THE ,

AMERICAN NATURALIST

Vou. LIV. January-February, 1920 No. 630

CERTAIN EVOLUTIONARY ASPECTS OF HUMAN

MORTALITY RATES!

PROFESSOR RAYMOND PEARL

THE JOHNS HOPKINS UNIVERSITY

Ir is the purpose of this paper to set forth some facts

regarding human mortality which appear .to lead with

great clarity to certain evolutionary generalizations of

interest to the biologist, which have hitherto been over-

looked so far as I am aware. The present fashion in the

study of evolution is towards the analytical discussion of

the factors. Synthetic general discussions of broad

phases of organic evolution, which occupied so prominent

a place in early post-Darwinian times, are now but rarely

found in biological literature. This may fairly be re-

garded as a blessing, but perhaps not an entirely un-

mitigated one. While much of the general discussion of

evolution of the period of fifty years ago was utter non-

sense, still a view of some of the aspects of the forest may

be at least occasionally stimulating, and particularly in

these present days when we are accumulating such a

mass of precise data about the characteristics of the trees.

It is in some ways remarkable that so little thought and

interest have been given by general biologists to the

phases of biology which form the working material of that

branch of applied science which is roughly but still suff-

ciently intelligibly labelled ‘‘vital statistics.” The data

1 Papers from the Department of Biometry and Vital RPE School of

Hygiene and Public Health, Johns Hopkins University, No.

In preparing this paper I have had the benefit in Seha of pathological

anatomy and embryology of the critical acumen and wide knowledge of my

colleague, Dr. W. T. Howard, to whom I am greatly indebted for this help.

6 THE AMERICAN NATURALIST [Von. LIV

of human natality, morbidity and mortality, when intel-

‘ligently and broadly studied, can, I am sure, throw a

great deal of light on some of the deepest and most sig-

nificant problems of general biology. If the facts pre-

sented in this paper succeed in some small degree in

demonstrating that this opinion is not an entirely idle

one, the purpose of this particular piece of work will

have been served.

By an international agreement among statisticians the

causes of human mortality are, for statistical purposes,

rather rigidly defined and separated into something over

180 distinct causes. It should be clearly understood that

this convention is distinctly and essentially statistical in

its nature. In recording the statistics of death the vital

statistician is confronted with the absolute necessity of

_ putting every death record into some category or other in

respect of its causation. However complex biologically

may have been the train of events leading up to a par-

ticular demise, the statistician must record the terminal

‘‘cause of death’’ as some particular thing. The Inter-

national Classification of the Causes of Death is a code

which is the result of many years’ experience and thought.

Great as are its defects in certain particulars, it never-

theless has certain marked advantages, the most con-

spicuous of which is that by its use the vital statistics of

different countries are put upon a uniform basis.

The several separate causes of death are grouped in

the International Classification into the following gen-

eral classes:

General diseases.

Diseases of the nervous system and of the organs

of special sense.

Diseases of the circulatory system.

Diseases of the respiratory system.

Diseases of the digestive system.

Non-venereal diseases of the genito-urinary system

and annexa.

dada 8p

No. 630] HUMAN MORTALITY RATES 7

VII. The puerperal state.

VIII. Diseases of the skin and of the cellular tissue.

IX. Diseases of the bones and of the organs of loco-

motion.

X. Malformations.

XI. Early infancy.

XIT. Old age.

XIII. External causes.

XIV. Ill-defined diseases.

It is evident enough that this is not primarily a biolog-

ical classification. The first group, for example, called

‘‘General diseases,’’ which caused in 1916, in the Regis-

tration Area of the United States approximately one

fourth of all the deaths, is a curious biological and clin-

ical melange. It includes such diverse entities as

measles, malaria, tetanus, tuberculosis, cancer, gonococ-

cus infection, alcoholism, goiter, and many other equally

unlike causes of death. For the purposes of the statis-

tical registrar it has useful points to make this ‘‘ General

diseases’’ grouping, but it clearly corresponds to,nothing

natural in the biological world. Again, in such part of

the scheme as does have some biological basis, the basis

is different in different rubrics. Some of the rubrics

have an organological base, while others, as ‘‘ Malforma-

tions’’ have a causational rather than an organological

base.

Altogether it is evident that if any synthetic biological

use is to be made of mortality data a fundamentally dif-

ferent scheme of classification of the causes of death will

have to be worked out.

Tit

For the purposes of this study? I have developed an

2 It should be clearly understood that this phrase ‘‘For the purposes of

this study’’ means precisely what it says. I am not advocating a new classi-

fication of the causes of death for statistical use. I should oppose vigorously

any attempt to substitute a new classification (mine or any other) for the

International List now in use. Uniformity in statistical classification is es-

sential to usable, practical vital statistics. Such uniformity has now become

well established through the International Classification. It would be most

8 THE AMERICAN NATURALIST. [Von. LIV

entirely different general classification of the causes of

death on a reasonably consistent biological basis. The

underlying idea of this new classification is to group all

causes of death under the heads of the several organ

systems of the body, the functional breakdown of which

is the immediate or predominant cause of the cessation

of life. All except a few of the statistically recognized

causes of death in the International Classification can be

assigned places in such a biologically grouped list. It

has a sound logical foundation in the fact that, biolog-

ically considered, death results because some organ sys-

tem, or group of organ systems, fails to continue its func-

tion. Practically, the plan involves the reassignment of

all of the several causes of death now grouped by vital

statisticians under heading ‘‘I. General diseases.’’ It

also involves the re-distributing of causes of death now

listed under the puerperal state, malformations, early in-

fancy, and certain of those under external causes.

The headings finally decided upon for the new classi-

fication ‘are as follows:

. Circulatory system, blood, and blood-forming

organs.

II. Respiratory system.

IU. Primary and secondary sex organs.

. Kidneys and related excretory organs.

. Skeletal and muscular systems.

VI. Alimentary tract and associated organs concerned

in metabolism.

VII. Nervous system and sense organs.

VIII. Skin.

IX. Endocrinal system.

X. All other causes of death.

It should be emphasized before presenting the tables

undesirable to make any radical changes in the Classification now. I have

in this paper made a rearrangement of the causes of death, for the purposes

of a specific biological problem, and no other. Iam not ‘‘ proposing a new

classification of vital statisties’’ S4 official or any other use except the one

to which I here put it. i

No. 630] HUMAN MORTALITY RATES 9

of detailed statistics on this new classification that the

underlying idea of this rearrangement of the causes of `

death is to put all those lethal entities together which

bring about death because of the functional organic

breakdown of the same general organ system. The

cause of this functional breakdown may be anything

whatever in the range of pathology. It may be due to

bacterial infection; it may be due to trophic disturb-

ances; it may be due to mechanical disturbances which

prevent the continuation of normal function; or to any

other cause whatsoever. In other words, the basis of the

present classification is not that of pathological -causa-

tion, but it is rather that of organological breakdown.

We are now looking at the question of death from the

standpoint of the pure biologist, who concerns himself

not with what causes a cessation of function, but rather

with what part of the organism ceases to function, and

therefore causes death. It is to be hoped that the novelty

of this method of looking at the causes of human mor-

tality will not per se prejudice the reader against it, to

the degree at least of preventing him from examining the

detailed results and consequences of such classification,

which will be presented in what follows.

There will now be presented in a series of tables the

statistical data as to deaths arranged in this classifica-

tion. The data given are in the form of death rates per

hundred thousand living at all ages from various causes

of death, arranged by organ systems primarily concerned

in death from the specified disease. The statistics pre-

sented are from three widely separated localities and

times, viz., (a) from the Registration Area of the United

States; (b) from England and Wales; and (c) from the

City of Sao Paulo, Brazil. The first two columns of each

table give the death rates, arranged in descending order

of magnitude in the first column, for the Registration

Area of the United States for the two periods, 1906-10

and 1901-05. The third column of each table gives the

death rate from the same cause of death for England and

10 THE AMERICAN NATURALIST [Vou. LIV

Wales in the year 1914. The fourth column gives the

rates for Sao Paulo for the year 1917. The;data for the

United States Registration Area were extracted from

the volume of Mortality Statistics for 1916, issued by the

Bureau of the Census. The English data were extracted

from the Report of the Registrar General of England

and Wales for 1914. The Sao Paulo rates were calcu-

lated from data as to deaths and population given in the

‘t Annuario Demographico’’ of Sao Paulo for 1917.

TABLE I

CIRCULATORY SYSTEM, BLOOD AND BLOOD-FORMING ORGANS

| r

; Registration Area, | p land

No.3 “Cause of Death” as per International UAA ee: ~a Paulo

Classification | rales 1917

1906-10 | 1901-05 1914

79 | Or cana diseaşod ol pA thi hoart i 133.2 | 124.2 | 137.3 | 130.0

81 | Disea if the artirina 17.7 9.4 23.5 59.7

78 | Acute napster vines ag ec uate dead pansies 12.2 11.2 5.1 6.5

T FROAN fever.) Uo isa vec ees 10.6 11.0 Tt 5.4

1504 | Congenital cae of the heart. . 9.0 6.7 4.2 4.65

80 | Angina pecto: Pouca ey Sarees 6.8 6.6 3.2 a:

82 | Embolism Aaa aka Ai, el, aa 3.9 4.2 8.9 8.3

20 | Purulent infection and septicemia..... 3.8 6.1 1.8 22.2

PIAS OND IOP ee a ee ee 3.5 4.5 4.4 2.6

WERT es a ee EEE A E 2.6 4.8 0.2 2.8

85 gponiemal pad oe diseases of the

A EEE I P 1.6 2.8 0.6 2.4

53 | Leuk 1.5 1.2 2.0 2.0

77 | Peri RIGS es E cues es ee eee es 1.3 2.1 1.2 it

54 | Anemia, Ton E E IN ies 1.0 0.5 6.4 8.7

83 Orta VOI. T es ce 0.6 0.6 1.0 0.7

84 | Diseases of the ‘mn a hae ae 0.3 0.2 0.9 0.2

116 | Diseases of the spleen............... 0.2 0.3 0.2 0.4

1O 1 SOON Teer eel ec ee as 0 0.3 0 0

1O i PIMOS ee Ao aa eee 0 0.1 0 0

e EV DR OVO es ER 6 6 0 0

3 Relapsing fever.. : P Ae e E 6 6 0 0

11 | Miliary fever.. 6 6 0 0

SOE ida ee 209.8 | 196.8 | 208.6 | 254.8

Nine of the items in Table I, namely items 77 to 85 in-

clusive, are those of rubric III of the International Class-

3 The numbers in this column in this and the following tables are the

numbers of the several causes of death in the International Classification.

4In part

5 The Gao ese statistics do not separate congenital malformations. This

is the total ra

6 Less than a 1 per 100,000.

No. 630] HUMAN MORTALITY RATES 11

ification, ‘‘Diseases of the circulatory system.’’ The

other items of Table I require some special explanation.

No. 7, ‘‘Searlet fever,’’ appears in the International

Classification under ‘‘General diseases.’’ It is placed

here in the organological classification because in the

vast majority of cases of fatal scarlet fever it is the clin-

ical form of the disease known as septic scarlatina which

is responsible for the death. Spengarn’ says that ‘‘sep-

tic scarlatine is responsible for most of the deaths.’’

‘‘The general condition is one of septicemia.’’ It, there-

- fore, seems best, on the present plan of biological classi-

fication, to put scarlet fever with the circulatory system,

blood and blood-forming organs, since septicemia is the

result of a breakdown and failure to function of the

normal defensive serologic mechanism of the body.

The item 150 in the International Classification is en-

titled ‘‘Congenital malformations,’’ and there includes

the following three subdivisions: Hydrocephalus, con-

genital malformations of the heart, and other congenital

malformations. The second of these subdivisions, ‘‘con-

genital malformations of the heart,’’ obviously belongs

here, and is consequently included, while the other sub-

divisions do not.

Item 20, ‘‘Purulent infection and septicemia,’’ is taken

from ‘‘General Diseases’’ and put here on the same rea-

soning as that just stated for scarlet fever.

Item 142, ‘‘Gangrene,’’ is placed here because nor-

mally in civilian life, under the conditions which pre-

vailed when these statistics were taken, most fatal gan-

grene is due to impairment of the circulation as a primary

cause. The arteries become occluded either from end-

arterial inflammation, due either to frank infection, or to

various somewhat obscure causes producing local obliter-

ative arteriosclerosis, or to trauma, or to thrombosis or

embolism, especially in association with cardiac disease.

Again some cases of gangrene, in the sense under con-

cua’ _ article ‘‘Scarlatine,’’? in Ref. Handbook Med. Sci., Vol.

VII, p. 658,

12 THE AMERICAN NATURALIST [Vou. LIV

sideration here, are doubtless due to extensive phlebitis

and primary thrombosis of veins. In any case it is a

part of the circulatory system which breaks down, and

therefore we are warranted in placing this disease in

Table I. :

Item 4, ‘‘Malaria,’’ is fundamentally a disease of the

blood, and hence is placed here from ‘‘ General diseases.’’

All the evidence that the pathological anatomist has

leads to the view that yellow fever, typhus fever, relaps-

ing fever and miliary fever are blood diseases. They

have the lesions of septicemias, or are transmitted by

biting insects, or both.

Items 53 and 54, ‘‘Leukemia’’ and ‘‘ Anemia, chlo-

rosis,’’ represent breakdowns of the blood or blood-form-

ing organs of the body. They are taken from Class I of

the International Classification.

In the International Classification item 116, ‘‘ Diseases

of the spleen,’’ is placed under the general rubric of

‘*Diseases of the digestive system.’’ This is a good

illustration of the biological absurdities which appear

in the statistical classification now used. Just what the

spleen has to do directly with digestion does not appear.

It is primarily a blood-forming organ.

Bubonic plague is a disease of the lymphatic system.

The great epidemics of fatal type are characterized by

the pneumonic and septicemie forms. On the whole, it

seems best to place this disease here.

It is evident from the data of Table I that where death

ensues from a breakdown of any part of the circulatory

or blood systems it is preponderantly the heart itself

which is at fault. Diseases of the arteries, which, gen-

erally speaking, mean arteriosclerosis, come second in

importance. The other causes listed are of relatively

minor importance. The relatively enormous rates for

diseases of the arteries and for purulent infection and

septicemia in São Paulo are noteworthy.

For the present no attempt will be made to discuss the

reasons for these differences, since the main object in this

No. 630] HUMAN MORTALITY RATES 13

section of the paper is to get the data as a whole before

he reader.

The question may fairly be raised as to whether item

22, ‘‘ Anthrax,’’ should not come in Table I with the blood

rather than with the skin in Table VIII. It is a difficult

question and one not capable of any absolutely precise

solution in the nature of the case. Most fatal cases of

anthrax, if not all, are septicemias, or, perhaps better,

haticvansias. due finally to failure of the defensive

mechanism of the blood. Furthermore, pneumonic and

intestinal forms of anthrax oceur. On the whole, how-

ever, the weight of evidence seems to be that in the

majority of cases at least the organism gains its entrance

and first victory through the skin, and that the biological

strength or weakness of that organ system determines

primarily what will subsequently happen. Fortunately,

the total rate from anthrax is so small as to be of no sig-

nificance in any general result.

The causes of death listed in Table II include all of

TABLE II

RESPIRATORY SYSTEM

| Registration Area, | p nd

No. “Cause of Death” as per International U. 8. A. = cnet

f Classification Wales 1917

1906-10 | 1901-05 1914

28&29 | Tuberculosis of lungs (including acute

miliary tuberciwiosis). 5 6. ka 146.8 | 170.7 | 104.5 | 119.8

92 | Pneumonia es sa and undefined)... .. 103.0 | 125.5 57.5 59.9

91 Bronchopneumonia...............--- 40.4 32.9 50.9 | 103.9

9 Diphtheria cad aos We eee Te Eta 22.4 29.6 16.0 9.6

10 Influenza Opp EEA E ERE EUEN 16.4 19.9 16.1 16.1

89 | Acute bronchitis. ee pe ama 15.2 21.4 | 108.75) 62.1

Bd Whoopin ng cough. . geese ey ck eee 10.9 21.8 9.1

90 | Chronic oabi pe aCe Le ee 168 a 3.9

6 | Me T AE PS ree ees 10.8 9.0 24.7 1.5

94 Boeri congestion and mame 5.6 8.6 4.5 9.4

93 | Pleuri , 4.1 4.9 $01. Ta

PO AnD: eee AÀ 2.9 3.7 4.9 2.8

98 | One respiratory diseases...........- 2.8 4.3 17 5.2

87 | Diseases of the larynx............... 1-7 2.3 3.2 0.9

97 | Pulmonary poate ee eee E 0.4 0.7 12 2.2

95 | Gangrene of the lungs.............-. 0.4 0.5 0.3 3.3

86 | Diseases of the Aes ise ea nA 0.2 0.2 0.2 0.2

| Totals. = „| 895.7 | 460.5 | 420.2 | 417.5

8 ‘Tackles acute and chronic ‘decanitte,

14 THE AMERICAN NATURALIST [Vou. LIV

those under the general heading IV, ‘‘Diseases of the

respiratory system’’ of the International Classification,

with a single exception, namely No. 88, ‘‘Diseases of the

thyroid body,’’ which goes elsewhere in the present clas-

sification. In addition, there are in Table II four causes

of death which are not included with the respiratory

system in the International List. These four we may

consider in detail.

Item 28, ‘Tuberculosis of lungs,’’ obviously belongs

with the řSspiratóry system, in a strictly organological

classification. The breakdown of the lungs as a function-

ing system is the biological meaning of death from pul-

monary tuberculosis. This item is taken from rubric I,

‘‘ General diseases,’’ of the International Classification.

Acute miliary tuberculosis has been included with pul-

monary tuberculosis here, rather than as a separate item,

for the reason that the English statistics treat these

items together. No significant error is introduced by

this procedure for two reasons: (a) the rate from miliary

tuberculosis by itself is very small; and (b) probably a

majority of cases of acute miliary tuberculosis have the

lungs as the chief organ affected.

Item 9, ‘‘Diphtheria and croup,’’ is again obviously a

respiratory category, on the basis of organs affected. It

does not seem to me to be to the point to argue that death

in diphtheria is in many cases due to a general toxemia.

To do so brings into prominence an aspect of the matter

foreign to our present point of view. The infecting

agent attacks a part of the respiratory system. If that

system were in man as in the insects, lined with chitin in

considerable part, presumably death from the clinical

entity known as diphtheria would never occur, because

the organism would not get the necessary foothold to

produce enough toxin to be troublesome. It seems to me

further that there is a fundamental biological difference

between the cases of scarlet fever and septicemia on the

one hand, and diphtheria on the other hand, which leads

to the placing of the former with the blood and the latter

No. 630] HUMAN MORTALITY RATES i 15

with the respiratory system. It is apparent, of course,

that the matter of the placing of diphtheria can be argued

from both sides, but on the whole I incline to the view

that it belongs here with the respiratory organs rather

than with the blood.

Item 10, ‘‘Influenza,’’ is so obviously respiratory as to

require no discussion. The same may be said of item 8,

‘t Whooping cough.”

The reason for including item 6, ‘‘Measles,’’ here is

clearly stated by Spengarn® when he says regarding

measles: ‘‘The mortality of this disease is largely due to

the pulmonary complications,’’ and further: ‘‘The high

mortality among the measles patients in children’s hos-

pitals is attributed to bronchopneumonia.”’’

Table II brings out very clearly one important point in

favor of the present classification. It is evident from an

examination of the four columns of rates that the usages

in respect of the diagnostic terminology of respiratory

affection, especially the pneumonias and bronchitis, differ

greatly in these three countries. Yet the totals for all

respiratory system deaths are closely similar for all

three countries and periods. In other words, the organ-

ological totals get rid to a large degree of one of the

greatest sources of error in vital statistics, the varying

terminology of disease in different regions.

The first and the fourth items in Table III present a

new angle of the problem of the classification of the

causes of death which needs particular discussion. These

items, ‘‘Premature birth’’ and ‘‘Injuries at birth’’ repre-

sent a part of the items 151 and 152 of the International

Classification. In the International Classification, item

151, which eomes under the general heading ‘‘ XI. Early

infancy,’’ has this general title ‘‘Congenital debility,

icterus and sclerema (total).’’ This contains two sepa-

rate subdivisions not numbered, the first being ‘‘Pre-

mature birth,” and the second ‘‘Congenital debility,

9 Spengarn, A., article ‘‘Measles’’ in Ref. Handbook Med. Sci., Vol. VI,

p. 283, 1916.

16 THE AMERICAN NATURALIST [Vou. LIV

TABLE III

PRIMARY AND SECONDARY SEX ORGANS

| Registration Area, | England |

No. “Cause of Death” as per International | U.S. A. and São

Classification ee oa ——| Wales | Paulo

| 1906-10 | 1901-05 1914 1917

151" | Premature birth Reise: 30.8 46.9 66.8

42 | Cancer of the female genital PEER | 10.8 10.0 12.9 6.5

137 | Puerper Soph ae i eS B72 6.5

1521! | Injuries a h. 6.6 5.0 2.8 2.1

43 oos = ‘as breast... 6.5 5.6 10.4 1.5

SE g S PE es Caer eee A a bor ie 4.1 5.8 15.010

126 | Diseases of the prostate 2.6 4.2 0.7

132 Salpingitis and other diseases af Q genic |

tal organs 4 22 2.1 0.5 0.2

129 | Uterine tum or (non-cancerous) . A aes 3 1.8 1.8 0.8 0

134 | Accidents re pregnancy. geben ves ty kee ce Ri 0.2

130 | Other diseases of the uterus EG Ri Sa ae 1.6 i eg 0.4 | 0.4

136 | Other accidents of labor............. te 0.9 4:1 0.7

440° 4 Following. childbirth. -A ia es Ses Pee Se: 1.5 0.1 | —

131 | Cysts and Serk nen of ovary. E LO 1.3 0.8 | 2

135 | Puerperal hemorrhage............... Beet 1.0 5 Be Bay ae a

125 rierien of mej urethra, urinary ab- | |

scesses, etc.. ; oyi # 0.4 EZ 0.7

38 | Gonococcus infecti E 0.3 0.1 0.2 0

128 ii eee rhage non-puerperal) Beal fe 0.3 0 0

127 | Non-venereal dise of g genita 1 |

Ca E OR ig een ocean SE N pees | 0.1 0.2 0

133 Non-puerperal diseases of breast —

cae 04 0.1 0.1 0

139 Persil ‘phiegmasia, ete. Msg ola oe eip ee I- Qi — U9 r O

1 |

eee eae ne Ce se ee

atrophy, marasmus, etc.” Item 152, coming under the

same general head of the International Classification has

the general title ‘‘Other causes peculiar to early infancy

(total).’’ This term contains two unnumbered sub-

divisions, the first being ‘‘Injuries at birth,’’ and the

other ‘‘Other causes peculiar to early infancy.”’

The question at once arises, why should these two items

‘‘ Premature birth’’ and ‘‘Injuries at birth’’ be included

with the primary and secondary sex organs, since it is

obvious enough that the infants whose deaths are re-

corded under these heads in the vast majority of cases,

if not all, have nothing whatever the matter with either

their primary or secondary sex organs. The answer is,

10 Including soft ci En — 1.5, and soft chancre 13.5).

11 In part. Cf. text h

No. 630] HUMAN MORTALITY RATES 17

in general terms, that on any proper biological basis

deaths coming under either of these two categories are

not properly chargeable organically against the infant

at all, but should be charged, on such a basis, against the

mother. To go into further detail, it is apparent that

when a premature birth occurs it is because the reproduc-

tive system of the mother, for some reason or other, did

not rise to the demands of the situation of carrying the

fetus to term. Premature birth, in short, results from a

failure or breakdown in some particular of the maternal

reproductive system. This failure may be caused in

various ways, which do not here concern us. The essen-

tial feature from our present viewpoint is that the repro-

ductive system of the mother does break down, and by so

doing causes the death of an infant, and that death is

recorded statistically under this title ‘‘ Premature birth.’’

The death organically is chargeable to the mother:

A considerable number of cases of premature birth are

unquestionably due to placental defect and the placenta

is a structure of fetal origin, so such deaths could not be

properly charged to the mother. On the other hand,

however, they would still stay in Table III, because the

placenta may fairly be regarded as an organ intimately

. concerned in reproduction.

The same reasoning which applies to premature births,

mutatis mutandis, applies to the item ‘‘Injuries at birth.’’

An infant death recorded under this head means that

some part of the reproductive mechanism of the mother,

either structural or functional, failed of normal per-

formance in the time of stress. Usually ‘‘injury at birth”?

means a contracted or malformed pelvis in the mother.

But in any case the death is purely external and acci-

dental from the standpoint of the infant. It is organ-

ically chargeable to a defect of the sex organs of the

mother. The female pelvis, in respect of its conforma-

tion, is a secondary sex character.

A practical difficulty arose from the fact that in the

Sao Paulo statistics items 151 and 152 are not subdivided.

18 THE AMERICAN NATURALIST [Vou. LIV

In the case of the first of these, item 151, I have ventured

to divide the total rate in roughly the same proportion

between the two subdivisions as exists in the United

States and England, namely 2 to premature birth and 2

to congenital debility, ete. While this is admittedly a.

hazardous proceeding, it seems to me less so than to omit

entirely so important a rate, which seems to me the only

other practical alternative. In the case of item 152 the

total rate is so small (3.3) that no particular difference

will be made whatever the basis of distribution used.

Consequently, I have again divided it roughly on the basis

of the American figures, calling 2 of the total due to

injuries at birth.

Table III also includes data which in the International

Classification are distributed under three different gen-

eral heads. First, ‘‘General diseases’’; second, ‘‘Non-

venereal diseases of the genito-urinary system and an-

nexa’’; and third, ‘‘Puerperal state.’’ In the Interna-

tional List all cancers are included under ‘‘General dis-

eases.” We have taken out for inclusion here the several

cancers of the primary and secondary sex organs, includ-

ing item 42, ‘‘Cancer of the female genital organs,’’ and

item 43, ‘‘Cancer of the breast.’’ Items 37 and 38,

‘‘Syphilis’’ and ‘‘Gonococcus infection,’’ are also taken

out of the class of ‘‘General diseases’’ of the Inter-

national List. The immediate reason for including these

diseases here is obvious, but particularly in relation to

syphilis the point at once needs further discussion. As

a cause of actual death, syphilis frequently acts through

the central nervous system, and the question may fairly

be raised why, in view of this fact, syphilis is not there

included. The point well illustrates one of the funda-

mental difficulties in any organological classification of

disease. In the case of syphilis, however, the difficulty in

practise is not nearly so great as it is in theory. Asa

matter of fact, most of the deaths from the effect of

syphilitic infection on the nervous system are recorded in

vital statistics by reporting physicians and vital statis-

No. 630] HUMAN MORTALITY RATES 19

ticians as diseases of the nervous system. For example,

it is perfectly certain that most of the deaths recorded as

due to ‘‘locomotor ataxia’’ and ‘‘softening of the brain”

are fundamentally syphilitic in origin. The rate included

in Table III of 5.4 for the Registration Area of the United

States in 1906-10 for deaths due to syphilis is far lower,

as any clinician knows, than the number of deaths really

attributable to syphilitic infection. These other deaths,

due to syphilis, and not reported under that title, are

reported under the organ which primarily breaks down

and causes death, as, for example, the brain, and will in

the present system of classification be included under the

nervous system. After careful consideration it has

seemed as fair and just as anything which could be done

to put the residue of deaths specifically reported as due

to syphilis under Table III, Primary and Secondary Sex

Organs. ‘The rate in any event is so small that whatever

shift was made could not sensibly affect the general re-

sults to which we shall presently come.

The question may be asked as to why puerperal septi-

cemia (item No. 137) is included here and not with the

diseases of the circulatory system and blood on the same

reasoning that general septicemia was put there. The

cases seem to be essentially different. Puerperal septi-

cemia arises fundamentally because of a failure of the

reproductive system of the female to meet in a normal

way the demands made upon it by the process of repro-

duction itself. In line with the general reasoning on

which we are working in this classification, it would

therefore seem that this cause of death belongs where it

has been put here, with the primary and secondary sex,

organs. The same sort of reasoning applies to the other

puerperal causes of death here included.

Item 125, ‘‘Diseases of the urethra, urinary abscesses,

ete.” is placed with the sex organs rather than with the

excretory organs in Table IV, because, with very few ex-

ceptions, the deaths in this item are sequele of gonorrhea.

Urinary abscesses are secondary usually to urethral

20 THE AMERICAN NATURALIST [Vonu. LIV

stricture, which in turn, except for an insignificant num-

ber of traumatic cases, is gonorrheal in origin.

Regarding the wade, of bringing together under one

rubric the causes of death listed in Table IV on a biolog-

TABLE IV

KIDNEYS AND RELATED EXCRETORY ORGANS

Registration Area, | England

No. “ Cause of Death” as per International 0-5-A- | and Sat

Classification | Wales 1917

1906-10 | 1901-05 1914

120 Bright's disease. D EN Pe hats a Serle 87.4 37.0 41.2

119 ae a 9.6 4 29.4

138 | Puerpe ral albuminuria and convulsions 3.4 2.8 Tz IZ

1 Diseases of the bladder i 3.1 4.3 33 1:3

121 &

122 | Chyluria and other pe ts of the.

‘kidneys. Kise ee ee 1.3 9.4

123 | Calculi of the. urinary. passage. pects | 0.6 0.5 0:7 0.4

Poa o a eee Ee | 107.2 | 107.4 | 49.4 | 83.4

ical basis, there would seem to be little doubt with a single

exception. This does present a very difficult problem.

Item 138, Puerperal albuminuria, is included here rather

than with other puerperal diseases under the sex organs,

or elsewhere, on the reasoning that the cause of death is

finally the organic breakdown of the kidneys and not of

the reproductive system, and bespeaks a fundamental

organic weakness of the excretory system, which weak-

ness is made to flare up into clinical nephritie trouble

under the strain of pregnancy. Basically these toxemias

are due to faulty maternal metabolism, of unknown

origin, which can not in the present state of ignorance be

properly charged against any particular organ or organ

system. It, however, remains a fact that many women

having organically sound excretory organs are able to

weather even very severe metabolic storms of this sort

near the end of pregnancy and survive. Others with

organically weak excretory systems go down. In view of

these facts it seems on the whole fairer to put these

deaths here than against any other organ system.

The ‘‘rheumatisms’”’ present another difficult ques-

No. 630] HUMAN MORTALITY RATES 21

tion. A precise and eritical decision on the point of

where these diseases belong in this present scheme of

classification is impossible of attainment. Weighing all

the evidence carefully, it seemed best to put chronic rheu-

matism and gout and acute articular rheumatism in

Table V, under ‘‘Skeletal and muscular system,’’ rather

than here with the kidneys. Much at least of the fatal

chronic rheumatism is really a chronic infective arthritis.

Gout is a disease due to fundamental disturbances of

general metabolism, but the statistical returns lump

deaths from this cause with chronic rheumatism. The

death rates from all of these diseases are, fortunately, so

small that it makes no essential difference to the final

synthetic result towards which we are working where

they are placed.

TABLE V

SKELETAL AND MUSCULAR SYSTEM

Registration Area, and |

No. “Cause of Death” as per International U. 8. A. pe 2 Phe

Classification | si 1917

1906-10 | 1901-05 1914

4 Acute articular rheumatism........ Laka Ai 5.2 5.6 2.6

146 | Diseases of the bones RAT fe 2.4 1.5 0.7

48 | Chronic rheumatism and gout: ae ewes 2:2 3.6 5.4 0

32 | Pott’s disease... SEA tl SHER. i" 1.5 1.6 2.6

33 | White swellings. . rer ee 0.7 0.7 0.9

147 | Diseases of the join oes aero ae -2 0.2 0.4 0

149 caw Karana of Ne organs of loco- :

ewer : eee oai 0.1 0.1 0

36 ctr PPE A a eas Galo 12 12 2.7 0.9

LOU A Gr cos ch. ok oe el oe 13.7 18.2 6.8

Item 47, ‘‘ Acute articular rheumatism,’’ and the two

tubercular affections, items 32 and 33 (Pott’s disease and

white swellings) are placed here because the essential

lesion produced by the causative agents is in either the

bones or the joints.

All of the rates in Table V are small, and any of the

causes of death listed therein could be shifted to other

rubrics without sensibly affecting any general result.

12 Not separately tabulated.

THE AMERICAN NATURALIST

[Vou. LIV

. In Table VI are included a number of causes of death

beyond those which are included in general heading ‘‘V.

Diseases of the digestive system’’ in the International

TABLE VI

ALIMENTARY TRACT AND ASSOCIATED ORGANS CONCERNED IN METABOLISM

| Registration Area, England sa

We “ Cause of Death ’ as per International U.S. A. ___| . and Panto

Classification Sees ales 1917

1906-10 | 1901-C5| 1914

104 | Diarrhea and enteritis (under 2)...... 2 89.0 63.64] 383.6

1518 Paisaia se atr Sar marasmus! 28.8 23.2 27.4 44.3

40 | Cancer of the stomach and liver...... 8.3 24. 36.5 28.1

1 | Typhoid fever Pe tls eee 32.0 4. 14.4

103 | Other diseases ‘of stomach. 6.8 | 17.7 | 10.9 1.3

105 | Diarrhea and ote s 2a and 1 over) « 16.7 20. —- 49.9

113 | Cirrhosis of the li 14.3 14.4 11.2 12.2

50: | Diabetes ose sie aes eerie poi 13:7. 11.5 12.2 5.4

109 | Hernia and pe renter oe eos 12.9 13.0 10.9 3.0

71 | Convulsions o 12.5 21.4 22:4 10.0

108 SARNE? ae typhi tis 11.2 11.0 T. 3.5

41 | Ca the peritoneum, ane,

8.8 rA i 21.3 4.1

14 | Dyse 6.5 8.6 0.7 9.6

117 Siola salon 6.1 10.8 1:4) 138

115 | Other diseases of die liver. 6.1 7.5 2.6 5.7

31 | Abdominal tuberculos Re es 6.0 6.0 9.4 17

150% | Other congenital sider andar 4.5 3.9 5.4 16

102 | Ulcer of the stomach. Pare kee 3.6 2.9 5.5 3.5

110 | Other AE of intestines, Pi cures 2.8 2.9 1.4 5.4

Ree) Mary Clout. a ow ss ei vere vine 2.8 2.2 2.3 0.4

3 Cancer of the buccal metai ENA a 2.6 mt 6.6 1.3

35 ated tuberculos 2.5 2.8 55 2.2

100 aaa of the chines, AP P IE GOP Ng 1.6 1.4 2.1 0.4

13 | Cholera nostras. ... 1.0 1.4 0.1 0.2

99 ases of the aaa 0.7 0.7 1.5 0.4

5 Other chronic doy 0.5 0.5 0 0.2

118 | Other diseases of the digestive system. 0.5 0.3 0.6 t1

111 | Acute Lise te coke ia Pee J Ds 0.4 0.2 0.4

101 | Disea sophagu Sepa pees 0.3 0.3 0.2 1.3

57 Chronic lead poisoniig 2.0.66 0.2 0.3 OF 6

ellagra ei 0.2 0 0 0

49 0.1 0.1 0.1 0.2

106 &

Blt Pe a A aa ee 0.1 0.1 0.1 6.3

112 Hydatid tumor OLIVER. oc. oes a 16 16 0.1 0.2

27 PEs re ys a ee ee ee 17 17 0 0.2

12 ‘auntie ORONA wee Ko cy eee 0 0 0 0

OBTAIN okies Ge ou) ude 334.9 | 340.4 | 274.1 | 613.8

13 In part.

14 Diarrhea and enteritis, all ages.

15 See footnote to Table I.

16 Death rate less than 0.1 per 100,000.

17 Not separately tabulated for period named.

No. 630] HUMAN MORTALITY RATES 23

Classification. Of these causes which have been brought

in from other parts of the International Classification the

first which demands attention is the second on the list

‘t Congenital debility, atrophy, marasmus.’’ This is a

part of item No. 151 of the International Classification.

As already pointed out, that item includes ‘‘ Premature

birth,’’ which has in the present classification been placed

under ‘‘Primary and secondary sex organs’’ for reasons

already stated, and ‘‘Congenital debility, atrophy, ma-

rasmus, ete.,’’ which is the part included here. The

reason for putting this portion of item 151 under the

present heading is the practical one that clinical expe-

rience shows that the vast majority of the deaths of in-

fants which are statistically recorded under this heading

‘‘ Congenital debility, atrophy, and marasmus’’ are actu-

ally due to deficiencies, functional, structural, or both,

in the alimentary tract. In probably more than 95 per

cent. of all cases ‘‘Congenital debility’? of an infant

means that something is wrong with the alimentary tract

in its immediate metabolic functions.

Item 50, ‘‘Diabetes,’’ includes deaths from a disease

which, while diagnosed from a disarrangement of the

excretory function, is primarily an affection of the organs

which have to do with the initial or early stages of

metabolism (the liver, the pancreas, ete.). It therefore

seems to belong properly in the classification where it is

now placed rather than with the kidneys. In the Inter-

national Classification it is included with ‘‘General

diseases.’’

Item 71, ‘‘Convulsions of infants,” is in the Inter-

national Classification placed with ‘‘Diseases of the

nervous system.’’ It is transferred from that location

to the present one in this classification because of the

well-known clinical fact that the vast majority of deaths

of infants recorded as due to convulsions are really due

to profound disarrangements of the alimentary tract,

which eventually lead to convulsions. Biologically, the

fundamental breakdown in such cases is of the alimen-

24 THE AMERICAN NATURALIST [Vou. LIV

tary tract and associated organs, and not of the brain or

central nervous system.

The part of item 150 of the International Classification

bearing the title ‘‘Other congenital malformations’’ needs

some discussion in regard to its inclusion here. In other

rubrics of the present classification we have taken ac-

count of hydrocephalus and congenital malformation of

the heart, both of which come under the general heading

“X. Malformations’’ of the International Classification.

The only other rubric under that heading in the. Inter-

national Classification is the one here under discussion

‘‘Other congenital malformations.’’ It is, of course, im-

possible to say in detail what these other congenital mal-

formations are. It seems fair, however, to assume from

general knowledge that after hydrocephalus and con-

genital malformations of the heart are deleted, the great

majority of the remaining congenital malformations will

relate directly to the alimentary tract or some of its asso-

ciated organs. Quantitative proof that this is the case

is not forthcoming for obvious reasons. The placing of

this item here is simply on the basis of the best informa-

tion it is possible -to get from those most familiar with

congenital malformations in infants. There is undoubt-

edly some error inherent in placing this title here, but

the net effect of such error must be insignificant for the

= reason that the death rate under this rubric is very small

in total, as will be seen from the table, and furthermore,

as has already been stated, it is certain on general grounds

that the vast bulk of deaths included here must be due to

malformations of the alimentary tract or its associated

organs.

Items No. 31 and 35 (Abdominal tuberculosis, and dis-

seminated tuberculosis) are placed here, because, while

these titles are somewhat indefinite, it is quite certain

that the major portion of the deaths recorded by health

officers under these terms are due to tubercular affec-

tions of the alimentary tract.

Items 57, 59, 26, 27, and 49 (chronic lead poisoning,

No. 630] HUMAN MORTALITY RATES 25

other chronic poisonings, pellagra, beriberi, and scurvy’)

present an interesting problem. The question is whether

they should go here or with external causes in Table X.

It can be argued that on the one hand, the poisonings are

due simply to the ingestion of a deleterious agent and

death has no biological basis any more than if a person

is struck by an automobile, and, on the other hand, that

deaths from the diseases like pellagra and beriberi again

simply arise from the fact that the victim lacked a proper

diet. But the case is not so simple as this argument

would imply. Not all workers in paint factories, nor all

inmates of insane asylums or prisons die from these

causes. Some survive. And it is reasonable, it seems

to me, to suppose that in many cases at least the deter-

mining factor in the survival is the relative organic

soundness or ‘‘strength’’ of the organs primarily con-

cerned in metabolism. On this basis, this group of causes

of death is included in Table VI. Fortunately, they are

all insignificant contributions to the total death rate.

Regarding the other items in Table VI, taken from the

‘General disease’’ class of the Titimatonsl Classifica-

tion, there is no need for discussion because it is suffi-

ciently evident that on a biological classification they

belong here rather than with any other organ group.

The enormous excess of the Sao Paulo death rate for

the total of the items in Table VI as compared with the

Registration Area of the United States and England and

Wales is noteworthy. Examination of the data will show

that it arises almost entirely from the excessive death

rate in Sao Paulo from diarrhea and enteritis (under 2).

In the main the causes of death included in Table VII

in addition to those which appear in class II, ‘‘Diseases

of the nervous system and of the organs of special sense”?

of the International Classification, so obviously belong

here as to require no special discussion. Two, however,

call for comment. Of these the most important is suicide.

In the International Classification suicides are placed

under ‘‘XTIT. External causes,” a singularly inept loca-

26 THE AMERICAN NATURALIST [Vou. LIV

TABLE VII

NERVOUS SYSTEM AND SENSE ORGANS

| Registration Area, | England Sho

No. | “ Cause of Death" as per International U.S.A. | and aulo

Classification Wales 1917

| 1906-10 | 1901-05 | 1914

64 | Cerebral hemorrhage and a ee pore ket. 69.6 65.3 32.9

61 oer (total). EES 19.4 81.7 11.5 43.1

66 | Paralysis orige specified « chud... 16.1 20.1 7.3 2.6

Suid (total) . Rees Matera sy whe 16.0 13.9 10.0 12.9

30 | Tuber eulous meningitis: . pe ae NG 9.1 8.9 12.6 0

56 | Alcoholis Reece 5.8 6.1 1.8 2.8

63 | Other paiia of ‘the spinal cord. Bae eas 5.8 4.9 7.6 4.4

73 &

74 | Neuralgia, neuritis and other diseases of

CHE HECVOUS rta. ick ee cai 5.5 6.9 7.0 2.0

67 | General badiiy of the insane ....... 55: 6.8 6.1 3.0

o PE S a 4 oc AONE ke rt E 4.2 4.4 7.6 4.8

68 | Other forms of mental alienation. ..... 3.6 3.6 2.7 0.7

24 | Tetanus ea We ice be erp acs 2.7 3:5 0.5 4.6

62 Locomotor atax A naas are sto ars 2.6 2.4 1.9 0.2

65 seers of the te 20 37 3.9 0.7

76 of the ea 1.6 1.3 3.3 0

15018 Hydrocephalus arg Or Nes Deer OE Ee 1.4 1.6 1.0 19

GO: | sineephialitiee ss eo esas ee. 1.1 1.9 0.9 1.3

70 Convulsions eee: ecole i 0.5 11 0.3 17

72 rats 0.2 0.3 0.5 0

ae: RONG iti ee a cee tas gtr 0.2 0.1 0 0.7

75 Disisi of the eye and annexa....... 0.1 0.1 0.2 0

17 20 20 0 5.9

TOE Oe ser ch ee 175.6 | 192.9 151.9 124.3

tion biologically. The immediate motivation of a sui-

cidal death is surely internal. A searching biological

analysis of the phenomenon of suicide has yet to be made,

but certain of its biological relations are clear enough.

In the broadest terms people commit suicide because

their higher cerebral mechanism breaks down under the

stresses of the world in which they live, and fails to con-

tinue its normal functioning. One of the deepest rooted

instincts of the individual among all living things, from

lowest to highest, is the instinct for the preservation of

the individual life. The only instinct which transcends

it, and that only in comparatively few cases in lower ani-

mals, is the instinct of reproduction. But the phenom-

18 In part.

19 See footnote Table I.

20 Less than 0.1 per 100,000.

No. 630] HUMAN MORTALITY RATES ei

enon of suicide in man marks the complete and total in-

hibition of this instinct of self-preservation. -Suicide is

always an act in some degree mentally deliberated before

its performance. A constitutionally and hygienieally

sound mentality weathers the environmental storm which

suggests suicide. On the basis of this reasoning suicide

death rate is put in Table VII.

Item 56, ‘‘ Aleoholism,’’ is included here because funda-

mentally deaths so returned would seem to be more truly

chargeable against the central nervous system than to

any other organ system. This opinion is founded on such

results as those of Barrington and Pearson,” who con-

clude, after a careful analysis of data regarding extreme

and chronic inebriates, that ‘‘there appears for constant

age little relation between alcoholism and physical fit-

ness,’’ while between mental defect (and poor education)

and alcoholism there is a sensible relation. ‘‘We con-

sider it probable... that the alcoholism is not due to the

poor education, nor is it to any marked extent productive

of the mental defect, but the want of will-power and self-

control associated with the mental defectiveness is itself

the antecedent of the poor education and of the alco-

holism.’’

The other cause of death needing special comment here

is leprosy. I am informed by my friend, Dr. G. H. de

Paula Souza, who has had unusual opportunities to know

leprosy in all its clinical manifestations, that when this

disease becomes fatal it is the nervous system which dis-

integrates and leads to death.

_ ‘The first five items in Table 8 are affections of the skin

about which there can be no doubt respecting the cor-

rectness of their inclusion here. -The last four items,

smallpox, anthrax, mycoses and glanders are all diseases

with very low death rates at the present time. Biolog-

ically, they represent diseases which either gain entrance

through the skin, or in which the principal lesions are of

21 Barrington, A., and Pearson, K., ‘‘A Preliminary Study of Extreme

Alcoholism in Adults,’’ Eugenics Lab. Mem., XIV, 1910.

28 THE AMERICAN NATURALIST [Vor. LIV

TABLE VIII

THE SKIN

| saa wart Area, |

| ? — | 4

No. | * Cause of Death” as per International | U.S. | San

$ Classification Sarsi | 1917

1906-10 | 1901-05 | 1914 |

18 | Erysipela aA O 4.2 4.5 al Ba

44 | Cancer of- the akin. Bc De oes -| DAPA 23 2.6 | To

144 | Acute abse aerer e e] Ti 1.4 21 | 0.7

145 | Other sieci abekin. 9 ae $0} 3t o 24

143 | Furune a a e G5 (207% 0.2

Smallpox : | 0.2 3.4 | ọ | 07

22 AN ee aaa a ea ofc ee Ot) -90 E E

ee OA VOOR ae ore. e a e eA — 0.1 Tek

2r A PAR Ge a a ko eed — 0.1 0 0

Po Tonk = ea ee a ages ee

the skin. It therefore appears that on the present

scheme of classification they may best be put here.

There is no doubt whatever that the three diseases of

Table IX belong biologically with the endocrinal system.

In the foregoing tables have been included all statis-

tically recognized causes of death which it is now possible

to classify on an organological basis, and which have a

TABLE IX

ENDOCRINAL SYSTEM

pigeon ae Area, England |

and | Pao

“ Cause of Death” as per International l- Paulo

JE A A E o E PEOS woe Wales | 1917

1906-10 | 1901-05 1914 |

51 | Exophthalmic iA: ime. aal A 0.7 13:1) 04

52 | Addison’s dise pO aaa, a te 0.5 00 ; 07

88 | Diseases of the thy ial body. Nee ae 0.4 0.3 OS | 0

Pa ee ee ee

significant death rate. The residue comprises in gen-

eral three categories (a) accidental and homicidal deaths;

(b) senility; and (c) deaths from a variety of causes

which are statistically lumped together and can not be

disentangled. Accidental and homicidal deaths find no

place in a biological classification of mortality. A man

organically sound in every respect may be instantly

killed by being struck by a railroad train or an automo-

No. 630] HUMAN MORTALITY RATES 29

bile. The best possible case that could be made out for

a biological factor in such deaths would be that contribu-

tory carelessness or negligence, which is a factor in some

portion of accidental deaths, bespeaks a small but definite

organic mental inferiority or weakness, and that, there-

fore, accidental deaths should be charged against the nerv-

. ous system. ‘This, however, is obviously not sound. For

in the first place in many accidents there is no factor of

contributory negligence in fact, and in the second place in

those cases where such negligence can fairly be alleged

its degree or significance is undeterminable and in many

cases surely slight.

Senility as a cause of death is not further classifiable

on an organological basis. A death really due to old age,

in the sense of Metchnikoff, represents, from the point of

view of the present discussion, a breaking down or wear-

ing out of all the organ systems of the body contem-

poraneously. In a strict sense this probably never, or at

best extremely rarely, happens. But physicians and reg-

istrars of mortality still return a certain number of

deaths as due to ‘‘senility.’? Under the circumstances it

is not possible to go behind such returns biologically.

TABLE X

ALL OTHER CAUSES

| seas” Bray Area,

| s Se A

i England São

No. Cause of Death ” as per International and Paulo

Classification Wales 1917

| 1906-10 | 1901-05 1914

iér All external causes (except suicide)... J 91.9 | 87.8 26.1 36.4

188 4 |

189 Ill-defined diseases. ie aa Ve ee 47.8 is 36.3

154 | Senility | 29.0 41.0 81.5 mi

45 Cancer of other organs | or r of organs not

POY A E oes Cenc ate ares 12.9 16.1 16.6 17.9

15222 Other auses peculiar to early infancy . 3.4 2.6 5.1 3.3

34 iroda sis of other organs 21 2.0 1.6 0.2

(

46 — umors (female genital ‘organs

es ake, ae

í 3.5

woa. i Euok ot oe o ee 0.3 12.3 0.6 0

19 | Other epidemic diseases 0.3 0.2 0.6 0.2

l To e a ' 171.3 H19 | 141.4 | 109.8

22 Less than 0.1 per 100,000.

30 THE AMERICAN NATURALIST [Vou. LIV

The second line of Table X, ‘‘Ill-defined diseases,’’

furnishes a striking commentary on the relative efficiency

of the medical profession in the United States and Eng-

land in respect of the reporting of the causes of death.

Only about one fourth as many deaths appear in the Eng-

lish vital statistics as due to ill-defined and unknown

causes as in the United States figures. Happily, the con-

_ ditions in this regard are constantly improving in the

Registration Area of the United States, due to the well-

conceived and untiring efforts of the officials in charge of

vital statistics in the Bureau of the Census. They de-

serve the warmest gratitude of every American vital

statistician for the improvements in registration they

have brought about.

Having now arranged, so far as possible, all statis-

tically recognized causes of death in a biological classifi-

cation, we may turn to an examination of the results

which such an arrangement shows. In Table XI the

totals of Tables I to IX, inclusive, are arranged in de-

scending order of magnitude. The results are shown

graphically in Fig. 1.

TABLE XI

SHOWING THE RELATIVE grant OF DIFFERENT ORGAN SYSTEMS IN

AN MORTALITY

Death Rates per 100,000

Groun _ Organ System KSK e să

wae | 7a

1906-10 1901-05 1914

II Banmer system 395.7 | 460.5 420.2 | 417.5

VI entary tract and associated | organs 334.9 | 340.4 | 274.1 | 613.8

I TN system, blood. ; 209.8 196.8 208.6 | 254.8

VII stem and sense organs..... 75.6 | 192.9 | 151.9 | 124.3

Yy Kidneys = ea excretory organs 107.2 | 107.4 19.4 83

II a sex organs .. if 7.4 95.4 | 103.2

y eT mre anand Waton... i... 12.6 13.7 18.2 8

VIIL | BE oia aa ee 10.1 13.3 12.0 7.9

I Eadocrinai system. 1.5 12 1. 11

Total death ei classifiable on a bio- |

Jopical basis oo oor ee a 1,335.5 |1,403.6 1,201.7 1,612.8

X | All other causes of death............. 1713 1 3119 ' 141.4 | 109.8

No. 630] HUMAN MORTALITY RATES 31

3957

gee ABOE

O 477.5

FrESPIRPATORY

ALIMENTARY 3 34.9

A AND

LLL.

ASSOCIATED ERRER N 613.8

CIRCULATORY )

SYSTEM. WML... 208.6

BLOOD MMMM +2246

NERVOUS

SYSTEM AND P

SENSE

ORGANS

SKIN

ENDOCRINAL

SYSTEM

US. REG AREA 1906-10 ENGLAND ano WALES 1914 SAO PAULO | 19/7

Diagram showing the relative importance of the different organ systems

e body in human mortality.

Fig. 1,

32 THE AMERICAN NATURALIST [Vou. LIV

From Table XI and the diagram a number of note-

worthy points can be made out.

1. In the United States, during the decade covered,

more deaths resulted from the breakdown of the respira-

tory system than from the failure of any other organ

system of the body. The same thing is true of England

and Wales. In Sio Paulo the alimentary tract takes first

position, with the respiratory system a rather close

second. The tremendous death rate in Sao Paulo charge-

able to the alimentary tract is chiefly due, as Table VI

clearly shows, to the relatively enormous number of

deaths of infants under two from diarrhea and enteritis.

Nothing approaching such a rate for this category as Sao

Paulo shows is known in this country or England.

2. In all three localities studied the respiratory system

and the alimentary tract together account for rather more

than half of all the deaths biologically classifiable. These

are the two organ systems which, while physically inter-

nal, come in contact directly at their surfaces with en-

vironmental entities (water, food, and air) with all their

bacterial contamination. The only other organ system

directly exposed to the environment is the skin. The

alimentary canal and the lungs are, of course, in effect

invaginated surfaces of the body. The mucous mem-

branes which line them are far less resistant to environ-

mental stresses, both physical and chemical, than is the

skin with its protecting layers of stratified epithelium.

3. The organs concerned with the blood and its circu-

lation stand third in importance in the mortality list.

Biologically the blood, through its immunological mechan-

ism, constitutes the second line of defense which the body

has against noxious invaders. The first line is the resist-

ance of the outer cells of the skin and the lining epithe-

lium of alimentary tract, lungs, and sexual and excretory

organs. When invading organisms pass or break down

these first two lines of defense the battle is then with the

home guard, the cells of the organ system which, like the

industrial workers of a commonwealth, keep the body

No. 630] HUMAN MORTALITY RATES 33

going as a whole functioning mechanism. Naturally it

would be expected that the casualties would be far heavier

in the first two defense lines (respiratory and alimentary

systems, and blood and circulation) than in the home

guard. Death rates when biologically classified bear out

this expectation.

4, It is at first thought somewhat surprising that the

‘breakdown of the nervous system is responsible for more

deaths than that of the excretory system. When one

bears in mind, however, the relative complexity of the

two pieces of machinery, it is perceived that the relative

position of the two in responsibility for mortality is what

might reasonably be expected.

5. In the United States the kidneys and related excre-

tory organs are responsible for more deaths than the sex

organs. ‘This relation is reversed in England and Wales

and in Sao Paulo. A return to Table III shows that this

difference is mainly due, in the case of England, to two

factors, premature birth and cancer. In Sao Paulo it is

due to premature birth and syphilis. The higher pre-

mature birth rate for these two localities as compared

with the United States might conceivably be explained in

either of two ways. It might mean better obstetrics here

than in the other localities, or it might mean that the

women of this country as a class are somewhat superior

physiologically in the matter of reproduction, when they

do reproduce. The first suggestion seems definitely more

improbable than the second. The higher apparent syph-

ilis rate of Sao Paulo probably means nothing more than

better reporting, a less prudish disinclination to report

Syphilis as a cause of death in Sao Paulo than in the other

two countries. It is by no means beyond the bounds of

possibility that if all deaths really due to syphilis and

gonorrhea were actually reported as such, the rate for

the sex organs would be decidedly higher than for the ex-

eretory organs in all countries.

6. The last three organ systems in the table, skeletal

and muscular system, skin and endocrinal organs, are

34 THE AMERICAN NATURALIST [Vou. LIV

responsible for so few deaths relatively as not to be of

serious moment.

7. In a broad sense the efforts of public health and

hygiene have been directed against the affections com-

prised in the first two items in the table, respiratory sys-

tem and alimentary tract. The figures in the first two

columns for the two five-year periods in the United States

indicate roughly the rate of progress such measures are

making, looking at the matter from a broad biological

standpoint. In reference to the respiratory system there

was a decline of 14 per cent. in the death rate between the

two periods. This is substantial. It is practically all

accounted for in phthisis, lobar pneumonia and bron-

chitis. For the alimentary tract the case is not so good

—indeed, far worse. Between the two periods the death

rate from this cause group fell only 1.8 per cent. Refer-

ence to Table VI shows how all the gain made in typhoid

fever was a great deal more than offset by diarrhea and

enteritis (under two), congenital debility and cancer.

Child welfare, both prenatal and postnatal, seems by long

odds the most hopeful direction in which public health

activities can expect at the present time substantially to

reduce the general death rate. This is a matter funda-

mentally of education. Ignorant and stupid people must

be taught, gently if possible, forcibly if necessary, how

to take care of a baby both before and after it is born.

It seems at present unlikely that mundane law will regard

feeding a two months old baby cucumber, or dispensing

milk reeking with deadly poison makers, as activities

accessory to first-degree murder. But we are moving in

that direction under the enthusiastic and capable leader-

ship of the Federal Children’s Bureau. And there is

this further comfort, that if that final Judgment Seat,

before which so many believe we must all eventually ap-

pear, dispenses that even-handed justice which in decency

it must, many of our most prominent citizens who in the

financial interests of themselves or their class block every

move towards better sewage disposal, water and milk

No. 630] HUMAN MORTALITY RATES 35

supply and the like, or force pregnant women to slave

over washtub or sewing bench that they may live, will

find themselves irrevocably indicted for the wanton and

wilful slaughter of innocent babies.

We come now to the final stage in this study. Having

arranged so far as possible all causes of death on an

organological base, it occurred to me to go one step fur-

ther back and combine them under the headings of the

primary germ layers from which the several organs de-

veloped embryologically. To do this is a task of consid-

erable difficulty. It raises intricate, and in some cases

still unsettled, questions of embryology. Furthermore,

the original statistical rubrics under which the data are

compiled by registrars of vital statistics were never

planned with such an object as this in mind. Still the

thing seemed worth trying because of the evolutionary

interest which would attach to the result, even though it

were somewhat crude and in respect of minor and insig-

nificant details open to captious criticism.

In Tables XII and XIII the death rates of Tables I to

IX are subsumed under the three captions, ectoderm,

mesoderm and endoderm, according as the organ con-

cerned developed from one or the other of these germ

layers. It will be necessary, however, before presenting

the tables, to set forth in detail how the figures they con-

tain were made up. :

A. Ectoderm.—Under this head were placed first, in

making up Table XII, the totals of Table VII (the nerv-

ous system and sense organs), and Table VIII (the skin).

To the sum obtained by adding these totals together

was added (a) item 39 (cancer of the buccal cavity) from

Table VI, on the ground that the lining of the buccal

cavity is ectodermal in origin; (b) 0.30 of the rates under

item 41 (cancer of the peritoneum, intestines and rectum).

The point here was that the lining epithelium of the rec-

tum is derived from ectoderm. The cancer rates for

36 THE AMERICAN NATURALIST (Vou. LIV

these three embryologically different organs, rectum, in-

testines and peritoneum are arbitrarily lumped together

by the registrars of vital statistics. It is necessary for

present purposes to unscramble the figures with as little

arbitrariness as possible. Data (admittedly rather

meager) given by Hoffman” (pp. 116-121) from the New

York State investigation indicate that in a lumped total

of cancer of the peritoneum, intestines and rectum, the

fractions incident upon each of the organs are about 0.04

for peritoneum, 0.30 for rectum, and 0.66 for intestines.

As these figures are much less arbitrary than a mere

guess, I have adopted them. It should be remembered

that in the final result it makes little difference what

fraction is adopted, because the total rate under item 41

is so small. A remarkable thing which comes out when

the lumped figures for cancer of peritoneum, intestines

and rectum are subdivided in the above-named propor-

tions, is the similarity, amounting practically to identity,

in the death rates in all four times and places studied,

from cancer of the buccal cavity and cancer of the rectum.

The figures are as follows:

U. S. A. England

sosto | swore | A Wai | OP

Cancer of buccal cavity............. 2.6 ot 6.6 1.3

Cancer of rectum (caleulated)....... 2.6 | 2.1 6.4 12

This identity can hardly be accidental, since it occurs

in all three different localities with quite different cancer

rates in each. It indicates that the fundamental embryo-

logical likeness between buccal cavity and rectum is ac-

curately reflected in their neoplastic pathology, provided

it can be safely assumed the portion of the rectum in

which cancers preponderantly occur is ectodermic. This

appears to be the fact. (c) Item 86 (diseases of the

nasal fosse) is added, because the lining membrane of the

nose is ectodermal in origin.

23 Hoffman, F. L., ‘‘The Mortality from Cancer throughout the World,’’

Newark, 1915.

No. 630] HUMAN MORTALITY RATES 37

B. Mesoderm.—Here the figures of Table XII were

reached by the following process. First, the totals of

Table I (circulatory system), Table III (sex organs),

and Table IV (kidneys), were added together, these

being obviously in general mesodermic. From the total

so obtained was subtracted item 124 of Table IV (dis-

eases of the bladder) since the lining epithelium, the most

vulnerable part pathologically, is endodermic in origin.

For the same reason item 125 of Table IV (diseases of

the urethra) was next subtracted. To the result so ob-

tained was added (a) the total of Table V (skeletal sys-

tem) and item 52 (Addison’s disease) from Table IX,

these representing organs mesodermie in origin; (b)

0.04 of the rate under item 41 of Table VI (cancer of

peritoneum) ; (c) item 117 (simple peritonitis); (d) item

93 (pleurisy). The pleura and peritoneum are meso-

dermic structures and therefore clearly belong here. The

final totals reached after the above described process are

those which appear under ‘‘Mesoderm”’ in Table XII.

Up to this point in the argument it has been assumed,

without discussion, that all the items in Table VII (the

nervous system and sense organs) go with the ectoderm.

There is, however, another point of view possible here,

which may be stated in the following way. Cerebral

hemorrhage and apoplexy (item 64) and softening of

the brain (item 65) are brain conditions brought about

by a precedent functional breakdown of a part of the

vascular system, namely the terminal arteries of the

brain. Cerebral hemorrhage is due to the rupture of an

artery or arteries in the brain, and may in and of itself

be a sufficient cause of death, just as would be a hemor-

rhage due to rupture of an artery in any other part of

the body. So far as anything now known can tell us, this

fatal accident is as likely as not to occur in a brain of

which the nerve cells (of ectodermic origin) are perfectly

sound organically. Should such a death be charged

against the ectoderm? ‘The case is at least open to

question.

38 THE AMERICAN NATURALIST [Vou. LIV

It might at first be supposed that the same argument

would justify the placing of cerebral hemorrhage with

the circulatory system in the primary organological

classification, but this does not seem to be warranted.

From an organological point of view the brain must be

considered as a whole organ, the machinery of its vascu-

lar supply being included as well as its proper nervous

components. So in this respect cerebral hemorrhage

properly belongs where it is placed in Table VII, with

the nervous system.

But the case is different from the embryological view-

point. Suppose it be granted for the moment that there

are specific differences between tissues originating from

the different germ layers in respect of their likelihood

to break down functionally under strain. Then clearly the

tendency to any such specificity would be obscured if we

charged to ectoderm the breakdown of any organ pri-

marily originating from that germ layer, but where in

fact the initial cause of the functional stopping of the

proper ectodermic tissue was the prior breakdown of a

part of the organ which was mesodermice in origin. This

is precisely the condition of affairs relative to the

pathology of cerebral hemorrhage.

Again, softening of the brain is really a necrosis of

brain tissue resulting from a cutting off of its nourish-

ment by stoppage of the circulation, which in turn may

be due to arthritis, thrombosis, embolism or pressure.

The same reasoning applies here as in the case of cere-

bral hemorrhage.

In so complicated a matter as the distribution of causes

of death to their embryological base probably the most

that can ever be hoped for, having regard to the enor-

mous complications of structural development, is to get

limiting values, within the range comprehended by which,

the true fact may be reasonably supposed to lie. To this

end Table XIII has been constructed. It with Table XII

gives lower and upper limiting values for death rates

chargeable to ectoderm and mesoderm.’ Table XIII is

No. 630] HUMAN MORTALITY RATES 39

made up in the same way as Table XII except that in the

former items 64 and 65 are transferred from ectoderm to

mesoderm. So far as I have been able to think the mat-

ter through it does not appear that the same complica-

tion may fairly be considered to arise in connection with

the embryological assignment of any other ‘‘cause of

death.’’

TABLE XII

SHOWING THE RELATIVE INFLUENCE OF THE PRIMARY GERM LAYERS IN

UMAN MORTALITY

(Items 64 and 65 charged to ectoderm)

| Death Rate per 100,000 Due to Functional Breakdown of

Toiy | Organs Embryologically Developing from

| Ectoderm % Mesoderm % Endoderm %

191.1 14.3 425.2 | 31.8 719.6 | 53.9

Sao Paulo, 1917 | 184.9 8.4 | 468.0 | 29.0! 1,009.9 | 62.6

England and Wales, 1914 ....| 177.1: | 14.4! 374.0 | 30.3 681.5 | 55.3

C. Endoderm.—The process of getting the figures here

was to add together first the totals of Tables II and VI

(respiratory system and alimentary tract) the organs

represented being mainly endodermal in origin. Then

there were subtracted from this total the following: (a)

items 39 (cancer of the buceal cavity) and 0.34 of item 41

(cancer of the. peritoneum, intestines, and rectum), leav-

ing 0.66 of this latter item here for cancer of intestines ;

(b) items 117 (simple peritonitis) and 93 (pleurisy) ; (c)

item 86 (diseases of the nasal fosse). All of these items

subtracted have been already placed with either ectoderm

or mesoderm. Finally, there were added items 124 and

125 (diseases of the bladder and of the urethra) which

were taken from the mesoderm for reasons already stated

under that heading. Also there were added items 51 and

88 from Table IX (exophthalmie goiter and diseases of

the thyroid body), because the thyroid arises from the

epithelium lining the inner branchial furrows. The re-

40 THE AMERICAN NATURALIST [Vou. LIV

sult finally obtained by the process described is that

which appears in Tables XII and XIII under ‘‘endoderm.”’

TABLE XIII

SHOWING THE RELATIVE INFLUENCE OF THE PRIMARY GERM LAYERS IN

HUMAN MORTALITY

(Items 64 and 65 charged to mesoderm)

Death Ta — 100,000 Due to Functional Breakdown of

| s Embryologically Developing from

Locality ES

Ectoderm % Mesoderm % Endoderm | a %

V i hse ep aimee Area, |

EE EE AE ME S | 116.9 8.7 499.4 37.4 719.6 | 53.9

U: yi y SRR AR Area, :

1901-05. | 137:3 9.8 | . 480.4 | 34.2 786.2 | 56.0

England and Wales, 1914 . 107.9 8.7 443.2 36.0 681.5 | 55.3

Sao Paul Paulo, 1 < 101.3 6.3 501.6 31. 1 | 1,009.9 62. 6

The data of Tables XII and can are shown graph-

ically in percentage form in Fig.

The final results shown in ete XII and XIII lead at

once to a generalization of considerable interest and sig-

nificance to the evolutionist. The figures show that in

man, the highest product of organic evolution, about 57

per cent. of all the biologically classifiable deaths result

from a breakdown and failure further to function of

organs arising from the endoderm in their embryological

development, while but from 8 per cent. to 13 per cent.

can be regarded as a result of breakdown of organ sys-

tems arising from the ectoderm. The remaining 30 to 35

per cent. of the mortality results from failure of meso-

dermic organs. Taking a general view of comparative

anatomy and embryology it is evident that in the evolu-

tionary history through which man and the higher verte-

brates have passed it is the ectoderm which has been

most widely differentiated from its primitive condition,

to the validity of which statement the central nervous

system furnishes the most potent evidence. The endo-

derm has been least differentiated in the process of evolu-

tion, while the mesoderm occupies an intermediate posi-

tion in this respect. An elaborate array of evidence

might be presented on these points, but to do so would be

No. 630] HUMAN MORTALITY RATES 41

supererogation. It would amount simply to repeating

any standard treatise on the comparative anatomy of the

vertebrates, a branch of biological literature which one

WM A S|

WMA

US. REGISTRATION AREA 1906-10

WSU rill

WME LAE!

ENGLAND and WALES I9/4-

RS O AEA

Wl Mea

SAO PAULO /9/7

ENDODERM MESODERM ECTODERM

Fie Diagram showing the ee ae of biologically classifiable human

Bait S Eih from breakdown of organs developi aei rom the different

germ layers. Upper bar of pair gives upper limit of mortality are AN to

ectoderm : lower bar gives lower limit of mortality chargeable to ectoderm

may fairly assume that the readers of this paper are

acquainted with, at least in general terms.

Degree of differentiation of organs in evolution implies

degree of adaptation to environment. The writings of

Darwin and Spencer, and in current times of Henry

Fairfield Osborn, have demonstrated this point beyond

question. From the present point of view we see that

that germ layer, the endoderm, which has evolved or

become differentiated least in the process of evolution is

42 THE AMERICAN NATURALIST [Vou. LIV

least able to meet successfully the vicissitudes of the

environment. The ectoderm has changed most in the

course of evolution. The process of differentiation which

has produced the central nervous system of man had as a

concomitant the differentiation of a protective mechan-

ism, the skull and vertebral column, which very well keeps

the delicate and highly organized central nervous system

away from direct contact with the environment. The

skin exhibits many differentiations of a highly adaptive

nature to resist environmental difficulties. It is then not

surprising that the organ systems developed from the

ectoderm break down and lead to death less frequently

than any other.

The figures of Tables XII and XIII make it clear that

man’s greatest enemy is his own endoderm. Evolution-

ally speaking, it is a very old-fashioned and out-of-date

ancestral relic, which causes him an infinity of trouble.

Practically, all public health activities are directed

towards overcoming the difficulties which arise because

man carries about this antediluvian sort of endoderm.

We endeavor to modify the environment, and soften its

asperities down to the point where our own inefficient

endodermal mechanism can cope with them, by such

methods as preventing bacterial contamination of water,

food and the like, warming the air we breathe, ete. But

our ectoderm requires no such extensive amelioration of

the environment. There are at most only a very few if

any germs which can gain entrance to the body through

the normal, healthy, unbroken skin. We do; to be sure,

wear clothes. But it is at least a debatable question

whether upon many parts of the earth’s surface we

should not be better off without them from the point of

view of health.

These tables indicate further in another manner how

important are the fundamental embryological factors in

determining the mortality of man. Of the three localities

compared, England and the United States may fairly be

regarded as much more advanced in matters of public

No. 630] HUMAN MORTALITY RATES 43

health and sanitation than Sao Paulo. This fact is re-

flected with perfect precision and justice in the relative

proportion of the death rates from endoderm and ecto-

derm. In the United States and England about 55 per

cent. of the classifiable deaths are chargeable to endo-

derm and about 9 to 14.5 per cent. to ectoderm. In Sao

Paulo 62.6 per cent. fall with the endoderm, and but 6.3

to 8.4 per cent. with the ectoderm. Since, as we have

already shown, public health measures can and do affect

practically only the death rate chargeable to endoderm

this result which is actually obtained is precisely that

which would be expected.

Finally, it seems to me that the results of this study

add one more link to the already strong chain of evidence

which indicates the highly important part played by in-

nate constitutional biological factors as contrasted with

environmental factors in the determination of the ob-

served rates of human mortality. Here we have grouped

human mortality into broad classes which rest upon a

strictly biological basis. When this is done it is found

that the proportionate subdivision of the mortality is

strikingly similar in such widely dissimilar environments

as the United States, England and Southern Brazil. It

is inconceivable that such congruent results would ap-

pear if the environment were the predominant factor in

human mortality. This conclusion does not overlook the

fact that in some diseases the environment, in a broad

Sense, is unquestionably the factor of greatest impor-

tance. Nor does it imply that every effort should not be

used to measure in every case the precise relative influ-

ence of constitution or heredity as compared with en-

vironment in the natural history of particular diseases.

This constitutes one of the most pressing and difficult

problems of medical science.

By way of summary it may be said that the purpose of

this paper is to rearrange the rates of human mortality

44 THE AMERICAN NATURALIST [Vou. LIV

as given in official reports of vital statistics, under the

code known as the International Classification, into

another classification upon a biological basis. The basis

taken is organological, each ‘‘cause of death’’ is charged

against that organ or organ system, the functional break-

down of which is fundamentally responsible for the death.

It is found that from 85 to 90 per cent. of all statistically

recognized causes of death can be subsumed under such a

biological classification. It is found when this is done

that the order of significance of the different organ sys-

tems in responsibility for human mortality is in general

that of the following list, the arrangement being in de-

scending order:

. Respiratory system.

Alimentary tract and associated organs.

Circulatory system and blood.

Nervous system and sense organs.

Kidneys and related excretory organs.

Primary and secondary sex organs.

Skeletal and muscular system.

Skin.

- Endocrinal system.

The arrangement differs slightly for different coun-

tries. If the further step is taken of referring the dif-

ferent organs and organ systems to the primary germ

layers from which they embryologically developed, it is

found that the death rates chargeable to organs of (a)

ectodermic, (b) mesodermic and (c) endodermic origin

stand to each other somewhere between the ratios of 1 to

2.3 to 4.4 and 1 to 4.4 to 7. The evolutionary and public

health significance of these results is discussed at some

length.

oe Se Se pre Go bo a

ON THE REACTION OF TISSUES TOWARDS

SYNGENESIO-HOMOIO— AND HETEROTOXINS,

AND ON THE POWER OF TISSUES TO

DISCERN BETWEEN DIFFERENT

DEGREES OF FAMILY

RELATIONSHIP

PROFESSOR LEO LOEB

(From the Department of Comparative Pathology, Washington Uni-

versity School of Medicine, St. Louis, Mo.)

In a series of papers our collaborators and ourselves

have analyzed the action of tissues upon each other after

transplantation carried out under varied conditions.

We wish now to suggest certain general conclusions of

wider significance which may be drawn from the facts

which have been previously published by us or which

will be published in the near future. No attempt will be

made here to review the facts on which our conclusions

are based and we must refer instead to our papers.!

In 1907 we first noticed that lymphocytes may appear

around or in transplanted tissue. Subsequently we ob-

served this occurrence in various tissues after transplan-

tation. We thought it possible that the action of lymph-

ocytes depended upon the relationship between host and

transplant. This was confirmed by our experiments.

1Leo Loeb, Archiv. f. Entwickelungsmech., 2897, Vi, 1; 1907, XXIV,

638; 1911, XXXI, 456; 1898, VI, 297.

Ran Loeb and W. H. F. Addison, Archiv. f. Entwickelungsmech., 1909,

XXII, 73; 1911, XXXI, 44.

Llewellyn Sale, Ibid., 1913, XXXVII, 248.

M. G. Seelig, Ibid., 1913, XXXVII, 259.

Max W. Myer, Ibid., 1913, XXXVIII, 1.

Cora Hesselberg, Journ. Kaj. Med., 1915, XXI, 164.

Cora Hesselberg, William Kerwin and Leo Loch, J. Med. Research, 1918,

XXXVIII, 17.

Leo Sanh: Journ. Am. Med. Asso., 1915, LXIV, 726.

Leo Loeb, Journ. Med. Reseorch, 1918, XXXVIII, 393; eee XXXIX,

189; 1918, XXXIX, 39; 1918, XX XIX, 71; 1918, XXXII, 3

45.

46 THE AMERICAN NATURALIST [Von. LIV

We found, however, that not only the lymphocytes, but

also the blood and lymph vessels and fibroblasts behaved

in a specific manner in accordance with the relationship

between host and graft.

We assume that all the tissues of an individual have in

common a certain chemical group which may be desig-

nated as individuality-differential. After transplanting

a piece of an organ into a near relative of the donor of

the tissue (syngenesiotransplantation), or into an unre-

lated individual of the same species (homoiotransplanta-

tion), or into an individual belonging to a different

species (heterotransplantation), the individuality-differ-

ential is no longer adapted to its environment and acts as

a syngenesio-, homoio-; heterodifferential, respectively.

In this inadequate environment the individuality-differ-

ential assumes injurious properties, either directly or

after interaction with the body fluids, some protein con-

stituent of which contains likewise the individuality-

differential or rather a group specifically combining with

the individuality differential. It is probable that the

second alternative represents the usual way in which the

individuality-differential becomes a syngenesio-, homoio-,

heterotoxin.

In certain cases the toxie character of the substance

which originates after homoiotransplantation is strong

enough to exert a direct injurious action on certain trans-

plantation is strong enough to exert a direct injurious

action on certain transplanted tissues, for instance, myx-

oid connective tissue and unstriated muscle. It can also

directly interfere with those metabolic processes which

lead to the production of epithelial pigment. In other

cases, however, the toxic substances, while strong enough

to modify the metabolism of the tissues, do not endanger

the life of the transplant. This occurs after transplanta-

tion of glandular structures like kidney or thyroid or

epithelial structures in general. But secondarily this

change in the metabolism of the transplanted tissue alters

the reaction of the host cells towards the graft. The

lymphocytes are attracted, the vascular supply is dimin-

No. 630] FAMILY RELATIONSHIP 47

ished; fibroblasts are given freer access to the trans-

plant, and moreover, the fibroblasts undergo secondary

changes; they form fibrous tissue, while after autotrans-

plantation the cytoplasm usually remains to a much

greater extent intact without undergoing the secondary

changes in contact with the grafted cells.

These toxic substances not only interfere with those

proliferative processes which are of a regenerative char-

acter in the more restricted sense, but also with others

caused by growth substances; thus they interfere with

the production of experimental deciduomata in the

uterus or with compensatory hypertrophy of the thyroid

after- homoiotransplantation, without however neces-

sarily preventing these growth processes entirely. Ulti-

mately they endanger the life of the exposed tissues,

usually indirectly through the action of the lymphocytes

and connective tissue cells, more rarely directly.

Furthermore the syngenesio-, homoio- and hetero-dif-

ferentials may act secondarily as antigens directly or

after interaction with the body fluids and then eall forth

the production of immune substances. Such immune sub-

stances however in most cases become demonstrable only

if the strangeness of the antigen used has been very

marked ; this is for instance the case if a hetero-differen-

tial serves as an antigen (Schoene, M. S. Fleisher). A

homoio-differential is only in some eases able to become

an antigen. Under certain conditions homoio-haemoly-

sins ean appear (Ehrlich and Morgenroth) or haemag-

glutinins (von Dungern and Hirschfeld) and further-

more homoio-immune substances can be produced against

growing tumors and embryonal tissues (Fichera, Peyton

Rous). In the case of tumor immunity lymphoeytes play

a very prominent part. This has been noted by a num-

ber of investigators. More recently the significance of

lymphoeytes in immunity has been demonstrated in

varied experiments especially by J. B. Murphy and his

collaborators. However, as we shall see presently, the

direct reaction of tissues (including lymphocytes) against

Syngenesio-, homoio- and heterotoxins is a finer bio-

48 THE AMERICAN NATURALIST [Vou. LIV

chemical reaction than any reaction known so far and

more delicate than the immune reactions.

These substances which function as individuality-dif-

ferentials are produced in the active metabolism of cells;

they can be demonstrated through their reaction after

transplantation of metabolically active tissue, but not

after transplantation of erythrocytes contained in a

blood clot. The syngenesiotoxins are least toxic. Usually

they call forth a lymphocytic reaction only slowly; but

ultimately the lymphocytes appear even here and invade

and destroy the strange tissue. At a time when the

vascular and fibroblastic reactions should occur, the

toxins may as yet be so weak that these two kinds of

tissues may behave normally. In other cases, however,

even the syngenesiotoxins may be strong enough to call

forth an altered reaction of vessels and fibroblasts; the

vessels may fail to be present in a large number by the

graft and the fibroblasts may produce more fibrous

tissue. This occurs typically. in response to homoio-

toxins; furthermore, in the presence of homoiotoxins

lymphocytes appear early and in large masses. They, as

well as the fibroblasts, may invade and destroy the

strange tissue. In the case of the heterotoxins the direct

injurious effect of the body fluids is much more pro-

nounced, and in a general way this effect is the greater,

the more distant the relationship between host and graft,

but in this case also the cellular reactions of the host may

secondarily contribute to the destruction of the strange

tissues. The fibroblasts of the host have a tendency to

form dense fibrous tissue around the graft and the blood

and lymph vessels are usually extremely sparse in the

direct neighborhood and in the interior of a heterograft;

apparently the strange cells do not exert an attracting or

stimulating influence on the growth of capillaries. While

thus in these two respects the heterotoxins produce an

effect which might have been foreseen from a study of

homoiotoxins, the behavior of the lymphocytes seems to

be different from what might have been expected. In-

stead of being attacked by lymphocytes even more actively

No. 630] FAMILY RELATIONSHIP 49

than the homoio-tissues, the lymphocytic reaction is on

the contrary decidedly weaker in the case of tissues of

other species. Lymphocytes do not usually invade and

destroy the tissue of a foreign species, although they may

collect in a considerable number in the neighborhood of

the graft and may occasionally invade it here and there

in small areas and destroy these. They may appear in

large quantities after the graft has been destroyed. This

relative inactivity of the lymphocytes is surprising, if we

consider the much greater strangeness between graft and

host which results from heterotransplantation. But it

may be just on account of the great strength of the hetero-

toxins that the reaction is weakened. We have seen above

that the development of the specifically attracting sub-

stances depends upon the active metabolism of the graft

as evidenced by the failure of the erythrocytes to at-

tract the lymphocytes. In the case of heterotransplan-

tation the action of the toxins may be so strong that it

interferes with these specific metabolic activities of the

transplanted cells, and thus the reaction would naturally

become weaker. It may also be that the scarcity of ves-

sels around and in the graft may contribute to this result,

these vessels acting as the channels through which the

lymphocytes reach the graft. But that this factor can

not be the only reason is clear from a study of certain

areas of the transplant occasionally found in which the

blood vessel supply may be somewhat better, but in

which, nevertheless, the lymphocytic infiltration of the

graft is absent or slight.

There is then a graded reaction of various tissues of

the host towards transplants. At one end of the series

we find the autotransplants; these are followed by the

various kinds of syngenesio-, by homoio- and hetero-

transplants. Autotransplants call forth a marked vas-

cular reaction. This reaction decreases in the direction

towards heterotoxins; it is already very weak in most

cases of homojotoxins. The fibroblasts remain relatively

well preserved, form least fibrillar material and tend to

the production of myxoid tissue uniter the influence of

50 THE AMERICAN NATURALIST [Vou. LIV

those conditions which prevail in the case of autotrans-

plantation. Here they are prevented at most places from

breaking into the glandular structures; in the presence

of homoio- and hetero- and even of syngenesio-toxins they

tend in a higher degree towards the production of fibrille.

Lymphocytes are attracted by syngenesiotoxins and still

more by homoiotoxins; here a maximum is reached. A

decrease occurs again in the region of the heterotoxins.

The number of fibroblasts invading the glandular trans-

plant is likewise greatest in the case of homoiotransplan-

tation. Again.a decrease seems to occur in the case of

heterotransplants.

We may express these facts also in a somewhat differ-

ent way. Under conditions of autotransplantation the

tissues give off substances which correspond to the iden-

tity of the individuality-differentials in the host and

graft. These substances, which may be designated as

‘‘auto-substances,’’ stimulate directly or indirectly the

vascular supply of the tissues belonging to the same indi-

vidual. And they also exert directly or indirectly a defi-

nite effect upon the fibroblasts, keeping them active and

preventing them from undergoing those processes which

probably represent a decline in normal metabolism and

which lead to the production of fibrous tissue at the ex-

pense of the healthy active cytoplasm. In the absence

of these auto-substances, the vascular supply is lessened

in direct proportion to the greater distance of the rela-

tionship between host and graft. To a certain extent

syngenesiotoxins still take the place of the auto-sub-

stances characteristic of the interaction between the own

tissues and body fluids. Some syngenesiotoxins however

can do so only to a very slight extent; homoiotoxins are

still less able to take the place of auto-substances and

least of all heterotoxins. In the case of homoio- and

heterodifferentials the stimulating effect of the ‘‘auto

substances’’ is lacking; they behave in certain respects

like foreign bodies.

On the other hand the autosubstances exert no attracting

influence on the lymphocytes, while the syngenesiotoxins

No. 630] FAMILY RELATIONSHIP 51

exert at first a very slight, but gradually cumulative,

effect; the homoiotoxins exert the maximum effect; and

then a decrease again takes place in the region of the

heterodifferentials.

It might be suggested that the same auto-substances

play a part in the interaction between the normal tissues

of an individual. It is quite evident that the effect of

the autosubstances would be beneficial to the tissues and

contribute to their nourishment. Thus the body would

possess a system of very finely acting chemical auto-

regulators which keep the vascular supply at the point of

greatest intensity and prevent the fibroblasts from form-

ing dense fibrous tissue which again would interfere with

the nourishment of the tissues and which insure such an

interaction of tissues that the normal structure results.

Strange tissues do not exhibit the effect of such auto-

substances, even if such strange tissues should tempor-

arily multiply mitotically, and therefore they perish in

the end.

On the other hand, autosubstances are indifferent, as

far as the lymphocytes are concerned, while syngenesio-

and homoio- and to some extent heterotoxins attract

them. The lymphocytes as well as invading fibroblasts,

are a destructive element and the effect of both is elimi-

nated through the action of autosubstances; again a bene-

ficial adaptation. Hypothetically we might thus explain

in part at least the changes of tissues in old age. The

effect of the autosubstances would be strongest in young

individuals and decrease in the less actively metabolizing

older tissues; and here we find, therefore, changes which

are characteristic of a decrease in the autosubstances, or

rather of specific metabolic substances which have the

‘‘auto’’ character and at the same time are characteristic

of the specific organ activity. Therefore in old age the

fibroblasts around the parenchyma from fibrous tissue

and the vascular supply decreases. In the embryo we

find least fibrous and most myxoid tissue and the best

vascular supply.

52 THE AMERICAN NATURALIST [Vou. LIV

Correspondingly we find least dense fibrous tissue

around actively metabolizing parenchyma, while around

the metabolically less active excretory ducts there is

usually a coat of much more dense fibrous tissue. Thus

it might be tentatively suggested that a decrease in these

autosubstances, to the existence of which the results of

tissue transplantation point, is at least partially respon-

sible for the changes which take place in old age. Other

factors of a different nature play certainly a part. Thus

the corpus luteum stimulates the activity of the uterine

connective tissue and epithelium. In later periods of

life this stimulating influence is lacking.

While the autosubstances increase directly or indi-

rectly the vascular supply, they very effectively limit the

growth of fibroblasts in contact with epithelial elements.

We have previously shown through transplantation ex-

periments that during regeneration the epithelium limits

the growth of the connective tissue.” In a similar way

perhaps the endothelium of the blood vessels limits the

growth of the connective tissue. Our further experi-

ments lead to the conclusion that this restraining influ-

ence exerted by endothelium and epithelium upon con-

nective tissue migration and proliferation is a specific

effect. The auto-substances possess it in the highest*de-

gree. It is less marked in the case of syngenesio- and

still less in the case of homoiotoxins. But even the

hetero-substances still exert a certain restraining influ-

ence, at least temporarily on the connective tissue and

they are thus in this respect more effective than foreign —

bodies. It is again clear that considering the tendency

of fibroblasts and lymphocytes to migrate actively into

parenchyma and to destroy it, the epithelial structures

can be assured of preservation only, if the auto-sub-

stances possess some kind of a restraining influence on

the connective tissue.

It is probable that not only in old age but also under

certain pathological conditions, the activity of these auto-

2 Leo Loeb, Arch. f. Entwickelungsmech., 1898, VI, 297 (p. 319).

No. 630] FAMILY RELATIONSHIP 53

substances is interfered with, and that thus cirrhotic

processes may be produced in various parenchymatous

organs. The usual assumption is that all these fibrous

changes are the result of an actual destruction of the epi-

thelium, that they are therefore due to regeneration in

the more restricted sense of the term. It is probable that

both these processes may occur in different cases,

As we have shown, various tissues, but particularly the

lymphocytes, are able to distinguish not only between

tissues belonging to the same and other individuals of

the same species, but even to recognize the difference in

degree of relationship. They behave in a graded man-

ner towards their own tissues, the tissues of a brother,

mother, the tissues of a not related individual of the same

Species and the tissues of an individual of a.different

species. ‘These reactions must be in response to specific

substances given off by these tissues, the autosubstances,

the syngenesio-, homoio- and heterotoxins. Whether

these substances are identical with the individuality-

differentials residing in the tissues or whether they are

due to an interaction between the individuality-differ-

entials residing in the tissues and adapted substances in

the body fluids can not be decided definitely at present;

however, the latter assumption seems to be more prob-

able. These responses represent to our knowledge the

finest biochemical reactions which are known at the

present time and surpass even the immune reactions

which permit us to distinguish only between different

Species and in a few cases only between individuals of the

same species.®

These reactions we may hope will contribute to an

understanding of the behavior and the functions of

tissues in general as‘distinet from the specific functions

of organs which under certain conditions are added to

*It is possible that a further development of the immunological methods

used by von Dungern and Hirschfeld and by Todd and White (Proc. Royal

Soc., 1910, LXXXIT, 416) will also lead to a differentiation in the relation-

ship of individuals of the same species.

54 THE AMERICAN NATURALIST [Vou. LIV

these more general tissue reactions, and thus they may

contribute to a physiology of tissues as contrasted with

the physiology of organs. Further experiments will

have to determine, how far the effect of the parenchyma

on the fibroblasts and blood vessels is a direct one and

how far secondary interactions between fibroblasts and

blood vessels enter into these reactions.

These various substances (autosubstances, syngenesio-,

homoio- heterodifferentials) have in addition to the func-

tions which concern the effect of cells upon each other

added functions of a specific nature. This is indicated by

the existence of specifically adapted substances like the

tissue coagulins which determine in a specifically adapted

manner the coagulation of the blood of various species.*

4Leo Loeb, Montreal Med. Journal, July, 1903; Virchow Archiv, 1904,

CLXXVI, 10; Biochem. Zeitschrift, 1910, XXVIII, 169.

THE INDIVIDUALITY-DIFFERENTIAL AND ITS

MODE OF INHERITANCE

PROFESSOR LEO LOEB

(From the Department of Comparative Pathology, Washington Uni-

versity School of Medicine, St. Louis, Mo.)

Ty a preceding communication we have shown that all

the tissues of an individual have in common a chemical

characteristic through which they differ from other indi-

viduals of the same species. 'This characteristic may be

designated as the individuality-differential. It is prob-

able that in the circulating body fluids these individuality-

differentials or substances specifically adapted to them

are likewise present. The interaction of cells and sub-

stances which possess the same individuality differential

leads to the production of autosubstances which are re-

sponsible for various conditions of tissues. But if,

through transplantation, the individuality-differentials

become converted into syngenesio-, homoio- or hetero-

differentials toxic substances are produced, the syn-

genesio-, homoio- or heterotoxins which lead to tissue

reactions of different kinds as we have described in the

preceding communication.

In the process of fertilization usually two homoio-dif-

ferentials combine to form a new individual. Through

transplantation of tissue it is possible to determine

whether the individuality-differential of the child is iden-

tical with the individuality-differential of one of the two

parents or whether its character is intermediate. If the

inheritance of the individuality-differential should be-

have like a simple Mendelian monohybrid character, all

the offspring of the first generation would have the same

individuality-differential and the individuality-differ-

ential of one of the two parents would probably dominate.

56 THE AMERICAN NATURALIST [Vou. LIV

Interchange of tissues between the children (brothers

and sisters) should give results identical with those of

autotransplantation, and transplantation of tissues from

one of the two parents to a child should in all children

give the same result, and the results should be those of

either auto- or homoiotransplantation. Or, it might be

possible that in the offspring a blending of the individu-

ality-differentials of both parents occurs. It might fur-

thermore be possible that in all children the same kind of

blending occurred or that all intermediate degrees of

blending of the differentials of father and mother be

found.

In using transplantation of tissue as a means of deter-

mining which of these possibilities is realized, we have to

take into account the difference in the situation of host

and graft. Under the usual conditions of transplanta-

tion the host is a selfsufficient organism and is not in any

essential manner dependent for his nourishment upon

the graft. The graft on the contrary depends upon the

host for its nourishment. ‘The relation between host and

graft is therefore not that of simple reciprocity. This

relation may be important in interpreting certain results

of transplantation as wè shall see later.

We have carried out two series of experiments in which

we analyzed the mode of inheritance of the individuality-

differential, one in the rat! and a second one in the guinea

pig.” In the former we transplanted simultaneously

pieces from different organs into rats; in the second we

used the thyroid gland for transplantation. We trans-

planted tissues from parents to children, from children

to mother and from brothers to brothers. Both series,

in the rat and guinea pig, gave the same result as far as

the main problem is concerned; the individuality-differ-

entials of the children are intermediate between those of

the two parents; but all kinds of intermediate conditions

1 Leo Loeb, Journ. Med. Research, 1918, XX XVIII, 393 (here the litera-

ture is discussed).

2 Leo Loeb, Journ. Med. Research, 1918, XXXIX, 39.

No. 630] THE INDIVIDUALITY-DIFFERENTIAL 57

are found varying between those approaching identity of

individuality-differentials on the one extreme and

homoio-differentials on the other.

In the guinea pig we analyzed further the difference in

the results after transplantation of tissues from brother

to brother, from mother to child and from child to mother.

We found transplantation from brother to brother to

give the best results, but even here the mixing of the indi-

viduality-differentials called forth the development of

toxins, syngenesiotoxins, which usually were relatively

mild, but in certain cases would be more severe. Trans-

plantation from child to mother led to the production of

toxic effects which were almost as marked as those pro-

duced by the homoio-toxins. Transplantation of tissues

from mother to child on the whole resembled that of

transplantation from brother to brother, but seemed to

be somewhat less favorable. In the rat there were like-

wise indications that the transplantation from child to

mother was more unfavorable than the others, but a de-

cided difference between transplantations from mother

to children and from brother to brother could so far not

be established. However, the indicator of effects which

we used in our guinea pig series was finer than that in

our rat series.

We have begun experiments to determine the behavior

of individuality-differentials in the second generation.

It seems that here too the results are intermediate, but

further experiments need to be carried out, before a defi-

nite statement can be made.

In a provisional way we may attempt to explain these

results as follows. In most cases each individual has at

least two sets of individuality-differentials, one inherited

from the father, the other from the mother. Each set

again consists of two kinds of differentials. There may

be added individuality-differentials from some further

distant ancestors, but this complication may be ignored

at present; in certain individuals the differentials of

either father or mother are lacking. We may assume

Pre eat

58 THE AMERICAN NATURALIST [Von. LIV

that several or all of the chromosomes of the father are

characterized by certain chemical groups which would be

the same in the cells of the same individual, but would

differ in the cells of different individuals. Each cell

of the child obtains a combination of chromosomes which

is the same in the same individual, but differs in the case

of different brothers or sisters. The chemical individ-

uality-character of the chromosomes should lead to

analogous chemical differences consisting perhaps in the

formation of chemical sidechains attached to proteins;

they should be present primarily in cell proteins and

secondarily in the proteins of the body fluids. While the

individuality-differentials in the tissues exist perhaps

even in the embryo, there are some indications that the

adapted substances in the body fluids originate after

birth. These side chains must be identical in all the pro-

teins of the same individual and differ in the case of

different individuals. We should then expect that the

individuality-differentials of the children, being a mix-

ture of those of the parents, however in proportions

which differ in the case of different children, should be

intermediate between those of the parents. Extremes in

the children may be almost identical with one or the other

parent. In transplanting tissue from one brother to

another the graft would in most cases find in the host the

same characteristic groups which its own cells possess,

but in a somewhat different quantitative relationship.

Therefore the life of the graft which finds all the char-

acteristic substances could be sustained; but the quanti-

tative differences which exist in most cases would grad-

ually lead to toxic effects which ultimately endanger the

life of the graft. In some cases, however, the host would

lack altogether some of the chromosomes or groups

present in the brother and then the result would be more

unfavorable, somewhat approaching that of homoio-

transplantation.

In the case of transplantation from child to mother on

the other hand the graft would lack one half the chromo-

No. 630] THE INDIVIDUALITY-DIFFERENTIAL 59

somes and therefore the corresponding chemical groups

present in the cells of the graft. The result should there-

fore approach that of homoio-transplantation, which we

indeed find to be the case. After transplantation from

mother to child the graft finds in the host in many cases

the chemical groups it possesses itself, but again the pro-

portion of chemical groups in host and graft (corre-

sponding to that of the chromosomes) differs here more

than in the case of two brothers and these quantitative

differences might lead. to a greater incompatibility be-

tween graft and host than in the case of transplantation

from brother to brother. On this assumption we might

furthermore expect that in certain rare cases even

homoio-differentials should show a similar constitution

and might therefore permit a successful transplantation

into a not related individual.

While the somatic tissues require for their normal’

life identity of individuality differentials with which they

come into contact, the germ cells on the contrary are

normally adapted to contact with homoio-differentials in.

the chromosomes and as T. H. Morgan? has shown in

Ciona secondary mechanisms ries even make auto fer-

tilization impossible.

In man, Landsteiner, Moss and others found a peculiar

- distribution of isoagglutinins into three or four groups,

which are apparently independent of the parentage of

the individuals concerned. Such a condition seems to be

peculiar to man and has not been found in animals

(Hecktoen).* In certain animals, however, von Dungern®

and Hirschfeld succeeded through immunization to de-

monstrate the existence of two kinds of isohemagglutin-

ins and of the corresponding antigens and thus of four

classes of individuals. As our transplantations show

conditions in the tissues cannot be the same as in the red

blood corpuscles, if we should judge the constitution of

* T. H. Morgan, Biological Bulletin, 1905, VIII, 313.

tL. Hecktoen, J. Infect. Diseases, 1907, IV, 297.

*V. Dungern, Munch. Med. Wok., 1910, Vol. 57, p. 293, p. 740.

60 | THE AMERICAN NATURALIST [Vov. LIV

the latter on the basis of these agglutination tests. In

the case of the tissues we have to assume the existence of

individuality-differentials which are composed of mul-

tiple chemical groups; therefore Mendelian heredity

would be that of multiple factors. It is not improbable

that even in the case of tissues the number of these

groups is limited and that all the individuals of the same

species have a choice only between a relatively small

number of groups which is characteristic of each species

and that the different individuals of a species differ from

each other through the combination of these groups which

each individual possesses. Other chemical groups would

be characteristic of species and in this case also the num-

ber of groups which constitute a species differential may

be limited.

The explanation for the facts of inheritance of the indi-

viduality-differentials which we attempted in this note

is regarded by us at present as of an entirely provisional

character. So far, however, it seems to agree with the

facts as they are known; but we have no doubt that as

investigations progress still further it may require cer-

tain, perhaps fargoing, modifications. It finds, however,

support in the investigations of Landsteiner, Pick and

Obermeyer and others who have shown that the immune

reaction-specificity of protein substances can be experi-

mentally altered through changes in chemical side chains

which are added to these proteins.

6 Karl Landsteiner u. Hans Lampl, Biochem. Zeitsch., 1918, LXXXVI, 342.

LINKAGE IN RATS!

HEMAN L. IBSEN

Kansas State AGRICULTURAL COLLEGE

At the present time there are at least five factor pairs

or series known in rats. Some of these have been de-

scribed only quite recently, and it may therefore be prof-

itable to tabulate all of them and to mention some of their

interactions.

_ These genes are:

1. R, black-eyed; r, red-eyed.

2. P, black-eyed; p, pink-eyed.

3. S, self; Sı, Irish; Sa, hooded.

4. A, agouti; a, non-agouti.

5. C, intense pigmentation; C+, non-yellow; Ca, albinism.

Color varieties homozygous for one or the other of the

first two recessive genes mentioned above were described

by Castle (1914). Both are yellow-coated. A PPrr ani-.

mal is yellow with eyes of a reddish tint, while animals of

the composition ppRR or pprr are yellow with pink eyes.

Pink-eyed yellows, therefore, may be of two kinds, those

carrying R and those lacking it. Animals carrying both

P and R are black-eyed and have black coats. Pink-eyed

yellows, carrying R (ppRR), mated to red-eyed (PPrr)

produce PpRr, black-eyed animals having black coats.

Pink-eyed yellows lacking R, and therefore of the compo-

sition pprr, when mated to red-eyed yellows (PPrr) give

p rr, or red-eyed yellows.

Castle and Wright (1915) and Castle (1916) present

evidence that the genes above described are linked. When

Pink-eyed yellows (ppRR) were crossed with red-eyed

1 Papers, from the Department of Genetics, Agricultural Experiment Sta-

tion, University of Wisconsin, No. 21. Published with the approval of the

Director of the Station. 4

62 THE AMERICAN NATURALIST [Vou LIV

yellows (PPrr), the p and R of the pink-eyed and the P

and r of the red-eyed tended to be linked, the crossing

over being about 17 or 18 per cent.

More recently Castle (1916) has given evidence indi-

eating that Irish pattern (Si), entirely pigmented except

for a white patch on the belly, is allelomorphic to both self

(S) and the hooded pattern (S). Whiting and King

(1918) have shown that the non-yellow condition (C+)

corresponds to that found in guinea-pigs and is similarly

allelomorphic to both complete pigmentation (C) and

albinism (Cc). Dilute pigmentation (Ca) has not as yet

been found in rats. Castle (1916) presents experimental

proof that the allelomorphs of pink-eyed (p) and red-

eyed (r), or P and R, are linked with albinism, Ca. This

would put the three genes on the same chromosome.

Castle’s data are too few for the exact degree of link-

age to be determined from them.

Up to the present no results have been published of a

direct attempt to determine the possible linkage relations

of self (S) and agouti (A) to each other or to the other

three linked genes. Data bearing on this point will be

presented in this paper. It will also be shown that so far

as our evidence goes the genes R and Ca are absolutely

linked.

The first crosses made were for the purpose of deter-

mining the linkage relations of the.red-eyed pair of allelo-

‘morphs (R and r) with the self series (S, Si and Sa).

Red-eyed selfs (rSPa) were crossed with black-eyed

hooded (RSiPa) and the resulting animals were there-

fore self?-blacks (rS-RS:).2 These self-blacks were then

bred back to the double recessives, red-eyed hooded

(rrSiS.). The offspring from this mating are shown in

Table I. From this it will be seen that red-eyed and self

are entirely independent in heredity.

2 With my animals every heterozygous self (SS8;,) had a white patch on

the belly.

3 P and a may be disregarded since both parents were alike with respect

to these genes.

No. 630] LINKAGE IN RATS 63

TABLE I

TS.RSp X rrSrS8p

Non-crossovers | Crossovers

| |

Black-hooded, RS), Self-yellow, 7S | Self-black, RS | Yellow-hooded, 7S),

49 42 | 49 | ` 48

Later the opportunity was offered for studying the

relation of agouti (A) to the above two genes. A red-

eyed self carrying agoutit (rSA) was mated to black-

eyed hooded blacks (RSia) and the resulting offspring,

self agoutis (rS.A-RSia), were bred back to the triple re-

cessives, red-eyed hooded (rrS:S:aa). From this mating

were obtained the animals shown in Table II.’ In this

case also there is no indication of linkage since all of the

classes are of approximately the same size.

TABLE II

rSA-.RS;a X rrS;8,aa

ARS | ARS, Arh | aRSh ars arSp

25 29 23 21 2a 24 25 26 196

If we disregard the agouti gene in the above cross, the

results from Table II may be combined with those from

Table I. This has been done and is given in Table ITI.

The combined results merely give added proof to the de-

ductions drawn from Table I, that no linkage has oc-

curred.

TABLE III

TABLES I AND II COMBINED

rS-RSp X rrShSh

Non-crossovers

RS, | rs ` RS rSh

102 i 100 97 | 95

*Red-eyed animals carrying agouti are of a decidedly deeper red than

those lacking it ae seem dilute in comparison) and are easily distin-

guishable from the latter

64 THE AMERICAN NATURALIST (Von LIV

We may therefore conclude that the known genes in ‘

rats arrange themselves into three groups. Into one may

be placed agouti (A) and its allelomorph, non-agouti (a);

into the second, self (9), with its allelomorphs, Irish (S:)

and hooded (S1); and into the third the three genes R, P

and C with their allelomorphs. °

As before stated, Castle showed that R and P were

linked to albinism (C.), but he did not determine the ex-

act degree of their linkage Evidence on this point

concerning the linkage of R and Cc will be presented in

the following pages.

Two of the heterozygous self agoutis (rSA-RSia) used

in determining the linkage relations of R, S and A, when

mated together produced some albino offspring. The

father of the self agoutis, ¢ 105A.1, a red-eyed self,

carrying agouti (rrSSAA), could not have carried al-

binism himself since he had 17 non-albino offspring when

mated back to one of his daughters, 2? 126B.4, known to.

be carrying the albino gene. The mother of the self

agoutis, 2 98A.2, a black-eyed black hooded, must there-

fore have been heterozygous for albinism, and accord-

ingly would be of the composition RRS:SiaaCCs. Her

offspring that gave birth to albinos would of necessity

have the zygotic formula RrSSi:AaCC.« These when in-

bred should have had albino offspring of various compo-

sitions, if there had been no linkage. For every albino

that was homozygous for a dominant gene we should have

expected two-that were heterozygous and one that was

homozygous for the recessive.

Since there were six albinos born from the agouti X

agouti mating, it seemed quite probable that one at least

would be found that was recessive for all the genes. Ani-

5In May, 1919, the author was informed by Professor Castle that he had

conclusive evidence that R and Ca were completely linked. At that time he

had obtained about 200 non-cross-over and no crossover gametes. While this

paper was going through the press Castle’s report (1919) on linkage in rats

has appeared as Publication No. 288 of the Carnegie Institution or Wash-

ington. In studying the linkage relations of albinism and red-eyed he ob-

tained 433 non-cross-over gametes and one somewhat doubtful crossover.

No. 630] LINKAGE IN RATS 65

mals of this sort could be used for further linkage work.

Even if none were found it seemed very probable that

from them albinos of this description could be produced.

Accordingly all six albinos were mated to red-eyed yel-

low-hooded animals (rrS:SiaaCC) in order to determine

their compositions. The zygotic formule of the six

proved to be as follows:

IRRS SAA,

2RR nS Áa,

IRRS Sraa,

IRRSSraa,

IRR? =

The one outstanding feature was that all six albinos were

homozygous for black-eyed (R), although without link-

age one should have expected that at least one would be

red-eyed (rr) and severalheterozygous (Rr). This gave

a very strong indication of linkage and so further work

was pursued with this in view.

To simplify matters we shall disregard all the genes

but R (and its allelomorph r) and C with its allelomorph

Ca, and we shall also assume complete linkage. When the

above six albinos (RRC.C.), therefore, were crossed with

red-eyed yellows (rrCC) their black-eyed offspring would

be of the composition RCa-rC. These black-eyed animals

when inbred, assuming complete linkage, would behave as

follows: 7

RCa-rC X RCw-rC =1 RCo-RCa (albino): 2RCa-rC (black-

eyed blacks): 1 rC-rC (red-eyed yellow).

® Black-eyed (R) animals may be distinguished from red-eyed (r) or al-

binos (Ca) at birth by the fact that their eyes already appear dark through

the skin, while red and albino eyes are as yet devoid of pigment. It is

only about two weeks after birth or just, before the eyes open that the red

eyes have enough pigment in them so that they can be distinguished from

albinos or pink-eyed (p). One of the albino females being tested had 11

black-eyed (R) young which through some oversight were disposed of before

their other characters were recorded.

66 THE AMERICAN NATURALIST [Vor. LIV

The albinos from this mating when mated to their red-

eyed yellow litter mates, or to red-eyed yellows from sim-

ilar matings, should give nothing but black-eyed blacks

(RCa-rC). This would prove for both albinos and red-

eyed yellows that each was the result of the union of two

non-crossover gametes. The black-eyed blacks when

mated together should behave just like their black-eyed

black parents, i.e., produce all three phenotypes. In this

case also this would prove that two non-crossover gametes

had united in the production of each black-eyed black

parent.

The above policy has now been pursued for some time.

From the mating together of RCo:rC black-eyed blacks

the following offspring have resulted:

23 albinos, 57 black-eyed’ blacks, 31 red-eyed yellows.

For some reason there is a deficiency of albinos. As

previously explained, black-eyed blacks may be distin-

guished at birth from either albinos or red-eyed yellows

by the color of their eyes. In the above cross five animals

died early, but none of them were black-eyed. They died

before one could be sure whether they were albinos or

red-eyed yellows. If there was selective mortality, and

they were all albinos, the deficiency of albinos would thus

be explained.

So far 13 albinos from RC«a-rC X RC.a-rC matings have

been tested and all proved to be RC.-RC.; therefore they

are the result of the union of 26 non-crossover gametes.

Similarly, 12 black-eyed blacks proved to be RCa-rC and

10 red-eyed yellows, rC-rC. The total number of non-

crossover gametes going into the production of the above

animals is 70, and is at least a fair indication that R and

Ca are completely linked. More results are necessary in

order to make this conclusive. Since the amount of cross-

ing-over between R and P is already known (17-18 per

cent.), and since R and Ca are completely linked, we

should expect to find the same percentage of crossing-

over occurring between P and Ca as between P and R.

No. 630] - LINKAGE IN RATS 67

LITERATURE CITED

Castle, W. E.

1914. Some New Varieties of Rats and Guinea-pigs and their Relation

to Problems of Color Inheritance. AMER. NAT., Vol. 48,

PP. '

1916. Further Studies of Piebald pes and PEK with pha beer

on Gametie Coupling. Pp. 163-192. In ‘‘Studies of Inher

tance in Guinea-pigs and a 2? Dy we E. Castle and Sewell

ege Carnegie Institution of Washington, Publication No.

Pp. iv+1

1919. Taen of heredity in rabbits, rats and mice. Carnegie Insti-

tution of Washington, Publication No. 288, 56 pp., 3 pls.

Castle, W. E., and Wright, Sewell.

1915. Two Color Mutations of Rats which show partial Coupling.

Science, N. S., Vol. 42, pp. 193-195.

Whiting, P. W., and King, H. D.

1918. Ruby-eyed Dilute Gray, a Third Allelomorph in the Albino

Series in the Rat. Jour. Exp. Zool., Vol. 26, pp. 55-64.

SOME HABITAT RESPONSES OF THE LARGE

WATER-STRIDER, GERRIS REMIGIS

SAX. IIT

C. F. CURTIS RILEY

THE New YORK STATE COLLEGE OF FORESTRY AT SYRACUSE UNIVERSITY,

Syracuse, NEw YORK

VI. Discussion or EXPERIMENTS AT WHITE HEATH

1. Rôle Played by Vision.—In regard to the experi-

ments at White Heath there is little to be said more than

already has been stated in the discussion in connection

with the responses of the water-striders, during severe

drought, in the dry bed of the stream. In general, the

majority of the gerrids found their way back to the brook,

when removed from it to distances of one, two, three, and

four yards. This was true whether they faced the brook,

were placed with their bodies parallel to its banks, or

faced directly away from the water. Water-striders with

their heads turned away from the stream took a little

longer time to reach the brook than was true of the other

hemipterons, and they also evinced more random move-

ments. Occasionally a gerrid wandered astray and

seemed unable to reach the brook. `

At such short distances away from the water, as have

been mentioned, it is very probable that the hemipterons

find their way back to it mainly through the sense of sight.

It is a well-known fact that many species of aquatic Hem-

iptera respond positively to light as a stimulus, indicating

that vision must play an important part in the behavior

of the members of this group. Among these are the

water-striders Gerris orba (Essenberg, 1915, p. 400),

Gerris remigis, Gerris marginatus (Riley, MS.), and prob-

ably Gerris thoracicus, Gerris tristan (Kirkaldy, 1899,

p. 110). Not only do certain water bugs respond posi-

tively to light, but Cole (1907, p. 387) has proved the truly

remarkable fact that Ranatra fusca possesses the ability

No. 630] HABITAT RESPONSES OF WATER STRIDER 69

to discriminate between two luminous areas of different

size, even though they are of the same intensity. Water-

striders may possess this sort of discrimination.

At this point I desire to direct attention to certain in-

teresting experiments of Parker (1903) on the butterfly,

Vanessa antiopa Linnzus, because of their probable bear-

ing on some of the responses of Gerris remigis. Accord-

ing to this writer (1903, p. 467),

Vanessa antiopa .. . [is able to] discriminate between light derived

from a large luminous area and that from a small one, even when light

from these two sources is of equal intensity as it falls on the animal.

These butterflies usually fly toward the larger areas of light.

He (1903, p. 465) remarks that in the sunlit spots in the

woods, this butterfly responds to the large areas of sun-

light rather than to the smaller ones. This form of re-

sponse applies also to the sun, although

the retinal image of the sun must be vastly brighter than those of all

other spots [of sunlight].

Furthermore, writing of the way in which Vanessa an-

tiopa finds a patch of sunlight, he (1903, p. 464) makes

the following statement :

; This patch [of sunlight] is found not through the accidental wander-

ing of the butterfly into it, but by the butterfly’s taking a direct course

to it, precisely as the insect finds a single light window in an otherwise

dark room. The directive influence, then, is not the intense sunlight that

makes the patch, but the much less intense reflected light radiating from

the patch. This must form a localized spot on each retina of the butter-

ATN it is the position of these spots that determines the direction of

The surface of the water in a brook forms an excellent

reflecting surface, either for moonlight or for sunlight,

and it is probable that the gerrids respond to such re-

flected light much in the same way that they do to arti-

ficial light. Or they may respond to water, or rather to

the reflections from its surface, according to the same gen-

eral principle that Vanessa antiopa responds to patches

of sunlight. These areas of sunlighted water in the

brook must have much the same appearance to insects

With image-forming eyes, such as water-striders, as do

70 THE AMERICAN NATURALIST [Vou LIV

the sunlit areas in the woods. The gerrids go toward

the water—not quite so directly as Vanessa antiopa

moves toward areas of sunlight—with but few prelimi-

nary random movements, except in the case of those

having their heads directed away from the brook, in

much the same fashion and probably for much the same

reason that Vanessa antiopa goes toward sunlit spots in

the woods. |

I observed, as early as the summer of 1911, that these

water-striders respond to moving objects and shadows

more promptly than they do to stationary ones. In the

early fall of 1918, I discovered that individuals of Gerris

remigis, confined in an aquarium, respond definitely and

in a pronounced manner to a moving incandescent electric

light and also to frequent changes in the position of such

a light. Essenberg (1915, p. 402) states that in Gerris

orba

The sense of sight: is keenly sybase the insects detecting a moving

object or a shadow very quickly.

The responses of Ranatra fusca to a moving light and

also to a light frequently changed as to position are well

known through the admirable work of Holmes (1905).

He (1907, pp. 160, 161) has also pointed out that the

young of Ranatra quadridentata respond to changes in

position of a light. Therefore, a brook with a current of

_ moderate velocity is more likely to be seen by the gerrids

than is still water. The riffles and small waves serve as

additional reflecting surfaces for diffuse daylight and sun-

light, which facts aid in making the position of the brook

still more noticeable to the water-striders.

2. Rôle Played by Moisture.—It is possible that mois-

ture from the brook diffusing through the atmosphere

may serve, to a certain extent, as a stimulus which may

produce a positive response when the water-striders are

in such close proximity to the stream as previously has

been indicated. However, I am much in doubt of such an

explanation. The plan to prevent the gerrids from seeing

No. 630] HABITAT RESPONSES OF WATER STRIDER 71

the water, or perhaps the reflections from it, and yet not to

obstruct the diffusion of moisture from the brook did not

produce results sufficiently definite from which to draw

conclusions. There is much doubt as to the role played by

moisture in influencing water-striders to move toward the

brook. ?

VII. Discussion or EXPERIMENTS aT SYRACUSE

1. Rôle of Vision—The experiments conducted near

the large pool in the brook at Syracuse added little infor-

mation to what has been stated concerning the work near

White Heath. I believe that vision was the main factor

in assisting the gerrids to reach the large pool of water.

There were no obstacles to obstruct the view of the ger-

rids, the surface of the ground being smooth and flat. The

water-striders facing toward the pool and also those

having the longitudinal axis of the body parallel with its

margin found the water very promptly and with consider-

able directness, again suggesting the probability that they

reached the pool according to the same principle involved

in the case of Vanessa antiopa in finding the areas of

bright sunlight. It must be recalled that the pool of

water was, comparatively, of large size and that reflec-

tions of light from its surface would be more readily seen

than from such a narrow brook as the one near White

Heath. It is true that, in the experiments in which the

gerrids faced away from the water, there was a little less

promptness in reaching the surface of the pool and also

Some random movements. However, in this series of ex-

periments, also, I believe that the sense of sight was the

chief factor involved in assisting the gerrids to reach the

Water. —

In the experiments when forty gerrids were used in

each trial, I believe that vision played the chiéf réle in

directing them to the water, at distances both of one yard

and of three yards. It is difficult to see what other factor

could have served as a stimulus in assisting the water-

_ Striders to reach the pool with such directness and prompt-

ness as was displayed.

72 THE AMERICAN NATURALIST [Vou. LIV

2. Rôle of Moisture.—During all of the experiments

performed at Syracuse, it is possible that moisture, evap-

orating from the pool and diffusing through the atmos-

phere, served as an additional stimulus in effecting a

positive response from the gerrids. Such a possibility is

more feasible in this connection than was true in the case

at White Heath, for the area of the water surface where

the experiments were carried on at Syracuse is very much

larger than the area of the water surface at the place in

the brook where the experiments were conducted at White

Heath.

VIII. Summary AND CONCLUSIONS

This paper treats of certain habitat responses of the

large water-strider, Gerris remigis Say. The work was

done partly near Urbana, Illinois, and partly near Syra-

cuse, New York. Observations were made of the re-

sponses of the water-striders trapped in stream pools,

during a period of severe drought, for the purpose of

discovering what became of them after the pools dried

up. These gerrids, being mainly apterous forms, were

unable to migrate by flight. Experiments, related to the

habitat responses, were performed for the purpose of

finding out whether water-striders were able to reach

their habitat, a brook of moderate size after having been

removed from it and placed on the ground certain dis-

tances away.

In the late summer, during a severe drought, with a

temperature from 90° to 100° F., water-striders, Gerris

remigis, frequently were found on stream pools, con-

nected by small riffles, at White Heath, near Urbana. As

food became scarce or when a scum formed on the surface

of some of the pools, the gerrids migrated, by way of the

riffles, to other pools that were free from scum. As the

drought progressed, the water-striders were congregated

on the few pools that remained. Often the scum, a bac-

terial growth, killed large numbers of the gerrids.

These stream pools were studied and the responses of

the water-striders were observed after the pools dried up.

No. 630] HABITAT RESPONSES OF WATER STRIDER T3

For an entire day particular attention was directed to one

small pool, dimensions 12 X 5 X 4 inches, which became

dry at that time. There were twenty gerrids on its sur-

face and they made no attempts to escape, as the pool

rapidly became reduced in size.

After the pool had become entirely dry, the water-

striders did not move away for a period of ten minutes.

The initial locomotor responses were due, primarily, to

the drying up of the water. This was the only change in

external conditions and there was no other evident stim-

ulus. Similarly, when gerrids were removed from

aquaria, where they had been kept in captivity, they be-

came very active when placed upon a solid surface away

from the water. This was true even if previously they

had been inactive. These water-striders moved with an

awkward stumbling gait on land, but they made fairly

rapid progress. Their methods of locomotion were by

walking and jumping. Not infrequently, when jumping,

the gerrids seemed to lose control of the orientation of

the body, and sometimes made a turn of 180 degrees.

The gerrids responded readily to contact stimuli, which

usually was evinced by them in coming to rest against

pieces of dry mud, driftwood, stones, and clumps of dead

leaves. They occasionally crawled underneath objects of

the character that have been mentioned. They did not re-

main there permanently, for even after carefully marking

the exact place, I never have been able to find them the fol-

lowing day. Shadé and a lower temperature, combined

with contact, probably were the factors which influenced

the water-striders to stay quietly in such places. They.

did not burrow into the mud, nor into the banks of the

brook for the purpose of estivating until the drought had

passed. So far as I was able to observe, the gerrids did

not xstivate.

Ten out of the twenty gerrids, or 50 per cent., reached

the nearest pool—dimensions 3 van. 2 yds: x 5 In

which was ten yards down the dry bed of the brook away

from the site of the former pool where the twenty water-

74 THE AMERICAN NATURALIST [Von. LIV

striders were entrapped. The first one to reach the pool

did so in 5 minutes and 30 seconds. Another gerrid re-

quired fifteen minutes to find the water. The last water-

strider to arrive at the pool completed the journey in

forty minutes. There was considerable variation as to

the time necessary to reach the pool on the part of the

others, the average being 14 minutes and 30 seconds.

The direction of locomotion, of the ten water-striders

that did not find the pool was mainly up the dry bed of

the brook. Four wandered so far upstream that there

was little probability of their reaching water. With ref-

erence to the six remaining gerrids, two of them jumped

into a large crack in the dry mud of the brook channel;

two crawled under some driftwood; one worked its way

into a clump of dead leaves; and one disappeared while I

was observing some other water-striders. The following

day I was unable to find any of these gerrids, although I

sought for them thoroughly, and had marked carefully

the various places where they were seen last on the previ-

ous evening.

There was considerable variation, by different indi-

vidual water-striders, as to the amount of time consumed

in traversing the distance between their former abode

and the large pool of water downstream. None of the

gerrids, that reached the pool, journeyed there along a

straight path. Those that were among the first to com-

plete the journey seemed to make the least number of

errors in direction. All of them made deviations from

the most direct route, and also evinced random move-.

ments. They found the pool of water through a blunder-

ing method of trial and error. The responses of the ger-

rids that moved downstream and found the water and

also of those that moved upstream and were not so suc-

cessful were, in the main, very similar, although the latter,

traveling a longer distance, made many more erratic `

movements. In general there appeared to be a lack of

definiteness in orientation with reference to the direction

of the pool and a lack of promptness in journeying to it.

No. 630] HABITAT RESPONSES OF WATER STRIDER "5

There appeared to be a tendency on the part of the

water-striders to keep moving along the path already

taken, unless some other stimulus diverted them. This

frequently occurred, and contact proved to be the com-

monest form of stimulus that brought about such diver-

sion. They wandered along a certain path until some

stimulus acted upon them. Then they changed their path

and tried another direction. There were times when it

was difficult to observe what was the stimulus causing the

change in direction. In fact on certain occasions there

appeared to be no new external stimulus, no change in the

external environment, and yet there occurred a change in

direction. Therefore the change in direction probably

was due to some disturbance of the physiological condi-.

tion of the animal brought about by some internal

stimulation.

Fifty per cent. of the total number of gerrids entrapped

on the surface of the stream pool were successful in

reaching water elsewhere. In this instance the water was

ten yards away from the site of the pool on which the

insects were trapped. So. large a number, I am con-

fident, is very unusual, for several other observations

of a similar character show that a very much smaller

percentage were able to find water after the pools on

which they were confined had become dry. In some

cases the water was at distances of less than ten yards,

while in other cases it was eleven, twelve, and fourteen

yards distant. I believe that large numbers of apterous

individuals dié during periods of long and severe

droughts. I have some evidence of this from out-of-door

observations. Further, I have found that water-striders,

frequently, soon die in the laboratory, when the water in

aquaria was permitted to evaporate to dryness. This

. ag "rela if the temperature was not higher than-

Experiments were carried on near Urbana for the pur-

pose of observing with what promptness and directness

water-striders, Gerris remigis, returned to their habitat

76 THE AMERICAN NATURALIST [Vou. LIV

after having been removed from it, and also for the pur-

pose of observing their responses while doing so. Twenty

water-striders were used at each trial. They were re-

moved quietly from the surface-film and then carefully

placed on the ground at distances of one, two, three, and

four yards away from the brook. In some experiments

the gerrids faced the water, in others they were parallel

with the current of the brook, and in still others they

faced away from the stream.

In all the experiments in which the gerrids faced the

brook, the majority of them regained the surface-film.

When they were placed on the ground one yard away

from the water, all those that reached the brook did so in

less than one minute. In no experiment were there more

than two gerrids that did not reach the water. When the

water-striders were taken two and three yards away from

the stream, they were back again on its surface within

2 minutes and 30 seconds. Those gerrids that were

placed on the ground four yards away from the brook dis-

played more random movements in reaching the water

than did those that were nearer to it and a slightly

smaller percentage succeeded in finding the brook. Those

that reached the water did so within four minutes. The

experiments with the gerrids parallel with the brook

showed that the majority of them reached the water at

distances from one to four yards inclusive. Some indi-

viduals required a little longer time to make the journey

than did those that faced the brook. Sometimes there

was a little delay before they began to jump toward the

water. Those that were taken four yards away from the

brook evinced more hesitancy and more random move-

ments than was the case with the gerrids placed on the

ground at points nearer the water. Experiments with the

water-striders facing away from the brook showed again

that the majority of the gerrids reached the water from —

all distances from one to four yards inclusive. There

were more random movements and less promptness on

the part of the water-striders in these experiments than

No. 630] HABITAT RESPONSES OF WATER STRIDER ‘17

in any of the previous ones. A slightly smaller percent-

age reached the water from a distance of four yards than

was the case in any of the other experiments.

Experiments were conducted in order to discover

whether vision, moisture, or both of these factors func-

tioned as stimuli in influencing the water-striders to find

the brook. A barrier was constructed to shut off the view

of the stream, but to be so arranged as still to. permit

moisture to pass through it. However, the barrier proved

to be defective in this respect. The water-striders were

a little less prompt in reaching the water when the barrier

was employed than was the case when it was not used.

The information that was obtained regarding the re-

sponses of the gerrids proved to be inconclusive. How-

ever, I am strongly of the opinion that vision is the impor-

tant factor in directing these hemipterons to find water.

Experiments, of a character similar to those that previ-

ously have been described, were undertaken near a small

rapid brook in the vicinity of Syracuse. Near the head-

waters was a large pool, its approximate dimensions

being 55 X 17 X 2 feet, formed by an artificial dam and

on its surface were thousands of gerrids. It was here

that the experiments were performed.

The gerrids used in the experiments were taken directly

from the surface-film of the pool. Different individuals

were employed in each experiment. In all the experi-

ments in which the responses of individuals were re-

corded, the distance from the pool to which the gerrids

were taken was one yard. Six experiments were grouped

together for convenience.

In the first, second, and third groups of experiments, the

water-striders were placed on the ground facing away

from the large pool. In the first group of experiments

the total time consumed by all the gerrids in reaching the

water was 12 minutes and 14 seconds. The average time

required to find the pool was 2 minutes and 24 seconds.

In Experiment VII, the gerrid had not yet reached the

water after ten minutes had elapsed. Omitting this ex-

78 THE AMERICAN NATURALIST [Vor. LIV

periment, the total time necessary for all the water-

striders to reach the pool was 2 minutes and 14 seconds,

and the average time consumed in finding the water was

264 seconds. In the second group of experiments the

total time used by the water-striders to reach the pool

was 3 minutes and 6 seconds. The average time required

to reach the water was thirty-one seconds. In the third

group of experiments the total amount of time that

elapsed before all the gerrids had reached the water was

17 minutes and 55 seconds. The average time necessary

for individuals to find the pool was 2 minutes and 30

seconds. The gerrid used in Experiment XXVI did not

reach the pool and it was observed for 15 minutes and

25 seconds. If this experiment is omitted the total

amount of time for all the water-striders to reach the

pool was found to be 2 minutes and 30 seconds, while the

average time required for the gerrids to find the water

was thirty seconds. The results of these experiments

are typical of many others. A large majority of the

gerrids were successful in reaching the water, only two

individuals out of eighteen failing to do so. There were

a number of random and trial movements, but in the main,

the gerrids returned to the surface-film with consider-

able promptness.

In the fourth, fifth, and sixth groups of experiments, the

initial position of the gerrids was facing the water. With

respect to the fourth group of experiments, all the water-

striders consumed a total amount of time of 2 minutes

and 40 seconds in reaching the surface-film. The average

time necessary to return to the water was 26% seconds.

The gerrid used in Experiment XXXIV consumed ninety

seconds of time before it succeeded in finding the pool.

Omitting this experiment the total amount of time re-

quired by all the water-striders to return to the brook

was 1 minute and 10 seconds, while the average time

neecssary to reach the water was fourteen seconds. In

the fifth group of experiments, the total amount of time

required by all the gerrids to find the pool was 1 minute

No. 630] HABITAT RESPONSES OF WATER STRIDER 19

and 52 seconds, and the average time consumed was 183

seconds. In considering the sixth group of experiments,

it was found that 1 minute and 24 seconds elapsed before

all the gerrids were back on the surface-film and that the

average time necessary to reach the water was fourteen

seconds. The results of these experiments are, in the

main, very similar to many others not recorded here. Out

of a total of eighteen gerrids not one failed to get back

to the water. The water-strider used in Experiment

XXXIV was the only one that took an unusual amount of

time to reach the pool. On the average, the gerrids used

in the second three groups of experiments required, ap-

proximately, only about one half the amount of time

that was required by the water-striders in the first three

groups of experiments in order to reach the pool of

water. The gerrids in the second three groups of ex-

periments made fewer mistakes and a less number of

random movements in finding the water than was the

case in the first three groups of experiments.

Just a brief statement will be made with reference to a

Series of experiments in which the bodies of the gerrids

were placed parallel to the shore of the pool. In other

respects the experiments were similar to the groups of

experiments, one to six inclusive, the results of which

already have been recorded. In general, the results were

very much like those obtained in the second group of ex-

periments, with the exception that a little more time was

required by the gerrids in reaching the water. There was

not quite so much promptness, on the part of the water-

striders, in moving toward the pool. They evinced a few

more trial directions before arriving at the water and

occasionally a gerrid did not succeed in reaching the pool. —

A series of experiments was carried out in which the

gerrids were not oriented, specifically, with reference to

the pool of water. The individual responses were not

considered in these experiments, as the water-striders

were used in large numbers, but records were made of the

number of gerrids that reached the pool and records also

80 THE AMERICAN NATURALIST [Vou. LIV

were made of the length of time that was necessary to

find the water. Forty gerrids were employed in each of

the experiments, which well might be considered as mass

experiments. They were placed on the ground one yard

away from the water in a number of the experiments, and

in the case of the other experiments, the water-striders

were placed on the ground three yards away from the pool.

The results of the different experiments one yard away

from the water were very similar in many instances.

Therefore the data will be given of only one experiment.

A great majority of the gerrids were back on the surface

of the pool within fifteen seconds from the time they were

placed on the ground. In thirty-five seconds all but two

individuals had reached the water, and in one minute of

time all the gerrids were striding back and forth on the

surface-film. The water-striders jumped toward the pool

with considerable promptness. They made comparatively

few errors in direction and few random movements.

Sometimes there was a gerrid that did not reach the pool.

In the experiments three yards distant from the pool

of water, a great majority of the gerrids were back on the

surface-film within forty seconds after they were placed

on the ground. In the majority of these experiments, all

the water-striders had returned to the water within 2

minutes and 5 seconds. A very few gerrids were not suc-

cessful in reaching the water. A fair degree of prompt-

ness and directness were evinced by the water-striders

in Jumping toward the pool. There were, perhaps, more

errors made in direction of movement than was the case

with the gerrids in the experiments one yard away from

the water.

In all these experiments conducted at the brook near

Syracuse, it seemed probable that the sense of sight was

the most important factor in directing the gerrids to the

water, although moisture also may have exerted an influ-

ence on their responses. :

No. 630] HABITAT RESPONSES OF WATER STRIDER 81

IX. ACKNOWLEDGMENTS

It is a pleasure to make certain acknowledgments to

various persons who have rendered assistance to me in a

number of different ways, while I was obtaining the in-

formation necessary for the preparation of this paper.

Dr. Charles. ©. Adams, professor of forest zoology in

The New York State College of Forestry at Syracuse

University, first directed my attention to the family

- Gerride as a suitable group for behavior and ecological

study. Some of the information recorded in this paper is

the result of certain work carried on under his general

supervision. If there are errors in the paper he is in no

Sense responsible for them. I have had free access to

his private library, and he has given me many useful

suggestions.

The late Mr. Charles A. Hart, systematic entomologist |

of the Illinois State Laboratory of Natural History at

the University of Illinois, identified many water-striders

for me. He gave me the opportunity to study the water-

strider collection of the State Laboratory of Natural His-

tory, and he also aided me in a number of other ways.

Dr. J. W. Folsom, of the Department of Entomology

at the University of Illinois, kindly loaned to me the

drawing of the water-strider which was reproduced as

Fig. 1 .

iw. I.

Mr. ©. A. Lloyde, photographer, of Champaign, Illi-

nois, rendered valuable aid in the taking of photographs

in the field, as did Mr. A. G. Whitney, of Syracuse, New

York.

Certain sums of money and a university fellowship, to

which I was twice appointed, were placed at my disposal

by the Graduate School of the University of Illinois.

These were of decided assistance in the prosecution of

investigations which made possible the preparation of

this paper. In this connection, recognition is due to Dr.

David Kinley, dean of the Graduate School and to Dr.

H. B. Ward, professor of zoology.

82 THE AMERICAN NATURALIST [Vou. LIV

BIBLIOGRAPHY

Abbott, C. H.

1918. Reactions of Land Isopods to Light. Jour. Exper. Zool., Vol.

XXVII, pp. 193-246.

Adams, C. C.

1915. An Ecological Study of Prairie and Forest Invertebrates. Bull.

Ill. State Lab. Nat. Hist., Vol. XI, Article II, pp. 33-279.

Bohn, G.

1903. De l’évolution des connaissances chez les animaux marins lit-

toraux. Bull. Institut Gen. Psychol., No. 6, pp. 1-67.

Cole, J. L.

1907. An Experimental Study of the Image-Forming Powers of Various

Sop = Eyes. Proc. Amer. Acad, Arts and Sci., Vol, XLII,

Comstock, J. B pi Comstock, A. B.

1895. A Mannal for the Study of Insects. (Ithaca, New York: Com-

stock Publishing Co.) Pp. x+ 701.

Drzewina, A.

1908. De l’hydrotropisme chez les Crabes. Compt. rend. Soc. Biol.,

T; V, pp. 1009-1011

Essenberg, C.

1915. The Habits of the Water-Strider, Gerris Remigis. Jour. Animal

Behavior, Vol. V, pp. 305-349.

Holmes, S., J.

1905. The pig of Random Movements as a Factor in Phototaxis.

j our. Comp. Neurol. and Psychol., Vol. XV, pp. 98-112.

/ 1905a. The aan of Ranatra to Light. Jour. Comp. Neurol. and

1907. Observations on the Yok ung of Ranatra Quadridentata Stal.

Biol. Bull., Vol. XII, pp. 158-164.

1916. Studies in Animal Behavior. (Boston: Richard G. Badger.)

4 + 266.

Jennings, H. -

: 1906. Piri of the Lower Organisme. (New York: Columbia Uni-

versity Press ss.) Pp. xiv + 366. '

Kellogg, V. L.

1908, American Insects. (2d ed., revised; New York: Henry Holt

and Co.) Pp. ee

- Kirkaldy, G: W.

1899. A Guide to N Study of British Waterbugs (Aquatic Rhyn-

chota). Entomologist, Vol. XXXII, pp. 108-115.

McCook, H. C. i

1907. Nature’s Craftsmen. (New York and London: Harper and

Bros.) Pp. xii+ 317

Parker, G. H.

1903. j Phototropism of the Mourning-Cloak Butterfly, Vanessa

Antiopa Linn. Mark Anniv. Vol., pp. 455-469 (separate).

No. 630] HABITAT RESPONSES OF WATER STRIDER 88

Shelford, V. E.

1913. The Reactions on Certain Animals to Gradients of Evaporating

` A Study in TT Ecology. Biol. Bull.,

Vol. XX, x a 79-120.

de . i Bueno, J.

The Cae oe the Atlantic States (Subfamily vrig

Trans. Amer. Entom. Soc., Vol

1917. sane -history and Habits of the Larger pdt Gerris

migis Say (Hem.). Entom. News, Vol. XXVIII, pp. 201-

Tower, W. L.

1906. An Investigation of Evolution in Chrysomelid Beetles of the

Genus Leptinotarsa. (Washington, D. C.: Carnegie Institu-

tion of Washington.) Pub. 14, pp. x + 320.

Uhler, P. R.

1888. nies! V,—Hemiptera. The Riverside Natural a (Cam-

bridge: The Riverside Press.) Vol. II, pp.

Weiss, H. B.

1914. Notes on the Positive Hydrotropism of Gerris Marginatus Say .

and Dineutes Assimilis Anbe. Canadian Entomologist, Vol.

XLVI, pp. 33-34.

SHORTER ARTICLES AND DISCUSSION

SEX-CORRELATED COLORATION IN CHITON

TUBERCULATUS!

1. Among mollusks the occurrence of clear-cut differential

characters associated with sex is rare. Differences of size in the

sexes of dicecious species are known, though in some instances

the larger size of the female is a consequence of protandric her-

maphroditism; there are also certain records of slight, and pos-

sibly inconstant, sex-differences in shell form; the hectocotylus

of dibranchiate cephalopods, however, is almost the only well-

defined instance of a ‘‘secondary sexual character’’ in mollusks

—and this is an accessory organ of copulation. Color differences

of this nature seem not to have been observed. Some importance:

may therefore be attached to the description of a pronounced

color difference, correlated with sex, which has been found in

the commonest placophoran at Bermuda, Chiton tuberculatus

Linné, particularly since this differential coloration seems

capable of interesting interpretation in several directions of

theoretic importance.

2. In adult chitons of this species there is noticeable what ap-

pears at first sight to be a considerable diversity in the degree

to which pigment, of a salmon-pink hue, is developed upon the

foot and other soft parts exposed in ventral view. Somewhat

less than half of the individuals have the foot, ctenidia, and

other soft parts of a pale buff color; in the remainder, the foot,

head, ctenidia and mantle are to various degrees tinged with

salmon-pink or orange-red pigment, the color being in some

eases startlingly vivid. This difference is most pronounced dur-

ing late spring, but persists to some extent throughout the year.

The pigmentation is not correlated in any way with size; indi-

viduals of any length from 3.4 to 9.2 em. may be either pale buff

or salmon-pink on the ventral surface; nor does the intensity of

reddish pigmentation, when present, depend upon size. In

dorsal view it is quite impossible to distinguish the two groups

of animals, unless the plates be artificially separated to an ex-

treme degree, and not even then with any certainty.

The differential coloration proves to be correlated with sex,

1 Contributions from the Bermuda Biological Station for Research, No. 109.

No. 630] SHORTER ARTICLES AND DISCUSSION 85

in the sense that the soft parts of male chitons are never colored

pink; whereas those of maturing females invariably are, the

intensity of the pigmentation depending to a large extent upon

the state of maturity of the ovary, to a lesser extent, it seems

probable, upon the quantity and the kind of the algal food avail-

able in differing environments. .

I have been at some pains to verify this conclusion by numer-

ous dissections and by microscopic examination of smears from

the gonad of 129 individuals. As in most chitons, the nature of

the single median gonad is readily distinguishable, when mature

or nearly so, owing to the fact that ovary and testis are differ-

ently colored. In the case of the young C. tuberculatus, and of

the immature gonad in animals of all sizes, testis and ovary are

macroscopically undistinguishable, being pigmented in the same

degree by a brick-red substance, which will be referred to in

what follows. These observations were made for the most part dur-

ing the week ending March 30, 1918, at which time motile sperms

and well-developed (but not mature) eggs were present. The

ripe testis differs in color from the ovary because the amount of

red pigment in the stroma of the male gonad does not increase

after a very early stage; so that the testis comes to appear as a

milk-white organ with innumerable interlacing threads of dull

crimson upon its surface. In the ovary, on the contrary, the

amount of this red substance increases enormously. No trace of a

gonad was detected in 72 animals less than 3.4 cm. total length,”

the smallest female being 3.4 cm., the smallest male 3.4 em. also.

A group of 67 individuals between 3.4 and 9.2 em. length, col-

lected at random, was examined by first carefully noting the

coloration of the tissues (foot, ete.), then investigating the con-

dition of the gonad. Among these 67, 27 were males containing

active sperm; the foot, ctenidia, and other parts were in every

_ ease pale buff in color. The remaining 40 were clearly separable

from the others by the presence of pink or orange pigment, and

were without exception females. A further group of 64 chitons

was first divided into two lots, ‘‘pale’’ and ‘‘pink,”’ respectively ;

smears and teased preparations of the gonads showed that in

only two instances was the expectation based upon the group

first studied defeated, and in these instances the animals were

small females with very immature ovaries. Summarizing the

2 An investigation of the adult life-history of C. tuberculatus, to be de-

seribed in detail elsewhere, shows that chitons of this size are at least two

years old

86 THE AMERICAN NATURALIST [Vou. LIV

results from both groups, it was found that the 131 individuals

with recognizable ovary or testis comprised 76 females and 55

males,’ the females, when mature, being distinguishable exter-

nally by the development of a salmon-pink or orange-red colora-

tion of the soft parts (foot, head, ctenidia, mantle) .*

3. The color difference between the sexes of Chiton is believed

- to be of special significance, for the following reasons: because

the coloration of the soft parts of the female is directly traceable

to metabolic activities associated with the growth of the ovary;

and because it provides an example of secondary sexual colora-

tion which has no conceivable utility, but is, on the contrary, so

far as color is concerned, of a thoroughly accidental nature.

Concerning the first point: the data previously summarized

show the definite manner in which reddish pigmentation is cor-

related with sex; there are also the facts, (1) that in animals

less than 3.4 em. length there is no trace of any pink body pig-

mentation, (2) that the intensity of such pigmentation agrees

with the state of development of the ovary, (3) that the blood

of female chitons is mahogany-red or deep orange in color (that

of males being dull yellow), and (4) that the reddish hue of

blood, external tissues, and ovary is demonstrably due to the

same pigment substance.

This pigment shows by its chemical behavior that it belongs

to the group of carotin-like ‘‘lipochromes,’’ and is unrelated to

the hemoglobin which colors the buccal musculature of both

sexes. It has also an absorption spectrum—one band in the

blue-green, another in the violet—of a kind supposed to be

characteristic of the ‘‘lipochromes.’’ The pigment is not soluble

in water, but is dissolved by either 95 per cent. alcohol, acetone,

xylol, or chloroform, and by the last named is extracted from

alcohol after treatment with alkalies; it is quickly decolorized

by standing in contact with air, in the light, and is bleached

(after passing through a deep blue condition) to lemon yellow

by strong nitric acid. Concentrated solutions are orange-red,

3 These figures give a sex ratio of males: females:: 1: 1.38; this is prob-

ably too high a proportion of females for the whole population, but there

seems undoubtedly to be, in some places, a preponderance of females. The

matter is worthy of further attention, in relation to the breeding habits of

Chiton.

4 For certain purposes in which eggs are required to be uncontaminated

with sperm, the external sex-difference in Chiton is a vaiuable aid in experi-

mental work; not only are the eggs abundant, of fair size, and easily ob-

tained, but males may be entirely excluded from the laboratory.

No. 630] SHORTER ARTICLES AND DISCUSSION 87

dilute solutions yellow. The lipochrome is present in the ccelomiec

fluids of the male Chiton, though in very small amount, and, as

previously stated, is present in the stroma of the testis. In the

female Chiton large quantities are present, in ‘‘solution,’’ in the

blood and cœlomic fluid, and in the ovary it is clearly associated

with the great quantity of fat globules there present; not all of

the fat globules are stained with the red pigment, multitudes of

the smaller ones being uncolored by it.

It seems clear that we have here another case where the de-

veloping ovary is associated with ‘‘fat metabolism’’; the red

lipochrome, accompanying a large volume of fatty materials, is

prominently concerned (perhaps by reason of its easy oxida-

tion) in the growth of the ovary, and both pigment and fat are

vastly important for the formation of sperms. The occurrence

of the ovarian pigment in much higher concentration in the

blood and juices of maturing females is‘comparable to the con-

dition found by Steche® in certain moths, whereof the blood of

the female was chemically differentiated in an obvious way from

that of the male.

That the pigment is concerned in the metabolism of the ovary

is shown by the fact that as the ovary becomes mature, but be-

fore it is fully so (i. e., early in May), it becomes of a deep green

color with imbedded streaks of maroon-red. In surface view the

ovary is then green, like that of most chitons, but the salmon or

deep orange coloration of the foot, muscle, blood, ete., does not

change. Hence, if these animals were to be examined in summer,

with the ovary nearly or quite mature, the causal connection

between ovarian pigmentation and body pigmentation would

hardly suggest itself immediately. It is easily shown, by ex-

tracting the pigment in acetone, that the green hue must be due

to a relatively simple modification of the original red substance.

Such extracts are orange-yellow, are decolorized by HNO,, i

give a green flocculent precipitate with alkalies. The ovarian

eggs themselves, at first colorless, are found by the middle of

May to have assumed a faint pink tinge, whereas toward the end

of June they become deep green.

4. Regarding the accidental character of the reddish color in

the tissues of adult female chitons, it is sufficient to point out

that the foot, where this character is most conspicuous, remains

throughout life firmly adherent to the substratum ; the gills also

5I quote at second hand, from Doncaster, 1914, ‘‘ The Determination of

Sex,’’ p. 101.

88 THE AMERICAN NATURALIST [Vou. LIV

are brightly pigmented, but the girdle of the chiton is never

raised more than a few millimeters from the surface upon which

the animal may be resting, and while above water, in the inter-

tidal zone, even this minute elevation occurs only along a short

length of the mantle at a time. If it be answered that these

chitons frequently creep over one another, it should be remem-

bered that in the Placophora there are no tentacular eyes upon

the head, and in the genus Chiton no extra pigmental megesthete

eyes upon the valves; so there is, after all, no opportunity for

sex-recognition through color (a fantastic idea, for other rea-

sons also). That the coloration of the soft parts is ever visible

to other animals seems equally improbable. Certain small isopods

(Spheroma) commonly frequent the mantle ‘‘chamber’’ of

Chiton tuberculatus, but they are found indifferently in the com-

pany of either sex. It is necessary to conclude that, so far as

color is concerned, the pink or orange hue of the body of the

female Chiton tuberculatus is of no ethological significance; the

nature of the pigment, its association with the growing ovary,

its progressive changes in the ovary itself, and its presence in

the blood, make of this case a most excellent illustration of the

‘‘metabolic-accident’’ conception of certain types of animal

coloration.

W. J. Crozier

DYER ISLAND,

BERMUDA

ON THE ALKALINITY OF THE SEA WATER IN

LAGOONS AT BERMUDA?

THE present land-form of Bermuda; resembling in certain

respects the configuration of many ‘‘coral’’ islands, was em-

ployed by Heilprin? as an example of atoll formation through

basic subsidence. The southeastern segment of the proto-Ber-

muda land mass, now the only area above water, in addition

exhibits three distinct ‘‘sounds,’’ or lagoons: Great Sound,

Harrington Sound, Castle Harbor. These lagoons Heilprin also

conceived to have originated through local subsidences. Fewkes?

had earlier considered the origin of these lagoons, stating his

belief that they, as well as the form of the islands as a whole,

1 Contributions from the Bermuda Station for Research, No. 114.

2 Heilprin, A., 1889, ‘‘The Bermuda Islands,’’ Philadelphia, [vi] + 231

pp, 17 pl.

3 Fewkes, J. W., 1888, Proc. Bost. Soc. Nat. Hist., Vol. 23, pp. 518-522.

No. 630] SHORTER ARTICLES AND DISCUSSION 89

were due to the erosive inroads of the sea. The collapse of

eaves and the general scouring action of tidal and other eur-

rents, as subsequently emphasized by Agassiz,* rather than very

local basal subsidences, were thus regarded as the forces respon-

sible for the lagoons.

So far as the general question of ‘‘coral’’ islands is con-

cerned, it is sufficient to note that, strictly speaking, Bermuda

is not, of course, a ‘‘coral’’ island at all, nor is its form that

characteristic of the islands commonly so termed.® The problem,

however, of this erosive action of the sea, its nature, and its réle

in the determination of land form in the case of a limestone

island, is insistently presented by the enclosed lagoons to which

I have referred. Murray’s idea of the solvent action of natural

waters in relation to the hollowing-out of lagoons and to the

building of barrier reefs has lately been attacked from several

aspects. Thus Mayer® has pointed out that at Tutuila (Samoa)

and at Oahu, the surface waters draining into the sea are prob-

ably too alkaline, and contain too much calcium derived from

the land, to be effective in dissolving the shoreward parts of the

coral reef-flat. In the case of lagoons, a great number of in-

fluences are at work to control the erosion of the rock and the

deposition and removal of silt.” The measurement of the al-

kalinity of the lagoon water provides but one of the factors

requisite for analysis of the thoroughly heterogeneous equilibrium

between the water and the limestone. Such determinations are

nevertheless valuable, and during a recent residence at the Ber-

muda Biological Station I had the opportunity of carrying out

estimations of this kind over a period of many months. At-

tention was chiefly given to the alkalinity of the semi-enclosed

waters as compared with that of the open ocean. The determi-

nations were made colorimetrically, by means of thymolsulpho-

nephthalein with borate standards,’ and phenolphthalein. The

alkaline reserve was not estimated

4 Agassiz, A., 1895, Bull. M. C. Z., Harvard Coll., Vol. 26, pp. 205-281,

0 pl.

5 Howe, M. A., 1912, Science, N. S., Vol. 35, pp. 837-842. Pirsson, L. V.,

1914, Amer. Jour. Sci., Ser. IV, Vol. 38, pp. 189-2

€ Mayer, A. G., 1917, Proc. Nat. Acad. Sci., Vol. 3, pp. 522-526

T Crozier, W. J., 1918, Jour. Exp. Zoöl., Vol. 26, pp. 379-389. Mayer, A.

G., 1918, Year Rook, Carnegie Instn. Wash., for 1917, pp. 186.

s A poaait for this work was obtained by a grant from the C. M. Warren

Fund of the American Academy of Arts and Sciences

® McClendon, J. F., Gault, ©. C., and Mulholland, S., 1917, Publ. No. 251

Carnegie Instn. Wash. . pp. 21-69.

90 - THE AMERICAN NATURALIST [Vou. LIV

Some distinct indications were had of a seasonal variation in

p, of the enclosed waters, but tidal and other diurnal complica-

tions in the lagoons would make it necessary to institute a long

series of studies for the complete description of this phenom-

enon.!° The general fact was quite apparent that the ‘‘inside

water (i. e., water within the sounds) was less alkaline than the

‘outside’ water over the reef flats, the latter likewise less alka-

line than the open ocean. Eight sets of estimations gave the

Pa of water taken at flood tide just beyond the outermost reefs to

the west and northwestward of Bermuda, as 8.25 (21°-23°), at a

salinity of 36.4 + per mille, agreeing with that found by other

observers for Atlantic water in this general region. The p" of

the ‘‘outside’’ water was at different times observed to lie between

8.09 and 8.23. Within the sounds, however, the range noted was

from 7.95 + to 8.15. The case of Harrington Sound, an almost

completely enclosed body of water, is the most interesting. The

waters of this lagoon are in communication with the outside sea

through but one surface channel, a narrow cut at Flatt’s Inlet;

there is also a smal] amount of subterranean communication.

Several specific examples will make clear the differences found.

he figures refer to samples taken with a tube of pyrex glass

from a depth of 2-3 feet below the surface. Samples obtained

from depths of several fathoms ran in about the same way.

Sept. 13th, 1917.

Great Sound, 9:40 A.M. Tide ebbing, Water temp. 26.9°; air 27.5° py 8.20

North shore, 9:55 A.M. Tide ebbing, Water temp. 26.8°; air 27.8° py 8.22

Harrington Sd., 10:55 A.M. Te ebbing, ‘Water temp. 27.4°; air 27.8°

Nov. peer 1917.

Great Sound, 9:05 A.M. Tide low, Water af 19.8°; air 24.0° px 8.08

North shore, 9:40 A.M. Tide low, px 8.20

Harrington Sd., 10:45 A.M. ‘Tide low, pu 7.95

Such results obviously speak for the view that the solution

of limestone by the sea within such lagoons as Harrington

Sound must be reckoned with. Exactly how important a part

it plays in the final adjustment of the land form can not, of

course, be said. The color of the sea water, I might note, varies

in correlation with the p". Within the sounds, color-readings

on the Forel scale" averaged 5.5 (17 per cent. yellow), whereas

10 Cf. Moore, B., Prideaux, E. B. R., and Herdman, G. A., 1915, Trans.

Liverp. Biol. Soc., Vol. 29, p. 233. McClendon, J. F., 1918, Publ. No. 252,

Carnegie Instn. Wash., pp. 21

11 Steuer, A., 1910, Plasktonkunde, xv + 723 pp., 1 Taf. und 365 Abb.,

Leipzig. [Pp. 84-98.]

No. 630] SHORTER ARTICLES AND DISCUSSION 91

out over the reefs to the northward the color index was 3.9

(8.6 per cent. yellow), that of the ocean beyond the reefs about

3.5 (7 per cent. yellow).

W. J. CROZIER

PHYSIOLOGICAL LABORATORY, ;

OLLEGE OF MEDICINE,

UNIVERSITY OF ILLINOIS.

June, 1919

A SIMPLE METHOD OF MEASURING THE RATE OF

RESPIRATION OF SMALL ORGANISMS

In view of the widespread interest at the present time in the

subject of respiration in the lower organisms, it is thought that

the following simple method of measuring the rate of carbon

dioxide production in small non-aquatic animals and plants

may be found useful not only by teachers who desire a quantita-

tive method suitable for class instruction but also by investiga-

tors who wish, without any material sacrifice in accuracy, con-

siderably to simplify the various procedures at present followed

in making determinations of small amount of CO,. The appa-

ratus required may readily be constructed by anyone in a few

minutes out of materials easily obtainable, and with it, it is

possible to measure, with a probable error well within the normal

uncontrollable range of variation of the material likely to be

studied, a few thousandths of a milligram of carbon dioxide—

an amount equal to that given out at ordinary temperatures by

a sprouting grain of wheat in perhaps three or four minutes and

by a house-fly in one or two minutes. It would be relatively

easy still further to increase the delicacy of the method, though

the gain in sensitiveness would be at the expense of the simplicity

which in its present form is its chief recommendation.

The method is based upon the well known indicator methods of

Haas! and of Osterhout,? but unlike the first, it is applicable to

small non-aquatic organisms, and unlike the second, it involves

the use of apparatus so simple in construction that it can be

duplicated any desired number of times and can therefore be

used even by large classes of elementary students. Furthermore,

provision is made not only for the comparison of relative rates

of carbon dioxide production but also for the measurement of

absolute amounts. Simplicity is secured by taking advantage of

1 Haas, A. R., Science, 1916, XLIV, 105.

2 Osterhout, W. J. V., J. Gen. Physiology, 1918, I, 17.

92 THE AMERICAN NATURALIST [Vou. LIV

two well-known facts: (1) that the carbon dioxide content of

out-of-door air varies only slightly from day to day, and scarcely

at all during the course of an ordinary series of experiments and

(2) that the distribution of a quantity of carbon dioxide between

given amounts of water and air may readily be calculated from

the known absorption coefficients for this gas at various tem-

peratures, which may be obtained from the Landolt-Bérnstem

Tabellen or elsewhere. ‘The first fact obviates.the necessity of

removing all of the carbon dioxide from the apparatus at the

beginning of the experiment and the second makes it possible,

with a minimum of trouble, to prepare standards for comparison

which contain any desired amount of carbon dioxide, thus enab-

ling measurements of quantity as well as of rate of production

to be made.

The apparatus in its simplest form consists of a Nonsol test

tube about 75 mm. by 10 mm., which has been drawn out in the

Bunsen flame somewhat above its middle into a constriction ap-

proximately 30 mm. long and 4 mm. in diameter. It is closed

with a well-rolled cork which has been thoroughly soaked in,

and coated with, acid free paraffin. The indicator solution is

placed in the lower portion of the tube; the constriction prevents

it, when the tube is agitated, from splashing on the organism con-

tained in the upper portion. To enable quantitative measure-

ments to be made, a series of standard tubes is required in which

known amounts of carbon dioxide have been added to the same

indicator solution as that used in the apparatus just described.

For the preparation of these standards the following device is

employed. A Pyrex or Nonsol flask with a capacity of about 150

c.c. is fitted with a well rolled cork through which a hole is bored

and one of the unaltered Nonsol test tubes forced in such a way

that when the cork is in the flask the bottom end of the tube pro-

jects freely upwards and its lip fits against the small end of the

cork. After being thus prepared, the sides and the lower sur-

face of the cork are thoroughly coated with paraffin of the best

quality, partly to prevent leaks but chiefly to protect the indica-

tor solution from actual contact with the cork, which would be

very likely to cause changes in its color. It is desirable, though

not absolutely necessary, to have as many of the flasks with the

prepared stoppers as the number of standards to be employed—

usually three to five. The only additional pieces of apparatus

required are a carbon dioxide generator, a box for comparing the

colors of the indicator tubes such as is commonly used in colori-

No. 630] SHORTER ARTICLES AND DISCUSSION 93

metric methods of determining hydrogen ion concentration (a

convenient form is supplied by the Hynson, Westcott and Dunn-

ing Co. of Baltimore, but it is easy to improvise one out of mate-

rials in hand in any laboratory) a fine-pointed pipette, a medium-

sized test tube, a large flask, and a few pieces of glass tubing.

For the pipette, tubing, ete., Pyrex or Nonsol glass should pre-

ferably be used; if ordinary glass be employed it should be

coated with paraffin where it comes in contact with the solutions.

The first step in making a determination is the preparation of

an indicator solution which is in exact equilibrium with the out-

of-door air. This may conveniently be done as follows: A two-

liter flask is filled with tap water, taken to an open window or

out of doors and all of the water except about 100 c.e. is slowly

poured out, great care being taken that neither the breath of the

operator nor any currents of air from the laboratory come near

it at this time. Enough of a concentrated solution of the indica-

tor (phenolsulphonephthalein) is added to give a color of the

proper intensity, the flask is stoppered and vigorously shaken for

several minutes. If the tap water is not nearly in equilibrium

with the carbon dioxide of the air, as shown by any decided

change in color on shaking, the solution should be poured into a

second flask from which water previously brought more nearly

into equilibrium with the air has been emptied, and shaken for

several minutes more. The solution, when in equilibrium with

air at 16° C. (where the absorbtion coefficient is approximately

equal to unity), and at a pressure of 760 mm. of mercury, con-

tains approximately 0.3 c.c. of CO, per liter, or 0.0006 mg. per

c.c. The exact amount need not be determined, however, since

it is a constant quantity in all of the tubes used, and it is the

amount added to it which is significant. To secure the benefit

of the most sensitive part of the range of the indicator, the solu-

tion thus prepared should have a p H of approximately 7.6 to

7.8, i.e., it should have a decided pink color with very little trace

of orange. If the tap water is not alkaline enough to produce

this result, a few drops of very weak NaOH may be added before

the final shaking. If the tap water is too alkaline, it may be

diluted with distilled water. The use of tap water rather than a

weak solution of NaOH in distilled water is recommended merely

for the sake of convenience and economy in those cases where it

is suitable.

The next step is the preparation of the comparison tubes in

which the indicator solutions, instead of being allowed to remain

94 THE AMERICAN NATURALIST [Von. LIV

in equilibrium with ordinary air and therefore to contain at

16° C. 0.0006 mg. of CO, per c.c., has received additions in the

various tubes of known amounts of this gas. This is accom-

plished as follows: A current of pure CO, from the generator is

allowed to pass through a few c.c. of distilled water in the

medium sized test tube until the water is saturated at atmos-

pheric pressure. It is convenient to use in the test tube a stop-

per with two openings, one for the inlet tube which carries the

gas below the surface of the water and the other for an open

glass tube projecting from the upper part of the tube through

the cork and several inches into the air. This permits the excess

gas to escape, and since CO, is heavier than air, the test tube

soon becomes filled with a pure atmosphere of it, the outside air

not readily entering through the long and narrow escape tube.

It is necessary that the current of CO, shall be slow enough to

give no more than atmospheric pressure in the test tube. If only

a few c.c. of water at a time are charged, the added pressure of

2 or 3 em. of water, due to the dipping of the inlet tube below

its surface, is not significant. The minimum time required to

saturate the water has not been determined, but it is the custom

of the writer when fresh water is taken to allow the current to

flow for at least thirty minutes; afterwards, by keeping the tube

corked between experiments, the water remains almost saturated

and exact equilibrium may easily be established in five or ten

minutes. It is, of course, very important that neither the test

tube nor the tube admitting the CO, shall give off appreciable

amounts of alkali, hence the recommendation that Pyrex or

Nonsol glass be used or the same result be secured with inferior

glass by means of a thin coating of paraffin.

Having a solution whose CO, content can accurately be calcu-

lated if the temperature and the barometric pressure are known,

the next step is to add measured amounts of it to successive por-

tions of the indicator solution. This is done as follows. The

first flask and the test tube in its stopper are filled with distilled

water, which by shaking has been brought into equilibrium with

out-of-door air, and emptied with the precautions already noted.

Five c.c. of the prepared indicator solution are then added, the

cork quickly inserted and the whole vigorously shaken. The

color of the solution should not change if the proper precau-

tions have been taken. The remaining flasks are then treated in

the same way. By inverting them, the color of the indicator

solution in their respective test tubes can be compared against a

No. 630] SHORTER ARTICLES AND DISCUSSION 95

white background. It should be the same in all. The first flask

is kept as a control, nothing being added. It is inverted, and

the cork with its test tube containing the indicator solution re-

moved and quickly stoppered with a paraffined cork. To the

second flask one drop of the carbon dioxide saturated water is

added, to the second two drops, to the third four, or any desired

number, ete. The stopper in each case is quickly replaced and

the whole apparatus shaken vigorously until the CO, has dis-

tributed itself between the solution and the air. The test tubes

are then removed and corked as described above. The amount

of CO, added to each c.c. of the solution may now readily be cal-

culated by taking into account the absorbtion coefficient for the

temperature in question and the relative amounts of water and

air. The volume of a single drop of the added solution has, of

course, previously been determined by counting the number of

drops required to give a volume of, for example, 5 c.c. In add-

ing the CO, it is convenient to use a fine-pointed pipette which

can be inserted in the escape tube of the test tube in which the

water has been charged. This makes it unnecessary to remove

the stopper of the latter or otherwise to disturb it. Unless the

pipette is first filled with CO, (which may, however, readily be

done and which is to be recommended), a little of the gas will

escape from the free surface of the liquid within the pipette. If

only a few drops are used from the lower portion of the pipette,

however, no error will result if one works quickly enough. To

drop the solution into the flasks without allowing any appreciable

amounts of CO, to escape into the air requires a little practice,

but after a few trials the best method is discovered and the nec-

essary skill acquired.

When the standards have been prepared, which requires only

a few minutes at the most, everything is ready for an actual

measurement. The procedure is as follows. After filling the

prepared test tube with out-of-door air, 1 e.c. of the indicator

solution is placed in its lower portion and the organism to be

studied in its upper portion, either free or attached to the cork

by a loop of thread. The tube is closed and agitated gently,

either continuously or at intervals, to mix the air and the indi-

cator solution thoroughly. It is neither desirable nor necessary

to shake the tube vigorously ; with a little practise it will be dis-

covered that a very slight movement of the proper sort will keep

the liquid filled with bubbles and the air in the whole apparatus

in circulation. From time to time the color of the solution is

96 THE AMERICAN NATURALIST [Vou. LIV

compared with that of the standards. It is obvious that since

the indicator solution is the same in each case and the starting

point is the same, the same color indicates the same amount of

CO, added. It is only necessary, from the relative volumes of

water and air in the apparatus and the absorbtion coefficient

under the conditions of the experiment, to calculate the total

amount of CO, produced by the organism to the time of the ob-

servation. Since the absorption of the CO, by the solution lags

a little behind its production, it is well not to consider the time

from the starting point to the first tube; from the first to the

second, however, and the second to the third, ete., this factor is

approximately the same in each case and therefore does not ap-

preciably affect the results.

As to the delicacy of the method, the indicator solution and

the air in the tube, if the temperature is 16° C. and the absorp-

tion coefficient therefore equal to 1, each contain 0.0006 mg. of

CO, per c.c. A ten per cent. increase causes a slight visible

change in the color of the indicator solution, so a production of

0.0003 mg. in the 5 c.c. tube ought theoretically to be detectable.

In practise, however, it is desirable to work with somewhat larger

amounts, e.g., 0.001 mg. or more. In measuring the time, it is

well instead of trying to determine the point at which the two

tubes exactly match to take the average between the last observa-

tion where the unknown tube is pinker and the first where it is

yellower than the comparison tube. To meet a possible objec-

tion, it may be said that when the carbon dioxide has increased

one hundred per cent., the oxygen in the tube has decreased only

approximately 0.2 per cent.; consequently changes in the amounts

of oxygen available for the organism during an ordinary experi-

ment are hardly significant. ;

In conclusion, it may be stated that the method has been

tested by comparing it with that of Lund? on the same organism

(a firefly) and the differences obtained were only of the order of

magnitude observed where two successive observations were

made on the same individual by the latter method alone; that is,

within the limits of uncontrollable normal variations of the

species in question.

: M. H. JACOBS

UNIVERSITY OF PENNSYLVANIA

3 Lund, Biol. Bull., 1919, XXXVI, 105.

THE

AMERICAN NATURALIST

Vou. LIV. March-April, 1920 ‘No. 631

ARE THE FACTORS OF HEREDITY ARRANGED

IN A LINE?

DR. H. J. MULLER

COLUMBIA UNIVERSITY

In the February (1919) number of the Proceedings of

the National Academy of Sciences, Professor Castle states

that he has ‘‘shown that the arrangement of the genes

in the sex-chromosome of Drosophila ampelophila is

probably not linear, and a method has been developed for

constructing a model of the experimentally determined

linkage relationships.’’! This declaration is so widely at

variance with the conclusions jointly agreed upon by all

Drosophila workers, that the arguments or assumptions

which it involves would seem to call for careful examina-

tion. It may be stated at the outset that the principle

upon which Professor Castle constructs his models ap-

pears exceedingly direct and simple—it is merely to

make a figure such that the distances between all the

points represented.on it are exactly proportional to the

frequencies of separation actually found between the

respective factors in the most reliable experiments. If

this is done, Castle contends, the models will be three-

dimensional instead of linear in shape.

1. The first argument which Castle gives against the

view that the groups of genes (which he admits, at least

1 Sturtevant, Bridges and Morgan also have published a defense of the

view of linear linkage, in the Proceedings of the National Academy of

Sciences (5, 1919, pp. 168-173) and Professor Castle has just replied to them

in the same journal (5, 1919, pp. 501-506). It is believed that the present

paper, although written and accepted for publication in the NATURALIST,

previously to this article, meets all the points therein brought forward.

98 THE AMERICAN NATURALIST [Vou. LIV

for purposes of argument, to be in the chromosomes) are

linear, is that ‘‘it is doubtful . . . whether an elaborate

organic molecule ever has a simple string-like form.”’

This argument is therefore based upon the unique as-

sumption that the whole chromosome (or that part of it

containing the genes) consists of one huge molecule.

Later, he speaks still more explicitly of this ‘‘chromo-

some molecule” and says, ‘‘the duplex linkage systems

of a germ cell at the reduction division must be . . . twin

organic molecules,’’ so that ‘‘a purely mechanical theory

[of crossing over] seems inadequate to account for inter-

change of equivalent parts between them.’’ The argu-

ment may therefore be paraphrased as follows: since (1)

the whole group of genes is but a single organic molecule,

and since (2) an organic molecule can not be linear, then

it must follow that (3) the group of genes is not linear,

and that the theory of crossing over is therefore erro-

neous. Although the premises of this argument are both

entirely gratuitous, it must be admitted that there is no

flaw in the reasoning, once the premises are admitted.

2. The second argument brought forward against the

linear arrangement of genes is that, in the linear maps,

the distances between widely separated loci are not

strictly proportional to the per cents of crossing over

actually found, being relatively too large, in comparison

with the per cents of crossing over. This he terms a

‘*diserepancy’’ in the map, which has required the ‘‘sub-

sidiary hypothesis’’ of double crossing over, in order to

harmonize it with the theory of linear linkage. The

answer to this is that it-has never been claimed, in the

theory of linear linkage, that the per cents of crossing

over are actually proportional to the map distances:

what has been stated is that the per cents of crossing

over are calculable from the map distances—or, to put

the matter in more mathematical terms, that the per

cents of crossing over are a function of the distances of

points from each other along a straight line. As will be

shown presently, this circumstance alone is sufficient to

No. 631] FACTORS OF HEREDITY 99

show that the factors must be bound together in a linear

series ; the precise nature of the function (involving coin-

cidence, etc.) will then determine for us precisely the

mode of incidence of the crossing over—i. e., granted the

linear series, it is then possible to calculate from the data

the exact frequency of single crossing over, double cross-

ing over of the various possible types, and multiple cross-

ing over. Double crossing over thus becomes, not a ‘‘sub-

sidiary hypothesis,’’ but a phenomenon directly demon-

strated.

It may, however, be noted in passing that, even if there

had been no experimental evidence at all in regard to the

nature of the linkage it could not have been conceded

that Castle’s alternative postulate—that no double cross-

ing over can ever occur at all—would have been any more

plausible a priori than that of the Drosophila workers

which admits the existence of double crossing over. For,

once the occurrence of single breaks in a chromosome is

admitted—a point agreed upon by both sides—it is just

as arbitrary to deny the possibility of double breaks as

to assert their existence. Although Castle nowhere does

explicitly admit that he has adopted this alternative

‘‘subsidiary hypothesis’’—the denial of the possibility

of double crossing over—yet an inspection of the theory

of linkage which he himself has proposed shows that in

this it has been tacitly assumed throughout, being neces-

sary for the purposes of the solid models. Were double

crossing over once admitted to occur, it could no longer

be claimed that the distances between the factors in the

three-dimensional models are exactly proportional to

their per cents of separation—a condition which it is the

sole aim of the existence of the models to fulfill.

We may now return to examine more carefully the

main argument upon which linear arrangement and its

corollaries (double crossing over, coincidence, ete.) is

based. The fact previously stated that the linkage rela-

tions between the genes are such that they are all cal-

culable from the positions of points in a linear series

dO THE AMERICAN NATURALIST [Vou LIV

may also be expressed as follows: given any three linked

factors, A, B and C, if any two of the linkages: between

them are known—say, the linkage AB and BC—then the

third linkage—AC—is determined (the most convenient

Reason method for calculating it is to make use of the

‘curve of coincidence’’ of the particular chromosome).

This is, two of the linkage values may be taken as ‘‘inde-

pendent variables’’ and the third is then ‘‘dependent’’

on them—in this sense we may say that B is linked di-

rectly to A and to C, but that A is only linked to C

through the linkage of each of these factors with B.

Since this is true of any combination of three-linked

factors (ABC, BCD, CDE, ACD, etc.) it can be shown

that the factors are all linked together in chain arrange-

ment, any one factor being linked directly to only two

others (those which we may regard as being on either

side of it), its linkage with the rest being entirely de-

pendent on these intermediary linkages.! This remains

true as a discovered mathematical fact of the linkage

relationships, shown first in experiments of Sturtevant’s

designed to investigate the problem, and this is what the

writer has designated as ‘‘the law of linear linkage.’’

Whether or not we regard the factors as lying in an

actual material thread, it must on the basis of these find-

ings be admitted that the forces holding them linked

together—be they physical, ‘‘dynamic’’ or transcend-

ental—are of such a nature that each factor is directly

1I. e. all the linkages (factorial (n— 1) in number) between the n

factors in a group, can be shown to be dependent on (functions of) only

n— 1 ‘‘primary’’ or ‘‘independent’’ linkages. To obtain the most perfect

expression of this dependency it is necessary to chose as the n— 1 inde-

pendent values the two strongest linkages involving each of the n factors

(what we should call linkages AB, BC, CD, DE, ete., as contrasted with

AC, AD, AE, BD, ete.). On this system, the other linkages all become

definitely determined, the secondary linkages being in each case a function

involving the sum of certain of the primary linkages. If, however, the pri-

mary T are not chosen according to the above rule, so as to consti-

tute a ‘‘chain formation,” no formula can definitely express the relation-

ships of the NaOH for the secondary linkages will then in some cases

depend upon the sum, in other cases upon the difference between e link-

ages taken as sears?

No. 631] FACTORS OF HEREDITY 101

bound, in segregation, with only two others—in bipolar

fashion—so that the whole group, dynamically consid-

ered, is a chain. This does not necessarily mean that the

spatial relations of the factors accord with these dynamic

relations, for it is conceivable a priori that factor A

might be far off from B, in another part of the cell, or

that both might be diffused throughout the cell, and that

they might nevertheless attract each other, during the

segregation division, by some sort of chemical or physical

influence. In the discussion that follows, no implication

as to the actual physical arrangement of the genes is in-

tended when the terms ‘‘linear series,’’ ‘‘distance,”’ ete.,

are used; these will refer only to the relations existing

between the points in the linear map, which may be re-

garded merely as a mathematical mode of representa-

tion of the data themselves. It will be shown, however,

at the conclusion of this article, that when the various

conditions which have to be fulfilled at segregation are

taken into consideration, any other explanation for these

peculiarly linear linkage findings than an arrangement

of the genes in a spatial, physical line proves to be haz-

ardously fanciful.

In the case of the larger distances, in order to a

what function of the distance the per cent. of separation

represents, it would be necessary to conduct extremely

delicate determinations, involving very extensive data in

experiments dealing with many points simultaneously.

Nevertheless enough has been done to show that even for

the larger distances the per cents of separation do de-

pend on the distance in the linear map—being less than

the distance by an amount which varies in a fairly regu-

lar manner according to the distance itself; hence it is

known that the higher per cents of separation certainly

involve some function of the linear distance.

In the case of the smaller distances, on the other hand,

the function has been rather accurately ascertained; it

is very close to the simplest one possible, that is, there 1s

an almost exact proportionality here between the map

102 THE AMERICAN NATURALIST [Von. LIV

distances and the per cents of separations. Just as dis-

tance AB plus distance BC on a line are equal to distance

AC, so the corresponding small frequency of separation

between A and B, plus the small frequency between B

and C, are found to be almost exactly equal to the fre-

quency of separation between A and C; for this reason

if the factors A, B and C are represented as points in a

straight linear map, the distances between any two of

them will represent the corresponding separation fre-

quencies in an almost proportionate manner. A few ex-

amples of this principle are shown in Table I; it has been

confirmed in innumerable other crosses, with many dif-

ferent factors. Moreover, it is found that the smaller

the distance involved, the more exact is the porportion-

ality that obtains, the less being the relative discrepancy

between the frequency AC as found by experiment, and

the value AC obtained, as on the map, by the summation

. of values AB and BC. The relationship which exists be-

tween the small separation values is hence just the sort

which Castle himself would demand, for a proof of linear

linkage. But whereas Castle would require this relation-

ship to. hold for all values, small or large, it may be

shown that its existence in the case of the small alone is

all that would be necessary for a complete proof of the

doctrine of linear linkage, even if the large values were

no sort of function of the linear series. For, if we pro-

ceed according to Castle’s own method, and construct a

map to represent the relations of the small values just

described, showing each of the frequencies by a propor-

tionate distance on the map, we necessarily obtain a map

each section of which is practically a straight line. In

the case, for example, of the data for v, g, and f, shown in

Table I, if we represent the separation frequencies by

proportionate distances in space, we must place point v

at 10.7 units from g, and g at 11.3 units from f; if these

two conditions are both to hold, then the only possible `

way of bringing f to its distance of 21.8 units from v is

to put the three points in a nearly straight line, as shown

No. 631] FACTORS OF HEREDITY 103

TABLE I

Back Cross OF FEMALES HETEROZYGOUS For v, g AND f. (PERFORMED BY

BRIDGES; REPORTED BY WEINSTEIN)

III. paik ge A By geiecoigae

I. Non-separa- II. Separations of of f from from v

tions vfromg and f and g Fy f V. Total Flies

2651 360 380 3 394

Resultant Per Cent. of Raren bbl tek = Resultant Per Cent. of

Separations Between Separ: s Betwi Separations Between

v and g ga aai. re v and f

GI Iv) (III + IV) ; (II+ IID

Vv y X

10.7 11.3 21.8

in Fig. 1. Other results indicute that the line would be

exactly straight if still smaller distances were studied.

Enough data have been obtained in the case of chromo-

some I of Drosophila to determine in this way the

‘“‘shape’’ of each part’ of the linkage group, and each

part, by itself, is thus found to follow the rules for linear

v J

. Direct ipten of the linkages in Table I. (vg, gf, and vf

are each represented by a line of length proportionate to the respective frequency

of separation.) The dotte curve shows the “ average ee deviation ” of the

factors from a straight line

distances in an extraordinarily rigorous manner. That

is, given the factors ABCDE, ete.,—or to take an actual

case, y, w, A, bi, cl,—it is found that the linkages of y, w,

and A are proportional to their distances in a straight

line, so are the linkages of w, A, and bi, for A, bi, and

cl, ete. But, since every part of the group is thus linear,

it must then be true that the entire group is linear. A

line all of the parts of which are straight is a straight

line. Any differences then observed between the size of

the larger distances and the per cents of crossing over,

even if they were so irregular that they could not be

thought of as a function of the linear system itself, would

then have to be regarded as due to peculiarities in the in-

cidence of the crossing over, superimposed upon a sys-

tem of genes which was really linear in formation,—

104 THE AMERICAN NATURALIST [Vor. LIV

modifications due to specific correlations between cross-

ings over in different regions. But since, as has been

stated, the differences between the larger per cents of

crossing over and the linear distances are not unregu-

lated, but do give clear evidence of being themselves a

function of the map distances, these larger per cents of

separation as well as the smaller ones can be used in

proof of the linear system of linkage. The systematic

differences between the frequencies and the map are

hence due to double and other multiple cross overs, which

vary in frequency in accordance with the distance in-

volved.

It is true that a certain amount of the differences actu-

ally found between the larger frequencies and their corre-

ée

. -

. .

A T NE PTEN POTT TY aai

figure that more remote factors, such as AE and J, are likely to be arranged

more nearly in a straight line than factors nearer together, such as AB and O.

sponding distances on a straight linear map might be

thought of as due to the cumulation of minor diserep-

ancies which existed between the small frequencies and

distances but each one of which was by itself too small

to be detected in the data for the smaller distances, being

within the limits of experimental error. As the small

discrepancies in such a case would, to be always cumu-

lative, all have to have a bias in the same direction, this

would amount to saying that the line along which the

points were really disposed had a slow, even curve, too

slight to be detected except when large distances were

considered. The straight line would then be sufficiently

accurate as a proportionate representation of all the

No. 631] FACTORS OF HEREDITY 105

small values but not of the large ones. If the validity of

the evenly curved figure were accepted, it would in no

way disagree with the finding of a linear arrangement of

the genes, but would merely substitute a curved line for

a straight one. In a really non-linear figure, such as

= shown in Fig. 2, the relations between the smaller dis-

tances would be (if anything) less of a linear type than

the relations between the larger distances,—factors

further apart in a thick rod, for example, would have to

be more in line than those near together. The fact that

the opposite relation holds in the actual data shows con-

clusively that the factors are in some sort of a line.

There is an a priori objection, however, to accepting a

curved line as an explanation of the linkage relations, in

that it is very difficult to imagine a plausible set of con-

ditions in the chromosome which would hold the factors

rigidly in this curved line but which would at the same

time determine the number of separations between the

factors according to their direct (straight) , distances

from each other, instead of according to their distances

along this line. But, quite aside from a priori reasons,

there is an experimental result absolutely fatal to the

curved line ‘‘explanation’’; this consists in the finding of

those classes which are termed by the Drosophila work-

ers ‘‘triple crossovers.’’ In the case of these classes the

separations are of such a type as to require the assump-

tion of .a break in the curved line at three points simul-

taneously. As it is obvious that a break in only one plane

could not cut the curve at more than two points, the triple

crossovers therefore would have to be due to a break in

more than one plane. The occurrence of breaks in more

than one plane, however, disturbs the assumed relation

of simple proportionality between separation frequencies

and map distances, which was the basie postulate upon

which the curved line was constructed. If the distances

are after all once admitted to be not exactly proportional

to the separation frequencies, then there remains no

reason to assume, just because the larger separation fre-

106 THE AMERICAN NATURALIST [Vou. LIV

quencies are out of exact proportion to the distances on a

straight linear map, that this is because the line is curved,

and the factors thus nearer together. If still more evi-

dence against the curved line idea be desired, it may be

added that when the curve is constructed so as to be in

good agreement (statistically) with the relations found

between the smaller frequencies, it is then not sufficiently

arched to permit the representation of the larger fre-

quencies by proportionate distances (see section 4). A

detailed compilation which I have made of all the data

has shown that experimental error will not well account

for the differences thus obtained between the two sets of

results. The curved line being abandoned, it vineinaian:

_ therefore, necessary to revert to ‘‘double crossing over,’

in explanation of the deviation of the large fı

from the straight map values.”

. If we examine further into Castle’s argument, how-

ever, we find that he objects, not only because the larger

separation frequencies are not proportional to the dis-

tances in linear maps, but also because he believes that

the smaller frequencies are not proportional; in fact,

according to his solid models, none of the kinds of fre-

quencies, small or large, could even be a function of the

distances in a linear map. In his solid, or rather, three-

dimensional, models, which purport to have the factors

so spaced that all distances between them are exactly

proportional to the corresponding linkages, the factors

are scattered about at all angles to each other, in such a

£ The fact that the P line which represents the linkages of the

factors should be taken as straight does not imply that the supposed physical

line in which the factors 5 is straight. So long as the fa etors lie in any

kind of physical line at all, then, if their linkages are determined, in some

way, by their distances as measured along this line, these patie should be

representable on the basis of a straight geometrical map, inasmuch as all

distances taken along a curved line must have the same interrelationships as

distances in a straight line. Hence the curving of the chromosome filament

is a matter entirely aside from the issue here involved, since the separation

frequencies of the factors in the supposed filament are not conceived of

dependent upon their direet distances from each other but rather upon their

distances along this filament. Thus the filament may, for these purposes, be

treated as if it were straight :

No. 631] FACTORS OF HEREDITY 107

way that their distances could never be represented as a

function of distances in a single line. The cause of this

discrepancy between Castle’s figures and the relation-

ships observed by the Drosophila workers lies in the

nature of the data which Castle uses, or rather, in his

manner of using the data. For Castle constructs his

maps, or models, on all the data obtainable, indiscrim-

inately, and regardless of the fact that most of the data

for the linkage values involved have been secured in as

many different experiments. On the contrary, it is nec-

essary, in order to determine exactly the relationships

existing between interdependent linkage values, that all

the data be obtained from the same experiment. This is

because the precise value obtained for any given linkage

is not only subject to the ordinary error of random sam-

pling but may vary significantly in different experiments,

in response to different environmental conditions, the

age of parents, genetic factors, and the amount of dis-

crepancy due to differential viability. Piling up enor-

mous counts does not eliminate these sources of varia-

tion. Any slight aberration thus produced in the abso-

lute value of one of the linkages (say AC) will then alter

so materially its relative value, as compared with the

other linkages (AB and BC), obtained in two different

experiments, that the different values no longer fit into

the linear system; they will not be expressible as any

sort of function of the system. That is why Castle found

that the Drosophila workers’ own data gave the per

cent. of crossing over between y(yellow) and w(white)

as 1.1, between w and bi (bifid) as 5.3, and between y and

bi as 5.5, a relationship quite at odds with their claims

concerning linear linkage for short distances. Castle

could have pointed out numerous similar ‘‘diserepan-

cies,’’ by similarly choosing to compare exactly (within,

Say, one unit of distance), the results of different experi-

ments. In fact, had we been allowed to select the experi-

ments for him, we could have chosen values such as the

following: Sb (frequency between star and black) 39.3;

108 THE AMERICAN NATURALIST [Vor. LIV

bp (frequency between black and purple) 5.9; Sp 0.4. If

Castle will follow his usual procedure here, and represent

these frequencies by proportionate distances in a model,

he will disprove not only linear linkage but both Euclidean

and non-Huclidean geometry and plain arithmetic. The

trouble in the case just cited arises in the fact that the

first two values are those obtained under ordinary cir-

cumstances whereas the third is a value obtained in the

presence of the factor CIIL which decreases enormously

the amount of crossing over. Clearly it will be unfair to

expect a single map to represent all three values simul-

taneously. Nevertheless, similar although less exag-

gerated, disturbing influences may be, and frequently are,

at work causing discrepancies between the results of

‘‘ordinary’’ experiments, so that it should be evident .

that the latter are not ordinarily fit to be subjected to

the delicate comparison which is necessary for the pur-

pose of determining the nature of the linkage system.

To some critics, it might at first sight appear incon-

sistent for the Drosophila workers to use the above argu-

ment against Castle’s system, in view of the fact that

these workers themselves also combine the results of dif-

ferent experiments in constructing their chromosome

maps. The answer to this is that the variations in link-

age between ordinary experiments are usually so small

absolutely, that, if all the data for independent linkage

values, like AB, BC, CD, ete.—are joined together and

represented in one linear map, the latter will be accurate

enough for the usual purpose of computing approx-

imately the per cents of separation: the factors will ap-

pear in their correct order, and with approximately the

correct distances between them. If, however, a study of

the nature of the system of linkage is to be made, much

‘more precise knowledge than this is required, for it is

necessary to know exactly the relative strengths of inter-

dependent linkages—like AB, BC and AC—as compared

with one another. In such a case the small absolute

deviations occurring in the different experiments become

No. 631] FACTORS OF HEREDITY 109

large relative deviations of the linkages as compared

with each other—this is particularly true the smaller the

absolute per cents of separation are—and so a totally

erroneous impression of the nature of the linkage system

may be produced. The nature of the linkage system—

whether it is linear and, if so, what function of a line is

involved—can only be studied to the best advantage in

experiments involving several factors at the same time,

but if our judgments regarding it have already been ar-

rived at, or verified, in this way, it is then quite legitimate

to use this knowledge for other factors, and to join the

results of different experiments involving them into one

linear map.

TABLE II

SEPARATION FREQUENCIES BETWEEN Every Two OF THE SIX SEX-LINKED

ACTORS y, bi, cl, v, s, B, AS SHOWN IN A CouNT OF 712 FLIES FROM

A CROSS IN WHICH TWELVE SEX-LINKED FACTORS WERE

)

OLLOWED SIMULTANEOUSLY. (MULLER

Sum of

Per

Directness of the Link- RESA, Ninh Poked sins a aaa ae f Bepa-

age, According to th f Sepa- Separations of Each from

Linear Maap. |) Commer. i aone (eee an hearde Ara Fasc | conan

; Inter-

mediate

Factor

and bi 39 5.5

‘Pi bi and cl 53 7.4

Primary" (or Sin cl and v 112 | 15.7

vands 57 8.0

sand B 95 13.3

y and cl 92 2.9 ybi+ bid = 92 12.9

Dependent on two! | biandv | 165 | 23.1 bicl + clv = 165 | 23.1

primaries ” cl and s 167 | 23.4 dv+vs=169 | 23.7

v and B 152 | 21.3 vs +s B= 152 21.3

De y and 198 .8 ye + el v = 204 28.6

= Seah a biands | 216 | 30.3| biv+vs=222 | 31.2

ie clandB | 240 | 33.7| clv+vB=264 | 37.0

Dependent on four| fy ands 247 | 34.7 y cl + cls = 259 36.4

primaries ” bi and B | 275 | 38.6 | biv+ vB = 2317 5

Dependent on fi 5 ee

“ primaries ” e {y and B 296 | 41.6 y v +v B = 350 49.2

In the experiments previously cited, the nature of the

linkage in various sections of the chromosome has been

110 THE AMERICAN NATURALIST [Von. LIV

studied by following the inheritance of three factors in

that region simultaneously. By a series of extensive

counts of this sort the nature of the linkage in each indi-

vidual section of the first chromosome has been studied,

and found to be linear. The data in Table II are derived

from an experiment which involves less extensive num-

bers than these, but illustrates to better advantage the

linear behavior of all parts of the chromosome at once.

These data are taken from Muller’s cross of flies hetero-

zygous for twelve mutant sex-linked factors. The re-

sults for six of these factors—those scattered most

evenly along the chromosome—are shown in the table, -

which gives the number and per cent. of separation be-

tween every one of these factors and each of the other

five. It will be seen that it happened that in this partic-

ular experiment, for all per cents of separation below 23,

the per cent. of separation between any two factors was

exactly equal to the sum of the per cents of separation of

each from a third factor lying between them, whereas for

factors less closely linked, the larger per cent. was less

than the sum of the other two by an amount varying

closely with the size of the large frequency itself. The

data obtained in this same experiment for the three

factors y, w and bi are given separately in Table ILI, in

order that they may be compared to better advantage

with the non-linear relation for these factors which

Castle claims, as a result of his combination into one map

of the results of separate experiments. Whereas Castle

obtained a triangular figure to represent the three fre-

quencies (y w 1.1, w bi 5.3, and y bi 5.5) it is seen that in

this experiment, where all three were followed at the

same time, an exactly linear relationship was obtained

(y w1.7, wbi3.8, y bi5.5). An experiment of Sturtevant’s

involving just these three factors is shown in the same

table (IIL); here too the relations are entirely linear.

In like manner the values obtained in the 12-factor ex-

periment for the loci of y w and A are given in Table

IV (yw 1.7, w A 1.4, y A 3.1) to be compared by the

No. 631] FACTORS OF HEREDITY 111

‘‘triangular’’ values (y w 1.1, w A 1.7, y A 2.0) claimed

by Castle. The numbers in Dies experiments are quite

sufficient to have revealed clearly any such triangular

relationships as shown in the data chosen and figured by

astle.

TABLE III

SEPARATION FREQUENCIES OF y, W AND bi

A. Data from the same experiment as that which furnished Table II.

uller)

III. Separations IV. Separations

I. Non-separa- II. Separations of of bi from y of w from y

tions y from w and bi and w and bi V. Total Flies

27 0 712

Resultant Per Cent. of Separa- — nt Per Cent. of Sepa- Resultant Per Cent. of Sepa-

tions Between y and w ations Between w and bi rations Between y and bi

I+IV) (II + IV) aI + MI)

y y

ET i 3.8 5.5

B. Data from a cross involving just these three factors. (Sturtevant)

I. Non-separa- II. Separations of III. Separationsof IV. Separations of

tions y from w and bi bi from y and w w from y and bi V. Total Flies

506

487

Resultant Per Sea of Sepa- Resultant Per Cent. of Sepa- Resultant Per Cent. of Sepa-

rations Between y and w rations Between w and bi rations Between y and bi

(III + IV)

oe v

0.6 3.2 36

TABLE IV

SEPARATION FREQUENCIES OF y, W AND A.

(From the same experiment as that which furnished Tables II and IHA.

Muller)

].Non-separa- II. Separations of m1. Separations ot Iv. piaekies S

tions y from wand A y and w from yand A V. Total Flies

690 12 0 712

Resultant Per Cent. Ap Sepa- Resultant Per Cent. of Sepa- Resultant Per Cent. of Sepa-

rations Between y and w rations Between w and A rations Between y and

I+ I)

X y +.

ay | 1.4 3.1

4. Although it has been shown that the linkage rela-

tions existing among the factors in any one experiment

are functions of a linear series it might still be ques-

tioned whether there might not, after all, be some ad-

vantage in using Castle’s system of graphic representa-

112 THE AMERICAN NATURALIST [Vou. LIV

tion—whereby each separation frequency is supposed to

be shown by an exactly proportionate distance on the

figure, no matter how many dimensions may be required

for this purpose. It will now be shown, however, that

such a system of representation is impossible, quite aside

from the fact that the models shown in Castle’s papers

are based upon data which can not legitimately be com-

bined together. That is, no matter whether the data used

are all derived from one experiment, or whether the re-

sults of different experiments are combined according to

Castle’s method, they could not be represented either in

a three-dimensional or in any other geometrical figurs,

in such a way that all the distances would be proportional

to the separation frequencies.

This may be illustrated by the data reported in Table

II. It has been seen that the per cent. of separations be-

tween y and cl is exactly equal to the per cent. of separa-

tions between y and bi plus that between bi and cl. If

then we represent these frequencies by actual distances,

we must make the distance between points y and cl ex-

actly equal to the distance between y and bi plus that

between bi and cl. The only possible way to do this, on

any kind of geometry—one-dimensional, three-dimen-

sional or n-dimensional—it to put these three points in

one straight line. In a similar manner we must place bi

cl v in a straight line, and also v s B. Cl v ands are in

almost a straight line, but there would have to be a slight

bend at v, owing to the fact that cl s is very slightly

shorter than cl v plus v s (on account of just one double

crossover having occurred between them); this is corre-

lated with the fact that cl s is a longer distance than the

others considered. The figure so constructed, on the

basis of Castle’s own methods, is shown in Fig. 3; it is

quite evident that this is the only figure which will repre-

sent directly (proportionately) the frequencies above

considered. If, however, we now measure the distance

on this figure between the extreme points, y and B, we

find that it turns out to be 49.3, or very nearly the sum of

No. 631] FACTORS OF HEREDITY 113

the intermediate distances (50.0), whereas the frequency

of separation found between y and B in the actual ex-

periment is 41.6. Similarly, the ‘‘model’’ shows too high

a frequency for the other longer distances involved.

(The long distances y s and bi B are 36.2 and 43.9 re-

spectively on the model, but only 34.6 and 38.6 in the

data; the moderately long distances y v, bi s, and el B

Ssa, B

. Direct F AA of the strongest and second strongest linkages

in Selo II. (y bi, cl, cl v, v 8, s B, and y cl, bi v, cb 8, v B, are each repre-

sented by a line of an aoak to the respective fre equmey of separation.)

e dotted curve shows the “average angular deviation” of the line i factors,

ahali to this miriadi

are 28.6, 30.8, and 36.6, respectively, on the model, but

27.8, 30.3, and 33.7 in the data.) It would, on the other

hand, have been possible to bring y and B clòse enough

together in the diagram, and at the same time have adja-

cent factors the correct distance apart, by giving the line

a curve, or bending it, as shown in Fig. 4. But if this is

Fic. 4. Direct marae of Bs strongest and weakest linkages ylides le

II. (y bi, bi cd, cb v s B, and y B are each represented by a line of pana

proportionate to the aad ive emma of ee m wd ty

the “average angular deviation” of the line of factors, according to this syst

done it is found that the distances of intermediate length

(y cl, bi v, cl s, and v B) are not properly represented,

all of them being relatively too short on the diagram.

It would be unsafe to attribute these discrepancies, so

uniform in direction, to the ‘‘errors of random sam-

pling.’’ The present experiment is cited, however, purely

114 THE AMERICAN NATURALIST [Vou. LIV

as an illustration, to show what kind of discrepancies are

meant. Discrepancies of exactly the same character and

direction appear when the diagrams obtained by this

method from experiments involving three points close

together are compared with those from other exper-

iments having three points far apart; that is, the former

figures are repeatedly found to be nearer in form to a

straight line than the latter; in such three-point exper-

iments, moreover, highly extensive counts have been

made, involving altogether (in the published experiments

on the first chromosome), approximately a hundred

thousand flies, and thousands of double cross overs.

5. The relation which has just been described, whereby

the larger frequencies’ of separation are relatively

smaller than could be directly represented in a curve

constructed on the basis of the small frequencies, is due,

according to the phraseology of the Drosophila workers,

to the fact that the relative frequency of double crossing

over (‘‘coincidence’’) is so much larger for large fre-

quencies than for small ones. Castle realizes to a cer-

tain extent the difficulty which this circumstance entails

for his models, and he endeavors to meet it by means of

the ‘‘subsidiary hypothesis’’ that the breaks in his

models are more frequent in certain directions than in

others. This assumption would, in some measure, ex-

plain away in a formal manner certain of the discrep-

ancies (although cases of ‘‘triple crossing over” still

remain an insurmountable obstacle), but the adopting

of any such hypothesis really amounts to cutting away

the ground from under the main theory of ‘‘propor-

tionate representation,’’ for the hypothesis involves an

abandonment of the claim that the model represents each

frequency by a proportionate distance between the nodes.

For it is evident that if, in a given region, breaks in one

direction are more frequent than in another, then points

in this region which are an equal distance apart will be

separated with different frequency according to the di-

No. 631] FACTORS OF HEREDITY 115

rection of the line joining them. A given distance then

no longer represents a given frequency.

6. It has been shown in the above two sections that a

single figure will not represent accurately, by propor-

tionate distances, the various linkage frequencies actu-

ally found in experiments involving many factors at

once. If, on the other hand, it had been attempted to

combine into one map the absolute frequencies obtained

in a series of different experiments with two factors at a

time, as Castle claims to do, the number and extent of

discrepancies irreconcilable with any possible geomet-

rical figure would have been much greater still. For,

since the absolute frequencies found in different exper-

iments necessarily have all sorts of irregular relation-

ships to each other, it follows that it would be even less

possible to show in one solid model separation frequencies

which were obtained in this way. One such irrecon-

cilable value has already been recognized by Castle—

namely, the frequency y B. He is forced to represent

this frequency by a curved wire in his model, because it

is longer (being 47) than the longest distance possible

(41) between these two points in any figure founded ona

proportionate representation of the other frequencies.

Of course, if distance on the model is to have any mean-

ing, it cannot arbitrarily be represented along a straight

line in some instances, and along lines having various

degrees of curvature in other instances. In this one case,

then, Castle is compelled to assume that the wrong value

has been obtained, owing to experimental error, even

though in all other cases: he has assumed that it is quite

legitimate to combine the results of different exper-

iments. It would have been strange if, in making a model

of this sort representing the separation frequencies of

so many combinations of factors, Castle had not encoun-

tered more of these refractory cases. He does not men-

tion any more, but it is noticeable that several other

curved lines appear in his model. Moreover there 1s :

conspicuous absence in the model of the factor lethal 2.

116 THE AMERICAN NATURALIST [Vou. LIV

It would have been inconvenient to represent the ob-

served linkage results for this factor by proportionate

lines in the model, for, according to the results, lethal 2

would have to be placed at 9.6 from w and 17.7 from v,

thus making the distance between w and v not greater

than 27.3, whereas the established distance between w

and v themselves is as much as 30.5; similarly, although

only 9.6 from w, lethal 2 must be placed only 15.5 from

m, although w and m are known to be at least 33.2 units

from each other. Hither the wv and wm lines would

have to be considerably curved, therefore, or the lines

between lethal 2 and the other factors would have to be

stretched in some way—perhaps dotted lines would meet

the difficulty! |

Although any scheme of representing linkage results

by exactly proportionate distances encounters the. con-

tradictions discussed above, it is noticeable that nearly

all the most extreme departures from a plane curved

figure (that figure which comes nearest to representing,

by strictly proportionate distances, the ratios resulting

from that type of linear linkage which actually exists)

occur in the ease of factors whose linkage ratios are dis-

torted by differential viability or difficult classification.

This is why the factors A, fr, sh, cl, bi, and the lethals

stand out from the fairly regular curved line which

Castle’s models would otherwise conform to. The first

two of the above factors are uncertain of classification,

the others mentioned affect viability markedly. In the

ease of nearly all the remaining factors of the model,

even though the results were taken from different exper-

iments, it was nevertheless found, when the data were

plotted, that they agreed pretty well with the expecta-

tions based on linear linkage. Moreover, the better the

experimental conditions are in regard to viability, cer-

tainty of classification, and size of counts,—the more

closely are these synthesized results of individual ex-

periments found to coincide with the linear findings of

experiments involving three or more points simulta-

No. 631] FACTORS OF HEREDITY 117

neously. (It is for this reason that Sturtevant was first

able to hit upon the general fact of linear linkage, on the

basis of numerous careful experiments involving only

two factors at a time.)

7.. Owing to the inherent inconsistencies of the methods

that were used to construct the solid models, it is to be

expected that any predictions regarding separation fre-

quencies which are deduced from them would be ex-

tremely unsafe. Castle states, however, that if any newly

discovered gene has been located in the model, by obtain-

ing its frequencies of separation from any three of the

other genes contained therein, then the relation of the

new gene ‘‘to all the others could be predicted by direct

measurement from the model.’’ In the case of two of

the four predictions which Castle has made in this way,

some evidence concerning the distance between the loci

involved is already in existence.

One of the frequencies of separation in question is that

between the loci of the recessive mutant factors glazed

eye and rugose eye, in Drosophila virilis. Castle pre-

dicts, on the basis of his model, that the per cent. of

crossing over between them should be found to be 4 or 5,

or ‘‘probably a little greater.’? The work of Metz, and

unpublished work of Weinstein, have shown, however,

that hybrid females which carry both mutant factors

exhibit the somatic character sterility possessed by the

more extreme mutant type. When this dominance of an

ordinarily recessive character in F, is taken together

with the close similarity between the unusual effects pro-

duced by the two mutant factors (both produce a similar,

peculiar effect on the eye, which is sex-limited, being

more marked in the males), and with the fact that there

is also a third mutant member of the series, with similar

peculiar effects and similar linkage relations, it becomes

highly probable that these factors are all allelomorphs.

In that case they occupy ‘‘identical loci,” and the fre-

quency of separation between them must be 0. A direct

determination of the per cent. of crossing over between

118 THE AMERICAN NATURALIST [Vou. LIV

them is obviously impossible to obtain, on account of the

sterility of the females carrying both factors.

Another prediction based on the solid models dealt

-with the frequency of separation between the factors

hairy and magenta, of Drosophila virilis. It had been

found by Metz that the per cent. of cross overs between

hairy and forked was 3.1 and between forked and ma-

genta 3.7; this would make the per cent. for hairy magenta

6.8 (or 0.6), if the factors were ina straight line. In the

solid model, however, the arrangement of these factors,

based on separate determinations of their frequencies of

crossing over with distant loci,—is shown as triangular;

and on the basis of this model Castle predicts that the

frequency hairy-magenta will be found to be 4 or 5. The

frequency has recently been determined by Weinstein,

who has kindly consented to allow its use in this connec-

tion. He finds it to be 6.6.

It should be pointed out that Castle has endeavored

to protect himself, in these predictions, by saying that-

they only hold, provided the relations given ‘‘have been

determined with sufficient accuracy’’!

8. One of Castle’s specific objections to the linear

maps, on which he lays much stress, is that on them the

distances between the extreme factors is much more than

50 units, whereas factors which are linked must have a

separation frequency of less than 50 per cent. It is only

necessary to point out here that since, as we have seen,

the linear maps, unlike the models, do not imply a pro-

portionate relationship between the distances and the

separation frequencies, these distances of over 50 do not

connote separation frequencies of over 50 per cent. On

account of the progressive reduction in separation fre-

quency, due to double crossing over, that occurs with in-

creasing distance, even distances of 100 or 110 in the

second chromosome do not connote separation frequen-

cies as high as 50 per cent. On the other hand, it should

_ also be remarked that separation frequencies of over 50

per cent. would not be impossible a priori, as Castle

No. 631] FACTORS OF HEREDITY 119

maintains; consequently any system of representing

linkage which permitted or showed such values would

not be ipso facto inconsistent. The mere fact that all

factors hitherto worked with in a single chromosome

have less than 50 per cent. of separation, and that those

in different chromosomes have just 50 per cent., does not

mean that factors can never be found which are so far

apart, and which lie in such a rigid chromosome (little

double crossing over) that they separate more often than

they remain together at segregation. Whether this

phenomenon should then be called linkage is but a ques-

tion of words; the chromosomes themselves would have

no regard for the 50.0 per cent. mark, or for the idio-

synerasies of our terminology.

The proof of the law of linear linkage, including all

the main aspects of it which have been given above, has

been stated on several previous occasions. It seems un-

fortunate that the argument has had to be repeated each

time that a new ‘‘theory of crossing over’’ has arisen,

for the discussion and data given in the original papers

supply all the material necessary for a decision of the

matter, at least so far as the germ plasm of Drosophila

is concerned.

Before closing, it may be desirable to supplement these

arguments for a mathematically linear mode of linkage,

by a statement of the considerations which indicate that

this mathematically linear linkage can have its basis

only in a linear physical connection between the genes.

If the genes are not spatially arranged, or physically .

connected, in the same linear sequence as that in which

they have been found to attract each other in linkage,

then the forces of linkage attraction must be such as to

‘fact at a distance.’’ But, although acting at a distance,

these linkage forces must nevertheless be extraordinarily

Specifie—binding each gene directly to just two specific

associate genes. Hence the forces could not be of an

electrical nature, for, since there are only two kinds of

electricity, electric forces could not be specific enough.

120 THE AMERICAN NATURALIST [Vou. LIV

Similarly, the attractions could not be magnetic, nor

could they be due to any kind of diffuse ‘‘physical’’

forces, such as those that emanate from centers of sur-

face tension change or from centers of vibrational dis-

turbanees. Those who deny linear arrangement, while

admitting the mathematically linear linkage results would

therefore be driven to assume that the linkage attraction

depended on the specific chemical nature of the genes,

which, by virtue of their chemical composition, exerted

a specific attraction at a distance, as the substances of

adsorption compounds are sometimes supposed to do.

But such a theory, as a method of accounting for linkage,

becomes stretched to the breaking point when it is re-

membered that each gene must be assumed to have such

an attraction for just two of the others, never more nor

less, and that when this attraction is broken it is always

exchanged for that of the allelomorph. Moreover, it

would be exceedingly hard to reconcile this theory with

the finding that changes in the nature of the genes—mu-

tations—alter in nowise the sequence of their linkage

attractions, and very rarely change even the strength of

the linkages. And when we come to analyze the linkage

relations in detail, and encounter the phenomenon of

interference, we find relations that are entirely at

variance with all our preconceptions concerning chem-

ical attractions or chemical activity in general,—results

that would force us to assume (1) that a breakage of the

attraction between two genes leads to an increased at-

traction between the other genes and (2) that the amount

of this increased attraction (‘‘interference’’) depends

solely on the directness of the connection (‘‘distance’’)

between these other genes and the one whose attraction

was broken, being not at all influenced by the chemical

nature of the broken attraction, or by the chemical nature

of the other attractions themselves. The facts of ‘‘inter-

ference’’ or ‘‘coincidence’’ are thus diametrically op-

posed to a chemical view of linkage, although they, like

all the other facts of linkage, are quite in accord with

No. 631] FACTORS OF HEREDITY 121

ideas of a spatial, physical linear arrangement, their in-

terpretation on the latter basis being natural and obvious.

The idea that the genes are bound together in line, in

order of their linkage, by material, solid connections

thus remains as the only interpretation which fits the

genetic findings. In view of the additional fact that the

chromosomes—themselves known to be specifically linked

to the factor groups—can, at certain stages of their his-

tory, be seen to have the linear structure required, it

would indeed be rash to adopt a different theory, with-

out most cogent evidence of a startlingly new character.

BIBLIOGRAPHY

Castle, W. E.

1919, Is Arrangement of the Genes in the Chromosome Linear?

Pro cad. Sc., V, 25-32.

1919. The Pinta mene of Bight Sex-linked Characters of Droso-

phila virilis.. Proc. Nat. Acad, 8c., V, 32-36.

Metz, C. W., and Bridges, C. B.

1917. Tneompatihility of Mutant Races in Drosophila. Proc. Nat.

cad. Sc., III, 673-678.

Metz, C. W.

1918. The Linkage of Eight Sex-linked Characters in Drosophila

virilis. Genetics, III, 107-

Morgan, T. H., and Bridges, 0. B

191 Sox hiked Takerin in Drosophila. Carnegie Institution of

W. :

Morgan, T. H., Sturtevant, A. H., Muller, H. J., and Bridges, C. B.

1915. The Mechanism of Mendelian Heredity. 262 pp. Henry Holt.

Muller, H. J.

1916. The Mechanism of Crossing Over. AMER. Nar., I, 193-221,

284-305, 350-366, 421-434.

Sturtevant, A. H.

1915. The Behavior of the Chromosomes as Studied through Linkage.

Zeitschr. f. ind. Abst. u. Vererb., XIII, 234-287.

Weinstein, A.

1918. Coincidence of Crossing Over in Drosophile melanogaster (am-

pelophila). Genetics, TII, 135-159.

INFLUENCE OF THE MALE IN THE PRODUC-

TION OF HUMAN TWINS!

DR. C. B. DAVENPORT

STATION FOR EXPERIMENTAL EvoLUTION, Corp SPRING HARBOR, L. I.

Ir is frequently pointed out that the father of twins

can have little influence in determining their production;

such production is purely a maternal quality, due to

double ovulation. One possible way, however, in which `

the male may influence twin production is recognized, but

this affects only l-egg twins. Thus, if we assume that

l-egg twins are due to an early fission of the embryonic

blastodise, or if they are due to a secondary budding (fol-

lowing the method of the armadillo), then the sperm cell

might carry the tendency to such fission or budding, as

well as the egg cell. This possibility, however, does not

help the statistical student of plural births, such as Wein-

berg, because he believes that the tendency to 1-egg twins

is not inherited at all.

In the following study, there will be considered only

the class of cases showing heredity most clearly, namely,

those in which the principal fraternity under considera-

tion has more than one pair of twins. Parents of such

fraternities are spoken of in what follows as repeater

fathers or mothers. Our query is then: ‘‘What is the

relative importance in twinning of inheritance from the

maternal and paternal sides, or what is the relative oc-

currence of twin labors in the close relatives of repeating

mothers and of their husbands? ’’

To get an answer to this question, all available figures

on twin repeaters were studied statistically. Of 355

labors occurring to the mothers of repeating mothers, 16

(4.5 per cent.) were twin labors. Of 289 labors occurring

to the mothers of twin-repeating fathers, 12 (4.2 per

cent.) were twin labors. These statistics thus indicate

1 Read before the American Society of Naturalists, at Princeton, Dec.

30, 1919.

122

No. 631] HUMAN TWINS 123

that the frequency of twins in the fraternities of fathers

of twins is almost the same as that of twins in the fra-

ternities of mothers of twins. Since the average propor-

tion of labors which are twin labors is 1.1 per cent. for

the population as a whole, we see that twins occur in the

fraternities of repeating fathers as well as repeating

mothers about four times as frequently as in the popula-

tion as a whole.

To make use of more extended pedigrees, we may com-

pare the tendency to have twin children on the part of

sisters of the father and the mother of twin fraternities

and on the part of brothers of the fathers and mothers of

such fraternities. Then we obtain the results shown in

the following table:

Per. Cent. of Births that

are Twin Births

Pather’s bistors? children’ 47 oio es et Oe es 8.2

Mother’s sisters”: children. -<-s 8.5 s5 ces tase 55

Wathor’s brothers children.cc . sso be i oa Chee 6.5

Mother's brothers’ Ghildren 2. 2) coe on ek ees oe 4.5

From this table, most of the items of which were based

upon ten or more twin labors, it appears that the sisters

of twin-producing parents are more apt to have twins

than the brothers of twin-producing parents; but the sis-

ters of twin-producing fathers are more apt to have twins:

than the sisters of twin-producing mothers; also the

brothers of twin-producing fathers are more apt to have

twins than the brothers of twin-producing mothers. In

all cases the proportion of twin births is very high, rang-

ing from 4 to 7.5 times the average proportion of twin

births in the whole population. These statistics then in-

dicate that there is no important difference in the hered-

itary influence to twin production on the part of the father

and the mother of offspring which include two or more

sets of twins.

If, instead of considering the cases of twins in general,

we pick out those of certain (or highly probable) identical

twins, then we find, in 30 families with such twins, that

the mothers came from fraternities in which (in 77 labors)

there were 13 per cent. twin labors, and the fathers came

from fraternities in which (in 38 labors) there were 13

124 THE AMERICAN NATURALIST [Vou. LIV

per cent. twin labors. Here we see that there is an eqality

of the maternal and paternal influence and that there is a

larger proportion of relatives of identical-twin producers

who are twins than of producers of twins in general. In-

deed, the occurrence of twin-offspring to the fraternities

of the parents of identical-twin producers is propor-

tionally 12 times as common as in the population at large.

Another way of testing the inheritableness of 1-egg

twins is by getting the frequency-distribution of the sex

of twins in repeater families—those in which the influ-

ence of heredity most clearly shows itself. In these,

therefore, we expect nearly an equality of twins of sim-

ilar sex and of dissimilar sex, provided 1-egg twins are

not found in these clearly inheritable strains. In 160

pairs of twins in repeater families, of which the sex is

given, there are 54 of unlike sex and 106 of like sex. Ex-

pectation in the case of binovular twins is that there will

be an equality of like and unlike sexed twins. Any excess

of like-sexed twins is to be ascribed to the occurrence of

l-egg twins. In the present case, there is an excess of 52

pairs of like-sexed twins out of 160 pairs of twins, which

indicates that about 1 in 3 of the twins in repeater fam-

ilies are identical twins, and this agrees approximately

with statistics obtained from the population as a whole.

From this we reach the conclusion that the tendency to

production of 1-egg twins is certainly not less common in

the case of repeater families than in the case of families

in which there is only a single pair of twins. The state-

ment, therefore, that there is no hereditary influence to

be detected in the case of 1-egg twins appears certainly to

be incorrect. In fact, the presence of heredity is more

striking than in the case of other twins and this leads us

to conclude that the hereditary tendencies toward unio-

vular multiple production so obvious in armadillo (Ta-

tusia) persists also in man.

Still another way of testing the relative influence of the

mother and father in twin production is the comparison

of cases in which the father of twins has married twice,

and the mother of twins has married twice. An examina-

tion of our records showed 30 families where at least one

No. 631] HUMAN TWINS 125

parent of twins has married twice. In 14 cases it was

the father who married twice, in 15 cases the mother, and,

in 1 case, both father and mother. In the 14 cases of

father of twins who had married twice, there were twins

by both marriages in 2 cases, or 14 per cent. of all such

cases. In the 15 cases where the mothers of twins had

married twice, there were twins by both marriages in 3

cases, or 21 per cent. of all such marriages. The numbers

are small, but, so far as they go, in view of the average

occurrence of twins in only about 2 per cent. of all mar-

riages (and hence if chance only were at work in 4 per

10,000 of both pairs of double marriages), they indicate

that the tendency to twin production is hereditary and

also that not only the mothers but also the fathers have

great influence in determining the production of twins.

` All the foregoing statistics speak strongly for the view

that the father has about as much influence in the produc-

tion of twins as the mother. This result at first sight

seems quite inexplicable and indeed to reduce the whole

matter to an absurdity. If twin production is due simply

to double ovulation, what can the father have to do with

the result? ;

The present paper does not attempt to give a final

answer to this inquiry. It attempts only to set forth a

hypothesis which suggests a line of experimentation to

answer the question more definitely. We have assumed

that 2-egg twins are due to the simultaneous bursting of

two Graafian follicles while single births result from the

bursting of a single follicle. There is, however, a good

deal of evidence that single births are not always the con-

sequence of the bursting of a single follicle merely. There

are indeed several other factors that determine a single

birth, such as the failure of one of two simultaneously

expelled eggs to be fertilized or the failure of one of

two simultaneously expelled fertilized eggs to develop

to maturity. That is, it may well be that two eggs are

simultaneously ovulated much more frequently than at

present recognized and that the comparative rarity of

twin-births is due either (1) to a failure of fertilization

of one egg or (2) to a failure of development of one egg.

126 THE AMERICAN NATURALIST [Vou. LIV

The conviction that not all eggs that are ovulated are

fertilized is borne upon one who compares the number of

corpora lutea in mammals that have large litters and the

number of embryos that one finds in the uterus. I have

recently made a number of counts in this respect in the

case of sows and give below results in tabular form:

Number of Recent Number of Embryos . Average Length of

Observation Number Corpora Lutea Found Embryos

1 3 3 15 cm

2 6 3 10 cm

7 8 7 6.5 cm

12 9 2 2.5 cm

13 8 7

34 22

Thus from 34 corpora lutea, or 34 eggs expelled, only

22 embryos were found, counting only those which had

reached a length of 2 cm., at which stage the chorion is

already so large that it seems improbable that it should

have been overlooked. :

There is some reason for thinking that in humans also

a certain proportion of the eggs ovulated fail of fertiliza-

tion even in families in which there is no prudential re-

striction—in which the size of the families indicates a

probability that nearly the maximum number of eggs

became fertilized. Conclusions are fortified by the ex-

amination of a good genealogy including families of chil-

dren born in the latter half of the eighteenth and the early

part of the nineteenth centuries. Thus in a genealogy of

the Gorton family, seventh generation, the intervals in

round years between births in various fraternities (all

related as cousins, are:

13 children—3, 1, 1, 5, 1, 2, 2, 2, 2, 2, 1, 5; all born 1795-

1821.

10 children—2, 2, 2, 2, 2,3, 2, 2,2. In this case there is no

unexpectedly large interval.

11 ehildren—-2, 2, 2,2, 2, 2, 2, 2. 1, 5.

6 children—4, 2, 4, 3, 4; all born between 1792-1809.

8 children—2, 2, 2, 2, 2, 5, 2; all born between 1796-1813.

13 children—1, 2, 1, 2, 2, 2, 3, 3, 3, 2, 2,4. In this case also

No. 631] HUMAN TWINS 127

there seems to be no failure of fertilization, except

at the end of the series. i

9 children—4, 2, 2, 2, 2, 2, 2, 2.

10 children—3, 1, 4, 2, 1, 2, 2, 2, 2.

9 children—1, 2, 3, 4, 3, 2, 2, 3; born between 1825-1845.

One gets the impression that the normal interval be-

tween births, assuming all eggs to be fertilized, is about

2 years. The frequent intervals of 3, 4, 5 and even more

years probably correspond to failure to fertilize, although

they may be due to miscarriages or even in some cases to

prolonged absence of the husband. In view of the fact,

however, that we have to do here with a prevailingly

rural population, chiefly farmers and millers in central

New York State, the latter contingency is improbable.

The failure of fertilized eggs to complete their develop-

ment is a real factor that must be taken into account.

Attention has been called to the importance of this factor

by John Hammond (Journal of Agricultural Science, VI,

1914) who has studied fetuses of rabbits and pigs and

finds among them many degenerating individuals. Thus

the number of degenerating fetuses in a large number of

uterine horns examined varied from 0 to 19 per cent. I

can confirm these results by observation made upon the

uterus of a sow (No. 3) in which there were 2 corpora

lutea in the left ovary and 5 in the right. In the left horn

of the uterus there was a well-developed embryo 8 mm.

long and one, evidently blighted, of 4 mm. The outlines

of the latter embryo were highly abnormal and shrunken.

The right horn of the uterus contained one embryo, 25

mm. long, a second 9 mm. long, and a third 6 mm. long.

Thus with 7 corpora lutea in the ovaries, there were only

5 embryos found, of which one was completely blighted,

another at 6 mm. length would probably soon have ceased

development and two others at 8 and 9 mm. were far be-

hind the best developed embryo, already 25 mm. long. :

Work on yellow mice, of which the yellow X yellow

matings give rise to 25 p. c. atretic embryos, and the far

more extensive experience of Morgan with lethal factors

in Drosophila, indicate that failure of ‘development is a far

128 THE AMERICAN NATURALIST [Vou. LIV

more common phenomenon than hitherto appreciated.

Lethal factors, it may be pointed out, are a probable solu-

tion of one of the mysteries of gynecology; namely, that

a woman who is sterile with one husband is often fertile

with another, even when examination has shown no defect

in the spermatozoa. ‘Similarly a husband may have no

children by one wife, but one or more by a second mar-

riage. Parallel phenomena are common in dairy cattle.

We conclude then that lethal factors are probably wide-

spread phenomena even in human germ cells, and ac-

count for a certain proportion of long intervals between

births, of early miscarriages, and of sterile unions.

The application of the foregoing two principles of fail-

ure of fertilization and failure of development to the ques-

tion of the réle of the male in twin production is now

fairly obvious. More eggs are laid, even without pru-

dential restraint, than come to development, and this is

true not only of eggs laid successively but of eggs laid

simultaneously; that is, twins that are born are the re-

siduum of a greater number of twins that are started in

their development and of a still greater number of pairs

of eggs simultaneously ovulated.

The literature of gynecology is indeed full of cases of

blighted twins. In a fairly large proportion of all twin

births, one of the twins has remained at a stage of devel-

opment of the third, fourth, or even earlier month. The

fetus is often found compressed and flattened; the name

is given of papyraceus twin. The number of blighted

twins which have been referred to in the literature

amounts to several score, but naturally is a very small

proportion of the whole. The vast majority of blighted

twins are simply lost unnoted with the afterbirth. A rec-

ord is made only of the larger blighted fetuses; the others

are entirely overlooked, since search is rarely made for

undeveloped embryos in the afterbirth, and the birth is

consequently regarded as a single one. We must believe

that a certain proportion, perhaps a large proportion, of

the fraternities which show two or three twin labors inter-

spersed with single labors are those in which pairs of eggs

No. 631] HUMAN TWINS 129

have been ovulated in each case, but one of the pair has

failed to develop, either through failure of fertilization or

early blighting.

Now the lethal factors show their influence first in cer-

tain combinations, just as in the matings of yellow x

yellow mice. The 4 of the embryos which die are those

which are derived from germ cells containing the genes

for yellow, whereas the other ? may develop fully. So

we concude that among humans the cases of twin-repeat-

ing fraternities are those in which there are no or few

lethal factors in the germ cells, so that there is a maxi-

mum fertilization and development of the eggs laid.t_ In

the case of families comprising only one pair of twins,

combined with a number of single births, it is probable

that in other cases there had been a double ovulation but

one of the pair had failed to develop. The additional fact

to be taken into account is that twins are found in a higher

ratio in large families than in small ones. Large families,

however, connote high fertility of the male as well as the

female. From all these facts we reach the conclusion

that families which readily produce twins do so not only

because in the mother the eggs were laid in pairs, but also

because in the father the sperm is active, abundant and

without lethal factors, so that the number of eggs fer-

tilized and brought to full term approaches a maximum,

To repeat, such fathers, experience indicates, belong to

strains which are exceptionally fertile and in which twins

are repeatedly produced both along male and female lines. :

Thus it comes about that the fathers of twins are about as ©

apt to belong to twin-producing strains as mothers of

twins and that twinning depends on constitutional—

hereditary—factors on both sides of the house.

1F, H. A. Marshall (1910), ‘‘ Physiology of Reproduction,’’ p. 618, rec-

‘ognizes that certain abortions in sheep ‘‘may be due to a want of vitality

on the part of the developing embryo.’’ Similarly gynecologists recognize

that a part of the 10 per’ cent. of barren marriages, and many of the early

miscarriages, have no explanation in pathology, but apparently only in

physiology.

INHERITANCE OF CONGENITAL PALSY IN

GUINEA-PIGS!

PROFESSOR LEON J. COLE

University OF WISCONSIN, AND

DR. HEMAN L. IBSEN

Kansas STATE AGRICULTURAL COLLEGE

CONTENTS

Introductory.

Origin of Palsied Stock.

Inheritance of the Palsy Character.

Etiology.

Discussion.

Pigeon.

Mouse and Rat.

References.

INTRODUCTORY

In 1914 a litter of two guinea-pigs was born in our lab-

oratory, one of which differed from the other in that it

appeared to lack nervous control. When this individual

was placed on its feet, attempts on its part to walk re-

sulted in spasmodic stiffening of the legs, causing it to

fall over on its side, where it lay helpless and unable to

get up. Although the animal appeared otherwise in good

physical condition, it was thought at the time that the

trouble might be due to temporary nutritional disurbance,

and attempts were accordingly made to feed it by hand,

1 Papers from the Department of Geneties, ‘Agricultural Experiment Sta-

tion, University of Wisconsin, No. 18. Published with the approval of the

Director of the Station.

130

No. 631] CONGENITAL PALSY IN GUINEA-PIGS 131

until it should be able to nurse. The effort was, however,

unavailing, the subject gradually becoming weaker and

the symptoms more pronounced, until death ensued in a

few days. <A second litter was produced by this pair on

May 19, 1914. This consisted of three young, which ap-

peared in all respects normal. On August 27, however,

another litter of two was produced and one of these was

like the abnormal individual described above. This gave

rise to the suspicion that the defect might be due to some

hereditary cause and consequently the mating of the same

parents was continued, with the following results: No-

vember 6, 1914, one defective offspring; March 24, 1915,

three offspring, 2 being normal and one born dead; and

June 20, 1915, 2 normal, 1 defective and 1 born dead. Not

counting the two born dead, since their condition with

respect to normal reactions could not be determined, this

pair then produced a total of 13 young, of which 9 were

normal and 4 defective. These results not only strength-

ened the presumption that we had to deal with a heritable

condition, but were so close to a three-to-one ratio as to

suggest that it might be a simple Mendelian recessive.

It may be stated at this point that further extensive ex-

periments have proven conclusively the correctness of

both of these presumptions.

Full discussion of the symptoms and of related condi-

tions in man and other animals will be reserved until the

experimental results have been presented. It is sufficient

to say here that the defective condition is always clearly

marked and easily recognizable, and that in no case have

there been doubtful intermediates. Furthermore, such

efforts as have been made as yet to rear the defective off-

spring have been uniformly unsuccessful; these individ-

uals always die within a short time, usually within two

weeks of birth.

ORIGIN oF Patstep Stock

Later in 1915 palsied offspring were produced by other

parents and studies of the pedigrees have shown that

such individuals have appeared in three distinct lines

132 THE AMERICAN NATURALIST [Vou. LIV

which are unrelated so far as the pedigrees show back to

‘our original stock. This stock came from two sources, a

few animals received from Professor Castle, of Harvard

University, and somewhat less than a dozen young ani-

mals supplied us by our veterinary department, but ob-

tained from a dealer. This stock had multiplied to about

forty individuals at the time records were begun on it.

The pedigrees show that in all probability there was only

one individual, a male, in the Castle stock which might

have brought in the palsy character, and since Professor

Castle informs us that he has never noticed it in his ani-

mals, this individual may with considerable certainty be

ruled out as the source of the defect in our experiments.

The young animals received from the dealer were all of

about the same age and were white spotted, very similar

in appearance, which suggests that they may have been

related. We are accordingly led to conclude that the

character was introduced with this stock and that in all

probability it may have traced back to one, or at least

only a few, heterozygous animals, and that, furthermore,

if there were more than one they were probably related.

INHERITANCE OF THE Patsy CHARACTER

The factor for normality appears to be completely dom-

inant and we have found it impossible to distinguish ani-

mals carrying the defective trait from those which do not

on the basis of observable behavior or any other char-

acters. The only method of separating the two classes is

therefore by breeding tests. Owing to the fact that the

affected (recessive) individuals always die, it has been

necessary to conduct the experimental tests by the round-

about method of always mating animals to be tested to

others known to be heterozygous. If the individual being

tested was a homozygous normal no defective offspring

would be produced by such a mating, whereas if it was

heterozygous they should appear in the usual ratio for

Mendelian recessives. We have therefore conducted ex-

tensive experiments to determine, (1) the ratio of palsied -

No. 631] CONGENITAL PALSY IN GUINEA-PIGS 133

offspring when two heterozygotes are mated, (2) the pro-

portion of homozygous to heterozygous individuals

among the normal offspring of such matings, and (3) the

ratio of homozygous to heterozygous offspring when

homozygote was mated to a heterozygote.

Since for practical reasons the number of offspring

which can be produced from any particular pair of par-

ents is limited, it became necessary to set a definite arbi-

trary number which should be taken as the minimum to

indicate a fair probability that the animal being tested

was homozygous for normality if no recessive young

were born. Five was chosen as this minimum, but in

every instance larger numbers were obtained where pos-

sible. All cases in which less than five normal offspring

were obtained without the appearance of a recessive are

discarded from the calculations. Furthermore, only six

of the thirty individuals rated as homozygous normals on

the basis of their breeding behavior had so few as five off-

Spring, and in most cases the number was considerably

larger, as is shown in Table I.

TABLE I

ANIMALS RATED AS Homozygous NORMAL AND THE NUMBER OF EXCLUSIVELY

ORMAL OFFSPRING ON WHICH THE RATING WAS BASED

No. of Normal Offspring

No. of Animals Tested Produced by Each Total Offspring

62 5 30

32 6 18

12 7 7

1 8 8

1 9 9

4 10 40

6 11 66

1 12 12

1 13 13

2 14 28

1 15 15

1 23 23

1 24 24

1 26 26

n 319

Total 30

2 Eight of these ten animals died before more offspring could be obtained,

one was discarded because of being a poor breeder, and one for some un

assigned cause.

134 THE AMERICAN NATURALIST [Vor. LIV

Further evidence that this test is fairly reliable is fur-

nished by the fact that in matings of heterozygote to het-

erozygote affected offspring appeared in litters before

five normal young had been born in 84 per cent. of the

cases, while in 22 of the 32 matings the recessive appeared

in the first litter. The complete data are given in Table II.

TABLE II

Number of Normai Offspring Produced before

Number of Matings Litter Containing Recessive

oar KH ©

fol bo wN

For present purposes we have adopted the symbol N to

represent a factor for normality; the recessive, palsied

animal is therefore nn.

1. Ratio of Palsied Offspring when two Heterozygotes

are mated.—As there appears to be no need of presenting

the detailed data of individual matings, the combined re-

sults of mating heterozygous animals together are given

in the left hand side of Table III. Of the total number

TABLE III

Matines Nn X Nn

Offspring Tested Normal Offspring

N | nn | Born Dead NN | Nn

Obearved fovea 183 | 63 | 36 |

Peron ee ee 184.5 61.5 = 73 14.6

of offspring alive when born (that is, when found) 183

were normal and 63 palsied, an almost exact three-to-one

ratio. We, therefore, feel safe in our assumption that

the palsied condition is based on a single unit factor dif-

ference. The question might be raised as to whether the

rather large number of offspring ‘‘born dead’’ might not

represent a disproportionate number of palsied young.

This does not, however, seem probable for a number of

No. 631] CONGENITAL PALSY IN GUINEA-PIGS 135 ©

reasons. In the first place, the palsied animals appear

as strong and vigorous when born, and in all respects ex-

cept for the nervous condition as fully developed as the

normal young. This is further borne out by the weights,

the weight of the palsied young being as great, indeed

averaging slightly more at birth than that of the normals.

The weights at birth of the living young from Nn X Nn

matings are shown in Table IV, from which it will be seen

TABLE IV

WEIGHTS AT BIRTH OF LIVE OFFSPRING Propucep By Matines Nn X Nn

| Nanni Average

um!

Waem Individuals

| Weighed Grams | Weighed

Ery a

a mala, oe ea a | gr i Beor] 4 95

Normal Tomales; reiki Ps oS e TO ts BEBB | 9 88

Normal males and females combined 170 | 88.65 | 13 | 183

peed males. O ee e 3 | 92.21 | 0 | 32

Paisied Jamals o. o roa aN. S | pat

| ll

Palsied males and females combined . . 61 | 90.19 | 2o o

that 170 normal offspring averaged 88.65 grams, whereas

61 palsied young average 90.19 grams. The slightly

greater weight of the latter is probably not significant.

These facts seem to indicate strongly that the congenital

death rate was not differential with respect to palsy.

2. Proportion of Homozygous to Heterozygous Individ-

uals among the Normal Offspring of Nn X Nn Matings.

—Further proof that we were dealing with a single factor

difference was provided by tests of the normal offspring

from matings of heterozygote to heterozygote. These

should, of course, consist of two heterozygous individuals

to each extracted homozygous dominant, which should

breed as free from the defect as any animals from non-

palsy stock. As shown in the right-hand half of Table

II, 22 of the 183 normal individuals were tested, of

which 7 proved to be NN and 15 Nn, the theoretical expec-

tations being 7.3 and 14.6, respectively.

3. Ratio of Homozygous to Heterozygous Offspring

from Mating NN X Nn.—One other type of test was

136 THE AMERICAN NATURALIST [Vou. LIV

made, namely, of the normal offspring resulting from the

mating of homozygous to heterozygous individuals. The

expectation in this case is equality of the classes, and the

TABLE V

Matines NN X Nn

Offspring Tested Offspring

| N | nn Born Dead NN | Nn

Oren a gre a 4 |

Eeected te a [B19 | 0 | a 12.5 12.5

actual numbers found in the 25 tests made were 14 NN

and 11 Nn, the expectation in this case being 12.5 in each

class (see Table V).

Additional evidence that the netraciad homozygous

normals are free from palsy ‘‘taint’’ is furnished by three

matings of such animals together, from which 31 living

offspring have been obtained, all normal.

The foregoing data would appear to be sufficient in

number and in closeness of ratios to demonstrate conclu-

sively that congenital palsy in guinea-pigs is inherited in

simple Mendelian fashion and depends on a single unit

difference, the normal condition being completely dom-

inant to the heterozygote.

SyMPTOMS

A brief description of the typical symptoms has al-

ready been given, but for comparison with the same or

similar conditions which may be observed by others, it

seems desirable to describe the symptoms of the palsy as

it occurs in our stock in somewhat greater detail.®

A word ought perhaps to be said at this point about the

use of the term congenital palsy. The congenital part is

evident enough and needs no explanation further than to

point out that we use it in the sense of being present at —

3 We wish to express our appreciation of valuable advice and assistance

rendered us by Dr. W. J. Meek in connection with this and the following

sections of this paper.

No. 631]: CONGENITAL PALSY IN GUINEA-PIGS 137

time of birth rather than of being contracted at time of

birth, which is the connotation sometimes implied in rela-

tion to certain infectious diseases. The word palsy is

used in the general sense to indicate the broad similarity

of the condition in the guinea-pigs to trembling palsy in

man. The term is intended to be a neutral one with no

implications as to the ultimate cause of the disturbance.

The condition perhaps in some ways more closely resem-

bles tetany as manifested in mamimals below man, but this

term has been avoided as having possibly too specific an

implication.

There is considerable variation in the degree to which

different individuals are affected. In most cases the vic-

tim when discovered shortly after birth is lying on its

side slowly moving the legs, twisting the body and lifting

the head as if in a vain endeavor to get on its feet. The

movement of the fore part of the body, head and forelegs

is much more pronounced than that of the hind quarters

and hind legs. Some individuals if placed gently on their

feet are able to stand, though usually in a strained tense

attitude. The difference between this and the normal

position may be observed in Fig. 1, 2 1089.1 being a pal-

sied individual, while the others are its normal brother

and sisters. The photograph is taken from directly

above. The affected individual has the feet somewhat

spread and the body slightly contorted, while the others

are in natural easy attitudes.

If left quietly to itself after being placed on its feet the

animal usually stands unsteadily for a few moments and

then when it starts to walk falls on its side, with charac-

teristic movements of the legs to be described presently.

Some animals are so little affected at birth that they are

able with effort to gain their feet themselves, and to walk

about in a clumsy, jerky, paralytic fashion. They expe-

rience the most difficulty in the control of the hind legs,

which appear to be in a hypertonic state and are com-

monly moved more in a hopping fashion than in steps. A

rough classification of 51 palsied antmals soon after birth

gives the following: 14 unable to rise and unable to stand

138 THE AMERICAN NATURALIST [Vou. LIV

when placed on their feet; 18 able to stand but unable to

walk; 5 able to walk when placed on their feet but unable

to arise unaided; and 14 able to get up and to walk. It

should be recalled that in all cases the symptoms grow

progressively worse, leading to the most severe condi-

tions, and to death in a week or two at most.

Breathing appears to be normal, as is also control of

the muscles of the jaws and throat, for the less affected

animals sometimes eat solid food, and those that are able

to walk may suckle the mothers. Such individuals increase

in weight for a time as rapidly as normal young, but with

the progress of the disease they become unable to obtain

nourishment, and consequently decline. We are unable

to state at present whether death is attributable finally to

starvation, or whether it is a direct sequel of the disease.

The most striking phenomenon in connection with the

disease is the reaction to stimuli, particularly to auditory

stimuli. This may be best observed in animals that can

stand when placed on their feet but are able to walk only

with great difficulty, if at all. If such an animal is placed

on its feet and a sharp sound is then made, such as clap-

ping the hands, snapping the fingers, or squeaking with

the lips, the reaction is definite and immediate—the sub-

ject jumps upward and forward, due to a sudden stiffen-

ing, particularly of the hind legs, then falls on its side,

the whole body shaking to some extent, but the legs ex-

hibiting strong clonic spasms. To the same stimulus nor-

mal individuals give merely a slight start, and then sit

unconcernedly as before. This result is clearly shown in

Fig. 2, which depicts the same litter as Fig. 1, but follow-

ing a stimulus which has thrown the affected individual

into a spasm as described. Fig. 3 is a short time-exposure

- of an animal in a spasm lying on its side. The photo-

graph shows clearly the movement of the feet.

Visual stimuli have relatively little effect in producing

the above-mentioned reaction. Even if the hand is

brought rapidly down to near the animal’s eyes it seldom

responds. The same is true for mechanical stimuli, the

reaction occurring only if the stimulation is severe. Af-

g 1089.3

i wa aa ? 1089.1 $1089.2

nooo nn Nn

798.1

INHERITANCE OF CONGENITAL PALSY IN GUINEA-PIGS,

140 THE AMERICAN NATURALIST (Vou. LIV

fected animals which are fairly able to walk may not fall

over even as a result of an auditory stimulus. They give

a jump, much more pronounced than the start of normal

individuals, but manage to stay on their feet. Further-

more, even the more affected ones become less sensitive

to repeated stimulation, and may after several reactions

fail to respond sufficiently to make them lose their balance.

In the more severe stages the reaction appears to simu-

late intentional tremor, in that it follows attempts at vol-

untary movements of the hind legs. In less severe cases

the animal can use the legs if free from other nervous

excitation. It would appear therefore that the condition

. is induced by sudden nervous excitement, the degree of

_ the stimulus necessary to cause complete lack of mus-

-cular control depending on the stage of progress of the

affection.

The severe spasms commonly last but a few moments.

If a guinea-pig stiffened out in one of the spasms is taken

in the hand it can soon be felt to relax, following which.

it either lies quiet or makes slow movements of the head

and to some extent of the legs as previously described.

ETIOLOGY

A number of possibilities suggest themselves as causes

of the disease described in this paper, and these will be

discussed in order.

= 1. As mentioned in the following section, digestive dis-

turbances may cause in sheep a condition very similar in

many of its symptoms to the spasm of our guinea-pigs.

Is it not possible that these were originally induced by

some similar cause? It is true that at times, especially

in the early part of the work, we have had some trouble

from improper feeding, notably when we attempted to.

substitute sugar beets for carrots and cabbage. While,

however, inadequate diet may cause scurvy and other

effects, we have no reason to believe that it ever produces

a condition which could be mistaken for the congenital

palsy. Furthermore, palsy never occurs in the descend-

No. 631] CONGENITAL PALSY IN GUINEA-PIGS 141

ants of two homozygous normal individuals, even though

their feeding and care is in all respects similar to that of

the others. In other words, the disease has behaved

strictly in accord with the known principles of heredity

since it has been under observation, and we have every

reason to believe that it has not appeared spontaneously

during that time. This would mean then that if the dis-

ease was due to nutritive conditions, it must have had its

inception in the stock before we received it, or within a

very short time thereafter at latest.

The evidence that heritable defects of this sort may be

induced by external conditions is very meager at best,

Stockard has produced somewhat similar nervous de-

fects in guinea-pigs by the administration of alcohol, but

while he claims that these are heritable, he has not, so far

as we are aware, shown that any of them are inherited in

strict Mendelian fashion as is the defect with which we

are concerned. We are therefore led to believe that this

character in our stock has not been induced by nutritional

or other environmental causes, but that it is due to a

factor mutation similar to those which have been studied

So thoroughly in domesticated and experimental animals

and plants in recent years, and for which there is at pres-

ent no assignable cause.

2. It might perhaps be assumed that the palsied indi-

viduals are due to unfavorable uterine conditions and con-

sequent abnormal fetal development. The occurrence of

‘“‘runts’’ in swine and in other animals which produce

large litters show that the uterine conditions are not the

same for all the individuals in a litter. Some doubtless

ave a poorer maternal blood supply than others, or they

may be crowded, or twisted into a position unfavorable

for growth. That these are not factors in the present

case seems demonstrated, however, by the fact that the

palsied animals are on the average fully as large and well

developed at birth as their litter mates (see Table IV).

3. The necessity of inbreeding the original stock a

order that the recessive palsy condition should appear 1s

apparent; but it might be maintained that this inbreeding

142 THE AMERICAN NATURALIST [ Vou.. LIV

in itself was perhaps the cause of the disease. All mod-

ern studies on inbreeding, however, seem to strengthen

the conclusion that while inbreeding may, by the ‘‘concen-

tration” or production of unfavorable character com-

binations, and particularly by the loss of important phys-

iological factors which are necessary to the well being of

the individual, result in lowered vitality and in the ap-

pearance of various defects, it is nevertheless a means

rather than a cause of bringing these into expression.

Further evidence that the palsy was not produced by

the inbreeding as such is furnished by the fact that the

lines in which it appeared were no more inbred than many

other lines that have been carried on in the laboratory in

connection with other problems, but in which no tendency

to such a defect has manifested itself. Our whole stock,

in fact, of some 2,200 litters and over 5,000 offspring has

all descended from not more than 50 original animals,

and as has already been stated, there is reason to believe

that some of these were related. In order to show the

intensity of the inbreeding in some cases, it may be men-

tioned that in one experiment a male was bred back to

his daughters for four successive generations, and with

no apparent ill effects. Inbreeding as a predisposing

cause may therefore be ruled out.

4. The spasms which form the characteristic reaction

of the palsied animals are clearly due to lack of nervous

control, especially when voluntary movements of the legs

are attempted, and under excitement. It may therefore

be that there is some heritable defect of the central nerv-

ous system. Examinations which have been made for us

by Dr. C. H. Bunting have, however, shown no lesions of

the nervous system to which these effects could be at-

tributed.

5. Disturbances of some of the glands which supply

internal secretions are known to produce nervous irri-

tability and conditions of spasm and tetany. Partic-

ularly is this true of the parathyroid, and some of the

symptoms accompanying disturbances of this gland re-

semble to a certain extent, at least superficially, the con-

No. 631] CONGENITAL PALSY IN GUINEA-PIGS 143

ditions in the guinea-pigs. Dr. Bunting is making a study

of this phase of the question, and reports that ‘‘thus far

the only anatomical difference between affected and nor-

mal animals of the same litter, that has been noted, has

been a definite hypoplasia of the parathyroid tissue in the

abnormal animals.’’ He will, however, report more fully

later.

For the present, therefore, we must be content with the

statement that the congenital palsy is due to a factor mu-

tation, the cause of which is unknown; nor do we under-

stand what its action is on the animal organism to pro-

duce the nervous symptoms described.

Discussion

A number of nervous defects are known in man and the

lower animals which have certain points of resemblance

to congenital palsy as it occurs in our guinea-pigs, but we

have been unable to find any condition which agrees

closely enough in details so that the two could be consid-

ered identical. A list of some of these follows, with brief

mention of resemblances and points of difference.

Pigeon.—Tumbling in pigeons appears to be due to lack

of nervous control of the muscles and associated to some

extent with certain voluntary efforts. This is especially

noticeable in Parlor Tumblers, which turn back somer-

saults when they attempt to fly. The condition is greatly

exaggerated by excitement. Further similarities are that

the tendency to tumble increases with age, to a certain

point at least, and that it behaves in a general way as a

recessive to normal flight, though the crossbreds are usu-

ally intermediate and there appears to be no sharp segre-

gation in F,. Tumbling, unlike congenital palsy, does

not seem to affect the legs particularly, and does not in-

terfere with normal life processes sufficiently to be lethal

if the birds are given adequate protection and care. ce

The condition described by Riddle (1918) as ataxia in

pigeons would appear to correspond very closely in symp-

toms to the more pronounced cases in Parlor Tumblers.

144 THE AMERICAN NATURALIST [Vou. LIV

There would appear to be also some resemblance to the

tumbling and shaking of the Fantail (French Trembleur).

Riddle states that the ‘‘character is, with some irreg-

ularities, a Mendelian recessive.” His inference that it

may have been produced by ‘‘reproductive overwork’’

seems inconclusive.

In connection with experiments on the homing ability

of pigeons Hurst (1913) speaks of obtaining ‘‘feeble-

minded’’ birds, as follows:

Results show that incompetent or feeble-minded pigeons may be

bred from competent or intelligent parents, and it is interesting to find

that feeble-mindedness behaves as a recessive character in birds as well

as in man

Foriunaiely, or unfortunately, it is much more difficult to get off-

spring from the feeble-minded in Pigeons than in

Mouse and Rat.—The well-known ee ha of the

waltzing mouse is probably of the nature of a nervous

disorder, either directly or indirectly. It is a simple

Mendelian recessive.

Bonhote (1912) at a meeting of the Zoological Society

of London ‘‘exhibited living specimens of rats (Mus

rattus) which he had bred in the course of his exper-

iments, and which showed the ‘waltzing’ character well

known in a variety of the domestic mouse, but which had

not hitherto been recorded in rats.’’

-Rabbit—We have in our possession a rabbit which is

now several years old, and which has since it was young

exhibited characteristic circus movements, or ‘‘waltzing,”’

very similar to the activities of the waltzing mouse. This

character appeared sporadically and we have been unable

to find that it is heritable, even though we have repeat-

edly bred this male’s daughters to their own brothers and

back to him. He appears normal in other respects except

that one eye seems somewhat distorted, which may have

something to do with his behavior. This case differs

from the waltzing mouse in that it is probably not her-

itable, and certainly is not a simple Mendelian recessive.

Guinea-Pig.—Some of the various defects in guinea-

No. 631] CONGENITAL PALSY IN GUINEA-PIGS 145

pigs described by Stockard and ascribed to the inherited

effects of alcohol treatment of the original parents, have

symptoms somewhat resembling those of congenital

palsy. His descriptions of the symptoms and behavior of

his animals are, unfortunately, inadequate for detailed

comparison of our cases with his. One point seems cer-

tain, however, namely, that while the symptoms exhibited

by our animals are relatively constant, he has obtained

in his affected lines a great variety of nervous defects and

anatomical abnormalities, all of which he attributes to

degeneration caused by the alcohol. To mention those

relating to nervous disorders, he speaks of the defective

animals as being ‘‘very shy and excitable’’ (1912, p. 22),

and says further: ‘‘it is a point of some interest that all

of the young animals that died showed various nervous

disturbances, having epileptic-like seizures, and in every

case died in a state of convulsion.” Again (1913, p. 663)

he speaks of an animal which died when one day old,

‘“‘having been in a constant tremor since its birth; an-

other lived for nine days but whenever it attempted to

walk it was seized with spasmodic contractions; the third

specimen exhibited the same nervous manifestation and

was completely eyeless.’? In a later paper (1916, p. 15)

he says that paralysis agitans is very common among the

F,, F,, and F, animals, apparently applying this term to

some of the symptoms mentioned in earlier papers, and

adds that ‘‘paralyzed limbs are often observed, the ani-

mals being unable to stand or walk.”

While some of the above symptoms approximate those

of congenital palsy, they seem to partake for the most

part either of a general nervous irritability or else of a

definite paralysis. Furthermore, while Stockard bases

his conclusion that the general defect that produces these

various conditions is hereditary on the fact that they con-

tinue to appear in his treated lines, but not in the parallel

control lines, he has not so far as we are aware, found any

tendency Pe the condition to be inherited in any definite

manner or proportions conformable with Mendelian rules.

146 THE AMERICAN NATURALIST — [Vow LIV

It is not clear, however, that he has made any systematic

matings in an endeavor to ascertain this point.

While we do not mean to imply that in Stockard’s ex-

periments the initiation of the various defects and abnor-

malities he describes may not have been due to the alcohol

treatment, it is nevertheless of interest to note that these

same defects and abnormalities appear from time to time

in our normal stock. We can, in fact, match his condi-

tions—almost case for case for all that he has described—

with offspring of our stock that has had the best care we

could give it. That our stock is as a whole in no way

degenerate is indicated by its prolificacy (average size of

863 litters = 2.71), its low mortality rate, and the fact

that our animals are if anything above the general run

of guinea-pig stock, as attested by reports from the

various hygienic and other laboratories to which our sur-

plus has gone. The point of special interest is that these

various abnormalities are entirely independent of the

congenital palsy, for they appear no more frequently in

the ‘‘palsy’’ stock than elsewhere.

Goat.—Hooper (1916) has described a case in goats

which has some strong points of resemblance to the be-

havior in the guinea-pigs, although in the former the con-

ditions are not so severe as to cause the death of the ani-

mals. He says:

There is a peculiar breed of goats raised in central and eastern

Tennessee. When suddenly frightened the hind legs become stiff and

the animal jumps along until it recovers and trots off normally or if

greatly frightened the front legs become stiff also and the goat falls to

the ground in a rigid condition. They have received the name of

“ stiff-legged ” or “sensitive ” goats.

Experiments were to be begun on the inheritance of the

character, but results have not to our knowledge been

reported.

Sheep.—A condition in sheep with symptoms somewhat

resembling those in ‘‘palsied’’ guinea-pigs and even more

the goats just mentioned is described by Jones and

Arnold (1917). Affected animals are able to walk, but

No. 631] CONGENITAL PALSY IN GUINEA-PIGS 147

when excited they run in a stumbling fashion and finally

the legs stiffen out and the animal falls on its side. This

affection is, however, not heritable, but has been demon-

strated by these investigators to be due to nutritional

disturbance, caused by a diet consisting too largely of

pampas grass.

When there is a liberal amount of grass the actual number of eases is

small. After a long continued drought when the fine grass supply is

short, the number of sick animals is large. The mortality varies con-

siderably, young sheep seeming to suffer most.

Man.—Among the numerous confusing and complex

nervous disorders in man there are several with certain

similarities to congenital palsy of the guinea-pigs. We

have not attempted an exhaustive survey of this field, but

list a few of them with remarks on resemblances or dis-

similarities. In some cases it is difficult to tell whether

the descriptions refer to the same or different affections,

the synonymy not being clear. The comparison with con-

genital palsy is also often uncertain owing to the indef-

initeness of the descriptions of symptoms. No attempt

at completeness has been made in the matter of refer-

ences, citations being added merely for giving authority

for the statements made.

Feeble-mindedness (Davenport, 1911), epilepsy (Dav-

enport, 1911; Davenport and Weeks, 1911; Weeks, 1915)

and some forms of insanity (Davenport, 1911) resemble

congenital palsy in being definitely recessive in inher-

itance, but show no close similarities in other symptoms.

SIMILARITIES DIFFERENCES

Paralysis agitans (Parkinson’s disease). (Curschmann, 1915.)

Tremor of muscles. Appears late in life.

Progresses in severity with course Constant trembling.

of disease. More often in male sex.

Habitual tremor. (Curschmann, 1915; Dana, 1887.)

Oceurs early in life. Not congenital.

Subsides when patient is at rest. Affects mostly hands and head.

Increased by voluntary movements Shallow oscillations

and excitement. May Gieappest.

pega to be hereditary? (Oc-

ostly in neuropathically

iaaa individuals.)

148 THE AMERICAN NATURALIST [Von. LIV

Familial tremor, (Curschmann, 1915.)

Heredit Not congenital.

Usually sain in youth. Sometimes improvement.

rest

Affects mostly arms and legs.

Progressive in its course.

Treatment powerless.

Tetany. (Curschmann, 1915.)

‘“<Tntentional’’ in some eases. Tonie spasms.

ha induced = stimuli. Hands and arms mostly.

often attacked. Spasm duration long.

Teele tetany incurable. Infection indicated.

eee lenticular degeneration. (Wilson, 1912; Spiller, 1916.)

Bilateral. Not congenital. .

ye both extremities. Accompanied by cirrhosis of liver?

Increase with volitional movement. Tonic spasticity of face and limbs.

Reflexes bie

Always

Familial.

Aplasia axialis extra-corticalis congenita. (Merzbacher, 1908; Batten and

Wilkinson, 1914.)

Congenital or in first three months, Affects chiefly males.

Hereditary. Slowly if at all progressive.

Symptoms constant.

Not so fatal.

Paramyotonia congenita. (Eulenberg, 1886.)

Congenital. Tonic spa

Hereditary. Not PENE bilateral

Last for

A aie hea diina.

It is clear that none of the above-mentioned conditions

can be considered as identical with congenital palsy. The

most common similarity is that several of them are known

to be recessive in inheritance, but they all differ in other

symptoms. Congenital palsy differs from any of the

_ other conditions in being definitely congenital and run-

ning a brief course terminating in death at an early age.

In conclusion it may be pointed out that while the data

may never be sufficiently complete in man, it may be pos-

4 According to Spiller the conditions attributed to disease of the lenticular

nucleus are numerous, including the pseudo-sclerosis of Westphall and

Striimpell, Huntington’s Wak Parkinson ’s disease, and a number of others.

No. 631] CONGENITAL PALSY IN GUINEA-PIGS 149

sible in animals where breeding experiments can be con-

ducted, to use the inheritance method for separating nerv-

ous diseases in which the symptoms are so similar as to

be confusing, or even identical. For example, let us sup-

pose that a recessive neurosis similar to congenital palsy

should appear in another line of guinea-pigs. If animals

heterozygous for it were mated to heterozygous individ-

uals of our stock and they produced affected offspring in

a one-to-three ratio, it would be good evidence that we

were dealing with the same heritable trait in both strains.

If, however, the disease in the new line was genetically

different, a different ratio of offspring would be expected,

presumably nine normal to seven neurotic individuals,

assuming that there was no linkage of the two genes con-

cerned. It is possible that even in man when the family

histories are sufficiently complete the method of genetic

analysis may help in the differentiation of neuroses char-

acterized by symptoms which are confusingly similar.

SuMMARY

1. A definite neurosis appeared in our guinea-pig stock

in 1914, characterized by clonic spasms, particularly of

the legs. When in a spasm the animals lie on their sides

in a helpless condition. This state is induced by various

stimuli, but especially by those of a sharp auditory

nature, and also by attempted volitional movements of

the legs.

2. The affected animals are fully up to average weight

when born, and appear to be normal in all other respects.

While different individuals vary with respect to the in-

tensity of the symptoms at birth, they are always easily

distinguished from normal young, and in all cases the

disease runs a short progressive course, terminating 1m

death within about two weeks at most.

3. This defect, which we have called congenital palsy,

is definitely heritable. It is a simple Mendelian recessive,

and normal and affected offspring are produced by two

150 THE AMERICAN NATURALIST [Vou. LIV

heterozygous parents in the ratio of three normal to one

affected. :

4. It has been shown that heterozygous animals mated

to normals produce offspring of the same classes as them-

selves in equal numbers. Furthermore, it has been

proven that homozygous dominants can be extracted from

heterozygous parents and that they show no more tend-

ency to transmit the disease than individuals of normal

unrelated stock.

5. Heterozygous animals are entirely normal in their

reaction and can be told from the homozygous only by

breeding tests. |

6. A survey of the literature relating to nervous de-

fects in man and other animals does not reveal any con-

dition corresponding exactly to congenital palsy. Some

of the conditions in pigeons, rodents and in man are sim-

ilar in that they are recessive in inheritance.

REFERENCES

Batten, F. E., and D. Wilkinso

1914 Un usual Type of Hereditary Disease of the Nervous System

(Pelizaeus-Merzbacher), sat PR Axialis Extra-corticalis Con-

n enita. Brain, Vol. 36, pp. 341-351.

Bonhote, J. L.

9 [On Waltzing Rats.] Proc. Zool. Soc. Lond., March, 1912,

pP. 6, 7.

Curschmann, H. (Editor.)

1915.. Text-book on Nervous Diseases. English edition edited by

Charles W. Burr. Philadelphia, 2 vols., xx + 11

Dana, C. L.

1887. Hereditary Tremor, a Hitherto Undescribed Form of Motor

Neurosis. Amer. Jour. Med. Sci., Vol. 44, p. 386.

Davenport, C. B

1911. Heredity in Relation to Eugenies. New York, Henry Holt and

1911, A “om Study of Inheritance in Epilepsy. Jour. Nerv. and

Mental Dis., Vol., 38, No. 11, pp. 641-670. (Bull. No. 4,

estate Record Office, pp. 1-30.)

Eulenberg, A.

1886. Über eine familiäre durch 6 Generationen verfolgbare Form

kongenitaler Paramyotomie. Neurol. Zentralbl., p. 265.

Hooper, J. J.

1916. A Peculiar Breed of Goats. Science, N. S., Vol. 43, No. 1112,

p. 571

No. 631] CONGENITAL PALSY IN GUINEA-PIGS : 151

Hurst, ©. C,

1913. British Association for the Advancement of Science. Birming-

ham Meeting. 1913. Visit of Sections D, K, and M, to the

Burbage Experiment Station of Applied Genetics, on Tuesday,

September 16. Notes on the experiments by the Director. 8 pp.

Jones, F. S., and J. F. Arnold.

1917. Stagger in Sheep in Patagonia. Jour. Exper. Med., Vol. 26,

805-823, 4 pls.

Merzbacher, k

1908. Weitere Mitteilungen über eine hereditiir-familiiire Erkrankung

es Zentralnervensystems. Med. Klinik., Bd. 4, pp. 1952-1955.

Spiller, W. G.

1916. The Family Form of Pseudo-sclerosis and other Conditions At-

tributed to the Lenticular Nucleus. Jour. Nerv. and Mental

Dis., Vol. 43, pp. 23-26.

Stockard, C. R.

1912. An Experimental Study of Racial Degeneration in Mammals

Treated with Alcohol. Arch. Internal Med., Vol. 10, pp. 369-

398

1913. The Effect on the Offspring of Intoxicating the Male Parent and

the Brae of the Defects to Subsequent Generatio ions.

1916. The Hereditary Transmission of Degeneracy and Deformities by

the Descendants of Alcoholized Mammals. Interstate Med.

Jour., Vol. 23, No. 6, pp. (of separate) 1-19.

Riddle, Osear.

1918. A Case of Hereditary Ataxia Ce in wr aly tie Proc. Soc. Exper.

Biol, and Med., Vol, 15, pp.

Weeks, D. F.

1915. Epilepsy with Special Reference to Heredity. Jour. Med. Soc.

New Jersey, pp. (of separate) 1-8.

Wilson, S. A. K.

1912, Progressive Lenticular Degeneration, a Familial Nervous Dis-

ease Associated with Cirrhosis of the Liver. Brain, Vol. 34,

pp. 295-509

ANIMAL LIFE AND SEWAGE IN THE GENESEE

RIVER, NEW YORK*

FRANK COLLINS BAKER

~ UNIVERSITY oF ILLINOIS

Ir is a hopeful sign of permanent improvement in our

rivers and streams when commonwealths and municipali-

ties turn their attention to the condition of these waters

and provide means for their purification where they have

previously been contaminated by sewage, refuse, or chem-

icals.

It has been known to biologists for many years that

sewage and chemicals were inimical to the life inhabiting

these waters, but political bodies have been slow to realize

or to admit that the pouring of millions of gallons of

crude sewage had any effect on the animal life living

in such waters. It is even probable in some cases that

those in authority cared little about the effect of such

contamination, if it provided an easy and economical

method of disposing of the sewage. The damage to fish

and other aquatic life has not been realized by the en-

gineers in charge of such work and hence this class of

scientific men has not protested or sought a better

method, at least not until recent years. The work of the

various conservation commissions of the several states,

as well as the efforts of natural history societies, univer-

sities, and private individuals, have brought into promi-

nence the danger from stream pollution and have awak-

ened widespread interest in this important subject.!

In Illinois, careful studies are in progress by the Nat-

* Contribution from the Museum of Natural History, University of Illinois.

1See in this connection, Henry B. Ward, ‘‘The Elimination of Stream

Pollution in New York State,’’ Trans. Amer. Fisheries Soc., XLVIII, pp.

1-25, 1918.

152

No. 631] ANIMAL LIFE AND SEWAGE 153

ural History Survey under the direction of Dr. S. A.

Forbes, for the purpose of ascertaining the effect in the

Illinois River of the large volume of polluted water from

the Chicago Drainage Canal, into which all of the sewage

of the city of Chicago is discharged.2 In other places,

studies of a similar character are being carried on.

In New York State, the Genesee River, at Rochester,

has afforded a striking example of stream pollution, of

the effect of this pollution on the animal life in the river,

and of the final return of this life after the amount of

pollution was notably reduced. It has been the writer’s

good fortune to visit Rochester every two or three years

(sometimes oftener) and to be able to study the condition

of the Genesee River during a period of nearly thirty

years. Collections were made before, during, and after

pollution, permitting comparisons to be made of the life

in the river during these several periods of varying con-

ditions.

The animal life in a body of water has been little used

as an indicator of the degree of pollution. Fish, espe-

cially young fish, have been used and are good indicators

because they cannot live in water polluted to any large

degree. The relative resistance of different species of

fish has been well shown by Shelford in a recent paper.

The writer is convinced that mollusks are also good in-

dicators of degrees of pollution. The intimate relation

of fish to the propagation of river mussels (Unionide),

so largely used in the manufacture of pearl buttons, is

also seriously affected by stream pollution.

The polluted portion of the Genesee River studied

(which was also the place of maximum pollution) lies

below the lower falls (Driving Park Avenue bridge), a

large sewer discharging some distance below these falls

just above the spot known locally as Brewer’s landing,

near Norton Street, on the east side of the river. Several

2? See Forbes and Richardson, ‘‘Some Recent Changes in Illinois Biology,’’

Ilinois Natural History Survey, Bulletin, XIII, pp. 139-156, 1919.

3 Bull, XIII., Ill. Nat. Hist. Surv., pp. 25-42, 1918.

154 THE AMERICAN NATURALIST [Vou. LIV

other sewers emptied into the river at the north end of

Maplewood Park on the west side of the river. The

stream for several miles below these points resembled

thick, dirty, greasy dish water, a heavy scum covering

the surface of the water as well as the shore and any

objects in the water.

At the time of maximum discharge, sewer outlets also

entered the river both above and below the falls and

The photograph was taken in the summer = e The white Aen in the

background are from the trunk line sewer east siđe of t er near

Norton Street. The light streak in the pene is the sewage cane oo outlet

on the west side of the river near the lower falls. A small island on the right

side of the picture hides a part of the sewage in the water on the east side of

be river. This place is six miles up the river from the mouth.

many manufactories also contaminated the water by dis-

charging chemicals and refuse into the river. At the

present time there are no sewers entering the river above

the falls. There are two sewer outlets at the northern

end of Maplewood Park, one from the residence section

west of the river (Dewey Avenue section) and one from

the Eastman plant. Sewage is also discharged into the

No. 631] ANIMAL LIFE AND SEWAGE 155

river at Charlotte near the mouth of the river. This,

however, does not enter into the present discussion. It

has not been possible to ascertain the amount of sewage

entering the river during the period of maximum dis-

charge, but at the present time the approximate quantity

of sewage discharged is one-eighth cubic foot per second

(data from Rochester engineering department). This

is a comparatively small amount which apparently has

little or no effect on the animal life in the river. On the

contrary, it may provide food for some organisms.

Sewage was turned into the Genesee River about the

year 1820. Collections of molluscan life were made in

July, 1897, and nine species were obtained, as noted

below:

Musculium transversum Physa gyrina

Musculium partumeium Physa sayi

Bythinia tentaculata Physa heterostropha

Galba catascopium Galba caperata (rare)

Planorbis trivolvis

Previously, in 1892-1895, collections had been made

which included about the same species as noted above.

Individuals were notably abundant, thickly covering the

rocks and the shore. At the time the above mollusks were

collected it was noted that the sewage was increasing in

volume and pollution was becoming more noticeable. It

was predicted at this time that in a few years the fauna

would be exterminated by the foulness of the water.

The river was visited and examined in 1898, 1900, 1901,

1904-1907, 1908, 1910, 1913, 1915-1917, and 1919.4 Each

year it was noted that the pollution of the water was

rapidly increasing. In 1907, the water-breathing mol-

lusks, Musculium and Bythinia, had succumbed and none

could be found. The air-breathers, Galba, Planorbis,

Physa, still held out, though reduced in number of indi-

mi i riter: ‘‘The Molluscan Fauna of

Won oe KES PE Saar iau, pe eh

**The Molluscan aia of the Genesee River,’’ AMER. NAT, XXXV, pp.

659-664, 1901,

156 THE AMERICAN NATURALIST [Von LIV

viduals. An examination made in 1910 failed to discover

a single living mollusk of any species. Apy e

water had reached such a state of concentrated polati

that even the air-breathing mollusks, which normally

come to the surface to take in free air, could not adapt

themselves to this unfavorable environment and were

either killed or compelled to migrate down the river to a

point where the pollution was not so great, a distance

of several miles. During the following two or three

years the river was visited but no mollusks could be

found.

On March 17, 1917, a large part of the city’s sewage

was diverted to the Irondequoit sewage disposal plant

located on the shore of Lake Ontario near the Durand-

Eastman Park. Here an average of 32 million gallons

of sewage are treated daily, and the treated sewage dis-

charged into Lake Ontario at a distance of 7,000 feet

from shore in water 50 deep (vide city engineer’s state-

ment). It may easily be seen that when this large amount

of sewage, untreated, was discharged into the Genesee

River, it could not but render the water totally unfit for

animal life and a menace even to the inhabitants who vis-

ited the beautiful parks bordering both sides of the river.

The result of the diminution of the amount of sewage

discharged into the river has been that the fauna has re-

turned and has rapidly taken possession of the favorable

environments which were in use previous to the maximum

period of pollution. Collections made in September,

1919, contained the six species noted below:

Musculium transversum Bythinia tentaculata

Planorbis trivolvis Galba catascopium

Physa integra

Physa oneida (previously reported as heterostropha)

It will be noted that practically the same species re-

turned to the Maplewood Park section of the river that

lived here before the polluted water exterminated the

fauna, indicating, probably, that they migrated up the

river from the less affected water below.

No. 631] - ANIMAL LIFE AND SEWAGE 157

Few data are at hand indicating how far the polluted

water must flow before it can purify itself enough to be-

come favorable for animal life. In the Illinois River, life

is being affected by the Chicago sewage at Peoria, a dis-

tance of 110 miles from the source of infection. A recent

study of the Salt Fork of the Vermilion River, into which

the sewage of Champaign and Urbana is discharged, in-

dicated that the polluted water was inimical to mollusean

life for a distance of 14 miles in which no living mollusks

were found, and one must pass down the stream for a

distance of nearly twenty miles before a normal mussel

fauna can be found.

In the Allegheny River, Ortmann found that whole

stretches of the stream and some of its tributaries had

been made into a desert by pollution, principally in the

form of chemicals from the numerous mines situated in

this part of the State. Ortmann remarks that ‘‘with re-

gard to the animal life in our rivers, sewage does not

seem to be harmful; on the contrary, certain forms

(fishes, crawfishes, mussels) seem to thrive on it’’ (p. 97).

This is probably true in a case where water is but slightly

contaminated; but in streams where pollution by sewage

is greatly concentrated (a condition reached sooner or

later in all streams used for sewage disposal) it is cer-

tainly inimical to the forms of life mentioned. It is very

true that a stream polluted by chemicals soon becomes

„destitute of the larger forms of animal life (if, indeed, not

all life) and in such waters the return of life will be very

slow and in many cases it may be impossible for life to

return on account of the chemicals which cover the bot-

tom and shores.

In the case of the Genesee River, we have a striking

example of the history of a polluted stream and its effect

on the animal life. Previous to the discharge of sewage

into the stream there was a varied molluscan fauna very

numerous in individuals. In the course of eleven years

the gill-bearing mollusks were forced out and after a

lapse of fourteen years all molluscan life ceased to live

158. THE AMERICAN NATURALIST [Vou. LIV

in this portion of the river. Seven years later, the

greater amount of sewage was diverted to another outlet.

Two years after this diminution of pollution we find that

the mollusean fauna has returned in as great number of

individuals as were found there before pollution began.

In other words, it required but two years (possibly less,

as the river was not examined in 1918, one year after the

conditions changed) for the river to become pure enough

to provide a favorable environment for mollusean life.

It has been reported that the sturgeon is again resorting

to the lower portion of the river for spawning purposes,

after an absence of several years, due to the heavy pollu-

tion of the water. The rapid return to a favorable con-

dition is partly due to the lower falls in the river which

abundantly aerates the water before it is mixed with the

small amount of sewage now flowing into the stream.

It may be affirmed without successful contradiction

that wherever sewage pollution occurs, sooner or later

the animal life will be affected, and finally driven out.

As this condition seriously concerns our food and game

fishes, which form so large a part of the meat food of our

population, it is a situation that demands immediate at-

tention and early remedy. That the fauna recovers so

quickly after pollution ceases is a matter of great interest

and satisfaction, showing what favorable returns may be

expected when these matters are taken up in all earnest-

ness by municipalities and commonwealths.

PoLLUTION IN THE GENESEE RIVER

Since writing the above account of the effect of sewage

pollution on the mollusean life of the river, Mr. John F.

Skinner, principal assistant engineer of the Rochester

Department of Engineering, who has been connected with

this department for upwards of twenty-eight years, has

kindly read the paper and has indicated several inac-

curacies in the historical matter, besides adding much in-

formation of value concerning the sewage disposal of the

city. The following data are all supplied by Mr. Skinner:

No. 631] ANIMAL LIFE AND SEWAGE 159

Rochester was settled in 1812, incorporated as a vil-

lage in 1817, and as a city in 1834. The first sewers were

built about 1820. All of the city west of the river and

roughly everything within a mile east drained into the

river. A sewer 4 by 6 feet in diameter was in operation

in 1863. In 1896 nine main outfalls were in operation,

five on the west side and four on thé east side. In 1897

the west side trunk sewer nine feet in diameter was put

in operation. Four of these sewer outfalls are below the

lower falls, two being above the point at which the mol-

luscan studies were made.

Fourteen stormwater sewers overflow into the river

above the lower falls. Refuse and waste matter, both

liquid and solid, enter the stream from a tannery, gas

works, breweries, garbage disposal plants and some other

manufacturing plants. The breweries do not now con-

taminate the water as formerly. This additional pollu-

tion is sometimes more harmful to animal life than the

Sewage itself. In March, 1917, the main (Irondequoit)

Sewage disposal plant was put in operation on the shore

of Lake Ontario. The outfall to this plant intercepts the

dry weather flow of all of the sewer outlets mentioned

above, except the Lake Avenue or Dewey Avenue outlet

on the west side about 6,000 feet below the lower falls.

There is also a large outlet further north, down the river,

from the Eastman Kodak plant and adjacent territory.

The overflows from the east and west side trunk sewers

enter below the lower falls, as will also that from the

Lake Avenue sewer after the Maplewood plant is com-

pleted. The clarified effluent of the last mentioned plant

will also enter the river, but the major portion of the

Solids (contained in the sludge) will be pumped across

the river to the east side interceptor.

In a report issued in 1913,° Mr. George C. Whipple,

consulting engineer, has published much valuable infor-

mation relating to the effect of the sewage pollution on

5**Report on the Sewage Disposal System of Rochester, N. Y.,’’ by

Edwin A. Fisher, city engineer. See pages 179-200.

160 THE AMERICAN NATURALIST [Vou. LIV

the river and on some of the animal and vegetal life.

This study was made in 1912 when the pollution was at

its maximum and during the period when mollusean life

had disappeared from the upper part of the river below

the lower falls. The dissolved oxygen in the lower river,

below the trunk line sewer, in July and August when the

temperature was high and the water low, varied from 5

to 41 per cent. of saturation. 'The water at the bottom of

the river almost always contained less oxygen than that

at the surface. This condition prevailed to within a short

distance of the mouth of the river when the reverse was

true, this change being due to the backflow of the well-

oxygenated water from Lake Ontario. Near the east side

trunk sewer, which is about half a mile below the lower

falls, the percentage of saturation varied from 5 to 60

between July 1 and August 13. On August 13, the per-

centage of saturation between the east side trunk sewer

and a point two and a half miles from the lake (a distance

of about three miles) did not exceed five per cent. This

area includes the shores examined for the Mollusca.

The percentage of dissolved oxygen saturation was usu-

ally higher at the surface than at the bottom of the river,

the heavier parts of the sewage falling to the bottom and

forming sludge banks. The percentage of dissolved oxy-

gen also did not vary directly with the amount of evident

pollution, for on a day in July when the most disagree-

able conditions existed for a mile and a half below the

east side outlet the dissolved oxygen at the surface varied

from 40 to 70 per cent.

A study of the plankton of the river indicated that

near the source of pollution, 54 miles above the mouth of

the river, there were on the average in July and August, ©

1,650,000 bacteria, 156 algæ, 209 Protozoa, and 57 Crus-

tacea and Rotifers per cubic centimeter. At the mouth

of the river the figures for these organisms per c.c. stood

as follows: 67,000; 363; 77; 233. It is unfortunate that

no discrimination was made between the foul water alge

and protozoa and those normally inhabiting pure water,

No. 631] ANIMAL LIFE AND SEWAGE 161

which would have made a difference in the number from

the standpoint of pollution. This has been done by

Forbes and Richardson in their studies of the Illinois

River pollution.®

A comparison of the report made by Engineer E.

Kuichling, Feb. 1, 1907 (1913 report, pp. 5-42) with that

of Mr. Whipple made in 1912 shows in a striking manner

the rapid increase of polluted conditions, the former au-

thor describing conditions as not very bad (pp. 10-11)

while the latter author, five years later, describes the con-

ditions as very bad (p. 182). It was between these dates,

1907 and 1912, that the molluscan fauna disappeared and

it is apparent that the distinct increase in toxicity is in-

dicated from these several angles of vision.

It should be stated in connection with the ill effects of

sewage pollution that it affects the population in an indi-

rect manner not usually recognized by sanitary engineers

who have not interested themselves in the problem of fish

culture. Such places as the six miles of shallow shore

bordering the Genesee River are the breeding and feed-

ing ground of such valuable food and game fish as the

sturgeon, black bass, sunfish, suckers, bullheads, pickerel,

pike, ete., and the young of these and other fish spend a

large part of their life in this kind of a habitat, to later

migrate into the open lake.

€‘‘Studies on the Biology of the Upper Illinois River,’’ Bull. Illinois

State Laboratory of Natural History, IX, pp. 481-574, 1913.

ALTERNATIVE EXPLANATIONS FOR EXCEPTIONAL

COLOR CLASSES IN DOVES AND CANARIES

DR. C. C. LITTLE

CARNEGIE INSTITUTION OF WASHINGTON

Doves and canaries have been shown to possess certain color

factors which are sex-linked in inheritance. The behavior of

these factors leads one to the conclusion that, unlike Drosophila,

cats and man, the female and not the male is the homozygous sex.

In this respect they resemble Abraxas, poultry and the domestic

pigeon.

In both doves and canaries, however, there occur exceptional

color classes in certain matings where the sex-linkage of the

factors in question manifests itself. To explain the appearance

of these exceptional color classes, Sturtevant (1912) (in canaries)

and Bridges (1913) (in doves) have suggested that the principle

of partial sex-linkage is involved.

Later, Bridges (1916), in discussing the phenomena of non-

disjunction in Drosophila, has reviewed briefly other forms to

which he considers non-disjunction may apply and among these

mentions doves and canaries as follows:

(Doves—p. 157) Exceptions to the inheritance of blond and the dark

types of pigeons have been explained as partial sex-linkage (Bridges,

1913) but non-disjunction offers an alternative hypothesis which seems

plausible.

(Canaries—p. 158) Exceptions to sex-linkage in the inheritance of

pink versus black eye colors have been reported (Durham and Marryatt,

1908). These exceptions are explainable by non-disjunction or by par-

tial sex-linkage.

In this papér an attempt will be made to show that the hypoth-

esis of partial sex-linkage and of non-disjunction expect certain

results from the crosses made, which have not been reported and

in the case of non-disjunction might, in addition, be fairly con-

sidered as involving sterility of certain color classes—a phenom-

enon not yet reported in any of the forms in question.

A further effort will be made to explain the observed facts on

an hypothesis of factorial change which involves neither a break

162 ©

No. 631] COLOR CLASSES IN DOVES AND CANARIES 168

in sex-linkage nor non-disjunction, and which expects no unusual

sterility nor the appearance within the crosses made, of other un-

recorded exceptions to the normal relation between phenotypic

color classes.

We may take up in order the three hypotheses of partial sex

linkage, non-disjunction and factorial change and may compare

them on the basis of the experimental results obtained.

PARTIAL SEX-LINKAGE

1. Doves.—The normal result obtained when white male and

colored female ring doves are crossed, is colored males and white

females. This may be explained as follows: Let W equal a factor

for the production of colored plumage and w, a factor allelo-

morphic to it for the production of white plumage. The male is

FFMM, the female FFMm in formula. W is linked with M in

inheritance.

te Male wwFFMM Colored Female WwFFMm

Formin wa gametes wFM WFM and wFm

Zygotes obtained: oe E males

wFFMm = white females

In addition, however, exceptional colored females are produced

infrequently and have been recorded by Staples-Browne (1912),

and by Strong (1912). These exceptional colored females have

been acounted for by Bridges (1913), as follows:

If in the female the sex-differentiating factor and the factor for

plumage color are placed close enough together in the same SEEE

to be linked, but not so close that linkage is complete “ crossing-over ”

would cause the two factors which entered in the same member of the

homologous pair of chromosomes to lie in different members and hence

to segregate to different gametes.

If this occurred we should have the following condition :

X Colored Female WwFFMm ] }

te Male wwFFMM WPM}

Prali gametes wFM

wen j commonly

wFM :

WFm } exceptionally

Zygotes formed: WwFFMM colored male

wwFFMm white female

WwFFMm colored female

wwFFMM white male

commonly .

* | exceptionally

164 THE AMERICAN NATURALIST [Vor. LIV

This would account for the exceptional colored females, re-

ported from this cross by Staples-Browne and by Strong. It also

expects an additional exceptional class—namely white males, and

these, though they should occur as frequently as do the colored

females, are conspicuous by their absence.

Further than this the hypothesis as just outlined supposes

that ‘‘crossing over’’ occurs in the heterozygous sex, between

chromosomes which correspond to the X and Y chromosomes of

Drosophila. This condition has not been observed in Drosophila

or in forms where a similar opportunity exists and it must there-

fore, be considered as entirely hypothetical and contrary to such

evidence as the most extensively investigated forms have given.*

2. Canaries.—In this form, the sex-linked inheritance of the

factor for dark-eyed color (P) having as an allelomorph pink

eye color (p) has been demonstrated by Durham and Marryatt

(1908) and reviewed by Sturtevant (1912). Here, however, as

in doves there is an unexpected color class which makes its ap-

pearance. The exceptional individuals are dark-eyed females

which oceur in a cross between pink-eyed males and dark-eyed

females where only dark-eyed males and pink-eyed females are

expected.

Sturtevant, in reviewing the case and in attempting to explain

it as the result of partial sex linkage says (p. 570) :

This hypothesis could be easily tested. If it is correct, then

the cross just discussed should, if large enough numbers be

reared, produce as many pink-eyed males as black females.’’ The

occurrence of such pink-eyed males has not been reported al-

though it seems almost certain that their appearance in this cross

would have been observed and mentioned by breeders did they

occur even very rarely. |

e may, therefore, say that should the missing color classes

appear in the dove and canary. matings as predicted by the

hypothesis of partial sex linkage, that hypothesis would have a

1 Cole and Kelley (1919) have studied the linkage relations between two

sex-linked factors in the domestic pigeon and have on the basis of consider-

able data, come to the conclusion that ‘‘ crossing over’’ occurs in the male

but not in the female. This result seriously invalidates partial sex-linkage

as a possible explanation for the exceptionally colored females in doves or

dark-eyed females in canaries. Furthermore, Goodale (1917) has shown that

‘‘erossing over’’ has occurred in the male and not in the female of the

domestic fowl—a point which also has a direct bearing on the work with

doves and canaries,

No. 631] COLOR CLASSES IN DOVES AND CANARIES 165

stronger claim to recognition as the correct one for explaining

the observed phenomena. Until such time, however, the explana-

tions of the observed exceptions by an hypothesis which requires

the appearance of an approximately equal number of exceptions

in the same cross, without any evidence that such exceptions exist

can not be considered as satisfactory. That this is the case for

doves has been suggested by Bridges in his more recent (1916)

paper on non-disjunction as already quoted.

NON-DISJUNCTION

In 1916 Bridges, in giving the data on which rests most of the

experimental proof of the existence of non-disjunction in Droso-

phila, suggested that the exceptions to sex-linked inheritance in

doves and canaries, might be the result of non-disjunction of the

sex chromosome.

If, however, the matings producing such exceptional individ-

uals are analyzed on the basis of non-disjunction, certain discrep-

ancies between expectations and actual results become evident.

These discrepancies suggest some fundamental difficulties in

applying the hypothesis of non-disjunction to the cases in ques-

tion. Thus if we assume as does Bridges that the sex formula in

both doves and canaries is FFMM in the male and FFMm in the

female we may represent the crosses made as follows: Theoret-

ically there may be either (a) no non-disjunction, or (b) non-

disjunction in the male, or (c) non-disjunction in the female. In

each mating we shall consider the three possibilities :

1. In doves:

White Male X Colored Female

White Male x ae. Bii

(a) If no non-disjunction; forms wFM WFM

gametes : wFm

(b) If non-disjunction in the male; wwF FMM WFM

orms gametes and — wFm

forms gametes: ; "m

In the three cases the zygotes formed will be as follows:

(a) If no non-disjunction:

(1) WwFFMM = colored males

(2) wwFFMm = white females

166 THE AMERICAN NATURALIST [Vou. LIV

This is the usual result obtained with, however, the addition of

exceptional dark females which we are trying to explain.

(b) If non-disjunction in the male: forms the following

zygotic classes:

(1) WwwFFFMMM= males? Colored? Probably die.

(2) WFM — = colored females? Sterile?

(3) wwwFFEMMm = white males (transmitting non- disjunction).

(4) wFm — = whites? Probably die.

It should be noted that non-disjunction in the male of Droso-

phila does not occur. Yet in pigeons the male is presumably the

‘‘homozygous’’ sex and this makes its chromosome condition in

respect to sex more closely analogous to the female Drosophila in

which primary non-disjunction does occur. The classes b(1)

and b(4) we may fairly suppose, fail to survive. The triple X

` condition of form b(1) is fatal in Drosophila as is the absence of

both X and Y seen in class b(4). The two classes b(2) and b(3)

are however, real difficulties. The sterility of class b(2), the ex-

` eeptional colored females has never been reported, as would un-

doubtedly have been the case, did it exist—just as their appear-

ance alone has excited comment and interest. Class b(3), more-

over, would certainly be white males and as we have already

seen there is no record of any such animals appearing in this

cross. Since these white males are the means of transmitting the

tendency for non-disjunction to further generations, their pres-

ence is necessary for the occurrence of secondary non-disjunction

and their absence is a serious handicap to the acceptance of the

hypothesis in this material.

(1) WwwFFFMMm = colored males Sages non-disjunction).

(2) wFM — = = white females? Sterile?

It will be seen that the exceptional colored females are neither

expected nor explained by this type of non-disjunction. Unless,

therefore, we are to assume that non-disjunction in doves is, in

almost all its fundamentals, different from the same process in

Drosophila, producing qualitatively different results, we must

agree that it fails to meet the experimental facts. If we do sup-

pose that it differs fundamentally, it may fairly be claimed that

no evidence of a conclusive nature either cytological or genetic

exists to lead us to say that non-disjunction is in any way involved.

No. 631] COLOR CLASSES IN DOVES AND CANARIES 167

Although the cross just considered is the one chiefly cited, it is

of interest to attempt to apply the three possibilities in question

to the reciprocal cross namely colored male X white female—

as follows:

Colored Male x bp Female

WWFFMM wFFMm

(a) If no non-disjunction; forms WFM «PM and

gametes: wim

(b) If non-disjunction in the male, WWFFMM and) (wFM and

forms gamete l )wFm

forms gametes wet

(a) No non-disjunction. A normal mating of this type gives

two classes of offspring as follows:

(1) WwF FMM = colored males.

(2) WwFFMm = colored females.

No exceptions have been recorded.

(b) Non-disjunction in the male: would expect four types of

zygotes as follows:

(1) WWwFFFMMM = colored males? Probably die

(2) WWwFFFMMm = colored mal ve Ghanaian & non-disjunction.

(3) wFM — ` = white females? Sterile?

(4) wFM — ` =— Whites? Probably die.

Did class b(3), sterile white females occur, their appearance

would undoubtedly have been noted and recorded. It should

further be noted that non-disjunction, namely in the male, is the

only type able to account for the appearance of exceptional

colored females in the cross reciprocal to that just considered.

In this cross, however, this type of non-disjunction expects a

color class which has not been recorded in matings of supposedly

homozygous colored males.

(¢) Non-disjunction in the female:

(1) WwwFFFMMm = colored males transmitting non-disjunction.

(2) WFM — = colored females? Sterile

Here, ETR gives no exceptions save the occurrence

of an Risen sterile colored female. This would undoubtedly

168 THE AMERICAN NATURALIST [Vou. LIV

be able to escape detection by breeders unless the most careful

individual records were kept. However, non-disjunction in the

female fails entirely to account for the occurrence of the ob-

served exceptions in the reciprocal cross and may for that reason

be disregarded.

Instead, therefore, of increasing the probability that non-dis-

junction is involved in the production of the exceptions noted, a

consideration of the above cross shows that it either fails to ac-

count for the exceptions which do occur or else expects additional!

color classes which have not been observed.

2. Canaries:

Here the conditions differ but slightly from those already de-

seribed for doves. The factors involved are P, dark eye color

epistatic to p, pink eye color. P is commonly considered as sex

linked. The possibilities of non-disjunction remain the same as -

in doves and may, therefore, be taken up under parallel headings.

Cross of Pink-eyed Male X Dark-eyed Female.

Pink-eyed Male x Dark-eyed female

ppFFMM PpFFMm

(a) If no non-disjunction; forming

pFM PFM and pFm

(b) If non-disjunction in the male:

forming gametes ppFFMM and— PFM and pFm

forming gametes pFM PpFFMm and —

The zygotes formed by these three processes would, in order,

be as follows

(a) No non-disjunction:

(1) PpFFMM = dark-eyed males.

(2) ppFFMm = pink-eyed females.

It is in this cross that exceptional dark-eyed females sometimes

occur.

(b) Non-disjunction in the male:

(1) PppFFFMMM = probably die

(2) PFM — = dark-eyed r Sterile?

(3) pppFFFMMm = pink-eyed males transmitting non-disjunction.

(4) pFm — = probably dies.

Here, as Durham and Marryatt who reviewed the case have

stated, although canary breeders have long noticed the occur-

No. 631] COLOR CLASSES IN DOVES AND CANARIES 169

rence of dark-eyed females, no mention is made of their sterility

nor of the occurrence of Class b(3), pink-eyed males, “although

the latter should have appeared with approximately equal fre-

quency. When one considers the amount of canary breeding

which has been done, and is still being continued and the fact

that breeders have long recognized the exceptional dark females,

the continued absence of the expected pink-eyed males becomes

a real objection to the acceptance of any hypothesis which calls

for their appearance.

(e) Non-disjunction in the female:

(1) PppFFFMMm = dark-eyed males transmitting non-disjunction.

(2) pFm — = pink-eyed females? Sterile?

It will be noted that this type of non-disjunction fails, as it did

in doves, to account for the observed exceptional dark-eyed

females.

Further if we now consider the reciprocal cross of dark-eyed

male X pink-eyed female, we shall find that the only type (b) of

non-disjunction which is able to account for the exceptional color

class above recorded demands a type of result as yet not reported.

Dark-eyed Male x Pink-eyed Female

PPFFMM

(a) If no. non-disjunction; forms ppFFMm

ga. : 7 PFM pFM and pFm

(b) If non-disjunction in the male; PPFFMM and pFM and

orms gametes oa } FM

orms gametes

(ppFFMm and

The following classes of zygotes will be expected :

(a) If no non-disjunction :

(1) PpFFMM = dark-eyed males.

(2) PpFFMm = dark-eyed females.

No exceptions have been recorded.

(b) If non-disjunction in the male:

(1) PPpFFFMMM = dark-eyed? Probably dies

(2) vin elidel = dark-eyed males tranenittiog non- —

(3) pFM == pink-eyed females? Sterile?

(4) pFm — = probably dies.

170 THE AMERICAN NATURALIST [Vou. LIV

Here it will be observed that pink-eyed females, probably

sterile, should be produced as frequently as were the exceptional

dark females in the reciprocal cross. We have no evidence that

this is the case.

(1) PppFFFMMm = dark-eyed males transmitting non-disjunction.

(2) PFM — = dark-eyed females? Sterile?

Here, as in doves, the result would possibly be masked because

no unusual color type is expected. Since, however, this form of

non-disjunction would fail to account for the dark females in the

cross of pink-eyed male X dark female it may be disregarded.

To sum up, we may say that non-disjunction is able to explain

part of the observed facts but expects sterility and other excep-

tional color classes in crosses where they have not been found.

If then, an explanation can be found which expects, in the crosses

made, the observed color classes and none other, it should in the

absence of stronger evidence for non-disjunction, be considered

to be fully as likely an explanation of the phenomena observed.’

FAcTORIAL CHANGE

1. In Doves.—In a paper now in press, I have attempted to

show that the occurrence of exceptional color classes in cats

(other than tortoise-shell males) which have been variously inter-

preted as due to partial sex-linkage or to the action of modifying

factors, may be satisfactorily explained by a process of factorial

change. Thus if in cats in some of the gametes of certain unusual

individuals the factor Y for the restriction of black pigment from

the coat, appeared in its hypostatic and allelomorphic form y,

the exceptional color classes would be accounted for. If a some-

what similar process occurred in certain rare individuals in doves,

between factors W and w, but in the reverse direction, namely,

from w white to W colored, we should have an explanation for

the exceptions observed.

If, then certain white male doves formula wwF FMM formed

2 Cole and Kelley (loc. cit.) believe that the exceptional colored females in

crosses between white male and colored female doves are simply mistakes in

observation or records, Because of the fact that they were obtained by two

entirely independent investigators and becduse a similar exception is found

in the case of canaries where even more extensive evidence exists, it is be-

lieved that the case demands explanation and cannot be merely disregarded

as Cole and Kelley imply.

No. 631] COLOR CLASSES IN DOVES AND CANARIES 171

among their gametes some that were WFM instead of wFM the

following result would be obtained in a cross between one of

them and a colored female.

White Male x Colored Female

wwFFMM WwFkFMm

Forming gametes: wFM commonly WFM

FM exceptionally

Zygotes expected: (1) WwFFMM = colored males (commonly)

(2) wwFFMm = white females (commonly)

(3) WWFFMM = colored males (exceptionally)

(4) WwFFMm = colored females (exceptionally)

Of the two exceptional zygotic classes (3) and (4) only the

latter represents a distinguishable phenotypic difference. The

other (3) would be merely individuals homozygous for the factor

W and therefore indistinguishable, except by proper breeding

tests, from the common heterozygous class (1). Such tests have

not been reported on as yet by investigators in whose stock, class

(4) individuals have appeared. The point to be emphasized,

however, is that the presence of homozygous colored males might

very easily escape notice unless sufficient numbers of young from

a critical cross were raised. It should further be noted that no

sterility is expected nor has any been recorded.

If a similar change occurred at rare intervals in certain white

females as we have a right to expect it possibly would, we should

have no phenotypically aberrant or unexpected color classes

formed:in crosses between such females and colored males. We

should however, obtain infrequently as a result of this process

homozygous instead of heterozygous ,colored males and mene

pepanaaltiee colored females as follows:

Colored Male x White Female

WWFFMM wwFFMm

Forming gametes: WFM wFM commonly

WFM exceptionally

WFm

Zygotes orpoen: (1) WwFFMM = colored males

(2) WwFFMm = colored females

(3) WWFFMM = colored males

(4) WWFFMm = colored females

commonly.

exceptionally.

Here again only careful individual breeding tests would be ex-

pected to reveal the presence of the exceptional homozygous

172 THE AMERICAN NATURALIST [Vou. LIV

colored individuals of classes (3) and (4) and no sterility above

the ordinary would be expected.

It is also interesting to note that theoretically the colored

females of class (4) would when crossed with ordinary white

males yield colored females of the normal type. Thus:

White Male x Colored Female Class (4)

wwFFMM WWFFMm

Forming gametes: wFM WFM

WFm

Zygotes expected: (1) WwFFMM = colored males.

(2) WwFFMm = colored females.

It may be objected that changes from a hypostatic factor to

its epistatic allelomorph are not frequent. This is admitted. On

the other hand, they have been several times reported by investi-

gators, among others by Morgan, in Drosophila, and by the writer,

in mice. In this connection it is interesting to note that the white

doves referred to are not totally unpigmented being merely

dilute, a fact easily observed in their eye color and found by

Strong (1912) to hold true for their plumage.

2. In Canaries.—The factors involved are the allelomorphic P

for dark eye color and p for pink-eye color. The quantitative

relation between the two is somewhat similar to that described in

doves though considerably less marked. The factorial change

appears to be extremely rare and to be from the p to the P condi-

tion. The following results would be expected if the ohanga

occurred in the pink-eyed male.

Pink-eyed Male x Dark-eyed Female

ppFFMM PpFFMm

Forming gametes: pFM commonly PFM

PFM exceptionally Pim

Zygotes expected: (1) PpFFMM = dark-eyed males

(2) ppFFMm =pink-eyed females f Commonly

(3) PPFFMM = dark-eyed

(4) PpFFMm = dark-eyed females toe tionally

Here as in doves the homozygous and heterozygous dark-eyed

males would be distinguishable only after a carefully controlled

breeding test. The dark-eyed females would be the only excep-

tional phenotypically distinct color class expected.

f the change occurred in the dark-eyed female instead of in

the pink-eyed male we should have the following condition.

No. 631] COLOR CLASSES IN DOVES AND CANARIES 173

Pink-eyed Male Dark-eyed Female

ppþFFMM X PpFFMm

Forming gametes pFM

PFM }

pFm commonly

s: fda m pexceptionally

Zygotes expected: (1) PpFFMM= dark-eyed males

(2) ppFFMm = pink-eyed females

(3) PpFFMM= dark-eyed males exe eptionally

(4) pPFFMm= dark-eyed females

} commonly

Here again dark-eyed females are the only unusual phenotypic

color class produced.

In the reciprocal cross we should have the following:

Dark-eyed Male x Pink-eyed Female

M Mm

PPFFM ppFF.

Forming gametes: PFM

pFM

pFm } commonly

Sin } exceptionally

Zygotes expected: (1) PpFFMM= colored males } es

(2) PpFFMm = colored females

(3) PPFFMM= colored males } exceptionally

(4) PPFFMm= colored females

As in doves the dark-eyed females of class (4) would be ex-

pected when crossed with ordinary white males, to produce dark-

eyed females, an unusual color class, as well as dark-eyed males, a

usual one.

It will then be seen that the hypothesis of factorial change ac-

counts for all the observed facts and unlike the hypothesis of

partial sex-linkage or that of non-disjunction expects neither

exceptional phenotypically distinct color classes as yet not ob-

tained, nor any exceptional degree of sterility. ;

On the hypothesis of factorial change it should be possible to

obtain at rare intervals colored doves from white parents. None

of those who reported exceptional colored females have reported

this event. Nor have breeders of pink-eyed canaries recorded a

dark-eyed bird from a pink-eyed X pink-eyed mating. In neither

case, however, have a considerable number of young from such

matings been reported by breeders from animals of the same stock

as that which gave the exceptional dark females. It therefore

remains quite probable that such a result could and would be ob-

174 THE AMERICAN NATURALIST [Vou. LIV

tained as it was in Morgan’s white-eyed flies and in my gray-

bellied agouti mice.

Further, it would appear that another possibility, visionary

though it may be, exists. If factorial change within a given locus

is in any way influenced by other genes or combinations of genes

within the cell either during gametogenesis or immediately after

fertilization, we should expect that the w or p gene, as the case

might be, would be subject to different intra-cellular environ-

ment when its allelomorph W or P was present, from that in

which it would be placed in a homozygous ww or pp individual.

Some of the differences which are bound to exist might well make

for its relatively greater instability in the former as compared

with the latter case.

Although such a relationship is highly hypothetical, it is sug-

gested that we should be continually on the alert for evidence of

possible effects of “intergenic and intra-cellular environment as

one of the most probable causes of genetic change.®

CONCLUSION

It is believed that the extension of the hypothesis of partial

sex-linkage and of non-disjunction, the effects of which have been

clearly demonstrated in Drosophila should be made to .include

ther forms only after confirmatory genetic and, wherever pos-

sible, cytological evidence have been obtained, and in the absence

of any other hypothesis which equally fits experimental facts and

is capable of experimental proof.

It is therefore suggested that the occurrence of occasional

colored females in a cross between white male and colored female

3 It should be recognized that sex-linked inheritance gives opportunity for

the fe soap of factorial changes should they occur, to a far greater ex

tent than ordinary crosses—for example: In in a case not involving sex

linkage we cross an individual homozygous or heterozygous for W with a w

individual, the small w might change to its epistatic allelomorph W in rare

eases without being recognized unless "each of the supposedly Ww zygotes

resulting from the cross were tested ars and sufficient young ob-

tained to determine whether they are exceptional WW individuals. This has

not been done on any very large scale with ones birds or mammals under

experimental conditions

If, however, the change occurred in a cross involving sex tg it would

be at once evident in at least one type of mating. This, as we have seen, is

the cross of white wwF FMM male by WwFFMm colored female where any

change in the w factor in the male would at once become evident by the pro-

duction of colored females otherwise not expected.

No. 631] COLOR CLASSES IN DOVES AND CANARIES 175

doves, and of dark-eyed females in a cross between pink-eyed

male and dark-eyed female canaries may be due to a rare fac-

torial change from the factor w to its allelomorph W in doves

and from the factor p to its allelomorph P in canaries. Such a

change would account for the observed results, except no sterility

nor additional unrecorded phenotypes and would be subject to

experimental tests.

LITERATURE CITED

pe 0: B.

1913. Science, N. 8., 37, 112-113.

1916 (a) Genities, J, 1-52,

1916 (b) Hanin 1, 107-163

Cole, L. J., and Kelley, F. J.

919. Gen sila 4, 183-203.

` Durham, F. M., and Marryatt, D.

1908. IV. Rept. Evol. d. Roy. Soc., 57—60.

Goodale, H. D.

1917. Science, N. S., 46, 213.

Little, C. C.

16 a Nar., 50, 335-349.

1913. a Nat., 47, 5-16.

Staples-Browne, R. H.

1912. Jour. Genetics, 2, 131-162.

Strong, R. M.

1912. Biol. Bwll., 23, 293-320.

Sturtevant, A. H.

1912. Jour. Exp. Zool., 12, 499-518.

SHORTER ARTICLES AND DISCUSSION

TRICHOMONAS AND BLACKHEAD IN TURKEYS

IN reading the introduction to Dr. E. E. Tyzzer’s contribu-

tion in the May issue of the Journal of Medical Research entitled

‘‘Developmental Stages of the Protozoon of ‘Blackhead’ in

Turkeys,’’ one is almost certain to be left with the impression

that the conception of the agency of the common flagellate,

Trichomonas, in producing pathological conditions character-

istic of blackhead in turkeys, as described in several papers by

the present writer, has no legs to go on, and would scarcely

receive the consideration of sane protozoologists. Of course this .

is not the impression that Dr. Tyzzer meant to leave; so that it

is fortunate that, in the experimental section of the paper re-

ferred to, he makes certain observations which are more favor-

able to the ‘‘flagellate hypothesis.’’ Fearing, however, lest the

hypothesis of tissue-invasion by Trichomonas might as yet be

too frail to survive long under the criticism of two such men as

Dr. Tyzzer and Dr. Theobald Smith (formerly chief proponent

of the ‘‘Amebic theory’’), the present writer, who first had the

misfortune seriously to mention Trichomonas in connection with

blackhead, wishes to point out a few instances in which Dr. Tyz-

zer’s criticisms, real or implied, are due either to careless read-

ing of the original papers, or to a too hurried examination of the

plates, or to both.

In way of introduction it may be said that Dr. Smith’s first

exposition of the blackhead disease, together with his original

description of the causative agent, Ameba meleagridis, appeared

in 1895. It is true that, at that time, as Dr. Tyzzer states, the

possibility of the relationship between Ameba meleagridis and

the flagellates was suggested by Dr. Smith. And the suggestion

was expressed in these words:

There is probably no genetic relation between this hypothetical organ-

ism (flagellate) and the true parasite of the disease under consideration.

For twenty years the ‘‘Ameba hypothesis’’ stood; and it was

not until this interpretation was called into question by Cole and

the present writer that (as Dr. Tyzzer states), Dr. Smith ex-

plained ‘‘that the name ‘Ameba’ is employed tentatively, and

No. 631] SHORTER ARTICLES AND DISCUSSION 177

that it may be necessary to change this when the nature of the

parasite is better understood.’’ The present writer would prob-

ably have been more cautious in his original criticisms of Dr.

Smith’s conclusions if that statement had been made by Dr.

Smith in 1895 instead of 1915. This will answer a criticism of

Dr. Tyzzer’s that is rather subtle and only implied.

Again, it is implied that something must be wrong with an

investigation that purports to demonstrate that Trichomonas is

the causative agent in an infection, when the investigator can

not put his finger on the species concerned, or even risk the

foundation of a new species. Who will come forward and give

us a clear, definite and usable classification of the Trichomonads!

And, speaking of new species in such a poorly known group, one

can not help wondering if it would not have been just as well, in

an earlier case, to leave the ‘‘meleagridis’’ off of Ameba. Can

one doubt that many unhappy hours and profitless discussions

have resulted from the necessity of piling up premature ad-

jectives after an innocent Latin noun? Why embarrass the

lexicographers until we are sure? And in the case under con-

sideration the present writer wasn’t sure.

Again Dr. Tyzzer states that it is obvious that the present

writer ‘‘does not consider the organism as primarily pathogenic

in nature, but as a normal inhabitant of the alimentary tract of

turkeys and fowls which may invade the tissue under conditions

which lower the resistance of the host.’ This is quite true.

Then Dr. Tyzzer continues,

Apparently this author attaches no importance to the fact that the

ase may be produced in healthy flocks by the introduction of in-

fected birds.

This is also quite true. The writer does not know of a care-

fully controlled experiment in which it has ever been conclusively

demonstrated that blackhead has been produced in healthy flocks

y the introduction of infected birds. During one year of ex-

perimental work in the field the writer made-it a point of remov-

ing the ceca and livers of poults which died of blackhead, chop-

ping them up in a meat cutter, mixing lightly with middlings

and feeding en masse to other poults as a partial substitute for

beef-scraps. The mortality from blackhead in the fed group

and in the control group was essentially the same. Most of the

poults died after several weeks with gape-worm infection, and

with no sign of pathologie changes in either ceca or liver. The

178 THE AMERICAN NATURALIST [Vou LIV

writer would have no apprehension in feeding to ‘‘healthy”’

poults any reasonable amount of pathologic material from black-

head cases, provided it were done in such a way as not to upset

the normal digestive equilibrium, and not to introduce pathogenic

bacteria nor bacterial toxins.

If Dr. Tyzzer had seen as much of blackhead in the field and

on the farm as he has seen in the laboratory, he might more

readily find reason in the writer’s viewpoint. Until a few years

ago, the writer held strongly the same views which Dr. Tyzzer

now holds. But here, as in some other branches of science, ‘‘field

work’’ and field experience has often wholesomely corrected mis-

guided laboratory theory; at least the writer has found it so in

his own case.

In another place Dr. Tyzzer states:

Contrary to Hadley’s claim Ameaba meleagridis should not be re-

garded as a cell parasite. . . . It does not oceur within cells except after

motility is lost, when it is soon phagocyte

Regarding the matter of cell-invasion Dr. Tyzzer quotes from

a passage from the author but stops prematurely. The passage

should be read as a whole to obtain the writers’ full meaning.

The writer states that, in tissue-invasion, we see Trichomonas in

a new role, and that here it may actively invade living cells. At

this point Dr. Tyzzer’s quotation stops, but in the original the

text proceeds:

One may remark that the type of cell invaded is a highly specialized

type [endothelial], and one that, by its nature, is more or less open to

nvasion. ;

The writer points out elsewhere that this invasion is not

passive but active. But nowhere in any of his published papers

(except in reference to the ‘‘goblet’’ cells) does the writer give

any expression of the opinion that Trichomonas is a cellular

parasite in the same sense that applies to the coccidia or other

sporozoa. In this respect, Dr. Tyzzer accidentally misrepresents

the writer’s views, Such little mistakes as always likely to

happen in the hurried reading of long and complicated papers.

A further criticism of Dr. Tyzzer’s is too good to omit.. The

circumstances are as follows: The epithelium of the cecum of the

turkey is thrown into folds. Sometimes they are deep and some-

times shallow. Within the folds, next to the cecal wall, are the

erypts. The projecting folds, with their accompanying tissues,

No. 631] SHORTER ARTICLES AND DISCUSSION 179

the writer has referred to as the villi. The author points out

that invasion of the submucosa is brought about by the passage

of the flagellates through the epithelium of the fundus of the

erypt, and that secondarily they invade (from behind) the villi,

and finally escape into the cecal lumen after pushing off the

epithelium of the villus tips. This phenomenon, which can be

followed clearly in suitable sections, the writer has referred to as

the stage of ‘‘reversed infection,” and has pointed out that it

constitutes a means whereby the parasites complete their para-

sitic cycle, rather than being buried and destroyed within the“

tissues as stated by Dr. Smith, who is of the opinion that the

parasite of blackhead lacks this essential feature of perfect

parasitism.

Here is Dr. Tyzzer’s criticism of this exposition:

The fallacy of such reasoning is quite apparent when the facts of the

case are considered. There are no villi in the portion of the cecum com-

monly involved in blackhead.

The writer had carefully explained in the text the appearance -~

of the invaded tissues; he had pictured it by hand-drawings, and

more in detail by a series of photomicrographs. No one could

fail to understand the definite histological structure to which the

writer referred, whether it is properly termed a ‘‘villus,’’ or

something else. Dr. Tyzzer may call the histological structure

what he pleases. The facts of the case with reference to Tricho-

monas remain the same.

But leaving aside the propriety of the term, villus, let us con-

sider what Dr. Tyzzer means by the balance of his sentence

‘“. . . in the portion of the cecum commonly involved in black-

head.” In the examination of hundreds of cases of blackhead

in turkeys and wild fowl the writer has found that blackhead

lesions may be initiated anywhere in the cecal wall; there is no

part of the cecum that is ‘‘commonly involved’’ except for this

circumstance: the majority of the lesions are observed in the

distal half of the cecum. Thus Dr. Tyzzer neglects clearly re-

ported facts to grapple with a technical triviality in nomen-

clature ; and at the same time, manifestly from lack of experience

with many cases of the disease, misrepresents one of the essential

facts relating to cecal infection.

In the next sentence Dr. Tyzzer attacks the statements of the

writer regarding the avenue of infection of Trichomonas. Re-

180 THE AMERICAN NATURALIST [Vou. LIV

ferring to the separation of the epithelium from the basement

membrane, he states:

In one ease the separation of the epithelium is taken as evidence of

invasion, and in the other it is taken as evidence of escape of the

flagellates from the tissue.

Dr. Tyzzer quite mistakes the point involved. It is not the

separation of the epithelium that is the important point (since

this is often an artifact), but the orientation and grouping of

a the parasites in the vicinity of this epithelium. By looking at a

church door we can scarcely: tell whether the last congregation

went in or out, but if we can find the congregation the question

will probably be answered.

And in further criticism of this point (avenue of infection

and of exit) Dr. Tyzzer has the misfortune to state,

The organisms interpreted by Hadley as encysted forms of the flagel-

late being discharged from the tissue are evidently Blastocystis derived

from the cecal content.

Did Dr. Tyzzer fail to examine the writer’s photomicrographs

(Bulletin 168, Figs. 30, 32 and 36) together with the complete `

description of these figures on a preceding page? Did he fail

to read the description of this ‘‘reversed infection’’ on page 26?

Are the writer’s photographs so poor as to make possible a con-

fusion between a flagellate trophozoite and ‘‘Blastocystis,’’ or

has Dr. Tyzzer an inadequate conception of what Blastocystis

really looks like? And, in addition, may it not be a little inac-

curate to affirm that ‘‘there is now quite general agreement that

they (Blastocystis) represent a distinct type of organism ...’’?

The matter is apparently still in controversy.

As to the statement of Dr. Tyzzer that the writer has failed

to establish the identity of the parasite with any species of

Aigi. or ‘‘to demonstrate any features characteristic of

the genus,’’—this must be left for others to judge. But the

author can not forbear to reiterate that he has no reason to

withdraw the evidence presented in previous papers. The

strongest evidence of all comes from the relatively rare cases in

which one can trace from the beginning the movements of the

parasites in the tissues, and follow clearly the morphological

changes that they undergo as the infection proceeds. It would

seem that Dr. Tyzzer, in his examination of only ‘‘five infected

turkeys,’’ has never seen such cases. The present writer eine

for many years before he found the ideal specimens. It is

No. 631] SHORTER ARTICLES AND DISCUSSION 181

hard thing to realize, in such an investigation where one is at-

tempting to ascertain the relation of two widely different enti-

ties, that a single average case, even though admirably sectioned

and stained, may mean very little. Dozens of cases usually

afford a more comprehensive view; and finally one comes to be

able to piece together bits of information which make the story

clear. It would be miraculous if the keenest pathologist could

make clear the evidence from ‘‘five cases.’’ Protozoan life his-

tories are not read in a moment, and a study of a hundred cases

for an hour means much more than one case for a hundred hours,

—unless that one case is exceptional.

In coneluding, it may be added that the writer hopes later to

consider more in detail the valuable constructive aspect of Dr.

Tyzzer’s paper. It is freely admitted that the life history of

Trichomonas in the tissues is not wholly clear, and it seems pos-

sible that some of the forms referred to by Dr. Tyzzer are new.

This is especially true of some of the motile stages which, in the

tissues, lose their flagella and, as Schaudinn says, ‘‘auch mit

stumpflobosen Pseudopodien umherkreicht.’’ It will probably

be some years before the last word is said on the blackhead

problem; and yet we are progressing. Under an efficient smoke

screen Dr. Tyzzer has given the last blow to the ‘‘ Amebic theory”?

-and already—though grudgingly—has yielded some support the

agency of the flagellates in cecal and liver infections. It may

be confidently expected that in the course of time his researches

will give more.

Dr. Tyzzer closes his critical introduction with the following

words: “It may appear that the above discussion is unduly

critical of the findings of other investigators. The confused

state of the subject, however, appears to warrant drastic methods

and the singling out of various misinterpretations and incon-

Sistencies, for it is quite evident that the enthusiasm of certain

investigators for their views has caused them to neglect impor-

tant facts.’’

How we all wish to be such champions of the truth! But, in

our war on ‘‘misinterpretations’’ and ‘‘inconsistencies’’ and on

“neglect of important facts,’’ would not our scientific world be

a happier place, and all our work of greater merit, if criticism

were tempered more with keen insight and less with the ardent

spirit of academic chivalry ? Pmr HADLEY.

KINGSTON, 5

October 9, 1919

| 182 THE AMERICAN NATURALIST [Von. LIV

THE INTENSITY OF ASSORTIVE PAIRING IN CHRO-

MODORIS?

THE pairing of the hermaphroditic nudibranch Chromodoris

zebra is accomplished in such a manner that there occurs a con-

siderable degree of assortive conjugation with respect to size. A

report? presenting evidence in support of this conclusion was

based upon the examination of Chromodoris population in Great

Sound, Bermuda, at a season when a considerable percentage of

CMS

Ollad

D œ o

NATURAL LENGTH

Z | | | | Lo | |

6 0o po R mo i0 Jea

ARTIFICIAL’ LENGTH. |

Fig, Curve relating the total length of Chromodoris of various sizes to the

“length ” as obtained from an “artificial” method of measuring the length

(see text).

the individuals exhibited injuries of the dorsal region of the

mantle. These injuries, resulting in a distortion of the dorsal

part of the body, made it necessary in estimating size to measure

the total length of the animals—from anterior edge of the buccal

veil to posterior termination of the foot. For practical purposes

it was necessary at that time to employ a somewhat artificial

_ 1 Contributions from the Bermuda Biological Station for Research, No. 115,

2 Crozier, W. J., ‘‘ Assortive Mating in a Nudibranch, Chromodoris zebra

Heilprin,’’ Jour. Exp. Zodl., Vol. 27, pp. 247-292, 1918 (ef. Proc. Nat.

Acad, Sci., 1917, Vol. 3, pp. 519-522).

No. 631] SHORTER ARTICLES. AND DISCUSSION 183

method in measuring this length. The animals were placed,

dorsal surface downward, upon a glass plate freshly wetted with

sea-water. It was recognized? that the soft body of these nudi-

branchs was by this procedure flattened out, and to some extent

increased in length, and that the proportionate amount of distor-

tion might be different for animals of different sizes. Oppor-

tunity was therefore subsequently taken to establish the relation

15 14 13 12 Nl 10 9 8 7 6

T i mt T T T T T

Beat

13 a 10 o p T 6 5 4

Regression plots; upper, from 148 pairs copulating in nature; lower,

classes; length measurements reduced by means of oi

are those previously found (see 2), employing the length as “artificially ” deter-

mined, and on the assumption that the regression is essentially linear.

between the ‘‘artificial’’ length as previously measured, and the

total length of the nudibranch as normally creeping on a flat sur-

face. The lengths of 74 individuals were determined in each of

these ways. The result of these measurements is exhibited in

Fig. 1.

| It is apparent that with nudibranchs of the larger sizes the

“normal’’ length is 1-2 em. less than the length as artificially

estimated ; further, that, as was to be expected, the extent of the

distortion introduced by ‘the latter method is proportionately

greater in larger specimens, the effect being negligible below 3

em. Accepting the curve as a measure of the relation desired,

184 THE AMERICAN NATURALIST [Von. LIV

Fig. 2 contains regression plots for my data? on pairs found in

nature and for laboratory matings in’ mass experiments, the

length-classes having been redistributed according to their re-

spective values in terms of the ‘‘normal’’ length. This procedure

involves the assumption that the proportion of flattening in the

‘‘artificial’’ method is the same for animals of the same size-class

at different seasons, which is probably not quite exact. The

original records were obtained in April-May, 1917, whereas the

data for Fig. 1 were secured in September, 1918. In the pres-

ence of so many possible sources of variation as these measure-

ments permit, it is sufficient to ‘‘average’’ the determinations

graphically, each original length-class, and the corresponding

mean length of the mates of individuals in this class, being treated

as units in reducing the old ‘‘length’’ figures to the more natural

ones obtained through Fig. 1.

According to Fig. 2, the apparent intensity of homogamy in

Chromodoris is but little affected, if anything perhaps slightly

improved, by the reduction of the original figures to the natural

scale.

W. J. CROZIER.

UNIVERSITY OF CHICAGO.

THE ORIGIN OF THE INTOLERANCE OF INBREEDING

N MAIZE

THE marked intolerance of inbreeding in maize has recently

been discussed by Collinst and brought to the support of the

hypothesis that this plant is of hybrid origin. But to those who

look for the origin of maize in another direction, the problem is

capable of a very different solution.

Briefly stated, Collins’ argument is this: Most varieties of

maize suffer from a few generations of self-pollination, but |

teosinte does not seem to be affected by this treatment. The

maize plant as a whole is usually synacmic, with a tendency

toward protandry, and self-pollination is in a large degree pos-

sible; such inflorescences of maize as have both stamens and

pistils are distinctly protogynous. In teosinte the large num-

ber of inflorescences on a single plant makes self-pollination a

common thing. If maize arose from teosinte, what was the origin

of its intolerance of inbreeding? The assumption that maize is

1 Collins, G. N., ‘‘ Intolerance of Maize to Self-fertilization,’’ Jour. Wash-

ington Acad. Sci., 9: 309-312, 1919.

No. 631] SHORTER ARTICLES AND DISCUSSION 185

of hybrid origin takes care of this difficulty by attributing this

genetic peculiarity to the unknown parent, which hybridized

with teosinte, and in which cross-pollination was probably

secured by protogyny.

Three fallacies render this argument inapplicable to the prob-

lem that it attempts to solve:

1. We are at once confronted with a question as to how maize,

embarrassed by its well-known intolerance of inbreeding and by

the extensive self-pollination with which Collins characterizes it,

has persisted through the ages. The answer is that self-pollina-

tion in the plant is not so common as would be inferred from

Collins’ discussion.

It is true that a single isolated plant is largely self-pollenized,

if pollenized at all, but data derived from the single-stalk culture

often practised in experimental work can not be accepted as a

criterion, for maize is normally grown in hills, and probably has

been for a very long time. This method of cultivation is de-

scribed by every early explorer and writer on Indian agriculture

and seems to have been the rule from the garden beds of the

Great Lakes region to the terraced mountain slopes of Peru. In

many instances as many as eight or ten plants were grown in a

single hill. This was the outgrowth of the Indian’s limitations

in the way of implements and domesticable animals, and the

plant was well adapted to it. The method was adopted by civil-

ized man and is extensively employed, with but few modifica-

tions, to the present day.?

If all the plants in a hill were synacmic and flowered at the

same time and the air were motionless, the chances for self-polli-

nation would vary inversely as the number of plants in a hill.

Tendencies toward protandry, coupled with slight differences in

the time of flowering of the individual plants of a hill, the pre-

valence of winds, and the proximity of other hills increase the:

chances for cross-pollination. Growing the plants in hills also

discourages the production of suckers, thus reducing the number

of inflorescences on a single plant, and consequently the chances

for self-pollination.

This massing of plants together in hills, and of hills together

in fields, is admittedly an artificial element of environment; but

its possible evolutionary effect in the ages during which it has

2 Cates, H. R., ‘‘Farm Practice in the Cultivation of Corn,’’ U. S. Dept.

Agr. Bull. 320, 1916, pp. 19-21.

186 THE AMERICAN NATURALIST [Von. LIV

prevailed can not be disregarded. What the condition was in

wild maize no one knows, and there is little basis for speculation.

But the plant has probably been in cultivation quite long enough

to have had its character shaped by agricultural practise.

Directly in accord with this theoretical consideration are

Waller’s researches,? which indicate that when corn is grown in

hills under ordinary field conditions, self-pollination occurs, on

the average, in only a little more than five per cent. of the seeds.

As Waller suggests, these figures may be modified by further

work on the problem. There is no evidence, however, that the

percentage of self-pollination will ultimately be found to be

significantly larger than this. The genetic complexity of the

average plant selected at random from any ordinary agricultural

variety of maize is a standing evidence of the prevalence of cross-

pollination.

2. The origin of protogyny in the androgynous inflorescences

of maize need not be sought outside the Maydex. This is the

regular condition in Tripsacum, at least in Tripsacum dacty-

loides, which is the only species that I have had opportunity to

examine in flower, and it occasionally occurs in Euchlena.

Collinst and Kempton® disregard or question the existence of

androgynous inflorescences in the latter genus, but the fact of

their occasional occurrence remains. The lowest inflorescences

of a teosinte plant are almost always wholly pistillate, and the

highest wholly staminate. Perfect flowers have not been ob-

served, but between the pistillate and staminate units andro-

gynous inflorescences often occur. These are regularly proto-

gynous. Androgynous inflorescences terminating the main culm

are often produced in the greenhouse. The difference between

greenhouse plants and those grown in the open in Mexico or

southern Florida is fully appreciated. Androgynous terminal

inflorescences are certainly of rare occurrence there, if they occur

at all; but I am not sure but that they are of less frequent occur-

rence also in maize grown in tropical or sub-tropical countries.

Moneecism in the Maydee is readily influenced by environment.

The physiological conditions conducive to androgyny in the

tassels of maize, and to a relative increase in the number of pis-

8 Waller, A. E., ‘‘A Method of Determining the sae of Self-polli-

nation in Maize,’’ Jour. Amer. Soc. Agron., 9, 35-37, 191

4 Loe. cit. Also Collins, G. N., ‘‘The Origin of Maize,’’ Vie Washington

Acad, Sci., 2: 520-530, 1

5 Kempton, J. H., ‘‘ The Aaii of Maize,’’ Jour. Washington Acad.

Sci., 9: 3-11, 1919.

No. 631] SHORTER ARTICLES AND DISCUSSION 187

tillate flowers in Coix and Sclerachne, also produce androgyny

in the inflorescence of teosinte. This fact may be of some signifi-

cance. Maize was doubtless originally a tropical plant. How

much of its erratic floral behavior when grown in temperate lati-

tudes is due to real, fundamental differences between it and

teosinte, and how much to environment?

It seems, then, that as to androgyny or as to protogyny of the

individual inflorescence, there is no fundamental difference be-

tween maize and the other American representatives of the

Maydex. When this fact is coupled with a reduction in the num-

ber of inflorescences, as in maize, it becomes unnecessary to as-

sume the introduction of the intolerance of self-pollination from

another group.

3. Collins leaves in this paper, as well as in an earlier one,°

the impression that the alternative to his hybrid origin hypoth-

esis is the theory that maize originated as a mutant from teosinte.

The latter idea is quite as chimerical as the former. We can not

reasonably hope to find the ancestor of maize in any modern

plant; phylogenetic histories seldom work out in this way. The

logical procedure is to look for other plants which may have

descended, coordinately with maize, from a common ancestor. In

Tripsacum and Euchlena we find two genera that fill the re-

quirements in all known details.”

The intolerance of inbreeding in maize is probably the plant’s

natural evolutionary response to its environment. The maize

plant is unique among the grasses in bearing but one pistillate

and one staminate inflorescence, or at most only a few inflor-

escences of each type, in having these widely separated, and in

having been grown in hills for untold centuries. These condi-

tions all tend toward extensive cross-pollination, and the data at

hand indicate that cross-pollination is the rule. More or less ad-

justment to these structural characters and this mode of living

would be expected; and the decline in vigor, resulting from in-

breeding, may be interpreted as the natural consequence of an

abnormal and unfavorable condition.

PAUL WEATHERWAX.

INDIANA UNIVERSITY,

BLOOMINGTON, IND.

® Collins, G. N., Angee Its Origin and Relationships,’’ Jour. Washington

Acad. Sci., 8: 42-4 ; i

t Westhorwax, Paul, pe Evolution of Maize,’’ Bull. Torrey Club, 45:

309-342, 1918,

NOTES AND LITERATURE

Orthogenetic Evolution in Pigeons. Posthumous works of C. O.

Whitman, edited by Oscar Rippitze. Publication No. 257, Car-

negie Inst., Wash. 3 quarto vols. with numerous colored plates

and figures. 1919.

In the opening sentence of volume 1 of this notable publica-

_ tion, Whitman says ‘‘Progress in science is better indicated by

the viewpoints we attain than by massive accumulation of facts.’’

The viewpoint which Whitman himself attained and beyond

which he saw no reason for advancing is that of ‘‘ orthogenesis.’’

His persistent industry also accumulated a mass of facts rarely

surpassed in amount concerning variation in a single group of

related organisms, the pigeons of the world.

The enormous task of setting these facts in order so as to illus-

trate his viewpoint, he was unable to accomplish. Death over-

took him while he was still busy accumulating facts. But he was

fortunate in having a loving pupil willing to devote his life, if

necessary, to rescuing from oblivion the work and words of his

beloved master. Few literary or scientific executors have shown

such self-forgetting devotion or have seen it crowned with such

success. Whatever we, living in a period of rapid advance in

biology, think at present concerning the value of Whitman’s

viewpoint, there can be no doubt that Riddle has preserved it

permanently, so that no one will be at a loss to know what Whit-

man’s ideas were about the factors of evolution, or on what data

they rested. :

Whitman took as the point of departure in his pigeon studies,

the plumage pattern of the wild rock-pigeon, Columba livia,

made familiar to everyone by Darwin’s use of it in his writings

on evolution. Darwin supposed that the wild rock-pigeon of a

slate blue color and with two black wingbars was the original

form from which all varieties of domestic pigeons had originated

through variation and selection. He showed that domestic vari-

eties when intercrossed frequently revert to this wild type and

he uses the manifold variation of domestic pigeons as a capital

illustration of evolution through descent with modification.

Whitman, in the true spirit of science which seeks to ‘‘try all

things and hold fast [only] that which is good,’’ made inde-

188

No. 6311 NOTES AND LITERATURE 189

pendent studies of wild rock-pigeons obtained from the ‘‘Caves

of Cromarty, Scotland.’’ He found that not all the wild pigeons

of this locality are of the simple two-wing-bar type, but that

part of them show a different pattern known as ‘‘chequered.’’

In these also the two black wing-bars can be observed, but they

are rendered less conspicuous by the occurrence of other black

spots scattered over other parts of the wing, giving the whole a

chequered appearance. The wing-bars are due to the occurrence

of a black spot on the tip or below the tip of each of two rows of

feathers that lie across the wing when it is folded. In chequered

birds other rows of feathers bear spots but the spots fall less

regularly and obviously into rows, so that the pattern is more

like that of a chequer-board. Further in young birds Whitman

observed that practically all the wing feathers may bear spots,

although in the later plumage some of the spots may disappear.

He concluded that this condition was the primitive one, rather

than the two-wing-bar type which Darwin regarded as primitive.

This conclusion seems well founded since the chequered type is

thus seen to be less specialized in form and earlier in ontogeny.

So far Whitman’s work supported Darwin’s general evolutionary

ideas, merely improving a detail in one of his illustrations, and

showing that there still exists among wild pigeons a pattern yet

more primitive than the one which Darwin had taken as the point

of evolutionary departure. But Whitman now extended his in-

vestigations to other species of pigeons and finally to those of

the entire world to see if he could work out more fully the evo-

lutionary history of plumage patterns in the group. As a result

of these studies he reached conclusions which did not enter into

Darwin’s scheme of evolution. The most important of these is

known by the name of ‘‘orthogenesis.’’ This is the idea that

evolution through natural selection does not result simply from

the selection of chance variations, that variations do not occur in

all directions but only in particular directions in straight lines

from the point of departure, hence the name orthogenesis. Whit-

man’s study of the plumage patterns of pigeons is probably the

most extensive, as it is the most recent, of the studies of a group

of animals made in the light of this principle, but to the general

body of biologists free from bias for any particular theory it

will scarcely be more convincing than its predecessors. It is

possible to arrange any group of related organisms in a graded

series and to assume that they have been evolved by orderly de-

velopment, from one end of the series (either end) to the other;

190 THE AMERICAN NATURALIST [Vou LIV

but this is no proof that such has actually been the historic

method by which the series has arisen. It may actually have

started in the middle and worked both ways, or in several direc-

tions. Only a study of contemporaneous genetic variation can

show what the method of evolution is. Color variation in mam-

mals is not unlike that of birds. We might arrange the color

varieties of any species of mammal or group of mammals in a

linear series and assume logically enough that evolution had

progressed from the darkest to the lightest form in orderly man-

ner, or vice versa, yet the study of contemporaneous variation

shows that this is not the case. A wild species, like the gray

rabbit or the brown rat, undergoes sporadically genetic variations

(‘‘mutations’’) some of which are lighter; some darker than the

parental form. They have no relation to each other as to the

order, time, or place of their appearance, so far as we can dis-

cover. Breeding evidence shows that they are genetically inde-

pendent one of another.

As an alternative to the hypothesis of orthogenesis in varia-

tion, the mutation theory of DeVries received much critical con-

sideration in Whitman’s writings. The lateness of publication

of much of this is to be regretted. Discussions which might have

been helpful a few years ago are now quite superfluous and out

of date in the light of critical experimental evidence since pro-

duced.

Mutation has practically ceased to be considered as a hypothet-

ical method of the immediate and direct origin of species. Even

as regards the origin of characters, mutation is no longer sup-

posed to be a simple process. Whitman maintains with entire

correctness that ‘‘ unit-characters’’ often have small beginnings

and may later be gradually increased by systematic selection.

Frizzling of the feathers in pigeons and fowls is an example cited

by him. He says, p. 151

Minute frills may occur in one or two feathers only, and they may

occur in any number, or in all of the feathers. . . . The full character

is reached, not by a jump, but by a process of ied itieditiall: carried

farther and farther, from the initial starting point. .. . It is well

known that characters often disappear by degrees, not all at onee. In

crossing species we rarely find the hybrid with pure characters. A ehar-

acter may be halved, quartered, ete., to any fractional part of the

original.

i passages such as these Whitman clearly shows that the muta-

No. 631] NOTES AND LITERATURE 191

tion theory as held at that time was untenable when applied

either to the origin of species or to the origin of characters.

What has since happened is that the mutation theory has been

frankly abandoned as applied to such origins and is now limited

to the origin of factors or genes. It is recognized that charac-

ters may change progressively and permanently (just as Whit-

man believed they did) under the guidance of selection. The

agency of such change is now supposed to be modifying or mul-

tiple factors, so numerous as singly almost to baffle detection and

so frequently coming and going that gradual modification of

characters in a desired direction is not difficult. This is the re-

siduum of truth which underlay the mutation theory as Whit-

man knew it and attacked it. In this marvellously modified form,

he would probably not have attacked the theory at all.

Volume 2 deals chiefly with inheritance, sex, and color in hy-

brids of wild species of pigeons. An enormous amount of exper-

imental data is here recorded, and scattered notes, briefs for

lectures, etc., have been brought together by the editor, dealing

with such general topics as heredity, Mendelism, sex determina-

tion and the like. As regards the hybrids, only F, individuals

were produced, for Whitman says, p. 3,

In the case of the wild species of pigeons, of which there are nearly

500, crosses are very often infertile, and fertile hybrids are so rare that

Darwin could not find a single well-ascertained instance of hybrids be-

tween two true species of pigeons being fertile inter se, or even when

crossed with one of their pure parents. The records since Darwin’s time

have not furnished the instance he vainly sought for.

Now every one to-day realizes that the F, or second hybrid

generation is all important for understanding or interpreting

heredity. Whitman accordingly, notwithstanding the boasted

superiority as genetic material of the pure species with which he

worked, since he was unable to produce in any case a second gen-

eration of hybrid birds, had no adequate basis for discussing

heredity in his hybrids, and no adequate basis for criticizing

Mendelism which is revealed only in the F, generation. One

characteristic of the large number of sterile F, hybrid birds

which Whitman produced is noteworthy. Their characters were

in nearly all cases blends or intermediates between those of the

respective parents. So long as doubt remained as to what the

Significance of blending is, whether it is essentially different in

nature from Mendelian inheritance, Whitman thought rightly

192 THE AMERICAN NATURALIST [Vou. LIV

that he had grounds for questioning the universality of Men-

delian inheritance. But strong evidence has now been produced

that blending inheritance is the regular outcome of crosses in-

volving multiple factorial differences. F, in such cases shows

increased variability with occasional segregation of the extreme

parental types, and in F, and F, such segregation becomes more

common. Had Whitman been able to raise F, and F, genera-

tions, he would undoubtedly have been convinced, contrary to

his expectations, as some of us have been, that blending inher-

itance finds adequate explanation in multiple factor Mendelian

inheritance. It is true that Whitman’s records of hybrid birds

reveal sex-linked inheritance, but these records did not suffice

for its discovery, which fell only to those experimenters who

worked with the despised ‘‘domestie breeds.’? The most val-

uable part of the work recorded in this volume is probably the

basis which it afforded for experiments on quantitative factors

entering into the development and expression of sex, if not its

actual determination. This work is due largely to the pupil and

editor, Riddle, though he generously brings the name of the

master to the front in dealing with the subject. These results

have been dealt with more fully in other publications by Riddle

and need not here be reviewed.

Volume 3 deals with very different subject matter from that

- contained in Volumes 1 and 2, viz., the behavior of pigeons.

Here is subject matter for the trained animal psychologist and

Dr. Riddle felt constrained to call in a competent psychologist to

edit this portion of Whitman’s writings. Professor H. A. Carr

has rendered this important service in a highly acceptable man-

ner. That a single biologist should be able to do distinguished

work in two fields so distinct as genetics and animal behavior

shows the breadth of Whitman’s capacities and interests. The

reviewer is unable to deal critically with the contents of Volume

3, but hazards the suggestion that it contains material of very

great interest and of permanent value not only to the psychol-

ogist but also to the naturalist, the one who is interested in ani-

mals as animals rather than as examples and products of one

evolutionary process or another.

It is much to be regretted that Professor Whitman was unable

himself fully to develop and round out the field of work here so

ably outlined and in part explored.

W. E. CASTLE

THE

AMERICAN NATURALIST

Vou. LIV. May-June, 1920 No. 632

CHIASMATYPE AND CROSSING OVER

PROFESSORS E. B. WILSON anv T. H. MORGAN

CoLUMBIA UNIVERSITY

Two short papers by Janssens, published in the

Comptes Rendus of the Société de Biologie for April and

May, 1919, outline an interpretation of the maturation-

phenomena in Orthoptera in agreement with his earlier

chiasmatype-theory (’09) based on the corresponding

phenomena observed in urodeles. It is a matter of so

much importance that all phases of this question be fully

discussed that we venture to report and examine the con-

clusions announced in these new communications. For

this purpose we have found it convenient to divide the

discussion into two parts, one dealing with the matter

more from the standpoint of strictly cytological observa-

vation, the other more from that of the possibilities sug-

gested by genetic analysis. In order to avoid repetition

we have numbered the figures consecutively, but each

author is responsible for the part under his name.

A CYTOLOGICAL VIEW oF THE CHIASMATYPE THEORY

E. B. WILSON

Professor Janssens’s results are as yet illustrated only

by diagrams, which leave us in doubt concerning some

very important details; nevertheless, a cytologist may be

permitted to indicate at this time how the conclusions

are related to those of other cytologists who have ex- |

193

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No. 632]. CHIASMATYPE AND CROSSING OVER 195

amined the phenomena in Orthoptera and other insects.

Incidentally I may remark that Janssens cites from one

of my own papers (’12) in support of his general theory

and also copies from another (’13) a series of general

diagrams by which the theory was illustrated. As he

a f]

T Ti 4

bj (|b

IG. 2. History of jan double rings (A-E, after Janssens). In each case ses

synaptic mates are ‘bla k and white, respectively, corresponding regions marke

osition of these rings as heretofore described; I and J, the two resulting

classes of chromatids, with no cross-

points out, these diagrams were too much simplified to

give an adequate representation of his views; but a erit-

ical account of cytological minutie was obviously inex-

pedient in a presentation intended only to make clear to

a general audience the nature of Janssens’s fundamental

assumption. I am glad however to see from these latest

196 THE AMERICAN NATURALIST [Vou. LIV

papers that he does not consider the diagrams to have

misrepresented the gist of the matter.

So far as can now be judged, Janssens’s latest studies

add nothing to his paper of 1909 that is new in principle.

They are in the main an elaboration of his earlier con-

clusions concerning the double-ring and double-cross

types of tetrads, which were illustrated in his former

work by diagrams XI, XVI, XIX and XX. These two

forms of tetrads are closely related, and each of them

shows in the prophases of meiosis a two-strand chiasma

—i. e., two threads which seem to pass over from one

synaptic mate to the other, crossing each other midway

between them, as in Fig. 5, I or 5, I1[—such as formed

the main basis of the original chiasmatype theory. It

may be needless to describe these tetrads, which are per-

fectly familiar to cytologists, but for the sake of clear-

ness I will briefly review their composition as now gen-

erally. understood.

aa aa ğ

| D AAAA-

3. Diagram to meg relation between the single rings, double crosses,

double ring and multiple ring types of tetrads, In each case the synaptic mates

are b and white Flinn. A, single ring with one ame of lateral arms;

B, same fee two pairs of arms; 0, double cross type with curved arms; D,

double ring, showing Sail piati eia (8, 8); E, multiple ring type (viewed

in somewhat different perspective) ; F, mode of division of such a tetrad

No. 632] CHIASMATYPE AND CROSSING OVER 197

Ring-tetrads may be single, or may consist of two or

more rings joined together in such a manner as to be suc-

cessively at right angles to one another, as is schemat-

ically shown in Janssens’s diagram, here reproduced in

Figs. 1 and 2 A-C. Single rings of the type here in ques-

tion (Fig. 3.4, B) were I think first clearly described and

figured in my laboratory by Paulmier (’98) in Hemiptera,

though he did not correctly make out their mode of origin.

Similar rings were subsequently studied in many other

animals, e. g., in Orthoptera by McClung, Sutton, Gra-

nata and others, in urodeles by Janssens, and in anne-

lids by the Schreiners, Foot and Strobell and others.

More recently they have been carefully examined by a

number of observers, in particular by McClung (’14),

Robertson (’16), and Wenrich (’16, ’17). ‘The single

ring-tetrad (Fig. 3 A, B) consists of a more or less open

ring, split lengthwise into two closely apposed halves and

cut crosswise at opposite points by two sutures which

divide the ring into two semicircular half-rings. The

latter are now regarded by practically all observers

(Janssens included) as the synaptic mates, joined by

their ends but elsewhere widely separated so as to lie on

opposite sides of the ring-opening, and each longitudi-

nally split. The longitudinal cleft lies therefore in the

plane of the future equation-division, the cross-sutures

in that of the reduction-division. At one of the cross-

sutures, less often at both, the longitudinal halves of

both synaptic mates are commonly drawn out at right

angles to the ring (in the manner made clear by’Fig. 3

A, B) thus forming two lateral arms, each longitudinally

double, so that this part of the ring, as seen in face view,

offers the figure of a double cross. If the ring be sup-

posed to break in two at the opposite suture and the half-

rings to straighten out completely it would become a sim-

ple double cross-figure with two short arms and two long

(Fig. 3 C or 5 III). If, on the other hand, the lateral

arms of a closed ring be supposed to elongate still more

and to bend away from the original ring until they meet,

198 THE AMERICAN NATURALIST [Vou. LIV

they would give rise to a second ring continuous with the

first but at right angles to it, as shown in perspective by

Fig. 3 D; and by repetition of this process would be

formed a series of three or more interlocking rings, each

at right angles to its successor (Fig. 3 E, F)1 How

many such successive rings may be formed is not known.

Double rings seem to be the most frequent; but in Chor-

thippus (Stenobothorus) both Robertson and Wenrich

describe and figure triple rings including at least one

case in which the lateral arms are long enough to form a

fourth ring, though their ends are in fact free. Jans-

sens’s diagram (Fig. 1) represents four complete rings

with lateral arms at both ends of the series; and it is

quite possible, as McClung has suggested, that some of

the forms that have been described as twisted or strep-

sinema stages may really be early conditions of such

multiple rings.

Janssens has found that in the heterotypie division

the double or multiple ring-tetrads lie on the spindle

with their longer axis transverse to that of the spindle,

and establish a lateral (atelomitic or non-terminal) at-

tachment; and since successive rings are always at right

angles to one another they lie alternately either in the

equatorial plane of the spindle or in a plane at right |

angles to it, 7. e., tangential to the spindle. In the ensu-

ing division the series is cut straight through in the equa-

torial plane (as shown in Fig. 1), rings which lie in this

plane being split lengthwise while those lying tangen-

tially are cut crosswise. This curious result is perfectly

in agreement with Robertson’s observations on Chor-

thippus (716, Figs. 179-182) and those of Wenrich on

Trimerotropis (717, Plate 3, Figs. 17, 18), and we may

probably accept it without hesitation, at least for some

tetrads of this type.

Thus far all observers are in agreement concerning the

external structure and mode of division of the compound

1 This account does not correctly describe the mode in which these com-

pound rings actually arise, but it is a convenient way of making clear their

structure.

No. 632] CHMASMATYPE AND CROSSING OVER 199

rings. As soon as we look further we encounter what

seems at first sight to be a hopeless contradiction be-

tween the conclusions of Janssens and those of others.

J +

A B _

j : :

| = T A i bi A a A ‘a

b ip b B B ë b B B

-t pd — :

. G ‘ca C | c: c ę c c

: d u D b D K ú d

e E e E | e E e E e

ij Í ‘ f F F A f F F

hor AG UJ

1 r l

A’ £

Fic. 4. Diagrams illustrating various possibilities concerning the compound

rings, following the outlines of Janssens’s figures, but showing also the relations

ft atids. At the left in each of the upper figures is the tu l

tetrad-rod from which the ring-series arises, showing results of assumed early

TOSS 1 or At mpound ring as conceived by McClung, Robert-

-overs) >

pound ring, such as

the results shown in B. ©, a compound ring giving the results

Janssens’s diagram (Fig. 1), resulting from a two-strand cross-over BRE two

pairs of threads, in regular alternation at successive nodes. The result (0*) is

four classes of chromatids, as shown in 0*

Janssens, holding fast to the general interpretation out-

lined in his earlier development of the chiasmatype-

theory, considers the compound rings to have resulted

200 THE AMERICAN NATURALIST [Vou. LIV

from a process of torsion of the synaptic mates about

each other, followed by a partial fusion between them at

certain points where threads from opposite sides of the

spiral have come together, crossing each other to form a

‘‘chiasma’”’ at each such point. By a subsequent read-

justment of position the regions between these points of

partial fusion have opened out to form rings disposed at

right angles to one another, and connected at the points

where the chiasmas have been formed. The general

nature of this rather complicated conception may better

be grasped by a study of Fig. 4C than from a description.

Janssens assumes, further, that at some period in their

history the rings are cut through at these points of fusion

in such a manner as to effect an exchange of correspond-

ing regions between the synaptic mates. The effect, as

conceived by Janssens, is shown in Fig. 1 (copied from

Janssens), and more in detail in my interpretative Fig.

4C,C’.

Janssens’s general interpretation (as will at once ap-

pear from his diagrams here reproduced as Figs. 1 and

2 A-E) includes two more specific assumptions on which

the whole matter turns. These assumptions are: (1) that

all the rings are essentially alike, the synaptic mates, or

corresponding regions of them (black and white in the

figure) lying in every case on opposite sides of the ring-

opening, the longitudinal cleft in each thus representing

the future equation-division; from this it follows (2),

that rings which lie in the equatorial plane of the spindle

(horizontally) are divided equationally, while the alter-

nate rings that lie tangential to the spindle are cut cross-

wise, and hence reductionally, by the same division. Both

these assumptions differ wholly from the results of pre-

vious investigators and hence call for critical exami-

nation.

The genesis and later history of the compound (espe-

cially the double) rings has been most fully studied in

the Orthoptera, having first been considered by McClung

and Granata, and more recently investigated with greater

No. 632] CHIASMATYPE AND CROSSING OVER 201

precision especially by Robertson (716) and by Wenrich

(716, 717). None of these observers, it is true, has traced

the history of the rings in every detail; but their results,

so far as they go, are entirely in harmony with the better

known history of the single rings and double crosses,

3 DA A

JI ch

A B

A — =

Fic. 5. Diagram ‘ice views, from ae models) of the origin of

— rings, double gp et and double crosses from a ou genera quadripartite

I, single rings; B leading to Da, and © to Db. II, double ring-formation.

IT, double pede Marat III, © Drebi from I, B k ad of the lower

‘ds of the synaptic mates. In each case ch marks an apparent crossing-point

or “ chiasma.”

both of which offer essentially the same problem as the

compound rings. These various forms of tetrads arise

from a diplotene thread that is at first longitudinally

double and sooner or later longitudinally quadripartite

202 THE AMERICAN NATURALIST [Vou. LIV

owing to the appearance of a second cleft at right angles

to the first. The evidence is nearly or quite conclusive

that one of these clefts coincides with the original plane

of synapsis or side-by-side apposition of the synaptic

mates (also the plane of the future reduction-division)

while the other is the equation-plane along which each

synaptic mate is longitudinally split.2 In any case it is

generally agreed that single rings arise by the separa-

tion and opening out of these threads along one of the

clefts (generally believed to be the synaptic, as in Fig.

5 I), their ends remaining united, while the second cleft

remains as the longitudinal cleft of the ring and repre-

sents the plane of the equation-division. The lateral

arms of these rings arise, as shown in the figures (5 I,

B, C) by separation and divergence of the free ends for

a certain distance along the second (equational) cleft,

thus finally giving the appearance of a double cross at

this part of the ring (5 I, D).

Double rings, coupled together (Fig. 5 IT) arise when

the rods separate along different planes in two adjoin-

ing regions, the opening of one ring representing the

expanded synaptic cleft (appositional or reductional)

that of the other the equation-cleft. Such rings are of

course at right angles to each other; and as the diagram

shows (Fig. 5 IT, B, D) when diane tetrads are viewed

obliquely they seem to show at certain points crossed

threads or chiasmas (ch.) in which two threads cross

over from opposite sides.’ It is of the first importance,

however, to bear in mind the fact that such figures are

shown in fore-shortened view. They are an attempt to

represent in two dimensions a figure which actually is in

three dimensions. Such tetrads can not adequately be

visualized until modeled in clay or by means of wires, so

as to be seen in three dimensions. When the models are

obliquely viewed they seem indeed to show at each node

2 This interpretation disregards the possibility (which I think is a proba-

bility). that recombination-phenomena or orderly exchanges of material be-

tween the synaptic mates may already have rene nian in thes quadripartite

rod; but for the moment we may leave this out of ace

3 This is clearly shown in McClung’s photograph, Vie. w (14).

No. 632] CHIASMATYPE AND CROSSING OVER 203

two threads that are connected by a chiasma and two that

are not thus connected; but if the model be rotated

through an angle of 90° the appearance is reversed, the

‘“‘chiasma’’ now appearing between the two threads that

previously seemed unconnected, and vice versa.

The same appearance, due to the same cause, is given

in early stages of the lateral arm-formation in the single

rings (5 I, B, C), and is shown with even greater clear-

ness in early stages of the double crosses. The latter

arise by separation of the free ends of the four threads

from each end towards the middle point, but along dif-

ferent planes (Fig. 5 III, B-D), i. e., from one end along

the equation-cleft, from the other along the reduction-

eleft—a process that is continued until all four threads

come to lie in a single plane in the form of a double cross.

Here, too, a ‘‘chiasma’’ (ch) is very clearly seen; but as

in the foregoing cases it is an optical illusion; the models

in three dimensions show at once that a straight split

through the tetrad involves no transverse break in the

chiasma, and that its two strands merely draw apart as

the division proceeds. In themselves these figures give

no reason whatever to assume that such a break (cross-

ing-over) has taken place at an earlier period or that the

Synaptic mates have been twisted about each other, as

Janssens assumes.

Such an origin of the double or multiple rings seems at

first sight wholly inconsistent with Janssens’s interpre-

tation; for if it be correctly determined the relation of

the synaptic mates to the ring-formation is wholly dif-

ferent in successive rings, as is shown in Figs. 3 D, E,

2-H, and 4-A. Specifically, in case of any two successive

rings one always shows the synaptic mates, lying on op-

posite sides of the ring-opening, and each longitudinally

split, while in the adjoining ring half of each synaptic

mate surrounds the’ entire ring-opening, lying in close

contact with the corresponding half of its mate. Only in

the first case, accordingly, does the longitudinal cleft of

the ring correspond to the equation-division. In the sec-

204 THE AMERICAN NATURALIST [Vou. LIV

ond case this cleft coincides with the apposition-plane of

the synaptic mates (i. e., that of the future reduction-

division) while the equation-cleft has opened out to form

the ring-opening; and so on in regular alternation. It fol-

lows, lastly, that if we disregard for the moment the pos-

sibility of an earlier recombination-process, a division

that cuts straight through the tetrad, as described alike

by Wenrich, Robertson and Janssens, does not in fact di-

vide certain rings equationally and others reductionally

in regular alternation but divides the whole series in the

same way, either equationally or reductionally as the case

may be (Figs. 2 H,J,3 HE, F,4 A).

In order to make clear the contrast between this con-

clusion and that of Janssens I have in Fig. 4 A followed

his outlines but have indicated the course of the four

threads (chromatids) in accordance with the account just

given. In Fig. 4 C, on the other hand, the chromatids are

shaded black and white in such a manner as to fit with

Janssens’s account. A similar comparison is shown for

the double-ring tetrads in Figs 2 F, G, which follow Jans-

sens’s outlines (2 A, B) as nearly as possible but are dif-

ferently shaded; while 2 H—J shows the double ring and

its mode of division in slightly oblique view, so as to

show the ‘‘chiasma.’’ In these various figures it is at

once evident that although a two-strand chiasma or

crossing (ch) appears at the junction of every two rings,

a straight longitudinal division of such a tetrad (separat-

ing black from white) involves on crossing-over, and di-

vides every ring reductionally; 2 .e., in such a manner as

to disjoin the synaptic mates. Here again it is also evi-

dent that the multiple ring need involve no twisting of

the synaptic mates about one another. It is true that

rings of this type, whether single or double, are not infre-

quently twisted in their earlier stages, and sometimes in

their later—a fact long known and easily verifiable; it is

shown unmistakably, for instance, in some of my own

slides of Phrynotettia (from material given me by Mce-

Clung several years ago). No evidence has yet been pro-

No. 632] CHIASMATYPE AND CROSSING OVER 205

duced, however, to show that such torsion leads to double

ring-formation by a process of chiasmatypy. On the con-

trary, the evidence thus far indicates that the torsion is

undone as the prophases advance; and it is a significant

fact that in these same twisted rings the free ends of the

chromatids (forming the lateral arms) show the typical

relation as described above, giving the appearance of a

chiasma at each end (as in Fig. 3 E, F, or 5 T1). Such

‘‘chiasmas’’ (like those seen at the junction of two rings)

are not for a moment to be confused with the appearance

of crossed threads given in side views of actually twisted

rings.

Such is the contradiction—at first sight it seems ir-

reconcilable—between Janssens’s conclusions and those

of other investigators of these tetrads. These latter re-

sults, in particular those of Robertson and of Wenrich,

are supported by very detailed and precise studies; and

my own observations, particularly on the double crosses,

are altogether in favor of their conclusions. Until Jans-

sens’s evidence is before us in greater detail it remains

to be seen whether the contradiction really is as great as

it now appears. In the meantime we may briefly con-

sider certain possibilities which may help to define the

issue more clearly.

The conflict of results has not, I think, grown out of

the fact that Janssens has worked with a different type

of compound ring, though this is possible, nor can we

assume that he has not reckoned with the results of other

observers. I incline to think that the contradiction may

be in ‘the main one of theoretical interpretation rather

than of known fact; for in theory all the observed facts

may quite logically be interpreted as the result of a chias-

matype that has been completed at a stage prior to the

ring-formation. Specifically we might assume that a

cross-over has earlier been completed at each node in the

series, causing an exchange of two longitudinal halves in

4 See for instance Granata (10, Fig. 29), Robertson (16, Figs. 150b,

175), Wenrich (’17, Pl. I, Figs. 8, 9), and Mohr (’16, Fig-131). The same

is clearly seen in my slides.

206 THE AMERICAN NATURALIST (Von. LIV

alternate rings—a process which would produce a condi-

tion identical so far as appearances go, in both structure

and mode of origin, with the compound ring as described

by Granata, McClung, Robertson or Wenrich, but one

which has a quite different morphological significance.

Such an assumption seems to me to be logically implied

by Janssens’s own account, though I am not sure that

such is actually his meaning. 3

‘ T have tried to illustrate this by the series of diagrams

shown in Fig. 4. A represents the compound ring in ac-

cordance with the results of McClung and his followers,

the synaptic mates being in black and white, respectively.

If, however, we assume this condition to have been pre-

ceded by a two-strand cross-over or chiasmatypy at each

node, the composition of the tetrad becomes that shown

in B or C. Hither of these figures realizes the two spe-

cific assumptions of Janssens earlier emphasized,

namely: (1) that the longitudinal cleft in every ring rep-

resents an equation-division (i. e., separates correspond-

ing halves of one synaptic mate in this particular part of

the tetrad), and (2) that a straight split through the

ring-series (such as is shown in Fig. 1 B) will now divide

half the rings equationally and the alternate rings reduc-

tionally. Both show recombinations in the same regions

(Aa, Cc, Ee) and in the same relative numbers in the

cross-over threads; but they are differently grouped,

owing to the fact that in one case (B) a cross-over has

taken place between the same pair of threads at every

node, while in C this occurs only at every other node, the

cross-overs taking place in regular alternation between

two different pairs of threads. As a comparison of Figs.

2 and 4 C will show, it is this latter form that corresponds

with Janssens’s interpretation.

Janssens does not make it clear in his preliminary

papers whether he assumes the chiasmas to be cut

through during the actual division of the tetrad, though

I think is what one would naturally infer from his gen-

eral account and from his figures, especially of the double

No. 632] CHIASMATYPE AND CROSSING OVER 207

rings (here reproduced as Figs. 2 A-E) and of the double

crosses (here Figs. 6 H-C). On the other hand a study

of my Fig. 4 will show that the results of the division, as

stated by Janssens himself (my Fig. 4 C) can only be

brought about by a split which passes straight through

the equational cleft of the horizontal rings and leaves the

chiasma untouched. I infer, therefore, that Janssens

does in fact consider the chiasmatypy to have taken place

Interpretations of the double crosses. A, B, Ja nssens’s interpreta-

I 5

tion (from his figures), showing four classes of chromatids, two with a single

figure of Janssens). D, E, the prevailing interpretation of the double cross, with

no cross-overs; F, early stage of the double cross. (Cf. Fig. 5 III, ©.)

at a stage prior to the opening out and division of the

rings; and this would be in agreement with his earlier

conclusions, as applied to the tetrads of urodeles, here

illustrated by Fig. 6 C (after Janssens).* At any rate, so

far as I can see, it is only by such an interpretation that

Janssen’s results can be reconciled with those of other

observers. More specifically, the assumption must be, I

5 See Janssens, ’09, p. 14 (Diagram, XXII): ‘‘We believe that in this

ease the threads which cross each other are those furthest apart, that is to

say, which occupy those parts of the chromosomes that undergo no spin

mixture. The threads which remain unconnected by a chiasma, on the

trary, are those which have undergone a secondary union at the ‘alan

where the chromosomes have interpenetrated aah other and fused.’

208 THE AMERICAN NATURALIST [Von LIV

think, that the chiasmatypy has taken place during a

strepsinema stage prior to the straight, longitudinally

divided threads from which the rings arise (Figs. 4 B, C,

at the left). If now, for the sake of argument, we accept

these assumptions, how does it come to pass that the sub-

sequent opening out of the rings exactly fits with the re-

combination-phenomena that have previously occurred

in the tetrad? Morgan.has already supplied an answer

to this in the ingenious suggestion that the mode of sep-

aration of the threads may be determined by their nature

—1. e., that the paternal and maternal threads (or por-

tions of threads) may always be the first to separate,

however they may lie in the tetrad. This is an impor-

tant addition which makes the whole series of assump-

tions logically complete.

All this constitutes a somewhat complicated train of

reasoning; nevertheless, if it be granted, it provides for-

mally an escape from the seeming contradiction and

leaves the chiasmatype-theory intact. The point, how-

ever, that I wish to emphasize is that we have now passed

over into a realm of hypothesis and logical construction,

based it is true on a vast assemblage of data of the high-

est importance, but derived from genetic experiment

rather than from cytological observation. No observer,

so far as I know, has yet seen a process of true crossing-

over (recombination) by means of torsion, chiasma-for-

mation, fusion, and secondary splitting apart. That such

a process takes place at all remains thus far an inference

based on the presence of a continuous two-strand chiasma

in later stages of meiosis and on certain resulting ap-

pearances in the late prophase- and metaphase-tetrads.

But as shown above, precisely the same appearance of a

two-strand chiasma is given by a process in which no tor-

sion need be involved. Both Wenrich and Robertson

have urged this fact against Janssens’s interpretation ;

and I am fully in agreement with them so far as the later

stages of meiosis are concerned. It may nevertheless be

pointed out that both these observers have figured stages

6 719, pp. 101-104.

No. 632] CHIASMATYPE AND CROSSING OVER 209

which at least suggest a process of torsion or strepsi-

nema-formation in the early diplotene prior to, or very

early during, the definitive opening out of the prophase-

figures—e. g., in Wenrich (’16), Fig. 75, or (717), Fig. 23,

and in Robertson (’16), Figs. 149, a and b. The case

seems, therefore, by no means closed; and we may await

the publication of Janssens’s new results in greater de-

tail, in the hope that more definite evidence may now be

produced concerning the critical point at issue.

My own doubts on this matter first grew out of obser-

vations on the origin of the double crosses, which, as

above indicated, involve a similar question concerning

the chiasmatype. Janssens’s earlier interpretation of

the double cross, which I believe he was the first to offer,

was in principle the same as that briefly indicated

above and schematically shown in Figs. 5, III and

6 D-E. Later this interpretation became the prevalent

one but was abandoned by Janssens himself (’09, 719) in

favor of one which assumes a process of chiasmatype to

be involved in the cross-formation. This interpretation

starts with a comparison of the double cross to the region

at which two rings join; and this is obviously correct

under any theory (ef. Figs. 3 D and 6 C, F). Janssens,

however, assumes the relation between the synaptic

mates to be essentially as shown in the diagram here

reproduced as Fig. 6 A—B, the two synaptic mates being

bent at right angles, and united by their apices to forma

cross which then splits straight through all four arms,

thus giving two cross-over chromatids out of four. I

seriously considered this interpretation in my own studies

on the double crosses of Hemiptera, but finally became

convinced (’12 and subsequently) that it does not corre-

spond with the facts. More recently Robertson, Wen-

rich and Mohr have demonstrated the same conclusion

in a very circumstantial and convincing manner in case

of the double crosses of Orthoptera, tracing their origin

step by step from the original diplotene in the manner

indicated in Fig. 5, III. According to all these observa-

210 THE AMERICAN NATURALIST [Vou. LIV

tions there is nothing in the history of these crosses, as

thus far made known, to suggest an earlier process of

torsion, chiasma-formation, and recombination. They

indicate rather that the cleavage of such a tetrad straight

through its two clefts involves simply one reduction-

division and one equation-division (Fig. 6 D-E).

Robertson has pointed out that many of those appear-

ances in the prophase- and metaphase-tetrads on which

Janssens’s theory was originally based are susceptible of

a much simpler explanation than is offered by the chias-

matype-theory, namely, that they are a result of ‘‘mis-

fortune in the prophase,’’ due to secondary displace-

ments of torsions at this time. Experiments with clay

models have convinced me that this point is well taken,

in respect to some at least of these appearances. It should

also be clear from the foregoing discussion that condi-

tions resulting from the persistence of the so-called two-

strand chiasma in the metaphase-figures are readily ex-

plicable without the assumption of an earlier process of

chiasmatypy.

In this brief review and critique of the cytological as-

pects of the question, I have not intended to take up an

attitude of opposition towards the chaismatype-theory

considered as an explanatory principle in genetics. On

the contrary, I am not able to escape the conviction that

somewhere in the course of meiosis some such process

must take place as is postulated by Janssens and by Mor-

gan and his co-workers, though I must admit that this

opinion rests less on cytological evidence than on genetic.

I have wished only to discuss the possibilities of the ex-

isting cytological situation and to offer a counsel of cau-

tion in respect to the chiasmatype-theory in so far as it,

is based on conditions seen in the later stages of meiosis.

This means no lack of appreciation for Janssens’s bril-

liant and fruitful work, which has opened up so remark-

able a new field of inquiry. But a theory of such funda-

mental importance calls for critical treatment, and on its

No. 632] CHIASMATYPE AND CROSSING OVER 211

purely cytological side too much has sometimes been

taken for granted by writers on genetics. It is, I think,

highly probable that the cytological mechanism of cross-

ing-over must be sought in some process of torsion and

recombination in the earlier stages of meiosis—perhaps

during the synaptic phase of slightly later—and that this

process may leave no visible trace in the resulting spi-

reme-threads. To accept this, of course, would mean that

such conventionalized diagrams as those here offered

(Figs. 3, 5, ete.) should be so modified as to indicate ex-

changes which have earlier taken place between the syn-

aptic mates. It must be said, on the other hand, that the

actual evidence of torsion during the process of parasyn-

apsis is still very inadequate and receives no support

from some of the most careful recent work. One can not

avoid a suspicion that some internal process of torsion

(or of rotation, as conjectured by Correns) may take

place in the early pachytene before the duality of the

diplotene becomes externally visible. Conjecture con-

cerning all this will however be less fruitful than

further cytological analysis. The truth is that for

the time being genetic development of the chromosome-

theory has far outrun the cytological. We are in no posi-

tion to predict when the plodding progress of cytology

may be able to close the gap; nevertheless we have every

reason to hope that the physical mechanism of the recom-

bination-phenomena may in the end prove to be accessible

to decisive cytological demonstration.

THE SPIRAL LOOPING OF THE CHROMOSOMES AND THE

THEORY or CROSSING OVER

T. H. MORGAN

In his two recent papers Janssens calls attention to

certain details relating to the application of the findings

of cytology to the interchanges between homologous sets

of linked genes. The first paper is a restatement of the

situation as it is generally understood to-day, and calls

212 . THE AMERICAN NATURALIST [Vou. LIV

for no special comment. It ends with the significant

statement

At our next meeting I shall point out that the theory of the chiasma-

type allows for an interpretation somewhat different from the view of

simple splitting of the threads in a single plane that passes through

the axis of the entwined threads.

Concerning the point here raised by Janssens I should

like to add that the ‘‘simple interpretation’’ was given

mainly to escape the somewhat complicated scheme in-

volved in Janssens’s theory. In this way it was hoped to

avoid a too detailed account of the process that calls for

pictures not readily understood except by cytologists

familiar with the changes that take place when the twisted

threads shorten and move apart. Unfortunately the

very simplicity of the statement led one critic to infer

that the interpretation must be wrong because at the

nodal points the plane of the split appeared as though it

cut obliquely through each chromosome itself. To avoid

this I represented in later diagrams the chromosomes as

made up of beads, and in this way tried to show that at

the node each bead and its allelomorph are not divided,

but go each to a pole. Even this diagram may prove too

simple; for, if at the time of twisting each thread is also

split lengthwise into two strands it is possible that only

two of the strands fuse at each node. In Janssens’s

scheme to be described below this secondary doubling of

each thread is seen to be an important factor in the

situation.

Janssens states that the matter is not simple:

The loops (Fig. 1 B) and the half loops (Fig. 1 C) that produce the

chiasma lead to profound modifications in the twisted threads. These

modifications are already indicated in the prophases, but they only

become evident in proportion as the dyads ripen and prepare to place

themselves on the spindle. We can not describe this here, but let us

state nevertheless that the chiasma segments are placed in planes per-

pendicular to the segments adjacent to them as indicated in diagram

II, Fig. 1. Once this fact is clearly seen it is not essential to add much

to Morgan’s phrase, since it expresses what really takes place. It need

only be said: (1) In both maturation divisions a cleavage takes place

No. 632] CHIASMATYPE AND .CROSSING OVER 213

only in the equatorial plane of the figure. The first of these cleavages

is here indicated by a dotted line in Fig. 1 A. ( 2) Moreover this plane

produces a longitudinal cleavage of the chromosome and hence is equa-

torial in each of the alternating chromosome segments (rin ) that lie

exactly at the equator of the spindle of the figure (like that which

occurs at a gonial mitosis), Fig. 1 A and B. (3) Finally, since the two

spindles of the two maturation divisions that follow rapidly are per-

pendicular to each other, one may further add that each dyad will be

split during the maturation (maiotiques) division by two planes at

right angles to each other. At the first division, the equatorial pasa

plane is perpendicular to the axis of the heterotypic spindle and durin

the second division the plane is in space, parallel to the original axis £

the same spindle.

Janssens suggests the following considerations that

have an application to Mendel’s laws.

Neighboring segments pass easily into the same chromosomes when

the direction of the twist is constant. When a segment is long it may

be considered as carrying a longitudinal series of qualities, in con-

formity with the ideas held by Morgan. On the other hand the qualities

supposed to be carried by the chromosomal segments are distributed

amongst the germ-cells as though they were carried by chromosomes

really independent confirming the law of disjunction of the characters

in the gametes (Mendel).7

Let us return to a further consideration of the dia-

grams that have been published to represent the methods

of crossing-over. In Janssens’s scheme, Fig. 1 A, four

complete rings are represented and the division plane ap-

pears to cut through each node, although the important

details of how this is done are not shown in the figure,

but may perhaps be inferred from Fig. 1 C, where the

four vertical strands show what is supposed to have

taken place. Crossing-over is represented as having oc-

curred at four nodes. In Drosophila the genetic evi-

7 In this sentence Janssens seems to imply that his chiasma theory ex-

will go over together in the segments between the nodes, or on each side of

node. Hence the phenomena of linkage that places a very great restric-

tion on Mendel’s second law of assortment. It is this feature that we have

always regarded as of the utmost significance in our theory of crossing over.

It is obviously implied in Janssen’s chiasma theory also, and I can not but

believe that Janssens must intend to apply his theory in the same way in

which we have applied our theory.

214 THE AMERICAN NATURALIST [Vou. LIV

dence shows that as much crossing over as this does not

usually occur. In our diagrams (Heredity and Sex,

1913), therefore, we represent only one or two real inter-

changes between the members of a pair of chromosomes

because the genetic evidence shows, as stated, that, in the

great majority of cases, this is what takes place.

Fie. 7. Diagram of the looping of a pair of chromosomes that are already

split lengthwise. A, two threads making one complete twist; B, the inner strands

tra

case that have broken and “crossed over.” The crossed strands in the figure

are not due to perspective.

The rings in two planes, as represented in Janssens’s

diagram, call for further analysis. We may call these

rings Bb, Ce, Dd, Ee (Fig. 1A). It will be observed that

No. 632] CHIASMATYPE AND CROSSING OVER 215

in ring Bb the dark double thread (half ring) at the right

separates from the light double half at the left. This is

a reduction division for this segment. On the other hand

in the ring Cc the division plane separates equationally

the halves of the dark and of the light half rings. Cross-

ing over takes place at the node between ring Bb and Ce,

and at the node between the rings Cc and Dd there is an-

other crossing over between the other two strands. Gen-

eralizing the result it may be said that crossing over of

two of the strands takes place at each node. In the sec-

ond division, that is supposed to take place here in the

plane of the paper, there is assumed to be no further

crossing over in either of the halves that have resulted

from the first division.

Janssens points out that on this new scheme there is

only half as much crossing over as on the scheme repre-

sented in our older diagram (1913) ; but it is obvious that

this is only because in the latter whole chromosomes

(each potentially or actually made up of two strands)

are represented as crossing over at each node. If, how-

ever, we compare this latest scheme of Janssens with the

figures that we have now recently published (‘‘Physical

Basis of Heredity,’’ 1919) in which, following some of

Janssens’s earlier diagrams only two of the strands

cross over at each node, it is perfectly clear that these

later schemes of ours give the same number of cross-

overs per complete twist as do Janssens’s present dia-

grams.

It may, therefore, not be without interest to compare

Janssens’s latest scheme with the one I have recently

suggested in my book on the ‘‘Physical Basis of Hered-

ity’’ (p. 105) where a figure is given that suggests an ex-

planation of the opening out of a twisted conjugated

thread in rings that lie in different planes. This figure

is here reproduced, Fig. 8 A-D, modified only so far as

to make it comparable with Janssens’s new diagram. In

A the two split threads are represented as looping or

overlapping in an open spiral (an earlier stage than

216 THE AMERICAN NATURALIST [Vou. LIV

Janssens’s first figure). At this stage where the inner

strands come into contact they are represented as fusing

with each other at three nodes. The threads may next be

supposed to flatten against each other to make the con-

jugated threads keep their spiral configuration and

then condense to make the thick threads. In this condi-

tion they pass to the equator of the spindle or they may

begin to open out before they reach the equator, Fig. 7 B.

-n

Fic. 8. Diagram showing how the twisted strands of Fig. 8, O, become

REESE out (untwisted) as the thread shortens, so that the former spiral

relati e resulting relation of the threads when they open out by t

reductional separation is shown in B this re shows the relation of the

strands the spiral in Fig. 8, O, untwists, i.e t hread shor B;

ment, the resulting figure, B, is the same as that of Janssens. In the middle of

the figure it appears as though two “ cross over ” strands were crossing. This is

here due to perspective

If the first division is reductional for every part of the

thread, the halves of the thread move apart in opposite

directions, and as a consequence of the way the twisted

threads have flattened against each other this opening

out may produce rings lying in different planes, Fig. 7

D, not necessarily at right angles to each other, but at an

angle with each other.

The rings are assumed to be due to the reductional

separation of the segments of the chromosomes along the

tetrad, but the further movements of the daughter chro-

mosomes after they have reached the equator of the

spindle must be referred to another mechanism that now

comes into play, namely, the forces that carry the chro-

mosomes to the poles. Under these circumstances the

No. 632] CHIASMATYPE AND CROSSING OVER 217

threads may be thought of as separating without assum-

ing stich a strictly symmetrical form as Janssens’s new

diagram indicates, or in other words the separation of

the chromosomes may take place as Janssens described

it in Batracoseps. The suggestion that I made to account

for the appearance of rings in different planes was made

to meet an objection raised by Robertson and by Wen-

rich, namely, that the crossed threads (the chiasma

threads) do not mean that crossing over has taken place

in that region. * They point out that the crossed threads

may mean no more than that a not-twisted tetrad has

opened out in different planes in consecutive regions.

This obviously may be the interpretation of the crossed

threads, but if as I suggested the opening out of the rings

themselves in different planes represents consistently a

reductional separation in a formerly twisted thread, then

the cross threads come to have a meaning, for they rep-

resent the level at which an earlier fusion and reunion of

the inner strands of the four strand stage took place.

From this point of view the cross strands, while having

nothing to do at this time with crossing over, neverthe-

less correspond to levels at which that process occurred.

I do not wish to appear to be advocating the scheme

that I suggested as the best or as the only one that is in-

volved in crossing over. Any scheme that accounts by

means of twisting threads for interchange between the

segments of homologous chromosomes will fulfill suffi-

ciently the present requirements of crossing over. Much

more cytological and genetic work too will be necessary

before it is possible to state when and how this process

goes on. One point alone seems at present to be indi-

cated with some probability by the genetic evidence,

namely, that it would appear simpler for the interchange

to take place when the lines of genes are extended to the

fullest extent possible, and this would seem most easily

to take place, in the accurate way indicated by the genetic

facts, when the leptotene threads have spun out to their

farthest extent. Whether Janssens also ascribes to this

218 THE AMERICAN NATURALIST [Vou. LIV

stage the essential step in the breaking and reunion of the

strands remains to be seen when his new results are pub-

lished. :

Until Janssens publishes a full statement as to how he

supposes the crossing over at the nodes to take place,

whether at the time when the looping of the threads is

present, or at an earlier stage, it is hazardous to make too

detailed comparisons, but one relation should not pass

unnoticed. In Janssens’s figure four rings seem to be

involved in one complete twist of the two chromosomes.

In order to place these rings in: such a position that a

single (vertical) plane can sunder successive rings trans-

versely and longitudinally in alternation, the rings must

be turned so that two are exactly vertical and two are

horizontal. A spiral relation of the threads can not be

brought into this relation unless the threads first untwist.

How this can be done is shown by a comparison of Fig. 7

with Fig. 8. In Fig 7 A, as explained, two chromosomes,

each of two strands, are represented as looped around

each other in an open spiral. In the middle of the spiral

the two inner strands that touch are represented as fus-

ing and reuniting to give the cross-over, and near the

ends, where the threads cross again, the other two strands

fuse, break, and reunite to cross over, Fig. 7 B. The

threads are then represented as flattening against each

other, still keeping their spiral configuration. When they

open out again, by a reductional separation of the seg-

ments, Fig. 7 D, the rings are formed, and if the threads

are still represented as keeping their spiral configura-

tion no single plane, as explained, will separate them

without cutting some of the strands. But if when stage

C is reached in Fig. 7 the threads straighten out as they

condense (i. e., if they untwist) the result will be that

shown in Fig. 8 A. If now the threads open out by a re-

duction division in each segment, the resulting figure will

be like that shown in Fig. 8 B. This figure is the same as

that of Janssens, and the halves can be separated in one

plane, as he explains. We may conclude then, if the con-

No. 632] CHIASMATYPE AND CROSSING OVER 219

jugated threads after crossing over do not untwist, they

will give figures like those in Fig. 7 D, and such threads

must be pulled apart as Janssens has explained for Ba-

tracoseps; but if after crossing over the twist is rectified

as in Fig. 8 A the threads can separate as Janssens ex-

plains for the grasshoppers. In both cases the crossing

over is represented as the result of twisting threads, and

if such loops tend to have a modal length, the mechanism

furnishes a beautiful explanation of interference which

is one of the crucial tests to which our explanation of

crossing over has been put.

REFERENCES

Granata, L.

1910. Le cinesi spermatogenetiche di Pamphagus marmoratus. Arch.

f. Zeliforsch., V.

Janssens, F. A

1909. La Deets de la chi Weer Nouvelle interprétation des

es de maturation. La cellule, XX.

19194. A propos x la POA mx li théorie de Morgan. Soc.

elg. Biol., 917-920.

1919b. hie Farmin simple exprimant ce qui se passe en réalité lors de

la ‘‘chiasmatypie’’ dans les deux cinèses de maturation. Ibid.,

930-934

McClung, C. E. è

1914. A Comparative Study of the Chromosomes in orthopteran Sper-

* matoge nesis. Jour, Morph., XXV.

Mohr, O. L.

1916. Studien über die Chromatinreifung der männlichen Geschlecht-

zellen bei Locusta viridissima. Lièg

Morgan, T. H.

1919. The Physical Basis of Heredity. Lippincott Co., Philadelphia.

Robertson, W. R. B.

1916. Chromosome Studies, I, Taxonomic Relationships shown in the

Chromosomes of Tettigide and Acridide, ete. Jour. Morph.,

XXVII, 2. i

Wenrich, D. H.

1916. The Spermatogenesis of Phrynotettis magnus, ete. Bull. Mus.

Comp. Zool., LX, 3.

1917. Synapsis and Chromosome Organization in Chorthippus, ete..

Jour. Morph., XXIX.

Wilson, E. B.

1912. poa on Chromosomes, VIII: Observations on the maturation-

enomena, ete. Jour. Exp. Zool.,

1913. tenait and Microscopical Research. Botence.

VARIATIONS IN THE SECONDARY SEXUAL

CHARACTERS OF THE FIDDLER CRAB

PROFESSOR T. H. MORGAN

CoLUMBIA UNIVERSITY

In species in which the ordinary individuals are

sharply separated into males and females there are occa-

sionally found abnormal individuals in which character-

istics of one sex are mixed with those of the other sex.

We are only at the beginning of the study of these cases,

but enough work has been done to make it more than

probable that there are several, or even many different

kinds of situations that call for separate treatment.

That this is generally becoming recognized is evident

from the different names that have been used in describ-

ing these cases, such as intersexes, sex intergrades, her-

maphrodites, gynanders, androgynes, pseudo-hermaph-

rodites, free martins, eunuchoids, protandrous hermaph-

rodites; moncecious, dicecious, tricecious plants, indiffer-

ent larve, neuter insects, éte. It seems to me not worth

while at present to attempt to classify such material until

we have learned more about it. Whether all or only some

of the aberrant types of fiddler crabs here described

should be called intersexes depends largely on the defini-

tion of what that term includes.

Tn the fiddler crabs the male (Fig. 1 A) and the female

(Fig. 1 B) show not only the characteristic differences of

other decapods, but one of the claws of the male is

enormously enlarged. It may be either the right or the

left one. If removed a new claw of the same kind regen-

erates from the stump although it may take more than

-one molt for the claw to become as large as the one re-

moved. In the fiddler ‘‘compensatory regulation’’ does

not take place as in some other decapods (Alpheus) ;

that is, after removal of the large claw, the smaller one

does not enlarge and substitute for it at the next molt.

220

No. 632] SECONDARY SEXUAL CHARACTERS 221

D dDouble clawed. F

Fig 1

222 ` THE AMERICAN NATURALIST [Von. LIV

Moreover, and this is important, the characteristics of

the new big claw are apparent as soon as the regener-

ated part begins to take shape, and even long before the

molt.

The other most characteristic difference in the exter-

nal parts between the male and the female is found in

the abdomen. In the male, Fig. 2 B, it is narrow, in the

female, Fig. 2 A, it is almost as broad as the ventral sur-

face of the thorax against which it is plastered. If the

abdomen of the male is lifted up, its anterior pair of ab-

dominal appendages, modified into copulatory organs,

can be seen (Fig. 2 B’ and Fig. 3 A). In the female the

abdominal appendages (Fig. 2 A’ and Fig. 3 B, B’) are

entirely different, and are used to carry the eggs. The

external genital pores can also be seen when the abdomen

is lifted up; those in the male on each side of the middle

line are in the segment that carries the last (5th) pair

No. 632] SECONDARY SEXUAL CHARACTERS 223

of legs, in the female they are further forward on the

segment that carries the third pair of legs.

In the summer of 1917, at Woods Hole, Miss Grace

Hays, while sorting out some fiddlers, found an individ-

ual that had a small first pair of legs like those in the

female, but an abdomen like that in the male. Another

collection of crabs was made and three other such indi-

viduals were found. In the summer of 1919 the col-

lectors at Woods Hole brought to me more fiddlers, and

from them more aberrant forms were obtained. It then

seemed worth while to find out how often such individ-

uals occur in this locality. Thanks to the interest shown

by Mr. Wm. Procter and Mr. Alfred F. Huettner a large

number of crabs were collected and carefully looked

over. As shown in the following table the number of

aberrant individuals was found to be about .0077 per

cent.

Normal * Intersex °

BOS = i 5 iia wis aeur es 5 June 24, 1919

ig BE a GO Sa ee: A 28

1849 er ey wee eee 6 30

Kotal 3 BER ee eu es 13

1 A few small intersexes were later obtained by Mr. Lionel Strong at Cold

Spring Harbor, L. I. Mr. Procter later collected 2,068 crabs at South

Wellfleet Cabs 4), but found no aberrant individuals amongst them.

224 THE AMERICAN NATURALIST [Vou. LIV

A cursory examination showed that two types of indi-

viduals were present. The larger individuals had the

abdomen of the male sex, but both claws were small and

No. 632] SECONDARY SEXUAL CHARACTERS 225

more like those of the female (Fig. 1 C). The other in-

dividuals had abdomens not quite so broad as those of

typical females of the same size, Fig. 4 B’, yet their

claws were generally small, like those of the female, and

showed no indications of a variation towards the male

type. Since the younger stages of some crabs, such as

the blue crab, have a narrower abdomen than that of the

adult female until the last molt, it seemed possible that

these ‘‘intersexes’’ might at a later molt turn into typi-

cal females. They were kept therefore and well fed for

two or three months during which time they molted once,

, Fig. 4 B”, or even twice. A comparison of the old skin

showed that the condition of the abdomen and claws had

not changed. It is evident that this condition can not be

explained as transitory. Nor is it juvenile because nor-

mal individuals of the same.size have the abdomen full

width.

A more detailed examination of these two types may

now be given. The most striking fact is that all of

the full grown crabs belong to one category, and all of

the smaller ones to another. The former of which there

are six, have a strictly male abdomen regardless of the

condition of their claws, and what is more significant the

external genital pores are at the base of the last pair of

legs, as in the normal male. As shown in Fig. 2 A’ and

B’, the abdomen is exactly like that of the male. On its

inner side it contains the two long copulatory appendages

of the male. The chele in three individuals are small,

Fig. 4 B, and of the same size, resembling those of the

female. In the other three one of the claws is somewhat

larger, Fig. 4 A, than the other and shows unmistakably

evidence of variation toward the male. The genital pores

are, as stated, in the same position as in the normal male,

and there are no indications of female pores further

forward. In two cases at least, the crabs molted, but did

not change their characters. In the second group, Figs.

A, B, C, D, there are sixteen individuals. There is

amongst these no obvious relation between the size of the

226 THE AMERICAN NATURALIST [Vou. LIV

crab and the relative width of the abdomen. Some of the

smallest have the narrowest abdomen. There is some

correlation between the character of the abdominal ap-

pendages, particularly the first pair and the width of the

abdomen. As shown in Fig. 6 A, B, this appendage does

not appear as much like that of the female of the same

size, Fig. 6 C, as would be expected were it strictly

female, yet it can not be said to be male-like, and the nar-

rowness of the abdomen may be responsible for the dif-

ference.

The claws are like those of the female in all cases.

After the foregoing account was written I have received

from Miss Rathburn a number of fiddler crabs, exactly

like those recorded above, from the collection in the Na-

tional Museum in Washington. They fall into the same

No. 632] SECONDARY SEXUAL CHARACTERS 227

two groups. One large male, labelled Uca pugilator

(18286), has a pair of small female like claws. It comes

from Northampton Co., Va. (1894). It belongs to a dif-

ferent species from those described above.

There are in this collection eight small female-like

erabs with the abdomen narrower than that of the nor-

mal female of the same size. AIl of them have both small

claws of the same size. In those with the narrowest ab-

: : aoe B ;

Fig'6

domen, the abdominal appendages are straighter and

less plumose than are those of the normal female of the

same size. This condition might be described either as

a juvenile, or as a less female-like condition, but not nec-

essarily more male-like. In size and shape the abdomens

of these crabs are like those of Fig. 5 4, B,C, D. In ad-

dition there is one small individual (17688) labelled

‘‘bugilator,’? with the abdomen about half the width of

a normal female of the same size of the other species.

There is also one further variation in the fiddler that

is different from the preceding ones. It is shown in Fig.

1 D. Mr. G. M. Gray found this male fiddler (Uca pugi-

latur), and with his permission I am able to figure it here.

It had two large claws, both like the claw of the normal

male. I find that Professor S. I. Smith, of New Haven,

recorded in 1869 a similar case of Uca pugnax.

228 THE AMERICAN NATURALIST [Vou. LIV

At present we are entirely ignorant as to what causes

determine in the normal male that only one side develops

a big claw. The asymmetry of the fiddler appears to be

analogous to that of the asymmetry of snails and of the

one-sided operculum of certain annelids (Hydroides), ete.

It is generally supposed that something comes in during

the development of the male crab that turns the scale

one way or the other; and once determined the relation

persists during life in fiddler crabs, although in other

decapods, as shown by Przibram, the initial difference

may be reversed during regeneration if the large claw is

removed and the small one left. Until we get further in-

formation concerning these matters it would be idle to

speculate as to what has led in this male to two large

claws.

It is interesting to note in the case of this male with

two large claws that it differs from the ordinary males

by doubling the kind of difference that distinguishes the

normal male from the female. It can scarcely be said to

be an inter-sex, for the difference is not in the direc-

tion of the opposite sex, but away from it. If some desig-

nation is called for, it might be said to be a super-male,

or at least an over-clawed male.

Discussion OF THE RESULTS

If we compare the results of parasitic castration of

certain decapods with the conditions described here in

the fiddler crab several resemblances and differences be-

come apparent. First in none of the cases of parasitized

crabs are the external genital openings affected. They

furnish a certain clue to the original sex of the individual.

Likewise in the large fiddlers the male external genital

pores are present, and there are no female pores. The

individuals have probably always been males. Whether

the condition of their claws is due to some disease, or

possibly to some internal parasite, or to a change in the

genetic complex, can not be stated. It is even possible

that it may be due to none of these, but to some ‘“‘acci-

dent’’ in the development, i. e., to some change in the em-

No. 632] SECONDARY SEXUAL CHARACTERS 229

bryology that determines the asymmetry of the normal

male. The occurrence of the male with the two large

claws may seem to favor the last interpretation; for here

we find the reverse relation and it does not seem prob-

able that such an over-clawed male could have arisen

through parasitism, or through disease, although the ar-

gument for a genetic change can not be entirely set aside.

In regard to the other group containing the small ab-

errant forms the situation is somewhat different. All of

these have started as females, as the location of the ex-

ternal genital pores clearly indicates. Yet some of them

show also an apparent change towards maleness by

the narrowing of the abdomen or possibly a retention of

the juvenile condition. Here the change, if it be achange,

is in the reverse direction from that. shown by most of

the intersexes described by Giard and by Geoffrey Smith,

since starting as a female the change is towards male-

ness, while in the parasitized crabs it is the female that

changes towards the male. The different degrees to

which the change has taken place in different individuals

may seem to indicate disease or parasitism. The ab-

sence of further change in the same direction in the next

or following molts is not perhaps so favorable to this in-

terpretation. But on the other hand the absence of adult

crabs of this sort, or at least their infrequency may mean

that these individuals do not reach maturity, and may

therefore be diseased or infected? or that in the adult the

full-sized abdomen is attained. These questions must be

further investigated before a decision can be reached.

GENERAL AND HYPOTHETICAL

It may seem, as stated above, that some of the changes

seen in the fiddlers may be similar in kind to some of

those brought about in other crabs by becoming para-

sitized. Giard has described several cases in crabs and

2 Geoffrey Smith has described changes in the crab Inarchus brought about

by inflection of a gregarine. The abdomen and claws of the male were

changed in much the same way as when this crab is parasitized by a barnacle.

Giard has deseribed an hermaphrodite amphiurian, parasitized by Orthenec-

tide, that cause the ovary to degenerate while the testes continue to function.

230 THE AMERICAN NATURALIST (Von. LIV

other Decapods parasitized by other crustataceans (Sac-

culina Portunion, Peltogaster, ete.), in which changes

take place in certain parts of the body that approach the

condition found in the opposite sex. These changes in-

volve most often the abdomen and its appendages, and

in one species at least the claws. The most marked

changes involved the male, producing in him alterations

in the direction of the female. In one case a female is

described as showing some effects of the parasite but if

I am correct Giard interpreted this change as resulting

from the retention of the juvenile condition. Giard con-

trasts the changes in the male crabs with those produced

_ by castration in the vertebrates. He seems to imply at

times that he supposed the effects are produced by the

loss of the gonads. At other times, however, he speaks

definitely of the changes as some sort of symbiotic rela-

tion between the host and the parasite—an idea similar

in many respects to the later and more elaborated hy-

pothesis of Geoffrey Smith. In fact, in summing up the

evidence Giard recognizes two classes of cases; those

due to the indirect action of the parasite by way of the

testes, and those due to the direct, by action on the host.

It was, of course, at that time natural to suppose that in

both groups, vertebrates and crustaceans, castration acts

in the same way, especially as the case of the vertebrates

had been long in the literature, and zoologists had be-.

come familiar with this kind of effect. Moreover at the

time other evidence was lacking to show in other groups

that the gonads have no influence on the development of

the secondary sexual characters. But the work of Oude-

manns that was later fully confirmed and extended by

Kopec and by Meisenheimer and by Kellog removed any

prejudice that the situation in the vertebrates had

brought about, so that at the time when Geoffrey Smith

wrote the field was clear for an independent judgment.

As stated Geoffrey Smith brought forward evidence that

seemed to him to show that the changes in the secondary

sexual characters in parasitized males were due to physio-

No. 632] SECONDARY SEXUAL CHARACTERS 231

logical processes set up by the parasite in the host. He

even went so far as to compare directly and in detail the

substances called forth in the host by the action of the

parasite. Without discussing these questions here (since

I have recently discussed them in my paper on ‘‘ The

Genetic and Operative Evidence Relating to Secondary

Sexual Characters,’’ Carnegie Publication No. 285, 1919)

it is evident that crucial experiments must be made on

the crabs themselves before a conclusive case can be

made out. This is by no means a simple matter as I have

found. During the last three summers at Woods Hole I

have tried to carry out experiments on crabs to test some

of these questions. All attempts to remove the gonads

in fiddler crabs have failed, because of the delicacy and

distribution of the organs, and the fatalities that result

when the carapace is lifted up. Attempts such as Sta-

mati made in 1880°to destroy or injure the gonads by in-

jecting substances through the genital pores have also

failed, because of the delicacy of the tubes and the dis-

tance of the gonad, in the male, from the external genital

opening.

Some important observations made by Kornhauser

(1919) on the effects of parasitism of the tree-hopper,

Thelia bimaculata, by the hymenopteron, Amphelopus

thelia, have a bearing on the preceding discussion. The

egg of the parasite is deposited within the body of the

nymph of Thelia from the first to the fifth instar. The

egg or eggs give rise to a number of ‘“polyembryonic”’

larve, that ultimately destroy the host. Infected males

show in the adult stages many of the characteristics of

the female, the degree to which the change takes place

being mainly dependent on the stage at which parasitism

occurred. The change involves the pigmentation, the

size, certain abdominal spines, the shape of the abdomi-

nal selerites that approach or even reach the condition

found in the female. The genital appendages do not

change into those of the female, but remain small and

lose their specific characteristics. `

232 THE AMERICAN NATURALIST [Vor LIV

Parasitized females do not assume any of the features

peculiar to the males.

The gonads in both sexes usually degenerate, and an

accumulation of fat takes place in the abdomen of the

host. Two exceptional cases have an important bearing

on the cause of the changes resulting from the parasitism.

One male was found that had been parasitized, and al-

though it had been considerably changed towards the

female in its somatic characters it ‘‘contained full-sized

normal testes with many spermatozoa.’’ Evidently then

the changes caused by the parasite are not due directly

to the destruction of the gonads as shown by this indi-

vidual in which the gonads had escaped. This accords

with the results of artificial castration in other insects.

The other exceptional case (fourth instar) had a ‘‘per-

fect female soma’’ but contained testes. The individual

had started as a female. There was evidence of this,

though it is not conclusive, in the chromosome counts of

the somatic cells. It must be supposed that at an early

stage something changed the cells of the germ-track, so

that its cells developed into testes. This conclusion is

borne out by a count of the chromosomes of ‘the testes

that show 21 cells in the spermatogonia, one of them

being the large X chromosome characteristic of the male.

An early ‘‘elimination’’ (loss) of an X chromosome from

the mother cell of the germ-track, such as occurs in Dro-

sophila, would seem to be the simplest explanation of

this case, as suggested by Kornhauser.

The conclusion from the evidence is quite convincing,

namely, that the several characters peculiar to the male

are changed into those peculiar to the female as a result

of the direct action of the parasite, and not through any

influence by way of the gonad.

FEEDING FIDDLER Crass ON THE GENITAL GLANDS OF THE

OPPOSITE Spx

During the summer of 1918 I carried out some feeding

experiments. The occurrence of hormones in the repro-

No. 632] SECONDARY SEXUAL CHARACTERS 233

ductive ‘‘glands’’ in other animals suggested the possi-

bility that the secondary sexual characters of fiddler crabs

might be affected if the crabs were fed on the organs of

the opposite sex during the period of regeneration of the

large claw. Male fiddlers whose large claw had been

previously removed, were fed exclusively, and at inter-

vals of two or three days, on the ovaries of female spider

crabs. The fiddlers were kept until they moulted about

a month or two later. The new claw showed all the char-

acteristic features of the normal large claw. Its regen-

eration had not been affected by the character of the food.

Female fiddlers, one of whose claws had been pre-

viously removed, were fed on the testes and the ducts

leading from them of the male spider crab. Other

females were fed on what appears to. be a large gland in

the posterior part of the abdomen of the male. No effect

on the regenerating claws were observed.

These negative results do not show that there is no

hormone in the gonads of the crab that affects the sec-

ondary sexual characters, for even if there were such, it

might not be able to produce its effect through the diges-

tive tract. Only positive results of this kind would be

important but none were obtained. As the results were

entirely negative they need not be further described.

A more promising test consisted in boring a hole in

the carapace of the male fiddler and inserting pieces of

the ovary of the female fiddler. Conversely for the

female. There are certain implications in Geoffrey

Smith’s views that seem to imply that male tissue can

not survive and grow in an individual with female metab-

olism, and perhaps conversely for the male. The small

grafted pieces often become lost, and it is difficult to de-

termine later by means of sections how far the tissues

degenerate and how far they become implanted and grow.

I have not had the time to carry out a detailed study of

the sections, but they seem worthy of further examina-

tion. No effect on the claws were produced.

234 THE AMERICAN NATURALIST [Vou. LIV

A PIECE or an Ovary PRESENT IN A MALE Crap

A normal male fiddler was opened to obtain pieces of

its testis. In the region where the left testis is supposed

to end there was found a small piece of ovary with its

purple eggs. These were sectioned and found to be nor-

mal eggs. This observation is significant in so far as it

shows that ovarian tissue can grow and differentiate in a

purely male environment. The explanation of this oc-

currence is not at hand. One is tempted to refer to it an

abnormal cell division in the testis of such a sort that the

chromosome combination (if such exists) to produce

eggs was formed, but in the complete absence of infor-

mation concerning the chromosome composition of the

male and female crustacea, such an attempt would ap-

pear premature.

INTERSEXES AND GYNANDROMORPHS IN CRUSTACEA

If it does not seem probable that the aberrant types

in the fiddlers, that have been described above, can be

safely referred to parasitism, it may not be without in-

terest to point out that there are many other queer cases

of sex mixtures in the crustacea, that do not appear in

any way connected with environmental changes—or at

least not directly.

Many cases of intersexes have been described in the

Cladocerans, in the genera Daphnia, Alona, Leptodora,

Simocephalus, under the name of androgynes, gynandro-

morphs, intersexes, ete. (Kurz, 1873. Grochowki, 1896.

Woltereck, 1908. Kutner, 1908. Ashworth, 1913. Agar,

Banta, 1918. De la Vaulx, 1915 and 1918). The anten-

næ more often show modifications characteristic of both-

sexes, but other organs are frequently involved, includ-

ing even the gonads. There are no indications of para-

sites in any of these cases, where owing to the transpar-

ency of the body they would be easily detected if present.

Kutner has recorded the sporadic occurrence of inter-

mediate forms through 12 generations of Daphnia pulex

—in a line having a relatively high percentage of these

No. 632] SECONDARY SEXUAL CHARACTERS 235

forms. No recognized form of inheritance can be de-

tected in these parthenogenetic lines. If, as generally

supposed, there is no elimination of chromosomes in the

parthenogenetic egg of Daphnians, the expectation would

be that all offspring of an intermediate would be like the

mother, whether the ‘‘character’’ were recessive or domi-

nant. It would seem then that if certain lines of parthe-

nogenetic Daphnians do produce more intermediate

types than occur in the general population, we must look

either to irregularity in the chromosome behavior or to

environmental influence. The latter seems excluded by

Banta’s results to be mentioned later. The former can

only be hypothetical until such differences are found.

Nevertheless the discovery of such cases in other groups

(Drosophila, @inothera) makes the suggestion at least

not so speculative as might have appeared several years

ago. :

The most important results are those recorded by

Banta, not only because he has obtained a much higher

percentage of intergrades, but because these appeared in

a pedigreed strain, and the appearance of the inter-

grades has been carefully followed through later genera-

tions. -In the 131st generation of one of the strains there

appeared males, females and sex intergrades. The last

group composed of ‘‘males with one or more female sec-

ondary sex characters, females with one to several male

characters and some hermaphrodites with various com-

binations of male and female secondary sex characters.”’

Highly male-like females produce only a few young or

are sterile. ‘‘A female intergrade with as many as six

strong male secondary characters rarely produces

young.” Males that have one or more female characters

have nearly always incompletely formed testes. The

strain was kept up by breeding from female intergrades

that continued to produce females, males, and sex inter-

grades for 16 generations with no apparent change in the

ratio of the various sex forms.’’ The picture here pre-

sented can not but suggest some sort of disintegration or

236 THE AMERICAN NATURALIST [ Vou. LIV

variation in the chromosome mechanism. At present we

do not know how a parthenogenetic female sometimes

produces. female (parthenogenetic) broods, at other

times male broods or sexual eggs. That such changes

may be brought on by environmental changes seems not

improbable from the large amount of data already col-

lected. The results in these respects are so similar to

those in rotifers where the situation is now under con-

trol (Whitney) that one can scarcely resist the convic-

tion that in both cases the environment acts in produc-

ing the changes. But while we have no explicit evidence,

as yet, even in Hydatina, that the environment acts only

by bringing about changes in the chromosome mechan-

ism, there is at least nothing known opposed to such a

view, and some general arguments that incline one to

anticipate such a discovery. Until these matters are set

straight not much is to be gained by speculating as to

how the sex intergrades of Simocephalus and other

Daphnia arise. But if it should be found that the nor-

mal cycle is caused by alterations in the chromosome

cycle, as has been shown in fact for Phylloxerans and

Aphids, then I think we may have to look to some aber-

rations in the same mechanism to explain these anoma-

lous cases. Indeed the kind of inheritance described by

Banta appears to be one that might be expected from

such a situation.

In the genus Cyclops, Mrázek (1914) has described

‘‘androgynes ” that have modifications in the antenne,

and Bremer (1914) has recorded two cases of ‘‘pseudo-

hermaphrodites’’ in Diaptomus.

In sharp contrast to these kinds of intersexes in the

lower crustaceans stand out the bilateral gynandro-

morphs that have been found in two genera of lobsters.

Nichols in 1734 described a lobster whose right side was

female and whose left side was male. Dissection showed

an ovary in the female side and a testis on the left. A

similar case was described for Palinurus in 1902 (Bur-

ger), but no dissection was made.

No. 632] ` SECONDARY SEXUAL CHARACTERS 237

In the Canadian Naturalist for May, 1919 (Vol.

XXXIII, No. 2), there is a description of another ‘‘her-

maphrodite”’ lobster. In reply to a letter of inquiry that

I sent to Mr. A. P. Wright, he states that the lobster was

sent to him by Mr. Halkett and that the animal is male on

the left side and female on the right side. There is an

ovary on one side and a testis on the other. These three

cases appear to differ from the preceding cases and sug-

gest a direct comparison with the bilateral gynandro-

morphs of insects. It is quite possible that they owe

their origin to some similar chromosome ‘‘elimination”’

in the course of development, but it should not be for-

gotten that sex-chromosomes have not been reported in

the lobster, although the cytology of the spermatozoa has

been often examined.

Another decapod, Gebia major, has been shown by

Ishikawa to be hermaphroditic. The anterior end of the

testes produces sperm and the posterior eggs. A pair of

ducts leads from each part to the exterior. Such indi-

viduals appear to function only as males. Spitschakoff

found in a crab, Lysmata seticaudata, that both ovaries

and testes are present with their ducts and external geni-

tal pores on the third and fifth pairs of legs. The an-

terior end of the gonad functions as ovary and the poste-

rior as testes, which is the reverse relation from that of

Gebia.

In crayfish belonging to the genus Parastacus, von

Martens, 1870, von Ihring, Faxon, 1898, and Lonnberg,

1898, have described genital pores on the third and fifth

pairs of appendages. Lonnberg has dissected some of

these individuals. He finds testes in some of them,

ovaries in others, but in both cases there are two pairs of

ducts lead to the genital pores on the third and fifth

pairs of legs. Here there is no true hermaphroditism,

but on the contrary separate sexes. Nevertheless the

ducts characteristic of the males and females in other

species with separate sexes are both present in all indi-

viduals of Parastacus.

238 THE AMERICAN NATURALIST [Vou. LIV

Selbie points out that Wollebaek (1909) showed that

Calocaris macandreeé is normally hermaphroditic, each

individual having testes and ovaries. The first pair of

abdominal appendages has its tip expanded in all indi-

viduals as in male decapods.

In some of the amphipod crustaceans, the occurrence

of ova in young males seems to be a normal occurrence

recalling the conditions in frogs. Nebeski (1880) stated

that the anterior end of the testis of Orchestia gamma-

rilus contained ova. DellaValle, 1893, never found

many eggs in Orchestia deshayesti, and none at all in

sexually mature males. Geoffrey Smith made some

further observations and attempted to explain the re-

sults on his anabolism-metabolism view. Ch. Boulenger

studied the two forms mentioned above. Out of 137

males of O. gammarellus, 135 had no ova and 2 had a few

ova anteriorly. Of small individuals, on the other hand,

nearly all contained ova in the testis (198 with and 19

without ova). ‘‘These results are therefore much at

variance with those obtained by Smith and I am at a loss

to explain how he arrived at his conclusions.”’

INTERSEXES AND HYBRIDIZATION

In recent years several cases in which intersexes ap-

peared in considerable numbers have been shown to be

due to intercrossing. This raises the question whether

some of the aberrant individuals here described may not

have been due to crosses between the two species of fid-

dlers Uca pugnax and Uca pugilator. It is true that the

latter is found most often in sandy stretches and the

latter on muddy flats, yet the two are not infrequently

found together or in nearby localities. The larger inter-

sexes appear to be unmistakably Uca pugnax; the smaller

are more difficult to identify. Miss Rathburn has exam-

ined both the large and the small individuals here de-

3 Ewing (’85) has described a blue erab in which the abdomen is inter-

mediate in width between that of the adult male and female. He thinks that

the individual is hermaphrodite, but as shown by Churchill, the peculiarity

described is the normal condition of the juvenile female before the last molt.

No. 632] SECONDARY SEXUAL CHARACTERS 239

scribed and reports that they all belong to the species

Uca pugnax, and show no signs of being hybrids.

The most interesting cases of intersexes are those pro-

duced by Goldschmidt in crosses between different races

of the gypsy moth. He describes some crosses that give

individuals showing only a slight tendency towards the

opposite sex; other crosses go further until finally the

male may be completely transformed into females, the

change even including the appearance of eggs in the

gonads. Conversely females may be changed towards

maleness in various degrees depending on which varie-

ties are crossed. His interpretation in general is that

the two kinds of sex genes have different values in dif-

ferent races, so that the hybrids are in these respects be-

twixt and between so far as the influence of the sex genes

isconcerned. As I have recently discussed at some length

Goldschmidt’s view (see Carnegie publication, No. 278,

1919, and No. 285, 1919), I need not go over the ground

again. :

Harrison has more recently described intersexes in

the offspring of different species of moths belonging to

the family of Bistonide.

In this connection it is interesting to note that some of

the phenomena seen in these moth crosses appear when

crosses are made between two species of Drosophila,

namely, D. melanogaster and D. simulans. Made one way

the cross gives only females as A. M. Brown discovered,

and as Sturtevant has verified. Reciprocally only males

are produced, as I have found, with a few females hatch-

ing late in the series. In both cases, however, the hybrid

males and females from the two crosses, although sterile,

are strictly one or the other sex both in their gonads and

in their secondary sexual characters, but as stated

the gonads are rudimentary. Sturtevant’s recent dis-

covery of real intersexes in a race of Drosophila simu-

lans has an important bearing on the interpretation of

intersexes. He finds in a certain line that individuals

appear that show characters both of the male and of the

240 THE AMERICAN NATURALIST [Vou. LIV

female, including especially the genitalia. They have

rudimentary gonads. Breeding from normal heterozy-

gous sisters and brothers he has shown that there is

present a recessive gene that gives the intersexes when

present in double dose in females. This gene is in an

autosome. The results are shown, therefore, not to be

due to a change in the gene or genes for sex, but to a gene

whose effects are superimposed on the influence of the

sex genes. It is evident that such a possibility must be

reckoned with in interpreting other cases.

Intersexes have been found in human lice, Pediculus,

by Keblin and Nuttall. The evidence makes it probable

that these arise most frequently when the body louse, P.

corporis, crosses with the head louse P. capitis. These

intersexes have both male and female gonads and geni-

talia in the same individual, differently combined.

It has long been known that crosses between Gallina-

ceous birds give rise to males that are sterile although

such males are not described as intersexes. Whether

only the male hybrids survive or whether the female hy-

brids are sometimes turned into males is not known.

Guyer has raised the question as to whether the individ-

uals in question if ever females might be classified as

males, because of the rudimentary condition of the ovary.

It is well known to-day that removal of the ovary of the

hen causes her to assume the male plumage (Goodale),

and also it is more than suspected that tumors in the

ovary or other diseases of that organ produce a like

effect on the plumage. But Guyer points out that in the

few cases examined by him testes were present. Riddle

has described many cases in hybrid doves in which the

sexual behavior of certain individuals showed them to

have opposite sex tendencies from that indicated by their

gonads. These he calls sex intergrades. It is well known

to poultrymen that birds in poor condition sometimes,

behave queerly in their sex relations. It is possible that

the weakened condition of these doves may have some-

thing to do with their anomalous behavior. But aside

No. 632] SECONDARY SEXUAL CHARACTERS 241

from this question it is possible to state that in one of

the crosses at least, in which a sex-linked character is in-

volved, there is good reason to believe that the normal

sex chromosome relations persist. It is scarcely legiti-

mate under these circumstances to suppose that the ordi-

nary mechanism of sex production is changed in such

cases in the sense implied or stated that males have been

turned into females and females into males. Moreover

it is sometimes overlooked that if such were the case very

anomalous sex inheritance would follow were it possible

to breed such hybrids. Unfortunately this is not pos-

sible in most of the cases at issue, since the hybrids are

Sterile, but in the few hybrids that have been bred no

such disorder of the machinery appears and the individ-

uals appear to be true to their sex. One must look, I

think, in other directions for an explanation of the results.

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1892. Uber innere Zwitterbildung beim Fluskrebs. Arch. f. mikrosk,

de la Vaulx, R.

1916. Anomalies antennularis de quelques Daphnies gynandromorphs.

ull. Soc, Zool. France, 40, 194-197.

1916. Sur les Daphnies androgynee. Bull, Soc. Zool, France, 40,

102-104.

1918. Observations sur L’apparition des Daphnies gynandromorphes.

l. Soc. Zool. France, 43, 187-194.

Wenke, K.

1906. Anatomie eines Argynnis paphia-Zwitters, nebst vergleichend-

anatomischen Betrachtungen über den ee hroditismus bei

Lepidopteren. Zeit. f. wiss. Zool., 84, 95-13

Wheeler, W. M.

1910. The Effect of Parasitie and Other Kinds of Castration in In-

sects. Jour. Exp. Zool., 8, 317-538.

1914. Gynandromorpos Ants Described During the Decade 1903-

1913. AMER. NAT., 48, 49-56.

ee ae W.

1889, Uber einen Fall von äuserem Hermaphroditismus beim Flus-

krebs. Travaux de la Soe, natural, de St. Petersbourg, Sect.

Zool., 20.

Selbie, C. M.

1914. The Decapoda Reptantia i the Coasts of Ireland. Part I.

Palinura astacura and anomura (except Paguridea). Fish-

eries, Ireland, Sci. ees I.

246 THE AMERICAN NATURALIST [Von. LIV

Smith, S. I.

1870. Notes on American Crustacea. Trans. Connecticut Acad., II,

113-176,

Smith, G. W.

1905. Note on a Gregarine (Aggregata mo n. sp.) which may cause

the parasitic castration of its host (Inachus dorsettensis).

Mitt. Zool., Stat. Neapel, 17, ae 06—409.

1906. Rhizocephala. Faun, Flor. Golf. Neap., Mon, 29, 1-123.

1908. Sex in the Crustacea with Special Reference to the Origin and

alge of Hermaphroditism. Rep. 77 Meet. Brit. Ass. Adv.

1909. Wades Cambridge Nat. Hist., 4, 1-217

1910. Soe in the Experimental Dosis of ‘Sex, Quart. Jour.

Vol. 54, 577-604,

1911. Pade in i ihe Experimental Analysis of Sex. Part 7. Sexual

ae nges in the Blood rie ed of Carcinus menas. Quart.

r. Micr. Sci., 57, 251-

1913. rk in the E y A of Sex. Part 10. The

Effect of Sacculina on the Storage of Fat and Glycogen, and

on the Formation of Pigment by its Host. Quart. Jour. Micr.

1914. Studies in the Experimental Analysis of Sex. Part 11. On

Stylops and Stylopisation. Quart. Jour. Micr. Sci., 60, 435-

461.

T: Th.

912. Lysmata seticaudata Risco, als Beispiel eines echten Hermaphro-

- ditismus bei den Decapoden. Zeit. wiss. Zool., 100, 190-209.

Wollebaeck, Alf.

1908. Remarks on Decapod Crustaceans of the North Atlantic and the

Norwegian Fiords. Bergens Mus. Aarbog, 12.

1909. Effektiv hermaphroditisme hos en decapod Crustace, Calocaris

macandree, Nyt. Magaz. Naturvid., 47.

v. Zograf, N

1907. Hatnapkroditisaaon bei om Männchen von Apus. Zool. Anz.

‘2

THE SABLE VARIETIES OF MICE

DR. L. C. DUNN

i BUSSEY INSTITUTION, HARVARD UNIVERSITY

THE variations in darkness of certain forms of fancy

mice have called forth different interpretations from the

various investigators who have studied them. The pres-

ent report is intended as a contribution of experimental

data, treating these differences as graded variations.

The varieties of mice most commonly exhibiting dif-

ferences in darkness comprise those races known as

sables. Such mice are distinguished by a yellow belly

and a back of some shade of black or brown with which

yellow may or may not be mixed. They were first re-

ported by Bateson in 1903 but Miss Durham (1911) was

the first to breed them experimentally and to catalog the

variations within the sable race. Little (1913) classed

sables as yellows with varying amounts of dark pigment

in the hairs on their dorsal and lateral surfaces. Dunn

(1916) offered the explanation that all sable varieties dif-

fered from ordinary yellow by a factor or factors deter-

mining the quantitative increase of dark pigments, so

that sables formed a continuous series of increasing dark

dorsal pigmentation from clear yellow to black-and-tan

in which the back was intense black while the yellow pig-

mentation was exhibited only onthe belly. Onslow (1917)

was ‘‘led to look upon sable as a pattern factor which

could give a yellow belly to a mouse of any color,’’ but he

did not publish the experimental evidence upon which

his conclusions were based. He criticized Dunn for

further involving the nomenclature of the sables through

the use of the names ‘‘black-and-tan,’’ ‘‘brown and tan,”’

“black sables,” and ‘‘brown sables,’’ to designate the

members of the sable series.

The use of the above term is, I believe, justified because

black-and-tan is recognized by the English fanciers as dis-

tinctly different from ordinary sable, and because none

of the sables described by Miss Durham behaved as did

247

248 THE AMERICAN NATURALIST [Vou. LIV

the mice used in my experiments. Miss Durham de-

scribed ‘‘black, blue, chocolate and silver fawn mice which

differ only from the ordinary forms by having yellow

bellies,’’ but they subsequently always moulted into ordi-

nary sables which have a ‘‘dark black or brown streak

down the middle of the dorsal region while the rest of the

mouse is yellow.’’ Black-and-tan however does not moult

to ordinary sable. Even at the age of twenty months

black-and-tan is entirely black except for the yellow belly

and yellow ticking on flanks and muzzle. Since these

mice were different from ordinary sables, they were

given a name to indicate the difference. Moreover when

they were crossed with various non-black-and-tan varie-

ties there were produced in the second generation mice

resembling the black-and-tan parent, others intermediate

between black-and-tan and yellow, and conforming to

Miss Durham’s description of sable. The latter were

called black sable or brown sable to indicate the color of

their non-yellow pigment. I am in sympathy with On-

slow’s desire to prevent a duplication of terms but I be-

lieve that the names employed are required by the pres-

ence of types which differ both genetically and somat-

ically.

Sooty yellows may likewise be included in the sable

series since these mice appear when black-and-tans or

sables are crossed with non-sable varieties. Sooties can

not be distinguished simply as yellows which are hetero-

zygous for black, for yellow mice which carry black may

show no trace of sootiness. Factors additional to the

black gamete are involved in the production of sooties

and these factors are present not only in the sooties but

in the blacks which they produce. Little (1916) used

blacks derived from sooties in crosses with wild agouti

and obtained agoutis which were much darker dorsally

than any wild agoutis. I have obtained similar results

from such crosses. Certain blacks with which yellows

have been crossed to produce sooties evidently carry

some of the factors for darkness which appear in greater

concentration in sables and black-and-tan as well as in

No. 632] SABLE VARIETIES OF MICE 249

the blacks derived from these varieties. Sooty, then, ap-

pears to be a lower stage of sable in the more complete

restriction of non-yellow pigments from the hair.

In addition to the varieties treated above it is neces-

sary to speak of light bellied mice which can not be in-

cluded in the sable series. I refer to the light-bellied

agouti variants reported by Cuénot and Morgan. These

variations have been shown to belong to a series of mul-

tiple allelomorphs in which the other members are ordi-

nary agouti, yellow, and non-agouti. The light-bellied

agouti also arose spontaneously in Little’s 1916 crosses

between gray-bellied agouti and dilute brown. Such

light-bellied agoutis bred true and when crossed with a

non-agouti variety they produced in F, only light-bellied

agoutis and normal non-agoutis. This result contrasts

strongly with the result of a cross of black-and-tan with

wild agouti which produces only sables and gray-bellied

agoutis in F,, while in F, there result yellows, sooties,

sables, black-and-tans, agoutis and darkened agoutis.

The difference is readily seen to be due to the yellow

gamete of the sable series.

To explain the results of the genetic behavior of sables

one is led to review the origin of the varieties concerned.

The wild house mouse is undoubtedly the ancestral type

from which all varieties of fancy mice have descended.

Its pelage contains the three fundamental pigments of

mice: yellow, black and brown, formed in the mosaic

known as the agouti pattern by the presence of a specific

gene ‘‘A.’? Each pigment is likewise determined by a

gene, Y for yellow, B for black, b for brown (absence of

black) and by loss of one or more of these genes, or by the

gain of other genes determining the distribution of the

pigments present, the whole array of fancy varieties has

resulted.

Yellow was shown by Cuénot to be due to a change in

the gene ‘‘A,’’ resulting in the presence of a restrictive

factor which limits the distribution and amount of black

and brown pigment, the eyes alone being dark pigmented

while black or brown pigments are present in the hair and

250 THE AMERICAN NATURALIST [Vou. LIV

skin in such small amounts as to leave the pelage clear

yellow. All three fundamental pigments are present in

yellow and it is essentially an agouti in which the dark

pigments are quantitatively restricted and reduced.

This gene acts as the dominant allelomorph of agouti,

light-bellied agouti, and non-agouti. Black mice, on the

other hand, represent no quantitative reduction in amount

of pigment but only the absence of the genes for yellow

and agouti. The sables contain a gene allelomorphic to

agouti and non-agouti. The evidence shows that this

gene is common to yellow, sooty, sable and black-and-tan

mice. This gene is a lethal. When it is present in both

gametes uniting to form a zygote it causes the death of

the zygote. This lethal gene (yellow) might conceivably

assume several forms and cause the differences noted

among the sable varieties. If such were the case, yellow

and sable varieties would be members of a series of mul-

tiple allelomorphs of a single gene. Such series have

been demonstrated in the gene for white eye in Droso-

phila by Morgan and his co-workers; in the color gene in

the guinea pig by Wright (1915); and in the agouti gene

in the mouse itself as quoted previously. But if the

black-and-tan mouse or a sooty were due simply to a dif-

ferent form of the yellow gene the difference of their

black recessives from ordinary blacks would still remain

to be explained. Moreover yellow and the members of

the sable series are more closely related to each other

than as mere members of a multiple allelomorphic series.

They do contain an identical gene, and unlike multiple

allelomorphs can be changed one into the other more or

less completely. Their difference rather inheres in their

possession of modifying genes determining the quantita-

tive increase of black or brown pigments not only in con-

nection with the yellow gene itself but: in connection with

the genes for black, brown and agouti.

Such modifying genes can not be merely changes in a

distributive gene such as agouti or the gene for restric-

tion which causes yellow, for their presence has been

demonstrated in non-agouti, non-yellow animals. They

No. 632] SABLE VARIETIES OF MICE : 251

must rather be related to the formative genes for black

and brown pigment, so that the number of black and

brown pigment granules is increased in proportion to the

number of modifying genes present. I have examined

microscopically hairs from the mid-dorsal region of a

black-sable mouse which was intermediate in color be-

tween black-and-tan and yellow, from pure black-and-tan

and from clear yellow mice of the same age. The cause

of the difference among the hair colors of these three

forms was clearly the varying number of black pigment

granules. In the yellow hair the dark granules were ex-

tremely rare and poorly defined, appearing in many cases

as partially mixed with the diffuse yellow ground color.

In the sable hair the black granules were more numerous,

occurring singly in the distal third of the shaft, while in

the proximal two thirds the concentration was greater.

Here the granules were large, one granule usually ex-

tending across the medullary space. In some cases two

granules appeared side by side, and in rare instances I

noted rows of three across the hair. In the hairs from

the black-and-tan the concentration of granules was three

to ten times as great as in the sable hair; the whole shaft

was filled with closely packed small black granules. One

row was rare; two was common; the rule was three or

four rows, while I sometimes found rows of six small

granules packed closely into the width of the hair.

If, as I have stated, there exist in mice genes determin-

ing the quantitative increase of dark pigments, it should

be possible by experiment to test their existence and to

determine whether they are Mendelian in behavior or not

and whether they are simple or multiple. The data which

follows is submitted as a test of the above questions.

According to the provisional hypothesis, black-and-tan

being the darkest member of the series should genetically

contain the greatest number of modifying genes. The

presence of such genes should become apparent if black-

and-tan were crossed with a race containing the dark pig-

ments but lacking entirely any of the modifying genes.

These conditions were satisfied only by pure wild house

252 THE AMERICAN NATURALIST [Vou. LIV

mice, caught at a distance to insure against any contami-

nation from crossing with fancy varieties. These wild

mice were regarded as lacking the darkeners; black-and-

tan as containing the maximum concentration of dark-

eners; and after some preliminary experimentation it

was decided that six stages in darkness could be distin-

guished of which the wild was regarded as grade 1 and

black-and-tan as grade 6. These did not represent all the

grades that actually appeared, for the variation from one

to six was practically continuous but such arbitrary

points had to be fixed for convenience in observation and

record. These grades were standardized by means of

type skins for each grade with which each mouse was

compared at the age of three weeks and at later intervals

throughout life.

The results of crossing black-and-tan with wild agouti

are seen in Table I and Fig. 1. The first generation con-

sisted of two classes of young, darkened yellows and dark-

ened agoutis. The mode of the F, yellows was at grade 3,

and their mean grade was 3.3 both practically midway be-

tween the parent grades. The mode of the F, agoutis

was at 2 and their mean grade was 2.8 showing that al-

though they represented a blend between the parental

types the agouti pattern affords a less favorable back-

ground for the development of darkness than does yellow.

Two F, generations were raised, one by inbreeding the

F, yellows, the other by inbreeding the F, agoutis. The

distribution of F, yellows shows the increased variability

which we have come to expect from such blending char-

acters as size and other quantitative measurements. Evi-

dence of segregation of parental characters appears from

the presence of a large number of grade 1 (yellows) and

the separation of this class from the other large class

(grades 3 and 4) by a small class (grade 2). Segregation

of darkness may also be inferred from the large class at

grade 5 which contained relatively few individuals in F,.

The mean grade of F, is 3.0 indicating that the average

darkness has not changed while the distribution has

changed considerably. The same is true in a lesser de-

No. 632] SABLE VARIETIES OF MICE 253

gree of the F, agoutis resulting from the inbred F, yel-

lows and of the progeny of the inbred F, agoutis. In the

‘latter class strong evidence of the segregation of the un-

darkened wild is apparent from the large size of grade 1

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THE AMERICAN NATURALIST

254

ILAODY CIM HLM NVI-ANV-AOVIg A0 Sassoup

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No. 632] _ SABLE VARIETIES OF MICE 255

(wild). The average grade of these F, agoutis is 2.2,

slightly lower than the F, grade while two new grades

have been added to the distribution, grade 1 (wild) and

grade 5 (very dark agouti). A few back crosses were

made of F, agoutis with wild, and of F, yellows with wild.

These showed likewise segregation of undarkened yel-

lows and undarkened agoutis and lower mean grades than

F’,—2.5 for yellows and 1.5 for agoutis.

The results thus far had established the presence of a

factor or factors for darkness, the formation of inter-

mediates in F, when crossed with animals lacking it, and

the incomplete segregation of parental types in F,. They

had not answered our questions regarding Mendelian be-

havior or number of factors involved. This failure may

have been due to incorrect observation, to the failure of

the grading scale to distinguish between the types pro-

duced or to the actual non-appearance of the types ex-

pected. By. constant application and ‘regrading it was

believed that the error from the first two reasons was low.

To consider the third, one must recall what is known of

the origin of the black-and-tan variety. It has been for

some years a standard breed of the English fancy, built

up probably through the constant selection by breeders

of the points it now possesses—clear yellow belly and

intensely black back with a sheen not duplicated in any

other variety or in the hybrids of black-and-tans with

other varieties. Since the variety breeds quite true these .

points must be heritable, and one can hardly expect to ex-

tract the pure type of black-and-tan from a cross with

wild without practising upon the segregates a selection

similar to that which perfected the variety. This involves

the supposition that the factors causing the darkness of

the black-and-tan are very numerous and extremely small

in individual effect.

The F, darkened agoutis were chosen as the starting

point of a selection for darkness which lasted through

several generations. These agoutis were easier to grade

because they were non-yellow; their litters were larger

for the same reason, and it was also desired to know

256 THE AMERICAN NATURALIST [Vou. LIV

whether the fact that black- id tans were always hetero-

zygous for black was a cause of their darkness. The re-

TABLE II

CROSSES OF DARK AGOUTIS INTER-SE

Srade Distribution ot Young

Parents Fan E O RE RE, T z y pey

Pie te lat a ea tee ee

Ab oe, 3 33. | 1.00 1

po Re oe Jape iia 11 | 21 33 | 1.60| 1

DEEA CE G2 sr, Il 038 6 3 38 | 2.02 2

XIV. 4X38. 6 5 11 | 3.45 1

De ee MO es oak 7 6 13 | 3.46 0

SVL Bb Xie. a a oe a 8 | 16 5 4 51 .83 13

AVIL SXG... & | iv-| 33} 28} 18 6 | 105 | 4.38 | 18

AVIE OXA 1 fe ad! a fe 6: 13 68 | 4.66

RIX. 56 X65. : 4 4 5 21 5.23 r

an ON Dia 6'| 20 | 41 | 47 | 21 | 135 | 5097 30

Wik. Oo Gs Se gS G |160 | 23 27 72 |. §.45 | 18

AAKI. OX I (wild)... 2. : 13 | 26 | 19 8 12 |. 2.55 0

I. Blk.-tan X wild.. 23 422 4:13 58 | 2.83 0

sults of mating together dark agoutis of various grades

is shown in Table II and Fig. 2

The table shows plainly that the variation in darkness

is practically continuous. Animals of grade 1 proved to

be pure wild segregates entirely lacking the darkeners.

Grades 2, 3 and 4 contained the darkener but never pro-

duced by recombination any animals darker than their

own grade. Grades 5, 5.5 and 6 produced grades both

darker and lighter than their own, proving them to be

heterozygous in the modifiers. None of these darkest

grades proved to be pure dark segregates. Even grade 6

which was entirely black with a gray belly and quite com-

parable in darkness to black-and-tan produced animals of

grade 1 (light segregates) when crossed with wild agouti.

These grade 1 agoutis were tested and found to lack any

modifiers for darkness. Therefore grade 6 in darkness

was not homozygous as regards the darkening modifiers.

The supposition that the darkness of the dark agoutis

might be due simply to their being heterozygous for black

was disposed of by the results of the dark agouti crosses,

for of eighteen F, dark agoutis thoroughly tested, twelve

were heterozygous for black and six were homozygous

No. 632] SABLE VARIETIES OF MICE 257

agoutis. In subsequent generations selection was in the

direction of darkness. That this was not accompanied by

selection of heterozygotes is shown by the figures for dark

agoutis of F,, F, and F, which were tested. In genera-

tions F, and F, there were twenty agoutis heterozygous

for black to 8 homozygous agoutis; in F, four heterozy-

gotes to three homozygotes, and the homozygotes com-

Grede | x Gradel Grede 2 x Grade2

Grades 1234 56 123456

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Fic. 2. Crosses of Dark Agouti Inter-Se.

prised some of the darkest mice produced. Another ex-

planation for the darkness of the agoutis must be invoked

and the data indicate that the only alternative is the ac-

258 THE AMERICAN NATURALIST [Von LIV

quisition by the dark agoutis of the peculiar and puzzling

darkness from the black-and-tan race.

Up to his point the data has involved crosses of dark-

ness with its absence—and crosses of dark animals of

various grades inter se. Multiple factors appear to be

involved and yet no evidence of Mendelian behavior has

been adduced except the segregation of lack of darkness

without accompanying segregation of darkness.

Many additional crosses have been made in which the

darkeners from the sable series have been transferred

into other varieties with results similar to those outlined

above. The most extensive of these secondary exper-

iments involved crosses of black-and-tan with brown

(chocolate) mice to test the black-and-tan (yellow) gamete

and to separate if possible the darkening modifiers (see

Table III and Fig. 3). This cross brought about the

union in the first generation of gametes with full dark-

ness (black-and-tan) with a uniform set of gametes from

the brown race all of which supposedly lacked the dark-

ener. The first generation from this cross showed, as

was expected, the dominance of black, all young being

black pigmented. Approximately one half were self black

which on being tested proved to be heterozygous for

brown. The other half were a lightened black-and-tan

(Table III, cross 23) with some variation but none were

as black as pure black-and-tan. The number of dark pig-

ment granules in the dorsal hairs was reduced and the

yellow pigment substratum was thereby allowed to show

at bases and tips of hairs especially in the older animals.

From these light black-and-tans was bred an F, genera-

tion (cross 26) consisting of’ mice with black pigment and

1 Morgan in 1914 reported the appearance in his experiments of mice to

which he gave the name ‘‘new gray,’’ which were noted first in the off-

spring of a pair of cinnamon mice. They ‘‘looked like chocolates, but

. . showed on later inspection distinctly ticked hair. One of these new

grays bred to black (heterozygous) gave some chocolates, black, new grays,

and one very dark, almost black, mouse.’? The above descriptions apply

quite accurately to cinnamon and agouti mice which I have raised from

erosses with one of the sable series and I have little doubt that the dark-

ness of Morgan’s new grays was derived originally from some mouse carry-

ing the ‘‘darkener.’’

No. 632] SABLE VARIETIES OF MICE 259

mice with brown pigment in approximately the ratio 3:1.

Of the blacks about one third were self black; the others

were yellows, sooties and black sables with varying

amounts of black in the fur, much like the F, array in the

TABLE III

CROSSES OF BLACK-AND-TAN WITH BROWN

Yellow and Black Young Yellow and Brown Young

Z F

a Parents | A futa Bia

2 2|3|4| 5 |5.5| 6 dlalélilalelalele 3 5

E 1 | 5 = |e | $ G a

A |

23 | Blk.-tan X Br..... |4|i7] 6 4.96 19 46 | |

24| Fi BTXE:BT..... 2/1) 2) 3 /12/26/14| 5.15)26) 86/02/11) 810 5.05 12 34

25 | Fi\BT Xbrown....|5|3{|11/2| 4| 2 3.00 30 57 9/27/0110 3.00 26/54

T X Br. and tan 6 |1 1} 0| 2 a7

27 | F. BT X F:BT from i | ;

P See |1| 2| 5117| 5.74 5.74) 7/82) 3) 3 | 5/11

black: and-tan X wildagouticross. In this F, distribution

were seen, besides all grades of intermediates, segregates

of both sorts, viz., yellows of grade 1 and black-and-tans

of grade 6, although the latter did not retain their dark-

ness throughout life and when bred proved not to be pure

segregates. The F, mice with brown pigment were sim-

ilarly divided into yellows and brown sables with varying

amounts of brown in the fur and self brown in the ratio

2:1. Of the yellow-browns some were evidently counter-

parts of black-and-tan with the black pigment replaced by

brown. To these the name brown-and-tan was given;

the other yellow-browns paralleled the yellow-black series

although the lower and intermediate grades were less well

represented, due perhaps to the difficulty of distinguish-

ing between yellows with considerable brown pigment and

yellows with smaller amounts of black pigment. Breed-

ing tests were used in doubtful cases. —

The F, light black-and-tans, when backcrossed to

browns (Table III, cross 24), gave equal numbers of all

four sorts, viz., yellow-blacks, self blacks, yellow-browns

and self brownė. The mode of these yellow-blacks was in

the middle class (grade 3) in contrast with the mode at

5.5 in the straight F,.

These crosses of black-and-tan with brown show the in-

dependence of the darkeners from black pigment for in

these experiments the modifiers have been detached from

260 THE AMERICAN NATURALIST [Vou. LIV

the black pigment on which they operate in the pure

black-and-tan and transferred to brown pigmented yel-

lows where their action is similar. Their independence

of yellow was illustrated by their action on ones mice.

‘ellow-blacks ell b

Yeni. sdble series) ig (Brown sabie. series)

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: (23456

Fic, 3. Crosses of Black-and-Tan with Brown, Yellow Young by Grades.

The intermediate nature of F, in the black-and-tan X

brown cross and subsequent segregation of dark and un-

darkened forms is not as clear as in the agouti crosses,

for it is probable that the brown parent contributed fac-

tors comparable to the darkeners which have acted to

make both F, and F, darker than if the darkening factors

had come only from the black-and-tan parent. The

browns used were derived from a yellow variety known

as red. Both the reds and their brown recessives are

more intensely colored than any other yellows or browns,

and in fact have given evidence in later experiments of

differing from ordinary varieties by intensity factors

similar to the darkening factors of black-and-tan.

No. 632] SABLE VARIETIES OF MICE 261

The results throughout indicate that we are dealing

here with genetic factors similar to those which have pro-

duced such quantitative differences as size in the races of

rabbits studied by Punnett. The results obtained from

crossing large and small races of rabbits agree in the pro-

duction in F, of animals genetically intermediate between

the parent races, and in the evidence of subsequent segre-

gation of the smaller size without segregation of the

larger. The same phenomenon appears in the present

study for light segregates have appeared but never the

ark. Placing the causes of darkness in mice in the same

category with the causes of size differences, which have

not yet been made clear, is an admission of the unsuitable-

ness of the material rather than of the insoluble nature

of the problem. Either the best material for the investi-

gation of such grade variations has not yet been found or

else the technique of observation and measurement of

such genetic differences as distinguished from non-her-

itable differences has not yet been evolved. The correct

interpretation of such differences must await an investi-

gation combining an optimum of material and method.

REFERENCES

Bateson, W.

1903. The Present State of a. of Color Heredity in Rats and

Mice. Proc. Zool, Soc

Cuenot, L.

1907. L’Hérèdité de la areen: chez les souris. (5) Arch. Zool.

Exp. et Gen.,

Dunn, L. C.

1916. ee gongs Behavior of Mice of the Color Varieties ‘‘ Black-

and ‘‘Red.’’? Amer. NAT.,

Durham, F. "s

Further TOE on the Inheritance of Color in Mice.

Journal of Genetics, Vol. 1.

Little, C. C.

191 he ee Studies of the Inheritance of in Mice. Pub.

No. 179 Carnegie Institution of Washingto

1916. Three Color Mutations in Mice. AMER. Nan, Vol. 50.

Morgan, T. H.

1914, Multiple Allelomorphs in Mice. Amer. Nar., Vol. 48.

Onslow, H.

1917. A note on Certain Names recently applied to Sable Mice. Jour-

nal of Genetics, Vol. 6.

SHORTER ARTICLES AND DISCUSSION

HYBRIDIZATION AND EVOLUTION

SoME years ago the writer made a cross between the two species

Nicotiana. rustica L. and Nicotiana paniculata L.t Since the

hybrids obtained through this mating are not completely sterile,

some biologists may perhaps maintain they are not distinct spe-

cies, but such a claim is wholly arbitrary. In a sense, a species

is a human concept and as such its definition may be carried to

any ridiculous extreme, yet there is no more striking biological

fact than that in general the great groups of living things do fall

into specific subdivisions which many criteria show to be distinct,

discontinuous, without intermediates. In two such groups fall

the above types. Though their ranges overlap, they differ from

each other in leaf, stem, flower and habit of growth much more

than do several other pairs of species within the same genus be-

tween which hybridization is impossible, or where the hybrid is

sterile.

The cross between these two species gives an F, generation in-

termediate between the two parents, and as uniform in each char-

acter as either parental group.

Few of the male or the female gametes are viable, vik by care-

ful attention to pollination, from one to twenty seeds can be

obtained in the capsules, where normally two hundred to three

hundred seeds are found. These seeds produce an F, generation

which is inordinately variable. No two plants are similar, and

numerous types can be picked out which if found in the wil

would undoubtedly be classed as different species. In genetic

terms, the behavior of the two species may be described as fol-

lows: They differ in an extremely large number of inherited

factors; and owing to these numerous differences, many of the

otherwise possible combinations of F, gametes, are not func-

tional. A huge percentage of expected combinations of both

gametes and zygotes are thus eliminated.

> The factors which in combination produce normal fertility,

1A detailed account of the genetic facts found in this study, has not yet

appeared. A preliminary paper was published in the Proc. Amer. Phil.

Soc., 54: 70-72, 1915.

262

No. 632] | SHORTER ARTICLES AND DISCUSSION — 263

recombine in the Mendelian sense, quite as do the factors con-

trolling the form of leaf and flower. The result is that after a

few generations of selection one may obtain a variety of strains,

uniform within each line, so fertile as to yield capsules with over

ninety per cent. of the normal quota of seed, and so different

from one another that the extreme types are more unlike than

_the two original species used in the cross.

After three years of selection (F;), eight such sain re-

mained out of a large series of selections studied earlier. It

seems hardly necessary to describe the differences they exhibited.

Suffice it to say that the smallest type was about 20 em. in height

with small smooth oval leaves, and the largest was nearly 200

em. in height with wrinkled cordate leaves some of which were

50 em. in length.

These eight strains were crossed in all possible combinations,

and every F, generation exhibited as high a degree of fertility as

that shown by the parents.

` To the writer it seems possible that these results have a bear-

ing on certain theoretical problems which may not be clear at

first sight.

A few years ago Lotsy? published an extended paper based on

a very limited number of crosses in the genera Nicotiana, Pisum,

Petunia and Antirrhinum, where partially sterile F, plants pro-

duced exceedingly variable progeny,—results wholly comparable

with our own. From these observations, neglecting all evidence

of the appearance of mutations in controlled pure lines, Lotsy

founded a theory of evolution. His arguments were based upon

five assumptions: (1) that all characters obey the Mendelian law

of heredity, (2) that acquired characters are never transmitted,

(3) that homozygotes are absolutely constant in succeeding gen-

erations, (4) that there has been no proof of variation inde-

pendent of crossing, and (5) that the variations observed after

crossing are sufficient te account for evolution.

Naturally numerous criticisms can be made against this ex-

treme interpretation. One need only inquire as to the source of

the original variations which are to form the basis of all Men-

delian recombinations, to show the untenability of the position.

On the other hand, it will be admitted by all that hybridization

has played some part in evolution, and it is of some importance

to endeavor to determine the limits of its rôle.

2 Lotsy, J. P., ‘‘La théorie du croisement,’’ Arch. Néerland. Sci. Exact.

et Nat., III, B, 2: 1-61, 1914.

264 THE AMERICAN NATURALIST [Vou. LIV

The observations of the writer on the enormous variability of

the F, generations arising from partially sterile F, generations

produced by crossing species, led him to suspect that such com-

binations might be the basis of a great deal of variability respon-

sible for evolution under domestication. A careful survey of the

evidence relating to the origin of modern horses, cattle, sheep,

swine, dogs, guinea pigs, fowls, ducks, and geese on the one hand,

and varieties of wheat, corn, barley, oats, rye, apples, grapes,

roses and begonias on the other hand, shows that in every case

several related wild or semi-wild species exist which will cross

together and yield partially fertile offspring. Doubtless many

other species which have shown great improvement under domes-

tication, would be found to have wild ‘relatives which behave sim-

ilarly, should they be investigated. Both the historical and the

experimental evidence, therefore, point to hybridization, and

particularly to species of hybridization, as the great single cause

of evolution under domestication.

At the same time, one must not confuse evolution under domes-

tication with natural evolution. The outstanding biological fea-

ture characteristic of the varied groups of domestic animals and

of cultivated plants, is the perfect fertility within each group.

A marked peculiarity of the great majority of natural species is

their sterility with one another, the origin of which has long

been a stumbling block to writers on evolutionary biology. Our

own experimental evidence, as far as it goes, and observations on

domestic forms which presumably have originated from com-

binations of two or more wild species, yield not the slightest in-

dication of a tendency toward the production of segregates that

exhibit either incompatibility in crosses or sterility of the indi-

viduals produced by hybridization.

E. M. East

BUSSEY INSTITUTION,

HARVARD UNIVERSITY s!

THE MEASUREMENT OF LINKAGE

LINKAGE is a name for that tendency sometimes shown by

genes to maintain in hereditary transmission their previous rela-

tions to each other. Thus if two linked genes, A and B, enter a

cross together, in the same gamete, they will oftener than not be

found together in the gametes formed by the cross-bred indi-

vidual. And if the same two genes enter the cross separately,

No. 632] SHORTER ARTICLES AND DISCUSSION 265

one in the egg, the other in the sperm, then oftener than not

they will be found apart, in different gametes formed by the

eross-bred individual.

Where no linkage exists between two genes, A and B, it will

be wholly a matter of chance whether they go together or not,

no matter what their previous relation was. We say that they

“‘assort independently,’’ as genes do in ordinary Mendelian in-

heritance, such as was known to Mendel. In such cases change

of relation occurs in the long run in half (or 50 per cent.) of all

cases. Such change of relation is called ‘‘crossing over.” Link-

age evidently will be shown by a falling below 50 in the per-

centage of cross-overs. The more cross-overs decline below 50

per cent., the stronger will be the linkage indicated, until when

no cross-overs occur, we call the linkage complete or perfect. Ac-

cordingly 0 and 50 per cent. will be the limiting values for cross-

overs indicating linkage. But it is conceivable that cross-overs

might occur in excess of 50 per cent. What would their signifi-

cance be? Not linkage, not a tendency to maintain relations

previously existing between genes, but a tendency to change

those relations, to go apart when previously together, and to get

together when previously apart. We are not acquainted with

any such tendencies as these, and it is difficult to imagine how

they might arise, but it is certain that they would be the opposite

of linkage and would need a different name, if observed.

It is evident that the strength of linkage increases, as the cross-

Over percentage decreases below 50. As a measure of the

strength of linkage, we might then take the difference between

50 and the observed cross-over percentage, as I have elsewhere

suggested (Castle, 1919). This would give us a numerical grade

of linkage strength on a scale of 50. But since we are more ac-

customed to grading on a scale of 100, it will perhaps be better

to double values thus obtained. Our grading scale of linkage

Strengths will then run thus:

Cross-over Percentage Linkage Strength

SO Sea bce whee ek Che sam ee 5 0

A ee a oe oe eee ees 20

BO T cea wee beet bah as 40

BOS iin Wa al Bec ba en we sees 60

J0 Ge MN Ae AO Mer San ON ae se: 80

Dek a as ee ee ee eee 100

By this method we can compare the linkage strength between

266 THE AMERICAN NATURALIST (vo LIV

any two pairs of genes without stopping to reverse the relations

indicated by cross-over percentages. For example the following

linkage relations are shown by the genes of rats and mice

(Dunn).

Cross-over Percentage Linkage Strength

Albinism—red-eye, rats .............. ? 96.4

Red-eye—pink-eye, rats .............. 18.3 63.4

Albinism—pink-eye, rats ............. 21.1(?) Res i Vict

Albinism—pink-eye, mice ............ 14.6 70.8

The strongest linkage here indicated is that between albinism

and red-eye in rats, next comes that between albinism and pink-

eye in mice. But albinism and pink-eye in rats show less linkage

than in mice. The three genes, albinism (c), red-eye (r) and

pink-eye (p) in rats are apparently arranged in linear fashion

thus:

This kind of a diagram is what Morgan, Bridges and Sturtevant

(1919) have made familiar to us under the name of ‘‘chromosome

map.’ Not to prejudice the case for or against the chromo-

somes, we might perhaps call it a linkage map or map of a link- `

age system. In its construction’ we use cross-over percentages

as direct measures of map distances, but in Drosophila at least

only distances relatively short have been found to be strictly

comparable. Beyond distances of about 5 units (cross-over per-

centages) it is found that double or triple cross-overs become

increasingly common and thus decrease the apparent number of

breaks in the linkage chain between two genes. So that long

map distances are based, not on directly observed cross-over per-

centages between the more distant genes, but on summation of

intervening short distances, it being assumed that the arrange-

ment is in all cases linear. While this latter assumption is not

to be accepted for all cases without proof, it must be admitted

that for Drosophila at least the evidence for a linear arrange-

ment is very strong and no insuperable objections can be raised

against it.

Map-distances have been found in the ‘‘first chromosome

linkage group of Drosophila exceeding 60, and in the ‘‘second

chromosome” group exceeding 100. But in no ease does the ob-

served cross-over percentage between two genes, however re-

mote, of the same linkage group exceed 50. This means that

No. 632] . SHORTER ARTICLES AND DISCUSSION 267

beyond very short distances cross-over percentages do not in-

crease in proportion to distance. The linkage group forms a

means of holding genes together, however distant they may be

from each other, so that, as one goes, all have a tendency to go.

The linkage map will give us a diagrammatic view of the rela-

tions to each other of the genes composing a linkage system. It

is based on the shorter observed cross-over percentages, or where

longer distances are used, they must be first corrected for double

and triple crossing-over. See in this connection the valuable

Table II. of Haldane (1919) which provides a ready means of

converting map distances into cross-over percentages or vice

versa, and so of predicting undetermined linkage relations. It is

based on a mathematical examination of the linkage system of

the first chromosome of Drosophila. A table of linkage strengths

will show us, without reference to distances involved, to what

extent the movements in gametogenesis of one gene are correlated

with those of any other gene. It is based on the unmodified

cross-over percentages observed, whether the map distances in-

volved are great or small. Linkage strengths can never exceed

50 on a scale of 50, 100 on a scale of 100, whereas map-distances

may be extended indefinitely with the discovery of new genes.

W. E. CASTLE

BUSSEY INSTITUTE,

HARVARD UNIVERSITY

LITERATURE CITED

Castle, W

1919. Studies of Heredity in Rabbits, Rats and Mice. Carnegie Inst.

sh., Publ. No. 288.

Dunn, L. C.

Linkage in Mice and Rats. (In press.)

Haldane, J. B. S.

1919. The Combination of Linkage Values, and the Calculation of

Distances anys the Loci of Linked Factors. Journal of

Geneties, 8, pp. ;

Morgan, T. H., Bridges, C. x and Sturtevant, A. H.

1919. C batahations to the Genetics of boaii melanogaster. Car-

’ negie Inst. Wash., Publ. No. 278.

IS THERE LINKAGE BETWEEN THE GENES FOR

YELLOW AND FOR BLACK IN MICE?

IN a recent number of this journal Dunn* has given data

showing a deficiency of black young in a family of yellow mice.

1 Am. Nat., 53: 558-560, 1919.

268 THE AMERICAN NATURALIST [Vou. LIV

Thus in a cross of two yellows, one of them probably hetero-

zygous for both black and brown and the other for brown only,

the offspring totalled fourteen yellow and four brown, the ex-

pectation being twelve yellow, three black and three brown.

The yellow descendents of this mating when bred to browns are

expected to give two yellows (one heterozygous for both black

and brown and one heterozygous for brown only) to one black

to one brown. The actual numbers obtained were eighteen

yellow, one black, and ten brown, and the expected numbers

fourteen yellow, seven black and seven brown. Dunn has sum-

marized these data according to the percentage of young of

each sort produced, as follows:

| Yellow | Black | Brown

Per cent. expected i 66.6 | 16.6 | 16.6

Per cant. obearvod: c.s. bcc tees 62.0 3.4 | 34.5

In the total number of young observed, the chances are equal

that the 16.6 per cent. expected black young might go as high as

30.8 per cent. or as low as 2.4 per cent. It is therefore apparent

that neither the 3.4 per cent. black nor the 34.5 per cent. brown

are aera outside the limit of probable variation due to

Aag not ncluding chance fluctuation as one of the three

theories capable of explaining his observed facts, Dunn evi-

dently feels the need for larger numbers of young before con-

sidering random sampling eliminated.

It is interesting however to see just what evidence there is in

Dunn’s data that black and yellow are linked. Apparently the

only facts in support of this hypothesis is the deficiency of

blacks and the slight excess of browns referred to. Significant

evidence for the expected excess of yellows carrying both black

and brown as compared with those carrying brown only is not

obtained. Of seventeen such yellows tested, ten carried both

black and brown and seven brown only—exact equality or 8.5 of

each is the Mendelian expectancy. The excess of yellows carry-

ing black and brown is 8.8 per cent. as against non-yellow browns

‘of 17.9 per cent. The deficiency of yellow carrying brown only

is 8.8 per cent. as against a deficiency of blacks of 13.3 per cent.

The sum of the departures from the expected equality in yellows

is 17.6 per cent., while in non-yellows it is 31.2 per cent., or

almost twice as much. The discrepancies in the yellow indi-

No. 632] SHORTER ARTICLES AND DISCUSSION 269

viduals are even more within the possibility of chance fluctuation

than those of the non-yellows.

Dunn states that linkage between Y and B ‘‘affords a satis-

factory explanation of the observed facts in harmony with other

cases of linkage.’’ However, one of the essential points of link-

age is that members of a multiple allelomorph series are linked

to a given gene in the same degree. Cuénot,? Morgan,’ Sturte-

vant,* and the writer,® have shown that the genes for yellow and

for agouti in mice are allelomorphic. Many investigators, in-

eluding Durham,’ Detlefsen,” and the writer,* ° have shown that

agouti and black are not linked in inheritance—yet according to

our present knowledge of linkage all genes in the same locus are

equally linked with any other given gene, and these crosses

should show linkage between agouti and black to a degree equal

to that of linkage between black and yellow. Dunn has not em-

phasized this point sufficiently.

Furthermore, if there is any significance other than random

sampling in the peculiar ratios reported, there is another pos-

sible explanation, not considered by Dunn, which avoids hypoth-

ecating linkage between yellow and black. If a lethal factor was

closely linked with black in the particular family under consid-

eration, and if this lethal was effective in a heterozygous condi-

tion in non-yellow mice—but not in yellow mice, the observed

results would be explicable as follows:

Let Y equal yellow, y equal non-yellow.

` B equal black, b equal brown

L equal lethal, 1 equal ey

Yy BL bl equals yellow heterozygous for black and lethal.

Forms gametes:

YBL YbL |

yBL ybL

yB] s l

Yb commonly YB rarely

ybl yBl

2 Archiv Zool. Exp. et Gen. (4), Vol. 8, 1911.

3 Am. NAT., 48, pp. 449-458, 1914

4AM. NAT., 46, pp. 368-371, 1912.

5 Sci., N. S., 38, p. 205, 1913.

* Jour. Genet., I, pp. 159-178, 1911.

T Genetics, 3, pp. 573-598, 1918.

8 Carn, Inst. of Wash., No. 179, 1913.

® AM, NAT., 47, pp. 760-762, 1913.

210°. THE AMERICAN NATURALIST [Vou. LIV

Crossed with brown normal yyblbl such a yellow would give the

following zygotes:

Yy BL bl; Yellow heterozygous for black and lethal

yy BL bl; Black lethal; dies*

only.

Yy bl bl; Yellow carrying brown normal ues 3

yy bl bl; Brown normal

Yy bL bl ; Veltow carrying brown and lethal

yy bL bl ; Brown lethal; dies*

a We rarely.

Yy Bl bl ; Yellow normal heterozygous for black

yy Bl bl ; Black normal

The death of the rare brown lethal individual would not be

noticed, for the common death of black lethals would leave a dis-

tinct excess of brown normals.

This hypothesis is capable of experimental test and involves a

lethal mutation in an entirely new factor which presupposes no

generality of the process in all yellows and agoutis; and simply

assumes that yellow, when present, hampers the action of the

lethal in much the same sort of way that it hampers the activity

of the black forming factor in the skin and hair.

The above hypothesis is advanced simply as an additional pos-

sibility for test in case something more than chance fluctuation

due to random sampling is involved.

C. C. LITTLE

COLD SPRING HARBOR,

Lone ISLAND, N. Y.

CREPIS—A PROMISING GENUS FOR GENETIC

: INVESTIGATIONS

To all who are familiar with the recent advances in our knowl-

edge of heredity, which were made possible largely through the

investigations of Morgan and others with ‘the fly, Drosophila

melanogaster, especially to those who have followed the develop-

ment of the chromosome theory of heredity with its correlative

theories of mutation and evolution, the urgent need of extensive

corroborative evidence from other animals and plants must be

forcibly clear. Although it appears inconceivable that the con-

clusions reached from the drosophila investigations are not ap-

plicable in all their essential features to all animals and plants,

No. 632] SHORTER ARTICLES AND DISCUSSION 271

yet it can not be denied that many biologists are not yet com-

mitted to the acceptance of these conclusions as of general ap-

plication. It is obvious that extensive corroborative evidence,

derived from other genera of animals and plants, would be o

paramount value in firmly establishing these far-reaching con-

clusions. It, therefore, becomes one, who allies himself with

those biologists who believe in the present importance and future

promise of this collection of genetic evidence, derived as it is,

almost entirely from a single species of insects, to consider most

carefully the selection of other material with which to test the

various hypotheses that have been proposed in order to interpret

the great mass of drosophila data consistently.

It is encouraging to note the energetic efforts of a number of

investigators to obtain a corresponding collection of data from

other species of Drosophila. As yet, however, little more than

a beginning has been made, particularly with the genetic inves-

tigations on these species, because it is necessary first to find

the comparatively rare mutant individuals with which to ex-

periment. No other genus of animals thus far reported upon

possesses so many features favorable to genetic study as does

Drosophila, although it is probable that other of the lower ani-

mal groups will in time furnish material just as valuable. In

plants, the only species in which genetic analysis has proceeded

far enough to establish the identity of a considerable number of

hereditary factors or genes, are the garden pea, sweet pea, snap-

dragon, maize, barley and wheat. In most of these and in some

other plants evidence of linkage of characters in inheritance has

been obtained, but in none has the number of linked groups been

shown to correspond with the number of chromosomes in the

germ cell and because of the relatively large number of chromo-

Somes in these species it will probably be some time before any

considerable body of corroborative evidence can be accumulated

from them. |

In addition to a low chromosome number there are several

other desiderata which the ideal form for genetic investigations

Should possess. It must display numerous germinal variations.

It must be prolific and easily reared. It should have a short life

eycle so as to permit of the maximum number of generations

within a given time. Furthermore, in the case of a plant, it

Should be self-fertile, so as to permit of establishing pure lines;

it should be easily hybridized ; and it should flourish when grown

under glass.

Ziz THE AMERICAN NATURALIST [Vou. LIV

A brief life cycle is extremely important because numerous

generations must be raised in order to secure adequate data for

the analysis of more complicated genetic problems. In this

respect, no sexually propagated flowering plants can compare

with the insects. On the other hand, certain highly desirable

features possessed by plants are either impossible or very

cult of realization in animals. For example, asexual jomodaoiion

can often be resorted to in plants when it is desired to fper-

petuate a particular individual for comparison with later gen-

erations. But the most important point of superiority of plants

over insects for genetic study is the greater possibility in plants

of ‘securing hybrids between different species. That this advan-

tage should receive considerable weight will be admitted by all

who recognize the need of studyińg hybrids between species hav-

ing different chromosome numbers. The desirability of such

investigations has been mentioned recently by Morgan (1919)

as follows:

The theory that the chromosomes are made up of independent self-

perpetuating elements or genes that compose the entire hereditary com-

plex of the race, and the implication contained in the theory that similar

species have an immense number of genes in common, makes the numer-

ical relation of the chromosomes in such species of unusual interest.

This subject is one that could best be studied by intercrossing similar

species with different numbers of chromosomes, but since this would

yield significant results only in groups where the contents of the chromo-

somes involved were sufficiently known to follow their histories, and since

as yet no such hybridizations have been made, we can only fall back on

the suggestive results that eytologists have already obtained along these

lines.

I have italicized one clause in the above paragraph in order

to emphasize the importance of extensive genetic analysis in those

particular species which are to be used in intercrossing exper-

iments. It is not sufficient that the species have low numbers

and different numbers; it is also necessary that the inheritance

of a sufficient number of characters in each species be studied so

as to establish the linked groups of characters or genes corre-

sponding to the chromosomes of each species. Only then can the

contents of the chromosomes involved be it lesa known to

follow their histories in the hybrids.

Thus we find several excellent reasons for seeking among plant

materials for a group of species which possess as many as pos-

es oa lle

No. 632] SHORTER ARTICLES AND DISCUSSION 273

sible of those features most favorable to securing the desired

results.

With this explanatory introduction let us consider briefly the

present state of our knowledge of Crepis with reference espe-

cially to its promise of usefulness in genetic studies.1 This genus

belonging to the chicory tribe of the Composite contains about

200 species (according to Index Kewensis) which are widely

scattered, the genus being represented by indigenous species in

every continent and in Australasia. Just how great is the diver-

sity in morphological characters within the genus remains to be

seen, but the wide distribution of the group as a whole and of

some of the individual species would lead one to expect a large

number of diverse characters and many different combinations

of the same. The descriptive connotation of many of the specific

names also indicates a remarkable diversity among these forms.

For example, there are giants and pigmies, there are forms with

bristly, woolly, floury, and glandular pubescence as well as

glabrous forms, there are four or more flower colors and one

species is named ‘‘bicolor.’? This expectation has been borne out

by such observations on preserved and living specimens as the

writer has been able to make. There are annual, biennial and

perennial species which should prove to be very interesting

forms for interspecific hybridization studies. Finally, within

at least two of the individual species, there certainly exists a

remarkable diversity of forms

But it is not for its wealth of variation alone that this genus —

is especially interesting to geneticists. The cytological investi-

gations which have been made on a dozen or more species of

Crepis reveal a most interesting situation as regards chromosome

numbers. There is at least one species (possibly two or three)

having only 3 for the haploid number of chromosomes, a group

of six or seven species with 4 chromosomes, another group of

four species with 5, a single species with 8, another with 9, and

still another with 20 chromosomes as the reduced number. The

absence of a common denominator greater than one for this series

of numbers has caused some interesting speculations as to the

= method of derivation of one species from another (Rosenberg,

1918). Several cytologists have also noted the fact that the chro-

is paper is a preliminary communication offered mainly for the pur-

pose of calling attention to this promising material. A few species have

been under investigation at the University of California for about three

years and will be discussed more fully in a future publication.

274 THE AMERICAN NATURALIST [Vou. LIV

mosomes themselves in these species are unusually favorable

objects of study, one of my correspondents going so far as to

predict that in time Crepis will become as famous and useful for

laboratory work as Ascaris is to-day. But the important consid-

eration in the present discussion is the fact that we have here

several species with the same chromosome number as Drosophila

melanogaster and at least one species with one less chromosome

pair. Obviously, if some of these species with the smallest

chromosome numbers are highly variable, existing in a large

number of distinct varieties or forms, they should serve as ex-

cellent material for genetic study especially if they possess the

other advantageous features already mentioned.

For at least two such species I can report very great promise

as objects of genetic research. Crepis capillaris (virens)? with

three chromosome pairs (Rosenberg, 1909, 1918; Digby, 1914)

and C. tectorum? with four pairs (Juel, 1905; Rosenberg, 1909,

1918). both exhibit polymorphism to a remarkable degree. This

is evidenced by the diversity of forms referred to these species

in the herbaria of the Royal Botanic Gardens at Kew and of the

Museum of Natural History in Paris. In both species it seems

to be merely a matter of sufficiently extensive seed collection

that is required in order to secure a sufficient number of allelo-

morphic pairs of characters to make possible the desired genetic

analysis. My cultures of C. virens, which have been grown from

seed secured from various foreign countries as well as in Cali-

fornia, have already yielded several pairs of contrasted char-

acters which will soon furnish a nucleus of genetic data on this

species.

These two pase are also very prolific, considering the plant

as a whole, there being several or many heads on a plant and

each-head bearing 5 to 15 fertile achenes in virens and 30 to 40

in tectorum. Unfortunately an individual flower produces but a

single seed and the flowers are so small as to make the work of

hybridization rather tedious when absolute control is exercised

through castration of the unopened flower. But, while this

method is essential in original crosses, it usually is not necessary

to castrate many flowers for any one cross, and when it comes to

2 The nomenclature of this species is somewhat in doubt. Both Robinson

and Fernald (1908) and Britton and Brown (1918) name it C. capillans

(L.) Wallr., but certain European botanists seem to have retained the name

T. virens L. for this species.

3 C, tectorum L.

No. 632] SHORTER ARTICLES AND DISCUSSION 275

making back crosses on a large scale, it may be practicable to

depollinate the flowers of the intended female parent with a

water jet instead of actually castrating the buds.

As regards other desiderata to be considered in selecting ma-

terial for genetic study these two species are very promising.

They are easily reared in greenhouse or field, the seeds ger-

minating quickly in glass germinators, thus permitting easy

manipulation and careful checking of viability when desired.

The life cycle varies from three to six months except in rare cases

of retarded development and little or no rest period is necessary

in the seed stage, so that it is possible to grow two or three gen-

erations in a year with proper facilities for culture under glass.

Partial or complete self-fertility is the rule in both these species,

although in some strains of virens the individual plant is nearly

self-sterile. No evidence of parthenogenesis or apogamy has been

found in these species. In general, therefore, it will be possible

to secure numerous sexually propagated pure lines, differing

from one another in one or more allelomorphie pairs, which will

Serve as the basic material for working out the ‘‘chromosome

content’’ in these species. It is only the problem of securing

seed from a large number of different localities and of growing

and carefully studying a sufficient number of plants that must

be solved in order to furnish the pure lines desired. The sooner

_ this can be accomplished the sooner can the extensive analysis

of the chromosome content of these species be gotten under way.

Finally the critical question as to whether these two species can

be hybridized has been answered in the affirmative by the pre-

liminary experiments of the present year.*

Sufficient has been said, I trust, to convince the reader that

we have in Crepis a wealth of material which may fairly be ex-

pected to furnish data of the greatest value in testing the gen-

erality of the chromosome theory of heredity, and that this group

is unique in the promise it holds of carrying out that test in much

shorter time than would be required if we should depend only

on the data which is slowly accumulating from other plants now

under investigation. It should be clearly realized, however, that

to accomplish the results aimed at, even with Crepis, will require

a considerable period of time, the length of the period being

largely conditioned by the number of investigators attacking the

t Since the above was written difficulty has been encountered in inducing

these hybrid seedlings to develop beyond the cotyledon stage. If this

difficulty can not be overcome both species will be crossed with still other

Species having low chromosome numbers.

276 THE AMERICAN NATURALIST [Von. LIV

problem and the facilities at their disposal or, in other words,

upon the amount of funds available for this project.

In order to advance the genetic analysis of Crepis virens and

C. tectorum now under way to a stage favorable to carrying out

the interspecific hybridization studies properly, calls for green-

house equipment, technical assistance, supplies and labor which

are not at present available. Some provision for the collection

of seed in foreign countries should also be made. There is no

prospect at this time that these facilities will become available

in the near future. It is recognized that the expansion of this

project will require a larger proportion of the time of the two

investigators now engaged on it and the workers concerned stand

ready to meet this requirement.

My purpose in going thus into detail is two-fold. First, so far

as I am aware, no other geneticists are working extensively with

this genus, and it should be clearly understood that under exist-

ing circumstances there is little prospect of rapid progress with

my own investigations. Yet the work has gone far enough to

accumulate material of very great promise. It is hoped, there-

fore, that means will be found to support adequately the investi-

gations of Crepis virens and C. tectorum now under way. Sec-

ond, it is highly desirable that other geneticists also contribute

to the analysis of the two species named above and especially

that they proceed with similar investigations, accompanied of _

course with cytological studies, on other species of Crepis.

Ernest B. BABCOCK

UNIVERSITY OF CALIFORNIA

LITERATURE CITED

1. Britton, N. L., and A. Bro

1918. Flora of North pa Nor.

2. aa L.

1914.. A Critical Study of the Cytology of Crepis virens. Arch. f.

Zelf., Bd. 12.

3. Juel,

1905. ie Tetradteilungen bei Taraxacum ~ — Cichorieen. K.

Svensk. Vetensk. Akad. Handl., Bd.

4. Morgan, T. H.

1919. The Physical Basis of Heredity. N. Y.

5. Robinson, B. L., and M. L. Fernald.

1908. Gray’s New Handbook of Botany.

6. Rosenberg, O.

1909. Zur Kenntniss von den gets ate der Compositen. Svensk.

Botanisk. Tidskrift., Bd. 3

1898. Chromosomenzahlen and oai mendimensionen in der Gattung

Crepis. Arkiv. för Botanik., Bd. 15, No. 11.

No. 632] SHORTER ARTICLES AND DISCUSSION 277

THE INHERITANCE OF CONGENITAL CATARACT IN

CATTLE

CATARACT in mammals may be due to environmental causes, or

it may be hereditary. The mode of inheritance has been debated.

In the case of man Bateson (1) and Davenport (2) regarded

cataract as a dominant Mendelian character, while Jones and

Mason (3) in an analysis of human pedigrees collected by Har-

mon (4) concluded that cataract is probably a simple recessive.

Danforth (5) raised some pertinent objections to this latter

hypothesis, and Jones and Mason (6) later admitted the validity

of some of these objections. There are a number of elements in

this analysis of human pedigrees which are no doubt perplexing,

but the preponderance of evidence seems to favor the hypothesis

that cataract in man is a Mendelian recessive.? Hereditary cat-

1 Paper No. 10 from the Laboratory of Genetics, Illinois Agricultural

Experiment Stat

2 The data as “uae by Jones and Mason seem Dig because of

the large value of P, a measure of goodness of fit of the observed to the

ETEA series. While there can be little doubt bat that the observed

e within reasonable limits of error when tested by any one of

aa approved methods, it should, pey be stated that Jones and

Mason’s use of Pearson’s criterion is hardly justified, inasmuch as Pear-

son’s iada applies to a correlated system PE ariables in which the sum

of the observed frequencies — sum of calculated frequencies, and the sum

of the errors = 0. Harris (7) of es out the value of Pearson’s formula

in relation to Mendelian ratios. Now in any complex Mendelian ratio of

fore be interpreted as consistent with their theory, if their method were

correct. By using the method adopted by Jones and Mason, one might

nevertheless obtain a better (%) fit in this case and thus a more satisfactory

result if one dealt with the series of normals in this population rather

than the series of cataractous. In any monohybrid ratio, the deviation of

the dominant class is — to the deviation of the recessive class. Hence,

if we divide the same series of deviations all the way through by a series

of larger calculated saben for normals, then X2 will be perceptibly smaller

and P larger (P= 0.71 in this case). This procedure would be somewhat

comparable to stating that in a single toss of 8 coins, 5 heads are more

likely to appear than 3 tails, or in a single throw of n coins (n-p) heads

are more probable than p tails.

278 THE AMERICAN NATURALIST [Vou. LIV

aract is known in some mammals other than man, but little is

known regarding its transmission. Hurst (8) stated that liabil-

ity to cataract-blindness in horses is a Mendelian character.

The data forming the basis of this paper arose through the

circumstance that a registered Holstein-Friesan bull, E. T. H.

(Holstein-Friesan Herdbook No. 62924) transmitted desirable

economic dairy characters to a marked degree, and consequently

attempts were made to fix his characters by inbreeding. A num-

ber of cataractous offspring resulted from these close matings.

The simultaneous occurrence of several cataracts in the progeny

of a single bull could not be attributed to chance environmental

or intrauterine conditions; hence the pedigrees of all animals

involved were carefully studied. There was no record of cat-

aract in any of the ascendants. The original bull, E. T. H., had

been mated to a large number of unrelated cows and produced

93 normal F, offspring. Thirty-two of these F, daughters were

mated to an F, son and produced 63 F, calves, of which 55 were

normal and 8 showed well-defined congenital cataracts of the

stellate type.* The ophthalmological aspects of these cases have

already been described by Small (8).

Cataract is evidently recessive in cattle and if it is a simple

Mendelian recessive then the original progenitor, E. T. H., was

heterozygous, Nn, where N= normal and n=cataractous.

Mated to unrelated normal females, NN, we should expect the 93

F, offspring to be perfectly normal, but of two genetic types in

equal numbers, NN + Nn. In selecting any F, son to breed to

the F, daughters, it was equally probable that he would be either

a homozygous normal, NN, or a heterozygous normal, Nn. A

single F, son, also a registered Holstein-Friesan bull, V. H. (Hol-

stein-Friesan Herdbook No. 158293), was chosen and he proved

to be heterozygous. Since half of the F, daughters were homo-

zygous and half were heterozygous, the former would produce

gametes, N+ N, and the latter would produce gametes, N + n.

The total population of F, daughters would therefore produce

three times as many normal as cataractous gametes. In Men-

delian notation the F, matings were as follows:

3N + Yn — gametes from F, females,

writers are indebted to Dr. ©. P. Small, of Chicago, Illinois, for

identifying the type of cataract and for much additional information, and

wish to express their appreciation of the deep interest Dr. Small has shown

in this case.

No. 632] SHORTER ARTICLES AND DISCUSSION 279

WYN + n = gametes from F, males,

ANN + Nn + nn =F, zygotes.

normal cataractous

That is, 7g of the F, calves should be normal and 1% should be

cataractous. The observed results agree with the calculated

rather better than one would usually expect, for the observed

= 55 normal -+8 cataractous and the calculated = 55.125 nor-

‘mal + 7.875 cataractous. The 8 F, cataractous calves were of

both sexes (2 heifers and 6 bulls).

All these facts clearly indicate that the original sire, E. T. H.,

was heterozygous, Nn. If mated to his own daughters he arid

give results similar to those of his son, V. H. He was thus tested

and produced 7 offspring of which 3 (1 bull and 2 heifers) were

cataractous. Collecting all matings of the sire, E. T. H., an

his son, V. H. (both were Nn)’ to F, daughters (NN + Nn) we

found

Normal | Cataractous | Total

a a ee a OD By re. | 11 | 70

Calculates th sibs kb ta R e 61.25. | 8.75 70

We may therefore conclude that congenital cataract in cattle is a

simple recessive Mendelian character.

To prevent the reappearance of cataractous individuals i in this

stock and to reduce the proportion carrying cataract as a re-

cessive is a matter of some economic importance. After all cat-

aractous individuals have been eliminated, there still remain one

half of the daughters and four sevenths of the granddaughters

of E .T. H. which carry a recessive factor for cataract. We can

not distinguish between the NN and Nn individuals, since N is

evidently dominant to n. Whatever the proportion of these two

types may be to each other, mating the cows to normal unrelated

bulls (which are almost unquestionably NN) will eventually re-

duce the cataractous-bearing individuals to a negligible mini-

mum. If we begin with r+ s individuals of the genetic consti-

tutions NN and Nn respectively, and we back cross to normal

stock, NN, any number of times, p, then the genetic composition

of the last generation produced after p such back crosses will be

[22r + (2? —1)s]NN + sNn.

280 - - THE AMERICAN NATURALIST [Vou. LIV

Since the first term becomes much larger than the second as p

increases, the number of homozygous normals becomes very great

compared with the heterozygous normals.

J. A. DETLEFSON,

W. W. YAPP

COLLEGE OF AGRICULTURE,

UNIVERSITY OF ILLINOIS

LITERATURE CITED

1. Bateson, Wm.

1913, Mendel’s Principles of Heredity. University Press, Cambridge,

2. pte Ge B

1911. Heredity in Relation to Eugenics. Henry Holt & Co., New

York.

3. Jones, D. F., and Mason, S. L.

1916, {abeditance of FOR Cataract. AM. Nat., 50: 119-126.

4. Harmon, N. B.

1910. eren of Human Inheritance. Eugenics Laboratory Me-

irs, XI. Part 10, Section XIIta: 126-169. Dulau and Co.

5. Danforth, o

1916. The Todeeritanes of Congenital Cataract. AM. NAT., 50: 442-

6. Jones, D. F., abd Mason, 8. L.

1916. Further emacs on the Inheritance of Congenital Cataract.

. Nat., 50: 751-757.

7. Harris, J.

1912. A pris Test of the Goodness of Fit of Mendelian Ratios.

AM. NAT., 46: 741-745.

8. Hurst, C. C.

1910. Mendelian Characters in Plants, Animals, and Man. Verh. d.

Naturf. Ver. in Brünn, 49: 192-213.

9. Small, C. P.

1919, Hereditary Cataract in Calves. Am. Journ. Ophth., 2: 681-

682.

FURTHER OBSERVATIONS ON SEX IN MERCURIALIS

ANNUA

In an earlier paper,’ I briefly mentioned the occurrence of so-

called moncecious forms in Mercurialis annua. I have since

then continued my studies upon such forms and this report deals

with the offspring of the so-called monecious plant, No. 3. It is

to be noted that Mercurialis annua is described as appearing in

1 Inheritance of Sex in Mercurialis annua, American Journal of Botany,

Dec., 1919.

No. 632] SHORTER ARTICLES AND DISCUSSION 281

three forms, male, female and monecious. Several hundred

seeds from plant No. 3 were sown in Fargo, North Dakota, in the

spring of 1919. Owing toa protracted drought only four plants

survived.

In their general habit of growth these plants were like the

females of my earlier observations—the flowers were clustered

At adh ,

Ai MWh

(

Fic. 1. Branch Mercurialis annua, a, male flower bud; b, female flower bud;

c, female flower; d, male flower; e, hermaphrodite flower.

in the axils of the leaves, either sessile or on more or less elon-

gated peduncles. In another paper (Mss.) I have described in

detail the various floral arrangements that appeared on these

plants. Female flower buds are conical. The male buds are

smaller than the female buds and they are spherical. The her-

maphrodite flower buds are like the female buds though some-

times smaller. Just prior to the opening of the hermaphrodite

282 THE AMERICAN NATURALIST [Vor. LIV

flower buds, the anthers may be recognized through the sepals.

These four plants are not monecious, since male, hermaphrodite

and female flowers appeared simultaneously on the same plant.

Plant No. 3-1 made a vigorous growth from the beginning.

Its foliage was dark green. The first flowers were female and

these were produced in increasing numbers. No attempt was

made to count the female flowers prior to the appearance of male

and hermaphrodite flowers. As can be seen from the table the

female flowers always outnumbered the male and hermaphrodite

flowers. Until September 10 the male flowers were more abun-

dant than the hermaphrodite. On September 12, there was a

sudden increase in the number of hermaphrodite flowers. This

rather sporadic appearance of flowers other than female flowers

shows how impossible it is to determine at one time the sex of

the individual. It is apparent that it is essential that such indi-

viduals be studied throughout their whole life history. Thus

through the first three months of its history this plant was fe-

male, after that it was polygamous, monecious, and gynomone-

cious. It was polygamous when beside the female flowers there

appeared male and hermaphrodite flowers, moncecious when only

male flowers appeared in association with the female flowers, and

gynomoneecious when hermaphrodite flowers appeared together

with female flowers. The total number of male and hermaphro-

dite flowers was about equal (table). This plant may be char-

acterized as a polygamous one.

While there were no definite points at which male or herma-

phrodite flowers appeared, there were branches that continued

to produce only female flowers throughout the life of the plant.

Thousands of seeds were collected from the plant.

Plant No. 3-2 like plant No. 1 made a vigorous growth. Its

foliage was much lighter than that of plant No. 1 but the plant

was healthy. As can be seen from the table the number of male

and hermaphrodite flowers that appeared at one time was rela-

tively larger than in any of the other plants. This condition

was maintained throughout the life of the plant. This plant

from the time of the appearance of male and hermaphrodite

flowers was decidedly polygamous, prior to that it produced fe-

male flowers like plant No. 1. During the period in which the

three kinds of flowers were counted, female, male, and hermaph-

rodite, the male flowers were in excess. It may be conceived

No. 632] SHORTER ARTICLES AND DISCUSSION 283

then that during a part of its life history the male elements pre-

dominated. This plant was a very prolific seed producer.

Plant No. 3-3 was a very vigorous grower and it behaved like

plants Nos. 1 and 2 until the time of the appearance of male and

hermaphrodite flowers. The total number of male flowers when

compared with the total number of hermaphrodite flowers showed

that the tendency of the plant was towards monecism. While

during most of its later history male and hermaphrodite flowers

appeared together, towards the end of the growing season (Octo-

ber 3-12) no hermaphrodite flowers were found and the plant

was decidedly monecious. This plant started out as a female,

became polygamous and towards the end became monecious.

Many seed were set.

Plant No. 3—4 started out as a vigorous plant producing in the

beginning female flowers in abundance. About the same time

that the other plants were producing increasingly large numbers

of male and hermaphrodite flowers this plant produced very few,

10 males and 4 hermaphrodites. After that the plant began

noticeably to lose in vigor, the leaves began to curl up. The

plant after that produced female flowers in abundance. These

however dried up very quickly and dropped off. The plant con-

tinued its sickly growth until it was killed by frost.

Pistillody and staminody occurred very abundantly in the

flowers of the first three plants. This condition I have described

in detail in another paper (Mss.). Many of the hermaphrodite

flowers had only a single stamen. The plants also produced a

large number of three-carpelled female and hermaphrodite flow-

ers whereas a two-carpelled flower is the rule.

While the number of plants is too small to warrant the draw-’

ing of any definite conclusions the following suggestive facts are

brought out.

1. Sex is not a fixed condition in these forms of Mercurialis

annua,

2. A plant may change its sex during the progress of its life

cycle.

3. Continued study with larger numbers of such plants will

very likely show marked variations and sex intergradations and

that a strict category of sex for these forms is untenable, so that

the terms monecious, gynomonæcious, gynodiccious, ete., can be

only arbitrarily employed.

284

THE AMERICAN NATURALIST [ Vou. LIV

sg ge oe Aug. 27 Aug. 30 Sept. 1 Sept. 4 Sept. 8

Only

tes nee 7 8 g ? 2 8 g Y £ é 8

duced Fls.} Fls.| Fls.| Fls.| Fls.| Fis.| Fis.) Fls.| Fls.| Fils.) Fls. Fls.| Fls.| Fis.) Fls.

3-1 œ co FII 2 | o 4|—|o2 1| œ 4 œ | 40| 10

3-2 (o) co | 25| 6 | © | 70 |36| æ |294/298) œ |158/163| œ |282)126

3-3 oo co} 5] L{ oo] 8] 4} 0 2| — |œ 9 o/ 15) 9

3-4 oo pla DY eon G At pf oOo te

Sept. 10 Sept. 12 | Sept. 16 Sept. 18 Sept. 22 Sept. 25

Pim 12IF/SIPIS1 8/214 P1S/BiP/S/ 8191s /8

Fis.| Fis.| Fis.| Fis.| Fls. | Fis | Fls.| Fls.| Fis. 1 og Fls.| Fls.| Fls.| Fls.| Fls.| Fls.| Fls

+i œ | 18| 8| æ | — |150'580| 50| 40 | 120| 40| — |200| 20/100

3-2 [750700450750 850 550 590/650) 350 301 550/512 165/225; 60

3-3 œ% | 22| 4/220/220) 60) ? | 20| ? | 60 200) 50/120/340| — |180/110| 30

3-4 Za ES

Sept. 27 Oct. 3 Oct. 12 | Total

punt | 9/3] 8] 9 TAPRE: 3 g

Fls.| Fls.| Fls.| Fils.) Fls.| Fls.| Fis. | Fis.) Fis. Fis. Fis. Fis.

3-1 102) 91| 24/500 100 000 200) 2 583 541

3-2 130/130} 80/400 480 500| 360/480120! œ -+3446 4892 3251

3-3 340,360, 20 200, 50 00 — 1920 1906 182

3-4 10 4

CECIL YAMPOLSKY

GRANTWOOD, N. J.

COMMENTS ON A RECENT CHECK-LIST

RESEARCH stations established in the past by scientific insti-

tutions, especially those in or near the tropics have generally

been devoted particularly to study of aquatic organisms. It was,

therefore, with great pleasure and with high hopes for its future

that naturalists all the world over have watched with keenest

interest the establishment and gradual development of the Trop-

ical Research Station of the New York Zoological Society.

Mr. Beebe has shown great acumen in selecting his locality.

His facile pen has drawn the wonders of his station’s environ-

ment in a way so splendidly vivid that I, for one, envy very

frankly his skill and his good fortune. These comments then are

offered here, on one of his recent papers, with a cordial apprecia-

tion of the debt which all naturalists owe to him for what should

in the future become the most useful workshop of its kind: in-

deed to be thought of always in future as bearing a relation to

the tropic rain-forest in the same way that one subconciously

recalls the Naples Station when thinking of or discussing the

fauna of the Mediterranean Sea.

No. 632] SHORTER ARTICLES AND DISCUSSION 285

Beebe has charmed many readers with essays which show that

he is gifted with a delightful diction and a romantic style most

convincing and hence to be most carefully used. To criticize

these essays unkindly is far too much like picking apart an

orchid. Nevertheless they sometimes have the defect of cap-

italizing supposed ‘‘new discoveries’ at a rather high adver-

' tising value when the history of our earlier knowledge has not

been. determined from the literature.

Thomas Penard, in an article of marked gentleness and cour-

tesy, has reviewed Beebe’s ‘‘Tropical Wild Life,’ in such a

way that further elaboration is happily unnecessary. Now, how-

ever, articles have appeared in Zoologica, which require more

careful examination. They purport to be usable lists, admitted

to be necessary, for any study of the higher vertebrates of British

Guiana with special reference to the fauna of the Bartica district

—the species which Beebe has actually found there being starred

with an asterisk.

Beebe introduces them as follows:

Finding no résumé available of the Amphibia, Reptilia and Mam-

malia of this colony, I have gone through the literature at hand and

made my own lists. These I offer as a preliminary enumeration of the

species thus far recorded in literature, or in my own collections, from

this British Colony. They form a tangible basis for future increments—-

the many new species and the radical extension of present known dis-

tributions which intensive study of these phyla in British Guiana is cer-

tain to achieve. Check-lists of mere names such as these are wholly

foreign to the future zoological work of the Tropical Station (italies

mine), but they are absolutely necessary as a basis for identification and

investigation, and it is in this spirit that this preliminary work has been

undertaken. :

I have made no attempt at a thorough search of literature for priority

or for confirmation of names or other similar phases of taxonomy, deem-

ing this the special province of the literary systematist. I have merely

sought to utilize the most recently accepted names of herpetologists and

mammalogists.

Now, generally speaking, the ‘‘literary systematist’’ does not

confine himself to this somewhat dry but entirely necessary voca-

tion, wholly from choice and he is saddened when his more foot-

free colleagues cast supercilious glances his way. It therefore

1 Auk, 36, 1919, pp. 217-225.

- 2Vol. 2, Nos. 7 and 8, 1919.

286 THE AMERICAN NATURALIST [Vou. LIV

behooves the now deservedly but still very highly vaunted ‘‘FIELD

NATURALIST’’ to write with care when he deliberately invades the

province of his more lowly associate. Systematists know that the

preparation of a good, useful check-list of a region like British

Guiana is no task to be entered upon lightly nor unadvisedly and

because the work is not spectacular, arouses little popular ac-

claim and is slow and tiresome, we sometimes wonder whether

these facts have not a high value in explaining the rather super-

cilious and scornful appraisal given to a mere check-list by the

modern field naturalist. Admittedly, however, this work if

worth doing at all, is worth doing well but this list of Beebe’s

is so phenomenally bad that we are loath to believe that Mr.

Beebe has tried to make it even moderately good. For example,

in so far as reptiles and amphibians—or mammals—are con-

cerned there is no evidence that specimens of many of the ob-

scure species discussed have ever been preserved for examina-

tion by a herpetologist.

We read of Bufo molitor. This name was given by Tschudi? to

a toad from high Peru. Naturalists in recent years have so far

as I know felt reasonably sure that this was a synonym of Bufo

marinus pure and simple. Stejneger has said recently:

Whatever may be the status of Tschudi’s Bufo molitor the half grown

toad [taken by the Yale Peruvian Exp.] collected at Santa Ana...

‘unquestionably belongs to Bufo marinus.

So also all the Peruvian examples collected by Mr. G. K. Noble

and now in the M. C. Z., Cambridge. Here then this name ap-

pears resurrected in literature and recorded from Bartica, of all

places, and no proof whatsoever offered to support so wholly

improbable a statement.

Bufo sternosignatus Keferst. The types came from western

Venezuela and Colombia. Giinther’s figure of this species shows

how easily it also might be taken for the young Bufo marinus.

Since apparently the species is not known from eastern South

America can this be called a valid record until Beebe’s specimen,

if it was preserved, falls into a herpetologist’s hands?

Hyla indris Cope. Another species, known apparently only

from Cope’s original description which strongly suggests that

it was probably nothing but an individual variant of Hyla

crepitans. ,

3 Fauna Peru, Herp., 1845, p. 73, PL 12.

No. 632] SHORTER ARTICLES AND DISCUSSION 287

Hyla punctata of Beebe’s list is probably Hyla helene Ruth-

ven, described from British Guiana and evidently entirely un-

known to Beebe.

Hyla fasciata here definitely recorded from British Guiana

although not captured (no asterisk), hence the record is prob-

ably copied from Boulenger’s Catalogue, where there is a large

question mark which is here omitted.

Hyla lineomaculata Werner is yet to be proved distinct from

Hyla rubra.

The Ceratophrys cornuta starred as having actually been taken

would indeed have been a prize had it fallen into appreciative

hands. For the finding of this species so far from home would

be worth most painstaking verification. Has Mr. Beebe saved the

specimen? It is not in the American Museum in New York,

whose reptile series suffers sadly through Beebe’s scorn of the

collector.

Specimens must be seen before the records. of Leptodactylus

longirostris Boulenger (type locality Santarem), Leptodactylus

ocellatus (Linné), widespread in the southern South American

grasslands and Leptodactylus gaudichaudii can be considered.

Suddenly using capitals for specific names, perhaps in a burst

of enthusiasm at the shock which he knows the ‘‘closet natural-

ist’’ will suffer, we read that he has found Otophryne ‘‘Ro-

busta’’ at Bartica, so also Atelopus ‘‘Proboscideus,’’ Atelopus

varius and Atelopus pulcher. In the same category of most

highly improbable records, among others, we find Anolis ortonii

of the Peruvian montaña and Anolis sagrei a native of Cuba and

the Bahamas. Ameiva surinamensis is referred to in an adjoin-

ing paper correctly as Ameiva ameiva, we wonder if they are

considered the same species. Prionodactylus we had always sup-

posed to be a characteristically Andean genus yet here the Equa-

dorian oshaughnessyi appears as actually occurring at Bartica!

Cophias should appear as Bachia but Beebe would probably con-

sider this as ‘‘in the special province of the literary systematist’’

or is this simply a case of where Mr. Tee-Van, in his ‘‘untiring

search’’ of the literature, got too tired before the pertinent ref- .

erence was found? The boas’ names are rather confused as we

use them now—another purely literary matter, however. The

nomenclature of the snakes in general is a mixture of earlier

usage with the acceptance of such a radical concession to neces-

sity as the use of Micrurus for Elaps, while in many other cases

288 THE AMERICAN NATURALIST [Von. LIV.

no attempt has been made to follow the now generally accepted

canons of the International Code of Zoological Nomenclature.

It is hard to review a paper of this sort without being personal,

for personality becomes most inexplicably pushed into what at

first sight is pure dry-as-dust. It is only fair to offer constructive

criticism also in such a case as this. Beebe should first learn

the value and importance—and the use—of an adequate library.

He should have attached to his staff trained taxonomists who are

also skillful collectors. These men should, taking the fauna

group by group, make careful determinations so that the ob-

servers at the station may know what they are working with.

Any reliance in the future on such a list as the one published—

admitted to be necessary—yet ‘‘wholly foreign’’ to the station’s

aim—will be regarded by sincere naturalists with pity at the

great opportunity lost and sorrow at the misuse of resources and

energy.

We may point our moral and adorn our tale with the wish

that: when that ‘‘little Danish flapper’’ in St. Thomas taught

Beebe that lizards may be noosed as he tells us, ‘‘Thus after

years of effort’ we wish that instead of only showing him what

every reptile collector learns from the first urchin he meets, if

he has not already devised the scheme by instinct, be the urchin

yellow, red, white or black, that she had said ‘‘Oh, kind Sir!

Do keep the lizard for your less happy colleagues at home will

still have much to learn from that poor despised little pickled

carcase.’”’

i THOMAS BARBOUR

THE

AMERICAN NATURALIST

VoL. LIV. July-August, 1920 No. 633

INHERITANCE OF CALLOSITIES IN THE

OSTRICH

DR. J. E. DUERDEN

PROFESSOR OF ZOOLOGY, RHODES UNIVERSITY COLLEGE, GRAHAMSTOWN ;

OFFICER-IN-CHARGE, OSTRICH INVESTIGATIONS, GROOTFONTEIN

SCHOOL OF AGRICULTURE, MIDDELBURG, SOUTH AFRICA

‘The problem of the method of evolution is one which

the biologist finds it impossible to leave alone, although

the longer he works at it, the farther its solution fades

into the distance. The central point in the problem is the

appearance, nature, and origin of the heritable varieties

that arise in organisms.” —H. S.’ JENNINGS.?

Twe ostrich has a shield-like sternum devoid of a keel,

a character it shares with the rest of the Ratitæ. The

middle forms a broad, rounded projection, while the cov-

ering skin is greatly thickened, devoid of feathers, and

constitutes a large, dense callosity on which the bird rests

when crouching. Moreover, the ostrich is unique among

birds in having a symphysis pubis, which forms a ventral

projection behind corresponding with the one in front,

only smaller, the skin over it likewise showing a strong

callosity (Fig. 1). The result is that when the bird

crouches the two median projections come into direct

contact with the ground and the thickened pads support

the greater part of the weight of the body, about 250 Ibs.,

in front and behind, while it is steadied laterally by rest-

ing upon the upper surface of the nearly horizontal meta-

1 The author is indebted to Dr. Raymond Pearl for seeing the paper

through the

2 Journ, WP ideation Academy of Sciences, Vol. VII, No. 10, May 19,

1917, p. 281.

289

290 THE AMERICAN NATURALIST [ Vou. LIV

tarsals and feet (Fig. 2). The sternal and pubie callosi-

ties may therefore be looked upon as a direct response

of the skin to the pressure and friction of the body

against the hard ground. Also in its frequent habit of

Fic. 1. Under surface of ostrich showing the large sternal callosity in front

and the small pubic callosity behind. The darkened surface of both is due to the

adherence of dirt. The bird is a young cock about eighteen months old in which

e white ventral feathers are not yet completely replaced by black.

taking a ‘‘dust-bath’’ the ostrich rolls from side to side,

the two projections being in the axis of motion, and this

serves further to extend the area subject to pressure and

friction.

In man and mammals generally a callosity usually con-

No: 633] INHERITANCE IN THE OSTRICH 291

sists of a single, smooth or papillose thickened area of

the skin, resting upon a bony support; but in the ostrich,

as in other birds and in reptiles, it is constituted of a

number of separate and distinct thickenings, somewhat

regular in their arrangement, which give the appearance

of a rounded or angular mosaic or tessellation (Figs. 5

and 6). This is typically shown on the under surface of

the toes of birds and lizards, where the elements tend to

Fig. 2. Group of young ostriches, about six months oe the one in the fore-

ground seen in a half-crouching attitude. The weight of the body is supported

upon the inside of the ankle and the partly upturned ‘ie. toes. When fully

crouching the bird lurches forwards and comes to rest upon the sternal and pubic

callosities, the tarsus and toes remaining in the same position.

be elongated and present a coarsely villous effect. Where

the skin is scaly each callous constituent corresponds

with an individual scale, but the latter has evidently no

determining influence upon the form assumed, for the

Same tessellated arrangement is found over the sternal

and pubic thickenings, though no scales are present. It

is probable that the typical form of the reptilian callosity

was first determined by the presence of. the epidermal

scales of the skin, and the latter still responds in the

Same manner in birds, not only on the legs and toes where

scales occur, but over other parts of the body from which

they are absent. The present interest lies in the fact that

the characteristic form assumed by a callous area in the

ostrich enables it to be sharply distinguished from the

292 THE AMERICAN NATURALIST [ Vou. LIV

surrounding parts of the skin which remain smooth. The

tessellation, along with the thickening below, gives it a

distinctive character as compared with the pads in mam-

mals, which are mere thickening of the skin, and whose

claim to be regarded as a ‘‘character’’ might at times be

disputed. Where a callosity assumes any considerable

thickness the underlying bone exhibits a correlated re-

sponse by likewise becoming thickened, as is well shown

on both the sternum and pubis of the ostrich.

The skin of all vertebrates appears to have the inherent

power of responding to frequently repeated pressure and

friction by the formation of thickenings over the bony

projections upon which it rests. The pads are special

protective adaptations to meet intermittent pressure and

friction, upon what would otherwise be soft vulnerable

parts of the body. They can arise at any part of the sur-

face of the skin and may slowly disappear when the

causal stimuli are no longer operative. Many of them

are temporary responses, acquired during a part of the

life-time of the individual, and come under the group of

adaptive somatic modifications which are non-transmis-

sible, though others, especially those on the under-surface

of the feet, are transmissible and may therefore be re-

garded as germinal in their origin. Thus similar char-

acters, alike in structure and function, may be either in-

dividually acquired and non-transmissible or germinal

and heritable.

The ostrich resembles man and other animals in hav-

ing the inherent power to produce special callosities over

parts of the skin not usually subjected to pressure and

friction, as the following observation proves. A chick

was hatched in the incubator with its legs widely apart,

in such a manner as to be incapable of supporting itself

upright in the normal fashion. A deformity of this

nature is not unusual among both ostrich and poultry

chicks as a result of imperfect incubation, but can gen-

erally be rectified by bandaging the legs and drawing

them nearer together for a day or two. In this instance

however advantage was taken of the deformity to deter-

No. 633] INHERITANCE IN THE OSTRICH 293

mine how far the skin would respond to unusual friction

and pressure. With its legs widely apart, the chick

naturally lay almost prone upon the ground, the inner

side of the ankle constituting a feeble support, the tarso-

metatarsus having here a projecting knob. The chick

was able to raise itself slightly upon the latter and also

to drag itself along the ground. It was kept alive for

about ten days, and in that time developed a very con-

spicuous callous thickening over the inside of the meta-

tarsal knob just below the ankle, the normal hereditary

callosity along the back of the ankle being unused. The

thickening was covered with the minute scales present

over the leg generally, but the degree of friction was too

intense and continuous for the skin wholly to adapt itself,

and a slight abrasion occurred at the apex of the thick-

ening, as in the human hand where pressure and friction

are applied too continuously for the callous formation to

keep pace with them.

The sternal and pubic callosities are not the only ones

in the ostrich which appear to represent adaptive re-

sponses to the special habits of the bird. When taking

its frequent sand-baths, it rolls about in the dry sand or

dust, from side to side, and at the same time uses its

wings in an oar-like manner. During the process the

under surface of the latter is dragged over the ground

and then turned upwards, inwards and backwards, scat-

tering the sand or dust over the body generally, first

from one wing and then from the other. The front or

pre-axial border of the wing is necessarily subjected to

much friction, and develops slight callous areas wherever

the internal bones project. Further, the third digit of the

wing, which is usually buried in the flesh, is occasionally

found projecting freely from the under surface, and its

tip naturally comes in for a good deal of rough wear as

the latter is dragged along the ground. In response, it

becomes knob-like and thickened, the surface showing the

characteristic callous markings (Fig. 3). The free tip

of the supporting phalanx is also knobbed.

Taking into account the responsive nature of the skin

294 THE AMERICAN NATURALIST [ Vou. LIV

along with the activities of the ostrich there appears no

reason why the sternal, pubic and alar callosities should

not be regarded as direct, structural responses to the

pressure and friction to which these parts of the body are

subject in the every-day activities of the bird. They

could be understood as acquired, adaptive characters.

The experiment given has served to prove, what would

naturally be expected from experience with other ani-

mals, that the skin generally is endowed with the power

Fic. 3. Under surface of wing pp Hean projecting ppa — pe clawed

ala apart a is seen above, the second fin is axial and a , while the

third projects freely from the under piae and is callous iad paral heb a

to make callous responses when migootod to the neces-

sary stimuli.

It was with some surprise therefore that in a series of

embryos, representing all the stages passed through dur-

ing the 42 days of incubation of the ostrich, the later ones

were found to possess a perfectly developed callosity over

both the sternum and the pubis, of exactly the same form

and nature as in the young chick and adult (Fig. 4). The

papillary outlines shown to be such a characteristic fea-

ture of sauropsidan callosities have the same variations

in size and distribution as in the adult, and serve clearly

to delimit the callous area from the remaining smooth

No. 633] INHERITANCE IN THE OSTRICH 295

surface of the body. Examination of chicks from the

time of hatching onwards leaves no doubt that the pre-

natal callosities become those of the adult, the elevations

becoming larger and coarser with use.

The rather insignificant callosities on the wing also

show themselves on unhatched and newly hatched chicks.

- ə

Fie. 4. Sternal ring of ostrich chick two or three weeks after hatching,

showing the biecninte A aot fully established and functional. The cut ends

of the feathers are seen surrounding the naked area

Fic. 5. Callosities on foot and ankle of ostrich chick a few days before hatch-

ing. The thickenings are already well developed, the asec elevations on the

toes being much narrower and closer than those on the an

They are hardly distinguishable by any special thicken-

ing of the skin, but by the appearance of a faint reticula-

tion in places corresponding with those in which they are

found in the adults, and which serves clearly to separate

them from the surrounding smooth surface. Even the

tip of the third digit where sufficiently projecting shows

a few markings, leaving no doubt they would later become

the functional callosity.

296 THE AMERICAN NATURALIST (Vou. LIV

We have therefore in the ostrich certain hereditary

structural characters whose independent formation could

in every respect be accounted for during the life-time of

the bird from the known responsive nature of the skin

and the habits of the creature. Examination of the adult

alone and a knowledge of its activities would have jus-

tified us in regarding them as acquired adaptive charac-

ters, had not observation proved that they appear on the

chick prior to hatching, and before the parts could have

„been subjected to the usual stimuli. The ostrich has

hereditary characters which could also be produced as

adaptive responses to the habits of the bird.

The old contentious question therefore arises as to

whether the character first appeared as a response of the

skin to the habits of the ostrich and has now become

hereditary, or whether, having arisen fortuitously in the

germ plasm, wholly apart from any adaptive need of the

bird, it is now utilized by it. Has the habit developed the

character until it has become transmissible or, the char-

acter being given, has it permitted of the adoption of the

habit? The reply is simple and free from doubt: the cal-

losity under any circumstances would develop pari passu

with the habit and need of the bird, and neither the cal-

losity nor the habit is dependent upon any antecedent

formation. If the character did not arise in the first in-

stance from the activities of the bird, subsequently be-

coming transmissible, it is manifest that it could originate

by two distinct and independent methods, namely, from

the germ-plasm and from post-natal stimuli.

It is not the first time that the presence of callosities

in the embryos of animals provided with them in the

adult has been adduced as evidence that characters orig-

- inating during the life-time may be transmitted to the

offspring. The best known ease is that of the wart-hog,

another African type—Ea Africa semper aliquid novi.

With reference to this Professor J. Arthur Thomson®

remarks:

3 t Heredity,’’ London, 1912, p. 180.

No. 633] INHERITANCE IN THE OSTRICH 297

The African wart-hog (Phacocherus) has the peculiar habit of kneel-

ing down on its fore-limbs as it routs with its huge tusks in the ground

and pushes itself forward with its hind-limbs. It has strong horny

callosities protecting the surfaces on which it kneels, and these are seen

even in the embryos. This seems to some naturalists to be a satisfactory

proof of the inheritance of an acquired character. It is to others simply

an instance.of an adaptive peata of germinal origin wrought out by

natural selection.

In the latter part of the above quotation Thomson

merely presents the two opposing views without afford-

ing us the advantage of his own. The last sentence is a

succinct expression of present-day orthodoxy, and we

may well consider how far it is justifiable in the case of

the ostrich. It is manifest that from their very nature

the callosities are outside the realm of competitive strife,

and therefore could not have been ‘‘wrought out by

natural selection.’’ If a character is such that it must

perforce be produced as a result of the every-day activi-

ties of an animal it is as wholly gratuitous to invoke

natural selection as it would be to seek an independent

germinal origin. As already shown, the skin of the

ostrich is of such a nature that it will form callosities

wherever friction and pressure are intermittently ap-

plied, just as surely as they will be produced on the

human hand as a result of manual labor, on the finger

tips of the harpist, violinist or rosary devotee, or on toes

encased in ill-fitting boots, with all of which natural selec-

tion has no concern. Originally natural selection may

have been operative in the survival of animals hav-

ing the inherent power to form the thickenings, but we

have abundant evidence that all the higher forms now

possess it.

When the ancestral ostrich first took to resting on

its sternum and pubis and rocking from side to side, the

callous thickenings would arise quite apart from any

antecedent formation and whether or not the germ-plasm

had anticipated the need. An inherent power is trans-

mitted, and nothing is gained by transmitting the cal-

losities themselves, since they are adaptations which

could arise in the natural course as needed. No selection

298 THE AMERICAN NATURALIST [Vou. LIV

is involved in producing the ‘‘horny hand of toil’’; it

forms in the individual in proportion to the need for it.

If fore-doomed to hard manual labor some advantage

may possibly be conceived in having the callosities in ad-

vance, but would be insufficient to be of any selection

value.

The position resolves itself as follows: From the known

responsiveness of the skin of the ostrich to intermittent

pressure and friction and the established activities of the

bird it is just as certain that the sternal, pubic and alar

callosities could be acquired in each generation inde-

pendently as that similar thickenings could develop on

the palm of the human hand engaged in labor. If we are

not prepared to admit that the callosities first arose as

somatic adaptations and then became hereditary, we have

to face the alternative that at some time in the history of

the ostrich a change took place in its germ plasm of such

a nature as to give rise to a directly adaptive character,

altogether similar to what could be somatically acquired;

we have to admit that an exactly similar character could

be produced in two wholly different ways: (a) directly as

a response to the activities of the bird; (b) as a result of

germinal changes. The same character could be soma-

tically acquired and could arise germinally.

Of course the same argument could be applied to the

strongly marked callosities on the toes and ankle of the

ostrich which are also hereditary (Fig. 5). But these are

not so peculiarly specific for the present purpose. Hered-

itary pedal thickenings occur in most animals, and even

Darwin‘ regarded the thickened sole of unborn infants

as ‘‘the inherited effects of pressure during a long series

of generations.’’ The thickenings on the sternum, pubis

and wings are confined to the ostrich, and therefore

afford a more circumscribed case for discussion, hered-

itary transmission from any other type being placed out

of consideration, though it is not unlikely that some of

the other Ratites may have corresponding structures.

An acquired, non-transmissible, callous ‘pad, presum-

ably due to a change in the crouching habit of the ostrich

4‘‘ Descent of Man,’’ p. 18. :

No. 633] INHERITANCE IN. THE OSTRICH 299

in the course of its phylogeny, remains to be noticed, as :

further instance of the responsive power of the skin.

Near the mesotarsal ankle-joint occurs a strong, elon-

gated, hereditary callosity covering the median part of

the broad, proximal end of the tarso-metatarsus (Fig.

5). This pad would naturally be used if the bird rested

Fic. 6. nkle region of young ostrich showing the symmetrical hereditary

allosity Posse and the accessory one forming below on ‘he inside (to the left).

FIG. 7. Ankle — of old ostrich in which the accessory ankle callosity (on

t right) has become coarse and broken up.

squarely upon its tarsus and foot when crouching, the

weight being mainly on the ankle. The ostrich however

makes little or no use of it, for even in young chicks

scarcely any evidence of contact with the ground can be

observed. Somewhat to the inside there appears a new

callous thickening, which begins to form by the time the

chicks are a month or two old, and remains as the func-

300 THE AMERICAN NATURALIST [Vor. LIV

tional pad throughout life, taking the place of the hered-

itary one which, though hardly used, persists structurally

(Figs. 6 and7). The new callosity is continuous laterally

with the old median one, and altogether resembles it in

character. No trace of it however appears in the chick

prior to hatching (Fig. 5), hence it represents an indi-

vidually acquired, adaptive character in the truest sense.

We have therefore an original part of the ankle callosity

which is hereditary, though now non-functional, and an

acquired part which is functional and non-transmissible.°

The main facts presented seem capable of interpreta-

tion only in one of two ways: (a) An acquired character

which represents a structural response to stimula result-

ing from the activities of the organism may become

transmissible. (b) A character may arise germinally of

a form and nature exactly similar to one which would

otherwise be acquired independently from the known

activities of the organism and the established responsive

nature of its structural parts.

5 tenga! in son course of its phylogeny some change has taken place

the manner of crouching of the ostrich, for instead of resting squarely

upon the median Ak of the ankle it has come to support itself mainly To

the inside. One ventures the suggestion that the change is to be associated

with the loss of the second toe in the course of the noah ai evolution

of the foot. During a part of its phylogenetic history the ancestral African

ostrich had unquestionably three toes like the living Rhea, the American

three-toed ostrich, representing the second, third and fourth of the penta-

RA series. The second has pee in the two-toed ostrich Struthio,

ugh AES PS traces exist in the embryo.

In its three-toed stage the ostrich wo Ha rest squarely upon its ankle, the

other extremity of the limb being steadied by the upturned three toes, a

smaller one on each side of the large middle third. A etrical median

eallosity would naturally form at the ankle-joint and, according to the view

here maintained, would become transmissible. With the loss of the inner or

second toe through degeneration the inside distal support for the tarsus

would disappear, and the latter would tend to tilt inwardly along its whole

length, in such a manner that the median part of the = would no longer

n the aap a callosity over it would be unnecessary, bu

one would form over the new area of support. In the geese of to-day the

era Carei ankle callosity, reminiscent of the three-toed stage, still

appears, though functionless; a new non-hereditary one is acquired afresh

with each mes the function of the old, becoming the

ankle support for the crouching two-toed bird (Fig. 7). The whole forms a

remarkable illustration of correlation between a phylogenetic change and an

adaptive ontogenetic modification.

No. 633] INHERITANCE IN THE OSTRICH 301

In adopting the first interpretation we depart from the

generally accepted opinion of biologists of the present

day and admit that an acquired character may become

transmissible; in maintaining the second we are exercis-

ing a credulity unjustified by biological experience.

In the voluminous literature of evolution and heredity,

case after case has been brought forward by advocates

such as Lamarck and Herbert Spencer, claiming to be

illustrations of the inheritance of acquired characters,

and just as surely has it seemed possible to interpret

them in some other fashion, as Weismann and others

have insistently done. The fate which has befallen these

should suffice to make the boldest hesitate in adducing yet

another. It is the apparently unassailable character of

the two opposing statements above which emboldens one

in all diffidence to re-open ‘‘the interminable question’’

of the late Professor W. K. Brooks, that leader and in-

spirer of so much American philosophical biology. The

peculiar justification for the present claim seems to be

that, were the callosities of the ostrich not transmissible,

they could be acquired just as effectively from the respon-

sive nature of the skin of the bird; also that natural

selection has no bearing on the question, for they are

adaptive structures which the organism has the inherent

power to produce as required.

According to Weismann (quoted from Walter*®) three

things are necessary to prove the inheritance of ac-

quired characters: ‘‘ first, a particular somatic character

must be called forth by a known external cause; second,

it must be something new or different from what was

already exhibited before, and not be simply the re-

awakening of a latent germinal character; and third, the

same particular character must reappear in succeeding

generations in the absence of the original external cause

which brought the character in question forth.’ It is

contended that all the cireumstances surrounding the

sternal and pubic callosities of the ostrich are in full

accord with these three requirements.

When assuming that an acquired character has become

ê H. E. Walter, ‘‘ Geneties,’’ Macmillan & Co., 1913, p. 94.

302 THE AMERICAN NATURALIST [Vou. LIV

transmissible it is usually held that in some mysterious

fashion it has so impressed itself upon the soma that it

becomes represented in the germ plasm by one or more

factors, determinants or genes which are able to repro-

duce the same character in the next generation. The

difficulties of conceiving this are so great as to convince

most students of its impossibility. On the other hand we

have to admit that we know little as to the means by

which a germinal factor arises and gains its expression

“as a somatic character. Apart from the accessory chro-

mosome in sex cells and the highly suggestive work of

Professor T. H. Morgan and his associates on germinal

loct in Drosophila, we only know of factorial represen-

tation by somatic expression. We are ignorant of the

relationships between the two, and of the measures by

which one gives rise to the other. Were it not that Thom-

son has shown the contrast to be hardly justifiable, one

would be inclined to ask: Is it not as difficult to under-

stand how a genetic factor arises and comes to have

somatic expression as it is to conceive how germinal rep-

resentation may be gained by an acquired somatic char-

acter? We accept the one without demur, but are prone

to deny the other as impossible. We must not forget the

warning of Professor Lloyd Morgan that because the

phenomenon of acquired transmissibility can not be un-

derstood it is not necessarily rendered impossible.

In considering the difficulty in the way of an acquired

character gaining factorial representation in the germ .

plasm it is legitimate to enquire whether a transmissible

character is necessarily germinal as present-day teach-

ing so consistently affirms, that is, whether it is neces-

sarily represented in the germ plasm by definite genetic

factors.” We have admitted that we know little or noth-

_7In a sense everything appearing in the soma may be regarded as s derived

from the germ, but the factorial hypothesis has given us a clear under-

standing as to “what is meant when we say that a character is germinal.

With the question of acquired characters before us there need be no con-

fusion as regards a germinal and a non-germinal character, and whether the

latter appears pre-natally or post-natally. On the considerations here set

forth a transmissible character is not necessarily represented directly by

germinal genetic factors.

No. 633] INHERITANCE IN THE OSTRICH 303

ing of the manner in which factorial Hic NNS in

the germ plasm gains expression in the soma; on the

other hand we have some experience, from observation

and experiment, of the production of somatic changes in

the life-time of the organism, as a result of environmental

influences and of stimuli due to the use and disuse of

parts. The production of callosities, the variation of

muscles and the skeletal changes in correlation there-

with, the direct modification of bones, ligaments and

mesenteries, are all adaptive changes which may result

as responses to the external and internal stimuli to which

the organism is subject during its life-time. They reveal

the inherent powers of responsive adaptability present

in the tissues and organs of the body. They are in truth

characters which arise independently of direct represen-

tation in the germ plasm, and indicate that the latter is

not the fons et origo of all structural changes. The power

of the tissues to respond to stimuli is transmissible; ir-

ritability, the power of responding to stimuli, is one of

8In a series of papers appearing in the Journal of Anatomy and Physi-

ology from 1886 to 1888, Sir W. Arbuthnot Lane presents a remarkable

series of adaptive changes which take place in the human body as a result

of continued occupational activities. _ They are probably the fullest and most

complete studies of this nature w we possess. One contribution, ‘‘A

remarkable Example of the manner in which Pressure-Changes in the Skele-

ton may Reveal the Labour-History of the Individual,’’ is a full account of

the changes which appear in the skeleton of the coal-trimmer.. The most

notable feature is the formation of an arthrodial joint in the fibro-cartilage

between the fourth and fifth lumbar vertebre and the division of the neural

arch of the fourth at two points, a result of the forcible rotation of the

spine on a vertical axis which takes place when coal is thrown with great

force to a considerable distance, as when the coal-trimmer is engaged at his

work on board ship.

A second paper, ‘‘The Anatomy and Physiology of ‘the Shoemaker,’’

describes the anatomical and osteological changes which had resulted from

the habitual performance of a definite series of movements entailing the

expenditure of a considerable amount of muscular energy, during the

greater part of a long life-tinie of seventy-three years. The most striking

change is the formation of a buttress of bone, which extends upwards from

the lateral mass of the atlas on ths à one s% and oe eg means of |

don, 3d ed., 191 PE

304 THE AMERICAN NATURALIST [ Vou. LIV

the fundamental attributes of protoplasm. The manner

of the response is adaptive, it is an individual effort, and

is usually non-transmissible. Whether the responses |

ever become transmissible, in that they appear without

the original stimulus, is the crucial point of the problem

of the transmission of acquired characters. That the

organism has the inherent power of forming new non-

germinal characters is however not questioned, and it is

well that the hard fact should be kept in mind. What we

desire is some evidence that stimuli are transmissible or,

if this be not forthcoming, some proof that the responses

may appear without the original stimuli. At first this

may be deemed to be looking for an effect without a cause,

a response without a stimulus.

he callosities in the ostrich and adaptive responses

generally lead one to submit that a character may become

transmissible without necessarily being germinal, in the

sense of having factorial representation in the germ

plasm. Acquired characters are such somatic modifica-

tions as are produced as responses of the organs and

tissues to stimuli, and are without direct representation

in the germ plasm. In the words of Weismann: ‘‘Ac-

quired characters are those which result from external

influence upon the organism, in contrast to such as spring

from the constitution of the germ.’”® They reveal an in-

herent power of response of the tissues and organs in a

more or less definite manner according to the differentia-

tion of the tissues and the nature of the stimulus. It

may be that much of the complicated development of

to-day was primarily of the nature of responses to stimuli.

The acceptance of Weismann’s germ plasm theory of

inheritance, strengthened as it has been by the factorial

hypothesis, has for the past two or three decades concen-

® Professor J. A. Thomson’s definition (‘‘ Heredity,’’ 1912, p. 173) is as

follows: ‘‘ An acquired character, or a somatic modification, may be defined

as a structural change in the body of a multicellular organism, involving

a deviation from the normal, directly induced during the individual life-

by a change in the environment or in function (use and disuse), and

such that transcends the limits of organic prp and therefore per-

sists after the — inducing it have ceased to operate.’’ ng his

iaaiiai he cites: ‘‘callosities induced on the skin by pressure.’’

No. 633] INHERITANCE IN THE OSTRICH 305

trated attention wholly on the germ plasm as the source

of heredity and variation in the animal world. Ordi-

narily in studying the origin of characters we start with

the germ and consider how factors arise and characters

come to be formed from them; but there is no reason why

we should not also contemplate their origin by observing

their manner of appearance in the soma, and from this

try to understand their transmissibility. Even if hitherto

the former has alone proved fertile in results and the

latter sterile it does not follow that renewed attacks on

the problem with additional armament will always fail.

Callosities are a definite response of the skin to stimuli

resulting from contact with some hard substance involv-

ing pressure and friction. They involve new inter-rela-

tionships of the structures concerned, and-may affect the

underlying tissues and even the bone on which they rest.

n the factorial hypothesis the multitude of character-

istics making up the complex organism are assumed to

have a measure of independence; yet it is allowed that

definite hereditary inter-relationships exist among them

when we contemplate the body as a whole. May not some

of the characteristics be directly factorial and others a

result of the inter-relationships brought about in their

establishment, just as in architecture certain subsidiary

structural parts have to be introduced in order to admit

of some major effect.° In any structural change, how-

ever simple, and whether germinal or somatic in origin,

the complex tissue inter-relationships of the organism

are involved. The old ties are disturbed and new ones

are established. It is conceivable that a continuance of

the application of fresh stimuli, from generation to gen-

eration, may result in a weakening of the old relation-

10 Mr. L. Doncaster (‘‘Heredity,’’. Cambridge, 1911, p. 97) expresses

much the same idea when he says: ‘‘The belief that ‘somatic’ changes

could not be m rests largely on the idea that every character is

determined by a ‘fac r determinant in the germ-cell, but it is clear

that any character is a inde directly from the germinal determinant,

but by the relation existing between the determinant and its surroundings,

viz., the body of the — If the surroundings are changed, this rela-

tionship may be altered, and the altered relation may be transmitted to the

offspring, so bringing about a a gett change in the character as it

appears in the next generat‘on.’

306 THE AMERICAN NATURALIST [ Vou. LIV

ships and a strengthening of the new, until in the end one

may supplant the other.

On a hypothetical conception of this kind it may be

understood that the continued production of sternal and

pubic callosities, generation after generation, has intro-

duced such fixed and intimate inter-relationships of the

structural parts concerned that in the end they come to

replace the old inter-relationships altogether and with

them the non-callous condition. The callosities are

formed antecedent to and apart from the primary stimuli.

Their appearance becomes accelerated, as it were, and

they arise even before the chick is hatched and the orig-

inal stimuli can be effective. They are not new charac-

ters which have come in, but are new as regards the onto-

genetic time at which they appear.

The possibility of responses occurring without the

original normal stimuli may be illustrated from certain

of the instinctive sexual activities of the ostrich. At the

breeding season the cock bird performs the sexual dis-

play known as ‘‘rolling.’’ He crouches on the ground

and with wings outspread rolls from side to side, his long

neck and head also taking part, the latter striking vigor-

ously against each side of the body alternately. Also as

he approaches sexual ripeness he begins to ‘‘bromm,’’

the seund having often been compared with the roar of a

lion. The mouth being closed he inflates the esophagus

until the neck as a whole becomes two or three times its

usual thickness and then forcibly expels the air through’

the nasal passages, producing a booming noise of great

carrying power, consisting of two short notes and a long

one, the sequence being repeated from one to six or seven

times, and serving as a guide to the farmer as to the state

of sexual ripeness of the bird. Again, during actual

pairing, the cock mounts upon the back of the crouching

hen with his right foot upon her back and the left upon

the ground, and sways the front part of the body and

neck to and fro as the act is consummated.

The above are three distinctive actions on the part of

the cock ostrich which are usually performed only at

sexual maturity, and may be deemed to be responses asso-

No. 633] INHERITANCE IN THE OSTRICH 307

ciated with stimuli from secretions or enzymes of the

sexual organs. Yet occasionaly very young chicks, per-

haps only a week or two old, are to be seen performing

the same, though in an imperfect manner. They can

‘‘roll’? almost perfectly; a chick can inflate its neck, but

has insufficient strength to expel the air with enough

force to produce a ‘‘bromm’’; and often one chick will

attempt to mount another which is resting on the ground,

and begin to sway from side to side in a ridiculous fash-

ion. May not these precocious activities be interpreted

as an acceleration of responses normally due to stimuli

of a sexual nature? Now they are performed wholly

apart from the usual stimuli and are of no adaptive nor

selection value at this early stage. They have become,

as it were, so integral a part of the organism that they

break out without the original stimulus; they have be-

come transmissible. They are hardly sufficiently general

to be comprised under the term ‘‘play’’ and, in the sense

of Carl Groos, to be regarded as preparatory to the real

business of life. Probably many activities of a similar

precocious nature could be brought forward where an

intensive study of an animal has been made. They serve

to show that a physiological action is not necessarily a

response to the stimuli which originally called it forth;

but may appear antecedent to and independently of them.

Just as physiological activities may make a precocious

or accelerated appearance so it may be that acquired,

morphological characters at times appear in advance and

apart from the stimuli which originally called them

forth; they may become transmissible, though not ger-

minal in the factorial sense. It is submitted that the for-

mation of callosities, ordinarily developed as responses

to pressure and friction in the life-time of the individual

bird, has become thus accelerated, so that they arise at a

much earlier period, even within the egg, and apart from

the usual stimuli. Arising in this way a character is not

germinal in the sense of having factorial representation,

but is nevertheless transmissible. Though appearing

before hatching it is no more germinal than it would be if

developed as a definite response to the post-natal stimuli

308 THE AMERICAN NATURALIST [ Vou. LIV

of friction and pressure. On this interpretation a new

character, to wit, a callosity, can arise either before or

after hatching as a result of the responsive nature of the

tissues, apart from any germinal representation.

Acquired adaptive characters, structural responses to

internal or external stimuli, are by their very nature

extra-germinal, and their appearance may well lead us to

hesitate in accepting the germ plasm theory as a complete

interpretation of everything somatic, or of everything

that is transmitted from generation to generation, des-

' pite the statement by Dr. ©. B. Davenport! that: ‘‘Upon

one point all geneticists are, however, agreed . . . that

we must interpret all our results in terms of genes alone.’’

So plastic and so responsive are the parts of the or-

ganism to stimuli that, in spite of such an embracive pro-

nouncement, it may still constitute a subject for enquiry

whether many of the adaptive relationships in organisms

are not such as were originally impressed upon the indi-

vidual as a result of its activities or subjection to former

stimuli and which have in time become transmissible.

The problem has been neglected for the past two or three

decades as a result of the firm hold which the germ plasm

theory of inheritance has gained over the minds of biol-

ogists and the general acceptance of the non-heritability

of acquired characters. Renewed search will probably

disclose many other instances of characters appearing

pre-natally which ‘could just as well be developed as

needed in the life-time of the individual, and thereby

throw suspicion upon their germinal origin. Callosities

are undoubtedly the most direct and simple instances of

this nature which could be adduced; we have both trans-

missible and non-transmissible examples in the same in-

dividual. Those whose transmissibility is established

could have been formed post-natally just as readily as

those produced where pressure and friction are applied

to surfaces not already callous. Knowing also the re-

sponsive nature of muscles, tendons, ligaments and osteo-

logical tuberosities and the readiness with which they are

modified through change of habits, it is not improbable

11 AMERICAN NATURALIST, Vol. 50, August, 1916, p. 463.

No. 633] INHERITANCE IN THE OSTRICH 309

that many now regarded as transmissible could also arise

as needed as direct responses. It will certainly be legit-

imate to question the germinal origin of those characters

whose formation can be interpreted as adaptive responses

to changes to which the organism is subject.

The germ plasm theory of Weismann and the factorial

hypothesis of Mendel, Bateson and others have been of

inestimable value in enabling us to appreciate many of

the facts of heredity. But no one imagines that they give

us the completed account of evolution and adaptation, as

many are beginning to feel now that their contributions

can be estimated more or less in their entirety, and we

get a true perspective of what they have to offer. They

are and will remain important chapters in the story of

variation, heredity and evolution, but they are not the

whole volume; nor are they the concluding chapters, as

their supporters themselves would doubtless admit. It is

submitted that something is yet to be gained from con-

sideration of how adaptive characters arise as a result of

stimuli from use and disuse of parts and from environ-

ment, and how they may become transmissible, though

. not necessarily germinal. The germ plasm theory to a

large extent and the factorial hypothesis in toto are

sterile when we come to questions of adaptation, and

natural selection has to be freely invoked, whereas prac-

tically every structure in the body bears witness to its

adaptive nature.

For an acquired character to become transmissible, so

that it appears independently of the stimuli which orig-

inally called it forth, is manifestly a difficult proceeding

when regarded from the point of view of the hereditary

structural relationships which have been established

through long ages. The natural and experimental

phenomena of regeneration show how deep is the tend-

ency to maintain the established relationships of the

various parts of the body. An acquired character repre-

sents some temporary disturbance of the normal rela-

tionships, but ordinarily the old correlations return with

the next generation and the new are but transient, per-

sisting for the generation only. When however these

310 THE AMERICAN NATURALIST [ Vou. LIV

new relationships are repeated generation after genera-

tion and maintained at their full vigor for the whole life-

time, it is conceivable that they become so impressed on

the organism that they gradually overcome the old weak-

ening relationships of parts and appear from the begin-

ning in place of them, in other words, the character be-

comes transmissible, the new ties become the heritage of

the organism. This, of course, is no proof of the in-

heritance of acquired characters, but may help us to con-

ceive its possibility in the light of considerations engen-

dered by the callosities in the ostrich.

The skin is more likely to show responses to environ-

mental stimuli and to the general activities of an animal

than the internal organs on account of its superficial,

exposed position, and callous pads are among the sim-

plest of structural responses and their formation is read-

ily understood. Where temporary, as on the human

hand, they are by no means likely to impress themselves

permanently as new interrelationships on the surround-

ing parts. Where, however, as in the ostrich, they would

form from the beginning and persist throughout life,

from generation to generation, it is more conceivable

that they would impress themselves on the constitu-

tion of the bird and their time of appearance would un-

dergo acceleration with an independence of the primary

stimulus.

.The accessory, non-transmissible callosity at the ankle

has not yet impressed itself so forcibly upon the gen-

eral structural relationships as permanently to disturb

the normal tendencies, and it has to be formed anew in

each generation from direct stimuli. The hereditary

median thickening is the primary one, and may well jus-

tify us in thinking that the three-toed, ancestral stage of

the ostrich was of long geological duration; the new pad

formed by the two-toed bird is more recent and has failed

as yet to attain transmissibility. It may be that in its

early days a race is more responsive to adaptive, struc-

tural changes than at a later period. In many respects

the ostrich now appears senescent, and may well be ex-

pected to be less plastic than in past ages.

No. 633] INHERITANCE IN THE OSTRICH 311

In general, correlated structural relationships, estab-

lished through long ages, will act as a vis inertie to the

introduction of acquired changes; they will represent so

much heritable, inherent tendency which has to be over-

come before any new relationship of parts can be estab-

lished. Life-time changes of habit or of environment, as

in the assumption by man of the erect habit, or the taking .

to water of a former terrestrial organism, are the con-

ditions which will be conducive to acquired changes be-

coming transmissible, compared with those under which

the responses are temporary, or continued for a few gen-

erations, or are the result of mutilation.12 Any tem-

porary structural relationship established, as in the de-

caudation experiments of Weismann and others, would

manifestly be incapable of overcoming those deeper rela-

tionships which, with each new generation, find their ex-

pression in a complete tail. As Professor T. H. Morgant’

points out, the theory of the inheritance of acquired char-

acters ‘‘is one that has the great merit of being capable

of experimental test,’’ but he allows that ‘‘modern La-

marckians are justified in claiming that the validity of

the theory can only be tested by experiments in which

the organism is subjected to influences extending over a

considerable period.’’ The hypothesis here submitted is

undoubtedly one which in most experimental cases would

demand long period for the effectiveness of its tests.

We need not expect mutilations to become transmis-

sible, nor most of the responses established during the

life-time of an individual; but this in no way precludes

the possibility for life-time responses which are con-

tinued for generations, or which may happen to strike a

race at some plastic period of its existence.

12In the adoption of a new habit during the life-time an adaptive char-

acter may appear from generation to generation as the habit comes to be

assumed, and give the appearance of being transmissible, whereas it may be

animal is in process of changing the stimuli to which it is subject will it

often be difficult to distinguish a transmissible from a responsive adaptive

character which is non-transmissible.

18 Morgan, T. H., ‘‘ Evolution and Adaption,’’ 1903, p. 230.

312 THE AMERICAN NATURALIST [ Vou. LIV

It is by no means anticipated that the conception of the

transmissibility of characters as so many accelerated

adaptive responses, involving new structural inter-rela-

tionships, and not necessarily with factorial germinal

representation, will apply to all the features of an or-

ganism and serve as an explanation of the origin of heri-

table characters generally. Its application may be lim-

ited to such as have an adaptive significance, and can be

assumed to have arisen in the first instance as a result of

internal or external stimuli acting upon the soma. As

will be shown in a later paper the ostrich itself, especially

in the details of its degeneration, presents us with many

character changes which have manifestly no adaptive

significance, but are the expression of germinal changes,

uninfluenced by external forces. Without question we

are short-sighted in attempting to reduce the methods of

evolution to some common term; as Professor H. F. —

Osborn points out in his new book: ‘‘The Origin and

Evolution of Life,’’* there are centripetal factors in or-

ganic evolution, there are centrifugal factors. Much of

the recent work on Mendelism and mutation strongly

supports the view so warmly advocated by Professor W.

Bateson and Professor T. H. Morgan that germinal char-

acters appear apart from any adaptive considerations,

and the degenerative changes in the ostrich are in full

accord with this; but it is by no means a complete answer

to the problems of evolution, where so much appears that

is directly adaptive and so little that is non-adaptive.

Most genetical work during the present century has been

unconnected with adaptation, yet it is one of the big

problems of biology which calls for solution as insistently

as ever, and it may be that a proper interpretation of the

eallosities in the ostrich will assist in some measure

towards an understanding.

14 Reviewed by Professor Lillie in Science, November 8, 1918.

THE SELECTION OF FOOD-PLANTS BY INSECTS,

WITH SPECIAL REFERENCE TO LEPI-

DOPTEROUS LARV Æ!

DR. CHARLES T. BRUES

Bussey INSTITUTE, HARVARD UNIVERSITY

Tae instinctive behavior exhibited by phytophagous

insects in the selection of their food-plants is always a

matter of interest to entomologists, and it is one of the

fundamental principles underlying the application of en-

tomology to agriculture, horticulture and forestry.

Nearly all insects show a great fixity of instinct in this

respect, but a most cursory examination of the habits of

almost any group will reveal a considerable variation

among different species, particularly with reference to

the number of plants regularly utilized as food and in

the selection of closely related or of very diverse plants.

The origin and development of the association between

insect species and plant host has been the basis for a

considerable amount of speculation which has increased

in proportion to the additional knowledge continually

added through field observation, collection, and rearing

of insects.

Before considering any of the theories advanced to ac-

count for the association of insects with definite plants, I

shall attempt to give a very brief account of the salient

facts concerning food-plants which appear to be suffi-

ciently definite for orderly arrangement, restricting the

discussion for the present, mainly to one of the better

known orders of insects.

The term phytophagous with reference to insects is

commonly employed in a considerably restricted and

rather inaccurate sense, including only those species that

feed upon the higher plants, meaning by these the ferns

1 Contributions from the Entomological Laboratory of the Bussey Institu-

tion, Harvard University, No. 168.

313

314 THE AMERICAN NATURALIST [VoL. LIV

and flowering plants. Only an extremely small, almost

negligible, proportion subsist upon ferns, so that from a

practical standpoint, we would include only those feeding

upon the Spermatophytes. This usage has developed on

account of the fact that the fungi which have many in-

sects feeding upon them, do not ordinarily engage the

attention of the economic entomologist, and for conveni-

ence it is acceptable in the present connection, as very

little is known concerning the specific hosts of insects

living in fungi. Furthermore, the food-plant is ordi-

narily understood to mean the species upon which the

larval or growing stages occur, for although it is com-

mon to find both the young and adult insects of the same

species subsisting upon the same plant, it occurs also

very frequently that the food of the larvæ and imagines

of holometabolous insects is of entirely different nature.

Among the many other truly phytophagous insects living

in fungi are a number of families of beetles, for example,

which develop in the tissues of the larger, fleshy fungi

and many of these mycetophagous insects undoubtedly

show a very close association with certain species of

fungi. In addition, some insects subsist upon the lower

fungi, yeasts and even bacteria. The biology of these

latter is very imperfectly known in nearly all cases,

owing to the greater difficulties attendant upon studies

dealing with them. The well-known fungous-growing

ants and termites and the ambrosia beetles actually cul-

tivate certain fungi for food and other insects (undoubt-

edly a far larger number than is now known) subsist

upon various microorganisms, although they are, to the

eyes of the casual observer, feeding directly upon the

substrata which really nourish the microscopic fungi,

yeasts or bacteria, that in turn form the actual food for

the insects. As already said, however, these symbiotic

relations are in most cases only very poorly understood,

and they are entirely outside the scope of the present

discussion.

As distinguished from those of predatory, parasitic

and saprophagous habits, the phytophagous insects rep-

No. 633] FOOD-PLANTS AND INSECTS 315

resent probably nearly half of the known species, and a

considerable proportion of the several orders of insects

contain at least some species that are phytophagous in

the sense indicated above. Some of these, like the Or-

thoptera, are very primitive, while others of probably

equal or even greater antiquity are not phytophagous, so

that it is difficult to say whether the earliest true insects

were vegetarian, predatory or saprophagous.2 This

question is perhaps not a very important one, for, as will

be pointed out later, a change from one type of food

habits to another has actually taken place independently

in several families of the highly specialized Lepidoptera.

As we might naturally expect, it is possible to point

out in a very general way a progressive specialization

in the selection of food-plants which parallels to some

degree what appears to have been the path of evolution

among insects, as determined from the criteria fur-

nished by comparative anatomy, development and pale-

ontology. Thus, the primitive Orthoptera appear to se-

lect their food-plants with but little discrimination, while

the Lepidoptera and phytophagous Hymenoptera exhibit

almost unerring accuracy in their instincts to choose cer-

tain plants and consistently to ignore all others. Beyond

this, however, it is not easy to make any broad state-

ments, for among the most highly specialized groups we

find a great variability, at least in the number of food-

plants admitted to the menu, as well as in regard to the

botanical relationships of the plants regularly selected.

It may be argued that selection of food-plants is a

somewhat dubious expression and that it may not accu-

rately represent the condition of affairs from the stand-

point of the larval insect. In most cases the larval food-

plant is really chosen by the adult female, who places her

eggs upon certain plants which then become of necessity

the food of the resulting larve, which could not very

readily migrate to another kind of plant even should they

2 This last term is rather ambiguous and is rapidly becoming still more

so in the light of studies recently made upon insects that subsist upon

microorganisms.

316 THE AMERICAN NATURALIST [Vou. LIV

be willing to do so. This objection is readily met by ex-

perimental evidence, for every entomologist is fully

aware of the fact that it is ordinarily quite impossible to

rear insects of restricted food habits upon other than

their normal food-plants. It is true that an acceptable

plant may sometimes be found by those familiar with the

vagaries of related species of insects, but in such cases

we may safely assume that the experimentally selected

plant may later prove, in at least some cases, to be one

sometimes picked out for food in nature.* It would be

an unwarranted assumption, therefore, to suppose that .

the maternal instinct of oviposition does not at the pres-

ent time represent fairly well the tastes of the larva. We

may reasonably ask, however, whether the selection of

the mother may not have impressed itself upon the larva

after continual repetition or whether the taste acquired

by the continual feeding of the larva may not persist

into the adult, just as fondness for sweets may become a

lifelong attribute in examples of the human species pam-

pered in youth by indulgent mothers. During the prog-

ress of evolution as food-habits have become fixed, it is

evident that any changing tastes on the part of the larva

must have become a part of the egg-laying instincts of

the mother, through the action of natural selection or

otherwise, before any change of food-plants could occur.

On the other hand, any change in the instincts of oviposi-

tion, not incompatible with larval tastes, might quickly

become a definite characteristic of the species. If any

adults should select unsuitable plants their progeny

would quickly perish. The maintenance of definite pref-

erences can thus be seen to be readily perpetuated

through the action of natural selection in the survival of

the fittest strains and the elimination of the unfit ones.

It will be evident later, however, that subsistence on

many food-plants would appear to have originated after

8It may also be noted that those experienced in rearing caterpillars are

frequently able to rear species of unknown habits on certain plants (e. g..

ehick-weed, Cerastium) on which they do not normally feed, but which are

acceptable to many larve in the absence of their natural food-plant.

No. 633] FOOD-PLANTS AND INSECTS 317

the manner of mutations, and it will, I think, be evident

that we should attribute these, at least in part, to chance

mutations or aberrations of instinct in the parent insects.

Before dealing specifically with the selection of food-

plants, it is necessary to classify in a general way the

types of food-habits generally met with in insects. Thus,

Reuter applies the terms Pantophaga to omnivorous in-

sects, Phytophaga and Sarcophaga to vegetarian and

carnivorous ones respectively and Necrophaga and Cop-

rophaga to those living upon dead animals and excremen-

titious material. Among the Phytophagous forms he

would further distinguish monophagous and polyphagous

species on the basis of the number of food-plants which

they utilize. Although satisfactory so far as it goes, this —

fails to include several categories commonly referred to

by entomologists and for the present purpose it ean be

readily enlarged as follows:

Pantophaga

Phytophaga Sacrophaga

Monophaga Harpactophaga

Oligophaga Entomophaga

Polyphaga

Saprophaga

(Partly subdivided as below)

{ Microphaga ‘Necrophaga

venue pea }

In this arrangement a distinction is made between

vegetarian species with a single food-plant (Monopha-

gous), those with several definitely fixed ones (Oligo-

phagous) and those with quite indiscriminate food-habits

(Polyphagous). On the other hand predatory species

(Harpactophagous) and entomophagous parasites are

distinguished, as each form a very large and important

group. Many necrophagous and coprophagous species

really subsist on bacteria, fungi, etc., and these may

perhaps be better designated as microphagous and

mycetophagous.

Among phytophagous insects, the polyphagous habit is

probably the most primitive and the monophagous one

315 THE AMERICAN NATURALIST [ Vou. LIV

the most highly specialized. It is not rare, however, to

find all three types represented in otherwise very homo-

geneous groups. The Lepidoptera, for example, form an

enormous complex of species, practically all of them phy-

tophagous, the majority feeding upon a very, restricted

series of plants and representing the oligophagous habit,

with a smaller series of apparently monophagous forms

and a few secondarily polyphagous ones. Fortunately

also, the food habits of this order as a whole, are better

known than those of other insects and it can be examined

with less chance of error than perhaps any other group

of equal extent. :

As already stated, nearly all of the larve of the Lepi-

doptera are phytophagous at the present time and there

can be no question that since the order has existed this

condition has prevailed. Owing to a change in the form

of the trophi during metamorphosis by which the adult

Lepidoptera develop haustellate or sucking mouthparts,

the food of the imagines is entirely different from that

of the larve and they subsist upon liquids, mainly the

nectar of flowers.

We may then classify the food- habits of the larvæ

roughly as follows:

Food Mater!lal y of Utilization

Pianta ois ie tie Saree bas cae Nearly all of page species

UOTE, ike i ces Probably none

BE Dir Oke Almost none

Tachen 6 CP e A very few, mainly in one family

Monsos kee Almost none

GINS. ee ks Ces ee cel eee Àv ery few

POWERING plants i esere ens ns Probably about 99 per cent.

On. foli a a ee Sree A large majority

Tn Bowo s-er A few ;

In saat PA (65. ck A very few

Tn i Re ee ear A few

In aah of herbaceous nag A rather small number

In wood of shrubs and trees...A rather small number

In dried seeds, fruits, etc. ....A very small number mainly in one

group

Animal food

On other living rati R R A few isolated cases

nimal origin

wool, horn, beeswax, ote -io A very few, mainly in one group

No. 633] FOOD-PLANTS AND INSECTS - 319

From this it will be seen that while the food-habits are

very homogeneous, isolated cases occur where certain

species have departed very strikingly from their more

conservative relatives. Among these, the most interest-

ing are those which have become carnivorous. Thus, we

have in the eastern United States, a small butterfly, Feni-

seca tarquinius, which feeds upon plant lice occurring on

alder. In our southwestern states there occurs also a

moth of the genus Epipyrops, typical of the family Epi-

pyropide, utterly unrelated to Feniseca, which feeds

upon Homopterous insects of the family Fulgoride, and

other species of Epipyrops are known to have quite simi-

lar habits in the orient. Also Thalpochares, a moth of

the family Noctuide, is known to feed upon aphids and

scale insects in Europe and Australia. Similarly the

:_ caterpillars of the Australian Cyclotorna is ectoparasitic

on Homoptera of the family Jasside, and the larve of

Zaphiodiopsis feed upon other caterpillars. A still fur-

ther and more extraordinary modification is in the larva

of the British butterfly, Lycena arion, which is herbivor-

ous in its early stages, but enters the nests of ants to

prey upon the ant-larve during its final period of growth.

Other scattered cases of predatory caterpillars are

known, including other butterflies and moths of several

families. With these the most striking feature is that

the prey almost always consists of Coccids or Aphids.

This association is probably due to the fact that these

Homoptera are sessile or slowly moving creatures, com-

monly present where caterpillars occur and therefore apt

to attract those of carnivorous instincts. Of interest in

cennection with this, is the fact that certain phytopha-

gous caterpillars may become temporarily carnivorous,

quite regularly or under the stress of circumstances.

Thus, the very abundant and destructive corn ear-worm,

Heliothis obsoleta, commonly lays a number of eggs on

the silks of a corn-ear, although nearly aways only one

caterpillar finally survives in the interior of the ear

where it does most of its feeding. Here the elimination

320 THE AMERICAN NATURALIST [Vou. LIV

is due to a cannibalistic instinct of the caterpillar which

results in the disappearance of the excess individuals,

notwithstanding the fact that there is food enough for a

considerable series in a single corn ear. A similar can-

nibalistic habit has been reported in Hadena and Agrotis,

two other genera of the same family, and no less than

75 species of European Lepidopterous caterpillars are

known to be occasionally predatory through temporary

aberrations of their trophic instincts.

With such plasticity of behavior in several diverse

families and even with Lycena arion and certain small

moths exhibiting a change in food habits during on-

togeny, it is not difficult to regard the origin of -sar-

cophagy in Lepidoptera as due to independent changes

which have become firmly fixed in individual species or

genera.

The habit of certain Tineid moths, including the

clothes-moth (Tinea) and some of its relatives, to feed

upon wool and other materials of animal origin is well

known, and other non-domesticated forms of the same

group exhibit similar food-habits. One African species

of Tinea lives at the base of the horns of a large water

antelope, where it forms tubes similar to those con-

structed by some other Microlepidoptera. The bee-moth,

Galleria mellonella, a commensal in the hives of the

honey-bee, subsists upon beeswax and bits of refuse said

to contain about 20 per cent. of nitrogenous matter.

Practically all of the caterpillars that subsist on foods of

animal origin are more or less closely related, but not

sufficiently so for us to entertain for a moment the belief

that the habit has not originated independently in numer-

ous instances. Why it should be restricted to a few

groups in one part of the order, may, I think, be ex-

plained on the following basis. Among the Microlepi-

doptera only do we find forms able to subsist upon plant

materials containing a very small amount of water (e.g.,

seeds, dry fruits, grain, flour, ete.) as distinguished from

the tissues of growing plants. Even in the wood of trees,

No. 633] FOOD-PLANTS AND INSECTS ; 321

tunneling larve remain in a moist burrow where evapora-

tion is very slow. Similarly the animal materials utilized

as food are very low in water content. That we do not

find Lepidopterous larve in moist material of animal

origin is no doubt due to the fact that they do not appear

_ to be adapted for subsistence upon the abundant micro-

organisms present in such materials.

Passing to a consideration of the phytophagous Lepi-

doptera, by far the greater part of the order remains to

be dealt with. As indicated in the tabulation, practically

all of these occur on the higher plants and feed almost

always upon living tissue. The latter is true almost with-

out exception of the leaf-feeding forms, although one of

our common moths of the eastern states, Pyromorpha, is

known to live upon dead and decaying fallen leaves and

another of our small moths avails itself of hemlock chips.

Among those which live in woody tissue, some prefer

weakened or sickly trees or unhealthy branches, but al-

most none occur in dead wood. .

Of those living on the lower plants, one small family

of moths, the Lithosiide, subsist upon lichens and they

are almost the only ones affecting these plants. This

family is far from primitive, so that its association with

a series of lower plants could have no significance, even

if it were definitely known that the lichens are a very old

group, which does not seem probable.

Mycetophagous forms of Lepidopterous caterpillars

are of very unusual occurrence, in spite of the fact that

several large series of beetle larve develop in fungi.

They are found, however, and there are in North América

at least two species of Tinea which have been bred from

these plants.

In spite of the similarity.of their foliage to that of the

flowering plants, ferns do not commonly serve as food

plants for insects. They are, in fact, strikingly immune

from insect pests of all sorts. This is hardly what might

be expected from the long presence of this group of

plants, their enormous development in the past, and their

oan THE AMERICAN NATURALIST [ Von. LIV

persistence at the present time in quite considerable

abundance. Why they should be so sparingly selected as

: food plants does not seem to have been adequately ex-

plained.

The use of Phanerogams as food-plants is so general

that it is possible to gain a much clearer insight into the

conditions pertaining to them than is the case with other

plants. In general the food habits of butterfly larve are

more fully known than those of the moths, on account

of the smaller number of species and the general interest

taken by amateurs in this group.

An account, very complete at the time, has been given

by Seudder of the food-plants of the butterflies of eastern

North America.* A tabulation of the food-plants in- .

cluded in this list shows several interesting features.

Fifty-five families of plants are included (not taking into

account several larve feeding on conifers and our one

predatory species) and the list contains a very repre-

sentative series, drawn from both the Monocotyledons

and Dicotyledons in approximate proportion to the num-

ber of species of these two sections. It is noticeable,

however, that several common families, the Iridaceæ,

Orchidacee, Caryophyllacee, Euphorbiacer, Vitacer,

Primulaceæ and Rubiacee are entirely omitted, that only

one species occurs in the Labiate, or on the Umbellifere,

and that only a very few affect Composite. We may

readily see that the generally strong-scented Labiate and

Umbellifere and the milky Euphorbiacee might require

great adaptation on the part of larve eating them, but

the omission of the other families if not entirely a matter

of chance must rest upon some less evident basis than

the foregoing. Among the other plant families the num-

_ ber of species of caterpillars compared to the number of

eastern American genera, included in each-family that is

4 This list has been used as a whole as it is complete in itself, and to

attempt to add to it and emend it by the present writer, sg more recent

literature, would improve it but little for the present purpos

5 This is true only of the butterflies in this list; many Ges leaf-eating

larve feed in abundance on these plants.

No. 633] FOOD-PLANTS AND INSECTS 323

fed upon, varies exceedingly, from 1:100 to 1:1 or even

1.6:1 in the case of the Rutacee. The average is about

1:4, but there is no tendency for the ratios to fall near the

mean and their distribution if not a matter of chance,

must have been determined in relation to their environ-

ment, no doubt to a great extent by their struggle for ex-

istence with other plant-eating forms.

If we examine the food-plants of the genera or higher

groups of butterflies, we find that most of them exhibit

well-marked preference for certain, usually related

plants. The food-plants of the British butterflies are un-

usually well known, and Tutt has recently given in his

work on ‘‘British Butterflies” a digest of their prefer-

ences which he finds to be closely similar to those of the

nearctic forms previously considered by Scudder. Gath-

ering his more definite data together and using his ter-

minology for the groups, the food- habits may be tabu-

lated as follows:

MR ee F508 Cow ox yc OS Urticacee Composite, ete

PV INS re Gh es E r Violaceæ exclusively

Brondi ro 65 3's vied Kune caw bn kas Violacee generall

Moda os ueni ea Esas Various plant

PR o a S wees Cruciferæ essentially

en og ti) Seana gpmeemmlrisey, “il ny ats Crucifere “asta

AMMAN T Ss O E oa eines Various plants

MUTA ea roye ok ss HRSG ERE RN - Various plants

ne at E E A E E E tapes Graminesw eae entirely

Gonepterygids E EER EEA T hamnaceæ

Bae aes E E ee TET Various plants Sie or less fixed in

e subdivisio o:

LN O o E rs a bedis food-h

TYBOOUGNIGR: Celie fs Oe as Polygonacee scat exclusively

si cect | veS a o a eae: a Various plants

Sub-groups Thymelicines ....... Graminee mainly

Urbicolines ...............Graminew mainly

Cyelopidines scesero Graminee mainly

Hesperiines ....... wan p eee Leguminose and various other plants

PADUIONIOS o oe cp ceria s Various plants; several groups with

particular food-plants

Viewed in this way, it is seen that barring many excep-

tions, there is a general tendency, much more pronounced

324 THE AMERICAN NATURALIST [ Vou. LIV

in some groups than in others, to select plants of very

specific families or even genera. This must not be under-

stood to mean that the individual species of insects affect

indiscriminately many or all members of the plant group,

but that their normal food-plant or plants do not fall out-

side the group. With the exceptions in mind, the fixity

of the instinct to feed on only certain kinds of plants is

all the more extraordinary, for we cannot readily dismiss

it as a physiological or nutritional necessity.

An interesting light upon the effect of the environment

in influencing the selection of food-plants, is furnished

by several widely distributed species and genera of but-

terflies. Thus several species of Vanessa have quite

identical food-habits throughout the entire holarctic re-

gion and the same is true of several very closely allied

palearctic and nearctic species belonging to the same

group, while, as mentioned above, the general food habits

of the larger groups run closely parallel among their rep-

resentatives on the two continents. Still more interesting

in this respect are the butterflies of the closely related

genera Catopsilia and Callidryas which restrict them-

selves to the Leguminous genus Cassia. These butter-

flies occur in the nearctic, neotropical, Indo-Malayan and

Australian regions and such species as have been reared

show this preference, which is probably universal. The

well-known genus Papilio supplies some similar peculi-

arities in that several world-wide groups of the genus

are restricted to certain closely related groups of plants

(e. g., Aristolochia, Citrus, ete.). On the other hand, one

North American species, the common Papilio glaucus, is

known to affect food-plants belonging to no less than fif-

teen different families of plants. With such constancy

in the most remote quarters of the globe among related

species of this genus and with one species in a single

region regularly developing on the most diversal plants,

we must believe that the fixed instincts of some species

are not to be led astray by the many temptations offered

even by the varied plants of widely separated zoological

No. 633] FOOD-PLANTS AND INSECTS 325

regions, while those of other species are so loose that

they restrict their owners only to a comparatively very

small extent. Such conditions certainly point to instinct

as the determining cause of food selection, rather than

physiological adaptation to specific kinds of plants.

In connection with cosmopolitan butterflies, Scudder

noted many years ago, that there are no species of re-

markable distribution known to feed upon Leguminose

or grasses, although these plants are cosmopolitan and

harbor many species. I am inclined to believe, however, ©

that this has no significance, particularly in view of the

aforementioned Coliads that feed upon Cassia in various

parts of the world. «

Many other groups of Lepidoptera conform quite

closely in food-habits to the butterflies, although some

show greater diversity, especially in affecting different

parts of the plant, and it may be said in general that the

larger moths are less apt to be monophagous than the

butterflies.

Among the hawk-moths or sphinx-caterpillars several

subfamilies show a restriction to groups of related plants,

while others do not. Thus in this cosmopolitan family,

one subfamily (Cherocampine) feeds-on Vitaceæ, with

an admixture of diverse other plants, another (Macro-

glossine) on Caprifoliacee exclusively, another (Sphin-

gineæ) to a great extent on Oleacee together with other

plants as different as Conifers, Solanacex, Euphorbiacee

and Labiate, while one (Smerinthine) exhibits no appar-

ent preference.

The family, Aegeriidæ, or clear-winged moths, live in

the larval stage in the interior of plants, tunneling

through the tissue. They affect a very wide series of

plants, herbs, shrubs and trees, as can be seen from

the following abbreviated list which represents the range

in habits of some of our eastern North American repre-

sentatives; stems of Cucurbits, Vernonia, blackberries,

currant, grape; wood of pine, willow, lilac, maple, oak,

peach; roots of Clematis, persimmon, blackberry, Eupa-

326 THE AMERICAN NATURALIST [Vou. LIV

torium; stumps of oaks cut the previous year; and oak-

galls. Notwithstanding such diversity within the family,

the individual species are nearly monophagous, or oligo-

phagous on related plants. Such a condition would seem

to have arisen through sudden mutations in instinct

rather than from numerous smaller variations having a

selective value, for in the latter case we should find poly-

phagous forms developing in some places at least.

Another, much smaller family of rather generalized

structure, the wood-boring Cosside, have habits similar

to many of the Sesiidæ, but their selection of food-plants

is very different. Typically they are oligophagous, but

some species, including the well-known and destructive

shade-tree pest known as the leopard-moth (Zeuzera

pyrina) introduced from Europe into the eastern United

States, has been bred in this country from an almost end-

less variety of shrubs and trees, as it has been in Europe

also. As listed by Chapman, the American food-plants

belong to twenty-two families of plants and to nearly

fifty genera. Almost all that can be said of the leopard-

moth’s bill-of-fare is that it includes no conifers.

Cossus ligniperda, another European species is strongly

polyphagous, but many of the exotic species appear to

avail themselves of a rather restricted diet. As this lat-

ter is perhaps due to lack of knowledge, it may be unwise

to draw any conclusions at present.

- In other families of moths the same phenomenon is fre-

quently encountered. The large group of Noctuide, com-

prising the owlet-moths, feed mainly upon the foliage of

a wide rang of plants, while the list of food-plants for

the numerous species varies greatly in extent. To at-

tempt to classify the food-habits of this group would re-.

quire much time and space, but it may be said that there

are species in certain genera, as, for example, the cotton

boll-worm, which appear to have rather suddenly en-

larged their range of food-plants as compared with that

of related species of the same genera.

In regard to the uniformity of food-plants during on-

No. 633] FOOD-PLANTS AND INSECTS 327

togeny, the statement has been made that some Lepidop-

terous caterpillars occur on a greater range of plants

when young, or at least that they will readily feed upon

certain kinds during the earlier instars, and refuse them

later, so that their diet becomes more restricted as

growth progresses. This statement has been in turn used

as an argument that oligophagous forms are derived

from more restricted feeders, and that they repeat in a

way their history by the limitation of their food-plants

during successive instars.

Some elaborate experiments on the feeding habits of

the gipsy-moth reported on by Mosher tend to discredit

this supposition, however. As is well known, the gipsy-

moth oceurs on a wide range of plants, but shows well-

marked preferences for certain among them which repre-

sent its favored food. These experiments were carried

out in the extensive detail possible only when dealing

with insects of great economic importance, and although

_planned for another purpose, furnish valuable data upon

this point. It appears that on a number of their numer-

ous food-plants, the gipsy-moth caterpillars show an in-

ability or at least an unwillingness to feed either during

the very early or during the later larval stages. On

some kinds of trees the early larve failed to develop and

on others the latter stages did not feed, although the

young ones did so. This diversity of behavior is in part

due to the fact that young larve cannot usually feed upon

conifers, while the older ones eat the foliage of these trees

voraciously; but it is by no means due to this alone, so.

that we can say that the juvenile preferences of the larve

become transformed or changed as growth progressed.

With an active polyphagous caterpillar like the gipsy-

moth in which the larve often migrate to other species of

plants during growth, it is possible for such changes in

diet to take place regularly in nature, although such could

not ordinarily occur with oligophagous species without `

tending greatly to reduce the chances of the species to

survive. As the necessity for migration is most acute in

the case of very abundant species, they are open to more

328 ` THE AMERICAN NATURALIST [Von. LIV

temptations to avail themselves of a variety of foods and

we find that it is usually the most abundant species of

any group that are polyphagous. Conversely we may

say also that polyphagy, when present, greatly increases

the chances for the larve to secure the necessary amount

of food for complete growth and tends to cause the spe-

cies to become excessively abundant. Once under head-

way, these two processes will act together and result in

the production of dominant species that tower above their

fellows. Examples of this are seen in the gipsy-moth,®

the Cecropia-moth, the army-worm, Papilio glaucus men-

tioned above, the woolly bear (Isia isabella), ete. We

must not lose sight of the fact, however, that this is only

one of many factors influencing dominance. The milk-

weed-butterfly, one of our most abundant native species

develops on a very common plant (Asclepias almost ex-

clusively) and is thought also to be a protected species.’

Its dominance may be interpreted, like that of many de-

structive agricultural pests, as due to a plentiful and un-

failing food supply, coupled with other pre-requisites in-

herent in the insect itself.

In spite of the many exceptions and variations which

have been enumerated, the fact stands out clearly that

the Lepidopterous insects show a very fixed instinct to

select definite plants for larval food; that many are ex-

tremely precise in this respect, some less so, and others

quite catholic in their tastes. Furthermore there is much

to show the existence of a so-called ‘‘ botanical instinct’?

in species, genera and even families, whereby evidently

related plants and these only serve as food. A few spe-

cies have departed from the general habit so far that

they have become carnivorous, and among the others we

find every gradation between the extremes of monophagy

and polyphagy.

It has been claimed that the food habits may be modi-

fied experimentally, in that caterpillars reared on a

6 This is true also in the native habitat of this species, aside from the

TRG by parasites which occurs more abundantly in Europe.

- e., distasteful to its enemies and exhibiting warning coloration.

No. 633] FOOD-PLANTS AND INSECTS 329

strange plant (where they could be induced to select it)

give rise to moths whose progeny more readily accept

the new plant. It is very difficult to accept such evi-

dence, at least as having any general application, with-

out very clear and incontrovertible proof. If such trans-

formations can occur so easily and become hereditary so

quickly they should have entirely destroyed the coherent

habits now existent, during the enormous period which

has elapsed, for example, since the violent-feeding Ar-

gynnids were differentiated, since the holarctic and neare-

tic Vanessids have been separated, or while the world-

wide Aristolochia-feeding Papilios were attaining their

present distribution. That such a change has actually

occurred in the case of other groups seems equally evi-

dent, although, as has been shown, we can more easily

believe that they may have arisen through mutations in

maternal instinct not incompatible with larval tastes and

then only in extremely rare cases and confined to certain

groups.

With a knowledge of the specificity of proteins in dif-

ferent living organisms and their apparent differentia-

tion as a replica of the genealogical history of the animal

and plant kingdoms, has come the suggestion that the

dependence of monophagous or oligophagous insects

upon specific plants rests upon a physiological basis, and

that particular proteins or vitamines are an actual neces-

sity for growth and development. A survey of the field

does not seem to bear out this supposition, however

plausible it may appear at first sight. With monopha-

gous larve, it will serve as a reasonable explanation, and

with oligophagous ones also so far as the individual spe-

cies are concerned, especially where such species select a

series of related plants. With those that select only a

few plants, however, and at the same time such as are

evidently not closely related, it does not seem so appro-

priate. It is when we compare the lists of food-plants of

several oligophagous species that it appears to fail com-

pletely to meet the requirements. Thus we find, referring

again to our North American butterflies, such combina-

330 THE AMERICAN NATURALIST [ Vou. LIV

tions as Leguminose with Pinaceæ, or with Rhamnacee,

Polygonacee, Cupulifere in the case of different larve.

More uniformity should certainly be expected if the se-

lection of diverse plants depended upon the actual chem-

ical characteristics of the plant tissue. We should have

also to assume that the digestive functions of the cecropia

caterpillar with its sixty-odd food-plants were funda-

mentally different from those of monophagous caterpil-

lars.

There is much in the behavior of certain species to

suggest that food-plants are selected on the basis of odor

by the parent female and also accepted on the same basis

by the larve. Experiments with cabbage butterflies by

Verschaffelt and others show that these insects are at-

tracted by the mustard oils present in these plants, and

it has also been shown that caterpillars will feed on other

plants which have been treated with one of these oils.

Similar behavior in the most diverse insects is also known

in the attraction exercised by specific fermentation prod-

ucts (e.g., to Stomoxys, Drosphila, ete.). The distaste of

mosquitoes for oil of Citronella is well known, as is also

the attractiveness of this same substance for fruit-flies

of the genus Dacus. That the same cabbage butterflies

have definite dislikes in the way of plant odors has re-

cently been claimed by the Russian entomologist Schrei-

ber, who found that Pieris brassice would not attack cab-

bages planted in close proximity to tomatoes. Pieris

rape does not seem to behave similarly, however, and this

dislike is probably not general among the crucifer-eating

Pierids.

Very recently MeIndoo has published some observa-

tions showing that caterpillars readily react to the odors

of several essential oils and to those of various plants.

This, taken together with the fact that Pieris will feed

upon strange plants treated with mustard oil, would sug-

gest that odor is an important factor in the selection of

food-plants. Queerly enough, however, he found that the

` response to their own food-plants was no more rapid

than to the other substances, and even slower in some

No. 633] FOOD-PLANTS AND INSECTS 331

cases. As the smearing of the oils of one plant on an-

other does not occur in nature, the important point to

discover is whether there is really any similarity of odor

in the several plants -of diverse groups that are some-

times utilized by a single species of insect. The facts

alluded to above in regard to the wide variety of selec-

tions made by different species would seem to answer

this question in the negative, as would our own human

sense of odor, which latter may, of course, not be reliable

when dealing with a group of animals so different from

man. We may, I think, rest assured that odor frequently

guides the insects to their food-plant, but we can not be-

lieve that oligophagous or polyphagous species have be-

come accustomed to a variety of plants due to a confusion

of similar odors. There does seem, however, to be one

very striking exception to this among the Pierid butter-

flies. As said before, these butterflies are confined to

Crucifere almost exclusively, but one of our species not

infrequently occurs on the garden ‘‘nasturtium’’ (Tro-

peolum). That the pungent taste of this plant is much

like that of a Crucifer is well known and further attested

by the common name, as the true nasturtium of the botan-

ists is a genus of Cruciferx, while the garden nasturtium

is a Geraniaceous plant.

On account of the very close biological association be-

tween insects and plants in many ways it is true that the

two have been mutally specialized until they have become

highly modified in reference to one another, but this is

not the case with food-plants, as no benefit ordinarily

accrues to the plants and any idea of parallel evolution

must be restricted to a development of undesirable at-

tributes on the part of the plants and adaptations on the

part of the insects to overcome such barriers to feeding. —

To avoid these numerous difficulties, it seems clear

that the selection of food-plants by the Lepidopterous

insects so far mentioned, must be considered as depend-

ent upon one or several of a number of factors. Among `

these we must include the following:

332 THE AMERICAN NATURALIST [Vou. LIV

1. The odor of the plant, and also its taste, which is

no doubt closely connected with odor. Associations rea-

sonably placed in this category would be the oligophagous

species occurring, for example, on various Crucifere,

various Umbellifere, and various Composite. An addi-

tional argument for the importance of this factor is seen

in the less common utilization by the same insect of sev-

eral plants in a family like the Solanaceæt where a more

or less similar odor does not become a family charac-

teristic.

2. Some attribute of the plant, perhaps an odor but

far less pronounced to our own senses than those men-

tioned above. Species restricted to plants like Legumi-

nose or Violacee may be considered in this category.

Undoubtedly there is some attribute of such plants which

insects can recognize in a general way and not as a

specific characteristic of some single plant species or

genus. The ‘‘ botanical instinct’’ of some caterpillars that

has frequently been commented upon would appear to be |

an exaggerated power of recognition of this sort.

: . A similarity in the immediate environment or gen-

pees form of the food-plant. The effect of something of

this sort is seen particularly in oligophagous and also

polyphagous caterpillars feeding mainly on trees or

shrubs, such as the gipsy-moth, Cecropia moth, ete., and

those of certain species like some of the Arctiid moths

that feed upon a great variety of low plants.

4. Apparently chance associations that have become

fixed, whereby diverse plants are utilized by oligophagous

species. Secondarily polyphagous species show these in

an exaggerated form. On account of their comparatively

` rare occurrence these seem to be analogous to structural

mutations, although they appear to be strictly modifica-

tions of instinct. As has been pointed out on a previous

page, these are much more apt to occur in some groups

(families and genera) than in others.

8 Possibly in this family, however, the matter may rest upon a physiolog-

ical basis, on account of the common occurrence of powerful alkaloids in

these plants.

THE MANIPULATION AND IDENTIFICATION OF

THE FREE-SWIMMING MASTIGOPHORA

OF FRESH WATERS

LEON AUGUSTUS HAUSMAN, Pu.D.

CORNELL UNIVERSITY

Nor the least among the problems that confront the

worker in systematic protozoology is the identification

of the minute, free-swimming Mastigophora, representa-

tives of which occur in all cultures, often in great num-

bers both of individuals and of larger groups. The

writer’s attempts to find some means of making their

identification easier and more certain have resulted in

the working out of several methods of dealing with these

elusive forms, methods which have been used with suc-

cess in the laboratory examination of material. They

are here presented with the hope that they may be a simi-

lar assistance to others.

For the purposes of identification it has been found

helpful arbitrarily to divide the Mastigophora into two

great groups, on the basis of size; placing those the ma-

jority of whose species measure about 12 microns or less

along the antero-posterior axis in one group, and those

of greater magnitude in the other. It is among the spe-

cies in the first group that the difficulties in identification

seem usually to occur, and it is with this division, there-

fore, that this paper deals.

The genera included within this first arbitrary division

fall within the first four orders of the mastigophora,

thus:

SUBPHYLUM MASTIGOPHORA

ORDER MONADIDA

Genera: Mastigamoeba

Cercobodo

Cercomonas

Physomonas

333

334 THE AMERICAN NATURALIST [Von. LIV

ORDER HETEROMASTIGIDA

Genera: Elvirea

Dinomonas

Pleuromonas

Spiromonas

ORDER PHYTOMASTIGIDA

Genera: Amphimonas

Hexamita

ORDER EUGLENIDA

Genera: Cryptoglena

Notosolenus

Almost all the mastigophora, but more especially the

minute forms, vary in size and shape within the limits of

the species. Individuals of apparently the same species

are often found half, and even a fourth, of the size which

is normal for that species, while abnormally large forms

are more rarely encountered. It is the smaller forms

which are the most puzzling. These are probably due

to: (1) the division of the adults, for binary fission along

the line of the antero-posterior axis is the prevailing

mode of reproduction among the Mastigophora. Where

division is occurring rapidly, in a crowded culture many

such forms will be found. Often the young again sub-

divide, even before reaching adult proportions. This

gives rise to individuals of a species varying widely in

size, (2) to the fact that the adults themselves vary in

size, even where division is not rapidly taking place, and

(3) to the possible production in some forms of swarm

spores. Possibly when the life histories of a greater

number of the smaller flagellates become known, it will

be found that many species multiply not only by binary `

fission, but by multiple fission as well, either within or

without the cyst. It is not unusual to find individuals of

a colonial form which have freed themselves, or have

been broken away, from the parent community, and

which are, temporarily, at least, living an independent

No. 633] FREE-SWIMMING MASTIGOPHORA 335

existence. Adventitious individuals may be derived

from such colonial mastigophora as Spongomonas, An-

thophysa, Dendromonas, Uroglena, and Ramosonema.

The following key, which was devised by the writer,

has been found helpful in the identification of the minute

forms, and in fixing in mind the characters that are the

most prominent, and that are useful, under the micro-

scope, in identification. The key includes practically all.

the forms of the minute mastigophora that are likely to

be found in the waters of bogs, ponds, roadside ditches,

creeks, and brooks, and putrefying infusions, in so far as. `

these have been accorded systematic place. These

forms occur over and over again, and their identification

has been found to be a matter of less difficulty than was

at first thought, before a definite plan for handling them

was formulated.

KEY TO THE MINUTE MASTIGOPHORA, THOSE ROUGHLY ABOUT OR BELOW

; CRONS

A, pron tae diameter. normally about, or less than 8

icrons.

B. “Papa 2, ae kidney-shaped, the smallest of the

* mastigop rine reer gary RUNES abate E yet get npn sae leuromonas

BB, Fiagella 3, ee trailing, one extended forward..... Elvirea

AA. Antero po or diameter normally greater than 8

B. With ¢ one flagellum

C. With greenish shecmatophores GP ae rae Cryptoglena

cC. Pap idi chromatophores

D. Flagellum stiff aasi Bb Ap oiea ro a Notosolenus

DD. Flagellum not stiff, aene present ....Mastigamoeba

C. With 2

E E E T E Cercomonas

ody

eee Both flagella at same extremity of body.

. Bo tk atii the anterior extremity the

Selva T E Dinomonas

EE. Sos in normally ovate. +

F., Body spherical ....---++--+e+++ seers Amphimonas

FF. Body not spherical.

G. Body ribbon-like, twisted .....-.--- Spiromonas

GG. Body not twisted.

336 THE AMERICAN NATURALIST [Vou. LIV

H. Body drawn out bluntly poste-

Cures os oa wei oo Physomonas

HH. Body drawn out into an acumi-

nate tip posteriorly, not trun-

‘ CAtod anteriorly sis 6s 5 ok Oe aces Cercobodo

CC. Flagella more than 2.

D. Fiagella 3, two trailing, one extended forward ..Elvireat

DD. Fiagella four, anteriorly extended; posterior

produced into 2 filamentous appendages... .Hexamita

In dealing with these minute, free-swimming forms, it

was of first necessity to devise some means of keeping

them quiet and within the field of the microscope when

‘the higher powers were in use. Several methods both

of retarding movement and of killing were used, but

those which gave the best results were the following.

For the first examination of any sample, a small drop

of the culture was taken and mixed on a slide with a drop

of very viscous gelatine solution,? and the whole thor-

oughly stirred together. Or often several drops of the

culture were mixed with an equal part of the gelatine

solution in a watch crystal and used on the slide when

needed. Such a preparation would not keep the pro-

tozoa confined within it alive for more than half an hour,

however, due to the occlusion of the necessary oxygen.

The drop on the slide was now carefully flattened out

and examined without a cover glass under a low power

(16 mm. objective and 10x eyepiece) to ascertain whether

the solution were of a viscosity great enough to check

sufficiently the movements of the flagellates. If not, it

was allowed to concentrate still more by evaporation

until properly viscous, and then covered with a cover

glass. Magnification with the 4 mm. objective and the

8x and 10x eyepieces was found to be great enough for

the identification of most of the forms.

. The gelatine used in this method must be of the best

grade and perfectly fresh and clear. It may be slightly

1 Elvirea, because of its variability, is placed both here and in division

AA of the key,

2See formulary of reagents at end of paper.

No. 633] FREE-SWIMMING MASTIGOPHORA 337

agitated before adding to the culture drop. This in-

cludes numerous minute air bubbles, around which the

animals may gather and so become concentrated, if the

solution is at first thin enough to allow them to make

their way through it. It was’ found that gelatine that

had stood ready made up for some time in a warm room

became cloudy in appearance and stringy in texture, due

to the growth of mould plants and colonies of bacteria.

Another method of retarding the motions of the flagel-

lates, which was partially successful with such minute

forms as Pleuwromonas jaculans and Elvirea cionae, was

to chill the slide and its water drop thoroughly on a block

of ice. This was tried in midsummer, when the sudden

reduction in temperature of water that had been quite

warm (the culture having stood in the sun) apparently

paralyzed the organisms, but they regained their wonted

activity after a few minutes’ time, since the slide could

not very conveniently be kept chilled under the micro-

scope.

The favorite method of the writer for quieting without

killing was to utilize a minute aquarium, of a sort that

might be used even under the high powers. This was

constructed by cutting outa circle of very thin typewriter

manifolding paper of good grade and firm texture of

slightly less diameter than that of the cover glass, and

then cutting from the center of this a concentric aperture

about 5 mm. in diameter. This was affixed to the slide

with a ring of thin balsam or castor oil, applied with a

fine camel’s hair brush; the water drop placed in the cen-

ter, and the cover glass, also ringed with thin balsam or

oil, carefully lowered thereon. The oil or balsam sealed

the cover glass, and the paper kept it from descending

far enough to crush the incarcerated organisms.

At first the flagellates in such an aquarium swim about

at their normal rates of speed, but after a time they be-

come stupefied, probably because of the gradual exhaus-

tion of the oxygen supply, and their movements become

progressively slower, until finally they cease altogether.

338 THE AMERICAN NATURALIST [ Vou. LIV

The flagella continue to beat for some little time after the

animal has come to rest.

This offers a good opportunity for the observation of

the natatory habits, and, as the animals quiet down, for

making a closer examination for identification, using

higher powers. The smaller the water volume in such a

micro-aquarium, the sooner the stupefaction of the con-

fined organisms takes place. The forms studied in the

micro-aquarium were usually stained intra vitam before

their incarceration.

The stains most frequently used for intra vitam work

were methylene blue (not methyl blue) and methyl green.*®

With each of these a saturated aqueous solution was pre-

pared and diluted to the desired strength.

The stains which were used for killed specimens were.

methylene blue (not methyl blue), methyl green, gentian

violet, and safranin.*

The examination of the imprisoned intra vitam stained

animals has the advantage over the killed and stained

ones that it shows the position and action of the flagella,

and so leads to a more correct idea of how this should be

represented in a drawing. Occasionally one meets with

the drawing of a form in which the flagellum is repre-

sented as thrown into graceful undulations, whereas, in

life, it may be only the tip of that organ that is motile.

It was found that frequently the killing reagents caused

the flagella to assume unnatural attitudes.

In both the killed and the intra vitam-stained animals

the flagella takes the stain least of all, often appearing

but very faintly, if at all, colored. In intra vitam stain-

ing, care must be taken not to kill the creatures with too

much stain in the attempt to make the flagella stain more

deeply.

Killing, in order that examination might be made with

the 1.8 mm. objective, using oil, was accomplished by the

use of the various well known reagents, such as tannic

3 See formulary of reagents at end of paper.

4See formulary of reagents at end of paper.

No. 633] FREE-SWIMMING MASTIGOPHORA 339

acid, osmic acid, acetic acid, formaldehyde, and mercuric

chloride solutions.* The best results, however, were ob-

tained by the use of a 1 per cent. aqueous solution of

copper sulphate, a reagent which was hit upon in the at-

tempt to find a medium in which death occurred with a

minimum of distortion of the flagella. Innearly all cases

the animals very gradually subsided into immobility

without any distortion whatever. A .5 per cent. solution

kills them much more gradually. These solutions must

be made up with accuracy, and may be most delicately

prepared by counting drops of water and of concentrated

copper sulphate solution, as they come from the tip of a

finely drawn out pipette. One hundred drops of water

from a pipette the diameter of whose tip measures about

2mm. makes a sufficient quantity to last for months.

The killing and staining was accomplished in either of

two ways, either by killing first and staining afterwards,

in which case any of the killing reagents given at the end

of the paper was used, followed by the stain, or by per-

forming both operations simultaneously. This may be

done by using strong stains. The material can be stained

either on a slide, or in larger quantities in a watch crys-

tal. Where the animals were extremely abundant, as '

they usually were in surface scums or decaying cultures,

the latter method was found to be the best, for with the

larger quantity of water both the killing reagent and the

stain could be more delicately controlled. Several watch

crystals were placed side by side and various gradations

_ of color secured. |

The killed specimens were examined at once, and fresh

preparations frequently made. Complete disintegration

of these tiny forms takes place a short time after they

have been killed. This is preceded by a distortion of the

body.

On the whole, intra vitam staining, with the animals

retarded in the gelatine solution, or stupefied in the

micro-aquarium, gave the best results. With animals

treated thus, the magnifications afforded by the 8x and

340 THE AMERICAN NATURALIST [ Von. LIV

10x eyepieces and the 4 mm. objective were found great

enough for the majority of the forms.

In the following descriptions of the genera and species

the attempt has been made to indicate the characters

which are the most prominent ones of the members of

each group, those by which the identification can usually

be made. Hitherto less attention than the subject seems

to deserve has been given to the manner in which these

lower forms make their way through the water—to what

may be called their natatory habits. Many forms show

natatory habits which seem to be of a constancy and a

distinctness sufficient to warrant their use as character-

isties for identification. This feature has been given at-

tention in the following descriptions because it has been

found a helpful one in identifying the forms.

It is here suggested that the vibratory motions which

some of the smaller flagellates, like Plewromonas and

Elvirea, exhibit, may be due in part to the influence of

pedesis, or Brownian movements. Carpenter states°

that all particles suspended in water below Yoo of an

inch (49 microns) exhibits this phenomenon, and it is a

matter of observation that the smaller the particle the

more pronounced the vibration.

ORDER MONADIDA

Genus Masticamorsa Schultze.

Body ameeboid, changing shape slowly as pseudopodia

are protruded, usually from the sides or posterior por-

tion of the body. Flagellum long, fine, and not easily

seen at first in its entirety, because of its rapid motion.

These forms move with either a true amceboid motion, or

swim by means of the flagellum. Conn states that in

swimming the pseudopodia are retracted, yet we have

noticed frequent exceptions in both species. The swim-

ming of these species is clumsy, due perhaps to the ir-

regularity of the body.

5‘*The Microscope and Tts Revelations.’’

Fig. 1. Mastigamoeba longifilum Stokes (10-15 u), 2 pai aps

Fig. 2. Mastigamoeba repetans Stokes (8—10 u), 2 individual

Cercobodo mutabilis Kent (8-12 u), 3 individuals, 1 + the pseudo-

podia-bearing stage.

Fic. 4. Cercomonas longicauda Dujardin (10-13 u), 3 individuals, 1 pro-

truding pseudopodia 1 ae the posterior extremity of the body.

5. monas crassicauda Dujardin (6-9 u), 1 individual of typical

Fig, 6. hana elongata Stokes (10-13 b> 3 individuals.

Fie. 7. Elvirea cionae Parona (5-8 u), 2 individuals.

Fig. 8. Dinomonas vorax Kent (8-15 uw), 3 individuals.

342 THE AMERICAN NATURALIST [ Vou. LIV

M. longifilum (Fig. 1) seems to be the most common

species in the waters about Ithaca, N. Y.,and New Haven,

Conn., though M. repetans (Fig. 2) was often seen. The

former is the larger, the more hyaline, and furthermore

possesses at least one quite prominent contractile vac-

uole. No difference in the length of the flagellum in the

two species could be observed.

Genus Crrcosopo Kraasilstschik.

Body changeable in form from almost globular to elon-

gate, with the posterior extremity usually more or less

drawn out, frequently acuminate. This latter form is

the one under which the species most frequently appears.

The two flagella arise from the anterior end of the body.

Often an ameeboid form of body is assumed, and locomo-

tion is effected by blunt pseudopodia.

Because of its instability of form, the one species which

is the most common has been relegated successively to

the genera Dimastigameba, Dimorpha, and Cercobodo.

The single contractile vacuole is usually present and

prominent. The one species observed seems to conform |

to the Cercobodo mutabilis of Stokes (Fig. 3).

Genus Cercomonas Dujardin.

Body globular to ovate, pointed at the anterior and

posterior extremities, from each of which arises a long

flagellum, the posterior of these being the stouter, a trifle

the shorter and less motile. The pseudopodia, which

are occasionally produced, are not as well defined as

those in the two preceding genera, and are limited to the

posterior fourth of the body. These were not frequently

seen.

Two species are fairly common: C. longicauda (Fig.

4), and C. crassicauda (Fig. 5). They may be distin-

guished by their difference in size.

Genus Puysomonas Kent.

Body changeable in form, though not possessing pseu-

dopodia, and varying from elongately ovoid to ovoid

No. 633] FREE-SWIMMING MASTIGOPHORA 343

pointed at the posterior extremity. The anterior portion

of the body is normally obliquely truncated, from which

arise two flagella of unequal length.

P. elongata (Fig. 6) is fairly common in all waters of

ponds and bogs, particularly among sphagnum, though

it seems never to occur in crowded cultures.

ORDER HETEROMASTIGIDA

Genus Exvrrea Parona.

The body is pear-shaped, and though it may elongate

and contract slightly during swimming, it is quite stable

‘inform. Of the three flagella which arise from the ante-

. rior extremity, the stouter, shorter one vibrates forward,

and is the organ of locomotion. The other two trail

behind.

'E. cione (Fig. 7) is apparently not a very common spe-

cies. It was found sparsely in the clear cold waters of

springs and creeks.

Genus Drnomonas Kent.

Members of this genus resemble those of the preceding.

one in the general shape of the body, but they are larger

and possess but two flagella, both of which extend for-

ward from the more acute anterior extremity. The con-

tractile vacuole is usually clearly Mes dn and located in

the rounded posterior region.

Fig. 8 was found abundantly in the scums of various

infusions of grasses and leaves, and conforms to the D.

' vorax of Kent. D. tuberculata (Fig. 9) was often found

in the same infusions with D. vorax. It is possible that

this may be merely another form of the latter species.

Genus Pievromonas Perty.

Body either kidney-shaped or ovate, the two long fla-

gella arising from a depression in the venter which is not,

however, invariably present.

P. jaculans (Fig. 10) is often very common in stagnant

waters wherever there is decomposing vegetable matter

344 THE AMERICAN NATURALIST [Vou. LIV

present. Some infusions will be colored a milky hue

from the multitudes of these forms within them. The

individuals of the species vary considerably in size, some

being no greater than 2 microns along the anterio-

posterior axis. The majority of the individuals, how-

ever, lie within the limits of 3 to 8 microns. They may

be recognized at once by their peculiar agitation and

habit of leaping or jerking about from place to place.

Individuals may sometimes be discovered lying quiet,

except for a gentle vibration—a motion which, it has

been suggested earlier in this paper, may be due to the

influence of pedesis. These quiet forms are to be found

usually near the edges of masses of disintegrating mate-

rial, where they are likely to be overlooked. The bodies

are often particularly hyaline, and the flagella difficult to

make out. Iodine (an alcoholic solution, with potassium

iodide, as given under No. 2, Section B of the Formulary

of Reagents at the end of the paper) as a stain after

killing was found to be the best for these minute forms.

In some eases the flagella could be made to take the stain

well, in others not. Those killed with the stain itself

‘seemed to be better colored than those stained after

having been killed with some other reagent.

Genus Sprromonas Perty.

Body leaf or ribbon-like, either flattened or more com-

monly twisted spirally, with one or two turns, very vari-

able. Kent says that these forms may even assume an

amceboid form of body. Of the two flagella that arise

from the anterior tip of the body, one trails, one extends

forward and vibrates with great rapidity.

The variable S. angustata (Fig. 11) seems to be quite

common in infusions of all kinds, but particularly abun-

dant in those of hay, swamp grasses, and the like.

ORDER PHYTOMASTIGIDA

Genus Ampuimonas Dujardin.

Body globular, either attached by a fine posterior pedi-

cel, or free-swimming—the latter being apparently the

sie

Fic. 1 Amphimonas globosa Kent (10-12 u), 2 individuals, 1 free, 1 at-

tached by a posterior pedicel.

Fig. 13. Hexamita inflata Dujardin eae nde 2 individuals.

Cryp ae 1 ptg

Fig. 14. toglena coni

Fie. 15. Oryptoglena pigra Ehrenberg ( , 1 individua.

Notosol 0 Stokes ae pa), 2 eativigenla 1 turned

Fic. 16.

sidewise to show the concavo-convex shape of the body. This latter form may

ies,

be, perhaps, another species.

346 THE AMERICAN NATURALIST [Von LIV

more common condition—by means of two long, fine,

equal, anterior, rapidly vibrating flagella. In the free-

swimming stage the posterior pedicel is usually absent,

_ though occasionally individuals may be seen trailing

after them pedicels of different lengths. These may be

pedicels in various stages of retraction into the body. .

A. globosa (Fig. 12) seems to be of rather rare occur-

rence in the waters of ponds and ditches among decaying

aquatics.

Genus Hexamita Dujardin.

Body very changeable in form, with two long, filamen-

tous appendages arising from near the posterior extrem-

ity of the body. Flagella four, anterior, active.

H. inflata (Fig. 13) was found in water containing

Ceratophyllum just beginning to decay.

ORDER EUGLENIDA

Genus Cryprocuena Ehrenberg.

Body oval, not changeable in form, nor varying greatly

among the members of the species; possessing one

greenish yellow, or greenish brown chromatophore, or

two. Flagellum stout at its base, there may be present

a red stigma. Swims rapidly, with an undulatory

course.

Two species, C. conica (Fig. 14) and C. pigra (Fig. 15),

seem to be quite common in pond waters among such |

smaller aquatics as Lemna, Elodea, etc. They are often

found in water in which there is decaying vegetation,

also, associated with Euglena and Phacus.

Genus Norosotenvs Stokes.

Body hollowed, resembling the bowl of a blunt, thick,

wooden spoon; hyaline, colorless, and filled with a large

number of large, globular, glassy granules or vacuoles.

We have observed but very few individuals which did not

contain these. Flagellum long, stiff, and stout, and rigid

except that its distal fourth only is motile. This pecu-

No. 633] FREE-SWIMMING MASTIGOPHORA 347

liar characteristic affords a good identification character.

During swimming it often turns over and over in the.

water, at which times the concavo-convex shape of the

body becomes appreciable.

Either individuals of the species N. orbicularis (Fig.

16) vary remarkably in size, or there is more than one

species, differing, apparently, only in this particular.

The form of the body is, however, constant.

These forms are Pound; unlike most of the flagellata,

most abundantly in fresh waters, particularly in the clear

cold waters of springs, that support little plant growth,

and they occur usually near the bottom, among the sands

and pebbles.

Their progression through the water is often slow and

deliberate, and at such times it seems as though the tip

of the flagellum were functioning as an exploratory

antenna.

FORMULARY OF REAGENTS USED FOR RETARDING, KILLING ANG STAINING

` 1. Retarding Solutions:

(1) Gelatine Solution.

NVM ook acco nee aNG E veo A 5 02

Gelato 5 20 Ps hace ees oe ee wl eck cee 1⁄4 oz.

Heat, to dissolve the gelatine; then allow to cool to the de-

sired viscosity.

(2) A 1 per cent. aq. sol. of chloretone nareotizes the animals, and

gave good results with certain forms, though its manipula-

tion was a trifle difficult.

2. Killing Reagents:

(1) 25 per cent. aq. sol. tannie acid.

(2) 5 per cent. aq. sol. acetic acid.

(3) 10 per cent. aq. sol. mercuric chloride.

(4) 1 per cent. aq. sol. form

(5) Invert slide with its ana drop over the neck of a bottle

containing a 2 per cent. sol. of osmice acid. The fumes kill

the animals at once.

(6) 1 per cent. aq. sol. copper sulphate. This gave the best re-

sults of any of the killing reagents.

3. Stains:

A, cil intra vitam staining. (Make up a quantity of the stain

, and then dilute with water to obtain desired

denih of color.)

348 THE AMERICAN NATURALIST [Von. LIV

(1) Sat. aq. sol. methylene blue.

(2) Sat. aq. sol. methyl green.

(3) Sat. aq. sol. APR violet.

(4) Sat. aq. sol. safran

B. For staining after killing, or for killing with the stain itself.

(Make up a quantity of the stain, and dilute with water for

desired color.

(1) Sat. alcoholic sol. methylene blue.

(2) Sat. alcoholic sol. methyl green.

(3) Sat. alcoholic sol. gentian violet.

(4) Sat. alcoholic sol. safranin.

(5) Sat. alcoholic sol. iodine, with 3 per cent. potassium

iodide. This gives excellent results. It is a very pow-

erful stain, and must be used in weak solutions.

NEOTENY! AND THE SEXUAL PROBLEM

DR. W. W. SWINGLE

DEPARTMENT. OF BIOLOGY, PRINCETON UNIVERSITY

Ir has long been known that the larvæ of certain Uro-

deles sometimes fail to undergo metamorphosis, yet be-

come sexually mature in the larval stage. Perhaps the

best known of such cases of neoteny, as this phenomenon

is called, is that of the Mexican axolotl, long regarded as

a separate species, now known to be an overgrown, sex-

ually mature larva of Amblystoma tigrinum. Several

other similar cases have been described, however. -All

neotenous amphibians hitherto reported, with the excep-

tion of Allen’s (1) thyroidless tadpoles, have been con-

fined to the tailed amphibians, and so far as the writer is

aware, the normal occurrence of precocious ripening of

the sex cells in larval Anura has never been described.

Oddly enough, it is the normal thing, and its occurrence

throws considerable light upon the obscure problem of

sex differentiation and development in the Anura, which

has long puzzled investigators of this subject. It will be

recalled that Pflüger (5) reported years ago, that there

occurs normally in newly metamorphosed frogs three

kinds of individuals, males, females and hermaphrodites,

the two latter forms much more numerous in early stages

than the males. In the course of further development the

hermaphrodites become either definitely male or female,

as the sex ratio for adult frogs is approximately 50-50.

The investigations of R. Hertwig, Kuschakewitsch and

Witschi (2) not only confirmed Pflüger’s work, but ex-

1 The choice of the word neoteny is perhaps not a fortunate one but be-

` cause it has come to be associated with the attainment of sexual maturity in

the larval stage, it will be employed here in that sense. Literally, neoteny

means the prolongation or extension of the period of youth, and it has no

necessary relation to sexual conditions.

349

350 THE AMERICAN NATURALIST [ Vou. LIV

tended it by showing that anurans apparently first de-

velop solely as females and sexual intermediates, the

males only later differentiating from the females and

hermaphroditic forms. Moreover, these investigators

described in great detail modification of the sex ratios by

environmental changes such as extremes of temperature

and late fertilization. All of these alleged facts have

given rise to the belief that anurans in their sexual de-

velopment differ greatly from other vertebrates.

For several years the writer has been engaged in

studying the germ cells of anurans, more especially Rana

catesbiana, with the object of testing the theories of sex

differentiation and development of the Pfliiger-Hertwig-

Kuschakewitsch school of German investigators. Al-

though at first inclined to admit their contentions, a more

careful survey of my material revealed several facts

irreconcilable with their views, but which could not be

satisfactorily interpreted. Fortunately an opportunity

presented itself of working with Professor E. G. Conklin

who suggested, after examining my material, that I was

probably dealing with a case of precocious ripening of

the germ cells in anuran larva, i.e., condition stimulating

neoteny, using this word in the sense applied above.

The suggestion proved correct, and it is a pleasure to

acknowledge my indebtedness to Professor Conklin for

giving the clue to correct interpretation of the problem

and for many other helpful suggestions as well. The

present paper is a brief summary of a more extensive and

detailed investigation scheduled for later publication.

In Rana catesbiana the larval period is very long, some

few individuals requiring four seasons to complete meta-

morphosis, though the usual period is about two years.

The sex of larve 55-65 mm. in length is not difficult

to determine by examination of the gross structure of

the gonads, but if such superficial examination is supple-

mented by a hasty survey of the microscopic appearance

of the germ cells, then oddly enough hopeless confusion

of the sexes results, and what were apparently males

from macroscopic evidence turn out to be apparent fe-

No. 633] NEOTENY 351

males. The sex ratios will vary greatly according to the

stress laid by the observer on the gross appearance of

the gonads (and it must be admitted that in early stages

the gonads of the two sexes are remarkably alike) or

upon the cytological evidence as it has heretofore been

interpreted. In larve of 80-100 mm. length the sex ratio

is approximately 50-50 when based on the evidence pre-

sented by the gross appearance of the gonads; on the

other hand, the cytological criterion, as it has been inter-

preted, practically does away with males, while most

of the animals are apparently female. It is probably

due to this erroneous interpretation of cytological condi-

tions that such confusion reigns in the literature regard-

ing sex in anurans.

The germ cells of larve 45 mm. and over, both male

and female, are found in early maturation stages. Such

animals are about 8 months of age. Practically all of

the female cells are in the leptotene or pachytene stage.

In the females the leptotene and pachytene stages do not

persist for any length of time, but give place to the period

of growth, in which the cells with pachytene nuclei in-

crease greatly in volume, are invested by a follicle of

peritoneal cells, and become typical oocytes. Those cells

bordering the lumen of the gonad, are first to enter the

growth period, and by reason of their great increase in

size, fill up the cavity. Around the periphery of the

gland a ring of cells with leptotene and pachytene nuclei

persists, giving rise later to oocytes. of a younger gen-

eration. Scattered through the gland are a few oogonia

with polymorphic nuclei.

The female gland increases greatly in size dué to the

growth of the oocytes, becomes much infolded and convo-

luted by inequalities of growth, thus taking on the char-

acteristics of the typical ovary of the adult. These typi-

cal ovaries are to be found in larve over 80 mm. long.

The gonads probably persist in this condition for several

years after metamorphosis, the oocytes growing very

slowly. According to the observations of Hertwig and

others, the females of Rana temporaria and Rana escu-

352 THE AMERICAN NATURALIST [ Vou. LIV

lenta do not become fully mature and ready for copula-

tion until the fifth season after metamorphosis. The

writer has captured two females of Rana catesbiana two

seasons after metamorphosis which were yet sexually

immature, hence it seems that the females of this species

also require a long period of time in which to develop

sexual maturity. The developmental history of the male

gonads and germ cells is quite different, and when rightly

interpreted fails to show female satiate transforming

into males and vice versa, or abnormal sex ratios.

It was stated that germ cells of the male larve begin

their maturation cycle simultaneously with those of the

females. This is a very unusual condition and probably

unique among the vertebrates though common enough

in the invertebrates. It will be recalled that in the verte-

brates—for example the mammalia, a very long period

of time, sometimes years, separates the maturation cycle

of the sexes. In many instances in the female, the initial

maturation changes preceding the growth period of the

oocyte, occur before birth, whereas the same nuclear

changes in the male cells do not make their appearance

until shortly before the attainment of sexual maturity.

It has become the custom for investigators of sexual con-

ditions in the Anura to use this fact of the early occur-

rence of maturation stages preceding the growth period

of the oocyte in the female as a cytological criterion for

differentiating the sexes in the larval stages. Unfortu-

nately this principle, though true enough for other verte-

brates is not applicable to Anurans and the result has

been hopeless confusion of the sexes because i in this group

maturation occurs in larval males.

From the period of formation of pachytene nuclei, the

history of the sexes is quite different in Rana catesbiana

and unmistakable if a complete series of larval stages is

obtained. In justice to other investigators whose results

the writer criticizes as based upon misinterpretation of

sexual conditions, it is fair to point out that of all exist-

ing species of Anura, Rana catesbiana is apparently the

only one in which precocious ripening. of the male germ

No. 633] NEOTENY 353

cells goes as far as the formation of the maturation divi-

sion in first year larve, and ripe spermatozoa in second

year animals. This is of course due to the extraordi-

narily long larval period. In Rana temporaria and Rana

esculenta the larval maturation changes apparently go

only up to and including the pachytene stages before de-

generation sets in. In Bufo, the precocious ripening of

the sex cells is confined entirely to the cells of Bidder’s

organ and continues up to the pachytene stage before

growth begins.

The male larve of Rana catesbiana undergo two dis-

tinct seasonal maturation cycles as larve. The first oc-

curs in young animals 45-60 mm. total length, despite the

fact that the germ gland is in an extremely undifferenti-

ated condition. The germ cells develop normally through

the leptotene, pachytene, diplotene and tetrad formation

stages, but invariably degenerate and go to pieces during

the late metaphase or early anaphase of the first matura-

tion division. The centrosomes fragment and the spindle

apparatus is aberrant. There are no second maturation

divisions, though occasional giant spermatid-like struc-

tures may form by the growth of axial filaments from the

centrosomes of first spermatocytes. The cells of the first `

larval maturation cycle degenerate. Through active

mitotic division the few primary spermatogonia scattered

throughout the gland give origin to those cells which

later undergo the second larval sexual cycle. This sec-

ond cycle occurs near the end of larval life, t.e., usually

about two years after hatching. Oddly enough the sec-

ond maturation cycle is normal, and gives rise to func-

tional spermatozoa in the larve, though the efferent ducts

of the testes are not yet fully formed. The germ cells

and tetrads of the first sexual cycle are aberrant in size

and character, those of the second cycle are normal in

every way.

The diploid chromosome number of the larve is twen-

ty-eight, the haploid number is fourteen. There is no

evidence of an accessory chromosome.

354 THE AMERICAN NATURALIST [ Vou. LIV

Probably the larval sexual cycle just mentioned is an

interesting example of a ‘‘carrying over’’ in ontogeny

of an earlier phylogenetic condition when the Salientia

were sexually mature and normally reproduced as larve.

It is interesting to note in this connection that male

anuran larve whose period of metamorphosis is indefi-

nitely postponed, as for example by thyroid extirpation,

readily mature sexually, in so far as the production of

ripe spermatozoa is concerned.

The male germ cells, unlike those of the female, do not

undergo growth, except in relatively rare instances to

be described later, and consequently do not fill up the

lumen of the gonad. This lumen later is obliterated by

the migration into the gonads of cells from the mesentery

and possibly from the cortical substance of the adrenal

gland. From this ingrowth the testicular interstitium

and rete apparatus develops. The efferent tubules at

the time of metamorphosis form a connection with the

mesonephros. The true sex cords of the testis arise as

proliferations of the germinal epithelium, and not as

so often claimed for amphibia, as ingrowths from the

mesonephros.

This phenomenon of precocious ripening of the male

germ cells of Rana catesbiana larve undoubtedly occurs

in other Anura, though is not carried so far as in the bull-

frog. The figures of Kuschakewitsch and Witschi show

clearly that this condition exists in Rana esculenta and

Rana temporaria. Indeed, it seems more than likely that

these writers have mistaken male frog larvte whose germ

cells were in early pseudo-reduction stages, for hermaph-

rodites and females. The so-called sexually indifferent

or sexually intermediate forms of the Pfliiger-Hertwig

school are very probably male animals whose germ cells

show precocious ripening as far as the pachytene stage.

This is plainly evident from their photographs, drawings

and descriptions. This probable misinterpretation of the

eytological data accounts for the transformation of such

so-called hermaphrodites into male animals, so minutely

described by these investigators. Using the chief eri-

No. 633] NEOTENY 355

terion of sex differentiation employed by Witschi, i. e.,

that all germ cells in the larval gonads showing pseudo-

reduction (leptotene and pachytene stages), are to be re-

garded as female, the writer obtains in his set of 2,000

animals, 96 per cent. females and only 4 per cent. males.

In larvæ of 85 mm. length the percentage of males is zero

if this criterion of sexual differentiation is employed.

The writer has found so far no evidence that the sex

ratios of Anure are any different from those of other

vertebrates, and is inclined to regard the confusion con-

cerning sèx differentiation and development in anurans

as a result of interpretating male animals showing pre-

cocious maturation changes of the germ cells as females

and hermaphrodites. Sex in the frog does not appear

to be nearly so labile and easily influenced as some in-

vestigators claim. Professor Hertwig’s ‘‘late fertiliza-

tion’’ experiments are more satisfactorily interpreted on

the chromosomal hypothesis of sex determination, than

on any other.

One reason so many workers dealing with anurans

have regarded these animals as possessing hermaph-

roditic tendencies is the occurrence of ‘‘oocytes,’’ so-

called, in the testes of larval and adult frogs and the

presence of the peculiar ovary-like structure, the organ

of Bidder, in the Bufonidæ. The origin of these apparent

oocytes in Rana catesbiana has not yet been worked out

as completely as the writer could wish; however, enough

data has been collected to warrant a tentative explana-

tion of their occurrence in this form and the same data is

suggestive as regards the nature of Bidder’s organ in

the male toad, at least suggestive enough to warrant a

reinvestigation of this structure, now generally regarded

as a rudimentary ovary.

In male Rana catesbiana larve, these large oocyte-

like cells are of frequent occurrence, and assume this

character while in the pachytene stage. Previous to the

growth period they are indistinguishable from the other

pachytene male cells of the gonad. During the growth

stage, which is later followed by their degeneration and

356 THE AMERICAN NATURALIST [Vou. LIV

disappearance, they are similar in every way to the cells

of Bidder’s organ. Their follicles are derived from sur-

rounding peritoneal or stroma cells. These follicles are

commonly observed surrounding isolated spermatogonia.

In certain male gonads a few cells grow to the size of

oocytes, and possess yolk nuclei. The presence of yolk,

however, is no sex criterion for the male germ cells of

many animals form yolk as for instance Ascaris, and the

apyrene spermatozoa of certain Prosobranchs, and the

degenerating cells of the frog.

The larval spermatocytes of the first maturation cycle

are in many instances of enormous proportions, scarcely

smaller than many organs of Bidder cells near the end of

their cycle. It is not impossible that there may be a

genetic relation between these two types of testicular ele-

ments. This question is reserved for further discussion

in a later paper.

The writer is of the opinion that these ‘‘oocytes’’ are

of the same nature as the cells of Bidder’s organ in Bufo.

It might be suggested as a possibility worthy of consid-

eration, that in male animals such cells may be of true

male character, but owing to the precocious sexual cycle,

itself a vestige of a primitive phylogenetic condition

when the Anura were sexually mature in the larval form,

a few of the germ cells are unable to complete their cycle,

and simply grow to an abnormal size, thus assuming the

unspecialized character associated with oocytes. These

cells degenerate during the second larval maturation

cycle when normal sex products are produced. It is

rather significant that the whole first larval sexual cycle

is abortive in almost every feature. For instance the

spermatocytes are abnormally large, the tetrads equally

so, the first maturation division never proceeds past the

anaphase, the centrosomes fragment, form polyasters,

and sometimes axial filaments. Entire cysts of perfectly

formed spermatocytes go to pieces in the very act of divi-

sion, and’ most of the germinal elements show marked

evidences of a deep seated protoplasmic disorganization.

In view of these facts it is possible that the cells of

No. 633] `- NEOTENY 357

Bidder’s organ in Bufo, and the oocytes-like cells of

anurans may not be true oocytes, despite their appear-

ance, but may be merely senescent cells, occurring in the

course of an abortive and degenerate larval sexual cycle.

Bidder’s organ on this assumption is the vestigial remains

of a primitive sex gland functional when the Bufonide

reproduced in the larval stage. The functional gonads

of present day toads represent recently acquired struc-

tures superimposed upon the phylogenetically older and

degenerate glands.

n Rana catesbiana, a more primitive anuran type

than Bufo, the entire larval male gonad might with some

plausibility be compared to an organ of Bidder in which

only a few cells assume the oocyte character whereas the

remainder develop a little further, 7.e., to the first matura-

tion anaphase, when they too go to pieces. The writer

suggests this view of Bidder’s organ tentatively, and

pending further investigation does not regard himself as

irrevocably committed to it. The facts are suggestive,

and that is all that can be said at present.

REFERENCES

1. Allen, B, M.

1918. Journal Exp. Zoology, Vol. 24, No. 3. The Results of Thyroid

Mystics in the Larvae of Rana pipiens.

2. Witschi,

1914 irdi. fur mikr. Anatomie. Bd. LXXXV. Experimentelle

Untersuchungen über. die Entwicklungsgeschichte der Keim-

drüsen von Rana temporaria.

3. Kuschakewitsch, 8.

1911. Festschr. R. Hertwig’s Bd. 2. Die Entwicklungsgeschichte der

Keimdrüsen von Rana esculenta

4. Hertwig, R.

1905-1906. Verhandl. der deutsch, Zool. ges. Breslau. Ueber dah Prob-

m der sexuellen Differenzierung.

5. Pflüger,

1882. ram f. phys. Bd. 29. Ueber die P

Uraschen und Geschlechtverhältnisse der Fröse

6. Penes W- W.

1918. Journal Expr. Zoology, Vol. 24, No. 3. The effect of inanition

upon the development of the germ glands and germ cells of

frog larvae.

7. King, H. D.

1908. Journal of Morph., Vol. 19, No. 2. The Structure and Develop-

ment of Bidder’s Organ in Bufo lentiginosus. `

SHORTER ARTICLES AND DISCUSSION

THE TABULATION OF FACTORIAL VALUES!

In Science for January 23? Dr. Ellis L. Michael discusses the

validity of the ordinary system of tabulation in the determina- ,

tion of the probable number of bacteria in an emulsion. He

argues in favor of the use of the logarithms of the measurements

instead of the direct measurements because the former give a

symmetrical distribution, while the latter give one that is dis-

tinetly asymmetrical. As Dr. Michael has invited discussion it

may be of interest to mention briefly a similar method used dur-

ing the last two years in a study of the germinal and environ-

mental factors affecting eye facet number in the bar races of

Drosophila. A report of the method was made at the St. Louis

meeting of the American Society of Zoologists and the results of

its application to the particular problems in hand are being pub-

lished in a series of papers.®

In working up the data it became evident that the demands of

the biological analysis were not adequately met by the system of

arrangement in classes with equal facet numbers. The wide

range in individual stocks and the still wider differences between

different races made it desirable to express relations directly in

terms of factorial units affecting . facet number rather than in

facet numbers. In dealing with a stock averaging 30 facets as

compared with one averaging 300 facets it became evident that a

one facet change at the mean in a 30 facet stock represents the

same factorial value as a ten facet change at the mean in a 300

facet stock and that a corresponding principle applies within the |

range of a single stock. Accordingly the classes were arranged

1 2 airy from the Zoological Laboratory of the University of Ili-

nois, No. 152

37i Concerning Application of the Probable Error in Cases of Extremely

Asymmetrical Frequency Curves,’’ Science, N. S., 51: 89-91.

_ 84 Change in the Bar Gene of Drosophila Involving Further Decrease

in Facet Number and Increase in Dominance,’’ J. Gen. Physiol., 1919, 2:

69-71. J. Exp. Zool., 1920, 30: 293-324, :

358

No. 633] SHORTER ARTICLES AND DISCUSSION 359

so that the ree range of each class is a fixed per cent. of the

mean facet value of its class. In other words the class facet

ranges vary in such a way as to give the same logarithmic range

to each class.

As an illustration eye facet counts in 488 females of the unse-

lected white bar stock may be taken. The following table gives

the frequency distribution obtained when the classes have the

same facet ranges:

Facet Counts Frequency in Per Cents.

1 0.2

GRO Rn Sa PEt pat SO eg

yO ene ea reas Bre oe wre WG ae rare oe 0.2

BB Bock. cae pos bb vba ig 2.9

Se AAT Tp Reels LO EP VR AOE E rr star 10.9

BOG ie pO cag cs si 14.3

nE EE TR GCE E Sra 12.3

ata g E E E E 12.9

DO Oe ve hee uri ety eee ee es 11,7

estima dA ed SI. ee i 9.2

COO ee ea ees 8.0

PA Veet BREESE NIMS E NT T ah Pee 3.9

BeBe iy ei EEN Dp were ewes 3.9

BU et Vea ven eee SAN w A's a's 3.3

Gh DO Re ess eh ee oles 2.9

AOO IOO ie Nis anew ee tee 6 1.4

OBL Lid E pe spies E E ara 1.6

RIPE Sow a nape eee eke ces 0.2

TIGIS re, ee aes eke Oy eee 0.0

BLE br wed EE A E 0.0

ROO PROG esa hees re RAEE E 0.2

The same arrangement is shown in graphic form in the following

figure:

mnie

rero :

There is a marked positive skewness. The next table uses the

Same original data but with the facet range in any class equal

to ten per cent of the mean of that class:

360 THE AMERICAN NATURALIST [Von. LIV

Frequencies in Factorial Units

Facet Counts Per Cents. from Mean

WOOF oe aa 0.2

Bie SO ieee oe ees as 0.0 — 8.93

BE BO isd oleae ore oe 0.2 — 7.93

ie BE oke eh eara 0.6 — 6.93

a U E E S A Ap E T 1.8 — 5.93

m a Oa ces cots We eet 3.1 — 4,93

OG Oe es ee er: oes 8.2 — 3.93

BOs Ge tie is iw eee sia 9.6 — 2.93

We cine ees i ELA — 1.93

MD E E Ga eee P EE 11.9 — 0.93

Or O ta eee ee a ba + 0.07

A FR hale oN ciate BOE 11.3 FLOT

FR a E O a 10.4 + 2.07

A iwc: 5.9 + 3.07

Ses Wie 5.1 + 4.07

SO oe a a ea 5.5 + 5.07

OB IU Tee eee eee s 2.3 + 6.07

weibo o a 1.4 + 7.07

Pee woe 0.0 + 8.07

ERO: Coa ae ee ee 0.2 + 9.07

The following figure is based on the same arrangement:

Fig. 2.

This is much closer to a normal distribution of frequencies than

in the ordinary method. It is correspondingly more reliable in

the determination of the various constants.

If the biological assumption upon which this tabulation is

based is correct the classes are of equal value as far as the factors

affecting facet numbers are concerned though the facet ranges

are different. In following out this view the intervals on the

variation scale have been expressed in terms of class units, each

unit being equivalent to a factor which produces a change of ten

per cent. in facet number. Some arbitrary point, for instance

the mean of the unselected stock, may be taken as the point of

reference or zero and every facet value has a corresponding fac-

torial value on the scale. The variation constants may be ob-

No. 633] SHORTER ARTICLES AND DISCUSSION 361

tained in the ordinary way but in terms of factorial units and

not facet units. The standard deviations are used directly as

coefficients of variation.

The biological validity of the factorial method as given is of

course dependent upon the correctness of the view that eye facet

numbers have such a relation to environmental and germinal

factors as is indicated. The normality of the factorial distribu-

tion has already been mentioned. General embryological con-

siderations favor proportionate action of factors rather than

action by accretion. But I wish to mention particularly the

definite experimental proof that at least one factor, temperature,

is in agreement with the hypothesis. Seyster* has shown that in

bar eye facet number decreases with increase in the temperature

at which the larve of Drosophila are reared. This decrease fol-

lows van’t Hoff’s law if an inhibitor of facet number is assumed

as the effective agent upon which the temperature acts. Krafka>

has demonstrated that this general law applies to ultra-bar as

well as to bar eye and that for the different bar stocks the effect

of a degree of change in temperature is roughly proportional to

the mean value of the stock and the same is approximately true

for the effects of a degree of change in temperature throughout

the range of a single stock. The following table gives the facet

values for ultra-bar, low selected bar and unselected bar at 15°

and 25°:

15° Facet Values | 25° Facet Values | Differences | Rati

51.5 25.2 26.3 | 1.0

189.0 74.2 114.8 | 4.4

269.8 | 120.5 | 149.3 5.7

Representing the effect of a ten-degree difference for ultra-bar as

unity, low selected bar has 4.4 times and unselected bar 5.7 times

this difference. It is obvious that difference in facet number is

not a good measure of the value of the temperature factor.

On the other hand, if facet values are reduced to factorial

values according to the method given above the results are as

ollows :

4Seyster, E. W., ‘‘Eye Facet Number as Influenced by Temperature in

the Bar-eyed Mutant of Drosophila melanogaster (ampelophila),’’ Biol.

Bull., 1919, 37: 168-182.

5 Krafka, Joseph, Jr., ‘‘The Effect of Temperature upon Facet Number .

in the Bar-eyed Mutant of Drosophila,’’ J. Gen. Physiol.,1920. (In press.)

362 THE AMERICAN NATURALIST [Vou. LIV

15° Factorial Values | 25° Factorial Values | Differences | Ratios of Differences

— 0.83 | —7.86 7.03 1.0

+12.17 | +2.79 9.38 1:3

+1572 > | +7.73 he ie aa

This is a much closer approach to unity for the ratios than in

the case of facet values and the units employed may be taken as

fairly close measures of the temperature factor.

A change of one facet is therefore not of equal factorial value

at different points on the variation scale as far as temperature is

concerned. A plotting of the data using facets as the units does

not give a uniform factorial scale. Suppose temperature to be

the only factor causing variation in the facet number of a par-

ticular stock but knowledge of the actual temperatures involved

in the production of a particular population to be lacking and it

is desired to derive the value of the temperatures from the facet

values. Obviously the closer approximation is obtained by the

tabulation in which each class has a facet range equal to a definite

per cent. of its facet mean. Krafka’s data show that even in

` this case the determination is not exact but certainly the error

is of a much lower order than that involved in using facets as

the units.

CHARLES ZELENY

UNIVERSITY OF ILLINOIS

AN EXPERIMENT ON REGULATION IN PLANTS!

Ir is a fundamental fact that of the enormous number of buds

on a tree only a few of these normally develop into branches.

Every bud, however, has the capability of growth and will grow

into a branch if the more apical bud or buds are removed. Even

normally, in uninjured trees, some of the lateral buds grow into

1 After this paper was written, my attention was called to an article by

Child and Bellamy (Science, N. S., L, 362, 1919), in which somewhat

similar experiments were reported ‘ina the same conclusion arrived at. —

Physiological isolation of two regions of a whole plant was produced by

low temperature instead of by actual killing of tissue as in my experi-

ments. In view of the importance of growth phenomena I believe it worth

while to again call attention to the conclusions to be drawn from these

facts, especially as the experiments of Child and Bellamy refer saat to the

influence of a growing stem on the growth of other stems and not to the

influence of growing roots on the development of roots in other regions

of a plant.

No. 633] SHORTER ARTICLES AND DISCUSSION 363

branches and the characteristic form and type of growth of a

plant are thus determined. It is a species characteristic.

An analysis of the factors which retard the growth of lateral

buds can best be made on plants with only a few buds, and an

excellent discussion of the problem has been given by McCallum.’

McCallum worked with the scarlet runner bean, Phaseolus multi-

florus. The cotyledons of this bean remain at the surface of the

ground and the buds in their axils never develop unless the

growing stem is injured or removed. en they invariably de-

velop and form shoots. No amount of wounding short of re-

moval of the growing tip will cause these buds to grow. They

never grow if the terminal bud is present, no matter how much

food or water is available with optimum light and temperature

conditions, and they always start to grow if the terminal bud is

removed and at the same time the plant is starved by cutting off

cotyledons and root systems or is practically dehydrated by plac-

ing it in a very dry atmosphere.

To describe the phenomenon we say that the tip inhibits the

growth of buds below it. Only a growing tip has this inhibitive

action, for McCallum showed that if the tip is kept in a hydrogen

atmosphere, which prevents its growth, the cotyledonary buds

begin to grow. Later if the tip is removed from the hydrogen

to air, it also will again grow.

The inhibitory influence of a growing stem tip on latent buds

is exerted only downward. A growing root exerts an inhibitory

influence on the development of roots above it and this influence

passes upward along the stem. If the roots of a bean plant are

removed, new roots will develop along the stem wherever there is

most moisture. ‘The new roots do not come from root buds as the

new shoots come from shoot buds, but they arise from unformed

regions of the stem. The inhibitory influence on root formation

which passes upward moves along the vascular bundles and is

restricted to that section of the stem immediately above in line

with the point of injury to the root. This, if the stem of a bean

plant is kept moist and a small notch is made (so as to cut the

vascular bundle) in the stem below this moist region, the inhib-

itory action of the main roots will be cut off by the notch and

secondary roots can now form in this moist region only on the

side above the notch (see Fig. 10, p. 116 of MeCallum’s paper).

The inhibitory action of a growing tip in the bean on buds

2 McCallum, Bot. Gaz., XL, 97 and 241, 1905.

364 THE AMERICAN NATURALIST [ Vou. LIV

below is not localized in the stem perhaps we may say is not

transmitted in a direct line in the stem. A notch cut half-way

across the stem will not cause the cotyledonary but directly below

it to grow. In Bryophyllum, however, Loeb’s*® experiments have

indicated that the inhibitory influence of a leaf on the growth of

axillary buds passes downward in the same sector of stem as the

leaf itself. Moreover the inhibitory influence appears to be of

the nature of material flowing, because the pathway of the in-

hibitory influence is affected by gravity. This is illustrated in

Figs. 11, 12 and 13, pp. 349 and 351 of Loeb’s paper. This in-

fluence of gravity is a fundamental fact whose importance for

the explanation of regulation phenomena must not be overlooked.

It is obvious to one who seriously contemplates: the facts of

regulation that the influence of one part over another in the

organism must be either similar to nerve influence and depend

on living protoplasmic continuity between the parts, or due to

the actual transport of material from one region to another.

Unless we are to assume the existence of a guiding all powerful

form-determining spirit or force, which is as difficult to prove as

to disprove, there is no other than these two explanations. These

we know to be two means of ‘‘action at a distance’’ in animals

and we might expect them to be operating in a plant also.

Let us consider the second of these possibilities—transport of

material. Two views are prevalent regarding the nature of this

transport. (1) A growing stem may be supposed to form ma-

terial which inhibits shoot formation and a growing root to form

material which inhibits root formation.t These special inhibi-

tion substances pass downward and upward in the stem respect-

ively. Polarity is a direct consequence of the formation of

these substances and their direction of flow. Loeb has pointed

out several instances of growing roots inhibiting the formation

3 Loeb, J., Journ. Gen. Physiol., I, p. 337 and 687, 1919.

4It has been suggested that a growing stem forms material which in-

hibits shoot formation but favors root formation. The root formative sub-

stances collect at the basal end of a cut stem and induce the formation of

roots there. That this assumption will not hold is indicated by McCallum ’s

experiments on root formation already mentioned. (Fig. 10, p. 116.) The

stem of a whole bean plant is surrounded near its upper end by water held

in a glass vessel. This gives favorable conditions for the development of

roots but none grow so long as the roots of the plants are intact. If they

are cut off new roots form, not at the base of the stem where the cut is

and where root forming substances should collect, but in the water high up

on the stem.

No. 633]

SHORTER ARTICLES AND DISCUSSION

365

of roots in other regions of a plant of Bryophyllum and of even

stopping the further growth of roots which had started to grow.

(2) In a whole plant, because of a cer-

tain morphological structure, the nutrient

channels are such as to carry food mate-

rial to growing regions. A plant grows

at both ends and so long as these are in-

tact and growing food flows toward them.

If removed, food flows to other points

and starts the growth of dormant short

buds or root primordia. Once a stem

or root has started growing Loeb’s® ex-

periments show very clearly that the

mass of growth formed is proportional

to the mass of materials available.

I believe that light is thrown on this

problem by some experiments which I

performed in 1910, while a student at

Columbia University, and repeated at

Princeton in 1912, but which have never

been published. They are designed to

divide a plant into two parts physiolog-

ically but not morphologically. A jet

of steam was directed against the stem

of a young bean plant between cotyle-

dons and first pair of leaves in order to

kill the tissue throughout the stem in

this region. In some plants the leaves

and growing tip above this region wilt

and die but in many cases not only does

no wilting occur but the tip continues

to grow and as rapidly or more rapidly

than control plants under the same

conditions which are unsteamed. Never-

theless the cotyledonary buds below the

steamed region begin to grow and roots

start to appear just above the steamed

region. If the air were sufficiently

Fic. 1. Drawing show-

ing condition of a bean

plant eight days after the

steamed.

oles of first pair of leaves.

moist or the region surrounded by water there is no rea-

son why these incipient roots should not grow out into a typ-

5 Loeb, J., Journ. Gen. Physiol., I, p. 81, 1918.

366 THE AMERICAN NATURALIST. > [Vou.LIV

ical root system. I have preserved the stems of plants steamed

in this way and Fig. 1 is a drawing of one of these. It will

be noted that the steamed region, which was exposed for.

three minutes in this plant, has shrivelled to a hard woody con-

nection about 24 mm. long. Table I gives the data regarding

the growth of control and steamed plants whose tops were not

killed by the steaming. The average growth for the three con-

trols is 40.5 mm., and for the steamed plants, 59 mm. It is evi-

dent from the table also that the terminal bud has grown in the

24 hrs. immediately after steaming so that we cannot say that

the steaming caused even a temporary cessation of growth of

the tip.

TABLE I

RATE OF GROWTH OF STEAMED AND CONTROL BEAN PLANTS

Mar. 7, | Mar. 8,

ie aro Tangi Length anak of Lapin Total

eek jeune ihv tbat a Internode | Internode gg

: in Sec- pe node | node i j Days,

in Mm.| fonves| Leaves | Ist. | 24 | 1st | 24 rhs

Controls, unsteamed. | 1 D LEI 7.5 26. 0 24.5

Cotyledonary buds {2 4.0 6.0 16.5, 3.5} 25.0) 14.0} 35.0

7 3 5.0 | 10.0 34.0, 2.0 a o 17.0) 62.0

| |

5 8.0 2.0 5.0 | 20.0 38.0. 36.0

March 7, 1912.||2 7 5.5 5.0 7.5 | 9.0) ve 0 15.5

Steamed. Cotyle-|} 3 10 9.5 7.0 11.0 | 39.0) 69.0, 11.0) 73.0

donary buds all||4 15 15.0 | 14.0 | 24.0 | 60.0 14.0) 66.0 47.0) 99.0

grow 5 20 |.14.0 5.0 8.0 | 37.0) 71.0 20.0! 86.0

6 | 180 | 24.0 | 13.0 | 18.0 | 47.0) 48.0 10.0| 45.0_

It is certainly true that sap must pass up the stem of these

steamed plants, otherwise the tops would remain turgid and

growth occur. Root inhibiting substances, if formed, must have

passed upward along with the sap. Nevertheless we find roots

developing above the steamed region despite the fact that the

plant has a normal living root system below. The evidence is

conclusively against the existence of definite root inhibitive sub-

stan sap can pass upward in a steamed area we might

expect that it could pass downward also. If inhibitive sub-

stances are formed by a growing stem these materials should

reach the cotyledonary buds below. Nevertheless these buds

develop. Since we can not necessarily argue that because ma-

terial can pass up a stem it must also pass down, the evidence

points against the existence of shoot inhibitive substances, but

is not unequivocal.

No. 633] SHORTER ARTICLES AND DISCUSSION 367

In a plant which has been steamed the nutrient channels are

the same as in a normal plant. The apical bud is growing and

attracting material to it so that we cannot say this food material

is now available for the cotyledonary buds as we might had the

growing tip been actually cut off or prevented from actively

growing by a hydrogen atmosphere. The evidence is conclu-

sively against the view that growing points prevent the growth

of dormant buds by attracting and utilizing the nutrient material.

It would seem that the inhibitive influence must be dependent

on living functioning protoplasmic connections. How are we to

conceive of an influence of this sort without invoking a vitalistic

explanation? I believe the explanation lies in the direction de-

veloped at length with the aid of metal models by Lillie. Grow-

ing points are of a different electrical potential as compared with

other points and the currents so generated passing through dor-

mant buds in the proper direction, prevent their growth. The

potentials are phase boundary or membrane potentials, possibly

dependent on selective ionic permeability or solubility of two

phases (cell and medium) to ions, and consequently dependent

or normal permeability conditions throughout the plant. Inter-

ruption of living protoplasmic connections, then, means merely ,

the interruption in continuity of semipermeable membrances in

longitudinal axes of the plant (vascular bundles?). While we

may be sure that the steamed portion of a plant will conduct an

electrical current, since its normal semipermeable membranes

have been destroyed there is no means of obtaining a return cir-

cuit. The plant is divided into two electrical systems instead of

one and behaves practically as two distinct plants. As Lillie’

has suggested the effect of gravity on the inhibitive influence of

growing stems, pointed out by Loeb, may be explained by move-

ment of sap downward and passage of a greater current through

this region because of increased electrical conductivity there.

Biological polarity thus becomes electrical polarity and a given

process at one region or pole is automatically accompanied by

the reverse process at the opposite region or pole:

E. Newron Harvey

PHYSIOLOGICAL LABORATORY,

PRINCETON UNIVERSITY

6 Lillie, R. S., Biol. Bull., XXXIII, 135, 1917.

7Private communication.

maa

368 THE AMERICAN NATURALIST [Vou. LIV

INHERITED PREDISPOSITION FOR A BACTERIAL

DISEASE

As soon as it can be demonstrated that in a process under in- -

vestigation a given factor has a very marked influence, this

factor is more often than not looked upon as the sole cause of

what happens. It is indeed very difficult not to overemphasize

the importance of a new link in a chain of causes, which has been

hitherto overlooked, and which one is fortunate enough to dis-

cover. To give a few instances from a field familiar to us, we

ean cite three factors in the evolution of species which have

each by one author been elevated to the rank of ‘‘the’’ cause of

species formation. Natural selection was the cause of evolution

in the eyes of Weismann, and every other factor was looked upon

as subordinate. In the same way Wagner overemphasized the

importance of isolation, and de Vries would have us believe that

mutation was the main, if not the sole, cause of evolution. The

greatness of Charles Darwin lies in the fact, that he was not led

away from a consideration of all the possible factors by the temp-

tation to pad out the importance of any one link in the chain of

causes. :

In a few instances the discovery of a new and very. important

factor in the causation of a process or set of phenomena sets all

the investigators working in the new field just opened up. And

often the attention is unduly taken away from other causes. In

pathology the discovery of the rôle which microorganisms play

in the causation of certain diseases has resulted in the almost

absolute neglect of the study of possible other factors in the

causation of these same diseases.

In the illness of an individual, infection by a specific micro-

organism is a very important factor in certain cases. But it is

clear that, besides this infection, other factors influencing the

qualities of the subject can be of great importance. Very often

we find that, besides the presence of the specific organism, pre-

disposing factors play an important rôle, such as the simul-

taneous presence of another infection (tuberculosis after measles)

special conditions (diabetes, possibly beri-beri) ; causes lowering

the vitality (exhaustion, inanition).

Besides factors of the environment, which in themselves are

not pathogenic factors, it is evident that factors given in the

composition of the individual, inherited factors, ean cooperate in

the causation of disease.

No. 633] SHORTER ARTICLES AND DISCUSSION 369

To make the statement general, we can say that illness is a con-

dition caused by the cooperation of a series of factors, of which

some are genetic, heritable, given in the composition of the indi-

vidual’s germ, and others are non-genetic, influencing the indi-

vidual from the outside. In different combinations of other

causes, individual factors can have a very different influence.

In certain cases, therefore, different factors can be looked upon

as the one which tips the scale, and consequently as ‘‘the’’

pathogenic moment.

The discovery of microorganisms and their rôle in Aaaa has

relegated other pathogenic causes to the background, and espe-

cially in those diseases where presence of the specific micro-

organism can always be demonstrated.

In some diseases the presence of a specific microorganism is

not demonstrated, and an important non-bacterial factor seems

to be the chief determining cause (some cases of carcinoma and

of traumatic diabetes). In other cases, presence of a specific

microorganism is certain demonstrable, but it seems as if other

factors play an important rôle. Tuberculosis is a typical in-

stance. And finally we know diseases, in which it appears as if

presence or absence of a specific microorganism constitutes the

almost exclusive cause of the difference between affected and

healthy individuals (plague).

In the first group, diseases in which microorganisms play no

rôle, the factors which cause the abnormal condition can be real

environmental factors, but in some instances they are clearly

genetic factors, developmental factors transmitted through the

germ, genes. We know real hereditary diseases, where an in-

herited, genotypic peculiarity seems to be the causating factor

(hemophily, Huntington’s chorea, Daltonism).

In the second group, in those cases, therefore, where predis-

position seems to have an influence comparable in its magnitude

to infection, this predisposition can have very different causes.

In some cases the cause of a predisposition is very clearly non-

genetic, environmental (pneumonia after influenza, tuberculosis

of the joints after trauma). In other cases, however, inherited

constitution is very probably an important factor.

The ‘‘inheritance’’ of tuberculosis has been a point of unend-

ing controversy. Very often tuberculosis occurs in families in a

way which makes us think of inheritance. According to many

authors this occurrence of tuberculosis in families is simply caused

by the greatly enhanced chances for a heavy infection. Others

370 THE AMERICAN NATURALIST [Vou. LIV

however believe in the possibility of a real inheritance of the dis-

ease. It is very evident that the discussion has been very much

hampered by a confusion of ‘‘inherited’’ and ‘‘congenital.’’

And it has seemed to a great many authorities as if the question

as to the existence of an inherited moment in tuberculosis could

be answered by an investigation into the possibility of pre-natal

infection.

Lastly, there are authors who believe in the inheritance of a

certain disposition for tuberculosis

From the fact that practically all persons above the age of

twelve react positively to von Pirquet’s test, it can be seen that

tuberculosis infection is not as inevitably the cause of tubercu-

losis, as for instance pneumococcus infection is the cause of septi-

cemia in the mouse. Every practising physician has seen cases

in which a joint became tuberculous after a trauma, in a patient

who showed no other evidence of a tuberculous infection. But

the fact that such cases are rare makes it probable that consti-

tutional, genetic, differences in resistance exist between indi-

viduals. The same holds true for traumatic carcinoma

It is evident that the study of the inheritance of constitutional

predisposition to a disease must be almost impossible, where in-

fection is so general as in the case of tuberculosis. We can only

hope to find instances of the inheritance of predisposition or re-

versely, of immunity to a bacterial disease in cases where we

are dealing with one, or with very few genetic factors, genes,

whose influence on the resistance happens to be very marked

indeed.

Now, in principle, there are reasons to believe in the possi-

bility of an inheritance of immunity or predisposition for bac-

terial diseases. In the first place we have those instances, in

which closely related varieties or species differ in resistance to @

specific bacterial infection. A classical instance is that of the

Algerian sheep, which are constitutionally immune to anthrax.

Another, similar instance was met by us in our work with rats.

We found that there was a striking lack of uniformity in the

practical results of the use of a paratyphus culture as distributed

by the State Serum-institute of Holland for exterminating rats.

In some parts of Holland the broth-culture was highly effective

and very well spoken of, whereas it was almost wholly inef-

fective in other provinces. It appeared to us that this difference

might depend upon the species of rats against which the culture

was used. It was discovered by some joint work of the Koloniaal

No. 633] SHORTER ARTICLES AND DISCUSSION 371

Instituut and ourselves, that the Norway rat, which is the com-

mon rat in most parts of Holland, was practically, if not wholly,

absent from parts of Friesland. In these parts Mus rattus is

the common rat. Whereas Mus norvegicus succumbs readily to

an ingestion of the broth culture as prepared by the Institute,

we found the Mus rattus animals immune. Before we started for

Java, we tried the pathogenic influence of the culture as fur-

nished to farmers, on some of our cultivated rats of the Mus

rattus group, on request of our ministry of colonial affairs. The

rats were fed on a broth culture of a virulent strain of para-

typhoid and bread, at the Serum-institute, and they remained in

good health on this diet. The same culture killed practically all

Mus norvegicus rats in a few days.

To our great regret we have never yet succeeded in obtaining

hybrids between the two groups of rats, norvegicus and rattus,

and for this reason the inheritance of this very marked immunity

of Mus rattus, or in other words predisposition of Mus norvegicus

can not be studied. We know of no case in the literature, of an

investigation of the inheritance of immunity to bacterial disease

in qnimals.

As is well known, Biffen found a ease of the inheritance of

resistance to rust in wheat, in which the difference between im-

mune and easily infected plants was proved to be due to pres-

ence or absence of one single gene. William Orton and Webber

have since found almost similar instances in cotton and water-

melons.

So far as known to the authors, the following ease of the in-

heritance of immunity, or predisposition for a microbial disease

in animals is the first one studied so far.

From Nagasaki, Japan, and Hong Kong, China, we brought

along some stock of a very minute domestic mouse. These mice

evidently belong to the same group as the commonly imported

oriental Waltzing mice. As a matter of fact, our Japanese ani-

mals of the second importation produced some waltzing offspring.

We used this material for a few series of experiments on the in-

heritance of weight, one series starting from the only fertile

Hong Kong female, and the others from diverse combinations of

the Nagasaki strain with large white mice. These white mice are

of a pure-bred strain used by T. B. Robertson in his experiments

on growth. We produced numerous hybrids, great numbers of

F, animals, and further we are grading back the hybrids both

to the dwarf and to the heavy strain. For our work individual

372 THE AMERICAN NATURALIST [ Vou. LIV

mice are frequently weighed, and from time to time the whole

series is weighed.

n the beginning of January an epidemic started in our

mousery. Our mice were at that time housed in approximately

seven hundred cages containing several thousand mice, both the

size-inheritance and other series of breeding experiments. The

cages of all the series were mixed and arranged on shelves in

three adjacent rooms. The infection apparently swept through

the entire colony, notwithstanding our attempts to limit it to one

room. The Japanese mice were distributed over all the stacks in

all three rooms, most of them mated to big mice or hybrids of

different generations. All these mice fell victim to the epidemic,

excepting three which we kept for a little while longer, by

taking them into the living house at the beginning of the trouble.

To our surprise the white mice of Robertson’s strain proved im-

mune. Even where the dead Japanese were partially eaten by

their mates, these latter remained in good health.

It is clear that the main circumstance, which made it possible

for us to see the clearcut segregation about to be described, was

the rapid spread of the epidemic. All the Japanese mice were

dead before the virulence of the microorganism was materially

altered. :

The rapid course of the disease made it possible to distinguish

simply between dead and surviving mice. As a rale we found

that animals contracting the disease presented the bunched up ap-

pearance and walked with the small, prancing steps familiar to

students of paratyphoid in small rodents. They would be visibly

ill for one, two, or exceptionally three days before death. We

do not remember having seen one recover.

Professor Hall, of the department of bacteriology, of the Uni-

versity of California, was kind enough to make a bacteriological

examination of the dying animals, and was able to isolate the

same staphylococcus from the blood of the heart of four animals.

If we count the proportion of the animals which succumbed

to the epidemic, we have to limit our countings to groups which

are comparable. Immunity can never be anything but relative,

and if we want simply to use the fact of survival as a criterion

for immunity we must exclude as far as possible other causes of

death. Of these the two main causes are death or illness of the

mother, causing starvation of the young, and troubles in par-

turition.

In our study of the inheritance of immunity to this staphylo-

No. 633] SHORTER ARTICLES AND DISCUSSION 373

coccus infection we have therefore limited our counts to animals

of the same age-group, that is to mice of at least four weeks old

and not yet used for breeding.

At the general weighing of January 4, 1919, no losses were

observed among the Japanese mice. Shortly afterward the

Japanese started to die off. And at the general weighing of

February 14, the last Japanese mouse was found dead.

The data given in this paper are taken from the records of

this’ general weighing of February 14, 1919. They include

litters of six kinds, pure Japanese, pure Robertson’s whites,

hybrids, F, hybrids, mice with one parent F, and the otier

Japanese, and such with one parent F, and one large parent.

As noted above all the Japanese left in the mousery died

between January 4 and February 14, 59 in all. Of these 23

were in the class of weaned young, not yet breeding.

TABLE I

Litters of Fz Animals Same — on Litters of F? Ani- Same Litters on

Jan 4 Febr. mals Jan 4 Febr. 14

USS Co Rone ES a a BS Sra ee

CT Ge Sate Se 2 Pieces iA T 3

OTE E R Bins 6 TTA Seas 3

AAR SE E RE AA 2 r REE P EAA Das E 2

Doda S bee 6 et Gk wage ae Ò 2

FS pice EO 2 Dos eho ee ee bea 4

Oca ene eS 4 MMe acs wes te we 4

7 EE R a ae 2. e Saeco Oraraea 2

Diva ky otek take io 2 Ds een al ale 1

SSL ED ew E E E A RPE 3 ERTSE Gig 1

Be eee ree I 3 Oe ewe eas 5

Do citys ens 4 e E pita, ica Saree N A 6

E E T A eG 3 e aes 3

Cee oe TER 4 Bei eee eee 2

a eee ce ey 1 eee ea ae 0

ie ee ee 3 Tost 180 5s. v ks 33s 91

As to the Robertson large strain, no deaths were observed

within this period of six weeks among mice of this age class. A

very considerable number of these weaned young were growing

up in cages together with Japanese of their age and sex.

Between January 4 and February 14 we lost no F, animals

after weaning age. Strictly comparable to the other lots were

only three litters, which were weaned within the critical six

weeks and not yet put to breeding. These litters contained

fourteen young. All were living on February 14.

374 THE AMERICAN NATURALIST [Vou LIV

This shows how the immunity to this staphylococcus disease of

the large albino strain as opposed to the predisposition to it of

the Japanese strain, is completely dominant in the hybrids.

To our great surprise we found that this difference between

immunity and predisposition was caused by presence or absence

of one single genetic factor. In other words, we found a very

clear monofactorial Mendelian segregation in F,. As we are

weighing non-breeding F, animals up to a relatively high age,

thirty-one litters containing 125 animals fell into this class be-

tween the two dates.

Of these 125 animals 91 were living on February 14, and 34

had died. (Theoretical expectation 93.75:31.25.) See Table I.

If in reality the ‘‘Robertson’’ mice have one gene, lacking in

the Japanese, whose presence protects them against death from

this infection, we would expect the hybrids to produce 50 per

cent. gametes with and as many without this gene. As the

Japanese lack this gene, we would expect 50 per cent. of the

young from matings between F, and Japanese to be immune,

and 50 per cent. to die. Fourteen such litters were available

for the test, with 57 animals. Of these 57 on February 14,

there were 25 left, 32 having died. (Theoretical expectation

equality.) See Table II.

TABLE II

Litters of Fi X Japanese Same Litters on rity pes 2 bay RE Same Litters on

on Jan. 4 Febr. 14 Febr. 14

i ie EEE EINA = RENE ay eee

TA eke bas tie a oe 1 RTE OTE a aetna 1

Bo ace eink ee cae 1 a SI E i We ee 1

pig eee E re 5 So yee ees 0

are ae eae ha nS br 4 E E Ses CN yet 1

Gp EE wes a ees 4 Precis ss PERL T 0

A ou E hoe cele 2 Ea e hain neice he 0

eas 25

In the same class with the other litters we had sixteen litters

of young, each from one F, and one ‘‘Robertson’’ parent. This

gave us 51 mice in this class. Fifty of these were living Feb-

ruary 14, one having died. (Theoretical expectation no deaths.)

will be seen in nearly every case the number of deaths

was slightly greater than expectation. Occasional mice will die

even when given the best of care. It is indeed remarkable that

not more of these vigorous mice, kept for the most part in com-

pany with several of their own sex, got killed fighting. It must

No. 633] SHORTER ARTICLES AND DISCUSSION 375

be remembered that these figures for deaths comprise all cases

of absence. Mice killed in fights and animals escaped are

classed as dead.

The numbers published in this note were collected only after

the epidemic had done its worst, and from our weighing records.

The epidemic seriously interfered with some of our planned

series in our breeding work on weight.

It was planned to start a series of infection-experiments with

the isolated staphylococcus strains on families of F, animals. It

may be possible at some future date to do this, when the mate:

rial will again be in the right condition for the experiment,

that is to say, free of spontaneous infection. At present, how-

ever, it is evident that the staphylococcus infection is still in

our mousery. The mortality in F, families remains high. It

is clear that, if we subjected F, animals to infection with a pure

culture of the staphylococcus, the group of animals would be

already a selected group, and the results would be quite mis-

leading.

We have refrained from publishing these data for some time:

hoping that we could free our mousery from the infection, so

that we could repeat under conditions of a laboratory experi-

ment the immunity tests of F, families. There seems no further

reason now to withhold the facts such as they are.

As far as we are aware no wholly Sopan pea is

known so far of a gene whose action has such a e effect

upon the resistance to a bacterial disease in animals. Ra evi-

dence for the inheritance of a differential susceptibility to trans-

planted tumors in Japanese and large mice in the work of

Tyzzer is scarcely as definite as our case.

_ In any case, this instance recorded here proves clearly that

the presence of a definite pathogenic organism as a factor in a

transmittable disease need not be the sole determining cause of

the disease. And it shows that the search for heritable factors

in the causation of bacterial diseases is neither hopeless nor

unscientific. We can only hope that cases such as the one just

given will encourage those medical investigators who believe

that predisposition is a factor not to be lost sight of in the

press of bacteriological and related discoveries.

A. C. Hagepoorn-LaBranp,

A. L. HAGEDOORN

BERKELEY, CAL.,

August 20, 1919

376 THE AMERICAN NATURALIST [Vou. LIV

BIBLIOGRAPHY

R. H. Biffen.

1915. rhe s Laws of Inheritance and Wheat Breeding. Journal of

ric. Science, Cambridge.

J. Grancher ma J. Comby.

04. — de l’enfance, Paris,

A. L. Hagedoor

1911. Antokatalytio Substances the Determinants ‘for the Inheritable

aracters. Roux’ series Aufsätze und Vort., Leipzig.

1914, Ratten. De Levende Natuur, Amsterdam

W. bin

Leube.

1908. Spezielle Diagnose der Inneren Krankheiten, Leipzig.

C. C. Little

1917. Evidence of Multiple Factors in Mice and Rats. AMER. NAT.

W. A. Ort

1911. he Development of Disease Resistant Varieties of Plants.

Comptes Rendus Conférence de Génétique, Paris.

E. E. Tyzzer.

1909. A Study of the Inheritance in Mice with Reference to their

Susceptibility to Transferable Tumors. Journal Med. Research.

NOTE ON THE PHOTIC SENSITIVITY OF THE

CHITONS?+

1. The remarkable sensory organs discovered by Mosely (1885)

in the tegmentum of the shell-valves of certain chitons are struc-

turally of such a nature that in their most highly developed

forms they were from the first recognized to be ‘‘eyes.’’ Prac-

tically nothing has been made known as to the functional values

of these organs, which in different genera occur in a great. diver-

sity of form, number, and arrangement. It has been shown,

however, that the tegmental æsthetes of Chiton tuberculatus are

indeed photosensitive (Arey and Crozier, 1919). But the shell-

eyes are in this genus generally represented by structures of an

intermediate degree of complexity. The ‘‘eyes’’ are supposed to

have been derived from large, relatively undifferentiated shell

receptors (macresthetes), and seem to reach their highest de-

velopment in those species of Schizochiton and Tonica which pos-

sess large complex eyes, each surrounded by a pigment cup (cf.

Plate, 1899; Nowikoff, 1907, 1909) ; in Chiton (at least in some

species of this genus) the eyes are ‘‘intrapigmental,’’ pigment

being contained within the receptor cells, whereas with the

‘‘extrapigmental’’ eyes the associated pigment occurs outside

1 Contributions from the Bermuda Biological Station for Research.

No. 633] SHORTER ARTICLES AND DISCUSSION 377

the receptor cells proper, in the integument. It seemed profitable

to attempt an analysis of the functional values of the several

types of photoreceptive elements to be found in different chitons.

Accordingly, in 1918 I made observations on the photic irritabil-

ity of representatives of several genera available at Bermuda.

- Pending the collection of more information on this subject, which

is necessary for a full discussion of the problem here suggested,

I give briefly the net result of these observations.

2. Ischnochiton purpurascens—found along the shores of

islands in Great Sound, and in bays on the south shore of Ber-

muda, usually in more or less exposed situations, but commonly

a little lower than the lowest reach of the tide (never between

tidal limits)—is quite sensitive to light. Individuals about 1 cm.

long were frequently obtained on bottles which had been on the

bottom long enough to acquire a film of algal growth; the under

surfaces of such bottles, and of smooth stones, provided most of

my specimens. These animals were photonegative to light of

any intensity used—from very weak diffuse light to direct sun-

light. This species therefore resembles I. magdalenensis (Heath,

1899). It is said that among the Ischnochitonine there are no

shell eyes. However, Boreochiton, also of this family, never oc-

curs ‘‘far from the light’’ (Pelseneer, 1906, p. 50).

I. purpurascens is an active creeper (Crozier, 1919). It

orients very quickly and precisely away from a source of illumi-

nation. At night its photic irritability seems decidedly en-

hanced, as I learned by comparing the rate of orientation of

single individuals to lamp light, in a dark room, at different times

during the twenty-four hours. (This would appear to be the

case with Chiton tuberculatus also—cf. Arey and Crozier, 1919.)

No evidence was had that I. purpurascens is reactive to

changes of light intensity.

3. Acanthochites spiculosus. Specimens about 14 mm. long

were found under stones, somewhat beneath low water level, in

Ely’s Harbor and at Spanish Point. In these places the water of

the open ocean is less modified than within the sounds. The re-

quirements of Acanthochites seems in this respect more rigorous

than are those of the preceding species, for A. spiculosus was not

found well within Great Sound. As in the case of Ischnochiton,

the present species is decidedly photosensitive, and orients pre-

cisely away from the light. It moves faster away from a bright

light than from a weak one, and comes to rest in the shade. It

is strongly thigmotactic, tending to settle in the angles at the

378 THE AMERICAN NATURALIST [ Von. LIV

corners of an aquarium, and once in such a situation is difficult

to move by light. Negative geotropism is also fairly well pro-

nounced.

If the intensity of light falling on am Acanthochites be sud-

denly increased, the girdle is depressed into contact with the sub-

stratum. Local illumination confined to the girdle leads to a

local response of the same character. The shéll plates seem not

to be sensitive in this respect.

As in the case of most Chitons (Sampson, 1895; Crozier,

1919; Arey and Crozier, 1919), the body may be strongly curved

to one side, the animal pivoting in a circle of short radius. Photic

orientation is often accomplished in this way. The ‘‘pivoting’’

of Acanthochites ceases instantly when the creature is shaded;

orientation is resumed when the light is increased. Since the

girdle does not respond to shading of this part alone, I am led to

believe that the shell plates are probably responsible for this

type of reaction (as with Chiton; Arey and Crozier, 1919).

4. As elsewhere described (Arey and Crozier, 1919), the shell-

plates of Chiton tuberculatus contain receptors activated by light

of constant intensity and by shading.

5. An unidentified species of Tonica, about 6 mm. long, com-

monly obtained in company with Ischnochiton purpurascens,

was found not to be reactive to shading, nor to increase of illu-

mination; but, like the latter, was decidedly photonegative.

This form is not so reactive to light as Ischnochiton, however.

6. Plate (1901) considered it possible that the order of evolu-

tion of the shell eyes of Chitons was from megalesthetes to intra-

pigmental eyes to extrapigmental eyes. In the present series of

species, this order would be represented by Ischnochiton, Chiton,

and Tonica, in respective sequence. The shell eyes are of course

not the only photoreceptors in these animals; for the girdle

` the ventral surfaces of the body (Arey and Crozier, 1919), and,

possibly, the bilateral larval ocelli (Heath, 1904) are functional

in this respect. But the experiments recorded in this paper show

that functions of a certain diversity are served by the tegmental

photoreceptors of the several species. Little can definitely be

said, however, regarding the correlation of structural features

with functional performance. It is noteworthy that members of

the Ischnochitonine—a group characterized by the absence of

shell ‘‘eyes’’ (i.e., with megalesthetes and micresthetes only)—

are quite as reactive to photic irritation as are members of Chiton

proper, where, so long as the tegmentum is uneroded, eyes of the

No. 633] SHORTER ARTICLES AND DISCUSSION 379

intrapigmental type are functional; they are also more reactive

- than Tonica is, although in the latter extrapigmental eyes are de-

veloped. Acanthochites, moreover, likewise with intrapigmental

eyes,’’ is reactive to shading, as in the case of Chiton, while

Tonica is not. We are therefore unable to assign definite types

of irritability to the several forms of shell photoreceptors.

he position taken by Nowikoff (1909), on morphological

grounds, that these organs are not related in genetic sequence, is

not inconsistent with such functional data as I possess. He re-

gards the intra- and extrapigmental eyes as being independently

derived from megalesthete structures. It is possible to consider

that the megalesthetes (or certain of them) are activated by

light, and that this kind of irritability is simply retained by eyes

of the extrapigmental variety, whereas eyes of the intrapigmen-

tal sort are in addition activated by shading. However, the local

activation of the girdle (of Chiton) by light and by shading

makes it necessary to believe that tegmental mireesthetes (e.g.,

of the girdle scales) may also be implicated in the photic irri-

tability of the shell-plates. As yet, experimental data for the

analysis of this problem is incomplete. The possible significance

of the number of shell-eyes present also needs to be investigated.

COLLEGE OF MEDICINE

UNIVERSITY OF ILLINOIS,

CHICAGO, 1919.

PAPERS CITED

meats F B., and Crozier, W. J.

9. "The Sensory Responses of Chiton.. Jour, Exp. Zool., Vol. 29, pp.

157-260.

Crozier, W. J.

1919. On the Use of the Foot in Some Molluses. Ibid., Vol. 27, pp.

359-366

Crozier, W. J., and Aier, L. B.

1918 On the Significance of the Reaction to Shading in Chiton.

Amer. Jour. Physiol., Vol. 46, pp. 487-492.

Heath, H. .

1899. The Development of Ischnochiton. Zool. Jahrb., Abt. Anat., Bd.

1904, The Larval Eye of Chitons. Proc. Acad. Nat. Sci., Philadelphia,

1904, pp. 257-259.

Moseley, H. N.

1885. On the Presence of Eyes in the Shells of Certain Chitonide and

on the Structure of These Organs. Quart, Jour. Micr. Sci.

N. 8S., Vol. 25, pp. 37-60.

380 THE AMERICAN NATURALIST [ Vou. LIV

Nowikoff, M.

1907. Uber die Riickensinnesorgane der Placophoren nebst einigen i

merkungen über die Schale derselben. Zeit. Wiss. Zool.,

88, pp. 153-186.

1909. Uber die Intrapigmentären Augen der Placophoren. Ibid., Bd.

j 68—680.

Pelseneer, P.

906. Mollusca, in Lankester, Treatise on Zoology, Part V, 355 pp.

London.

Plate, L.

1899. Die ae und Phylogenie der Chitonen (Theil B). Zool.

Jahrb., Suppl., Bd. 4 (Fauna Chilensis, s ee p. 15-216.

1901. Fan (Theil C). Ibid., Bd. 5, pp. 508-6

Sampson, L.

1895. The Musculature of Chiton. Jour. Morph., Vol. 11, pp. 595-628.

THE BIONOMICS OF PORICHTHYS NOTATUS GIRARD

Porichthys notatus is a batrachoidid fish, which is known to

range from southern Alaska to the Gulf of California, and from

depths of at least 62 fathoms to just above the lower low-water

level of the reefs. During the fall and winter months it inhabits

comparatively deep water, where nothing definite is known con-

cerning its life, beyond the fact, recorded by Dr. and Mrs. Eigen-

mann (1889, p. 132), that it is at least occasionally preyed upon

by rock-cods (Sebastodes). In the late spring and early summer

a shoreward migration apparently takes place (Greene, 1899).

Along the coasts of Lower California and on the mainland shore

of southern California, it is usually found in shallow bays at this

season; at Santa Catalina Island Holder (Holder and Jordan,

1909) has mentioned hearing numbers just off rocky shores.

There is but one record of the occurrence of the species in the

reef-pools south of the vicinity of Pt. Conception in California,

= Hilton (1914) having found a specimen in a pool on the reef at

Laguna Beach, California.

From Pt. Conception northward, on the contrary, this species,

while never abundant is by no means rare along the reefs within

tidal limits, during the breeding season. Here it occupies very

shallow, often sandy pools, either those containing boulders or

those with horizontal crevices in the rocky sides. It is here a

fish of sluggish and retiring habits, swimming slowly with an

undulating motion; when disturbed it usually seeks shelter, but

sometimes swims off a short distance only, coming to rest and

No. 633] SHORTER ARTICLES AND DISCUSSION 381

partially covering~itself with sand by a lateral twisting of the

body. It is able, by a sudden movement of the body, to inflict

a rather painful wound with the opercular spine.

The stomachs of the specimens examined from reef-pools were

mostly empty ; one contained some sand and an empty snail shell,

while another had eaten a crab (Petrolisthes), of a species which

abounds beneath stones along the fore-shore. Eigenmann (1892)

found an anchovy in the stomach of a Porichthys from San Diego

Bay, and the writer found a sardine (Sardinia cerulea) in the

stomach of a specimen from San Diego County.

The adult is dull brownish, varying very little in color and

not much in shade. The photophores are evident as silvery spots,

due to the reflection of external light. There is a whitish trans-

lucent spot below the eye, and another behind the pectoral fin,

in the position of a large pore in Batrachus tau. Owing per-

haps to a greater development of black pigment, the males retain

more of the dark pattern of the young than the females do.

The coloration of specimens 26 mm. long was described in the

field as follows. Eight greenish black bars extend from the

mediodorsal line to the upper edge of a broad silvery stripe with

metallic reflections, which occupies the middle third of the body.

The fins are clear, excepting a basal caudal bar, and the two

dorsal spines. The head is mottled with dark above, and is

silvery on the sides and clear below, excepting the dark ring sur-

rounding each photophore. A conspicuous narrow black streak,

located below the eye, branches once or twice posteriorly.

Parental care is generally practised in the Batrachoidide.

Porichthys notatus, as noted above, after migrating shoreward

during the late spring and early summer, breeds in shallow

water, within tidal limits from the region of Pt. Conception

northward, where all of the following observations were made.

No details of the breeding habits prior to the guarding of the

eggs have heretofore been published. Males with enlarged testes

were taken by the writer on several occasions from June 2 to

June 15, in no case guarding eggs, and in one instance, on June

20, one was found in company with a female containing matured

eggs. A male with ripe testes was found washed up on the

beach near the reef of Government Pt., near Pt. Conception, on

July 15. The females must leave the pools as soon as, or soon

after, the eggs are laid, as none other than the one just men- —

tioned was observed in the tidal zone. As Greene (1899) has

already remarked, it is the males which guard the eggs and

382 THE AMERICAN NATURALIST [Vor. LIV

young, remaining within a few feet of them even when dis-

turbed. The eggs are cemented to the roof overlying a shallow

crevice in the rocks or a space beneath a flat boulder. They

somewhat suggest the familiar egg of the Pacific salmon in color,

and vary in the larger diameter from 4.0 to 6.0 mm. They are

slightly compressed, as though by pressure against the rock, and

are broadly elliptical in outline.

The young hatch out during the summer. Jordan and Starks

(1895, p. 840), in discussing the species as found in Puget

Sound, remark ‘‘the young fasten themselves to the rocks by

means of a ventral dise which soon disappears.’ They mention

further that ‘‘the adult remains with the young until they are

quite well matured.’’ On October 25 the writer found a single

grunting male under a large flat stone in a pool about two feet

square, with numerous young all about 26 mm. long. Other

young, 22 to 28 mm. long, were caught in a larger pool on Octo-

ber 26. None has been obtained on the reefs in the winter or

spring; young as small as 23 mm. have been taken by the Scripps

Institution for Biological Research, at La Jolla in depths as

great as forty fathoms. Except for their proximity to the eggs,

the males show no special habits which might be construed as

definitely protective.

Porichthys is one of three genera of phosphorescent shore-

fishes, the other two being Anomalops and Photoblepharon of

the East Indian reefs. In each of these East Indian fishes the

single large light-producing structure is located below the eye

(Steche, 1909), while in Porichthys a large number of photo-

phores (in P. notatus Greene found an average of about 700)

are developed in connection with the several lateral lines (except

the uppermost, which is only rarely accompanied by a few rudi-

mentary light organs), one photophore being opposite each pore.

The photophores are most abundantly developed on the ventral

surface, and all are oriented downward. The same condition

holds true in the several other diverse groups of fishes, mostly

pelagie or bathypelagic, in which the power to emit light has

obviously been independently acquired, as well as in certain

other phosphorescent animals, such as the bathybial cephalopods.

This general downward cast of the light of luminescent marine

animals, a point regarded by the writer as of critical significance,

has apparently not beem duly considered by any of the authors

who have proposed such varied theories to explain the biological

significance of biophotogenesis.

No. 633] SHORTER ARTICLES AND DISCUSSION 383

The histology of the photophores of Porichthys notatus has

been reported upon in detail by Greene (1899), and ten years

earlier by Eigenmann and Eigenmann (1889), and by Test

(1889). These organs were found by the writer to be com-

pletely and typically developed in young about 25 mm. long

(sectioned at Stanford University). Each photophore lies deeply

imbedded in the dermis. It consists essentially of a more or

less parabolic reflector surrounded by a mass of melanophores,

and enclosing the photogenic gland cells, which are richly sup-

plied with blood vessels, but according to Greene not. specifically

enervated. The light passes downward either directly from

these cells, or indirectly from the reflector, through the large

lens and the cornea-like epidermal covering of the organ. The

ventral aspect of the illuminated fish is striking, the hundreds

of dots of light being arranged in a symmetrical pattern.

The light of Porichthys has been observed only in the labora-

tory, where it has been produced as a response to intense elec-

trical or chemical stimulus. Green records but one instance of

a slight glow of the photophores being produced by mechanical

stimulus. In experimenting with two specimens from rather

deep-water, the same author was unable to produce any reaction

of the photophores, although he applied stimuli successful in

the case of individuals from the reefs. This observation, while

of course insufficient, perhaps indicates that the luminescence may

be characteristic of the breeding season. In this connection it

is also significant to note that Holder’s observations (Holder and

Jordan, 1909) indicate that the species is of nocturnal habits, its

grunting being heard chiefly at night, or in the evening or early

morning.

The peculiar humming sound produced by this species during

the night, or during the day when disturbed, is another of its

remarkable characteristics. The sound (which by some has been

called a ‘‘song,’’ an expression which seems quite figurative) is

produced in the air-bladder, which has a very thick muscular

wall, and is enervated by the thickest ramus of each vagus nerve.

Upon opening a live specimen the air-bladder was observed by

the writer to vibrate rapidly while the. fish was grunting, and

the sides of the body were felt vibrating at the same time. The

abdomen of young about 25 mm. long was also felt vibrating, but

the sound produced, if any, was inaudible.

384 THE AMERICAN NATURALIST [ Von. LIV

BIBLIOGRAPHY

Eigenmann, Carl

1892. The nas of San Diego, California. Proc. U. S. Nat. Mus.,

Vol. 15, pp. 122-178.

Eigenmann, Car! H., and Eigenmann, Rosa Sm

1889. On fi E E Spots of ea E margaritatus. West

Am. Sci., Vol. 6, pp. 32-34 (see also p. 132).

Girard,

58. General Report on the Fishes. U. S. Pac. R. R. Surv., Vol. 10,

t. 4 (p. 134, pl. 25).

Greene, Es Wilson.

18 a Organs in the rine Fish, Porichthys

notatus Gir Jour. Morph., Vol. 15, pp. 667-696, pl

5 e sprinted | as: alee Biol. ka Seaside Lab., No. 18,

H[ilton], W. k

1914. Record of Two Fishes not before Mentioned, from Laguna.

Jour. Ento. and Zool., Vol. 6, p. 233

Holder, Charles Frederick, and Jordan, David Starr.

1909. Fish AL (New York) (pp. 315-318).

Jordan, David Sta

1905. Te a the Study of Fishes (Holt & Co.), 2 Vols. (Vol. 1,

0-197, Figs. 146-148; Vol. 2, ae 526, Fig. 481).

Ta David hace and Evermann, Barton Warr

ses oe of North and Middle fine. Bull. U. S. Nat.

, No. 47 (Pt. 3, pp. 2321-2322).

Jordan, sea mi per Gilbert, Charles H.

881. Notes on the Fishes of the Pacific Coast of the United States.

Proc. U. S. Nat. Mus., Vol. 4, pp. 29-70 (p. 65

1883. Synopsis of the Fishes of North America. Bull. v. 8S. Nat.

Mus., No. 16 (pp. 751-752).

Jordan, David Starr, and Starks, Edwin Chapin

1895. The Fishes £ ae Sound, Proc. Cal. Acad. Sci., Ser. 2, Vol.

85-

Prince, E.

1910. ‘aia of Gill’s paper on the habits of fishes.] Bull.

S. Bur. Fish., Vol. 28, pp.- 1068-1069.

Steche, Otto.

1909. Die Leuchtorgane von Anomalops katoptron und Photoblepharon

palpebratus, zwei Oberflächenfischen aus dem malaiischen

Archipel. Ei g zur Morphologie und Physiologie der

Leuchtorgane der Fische. Zeitschr. Wiss. Zool., Vol. 93, pp.

349-408, 3 pls., 5 fi

Test, Frederick C.

1889. New Phosphorescent SRN in Porichthys. Bull. Essex Inst.,

Vol. 21, pp. 43-52, pl. 4

CARL L. HUBBS

MUSEUM OF ZOOLOGY, UNIVERSITY OF MICHIGAN

THE

AMERICAN NATURALIST

Vou. LIV. September— October, 1920 No. 634

STENOTHERMY AND ZONE-INVASION?!

PROFESSOR WILLIAM ALBERT SETCHELL,

UNIVERSITY OF CALIFORNIA

THE conception of geographical distribution seems to

have come to the botanists of the later fifteenth and ear-

lier portions of the sixteenth centuries as a distinct and

gradually developing idea. They began to realize-that

the plants of central and northern Europe were different

from those of Greece and Italy as treated of by Theo-

phrastus and his successors and were worthy of study

for their own sakes. With the revival of learning, the

discovery of the ‘‘New World’’ and the attention paid

to the plants and animals of the different countries being

made known through the visits of the various voyagers,

both the knowledge of the different countries and that of

the natural objects brought back from them emphasized

more and more the idea of geographical differences in

flora and fauna and the gradual perception that there

might be some general laws or principles governing

them. It remained for Humboldt in a series of papers in

1805, 1807, 1816, 1817 and 1820, to place the matter of

the geographical distribution of plants on a firm scientific

basis. After Humboldt’s preliminary work, came the

studies of a number of leading botanists and gradually

there have arisen various points of view, especially as to

factors concerned and as to the division of the subject

into various categories according to the special factor, or

set of factors, emphasized. The studies in ecology, which

have come more recently to represent the activities

1 Annual lecture before the Barnard Botanical Club, New York City, de-

livered March 12, 1920.

385

386 THE AMERICAN NATURALIST [Vou. LIV

toward solutions of the problems of distribution, are

founded more particularly on the influence and control

of distribution by edaphic factors, or those more particu-

larly connected with the substratum and concerned in

the studies of association and formations, in other words

having to do particularly with topographic distribution

as contrasted with climatic distribution.

Humboldt’s publications concerned themselves partic-

ularly with climatic distribution, although, incidentally,

he necessarily touched upon topographical distribution.

The chief factor of control in climatic distribution recog-

nized by Humboldt and his successors is temperature,

and Humboldt called attention, in most graphic ways, to

the resemblances between the climatic zones of latitude

over the earth’s surface and those of altitude passed

through in the ascent from sea-level to thousands of

meters above it. Those of us who are older remember

the reproductions of Humboldt’s diagrams of the various

zones (or perhaps better, belts) of vegetation of moun-

tain peaks situate in different latitudinal zones which

were reproduced in the various atlases and older geog-

raphies. Lamouroux, in 1825 and 1826, applied the gen-

eral principles of Humboldt, DeCandolle and Robert

Brown, to marine plants, especially to the alge, and dis-

tinguished latitudinal zones and differences of distribu-

tion in depth (belts), as well as-the effect of certain fac-

tors on topographical distribution. Lamouroux was

followed by Greville and Harvey in the attempts to dis-

cuss the distribution of marine algæ and the latter (1852)

divided the Atlantic coast of North America into 4 divi-

sions and emphasized the position of Cape Cod as a de-

marcation point. These authors and their ideas may be

taken as starting points of the discussions more or less

contemporaneous and later.

A definite attempt to determine the criteria of a cli-

matic zone was made by C. Hart Merriam (1894, 1898)

in his papers on ‘‘life-zones’’ and ‘‘crop-zones’’ of the

United States. Merriam used summation indices com-

piled for a large number of stations and divided the

No. 634] STENOTHERMY AND ZONE-INV ASION 387

country into life-zones in accordance with the indices

thus obtained. Merriam also shows that, by plotting

the isotherms of 18°, 22°, and 26° C., for the six hottest

weeks of the year, divisions are separated from one an-

other corresponding in all essential details to those ob-

tained by plotting summation lines. This is practically

the method I have used in separating climatic zones of

the surface waters of the oceans. Livingston and Liv-

ingston (1913) have discussed the system of Merriam

and proposed a system of efficiency temperature coeffi-

cients which are claimed to represent something more of

the basic principles.of physiology upon which the final

explanations of distribution should be based. A com-

parison between isoclimatic lines plotted for the United

States on the direct summation basis and isoclimatic lines

plotted on the efficiency indices basis shows a strong, but

not absolute tendency toward agreement. The Living-

stons, however, do not discuss the interpretation of their

charts as regards plant distribution in detail.

Nearly 30 years ago, while attempting to obtain some

idea of the temperature relations of the geographical

distribution of the Laminariacex, I noticed a seemingly

definite relation to the lines of mean maxima (summer

lines or isotheres) of surface temperatures. Some brief

remarks on these relations were published in 1893. Far-

ther studies seemed to emphasize the relation between

the 10, 15, 20, and 25 degree (Centigrade) isotheres or

lines of mean monthly maxima and the limits of distribu-

tion of various floral groups, and in 1914 I read a paper

at the Twenty-fifth Anniversary Celebration of the Mis-

souri Botanical Garden (published 1915) as a prelimi.

nary communication on the temperature relation of the

distribution of the marine algæ as expressed in terms of

mean monthly maxima and minima (isotheres and iso-

crymes). In this paper, I made a tentative division of

the surface waters of the oceans, etc., into zones accord-

ing to the courses of the 10°, 15°, 20°, and 25° C. iso-

theres, and announced that a rough tabulation indicated

that the great majority of species are confined to one or

388 THE AMERICAN NATURALIST [Vou. LIV

another of these zones, that a considerable number of

species extend over two of these zones, that a compara-

tively small number are found to extend over three zones,

while the number credited with extending over four or

five zones are extremely few and almost always doubt-

fully so accredited. It was also suggested that the dis-

turbance of zonal distribution, so far as the occurrence

is concerned, is probably due to spot distribution, t.e.,

where waters of a higher or lower temperature than that

of the zone in which they are placed exist due to local

physical conditions, and to seasonal lowering of the

temperature normal to the zone. In 1916, in another ad-

dress (published 1917), I reasserted these statements

and added something as to the significance of the isocry-

mal lines, or lines of monthly mean minima. I suggest

using the latter lines to divide the zones into proper

provinces.

Since writing the last paper I have investigated the

floras of the coast of New England and have found that

the species may be readily arranged in two categories,

one of the colder waters (20° C. or less) and the other of

the warmer waters (20° C. or over), and while some of

these are found only north of Cape Cod and others only

south of Cape Cod, the majority are found on both sides

of the cape, which is, however, the natural dividing point

and approximating closely to the position of the 20° C.

isothere. The separation is made by ascertaining

whether a given species of the last group in particular

inhabits warmer localities to the north or is found only

in cold localities or appears or fruits only in the colder

season to- the south. Similar examinations of other, but

less perfectly known floras, add to the conviction that

species of marine alge, at least, are normal to only one

zone of 5° C. amplitude as to mean maxima, except in

the cases of those of the very coldest waters and it may

be that they are no exceptions to such a rule. Further-

more, it may be assumed, from observing the isotheres

and isoerymes in favorable portions of the surface waters

of the oceans, viz., those undisturbed by the larger ocean

No. 634] STENOTHERMY AND ZONE-INV ASION 889

currents, that the normal, or at least the minimum sea-

sonal variation in temperature is closely approximating

to 5° C. This, added to the amplitude of 5° C. mean

maximum variation, makes the normal amplitude of tem-

perature within each zone about 10° C. and the tempera-

ture interval favorable to the persistence of a species

within a given area, so far as active growth is concerned,

is very little, if any, over 10° C. The seasonal range in

some portions of the surface waters of the oceans may

amount to as much as 18° or 20° C. In such localities as

may have such an extreme range of temperature, we may,

I think, assume that a condition of quiescence, or rigor,

may exist, at least in the perennial species, such as exists

in the case of perennial plants in zones on land where

there is an alternation of a frost with a frostless season,

as it does particularly in the polar and most of the so-

called temperate regions.

It will appear from a careful consideration of what I

have been saying, that the temperatures for normal per-

sistence of any particular species of marine plant lie

within narrow limits, although many marine plants are

credited with extending over fairly wide ranges of tem-

perature. We are, consequently, brought directly to a

consideration of the ideas implied in the use of the terms

stenothermal and eurythermal. The proposal of these

terms, or rather their equivalents in German, rests with

Karl Moebius who, in 1877, published a paper in Die

` Natur on the external factors of life of marine animals.

According to Moebius the eurythermal animals can en-

dure wide ranges of temperature and continue their

occupation of extensive zones and range in depth be-

cause they are able to reproduce under such conditions.

It is this conception of being able to reproduce at widely

separated temperature limits that I wish to call particu-

lar attention in order that I may discuss it later. Moe-

bius states that the eurythermal animals are much less

numerous than those which normally occur and with-

stenothermal animals. The latter seem to be the more

390 THE AMERICAN NATURALIST [Vou. LIV

usual type and this agrees with what I have found in my

attempts to tabulate the marine alge as I have already

mentioned with emphasis. To repeat the idea of Moe-

bius, in a rather free translation of his own words, eury-

thermal animals are those which in the surface waters

of the temperate zones are able to exist and to continue

their kind through reproduction under all of the various

temperature relationships of the different seasons of the

year.

The terms eurythermal and stenothermal have not

come into any noticeable use in botany and are not wide-

spread even in zoological literature, although they are

very convenient. They are-both to be found in the later

editions of Webster’s and in the supplement to the Cen-

tury Dictionary. They are discussed in the latest edi-

tion of the Encyclopedia Britannica by G. H. Fowler,

under the article on ‘‘Plankton.’’ Fowler says: ‘‘In

relation to temperature the wide-ranging species are

termed eurythermal, the limited stenothermal (Moe-

bius); the terms are useful to record fact, but not ex-

planatory. It seems to be the case that to every or-

ganism is assigned a minimum temperature below which

it dies, a maximum temperature above which it dies and

an optimum temperature at which it thrives best; but

these have to be studied separately for every species.”’

The definitions of Moebius and the comments of Fowler

are exactly to the purpose of our consideration, since the

one is from the purely distributional point of view ex-

pressing a fact only, while the other seeks to link the

fact with some explanation, preferably physiological.

Our own discussion of these terms and the underlying

conceptions must necessarily proceed on a somewhat

middle course, largely from the distributional point of

view, but with such regard for the interpretation of the

physiological basis as may be possible from our present

knowledge.

It will be of the greatest assistance, I think, to consider

some concrete cases of eurythermal species and to in-

quire into the conditions of their continued persistence

No. 634] STENOTHERMY AND ZONE-INV ASION 391

under different temperatures. One constituent of the

marine flora of the northern hemisphere which has inter-

ested me very much indeed, is the common eel-grass,

Zostera marina, a marine spermatophyte. As commonly

regarded as to specific limits, this plant extends from

the northern coasts of Europe down along the western

coast and enters the Mediterranean Sea, occurring spot-

wise in the northwestern portion of it and being repre-

sented also in the northern Adriatic. Zostera marina is

represented in one or two localities in southwestern

Greenland and, reappearing at the Strait of Belleisle, it

seems fairly continuous in its distribution thence down

to the coast of North Carolina, at least, and is reported

from West Florida and the Bermuda Islands, although

I can not make certain as to whether it actually grows in

either of the last mentioned stations. Zostera marina is

reported from both the North American and the Asiatic

coasts of the North Pacific, but the exact limits of its oc-

cupancy of these shores is in doubt. The greatest range

of temperature experienced by the Zostera is that on the

Atlantic coast of North America, where it extends from

waters of a mean maximum of 0° C. to those of a mean

maximum of somewhat over 25° C. It is also found in

localities where the seasonal temperature range of the

surface waters is from somewhat below 0° C. to 15° C.

It ranges through all the temperature zones of surface

waters from the Upper Boreal (0°-10° C.) to the Trop-

ical (25°-30° C.), i.e., five zones in all. I shall discuss

the reasons for this wide extension of the range of Zos-

tera marina later, but desire to call attention here to the

facts that we are dealing with a perennial plant with un-

usually effective methods of vegetative multiplication

and devices for wide dispersal.

Another eurythermal marine species is Ascophyllum

nodosum, one of the bladder-bearing Fucacee or Rock-

weeds. On the Atlantic coast of North America, this

species is found in some abundance from well up on the

west coast of Greenland down to the northeastern coast

of New Jersey, or on coasts having a range of mean

392 THE AMERICAN NATURALIST [Vou. LIV

maximum temperature from 0° C. or below to about 22°

C. and seasonal ranges of about 17° C. maximum. Asco-

phyllum nodosum is also a perennial species. Rhodo- |

chorton Rothi is a delicate red alga which, nevertheless,

seems to be a perennial and Monostroma Greville: a mem-

branous green alga, and Polysiphonia urceolata, a fila-

mentous red alga, are annuals, but with the same range

as Ascophyllum nodosum. Grinnellia americana is the

last example of many eurythermal alge of the Atlantic

coast of North America I desire to bring forward. It is

a strikingly beautiful annual membranous red alga and

extends from northern New England (North Temperate

Zone, 15°—20° C., mean max.) to the coast of North Caro-

lina (Tropical Zone, 25°-30° C., mean max.). Other ex-

amples of eurythermal species might be given, but those

I have mentioned are typical and reasonably well known.

They will serve as a good representative basis for dis-

cussion with the idea in mind that what is indicated by

the eurythermy of one and another of them will, by an-

alogy, also seem extremely possible to be the case with

all other types and individual species extending over

ranges of temperature of more than 10° :

Stenothermal species are particularly characteristic

of the Tropical Zone, in very few portions of which. the

seasonal variation in temperature is over 10° C. Species

confined to the Upper Boreal or to the Upper Austral

Zones are also narrowly stenothermal, since the entire

range of temperature in these zones is not over 10° C.

The temperate and subtropical zones are usually suffi-

ciently affected by seasonal changes to show a range

of temperature greater than 10° C., but in the southern

hemisphere in particular, there are portions of these

zones, at least, that show only a 10° C. range and conse-

quently may possess stenothermal species. The annual

species of any particular zone, and even perhaps all an-

nual species, are stenothermal so far as their actively

vital processes are concerned, but may endure tempera-

tures of more extended range in the resting seed or spore

condition. This:naturally brings us to inquire as to the

No. 634] STENOTHERMY AND ZONE-INV ASION 393

nature of the fundamental differences between the eury-

thermal and the stenothermal species, and this, in turn,

is closely connected, as I shall hope to make plain, with

the second topic of this paper, viz., zone-invasion.

I have already tried to make clear the fact that my in-

vestigations have tended very strongly to convince me

that each and every species of marine plant is normal

to only one zone, and that, when a species is credited to,

or found to occur in, two zones, it is normal to only one

of them and is to be found in the other because for some

reason it finds in the second zone the temperature con-

ditions, both as to degree of temperature and as to dura-

tion of that degree of temperature, of the zone to which

it is normal. In a similar fashion, if a species is found

to inhabit three, four, or even five zones of different tem-

perature relations, it is possible to make certain that it

is normal to only one of these and invades the other

zones because it finds the proper temperature conditions

for its continuous existence. The proper temperature

seems certainly to be that which is most intimately con-

nected with reproduction, since it is this function that is

most necessary to persistence in the particular locality.

In the laboratory, under controlled conditions, alge, in

particular, have been found to be very sensitive to even

slight changes of temperature, as Ewart (1896) has dem-

onstrated. It does not seem as if the same alge, in their

ordinary environment, could be thus sensitive as West

and West (1898) have held, but Ewart (1898) has an-

swered their objections, claiming that, in nature, they

are probably equally sensitive, but withstand seemingly

great changes for reasons that prevent these changes

actuating. This is something of the truth in the case of

species invading colder from warmer, or warmer from

colder ‘zones in that they find in the invaded zones the

temperatures, both as to intensity and duration, which

are favorable to their growth and reproduction and

which are the same as they find normally in their proper

zone. :

Zone-invasions proceed in one of two directions, or,

394 THE AMERICAN NATURALIST [Von. LIV

occasionally, in both. They may proceed from warmer

to colder zones, they may proceed from colder to warmer

zones, or they may proceed from a zone of intermediate

temperatures to both colder and warmer zones. Where

warmer spots or areas exist in the midst of cooler waters,

species of warmer zones may exist spotwise in the cooler

zone. Where certain portions of the waters of a warmer

zone are depressed in temperature by cold currents or

upwellings, or, for certain seasons of the year, suffer a

general lowering of the temperature, there and then may

species from cooler zones be expected to put in an ap-

pearance. The extent of such invasions will depend

naturally upon the intensity and duration of the unusual

temperature. A consideration of the examples I men-

tioned as typically eurythermal may serve to make this

idea more clear.

Zostera marina seems, on careful study of its occur-

rence and habits on all the coasts where it is found, to be

normal to the North Temperate Zone with the mean

maxima for the hottest month from 15° to 20° C. If this

is the case, we are dealing with a species which extends

in both directions from its normal zone. The more

northern extensions may be explained by the fact that

the very shallow and protected lagoons and interiors of

prolonged and narrow bays preferred by this species

may have the temperature of their waters raised through

the action of the air and of the sun. In such waters,

insolation undoubtedly is the most effective agent in

raising the temperature as much as 10°-12° C. or even

higher. To the south, the invasions of Zostera marina

may be assumed to be made possible by the seasonal

lowering of the temperature of the waters through the

lower winter temperatures, e.g., the winter temperatures

on the coast of North Carolina is somewhat under 20° C.

and the winter temperature on the coast of West Flor-

if the seasonal lowering of the waters south of the lower

limits of the North Temperate Zone allows the eel-grass

to find its normal temperature for fruiting in an earlier

No. 634] STENOTHERMY AND ZONE-INV ASION 395

season of the year than late summer, that the farther

south the species grows, the earlier will be the fruiting

season. Unfortunately, it is impossible to obtain any

extensive data on this subject, but reliable testimony

indicates that it flowers and fruits somewhat over a

month earlier on the coast of New Jersey than it does on

the coast of northern New England. It seems therefore

that the critical temperature for persistence of this spe-

cies, at least through flowering and seeding, is the same

throughout its limits and that the species does not differ

from a typical stenothermal species from this point of

view. Zostera marina, however, is one of the most typi-

cal of the eurythermal species in that it must endure

extremes of both heat and cold in various portions of its

extensive range and in the various seasons of the year in

each and every portion of its habitat. It is not known

as to the temperature limits of the vital activity of the

vegetative portions of the Zostera, but it does not seem

possible that their separation can possibly be as wide as

the differences between the extreme limits of the tem-

peratures of endurance and probably are very much less.

~The Zostera probably has rather narrow limits to the

temperature range of its vegetative activities and un-

doubtedly passes into a resting or hibernating condition,

a condition of cold-rigor or of heat-rigor as the case may

be, at the upper as well as at the lower portions of its

temperature range. The land perennials of temperate

zones do this and it seems safe to assume that Zostera

does the same.

The case of Ascophyllum nodosum, a perennial brown

alga of complex structure, is a very excellent one for

study. This species ranges from the western coast of

Greenland to that of New Jersey and it has a similar

range on the northern and western European coast. On

the coast of Greenland, it fruits in summer and it fruits

earlier and earlier in the season as it proceeds towards

the south, until, in the region of Long Island Sound, it

fruits in late winter and early spring. The frond, or

396 THE AMERICAN NATURALIST [Vou. LIV

vegetative portion, of Ascophyllum does not seem at all

vigorous during the summer of the southern portion of

its range. It seems perfectly evident that Ascophyllum

is normal to the Upper Boreal Zone and invades the

zones to the south because it finds, even on the north-

eastern coast of New Jersey, seasonal temperatures of

isotherm, of 5° C. touches the coast of New Jersey at

about the point that marks the southern limit of the

range of Ascophyllum nodosum. We have in this spe-

cies, then, a eurythermal species whose critical tempera-

ture and amplitude for persistence range from 0° to 10°

C. and which undoubtedly passes into a condition of heat

rigor during the hotter months of the year in the south-

ern portion of its range. It differs from the last ex-

ample, in that its course of invasion is in one direction,

viz., to the south.

Rhodochorton Rothii is a very delicate, filamentous,

perennial red alga of very lowly stature. It has a range

very similar to that of the last species and, in the south-

- ern portions of its range, fruits only in winter. The

same things may be said of this species as were said of

Ascophyllum. Rhodochorton, however, is a shade or cave

plant in the more southern portions of its range, seek-

ing the cooler portions of the warmer districts. This is

doubtless its only opportunity of surviving the heat and

is of great benefit to its delicate structure.

Monostroma Grevillei and Polysiphonia urceolata are

annuals, with about the same- range as the last two.

They are summer annuals in the waters of Greenland,

but are winter and early spring annuals of the southern

portions of their range. With the exception, then, of the

temperatures endured by their resting spores, they are

confined to the temperature range of the Upper Boreal

Zone and are practically stenothermal.

The last example quoted is Grinnelia americana, an

annual red alga, apparently normal to the Long Island

Sound district and therefore of the North Subtropical

No. 634] STENOTHERMY AND ZONE-INV ASION 397

Zone (20°-25° C.). North of Cape Cod, it is to be found

only in certain warm protected spots where the insola-

tion is sufficient to raise the temperature to that of the

subtropical zones while the waters outside are those of

the temperate zones. To the south of the North Sub-

tropical Zone the species is a winter annual and follows:

the 20° C. isoeryme. Grinnelia is, therefore, a steno-

thermal and not a typical eurythermal species and in-

vades both colder and warmer zones, the colder because

of warm spots and the warmer because of favorable sea-

sonal conditions.

- Farlow, in his Marine Alge of New England, has am-

ply explained still a different type of invasion, viz., from

a colder zone into a warmer and I have some additional

details in a paper soon to be published. The Laminari-

acee, or kelps, a number of species of perennial red

alge, some other browns, greens, reds, etc., pass Cape

Cod and are to be found in the colder waters which are

usually the deeper waters to the south of it. This seems

to be an invasion from the North Temperate into the

North Subtropical. It does not mean, however, as is

the case also with the examples I have mentioned and

discussed, that these seeming invaders are living in

waters of a different range of temperature from that of

the normal zone. Their eurythermy is but seeming, at

least so far as this particular invasion is concerned.

- In conclusion, I may say simply this: stenothermy is

the rule both from the point of view of distribution and

of physiology, at least so far as effective reproduction is

concerned; eurythermy is largely, if not entirely, a

matter of endurance of a wide range of temperature,

much of which endurance is due to the power to enter

into a condition of rigor after certain extremes of tem-

perature of either direction are passed ; and a study of

the various reasons for zone invasion assists Soy i in

making these facts apparent.

PHYLOGENY OF THE ARTHROPODA WITH ES-

PECIAL REFERENCE TO THE TRILOBITES!

PERCY E. RAYMOND, Pu.D.

HARVARD UNIVERSITY

THE phylogeny of the Arthropoda has been discussed

so often that merely to summarize previous opinions

would require an article of considerable length. In a re-

cent number of the Narurauist,? Professor Crampton has

reviewed the subject from the standpoint of a student of

insects, the most specialized Arthropoda. It may be of

interest to see what results are reached when approached

from the point of view of a student of the trilobites, the

most ancient members of the phylum. The characteris-

tics of trilobites may be summarized as follows:

APPENDAGES

During the last two years I have had occasion to re-

study practically all of the known specimens of trilobites

whose appendages are preserved. The limbs of twelve

species, representing nine genera, are now more or less

fully known. Those which leave least to be desired are

Neolenus from the Middle Cambrian, Triarthrus, Caly-

mene, Ceraurus, and Cryptolithus from the Middle Ordo-

vician, and Isotelus from the Upper Ordovician. Repre-

sentatives of all three of the orders into which the class

is divided are included in this list, which contains exam-

ples of both ‘‘primitive’’ and ‘‘specialized’’ trilobites.

The appendages of all these genera, with the exception

of Isotelus, whose exopodites are still unknown, prove to

be constructed on one plan. An articulatory segment

1 This is an abstract of a more extensive discussion of the affinities of

the trilobites now being published by the Connecticut Academy of Arts and

Sciences,

2 AMERICAN NATURALIST, Vol. 52, 1919, p. 143.

No. 634] PHYLOGENY OF THE ARTHROPODA 399

(coxopodite) supports the proximal ends of two branches,

an ambulatory endopodite and a setiferous respiratory

exopodite. The endopodite consists in all cases of six

segments, the terminal one with movable spines on the

distal end, usually three in number, but occasionally sev-

eral, The proximal segment of the endopodite is a basi-

podite and gives rise to the exopodite, although both

branches articulate with the coxopodite. The method of

articulation of coxopodite, exopodite, and basipodite is

similar to that of the second thoracic limb of the recent

Anaspides, as figured by Calman. The exopodite is in all

cases composed of a flattened shaft, along the posterior

margin of which are delicate flattened sete. The form

of articulation of the basipodite, exopodite, and coxo-

podite indicates that when one of the outer branches

moved the other accompanied it, but as the exopodites

were always above the endopodites, they appear to have

been of comparatively little use in swimming, and were

probably chiefly respiratory organs.

All of the trilobites mentioned, so far as their state of

preservation will allow determination, have four pairs of

limbs of this sort on the cephalon, a pair on each segment

of the thorax, and as many pairs on the pygidial shield

as there are annulations on its axial lobe. In front of

the biramous limbs there is one pair of uniramous, richly

segmented, tactile antennules. The ventral membrane of

the trilobite was very thin and feebly supported, so that

the articulation of the limbs was not with it, but with

infoldings of the dorsal shell which extended downward

beneath the glabeller and dorsal furrows. The distal end

of each of these appendifers fitted into a notch in the

upper side of the corresponding coxopodite. A projec-

tion of this latter segment extended mesally nearly to the

median line, forming endobases which on the cephalon,

and usually along the whole of the body, functioned as

food-getting organs.

No other parts of the limbs have yet been found, al-

though I have searched diligently through all of the

400 THE AMERICAN NATURALIST . [ Vou. LIV

known material preserving the ventral anatomy. There-

fore it seems to me that Walcott has not sufficient evi-

dence for the structures he illustrates and describes as

epipodites and exites in Neolenus, epipodites in Triar-

thrus, Calymene, and: Ceraurus, and spiral gills in the

last two. The presence of none of these things can, in

my view, be proved.

There is little modification of the appendages of differ-

ent parts of the body. The gnathobases of the coxopo-

dites on the cephalon of Triarthrus are more jaw-like

than those on the remainder of the body, and in the same

species the segments of the endopodites of the pygidium

and posterior part of the thorax are more triangular than

those of the anterior ones. Cryptolithus has the thoracic

legs bowed backward to form more efficient pushing or-

gans, and in all species with long hypostomata the an-

. terior biramous appendages seem to be more or less

degenerate. Thus, Calymene appears to have two pairs

of very delicate biramous appendages back of the anten-

nules, and the first one or two pairs of gnathobases of

Calymene, Ceraurus and Neolenus seem to be somewhat

reduced, but there is no evidence that any pair of ap-

pendages is entirely lost. All the evidence seems to

indicate that Beecher correctly homologized the cephalic

appendages with the antennules, antenne, mandibles,

maxillule, and maxille of the Crustacea.

Form or Bopy

Trilobites are always depressed, flattened animals,

with a broad head composed of at least five fused seg-

ments, a thorax of from two to forty-four free segments,

and a pygidium made up of a variable number of undif-

ferentiated segments. The anal opening is at the pos-

terior end of the pygidium, and the growing point just

in front of it, as in other arthropods. New segments are

introduced into the posterior end of the pygidium during

moults, are pushed forward by the introduction of others

2 Smithsonian Miscl. Coll., 1918, Vol. 67, No. 4.

No. 634] PHYLOGENY OF THE ARTHROPODA . 401

behind, and eventually a certain number are freed from

the anterior end of the pygidium to form the thorax.

Trilobites with an elongate worm-like form have numer-

ous thoracic segments and small pygidia, while many

others have few free segments and the pygidium nearly

as large as the cephalon. These latter have usually been

called more specialized than the former, but it is obvious

from the method of introduction of new thoracic seg-

ments that the reverse is the case. This opinion is con-

firmed by a study of the ontogeny, for it is found that in

the protaspis the pygidium of any species is proportion-

ally larger than at any later period in life, and that many

species pass through a stage in which they are isopygous.

There is a certain amount of evidence that the pygi-

dium was used as a swimming fin, and some species seem

to have had sufficiently strong muscles to enable the ani-

mal to dart away suddenly when attacked. Trilobites

with large pygidia would thus have a certain advantage

over the others, and, as a matter of fact, it was this type

which persisted longest. The broad depressed body was

not as well adapted for a nectic mode of life as a com-

pressed fishlike one would have been, but it is the form

which could most easily be kept afloat and propelled with

the minimum of effort. The young of all species are cir-

cular or broadly oval in outline, and those adults with

subequal shields depart least from that form. A fair

inference from the above would be that the elongate

crawling trilobite was more specialized than the isopyg-

ous swimming one.

[INTERNAL ANATOMY

Naturally knowledge of the internal anatomy is not as

full as could be desired, but what follows appears to be

based on reasonably clear evidence.

The mouth is ventral and usually situated back of the

middle of the cephalon. Its position depends upon the

length of the ‘‘upper lip’’ or hypostoma, and in extreme

cases may be at the posterior end of the cephalon. There

402 THE AMERICAN NATURALIST [Vou. LIV

is evidence from ontogeny and phylogeny of a backward

migration of the mouth, coincident with the same move-

ment of the eyes. In both cases this is probably due to

the enlargement of the anterior end of the mid-gut.

From the mouth the esophagus extends upward and for-

ward to the enlarged mesenteron which occupies the

greater part of the large cavity between the hypostoma

and glabella. The intestinal canal tapers backward, but

no differentiation of the posterior portion has yet been

made out. The anus is beneath the posterior end of the

axial lobe. The heart is elongate, chambered, branchio-

pod-like, and in the one species in which it is preserved,

extended from the middle of the cephalon to the anterior

end of the pygidium. The principal muscles were a dor-

sal pair of extensors, attached at the posterior margin

of the cephalon and anterior ring of the pygidium, and a

ventral pair of flexors, both with branches inserted in

each segment. All of these organs were within the axial

lobe.

CoMPARISON WITH OTHER ARTHROPODA

Having thus briefly stated the principal characteristics

of the trilobites, the method will be to indicate briefly

the similarities which exist between the trilobites and

other arthropods, and to show that there is nothing about

the bodily form or characteristics of the appendages to

negate the possibility of a derivation directly or indi-

rectly of all other classes from that under discussion. It

is obvious that in this short paper each class can be

treated but briefly.

CRUSTACEA

The trilobites are themselves crustaceans, as is amply

proved by their biramous appendages. An attempt will

be made to show that they may have been ancestral to

the other crustaceans.

In recent years it has been fecal considered that

the Branchiopoda were more nearly allied to the trilo-

bites than any other living animals. Bernard, the chief

No. 634] PHYLOGENY OF THE ARTHROPODA 403

proponent of this association, did not consider either sub-

class derivable from the other. Walcott has more re-

cently stated that the trilobites were derived from the

branchiopods and in this has been followed by Crampton.

The points of relationship are: in both subclasses the

number of segments is not fixed, and in both there are

some species which have large numbers of them; both

have a well-developed labrum (hypostoma); both have

functional gnathobases along the body; the change in

metamorphosis of the branchiopod is comparatively

small, although A pus is by means a ‘‘grown up nauplius,”’

as Bernard put it.

So far as these similarities are important, they do show

a close relationship of the two groups, but none of them

indicates that either is more primitive than the other.

When a closer comparison is made, it at once becomes

evident that the trilobites are much more primitive than

the branchiopods. For example: trilobites have no cara-

pace; some branchiopods do; trilobites have serially sim-

ilar appendages on all segments, branchiopods have very

different appendages on the head from those on the

thorax, and some of the abdominal segments lack them

entirely; trilobites have antenne like the other cephalic

and trunk appendages, branchiopods have the antenne

highly modified, degenerate, or absent. In other words,

branchiopods are in all these respects much more spe-

cialized than the trilobites. Finally, the limbs may be

considered. Lankester has shown that the schizopodal

limb of the higher Crustacea may be explained as derived

from one like that of the thorax of Apus, and most stu-

dents of the Crustacea have followed him in considering

the phyllopodous limb the most primitive among the

Crustacea. This theory has now been completely upset,

for Walcott has found several undoubted branchiopods

with appendages in the Middle Cambrian, and the best

preserved of them (Burgessia) show that the limbs were

not phyllopodan, but like those of trilobites. The ancient

branchiopods having had simple trilobite-like limbs, it

404 THE AMERICAN NATURALIST [Vou. LIV

can no longer be held that phyllopodan limbs are primi-

tive, and, stripped of their trilobite-like disguise, these

wormlike crustaceans may no longer be considered most

primitive. The possession of biramous limbs by the

branchiopods of the Middle Cambrian, added to their

other undoubted likenesses, indicates the possibility that

they were derived from the trilobites, although some of

them had then already attained the specialized carapace,

pedunculate eyes, and limbless hind-body. This possi-

bility is converted into strong probability when one con-

siders the structure of the beautiful Marrella splendens

Walcott. The head of this ‘‘lace-crab’’ of the Middle

Cambrian is obviously highly specialized, but the struc-

ture as a whole proves it to occupy an intermediate posi-

tion between the trilobites and more specialized crusta-

ceans, including the branchiopods. It resembles the

higher crustaceans in having the antenne uniramous, in

lacking exopodites on the cephalic appendages, gnatho-

bases on those of the thorax, and in the absence of pleural

lobes from the test of the trunk. This animal retains

enough characteristics of the trilobites to show that it

was derived from them, and has attained enough charac-

teristics of the higher Crustacea to show that it belongs

with them. A better connecting link can hardly be ex-

pected.

The Copepoda prove, on analysis, to be much more

closely allied to the trilobites than had been supposed.

All students have remarked upon the many primitive

features of the non-parasitic members of this group, but

have generally explained them by the sweeping assertion

that they must be degenerate. Why, if they are degen- _

rate, do the Copepoda show fewer modifications during

development than any other Crustacea except the trilo-

bites? They, instead of Apus, represent the ‘‘grown up

nauplius.’’

These animals resemble the trilobites in lacking a cara-

pace, in possessing pleural lobes, which, however, are in-

curved instead of being flattened. The greatest resem-

No. 634] PHYLOGENY OF THE ARTHROPODA 405

blances are, however, in the appendages. All these,

except the antennules, maxille, and maxillipeds, are bira-

mous, the antenne and mandibles being especially like

those of trilobites. The Copepoda are easily derivable

from the latter, even though there are no fossil forms to

connect the two groups. Since they lack compound eyes,

and show very slight evidence of having ever possessed

them, it is even conceivable that they branched off from

the Hypoparia, the most primitive of trilobites.

The Ostracoda and Cirripedia are of course highly

modified by their somewhat peculiar method of life, but

when the young are studied, the characteristics of trilo-

bites are readily observed. In fact, it is really surpris-

ing that the trilobite-like character of the crustacean nau-

plius is so consistently ignored. It has a broad depressed

form like a trilobite. It has simple antennules, biramous

antenne, and mandibles like a trilobite, and the gnatho-

bases of the last two function as mouth-organs. An hy-

postoma is present, and there is a growing point, as is

evidenced by the way new segments are added. It is not,

it is true, a trilobite, but it looks like a trilobite modified

by suppression, and taken in connection with other. evi-

dence, certainly does no injury to the theory that the

higher Crustacea were derived from the trilobites.

The Malacostraca can be mentioned but briefly. Their

most ancient representative whose appendages are

known, Hymenocaris from the Middle Cambrian of Brit-

ish Columbia, had biramous appendages like those of the

trilobites, and most of the modern members of the group

have similar ones on some part of the body. As in lower

crustaceans, when the exopodites are lost or degenerate,

epipodites are developed to replace them, and thus the

limbs become variously modified. It is remarkable, how-

ever, how close a resemblance there is between the ap-

pendages of a trilobite and those of fresh-water syn-

carids from Tasmania, and even in the Decapoda the

seven segments of the walking leg are serially homolo-

gous with the seven segments of that of the trilobite. It

406 THE AMERICAN NATURALIST [Vou. LIV

has frequently been objected to the trilobites as ancestors

of the Crustacea, that they had wide pleural extensions

and a large pygidium. To the first it may now be replied

that some trilobites did get rid of the pleural extensions,

but that, on the other hand, most Crustacea retain some

remnants of them. I have already shown above that the

large pygidium in trilobites was more primitive than the

trunk with numerous free segments, and it may further

be pointed out that some orders of Isopoda do have a

pygidium.

ARACHNIDA

My task in this class is rendered somewhat easier by

the fact that the followers of Lankester appear to have

accepted his explanation of the descent of the class from

the trilobites. While I agree with the general thesis, I

must point out that a certain amount of caution must be

used, for the connecting links are not nearly so satisfac-

tory as one would like them to be, and the trilobites are

not nearly so closely related even to the Merostomata, as

they are to the higher Crustacea.

In the first place, while the Trilobita were probably

the ancestors of the Arachnida, they do not themselves

belong to that class. Lankester advanced six reasons for

placing them in the Arachnida, but the first is the only

one having any considerable weight, and is the only one

which will be discussed here. This point was that they

had only one pair, apart from the eyes, of pre-oral ap-

pendages, while the Crustacea have two pairs. Re-

searches since Lankester’s article was written seem to

show that this apparent difference between the Arach-

nida and Crustacea is not fundamental, for the chelicere

of the former are probably to be homologized with the

antenne, not the antennules of the latter, so that the

mouth is in the same position in relation to the append-

ages in both groups. Further, the mouth does not occupy

a constant position in the trilobites, but with the elonga-

tion of the hypostoma, is pushed backward, so that from

one to four pairs of appendages may be attached in front

of it.

No. 634] PHYLOGENY OF THE ARTHROPODA 407

If dorsal tests only be considered, one can pick out an

excellent series showing gradations from a trilobite into

Limulus. Thus, there are in the Middle and Upper Cam-

brian the Aglaspidex, with Limulus-like head, trilobite-like

free thoracic segments, and Limulus-like telson. Follow-

ing the history of the group through the Paleozoic, there

is, in the Silurian, Neolimulus with a head which is surely

that of Limulus but which has vestigial facial sutures,

and free thoracic segments are present. By Devonian

times, the thorax had begun to fuse into a shield, although

some of the Pennsylvanian species retained a few free

segments at the anterior end of the thorax. This series

is so convincing that one must believe that the Xiphosura

developed from the trilobites, but a study of the append-

ages shows that there are greater differences between

those of a trilobite and Limulus than between those of a

trilobite and one of the highest Crustacea.

The greatest difference is in the complete lack, at any

stage of development, of the antennules, from which it

follows that the anterior shield in the Xiphosura is a

cephalothorax in which at least seven segments are in-

corporated. It is, of course, entirely possible that in one

line of evolution of the trilobites the antennules were lost

and the antenne developed as chelicere, but if the test be

applied to the Aglaspide, the results are at variance with

the expectation. Walcott has found Aglaspide with ap-

pendages in the Middle Cambrian, and they seem to have

five pairs of appendages on the cephalon, two pairs of

which are elongate, multi-segmented, tactile antenne, and

biramous appendages are present on the thorax. These

animals were still Crustacea, and the development of

elongate antenne instead of chelicere shows that they

were not tending in the direction of the Xiphosura. It is

possible, however, that when the appendages of more

Aglaspide are known, it will be found that some of them

showed a tendency to lose the antennules and develop

chelicerer.

#Smithsonian Miscl. Coll., Vol. 57, No. 6, 1912.

408 THE AMERICAN NATURALIST [Vou. LIV

Some progress has been made toward the connection

of the trilobites with the Merostomata, as the Limulava

of Walcott are, in a certain sense, intermediate between

the two. The Limulava are, however, true crustaceans,

for they have five pairs of cephalic appendages, the first

of which are elongate uniramous antennules, and also bi-

ramous, trilobite-like limbs on the anterior part of the

thorax. They are especially trilobite-like in the fact that

the antenne are not elongate tactile organs, but, in Emer-

aldella at least, are biramous. The relationship to the

Merostomata is expressed in the shape of the head, body

and telson, and the grouping of the cephalic appendages

about the mouth. If these animals lost the antennules,

developed the antenne into chelicere, added two thoracic

segments to the cephalon, modified the appendages, and

added a sternal operculum, a merostome would be pro-

duced. I think it is obvious that to change a trilobite

into a marine arachnid is a more complicated process

than to change one into a crustacean of any kind.

To compare the spiders directly with the trilobites may

seem somewhat fanciful, yet in some respects the spiders

are more trilobite-like than Limulus is. On the germ

band there is a pair of buds in front of the mouth which

probably are antennules. These later fuse to form the

rostrum, and the chelicere move into a pre-oral position.

Moreover, Jaworowski has shown that the pedipalps on

the germ band of Trochosa singoriensis are biramous.

In young spiders the abdomen is segmented, and the an-

terior segments bear pairs of limb-buds, some of which

are later lost, while others develop into lung-books or

spinnerets. The number of abdominal segments appears

to be variable, from eight to fourteen, another feature

which suggests the trilobites. The spiders very probably

did not spring directly from this group, but will eventu-

ally be traced to it, and not through the Xiphosura.

No. 634] PHYLOGENY OF THE ARTHROPODA 409

INSECTA

I quite agree with Crampton that Handlirsch has pre-

sented little or no evidence that the Insecta were derived

directly from the trilobites. His chief point was that the

most ancient known insects, the Paleodictyoptera, were

amphibious, and that their larvae, which lived in water,

were very like the adult. His second was that the wings

of the Paleodictyoptera probably worked up and down

only, and that the two main wings were homlogous with

rudimentary winglike outgrowths on each segment of the

body. These outgrowths resemble the pleural lobes of

trilobites, and were considered to have been derived from

them. Comstock, who has recently reviewed the ques-

tion, does not see any evidence that the Paleodictyoptera

were amphibious, and I do not think any entomologist

or paleontologist has accepted the idea of a direct trans-

formation of pleural extensions of segments of trilobites

into wings. The ‘‘para-notal’’ theory certainly does not

involve any such conception. That the insects are de-

rived indirectly from the trilobites is, however, entirely

possible, and Professor Crampton has marshalled the

data for one such possible line of derivation through the

Crustacea in the article to which allusion was made in

the opening sentences of this essay. Another theory is

that advanced by Tothill, who suggested that the Insecta

arose through some chilopod-like tracheate, rather than

directly from a marine organism. Tothill® has pointed

out that in the germ band, spiracles appear as early as

the limb-buds, and may thus indicate a tracheate ancestor

for the insects. This is, of course, discounting the pos-

sible effect of acceleration on the embryo, but the whole

anatomy of the insects indicates long separation from

the marine ancestor. The germ band of the chilopod is

somewhat more primitive than that of the insect, for in

Some species both antennules and antenne are present,

and the maxille and first maxillipeds are biramous. The

5 Am, Jour. Sci., Vol. 42, 1916, p. 373.

410 THE AMERICAN NATURALIST [ Vou. LIV

presence of two pairs of antennae does not point directly

to the trilobites, but to some offshoot like Marrella, and it

is possible that the line has been: trilobite, Marrella-like

marine animal, chilopod-like tracheate, insect.

There remain only the Diplopoda, which show a few .

trilobite-like characteristics, notably their lateral out-

growths and the endopodite-like walking legs on every

segment. Antennules are present, antenne absent, man-

dibles and maxillule much modified, the latter possibly

biramous, and maxille absent. The most characteristic

feature, the possession of two pairs of limbs on each seg-

ment on a part of the trunk, can be shown to have arisen

comparatively recently (geologically), for Silurian and

Devonian fossils which are undoubted diplopods have a

test like that of a trilobite and eyes much like those of a

Phacops. While there are no close connections, there is

nothing to show that the Diplopoda could not have been

derived from the Trilobita.

SuMMARY

After the above survey, it should appear that the trilo-

bites, particularly in respect to their appendages, are

more primitive than any other Arthropoda. The chief

modifications in other groups are in the nature of reduc-

tions, in the loss of whole appendages, of branches or of

segments. Extra segments are sometimes added in cer-

tain appendages, and new outgrowths, epipodites, are

common among the Crustacea. The trilobites have what

seems, at first sight, a peculiar and specialized dorsal

test, but now that it has been shown that the pleural lobes

may be lost and the pygidium reduced to a single seg-

ment, and, chiefly, that the wormlike form is not primi-

tive but secondary, they may be viewed in an entirely

new light.

In the oldest fossiliferous rocks, Lower Cambrian,

trilobites are plentiful, branchiopods rare, and no other

arthropods present. A greater differentiation is seen in

the Middle Cambrian fauna, due, however, entirely to the

No. 634] PHYLOGENY OF THE ARTHROPODA 411

remarkable assemblage found by Walcott at a single lo-

cality in British Columbia. In this fauna the Crustacea

are represented by trilobites, anostracan and notostracan

branchiopods, Marrella, Limulava (possible ancestors of

the merostomes), Aglaspide (possible ancestors of the

Xiphosura), and Leptostraca, the most primitive Mala-

costraca. The Upper Cambrian brought the first true

Merostomata. In the Ordovician, Ostracoda and Cirri-

pedia first appear, and in the Silurian the first undoubted

Xiphosura, primitive Diplopoda, and Scorpiones. In-

secta and air-breathing Arachnoidea, including Araneæ,

appear suddenly in the Pennsylvanian (Upper Carbonif-

erous), and the oldest known Chilopoda are found with

them. All of the tracheates probably have a long pre-

Pennsylvanian history, however, and the record of the

fossils is liable to be amplified by new discoveries at any

time.

The geological record, so far as it is now available, is

in favor of the theory that the other Arthropoda were

derived from the trilobites, for although Crustacea were

highly diversified by the Middle Cambrian, all other than

these were rare, and the trilobites, while they had not

reached their highest development, were exceedingly

abundant and varied.

If the trilobites were the most primitive arthropods,

the question of the ancestry of the phylum resolves itself

into a search for the progenitors of the former. What

would be the form of the animal from which the trilobite

was derived? The depressed form universal in the sub-

class and the equally universal lateral (‘‘pleural’’) lobes

have already been commented upon. From a study of

comparative morphology, it appears that the more an-

cient trilobites, and the more ancient members of higher

families within the subclass, have the most nearly flat

form, the narrowest axial, and the widest pleural lobes.

Turning to ontogeny, it is found that in most cases the

protaspis of any species shows the same characteristics.

All these suggest a broad depressed animal with narrow

412 THE AMERICAN NATURALIST [Vou. LIV

axial portion as the ancestor. Only a few specialized

trilobites like the Remopleuride and one subfamily of the

Cheiruride show extensive reduction of the pleural lobes.

A study of the ontogeny of trilobites with both large

and small pygidial shields shows that the pygidia are

proportionally larger in the protaspis than in the adult,

and the more ancient forms pass through a stage in which

they are practically isopygous. This suggests that the

ancestor had subequal cephalic and abdominal shields.

Since the thorax grows by the breaking down of the pygi-

dium, the ancestor should lack free thoracic segments.

Curiously enough, among Walcott’s remarkable finds in

the Middle Cambrian there is an isopygous crustacean

without free thoracic segments. It was named Naraoia

and referred to the Branchiopoda by Walcott,® but since

it satisfies the theoretical considerations and evidently

can not be referred properly to any other subclass, I am

inclined to look upon it as the simplest of all trilobites.

The specimens so far described are not fully preserved,

but the appendages are apparently biramous and trilo-

bite-like, and there are at least three pairs on the head

and fourteen on the pygidium. From Agnostidae with

subequal shields and two thoracic segments to Naraowa

with subequal shields and no thoracic segments is but a

step. If the pygidium were built up by the coalescence

of once free segments, that step would be in the direction

of specialization, but since the reverse is the case, the

extraordinary conclusion is reached that the simplest

trilobite did not look at all like the traditional benthonic

round annelid.

The study of the ontogeny of many species of trilobites

long ago established the fact that in the ontogeny the

eyes, which may be entirely absent in the very young of

the simplest oculiferous species, appear first on the an-

terior margin and during growth move backward on the

head. A point which has not been noted is that this

movement is correlated with a backward movement of

® Smithsonian Miscl. Coll., Vol. 57, No. 6, 1912, p. 175.

No. 634] PHYLOGENY OF THE ARTHROPODA 413

the mouth, as indicated by the increase in length of the

hypostoma, and an increase in size of the anterior part of

the glabella. There is nothing mysterious about the

process, as it is probably due to the increase in the size

of the anterior (digestive) portion of the ‘‘ stomach.’’

This indicates that in the ancestral form the mouth and

eyes were close to the anterior margin, and does away

with the necessity of the bent annelid to explain their

migration. Many of the simpler trilobites are of course

blind, as is Naraoia.

It is true that much of the argument involves the use

of principles drawn from the study of ontogeny, but

where the ontogeny points to animals which actually exist

and helps to explain observed facts, its use seems to be

justified. Swinnerton has recently suggested that stu-

dents of the ontogeny of trilobites have been led into an

entirely wrong interpretation because they have not real-

ized that the protaspis, like the nauplius, is a specialized

larva adapted to a nektonic mode of life. Since Swinner-

ton believes that the trilobites are descended from ben-

thonic annelids, one can not but wonder why the nektonic

trochophore was not carried over instead of requiring

the development of a new and totally different free-swim-

ming larva by the trilobites. All indications derived

from the present study are that the primitive trilobites

were floating and swimming animals, that their adoption

of a crawling habit was a specialization, that the protas-

pis was nektonic because the adults were, and that the

nauplius of recent Crustacea is a similar free-swimming

larva because it harks back to ancestral conditions.

THE UTILIZATION OF ECHINODERMS AND OF

GASTEROPOD MOLLUSKS

H. P. KJERSKOG-AGERSBORG, B.S., M.S.

DEPARTMENT OF ANATOMY, LONG ISLAND COLLEGE HOSPITAL,

BROOKLYN, New YORK

Tue Puget Sound region, in the State of Washington,

is noted for the wonderful abundance and diversity of its

fauna. The region is also noted for its several groups of

archipelagoes, of which the San Juan Archipelago is an

especially beautiful one.

Around the shores of these islands, echinoderms are

found in great profusion. Particularly noticeable are

the common forms of starfish, sea urchins, and sea cu-

cumbers. The most common starfish are Piaster ochra-

ceus and Evasterias troschelli, which show, respectively,

considerable substantive and merestic variation. In the

environs of Bremerton, the latter finds more congenial

conditions than any of the other common species, and

there it occurs in a ratio of 25 to 4 of the former, while in

the San Juan island group, P. ochraceus is by far the most

numerous. Besides these two species, P. paucispinus and

many others are also found, but in smaller numbers. The

twenty-rayed starfish, Pycnopodia helianthoides, occurs

quite plentifully at various places, e.g., Bremerton, Grif-

fin Bay, East Sound, etc. Sea urchins, Strongylocentro-

tus drébachiensis, S. purpuratus, S. franciscanus are very

numerous, especially the former. At low-water, S. dro-

bachiensis may be seen in the bays of the northern part

of the sound in large patches, and at a depth of only four

meters. S. franciscanus, which becomes very large—7 to

13 centimeters in diameter—is found just below low-water

mark; I have seen it in large numbers in the vicinity of

the Biological Station at Friday Harbor. The most

noticeable species of sea cucumbers are Cucumaria japon-

ica (Semper), C. chrondjelmi (Theil), and Stichopus cali-

414

No. 634] ‘UTILIZATION OF ECHINODERMS 415

fornicus (Stimpson) Edwards. C. chrondjelmi is exceed-

ingly abundant near the Sucia Islands. All these species

may be obtained by dredging, and C. japonica may be

picked by hand at low-tide.

Of all the echinoderms, common starfish, Piaster, Evas-

terias, etc., are most easily obtained. They occur within

the lower limit of the average ebb-tide, and sometimes in

such profusion that, especially when the stars are brightly

colored, they may be seen at half a mile’s distance. Their

occurrence is independent of town sites, being determined

by the nature of food available. Shores well supplied

with barnacles usually have a large number of starfish.

And the fact that they are abundant at a distance from

towns adds to the desirability of their use as a food prod-

uct. The parts of the starfish and sea urchins utilizable

as food are the gonads. During the breeding season,

these grow enormously, so that in the starfish the body

becomes twice its normal size, the gonads completely fill-

ing the gastric cavity. The part of the sea cucumber

utilizable as food is the muscles,

Echinoderm gonads as a food commodity would be the

object of an industry of annual periodicity like the salmon

industry. As the spawning season of starfish and sea

urchins comes in the spring, the canning of the roe could

be well completed before the salmon season begins; or the

making of echinoderm gonads into caviar might well be

done along with the canning of fish, whether salmon or

otherwise. The gonads of the various species of the

larger starfish are ripe in April; those of the sea urchin,

in June, as regards species of the north Pacific coast

(Figs. 1-3).

There can be no question about the advisability of using

the spawn and muscles of echinoderm as food, even in a

country where all kinds of food are as plentiful as in the

United States. The question is rather how to utilize this

part of nature’s storehouse to the best advantage for

mankind. :

Barbier (1908) states that the natives of Madagascar

416 THE AMERICAN NATURALIST [Von. LIV

have developed a considerable industry in the utilization

of starfish, sea urchins, and sea cucumbers as food. In

1902, the marketable quantity of sea cucumbers repre-

sented a value of 175,000 francs. The province of Tulear

produced alone 30 tons, but the lack of necessary labor

prevented further production that year.

Taylor (1908) reports an interesting fact, namely, that

natural size. (Photo by

Fic. 1. Mature ovary of Hvasterias troschelii, %

author.)

the Arctic Fox of the Aleutian Islands, so highly valued

for its beautiful fur, feeds, in winter, on echinoderms, e.g.,

sea urchins.

Reagan (1907) claims that the sea urchin (Strongylo-

centrotus drébachiensis) is used by the Pacific coast In-

dians as food.

In conversation with the United States Commissioner

of Fisheries (1916) I learned that the roe of starfish is

being used in France as food and also as bait in the sar-

dine fisheries; and through Professor Kincaid, I am in-

formed that certain species of sea urchins, which in the

market of Naples are called ‘‘Frutta di Mare,’’ and in the

West Indies ‘‘Sea Eggs,’’ are sold as food, but I have not

No. 634] UTILIZATION OF ECHINODERMS 417

had the opportunity to consult literature on these points.

Brunchorst (1898) shows that a number of excellent

food fish common to the coast of Norway feed on echino-

derms, and mentions especially: Anarrhichas lupus, and

A. minor; Lycodes esmarckii; Pleuronectes microceph-

alus, and P. platessa; others not used as food fish but

which feed on echinoderms are, A. latifrons, P. cynoglos-

sus, and Galeus vulgarus. Perhaps other food fish such

as Gadus callarias and G. pollachius also feed on echino-

derms, as I have at least found at times small starfish in

their stomachs.

Carr (1907) found that out of 150 starry rays (Raia

radiata) ten contained echinoderms (Asterias, Echinus,

Fic. 2. Semi-mature ovary (largest) and spermary (smallest) of Piaster pauoi-

spinus, 24 natural size. (Photo by author.)

and Ophiocoma), and out of 12 haddock (Gadus eglefinus)

two contained echinoderms (Ophiocoma). Three out of

13 wolffish (Anarrhichas lupus) contained echinoderms.

In 1908, the same author tabulated observations on 370

common dab (Pleuronectes limanda) and showed that out

of this number, 56 contained echinoderms, e.g., Ophiuroids

and Echinoids; 5 long rough dab (Hippoglossus liman-

418 THE AMERICAN NATURALIST [Vou. LIV

dioides) out of 60 fish contained Ophiuroids; 10 out of 25

G. eglefinus, contained echinoderms (Ophiuroids and

Echinocyamus), and one gray gurnard (Trigla gur-

nardes) out of 150 fish also contained echinoderms.

From the findings of Brunchorst and Carr it is seen

that various kinds of fish feed on echinoderms, whence

the suggestion that echinoderms be used as bait. How-

Mature ovary and spermary of medium-sized twenty-rayed starfish,

Fie. 3.

Pycnopodia Pa e 24 natural size. (Photo by author.) N.B. The alveoli

are larger in the ovary.

ever, it may be that for a number of forms echinoderms

are resorted to only when other food is out of reach,

though the common dab, according to Carr, appears to

eat them during the greater part of the year. The long

rough dab feeds less on echinoderms than the common

dab, perhaps owing to a difference in migration habits of

the two.

A large part of an echinoderm industry would be bi-

products, since the main bulk of the starfish consists of

material best suited for guano. No absolute waste ma-

terial need remain; all of the animal may be utilized. In-

directly, the shell- fish industries would be benefited by

No. 634] UTILIZATION OF ECHINODERMS 419

reducing the number of starfish in regions where shell-fish

live, as various forms of starfish feed on marketable shell-

fish. Lebour (1916) makes an interesting statement:

The mussels on this coast have not many enemies, but by far the most

important of these is the starfish, Asterias rubens, which constantly

preys upon them. A formerly flourishing bed near the Tyne has lately

been exterminated by this starfish and it is a bad enemy everywhere.

Purpura lapillus [a small gasteropod] devours the mussels on the scaup,

Holy Island, and here in parts the devastation caused by this small and

very destructive mollusk is great. It does not, however, appear to be a

scourge elsewhere. The only possible way of dealing with such foes

would be to destroy all starfish whenever found, and to collect the Pur-

pura lapillus systematically, and also its spawn, and destroy both.

Kellogg (1910) records nothing favorable about the star-

fish. To him it is a pest.

The removal of these pests has always been a very difficult matter, and

no entirely satisfactory method has been devised for accomplishing it.

When the economic value of starfish is realized, depletion

of starfish may result from overfishing, and ‘‘to destroy |

all starfish whenever found’’ will be out of the question.

If it prove necessary to protect starfish, where only the

gonads are to be used, these may be removed on the

grounds, while fishing, and the starfish at once put back

into the water below low-tide level to avoid unnecessary

exposure. The operation of removing the gonads could

be carried out successfully without killing the animal,

since echinoderms possess great regenerative powers.

As male gonads may be unfit for caviar, it is worth noting

that they can be easily distinguished from the female

since the latter are of pinkish color while the former are

of light yellowish hue. The reproductive power, and

growth of starfish, are very great. According to Kellogg,

“A female starfish may, if large enough [depending on

amount of food] begin to extrude eggs during its second

summer, and many by that time attain the required size.’’

As echinoderms, on the north Pacifie coast, can be more

easily caught than any other kind of sea food, the star-

fish and some of the sea cucumbers may simply be picked

420 THE AMERICAN NATURALIST [Vou. LIV

up at low-tide, and sea urchins and certain sea cucumbers

may be obtained by dredging, the expenses connected with

their utilization as a whole should be comparatively low,

Fig. 4. Live shells of Polynices lewisii, natural size. (Photo by author.)

making it possible to sell the products at a reasonable

price.

In quoting Lebour, I mentioned Purpura lapillus as a

destructive enemy of bivalve mollusks. I now wish to

point out the possibility of utilizing destructive gastero-

pods:

Polynices lewisii, a very large gasterpod (Fig. 4), is a

great destroyer of mollusks of commercial value. Its foot

may reach the length of 21 centimeters and a width of 13

centimeters, and a depth of the body about 104 centi-

meters. It destroys oyster beds by its burrowing in them

in search of clams, but it is not known whether it attacks

oysters directly. On account of its burrowing habits, the

oystermen, at the head waters of Puget Sound, destroy

large numbers of them.

Keep (1888), speaking of Lunatia lewisii Gld., now

merged in Polynices, claims that it possesses a flint drill

No. 634] UTILIZATION OF ECHINODERMS 421

which it carries in its mouth, and by use of which it drills

into the clam or whatever mollusk it may encounter, kill-

ing the same. This, it is claimed, i§ a common habit of

members of the family Naticide of which the genera

Natica and Lunatica are best known. Daugherty (1912)

says:

Natica is another drilling sea-snail common to our coast. It burrows

in the sand for clams and bores a hole with its radula, rotating its own

body in the action.

Agersborg (1918), during the summer of 1916, observed

a number of specimens of Polynices in the actual act of

killing and eating clams. At low-tide, when rowing along

the shores of Dyes Inlet near Chico, Washington, a large

number of Polynices was found. As the tide was very

low it was possible to pick them up by using a dip-net.

Some of them, however, were not so easily removed from

the bottom as others, holding to the same by means of the

enormous foot, or having sucked down into the sand to

the depth of about ten centimeters, leaving only part of

the shell uncovered in the middle of a pit. It was soon

found that there was a definite cause for their holding on

to the bottom so firmly; these individuals of Polynices

were feeding. The process of feeding was found to be

somewhat different from that described by Keep, and

Daugherty.

As Polynices crawls along the bottom it kills any clam

it encounters by suffocation. The soft-shelled clam, Mya

arenaria, which is quite numerous in the bays of Puget

Sound, is a common victim. Hard-shelled clams, Paphia

staminea, Cardium corbis, are also an easy prey for this

ravener. In the case of Mya, the gasteropod sucks itself

over the syphon down into the sand until its victim is dead

from suffocation, and then when the clam has opened,

Polynices simply sends its proboscis between the valves

and devours the content. As for the hard-shelled clams,

the process of feeding is similar to that used when eating

a Mya but the method of killing is different. In this

case the prey is held in the ‘‘sole’’ of the foot until the

422 THE AMERICAN NATURALIST [Vou: LIV

adductor muscles are relaxed or the victim is dead, when

the feeding begins. Several dead clams, of these species

mentioned, were found in possession of Polynices, but

none of them were drilled. It is thus seen that this gas-

teropod is very decidedly an enemy of the bivalved mol-

lusks, but its method of killing clams is different from that

described by Keep and Daugherty.

Several specimens of Polynices lewisii were obtained

and brought to Bremerton, where experimentation on the

possibility of utilizing them as food was carried out. Two

methods of preparing the animals for the table were

used: first, steaming in the moisture contained within its

swollen foot, and second, breaking the shell and frying

the animal alive in butter. Hither of these methods gave

good results. By the former, a delicious broth was the

principal result; by the latter, a large piece of variant

meat. The foot, however, by either method, becomes

rather tough when cooked. As some one has held that the

meat of Polynices is poisonous, not so very much was

eaten; no ill effects, however, were felt from that con-

sumed. The idea that Polynices is unfit for food is of

course baseless, as I am informed by Professor Kincaid

that thousands of Polynices shells may be found in the

Indian kitchen-middies, which indicates that the Indians

used this mollusk as food, and as the Polynices’ shells are

found in these remains in much greater proportion than

any other shells, this gasteropod must have been widely

sought by the Aborigines; or it may be that Polynices

was formerly more abundant than any other mollusk on

our western coast. At any rate, this gasteropod seems to

have been a common diet of the Indians who lived along

Puget Sound. The tastes of Indian and white man are

not unlike in these matters, for white people eat various

species of clams, also an Indian diet, and seem to delight

in such food, as is well demonstrated by the establishment

of shell-fish canneries on our coasts.

It does not seem unreasonable, therefore, that Poly-

mnices as well will find a ready market. In fact, it might

No. 634] UTILIZATION OF ECHINODERMS 423

well be prepared as an extra delicacy and sold as such,

and in that way made to make up partly for injuries that

it inflicts on the bivalve-mollusks.

Barbier (1908) enumerates a large number of gastero-

pod mollusks used by the natives of Madagascar in va-

rious ways. Not only is the animal matter used as food,

but the shells are commercialized as well. Having enu-

merated ten species of the genus Murex, and 139 species

from different genera including Littorina, Nerita, Cyp-

rea, Pterocera, Strombus, Neritina, Turbo, Conus, Tere-

bra, Natica, Cassis, Harpa, Mitra, Voluta, Vasum, Oliva,

Fasciolaria, Purpura, Rapana, Eburna, Nassa, Ranella,

Triton, Fusus, Neptuna, Busycon, and Pyrula, all of

which are marine forms, he adds the following terrestrial

and freshwater gasteropods: Helix hemastoma L., Buli-

mus perversus L., Mulimulus multilineatus Say, Pupa uva

L., Clausilia cana Qld., Auriculus auris Mide L., Tudora

versicolor Pfr., and Helicina miltochila Cross, and says:

Tous ces coquillages servent à la nourriture des indigènes qui mangent

leur chair cuite dans la coquille sur un feu ardent sans acun assaisonne-

ment.

It is worth noting that genus Purpura which causes

great destruction of the mussel beds on the English coast,

and which was suggested by Lebour to be systematically

collected and destroyed, serves the Indians of Madagas-

car as food. Murex, Natica, Nassa, Busycon, and others

related to the gasteropod types on our coasts are being

utilized as food by the natives of Madagascar. Cycotypus

canaliculatus Verrill & Smith, 1873 (Busycon canalicu-

latus Say, or Fulgur canaliculata Gould, 1887, Dall, 1889),

is a very pernicious enemy of oysters. According to

Sumner, Osburn and Cole, 1908,

It is abundant in shallower water generally . . . pretty generally dis-

tributed throughout Buzzard Bay and Vineyard Sound. It preys upon

mollusks and is said to be destructive to oysters (p. 707).

It is still of little commercial value save that of being used

for dissecting purposes, and some Europeans, in New

424 THE AMERICAN NATURALIST [Vou. LIV

England, have ventured to use it as food, but this is by no

means a common practise. The genus Urosalpinx is

closely allied to Murex; several of its species are found

on the east coast of the United States. Arnold (1916)

says of Urosalpina cinerea:

This well-known species is regarded by Chesapeake and Long Island

Sound oystermen much in the light of a plague. These active preda-

ceous mollusks live upon bivalves, and preferably upon oysters. They

bore a small hole through the shell of their helpless victims, and then

proceed to extract the succulent, fleshy animal from within. The oyster-

men call them by the suggestive name of “ drill,” and wage incessant

warfare upon them.

Daugherty claims: ‘‘It is a feeder upon oysters;’’ and

Kellogg says in part:

There are several species of the snails that are destructive to bivalves.

Among these the large winkles or conchs of northern shores do very

The drill, or Urosalpinz, is most destructive to young oysters. It seems

to be unable to bore through the shell of large individuals. . . ik

starfish, oyster drills were formerly not numerous on the New Biisland

oyster beds, but in recent years have increased greatly. In New York

Bay, and in the Chesapeake, they are abundant ... in Louisiana, a

larger drill, Purpura floridana, is sometimes very destructive.

Opinions thus seem to vary as to the destructive habits of

some of the gasteropods upon bivalve mollusks, but the

findings of Dr. Copeland (1916) are very conclusive:

Busycon reacts positively toward oyster juice, in fact, the

oyster often forms a conspicuous part of its natural diet.

All the investigators, however, seem to agree about the

habits of Urosalpinz. In view of the fact that these gas-

teropods are esculent, injurious to other marketable mol-

lusks, near large cities, and generally easily obtained, it

seems rather strange that they are seldom found in the

market. Polynices lewisii, which is still quite abundant

in the upper part of Puget Sound, is generally destroyed

by the oystermen whenever found in the vicinity of oyster

fields. Asa natural enemy, P. lewisii seems to have none

more dangerous than the twenty-rayed starfish ( Pycno-

No. 634] UTILIZATION OF ECHINODERMS 425

podia helianthoides). As a matter of fact, bays that have

none or very few Pycnopodia may have a large number

of Polynices, and bays that are well populated with this

starfish have remarkably few Polynices present. When

I later experimented on the sensitivity of Polynices to

Pycnopodia (Agersborg, 1918) I found in all instances,

that when the slug came into contact with the star, it

withdrew its foot at once. The monstrous foot, though it

seemed impossible that it could be withdrawn within the

shell, was very quickly covered thereby. Upon with-

drawing the foot in a hurry, as it does when in contact

with Pycnopodia, the periphery of the foot, which is per-

forated, throws a spray like a garden sprinkler with the

holes in the spray-disk plugged except those around the

periphery. No matter how much larger the animal is than

its shell, when all the water is squeezed out of the foot,

the former can be completely covered by the latter. In

such a condition, however, Polynices can not live very

long. It is itself easily exhausted when completely shut

up within its shell. If it is not allowed to take in fresh

water supply when it comes out to breathe it soon relaxes,

an easy prey to the gluttonous Pycnopodia. In fact, when

leaving Polynices with Pycnopodia in an aquarium, two

of the former were killed and eaten by the latter within

three days, leaving the shells and opercula.

The absence of Polynices where Pycnopodia abounds,

together with the facts observed when keeping the two in

the same aquarium, seems to indicate definitely that

Pycnopodia preys on Polynices. As mentioned above,

Polynices is a nuisance to oyster growers, even if it does

not feed on oysters, for it destroys the oyster beds by

burrowing in them; primarily Pycnopodia is a gastero-

pod feeder, and though it is quite omnivorous and may

feed on anything it happens to encounter, it is not known

whether it feeds on oysters. The question then is: might

not Pycnopodia be used as a check against Polynices in

the oyster beds? This could easily be tested out experi-

mentally: Pycnopodia could be placed on oyster beds to

426 THE AMERICAN NATURALIST [Vou. LIV

see whether it remains there or crawls away. If the latter

was found to be the case then Pycnopodia is not adapted

to feed on oysters and might then be kept on the outside

of the oyster beds as a guard against the inroad of

Polynices.

: REFERENCES

Agersborg, H. P. Kjerskog.

1918, Bilateral Tendencies and Habits in the Twenty-rayed Starfish,

Pycnopodia helianthoides (Stimpson). Biol. Bull., Vol. 35,

No. 4, pp. 232-254

Arnold, Augusta Foote.

1916. Sea-beach at Ebb-tide. Pp. 305-404. New York.

` Barbier, Camille le, M.

1908, Baquisse sur la Féche dans la province de Tuléar. Ann. Mus.

Colonial Marseille, 2 sér., 6 vol., pp. 23-

Brunchorst, Dr. J.

1898. Norges fiske deres udbredelse og levevis. Bergen.

Carr, A. M.

1907-1908. ocho of Fishes. ve Northumberland Sea Fisheries

-» Pp. 68-71; pp.

Copeland, Man

1918. jas “Oltseley Reactions and Organs of the Marine Snails Alec-

trion obsoleta Say and Busycon canaliculatum Linn. Jour.

Ezp. Zool., Vol. 25, No. 1, pp. 177-227.

ee L. S, and M. C

912. Principles of Economie Zoology. Pp. 78, 82-83. Philadelphia.

pions aed

1888. West Coast Shells. Chapter 7, pp. 45-46. San Francisco.

Kellogg, James L.

1910. Shell- fish Industries. Pp. 154, 156, 157, 289, 294-295.

Lebour, Marie V.

Dea. The Mussel Beds of Northumberland. Rept. Northumber-

land Sea Fisheries Comm., pp. 28—48, 1906.

Reagan, A. B.

1907. Some Sea Shells from La Push, Washington. Trans. Kansas

Acad met Vol. 21, Part 1, 9.

Sumner, Francis B., Osburn, Raymond D. anil Cole, Leon J.

1913. A Biographi Survey o f the Waters of Woods Hole and

nity. Part 2. Bull. United States Bureau Fisheries, Vol.

eg pp. 707-713.

Taylor, H. H.

1908. A Group of Arctic Foxes. The Museum News, Vol. 3, No. 4,

p. 59

THE VIBRATILE ORAL MEMBRANES OF

GLAUCOMA SCINTILLANS, EHR.

LEON AUGUSTUS HAUSMAN, Px.D.,

CORNELL UNIVERSITY

Glaucoma scintillans was first described by Ehrenberg

in 1838, and has received since that time but little notice,

Save as a species to be included in catalogues of micro-

fauna. The writer has found it of interest because of

the peculiar appendages borne about the mouth, i.e., the

vibratile oral membranes. Other species also bear either

one or two oral membranes, but Glaucoma is distinct in

this respect: that the membranes completely encircle the

oral aperture; are distinctly bilabial in form, and are

usually in active, characteristic motion. So rapid is the

motion of the membranes that, due to the reflection and

refraction of the light rays from the microscope mirror

which is produced, a twinkling or scintillating appear-

ance results. It is from this phenomenon that the crea-

ture has received its specific name, scintillans. —

The body of Glaucoma is ovate (Figs. 1 and 2), the

ventral surface flattened and entirely ciliated; the dorsal

surface arched, and naked. The cuticle is everywhere

longitudinally striated. The oral aperture lies in the

anterior half of the ventral surface, its longer axis

slightly oblique, though in many individuals the longer

oral axis is practically parallel with the longer axis of

the body. The nucleus is spherical, its diameter being

approximately equal to the long axis of the mouth, and

situated in the central portion of the body, often, how-

ever, slightly nearer the posterior extremity, A sec-

ondary nucleus, roughly a fifth or sixth of the diameter

of the primary one, can frequently be made out. The

contractile vacuole is usually single, rarely double, and

situated in the posterior third of the body. In shape,

Glaucoma is more constant than many of the other cili-

427 :

428 THE AMERICAN NATURALIST [Vou. LIV

ates. The adults are usually almost perfectly oval or

ovate; the young are apt to be often spherical. In size

the adults vary between 70 and 75 microns in length.

The writer has noted a few individuals that were 78-80

No. 634] ORAL MEMBRANES OF GLAUCOMA 429

microns.' These, however, were very rare, and did not

number more than perhaps a dozen individuals among

several hundred.

Glaucoma is a fairly common protozoan. Its usual

habitat is in stagnant water, particularly pond water in

which there is considerable decaying aquatic vegetation.

The writer has found it abundant in the brackish water

of a peat swamp. It commonly occurs wherever there

are also numbers of small flagellates. Samuelson (’57)?

says that he has reared large numbers of them in an in-

fusion made from cabbage leaves and distilled water.

Cultures of Glaucoma were prepared in the laboratory

by the writer by allowing water, containing cattails, ponds

lily leaves, and Elodea to become putrid. Numerous

Glaucome were found congregated in the grayish scum

that overspread the surface of the infusions, where they

were engaged in feeding upon the bacteria, which seems

to form the bulk of their food.

It was necessary to keep individual Glaucome under

observation over extended periods of time, and this was

accomplished by means of a device whose utility was such

as to warrant a description of it here (Fig. 3). A piece

of lens paper, or of thin typewriter manifolding paper,

Fic. 1. Mature Glaucoma erare D, sealing material (parafin or

ventral aspect. A, = Canada balsam).

let; B, vibratile oral SPERIA Fic. 4. The vibratile oral membranes,

or outer lips; O, ing to bseat or outer shea with the opening

cavity (or mouth proper), or inner of the mouth ioe beneath them.

ips; D, nucleus; Æ, contractile Raunt Gin gcat

vacuole ; striations of the Fie. 5& The scans oe dissociated

cuticl viene peek ea a o»

cu e. ine rep

Fic. 2. Outline drawing of the lat- konta the position: of the wurtace pat

i aspect of Glaucoma scintil- the caticla.

B, ter lips; D, nucleus; Fic. 6

the ventral surface may often be

depressed.

Fic. 3. Micro-aquarium. A, circle of

thin lens paper, bearing a src

lar opening; B, O, the cover glass:

1Eyferth (1909) ie the length of Glaucoma s

0 microns!

tween the extremes, 2

the length of toy alae just afte

2 Quart.

A single outer a showing

tions

k seen

A, outer lips; B,

opening of mouth

cintillans as lying be-

The lesser figure probably refers to

r division.

r, Mic. Sci., Vol. 5, 1857, p. 19.

430 THE AMERICAN NATURALIST [Von. LIV

the shape and size of the cover glass, with a small cir-

cular opening cut in its center, is soaked in hot parafin,

drained, and placed upon a glass slide. After the parafin

has cooled a drop of water containing the organisms

is placed in the center of the circular opening, and the

cover glass applied. The drop should flatten out just

sufficiently to fill completely the space between the cover

glass and the slide inside the circular opening. The

cover glass must now be sealed down about its edge by

means of a camel’s hair brush dipped in hot paraffine.

Such a device the writer has called a micro-aquariwm and

has found its employment of the utmost use. In it scores

of Glaucome were kept alive for as long as eight hours.

For quieting the movements of Glaucome thick gela-

tine solution was used, and a drop, mixed with a drop of

water containing the organisms, placed on a slide and

examined under the 16 mm. objective and allowed to re-

main uncovered until evaporation had rendered the mix-

ture of such viscosity as to retard the animals suff-

ciently. The cover glass was then applied and sealed

down with either hot paraffine or castor oil to prevent

further evaporation.

For killing without staining and without distortion

either a one per cent. aqueous solution of copper sulphate,

a ten per cent. solution of alcohol, or a fifteen per cent.

solution of chloretone was found satisfactory. The best

of all killing reagents for Glaucoma, however, was found

to be a two per cent. aqueous solution of alum.

Intra-vitam staining was accomplished with an aqueous

solution of Bismarck and methyl green; while for stain-

ing after killing there were utilized: iodine, methyl green,

methyl blue, Bismarck brown, and safranin.

The appendages which make Glaucoma of especial in-

terest are the oral membranes. These are present in the

form of two hyaline, lip-like structures, lying one on

either side of the buccal evaity (Fig. 1). For conveni-

ence these will be referred to as the lips. In form they

are roughly rectangular, and approximately twice as

No. 634] ORAL MEMBRANES OF GLAUCOMA 431

long as broad, with one extremity enlarged and rounded,

and the other slightly narrowed and with a crescentric

edge (Fig. 4). They are joined at their base, at either

end, and project outward from the body so as to be

plainly visible in profile (Fig. 2). Usually the lips are

in constant motion, but occasionally may be seen inac-

tive, and when so are normally closed (Fig. 1).

When the body of Glaucoma is disintegrated with

strong alum solution, or copper sulphate, it is sometimes

possible to isolate the two lips together, they apparently

being more resistant than the rest of the body. When

this is done, it can be seen that they are more nearly oval

in outline, possessing an extended, fin-like portion, which

projects into, or beneath the cuticle (Figs. 4 and 5).

That the origin of these membranes may be sought for

in the fusion of rows of cilia situated on either side of

: the buccal cavity, is suggested by the fact that each lip

exhibits striations running at right angles, or nearly so,

to the longitudinal axis (Fig. 6). These striations are

broadest at their bases, and narrowest at their tips, and

recall to mind the rows of stout oral cilia found among

so many of the infusoria.

Between the bases of the lips lies the opening of the

buccal cavity, or mouth proper. Its edges, which may

be termed the inner lips, are also capable of a motion

which will be described later (Fig. 7).

The movement of the outer lips consists of a rapid

opening and closing, and is best described by the word,

beating. The rate of the beating is apparently under

control of the animal, and varies at different times.

Under normal conditions the beating of the lips is very

rapid. The hyaline membranes, even when at rest, seem

to glisten, possibly due to the striations which refract

the light in different ways, and when in rapid motion

produce the pretty scintillating effect which has given

the creature its name. Observations made by the writer

of the rate of opening and closing of the lips, showed

that it varies from eight or nine times per second, through

432 THE AMERICAN NATURALIST [Vou. LIV

all the lessening degrees, to actual cessation. Usually

the beating, no matter what the rate, is regular, t.e., the

durations of opening and closing being of equal longus

This, however, is subject to modification, apparently at

will, and individuals are sometimes, though not fre-

quently, encountered in which the lips beat with great

SECOND BEAT THIRD BEAT FOURTH BEAT

i o

UNK

| FIRST SECOND ; | SECOND SECOND |

| | |

No. 634] ORAL MEMBRANES OF GLAUCOMA 433

rapidity for a few seconds, then flutter slowly, then close

for a second or two, and then begin slowly to beat again.

From experiments which have been made the conclusion

is drawn that the rate of the beating of the oral mem-

branes in Glaucoma is directly proportional to the

strength of the food stimulus received in the buccal cav-

ity, or possibly through the cilia in the region of the

mouth.

The lips do not open and close with their ectal edges

parallel. The process of closing takes place with a wave-

like motion, the anterior edges of the lips meeting first,

and the wave of motion thus initiated traveling toward

the posterior ends, until, when these finally meet, the an-

terior edges are open again. The process of opening,

therefore, takes place in the reverse direction. Fig.

diagrams six stages in a single beat of the lips, and in

Fig. 9 are represented four beats analyzed with respect

to their cycles of contacts and partings.

The opening and closing of the inner lips, or edges of

the mouth proper, take place, apparently, in a similar

wave-like manner, and in the reverse order or motion

from that of the outer lips. This sequence of motion

may aid in forcing food into the buccal cavity, since

whenever any given portion of the buccal cavity is open

Fig. 8. Six stages in a cycle of the of the lips are in contact. Stages

opening and closing of the aye 1, 2, 3, 4, 5, in this figure cor-

lips. The edges of the lips respond respectively to stages 1,

represented diagrammatically ee 2, 4, 5, 6, in Fig. 8.

show how the waves of contact Fic. 10. Five stages of the cycles of

nd parting follow each other opening and closing of both the

Stage 7 begins the cy ane outer and inner lips diagram-

Fic. 9. Graphic representation of the matically represented, and super-

relations of the cycles of opening imposed to show their reverse re-

and clos of the outer lips. lationshi he o-lines r

sng og ae aaa each S the of the aps ips, and

the lines rosses and circles Fics, 11, 12, 13 show the various

show how the waves of contact and directions from which water cur-

parting sweep up and down them. ts, b food, can urged

Four stages are given for each towards an individual by the

beat—represented by the four action of the cilia.

vertical lines of the lips in each Fig. 14. Group of Glaucome clustered

beat. The longer vertical lines about a mass of debris and bac-

represent the stages when no part teria, feeding.

434 THE AMERICAN NATURALIST [Vou. LIV

to receive food, the corresponding portion of the lips

above is closed, to force it in. Fig. 10 shows diagram-

matically the relationship of the cycles-of opening and

closing of the outer and inner lips. It will be noted that

once during each cycle (at its middle) both the outer and

inner lips correspond, for. an instant, in attitude, the

same portions of each being in contact (Stage 3, Fig.

10). In some individuals the inner lips seemed not to

open and close at all, but appear to remain permanently

open. Observations on the motions of the lips were made

while the animals were incarcerated in very thick gela-

tine, and all of their movements much retarded.

The ciliary action of the anterior portion of the body

can apparently be regulated according to the desires of

the animal and water currents, bearing food, can be

drawn toward the mouth either from directly in front of

the creature, from the side, or from behind (Figs. 11, 12,

and 13).

Glaucoma feeds upon minute flagellates and other

minute protozoans, fragments of débris, tiny diatoms

- and desmids, but the bulk of its food seems to consist of

bacteria. Fig. 14 shows what may frequently be ob-

served in a culture, i.e., a group of individuals clustered

about a mass pomponed mainly of bacteria, . pressing

their lips against the substance, and urging portions of

it into the buccal cavity by the combined action of the

lips, and oral cilia. When feeding in this fashion the

movements of the outer lips resembles somewhat the

biting and chewing motions. of the mouths of the higher

animals.

Curiously enough the complex development of the ex-

terior oral appendages seems to have no parallel within

‘the buccal cavity, since neither supporting pharyngeal

rods, nor even any definite pharynx, could be discerned.

NOTES ON THE BIONOMICS OF MELLITA?

DR. W. J. CROZIER

UNIVERSITY OF CHICAGO

OBSERVATIONS already recorded? led me to devote some atten-

tion to the movements and the coloration of Mellita sexies-per-

forata, and to the injuries which are in nature inflicted upon the

individuals of this species. The findings incidentally supple-

ment and confirm some deductions made in the notes cited,’

and serve to indicate several directions in which further study

would seem promising.

Mellita lives more or less completely buried in the sand, in

channels between islands, at the outlets of sounds, and between

the shore and the inner reefs; but always in places where there

is a tidal current. The character of the bottom, which may lie

2 to 6 fathoms beneath low water, varies from shell-sand, gray-

white and usually muddy, to dark brownish mud. Young and

adults of all sizes up to 13 em. transverse diameter occur in

company. The older individuals burrow more deeply than the

young ones, the latter frequently lying freely exposed on the

surface of the sand. In stormy weather, all the Mellitas dig

themselves deep into the mud, to a depth of perhaps 8-9 cm.

In the laboratory the older individuals burrow more quickly

when exposed to bright sunlight than they do in the dark. He-

liotropism, when horizontal light is used, is not precise; younger

individuals tend, on the whole, to move away from a source of

horizontal light. Normally, light coming from above may be a

significant source of stimulation; this was not adequately tested.

The low degree of photic irritability toward horizontal light

probably accounts for the fact that no photic orientation, strictly

speaking, was noted; such orientation might be expected, since

the nature of Mellita’s locomotion would make it possible.

In locomotion on a solid surface, that part of the body ana-

tomically the anterior is always carried ahead. The ‘‘leading’’

1 Contribution from the Bermuda Biological Station for Research, No. 118.

2 Crozier, W. J., 1918, ‘‘On the pigmentation of a Clypeastroid, Mellita

sesquiperforatus Leske,’’ AMER. NAT., 52, 552-555. 1919, ‘‘On Rege

tion and the Re-formation of Lunules in Mellita,’?’ Amer. Nart., 53, 93-96.

435

436 THE AMERICAN NATURALIST [Vou. LIV

point may shift progressively from side to side during an ex-

tended act of creeping, but at all times some part within the two

anterior interradii is in advance. Mellita can, however, pivot

in complete cireles, in either direction, about its mouth as a

center; it also carries out successive incomplete swings, alter-

nately opposite in direction. Movements of the latter type,

together with the relatively fixed direction of creeping, namely

anteriorly, are important for the act of burrowing, and are cor-

related ki some notable growth-changes in the form of the

whole

During burrowing the anterior end is in advance. The process

of concealment is a fairly rapid one, a large specimen being able

to disappear completely in less than 15 minutes, although two

to three times this interval may be employed. Not only do the

spines and tube feet assist in clearing a way through the sand,

by moving the individual sand grains, but, in addition, the

body as a whole is used as a digging instrument. The disk is

repeatedly rotated 30° or more to either side of the sagittal line,

Fic. 1. Outlines of three young Mellitu sexies-p ta, showing the approx-

imately circular outlines of the body; between the ‘s pecimen ens of intermediate

and largest size is an antero-posterior section of the former. Attention may

ambulacral lunules, although these lunules, in M. sewxies-perforata, are formed

by the meeting of dorsal and ventral invaginations, not by biog inclusion of

reéntrant marginal notches—as is the case in other Mellitas., 1

with the result that, since the very numerous spines and tube

feet are simultaneously pressing the disk forward, the animal is

actually insinuated, or ‘‘slid,’’ into the ground. This maneuver

is especially effective upon a muddy bottom, where movement of

sand by the tube feet and spines would be a slow and inefficient

‘process.

The young Mellita is quite thin and wafer-like, its outline

practically circular (Fig. 1). As the animal grows, the thick-

ness of the body increases, although the edge of the disk remains

thin. In many cases the outline of the disk is still almost cir-

No. 634] BIONOMICS OF MELLITA 437

cular even in specimens of maximal size, and the ventral surface

of the disk practically flat (Fig. 2).» It frequently happens,

however, that the central region of the body becomes relatively

thicker than in the flat, circular sea-plates, and in these indi-

viduals there are several noteworthy departures from the typical

structure. Anteriorly the disk is more wedge-shaped in vertical

Fic. 2. Outlines of two individuals with circular type of margin, with a

Sagittal section of one of them (A). (x2%.) Im this section, and in the

following ones, it will be observed that the anterior margin of the disc is more

bluntly rounded than that at the posterior edge—an advantage, presumably,

Since the burrowing portion of the periphery is thus made stronger.

section ; the anterior antimere projects forward, forming a sharp

‘nose,’’? or entering point, which presumably facilitates bur-

rowing (Fig. 34). The antero-lateral radius on either side

438 THE AMERICAN NATURALIST [Von LIV

sometimes forms, in addition, a more or less projecting ‘‘shoul-

der” (Fig. 4). These departures from the smoothly circular

form, together with the ‘‘arched’’ construction of the test in

some older specimens (Fig. 4), derive their effectiveness for

Fie, 3. Outlines of ee individuals with aera anterior radii, and a sagittal

one of them. (x %.)

burrowing from the partial rotation or ‘‘swinging’’ of the disk

during this act.

The changes here noted i in the form of the body. of some jidi

viduals with advancing growth, are not detectably correlated

with peculiarities of habitat. The different types occur with

about the same relative frequency whether the bottom is of shell

sand or of brownish mud. The local character of the bottom

No. 634] BIONOMICS OF MELLITA 439

changes somewhat, however, from time to time, being more

muddy and less sandy in some years than in others. One may

nevertheless entertain the idea that genetic factors are con-

eerned in determining the growth-changes in the body-shape of

some individuals. This matter should be studied in a larger

series of specimens than I have been able to secure in the time

devoted to this work. Especially interesting is the fact that this

I . Outline and sagittal section of a Mellita pointed anteriorly and with

lateral “shoulders” ; the section shows the tendency toward an arching of

the test in some of these cases. p

species occurs in the fossilized state above the beach zone along

the shores of islands in Great Sound. The seven large fossil

tests I have examined were all of the almost perfectly circular

type (cf. Fig. 1).

In order to follow more precisely the course of growth-changes

in Mellita, I endeavored to derive the curve of its growth, and to

fix the average duration of its life. The results, which are pro-

yisional only, are given in Fig. 5. Specimens were measured

from one locality—Cobbler’s Cut, Spanish Point—in September.

The transverse diameter was measured, since it is less subject

than is the antero-posterior to fluctuations induced (a) by the

tendency, already noted, to form a projection at the anterior

antimere,. and (b) through injuries suffered at the posterior

inter-radius. From the modes in the frequency distribution of

Sizes, it was deduced that at 6-months M. sexies-perforata meas-

ures 2.2 em. in transverse diameter; at 1.5 years, 5.7 cm.; and so

on, as indicated in Fig. 5. It seems possible that the average

duration of life is about 4 years, according with the fact that

440 THE AMERICAN NATURALIST [Vou. LIV

the majority of the dead tests, which may be collected in quan-

tity, are about 10 cm. in transverse diameter. From these esti-

mates of age in Mellita, the described growth-changes in the

form of the body begin to become obvious during the third year

of an individual’s life; in some specimens they do not occur

at all.

During the middle years of its life, Mellita has a considerable

capacity of withstanding injuries (cf. Fig. 6) and of repairing

damage done to the periphery of its body. I have already noted

the fact that injured and regenerating individuals are found to

have been damaged at the posterior end only; the wound illus-

| TRANSY. DIA.,

CMS.

10 >

= °

a Pe ee

1 2 3 4.9

Fic. 5. Possible growth curve of M. sevies-perforata.

trated in Fig. 6 is unusually far forward. It was previously

suggested (Crozier, 1919) that the posterior incidence of in-

juries resulted from the circumstance that the posterior end was

more freely exposed than the rest of the body. Observations in

aquaria and on sand-beaches have shown this explanation to be

probably correct. Burrowing takes place with the anterior end

in advance, the edge of the posterior inter-ambulacral area fre-

quently remaining exposed long after the rest of the creature

has been concealed beneath the sand. The experimental tests

were made with active, healthy, specimens exhibiting no green

areas upon their surface (cf. Crozier, 1918). During burrow-

ing, the body of the sea-plate is moreover tilted, anterior end

down, at an angle of 10°-20° with the surface of the sand; so

No. 634] BIONOMICS OF MELLITA 441

that the exposed posterior or postero-lateral margin projects in a

not inconspicuous way above the general level of the sand.

In the light of this behavior, and particularly because of the

injuries found to have been suffered by the sea-plates, it be-

comes pertinent to inquire whether an adaptive (concealing)

value attaches to the pigmentation of these animals. The oc-

currence of injured specimens, and that in some degree of fre-

quency (about 60 per cent. of those above 9 em. transverse diam-

eter), would seem in itself to be valuable evidence upon this

point. There are several other important considerations to be

derived from the nature of the pigmentation of Mellita.

Until it has attained a diameter of 7 to 8 cm., the young M.

sexies-perforata, seen from above, is practically colorless; the

integument contains no pigment,

although the yellow-brown stomach

may show faintly through the test.

Upon attaining this size, a light coffee-

tint, evenly distributed upon the

dorsum, makes its appearance; previ-

ously, at about 5.7 cm. diameter, dark

brown pigment begins to show on the

ventral surface, on each of the poly-

gonal areas surrounded by the tube-

foot channels. Pigment thus begins rye, 6. Illustrating natural

to be deposited on the ventral side; i a e i

and it continues to be denser (darker) (x 14.)

on this side than dorsally. The in-

tensity of pigmentation increases progressively with age, until,

in animals on 12-13 cm. diameter, a very dark brown hue is

attained.

M. sexies-perforata, at Bermuda, does not frequent bottoms

supporting a good growth of eel-grass. If in other regions it

Should be found to do so, the alkali-greening substance occur-

ring in this species (Crozier, 1918) and in Clypeastroids gen-

erally, might be adaptively concerned in pigmentation. But no

green hues are normally evidenced by this species at Bermuda.

If the somewhat uncertain records of a green coloration in nor-

mal mellitas of this species at more southerly stations are con-

firmed, and found related to an eel-grass habitat, a direct phys-

ical explanation is at hand to account for the greening (cf. Cro-

zier, 1918). The normal brown hue seems due to the integu-

442 THE AMERICAN NATURALIST [Vou. LIV

mentary accumulation of some metabolic waste. This view in

itself does not preclude the possibility of an adaptive deter-

mination of the pigmentation; it would be curious indeed if an

internal coloring-matter were not the result of metabolism. In

order to remove the possibility of an explanation for the colora-

tion in the customary terms of adaptation, it must be shown that

the pigmentation in question is an wnconditioned result of

metabolic processes—unconditioned, that is, by the ‘‘need’’ for

concealment and the like. It is, therefore, important to observe

that: (1) the degree of pigmentation increases with age; (2)

the variously colored individuals live side by side; (3) the tilt-

ing of the body exhibited during burrowing, and the exposure

of the posterior margin of the body owing to the incompleteness

of this act, are not compensated by counter shading—the ven-

tral surface is more darkly colored than the dorsal; and (4), the

region known to be differentially exposed inthis way is found

actually to bear evidence of. damage, in a goodly proportion of

individuals. The exact origin of these injuries remains obscure,

but is not of primary importance here.’

The general physiology of ;pigmentation in the muna dallare

and sea-plates, and the possible evolutionary significance of the

growth changes in body-form noted in. this paper, should. be

made the topics of further studies:

DYER ISLAND, BERMUDA, 1918.

3I have good reason to believe that the injured mellitas ‘were not dase

aged as the result of antecedent dredging operations in the same areas.

THE INSECT ENEMIES OF POLYPOROID FUNGI

DR. HARRY B. WEISS

N. J. STATE DEPARTMENT OF AGRICULTURE

In the past, entomologists have paid littlé or ‘no attention to

the fungus hosts from which they collected insects, and their cap-

tures are usually recorded as having been taken on or in a

‘“‘fungus.’’ This is a very indefinite term which includes a large

number of species and gives no clue whatever as to the identity

of the host. Years ago when mycologists were few and far be-

tween, it was undoubtedly difficult for entomologists to have the

fungi identified but at present this excuse will no longer hold

and there is no reason why such hosts should not be specified.

What appears to be a definite relationship between certain

fungi or their fruiting bodies and insects has been observed in

the past by both entomologists and mycologists.. The spores of

certain fungi were found to germinate in certain insect burrows

and infection in some cases took place through insect apertures.

In other eases, certain’ insects were observed to be present with

certain fungi, both on a common host. Whether they acted to-

gether, independently, or followed each other i in | connection with

the death of the host is a subject for further, stu

The main object of this paper is to call ton. to the differ-

ent groups of insects which are found associated with polyporoid

fungi and to urge that the hosts be recorded specifically or as

near that as possible so that future workers will be in a position

to digest the information intelligently after a large enough mass

has accumulated. This paper is really a summary of the ob-

servations made during a year’s collecting pf fungus insects in

New Jersey. i

The Polyporacee includes those forms in which: ‘the hymeneal

surface is generally spread over the inner.surfaces of pores or,

narrow tubes, sometimes over folds or shallow depressions be-

tween vein-like reticulations occasionally more or less lamel-

loid.’": The sporophores vary considerably, are often very large

and usually tough, and found chiefly on wood in the form of

brackets. of various sizes and shapes. The members of this family

are found on both living and dead wood of deciduous and- coi

1 Duggar, B. M., ‘‘ Fungous Diseases of Plants.’’

443

444 THE AMERICAN NATURALIST (Vou. LIV

A, Fruiting bodies of Polyporus sulphure

B. Horosi iad of Dædalia quercina on she yo ae tie; rarely attacked by

insects.

0. Sporophore of Polyporus betulinus on birch

omes igniarius on aspen

( gures er Von Schrenk and Spaulding, Bul. 149, U. S. D. A. Bur.

dus.)

No. 634] INSECT ENEMIES OF POLYPOROID FUNGI 445

niferous trees and as a class are very destructive to trees and

timber.

New Jersey is not particularly rich in this group, only some 50

species having been found up to the present time and the state

has been fairly well collected over. Many of these were taken in

what is known as the Piedmont Plain section and while this area

is largely under cultivation, it has many large swamp areas and

the forests are deciduous. The Pine Barren section of the state

was almost devoid of polypores and in the other sections they

were found in carying numbers, depending on the size and loca-

tion of the forested area. Several sections of the Piedmont Plain

yielded the most and the species were by far more numerous here

than in any of the other sections of the state.

Of the 50 different species of polypores collected 80 per cent.

were found to be infested by insects, which were distributed as

follows: Of a total number of 74 species, 59 belonged to the

Coleoptera, 1 to the Hemiptera, 3 to the Lepidoptera, 5 to the

Hymenoptera and 6 to the Diptera. Of the 6 species of Diptera,

2 were crane flies found associated with soft, watery polypores,

3 were fungus gnats and 1 was a member of the Ortalide.

of the Hymenoptera were parasites of beetles. The 3 species of

Lepidoptera belonged to the family Tineid@ and the one hemip-

teron was the flat bug Aradus similis found on Polyporus betu-

linus and Fomes pinicola. In the Coleoptera 17 families were

represented, according to the following table:

COLEOPTERA ASSOCIATED WITH POLYPORES

Number of Species Found

‘amily on or in Polypores

FIFGTOMRIUG ci inne creisteis iski

SCALING GR ss as See ees 3

SOMONE ec Os cs ee aes 2

BOUD sie a oo ee 4

MycetophagidD oo. orice ek 3

EE O 2 bes, owes eee cs 1

PSO no ska eh eed nee 3

ME foo ee cy ae ea 6

pan an D oo i et eee 2

Pree ee a ra Pe 3

ORO PON GN 0 i ee eee 1

OMO ican Sees e Pos ar 16

ae e E TaD A E re ce 2

LOODI Go ole tee ss vast 6

PROTA VIG ee i cae 4

Moriglbdae is aeo aee Os 1

Anthribide oe ees os a 1

446 THE AMERICAN NATURALIST _ [Vou LIV

With the exception of the species belonging to the Histeride

and part of the Trogositide, which are predaceous, it is extremely

probable that most of the remainder are fungus eaters; as some

were taken breeding in and others on or in the fungi. In addi-

tion to what might be called the fungus habit of some of the

members of the above named families, it might be of interest to

note other family habits in a general way and this can be pre-

sented best in a tabular form.

OTHER FAMILY HABITS OF COLEOPTERA FOUND IN POLYPORES

Family l Habits of M

Hydrophilide ......... Aquatic and terrestrial, found in moist earth,

ng, decaying vegetatio

Staphylinidw .:.......: Varied, predaceous, eni on decayed vegetation.

oaphidiidæ 6.660.084 Living in rotten wood, gill fungi.

Seroty lide aias iaaa In fungoid growths, stems of plants.

iio ora towne « Under bark and in fun

Dermestide ........... n dry animal matter aia vegetable products.

Histeride aay ees 6 Traas:

PON o Sees Varied, Fig beetles, in fungi or dry animal and

veget rane

Progositid®. yes cece css Preðaceous, a few in granaries, fungi.

E oas eoa h On dry animal iua ESER ‘pibdaslé

Oey Gam 2 yen ea as ys In dry “oi.

CNA aa In fungi or wood penetrated by fungi.

Scarabadide .......... Varied, in excrement, decaying vegetation, etc.

Tenebrionide ......... Scavengers, on dead or dry wood, vegetable prod-

ucts, in granaries.

Melandryide .......... In dry vegetable matter

MordoMaw oa.n On flowers, dead trees, in plant stems.

Aithrihide saan On dead wood, on fungi.

The members of the Cisidæ and Mycetophagidæ appear to be

the only ones confined almost exclusively to fungi. It is quite

probable, however, that such members of the other families as are

listed as occurring under bark and in dead wood are feeders on

the fungus hyphae which penetrate such places.

Many of the polypores, especially after they have matured, are

dry, tough, woody or leathery, although some are soft and watery.

In most cases the entire sporophore is consumed by the beetles

and their larvæ, or so riddled that it weathers away rapidly. In

many instances the partly eaten sporophore affords hibernation

quarters for the larve or adults during the winter and food the

next season until fresh fruiting bodies are produced.

Certain species of polypores appear to be more attractive to

insects than others and the following table gives a list of

fungi, together with the numbers of insects in different orders

found associated with each fungus.

No. 634] INSECT ENEMIES OF POLYPOROID FUNGI 447

_POLYPORES AND INSECTS FOUND ASSOCIATED WITH THEM

oleop- | Lepidop- = Hemip-

Fungus tera No. | tera No. tera No, Total

Species | Species | Paate Species

Polyporus sooner gene bree ee 1 1

malis gate ea bers 1 1

4, rag tania Bul. PETRE RE 8 1 9

s lnt Eroa N ii 11

i sulphureus Bul........ 2 1 3

sae fumosus Per. s... us, 2 2

a amorphus Fr.......... 2 2

ny, ifer Schw...:.... 1 1

2 tulipiferus Schw....... 1 1

T amenus Fr........ 3 3

x BLCOLOT Tas ."ow sika shires 23 23

m hirsutus WE, ia: 5 1 6

ne RCRTOUR ET 644 4 cs 4 2 6

Ni borealis Fre ecco sc nies 1 i

x chioneus Fr........... 2 2

7 albellus Peck ........'. 6 1 7

i galactinus Peck....... 1 1

F cinnabarinus Jacq. .... 3 3

n lucidus Leys:......... 3 1 4

$ curtist Berk. ......... 1 1

u WO Mar iroi 3 1 1 5

pr graveolens Schw. ...... 1 1

4 hispidus Bul.......... i 1

“i gilvus Schw...:......- 10 10

cuticularis Bul........ 4 4

Fomes pinicola Swen.........4.: 1 1 2

PT DRO oe es R 1 1

“fomentarius L............ 1 1

narium n, e is ss 2 1 3

i lobatus Bebe or o a 1 1

“ - applanatus Per,.......+.- 3 3

“om GE a ee E 1 1

S WELAN eek 1 1

Dedalia unicolor Bul. .......... 1 1

athe tlgs Babee ee 3 :

es WG pay Gta ets 1

Livia earning Bs oe a 8 £ 2 1l

PRTG PY. occ sc 6 3 2 1 ”

Baie (eee ee ieee 2 2

From this table it will be seen that Polyporus versicolor, Poly-

porus berkleyi, Polyporus betulinus, Polyporus gilvus and Len-

zites betulina are all insect favorites, especially Polyporus versi-

color with 23 species to its credit. Just why these species are so

attractive to the Coleoptera is a subject for further study. In

fact any discussion at this time of the relationship between in-

sects and fleshy fungi would be unwise on account of a lack of

suitable data and the above material has been presented in the

hope that it may stimulate interest in a subject which has long

been neglected and which contains interesting and perhaps eco-

nomic possibilities.

SHORTER ARTICLES AND DISCUSSION |

NOTES ON THE NEMATODE GENUS CAMALLANUS

RECENTLY a paper by Dr. G. A. MacCallum entitled ‘‘ Notes

on the Genus Camallanus and Other Nematodes from Various

Hosts’’ has come to my attention. It is dated July, 1918, and

appeared in Zoopathologica. I have carefully investigated the

date of the paper and find that although it appeared in the July,

1918, number of Zoopathologica it was not received at the Library

of the Bureau of Animal Industry until August, 1919, and at

that time neither the John Crerar, the National Museum Library,

the Library of Congress, nor the New York Public Library had

received their copies. The Secretary of the New York Zoological

Society stated that the edition was sent to Dr. MacCallum, Oc-

tober 14, 1918, and as nearly as I can learn was not mailed out

until August, 1919. In a personal letter Dr. MacCallum stated _

that the paper was ‘‘partly issued on July 1, 1918.’’ My paper

on Camallanus americanus was mailed out on August 13, 1919,

and since I can not obtain a definite statement as to the date on

which MacCallum’s paper was mailed, it is impossible for me to

state which paper actually has priority of date. MacCallum’s

paper was unknown to me at the time my monograph on C. amer-

tcanus (1919) was published; hence it seems that I should dis-

cuss the form described by MacCallum, since some of my con-

cepts concerning the genus and its species do not conform with

his observations.

In the first place, attention should be called to the fact that

MacCallum was undoubtedly misled by the brevity of a prelim-

inary paper by Ward and Magath (1917) into thinking that we

believed the two species described were the first from America,

as MacCallum asserts. We were well aware of the fact that Leidy

(1851) had found the genus, under another name, many years

before and had named several species from America. At the

time we had many records of it and a great deal of material and,

in fact, considered it a common parasite. I have gone over the

paper quite carefully and can not see why MacCallum should

say that the ‘‘general tenor’’ of our paper implies that the worm

is rare.

MacCallum apparently places the genus Camallanus in a sub-

448

No. 634] SHORTER ARTICLES AND DISCUSSION 449

family within the family Strongylide; I am sorry to disagree

with him, however, on fundamentals. He bases his argument on

four statements:

1. These worms live in the same organ. However, so do many

other worms, trematodes, cestodes, and so forth.

2. They have identical habits and attach themselves to the

mucous membrane in the same manner. The true situation is

clearly set forth in Looss’s (1905) monograph on the hookworm

and in my paper on Camallanus americanus. Ward (1917) has

called attention to the fundamental structural difference in the

buccal apparatus of the Strongylide and I have pointed out the

various methods of attachment to the mucous membrane. The

members of the genus Camallanus are blood suckers; this may be

true of some strongyles, but not of the hookworm. Looss has

shown clearly that it is not a blood sucker and gets blood only

incidentally as it feeds on the mucous membrane of the host.

3. The muscular pharynx or upper part of the esophagus is

essentially the same in both types. This part of the esophagus is

the same in all the Myosyringata.

4. The structure of their mouths MacCallum believes to be

essentially the same. Ward and I have called attention to the

basic fact that the mouths of the strongyles are built up on the

circular plan, that they hold fast by suction and then shave off

the mucous membrane with additional structures, such as in-

ternal cutting plates of the hookworms. In the genus Camallanus

the mouth is built up on a lateral plan. The valves are in truth

jaws and bite; suction is secondary and is produced, as in all

Myosyringata, by the action of the esophagus. >

It would lead me too far astray to take up all the differences

between the families Camallanide and Strongylide because they

even belong in different superfamilies, but I may point out the

fact that the former are viviparous forms, while the latter are

oviparous, that the Camallanide have but one single ovary and

the males genital ale, while in the other family the females have

two ovaries and the males have burse. These are such im-

portant facts in the structure of nematodes that were there no

other points of difference, such as the double character of the

esophagus in the Camallanide, the heavier character of the

spicula, and the lack of gubernacula, that they could not be con-

sidered in the same subdivision.

I must call the reader’s attention to the following points in

MacCallum’s brief description of the genus Camallanus

450 THE AMERICAN NATURALIST [Vou. LIV

1. The length of the worms as given does not embrace enough

variation, nor does the recorded width. Worms within this genus

have been recorded nearly twice the greatest dimensions which

he gives, and mature females have been found much smaller than

those which he describes.

2. The ridges in the valves are not always ‘‘six main ribs on

each side of the central line.

3. My experience is that the worms are dislocated from the

mucous membrane with difficulty and that often they are pulled

in two or a plug pulled out of the intestine before they can be

loosened.

4. I presume that ‘‘the bar of chitin across the anterior ends

of the median four’’ ridges is the structure that I have called the

anterior wing and its purpose is the attachment of the giant

buccal muscles primarily and not for ‘‘stiffening them” only, if

at all.

5. Certainly not all the males have ‘‘three pairs of post-anal

papille, and one pair of pre-anal.’’ In fact, I am sure that most

if not all members of this genus have seven pairs of pre-anal

papille and five pairs of post-anals, with two para-anal pairs.

6. ‘‘The semicircular flap’’ does not act like a bursa. The

action of this structure, correctly called ‘‘ale’’ has been ex-

plained by Magath (1919) and its difference from the action of a

true bursa shown.

With regard to the new species; MacCallum identified C. osy-

cephalus from a Mississippi alligator. It is impossible to know

whether or not he really had a worm belonging to this species.

It would be interesting to know that a species harbored in fishes

could live in an alligator. If, as he says, the ‘‘general descrip-

tion’’ from the genus will answer for this species he can not be

certain that he had C. oxycephalus because there is nothing in

his general description that is specific for this worm or any other

species.

MacCallum’s descriptions of C. scabre and C. troosti are so

indefinite and meager that either species can not be identified

positively from the descriptions and figures. He gives very few

measurements and the magnification of the figures is not stated.

I had hoped to be able to compare his species with C. americanus

but I can ha no definite data in his paper on which to base the

compariso

‘The sealable of C. chelydre i is passed over with the state-

No. 634] SHORTER ARTICLES AND DISCUSSION 451

ment that ‘‘there is no appreciable difference between these and

the general description’’ of the genus which MacCallum states

also fits C. oxycephalus. The status of this new species seems to

me to be doubtful.

MacCallum’s basis for describing C. floridiane as new seems

to lie in the fact that

the rods are placed on two levels, one set of four being in front and the

other set of four placed behind, and diagonally across the first. Whether

this condition is only an exemplification of the way in which they act

normally by a sawing motion, I do not know, but this would be reason-

able. They may act like a pair of hair clippers and were caught in this

position when death took place.

The action which MacCallum assumes is probably not the method

of action of these jaws. Since I have previously pointed out the

method of action of the jaws, no more needs to be said here on the

subject. The criss-cross arrangement of the ridges in the mouth

apparatus is well explained on the basis of MacCallum’s draw-

ing, which shows that the head of the worm was tilted; I have

often seen the same condition in poor mounts of other members

of this genus when the heads are twisted a trifle. The appear-

ance is purely an artifact. MacCallum’s next point is that this

worm has only two parts of the trident present, or that it has,

in other words, a bident. The figure does not bear out this as-

sertion ; two typical tridents are shown, each with three prongs.

MacCallum states that the males have six pairs of pre-anal

papille and three post-anal pairs.

The description of C. elegans is quite brief. The author could

not determine whether or not the males have one or two spicula,

and because the male tail is ‘‘not so complete and pretentious as

in C. floridiane’’ he believes that the worms deserve a new name.

In C. ptychozcondis the only feature MacCallum noted that

seems at all distinctive is the fact that the intestine follows imme-

diately after the muscular esophagus. If this is the case this

worm is not a member of the genus Camallanus. The anus is on

the left of the worm described. If the observation is correct it is

the first recorded instance of which I know in the literature on

nematodes in which the anus does not lie in the sagittal plane.

I am of the opinion that the worm or worms studied were twisted

in mounting or handling. Unless a series of sections of this

worm can be shown in which the lateral lines are in the same

452 THE AMERICAN NATURALIST [Von. LIV

plane with the anus, I can not accept MacCallum’s conclusion.

He says ‘‘that the vagina has not been seen, but appears to be

very near the mouth on the left side.’’ If it were not near the

middle of the body and in the mid ventral line I would accept

with some caution his conclusion, because this is the character-

istic position of the vulvar opening in this genus.

MacCallum’s C. cyathocephalus is clearly the fourth stage of

his C. scabre. I have described in detail this same stage for C.

americanus.

Unfortunately the description of C. bungari is so incomplete

and the drawing so obscure that it is impossible to locate the

worm even with regard to its genus. Certainly with the slight

description given it could not be placed in the genus Camallanus,

because of the single portion of the esophagus and the type of

the oral apparatus. The picture seems to show eggs in the ter-

minal portion of the uterus; if the worm were mature, larvae

only would be found in this portion of the uterus if it belonged

to the genus Camallanus.

Since I have found C. americanus in many different species

of turtles in the United States, I have tried to decide whether or

not MacCallum found this species and described it as one of his

new species. In going over his paper carefully I am unable to

admit that from his descriptions and figures he described the

worm I recorded under the name Camallanus americanus, al-

though it is possible that he might have had the worm. One can

not be certain whether or not he had some of the species described

by Leidy, nor can one be certain of the validity of any species

which he describes.

In the face of these facts it seems to me that at present it

would be impossible to accept these species in the genus Camal-

lanus and hence I suggest that they be considered as species in-

quirende. Camallanus is such an important genus that the

species described within it should be established without any

doubt whatsoever. It is unfortunate that MacCallum did not

publish more definite data concerning the forms and it is to be

hoped that he will follow up his paper with a complete descrip-

tion of each worm, based on the study of more material and his-

tologie sections.

In the past, nematode descriptions have for the most part been

rather superficial and a great deal of confusion has arisen con-

cerning the identification of genera and species. The worms are

No. 634] SHORTER ARTICLES AND DISCUSSION 453

so difficult to study on account of the problem of proper technic

that it is not surprising that many incomplete descriptions should

have been published. It is to be hoped, however, that the day

will come when nematodes will be as thoroughly studied and de-

scribed as other parasitic worms have been and that their classi-

- fication and identification will be made more certain.

THomas Byrp MAGATH

Mayo CLINIC,

ROCHESTER, MINN,

BIBLIOGRAPHY

1, Leidy, J.

1851. Contributions to Helminthology. Proc. Acad. Nat. Sci., V, 239-

2. Looss, A

1905. The Anatomy and Life History of rit gras duodenale Dub. I.

Rec. Egypt. Govt. School Med., 11-

. MacCallum i A.

1918. Notes on the Genus Camallanus and other Nematodes from Vari-

ous Hosts. Zoopathologica, I, 123-134

4. Magath, T. B.

1919. Camallanus americanus nov. spec. Tr. Am. Microsc. Soc.,

XVIII, 49-170.

5. Ward, H. B.

1917. On the ieharowis and Classification of oe American Parasitic

orms. r. Parasitology, IV, 1-1

6. Ward, H. B., and ight, X

1917. renee on Some emeaans from Fresh-water Fishes. Jour.

Parasitology, III, 57-64.

AN AMICRONUCLEATE RACE OF PARAMECIUM

CAUDATUM

PROBABLY no representative of the Protozoa has received more

attention in matters relating to life cycles, reproduction, hered-

ity and cytology than has Parameciwm. It should be of general

interest, therefore, to record the occurrence of a race of Para-

mecium caudatum which appears to be entirely devoid of a

micronucleus. The recent studies by Dawson (1) on an amicro-

aie race or species of Oxytricha add interest to the present

discover

In ne ‘fall of 1914 Doctor M. H. Jacobs of this —

used, in certain heat experiments, some Paramecium caudatw

derived from a culture which exhibited great viability. During

the following January Hance (2), in examining some of the sur-

454 THE AMERICAN NATURALIST [Von. LIV

viving Paramecia, found that a few were characterized by the

presence of three contractile vacuoles instead of two, the normal

number. Several of these animals were isolated and became the

progenitors of the multivacuolate race studied by Hance (2).

In speaking of the cytology of the race Hance mentions the -

great difficulty experienced in staining the micronucleus and

states that ‘‘the depression in the macronucleus where the micro-

nucleus usually lies is frequently visible but it appears quite

empty.’’ He decided, however, that there was one micronucleus

present.

The greater viability and the slightly larger size of this race

as compared with the wild races led to its use for class work

Having occasion, during November, 1919, to filter about four

hundred cubic centimeters of classroom culture densely popu-

lated by this race of Paramecium the writer fixed the animals so

obtained in warm Schaudinn’s sublimate alcohol and subse-

quently stained them with Delafield’s hematoxylin. On ex-

amination it was discovered that in none of the individuals

could a micronucleus be found. This observation in itself was

not conclusive since the seeming absence of the micronucleus

might have been due to faulty technique. The same material

was stained with borax carmine and the absence of the micro-

nucleus as a staining body was confirmed. Later four different

fixatives were used and the material stained with Carmalum

and in no case was the micronucleus found. Material was then

fixed daily from a series of four cultures for periods ranging

from two to four months. Throughout this period the character

of the Paramecia remained constant in that no multivacuolate

animal possessed a micronucleus.

For obtaining pure lines of amicronucleate animals with

which to make further observations twenty multivacuolate indi-

viduals were isolated. Some of the progeny of each of these

were stained in aceto-carmine and in each case the micronucleus

was absent. The question as to the identity of the multivacuo-

late race and the amicronucleate race then arose. The fact that

the progeny of twenty multivacuolate individuals showed no

micronucleus supported this supposition. _A number of slides,

made before the discovery of the multivacuolate race by Hance,

were found in the Laboratory by Doctor D. H. Wenrich, to

whom the writer is greatly indebted for his constant interest,

valuable advice, and criticism throughout this preliminary work.

Both micronucleate and amicronucleate individuals are to be

No. 634] SHORTER ARTICLES AND DISCUSSION 455

found on these slides. Several amicronucleate individuals con-

tain three distended contractile vacuoles. All the micronucleate

individuals contain only two. There is reason to believe that

these slides were made from the same cultures from which Doc-

tor Jacobs obtained his animals for experimentation. There-

fore these slides also indicate the identity of the two races. Ap-

parently both the extra vacuoles and the absence of a micro-

nucleus were characters present before the heat experiments

referred to.

Throughout the entire history of the cultures observed the

lightly stained, comparatively large, very irregular, and ex-

panded macronucleus is characteristic of the race. Under poor

cultural conditions animals with regular nuclei are few in num-

ber and these nuclei are usually oval in shape and proportion-

ately larger, more lightly stained than others and often blending

with the cytoplasm. Under the same conditions condensations

of the chromatin material are of frequent occurrence and consist

of three types: (a) small or large tongues of chromatin, com-

pact and darkly stained throughout or only around the edges,

usually lying in a concavity of the macronucleus, (b) small, cir-

cular, dense masses of chromatin, usually flattened and near the

surface of the macronucleus, (c) bar-shaped condensations, many

times longer than broad, ranging from very loose aggregations

of granules to very compact masses.

In the early part of the work the writer often experienced

difficulty in deciding whether or not a micronucleus was present

because macronuclear condensations frequently resembled micro-

nuclei. But after observing many specimens they were easily

distinguishable since neither condensations, lobes, nor detached

portions of the macronucleus possessed the detailed structure

typical of a micronucleus. They could always be identified on

very careful examination as portions of the macronucleus by

the arrangement of the chromatin. It is possible that Hance

may have seen macronuclear condensations resembling a micro-

nucleus or small detached portions of the macronucleus which

at certain times are rather common.

Other differences between the nuclei of micronucleate and

amicronucleate animals were noticed. The macronucleus of the

wild, micronucleate races is compact, comparatively small and

darkly stained with a distinct concavity for the micronucleus,

The nucleus of the amicronucleate race is large, expanded, and

lightly staining.

456 THE AMERICAN NATURALIST [Vou. LIV

In addition to these characters there are also certain other

morphological characters which distinguish the race. The ami-

cronucleate race is larger than the wild ones so far observed.

The curve of the buccal groove is slightly greater than that of

the micronucleate animals. The posterior tip is slightly bent

toward the aboral side and the buccal groove itself is shal-

lower since the sides of the groove are bent outward. All evi-

dences so far indicate that the amicronucleate race has the poten-

tiality of forming from three to seven contractile vacuoles.

Attempts have been made by the writer to induce conjugation.

A flourishing culture has been allowed to evaporate to half vol-

ume and small mass cultures have been submitted to various

experimental conditions but so far the writer has been unable

to induce conjugation in this race. Hance (2), however, in-

duced conjugation in the multivacuolate race by the method first

mentioned. Amicronucleate animals in conjugation are to be

found on the slides (made before Hance’s discovery of the extra

vacuoles) mentioned above. Hence the race has conjugated in

the past and attempts will be made to induce conjugation in the

future.

The main question in the future study of this race will be the

eytology of the conjugation process. This will require exper-

imental work on methods of inducing conjugation in the race

and the study of the conjugants so obtained. The effect, if any,

of the absence of the micronucleus on the division process will

also be observed.

The maintenance of pure lines and the study of the nuclear

changes which proceed in ordinary vegetative existence will also

be an important part of the future work. If there is a process

of endomixis the same means will provide a basis for the study

of that phase.

These two matters are the most interesting from the stand-

point of cytology, especially since the work of Calkins and Cull

(3) on conjugation, and Erdmann and Woodruff (4) on endo-

mixis, in Paramecium caudatum show that the active body is the

micronucleus and that the macronucleus breaks down and dis-

appears in both processes. :

Is the macronucleus affected by different cultural conditions

in any definite way and how does the behavior of the nuclei of

the micronucleate race compare with the behavior of the macro-

nucleus in the newly discovered race? The preliminary work

done so far indicates that there is a definite relation between

No. 634] SHORTER ARTICLES AND DISCUSSION 457

environment and the behavior of the macronucleus and that the

macronucleus assumes different shapes and appearances under

different cultural conditions.

Is this amicronucleate paramecium able to exist indefinitely

without conjugation involving a micronucleus and without re-

organization of nuclear material, or is there another type of reor-

ganization in this race? A nuclear reorganization, if present,

must evidently be of a different type from that described by

Erdmann and Woodruff

These and similar problems are interesting, not only in them-

selves, but because Paramecium has been studied in great detail

by Jennings and others with reference to the occurrence of cyto-

plasmic variations. The amicronucleate race, however, is impor-

tant because the variation is one of nuclear structure. The

importance and interest of the study is increased by the fact

that the micronucleus is usually considered to be an aggregation

of generative or hereditary chromatin and the body which sup-

posedly initiates reproductive processes of all types and from

which, in sexual reproduction, the new nuclei are formed.

EvuGene M. LANDIS

ZOOLOGICAL LABORATORY, ‘

UNIVERSITY OF PENNSYLVANIA

REFERENCES,

1. Dawson, J. A. 1919. An Experimental Study of an Amicronucleate

Oxytricha. 1. Study of Normal Animal with an Account of Canni-

ism, Jour. Exp. Zool., Vol. 29, No. 3.

2. Hance, R. T. 1917. Studies on a Race of Paramoecium Possessing Ex-

tra Contractile Vacuoles. 1. An Account of the Morphology, Physiol-

ogy, nape and Cytology of this New Race. Jour, Exp. Zool.,

Vol. 2

3. Calkins, a and Cull, S. W. 1907. Conjugation of Paramecium

aurelia a, Arch f. Protistenkunde, Bd. X.

4. Erdmann, R. and Woodruff, L. L. 1916. Periodice Reorganization

Process in Paramecium coudatwn. Jour. Exp. Zool., Vol, 20.

NOTE ON THE OCCURRENCE OF A PROBABLE SEX-

LINKED LETHAL FACTOR IN MAMMALS

THE occurrence of sex-linked lethal factors in Drosophila is a

matter of common knowledge to most biologists. Since mammals

have an essentially similar type of sex determination in so far

as their dimorphism of sperm is concerned, it is theoretically

possible that sex-linked lethal factors should occur among them.

458 THE AMERICAN NATURALIST [Vou. LIV

Inasmuch as only a few sex-linked factors of any sort are

known in laboratory mammals where numerous other genetic

differences have been recorded, breeding tests of linkage rela-

tions by ordinary methods are precluded. The first indications

of a sex-linked lethal factor would therefore be expected to con-

sist of an abnormal sex ratio at birth and a reduction in the size

of litters.

Such conditions are met with in certain Japanese waltzing mice

derived from a remarkably closely inbred race. This particular

strain of Japanese mice has been inbred from the descendants

of a single pair of animals for approximately fourteen years. The

animals are difficult to raise and the litters are frequently dis-

tinctly smaller than those of non-waltzing mice of inbred races.

The great majority of animals of this strain have been bred by

Mr, George Lambert of Boston, who has provided adult or young

adult animals to the writer for several years. Mr. Lambert is

now engaged in recording sex ratio data at the birth of litters

and states that at present an excess of females is being produced

in his stock. While awaiting increased numerical data from his

records, however, it appeared advisable to make a short note of

the sex ratio and belavior of this strain in the animals raised

under controlled observation.t The sex ratio of inbred non-

waltzing mice is 103.1 + 2.8, showing a slight excess of males.

The sex ratio obtained from Japanese waltzing race of the Lam-

bert strain is 53.2 + 5.7. The difference between these ratios is

7.9 times its probable error and is certainly significant.

Since recessive sex-linked lethal factors are transmissible

through a female to one half of her male offspring, the sex ratio

among the progeny of females carrying sex-linked lethal factors

should be theoretically 50.0. Males of the Japanese waltzing

race can not, of course, transmit the lethal factor, since if they

possessed the factor it would result in their death. If then ani-

mals of the Japanese waltzing race are crossed with non-waltz-

ing mice of a race presumably free from lethals, the reciprocal

crosses should give markedly different sex ratios. Such is actu-

ally the case. Non-waltzing females by Japanese waltzing males

should give a sex ratio free from the effect of lethal factors.

The observed sex ratio in the F, generation of this cross is 118.2

1Dr. H. J. Bagg, of the Memorial Hospital, New York City, has kindly

placed at my disposal data collected by him while breeding Japanese waltz-

ing mice of the same (Lambert) strain. These data are included with my

own in this publication.

No. 634] SHORTER ARTICLES AND DISCUSSION 459

+ 3.8 and in the F, generation 113.3+3.0. The combined

ratios are 115.9+ 2.7. The significant excess of males above

that found in the inbred non-waltzing stock is a common result

of hybridization. The reciprocal cross gives a most interesting

contrast. When Japanese waltzing females are crossed with

non-waltzing males the sex ratio is 44.0+ 7.4. This differs from

the sex ratio of the reciprocal cross by 8.9 times the probable

error of the difference.

Certain other evidence is obtainable from the vocals of mat-

ing Japanese waltzing females or their female descendants with

hybrids of the F, or back cross generation. Such crosses give

opportunity for a lethal factor to be transmitted and to ex-

press itself. We should expect, therefore, that an excess of

females would be obtained in the progeny of such crosses. Such

is actually the case, the ratio being 78.7 + 2.9. The exact ratio

to be expected would depend upon the numerical relation of

young in a given population, obtained from homozygous normal

females, to those from females carrying the lethal factor.

The size of litters given by Japanese females irrespective of

the sire is distinctly smaller than that of litters from non-waltz-

ing females. The average of 58 litters from Japanese waltzing

females is 3.38 and from non-waltzing females (100 litters) 5.93.

The litters from Japanese females are therefore .57 times the

size of those from non-waltzing females. This result is in gen-

eral accordance with the presence of a sex-linked lethal factor.

x* test of the frequency distributions of litters in the two cases

shows that the odds are less than one in 1,000,000 that they are >

the same.

While it is realized that the above evidence is preliminary, its

entire consistency and the controlled nature of the material

makes it seem likely that the observed figures indicate the pres-

ence of what is apparently the first case of sex-linkage in rodents

and of a sex-linked lethal factor in mammals. The possible ex- .

ceptions to this statement? are to be found in the case of hemo-

philia recently reviewed by Whitman? and in the possible dif-

ference in reciprocal crosses between Epimys rattus and Epimys

alexandrinus reported by De l'Isle and reviewed by de Meijere.*

2 Progressive muscular atrophy in man has a lethal action. Its action is,

however, so delayed that it seems searcely to fall into the same category

with what have hitherto been considered as sex-linked lethals,

8 Jour. Cancer Research, 1919, 4, 181.

4 Archiv. f. Rassengesell. u. Biol., 8, 697.

460 THE AMERICAN NATURALIST [Von. LIV

In order to explain the case reported by Whitman an entirely

new and unsupported behavior of the lethal factor is hypothe-

sized. This consists in a supposition that females possessing two

does of the lethal die. Inasmuch as a female with two doses of

a sex-linked lethal could not be formed except by mutation, pro-

vided the relations observed in Drosophila hold true, the pres-

ence of a sex-linked lethal factor of the accepted type does not

appear to be strongly supported. In the case of the rats a

simple statement of a difference in reciprocal crosses is the sole

evidence. In this case no lethal action is apparently involved;

but sex-linkage might possibly account for the result. Until

actual experimental evidence on this matter is available, how-

ever, it seems as though it was not sufficiently definite to be con-

sidered as having previously established the existence of sex-

linkage in rodents.

C. C. LITTLE

CONCERNING THE FOSSILIZATION OF BLOOD

CORPUSCLES

RECENTLY, while studying a series of microscopic preparations

of fossil material in connection with paleopathology, I observed

in sections of a dinosaur bone (possibly Apatosaurus) which I

had collected in the Como beds of Wyoming in 1906, some ovoid

bodies, arranged around the periphery of vascular spaces and

Haversian canals, which looked remarkably like blood corpuscles.

Close scrutiny of the available material, however, did not satisfy

me that the objects might not be the products or by-products

of incomplete crystallization. The majority of the bodies had

the size and shape of modern reptilian erythrocytes; the nucleus

of course not being evident, since only the outward form of the

corpuscle was to be seen. Other bodies, apparently similar,

were irregular in shape and hard to distinguish structurally

from the regular bodies. These latter, however, may be masses

composed of several corpuscles which had become agglutinated.

Not being satisfied with the results of my observations, I should

not have published anything about it had I not seen in a memoir

by Seitz’ a description of similar bodies in sections of normal

1 Adolf Leo Ludwig Seitz, 1907, ‘*Vergleichenden Studien über den mikro-

meinen,’’ Nova Acta, Abh. der Kaiserl, Leop.-Carol. Deutschen Akad. der

Naturforscher. Halle, Bd. LXXXVII, No. 2, 329-330, Tab. XXI, Fig. 61,

where the corpuscles are shown in a photomicrograph in 365 diameters.

No. 634] SHORTER ARTICLES AND DISCUSSION 461

Fig. A vascular space in a normal metatarsal of Apatosaurus, or some re-

lated Aarie Y from the Como Beds of Wyoming, showing in e peng mar-

ginal bodies, the preservation of supposed blood scat ban: — fied 2 200 diame-

ters. These are the same bodies that Seitz saw in European poate osaurs. The

light area is the vascular space filled with paki? quartz. ke dark ma vo areas

are osseous trabecule rendered dark by i The sharp indentations the

border of e vascular space are tac by Seitz as Howship’s ohn in

which case the rounded bodies would be osteoclasts and not blood corpuscles.

1 the Per-

but failed to find, blood corpuscles in bone fron

Mian of the Autun basin of France

bone from the European dinosaur, Iguanodon Bernissaertensis

from the Wealden of Bernissaert, Belgium. Seitz’s description

of the blood corpuscles follows:

A larger part of the Haversian canals of Iguanodon is empty. A

part of them, however, contain small, round, biconvex bodies, apparently

with flat surfaces, which occur regularly or scattered about in the lumen

of the vessels, with an occasional one near the periphery. Not seldom

a compact mass of them entirely fills the blood-vessel. Professor

Solereder of Erlangen declares that the bodies are not of plant origin

462 THE AMERICAN NATURALIST [Vou. LIV

(spores), and by polarization it is determined that the bodies resemble

somewhat crystalline concretions, so that we are forced to the conclusion

that we have here some fossilized blood corpuscles. The partial filling

of the blood vessel may be due to coagulation or a peripheral thrombus.

There is also to be found frequent accumulations of reddish erystals

which resemble hematoid crystals, and which support the suggestion as

to the nature of the material. I give these observations with some

reservation.

We may gain an insight into the possibility of the fossilization

of blood corpuscles by studying the results of the researches

into the nature of the mummified brain material of the ancient

Egyptians. This subject has been studied by Mair,? who finds

that the lipoids of the brain from Coptic bodies, 500 B.c., had

been changed into cholesteryl stearate and palmitate.* Mair ob-

tained cholesteryl stearate by heating cholesterol with stearic

acid, and one may infer that the heat of the desert sands in

which the bodies were buried may have been an important factor

in the conversion of the brain lipoids into the two relatively re-

sistant substances, palmitate and cholesteryl stearate. These

brains, even those dating from a period prior to the process of

embalming (4500 B.c.), are frequently so well preserved, though

greatly shrunken, that practically all the gyri may be accurately

determined. This item from more recent times may aid in an

explanation of processes occurring in geological ages.

The studies on Egyptian mummies have not resulted in the

discovery of blood corpuscles. Schmidt* examined bodies dat-

ing from 1000 years before Menes (3400 B.c.) to 500 B.c. (mum-

mified material from Coptic bodies) and was unable to find a

positive hemin reaction, tending to show the complete disap-

pearance of all blood in the process of time. Wood Jones,° how-

ever, is convinced that traces of blood are readily discernible.

Elliot Smith has referred to blood stains on bandages used in

2 W. Mair, 1913, ‘‘On the bei fe of Ancient Egyptian Brains,’’ J. Path.

and Bacteriol., XVIII, 179-184;

3 Mair’s results are donka te atait by Lapworth and Royle, 1914,

**The Lipoids of Ancient Egyptian Brains and the Nature of Cholesteryl

To A Path and Bacteriol., XIX, 474—477.

PE 1907, ‘‘ Chemische und biologische Untersuchungen von

a Mumienmaterial, nebst Betrachtungen über das Einbalsamie-

rungsverfahren jee alten Aegypter,’’ Ztschr. f. allgem. Physiol, VII,

369-392.

5 F. Wood Jones, 1908, ‘The Post-mortem Staining of Bone Produced by

the Ante-mortem Shedding of Blood,’’ Brit, Med. J., 1, 734-736.

No. 634] SHORTER ARTICLES AND DISCUSSION 463

the primitive surgery of Egypt. Ruffer in his extensive studies

into the histology of Egyptian mummies did not discover any

definite corpuscles.

It may be of interest to note that Friedenthal® announced to

the physiological society of Berlin the discovery of red blood

in the body of a mammoth from eastern Siberia which had been

frozen in the tundra since Pleistocene times. The precipitin

reaction of the blood is similar to that of the modern elephant.

No record is made of the preservation of blood corpuscles.

While this is an extremely interesting discovery, it must be re-

called that cold brings many chemical reactions to a halt, and

there may have been little change in the blood of this mammoth

during its 175,000 years of cold storage in the Siberian mud.

The body had been so well frozen that the flesh was still fresh

enough to satisfy the hunger of wolves and dogs.

Hoppe-Seyler has shown that dried red blood corpuscles of

man contain 2.5 parts of cholesterin in 1000. While this is an

extremely small amount of lipoid substance, since it is chiefly

in the cortex of the corpuscle, it occurred to me that this might

offer an explanation of the preservation of blood corpuscles.

That is, under favorable conditions, the lipoids of the blood

might be changed into some resistant substance like palmitate

or cholesteryl stearate and thus retain the form of the cor-

puscles and delay their destruction long enough for fossiliza-

tion to set in; these substances being replaced later by the min-

eral crystals from the magma in which the body was immersed.

The beautiful little ganoid fish brains described by the writer’

some years ago from the Coal Measures may have been preserved

in a similar way. The resemblance between brain substance and

blood corpuscles is close in this respect that each has a small

amount of resistant substance, a large amount of water and a

relatively similar proportion of lipoids which may have become

transformed, under proper conditions, into resistant substances

which carried the part over the critical period of destruction.

In view of the fact that so many soft-bodied animals are so

beautifully preserved in the rocks, that the histological nature

of Paleozoic muscle tissue has been determined, that bacteria

and the delicate parts of flowers are so frequently fossilized, it

6 Deutsche Med. Wochenschrift, 1904, p. 901

T Roy L. Moodie, 1915, ‘‘A new Fish Brain from the Coal Measures of

Kansas, with a Review of other fossil Brains, Á Comp. Neurol., XXV, No. 2,

135, 17 figs.

464 THE AMERICAN NATURALIST [Vou. LIV

is certainly not beyond reason to expect the preservation of

blood corpuscles. The subject is still an open one but this con-

tribution to the theory of fossilization, it is hoped, may help to

clear up the matter of the preservation of delicate objects.

The fossilization of any of the blood crystals as suggested by

Seitz? is extremely improbable, since the evanescent nature of

the crystals of hemoglobin is well known. Whether the crystals

seen with the supposed blood corpuscles have resulted second-

arily from the disintegration of hemin crystals or whether the

whole appearance is due to chemical reactions in the incomplete

crystallization of inorganic substances is an open question. Still

we must not close our eyes to the possibility of discovery and

block the way to progress by saying it is either one or the other.

This paper merely opens the field.

Roy L. Moopir

DEPARTMENT OF ANATOMY,

IVERSITY OF ILLINOIS,

CHICAGO

| THE

AMERICAN NATURALIST

Vou. LIV. November—December, 1920 No. 635

TYPES OF WHITE SPOTTING IN MICE!

L. C. DUNN

Storrs AGricuururAL EXPERIMENT STATION, Storrs, Conn.

THE occurrence of white spotting in the coats of col-

ored mammals is one of the commonest phenomena en-

countered by the student of variation and heredity. For

a long time spotting was thought to be of the same nature

as albinism, a condition in which no pigment is present in

the fur and eyes, leaving the pelage clear white and the

eyes pink. Many specimens of white spotted animals

are still to be seen in museums masquerading as ‘‘ partial

albinos.’’

As soon as the methods of experimental breeding were

employed in studying such variations, albinism and white

spotting were found to be genetically distinct. Albinism,

because of the striking nature of the variation and its

almost identical appearance wherever encountered was

one of the first mammalian variations to be analyzed and

its mode of inheritance is now well known. The case of

white spotting is quite different. The spotting of most

animals presents an extremely wide range of variation.

An almost continuous series may be traced by the casual

observer from the extreme spotting of white dogs with

black eyes to the small star or blaze on the foreheads of

some colored horses. The solid colored condition, gen-

erally known as self, and spotting may thus in some in-

stances be distinguished only by the presence of a few

white hairs. Moreover, the inheritance of white spot-

ting in different animals and of the various grades of

1The experiments reported in this paper were performed at the Bussey

Institution, Harvard University, Forest Hills, Mass.

465

466 THE AMERICAN NATURALIST [Von. LIV

spotting in the same animal has been found by exper-

iment to be distinctly different. Our knowledge of the

hereditary factors and of the processes concerned with

the development of pigment in the coat is still too frag-

mentary for a satisfactory comparative exposition of

the nature and causes of white spotting. The need at

present appears rather to be for intensive experimental

studies of variations in the most favorable species in

which they occur. The white spotting of some species

` also provides excellent material for the study of the

nature of genes with small quantitative effects either as

main or as modifying factors. As a contribution to these

ends the present report of experiments with white spot-

ting in mice is offered.

In the house mouse the whole range of variability in

white spotting is found. At one extreme are black-eyed

whites, with pigment occurring only in the eyes; at the

other extremes are colored mice which have only a few

white hairs on forehead, feet, tail or belly. The appear-

ance of all possible intergrades between black-eyed

whites at one end of the scale and animals closely resem-

bling self at the other led Cuenot to suppose that all

spotted mice differed from self by a single main spotting

factor (P) which might be present in various conditions

represented by factors with minor effects which caused

the more apparent differences in amount of pigmented

areas. The finer details and intergrades of spotting he

regarded as purely somatic variations with no germinal

(hereditary) cause. Later, however, Little (1915) bred

spotted mice and classified all parents and offspring by

estimating the percentage relations between white and

colored spaces. He found that the ‘‘continuous’’ series

of spotted forms consisted of two main types. One of

these, black-eyed white, was characterized by a pelage

practically all white with dark eyes. The other, piebald,

was distinguished by the greater extent of pigmented

areas down to and including mice with only a few white

hairs dorsally and a small patch of white on the belly.

Another type of spotted mouse known as ‘‘blaze’’ and

No. 635] WHITE SPOTTING IN MICE 467

characterized only by a small white spot between the

eyes was also removed from the continuous series by

the work of Little (1917). This variation was apparently

heritable, although subect to some variability in expres-

sion. Two types of piebald spotting, one with more and

one with less white were likewise indicated in Little’s

data. He regarded these differences as possibly due to

two distinct modifying factors of the piebald gene. In

addition, crosses of black-eyed white with self-colored

mice had produced two new spotted types, one with more

and one with less white. The continuous series of

spotted forms has thus been broken up on the basis of

amount and distribution of spotting into a large number

of fairly distinct types, two of them due to genes the in-

heritance of which is known. The process of resolution

has not reached its end yet, for a great deal of variabil-

ity exists within the various types, and the resolution of

these variations into still more sub-types is possible.

The specific objects of this study are to redefine the

ranges of the main types of spotting in the light of in-

creased data; (2) to find out, if possible, whether the

conditions of spotting in the sub-types are due to dif-

ferent combinations of the main genes or to distinct

genes which modify the expression of the main genes.

The two main types of spotting in mice are known re-

spectively as black-eyed white and piebald. Little at

first described black-eyed whites as spotted mice which

this limit to include mice which are 80 per cent. or more

white dorsally. Certain yellow black-eyed whites were

described by Little (1917) as exhibiting as little as 60

per cent. of white in the dorsal surface. Evidence will

be presented later to show that the range of black-eyed

white variability is even greater than this and may in-

clude mice with as little as 50 per cent. of dorsal white.

Piebalds are much darker, i.e., have less white spot-

ting than black-eyed whites. The piebalds born in my

experiments have, with one or two exceptions, been less

than 50 per cent. white dorsally with belly spotting rang-

468 THE AMERICAN NATURALIST [Vou. LIV ~

ing from 12 per cent. to 85 per cent. of white. Other in-

vestigators have recorded piebalds whiter than this? and

one or two of my crosses indicate that piebalds may ex-

hibit as much as 60 per cent. or 65 per cent. white, al-

though such animals site been extremely rare in these

experiments.

Genetically these two types of spotting are distinct,

and each is due to a gene distinct from and independent

of the other. When black-eyed whites are crossed with

piebalds equal numbers of black-eyed whites and piebalds

result. When black-eyed whites are bred inter se, black-

eyed whites and piebalds result in the ratio of 2:1. The

black-eyed white condition is therefore due to a gene

(symbol W) acting with the gene for piebald (symbol s).

Black-eyed whites are heterozygous for the gene W and

are homozygous for s. Genetically they are Wwss. Pie-

balds may be represented by the formula wwss, where w

stands merely for ‘‘not-black-eyed white.’? These two

genes, as is known from previous data (Little, 1915;

Dunn, 1920), are neither allelomorphic nor linked, but

entirely independent.

As additional evidence of the distinctness of these

types and to illustrate the comparative ranges as re-

gards amount of white spotting on the dorsal surface,

the data from a number of crosses between black-eyed

whites and piebalds are presented in Table II, Cross 1,

and Fig. 1 solid line. All mice in this as in other dis-

tributions to be discussed were graded by estimating

the amount of white in the coat. The two surfaces, dor-

sal and ventral, were graded separately, the total of each

surface being regarded as 100. The percentage of dorsal

white was expressed as the numerator and the per-

centage of ventral white as the denominator of a fraction.

Thus a mouse entirely white dorsally and ventrally (ex-

cept for pigment in the eyes) was graded as 100/100;

while one with only a small patch of white ventrally was

2 For instance, the race of pure Japanese piebalds described by Little

_ (1917) which varied from 100 per cent. to 64 per cent. white dorsally and

osely resembled black-eyed whites in amount of spotting.

No. 635] WHITE SPOTTING IN MICE 469

graded 0/1, or 0/3, etc. The results can be easily trans-

posed into Little’s scale by simple subtraction of any

grade from 100, since his percentage expressed the

amount of color. For convenience, only the dorsal

grades have been used in the tabulation, since the results

60 Poa

—

man

Number of Individuals

—a_

s..

k ai

ie che

Reames See. Sin

00° 7907 Teo 1% 7 Teo’ Ts0’ Tan Igo” 20” tao!

Percent of dorsum white

ng graphically the distribution as regards amount of white

Spottin. ag of (1) a black-eyed white mice (dotted line) ; (2) offspring of crosses

of black-eyed white by piebald (solid line); (3) offspring of cross of black-eyed

white by self (broken line).

obtained by using the ventral grades are in all respects

similar.

Of 323 mice raised from crosses of black-eyed whites

by piebalds, approximately half (160) were 50 per cent.

white or more; the other half (163) were spotted mice

with less than 50 per cent. white; expected 161.5 of each.

No mice were obtained early in the experiment which

were from 55 to 51 per cent. white and it was thought

that this zero class indicated a clear discontinuity be-

_ tween the types. With larger numbers, however, three

mice of this sort were born. That the division between

black-eyed white and piebald at 51 per cent. is, however,

470 THE AMERICAN NATURALIST [Vou. LIV

not an arbitrary one is shown by the bimodal nature of

the curve (Fig. 1, solid line), which divides itself near

50 per cent.; by the closeness with which the actual as-

sortment of W and w (assuming the lower limit of W

spotting as 51 per cent.) approaches the expected and by

breeding tests of spotted mice slightly more and slightly

less than 50 per cent. white. Those more than 50 per

cent. white proved to be black-eyed white and those less

than 50 per cent. white proved to be piebalds.

The mode of the black-eyed whites in this distribution

is at 95-86 per cent. white, although when all other black-

eyed whites are added (Table II, Cross 8, Fig. 1, broken

line) the main mode is found to be at 90-86. The range

is from 100 per cent. to 51 per cent. and the mean of all

black-eyed whites is 83.5 per cent. + .4 with a standard

deviation of 11.4 per cent. + .3. :

This establishes a wider range of variability for the

black-eyed white variation than has been current hereto-

fore, by the addition to the distribution of the classes less

than 80 per cent. white. It will be shown later in the sec-

tion on modifying factors that these darker classes are

not merely somatic fluctuations in the expression of the

gene for black-eyed white (W) but represent genetic

variations. They may be regarded as sub-types of black-

eyed white.

PIEBALD

The piebalds produced by the cross of black-eyed white

- with piebald are represented by that part of the solid line

(Fig. 1) lying between 50 per cent. and 0 per cent. Un- `

like black-eyed whites, piebalds are not always distin-

guishable on the basis of dorsal white alone, for some pie-

balds have no white at all dorsally. In such cases the

ventral white must be used as a criterion, and of the pure

piebalds produced in this cross none had less than 12 per

cent. of ventral white and this was used as the limit of

piebald variability. All animals with 12 per cent. or

more of ventral white and with from 0 to 5 per cent. of

dorsal white were placed in the 0-5 per cent. class. The

correctness of this classification can be inferred from the

No. 635] WHITE SPOTTING IN MICE 471

closeness with which.the numbers of piebalds resulting

from various crosses (Table II) agree with the numbers

expected on the assumption that the gene s segregates

at random with regard to S, W, and w. It is certain,

sTenpyatpul ` Jo aqy

-em

40 30 20

Percent of dorsum white

Fic. 2. Showing graphically the distribution as regards amount of white

spotting of (1) all piebald mice (solid line); (2) piebald mice resulting in the

second generation from a cross of piebald by self (dotted line); (3) piebalds ex-

tracted from black-eyed whites (broken line).

nevertheless, that all possible variations of piebald have

not been met with in the distributions presented in Table

II and Fig. 2. Little (1917) bred a race of pure piebalds

which varied from 100 per cent. to 64 per cent. white dor-

sally. These piebalds are entirely outside the range of

the piebalds bred in the present experiments. Moreover,

472 THE AMERICAN NATURALIST [Vou. LIV

since the conclusion of these experiments I have been

able to isolate one family of piebalds characterized by

from 0-10 per cent. of white dorsally and from 0-12 per

cent. of white ventrally. They have even produced a

small proportion of solid colored young which probably

represents an extreme condition of piebald in connection

with other subsidiary factors for the increase of pig-

mented areas. Thus aside from the piebald mice ob-

served in these experiments it can be seen that the geno-

type ‘‘ss’’ (piebald) may vary somatically from solid

colored to all white with dark eyes.

As regards only the piebalds observed in this investi-

gation (and this includes all the piebalds in the experi-

ment, 437 in number) it can be seen by a glance at Table

II, Cross 11, and Fig. 2 that they constitute a well-defined

class ranging from 50 per cent. to 0 per cent. white dor-

sally. Of the total (487) 295, or 67 per cent., are less than

10 per cent. white. They are less variable than the black-

eyed whites, since the standard deviation of 302 black-

eyed whites is 11.4+.3, while the standard deviation of

437 piebalds is 8.6+.2. This difference is not due to the

range which is 50 per cent. in each case, but to the group-

ing of the piebalds in the two darkest classes while the

black-eyed whites are distributed more evenly through-

out the distribution. The mean and standard deviation

of piebalds out of crosses with self (Table II, Cross 10)

are significantly lower than the same constants from pie-

balds out of crosses with black-eyed white. An inter-

pretation of these differences is offered below in the sec-

tion. on modifying factors.

The main difference between the black-eyed white and

piebald condition is due to the presence in the black-eyed

whites" of a dominant gene (W) which the piebalds lack.

This gene in single dose, and in connection with the gene

for piebald, limits the formation of pigment to, on the

average, about 10 per cent. of the dorsal surface, though

mice possessing this combination of genes may vary from

all white with dark eyes to about 50 per cent. white.

The piebald gene in double dose and acting alone per-

No. 635] WHITE SPOTTING IN MICE 473

mits the formation of pigment on the average, in about

85 per cent of the dorsal surface, although such mice may

vary from solid colored dorsally (0 per cent. white) to

100 per cent. white dorsally.

There are certain other combinations of these genes

possible, and by experiment these other combinations

have been found to produce other spotted types. Some

of these types have been found to be indistinguishable

somatically from piebald, although differing from pie-

bald in genetic constitution. The experimental evidence

bearing on the appearance, constitution and variability

of such additional types follows.

Typs ‘‘A’’ SPOTTING

When black-eyed white is crossed with self approxi-

mately half of the progeny are spotted and half are self

or exhibit at most only a small white ventral spot. From

such a cross in the present experiments 76 young have

been born, of which 40 were spotted and 36 were self col-

ored (Table II, Cross 2). Little found that the self (or

nearly self) young from sueh a cross were ordinary

heterozygotes between self and piebald. The spotted

young he found to be due to unions of gametes carrying

black-eyed white and piebald (Ws) with self gametes

(wS) producing the double heterozygote WwSs. He

called such spotted mice Type ‘‘A’’. The somatic ex-

pression of this combination of genes has produced

spotted mice varying from 0 to 45 per cent. of white dor-

sally (Fig. 1, broken line, and Fig. 3, dotted line). The

distribution as regards amount of white dorsally is seen

from this figure to resemble closely the distribution of

piebald in range, while the mode of Type ‘‘A”’’ is at 5-0

per cent. and the mode of all piebalds is at the same point.

The mean of all Type ‘‘A’’s raised (83 in number) was

7.9 = .6 per cent. white dorsally with a standard devia-

tion of 8.4+.4. This is very close to the mean of all

piebalds (9.7 per cent. white) and almost identical with

the mean of piebalds extracted from crosses of piebalds

with self (8.05 +.3). Moreover, Type ‘‘A’’s which have

474 THE AMERICAN NATURALIST [Vou. LIV

no dorsal white may be characterized by an extremely

small amount of ventral white. Ordinarily mice with less

than 12 per cent. of ventral white may be classed as self.

I mated together two such apparently self animals out

of a cross of Type ‘‘A’’ by piebald. Each had a small

white spot on the belly only covering 4 per cent. of that

surface in one of the mice and 5 per cent. in the other.

They produced two litters, each of which contained two

black-eyed white mice. They were Type ‘‘A’’ mice and

not selfs as they had been recorded. A similar case has

been reported by Little (1917) in which eleven yellow

mice with 6 per cent. and more of ventral spotting proved

on breeding tests to be Type “A”. That an extreme of

Type ‘‘A’’ spotting approached the self condition so

closely was not discovered until most of the animals had

been graded. It is possible, therefore, that where Type

“A” and self animals appear in the same distribution,

_ the self class may be factitiously enlarged at the expense

of the Type ‘‘A”’ class, due to errors in grading. Type

‘A’ spotted mice are hence indistinguishable somatically

from piebalds, and in certain cases, from selfs, although

possessing a genetic constitution entirely different from

either of these latter forms.

Ter O?

There remains one other type of spotting to be dis-

cussed which like Type ‘‘A’”’ and piebald has a different

genetic constitution, but which is difficult to distinguish

from either Type ‘‘A’’ or piebald. Such mice are pro-

duced when Type ‘‘A’’ animals are interbred. Each

Type ‘‘A’’ produces gametes WS, Ws, wS and ws which

by random union give the following array of zygotes:

4 pure for W which are non-viable and die in utero.

4 WwSs—Type “A” l

2 wwS's

1 wwss\selt

2 Wwss—black-eyed white :

2 WwSS—dark spotted (Type ‘‘C’’)

No. 635] WHITE SPOTTING IN MICE 475

1 wwss—piebald

The visible distribution should consist of approximately

2 black-eyed whites, 7 spotted, and 3 self. The experi-

mental numbers for this cross (Table I, Cross 4) in the

present study are 16 black-eyed whites, 27 ‘‘spotted,’’*

and 18 selfs. Among the spotted forms is included a new

genotypic class consisting of mice which are heterozygous

for W but pure for self. Little called this genotype

‘‘dark spotted,’’ but since somatically it is no darker than

other spotted types I shall refer to it arbitrarily as Type

«C. Some of the spotted mice from the above cross (4)

were tested by crossing them with piebalds. If the mouse

tested were piebald, it should produce only spotted (pie-

bald) mice; if it were Type ‘‘A”’ it should produce black-

eyed whites, spotted and selfs; while if it were Type ‘‘C”’

it should produce only spotted (Type ‘‘A’’) and self.

Out of a number of mice so tested only seven proved to

be Type ‘‘C”’ and the only evidence available on the ap-

pearance of Type ‘‘C’’ mice is from the appearance of

these tested animals. Five were less than 5 per cent.

white dorsally; one was 7 per cent. white and one was 8

per cent. The white spotting in all of them was confined

to the head, either as a spot on the nose or between the

eyes (‘‘blaze’’). It is to be regretted that no animals

from this cross with less than 12 per cent. of ventral

white were tested, since it seems probable from the ex-

cess of selfs recorded that some mice graded as self and

were really Type ‘‘C.’? The same excess of selfs was

noted in a larger amount of data on this cross reported

by Little, Its significance is probably the same, that is,

it is due to the production of an extremely small amount

of spotting by the genetic Types ‘‘A’’ and “C.”

Crosses of Type ‘‘C’’ with piebald produced a total of

85 offspring (Table II, Cross 6), of which 43 were spotted

and 42 were self (expected 42.5 of each). The spotted

3 Under the general term ‘‘spotted’’ are included all those genotypes

which are somatically indistinguishable when occurring in the same distri-

bution, viz., Type ‘‘A,’’ Type ‘‘C,’’ and piebald.

476 THE AMERICAN NATURALIST [Vou. LIV

mice were genetically Type ‘‘A’’ (WwSs) and their dis-

tribution is shown graphically in Fig. 3, broken line.

This distribution resembles that of the Type ‘‘A’’s pro-

duced by crossing black-eyed white with self, except that

the former are somewhat less variable, due to the ab-

Number of Individuals’

i Percent of Dorsum white

Fic. 3. Showing — the pledge as mount of white

spotting of (1) offspring from crosses of Type | eee "ald line) ; (2). of

all Type A mice (aovted Shoat (3) offspring oy pinea of t Fros C by piebald

(broken line).

sence of classes lighter than 25 per cent. white, and their

mean is somewhat lower for the same reason. These

differences, are probably due to the selection of dark Type

Opn parents and it will be seen later that the darker

No. 635] WHITE SPOTTING IN MICE 477

spotted types probably carry modifying genes which

have a pronounced effect in increasing the amount of

pigment present.

Many crosses were made between Type ‘‘A’’ and pie-

balds with the object of determining whether the genes

W and s were linked or independent. All offspring from

this cross were also graded for variation in amount of

white spotting. The distribution of the 443 offspring

(Table II, Cross, and Fig. 3 solid line) indicates the cor-

rectness of the ranges already established for three types

of spotting, since black-eyed whites, ‘‘spotted’’ (Type

‘A’? and piebald) and selfs resulted in the expected ratio

of 1:2:1. The range of the black-eyed whites was from

100 to 56 per cent. white; and ‘‘spotted’’ from 50 to 0 per

cent. white. The mean of the black-eyed whites was 84.7

per cent. + .6 of white dorsally with a standard deviation

of 10.3 + .5, which values correspond closely to those cal-

culated for the cross black-eyed white X piebald (Table

I, Cross 1). The mean of the mixed spotted was at 11.6

per cent.+.5 compared with 12.5 per cent.+.6, the

mean of the piebalds in Cross 1. It may be inferred from

this that the residence in the same Type ‘‘A’’ zygote of

the genes W and self has had per se no darkening effect

on the black-eyed whites and spotted subsequently ex-.

tracted.

SELF

Data on the ranges of variability of white spotted mice

would not be complete without some reference to the

variability exhibited by mice which by all tests which

have been applied to them are genetically self mice, i.e.,

lacking the genes at present known to cause white spot-

ting. The heterozygote between self and piebald is gen-

erally regarded as self, that is, self is supposed to be

completely dominant to piebald. But in a number of

cases in these experiments heterozygotes between self

and piebald have exhibited a small spot of white on the

belly, covering never more than 12 per cent. of the ven-

tral surface. This occurrence has been remarked by

Little in the case of Type ‘‘B’’ mice resulting from the

478 THE AMERICAN NATURALIST [Vou. LIV

cross black-eyed white by self. Further reference will

be made to these mice in the section on modifying factors.

In addition certain mice have appeared which exhibit

only a small white spot in the form of a ‘‘blaze’’ of white

hairs between the eyes which may or may not be accom-

panied by a small belly spot. Such mice have proved to

be self in distinction from piebald since when mated inter

se they have produced 15 self-colored mice lacking any

spotting and 6 piebalds, indicating that both ‘‘blaze’’

parents were selfs heterozygous for piebald. When

tested by crossing with pure piebalds, such ‘‘blaze’’ mice

have produced 55 selfs and 39 piebalds. Certain of the

selfs had a small white spot (always less than 10 per

cent.) ventrally, and it is possible that these may be pie-

balds. If so, the ratio of 1 self:1 piebald may be more

closely approached, indicating that the small white dorsal

spot is a non-genetic imperfection of dominance occurring

in self mice heterozygous for piebald. None of the ‘‘self”’

progeny from crosses of blaze with piebald exhibit any

dorsal spotting. One other possibility is that the blaze

may be due to a separate gene either identical with or

similar to the gene which differentiated the blaze mice

reported by Little. The second or other segregating gen-

eration which is critical for determining this point has

not been bred. Of course the term self should apply

properly only to mice which show no trace of white spot-

ting. Genetically it is the sum of the factors producing

‘the normal solid coat of the wild mouse and as such

should be always the same unless new mutations take

place or unless certain somatic variability exists uncon-

nected with a germinal cause. Sufficient data in the case

of the dorsal spotting of apparently self mice are not at

present available to decide between these alternatives.

In the case of the small belly spotting, as will be seen

later, the case is somewhat different.

For convenience in reference the range of variability

of each of the several genotypes discussed above has

been placed in tabular-form (Table I). All ranges ex-

cept that for piebald (line 3) have been drawn from ob-

No. 635] WHITE SPOTTING IN MICE 479

servations by the writer and all data in the tables and

figures of this report have been tabulated according to

thesé ranges. Such a table is approximate and may be

only temporary, for the breeding of larger numbers of

Summary oF Rance Data

TABLE I

Type of Spotting | Genotype iss eae peti e ya

l; "en ad dw See ees | Wwss |, 100 to 50 | 100 to 85

2. Pie T oait, BOries) 2.5. 2038 | wwss 50 to 0 | 85 to 12

3. Piebald (other data) ovo ouei | wwss 100 to 0 | 85 to 0

A Ton A. o cat ese. | WwSs 45to 0 | 90to 4

Siecle | WwSS 8to 0 | 50tol5

SA Mehta ak EE E ET A O AES | wwSS or |

wwss 3 to 0 | 12 to 0

spotted mice may increase the range now attributed to

each type. Whether the ranges of variability represent

the norm for each type is not at present known, nor can

it be known until each type by inbreeding or other suit-

able methods has been separated from the subsidiary

factors which, as it will appear, alter the expression of

the main spotting factors.

Mopiryine FACTORS

The general result of the foregoing discussion is sim-

ply an exposition of the great amount of variability ex-

istent within each type of spotted mice, all of which are

identical as regards the main genes now known to deter-

mine white spotting. The question naturally arises, if

a mouse with a coat entirely white except for pigment in

the eyes and a mouse in which the dorsal surface is

equally divided between pigmented and white spaces are

genetically identical as regards the main genes W and s,

how then do they differ? Is each merely a somatie va-

riation (fluctuation) of a genetic complex determining a

combination of colored and white spaces halfway between

these extremes? Or do other genetic factors in com-

bination with the main spotting genes determine greater

or less amounts of pigment in the coat?

If we adopt the fluctuation hypothesis then we must

480 THE AMERICAN NATURALIST [Von. LIV

demonstrate that the amount of spotting in the offspring

is not correlated with the amount of spotting in the

parents. Being due to non-genetic causes, the variations

within the type should appear purely at random. An ex:

cellent example of this kind of variation has been com-

municated in a paper read before the American Society

of Naturalists at their December, 1919, meeting by Dr.

Sewall Wright. The piebald pattern of guinea pigs ap-

peared in his experiments to be determined primarily by

one recessive Mendelian gene, the expression of which is

altered through extremely wide ranges by environment,

sex and the uncontrolled vagaries of development.

The second explanation presumes the occurrence of

modifying genes separable in heredity from other genes

for spotting, yet only coming to expression in the pres-

ence of the main gene or genes for spotting. If this be

true, the various grades of spotting within any type such

as black-eyed white should be heritable. The amount of

spotting in the offspring should be definitely correlated

with the amount of spotting in the parents. Whiter

black-eyed whites, for example, should have whiter off-

spring; and darker black-eyed whites should have darker

offspring. Little has found some evidence that this may

be true of certain grades of piebald, for he noted that the

offspring of hybrids between selfs and piebald tended to

cluster about the mode of the particular piebald grand-

parents. :

The experimental test of these diverse explanations

has in the present experiments consisted of crossing

mice of one spotted type with lighter (much spotted)

and darker (little spotted) mice of another type. The

offspring of the lighter and darker matings have then

been compared as to mean and range. Some matings

of lighter types inter se and darker types inter se have

been made, and while these have not yet yielded enough

offspring to have a decisive bearing on the question,

they indicate that black-eyed white and piebalds with

more white spotting than the mean of their respective

types and with amounts of spotting below the mean

No. 635] WHITE SPOTTING IN MICE 481

breed fairly true to these different conditions. The re-

sults of the first mentioned matings have shown in gen-

eral that the altered expression of the spotting factors

W and s in the direction of more or less white spotting is

definitely transmitted to the offspring. The evidence on

this point is presented in Table II.

Cross 1 of this table presents the distribution of off-

spring of crosses of black-eyed whites with dark pie-

balds, viz., those with dorsal white spotting ranging

_ from 0-10 per cent. Among the black-eyed white parents

all grades of spotting were approximately equally rep-

resented. The mode of the black-eyed white offspring is

at 85-81 per cent. of white, the mean of white spotting

is 80.5 per cent. +.7 per cent., and they range from 100

to 51 per cent. white, with a standard deviation of 11.65

+.. The piebald young have a mean grade of 10.9 = .4

per cent., a standard deviation of 8.1 + 3, and all grades

of piebald from 0 to 50 per cent. white are represented,

although the majority is less than 20 per cent. white.

With these crosses are to be compared the offspring of

Cross 2, of which the parents were black-eyed whites of

the same grades as were used in Cross 1, and light pie-

balds, viz., those which were more than 10 per cent. white

dordalty. The black-eyed white young were centered

about a mode at 95-91 per cent. white; their mean is

88.5 per cent. +.8 per cent., and their standard devia-

tion 7.8 +.5. Their range is considerably less than the

range of black-eyed whites in cross 1, due to the absence

from the distribution of all.classes less than 70-66 per

cent. white. The piebald young from Cross 2 have a

mean of 16.4+ 1.2 per cent. white and a standard devia-

tion of 12.1 +.8. The range of the ‘piebalds is the same

as in Cross 1, but the lighter classes are more heavily

represented than in Cross 1, and this is reflected in the

higher standard deviation.

These crosses are a test of the nature of the differ-

ences between darker and lighter piebalds. That such

differences are genetic is clearly shown by the results, for

the lighter piebalds have appreciably lighter offspring

[Vou. LIV

482

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484 THE AMERICAN NATURALIST [Vou. LIV

than the darker piebalds. The difference in the means

of white spotting in the offspring of the two crosses is

significant when the errors are considered. When we

consider the kinds of individuals produced, we find that

the darker piebalds produce certain classes of young

which the lighter piebalds do not produce. The darker

piebalds appear to possess then a factor or factors deter-

mining an increase in the amount of pigment produced

and a consequent decrease in the amount of the white

spotting. The lighter piebalds do not give evidence of

possessing these genes or if they do possess certain of

: them they do not at any rate possess the number or the

kinds which are apparent in the darker piebalds. It is

to be especially noted that such modifying genes produce

effects equally on the amount of black-eyed white spot-

ting and on the amount of piebald spotting.

In the above case the assumed modifying genes came

from piebalds differing in amounts of white spotting.

In crosses 3 and 4 (Table IIT) their effect has been tested

when entering in connection with black-eyed white spot-

ting. The spotting produced in Type ‘‘A’’s (Ww/Ss)

must be due to the gene W for animals of the formula

Ss are not spotted except for certain imperfections of

dominance already noted. Darker Type ‘‘A’’s (0-10

per cent. white dorsally) and lighter Type ‘‘A’’s (more.

than 10 per cent. white) were tested by mating with pie-

balds of various grades ranging from 20 per cent. white

to 0 per cent white. The young from darker Type ‘‘A’’s

X piebald (Cross 3) were of three sorts as expected,

black-eyed whites, ‘‘spotted’’ (comprising Type ‘‘A’’s

‘and piebalds) and selfs in the approximate ratio of

1:2:1. The mean of the black-eyed whites was 81.3 + .8

per cent. white, which is about the same as the mean of

black-eyed whites out of dark piebalds. They varied

from 100 per cent. to 56 per cent. white with a standard

deviation of 10.3+.6. The ‘‘spotted’’ young from this

cross had a mean grade of 8.6 per cent.+.5, a range

` 4 The difference in mean grade of offspring of lighter and darker parents

is 8.0 + 1.06, or more than 7 times the probable error.

WHITE SPOTTING IN MICE

485

No. 635]

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— 486 THE AMERICAN NATURALIST [Vou. LIV

from 50 to 0 per cent. white and a standard deviation of

8.9 +3.

In Cross 4 the piebald ‘parents were of similar grades

to those used in Cross 3 while the Type ‘‘A’’ parents

were all more than 10 per cent. white dorsally. The

black-eyed white young from this cross had a mean grade

of 91.7 +.7 per cent. white. They varied from 100 per

cent. to 76 per cent. white with a standard deviation of

6.19+.5. The ‘‘spotted’’ young (Type ‘‘A’’ and piebald

mixed) were of mean grade 17.2+1.0 per cent. white,

and varied from 50 per cent. to 0 per cent. white, with a

standard deviation of 13.2+.7. In general the offspring

of the lighter Type ‘‘A’’ parents were characterized by

about 10 per cent. more white spotting than the offspring

of the darker Type ‘‘A’’ parents. The difference of the

parents in amount of spotting is thence reflected in sim-

ilar differences in their respective offspring. _

The indications from the tests of Type ‘‘A’’ spotted

mice are that the same modifying factors which were

assumed to cause the variation in the amount of spotting

in piebalds cause also the variation in the expression of

the gene W as evidenced in Type “A” spotting. Here

also certain classes of dark black-eyed whites appear

when dark Type ‘‘A’’s are bred which are absent from

the young produced by lighter Type ‘‘A’’s. -This ab-

sence is witnessed by the significantly lower variabilities

of the black-eyed white offspring of both lighter piebald

and lighter Type ‘‘A’’s. The effect of the modifiers is

the opposite when acting on the piebald and spotted off-

spring of these crosses. The piebald offspring of lighter

piebald and Type ‘‘A’’ parents have a greater range

and consequently a higher standard deviation than the

piebald offspring of darker parents. The darkening

modifiers add darker classes to the black-eyed white

range but subtract from the lighter classes of piebald,

lowering in general the amount of white in each type. A

‘‘light’’ piebald, namely, one near the upper limit of pie-

bald spotting and lacking the dark modifiers, may thus

be similar in appearance to a ‘‘dark’’ black-eyed white,

No. 635] WHITE SPOTTING IN MICE 487

namely, one near the lower limit of black-eyed white

spotting and possessing the dark modifiers. Such con-

fusion is not apt to occur in the progeny of single pairs,

for if the parents possess the modifiers dark black-eyed

whites will be produced, but also dark piebalds, leaving

an appreciable gap between the two types.

THE NATURE oF THE MODIFIERS

The effect of the same modifying genes upon the ex-

pression of both black-eyed white and piebald spotting

furnishes certain information concerning the nature of

the modifying genes themselves. The main spotting

genes W and s have been found to be properties of dis-

tinct loci in different chromosomes (Dunn, 1920). There-

fore the gene or genes which modify both W and s must

determine the general conditions underlying the forma-

tion of pigment in the coat rather than specific condi-

` tions associated with a particular spotting gene. From

the present evidence it appears to the writer that these

modifying genes alter the internal environment of en-

zyme and chromogen upon which the main spotting genes

W and s act to bring about their specific effects. The

darkening modifiers appear to increase the general

amount of color forming substance. In the presence of

such modifiers both W and s produce relatively less than

the normal amount of white spotting.

THE Source or THE MODIFIERS

The genes modifying the amount of white spotting in

the mice used in these experiments appear to have come

from certain self mice with which black-eyed whites and

piebalds had been crossed. The black-eyed white stock

used was originally bred by Dr. J. A. Detlefsen and

reached this laboratory through a fancier. When first

bred inter se no grading records were kept, but I am cer-

tain that no black-eyed whites were produced which were

less than 70 per cent. white. This agrees fairly well with

the range of the black-eyed whites bred by Little. The

488 THE AMERICAN NATURALIST [Von. LIV

piebalds used were obtained originally from fanciers.

Sixty-five such piebalds varied from approximately 50

per cent. white to 0 per cent. white dorsally, with a mean

grade of about 22 per cent. white dorsally. When these

had been crossed with self mice 278 piebalds extracted in

the second generation averaged 8 per cent. white dor-

sally. Their range was approximately the same as that

of the original piebalds but the darker classes between

0-10 per cent. white had been greatly enlarged. It is

probably from this cross that the darkening modifiers

were introduced into the piebald stock, for the piebalds

used in all subsequent crosses were descended from these

extracted piebalds, most of which showed but little white

spotting. It might be supposed that the darkness of the

extracted piebalds could be explained on the basis of con-

tamination of the piebald gene during its residence in

self animals. That this is not the true explanation is in-

dicated by other results. The cross of black-eyed white

X piebald (Table II, Cross 1) yields black-eyed white

progeny with a mean grade of 82.8 per cent. and pie-

balds averaging 12.5 per cent. The cross Type “A”

X piebald (Table II, Cross 3) yields black-eyed white

young with a mean grade of 84.8 per cent. white and

‘‘spotted’’ young, with a mean grade of 11.6 per cent.

white. The means in the two crosses do not differ sen-

sibly. Yet Type ‘‘A’’ is heterozygous for self and the

young it produces should exhibit contamination if any

takes place. Certain of the selfs with which piebalds

were crossed originally, and certain selfs with which

black-eyed whites were crossed later to produce Type

‘*A’’s appear to have contributed modifying genes which

could have had no expression in the self mice, since these

lacked the main spotting genes. Not all selfs are geno-

typically similar in respect to the modifiers, since from

crosses of black-eyed whites with certain selfs has arisen

a lighter strain of black-eyed white which is now being

bred, while from other selfs has come a darker strain of

black-eyed white which probably possesses the modifiers.

The probable existence of additional genes in mice of

the nature of modifying factors has been stressed be-

cause it is felt that animals which can be easily bred in

the laboratory should be thoroughly explored genetically,

in order to find out.characters not known at present. As

the number of genes approaches the number of chromo-

somes, the probabilities of finding linkage become greater

and it is through the investigation of linkage and the

localization of the hereditary determiners that the most

exact knowledge concerning the nature of the hereditary

material can be secured.

INHERITANCE OF BELLY SPOTTING

Before concluding this discussion of modifiers of white

spotting in mice some evidence may be added which bears

on the appearance of a small amount of white spotting

on the bellies of mice which are genetically self as re-

gards W and s. Piebald spotting has been regarded as

the recessive allelomorph of self or uniform coloration,

and all the evidence from crosses between these two

varieties supports this view. It has been noticed, how-

ever, that the heterozygotes resulting in F, are not al-

ways exact duplicates of the self parents. Where large

numbers have been bred, investigators have always

found F, animals with some white spotting, usually con-

sisting of a patch of white on the belly not exceeding 12

per cent. of the ventral surface.

Records of experiments in the present investigation

disclosed this apparent imperfection of dominance, and `

all animals resulting from the cross of piebald with self

have been graded according to the per cent. of white

spotting exhibited. A tabulation of these records shows

that out of 51 pure piebalds bred to self mice, 36 pro-

duced only self mice with no white hairs; 15 produced

some perfect self and some with white hairs. Of these 15

parents only 7 produced more than one young showing

any white spotting. 557 young resulted from all piebald

X self matings, of which 524 showed no trace of spotting

490 THE AMERICAN NATURALIST [Vou. LIV

while 33, or about 6 per cent., showed one or more white

hairs. The spotting in the F, mice was confined to the.

ventral surface,* usually in the center of the belly. The

minimum size of this spot was a few white hairs, its

maximum extent was 12 per cent. of the ventral surface,

and its average extent was 3 per cent. of the ventral sur-

face. All young produced by this cross must be regarded

as selfs since all produced young, when interbred, in the

ratio of three selfs to one piebald. What, then, is the

cause of the appearance of certain animals in F, which

show some characteristics of the recessive parent?

There may be two answers to this question: (1) the

apparent imperfections of dominance in F, may be due

to fluctuations in the somatic expression of the piebald

gene when present singly in the zygote; (2) they may be

due to a definite gene or genes for a small amount of

ventral spotting in mice heterozygous for piebald.

As evidence for the first. view we have relevant data

in the experiments just reported. An analysis reveals

that the production of young with small amounts of

white spotting is not correlated with the somatic appear-

ance of the piebald parents since in amount and distribu-

tion of spotting these parents as a class are not distin-

guishable from the parents which produced only true

self young. On the other hand, practically all the spotted

F,s which were produced by individual piebald parents

had for their other parent a particular self animal. Ap-

parently the selfs as well as the piebalds varied in the

-~ power of producing slightly spotted young. Causes in-

fluencing the production of this small amount of spotting

in F, may have been contributed by the self parents, al-

though the posibility that part of the causes came from

the piebald parents is not excluded by the evidence. If

this be accepted as evidence that selfs share in the pro-

duction of slightly spotted mice, then certain selfs must

differ genetically from other selfs, and the point of dif-

ference may be a separate recessive factor for ventral

5 With the exception of the few dorsally spotted mice referred to on p. —-

No. 635] WHITE SPOTTING IN MICE 491

spotting, which is expressed in the presence of but one

dose of piebald.

On this view, self animals which, when bred to pie-

balds, produce animals with small amounts of ventral

spotting, must be heterozygous for a recessive gene for

such spotting. Moreover, the piebald parents must also

be heterozygous in the same gene. This is required by

the evidence. 15 pairs of parents producing young with

some white gave a total of 151 young, of which 33, or 21

per cent., showed some white. This is nearly a ratio of

three perfect selfs to one with some white, and if the

cause of the small spotting is a gene, both piebald and

self parents must have been heterozygous for it. The

presence of such a gene in piebald mice is difficult of

demonstration, since when bred together piebald mice

produce only piebalds, with their characteristic dorsal

and ventral spotting, which obscures the action of any

genes for spotting of the ventrum only.

A summary now partially completed shows that the

peculiarity of small belly spotting in ‘‘self’’ mice does

not breed true. Matings of ‘‘belly spot’’ X ‘‘belly spot’’

have produced 70 young of which 57 were graded as self

(viz., having either no white spotting or less than 12 per

cent. white ventrally) while 13 were clearly piebald. In-

dividual tests showed that all belly spotted mice bred

were heterozygous for piebald, so this ratio is probably

a deviation from a 3:1 ratio. Of the 57 ‘‘selfs,’’ 41 had

some ventral spotting like the parents, while 16 were true

selfs without any white hairs. The appearance of these

true selfs, and the fact that all belly spotted mice tested

were heterozygous for piebald indicate that the assumed

gene for belly spotting is only expressed by mice which

are heterozygous for piebald. The total distribution

from the matings just referred to resembles somewhat a

1:2:1 ratio, which would be expected if selfs hetero-

zygous for piebald show by reason of an imperfection in

dominance, a small amount of ventral spotting. The

distribution tabulated on this assumption follows:

492 THE AMERICAN NATURALIST [Vou. LIV

| Self (SS) i Eana Piebald ss Total .

Obwerved ai L i6 Al 13 70

Rae o Do 35 17.5 70

That the variation is inherited is argued by the much

greater frequency of belly spotted individuals in the off-

spring of parents showing the characteristic than in the

total progeny of all self X piebald matings. In the prog- -

eny of belly spotted mice 71 per cent. of all selfs were

belly spotted, while of all selfs heterozygous for piebald

only 6 per cent. were belly spotted. The problem is

doubtless complicated (as are probably all spotting prob-

lems) by the occurrence of a certain amount of uncon-

trollable somatic variation in the expression of the genes,

by reason of which the truly genetic variations cannot

always be isolated with certainty. In addition the last

mentioned modifier seems to be dependent for expres- |

sion on a particular complex of genes, namely, the pres-

ence in one individual of one dose of piebald and c one of

its normal allelomorph (Ss).

SUMMARY oF MODIFIERS OF AMouNT OF WHITE SPOTTING

1. The expresson of the complex of genes producing

- black-eyed white spotting (Wwss) is subject to modifica-

tion by a gene or genes determining an increased amount

of pigment and a decreased amount of white spotting.

The normal range of black-eyed whites being from 100 to

70 per cent. white dorsally, the addition of such darken-

ing modifiers decreases the mean amount of white spot-

ting in such a fashion that the range is extended to as

low as 50 per cent. white. |

2. The expression of the gene for piebald spotting is

subject to modification in the same direction and by the

same gene or genes which modify the expression of black-

eyed white. When these darkening modifiers are pres-

ent in mice pure for piebald (ss) most of the mice are

No. 635] WHITE SPOTTING IN MICE 493

about 10 per cent. or less white dorsally, while those with

larger percentage of white are much rarer than among

piebalds lacking the darkening modifiers.

3. The genotype Ss ordinarily produces the self coat,

but in the presence of an additional modifying gene pro-

duces a small amount of white spotting on the ventral

surface, varying in size from a few white hairs to 12 per

eent. of that surface.

MODIFIERS AFFECTING LOCALIZATION OF WHITE SPOTTING

IN PIrEBALD MICE

- The presence of separate genes for certain localiza-

tions of spotting in piebald mice has been suspected for

Some time. Fanciers, for instance, have given separate

ħames to such types as ‘‘Dutch belted” mice and have

claimed that they bred true to this condition, which re-

sembles the Dutch belted pattern of cattle. Consequently

when piebald mice showing distinct localization of white

spotting in the pelt have been born in these experiments

they have been saved for further study.

- The most striking of these localized spotting types

has appeared sporadically in the piebald stock. From

its appearance I have called it ‘‘white face” although

it varies from a small blaze of white on the forehead to

a white spot which covers the whole head back as far as

the ears. The belly is spotted with white as in ordinary

piebalds. The strain of white face which has been iso-

lated breeds true to this condition, 8 matings of white-

face by white face having produced 46 young, all of them

white faced. The offspring of one pair of white faced

mice which were brother and sister, have been inbred,

brother to sister, for four generations and there have

been born in these matings to date 36 young, all white

faced, and varying but little in the amount and distribu-

tion of the white spotting on the face.

_ One other sub-type of piebald is perhaps also sep-

arable. This is the type known as belted. It varies

494 THE AMERICAN NATURALIST [Vou. LIV

from a wide white belt covering all of the back from

shoulders to hind limbs (about 45 or 50 per cent. of

the dorsal surface) down to a small spot located like-

wise on the back within this same area. The rest of the

dorsum including the face is colored. The belly is

spotted with white as in ordinary piebalds. Several

good examples of this type have been saved and a few

matings have been made recently. Only two matings of

belted by belted have produced young. All of these

young (four in number) are belted, with no spotting else-

where on the dorsum. This is hardly a sufficient test of

the separateness of this type, but more data are being

accumulated.

It seems fairly evident that the production of the pat-

tern of piebald mice is due to a complex of genes modi-

fying the expression of one main gene. It is probable

that each such gene in the complex determines the non-

development of pigment in one part of the pelage. Asa

means of testing these hypotheses and of separating, if

present, the various causative factors, the inbreeding

method advanced by East warrants a trial as the most

likely to bring results. Piebald mice of several different

types should be inbred and the inbreeding continued in

the various lines, brother to sister, for seven or eight

generations. This should result in the purification of

the types by the elimination of heterozygotes, and the

resulting pure recessives should exhibit, if present, the

effects of the separate factors. Such inbreeding is now

under way on the white face and on the belted types.

LITERATURE CITED

Dunn, L. C.

1920. Independent Genes in Mice. Genetics, 5: 344-361.

Little, C. C.

1914. Dominant and Recessive Spotting in Mice. AMER, NAT., 48:

74-83.

Little, C. C.

1915. The Inheritance ah Black-eyed White Spotting in Mice. AMER.

NAT., 49: 727-7

No. 635] WHITE SPOTTING IN MICE 495

Little, C. C.

1917a. Evidence of ra Factors in Mice and Rats. AMER. NAT.,

51: 457-4

ar CG,

1917b. The Relation of Yellow Coat Color and Black- Seagal Wer Spot-

ting of Mice in Inheritance. Genetics, 2: 433-4

STRUCTURAL CHARACTERISTICS OF THE

HAIR OF MAMMALS

DR. LEON AUGUSTUS HAUSMAN

ZOOLOGICAL LABORATORY, CORNELL UNIVERSITY

THE microscopic structures in the hairs of mammals

offer certain definite and unchanging characteristics

which have been found useful for the purposes of iden-

tification The present paper aims to be an answer to

numerous inquiries which the writer has received re-

garding: (1) the structure of a large number of mam-

. mal hairs, with especial reference to the possibility of

systematically classifying them upon some morphologi-

cally accurate basis; (22) the relationships between the

various elemental structures of the hair shaft; and (3)

the methods employed in the preparation of the hairs

for microscopic analysis.

The primary development of the hair begins as a local-

ized proliferation of the cells of the outermost layer of

the skin, known as the epidermis, forming a dense aggre-

gation of cells which elongates downward into the

corium, or dermis, beneath. Directly underneath this

downward-élongated, flask-shaped depression of the cells

of the epidermis there is formed a dense mass composed -

of cells of the corium, or dermis, which ultimately be-

comes the papilla of the hair (P, Fig. 178). The flask-

shaped depression now becomes lined with cells of the

epidermis, and is called the follicle. The epithelial con-

tents of the growing follicle elongate into an avial strand

of fusiform, spindle cells, which later undergoes keratini-

zation, or becomes horny, and forms the hair shaft. The

lower portion of the shaft expands into a bulb which en-

1 Hausman: (1) ‘*‘The Microscopic Identification of Commercial Fur

Hairs,’’ Scientific Monthly, Jan., 1920, pp. 70-78; (2) ‘‘A Micrological

Investigation of the Hair Structure of the Monotremata,’? Am. Journal

of Anatomy, Sept., 1920, (3) ‘‘The Microscopie Identification of Mammal

Hairs Used in the Textile Industry,’’ The Scientific American, Feb, 21, 1920.

No. 635] _ THE HAIR OF MAMMALS 497

wraps the papilla (Fig. 178). The shaft elongates up-

ward, and emerges through the epidermis, an aperture

thereafter known as the mouth of the follicle, and con-

tinues to grow, the growth being exclusively confined to

the bulbous lower, or proximal portion of the shaft.

Here the conversion of matrix cells into keratinized hair

shaft cells continually progresses. Mammal hairs are in

general either circular or ‘elliptical in cross section.?

Those which are circular are straight, or but slightly

curved, while those of elliptical cross section are curly

or kinky, the amount of curl being dependent upon the

flatness of the ellipse.

The hair shaft consists of four structural units (Figs.

167 and 168): (1) the medulla, sometimes termed the

pith, from a somewhat analogous structure in plant

stems, and which is built up of many shrunken and vari-

ously disposed cells or chambers, representing dried and >

cornified epithelial structures connected by a branching

filamentous network, which sometimes completely fills

the medullary column, but which is interrupted in many

cases; (2) the cortex, or shell of the hair shaft, surround-

ing the medulla, and composed of elongate, fusiform cells

or hair-spindles, coalesced together into a horny, almost

homogeneous, hyaline mass and forming in many cases,

where the medulla is reduced, a large proportion of the

hair shaft; (3) the pigment granules, to which the color

of the hair is primarily due (though in some hairs the

pigment is diffuse and not in granular form), scattered

about within or between the hair spindles, and in some

hairs arranged in definite patterns; and (4) the cuticle,

or outermost integument of the hair shaft, lying upon

the cortex, and composed of imbricated, thin, hyaline,

colorless seales of varying forms and dimensions. It is

the forms, relationships, and measurements of these four

elements, together with the measurements of the diam-

cats pioneer work in the relation of the shape of the cross section of

man hair in its waviness to Dr. Pruner-Bey’s ‘‘De La Chevelure comme

Oharaet odn kah des Races Humaines, d’après des Recherches Microsco-

Piques,’’ in Mémoires de la Société d’Anthropologie de Paris, Vol. 2, p. 1.

No. 635] THE HAIR OF MAMMALS ' 499

eter of the hair shaft itself, in micra* which constitute

the series of determinative criteria for each species of

air.

Medullas can be conveniently grouped, according to

their forms, as they: (1) discontinuous, as in the hair of

the Botta’s pocket gopher (Thomomomys botte) (Fig.

3); (2) continuous, as in the hair of the kinkajou (Cer-

coleptes caudivolvulus) (Fig. 7); and (3) fragmental, as

in the hair of the wombat (Phascolomys ursinus) (Fig.

64).

The cuticular scales fall readily into two well-marked

types, the: (1) imbricate, represented in the hair of the

civet (Arctogalidia fusca) (Fig. 1); and (2) coronal, rep-

resented in the hair of the majority of the bats, e.g., the

mastiff bat (Molossus sinaloe) (Fig. 105).

The cortex element of the hair shaft structure exhibits

few or no traces of the form of its component fusiform

EXPLANATION OF PLATE I

Fie. 1. Civet (Arctogalidia hg 21.00 u.

Fie. 2. Pocket Kangaroo Rat (Dipodomys m. stern a eS

Fic. 3. Botta’s Pocket Gopher ( tir ys botte), -50 u

Fic. 4 Coypu Rat (Myocastor coypus), 11 be

Fig. 5. lack Lemur (Lemur kaka), 20.00 u.

Fic. 6. Chimpanz (Anthropopithecus tr Se trees: 119.00 u.

Fia. T. Sinkajow (Cercoleptes caudivolvulus),

Fie. 8. Rocky Jump Mouse (Zapus princep a

Fic. 9. Sierra Jumping Mouse (Zapus trinotatus a 17. 00 u.

a. 10. tes (Orolestes obscurus), 1

ro 0.0

Fic. 11. Caeamixtli (Bassariscus astut ue flavus), 17.00 u.

Fig, 12, Striped Bandicoot (Perameles pesto bougainvillei), 17.00 u

Fic. 13. European Mole (Talpa europea), 17.00

Fig. 14. Platypus ee eae anatinus), 8.00

Fie. 15. Star Nosed Mole (Condylura cristata), 25.50

Fie. 16. Pigmy Fl slep its er eag pygmea), ‘17. 00 u.

Fig. 17. Black Bear (Ursinus americanus), 2 p

Fig. 18. ed Kangaroo (Macropus jasna an

Fic. 19. Microgale reaala an ht

Fic. 20. Aye aye (Chiromys agancrient) 24.00 p.

Fig. 21. Koala a tae sh om ereus), 20.40 u

Fic. 22. Dormouse (Muscardinus Sars: nae 00 p.

Fie. 23 oe. 3 Mose (Mus musculus), 17.00 p.

Fig. 24. ien p paee gymnura gymnura), 19.00 u.

Frc. 25. oodland Jumping Mouse (Napeozapus insignis insignis), 21.00 u

Fig. 26. abe (Glis glis pon 30.00

Fig. 27. Rat (albino) (Mus n orvegious), 17.50 u.

Fic. 28. Hoy’s Shrew (Microsorex hoyi), 18.00 u.

3 One micron (#) is 1/1,000 of a millimeter, or circa 1/254,000 of an

No. 635] THE HAIR OF MAMMALS 501

cells, or hair spindles, except under dissociative treat-

ment with caustic soda, caustic potash, or acids of vari-

ous sorts, and hence is of very little value as a criterion

for determining the species of the hair.

The coloring matter, or pigment, of the hair shaft is

either distributed diffusely and homogeneously through-

out the cortex, or exists as an aggregation of granules

between or within the fusiform cortical cells, or hair

tween or within the fusiform cortical cells, or hair

spindles. Where the latter is the case the granules ap-

pear to be of definite form and mode of placentation for

each species of hair. In many eases, it is believed that

the characteristic patterns formed by the arrangement

of the pigment granules, as well as the form of the gran-

ules themselves may offer a valuable character for iden-

tification. Figs. 190, 191, and 192 show respectively por-

tions of the hair shafts of the mandril (Cyanocephalus

maimon), badger (Taxidea americana), and wolverene

(Gulo luscus), very highly magnified, illustrative of the

differences which may exist in the configuration and ar-

EXPLANATION OF PLATE. II

Fig. 29. Geogale (Geogale aurita),

Fic. 30. Potamogale (Potamo: ee veton) 10. fd

Fig. 31. Golden Mole (Amblys rie),

Fig. 32. Heliophobius THES kapiti), sed 00 a

Fic. 33. Marsh Shrew (Neosorer palustris Anir, 11.30 u.

Fic. 34. Rock Runner (Petrodromus tetradactylus), 37.00

Fic. 35. Speke’s Jumping Mouse Jaded spekii), 25.00 a

Fig. 36. Walrus (Trichechus ros

Fie. 37. American Wapiti (cereus canadensis), ae ig

G. 88. Mongoose Lemur ur oz)

Fic. 39. Colugo ( aas E, 20 ia

Fic. 40. Coendou (Coendou sanctemarte)

Fig. 41. Flying Squirrel (Sohireteras voluectia), 1 a,

Fig. 42. Bactrian Camel (0 Be S bactrianus),

Fic. 43. Tiger (Felis tigris), 6

Fig. 44. Bruce’s Dassie e Sona rudolphi), 22.00 u.

`25.50 u.

Fig. 49. de S Kangaroo _taeororne giganteus), re a vio

re (D viverrinu vpi

. asyu

Fig, 51. Dansar Uai ea s capybara), 3 rei RR

Fic. 52. Small Three-Spined Tenrec (H miventates variegatus), 28.00 u.

Fıc. 53. Unau (Cholepus capitalis), pe

Fic. 54. European Porcupine (Hystris prtatate). 140.00 p.

Fie. 55. Spiny Anteater (Tachyglossus oo 103.00 u.

Fie. 56. Agouti (Dasyprocta urucuna), 150

No. 635] THE HAIR OF MAMMALS 503

rangement of the pigment granules. There seems to be

also a wide variation in color value and color depth of the

pigment granules, a variation which is especially well

brought out by the use of reflected light, or of dark field

illumination. These methods of examination will be ex-

plained later.

In a recent contribution to the structure of the mam-

malian hairt the author has pointed out that mammal

hairs may be conveniently classified, on the basis. of the

configuration of the cuticular scales and medulla, as

follows:

CUTICULAR SCALES

I. Imbricate

1. Ovate, represented by Figs. 1 to 7

2. Acuminate, represented by Figs. 8 to 20

3. Elongate, represented by Figs. 21 to 35

4, Crenate, represented by Figs. 36 to 67

5. Flattened, represented by Figs. 68 to 92

PXPLANATION OF PLATE III

Fig. 57, African Elephant (Lorodonta africana capensis), 80.00 u.

Fic, 58. Ethiopian Aard Vark (Oryc sad @æthiopicus), 252.00 u.

Fig. 59.. Hyena (Hyena hyena schillingsi), a

Fıc. 60. Richard’s Seal (Phoca richardi), 232:

Fic. 61. Two-Horned Rhinoceros (Diceros Da bicornis), 147.00 u.

be.

Fic. 66. Dinomys (Dinomys At i td 120.00

Fic. 67. Wild Boar (Sus scrofa), 680.00 u.

Fic. 68. Two-Toed Anteater CE es 17.00 u.

Fig. 69. Bilack-Faced Bat (Melanycteris melanops), 10.00 u.

Fic, 70. Small Long-Tongued oe it Bat east eh minimus), 13.00 u.

Fie. 71. Chevrotain (Tragulus boreanus), 00 u.

Fig. 72. Llama (Lama glama), 32.00 u.

Fic. 73. Fox Terrier, .60

Fic. 74. | Ingraham’s Hutia (Oen ingrahami), 76.50 u.

Fira. 75. Jerse az. $

Fic. 76. American Bison (Bison amaia Aia

Fic. 77. Manatee (Manatus ess phn 136.00 u

Fig. 78. Pinehs (Midas oe 0

Ete: T9. Boschbok (Tragelephus som aly 119.00 u.

Fria. 80. Sumatran Chevrotain (Tragulus eagle 55.70 ġ

G. 81. Hispid Pocket Mouse (Perognathus AS g 127.00 p-

Fig. 82. Squirrel Monkey (Chrysothrix sciurea).

Fic. 88. Agouti (Dasyprocta variegata), 127.50 u.

Fic. 84. Tamandua (Tamandua tetradoctyla etensis), 85.00 u.

4 Hausman: ‘‘A Micrological Investigation of ril Hair ‘Structure of

the Monotremata, ”? Am. Journal of Anatomy, Sept.,

No. 635]

THE HAIR OF MAMMALS

II. Coronal

1. Simple, represented by Figs. 93 to 102

2. Serrate, represented by Figs. 103 to 107

3. Dentate, represented by Figs. 108 to 113

A, Simple

MeEDULLAS

I. Discontinuous

1. Ovate, represented by Figs. 114 to 126

2. Elongate, represented by Figs. 127 to 128

3. Flattened, represented by Figs. 129 to 135

B. Compound

1. Ovate, represented by Fig. 136

2. Flattened, represented by Fig. 137

II. Continuous

. Nodose, represented by Figs. 138 to 147

a Homogeneous, represented by Figs. 148 to 153

II. Fragmental

Represented by Figs. 115 to 166

EXPLANATION OF PLATE IV

Gorilla (Gorilla gorilla), 37.40 u.

Virginia Deer (Odocoileus maar te

Ham

Bicolored Leaf-Nosed Bat “(iinposiaeru ioii, aie u

Indian Vampire Bat (Lavia frons), 12.00 p.

Leaf-Nosed Bat( Rhinolophus hainanus), 10.00

Horseshoe Bat (Rhinolophus acuminatus), 10. 00 p pe

= ea (Pipistrellus subflavus), 6.80 u.

a Vampire Bat (Petalia capensis), 10.00 u.

Cpe Mole Rat (

Phyllops (Phyllops falcatus), 10.

Mastiff Bat (Molossus sinaloae), 9.00 u

Wrinkled-Lipped Bat Rr i863 agen ns [he

Intermediate Bat (Mormops intermedia), 6.8

Chief (Och princep k 13.60 u.

Pika (Ochotona figginsi), 11.30

Pik tona wardi), 11

(Och 80 u-

Alpine Chinchilla (Lagidium pernarum), 11.30

Little Banded Anteater (Myrmecobius Tasoh. 20.40 u.

505

Porto-Rican Bat ae pernetit chattel pA 8.50 u.

anuru 11.0

No. 635] THE HAIR OF MAMMALS 507

The hair type chosen to be shown as the most repre-

sentative of each species is that type which, it was found,

in most cases constitutes the major portion of the body

covering, t.e., the fur, or under hair. This usually under-

lies a comparatively more or less sparse growth of

longer, coarser, stouter hair, which is termed the pro-

tective, or over hair. In typically aquatic mammals, such

as the seals, walruses, etc., the protective hair is thicker

than in those forms which are merely amphibious, such

as the platypus, muskrats, beavers, ete. In such mammals

as the whales, porpoises, etc., which are wholly aquatic,

the fur hair has apparently vanished altogether. The

only remaining hairs upon the body are, as a rule, con-

fined to a very few stout stubs of hairs, located commonly

in the region about the muzzle. In such hairs the cuticu-

lar scales are always of one type, illustrated by the muz-

zle hair of the dugong (Dugong dugong) (Fig. 159).

In identification, however, it is sometimes necessary

to prepare for examination shafts of both the fur and the

EXPLANATION OF PLATE V

Fig. 113. pean Otter (Lutra vulgaris), 10. es

Fig,. 114. ahr (Chinchilla lanigera), 16.00

Fig. 115, sky-H rsius fus

Fig. 118. Sewell el (Aplodontia rufa), 17.00

Fig. 119. Marsupial Mole ahtaista Pa 17.00 u.

Fig. 120. Galeopterus (Galeopterus gracilis), 22.00 u.

Fig. 121. Beecroft’s eaters ed Squirrel Peyrat beéorority, 18.00 yu

. Fic. 122. Viseacha FS eet Ry 41.00 u

Fic. 123. Black-Footed Ferr nigripe a

Fig. 124. Nail-Tailed Wally AP hate De re 50 u-

5. Foussa (Cryptoprocta fer soi mes tas

Fie. 126. Cavy Dolent salinicola),

Fic. 127. Peters’ Shrew (Rhyncocyon peter 26.00 u.

Fic. 128. Racoon (Procyon lotor), 20.

Fic. 129. Philippine Tarsier (Tarsius philippinensis), 18.00 u.

Frc. 130. Great Mole Rat (Spalax typhlus),

$ . Ne

Fig. 133. Gray Rabbit (Lepus nutalli agada A

Degu ( 4

Fig. 138. Agouta (Solenodon paradozus), A

Fic. nadensis), 19.

Fic, 140. European Hedgehog Faen ani ieg 85.00 u.

r ia i a ay al

y y 1} Ff A S F.

iif LA

maana saa bd E

eae mB AE a

No. 635] THE HAIR OF MAMMALS 509

protective hair. And since the structural elements in

these two types of hair usually differ considerably,

greater number of distinctive characters is thus avail-

able for comparison. However, the greater thickness

and deeper pigmentation of the protective hair shafts

make them much more difficult to work with than the

finer, clearer fur hairs. Moreover, the scales of the pro-

tective hair are often worn off to such an extent as to

make them also valueless as identification criteria. Figs.

175 to 177, and 169 to 171 show, represented to scale, the

structure of the scales and medulla of the fur and pro-

tective hair of the skunk (Mephitis mephitica), and the

European beaver (Castor fiber). The protective hair of

mammals in general, in most cases, bears cuticular scales

of the flattened or crenate type, and medullas of the con-

tinuous nodose or continuous homogeneous type.

In identifying hair species it is necessary to compare

the scales and medulla from the same parts of the hairs®

EXPLANATION OF PLATE VI

Fic, 141, Polar Bear (Thalarctos maritimus), 68.00 u.

. 14 Hyena (Hyena hyena bergeri), 157.00 u.

Fic. 143. Old World Tapir (Tapirus terrestris), 104.00 u.

Fie. 144. American Tapir (Tapirus americanus), 74.00 u.

Fig, 146. Central American Tapir (Hlasmognathus ple 96.00 u.

Fic. 147. Rush Mouse (Thryonomys gregorianus), 165.0

Fig. 148. Hoffman’s Sloth (Chotepus ee nog fs

Fie. 149. Ass (Equus asinus),

Fie. 150. Water Deer (Hyomo theo one uaticum), 122

Fig. 151. Thompson’s Gazelle seein repay a. 105.40 u.

Fie. 152. Cape Giraffe (Giraffa ensis

Fie. 153. Quagga (Mesai quagga b hab, u

. 154. Mongoose (Helog ale hirtula nen, 24.00 u.

Fie. 155. Wart Hog (Phacocherus ethiopicus), re 00 u.

Fig. 15

i -00 u.

Fic. 161. Indian mht k Onena indiens), te 00 u.

Fic. 162, Coendou (Cendou mevicanus),

Fig. 163. sre = eiaeia ay 185. 00 u.

Fic. 164. Vicuna (La cuna), 11.00 u.

Fie. 165. Ma ara edits (Manis javanica), 290.00 u.

Fig. 166, Mammoth (Elephas primigeni ius), from Alaska, 50.00 u.

5 The fur hair of many species of mammals varies upon different parts

of the body, apiece with respect to the configuration of the scales and

medulla. Hence samples for rasa eae mist be taken, as, far as possible,

from the same regions.

anas a CA

P E ai a a si E r

~ zya a an Si ease Er

Nrt

E -- ——

mS ccereaocaccereconae

SONG

SANNA

ar ae

í S.

NACE HT

Sis SAY

No. 635] THE HAIR OF MAMMALS 511

EXPLANATION OF PLATE VII

Longitudinal section through an ideal general ized mammalia

hair, es Fa discontinuous medulla variety, to show the relation of its sage

elements.

CU, cuticle,

CO, cortex

MC, m medulla ary cell or chamber,

1, inters ce oe space,

MS, medullar haft or column,

FOU, free note edge - igen scale,

igment gra

Fic. 168. Stereogram of ideal Schack mammalian hair of the continu-

ous modula variety.

OS, cuticular scales,

Cc, cuticle,

O, cortex

o medulla,

, pigment granules.

. 169. Protective oe of European Beaver (Castor fiber) to show

rien scales

Fie. 170. ‘Protective hair of European Beaver (Castor fiber) to show

medulla:

slg 171.. Fur hair of European Beaver (Castor fiber).

Fur hair of Platypus (Ornithorhynchus anatinus) just above the

mouth a the follicle.

Fig. 173. Fur hair of Platypus (Ornithorhynchus anatinus) one third of

the aranes from the base to the tip.

I Fur hair of Platypus (Ornithorhynchus anatinus) near the

me extremity, or or tip.

. 175. Protective hair of Skunk (Mephitis mephitica) to show cuticu-

. 176. Protective hair of Skunk (Mephitis ger, to show medulla.

Fie. 177. Fur hair of Skunk (Mephitis mephitic

Fig. 178. Stereogram of an ideal generalized Seiad hair in its follicle.

cuticle,

SO, stratum corneum of epidermis,

SM, stratum malphigii of epidermis,

D, ari rapra

G, sebac

palit Taser

outer layer of ae sheath,

apilla,

, muse sng ip erect the hair shaft,

of sheath,

NON >

inner layer of follicle,

os outer layer of follicle,

blood and nerve supply to the bulb of the hair

pte 179 to ma Various types of im oes scales (referred i in text).

187. Hair shaft showing teased-out cortical element.

CO, cortical cells or hair spindles.

Fig. 188. Transverse sates oe ogg with compound medulla.

QU,

se te te

M, pestis

co, cortex.

Fic. 189. Transverse through a hair with simple or single medulla.

CU, cuticle,

M, yore

Co, cortex.

190. Portion of shaft of fur peste of Mandril (Cyanocephalus maimon)

the Ba adger (Tasgi-

dea aih rtbaha) to show the configuration and disposition of the pigment

anul

Fig. 192. Portion of the shaft for the fur hair of Goa DD luscus)

to goon! the configuration and se an cage of the pi

t gran

Figs. 193 to 199. Various types of corneal scales gp ee to in text).

512 THE AMERICAN NATURALIST [Vou. LIV

under examination, since the form of the scale (more

especially) undergoes alteration from the base to the tip

of the hair shaft. As a rule the scales at the base of the

hair are of greater longitudinal than transverse diam-

eter, while the converse is true of the scales at the tip of

the shaft. Figs. 172, 173 and 174 illustrate the nature of

the change in form which is normally met with in the

hairs of mammals as it occurs in the fur hair of the pla-

typus (Ornithorhynchus anatinus). This modification

in the form of the scales is believed to be due to the in-

creasing amount of wear to which the hair shaft is sub-

jected the farther away it is pushed from the. follicle.

That external friction is the cause of scale alteration in

form is likewise suggested by the fact that the stiffest

hairs possess, usually, scales of a much flattened type

(ef. Figs. 57 to 67, inc.), while the finer hairs show the

delicate, free ectal edges of the scales unchanged for at

least the proximal three fourths of the length of the

shaft. This is especially well illustrated in the hair of

the bats, notably in such species as the mastiff bat (Mo-

lossus sinaloe) (Fig. 105); the wrinkled-lipped bat (Nyc-

tinomus bocagei) (Fig. 106); and the intermediate bat

(Mormops intermedia) (Fig. 107).

The fur hairs shown in the plates* were chosen with

the view of bringing out most clearly the nature of the

forms of the simple varieties of scales and medullas, and

of their various common modifications, as they exist one

third of the distance from the mouth of the follicle to the

top of the hair shaft. For convenience, therefore, the

scales and medulla in this portion of the hair shaft have

been termed mature scales and mature medulla. The

scales at the distal extremity of the hair shaft, whose

modification in form is considered to be the result of ~

attrition, are called the attritional scales, and the pinched

out medulla of the same region, the fragmentary medulla.

Inasmuch as the hair shafts represented in the plates

ê The fur hair shown in the plates were taken, where possible, from

the region of the median line of the dorsum, just below, i.e., caudad of, the

shoulders.

No. 635] THE HAIR OF MAMMALS 513

vary so widely in diameter (6.80 in the hair of the in-

termediate bat (Mormops intermedia) (Fig. 107); and

1,177 » in the hair of the dugong (Dugong dugong) (Fig.

159), to draw them to the same scale, and at the same

time to make the smaller hairs of sufficient size to show

clearly the cuticular scales and medullas, was obviously

impracticable. The arbitrary expedient was therefore

adopted of drawing all the hairs whose diameters were

equal to, or less than, 50 to one size, and drawing all

those hairs whose diameters were greater than 50» to

another size. In the figures the latter hairs are repre-

sented as being slightly greater in diameter. Such a di-

vision into coarse and fine hairs is not without its basis

in common use, for it was found that as hairs are greater

or less than 50» in diameter they are called respectively

coarse or fine, or stiff and soft, by perhaps the majority

of persons. The true spines form still a third division,

with which, however, we shall have nothing to do.

Such an arbitrary representation of hair shafts, how-

ever, affords no appreciation of the relative or actual

magnitudes of the hairs. In order that this might be

had, therefore, the actual diameter of the fur hair of

each species, in micra, is given after the name in the ex-

planation of the plates. In each case this, obviously, is

approximate only, the result of averaging a large num-

ber of individual measurements. It was found that the

diameters of the hair shafts of any given individual vary

considerably, and that a somewhat less range of varia-

tion occurs among the averages of different individuals

of the same species. Hence it is inferred that only a

meager amount of significance should be attached to hair

magnitudes, except possibly, in large averages, and be-

tween large groups, i.e., families or genera.

It must also be borne in mind that the prepared hair

shaft, underneath the microscope, does not reveal at any

one time the complete contour of the cuticular scales, or

medulla, as it is represented in the figures. This is due

to the fact, that with the objectives of sufficiently high

514 THE AMERICAN NATURALIST [Vou. LIV

power to resolve the scale outlines, or the structure of

the medulla, but one portion of the cylindrical hair shaft

can be brought into exact focus at a time. The objective

must in focusing follow around the hair, as it were, up

one side, and down the other, revealing, as it goes, the

course of the outline of the scale, or of the irregularities

of the medulla. The resulting curves are then drawn on

the single plane of the paper, as though the hair had, by

some means, been crushed out flat without distorting its

structure. It is because of this rotundity of the various

elements of the hair shafts that it is often impossible to

secure adequate photomicrographs of hair shafts, since

it is necessary to employ high-powered objectives with a

consequent very limited focal depth. Moreover the

various different indices of light refraction and reflec-

tion among the hyaline elements of the shaft produce,

upon the finished photograph, various striations and

markings of one sort and another, which have no anal-

ogue in the actual structure of the hair shaft itself. It

is possible, however, that photomicrographs of small,

highly magnified portions of the hair shaft, cortex may

be very useful in determining the form and placentation

pattern of the pigment granules.

The figures of the fur hairs are arranged with the sim-

ple form of each type of scale, or medulla, coming first,

followed by its various common variations. The hair of

the civet (Arctogalidia fusca) (Fig. 1) represents the

simplest form of the imbricate scale, termed the ovate.

Fig. 179 shows the normal appearance of a single isolated

scale of this type. Figs. 2 to 7 show the commonest modi-

fications which the ovate scale undergoes. Of all of the

imbricate scales whose longitudinal axis is equal to, or

greater than, the transverse axis, the ovate is the most

common.

Between the ovate scale and the acuminate, no definite

line of demarcation can be drawn. I have considered

Figs. 8 and 9 to represent perhaps the simplest form of

the acuminate type. Figs. 10 to 17 show scales of in-

No. 635] THE HAIR OF MAMMALS 515

creasing acuminateness, while Figs. 18 to 20 show curious

anomalous varieties.

In Figs. 181 and 182 are shown two isolated acuminate

seales of characteristic outline.

The elongate type of cuticular scale (Figs. 21 to 35)

is one least often met with, especially in its typical form,

as shown in Figs. 29 to 31. The simplest variety (Fig.

21) possesses a longitudinal axis only a trifle greater

than the transverse one. Figs. 29 to 31 are the typical

varieties, and Figs. 32 to 35 show forms difficult to group-

They are, however, tentatively put with the elongate

forms. A single dissociated elongated scale is shown in

Fig. 183.

By far the commonest types of scale which one encoun-

ters are the crenate and flattened types. The former are

illustrated by Figs. 36 to 67. In this form of scale the

transverse axis is much greater than the longitudinal,

and the free ectal, or outermost edge of the seale is ir-

regularly waved or crenulated. Of this type, a confusing

multiplicity of variations occur. Some of the plainest

and most easily interpreted of these are shown. Fig. 36

is considered to represent the simplest form. Seales

like those shown in Figs. 57 to 67 are usually associated

with the hairs of the greatest diameter, i.e., the coarse,

or stiff hairs, or bristles. This form is also character-

istic of the majority of the spines. Two typical crenate

seales, dissociated from the cortex, are represented by

Figs. 185 and 186.

The flattened type is equally common and differs from

the crenate only in exhibiting an ectal edge smooth and

comparatively free from sudden irregularities. The

longitudinal axis, however, is frequently but little greater

than the transverse one, as can be seen in such hairs as

are represented by Figs. 69 and 70. Fig. 68 represents

the simplest form, and Fig. 184 a single scale of the same

type.

In the coronal scale we have a scale fundamentally dif-

ferent from the imbricate. Here the scale usually com-

516 THE AMERICAN NATURALIST [Vou. LIV

pletely surrounds the hair. The cuticular portion of the

hair may be likened to a pile of tall tumblers placed one

within the other, the upper rims representing the free

ectal edges of the scales. Isolated coronal scales of

various types are represented in Figs. 193 to 199. Fig.

93 represents a form which may be regarded as one of

the simplest of the coronal scales. An isolated scale of

this form is also shown in Fig. 193. The numerous varia-

tions of this type of scale are usually in the direction of

a more flaring and more irregular ectal edge, as can be

seen by comparing Figs. 93 to 113, and Figs. 193 to 199.

The coronal scales may be subdivided into simple

(Figs. 93 to 102), serrate (Figs. 103 to 107), and dentate

(Figs. 108 to 113). The simple scales, as well as the

serrate are the forms usually found among the bats,

which are fairly constant in this regard. Figs. 106 and

107 represent, perhaps, the maximum of scale decora-

tion among the mammals. These scales, isolated from

the cortex, are shown in Figs. 196 and 197. The inter-

mediate bat (Mormops intermedia) whose hair is illus-

trated by Figs. 107 and 197, possesses, possibly, the finest

of mammalian hair. The shafts of the fur hair average

6.80 in diameter, and often shafts of as small a diam-

eter as 4.30» can be found. In these hairs, apparently,

the cuticle has become greatly thickened, and the medulla

has been lost. This seems to be true of the majority of

the bats, more particularly of those bearing the serrate

type of cuticular scales. The dentate type of scale is not

- found among bats, but seems to be scattered among sev-

eral orders of mammals. It occurs most frequently

among the members of the glires, or rodents. The sim-

plest form is shown in Fig. 108, and other typical forms

in Figs. 109 to 112. There seems to be not a great range

of variation in this type of scale, the majority of species

which bear this type of hair approximating very closely

to the forms shown in Figs. 109 to 112. Fig. 113, how-

ever, shows an anomalous form of scale characteristic

of both the American and European species of otter. In

No. 635] THE HAIR OF MAMMALS 517

this form the scale reaches its greatest length, as can be

seen by the isolated scale, Fig. 198. The shorter scale,

of the usual dentate type is shown in Fig. 199.

Of the three great groups of medullas: the discontinu-

ous, the continuous, and the fragmental, the first seems

to be subject to the greatest range of modification. This

has been subdivided into simple, and compound types.

The simple, furthermore, can be grouped as: ovate, rep-

resented by Figs. 114 to 126, elongate, shown by Figs.

127 to 128, and flattened, illustrated in Figs. 129 to 135.

-= The ovate type, in its various modifications, is met

with usually, in hairs of small diameter. Thus the hairs

of the shrews, moles, small rodents, one or two bats, ete.,

possess hairs of ovate medullas. The form usually en-

countered is apt to be more nearly like those shown by

Figs. 114 to 118, than like the remainder of the ovate

types (Figs. 119 to 126). The latter, especially such

partially fused forms as shown in Figs. 120 and 121, are

infrequently seen.

Still less common than these forms are the forms of

the elongate medullas (Figs. 127 to 128). These must

not be confused. with the various fragmental types (Figs.

155 to 166). In the latter the divisions do not represent

regularly placed cells or chambers as in the former.

The compound medullas, at least in the fur hairs, are

the least common of all. Two varieties can be easily dis-

tinguished; the cells of one being ovate (Fig. 136), and

the cells of the other flattened (Fig. 137). No instances

of elongate cells were observed.

The continuous medulla (Figs. 138 to 153) seems to be

the one characteristic of more than half of mammal

hairs, particularly of those which are greater than 50 p

in diameter. It is found in nearly all of the protective,

or over hairs, and is present in all spines and bristles, in

some portion of the shaft. Fig. 168 shows a hair of this

type as it would appear if sectioned to show the longi-

tudinal and transverse appearance of the continuous me-

dulla. The whole interior of the medullary column or

518 THE AMERICAN NATURALIST [Vou. LIV

shaft (MS, Fig. 167) is filled with an anastomosing mass

of cornified filaments, which probably represent a

closely compressed aggregation of small medullary cells

(Fig. 178). A type of medulla in which the component

cells are still preserved so that their individual nature

can still be seen, is shown in Fig. 147. Two divisions of

the continuous medulla can be readily recognized; the

nodose (or irregular) (Figs. 138 to 147), and the homo-

geneous Figs. 148 to 153). Between these two forms, all

sorts of intergradational varieties exist.

The fragmental medulla (Figs. 155 to 166) represents

perhaps various stages in the reduction of this element

of the hair shaft structure, and seems to have been de-

rived from the continuous type. Where the medulla

seems to be lacking altogether, minute traces can still be

found in various portions of the hair shaft, particularly

in the region just below the mouth of the follicle. Struc-

tural indications seem to suggest that the development

of medullas is from the discontinuous, through the con-

tinuous, to the fragmental, and finally, as is the case in

the bats, to no medulla at all. `

To prepare hairs for microscopical examination care

must be exercised that the reagents used in cleaning,

staining, etc., do not soften the cuticle, and thus distort

the form of the scales, or that the cover glass is not made

to press too heavily upon the hair, and thus flatten it out,

deforming both the cuticular scales and medulla as well.

The simplest treatment for scale examination consists

in washing the hair thoroughly in a solution composed of

equal parts of 95 per cent. alcohol and ether (or chloro-.

form). The hair may then be dipped into pure ether, or

chloroform, to insure rapid drying, and when thoroughly

dry placed upon a slide and covered with a cover glass

for immediate examination. Some hairs, e.g., those of

sheep of most varieties, the fur hair of the camels, and

the protective hair of many of the bats, notably the sil-

very bat (Lasionycteris noctivagans), exhibit the scales

very well after this simple treatment. The 8x or 10x eye-

No. 635] THE HAIR OF MAMMALS 519

piece, and the 4 mm. objective with transmitted light,

preterably from.a blued glass, or better, daylight glass,

gives the best results. Indirect lighting, with the mirror

swung to one side, may be used where the scale edges are

not easily seen. Reflected light has been found excellent,

but only in a very few cases. ;

With hairs like those of the rabbits and hares, shrews,

moles, the fur hair of bats, and the like other manipula-

tions of the hair must be brought into requisition. One

of the most generally useful of the various staining

preparations consists in immersing the hair, after its

ether-alcohol bath, in a solution of gentian violet, methyl

blue, methyl green, or safranin, in 95 per cent. alcohol.

The stain is prepared by making up a saturated solu-

tion of the stains enumerated, and then diluting each

with 95 per cent. alcohol to the desired degree of

color depth, which must be empirically determined

for each different species‘ of hair. The evaporation

of the aleohol, which must be accomplished rapidly in a

warm current of air from a bunsen flame, deposits in the

depressions just ectad of each cuticular scale edge, a

tiny bit of the stain, which therefore clearly outlines the

contour of each individual scale. This method is diffi-

cult, and the writer has found that repeated trials with

the same hairs were frequently necessary before satis-

factory results were secured. In working with hairs it is

better to use a tuft of 25 or 50, rather than try to work

with but a few.

The preparation of the a is, however, of but slight

‘importance compared with the manipulation of the

proper lighting and the proper combination of objective

and ocular. Where the cuticular seales remain obstin-

ately invisible, or only faintly seen, various sorts of il-

lumination must be tried; transmitted vertical light,

transmitted oblique light, dark field illumination, re-

flected light, and polarized light. Dark field illumination,

e writer is aware that ‘‘species of hair’’ is hardly admissible, yet the

convenience must be the excuse for its use

520 THE AMERICAN NATURALIST [Vou. LIV

with the 1.8 mm. objective and 4x eyepiece was found ex-

cellent for a large number of hairs. It must be borne in

mind that, in using this combination of immersion ob-

jective with the dark field illuminator, an oil connection

must also be formed between the upper surface of the

condenser and the lower surface of the slide.S HExigency

of space forbids the descriptions of the various types of

lighting which have been found most satisfactory with

the various species of hairs. These must be empirically

determined by each investigator. The degree of success

obtained with the microscope usually depends as much

upon the preparation of the instrument and its lighting,

as upon the preparation of what is to go under it for ex-

amination.

For examination of the medulla all that has been said

regarding lighting, etc., applies. However, the various

treatments given the hair and used to render visible the

cuticular scales, obscure the medulla. The simplest and

most generally useful method of rendering the medulla

clear, consists in reducing the visibility of the cuticular

scales to as near zero as possible by mounting the hair,

beneath the cover glass, in some light microscopical oil,

such as oil of bergamot, of cedar, or origanum, of amber,

of cloves, etc., after having washed it, as before, in the

ether-aleohol solution. Such a treatment renders the

hair, in effect, a glassy cylinder, within which the medulla

can be clearly seen, provided the cortex is not thickly be-

sprinkled with pigment granules, or rendered dark in

color by diffuse pigment. Fortunately most of the fur

hairs are lightly pigmented. Many of the protective

hairs, however, are so heavily colored that the medulla

is partially, or almost wholly, obscured.

Some of the finer hairs can be examined with advan-

tage i in a mount of clear water, or xylol. The best treat-

“8 For directions for all sorts of microscope SApS ena; apparatus,

microscopical principles, ete., consult Professor S. H. Gage’s comprehensive

‘‘ The Microscope, and Introduction to Microscopic Methods and to His-

tology,’’ Ithaca, N. Y., 1917. A new edition of this valuable work is now

ready to leave the press.

No. 635] THE HAIR OF MAMMALS 521

ment, however, was found to consist in washing the hair

` in the ether-alcohol, drying, immersing in xylol, and then

mounting in very thin Canada balsam. This makes a

permanent mount.

Lighting with the dark ground illumination was found

to give the best results in the examination of the external

configuration of the medulla.

In the case of hairs where the heaviness of the pigmen-

tation obscures the medulla, or in compound-medullated

hairs, or in those cases where an accurate knowledge of

the form of the cross section of the medullary column is

desired, it is necessary to prepare cross sections of the

hair shaft, by the usual methods of imbedding in paraffin

or celloidin.? Figs. 188 and 189 show the manner in

which the form of the medulla is shown in transverse

sections, as well as its relations to the thickness of the

cortex and of the cuticle.

The methods used to make clear the medulla serve well

also to reveal the pigment granules. In examination of

the shaft for these tiny bodies the 1.8 mm. objective and

the 10x eyepiece with the draw tube of the microscope

extended its full length was found to be the lowest power

which could be satisfactorily employed. Lighting with

daylight glass and a 200-watt tungsten-filled bulb was

apparently a necessity.

The cortex, because of its nearly homogeneous struc-

ture, was not found to exhibit characters which could be

used as criteria for identification. Fig. 187 shows a hair

macerated in caustic soda, and with the cortex teased out

to show the distorted, elongated cortical cells, or hair

spindles.

The use of caustics and strong acids for dissociating -

the cuticular scales is not recommended. The softening

of the scales distorts their form and thus renders them

useless for delicate determinative purposes.

It very often becomes necessary to distinguish the dis-

9 For histological methods consult Professor M. F. Guyer’s ‘‘ Animal

Micrology,’’ Chicago.

522 THE AMERICAN NATURALIST [Vor. LIV

tal from the proximal end of some one hair shaft. This

can be done under the microscope, remembering: first

that the image is reversed, and second, that the free

edges of the cuticular scales lie always at the ectal, or

distal portion of the scale, and so indicate the direction

. of the distal extremity of the hair. A much more simple

method is to rub the hair in question between the thumb

and finger, when it will always travel in the direction of

the bulb, i.e., in the direction of its proximal extremity.

This fact that the free ectal edges of the cuticular scales

develop in such a way that they are always directed out-

ward from the animal, suggests that they may afford pro-

tection against the intrusion between the hairs, and so

on to the skin itself, of foreign bodies, parasites, and

water. Furthermore any such extraneous elements

which may have gained entrance, apparently would tend

to be worked outward away from the skin to the outer

surface of the hair covering by the motions into which

the hair is thrown by the movement of the muscles of the

body during locomotion.

In preparing a series of animal hairs to be used as

type specimens for determinative comparisons with un-

known hairs it is well to have a series of slides prepared

to show the medulla (mounted in balsam as previously

directed), and another series of slides with the hairs

mounted thereupon in dry cells? (washed in the ether-

alcohol, and stained or not as each requires), to show the

cuticular scales. Since this later method of preparing

hairs seems to be attained with little suecess (too much

dust gathering upon the hair, the fibers obscuring the

sculpturings of the cuticular scales), it is better, per-

haps, to keep a tuft of each species of hair in a small phial

or double envelope, and make fresh preparations when

necessary. Both the balsam-mounted slides and the un-

treated hair samples should be filed away following the

classification scheme for the scales and medulla given

in this paper. This facilitates the immediate selection

of the particular group of hairs possessing the charac-

No. 635] THE HAIR OF MAMMALS 523

teristics of the unknown sample, and makes identification

much easier and quicker. For each species of mammal

samples of the hair from several:regions of the body

should be had, as well as samples of both the fur and pro-

tective hairs of various regions. From his own experi-

ence, however, the writer is well aware that this is an

ideal more easily recommended than realized.

THE EFFECT UPON THE WHITE RAT OF CON-

TINUED BODILY ROTATION

COLEMAN R. GRIFFITH

PSYCHOLOGICAL LABORATORY, UNIVERSITY OF ILLINOIS

Everyone knows that a rapid turning-about upon the

heels usually leads to dizziness and that a like state is in-

duced in the revolving chair or the turn-table of the lab-

oratory or in the merry-go-round of street fairs. It is

also known, especially among those who have attempted

to analyze the complicated experience of dizziness, that

an important constituent of this disturbed state of mind

and body is a characteristic movement, to-and-fro, of the

eyes. To this ocular twitching, which is sometimes called

‘‘nystagmus,’’ is due, in large measure, the apparent

swimming movement of surrounding objects. The twitch-

ing appears soon after rotation begins and it continues,

with characteristic modifications, for a short period after

the body comes to rest.

The bodily and mental effects of sted dn in man and

in other animals have for a good many years been made

the subject of investigation by physicists, anatomists,

physiologists, psychologists and medical men. It is sup-

posed that rotation produces a specific effect upon the

neural end-organs of the semicircular canals, and it is

definitely known that, in addition, pretty much the entire

organism is involved in the general disturbance. Concern-

ing the ocular movements themselves, a good deal has

been learned. We know, for example, that the character

and the duration of the nystagmus depend upon a large

and heterogeneous group of conditions, among which may

be named the general state of the organism, the state of

attention, the associative connections, the rate, regularity

and duration of the rotational movements, repetition and

practise, and other mental and physical conditions. Of

524

No. 635] BODILY ROTATION 525

these conditions, we are here concerned with one only,

i. e., with the effect of regular and continued repetition

upon the ocular movements in question.

It has been commonly observed that long persistence in

whirling movements may reduce in intensity the distress-

ing symptoms of dizziness. This reduction under repeti-

tion has suggested that the accompanying ocular

movements may also tend, under persistent practise, to

disappear. The testimony of whirling dancers and gym-

nasts, who are frequently undisturbed by the swimming

and the giddiness, points in this direction,’ and further

evidence, of an experimental sort,? has recently been de-

rived from subjects who were rotated about three min-

utes daily for two or three weeks. At the end of this

period the subjects had lost, either wholly or in part, the

‘‘after-nystagmus’’ which usually persists, as we have

seen, when the body has come to rest.

Now these experimental results have been sharply crit-

icized by two otologists, Drs. Fisher and Babcock,? who

are distressed that the stability of such a ‘‘reflex reac-

tion’’ as nystagmus should be called in question. ‘‘Clin-

ical medicine has,’’ as they observe, ‘‘for years relied

upon the permanency and the constancy of reflex phe-

nomena.’’ As for the results just referred to, they set

them down as ‘‘pathological.’’ Professing to repeat the

experiments, but wholly missing the essential point of

the method which they criticize, these men have come, not

unnaturally, to a conclusion which is not antagonistic to

the dogma of the invariable reflex. Despite the miscar-

riage of their method, however, they do find a certain

amount of reduction in time of nystagmus and this re-

duction they propose to explain by the voluntary ‘‘gaze-

fixing’’ of ‘‘a few subjects.’’ Although the abortive

1 Parsons, R. P., and Segar, L. H., ‘‘A Correlation Study of Bárány

Chair Tests and Flying Ability of One Hundred Navy Aviators,’’ J. Amer.

Med. Ass., 1918, 70, 1064,

2 Manual of Medical Research Laboratory, Washington, D. C., 1918, 186 ff.

3 Fisher, L., and Babcock, H. L., ‘‘The Reliability of the Nystagmus

Test,’? J. Amer. Med. Ass., 1919, 72, 779 ff. .

526 THE AMERICAN NATURALIST [Von. LIV

attempt of Fisher and Babcock affords no positive evi-

dence against the demonstrated reduction of nystagmus

under repetition, it has suggested an experimentum

crucis which is designed to show that the reduction is not

an artefact produced by the ‘‘wilful gaze-fixing’’ of in-

convenient subjects who acquired ‘‘the art of holding

the eye more or less fixed voluntarily’’ upon a ‘‘distant

object.’’ .

We have chosen the white rat as a subject in our crucial

experiment. The rat is admirably adapted to this sort

of problem. It is docile and easy to handle. The lack of

a fovea and of distant vision and the probable absence of

all clear-cut retinal images® seem to provide the optimal

conditions of non-fixation as suggested by the otologists’

contentions. On the other hand, the pupil of the rat’s

eye is easily observed, as well as those portions of the

sclerotic coat which project beyond the surrounding

cutaneous and hairy tissues.

e following method of rotation and observation was

employed. Upon a pivoted wooden platform, 11 em. X 20

em., was set a glass bell-jar 11 em. in diameter and 12 em.

in height. The rat was so placed under the glass jar that

its center of gravity lay over the center of rotation. A

small motor, governed by means of a friction-brake,

served to provide a very regular and easily controlled

means of rotating the platform and the jar. Records o

the time of after-nystagmus were at first made with a

stop-watch, but later with a key connected to an electric

signal-marker which registered on a revolving smoked

4 As a matter of fact, these authors unwittingly furnish the most delicate

and unimpeachable evidence for the very reduction which they deny. Al-

though they apparently omitted to repeat at each sitting, giving each of the

ten subjects included in their Table II only one turning to the right and

one to the left, in every single case the average nystagmus-time is less for

he second five days than for the first five days. That is to say that a single

turning each day (not a series) is sufficient to reduce the time for subse-

quent days. The tendency to reduction must, then, be moch greater than

the first experimenters had contended or su

5 Vincent, S. B., ‘‘The Mammalian Eye,’’ J. of Anii Behavior, 1912, 2,

249-255. See table and also references to the literature.

No. 635] BODILY ROTATION 527

drum.® It was found, by preliminary trials, that the ap-

pearance of the nystagmus was directly proportional to

the number of rotations and to the speed of rotation.

For experimental purposes, an arbitrary choice was made

of a speed of ten revolutions in fifteen seconds. Ten

trials of ten rotations each were repeated two or three

times a day, save for subjects: ‘‘I’’ and ‘‘J,’’ which were

given twenty trials twice a day. The subjects were ten

white rats, five males and five females, all about three

months old. The functional integrity of the mechanisms

of equilibrium‘ was roughly determined by observing the

rats’ behavior under daily conditions of life, and by

throwing them into the air and dropping them. All of

the subjects responded quickly and positively to such

tests. In the subsequent experiments each rat was ro-

tated a like number of times to the right and to the left,

and averages of the duration (in seconds) of the nystag-

mus after stopping were computed. A comparison of

these averages from day to day may be made from

Table I.

The outstanding feature of the investigation is the

rapid decrease of after-nystagmus from day to day, as is

clearly indicated in Table I. Within ten to eighteen

periods of rotation the nystagmus had completely disap-

peared. The number of ocular movements after stopping

the platform was also observed. Upon the first rota-

tion for each rat, the number of movements varied be-

tween 18 and 25. This number rapidly decreased during

the first four or five periods to between 5 and 8, and soon

became reduced to a single movement which generally

hung on for some time. As the rotation was stopped, the

eye gradually moved in the direction of the preceding

rotation and then jerked back to normal position. The

6 This latter method was used by the Psychological Department of the

Mineola Research Laboratory. It is a decided improvement over the clinical

method of observation by the stop watch. See ‘‘Manual,’’ p. 190.

7 The semicircular canals of Rodentia are well developed and quite regu-

lar in form. See Gray, A. A., ‘‘The Labyrinth of Animals,’’ 1907, Vol. I,

pp. 165 ff. ; :

[Vou. LIV

THE AMERICAN NATURALIST

528

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No. 635] BODILY ROTATION 529

disappearance of this one movement accounts for the sud-

den falling off of the time-values at the end of the various

series. The average initial time of after-nystagmus for

all subjects was 5.57 sec. for rotation to the left and 5.74

sec. for rotation to the right. Other averages testify to

this difference in time for the two directions of rotation.

This seems to be a genuine case of individual difference

quite comparable to similar differences found in human

observers.®

The fact of decrease from day to day is incontestable.

Each column in Table I shows it. It is just as apparent,

if, in each day’s series, an average of the first two trials

is taken and compared with corresponding values for

subsequent days. That is, each day begins at just a little

lower nystagmus-time than the preceding day began.

Furthermore, the decrease is of a characteristic kind.

Table I indicates that at least one half of the total de-

crease commonly occurs in the first few days of exper-

imentation. The exceptions, subjects ‘‘G’’ and “H,”

will be considered later. In this respect, a ‘‘nystagmus

curve’’ is quite comparable with the common ‘‘learning

curve,’’ save for the absence of plateaus.

Again, the figures make it plain that there is also a gen-

eral decrease in the time of after-nystagmus within any

_ single day’s turning. Table II indicates that this de-

crease was constant for all subjects, save ‘‘G’’ and ‘‘H.’’

An analysis of the material upon which the table is based

shows that the main decrease within any single day falls

early in the series—a result consonant with the early fall

in time from day to day, as just mentioned.

It must be emphasized that any decrease is for one set

of conditions only. Only those values are given which

resulted when the rat rested quietly on the floor of the

rotated platform. Occasionally the rat would stand al-

most upright, in which case the nystagmus was almost

invariably longer. Even after the disappearance of the

8 See ‘‘Manual,’’ passim, and also articles in the J. Amer. Med. Ass.,

cited above.

530 THE AMERICAN NATURALIST [Vor LIV

TABLE I

L R

Subject 5 EE ALGO ESS Se GEESE SAN EE ELD :

| I II III IV

A | 2.81 2.49 2.84 2.51

B 2.84 2.30 2.81 2.51

C 2.31 2.74 2.66

D 3.18 2.89 3.13 3.00

M 2.59 2.48 2.50 2.02

F 2.57 2.23 2.56 2.03

G 3.46 3.50 3.40 3.30

H 3.26 3.41 3.44 3.55

I 2.98 2.18 2.93 2.23

J 2.98 2.33 3.28 205° o

Column I, averages of all the first two rotations to the left for all series;

column II, the average of all the last two rotations to the left for all series;

columns III and IV, the same for rotation to the right.9

nystagmus under usual conditions, this upright posture

induced some after-nystagmus; but it is important to note

that the time and the intensity of it were never so great

(by more than half) as the original nystagmus in these

positions. That is, there seems to be a ‘‘transfer’’ effect

from one set of conditions to another. Changing the

speed or the number of rotations at any time produced a

similar reappearance of nystagmus, but never in its orig-

inal intensity or temporal duration. Several of the sub-

jects gave a nystagmus varying between twelve and

twenty-five seconds when rotated once a second for thirty

seconds before. the practise series. After the practise

series, these values were reduced to about the level of the

original values for the rotation-rate used in the investi-

gation, viz., 5-6 seconds. The change of position of the

rat during and after rotation had to be carefully re-

garded; for such a change was frequently responsible

for an increase of nystagmus-time that obscured a real

decrease.

There are several special points of importance.

1. It has been noted above that subjects ‘‘G’’ and “H”?

offer certain exceptions to our conclusions. Table I indi-

9 Mean variations from the averages given in the tables were computed,

but since they were not of sufficient magnitude to affect the significance of

the figures as given they have been omitted.

` No. 635] BODILY ROTATION 531

cates that the length of their total series was greater than

that of any of the other rats. These two subjects were

females rotated during the period of gestation. Their

rotation was marked by frequent and severe retching

movements, defecation, and micturition. The period of

gestation of subject ‘‘G’’ was three days short. ‘‘@’’ þe-

came too sick during the last reported turning to be used

further, and a day later, during which time she did not

seem to recover, a litter of two were born. These coin-

cidences point directly to the fact that nystagmus is

closely related to the organic condition of the individual

rotated and they at least suggest the fruitfulness of

further work upon this matter.

2. The fact that the white rat is a nocturnal animal’

suggested that the time of day might make a difference

in values. Accordingly two rats, ‘‘I’’ and ‘‘J,’’ were ro-

tated twenty times twice a day, early in the morning and

late in the afternoon. The results were as follows:

I J

Morning trials, rotation to left (ave.) neos rosie 2.24 2.81

rotation to right Cave.). -< ocr aou 2.37 3.17

Evening trials, rotation to left (ave.) .................- 1.70 2.44

rotation tö Tight Cave... ines eas 1.88 2.40

The morning nystagmus is invariably longer, the dif-

ference being most pronounced early in the series. Addi-

tional evidence of this diurnal difference is being sought

with both human and animal subjects.

3. Other responses than the nystagmus were scrupu-

lously noted in our observations. During the first days,

most of the subjects showed a tendency to excessive defe-

cation and micturition. Frequently the feces were not of

the solid character of normal life but were quite liquid,

suggesting that the rotation had induced some sort of

temporary organic shock. This supposition is supported

by the facts that neither micturition nor defecation ever

occurred late in the series and that the rats, although

“ 10 Slonaker, J. R., ‘*The Normal Activity of the Albino Rat, etc.,’’ J. of

Animal Behav., 1912, 2, 20-42.

532 THE AMERICAN NATURALIST [Vou. LIV

hungry, frequently refused to eat immediately after

earlier turnings, although later they eat quite readily.

Other evidence of a general organic disturbance is found

in the violent trembling which frequently seized some of

the rats during a given series. This trembling was dis-

tinct from that behavior mentioned before which reminds

one of nothing so much as the retching of nausea in

human beings. I have failed to find a single case of nau-

seation in the rat which resulted in an esophageal dis-

charge. The retching did not seem to occur so readily if

the rat had had food before the rotational period. The

trembling was by far the most characteristic performance

and was common to most of the subjects. That the trem-

bling was organically based could be determined by hold-

ing the rat just after turning. The visceral organs

seemed to be convulsed. The eyes were partially closed

and the vibrisse trembled violently because of the trem-

bling of the mouth parts. This behavior occurred for

two or three days after the series had been started and in

the case of some of the subjects was the last observable

response to the rotation.

4. It is difficult to get a quantitative test for these or

for more specifically kinesthetic responses. The only test

used in this connection was an enumeration of the num-

ber of spontaneous movements made before, during, and

after rotation, as the series progressed. Prior to all rota-

tion, the exploratory movements are prominent. As rota-

tion takes place for the first time two kinds of response

are in evidence. First, the rat may make frantic efforts

to move in the direction contrary to rotation so long as

the platform moves. When the movement ceases the rat

turns and attempts just as vigorously to move in the oppo-

site direction. These attempts always cease in five or

six seconds: they seem to reach their term with the after-

nystagmus. The other characteristic response is illus-

trated by those subjects which squat tensely on the floor

of the rotating platform with the head turned far in the

direction against rotation. There seems to be a specific

No. 635] BODILY ROTATION 533

inhibition of all movement and a tenseness of position

leading to what one might call the ‘‘rotational posture.’’

There is no change in the position until the end of the

after-nystagmus, save that the head swings to the oppo-

site side as rotation ceases. This second type of response

can be easily induced in subjects manifesting the first

kind by slightly increasing the speed of rotation. As the

series proceeds, the more striking features of the rota-

tional posture begin to drop out. The head tends to swing

less and less in the direction opposite to rotation and very

early the return movements—even the bringing of the

head back to a straight position—disappear. Finally,

the original swing itself becomes quite listless and may

not occur at all provided the attention of the rat is else-

where directed. The exploratory movements return

slowly, beginning with the post-rotary period and finally

entering the rotary period itself.

5. The scratch-reflex affords an excellent indication of

the extensity and intensity of the bodily disturbance pres-

ent during, and subsequent to, rotation. Early in a series,

a scratch movement initiated before rotation is suddenly

arrested as rotation begins. I have not observed any

seratching during the earlier trials of a series. Subject

‘* J’? endeavored to scratch on the fourth day’s rotation;

but the effort was poorly localized | and uncoordinated.

At the end of the series, an’ “accurately localized scratch-

movement was begun and carried to completion by sev-

eral subjects, and successful attempts were frequently

made to cleanse the face, ete., in spite of rotation or stop-

ping. As the exploratory movements came back to their

own, the rat frequently stretched up on its hind legs. In

Such a position, the stopping of rotation caused a definite

compensatory reaction on the part of the rat; but there

was nothing here to indicate that this was more than a

natural response to the effect of inertia. All of the spas-

modic and uncoordinated qualities of an early event of

this kind were gone. The tendency of some of the sub-

jects to run in the direction opposite to rotation com-

534 THE AMERICAN NATURALIST [Von. LIV

pletely disappeared after a few trials. In brief, the whole

series of any one of the subjects here reported displayed

an increasing degree of freedom and precision of move-

ment, as time went on. All subjects were tested for

equilibration after a series had been completed and all

responded to being thrown and dropped just as alertly as

before rotation.

It is hazardous to draw general conclusions from an in-

troductory study of this kind. Our problem does, how-

ever, bear directly and significantly upon the liio

integrity of the equilibratory mechanisms. The facts

above presented support. the contention that nystagmus

is closely related to the other organic responses to rota-

tion and that it is dependent, as are these other responses,

upon a large group of factors. Furthermore, we have

found that after-nystagmus in the white rat decreases in

intensity and duration (a) from day to day and (b)

within the series of a single day. Either intensity or

duration may be modified also by certain organic condi-

tions, e. g., nausea, by speed and number of rotations, and

by such general conditions as antecedent rest and fatigue.

The decrease and disappearance of nystagmus are accom-

panied by a disappearance of the characteristic rotational

posture and of other bodily disturbances, the disappear-

ance being signalized by. the reappearance of the usual

exploratory movements and i pach specific events as the

scratch-reflex. :

Fisher and Babcock tried to explain away the demon-

strated loss of after-nystagmus under repetition (a) by

charging that the human subjects were ‘‘pathological’’

and (b) by referring the observed decrease to a vicious

practise acquired by ‘ta few subjects’’ of “ gaze-fixing’’

upon a ‘‘distant object.’ It is not clear just how ee

explanation can be extended to the white rats.

NOTE ON THE ‘‘PELVIC WING” IN POULTRY?

PROFESSOR WILLIAM A. LIPPINCOTT

KANSAS AGRICULTURAL EXPERIMENT STATION:

Quire recently Beebe (1915) proposed a four-wing

theory of the origin of flight in birds in the stages suc-

ceeding the arboreal phase of their evolution. Osborn

(1918) raises this theory to the position of an alternate

with the older two-wing theory developed from studies

on the Archeopteryx (see Heilmann, 1913).. Beebe bases

his theory on observations of nestlings of the white-

winged dove (Melopelia asiatica) and the domestic

pigeon (Columba livia Bonn.), an embryo of the jacana

(Jacana jacana), a living specimen of the great horned

owl (Bubo virginianus) and studies of photographs of

the Berlin specimen of the Archeopteryx..

The purpose of this note is to report the presence of

the structure described by Beebe, in glee eae

birds. In reporting his discovery of a ‘‘pelvie wing”

nestling birds Beebe (p. 42) makes the following Stabe:

ment:

Recently while examining the fresh body of a four-days-old white-

winged dove in the New York Zoological Park, I observed on its al-

most naked body a remarkable development of sprouting quills across

the upper part of the hind-leg, and extending toward the tail across

the patagium just behind the femur. A second glance showed that this

was no irregular or abnormally precocious development on the part of

the femoral pterylum, but a line of primary like sheaths, many of

which had a very definitely placed covert.

He then proceeds to a rather detailed Cri prion of the

structure which he called a ‘‘pelvic wing.’

What appears to be the same structure, judging from

Beebe’s description and from the figures accompanying

_ his paper, may be readily observed on most chicks of the

1 Contribution No. 14 from the Department of Poultry Husbandry.

535

IT™ 536 THE AMERICAN NATURALIST [Vou. LIV

No. 635] “PELVIC WING” IN POULTRY 537

American and Mediterranean breeds at three weeks of

age or younger and on English and Asiatic chicks a week

or two later.

In the routine of describing three-weeks old chicks in

connection with certain genetic studies, the writer has

noted and recorded the presence of this structure on sev-

eral hundred individuals. It has seldom been lacking on

chicks of the Mediterranean breeds and crosses, and is

usually found on chicks of the American breeds, and fre-

quently on those of English and Asiatic breeds of this

age. Its non-appearance in chicks of the lighter breeds,

by the time they are three weeks old, is usually asso-

ciated with low vitality and general slowness of feather-

ing. The heavier breeds are naturally slower in passing

from the down to the feather stage and its failure to de-

velop in the first three weeks is more frequent.

While not all of the individuals which failed to show

the so-called pelvic wing in three weeks were reexamined,

many of them were and in every instance the structure

was found at some stage of development. The parents

of the chicks observed were not only of several distinct

breeds and classes but were frequently from widely sep-

arated sections of the country. The number of observa-

tions made and the various sources of the breeding stock

seem to warrant the belief that the ‘‘pelviec wing’’ in the

young domestic fowl is of fairly constant occurrence.

It is interesting to note in this connection that the

BPXPLANATION OF PLATE I

- ic. 1. Pelvic wing of Rhode Island Red chick hatched February 4, 1919,

photographed March 27, 1919. Age hee one days.

Fic. 2. Pelvic wing of bronze poult hatched June 7, 1919, photographed

ord 11, 1919. Age thirty-four days. Some down feathers plucked to show

eee more clearly.

. 8. Pelvic wing of Blue Andalusian chick hatched February 25, 1919,

photographed March 27, 1919. Age thirty days

Fie. 4. Pelvic wing of Blue Andalusian chick hatched March 18, 1919,

photographed March 31, 1919. Age thirteen Down plucked to show

ructure more clearly. Leg extended.

SP he same individual shown in 4, with leg flexed,

Fic. 6. Pelvic wing of White Plymouth Rock chick hatched March 4, 1919,

page” aaa March 27, 1919. Age twenty-three days.

Fig. 7. Pelvic wing of Barred Plymouth <6, ar hatched March 4, 1919,

photographed March 27, 1919. Age twenty-

538 THE AMERICAN NATURALIST [Vou. LIV

‘‘nelvic wing’’ is clearly illustrated in two photographic

figures of four weeks old White Leghorn chicks in Rice,

Nixon and Roger’s (1908, pp. 25-26, Figs. 6 and 7) paper

on ‘‘The Molting of Fowls.’’ The structure is referred

to by these writers as ‘‘the thigh tract.’’

In chickens the ‘‘pelvic wing’’ occurs along the pos-

tero-ventral border of the femoral or lumbar tract, as

described by Nitzsch (1867, Plate VII, Fig. 6) for Gallus

bankiva and appears to be a part of it. In its develop-

ment it is synchronous with, or slightly preceded by, the

feathers of the humeral tract and has so much in com-

mon with the latter as to suggest that the two tracts may

be homologous structures of the hind and fore-limbs, re-

spectively. The ‘‘pelvic wing’’ extends across the upper

part of the hind limb and a more or less well-marked

patagium just behind the femur. The humeral tract ex-

tends across the upper part of the fore limb and the

patagium behind the humerus.

The appearance of the ‘‘pelvic wing’’ of chicks of dif-

ferent breeds is shown in Plate I, Figs. 1, 3, 4, 5, 6, and 7.

The structure in the Bronze turkey (Fig. 2) is essen-

tially the same as in chickens. This breed is the largest

and commonest variety of domestic turkeys and most

nearly resembles their native wild progenitors. |

In the waterfowl the structure has not been found.

This was perhaps to be expected from the figures of

Nitzsch (1867, Plate X, Figs. 5, 6, and 7). The birds ob-

served were domesticated Mallard ducks and White `

Embden geese. In neither could any feathers be discov-

ered which were set off from the others of the femoral

tract, either in size, or precocity of development. There

is however in both species a group of feathers whose de-

velopment is simultaneous with that of the feathers of

the humeral tract. These are situated on a branch of the

inferior tract which extends beyond the breast along the

sides of the trunk almost to the knee. The feathers of

both these tracts precede the remiges in development.

Nitzsch (1867, p. 146) makes note of the fact that ‘‘this .

No. 635] “ PELVIC WING” IN POULTRY 539

short outer branch (of the inferior tract), and the broad,

obtuse axillary tract, constitute the strongest portion of

the entire plumage of the trunk.’’ The position of these

feathers is such as to suggest a pelvic wing to a casual

observer. He further (p. 177) calls attention to the un-

usual development of this branch in Crypturus, where it

‘‘nasses through the lateral space of the trunk and unites

with the extremity of the lumbar tract of the same side.’’

The conditions found in Crypturus (see Nitzsch’s

Plate VII, Figs. 11 and 12), ducks, geese and chickens

might suggest the possibility that the ‘‘pelvic wing’’ in

the chicken, and the branch of the inferior tract in the

duck and goose are both vestiges of what was once a con-

tinuous row of rather large feathers extending from

below the shoulder along the edge of the breast and out

over the thigh. Such a suggestion, however, presents

‘difficulties if the homology of the pelvic wing and the

humeral tract is seriously considered. Judging from

Nitzsch’s figures of Crypturus (Plate VII, Figs. 11 and

12), there is probably no connection between this branch

and the humeral tract. |

BIBLIOGRAPHY

Beebe, C. William.

1915. A Tetrapteryx Stage in the Ancestry of Birds. Zoologica, Vol.

I, No. 2, pp. 3

Heilmann, Gerhard.

1913, ee Nuvaerende Viden om Fuglenes page: Dansk Or-

ithologisk Forenings Tedsskrift, Aarg. 7, H I, II, pp. 1-71.

Nitzsch, Christi an Ludwig.

1867 tas iprnpea® Ed. by Sclater. xi-+18lpp. Plates

Et Pub. for the Royal Society by Robert Hardwick.

Lon fe n.

Osborn, Henry Fairfield.

1918, The Origin and Evolution of Life. Chas. Seribner’s Sons. New

York. xxxi + 322 pp. 136 illustrations.

Rice, James E., Nixon, Clara, and Rogers, C.

‘1908. The Molting of Fowl Cornell Bull, No. 258, pp. 68, Figs, 22.

SHORTER ARTICLES AND DISCUSSION

ON THE NUMERICAL EXPRESSION OF THE DEGREE

OF INBREEDING AND RELATIONSHIP IN A

PEDIGREE!

Dr. Raymond PEARL has given in a series of papers (‘‘ Studies

on Inbreeding,” I-VIII)* published in the AMERICAN NATU-

RALIST during the years 1913 to 1917 a system of measuring

numerically the degree of inbreeding and relationship in a

pedigree.

It will not be necessary to describe the method in any length

as it may be familiar to most readers or can easily be found in

the original papers.

The starting point is the fact, that all inbred individuals, not-

withstanding the special system of inbreeding involved, have

fewer different ancestors in a certain generation than the gront-

est possible number.

The degree of inbreeding is measured by the extent of this

reduction in numbers of different ancestors. For that purpose

a coefficient of inbreeding is determined for each generation ac-

cording to the formula

aa 100(pa41 — Gn41) :

Pn4+1

where Pn, indicates the greatest possible number of different

ancestors in the n 1st generation and qn, means the actual

number of different ancestors in the same generation.

Plotting the series of values obtained for Z over a base indi-

eating the series of generations, the inbreeding curve can be

awn. aximum values for the coefficient of inbreeding are

obtained when continuous brother and sister mating is involved.

The brother and sister inbreeding curve has therefore the im-

portance as the limit, which no other inbreeding curve can

surpass. l i

The proportion of the actual inbreeding during a number of

generations to the highest possible inbreeding in the same num-

ber of generations then offers a fairly good measure for the

1 Papers from the Department of Biometry and Vital Statisties, School of

Hygiene and Public Health, Johns Hopkins University, No. 12

540

No. 635] SHORTER ARTICLES AND DISCUSSION 541

total inbreeding. This proportion can be found by determining

the proportion of the area included by the actual inbreeding

curve in percentage of the area included by the maximum in-

breeding curve. The area of the latter can be calculated by inte-

gration. The actual curve is usually so irregular that no inte-

gration is possible. To get an approximate value the series of

values for Z is simply summed. The formula for the total in-

breeding coefficient is then the following:

1002 ZL

= Fro

the = denoting the summation of i values between and includ-

ing the limits indicated, and Fy, the area included ‘by the

maximum curve, the same mana ‘of encian being involved.?

A question of considerable genetic bearing is the degree of

relationship between the parents of the individual, whose pedi-

gree is being examined. Relationship is indicated by the reap-

pearance of individuals from the pedigree of one individual in

the ancestry of another.

s a measure of degrees of relationship Pearl proposed a co-

efficient of relationship. This is calculated in two slightly dif-

ferent ways according to whether it is measured with the coeff-

cient of inbreeding, where the relationship of the sire and dam

of the inbred individual is being calculated, or separately, when

relationship of any two individuals is measured. The formulæ

are as follows:

(1) Koa 100(pn41 — qn4:) — (sZn_1-spn + dZn_1-dpn

1/2pn4i y

100(pn41 EN Tn41)

2 =

(2) Kn =e

where a prefixed s or d indicates that the following letter refers

to the sire’s or the dam’s pedigree only, and (pn.,;—Tn,,) means

the number of common ancestors for both pedigrees in the

n-+ Ist generation.

As a measure of the proportion of the actual inbreeding due.

to relationship between the sire and dam of the individual Pearl

has proposed to give a series of partial inbreeding indices cal-

culated according to the formula

KZa = Ke)

2 The values of Fyn are given in ee ‘‘ Studies on Inbreeding,’’ VIII,

1917 (Pearl).

542 THE AMERICAN NATURALIST [Vou. LIV

In this paper I wish to give a modification and some extensions

to the method worked out by Pearl with the purpose of bringing

all the measurements of inbreeding and relationship on the same

scale and using total coefficients based on calculations of areas

as. the fundamental method in expressing degrees of kinship

numerically.

I. DEFINITION OF THE COEFFICIENT OF RELATIONSHIP

If we plot the values of the coefficient of relationship obtained

in accordance with the above indicated method together with

the values of the corresponding coefficients of inbreeding for a

given pedigree, we shall find that these corresponding values

are not directly comparable as they are not worked out in rela-

tion to the same scale. To obtain this we need to change slightly

the definition and formula of the coefficient of relationship.

Pearl’s definition is the following: The coefficient of relation-

ship indicates the number of ancestors common to both pedigrees

of the two individuals whose relationship is being measured in

proportion to the greatest possible number of common ancestors

in this generation.

The proposed definition is this: The coefficient of relationship

indicates the number of ancestors common to both pedigrees of

the two individuals whose relationship is being measured in

proportion to the total maximum number of different ancestors in

the two pedigress taken together in the generation in question.

The formulæ are now the following :

(1) (When the relationship between the sire and dam of an inbred indi-

vidual is being measure

Eo 100(pn 41 — Qn 41) sata (sZn_1*sp2 + dZn_‘dpn) j

: pn4ı ;

(2) (If any two different individuals are concerned)

Ka 100(pn41 — Tn4ı)

cae .

Ppn+ı

The difference between these formule and the first mentioned

is only that the denominator in the fractions is multiplied by

two. The total values, therefore, are exactly one half of Pearl’s.

The maximum value of the coefficient of relationship will in

every generation be 50, as no more than 50 per cent. of the indi-

viduals in a generation of a pedigree can appear in both halves

of the pedigree.

No. 635] SHORTER ARTICLES AND DISCUSSION 543

Il. THe TOTAL RELATIONSHIP COEFFICIENT

To measure the total degree of relationship during a number

of generations I propose to use a total relationship coefficient

based on the same common principles as the total inbreeding

coefficient.

The areas to be compared are the area included by the rela-

tionship curve (corresponding to the inbreeding curve) and

the area included by the maximum relationship curve. Now the

maximum values of the coefficient of relationship are 50 in every -

generation beginning at K, and the area in question is for that

reason simply 50 times the number of generations involved.

The formula of the total relationship coefficient for n genera-

tions is then the following:

100ZK; _ 22K

Pa hy

Krn ip

III. TOTAL RELATIONSHIP INBREEDING INDEX

To indicate the proportion of the inbreeding that is due to

relationship between the sire and dam of the individual, whose

pedigree is being examined, I wish to propose a single numerical

expression, the total relationship inbreeding index indicating

the proportion of the area included by the relationship curve

to the area included by the ameen curve, the formula being

the following:

Calculation of the Coefficient Indicating the Degree of Inbreed-

ing and Relationship in the Pedigree of the Jersey Bull

King Melia Rioter 14th (103901)

To show the calculation and significance of the described co-

efficients I have selected the pedigree of King Melia Rioter

Fourteenth including eleven generations. Table I gives the

TABLE I

Z, = 25.00 K, = 25.00

Z, = 37.50 K, =31.25

Z, = 50.00 K, = 37.50

2, = T188 KE, = 43.75

544

THE AMERICAN NATURALIST

Zs = 81.25

4, == 90.63

fe = 02T

Z, = 93.65

Z = 93.85

Total 661.53

K, = 46.09

K, = 46.48

K, = 46.88

10 = 46.88

Total 395.71

[Vou. LIV

values of the series of the coefficients of inbreeding and relation-

ship for each generation.

The calculations of the total coefficients are now the following:

ZT ey

KZ71,, =

_ 2X 395.71

100 X 661.53

900.10

100 X 395.71

= 73.50,

= 79.14,

= 59.82,

Or expressed verbally: In eleven generations King Melia Rioter

Fourteenth is 73.50 per cent. inbred, his sire and dam are 79.14

100 E

90 —

8O ened

70 am

6O —

50 D Y

a ” Yi

4 f 7 Yj

20 WY YY Yyy Wy

fi 7 Aj OME, tf,

Yy YY Yj

10 HG A

fy Yy Yy

Eg 8

Fic. 1. For explanation see text.

No. 635] SHORTER ARTICLES AND DISCUSSION 545

per cent, related, and the part of the inbreeding due to relation-

ship between his sire and dam is 59.82 per cent. of the actual

total inbreeding.

n Fig. 1 the inbreeding curve and the relationship curve are

plotted, based on the figures given in Table I, the former as a

solid line, the latter as a broken line. The smooth curve indi-

cates the maximum inbreeding curve; the broken line, that

divides the area in two equal halves, indicates the maximum

relationship curve. These four curves taken together give a

fairly good graphical demonstration of the facts in question.

1. The area OABX in relation to the area OAEX gives the

proportion of the actual to the maximum degree of inbreeding:

The total inbreeding coefficient.

2. The area OACX in relation to the area ODFX indicates

the proportion of the actual to the maximum degree of rela-

tionship: The total relationship coefficient.

3. The area OACX in relation to the area OABX gives the

proportion of the inbreeding that is due to relationship: The

total relationship inbreeding index.

In bringing all measurements of degrees of inbreeding and

relationship to the same scale and using areas as the measures

we get a uniform and significant series of coefficients that nu-

merically express the degree of inbreeding and relationship in

a given pedigree. TAGE ELLINGER

COPENHAGEN.

SOME OBSERVATIONS CONCERNING THE

PERIODICAL CICADA

Durine the recent visitation of the periodical cicada, their

great abundance on the writer’s home grounds at Vinson Sta-

_ tion, Va., afforded an excellent opportunity to observe some of

the habits of these interesting insects. During the months of

January, February and March, the writer was engaged in clear-

ing off all trees and brush from several lots immediately adjoin-

ing his home grounds. In the course of this work, several large

oak trees were completely dug up by the roots. Even during the

winter months, many of these benumbed creatures were encoun-

tered in their burrows in the soil around the roots. As warmer

weather approached, their burrows became more numerous in

the soil and it was evident that they were approaching the

warmer, uppermost layer in ever-increasing numbers. Finally,

546 THE AMERICAN NATURALIST [Vou. LIV

on May 18, the first adult was seen making its weak flight over

my garden, having emerged some time during the previous night.

A few evenings later the great exodus had begun in earnest and

thousands of pup were issuing from the ground after sundown

and ascending all the bushes, trees and posts in the vicinity to

transform.

Although the actual exodus from the ground does not take

place until after sundown each evening, the pup, in preparation

for the event, excavate their burrows to the very surface of the

ground and await the setting of the sun. In some instances the

creatures burrow just to the surface, leaving a very thin layer

of soil undisturbed over the exit. Frequently a tiny hole is punc-

tured in the center of this thin surface layer. If these burrows

are cautiously approached late in the afternoon long before sun-

down, the heads of the creatures may be seen near the surface.

As the light intensity wanes with the oncoming of evening, the

creatures come to the very surface, but quickly retreat if ap-

proached or disturbed. It is evident that the pup are nega-

tively phototropic. If a pail or box is inverted over their bur-

rows long before sundown so as to exclude the light, the creatures

will shortly emerge as if night were really at hand. In this way

I have brought many pup out of their burrows in broad day-

light.

Although the pupe quickly transform after emerging from the

ground, it would be of interest to know just what conditions, ex-

ternal or internal, determine the impulse to prepare for the adult

stage. If the creatures are prevented from leaving the ground

or soil, the following experiments indicate that the pupe will

remain as such at least a day or two longer than when allowed to.

ascend trees and shrubs in the normal manner.

On the evening of May 24, five pupe just emerging from the

ground were captured and placed on the damp bare ground be-

neath a large inverted flowerpot, the drainage hole at the bottom

of which had been closed. In addition to these, six other pupæ

were captured and placed in a large flowerpot of similar size

filled even to the top with loose soil. This pot was covered with a

board. Both pots were examined next morning. The pup

placed on the bare ground beneath the inverted, empty flowerpot

were still crawling around, and none had transformed. Of the

six placed in the pot containing soil, one had died. The remain-

ing five were alive and active, and likewise none of these had

transformed.

No. 635] SHORTER ARTICLES AND DISCUSSION 547

On May 25, the following experiment was made with these

creatures. Early in the evening before the time had arrived

when the creatures usually emerge in response to the low light

intensity prevailing after sundown, many were captured by in-

verting boxes, etc., over the burrows. Later in the evening many

more pup were captured as they were emerging from the

ground in response to the normal darkness following sundown.

Six were again placed on the damp earth beneath an empty, in-

verted flowerpot. Nine were placed as before in a full pot of

soil, over which a board was placed to prevent their escape. As

controls, six were placed on the branches of a shrub and kept

under observation. One of the controls fell off and escaped. The

remaining five soon transformed in the normal manner. The

next morning, May 26, the pupe kept beneath the empty, in-

verted pot and those in the soil were examined. Of the six placed

on the bare soil beneath the empty, inverted pot, one had died

but the rest were active. None had transformed. All nine pupe

placed in the pot containing soil were alive and crawling over

the top of the soil. Likewise none of these had transformed. On

the evening of May 26, three of these had died, but the remaining

six were as lively as ever. These were then given their freedom

and were allowed to crawl up into the branches of a small fringe:

tree nearby. One fell off and was lost, but the remaining five

completed their transformations in the normal manner. Whether

this temporary inhibition of the act of transformation is voli-

tional or depends upon some factor of the soil environment act-

ing upon them is not definitely established by these experiments.

After the pups ascend the shrubs and trees, rigidity sooner or

later takes place, and the adult begins its emergence from the

dorsal slit which opens in the pupal skin. It is not long until the

lax, soft-bodied creature is hanging head downward by the tip

of the abdomen. At this stage of its emergence, when it appears

as if the helpless, soft-bodied creature must fall to the ground

and perhaps suffer injury, it becomes very active, actually bend-

ing up to catch the exuvium or other near object with its legs,

just before the tip of the abdomen is released. Not all pupe are

fortunate in their travels and transformations, however, for

many come tumbling to the ground from the trees while they are

making their way up the trunk and limbs. The almost helpless

transformed adults also sometimes fail to secure a foothold and

fall to the ground. It is interesting to note how quickly pigmen-

548 THE AMERICAN NATURALIST [Vor. LIV

tation is completed after transformation. Immediately after

emerging from the pupal shells, the adults are pale yellowish

white, with two large conspicuous jet-black areas on the yellow-

ish white prothorax. In a few hours the entire prothorax de-

velops this same black pigment and becomes almost uniformly

black.

In some localities the pup, in response to special conditions,

construct neat little chimneys of earth several inches in height

into which their burrows lead. . I did not, however, find a single

specimen of these unique structures in my locality, although the

soil conditions varied greatly.

At Vinson Station, I was afforded an excellent opportunity to

observe the occurrence, habits and notes of the dwarf or casinii

form as well as the typical, much larger form, since both oc-

curred here. Although the earliest musical expressions of the

larger form were heard at my home on May 24, the distinctive

notes of the dwarf form were not heard until nearly a week later.

A rather well-defined colony of these smaller cicades appeared in

some low, shrubby oaks only a few rods from my home, and re-

mained locally abundant here throughout the period of their

visitation. It was here that I spent much time in observing their

habits. Although the pupe of the larger and the dwarf form

emerged from the ground within the same area in some places,

and both forms were singing in the same trees and shrubs, both

species appeared to mate among themselves. At no time did I

observe a single instance of cross-mating. Although now and

then I heard an occasional casinii form singing in the nearby

woods, this form confined itself almost entirely to the narrow

limits of the shrubby oak growths where it first appeared.

It now remains to consider the ‘‘songs’’ or musical notes of

the larger and the smaller forms, for they are entirely different

in character. The song of the larger form is a low, and to my

ear usually pleasing, droning,—ah-oo—ah-o00o—ah-o00o—ah-oo—

ah-oo. The first, or ‘‘ah’’ syllable is higher in tone and slurs

down to the much lower pitch expressed by the syllable ‘‘oo.”’

Each phrase ‘‘ah-oo’’ requires about five seconds, and the entire

series may be prolonged for many seconds. During the act of

‘*singing,’’ the abdomen is noticeably raised toward the wings

on every ‘‘ah’’ syllable, and is lowered on the lower-pitched

**o0’’ syllable.

The ‘‘song’’ of the small Casinii form is a dry, lisping, tone-

No. 635] SHORTER ARTICLES AND DISCUSSION 549

less series of sounds, which to me seem best described by the syl-

lables _— ‘‘it-see—it-see—it-see—it-see—it-see—it-see—see—see—

The entire series of notes is hurriedly delivered and

does not usually last over 8 to 10 seconds. The first notes of the

_series—‘‘it-see—it-see ’’—usually begin slowly and are somewhat

subdued in character. The syllables ‘‘it-see’’ gradually increase

in loudness, and finally decrease somewhat in intensity, as they

run into the shorter, more subduel syllables ‘‘see—see—see—

see” which terminate the complete ‘‘song.’’ The notes of this

form are soft and lisping in character, and remind one of the

noise of steam escaping intermittently, as one sometimes hears it

around a locomotive.

During the height of the ‘‘song’’ season, one could rarely dis-

tinguish the notes of any individual, for the myriads of ‘‘ voices’’

blended into a volume of soft, murmurous sound—a veritable

atmosphere of sound which seemed everywhere to invest the trees

and landscape from daybreak till darkness. It was a steady,

droning, unceasing hum like the even whirr of machinery. The

trees in the National Cemetery were fairly swarming with these

creatures and their steady, murmurous chorus could be heard

from morning until night, at a distance becoming softened and

subdued, and reminding one of the soft murmurs heard when a

big sea shell is held to one’s ears.

Although the periodical cicada usually becomes silent after

sundown, a great nocturnal chorus is sometimes initiated and a

remarkable wave of sound invests the night for a time. On the

night of May 31, I heard a most memorable, nocturnal chorus of

this character, which began just before 2 A.M., solar time. One

or two singers in the oak trees in my back yard initiated the con-

cert. Others joined in, and there was a gradual swelling in the

volume of sound until it seemed as if all the creatures in these

trees were in full song. The concert did not stop here, for I

heard it passing on to the big woods toward tulip poplar swamp,

until the nighttime was fairly filled with murmurous sound.

Gradually the crest of the wave passed outward into the more

distant. woods, while it subsided slowly in the trees in my back

yard where the musical impulse appeared to originate. After

some minutes all was quiet again around me, although I could

just hear the great wave of sound receding or dying away in the

distance. It was the most weird and remarkable chorus I have

550 THE AMERICAN NATURALIST [Vou. LIV

ever heard. Hopkins describes a similar instance of this spec-

tacular, nocturnal singing which he once heard.*

Many species of birds appeared to find these cicadas especially

acceptable morsels. The blue birds in my boxes fed their young

upon them extensively, as did a pair of song sparrows which had

their nest in a pile of roots in my back yard. House wrens, Eng-

lish sparrows, red-headed woodpeckers and cuckoos fed upon

them greedily. Some birds appeared frequently to snap them-up

in mere play as I once saw a cuckoo doing in the branches of a

maple tree over my head. This bird snapped up first one then

another in quick succession, quickly dropping them one by one,

in a badly injured, helpless condition.

It is of interest to note that indsvideals differ in eye color. I

have noted the following:

1. Males and females with red eye color.

2. Males and females with orange eye color.

3. Males and females with light buff eye color.

4, One male with noticeably white eye color. This individual

was distinctive in other respects, since the large veins of the

wings, markedly reddish in the common, red-eyed form, were

pale yellowish in color. Red-eyed individuals predominate.

Some of the more important dates in the occurrences of the

periodical cicada at Vinson Station I have recorded in my jour-

nal as follows:

May 18—First adult seen on the wing. The great exodus from

the soil began during the next few days.

May 24—First ‘‘singing’’ of larger form heard. First singing

of smaller Casinii form heard some days later, about May 27 to

May 30.

May 30—Large form in copulation conway First female

noticed laying eggs in tw

June 5—Ege-laying spa at their height.

June 14—Creatures becoming very rare, and individual singers

only occasionally heard.

une 20—All silent.

June 27—A single, belated individual of the larger form heard

in ‘‘song.”’

` Although the incessant concerts of the periodical cicadas per-

sisting from morning until night became almost disquieting at

1See ‘‘The Periodical Cieada,’’ by C. L. Marlatt, Bull. No. 14, Div. of

Ent., U. 8. Dept. of Agr., 1898, page 58.

No. 635] SHORTER ARTICLES AND DISCUSSION 551

times, I felt a positive sadness when I realized that the great

visitation was over, and there was silence in the world again, and

all were dead that had so recently lived and filled the world with

noise and movement. It was almost a painful silence, and I could

not but feel that I had lived to witness one of the great events of

existence, comparable to the occurrence of a notable eclipse or

the visitation of a great comet. Then again the event marked a

definite period in my life, and I could not but wonder how

changed would-be my surroundings, my experiences, my attitude

toward life, should I live to see them occur again seventeen years:

later.

H. A. ALLARD

WASHINGTON, D. C.

THE BEHAVIOR OF FUNDULUS HETEROCLITUS ON

THE SALT MARSHES OF NEW JERSEY

Durme the year 1914—’15 the writer was retained as consult-

ing zoologist to the department of entomology of the New Jersey

Agricultural Experiment Station and engaged in studying the

fish enemies of the salt marsh mosquitoes. At that time it be-

came evident that Fundulus heteroclitus is the most important

predatory fish attacking the salt marsh mosquitoes of northern

waters. Much evidence of the efficiency of Fundulus heteroclitus

as a mosquito exterminator has already been published (Chides-

ter, 1916). Certain notes on its behavior under varied condi-

tions have been amplified by more recent observations and are

herewith presented in connection with the problem of migration

in fishes.

In New Jersey the fish were studied under natural conditions

for over a year on the salt marshes near the city of New Bruns-

wick. Through the report system of the state inspectors of the

Mosquito Commission, much important information was secured

regarding conditions in other parts of the state. Experimental

conditions were induced in the field by drainage ditches and in

the laboratory by the use of aquaria. Other studies were made

at Woods Hole, Mass., for several years during a portion of the

month of June.

MATERIAL AND METHODS

On the salt marshes where the chief study was made there

were numerous pools, some permanent, others easily differenti-

552 THE AMERICAN NATURALIST [Vou. LIV

ated as temporary. The bottoms of the permanent pools were

covered with soft mud and strewn with sedge and eel grass fre-

quently dispersed in windrows as a result of repeated wave

action. The bottoms of the temporary pools were covered with

matted grass bound together by hardened clay.

At the Bonhamtown marshes near New Brunswick, intensive

study was made of three large permanent pools, one of which

was partially drained by a ditch connecting it with the Raritan

River. Additional studies were made of conditions in many

other permanent pools, temporary pools and ditches.

The three permanent pools studied most intensively were quite

different in their character. The largest one was about 40 feet

long and ranged from a foot to 10 feet in width, but its depth

varied considerably with the tides. At its larger end it was

connected with the Raritan River by means of a long narrow

drainage ditch. The second was an almost circular pool about

25 feet in diameter and in no place more than 18 inches deep;

much of the time it was only about 6 inches deep. The third

pool was about 30 feet long and about 10 feet wide. At one

end it was 20 inches in depth and at the other about 12 inches.

Collections were made by means of a 20-foot minnow seine and

several small dip nets. Fish were frequently preserved in weak

formalin in the field when it was desired to examine their stom-

achs at leisure. Usually, however, they were brought to the

laboratory and examined freshly killed or else liberated in

aquaria. 3

Records of temperature, salinity and specific gravity werc

taken with each collection, while the height of the tidal flow and

the depth of the pools were approximately recorded.

SPRING MIGRATION

In the early spring, usually during the latter part of March,

Fundulus heteroclitus begins its migration from the mouth of the

Raritan River up beyond the salt water to the slightly brackish

water of the salt marshes and even into fresh water creeks.

At first large numbers of medium-sized males appear, followed

soon after by the medium-sized females (three or four years old)

and later by the large and small of both sexes. By the middle

of April great shoals of small fish crowd the streams and pene-

trate to the shallows. They seem undeterred by the sewage pollu-

No. 635] SHORTER ARTICLES AND DISCUSSION 553

_ tion of the river and are apparently impelled to seek out the

farthest limits of tidal water.

Spawning takes place in April and continues until July in the

region studied.

The factors influencing inland migration in the spring are sev-

eral. The temperature of the inland waters which is at that

time slightly higher than that of the ocean, and will later con-

tinue to increase, undoubtedly plays an important part. The

fresh water teeming with life and the salt marshes with myriads

of insect larve, shrimps, and young fish furnish food for the

vigorous hungry fishes. The currents of fresh water have become

stronger and as the fish needs must react to a stream of water not

absolutely toxic to it, there is thus a pressure stimulus which

powerfully attracts. Of perhaps less importance is the fact that

the fresher waters when not too greatly contaminated by sewage

pollution are richer in oxygen. Certain it is that many fish not

anadromous come near the shore to spawn. Possibly the greater

metabolism incident to the development of eggs and sperm causes

them to seek out water which has a higher oxygen content. Roule

(1914) believes that salmon migrate to a richer supply of oxygen.

Wells (1915) has shown that starvation may cause certain fishes

to seek water of lower concentration of salts and other species

to behave in the opposite manner.

SUMMER HABITS

During the summer until early August there is continual mi-

gration inland with the tides, many of the fish returning to the

brackish water of rivers and creeks as the tide ebbs from the

marshes. Some few individuals of the species Fundulus hetero-

clitus find sanctuary in the marsh pools, and in all probability so

habituate themselves that they remain until cold weather. From

the three permanent pools not partially drained by ditches, col-

lections made during the year furnished the following species.

Number of

Collections Fundulus het. Cyprinodon var. Apeltes quad. Anguilla

1,581 105 19 22

E E ee ee ore ee a

Since Fundulus majalis did not appear on the Bonhamtown

marshes it was not feasible to repeat with that species the ob-

servations of Mast (1915), who found that it is not only prone to

move with the tides, but that if the outlet to the ocean is plugged,

554 THE AMERICAN NATURALIST [Vou. LIV

the fish will convey themselves overland by flopping in the gen-

eral direction of the ocean. Mast shows that the fish are able to

keep their sense of direction in the overland course and concludes

that they remember the outlet. He believes that since there are

apparently no external factors capable of guiding them, the

behavior is dependent on internal factors.

Fundulus heteroclitus does not as a rule leap from pools, when

left by the gradually receding tides. ` Two permanent pools were

available for the study of the reactions of this species, one of

them being connected with the Raritan River by a drainage ditch

during the course of the study. This pool had been under con-

tinuous observation in an undrained condition and through an

error workmen ran a drainage ditch to it, which did not, how-

ever, completely remove the water. After two days of the re-

sultant condition the ditch was plugged with heavy sods and

observations continued as before. The day after the ditch was

plugged it was noted that there were many F. heteroclitus scat-

tered all around the margin of the large oval pool. Although it

was 25 X 15 ft., there was no marked variation in the distribu-

tion of the dead fish, except that there were none at the end

farthest from the outlet. The banks were gently sloping and

afforded an easy egress in any direction. The second pool with

an outlet was long and narrow with high banks and was partially

drained at the ebbing of the tide. When the receding water had

left certain of the fish near the shallows at the exit, there was

the usual attempt of the majority of fish to follow an outflowing

current. But few individuals were caught in the mud, the ma-

jority returning to the deeper pool.

Since there is one predominant. reaction in fishes, that to cur-

rents, it is quite probable that with Fundulus heteroclitus there

is a less marked reaction to ebb tide. In the case of Fundulus

majalis under natural conditions there must be an extremely

rapid reaction to the condition of slack tide. Their disturbance

under “experimental conditions induced by Mast (1915), who

plugged the entrance of the tide as it was coming in, indicates

that this species does not normally accommodate itself to still

water and that its stay inland is determined only by the tidal

rise.

In the case of Fundulus heteroclitus, which migrates inland

to the extremely shallow water covering the salt marshes at high

tide, there is no such immediate response to receding water. The

No. 635] SHORTER ARTICLES AND DISCUSSION 555

fish return less quickly and seem to become readily acclimated

to the still waters of permanent or even temporary pools to

which they are directed as the tides recede.

In August there is a period of over two weeks when actively

feeding killifish are almost completely absent from the marshes,

That temperature plays a most important part in this behavior

is indubitable. Shelford and Powers have shown (1915) that

the herring is sensitive to temperature differences as small as 0.2°

C. They have demonstrated that alkalinity and acidity are

more important than salinity. The herring and salmon experi-

mented with reacted to small fractions of a cubic centimeter per

liter of H,S and became negative to sea water which was slightly

more acid than the fresh. It is possible that increased tempera-

ture may bring into solution organic substances which alter the

alkalinity of the sea water or even render it acid near sources

of pollution. Johnstone has shown (1908) that the migration

of herring in Europe is closely associated with the salinity and

temperature of the sea.

We may safely assume that Fundulus heteroclitus has an op-

timum temperature for its metabolism which will be higher when

the animal is weak and poorly nourished, but lower when it is

well fed. Thus a gradually increasing temperature while the

animal is feeding will finally result in such warmth that normal

metabolism is no longer possible and there will be no return to

the fresher waters until they become cooler. Another factor of

great importance in the inland movements of Fundulus is the

fact that after spawning, the animals are sluggish and hence in

no condition for a battle with the tides. This factor is probably

the one that causes almost complete disappearance of the larger

and the medium-sized Fundulus during August in the area

studied.

FALL MIGRATION

Early in September large numbers of Fundulus kaar iis

of small and medium size return to the marshes with the tides,

and they continue to run in and out until the water becomes

extremely cold. There are fewer individuals remaining in the

pools between tides, but many are still found variously dispersed

among temporary pools far inland.

Their food is somewhat reduced so far as mosquito larvæ are

concerned, but there are many other insects available, besides

small eggs and shrimps.

556 THE AMERICAN NATURALIST (Vou. LIV

WINTER HABITS

The habits of Fundulus heteroclitus in the ocean in winter are

not fully known. The late Vinal Edwards of the U. S. Bureau

of Fisheries, Woods Hole, Mass., stated to the writer that it was

his observation that they spend a large part of the winter near

the mouths of rivers in water which is moving and which is at a

salinity slightly lower than that of the sea.

In November, when the temperature of the water on the

marshes goes down to 40° F., the migration inland is much re-

duced. Field observations showed that fish in temporary pools

at this time attempted to burrow in the bottoms and being of

course unsuccessful on account of the hardness of the clay died

during the night as the temperature went down to nearly the

freezing point. In the case of permanent pools whose bottoms

were covered with soft mud, the fish burrowed down during the

night and emerged when the sun came out and warmed the water.

At about the time that ice begins to form over the permanent

pools, migration ceases so far as the marshes are concerned. In

the pools, fish were found burrowed in the mud at a depth of

from 6 to 8 inches in the middle of the winter. The temperature

of the mud was from 40° F. to 45° F. and that of the water

ranged from 32° F. to above 40° F., even in February, since the

shallower pools were warmed considerably by the sun. On

bright days when the sun was most effective, a few hardy fish

ventured forth from hibernation and swam slowly around under

the ice, feeding but little. Associated with them were shrimps,

myriapods, eels and another minnow (Cyprinodon var.), all of

which were burrowed in the mud during most of the winter.

Examinations of the stomach contents of Fundulus showed

that the food during the winter was largely algal matter in those

individuals that became active. By far the majority of the fish

remained torpid until early spring, beginning to feed again in

March, and reassuming complete activity early in April.

SUMMARY

1. Field studies of Fundulus heteroclitus were made through-

out one entire year on the salt marshes of New Jersey.

. Spring migration begins in March and is probably caused

by several factors, including the higher temperature of the in-

land water; currents due to high tides and rainfall; the need

No. 635] SHORTER AnTICLES AND DISCUSSION 557

for food available in fresh water; greater metabolic activity due

to gonad development which demands a greater oxygen supply.

3. Summer activities consist in spawning, feeding, lazy move-

ments from the marshes to the brackish water and back again.

4. In the autumn, migration is less constant and the larger

fish are less numerous.

5. In the winter, migration ceases entirely as the marsh pools

are scumming with ice. Some landlocked individuals burrow

into the mud of permanent pools, coming out occasionally as the

sun warms the water. Many fish are killed by the cold as they

remain in temporary pools with bottoms composed of caked mud

and grass offering no shelter.

6. The majority of Fundulus heteroclitus return to salt water

in the winter, probably remaining near the mouths of rivers

until spring.

F. E. CHIDESTER

WEST VIRGINIA UNIVERSITY.

BIBLIOGRAPHY

Chidester, F. E.

1916. A Rascal Study of the More gp of the Fish Enemies

of the Salt Marsh Mosquitoes. Bull. 300, N. J. Ag. Exp.

aa pp. 1-16.

Johnstone, J.

1908. Conditions of Life in the Sea. 332 p. Cambridge.

Mast,

1915. “The Behavior of Fundulus with Especial Reference to Overland

rae ag Tide- as and Locomotion on Land. Jour. An.

, Vol. 5, pp. 341-350.

Meek, A.

1916. The Migrations - Fish. 427 p. London.

Shelford, V. E., and Allee, W. C.

1914. Rapid Modification of the Behavior of Fishes in Contact with

Modified Water. Jour. An. Beh., Vol. 4, pp. 1-30.

Shelford, V. E., and Powers, E. B.

1915.. An ete Study of the Movements of Herring and

Other Marine Fishes. Biol. Bull, Vol. 28, pp. 315-334.

Wells, M. M.

1914. ga pT and Resistance of Fishes to Temperature. Trans.

ad. Sci., Vol. 7.

1915. a Baiia and Resistance of Fishes in their Natural En-

vironment to Salts. Jou ap. Z 10, pp. 243-283.

1915. Reaction and Resistance of Fishes in their Natural Environ-

ments to Acidity, Alkalinity and Neutrality. Biol. Bull., Vol.

29, pp. 221--257.

INDEX

NAMES OF CONTRIBUTORS ARE

AGERSBORG, H. P. K., Utilization =

chinoderms and Gasteropod Mol

lusks, 414

Alkalinity of Sea Water,

Cro 88

Ataano, “HL. A., Periodical Cicada,

Weeds

Amieronaeloate mia of Paramecium

audatum, EUGENE M. LANDIS, 453

Ponsa Lit fe oe geet FRANK

‘OLLINS BAKER, 152

Assortative Pairing in Chromodoris,

W. J. Crozier, 182

Bascock, Ernest B. Chih Aea and Ge-

netic ratiga don, 270

BAKER, FRANK COLLINS, Animal Life

and ‘Sewage e, 15)

gege THOMAS, A Recent Check-

284

mace sa Fundulus heteroclitus,

DESTER, 551

a Porichthys notatus

Girard, 380; of Mellita, W. J

CROZIER, 435

Bass, CHARLES T., Plants and In-

313

pep sonata aar in Guinea- -pigs,

LEO CoLE, 130; Cataract in

Cattle, E A DETLEFSON and W.

W. YAPP, 277

CASTLE, W. E., man and Castle

on Orthogenetie Evolution in Pi-

geons,

Cheek-list, THOMA S BARBOUR, 284

Chiasmatype and Crossing-over, E.

N, T. H. MORGAN, 193

CHIDES R, E., Behavior ‘of Fun-

dulus + betercotitics

Chitons, Coloration, FE ipe Sen-

py 6

COLE, LEO "d mare ’Palsy in

Guinei Pa. 130

Color Classes, Exceptional, in Zoe

nd Canaries, C. C. LITTLE, 162

Crepi omg Genetic Investigations,

a BABCOCK, 270

Ww. J., Sex- correlated Cor-

ia sa Chiton tuberculatus,

4; Alkalinity of Seawater, 88;

eaae. Pairing, 182; Photie

559

PRINTED IN SMALL CAPITALS

Sensitivity of the Chitons, 376;

Bionomics of Mellita, 435

DAVENPORT, C. B., Human Twins,

Det LEFSON, J. A., an ad W. W. oar

Congenital Cataract in Cattle, 277

U. r i 4 Oaa of

the Ostrich, aS

DUNN ., Sable Varieties of

Mice, 247; White- -spotting in Mice,

456

East, E. a a and Evo-

Eohinedarms and Gasteropod Mol-

rey ra . KJERSKOG-AGERSBORG

iea NGER, TAGE, Numeral Expres-

sion of the Degree of Inbreeding,

540

Evolutionary Aspects of Human Mor-

tality Rates, RAYMOND PEARL,

Factorial Values, C. ZELENY, 358

Fossilization of Blood Corpuseles,

Roy L. Moopte, 460

GRIFFITH, COLEMAN R. aged Rota-

tion igi the White Rat,

gyae ea ra C. F. Curtis

ao;

HAD oe ILIP, een oy and

Blackhead i in ingest

eer of Mamma ait il H Havs-

AN, 496

Dat, E. Newton, Regulation in

., The Free-swim-

ibra

tillans, 427; Hair of Mammals,

HAGEDOORN, A. L., and A. c. HAGE-

RN-LABR RAND, White Rat and

Bacterial Diseases, 368

Heredity, MULLER,

HUBBS, CARL e asada of Po-

richythys tatus Girar d, 380

Hybridization and Evolution, E. M.

East, 262

560

IBSEN, HERMAN I., Linkage,

Inbreeding in in Maize, 1 rr da of,

Individuality. Differential and its In-

EB,

Inheritance of Congenital hye 2 in

nea-pigs N J. COLE,

Inherited Predisposition for à ‘Bac.

terial Disea . C. HAGEDOORN,

LABRAND a

368

ger Enemies of iy ship Fungi,

y B. Wess, 443

at a L. HAGEDOORN,

Jacoss, M. H., Rate of aoe

in Small 1 Organisms, 9

LANDIS, EUGENE M., Amicronucleate

Race of Paramecium caudatum,

453

Linkage in Rats, HERMAN I. IBSEN,

61; Measurement of, C. C. LITTLE,

LirpPINcorr, WILLIAM A., Pelvic

Wing in Poultry, 536

Lırrue, C. C., Exceptional Daer

Classes in Doves and Cana

162; Linkage, 264

Tissues and Degrees of

Family ‘Relationships, | bo Indi-

viduality-Differential a d its Mode

of Inheritance, 55

MAGATH, THOMAS Byrp, The Nema-

tode Genus Camallanus, 448

Fossilization of

ondary Sexual

Characters of the Fiddler Crab,

po and E. B. Winson, Chiasma-

Crossing-over, 193

Mevulity ea Human, RAYMOND

PEARL

MULLER, H. J., Heredity, 97

Nastigophora, the Le haga

Leon A. HAUSMAN, 333

Nematode nus, Camallanus,

OMAS Byrp MAGATH,

Neotony and the Sexual Problem, W.

W. SWINGL

Numeral Expression of

of Inbreeding, Tage ETTINGER,

540

nee of ee Callosi-

Ostrich, Inherita

ties of, J. E. DUERDEN, 2

2 a O Evolutionary As-

oy age

—a

THE AMERICAN NATURALIST

the Degree

‘Zeteny, C.,

Zone Invasion and Ste

LIAM ALBERT

[Vou. LIV

Periodical Cicada, H. A, ALLARD,

545

RAYMOND, Percy E., Phylogeny of

the Arthro opoda, 398

ap eg in Plants, E. NEWTON

Harvey, 362

Relationships, Family, Tissues and

ine e Leo LOEB, 45

RILEY, C. F. CURTIS, Habitat Re-

ada s, 68

Preen Measuring rate of, M.

Rotation, Continued Bodi ily, of

White Rat, COLEMAN R. GRIF-

FITH, 542

Sable Varieties of Mice, L. C. DUNN,

Secondary Sexual Characters of the

Fiddler Crab, T. H. MorcaxN, 220

SETCHELL, WILLIAM ALBERT,

thermy eraa Zone Invasion, 385

Sex in Mercurialis annua, CECIL

Samer, 280

Sex-linked Lethal Factor in Mam-

mals, C. C. LITTLE,

Swinete, W. W., Neotony and the

Sexual Problem, 349

Trichomonas and sopas in Tur-

keys, PHILIP HADLEY, 17

Twins, Human, Production of, C. B.

DAVENPORT

Vibratile Membranes of Glaucoma

scintillans, LEON A. HAUSMAN,

WEATHERWAX, PAUL, Intolerance of

nbreeding in Maize, 1

Weiss, Harry B., aadh Enemies of

Polyporoid Fungi, 443

456

Whitman and Riddle, Evolution in

Pigeo E. CASTLE, 188

|. MORGAN,

. Crossing-over,

YAMPOLSKY, CECIL, Bex in Mercu-

rialis annua, 280

Factorial Values, 358

tenothermy, WIL-

385