and myself!® have

produced in somatic cells, a change which is transferab'e to

the following cell generations and is therefore hereditary,

and which, while it would be pronounced non-specific, if

we should use ordinary criteria, can through the use of

special methods be shown to possess a definite, character-

istic relationship to the external factor that caused this

change and must therefore be called specific. The obser-

vations on which these conclusions are based are briefly

as follows:

If we inoculate mice with the mouse carcinoma used by

us in our experiments and from the ninth to the fourteenth

day after inoculation give on successive days four intra-

venous injections of such substances as colloidal copper

or hirudin, a marked inhibition in growth takes place

during the period of injection. The intensity of this

inhibition varies in different cases and it is possible for

us by using a combination of two substances to cause a

retrogression of a considerable number of tumors. Now,

15 Moyer S. Fleisher and Leo Loeb, Jour. Exper. Med., Vol. XX, 1914,

p. 503. Moyer S. Fleisher, Miguel Vera and Leo Loeb, Jour. Exper. Med.,

Vol. XX, 1914, p. 522. Moyer S. Fleisher and Leo Loeb, Jour. Exper. Med.,

Vol. XXI, 1915, p. 155.

No. 581] GERM CELLS AND SOMATIC CELLS 301

if we inject daily from the second to the fifth day after in-

oculation mice with either of these two substances, tumor

growth is not noticeably retarded through the injections.

Tumors, in an early stage of development, are resistant

to this inhibiting effect. If we now give four intravenous

injections, one on each successive day, from the second to

the fifth day, and later again to the same mice four injec-

tions from the ninth to the thirteenth day, the latter series

of injections which had been effective in other animals not

previously injected from the second to the fifth day, have

now almost completely lost their efficacy. The mice have

through the first set of injections become immune against

the action of colloidal copper and hirudin as far as the

effect of these substances on tumor growth is concerned.

We next inquired into the mechanism of this immunity,

and especially were we concerned with the place where

this immunity is produced. It was conceivable that this

took place either in some organ of the injected animal or

in the tumor cells themselves. The following experiments

showed that both possibilities were realized: If we inject

the mice on the four days preceding inoculation with

tumor, immunity is produced, at least in the case of col-

loidal copper. This proves that some organ in the host

animal contributes to the immunity, inasmuch as in this

case the preliminary injections exerted their influence

without having had a chance to act on the tumor cells.

But the tumor cells themselves also become actively im-

mune, as shown in the following manner: We inject ani-

mals with either colloidal copper or hirudin from the

second to fifth day, and again from the ninth to the

thirteenth day after inoculation. Two days after the last

injection we used the tumors of some of the injected ani-

mals for reinoculation into a new set of mice. Nine to

thirteen days after this second inoculation the mice be-

longing to the second set are injected with colloidal copper

and hirudin, respectively. Now we find that these tumors

also are almost entirely resistant against the effect of

colloidal copper and hirudin, although i in this case no pre-

liminary injections had been given to the animals which

302 THE AMERICAN NATURALIST [Vou. XLIX

are now the bearers of the tumors. It is therefore neces-

sary to conclude that the tumor cells used for transplanta-

tion are in this case the sole bearers of the immunity, and

that the tumor cells themselves have been actively immu-

nized. From the latter experiments we may furthermore

conclude that the immunity acquired by tumor cells is

transferred to the following generations of tumor cells,

and that therefore a hereditary transmission of a char-

acter acquired by somatic cells under the influence of

external conditions takes place. The conclusion is based

on the following consideration: The process of tumor in-

oculation consists in the transfer of a very small particle

of tumor. Very soon after transplantation most of the

transplanted tumor cells become necrotic and only a rela-

tively small number of peripheral tumor cells remain

alive. These very soon begin to proliferate, and through

their proliferation give origin to the developing tumor.

If therefore the tumors developing after transplantation `

in the new hosts are immune, the immunity must have

been transmitted from the few cells remaining alive after

inoculation to the new cell generations to whom they give

origin. A fully developed tumor represents a combina-

tion of a large number of generations of tumor cells and it

may be assumed that the later generations of tumor cells

preponderate numerically very much over the earlier

generations. Through how many generations of tumor

cells this transmission of the acquired immunity can be

propagated remains yet to be determined. From our

preliminary experiments, which are, however, not yet

definite, it appears not improbable that it extends at least

through several series of transplantations.

Both colloidal copper and hirudin inhibit tumor growth.

The sign by which we judge the effect of these substances

is therefore essentially the same in both. We might thus

be inclined to conclude that their action is identical and

that likewise the immunity which they produce is the

same; that animals having received preliminary injections

of colloidal copper would therefore be immune not only

against the action of colloidal copper but also against

No. 581] GERM CELLS AND SOMATIC CELLS 303

hirudin, and that those having received preliminary in-

jections of hirudin would also be immune against colloidal

copper. We wished to test this conclusion and undertook

therefore experiments in which we immunized animals

with one substance and examined later their immunity

not only against the substance with which they were

immunized, but also against the other substance. These

experiments showed that animals immunized with col-

loidal copper are essentially only immune against the

effect of colloidal copper, not of hirudin, and those immu-

nized with hirudin are immune against hirudin, but not

noticeably (very weakly, if at all) against colloidal copper.

The acquired immunity is therefore a specific one. This

specificity can be shown to exist if after preliminary in-

jections given from the second to the fifth day after inocu-

lation the immunity is tested through cross injections

given from the ninth to the thirteenth day. It can also

be demonstrated in the tumors transplanted into other

animals after preliminary injections in the first set of

animals. The specificity concerns therefore the immunity

which is produced in the tumor cells and probably also the

immunity in the organism of the injected animals. These

investigations prove then (1) that an acquired immunity

against the injurious. action of certain substances can be

localized in the cells concerned; (2) that this immunity

can be transferred to later cell generations; and (3) that

although the effect of two substances on the cells is appar-

ently the same, the mechanism through which this effect

is produced differs in the case of each substance, and that

therefore the immunity produced against the injurious

action of these substances is a specific one for the sub-

stances injected. We see therefore that in a similar

manner as in germ cells an effect produced through an

external agency can be transmitted to later generations;

a transmission of changes produced through an external

(chemical) agency may be transmitted to later genera-

tions also in the case of somatic cells. But the further

results we obtained in the case of somatic cells suggest the

question whether the lesion produced and transmitted

304 THE AMERICAN NATURALIST [Vou. XLIX

in germ cells may not also be specific, although different

chemicals produce apparently the same results. May

there not in germ cells, just as in somatic cells, exist a

difference in the mode of production of these lesions

through the different substances and consequently a speci-

ficity in the acquired lesion, notwithstanding the appar-

ently unspecific character of the lesion? Our work makes

it possible that this question which seems of considerable

theoretical interest may be solved in a similar manner as

in the case of the somatic cells, viz., through testing the

immunity produced through the action of chemical sub-

stances.

SuMMARY

1. It is shown that evidence similar to that which makes

probable the potential immortality of protozoa and germ

cells also exists in the case of somatic cells of metazoa.

As far as the protozoa are concerned, the discussion does

not, as seems to be assumed, concern their potential im-

mortality so much as the question whether protozoa cor-

respond to germ or to somatic cells of metazoa or repre-

sent perhaps a combination of both.

2. While in the case of tumor cells the potential immor-

tality of somatic cells has been demonstrated as definitely

as the character of the problem will ever permit, the diff-

culties standing in the way of a similar demonstration in

the case of certain other somatic cells and the means of

overcoming these difficulties are analyzed. It is partic-

ularly shown that chemical differences existing between

the body fluids of individuals belonging to the same spe-

cies are the basis of these difficulties, and that as a result

of these differences the metabolism of cells in a new envi-

ronment is modified in such a way that the behavior of

connective tissue cells and of lymphocytes is altered, and

that as a result of these alterations the death of the tissue

is brought about where it could probably have lived indef-

initely. Besides altering the character of the body fluids,

transplantation of tissues furthermore has usually an

additional injurious effect; it changes the way in which

nourishment is carried to the transplanted cells, and this

No. 581] GERM CELLS AND SOMATIC CELLS 305

may also lead to alterations in metabolism calling forth a

destructive activity of connective tissue and lymphocytes.

Thus there exist difficulties in the case of certain tissues

in demonstrating through serial transplantation their

potential immortality, in a similar manner as it has been

demonstrated in the case of strongly proliferating somatic

cells (tumor cells).

It is also shown that in the case of the germ cells which

really represent a foreign individual within a host organ-

ism mechanisms exist which prevent these injurious agen-

cies from becoming effective.

3. We must sharply distinguish between the power of

cells to grow and their power to live. While the former

seems to be destroyed through differentiation, the latter

may still exist, and we can therefore at present not deny

the possibility that even highly differentiated somatie

cells may still possess the potentiality of immortal life.

4. While in the case of protozoa and germ cells definite

cycles exist, manifesting themselves either through the

oceurrence of rhythmically occurring depressions of vital-

ity or of typical changes in the nuclei, such cycles have so

far not been demonstrated in the case of somatic cells,

particularly of tumor cells.

5. In the case of germ, cells external factors can pro-

duce certain changes, and these changes (not necessarily

identical with those originally produced through the ex-

ternal factors) can be transmitted to the offspring. It is

shown that in a similar way in the case of somatic (tumor)

cells a transmission of characters acquired under the in

fluence of external agencies to the succeeding cell genera-

tions may take place. It can be shown in the case of the

somatic cells that apparently similar changes produced

through different external agencies are really not iden-

tical, but specific. It is suggested that such a specificity

of transmitted characters may also exist in the case of

germ cells despite the apparent identity of changes pro-

duced through different external agencies.

MENDELIAN INHERITANCE OF FECUNDITY IN

THE DOMESTIC FOWL, AND AVERAGE

FLOCK PRODUCTION 1

Dr. RAYMOND PEARL

In 1912 I showed,? from extensive experimental data

that, in certain breeds of domestic poultry, winter egg

producing ability is inherited in a strictly Mendelian

manner. It was pointed out that there was much evidence

indicating that winter production was, on the whole, a

rather reliable index of total fecundity capacity. As was

to be expected, the novelty of the results presented in the

papers referred to led to their criticism from various

points of view, including that of the practical poultryman.

Most of these criticisms have been based upon some mis-

understanding of the nature of the results themselves.

Others, and particularly those of the poultry press, have

apparently been based on a purely conservative instinct

to resist the intrusion of any new idea which seems to

threaten those solid personal and editorial assets of (re-

puted) infallibility and ‘‘safe and sane’’ judgment.

It has seemed to the writer more likely to conduce to

the advancement of knowledge in this field if he went

steadily about collecting more and more concrete objec-

tive evidence rather than engaging in polemic disputa-

tions with everyone whose opinion in regard to the valid-

ity or interpretation of the earlier results chanced to

differ from his own. As a result of this policy there has

accumulated a large mass of additional experimental data

confirming and extending the results of the earlier work.

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

periment Station, No. 81.

2 Pearl, R., ‘‘The Mode of Inheritance of Fecundity in the Domestic

Fowl,’’? Jour. Exper. Zool., Vol. 13, pp. 153-268, 1912. Cf. also ‘‘The Men-

delian Inheritance of Fecundity in the Domestic Fowl,’’ AMER. NAT., Vol.

XLVI, pp. 697-711, 1912.

306

No. 581] INHERITANCE OF FECUNDITY 307

This material will be published as opportunity offers.

It is the purpose of the present paper to record certain

facts which are pertinent to a general consideration of

the problem of inheritance of fecundity, but at the same

time do not fall in the direct line of the experimental

inquiry. They are matters, in other words, which are

essentially by-products of the investigation but still have

a more or less important bearing on the interpretation,

in a broad sense,-of the whole.

I. Tue Seasonat DISTRIBUTION or A Frock Ece Propvc-

TION UNDER A MENDELIAN SYSTEM OF BREEDING AS

COMPARED WITH SIMPLE Mass SELECTION

The mean egg production per bird in the different

months of the laying year has been given by Pearl and

Surface’ in an earlier paper. Those results are based on

the weighted mean production of the flocks of Barred

Plymouth Rocks at the Maine Agricultural Experiment

Station during the ten years that a system of mass-selec-

tion was followed in breeding for egg production.

It is an obvious deduction from the results of the Men-

delian experiments recorded in the earlier papers already

referred to, that by their application it should be possible

to modify the average production of a flock over a rather

wide range, the modification being of a fixed and perma-

nent character under any definite conditions of environ-

ment and breeding. To many practical poultrymen the

only test of the validity of the conclusions reached which

has any significance, is that of average flock production.

It is obvious that from a technically critical point of view

such a test has, of itself, relatively small value in helping

to judge of the correctness of a Mendelian interpretation.

At the same time it is clear that if one takes a flock of

poultry of mixed genetic constitution in respect of fecun-

dity and aims to preserve in his breeding only animals

carrying both the factors L, and L, necessary for high

3 Pearl, R., and Surface, F. M., ‘‘A Biometrieal Study of Egg Production

in the Domestic Fowl.’’ II. Seasonal Distribution of Egg Production,’’

U. S. Dept. of Agr., B. A. I. Bull. 110, Pt. II, pp. 81-170, 1911.

308 THE AMERICAN NATURALIST [Vou. XLIX

production, there ought to result a marked and immediate

improvement in average flock production no matter what

the size of the flock.

This, as a matter of fact, is exactly what has been done

in the breeding of the flock of Barred Plymouth Rocks at

the Maine Station for several years past. No attempt has

been made to propagate low fecundity strains, after it had

once been demonstrated that this could be done. In the

work since 1912 the experimental aims have been such as

not to be at variance with the practical one of getting the

most eggs with the least trouble and expense, so far as

has concerned the Barred Plymouth Rock stock. Conse-

quently in making the matings from which the founda-

tion Barred Plymouth Rock stock was being maintained

I have each year endeavored to keep a number of differ-

ent blood lines comparatively pure for the factors L, and

L,, and then intercross these lines with one another.

The results have been highly successful from a prac-

tical point of view. This is indicated by the figures shown

in Table I and graphically in Fig. 1. These compare the

mean egg production per bird month by month under the

old system of mass-selection and under the new system

of breeding which recognizes the Mendelian inheritance

of fecundity with sex-linkage of the factor on which high

production depends. The figures for the new system are

those of the laying year 1913-14. In the laying year

1912-13 the flock had not yet attained any considerable

degree of homogeneity in respect of fecundity factors

since up to and including the preceding year low produc-

ing genetic combinations had been deliberately propa-

gated and therefore an average which included all birds

in the flock would be manifestly unfair as a test of the

practical worth on a large scale of the new systems of

breeding. The laying year 1913-14 is then the first com-

pleted year on which records are available for a fair test

of the Mendelian plan on a total flock scale.

The Barred Rock flock of the year 1913-14 included 192

birds which completed the year’s work. A number of

other birds (about 20) began the year but died before its

No. 581] INHERITANCE OF FECUNDITY 309

completion. These 192 birds were divided among three

flocks of 125 each, the other birds in each flock being cross-

breds of various sorts.

It is possible to compare these 1913-14 flock with the

old records during nine months of the year only. The

reason for this is found in the fact that the trap-nesting

season is, under the present system of management,

brought to a close with August. Furthermore a record is

now kept of the laying of the pullets in October at the

beginning of the year, whereas formerly the season’s

records did not begin until November 1. This comparison

is made in Table I. Also in this table the production for

1913-14 is compared with the best single year during the

mass selection experiment, when anything approaching a

corresponding number of birds were included,‘ and for

which all environmental conditions may be regarded as

approximately normal.’ The single year records which

come nearest to fulfilling all the conditions for a fair com-

parison with 1913-14 are those for the 100-bird pens in

the laying year 1905-06. There were two such pens and

182 birds survived through the year. There was one

small environmental accident in that year which reduced

the production in May somewhat. There were adverse

environmental influences in 1913 probably quite as effect-

ive in reducing production as anything that operated in

1905-06. The seasonal conditions, size of flock, ete., were

all fairly closely comparable with those obtaining in 1913-

14. At that time (1905-06) the flock had been under con-

tinuous mass selection for eight years.

There are a number of difficulties in the way of making

a comparison between any single year now, and the ‘‘best

4 The absolutely best single year under mass selection was 1901-02. That

year there were only 48 birds for which records are available. These were in

several respects a special lot, and can not fairly be compared with large

flocks kept under ordinary flock conditions. Cf. Pearl and Surface, loc cit.

5 Cf. Pearl, R., and Surface, F. M., ‘‘A Biometrical Study of Egg Produc-

tion in the Domestic Fowl. I. Variation in Annual Egg Production,’’ U. $.

Dept. Agr., B. A. I. Bull. 110, Pt. I, pp- 1-80, 1909, for an account of the

environmental difficulties in certain of the earlier years.

ê See Pearl and Surface, loc. cit., p. 18.

310 THE AMERICAN NATURALIST (Von. XLIX

year’’ made under the mass-selection system. In the first

place in order to make the comparison at all fair the

flocks in which the birds were kept when the records were

made must be of approximately the same size. It has

been conclusively demonstrated by earlier work in the

laboratory that egg production becomes reduced as flock

size increases. It would be idle to compare the results

now where the birds run in flocks of 125 to 150 birds per

pen with the ‘‘best’’ of those prior to 1904, when the

flocks were never larger than 50 birds each and were some-

times smaller. This restricts single year comparisons

then to the period after 1904.

In the second place, if we take the year when the total

production was highest, as the ‘‘best’’ year, we shall find,

in practically every case, that some particular month or

months of this year.will fall below the average for that

month or months. There are then two alternatives,

either, on the one hand, to take for comparison with a

single year now that year under the old system of breed-

ing which, on the whole, is the best and then make allow-

ances for disturbing factors in particular months, or, on

the other hand, to compare a single year now, month by

month, with an artificial year’s record made up by pick-

ing out the best record of each individual month regard-

less of the year in which it occurred or of the size of

flock. The second of these comparisons is obviously

artificial, since it is continued high production month

after month in the same laying year which is important.

It is of interest, however, to see the results of the com-

parison on both bases. These comparisons are made in

Table I.

The best single year 100-bird pen record in the earlier

period is, as already pointed out, that for 1905-06, having

regard to the months here compared (November to July,

inclusive). The 100-bird pen of 1904-05 made a better

record during the summer than the corresponding pens

of 1905-06, but fall considerably below in winter pro-

duction. In 1905-06 there was an environmental accident

No. 581] INHERITANCE OF FECUNDITY 311

TABLE I

MONTHLY DISTRIBUTION OF MEAN EGG PRODUCTION PER BIRD UNDER DIF-

FERENT BREEDING SYSTEMS

Weight- 1918. 14 (oe |

ed Mean org

Month Under | zed Best Month in Any Year of Mass Selection; Any | Year

ont Mass |Flocks Un- Size Flock 1913-14

elec | der Mass

tion Selection

1905-06

| 100-bird

ens )

November.| 4.63 | 5.38 6.45 (1904—05, 100-bird flock) 10.76

i ; | 9.91 (12.02 (1901-02, only 48 birds in small flocks); 14.19

January...| 11.71 | 13.27 {15.21 (1901-02, only 48 birds in small flocks)| 13.88

ocks) 13.

February. .| 10.87 | 13.39 14.46 (1905-06, n 87

March. ...| 16.11 | 17.33 18.29 (1905-06, 50-bird flocks) 19.22

April, os... 15.85 | 16.48 487 nc 50 (1901-02, oe 8 birds in small hata 18.44

May... T: | .02 (1902-03, 147 birde in small floc 16.88

R ANS ar 477 #4 "88 (1901-02, only 48 birds in small pee 14.56

Wy 0. a7 | 10.498 [14.90 (1901-02, only 48 birds in small flocks)| 14.62

(overfeeding of green food) in the latter part of April.

This adversely affected the May production. The 100-

bird pens were more affected than the 50-bird pens. Con-

sequently, in order to give every possible advantage to the

earlier period of the work, I have taken the 50-bird pen

averages for April, June and July and have graphically

interpolated the figure for May in the diagram.

The data in Table I are set forth graphically in Fig. 1.

From the table and the diagram the following points

are to be noted:

1. It is apparent that the laying in the part of the lay-

ing year covered by the statistics was distinctly better

in 1913-14 than either the weighted mean of the whole

period of mass selection, or than in the best comparable

year of the earlier period.

2. The difference is somewhat more pronounced in

respect of winter production (i. e., the laying prior to

March 1) than for any other cycle. Under the earlier

plan of breeding the average winter production was 36.12

eggs. This production corresponds reasonably closely to

the division point at 30 eggs between genetically high and

7 Average from 50-bird pens of same year (1905-06). See text.

8 Average omitted because of abnormal conditions. See text.

312 THE AMERICAN NATURALIST [ Vou. XLIX

genetically mediocre winter producers which was used in

the Mendelian analysis. In the year 1905-06 the mean

winter production was 41.95 eggs. In 1913-14 the pro-

;

EGG PRODUCTION

NOV DEC JAN FEB MAR APR MAY JUNE JULY

Fic. 1. Diagram comparing mean monthly egg production under different sys-

tems of breeding. The light continuous line gives the weighted means for the

earlier years, the heavy continuous line the means for 1913-14, and the dotted

line the means for 1905-06 100-bird pens. The cross-hatched area in comparison

with the Bys area indicates in the increase of the 1913-14 averages over the

earlier figure

duction in the corresponding months was 51.20 eggs

per bird.

3. It was shown by Pearl and Surface? that, on the

average, a flock of hens produces 81.73 per cent. of their

total annual yield between November 1 and August 1.

Applying this figure to the 1913-14 nine-month total of

135.82 èggs, we get for the probable production of this

9**Biometrical Study of Egg Production in the Domestic Fowl. II. Sea-

sonal Distribution of Egg Production,’’ U. S. Dept. of Agr., B. A. I. Bull.

110, Pt. II, p. 89, 1911

No. 581] INHERITANCE OF FECUNDITY 313

flock of 192 birds from November 1 to November 1 a total

of 166.18 eggs. This value, as a matter of fact, is very

close to the average production per bird of those (53)

out of the 192 which were kept over for experimental pur-

poses a second year. The corresponding total for the

weighted mean annual production over the whole period

is 128.86.

4. Taking the artificial year given in next to the last

column of the table it is seen that in 1913-14, with 125-bird

flocks, the November, December and March averages were

higher than the highest made in the corresponding months

during the mass-selection period, regardless of size of

flock or other conditions. The April, May and July aver-

ages in 1913-14 were substantially equal to the highest

made in the corresponding months under mass-selection.

The highest January, February and June averages in the

mass-selection period were from 1 to 2 eggs higher than

the corresponding months in 1913-14. Taking the totals

of the whole 9-month period compared, we have for the

artificial year, made up of the highest mean monthly pro-

duction under mass selection for each month regardless

of the year or the flock size, a total of 133.73 eggs per

bird, while that for the single year 1913-14 is 135.82.

Another comparison, which brings out some additional

facts, is set forth in Table II. Any bird laying 18 or more

eggs per month in the months November, December, Jan-

uary and.February may certainly be regarded as a high

winter producer. The proportion of such high pro-

ducers in the whole flock gives valuable additional infor-

mation to that furnished by the means, since the monthly

egg production variation curves are distinctly skew. The

TABLE II

SHOWING PROPORTION OF FLOCK LAYING 18 oR MORE EGGS IN THE SPECIFIED

MONTHS

a ` | Total Flocks 1899-1907,| _ 100-bird Flocks Flock of 1913-1914,

Month | 7 Pie Sent; 1905-1906, Per Cent. Per Cent.

November....... | 7.0 5.5 26.0

December........| 19.0 30.2 47.4

amay ee | 24.2 36.3 42.2

February........ | 22.6 36.3 31.8

314 THE AMERICAN NATURALIST [ Vou. XLIX

mean and median do not coincide. In Table II is shown

the percentage of the whole flock laying 18 or more eggs

in the months specified.

This table shows in an even more striking way than

the means in Table I the marked difference between the

flocks of the present time and those of the earlier years.

In 1913-14 nearly half the flock laid 18 or more eggs each

during December and January.

The data presented in this paper establish, I think,

the following facts:

1. There is a marked difference in the average produc-

tion per bird of Barred Plymouth Rock pullets of the

Maine Station strain at the present time, as compared

with what obtained in the earlier trap-nesting work of the

Station described by Pearl and Surface (loc. cit.).

2. This difference is in the direction of a substantially

higher mean flock production at the present tame.

3. The increase in flock production is most pronounced

in respect to winter production.

The most probable explanation of the above results

appears to the writer to be that the plan of breeding now

followed is more nearly in accord with the biological facts

regarding the inheritance of fecundity than was the plan

followed in the earlier years.

The reasons for this opinion, while not constituting

complete proof of the suggested explanation, certainly

make a strong body of evidence in its favor. They are,

summarily stated:

(a) That the increases in flock productivity have been

synchronous with changes in breeding practise.

(b) That the increases give every indication of being

permanent, there having been no tendency towards a de-

cline in flock productivity since 1908, when the simple

mass selection was stopped and breeding begun on a

progeny-test basis.

environmental circumstances synchronous with the in-

creases in flock production and capable of accounting for

them. The hens are housed to-day in the same houses

No. 581] INHERITANCE OF FECUNDITY 315

that they were in 1904; are fed substantially the same

feed, the only modification of the ration having been in

the direction of one less stimulating to production than

the one formerly used; are hatched in the same sort of

incubators; reared in the same yards, ete.

(d) That the most marked gains have been in that

cycle of production (winter laying) to which especial

attention was paid in the breeding.

(e) That when analyzed in terms of individual matings

the results obtained in egg production have been the re-

sults to be expected on the Mendelian hypothesis of the

inheritance of this character earlier set forth, with only

minor exceptions for which the explanation is in nearly

all cases apparent.

Il. Aw InpEPENDENT CONFIRMATION OF THE SEX-LINKAGE

OF THE FACTOR ror Hıcam FECUNDITY

Besides the results with large flocks which have fol-

lowed the practical application of the Mendelian hypoth-

esis of fecundity inheritance at this Station, numerous

poultrymen in various parts of the world have obtained

similar results. Several instances of this sort might be

cited from private correspondence. The writer has felt,

however, that such cases really contributed nothing new

in principle, and that therefore there was no special need

of calling attention to them.

There lately appeared, however, in an English poultry

paper, a note which seemed to me to be of interest on

several grounds. In the first place, it is evident that the

writer, Mr. E. N. Steane, is a careful observer, and an

experienced poultryman. In the second place, his ob-

servations on inheritance of egg producing ability appear

to be, from his point of view, entirely original and unin-

fluenced by any earlier work.

The parts of Mr. Steane’s note” which are pertinent in

the present connection are these:

10 Steane, E. N., ‘‘The Production of ‘Best Layers,’’’ The Feathered

World (London), Vol. 52, p. 285, 1915.

316 THE AMERICAN NATURALIST [ Von. XLIX

My own experience, and that of many other breeders, tends to show

that the birds hatched from high pedigree hens are not such prolific

layers as those hatched from healthy hens of an indifferent laying strain

mated to high pedigree cockerels.

For three or four seasons I bred from two-year-old white Leghorn hens

of a gold-medal laying strain mated to a cockerel of equally-good descent,

and the results, to my mind, were disappointing, and did not yield an

adequate profit on the money spent. The pullets were less prolific than

their parents, and inclined to be delicate and more or less undersized,

while the percentage of fertile eggs was lessened.

Then by a lucky chance one season I had not enough eggs from a pen

of Rhode Island Reds to fill up an ineubator, and I made up the defi-

ciency from a pen of good-sized healthy Leghorn hens of no particular

laying strain mated to a pedigree cockerel. Practically every egg from

this pen was fertile, the chickens proved strong, and the results seemed

in every way satisfactory,

This, of course, led to my systematic mating of healthy, well-grown

birds of indifferent laying strain to high pedigree cockerels, with ve

successful results. The fertility of the eggs was extremely satisfactory,

the chickens turned out strong and healthy, and the pullets on arriving

at maturity were highly prolific layers, each pullet averaging 200 eggs

and over during the first twelve months, as against about 130 from the

pullets of the high pedigree hens, many of whom also died off. In the

second year the birds did equally well, the number of eggs being main-

tained and all being of a good size.

Later, I tried the result of mating high pedigree hens to a healthy

cockerel of no special laying strain, but without success, the chickens

being healthy, but the laying results much below the average, so that

nothing was to be gained by further trials in that direction.

While being quite aware that many breeders do not agree with my

conclusions, and that a great deal also depends on the condition and en-

vironment of the birds—prolificacy being always greatly improved by

the birds having a free range, I am myself firmly convinced that such

mating makes for the production of best layers. All my experiments

were, of course, carried out under the same conditions in each ease, the

birds being kept in runs of 20 yards by 10, on well-drained, sandy soil,

with a house and scratching shed attached, and fed on the same diet as

that adopted in the recent laying competitions.

It is evident that Mr. Steane’s experience was exactly

parallel to the results of the present writer’s investiga-

tions reported in earlier papers. High producing females

did not transmit that quality directly to their daughters.

The character is sex-linked.

he only point of difference is that noted in the second

No. 581] INHERITANCE OF FECUNDITY 317

paragraph of the quotation, and I think that the explana-

tion of the discrepancy there is contained in the closing

words of the paragraph where Mr. Steane says:

The pullets were .. . inclined to be delicate and more or less under-

sized, while the percentage of fertile eggs was lessened.

This would indicate that other causes besides the breed-

ing operations were working to bring about a poor physio-

logical condition of the progeny, which is of course incon-

sistent with high productivity. Lowered fertility of eggs

is one of the best indicators of reduced vitality which can

be found.

We appear to have, in this case, a rather complete inde-

pendent confirmation by a practical poultryman of one of .

the present writer’s chief results in regard to the inher-

itance of fecundity.

II. Summary

In this paper it has been shown that:

1. There is a marked difference in average egg produc-

tion per bird of Barred Plymouth Rock pullets of the

Maine Station strain at the present time as compared

with what obtained during the period of simple mass-

selection for this character.

2. This difference is in the direction of a substantially

higher mean production at the present time, when tested

on flocks of large size.

3. The increase in flock average productivity is most

pronounced in respect to winter production, which is the

laying cycle to which especial attention has been given in

the breeding.

4. The cause of this increase in flock productivity ap-

pears, with a degree of probability which is very high and

amounts nearly to certainty, to be that the method of

breeding the stock now followed is more closely in accord

with the mode of inheritance of fecundity than was the

simple mass-selection practised in the earlier period.

5. The result announced in earlier papers that high

fecundity is a sex-linked character, for which the female

is heterozygous, has been confirmed by practical poultry-

men in their breeding operations.

SHORTER ARTICLES AND DISCUSSION

THE APPEARANCE OF KNOWN MUTATIONS IN OTHER

MUTANT STOCKS

In Drosophila ampelophila the reappearance of known muta-

tions in stocks that appear to be uncontaminated is a not un-

familiar occurrence, but we discount all such cases unless in some

way the occurrence can be controlled, because the chance of con-

tamination even with extreme care might be claimed to be greater

than the chance of mutating.

In the stock of sepia-eyed flies a few individuals with very pale

(yellowish red) eyes appeared. Sepia eyes are very dark or

black brown in color. So that the flies with the new eye color

stood out conspicuously amongst the dark-eyed sepias.

From the color of the eye it was suggested that it might be

vermilion-sepia. If this were the case it should give, when bred

to vermilion flies, vermilion-eyed offspring, because the factor for

vermilion would be common to both stocks and the stock ver-

milion would carry the normal (dominant) allelomorph of sepia.

When the test was made the offspring were vermilion. These F,’s

inbred gave in F, 122 vermilion to 39 vermilion sepia, approxi-

mately 3:1, which is the expectation for one factor difference.

The result shows that a mutation to vermilion eyes had taken

place in stock that had already sepia eyes. The resulting flies

were the double recessive vermilion sepia.

That the result is not due to contamination is evident, for had

a vermilion-eyed fly got into the sepia stock it would have

produced red-eyed (wild type) females or vermilion males. As

no red- or vermilion-eyed flies were present this explanation is

excluded.

A similar mutation took place in stock having purple eyes.

Like sepia the eye color of these flies is dark but in this case

has a distinct purplish-red tinge. Among the offspring from a

cross of a female heterozygous for purple with a pure purple

male a fiy with very pale orange-colored eyes appeared. This fly,

which was a male, was also conspicuously unlike the remainder

of the red or purple offspring of this pair.

It was at first thought possible that this was the appearance

of a mutation to cherry in a mutant stock. If this had been the

case we should expect that in a cross to a cherry female all of F,

offspring would be cherry. The test showed instead all cherry

-818

No. 581] SHORTER CONTRIBUTIONS AND DISCUSSION 319

males and all red females—the normal dominant color. This

proved then that the new fly did not contain the factor for cherry.

It was then suggested that this was a second case of the appear-

ance of vermilion in mutant stock. Since the fly was a male

several matings were possible, and it was therefore crossed to a

vermilion female. As in the previous case if vermilion were

common to both stocks, the offspring should be all vermilion.

This condition was actually found in all the F, offspring of this

second cross, and the F,’s gave vermilion and the orange-eyed

fly—now shown to be vermilion purple—in approximately 3:1

classes. This demonstrated that a mutation to vermilion had

taken place in a fly already having purple eyes, for as the cherry

cross indicated, the pure mutant stock contains the normal

dominant allelomorph to every factor except the one it shows.

In order to demonstrate that the purple factor was still pres-

ent unchanged in the germ cells of the double recessive (ver-

milion purple) fly, the original male was also mated to pure

purple-eyed stock. As in the other cases if both parents contain

the factor for purple all the offspring should be purple. This

was the actual result obtained, and it proves the original mutant

to have been the double recessive vermilion purple.

In this case also it is not possible that the result could have

been due to contamination. This would indeed be highly im-

probable when the original parents were a single isolated pair,

the female of which was a virgin when first mated. But even

had a vermilion male been able to mate with the heterozygous

female only red-eyed flies could have been produced. The ver-

milion purple combination could not occur because the germ

cells of each animal carry the normal dominant allelomorph of

the mutation in the other.

Our results in these two cases show that mutations within other

mutant stocks occur, and they also indicate that in the case of

vermilion we have a mutation which has recently reappeared

twice, T. H. MORGAN,

COLUMBIA UNIVERSITY HAROLD PLOUGH

THE EVENING PRIMROSE VARIETIES OF DE VRIES

No explanation of the ‘‘variation’’ of heterozygous plants had

presented itself until Mendel went back to the haploid generation,

and referred the differences in the progeny of heterozygotes to the »

Segregation of differences in the pollen-grains and embryo-sacs

from which the plants had arisen. He dealt, however, with plants

320 THE AMERICAN NATURALIST [ Vou. XLIX

in which all the young pollen-grains and embryo-saes had pre-

sumably an equal chance to mature.

Perhaps a parallel state of affairs exists to-day. De Vries and

others have brought to light, in the progeny of Œnotheras, a cer-

tain amount of ‘‘variation,’’ by no means so striking as can be

seen in the progeny of many variety or species crosses, but re-

markable chiefly because it could not be explained. In my opin-

ion, this ‘‘variation’’ can perhaps be explained by going back,

as Mendel did, to the haploid generation. We may, I think, pre-

sume that there are certain genetic factors concerned with the

development of the young microspore into a complete pollen-

grain, and the young megaspore into a normal embryo-sac. If

the plants are heterozygous for one or more of these factors, we

get definite ratios of normal and aborted pollen-grains, or normal

and aborted embryo-sacs. We thus have a population of haploid

individuals (microspores or megaspores) which show segregation

into viable and non-viable. We may expect ratios of normal and

aborted haploid individuals of 1:1; 1:3; 1:7; 1:15, ete., apply-

ing to either pollen-grains or to embryo-saes, or to both. When

we thus have heterozygosity of one or more factors essential for

the development of the individuals of the haploid generation, the

laws and ratios for certain characters of the diploid generation

may become very different.

According to Geerts, who seems to have made the only accu-

rate study of the point, the typical Gnothera lamarckiana aborts

one half its microspores (two from each tetrad) and one half

its embryo-saes. The simplest hypothesis demands two factors,

one essential for the development of pollen-grains, and one for

the development of embryo-saes, which factors show complete

(or nearly complete) repulsion. Then, of course, the offspring

will be permanently heterozygous for these two factors, and

also more or less for any other factors which may be linked with

them. (Linkage has been shown to exist, I think, in all plants

where it has been looked for.) With more than two such fac-

tors heterozygous, the aborted pollen-grains or embryo-sacs may

increase, and the ratios in the progenies of crosses become al-

tered. Hence, in my opinion, a promising step towards the in-

vestigation of inheritance in Œnotheras is the correct determina-

tion of the ratios of aborted and normal pollen-grains and

embryo-saes in the different amet of @nothera lamarcki-

ana, and related species. JOHN BELLING

FLORIDA AGRICULTURAL EXPERIMENT STATION

E, 1915

VOL. XLIX, NO. 58

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THE

AMERICAN NATURALIST

Vout. XLIX June, 1915 No. 582

THE naira Stal OF CERTAIN INTERNAL

CONDITIONS OF THE ORGANISM IN

ORGANIC EVOLUTION

First Parer. Tue REGULATION oF THE PuHysico-CHEM-

ICAL CONDITIONS OF THE ORGANISM!

F. H. PIKE AND E. L. SCOTT

DEPARTMENT OF PHYSIOLOGY, COLUMBIA UNIVERSITY

I. Introductio

II. The anias hinis of internal ipasa in the higher organisms.

. Thermo-regulation in the higher organis

The cardiac and vascular mechanisms.

The concentration of sugar in the blood.

The osmotic pressure of the body fluids.

The digestive tract.

The epidermis an nd sere mechanical protective mechanisms.

. The internal secretions.

The mechanisms of er

IKL The laws of chemical equilibrium.

1. The law of mass action.

- Van’t Hoff ’s law.

. The phase rule.

IV. The interpretation of the regulatory mechanisms in terms of chemical

equilibrium.

ee T

w bo

. Applications of Van’t Hoff’s law.

. The general conditions of the reactions in the cells.

3. Stimulation in terms of chemical equilibrium.

V. General considerations and summary.

bo =

Tue desirability of an attack on the general problems

of evolution from the point of view of physiology, as well

as the general deficiency of literature in physiology bear-

1 Read before Section F of the American Association for the Advance-

ment of Science, December 30, 1914.

321

322 THE AMERICAN NATURALIST [Vou. XLIX

ing on these problems, has been recognized for some time.?

The considerations to be presented in the papers of this

series are in part the outgrowth of experimental work

on the central nervous system and its relation to the proc-

esses of evolution ;? they were in part suggested by Black-

man’s‘ paper on the manifestations of the principles of

chemical mechanics in living matter; and they have grad-

ually grown up in our minds as our attention was at-

tracted more and more to the questions involved. The

bearing upon the processes of evolution of certain of the

facts drawn from the experimental study of the compara-

tive physiology of the nervous system will, for the most

part, be presented in separate papers embodying the

experimental data. The relation of the physico-chemical

conditions of the organism, together with those nervous

mechanisms with which the maintenance of the physico-

chemical conditions is inextricably bound up, to the ques-

tions of adaptation and fitness of the organism will con-

stitute the greater part of the subject matter of this and

following papers on the general problems of evolution

from the point of view of the physiologist.

Since the inception of the work, there have appeared,

in addition to Blackman’s paper, several other papers of

interest to physiologists on certain phases of the problem

of evolution.

Woods?’ has collected the better-known cases of modi-

fication in animals and plants induced by changes in the

environment or in the general conditions of existence, as

shown by changes in the rate of growth, changes of the

external form of the body, the occurrence of artificial

2 Howell, ‘‘Problems of Physiology of the Present Time,’’ Congress

of Arts and Sciences, Universal Exposition, St. Louis, 1904, Vol. V, p.

11 of the reprint.

3 Pike, American Journal of Physiology, 1909, XXIV, p. 124; Ibid.,

1912, XXX, p. 436; Quarterly Journal of Experimental dareng AN

VII, p- 1; Popular Science Monthly, 1914, p. 403; Science, N. S., Ey.

805.

4 Blackman, Nature, 1908, LXXVIII, p. 556; AMERICAN NATURALIST,

1908, XLII, pp. 633-664,

5 Woods, Popular Science Monthly, 1910, p. 313.

No. 582] SIGNIFICANCE OF INTERNAL CONDITIONS 323

parthenogenesis, the modification of mental and moral

traits, and the extent of regeneration of lost parts.

When arranged in the order of their position in the

taxonomic scale, organisms show a steadily decreasing

response, with reference to these phenomena, to changes

in the environment. Woods does not indicate, except in

very general terms, the physiological mechanisms in-

volved in bringing about this diminishing effect of the

environment. Some years earlier Donaldson® had called

attention to the general lack of influence of formal edu-

cational training upon the course of later life of talented

individuals.

Julian Huxley’ in his discussion of the individual in

the animal kingdom, points out that the individual

acquires an increasing independence of the environment,.

or that the environment has a diminishing effect. Hux-

ley assigns mere increase in size and the increasing com-

plexity and efficiency of the nervous system as two of the

factors involved in the attainment of the freedom from

mere accidents.

Mathews’ has pointed out more specifically some of the

various internal mechanisms which are involved in the

acquisition of independence of the environment on the

part of the higher animals. These are, according to him,

(1) the heat-regulating mechanism, (2) the mechanism

of immunity, (3) the mechanism for rendering animals

independent of external conditions of moisture, (4) the

mechanism which renders them independent of barometric

pressure, (5) the mechanisms for reproduction and car-

ing for the young, (6) the alimentary mechanism, and (7)

the nervous system.

Henderson? has shown that the environment is an ex-

ternal thing in which certain physico-chemical conditions

are kept relatively constant, while others may vary

® Donaldson, ‘‘Growth of the Brain,’? London and New York, 1895, pp.

347, 355, 360, 365.

t Huxley, J. S., ‘‘The Individual in the Animal Kingdom,’’ Cambridge

and New York, 1912.

8 Mathews, AMERICAN NATURALIST, 1913, XLVII, pp. 90-104.

? Henderson, ‘‘ Fitness of the Environment,’’ New York, 1913.

324 THE AMERICAN NATURALIST [Vou. XLIX

widely, even in the same region. As long as organisms

live in the ocean or in the water generally, they are sub-

jected to certain relatively constant conditions dependent

upon the physico-chemical properties of the environment.

But it should be recognized that with organisms which

have migrated out upon the land the case is somewhat

different, as all conditions, except oxygen concentration

and pressure, vary more markedly on the land than in the

water. Temperature, in particular, varies greatly over

the land, and the poikilothermal animals have their activ-

ities greatly limited by the temperature conditions.

From Henderson’s premises, the conclusion follows

that life is what it is because the environment is what it

is. A different environment might, and in all probabil-

ity would, have resulted in, or been associated with, a dif-

ferent form of life on the earth. Certain characteristics

commonly called adaptations are, as Henderson shows,

the automatic and inevitable results of the physico-chem-

ical conditions obtaining in the environment. If suc

a view assumes that an adaptation ceases to be an adap-

tation when the manner of its origin is discovered, it

would seem that we were in need of a more precise defini-

tion of adaptation. The question arises whether other

similar characteristics that have been called adaptations

are not also the inevitable and automatic result of the

physico-chemical conditions of the environment. We may

therefore consider the question of the reality of adapta-

tion, and also whether some of the characteristics of or-

ganisms are not really adaptations,’° even if they arise

from the action of physico-chemical conditions in the en- °

vironment. Again, since, in a given environment, with es-

-= sentially the same physico-chemical conditions for all its

inhabitants, there are many animal types, it would appear

that there were some influences operative within the or-

ganism itself to produce certain characteristic reactions,

known as adaptations, to the environment. As we will

show subsequently, these facts do not in any way pre-

clude an explanation of their origin on some hypothesis

10 Mathews, loc. cit.

No.582] SIGNIFICANCE OF INTERNAL CONDITIONS 825

other than vitalism. The organisms may be, under cer-

tain conditions at least, more variable than the environ-

ment. These considerations apply also to those simple

organisms which are the cellular constituents of a larger

body. Certain of the higher vertebrates, in which, as

has been indicated, the influence of the environment is

probably less than in some of the lower forms, are more

variable than certain of the lower vertebrates.

It is a fair inference from the facts cited in the various

papers referred to, that certain characteristics of living

matter, such as its slight degree of alkalinity, and its rel-

atively great specific heat, may be regarded as the direct

automatic and inevitable results of the properties of the

environment. Other characteristics, as the peculiar type

of the nervous system, are not so obviously the direct and

inevitable result of the environment, and these may be

regarded, for some time to come, as adaptations to the

environment or to the general conditions of existence in

which the particular organism is able to live and perpetu-

ate itself. .

A statement of the general problem may now be made.

Two general classes of organisms live in a relatively con-

stant environment, so far as the general internal condi-

tions of the organism are concerned. (1) For example,

the lower marine organisms of fairly limited distribution

live in an external environment which changes but little

in temperature, osmotic pressure, inorganic salt content,

neutrality or faint alkalinity, oxygen and carbon dioxide

concentration, and soluble nitrogen compounds. Tem-

perature and amounts of light may vary somewhat

throughout the year, but the temperature changes in the

given region of the ocean are less in magnitude than the

temperature changes over a corresponding area of land.

The osmotic and inorganic salt relationships of organism

and environment alike vary but little. Nor does the or-

ganism, in general, maintain within itself, any purely

physico-chemical condition differing greatly from that in

the general external environment. This does not pre-

326 THE AMERICAN NATURALIST [Vou. XLIX

clude the origin within the marine organism of stereo-

chemical isomers, the great importance of which has re-

cently been pointed out by Reichert. Stability of con-

ditions would even favor the perpetuation of such com-

pounds as could be formed under a given set of condi-

tions. (2) On the land, as has already been indicated, the

higher animals—birds and mammals—have acquired a

relative independence of the environment as shown by

their wide distribution. Their internal conditions of tem-

perature, moisture and the like, may not only differ

greatly from the same conditions in the environment at

any given time, but the internal conditions, as we shall

show, do not change greatly when the external conditions

change. Intermediate between these two types is a third

type which lives in an environment subject to wide varia-

tions of temperature and moisture, and whose internal

temperature varies with the change of external tempera-

ture. While some of the internal conditions of these or-

ganisms remain relatively stable, others are subject to wide

variation. We have then to explain, in terms of function,

(1) what are the various mechanisms by which the higher

animals have attained this relative independence of the

environment and (2) what has been the rôle of these

mechanisms in organic evolution.

II. THE GENERAL Constancy or INTERNAL CONDITIONS IN

THE HIGHER ORGANISMS

The study of the internal physico-chemical relationships

of higher animals has led to the acquisition of a consid-

erable mass of facts concerning this phase of animal or-

ganization. These facts show that in the higher animals

there exist a number of mechanisms which interact to

bring about a remarkable constancy of internal physico-

chemical conditions during the life of the animal. It ap-

pears justifiable again to call attention to some of these

facts with a brief description of some of the mechanisms

involved in order better to emphasize some of the inter-

pretations of, and inferences drawn from, them in so far

11 Reichert, Science, 1914, N. S., XI, pp. 649-661.

No. 582] SIGNIFICANCE OF INTERNAL CONDITIONS 827

as these interpretations and inferences have to do with

the general problem of evolution. We may, then, first of

all briefly review the more salient of these facts, and after-

ward attempt their interpretation in terms of well-known

physico-chemical laws—e. g., the law of mass action and

the phase rule.

1. Thermo-Regulation in the Higher Organisms

We may divide the vertebrates into two general groups

on the basis of their internal or body temperature; (1)

those which maintain a relatively constant internal tem-

perature and (2) those whose internal temperature is

variable. These groups may be tabulated as follows:

TABLE I

I. Animals with a constant body temperature.

about 42° C. or 107° F. Birds.

a bi about 39° C. or 102° F. Mammals.

yeri about 37° C. or 98.6° F. Man.

II. Animals with an inconstant body temperature.

Adults or partly grown mam-

rds

(a) Animals which die when

the temperature falls? Newborn mammals and birds,

below 20° C.

(b) Animals which become

korpit Npe te me Hibernating forms—some mammals.

perature falls below

a Aan O Reptiles, batrachians, fishes, amorg

vertebrates; molluses, insects, and

the invertebrates generally.

active when the tem-

perature falls below

20° C. L

Looking now to the differences between lower and higher

vertebrates, to restrict ourselves at the start to a rela-

tively small part of the animal kingdom, one of the most

noticeable changes has been the development of a very

constant body temperature in the so-called warm-blooded

or homoiothermal animals (Table II). The detailed

enumeration of the body temperature of all the animals

so far observed would require too much space, but the fol-

lowing data will be sufficient to show upon what basis of

fact the statements rest:

12 Richet, Dictionnaire de Physiologie, 1898, t. III, pp. 85-86.

328 THE AMERICAN NATURALIST [Vou. XLIX

TABLE IT

TABLES OF BODY TEMPERATURE

1. Birds

No. of

Genus or Species | Observa- Temperature Observer

tions

Spairow....:-.. 1 42.1° O Davy.

UEROy A 1 42.7 avy.

Peacock. i543 2% 1 40.5 to 43.0 Davy.

Guinea fowl..... 1 43.0 Davy

Duck, domestic 110 (Mean) 42.07 Martins

Mas S RE 179 (Mean) 42.3 Marti

Te POE E, (Maximal) 43.45 Martins

ew E (Minimum) 40.8 Martins

saN Davy, Eydoux,

Mikao SE A 9 40.6 rown-Sequard,

longipennes 69 40.6 Souleyet.

Peasant). 23. . 5 42.5 ichet.

yo Ro E S 17 42.5 Mantegazza, De

rquay, Dumeril,

Davy, Prevost and

Dumas.

Pigeon oaa 600 (Mean) 41.9 Chossat.

(Noon) 42.22

(Midnight) 41.48

Piom. ese 10 ( 41.2 Corin, Van Beneden.

(Maximum) 43.6

(Minimum) 39 Daily variation 2.2

Pigeon 355.5 2: 31 (Mean) Zander.

(Maximum) 44

42.0

Pee We aie ec aD ee Se a ee

Richet!® considers it probable. that the temperature of

birds is always above 40° and never, except under ex-

treme conditions, above 44° C.

Further measurements are given by Sutherland

Simpson.'4

2. Mammals15

Genus or Species. Temperature.

Pe oe ess ee ee ee ee 89.7° C.

SOOO siao iae es ea pe pe ee 39.6

Oe co eee ee ks Ua ee 39.5

Rabla -oe Fs ies es a ee es 39.5

OGG ie ce ree b eee r tree teas ety oboe 39.2

es i cossos irriparre or re a xy ein Fk 39.2

Monkeys ...... PVub a betas E eu eee 38.3

Horsen i a a ee ee 37.7

DEOHOUKENIRG soenan As a a ee ok 30.0

13 Richet, loe.

, loe. cit., p. 87.

14 Proceedings of the Royal Society of Edinburgh, 1911-12, XXXII, pp-

19-35.

15 Richet, loc. cit., t. TII, p. 91.

No. 582] SIGNIFICANCE OF INTERNAL CONDITIONS 329

The monotremes occupy a peculiar position in the scale

(Table III). Their internal temperature, while relatively

constant and considerably above that of the external air, is

notably lower than that of mammals generally.'® This

group probably presents a transition stage between the

thermal animals and the homoiothermal animals

with a higher body temperature.

TABLE III

SHOWING Bopy TEMPERATURE OF THE MONOTREMES

Temperature

| Cloacal Peritoneal | External

Echidna aculeata, var. typ............ e E. WC: SLS C:

Echidna aculeata, var. typ............ | 29.5 31.5 22.0

Echidna aculeata, var. typ............ | 380.5 31.5 18.0

hidna aculeata, var. typ............ | $81.5 31.5 18.0

Echidna aculeata, var. typ. young..... 31.0 31.5 24.0

Echidna aculeata, var. typ. young..... 34.2 31.5 22.5

Echid Cuba VOR ty. oe i 34.0 36.0 31.5

Echidna aculeata, var. typ..........-. 28.3 30.0 31.5

Echidna a op WEP EV Pet es 28.3 26.9 20.0

rnithorh radost ne 24.4 26.9 20.0

ertain paradou sin es i 25.2 25.2 23.0

The normal diurnal variation in temperature of the

human has been studied by many observers. The temper-

ature varies not only with the time of day, but with the

taking of food, with age, with external temperature and

with other conditions to which we will return later. On

the average, the highest temperature is attained in the

evening between five and eight o’clock, and the lowest in

the early morning between two and six, with upper and

lower limits of 37.5° C. (99.5° F.) and 36.3° C. (97.4° F.),

respectively. The body temperature may, of course, be

greater or less without any necessary implication of dis-

ease processes, but the figures given may be considered as

fairly representative.’7 It seems well established that, in

conditions of health, the daily variation in temperature

is about one per cent. of the mean—98.4° F.—expressed in

the Fahrenheit scale. It is a peculiar fact also that the

16 Richet, p. 90, Table II, and C. J. Martin, Philosophical Transactions of

the Royal Society, London, 1903, Series B, Vol. CXCV, p. 1

17 Stewart, ‘‘ Manual of Physiology,” 6th ed., New York, 1910, p. 605.

330 THE AMERICAN NATURALIST [Vou XLIX

normal body temperature is fairly close to the upper

limits of body temperature compatible with life. A varia-

tion of five per cent. from the mean, expressed in degrees

Fahrenheit, is often cause for grave anxiety, and a varia-

tion of ten per cent. is usually fatal. Compared with this,

the variation in body temperature of fishes which live in

the water only a few degrees above the freezing point

in the winter and in the tepid water of a shallow stream

in the summer is enormous.

The highest temperatures recorded in the human, after

which recovery has occurred, are shown in Table IV

vae IV

Temperature

AE RN o e rA erino dai, ‘cited by Lom-

broso.

AB ohea enn kiar Oe Alvarenga

SEI aan Searlat Bouveret.

SSO fi. eera earlat Vicente et Bloch.

CES. ee Periostitis and pyemia Weber

43.3 .......Intermittent fever Meter cited by Seguin.

ee eee Intermittent fever Hirtz.

eens Intermittent fever Alvarenga.

Ee Intermittent fever Riess.

J Peeper ne Intermittent fever Bassanovitz.

B eee Intermittent fever Diez Obelar.

Me wis Intermittent fever ay eo cited by Richet.

BA Bo i hin Intermittent fever

OSB) Cece, Rheumatism Witson Tos cited by Seguin.

449 nan Hysterical icterus Loren

dileas Hysteria miem ka by Gilles de la

Tourette.

SD eens Hysteria Lombroso

SO Rush . Hysteria R. Visioli

BS Ge Hii . Hysteria Sciamanna.

REO ix, Cane Fracture of the cervical Brodie, Lorain.

vertebra

Se A Fracture of the 12th a Simon.

vertebra and deliriu

tremens

S98 ae a Fracture of the 6th cer- Frerichs.

vieal (19 hours after

traumatism)

The somewhat alarming but relatively innocuous mani-

festations of hysteria are attended by a high temperature

without the complicating factor of an infection, and pres-

No. 582] SIGNIFICANCE OF INTERNAL CONDITIONS 331

ent, therefore, the effects of temperature alone. It will

be noted that the body temperature attained in hysteria—

45° C. or 113° F.—and 46° C. in a case of intermittent

fever with recovery is nearly as high as we have found

recorded—45.7° C. or 114.3° F. after death in a case of

tetanus, and is next to the highest recorded, as far as

our observation goes, with recovery of the patient. The

temperature of the body may, however, rise still higher

under the influence of external agents. Thus, in death

from strong electric currents, Klein'® reports a body

temperature of 132° Fahrenheit (55.5° C.) or even 140° F.

(60° C.) immediately after death.

The effect of temperature upon the contractile mani-

festations of protoplasm has been summarized by

Schäfer :19

In warm-blooded animals the phenomena cease altogether to be ex-

hibited if the protoplasm which is under observation is cooled to below

a temperature of about 10° C., although they will be resumed on warm-

ing the preparation again, and this even if it has been cooled to 0° C.,

or a little lower. And when warmed gradually, it is found that the

movements become more active as the temperature rises, attaining a

maximum of activity a few degrees above the natural temperature of the

body, although if maintained at an abnormally high temperature they

are not long continued. A temperature a little above this maximum

rapidly kills protoplasm, at least that of vertebrates, producing a stiff-

hess or coagulation in it (heat-rigor), which is preceded by a general

contraction; from this condition of rigor. the protoplasm can not be

recovered. But the protoplasm of some organisms will stand tempera-

tures approaching that of boiling water without passing into heat-rigor.

Freezing may cause destruction of protoplasm in higher animals, but

that of certain of the lower animal and plant organisms is capable of

resisting extreme cold, apparently for an indefinite time. This has also

been found true for seeds of plants (Dewar).

Frog’s muscle (gastrocnemius) reaches its maximum

efficiency at about 35° C., after which a falling off occurs

as the temperature is increased. Heat-rigor makes its

appearance at about 41° C.—about two degrees Centi-

grade above the usual body temperature of a dog (an

18 Klein, New York Medical ‘Journal, May 30, 1914.

19 Schäfer, ‘*Text-Book of Microscopic Anatomy,’’ London and New

York, 1912, pp. 68-69,

332 THE AMERICAN NATURALIST [Vou XLIX

average of 39.38° C. for 176 measurements), or slightly

less than the usual body temperature of birds (42° C.).”

The maintenance of a constant temperature is depend-

ent not upon one mechanism alone, but upon the coordi-

nated interaction of several mechanisms. The presence

of a coat of fur or feathers has long been recognized as a

factor in maintaining the constant temperatures of mam-

mals and birds. The development of such a protective

covering has many times been emphasized by evolution-

ists, and seems to be well accounted for on the theory of

natural selection. The fur or feathers tend to diminish

heat loss from the surface of the body, but have nothing

to do with the production or distribution of heat within the

body. A subcutaneous layer of fat may still further re-

duce the heat loss from the surface, as in the Cetacea.

The production of heat is directly dependent upon oxi-

dation in the muscles and glands of the body. A fall of

general body temperature is attended by increased muscu-

lar activity, as shivering, when the temperature tends to

fall unduly low. The muscular activity is dependent in

its turn upon the nervous system, and upon the supply of

oxygen and oxidizable substances through the blood.

The effect of the blood in maintaining a more nearly

constant temperature of the muscles, as well as the pro-

duction of heat by the muscles themselves, is shown by

Meade Smith’s experiments on mammalian muscles.”

Although more heat is produced in a muscle which is ĉon-

tracting than in a resting muscle, there is still some heat

production while at rest. When the artery going to a

resting muscle was tied off, the difference in temperature

between muscle and blood due to heat production in the

muscle might be as much as 0.6° C. at the end of a five-

minute period. When the circulation is intact, this dif-

ference in temperatures does not become so great. Te-

tanic stimulation of a muscle may lead to a considerable

increase in the temperature of the venous ee oe

20 Richet, ‘‘ Dictionnaire de Physiologie,’’ 1898,

21 Meade Smith, Archiv für (Anatomie und) ‘Physiologie “(Du Bois

Reymond), Physiol. Abt., 1881, pp. 105-152.

No. 582] SIGNIFICANCE OF INTERNAL. CONDITIONS 333

directly from the muscle as compared with arterial blood.

The distribution of heat is accomplished by the circu-

lating fluids of the body, and particularly by the blood.

When the heat loss by radiation from the surface of the

body becomes too rapid, the contraction of the walls of the

peripheral blood vessels cuts down the quantity of blood

going to the surface and, hence, the loss of heat as well.

The constriction of the peripheral blood vessels and the

contraction of the muscles tend to restrict the lower limit

to which the body temperature may fall. The lower

the external temperature, the greater the supply of

heat from internal combustion needed to maintain the

usual temperature of the body unless the radiation be

checked by clothing or by artificial heat. It is generally

stated that the temperature of the unclothed human body

at rest may be maintained until the external temperature

falls to 27° C. (Senator). This statement, as will be

shown in a later paper, may be open to question. When

the external temperature falls below this point, shivering

or other involuntary muscular movement begins. This

relation between temperature and metabolism accounts in

large measure for the large amounts of food sometimes

consumed by Eskimos. A young vigorous Eskimo may

eat as much as four kilograms (nine pounds) of meat in

a day.??

K. E. Ranke gives another illustration of the effect of

climate upon diet in Germany and in Brazil. Allowing

himself a free choice of food, the controlling influence

being his appetite, his food requirements were 3,300 to

3,500 calories a day, when the external temperature range

was from 15° C. to 22° C. Ina dry atmosphere at 25° C.,

the fuel value of the diet fell to 2,800 calories. In an at-

mosphere with a temperature of 25° C. to 28° C. and a hu-

midity of eighty-three per cent., the heat value of the diet

fell to 1,970 calories in.a day. This diet was insufficient

22 Rink, cited by Lusk, ‘‘ Fundamental Basis of Nutrition,’? New Haven,

1914, p. 28

334 THE AMERICAN NATURALIST [Vou. XLIX

to maintain his body weight, and disturbances of his gen-

eral health appeared.?*

The cold-blooded and warm- keki animals react dif-

ferently to changes in external temperature. Thus, the

carbon dioxide output of a frog rose from 0.015 gram

per kilogram of body weight per hour when the external

temperature was 1.6° C. to 0.639 gram when the external

temperature was increased to 34° C. (H. Schultz). But

as was first shown by Pflüger and his pupils, the metab-

olism of a warm-blooded animal increases as the external

temperature is lowered. If, however,the body tempera-

ture is raised there is likewise an increase in the metabo-

lism of the warm-blooded animals. Pflüger regarded the

increase in metabolism of the warm-bloodedanimalsaccom-

panying the decrease of external temperature as a later

acquisition or as a mechanism which has gradually been

evolved in the special interest of a constant temperature.

Rubner’s measurements of the metabolism in a dog showed

an increase from 30.8 calories an hour when the external

temperature was 27.4° C. to 40.6 calories an hour when the

external temperature was lowered to 11.8° C.,—an in-

crease of about thirty-three per cent. These considera- -

tions are sufficient to suggest that the effect of similar

changes in the environment may not only not have effects

of equal magnitude upon organisms at different levels in

the taxonomic scale, but may even have opposite effects at

the two extremes of the scale.

The upward march of the body temperature is re-

stricted by the greater access of blood to the periphery

and the increased loss of heat by radiation from the sur-

face. A still greater loss of heat, in addition to the rather

constant amount lost by evaporation of water from the

lungs, is brought about by evaporation of water from the

skin or other surface of the body, such as the tongue in

dogs. The amount of water on the skin is regulated by

the activity of the sweat glands, and these, in their turn,

are under nervous control.

23 Tigerstedt, ges Book of Physiology,’’ translated by Murlin, New

York, 1906, p.

No.582] SIGNIFICANCE OF INTERNAL CONDITIONS 385

Animals unable to maintain this constant body temper-

ature throughout the year may maintain a constant tem-

perature during the warmer seasons of the year and hiber-

nate during the winter. This is particularly the case with

small mammals, whose relatively large ratio of surface to

mass may greatly facilitate heat loss, and with animals

whose supply of food is difficult or impossible to obtain

during the colder season. The body temperature of the

animal falls greatly during hibernation. The importance

of size in its relation to metabolism may be shown from

the specific energy requirements of various animals. In

general, the heat requirement of all well-nourished warm-

blooded animals is about 35 calories per hour for each

square meter of body surface. But since the surface va-

ries as the square of the dimensions of the body, and the

mass varies as the cube of these dimensions, the ratio of

surface to mass is much greater in small animals than in

large. A mouse requires 452 calories per kilogram of

body weight in twenty-four hours, while a horse requires

but 14.5 calories and a man about 24 calories in the same

time.24 To sustain a number of mice equal in weight to

a man would require more than eighteen times as much

food, measured in calories, as a man would need; and

more than thirty horses could subsist upon the same

amount of food that would be necessary to sustain a num-

ber of mice whose aggregate weight was equal to that of

one horse. This is very different from saying how much

food one mouse as large as a man or a horse would need,

and should not, under any conditions, be confused with

such a statement.

Milne-Edwards observed that in a small bird such as

the sparrow, the body temperature might be lower in

winter—40.8° C.—than in summer,—43.77° C.—the dif-

ference in temperature amounting to about 3° C.

The heat regulating mechanism of the body is, then,

not a simple one but a complex one, involving muscle and

gland, food supply and distribution of the blood, the nerv-

24 Lusk, loc. cit., p.10. `

336 THE AMERICAN NATURALIST [Vou. XLIX

ous system and the oxygen tension in the blood. We

may next consider some of these subsidiary mechanisms.

2. The Cardiac and Vascular Mechanisms

The mechanism for the distribution of the blood is in

itself a complex one, and involves (1) the mechanism con-

trolling the rate and force of the heart beat and (2) the

mechanism controlling the caliber of the blood vessels.

When the cardio-regulatory and vasomotor nervous

mechanisms are intact, a fall in blood pressure is attended

by an increase in the rate of the heart beat; and, con-

versely, when the blood pressure tends to rise, the rate

of the heart decreases. When the extrinsic nerves to the

heart are cut, these changes in the pulse rate no longer

occur as an accompaniment to the changes in blood pres-

sure. The importance to the animal of these changes in

heart rate with changes in blood pressure is shown by

the fact that rabbits and dogs whose extrinsic cardiac

nerves have been cut soon get out of breath on attempting

to run.2° Through the combined agencies of the vaso-

motor and the cardio-regulatory nervous mechanisms,

the blood pressure in all mammals so far investigated?’

and in some birds, e. g., ducks and fowls,?7 is very much

the same, that is, about equal to a pressure of one hun-

dred and twenty-five millimeters of mercury. Changes

in the caliber of the blood vessels or in the rate of the

heart beat equalize the local changes of pressure. due to

changes in muscular activity. Working glands or muscles

receive, as a rule, more blood than similar organs at rest.

This increase in blood-supply may be due in part to the

action of metabolites upon the walls of the blood vessels

of the active structure (Barcroft).

The blood pressure in the homoiothermal animals, or

the blood pressure during the periods of activity of such

25 See Guthrie and Pike, American Journal of Physiology, 1907, XVIII,

pp. 27-28, for the earlier literature.

26 Porter and Richardson, American Journal of Physiology, 1908, XXIII,

p: 131.

27 Riddle and Matthews, American Journal of Physiology, 1907, XIX,

108.

No. 582] SIGNIFICANCE OF INTERNAL CONDITIONS 837

of them as hibernate, is significantly higher than in the

poikilothermal animals. The precise significance of this

higher pressure in the homoiothermal animals is un-

known. It has been suggested that a certain pressure is

necessary to overcome the friction of the blood against

the walls of the blood vessels. It would appear that fully

as much friction might be encountered in the vessels of a

turtle weighing thirty or more kilograms as in the vessels

of a guinea-pig weighing less than one kilogram. Yet

the guinea-pig has the higher blood pressure. Nor does

the difference in blood pressure appear wholly due to

mere differences in viscosity of the blood of the two

forms.

The general stages, from the point of view of function,

in the phylogenetic development of the vascular system

have been indicated elsewhere.?®

In connection with the question of the rôle of a more

or less constant blood pressure in the animal economy,

we may mention the experiments of Legallois, Schiff and

Goltz.?° These investigators found that, while the cells

of an animal do not die immediately after the blood pres-

sure reaches a low level, the life of the cells in such an

animal as the frog is not possible for indefinite periods of

time, and in rabbits or dogs, death is a matter of hours.

We may, perhaps, imagine that the low blood pressure

may give rise to changes in the chemical systems in the

cell that are incompatible with indefinite existence.

3. The Respiratory Mechanism

The respiratory movements in mammals, and probably

also in birds, are, as Haldane and Lorraine Smith have

shown, kept up at such a rate as will maintain a constant

tension of carbon dioxide and oxygen in the alveoli of the

lungs, and presumably in the blood leaving the lungs.

The oxygen and carbon dioxide content of arterial blood

may be supposed to be fairly constant in any one indi-

28 Pike, Quarterly Journal of Experimental Physiology, 1913, VII, p. 23.

29 The literature on the effects of low blood pressure has been given

in the American Journal of Physiology, 1912, XXX, pp. 444-446.

338 THE AMERICAN NATURALIST [ Vou. XLIX

vidual. The reaction of the body fluids is likewise de-

pendent, in some degree at least, upon the tension of

oxygen and carbon dioxide in the blood.

The reaction of the body fluids, particularly the blood,

remains remarkably constant during the life of the ani-

mal. This is not so much the peculiarity of the higher

organisms as is the constant temperature. The process

of regulation of neutrality, as Henderson has shown, is a

physico-chemical process and depends upon the proper-

ties of carbon dioxide, bicarbonates and phosphates in so-

lution. The changes in concentration of hydrogen and

hydroxyl ions in the blood are, in their turn, related to

the respiratory rhythm.

The whole subject has been so well summarized by

Haldane* that I venture to quote his statement entire.

To illustrate this point I may perhaps refer to a subject which we

have recently been investigating at Oxford. We have found that the

respiratory center is so extremely sensitive to any increase or diminu-

tion of the partial pressure of carbon dioxide in the blood that a

diminution of 0.2 per cent. of an atmosphere, or 1.5 mm. of mereury will

cause apnea, while a corresponding increase will double the breathing.

The recent researches of Hasselbach have afforded experimental evi-

dence of what had already seemed very probable—that the stimulus to

which the center responds is the difference in hydrogen ion concentra-

tion, or acidity, brought about by the very slight deficiency or excess of

earbon dioxide. He has also investigated quantitatively the effect on

the hydrogen ion concentration of the blood of varying the partial

pressure of carbon dioxide. From his results and ours it follows that

the hydrogen ion concentration of the blood during rest is extraor-

dinarily constant, and remains so day by day and year by year. As

the amount of acid and alkali passing into the blood from the food and

other sources is constantly varying, it follows that the regulation of

hydrogen ion concentration is mainly brought about by the kidneys.

It has been known for long that the urine varies in acidity or alkalinity

aceording to the diet; but Hasselbach has measured the actual varia-

tions in hydrogen ion concentration. Putting together his conelusions

and ours, it appears that during ordinary resting conditions the varia-

tions in hydrogen ion concentration of the urine are about a hundred

thousand times as great as those of the arterial blood.

Thus the kidney epithelial cells react so delicately to variations in

30 Haldane, ‘‘ Mechanism, Life and Personality,’’ New York, 1914, pp.

9-51.

No. 582] SIGNIFICANCE OF INTERNAL CONDITIONS 389

hydrogen ion concentration of the blood, that the very smallest varia-

liquid which is, filatinniy speaking, intensely acid or alkaline, the net

result being that the normal hydrogen ion concentration of the blood

remains practically constant.

en we have such figures before us we realize the marvellous fine-

ness of the regulation by the kidneys and respiratory center. Physi-

ologists are still so much under the influence of the old gross mechanical

theories of secretion that attempts at exact measurements of the delicacy

of regulation by the kidneys have hitherto scarcely been made in the

ease of regulation in other directions, though we have every reason to

believe that similar delicacy exists as regards the regulation of the water,

salts, and other blood constituents. It is hard to realize that something

which looks under the microscope like nothing more than a somewhat

indefinite collection of gelatinous material can react, and continue

throughout life to react, true as the finest mechanism of highly tem-

pered steel, to the minutest change in its environment.

TABLE V

SOLUBILITY OF GASES IN WATER; VARIATION WITH THE TEMPERATURE

The table gives the weight in grams of the gas which will be absorbed

n 1000 grams of water when the partial pressure of the gas plus the vapor

pressure of the liquid at the given temperature equals 760 mm.

Gas 8°: C: 10°. C. 20° C. 80° C. 40° C. 50° C.

Ope .0705 0551 0443 .03 1 0263

mo .00192 00174 .001 .00147 00138 00129

Mona, .0293 0 .0189 .0161 0139 0121

Bae a 431. 248 & :

Cl 9.97 7.29 5.72 4.59 3

Oe opr is: 3.35 2.32 1.69 1.26 0.97 0.76

5...) 7.10 5.30 3.98 —- TOTA

Na 987. : 535. 422. — —

DO oa. 228. 162. 113. 78. 54. VEGRE

Whether such a constant O, and CO, content of the

blood of all poikilothermal animals is to be found under

all conditions of existence is unknown, but the coefficients

of absorption of oxygen and carbon dioxide at varying

temperatures would indicate that the carbon dioxide and

oxygen held in solution in the body fluids would be sub-

ject to change with a change in temperature." In the

higher forms, the iron-bearing respiratory pigment, hemo-

globin, absorbs all the oxygen with which it combines

31 Table V, from Table No. 130, p. 142, Smithsonian Physical Tables.

340 THE AMERICAN NATURALIST [Vou XLIX

within wide ranges of barometric pressure. There is

some difference in the processes of absorption at high and

low barometric pressures (Haldane), but the end result is

essentially the same. No more oxygen is taken up by the

hemoglobin at pressures of two or three atmospheres

than at a pressure of half an atmosphere although the

amount of oxygen dissolved in the fluid portion of the

blood niay be greater at the higher pressures. This dif-

ference is insignificant compared with the total oxygen in

the blood. In the lower forms, manganese in the Echino-

derms, and copper in certain Crustaceæ take the place of

the iron in the respiratory pigment. The general condi-

tions under which the oxygen is carried in the blood are,

however, essentially the same in the various forms.

4. The Concentration of Sugar in the Blood

It has been stated since the time of Claude Bernard

that the blood in the portal vein at the height of digestion

contains more sugar in unit volume than the blood in the

hepatic vein. The liver of the homoiothermal animals

converts sugar to glycogen and stores it up in that form.

Further extensive storage of glycogen occurs in the

muscles.

While, under ordinary circumstances, there is good

reason to believe that the concentration of sugar in the

blood of a given animal is fairly constant for a given set

of conditions, it is known that the amounts of sugar in the

blood may vary under other conditions. Excessive

amounts of sugar in the blood are eliminated by the kid-

neys. If the concentration of sugar falls, the transfor-

mation of glycogen to sugar makes up the deficiency. The

concentration of sugar in the blood is not necessarily the

same for any two species of animals under essentially the

same conditions. Nor does the concentration of the sugar

in the blood remain constant in any one individual, cat,

dog, or human, under all conditions.**

32 Cannon, American Journal of Physiology, 1914, XXXIII, p. 257;

Seott, Ibid., 1914, XXXIV, p. 271; Shaffer, Journal of Biological Chem-

istry, 1914, XIX, p. 297:

No. 582] SIGNIFICANCE OF INTERNAL CONDITIONS 341

It is probable that an organ or organs having a glyco-

genic function exist in some invertebrates, e. g., the

oyster, since glycogen may be obtained from these ani-

mals. Whether such a delicate adjustment similar to

that obtaining in the higher animals between stored glyco-

gen and circulating carbohydrate exists in these forms is

unknown to us.

5. The Osmotic Pressure of the Body Fluids

In many species of homoiothermal animals, the osmotic

pressure of the blood, as measured by the depression of

the freezing point, is very constant, nor can it be easily

influenced by changes in the environment. The ingestion

of large quantities of water may be followed by the secre-

tion of large quantities of dilute urine or by profuse per-

spiration. A shortage of water to drink leads to the se-

cretion of small quantities of more concentrated urine.

Both qualitatively and quantitatively, the physico-chem-

ical constitution of the blood varies within relatively nar-

row limits. ne boa

6. The Digestive Tract 4

The mechanical and chemical processes of the alimen-

tary tract reduce all the food, or its digestible portions,

to water-soluble substances, in which form they are ab-

sorbed. The proteins of the food are reduced to the

amino acids or polypeptids, the starches and sugars to

monosaccharides and the fats to soaps before being ab-

sorbed.

The introduction of foreign proteins, e. g., egg albumen,

as such directly into the blood of the host is injurious.

But the amino acids and polypeptids to which this pro-

tein is hydrolyzed by the action of the digestive enzymes

are, in general, qualitatively the same as those in the blood

of the host. The difference in proteins depends upon the

difference in the quantitative relations of the amino acids

in the protein molecule as well as upon the qualitative

differences. The hydrolysis of all proteins to their

342 THE AMERICAN NATURALIST [Vou. XLIX

simpler splitting before absorption is a mechanism of

protection against the entrance of foreign protein into

the blood. ; :

The alimentary tract to a certain extent renders the

individual independent of the quantitative or stereo-

chemical constitution of the proteins of its food, the only

necessity being the presence of certain amino acids in the

od.

But efficient as the alimentary tract is, it does not ex-

clude all foreign or inutilizable substances. Cholohema-

tin for example, from sheeps’ bile, characterized by a

peculiar spectrum and hence susceptible of easy identifi-

cation, is absorbed by the dog and at least some of it is

excreted in the dogs’ bile without change.

The protection due to changes in the mucous membrane

of the alimentary tract is well shown in the case of ar-

senic. It was long supposed that the arsenic-eating

peasants of the Austrian Tyrol had become immune to

the effects of a considerable concentration of arsenic in

the blood, since they were able to take large quantities of

it by mouth without suffering the usual effects of an over-

dose. It was shown by Cloetta? that the apparent im-

munity arose from changes in the intestinal mucosa which

prevented the absorption of all but a small percentage

of the arsenic taken.

If the lower members of the fatty acid series be fed to

a dog the body fat which is stored up is softer and of a

lower melting point than usual. Excess fat in the food

may be stored up as body fat, but under certain condi-

tions, the animal may use as much fat as is taken in the

food, and the animal remains in metabolic equilibrium so

far as the fat is concerned.

Although the amount of protein necessary to sustain

life in an adult or to provide for growth in a young animal

varies with the nature of the protein taken in the food,

the animal is able to build up its own body protein from

33 Cloetta, Archiv für Experimentelle Pathologie und Pharmakologie,

1906, LIV, p. 196.

No. 582] SIGNIFICANCE OF INTERNAL CONDITIONS 343

any food which contains the requisite amino acids. The

power of synthesis of new amino acids in the body is

limited. Glycocoll, for example (amino-acetic acid), may

be synthesized in the body. More protein is needed as

food if its content in certain of the amino acids is low

than if its content of these necessary acids is high.** But

under all the varying conditions, within wide limits, the

animal may maintain itself in nitrogen equilibrium,

neither storing up any nitrogen in its flesh nor losing any

from its tissues. The excess of any particular amino

acid above that necessary for tissue growth or repair is

eliminated from the body. Voit’s famous 35 kilo dog

was able to maintain nitrogen equilibrium when fed on

amounts of protein varying from 480 grams of meat a

day as a lower limit up to 2,500 grams a day.

The quantities of fluid, fat and protein in the blood,

while undergoing some changes with the varying condi-

tions of nutrition, starvation and fasting, remain close to

a standard concentration as long as life lasts. Variations

of great magnitude are incompatible with the prolonged

life of the organism.

7. Epidermis and Other Protective Mechanisms

In addition to absorption, the limiting membranes of

the body have other and important functions. The en-

trance of many harmful foreign substances into the or-

ganism is prevented by the protecting epidermis, the al-

veolar mucous membrane, and the intestinal mucosa, al-

ready noted.

But, however important the exclusion of harmful sub-

stances may be, the protection of the organism through

the retention of valuable material is also of importance

and must be provided for. —

The escape of useful substances is prevented by the

skin, the liver, the alimentary tract, the lungs and the kid-

neys. The splitting products of the hemoglobin arising

from the death of the red blood cells are separated by

34 Lusk, loc, cit.

344 THE AMERICAN NATURALIST [ Vou, XLIX

the liver in the form of bile pigments, but the iron is con-

served for use in the formation of new hemoglobin. But

little iron is eliminated by the liver, although much iron

may be stored there. The milk of higher animals con-

tains but little iron, and the young mammal needs much

iron for the formation of new blood cells during the rapid

growth of early life. Provision is made for this by the

storage of iron in the liver of the fetus. As postpartum

growth proceeds, the amount of iron in the liver is re-

duced and the amount occurring in hemoglobin is in-

creased.

8. The Internal Secretions

The internal secretions form another group of chemical

conditions which vary within narrow limits in a state of

health. Many years ago Caspar Friederich Wolff ex-

pressed the idea that each organ of the body stood in the

relation of an organ of internal secretion to some other

organ in the body. The liver liberates sugar which is

necessary for the action of the muscles, and it also lib-

erates urea which has a definite relation to the action of

the kidneys. The muscles set free carbon dioxide which

acts upon a particular group of cells in the nervous sys-

tem, and nitrogenous waste products, some of which are

transformed to urea in the liver. But apart from these

more general relationships, a system of ductless glands

sets free a variety of chemical substances which bear a

rather different relation to the development and activity

of many other organs and tissues of the body.** The

relation of the adrenal gland to the myo-neural junction

of sympathetic and smooth muscle fiber*® is well known.

The dependence of the development of the secondary

sexual characters upon the internal secretion of the sexual

glands is also familiar to biologists. The internal secre-

tions in general have become a part of the internal con-

ditions of the organism and of the chemical environment

of the cells of the organism.

35 Mathews, Science, 1897, N. S., V, pp. 683-685.

86 Elliott, Journal of Phisiologs. 1905, XXXII, p. 401.

No. 582] SIGNIFICANCE OF INTERNAL CONDITIONS 345

9. The Mechanisms for Elimination of Waste Products

The elimination of waste products occurs promptly and

surely. The liver of higher animals not only separates

out the useless portions of the hemoglobin derived from

worn-out corpuscles (with retention of the iron-bearing

part), in the form of bile pigment, but also transforms

the ammonia compounds arising from nitrogenous metab-

olism to the relatively non-poisonous urea. The known

chemical functions of the liver? are numerous. The kid-

neys promptly remove the urea and uric acid from the

blood as these and other products of metabolism accumu-

late following activity of the cells. Certain mineral salts,

e. g., iron, are excreted by the intestinal mucosa. Some

fat, in addition to that which is not absorbed from the

food, is also excreted from the intestine.

The attempt to tabulate the various excretions of the

body reveals the fact that, although the qualitative com-

position of the bile and the urine is relatively constant,

the quantitative variations are very wide under different

conditions. The quantity of carbon dioxide exhaled dur-

ing twenty-four hours depends upon the diet and upon

the amount of muscular activity during the day. Al-

though somewhat disconcerting at first sight, in view of

the constancy of internal conditions, this very inconstancy

of the excretions is to be regarded as a consequence of the

maintenance of constant internal conditions. For it is

only by the conservation of those necessary elements or

substances whose supply is limited, and the free elimina-

tion of waste products or of other substances in excess

that the constancy of internal conditions can be main-

tained. Intake and outgo of matter and energy are

such as to maintain relatively constant physico-chemical

conditions within the organism. The greater the energy

requirements of the organism, the greater must be the

intake to meet these requirements, and the cba the

amount of waste products eliminated.

87 Hofmeister, ‘‘Chemische Organization der Zelle,’’ ein Vortrag; Braun-

schweig, 1901,

346 THE AMERICAN NATURALIST [Vou. XLIX

The list of mechanisms, organs and tissues of the animal

body and of specific organic or inorganic substances

within the body, whose conditions and concentration re-

main relatively constant, could be extended. The descrip-

tion of these phenomena bulks large in the extensive lit-

erature of physiology of to-day. Sufficient data have been

adduced to show that there is a considerable basis of fact

for the interpretations which we now wish to present.

A summary of the known facts of the internal conditions

of the organisms permits of the statement that in the

homoiothermal animals, there are, then, several mech-

anisms of extreme delicacy and great constancy under

similar conditions and varying but little under wide

changes of external conditions. The tracing out of their

development constitutes a large part of the subject matter

of comparative physiology. But their interpretation

rather than their development is the thing of main in-

terest at present. We will return to the questions of the

origin and development of these mechanisms in later

papers.

What point of view will give us the best insight into

the rôle of these mechanisms in the evolution of the verte-

brate phylum? Of what use have they been? Or are

they simply mechanisms which have arisen in the course

of evolution apparently through correlation with other

phases of development but without obvious significance

to the organism?

HOI. Tue Laws or CHEMICAL EQUILIBRIUM

Before attempting the interpretation of these mech-

anisms, or pointing out their rôle in evolution, we may

very briefly review the laws of chemical equilibrium as

exemplified in the ‘‘slow’’ reactions of the physical chem-

ist. For our present purpose, these laws may be included

under the law of mass action, Van’t Hoff’s law and the

phase rule. A fuller statement is given in Blackman’s

paper and in the text-books of physical chemistry.

No. 582] SIGNIFICANCE OF INTERNAL CONDITIONS 847

1. The Law of Mass Action

The mass law or law of mass action expresses the re-

lationship between the molecular concentration and the

speed of the reaction. The concentration of the substance

is usually expressed in terms of the number, either whole

or partial, of gram molecular weights or gram molecules

present in one liter of the solution. On the basis of Avo-

gadro’s law, there is the same number of molecules of

sodium chloride in a gram molecule (58.4 grams) of

sodium chloride as there are molecules of cane sugar in a

gram molecule (342 grams) of cane sugar or molecules

of oxygen in a gram molecule (32 grams) of oxygen. If

equal fractions of the gram molecular weights of two dif-

ferent substances are each dissolved in a liter of water,

there will be the same number of molecules in each of

the two solutions.

Let two substances, A and B, be present in a solution

in the concentrations (expressed in gram molecules) of

c, and Cz, respectively, at any stage of the reaction

A+B—>C-+D and let the temperature remain constant

throughout the action. The speed (S) of the forward ac-

tion expressed in gram molecules of A and B transformed

in unit time is defined by the relation c, X¢sXF=S

where F is the affinity constant. As the reaction pro-

ceeds, c, and cs and, hence S, steadily decrease, since A

and B are being continually used up. S may therefore be

taken at any time as the quantity of A and B which would

be transformed in the unit of time if the concentration

Ca and cp were maintained at a constant value by the con-

tinual addition of new substance. F is the measure of

the intrinsic activity (affinity) which is the driving force

in the reaction, and is independent of the concentration.

If unit concentrations are taken, c, = Cs =1 and F =S.

The activity, F, is thus represented numerically by the

number of gram molecules transformed in unit of time

when each reacting substance is present in unit concentra-

348 THE AMERICAN NATURALIST [Von, XLIX

tion. Since c4, cz and S may be measured at any time,

F may be calculated for any action.*®

The law of molecular concentration or law of mass ac-

tion is: In every chemical experiment, the speed of the

action at any moment is proportional to the first, or some

higher, power of the molecular concentration, at that time,

of each interacting substance and to the intrinsic activity

(affinity) of the substances.

2. Van’t Hoff’s Law

But the speed of any reaction at any concentration

varies with the temperature. In general, the increase in

speed is about ten per cent. for each increase of one de-

gree Centigrade, or, as it is sometimes expressed, the

speed of the reaction is doubled when the temperature is

increased ten degrees Centigrade. This is known as Van’t

Hoff’s law. The actual change in the speed of the re-

action may be greater or less than ten per cent. for each

change of one degree Centigrade, and is usually expressed

by a coefficient. When the coefficient is 1.2 or less, that

is, when the change in speed is two per cent. or less for

each change of one degree Centigrade, the action is

usually considered to be a physical and not a chemical

action. When the temperature coefficient is greater than

1.2, the action is commonly considered to be a chemical

action. No theoretical explanation of Van’t Hoff’s law

of change in speed with change in temperature has so far

been advanced.

These laws apply to reactions which go on at a measur-

able speed and which have been called ‘‘slow’’ reactions

by the physical chemists. These ‘‘slow’’ reactions are to

be distinguished from those reactions which proceed so

rapidly that no measurement of their speed at different

intervals is possible, or reactions of the explosive type.

38 Smith, ‘‘ Gereral Inorganie Chemistry,’’ 1st ed., New York, 1906, p. 251.

No. 582] SIGNIFICANCE OF INTERNAL CONDITIONS 349

3. The Phase Rule

One other principle of physical chemistry finds frequent

application in biology, and that is the phase rule devel-

oped by Gibbs. The phase rule defines the condition of

equilibrium existing in a system by the relation between

the number of coexisting phases and components. ‘‘Ac-

cording to it a system made up of n components in n + 2

phases can only exist when pressure, temperature and

composition have definite fixed values; a system of n

components in »+1 phases can exist so long as only

one of the factors varies and a system of n components

in n phases can exist while two of the factors vary. In

other words, the degree of freedom is expressed by the

equation

PPaCtoor P= C+3—2

where P designates the number of phases, C the number

of components, and F the degree of freedom.’’*® In other

words, F' represents the number of conditions which may

be varied without causing one of the phases to disappear.

An example of the phase rule, based upon the proper-

ties of a familiar substance, is that of ice, liquid water and

water vapor existing together in a closed vessel from

which the air has been exhausted. Ice, liquid water and

water vapor each constitute a phase of the system, and

there is but one component or substance—water—present.

Here, one component exists in three different phases.

We have, then, n components and n +2 phases. The es-

sential conditions for the existence of the system are

temperature and pressure of the water vapor. In the

notation quoted above, P=3, C=1. Hence, F=1+2

—3=0. Neither of the conditions—temperature or

pressure—of the system can be changed without causing

one of the phases to disappear. There is no degree of

freedom, or, as it is sometimes expressed, the system is a

non-variant system. The exact conditions for stability

39 Morgan, ‘‘ Physical Chemistry,’’ New York, 1911, p. 119.

350 THE AMERICAN NATURALIST [Voi XLIX

of such a system are a pressure of water vapor equal

to 4 mm. of mercury and a temperature of .007° C. above

0° C.—the freezing point at atmospheric pressure.

Many applications of the phase rule to living matter

have been made. We will cite but one. The globulins—

typical proteins found in the blood of animals—are in-

soluble in distilled water, but are soluble in dilute solu-

tions of the inorganic salts, such as sodium chloride. The

globulin may exist in a system of water, sodium chloride

and globulin, as globulin in solution or as precipitated

globulin. The globulin is the only component existing

in more than one phase under the conditions of the ex-

periment.*** Addition of water to the system to such a

degree that the concentration of the inorganic salts falls

below a certain minimum leads to a precipitation of part

of the globulin in solution. The removal of the mineral

salts, keeping the volume of the solution constant, will

also lead to precipitation wholly or in part, of the globulin

in solution. But whether water be added or salt removed,

the essential condition which undergoes changes is the

concentration of the salt.. Pressure does not enter in as

one of the conditions of the system. And if the tem-

perature of the system be raised above a certain point,

depending upon the globulin present in the system, the

globulin will be precipitated. In this system, the number

of components is one (globulin) and the number of phases

is also one, dissolved globulin. We have, therefore, a

system of n components with n phases, and two of the

conditions may vary, within certain limits, at the same

time, viz., the concentration of the sodium chloride and

the temperature. In the terminology of the quotation

above, P=1, C=1 and F=1+2~—1, or 2. This 16

also expressed by saying that the system is divariant.

This system is of interest because of the fact that it also

illustrates the phenomena of maximum points.

39a While globulin is not the only component entering into the system, we

have restricted the discussion to the department of the globulin for reasons

of space and simplicity.

No. 582] SIGNIFICANCE OF INTERNAL CONDITIONS 351

Further details should be sought in the text-books of

physical chemistry, and especially those by Bancroft and

Findlay on the phase rule.*°

IV. THE INTERPRETATION OF THE REGULATORY MECHAN-

ISMS IN TERMS OF CHEMICAL EQUILIBRIUM

But what evidence is there that the laws of mass action

or of chemical equilibrium apply to living matter? Is

there any evidence that the reactions occurring in the

cell are ‘‘slow’’ reactions similar to those of the physico-

chemical laboratory? The answer to these questions is

decidedly in the affirmative. Much evidence in favor of

such a view was presented by Blackman. Hofmeister,

Bredig and others regard the cell as a congeries of en-

zymes, each one, according to Hofmeister,“ acting in its

own compartment upon its own peculiar substrate.

1. Applications of Van’t Hoff’s Law

As further evidence of the nature of the reactions in

living matter, we may cite the work of Shelford‘? on tiger

beetles, in which the length of the combined quiescent

periods of the pupal and the prepupal stages was in-

creased from four or six weeks at a temperature of 28°

to 30° C. to ten or twelve weeks at a temperature of 15°

to 17° ©. Riddle! found that the temperature coeffi-

cients for digestion in Amia, Rana, Necturus and the

common turtle (Emydoidea) ranged from 0.93 in Nec-

turus to 7.81 in the turtle. Rogers and Lewis* have re-

cently shown that the temperature coefficient of the rate

of contraction of the dorsal blood vessel of the earthworm

is of the order of magnitude to be expected if the processes

40 Bancroft, ‘‘ The Phase Rule,’’ Ithaca, New York; Findlay, ‘‘ The Phase

Rule and Its Applications,’’ 3d ed., 1911, London and New York.

41 Hofmeister, loc. cit.

42 Shelford, Linnean Society’s Journal, 1908, XXX, p. 176.

43 Riddle, American Journal of Physiology, 1909, XXIV, pp. 447-458.

44 Rogers and Lewis, Biological Bulletin, 1914, XXVII, p. 269. See also

Lehenbauer, ‘‘ Physiological Researches,’’ 1914, I, pp. 247-288,

352 THE AMERICAN NATURALIST [VoL XLIX

concerned are of the nature of slow chemical reactions.

The application of Van’t Hoff’s law in these instances

is sufficiently plain.

Considering the processes in living matter, from this

point of view, we may gain some insight into the reason

why so many of the factors or conditions entering into

the reactions occurring in the body of a higher organism

should be kept as nearly constant as possible.

2. The General Conditions of the Reactions in the Cells

_ In determining the velocity of a reaction, we may deter-

mine (1) what quantity of the reacting substances com-

bine or react in unit time, the usual method of the labora-

tory, as has been shown above, or (2) we may determine

what quantities of material must be added in unit time

to keep the reaction going at a constant rate. Recalling

now the nearly constant factors in the higher mammalian

organism, the oxygen content, the temperature, and the

hydrogen ion concentration all varying within relatively

narrow limits, and the variations usually being in such a

direction as to get more material to an active or working

structure in unit time, we can see that there are certain

very effective devices for maintaining a reaction at a

constant speed, which are the counterparts of the appara-

tus employed in the chemical laboratory. But the mech-

anisms in the living organism are capable of reguiating,

with a great degree of exactness, more conditions than

any artificial mechanisms so far devised in the laboratory

can control.

In the evolution of the organism the development of

the various regulating mechanisms which we have de-

scribed has brought about a set of conditions which tend

to keep the environment surrounding the cells relatively

constant. The analogy beween the reactions in the cells

and the slow reactions of the physical chemist becomes

clear. The temperature of the body being constant, the

reactions in the cells, dependent as they are, upon a con-

stant supply of material, go on at a relatively constant

rate, or at such a rate as is determined by the needs of

No. 582] SIGNIFICANCE OF INTERNAL CONDITIONS 358

the organism, and a rate which is provided for by the

changing distribution of the blood.

Not all the physico-chemical conditions of cell activity

are as constant as those discussed in the second division

of this paper. Nor does the experimental interference

with certain body structures leading to known departures

from the usual conditions always entail serious results.

As an instance of this we may cite the experiments of

Ogata, who investigated the rate of absorption of pro-

tein when fed by the mouth as compared with its rate of

absorption when introduced directly into the intestine

through a fistula. Taking the nitrogen output in the

urine as the expression of the rate of absorption, the

nitrogen output rose much more rapidly after direct in-

troduction of the meat into the intestine than it did when

the meat was fed by mouth. Although the absorption of

the food was apparently more rapid than usual, the capac-

ity for adjustment on the part of the organism was not

exceeded. We may mention in passing that one function

of the stomach may be to act as a storehouse and provide

for a more gradual absorption of food than would other-

wise occur. In the terminology of this paper, there is a

less sudden entrance of constituents tending toward a

disturbance of the equilibrium when the stomach is

present than when it is absent. If food is administered

in small portions and in a finely divided state after com-

plete removal of the stomach, life goes on as usual

(Czerny). But one is hardly justified in saying that, be-

cause great and profound changes do not occur in the

organism after extirpation of the stomach, the stomach

has no important function.

A detailed consideration of the inconstant or variable

conditions and of the manner and extent to which changes

in the environment can influence all internal conditions,

must be deferred for another communication. Enough

has been said in these pages to show, in outline at least,

the essential uniformity of some important internal con-

45 Ogata, Archiv fiir Anatomie und Physiologie, 1883, p. 89.

354 THE AMERICAN NATURALIST [Vor. XLIX

ditions of the higher organism and to indicate their rôle,

on the assumption that the internal mechanisms of the

organism are physico-chemical mechanisms.

In the response of the respiratory mechanism to the

increased concentration of carbon dioxide or to lack of

oxygen in the blood, we have an instance of adaptation

which is not at once seen to be an obviously automatic

and inevitable result of the physico-chemical properties

of the environment. A striking characteristic of the re-

spiratory center is at once its sensitiveness to slight

changes in the concentration of carbon dioxide and its

tolerance to the accumulation of carbon dioxide in the

blood. The respiratory cells react to an extremely slight

increase of carbon dioxide which is insufficient to affect

the other cells, and remain sensitive to this increase after

the concentration has risen so high that the visible re-

sponses of certain other cells have ceased. The common

excitability of the respiratory and other motor nerve cells

to carbon dioxide may ‘be supposed to result from the

disturbance or change produced in a complex system by

the accumulation of one end product of the reaction, and

to this extent to be an automatic result of the physico-

chemical constitution of the cell.

The question raised by Mathison*® as to whether car-

bon dioxide is a stimulant for all nerve cells is of interest

in this connection. Carbon dioxide is certainly a stimu-

lant for the central nerve cells of the respiratory mech-

anism, but it is not necessarily a stimulant to the same

degree for all nerve cells. It is probable that all living

matter is more or less sensitive to the accumulation of

carbon dioxide since it is one of the waste products of

all destructive metabolism. The cell bodies of the respira-

tory neurones, by reason of the development of this

common property of excitability to carbon dioxide, have

become especially adapted to respond to slight variations

in carbon dioxide. The adaptation undoubtedly depends

upon a physico-chemical change in the respiratory neu-

46 Journal of Physiology, 1910, XLI, p. 448.

No. 582] SIGNIFICANCE OF INTERNAL CONDITIONS 3855

rones. The persistence of the common property accounts

for the asphyxial convulsions of the spinal animals and

for the movements which are sometimes considered to be

respiratory movements and commonly attributed to so-

called respiratory centers. But whether we consider that

the cells of the respiratory group have gradually acquired

a lower threshold value for stimulation by carbon dioxide

than the other cells of the nervous system, or that the

cells of the respiratory group have simply retained the

the common excitability of protoplasm in general to car-

bon dioxide, and the remaining cells have undergone modi-

fications which have raised their threshold value, makes

little difference from the theoretical point of view. In

an environment which is, so far as one can determine,

uniform, certain quantitative variations have occurred

which have resulted in a differential sensitiveness to car-

bon dioxide or to lack of oxygen. The changes have not

been qualitative, since asphyxial convulsions involving

muscles innervated from other parts of the central nerv-

ous system, may be brought on by a reduction of the

oxygen supply.

The usefulness of the lower threshold value for lack

of oxygen in a particular group of cells is at once ap-

parent. Oxygen generation of the blood and elimination

of carbon dioxide proceed without attention, and without

noticeable excitation of any other group of nerve cells.

There is no disturbance of the precision of movement of

any group of muscles aside from those actually engaged

in the respiratory act, nor the slightest effect upon the

neurones involved in mental processes, resulting from the

decreased oxygen or increased carbon dioxide tension in

the blood sufficient to provoke a respiratory response.

3. Stimulation in Terms of Chemical Equilibrium

This brings us to a consideration of the nature of stimu-

lation in general. Lack of space precludes all but the

briefest mention at this time. We may here simply in-

dicate the consideration in terms of the laws of mass

356 THE AMERICAN NATURALIST (Vou. XLIX

action and of the phase rule. That changes in the speed

of reaction depend upon the concentration of the reacting

substances or of the end products of the reaction has

been shown in the discussion of the laws of mass action.

It is not difficult to see that the respiratory movements

owe their origin largely to changes in concentration of

carbon dioxide and oxygen, and, since these changes result

in a slight change in the concentration of the hydrogen

ions it is not difficult to imagine that the law of mass

action may be involved in the stimulation of the respira-

tory cells in the medulla oblongata. We have given in the

third section of this paper two illustrations of conditions

coming under the operation of the phase rule. It is true

that living matter undoubtedly comprises vastly more

complex systems than those described, but that the general

principles underlying the reactions are similar in most

important respects to the systems employed in labora-

tory experiments is scarcely to be doubted. The with-

drawal of water from a cell or nerve fiber by osmosis or

drying, entailing a quantitative change in the amount of

water in the cell, is followed by other changes in the cell

which tend to bring about a reestablishment of conditions

in accordance with the laws of chemicalequilibrium. That

a change of phase of some of the components occurs in

the process is probable.

Such influences as drying, applications of heat or me-

chanical pressure, whether occurring in the laboratory or

in nature, are known as stimuli, and the changes asso-

ciated with their operation in the organism are responses

to stimulation. As Jost? has pointed out, the formal

conditions of existence may act as stimuli to organisms.

Although we must admit that a wide gap still exists, it

seems to us that the discussion of stimuli and the proc-

esses of stimulation in terms of the law of mass action

and the phase rule will enable us to meet in some degree,

however small, Haldane’s objection*® that no causal con-

47 Jost, ‘‘ Pflanzenphysiologie,’’ zweite Aufl., p. 618, Jena, 1908.

48 Haldane, loc. cit., p. 37.

No. 582] SIGNIFICANCE OF INTERNAL CONDITIONS 357

nection has been shown between stimulus and response.

And we may hope that here as elsewhere in biology the

limits to our knowledge of nature will gradually be broken

own.

The accumulation of waste products in the blood or body

fluids through increase of their concentration in these

fluids, leads to modified activity of the excretory and

other organs. We cite a few examples.

The kidney, in addition to the elimination of water, fol-

lows the law of mass action in other ways. The volume

of urinary secretion, other things being equal, is propor-

tional to the volume of blood flow through the kidneys in

unit time. The greater volume of blood carries with it a

greater volume of waste products in unit time, and hence

a greater volume of secretion is the result to be expected if

urinary secretion is a physico-chemical process following

the general provision of the mass law.

The accumulation of waste products arising from the

slow reactions in the cells gives rise to the phenomena of

fatigue, and the general slowing down of the cell proc-

esses, just as the accumulation of the end products of

any slow reversible reaction decreases the amount of

chemical transformation in unit time, in accordance with

the mass law.

Excess of carbon dioxide, a typical waste product, even

of the activity in nerves,*® decreases or abolishes the con-

ductivity of a nerve fiber. A stimulus (geotropic) may be

applied to a plant in an oxygen-free atmosphere, but the

responses will not occur until the plant is moved to an

atmosphere containing oxygen.*°

But even waste products in a certain concentration

may be necessary for the optimum conditions of activity

of an organ. Baglioni®! points out that the selachian

heart maintains its activity better in a solution of the

inorganic salts containing two per cent. urea—the normal

49 Tashiro, American Journal of Physiology, 1913, xxxii, p. 107.

50 Jost, ‘‘ Pflanzenphysiologie,’’ zweite Aufl., p. 524, Jena, 1908.

51 Baglioni, Zeitschrift fiir allgemeine Physiologie, 1906, VI, p. 71.

358 THE AMERICAN NATURALIST [Von XLIX

concentration of this substance in selachian blood—than in

more readily recorded.

The hens investigated were in the egg-laying contest

located at Storrs, Conn. Pullets enter the contest Novem-

ber 1 and remain for one year. They are housed in pens

of 10 birds each, are fed the same ration and so far as

5 Circular 499, Maine Agrie. Exper. Station. This is listed as an abstract

of Bulletin 232.

® Woods, P. T., Amer. Poultry Jour., p. 35, January, 1915.

362 THE AMERICAN NATURALIST — [Vou XLIX

possible are handled exactly alike.” The influence of

different environmental factors, therefore, can be largely

neglected.

A preliminary test was made the middle of last Septem-

ber by taking from each of a number of different pens a

pair of birds representing the extremes of yellow pig-

mentation and comparing their egg records. This test

indicated that the extremely pale birds were laying and

the extremely yellow ones were not. It indicated also that

the ear-lobes were much more easily graded as to color

and in addition were apparently more indicative of egg-

laying activity than the beaks and legs. The ear-lobes of

the American breeds are red like the comb and wattles and

do not show yellow pigment. The ear-lobes of certain

other breeds, like the Blue Andalusians, are white but

apparently remain without any appearance of yellow ever

taking place. The Leghorns, including Browns, Blacks,

Buffs and Whites, show marked changes in the amount of

yellow in their ear-lobes. White Leghorns, of which

there were over 300 in the contest, were accordingly

chosen for closer study.

Ear-lobe Color in White Leghorns.—Color can be con-

veniently measured quantitatively by means of the Milton

Bradley color top, which, when spinning, acts as a color

mixer. In matching ear-lobes, only yellow and white

sectors have been used. The matching is not perfect.

especially in the lower grades, since a certain amount of

bluish tinge is often present. The amount of yellow, how-

ever, has probably been more accurately measured than

if the other color components were considered. By the

method used, it appears possible under proper illumina-

tion for one to repeat readings with a change of seldom.

more than 5 per cent. yellow above or below the mean

observation. :

Top readings were taken of the White Leghorns listed

7 Four pens of White Leghorns and four of White Rocks, belonging to the

Experiment Station, had sour milk substituted for different ingredients of

the normal ration, but, since they showed no apparent differences in color

that could be attributed to the change in the feed, they were included in the

tabulations.

No. 582] EGG-LAYING ACTIVITY IN DOMESTIC FOWL 368

TABLE I

AVERAGE EGG RECORDS FOR DIFFERENT AMOUNTS OF YELLOW IN EAR-LOBES

OF 312 WHITE LEGHORNS

| l

5-10 | 7 | 23.1 | 21.3 | 19.7 | 15.3 | 9.9 | 9.9 | 9.29 | 6.00 | 197.1

11-15 | 36 | 21.8 | 22.1 | 182 | 142] 94 | 88 | 814 | 6.03 | 187.9

16-20 | 40 | 22.2 | 20.7 | 169 | 11.7} 88 | 82 | 7.50 | 4.17 | 184.3

21-25 | 19.8 | 214 | 164 | 81 | 81 | 8&3 | 5.56 | 2.50 | 164.3

26-30 | 20 | 195 | 189 | 103 | 3.2 | 55 | 4.8 | 2.75 | 0.45 148.5

31-35 | 180. 17.7 |} $ 0.5 | 3.5 | 2.1 | 0.45 | 0.00 | 139.1

338° | 197 |173 | 61.) 0232p 42 | 19 | O16 F 0.00 11906

41-45 | 41 | 182 | 16.2 | 4. 0.2 | 34 | 1.6 | 0.22 | 0.00 | 134.2

46-50 | 39 |. 180 | 15.6 | 4. 0.2 | 26 | 1.4. | 0.18 | 0.05 | 138.2

51-55 | 30 | 184 / 161] 3.6 | 0.1 | 29 | 0.7 | 0.00 | 0.07 | 137.8

56-60 | 13 | 148 | 10.7 | 24] 0.0 | 22 | 0.2 | 0.00 | 0.00 | 124.7

61-65; 4 |145)| 88| 13) 03] 03 0 | 0.25 | 0.00 8

66-70 | 1 | 30 00) 00] 0.0) 00 | 0.0 | 0.00 0.00 70.0

71-75 | 1.| 00! 00] 0.0] 00] 0.0 F 0.0 | 0.00 | 0.00 | 83.0

TABLE IT.

coe. OF HENS LAYING AND AVERAGE NUMBER OF pine SINCE LAYING

R DIFFERENT AMOUNTS OF YELLOW IN EAR-LOBES

White Se aaa: total number of records, 932; total number of birds, 317

eS S48 Pa ae 3 A meat chet ee

Per Cent. Yellow Zial Ki | Ai J 4 i | ap es Ge oe $i 3

| j |

No. records. .... 41 | 125; 80 | 67 | 62 92| 94| 94/108 84| 44| 28; 9 | 4

Av. days since ]

TS oe 0.4 1.6 7.3/17.1 26.2 37.9 41.5 44.0 45.1 51.3 55.9 61.4 50.3 71.0

No. records = |

He eee) 86| 98/ 44| 17/3 0|1}012]0/0]0]0]0

Per cent. records i

=laying. .. . .|87.8/78.4 55.0/25.4|04.8! 0 101.0! 0 019 0/01/0100

in Tables I and II at three different periods. The first

recording took from October 7 to October 14, the second

from October 19 to 21 and the last was completed in one

day, October 28. The top records were all made by the

same one of us (B), except for 197 records on October 28.

The men who took these records had already acquired

familiarity with the method, and while their readings are

not absolutely comparable with the others, they probably

are sufficiently so to be included in Table II. The three

top readings were taken on separate sheets and the egg

records were investigated after the readings were all

taken and the birds had left the contest. Personal bias

that might have influenced the readings was thereby

avoide

Table I shows the percentage of yellow in the ear-lobes

364 THE AMERICAN NATURALIST [Vou. XLIX

of 312 birds according to the records of October 19-21,

together with monthly and yearly egg records for the

different color groups. The months of October and Sep-

tember are each divided into halves. It will be seen that

in general as the percentage of yellow increases, the egg

production falls off, and that the correlation is most

marked during the periods nearest the time when the

records were taken. A distinct though slight correlation

seems to show as far back even as July and is strikingly

evident in the yearly averages. For months before Sep-

tember and October, the correlation with color is probably

an indirect one. Itis generally only the best birds—those

that make the large yearly records—that are laying in

October. Therefore, any method that selects the laying

birds at this season will select, at the same time, the birds

laying above average throughout the year and conse-

quently give high yearly totals. It will be observed that

30 per cent. seems to be a critical amount of yellow.

Above this amount comes the sudden drop in egg produc-

tion for the months of September and October and also

above 30 per cent. yellow the yearly totals fall to between

130 and 140, with but slight change thereafter.

In Table II, the records at the three different readings

have been used. A bird laying on the day of record or on

a later day within the month is considered to be laying and

credited with a zero. If she laid on the day before the

record but not later, she is credited with one ‘‘day since

laying,” and in a similar way a longer period of inactivity

in laying is indicated by a larger number of days since

laying. With the exception of a few cases where this was

not possible, three records were taken of each bird. Since

October is the season of decreasing egg production, the

majority of the birds increased their quantum of yellow

and consequently most birds are listed in more than a

single color grade. Beginning with the 41 records in the

5-10 per cent. color grade which show an average of only

0.4 day since laying, the number of days increases con-

sistently with the amount of yellow in the ear-lobes, the

irregularity at 70 per cent. being probably due to the

No. 582] EGG-LAYING ACTIVITY IN DOMESTIC FOWL 365

smallness of the numbers in this group. The percentage

of records that indicate actual laying drops rapidly from

87.8 per cent. for 5-10 per cent. yellow to zero for grades

of yellow above 30 per cent.’ The table shows that it is

practically certain that a bird with an ear-lobe showing

more than 30 per cent. yellow at the time of the records,

is not in a laying condition.

TABLE III

AVERAGE EGG RECORDS FOR DIFFERENT GRADES OF YELLOW IN BEAKS AND

LEGs OF 256 WHITE LEGHORNS

(P, M and Y are abbreviations for Pale, Medium and Yellow)

Phe Beak Legs Suly | Aug. | Sept. | Oct. 1 Sept. Pl ‘Toet Oct.| Year

51 P P 22.0 | 20.9 | 18.6 | 14.3 | 9.6 | 9.0 | 8.0 | 6.3 |186.4

17 | M M 18.5 | 17.8 | 11.4 4.8 | 6.5 | 4.9 | 3.4 | 1.4 | 146.4

ik X 16.6 |142| 29) 04| 2.2 | 0.7 | 0.3 | 0.1 |1293

P 51 |

S i P M2 $| 22.1 | 21.0 18.3 | 14.0 | 9.4 | 88 | 7.9 | 6.1 | 185.3

; Y 0

P 25 |

43| M M17 + 20.1 | 20.6 | 13.7| 67| 7.4 | 6.3 | 4.2 | 1.5 | 164.6

Yi |

P14 |

160 | Y M49 } | 17.7 | 16.1 | 4.8 | 0.8 | 3.2 | 1.7 | 0.6 | 0.2 |135.0

Y 97 |

P51 |

90 | M25 P 21.6 [213 117.0 | 10.4 | 8.9 | 8.2 | 6.3 | 4.1 | 179.9

Y14 | | |

P 2 | | | | |

68 |{M17}| M | 19.2 | 18.3 | 7.7 | 2.1 | 4.7 | 3.0 | 1.5 | 0.6 | 142.0

Y49 | | | | | |

P O | | | | |

98 |M 1 7 16.6 | 14.3 | 2.9 | 04) 2.1 | 0.7 | 0.3 | 0.1 | 129.2

lyo7 oe oe bel

256 |Averages of totals | 19.0 | 17.8 | 9.1 | 4.3 5.2! 3.9 | 2.7 | 1.6 1504

Beak and Leg Color—The beak and legs are more

dificult to grade quantitatively than the ear-lobes. The

color is less uniform in its distribution and has more of

an orange hue, requiring the manipulation of at least one

8 The three cases of laying, among the 557 records in the grades above 30

per cent. yellow were for sporadic layers. The one in the 40 per cent. group

laid October 18, but at no other time in October or September. This case

and 19th and had no eggs to her credit in the second half of September.

366 THE AMERICAN NATURALIST EVou. XLIX

extra color disk in taking the records. A rough grouping

by inspection into the three grades, pale, medium and

yellow, however, gives a striking corroboration of the re-

sults obtained by the more accurate records on the ear-

lobes and is applicable to breeds in which ear-lobe yellow

is not present. The grading was always done by the same

one of us (W.) who has had some familiarity in handling

poultry. Probably no two observers would entirely agree

in recording the colors but the difficulty comes in delimit-

ing the grade medium,and not in deciding between the

extremes, pale and yellow. The color records were taken

on October 31 and November 1 to 4, as the birds were

being packed for shipment and their egg records were

looked up for tabulation after they had left the contest.

Table III corresponds to Table I. In the first three

rows are listed the birds that agree in beak and leg color.

In the second three rows the birds are grouped according

to their beak colors without regard to their leg colors,

while in the last three rows they are grouped according to

leg color alone.

Table IV corresponds to Table II. Since egg records

for these birds stopped on October 31, a bird laying on

October 29 is counted among the layers even if she failed

to lay on the 31st—the day she left the contest.

It will be noted from Table III that, in the Leghorns at

least, where the numbers are large enough to make com-

parisons significant, the beaks, considered alone, seem to

form a slightly better criterion for picking out the hens

with high records, while the legs alone are better in select-

ing the poorest layers. In the great majority of cases in

all the breeds considered, if the beak and the legs fail to

agree in color it is the beak that is listed the yellower. In

October the hens are falling off in laying and in conse-

quence increasing in yellow pigment. Apparently the ear-

lobes and beak are more quickly responsive to this change.

In only 97 out of 160 Leghorns for which the beak was

listed as yellow had the legs reached a similar grading

in color. :

Of the 51 White Leghorns listed in Table III as pale in

No. 582] EGG-LAYING ACTIVITY IN DOMESTIC FOWL 367

both legs and beak, 31 had ear-lobe records of 20 per cent.

or less yellow on October 28. These averaged a yearly

total of 191.9 eggs. The 40 birds of those in Table III

that on this date had 20 per cent. or less yellow in ear-

lobes, irrespective of the color of other parts, averaged a

yearly total of 189.4 eggs. It appears therefore that hens

with a higher yearly average may be obtained by selecting

those that are pale in all parts—ear-lobes and beak as we'l

as in legs—than if only one of these parts is considered.

TABLE IV

PERCENTAGE OF BIRDS LAYING, AVERAGE NUMBER OF Days SINCE LAYING

AND YEARLY TOTALS FOR DIFFERENT COLOR GRADES OF BEAKS AND LEGS

(P, M and Y are guint for Pale, Medium and Yellow; the color of

beak is written first, followed by color of legs

White beakers (256 birds with yearly average of 150.4 eggs)

P.P."| M.M.| Y.Y.| P.M. | #.Y. | M. P Er Y.P. | Y.M.

Ro bies 60 5 17° ior Gos lil ila

Av. days since laying.. a 30.4 | 57.8! 30.5} — | 20.8 64.0 | 28.6 | 45.9

No. birds laying. :...... 2 1 a

Per cent. birds laying... . rt Si 18.8) 10 0 | 12.0 0.0 | 7.2 .0

Yearly averages........ 186.4 146.4 129.3 |150.5 | — 178.7 (122.0 158.4 139.9

White, Buff and Columbian Wyandottes (79 birds with yearly average of

144.8 eggs)

| p.p. | Mm. | Y.Y. | P.M. | P.Y. | M.P. | M.¥.| Y.P. | YM.

No. bras 7 los |13 ai rilo ee ooro.

Av. days sincs laying...| 6.5| 17.5| 48.9| 0 | — | 7 | | | 287

No. bi L agile ae | 16 5 0 1 — 2 — — 1

Per cent. birds laying 57.2| 38.5) 0.0/100.0} — | 50.0 — | — |111

Yearly averages........ 178.3 1130.7 1C8.4 1194.0! — 161.51 — | — 1145.6

P.P; | M.M. | Y.Y:

P.M.

M.P.

| MY.

No.

irds

cent. birds slaying.

Yeuty av

15 | 22

25.9 | 51.6

11.3 |

wo b]

55.5 20.0) 0.0

: 1153.7 149.7 123.0

1.0

66.6

163.7 |

100.

204.0 |

33.8

0.0

138.8

117.5

6.0

(114 birds with

yearly average of 128.8 eggs)

P.P. | M.M. | y.y.| P.M. | P.Y. | M.P. | M.Y.| Y.P. | Y.M.

To Ma E Ss 3 Tis +6 1 0o03 4-19

Av. days since rame.. 14.5. 155 50.4|.— | — | 19.0| 38.0] 183) 41.2

No. birds laying ........ 2 — — 0 1

Per cent. birds ig 53.9 46.7) 36,5 — — 00i 6.0! 96) 11

Yearly averages........ - 146.3 142.5 109.8! — | — 159.0 178.0 162.0 139.2

368 THE AMERICAN NATURALIST [ Vou. XLIX

The method of grading beak and leg color may appear

crude, but that it is capable of giving valuable evidence of

previous laying activity is further shown by data kindly

turned over to us by Professor C. A. Wheeler. On Octo-

ber 26, 1912, under his direction a series of measurements

of 132 White Leghorns from the contest was taken by Mr.

R. E. Jones. Among other records, the ear-lobes were

graded as white, cream or yellow and the legs as pale or

yellow, but no connection was worked out between the

color and the egg records. These 132 birds we find to

have a yearly average of 155.1 eggs. The 34 birds with

pale legs averaged 188.9 eggs; the 98 with yellow legs,

143.5 eggs. The 33 birds with white lobes averaged 190.1,

while the 99 with cream or yellow lobes averaged 143.5.

The 21 birds that had both white ear-lobes and pale legs

averaged exactly 200 eggs.

The data presented in the foregoing pages indicate a

connection between the amount of yellow pigment showing

in a hen and her previous laying activity. The most nat-

ural assumption is that laying removes yellow pigment

with the yolks more rapidly than it can be replaced by

the normal metabolism, and in consequence the ear-

lobes, the beak and the legs become pale by this subtrac-

tion of pigment.

Environmental factors, other than laying, may be of

more or less influence on yellow pigmentation. In fact,

birds obviously sick have been observed to be pale al-

though not in a laying condition. In the material investi-

gated, however, variation in the laying activity seems to

be the prime cause of the changes in yellow pigmentation

in the domestic fowl.

The data of the present paper have been summarized

in a preliminary report in Science, March 19, 1915. Pho-

tographs showing differences in yellow pigmentation in

fowls are given in an article in the Journal of Heredity,

April, 1915.

The change in yellow pigmentation is being further

studied by a twice weekly top record of a flock of birds

throughout the year.

SOME RECENT STUDIES ON FOSSIL AMPHIBIA

Dr. ROY L. MOODIE

DEPARTMENT OF ANATOMY, UNIVERSITY OF ILLINOIS, CHICAGO

THe anatomy and relationships of the earliest air-

breathing vertebrates have interested students of fossil

animals so greatly since Georg Jaeger described the first

Labyrinthodont in 1828, that the result to-day is a biblio-

graphic list of over 600 titles, varying in importance from

the magnificent work of Fritsch (‘‘ Fauna der Gaskohle’’)

issued in four folio volumes with scores of lithographic

plates, to short notices of a few lines. Many of the mem-

oirs are handsomely illustrated and beautifully printed.

The material so far described has been extremely frag-

mentary and the greater number of the contributions is-

sued have been dedicated to the description of species

based on incomplete material. The fauna was exceed-

ingly diverse like the plesiosaurs of a later period, and

new discoveries tend to confuse rather than to unify our

ideas of amphibian morphology. The few papers re-

viewed below form no exception to the statement made

above. Many new and importants facts are brought forth

in the contributions made during the past few months and

these are well worthy of consideration. Attention in

these reviews will be paid especially to new facts of struc-

tural importance.

Broili (1) in a short paper has added to our knowledge

of the Permian fauna of Texas by the description of two

new species of Amphibia based on incomplete skulls.

One of the species is very small, the skull measuring

scarcely half an inch in length. The same writer (2) ina

more extensive paper has given a popular review of the

chief work done during the past ten years on the early air-

breathing vertebrates and has listed the important papers

from which he has used illustrations to elucidate his re-

marks. This paper should be consulted by any one who

wishes a convenient and accurate survey of the earliest

land vertebrates. Doctor Broili refers to Micrerpeton,

the first branchiosaur known from the western hemi-

369

370 THE AMERICAN NATURALIST [ Vou. XLIX

sphere, as a microsaur. The distinction between these

two groups is clear, the former undoubtedly being .ances-

tral to the modern Caudata and the latter having reptilian

affinities. Likewise the author refers to Lysorophus'

as a reptile, while the majority of paleontologists regard

the form as Amphibian; Williston! even going so far as

to locate it in the suborder Ichthyoidea of the Caudata.

In conclusion Doctor Broili says:

Im übrigen haben wir im Laufe der letzten 10 Jahre über die ältesten

Tetrapoden so viel neues und wichtiges kennen gelernt, wie wohl in

relativ keinem anderen Zweige der Wirbeltierpaliontologie. .. .

Broom (3) has given the results of his studies on Per-

mian vertebrates in the American Museum. His reason

for again describing and studying this much described

and much studied material is that structural characters

are difficult to determine in these forms on account of the

very closely adherent matrix which has in many cases ob-

secured all sutures in the skull. His discussion is accom-

panied by restorations of the skulls of the chief Permian

- genera, indicating most of the sutures, something which

Cope was unable to do. He discusses some elements in

the mandible not previously observed among Amphibia

and suggests homologies between them and elements of

the reptilian mandible. Unfortunately, Broom has paid

no attention to the occurrence of lateral line canals on the

skulls of these forms. It is highly important that this

system of sense organs be distinctly understood. In view

of Herrick’s studies? on this structure in the catfish it is

certain that this system of sensory organs has a distinct

influence on the location of the peripheral osseous ele-

ments of the skull and mandible. I do not recall that

Herrick’s result have been noted by any paleontologist,

but they should be taken into consideration. Broom says

in regard to Eryops, the large Permian stegocephalian:

. Every detail of the cranial structure can be clearly made out.

He criticizes Huene’s (1913 b) work on the brain-case,

however, and makes no statement concerning the lateral

Aegae Bull., Vol. XV, No. 5, p. 229, 1908.

2 Jou ri. Comp: Neurol., Vol. 11, p. 224, 1901.

No.582] RECENT STUDIES ON FOSSIL AMPHIBIA 371

line organs which were imperfectly studied some years

ago? by the reviewer; so it is yet too soon to say that

every detail of structure is known. The palate is very

completely known and is figured by Broom. He has fig-

ured also very imperfectly, but for the first time, sections

through the ear and brain-case showing the probable size

of the dural cavity. He says that the portion of the par-

occipital which lodges the labyrinth was cartilaginous, but

does not give his reasons for this statement. In view of

the almost perfect preservation of the semicircular canals

in fishes, cotylosaurs and pterodactyls we should expect

a favorably preserved specimen of an amphibian to show

this structure also. He describes a pit in the basisphe-

noid for the reception of the hypophysis. He also figures

for the first time the complete osteology of the mandible

of Eryops. The author likewise describes and briefly

figures two new species of stegocephalians. The same

author (4) has given considerable attention to the study

of the osteology of the mandible in Trimeorohachis, the

discussion being very similar to that given in the above

paper. The discussion has especially in view the problem

of the derivation of the Amphibia from the Crossopte-

rygia, and he figures the mandible, shoulder girdle and

pectoral fin of Sauripteris taylori on account: `

. of (the) extreme interest from having the pectoral fin more closely

resembling the tetrapod limb than in any other known form

Case (5) reviewed before the American Paleontological

Society the recent trend of studies on the air-breathing

vertebrates of the Paleozoic. He states there are two

general conclusions which have been reached by students

of these early vertebrates. First, Baur initiated the idea

of the crossopterygian ancestry of the Amphibia, and

later workers have so far confirmed his suggestion as to

make it extremely probably that the land vertebrates arose

from these fishes. The intermediate stages are unknown.

The second conelusion is

that the primitive reptiles—the Cotylosauria—were derived directly

from the Stegocephalia.

So we are thus in possession of partial proof at least of

3 Journ. Morphol., 1908, Vol. XIX, p. 511.

372 . THE AMERICAN NATURALIST (Vou. XLIX

the origin of reptiles from fishes through the Amphibia.

We owe to Doctor Fraas of Stuttgart many important

contributions to the knowledge of the early air-breathing

vertebrates and he has recently (6) issued another memoir

on the labyrinthodonts of the Trias, the first study of

these animals since the appearance of his large memoir in

1889.4 The present contribution is devoted to discussions

of new species and new facts concerning previously de-

scribed species. The Plagiosternum granulosum is found

to be the most peculiar labyrinthodont yet described, in

that it is extremely frog-like in appearance, especially in

the huge size of the orbits and the expanded occiput. It

is interesting, furthermore, in the apparent absence or

indistinct preservation of the lateral line canals. The

photograph (Plate XVI, Fig. 1) of the dorsum shows

portions of the supra- and infraorbital canals. The re-

mainder of the cephalic system of sense organs was prob-

ably contained in pits, which, in the fossilized skull, are

not to be distinguished from the ornamental scrobicula-

tions of the membrane bones of the face. The auditory

meatus is on the posterior edge of the skull and is quite

large for the size of the skull. Doctor Fraas has given in

a drawing (Plate XVI, Fig. 3) the complete osteology of

the occiput of this unusual labyrinthodont. The re-

mainder of the memoir is devoted to a discussion of new

or disputed points in the osteology of various genera and

species of Triassic labyrinthodonts.

Gregory (7) has reviewed the studies which have thrown

light on the crossopterygian ancestry of the Amphibia,

dealing especially with Watson’s (11) recent paper on the

Larger Coal Measures Amphibia, and giving a list of thir-

teen contributions which deal directly with this derivation

of the Amphibia.

Huene (8) has again described the mandible of the pe-

culiar Permian genus Diplocaulus although it has been

many times studied, described and figured. He states, in

his introductory paragraph:

Gattungen, wie Diceratosaurus, Eoserpeton, Stegops, Amphibamus,

vieleicht auch Tuditanus zeigen Verwandtschaft mit Diplocaulus.

4‘‘Paleontographica,’’ Bd. XXXVI.

No.582] RECENT STUDIES ON FOSSIL AMPHIBIA ore

Just what the basis of this relationship is he does not

state. The reviewer® has previously stated that these

above-mentioned microsaurian genera exhibit no struc-

tural features which would ally them, except remotely,

with Diplocaulus. This Permian genus has no relatives

among the Coal Measures Microsauria, the reasons for

this statement being given in the above-mentioned essay®

and need not be repeated here. The material on which

von Huene bases his paper was collected in Baylor County,

Texas, and formed a part of a collection purchased by

Doctor von Huene from Charles Sternberg at Lawrence,

Kansas. The same writer (9) has again studied the Per-

mian Lysorophus, which is regarded by Williston as

closely akin to the salamanders.’ Huene bases his dis-

cussion on twenty-four skulls in the collection of the Uni-

versity of Tübingen. He describes and figures some mi-

nute limb bones, thus partially confirming Miss Finney’s

results.” He agrees with Williston that Lysorophus is

related to the Urodeles though suggesting : 4

Mit den Temnospondylia hat der permische Urodele Lysorophus:

noch grössere Ahnlichkeit als die jetzigen Urodelen. Sie liegen in der:

Schiidelbasis und der grosseren Anzahl der hinteren Schiideldeckknochen.

The same author (10) gives the results of his studies of

Permian vertebrates at the American Museum. The

paper is illustrated by sketches of various skulls and parts.

of skulls made by the author and showing his interpreta-.

tion of the elements composing the cranium of American

Permian amphibians and reptiles. He describes and fig-

ures a stapes in a skull of Eryops and gives the results

of his study of the brain-case of this genus. The stapes

has a length of 4 em. and in shape is not unlike a human

clavicle. His studies of Lysorophus, Gymnarthrus, Di-

plocaulus and other genera confirm the results of pre-

vious students of these forms. He concludes his paper

with a discussion of morphological results, and appends

a bibliography of twenty papers.

5 Journ. Morphol., Vol. 23, p. 31, 1912.

< 229,

€ Biol. Bull., XV, 1908,

7 Journ. Morphol., 23, p. 664, 1912.

374 THE AMERICAN. NATURALIST [ Vou. XLIX

Watson (11) has restudied the skulls of some of the

European Carboniferous labyrinthodonts, Loxomma, Pter-

oplax, and Anthracosaurus, and compared them with the

Coal Measures fish, Megalichthys. His results have

already been reviewed by Gregory (7), so that it will only

be necessary here to say that these genera approach the

crossopterygian type of structure in various features.

The same author (12) has redescribed an interesting mi-

crosaur in which he is able to give a very complete account

of the structure of the dorsal and ventral surfaces of the

skull and pectoral girdle. He compares the newly recon-

strueted microsaurian with Diplocaulus and Ceraterpeton.

It is very important that these little-known species from

Europe be restudied and redescribed, so that former ob-

servations may be corrected, corroborated and extended.

The status of

The classification of the smaller stegocephalian Amphibia, so abun-

dant in the Coal Measures and Permian Rocks of Europe and North

America, is in such confusion, to which some recent work has added,

that it is at present only possible to proceed by reference to individual

specimens which have been well described.

The reviewer finds himself in hearty accord with these

statements, although he must plead guilty of having

thrown some confusion into the classification of these ani-

mals in the hope that thereby order might ensue.

Doctor Williston (14) has determined the complete os-

teology of the mandible in the early reptiles and amphib-

ians, working especially with the material from the Per-

mian of America. He says:

In the structure of the mandible the amphibians are remarkably in-

termediate between the early reptiles and the contemporary cross-

opterygian fishes, differing from the latter chiefly in the reduced num-

ber of coronoids, and from the former chiefly in the possession of two

additional coronoids and a splenial.

These results are corroborated by the studies of Doctor

Broom on similar material, so that any doubts as to the

real structure of the stegocephalian mandible are placed

at rest by the results arrived at by these ee investi-

gations.

No. 582] RECENT STUDIES ON FOSSIL AMPHIBIA 375

The mandible of the primitive amphibians differs chiefly from that

of the early reptiles in the division of the coronoid into three elements,

or possibly four, and in the division of the splenial into two.

Wiman (15) within the past three years has become

much interested in the amphibian fauna of the Trias of

Spitzbergen. In the present paper he reviews the work

which has been done on the structures of the occiput of

seven genera of Permian and Triassic stegocephalians,

figuring the anatomy of this region of a new laby-

rinthodont from Spitzbergen. He describes this new

genus in a later contribution. In this latter paper (16)

Wiman discusses the occurrence of amphibian remains in

the deposits of Spitzbergen, accompanying his remarks

by photographs of the bone-bearing horizons. His paper

deals largely with new forms from Spitzbergen, which are

illustrated in four text figures and nine photographic

plates. One is at once struck, in the examination of

Wiman’s plates, by the clearness of preservation of the

cephalic lateral line canals. The author refers to these

structures as ‘‘ Schleimkaniile ’’ and gives a very careful

description of their occurrence; the only writer of recent

date who has done so. The term Lyrocephalus euri is

proposed for the new genus and species.

Der Gattungsname bezieht sich auf die ausserordentlich kräftig

entwickelten Schleimkanile des Kopfes. .. .

He refers to the various canals as ‘‘ Tremalkanile,’’ ‘‘ Na-

sofrontalkaniile,’’? ‘‘Temporalkanal’’ and ‘‘Maxillarka-

nal,’’ but makes no attempt to homologize them on the þa-

sis of the work of Allis’ (1889) and the reviewer (1908).

The lateral line canals are so unusually well preserved in

Lyrocephalus that it is thought worth while to give an

outline figure in another place of their occurrence and to

homologize them on the basis of previous work. The

columella auris is described and figured (Plate II, Figs.

4-5) in this species. It is unusually large. Other new

forms are described from these interesting deposits, many

of the specimens showing much of interest in a structural

way. The material described is chiefly cranial, although

a few thoracic plates (interclavicles), of the typical laby-

8 Journ. Morphol., II, 1889, p. 463; 1908, p. 511.

376 THE AMERICAN NATURALIST [VoL. XLIX

rinthodont form, are described and figured. Doctor Wi-

man is to be congratulated on his contributions to our

knowledge of these early vertebrates. His future papers

will be looked for with much interest.

oan

BIBLIOGRAPHY

Broili, F. 1913 a. Uber zwei Stegocephalenreste aus dem texanischen

Perm. Neues Jahrbuch f. Mineral., Bd. I, Jahrgang 1913, pp. 96-1

Taf. IX.

1913. Unser Wissen ia die ältesten Tetrapoden. Fortschr.

d. Naturwissenschaftl. Forschung, herausgegeben v. Prof. Dr. E. Abder-

halden-Hall. ae Bd. VIII, pp. 51-93, figs. 14-62.

room, R. 1913. a. Studies on the Permian Temnospondylous Stego-

cephalians of Ra th America. Bull. Amer. Mus. Nat. Hist., XXXII,

II, pp. 563-595, with 21 ia

On the Structure of the Mandible in the Stegocephalia.

Anat. Anz., Bd. 45, No. 2/3, pp. 73-78, with 4 figs

Case, E. C. 1912. Paleozoic apaiia and gh, Bull. Geol. Soc.

aige a 23, pp. 200-

raa 913. Neue Labyrinthodonted aus der schwibischen Trias.

Sai ran Bd. LX, pp. 275-294, pls. XVI-XXII, with text-

1-5

. Gregory, wm. K. 1913. Crossopterygian Ancestry of the Amphibia.

VII, No. 960, pp. 806-808.

Science, N.S., Vol. XX

Huene, Fr. von. 1912. Die Unterkiefer von Diplocaulus. Anat. Anz.,

Bd. “a No. È p- 472-475, Figs. 1-3.

13 a. Über Lysorophus aus dem Perm von Texas. Anat. Anz.,

Ba. a No. 14/15, pp. 389-396, Figs. 1-5, with bibliography.

. —— 1913 b. The Skull Elements of the Permian pagite in the

. Mus.

American Museum of Natural History, New York. Bull. Am

Nat. Hist., XXXII, Fork XVIII, pp. 315-386, Figs. 1-57.

. Watson, D. M. 8, The Larger Coal Measure ee Mem.

and Proc. loa ii and Philos. Soc., Vol. 57, ; Dee.

1913. Batrachiderpeton lineolatum, a Coal Measure Btegocóplia-

figures in th See als :

tion of the ae Rept. 83 Meet. British Assoc. Advance. Se. Bir-

mingham, 1913, p. 532.

1914. The Cheirotherium. Geol. Mag., Dec. VI, Vol. I, No. 603,

pp. 395-398.

. Williston, S. W. 1913. The Primitive Structure of the Mandible in

Amphibians and Reptiles. Journ. Geol., Vol. 21, No. 7, pp. 625-627, 1

See also same EE further notes: eit: Geol., Vol. XXII, No.

Wiman, Carl. 1913. ier das Hinterhaupt der Labyiinthodonten,

Bull. of the Geol. Instit. of Upsala, Vol, XII, pp. 1-7, Figs. 1

Uber die Stegocephalen aus der Trias Spitzbergens. ‘Bull,

of the Geol. Instit. of Upsala, Vol. XIII, pp. 1-30, Pls. I-IX, Figs.

1- e Villines aphy.

SHORTER ARTICLES AND DISCUSSION

THE RESEMBLANCE OF YOUNG TWINS IN

HANDWRITING

By each of 144 children 7 to 15 years old, forming 72 twin

pairs, the first name (and usually also a word or so like ‘‘years

old’? or March or grade) was written. These were pasted on

cards identified by chance numbering. Twelve men and women

of good general education, but of no special experience in identi-

fying handwritings, were shown the 72 specimens belonging to

72 first members of twin pairs and asked to match each by the

specimen of the remaining 72 which most resembled it.

There was thus one chance in 72 of a correct match by chance,

or 12 chances for all judges combined. There were in fact 6, 4,

8, 4, 6, 6, 7, 1, 3, 6, 3 and 4 correct pairings made by the twelve

judges, respectively, or 58 in all.

It would be possible by the same method to derive a scale for

unintentional resemblance in specimens of handwriting as shown

roughly below. Such a scale might indirectly be of use in the

study of questioned documents, since the resemblance of one speci-

men of an individual’s writing to another specimen by himself

may be regarded as the limiting case of the unintentional re-

semblance found amongst different individuals. A scale for re-

semblances produced intentionally would presumably form a

Series in which the resemblances would, upon analysis, be found

characteristically different from the unintentional or natural re-

semblances, The genuineness of a questioned specimen of writing

might thus be determined in part by measuring its resemblance

to the unquestioned specimen in the different elements character-

istic of the two scales. Resemblances of certain sorts might thus

be used as actual evidence of forgery, and differences of certain

sorts as evidences of genuineness, more systematically and ob-

jectively than is now the ease.

Specimens 145 and 147 have a curious interest as a result of

possessing nearly as close resemblance between two ‘‘natural’’

writings by two different persons as is likely ever to be found.

It is probable that if the individuals in question had each written

378 THE AMERICAN NATURALIST (Vou. XLIX

Fic. 1. Rough Scale of Resemblances in Handwriting. 145 and 147 were

regarded as matches by 11 of the 12 judges; 19 and 65 were so regarded by 5

judges; 38 and 90, by 2 judges; 4 and 96 by none.

a hundred natural specimens of the same two words, and if judges

of the training of tellers in banks had been given the task of sepa-

rating the two hundred specimens into the hundred by individual

A and the hundred by individual B, the percentage of failures

would have been considerable. These specimens, that is, may

illustrate the possibility of successful forgery without artifice.

In general, of course, the experiment shows how very, very

rare the case of substantially perfect resemblance of two natural

signatures by different individuals will be. One case amongst 72

pairs of twins probably signifies less than one-case in a thousand

amongst the general population of as close resemblance as 145

No. 582]. SHORTER ARTICLES AND DISCUSSION 319

and 147. Twins are probably distinguishable by their hand-

writing oftener than by their physical appearance; for I am con-

fident that the bodies of at least five and probably more of these -

72 twins would have been as hard to tell apart from a minute’s

visual inspection as specimens 145 and 147. Of people in general

this would probably not hold true, but the distinguishing value

of a specimen of natural writing is very high even for them.

EDWARD L. THORNDIKE

TEACHERS COLLEGE,

COLUMBIA UNIVERSITY

ALLELOMORPHS AND MICE

In the February number of this journal, C. C. Little points out

that Cuénot (1903) recognized certain factors in mice as allelo-

morphic,* and that in my paper of 1914 I not only failed to men-

tion that Cuénot had treated these factors in this way, but that I

claimed to have brought forward for the first time a demonstra-

tion of the allelomorphism in question. In fact, I did overlook or

had forgotten that Cuénot interpreted these types in this way;

and curiously enough, my work was undertaken because Little

on the alleged results of some of his own earlier experiments

denied that the factors for yellow and gray are completely linked,

despite Cuénot’s evidence, then published, which Little now says

established from the ratios obtained that the factors in question

are allelomorphic.? Little wrote as late as 1913:

“Yellow” in mice is no more alehenirniee to gray than is gray

allelomorphie to black.

If this is the conclusion at which he arrived after his elaborate

series of experiments and after Cuénot’s work had been done,

the need of further work would seem to be obvious.

The failure of several of us to fully appreciate the significance

of Cuénot’s statements and evidence in regard to allelomorphism

may in part be due to the fact that in his second paper Cuénot had

used the symbols G (gray) and N (black) as allelomorphs, and had

besides used the symbols A (albino) and G (gray) as allelomorphs

without, however, intending to mean that there was here a set of

1 Note 1903, Archiv. Zool. Exp. et Gen. (4), I.

2 The numerical results are the same for complete linkage and for multiple

allelomorphs. The evidence that would ites the one would also disprove

the other.

380 THE AMERICAN NATURALIST [ Von. XLIX

three allelomorphs, but using G in each of the two cases to rep-

resent a different factor of the gray mouse.’ This method is in

itself quite legitimate, but as a result when Cuénot later spoke of

the factor for gray, gray white belly, yellow, and black, all as

allelomorphic, some of us, it appears, failed to appreciate that in

doing so Cuénot was treating this set of terms in an entirely differ-

ent way from the way in which he treated the other cases, where

he had represented factors as allelomorphiec to each other. In the

second place, the full significance of multiple allelomorphs in mice

was not, I think, fully appreciated until its relation to complete

linkage became apparent, and in fact even now this relation is not

sufficiently understood by many geneticists themselves. Even,

however, had I taken fully into account all that Cuénot had done,

the somewhat extensive experiments that I undertook in order to

prove that the factors in question are allelomorphie would have

seemed to me necessary, as they still do, to establish that this

series of factors bears this relation to each other. Let us ex-

amine, therefore, the evidence, which, according to Mr. Little,

rendered my experiments a work of supererogation.

1. Little says:

As early as 1903 Cuénot recognized that albinos, potentially yellows,

when crossed with black gave besides yellow offspring either black or

agouti young but not both. This is, of course, evidence that yellow,

agouti and black‘ are all allelomorphiec to one another.

But the evidence proves nothing of the sort, unless Cuénot had

shown that his albinos should have been expected from their

history to contain all three factors in question. However likely

it may seem, to one so inclined, that such triple forms must sooner

or later have been met with by chance, the fact remains that

Cuénot had, as the offspring showed, used only double types, and

such a fact in the absence of explicit evidence as to the history

of the forms used can not be said to demonstrate anything in

particular.

2. Little continues:

At the same time he gives the ratios produced by crossing an albino

3 The ‘‘examples’’ given on page vii of the second memoir are also in-

structive in the present case.

4 Probably Little means here by ‘‘black’’ what he later calls the non-

f so he refers to a different AE from that which he

agouti factor.

. is, moreover, clearly

called black, when, in 1913, he wrote:—‘ Blac

a positive character which is dominant over its pecans

No. 582] SHORTER ARTICLES AND DISCUSSION 3X1

potentially a heterozygous gray (agouti) with a yellow carrying black

but no agouti and albinism. . . . Cuénot recognized that the ratio ex-

pected from the cross was 2 valine: 1 black and 1 agouti (gray).

If one turns to Cuénot’s experiment® he finds that Cuénot

crossed an albino carrying black (AN) to an albino carrying gray

(AG) in order to obtain a ‘‘dozen’’ white mice with the formula

AGAN, and similarly he crossed a black mouse (CN) to a white

mouse carrying yellow (AJ) in order to obtain another ‘‘dozen’’

mice with the formula CNAJ. We are not told whether each

dozen came from the same parents, or from several similar com-

binations. It will be observed that the yellow (J) and black (N)

were brought together to make one F,, and that gray and black

were brought together to make the other F,, hence since gray was

in one F, and yellow in the other F, it is not possible to tell

whether they behave as allelomorphs to each other. There is no

reason, then, for making gray and yellow both allelomorphie to the

same factor (N), black; for, in the first cross the gametes (omitting

A and C) might have been Gj (gray) and gj (black) and in the

other cross gJ (yellow) and gj (black). The numerical results

would then be those obtained by Cuénot, which would prove noth-

ing in regard to the allelomorphism of gray, yellow and black.

In other words, the letter N stands in this cross simply as a sym-

bol for anything in the black mouse that could be treated as

allelomorphie to G in the one ease, and to J in the other; just as

at first when rose comb in fowls was found to give a 3 to 1 ratio

with single comb it was treated as an allelomorph to single; and

likewise when pea was found to give 3 to 1 with single it too was

regarded as allelomorphie to single. Later it was found that S

(single) stood for two factors (‘‘absences’’), small r and small p.

3. Little thinks that both Cuénot and I have fallen into the

Same error in regard to black; but he fails to see that from our

points of view in regard to the other colors it was inevitable that

we should come independently to the same conclusion. Little

says that the ‘‘true’’ series of allelomorphs is yellow, white-

bellied gray, gray-bellied gray, and non-agouti (not ‘‘black’’).

The factor that Little prefers to call non-agouti, I call the black

factor. He regards a non-factor as a member of an allelomorphie

series, while I regard the black mouse as the result of the action

of a factor for black. By the same criterion as that by which

Little speaks of a non-agouti factor, he might equally well claim

5 Third note, p. xlix.

382 THE AMERICAN NATURALIST [Von. XLIX

that the ‘‘true’’ series is black, gray gray belly, gray white belly

and non-agouti (instead of yellow).

The race of white-bellied mice that I have kept for several

years does not correspond in all respects to Cuénot’s description

of those that he has studied. His account of them in 1908? is as

follows:

La Souris reste grise sur le dos, mais le ventre prend une teinte blane

roussatre, avec un bouquet de poils plus roux entre les deux pattes de

devant, et une bordure un peu plus rousse sur les flanes; elle resemble

d’une façon frappante ‘4 Mus sylvaticus, L.

Again in 19117 Cuénot says:

La première diffère de la Souris grise sauvage par la teinte du ventre,

qui, au lieu d’étre gris-clair, est blane roussâtre, avec un bouquet de

poils roux entre les deux pattes de devant et une bordure un peu plus

rousse sur les flanes; cette Souris a souvent de gros yeux saillants, de

sorte qu’elle ressemble d’une façon frappante au Mulot (Mus sylvat-

icus, L

In my race of white-bellied mice there is not a bouquet of rus-

set hairs between the front legs, and I have not observed that the

eyes are large and protruding more than occurs at times in other

mice. At present, however, I have two old mice that were re-

cently found that have a tuft of faint russet hairs between the

forelegs. Whether we have‘here still another allelomorph, or

whether a particular genetic constitution makes apparent the

bouquet in conjunction with the white-bellied factor, remains to

be worked out. While it seems probable that Cuénot’s type of

white-bellied mouse and that which I have studied are the same,

it is not certain that such is the case until further work has been

done.

Cuénot has not published as yet any conclusive evidence to

show that the gray mice with white belly belong to the series of

allelomorphs, although it is true he states that this type is allelo-

morphic to the three other types. Finally, I should like to add

that I am far from wishing to appear to minimize the importance

of Cuénot’s work, and it is now evident that he should have

received full credit for his recognition of the allelomorphic

nature of the four factors in question.. I still think, nevertheless,

6 Sixth note, II, p. xv.

7 Seventh note, p. xlvii.

No.582] SHORTER ARTICLES AND DISCUSSION 383

that there was room, as matters stood, for the analysis that Stur-

tevant published and for the work that I carried out.

T. H. MORGAN

COLUMBIA UNIVERSITY

A METHOD OF CALCULATING THE PERCENTAGE OF

RECESSIVES FROM INCOMPLETE DATA

In the very interesting article on ‘‘The Inheritance of Left-

handedness’’ by Professor Ramaley in the December number of

the NATURALIST, a table is given on page 736 showing the propor-

tion of right- and left-handed children in families where both

parents are presumably heterozygous for right- and left-handed-

ness, including only families with left-handed children. In 93

such families there are 282 right-handed and 116 left-handed

children. This gives 29.13 per cent. of left-handedness in these

families. It is clear, however, that this does not represent the

TOTAL NUMBER OF CHILDREN FROM PARENTS HETEROZYGOUS FOR RIGHT- AND

LEFT-HANDEDNESS, BASED ON THE NUMBER OF FAMILIES OMITTED

BECAUSE OF ABSENCE OF LEFT-HANDED CHILDREN IN PROF

RAMALEY’S TABLE 4

Children per Actual Number Actual Number} Corrected Number | Corrected ee

Family of Families of Children of Families’ | of Childre

1 4 4 16 16

2 14 28 32 64

3 if 51 294

4 23 92 33.63 134.5

5 18 90 23.6 118.0

6 5 30 .08 36.45

7 1 7 1.154 8.

8 6 48 6.666 53.35

9 4 36 4.325 38.

12 1 12 1.032 12.39

Total 569.87

true Mendelian proportions if right-handedness is a simple Men-

delian dominant over left-handedness. For instance, in families

where both parents are heterozygous and in which there is only

one offspring, the probabilities are that only one family in four

will show the recessive character. From the total population re-

8 Archiv. de Zool. Exp. et Gen. (4), IX; (5), VIIL

1 By oversight in Professor Ramaley’s additions one column of right-

handed children was omitted, so that the numbers given in the table are

incorrect,

384 THE AMERICAN NATURALIST [ Von. XLIX

sulting from such matings, we therefore leave out three fourths

of the families when we include only those showing the recessive

character in the offspring. In families of two children nine

sixteenths of the families are omitted. In general, the number of

families omitted in such a study is 3"/4", where n is the number

of children per family. In order to get the true Mendelian pro-

portions we must take account of these omitted families. The

accompanying table shows the most probable results in Professor

Ramaley’s study had he been able to include the proper propor-

tions of families in which left-handed children might have oc-

curred.

Thus if Professor Ramaley had had at his disposal the full

number of families of this character there should have been

about 570 children in them, 116 of which were left-handed, or

20.37 per cent.

This is somewhat lower than the theoretical 25 per cent., and I

would suggest as a possible cause of this the fact that so many

children who are naturally left-handed are from early infancy

trained to be right-handed. Hence the number of left-handed

children reported is probably less than the true number of

recessives in these families.

W. J. SPILLMAN

U. S. DEPARTMENT OF AGRICULTURE

VOL. XLIX, NO. 583 JULY, 1915

THE

AMERICAN

NATURALIST

A MONTHLY JOURNAL

Devoted to the Advancement of the Biological Sciences with

Special Reference to the Factors of Evolution

CONTENTS

Page

I. The Role of the Environment in the Realization ns a Sex-linked Mendelian

aracter in Drosophila. Professor T. H. M -3

Ii. On a Criterion of Substratum Homogeneity (or ee in Field Ex-

eriments. Dr. J. ARTHUR HARRIS 430

Ill. Shorter Articles and Discussions: A Note on a Gonads of ETEEN

of Drosophila ampelophila. F.N. DUNC 455

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THE

AMERICAN NATURALIST

Vou. XLIX. July, 1915 No. 583

THE ROLE OF THE ENVIRONMENT IN THE

REALIZATION OF A SEX-LINKED ME

DELIAN CHARACTER IN DROSOPHILA

Proressor T. H. MORGAN

COLUMBIA UNIVERSITY

CONTENTS

i The Influence of the Environm

The Linkage of the Factor for Abnormal ar ole Sex-Linked Factors.

(a) The Linkage of Abnormal and White.

lack, Red, Abnormal by Gray, White, Normal.

Gray, Red, Abnormal by Black, White, Normal.

(6) The Linkage of Abnormal, Yellow, and White.

ray, Red, Abnormal by Yellow, White, Normal.

Gray, White, Abnormal by Yellow, White, Normal.

a White, Abnormal by Gray, Red, Normal.

low, S Abnormal by Gray, White, Normal.

2. Change ay aa as the Culture Grows Older.

ests of Changed over Classes

. Influence of the Factor for Black on the Realization of the Abnormal

P 2

aracter.

- Influence of the Factor for Yellow on the Realization of the Abnormal

haracter.

- The Relative Influence of the Egg and of the Sperm on the Condition

of the Heterozygote.

7. Presence and Absence.

8. Other Types of Abnormal Abdomen.

9. The Non-Inheritance of an Acquired Character.

10. The Non-Contamination of Genes.

INTRODUCTION

THE mutant, from which the stock with ‘‘abnormal ab-

domen” was derived, appeared in 1910. It is charac-

terized by a peculiar condition of the pigment bands and

segments of the abdomen as shown in Fig. 1. The range

of variation of the character is very great; in its most

385

386 THE AMERICAN NATURALIST [Vou. XLIX

Fig. 1.

extreme condition not only do the pigment bands totally

disappear, but even the lines between the metameres are

broken up, and the location of the external genitalia may

be shifted to a more terminal position. All stages exist

between this extreme modification and a condition that

can not be distinguished from the normal. Owing to

this wide range of variability the study of the inher-

itance was very difficult until it was found that the reali-

zation of the type is a function of the environment.

the more extreme types the abdomen is deformed to

such an extent that copulation is difficult or impossible.

The sterility caused in this way helped also to make the

work burdensome, especially when breeding was made

with pairs. Instead of pairs, cultures of ten to twenty

individuals of the more extreme type were resorted to,

as a rule insuring the successful mating of some indi-

viduals. Aside from this mechanical difficulty in mating,

the mutant race is quite vigorous and of good size.

No. 583] ROLE OF ENVIRONMENT IN DROSOPHILA 387

Two principal obstacles delayed the formation of a

pure strain. The new character is a sex-linked domi-

nant,’ but both the heterozygous and the homozygous

condition overlap the normal type which makes the selec-

tion of pure females difficult. Any male, however, that

shows abnormal abdomen at all is pure, for the charac-

ter is borne by the X chromosomes of which he has but

one.

The other obstacle was what at first appeared to be a

perpetual reversion of stock, seemingly pure, to the nor-

mal. So constantly did this occur, that, for some time, I

thought that I had an ‘‘ever-sporting’’ variety—one

that reverted to the normal without apparent provoca-

tion. I found, however, that the first flies that hatched

in the best-fed cultures were entirely abnormal, while

those that emerged later were less abnormal, until finally

those that emerged when the cultures were nearly at an

end were invariably normal flies. It seemed at first pos-

sible that such stock might be impure, and that the ab-

normal flies hatched sooner than the normal, but this view

was negatived by the fact that normals hatch as soon as

do the abnormal flies.

The one remaining possibility seemed to be that de-

velopment of the abnormal abdomen depended on some

definite condition of the culture—one that was present

when the food was fresh and the bottle wet, but which

disappeared as the food was used up and the bottle got

dry. I tested this hypothesis in many ways. Stock was

used that had been pure for nine generations. As a

bottle dried up an ever increasing proportion of normal

flies appeared. At intervals lots of flies were taken out

and put into new bottles where they were abundantly fed.

Their first progeny, as recorded below, shows that under

the new conditions the offspring were sometimes ex-

tremely abnormal irrespective of the general condition

of the original stock when used.

1 Morgan, T. H., ‘‘A Dominant Sex-Linked Character,’’ Proceed. Soe.

Ezp. Biol. and Medicine, IX, October 18, 1911.

388 THE AMERICAN NATURALIST [Vou. XLIX

Condition of Parents Next Generation

Feb. 26. Most flies abnormal—a few were normal.. Very abnormal.

Feb. 27. More than half were normal........... Flies fairly normal.

Feb. 28. About half were normal............:.. Nearly all abnormal.

Feb. 29. Practically normal <2... 0.06. eee tse os Very abnormal

Mohd. Nanri Orai o is i. 8 se oo 88 Abnormal, a few normal.

Mok A DORA ss fale ee lig a eee ee ee Very abnormal.

Men. De OPI ep eck de bse ece ee Very abnormal.

The preceding case shows that there is no necessary

relation between the development of the abnormality in

the parent and that in the offspring. This is only a

sample of a large amount of similar data. But this evi-

dence does not show what special conditions make for ab-

normality. In order to study this problem I generally

used heterozygous females which were obtained either

by mating an abnormal male to a wild (virgin) female

(in which case the daughters will be abnormal under suit-

able conditions and the sons normal), or reciprocally by

mating a normal male to an abnormal female (when all

the daughters will be abnormal (heterozygous) and all

the sons pure abnormal). Many experiments had shown

that the heterozygous female changes over more promptly

to the normal character than does the homozygous male

and the latter sooner than the homozygous female.

The one outstanding fact for some time was that as a

bottle crowded with flies gets old there is always a change

from day to day from abnormal towards normal, but it

remained to be shown whether the change was due to

the drying out of the culture, or to any one of a dozen

other parallel changes that obviously are going on at the

same time. The more significant results of a prolonged

set of experiments may be summed up as follows:

_ 1. Starvation.—Lack of food does not bring about the

change from abnormal to normal. Flies that are so

starved as to be extremely small may be very abnormal.

: 2. Acid, Alkali or Neutral Condition of Food Stuff. —

Most cultures change in the course of the ten to twelve

days from an acid through a neutral to an alkaline con-

dition. Fresh fermenting banana (in the old and acid

No. 583] . ROLE OF ENVIRONMENT IN DROSOPHILA 389

medium) was made more acid (and liquid) by adding an

equal amount of a 5 per cent. solution of acetic acid.

Other food was made alkaline by adding dry sodium

bicarbonate, or a 1 per cent. solution of sodium hy-

droxide. The acid food gave very abnormal flies; the

alkaline food was difficult to control as the flies refused

in most cases to lay eggs on it, if it remained alkaline,

and the food often dried up, or putrified, or grew mouldy.

Moreover, the highly alkaline food often became acid

over night owing to fermentation changes taking place

within the pieces of fruit used for food. But several

times good results were obtained with cultures that had

been strictly neutral and often alkaline throughout the

time of the experiment and from these the flies were ab-

normal, Omitting all details it may be stated that an

acid or alkaline (neutral) condition as such is not the

cause that conditions the character.

3. Food of Parents.—At one time it seemed possible

that the kind of food that the female was supplied with

might for a time continue to affect her eggs, even al-

though the parent was transferred to a medium that

acted in the opposite direction. Careful tests showed

conclusively that such was not the case. Some of the

evidence for this statement will be given later.

4. Egg versus Sperm.—Heterozygous females may be

produced either by using a normal female and abnormal

male, or conversely an abnormal female and a normal

male. Certain cultures seemed, at one time, to show that

when the egg parent was abnormal the offspring were

more abnormal than when the egg parent was normal,

but careful tests disproved this view. The difference in

the cultures, that led to the suspicion mentioned, was due

to the large number of eggs laid by the normal females,

hence greater crowding and more rapid disappearance

of the moist food.

5. Influence of Genetic Factors.—Certain mutant stocks,

notably black, seemed at times to show the abnormality

less strongly than other stocks, but here, as in the last

390 THE AMERICAN NATURALIST [Vor. XLIX

ease, the results were found to be due, when carefully

tested, to the number of eggs laid and the promptitude

with which they are laid when the food is fresh. The

question will again come up in certain of the crosses.

6. Amount of Water in Food.—Normal cultures lose

much of their water as the brood of flies develops. It

was a fact noticed at the start that in ‘‘wet’’ bottles the

abnormal characters appeared to best advantage, and in

most of the work on linkage that knowledge was utilized.

But whether the wetness was only incidental to other

changes, or in itself the normal condition was not pre-

cisely determined. Under all conditions the air in the

bottles must be completely saturated with moisture so

that we must be dealing with the water taken in with the

food and not with the amount of water in the inspired

air. In three ways the effect of water was studied. (1)

Food that had been fermenting for two or three days in

the old acid medium was squeezed until freed of much

of its water. The solid part was then further dried su-

perficially by pressing between pieces of filter paper, and

finally put into a bottle with more dry filter paper. The

fluid squeezed out was diluted with an equal amount of

water, and put into another bottle. Virgin normal flies

and abnormal males of pure stock were set free in these

two bottles. The results at the end of nine days were

most striking. In the dry bottles the F, females were

all normal; in the wet bottles the F, females were ex-

tremely abnormal.

7. Changing the Adult from Wet to Dry and Vice

Versa.—In this same series the old (P,) flies that had

been in the wet bottle were transferred to dry food, and

conversely the ‘‘dry’’ flies to wet food. Their progeny

showed the influence of the food that they were reared

upon, and no effect of the feeding in the previous bottle.

Once more they were changed, the wet to dry, the dry to

wet, and the results were the same as before, i. e., the

actual conditions, not the preceding ones, ba acnounted

for the results that were obtained.

No. 583] ROLE OF ENVIRONMENT IN DROSOPHILA 391

8. A culture that was giving F, normal females (that

were heterozygous for abnormal) was made extremely

wet; into a sort of swamp. The flies that emerged dur-

ing the next six days were normal, on the seventh day

the flies were slightly to fairly abnormal, on the eighth

and ninth days the flies that emerged were slightly to

quite abnormal. It is evident that the influence of the

wet conditions does not appear unless the flies are sub-

jected to it throughout most of the larval life, or else that

the first few days of larval life is the critical period.

9. Larve that were about ready to pupate were trans-

ferred to very wet new food, where they pupated, in

from 12 to 24 hours. The pupe remained in the same

bottles until the flies emerged. These flies were entirely

normal in appearance; the stock from which the larve

came were also giving rise to normal flies. The sojourn

of one or two or even three days in a wet environment

at the end of the larval life does not suffice to alter the

effects that have already been induced in an earlier stage.

Conclusions.—The preceding evidence makes clear

that the amount of water in the food, determines the

realization of the ‘‘abnormal’’ type. The water may

produce its effect either by being taken in with the food,

or by being directly absorbed; or it may determine the

nature of the bacterial or yeast flora that in turn deter-

mines the nature of the fermentative changes that take

place within or without the larve. It would be a very

difficult matter to find out in which one of these ways the

effects are brought about. However this may be, it is

possible for the experimenter to determine at will the

nature of the flies that will be produced in his cultures

by controlling the food supply.

THE LINKAGE OF THE FACTOR FOR ABNORMAL ABDOMEN

WITH OTHER SEX-LINKED FACTORS

Owing to the overlapping of the abnormal and normal

types, the study of the linkage has presented unusual

difficulties. The following experiments were made for

the most part during the second year when the influence

392 THE AMERICAN NATURALIST ~— [Vou. XLIX

of the environment was not fully under control. The

conditions under which the experiments were made were,

however, favorable for the appearance of the abnormal

condition, at least in the first counts of each brood, for

the bottles were supplied with an abundance of wet fer-

mented food.

The linkage of abnormal abdomen with white eyes and

yellow body color was studied in different combinations;

and since the factor for abnormal abdomen proved to be

quite near the other two factors the choice was a favor-

able one in certain respects. A special method by means

of which the error, due to the variability of the charac-

ter, can be largely eliminated will be given after the evi-

dence has been presented.

THE LINKAGE OF ABNORMAL AND WHITE

When red-eyed (R) abnormal (Ab) females were mated

to white-eyed (W) normal (N) males, red abnormal

males and females were produced.? When these were

mated the results recorded in the next table were ob-

tained

By means of the following diagram, I have tried to

WE PE

wW N

DIAGRAM I.

show what the expectation is for this combination. The

two parallel lines are intended to represent the two sex

chromosomes of the F, female. From her mother she

2 Throughout this paper I have used the letters R for red eyes, W for

white-eyes, N for normal abdomen, Ab for abnormal abdomen, Y for yellow,

B for black instead of using the allelomorphic system; because for present

purposes, where analyses are unnecessary, these letters suffice most simply

to indicate the operations that are involved. For comparison with other

papers the allelomorphie symbols for the same neti would be:

w= the factor for white. W =its normal allelomorph = red.

A'b = the factor for abn. abd. a’b—Zits normal oo = normal abd.

y= the factor for yellow. Y=~its normal allelomorph = gray.

b= the factor for black, B=its normal enara gray.

No. 583] ROLE OF ENVIRONMENT IN DROSOPHILA 393

got the sex chromosome bearing the factors for red and ab-

normal (RAb), from her father the homologous sex

chromosome that carries the factors for white and nor-

mal (WN).

TABLE I

ParRENTS: RAD? BY WN g

F,: RAb9—RAb ¢

RAb WN | RN WAb |

seas | POV EREE] TEESE E RR gli EETA RIT EAR No. of Culture

A9 F | toe | 9 J | g

Fs deat ae.” ie or ee Ha 2 ee tea Ih

148) ee | ee AS | 6 1 eh eee Ils

106 | 3 is ee or. 3 ea, Ils

ee Gece R - ae peed vee MS sss aa a Il;s

B | Ob A081 EP E e Iza

a a eee a eee eer 4 Tiss

GO 6 BOs ieee 1 “hee pet Ti»

647 i 17 el o. kæde han n

If these chromosomes unite at synapsis without ex-

change of materials, half of the eggs that result (one

chromosome being eliminated in the polar bodies) will

contain the red normal combination, the other half the

white normal. These represent the ‘‘non-cross-over’’

gametes. If, however, these chromosomes should cross

and reunite, as in the diagram (the crossed lines indi-

cate where the crossing over may occur, not how it oc-

curs), the two resulting chromosomes will be red-normal

RN, and white abnormal, WAb, which represent the

other (the cross-over) kinds of gametes of the F, female.

The ratio in which they are produced is the gametic

ratio and is a measure of the linkage.

In the F, males there is but one X chromosome, hence

there is no opportunity for interchange here between

the X chromosomes. The mate of the X chromosome is,

in the male, the Y chromosome. Other experiments have

shown that the Y chromosome carries no factors; hence

interchange seems precluded; and, so far, no loss of X

chromosome factors to the Y chromosome has ever been

observed. The X chromosome passes into the female-

3 An unexpected individual that can be accounted for by equational non-

disjunction.

394 THE AMERICAN NATURALIST [Vou. XLIX

producing spermatozoon, which carries therefore an X

chromosome received from the mother of the F, males

and bears her character. In the present case the male

carries the chromosome bearing red abnormal.

Since red and abnormal dominate, all the F, females

should be red abnormal, except in so far as the conditions

suppress the abnormal and induce the normal type. The

experiment, Table I, shows that very few normal females

were present.

Four classes of males are expected—the large class of

non-cross-overs RAb and WN, and two small classes of

cross-overs RN and WAb. It will be observed (Table I)

that the linkage between R and Ab is very strong, since

nearly all of the males are either RAb (647) or NW (664).

Only a few crossovers RN (25) and WAb (13) males

were present. The percentage of crossing over is 1.97

per cent. when the abnormal males alone are used for

calculation.

In the reciprocal cross the RAb male was mated to

WN female, and gave in F, RAb females and WN males.

The F, record is given in Table IT. —

TABLE II

PARENTS: RAb g By WN?

F,: RAb9—WN ¢

RAb WN RN WAb

By 9 J 9 a g Ty

68 62 59 47 1 0 2 1 Il:

38 69 68 0 3 0 1 II20

115 170 130 147 2 2 2 2 IIa

03 103 97 103 3 7 4 2 II

75 96 94 49 2 1 5 0 Tis

399 486 449 194 8 13 i ro Gt

Since the same two pairs of factors enter as before,

the same chromosome diagram will suffice for the gametes

of the F, female. The F, male is, however, a double re-

cessive (WN); in consequence four classes of females

are expected as well as of males. The gametes of the

F, female are as before the following:

No. 583] ROLE OF ENVIRONMENT IN DROSOPHILA 395

Non-cross-over RAb Crossover RN

gametes WN gametes WAb

The percentage of crossing over as calculated from

the abnormal classes (males and females) is 2.1.

In order to obtain further data for linkage the pre-

ceding experiment was repeated in the winter of 1914,

but the linked factors entered differently combined. The

experiment was begun by crossing white abnormal fe-

males to wild males which gave red abnormal females

and white abnormal males. These were inbred and gave

the following results in five different cultures (kept with

abundance of moist food).

TABLE III

PaRENTS: WAb? By RNG

F,: RAb 9—WAb g

RAb | WN RN | WAb

No. | RESCUERS US ARLENE reas

a | 9 Pee ce fhe ee ee ee

1 0 44 0 2 33 0 52 55

2 4 66 0 0 Sl s 57 50

3 1 38 0 0 62 0 37 48

4 1 lil 7 1 95 0 77 100

5 1 65 2 0 65 0 | 34

Total | 7 | 324 oe 312 4 | 251 | 287

The sum of the two non-cross-over males (251 + 312 =

563) plus the cross-overs (16) divided into the sum of

the cross-over males (7 +9—16) gives 2.7 as the percent-

age of crossing over. Since the white normal males

may receive contributions from the changed white ab-

normal, the result may be freer from error if the two

correlative abnormal male classes, viz., red abnormal (7)

and white abnormal (251), be utilized to calculate cross-

ing over. Dividing the former by the total (251 +7) —

gives 2.7 per cent. of crossing over which is the same as

the preceding estimate.

The reciprocal cross, RN 2 by WAb ¢, was also made

once and the results in F, combined with other similar

results are as follows:

WAb RAb WN

a ọ g g g g

1,220 (withRAb) 854 20 1,323 89

396 THE AMERICAN NATURALIST — [Vou. XLIX

The other results were obtained in the following way:

The abnormal red eyed F, females obtained from the

first experiment are heterozygous for abnormal (AbN)

and white (RW), except in so far as this class may

contain cross-over flies that are heterozygous in white but

homozygous in abnormal AbWAbR. Except for these

flies, these F, females are like the F, females, and if

mated to abnormal white males will continue in each

successive generation to give the same linkage data as

do the F, classes above. If bred in pairs exceptional

females homozygous for abnormal will be at once de-

tected, and can be thrown out; but even if bred in small

batches of four or five females the chance is small of in-

cluding homozygous abnormal females.

In these counts no separation of the normal red fe-

males (when they occurred) from the abnormal red females

was made but the red females were put into the latter

class. Since the females were not intended to be used

for comparison this grouping does not affect the prob-

lem involved. If we divide the cross-over red abnormal

males (20) by the abnormal white males (854) plus 20

abnormal red males, we get the per cent. of cross-overs

which is here 2.3. This is slightly lower than that ob-

tained for the preceding data.

Black, Red, Abnormal by Gray, White, Normal

Another series of experiments, carried on for a some-

what different purpose, may be utilized here for further

data. Gray, white, normal females were mated to black,

red, abnormal males. The daughters were gray, red,

normal (or slightly abnormal), and the sons gray, white,

normal. Inbred they give the results shown in Table

IV. Since the factor for black is not sex-linked, the

gray and the black classes may be added together as

shown in Table V.

The results differ from those of Table II in the follow-

ing points: There are relatively more red normals which

may be assumed to be due to the external condition pre-

No. 583] ROLE OF ENVIRONMENT IN DROSOPHILA 397

TABLE IV

PARENTS: BRAb g By GWN 9?

F,: GRN or SLIGHTLY Ab9—GWN g

GRAb | BRAb | GWN | BWN GRN | BRN ama

ll SP Sat aes

PPL A] Ph Pe ta pigaa e|elelale|

35| 63) 7| 8| 160| 170] 48| 58|126 |146| 54| 43|...]...| IIs

50| 78} 6| 16| 111| 104| 34| 18| 48| 30| 34| 28 efes III29

65 | QO} 1] 221) 187| 13| 7/181}159| 11] 16; 1: Hi

187 |152| 27| 36| 254) 268| 58| 72|,102| 99| 45| 65 4/1) UR

33| 56| 12| 12| 37| 63| 15| 10 0] 0] o|...|...} Ie

103 |140| 34| 34| 146| 191) 52) 42| 54| 52| 21| 14| 6| 1| IIIs

50| 33| 14| 10] 93| 69| 22| 24| 30| 24| 7| 6j 1|...| Ils

8} 71| 0 2) 76 123) 20 40| 80| 66| 27| 61]...|...| IIs

91| 74| 17|- 16| 89| 89|-30| 45| 75 | 66| 79| 59| 1|...| Ie

92| 88|:27| 24| 135| 153| 33| 59| 62| 76| 19| 20|...| i | Tse

2 8 3 7] | 4 0) 0; 0)...)...) Ex.

_82| 95| 32| 23| 195) 191| 47| 65| 66 66 | 94| 34 29}... 1 | ihe

| | |

798 899 182 |185 1,524 1,625 375. PEE

vailing at the time, or else the black factor may have had

some influence that is favorable to the normal condition

in the heterozygous abnormal flies. If the latter were

the true explanation we can understand the large num-

ber (here) of the GRN class (for two thirds are hetero- -

zygous in black and intermediate in color) and the com-

plete absence of the BW Ab class which should be one third

as frequent as the GWAb class.

was made to test this possibility and will be described

TABLE V

PaRENTS: BRAb BY

A special examination

GWN?

F,: GRN or sLIGHTLY Ab9—GWN ¢

RAb WN RN WAb |

F Q F ọ F Q oo]

42 60 208 237 179 1960 E (oT

56 94 145 122 82 PE ean Saliva! Iie

65 53 234 194 142 175 ii Dhi

214 188 312 340 148 64 4 1 | Ile

45 68 52 } GE rr i ae II Tio

137 192 198 233 75 66 6 i | die

64 43 115 93 37 30 Looe Wa

8 73 96 163 107 iT peo | Ils

108 90 119 134 154 125 io) Die

119 112 168 212 81 E Í IIIso

8 11 10 cy Oe RE E © POC cee A Cana, Extra

105 118 242 256 100 cj to B

S41 | 1,102 {| 1,809 | 2065 { 1,105 | 1,168 | 13 | & |

398 THE AMERICAN NATURALIST [Von XLIX

later, but it may be stated beforehand that no certain

evidence could be found in favor of this view. The num-

ber of larvæ in a culture brings about a rapid alteration

in the condition of the food, so that it changes more

quicky from an acid to a neutral or alkaline condition.

If the black flies used gave vigorous F, offspring the

effect in question could be explained as due to numbers,

and not as connected with the black factor.

Gray, Red, Abnormal by Black, White, Normal

The results of this cross and of its reciprocal are given

in Tables VI and VII. The RN class (cross-over) is

relatively too large, but the increase is due to the transi-

tion from abnormal to normal.

TABLE. VI

PaRENTS: GRAb@? By BWN GC

F,: GRAb 9—GRAb J

Grab | BWN | GwN | BRAb | GRN | BWAb| GWAb | BRN _

glelalelalelalelalelalele|e lal 2

95 |194| 49 | 2 |163| 1 | 20| 32 | 56] 71 |...1...| 4 |..... | 24 | 45

PARENTS: BWN 9 By GRAb¢

F,: GRAb d—GWN 9°

215 |143| 91 | 91 |314 |276| 56 | 11 | 28 [azol...[...)9 | 2] a | 50 _

THE LINKAGE oF ABNORMAL, YELLOW, AND WHITE

, 2

In the following crosses three pairs of sex-linked fac-

tors characters are involved, viz., yellow, white, abnor-

mal and their normal allelomorphs whose location at one

end of the X chromosome is shown in Diagram II.

DIAGRAM II.

Gray, Red, Abnormal by Yellow, White, Normal

When a YWN @ is crossed to a GRAD ĝ the daughters are

GRAb and the sons YWN. The F, male is a triple re-

No.583] ROLE OF ENVIRONMENT IN DROSOPHILA 399

cessive, hence, neither his female-producing nor his male-

producing sperm affect the dominant characters that the

eggs carry, and in consequence the entire F, count, fe-

males as well as males, are indicators of the gametic

composition of the eggs of the F, female. The F, results

are given in Table VII.

TABLE VII

Parents: GRAb g By YWN 2?

F,: GRAb 9—YWN ¢}

YWN GRAb |YRAb| GWN | YWAb| GEN | YRN | GWAb |

gleleleleleleleleleleleleleiele!|

1; 45| 59| 44| 51 | Be ee ae a ee Se ae Iı

21 831 OO) a BB. T W iss diesters Is

3| 115| 107| 132) 150 1} 2|-..]...1 @| 6] 4} T I;

4| 174| 177| 152| 205 2| 5| 2] 4...) 6 9...) 1)...)... Iio

5| 100| 128| 108| 150 TiS Sra a o oa In

G| 42| -52| 58| 4 SR Ge Bee ie cee ne ee 3

7| 92| 94| 105| 114 WI r A r. 6

8| 105) 180| 123| 97 B41 die AB oe es) Basle s

9| 83 78| 92 eit Sore a> S ak bone 9

10; 83) 81) 90| 107 Lt Bt A e 10

11| 375| 374| 441| 443| 1| 6| 4| 3| 5| 7| 22| 14)...)...|...)... u

12| 103| 127] 125| 136| 1|...|...|...| 2]...] 7 81|- 12

13) 135) 116| 119| 169/ 1] 1}...) T T 9) Bo 13

14/ W01; 92] 116] 105) 1| Irop e 4} WA a 15

15| 29) 56 Pic th wie Sa 18

16; 45; 58, 50| 77 $d AB linet ales sie o 19

ee Se me a | ae aD pee Ge ees A | as A A a a

t8; 31) 45; 30 1 Pia ifi cae 1 | Iss

19| 236; 231| 283| 276| 6| 2| 4| 3| 9} 1) 6 6...) 1)...|... 27

20, 47) 31 eres ee ren ee eo 30

21; 66; 79; 101| 64/...|...) 2] Apin 17) 52)...).-.)--.)--- a

22| 325; 307| 209| 250| 1| 1| 3| 2| 1)|.../139/251) 2 | 1 |. | IVs

23| 286| 184| 233| 321| 6| 2| 5| 3| 2| 2j197/191| 1 | 1 |...| 1 |IVs

2,734 2,744 2,773 3,008 | 22 | 45 | 30 | 33 | 43 | 21 |478/644, 4 | 8/0 2

a | Ba khob a {oOo

The relation of the classes to each other is evident from

the following diagram (III) which represents (as before)

G Ab

EMD EE nas

DracRaM III.

the sex chromosomes of the F, female. The classes of

gametes of the F, females are the following:

400 THE AMERICAN NATURALIST [Von XLIX

Non-Crossovers Single Crossovers Double C

YWN YRAb YRN

RGAb GWN GWAb

YWN

GRN

In this and in the following tables the order of the cross-

over gametes is always given the same, viz.: the first

factor to the left above (Y) joins the two following below,

R and Ab, (taking the switch as it were at the first cross-

over). Then follows the cross-over that is the converse

of the preceding (the first factor to the left below switch-

ing over to join W and N). The second crossing is taken

in the same way, thus Y and W switch over to Ab, and

conversely G and R switch over to N. The double cross-

over takes the switch twice; thus Y to R and then to N;

and conversely G to W and then to Ab. The F, flies

should correspond to these gametic classes (since the F,

male was a triple recessive) except in so far as the ab-

normal classes change to phenotypic normal types. Thus

the non-cross-over class GRAb will, in this sense, con-

tribute to the single cross-over class GRN; and the single

cross-over class YRAb to the double cross-over class

YRN. The last-named class can not, therefore, be used as

a measure of the double crossing over, since it is more

probable that any flies of this kind that appear will be

only phenotypic YRN, than that they should belong to

the YRN class genetically. Only the GWAb class may

be used as a measure of double crossing over, and, as will

be shown below, much caution must be used even in this

case.

It will be seen in the table that only relatively few of

the GRAb type have changed to the normal type, because

the conditions were favorable for abnormal although the

cultures ran in most cases for ten days, but during this

~ time they still contained plenty of wet food. It will be

noticed that the changed class GRN corresponds to one

of the single cross-over classes, consequently GRN is a

mixed class, and can not be used to base any calculation

on. It is true, one may roughly determine how many

No.583] ROLE OF ENVIRONMENT IN DROSOPHILA 401

cross-overs are expected in this mixed class by compari-

son with the other single cross-over class (YWAb).

these are subtracted, the remainder shows how many of

this GRN class are due to a change from the abnormal to

normal. Another point to note is that one of the double

cross-over classes, viz., YRN, is likewise subject to addi-

tion from the single cross-over class, YRAb, and can not

itself be taken as a measure of double crossing over, while,

on the contrary, all cases in the other double cross-over

class, viz., GWAb, count for their full value. Only two

such double cross-overs occurred.

On the basis of the amount of single crossing over it is

possible to calculate, as Sturtevant has shown, the ex-

pected number of double cross-overs. The number of

the double cross-overs (two) in Table VIII is larger than

expected. I repeated (December, 1913) the last experi-

ment to test the question because abnormal arrangement

of the rings of the abdomen is not a very rare occurrence

and may sometimes be the result of injury to the larva or

to the pups, or in still other cases may be due to other

mutations, some of which will be described later. The

abnormal mutation itself occurs not infrequently under

conditions precluding contamination. In repeating the

experiment extreme care was taken not to classify any fly

TABLE VIIT

ParENtTs: GRAb g BY YWNQ

F,: GRAb 9—YWN ¢

| YWN GRAb YRAb GWN YWAb GRN YRN | GWAb

lelelelelalelale|elele|elielelale

A 58| 64| 57 6L O06 1067 8 1-oy i

D 60) O71 461 O81 oi 45 1 OT OTe rf i

E 79) l 601 7601-86 OB 1) 8 8

F O7| 921 SB) 7111] 91119] eo 3f 1] $

H Sti 40) 47) ilr oroo 0r eT a

J O71 SO) Set BOT it 72 te Or 1i eS

K 65 Bist OF11o} 21 OF: 1] 2

L 83 901116 [126° 9 6-04 1 Oa Liù 4i 3

M 74 765101 9100] 3| $| 6] 3

N 40; 51| 3881 6710] 01010] 0} 1} 3) 8

Totals .| 605 |675 |625 |683| 9 | 10| 5 |5 | 16 | 12 | 24/| 24,/0/0/0) 0

402 THE AMERICAN NATURALIST [ Vou. XLIX

in the double cross-over class as abnormal unless there

could be no reasonable doubt as to the nature of the char-

acter. In case of doubt the flies were tested by crossing

again.

As before, yellow white normal (abdomen) females were

crossed to gray red abnormal males. These gave in F,

YWN ¢ and GRAb 2 which inbred gave the results shown

in Table VIII.

The double cross-over class is GWAb. The combina-

tion did not appear once amongst the 2,690 flies that are

recorded in F,. The percentage of crossing over between

Y and W is 1.0; that between W and Ab was 2.1. The

expectation of double crossing over on this basis (without

interference) would be .02 per cent., or about 1 in 5,000.

But the expectation would be far smaller than this be-

cause of a principle that we call interference. We mean

by this term that should a cross-over occur at one point

the chance of another occurring near it is greatly dimin-

ished, because if crossing over is due to twists of the

chromosome the length of a twist would usually preclude

the occurrence of two cross-overs near one another. In

other words, if the loop that makes the twist is more likely

to be of a certain length then the likelihood of the occur-

rence of a small loop necessary for a double cross-over is

very small. In two cases, B and C, the F, counts (from

pairs of F, flies) gave no YWN males as shown in the

next counts.

| -YWN GRAb YRAb GWN YWAb sires

le@[efele|e| Ps ee

pei

a o| | | at |i pee fed due

49 | 47 | 47 | 0 t2 be 1S.

The absence of the YWN males, when the other classes

showed that no error in the experiment had been made,

was not understood until the occurrence of lethal factors

was worked out. Here clearly a lethal factor in the YWN

grandmother has been carried over into her GRAD

daughter. The lethal factor must have been closely

eo;

oo] +70

No. 583] ROLE OF ENVIRONMENT IN DROSOPHILA 403

linked with yellow and with white. The F, YWN son of

the original YWN female must have come from the other

sex chromosome of the YWN female—the one that did

not carry the lethal. The count of the males in the F,

gives both in B and in C a 2:1 ratio which is the charac-

teristic ratio for a sex-linked lethal. The reciprocal cross

was also made, but only twice; the F, counts are given

in Table IX.

TABLE IX

PARENTS: GRAb? By YWN g

F,: GRN@ (or suicHtLy Ab)—GRAb ¢

gigialelalelale|alel a] jalelale

141 |---| 165 | 339 | we CA eee k 59 [10 AR

202 Joo: O86 1:86) [8s |. e be Fao Ie ME Se es Boe

The expected gametes of the F, female are the same, of

course, as before, but the male contains all three sex-

linked dominant factors, GRAb. Consequently in F, half

of the GRAb female class is pure and half is heterozygous

for abnormality. The GRAb F, males, on the other hand,

are all pure, in the sense that they have only one factor

for abnormal and no factor for normal. It is probable

that most of them here are phenotypically abnormal.

The relation of the non-cross-over and the cross-over

gametes is the same as in the reciprocal cross, since only

sex-linked factors are involved, but the cross-over classes -

given in Table IX are different in the female classes in so

far as the female producing sperms, that carry GRAb,

contain three dominants. In one of the two counts given

in the table the cross-over class that has changed to

phenotypic normal is relatively large; in the other count

it is small.

Gray, White, Abnormal by Yellow, Red, Normal

The next largest series of experiments involves the same

three pairs of characters but combined in a different way.

The results are shown in Table X. Diagram, IV shows

the relative positions of the factors in this combination.

404 THE AMERICAN NATURALIST — [Vou XLIX

Y R N

Pe (eS

G:. W Ab

DIAGRAM IV.

The gametes produced by the F, female are the following.

Non-Crossover Single Crossover Double Crossover

Gametes Gametes Gametes

R YWA WN

GWAb GRN GRAb

YRAb

GWN

The classes of special interest are non-cross-over GW Ab

males which change as the culture gets old into GWN

(which is a single cross-over class), and GRN which is

the corresponding female class (but heterozygous).

TABLE X

PARENTS: GWAb ¢ By YRNQ

F,: GRAb? (to N)—YRN ¢

YRN GWAb YWADb GRN YRAbDS; GWN YWN GRAb

Cre CPI eit Se Ss Se eee reer ee

Yee” 7g Dg ei thy ete 2145/1 Bh ea Oe ae

410) 404) 3201.. Tt. J101 185i Pie et Tr. Aa] 90i

G2) OTE WWE er e e Eeo e l 124 | IIIa

327) 123) 50 St p 1 56 T. 130 | IIIs

196| 181 1i eae) 8 Saol 239 | Iles

234| 286! 168 Te 166. bk 69 Ad 151 | IIs

108! 149 1k ae. 49 in er 79| III;

321| 381| 218 Lit St 90i 3) 208) ie 259 | IIIsz

158; 167 Pt Oe ee eee ie 96| III

178| 169 1-81 m6 3i 10 Pe 62) IIL

185| 181| 107 ele Ciera: igs ee 119 III

109 H ai oor a4 I 28 t 114 | IIIs

189} 185| 141 ie Tt 4a 27 De 172 | IIIs7

332| 322) 233 SiO) mi3 i 27l. a 309 | IITs

279| 19 .| 6| 324]. 1s FOS Fees: 14| IIe

147| 144) 98 .| 6} 169). 661... a Is7

236| 221| 244 Sl Iba: 56). Lia, 241 | Illes

30} 25) 19 ees ti. GSE Gee Be 19 IIIz7

230| 227| 97 bie | 16i... V6 3h 86 | III79

106} 80| 74 ip aii 43 $i; 30 | IIIo

130| 115 Ta iL: ERL 64 IIl»

111| 128| 82 2 e 42i ti 2 61 | III»s

83 Hai g ooo Peg 47

225| 202! 100 SoTa IB a: 94

4,205/4,409/2,677 |. ..| 13 |. . .| 85 (2,521 |61 | 8 |1,552| 5 |20|...| 2 |2,817

No. 583] ROLE OF ENVIRONMENT IN DROSOPHILA 405

An examination of Table VI shows how extensively

changing took place in almost every one of the experi-

ments. The contrast with the result of Table V is very

striking.

w Ab

G R | N

Yellow, White, Abnormal by Gray, Red, Normal

The experiment was made once one way (Table XI) and

seven times reciprocally (Table XII). In the first case

TABLE XI

ParENTS: YWAb? By GRN J

F,: GRN 9—YWN ¢

_GRab | ywn | GwN |YRab| GRN | ywab | GWAb| YRN |

glelalelalelalele|ele|eialelale|

3 |105| 58 | 25 {11/1 |...1 2 |167/145| 741 47 |...131 5110 | Tes

nearly all of the GRAb females are of the normal type.

The only GR males that are abnormal are single cross-

overs (Diagram V). This means that the heterozygous

females are affected more easily than are the pure males;

TABLE XII

PARENTS: YWAb<o By GRNQ

F,: GRN 9—GRN g

GRAb YWN GWN YRAb GRN | YWAb GWAb YRN

a |elelelelelelela|elalelelelale

j f pe

re tb Si. cL e sw ck is a s

ost s] I i 4 OUR ais gi oe El i

idee. alila na er a e e ae

1 aiak do oed A AOS a a

3 69| 40|...| 5]. 488! 648| 59/...) 6 |...) 3 III;

a7 i. at 67| 113|.. aata IIs

1 OL sko Jr. ; 219| 249| 36 1 | 1|...| Uls

| j |

Total S 174 s08 1 isi a. 1,489/2,320| 169 !...| 9 Be a.

4 There is an exceptional case in the table, viz., two GWN 9.

406 THE AMERICAN NATURALIST [ Vou. XLIX

but even amongst the females a large percentage of gray

reds are normal. The yellow white abnormal class is

relatively much more abnormal, i. e., relatively fewer

have undergone the transition.

The results from the reciprocal cross are given in the

next table. Here the F, male contains two dominants

(GR) and one recessive factor (N). The females GRN

YWAbD carry only one dose of Ab, yet they are largely

abnormal. The GRAb are single cross-overs.

Yellow, Red, Abnormal 2 by Gray, White, Normal 3

Only one experiment of this kind was made, but as the

number of F, flies was rather large the results may be

given (Table XIII).

Y R Ab f

DiacramM VI.

TABLE XIII

PARENTS: seperated BY GWN 9?

: GRAb9—GWN ¢

O GWN y YRAb GRAb YWN GWAb YRN GRN YWAb

S/S Pi ePlaelegilelelalelaelelale|e| 9

166 | 171 135 |.. a A oe a ala a 1 | 36

taisi a hee ee a a | 31

31013151179... J. ee ee ie 2 8

217 (223| 165 |...-| 1 |1aO | Pee Bole. hes 1 | 101

791 | 824| 662 |....|...,1718] 8 |....1 7.18 lect...) 2 1268

In this cross the gametes are as follows:

Non-Cross-over Single Cross-over Double C er

GRAb GRN

YRAb YWN YWAb

GWAb

YRN

The F, male is @WN and contains, therefore, one domi-

nant sex-linked factor, viz., G. Therefore, all of the F:

No. 583] ROLE OF ENVIRONMENT IN DROSOPHILA 407

females are gray. The F, male classes alone can be used

for testing the extent of crossing over.

CHANGE OF TYPE AS THE CULTURE GROWS OLDER

The preceding tables do not bring out the change that

takes place as the culture gets older—a change by which

the abnormal classes become replaced by the normal

classes. A few results will therefore be given in detail to

illustrate this relation.

In none of the relatively few counts in Tables I, and II,

involving two pairs of factors (RN and WAb), was any

change in type during the time of the experiment noticed;

but in other cases a very marked change was observed as

the cultures grew older.

In the two following tables consecutive counts of the F,

flies (from YRAb g by GWN @) emerging from day to day

from the same culture are given. The change of the

YRAb to the YRN and of GRAb to GRN is very striking.

TABLE XIV

PARENTS: YRAb¢ By GWNQ

F,: GRAb 9—GWN ¢

YRAb | GWN | YWN | GRAb | YRN | GWab |YWAb| GRN

essere | | | AD EEEE

giejalelalelalelale/a|ejaleja|e¢

eS ME Ob ae, a) OB) Fo Pa

AFA) Md i BO Be A ee othe

7 19| 34|. Ba ee haa ae ed

135| | 116/171 16618 PS

Tins t ak BLY sl.) | 1

38|...| 39| 39| 1 43

33| 38 64. 1

40 36| 27 36 +

63| 51 6| 74 81

179|...1216|210| 2 |...|...1992| 74 |...| 2 | E A 88

In the next table two F, counts are given derived from

GWN È? by BRAb ¢ grandparents. The GRAb changes

to GRN and BRAb to BRN.

408 THE AMERICAN NATURALIST [Vou. XLIX

TABLE XV

PARENTS: BRAb¢ By GWN@

F,: GRN@ (or sLIGHTLY Ab)—GWN g

GRAb GRN BRAb | BRN | GWAb | GWN | BWAb | BWN |

Counts ' r i |

g|alelalelale|alelaleialelae.

| I

E T T a a Ea TrA

e oie) Oli! Bet ar at.. 0t. | 2]

3 | 1| 0| 17/24] 0| ot 6| 7|...|...|15|24 21 /6| HIG

4 | O| 0} 36|40| 0| of15|12)...]...)41)30]...|...]15 | 22

5 | 6| 3/76 \71 o| ol31 20/...|.../67)81)...|.../28 21

1 | 19} 24] 1] o/11| 6| 2| o.. 23 |20 .| 10 | al)

2 | 26|28| 0| 0| 7\10| 0| ol.. 60|20| 1 |...| 912|

3 |29|30| 0| o| 8| 2| 3| 0l.. 28 |37 lth Titans

4 | 8/13] 2] 0] 6| 5 Shet 11 |14 | 4| 4|

5 | o| o| 27 |43| 0} opn.. 32 42 Telr

6 | o! olis oO! of17/16|...'... 51/49 [10 21 |

In the next case eight consecutive F, counts are given. The

GRAb changes to GRN. In the first three counts there

are 221 GRAb to 76 GRN, or 3 to 1. In the last three

counts there are 148 GRAb to 296 GRN or 1 to 2.

TABLE XVI

arrr GRAb ¢ By YWN 9

RAb 9—YWN

e SAIL O1AIL O14] 9 9 | FIO AIL APIA] G

106 | 90}. 011100! 0 | 6.1 4.1 Eroro 1-167 BE) Ett

301-37) -17)-190)-0-1.6 1616 1-04-06 o 397 0 4:0

O21 36 281-611-076 i eT 81 6 aj 400

PID e Hororo 00o or aloro

5-4- 1i 1 04.6 | oloo] ó 37414 E,

6zi GB) 14) l0 loiil 1i 0i olizo

47| 28| 23| 27 0 | 0 | 0 | 0 | 0 | 0 | 18| 36] 0 | 0

42| 63| 35 39 | liit Oio 0o] 4160 01-0)

} * f —

325 | 307 | 219 250| 1 iiaia Lo oam of 0 1 8

Finally six cultures are given in the following table of Fz

flies from YRN 2 by GWAb ¢ grandparents. The GWAb

males change to GWN males and the GRAb females to

GRN females. In both cases the increase in the normal

flies in the last two or three counts is marked.

No. 583] ROLE OF ENVIRONMENT IN DROSOPHILA

F,: GRAb 9—YRN ¢

TABLE XVII

PARENTS: GWAb od By YRN?

409

YRN | GWAb |YWAb| GRN | yrab| GWN | YWN | GRab

ue alelalele|elele|alelelela|e¢

ics} 4) 48) a ak i a Da Bae ee ee S | 46

w 88) SS aes Pap ee Nee ar hat ee | 73

ee ai aes Nr ae oe rp eta ES Gage eS Oe ae A 57

me err oe es Be Re ade ae 35

| sej OB) SBP Lee see 31}. | 1 | 3

25} 88) OO a 1| 10). EME Ree OS oo 3

60} 49] 49|...]...|... ‘eee oe age Meeks Sah EH 11

87) AO) BBL daia: Sea ee ie Wit a

38; 43/2...) 1)... seen ae rd te a ek a re

T E et Be ST ae We es te ee oe ee sais

: | |

Wisc.) a r nie r. a a | 80

36| 43] 28). Ee E a 44

50| 46| 20). ...| 29 es ye en 24

29| 48] 6l. xag a. z

75| 98} 53l. 14] 88 ro eae 3

His... 28 33 oii; he e ee pera a | Dn RN E 46

art a a ee as mt pee | eas coe 48

arte See LS Gand lol 2

42| 31 Shei 4a. a ee e Meee Sir mcr) Sean

10} skad hash as 26 30 2).

Mia. 36) w aklo 6| 2 re oes bed Sar 39

96) 994 gels Bed. 47 |. a ree aS i

Syl dil al did i. 1g RO a O82 4

63} 68| ol. whe ae a Og T aN ee ae

g a pk 8| 23 pale

Tw) s AL wk da eh a

144| 181, 126 oo E Pe Be 8 41

97 78 2. 16l VEEL AE 3 Ji. 187

43] 2l l. ad ds al eat SE 81

IIIz9... 46 39 47)|. OAS BE || Bt Be) Saray came A 65

23| 24| 28 ila eek Ba 19

18| 12] 17) CAL el aod: 1

il B 8 ke 1| 12 iat 1

$2) w o. bes ee 56 i. 2

62 erie oe Oa, ae 46 . 63 i

a a o l 1| 9.. 40l il

1,431 |1,608 |1,101 |...| 6 |...137/687| 7 | 2 1631! 0 |11' 0 | 0 | 938

TESTS OF CHANGED-OVER CLASSES

In a number of cases in which some members of an ab-

normal class changed over to become phenotypically

members of a normal class; some of these apparently

normal flies were tested under conditions favorable for

the appearance in the next generation of abnormality.

410 THE AMERICAN NATURALIST [Vou. XLIX

These cases may be given. Two kinds of crosses are ex-

pected. In a few cases the normal will be found to be a

true normal (single cross-overs) and give therefore only

normal offspring when bred to normal (recessive). In

other cases the expectation is for abnormal offspring,

and where change of type has been extensive, these kinds

will be in the majority.

In experiment II,, one gray red normal female when

tested gave GRAb J and 9.

In experiment I, seven GRN 2 were bred to BWN g.

Four gave some abnormal offspring and three gave only

normal offspring.

In experiment I, five GRN 2 were tested. Three gave

some abnormal, two gave only normal offspring.

In experiment II; seven GRN 2 were tested. Four

gave some abnormal offspring, and three gave only nor-

mal offspring.

In experiment IIT, one GRN ¢ tested gave some ab-

normals,

In III, one GRN 2 bred to YRN g gave some GRAb gg

and 99.

In III; some BRN ¢ were bred to their BRN sisters.

All BR offspring were abnormal.

In IIT,, GRN 2 paired to GRN ¢ gave GRAb ¢ and &.

In III, GRN Ẹ bred to GWN brothers gave GRAb 2

and GWAb ¢ and 9.

In III,,; GRN ¢ to GRN ¢ gave GRAb ¢ and 9.

In III,, GRN 2? by GWN ¢ gave GRAb 2 and GWAb 3

and 9.

In III, GRN 2? by GWN ¢ gave GRAb 2 and GWAb J

and 9.

In III,;, GRN 2 (17) by GWN ¢ (4) gave the same re-

sults as the last. .

In III,;, GRN 2? X YWAb ¢ gave GRAb ¢ and 8.

In I.s, GRN 2? to GWN ¢ gave GRAb ¢ and 2 and

YWAb ¢ and 9.

In II, GRN 2 to GWN ¢ gave GRAb ? and GWAb 3

and Ẹ in three different tests.

No. 583] ROLE OF ENVIRONMENT IN DROSOPHILA 411

In IIT,, one GRN ¢ (the only one present) when tested

gave GRAb J and 2? and GWAb g and 9.

In ITI,,, GRN 2? to GWN ¢ gave GWAb ¢ and @ and

GRAb 2.

These results show without any question that in the

great majority of cases the phenotypic normal class (when

abnormality is expected) is in reality made up largely

(entirely, except for cross-overs according to expecta-

tion) of genotypically abnormal individuals. Their ab-

normality is shown by suitable breeding tests such as

those here recorded.

INFLUENCE OF THE FACTOR FOR BLACK ON THE REALIZATION

OF THE ARNORMAL CONDITION

Some of the evidence seemed at times to indicate that

flies heterozygous in black are less likely to show the ab-

normal abdomen, but even if this is true it is still uncer-

tain whether this might not be due to other conditions

than those caused directly by the heterozygosity for black.

It might be that the black stock contained other factors

that influence the cross. Moreover since the number of

eggs laid by a given kind of female determines how many

larve will appear in a given time, and since the relation

of the larve to the food is an important factor in the

results, it seemed hazardous to put any emphasis on such

results.

In order that the heterozygous flies might be reared

under conditions that the control showed were favorable

for development of the abnormal condition in homozy-

gous forms, some black, red-eyed normal females were

mated to gray, white-eyed abnormal males. After the fe-

males were fertilized they were put into a new bottle with

some of the stock white-eyed females (fertilized). Some

‘of the daughters were red- and some white-eyed; all of

the latter were very abnormal, but the red-eyed females

(heterozygous) were all normal through five counts. At

the fifth count the white-eyed males that had been ab-

normal up to this time became normal. The result is in

accord with many similar observations; for as conditions

412 THE AMERICAN NATURALIST [Vou. XLIX

alter, the abnormal males first change to normal, then the

heterozygous females, and lastly the homozygous females.

Several attempts were made to find out if, when the

F, female, heterozygous for abnormal abdomen, is her-

self abnormal, her offspring are more likely to be abnor-

mal than when she is normal. There is evidence every-

where throughout the tables to show that the condition

of the mother has absolutely no effect on her offspring.

In December—January, 1914, the following experiments

were made which are the converse, in one respect, of

some of the preceding experiments since black abnormal

females were used. The crosses are indicated below.

(1) Black, white, abnormal 2 by gray, white, normal g.

(2) Gray, red, abnormal 2 by gray, white, normal ¢.

(3) Black, white, abnormal ? by black, white, normal JZ.

(4) Gray, white, abnormal 2 by black, white, normal g.

The F, females from (1) compared with (2) should

show whether females heterozygous for black (and ab-

normal) are less abnormal than those pure for gray;

provided, white and red eye make no difference in the

development of abnormality. The F, female from (3)

compared with (4) should reveal whether pure black

heterozygous for abnormal are less abnormal than flies

heterozygous for gray as well as abnormal.

The results need not be given in detail. It was found

that the (F) daughters from (1) show the same degree

of abnormality as those in (2). Hence heterozygosis in

black need not have any influence on the realization of ab-

normality. The mothers were not, however, in the same

bottles, but in different cultures kept as much alike as

possible. To this extent the experiments are unsatisfac-

tory. It was found that F, females from (3) were like

those from (4), hence no evidence was found that the

heterozygous type is more affected than the homozygous

black. But here also the flies were reared in different

bottles. In order to overcome this difference, some ab-

normal females that were heterozygous for black were

bred to black normal males (both having white eyes).

No. 583] ROLE OF ENVIRONMENT IN DROSOPHILA 413

The daughters were either heterozygous for black or pure

black, likewise the sons. Hence, direct comparison could

be made. The following protocol gives the results for

four successive counts:

1. Black 9 quite abnormal. Intermed. 2 quite abnormal.

Black ¢ quite abnormal. Intermed. ¢ quite abnormal.

2. Black Q quite abnormal. Intermed. ? quite abnormal

Black ¢ quite abnormal. Intermed. jf quite abnormal.

3. Black Ọ fairly abnormal. Intermed. ? fairl a

Black ¢ very abnormal. Intermed. i very abnormal.

4. Black 2 none present. Intermed. 2 fairly abnormal.

Black g fone quite, Intermed. ¢ quite abnormal.

one fairly abn.

The evidence shows no difference between the extent of

development of abnormality in the homozygous black and

heterozygous black females and males.

In another way an attempt was made to get light on the

same question. Red black females were mated to white

abnormal males; and, simultaneously, red gray females

were mated to white abnormal males. The females were

later put into the same bottle and their offspring reared

together. All the daughters for four counts were normal.

At the fifth count an attempt was made to separate the two

classes of daughters, which is possible, because the off-

spring heterozygous for black are darker than the grays.

The heterozygous pairs were normal or slightly abnormal

while the pure grays appeared a little more abnormal ;

but the difference is hardly to be relied upon, since the

abnormality is less striking in the black flies.

To test this possibilty some of the preceding experi-

ments were carried to F,, when pure abnormal grays, in-

termediate and pure abnormal blacks appear. The most

abnormal grays were no more abnormal than the most ab-

normal blacks, which so far as it goes shows that the

homozygous black flies themselves may be as abnormal as

the grays under the same conditions and with the same

ancestry.

414 THE AMERICAN NATURALIST [Vou. XLIX

INFLUENCE OF THE FACTOR FOR YELLOW IN THE REALIZA-

TION OF THE ABNORMAL CONDITION

Experiments similar to those with black were made

with yellow. Yellow, white-eyed normal flies were bred

to gray, white-eyed abnormal. In ten tests, the F, fe-

males were abnormal in eight cases, and normal in two.

It is not apparent that the yellow factor has any decided

influence on the results. :

In order to compare the females heterozygous in black

and in yellow, and others also homozygous in both, the

four following tests were made. By utilizing the red and

the white eye colors it was possible to distinguish be-

tween the different classes of females. Previous experi-

ments, described above, had made it highly probable, that

no effects are produced by red and by white, but by making

reciprocal crosses here this possible effect was more cer-

tainly eliminated. In all cases the females were mated

separately for a few days to gray, white-eyed abnormal

males to better ensure fertilization and were then brought

together in one bottle.

(1) (2)

Han 2 by GWAb g. ena 2 by GWAD J.

BRN 2 by GWAb Z. YRN@ by GWAb J.

1.{GR 9 Fairly Ab. 1f 3 GRN 9.

GW 9 Fairly Ab. 1 GWN 9.

o (GR Ọ Like last 3 12 GR slightly Ab 9.

GW @ Like last. ‘| 3 GW slightly more Ab 9.

3 {GRQ Like last. 1 GRN 9.

‘GW @ Like last. 3.) 8 GW slightly Ab 9.

| 4 GRNQ.

4) 8 GWNQ

_§ 1 GRN

9-110 GWN 9

{ 2 GRNỌ

6.114 GWNQ

In (2) the females heterozygous in yellow were slightly

more abnormal than those heterozygous in black or at

least they gave such an impression.

No.583] ROLE OF ENVIRONMENT IN DROSOPHILA 415

(3) (4)

em 9 by GWAb g. ee 2 by GWAb g.

GWN? by GWAb g. GRN 9 by GWAbD &.

1.{GR slightly Ab 9. 1 5 GR slightly Ab 9.

ə N or nearly NỌ ‘] 2 GW nearly N 9Q.

"(GW fairly Ab 9. o |14 GR fairly to slightly Ab 9.

3) 5 GRN and 4 GR quite Ab 9.) 6 GW nearly N 9.

L On T quite to fairly Ab. 3.{GR slightly Ab to N9

ra 13 GR i 28 GRN 9.

"F16 ae quite to slightly Ab 9. 3 GWN Q.

5 15 GRN |17 GRN 9.

‘1 9 GW fairly Ab to NQ. ") 2 GWN 9.

K 6 GRN 6.{ 6 GRN 9?

‘110 GWN Ọ.

In (3) the females heterozygous in black were slightly

more normal than the grays. In (4) there is hardly any

difference, but so far as difference is noticeable the hetero-

zygous type (GW) is again more nearly normal. This

difference was even more apparent in a second culture

from the same parents.

THE RELATIVE INFLUENCE OF THE EGG AND OF THE SPERM

ON THE CONDITION OF THE HETEROZYGOTE

At the time when the F, generation began to hatch

the extent of the abnormality in the females was noted.

This was at the time when the flies were taken out to be-

come the parents of the F, generation. The terms used

were necessarily somewhat vague, but give a fairly ac-

curate idea of the condition of the cultures as a whole.

If most of the flies were distinctly abnormal this was indi-

cated by Ab to N, if more of the flies were normal or nearly

so but some were abnormal this was indicated by N to Ab.

If the flies were normal in appearance this was indicated

by N. The results for many of the cases recorded in the

preceding tables are brought together in the next table.

he results are far from uniform, as was to be expected,

but in most cases it will be noted that when the female

was normal and the male abnormal, the daughters were

frequently normal or nearly so, while in the reciprocal

cross the tendency was in the opposite direction, i. e., the

416 THE AMERICAN NATURALIST [ Vou. XLIX

daughters were more likely to be abnormal. These

records were made at a time when no suspicion of such a

relation was present in my mind. If these observations

are to be trusted they mean that when abnormality comes

| abn. | Abn.toN. | N.toAbn. | N.

YWAbg fo CSS Ee eis | 1 7

GRN foc [Gogooonoodns Coen ccc econ 2 (few)

GRAbg fcc 14 2 6 1

YWNo fic rer ease 1 1

BRAbg foc | 3 3 4

YWN9? | >

anisat R A Se iO,

in with the egg the heterozygous female is more likely to

show abnormality than when the abnormality comes in

with the sperm. Conversely the result may be stated in

this way—when normality comes in from the egg the

daughters are more likely to be normal than when the

normality comes in from the sperm. In other words, we

might extend this conclusion and state that the cytoplasm

of the egg has an influence on the soma of the individual

which arises from it, or the cytoplasm plus the nucleus

of the egg has more influence on the next generation than

the nucleus of the sperm.

When this possibility was realized it was evident that

some of the experiments must be repeated under condi-

No. 583] ROLE OF ENVIRONMENT IN DROSOPHILA 417

tions where a more exact comparison between a cross and

its reciprocal could be made. In the autumn of 1913

I went over the ground again with this object in view. It

was found that the F, females heterozygous for abnor-

mality are just as likely to be abnormal when their ab-

normal factor comes from the father as when it comes

from the mother. The extent to which the abnormality

is realized depends on the condition of the food. This in

turn will depend in part not only on its amount but to

what extent it is worked over by the larva which again

depends, in large part, on the number of eggs laid by the

female. To this extent and only in this sense does the

condition of the mother affect the condition of her daugh-

ters. If the females lay too many eggs for the amount

of food thatis present, crowding results and the daughters

show abnormality to a less degree than when fewer eggs

are laid (that hatch) and little competition takes place.

Now the normal female is more likely to lay more fertile

eggs than the abnormal female. Hence other things be-

ing equal the heterozygous daughter of a normal mother

is more likely to be normal than the heterozygous daugh-

ters of an abnormal female (which are therefore again

more like their mother—very abnormal in this case, be-

cause the former mother is more likely to lay more eggs

than the latter). The relation between the two cases is

therefore not owing to the egg transmitting abnormality

to the daughters better than the sperm, but to the number

of eggs likely to be laid by the mother in question.

In order to examine further whether when abnormality

comes in with the egg it is more likely to be shown in the

F, heterozygote, a number of parallel experiments were

made, of which the following are samples:

Gray Rep ABN. ? py Wip g. Gray Rep ABN. ji By Wi 9.

(1) Very abn. g and 9. (1) Fairly abn. 9.

(2) eons (a few slightly ab- (2) Most fairly, a few very abn.

rmal). (3) Most fairly, a few very abn.

(3) Mohini (a few slightly ab- (4) Slightly abn

normal), (5) Slightly abn.

(4) Normal (a few slightly ab- (6) NỌ (40) 1 slight abn. 9.

normal). (7) NQ.

418 : THE AMERICAN NATURALIST [Vou. XLIX

While it is true in the first count above that when ab-

normality entered through the egg there was greater ab-

normality in the offspring, yet this is offset by the counter

evidence in this set that the change to the usual pheno-

type took place sooner in this set than in the others.

This point will be taken up again in connection with other

data.

In order to compare, under changing conditions, hetero-

zygous and homozygous females, some white abnormal

females were mated to red abnormal males, and, inde-

pendently, some other white abnormal females were

mated to red normal males. After several days both

kinds of females were separated from their respective

males and put together into a single new bottle. All of

the daughters had red eyes. In the first count two types

of females could readily be distinguished. Some were

quite abnormal, others were slightly abnormal or normal.

In the second count (next day) again two types appeared,

one quite abnormal and the other slightly abnormal fe-

males. In the third count some females were fairly ab-

normal, the rest normal and this held for the fourth

count. The result leaves little doubt that under these con-

ditions, the homozygous were abnormal and the hetero-

zygous less abnormal or quite normal.

In order to see if the factors for red and for white

affect the condition of the zygote, homozygous for ab-

normal; white abnormal females were mated to red ab-

normal males, and, separately, other white abnormal fe-

males to white abnormal males. After several days the

females were put together in a new bottle and the males

removed. Through five consecutive counts the red and

the white daughters were alike, at first quite abnormal,

later nearly normal. Red and white abnormal females

therefore behave alike.

PRESENCE AND ABSENCE

It is not without interest to examine the bearing of

these results from the point of view of the ‘‘presence

No.583] ROLE OF ENVIRONMENT IN DROSOPHILA 419

and absence’’ hypothesis, even although I myself prefer

a more non-committal form of factorial interpretation

than that offered by the ‘‘presence and absence” theory.

The abnormal male (Ab) has one dose of abnormality

and the degree of his abnormality is the same as that of

the female (Ab, Ab) with two doses. But the hetero-

zygous female, AbN, has only one dose (or factor) for

abnormality. The degree of abnormality that she shows

is very variable ; she is less abnormal on an average, than

the abnormal male.

Which condition is to be interpreted as absence—the

real absence of one Ab in the male, or the absence of one

Ab in the other (normal) chromosome of the female? A

moment’s thought will show, however, that nothing of any

value can come from a discussion of this question, be-

cause the heterozygous female (AbN) differs from the

male not simply by the factor N, but by a whole chromo-

some including amongst other factors a factor which in

duplex produces a female. Moreover, an advocate of

presence and absence might maintain that the relation

of a dominant to the normal allelomorph is not the same

as the relation of a normal allelomorph to a recessive for

it is the latter that is ‘‘absent.’’ In other words, he might

conceivably accept the hypothesis of absence for a reces-

„sive, but reject it for a dominant mutation.

I have pointed out elsewhere that it seems to me un-

warrantable to interpret the absence of a character to

mean necessarily an absence of a factor in the germ

plasm.” Yet this literal interpretation of the presence

and absence hypothesis has often been made. If the

linear arrangement of factors in the chromosomes be ad-

mitted as a plausible hypothesis the absence of a factor in

this literal sense would mean a hole in the chromosome,

and a corresponding displacement of the linear sequence

of factors. The evidence does not support this hypothe-

sis. On the other hand, if the locus of a factor be con-

5 Although of course a changed factor might cause the failure of some

substance to develop that is necessary for a given reaction.

420 THE AMERICAN NATURALIST [Vou XLIX

ceived as a particular chemical body at a given level in

the chromosome then any change in this body would be

expected to affect one, or more, or even, at times, all

characters of the complex that gives rise to the body

character or characters. The particular change might

involve no more than a rearrangement of the materials

of the locus or the addition of a chemical element (or com-

pound) or the loss of a chemical element (or compound)

—any one of these changes might lead to the loss of a

character in the soma. As to what happens in the locus

we can form no idea, and so far as the mechanism of

heredity is concerned it is a matter of no immediate im-

portance. If, however, any one finds a greater satisfac-

tion in the view that a loss of something from the locus

(an atom or a molecule) leads to a recessive character,

there is not the slightest objection to his doing so, unless

by loss he means the loss of the entire locus. He may do

this if he rejects the linear arrangement of different

material in the chromosomes, but if he accepts the latter

view the assumption of a literal absence involves him in

unnecessary difficulties. It is not as generally under-

stood as it should be that the facts which the presence

and absence theory was constructed to account for do

not require the assumption that the absence of a char-

acter means the absence of a factor in the germ-plasm. °

It is entirely gratuitous to involve the theory of Mende-

lian heredity in such an interpretation which adds noth-

ing to the theory and by bringing in a new hypothesis may

involve the Mendelian theory in further difficulties. An

example may make this clear. It is known that when a

chocolate mouse is bred to gray and the F, grays that

result are bred together there appear in F, grays (9),

cinnamons (3), blacks (3) and chocolate (1). Gray was

written GBCh and chocolate gbC, which gave in F, @BCh

(9) GbCh (3) gBCh (3) and gbCh (1). The occurrence

of the black class of gBCh is accounted for through re-

combination. But the same end is accomplished if we

No.583] ROLE OF ENVIRONMENT IN DROSOPHILA 421

suppose that a factor in the wild or agouti mouse mu-

tated so that the recessive black was produced as a result

of the activity of the new gene. Then bl—black, and Bl

= gray with respect to black. Likewise cinnamon agouti

may be represented by ci, and gray, with respect to cin-

namon, by Ci. Chocolate is then the double recessive

blei and the symbol Ch for ‘‘chocolate’’ becomes super-

fluous. All the experimental results may be explained

on this basis.

It is not necessary to try to state what kind of a change

in the germ-plasm led to these two mutations. The fac-

torial hypothesis should be entirely non-committal as to

the kind of change that took place, for we can know noth-

ing about the nature of the change, yet the results are

predictable as well on one view as on the other.

There is another way to interpret a dominant factor

like this one that gives abnormality, namely, that there is

present in the normal fly a factor that restricts the yellow

of the abdomen to the bands. When this restrictor, ab,

changes (Ab) the yellow is dispersed over the abdomen

and the black bands fail in part or entirely to appear.

The new factor, acting with the rest of the cell, gives ab-

normality, just as the normal restrictor or inhibitor (ab)

acting with the rest of the cell gives normality or band-

ing. The interpretation is non-committal in regard to

the nature of the change, which is an advantage in the

direction of simplification. In contrast to this view, a

different interpretation of the meaning of a restrictor

might be entertained on the presence and absence view.

It might be said that a restrictor factor has been ‘‘lost’’

from the normal fly, which failing to restrict the color

has given rise to abnormality. The first objection to this

hypothesis is that it postulates (as above) the nature of

the change in the germ plasm, because it says something

has been lost. The second objection is that the facts

show that a restrictor has not been lost sensu strictu

because there is a wide range of variation in regard to

422 THE AMERICAN NATURALIST [ Vou. XLIX

the loss of banding and in certain environments there ts

a return to the normal banding to the extent that the fly

can not be distinguished somatically from a normal

banded fly. My contention is that since we know noth-

ing of the nature of the change in the germ-plasm that

leads to the appearance of a new or the loss of an old

character, any assumption that is based on the nature of

that change involves the Mendelian interpretation in un-

necessary implications. We need only assume that some

change has occurred, as the result indicates; my formulas

give the same results as do those of presence and ab-

sence and serve the purpose of briefly indicating a change,

the machinery involved, and the necessary consequences.

OTHER TYPES OF ABNORMAL ABDOMEN

Irregularities in the arrangement of the rings of the

abdomen are not uncommon in Drosophila. Sometimes

they appear to have been caused by injury to the

larve or pups, but still other abnormalities are inherited

in the sense that they occur in certain stocks in more or

less definite percentages. Several times I have bred ab-

normal types: some of them have failed to reappear;

others have reappeared in a certain percentage of cases.

Two stocks of the latter kind may be referred to here.

My main purpose in describing them is to anticipate the

possible confusion that might arise if some one finding

these or similar ones should suppose them to be the same

types as those described as abnormal abdomen in this

paper.

The six drawings in Fig. 2, a-f, represent some of the

characteristic types of a certain stock. The failure of the

third abdominal ring to extend across the middle line, as

e It is not an objection to this hypothesis that an absence (loss of re-

strictor) appears to dominate presence. This interpretation rests on a com-

plete misunderstanding of the nature of the factorial hypothesis; for, ab-

sence here means only that the rest of the cell fails to produce banding

when a certain factor is lost, or, when as in the female, one of the inhibitors

is lost.

No.583] ROLE OF ENVIRONMENT IN DROSOPHILA 423

Fig, 2.

seen in the first two figures, is the more usual form of

abnormality in this stock; but modifications of other

rings shown in the other figures are probably due to the

Same cause or causes. Two consecutive rings may form

a spiral as shown in c or half of a ring may be absent

as in e, or an entire ring may be lacking as in f. Indi-

viduals with abnormalities like those shown in the figures

were bred to each other usually three or four together.

Their progeny was examined and the normal and the ab-

normal types recorded. The latter were again used to

breed from for three or four generations. As no increase

in the proportion of abnormal offspring appeared, the

breeding was abandoned. The results given below are

in the order in which they were obtained without regard

to the generation in which they appeared.

424 THE AMERICAN NATURALIST [Vou. XLIX

In these counts there were normal to abnormal flies both

of whose parents were abnormal. Since the normals also

throw some abnormals it is probable that there is here a

case of multiple factors like that of beaded and truncate.

Special tests will therefore be necessary to work out the

case.

N a a ae N Ab N Ab

85 E ee oa et 40 0 73 0

6 1 Woe B p il

28 5 33 2 52 7 32 5

32 10 20 2 15 5 105 3

15 3 13 4 w l i 37 10

40). [8 ee G eee

yin ey | | | |

The abnormal abdomens shown in Fig. 3, a-f, are from

another stock, discovered by Mr. Bridges. While some of

the types are not unlike those of the last series, they are

more extreme and there can be no doubt but that the two

stocks have a different composition.

In the last drawing the entire fly is figured (the one

wing present has been cut off at the base), the upper half

of the thorax is absent. This same condition appears in

rather high proportions in certain other stocks, notably

in vestigial stocks. Even both sides of the thorax may

be absent so that the head rests above on the abdomen.

Although I have tried a number of times to obtain pure

stocks of this thoracic abnormality, I have never suc-

ceeded in getting a stock that did not throw a high per-

centage of normal individuals.

This type of abnormal abdomen appeared in a cross

between a cream male and an eosin female as a single

female, Fig. 1, a, which had only three instead of five

bands in the abdomen. She was mated to one of her

brothers, and produced offspring all of which as far as

known had normal bands. A pair of these offspring gave

in the next generation abnormal bands in about half of

the flies. The abnormal band acted as a recessive. In

subsequent generations the character behaved in an irreg-

No. 583] ROLE OF ENVIRONMENT IN DROSOPHILA 425

Fie. 3.

ular manner though no serious attempt was made to dis-

cover the cause of the irregularity. A stock of cream eye

color was made up from this strain and selection against

the abnormal was carried out in a rough way for several

generations, but this selection failed to eliminate the ab-

normal condition, and a recent examination of the stock

showed that for a year the abnormal abdomen had main-

tained itself and was still present in about half of the

ies.

A male was again crossed to a wild type female and

gave normal F, flies. In F, there were 128 red normal

females, 29 red normal males, and 28 eosin normal males.

No abnormals appeared. Crossed to eosin the F, were

426. THE AMERICAN NATURALIST [Vou. XLIX

PARENTS: AbE By NE

F,: NE

EN ọ EN ¢ | EAb ọ | EAb ¢

78 56 1 1

13 14 0 2

46 40 0 2

6 pi 0 0

35 32 0 1

39 46 7 1

217 195 | 8 | 7

all normal; these inbred gave in F, the classes given above:

Two eosin females heterozygous for white were crossed

each to an abnormal male. The normal F, daughters

were bred to those sons that had white eyes, and gave the

following kinds of offspring:

PARENTS: E-WNQ By EAb ĝ

F,: EN? (By WN ĝg)

18 26 1 1 20 15 1 1

34 28 1 $s 25 2 1

52 | 54 2 2 | 8 woa 2

Abnormal males were bred to eosin females and gave, as

before, normal F, sons and daughters. Some of the

daughters were backcrossed to eosin cream abnormal

males and gave the following results:

PARENTS: AbE BY NE

F,: NE (BY AbE ĝ)

EN 9 ENG EAb ọ | EAbg

35 32 0 1

21 4 1 2

48 40 0 1

72 72 8 6

176 149 9 10

These tables show that the abnormal condition rarely ap-

pears in F,. Its realization must be due therefore either

No. 583] ROLE OF ENVIRONMENT IN DROSOPHILA . 427

to multiple factors or to environmental effects. That

the former rather than the latter is the main explanation

is shown in the frequency with which the abnormal flies

appear in the inbred stock (where the conditions are the

Same as in the experiments) and the rarity with which

the character appears when the stock is outcrossed.

THE NON_INHERITANCE OF AN ACQUIRED CHARACTER

The acquirement of a new character by a pure stock

implies by definition the capacity of this stock to respond

to the imposed conditions. Conversely if an animal does

not acquire a new character in a changed environment it

does not come within the scope of the definition of an

acquired character, and even should its offspring show

new characters as a result of the new environment in

which the parents have been placed the result is still

excluded by definition from being a case of the inheri-

tance of an acquired character. At least this is my un-

derstanding of the use of the term and the way in which

I shall use it in the following statement.

The mutant stock of abnormal abdomen offers an ex-

ceptional opportunity to examine the possible influence

of an acquired character on the offspring. As the experi-

ments have shown this stock is very susceptible to en-

vironmental influence, and the effects produced pro-

foundly affect the structure of the organism. Moreover

it is possible to carry the stock through several genera-

tions in either of the phenotypic conditions, and then, at

will, to cause the other type to appear at once in its com-

pletest form, by regulating the external conditions in

which the young are reared.

No better material could be found for studying the

possible influence of the environment through its effects

on the soma of the individual. The evidence shows in the

clearest manner that the condition of the parent, whether

normal or abnormal in type, has no effect on the charac-

ter of the offspring. The evidence is so clear and so

positive that it seems unnecessary to elaborate the point.

428 THE AMERICAN NATURALIST [ Vou. XLIX

THE NON-CONTAMINATION OF GENES

Recently the question of the possible contamination of

genes (or factors) has been under discussion. Were

such contamination possible one might expect to find

some evidence of it in a case like this one of abnormal

abdomen, if one is justified, at all, in drawing infer-

ences from the nature of the character to the nature of the

gene that stands for that character. I do not myself

think that there is the slightest justification in drawing

such conclusions, but let us assume for the moment that

such an inference is justifiable in order to examine the

bearing of the evidence furnished by this mutant type.

The heterozygous female carries a factor for normal

and one for abnormal. She herself may be either normal

or abnormal according to the environment in which she

was reared. It might be supposed, since she is abnor-

mal, that her normal gene might be more predisposed

to contamination by the abnormal gene. The evidence

shows that this does not occur; for, by means of the link-

age we can identify the normal flies that should carry the

normal, or the abnormal genes, and we find that the re-

sults conform completely to expectation; 7. e., they are in

full accord with all other linkage results where there is

no reason to suppose that contamination takes place.

Conversely it might be supposed that if the hetero-

zygous female were normal in type her abnormal gene

might be predisposed to contamination by the normal gene,

but again the evidence contradicts the assumption.

If, on the other hand, it is not supposed that the pheno-

typic condition of the female has any part in bringing

about contamination (or in serving as an indicator, that

conditions are favorable for contamination) but that con-

tamination is due merely to juxtaposition of genes in the

same cell, then in refutation of the contamination of genes

I may cite the evidence cited above, where in several suc-

cessive generations the breeding took place from hetero-

zygous females bred to recessive males and the gametic

No. 583] ROLE OF ENVIRONMENT IN DROSOPHILA 429

ratios were the same in the late as in the earlier gen-

erations.

Lastly the tests made of individuals that were pheno-

typically normal, but genetically abnormal, showed in all

eases the validity of the genetic evidence, which would

not have been the case if the apparent exceptions had been

due to contamination of the genes. I may also cite the

two peculiar matings, B and C, recorded on page 402,

where an expected class did not appear. It might have

appeared that here actual contamination had occurred.

In reality, the result turned out to be due to a lethal

factor. Our study of these lethals, that give verifiable

results, fully under control, made it possible to interpret

this case that otherwise would have been inexplicable, and

might have been cited in favor of the view of contamina-

tion of genes. Taken all together the results obtained

with this mutant type make out a strong case against the

supposition that genes become contaminated through jux-

taposition. I shall not discuss here, therefore, the un-

pragmatic character of such a supposition, but rest the

case on the evidence from the experiments.

ON A CRITERION OF SUBSTRATUM HOMOGE-

NEITY (OR HETEROGENEITY) IN FIELD

EXPERIMENTS

Dr. J. ARTHUR HARRIS

CARNEGIE INSTITUTION OF WASHINGTON

I. INTRODUCTORY REMARKS

Every one who has had practical experience in variety

or fertilizer tests or in any other experiments involving

the comparison of field plots must have been impressed

by the great difficulty of securing tracts with uniform soil

for their cultures.

A careful examination of the agricultural literature

bearing on the question of variety tests will reveal many

cases in which the experimenters have noted the difficulty

of securing a uniform substratum, or in which there is

internal evidence for the influence of mubeatum hetero-

geneity upon the result.

For example, in 1894-1895 tests of varieties of wheat

were made on 77 plots at the University of Illinois.! As

a check on the other strains, the variety known as Valley

was sown on nine different plots ‘‘well distributed over

the area sown.’’

the yields of this variety varied from 11.7 bushels to 24.1

feahelac an average of 19 bushels which is remarkably close to the

average of all the varieties, It is again remarkable that but eight yields

were above the highest of the Valley, and but three below the lowest

of the same variety, . .

The only reasonable explanations that can be given for

such results are either (a) that the plots were so small

that the results are due purely and simply to the errors of

random sampling, or (b) that the wide divergences in the

1 Bull. Univ. TU. Agr. Exp. Sta., 41, 1896.

430

No. 583] ON SUBSTRATUM HOMOGENEITY 431

results for the individual variety are due to substratum

heterogeneity.

In either case, the results secured are obviously worth-

less as indicating differences in the value of the individual

varieties.

Seventeen years ago, Larsen? reached the conclusion

that the results of experimental tests were much more

exact when a given area is divided into a large number of

small plots upon which the tests are made than when it is

divided into a few larger plots.

Hall’ has laid great emphasis upon irregularities of ex-

perimental fields. Mercer and Hall in their interesting

paper on ‘‘The Experimental Error of Field Trials’

discuss at considerable length various phases of the influ-

ence of soil heterogeneity upon field results. In an ap-

pendix to their paper, Student® takes up the problem of

the method of arranging plots so as to utilize to the best

advantage a given area of land in testing two varieties.®

The influence of substratum heterogeneity is also read-

ily seen in Montgomery’s interesting experimental data

for wheat.”

Indeed, it is quite possible that without special precau-

tions irregularities in the substratum may have greater

influence upon the numerical results of an experiment

than the factors which the investigator is seeking to com-

pare. Elsewhere® I have shown that the sac aaeadan

ring B. R., ‘‘Andra nordska Landbrakskongressen i Stockholm,’

1897, I, Ý. 72; fide G. Holtermark and B. R. Larsen, Lanwirtschaftl. e ;

such- Stationen, p a, 190.

3 Hall, A. D., ‘‘The Experimental Error of Field Trials,’’ Journ. Board

Agr. Great Britain, 16, 365-370, 1909

4 Journ. Agr. Sci., 4, 107-127, 1911.

5 Student, Journ. yas Sci., 4, 128-132, 1911.

6 For several years, I have a eareful tests labelled each seed individually

and scattered them at random over the field to eliminate the influence of soil

een

7 Montgomery, E. G., ‘‘ Variation in Yield and Method of Arranging

Plots to Secure Comparative Results,’? Ann. Rep. Neb. Agr. Sta., 25, 164-180,

1912,

8 Harris, J. Arthur, ‘‘An Illustration of the Influence of Substratum

Heterogeneity upon Experimental Results,’’ Science, N. S., 38, 345-346.

1913.

432 THE AMERICAN NATURALIST [ Vou. XLIX

in an apparently uniform garden plot may be sufficient to

mask entirely the influence of the weight of the seed

(Phaseolus vulgaris) planted upon the size of the plant

(as measured by the number of pods) produced. It is

very probable that certain pure-line experiments and con-

clusions are entirely invalidated by the fact that the in-

fluence of irregularities in the substratum were not suff-

ciently guarded against.®

Several authors have tried to obtain some measure of,

or some corrective term for, substratum heterogeneity.

For example, Mercer and Hall (loc. cit.) have plotted the

yields across the field in both directions. Such methods,

however, give but a very imperfect idea of irregularities

in the soil. Heterogeneity is perhaps more likely to occur

as a spotting of the field than as a relatively uniform

change from one side to the other. This is clearly indi-

cated in the diagrams published by Montgomery. The

mere plotting of yields in any line across the field can not

adequately take into account such irregularities. Fur-

thermore, some quantitative measure (and some probable

error of this measure) of the amount of irregularity, not

merely a demonstration of its existence, is required.

Some generally applicable measure of the degree of

homogeneity of the soil of a field (as shown by actual ca-

pacity for crop production) seems highly desirable. Such

a criterion should be universally applicable, comparable

from species to species, character to character or experi-

ment to experiment, and easy to calculate.

I believe we may proceed as follows. Suppose a field

divided into N small plots all planted to the same variety

of plants. Let p be the yield of an individual plot. The

variability of p may be due purely and simply to chance,

since the individuals of any variety are variable and the

size of the plots is small, or it may be due in part to differ-

entiation in the substratum. If the irregularities in the

experimental field are so large as to influence the yield of

9 See ‘‘The Distribution of Pure Line Means,’? AMER. NAT., 45, 686-

700, 1911.

No. 583] ON SUBSTRATUM HOMOGENEITY 433

areas larger than single plots’? they will tend to bring

about a similarity of adjoining plots, some groups tend-

ing to yield higher than the average, others lower.

Now let the yields of these units be grouped into m

larger plots, Cp, each of n contiguous ultimate units, p.

The correlation between the p’s of the same combination

plot, Cp, will furnish a measure (on the scale of 0 to 1)

of the differentiation of the substratum as expressed in

capacity for crop production. If this correlation be sen-

sibly 0, the irregularities of the field are not so great as

to influence in the same direction the yields of neighboring

small plots. As substratum heterogeneity becomes greater,

the correlation will also increase. The size of the co-

efficient obtained will depend somewhat upon the nature

of the characters measured, somewhat upon the species

grown, and somewhat upon the size of the ultimate and

combination plots. A knowledge of the values of the cor-

relation to be expected must be determined empirically.

Fortunately, very simple formule are now available for

calculating such coefficients."

Let S indicate a summation for all the ultimate or com-

bination plots of the field under consideration, as may be

indicated by the capital Cp or lower case p. Then in our

present notation which is as much simplified as possible

for the special purposes of this discussion

{LS(C,?) — S(p?)]/m[n(n — 1) 3} — 7

T pipa Er

where P is the average yield of the ultimate plots and op

their variability, and n is constant throughout the m com-

bination plots.!?

10 Trregularities of soil influencing the plants of only a single small plot

may in most work be left out of account, since they are of the kind to

which differences between individual plants are to a considerable extent

due, and are common to all the plots of a field.

11 Harris, J. Arthur, ‘‘On the Calculation of Intra-class and Inter-class

Coefficients of Correlation from Class Moments when the Number of Pos-

sible Combinations is Large,’’ Biometrika, 9, 446-472, 1913.

12 For the benefit of those who are frightened by formule, it may be

paraphrased as follows: One merely adds together the yields of a chosen

434 THE AMERICAN NATURALIST [Vou. XLIX

Ultimately, I hope to present experimental data of my

own bearing on this problem. For the present, the method

is admirably illustrated by a number of published records.

IJ. ILLUSTRATIONS or METHOD

A. Cases in which the Combination Plots are Equal in

ize

Illustration 1. Influence of substratum heterogeneity

on yield of experimental plots of mangolds.

TABLE I

YIELD OF COMBINATION PLOTS FOR MANGOLDS, OBTAINED BY COMBINING THE

ENTRIES OF MAP A BY FOURS AS INDICATED BY THE HEAVIER LINES

1,209 1,175 1,215 1,239 1,276

172 183 171 175 205

1,250 1,321 1,274 1,293 1,310

185 191 187 184 207

1,204 1,333 1,268 1,290 1,268

159 188 172 185 200

1,300 . 1,272 1,222 1,272 1,388

172 177 167 173 215

1,385 1,375 1,314 1,260 1,373

ies 194 193 180

1,380 1,387 1,309 1,314 1,380

204 202 177 188 229

1,320 1,295 1,304 1,332 1,397

180 188 187 194 226

1,331 1,264 1,310 1,325 1,337

183 183 188 203

1,404 1,325 1,334 1,335 1,312

194 190 190 ' 1 2

1,418 1,373 1,339 1,403 1,401

193 196 189 198 226

number of contiguous p plots to form a number m of Cp plots. The sum

of the squares of p is subtracted from the sum of the squares of C. d

he result divided by m[n(n—l)] where n is the number of ultimate

plots in each of the m combination plots. The quotient is reduced by sub-

pine required. Thus the calculation m the eriterion is very simple

435

No. 583] ON SUBSTRATUM HOMOGENEITY

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Map A. Pounds per Plot of of Mangolds. Data of Mercer

Roots and Leaves

and

Hal

436 THE AMERICAN NATURALIST [ Vou. XLIX

Map A represents the Rothamsted field of mangolds

grown by Mercer and Hall (loc. cit.). The upper entries

are for pounds of roots, the lower for pounds of leaves.

I now reduce the 200 areas to 50 by combining the ad-

joining plots by fours, as indicated by the heavier lines on

the map. Thus for leaves the Southwest combination

plot, Cp, is 67 +52 +56 + 51—226. Table I gives the

result.

This gives for roots:

s p) = 65715, S(p”) = 21674871, N = 200,

== $28.575, op? = 4132.8243

S (Cry = Sa, m[n(n — 1)] = 50 X 4 XxX 3 = 600,

[S (Cp?) — S(p?)]/m[n(n — 1) ] = 108104.280,

and

_ 108104.280 — (328.575)?

Pips = 412.824

= .346 + .042."

The results for yield of leaves are

S(p)==9541, S(p?) —45941, N—200,

p==47.705, cp? == 23.938,

S (C?) = 1832095, m[n(n —1)]—50 x 4 X 3= 600,

[S(C,?) — S(p?) ]/m[n(n — 1)] = 2286.923,

whence |

= 2286.923 — (47.705)?

IPE, B

Illustration 2. Influence of Substratum Heterogeneity

upon the Yield of Straw and Grain in Experimental Plots

of Wheat.

18 The standard deviation is most conveniently calculated in eases like the

present, in which one requires the summed squares of actual values for other

purposes from

= .466 + .037.

Op? = = (p*)/N — [E (p)/N F.

14 The probable errors have in all cases been calculated upon the actual,

not the weighted, number of ultimate plots as N.

No. 583] ON SUBSTRATUM HOMOGENEITY 437

The wheat field of Mercer and Hall is divided into

25 X 20—500 plots, Map B. Combining the plots by

fives from east to west and by fours from north to south,

I have condensed this into 5 X 525 Cp plots, each of

20 ultimate plots as shown in Table II.

TABLE II

YIELDS OF COMBINATION PLOTS OF ROTHAMSTED WHEAT, 4 X 5 GROUPING.

ORIGINAL AREAS SEPARATED BY DOUBLE LINES IN MAP B

82.89 | 83.05 | 78.63 78.76 74.70

139.36 13241 | D2% 120.53 114.58

7i | $4.34 | 75.61 | 80.32 74.87

130.60 | 140.31 alo ear eat

79.80 | $4.70 | 74.94 81.50 77.34

13331 | ls | X 133.28 | p

84.36 | 82.42 7300 | 71.35 75.81

142.79 | it iwo o PiB ? 0

85.19 | 84.56 | 82.25 | 68.52 | 76.69

147.95 | 146.78 13842 | 12009 | 124.88

Summing the actual yields and the squares of yields

for the ultimate plots and the squares for the combination

plots, I find the following values:

For wheat grain

S(p) = 1974.32, S(p) = 7900.6790, N=500,

p=3.949, op? = .209600,

S (C2) = 156419.3106, m[n(n — 1)] = 25 X 20 X 19

= 9,500,

LS(0:2) — S(p?)]/m[n(n — 1) ] = 15.633540,

which leads to

15.633540 — (3.949)? _

R Boe = .186 + .029.

a 20

For wheat straw

S(p) = 3257.40, S(p?) = 21623.9802, N= 500,

p=6.515, 7 = .805341,

S'(C,? — 427479.9920, m[n(n—1)] 9500,

[S(Cp?2) — S(p?)]/m[n(n — 1) ] = 42.721685,

THE AMERICAN

2 3

NATURALIST

[Vou. XLIX

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Map B. Wheat Yields, Upper Figures Grains, Lower F

‘

igures Straw,

No. 583] ON SUBSTRATUM HOMOGENEITY

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4 A N N

on Rothamsted Acre.

whence

THE AMERICAN NATURALIST

_ 42.721685 — (6.515)?

805341

[ Vou. XLIX

- = 343 + .027.

Illustration 3. Influence of Substratum Heterogeneity

upon Yield of Grain and Nitrogen Content in Experi-

mental Plots of Wheat.

Table III is condensed from Map C of Montgomery”

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Map C. Yields

15 Montgomery, E. G.,

164-177, 1912.

Grain in Grams

Wheat Plots. The e Entries a

ay perg of Nitrogen

e Yield

Percentage glastag Cont

in M r GOAL!

n Grams of Grain, the Low

ent.

‘Variation in Yields and Method of Arranging

Plots to Secure Comparative Results,’? Ann. Rep. Neb. Agr. Exp. Sta., 25,

No. 583] ON SUBSTRATUM HOMOGENEITY 441

by combining adjoining plots 22. The following are

the numerical values.

For grains produced,

S(p) =123429, S(p?) = 70112319, N= 224,

p=—551.022, op? = 9375.826,

S (C?) = 277945243, m[n(n — 1)] = 642, |

[S (Cr?) —S(p?)]/m[n(n — 1)] = 309275.184,

whence

fipa = .603 + .029.

For percentage nitrogen, .

S(p) = 465.29, S(p?) = 968.3721, N = 224,

p=2.077187, op? = .008383,

S (C?) = 3868.5047, m[n(n—1)] = 672,

[S(Cp?2) — S(p?)]/m[n(n — 1) ] = 4.315673,

and

p43 == AL i 044,

TABLE III

COMBINATION PLOTS OF MONTGOMERY’S WHEAT, 2 X 2-FoLD GROUPING AS

INDICATED BY HEAVY LINES IN MAP

2,168 2,016 2,029 1,819 | 1,689 1,702 1,788

8.22 8.20 8.56 8.30 8.12 8.31

2,090 2,126 1,700 1,667 1,652 1,661 1,769

8.33 8.38 8.29 8.52 8.12 7.98 7.93

2,242 1,981 2,071 1,955 1,785 1,886 1,985

8.45 8.42 8.16 8.24 8.00 7.98 7.95

2,074 2,140 2,004 2,271 | 2,793 2,208 2,429

8.34 8. 8.26 8.37 8.27 8.09 7.88

2,043 1,928 2,406 2,280 2,628 2,802 2,682

8.23 .32 8.87 8.68 | 8.38 8.38

2,339 2,528 2,271 2,363 2,730 2,809 2,582

8.3 .0 8.39 8.04 8.36 8.21

2,573 2,456 2,470 2,286 2,498 2,524 2,540

1 8.27 8.46 8.43 8.32 8.88 8.45

2,450 2,322 2,591 2,097 2,326 2 2,200

8.26 8.54 8.37 8.67 8.32 7.98

442 THE AMERICAN NATURALIST [ Vou. XLIX

Illustration 4. Influence of Substratum Heterogeneity

upon the Yield of Experimental Plots of Timothy Hay.

I take as a final illustration of the application of the

criterion of substratum heterogeneity here proposed, the

plot data for timothy hay published by Holtermarck and

Larsen, loc. cit. By combining their plots into groups of

4 Table IV is secured,

S(p) = 4268.8, S(p?)=77968.50, N = 240,

p= 17.787, o,’ = 8.503,

S(C:2) = 309491.48, m[n(n—1)] =720,

whence

1p192 = -609 + .027.

TABLE IV

COMBINATION PLOTS 2 X 2, SHOWING YIELDS OF TIMOTHY HAY SECURED IN

| THE EXPERIMENT oF LARSON

The original field is not mapped here

a 87.4 99.0 | 78.5 65.8 67.2 63.3

76.4 72 | 750 73.1 67.7 59.7

76.9 65.2 64.2 89.7 72.1 64.3

65.1 54.1 66.4 98.9 83.3 64.3

57.9 64.7 61.1 88.6 72.2 64.8

73.0 55.6 62.2 75.6 82.8 71.1

71.7 “s © M 64.8 81.6 75.2

68.8 70.4 | 617 81.2 72.8 61.4

77.5 ne | 669 | s 73.9 | 685 _

B. Cases in which the Combination Plots Vary in Size

In the foregoing illustration the combination plots have

been of uniform size, i. e., have contained each the same

number of ultimate plots. It may be desirable or neces-

sary to have some of the combination plots smaller than

the others. Thus the wheat field of Mercer and Hall is

No. 583] ON SUBSTRATUM HOMOGENEITY 443

laid out in a 20 X 25 manner. This permits only 2 X 5,

45 or 5X5 combinations of the same size throughout.

Montgomery’s experiment comprises an area of 16 X 14

plots which may be combined in only 2 X 2 or 4 X 2 equal

areas suitable for calculation. In each of these cases

other groupings are desirable.

The formule are quite applicable to such cases: the

arithmetical routine is merely a little longer. The for-

mula is again

{[S(C,*) — S(p*)]/SIn(n — 1)]} -

Tryp, cee

but p and cp are obtained by a (n —1)-fold weighting of

the plots,1® where n is the number of ultimate plots in the

combination plot to which any p may be assigned, i. e.,

p=S[(n—1)p]/S[n(n—1)],

Me = Da (Aeru,

T Sina- 1)] ~ Sha- 1))

The point may be illustrated in detail on the wheat data

of Mercer and Hall. I adopt a combination by twos from

north to south, 7. e., arrange the data in 10 rows of com-

bination plots instead of 20 rows of ultimate plots. From

east to west there are 25 rows of ultimate plots; these can

be only reduced to a 2 X 2-fold grouping for the first 22

rows. The lines of division are indicated on Map B by

marginal arrows.

Row 23-25 must be thrown into combination plots each

of 6 units. The possible permutations within a combina-

tion plot are 1/2 n(n — 1), but since the surfaces are ren-

dered symmetrical, the total permutations for the whole

field is S[n(m—1)]. There are only two sizes of combi-

nation plots, of which 110 have 4 and 10 have 6 ultimate

plots each. Thus the weighted population N is

16 That is, each ultimate plot is multiplied by the number less one of the

plots in the combination plot to which it is assigne

444 THE AMERICAN NATURALIST (Vou. XLIX

S[n(m—1)] = (110 x 4 x 3) + (10 x6 X-5)=1620;

In the calculation of the weighted means and standard

deviations each entry, and the square of each entry, in the

first 22 rows must be weighted in an (n — 1)-fold=3-fold

manner, while those for the last three rows must be

weighted in a 5-fold manner.

The numerical values are:

For grain,

Sl(n— dae = 6378.72, S[(m—1) p*] = 254524154,

==3.937, dp? = 207610,

S o = 33129.7080, Ə (7) = 1900.6790,

whence

Tssa — .354 + .026.

Note that S(p?) is constant for all groupings.

For straw,

S[(n — 1)p] = 10474.52, S[(n — 1)p?] = 69042.7194,

p = 0.466, op*== 813000,

S (C2) = 89985.8976, S(p?) = 21623.9802,

whence

Taro ™= ALD + 028.

Weighting has not materially changed the physical con-

stants from the values given under illustration 2 above.

The reasons for the conspicuous differences in the corre-

lations will be taken up presently.

Montgomery’s wheat data have been grouped into 2 X 2-

fold combination plots in the illustration above. If we

again combine the entries of Table III by twos, beginning

at the upper left-hand corner, we have 12 combination

plots each 4 X 4, or of 16 ultimate plots, and 4 combina-

17 Since each individual ultimate plot is compared once as a first (or as

a second) number of a pair with every plot classed with it, the weighting

of the ae plots for means and standard deviations is an (n—1)-

fold o

No. 583] ON SUBSTRATUM HOMOGENEITY 445

tion plots each of 2 X 4=8 ultimate plots. The method

of dividing up the field is indicated by the marginal ar-

rows on Map C.

S[n(n —1)] = (12 X 16 15) + (4&8 X 7) = 3104.

For grain,

S[(n — 1)p] = 1707635, S[(n — 1)p?] —9683408.57

p=550.140, op? = 9311.307,

S (C?) — 1023184887, S(p?) = 70112319,

whence

rae == 412 036:

For nitrogen,

S[(n —1)p] = 6458.63, S[(n — 1)p?] = 13464.6031,

p=2.080744, op? = .008327,

S (C2) = 14409.6095, S(p?) —968.3721,

and

1192 = .096 + .045.

Again the weighted means and standard deviations do

not differ widely from those used above. The differ-

ences in the correlations will be discussed below.

In concluding this section it may be pointed out that

all of the foregoing values are surprisingly high. They

indicate clearly that the irregularities of an apparently

uniform field may influence profoundly the yield of a

series of experimental plots. They also bring out an-

other interesting point. In the three cases in which two

different characters were measured on the same species

they show very different susceptibilities to environmental

influence. Thus, for example, the correlation of man-

gold roots is r = .346 + .042 as compared with r==.466 +

-037 for leaves. For grain on the Rothamsted field with a

4 X 5-fold grouping the correlation is r=.186 + .029 as

compared with r= .343 + .027 for straw. For Montgom-

ery’s data for yield and composition the differences are

446 THE AMERICAN NATURALIST [Vou. XLIX

even more conspicuous. The correlation for per cent. ni-

trogen is r=.115-++.044 as compared with r= .603 + .029

for weight of grain produced.

This point will not be discussed in greater detail here,

since the problem of the relative susceptibility of various

characteristics of the individual to environmental influ-

ence has been the subject of experimental and statistical

studies which have been under way for several years and

will probably eventually be published.

III. ON THE Nature OF THE REGRESSION or ASSOCIATED

PuLots

The correlation coefficient is strictly valid as a measure

of interdependence only when regression is linear, i. e.,

when the means of the second variable associated with

successive grades of the first lie in a sensibly straight line.

The equation for the regression straight line

poe Op para Op,

ps Pes (P: — pps >) F pipe pı

Tp, Tp,

for the second on the first ultimate plot of the same com- —

bination plot reduces to

Pp — 18) +10,

when symmetrical tables in which p, = Po, op; = Fpa are

used.

The testing of the linearity of regression in any indi-

vidual case is rendered somewhat difficult by the necessity

TABLE V

YIELD OF GRAIN IN ROTHAMSTED WHEAT EXPERIMENT

Mean Yield Mean Yield

Yield of First | Weighted pone Yield of First |` Weighted

Plot Frequency ot —— Plot a Frequency " —

2.75-2.99 133 3.76 4.00-4.24 1786 3.99

3 3.24 75 3.78 4.25-4.49 1444 4.07

3.25-3.49 1026 3.81 4.50-4.7 03 04

1634 3.89 4.75—4, 247 4.05

3.75-3.99 1919 3.93 5.00-5.24 BIG

No. 583] ON SUBSTRATUM HOMOGENEITY 447

of actually forming a correlation table from which to com-

pute the means of arrays. The labor is greatly lessened

by the use of some such scheme as that described for the

formation of condensed correlation tables.1®

TABLE VI

YIELD OF STRAW IN ROTHAMSTED WHEAT EXPERIMENT

Plot Frequency Plots Plot {Frequency Plots

4.00-4.24 19 6.11 6.50-6.74 608 6.56

4.25-4.49 19 5.68 6.75-6.99 817 6.69

4.50-4.7 133 6.08 re 779 6.86

4.75-4.9 171 6.07 7.25-7.49 65 6.84

5.00-5.24 304 6.19 7.50-7.74 627 04

5.25-5.49 418 6.13 7.75-7.99 323 6.96

5.50-5.74 6.18 8.00-8.24 247 7.14

5.75-5.99 1121 6.20 8.25-8.49 09

6.00-6.24 1273 6.31 8.50-8.74 152 6.75

6.25-6.49 969 6.38 8.75-8.99 76 7.28

™~

20 | 27 |22 |23 |24 |25 |26 |27 | 28 |29 30 |37 [32 |33 [a+ |35 |36

Ioi

Wha T T U T U T T T T T T

oR BoE Boe TE a ee a

= & a

= $ eee.

-20 z

L L L L L L L L 1

Figure A Figure 2

Figs. 1 AND 2. Mean Yields of Grain and Straw on Ultimate Plots Asso-

ciated in the Same Combination Plots of a Given Yield. Rothamsted Wheat.

Empirical Means and Fitted Straight Line. Units are Quarters of a Pound.

18 Harris, J. Arthur, ‘‘On the Formation of Condensed Correlation Tables

when the Number of Combinations is Large,’ AMER. NAT., 46, 477-486,

1912,

448 THE AMERICAN NATURALIST (Vou. XLE

For the 5 X 4 grouping of the 500 wheat plot of Mercer

and Hall I find the values given in Tables V—VI.

For the regression of the second on the first plot the

equations are:

For grain, g, g =3.214 + 186 9;.

For straw, s, Sy = 4.280 + .343 S1-

Figs. 1 and 2 exhibit the usual irregularities of sam-

pling in the means, but show no certain departure from

linearity.

TABLE VII

YIELD OF GRAIN IN MONTGOMERY’S WHEAT EXPERIMENT

hes Plot g | Fisaneine | at gh $ Plot pet Pes eney_ | * = reas

325-374 | 9 | 516.88 575-624 liL | 579.82

375-42 | 63 440.22 625-674 90 | 616.21

425-474 | 93 471.23 675-724 45 656.37

475-524 | 108 | 540.24 725-774 30 | 628.80

525-574 | 120 l 548.24 775-824 3 | 574.00

350 | #00 | +50. | 500 sso | 600 | 650 | wo | 750 | 800

Figure s

Fic. 3. Grain Yields in Nebraska Wheat. See Figs. 1-2 for Explanation.

No. 583] ON SUBSTRATUM HOMOGENEITY 449

Table VII gives the first plot character, weighted fre-

quencies and empirical means for associated plots for

2 X 2-fold combinations from Montgomery’s grain yield

data in wheat.!®

The equation is

For grain, g, 9, = 218.993 + .603 g4.

The graph figures indicate sensible linearity.

IV. INFLUENCE or NUMBER or ULTIMATE PLOTS COMBINED

If an experimental field exhibit irregularities of condi-

tions which influence in a measurable degree the yield of

TABLE VIII

5 X 2-FoLD COMBINATION OF PLOTS OF ROTHAMSTED WHEAT

divisions of the field are indicated by the double vertical lines and

the arrows along the right margin in map

41.11 42.51 40.32 38.53 36.65

68.19 66.59 62.22 59.52 54.45

41.78 40.54 38.31 40.23 38.05

71.17 65.82 60.62 61.01 60.13

40.35 41.92 37.77 40.01 39.48

69.10 70.37 60.65 58.10 58.00

37.80 42.42 37.84 40.31 35.39

61.50 69.94 59.46 61.17 54.21

40.42 42.03 36.69 41.84 38.83

65.95 71.09 59.97 64.09 56.99

39.38 42.67 38.25 39.66 38.51

67.36 78.49 65.30 69.19 63.10

42.77 42.17 38.07 38.05 40.22

71.95 75.20 66.92 64.05 63.45

41.59 40.25 | 35.53 33.30 35.59

70.84 72.24 | 64.88 57.13 58.57

41.75 41.44 40.12 34.00 38.13

71.84 71.92 67.99 60.55 62.36

43.44 43.12 42.13 34.52 38.53

ae tT 70.43 59.54 62.52

19 Because of the many differences in the two experiments it is inadvisable

to attempt drawing the regressions lines in a strictly comparable form.

450 THE AMERICAN NATURALIST [ Vou. XLIX

neighboring small experimental plots, this heterogeneity

should become apparently less when expressed on a scale

of correlation between plots as the number of ultimate

plots combined increases. The reason for this condition

is quite simple. If the irregularities are very local in

nature they will influence in the same direction the yield

of only a very few neighboring plots. If too many ulti-

mate plots be combined the correlation will tend to vanish

because of the increased frequency of association of un-

like conditions due to the fact that the combination plots

have been made so large that they themselves have become

heterogeneous.

That these conditions have been observed in actual ex-

perimentation is shown by the following constants based

on different groupings of the data used above. .

Consider first the Rothamsted wheat. For a 4X5

grouping of the plots the results were found to be

For grain, 1 9199 = 186 + .029,

For straw, Tpyp9 == 043 + .027.

If the plots be grouped by fives from east to west and

by twos from north to south, Table VIII is obtained. The

values S(p), p and op are the same as in the preceding

case,

m[n(n —1)] =50 X 10 x 9 = 4500.

For grain, S$(C,?) =78265.2822, rpp = .214 + .029.

For straw, S(C>?) = 213939.8774, ryp: =.365 + .026.

If the combination plots be made even smaller by group-

ing in a 2 X 2-fold manner for all but the last three north

and south rows, where a 2 X 3-fold combination must be

adopted, the results are, as illustrated above,

For grain, Tpi = -394 + .026,

For straw, 9199 = A19 + .023.

For Montgomery’s wheat data the results for a 4 X 4

fold grouping (in as far as the nature of the records will

permit) have been shown to be

No. 583] ON SUBSTRATUM HOMOGENEITY 451

For grain, fpa = 472 + .035,

For nitrogen, p19 = -096 + .045,

as compared with the following values for a 2 Xx 2-fold

grouping

For grain, 492 = -603 + .029,

For nitrogen, Y'pypq = -115 + .044.

Finally consider the constants deduced from the hay

yields published by Holtermark and Larsen.

For a 2 x 2-fold grouping, tars = .609 + .027,

For a 2x 4-fold grouping, — fma = .471 + .034,

For a 2 X 8-fold grouping, fpina = .278 + .040.

Thus for every species of plant and every character con-

sidered the correlation between associated ultimate plots

decreases as the number of plots grouped increases.”°

TABLES IX AND X

2 X 4-Forp AND 2 X 8-FoLD COMBINATION OF THE DATA FOR PLOT YIELD

IN TIMOTHY HAY, TABLES DERIVED FROM TABLE IV

163.8 169.2 153.5 138.9 134.9 123.0 p

305.8 288.5 284.1 352.8 310.4 264.5

20 Of course, the same effect would be produced if comparisons were

drawn between tests for substratum heterogeneity on fields Sree

in every regard except for the size of the ultimate plots. Possibly, t

plains in part, at least, the striking differences in the correlations for grain

yield found from the records of Montgomery and of Mercer and Hall.

The Rothamsted plots were 1/500th acre in area or 87.12 square feet.

Montgomery’s plots were 5.5 X 5.5==30.25 square feet, or only about 1/3

of the area of the Rothamsted plots.

452 THE AMERICAN NATURALIST [ Von. XLIX

V. RECAPITULATION AND DISCUSSION

If the methodical production of new varieties of animals

and plants to be made possible by the laws discovered

in experimental breeding is to be of material practical

value, more attention must be given to the development

of a standardized scientific system of variety testing.

From the practical standpoint, nothing is to be gained by

the formation of varieties of plants differing in discern-

ible features of any kind unless some of these varieties

ean by rigorous scientific tests be shown to be of superior

economic value.

It is equally true that if tests of fertilizers or of dif-

ferent methods of irrigation carried out on an experi-

mental scale are to have any real value as a guide to a com-

mercial practise, the differences in the experimental re-

sults must certainly be significant in comparison with

their probable errors.

The problem of plot tests has several different phases,

all of which must ultimately receive careful investigation.

The purpose of this paper has been to consider one of the

problems only. To what extent do the irregularities of

an apparently homogeneous field selected for comparative

plot tests influence the yield of the plots?

The question has been far too generally neglected,

although indispensable to trustworthy results. It is ob-

viously idle to conclude from a given experiment that va-

riety A yields higher than variety B, or that fertilizer X

is more effective than fertilizer Y, unless the differences

found are greater than those which might be expected

from differences in the productive capacity of the plots

of soils upon which they were grown.

The first problem has been to secure some suitable

mathematical criterion of substratum homogeneity (or

heterogeneity). Such a criterion should be expressed on

a relative scale ranging from 0 to 1, in order that com-

The 2 X 2-fold grouping of Montgomery’s plots gives a correlation of

.603 + .029 as compared with r = .354 + .026 for as nearly a perfect 2 X 2-

fold grouping as the Rothamsted records permit.

No. 583] ON SUBSTRATUM HOMOGENEITY 453

parisons from field to field, variety to variety or character

to character, may be directly made. It should also, if pos-

sible, offer no difficulties of calculation.

The criterion proposed is the coefficient of correlation

between neighboring plots of the field. An exceedingly

simple formula for the calculation of such coefficients has

been deduced.

The method of application of this coefficient is here il-

lustrated by four distinct series of experimental data.

The remarkable thing about the results of these tests

is that in every case the coefficient of correlation has the

positive sign and that in some instances it is of even more

than a medium value. In short, in every one of these ex-

perimental series the irregularities of the substratum have

been sufficient to influence, and often profoundly, the ex-

perimental results.

It might be objected that by chance, or otherwise, the

illustrations are not typical of what ordinarily occurs in

plot cultures. But they have been purposely drawn from

the writings of those who are recognized authorities in

agricultural experimentation, and who have given their

assurance of the suitability of the fields upon which the

tests were made.

For example, Mercer and Hall state the purpose of

their research to be, ‘‘to estimate the variations in the

yield of various sized plots of ordinary field crops which

had been subjected to no special treatment and appealed

to the eye sensibly uniform.’’ Their mangolds ‘‘looked

a uniform and fairly heavy crop for the season and soil,’’

while in their wheat field ‘‘a very uniform area was se-

lected, one acre of which was harvested in separate plots,

each one five hundredth of an acre in area.” The data

of Larsen were drawn from an experiment ‘‘auf einer

dem Auge sehr gleichmissig erscheinenden, 3 Jahre alten

Timotheegraswiese.’’ Montgomery’s data were secured

from a plot of land only 77 X 88 feet in size, which had

been sown continuously to Turkey Red wheat for three

454 THE AMERICAN NATURALIST [Von XLIX

years, ‘‘and was of about average uniformity and fer-

tility.’’

Nothing could, it seems to me, emphasize more emphat-

ically the need of a scientific criterion for substratum homo-

geneity than the facts that correlations between the yields

of adjacent plots ranging from r= .115 to r= .609 can be

deduced from the data of fields which have passed the

trained eyes of agricultural experimenters as satisfac-

torily uniform.

December 12, 1914

SHORTER ARTICLES AND DISCUSSION

A NOTE ON THE GONADS OF GYNANDROMORPHS OF

DROSOPHILA AMPELOPHILA

Five gynandromorphs of Drosophila amelophila were sec-

tioned and their gonads studied in order to determine whether

the gonads corresponded to the secondary sex characters ex-

pressed by the somatoplasm. The specimens were either lateral

or fore and aft gynandromorphs.

I. This gynandromorph arose from a cross between a white

eyed fly and a fly of the wild type. On one side of the body the

eye was red, the wing long, the sex comb lacking, and the ab-

domen characteristically female. The other side had a white

eye, short wing, sex comb and male abdomen. The external

genitalia were abnormal.

The fly would not mate, not only because of the abnormality

of the genitalia, but because its mating instincts were indifferent.

It was courted by males but, in turn, it itself did not court

females.

Since the fly was externally a bilateral gynandromorph one

would expect to find that the gonads on one side were male and

on the other side female. This, however, was not the case. The

gonads on both sides were male and the testes were filled with

ripe spermatozoa.

II. This fly arose from a cross of cherry club vermilion with

the wild type. The left side had a cherry eye, sex comb, long

wing and an abdomen of the female type. The sex comb is

characteristic of the male and the long wing of the female. The

right side had a red eye, no sex comb, short wing, and abdomen

of the male type. The absence of the sex comb is characteristic

of the female while the short wing and dark abdomen on this

side were male. This is lateral and, at the same time, a fore and

aft gynandromorph. The left side was male anteriorly and

female posteriorly while the right side was female anteriorly

and male posteriorly. The gonads were male but immature.

No ripe spermatozoa were seen.

III. The origin of this fly was the same as the last. Both

456 THE AMERICAN NATURALIST [ Vou. XLIX

eyes were red, sex combs lacking, left wing long, and the ab-

domen characteristically male. The external genitalia were

apparently half male and half female. This is not a fore and

aft gynandromorph but a lateral one in which the parts involved

are restricted to the abdomen and the posterior part of the

thorax.

The fiy was courted assiduously by males but it would not

mate. The gonads on both sides were female and ripe eggs were

present. It is probably true that the eggs could not be deposited ©

on account of some defect in the oviducts.

IV. The origin of this fly was the same as the last two, i. e., it

came from a cross of cherry club vermilion with the wild type.

The eyes were red, sex combs lacking ; the wings were of the same

length; the abdomen was divided into a female and a male side

and the external genitalia were apparently half female and half

male. Anteriorly the fly was female, and posteriorly it was half

male and half female.

A male courted this gynandromorph as long as the male re-

mained in front of it. When the male with one wing vibrating

made a half circle to the tip of the abdomen, it immediately

dropped its wing and turned and ran. Sections showed mature

spermatozoa in both testes.

. This gynandromorph arose from the cross of an abnormal

form, a possible mutant, with the wild type. The eyes were

red, but on one side there was a sex comb and a short wing,

while on the other side the sex comb was lacking and the wing

was long. The abdomen was characteristically female. The

gonads were of the female type on both sides.

The conclusion, if one is justified in drawing a conclusion

from so few data, is that the gonads of lateral gynandromorphs

do not follow the separation of the somatic cells into a male and

a female side, but are always the same on both sides, either male

or female. Since the cells of an early embryo must be either

male or female producing, we can understand why the gonads

of a gynandromorph should be alike on both sides, regardless of

the somatic condition, if we suppose that the gonads are derived

from a single cell of the embryo.

F. N. DUNCAN

COLUMBIA UNIVERSITY

VOL. XLIX, NO. 584 AUGUST, 1915

THE

AMERICAN

NATURALIST

A MONTHLY JOURNAL

Devoted to the Advancement of the Biological Sciences with

Special Reference to the Factors of Evolution

CONTENTS

Page

I. The Chromosome View of Heredity and its Meaning to Plant Breeders. Pro-

am a a a me a ea ae

- — -495

Regeneration Posteriorly in Enchytræus albidus. H. R. HUNT

The Origin of Bilaterality in Vertebrates. Professor A. C. EYCLESHEIMER - 504

Shorter Articles and Discussion: The Tortoiseshell Cat. Dr. PHtngas W.

ee a a ke a o

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THE

AMERICAN NATURALIST

VoL. XLIX. August, 1915 No. 584

THE CHROMOSOME VIEW OF HEREDITY AND

ITS MEANING TO PLANT BREEDERS!

E. M. EAST

BUSSEY Institution, HARVARD. UNIVERSITY

DEFINITE advice as to practical procedure must be based

on a firm foundation of fact if the leaders in the applied

science are to retain any confidence in those who lay the

first stones in the pure science. At the same time, if it is

clearly understood that science only approximates truth,

that so-called ‘‘established laws’’ are only highly prob-

able and never absolute, it can hardly be said to be unwise

if an inventory of fact is taken at any time. The hand-

writing on the wall is never finished; some words are dim

and the erasures and omissions are many, but that is no

reason why one should not try to read it and to see what

it directs if he has translated aright.

This preliminary justification of the title of this article

is made because our present stock of facts regarding

heredity points clearly to the chromosomes as vital parts

of the mechanism, and I wish to emphasize some impor-

tant practical deductions in case this position continues to

become more firmly established.

A just and complete dissertation upon the rôle of the

1 This paper is based upon two lectures delivered at Harvard University

in 1914. I hope that any cytologists who may have their attention called

to it will overlook the repetition of some well-known facts in the first few

pages, as it is intended to be merely a general statement of a particular

point of view with certain deductions that follow if it be accepted. I wish

to thank Doctors O. E. White, T. H. Morgan and R, Goldschmidt for their

kindness in giving me many suggestions, but in justice to them I should state

that they are not responsible for the conclusions drawn.

457

458 THE AMERICAN NATURALIST [Vor. XLIX

chromosomes in heredity not only would fill many pages,

but would expose numerous gaps in our present knowl-

edge, gaps that leave several important questions in the

balance. We shall assume frankly therefore that the

chromosomes are the bearers of the determiners of prac-

tically all of the hereditary characters that have been in-

vestigated by pedigree culture methods, acknowledging

freely our ignorance on many points, but maintaining that

while no facts have been discovered which offer insur-

mountable arguments against the viewpoint taken, the

following logical sequence of truths discovered at various

times and by different methods of research make a pretty

sound case upon which to base our practical conclusions.

RELATIVE Importance OF NUCLEUS AND CyTOPLASM

There are several reasons for believing that of the two

parts of the cell, the nucleus and the cytoplasm, the former

plays the greater rôle in heredity.

In general it is believed that the two parents contribute

equally in the production of offspring—that the male and

female contribution of potential characters is practically

the same. If there were a difference it would be shown

by divergent results in reciprocal crosses, but the investi-

gations following Mendel’s method make it probable that

with the exception of sex and sex-linked characters, the

results of reciprocal crosses are generally alike. This

being true, it would appear that the principal basis of

inheritance must be sought elsewhere than in the cyto-

plasm, for in most observed cases the sperm is very much

smaller than the egg, and this difference is largely a dif-

ference in the amount of cytoplasm each carries. Is one

not to look for some significance in this disparity in size?

Strasburger, as well as other botanists, has even gone so

far as to declare the male generative cell in certain angio-

sperms to be simply a naked nucleus that slips out of its

cytoplasmic coat into the embryo sac, leaving the dis-

carded coat behind, and that stimuli proceeding from the

nucleus control the assimilation of food in the cell and

determine even the character of the cytoplasm itself.

No. 584] HEREDITY AND ITS MEANING 459

This belief may be too radical. The machine must have

, all of its parts to do proper work; and it may be, as Conk-

lin suggests, that such characters as polarity, symmetry

and localization of organ bases in the egg have their chief

seat in the cytoplasm. This is only a possibility and not

a fact, however, for one must admit that cytological inves-

tigation has not disclosed the presence of a material basis

of heredity in the cytoplasm, though he may not be con-

vinced that it is unimportant. Does the same statement

hold for the nucleus?

The nuclear cavity contains four substances as they are

ordinarily described in connection with morphological in-

vestigations. These are nuclear sap, linin, nucleolar ma-

terial and chromatin.

Nuclear sap probably belongs as much to the cytoplasm

as to the nucleus, and we know nothing as to its possible

significance and importance within the nucleus.

Linin by some investigators is regarded as very similar

to chromatin. Others (Strasburger) consider it to be

the framework of the chromosomes, and the only real sub-

stance within the nuclear cavity that is continuous from

generation to generation. It is a thread-like material

staining lighter than chromatin upon which the chromo-

somes appear to be strung in the early prophases of nu-

clear division.

Nucleolar substance, though it stains in a different

manner from chromatin, is considered by many to be

chromatin-like in its nature. It is the substance of which

the nucleoli are composed; but as these bodies become

vacuolated and finally disappear during nuclear division,

one is led to believe with Strasburger that they are tem-

porary storehouses of some necessary food material.

Chromatin, however, as the material of which the

chromosomes are composed, plays such a peculiar part in

the activities of the cell, that hypotheses as to the méan-

ing of its behavior are certainly more than shrewd guesses,

as will be seen.

The chromosomes may be described as morphological

460 THE AMERICAN NATURALIST [ Vou. XLIX

elements, of various shapes and sizes that are found

within the nucleus; they are especially demonstrable as

deeply staining bodies, definite in number for each cell at

the period of division. In many cases in both plants and

animals they have been found to be made up of small

particles, the chromomeres, and various investigators

have expressed the belief that these, too, are definite in

number and play an important part in the larger collective

entity, the chromosome.

Almost from their discovery, the chromosomes have .

had an especially important part assigned to them in the

drama of heredity because of the previous philosophical

deductions of Weismann. Weismann reasoned that if

there were no reduction of heritable substance in the life

cycle of an organism, it would pile up indefinitely because

of the nuclear fusion at fertilization. He, therefore, pre-

dicted the discovery of some mechanism by which the

character conserving substance would be divided. A few

years later his prediction was verified in its important

details by actual observation of the chromosome reduc-

tion in the formation of germ cells in Ascaris. From this

discovery and from the facts that a specific number was

found for the cells of each species, that all the cells of an

individual appeared to possess the same number (except

when they were halved at gametogenesis), that they were

apparently permanent organs, that they were longitudi-

nally halved in division so as to give each daughter cell

the same number as well as an exact half of each chromo-

some possessed by the mother cell, investigators were

early tempted to place upon chromosomes the whole

burden of inheritance.

Our observations regarding chromosomes and the re-

duction divisions in plants now rest on a basis of cyto-

logical investigation of over 250 species, representing

over 150 genera and divided among the four great groups

of this kingdom. Montgomery’s 1906 list of chromosome

numbers in animals represents investigations on 185 spe-

cies, comprised in about 170 genera, distributed among

No. 584] HEREDITY AND ITS MEANING 461

nearly all the phyla of the animal kingdom. Sex chro-

mosome studies have undoubtedly increased these figures

for the animal kingdom to date, by hundreds of species.

Variation in chromosome number among the cells of an

individual plant or animal is a recognized fact among

cytologists, but this variation is not regarded as of par-

ticular significance, as commonly it is held to exist only

among old cells, cells highly specialized, or, at any rate,

cells which will never have anything in common with re-

production. To quote from Strasburger,

the number of chromosomes in the nuclei of the somatice cells of both

the sexual and the asexual generations have been found to vary. But so

far as my experience goes, these observations are always to be observed

in the nuclei of cells which are no longer embryonic, like those in an

embryo or growing point, but which, on the contrary, are to some ex-

tent histologically specialized and are not destined eventually to give

rise to reproductive cells. The determinate number is still more fre-

quently departed from in nuclei which are definitely excluded from the

sphere of reproduction.

In the reproductive cells, chromosome division is, on

the other hand, very exact, and the numbers found, almost

invariable, with one exception. This exception is the so-

called accessory chromosome or chromosomes, that ap-

pear to be coupled with sex differentiation. And the

very fact that such accessory chromosomes do exist and

by their presence or absence parallel sex distribution,

forms one of the most unanswerable arguments in favor

of the chromosomes being the chief bearers of character

determinants.

MORPHOLOGICAL InpIvIDUALITY OF THE CHROMOSOMES

The next topic to consider is whether there is sufficient

evidence to support the idea that these bodies—the chro-

mosomes—are morphological entities persisting from one

cell generation to another.

Prochromosomes are deeply staining bodies found in

the resting cell nuclei of plants, which probably corre-

spond in number, but not in size, to the chromosomes

which are found in the dividing nuclei. These bodies are

462 THE AMERICAN NATURALIST [ Vor. XLIX

thought to represent the resting nuclear condition of the

chromosomes. Prochromosomes have been found in at

least sixty species of plants, and various structures com-

parable to them in many others. These investigations

favor the thought that the chromosomes are persistent

morphological entities; nevertheless they are not suffi-

cient to establish the matter if there were no other data

at hand.

There is a series of facts, however, which is more con-

vincing. We are told that in addition to each species of

animal or plant having in the larger part of its cells a spe-

cific number of chromosomes, there is a constant reap-

pearance of the different shapes and sizes of these chro-

mosomes in the same positions relative to one another

during cell division after cell division.

Strasburger says: ‘‘The observation of such a series

of stages of nuclear division as can be obtained by the

laying open of embryo sacs in which development of

endosperm tissue is commencing, makes it difficult to re-

sist the impression that it is always the same chromo-

somes which make their appearance over and over again

in the repeated divisions. In the prophase, the chromo-

somes are seen to appear in precisely the same position

that they occupied in the preceding anaphase, and if the

picture of the anaphase were proportionally enlarged, it

would exactly correspond to that of the succeeding pro-

phase.’’

The facts from which these general conclusions have

been drawn can not be denied. Baltzer found odd-shaped

chromosomes of similar shape in many maturing eggs of

sea urchins. Boveri, Montgomery and later Schaffner

pointed out a constant difference in the form and the size

relations of the two chromosomes of Ascaris megalo-

cephala univalens. Sutton thought he could recognize

each individual chromosome in eleven consecutive cell

generations of the maturing germ cells of the lubber

grasshopper Brachystola magna. The so-called sex chro-

mosome which has been found in so many insects and

No. 584] HEREDITY AND ITS MEANING 463

other animals, is a clear case of constancy in appearance.

In plants the same phenomenon has been observed. Ro-

senberg investigated the pollen mother cells of Crepis

virens and in certain stages in division invariably found

two long, two intermediate and two very short chromo-

somes. Division figures in the somatic cells showed the

same differentiation, and in an examination of the nuclei

of the pollen grain he found only one chromosome of each

kind present. Such other species of this genus as have

been investigated also show some variation in chromo-

some form, although it is not so striking as in C. virens.

Hieracium venosum, exceptionally good material also in-

vestigated by Rosenberg, has shown the same thing.

Edith Hyde remarks on the fact of the constant reappear-

ance of certain chromosome forms among hundreds of

division figures which she observed in Hyacinthus orien-

talis. Sauer mentions a very long chromosome constantly

present in pollen mother cell preparations of the lily-of-

the-valley, and Strasburger and Lutz found a large

chromosome among many small ones in Lychnis dioica.

In certain species of Yucca this chromosome differentia-

tion takes on a dimorphic aspect, ten of the chromosomes

being very large and about forty-five very small.

Taking into consideration all of these facts, of which

hardly more than a random sample has been given, one

is clearly justified in concluding that these cell characters

are reproduced generation after generation. Why this

constancy if they are not important?

PHYSIOLOGICAL INDIVIDUALITY OF THE CHROMOSOMES

There is also considerable reason for believing that the

various chromosomes of a cell may have different func-

tions.

Boveri was the first to endeavor to test this hypothesis

by allowing sea-urchin’s eggs to be fertilized by two sper-

matozoa. Three nuclei, each with eighteen chromosomes,

were thus present in the same egg, two male and one

female. Although cytoplasmic division seemed to pro-

464 THE AMERICAN NATURALIST [Vor. XLIX

ceed normally, the chromosomes were usually distributed

irregularly by a three-poled or a four-poled spindle. As

a result three or four cells were produced at the first divi-

sion of the doubly fertilized egg, instead of the two cells

that arise after normal fertilization. Various abnormal

larvæ were produced later. In such embryos, Boveri found

the organism to be divided into definite regions, thirds or

fourths, each part traceable to one of the three or four

original cells, and the cells of each part differing from

the cells of the other parts in their combination of chro-

mosomes and usually in their chromosome number. In

rare cases normal embryos were produced, but these were

more commonly developed from a doubly fertilized egg

which in its first division was three-celled, than from one

in which it was four-celled. The thought occurs at once

that three cells have a better chance than four cells in

securing a full set of chromosomes, both as to number and

kind. If the division were normal, each nucleus would

receive a full set in the case of the chromosome distribu-

tion to three cells, but the division is usually irregular,

and because of this irregularity each cell does not usually

secure its normal set of chromosomes. Nevertheless it

is clear that the embryo parts developed from the three-

celled cleavage stand a much greater chance of being

normal than those from the four-celled type, although

through irregularities in division an eighteen-chromo-

some-celled region might be formed even where the first

division was four-celled.

In some cases, the embryo was completely normal as

regards skeleton and pigmentation in one or even two of

its thirds, while the remainder was entirely lacking in

these characters. Nearly normal embryos occurred which

were perfect as to parts and specific characters, but indi-

vidual variations which normally should have appeared

in separate larvæ were present among the thirds. Asym-

metrical larvæ also were formed.

More important still are the results Boveri obtained by

isolating the three cells of the three-fold type and the

No. 584] HEREDITY AND ITS MEANING 465

four cells of the four-fold type and allowing them to de-

velop into larve. When the four cells of a four-celled

stage of a normal embryo are separated, each cell pro-

duces a normal dwarf embryo alike in every respect, but

the three- or four-celled embryos from double fertilized

eggs, when treated in the same manner, never produce

normal dwarfs even when the chromosome distribution

has been numerically equal. Large numbers of larve

brought into existence through this experiment showed all

possible combinations of characters, just as all possible

chromosome combinations were found in their nuclei,

and from these and other data the conclusion is drawn

that ‘‘not a certain number, but a certain combination of

chromosomes is necessary to normal development, and

this clearly points out that chromosomes have different

qualities.’’ In other words, the sea urchin has a set of

eighteen chromosomes, each chromosome performing at .

least some different functions from its neighbors, making

it necessary for the whole set to be present in order to

Insure normal development.

In further investigations, Boveri placed sea-urchin eggs

which had been normally fertilized and were about to di-

vide under pressure. As a result, division of the nucleus

took place, but often no division of the cytoplasm. Such

eggs on again dividing often formed more than two poles,

resulting in inequalities in chromosome distribution and

abnormal larval development. Boveri puts upon these

cases an interpretation similar to that of the preceding

experiments, as the irregular chromosome distribution

seems to be all they have in common.

Morgan comments on Boveri’s experiments as follows:

The evidence makes probable the view that the different chromosomes

may have somewhat different functions and that normal development

depends on the normal interactions of the materials produced by the

entire constellation of chromosomes.

Artificial parthenogenesis and experiments with enu-

cleated eggs have proved that only one set of chromosomes

is necessary to normal development of embryos, but it is

466 THE AMERICAN NATURALIST [ Vou. XLIX

important, in considering these experiments, to note that

two sets of similar chromosomes are present in a normal

sexually produced organism.

Pairs of chromosomes of each shape and size (if they

differ in shape and size) are nearly always found in the

somatic cells—the exception being when the so-called

accessory chromosomes are present. And since but one

of each kind is found in the two gametes that fuse to form

the new organism, it is only natural to suppose that one

set was contributed by the maternal parent and the other

by the paternal parent.

_ The numerous cases in which this phenomenon has been

demonstrated are to many the most convincing evidence

of some sort of a morphological individuality of the chro-

mosomes. To them the fact implies pairs of freight boats

loaded with the essential materials of life, to others—the

minority—it is no more wonderful than the constant re-

currence of other plant organs. At any rate, it has been

shown that these sets of chromosomes continue an appar-

ently independent existence for some time. Moenkhaus

produced hybrids between the two species of fish, Fundu-

lus heteroclitus with long straight chromosomes and

Menidia notata with short curved chromosomes, and the

early divisions of the fertilized egg showed clearly com-

plete sets of chromosomes from each parent. Rosenberg

obtained similar results in crosses between the two sun-

dews, Drosera longifolia, which has forty small chromo-

somes, and Drosera rotundifolia, which has twenty large

chromosomes. In some eases similar to the latter, where

one parent contributes a greater number of chromosomes,

it should be noted that the organism seems to have regula-

tory powers. The chromosomes unnecessary for a double

set are either thrown out or take no part in the activities

of cell division. For example, in the supposedly hybrid

sundew, Drosera obovata, Rosenberg found that its thirty

chromosomes behaved in the following peculiar manner.

Ten of them paired with another ten, but the other ten

remained unpaired and acted in a very abnormal fashion

No. 584] HEREDITY AND ITS MEANING 467

in the reduction divisions. The ten pairs separated nor-

mally, one of each pair going to each pole; but the ten

unpaired were irregularly distributed, sometimes nearly

all of them going to one pole, sometimes most of them be-

coming lost in the cytoplasm and forming small nuclei.

Embryos were produced in a very few cases and these

only through back-crossing with pollen of D. longifolia.

Unfortunately these embryos only developed through a

few cell divisions.

These chromosome pairs have been distinguished by

the name homologous chromosomes. For a long time it

was thought that the paternal and the maternal set of

chromosomes separated from each other bodily at the re-

duction division. Now it is believed to be only a matter

of chance which chromosome of a pair passes to a particu-

lar daughter cell. There is some cytological evidence for

this view, but the main argument in its favor is that this

behavior is all that is necessary to fit nearly all the known

facts of heredity, with the chromosomes playing the

part of the active heredity machinery as will be seen

shortly. This statement is true in a broad sense, but the

word nearly is used because there is an exception to it.

Chance apportionment of either member of a homologous

pair of chromosomes to a daughter cell accounts for all

facts of alternative (Mendelian) inheritance except where

there are breaks in the correlation between characters

usually inherited together. Since such breaks in corre-

lation are common, it is clear that there must be a period

when chromosome pairs have such an intimate relation

that material can be exchanged. Many biologists believe

that such a period is found during the maturation of the

sex cells. The particular point at which such a conjuga-

tion or approximation of chromosome pairs takes place is

called synapsis; it occurs as a part of the prophase or

first stage of the reduction division. Some investigators

have been unable to demonstrate any real chromosome

fusion at this time, but all agree that there is an approxi-

mation between the two sets, and a chance for some kind

of an exchange or interaction to take place.

468 THE AMERICAN NATURALIST [ Von. XLIX

Evidence of the physiological individuality of the chro-

mosomes may be concluded by referring briefly to the so-

ealled accessory chromosome. This fraction of a chro-

mosome, whole chromosome, or in some cases, group of

chromosomes, pessesses no true synaptic mate, and there-

fore at reduction division two types of daughter cells are

found. The presence or absence of the ‘‘accessory’’ is so

closely associated with sex determination that most biolo-

gists now regard it as the morphological expression of a

germinal sex determinant. The essential result of re-

searches on this body may be summed up in the following

words of Wilson.

They have established the existence of a visible difference between the

sexes in respect to these chromosomes, and have shown that it is trace-

able to a corresponding difference in the nuclei of the gametes of one

sex or the other.

The simplest type of accessory chromosome, where the

male possesses an unpaired chromosome which passes

to one pole undivided in one of the spermatocyte divisions

and hence enters but half the spermatozoa, was discovered

by Henking (1891) in Pyrrhocoris. This work was con-

firmed in certain species of Orthoptera in 1902 by Mc-

Clung, who advanced the hypothesis that the odd chromo-

some was a sex-determiner. Shortly afterward this was

made more probable by Wilson and by Stevens who

proved for several species of Hemiptera that the body

cells of the males contain one less chromosome than the

females. Two accessory or X chromosomes are present

in the female, while but one is present in the male.

About the same time, both Wilson and Stevens inde-

pendently discovered another kind of dimorphism in male

germ cells of certain Hemiptera. Here the X chromo-

some of the male has a smaller synaptic mate Y. The

body cells of the female, however, show two of the large

X chromosomes. The sexes, therefore, both contain the

same number of chromosomes, but have the same type of

chromatin difference as was first discovered. The female

is XX and the male XY.

No. 584] HEREDITY AND ITS MEANING 469

Baltzer claimed in 1909 that in the sea urchins Sphere-

chinus and Echinus the sex with the dimorphic germ cells

is the female instead of the male, but the work of Tennent

has shown him to be in error and he has retracted the

statement. There is, therefore, no undisputed cytological

evidence demonstrating this type of dimorphic eggs; but

since breeding results on certain species of birds and of

lepidopters can be interpreted only on such an assump-

tion, it is safe to assume that sooner or later they will be

found.? Whether or not there are animals of this type,

however, is of no particular importance in the present

discussion. What we desire to emphasize is that a large

number of animals, including man, have been shown to have

a chromatic difference between the sexes, and that this

difference is readily explained by the fact that the eggs

are of a single type and the spermatozoa of two types.

In dicecious plants no such morphological differentia-

tion has been found. But this fact does not negate the

idea that the visible differences found in animals are really

sex-determining differences. We have only to suppose

that the dimorphism is primarily qualitative and second-

arily quantitative. Indeed Wilson has found that the Y

chromosome—the synaptic mate of the X—may vary in

different species from a size equal to that of X until it

disappears entirely, leaving X without a mate.

There is only one criticism in this whole matter. One

may admit these cytological differences between the sexes,

but hold that they are early appearances of secondary sex-

ual characters. Morgan, von Baehr and Stevens have

answered this impeachment. In the phylloxerans and

aphids all the fertilized eggs produce females; males arise

only by parthenogenesis, though females may arise in this

manner. The cytological facts are as follows: Under

favorable external conditions eggs develop without reduc-

tion and females are formed. Under unfavorable condi-

tions one or two chromosomes (the sex determiners) are

thrown out. If these eggs develop without fertilization

2Dimorphie eggs in Lepidoptera have recently been demonstrated by

both Doncaster and Seiler.

470 THE AMERICAN NATURALIST [ Vou. XLIX

males arise. The somatic condition of the females may

therefore be termed XX and that of the males XY. If

both reduced normally at any time, ordinary fertilization

might be expected to give both males and females. But

the spermatocytes without X degenerate, leaving only one

type of functional spermatozoa, which produces females.

Thus actual causal connection between the X chromosome

and sex determination appears to have been demonstrated.

These are the main cytological arguments in favor of

the chromosome view of heredity that seem to me to be

insuperable. There are minor arguments both pro and

con, which, as I said in the beginning, we have not space

to consider. Instead it seems more profitable to- show

how Mendelian results interlock with those from cytology

like the parts of a jig-saw puzzle.

CHROMOSOMES AND MENDELIAN INHERITANCE

The principal phenomena of Mendelian inheritance are:

(1) characters that breed true; (2) uniformity of the

population of the first hybrid generation in particular

traits in which homozygous parents differed; (3) inde-

pendent segregation of certain character determiners;

(4) recombination of certain characters; (5) perfect

coupling between certain characters; and (6) partial

coupling between certain characters. Let us see how

plausibly one čan picture the mechanism through which

such phenomena may result without imputing to the

chromosomes any behavior that is not known to occur.

To do this simply let the imagination portray a plant spe-

cies having four chromosomes, each chromosome having

three character determinants that can be followed through

the breeding results that are obtained.

Our figures represent the immature germ cells of the

plant just previous to the reduction division. Fig.

shows the germ mother cell with a duplicate set of heredi-

tary determinants. The mature germ cells are exactly

alike, therefore the plant breeds true to the characters.

concerned.

No. 584]

HEREDITY AND ITS MEANING

Q W p

Meo

Fig. 1

Fic. 2

Que

Meo

aos

Meo

471

Suppose, however, that a change in the germ plasm has

occurred (Fig. 2) at some time or other.

In one member

of the first pair of chromosomes, determinant ‘‘A’’ has

The mature germ cells differ from each

other by one factor.

become ‘‘a.’?

Q Wp

=" ug

Fie. 3

mo]

For this reason the plant does not

breed true, but gives a mono-hybrid Mendelian result.

472 THE AMERICAN NATURALIST [Vou XLIX

Again, if such a change occurs that A becomes A’ (Fig.

3), a series of triple allelomorphs giving monohybrid re-

sults with each other, is formed. ‘‘A’’ is allelomorphic

to 66 Ar? or &tg 2?

Qov

O p

Aad

Eng e.

giok»

FIG. 4

But there are other character determinants in the first

pair of chromosomes. What happens if both ‘‘A’’ and

“B” become changed? There are two possibilities, as

shown in the two parts of Fig. 4. If one of the members

of the pair of homologous chromosomes becomes abC

while the other remains ABO, there is a positive corre-

lation between the inheritance of ‘‘A’’ and ‘‘B.’? On the

other hand, if the change is such that the two chromo-

somes are aBC and AbC, there is a negative correlation

between A and B. In other words, the determinants re-

main correlated in the same way they entered the com-

bination. There may be breaks in these correlations,

however, as Morgan has shown in Drosophila; and these

breaks in correlation occur in a constant ratio. Diagram-

matically, it may be said that A and B are always the same

distance apart in the chromosome structure and that the

determinants ‘‘cross over’’ from one member of a pair

to the other every so often. All of the gametes in the

first case are not ABC and abC, for example. Some of

them will be AbC and aBC. And the same percentages

of these cross overs are found in the second case where

“A” and ‘‘B”’ are correlated negatively. Furthermore,

No. 584] HEREDITY AND ITS MEANING 473

if C should become ec, and the chromosome pair take the

form ABC and abe, there are definite relations between the

three determinants. Breaks in correlation occur, and this

ratio is constant, so that if given the percentage of breaks

of correlation between “A” and ‘‘C’’ and “B” and ‘‘C,”’

the percentage of breaks between ‘‘A’’ and ‘‘B’’ can be

predicted. If there is a break in the correlation between

“A” and ‘‘C’’ 30 times in 100, and a break between ‘‘B’’

and ‘‘C’’ 10 times in 100, then there will be breaks in the

correlation between ‘‘A’’ and ‘‘B’’ 20 times in 100.

QW b&

QWs

Yeo

Fie. 5

Likewise, the determinants in the second pair of chro-

mosomes are coupled together in their inheritance. D, E

and F have each their peculiar linkage to the other, a link-

age that remains comparatively constant. Yet the de-

terminants in the second pair of chromosomes are entirely

independent from those in the first pair in their inheri-

tance. For example, if, as shown in Fig. 5, ‘‘A’’ should

become ‘‘a’’ in either member of pair number one, and

“D” should become ‘‘d’’ in either member of pair number

two, Mendelian dihybridism would result. Furthermore,

if “A” and “D” should each have the function of affect-

ing the same general character complex in somewhat the

Same manner, there would be an apparent 15:1 ratio if

dominance were complete or a series of types ranging

from the type of one grandparent to that of the other, if

dominance is lacking.

These are the main features that have been established

474 THE AMERICAN NATURALIST [ Vou. XLIX

by recent work on hybrids. We have pictured them as

actual chromosome functions, because every part of the

description has been actual fact as far as the breeding

experiments go. Our picture, it is true, is fictitious, for

we do not know absolutely that the heredity mechanism is

of this nature. But the facts do fit perfectly all that is

known of chromosome behavior. It seems impossible,

therefore, that there should be so many coincidences.

There are also two other pieces of evidence that fit in

and round out the case. Bridges has shown that females

occasionally occur in Drosophila bearing the sex-linked

characters borne by the mother but showing no influence

of those borne in the father. Such exceptional females

were found to inherit directly from their mother the power

of producing like exceptions, and it was proven cytolog-

ically after the prediction had been made from the breed-

ing facts that these females resulted from the non-disjunc-

tion of the X chromosomes at the maturation of the eggs

from which they came, and that one half of their daughters

did in fact contain a Y chromosome in addition to two X

chromosomes. This appears to be definite proof that sex-

linked genes are borne by the X chromosomes.

The other important basis for regarding the chromo-

somes as the material basis for heredity also comes from

Morgan’s work on Drosophila ampelophila, this being the

only species upon which sufficient work has been done to

give a reasonable basis for the conclusion. All of the hun-

dred and thirty or so mutations in this species wpon which

Morgan and his students have worked are so linked to-

gether in heredity that they form four groups correspond-

ing to the four pairs of chromosomes found in the species.

If one single character should be found that did not fit into

one of these four groups, the whole theory would break

down. But no such character has appeared.

This completes the case for the chromosomes as regards

the main facts, and it seems only proper that a fair-

minded jury of scientists should render verdict for the

plaintiff. No case is so bad, however, that a lawyer can

No. 584] HEREDITY AND ITS MEANING 475

find nothing to say for the defense and scientists in this

respect resemble the men of the bar. Certainly there are

some outlying facts, but they are comparatively unimpor-

tant. If a series of important facts should at any time

be found which do not fit, the chromosome mechanism

should be looked into. It is likely that the explanation

will be found in an abnormal chromosome behavior as was

the case in the aphis.

_ PRACTICAL CONCLUSIONS AND Discussions

If now it be accepted as a reasonable premise that the

chromosomes are the chief if not the sole bearers of he-

reditary determinants of body characters, and that their

behavior is a rough indication of the mechanism of he-

redity; what cytological facts, if any, can be made useful

at present or in the future to plant and animal breeders?

If such data exist, they should be put to service; if it is

likely that such facts can be found, investigations should

be undertaken. The broad question may be divided into

three parts which will be discussed in regular sequence :

1. What are the relations of chromosomes to somatic

characters?

2. What are the relations of normal chromosome beha-

vior to the transmission of characters?

3. What are the relations of peculiar or unusual chro-

mosome behavior to the transmission of characters?

RELATIONS OF CHROMOSOMES TO INTERNAL CHARACTERS

Some very interesting observations have been made on

. the relations of internal and external characters to chro-

mosome number.

Farmer and Digby in a comparative study of the cells

of a fern of the genus Athyrium with similar cells of three

of its varieties, found that the measurements were suc-

cessively larger in the three varieties than in the species,

and that there was a corresponding increase in the number

of chromosomes, the gametic numbers for the species and

its varieties being estimated at 76-80, 84, 90 and 100,

476 THE AMERICAN NATURALIST [Vou. XLIX

respectively. Investigations on another fern, Lastrea, did

not corroborate these results, however, in one variety the

chromosomes being more numerous and the cells smaller -

than in the parent type.

Gates by comparing nuclei and cells of different tissues

of Enothera Lamarckiana and similar structures in its

‘mutant’ O. gigas with double the number of chromo-

somes, found that the O. gigas cells and nuclei were always

larger, varying from a comparative ratio of 1:1.5 to 1:3.

At the same time, it would hardly be wise to maintain that

this is always the case, for ~~ a few individuals were

investigated.

Primula sinensis has two foxstia in cultivation, similar

except as to size. The giant form has flowers about one

and one half times the size of those produced by the ordi-

nary form. Gregory investigated these two forms cyto-

logically to determine the cause of this increase. The

nuclei and the chromosomes of the giant form were a little

larger, though the difference was hardly a measurable one.

The chromosome number was the same in both the forms.

In a later investigation he has found that some exceed-

ingly large plants with nuclei distinctly larger than those

of the normal form had double the number of chromo-

somes normal to the species.

Boveri investigated this same relation of cells and nu-

clei to chromosome number in N, 2N and 4N larve of the

sea urchin. From these studies, he concludes that chro-

matin is non-regulatory, and in the case of decrease, un-

regenerable, the cytoplasm in contrast showing the fullest

regulatory activity. Further, the size of the larval cells

is governed by the chromosome mass and the cell volume

is directly proportional to the chromosome number. On

the other hand, Conklin’s investigations on annelids, mol-

lusks and ascidians lead him to take a position opposed

to that of Boveri. He says:

The size of the nucleus, centrosomes and chromosomes is dependent

upon the volume of the cytoplasm is clearly shown in Crepidula, where

in large and small blastomeres, these structures are invariably propor-

tional in size to the volume of cytoplasm.

No. 584] HEREDITY AND ITS MEANING 477

_ Neither chromosomes nor nucleus control, the size of the

cell in annelids, mollusks or ascidians.

RELATIONS BETWEEN CHROMOSOMES AND EXTERNAL

CHARACTERS

Thus there seems to be no constant relationship even

between nuclear or cell size and number of chromosomes,

and bonds of union between external taxonomic charac-

ters and chromosome number seem to be still more tenu-

ous. It is true tliat certain giant Primulas and Ginotheras

had more chromosomes than were characteristic of the

normal forms, but it is just as clear that all giant Primulas

(and the same is probably true of Ginotheras, from the

work of Heribert-Nilsson and of Geerts) do not have ab-

normal chromosome numbers.

Results on several species of both animals and plants

are interesting in this connection.

The thread worm, Ascaris megalocephala, has two va-

rieties, bivalens and univalens, the former having as a 2N

number four chromosomes, the latter two chromosomes.

Nothing is known as to the origin of these two forms.

They are found parasitic in the same host individual and

neither form is rare. According to Herla, they hybridize

freely and produce embryos whose cells have three chro-

mosomes, but no mature hybrids have ever been found.

Meyer could distinguish no anatomical differences þe-

tween the two varieties.

Rosenberg investigated the reproductive structures of

two species of sundew and found one to have double the

chromosome number of the other. A subsequent com-

parison of anatomical and taxonomic characters failed to

show any sharply marked differences between them ex-

cept in size. The form having the smaller chromosome

number was smaller and less robust. They inhabit the

same territory and produce natural hybrids which are

sterile.

Rosa canina has two varieties which have the same taxo-

nomic characters, but one form has thirty-four while the

478 THE AMERICAN NATURALIST [VoL XLIX

other has only sixteen chromosomes. The form with

thirty-four chromosomes is apogamous and reproduces

without fertilization, but that one must not conclude that

apogamy is necessarily associated with a double or an in-

creased chromosome number, is clear from the case of

Rumex. Rumex was investigated by Roth; one species,

R. cordifolius, having forty chromosomes as its 2N num-

ber, required fertilization to produce offspring; another

species, with only sixteen chromosomes, was apogamous.

A short list of nearly related species or species with two

varieties varying in their chromosome numbers with their

character differences, if present, is given below.

Name Date | N | 2N Characte rs Investigator

Alchemilla SSAB 1904 |32| 64 |Apogamous Strasburger, E.

aphanes....... 1904 | 16| 32 > =

Ascaris ioe hap 1883 | 2| 4 |Alike externally |Van Beneden

s4 e e rg 1895.{| 2| 4 Meyer, O.

rh Ne Ge eee 1 99 T “ and others

Ascaris lumbricoides....... 1887 24 Boveri, T.

n De eee 1887 48 S 4

Dahlia variabilis S E 1911 |16| 32 Ishikawa, M.

vee ee 1911 | 32} 64 3 S

Drosera Baramin P T 1909 |10| 20 Rosenberg, O

ola... 20 | 40 More robust, ete. i s

Echinus microtuberculatus 1888 | 9| 18 Boveri, T.

1902 |18| 36 oh A

Heliz pomatia...........: 1903 |24 | 48 |Alike externally |Ancel, P.

: ie eee iat oe 1896 |12| 2 v. Rath, O.

N ephrodium molle onas 1908 |64 |128 None mentioned | Yamanouchi, 8.

ree ane 1908 66 132 :

Cnothera seul shame ay 191) rn Gates, R. R.

eh 909 | 14 |. 28 Large and 2 ERS

coarser j

FUA sinensis wa 1909 |12| 24 Gregory, R. P.

t form ing ROK 1909 12| 24 More robust n ee

a ee 1914 |24| 48 = Ly g ee

Rosa canina Pa aah ian ap a 1909 34 |Apogamous Rosenberg, O

Cie eis OS c Les 190: 8} 16 Strasburger, E

Thalictrum WRUNG os 1909 | 12 | 24 Overton, J

rpuras 1909 |24 | 48 |Apogamous a $6:

Zea was meee Flint’ a 1911 !10 Kuwada, Y. “

r e Bo e ooo, 1911 |12 | he

What conclusions can be drawn from these facts? Cer-

tain botanists have attempted to connect chromosome

doubling with apogamy, as usually the chromosome num-

ber in apogamous species is higher than in the normal

species of the same genus; but there is no evidence of

No. 584] HEREDITY AND ITS MEANING 479

apogamy in @nothera gigas, and in Rumex the form with

the low number of chromosomes is apogamous while the

form with the high chromosome number requires fertili-

zation. On account of these exceptions, therefore, it |

seems probable that the cause of apogamy is deeper than

a mere doubling of the chromosomes, even though doub-

ling may usually accompany such a change in reproduc-

tive habits.

Variation in chromosome number in the same species

has been proposed as a cause of general variation in so-

matic characters, but the evidence is not clearly in favor

of such a theory. In the fern Nephrodiwm molle Yama-

nouchi found spermatid cells to be of two sorts, those with

sixty-six and those with sixty-four chromosomes. This

would mean that Nephrodium has two gametophyte forms

and two sporophyte forms, externally identical, so far as

our present knowledge goes, but differing in their chro-

mosome numbers.

Further, sporophytes developing from the prothallia of

ferns without the intervention of a sexual process have

the N instead of the 2N chromosome number, yet apoga-

mously developed fern sporophytes, except as to chromo-

some number, are indistinguishable from normal sexually

produced individuals of the same species.

Many writers have been tempted to postulate a causal

relation between the numerical variation of chromosomes

among the species of a genus and the genera of a family

and their specific and generic characters. The thirty or

more species of Composite investigated have shown a

remarkable variation in their chromosome numbers, the

2N numbers ranging between six and sixty, and, as is well

known, the Composite possess an infinite variety of

sharply contrasting characters. But the lily family also

has an enormous number of characters in its species and

genera, and the genus Liliwm, with its great variety of

characters distributed among forty-five species, is typical

of the other genera of the family, as far as present inves-

tigations go, in having the same chromosome number for

480 THE AMERICAN NATURALIST [Vor. XLIX

all of its species. Others suggest that the more chromo-

somes a plant species possesses the greater is its varia-

bility. Thus Spillman? speaks of the low variability of

rye, suggesting its small chromosome number (six or

eight) as a possible reason; for maize, having probably

from twenty to twenty-four chromosomes, is infinitely

more variable than rye. However, Britton’s ‘‘Manual’’

selects Crepis virens for special mention as an extremely

variable species from among the four or five other species

listed under that genus, and it is known that C. virens

has only six chromosomes, while three other species of

Crepis investigated all have higher numbers. Again, ac-

cording to Wiegand, the Canna has only six chromosomes,

yet every gardener is well acquainted with the infinite

variety in Cannas.

THE CHROMOSOMES AND VARIABILITY

After a consideration of the above facts, one may well

hesitate to state that there is even a high degree of corre-

lation either between variability in chromosome number

and general variability, or between high numbers of chro-

mosomes and a high degree of variability in specific char-

acters. On the other hand, it is not certain that the data

upon which our discussion is based are relevant to the case

in hand. We have discussed a possible relationship be-

tween chromosome numbers and species complexity and

variability as found in the wild. This is not at all the

same thing as discussing the relationship between chro-

mosome number and true variability. It is true that com-

plexity and specialization of plants and animals seem to

have no connection with chromosome number, and that

within a family a genus or a species profusion of taxo-

nomic characters do not go hand-in-hand with high chro-

mosome numbers. But in these cases our data come from

persistent forms. What the actual inherent variability

of the protoplasm is in most cases we do not know. Dro-

sophila ampelophila, a species with only four chromo-

3 Six according to Westgate’s unpublished data; eight according to Nakao.

No. 584] HEREDITY AND ITS MEANING 481

some pairs, is considered to be very constant in its char-

acters from the taxonomist’s standpoint, yet by careful

continued observation Morgan has succeeded in detecting

over 130 mutations.

From a strictly mathematical standpoint, it would seem

that if other things are equal, variability would take place

in proportion to the number of chromosome units. The

difficulty is that in no case do we know anything whatever

about the relative complexity of any particular chromo-

some unit. One must infer, however, that the 47—48 chro-

mosomes in man are individually much more complex than

the 128-132 chromosomes in the fern Nephrodium molle.

If this inference be correct there are reasons why altera-

tion in determinants may occur in direct proportion to

the number of chromosomes or rather to the mass of chro-

matin without there being visible somatic variability in

the same ratio. Let us construct an imaginary plan for

preventing visible variation without preventing change

in chromosome determinants. Unquestionably the sim-

plest means is to double the chromosome number. Se-

lecting, for example, a species with four chromosomes, let

us suppose that fertilization occurs without a reduction

division at some time or other. Then instead of a dual

organism with two sets of chromosomes of similar func-

tion, one from the male and one from the female parent,

there would be a quadruple organism with two sets of

similar chromosomes from each parent. Any germinal

change which would produce a new dominant character

would be apparent immediately, but for a recessive change

to appear—and these are many times as numerous as the

others—it would be necessary to have identical changes

occur in two chromosomes. Following out this line of

reasoning, it is not hard to see what a great possibility

for uniformity there is in further chromosome duplication,

provided the actual fact of duplication makes no great

change in the organism. That chromosome doubling has

no decided visible effect we have seen from the cases

already described; and since so many nearly related spe-

482 THE AMERICAN NATURALIST [ Vou. XLIX

cies and varieties have their chromosome numbers in

series 1:2:3:4, ete., it seems by no means improbable that

what we have imagined above has actually occurred many

times. And if one may believe that the eyent has the

result supposed, all the worry about relationships between

chromosome number and height of species in the scale of

evolution may be eliminated.

Norman CHROMOSOME BEHAVIOR AND HEREDITY

The second query, concerning the relation of normal

chromosome behavior to the transmission of characters,

is much more important than the one just examined, but

it can be discussed more briefly. By normal ‘‘chromo-

some behavior’’ is meant a reduction division where ma-

ternal and paternal chromosomes approach each other in

definite pairs (if homologous pairs are present), chance

only governing the passage of either to a particular

daughter cell. This is probably the usual behavior in the

higher plants and animals, and upon this behavior depends

Mendelian heredity in the narrow sense. The thesis to be

submitted and scrutinized is the following: The maximum

possible difficulty in the improvement of animals and

plants by hybridization usually depends directly upon the

chromosome number.

When a mutation in a single determinant takes place in

the germ cells of a plant, such as may cause the loss of

red color in the corolla, crosses between such a form and

the normal give a monohybrid Mendelian result. Two _

mutations in non-homologous chromosomes gives in a

similar way a dihybrid result. Such simple conditions,

however, are not met with very frequently. For example,

White found that a fasciated tobacco when crossed with

the type from which it sprang and from which it probably

differed only by this single determinant, gave a mono- —

hybrid Mendelian ratio in the F, generation; but when the

fasciated type was crossed with other types the result was

a complex F, population. This population was suscepti-

ble of analysis, nevertheless, and showed that the various

No. 584] HEREDITY AND ITS MEANING 483

varieties with which the fasciated type was crossed dif-

fered from it by several determinants, each of which was

transmitted independently though they every one aff ected

the development of fasciation. This illustration is not

one of a rare phenomenon. It is what geneticists find

constantly in their experiments. Presence or absence of

a particular character may depend upon the presence or

absence of a particular essential determinant, but, given

this determinant, sooner or later the investigator finds

several other determinants which modify the expression

of the character. The existence of these modifiers has

been the cause of a great deal of confusion in the analysis

of breeding results, but in reality the inheritance is sim-

ple. The experience that all investigators who have

worked intensively have had with them shows that prac-

tically all somatic characters are due to multiple determi-

nants in the germ cells. It merely depends on the rela-

tive difference between the germ plasms brought together

in crosses, how complex the resulting F, populations ap-

pear. Since even apparently simple characters are thus

due to complex germinal interactions, that results of

crosses made for the purpose of improving such intangi-

ble things as yield, size, quality, etc., should be complex,

is not astonishing. In the comparatively extensive expe-

rience that the writer has had in breeding tobacco, maize,

peas and beans the wide variability of the F, population

in crosses between distinct varieties leads him to think

that it is extremely common for such varieties to differ

qualitatively in every chromosome. Furthermore, the

relative complexity of the segregating populations is

much greater in tobacco than in corn and greater in corn

than in peas or beans. What can this mean but that when

varieties are found that differ qualitatively in all of their

chromosomes, the complexity of the result varies directly

with the number of chromosomes present.

In Mendelian inheritance the number of actual types

(both homozygous and heterozygous) present in the F,

population when all are represented is 3", and the number

484 THE AMERICAN NATURALIST [ Vou. XLIX

of individuals that must be present to give an equal chance

for the presence or absence of an individual of every type

is 4", where n represents the number of allelomorphic

pairs. This being true, if differences in all of the chro-

mosomes are predicated in tobacco and in pea crosses, the

maximum number of individuals necessary in the F, gen-

eration to allow for one reproduction of each of the grand-

parental forms is 42 in the first case and 47 in the second

ease. It is clear that there is an absolutely overwhelming

difference in the difficulty of recovering the grandpar-

ental forms in the two examples.

Now this is about what one wishes to do in many plant-

breeding problems. It is desired to combine one or two

characters from one parent with all of the other qualities

of the second parent. And such has been my experience

that I believe that this maximum possible difficulty in the

operation as predicated by qualitative differences in all of

the chromosomes often occurs. There can be no question

on these grounds of the importance of determining the

number of chromosomes in a species before beginning

a complex plant-breeding problem, and thus being able to

comprehend the maximum possible difficulties that may

be encountered. How greatly these difficulties vary may

be seen in the very incomplete list of chromosome counts

in common plants that is given below.

Common Name | Scientific Name ee 2N Date Investigator

Banana..... Musa sapientum, "dole 8 16" 1910 |Tischler, G.

ree gi ald Musa sapientum, |

"Radjah Siam’”’...... i 26 a 1910 z md

T eas aor anime Ss 24 48 1910 oe Mi

Bean; oY. Phaseolus vulgaris......| 8 16 1904 |Wager, H.

Calla lily.. pps Africana.....| 8 16 1909 (Overton, J. B.

chy eRe Can indica Cat eee es ge 6 1900 |Wiegand, K. M.

Cee ee en eee eet | 8&8 more than

| 10 1904 |Koérnicke, M.

Coti. ss cee Zea Mays, * ‘yellow

starchy” ‘‘amber

pop,” “black ma nage

“golden broach field,”

Cahita Mat coo, 10 “op? 1911 |Kuwada, Y.

cece, 9-10 | “18-20” | 1911 j T

RD Eo pruebas 9-12 1911 585 2

No. 584] HEREDITY AND ITS MEANING 485

Common Name. Scientific Name N 2N Date | Investigator

Pes A ye ei Zea M ays, re sugar.. 12 1911

Cottone cc] Gossy ypium hybrid’. ..] 28 “567 1903 bai W. A.

ob he diane! ti i “Egyptian” 20 1910 Balls, W. L.

EE ATA ER E E bt “16” | 1906 |Tischler, G.

Dandelion. ` Tarazacum confertum.. 8 “16” 1909 Rosen i,

Pi ere ener) O .|120r13, about 26 | 1905 (Juel, H. O.

Elderberry.. 3 Sambucus 2 PO une eee 18 38 1909 Lagerberg, T.

Ev vening |

primrose .. \@nothera grandiflora... ra 14 1909 Davis, B. M.

Evening | |

primrose... O. lamarckiana........ “Jy 14 1907 Geerts, J. M.

| 7 1911 Gates, R. R.

Evening | |

primrose. . . 0. gigas... i. 5 arous 14 28 1909 Gates, R. R.

eae pee N ia i II RNT E a 64 128

or or 1908 Yamanouchi, 8.

66 132

okies as squalens...........| 12 2 | 1900 Strasburger, E.

tea WRT 7 ae lanceolata var. | |

platyphylum......... 5 10 2014 Tahara, M., and M.

| Ishikaw:

we (Grupis WORE aan 3 6 | 1909 Rosenberg, O

p \Crepis tectorum........ 4 8 | 1905 el, H. O.

=e Crepis japonica........ 8 16 1910 Tahara, M.

NAGS cae & Lilium martagon.......| 12 24 | 1884 Guignard, L.

Lily-of-the- |

alley . Convallaria majalis 18 “36” | 1899 Wiegand, K. M.

Lily-of-the- :

Valley os oe ue majalis..... 6 3 09 Sauer, L. W.

berry... -Morus orus alba, ‘‘Shirowase’’ 17? 40-50 1910 Tahara, M

rS orus indica.......... 14 28 1910 Tahara,

Nightshade Solanum nigrum....... 36 72? 1909 inkler, Hans

D E ein Cone. E AT E y A "107 1898 Schaffner, J. H.

Pees see See Paeonia spectabilis..... i2 oe" 1893 |Overton, E.

eee isum sativum......... 7 14 903 (Cannon, W. A.

Persimmon. .|Diospyros virginiana 30 or

more 1911 (Hague, Stella M.

Bg) RR ah dea, Pinus cate SOA 12 24 1899 Cha ST n, ©. d.

ren PA E Orana oliot. inari 12 244 1910 Kuwada, Y.

irer Rosa va 3 species..... 8 16 1904 retni eane E.

Tobacco..... Nicotiana ap: .. 6.45 ss: 24 48 1913 |White, O. E.

hea bees pasan eA.. 12 24 1909 Winkler, Hans

Eeoae ulipa Gesneriana......| 12 24 1901 t, A.

Wake-robin Trillium grandiflorum 6 3 1899 Atkinson, G F

Seok Triticum vulgar Sees « 8 16 Koérnicke, M

a See re 8 STE" 1893 (Overton, E.

e PE a Pe piu ee ee 8 ek | 908 (Dudley, A. H.

Among these figures are found four of our most impor-

tant crops—wheat, tobacco, corn and cotton. They con-

trast strikingly in their chromosome numbers.

eat

and tobacco, species in which the flowers are naturally

self-pollinated, have 8 and 24 chromosomes, respectively,

4‘*But we often find a larger number.’’ Quotation marks refer to in-

ferred numbers rather than actual countings.

486 THE AMERICAN NATURALIST [ Vou. XLIX

in their gametes. Corn and cotton, species usually cross-

pollinated, have 10-12 and 20-28 chromosomes, respect-

ively, in their germ cells. These species all have been

under cultivation since before there has been recorded his-

tory. Many varieties of each exist. It is not at all im-

probable that with thousands of years of cultivation and

selection under diverse conditions, mutations in most of

their chromosomes have persisted. If, then, improvement

means working on character complexes that involve al-

most all of the plant functions, it does not seem improb-

able that the actual difference in the difficulty of improving

wheat and tobacco is as 48:44, or about 1 to 4,295,000,000.

In like manner corn and cotton compare in the ratio

41°: 428. or 1 to 68,720,000,000. And is it not true that

modern improvement in most of these crops does involve

nearly all the plant functions? Yield in wheat involves

number and size of grain, and number of culms, with all

that these things include in plant economy; yield of to-

bacco involves number, size and thickness of the leaves.

Quality, a mystical word, is perhaps still more complex.

In wheat, it takes in habit of growth of both root and stem

and such other characters as go to make up strength and

hardiness, thickness of pericarp, size of aleurone cells, and

the physical and the chemical character of both endo-

sperm and embryo, as well as their size ratios in regard

to each other. In tobacco, it includes thickness and

strength of leaf, color, texture and all chemical and physi-

eal characters that make for flavor and ‘‘burn.”’

One may say that this is all very well as a theory, but

that it is all theory, and ask what support is given to it by

practise. I have had personal experience with but two

of these four crops. I have worked extensively and in-

tensively with corn and tobacco for some ten years. But

I have followed carefully the published experiments in

breeding wheat and cotton and have seen several of the

more important experiments. And I may say that it was

my observation of the extreme difficulty in the experi-

ments with cotton and tobacco as compared with corn and

wheat that led to this theory of the cause.

No. 584] HEREDITY AND ITS MEANING 487

In proposing this thesis, the chromosomes have been

considered as pairs of freight boats loaded with character

determiners, shifted bodily to the daughter cells by in-

ternal forces of which we are ignorant. Yet this is not

the whole truth. The determiners in particular chromo-

somes seem to be tied together more or less tightly, but

they are not always transferred as one package. They

are coupled in their transmission to the next generation,

but this coupling is not perfect. Breaks in the coupling

occur and there is order and regularity in these breaks.

Our knowledge on these matters rests upon the researches

of Morgan on Drosophila, Bateson on the sweet pea, and

Tanaka on the silkworm, so it is not certain whether these

are common grounds for this regularity or whether each

species has regular laws which control the breaks in cor-

relation. But in either case, these breaks do not inter-

fere with our proposition. They only complicate matters.

In most of the cases in Drosophila, where they are best

known, linkage is comparatively tight, 7. e., breaks are

somewhat rare; but they may become so frequent as to

simulate inheritance from separate chromosomes. In

those cases our theory is of no value, but if Drosophila

is any criterion by which to judge, such conditions are

very unusual.

ABNORMAL CHROMOSOME BEHAVIOR AND HEREDITY

The third query concerning the relations of peculiar or

unusual chromosome behavior to the transmission of

characters may be passed over with a word. In certain

insects, for example, bees, wasps, aphids, phylloxerans,

etc., odd sex ratios and attendant complexities have long

been known. These have been cleared up more or less

-completely by cytological studies. They depended upon

chromosome behaviors that are not usual in animals or

plants. Similar peculiar chromosome mechanisms may

be present in many other species. Attention is merely

called to the fact that if experiments on any plant species

appear to show that its characters do not obey the laws

that have been demonstrated for so many types, their

488 THE AMERICAN NATURALIST [ Vou. XLIX

cytological eccentricities should be looked into. In them

will probably be found the key to the situation. The

(Enotheras may be mentioned as a ease in point. Their

heredity in many cases is not what would be expected by

analogy with other plants. We know that in some ways

the behavior of their chromosomes is irregular. Further

study will probably show that this is the sole cause of their

anomalous heredity.

LITERATURE CITED

Allen, C. E

1905. Nuclear nsike in the Pollen Mother-cells of Lilium canadense.

An , 19: 189-258.

Atkinson, G. F.

899. Studies on Reduction in Plants. Bot. Gaz., 28: 1-26.

W.L

1910. The Mechanism of Nuclear Division. Ann. Bot. 24: 653-665.

1910. Ueber die ag! zwischen dem Chromatin und der Ent-

een und Vererbungsrichtung bei Echinodermenbastar-

den. v. f. Zeliforsch., 5: 497.

gerse W.

1909. iDa ’s Principles of Heredity. Cambridge, R Uni-

sity Press. See bibliography reported ther

Bonnevie, K

1909. Chromosomenstudien I. Archiv. f. Zellforsch.,1: 450-514, 1908.

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REGENERATION POSTERIORLY IN ENCHY-

TRÆUS ALBIDUS!

H. R. HUNT

THE primary object of the following experiments was

to determine whether Enchytreus albidus can regenerate

posteriorly, when cut at regions of the body varying from

near the posterior end to near the anterior end. Sec-

ondly, an attempt was made to compare the rates of re-

generation per day posteriorly at the different levels at

which the worms were cut in two.

No experiments have been published in which the ca-

pacity of this species to regenerate posteriorly has been

tested. Nusbaum (’02; ’04) studied the histological

processes in the regeneration of the Enchytreide ante-

_ riorly and posteriorly. He found that regeneration ante-

riorly does not take place as readily as regeneration pos-

teriorly, and that never more than two or three segments

regenerate anteriorly.

The animals used in the present experiments were col-

lected in abundance from the coarse gravel of the tidal

zone on the seashore at Cold Spring Harbor, Long Island,

New York. Six sets of experiments were conducted.

Each of the worms was cut into two pieces, the anterior

and the posterior pieces being preserved. The average

number of segments in this species is not far from sixty.

The regions selected for cutting were such as to give

fairly comprehensive data as to the regenerative capacity

posteriorly at different levels. In the first set of experi-

ments the worms were so cut as to leave only about eight

anterior segments; in the second set about sixteen anterior

segments; and in the third set about twenty anterior seg-

ments. In the fourth set the cut was made near the

middle of the worm; in the fifth about sixteen posterior

1 Contributions from the Zoological Laboratory of the Museum of Com-

parative Zoology at Harvard College, No. 260.

495

496 THE AMERICAN NATURALIST [ Vou, XLIX

segments were removed; and in the sixth eight posterior

segments. The worms were anesthetized with chloretone,

and the operation was performed under a dissecting mi-

eroscope. The pieces were placed in small sterilized glass

bottles, each containing a strip of filter paper and enough

sterilized sea water to keep the animals well moistened. -

Ten pieces of approximately the same length were kept

in a single bottle. Throughout the experiment the bot-

tles, each one stoppered with a cork, were kept in an ice

chest to restrict the growth of bacteria. The work was

begun early in July, 1913, and was continued until the

first of October. At the middle of August it became nec-

essary to carry away from the seashore the material then

living. After this, fresh water was used for moistening

the worms and cleaning out the bottles. The worms,

however, seemed to regenerate as well in the fresh-water

as in the salt-water environment. The analysis of the

results of the experiments was done in the zoological labo-

ratory of Harvard University.

It was found that the length of the regenerated seg-

ments, as compared with that of the segments in the adja-

cent unregenerated part of the worm, was a fairly accu-

rate criterion for determining the number of regenerated

segments. To test the accuracy of this criterion, parts

of eight worms consisting of the twenty most anterior

segments were allowed to regenerate for about eight

weeks. Having taken the precaution to determine accu-

rately the number of segments in each of the pieces at the

time of the operation, it was easy to determine how many

segments had regenerated, for of the total number of seg-

ments at the end of the experiment all except the original

twenty were, of course, regenerated segments. The re-

sult thus obtained was compared in each worm with that

obtained by counting in the same worm the number of

segments posterior to the point where there was an abrupt

change in the length of the segments, that point indicat-

ing the region of the cut. Table I gives the data for this

comparison. The results show that the method which

No. 584] REGENERATION IN ENCHYTRAEUS 497

was used to determine the number of regenerated seg-

ments is accurate to within one or two segments, for it

will be noted that the results by the two methods never

differ by more than two segments, usually by only one.

The worm’s body is so short that it was found impracti-

cable to secure exactly eight, sixteen, etc., segments in

every piece used in the whole series of experiments.

TABLE I

Number of Segments Regenerated :

As Determined by e

Number of the Worm Total Number Minus 20 Segment Length

1 6 rf

2 18 18

3 20 22

4 23 24

5 21 22

6 15 14

7 18 17

8 10 12

The results obtained in each of the six sets of experi-

ments have been condensed, for convenience, and are

shown in Table II. In the first vertical column of this

table the Roman numerals designate the number of the

set of experiments. The horizontal lines corresponding

to each of these sets give in succession, (1) the number of

segments in the pieces used in the experiments, (2) the

number of worms operated on, (3) the number that sur-

vived long enough to be observed, (4) the per cent of

worms that survived and were observed, (5) the period

during which the regeneration took place, (6) the number

of segments (0 to 24) regenerated by the surviving worms,

(7) the average number of segments regenerated in each

set of experiments, and (8) the mean rate of regeneration

per day of the worms in each set expressed in segments.

This mean rate of regeneration was obtained by first com-

puting the rate of regeneration per day (in segments)

for each worm in the set, and then averaging all the re-

sults. In some worms the number of segments regen-

erated was observed twice, several weeks elapsing be-

[ Vou. XLIX

THE AMERICAN NATURALIST

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No. 584] REGENERATION IN ENCHYTRAEUS 499

tween the two observations, so that the total number of

observations recorded in any one set of experiments may

be larger than the number of worms observed in the

same set.

The results of these experiments are summarized in the

graph shown in Fig. 1, where the rates of regeneration

per day (expressed in hundredths of the length of one

segment) are measured on the axis of ordinates (Y),

and the length (in number of segments) of the pieces that

produced the regenerated parts, are measured on the axis

of abscisse (X). Since sixty is about the average num-

ber of segments in this species, that is the value which

has been used in plotting the curve. A mathematical

analysis of the rates of regeneration at the different levels

shows that the difference in the mean rates of regenera-

tion at any two successive levels is significant. But the

temperature of the worms was not carefully controlled,

and the periods during which the wounds were healing

and the worms preparing to form new segments were in-

cluded in the computation of the mean rates of regenera-

tion. Therefore, the ratio between the rates of regenera-

tion, as here computed, at any two of the six levels only

approximates the ratio which would have been obtained

between the rates at these two levels by subjecting all the

worms to the same temperature conditions and by using

in the computation of the mean rates of regeneration only

the periods during which the segments were being formed.

The curve suggests, however, that the rate of regenera-

tion for the posterior half of the body is proportional, or

nearly so, to the number of segments removed. Anterior

to the twentieth segment the rate of regeneration de-

creases. May we not have here a curve depending on two

opposing sets of factors; one which tends to increase the

rate of regeneration as more segments are removed, the

other to decrease the rate? In the latter set of factors

the amount of available building material may be the most

important element.

500 THE AMERICAN NATURALIST [ Vor. XLIX

The worms seemed to regenerate equally well in a frei

water or in a salt-water environment. Thirty-one of the

one hundred and sixty surviving worms lived for about

forty days in a fresh-water environment and regenerated.

Twenty-six worms from which the sixteen posterior seg-

8 i6 2 30 44 52

Fic, 1. Curve showing the daily seme of pon Bae by pieces of six dif-

ferent lengths. The unit selected to measure the mean rate of regeneration at

each of the six levels was 1/100 of a catia ent, nent that oh to measure nse

lengths of the pieces which produced the regenerated segments was one segment

ent (on axis Y) was the same as that chosen = EE one segment (axis

of X) of the pieces mea nth yp reniawnee par

ments had been removed, and twenty-six others from

which the posterior half had been removed, regenerated

almost contemporaneously for about thirty days in the

same ice chest, and in a salt-water environment. Later

in the season in a different ice chest eighteen worms from

which the sixteen posterior segments had been removed,

and thirteen from which the posterior halves had been re-

moved, regenerated contemporaneously for about forty

days in a fresh-water environment. When the sixteen

posterior segments were removed the rate of regeneration

in the salt-water environment was 0.02 segments per day

less than in the fresh-water environment, while when the

posterior halves were removed the rate of regeneration

in the salt-water was 0.07 segments per day greater than in

No. 584] REGENERATION IN ENCHYTRAUS 501

the fresh-water surroundings. These facts show that

the worms regenerate in both fresh and salt water. This

is not surprising, since individuals of this species are

normally found both on the seashore, where they live in a

salt-water environment, and also in earth moistened with

fresh water. Furthermore, with the exception of the sa-

Fic. 2, Camera lucida iawii of the posterior end of a normal worm. Magni-

fied 17 diameters.

Fig, 3. Camera lucida drawing pags the pe regenerated posterior a ho a worm,

The region posterior to X is regenerated gnified 17 diam

Fie. 4. Sketch of a Aa double tail, pero about 17 pagia EA

linity of the water used to moisten the worms, the worms

which regenerated in the fresh-water surroundings were

probably subjected to about the same conditions as those

which regenerated in the salt-water. Therefore, the sa-

linity of the water in the environment does not seem to

affect the rate of regeneration. The data used in plotting

502 THE AMERICAN NATURALIST [Vou. XLIX

the curve shown in Fig. 1 were secured from worms which

regenerated in the fresh-water, as well as from those

which regenerated in the salt-water, environment. The

above observations make it seem probable, therefore, that.

the form of the curve does not differ fundamentally from

the form which it would have had if all the worms had

regenerated in salt-water surroundings.

In. Fig. 2 is shown the normal appearance of the ven-

tral aspect of the posterior end of a worm in which there

has been no regeneration. It will be noticed that the

length of the segments gradually decreases toward the

posterior end; but in Fig. 3, which is a camera lucida.

drawing of the posterior portion of one of the regen-

erated worms, the length of the segments decreases ab-

ruptly at the point X, showing that to be the point at

which the tail was removed.

Three worms from which eight posterior segments were

removed regenerated double tails. Morgan (’97) and

Michel (’98) observed the same phenomena in Allolobo-

phora fetida. One of these worms is shown in Fig. 4.

Some attempts were made to determine the rate of

regeneration anteriorly at different levels on the worm’s

body. At present all that can be said is that regeneration

posteriorly takes place much more frequently and rapidly

than anteriorly.

The conclusions that follow from these experiments are:

1. Enchytreus albidus regenerates posteriorly when

cut off at any level between eight segments from the pos-

terior end of the body and eight segments from the an-

terior end. It will be noticed that although the mortality

in pieces containing only the eight most anterior segments.

was about 94 per cent., yet those that did survive regen-

erated from three to eleven (on the average seven) seg-

ments. In other words, a piece from the extreme anterior

end, containing only one eighth the number of segments.

in the whole worm, can regenerate nearly as many seg-

ments, on the average, as it had at the beginning of the

experiment. Morgan (’97) found that in Allolobophora:

No. 584] REGENERATION IN ENCHYTRZUS 503

fetida anterior pieces of less than thirteen segments

rarely, if ever, regenerate posteriorly. In Enchytreus

the anterior limit of the capacity to regenerate posteriorly

was not found.

2. The rate of regeneration seems to increase from the

posterior end of the worm up to its middle almost in di-

rect proportion to the number of segments removed. An-

terior to about the twentieth segment the rate decreases.

3. Regeneration can take place either in a fresh-water

or in a salt-water environment. Also, the salinity of the

water seems to have little or no effect upon the rate of

regeneration.

4. Double tails can be regenerated when the eight

most posterior segments are removed.

5. Regeneration posteriorly takes place more readily

than it does anteriorly.

I am indebted to Professor C. B. Davenport for pro-

posing the problem and for making many helpful sugges-

tions. I also wish to express my gratitude to Professor

E. L. Mark and to Professor H. W. Rand for corrections

and suggestions in the preparation of the manuscript.

REFERENCES CITED

Michel, A.

1898. Recherches sur la Régénération chez les Annélides. Bull. sci.

France et Belgique, Tome 31, pp. 245-420, pl. 13-19.

Morgan, T. H.

1897. Regeneration in Allolobophora fetida, means = Entwick-

lungsmechanik, Bd. 5, Heft 3, pp. 570-586,

Nusbaum,

1902. Veber ks morphologischen Vorgänge bei der Regeneration des

lich abgetragenen hinteren Körperabschnittes bei Enchy-

seo Arch. polonaises Sci, biolog. et med., Tome 1, pp,

292-347, (Cited from Zoologischer Jahresbericht, 1902.) Pre-

preii account in Biologisches Centralblatt, 1902, Bd. 22, pp.

—298.

1904. Veber ni Regeneration des Vordertheiles si D

körpers nach einem künstlichen Operation. lonaises

8. Diolog. e t Med., Tome 2, pp, 233-258. ovis frum Zoolo-

gischer Jahresbericht, 1904.)

THE ORIGIN OF BILATERALITY IN

VERTEBRATES:

Proressor A. C. EYCLESHYMER

DEPARTMENT OF ANATOMY, UNIVERSITY OF ILLINOIS

Many attempts have been made to determine how early

in development the vertebrate egg becomes bilaterally

symmetrical. The conclusions have been as varied as the

attempts.

Before the subject can be discussed it is necessary to

consider two fundamental propositions. The first is that

there exists an active pole in the egg, and the second is

that the anterior end of the embryo develops in this

region, or at least in the active hemisphere.

The active pole is indicated at an early period by cer-

tain phenomena, such as secretory activity, accelerated

yolk metabolism, formation of pigment, position of

nucleus, expulsion of polar bodies, ete. Hatschek says

that ‘‘it is probable that a polar differentiation is present

in the unfertilized ova of all the metazoa, through which

the most active and least active poles can be determined.’’

Whether or not Hatschek’s statement be true, it is certain

that if the area in which cleavage grooves first appear

be traced backward a differentiation in this area can

be found in a very early stage. We are thus enabled to

speak of an active pole and an opposite inactive pole. A

line passing through the two is designated as the primary

ovic axis.

That the active pole or hemisphere gives rise to the

embryo was first pointed out by Jan. Swammerdam

in his ‘‘Bibel der Natur.’’ This view was later supported

by Prevost and Dumas, von Baer, Reichert, Cramer, New-

port and others. Pfliiger, however, believed that the

greater portion of the embryo was formed from the in-

active hemisphere and his view was supported by Roux,

O. Hertwig and others. Most of the later investigators

1 With observations by C. O. Whitman on Bufo.

504

No. 584] BILATERALITY IN VERTEBRATES 505

including Morgan and Tsuda, Assheton, H. V. Wilson,

King, Smith and others have generally agreed that the

head end of the embryo forms from the active hemi-

sphere and the caudal portion from the inactive. My

own experiments on a considerable number of Amphibia

have led to the conclusion that the head of the embryo

forms from material which lies at, or near, the active pole

of theegg. It thus seems fair to assume that the cephalic

portion of the embryo is formed from the active hemi-

sphere.

As stated there have been many attempts to deter-

mine how early in development the egg shows bilateral

symmetry. Some claim bilateralism for the primitive

ovum. Others hold that this condition is not present

from the first, but originates at some later period. This

period may precede or follow the deposition of the egg.

Those who regard the egg as bilaterally symmetrical

before deposition claim that this is manifested either

through an excentric position of the egg nucleus, or an

excentric pigmentation. Those who regard it as fixed

after deposition are not in accord. By some the path of

the spermatozoon is considered as the determining factor,

by others the first or second cleavage groove, and by still

others areas of accelerated segmentation.

The assumption that the egg is bilaterally symmetrical

from the beginning is based upon nothing more than

plausible hypothesis and naturally falls beyond the range

of experimental proo

Some (Schultze) hold that the excentric position of the

egg nucleus together with the primary ovic axis deter-

mine bilaterality. The work by Roux, Jordan and others,

shows that this is highly improbable.

Others (Roux, Morgan and Tsuda) maintain that the

excentric arrangement of pigment enables one to deter-

mine bilaterality. Professor Whitman’s observations

which are recorded in a later paragraph, together with

his drawings, indicate that the arrangement of the pig-

ment is of significance in Bufo. The observations of

Moskowski on Rana, Morgan’s later observations on

506 THE AMERICAN NATURALIST [ Vou, XLIX

Bufo, together with my own on Amblystoma, have thrown

doubt upon this conclusion.

Still others (Newport, Roux) believe that the path of

the entering spermatozoon and the primary ovic axis

determine bilaterality. Jordan has shown that this view

is untenable for Diemyctylus. Professor Whitman’s ob-

servations, recorded in a later paragraph, show that this

is not true in Bufo.

Thus each of these assumptions has been met by

serious objections.

The idea that the first plane of cleavage determines

the axis of the embryo was expressed as early as 1853 by

Newport in the following words:

I have long been aware that the axis of the embryo was in the line

of the first cleft of the yolk.

From a series of experiments on the frog’s egg Roux

came to the conclusion that the first cleavage plane coin-

cides with the median sagittal plane of the embryo. In

the same year Pfliiger reached the same conclusion. Sup-

ported by these eminent investigators the theory was very

generally accepted. In working over the same field

Rauber found that in the axolotl and frog the median

plane of the embryo coincided with the second cleavage

groove instead of the first. Shortly after the publica-

tion of Rauber’s work, O. Hertwig working on the egg

of Triton confirmed the observations of Rauber. In 1892

Roux modified his earlier view and stated that the second

groove as well as the first often coincided with the median

plane of the embryo. ;

In the following April the writer found from a series

of puncture experiments on the egg of Amblystoma that

exovates on opposite sides of the first cleavage groove

were later found on one side of the embryo. The conclu-

sion was that in these cases the first cleavage groove did

not separate the right and left halves of the embryo.

In 1893 Jordan and the writer reviewed the experi-

ments up to this date. We found that even in the de-

scriptions and figures given by Newport, Roux, Rauber,

there was evidence sufficient to show that the median

No. 584] BILATERALITY IN VERTEBRATES 507

plane of the embryo often deviated widely from the first

or second cleavage planes. We accordingly undertook

ansextended series of observations on the living segment-

ing eggs of Amblystoma, Diemyctylus, Rana and Bufo.

Our conclusions were as follows:

The first and second cleavage planes undergo, even in the earlier

stages, extensive torsion. Everything indicates that the extent of this

shifting increases greatly in later stages. This led us to conclude that

the earlier cleavage planes and the embryonie axes have no vital con-

nection and that the coincidence where it exists is of no fundamental

significance.

The later observations by Grönroos, v. Ebner, Morgan

and Tsuda, Kopsch and others have likewise emphasized

the significance of these variations.

It is scarcely necessary to state that if these cleavage

planes mark embryonic areas, the amount of material

set apart in different eggs for similar parts of their re-

spective embryos, must be exceedingly variable, and these

excesses and deficiencies must be corrected by a corre-

sponding retarded or accelerated growth until the norm

is reached, but there is not the slightest evidence that

such corrections occur.

These wide variations have been repeatedly observed

not only in various amphibia but also in practically all

classes of vertebrates: in Amphioxus by Wilson; in

Petromyson by McClure, Kupffer, Eycleshymer; in Dip-

noans by Semon; in Ganoids by Salensky, Dean, Whit-

man and Eycleshymer; in Teleosts by Coste, Hoffmann,

His, Agassiz and Whitman, Kingsley and Conn, Clapp,

Sobotta and others; in Reptiles by Agassiz and Clark,

Oppel, Sarasin; in Aves by Coste, Koelliker, Kionka ;

in Mammals by Duval, v. Beneden, Assheton, Sobotta

and many others.

The inevitable conclusion from such a mass of evi-

dence can not be other than that neither the position or

direction of cleavage grooves has the slightest signifi-

cance as far as the setting apart of definite embryonic

areas is concerned.

If then it may be considered an established fact that

508 THE AMERICAN NATURALIST [ Vou. XLIX

neither the position nor the direction of the cleavage

grooves enables one to predict the long axis of the em-

bryo, we are naturally led to look for other phenemena

which may be of significance. As stated in an earlier

paragraph my experiments showed that the head end of

the embryo is formed at, or very near, the active pole,

and since this area is the one in which cell division is

most rapid, it was concluded that the anterior end of the

embryo, which is the first to differentiate, was indicated

by this increased cellular activity. I accordingly stated

that an area of increased cellular activity indicates the

position of the head end of the embryo. As is well

known, this area can be located with the advent of the

first cleavage groove.

While the head end of the embryo may thus be readily

located, the median plane of the body may lie in any one

of an indefinite number of meridians. The question

which now arises is which one of these meridians will

represent the median plane of the future embryo.

The writer’s studies on Rana, Bufo, Acris, Ambly-

stoma, Necturus have shown that in another portion of

the egg there is an area of smaller cells, and that this

area of smaller cells always marked the region of the

forthcoming blastopore. The blastopore in turn defi-

nitely fixes the posterior portion of the embryo.

With the recognition of these areas of accelerated cel-

lular activity, the one at the active pole, indicating the

position of the future head of the embryo, the other at

the side of the egg, indicating the position of the forth-

coming blastopore, it necessarily follows that the median

plane of the embryo must coincide with a line passing

through the centers of the two.

When these observations were first published in 1898,

many questioned the existence of such a secondary area

of cellular activity. Yet a search through the literature

showed that such an area had been observed in many

groups of vertebrates. Lwoff found such an area at the

posterior end of the embryo of Amphioxus. The figures

of the segmenting blastodises of Elasmobranchs, given

No. 584] BILATERALITY IN VERTEBRATES 509

by Balfour, Riickert, Gerbe and Sobotta all show that in

these forms such an area is present. In the Reptilia,

Vay’s studies on Tropidonotus show that an area of small

cells represents the posterior end of the embryo. v.

Koelliker first called attention to such an area in the

blastodise of the chick and suggested that it determines

the position of the posterior end of the embryo. The

later investigations of Duval and Kionka leave no doubt

as to the frequent and probably constant appearance of

this area in the locality which later becomes the posterior

end of the embryo.

In 1904 the writer made a study of the egg of Necturus,

which from its size is especially favorable for surface

study. This work was undertaken with a view of ascer-

taining how early this secondary area could be located.

It was found that as early as the fourth or fifth cleavage,

the cells on one side began to divide more rapidly than

any others, excepting those of the primary area. It was

possible to predict in this form the median plane of the

forthcoming embryo at an extremely early stage of

cleavage.

The following year de Bussy from his studies on the

Japanese Cryptobranchus emphasized the fact that he

could find no secondary area of accelerated cell division

such as had been described by the present writer. Yet

Smith working on the American Cryptobranchus says

that he finds ‘‘an accelerated cell division about a radius

ef the blastodise which gives a condition of bilateral sym-

metry.

The writer felt that it was scarcely necessary to follow

the subject further and should not have rehearsed the

findings had it not been that certain material came into

his hands last year which bears directly upon this sub-

ject. This material consists of unpublished descriptions

and drawings made by the late Professor C. O. Whitman

in June, 1894. These were turned over to me by the de-

partment of zoology of the University of Chicago. Pro-

fessor Whitman ’s notes run as follows:

510 THE AMERICAN NATURALIST [Vou. XLIX

Hitherto we have obtained eggs the first week in June. This year

we could find none until July 1. We had several night rains, enough to

flood the low ground behind Breakwater Hotel. On the evening of

June 30, the day after the rain fell copiously, the toads swarmed in this

place, and had a carnival of noise; the whole place rang with so many

voices as to be almost deafening. On the morning of July 1, we found

a great many eggs. The following night the singing followed but much

reduced, and only two pairs of toads were captured. The next night

the water had gone except in one of the ditches and no toads were to

be heard, and of course no eggs. It would seem that rains stimulate

them to lay; and the lateness of the season may have been the reason

that the egg-laying was confined almost entirely to a single night.

The unfertilized eggs are by some said to be unoriented, that is they

are said to be unable to take the normal position assumed by the fer-

tilized egg. The sperm is supposed by some observers to mark the first

plane of division and to give the egg the power to right itself. I find

that it is not true that the eggs will lie just as they happen to fall,

although they do so more nearly before fertilization than after it. I

an egg be separated from the rest and turned about for some moments

with needles, so as to loosen its adhesion to the membrane, and then

rolled to one side so that the equator is vertical, one observes that it

slowly turns and in the course of a minute, or sooner, it takes the

normal position with the blacker pole uppermost and the whiter show-

ing a little on one side, when viewed from above. This was repeated

several times and on several eggs with the same result. The motion is so

slow that one does not notice it until after the lapse of some seconds.

I cannot affirm that all unfertilized eggs will right themselves; ordi-

narily they do not if left to themselves. They assume an irregular

wrinkled appearance and have so little power of righting that they stick

to the membrane enough to prevent it. When fertilized they contract

and round up and get freedom of space to move in, The entrance of

the sperm evidently increases the disproportions between the weights of

the upper and lower pole. The upper pole becomes lighter and the egg

rights itself more readily and quickly. The orientation of the egg is

complete before fertilization.

e eggs which are in the stage of first cleavage there is a small

depression which I have found by examination of earlier stages is the

“fovea germinativa” of Max Schultze, or the “fosette germinative ”

of Bambeke. I find further after fertilization, a second point or de-

pression, which probably is the place of penetration of the spermato-

zoon. The fovea marks the upper pole, but is not placed at the middle

of the upper hemisphere; it is excentric.

I followed two eggs which showed both the fovea and the spermatic

dent. In neither did the first cleavage plane pass through this dent.

In one case it passed far from it while the second cleavage passed near

to it. In another ease the dent is in the middle of one of the first four

No. 584] BILATERALITY IN VERTEBRATES 511

cells, and on the darker side of the upper hemisphere. If this be the

sperm track it does not determine the median plane of the embryo.

CLEAVAGE

The eggs were obtained in the two-cell and four-cell stages. At this

time the pigment is excentric, falling a little short of the equator on

the one side and a little beyond it on the opposite. [The notes nowhere

state that the antero-posterior direction of the embryo is indicated by

the distribution of pigment, yet I think an examination of the figures

ean not fail to convince all that their interpretation can not be other-

wise.—A. C. E.] When the first cleavage groove runs in the plane «f

symmetry the second cleavage grooves are at right angles and appear

at about the same time in both halves as shown in Figs. 3 and 4. When |

the first cleavage groove is transverse to the plane of symmetry the

second cleavage grooves do not appear at the same time, but the one

upper ais on the blastoporie (posterior) side, but leaves considerable

below the upper cells on the opposite (anterior) side. e secon

equatorial usually cuts off all the pigmented cells on the anterior side

of the egg and non-pigmented cells on the posterior (blastoporic) side.

The blastomeres on the posterior (blastoporic) side are smaller than

on the anterior side, from the very first. It is the blastoporie side that

takes the lead in division and the cells are smaller here all the way up

to the time when the blastopore appears.

It is thus obvious that the findings by Professor Whit-

man not only lend confirmation to my observations on

bilaterality, but that they in reality anticipate them.

It may be said with added confidence that bilaterality

in the vertebrate egg is revealed through the early cleav-

age grooves. The cephalic portion of the embryo is in-

dicated by the area in which cleavage grooves first appear

and in which cellular division is most rapid. The caudal

portion is indicated by a secondary area of cellular activ-

ity in the blastoporic region. These two areas pass into

each other constituting an embryonic tract.

In addition to the above observations, Professor Whit-

man’s manuscript and drawings give the results of a

series of puncture experiments in the blastoporie lip.

Since these observations have an important bearing on

the question of epiboly, emboly and concrescence, they

are appended,

512 THE AMERICAN NATURALIST [ Vou, XLIX

No. 584] BILATERALITY IN VERTEBRATES 513

EXPERIMENTS

On June 5, 1894, sixteen eggs in the thirty-two cell stage were punc-

tured at the equator, in the middle of the white cells, as shown in Fig.

11. In twelve the blastopore appeared near the puncture as shown

in the accompanying cut. The extraovates were found in the positions

shown in A, 1-12, at 10:00 a.m. the next morning. The variations in

positions are doubtless due to my punctures falling at different points,

sometimes hitting as in Fig. 12, at other times in the very edge of the

pigment. In the four remaining eggs two showed no extraovate and

two showed no blastopore.

On June 4, 1894, pricked egg B at middle of lower pole, soon after

the blastopore was sharply marked on the side of the embryo. Ven-

trally this outline was not clearly marked. At 4:30 this blastopore was

outlined all around and nearly circular or about 1% diameter observed

at 3:00. At 6:30 the blastopore was far advanced and nearly circular.

At 8:30 it was nearly closed. It will be noted that the extraovate re-

mained central throughout.

Another egg C was punctured in the ventral edge of the blastoporie

rim, and the extraovate was carried along by the closing blastopore.

I ought to have made two punctures, one in the middle as well, so that

this approach could have been seen. However, my notes show that the

blastopore advanced evenly. In this case the extraovate is carried

point, approached by the blastopore from the opposite side.

June I pricked a number of eggs in the early cleavage stages

(8-64 cells) at lower pole. In most of these eggs the extraovates were

found after two to three hours to lie at or near the equator of the egg.

This was long before the appearance of the blastopore. The extra-

ovate has evidently moved and if one should leave the egg until the

blastopore appeared and then look at it, it might be found at the middle

of the body; and thus it might appear as if the embryo had lengthened

across the lower pole (Roux). Sometimes extraovates have moved and

the punctures healed.

514 THE AMERICAN NATURALIST [ Von. XLIX

No. 584] BILATERALITY IN VERTEBRATES 515

EXPLANATION OF PLATES

Since no explanation of the figures could be found

other than those included in the preceding pages, I have

endeavored to give an explanation in accord with the

text. It should be remembered however that the figures

may be open to other interpretations than those pre-

sented. The figures show the distribution of pigment

and the relation of the embryo and the cleavage planes

to the pigment. It will be noted that the eggs when

viewed from above show a lighter area or crescent on

one side. This excentric position of the pigment is like:

wise well shown in profile. The arrows in all cases show

the direction of the forthcoming embryo.

Shows the upper hemisphere of an egg in which e embryonic

axis is indicated by a line passing through the centers of the noe erescent and

the e deeply pigmented area. In this case the first cleavage plane (I)

passed at right angles to the embryonic axis. It is of interest to pbk that the

second cleavage (II) has appeared in that portion of the egg nearest the og y

crescent and prera Agere it coincides with the median plane of sha mbry'

Fig. 2. Sho profile view of an egg in which the first cleavage s

with tie recog piane rae the embryo while the second is at right angles to the

sam loss to understand the extent of the arrow in this and the

MEER a pineg views. It may be ea bata Ww hitman intended thus to

indicate the limits hee the embryonic

Fic. 3. Shows the upper ae ct an egg in the four cell stage. In

this case ae median plane of the forthcoming embryo coincides with the first

cleava i

s the upper hemisphere of an egg consisting of eight cells.

It is fi be noted that the formation of the first equatorial sharply ego cer the

prs shies our vege stag of the egg on the one side but not on the opposite

In t case the median plane of the embryo cotachiak with either the

groove.

1G. 5. Represents the profile view of either the same egg or another egg

in the same stage. In this case the differences in the distribution of the pigment

are again shown.

Fic. 6. Shows the upper hemisphere of an egg in koria TE the sa

nor the second cleavage grooves coincide with the median

Fie. 7. Shows the upper hemisphere of an egg at a Se when ot scare

cleavage grooves are present. It is impossible to say whether the median T

of the embryo coincides with either the first or the second cleavages.

pearance of the cleavage grooves leads me to infer that the direction res 68

arrow is parallel with either the first or pt second,

Fic. 8. Represents a profile view Aui api the same egg or another egg in the

Fig. 9. agga the a hemisphere of another egg in which the fourth

cleavage grooves are present. In egg the median plane of the embryo

coincides with bee eg or second Psa groove.

516 THE AMERICAN NATURALIST [Vou. XLIX

No. 584] BILATERALITY IN VERTEBRATES 517

Fic. 10. Shows the upper hemisphere of an egg in a later stage of cleav-

age. It should be noted that the lines representing the primary grooves are

entirely pra by a “ee of the blastomeres.

Fie epresents a profile view of the same (?) egg, viewed from the

e on wh i the blastopore is forthcoming. The small crossed lines represent

the localities in which Professor Whitman punct the of this stage.

nts a profile of the opposite side of the same (?

the u hemisphere of an eg a later stage of cleav-

age. It should again be glee that it would be impossible to

two grooves it must be setae irregular.

Fic. 14. Represents a profile view of the same (?) egg viewed from the

side in which the blastopore will por appear. On this side cell division is

decidedly in advance of the opposite

Fig. Represents a profile view Ne "the opposite side of the same (?) egg.

10. 1

Represents a profile view = an Pea in roy segmentation. The

side ph Niak the Trea will appear indicated not only = the dis-

Oe ae x pigment but also by a ESE paaien in cell divisi

b Neurite a gana view of an egg at the time when ane pE SE

appears. on figure shows that it appears on the side of the egg which is least

pigmen

SHORTER ARTICLES AND DISCUSSIONS

THE TORTOISESHELL CAT

In The Journal of Genetics (June, 1913), Doncaster has sum-

marized genetic data dealing with the tortoiseshell cat. The

records are collected from fancy breeders and from the work of

Dr. C. C. Little

Aside from certain disputed points the inheritance is in ac-

cordance with simple sex-linkage and is analogous to the human

defeects—color-blindness, night-blindness, nystagmus, and hemo-

philia, and to the thirty or more sex-linked factors of Drosophila.

If the factor for yellow be represented by Y and its allelo-

morph, the factor for black, by B, the lack of either by b, the

sex factor by X, and the allelomorph of X by x, the normal

zygotic possibilities are as follows: YX—bx=—yellow male.

BX —bx=black male. YX—YX=yellow female. BX—

BX = black female. YX—BX-=tortoiseshell female.

It is obvious then that there can be but two classes of males,

while there are three classes of females. Difficulties arise when

it is attempted to explain the occurrence of black females pro-

duced either by the mating of a black female to a yellow male

which should give only tortoiseshell females and black males.

or by the mating of a tortoiseshell female to a yellow male,

which should give only tortoiseshell and yellow females and

black and yellow males. The occurrence of the rare tortoiseshell

male is also the cause of considerable difficulty. In one mating

out of seventeen of yellow females to yellow males there were

produced three tortoiseshell females. There are recorded in

addition from the seventeen matings forty yellow females and

forty-eight yellow males which are in agreement with expectation.

In order to explain these discrepancies it is suggested that

possibly the linkage of Y with X is not absolute. Yellow males

may then produce gametes bX and Yx in addition to the normal

or more frequent gametes YX and bx. Gamete bX is female

determining, while gamete Yx is male determining and yellow

bearing. The latter gamete should produce a tortoiseshell male

when it meets an egg BX.

On this hypothesis we should expect the tortoiseshell males to

be as frequent as the anomalous black females from yellow

fathers. From the matings recorded there are eighteen anoma-

lous black females and only three tortoiseshell males, and one

of these tortoiseshell males had a black father. There is a fur-

518

No. 584] SHORTER ARTICLES AND DISCUSSIONS 519

ther objection to this hypothesis inasmuch as it is not explained

how gamete bX differs from BX. Doncaster admits these diff-

culties, stating that further work is necessary before a definite

conclusion can be reached.

In a more recent paper! Doncaster has suggested non-disjunc-

tion of the sex-chromosomes in oogenesis as a possible explana-

tion. This explains the matroclinous black females, but fails to

account for the lack of an equal number of patroclinous yellow

males. It also fails to account for the tortoiseshell male and

the occurrence of tortoiseshell females among the offspring of

yellow by yellow.

In a series of experiments begun upon cats at the University

of Pennsylvania during the last year, the tortoiseshell problem

has been especially investigated. A yellow Persian male was

crossed with common cats—black, maltese and tabby. The re-

sults, although not at present extensive, are sufficient to explain,

at least in part, the anomalies observed, and to suggest a simple

explanation for the occurrence of unexpected classes.

When the yellow male was crossed with a maltese female, a

maltese male and two blue and cream females were produced.

The blue and cream is the maltese or dilute tortoiseshell. When

mated to a black female the yellow male produced both dark and

dilute kittens. This shows that the black female was hetero-

zygous for dilution. Two of the males were black and two mal-

tese. The two females were dark tortoiseshell. When the yel-

low male was crossed with a dark tabby, there were produced

dark and light tabbies and maltese. Blacks are also to be ex-

pected from this mating. The mother is evidently hybrid be-

tween tabby and black and between black and maltese. The

female offspring showed yellow: the male offspring were without

yellow except for tabby striping.

The female offspring obtained from these matings may be ar-

ranged in a series, ranging from one that is predominantly

yellow to one that is maltese except for a few cream-colored hairs,

The maltese with a few cream hairs occurred in the litter of

three above mentioned, which included also a maltese male and a

maltese female with a small cream patch.

It may be readily understood how a maltese cat with a few cream

hairs or its intense form, a black cat with a few yellow hairs, would

be recorded as maltese or black, and it is reasonable to suppose

that further segregation of distribution factors in the direction

of black would have produced a fully black female. This may

1 Quarterly Journal of Microscopical Science, February, 1914.

520 THE AMERICAN NATURALIST [ Vou. XLIX

be compared with conditions in the guinea-pig in which yellow

spotting is continuous with total black. The essential differ-

ences are that in the cat we have a factor for yellow allelomor-

phic to a factor for black, that these allelomorphs are sex-linked,

and that either alone is sufficient to produce its expected color,

but that when one is balanced against the other, as in the tortoise-

shell female, other factors governing the relative amounts of the

two colors can act and produce continuous variation from yellow

to black.

The three tortoiseshell females from the mating of yellow by

yellow may be explained by supposing that the mother was

gametically a tortoiseshell plus a sum of yellow extension factors

and minus a sum of black extension factors.

The occurrence of the tabby factor brings in a restriction of

the black pigmentation producing yellow stripes. It is there-

fore much more difficult to distinguish a tabby from a tabby-

tortoiseshell than a black from a tortoiseshell. We have had a

few tabby-tortoiseshells that would have been recorded as tab-

bies if close examination had not been made.

Another source of error in records involving the tortoiseshell

pattern may be introduced by the occurrence of white spots.

Doneaster makes no mention of these in his paper, so that it is

possible that they did not occur in the animals recorded. In

what is genetically a tortoiseshell and white cat the incidence

of the white spotting may happen to be at just those points

which would otherwise be yellow. Thus the occurrence of black

and white daughters from yellow males may be explained. It

is possible also that the yellow mother of the three tortoiseshell

kittens recorded from the mating of yellow by yellow may have

been white at points which, if pigmented, would have been black.

She would then have been genetically a tortoiseshell and white

and some tortoiseshell kittens would have been expected.

I would suggest as a plausible hypothesis that the rare tor-

toiseshell male is genetically a yellow with an extreme of black

extension factors or a black with an extreme of yellow extension

factors. This hypothesis is rendered more probable by some

slight evidence showing that male tortoiseshells breed like

yellows.

There is then no need for assuming in the cat either breaks

in sex-linkage or non-disjunction of the sex chromosomes in

oogenesis. PHINEAS W. WHITING

UNIVERSITY OF PENNSYLVANIA

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THE

AMERICAN NATURALIST

VoL. X LIX. September, 1915 No. 585

A STUDY OF ASYMMETRY, AS DEVELOPED IN

THE GENERA AND FAMILIES OF

RECENT CRINOIDS

AUSTIN H. CLARK

PHOLSCG yok os coh tenes Me Cae oe es a he ee fe eH a os ws 521

The Different Types of as AMOS 6 9 wae tarse INESS sc : 523

The Asymmetrical Crinoids ..........-+. 22 esseenes WE D Se ee 524

The Phylogenetic iisa of Moy tishatty elie pepe mec ea Vee oe 526

The Geographical Distribution of Asymmetry ....................-- 527

Bathymetrical Distribution of the Asymmetrical Crinoids ............ 530

Thermal Distribution of the Asymmetrical Crinoids ................. 535

The Asymmetrical Features in Detail ..... 250.202. secs ces cces sae 538

Jamar a eee BN eRe EA a Eh Sp i ew NA 546

PREFACE

In the animal kingdom there are few, if any, forms

which can be properly described as perfectly symmetrical,

either from a bilateral or a radial standard. We have,

however, become accustomed to refer to many types as

“asymmetrical.” In the sense in which we employ this

word we do not intend to convey the meaning that these

types alone of their respective classes depart from true

bilateral or radial symmetry, but rather to indicate that

they exhibit more asymmetry than the maximum contem-

plated in our generalized concept of, or arbitrary stand-

ard for, those classes.

Thus we readily recognize and confess the asymmetry

in the skull of the narwhal (Monodon) with its single

greatly elongated and twisted incisor, and the asymmetry

in the bones in the skull of the whales, while at the same

time we commonly consider man to be symmetrical,

though careful measurement shows the right arm and

521

522 THE AMERICAN NATURALIST [Vot. XLIX

hand to be larger than the left, and the left leg and foot to

be larger than the right.

It is clear, therefore, that in dealing with asymmetry in

any group we must work inward from the most asymmet-

rical types toward the least asymmetrical, arbitrarily

erecting a barrier between what we call asymmetry and

what we are pleased to consider as ‘‘symmetry’’ at any

point we choose.

Asymmetry—that is to say the maximum departure

from perfect bilateral or radial symmetry—appears to

follow certain definite lines wherever it appears, quite

regardless of the type of animal, or the form, in which

it is manifested.

In the following pages we shall consider the wider

variations from the typical pentamerous symmetry among

the recent crinoids, which is phylogenetically most exten-

sively developed at the consummation of the phylogenetic

lines, and physico-economically most extensively devel-

oped in the situations most unsuited to crinoidal exist-

ence, particularly in the very warm water of the Hast

Indian and north Australian littoral, and the very cold

water of the Antarctic regions and the deep abysses of the

oceans, and is least evident among phylogenetically con-

servative types, and in the situations which appear to be

best suited for crinoid life.

As an indication of the possible fundamental impor-

. tance of the light thrown on the study of asymmetry by an

examination of the data offered by the recent crinoids, it

may be noticed and borne in mind that among the mam-

mals the phylogenetically aberrant asymmetrical narwhal

(Monodon) is exclusively arctic; the phylogenetically

aberrant asymmetrical whales occupy a habitat very aber-

rant for the class; and the anthropoid apes, which are

pronouncedly right or left handed, live in very warm

regions; that among the birds the curious crook-billed

plover (Anarhynchus), with the beak twisted to the right

and one side of the body lighter in color than the other,

occurs only in New Zealand, the home of many phyloge-

No. 585] A STUDY OF ASYMMETRY 523

netic oddities; the hornbill Rhinoplax, with an asymmet-

rical tail, further peculiar in having a solid casque, an

elongate central rectrix, and a naked patch on the back

extending to the sides of the head, is found in the warm

Malayan region; the crossbills (Loxia), with the tips of

the mandibles crossed and a corresponding distortion in

the bones of the head are all subarctic or cold temperate

forms; and the owls with one ear greatly larger than the

other, so far as has been determined are, like the cross-

bills, birds of the colder regions; and that among the

fishes and similar types the very asymmetrical Anableps

lives in the warm tropical littoral, while the flatfishes

(Pleuronectidæ) are chiefly developed in the warm trop-

ical littoral, and in cold and shallow water, and the asym-

metrical forms of ‘‘ Amphi ’? (using the term in its

broadest sense) occur in warm and shallow water.

Further it is interesting to recall that animals under

domestication—that is, living under conditions which

typically lead to a more or less degenerate diversity in

form and color—commonly develop asymmetry of action

which, though usually occurring in the form of individual

variation, may become very marked as in the case of the

Japanese waltzing mice, as well as pronounced, though

irregular and sporadic, asymmetry in color pattern, denti-

tion, and other features.

More or less pronounced asymmetry undoubtedly exists

in many types in which up to now it has been overlooked,

and the conclusions reached in the present paper may be

modified somewhat when a better knowledge of the sub-

ject is attained; but on the other hand it is scarcely prob-

able that many instances of marked asymmetry have es-

caped the notice of naturalists.

THE DIFFERENT Types or RINOIDAL ASYMMETRY

In the great majority of the recent crinoids the body is

almost perfectly pentamerous, being composed of five

similar sectors. The presence of a small muscular cone

in the posterior interradius, at the summit of which is

524 THE AMERICAN NATURALIST [ Vou. XLIX

the posterior opening of the spiral digestive tube, gives

the only visible indication of a departure from true pen-

tamerous symmetry.

In certain types, however, a more or less marked devia-

tion from the characteristic symmetry occurs. This devi-

ation follows four different lines:

1. A rearrangement of the five primary groove trunks

upon the disk whereby (a) the left posterior increases in

size and gives off more branches than any of the others;

(b) as a result of the anterior migration of the mouth,

the two posterior become much longer and the anterior

much shorter than the others and a condition of bilateral

symmetry is attained; (c) correlated with the anterior

migration of the mouth, all of the primary groove trunks

become merged into a horse-shoe shaped ring which

skirts the lateral and anterior borders of the disk, giving

off branches to the arms, the mouth being in the right

center of the ring so that the ambulacra on the left are

more developed than those on the right, or the ambulacra

leading to the left posterior arm disappearing altogether

so that the ambulacra on the right are more developed

than those on the left;

2. A dwarfing, or an overdevelopment, of the left poste-

rior, more rarely of both, posterior radials with their

post-radial series;

3. The intercalation of additional radials and post-

radial series which alternate with the original five, and

the associated dropping out of one of the five radials; and

4. The suppression of two of the primarily five basals.

THE ASYMMETRICAL CRINOIDS

In the following list are given all the families and

genera of recent crinoids which include asymmetrical

species.

After the families the bathymetrical and thermal

ranges are given, and after the genera the bathymetrical

range.

Certain families are represented in the warm littoral

No. 585] A STUDY OF ASYMMETRY 525

water of the Malayan region and northern Australia, but

the highest actual temperature record is considerably less

than the temperature of this water; in these cases the

temperature 80.5° is given after the gadertapied maximum

as more nearly representing the true maximum.

Of the nine families the four in which asymmetry is

most markedly developed are marked with an asterisk

(*); and of the twenty-seven genera the sixteen which

include the most notably asymmetrical species are simi-

larly distinguished.

Depth (Fathoms) Temperature (F.)

Capillaserings: 00s 0s a co a ie 0-830 44.5-78.5 (80.5)

ETT he) Creo: BER MIRE AU EE ioe ERR E Marner 0-106

N pooma 2. SiS ks Ba 10-830

OOO WIECH oo ss 8 ee ee E 140-153

CODIR 64 a ae as 0-160

A I ic Ne OEE Oc PEER LS oS 0-194

CERRO Ste eas oa 100

LOONE OO Oe oe ee ee 42-163

Ean oa os oi ces es. a ee 0-288 62.0-71.9 (80.5)

Comot cock ts ES a A 0-160

Damien: ian aa e 10

ONAN E E E EEE ee ee 0-288

COMA Se cr a can vee 262

“CRONIN SS e a ie eee a 0-140 52.3-80.0 (80.5)

E AE A ic ahs cee eS 0-95

PCOMURTNOTUE © 6 orci oe es ere 0-83

COMONINRA GS, Se cae ec ees 2

POCORN oo a a 0-140

TROOP es ok en os 2-—1,600 28.7-60.5

ESA E RER I C E E S 10-222 28.7

FPentamotroiaide <... oee 103-1,800 33.5-60.6

WE RAmIOtOCHINEN Ooo. cas ce chen 861-1,800

VIN ons oo ak as oo eee 565-940 36.7-38.1

Nk TOMMOCTTNER oe ey ob en a ss 40

SCOTPOREOPOOTINUE o enana eed es 565

Bourgueticrinide aa Ca open bay ue ee 62-2,690 29.1—70.7

P RMNO ee ss CAs Bs he 77-1,300 32.2-48.7

RENOOTURNG oi os in Waka es Coens’ 687—2,419 37,4—40.0

*Rolopodido oae, «aed ee 5-120 71.0

ODER i E E oe Cie ees awake 5-120

"PF iedioerinide ... OS eG 266-2,575 31.1-43.9

"UGIOMIOONAUE -n.a oc Vs eee 392-782

"Pe Oerioe. ia Ca is es Ak 266-2,485

sf GNU cc Su Fis Soe a ee a 575

,103

526 THE AMERICAN NATURALIST [ Vou. XLIX

TEE PHYLOGENETIC DISTRIBUTION OF ASYMMETRY

The phylogenetic distribution of the asymmetry among

the recent crinoids is very interesting.

Asymmetry is almost universal in the comatulid family

Comasteridæ, which includes the most specialized of all

recent forms; in this family the first and second types

occur, though the latter is much less common.

Asymmetry is characteristic of the genus Promacho-

crinus, which is probably rightly considered as the most

specialized genus in the subfamily Heliometrinæ, the

largest and most universally distributed subfamily of the

at present dominant family Antedonidæ; in the genus

Promachocrinus the first and third types occur.

Asymmetry is equally characteristic of the genus Thau-

matocrinus, the most specialized genus of the family

Pentametrocrinidæ; in this genus the third type is found.

Asymmetry exists in all of the genera of the Plicato-

crinidæ, which includes the last highly specialized expo-

nents of the ancient order Inadunata, which flourished

from the Ordovician to the Carboniferous, with one

family extending into the Permian and Trias and another

(the present family) appearing in the Jura; in the Plicato-

crinidæ the first, second and fourth types occur in recent

genera, while the third is also found in fossil genera.

Asymmetry is characteristic of both of the recent gen-

era of Apiocrinidæ, which are the most specialized genera

in the family; in these the second type occurs.

Asymmetry of the second type is characteristic of the

only recent genus of the Holopodide.

Asymmetry characterizes both of the species of Rhizo-

crinus—which is at least as highly specialized as any of

the genera of the Bourgueticrinide—existing in the pres-

ent seas, and one of the species of Monachocrinus, a genus

of which the exact phylogenetic position is uncertain,

although it is probably on a par with Rhizocrinus; in

these the third type occurs.

In the following list the recent asymmetrical types are

No. 585] A STUDY OF ASYMMETRY 527

given in the order of the extent of their departure from

the normal pentamerous symmetry:

Plicatocrinide: Asymmetry of Types 1, 2, (3) and 4.

Comasteride : Asymmetry of Types 1 and 2.

Promachoerinus: Asymmetry of Types 1 and 3.

Apiocrinide Asymmetry of Type 2

Holopodide Asymmetry of Type 2

haumatocrinus Asymmetry of Type 3

Rhizocrinus Asymmetry of Type 3.

Monachecrinus : Asymmetry of Type 3.

The asymmetry of the Comasteride is considered more

fundamental than that of Promachocrinus for the reason

that it is characteristic of practically the entire family,

and also because it results in a much greater degree of

irregularity. It is interesting to note that asymmetry

of Type 3 is not uncommon among the Comasteride, in

the form of individual variation.

The asymmetry of the Apiocrinide and Holopodide is

considered more fundamental than that of the genus

Thaumatocrinus for the reason that it affects the entire

family, at the same time inducing a greater departure

from the normal form.

The asymmetry of Rhizocrinus is considered less funda-

mental than that of Thawmatocrinus because, though

affecting all of the species, exactly as in Thaumatocrinus,

it is less extensively developed.

The asymmetry of Monachocrinus affects only one of

the seven species of the genus.

Briefly stated, it appéars that, no matter in what form

it may manifest itself, metameric asymmetry in the recent

crinoids is an attribute of the most specialized types in

the groups in which it occurs.

From the conditions in the Plicatocrinide, the last

remnants of the once abundant Inadunata, it would appear

that asymmetry is an attribute of phylogenetically deca-

dent types—types in which type senescence has so far ad-

vanced as to inhibit the normal course of development.

THE GrocrapHicaL DISTRIBUTION oF ASYMMETRY

The geographical distribution of asymmetry is as inter-

esting as the phylogenetical distribution.

528 THE AMERICAN NATURALIST [ Vou. XLIX

Although occurring everywhere except in the Arctic

Ocean and in the Mediterranean, Bering, Okhotsk and

Japan seas, asymmetrical types are most frequent and

most highly developed (1) in warm shallow water from

southern Japan southward throughout the Malay Archi-

pelago to northern Australia and westward to Ceylon, and

(2) in the Antarctic and in the cold abysses.

Though present among species inhabiting the west

Atlantic from North Carolina to Brazil, and characteristic

of many forms living at intermediate depths in the west-

ern Pacific and in the Indian Oceans, in these it is never

more than slightly developed, even though they be very

closely related to types in which it is, in other situations,

carried to an extreme.

Depth (Fath Number of Number of ati gr va une

re Torrens Asymmetrical Genera | Symmetrical Genera | ‘or = eT mara

0-50 16 50 32%

100 15 53

100-150 13 51 25

150-200 10 44 22

200-250 5 39 13

250-300 5 34 14

300-350 3 30 10

350—4 4 32 12

400-45! 5 29 17

450-500 5 27 18

500-550 5 26 | 19

550-600 6 26 23

5 26 19

650-700 6 22 27

700-750 6 22 27

750-800 6 18 33

800-850 5 18 28

850- 4 18 22

5 19 26

950-1,000 5 1 31

1,000-1,100 5 16 31

1,100-1,200 5 12 41

1,200-1,300 5 9 55

1,300-1,400 4 9 44

1,400-1,500 4 7 57

1,500-1,600 4 7 57

1,600-1,700 5 3 166

1,700-1,800 5 3 166

1,800-1,900 4 3 133

1,900-2,000 4 3 133

2,000-2,500 4 3 133

2,500-3,000 1 3 33

In short, though almost universal, occurring every-

Genera with and without Asymmetrical Spe-

with very Asymmetrical and without As

metrical Species at Different Depths (===),

Genera with Depth,

ym-

and the Decrease in the Number

expressed in Percentages of the Total Number (- - - -).

Fic. 1. The Relation between the

cies at Different Depths (

5380 THE AMERICAN NATURALIST [ Von. XLIX

where except in inland seas, asymmetry is especially

developed in the warm waters of the eastern tropics, par-

ticularly in the Malayan region and in northern Australia,

and in the Antarctic and the cold abysses.

BATHYMETRICAL DISTRIBUTION OF THE ASYMMETRICAL

CRINOIDS

The number of genera of recent crinoids including

asymmetrical species, the number of genera including

| Number of | Per Cent. of the

Depth (Fathoms) Asymumetrical Genera | , Number of | Latter ———

Which Are Marked * | 5 bs | by the Former

0-5 7 50 | 14.0

50-100 7 53 | 13.2

100-1; 5 51 | 9.8

150-200 3 44 6.8

200-250 2 39 5.1

250-300 2 34 5.8

300-350 2 30 6.6

350-400 4 32 12.5

400-450 4 29 13.8

450-500 4 27 14.8

500-550 4 26 15.4

550-600 5 26 19.2

600-650 | 4 26 15.4

650-700 | 4 22 18.1

700-750 | 4 22 18.1

50-8 | 4 18 22.2

00- 3 18 16.6

850-900 3 18 16.6

900-950 4 19 21.0

950-1,000 4 16 25.0

1,000-1,100 4 16 25.0

1,100-1,200 4 12 33.3

1,200-1,300 4 : 9 44.4

1,300-1,400 3 9 33.3

1,400-1,500 3 ff 42.8

500-1, 3 7 42.8

,600-1, 4 3 133.3

1,700-1,800 4 3 133.3

1,800-1,900 3 3 100.0

1,900-2,000 4 3 100.0

2,000-2,500 3 3 100.0

2,500-3,000 1 3 | eee

only symmetrical species, and the percentage of the num-

ber of symmetrical genera represented by the number of

asymmetrical genera at different depths are given in the

table on page 528 and shown in Fig. 1.

Considering the percentages only, these may be re-

grouped as follows:

No. 585] A STUDY OF ASYMMETRY 531

ee Ri ek a a a a a S a 27

v00- G50 irs eo cle se Fs 5 ORs Cece ew ae Ce thew wa cee 16

GOO) 100 so ea cs eee ee a ee 28

py Nt, | Ee erg rr emma RE ee I angen 7 oes Senet aa 92

Considering only the genera marked with an asterisk

(*) we find the representation at different depths given

in the table on page 530 and in Fig. 1.

Considering the percentages only, these may be re-

grouped, as follows:

I ace aie ee CHa we eo owe a ey cakes 13.6

100e S00 se Ceres er ek ag a vag be ee ee hss eed Gate

BO 900 ae ee ee OU as as eh ek A ee ees 16.6

P003,000 -aoea ko ee ee sl heer 61.8

The number of families of recent crinoids including

asymmetrical species, the number of families including

only symmetrical species, and the percentage of the num-

ber of families including only symmetrical species repre-

sented by the number of families including asymmetrical

species at different depths, are shown in the table on page

933 and in Fig. 2.

The proportion of the genera including asymmetrical

species to those composed entirely of symmetrical spe- —

cies, about one third between the shore line and 50

fathoms, decreases to a minimum of one tenth at from 300

to 350 fathoms, and then increases, with greater and

greater rapidity, to 1,600 fathoms and below.

It is everywhere less than one quarter between 100 and

650 fathoms. Thus it is evident that the genera including

asymmetrical species are chiefly developed in shallow

water, and in deep water, and are least developed in water

of intermediate depth.

Taking the ocean as a whole, the temperature at 100

fathoms is 60.7°, and at 650 fathoms 38.6°; the optimum

temperature for the recent crinoids appears to be between

50° and 65°; when we remember that most of the asym-

metrical species, and all of the most asymmetrical ones, in

the genera which give us our numbers for 0-50 and for

50-100 fathoms, are confined to a littoral belt of scarcely

more than 50 fathoms, it becomes at once evident that

asymmetry among the crinoids is developed chiefly in

Ne — ee ee

6008-0062

Proportion of Families with and without Asymmetrical Species

Fia. 2. The

at Different Depths (

), and the Percentage of the Total Number of ©

at Different Depths (- - --).

Crinoid Families represented

No. 585] A STUDY OF ASYMMETRY 533

| t. of Sym-

| Number of The Families Number of metroa r siiis

(rations) | Abymmstrical |yarkod wih ane | SZameirionl |Hepresentd by

0-50 5 2 i 33

50-10 6 - as 4

100-150 7 2 u H

150-200 | 5 0 : “

200-250 | 5 0 0 oa

250-300 | 6 0 : ae

300-350 | 5 0 8 62

350-400 5 0 : n

400-450 5 0 : li

450-500 | 5 0 i n

500-550 | 5 0 5 >

550-600 | 6 1 : ie

600-650 6 1 : s

650-700 | 6 1 :

700-750 | 6 1 7 a

750-800 | 6 1 : a

800-850 | 6 1 ~ n

850-900 | 5 1 ` =

900-950 5 1 :

50-1, 4 0 é -

1,000-1,100 4 0 : =

1,100-1,200 4 0 : bes

1,200-1,300 4 0 $ 10

,300-1, 4 0 í sh

1,400-1,500 4 0 : i

1,500-1,600 4 | 0 : po

1,600-1,700 3 | 0 : xo

1,700-1,800 3 | 0 } | ps

1,800-1,900 2 | 0 : -

1,900-2,000 2 | 0 : re

1,900-2,000 2 | 0 l -=

2,000-2,500 2 | 0 : | ~

2,500-3,000 2 0

water above and below the optimum, and least at and just

below the optimum temperature. :

Onia only the genera marked with an asterisk

(*), that is, the genera with the most highly developed

asymmetry, we find the same general facts emphasized as

in the case of all the genera including asymmetrical

forms; but here the minimum is between 50 and 400 fath-

oms instead of between 100 and 650 fathoms. The tem-

perature at 400 fathoms is 41.8°. This approximation of

the minimum to the zone of optimum temperature when

only the most asymmetrical. types are considered

strengthens the hypothesis that the zone of optimum

temperature really represents the zone of least-developed

asymmetry.

534 THE AMERICAN NATURALIST [ Vou. XLIX

Comparing the proportionate abundance of asymmet-

rical genera at different depths with the frequency of all

the genera expressed as percentages of the total, we find

that the former decreases while the latter increases to

50-100 fathoms; from this point the two run roughly

parallel to 300-350 fathoms, after which the former in-

creases with progressively greater rapidity. while the

latter decreases steadily and gradually to 3,000 fathoms;

the two cross each other between 600 and 700 fathoms.

The proportion of the families including asymmetrical

species to those composed entirely of symmetrical species

increases from one third at 0-50 fathoms to three times

as many at 1,600 fathoms and twice as many at 1,900

fathoms and over. The increase, though irregular—

largely as a result of the small numbers involved at the

greater depths—is constant.

The number of families at different depths, expressed

as percentages of the total number, increases from 0-50

to 50-100 fathoms, and then decreases to 1,800 fathoms

and beyond. Except for a minimum between 350 and

500 fathoms the decrease is fairly regular.

The two lines cross between 200 and 300 fathoms.

The reversal of the direction of the line representing

the frequency of the families including asymmetrical spe-

cies as a percentage of the number of the families not in-

cluding asymmetrical species at different depths, as com-

pared with the line representing the frequency of the

families at different depths expressed as percentages of

the total number, indicates that the less favorable the

environment for crinoids as a whole the greater becomes

the proportion of asymmetrical forms.

In the proportion of genera including asymmetrical

species to those composed entirely of symmetrical species

we find a minimum between 100 and 650 fathoms or, con-

sidering only the most markedly asymmetrical types, be-

tween 50 and 400 fathoms, the numbers above 100 (or 50)

fathoms and below 650 (or 400) fathoms being greater.

Considering families in the same light we appear te

No. 585] A STUDY OF ASYMMETRY 535

have an increase between 350 and 500 fathoms—that is,

more or less coinciding with this minimum.

In the frequency of families at different depths ex-

pressed as percentages of the total number we notice a

minimum between 350 and 500 fathoms which reaches a

point not again touched until 750-800 fathoms and beyond.

This indicates the occurrence here of a proportion-

ately large number of families including asymmetrical

species, but at the same time a proportionately small

number of genera including asymmetrical species within

those families.

THERMAL DISTRIBUTION oF THE ASYMMETRICAL CRINOIDS

In examining the thermal distribution of asymmetry

among the recent crinoids we find it advisable to employ

family instead of generic units, for the reason that our

records are insufficient to furnish us with even approxi-

mate thermal ranges for many of the individual genera,

though in most cases these may be estimated with rea-

sonable exactness. The records for the crinoids of the

deeper water are far more satisfactory than the records

for the crinoids of the littoral, and this is very fortunate,

for it justifies us in assigning a temperature of 65° and

‘Over to a number of species and genera which are of

great importance in the present study.

In considering asymmetry in relation to temperature

by family units it must constantly be borne in mind that,

whereas certain families (Capillasterine, Comactiniine

and Comasterine) extend from the warm littoral into

moderately deep water with a relatively low temperature,

the asymmetry among their component genera and species

is strongly marked only in very shallow water of high tem-

perature, and is only slightly marked—indeed not infre-

quently entirely absent, as in Comatilia—in genera and

species inhabiting deep and cold water.

Thus through a study of family units the amount of

asymmetry shown at intermediate temperatures is really

exaggerated, and appears in its relation to the higher

536 THE AMERICAN NATURALIST [Vor XLIX

and to the lower temperatures considerably greater than

it really is.

In the subfamily Heliometrinæ, the largest and most

widely distributed subfamily of the Antedonidæ, which

itself is the dominant crinoid family of the present seas,

the range of temperature is very great; but as only one

out of the ten genera of the Heliometrinæ is asymmetrical

it has seemed sufficient to consider and to tabulate the

temperature of this genus (Promachocrinus) alone.

he frequency of the families including asymmetrical

crinoids at different temperatures is as follows:

r eS Ae 4

Ce re E 4

e 2 oa i Peon th his ous Mae hae 4

T a ei a 3

ee a ee 4

OO a 3

owl A y E A 3

Da ee et a 3

SOE EE Ee S 4

OOS a ee re ee 5

aD ce OnE SUE up i TE Neen reese EO 4

Me a 1

Polow TE pa Soc bo Vins & Vdiein 6 oe Fie ee ORS VR ET SE 1

DUM E N A A E AT 4.3

BB -OD rs eta cick ce es weed eed bees aa were een 3.2

COBO. tinh ib hc ess RR EEE Oa Cie hee CER es Ve 3.7

or,

MUONS Dos og kw 6 oa Od ie oes aS T E 1

= oe APRESS GSES GRRE a eM Me mA at 4.3

ME I Sek Bei ea re NON Boa eRe oes ese tae 3.2

UPC CEU beeen cues os ae Ces mee cue Ly a eee 4.0

Considering the zone of optimum temperature (50°-

65°) in contrast to the temperatures above and below, and

omitting the exceptionally low temperatures below 30°,

we have:

No. 585] A STUDY OF ASYMMETRY 537

Bearing in mind always that the frequency between the

warm littoral and the cold abyssal temperatures is exag-

gerated because of the segrega-

tion in the warm littoral zone of

the most asymmetrical genera

and species in many of the fam-

ilies inhabiting intermediate tem-

peratures, it is clear that asym-

metry is least developed at the

optimum temperature for crinoid

life, and most developed in tem-

peratures which are phylogenet-

ically too warm or too cold.

This agrees perfectly with what

we found from an examination of

the bathymetrical distribution of

asymmetry.

A comparison between the fre-

quency of the families of crinoids

represented in the recent seas,

including only symmetrical spe-

cies, given in the actual numbers

and also as percentages of the

total numbers, and the frequency

of the families including asym-

metrical species, given in the same

way, follows (Fig. 3):

l \

nee eee

Te ome a

ow co 0

owe

: Li i]

Fie, 3. Frequency at Dif-

ferent Temperatures of the

Families eterna As epee”

rical Species (

those erapl Symmetriea

Species only (- - - -).

Families with — with

mperatur a Per Cent.

(Fate ubeit) Svecee Saiy ps ae a Total”

85°-80° 2 13 4 | 44

80 -75 2 13 4 | 44

75 -70 9 60 4 | 44

70 -65 9 60 3 | 33

—60 14 93 4 | 44

60 -55 12 80 3 | 33

55 —50 | 11 73 3 | 33

50 -45 | 7 47 3 | 33

45 —40 | 47 4 | 44

40 -35 | 7 47 | 5 | 55

35 -30 3 20 e 4 | 44

30 -25 1 7 | 1 | 11

538 THE AMERICAN NATURALIST [Vor XLIX

THE ASYMMETRICAL FEATURES IN DETAIL

In the following list are given the four types of asym-

metry occurring in the recent crinoids, with their geo-

graphical distribution and the genera in which they are

found.

1. Disk Not Radially Symmetrical

Geographical Distribution—Southern Japan south-

ward to Samoa, Fiji and southern Australia, thence west-

-l

“i

Soa.

-_-—

—

-_-—

—_—

_—

p= e

pen

oe ee ee

(————-), the Genera with One or More Rays

the Genera with Six to Ten

( exp

d or gp rged (——

Rays (- -), and the Genera with Three Basal

ressed as Percentages of the “otal heuer in Each Clas

ward to east Africa, from the Red Sea to the Cape; north-

western Africa and southwestern Europe (in moderately

deep water), and from South Carolina to Brazil; antarctic

regions, littoral to abyssal, and northward along the

No. 585]

A STUDY OF ASYMMETRY

539

eastern shores of the Pacific (in deep water) to British

Columbia.

This character is most strongly

marked in the shallow water

from the Marshall Islands and

New Caledonia through the Malay

Archipelago and along the north-

ern coasts of Australia, and

thence westward to Ceylon; and

again in the antarctic regions and

the abysses of the east Pacific.

Systematic Distribution —

Capillasterinz

Comatella Capillaster

Neocomatella Ne

Paleccomatella

Comactiniine

omatula Comint

Comatulella Comantinta

Comaster Comanthina

Comantheria omanthus

inept

machocr

AETR

Ptilocrinus

2. One or More Rays Dwarfed,

or Enlarged

Geographical Distribution. —

Malayan region and north Aus-

tralia, and Caribbean Sea, bu

only in warm and shallow water;

oo oO

ow at]

[J ' J

led »

O O 0

rts.

ul ee S

nO n oO

oO eteo

bgd

Frequency at Dif-

Temi mperatures of Fam-

tae Species in

e Disk is not Radially

including Species with

or More Rays Dwarfed or

eeh ed ( Fam-

ves inc ppc: Species with

m Six to T =-=- -),

s (-

a Pantie including Species

a Three Bas

and the Total ot a these t

regularities.

Malay Archipelago to

southern Japan, and Galápagos Islands to Central Amer-

ica in deep cold water.

Systematic Distribution.—

Capillasterinz

Capillaster (part)

Comactinii

ine

Comasterine

Comaster (part)

Comanthina

540- THE AMERICAN NATURALIST [Vou. XLIX

Comanthus (part)

Apiocrinidæ

Carpenterocrinus

Holopodidæ

Comantheria (part)

Proisocrinus

Holopus

Plicatocrinidæ

amocrinus

3. Six to Ten (Sometimes Four) Rays

Geographical Distribution—Southern Japan and the

Hawaiian Islands to the Malay Archipelago, in rather

deep water; abysses of the Indian Ocean and the Ant-

arctic; Florida northward and northeastward to Iceland

and Norway in deep and cold water.

hie a

(

-i

wwe meme

@----

steerer

aoe essameser==

wow eee

SEEN

a“

Ste wm

1G. 6. Proportion at Different Depths of Genera only Symmetrical Species,

and Genera including Species Asymmetrical Disks ( ), Genera in-

cluding One or More of the Rays Dwa

Genera including Species with from Six to Ten Rays (—— — -), and Genera in-

cluding Species with Three Basals (--- - -- j.

No. 585] A STUDY OF ASYMMETRY 541

This feature as an individual variant occurs in the

warm water of the Malayan region, in the shallower por-

tions of the Caribbean Sea, and very commonly on the

tropical Brazilian coast:

Depth R Ite ap ee Dr cpr be Six to Ten Three Total (35

(Fathoms) | metrical (17) lorkelarged(10)| Rays (4) Basals (4) 04a: (25)

0-50 (15) 88 (7) 70 (1) 25 0 (23) 66

50-100 (13) 76 (6) 60 (2) 50 0 (21) 60

100-150 (11) 65 (4) 40 (2) 50 0 (17) 49

150-200 (9) 53 (2) 20 (2) 50 0 (13) 37

200-250 (4) 23 0 (2) 50° 0 6) 17

250-300 (4) 23 0 (1) 25 (1) 25 6) 17

300-350 (2) 12 0 (1) 25 (1) 25 4) 11

350-400 (2) 12 (1). 10 2) 50 (1) 25 6) 17

(2) 12 (H) 10 2) 50 (1) 25 6) 17

450-500 (2) 12 @) 10 2) 50 (1) 25 6) 17

500-550 (2) 12 (1) 10 2) 50 (1) 25 6) 17

550-600 (2) 12 (2) 20 2) 50 (1) 25 7) 20

65 (2) 12 (1) 10 (2) 50 (1) 25 6) 17

650-700 (2) 12 (1) 10 75 (1) 25 ) 20

700-750 (2) 12 (1) 10 75 (1) 25

750-800 (2) 12 (1) 10 75 (1) 25 ) 20

800-850 (2) 12 0 ) 75 (1) 25

850-900 (i). 6 0 75 (1) 25 ) 14

950 BD G (1) 10 ) 75 (1) 25 ee ys

950-1,000 (ly 6 0 ) 75 (2) 50

1,000-1,100 (1) 6 0 ) 75 (2) 50 17

1,100-1,200 Uy. 9 0 ) 765 (2) 50

1,200-1,300 (1) 6 0 ) 75 (2) ar

1,300-1,400 (1) 6 0 ) 50 (2) 50 ) 14

1,400-1,500 W 6 0 ) 50 (2) 14

: ,500-1,600 U6 0 (2) 50 (2) 50 (5) 14

1,600-1,700 1) 6 0 (2) 50 (3) 75 ) 17

: »700—1,800 (6 0 (3) 75 (6) 17

800-1,900 (i) 6 0 (1) 25 (3) 75 (5) 14

oa ,000 G) © 0 (1) 25 (3) 75 (5) 14

2,000-2,500 () 6 0 (1) 25 (3) 75 (5) 14

2,500-3,000 0 0 (1) 25 (1) 3

Disk Not | Oneor More |

Temperature Radially | Rays Dwarfed| Six to Ten Three Basals Total

(Fahrenheit) Aranaren | | or Enlarged Rays

80°-75° 2 | 3 0 0 5

-70 3 | 4 0 0 T

70 -65 3 | 3 0 0 6

65 -60 3 | 3 1 0 ri

60 -55 2 | 2 X 0 5

—50 2 | 2 1 0 5

50 —45 1 | I 2 0 4

45 -40 2 | 2 2. 1 7

40 -35 1 | 2 3 1 7

35 -30 1 | 1 2 1 5

30 -25 1 | 0 | 1 0 2

542 THE AMERICAN NATURALIST [Von XLIX

Systematic Distribution. —

Heliometrinæ

Promachocrinus

Pentametrocrinidæ

haumatocrinus

Bourgueticrinide

Monachocrinus (part) Rhizecrinus

The Numb f Genera

Number of Genera Number of Genera Dube accessed es os

Depth (Fathoms) with ee with p Fe geen Percentage of the

isks isks Number with Symmet-

ri isks

0-50 15 51 29

50-100 13 55 23

100-150 pS 53 21

150-200 9 45 20

200-250 4 40 10

250-300 4 35 11

00-3 2 31 6

350-400 2 34 6

00-4 2 32 6

450-500 2 30 7

500-550 2 29 7

550-600 2 30 7

600-650 2 29 7

650-700 2 26 8

700-7 2 26 8

750-800 2 22 9

800- 2 21 9

850-900 1 21 5

900-950 1 23 4

950-1,000 1 20 5

,000-1,1 1 20 5

1,100-1,200 1 16 5

1,200-1,300 1 13 A 8

1,300-1,400 1 12 8

1,400-1,500 1 10 10

1,500-1,600 1 10 10

1,600-1,700 1 7 14

1,700-1,800 1 7 14

1,800-1, 1 6 16

1,900-2,000 1 6 16

2,000-2,500 1 6 16

2,500-3,000 0 4 D

4. Three Basals

Geographical Distribution.—Antarctic regions, and

northward to northwestern Africa, the Caroline Islands,

and British Columbia, except in the antarctic always in

very deep water.

No. 585] A STUDY OF ASYMMETRY 543

Systematic Distribution.—

Plicatocrinide

Ptilocrinus Gephyrocrinus

Hyocrinus Thalassocrinus

The frequency of each of these four types of asymmetry

at different depths and temperatures is given in the

tables on page 541 and in Fig. 4.

The rg mber of —

: wi symmetric:

Dopik Puika | ete Aar aonn | GIER DPS ppi pape gior g

Rays Number with Sym-

metrical Rays

0-50 7 59 12

50-10 6 62 9

100-150 4 60 6

150-200 2 52 4

00-250 0 44 0

250-300 0 39 0

300-350 0 33 0

350-4 1 35 3

400-450 1 33 3

450-500 1 31 3

00-550 1 30 3

550-600 2 30 6

00-650 1 30 3

650-700 1 27 4

700-750 1 27 4

750-800 1 23 4

800-850 0 23 + 0

0-9 0 22 0

00-9 1 23 4

950-1,000 0 21 0

1,000-1,100 0 21 0

1,100-1,200 0 17 0

1,200-1,300 0 14 0

,300-1,4 | 0 13 0

1,400-1,500 | 0 11 0

,500-1,6 | 0 11 0

1,600-1,700 | 0 8 0

1,700-1,800 | 0 8 0

1,800-1,900 0 7 0

1,900-2,000 | 0 7 0

2,000-2,500 0 7 0

2,500-3,000 | 0 4 0

In the table showing the frequency at different depths

the numbers in parentheses represent the actual cases, the

other numbers being the percentage of the total number

of genera in which the feature under consideration is

found. This last is given in parentheses at the head of

each column.

544 THE AMERICAN NATURALIST [ Vou. XLIX

For a graphic representation of the data in the table

on the lower part of page 541 see Fig. 5.

These frequencies group themselves as follows:

Wei i ee See 6.2

Ga cp ee cet ee . nel eae Ree 4.7

aa, ee ee ri 6.3

A E Cor oN Ge er a oe ee Varese 2.0

or, segregating those occurring at the optimum tempera-

ture:

o o

BOBS E E SEN we NN RE EE E eK Ewe 6.0

iting ee TE Oe OR Se ae PEE eee Pe 5.6

yp OR EEE OTe ee ee E ee ee eee 5.7

NOE Dee Ee Ona fey ERTE E rip rere 2.0

he Number of Genera

Number of Genera Number of Genera rich More Than Five

Depth (Fathoms) with More Than with Always Rays Expressed as a

Five Rays Five Rays Poe of the Num-

h Five Rays

0- 1 65 1

50-100 2 66 3

100-150 2 62 3

150-200 2 52 4

200-250 2 42 5

250-3! 1 38 3

300-350 1 32 3

350-400 2 34 6

400-450 2 32 6

450-500 2 30 6

500-550 2 29 7

550-600 2 30 6

5 2 29 t

650-700 3 25 12

700-7 3 25 12

7 3 21 14

00- 3 20 15

850-900 3 19 16

900-950 3 21 14

950-1,000 3 18 16

1,000-1,100 3 18 16

1,100-1,200 3 14 21

1,200-1,300 3 11 27

1,300-1,: 2 il 18

1,400-1,500 2 9 22

1,500-1,600 2 9 22

1,600-1,700 2 6 33

1,700-1,800 2 6 33

1,800-1,900 i 6 16

1,900-2,000 1 6 16

2,000-2,500 1 6 16

2,500-3, 0 4 0

No. 585] A STUDY OF ASYMMETRY 545

The relation at different depths between the crinoids

in which the disk is not radially symmetrical and those in

which it is radially symmetrical is shown in the table on

page 542 and in Fig. 6.

The relation at different depths between the crinoids in

which one or more rays are dwarfed, or, more rarely, en-

larged, and those in which all of the rays are of the same

size is shown in the table on page 543 and in Fig. 6.

e boca a

5 x wi ree Basals

Depth (raa | A Ee | ee foe aape y frale i

ber with Five Basals

0-50 0 66 0

50-10 0 68 0

100-150 0 64 | 0

150-200 0 54 | 0

200-250 0 44 | 0

250-300 1 38 | 2

300-350 1 32 3

350-400 i Sa 3

400-450 1 33 3

50-500 1 31 3

500-550 1 30 3

550-600 1 31 3

00-650 1 30 3

650-700 1 rt § 4

700-750 1 27 4

50-8! 1 23 4

800-850 1 22 4

0-9 1 21 5

900-950 1 23 4

950-1,000 2 19 10

1,000-1,100 2 19 10

1,100-1,200 2 15 13

,200-1,300 2 12 16

1,300-1,400 9 11 18

,400—1,500 2 9 22

1,500-1,600 2 9 22

1,600-1,700 3 5 60

1,700-1,800 3 5 60

1,800-1,900 3 4 75

1,900-2,000 3 4 75

,000-2,500 3 4 75

2,500-3,000 1 3 3o

The relation at different depths between the crinoids

with more (less frequently less) than five rays, and those

with five rays, is shown in the table on page 544 and in

Fig. 6.

The relation at different depths between the crinoids

with three basals and those with five is given in the table

given above and in Fig. 6.

546 THE AMERICAN NATURALIST [Von XLIX

SUMMARY

Among the recent crinoids any wide departure from the

normal close approximation to true pentamerous sym-

metry indicates unfavorable conditions of one or other of

two main types, which are not mutually exclusive.

These two types are

1. INTERNAL UNFAVORABLE CONDITIONS, induced by incip-

ient phylogenetical degeneration through type-senescence,

as in the Plicatocrinide, which in the recent seas repre-

sent the almost exclusively paleozoic Inadunata; and

2. EXTERNAL UNFAVORABLE CONDITIONS, taking the

form of

(a) Phylogenetically excessive cold, which, to

cite one example, appears to be the determining

factor in the asymmetry of the genus Promacho-

crinus; or of

(b) Phylogenetically excessive warmth, which

appears to be the determining factor in the asym-

metry of the family Comasteride.

INHERITANCE OF HABIT IN THE COMMON BEAN

JOHN B. NORTON, M.S.

MASSACHUSETTS EXPERIMENT STATION

Hasır is the external form of a plant taken as a whole.

It is usually described by a few general adjectives, such

as erect, open, spreading, etc. However, to study the

inheritance of plant habit, a detailed analysis of the real

characters underlying habit must be made. It is usually

found that the general outer appearance of a plant, its

habit, is the result of a combination of independent char-

acters, units, the recombination of which by crossing

often results in plants much altered in appearance from

the parent varieties. Characters usually unimportant

may be found of primary importance in the formation of

plant habit.

An example of such inheritance of habit is found in one

of Webber’s pepper hybrids (6). A cross was made be-

tween Red Chili, a variety with many erect fine branches,

and Golden Dawn, with few, horizontal, coarse branches,

both being of medium size. In the second generation re-

combination and segregation of the three character pairs

occurred, although not in strict Mendelian proportions.

The important feature of the results, however, lies in the

apparent creation of a giant and a dwarf type, not by the

appearance of new units by mutation, but simply by the

transference of the characters fine and coarse branches.

Hybrids having erect, many and coarse branches were

giants, while those having few, horizontal and coarse

branches were dwarfs. Other combinations of these

characters gave intermediate forms.

The study here reported was made largely on third and

fourth generation plants and a few second generation

plants of hybrids made primarily for the study of pig-

547

548 THE AMERICAN NATURALIST [Vou. XLIX

mentation. The material worked with, owing chiefly to

lack of knowledge of earlier generations, offered many

limitations and is unsuited to a detailed analysis of the

characters in question. As the plants were usually not

more than six inches apart in the rows, the crowding in

the later stages of development hindered accurate judg-

ment of the habit type.

With reference to general habit bean plants are either

pole or bush. Pole beans are commonly long twining

vines, climbing when provided with poles or other sup-

port. The true bush type is usually short, erect and non-

twining. There are also certain races of beans really in-

termediate between the true bush and pole types, the run-

ner beans, which are non-climbing. Types classed as

bush beans also occur, which are spreading and possess

outstretched branches of a more or less runner-like char-

acter.

The following table contains a description of habit of

varieties of beans considered in this discussion. The de-

scriptions are from ‘‘American Varieties of Garden

Beans’’ (5). The varieties observed agree with these

descriptions except in the case of Mohawk, which is de-

seribed as without runners. The strain of Mohawk iso-

lated here produces runners.

TABLE I

DESCRIPTION OF BEAN VARIETIES

Pole Beans ALT1

Golden Carmine—Small, good climber

Creasback—Small, at first bush-like, poor climber when young.

Runner Beans ALt

White Marrow—Very large, very spreading, many runners.

Bush Beans AIT

Burpee Stringless—Large, medium, very erect when young, with a few shoots

high above the plant, = more or less spreading when mature; no runners.

Giant Stringless—Same as

1 For the meaning of these letters see page 550.

No. 585] INHERITANCE OF HABIT 549

Semi-runner Forms Alt

Refugee—Very large, very spreading, many semi-runners.

Refugee Wax—Large, medium, very spreading, many runner-like branches.

Spreading Forms aLT or alt

Longfellow—Large to medium, somewhat spreading, many outstretched

branches, no real runners.

Kenny Rustless—Large, very pee almost runner-like bran

Prolific Black Wax—Medium, more or less spreading, arc oa out-

stretched branches, no real runners.

Erect Forms alT or alt

Black Valentine—Large, medium, fairly erect, occasional drooping branches,

no real runners

Blue Pod—Medium, erect, no runners or spreading branches.

Ta rge, medium, fairly erect when y m but drooping when ma-

no runners or decided spreading branc

Bet Kidney—Large, no runners, but as drooping with fruit-laden

branches and spreading when mature

ee Maer Wax—Large, sometimes ‘with drooping branches, but no real

Challenge Black Wax—Very small, erect, no runners or spreading branches.

Cu rries—Medium , erect, no runners or — branches.

ax—La ine. medium, erect, no runners.

Early Refugee—Medium, very erect, no runners or spreading branch

German Black Wa Bg Fis ek erect when er usually borne pen with

fruit laden branches when mature, no runners.

Long Yellow Six Weeks—Medium, very cae. no runners or spreading

ranches

Low Champion—Very large, usually erect, no runners or — branches.

Mohawk—Large, very erect, no runners, sometimes drooping w

Red Valentine—Medium, erect, no runners or spreading branches,

Round Yellow Six Weeks--Ginall; medium, very erect, no runners or spread-

ing branches,

Wardwell—Large, medium, fairly erect, no runners.

Warren—Very large, usually erect, no runners or decided spreading

branches

Wa RART a erect, no runners or spreading branches.

R. A. Emerson in his experiments on heredity of plant

habit in beans found three main character pairs con-

cerned, namely, length of plant axis, developed in vari-

ous degrees; ; twining habit or circumnutation developed

in various degrees or not at all; and lastly, the position of

pods, axial or terminal. His data involve chiefly the

latter character pair, which is inherited in a 3:1 propor-

550 THE AMERICAN NATURALIST [Vor. XLIX

tion, the axial position of pods being dominant. The posi-

tion of pods or flowers influences plant habit in this man-

ner: when flowers are formed at the growing tip of a

main stem or branch, such a stem or branch must neces-

sarily cease to elongate; on the other hand, if no flowers

or fruits are formed at that point it may continue to grow

indefinitely.

The habit of all the varieties of beans can be accounted

for easily with only these three character pairs. In

Table I the varieties here concerned have been grouped

according to the probable presence or absence in them of

the characters mentioned.

I have designated the axial position of the pods as A,

the terminal position by a; long plant axis by L, short

by 1; a long axis was shown to be dominant over short in

some of Mendel’s crosses of beans (1). I have designated

circumnutation by T and its absence by t, as, judging

from Emerson’s statements, and according to my own

observations twining habit is dominant. The possible

combinations of these characters are as follows:

HABIT TYPES

Type a, ALT....Pole beans.

Type b, ALt.....Runner beans.

Type a comprises the pole beans, as the vines are of

great length, both on account of long axis and not being

checked by any terminal inflorescence, and as they can

climb by virtue of cireumnutation.

Type b comprises the runner beans. They aredlike the

pole beans except that the climbing habit is not developed

to any great extent, if at all. Between these two types

it is difficult to draw sharp distinction, but the true

runner probably lacks the factor for twining.

No. 585] INHERITANCE OF HABIT 551

Type ¢ probably represents the varieties which early

send up a few shoots high in the air like Burpee String-

less. In such beans the growth of the main stems or

branches is not entirely prevented by the absence of

the character which produces a long axis, and as the

climbing habit is more or less developed, the characteris-

tic shoots are sent up.

Type d represents the semi-runners, caused by the

short axis.

Combinations of type e and e, are the spreading varie-

ties, with long outstretched branches. They are to be

distinguished from runners by terminal inflorescences.

Kenny Rustless is a representative of the e type of habit

and probably Prolific Black Wax also.

The last two combinations, f and f, are the typical

erect bush form, such as Blue Pod Butter and Challenge

Black Wax.

Table II gives the possible crosses of these types and

the F, proportions to be expected when the forms crossed

are the most nearly typical. In the cases of typical

forms, the F, types should be differentiated without

much difficulty. A circumstance that must be looked

upon as a possible cause of exceptions is the presence of

unknown factors that cause variations in the intensity of

the development of the twining habit and of the inter-

mediate lengths between long and short axis. If there

are various factors for length, as Emerson assumes to be

the case in all quantitative characters (3), and if the

twining habit is to be explained in much the same way,

results may be considerably at variance with the expecta-

tions indicated in Table II. It must be remembered that

the constitutions given for the varieties are only as-

sumed.

At present, owing to circumstances mentioned before,

TABLE II

Constitution Type F: Proportions

ALTX ALT axo a

ALT xX ALt axb 3a: 1b

ALT xX AIT aXe 3a: le

ALTX Alt axd

Ae wrrs

552 THE AMERICAN NATURALIST [ Vou. XLIX

ALT 7a

ALt 2 3b

AIT gametes 3c

Alt] 1d

5 ALT X aLT aXe 3a: le

6 ALT X aLt aXe

ALt 2 3b

aLT gametes 3e,

aLt le,

Qa: 3b: 4e

vå ALT X alT axf 7a

ALT 2 3b

AIT 3e

aLT gametes if

alT Qa: 3b: 3e: 1f

8 ALT X alt ax? 15a

ALT O- 19

ALt 4 Te

AIT So Eos Sad

Alt Te

aLT 5

aLt 3f

alT 1

alt 27a: 9b: 9c: 3d: 12e: 4f

9 ALt X ALt bXxXb b 5

10 ALt X AIT bXe 9a: 3b: 3c: 1d as in type No. 4.

11 ALt X Alt bxd 3b: 1d

12 ALt X aLt bXe 3b: le

13 ALt X aLT bXe Ta

AL 2 3b

ALt 3e

aLT gametes 1

aLt S S 4

14 ALt X alT bXf 27a: 9b: 9c: 3d: 12e: 4f as in type No. 8.

15 ALt X alt bxf

ALt

No. 585]

16 AIT X AIT exe

17 AIT X Alt cxd

18 ATT X aLT exe

19 AIT X al? cxf

20 AIT Sait oxe

Si: AIT X ale cxf

AIT

Alt

alT

alt

22 Alt X Alt axd

23 Alt X aLT aXe

24 Alt X aLt aXe

ALt

Alt

E gametes

alt

25 Alt X alT dxf

AIT

Alt

alT gametes

alt

26 Alt X alt aX f

27 aLT X aLT exe

28 aLT X aLt exe

29 aLT X alT xT

30 SLT X alt exf

aLT

aLt

alT gametes

sit}

31 aLt X alt ixe

32 alt Xx alT éxf

33 aLt X alt EXT

834 alT X alT PAT

35 alT X alt I XF

36 alt X alt [xf

INHERITANCE OF HABIT

9c: 3d: 4f

27a: 9b: 90: Sd:

3e: 1f as in type 30.

3: If

: 9e: Id: 12e:

12e:

553

d !

: 3e: 1f as in type No. 7.

4f as in type No. 8.

only general notes on the behavior of various types of

crosses can be given.

554 THE AMERICAN NATURALIST [Von XLIX

Tyre 2. ALT X ALt

In the third generation of a cross of Creasback, a typ-

ical pole bean with White Marrow, a runner bean with

probably a weak character for circumnutation, all lots

were of axillary inflorescence. The habit of climbing

was developed in various degrees so that classifications

of types was difficult.

Cross Tyre 6 or 7. ALT +aLT or alt

Notes on an early cross of Creasback by Prolific Black

Wax indicate that the generation F, were pole beans, the

generation F, segregating into 33 pole and 8 bush. The

latter is probably a 3:1 proportion as expected. Whether

all plants described as bush were of the spreading type

does not appear from our records.

Cross Tyre 8. ALT X alt or alT

In a cross of Creasback with Blue Pod, a typical bush

bean, there occurs one strain of homozygous pole plants,

and also in the F, generation heterozygous types. Pole

and runner forms and bush forms of various types occur

in the proportions of 9:7 in one lot and in another of 3:1,

as might be expected in an F, generation. In another

small lot occur plants with long outstretched branches,

in another two plants of c type of habit. Evidently

Blue Pod has the constitution alt.

The date from a cross of Creasback with Blue Pod do

not signify much, as the types isolated happen to be con-

stant, one a pole type and bush types, of which several

are described as somewhat spreading. In one there

occurs a runner bean.

Creasback and Warwick crosses in the F, generation

behave consistently with the cross type, as assumed. In

one lot, 1 2 have axial inflorescence and three terminal.

Lots with spreading plants occur and one plant was noted

which possessed a very long axis, along with a twining

habit, but also terminal inflorescence. According to the

No. 585] INHERITANCE OF HABIT 555

explanation of habit characters assumed, such a plant

would have the formula aLT. Without a support which

happened to have been placed near it, the peculiarity of

the plant would not have been so noticeable.

A cross of Mohawk and Golden Carmine, a pole bean,

gave in the F, generation 7 plants of the bush type and

28 plants more or less pole like. In the notes no separa-

tion of pole and runner beans were made, probably due

to a lack of clear distinction between the two as occurs

in many crosses.

Cross Type 10. ALt x AIT

White Marrow by Burpee Stringless is presumably a

cross of this type. In one case the F is described as a

pole and in another as a runner bean. The F, genera-

tion results in 38 bush to 108 described as runner beans.

This is consistent with expected results when the plant

is described as a whole. The expectations are 12 pole

and more or less pole like beans and four more or less

bush like forms.

Cross Type 12 or 13. ALt+aLT or aLt

A cross of White Marrow, a runner variety, with Pro-

lific Black Wax, which belongs to the type with spreading

outstretched branches, gave 20 bush plants and 58 plants

of the runner and pole types, no differentiation being

made between the two. This is consistent with the as-

sumed constitutions.

Cross TYPE 14 or 15. ALt X alt or alT

White Marrow with Currie behaves according to ex-

pectation, giving in the F, generation 41 bush plants e or

f in type, and 52 of the runner or semi-runner type.

In the cross of Blue Pod by White Marrow and its recip-

rocal, neither variety being pole in type, climbing plants

apparently occur as well representative of most if not all

of the other habit types. Some lots isolated were very

erect, others spreading in various degrees; one lot is de-

556 THE AMERICAN NATURALIST [ Vou. XLIX

scribed as having long tendril-like shoots above the plant,

another along side of this had shorter shoots, perhaps

AIT. Among the lots, all degrees of climbing were devel-

oped; one plant encountered was evidently aLT like the

one mentioned in a previously discussed cross; plants

with more or less outstretched branches were noted.

Type notes on F, and F, generations of an earlier cross

in type; F, segregates into 25 bush forms and 62 runners,

are significant. The F, generation is described as pole

probably including pole beans of the F, type. The ratio

is disturbed by the lack of a clear understanding of the

true basis for classification of plant type in beans. ‘The

F, of another cross involving the same varieties is noted

as having 41 bush and 5 runner beans.

White Marrow and Burpee Kidney yielded two lots of

bush beans and two heterozygote lots giving 6 plants with

terminal inflorescence and 15 with axillary.

Red Valentine and White Marrow crosses give similar

results. In an early cross, the F, generation plants have

been grouped according to the general plant type, no at-

tempt being made to separate intergrading types. The

notes give the results of segregations as 75 bush and 136

runner beans. Later generation heterozygotes approach

a proportion of 9 runner to 7 bush beans. The apparent

behavior probably depends on whether the intermediate

types are classed as runner or bush. In the cross in

which only the F, generation was observed, only constant

bush types seem to have been isolated.

Cross Tyre 19 or 21. AIT X alt on alT

Blue Pod crossed with Burpee is a representative cross

of this type. Only in a few cases was the Burpee type,

plants with shoots high in the air, observed, as most lots

isolated were homozygous and erect. In the F, genera-

tion of an early cross, plants described as runners ap-

peared. The proportion was 3 runners tolbush. Heter-

ozygote lots descended from these plants segregated in

the same manner, totaled 18 bush and 71 so-called run-

No. 585] INHERITANCE OF HABIT 557

ners. The runners are probably really c in type or c

and d.

In the cross of Giant Stringless and Blue Pod the

parent types were both isolated. No semi-runners were

noted, as would be the case if the cross were No. 21 in

type.

Cross Type 25 or 26. Alt X aLT or alt

Refugee Wax is a semi-runner bean. The F, isolated

lots of this variety crossed with Blue Pod were all more

or less erect. Some lots homozygous for axial branch-

ing were isolated, many individuals of which showed

signs of climbing. The semi-running and climbing

branches were short, confirming the assumption that

neither variety used possesses the factor for a long axis.

The climbing tendency exhibited shows that there must

be strains of Blue Pod that possess T. Previous data are

in harmony with this.

Cross Tyre 29, 30, 34 or 35. aLT or aLt X alt or alT

Many crosses of bush beans with those of spreading

type give a 3:1 proportion in the F, and later hetero-

zygous lots.

In Keeny Rustless, a variety of the spreading type,

with its almost runner-like branches, by Red Valentine

some lots with the spreading habit have been isolated,

also more or less runner-like forms and one with the erect

habit of Red Valentine. The axial and terminal inflores-

cence is inherited in a 3:1 proportion. Notes on type in

one heterozygous lot show five erect and 10 plants with

outstretched branches.

In the cross of Black Valentine and Prolific Black Wax

one lot with outstretched branches was isolated; all

others were of the erect type.

In the cross of Blue Pod Butter and Prolific Black Wax

no spreading types with outstretched branches were

noted, but this is not surprising, as in an F, generation

the parent plants selfed for planting may not have hap-

558 THE AMERICAN NATURALIST [ Vou. XLIX

pened to be of the spreading type, thus giving homo-

zygous erect offspring.

In the cross of Golden Eyed Wax with Prolific Black,

outstretched branches due only to axial inflorescence

were noted.

Spreading plants of this nature also occur in the cross

of Bountiful and Prolific Black Wax. In the latter two

crosses the twining habit was more or less developed in

the longer branches.

Cross Type 34, 35, or 36. alT Xx alT, alT X alT, on

alt X alt

In the crosses of this type only erect bush beans with-

out runners or spreading branches, should occur, al-

though contorted stems might possibly appear. Such is

the behavior of the following crosses of this type:

Low Champion X Blue Pod Butter

Blue Pod Butter X Golden Eyed Wax and reciprocal

Blue Pod Butter X Mohawk and reciprocal

Challenge Black Wax X Warwick

Currie X Mohawk and reciprocal

Currie X Red Valentine

Blue Pod Butter X Warren

Bountiful X German Black Wax

In the crosses, Challenge Black Wax by Davis Wax and

Blue Pod Butter by Davis Wax, lots have been isolated

with short shoots above the plants somewhat resembling

the habit of Burpee Stringless and Giant Stringless.

This behavior is unexpected if such a plant type is to be

described by the formula AIT. The Davis Wax type

used in the crosses may, however, have been of a different

strain from that described in the table. This variety is

the only one used in the crosses that was not under the

observation of the writer, as its growth was discontinued

the year in which these notes were taken.

While the factors discussed above primarily determine

the plant habit, there are several others of secondary con-

sideration. No special notes were taken with regard to

No. 585] INHERITANCE OF HABIT 559

these. Some of them are mentioned in the following

paragraph.

The character of the habit type is somewhat influenced

by the amount of branching the plants exhibit; open,

loose, bush beans are the result of few branches; the

close, dense habit of some forms is caused by profuse

branching. The size of a plant to some extent influences

the habit, although not as much in small ones like Chal-

lenge Black Wax. In Warren the size of the plant prob-

ably causes it to droop. In some varieties the number

and weight of the pods, as well as their position, cause

some plants to droop and assume a spreading habit when

old. Perhaps fineness and coarseness of branching

affect habit.

One further matter that comes up for consideration is

the question of the effect of environment upon plant

habit. Its greatest effect, as would be supposed, seems

to be upon such quantitative characters as length of the

plant axis and probably the twining character to some

extent. Instances of adverse conditions resulting in the

almost total suppression of a character were noted in

plants grown on poor soil. They exhibited the slender

tips, typical of vines with axial inflorescence, but were

otherwise bush-like and erect. The accelerating effects

of very fertile soil on the growth of runner was also

noted. However, the environmental explanation for the

sudden appearance of runners among bush beans or of

pole beans among typical runners is open to question.

The most probable cause of such phenomena lies pri-

marily in the regrouping of the unit characters of habit,

combined at times with checking and accelerating factors

external to the plant.

The investigations here reported offer a foundation

upon which more extensive study on the subject might

be based.

The following table suggests a few important cross

types and the varieties which might be used to ad-

vantage:

560 THE AMERICAN NATURALIST [ Vou. XLIX

CROSSES FOR FURTHER STUDY

Type Plant

Number Varieties Type

2 Golden Carmine X White Marrow and reciprocal aXb

3 Golden Carmine X Burpee Stringless. and reciprocal aXe

+ Golden Carmine X Refugee and reciprocal axd

5or6 Golden Carmine X Keeney and reciprocal axe

7ors8 Golden Carmine X Challenge Black and reciprocal aX f

10 White Marrow X Burpee Stringlessand reciprocal b X ¢

þei ped jed pi p eed

AkReneoocwmrannwnne 2

bad

11 White Marrow X Refugee and reciprocal xd

120r13 White Marrow X Keeney and reciprocal bxXe

White Marrow X Challenge Black and reciprocal b Xf

17 Burpee Stringless X Refugee and reciprocal exXd

180r19 Burpee Stringless X Keeney and reciprocal cxe

20or21 Burpee Stringless X Challege Black and reciprocal cxf

23 0r24 Refugee Keeney and reciprocal axe

25 0r26 Refugee X Challenge Black and reciprocal d Xf

290r30 Keeney X Challenge Black and reciprocal exf

The Burpee crosses should be particularly watched to

determine if the assumed set of factors AIT is the cause

of the shoots and later spreading habit of the plant.

The axis should be studied by means of accurate meas-

urement as far as possible. The judgment concerning

circumnutation would probably be necessarily more or

less indefinite.

In crosses 4, 5, 8, 9, 11, ete. the type number should be

determined.

The conclusions that can be drawn from observations

reported in the preceding pages are:

1. That plant habit in beans is largely determined by

the presence or absence of three characters which have

been designated by the letters A, L, and T.

1. A, the presence of axial inflorescence permitting an

indefinite growth, of the main stem and main branches,

and a terminal inflorescence causing definite growth.

2. The length of the axis L, an important factor con-

trolling plant habit and probably governed by a series of

two or more factors for a length L,, L,, ete., which behave

after the fashion of Emerson’s hypothesis for the inherit-

ance of quantitative characters.

3. The climbing habit is due to a factor for circum-

No. 585] INHERITANCE OF HABIT 561

nutation. This factor may be called T. The cause of the

various degrees of the climbing habit has not been deter-

mined with any degree of certainty. The contorted stems

of erect bush forms are probably caused by T.

II. The factors A, L and T may be present in any

possible combination, giving rise to the various habit

types of beans.

III. When the types are crossed among themselves

they behave approximately after the manner sketched in

Table IT.

BIBLIOGRAPHY

1. Emerson, R. A. Pie in Bean Hybrids. Rpt. Agr. Exp. Sta. Neb. 17

(1904), p 34—43.

2. Emerson, R. A. Inheritance of Sizes and Shapes in Plants. AMER. NAT.,

44 (1 910), pp. 736-46 (1910).

. Emerson, R. A., and East, E. M. Inheritance of Quantitative Characters

in Maize. Wuiversity of Nebraska Agr. Exp. Sta. Research Bulletin 2

913).

4, Jarvis, C. D aang Varieties of Beans. Cornell Uniyersity Agr. Exp.

ta. Bulletin 2

5. Tracy, Jr rican Varieties of Garden Beans. U. S. D. A.

in No. 109.

6. Webber, H. J. Preliminary Report on Pepper Hybrids. A. B. A.

Reports, VII and VIII, p. 188.

ON THE MODIFICATION OF CHARACTERS BY

CROSSING!

R. RUGGLES GATES

UNIVERSITY OF LONDON

Iw the early years of Mendelian discovery there was

much discussion concerning gametic purity in hybrids,

and the question whether unit characters are modified on

crossing was keenly debated. Convinced by the numer-

ous instances in which Mendelian characters appear to

be unmodified by crossing, many writers came to the con-

clusion that characters universally segregate without

being modified or ‘‘contaminated’’ by association with

other characters in the hybrid. That such a conclusion is

far too sweeping is, however, indicated by many later

results, and there is now a disposition to admit that

changes in a character or the breaking up of a character

may be effected through crossing. But some writers con-

tinue to look upon a unit character as an entity, which is

unmodifiable and indestructible by hybridization.

Notwithstanding the admitted belief of Bateson and

others that characters may be modified by crossing, I

know of no extensive body of evidence that such modifica-

tions take place except the work of Castle and Phillips

(1914) whose conclusions have not been fully accepted

and are chiefly concerned with modification by selection.

It therefore seemed worth while to direct attention to

certain experimental results of a somewhat different kind

which appear to show beyond cavil that modifications of

characters sometimes result from crossing. The matter

is an important one because it affects the old question of

the swamping of new characters through crossing, as well

as various other aspects of evolutionary theory.

1 Read before the American Genetic Association, San Francisco meeting,

August 3, 1915.

562

No. 585] MODIFICATION OF CHARACTERS 563

Anticipating the conclusions which will be reached in

this paper, it may be pointed out that the swamping effect

is not so serious a check upon progressive evolution as

might be supposed, (1) because blending or modification

of a new character only takes place in certain crosses and

may be accompanied by segregation even in some of

those, and (2) because Mendelian characters usually come

out ‘‘pure’’ when crossed with the form from which they

were derived. Hence when Mendelian characters arise

through mutations in nature it may be expected that they

will be able to perpetuate themselves and spread, espe-

cially when dominant, unless they place the organism at a

disadvantage in the struggle for existence. The modifi-

cation of a Mendelian character will come, not from cross-

ing with its parent form but with a more distantly related

species.

Some writers appear to believe that it is practically

impossible to modify a unit character because it is repre-

sented in the germ plasm by a ‘‘gene’’ whose essential

characteristic is its unmodifiability. But if we consider

that each unit character is a difference which has arisen

through a change in one element of the germ plasm, prob-

ably in a chromosome, then it would seem possible that if

introduced into a foreign cytoplasm the chromosome may

become subject to permanent modification.

Castle and Phillips (1914) have produced evidence

from hooded rats tending to show that selection may

modify a unit character in certain cases, although the

nature of this result is not yet fully analyzed. They

moreover show that the hooded character is modified by

across. Davenport (1906) in his experiments with poul-

try, concluded that unit characters are frequently modi-

fied by crossing. He says (p. 80):

Very frequently, if not always, the character that has been once

crossed has been affected by its opposite with which it was mated and

whose place it has taken in the hybrid. It may be extracted therefrom

to use in a new combination, but it will be found to be altered. This we

564 THE AMERICAN NATURALIST (Vor XLIX

have seen to be true for almost every characteristic sufficiently studied—

for the comb form, the nostril form, cerebral hernia, crest, muff, tail

length, vulture hock, foot feathering, foot color, earlobe and both gen-

eral and special plumage color. Everywhere unit characters are changed

by hybridizing.

In crosses between Ginothera rubricalyx and Œ. grand-

iflora I have studied with care the modifications which

take place in the expression of the various character-

differences in F,, F, and later generations. Many of the

results have been recorded in detail elsewhere (Gates,

1914, 1915a, pp. 250-282). It need only be said that the

foliage characters in F, form an absolutely continuous

series so that it is impossible to apply to them usefully

the unit-character conception. In F, a large number of

races were obtained differing in many ways as regards

their foliage, many of them breeding true and others

varying within wide or narrow limits. Occasionally in

back-crosses an apparently complete reversion takes

place to one or other of the parents, but blending and

fractionation of the characters is the rule.

It is, however, difficult to obtain critical evidence from

the foliage because, while the original differences are

sharply marked, yet it is always possible to assume that

the continuous F, series and the numerous F, races result

from the presence of many independent units.? I will

therefore confine my attention to the sharp pigmentation

character (R) of rubricalyx, for in the inheritance of this

character crucial evidence may be obtained. The origin

of this dominant unit-character through a single muta-

tion, and the subsequent attainment of the duplicate con-

dition (RR’) for this character in some of the offspring

of later generations (1915b), have been pointed out else-

where. Here we will examine the modifications of R

which take place when rubricalyx is crossed with Œ.

grandiflora.

The main facts regarding the variability of R in these

2 The inheritance of pubescence-differences shows similar features and can

not be reasonably interpreted in terms of numerous units.

No. 585] MODIFICATION OF CHARACTERS. 565

crosses have already been published (Gates, 1914, p. 244

and 1915a, p. 257) and need only be summarized here, to

emphasize their significance. In the publications cited

I had not yet reeognized that the occurrence of 15:1 ratios

in later generations of rubricalyx is significant as indi-

cating that in such families the duplicate condition for R

had been reached, even although other ratios such as

5:1 occur as well.

The F, generation of the crosses between rubricalyx

and grandiflora contained 2,794 plants, in 20 of which the

red bud-character R showed decided modification so as to

be more or less intermediate between the two parents.

Since each plant in bloom produces scores of buds simul-

taneously, and hundreds during the season, there is ample

material for determining the exact degree of modification

or development of the character in every individual. As

will be seen from the original records, the 20 plants in

which the color pattern was more or less modified were

not all alike but formed a series, some being nearer the

normal R than others. In most other F, plants sharp

segregation took place, the buds being entirely either R

or r without the slightest doubt in classification. In addi-

tion to the 20 plants above mentioned, there were, how-

ever, a certain number in which the character R was more

or less underdeveloped, so that it was impossible to be

certain whether they represented mere fluctuations or real

modifications of the character.

The crucial test of modification is supplied by the F,

generation. Two of these last-mentioned intermediate

plants self-pollinated yielded offspring like themselves,

without any tendency to segregate into the R and r types.

These families numbered, respectively, 283 and 20 plants,

so that in the former case at least any tendency to segre-

gation could not fail to be observed. The buds of these

plants were intermediate, the pigmentation was pale and

was never fully developed on the hypanthium as is the

case in rubricalyx. The whole population was then inter-

mediate like the parent.

566 THE AMERICAN NATURALIST [Vou. XLIX

Another F, family (No. 149) was derived from an F,

plant (65. III. 12) having sepals weak red with the color

pattern as extensive as in rubrinervis 6 (i. e., nearly the

extreme condition), and in addition streaks of pale red

on the hypanthium. This plant was therefore nearer r

than R, and one may account for its occurrence through

‘‘contamination’’ before segregation took place in the

germ cells of the previous generation. In pure rubri-

nervis or grandiflora I have never found even a trace of

red on the hypanthium until the flower fades. The off-

spring of this plant numbered 186 individuals and their

pigmentation fluctuated about that of the parent plant as

amean. This condition closely approximated that in Œ.

rubrinervoides (1915c, p. 390), which may have orig-

inated in a similar way.

We must, therefore, conclude that plants which are

intermediate in pigmentation breed true, at least in all

cases tested, and that the degree of pigmentation in the

parent is adhered to in the offspring whether the parent

plant is an under-pigmented R or an over-pigmented r.

In this aspect, the inheritance in such cases is quantita-

tive and the offspring vary only within narrow limits.

The quantitative aspect is further emphasized when F,

and F, hybrids of Œ. grandiflora and Œ. rubricalyx are

crossed back with either parent. The pigmentation is

much intensified when crossed back with rubricalyx, and

greatly diluted when crossed with grandiflora, Thus in

(rubricalyx X grandiflora) < grandiflora if the female

parent is heterozygous for R, segregation into R and r

plants will occur in the offspring, but the R plants will

be much paler than in the selfed offspring of the female

parent.

Hence there are two somewhat antagonistic effects

which have to be considered, (1) the segregation of R and

r individuals, and (2) a permanent dilution of the pig-

mentation of the R individuals. The former effect can be

explained by the meiotic mechanism which segregates

No. 585] MODIFICATION OF CHARACTERS. 567

chromosome pairs. The latter effect may be due to a

modification of the chromosomes themselves, or perhaps

of the surrounding cytoplasm, or the inhibition in pig-

mentation may be explained by the presence of more

numerous grandiflora chromosomes. Everywhere, in an

accurate study of the inheritance of R, the quantitative

as well as the qualitative (presence or absence) aspect

has to be considered.

The dilution effect from crossing back with grandiflora

has been tested in six families numbering 673 individuals

and is always essentially the same. Although segregation

into the R and r types takes place when the parent is

heterozygous, yet R once diluted always remains so and

apparently never gives rise to the original deeply pig-

mented condition. In other words, a permanently blended

condition arises as regards the depth of pigmentation,

although this will still segregate from the unpigmented

- eondition in heterozygous plants.

It is not easy to furnish a complete explanation for this

diluting effect. The permanent dilution of R through

union with a grandiflora germ cell may perhaps be ac-

counted for by the fact that in the heterozygote the chro-

mosomes of grandiflora are closely associated in the same

nucleus with those of the other parent. The chromosomes

which are finally dissociated in the germ cells, after thou-

sands or millions of mitotic divisions in association,

might then be supposed to be somewhat modified. There

are, however, difficulties with this view, since the absence-

character, r, is usually not contaminated, but splits out

sharply and almost invariably without any trace of red-

production.

It is also difficult to account for the facts on the

assumption that the cytoplasm has been permanently

modified.

There is, however, one hypothesis which appears to

meet the case. If all the grandiflora chromosomes are

equally effective in inhibiting anthocyanin production in

568 THE AMERICAN NATURALIST [ Vor. XLIX

the hybrids with rubricalyx—a not improbable hypothesis

—then the dilution effect will be the same in F, or in cross-

ing back, whenever an R chromosome is present in the

next generation; and when such a chromosome is not

present there will of course be complete absence from the

buds of the rubricalyx pigment. On this hypothesis, in an

original cross between rubricalyx and grandiflora a cer-

tain (observed) reduction in pigmentation occurs. When

the F, hybrid is crossed back with grandiflora the addi-

tional grandiflora chromosomes thus introduced dilute or

inhibit the color still further, while the presence or ab-

sence of the diluted R will depend upon whether or not

the R chromosome from rubricalyx is present. It would

_ thus appear to be unnecessary to assume that this chromo-

some is itself modified by its different nuclear and cyto-

plasmic environment.

In other words, the grandiflora chromosomes may be

supposed to exert a mass effect in inhibiting the influence

of the R chromosome. It is, of course, possible that in

these circumstances the R chromosome itself may be

permanently modified, but it seems possible to explain all

the facts without making this assumption. In any case,

whatever the modus operandi, there can be no question

that the R character is permanently diluted by crossing

with grandiflora, and the degree of dilution is increased

every time the hybrid is again crossed back with that

species.

Another noteworthy fact is that as the pigmentation

becomes more dilute its morphological expression is more

irregular. The color pattern of the bud begins to break

up, and instead of continuous pigmentation of the whole

bud a patchy effect will be produced. This spotted condi-

tion of the buds is very marked in certain families, e. g.,

in the second generation of offspring from (rubricalyx X

grandiflora) X grandiflora (see Gates, 1915a, Fig. 113, p.

280). When it appears it is found to persist in later

generations. To account for this condition through the

No. 585] MODIFICATION OF CHARACTERS. 569

accession of a ‘‘spotting factor’’ is a gratuitous assump-

tion. Spotting appears rather to be the manner of ex-

pression of the character when the amount of pigment is

small. It must be said, however, that in some families

having no greater quantity of pigmentation there is a

strong tendency for it to remain uniformly distributed,

so that the whole bud is very pale red.

LITERATURE CITED

Castle, W. E., and Phillips, John C. 1914. Piebald Rats and Selection; an

p A Test of the Effectiveness of Selection and the

siy ory of eaor ne in Mendelian Crosses. Carnegie

ubl. No. 195, pp. 56, pls. 3.

Davenport, C. z 1906. sii te in Poultry. Carnegie Publ. No. 52, pp.

136, pls. 17.

Gates, R. R. 1914. Breeding Experiments which Show that ape

and Mutation are Independent Phenomena. Zeitschr. f. Abst

. Vererb., 11: 209-279, Figs. 2

1915a. The Matation Factor in Evolution. Macmillans, London, pp. 353,

19156. On Successive teil casey pie Biol. Bull., 29: In press.

1915c. Some Cénotheras from Cheshire and Lancashire. Annals Mo.

Bot. Gard., ii por Pie 20-22

SHORTER ARTICLES AND DISCUSSION

STUDIES ON INBREEDING. VI. SOME FURTHER CON-

SIDERATIONS REGARDING COUSIN AND

RELATED KINDS OF MATING?

IN the first of these studies? the writer dealt with the results,

in so far as concerned coefficients of inbreeding, which would

follow continued brother X sister, parent X offspring, and cousin

X cousin mating. Regarding matings of the latter type it is de-

sired now to record certain further facts.

PEDIGREE TABLE I (HYP L)

To ILLUSTRATE THE CONTINUED BREEDING OF First-CousIN X First-CousIN

— SINGLE COUSINS

ae poe Ney

. > 2

ee ae =

oe ee ee ee

A <

Ta P

i m

Generation number 1 2 3 4

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

ment Station No. 85.

2 AMER. Nat., Vol. XLVIII, 1913, pp. 577-614.

570

No. 585] SHORTER ARTICLES AND DISCUSSION 571

There are, of course, two possible sorts of first cousins, single

and double. In the first case one of the parents of any individual

is a brother (or sister) to the one of the parents of the other indi-

vidual in the mating. In the second case, both the parents

occupy this relation to the parents of the other individual in the

mating.

These two sorts of first cousinship are shown in Pedigree Tables

I and II.

PEDIGREE TABLE II (HYPOTHETICAL)

To ILLUSTRATE THE CONTINUED BREEDING OF First-CousIN X First-Cousin

— DOUBLE COUSINS

k oe

g |, ja

i oe

a tr

k G

i 1, f

; P

A, < i jo

g |

m ee

+ ala

ta 4 r

i | tp

J U

Ae {p

n {4

Generation number 1 2 3 | 4 5

The values of the coefficients of inbreeding for continued single

and double cousin mating are shown in Table I.

It will be seen that Pedigree Table I and the third column of

Table I are different from the corresponding values given on

pages 591 and 592 of the earlier paper. The present values

should be substituted for the earlier ones, which were based upon

572

THE AMERICAN NATURALIST

[ Vou. XLIX

the erroneous assumption that half the double-cousin values

would give single-cousin values.

TABLE I

VALUES OF THE SUCCESSIVE COEFFICIENTS OF INBREEDING IN THE CASE OF

CONTINUED COUSIN MATING

Coefficient of Ancestral Generation Coefficient fo for Single | Coefficient for Double

Inbreeding Included Pins usins — _ Cou usins

Zo 3 0 o

Z, 2 0 0

Ze 3 25.00 50.00

Z; 4 50.00 5.00

Z, 5 68.75 87.50

Z; 6 81.25 93.75

Ze T 89.06 96.98

Z, 8 93.75 98.44

Zs 9 96.48 99.22

Zo 10 98.05 99.61

Zio 11 98.93 99.80

VE 12 99.41 99.90

Zy> | 13 99.68 99.95

Zis 14 99.83 99.98

Ziu 15 99.91 99.99

Zis 16 99.95 99.994

00 — ee

se as ee eatin

Dg oe

0 A Ka re y

Ere 7

ys Pa

9 Y ` Sa

K % t

Š oo | S

N / f ri

Ñ 3

T ig)

Sy 4

v i Í

/ r

p? /

20 + l É

/ i

‘WV

4 E 2 70 7 74

GENERATIONS

Curves of inbreeding, showing (a) the limiting case of continued

Fic. 1.

brother x sister breeding, fodder the successive coefficients of hoj have the

aximum values; (b) c ued p ing ma cng fe) continued first-

pei first-cousin aces pane the cousinship a double (C2 x C?), ang a con-

tinued first-cousin x first-cousin m e the cou ate is single (Ctx Ct’).

The continued mating of Se pam Sdan re same curve a

No.585] SHORTER ARTICLES AND DISCUSSION 573

The data of Table I are given graphically in Fig. 1, together

with the curve for brother X sister and parent X offspring.

From the table and figure it is seen that with continued in-

breeding according to any one of these four types the coefficient

approaches the value 100. The rate of approach is different,

however, in the different cases. The curves fall into two pairs.

The brother X sister and the double cousin curves are precisely

alike so far as concerns their curvature or shape at any given

point. Similarly, the parent X offspring and single cousin curves

are of the same shape. The essential point of difference is that

the cousin curves lag a generation behind the others.

Let us now consider the question of the degree of inbreeding

following continued matings of the avuncular type of relation-

ship. Pedigree Table III gives a pedigree in which each mating

is of uncle X niece.

PEDIGREE TABLE III (HYPOTHETICAL)

To ILLUSTRATE THE MATING OF UNCLE X NIECE

| | fu

| m is

poco

c A

h | n

i k

t 5 je

d í i?

j |

>. 4 4 1s

; í ts

h i

: s

: i +.

b 4 r

pa fe

te | {

f i (i

l d

Generation number 1 2 a4

574 THE AMERICAN NATURALIST [Vot XLIX

From this table it appears that the values of the coefficients of

inbreeding will be exactly the same for this type of mating as in

the case of single cousin mating. Or, in other words, Z’s form

the following series.

TABLE II

VALUES OF COEFFICIENTS OF INBREEDING FOR CONTINUED

X NIECE MATING

Coefficient Number of Ancestral Generations Value of Coefficient

Zo 1 0

Z, 2 0

Z, 3 25.00

Ze 4 50.00

7A 5 68.75

B 6 81.25

ete. ete. etc. as in Table I

From the data presented in this and former papers it is clear

that inbreeding continued for about ten generations, quite re-

gardless of the type of mating, provided only it be continuously

followed, leads to within one or two per cent. of complete ‘‘con-

centration of blood.’’ The bearing of this result upon the general

question of the degree of inbreeding which exists in the ancestry

of our domestic animals to-day is obvious. To consider but a

single case: In 1789° a law was passed prohibiting the importa-

tion of cattle into the Island of Jersey. Hence it follows that all

pure-bred Jersey cattle of the present time must be of the

descendants of the relatively few animals on the Island in 1790.

Taking three years as about the average generation interval in

eattle, this means about forty generations since the Island was

closed to importation. The concentration of lines of descent

which must have occurred in this time merely by the dropping of

lines and quite regardless of the type of mating is obvious. This

is not the place to go in detail into the discussion of inbreeding in

Jerseys, especially as I hope shortly to publish the results of an

extensive study of this matter, but it seems desirable to emphasize .

the bearing of such hypothetical pedigrees for particular types

of mating as are given in this and earlier papers, on the general

problem of inbreeding.

It is possible to extend now somewhat the table of general

equations given by Jennings‘ for coefficients of inbreeding after

8 Teste Rees’s odo Sagas and H. S. Redfield, Natl. Stockman and

Farmer, December 15, 1892.

4 Amer. NAT., Vol. XLIII, p. 695, 1914.

No. 585] SHORTER ARTICLES AND DISCUSSION 575

m generations of each particular type of mating. We have the

following values, where n denotes the number of ancestral gen-

erations concerned, or, as Jennings puts it, the number of suc-

cessive inbreedings which have taken place.

Type of Mating Coefficient of Inbreeding

2n — 1

E aT an a O E O a eee on

2n — 2

BrOK Or OC MSLOY eLan a i ees ek

Ən

Gow i z 2n — 2n

omn X COUMM, MINIS cii: ccc s wee e neces’ SE TEF

x i Qn — 22 (from n==2

Cousin X cousin, GOW oe ec es eae E ek ln a i nao

r on — Nn — I

Parent X offspring ........... Serre re on

Vacio x Pow o no an on es

RAYMOND PEARL .

AN ATTEMPT TO PRODUCE MUTATIONS THROUGH

HYBRIDIZATION

THERE is no more interesting problem to the experimental

evolutionist than the one relating to the cause or causes of the

origin of mutations. Until we are able to solve this problem we

can only accept what the gods give in our breeding experiments.

When a mutation arises it is usually a simple process to produce

a pure stock. By mutation is meant any deviation from the

normal type which reappears in some of the descendants. In

the following experiment most of the abnormalities that were

found never reappeared in the offspring.

My experiments have been confined to the fruit fly, Drosophila

ampelophila, a species kept for years ‘‘under cultivation’’ at

Columbia University. This species has proved to be very plas-

tic, throwing off great numbers of mutant forms. At the sug-

gestion of Dr. T. H. Morgan I crossed some of these mutants

with wild stock of the same species from widely separated locali-

ties in order to test whether through hybridization mutations

arise in greater numbers than in inbred stock.

The idea that new forms arise from crossing more or less

closely related species is an old one. One finds many references

in Darwin’s works to this conception. For instance, in the

** Origin of Species °? Darwin says:

576 THE AMERICAN NATURALIST [ Von. XLIX

When mongrels and the more fertile hybrids are propagated for

several generations, an extreme amount of variability in the offspring

in both eases is notorious; but some few instances of both hybrids and

mongrels long retaining a uniform character could be given. The vari-

ability, however, in the successive generations of mongrels is, perhaps,

greater than in hybrids.

One of the causes of ordinary variability ... is ... that the repro-

ductive system from being eminently sensitive to changed conditions of

life, fails under these circumstances to perform its proper function of

producing offspring closely similar in all respects to the parent form.

From ‘‘ Plants and Animals under Domestication ’’ we find

the following.

Crossing, like any other change in the conditions of life, seems to be

an element, probably a potent one, in causing variability.

A variation to be effective in species formation must reappear

in some of the descendants. That a variation could, through

selection within a pure strain be increased or decreased in the

direction of selection to form a stable species has been seriously

questioned since Johannsen’s classic experiments. It is well

understood, on the other hand, how selection in a mixed popula-

tion could cause the variation to move in the direction of selec-

tion up to a certain point.

The first mutant stock selected for the experiment was cherry

club vermilion. The factors for these three characters are

linked together and are also linked with sex; the second stock

was black pink bent, which has the three factors independent of

each other and none is linked with sex. These factors are sup-

posed to lie in the second, third and fourth chromosomes, re-

spectively. The third stock was black purple vestigial are speck,

which has the five factors linked together. They lie in the sec-

ond chromosome. A stock from France was crossed to the mu-

tant stock several months after the other crosses were made, and

eosin tan vermilion was substituted for the cherry club ver-

milion, and pink kidney sooty rough for the black purple ves-

tigial are speck stock because flies of these particular stocks

were not to be had at the time desired.

These forms were chosen because it was thought that if muta-

tions do arise from hybrid forms there would be more probability

of their origin from a mutant varying in several characters when

crossed to wild than if it varied in only one character. Also by

, using stock containing several recessive characters a check could

No.585] SHORTER ARTICLES AND DISCUSSION 577

be placed upon any variant from the expected classes due to

contamination; for the variant, if arising from the cross, would

give some offspring in the F, generation with some of the reces-

sive characters. However, extreme care was taken to avoid con-

tamination and at no time was there reason to suspect it in any

of the cultures.

The wild stocks used were from Arkansas, California, Massa-

chusetts, Illinois, Minnesota, Ohio, Wyoming, Porto Rico, Cuba,

Australia and France. The totals of the F, generations are as

follows:

Ch. Cl. Ver. Bi. Pk: B: Bl. P. Vg. Are. Sp.

pe eee ave ts 1,162 307 198

California S20) Deri e od 859 715 332

iois <2. 5 eaaa serene 211 287

Massachusetts ..........». 1,078 681 1,013

PEO Ss oes vues Fags s 771 274

Me eo ee pres eer 506 1,612 370

Wyoming o oo). PEERS Hes 925 150

Porka Aeteo sons ei a 151 207

CRBS se sean aon es Gena 819

PTE o ety « s 469 401 548

PPBNCG oe ce tes 814 ‘951 826

OO eas cee 6,946 “5,298 4,393

This gives a grand total of 16,637 flies. It should be noted

that these flies were examined with the greatest care under a

binocular microscope. Each fly was turned over separately and

every part carefully examined.

From the cherry club vermilion crosses the following ab-

normal forms were found; three gynandromorphs; twenty-four

flies with more or less beaded wings; two flies with three cross

veins on the wings; one truncate; and two flies with abnormal

abdomen.

The abnormal forms from the crosses with black purple ves-

tigial are speck were, sixty-three with more or less beaded wings;

one truncate; one abnormal abdomen; one fly with five legs; and

four flies with a projection from the posterior cross vein toward

the base of the wing.

From the black pink bent crosses were found two beaded; one

abnormal abdomen; three truncate; and one called furrowed be-

cause of the furrows in the eyes due to the foreshortening of

the head.

This gives a total of 109 abnormal forms or one abnormal in

578 THE AMERICAN NATURALIST [ Von. XLIX

every 152 flies. But 89 of these abnormals were flies with beaded

wings. This character is very variable; some of the flies had

only a few bristles missing from the margin of the wings, while

others had both the outer and inner margins of the wings ser-

rated. The character has been recurring in the stock so fre-

quently that it can scarcely be ascribed to outcrossing. Many of

these flies were mated, but they either did not leave offspring,

or the character did not reappear in the F, generation.

The three gynandromorphs are not to be considered as mu-

tants. The data here show that gynandromorphs occur once in

about five thousand five hundred times.

Flies with truncate wings are of occasional occurrence in the

laboratory stock, as are also those with abnormal abdomen; hence,

flies with these characters are not to be considered as due neces-

sarily to the outcrossing. The truncate would not breed and the

abnormal abdomen character did not reappear in the F, genera-

tion. If a character does not reappear in the F, generation it is

considered to be of somatic and not of germinal origin, unless

an environmental condition is necessary for the expression of

the changed character. -

The abnormality of the fly with five legs may have been the

result of accident, for the character did not reappear in the F,

generation.

Three characters were found to be inherited; the one called

‘‘furrowed,’’ which arose from the cross of black pink bent with

wild stock from Massachusetts; the one with a projection from

the posterior cross vein toward the base of the wing, called

‘* tau,’’ which arose from the cross of black purple vestigial are

speck with wild stock from Illinois; but since this stock had

just been received from Illinois, and since the character appeared

in four of the flies, it is suspected that the character was reces-

sive in the wild stock and not due solely to the cross. Also from

cherry club vermilion crossed to stock from Arkansas arose two

males with three cross veins on the wings and a disturbance of

the ommatidia of the eye. This character is called ‘‘ warty.’’

Pure stocks of flies with these characters have been bred for

many generations and each continues to breed true. ‘‘ Warty ”

has many other characters than the modification of the eyes,

e. g., beaded wing, spread wing, from two to five cross veins

on the wings, abnormal abdomen and disarranged hairs on

the thorax. The females are sterile and the race is maintained

No. 585] SHORTER ARTICLES AND DISCUSSION 579

by crossing the males to their heterozygous sisters. The char-

acter is not sex linked; it decreases the viability of the flies, but

more than this can not be said at present. Work is being con-

tinued on this character and on flies with the character ‘‘tau.”’

‘‘Furrowed’’ is characterized by having the head foreshort-

ened, which causes indentations or furrows in the eyes; also the

spines on the scutellum are stumpy. The last character is of

importance in determining some of the flies, as a female will

sometimes occur without any disturbance of the eyes.

This character arose in a male which was crossed to a wild

female. The F, generation gave normal females and half the

males were normal and half were furrowed. This established

the fact that the character followed the distribution of the sex

chromosome. The position of the gene in the chromosome was

next determined according to the theory that the genes in any

chromosome are arranged in a linear series.1_ Crosses were made

with eosin miniature, sable forked, and with vermilion barred.

Because of the low fertility of the furrowed females the cross

was always made with the furrowed males. Consequently, the

males alone are considered in the counts given below.

EosIN MINIATURE? By FURROWED ĝ

MOPE sS u aides ck why S POONA it a. esas 67

Eosin miniature furrowed. 1 Eosin miniature ........... 75

F, males.. : ps

Wom Tone sue. io SMA oe ek es 31

Miniature furrowed ..... 0 Eosin long furrowed ....... 28

In the first column are the cross-over classes between mini-

ature and furrowed and the per cent. of these to the whole

number is 3.4. Then the gene which determines the character

‘‘furrowed’’ is supposed to lie 3.4 points beyond miniature, or

at 39.6.

SABLE FORKED 9 BY FURROWED ¢

Furrowed sable forked... 1 Sable forked ...........:.. 61

F Í MOP eekan o TO o tein clea shes 105

2 males.. Worked N E a 3 Furrowed forked ........... 1

pisa Ma sieves O Gable (oo a et 16

In the first column are the cross-over classes between furrowed

and sable and these are 5.7 per cent. of the entire number.

Then furrowed lies at a point 5.7 to the left of sable, or at 37.3.

1 Sturtevant, Jour, Ex. Zool., 713.

580 THE AMERICAN NATURALIST [ Vou. XLIX

VERMILION BARRED 9 BY FURROWED ¢

f PET ee eek ee 6 Vermilion Bar. oer GG 86

Vermilion furrowed ..... Do Worrowed siok ae 102

F, males.. Mom i aa 0O Furrowed bar.. asina na 15

Vermilion furrowed bar... 0. Vermilion ................+ 28

The cross-over classes between vermilion and furrowed are

the bar and vermilion furrowed classes of which there are nine,

which is 3.75 per cent. of the entire number. Vermilion is at

33, hence the gene for furrowed lies at 36.75.

The cross-over classes between furrowed and bar are the fur-

rowed bar and the vermilion classes of which there are 43 which

is 18 per cent. Then furrowed lies/18 points to the left of bar

or at 39.

The discrepancy in these results is due to the low viability of

the furrowed flies, yet the results agree fairly well, varying from

36.75 to 39, giving an average of 38.1, which is considered as the

relative position of the gene for furrowed in the sex chromosome.

` H Br

The accompanying diagram will aid in understanding the

cross-over classes. The heavy straight lines represent the paired

sex chromosomes which a heterozygous female has received from

her parents. The upper one, which carries vermilion bar, was

received from the female parent and the lower, carrying fur-

rowed, was received from the male parent. Each of the sons

of this heterozygous female receives one of these chromosomes

which determines what it shall be with reference to these special

characters. In about 75 per cent. of the cases the sons receive

ese chromosomes without any interchange of substance be-

tween the two as is shown by the two straight lines which rep-

resent the non-cross-over classes. When there is an interchange

No. 585] SHORTER ARTICLES AND DISCUSSION 581

of material between the two chromosomes as indicated by the

crossed lines, then males arise with a different arrangement of

the characters from that which had appeared in the grand-

parents.

In the diagram v, f and Br stand for vermilion eye, furrowed

eye, and bar eye, respectively; while V, F and br stand for

the normal allelomorphs of these characters, i. e, red eye, not

furrowed and not bar. Reading from the left the top dotted

line includes v, F and br, but since F and br are normal the flies

will differ from normal forms in the one character alone, viz.,

vermilion. The dotted line below includes V, f and Br, hence

the males receiving this chromosome are furrowed bar. Re-

ferring to the table showing the cross between a vermilion bar

female with a furrowed male we see that there were 28 vermilion

and 15 furrowed bar flies. Reading from the left again and

omitting the normal allelomorphs, the upper dash line includes

vermilion and furrowed and the lower dash line includes bar

alone. The table shows that there were only three vermilion

furrowed and six bar males, hence the interchange of material

between vermilion and furrowed took place less frequently

than it did between furrowed and bar. Since the per cent.

of crossing over between any two genes is taken as the index of

the relative distance between those genes, then furrowed lies

much closer to vermilion than it does to bar.

The fine lines represent double crossing over, of which no

representatives were found in this cross.

SUMMARY AND CONCLUSIONS

Crosses were made with mutant stocks of Drosophila with

wild stock from many localities in the United States, from the

West Indies, France and Australia in order to discover, if pos-

sible, if hybridization is an essential factor in the formation of

mutant races. From 16,637 flies of the F, generation seven

flies arose which varied from the normal type and which bred

true. If we discard the four with the character ‘‘tau’’ for

reasons given above, then the result is narrowed to three flies

with two characters. This gives one mutant to every 5,545 flies.

Therefore, a mutation has occurred so seldom that we can

scarcely attribute hybridization as its cause. It is highly prob-

able that if the same number of wild flies had been reared under

582 THE AMERICAN NATURALIST [ Vor. XLIX

favorable conditions for the survival of any new forms that ap-

peared just as many mutations would have been found as in the

above experiment. In the light of these results we can attribute

the origin of mutations only to chance, since hybridization as a

causal agent does not occupy a privileged position relative to

the effect.

F. N. DUNCAN

COLUMBIA UNIVERSITY

wt i

LINKAGE AND SEMI-STERILITY

Tue Florida velvet bean (Stizolobium deeringianum) has nor-

mal pollen and embryo-sacs; it flowers (when sown in May)

early in September; and has pigmented (mottled) seed-coats.

The Yokohama bean (Stizolobium hassjoo) has also normal pol-

len and embryo-saes; it flowers in July; and has its seed-coats

unpigmented. The first-generation hybrids of Florida by Yoko-

hama had half their pollen and embryo-saes aborted (1, 2);

flowered at the end of August; and had more or less pigmented

seed-coats. In the second generation, half of the plants had

normal pollen and embryo-sacs, and half showed semi-sterility

(1, 2). These plants flowered from July to September, the ma-

jority being late. About three-quarters had pigmented seed-

coats; and one-quarter, colorless seed-coats.

Most of the semi-sterile plants, and also most of the plants with

pigmented seed-coats, were late in flowering. The semi-sterile

plants, however, were not later than the fertile, in the second

generation of the Florida by China cross. Hence there is no

necessary connection between semi-sterility and lateness. A ran-

dom sample of five second-generation plants of the Florida by

Yokohama cross gave one family with pigmented seed-coats, one

family with colorless seed-coats, and three families segregating

into pigmented and colorless in about the ratio 3:1. Hence the

pigmentation of the seed-coat is not a mere physiological conse-

quence of lateness, but is determined by a definite factor. If K

is the factor from the Florida concerned with semi-sterility ; P,

a factor concerned with pigmentation of seed-coat; and H, the

main factor for lateness; then K and H are strongly coupled in

the gametes of the first-generation plants, as are also P and H.

K and P show secondary coupling.

No.585] SHORTER ARTICLES AND DISCUSSION 583

The data follow.

SEMI-STERILITY AND LATENESS

Second generation of Florida by Yokohama

eeds n early in May

(Classes are approximately fortnights)

oe ee eee M

Fertile plants .............0-+- uio n]? Bing | u

Semi-sterile plants ...... 6 10 11 29 10 | ie

The average of the semi-sterile is about a fortnight later than

that of the fertile. If we divide the plants into those flowering

before and after August 11, we have:

| First Month | Second kud Third Mouths

Fertile | 43 38

Semi-sterile .... | 16 59

A calculation, based on the hypothesis used for semi-sterility

(1), shows that the crossing-over (3) between K and H is prob-

ably less than 17 per cent.

SECOND GENERATION OF FLORIDA BY YOKOHAMA

Seeds sown early in June

ajej a| | e | tek

Fertile tilaisi’ 8 oe

Semi-sterile A TiS ae ee 88

The fertile plants are earlier than the semi-sterile; though the

average difference is less than in the early planting, because, as

usual, the first-early plants are more affected by late planting

than are the later plants. .

PIGMENTATION OF SEED-COAT, AND LATENESS

Second Generation of Florida by Yokohama

arly sowing

eros Le | 5 | 6 | Totals

Unpigmented seed-coats .. | 16 | m6 | ol b | rio

Pigmented seed-coats........ 4 | 22 | 25 tR DI m

Thus most plants with unpigmented seed-coats are early. A

calculation again shows that the amount of crossing-over is prob-

ably under 23 per cent.

584 THE AMERICAN NATURALIST [ Vou. XLIX

SECOND GENERATION OF FLORIDA BY YOKOHAMA

Late sowing

6 | Totals

Unpigmented seed-coats ............ | 8 | 20 | 12 |

$1 eae |

1 43

Pigmento saisir itirirdi iraa | 17 3 HS

This confirms the results from the early sowing.

PIGMENTATION OF SEED-COAT AND SEMI-STERILITY

The coupling between K and P is given from the following:

SECOND GENERATION OF FLORIDA BY YOKOHAMA

Pigmented | Totals

| Unpigmented

| meae

Site o | me 110 | 155

Bemisterile 2 arare 39 120 | 159

The excess of pigmented semi-sterile and of unpigmented fer-

tile testifies to a slight coupling, and calculation shows that there

is probably about 35 per cent. of crossing-over.

According to the hypothesis (1), fertile second-generation

plants should be mainly homozygous for H (or h) and P (or p);

while semi-sterile plants should be mainly heterozygous for these

factors. This is being further tested.

JOHN BELLING

FLORIDA AGRICULTURAL EXPERIMENT STATION

REFERENCES

1. Belling, J.

1914. The mode of inheritance of semi-sterility in certain hybrid

plants. Zeitschr. f. ind. Abst.- u. Verebungslehre 12; 303-

342.

2. Belling, J.

1915. Inheritance of partial sterility. Report of Fla. Agr. Exp. Sta.

for 19 Pp. 96-105.

3. Sturtevant, A. H. -

1915. The Behavior of the Chromosomes as Studied through Linkage.

Zeitschr. f. ind. Abst.- u. Vererbungslehre 13: 234-287.

VOL. XLIX, NO. 586" OCTOBER, 1915

Ham

. Shorter Articles and EEE » Anticipatory Mutationist. Dr. R.

THE

AMERICAN

NATURALIST

A MONTHLY JOURNAL

Devoted to the Advancement of .the Biological Sciences with

Special Reference to the Factors of Evolution

CONTENTS

Early Portrayals ofthe Opossum. Dr. CHARLES R. EASTMAN. - —- - 586

Seventeen Years Selection of a Character. Dr. RAYMOND PEARL - - -595

Specific and Varietal Characters in Annual Sunflowers. Professor T. D. A.

omen -=

The Inh Dl in Matthiol d Petunia. I. The Hypotheses

HowaRD B. FROST - -=

The Coal Measure Amphibia, and EE Dr. Roy L. MOODIE - 637

RUGGLES GATES ~ 645

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THE

AMERICAN NATURALIST

VoL. XLIX. October, 1915 No. 586

EARLY PORTRAYALS OF THE OPOSSUM

DR. CHARLES R. EASTMAN

AMERICAN MUSEUM OF NATURAL History

THE quaint animal figures found in olden time works

on natural history are interesting not only as bearing

upon the contemporary state of zoological science and the

art of book-making, but also because many of the illus-

trations belong to a regular sequence or lineage which can

be traced back, like the textual descriptions, to primitive

sources. To a certain extent this has already been done,

or at least indicated, in the work by John Ashton, entitled

‘‘ Curious Creatures of Zoology.”

A subject deserving of the attention of naturalists but

which appears to have been neglected, is an historical and

systematic investigation of animal figures introduced in

early American cartography. Thanks to the magnificent

facsimile reproductions of sixteenth century maps which

have been published during recent years in this country

and abroad, abundant materials for this purpose are now

easily accessible. As for the ‘‘relaciones’’ of early voy-

agers and travelers in the western world, very few of

these have been published with scientific commentaries,

and among the really important seventeenth century writ-

ers on Central and South American natural history, only

the works of Hernandez (1628) and Maregrav' (1648)

have been systematically annotated. The first letter

1See the commentaries on these authors by Lichtenstein and Martius,

1827 and 1853, in the publications of the Berlin and Bavarian Academies

of Science.

£85

586 THE AMERICAN NATURALIST [Vou. XLIX

written from the newly discovered world, by Dr. Chanca,

companion of Columbus, was not adequately edited and

annotated until after four centuries had passed. Ves-

pucci’s letters also are deserving of mention in this con-

nection.”

In view of the fact that several communications have

appeared in Nature during the past year concerning the

first mention of the opossum in literature, it may not be

inopportune to trace the pedigree of some of the early

illustrations of this animal, both in maps and in printed

works. At the same time a few of the older printed de-

scriptions of American marsupials may be noticed. And

we will observe first of all that the earliest reference to

the common American opossum is found in the famous

collection of voyages published in 1504 by Angelo Trivi-

giano, under the caption of ‘‘Libretto de Tutta la Naviga-

tione de Re de Spagna, de le Isole et Terreni Novamente

Trovati.” In Chapter XXX of that work it is mentioned

that a live specimen, taken by the Pinzons in Brazil in

1500, was exhibited in Granada.

In Decas II of Peter Martyr’s ‘‘De Nove Orbe,’’ pub-

lished in 1511, occurs the first published description of

the American tapir; and immediately following this the

opossum is referred to in these words:

There is also an animal which lives in the trees, feeds upon fruits,

and carries its young in a pouch in the belly; no writer as far as I know

has seen it, but I have already sufficiently described it in the Decade

which has already reached Your Holiness before your elevation, as it

was then stolen from me to be printed.

In 1547 and 1548, and again from 1549 to 1555, Hans

Stade of Homburg, Hesse, passed some time in Brazil,

and wrote or dictated an account of his strange adven-

tures, which was published at Marburg in 1557. Under

the caption of ‘‘Servoy,’’? Chapter XXXII, we read:

2 See Fernandez de Ybarra in Journ. Amer. Med. Assoc. for September,

1906, and in Mise. Coll. Smithson. Inst. for the same year. Vespucci’s first

letter (1497) was republished in facsimile by Varnhagen in 1893, having

for frontispiece a design by Stradanus dating from about 1580, in which

various South American animals are well represented. Mention occurs 1

this letter of the iguana, puma and ocelot from the coast of Tampico.

No. 586] EARLY PORTRAYALS OF THE OPOSSUM 587

There is also a kind of game, called servoy, which is as large as a

eat, and has a tail like a cat; its fur is gray, and sometimes grayish

black. And when it breeds, it bears five or six young. It has a slit in

the belly about half a span in length. Within the slit there is yet

Dic Fugnr Datt, Cop. vevi

Tiaka Cap. pvei.

S bat auch eyn art Wiless peyffet Gerwoy/ift (o grof

E wie cyn Fane/weifaraw vobarensauch (d eps sive

bat enen (hwang wiseyntass. Unnd wann es gtberet/

Fic, 1. The “ Dattu” (tatou or armadillo) and “ Servoy” (opossum); after

Hans Stade, 1557.

another skin; for its belly is not open, and within this slit are the teats.

Wherever it goes, it carries its young in the pocket between the two

skins. I have often helped to catch them and have taken the young

ones from out of the slit.

588 THE AMERICAN NATURALIST [Vor. XLIX

In the original edition of the work just quoted wood-

euts are given of both the opossum and armadillo (Dasy-

pus novemcinctus Linn.) and these are reproduced in the

present article (Fig. 1) from a copy belonging to the New

York Public Library. The armadillo is thus described in

Stade’s ‘‘ Wahrhaftig Historia’’:

There is another sort of animal found in

savages call dattu; it stands about six inches high and is nine inches

long; its body is covered all over, except underneath, with a kind of

armor. This covering is horn-like, and the plates overlap one another

like those of chain armor. This animal has a very long snout, and 1s

usually found on rocks. It feeds on ants. Its flesh is sweet and I have

often eaten of it.

Two works published at about the same time as the

narrative of Stade also contain mention of the opossum,

the name of ‘‘Simivulpa’”’ or Fox-ape and ‘“‘Su” being

this country which the

applied to the creature. In the Italian edition (1558)

of Sebastian Miinster’s ‘‘Cosmographia’’ occurs this

passage, accompanied by an illustration which we have

reproduced in Fig. 2:

No. 586] EARLY PORTRAYALS OF THE OPOSSUM 589

Trovasi in quel luogo [Brazil] un animal prodigioso, le cui parti

davanti si rassomigliano a volpe & quella di dietro à Simia mai suoi

piedi sono como di huomo, ha le orecchi di civetta, & sotto le ventre

como una borsa, nella quale tien nascosti suoi figliuoli, finche crescono

di sorte che possino caminare securamente da lor stesi, & procurarsi il

cibo senza tutela della madre, ne mai escono di quella borsa se non

quando lattano. Quest’ animale mostruosa con tre suoi figliuoli fu

portato in Sibilía & indi in Granatá.”—p.

Münster’s illustration of the PE is evidently

derived from figures of the opossum appearing in several

editions of Ptolemy’s ‘‘Geography’’ from 1522 onward,

ae: npud of tesa

Sop

Cangila

Fig. 3. Earliest known figure of the opossum; from the Waldseemüller world-

map of 1516.

and other early maps of South America, all traceable in

the first instance to Waldseemiiller’s world-map of 1516,

where the same representation occurs (Fig. 3). It is

there accompanied by essentially the same legend as one

finds in the ‘‘ Tabula Terre nove” of the 1522 Ptolemy,

and in later maps and atlases,’ such as Cornelius de

Jode’s (1585), and van Linschoten’s (1598).

3 Modern reproductions of South American maps showing these figures

may be seen in Winsor’s ‘‘ Narrative and Critical History of America,’’

and in the magnificent na published by the Brazilian government

under the direction of Baron de Rio Branca. The representation of a Bra-

zilian landscape in the Ca sae no map of 1500, shown in our Fig. 4, is from

a photograph of Harrisse’s colored reproduction.

THE AMERICAN NATURALIST [Vou. XLIX

Jae ee

Whos w er yp va v be

YW obs oP W2 :

Fic. 4. One of the earliest representations of an American landscape; from the

Cantino map of 1500

André Thevet, who sojourned for a short time in Brazil,

published his ‘‘Singularitez de la France Antarctique”’

in 1558. His description of the ‘‘Su,’’ in reality the

opossum, is paraphrased by Conrad Gesner, Edward

Topsell, J. E. Nieremberg and John Jonston under that

caption, and his grotesque caricature of the beast is re-

produced by these authors. It is also introduced in

sixteenth century cartography of the two Americas.

Blaeu, in his world-map of 1605, places the ‘‘Su’’ and

its descriptive legend in the region of Nova Francia;*

and in the La Plata region of the same map occurs still

another figure of the opossum, based upon the century-old

drawing which appears in the Waldseemiiller world-map.

Our Fig. 5 is taken from Thevet, and Fig. 6 from Nierem-

berg, whose ‘‘ Historia Nature’’ was published in 1635.

In Wolfe’s English edition of van Linschoten’s ‘‘ Voy-

ages,” figures of the sloth and ‘‘Simivulpa”’ are intro-

4See the new facsimile edition (1914) published = Dr. E. L. Stevenson

under the auspices of the Hispanic Society of Amer

No. 586] EARLY PORTRAYALS OF THE OPOSSUM 591

Fic. 5. The “Su” (common opossum) ; after André Thevet, 1555.

RN Wess y

SI BS N\ WSS

Fig. 6. The “ Flaquatzin” (wooly opossum); from Topsell, after Nieremberg,

1635.

duced in the Brazilian and Argentine region of the map

of the South American continent, and at page 232 of this

work occurs the following description of one of these

asts:

592 THE AMERICAN NATURALIST [Vou XLIX

There is likewise another wonderful and strange beast of Gesnerus

called a Foxe ape, on the belly whereof Nature hath formed an other

belly, wherein when it goeth into any place, it hideth her young ones,

and so beareth them about with her. This beast hath a body and mem-

bers like a foxe, feete like mens hands, or like sea cattes feete, eares

like a batte. It is never seene that this beast letteth her young ones

come forth but when they sucke, or ease themselves, but are alwayes

therein, until they can gette-their own meate.

Passing now to the seventeenth century writers, we find

this account of Didelphis in Raphe Hamor’s ‘‘True Dis-

course of the Present Estate of Virginia’’ (London,

1615):

For true it is, that the Land is stored with plenty and variety of wild

beastes, Lions, Bears, Deere of all sorts. . . . Beavers, Otters, Foxes,

Racounes, almost as big as a Fox, as good meat as a lamb, Hares,

wild Cats, Muske rats, Squirrels flying, and other of three or foure

sorts, Apossumes, of the bignesse and likenesse of a Pigge, of a moneth

ould, a beast of as strange as incredible nature; she hath commonly

seauen young ones, sometimes more and sometimes lesse, which she

taketh vp into her belly, and putteth forth againe without hurt to her

selfe or them.

Of each of these beasts, the Lion excepted, my selfe have many

times eaten, and can testifie that they are not only tastefull, but also

wholesome and nourishing foode.

oF >?

Fic. 7. The opossum and young; after César de Rochefort, 1658.

About the same time Captain John Smith wrote the fol-

lowing brief characterization of the opossum, in his ‘‘De-

scription of Virginia” (1612):

An opossum hath a head like a Swine, and a taile like a Rat, and is

of the bignesse of a Cat. Under her belly she hath a bag, wherein she

lodgeth, carrieth, and suckleth her young.

After Nieremberg, a Jesuit professor at Madrid, whose

work on natural history (1635) is chiefly a compilation,

we come to George Marcgrav and Wilhelm Piso; and

No. 586] EARLY PORTRAYALS OF THE OPOSSUM 593

their contributions on Brazilian natural history, pub-

lished in 1648, are recognized as highly meritorious.

Ulysses Aldrovandi’s large posthumous folio on Quad-

rupeds (1637, p. 103) also contains a figure of the opos-

sum (otherwise interpreted, however) which is clearly

traceable to the early carto-

graphic designs. But it is unnec-

essary to pursue the subject fur-

ther, except to state that Fig. 7 is

copied after Charles César de

Rochefort’s engraving of an opos-

sum (‘‘ Histoire des Îles Antilles,”’

1658), and Fig. 8 shows the same

animal, acording to Eduard Sel-

er’s interpretation, as depicted in

one of the Maya Codices (Nuttall,

71). j Fic. 8. Maya representa-

Among other mammalian fig- tion of the opossum (?) From

ures in pre-Columbian Maya and Gwe

Mexican colored drawings® that

have been preserved are several that represent a spotted

dog, probably one of the varieties of ‘‘ Aleos’’ mentioned

by Hernandez. The occurrence of an indigenous spotted

dog in Central America is of interest in view of the fact

that a similar race is depicted in ancient Egyptian, As-

syrian and Pelasgian animal effigies and paintings, some

of the figures dating as far back as about 3000 s.c.

The oldest known representations of the hunting dog

of the ancient Egyptians, together with a number of

large African mammals, are inscribed in a palette dis-

covered a few years ago at Hierakonpolis.

| Fr

a UO

TE n e

5See Edward Seler, ‘‘Die Tierbilder der EE und Maya

Broin >’? Zeitschr. f. Ethnol., Jhrg. 41, 1909. A. M. Tozzer and

. Allen, ‘‘ Animal Figures in the Maya Codices,’’ papers of Peabody

Mosii iā; Ethnol., Vol. 4, No. 3, 1910. References to the literature

on ancient Egyptian and Assyrian animal effigies will be found in Amer.

Journ. Philol., Vol. XXX, 1909, pp. 322-331. The early history of the

rhinoceros is triood by B. Laufer in Publication 179 of the Field Museum,

and medieval ideas of the elephant are portrayed by E. D. Cuming in a

recent number of Field (April 3, 1915).

594 THE AMERICAN NATURALIST [Vor. XLIX

Concerning the several varieties of ancient Inca or

Ancon dog that are known from well-preserved Peruvian

mummies, Nehring® is of the opinion that their remote

ancestry is traceable to the North American wolf (Lupus

occidentalis var. mexicanus and rufus). The great an-

tiquity of domesticated dogs in South America is indi-

cated also by a canine skull which R. Lydekker has de-

scribed from the superficial deposits of Buenos Aires.

This dog, according to Dr. Lydekker,” ‘‘though appar-

ently contemporaneous with many of the wonderful ex-

tinct mammals of the Pampas, yet shows unmistakable

signs of affinity with domesticated breeds, although the

precise relationship has not been established.”’

Reference having already been made to animal figures

in early American cartography, we may call attention in

closing this sketch to a memoir by Anibal Cardoso in the

Anales of the Buenos Aires Museum for 1912 (Vol. XV),

on the origin of Argentine horses. The writer endeav-

ors to show from historical evidence that large numbers

of horses existed in the interior of the country prior to

the Spanish Conquest, and a figure of one of these ani-

mals drawn by Sebastian Cabot in his world-map of 1544

is interpreted as indicating that wild herds were seen by

that navigator in 1531. A portion of Cabot’s map is re-

produced in Sefior Cardoso’s memoir (p. 379), and also

in one by J. T. Medina on the voyage of Sebastian Cabot.

Nevertheless the conclusion appears unavoidable that,

had the horse actually persisted in the western hemisphere

down to the time of the advent of Europeans, some traces

of it would certainly appear in the culture of the primitive

inhabitants.

6 Sitzungsber. ges Naturf. Freunde, Berlin, 1884.

TR. Lydekker, ‘‘ Mostly Mammals,’’ London, 1903, p. 204.

8‘‘ Antigüedad del Caballo en el Plata.’’ On the horse in post-con-

quistorial times in North America see Clark Wissler, ‘‘ The Influence of the

Horse in the Development of Plains Culture,’’ in Amer, Anthropol., Vol.

XVI, 1914.,

SEVENTEEN YEARS SELECTION OF A CHAR-

ACTER SHOWING SEX-LINKED MENDELIAN

INHERITANCE!

RAYMOND PEARL

In 1898 there was begun at the Maine Agricultural

Experiment Station an experiment in breeding Barred

Plymouth Rock fowls, having for its purpose the improve-

ment by selection of the character winter egg production.

This investigation has continued to the present time. A

résumé of the results to date, considered with reference

to their bearing upon the general biological problem of

selection, may be of some interest.

The experiment has fallen into three divisions or pe-

riods: viz., (1) the period from 1898 to 1907, (2) the

period from 1908 to 1912, and finally (3) the period from

1912 to date. Detailed reports on the methods of breed-

ing in operation have been published elsewhere? For

purposes of clear orientation in the present discussion it

will be well here briefly to review the facts as to the

methods of breeding used in each of the periods. With

these facts definitely in mind we may then proceed to an

examination of the results.

1. The Period from 1898 to 1907.—During this period

the breeding followed the plan outlined at the beginning

by Woods and Gowell. Essentially it consisted of the

following elements.

1. Trap-nest record of the performance of each indi-

vidual female.

2. Selection as breeders of all females which laid more

than a definite number of eggs (150) in the first

laying year.

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

periment Station, No. 87.

2 Cf. particularly Woods, C. D., and Gowell, G. M., U. S. Dept. Agr.

Bur. Anim. Ind. Bulletin 90, 1906, pp. 42; Pearl, R., and Surface, F. M.,

Ibid. Bulletin 110, Part I, 1909, pp. 80; Pearl, Me. Agr. Expt. Stat. Ann,

Rept., 1911, pp. 113-176; and Pearl, Jour. Exp. Zool., Vol. 13, 1912, pp.

153-268.

595

596 THE AMERICAN NATURALIST (Von. XLIX

3. Selection as breeders of males whose dams had laid

more than another definite number of eggs (200).

4. The indiscriminate mass breeding, without individ-

ual pedigrees, of all individuals selected as de-

scribed under 2 and 3, and, in consequence,

5. No test of the progeny we particular matings with

respect to their laying ability.

This may be designated as the period of mass selection.

The following statement regarding the methods used

in this period was made by Woods and Gowell (loc. cit.,

p. 8):

The plans followed in this breeding work are based upon everyday,

practical common sense, and are the same as would be used in building

up a high-producing strain of dairy animals. Individual records of

performance are kept. The large producers are mated with sons of

large producers in the hope of obtaining a race of improved layers. In

the first year’s work three birds laid over 200 eggs each, and this fact

led to the adoption of that number of eggs as the minimum perform-

ance for a “registered” bird. Other than this there was no reason for

selecting 200 as the number of eggs necessary to entitle a bird to regis-

tration. Any other number, as 190 or 210, might have been taken with

equal propriety, just as horsemen might have selected some other time

than 2.30 by which to determine a standard horse.

2. The Period from 1908 to 1912.—For reasons which

have been fully set forth elsewhere? it was decided not to

continue the breeding along the same plan after 1907.

he new plant, put into operation first in the breeding

season of 1908, was calculated primarily to furnish defi-

nite information regarding the mode of inheritance of the

character winter egg production. It involved essentially

the following items:

1. Trap-nest record of the performance of each indi-

vidual female.

2. The selection of both males and females was made

on a double basis, including in addition to the

individual’s own performance as in the earlier

plan, also the idea of progeny performance. In

practice this worked out for hens in the following

way: Plans were made to see whether there could

3 Pearl and Surface, loc. cit.

No. 586] SELECTION OF A CHARACTER 597

be formed by selection and propagated three dis-

tinct strains of winter egg producers, namely, high,

mediocre and low. This involved, on the individ-

ual performance side, the separate selection in the

first years of three classes of females as breeders:

(a) good winter producers, with records before

March 1 of above 30 eggs; (b) mediocre winter

producers, with records below 30 eggs; and (c)

poor winter producers, which laid no eggs before

March 1. The division at 30 eggs was, after the

first year, merely a nominal one in the selection of

high producers. Actually only birds were used

in the a class whose records materially exceeded

30 eggs, running up to over 100 eggs in some

cases. :

The progeny performance idea was carried out in

two ways in the breeding. In the first place, no

female was selected for the high winter produc-

tion breeding pens, for example, unless, in addi-

tion to her own high winter record, all her sisters

and her dam were high producers. In the second

place, of all females fulfilling the above qualifica-

tion only those were bred a second time whose

progeny from the first year’s mating had proven

to be all high producers. Similar types of selec-

tion were followed by the mediocre and low lines,

except that segregating families were put in the

mediocre class.

3. The selection of males was along essentially the

same lines, with only such difference as is in-

volved in the fact that the male makes no per-

formance record himself. Males were put into

the breeding pen the first time on the basis of the

records of their dams, on the one hand, and of

their sisters, on the other hand. Those whose

progeny proved that they were transmitting the

character to which selection was being made were

used a second or even third time as breeders.

4. Complete individual pedigrees, whereby each off-

598 THE AMERICAN NATURALIST (Vón XLIX

spring individual’s parentage, both male and fe-

male, was known.

d. The records of production of the progeny of each

mating separàtely recorded and studied as a unit.

It will be noted that there are but two essential differ-

ences between the plan in this period and that followed

in the earlier one. These are: first and most important,

that in this second period the principle of progeny testing

was introduced into the scheme of breeding. The second

difference was that selection was carried on for low pro-

duction as well as for high, which had not been previously

done. A third difference is apparently found in the fact

that in this second period of selection the winter record

rather than the yearly record is made the basis of selec-

tion. This is in no way an essential difference. The

reasons for adopting the winter period have been set

forth in detail elsewheret and need not be repeated. It

suffices to say here that essentially the same results and

conclusions will be reached if one uses winter production

or annual production.

As a result of the studies made in this period on the

plan of breeding outlined the mode of inheritance of the

character winter production was definitely determined,

and has been confirmed by subsequent work.’ The char-

acter was shown to be Mendelian in its genetic behavior,

depending upon two factors, one of which is sex-linked.

3. The Period from 1912 to Date—The only difference

in the mode of breeding the stock of Barred Plymouth

Rocks in this period, as compared with the preceding one,

is found in the fact that during this last period all selec-

tions for low and mediocre production have been dropped.

The breeding for high production alone continues, with

only such differences in the details of manipulation of

the breeding stock as would naturally follow a definite

knowledge of the mode of inheritance of the character,

t Pearl, 1912, loc. cit., and Me. Agr. Exp. Stat. Ann. Rept., 1914, pp. 217-

ay Cf. also Wilson and Murphy, Jour. Dept. Agr. Ireland, Vol. XIV,

5 Pearl, 1912, loc. cit., also Amer. Nat., Vol. XLIX, 1915, pp. 306-317,

and Curtis and Pearl, Jour. Exp. Zoology, Vol. 19, 1915, pp. 45-59.

No. 586] SELECTION OF A CHARACTER 599

and of the gametic constitution of particular individuals

with reference to that character. As a matter of fact, all

low-producing lines were dropped at the end of the laying

year 1911-12. Certain of the mediocre lines were contin-

ued a year longer. In the laying flock of 1913-14 there

were no birds which had been bred for anything other

than high production, so far as the breeder’s deliberate

intention went.

The results of this seventeen year selection period are

set forth in Table I.

TABLE I

MEAN WINTER PRODUCTION PER BIRD OF THE BARRED PLYMOUTH Rock

FLOCKS FROM 1899 To 1915

Mean Winter Mean Winter

Mean Winter No. of Birds Production of Production of

Laying Year Production of |Making Winter| All Birds Se- All Birds Se-

All Birds Records lected for High | lected for cow

oduction Production

1899-1900 41.08 eggs 70 — ae

1900-1901 37.88 85 — —

1901-1902 45.293 “ 48 — —

1902-1903 26.01 = 147 — —

1903-1904 OO hb: ** 254 — —

1904-1905 35.04 “ 515 — —

1905-1906 40.65 ‘ 635 — —

1906-1907 yea * 653 — =

1907-1908 19.93 * 780 — —

1908-1909 26.69. “ 359 54.16 22.06

190 10 OLO rhe 247 47.57 25.05

1910-1911 30.49 ‘* 64 50.58 17.00

1911-1912 35.98: . ** 232 57.42 16.48

1912-1913 43.01 ** 182 52.61 —

1913-1914 52,2% *“ 192 52.20 —

1914-1915 45.89 ‘°° 179 45.89 '—

ToS rangs ;

eak 35.05 “ 4,842 51.49 20.14

The data of this table are shown graphically in Fig. 1.

From the table and diagrams the following results

appear:

1. The number of individuals involvedin this experiment,

on each one of which exact trap-nest records have been

kept, is large, amounting nearly to five thousand. This

number is large enough to lead to conclusions which are

trustworthy. It will be shown presently that wherever

it has been possible to compare the results on egg produc-

or)

THE AMERICAN NATURALIST [Vou. XLIX

™

> MEAN WINTER PRODUCTION

` N w A Q ®

S S S S S Ò

8 2

S /

X ers

g / k

& i —— — — a a cS

` an ARC A

ae “o

: ~X E

3 ` a

« y 8 Ha

a \

Š < :

i N

~ H

rnd á

X A 7

al re

Ñ /

ii °

& |

EN P

x| !

Fic. 1. — showing the course of mean winter egg Pearcy ate the

years 1899 and 1915. The solid lines and circles give the total flock m The

two straight aie. fitted by the method of least squares to the seas flock

ans, have ations = 5 — 2.1812, 17, 4 e

0 circles and broken (dash) line give the means of the lines selected for high

winter production betwe h 19 5. dotted line and

open cireles give the mean winter production of the lines selected for low produc-

tion between the years 1908 and 1912,

No. 586] SELECTION OF A CHARACTER 601

tion obtained in this experiment with independently de-

termined norms the general trustworthiness and normal-

ity of the present data have been demonstrated.

2. From the beginning of the experiment through the

laying year 1907-08 the general trend of mean produc-

tion was downward, with minor fluctuations from year to

year. In other words during the period in which the sys-

tem of breeding was mass selection for high production

without progeny test there was no change of the mean in

the direction of the selection. The fluctuations in mean

production during this period were, in the main, due prob-

ably to two sets of causes: (a) environmental differences

in different years acting at one point or another in the

life history of the birds; (b) random fluctuations in the

genetic constitution of the male birds used as breeders in

successive years, brought about because of the ignorance

of the breeder, in the absence of any individual progeny

testing plan, of the ability of any particular male to trans-

mit high fecundity to his daughters. The first of these

factors needs no special discussion and is relatively of

minor importance. The second will be dealt with in detail

farther on in the paper.

3. Since the laying year 1907—08 there has been a steady -

increase in mean winter production for the whole flock, ex-

cept for the years 1910-11 and 1914-15. Inthe former year

the decline in the mean is slight, and is probably due to

unfavorable environmental influences. In 1914-15 the

decline is certainly due to such causes. In the hatching

season of 1914 an inexperienced man was in charge of

the incubation and rearing. He had very poor success,

and the Barred Plymouth Rock pullets available for the

laying houses in the fall were relatively few in number,

of a relatively late average date of hatching, and poorly

grown. It is remarkable, not that the mean winter pro-

duction was lower in 1914-15 than in 1913-14, but rather

that it was so high as it was, taking all the circumstances

into account. It appears that the system of breeding

which made the selections on a progeny test basis was

immediately and, to date, continuously effective.

602 THE AMERICAN NATURALIST [Vou. XLIX

4. That selection on a progeny test basis was effective

is demonstrated not only by the general flock averages,

but also by the fact that it was possible to propagate sep-

arately high and low producing strains. The high pro-

ducing strains differed widely from the low producing in

mean winter production. Taking the average for seven

years in the case of the high, and four years in the case of

the low, it appears that the mean winter production of the

high producing strains was approximately two and a half

times that of the low producing strains. At the end of

the laying year 1911-12 the low producing lines were

dropped. In the next year (breeding season of 1913) no

birds were bred which were known to belong to segregat-

ing lines. Of course some were included which proved

afterwards to have been segregating, but this fact could

not, in any such case, have been told in advance from the

records in hand. The propagation of low producing

strains was attended with a great deal of practical diffi-

culty with the environmental conditions under which one

has to operate at this station. The growing season is

short. In order to grow properly a pullet for laying pur-

poses it is necessary that she be hatched after April 1 and

- before June 1 at the latest, and preferably before May 15.

If, however, one selects birds which produce no eggs what-

ever before March 1, and use up some valuable time be-

fore they get well started in the spring cycle of laying it

becomes perfectly clear that one is automatically pre-

vented from getting any considerable number of early

hatched chicks from such mothers. If late hatched chicks

are used the results obtained as to winter production

later will not be critical. These cireumstances make the

propagation of a low producing strain on a large scale

really a difficult proposition. There is of course no diffi-

culty in breeding birds which will not be winter layers.

One only needs to hatch in June, July or August. But

such birds will furnish no critical evidence regarding the

inheritance of winter production.

5. The mean winter production for whole flocks over

the entire period of the investigation is 35.05 eggs. In

No. 586] SELECTION OF A CHARACTER 603

the writer’s opinion, based upon rather extended expe-

rience in the study of egg records, approximately this fig-

ure may be taken as representing the general average

winter production of mixed flocks of Barred Plymouth

Rocks (or of American birds generally with the probable

exception of White Wyandottes), which have been hatched

at the proper time and well reared. As evidence on this

point the data presented in Table II have pertinent bear-

ing. These data give the mean winter production of birds

of the different American breeds obtained in the Fourth

Philadelphia North American International Egg-Laying

Competition, carried on at the Delaware Agricultural

Experiment Station in 1914-15. The conditions under

which these records are made are such as to safeguard

their essential accuracy. The figures here given are the

mean productions per bird up to the end of the eighteenth

and seventeenth week of the laying after November 1,

1914. Owing to the fact that the original records as pub-

lished are compiled by calendar weeks it its not possible

to give the exact production from November 1 to March

1. Eighteen weeks gives 5 days laying over this period,

and seventeen weeks gives 2 days under. Both sets of

means have therefore been tabled. It should be said that

the birds were kept in flocks of 5 birds each, thus tend-

ing to the most favorable condition for high individual

records.

TABLE II

MEAN WINTER PRODUCTION OF FOWLS OF THE AMERICAN BREEDS, CALCU-

LATED FROM RECORDS OF THE FOURTH INTERNATIONAL

AYING COMPETITION, 1914-15

Breed No. of Birds meee geadas Nov.1 Moa. a gg 1

Barred Plymouth Rocks caste 45 29.20 25.47

All Plymout y # rare o CONE N 80 32.39 28.39

All fja D TE E saaes! 55 48.20 44.00

IR 75 38.37 34.42

All peck ae Droóds.isscsrsse 210 38.67 34.63

From this table it is clear that the records presented in

Table I average about the same as those of the 210 birds

of the American breeds in the Delaware competition.

604 THE AMERICAN NATURALIST [Vow. XLIX

The Wyandottes alone give a distinctly higher mean,

and this the writer has also found to be true of Irish egg

records. The Barred Rocks in the competition this year

give a somewhat abnormally low winter mean. Irish

records® give a winter mean for 48 Barred Rocks, in flocks

of 6 each, of 36.54 eggs per bird which is more nearly

normal.

iit

Let us now turn to the question of the interpretation of

the data set forth in the preceding section. Broadly

speaking what the facts gleaned from this seventeen-year

experiment show is that mass selection for egg produc-

tion was not effective, while selection which was based

upon the performance of the progeny was extremely and

quickly effective. What is the explanation of the differ-

ence? The facts are purely objective realities, about

which dispute or question is idle. They are real and

obvious matters. Regarding the interpretation of such

facts as these there have been, and no doubt will continue

to be for some time to come, differences of opinion

amongst biologists. Under these circumstances, the

writer will, then, with all respect and consideration for

the differing opinions of others endeavor to make clear

the view of the meaning of these results which he has

come to hold.

In the first place we may definitely put aside any inter-

pretation which bases its explanation of the results on

environmental action. In an earlier paper the writer‘

has shown in detail the impossibility of this explanation

for the results during the period of mass selection (the

descending limb of the curve). The totality of the results

here presented make it still more apparent that such an

explanation can have no place here. We should have to

suppose that the environmental influences were adverse

throughout the period of mass selection, but suddenly

became favorable when the method of breeding was

changed, and have ameliorated at an ever increasing rate

6 Murphy, L., Jour. Dept. Agr. Ireland, Vol. XIV, pp. 8-30, 1913.

7 Pearl, R., Me. Agr. Expt. Stat. Ann. Rept., 1911, pp. 113-176.

No. 586] SELECTION OF A CHARACTER 605

as time has gone on. Nothing of the sort was, in fact,

the case. The only explanation which can satisfy the

case is one which is based upon or at least takes full

account of the changing genetic constitution of the flock.

It appears to the writer that the essential key-note to

the explanation of the results of this long experiment

is found in the fact that phenotypic variation of the char-

acter fecundity, in fowls, markedly transcends, in extent

and degree, genotypic variation. It is quite impossible

in the great majority of cases to determine with preci-

sion what is a hen’s genetic constitution with respect to

fecundity from an examination of her egg record alone.

In this case, as in so many others, but in an unusually

pronounced degree, where the phenotypic distributions

overlap, a sure diagnosis of genetic constitution can only

be made by means of the progeny test. Lacking this the

phenotypic performance becomes an always uncertain

and at times very misleading guide.

It can be shown that if, during the period of mass se-

lection, all the hens used as breeders had been, as they

were supposed in the theory of the originators of that

part of the experiment to be, either Type 1 or Type 2

females (fL L,- Fl, or fL,L,- Fi,L,) then the continued

mass selection must have resulted in improvement. The

only criterion of constitution which was used, however,

was the bird’s performance. But, taken by this criterion

alone, there would be constantly chosen a proportion of

birds whose genotype was for mediocre fecundity, but

which made a performance record (phenotypic) suffi-

ciently high to be selected. That this is what actually

happened is evident from the curve (Fig. 1), but the fact

was experimentally proved in 1909.8

Put in the fewest words, then, the reason why no effect

was produced during the first ten years of selection and

a marked effect was produced during the last seven, was,

in the writer’s opinion, because genotypically high pro-

ducers were uniformly selected (in the high lines) during

8 Pearl and Surface, Me. Agr. Expt. Stat. Ann. Rept., 1909, pp. 49-84,

606 THE AMERICAN NATURALIST [VoL. XLIX

the latter period, and were not uniformly selected in the

former. By the introduction of the progeny test as an

essential part of the selection the whole process of the

creation of a highly fecund race of hens was transferred

from the realm of blind chance to that of precise and defi-

nite control. And it becomes increasingly clear that

mass selection, on the basis of performance (phenotypic

appearance) alone, is in its essential nature a blind and

haphazard process, no matter with what precision and

stringency it is carried out, just so long as the correla-

tion between the gametic and somatic conditions of the

character selected is not perfect. And it is an outstand-

ing result of the Mendelian investigations of the last 15

years that the gamete-soma correlation is very rarely, if

ever, perfect.®

It appears on this view that selection for high egg pro-

duction in the fowl is effective when it is real. That is,

if one selects genetically high producers by means of the

trap-nest plus the progeny test, he succeeds very rapidly

in fixing a high producing strain. If on the other hand

he merely selects high layers by the trap-nest record

alone, he is not really selecting genetically high pro-

ducers except in a portion of the cases. Under these cir-

cumstances he makes no progress in building up a highly

fecund strain. To be effective in changing the average

productiveness of a flock of poultry selection must pick

out those birds as breeders which carry the factors for

high fecundity genetically, i. e., as an integral part of

their hereditary make-up, and not any other birds.

With the above interpretation of the results of seven-

teen years’ continuous selection of the character fecundity,

all the facts known to the writer are in complete accord.

No other interpretation of the results of this experiment

has yet been suggested which will meet all the facts.

® Complete citations on this point would make a tolerably full bibliog-

raphy of Mendelism. The methodological or the strictly quantitative aspects

of the problem have been but little dealt with. In this connection ef. W

F. R. Weldon, Biometrika, Vol. I, pp. 228-254, 1902, and R. Pearl, Biol.

Bulletin, Vol. XXI, pp. 339-366, 1911.

No. 586] SELECTION OF A CHARACTER 607

What bearing have these results upon the general prob-

lem of the effectiveness of selection in modifying ger-

minal determiners? Let us at the outstart endeavor to

be quite clear as to the problem. It has been shown in

what has preceded that in the long experiment a change

in the average condition of the population has occurred,

and has been coincident with selection. The writer has

no hesitation in saying that the increase in average pro-

ductiveness since 1908 has been caused by the particular

kind of selective breeding practised. Furthermore the

average productiveness at the present time transcends

any average known in the previous history of the stock.

Granting all this, however, as plain matter of fact, it

does not, in the writer’s opinion, afford one iota of evi-

dence that through the process of selection the hereditary

determiners of fecundity either have been or can be

changed. All that the selection has done, so far as we

have any evidence, is to change the constitution of the

population in respect of fecundity genotypes. There is

no evidence that the genotypes themselves have been

changed. On the contrary, everything indicates that they

have not been changed. During the last seventeen years

we have merely sorted out from a mixed population, by a

systematic method of breeding, those individuals which

were alike in one respect, and have sold all the rest to the

butcher. That one respect was that each individual bore

progeny which were high producers.’® Those individuals

chosen as breeders in 1908 and 1914 were precisely alike

in this particular There were more of them available

in proportion to the whole flock in 1914 than in 1908, but,

as individuals, I am unable to discern any particular in

which they were different in 1914 from what they were in

1908.

The general point here involved is essentially the same

as one with which we are more familiar in demographic

10T am, of course, referring to the high line selections only, merely for

the sake of verbal economy. The same reasoning mutatis mutandis applies

to the low lines.

608 THE AMERICAN NATURALIST [Vor. XLIX

statistics. The constitution of a population does not di-

rectly affect the individual. My expectation of life will

not be materially increased if I chance to move into a

community in which all the other inhabitants are of ad-

vanced age. To this everyone will agree. But the ex-

treme selectionist appears to believe that in some mys-

terious way the act of continued selection, which means

concretely only the transference of each selected individ-

ual from one cage or pen to another to breed, will in and

of itself change the germ-plasm, so that after the act it is

different from what it was before! It does not seem that

the evidence that such is in fact the case is critically valid.

A careful study of the very interesting and valuable work

of Castle and Phillipsi! with rats leaves the writer with

the feeling that those experiments prove no more than do

the experiments here reported: namely that the compo-

sition of a population may be altered by selection. It

does not appear to be proven that selection has essentially

altered the constitution of the germ-plasm of any partic-

ular individual as compared with the germ-plasm of that

individual’s ancestors, making due allowance of course

for the phenomenon of segregation. That selection can

alter the composition of a population with respect to

genetic determiners, by a process of sorting over what is

already there and rejecting some portion, no one can

doubt. But it still appears to the writer to be true that:

‘< It has never yet been demonstrated, so far as I know,

that the absolute somatic value of a particular hereditary

factor or determinant (i. e., its power to cause a quanti-

tatively definite degree of somatic development of a char-

acter) can be changed by selection on a somatic basis,

however long continued.’’!?

11 Castle, W. E., and Phillips, J. C., ‘‘Piebald Rats and Selection,’’

Carnegie Institution of Washington Publication No. 195, 1914.

12 R. Pearl, Jour. Exp. Zool., Vol. 13, p. 264, 1912.

SPECIFIC AND VARIETAL CHARACTERS IN AN-

NUAL SUNFLOWERS

PROFESSOR T. D. A. COCKERELL

UNIVERSITY OF COLORADO

THe group of Helianthus annuus, the typical, annual

sunflowers of North America, is not a large one. The

annual habit seems to have been acquired independently

by several different Helianthine stocks, so that H. bolan-

dert Gray, H. exilis Gray, H. floridanus Gray and H.

tephrodes Gray are to be excluded from the H. annuus

group. The subgenus Helianthus s.str., or Euhelianthus,

contains the following:

1. H. annuus Linn. Based on the large cultivated form

(H. macrocarpus D. C.), Dr. A. H. Church of Oxford has

investigated the history of this plant, and I take the

liberty of quoting from a letter he wrote on March 4,

1915:

The published accounts of the giant sunflower in Europe in the six-

teenth century are so precise that it is interesting to remark that this is

in fact the oldest mutation known, which is still with us, quite unaffected,

though still never quite a pure strain, owing to insect pollination. The

facts are quite simple. The first description of the plant, by Dodonzus

(1567), tells us it grew in the Botanic Garden at Madrid, 24 feet. At

the Padua Garden, indoors, in a viridarium or orangery, 40 feet! The

usual height was 20 ft. The first English specimens, grown in London

by Gerard, were 14 ft.; and 15 ft. is the local record here. The giant

form is known by earrying one head, and having no trace of axillary

buds, Liar cadushalle strain, as opposed to reverting branching indi-

viduals. . The next point is, where did it come from? From Peru,

say the lls: but all Spanish things from America came via Peru,

because this was the last port of call. Hence Mexico is regarded as the

home. On the other hand Ximenes, who lived in Mexico several years,

and Hernandez after him, call it the Chimalacak del Peru; “acak” I

find means a reed, and thus refers to the long tall single stem of the cul-

tivated crop. The inference is that the plant as we know it was evolved

by ages of selection in Peru, by guano fed cultivation, possibly long be-

fore Inca rule, the plant having been taken by all migrating tribes from

the Mexican district. . Regarded as a product of Peruvian agricul-

ture the sunflower is aas parallel with the maize. . . . It was the

oil crop of ancient America.

609

610 THE AMERICAN NATURALIST [Vou. XLIX

The true H. annuus appears to be quite unknown in

the wild state, but nevertheless the monocephalic char-

acter may have arisen among wild plants. Dr. Church

makes the following suggestion:

If the monocephalic form is the giant of cultivation derived from the

Prairie form, it should be possible to repeat the history, by growing

Prairie forms in quantity, and selecting the suitable mutations when they

appear under the stimulus of excess manure (guano for choice). My

idea has been that, knowing what to look for, it might be possible to get

somewhere near it in say 10 years; though the Indians possibly took

2,000. General structural evidence alone suffices to show that the mono-

cephalic strain is the response to selection for close cultivation (about

two plants per square yard). The solitary heads are required for simul-

taneous harvesting.

2. H. lenticularis Douglas. The prairie sunflower,

much branched, and normally with dark disce. It has

been regarded as the wild type of H. annuus, but Ryd-

berg treats it as a distinct species. In crosses with

typical annuus, the F, is intermediate, often with a

tendency to fasciation. If annuus and lenticularis are

considered specifically distinct, we have to face the diff-

culty that the former is known only in cultivation, and its

one ‘‘ specific’’ character, the monocephalous habit, is

not constant.! The color of the dise is not a reliable

distinction, since yellow disces occur in wild plants.

Possibly the variation shown by H. annuus may be ex-

plained by contamination with lenticularis, since some

strains, at least, are constant in their characters. At

present, however, it seems probable that no wild species

ever existed with typical H. annuus characters; the actual

facts would probably be best represented by considering

lenticularis the species, and annuus a cultivated variety

derived therefrom. Since, however, the latter was first

named, the species-aggregate will have to be called H.

annuus, and the nomenclatural outcome will be as fol-

lows:

1 Shull, Botanical — 45, 105, figures a much branched form which is

not the wild lenticularis

No. 586] ANNUAL SUNFLOWERS 611

Helianthus annuus L.

(a) lenticularis (Dougl.)

v (b) macrocarpus (D.C.) = annuus L., s. str.

At the same time, for ordinary purposes, it may be per-

missible to simply write H. lenticularis when referring to

the wild plant.

3. H. aridus Rydberg. Like H. lenticularis, but

leaves lanceolate or narrowly deltoid, minutely toothed

or entire. Montana to New Mexico. Nelson calls this

a synonym of H. petiolaris, which it certainly is not. It

must be called H. lenticularis aridus (Rydb.) or H.

annuus lenticularis var. aridus, since it is a variable

form of lenticularis, which may possibly be due to cross-

ing with H. petiolaris, the hybrid having crossed back

with lenticularis. From the mode of its occurrence it is

nearly certain that it is not a simple lenticularis X peti-

olaris hybrid, petiolaris being often absent from the

immediate vicinity.

To give an idea of the actual condition of affairs

where H. aridus occurs in Colorado, I present a synopsis

of the forms found at Longmont, August 30, 1914:

(4) H. aridus type; smaller and more ra hte cuneate bases to leaves.

(a) seas with yellow disc; two plan

Dis m. diameter, light a aia entirely dull light

“alow ; rays ordinary; foliage unusually pale; base of

rather broad-cuneate, marginal teeth feeble.

(b) Dise ae (col lobes dark reddish). Leaves with cuneate base

subentire margins; typical aridus. Involucral bracts

sti broad and bristly. ay rather slender plants

have small discs (17-21 mm. diam.) and very ample

rays, which are not very numerous (10-13); color of

rays rich orange yellow; stems lightly speckled with

purplish.

(i) Rays longer, about 38 mm. long and 15 broad.

(ii) Rays shorter, about 28 mm. long and 14 broad.

(This difference in size of rays is probably environmental.)

(B) H. neal type; bases of leaves truncate or cordate; plants usually

robust; dise dark.

(a) ii of aridus, being rather slender, with small (diam. 23.5

mm.) dise and long rays; but leaves broadly truncate at

base and rather strongly toothed, quite lenticularis style.

This is a very pretty form, with long rays (about 40

mm, long and 11 broad), more or less twisted at end, and

rather narrow. The rays number about 15.

612 THE AMERICAN NATURALIST [Vou. XLIX

(b) Aspect a o ; more or less robust, rays rather short and

(i) “ng comparatively short and broad (about 22 mm. long

and 1 oad on a small head), the middle third

= with its apical half variably light brown-

ish-red. Leaves thick, with broad petioles.

(ii) Rays normal.

(a) Upper leaves ovate, scarcely at all dentate, inequi-

lateral. Dise small (22 mm. diam.), rather paler

than usual, the corolla lobes showing less red.

Rays 14, about 31 mm. long and 11.5 broad.

(B) he sis ae broad at base, but somewhat cuneate,

ly dentate. Disc 20-23 mm. diameter.

i ra had (dise 20 mm.) with many (21) quite

short rays, about 17 mm. long and 7 broad.

(y) Typical lenticularis, with broad-based strongly den-

tate leaves. Disc 37 mm. diameter; rays 37 mm.

long, numerous (about 33).

It would of course be possible to maintain that H.

aridus was originally a distinct or isolated species, which

has now lost its purity by crossing with lenticularis. We

ean at least say this, that if annuus, lenticularis and

aridus, in their pure forms, inhabited three different

aiaga, few would hesitate to regard them as perfectly

‘good species.” Also, if they grow mixed for any

length of time, they are sure to suffer from ‘‘ vicinism ’’

to such an extent as to lose their supposed original dis-

tinctness. At present, however, we have no assurance

that H. aridus has ever constituted a distinct species, in

the sense of occupying any considerable area in its pure

form. On the other hand, it is manifestly not a ‘‘ fluctuat-

ing variation,’’ due to mere environmental conditions.

4. H. petiolaris Nuttall. Described by Nuttall in

1821, from ‘‘the sandy shores of the Arkansa,’’ and

recommended as ‘‘an ornamental annual of easy cul-

ture.” It extends from British America to the State of

Chihuahua. It differs from H. lenticularis by (a)

smaller stature, (b) leaves differently shaped, lanceolate

or broad-lanceolate, not dentate, more or less shiny above,

those of lenticularis being quite dull, (c) bracts of invo-

lucre lanceolate, with margin very short-ciliate. Stem

rough, with a little purplish color; basal third of rays

deeper orange than the rest.

No. 586] ANNUAL SUNFLOWERS 613

This is a good species in the ordinary sense; in Colo-

rado it is often found abundantly in the cafions of the

foothills, growing without admixture of other species.

Lower down, it frequently oceurs with lenticularis.

The variety patens (Lehm.) Rydb. is said to differ by

having the heads larger, long-peduncled, the peduncles

fleshy toward the top; leaves large, long-petioled. Nut-

tall described his original petiolaris as having the pedun-

cles ‘‘of great length,’’ and the petioles ‘‘of an ex-

traordinary length,’’? though the leaves were ‘‘rather

small.’? Probably patens is not far from the original

petiolaris. Gray considered patens a synonym. Ac-

cording to Rydberg, the leaves of patens are broadly

ovate or subcordate, much in the style of lenticularis,

while the bracts are those of petiolaris, thus reversing

the condition of aridus. It is possible that aridus and

patens are both remote results of the lenticularis X petio-

laris cross, but in the vicinity of Boulder, when aridus is

common, I have not found patens.

5. H. canus (Britton) Wooton and Standley. A

species of New Mexico, Chihuahua, and adjacent regions,

close to petiolaris, but with abundant white pubescence

on leaves and stems. The involucral bracts are of the

petiolaris type. This is to petiolaris much as H.

argophyllus is to lenticularis, but the pubescence is long

and spreading, not subappressed and silky.

6. H. argophyllus Torrey and Gray. Discovered by

Drummond in dry soil in Texas. This has the form and

leaves of lenticularis, but is very remarkable for the long

subappressed silky white hairs, totally different from

those of any other Helianthus known to me. Gray re-

marks that it ‘‘ degenerates in cultivation apparently into

H. annuus,” which merely means that it suffers from

vicinism. Old cultivated stocks, kept pure, are quite con-

stant. A remarkable feature of H. argophyllus is the

extremely slow growth, at least until near flowering time.

This peculiarity is dominant in a cross with H. annuus X

lenticularis.

614 THE AMERICAN NATURALIST [Vou XLIX

7. H. debilis Nuttall. Florida to Texas.

8. H. praecox Engelm. and Gray. Florida to Texas,

near coast. Differs from debilis by being strongly

hirsute.

9. H. cucumerifolius Torrey andGray. Texas. Differs

from debilis and precox by having the branches mottled

with purple.

The last three were eventually reduced by Gray to a

single species, but Small keeps them separate.- My wife

and I have grown H. cucwmerifolius for several years,

and have crossed it with annuus X lenticularis. The

first cross is quite fertile, but it is impossible to get any

quantity of F, seed. Mr. Leonard Sutton in England

has had the same experience; he writes (April 3, 1915)

We are arranging for a large breadth of the cucumerifolius crosses

this season, but we have found as you mention that very little seed is

produced, and we are hoping that the plant will improve in this respect

if grown for a few years, and the best seeding plants are selected for

stock.

These hybrids are of considerable horticultural value,

especially those derived from crosses with the red sun-

flower, so it is desirable to secure fertile strains if pos-

sible. Something may be attained by crossing back with

the parent species.

The H. cucumerifolius type is dwarf, freely branching,

with broad bright green leaves, shiny on both sides. The

involucral bracts are long and narrow. The bulb or

swelling of the dise corollas is minutely puberulent,

whereas that of the lenticularis forms is long hairy. In

the F, hybrid the bulb is long-hairy as in lenticularis, the

character being dominant. Although H. cucumerifolius

is very unlike the other species (except debilis and

precox) in apperance, its constant structural differ-

ences are very few. The base of the leaves, as in the

annuus forms, may be auriculate or truncate. The dise

bracts may be long-ciliate, or with the margins merely

appearing scurfy. It is proper to state that my material

belonged to cultivated strains; possibly the wild plant is

less variable.

No. 586] ANNUAL SUNFLOWERS 615

Thus we have at the most nine species, which can prob-

ably be reduced to five. They belong to the region which

used to be marked in old geography books as the ‘‘ Great

American Desert,’’ though members of the debilis group

extend along the Gulf States to Florida. The dominant,

widely distributed form is lenticularis, a plant of sandy

river-bottoms and similar places, which has spread as a

weed in cultivated areas. Prior to the era of cultivation.

it is probable that H. petiolaris occupied a greater area,

at least in acreage. At the present time H. lenticularis

is common in California, but I suspect that it has been

introduced into the Pacific coast region by man.

In order to give an idea of the cultivated forms of our

group, I have made a table from Sutton’s Catalogue for

1915.

Silver-leaved (argophyllus- dai ; rays yellow;

iso blaok: G Th cornea Silver- FE

Not DAVOS ORE a air Vona E Oa a a Mie er araa ‘

1. Cucumerifolius-type, none over 4 ft. high.........-.-+-eeeee reer ees i

AMNU YDE Mostly tall osese resas es Conners tai iN ay 6.

my: Only 12 mehes hiph: (Onpa ioe erre Dwarf Miniature.

Four Coot kgh -oeer rae Rine e ra nh LES a 3.

S: munya tolled, ‘Tike the eactie dahla s: isc. sce suas i eas n esa Orion.

FORTE MOG POU oo a Fo es oa a a Eb Pe he ek hoc pas Ceeepes

4, Bays pale primrose, dise dirk ....0.00 6s eecec cies ss Primrose Stella.

Kays pripit FOHOW oso in ees ook bi ei sce laws eck e ay peru eee 5.

5: Heads email, with dark Qine sissu- oiera senstepevcsssss Miniature.

Heads larger, rays long ...........-+. acne T E S ees Stella.

6. Bays Wholly OF partly chootant red i... oioi ioe ae et Red.

Rays Toa OF DATUY VINORS ioei fh aes ees oe 28 Langley Gem

Haye primos e as sos as ho 0s 8 oe ks ee sk Na, T

Rays kiai pi u a A E a 9.

7. Double (i. e., dise florets Aglio) E E A eee Double Primrose.

Single; iad Pale E es We es Os Se ee

8. Tall, 6 POG esi es Vika kes es A R Primrose Datodinn

STORIE, Sarre Re cio cv ong iek he cee Single Dwarf Primrose.

9. Double (i. e., disc florets ligulate). ...........eesesroseseeserese. 10.

Singlo (i 0., normal heads). 06.5 ees eee eevee eria 11.

10. Flowers orango; 6 ft: ioii ouir nce os Double (also a pa 5 ft. high).

Compact habit: a ft. 6 cone iia sche 05 <i tied on wh 8s arf Double.

11. Heads extremely large; height 8-10 ft. ............0cseeeeeee Giant.

Heads ordinary or smallish; dise dark; height 6 ft. ............... 12.

12. Heads medium size ..............+ Aisthetic al (J. Veitch & Sons).

PURVES Owen sis oi ds rossii aes ssa ess Earliest of All.

616 THE AMERICAN NATURALIST [Vou. XLIX

Of the above Red is coronatus, and Langley Gem is

vinosus, both derived from our Boulder cultures. The

seed offered as Langley Gem was grown in Boulder. The

Primrose variety I have called primulinus.

An old cultivated variety is H. annuus var. indicus

(Helianthus indicus Linn., Mant. I, 117), peculiar for the

foliar expansion of the involucral bracts. It did not come

from India, but from Egypt. Tithonia speciosa, once

regarded by Hooker as a Helianthus, has the bracts nor-

mally foliaceous. In 1913 I witnessed the appearance of

foliaceous bracts in the F, generation from primulinus X

coronatus. The plant in question was a very abnormal

dwarf, wholly unlike the rest of its generation, or any

known parents. It was described as follows:

Dwarf, about 28 mm. high; slender, fasciated at top of

stem; rays vinous, but on nearly all the heads a very

dilute and dingy color; dise dark, stigmatic branches dark

red; apical part of dise corollas dark greenish, tipped

with red, and very hairy; anthers not projecting, but not

shrivelled, almost wholly without pollen, and what there

is probably no good; achenes hairy, usually with super-

numerary pappus scales; pappus scales stained with pink;

involucral bracts long and tapering, strongly hirsute,

curled over, one or two outer ones long and foliaceous;

stem hirsute; leaves long and narrow, narrowly cuneate

at base; margins irregularly, sharply dentate, entire on

small very narrow leaves; sometimes one of the large

lateral veins of the leaves, and its supporting tissue,

absent.

Such a plant may result from some unwonted combina-

tion of genes, whereby the normal constitution is broken

down and in the resulting disruption characters usually

suppressed appear. Such monstrosities quickly perish,

but during their transient existence may reveal, like a

drunken man, matters which in the well behaved would

never reach the surface.

One of the most remarkable of cultivated varieties is

the Chrysanthemum-flowered, of which we obtained a

No. 586] ANNUAL SUNFLOWERS 617

perfectly constant and uniform strain from Dreer. It

may be named var. chrysanthemoides; plants of the same

general type have passed in horticulture as var. califor-

nicus (not H. californicus D.C.)

Helianthus annuus var. chrysanthemoides

Manner of growth.—(Tested in two seasons). Grows

much more slowly than the other forms (except argophyl-

lus), but is very robust. Nine plants studied were 15-17

inches high July 14, about 36 inches July 30, and coming

into flower at about 5 ft., 6 inches, August 15.

Foliage.—At first (June 8) leaves are narrow and long;

very uniform. Later, the upper (small) leaves are con-

spicuously pallid. At time of flowering the leaves are

broad, cordate, with auriculate base; surface very

strongly crinkled; margin moderately dentate.

Pubescence.—Leaves soft with very scanty pubescence;

petioles somewhat scabrous; stems, especially toward

the top and under the heads, with abundant and con-

spicuous soft white pubescence.

Heads.—Stalks greatly broadened under heads, diam-

eter about 27 mm. just under bracts; involucral bracts

hairy, the marginal hairs not longer than those covering

the backs of the bracts, five strong veins, and others

weak; basal half of bracts about 15mm. broad, gradually,

not abruptly, tapering to acuminate ends; bracts extend-

ing about 18 mm. beyond outer florets, which are like the

inner ones; heads entirely double (i. e., corollas ligulate),

rays very bright orange or saffron, dises light green

before they come into flower; immature achenes with

‘much silvery hair. -

This plant is so distinct, structurally and physiologic-

ally, that if it were not known to have originated in cultiva-

tion, it might well pass as a distinct species. Although I

have no information concerning its history, I can only

suppose that it is part argophyllus. Mr. Leonard Sutton

writes me that the similar Double catalogued by him,

which is of continental origin, does not grow more slowly

618 THE AMERICAN NATURALIST [Vou. XLIX

Fic, 1, above, Double

Red Sunflower.

Fig. 2, below, Helianthus von tortuosus.

No. 586] ANNUAL SUNFLOWERS 619

than other sunflowers in its early stages. The var.

chrysanthemoides was found by us to cross freely with

the annuus X lenticularis varieties, producing a series of

semi-doubles. The double and semi-double forms ex-

tracted from this cross and from crosses with Sutton’s

various double forms need not be described here, but in

order to illustrate the double type, I give a figure of a

full double with chestnut color, the red being derived

from the variety coronatus (Fig. 1).

MODIFICATIONS OF THE Rays

Number.—Halsted (Rept. Bot. Dept. N. J. Agric. Exp.

Sta. for 1911, pp. 335-337) has given elaborate data from

the branched form of the cultivated H. annuus, showing

that the terminal heads have most rays, and when there

are many lateral branches, the rays on these are com-

paratively few. Nevertheless, there are inherited differ-

ences in the number of rays, not depending on conditions

of nutrition. I observed a striking case by the roadside

in Boulder, where three wild lenticularis plants, growing

close together, differed thus:

(a) Rays normal, at right angles to axis; number of rays

in well-formed heads, 21, 21, 21, 21,.20, 21, 21.

(b) Rays normal, elevated, their plane oblique in rela-

tion to the axis of head; rays in well-formed heads,

14, 13, 14, 14, 14, 11, 15.

formed heads, 18, 18, 18, 19. In this plant many of

the rays were modified by quilling and splitting, some

being completely quilled, i. e., hollow and tubular.

The normal rays were very obtuse, and distinctly

emarginate at end. Some showed a little red color on

apical part of middle third beneath.

Length.—The length also differs, the differences due

sometimes to race, sometimes to illumination or nutri-

tion. In our cultures mutational forms have arisen with

unusually short rays, thus:

(a) Var. vinosus with dise 55 mm. broad, rays only 35

mm. long; dise unusually convex.

620 THE AMERICAN NATURALIST [Vot. XLIX

(b) Var. bicolor with disc 64 mm. diameter, rays only 29

mm. (Next to it, in the same lot, grew a plant with

dise diameter 38, rays 47 mm.)

These measurements represent average heads from the

respective plants. A quite analogous variation was seen

in two plants of Ratibida columnifera, growing at Boulder

along with the typical form (var. nov. breviradiata, rays

yellow, only about 10 mm. long, about half the normal

size).

Torsion.—A peculiar form which appeared in our cul-

tures is the variety tortuosus, in which the ends of the

rays are twisted, as though in curl papers. This is

wholly unattractive, but other variations have the long

rays moderately curled or twisted, promising the develop-

ment of a series of forms analogous to the cactus dahlias.

As with the cactus dahlias, the rays may be rolled instead

of twisted; a wild form of this type may be described

thus:

Helianthus lenticularis var. n. angustus. Rays about

20, narrow, rolled, so that they are separated by wide in-

tervals. The rays were 36 mm. long and 5 wide (a normal

-lenticularis ray 30 mm. long is 9 wide). Disc 26 mm.

‘diameter. Goodview, Colorado, July 28, 1913.

Tubular Rays.—Under the heading ‘‘Number’’ above,

‘a case of completely quilled rays in a wild sunflower is

recorded. This peculiar modification indicates some

deep-seated tendency in the Composite, since it appears

in several genera, e. g.:

(a) Ratibida columnifera var. n. tubularis. Rays of the

usual orange color, about 25 mm. long and 3.5 broad,

completely quilled, being hollow cylinders. Flag-

staff Hill, Boulder, Colorado, July 19, 1914.

(b) Rudbeckia hirta var. tubuliforme S. H. Burnham

Amer. Botanist, Feb., 1914.

Emarginate and Cleft Rays.—This is another common

modification, also observed in other genera, as Ratibida

` {R. columnifera var. n. incisa; rays with one or two deep

No. 586] ANNUAL SUNFLOWERS 621

incisions, and also some narrow supplementary rays;

Boulder, Colorado, August 8, W. P. Cockerell).

Double Rows——The dise remaining normal, the rays

may be in two rows, indicating an approach to a type re-

sembling the star dahlias.

Color.—The yellow may be of various shades from

deep orange to very pale, approaching white. This has

already been discussed in Science, August 21, 1914, pp.

283-285. It may be possible eventually to get a pure

white. Dr. Church (in litt.) refers to a white form as

having been mentioned long ago by Hernandez. There is

also the development of the soluble (anthocyanin) red

pigment, giving us the chestnut red and wine red vari-

eties.

CONCLUSIONS

It is impossible at the present time to give all the evi-

dence on which opinions have been formed, but such facts

as are reported above, and others, seem to suggest the

following generalizations :

1. The number of genes or determiners in Helianthus is

not infinitely great; it is probably very much less than

exists in most animals, and the study of the processes of

heredity is relatively simple.

2. In the history of the sunflowers of the H. annuus

group, there have been few really new developments.

Species which seem very distinct prove on examination

to have few special characters of their own.

3. It is quite common for variations to arise, in wild

and cultivated plants, which appear to break the type,

and initiate something altogether new. When, however,

we begin to gather data on the variation of the Compositæ,

we find that practically all these ‘‘ new ”’ variations re-

peat themseles in various species, and at various times,

indicating that they represent deep-seated common tend-

encies. Their occurrence among wild plants shows that

they are not necessarily connected in any way with culti-

vation, and it is equally evident that they need not indi-

622 THE AMERICAN NATURALIST [Vou XLIX

cate any sort of hybridization. For example, Ratibida

columnifera presents many variations parallel with those

of Helianthus, in localities where it is the only species of

its genus.

4. We are led, then, to think of the annual sunflowers as

plants representing a certain complex of potentialities or

genes (of which we may hope at length to make a reason-

ably complete catalogue), offering these in different com-

binations at different times, usually failing to register

any permanent advance, but once in a long while reaching

a new position of stability, suited to a particular en-

vironment. These positions of stability represent what

we call the species. As with the dahlia, the horticulturist

may expect to be able to produce many interesting varie-

ties by selecting and saving the various possible combina-

tions, but analysis shows that the genes going into these

are the old ones, the effects of which may be seen from

time to time even in wild plants.

The perennial sunflowers appear to offer a more com-

plex problem. Mr. S. Alexander has found hundreds of

what are considered ‘‘ elementary species ” in Michigan.

He has been good enough to send me a large number of

these, and I ean testify that they are appreciably differ-

ent; yet they seem to represent recombinations of old

characters, already known to exist in the species of the

manuals. Some would dismiss them, along with the mul-

titudes of Crategus, as hybrids; but it does not seem justi-

fiable to assume hybridization without better evidence.

We have sufficient proof, I think, that all sorts of new

combinations of characters may arise within a type, with-

out hybridization.

Undoubtedly new determiners are formed (how, we

need not here speculate) from time to time, but the oc-

currence must be so rare and so difficult to demonstrate

that we can hardly hope to obtain satisfactory evidence

concerning it.

THE INHERITANCE OF DOUBLENESS IN MAT-

THIOLA AND PETUNIA. I. THE HYPOTHESES*

HOWARD B. FROST

Citrus EXPERIMENT STATION, UNIVERSITY OF CALIFORNIA

THE peculiar inheritance of ‘‘doubleness’’ in stocks

(Matthiola) has long been a matter of special interest.

Some races produce only single-flowering plants. A pure

double-flowering race, on the other hand, is an impossihil-

ity ; the doubles are absolutely sterile, stamens and pistils

Matthiola plants, unselected progeny of two porene showing the

s i

for photographing. The singles are plants 1, 2, 3, and 11 (mis aa). from the

left side, in the upper row, and plants 1 to 5 in the lower sary

being entirely absent. Certain races, however, consist of

both singles and doubles, in nearly equal numbers,’ each

generation being descended from the singles of the pre-

* Paper No. 17, Citrus Experiment Station, College of Agriculture, Univer-

versity of California, Riverside, California.

1 The usual proportion of doubles in large cultures seems to be near 53

per cent., or perhaps slightly higher in some cases,

623

624 THE AMERICAN NATURALIS1 [Vou. XLIX

ceding generation (see Fig. 1); the following diagram

shows the mode of inheritance in such races:

Single

i |

Double Single

(sterile) i

ouble Bingi

(sterile)

Miss Saunders (1911; 1913; Bateson, 1909, pp. 201-204)

has done a great amount of work on heredity in Matthiola,

and has developed an ingenious hypothesis to explain the

peculiar behavior of doubleness. Goldschmidt (1913) has

given another explanation, which has been vigorously

criticized by Miss Saunders. Several years ago (per-

haps in 1909), largely on the basis of Miss Saunders’s evi-

dence, I formulated a hypothesis somewhat simpler than

either of those just mentioned.

In view of the special interest of the case at present,

and the fact that one or both of the essential points of

my explanation have been suggested incidentally by an-

other writer (Belling, 1915, 1915a), it seems desirable to

give a general review of the hypotheses at this time.?

As Miss Saunders’s (1911; Bateson, 1909, p. 201-204)

crosses have shown, the EEE E singles are

heterozygous, the approximately 1:1 ratio being due to

the fact that the functional pollen is all double-carrying.

This is shown by Miss Saunders’s crosses between double-

throwers and pure singles. When the double-thrower

is the seed-parent, about half the F, progeny are hetero-

zygous, the rest being pure singles ; about half the double-

thrower eggs, then, are ‘‘double-carrying.’? On the other

2 My own data bearing on the problem have largely been published (Frost,

1911) or will be published in two papers (Frost, unpublished) soon to ap-

pear; some further evidence, relating to the proportions secured with some

8,000 plants of. one variety, together with a summary of my other data, is to

be presented in a paper to follow the present one. Aside, however, from one

important general feature of these results, to be briefly stated below, the

view given here is dependent on Miss Saunders’s evidence and that cited

by her.

No. 586] THE INHERITANCE OF DOUBLENESS 625

hand, when the double-thrower is the pollen-parent, all

the F, progeny are heterozygous; hence all the double-

thrower-pollen is double-carrying. These facts are il-

lustrated by the two following diagrams (adapted from

Goldschmidt) :

P: Double-thrower ?

Pure single d

| Í

F: Single (3) Single (4)

] J l

F- Single Single (4) pi (4) Double (4)

| | l

F: Single Single Single (4) Single (4) Double (3)

(pure) (pure) (pure (heterozygous) (sterile)

Pi Pure single Ẹ Double-thrower ¢

F: Single

| | |

F: Single (4) Single (3) Double (4)

g I |

F: Single Single (4) Single (4) Double (4)

(pure) (pure) (heterozygous) (sterile)

In these two crosses, where the ‘‘ singleness ”’ in the F,

(or later) heterozygotes comes entirely from the pure

single parent, we get what seems to be an ordinary Men-

delian® result in F,; the pollen of these heterozygotes

must carry both ‘‘singleness’’ and ‘‘doubleness.’’ The

absence of singleness from the double-thrower pollen is

taken by Bateson (1914, p. 292, foot-note) as almost con-

clusive evidence of somatic segregation of factors, occur-

ring in such a way that the pollen-mother-cells receive.

only doubleness. Neither he nor Miss Saunders, how-

ever, gives any reason why singleness, rather than double-

ness, should be thus eliminated. Goldschmidt (1913)

and Belling (1915, p. 126) have stated that selective

sterility of pollen will also explain the case, and definite

evidence for this view is presented below.

3In some crosses the proportion of doubles is smaller, possibly 1/16

instead of 1/4.

626 THE AMERICAN NATURALIST (Vor. XLIX

To explain the slight but constant excess of doubles

over singles, Miss Saunders assumes that two comple-

mentary linked factors, X and Y, are essential to single-

ness, and that these factors cannot be carried by the male

gametes of the double-throwers, which are all xy. X and

Y are supposed to be so linked in the ovules that the four

kinds of eggs are produced, not in equal numbers, but in

the ratio 7XY:1Xy:1xY:7xy—or else in the ratio 15:1:

1:15. Fertilization by xy pollen will give, in the former

case, TXY -xy +1Xy-xy+1xY-xy-+7xy-xy; if only

zygotes having both X and Y are single-flowering, only

the first class will consist of singles, and the doubles will

constitute 9/16, or 564 per cent., of the total. Linkage

on the 15:1 plan would give 17/32, or 534 per cent., of

doubles.

- For certain cases where crosses with pure singles have

given much less than 25 per cent. of doubles in F,, Miss

Saunders assumes the presence of a second set of two

linked factors, X’ and Y’; then any zygote receiving X or

X’ together with Y or Y’ is a single, and the proportion

of doubles is correspondingly reduced.

Von Tschermak (1912) favors Miss Saunders’s hypoth-

esis; he suggests the possibility of selective elimination

(in a dihybrid scheme), but does not consider this expla-

nation probable. It would seem, however, in view of con-

siderations stated below, that any dihybrid scheme to ex-

plain the usual slight deviation of the double-throwing

races from a 1:1 ratio is unnecessarily complex.

Goldschmidt’s (1913) hypothesis assumes selective

degeneration or sterility of pollen in the double-throw-

ers, and considers the case to be one of sex-linkage, class-

ing the slightly aberrant ratio with the known cases of

slight deviation in the sex-ratio in animals. He supposes

that this ‘‘ hermaphroditic ’’ plant is homozygous for a

distinct factor for femaleness (F), producing eggs all of

which carry this factor. He assumes that singleness is

4 Miss Saunders (1911) rather favors the latter gametic ratio, which also

corresponds closely to my own data.

No. 586] THE INHERITANCE OF DOUBLENESS 627

determined by one dominant factor, S; the eggs of the

double-thrower, then, are SF (‘‘single’’) and sF

(‘‘double’’). He assumes, also, that half the pollen-

grains or microspores, in all races of Matthiola, lack F,

probably because of elimination of part of an X-chromo-

some, and that these pollen-grains degenerate or at least

are non-functional, so that no staminate plants are pro-

duced. It is necessary to assume, then, that in the

double-throwing races S (or s) and F are carried by the

same chromosome, and that the S-carrying chromosome

is always the one to eliminate F. The S-carrying chro-

mosomes will then be the ones destined to degenerate.

The pollen resulting is of two kinds, Sf (‘‘ single,’’ non-

functional), and sF (‘‘ double,’’ functional).

The double-throwing plant, then, is SFsF ; its eggs are

SF and sF, while its pollen-grains are Sf (non-fune-

tional) and sF. Self-pollination gives, then, SFsF

(heterozygous or double-throwing singles) and sFsF

(homozygous sterile doubles).

The factor S, however, can not in itself, in general, in-

sure pollen-degeneration, since homozygous singles (SS)

produce fertile pollen. Nor can the case be one of degen-

eration of all pollen-grains receiving a maternal X-chro-

mosome, as is proved by the results of crossing SS and Ss

races. Heterozygous singles (Ss) which get the S factor

from a pure single (SS) parent, either through egg or

through sperm, produce good S pollen, as is shown by the

ordinary Mendelian ratio among their progeny (1 homo-

zygous single (SS) :2 heterozygous singles (Ss) :1 homo-

zygous double (ss). Goldschmidt is driven to assume,

therefore, that the singleness factor (S,) in the double-

throwers differs from that in the pure singles (S)—or

else to suppose that another factor interferes in the

former type.

It will be seen that Goldschmidt gives, at most, only an

indefinite implied explanation of the deviation of the

double-single ratio from equality in the double-throwing

races. And it is hard to see what advantage is secured

628 THE AMERICAN NATURALIST [Vot. XLIX

by introducing sex-factors into the discussion at all, when

all actual individuals have both stamens and pistils, or

else neither. When we assume—as Goldschmidt does—

that the factor S is so modified in the double-throwing

races as to insure the sterility of pollen-grains receiving

it, the known facts must follow; it seems wholly superflu-

ous to refer the sterility to linkage of S, with a sex-factor.

The hypothesis seems quite unnecessarily complex; there

is no real evidence here for the existence of a distinctly

heritable femaleness factor, or for any elimination of sex-

factors in pollen-formation, or for the occurrence of non-

functional pollen in ordinary pure single (SS) races.

In a reply to Goldschmidt, Miss Saunders (1913) gives

a very clear presentation of both her formulation and

that of Professor Goldschmidt, urging most of the ob-

jections to the latter scheme which are stated above, but

especially emphasizing its failure to explain the excess

of doubles over 50 per cent. She also objects to the as-

sumption of the existence of non-functional pollen, but I

can not agree with her on this point.

I have sectioned anthers prepared for cytological

study, and have frequently observed stages subsequent to

the reduction divisions. The spore-tetrads appear nor-

mal, and there seems to be no early and conspicuous evi-

dence of later degeneration. The ‘‘single’’ pollen, how-

ever, might even germinate and yet be strictly non-func-

tional because of weak growth; and, as is shown below,

the singles are actually inferior to the doubles in vigor.

Selective partial sterility seems to be a rather common

phenomenon, and it very probably occurs here.

The only other recourse seems to be the hypothesis of

somatic segregation mentioned above, and somatic segre-

gation, except as a rare accident of abnormal cell-divi-

sion, has no decisive evidence in its favor® and an over-

whelming convergence of probabilities against it. Bel-

ling (1915) calls attention to decisive evidence against

. 5 Bateson’s (1914, p. 292) positiveness in its favor seems to depend on

just such cases as that here in question.

No. 586] THE INHERITANCE OF DOUBLENESS 629

it in five genera representing as many distinct orders.

Bateson himself (1909, chap. 9) reports a fact which

seems to exclude it in the sweet pea, although his redu-

plication hypothesis? (Bateson and Punnett, 1911) would

require it there if anywhere.

This phenomenon is one to which East (1915, p. 87) has

recently referred, the ‘‘ zygotic ’’ nature of certain pol-

len-grain characters. In the sweet pea, for instance, F,

hybrids between certain races with long (dominant) and

round pollen have the pollen all long, although segrega-

tion, on any hypothesis, must have already occurred

before the shaping of the pollen-grains. If segregation

takes place as a result of chromosome-reduction, in the

formation of the spore-tetrads, it is not strange that the

cytoplasm of the young pollen-grain still retains the im-

press of the diploid maternal set of chromosomes, so that

the pollen-grains give no evidence in their shape of the

segregation that has just taken place. On the other

hand, if segregation takes place early enough to permit

of extensive ‘‘ reduplications ’’ of the cells carrying cer-

tain combinations of factors, it is very strange that the

cytoplasm of the pollen-grain should be essentially

maternal in nature. Especially does this evidence nega-

tive any hypothesis of cytoplasmic segregation—and if

segregation is nuclear, surely we have reasons enough for

connecting it with the reduction of the chromosomes.

It is due to Goldsckhmidt’s hypothesis to note that a

factor ‘‘ completely coupled ’’ with S, completely lethal

for pollen and only slightly so for the embryo-sac, would

explain the peculiarities of the case in Matthiola, both the

non-functioning of the S-ecarrying pollen and the excess

of doubles over 50 per cent. This is an amplification of

his suggestion, in a passing reference (1913, p. 81), of a

6 Bateson and Punnett explain linkage of genetic factors by means of the

hypothesis of somatic segregation. They assume that a period of cell-divi-

sion intervenes between the segregation of Mendelian factors and the

formation of the germ-cells, and that the cells bearing certain sets of factors

divide more often than the rest. This would result in making some classes

of germ-cells more numerous than others.

630 THE AMERICAN NATURALIST [Vou. XLIX

possible ‘‘ further distinct hereditary factor ’’; I merely

omit the sex-factor, and suppose the other factor to be

lethal in itself. He evidently does not notice that this

sort of factor might well explain more than the sterility

of the pollen. It amounts to the same thing, however,

to suppose the double-thrower S (or §,) to be itself the

lethal factor. The introduction of sex-factors seems en-

tirely unnecessary here, and the supposed lethal elimina-

tion of an F tactor can not be general in hermaphroditic

plants, since it would involve the universal occurrence of

sterile microspores or pollen.

Our case appears to be merely one of a hybrid showing

selective sterility of pollen-grains, a sterility due to the S

factor or to a lethal factor linked with S. Further, if

there is also a slight tendency to selective elimination of

S-carrying eggs, we have a simple and direct explanation

of the excess of doubles over the expected 50 per cent.

Or, if the s-carrying eggs are more often fertilized, the

excess of doubles is explained. Once more, selective

elimination of single (Ss) embryos might produce the

same result.

There are several facts which are extremely suggestive

in relation to all these possible forms of selective elimina-

tion. First, it is known that, in a double-throwing race,

the doubles are longer-lived than the singles in the seed

stage; Miss Saunders (1911, p. 362) has definitely con-

firmed the common belief that the proportion of doubles

tends to increase with the age of the seed. Second, Miss

Saunders (1911, p. 364) has obtained a higher proportion

of doubles from seed of lower viability, even with fresh

seed. Third, some seed-growers (deVries, 1906, p. 335)

regularly ‘‘ starve ’’ the seed-bearing plants, in the belief

that they thus increase the percentage of doubles among

the progeny. Fourth, the writer (Frost, 1911) has found,

with one variety, that inhibition of flowering by high tem-

perature is much more marked with singles than with

doubles; in field cultures, in many cases, hot weather

greatly delayed or entirely prevented flowering, the

No. 586] THE INHERITANCE OF DOUBLENESS 631

difference there being very much greater than that shown

in the tables in the paper cited.” Fifth, in the cultures

just mentioned the doubles had larger leaves than the

singles and evidently were decidedly larger as young

plants. It seems that the double form (ss) is superior to

the heterozygous single (Ss) of this double-throwing race

in general vegetative vigor, and a similar difference may

exist between s and S gametes; on these facts probably

depend the peculiarities of the observed ratio.

In order to make the case of doubleness in Matthiola

as clear as possible, let us consider a brief summary of

the formulations that have been proposed. There are

two essential points to be explained, namely: (1) the fact

that the singleness factor or set of factors of the double-

throwing races can not be carried by functional pollen,

although the corresponding factor or factor-group of the

pure single races so far tested is normal in relation to

pollen, even in single-double hybrids; (2) the fact that

the double-throwing races show a small but feini con-

stant excess of doubles over 50 per cent.

Miss Saunders gives a formally adequate but rather

complex factorial hypothesis for (2). She leaves (1),

however, essentially unexplained; she evidently relegates

it to the realm of somatic segregation, and in any case

makes no suggestion as to the real cause of the uniform

elimination of singleness.

Goldschmidt, on the other hand, gives for (1) a hypoth-

esis of selective sterility which is adequate, though of

obviously unnecessary complexity, but fails with (2)

about as completely as Miss Saunders does with (1).

It is here maintained that an extension of the general

idea of selective elimination or viability, in any one of

the several forms consistent with the evidence, complies

with all the requirements, adequately explaining both (1)

and (2). It might seem, at first thought, that the as-

sumption of a difference between S and §,, or of the exist-

7 This evidence is to be published mainly in my forthcoming paper on

‘‘ Mutation in Matthiola. ”?

632 THE AMERICAN NATURALIST [Vou XLIX

ence of a distinct linked lethal factor, makes this scheme

as complex as that of Miss Saunders; this is not the case,

however, since Miss Saunders’s scheme simply omits any

attempt at real explanation of the peculiarity of the

double-thrower pollen; her formulation imperatively re-

quires the addition of the hypothesis of selective via-

bility, or of some definite equivalent for it.®

The real puzzle of the case lies in the fact that the

double-throwers plainly differ from the pure singles so

far tested in at least two respects—heterozygosity for

singleness (ability to form sporophylls) and the associa-

tion of some peculiarity with the remaining singleness.

This, however, is essentially a problem of the origin of

the double-throwing races, and is, in any case, nowhere

simpler than with the hypothesis here suggested. Miss

Saunders’s scheme really implies four factorial or linkage

differences between pure singles and double-throwing

singles, and for certain cases six such differences, in place

of the two or three required by the hypothesis here

favored. That is, the double-thrower is supposed to

differ from the pure single in the following points: (1)

that it is heterozygous for two complementary factors

(X and Y) for which the pure single is pure, and in some

cases also for a second set of such factors (X’ and Y’);

(2) that its ‘‘ singleness ’’ can not be carried by func-

tional pollen; (3) that X and Y are partially instead of

completely linked. It is here proposed to drop half the

factors of (1), and this makes (3) superfiuous.

8 She supposes (Saunders, 1911, p. 334) that X and Y are completely

linked in the pure singles, but only partially so in the double-throwers; this

explains why, with self-pollination, the latter give 50 + per cent. of doubles

rather than 50 per cent., but not why they approximate 50 per cent. instead

of 25 per cent. It would seem, however, that the Ss hybrid between pure

single (SS) and eian thrower (S,s) may usually give double progeny

approximating, not the 25 per cent. assumed, but a slightly lower ratio.

A possible general slight deficiency of doubles in this cross is not provided

for in Miss Saunders’s hypothesis, complete linkage of X and Y explaining

why there is not an excess of doubles; whether the viability-hypothesis is

adequate depends on the general viability-relations of the S factor (as dis-

tinguished from S,), which quite possibly is even superior to s in respect to

vigo

No. 586] THE INHERITANCE OF DOUBLENESS 633

It must be admitted, however, that (3) is not in itself

improbable if (1) is true, in view of Miss Saunders’s

evidence. A similar difference between races, with re-

spect to linkage, occurs with ‘‘cream’’ flower-color,

which is partially linked with doubleness in the sulfur-

white races, but completely linked in the pure-cream

races. The essential difference of the viability-hypoth-

esis, as here presented, relates to (1); the demon-

strated lower viability of the singles, evidently the basis

of (2), makes possible the simplification of (1).

If we accept this viability-hypothesis, there seem to be

two general possibilities as to the origin of the double-

throwing races. One is that the mutation by which Ss

(double-throwing) races arise from SS (pure single)

races involves a simultaneous or consequent alteration

in the remaining S factor (or the production of a lethal

factor completely linked with S), by which the presence

of S becomes incompatible with pollen-formation.

Second, it may be that the particular race or races in

which our double-throwing forms originated had an S

factor originally different from that of the pure single

races which have been used in crossing with double-

throwers—that is to say, an S factor originally incompat-

ible with the formation of good pollen in an Ss plant—

or else that they originally possessed the lethal factor

suggested. If the second supposition is correct, such

pure single races may be found,—races which in crossing

with double-throwers never give the F, ratio 3 singles:1

double, but only approximately 1 single: 1 double.

With Petunia, if we ignore the new seed-producing

double (Francis, 1913), which has a distinct type of

flower, the general case would seem to be similarly

simple. Here, as is well known, the doubles are pro-

duced only when singles are pollinated by doubles, the

ordinary doubles having stamens but not pistils, or, at

most, non-functional rudiments of pistils. In this case

the doubleness factor (D) is plainly dominant, and is

perhaps to be considered an inhibitor; the single, then, is

634 THE AMERICAN NATURALIST — [Vov. XLIX

dd, and the double Dd, cross-pollination giving 1dd:1Dd.

There is usually (Hamüdort, 1910) an excess of singles;

here, as in Matthiola, the heterozy gous form is the one

deficient in numbers, and it is also the one which appears

inferior in vegetative vigor.? Probably the deviation

from the 1:1 ratio is due in Petunia to selective elimina-

tion of doubleness.

We have, then, in Matthiola and Petunia, hybrids

evidently due, not to the crossing of widely different

forms, but to mutation within the race,” and yet they

are partially sterile, and perhaps even lacking in vegeta-

tive vigor because of their hybridity! In connection with

the vigorous discussion of mutation now going on, it

seems worth while to ask whether, in a case like that of

(Enothera, hybridization is the cause of mutation or

mutation one great cause of hybridity; apparently both

views may be in part correct.

Miss Saunders favors a dihybrid scheme for Petunia,

evidently supposing the difference here also to depend on

two complementary factors, both necessary for single-

ness. Her assumption that singleness is dominant, as in

Matthiola, seems absolutely untenable. In considering

the last point, we may ignore the dihybrid feature, since

this evidently concerns only the deviation of the ratio

from 50 per cent.

Her formulation, as thus simplified, makes the singles

Ss and the doubles necessarily ss; the data then indicate

that the functional single pollen is all S-carrying (the

reverse of the case in Matthiola), since self-pollinated

singles produce no doubles. Then, either the single eggs

are S + s, and the double pollen s + s, or the single eggs

are s-+s, and the double pollen S+s. The latter

assumption is obviously impossible, since it not only con-

tradicts the assumption that singleness is dominant, but

® Theodore Payne, a seedsman of Los Angeles, California, says in his ~

1914 seed-catalogue, ‘‘The weaker seedlings should be carefully saved, as

these invariably produce the double flowers.’’

.10 This is not to assume that some disturbance due to crossing of two

single-flowering forms might not have led to the ‘‘mutation.’?

No. 586] THE INHERITANCE OF DOUBLENESS 635.

makes both singles and doubles heterozygous (Ss); the

former assumption, however, is also excluded, as Miss

Saunders shows, by the fact that all singles tested pro-

duce some doubles when pollinated by doubles—that is,

the expected class of pure singles (SS) does not occur.

Evidently, as both Goldschmidt (1913) and Belling (1915)

assume,!? doubleness is dominant in Petunia, and selective

viability probably completes the explanation.

BIBLIOGRAPHY

Bateson, Willia

1909 indat Principles i Heredity. 14+ 396 pp. Cambridge,

Univ. Press. 6 pl. a

1914. The Address of the President of the British Association for the

Adva slope of Science. [Heredity.] I. Science, N. S.,

Bateson, blest m, and 3 R. C.

911 n Gametie Scam Involving Reduplication of Certain Terms.

Jour. of Genetics, 1: 293-302, 1 pl. and 1 fig.

Belling, John.

1915. On the Time of Segregation of Genetic Factors in Plants. AM.

Nar., 49: 125-126, Bibliog.

1915a. "Coniitions of Mendelian Inheritance. Jour. of Heredity, 6: 108..

East, Edward M.

. The Phenomenon of Self-sterility. Am. Nart., 49: 76-87, Bibliog.

Francis, ede Shepherd.

191 A New Creation in Floriculture. The Rural Californian, 37:

397-399, 410, 411

11 In the dihybrid scheme, here, if linkage is to be invoked, as in Matthiola,

to explain the deviation from 50 per cent. of doubles, both the singles and

the doubles must carry both factors—since the singles possess both by

hypothesis, and we are supposing the pollen of the doubles to show linkage!

Further, doubles, not singles, would be expected to be in excess of 50 per

cen eam e fact, no self-consistent dihibrid scheme seems to be possible with

Petu

12 Gádsihaidi ’s statement (1913, p. 84) seems to segues that Miss

Saunders herself made this change, especially as he refers to ‘‘ Journal of

Genetics, 1, 1911’; apparently, however, he intends the alone article, pub-

lished in 1910, and I have failed to find any reference to the matter in the

part of the volume published in 1911. The explanation peat above was

stated in a letter sent to her in May, 1914, but no reply has been received.

Bateson (1913) considers singleness to be dominant, admitting the necessary

conclusion that all cultivated singles appear to be heterozygous. How this

universal heterozygosity could be maintained in self-pollination of the singles

(S +s eggs X S pollen, since the opposite assumption is untenable), he does

not explain.

636 THE AMERICAN NATURALIST [Vou. XLIX

Frost, Howard B.

1911, Variation as Related to the pager Seite Am.

Breed. Assoc, R

ept., 6: 384-395, 4 tables, arts.

[In Ms.] The Relation of Pemperatare to valves: in Matthiola.

[In Ms.] Mutation in Matthiola.

Goldschmidt, Richard

Der Vererbungmodus der gefüllten Levkojenrassen als Fall

ee oe Vererbung. Zeitsch, f. indukt. Abstam.-

. Vererbungsl., 10: 74-98. Diagr.

a Maith R.

Studies in the Inheritance pi poseg. in Flowers. I. Petunia.

Jour. of Geneties, 1: 57-69, 5 tables,

1911, i Re HI on F p AA of Doubleness and Other

acters in Stocks. Jour. of Genetics, 1: 303-376, 8 tables.

1913. pe pene Mode

of sed Si of Certain Characters in Double-

throwing jag A Reply. Zeitsch. f. indukt. Abst

aa 06s : 297-310.

Tschermax, Erich v

stam.- U.

1912. fis ida Miatleieneeeckc an Levkojen, Erbsen und Bohnen mit

iicksicht auf die Faktorenlehre. Zeitsch. f. indukt. Abstam.-

u. Vererbungsl., 7: 81-234, tables.

de Vries, Hugo

190 tieeaion and Varieties: Their Origin by Mutation. 2d ed.,

18 + 847 pp. Chicago, Open Court Pub. Co.

THE COAL MEASURES AMPHIBIA AND THE

CROSSOPTERYGIA

DR. ROY L. MOODIE

DEPARTMENT OF ANATOMY, UNIVERSITY OF ILLINOIS, CHICAGO

Ir has been assumed for many years that the crossop-

terygian ganoids are more nearly in the direct line of

descent of the amphibia than any other known group of

fishes. Recent work along this line adds considerable

evidence to support this assumption and it is fast becom-

ing accepted as practically proven that such was the line

of descent of this group of vertebrates. Watson (1),

Broom (2), Gregory (3-4), Pollard (5), Klaatsch (6),

Budgett (7), the writer (8), and others have added to our

knowledge of this relationship, which is based on the

structure of the skull, the limbs and the mandible, so far

as these anatomical features are known. Our knowledge

of the osteology of neither group is satisfactory and it is

to be hoped that additional material will do much toward

a solution of this problem.

It is our purpose here to state in a brief manner what

the Amphibia from the Coal Measures add toward the

solution of the problem of the derivation of the amphib-

ians from the crossopterygians.

The fish characters of the larval stages of the Amphibia

have been often cited as evidence of this relationship.

Budgett (7) says:

It has been admitted by the most competent paleontologists that the

structure of the dermal bones of the head and shoulder girdle of Poly-

pterus is so like that of certain Stegocephali, that it must be regarded

as more than a mere resemblance while there are many points in the

development of the skeleton that distinctly approach the condition of

the Amphibia. The only possible interpretation of these facts appears

to me to be that the living crossopterygians form a central group among

recent forms, having some characters in common with most of the great

groups.

The writer (8) has called attention to the similarity of

arrangement of the lateral line canals in Amphibia and

Crossopterygia and has attempted a correlation of the

cranial elements. In that essay it is stated:

637

638 THE AMERICAN NATURALIST [Vou XLIX

H ali

Sguali Paji

Mi T e

Cycjostomata

Osira rE

Aimphioxus tike ancestor

Tunicata

Posible invertebrtles ancestral frn

A phylogenetic scheme illustrating in a tentative way the possible relationships

“of the Coal Measures Amphibia to the other Chordata. The Crossopterygia may

have had more immediate ancestral relations than the diagram idicates.

No. 586] THE COAL MEASURES AMPHIBIA 639

The following elements of the stegocephalan cranium are homologous

with the same elements in (the crossopterygian) fishes: premaxille,

maxille, nasals, frontals, prefontals, parietals, squamosals, and post-

frontals. The epiotics and supraoccipitals of the Stegocephala are

homologous with the supratemporal elements of fishes. The quadrato-

jugal is homologous with the suboperecular of fishes. The supratem-

poral is homologous with the preopereulum (8).

Wilder has commented on the close relationship of

these two groups and even goes so far as to say: ‘‘that

terrestrial vertebrates were originally. derived from a

single form, perhaps a single species’’ (i. e., of the Cros-

sopterygia) (9). It will be interesting in this connection

to give a brief résumé of the geological history of the two

groups of vertebrates. The history of the Amphibia is

briefly this:

Devonian: Thinopus antiquus Marsh, footprint from

Pennsylvania.

Mississippian: Footprints from eastern North America.

Pennsylvanian: Five orders of Amphibians represented

by hundreds of more or less complete skeletons from

Europe and North America.

Permian: Four orders of Amphibia, known from an abun-

dance of material from Europe, Africa, Asia, and

North America.

Triassic: Two orders of Amphibia, the species of which

may be compared very favorably with modern spe-

cies; North America and Europe.

Comanchean: None known in North America.

Cretaceous: Caudata known from imperfect fragments,

North America.

Eocene to Recent: Frogs and salamanders as in modern

times. |

Recent: Salientia, Caudata, Gymnophiona.

The geological history of the Crossopterygia is briefly

summarized by Huxley! in the following:

The group of Crossopterygide as thus established appears to me to

have many remarkable and interesting zoological and paleontological

relations. Of the six families which compose it, four are not only

Paleozoic, but are, some exclusively and all chiefly, confined to rocks of

1 Scientifie Memoirs, IT, p. 445.

640 THE AMERICAN NATURALIST [Vou. XLIX

the Devonian age,—an epoch in which, so far as our present knowledge

goes, no fish belonging to the suborders Amiadz or Lepidosteide (unless

Cheirolepis is one of the latter) makes its appearance. Rapidly dimin-

ishing in numbers the Crossopterygide seem to have had several repre-

sentatives during the Carboniferous epoch, but after this period...

they are continued through the Mesozoic age only by a thin, though

continuous line of Celacanthini, and terminate, at the present day, in

the two or three known species of the single genus Polypterus, now

recognized under two genera: Polypterus and Erpetoichthys (Calam-

oichthys).

Such, in brief, is the geological history of this peculiar

order of fishes. At the time of the publication of Hux-

ley’s essay the fact of the geological distribution of the

group was of the greatest interest, since it proved the

transition of a vertebrate group from the Paleozoic to

later times in practically unchanged form.

Tt will thus be seen that in the Devonian we have repre-

sentatives of these two groups; one of which has been

supposed to have given origin to the other. The oldest

known Crossopterygian coexisted, in the Devonian, with

well-developed Amphibia-like forms if we may trust the

evidence of the single imprint of Thinopus antiquus

Marsh from the Devonian of Pennsylvania. That the

impression described by Professor Marsh is in reality a

footprint no one, who consults his figures, can doubt.

Its geological horizon is vouched for by the late Dr.

Charles E. Beecher, whose interpretations of geological

facts have never been impeached. So that we may say

with perfect assurance that the oldest known Crossop-

terygia existed side by side, geologically, with well-devel-

oped air-breathing, quadrupedal vertebrates. Whether

the latter were Amphibia or not is a matter which no one,

in the light of our present knowledge, can decide. The

inference, however, is that they were such.

In order that all the facts of the case in regard to the

origin of the Amphibia may be given, the following defi-

nition of Crossopterygia is given. It is based on the

first definition by Huxley and the definition contained in

Zittel’s ‘‘Paleontology’’ (ed. by Eastman).

Dorsal fins two, or if single multifid and very long; the pectoral and

Waly the ventral fins lobate; no branchiostegal rays, but two prin-

No. 586] THE COAL MEASURES AMPHIBIA 641

cipal with sometimes lateral and median jugular plates situated be-

tween the rami of the mandibles; caudal fin diphycereal or hetero-

cereal; scales cycloid or rhomboid, smooth or sculptured.

These characters may be supplemented by the follow-

ing: Notochord persistent or vertebre slightly ossified,

infraclavicle present. Teeth dendritic in a few forms.

The following list contains brief statements concerning

the structures in these two groups which are usually re-

garded as of great taxonomic importance in all vertebrates.

4. COMPARATIVE TABLE OF STRUCTURES IN AMPHIBIA AND

CROSSOPTERYGIA

Amphibia

I. Typically quadrupedal tetra-

and pentadactyl, aquatic or terres-

trial vertebrates. Body usually

provided with ventral armor of

ossified, calcified or chondrified

Body completely sealed in

one species. Seales present in

other species but incompletely

own.

II. Teeth labyrinthine in some

species.

II. Vertebre always ossified,

sometimes highly developed; as-

suming various forms. Notochord

incompletely persistent as inter-

_ central masses.

IV. Skull covered with dermal

bones, which are at times variously

sculptured and grooved by pits

and canals.

V. Lateral line canals present

as distinct impressions in the der-

mal elements.

VI. Parasphenoid largely de-

veloped.

VII. The following cranial ele-

ments correlated wit of the

Crossopterygia: Supraoccipital,

epiotie, parietal, frontal, prefron-

tal, nasal, premaxilla, maxilla,

Crossopterygia

Aquatie, fring-fined, completely

sealed, fishes with dorsal, ventral

and caudal fins

Dentine of the teeth dendritic

in a few forms

Vertebre usually unossified or

incompletely. Notochord largely

persistent and but slightly con-

stricted.

Skull covered by dermal bones

which are seldom sculptured al-

though possessing a similar type

of lateral line system contained

within the s

Lateral foe ee not always

impressions in bones, but similar

in arrangement to the Amphibia.

Parasphenoid largely developed.

The following elements absent

in Amphibia but present in the

Crossopterygia: Supratemporal os-

sicles, ethmoid, hyomandibular,

jugular plates, opercular appara-

tus consisting of opereulum and

subopereulum.

Pineal opening present in at

least one genus.

Air bladder present, with at

times calcified walls

Pelvie girdle composed of rhom-

boid plate of two parts which may

correspond to the ilia.

642

quadrate, pterygoid,

supratemporal, para-

Ethmoid

squamosal,

palantine,

sphenoid, postorbital.

present .in Gymnophiona.

ineal opening present

in most extinet species.

X. No air bladder. Lung an-

lagen on ventral surface of phar-

ynx

XI. Pelvic girdle composed of

osseous ilium, ischium and car-

tilaginous or osseous pubis.

m consisting of hu-

merus, ios ulna, carpals (some-

times cartilaginous), metacarpals

and phalanges.

XIII. Leg composed of femur,

yore fibula, tarsus (sometimes

artilaginous), metatarsus and

XIV. Ribs single, long or

short, heavy or slender, inter- or

intracentral.

Form of body not fish-

like.

XVI. Mesonephros functional

in adult

XVII. External gills slender

and thread-like in the young of

all living and some of the ancient

forms.

THE AMERICAN NATURALIST

(Vou. XLIX

Pectoral fin composed of pro-,

meta—, and mesopterygium, acti-

nosts and fin rays. Broom (2) ha

correlated the elements in the arm

of Sauripteris taylori with those

of the amphibian arm down to the

actinosts, which he regards as car-

pals. The fin rays would repre-

sent phalanges

Pelvic fin composed of basiost

which represents the femur, and

meta- and mesoptergyia and fin

rays.

Ribs double; dorsal, arising in-

dependently of transverse proc-

esses; ventral one an exogenous

process of vertebra, which in the

tail becomes the hemal arches by

fusion of the tips.

Form of body always typically

fish-like.

Mesonephros functional in adult.

xternal gills of young, slender,

thread-like, recalling those of lar-

val salamander.

It will be seen from the above list of comparative struc- .

tures that there are a variety of instances in which the two

groups approach each other. It is, however, to be clearly

kept in mind that the oldest known Amphibia, as indi-

cated by our present knowledge of these forms, are more

like the modern forms of Amphibia than they are like

the ancient types of fishes from which they supposedly

have been derived. In other words, a more complete

knowledge of the Coal Measures Amphibia has not served

to simplify our ideas of amphibian descent in the least,

but rather to confuse them.

All of the early Amphibia have well-developed ambula-

tory or natatory limbs and none of them are fish-like in

No. 586] THE COAL MEASURES AMPHIBIA 643

external form. Many of the representatives of the Am-

phibia in the Coal Measures of North America are highly

specialized and adapted for a variety of modes of life.

One of the most significant factors in the derivation of the

early land vertebrates from the fishes is the question of

the origin of limbs from fins, on which much has been

written from a theoretical standpoint, but nothing has

been seen in the nature of material supporting and defin-

ing the details in the process of evolution. It must be

remembered, however, that the Coal Measure forms are

Amphibia in a high stage of development and when new |

discoveries show us the anatomy of the forms from the

Mississippian, Devonian and possibly the Silurian, then

we shall be in better shape to discuss the question of the

origin of tetra- and pentadactyl limbs.

The evolutional status of the Coal Measures Amphibia

may be briefly stated. They were an assemblage of

forms, highly developed and highly specialized, with few

primitive characters which would tend to ally them di-

rectly with any known group of more primitive verte-

brates. We should expect to find among these Paleozoic

Amphibia some evidence of a transitional type of limb

(11) structure between that of Eusthenopteron (12), or

allied Crossopterygian, on the one hand, and the penta-

dactyl terrestrial vertebrate, on the other. But such evi-

dence is not forthcoming among the material at present

available. Evolutional forces had brought about a wide

diversion of faunas in the Coal Measures, so that the spe-

cies are easily separable into distinct geographic groups,

which are more distinct than are the species of Amphibia

inhabiting the same regions to-day.

The living Amphibia are much more commonly iden-

tical in eastern Ohio and northern Illinois than were the

species of the same order during the Coal Measures.

Species of Necturus, Amblystoma, Rana and Bufo are not

widely different in the two localities referred to; yet the

species of Amphibia during the Coal Measures at Mazon

Creek, Illinois, and Linton, Ohio, are widely distinct.

They are, in fact, more widely distinct than the species of

644 THE AMERICAN NATURALIST (Vor. XLIX

modern Amphibia existing in New York and in Cali-

fornia; for in these states we find modern genera in com-

mon. This wide diversion of structure between the faunas

of Linton and Mazon Creek is not due to difference in age,

since it is almost assured that eit were nearly contem-

-poraneous geologically.

The high degree of specialization attained by various

members of the Coal Measures Amphibia is remarkable.

They had become adapted to nearly every condition of

vertebrate existence, which animals of later times have

adopted. There were strictly aquatic, fossorial, terres-

trial, climbing, crawling, worm-like, snake-like, lizard-like,

crocodile-like, all living ecntomporaneously. The absence

of fish-like forms is noteworthy.

1. Watson, D. M. S. 1912. The Larger Coal Measure es seme Mem.

and Proc, Manchester Lit. and Philos. Soc., LVII, No. 1, pp. pl.

ch R. 1913. On the Structure of the Mandible in a ria

alia. Anat. Anz., Bd. 45, No. 2/3, pp. 73-78, figs

3. Gregory, W. K. 1911. The Limbs of Eryops ed the ig of Paiređ

Limbs from Fins. Science, N. S., 33, No. 848, pp. 508-9.

4. Gregory, yeh K. 1913. The Orois Ancestry 5 the Amphibia.

Science, N. 8., A No. 960, pp. 806-8.

5. Pollard, H. B. 1. On the Anatomy and Phylogenetic Position of

Polypterus, Fak. Po Bd. VI, p. 338; Zool. Jahrb. (Morphol.

Abth.), V, oe 7m 387-428, with pl.

6. Klaatsch. Herm 896, Die Brustflosse der Crossoptyeygiaer. Fest-

schr. fiir ei Bd. I, pp. 259-391, Taf. I-IV.

. Budgett, J. S. 1902. On the Structure of the Larval Polypterus.

Trans. Zool. Soc., London, XVI, Pt. VII, October; Works, pp. 154-

176, pls. X-XIII 1 907.

8. diate: R. L. 1908. The Lateral Line System in Extinct Amphibia.

Journ. Morph., XIX, No. 2, 511-540, 17 figs.

9. Wilder, H. H. 1909. ‘His story of the tities Body. New York, Henry

Holt and Co. Amphibia, pp. 541-2

10. Moodie, R. L. 1915. The Sealed Amphibia of the Coal Measures.

- , pp. 463-464, 1915.

ahi si W. K. 1913. Crossopterygian ape p the Amphibia.

Science, N. S., XXXVII, No. 960, pp. 806-808.

12. Patien. Wan. 1912, Evolution of the Vertebrates and their Kin, p,

391, Fig. 265.

SHORTER ARTICLES AND DISCUSSION

AN ANTICIPATORY MUTATIONIST

WHENEVER any new view gains acceptance it is usually found

to have been partially anticipated in the writings of various au-

thors. The mutation theory is no exception to this rule, and the

purpose of this note is to direct wider attention to the anticipa-

tion of mutationist views by Thomas Meehan. While it is known

to some that Meehan held such views, it is not, I think, generally

realized how consistently and persistently he advocated them

throughout the course of his life.

Thomas Meehan was born near London in 1826, was trained

as a gardener at Kew and afterwards came to America. He

settled in Philadelphia as a horticulturist, became a prolific

writer for agricultural and horticultural journals and finally, in

1891, established Meehan’s Monthly, a journal devoted to garden-

ing. He traveled as far as the Rocky Mountains and Alaska,

Was appointed state botanist for Pennsylvania, and was in 1875

elected a fellow of the American Association for the Advance-

ment of Science. His publications included ‘‘Native Flowers

and Ferns of the United States,’’ in four volumes, and the cur-

rent of his work continued until after his death in November,

1901.

But the phases of his active life which I wish to emphasize here

were (1) his keenness and accuracy as an observer, and (2) his

constant advocacy of discontinuity in the variations of species on

the basis of his own observations, at a time when such views were

by no means popular. Meehan was particularly active in the

Philadelphia Academy of Science, and he contributed in all no

less than 257 papers and notes to the Proceedings of that society

between the years 1862 and 1901.

Although Meehan accepted evolution with his contemporaries

and with Darwin, yet he never lost an opportunity to emphasize

the probable significance of the wide variations which he fre-

quently observed in nature, as opposed to the insensible changes

which were believed to furnish the material for evolution. The

character of his observations as well as the trend of his views,

may be indicated by a few quotations from his writings.

645

646 THE AMERICAN NATURALIST [Vor. XLIX

In a paper entitled ‘‘Change by Gradual Modification not the

Universal Law,’’? he begins as follows:

Natura non facit saltum has been accepted as a grand canon by most

naturalists, and the evident absence of connecting links has been thought

fatal to theories of evolution. My studies in plant life lead me to the

belief that one form will spring from another essentially different, and

without any gradual or insensible modifications uniting them.

He then describes a variation in Halesia tetraptera.2, The new

form had undergone a change in leaf shape and the veins were

rugose. The fiowers, instead of having a narrow tube at the base,

were open, cup-shaped, the pistil wholly enclosed and not ex-

serted. This form produced good seeds and if found wild would

be considered a new species.* He then refers to a variation in

Yucca filamentosa. One plant in hundreds threw out a more

branching panicle which opened two weeks earlier. Its charac-

ters remained and were continued in the progeny. After citing

other eases, Meehan says:

Not only do strikingly distinct forms come suddenly into existence but

once born they reproduce themselves from seed, and act in every respect

as acknowledged species.

He states that a ‘‘weeping’’ variety of the peach came into

existence ‘‘about 30 years ago,’’ and also ‘‘ten years ago a deep

blood-leaved variety appeared.’’ The following quotations from

the same paper will serve further to illustrate his views:

In over a quarter of a century of experience among living plants, I

have rarely known any striking form to have originated by gradual

modification, but always by one great leap. The slight changes are

generally in efforts backwards; as when we sow purple beech seed, some

few are a trifle paler than their parents; there is little or no hesitation

in the forward leap... .

Forms are not only called into existence suddenly, widely different

from their parents, and can reproduce themselves from seed, but they

come into existence without seed agency, and the same or similar form

in widely separated localities, and not all necessarily by seed from one

individual.

Flowers of Viola pedata were sent to him from five localities

in Pennsylvania, New York, Illinois and Indiana, having ‘‘the

two upper petals a beautiful maroon color as in the pansy.’’

1 Proc. Amer, Assoc, Adv. Sci., 1874, B. 7-12, 1875.

2 Now known as Halesia carolina L

3 This fuller account is taken from his later paper, ‘‘ Variation in

Halesia,’’ Proc. Phila. Acad., 1884, 32-33, Figs. 4, 1885.

No. 586] SHORTER ARTICLES AND DISCUSSION 647

Among the conclusions of this paper, which pretty well sums

up his views, we find,

Morphological changes in individual plants are by no means by grad-

ual modification,

and

New and widely distinet species may be suddenly evolved from pre-

existing forms without the intervention of connecting links.

A discussion followed in which Professor Morse, C. V. Riley,

Professor Gill and Asa Gray took part, but although some agreed

that there was no reason why marked changes and gradual modi-

fications should not both play a part in evolution, yet the tend-

ency was rather to look upon the former as sports which were of

little evolutionary significance. Meehan afterwards referred to

this paper as showing that:

New forms “ jumped ” into existence, and frequently these new forms

were diverse from each other, under precisely the same “ environment ”

as far as human knowledge had yet reached, as had been the surround-

ing circumstances of the parent form.

Quotations of a few of Meehan’s other papers, with notes upon

them, will serve to show the range of his ideas and the accuracy

of his observations.

“‘On the Agency of Insects in Obstructing Evolution,’’ Proc.

Phila. Acad., 1872, 235-37, 1872.

‘On Rapid Changes in the History of Species.” Proc. Phila.

Acad., 1884, 142-43, 1885.

‘‘ Persistence in Variations Suddenly Introduced,” Proc. Phila.

Acad., 1885, 116, 1886.

We see that identical forms may appear simultaneously in loealities

widely separated; and, the circles meeting, cover a district in a compara-

tively short time.

‘‘Spicate Inflorescence in Cypripedium insigne,’’ Proc. Phila.

Acad., 1885, 30-32, 1886.

Such a belief [in jumps] would tend materially to remove difficulties

in the way of theories of evolution, that now prevented a full acceptance

thereof. :

‘‘On a White-seeded Variety of the Honey Locust,” Proc. Phila.

Acad., 1885, 404, 1886.

In this paper he describes a tree of Gleditschia triacanthos

growing near Germantown, Pa., which had seeds white instead of

dark olive-brown. They also differed in shape, being nearly

648 THE AMERICAN NATURALIST [Vou. XLIX

orbicular, instead of narrowly ovate, and twice as long as broad.

He remarks in this paper:

When variations occur it is difficult for some to believe that cross-fer-

tilization, a return to some characteristic of an ancient parent, or some

accident of climate or soil had not [been] an agency in the change.

This type of difficulty is still formidable in the minds of some.

In the case he describes such explanations are excluded as in-

applicable,

‘*On Parallelism in Distinct Lines of Evolution,’’ Proc. Phila.

Acad., 1886, 294-95, 1887.

Meehan refers* to a paper given by him at the Troy meeting

of the American Association (1870), ‘‘On the Introduction of

Species by Sudden Leaps.’’ But there is no such paper in the

report, although he gave three other papers dealing respectively

with fasciation, pollination by insects, and the influence of nu-

trition on sex. His last paper, published posthumously, in Proc.

Phila. Acad., 54, 33-36 (1902), is in two parts, dealing with

“‘The Bartram Oak, in Connection with Variation and Hybrid-

ism’’ and ‘‘Observations on the Flowering of Lobelia cardinalis

and Lobelia syphilitica.’’ He may well be described with justice

and accuracy as an anticipator of the mutation theory, not on

theoretical grounds but on the basis of his own keen observations.

Meehan also contributed to the earlier volumes of the AMERI-

CAN NATURALIST, the Botanical Gazette, Torrey Bulletin and

other journals during his active life. One of these® character-

istically sets forth his mutationist views.

; R. RUGGLES @ATES

4 Proc. Phila. Acad., 1885, 30.

5 On the Relation Between Insects and the Forms and Character of Flow-

ers,’’ Bot. Gazette, 16, 176-77, 1891.

“

VOL. XLIX, NO. 587 NOVEMBER, 1915

THE

AMERICAN

NATURALIST

A MONTHLY JOURNAL

Devoted to the Advancement of the Biological Sciences with

Special Reference to the Factors of Evolution

CONTENTS

Page

I. Variability and Amphimixis. Professor L. B. WALTON - - - - - 641

TI. Genetic Studies of Several 2 atest Races of California Dear Mice: Dr.

Francis B. SUMME - - -= - -688

I. Shorter Articles and Discussion: Additional Evid f Mutation in Oenot

Dr. BRADLEY M. Davis; The Value of Inter-annual Correlations: Dr.

J. ARTHUR HARRIS - - ~ - -702

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THE

AMERICAN NATURALIST

VoL. X LIX. November, 1915 No. 587

VARIABILITY AND AMPHIMIXIS

PROFESSOR L. B. WALTON

KENYON COLLEGE

A Comparative Stupy oF THE VARIABILITY IN ZyGo-

SPORES OF Spirogyra inflata (VAUCH.) FORMED BY LATERAL

(CLOSE BREEDING) AND BY ScALARIFORM (CROSS BREEDING)

CONJUGATION, AND ITS BEARING ON THE THEORY OF AMPHI-

MIXIS AND CoRRELATED PROBLEMS

Rt Prenminity onilin a. eas i io cod ae ae ERP ER es en cae 650

1. Introduction

2. Historical b

3. Material `

4. Methods

Ii Conmdorntion Of Touha iocis Aa r ea 658

1. Comparative variability in length of totaal

2. Comparative variability in diameter of zygospor

3. Comparative correlation praia length and a

4. Comparative size of zygospor

Reds UIA OL TOON ooe i ee a keel eee s cea Chenu ee es « 668

1. Comparative oe

2. Comparative

3. Comparative pep RA

4. Origin of amphimixis and of death

LV. A working hypothesis of OVOIULION s. essersi si oron irera 680

Ws I A E T E bop E REE Sass 682

AA I a E a aE O a A A E E O Oh E 80's oes a ae 684

650 THE AMERICAN NATURALIST [ Vou. XLIX

I. PRELIMINARY OUTLINE

1. Introduction

Comparative studies along statistical lines of the results

produced by cross breeding and close breeding afford

data of value bearing on the problem of evolution as well

as the subsidiary problem of the origin of amphimixis.

It has long been assumed (Weismann, ’76) that sex existed

primarily to increase variability and with the further as-

sumption that the variations thus produced were heritable

and accumulated, the differentiation of organisms was

logically explained. As a corollary to such a conclusion

the belief has long been prevalent that the offspring of

organisms produced by cross breeding were as a group

more variable than those produced by close breeding, an

idea which gained further acceptance in connection with

the investigations of Castle (’06), Jennings (’08, ’09, 712,

713) and others interested in problems of genetics. That

there was excellent evidence for exactly an opposite view

and that an analysis of the results presented by the in-

vestigators mentioned above did not bear out the conclu-

sion that variability was increased by cross breeding has

been pointed out by the writer (Walton, ’08, 712, 714) in

some earlier papers.

The importance of arriving at a correct conclusion con-

cerning the part played by hybridization and cross breed-

ing in evolution can not be overestimated. If units are

merely redistributed and form characters resulting in no

actual evolutionary progress, work along Mendelian lines

tends rather to obscure the facts of value toward solving

the problem of the origin of species as well as that of evo-

lutionary control in animal and plant breeding. It is

therefore well to obtain data from as many sources as

possible bearing on the question.

Among the species of Spirogyra, a group of alge be-

longing to the class Conjugate, there are several which

reproduce both by lateral conjugation (Fig. 1, 4) where

No. 587} VARIABILITY AND AMPHIMIXIS 651

the adjacent cells of a single filament unite to form the

zygospore, itself a young individual, and at the same time

by sealariform conjugation (Fig. 1, B) where the cells of

two distinct filaments unite to form the zygospore. Thus

1. FORMATION OF pegs gen IN Spirogyra inflata (Vauch.) by lateral

conjugation (A) close bred from the same filament, and by scalariform conjuga-

n (B) cross bred from two distinct proren z = zygospore.

there is an example of a population producing under

the same environment two groups of individuals, one

by close breeding (lateral conjugation) and the other

by cross breeding (scalariform conjugation), and a com-

parison of the variability by statistical methods should

afford evidence toward the solution of the problem pre-

sented where the offspring have arisen from a common

ancestor as indicated in the material studied.

2. Historical

Much has been published concerning hybridization,

cross and close breeding, amphimixis and parthenogene-

sis, all of which are distinguishable from one another

merely by degree, nevertheless so far as the subject under

652 THE AMERICAN NATURALIST [ Vou. XLIX

discussion is concerned, the conclusions in general have

largely been assumptions based on little or no evidence.

It was Weismann (’76) who was evidently the first to

definitely express the importance of sex in producing

variations, an idea to which he consistently held in his

subsequent papers, while Nägeli (’84), Strasburger

(’84), Hatscheck (’87), Hayeraft (’95), ete., believed like-

wise on theoretical grounds that variability was reduced

by amphimixis.

The first paper presenting tangible evidence upon the

subject was that of Warren (’99) who found that par-

thenogenetically produced Daphnia magna were slightly

more variable as measured by the ‘‘Standard Deviation’’

which had a value of 2.95, than the mothers whose ‘‘Stand-

ard Deviation” was 2.22. The small number utilized,

96 in the first instance and 23 in the second instance, to-

gether with the fact that the mothers represented a se-

lected class, only those Daphnia producing young being

included, did not allow placing much reliance in the re-

sults. Warren (’02) compared 60 parental aphids (Hya-

lopterus trirhodus) and their 368 offspring as well as a

series from 30 aphid grandparents and their 291 grand-

children. The variability was found in a comparison of

grandparents and grandchildren (parthenogenetic) to

have slightly decreased in respect to frontal breadth and

considerably increased in respect to length of right

antenna, but again objections similar to those in the pre-

ceding paper render the conclusion of little value, as

Warren himself observed.

Casteel and Phillips (’03) measured drones and workers

of Apis mellifica, the honey bee, selecting individuals at

random from different colonies, and tabulating classes

and frequencies without, however, a further application

of biometrical methods. The ‘‘range of variability” was

found to be greater in the drones than in the workers.

Lutz (’04) criticized the methods utilized in the paper,

nevertheless.variation as measured by the standard devia-

No. 587] VARIABILITY AND AMPHIMIXIS 653

tion upon calculation by Wright, Lee and Pearson (’07) »

was found greater in the drones by a difference ranging

from 0.22 to 2.63 in respect to all five characters studied

in the single group of 50 Italian workers and 50 drones

of real value for comparative purposes.

Kellogg (’06), in a preliminary paper dealing with

drones and workers of bees and also with female aphids,

concluded that not only was there no evidence that amphi-

mixis produced increased variability, but that it was an

unnecessary factor in the production of Darwinian varia-

tion. The results were summarized as follows:

(a) In all but one of the characteristics studied, the amount of varia-

tion both quantitative and qualitative, is markedly larger among the

drone bees than among the workers, and in the one exceptional char-

acteristic it is no less; (b) no more variation in wing characters is

apparent among drones or workers that have not been exposed in

imaginal condition to the rigors of personal selection than exists among

bees, drones or workers, that have been so exposed; (c) the variation

in wing characters in drone bees reared in worker cells is no greater

than that among individuals reared among drone cells; (d) the varia-

tion among drones hatched from worker laid eggs is "o larger

than that among drones hatched from queen laid eggs.

Eleven ‘‘lots’’ were studied with a small number (No.

3, 48; No. 7, 54; No. 8, 75; No. 9, 26; No. 11, 60) in many

of the ‘‘lots.’’? Even though the probable errors would

have been large and while the material was heterogene-

ous, the facts brought out are of extreme interest, par-

ticularly when considered with the results obtained by

Casteel and Phillips (703).

Wright, Lee and Pearson (’07) made a comparative

biometrical study of 129 queens, 130 drones, and 129

workers taken from a nest of the common wasp Vespa

vulgaris in Charterhouse, England. In connection with

the wing dimensions, the coefficient of variation was found

to be greatest in the worker, less in the drone, and least

in the queen, differing from the bee as noted above where

drones were more variable than workers. The conclu-

sion here of interest was:

654 THE AMERICAN NATURALIST [Von. XLIX

There is no evidence in favor of parthenogenesis resulting in a smaller

variability than sexual reproduction, for if the workers be more, the

queens are less, variable than the drones.

It was suggested by the writers that the large variabilities

of the workers might have resulted from subclasses

among them due to differentiated functions or nurtures.

Castle, Carpenter, Clark, Mast and Barrows (’06) made

observations on the variability and fertility of Drosophila

ampelophila Loew, the small fruit fly, as modified by in-

breeding and cross breeding. They found that ‘‘inbreed-

ing does not affect the variability in number of teeth on

the sex comb of the male, nor the variability in size.’’

While the conclusion is not in accord with an earlier ob-

servation (p. 780) that variability would seem to have

been increased by inbreeding so far as a comparison of

the sixth inbred generation with the sixty-first genera-

tion, the small number utilized in the sixth generation

(40 males in series A-6, B-6, C-6 each) was ground for

the opinion that such a conclusion had little value in com-

parison with data pointing in the reverse direction. If

however we calculate the coefficient of variation for the

length of the tibia, an unfortunate omission on the part

of the writers, it may be noted that the flies produced by

inbreeding are decidedly more variable than those pro-

duced by cross breeding. Data for this conclusion are

given in a subsequent part of the present paper.

Walton (’08) noted that the results of measuring zygo-

spores of Spirogyra indicated that the close-bred indi-

viduals were more variable than the cross-bred individuals

and furthermore that the data went far toward confirm-

ing the theory that sex existed for the purpose of limiting

instead of augmenting variability.

Emerson (710) found that crosses between races of

plants (maize, squash, beans, gourds) differing in size and

shape had the variability of the second (F,) generation

approximately twice as great as the variability of either

parental form or of the first (F,) generation. This he

No. 587] VARIABILITY AND AMPHIMIXIS 655

explained on the basis of the segregation of size and shape

characters. Similar results were obtained by East (711)

for maize and Hayes (’12) for tobacco.

Jennings (’11) extending and summarizing his breed-

ing experiments on Paramecium concluded that

The progeny of conjugants are more variable, in size and in certain

other respects, than the progeny of the equivalent non-conjugants.

Thus conjugation increases variation.

Later (’13) continuing his investigations he stated that

conjugation increased the variability in the rate of repro-

duction. In a subsequent part of the present paper a

somewhat critical review of the data and conclusions

therein noted is presented.

3. Material

In obtaining material early one April for the labora-

tory work of a class in biology, the collection being made

in a small pool resulting from the overflow of a rivulet, a

peculiar species of Spirogyra was noticed in which both

lateral and scalariform conjugation was taking place often

in the same filament. It was at once suggestive that a

comparison of the variability in the two groups of zygo-

spores would present facts of interest in connection with

the effect of close breeding and cross breeding on varia-

bility as well as affording evidence as to the theories of

amphimixis.

The species was first determined as Spirogyra quadrata

(Hass.) but subsequent examination indicated that it

should be classified as Spirogyra inflata (Vauch.).

The material utilized for the measurements was all pro-

cured at one time from a restricted area one or two inches

square on the surface of the pool and included only the

one form of Spirogyra, that alone being present as a mass

3 or 4 inches in diameter. Inasmuch as both lateral and

scalariform conjugation occasionally took place in the

same filament (Fig. 2) a suggestion that two species were

656 THE AMERICAN NATURALIST [ Vou. XLIX

represented can not be made for the filaments are alike in

every characteristic. Of the 500 zygospores observed 45

per cent. were produced by lateral conjugation.

G. 2. Spirogyra inflata (Vauch.) x 800, with both scalariform and lateral

conjugation in the same filament. (a) Zygospore formed by lateral conjugation.

‘ male

lateral conjugation. (e) Cell from which the protoplasm has passed to form the

zygospore in (b). Obj. 1/12, Ocul. 2. Camera lucida drawing.

4. Methods

In considering the variability of large numbers of

microscopic forms, rapid and accurate measurements are

a necessity. Pearl and Dunbar (’03) in measuring Ar-

cella used a camera lucida, marking the dimensions by

means of a needle point, and reducing to microns. Pearl

(°06) adopted a similar method for Chilomonas, using a

magnification of 689.7. Pearl (’07) in measuring Para-

mecium used a 2/3-inch objective and a No.1 ocular. By

means of a camera lucida the points to be measured were

projected on cards, marked, and measured with a vernier

calipers to tenths of millimeters. Multiplying the meas-

urements so obtained by the proper reduction factor found

by calibrating with a stage micrometer, they were re-

uced to microns and recorded. Jennings (’11) at first

measured Paramecium from a slide with an ocular mi-

crometer. Later an Edinger drawing and projection ap-

paratus was used, the projected images of the specimens

on a slide in a flat drop of 25 per cent. glycerine, with-

No. 587] VARIABILITY AND AMPHIMIXIS 657

out a cover glass which by pressure would have caused

distortion, were enlarged to 500 diameters and measured

with a milimeter ruler.

In the present study, the material was preserved in 2

per cent. formalin, the first series of measurements! being

made April 2, while measurements of 358 were completed

before May 16, and the remaining 42 finished Aug. 21 of

the same year. Swelling of the zygospores did not occur

to an appreciable extent, a possible error considered

in a subsequent part of the paper. Using a B. and L.

BB-6 microscope with a No. 1 ocular and a 1/12 oil immer-

sion, a slide with a couple of drops of fluid containing the

material was covered with a No. 2 coverglass, the super-

fluous liquid drawn off by means of a pipette, and the

preparation placed on the mechanical stage. Beginning

at the lower right-hand corner the slide was moved from

left to right and each zygospore presented in the field in

a uniformly horizontal condition, was measured. On

reaching the left margin of the preparation, the slide was

returned to the first position, moved sufficiently toward

the observer so that a new path would be traversed, and

the operation repeated. . Thus the selection was at random

and no zygospore measured twice. The dimensions were

marked on note paper by means of a camera lucida at a

magnification of 1,460 diameters, the two cross lines

representing length (a) and diameter (y) having at the

point of juncture an ‘‘S’’ or an ‘‘L’’ for scalariform or

lateral conjugation. Only those zygospores having defi-

nitely formed membranes were considered.

In the reduction of data, so soon as the projections of

the apparent dimensions were completed, the length of the

lines æ and y were measured with proportional dividers

(Keuffel and Esser No. 441 special) adjusted at the ratio

1,460 to 1,000, thus giving a reading in tenths of microns.

Accurate adjustment was made possible by means of a

1I am indebted to Dr. C. C. W. Judd, of Baltimore, Md., at that time a

senior in Kenyon College, for work in part in obtaining the first series of

measurements.

658 THE AMERICAN NATURALIST [ Vou. XLIX

micrometer screw, on the basis of the equation for similar

triangles;

1,460 mm. : 1,000 mm.— 160 mm.— x mm.: x mm.

where 160 represented the total length of the dividers,

and aw or 65.04 mm. the point of adjustment. Having

checked the adjustment, it only became necessary to note

the size of a given zygospore with the longer legs of the

instrument, then by applying the shorter legs to a milli-

meter scale, to read the result. The various constants

were then computed on the basis of the work of Pearson

and of Elderton by means of a Brunsviga calculating ma-

chine. I am indebted to Dr. H. H. Mitchell of the Uni-

versity of Illinois for checking the mathematical data.

II. ConsmERATION oF RESULTS

The direct results obtained by the statistical methods

employed are here presented. These furnish the basis

for the general discussion and conclusions which follow.

The problems of biology relating to evolution need the

application of statistical methods to studies in genetics.

In no other way will it be possible to clearly demonstrate

the relative efficiency of the different types of variation—

fluctuation, amphimutation, cumulation, ete.—in originat-

ing and maintaining the diverse forms of life that exist.

Similarly the importance or unimportance of small varia-

tions in animal and plant breeding may only thus be ex-

plained. The refinements of curve fitting are by no

means necessary, nevertheless values are thus exhibited

which are presentable in no other way.

1. Comparative Variability in Length of Zygospores

In the frequency distribution for lengths of the two

groups of zygospores (Table I) the class range adopted

was two microns as compared with a range of one micron

in the distribution of diameters. The more extended as

well as the more irregular distribution of lengths of the

lateral zygospores when compared with the scalariform

No. 587] VARIABILITY AND AMPHIMIXIS 659

zygospores is at once suggestive that the group thus

close bred, is the more variable one. It is also of some

interest to note that the empirical range of variation for

the laterally formed zygospores,—with length from 49 m.

to m.,—is considerably greater than in the scalari-

form zygospores with lengths from 47 m. to 79m. While

this is not a measure of statistical variability, it un-

doubtedly has a genetic value.

TABLE I

LENGTH OF 400 ZyGOSPORES FROM Spirogyra o (VaucH.), 200 PRO-

DUCED BY LATERAL CONJUGATION AND 200 PRODUCED BY SCALARIFORM

CONJUGATION, ARRANGED IN CLASSES ACCORDING TO FREQUENCIES.

MAGNITUDES IN 1/10m

Length of zygospores in microns.

L 1 Conjugati Scalariform Conjugation

Frequency Frequency

Class ius

Observed Calculated Observed Calculated

38.0-39.9 1 0.21 0 0.

40.0-41.9 0 0.43 0 0.

42.0—43.9 1 0.84 0 0.

44.0-45.9 8 1.49 0 0.

6.0—47 2. 2.56 3 1.17

8.0-49. 0 4.18 3 3.14

50.0—51.9 4 6.44 6 6.76

52.0-53.9 16 9.34 16 12.65

24.0-55.9 10 42.71 20 19.82

56.0—57.9 26 16.16 25 1

58.0-59.9 11 19.17 25 29.40

60.0-61.9 19 21.15 26 28.41

62.0-63.9 22 21.67 25

-0-65.9 20 21.18 18 18.30

66.0—-67.9 21 18.10 11 12.66

8.0-69.9 13 14.72 7 8.12

70.0-71.9 16 11.08 6 4.90

72.0-73.9 6 2.83

74.0-75.9 1 4.98 1 1.57

76.0-77.9 5 1 .85

78.0-79.9 2 1.66 1 45

80.0-81.9 1 .86 0 0.

82.0-83.9 1 42 0 0.

ToM aa 200 200.06 200 201.04

The general constants for the variability in the length

of the zygospore of the two groups are shown below

(Table II). It may be noted that the mean (M.) or aver-

660 THE AMERICAN NATURALIST [ Vou. XLIX

TABLE II

GENERAL CONSTANTS FOR VARIATION IN LENGTHS OF ZYGOSPORES BASED ON

200 FORMED BY LATERAL AND 200 FORMED By SCALARIFORM CONJUGA-

TION WITH A CLASS RANGE oF 2 MICRONS. STANDARD

DEVIATION IN MICRONS

Constant ase meaner oe

Name Symbol Value Prob. Error Value Prob, Error

PUI OR eh i N. PO ee es yd E ee a ae

Mean ee M. 62.38 +0.1776 60.44 +0.1345

Modes. aaa Mo. ORDES lo orae SOGLO i;e

peer deviation........ e. 7.4460 | +0.1304 5.7474 | +0.1104

at t of variation.... CV. 11.9364 | +0.0330 9.5093 | +0.0330

Bkewness. 65] 3 oe Sk. —.0356 | +0.0468 .1589 .0464

age length of the zygospores produced by lateral con-

jugation exceeds the mean of the scalariform conjugants

by 1.94 microns, while the probable error for the first

constant is +.1776 and for the second constant + .1345.

The difference is therefore a significant one so far as the

present material is concerned.

It is in the comparison of the standard deviations (c)

and the coefficients of variation (C. V.) that the results of

most interest appear, however. The former constant in

lateral conjugation has a value of 1.6986 in excess of the

same constant in scalariform conjugation, or relatively

29 per cent. This is more than thirteen times the prob-

able error. In the coefficient of variation, an abstract

number permitting comparison with similar constants in

other organisms, the results indicate that the variability

in lateral conjugation exceeds that occurring in scalari-

form conjugation by 2.4271 or relatively 26 per cent., a

result corroborated by the distribution of the diameters.

The probable errors are sufficiently small in comparison

with the differences noted, that they may be considered

negligible.

Skewness is negative in the curve for lateral conjuga-

tion, the mean being on the left side of the mode, but its

value is less than the probable error. In the curve for

scalariform conjugation skewness is positive with a value

No. 587] VARIABILITY AND AMPHIMIXIS 661

slightly more than three times the probable error. There-

fore the differences of the two constants appear to have

no particular value so far as the present material is

concerned.

The analytical constants (Table III) necessary for the

TABLE III

ANALYTICAL CONSTANTS FOR VARIATION IN LENGTH OF ZYGOSPORES FORMED

BY LATERAL SCALARIFORM CONJUGATION,

Scalariform

Constant Conjugation Conjugation

Wee ee T 13.8606 8.2583

Whe oo 8 ey eto tee — 3.9024 9.2989

Meee ver eeks wis Ces T 606.8690 245.0223

De ae ol epi NaS FeS .0057 1535

MS Po oe wei ee Ge aks .0756 3918

Bee ee O 3.1068 3.5928

Meals E des .0219 .1654

fitting of the curves indicate that type IV curves may be

used for each method of conjugation. In lateral con-

jugation the equation is

a” en 9.5995 tan —1(z/29,2687)

= : TAE SRA OR -—-9.« n —1( 2/29.

= 10.842 (1 + aage) Xe

and in scalariform conjugation similarly the equation is

—11,0945

ial a —8.9889 tan —1(«/11.50)

y= 5.0014( 1+ 555 ) Xe

while the frequency polygons and the fitted curves (Figs.

3, 4, and 5) illustrate the conditions diagramatically.

2 The following formule as the basis of the probable errors, may be noted:

PEs. = 67449 £ ha Vi + 3(8k.)2.

or)

THE AMERICAN NATURALIST [ Vou. XLIX

EU SRRY

r—

-x

P<]

e—

A p

r Pa \

4 A fi

: Z AL

\ ~

37 39 W 43 YS 47 49 50 53 55 57 59 6i 6&3 OF 67 OF V B 75 717 17 BI 3 bs 7 89

a 3. FREQUENCY POLYGON AND FITTED CURVE R VARIATION IN LENGTH

ZYG ORES PRODUCED BY LATERAL CONJUGATION peirar IN gree

pet (Vauch.).

JAM

3 ELS

4 I SESE

E F A

bae

w | HE N

: J \

6 f à

is N

2 JH |

o A

N B u B YS 47 4q SI 5> 55 57 59 GI 63 GS 67 CF U 13 75 77 79 81 83 £5

Fic. 4. FREQUENCY POLYGON AND FITTED CURVE FOR VARIATION IN LENGTH OF

ZYGOSPORES PRODUCED BY SCALARIFORM CONJUGATION (CROSS BREEDING) IN Spiro-

gyra inflata (Vauch.).

2. Comparative Variability in the Diameter of the

Zygospores

The class range adopted in the frequency distribution

for diameters (Table IV) of the two groups of zygo-

No. 587] VARIABILITY AND AMPHIMIXIS 663

74 a8

7 é N

PY N

Fe a N

to j fi N \

7 x

fie \

ww ig K

f Z i A

3 "i N

T L 4 2 %

£ É £ a

(5 A d w

+ N,

: 47 TL

a My

> ae Fi A SN -

e d S ne

Pre a — ere

317 34 W u3 y5 yt Ye St 53 55 57 59 68 be 65°60 8 ENMANE GA

Fie. 5. CE a OF FITTED CURVES FOR Ks conan IN LENGTH OF ZyGo-

SPORES PRODUCED BY LATERAL CONJUGATION (CLOSE BREEDING) AND BY SCALARI-

FOR anne oxsuaamioN (CROSS an G) IN spirogvra iniata ea, Lateral

eonin

Scalarifor

spores was one micron, measurement being made at the

maximum diameter. An inspection of the distribution

shows at once the greater concentration of the variates

TABLE IV

DIAMETERS OF 400 ZYGOSPORES FROM Spirogyra quadrata (Haas.) 200 PRO-

DUCED BY LATERAL CONJUGATION AND 200 PRODUCED BY SCALARIFORM

CONJUGATION, ARRANGED IN CLASSES ACCORDING TO FREQUENCIES.

MAGNITUDES IN

DIAMETER OF ZYGOSPORES IN MICRONS.

Lateral Conjugation Scalariform Conjugation

Class Frequency Class Frequency

23.0-—23.9 0 3.0-23 x

24.0-24.9 3 24.0-24.9 0

25.0—25.9 4 25.0-25.9 3

26.0-26.9 12 26.0-26.9 9

27.0—27.9 22 27.0-27.9 13

28.0-28.9 44 28.0-28.9 38

29.0-—29.9 40 29.0-29.9 46

30.0-30.9 25 30.0-30.9 46

31.0-31.9 16 31.0-31.9 30

32.0-32.9 15 2.0-32.

33.0-33.9 10 33.0-33.9 4

0-34 9 34.0-34.9 1

To 200 ToM. es 200

664

TABLE V

THE AMERICAN NATURALIST

[Vou. XLIX

GENERAL CONSTANTS FOR VARIATION IN re eect: OF ZYGOSPORES BASED

200 FORM By SCALARIFORM

ON FORMED BY

2 LATERAL AND

CONJUGATION WITH A CLASS RANGE OF 1 MICRON

Lateral Conjugation,

Scalariform Conjugation,

Cross Bı reedi ng

POORINON ~ e opo Breeding |

Name Symbol Value | Prov. Error | Value Prob. Error

Taa ac A PEP URN N. C e eaan | Fao s

on TEE Sie aka oe BE Ce e M. | 29.66 +.1049 29.725 +.0801

bas ee ye Seas, Dts BOL EOS fi kins Ga | > eR IOO be a ec es ok

adad deviation........ o. | 2.1980 | =.0688 | 1.6796 | +.0583

icy of variation. CY | 7.5376| +.0339 5.7471 | +.0338

a egies Waa aes Sk. | .2285 | +.0505 | —.1480| +.0566

mamma core

uy a

ry |

o zk >

4 r 7

I \

36 > ‘

32 h À

i | Ree

2S f N \

I \

l o

24 j k

d \

90 a | X \

i | N \

z \

\6 f- y

f | Yh

12 bf ae

i E | y%

+ P=

7 A

4 s \

E E ‘

o Pog ‘

a a Ae ee

GRAM SHOW

7 WING FREQU

F ZYGOSPORES IN Spirogyra subse (Vauch.

sera FORM Gouieaies:

THE

DIAMETER

Coxsvoatiox (INBREEDING) AND

NG e uni

Sth Pore breeding),

abscissa is one mikro

cy POLYGON FOR THE VARIATION IN

) PRODU LATERAL

conjugation (cross breeding)

No. 587] VARIABILITY AND AMPHIMIXIS 665

in sealariform conjugation, and thus their smaller varia-

ility. In considering the general constants of varia-

bility (Table V) based on the diameters it is to be noted

that the means (M.) do not differ, as was found when

considering length. The standard deviation (e) and

the coefficient of variation (C. V.) once more demonstrate

the greater variability of the laterally formed zygospores.

The values of the constants for skewness (Sk.) are not

sufficient, however, when considered with the probable

error, to be of importance. The frequency polygons

(Fig. 6) illustrate conditions, although no curves have

been fitted.

3. Comparative Correlation of Length and Diameter

In view of the results obtained in a consideration of the

variability, it will be of some interest to ascertain whether

TABLE VI

CORRELATION BETWEEN LENGTH AND DIAMETER OF 200 ZyGOSPORES OF

Spirogyra inflata ei ) PRODUCED BY LATERAL CONJUGATION

1 oO |

Pam gg] 3] 2) 8/8] 2] 8) ai el 3] 3

oo Se: 21 ejej jd dj 4] dj d| d| 4] | Totas

Length ~ | 8) 8) 8) 8) R R| 3 5/8) 8) 8

| |

38.0-39.9 Lie ES Bien Bias Gone OSE 1

40.0-41.9 Ber tie ee Ree ee o 0

42.0-43.9 eee) ee bb ede dee. 1

44,0-45.9 ee e eg eed ae a 3

46.0-47.9 He oe a a a Cea eo ee 2

48.0-49.9 | BREN oes ae aN Bel ot BS 0

50.0-51. Petri. 1 TE eats FO ee

52.0-53.9 1| 2) S| 21 8/2. 2 T.J] 16

0-55.9 ple a a 10

COSTS E R (eRe é 1} 4| 6| 5| 3| 2| eS eer

58.0-59.9 akaa Cel Si 402) Sina i ek

.0-61.9 ee pat ilei 6) ailal

62.0-63.9 fe ten eg 7.6 4l.. Bl Rd 2

64.0-65.9 1 Bike 2| 5| 3| 1) 3) 2| 2/1] 20

66.0-67.9 ee Creer ee ea i aTa ii a

68.0-69.9 S a 44242

WoT e ae eg f 2] 1) 8] 1] 3] 1]...1 2] 16

72.0-73.9 geste gee Eoi 87 iaia’ &

74.0-75.9 ee Leads de a Cs Oe

6.0-77.9 Ppa Ree ids LAL Se BL les: 5

78.0-79.9 Baer cide! Theses Fe ae Cee 2

.0-81.9 ceefece cesleseens tee | do pid zà

82.0-83.9 eepepebepepepepep Heere] 1

— tele oo | 3 | 4 [12/22 |44|40|25|16|15|10| 9 | 200

666 THE AMERICAN NATURALIST [ Vou. XLIX

the inbred zygospores produced by lateral conjugation

will be more or less correlated than the cross bred zygo-

spores produced by scalariform conjugation so far as

length and diameter are concerned.

The value of perfect correlation as measured by the

constant (7) is unity, while absence of correlation allows

the value to become zero. Length is taken as the subject

class (y) and diameter (x) as the relative class in the

accompanying tables (VI and VII).

TABLE VII e

CORRELATION BETWEEN LENGTH AND DIAMETER OF 200 ZYGOSPORES OF

Spirogyra inflata (VAUCH.) PRODUCED BY SCALARIFORM CONJUGATION

Diameter (2/Sigieigigigig¢iaiaisl¢

v N N nN N AN o> | N r] c] oO | V oD

m AEE hE ra i a k PIPE E

Length E E E EE AE E

38.0-39.9 Pas o ai f 0

40.0-41.9 ae es r E A ES 0

42.0-43.9 e As ee L. 0

44.0-45.9 E Cee, oe a ae BO ee 0

46.0-47.9 Pe ee o ge eke sles ee 3

0-49.9 Wot Se A ee 3

0-51. tel eb at ge 6

52.0-53.9 1 et 2| 5| 4| 2... 16

0-55. EO) ol 6) @) ab is i 20

56.0-57.9 Piet a6) 8) Bl al ok 25

58.0-59.9 Jal Jal blis |.. J1 2

.0-61.9 Meh ry er eee 4 26

62.0-63.9 1 siell 3| 6...) 1 25

.0-65.9 LiOt 8) 4 eal gis 18

66.0-67.9 are aera eee 11

68.0-69.9 1L Sl et 1) abe 7

70.0-71.9 iali. ees ae 6

72.0-73.9 ALT AS be. 6

74.0-75.9 fen eek eL 1

76.0-77.9 es T 1

78.0-79.9 1 ne 1

Woas <. s: 1/0/13) 9 |13'38|46/46/30| 9 | 4| 1! 200

While one might infer that the longer a zygospore the

greater the diameter, such a condition is not apparent by

mere inspection of the tables in either case. Conse-

quently on solving the equations we are prepared to find

that the coefficients have an extremely low value in each

group.

No. 587] VARIABILITY AND AMPHIMIXIS 667

Lateral Conjugation ... 6.0.0.0... 60005 r = .1894 + .0460

Scalariform Conjugation ........... r= .0934 + .0473

Although in lateral conjugation the value is more than

four times the probable error, one is scarcely prepared to

state that there is greater correlation between characters

in close breeding than in cross breeding on the basis of

the data noted above. When considered with the results

presented in Table XII, the conclusion seems fully estab-

lished, however.

4. Comparative Size of Zygospores

The term ‘‘size’’ as noted in the subsequent discussion

is open to various interpretations dependent as to

whether length, diameter or volume is being considered,

a condition which to some extent complicates the inter-

pretation of size characters among multicellular organ-

isms which are in general dependent on the number

rather than the dimensions of the component cells.

Those zygospores produced by lateral conjugation

(close bred), so far as the present material is concerned,

have an average length considerably exceeding those

produced by scalariform conjugation (cross bred) while

the diameter is approximately the same. This is illus-

trated in Table VIII.

TABLE VIII

COMPARATIVE LENGTH, DIAMETER AND VOLUME OF ZYGOSPORES PRODUCED

)

BY LATERAL (CLOSE BRED) AND By SCALARIFORM (Cross BRED

CONJUGATION

Method Produced | Mean Length | Mean Diameter | Mean Volume

62.380 m. +.178) 29.660 m. +.105| 28,733 cub. m.

Lateral conjugation........

60.440 m. +. 135, 29.725 m. +.080 27,972 cub. m.

Scalariform conjugation. ....

Differences RENNY lateral |

CODIUGAOR asaos erin +1.940 m. | —.070 m. | +771 cub. m.

Consequently, here, the average zygospore produced by

lateral conjugation has a greater volume than that pro-

duced by scalariform conjugation. Utilizing the formula

668 THE AMERICAN NATURALIST [ Vou. XLIX

for computing the volume of a prolate spheroid (V =

1/6zld?) the difference is 771 cubic m. in favor of the

former, although relatively this approximates only 3 per

cent.

A question of some interest is at once suggested,

namely, the possibilities for nourishment and develop-

ment in cells of large and of small volume, inasmuch as

one with a maximum volume has relatively less surface

through which nourishment may be obtained. Thus

growth may be retarded.

III. Discussion or RESULTS

The close bred forms on the basis of the characters

studied in the given population have been found more

variable as to both length and diameter, more highly

correlated, and larger taking into consideration length

and volume. The value of the conclusions in their ap-

plication to the solution of problems of evolution is de-

pendent on the logical application of cause and result as

well as the methods of the investigation.

That the two groups of zygospores are comparatively

close bred and cross bred will scarcely be denied, par-

ticularly when it is remembered that in lateral conjuga-

tion nearly all adjacent pairs of cells in a filament had

united in the process, each pair producing a zygospore,

all pairs having originated from the same cell. With

the material taken from a part of a mass a few cen-

timeters square, a sample of a whole population has been

utilized, and from what is known of the reproduction of

Spirogyra, it may be assumed with reasonable certainty

that the entire mass had its origin from zygospores pro-

duced in a few filaments the preceding year. With prac-

tically all zygospores measured in each filament, the

eriticism that isolated zygospores of mixed descent were

studied, and that greater variability would be expected in

those produced by lateral conjugation, loses its force.

Furthermore it is believed that all investigations thus far

No. 587] VARIABILITY AND AMPHIMIXIS 669

made, upon analysis support the direct conclusions which

follow.

It may be objected that cells of mature filaments

originating from the zygospores should have been studied.

While this would have been of interest, the zygospores

themselves are individuals in the cycle of development,

and the differences as represented in the groups chosen

can not be said to have less value than data from another

part of the life cycle.

The possibility of the results being affected by the

swelling of zygospores due to the 2 per cent. formalin

used in preservation, became apparent when other duties

prevented measurements within the anticipated time.

The first series of 358 zygospores was measured between

April 2 and May 16, while the remaining 42 were meas-

ured between August 17 and 21. The question seemed

an important one, and in order to test the extent of such

an error if present, the average diameter of the last lot

was compared with that of the first lot, the values being

29.15 m. and 29.08 m., the difference of 0.07 m. being well

within the limits of the probable error. The 42 zygo-

spores measured August 17—21 happened to consist of an

equal number of lateral and scalariform individuals,

which would thus tend to eliminate an error should it

have occurred. Consequently the use of the formalin

does not appear to have affected the results.

Some evidence has been presented that new phylo-

genetic characters are more variable than older char-

acters. Thus if lateral conjugation was a recent acquisi-

tion the greater variabitiy might have been expected.

Pearl and Clawson (’07) found a higher variation in the

great chela of the crayfish, Camburus propinquus Girard,

than in the protopodites of the 2 and 3 legs, nevertheless

they preferred to attribute the result to ontogenetic

rather than to phylogenetic factors. MacDougall, Vail

and Shull (’07) stated that

the greater variability of P new characters as compared

with older ones .. . is confirme ip

670 THE AMERICAN NATURALIST [ Vou. XLIR

The conclusion is open to objection inasmuch as they

were comparing a hybrid with a single parental type and

in general the greater variability would be expected.

Consequently even admitting that lateral conjugation has

been a more recent development than scalariform con-

jugation, it would not be demonstrated that an error had

thus arisen.

1. Comparative Variability

Within the limits of the characters studied so far as

the present material is concerned, it is evident that the

zygospores produced by close breeding are more variable

than those produced by cross breeding. While it tis

another proposition to extend the conclusion and insist

that organisms produced asexually, by pure lines, or by

close breeding, are more variable than those produced

sexually or by cross breeding, it would seem that the facts

strongly support such a conclusion and in connection with

the evidence afforded by the investigations of Warren,

Casteel and Phillips, Kellogg, and Wright, Lee and Pear-

son, it certainly may be denied that amphimixis or cross

breeding as compared with other types actually produces

variations, as has long been the prevalent belief.

The question here of particular interest, however, is

that of the excess type of variability represented in

Spirogyra. Inasmuch as the material was homogeneous

in every way, it may be asserted that the greater vari-

ability exhibited by the close-bred forms is not fluctu-

ability due to environment. It is also evident that, theo-

retically, cross breeding produces a greater number of

combinations than inbreeding, nevertheless that the vari-

ability thus resulting is overwhelmed by that of another

type in nature, is clear from the results noted in the pre-

ceding pages. An excellent demonstration of such con-

dition is obtained by recalculating constants obtained by

Hayes (712) as shown in the accompanying table (Table

TX) based on data obtained in connection with the breed-

ing of Nicotiana tabacum.

No. 587] VARIABILITY AND AMPHIMIXIS 671

TABLE IX

COMPARISON OF a ois oF Nicotiana tabacum IN COMBINED PARENTAL

Types (No. 3 8) WITH VARIABILITY IN SEPARATE PARENTAL TYPES

(No. 1, 2, 6 AND a IN THE First HYBRID oe. (No. 4 AND 9)

AND IN THE SECOND HYBRID GENERATIONS (No. 5 AND 10). No. 3 AND 8

CALCULATED FROM DATA By HAYES IN TABLES NOTED. OTHER CONSTANTS

S GIVEN BY HAYES

No. Table Type | Character Ss. D; | E | Cc. Vv. E

1 AV 401 | Number of leaves 0.96 | +.037| 5.00 |+.189

21 XVI 403 | 1.49 |+.058| 5.27 | +.578

BRR pe | “ . 4.70 |+.129| 19.55 | 4.129

di 2 4 n 1.30 | +.056| 5.51 |+.215

& i XVIII ede Oey la os 2.24 | +.103| 9.40 |+.551

6 XV pet | Height of plant | 3.85 |+.150! 7.00 |+.150

7 XVI es ™ .55 |4.177| 5.98 |+.177

8 | XV-XVI 1014-408 s x 11.31 14.311] 17.35 |+.312

9| XVII 403 X ale oe 4.54 |+.177! 6.41 | +.249

10 | XVIII “403x401 — 1-F,| e a 7.22 | +.333 13.60 | +.333

Here the constants of No. 3 and No. 8 have been ob-

tained by combining the two parental types (401 and 403)

both for the number of leaves and the height of the plant,

and it may be noted that the coefficient of variation has

dropped from 19.55 to 9.40 in the one case and from 17.35

to 13.60 in the other case. Thus variability as measured

statistically has decreased. Those who have advo-

cated an increased variability as the result of hybridiza-

tion are correct when comparison is made of the F, gen-

eration with the F, generation or with a single parental

generation. They are not correct, however, in making a

general statement that cross breeding increases varia-

bility since the variability of the group composed of both

parental types must be considered and upon so doing, it

may normally be found that there has actually been a

decrease in variability.

The possibility exists however that the variability will

appear to have been increased when forms having the

same phenotype but different genotypes are bred together.

Such a condition may be illustrated by the two strains of

white sweet peas crossed by Bateson which produced

purple flowers in the first (F,) generation, and purple,

™~

672 THE AMERICAN NATURALIST [Vou. XLIX

pink, mixed and white flowers in the second (F,) genera-

tion. New combinations had arisen, but only as an ex-

pression of that which already existed in the phenotypes,

for there is no evidence of an increase in unit characters

nor was there an actual increase in variability.

There are only three papers of a statistical nature in

which it has seriously been asserted that cross-bred forms

or conjugating forms produced greater variability than

resulted in close-bred forms or non-conjugating forms.

The first is that of Castle, Carpenter, Clark, Mast and

Barrows (’06) based on a series of observations as to the

effect of cross breeding and close breeding on the varia-

bility and fertility of the small fruit fly Drosophila

ampelophila Loew. In conclusion it was stated that

‘inbreeding did not affect the variability in the number

of teeth of the sex comb of the male, nor the variability

in size,’’ the first opinion resulting from the value of the

coefficient of variation in the number of tibial spines, the

second from the standard deviation in the length of the

tibia. In the former case the data certainly do not

permit a clear conclusion one way or the other. In the

second case, however, if the value of the coefficient of

variation is computed for the length of the tibia—which,

strange to say, was not done in the original investiga-

tion—and thus allowance made for the greater length of

TABLE X

ILLUSTRATING COMPARATIVE VARIABILITY OF CROSS BRED AND INBRED FORMS

OF Drosophila AFTER COMPUTING THE VALUE OF THE COEFFICIENT OF

VARIATION FOR THE LENGTH OF TIBIA FROM DATA BY CASTLE

AND OTHERS , i

S.D. = Standard Deviation. C.V. = Coefficient of Variation.

Group Spines of Sex Comb Length of Tibia

Generation — cs Qv so ee a

Cross bred (X-1)...... 100 | 1.749.083 | 16.23 | 1.461+.070 | 3.531 +.168

Inbred (M-31)........ 100 i 568. plied | 15.51 | 1.723 +.082 | 4.452 +.212

Inbred (N-30)......... 100 | 1.684+.0 80 | 17.38 | 2.842 +.136 | 8.167 +.389

Inbred (A-61)......... 100 | 1.857+.089 17.60 | 2.041 = 097 | 5.245 +.250

No. 587] VARIABILITY AND AMPHIMIXIS 673

tibia in the cross-bred forms (Table X) the average

variability of the three inbred groups is 68 per cent.

greater than that of the cross-bred group. Consequently,

the results decidedly support the facts in the present

paper.

The remaining papers are those of Jennings (711 and

713) in a study of Paramecium. In the first paper the

breeding experiments are summarized as follows:

The progeny of conjugants are more variable, in size and in certain

other respects, than the progeny of the equivalent non-conjugants.

Thus conjugation increases variation.

It seems difficult to account for this conclusion if one

subjects the data to a critical review. So far as a ‘‘pure

race’’ is concerned the non-conjugants and their progeny

were decidedly more variable than the conjugants and

their progeny (Table 28, p. 94), although the small number

utilized March 31 for the statistical work (42 and 34) is

not sufficient to justify a conclusion in either direction.

Even in a ‘‘wild eulture’’ (Table 32, p. 99) the evidence

is too conflicting to justify a definite expression of

opinion. Of the seven comparisons here made among

the progeny, five showed an excess variability for the

conjugants, but in only one case did the difference exceed

three times the probable error, while two cases showed

an excess variability for the non-conjugants, the differ-

ence in one case exceeding twice the probable error.

Data from numbers so small (22-95) can scarcely be con-

sidered reliable. The comparison of the variability of

‘all pairs’’ and ‘‘all unpairs’’ on June 22 and June 23

denotes an excess variability for those completing con-

jugation at the beginning of the experiment.

In the second paper Jennings concluded (p. 363) that

conjugation increased the variation in the rate of repro-

duction. The variation was increased, but the explana-

tion of such increase seems comparatively simple when

it is noted that among the conjugants there were many

with a low rate of fission with death occurring. As com-

674 THE AMERICAN NATURALIST [Vou. XLIX

pared with the more normal rate of fission among non-

conjugants, this could result in nothing but an increased

variability, having, however, no bearing on the question at

issue.

At the present time, therefore, it would seem that the

preponderance of evidence demonstrates that variability

is decreased in cross breeding.

2. Comparative Size

The zygospores produced by close breeding have a

mean length of 62.38 ». + .18 ». with a mean diameter

of 29.66 ». + 10 p. and those produced by cross breeding

have a mean length of 60.44 » + .13 m. with a mean

diameter of 29.725 ». + .08 a. Thus so far as length is

concerned the close bred zygospores are relatively 3.2

per cent. larger and although slightly smaller in diameter,

when volume is considered by utilizing the formula

(V =4Anld*) the close bred forms are also 2.8 per cent.

larger. Since these results are not in accord with the

general belief that cross fertilization increases size and

vigor, terms which have a diverse usage, however, it will

be well to consider other evidence bearing on the problem

with a view of attempting an explanation which may meet

the conditions imposed.

Pearl (’07) in studying the conjugation of Paramecium

with particular reference to assortative mating, notes

that ‘‘the conjugant individuals when compared with the

non-conjugant, are shorter and narrower’’ and stated in

accordance with Calkins (’02) that the reduction in size

was quite probably dependent on functional changes con-

nected with reproduction. In Spirogyra, however, both

the close-bred and the cross-bred zygospores go through

similar reproductive processes in consequence of which

one may question the theory that the method of conjuga-

tion is the decisive factor in bringing about the result

even in Paramecium.

Jennings (711) in comparing the size of conjugant and

non-conjugant Paramecium stated that

No. 587] VARIABILITY AND AMPHIMIXIS 675

The progeny of conjugants . . . were a little larger than the progeny

of non-conjugants and the difference appears to be significant.

This conclusion was based on measurements of length and

diameter, the volume not being computed. When this is

done as shown in the accompanying table (Table XI) by

TABLE XI

COMPARISON IN SIZE OF CONJUGANT AND NON-CONJUGANT ForMs oF Para-

mecium aurelia AND THEIR PROGENY BASED ON VOLUME

(V =1/6,ld2)r FROM LENGTH AND DIAMETER MEASURE-

MENTS BY JENNINGS, 1911

| |

Experiment Non-conjugants and Progeny | Conjugants and Progeny | Non R

| -|

Diam. | Volume | | Volume | Exceed the

Date, — Length | Diam. | Conjugants

Culture No. Mi- Cub. | No. Cub. 1

1908 rons | crons | Micro ons | panos RS Microns ume

| Nf» |Mar. 31| 34| 144.59|34 87, sil 48 136.95) 35.52 | 90,471 — 2,953

Table |Apr. 10| 65) 137.97/44 139,859 61 148.20 42.30 |138,844 + 1,015

28 |Apr. 20/103) 156.48) 43.82|157, 327 108, | 160. 85 42.04 148 „849 + 8,478

C: |Sept. 16/110} 132.18] ? ? h 38 121.91 ? C hey

Table |Sept. 18| 70| 116.17|31.20| 59,211, 15 1 31.20 | 65,241 — 6,030

29 |Sept. 26| 52| 122.15/34.81) 77,500 ay 112.36| 29.50 51,198 + 26,302

g (Sept. 27/118) 135.35] ? ? F 174| 118.28| ? rot

Table (Sept. 29| 10, 156.40/49.60/201,465| 6 135.33 36 | 91,833 +109,633

30 | re

œo

kz]

per rou on ee

e a)

k Sept. 12/100/ 140.20 Re ? =|336) 129. | ?

d | Table |Oct. 28| 10 136 7.60 100 673 39 131.38) 35.49 | 86,644| + 14,029

31 jOct. 30| 28 123.71| Hi 14, 75 °497| 25| 128.16) 36.32 88,520| — 13,023

utilizing the formula V = 1/6z/d?, thus allowing for slight

decreases in diameters, the facts present a different in-

terpretation.

Three (a, b, c) of the four experiments dealing with a

‘‘pure race’’ of P. aurelia indicate that the progeny of

the non-conjugants become larger, even when as a group

they are smaller (a, b?) at the beginning of the experi-

ment. While the fourth (d) indicates a reverse condi-

tion so far as the measurements of October 30 are con-

cerned, the measurements of the sixth and seventh genera-

tions immediately preceding, demonstrate that the non-

conjugants were larger. The result on October 30, where

the non-conjugants became smaller, may have depended

676 THE AMERICAN NATURALIST [ Vou. XLIX

on the elimination suggested by ‘‘all existing progeny.’’

The extraordinary diminution in length (140 ». to 123.71

p.) Suggests some disturbing factor of metabolism.

The results of the experiment with a ‘‘wild culture’?

where progeny of ‘‘unpaired’’ and ‘‘paired’’ forms of P.

caudatum (?) were considered, again suggested to Jen-

nings the greater size of the progeny of the paired indi-

viduals (conjugants), a condition which was particularly

evident in the first generation. But it must be noted that

the disturbance of the function of conjugation in ‘‘un-

pairing’’ may have produced the result. The progeny of

the ‘‘unpairs’’ were relatively becoming larger from the

first to the seventh generation. These facts taken to-

gether with the absence of measurements of mean diam-

eters by which to caleulate the mean volumes, suggest

that such a conclusion based on that part of the work

could not be accepted, and that the data strongly support

the proposition directly contrary to Jennings that the

progeny of conjugants tend to become smaller than the

progeny of non-conjugants although the latter may be

larger directly after conjugation as a result of slower

fission. Thus the evidence from various sources,

although incomplete, suggests that cross-bred unicellular

organisms are smaller than close-bred forms.

Among multicellular organisms however it has long

been recognized that hybrids usually grew to a larger

size than either parental form, as has been observed by

Kohlreuter (’63), Knight (’99), Gartner (’49), as well

as Darwin, Mendel and others, although the cause of the

increased growth has been purely conjectural. It is quite

evident that the result is due to either the increased num-

ber of cells, a suggestion made by East, to the increased

size of the cells, or to the combination of both conditions.

The question immediately arises as to the cause of the

increased size and vigor among cross-bred multicellular

organisms when the evidence indicates that cross-bred

unicellular organisms are smaller instead of larger.

No. 587] VARIABILITY AND AMPHIMIXIS 677

Some investigations in progress? suggest an answer

meeting the conditions, although more than a provisional

opinion may as yet not be ventured. This is to the effect

that the cells of cross-bred multicellular organisms are

actually smaller than the cells of pure line or inbred

organisms, and that the more rapid division is a function

of the greater ratio surface has to volume in a small cell

with the better opportunity this afforded for an increased

metabolism.

The increase of size in plant and animal forms to the

physiological limit has great importance for the future

of agriculture and stock breeding, but many subsidiary

problems must be solved before practical results are at-

tained in this direction. The relative rate of growth,

number and size of the constituent cells of pure line and

of hybrid individuals is one of the problems.

3. Comparative Correlation Resulting from Close

Breeding and Cross Breeding

‘The close-bred zygospores are more correlated as to

length and diameter than the cross-bred zygospores, but

since the difference only slightly exceeds twice the prob-

able error, the value of the result here is questionable.

Considering other investigations (Table XII), it may be

noted that the group containing close-bred, asexual or

non-conjugating organisms, is more highly correlated in

respect to characters than the group consisting of cross-

bred, sexual, or conjugating organisms, although two

exceptions, No. 12 and No. 14, are presented. An in-

teresting fact, although possibly only a coincidence, is

that cross bred zygospores of Spirogyra and of conjugat-

ing Paramecium have approximately only one half the

correlation exhibited by close bred er ECeporee of Spiro-

gyra and by non-conjugating Parameen

The explanation of the conclusion here’ reached, that

the value of a character ‘‘x’’ in cross-bred forms does

not have the same tendency t change that the value of a

8 Walton (’14).

[ Vou, XLIX

678 THE AMERICAN NATURALIST

TABLE XII

COMPARATIVE CORRELATION OF CHARACTERS IN CROSS-BRED AND CLOSE-BRED

ORGANISMS INCLUDING CONJUGANT AND NON-CONJUGANT Paramecium,

PARTHENOGENETIC AND SEXUALLY PRODUCED WASPS

Organism Authority pes naa Type of Development ‘oo

Paramecium | Pearl, ’07 Length and oa Ser. A| .589-+.03

e , a diameter. .278 +.04

Drosophila Barrows, ’06 | Number of Close bred, fer. A-61. 469 +.05

= _ s spines and Ser. M-31. 8+.05

Sa P "a length of F ie r. N-30. | .708+.03

aa s: " tibia. Cross bred, Ser. X-1. 41+.07

Nicotiana Hayes, ’12 Number of Close bred, aia 2 368 +.05

ph = T leaves and s 631 +.03

e i ps height. Cross bred, 403 x01. 406 +.05

ts 5 Length and Close bred, No. 4 +.0

? A pa breadth of No. os 497 +.04

1 A = ie eaf. — — 403 X401. | .818+.02

Vespa vulgaris ime Lee, | Length and | Dro 772 +.02

4 ai isi erm of iter tee 912+.01

15 E Pearson, pa aie 8+.04

Spirogyra | Walton, n, Length ‘and Close bred (Lat. C.) .189 +.05

7 fe | diameter. | Cross bred (Seal. C.) |.093+.05

related character has in eclose-bred forms, appar-

ently rests on a Mendelian basis. Its importance in

evolution, beyond the idea that more pronounced tempo-

rary combinations are thus allowed in the trial and error

plan of nature, is conjectural.

6.27

4. Amphimixis and Death

With the assumption that the results obtained in the

preceding investigation, together with the data presented

by other writers, when correctly analyzed, strongly sup-

ports the view that asexually produced organisms tend to

be more variable than those produced by the union of two

gametes, there is furnished evidence for the interpreta-

tion of the origin of sex—amphimixis and also for the

origin of death that would seem to rest upon a much more

secure basis than the purely speculative theories of Weis-

mann, Nägeli, Hatscheck, Metschnikoff, Minot, ete., which

have previously been advano

The chief advantage wéinied 3 in the reduction of varia-

bility, while somewhat conjectural, would appear to be

No. 587] VARIABILITY AND AMPHIMIXIS 679

that of holding organisms within limited bounds, or in

other words, asexually produced organisms in general

tend by their variability to exceed the limits of their

environment and thus perish, while organisms produced

by the mingling of two diverse lines of germ plasm with

their lessened variability meet the conditions of the com-

paratively slowly changing environment and their race

persists. This idea was proposed entirely upon specula-

tive grounds by Hatscheck (’87) who suggested that

variation would run riot if not controlled by the union of

germ cells, and it would now appear that the facts sup-

port such a proposition. While it has been suggested

that the chief function of amphimixis was that of re-

juvenation, a consideration of the discussion on ‘‘Com-

parative Size’’ as well as the recent experimental results

obtained in the production of Paramecium do not support

such an opinion to the exclusion of the hypothesis here

put forward. East and Hayes (’12) have advanced the

theory that recombinations in accordance with Mendelian

principles were the chief purpose of amphimixis. While

new combinations are thus brought about, apparently

there exists a real difficulty in understanding how transi-

tory heterozygotic forms could become of selective value

in originating and maintaining such a process.

The acceptance of the conclusion that asexually pro-

duced organisms are more variable than those produced

by amphimixis, and that thus some of the units are more

readily subject to the eliminating influences of the en-

vironment, affords a comparatively simple explanation

of the origin of death in multicellular forms which are

built up of such units—the cell. Consequently the infer-

ence is that* death occurs as the result of the continually

forming body cells becoming so variable through the

absence of control by amphimizis, that eventually some

one group fails to meet the limits imposed by the environ-

ment, and these together with the remainder of the colony

4 Walton, Science, p. 216, 1909.

680 THE AMERICAN NATURALIST [ Von. XLIX

—the individual—perish. The experiments of Wood-

ruff (711, ete.) who in extending the work of Maupas and

of Calkins was able to rear several thousand generations

of Paramecium without conjugation, as well as the in-

vestigations of Harrison subsequently elaborated by

Carrel, where human and other animal tissues main-

tained cell division for a prolonged time in an artificial

medium, are here of much interest. In each case the

result is brought about by the favorable artificial environ-

ment, and it is made more clear that death itself is wholly

or in part due to the unfavorable conditions surrounding

an organism.

IV. A Worxkine HYPOTHESIS oF EVOLUTION

Investigations during the last fifteen years, instead of

establishing evolution as the simple process of natural

selection conjectured by Darwin and others, have made it

evident that the results are due to many factors of much

complexity. While the diversity of organisms depends

on variation—their inheritance and non-inheritance—it

is becoming more and more apparent that the term is too

comprehensive and covers variations arising in organ-

isms from causes quite different from one another.

The results reached in the preceding pages indicate the

need of extending the older terminology as used by Plate,

13, and others where variations are separated into

‘*somations’’ or fluctuations induced by the environment

and not inherited, and ‘‘mutations’’ or blastovariations

arising in the germ plasm and inherited, if a clearer —

understanding is to be obtained of evolution and its ap-

plication. Therefore the following scheme is proposed.’

5 Several interesting groupings of variations have been suggested by Spill-

man, Baur and others, none of which, however, appear to meet present con-

ditions,

No. 587] VARIABILITY AND AMPHIMIXIS 681

VARIATIONS

Al, adage originating in accordance with definite

law

Bi, Talend by general environmental stimuli,

(food supply, use and disuse, ete.), but not in-

r s

B2. Notinduced by environmental stimuli; inherited.

C1. Arising through the transference of factors

by the combination of two ancestral lines in

accordance with Mendelian principles, but ex-

hibiting ‘‘per se’’ no definite progress. ..... 2. Amphimutations

‘< mutations’? in part).

C2. Arising through causes at present unknown,

but which, from the progressive results ob-

tained, may be assumed to originate in accord- :

DUNE with dofimte I8WS ea is Oo eiren 3. Cumulations.6

A2, Apparently not originating in accordance with

RE ANER oo dada sci ce oe B. Abnormations.

Bı. Induced during early developmental stages of

the embryo from intracellular (?) stimuli, and

inherited.

C1. Arising through the abnormal segregation

of the hereditary material Sarian .. 4. Malsegregations

‘*mutations’’ in part).

C2, Arising by the loss of hereditary qualities,

Di, Resulting from the functional loss of

factor controlling a character ........... Defactorations

(3 aiid in part).

D2, Resulting from the partial functional

loss of a factor controlling a character. ... 6. Fractionations

is amiata) in part).

B2. Induced during the early developmental stages

of the embryo from extracellular (?) stimuli and

Hot Mhona = oe Sas Se ee a 7. Malformations.7

While any scheme presented must change as new facts

are obtained, a terminology is of value in proportion as it

gives a basis for future progress. The objection that it

is not possible to point out a specific cumulation by no -

means indicates the absence of such progressive varia-

tions taking long intervals of time, by the haphazard

6 Cumulations—from cumulo, to increase—including the names of the

following groups, with the exception of fractionations proposed by Bateson,

are based on the apparent origin of the variations.

7 Many so-called malformations originate as hi siscitiens: ete.

682 THE AMERICAN NATURALIST [ Vou. XLIX

method of nature, in which to bring about a change evi-

dent to mankind. That the weight of evidence, so far as

investigations have gone, is against evolution by means

of the other variations noted, makes the explanation the

more plausible. While it is true that Bateson (714) has

urged the consideration of the proposition that organic

changes occur through the loss of inhibiting factors—de-

factorations—such a double negative theory assumes a

decreasing complexity instead of an increasing com-

plexity of protoplasm, as already pointed out by Castle,

(715) and seems impossible to maintain.

On the interpretation here presented, the diversity of

organic forms is more complex than earlier imagined,

and the problem of positive racial improvement is still

far from solution. Loss as well as segregation factors

may add new forms which really contain nothing new.

To build up and not to break down is the desideratum,

and the data obtained would seem to suggest that pure

line breeding with the employment of statistical methods

to show any progress would be the path leading most di-

rectly to the goal.

VI. Conciusions

1. Direct Conclusions

The following conclusions drawn from the investiga-

tion are primarily statements of fact.

1. Zygospores of Spirogyra inflata (Vauch.) produced

by lateral conjugation or close breeding (quasi-partheno-

genesis) are relatively 26 per cent. more variable in

length and 31 per cent. more variable in diameter as

measured by the coefficient of variation, than those pro-

duced by scalariform conjugation or cross breeding

(sexual reproduction).

2. The size (volume) is greater in the average (mean)

zygospore close bred by lateral conjugation, where the

mean length is 62.38 ». + .178, than in the average zygo-

No. 587] VARIABILITY AND AMPHIMIXIS 683

spore cross bred by scalariform conjugation, where the

mean length is 60.44 u. + .135, The diameter is approxi-

mately the same in both types.

3. In zygospores produced by lateral conjugation there

exists a positive correlation between length and diameter

of .1894=.0460, while in sealariform conjugation the

value is .0934 = .0473. This is in general agreement with

results obtained by others although here the difference is

not significant when the probable error is considered.

4. In the material studied approximately 45 per cent.

of the zygospores were formed by lateral conjugation, the

remaining 55 per cent. by scalariform conjugation.

5. The material studied was strictly homogeneous, and

evidently arose from the same parental stock, both types

of filaments being intermingled with no structural dif-

ferences except those of conjugation. Consequently the

differences in variability are not the result of fluctuability.

2. Indirect Conclusions

The conclusions here presented are generalizations

based on the present investigation as well as the work of

others, and represent propositions concerning which dif-

ferences of opinion may exist.

1. Amphimixis, cross-breeding, etc., decreases and does

not augment variability (cumulability) although amphi-

mutability may temporarily be increased.

2. Close bred forms are more highly correlated in re-

spect to related characters than cross-bred forms.

. Variations, so far as their origin is concerned, may

be separated into (A) Normations consisting of (1)

fluctuations, (2) amphimutations, and (3) cumulations,

and into (B) Abnormations consisting of (1) malsegrega-

tions, (2) defactorations, (3) fractionations, and (4) mal-

formations.

4, Cumulations may best be investigated among organ-

isms produced asexually, by pure lines, or by close breed-

ing than by cross breeding, ete.

684 THE AMERICAN NATURALIST [ Von. XLIX

5. Sexual reproduction and cross fertilization have

been advantageous in the evolution of organisms by limit-

ing ecumulability and thus confining the progress of the

group to a path bounded by the more permanent en-

vironment.

6. Death occurs as a result of the continually forming

body cells becoming so variable through the absence of

control by amphimixis, that eventually some one group

fails to meet the limits imposed by the environment, and

these together with the remainder of the colony—the

individual—perish.

3. Hypotheses

The following opinions in the nature of hypotheses

based to a large extent on the preceding work may be

confirmed or invalidated by future investigations.

1. Variability (cumulability) will be greater in a small

and isolated population than in a large and less isolated

population.

2. Progressive evolution has resulted from factors aris-

ing through cumulations without reference to amphimuta-

tions (Mendelian combinations).

3. Characters once established by cumulations produce

by fluctuations, amphimutations, etc., the diversity of

organic life. Such secondary variations are only in-

directly the products of evolution.

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686 THE AMERICAN NATURALIST [ Von. XLIX

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21, pp. 263-266.

GENETIC STUDIES OF SEVERAL GEOGRAPHIC

RACES OF CALIFORNIA DEER—MICE?

DR. FRANCIS B. SUMNER

SCRIPPS INSTITUTE, LA JOLLA, CAL.

Some of those present may recall a resolution which

was adopted at a meeting of the Biological Society of the

Pacific, held in Berkeley, in April, 1913, endorsing a

project for the study of certain problems, related both to

genetics and to geographical distribution. During the

same year, the Scripps Institution for Biological Re-

search found it possible to undertake the execution of this

project, and the author of the present paper was chosen

to carry it out. It is my object to-day to offer a pre-

liminary report upon the results of these studies.

To those who have been so fortunate as to work in

fields which yield quicker returns than does that of ex-

perimental breeding, it may seem that something more

than a ‘‘preliminary report”? might reasonably be ex-

pected after the lapse of a year anda half. If any justi-

fication is needed for such seeming slothfulness, I need

only remark that my studies have already necessitated

the trapping of about 600 living mice, of my chosen

species, in four widely distant parts of the state, together

with the rearing of several hundred others which were

born in captivity; and that I have made measurements

of some 500 of these animals, including skeletal measure-

ments of over 400. Care of this rather large family of

pets, statistical treatment of the measurements, continu-

ous meteorological observations at several points, and the

preparation of a certain number of skins and color photo-

graphs, are also to be included in the technique of this

1 Read before a joint meeting of the American Association for the Ad-

vancement of Science (Section F), the American Society of Naturalists,

the American Society of Zoologists, the American Genetic Association, and

_ the Eugenie Research Association, at Stanford University, August 4, 1915.

: 688

No. 587] CALIFORNIA DEER-MICE 689

project. Without’the generous opportunities afforded

me by the Scripps Institution, the work could never have

been undertaken. And of an importance only second

in order I must’ mention the assistance rendered me

throughout these studies by the Museum of Vertebrate

Zoology at Berkeley.

The resolution to which I have referrsd above formu-

lated four questions which were regarded as especially

worthy of consideration in the investigations contem-

plated. These were:

1. To what extent do influences such as external condi-

tions, the exercise of organs or faculties, ete., which pro-

duce modifications of structure or function in the parent,

result in bringing about parallel changes in the offspring?

2. If such changes are, in reality, found to reappear

in the offspring, do they constitute true examples of

heredity?

3. Are the subspecies or geographical races of the sys-

tematic zoologists fixed, in the sense of being hereditary,

or do the differences by which they are distinguished

depend upon conditions which must act anew during the

lifetime of each individual?

4. If these subspecific characteristics are actually found

to ‘‘breed true,’’ do they owe their existence at the outset

to ‘‘mutations’’ or to the cumulative effect of environ-

mental influences, or to the mere fact of isolation, acting

in some way independently of those influences?

To a large section of experimental breeders in this

country, to whom ‘‘genetics’’ is synonymous with Men-

delism, such a formulation of problems as this doubtless

seems hopelessly archaic. ‘‘What is the use of raising

all these dead issues,’’ they will ask, ‘‘as if Weismann

and De Vries and Johannsen had never lived?’’ And as

for the question of subspecies, I suspect that some of our

critics would grant them no existence whatever, outside

the overwrought imagination of certain taxonomists.

Those, however, who have read dispassionately such

able compilations of evidence as are offered us, for

650 THE AMERICAN NATURALIST [ Vou. XLIX

example, by Plate? and Semon? are not likely to fall into

the shallow dogmatism which dismisses the whole ‘‘ac-

quired characters’’ question as once for all settled. And

those who have taken the trouble to carefully examine a

few trays of specimens, representing the subspecies of

some widely ranging bird or mammal, will not so readily

resort to a subjective interpretation of the phenomenon

of geographic variation.

I shall give chief attention to-day to the case of a single

species of white-footed mouse, or deer-mouse of the genus

Peromyscus. According to Osgood,‘ the chief monog-

rapher of this genus, the species maniculatus comprises

about 40 distinguishable geographic races, many of which

are so unlike that they would be given full specific rank

but for the fact that they intergrade insensibly with one

another.

My own special studies have had to do chiefly with

those subspecies of Peromyscus maniculatus which fall

within the limits of the state of California. The first

investigations have naturally been directed toward a

careful examination of mice representing each of these

local races, together with a determination, so far as pos-

sible, of the meteorological conditions to which they are

subjected in nature. <A search for correlations of any

sort between structural and environmental differences

was, of course, early undertaken.

Mice were collected at four points within the state:

Eureka, Berkeley, La Jolla, and in the Mojave Desert

near Victorville. At Eureka, Berkeley and Victorville,

self-recording instruments (thermographs and hygro-

graphs) have been left in charge of assistants for nine

to fifteen months, and recording instruments will be in-

stalled at La Jolla this summer. It is planned to con-

tinue these records for at least two years. The instru-

2 ‘<Selektionsprinzip,’’ vierte Auflage, Engelmann, 1913.

3 “í Das Problem der Vererbung ‘erworbener Eigenschaften,’ ’’ Engelmann,

1912.

4‘‘ Revision of the Mice of the American Genus Peromyscus,’’ U. S. De-

partment of Agriculture, Biological Survey, 1909.

No. 587] CALIFORNIA DEER-MICE 691

ments are placed in positions more nearly representing

the natural environmental conditions of the animals than

is customary for regular Weather Bureau stations (e. g.,

in a redwood forest on the outskirts of Eureka).

The Eureka mice are assigned to the subspecies ‘‘rubi-

dus,’’ those from the desert to ‘‘ sonoriensis,’’ while those

EVREKA

DISTRIBUTION MAP

MUSEUM OF VERTEBRATE

fi i j| Ji fi

AND NEVADA, BASED UPON THE pps BUTION MAP OF Osaoop (1909). The ae.

iest shading denotes the range of P. m. rubidus, the intermediate shading that of

gambeli, the lightest that of sonoriensts. Areas of intergradation between two

races are indicated by dotted lines.

692 THE AMERICAN NATURALIST [ Von. XLIX

from Berkeley and La Jolla are assigned by Osgood to

the same subspecies ‘‘ gambeli,’”’ although, as I shall point

out, there are certain slight differences of type between

the two.

Now, as to characters, I have made 14 measurements of

each completely measured mouse. Certain color char-

acters, not capable of quantitative expression, have also

been taken into consideration. I shall first consider the

measurable parts. I must introduce this discussion by

stating that my comparisons are entirely between animals

of the same body length. When I say that P. m. rubidus

has a longer tail than sonoriensis, I mean that this is true

for mice of equal size. Owing to the impracticability of

giving you a mathematical justification of all the steps

which I have taken, I will ask you to credit me with a

knowledge of the more elementary statistical methods.’

I must also explain that I have thus far failed to kill

and measure many animals from which I shall before

long have full data. At present these are being retained

for breeding purposes. Hence my series of measure-

ments, in certain cases, is very small.

To present these subspecific characters briefly, I may

say that, in respect to tail and foot length, rubidus stands

in a class by itself. It does not require the trained eye of

a systematist to detect the fact that this northern race.

has conspicuously longer tail and feet. In the case of

the tail, this difference is due almost wholly to a differ-

ence in the length of the individual vertebra, not to an

increase in the number of these. The other three races

(sonoriensis and the two lots of gambeli) show no statis-

tically certain differences in either of these characters.

P. m. rubidus likewise has a significantly greater skull

length and probably also a greater cranial capacity.”

5 The detailed data must be deferred until a somewhat later stage of the

work. Some of these were presented to the meeting in the form of graphs.

ê The same was found to be true of the soiree induced modifications

in tail length, described by me elsewhere for white

7 Determined by suitably cleaning and then aaie the skulls, and

weighing the volume of mercury which i filled the cranial cavity.

No. 587] CALIFORNIA DEER-MICE 693

The La Jolla race of gambeli seems to fall second in the

list in this regard.

The only significant difference in ear length is that be-

tween the two races of gambeli, the La Jolla stock having

noticeably longer ears than the Berkeley stock, while

rubidus and sonoriensis appear to be intermediate in this

respect.

As regards color differences, these relate chiefly (1) to

the depth of shade, and (2) to the extensity of the pig-

mented areas. A careful comparison of large numbers

of the Berkeley race (gambeli) and the desert race

(sonoriensis) revealed at least ten recognizable differ-

ences of this class, though in many cases these were

merely different expressions of the same fundamental

difference. None of the distinctions between these two

races are absolute ones, holding between any two individ-

uals of the contrasted races. Rather they are distinc-

tions ‘‘on the whole,’’ expressed by differences of mode

or mean. Taken collectively, however, it is likely that

these characters form an ensemble sufficiently distinct to

reveal the identity of practically every specimen.

The most widely separate of the races, in respect to

color, are rubidus and sonoriensis, the former race being

very much darker than the latter. The two lots of

gambeli occupy intermediate positions between the others.

METEOROLOGICAL Data AT Four CALIFORNIA STATIONS.

Temperature (°F.) Humidity Rainfall

Annual Annual Annual Daily Annual

Mean Range Mean range total

SPOR Ae ook os bs ea 51.6 8.9 86 Very 45

small

SED a BODE DG eae aes 56.19 14,49 838 | Small 26°

Seg ried (San ey hda 60.6 14.7 75 Small 10(—)

Mojave Desert. .......... (Mo- (Mo- (Victor- | High (Victor-

jave)! jave)! ville)!° ville)

63.6 40.4 45+ 6

8 U. S. Weather Bureau.

9 University Observator

10 Computed from observations during present experiments (only one

half year at this station).

11 Rain-gauge records of Mr. Reginald Frost.

694 THE AMERICAN NATURALIST [Vou. XLIX

Now do we find any instances of correlation between

these differences of structure or color and differences in

environmental conditions? The most conspicuous of the

structural differences relate to the greater length of the

tail and foot of the Eureka race (rubidus) as compared

with any of the other three races here considered. It is

of considerable interest to note that there is here an in-

crease in the length of these appendages as we pass to the

northward, a circumstance which is still further empha-

sized by the condition of certain Alaskan subspecies. In

fact, so far as these coastal subspecies of Peromyscus

are concerned, there seems to be, within certain limits, a

reversal of Allen’s principle of the shortening of ‘‘ periph-

eral parts’’ as we pass from south to north. The facts

here revealed are likewise out of harmony with my own

experimental results from white mice, which showed con-

clusively that low temperature and high humidity led to

a decrease, rather than an increase in the length of the

tail and foot.12 A little later I shall point out the pro-

nounced effect of certain other artificial influences upon

the length of these appendages in Peromyscus, though I

must admit that these later experimental results furnish

no more satisfactory clue to the origin of these differ-

ences in nature.

= On the whole, then, these preliminary researches do

not offer much ground for believing that the differences

found in the tails and feet of these wild races of Pero-

myscus result directly from any differences in environ-

mental stimuli, or for expecting that they will respond

appreciably to artificial climatic changes.

Passing to color differences, we seem to have here a

good illustration of that correlation between atmospheric

humidity and depth of pigmentation which has long been

recognized to hold for mammals, birds and some other

animals. If we arrange our four environments in ascend-

ing order with respect to their atmospheri¢ humidity

12 Cf. Journal of Experimental Zoology, April, 1915, and earlier papers

therein cited.

No. 587] CALIFORNIA DEER-MICE 695

(the same order holds with respect to their rainfall), we

have the series: (1) Victorville, (2) La Jolla, (3)

Berkeley and (4) Eureka. Correspondingly, the desert

mouse (sonoriensis) is the palest of the lot, while the La

Jolla mouse, the Berkeley mouse and the Eureka mouse

follow inthe order of increasing pigmentation. This

relation, when viewed in connection with a wide range of

known facts, and with certain experimental data to be

noted later, can hardly be regarded as accidental. Any

exact quantitative determination of the density of pig-

mentation would of course be difficult, and it has not yet

been attempted. But the width of the dorsal median

stripe of the tail is found to serve in some measure as an

index of the extension of the darkly pigmented areas. It

is interesting to note, in order of increasing width:

sonoriensis (28 per cent.), gambeli (32 per cent.) and

rubidus (43 per cent.). (The gambeli considered are

from La Jolla.)

Let us grant then, provisionally, some sort of causal

relationship between atmospheric humidity and the quan-

tity of pigment in the hair or feathers. Now, aside from

our ignorance of the physics and chemistry of the proc-

esses here involved, there is still a most important bio-

logical question left unsolved: Are these differences in

pigmentation between the various geographical races

germinal in their origin or are they purely somatic and

individually acquired?

It was but a few years ago that Mr. J. A. Allen’? was

shocked by the very moderate suggestion of President

Jordan’s'* that perhaps some of our subspecific differ-

ences were ‘‘ontogenetic,’’ and not racially fixed. Mr.

Allen was shocked, though unable to offer any really sub-

stantial evidence in reply. In this uncertainty over so

elementary a matter of fact, everybody suggested decisive

experiments for some one else to perform, but somehow

` no one seemed disposed to perform them. At least the

13 Science, January 26, 1906.

14 Science, December 29, 1905.

696 THE AMERICAN NATURALIST [ Von. XLIX

question of the fixity of the subspecies of mammals and

birds has, to my knowedge, never before been put to ex-

perimental test.*®

Now, in view of the subject matter of the present paper,

it would ill become me to underrate the value of such

tests. But I think that I have had enough to do with the

experimental method in zoology to make me realize its

rigid limitations. It is seldom indeed that we are able

to perform a really crucial experiment and to obtain un-

equivocal results. Moreover, the mills of the gods grind

slowly, while the single human life is short.

I am therefore disposed to attach considerable impor-

tance to what have been called ‘‘Nature’s experiments.’’

Certain of these have been cited by Grinnell and Swarth’®

in their bearing on the subspecies question. For ex-

ample, two well-marked local races or subspecies of song-

sparrow occur in southern California, on opposite sides

of the high mountain range which divides the coastal

plain from the desert interior. These races are sepa-

rated nearly everywhere by the mountain barrier, but at

certain points passes through the latter occur, permitting

of migration from one side to the other.

Now these authors find localities in which the coast

form of song-sparrow has penetrated, for considerable

distances, into the desert and has become established

there. Nevertheless, these invaders, which have perhaps

been exposed for many generations to the desert at-

mosphere, have retained the darker pigmentation and

other characteristics proper to the coastal plain.

- Again, both Grinnell and Taylor’? have taken speci-

mens of Peromyscus maniculatus, which they believe to be

typical representatives of the desert race sonoriensis,

15 It is interesting to note that the often cited case of the Porto Santo

rabbit has been recently put in quite a new light by the investigations of

G. S. Miller, who finds that this transplanted race is merely the unmodified

rabbit of southern Europe. (Catalogue of the mammals of western Europe,

in the British Museum, London, 1912.) |

16 University of California Publications in Zoology, Vol. 10, No. 9, 1913.

17 University of California Publications in Zoology, Vol. 7, No. 7, 1911.

No. 587] CALIFORNIA DEER-MICE 697

high up in the mountains of California and Nevada.

These points are continuous with the main habitat of the

subspecies in the desert lowlands and plateaus, in the

sense that no abrupt barriers intervene, but they present

very great differences in climate and vegetation.

Facts of this sort—‘‘natural experiments,’’ as we may

call them—seem to show that these subspecific differ-

ences manifest themselves in a large degree independ-

ently of climatic conditions, in other words, that they are

of germinal rather than of somatic origin.

But these ‘‘natural experiments’’ are not entirely con-

clusive, for we can never be quite certain what the actual

condition are which Nature has imposed in a given case.

Granting that these darker song-sparrows in the desert

are actually invaders from the coastal plain, we have no

means of knowing how long they have been exposed to

the desert conditions. Also is it definitely known that

their restricted habitat in certain portions of the desert

does not agree with their original habitat in respect to

those factors which are really essential in determining

their characteristic coloration?

My own first attempt at transplantation consisted in

bringing a considerable number of specimens of P. m.

sonoriensis from the vicinity of Victorville to Berkeley.!8

At the latter point, the mice were kept in cages, freely

exposed to the air, and under atmospheric conditions as

nearly natural as possible. For control, numbers of the

Berkeley race were reared in neighboring cages. The

result of this experiment I can state briefly: Neither

the originally introduced animals nor their offspring,

nor their grandchildren, have thus far shown any per-

ceptible approach to the local type. They are still

obviously of the sonoriensis race. If there is any tend-

18 The contrast between the climatic conditions at the two points is indi-

cated, to a certain extent, in the foregoing table. But this does not show

one of the most characteristic differences, namely, the relatively enormous

diurnal fluctuations of temperature and humidity in the desert, as com-

pared with those in the coastal region.

698 THE AMERICAN NATURALIST [ Vou. XLIX

ency for these mice to be modified in the direction of

gambeli, this tendency is not sufficiently great to be de-

tected through any mere gross comparison, based upon

qualitative characters. Unfortunately, these two races

differ significantly in color characters only, so that an

exact quantitative test of this question is not here possible.

But I am now rearing P. m. rubidus at La Jolla, an ex-

periment which would seem to be much more promising

of decisive results than the one just described.

Enough has been done, therefore, to prove that the color

differences between sonoriensis and gambeli are at least

in a large degree germinal and independent of environ-

mental influences acting during a single lifetime.

Whether or not they are wholly germinal, and if so,

whether they can resist change for an indefinite number

of generations, remains to be learned. Suppose that we

had a shifting of the mean to the extent of one per cent.,

or even ten per cent., in the direction of gambeli. Amid

all the natural variability, we certainly should not be able

to detect such a change with the unaided eye.

In interpreting the facts that I have offered as to the

relative fixity of these color differences of Peromyscus,

we should have due regard for various other experiments

which show that environmental influences may produce

notable changes of coloration in the lifetime of an indi-

vidual. As especially comparable with these tests of my

own, though differing completely in the outcome, may be

cited the experiments of Beebe.1® This author produced

a marked increase of pigmentation in the feathers of three

species of birds by rearing them in an atmosphere of

abnormally high humidity.

Beebe’s experiments seem to show that pigmentation

may in some cases be altered during a single lifetime by

changes of humidity. The generally known facts of geo-

graphic distribution show that there is in nature a dis-

tinct correlation between pigmentation and humidity.

My own experiments show that these geographic differ-

19 Zoologica, N. Y. Zool. Soc., Sept. 25, 1907.

No. 587] CALIFORNIA DEER-MICE 699

ences of pigmentation are capable of being relatively fixed

germinally. Bringing these three sets of facts together,

they are, in my opinion, most readily harmonized on the

assumption that the direct effects of humidity upon the

organism may finally become fixed through heredity.”

But I grant that this assumption is as yet far from

proved.

A study of the effects of captivity forms a new line of

inquiry which was hardly considered when the present

researches were undertaken. For some reasons, how-

ever, this line of investigation now seems quite as prom-

ising as the search for climatic effects. In the first place,

my comparatively meager results in this field already re-

veal striking differences between the wild stock and the

individuals of the first generation reared in captivity.

These differences relate to absolute size (the domesti-

cated generation being smaller), to length of tail and foot

(both shorter in the domesticated) and to the length of

the femur and the pelvis, which differ in the same direc-

tion. In the case of the femur, in particular, the differ-

ences are striking, even upon the most casual inspection,

and they are absolutely certain statistically. They hold

for both sexes and for both of the subspecies which have

thus far been tested in this regard. Thus far, no certain

effects upon the cranial capacity of the captive lots have

been detected.

Such differences as those found probably have nothing

to do with the direct effects of external conditions, but

are due to the activities of the animal. For this reason,

they are of much higher value as a test of the Lamarckian

principle, which could help us most in explaining the per-

fecting of active parts through use or of their degenera-

tion through disuse.

The experimental results just referred to suggested

the possibility that some of the differences found to occur

in nature might have had a functional basis. The larger

20 Whether this results from ‘‘somatic’’ or ‘‘ parallel induction’’ need

not concern us here.

700 THE AMERICAN NATURALIST [Vou. XLIX

feet and tail of P. m. rubidus, for example, might be at-

tributed to its (assumed) greater activity. Unfortu-

nately for this theory, the pelvis and femur of rubidus is

no greater (slightly smaller, it would seem) than in the

other races. Had the enlargement of the foot been

due to greater functional activity the skeletal parts named

would probably have also undergone an increase in size.

From a series of measurements upon the skeletons of

wild and domestic fowls and rabbits, Darwin inferred a

relative decrease in the size of the wings of the former

and of the cranial capacity of the latter, under the in-

fluence of domestication. These conclusions may well be

true, but the evidence offered seems to be open to several

objections. (1) They are based on too small numbers

and lack the precision demanded by modern statistical

work. (2) We can only infer the exact nature of the wild

stock from which the domesticated races are descended.

(3) We can not judge of the extent to which artificial se-

lection may have played a part in bringing about these

differences. It was perhaps considerable. (4) We do not

know how much of this modification results from use or

disuse during the animal’s own lifetime. It might be

contended that the change was not congenital at all.

Lapicque and Girard have, in the main, demonstrated

a smaller cranial capacity in domesticated animals as

compared with wild ones, but aside from the more rig-

orous statistical methods employed by these authors, the

biological significance of their results is open to the same

objections as I have stated in the case of Darwin’s.

Hatai™ has shown that the albino rat has a smaller

brain than the wild Norway rat, when individuals of the

same size are compared. This proves nothing definite,

however, as to the effects of domestication, a fact which

the author recognizes. The deficient brain of the albino

may have been part of the same. mutation which brought

about the albinic condition. Or it may have resulted

in part from the selection of tamer individuals. Or the

21 Anatomical Record, Vol. 3, 1909, p. 245.

No. 587] CALIFORNIA DEER-MICE 701

difference between the two races may be purely onto-

genetic. Indeed, Donaldson?? seems to have demon-

strated the effects of exercise upon the weight of the

nervous system of the rat.

By taking a known stock of wild mice and measuring

each successive generation reared in captivity, and by

being careful to avoid selection, it would seem that the

foregoing ambiguities of interpretation might in a large

degree be obviated. It is possible, therefore, that this

phase of the subject deserves quite as much attention as

the problems relating to the physical environment and

the distribution of subspecies.

Hybridization has thus far failed completely between

rubidus and gambeli (48 matings). The Berkeley gam-

beli has, however, been successfully crossed with sonori-

ensis and some young of an F, generation have already

been obtained. Owing to the intergrading and widely

overlapping character of the differences between these

two races, it does not seem likely that they will lend them-

selves well to Mendelian analysis. But it would be idle

for me to discuss the results of these crosses at the present

stage of the experiments. Further attempts will, of

course, be made to obtain hybrids between the more widely

separated races.

(Since writing the foregoing, several successful mat-

_ ings between rubidus and sonoriensis have been effected.)

22 Journal of Comparative Neurology, Vol. 21, No. 2, 1911.

SHORTER ARTICLES AND DISCUSSION

ADDITIONAL EVIDENCE OF MUTATION IN GNOTHERA

IN a group of recent papers Bartlett reports on the remarkable

behavior of certain wild species of Ginothera grown in large cul-

tures, which behavior he regards as strong evidence for the muta-

tion theory of De Vries. The facts are presented very clearly,

but there is, however, a point of view which has not been consid-

ered in the interpretation of the conditions in his material, certain

possibilities that must be reckoned with in the critical examina-

tion of such evidence. The suggestions that I shall offer will

eoncern chiefly the genetic purity of the forms studied, a condi-

tion which is of course basic to studies on mutation as well as to

Mendelian experimentation.

nothera pratincola Bartlett! is a small-flowered, close-polli-

nated species apparently common in the North Central States.

Seven strains derived from wild mother plants at Lexington,

Kentucky, gave rise to a variant, nummularia, which differs from

the parent type in the form of the seedling leaves, foliage, pubes-

cence of the ovary and calyx, and in the manner in which the

calyx is ruptured in the opening of the flower. Nummularia

appeared with a frequency of about 1 plant to every 400 seeds

sown and 1 plant to every 250 seedlings since the germination of

the seeds in the earth was 66 per cent. Two of the strains pro-

duced nummularia in both the F, and F, generations. Further

studies will be undertaken to determine whether pratincola will

continue to give nummularia or whether it may perhaps in later

generations produce stable individuals. Nuwmmularia develops a

low percentage of good pollen (less than 50 per cent.) while

pratincola has a high proportion (90 per cent.) ; nummularia also

forms very few good seeds to a capsule, and of these only 34 per

cent. are viable. Small cultures grown from nummularia seeds

gave no plants of pratincola, but certain new forms appeared.

The high degree of sterility both gametie and zygotic shown by

nummularia is striking and demands study, for it will make a

difference in the interpretation of the behavior of this plant

whether the sterility is physiological or genetic in character.

1 Bartlett, H. H., ‘‘ Additional Evidence of Mutation in Mnothera,’’

Bot. Gaz., Vol. LIX, p. 81, 1915.

702

No. 587] SHORTER ARTICLES AND DISCUSSION 7038

Cultures of pratincola and nummularia should be grown from

germinations established experimentally to be complete, with

records of the residue of sterile seed-like structures, and the two

forms should be crossed with the purest Gnothera known to

determine whether or not the F, hybrid generations are uniform.

Should F, hybrid generations consist of distinct classes we would

be justly suspicious of the purity of the stock.

A second paper of Bartlett? describes a series of cultures of

Ginothera stenomeres, a cruciate-flowered species from Mont-

gomery County, Maryland. Two sharply marked new types were

produced by the typical form of the species, gigas represented by

one specimen with 28 chromosomes, and lasiopetala with hairy

petals. The gigas plant appeared in the F, generation of a line of

stenomeres. The peculiarities separating it from stenomeres are

similar to the distinctions between Lamarckiana and its deriva-

tive gigas. Thus both gigas forms are more persistently biennial

in habit than their parents, both have thicker, broader leaves,

stouter stems, larger buds, thicker fruits, 4-lobed pollen grains,

and twice as many chromosomes. A progeny of 63 individuals

from the original gigas plant consisted of 54 typical gigas, 6

narrow-leaved variants, and 3 ‘‘secondary mutations’’; the form

thus, as with the gigas from Lamarckiana, produces a varied off-

spring. Two of the ‘‘secondary mutations’’ were dwarfs and one

had the characters of lasiopetala, hairy petals, and in addition

certain of the stamens were also hairy. :

Lasiopetala was noted in an F, generation and also in two cul-

tures of an F,; it is of infrequent occurrence, only 5 plants in all

being observed. The plants formed persistent rosettes (steno-

meres being annual) and only one branch produced flowers, these

with hairy petals. The pollen of lasiopetala is 40-50 per cent.

perfect; that of stenomeres 60-80 per cent. An F, progeny of

116 plants from selfed lasiopetala gave 60 per cent. typical

stenomeres and 40 per cent. lasiopetala, thus behaving like

@nothera lata and O. scintillans in throwing their parent form

Lamarckiana.

Of these two new types derived from O. stenomeres the gigas

plant is remarkable as being another of the very few cenotheras

discovered with the quadruploid number of chromosomes (28) ;

triploid forms usually named semigigas have been described from

a number of lines. The hairiness of the petals in lasiopetala is

2 Bartlett, H. H., ‘‘The Mutations of Mnothera stenomeres,’’ Amer.

Jour. Bot., Vol. II, p. 100, 1915.

704 THE AMERICAN NATURALIST [ Vou. XLIX

regarded by Bartlett as a character new to the genus. Bartlett

emphasizes the fact that the characters of neither type could be

interpreted as the result of segregation following hybridization,

which may be true, but I do not think from this that it follows

that neither type can be the result of hybridization. I am not

willing to admit that hybrids present only combinations of char-

acters derived from their parent lines. It seems to me reasonable

to believe that in hybrids at times the interaction of elements

modifies the old or produces new factors. The species stenomeres

and the derivatives gigas and lasiopetala have not been tested for

genetic purity by cross-breeding with relatively stable types and

the problems of gametie and zygotic sterility have not yet been

attacked.

The final paper of this group of Bartlett’s* deals with an ex-

tremely interesting situation developed in cultures of Gnothera

Reynoldsii from Knoxville, Tennessee. This is also a small-

flowered, close-pollinated species, and its peculiarity lies in an

ability to throw extraordinarily large classes of dwarfs. There

are two types of dwarfs: (1) semialta somewhat smaller than the

typical Reynoldsit and intermediate between it and the smaller

dwarf; (2) debilis. A plant of Reynoldsii in the F, produced 29

individuals like itself, 32 plants of semialta, and 18 of debilis,

i. e., 60 per cent. of its offspring were dwarfs. Semialta throws

debilis, but no Reynoldsii. Debilis apparently can produce no

Reynoldsii or semialta and breeds true except for an occasional

variant bilonga which was also found in one culture from typical

Reynoldsii.

With respect to the dwarfs we have here presented a beautiful

series leading from the unstable parent type Reynoldsii through

the more stable semialta to the most stable and most extreme

dwarf debilis. Bartlett calls the behavior mutation en masse, but

confesses that it bears a certain degree of resemblance to Men-

delian segregation. We should very much like to see this study

repeated on a larger scale and with experimental germination of

the seed so that we may be sure of the ratios and also certain that

the cultures have given us all of their possible progeny. Segre-

gation en masse seems to the writer likely to be a more probable

explanation of the phenomena than mutation.

The form bilonga derived from the dwarf debilis offers a partic-

ularly interesting problem. It is similar to semialta except that

3 Bartlett, H. H., ‘‘Mutation en masse,’? AMER. Nat., Vol. XLIX,

p. 129, 1915.

No.587] SHORTER ARTICLES AND DISCUSSION 705

the fruits are twice as long. The capsules sometimes reach the

length of 70 mm. and average above 60 mm.; they are very much

the longest fruits reported in the subgenus Onagra. Bartlett re-

gards this large size of capsule as the origin of a new character.

Now capsule size obviously depends upon the number of ovules

produced which develop into seeds. It thus becomes an impor-

tant matter to obtain the data on ovule sterility in the species

Reynoldsii and the derived forms semialta, debilis and bilonga.

Ovule sterility is widespread among the Œnotheras as all stu-

dents of the genus know. Should it be found that bilonga pro-

duces a very much greater number of ovules than debilis and the

other types this fact would indicate a true progressive advance.

It may, however, be found that the smaller size of the capsules of

Reynoldsti semialta, and debilis is due to ovule sterility, i. e., to

the inability of a large proportion of the ovules to set seed. This

would.point to a very different interpretation of the conditions in

bilonga, and might indicate that bilonga is an example of rever-

sion towards an ancestral type in which a large capsule was corre-

lated with a high degree of ovule fertility.

In the comments which I have presented on the extremely

interesting facts discovered by Bartlett no attempts have been

made to offer exact explanations in line with Mendelian analysis.

It is not difficult to spin hypotheses on assumptions which have

been neither established nor disproved, but such creations are

hardly worth the effort when the facts are within grasp. My

main point is a constant questioning of the genetic purity of the

material with which Bartlett has worked from the standpoint

developed in my forthcoming paper ‘‘The Test of a Pure Species

of Gnothera.’’* It is impossible to discuss this subject in the

short space of a review. The most important test is that of cross-

breeding with the purest species known, to judge from the uni-

formity of the F, hybrid generation whether or not the parent

types are pure. I also firmly believe that all exact genetical work

on cenotheras must make use of methods of experimental germi-

nation to ensure complete progenies from the viable seeds and tc

permit the preservation of a residue of ungerminated structures

that may be examined.® There is in addition the determination

4To “apo in the Proceedings of the American Philosophical Society,

Vol. LIV, 1915.

5 Davis, x M., ‘‘A Method of Obtaining Complete Germination of Seeds

in Enothera and of Recording the Residue of Sterile Seed-like Structures,’’

Proc. Nat. Acad. Sci., Vol. I, p. 360, 1915.

706 THE AMERICAN NATURALIST [Von. XLIX

of degrees of sterility both gametic and zygotic, and the consid-

eration of whether such sterility is genetic or physiological.

From such tests it is possible to reach much clearer conclusions on

the genetic purity of @nothera material than has been possible

in the past.

Finally reference should be made to the important confirmation

by De Vries® of the studies of Stomps on @nothera biennis L.

In large cultures totaling 8,500 plants from Stomps’s selfed line

De Vries obtained 8 plants of a dwarf biennis nanella about 0.1

per cent., 4 plants of biennis semigigas (21 chromosomes) about

0.05 per cent., and 27 plants of the color variety biennis sulfurea

about 0.3 per cent. Since the percentages from Lamarckiana

are for nanella 1-2 per cent. and for semigigas 3 per cent., it

would appear that biennis is the more stable of the two species,

although the color variety biennis sulfurea is a new type in

experimental studies in @inothera. A culture of over 1,000

plants from selfed seed of biennis sulfwrea, all with pale yellow

flowers, produced 2 dwarfs, thus giving what De Vries calls a

‘‘double mutant,’’ O. biennis mut. sulfurea mut. nanella.

This behavior of Gnothera biennis is to the writer much more

trustworthy evidence for mutation than that presented from the

studies on Lamarckiana since biennis has a record of a long

history as a species on the sand hills of Holland, where there ap-

pears to have been little probability of recent contamination.

However, the showing of ‘‘mutants’’ from biennis does not ap-

pear very encouraging for the mutation theory of organic evolu-

tion when it is remembered that biennis nanella is frequently

weakly or diseased, that biennis sémigigas is self sterile, and that

biennis sulfurea appears to be a retrogressive form having lost the

power of producing normal yellow flowers. Although the Dutch

biennis of all the cenotheras so far brought into the experimental

garden still seems to me the form most free from suspicion of

genetic impurity, nevertheless, the line of Stomps’s has not, so

far as we know, been subjected to all of the tests of a pure species.

Until these tests are made it is not safe to assume that this mate-

rial is wholly pure. It seems to me not improbable that other

species of @nothera will eventually be isolated more stable than

the Dutch biennis. BRADLEY Moore Davis

UNIVERSITY OF PENNSYLVANIA,

June, 1915

6 De Vries, Hugo, ‘‘The Coefficient of Mutation in @nothera biennis L.,’?

Bot. Gaz., Vol. LIX, p. 169, 1915.

No.587] SHORTER ARTICLES AND DISCUSSION 707

THE VALUE OF INTER-ANNUAL CORRELATIONS

IF £1, £a, Lz +++ Zn be measures taken on the n individuals of a

series in a given year and 2,', £3, £, +++ Zn’ be similar measures

taken in a subsequent year, the correlation between the first and

second measures on the same individual rss’, may be designated

as a direct inter-annual correlation.1 The purpose of this review

is to illustrate the usefulness of such constants, with a view to

extending their application, by bringing together examples of

inter-annual correlations from various fields.

The immediate value of such coefficients may be purely scien-

tific, economic, or both theoretical and practical.

Practically such means of prediction as correlation and regres-

sion formule should find wide application in breeding operations

where it is desirable to weed out or send to the butcher at the

earliest possible moment those individuals which can not be kept

with the maximum profit. If the correlation between the egg

production of a fowl in her pullet year and her laying capacity

in any subsequent year be high, it is clear that those which on the

average are to prove unprofitable may be sent to the pot when

most desirable for that purpose, and before they have consumed

two or more years’ feed without yielding the maximum return in

eggs. If, on the contrary, there be no correlation, the labor of

selection in the pullet year is an unnecessary expense. Ifa cow’s

milking capacity be closely correlated with her milking record in

her heifer year, the culling of dairy herds may be profitably

carried out in the first year. In plant breeding experiments,

involving either sexual or vegetative reproduction, selection of

individuals for future propagation must be made, and at as early

a date as possible. If the future yield per plant of hay can be

estimated with considerable accuracy from a first year’s culture

the process of selecting clonal strains can be carried out with far

greater rapidity than if one must wait for the results of subse-

quent years’ tests. In all such cases the finality of a first judg-

ment must depend in large degree upon the closeness of correla-

tion between the results of successive experiments—in short upon

the value of the inter-annual correlation coefficient.

1 Cross inter-annual correlations in which the measures taken are of a

different sort are sometimes useful, but examples of such are not consid-

view,

708 THE AMERICAN NATURALIST [ Von. XLIX

In dealing with egg production Pearl and Surface? give as the

correlation in number of eggs for first and second year

r= .032 + .083,

a value which, though positive, is clearly insignificant with re-

gard to its probable error.

Thus in this particular case the performance of the first year

furnishes no clue to that of the second. With respect to egg-

laying capacity, the record of the pullet year furnishes no cri-

terion for elimination from the flock.

For milk yield in cattle the case seems to be quite different.

Gavin? has found that there is a medium correlation between (a)

the ‘‘ revised maximum ’” yield in quarts of successive lactations,

and (b) between the ‘‘ revised maximum ’’ of the individual

lactation periods and the highest revised maximum reached by

the animal.

So far as I am aware the only worker who has published

correlations between the characters of the same plant individuals

in different years is Clark® whose results have been noted in these

pages by Pearl.®

The correlation tables and constants show that plants of a

given class in any year (height or weight of hay produced) will

be highly variable in a subsequent year, but will on the average

deviate from the mean of the whole culture of the year in the

same direction and to about half the extent of the type selected

in the preceding year. Thus if selection were made on the basis

of a single year’s test only, many individual plants of low yield

would be discarded which in a subsequent year would have taken

higher rank, while high-yielding plants would be retained which

subsequently would give disappointing results. On the whole,

however, the yield of a hay plant one year does furnish a valu-

able index to its yield in a subsequent year.

2 Pearl, R. and F. M. Surface, ‘‘A Biometrical Study of Egg Produc-

tion in the Domestic Fowl,’’ I, Bull. Bu. Anim. Ind., 110, 66, 1909.

3 Gavin, Wm., ‘‘Studies in Milk Records: On the Accuracy of Estimat-

ing a Cow’s Milking Capacity by Her First Lactation Period.’’ Jour. Agr.

Sci., 5, 377-390, 1913.

4‘‘ Revised Maximum’’ milk yield is «a maximum day yield which is

three times reached or exceeded in a lactat

5 Clark, C. F., ‘‘ Variation and paca i in aS ? Bull. Cornell Agr.

Exp, Sta, 279, 1910.

€ Posti, R., Aune. Nar., 45, 418-419, 1911.

No.587] SHORTER ARTICLES AND DISCUSSION 709

That we are dealing with a real measure of the relatively per-

manent differentiation of individuals, and not with merely tem-

porary differences due to growth, is indicated by the fact that

the correlations between a first and a third year are about the

same as those between a first and a second or a second and a

third.

In other fields of plant industry such methods may be profit-

ably applied. For example Sievers’ after discussing at some

length the question of the differentiation of belladonna plants

with respect to alkaloidal content, warns the reader that ‘‘ the

investigation has hardly progressed far enough to yield any defi-

nite conclusions ’’ but says in summarizing his data:

A considerable number of plants with leaves rich in alkaloids in one

season are found to have equally rich leaves in the following season.

Furthermore, they frequently manifest the same characteristics at the

various stages of growth during the season in eomparison with other

plants. The same facts are true with regard to plants which bear

leaves with a low percentage of alkaloids.

How much more definite is the information conveyed by the

simple statement that the inter-annual correlation! between the

alkaloidal content for 1911 and 1912 is

r==.513 + .066!

Such studies as those by Stockberger on individual perform-

_ ance in hops? may be facilitated by the use of inter-annual corre-

lation coefficients. He gives only the extremes of his series of

individuals, but from these the correlations between yield per

hill for different years are:

Lowest Hills Highest Hills

1909 and 1910 ..:...... 29 + 17 59 + .18 =

1910 and 390)... a. 55 + 13 52 + 14

1009 tnd WIL... 43 + 15 30 + .18

Such constants, deduced from materials which almost certainly

T Sievers, A. F., ‘‘ Individual Variation in the Alkaloidal Content of Bel-

ladonna dae! Jour. Agr. Res., 1, 129-146, 1913.

8 In computing this coefficient a number of inconsistencies in the data

table were issand. The constant as given is probably as nearly correct

as can be found from the available da

9 Stockberger, W. W., ‘‘A Study of Individual Performance in Hops,’’

Prac. Amer. Breed. Ass., 7, 452-457, 1912.

710 THE AMERICAN NATURALIST [Vou. XLIX

do not show the full strength of the correlation, remove at once

all question concerning the relatively permanent differences in

productiveness of the individual hills.

Consider next an illustration from hybridization of measur-

able characters.

Goodspeed and Clauson’ have given the mean values of meas-

urements of the flowers of individual plants of Nicotiana hybrids

cultivated in 1912 and of corollas of the same plants cut back

and flowered in 1913. The correlations between the mean di-

mensions for the two years I find to be:

N. Tabacum var. macrophylia 2 X N. sylvestris g

F, plants, N = 21.

For spread of corolla, r = .044 + .147.

For length of corolla, r==.169 + .143.

Hybrid produced by crossing F, of the hybrid N. Tabacum

** Maryland ” 2 by N. Tabacum 4, with N. sylvestris, N=19.

For spread of corolla, r==.560 + .106

For length of corolla, r==.788 + .059.

These correlations show at once the high degree of uniformity

of the F, of the first as compared with that of the second series.

In all four cases the signs of the coefficients are positive, but

those of the first class are insignificant in comparison with their

probable errors. In both cases length of corolla is more closely

correlated than breadth. Possibly this is due to errors of sam-

pling only, or to greater difficulty in obtaining an exact measure .

of the spread of the limb. It may, however, indicate that some

characters are more sharply and permanently differentiated

from individual to individual than others.

That the latter may sometimes be the case is clearly shown by

unpublished data of my own for the ligneous perennials Staph-

ylea trifolia and Hibiscus Syriacus.*?

10 Goodspeed, J. H., and R. E. Clauson, ‘* Factors Influencing Flower Size

in Nicotiana with Spøeial Reference to Qisim of Inheritance,’’ Amer.

Jour. Bot., 2, 232-274, 1915

11 The AREA are based in all cases on mean values of the characters

of ovaries of shrubs well established in the Missouri Botanical Garden. In

such work the number of individuals can never for practical reasons be very

large, if a fairly large number of countings be made for each shrub. Fur-

thermore much of the work which one does may be lost by some accident

which precludes the securing of countings from each individual every year.

. If an individual is not represented in both of a pair of years it must be

omitted entirely.

No. 587]

SHORTER ARTICLES AND DISCUSSION

711

The accompanying tables show the correlations deduced for

the characters indicated.'”

INTER-ANNUAL CORRELATIONS FOR FRUITS OF STAPHYLEA

Correlation for | Correlation for pa ergo for

Relationship 1906 an sa pen Be 1007's ae 1908, 1908 1909,

tes ong srg ovules .445 = .069 | .816 = .058 | 872 = 036

Seeds seeds .063 = .154 | .064+.173 | .056 + .150

Ravan d asymm 748 + .068 | .102.+ .172 | .205 + .145

Libsilacs composition ae y lens A com-

TOON on ee a a ahs ss .601 + .099 | -294 = .159 | 335 = .134

INTER-ANNUAL CORRELATION FoR Fruits or HIBiscus, n= 23.

Correlation for

Relationship 1907 and 1908

PUPS BU OIE os. co Carra aa ie is eke es 451 + .112

Brors and PINE oo ee a e a .836 + .042

yale And OO aoc e ea et eee aa e 941 + .016

Goods and PoE ee cia 630 + .085

Asymmetry ANG IMMO -e ok ic Fi ayes 747 + .062

Locular composition and locular composition ........ 725 + .067

POP BOG LOr oe 6 seas beet bsuctveteas yey 610 + .088

COTTE EON BNO SONORON >.: iruek koraan .035 2 141

The constants are very irregular in magnitude, but are with-

out exception positive in sign. In many instances they are large.

Thus in these individual shrubs which taxonomically show no

differences® there is nevertheless a distinct differentiation in

respect of the great majority of the characters examined.

While the probable errors are large the evidence warrants the

conclusion that some are decidedly more highly correlated than

others.

12 Sepals = mean number of sepals in calyx.

Bracts = mean number of bracts in involucre.

Ovules = mean number of ovules formed per fruit.

Seeds — mean number of seeds matured per fruit.

Asymmetry = average radia] asymmetry in the distribution of the num-

ber of ovules per locule. For method of computation see Biometrika, Vol.

VII, pp. 477-478, 1910, and AMER. Nat., Vol. XLVI, p. 480,

Locular composition = average number of locules per frait with an odd

number of ovules. See citations above.

Fertility — coefficient of fertility (mean seeds per fruit) (mean ovules

per fruit).

Correlation = sigma of correlation between number of ovules and

number of seeds per loc

13 I believe one of the Hibiscus shrubs had lighter flowers than the rest.

712 THE AMERICAN NATURALIST [ Von. XLIX

In Hibiscus the differentiation of the individuals with respect

to number of bracts seems to be greater than that for number of

sepals. For both Staphylea and Hibiscus the correlation for

ovules is generally high. It is in every instance higher than

that for mean number of seeds matured per fruit. Correlation

for both mean number’ of seeds per fruit and relative number

of seeds matured has a moderately large value in Hibiscus, but

in Staphylea it is sensibly 0. In both species such character-

istics of the ovary as radial asymmetry and locular composition

seem to be rather sharply differentiated from individual to indi-

vidual. This is probably due in part to differentiation with

respect of number of ovules per fruit, but further discussion of

the problem would be out of place in a note, the only purpose

of which is to call attention to the usefulness, in both applied

and pure science, of a quantitative means of detecting and ex-

pressing permanent differentiation.

In this brief review I have made no attempt to discuss fully

all the biological phases of the problems suggested. The analysis

of the data may in several instances be carried much further by

the use of the statistical tools. Perhaps enough has been said to

indicate that inter-annual coefficients may be of real service in

practical animal husbandry, in plant breeding and in mor-

phology and physiology. More than usefulness is not to be ex-

pected of any method.

J. ARTHUR Harris

THE PHENOMENON OF SELF STERILITY

In my paper which appeared in THE AMERICAN NATURALIST,

Vol. XLIX, p. 79, the last seven lines on page seventy-nine

should read as follows:

Self-sterile plants crossed with self-sterile plants gave only self-sterile

offspring. Certain self-fertile plants, however, gave only self-fertile off-

spring either when self-pollinated or when crossed with self-sterile plants.

Other self-fertile plants gave ratios of 3 self-fertile to 1 self-sterile off-

spring when self-pollinated, and ratios of 1:1 when crossed with pollen

from self-sterile, ete.

E. M. East.

VOL. XLIX, NO. 588 “ DECEMBER, 1915

SHe.

. The F, Blend accompanied by Genic Purity. Dr. H. H. LAUGHLIN

THE

AMERICAN

NATURALIST

A MONTHLY JOURNAL

Devoted to the Advancement of the Biological Sciences with

Special Reference to the Factors of Evolution

CONTENTS

Page

Some Experiments in Mass Selection. Professor W. E. CASTLE - - -713

The Inheritance of Black-eyed White Spotting in Mice. Dr. C. C. LITTLE - 727

- ~ 741

The ne TREC of the “Blanket Te of Freshwater Pools. EX perem

PLA 752

Shorter pee and Discussion: Practical Vitalism. Dr. A. GURWITSCH - 763

Index to Volume XLIX = - - = ~ - = 771

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THE

AMERICAN NATURALIST

VoL. XLIX. December, 1915 No. 588

SOME EXPERIMENTS IN MASS SELECTION

PROFESSOR W. E. CASTLE

Bussey Institution, HARVARD UNIVERSITY

Ar the close of an interesting review of ‘‘seventeen

years selection’’ of the character winter egg production

in Barred Plymouth Rock fowls, made at the Maine Agri-

cultural Experiment Station,’ Dr. Pearl compares his re-

sults with those of Phillips and myself? in selecting for a

like number of generations the hooded pattern of rats and

concludes that the same interpretation should be given to

both series of experiments, viz., that selection can change

a population but not a character.

Without discussing for the moment the validity of the

now world-famous generalization of Johannsen, which

Pearl here accepts for his fowls and seeks to extend to

our rats, I wish to point out some differences between the

two cases which make a direct comparison between them

difficult and conclusions based upon them of unequal

validity.

The character winter egg production in fowls is on

Pearl’s showing extremely difficult to determine. It is

necessarily an unknown quantity in all male birds, which

themselves produce no eggs, and any influence which

1‘‘ Seventeen Years Selection of a Character Showing Sex-linked Mendel-

ian Inheritance,’’ AMERICAN NATURALIST, Vol. 49, pp. 595-608, 1915.

2**Piebald Rats and Selection,’’ Publ. No. 195, Carnegie Institution of

Washington, 1914,

713

714 THE AMERICAN NATURALIST [Von XLIX

males may exert on the egg-production of their daughters

can be tested only by an indirect and rather uncertain

process. Only in the case of females is the character di-

rectly measurable and then only for such females as (1)

are hatched ‘‘after April 1 and before June 1,’’ (2) sur-

vive all the accidents of chickhood and adolescence, (3)

escape all attacks of disease and are kept continuously

free from parasites, and (4) are properly fed and housed.

For any bird which dies, is disabled or becomes seriously

ill under ten months old, the character is an unknown

quantity. These limitations make the proportion of

birds which can be accurately rated as regards the char-

acter extremely small, and reduce correspondingly the

material on which selection can be practised.

Contrast with this situation that regarding the hooded

pattern of rats. This character is possessed by every in-

dividual of both sexes and is inherited equally through

either sex. The character is fully developed in its final

form within a week after birth, months before sexual

maturity is attained. This makes it possible to grade the

animals accurately while they are still very young and to

discard at once all individuals which fall below the

adopted standard. Selection thus has a vastly greater

amount of material to work with, and the variation in

each generation can be ascertained with a completeness

and accuracy quite impossible in the case of winter egg

production in fowls.

It is scarcely necessary to point out that upon the com-

pleteness of one’s knowledge of the character and extent

of variation depends his ability to take advantage of that

variation by systematic selection. By this criterion win-

ter egg production is very poor material on which to base

an experimental test of ‘‘mass selection,” whereas the

hooded pattern of rats is material admirably adapted for

the purpose. Many times has the fact been commented

upon that Mendel’s fortunate choice of peas as material

for his studies of hybridization was largely responsible

for his success where others failed. If one wishes to test

No. 588] EXPERIMENTS IN MASS SELECTION 715

a theory he must choose material suited to the purpose.

No adequate test of the efficacy of mass selection can be

obtained from material which can not be accurately

judged in the mass.

Pearl points out further limitations of his material in

the statement ‘‘that phenotypic variation of the character

fecundity, in fowls, markedly transcends, in extent and

degree, genotypic variation.” That is, non-heritable

causes of fecundity are in excess of heritable causes and

serve to obscure the occurrence of the latter. Further,

Pearl says:

It is quite impossible in the great majority of cases to determine with

precision what is a hen’s genetic constitution with respect to fecundity

from an examination of her egg record alone.

If then one has reared his pullets to the age of one year,

has kept them free from disease and parasites, has fed

and housed them properly and has even trap-nested them

and recorded their eggs all winter, still he has no suff-

cient basis on which to base a selection. He must first

rear and test their progeny in the same way. Pearl’s

statements on this point, the accuracy of which I do not

question, are sufficient to show the entire unsuitability of

his material for testing the efficacy of mass selection.

One might with propriety even question whether such

a thing as inherited capacity for winter egg production

exists in fowls, but on this point, I think, another inves-

tigation? made by Pear] is conclusive, in which he crossed

Cornish Indian game fowls, which are poor winter layers,

with Barred Plymouth Rocks which are fairly good winter

layers. Reciprocal crosses were made in both of which

the daughters showed resemblance to the racial winter

egg productiveness of the sire’s race. This result indicates

that a sex-linked genetic factor of some sort exists which

affects winter egg production in fowls. But since the fe-

cundity of the offspring was obviously influenced by the

mothers’ race as well as by the father’s race, Pearl was

3‘‘The Mode of Inheritance of Fecundity in the Domestic Fowl,’’ Jour.

Exp. Zool., Vol. 13, p. 153, 1912.

716 | THE AMERICAN NATURALIST [ Vou. XLIX

led to suggest the existence of a second fecundity factor

which was not sex-linked. He assumes that this second

factor, like the first, is a Mendelizing factor, but without

any sufficient published evidence for either conclusion.

To this I called Dr. Pearl’s attention soon after the pub-

lication of his paper and suggested that if possible the

data be put on record in such form as to allow of testing

this and other hypotheses concerning the genetic factors

concerned. For one-factor, two-factor, ten-factor and

infinity-factor Mendelian hypotheses would call for very

different ratios and distributions of fecundity among the

offspring. He replied that the data could not be so given

without an amount of work which he considered unprofit-

able. We are left, therefore, with only this information

concerning Pearl’s pullets, whether each one laid more or

less than 30 eggs in its first winter. If we knew what

number each one laid, we might form an intelligent

opinion as to whether Mendelian factors are involved,

and if so how many, in the same way that we can test

Mendel’s conclusions concerning the independent inheri-

tance of yellow cotyledon color and round seed form in

peas because he tells us the actual proportions of the

various sorts of peas reported for each plant. Being

denied such information by Pearl, it is useless to dis-

cuss his two-factor hypothesis, for its correctness can be

neither proved nor disproved.

Leaving aside the question whether any inherited factor

has changed as a result of selection in Pearl’s experi-

‘ments, which we have no means of investigating, we can

consider only the question whether the gross winter egg

production has changed. As a basis for judgment he

gives us the averages of winter egg production year by

year for sixteen years. Pearl’s graphic presentation of

the data (assuming that the considerable fluctuation re-

corded is not significant) indicates a steady decline of

the general flock average during the first nine years of

the experiment and a steady recovery and further in-

crease during the next seven years, which he ascribes to

No. 588] EXPERIMENTS IN MASS SELECTION 717

the different basis of selection in the two periods. But

it is hard to believe that this entirely explains the dif-

ference in result. One notices for example that during

the period of ostensible decline the highest average fecun-

dity (45.23) is recorded when the number of birds under

observation is smallest (48) and the lowest average

(19.93) is recorded when the flock is largest (780). Fur-

ther, in the later seven-year period of ‘‘improvement,’’

the number of birds tested declines as their average

fecundity rises. Has not the better environment and

lessened competition of small numbers possibly some-

thing to do with the changes noted? Is it certain that

genetic agencies are responsible for the differences ob-

served? Pearl himself nowhere states that the selection

practised during the earlier period had produced posi-

tive deterioration; he merely states that ‘‘there was no

change of the mean in the directon of the selection’’ dur-

ing this period when selection was based on high produc-

tion without progeny tests. But as soon as progeny tests

were made an additional feature of the basis for selection

Pearl notes immediate results, viz., the immediate isola-

tion of a strain which in its first year made a record for

high productiveness only once equalled in the six subse-

quent years. How many successive selections were made

in this period, we are not informed, but since it would

require at least two years to make a combined perform-

ance and progeny test, it would seem that not more than

three successive selections can have been*carried out on

this basis in the seven year period from 1908 to 1915. It

may fairly be questioned whether this is an adequate test

of the effectiveness of mass selection. The total number

of individuals tested during this period is, according to

Pearl’s table, 1,655. For the entire seventeen years of

selection it is 4,842.

The total number of animals graded in our selection

experiments with rats heretofore published is 20,645, and

the number of generations involved 13. Since those

figures were compiled, four additional generations of

718 THE AMERICAN NATURALIST [ Vou. XLIX

rats have been reared in the straight selection series,

bringing the total number of animals observed in this ex-

periment up to 33,249, and the total number of genera-

tions of selections up to 17, numbers certainly more nearly

justifying the term ‘‘mass selection’’ than those studied

by Pearl. As no previous account of this experiment has

been given to readers of the Naruratist, a brief review

of its salient features may be appropriate here.

Experiments made by MacCurdy and by Doncaster

had shown that the hooded pattern of rats is a Mendelian

recessive character dominated in crosses by the ‘‘self’’

or entirely pigmented condition of wild rats and of cer-

tain tame races. The F, ratio obtained in crosses be-

tween hooded and self rats is an unmistakable mono-

hybrid ratio, viz., 493 hooded: 1,483 self, or 24.9 per cent.

hooded. The hooded pattern is subject to slight fluctua-

tions in the relative amounts of pigmented and unpig-

mented surfaces, and though these slight plus and minus

variations are such as are usually disregarded in Men-

delian analyses, MacCurdy’s investigations had indicated

that they are to some extent inherited. It was our pur-

pose in starting the selection experiments to ascertain

whether the observed fluctuations were capable of in-

crease and summation through the action of repeated

selection, a possibility denied for all such cases by de

Vries and Johannsen on theoretical grounds and quite

incompatible with notions prevailing then as to the

‘‘oametic purity’’ of recessives. This ‘‘pure line” idea

Pearl still maintains on the basis of his observations of

the winter productiveness of his pullets. But, as I have

tried to show, his material is no more adequate than that

of Johannsen, which involved no demonstrated Mendelian

character whatever. For, though Pearl asswmes that

winter egg productiveness of fowls involves a ‘‘sex-

linked Mendelian character’’ he has withheld from pub-

lication the only facts on which such an assumption may

legitimately be based.

Our selection experiments with hooded rats began in

No. 588] EXPERIMENTS IN MASS SELECTION 719

1907. The initial stock consisted of less than a dozen indi-

viduals all ‘‘pure recessives,’’ which produced only ‘‘

cessive’? hooded young, in accordance with Mendelian

expectation. But though all the young were recessive

(hooded), all were not exactly alike, and to assist in their

classification we devised arbitrary ‘‘grades’’ of increased

(plus) or decreased (minus) pigmentation as compared

with the modal (zero) condition in our hooded race. The

scale of ‘‘grades’’ is shown in part in Fig. 1. It has

AEMT set of grades used in classifying the fluctuating variations

uke

of oa

been found necessary to extend it in both directions,

beyond the range shown in the figure, in order to

admit the new grades of rats which have made their ap-

pearance as the experiment progressed. The first plus-

selected parents produced 150 offspring ranging in grade

from + 1 to +3, mean + 2.51. The first minus-selected

parents produced 55 offspring ranging in grade from — 2

to + 4, mean —1.46. It will be observed that the ranges

of the young produced in the two selections were prac-

tically continuous with each other, though they did not

actually overlap. But actual overlapping did occur in the

following generation, in which no advance was made in

the mean grade of the parents, practically all the available

females being used as parents in an effort to increase the

stock. The grade of the offspring also remained prac-

tically stationary in this second generation (see Tables I

720

THE AMERICAN NATURALIST

TABLE I

[Vou. XLIX

RESULTS OF THE PLUS SELECTION OF HOooDED RATS CONTINUED THROUGH

SIXTEEN SUCCESSIVE GENERATIONS

Lowest Highest Standard Number of

Mean Grade | Mean Grade

1 2°51 2.05 +1.00 +3.00 .54 150

2 2.52 1.92 — 1.00 +3.75 to 471

3 9.78 2.51 + .75 +4.00 Oo 341

4 3.09 2.78 + .75 +3.75 47 444

5 3.33 2.90 + .75 +4.25 .50 610

6 3.52 a1 +1.50 +4.50 49 861

T 3.56 3.20 +1.50 +4.75 .55 1,077

8 3.75 3.48 +1.75 +4.50 44 1,408

9 3.78 3.54 +1.75 -4.50 "30 1,322

10 3.88 3.73 +2.25 +5.00 .36 776

11 3.98 3.78 +2.75 +5.00 -29 697

12 4.10 3.92 +2.25 +5.25 soL 682

13 4.13 3.94 +2.75 +5.25 -34 529

14 4.14 4.01 +2.75 +5.50 -34 1,359

15 4.38 4.07 +2.50 +5.50 .29 3,690

16 4,45 4.13 +3.25 +5.87 29 1,690

16,107

TABLE II

RESULTS OF THE MINUS SELECTION OF HoopED RATS CONTINUED THROUGH

VENTEEN SUCCESSIVE GENERATIONS

Mean Grade | Mean Grade — Biphost ere Number of

See | ot Parents | ct Oftepeton Oa pst ge Posed Offspring

1 — 1.46 — 1.00 + .25 — 2.00 51 55

2 — 1.41 — 1.07 + .50 — 2.00 AQ 132

os —1. —1.18 0 —2.00 48 195

4 —1.69 —1.28 + .50 22o 46 329

5 —1.73 —1.41 0 — 2.50 50 701

6 — 1.86 — 1.56 0 — 2.50 44 1,252

rd —2.01 — 1.73 0 — 2.75 .35 1,680

8 — 2.05 — 1.80 0 Zio .28 1,726

9 —2.11 —1.92 — .50 —2.75 28 1,591

10 — 2.18 — 2.01 — 1.00 3:25 -24 1,451

11 — 2.30 — 2.15 — 1.00 — 3.50 .35 984

12 — 2.44 2.23 — 1.00 —3.50 ot 1,037

13 —2.48 — 2.39 —1.75 —3.50 .34 1,006

14 — 2.64 —2.48 — 1.00 3.50 .30 Viz

15 — 2.65 — 2.54 —1.75 —3.50 .29 1,438

16 — 2,79 — 2.63 —1.00 — 4.00 ae 1,980

17 —2.86 — 2.70 —1.75 —4,25 -28 868

No. 588] EXPERIMENTS IN MASS SELECTION 721

and IT). In the third and all subsequent generations selec-

tion was made as rigorous as possible consistent with the

maintenance of a strong colony from which to make fur-

ther selections. Following each selection an advance in

the average grade of the offspring took place attended by

a steady movement in the direction of the selection on the

part of both the upper and the lower limits of variation.

The sixteenth plus selection produced 1,690 offspring (a

larger number of individuals than is contained in Pearl’s

entire seven-year series) every one of which fell beyond

the original range of variation, which was from + 1 to + 3

in the first plus selected generation and from + 34 to +5

in the sixteenth generation. What this change signifies

will be better appreciated when I state that +6 in our

grades is a wholly pigmented or ‘‘self’’ rat, and that the

extreme variation noted, + 53, signifies a rat wholly pig-

mented except for a few white hairs between the front

legs. The whole race has accordingly been changed so

that no individual is longer produced which falls within

the original range of variation. Not a dozen rats in this

entire generation would be allowed by a fancier in the

category of ‘‘hooded”’’ rats.

In the minus selection series the results secured are

scarcely less striking. Only a very few individuals of the

1,980 sixteenth generation rats, or the 868 seventeenth gen-

eration rats fell within the original range of variation,

which in generations 1-3 went no farther than grade — 2.

In all other individuals of the sixteenth and seventeenth

generations the ‘‘hood’’ was reduced to an extent never

seen in the hooded rats of the fancier, the white areas

having covered the neck and in extreme cases the fore-

head also, leaving only the nose and a patch round the

eyes and ears still pigmented.

Pearl (p. 607) commenting on the results of his selec-

tions states that he had no reason to think that at the close

of the series any individual had been produced superior

in productiveness to those which occurred at the outset,

but that he had merely secured more of them, thus raising

T2: THE AMERICAN NATURALIST [ Vou. XLIX

the average. With the rats, however, a very different

condition exists. The average is not changed by increase

of high-grade individuals merely or chiefly. At the pres-

ent time every individual in the plus selection series and

nearly every individual in the minus selection series is of

higher grade (plus or minus respectively) than any indi-

vidual in the race at the outset. It is not a fallacious

change of averages which has taken place; a genuine and

permanent racial change has occurred, following step by

step upon repeated selection. Generation by generation

new grades of offspring have come into existence, more

extreme in character than any which existed before, and

simultaneously with the advance of the outer limit of vari-

ation the inner limit has receded. No great change in

variability has attended the selection. The standard devi-

ation has decreased somewhat to about three fifths of its

original amount, but has scarcely altered in the last eight

or ten generations (see Tables I and IT). Rather there has

occurred a change in the modal condition of the character,

about which fluctuation continues very much as before.

When the position of the mode changes, as a result of

selection, the position of the average and of the upper and

lower limits of variation change with it. In a word the

character changes.

In our 1914 publication Phillips and I were conservative

about asserting a change in the single Mendelian unit-

character manifestly involved in the hooded pattern. We

suggested the possibility that other as yet undiscovered

factors might be responsible for the apparent changes

observed and awaited the result of experiments then in

progress to show whether such a possibility was admis-

sible. I have no hesitation now in saying that it is not.

All the evidence we have thus far obtained indicates that

outside modifiers will not account for the changes ob-

served in the hooded pattern, itself a clear Mendelian

unit. We are forced to conclude that this unit itself

changes under repeated selection in the direction of the

selection; sometimes abruptly, as in the case of our ‘‘mu-

No. 588] EXPERIMENTS IN MASS SELECTION 723

tant’’ race, a highly stable plus variation ; but much oftener

gradually, as has occurred continuously in both the plus

and the minus selection series. The permanency of these

cumulative changes we have tested by repeated crossing

of both selected races with the same wild race. The first

cross seems to undo to a slight extent the work of selection,

causing regression in both plus and minus selected races,

but a second back cross with the wild race causes no fur-

ther regression. Thus, plus-selected rats of mean grade

3.45 were crossed with wild rats and the recessive char-

acter was recovered in F, in 75 individuals, 24 per cent.

of the entire generation. These 75 extracted hooded rats

were of mean grade 2.89, a regression of .56 on the mean

grade of their hooded grandparents, which is about double

the regression shown by the plus selected race when not

crossed with wild rats. It seems proper therefore to at-

tribute to the wild cross a part of the regression observed

in this case and this I have expressed by saying that cross-

ing the selected race with wild rats tends to undo the work

of selection. The suggestion was tentatively adopted by

Phillips and myself that this wndoing consisted in the re-

moval of ‘‘modifiers’’ of some sort, possibly independent

Mendelizing factors. If this explanation were correct,

further crossing with wild rats should tend still further

to ‘‘undo’’ the work of selection, so that ultimately the

extracted hooded race should return completely to its orig-

inal modal state, the zero grade. To test this matter,

extracted hooded rats ranging from grade +2 to +4

(mean grade 3.01) were crossed back a second time with

pure wild rats. The theory of independent modifiers

would lead one to expect further regression as a result of

this cross, but no regression was this time observed. In-

stead an advance of .32 took place bringing the mean of

the twice extracted hooded recessives back to about the

grade of the uncrossed race. The mean grade of the once-

extracted grandparents, loaded in proportion to the num-

ber of their twice-extracted hooded grandchildren, was

3.01; the mean of the 263 hooded grandchildren was 3.33.

724 THE AMERICAN NATURALIST [ Vou. XLIX

The number of these grandchildren is large enough to

leave no doubt as to the conclusion that no further regres-

sion attended extraction of the hooded character a second

time from the wild cross. The proportion of hooded in-

dividuals to non-hooded is also an unmistakable mono-

hybrid ratio, viz., 263 hooded to 759 non-hooded, or 25.7

per cent. hooded in a total of 1,022 individuals.

This result indicates clearly the untenable character of

our provisional hypothesis to explain the altered grade of

hooded rats under selection and crossing, by invoking the

action of independent modifying Mendelian factors. No

evidence is forthcoming from further and more extensive

experiments that such modifying factors are concerned in

the result. It seems rather that the hooded character,

which is a mosaic or balanced condition of pigmented and

unpigmented areas, is slightly unstable. It oscillates reg-

ularly about a mean condition or grade, these oscillations

being not phenotypic merely but in part genotypic so that

selection brought to bear upon them is immediately and

continuously effective.

There may exist cases of continuous variation purely

phenotypic, as that of Johannsen’s beans seems on his

showing to be. In other cases phenotypic variations may

so largely exceed genotypic variations that it is difficult to

discover and isolate the latter, as has been Pearl’s ex-

perience. But our experiments with rats show beyond

reasonable doubt that genotypic variation, as well as phe-

notypic, may assume a continuous form, and if it does no

one can question its further modifiability by selection. In

denying effectiveness to selection in the case of continuous

variation, it has been assumed, tacitly by DeVries and

expressly by Johannsen, that continuous variation is

wholly phenotypic. This assumption being disproved,

the pure-line theory which rests upon it lacks adequate

support.

It seems strange looking backward that the idea should

have become so widely accepted that continuous or fluctu-

ating variations are wholly phenotypic. For a continu-

No. 588] EXPERIMENTS IN MASS SELECTION 725

ous variation signifies only the combined result of several

independent agencies. In purely phenotypic variation

(such as possibly Johannsen has observed) these agencies

are obviously environmental and so do not affect the in-

heritance. But in a case of multiple genetic agencies (the

existence of which everyone recognizes) a continuous

series of variations may result which would be amenable

to selection. Pearl and all other pure-line advocates ad-

mit the existence of such cases. But the same thing would

result if, aside from purely phenotypic variations in a

character, its single factorial basis should undergo quanti-

tative variation. It is precisely this last named category

of cases which alone can explain our rat results. And it

is precisely this category of cases which the pure-line ad-

vocates, unable to disprove, boldly deny. Driven from all

other defences they cling to.this as their last line and

solemnly repeat challenges issued years before in mo-

ments of greater confidence. Thus Pearl closes his paper

with a renewal of the opinion expressed by him in 1912.

It has never yet been demonstrated, so far as I know, that the abso-

lute somatic value of a particular hereditary factor or determinant (i. e.,

its power to cause a quantitatively definite degree of somatic develop-

ment of a character) can be changed by selection on a somatic basis,

however long continued.

Our observations on rats are submitted as a sufficient

answer to this challenge.

I do not suppose that Pearl means to be taken seriously

when he says (p. 608):

The extreme selectionist appears to believe that in some mysterious

way the act of continued selection, which means concretely only the

transference of each selected individual from one cage or pen to another

to breed, will in and of itself change the germ-plasm.

I have never heard a selectionist, however extreme, ex-

press such a view; certainly I, whose views are attacked

in the next sentence, have never entertained such an idea.

But Dr. Pearl knows, as well as I do, that while the germ-

plasm of the individual remains unmodified upon its trans-

726 THE AMERICAN NATURALIST [Vou. XLIX

fer from one cage to another, the character of the germ-

plasm of its descendants, and so of the race, depends very

largely upon what mates are transferred to the same cage

with it. This is where the selection comes in and there is

nothing ‘‘mysterious’’ about it either.

The idea that selection can bring about no change in the

germ-plasm of the race ‘‘except by sorting over what is

already there,’’ to which Pearl gives expression, rests on

the assumption that the germ-plasm never changes. What

ground have we for such an assumption? No more than

for the idea of the unchangableness of species, which for-

merly prevailed. Even Johannsen admits that large

germinal changes (‘‘mutations’’) sometimes occur. He

himself records having observed them. Why should we

be so skeptical about the occurrence of minor germinal

changes? Itis easy to overlook them when purely somatic

changes are associated with them and outnumber them as

they possibly do in Johannsen’s beans and Pearl’s fowls

but a single clearly established case should suffice to estab-

lish their existence and their importance in evolution.

THE INHERITANCE OF BLACK-EYED WHITE

SPOTTING IN MICE

C. C. LITTLE

Buack-EYEeD white varieties of rodents have long been

recognized and used as material for genetic investigation.

Cuénot, Morgan and Durham with mice and Castle with

guinea-pigs have utilized this particular color variety in

breeding experiments. For the most part they are agreed

that black-eyed white varieties represent an extreme con-

dition of the ordinary ‘‘spotted’’ or ‘‘piebald’’ series.

Cuénot (1904) in treating the inheritance of spotting

concludes that there exists a continuous series of partially

pigmented forms extending on the one hand from mice

with white on the tail, or with a small white ventral patch,

or with small white forehead spot, through a series of

decreasingly pigmented forms until the black-eyed white

form is reached at the other end of the series. As toa

factorial explanation for the phenomena observed in the

inheritance of spotting, Cuénot feels that there are nu-

merous stages of the spotted condition (P) which he desig-

nates by pt, p°, p?, p* as progressively whiter forms are

considered. He believes, however, that the details of

spotting are not represented in the germ cell. He further

mentions the failure to obtain any particular stage of

spotting in a true breeding condition. Selection of nearly

solid-colored forms has enabled him to obtain animals

with greatly increased white areas.

Durham (1908) has obtained some evidence for two

different types of spotting, one recessive to solid-coated

forms and one dominant to them. She has reported sev-

eral crosses which I have considered in more or less detail

in another paper (Little, 1914). None of the crosses pre-

sented by her can be considered as critical tests of the

presence of two distinct spotting factors. Morgan (1909),

727

728 THE AMERICAN NATURALIST [ Vou. XLIX

who has worked with the same types as Durham, feels

uncertain as to the real significance of black-eyed whites

and as to the occurrence of a distinct factor for dominant

spotting. This uncertainty I also felt and have tried to

show further reasons for not considering Miss Durham’s

work as establishing the existence of a dominant spotting

factor.

Castle (1905) has found that in guinea-pigs black-eyed

whites behave in inheritance in much the same way that

the same type of mouse behaves, namely that black-eyed

whites do not breed true but give, when crossed inter se,

a whole range of spotted forms in addition to some like

themselves.

One can by selection progress in either direction through

a series of spotted forms, decreasing or increasing the

number and extent of pigment patches. Great difficulty,

however, was encountered in trying to fix the color pat-

tern at any particular stage in the series. Up to the

present time this has not been proved possible.

EXPERIMENTAL

In the early winter of 1913 Dr. Castle obtained from a

fancier in England two pairs of black-eyed white mice.

These he kindly handed over to me for investigation.

From the outset the progeny of these mice e to be

extremely healthy and vigorous.

1. Black-eyed White Crossed Inter Se

This cross gave two distinct classes of young, black-

eyed white and ‘‘piebald.’’ The distinction between the

two classes can best be shown by the tabulation of their

progeny on the basis of the amount of dorsal pigmenta-

tion they possess. I have for some time estimated the

per cent. of the dorsal surface pigmented in the case of

all spotted animals recorded. This gives a basis for clas-

sification which, though it may at first glance seem to

inexact, nevertheless has been shown by comparing the

No. 588] INHERITANCE OF SPOTTING IN MICE 129

estimates of two or more investigators on any one animal

to be surprisingly exact and fully as satisfactory as any

other system of grading.

TABLE I.

Per Cent of Dorsal Pigmentation

Type of Cross S| 3) S/8| 8/3| S| 9| 3| 3| 3| 3 £| £| 3| 3| 8| 28| 2

g/g agai g/e gi aigggaigaddigiiiz

Black-eyed white in-

ter se 56 1/0/1/3| 5} 6) 7| 4) 3/11; 0}1/0/0/ 2) 1| 0/1] 0

— ae white X

iebald 105; 0} 0} 1 |1/12) 8)11) 5) 6) 4) 4/1)3)4)] 9 4; 913) 0

Pisbald X piebald ARI 0.0} 0/9/0} 4| 6| 7/13) 6 2| 9/4|6|2| 5 8/15) 2) 0

Total 161; 1/0 2 [4/21 0 /25)28)15) 7 |18 619) 6 /16)13'24) 6| 0

From Chart I it will be seen that 44 of the 75 young

obtained fall in the class between 0 and 5 per cent. of

dorsal pigmentation. These are the black-eyed whites.

CHART 1

0-5 6-0 WAS WO 31-25 1630 3-3F KNO W-VF USP -SF bo S-S Go THIS N-S -IS FOR 9-95 Tew

730 THE AMERICAN NATURALIST [Von XLIX

The remaining 31 young are more or less scattered along

the range of ‘‘piebald’’ forms. The gap between the two

classes is a considerable one and is certainly significant.

b N

Fig. 1 Fic. 2

Figs. 1—4 are diagrammatic and are intended to show

the two groups of spotted animals. Figs. 1 and 2 show

No.588] INHERITANCE OF SPOTTING IN MICE 731

the common range of variation within the black-eyed

white type and Figs. 3 and 4 the same for the ‘‘piebald’’

type.

2. Black-eyed White X Piebald

This mating brought out two interesting facts. First,

all black-eyed whites behaved in essentially the same way,

approximately an equal number of black-eyed white and

piebald young being produced. Second, the same dis-

tinctness between the two types held good, as will be seen

from the chart given below (solid line).

3. Piebald « Piebald

Piebald animals from black-eyed white parents and

from the cross of piebald X black-eyed white were mated

inter se. They produced only piebald young, 93 in

number.

The distribution of these young according to the degree

of dorsal pigmentation they possessed is shown by Chart

2 (dotted line).

It will be noticed that there is no approach to the black-

eyed white condition (0-5 per cent.). There are also in-

dications of two main modal points, one at 41-50 per cent.

and one at 80-90 per cent. A complete curve formed from

the sum of all piebald animals included in Table I, is

given in Chart 2 (broken line).

This further emphasizes the bi-modal nature of the

curve in the case of piebald mice and makes it seem likely

that there are two genetically distinct grades of this

variety. It is hoped that opportunity will arise in the

future to investigate this point more accurately.

4. Discussion

From the three types of matings given above the fol-

lowing facts may be deduced: (1) The inheritance of the

characters in question is alternative, not blending in

nature; (2) black-eyed white is epistatic to ordinary pie-

bald spotting.

732 _ THE AMERICAN NATURALIST [ Vou. XLIX

e CHART 2

BLACK- EYED WHITE Aang (SOLID LINE) —

PIEBALD X PIEBALD (DOTTED Line ).....

COMBINATION OF ALL means hers LINE)—-—

a-r GH TT (M-10 tu-a 426-30 31-95 "36-40" Hi 4s! e-m! prs R-lo GIGS! bé-70 6 I-75 ' T6- fp Bie BS! g6-fo Mirar” 9-ta)

The behavior of black-eyed whites in crosses 1 and 2,

Table I indicates that they are always heterozygous domi-

nants and that they can not, therefore, be obtained in a

condition to ‘‘breed true.”

With this in mind it is interesting to calculate the ex-

pected ratio when black-eyed whites are crossed inter se.

If black-eyed white is due primarily to a dominant factor

No.588] INHERITANCE OF SPOTTING IN MICE 733

which obeys the ordinary laws of mendelian inheritance,

we should expect that black-eyed whites would be obtained

of two genetic types, homozygous and heterozygous. If

now black-eyed whites were mated together at random,

the matings should be either (1) DD x DD, (2) DD x DR

or (3) DRX DR. In the case of (1) and (2) only black-

eyed white young should be produced, while type (3)

should give approximately 3 black-eyed whites to one pie-

bald. Random matings would therefore produce a ratio

of black-eyed whites to piebalds considerably in excess

of 321.

If, on the other hand, the DD form of black-eyed white

mice behaves in a fashion similar to the homozygous yel-

low mice, failing to develop, we should expect a ratio of 2

black-eyed whites to one piebald young, no matter what

the origin of the black-eyed white parents might be, when-

ever two black-eyed whites are bred together.

The results are as follows:

Black-Eyed White X Black-Eyed White

Black-eyed White Piebald

Obsörvod nci aie ORS eS 57 39

Expectod 8:1- ratio «6. cei. eee 64 32

expected 3:1 tso Gis sikiwiecns 6 72 24

When one realizes that the ratio in one case should be

considerably higher than 3:1, it seems that the results in-

dicate a 2:1 ratio and the heterozygous nature of black-

eyed whites.

To further test this hypothesis individual tests of

twenty-one black-eyed whites coming from black-eyed

white parents were made by crossing with piebald

animals. If the DD combination is possible, approx-

imately seven of the twenty-one tested should be of that

constitution. All of them, however, proved to be hetero-

zygous. While the numbers should be supplemented by

further tests, they are certainly sufficient to serve as a

basis for a tentative conclusion that black-eyed white

mice are always heterozygous. :

734 THE AMERICAN NATURALIST [Von XLIX

The numbers from the cross of piebald X black-eyed

white are more extensive and closely approximate a 1:1

ratio. The numbers obtained are 105 black-eyed whites

and 102 piebald, while the 103 of each would have been

exactly an equality ratio.

The behavior of the piebald animals when crossed inter

se is exactly what would be expected if piebald was hypo-

static to black-eyed white and distinct from it in inheri-

tance.

The next question to be considered is the relation of

black-eyed white to ‘‘self’’ or solid coat, in inheritance.

RELATION oF BLACK-EYED WHITE TO SELF

A preliminary investigation of this question has been

made. The ‘‘self’’ race used was really technically not

a ‘‘self” but genetically it carried neither the black-eyed

white nor piebald spotting factors. Somatically the self

race used was a ‘‘blaze’’ race of the type which I have

previously put on record. Further crosses which I have

made between black-eyed whites and true selfs have

‘shown, even in early stages, clear evidence that the be-

havior of the blaze and true self races is directly com-

parable.

1. “Self”? X Black-eyed White

The F, generation produced by crossing self (blaze

F6B) animals with black-eyed whites consists of two very

distinct forms. These have been produced in a ratio of

50 Type ‘‘A’’ to 47 Type ‘‘B.’’ The first of these, Type

**A,’’? is shown in Fig. 5. While the percentage of dorsal

pigmentation of this type is subject to some variation

(see table), it will be noticed that they are ordinarily be-

tween 80 and 90 per cent. colored. The spots of color

$/3/3|3|3|/2|8|8|3|3|2|3

Type “A” t a: Tis

: PLP Desa 2) f/E/22]3

Black-eyed white X self (blaze))0/1/2/0/1}1/2 0/9 |15)10)8/}1

No.588] INHERITANCE OF SPOTTING IN MICE 735

appear to have slightly more irregular and less clearly

defined outlines than do those of the ordinary piebald

mice and many of the spots are distinctly smaller in size

(compare Figs. 3, 4 and 5). Just how much of this ap-

——— N oe : aa

= OO

D V D v

Fic. 5 Fie. 6

pearance is due to true genetic difference between the two

types of spotting is of course problematical and must

remain so until a larger mass of data is available.

Concerning class ‘‘B’’ (Fig. 6) little need be said save

that they appear in every way identical with heterozy-

gotes ordinarily obtained in a cross between ‘‘self’’ and

‘‘niebald’’ animals. They vary from entirely solid colored

animals to those having approximately 20 per cent. of the

ventral surface white. They may be tabulated as follows:

Per Cent of White on Ventral Surface

5 0 | 1-5 | 6-10 | 11-15 | 16-20 | 21-25 | 26-30

fee SB? o n eee a eee ad

2. Type “A” Animals Crossed Inter Se

Type ‘‘A’’ animals obtained in F, are distinctly ‘‘spot-

ted.” They have a clearly discernible amount of white

736 THE AMERICAN NATURALIST [Vou. XLIX

and are not in the least like heterozygous ‘‘selfs’’ of any

recorded type. When crossed together they give three so-

matically distinct classes of young, ‘‘self,’’ ‘‘piebald’’ or

like class ‘‘A,’’ and black-eyed white. The numbers ob-

tained are 15 ‘‘self,’’? 31 spotted (piebald or like class

**A’’) and 11 black-eyed whites.

3. Type ‘‘A’’ X Piebald

To test them further type ‘‘A,’’ animals of this class

were crossed with homozygous piebald mice extracted

from the black-eyed white crosses. Again three general

classes of young were obtained as follows: 45 ‘‘self,’’

54 spotted (piebald or like type ‘‘A’’) and 29 black-eyed

whites.

4. Type ‘‘B’’ X Piebald

To compare the behavior of types ‘‘A’’ and ‘‘B”’ this

cross was made. Only two classes of young resulted as

follows: 82 class ‘‘B’’ and 78 piebald. No black-eyed

whites were obtained.

Discussion

The question now arising is whether the factors for

self, black-eyed white, and piebald are allelomorphic or

independent in inheritance.

From the nature of the F, generation it is certain that

the black-eyed white animals are forming two kinds of

gametes in respect to their spotting factors.

If now the conditions ‘‘self’’ coat, ‘* black-eyed white”?

and ‘‘piebald’’ are all related as members of a system of

triple allelomorphs, we can express the cross as follows:

S=self factor.

W= black-eyed white factor.

sp=piebald factor.

Then

S S=self X Wsp=black-eyed white

gametes § WwW

F, Generation S W= Type A, Fig. 5

S sp = Typo B, Fig. 6

No.588] INHERITANCE OF SPOTTING IN MICE 737

If now animals of Type A are bred inter se we should

expect

S|wWxS W

LSS self

2 SW =like Type “Ar”

1 WW = (not formed because homozygous)

The one WW individual could not be formed since by

experiment it has been shown that W can exist in only

one of the two gametes forming a zygote. When W meets

S, an animal like Class A is produced, when it meets sp

a black-eyed white results.

The expectation therefore is that, if a system of triple

allelomorphs is operative here, we should have no black-

eyed whites formed from mating together class “A”

animals.

The result of this mating quickly settles the above hy-

pothesis for 15 ‘‘self’’ colored, 31 spotted (like or nearly

like Type ‘‘A’’), and 11 black-eyed whites have been

obtained.

It is clear, therefore, that ‘‘ black-eyed white’’ depends

upon a factor which is at least partly independent of that

producing ‘‘piebald’’ spotting. Let us suppose that this

is the case and that ‘‘black-eyed whites” always carry

piebald in all of their gametes and an epistatic inhibiting

or restrictive factor producing increased whiteness in one

half their gametes. If W equals restrictor and w its ab-

sence and sp equals the factor for piebald spotting, all

black-eyed whites will be Wwspsp, in zygotic formula and

will form two sorts of gametes, Wsp and wsp.

This will account for the results in mating black-eyed

whites inter se due to the failure of the WWspsp zygote

to continue its mee Mncose ‘nbd because of the double dose

of W.

If now black-eyed whites Wwspsp are crossed with selfs

wwssS, two classes of F, zygotes will result, WwSsp and

wwSsp. The former will produce a new zygotic combi-

738 THE AMERICAN NATURALIST [ Vou. XLIX

nation really differing from the black-eyed whites in the

substitution of a ‘‘self’’ bearing gamete for a ‘‘piebald’’

one in the zygotic formula. The result is an animal like

Type ‘‘A,’’ Fig. 5; Type ‘‘B,’’ Fig. 6 shows the other F,

type which is entirely free from the W factor and which

is merely a heterozygote between ‘‘self’’ and ‘‘piebald.”’

If class ‘‘A’’ animals are crossed inter se we should on

this new hypothesis expect the following results.

OW WS oora not developed

S EWE Fs cnc very dark spotted

2 WWD siari not developed

2 WD ices os not developed

2 Wwspsp ....... black-eyed white

I WROSD iia ceu ‘self’?

2 WWD s.is :oe ‘‘self’?’ or ‘‘self’’'with white ventral patch (type ‘‘B’’)

1 wwspsp ........ ‘*piebald’?

Four of the 16 zygotes in F, would have two doses of

W and would not develop. Of the remaining 12, seven

would have some degree of white spotting depending upon

whether they were WwSS, WwSsp or wwspsp in formula;

three would be ‘‘solid’’ colored or like type ‘‘B’’ of F,

and two would be black-eyed whites.

On this hypothesis the F, generation would be as fol-

lows:

Observed Expected

DOR -oree ea ee eG 15 15

OOO -e iirrainn ra 31 35

Biack-oyod. whitòs 66 ei id ce ec cues 11 10

57 60

A further test of the nature of type ‘‘A’’ is possible.

If they are bred to piebald animals, four classes of young

should result as follows.

WOD 0G oa iv nee yk cel ks Cinna kiss like class ‘A

OU ices oh oes ed ce ke hes aaa black-eyed whites

NS i si as oi edn os Wee aaa solid colored

MONI 6 cei nec cs sé vee peensiciveses

Lumping together the WwSsp and the wwspsp animals

No.588] INHERITANCE OF SPOTTING IN MICE 739

we should have 2 spotted, 1 black-eyed white and 1 self.

The results are as follows:

Observed Expected

MIOCENE S ae ee Ges es 64

OE ge i Oro ce oe eee as 45 32

Hlack-eved: White: oss sad fy. Cosix% 29 32

128 128

Whether the excess of ‘‘self’’ animals is significant is,

of course, a question to be borne in mind but it is ex-

tremely doubtful whether it is due to anything more than

a chance deviation. |

Type ‘‘B’’ animals have, upon mating with ‘‘piebald’’

individuals, given very close to the expected ratio of 1

type “B to 1 ‘‘piebald.’’ The exact numbers are

82:78; expected ratio 80: 80.

Is BLACK-EYED WHITE IN Mice an ALLELOMORPH OF

ALBINISM?

The experiments of Castle and Wright have shown that

a dark red-eyed variety of guinea-pig exists which is an

allelomorph of dilute pigmentation and of albinism. This

possibility in the case of mice is eliminated by crossing

black-eyed white with albino, when on the supposition

that the condition found in guinea-pigs holds true in mice

all the young should be either black-eyed white, albino or

dilute pigmented. Actually there were obtained from a

single mating of this sort five young, all intensely pig-

mented, two blacks and three browns; thereby eliminating

the possibility that black-eyed white, in mice, is an

allelomorph in the albino series.

CoNCLUSIONS

The fact that black-eyed white spotting in mice ap-

pears to be due to a factor independent of and supple-

mentary to the factor for ‘‘piebald’’ spotting leads to

interesting speculation as to the nature of spotting and

740 THE AMERICAN NATURALIST [ Von. XLIX

indicates that spotting in mice is dependent upon more

than one pair of clear-cut mendelizing factors. Modify-

ing factors which may be more or less difficult to analyze

but which nevertheless are certainly present, contribute

to the extent of variation in spotted races.

‘*Blaze’’ or forehead spotting is apparently independent

of ordinary ‘‘piebald’’ spotting, as I shall hope to show

in a future paper; ‘‘black-eyed white’’ is primarily due

to an independent genetic factor and ‘‘piebald’’ makes a

third independent type. If now in the ‘‘piebald’’ stock

there exist at least two genetic races as are indicated by

the curve of all piebald animals obtained in the ‘‘black-

eyed white’’ crosses, the condition is still further com-

plicated. At all events one can truthfully say that the

distribution of pigment occurring as it does along a series

from ‘‘self’’ colored to ‘‘ black-eyed white’’ animals, offers

a field for the activity of many mendelizing factors.

There is no a priori reason why this should not be true,

there are many experimental reasons steadily increasing

why it appears to be true.

Spotting in rodents is tempting as genetic material be-

cause of the clear patterns and contrast between colored

and white areas. It is, however, as a character extremely

sensitive to minute quantitative and qualitative changes

and its apparent genetic simplicity is a snare and a de-

lusion.

LITERATURE CITED

Castle, W. E. 1905. Carnegie Inst. of Wash. Publ. No. 23, 78 pp.

Castle, W. E. 1914. Am. Nar., Vol. 48, pp. 65-73.

Cuénot, L. 1904. Arch. Zool. Reo. et Gen., Notes et Revue (4), Vol. 2,

Durham, F. M. 1908. Rept. Evol. Comm., No. 4, p. 41.

Morgan, T. H. 1909, Am. Nart., Vol. 43, pp. 493-512.

Wright, S. G. 1915. Am. Nart., Vol. 49, pp. 140-148.

THE F, BLEND ACCOMPANIED BY GENIC

PURITY

A Description OF MECHANICAL CHARTS FOR ILLUSTRATING

Menpevian Hereprry 1x Hacw or Tares WELL-

KNOWN Cases oF BLENDING INHERITANCE IN

THE First HYBRID GENERATION

HARRY H. LAUGHLIN

EvGENICcS Recorp Orrice, Coup SPRING HARBOR, N. Y.

THE mechanical charts herewith figured are the first of

a series prepared for the purpose of presenting graph-

ically and schematically the established facts of heredity.

These particular mechanisms, illustrating blending in-

heritance, consist essentially of wooden slabs on which the

gametic formule of the several generations are charted

while that for F, is inscribed on cylinders which turn

freely. A capital letter represents a gene; the corre-

sponding small letter the absence of that gene. The lo-

cation of genes, whether they lie in the same chromosome

i. e., are linked, or in different chromosomes, is shown’

graphically by placing their symbols in the same or in

different squares, or upon the same or different half-

cylinder surfaces. In each of these selected cases the

individuals of the P, generation are homozygous in re-

spect to both of the traits or allelomorphic phases con-

cerned. The genes contributed by the P, generation to

the F, zygote are charted on the starred faces of the

freely turning cylinders. The back of each spool contains

the same inscription as the face of its partner cylinder.

Each face of a cylinder represents a chromosome—the

two faces the two chromosome types in reference to the

741

[Von. XLIX

fag

É i

THE AME

No. 588] F, BLEND AND GENIC PURITY 743

traits lying in that particular chr , which each F,

individual as a parent is capable of passing on. There-

fore, by turning the spools so that all possible combina-

tions are made, one can read off directly all of the dif-

ferent hereditary potentialities to be had by inbreeding

the F, generation. Consequently the F, line (which is

charted on a flat surface) is simply a record of such

combinations.

For the purpose of this study a case of blended inher-

itance is one in which the development in F, of a given so-

matic trait—regardless of whether it develops from one

or more genes—is about midway between its development

in the two parents, each of which is of pure stock in refer-

ence to the trait concerned. Until about the year 1910

students of heredity were unable to coordinate the general

rule of dominance and segregation on one hand, with the

frequent exception of blending and segregation on the

other. Now the existence of at least three different routes

by each of which nature arrives at the somatic blend in F,

are recognized, and each finds ready interpretation in con-

sonance with the theory of the pure gene. The first of

these is the dilution or true blend route, by which nature

appears to travel in the classical cases of the Blue Anda-

lusian' fowl resulting from the crossing of splashed-

white and black parents, and of the pink four o’clock

(Mirabilis jalapa) resulting from the crossing of red and

white parents.

The ordinary mode of inheritance is strongly duplex—

that is, the zygote normally possesses two genes for each

trait, either one of which genes is usually sufficient—with

possibly a liberal surplus of valence—to give full somatic

expression to its correlated trait. In such cases complete

dominance in F, and clear-cut segregation in F, are the

rule. Occasionally, however, in cases wherein a duplex

parent possesses a strong somatic development of a trait,

1‘*Mendel’s Principles of Heredity’? (3d Impression, 1912), p. 51, by

W. Bateson.

744

THE AMERICAN NATURALIST

Plumage Color in Andalusian

tically equalValenc

or o affecting t yh ae ha

Bath of thead ir inthe

eco

Somat Soma:White

Rac.

Ww Wii i.

Fann Eas

sii sdad lak ia dae Cowes which

somatic peg waged womens, Se eel areas from patches

on is aor ots i

HM whe show a black or blue ji

pee i EA

foie wants

by one equally post

blue because of Ad mtrinsic pir aeni a gn ar that hai

the genes N and WX le in the same chromogome.

+ N nigrum) i.e.black

Fowl:-

4s due to lwo inten oe poen for dom-

inant while and me ck- of atang

the

Mechanism for lllust

Inheritance of

[Vou. XLIX

SSS

Nar|

—_

conus ts ting the Party nt ai,

Fic. 2. Chart showing the F, Blend Associated with Genic Dilution—the True

Blend

No. 588] F, BLEND AND GENIC PURITY 745

a single gene—from the paternal or the maternal line only

—for such trait, in the zygote, is not sufficient to give a

somatic development of the trait equal to that possessed

by the duplex parent. In such cases, therefore, the unit

trait in question is blended in the F, soma—a case of

imperfection of dominance.? Nevertheless, in such cases

segregation is just as clean-cut in the germ-plasm as it is

in the cases accompanied by strong somatic dominance.

In Andalusian fowl ‘‘W’’—dominant splashed-white—

and ‘‘N’’—(nigrum) black—are two opposing and allelo-

morphic genes of nearly equal valence in ontogenesis.

Their combination and interaction determine plumage-

color in the offspring. The black Andalusian is duplex

for black plumage-pigment, while the splashed-white is

duplex for dominant splashed-white. The F, offspring

are ‘‘blue’’—a shade really intermediate between: the

white and the black. Moreover, the genes ‘‘W’’ and “N”

evidently lie in the same* chromosome. The evidence for

this consists in the fact that in the F, generation, result-

ing from inbreeding two blue Andalusians, neither albinic

white nor jungle‘—pure or modified—patterned fowl re-

sult, which would be the case if ‘‘N’’ and ‘‘W”’ lay in

different chromosomes, permitting, in some F, zygotic

combinations, the elimination of both ‘‘N’’ and “W.”

For further explanation of this particular type of blended

inheritance see the accompanying figure descriptive of the

mechanical chart ‘‘Plumage-Color in Andalusian Fowl.’’

The second type—that of multiple factors—is typified

by the inheritance of black skin-pigment in man. It isa

matter of common knowledge that a mulatto of the first

generation is about intermediate in density of black skin-

pigment between his white and his black parents. In 1913

2‘*Tmperfection of Dominance,’’ American Breeders Magazine, No. 1,

Vol. 1, p. 39, 1910, by C. B, Davenport.

3‘‘ Heredity and Sex,’’ p. 93 et seq. (Columbia University Press, 1913),

by Thomas H. Morgan.

4‘*New Views about Reversion,’’ Proceedings of the American Philo-

sophical Society, Vol. XLIX, No. 196, 1910, by C. B. Davenport.

746

THE AMERICAN NATURALIST

Black Skin-Pigment in

Ma Ti:=

i/sdue to two segregable genes in

each gamete. :

2The potentiality ofe each gene finds

Le ed

PIIGAD

regardless of the presence or ab-

sence of other genes.

Awhile man A woman

6% Ni in skin. 70% N M skin.

as 9 a : ww

z Jez ae

HR-

tie

s not found in PaiFim- Gametic types sat keratin

Ne hak DAR

oe figures 1 the pigment, ‘producing power (in per-

gw} ion ai au Scie shines families Da t found

dian Negro- venpor:

five freque m densily of skin- pigmenti-

554N 462N youn

[Vou. XLIX

there s sible is

‘ack Sare pr tle uc malingo, pare paces the de

Mechanism for illustrating the of the

s manner

ape e, madre gae g ak Po tir a y mi « m marn.

Negro-While Grosses’-Davenpart

Fic, 3. Chart showing the F, Blend Associated with Multiple Factors for One

omatic Trait

No. 588] F, BLEND AND GENIC PURITY 747

Dr. C. B. Davenport® found, by analyzing data on the

family distribution of black skin-pigment measured quan-

titatively (by the color-top) among the mixed white-and-

black families of the Island of Jamaica, the Island of

Bermuda, and in our own Southern States, (1) that black

skin-pigment in man is the somatic working out of two

segregable genes in each gamete, and (2) that the poten-

tiality of each gene finds definite measurable somatic ex-

pression, regardless of the presence or absence in the

zygote of other genes. Now these two genes appear to

be of different valence; they appear also to lie in differ-

ent chromosomes. The scheme outlined by the mechan-

ical chart ‘‘Black Skin-Pigment in Man”’ is quite conso-

nant with the facts of inheritance which Dr. Davenport

found in nature. The facts seem to be that in white per-

sons one of these genes will develop from practically none

to about 1 per cent. of blackness in skin-color, and the

second from very little to about 2 per cent., thus resulting

in a blackness of skin-color of 6 per cent. or less in the

somas of members of the light races. He found that some

races of negroes show about 70 per cent. black in skin-

color. In such races one gene for black skin-color seems

to be potential to developing approximately 16 per cent.

of black skin-color, the other about 19 per cent. The evi-

dence that there are two such genes, and that they are

segregable, i. e., that they lie in different chromosomes,

and that their values among the strains studied are about

as described above, lies in the fact that, in the hybrid

families in Bermuda, Davenport found 5 frequency max-

ima in intensity of black skin-pigmentation, and that his

analysis of the family distribution of this trait, quanti-

tatively measured in many mongrel families of known

pedigree, demanded the existence in nature of the scheme

above outlined.

Darwin, whose method of study was essentially obser-

vational, knew that the F, generation was quite generally

5 ‘*Heredity of Skin-Color in Negro-White Crosses,’’ published by the

Carnegie Institution of Washington, 1913, by Charles B. Davenport.

748 THE AMERICAN NATURALIST [ Vou. XLIX

remarkably uniform, but among and beyond the F, gen-

eral observation found no rule of inheritance. It re-

mained for the application of the analytical or Mendelian

study to discover order in the apparent somatic tangle of

F,. The skin-color story just related is a striking case

in point.

The third class of blended inheritance—the particulate

or mosaic—is typified by the behavior in heredity of coat-

color in short-horn® cattle in which, in the F, soma, the

Black Man Yellow Man White Man

Louis 5. rie

«The red of these aga carmine wW which accordi

to Riòway’s Color Standards is composed 552 of spectrum

red, 45z of black.

Fie. 4. Composition of Skin-pigmentation in Representitives of Three Races.

_Jamaicans- of the Moneaque Holel, Monea Jamaica.

Mimie Webster Victer Webster David MacDonough CLlewellyn

N.162

R pas Be R.44%

Y. 292 Y.252z Y.162 y. sor

W. 272% W277 We4ex W. 192

1002 10027 “O07 hoor

Broca's Scale Brocas Scale Brocas Scale Scale Broca's Scale Broca's Scale

E T E ese TEE y SIE ORA #3.

Fie, 5. Variation in Skin-pigmentation Among Jamaicans

6 ‘‘ Inheritance of Coal-Color in Short-horn Cattle,’? AMERICAN NATURAL-

ist, December, 1911, January, 1912, by H. H. Laughlin

No. 588] F, BLEND AND GENIC PURITY

Coat Color in Short-horn

Caltle:-

is dependent upon ive ae “the”

inheritance areas

conlrol of which lie in the same@ch

mosome.

@)1Hrea cavers two flank belts, the underline, the

median line of the face, pou a mosaic, either coarse

or fine, sagas. 3 the remainder

2.Area twa cove s the neck, the sides, the back, hina

quarters and and a mosaic either coarse,

covery; remainder of the i Pony oe omen or of area

ay ee

one the breed white c

as He tae recessive alelormorph Cs te note)

> re area twe pea breed a over:

8) The, I The proof consists in the fact GEO indiridon] Shot

nd while in area twa

& pan stands for any mosaic- either fine or coarse-

of red and white.

Nete~

‘Ry is dom, is Sorina piad ti mall r for

nally a as frequen ared

are coe will produce a spotted ora roan

Vif are Se oak po cae than Bme strai Pa

same aren jn another strain, fines caff produced

bya mating would the following

g Area one WR-opposing positive genes allelo-

mor, $

he this

Pis > aaee herewith vith deacrited, including th

the allelo s for o that

E morphic genes f ra-sygotic reaction i

a fluctuation thru the criti paint of somale

Servet abe te a auth feller actos oF

coat-color in Shorthorn cattle,

EER oe jy Paw) Sone ay: Tid nea e-

749

Lellers identify spools.

aa)

Fic. 6. Chart showing the F, Blend Associated with Particulate Inheritance—

a Patent Mosaic

750 THE AMERICAN NATURALIST [ Vou. XLIX

character concerned is, in its grosser aspect, clearly mid-

way between the corresponding traits of its two parents,

although a closer inspection reveals a mosaic the elements

of which are the parental traits quite unchanged. The

difference between the Andalusian fowl and the short-

horn cattle cases seems to be as follows: In the Anda-

lusian each gene influences the entire plumage-color, and

appears to be struggling unsuccessfully, as it were, for

the supremacy in somatic expression, thus resulting in a

very fine and quite generally distributed blend or mosaic;

while in short-horn cattle the controlling genes are double

the number, each pair being confined to specific coat

areas in somatic expression, and the resulting mosaic,

although quite variable in coarseness, is always relatively

coarse and is also quite definitely patterned.

Thus, normally (for the exception see the note in Fig.

6) in Area 1 the gene ‘‘W”’ is clearly dominant over the

gene ‘‘R.’’ In Area 2 the gene ‘‘R”’ is dominant over its

absence. There seems to be in Area 2 no competing or

allelomorphic gene whatever—it is simply “R?” or its

absence, i. e., albinic white; whereas in Area 1 the ‘‘W,”’

which is epistatic to ‘‘R,’’ will leave ‘‘R’’ by its absence.

The evidence for all this consists in the fact that a white

short-horn (which is evidently dominant white, always

duplex, in Area 1, and always recessive white in Area 2)

will, when crossed with a black Angus, which is dominant

black for its entire coat, give in the offspring a calf domi-

nant white, simplex, in Area 1, and black, simplex, in Area

2—the familiar ‘‘blue roan” in cattle. That in short-horn

cattle the genes ‘‘W”’ and “R” lie in the same chromo-

some is sufficiently proved by the fact that the color

pattern is never reversed, that is to say, in bi-colored indi-

viduals of whatever coarseness of mosaic, Area 1 is

(Note:—When this paper on coat-color was written it was pointed out that

coats red in Area 1 and white in Area 2 were never observed. Now the

modified interpretation, involving linkage and a variation in genic valence,

as explained in the text and Fig. 6 of the present article, accounts for prac-

tically all of the observed facts.)

No. 588] F, BLEND AND GENIC PURITY 751

always dominant white, and Area 2 is always red, and we

never find an individual red in Area 1 and white in Area

2, although solid whites and solid reds, and bi-colored

individuals of the first specified type are common. The

reversed pattern, i. e., red in Area 1 and white in Area 2,

would occur if the genes ‘‘W’’ for Area 1 and ‘‘R”’ for

Area 2 were completely segregable, i. e., if they lay in dif-

ferent chromosomes. For a further explanation of this

mode of blending inheritance see the accompanying chart,

‘*Coat-color in Short-horn Cattle.’’

THE POPULATION OF THE ‘‘BLANKET-ALGO”’

OF FRESHWATER POOLS!

' EMILIE LOUISE PLATT

CoRNELL UNIVERSITY

Tis is a study of the community of life that is bound

up with the floating masses of filamentous alge, popularly

known as ‘‘blanket-alge.’? An acquaintance with this

population is worth cultivating for the sake of the variety,

beauty and interesting peculiarities of the plants and ani-

mals found in this unique habitat. It may be of utili-

tarian value as well, for there exists a relation between

plankton production, algal growth and fish culture. Fur-

thermore, it may be a help to students and to teachers of

biology when they are in search of certain laboratory ma-

terials, which in these alge masses flourish.

Method of Collecting.—A fine silk hand net of No, 12

bolting cloth was used to lift the alge from the surface of

the water. The largest collection covered about 2,800

sq. cm.; the smallest about 10 sq. cm., but most of them

were from 200 sq. em. to 800 sq. em. in area. Doubtless,

many active and comparatively large foraging animals,

such as small fishes or adult insects, escaped while the

net was surrounding and enveloping the mass. Probably

comparatively few of the smaller forms were lost through

the fine silk mesh of the net. The volume of the mass

was then computed in cubic centimeters. As the mass

sometimes lay in thin layers and sometimes in thicker

masses, the proportion of volume to surface was seldom

the same. About 200 cu. cm. was the average. The com-

ponents of the ‘‘blanket’’ were determined and all forms,

plant and animal, were listed and their size and relative

abundance noted. The collections were made during the

fall and early winter of 1912 and the spring and early

summer of 1913.

Location and Character of the Pools.—The pools are

all located in the vicinity of Cornell University campus at

1 This study was carried on in the limnological laboratory of the depart-

ment of entomology of Cornell University under the direction of Professor

James G. Needham.

752

No. 588] POPULATION OF “ BLANKET-ALGÆ ” 753

Ithaca, N. Y. (see map). They varied from shallow,

transient collections of ditch-water to large, permanent,

usually stagnant pools. Those lettered B, C, D, G, J, M,

and N belong to the first category. Pools x, x’, x”, x, x*,

CAY.: ;

Fp / |

wer Ny = — Nas

[>]

„$

“o

‘ \

MIL Š

CONTOUR INTERVAL £00 FEET

Pools in the Vicinity of Cornell University Campus.

and y, y', E, K, I, and L are permanent pools and measure

from four to thirty or more inches in depth. Pool H is a

quiet part of a large stream. Pools F and A are artifi-

cially enclosed and are filled from pipes. The pools of

the lowland of Cayuga Valley (about 400 ft. above sea-

level) are A, B, C, D, and E. The others are among the

hills (about 800 feet above sea-level).

The Filamentous Alge of the Floating Mass.—Although

there was such variety in seasonal conditions and in the

754 THE AMERICAN NATURALIST [ Vou. XLIX

location and character of the pools, nevertheless some

forms appeared constantly. Among the filamentous alge,

Spirogyra was almost uniformly present, appearing

twenty-eight times out of thirty. The species were not

identified until March, but in the twenty collections taken

in the spring and early summer, the most frequent species

was Spirogyra varians. Spirogyra insignis was found

five times. Other species seen less frequently were:

S. tenuissima S. communis

S. sticticum S. fluviatilis

S. grevilliana S. bellis

S. weberi S. nitida

S. quinina S. inflata

S. crassa S. decimina

S. majuscula S. rwularis

Usually the masses contained several species of Spiro-

gyra, often withalarge proportion of one species, and the

Spirogyra was almost invariably associated with other

filamentous alge. Among the most frequent of these

were Mougeotia and Zygnema. Vaucheria was found

frequently in the autumn and early winter. Oscillatoria

was quite constant after its first occurrence in early

March, but it was usually in very small quantities. Ulo-

thrix Draparnaldia and Microspora were seen occasion-

ally, but not in abundance, while Anabena oscillaroides

was found only once. In general, the large permanent

pools produced the greatest variety of genera and species

of these alge, but otherwise there was no apparent rela-

tion between the genera of alge produced and the char-

acter and location of the pools; with the possible excep-

tion of Draparnaldia plumosa, which was found four

times out of five in shallow ditches.

Diatoms, Desmids and Other Alga.—Diatoms were in-

variably present. Of these, there were four that were

constant and always in greater quantity than other kinds.

These four were Navicula, in great variety, Synedra, Coc-

conema and Gomphonema. Other diatoms were seen ir-

No. 588] POPULATION OF “BLANKET-ALGZ ” 755

regularly as to quantity and time of occurrence and in-

cluded the following:

Tabellaria Cocconets

Fragillaria Campylodiscus

Meridion Amphora

Asterionella Pleurosigma

Diatoma Nitzschia

Encyonema Odontidium

Cymbella Cyclotella

Most of these were free but often Gomphonema, Cocco-

nema and Cymbella were in colonies attached by branched

or simple stalks to larger forms. Encyonema is found

end to end in colonies enclosed in long filament-like gelat-

inous envelopes. Navicula as well as stalked diatoms

sometimes covered the bodies of larvæ and smaller crus-

taceans and also the cases in which the chironomid larvæ

spent part of their time. Variation in occurrence of dia-

toms is apparently due to seasonal changes, which will

þe considered later.

Other algæ were less constant, the most regular one be-

ing Closterium, which occurred in eight collections, show-

ing a number of species. Of the other desmids that ap-

peared, Cosmarium, Penium and Staurastrum were

usually in small quantities. Twice, however, Cosmarium

and Closterium both appeared in abundance, the first

time being in a permanent but shallow pool (I) where

Ulothrix predominated, and the second time in a shallow

but probably permanent roadside pool (G) covered with

Spirogyra. The Volvocaceæ were represented by Volvoz,

Eudorina, Pandorina, Spherella and Chlamydomonas.

Two Phæophyceæ, Dinobryon and Synura, and four Pro-

tococcaceæ, Dictyospherium, Kirchneriella, Protococcus

and Scenedesmus, added variety but did not appear fre-

quently. Peridinium, Pediastrum and Ophiocytium were

rare. :

The pools (Z and Y) that had the greatest variety in

desmids and kindred forms were also rich in diatoms.

756 THE AMERICAN NATURALIST [Vou. XLIX

These pools are large and one or two feet deep and have

thin mud overlying rock bottom. Both lie near Fall

Creek.

The pools (K, x, 21, x’, x+) near Cascadilla Creek pre-

sented the only specimens of Dinobryon that were seen.

These pools are permanent and deep and have stony

bottom. |

It may be significant that in the low-ground pools there

were few kinds of diatoms and in only one such pool (A)

were there any desmids.

The Animal Population.—The floating and entangled

vegetation of these masses supports a large animal popu-

lation. The protozoans found were particularly varied

and interesting. Ameba, Arcella and Difflugia appeared

irregularly in the upland pools. Cochliopodium and Mas-

tigameba were rare. No other Rhizopods were observed.

The ciliates were not determined before March, with the

exception of Paramecium, which was listed from the first.

In the twenty collections made since March first, fifteen

genera of ciliates have been observed. Paramecium was

constant and abundant. Among the larger representa-

tives of the group, Coleps, Chilodon, Colpidium, Stylo-

nychia and Vorticella appeared frequently and in large

numbers. Stentor, Dipleurostyla and Amphileptus were

less frequent, as were the smaller members of the group,

namely, Euplotes, Halteria and Askanasia. Coleps was

especially noticeable in pool y', while Vorticella was plen-

tiful in pools D and G. Pools D, G and J, which supplied

the largest number of genera and of individual ciliates,

are shallow ditch-pools with muddy bottom, while A and

Y in which smaller numbers were found, but still many

genera, are larger and deeper, but have muddy bottom or

muddy water. From this it seems evident that these

protozoa prefer water with inorganic material in suspen-

sion, although they are said to avoid water polluted by de-

caying organic matter. These tiny creatures forage bus-

ily among the algal filaments, some swimming and rotat-

ing smoothly, others, such as Halteria and Stylonychia,

No. 588] POPULATION OF “ BLANKET-ALGZ ” 757

moving by jerks and sudden dartings hither and yon.

The minute form, Euplotes, has a peculiar method of loco-

motion that looks like walking along a filament, though it

is merely forward progress by means of cilia.

The flagellates were represented by Euglena, Distigma

and Phacus, of which the first was fairly constant. Three

heliozoans, Actinospherium, Actinophrys and Vampyrella,

appeared infrequently. Hydra was found in one collec-

tion only, and no other ccelenterates were seen.

Various worms, mainly the microscopic nematodes as

well as unidentified planarians and turbellarians, also

three kinds of oligochetes, namely Nais, Tubifex and

Chetogaster, were frequent but not regular inhabitants of

the alga-mass.

The rotifers were regularly a part of the population,

furnishing species of eighteen genera. Determination of

genera was not undertaken until March The genus most

constantly in evidence was Diglena, especially in dirty

water, foraging industriously, nibbling and pulling at the

alge. A species of Metapidia with a broadly curved

lorica was seen several times. It clung by its toes to

debris, while the flow of water carried food-particles past

the rotating cilia into the mastax. Anuwrea, Salpina and

Syncheta were found exclusively in the pool nearest Cay-

uga Lake, pool A. Also in this pool, as well as elsewhere,

were found Polyarthra, Rotifer, Adineta, Diglena, Noth-

olca labis and a long-spined species of Rattulus. This

permanent pool and a similar pool (X!) of the highland

were richest in rotifer life. Forms found in the latter

pool and not observed elsewhere, were Notommata and a

species of Stephanops with a fan-like anterior projection

of the lorica. Other genera identified were Brachionus,

Philodina, Mytillina, Mastigocerca and Diaschiza. Cheto-

notus, a representative of the Gastrotricha, was seen a

few times.

The Gastropoda, the only mollusk group represented,

did not furnish a constant element, since only eight collec-

tions contained any snails. Lymnea appeared once,

758 THE AMERICAN NATURALIST [ Vou. XLIX

Physa five times and Planorbis four times. These snails

varied in size from two to twenty-five mm. long. Except

in one instance, they were in shaded pools or came out on

cloudy days. The exceptional case may be considered as

similar because the luxuriant growth of watercress near

the algae furnished spots of shade, although most of the

“blanket” was in sunlight. It seems fair to assume that

snails are not regular inhabitants of the surface alge, but

merely forage there when there is little or no sunlight.

Many small crustaceans were observed. Chydorus and

Bosmina were numerous, while two other Cladocera, Daph-

nia and Simocephalus, were less in evidence The ostra-

cods found were in eleven collections and quite numerous.

They have not been identified. Cyclops, Canthocamptus

and Diaptomus were the copepods identified. Cyclops

was remarkably constant and abundant. Many females

bearing paired egg-sacs and many copepod nauplii, pre-

sumably young cyclops, were among the number. The

adults were from one to three mm. long. The Isopod,

Asellus aquaticus, was found only once and then in a mass

of alge close to a mud bank. Two amphipods, Gam-

marus and Hyalella, were observed several times.

The last group of foraging animals and the one to which

the largest individuals of this population belong is the

Insecta. In this class were found larve, nymphs and

adults, representing five orders of insects. Three nymphs

of Callibetis, in pool A, one of Betis, in pool M, and ten

of undetermined genera of Ephemerida in Pool F were

the only may-fly nymphs found. The Odonata were more

frequent. There were a few Libellulids, and a number of

nymphs of Enallagma and Ischnura. The Hemiptera had

only one representative, Corisa, the water-boatman, which

was caught twice but was frequently seen swimming on the

clean surface of the pool. It can hardly be considered a

regular inhabitant of the alga-masses.

Four different larve of the order Diptera made up the

greater part of the insect population. Chironomus was

particularly conspicuous, since the larve were found con-

No. 588] POPULATION OF “BLANKET-ALGH ” 759

stantly, and were generally very numerous. Masses of

eggs of Chironomus cayuge Johannsen were found en-

closed in an oval mass of gelatin anchored to some of the

alge, also myriads of newly-hatched, almost microscopic

larve were seen, so it is reasonable to assume that, for

these pale pink or yellowish chironomus larve (1-18 mm.

long), this environment is the normal one. A few larger

species, some of them blood-red, were found also. Larve

of the ‘‘punkie’’ Ceratopogon and of the soldier-fly, Odon-

tomyia, were seen occasionally. Although mosquito-larve

are found regularly in stagnant pools, it is surprising to

note that only twice were these larve found among the

filaments of the floating alge. These larve were not

identified.

A few larval beetles and a few adults made infrequent

appearances. Undetermined Hydroporus and other dy-

tiscid larve were among these. Although known as a

dweller among filamentous alge, the Haliplid beetle larva,

Peltodytes, was seen only once, its long spiny hairs

tangled in the vegetation. _ Adults of two genera of Hy-

drophilid beetles were identified as Helophorus and

Crenophilus and a few other diving-beetles were seen but

not identified.

Although tadpoles, and once a young salamander, were

found in the collections, they can hardly be reckoned as

members of the society under consideration.

Dominant Forms.—In this diverse population the con-

stant and abundant forms have been few. Spirogyra,

especially Spirogyra varians, Mougeotia and Zygnema,

were the principal constituents of the ‘‘blankets.’’

‘Among the Diatoms, the dominating forms were Cocco-

nema, Navicula, Gomphonema and Synedra. Other alge

were best represented by Closterium, Dictyospherium

and Dinobryon. Among the animals Paramecium,

Euglena and the rotifer, Diglena, were quite constant.

The forms that appeared most regularly were Cyclops

and the larve of Chironomus. Some of the less constant

forms showed the influence of seasonal variation.

760 THE AMERICAN NATURALIST [ Vou. XLIX

Seasonal Variation.—In the autumn and early winter

Vaucheria was usually present, but appeared only twice

in the spring. Pandorina and Peridinium also appeared

late in the year. At that time fewer protozoa were seen

than in the spring, but, as has been said, variations here

seem to be more closely related to the character of the

water than to the temperature. Gammarus and the

nymphs of may-flies and dragon-flies were most numer-

ous in October, November and December.

The spring season also had its special forms. Oscil-

latoria appeared first in March and was constant there-

after. Diatom production was at its height in April and

May at water-temperatures varying between 8° and 16°

C. and there was a marked decline in diatom appearances

toward the end of June. In contrast to diatoms, desmids

seem to require higher temperatures, since most of the

Closterium and all of the Cosmarium and Staurastrum

that were seen appeared in June, in water at temperatures

between 15° and 20° C. The proportion of Dinobryon

in collections became noticeably greater during the latter

part of June. The smaller crustaceans, excepting the

ever-present Cyclops, showed marked increase in num-

bers as well as in diversity during May and June. The

Same seasonal increase was noticed for Anguillula and

the rotifers. Most of the coleopterous and dipterous

larvæ were found in May and June, except Chironomus

which was present at all seasons. °

Another point of interest in connection with seasons is

the time of reproduction. Spirogyra was found conju-

gating in October, April and June; M ougeotia in Novem-

ber, December, May and June. Young, sessile plants of

Ulothria were seen in April and May. All through the

year, copepod nauplii and female Cyclops bearing egg-

Sacs were observed. Chironomus eggs were found in

April and early in June, while very young larve were

abundant during April, May and June.

In view of the fact that floating alge were found in

large quantities in December, even under ice, it was sur-

No. 588] POPULATION OF “BLANKET-ALGA” 761

prising to find some of the pools totally devoid of this

kind of vegetation in spring. Pools K, M, 2, x', x, x, x*

showed this peculiarity. Their ‘‘blanket-algw’’ did not

reappear until May. This disappearance of surface

vegetation may have been due to spring freshets, as the

pools mentioned are in the flood-plain of Cascadilla Creek,

although not in the stream-bed.

_ The Natural Balance.—Like other societies, the popu-

lation of the ‘‘blanket-alge’’ has its producers and its

consumers, its hunters and its hunted, each readily ex-

changing rôles as occasion demands. The synthetic or-

ganisms include with the phytoplankton a few chlorophyl-

bearing organisms of the zooplankton; that is, forms like

Euglena, Phacus and Distigma, which, in sunlight, have

the holophytie method of feeding (Stokes, 1895). Dia-

toms require nitrates, silica and some salts to make their

dainty and beautifully marked shells. Since they are

comparatively heavy, they sink slowly, but are brought to

the surface during the spring and fall circulation of the

water. In spring they multiply rapidly near the surface,

since they need oxygen and sunlight.

_ Many of the tiny creatures, including ciliates, Clado-

cera, rotifers and nymphs and larve of some insects are in

search of diatoms. These animals eat other tiny food

particles as well as diatoms. The rhizopods, Arcella and

Ameba, ingest diatoms, desmids, small protozoans and

even rotifers. Vampyrella consumes the cell-contents of

alge. Actinophrys prefers the spores of alge, but takes

small protozoa. Actinospherium is omnivorous (Stokes,

1895). ‘Many of the ciliates eat diatoms and other ciliates.

The food is drawn into the oral opening by means of cur-

rents of water which are directed toward the opening by the

constant motion of cilia. One ciliate, Chilodon, has a pe-

culiar method of feeding. It protrudes a broad flexible

lip-like expansion of the anterior end and gathers up

food particles with a sweep of this organ.

Turbellarian worms feed on rhizopods, ciliates and —

rotifers. Rotifers eat diatoms and some nibble alge,

762 THE AMERICAN NATURALIST [Voi XLIX

whereas the closely related Gastrotricha, Chetonotus,

eats minute particles of decayed animal and vegetable

matter, rarely taking diatoms.

The smaller crustaceans in general and the snails are

scavengers, removing decaying algæ and bits of dead in-

sects or other animal matter. The Cladocera, however,

are said to eat diatoms and many of the smaller algæ.

Ostracoda are omnivorous and often attack their own

species.

Among the insect members of this society, the larvæ of

the may-flies and midges are the great herbivores, al-

though, in addition to algæ, diatoms and leaves of higher

plants, consuming a great variety of vegetable sub-

stances, both living and dead. The great abundance of

Chironomus larvæ make this genus an important factor,

both as a consumer, and as food for other animals.

Chironomus larvæ and pupæ are, in turn, eaten by dragon-

fly nymphs, and other predaceous larvæ. They are of

much importance as fish-food.

Dragon-fly nymphs are predatory. Some species eat

back-swimmers and water-boatmen, small crustaceans

and snails, coleopterous and dipterous larvæ and even

young dragon-fly nymphs. The larger nymphs are eaten

principally by fish, occasionally by water-birds.

This brief account of some of the feeding-habits will

serve to show how much all the members of this society

are dependent upon the others, and, at the same time,

are in constant danger of extinction. Each form acts as

a check upon too rapid multiplication of some other form.

Since the most prolific animals in this population are

Cyclops and Chironomus, each must have peculiarities

that enable it to survive in this environment and to com-

pete with other animals. Cyclops adapts itself easily to

changes. Its prolific reproduction, seasonal constancy,

and plasticity, give it great advantage over other small

crustacea. Chironomus, also constant, prolific and adapt-

able, finds abundant food and comparative shelter among

the algal filaments.

SHORTER ARTICLES AND DISCUSSION

ON PRACTICAL VITALISM

In a series of critical and polemical essays, published during

the past few years in American journals by diverse authors, par-

ticularly by Jennings, the problem of vitalism has been dis-

cussed in a manner that may seem exhaustive.

There would appear to be no possibility of adducing new ar-

guments in the matter. If in spite of this a new presentation

is here attempted, it is because the author holds a standpoint

entirely divergent from what has been thus far set forth in the

discussion.

If it is true that the argumentation of the promoter and

leader of the new scientific vitalism—Driesch—becomes at times

somewhat metaphysical, it appears to me also that the criticism,

as made by Jennings, tends at times to become dialectical and

sophistical.

I can not otherwise characterize the tendency to efface any

specific difference between the living and the non-living. By

isolating at random a feature of the living and comparing it

with an inorganic model one can indeed seem to show the iden-

tity of the two. But in this procedure we recognize the typical

method of the ancient sophists. I can find nothing of interest,

= for example, in such an argumentation as the one cited below

from Jennings.’

In a rejoinder to Lovejoy, who insists ‘‘that the same phenom-

ena occur in a given organism in spite of profound modifica-

tions of the composition and configuration of the parts’’ Jen-

nings objects that we have here

a proposition that holds for things in general. An iron body of a certain

form moves toward the earth. We may change the form in most varied

ways . . . change the material, substitute lead, brass, stone . . .; it still

moves toward the earth.”

Nothing is easier than to prove that black and white, plant

and animal, man and monkey, are ‘‘fundamentally the same.”’’

1A typical one for the antivitalistic criticism.

2 AMERICAN NATURALIST, 1913, p. 395.

763

764 THE AMERICAN NATURALIST [ Vou. XLIX

But does an affirmation of this sort annihilate in any way the

specific difference between man and monkey, or diminish the in-

terest of science in this specificity ?

The innumerable attempts of the critics of vitalism to prove

by comparison of certain isolated features that the living is

nothing more than an extreme complication of the non-living

fail, because the analysis in such cases is never exhaustive. One

may prove that living and inorganic coincide in many points;

he can not prove more.

I do not see why these points of coincidence are of more im-

portance and interest for our conception of the matter than the

points of undeniably distinctive = even though the latter

are as yet unanalyzed.

The best way to test the validity of an idea or hypothesis is to

follow it to its most extreme but logically inevitable consequences,

taking these as a statement of the proposition involved.

If we follow this method in order to obtain an objective and

exact formulation of the essence of vitalism (or of its antithesis,

mechanism), we can say that what mechanism asserts is this:

Whenever a certain configuration of matter occurs or is given,

there also what we call ‘‘life’’ is found; or in more popular

terms, the artificial production of a living organism from ‘‘non-

living’’ matter would theoretically be possible.

Vitalism, on the other hand, is a standpoint that in last in-

stance denies such a possibility.

It is clear that both the assertion and the negation are un-

provable, and as such are matters of faith, not of emprical

science,

If one attempts to give an estimate of the two from the stand- —

point of science, sympathy must, it appears to me, incline to the

vitalistie view, since scepticism is the very palladium of exact

science.®

It is generally overlooked that if one of the two opponents is

to be reproved as aggressive, that one is the mechanist rather

than the vitalist. The mechanist in asserting that he knows

more than can be proved is filled with a scientific optimism of a

somewhat frivolous character.

Yet it is the moderate agnostic standpoint, declaring no belief

3 It may be objected that a negation is dogmatic to the same degree as an

assertion. This may be true. But one can ropie the term ‘‘negation’’ by

some other less radical expression, such as ‘‘doubt,’’ without altering the

essence of the standpoint.

No.588] SHORTER ARTICLES AND DISCUSSION 765

in the possibility of artificial synthesis of the living so long as

that is not proved, that is subjected to ridicule as a dogmatic,

obscurantist and non-scientific doctrine.*

The entire problem to me falls in the domain of ‘‘ Natur-philos-

ophie,’’ that branch of our knowledge which can not directly

prove the truth or logical necessity of the results of investiga-

tions made in its field; can do no more than to make them plaus-

ible; and thus give to us a genuine sensation of mental satis-

faction.

There is no intention here of participating in the endless dis-

pute above sketched; I do not know what could be added in this

direction, from a vitalistic point of view, to the formulations, of

Driesch.” Our purpose is the defense of the right to a prac-

tical vitalism, as a method of exact empirical (although not

necessarily experimental) investigation.

e do not care whether the methods demanded by such a

vitalism are or can be proper also for inorganic investigation.

It appears that they are not, for the mechanists oppose their

‘‘veto’’ in the name of exact science to all constructions of the

vitalistie system, even though not fully analogous with that

which will be detailed below.

Practical vitalism claims the right to be restricted in formulat-

ing hypotheses only by postulates of logic and of the general

theory of knowledge, and by nothing else.

4 The same point can be made with regard to the other aspect of vitalism

—the so-called ‘‘experimental indeterminism.’’ As to this, it must be ad-

mitted that the empirical evidence seems to favor the vitalistic standpoint.

The assertion of the mechanists, that experimental indeterminism can not

hold for the living, is likewise a matter of faith, and the burden of proof

falls upon those who make it.

5I must nevertheless confess, despite my profound admiration for

Driesch’s work, that nd that his chief experimental foundation of vital-

ism, by means of his masterly analysis of certain cases of regulation, fails

to produce the desired effect; chiefly because the entire argument rests upon

certain experiments that are, as one may say, a lucky chance in biological

investigation. It would be quite possible that no organisms having the mar-

velous powers of regulation and equipotentiality shown by Tubularia, the

sea-urchin or Clavellina, should ever be discovered. Can it be admitted that

a scientific proof of vitalism as the basis of biological research would there-

fore remain inaccessible? The argument in such a capital problem must, I

think, rest on a more general basis, one resulting from an adequate analysis

of essential and genuine vital phenomena. I incline therefore to consider

Driesch’s further analysis, as presented in his ‘‘Science and Philosophy of

the Organism’’ as a no less valuable part of his work. :

766 THE AMERICAN NATURALIST [ Vou. XLIX

We hold as a justified demand of the theory of knowledge

that every hypothesis must be fruitful; that is, it must give a

number of deductions that can be verified empirically. Every

hypothesis which permits us a prediction is to be considered a

step in the progress of knowledge, until such time as it is re-

placed by a new one, more suitable or more fruitful.

Biological, and particularly embryological, investigation needs

sometimes to introduce as a hypothesis for the explanation of

certain empirical facts the idea of so-called ‘‘immaterial’’ (or

in Jennings’s terminology ‘‘non-perceptual’’) factors.

This is the chief point on which are based the recriminations

of most critics of vitalism, especially of Driesch’s vitalism.

The belief in such ‘‘non-perceptual’’ factors is in Jennings’s

mind synonymous with obscurantism or dogmatism. To Ritter

‘‘the vitalism . . . is the belief that organic phenomena can not

be fully explained by referring them to the material elements of

which organisms are composed, but that something not really

belonging to the natural order [?] ... is present in living

things’’ (italics mine).

si me it is entirely obscure why the term ‘‘non-perceptual fac-

tor,” employed by Jennings in a logical and consistent manner,

is by him rejected as nonsense.

His formulation of the non-perceptual is very clear.

Conditions subject to diverse physical tests will here be called either

perceptual or physical.®

A non-pereeptual agent would be one which though producing at a

particular time a particular physical event, was not subject to other

physical tests for its presence.”

I have given a formulation much resembling this, of what I call

the ‘‘immaterial factor’’ in my paper bearing that title, printed

in the ‘‘Festschrift fiir Schwalbe.’’

This work was to have been published the first of August,

1914, at the very moment of the outbreak of the war. Whether

it has been issued I do not know.

My definition is as follows:

Als materiell gilt uns im allgemeinen ein Objekt unserer Erkenntniss

welches eine Mehrzahl von einander unabhängiger Eigenschaften (se.

Wirkungsweisen) in sich vereinigt und sowohl in Tätigkeit als in Ruhe

befindlich wenigstens gedacht werden kann.

6 Johns i University Circular, 1914, No. 10, p. 8.

7 Ibid., p

No.588] SHORTER ARTICLES AND DISCUSSION 767

Ein zur Erklärung bestimmter Wahrnehmungen ersonnener Factor

von dem eine derartige Annahme d, h. ein Zustand der Nichtbetätigung

widersinnig wäre mag folgerichtig als “nicht materiell” bezeichnet

werden.

Neither Jennings’s ‘‘non-perceptual’’ or my ‘‘immaterial’”’

can be considered an illogical or contradictory conception.

Criticism must, so far as my own doctrine is concerned, be there-

fore concentrated solely on the strength of the empirical founda-

tion for the hypothesis of immaterial factors in any given case.

Besides the logical definition given above, an examination is

required of the question; What exactly can be meant by, or how

can one be led to assume, an ‘‘immaterial factor” as a result of

experimental investigation, or at least as a hypothesis impelled

by such a result?

To Jennings the assumption of a ‘‘non-perceptual agent’’

leads directly to, or is synonymous with, the so-called ‘‘experi-

mental indeterminism,’’ as admitted by Driesch.

He seems to neglect every other possibility of the action of an

‘‘immaterial factor.’’ I do not see that this is inevitable.

To me the essential point of the problem lies in the question

of the ‘‘bearers’’ for any sort of empirically detectible action

(induction, force, or the like).

Suppose that it were found that the factors directing the

movements of a given element of a living organism (for example,

the cell of an embryo), in a given direction m to the point n, lie

outside itself.

e will then assume at the point n a center of forces.

Suppose now that we can deduce from this assumption certain

consequences that will be subsequently verified empirically.®

Our assumption that gives us possibilities of prediction becomes

then a scientific reality. We say ‘‘reality,’’ although it may

remain somewhat hypothetical. We find the same condition of

affairs in the imperceptible but strongly inferred realities of

physies, ete.

8 I find that there is a point at which Jennings’s conception of the ‘‘non-

perceptual’’ seems to lead us wrong. It is well to say with Jennings that

such an agent is one producing at a particular time a particular physical

event but not subject to other physical tests for its presence (italics mine).

But Jennings seems not to take into consideration that a ‘‘ particular phys-

ical event’’ or a ‘‘single mode of action’’ (in my formulation) can lead to

many empirically verifiable consequences.

768 THE AMERICAN NATURALIST [Vou. XLIX

Suppose now that at the point of space where we have pro-

jected the center of forces there lies some element of the embryo,

such as a cell. The scientific routine will call this element the

‘‘bearer’’ of the forces in question.

But it is also possible that no element and no matter is to be

found at this point.

The first impulse will be to search for some other element of

the embryo, situated elsewhere, that can act as such a center, by

irradiating certain ‘‘lines of force,’ which influence in some

manner the movements of the first considered element. We will,

however, assume a case where no such element acting at a dis-

tance can reasonably be supposed. What now?

If the fundamental assumption holds true, that the factors

determining the movements of the element lie outside of itself,

we find ourselves confronted by the following alternative:

Hither the presumed factors have a bearer that is not cogniz-

able, or they have no material bearer at all!

It is clear that if we deny the existence of bearers that are

evidently perceptible, we can also exclude the possibility that

such bearers exist, but are invisible owing to their minuteness;

for the presumed center of forces lies according to our assump-

tion outside the organism; or in a district of it where there is

no formed embryonic matter at all.

Thus under the circumstances our two alternatives signify

the same thing, for to say that there is a bearer of factors

that is cognizable solely as the factors themselves involves

a tautology; an assumption of the sort so well character-

ized by the French as a ‘‘hypothése gratuite.’’ While any one

is free to make such an assumption, no scientific use can be made

of it. Methodologically it is perhaps comparable to Kant’s

‘‘Ding an sich,’’ which likewise must remain without empirical

content.

As a fundamental postulate of biological (and especially of

pele ot al research, there can therefore arise the concep-

ton of factors which, although spatial and localized in space,

e no material bearers, and as such may be denominated im-

material.

Is such an idea indeed nonsense; something that proves the

obscurantism of its promoter ?

I am well aware that the ‘‘immaterial’’ factor here presented

is far from coinciding with Driesch’s Entelechy or with any

No.588] SHORTER ARTICLES AND DISCUSSION 769

analogous agent that is e definitione not solely immaterial, but

also non-spatial.

If the entire weight of antivitalistic criticism is directed and

concentrated wholly against such ideas as that of Entelechy;

and if the mechanist will agree with me that a spatial localiza-

tion of a center of forces may be assumed without necessarily

combining this with a material bearer, I shall be much gratified.

But I fear that this is not the case. The ‘‘dynamical prefor-

mation of the morphe,’’ as I have elsewhere called the imma-

terial but spatial factors of morphogenesis,® must, I fear, fall

under the same anathema as the classical vitalism.

To resume the chief postulate of my own ‘‘vitalism’’: if mor-

phogenetic investigation is led in a rigorous inductive way to

assume a spatial factor at a definite point inside or outside the

asc no difficulty or contradiction or nonsense arises if no

‘embryonic’’ matter, or what is the same, no material ‘‘bearer’’

for this factor can be found at that point. Yet of course no

one can be prohibited from forming any sort of hypothesis as

to such functionless bearers, It may be even a psychological

necessity to form such hypothesis, for we love a ‘‘Ding an sich.’’

But such will form no part of empirical research.

The right to work with such immaterial factors, and in the in-

ductive way set forth above, is, for me, the essence of practical

vitalism.

We have now to examine consequences and postulates de-

rived from our fundamental assumption, which seem to present

very great difficulty. If we admit a dynamical factor localized

in space but not derived from a material bearer, it will be asked,

whence comes and how arises this factor?

The question of causation is based on a postulate of knowledge

that can not be eluded; it must be answered in some manner.

I will attempt to point out briefly how one can think the

origin or evolution of such an immaterial morphogenetic factor,

although it must be insisted that we have here a problem which

does not stand in immediate connection with the purely empir-

ical method of investigating the factors considered, so to say,

per se in their activity.

I see no difficulty in assuming an immaterial causality; that

is, the arising of an immaterial factor having a certain property

9 Biologisches Centrablatt, Bd. 32; Archiv. f. Entwicklungsmechanik, Ba.

39; Festschrift fiir Schwalbe, 1914

770 THE AMERICAN NATURALIST [ Vou. XLIX

(for example, configuration) from another less complicated im-

material factor, and so on.

The chain of immaterial factors could in this manner logically

be pursued backward to the beginning of the embryogenesis, or

to the egg.

As to the relation of such immaterial factors to Driesch’s

entelechy, they can be ranged solely in the category of ‘‘means’’

(Mittel) of the latter for the purpose of morphogenesis.

But I repeat that this is for me a matter belonging for the

present not to experimental investigation, but to the domain of

‘“Naturphilosophie.’’

If it appears as if I agree in this point with the ‘‘standpoint

of radically experimental analysis’’ of Jennings, this is not

really the case. The latter author seems to reject all that does

not belong to experimental investigation.

I think, on the contrary, that vigorously logical considerations,

deductive and even inductive, on the given empirical data form

a legitimate and integral part of our science of nature.

A. GURWITSCH

THE WOMAN’s UNIVERSITY,

PETROGRAD,

April, 1915

INDEX

NAMES OF CONTRIBUTORS ARE PRINTED IN SMALL CAPITALS.

age Hen’s Egg, F. E. CHI-

TER

Albino ‘Series of Allelomorphs in

“TAI ket,’? of Freshwater

ia The oly arg oe the,

MILIE LOUISE PLATT

Allelomorphs, Multiple, the ‘Signi

ca of, oes E. es and

H D. FisH, 88; i "0. C.

LITTLE, 122; : The Atbing Series of,

in Guinea-pigs, SEWALL WRIGHT,

140; and Mice, T. H. MORGAN,

Er Fossil, Some Recent Stud-

ies on, Roy L. Moopie, 369; Coal

Sauk me Tage Crossopterygia,

Roy 63

Amphinixis tea Variability, L R.

WAL 6

Aa Mutationist, R. Rue-

TES, 645

Asterias tenuispina Lamk. at Ber-

muda, On the Number of Rays

W. J. rE T.

Asyhmetsy, A

Stud y of, as devel-

oped in the Psa and Families

of Desni Crinoids, AUSTIN H

CLARK,

er wea, HARLEY Harris, Muta-

tion en Masse, 129

Bean, Seed, The Influence of Posi-

tion in the Pod u upon the Weight

of the, J. ARTHUR Harris, 44;

Common, Inheritance of Habit in,

N B. Norron, 547

BELLING, Jo: On the

egregation of Genetic Factors

a Plants, 125; The E

ose Varieties of de Vries,

319; Linkage and Semi-Sterility,

582

Bermuda, On the Number of Rays

in Asteria nr Spe Lamarck at,

Bilaterality in Vertebrates, The

Origin of, A. C. EYCLESHEIMER,

504

Black-eyed White Spotting in bene

727

BLAKESLEE, A. F. and D. E. War-

NER, Correlation between Egg-

of Freshw

ools, Population of the,

EMILIE LovIsE PLATT, 752

ayester amas the Percentage of Re-

rom Incomplete Data,

W. J. SPILLMAN, 383

CALKINS, GARY N., Cycles and

Rhythms and the Problems of

‘‘ Immortality’? in Paramecium,

Mr. Muller

CASTLE, W., E., on the

- Mass Deena 713;

aad Th e Eng-

lish Rabbit and ee. Hinata of

Mendelian nese gar oat Con-

stancy, 23;

Black-and- Tan Rabbit and e

Significance of Multiple Allelo-

morphs, 88

Cat, chad ‘Tortoiseshell, PHINEAS W.

Wu HITING, 518

Girant “showing Sex-linked vent

delian Inheritance, Seventee

Years Selection of, cht

“re Origin of, as

PEARL,

Characters,

observed Fossil and Living

Chromosome, of ash geri Another

Gen the Fourth, RED A,

Hoge, 47; View of ‘Horedity . and

Its Meaning to Plant Breeders,

E. M. East,

A sTIN H., A Study o

Asymmetry, as developed in the

Genera and Families of Recent

Crinoids, 521

Coal Measures Amphibia and the

T12

Crossopterygia, Roy L. Moopiz,

Coc T. D. A., Diptera from

the § Seychelles, 251; Specific ani

Var iets Characters in Ann

Su aan

Correlation Toiora Egg-laying Ac-

Yellow spom in the

iien Fowl, A. F. BLAKESLEE

nd D. AR “360.

Correlations, Value of Inter- annual,

J. ARTHUR Harris, 707

RE pae S The meen

of the Best Value of the, fro

, p Set of Data, F. da E.

CUa OR

Crinoids, Recent, A Study of Asym-

metry, as developed i in the Gen-

era and Families of, AusTIN H.

CLARK, 521

Crossing, Over, None in the Female

of the Silkworm Moth H.

STURTEVANT, 42; Modification of

Characters by, R. RUGGLES GATES,

562

Crossopterygia, and Coal or

Am mobs, Roy L. Moopiz, 637

CROZIE w. dij the pn as of

Rays i in in Asterias tenuispina Lamk,

hagis pee Rhythms and the Prob-

lem of ‘‘Immortality’’ in Para-

mecium, Gary N. CALKINS, 6

Davi ; , BRADLE Y Moors, Additional

the Probable Top of Œnothera

Lam

Dvr, ARTHUR, AEE Evolu-

pe and the Origin of Species,

149

Piskent? New Standard,

Gene e aa in, a H.

SHUL

ari from n e Seychelles, T. D.

A. COCKER Bis

Doubleness, Tnhorita e of, in Mat-

and Poteet. HOWARD B.

Fros'

Drosophila Another g in esa

A. Hogs, 47; ampelophila, A Pe.

culiar Mende lian Ratio in, JOSEPH

Lirr, 97; The Origin of a New

Eye-color. in, and Its Behavior in

Heredity, Ros

A wing Mutation in a S

cies o E.R. Hype, 185;

Mutations in Two Species of, c.

THE AMERICAN NATURALIST

coe R. Hypz, 183;

[ Vou. XLIX

W. and B. S. Merz, 187; repleta,

A Sex-linked Character in A.

STURTEVANT, 18 ; The Infertility

zation of a Sex-linked Mendelian

Character in, T. H. MORGAN, ;

Note on the Gonads of Gynan-

i dg of, F. N. Duncan,

Dunc F. N, A Note on the

Gon ab of Gynand

eroana pepa,

Attempt produce aa

through Hybridization, 575

HE. F. L. and G-U., ¥., The De-

termination of the Best Value of

the Coupling-ratio from a Given

Set of Data, 127

Early Portrayals of Says Opossum,

Peleg on R. EASTMAN, 585

M., The Paani of

Selt sterility, 76, 712; The Chro-

Vie of Heredity and its

Fr E

z On the ee A

the Conditions which determ

or prevent the Entrance of the

foe into the, JACQUES

Egg-laying „Activity and Yellow

the Domestice Fowl,

Correlation between, A. F.

AKES and D. E. WARNER,

360

Enchytræus albidus,

Regeneration

Posteriorly in, é

EN Ww,

UNT, 495

L., Repulsion in

eat, 127

Environment, The Role of the, in the

Realization of a Sex-li nked Char-

acter in Drosophila, T. H. MORGAN,

Varieties of de

i gnificance of

rid fon Internal Conditions of the

Organism in, F. H. and E,

L. Sco

EYcLESH

EIMER, The Origin

of Bilaterality: i in » Vertebrates, 504

Eye-color, New, Origin Drosophila

repleta, and. its Behavior in He-

redity Roscoe R. HYDE, 1

No. 588]

F, Blend accompanied by Genic

H. H. LAUGHLIN, 74

urity,

Fecundity in the feaa n,

deli

of,

Average Flock Production, as

MOND PEARL, 306

Field Experimen nts, On a Criterion

of Substratum Homogeneity sa

Heterogeneity) in, J. ARTHUR

Harris,

1sH, H. D. and W. E. CASTLE, The

Black-and-Tan Rabbit and the

Significance of Multiple Alelo-

morphs, 88

Flock Production, Average, and

Mendelian Inheritance of Fecun-

ay in ~~ omestic Fowl, RAY-

MOND PEARL, 306

Flower Pigments, M. W., 256

and ivin Anim als

Amphibia,

Some. Mpo: Studies in, Roy L.

Moopiz, 3

Fowl, _Domestic, Mendelian Torpe

tance of Fecundity in and are

ago F “Flock icere RAYM a

; Correlation Sarees

Ege ls laying Activity and Yellow

Pigment > i F. BLAKESLEE and

Freshwater Tal Population of i

‘*Blanket of

e Inheritance

Paturs, I. The Hypotheses, 623

Gates, R. Rueetes, On the Modifi-

cation of Characters by Crossing,

tay a Anticipatory Mutation-

Genk eek in the Fourth Chro-

reg ee of Drosophila, MILDRED

Genetic, Definitions in the New

Standard Dictionary, G. H. S i

52; Factors in Plants, On the

Time of Se on of, Jo

Deer Mice, Francis B. SUMNER,

688

Genie Ribas a Tod Blend accom-

panied by, LAUGHLIN, 741

Germ Cells a oes tie Cells, LEO

LOEB.

Gonads of ewer ongs s of Dro-

sophila ampelophila, F. N. Dun-

CAN, 455

INDEX

773

Guinea-pigs, The Albino Series of

Allelomorphs in, SEWALL WRIGHT,

140

GurwitscH, A., Practical Vitalism,

Gynandromorphs of Drosophila am-

pelophila, Gonads of, F. N. Dun-

CAN, 455

Habit, Inheritance of, in the Com-

mon Bean, JOHN B. Norton, 547

HADLEY, PHILIP an W. E.

CASTLE, The English Rabbit and

t on of Mendelian Unit-

character Constancy, 23

ing, The Resemblance of

ins in, EDWARD L

hori of Inter-annual Correla-

tio 707

Heredity, The Origin of a New Eye-

color in Drosophila hg Spe and

183; The romosome View of,

and its Meaning to Plant Breed-

, E. M. East, 457

Hose. MILDRED A., Another Gene =

the Fourth Chromosome of Dros

YRON B., Sterility in a

252

. R., Regeneration Posteri-

orly in Enchytræus albidus, 495

E coE R

ity, 183; A Wing Mu

New Species of Drosophila, 185

tt Immortality’? in Parameci

Cycles and R

Problem of, Gary N.

Sabrane Studies in, RAYMOND

PEARL

Infertility of Rudimentary Winged

ales of Drosophila ampelo-

phila, T. H. MORGAN, 240

grw, itance, Mendelian, of Fecun-

dity in the fee eg Fowl, and

Average Fi Flock Production, RAY-

, 806; of Habit in the

` Common

acter showing, RAYMOND PEARL,

7174

595; of i get in Matthiola

and Petunia, Howarp B. Frost,

ot of Black: -eyed Birer Spot-

n Mic , 127

Inte annual Chavelations, F "ARTHUR

, 107

Titersal Conditions, Certain, o e

Organi Organic Evolution,

The Signifieance of, F. H. Pike

and E. L. Scort, 321

JEFFREY, EDWARD C., Some Funda-

mental Morphological Objections

to the Mutation Theory of de

Vries, 5

LAUGHLIN, H. H., The F, Blend ac-

companied by Ge

JOSEPH, Data on

Mendelian Ratio in Drobojhila

ampelophila,

Linkage and Semi- -sterility, JOHN

a , 582

E A Note on Lo s

pere eA in Mice,

Inheritance of ae -eyed White

Spotting in Mice,

727

LOEB, JACQUES, On the Nature of

matozoon into the Egg, 2

LOEB Bo Sea Cells and Bitte

Cells,

aey ee cn co Experiments

Matthiola and Petunia aces tt

ess How. B.

The English Rabbit

Sio Ost, 623.

Mendelian, Unit-character Constancy,

and the Ques-

aan of, W. E. CASTLE and PHILIP

-li ee AN, 385

-, Mutations

pecies of Drosophila, 187

sae “ad Allelomorphs, T. H. Mor-

GAN, 379 ornia Deer, Genetic

Studies graphie

of, Francis B. SUMNER,

688; The ritance of Black-

THE AMERICAN NATURALIST

[ Vou. XLIX

eyed ‘aby Spotting in, C. C.

LITTLE, 7

Some Recent Stud-

ies on Fossil “Amphib ia, 369; The

oal Measures Amphibia a and the

Crossopterygia, 637

Morean, T. H., The Infertility of

Rudimentary "Winge Females of

Drosophila ampelophila, 240; Al-

rphs

OUGH, e sap ironed

of own Mutations in Othe

Mut an Stocks, 318

orm, ’ No a h ar

Moth, Silkw

in the Female of, A. H.

VANT

Muller, Mr., on the Constancy of

Mende = Characters, W. E.

CASTLE,

Multiple Aiie orphs, The Black-

122

Mutant mag ie The Appearance of

Known Mutations in Other, T. H.

; Wing, in a

mise er of Drosophila, Ros-

j pe a a

Additional 1 Bvidence of, Brap.

Matetionist, Anticipatory, R. Ruc-

GLES GATE

Mutations, in rwo Species of Droso-

phi we C. W. and B. S. Merz >» oats

Kno a Aoi in Other Mu-

vee Stocks, T H M ORGAN and

HAROLD 31 n At-

tempt to Produce, reen Hy-

bridization, F. N. Duncan, 575

NORTON, Tpi B, y stern of

Habit e Common Bean, 547

Notes ond These "32, 127, 251

(Enothera Lamarckiana, Professor

de Vries on the Probable Mie a

of, Y Moore Davis, 59;

Additional Evidence of Mutation

in, BRADLEY Moore Davis, 702

Oran, Early Portra: rayals of,

R. EASTMAN, 585

Ges. The Significance of Cer-

No. 588]

tain Internal Conditions of, in

wii oa porna F, PIKE

d E. L. Sco , 321

Origin: of Boodlea, "i ecb. rg

Evolution, ARTHU

of a New Bye-color in " Drosophila

repleta and its Behavior in He-

ora Roscoe R. HYDE, 183

OsBo HENRY FARFE FIELD, Origin

of ‘Si ingle Characters as observed

in Fossil and Living Animals and

Plants, 193

Paramecium, Cycles and Rhythms

and the Problem of ‘‘Immor-

tality?’ in, Gary N. CALKINS, 65

PEARL, RAYMON n Inh r-

ERE of Fecundity i in a Domes-

owl, and are Flock Pro-

s Selec-

ring -

nee, 595

mheritance

oubleness in: sg

Pudar 62

IKE, F. H. and E. L. Sco The

of Certain Taternal

a Heredity and its Mean-

ingt EAST, 457

LATT, p aie Lovise, The Popu-

lation of the “Blanket Alge’’ of

Freshwater Pools,

ae HAROLD and T e pager

e Appea a of K

tations in Other Mutant "ae

Practical Vitalism, A. GuRWwITSCH,

762

~~ The English, and the Ques-

of Mendelian Unit-character

Coney, STLE and

Pup B. H , 23; The Black-

and-Tan, and the ificance of

CasTLe and H. D. FISH, 88

Rays in Asterias tenuispina

at nia Number of, W. J.

e s re Method of Calculating

the Percentage of Eaa Incom-

plete Data, LMAN, 383

Regeneration Patis in Enchy-

træus albinus, H. B. Hunt, 495

gee oma in "Wheat , F. L. ENGLE-

, 127

ianiai of Young Twins in

INDEX

Semi- -sterility,

, 582

775

Handwriting, EDWARD L. THORN-

DIKE, 377

Scorr, E. L. and F. H. Pixs, The

Significance of Certain Internal

Conditions of = Organism in Or-

ganic Evolution, 321

Segregation of "Genetic Factors in

On the Time of, JOHN

Be a 125

Selection, ’ Sugar- -beets — gprs

W. E. Castiz, 121; Some

Experiments in, W. E Tana,

Self-sterility, The Phenomenon of,

. East, 76, 712

and Linkage, JOHN

BELLING

Sexlinked, Character in ene TF

repleta "A. H. STURTEVAN 189;

Waridi Inheritance, Bewcubail

Years Selection of a Character

owing, RAYMOND PEARL,

Seychelles, i i fiom, T. D.

COCKERELL, 2

T Articles and Discussion, 121,

, 318, 455, 518, 570, 645, 702,

rts

SHULL

, G. H., Genetic ipa in

the New Standard Dictio ary, 52

Somatic Cells and Germ Cells, LEO

LOEB

Species — Sterility in, Byron

B. Horton, 252

Spermatozoon, On the Nature of the

Conditions which determine or

prevent Ponin into the Egg,

JACQUES ;

SPILLMAN, W. J., A Method of Cal-

culating the Percentage of Re-

cessives from Incomplete Data,

383

gora Black-eyed White, Inher-

of, in Mice, C. C. ' LITTE ITTLE,

Sterility, Self, The Phenomenon of,

E. M. EAST, 76; in a Species

B. Horton,

Moth, Sex-linked

Character in Dreaophiin repleta,

Substratum Homogeneity (or Het-

erogeneity) in Field Experiments,

J. ARTHUR Harris, 430

Tibia Selection and Thrips,

W. E. CASTLE

SUMNER, FRAN ae B., Genetie Stud-

ies of Races

Several Geograp hic

of California Deer Mice, 688

776

Sunflowers, Annual, hee and

Varietal. Characters in, T. D. A.

COCKERELL, 609

THORNDIKE, Epwarp L., The Re-

semblance of Young Twins in

Handwriting, 37

Thrips, Sugar-beets and Selection,

W. CASTLE, 121

Tortoiseshell Cat, PHINEAS W.

ung, Resemblance =

andwriting, Epwarp L. THO

DIKE, 377

je repai and Amphiontxi li B.

N, 649

Vertebrates, The Origin of Bilat-

lity in, A. C. EYCLESHEIMER,

Vitalis, Practical, A. GURWITSCH,

Vries, Hugo de, Some Fundamental

Merpholewies! Objections to the

Mutation Theory of, Epwarp C.

J EFFREY, 5; on the Probable Or-

igin of CEnothera Lamar ckiana,

THE AMERICAN NATURALIST

[Vou. XLIX

BRADLEY Moore Davis, 5

Evening Primrose Varieties ey

JOHN BELLING, 319

W., M., Flower Pigments, 256

WALTON, L. B., Variability and Am-

phimixis,

Warner, D. E. and A. F. BLAKES-

LEE, Correlation between Egg-lay-

Wheat, Repulsion in, F.. L. ENGLE-

camel ard

WH PHINEAS W., The

teisoahall Cat, 518

RIGHT, SEWALL. e Albino Series

of Allelomorphs in Guinea- “pigs,

140

Tor-

and F. L. E., The Deter-

of the Best Value of

a peer bale from a Given

Set of Data, 127

Y, & v.