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^Heredity of Coat Characters in
Guinea-Pigs and Rabbits,

W. E. CASTLE

Assistant Professor of Zoology, Harvard University
Associate, Station for Experimental Evolution

Drf

PUBLISHED BY THE CARNEGIE INSTITUTION OF WASHINGTON
FEBRUARY, 1905

CARNEGIE INSTITUTION OF WASHINGTON, PUBLICATION No. 23.

PAPERS OF STATION FOR EXPERIMENTAL EVOLUTION AT
COLD SPRING HARBOR, NEW YORK. No. 2.

CONTRIBUTIONS FROM ZOOLOGICAL LABORATORY OF MUSEUM OF COMPARA-
TIVE ZOOLOGY AT HARVARD COLLEGE. E. L. MARK, DIRECTOR. No. 158.

PRESS OF GIBSON BROS.,
WASHINGTON, D. C.

CONTENTS.

Introduction, , 5

Experiments with guinea-pigs, . 6

Heredity of coat color, . . . . 6

Coat of the wild cavy, 6

Color varieties of the domesticated cavy or guinea-pig, .... 7

Agouti, . ... . 7

Yellow, 7

Chocolate, 7

Black, .....,_ 8

Albino, ..'.'. 8

Spotted, . . . ..'.".• 12

Brindled, 13

Roan, and Silvered, . . ... . . . . -14

Results of crossing the elementary color varieties, . . . . .14

Albinos and pigmented animals, . . • . , ', . . .14
Albinism and the "Law of ancestral heredjty," .»••:. . « . 16
Albinism and sexual prepotency, . . . . . . . . 33

Albinism and latent pigment characters, . . . ; . 34

Intercrossing of different pigment types, . . . . . a6

The agouti type, . . . . ..... . .26

Agouti X agouti, 26

Agouti x black, ..... .26

Agouti X red. . . , . . .28

Agouti x albino, . . . .28

The black type, 31

Black x red, 31

Black x albino, . . . . ... . . -34

The red type, . . . . . . . . % . .36

Red x albino, 37

Black-eyed white, -37

Comparison with pink-eyed mice, . . ; . . -47

Heredity of rough coat, 56

Prepotency and dominance, . . .58

Heredity of long coat 64

Correlation among coat characters, . ...... 67

Experiments with rabbits, 70

Cross between two different types of albinos, .... .• . .70
Heredity of long or Angora coat, «, • • • • • • -73

Herediiy of lop-ears, . . . , * . • 74

Summary, . . • • • 75
Bibliography, 77

HEREDITY OF COAT CHARACTERS IN
GUINEA-PIGS AND RABBITS.

BY W. E. CASTLE.

INTRODUCTION.

The experiments to be described in this paper have been in progress
in the Zoological Laboratory of Harvard University since the year 1900 .
They were begun for the study of conditions governing sex in the higher
animals, but have yielded results bearing on certain other questions,
which alone will be considered in this paper.

The animals used, guinea-pigs and rabbits, were selected because of
their early maturity and fecundity. To provide them with food and
shelter and to give them the necessary daily care, in addition to keep-
ing records as full as possible, have been no small task. In this con-
nection I am indebted for invaluable assistance to a number of per-
sons. First of all to Prof. E. L. Mark, director of the zoological
laboratory, without whose encouragement and support the experi-
ments could never have been undertaken, and who has more than
once come to the rescue when the material resources at my command
were exhausted and further progress seemed impossible. The director
and other officers of the Museum of Comparative Zoology, and the
President of the University, have generously provided quarters for the
animals and in other ways have aided the enterprise. Finally, when
the increasing cost became a burden too heavy for the laboratory to
bear, it was assumed by the Carnegie Institution of Washington in the
form of a grant to Professor Mark and myself for experimental studies
in heredity. Under the auspices of the Carnegie Institution the work
has been in progress since January, 1904, and this paper is presented
as a first detailed report upon it.

In the course of the experiments about 3,000 guinea-pigs and several
hundred rabbits have been reared.

For valuable guinea-pigs and excellent practical suggestions I am
indebted to Miss Jeannette Soule, secretary of the National Cavy Club ;
for an interesting stock of albino rabbits I am indebted to Prof. R. T.

6 COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

Jackson. During the academic year 1903-1904, Mr. R. C. Kibbey has
given me valuable assistance in the breeding experiments, and Mr.
A. D. Howard in the study of the hair pigments.

EXPERIMENTS WITH GUINEA-PIGS.
HEREDITY OF COAT COLOR.

In the coat of many mammals there occur two or more distinct pig-
ments associated together in the same individual hair, and according
as one or the other of these predominates in particular regions of the
hair or of the body, a distinct " ticking" of the hair is produced, or a
color-pattern of the body. Familiar examples of " ticked" or parti-
colored hairs are those of mice, squirrels, and foxes. Body color-pat-
terns of the sort mentioned occur in cats, tigers, leopards and the like.

In mice Bateson ( : 03)* has shown that there occur three different
pigments — black, chocolate, and yellow. In the wild mouse all these
pigments occur together in the same individual hair, but in fancy mice
the pigments may occur singly or combined in pairs, when they pro-
duce the color varieties most sought by fanciers. Bateson's observa-
tions have been confirmed by Allen ( :O4).

COAT OF THE WILD CAVY.

In wild guinea-pigs (or cavies) occur the same three pigments as in
mice, viz, black, chocolate, and yellow. A skin of a young Cavia aperea
Linn, from Brazil, which lies before me, shows a coloration similar
to that of the " agouti " variety of the domesticated guinea-pig. On
the back and sides of the body the ordinary hairs have a tip, about 2
mm. long, of a deep brownish-black color. Below this comes a yellow
band of about the same length. The rest of the hair appears black,
but is less heavily pigmented than the tip, and grows lighter toward
its base, which is of a dull leaden color. Microscopic examination
shows that the medulla of the hair, throughout its length, contains fine
pigment granules of an intense black color, and associated with them
others of a chocolate-brown color. The former are much more
numerous than the latter, and both are much less abundant toward the
base of the hair than at its tip. The cortex of the h'air contains
throughout the greater part of its length, where it is relatively thin, only
some chocolate pigment with a very little black. But in the distal part
of the hair the cortex is much thicker and more heavily pigmented.
Its terminal 2 mm. has the combination of chocolate and black already
described, but in the region just proximal to this it contains only bright
yellow pigment, which produces the yellow ticking of the coat.

The longer, so-called contour hairs, found on the back and sides of
•The figures in parentheses refer to the Bibliography, p. 77.

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 7

the animal, are black throughout their length, lacking entirely the
subapical yellow band. On the lower side of the body the hairs have
a pigmentation similar to that of the ticked hairs of the back, but the
yellow band is longer and less sharply limited, and the black tip is
inconspicuous, so that the fur appears superficially of a dull yellow
color, but when parted is seen to be leaden black at the base.

COLOR VARIETIES OF DOMESTICATED CAVY OR GUINEA-PIG.
In the various color varieties of domesticated cavies the same three
sorts of pigment found in the wild animal exist singly or in combina-
tions sometimes identical with those found in the wild animal, some-
times different.

AGOUTI.

In the agouti variety, of which there are two distinct sub-varieties,
known respectively as golden and silver agouti, all three pigments are
present, distributed as in the wild cavy. In the golden agouti the
pigments of all three sorts are abundant and dark, so that the yellow
band becomes a red of the sort found in a sorrel horse, while the
remaining portions of the hair are fairly deep black. In silver agouti
the pigmentation is less heavy. It may fairly be described as a dilute
condition of the golden agouti. The yellow band is of a pale yellow
color, and the black portions of the hair are a pale or bluish black.
Silver agouti may be produced by crossing golden agoutis with albino
animals of a particular sort, as will be explained presently.

YELLOW.

Yellow-coated varieties, with hair containing neither black nor*
chocolate pigment, are distinguished according to the depth of their
color, as red, yellow, or cream.

In the lighter shades, as compared with the darker ones, the pigment
granules are smaller and possibly less numerous. The skin covering
the feet and ears of animals of this variety contains chocolate pigment,
and, at least in some cases, black also ; the eye, too, certainly contains
chocolate pigment as well as black, yet the hair, as stated, never con-
tains black or chocolate pigment.

CHOCOLATE.

Of the chocolate variety I have made as yet a very incomplete study,
for lack of material. The two animals which I. have had bore one a
spot of red, the other a spot of yellow. Neither bore any black hairs.
The chocolate hairs apparently contain no other pigment. Theoretically
it should be possible to obtain a chocolate-colored animal entirely free
from yellow as well as from black pigment, as is possible with mice
(see Allen, : 04). My experiments have not progressed far enough to
show whether this expectation can be realized.

8 COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

BLACK.

In the black variety, black pigment predominates over the other two
torts and obscures them. But I have never been able to obtain it in
a pure state. Chocolate is invariably associated with it, and usually
hairs can be found somewhere on the body which show the presence
of the red-yellow pigment also.

In the ordinary black hair chocolate pigment predominates in the
cortex, black in the medulla. I am unable to say whether the red-
yellow pigment is present with them or not, but I am inclined to think
that in some cases at least it is, for here and there on the body one can
frequently find a hair devoid of the black and chocolate pigments, and
such a hair commonly shows a red or yellow pigmentation. Still there
are reasons for supposing that with proper attention a black variety
could be produced which would have no red or yellow in its coat, just
as red or yellow animals are obtained free from black and chocolate.

The black, like the red-yellow variety, occurs in forms more or
less heavily pigmented, the lighter shades being known as blue. The
latter can be produced by crossing black animals with red or yellow
ones, or with albinos of certain sorts. Blue animals bear the same
relation to black ones as silver agoutis to golden agoutis. Blue and
silver agouti are dilute forms of black and golden agouti, respectively.
In a blue animal the black and chocolate pigments are less abundant,
and the red-yellow pigment, if it appears on separate hairs, is of a light
(yellow) shade.

ALBINO.

P The albino or white variety, though apparently the simplest as re-
[ gards pigment characters, is in reality the most complex. Albinos
\ have pink eyes, the color of which is due not to a pigment, but to the
blood seen through the transparent eye. The hair is likewise unpig-
mented at birth, and may remain of this character throughout life
over the greater part of the body. Albino mice and ordinary albino
rabbits apparently never develop pigment in any part of their coat, but
such is not the case in cavies. Though I have carefully sought them,
I have never yet seen albino individuals which in adult life did not
form pigment in some region or other of their coat. This pigment
makes its appearance first and chiefly at the extremities of the body —
on the ears, the feet, and the nose — but may in extreme cases extend to
the hairs of the body coat also. To the unaided eye the hairs of the
extremities are of a sooty black color ; the microscope shows them to
contain chocolate pigment, with an occasional granule of black.

In the body hairs I have in one case identified reddish-yellow granules
without those of other sorts. They are not at all abundant and are
found principally at the tip of the hair, so that the coat looks like an

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 9

ordinary white one which has become dirty. For a long time I so
accounted for the condition seen in a particularly unattractive albino
in my flock, but finding that no change occurred in her coat, I investi-
gated the case with the result noted. So-called Himalayan rabbits
are albinos with peripheral pigmentation similar to that just described
for cavies. But there occur also albino rabbits without peripheral
pigmentation. In the Himalayan rabbit, as in the albino cavy, the
coat of the young is commonly white at first all over the body, but
soon becomes pigmented at the extremities. In some cases the first
coat on the general body surfaces is slightly pigmented also, the pig-
ment being found chiefly in the hair tip. This pigmentation is already
forming at birth, and can be recognized by the deeper red color of the
skin, as compared with that of normal individuals.

I have never seen a case in which this pigmentation of the hair-tips
persisted in the adult animal, though that of the extremities regularly
does. It is apparently in rabbits restricted to the first coat, though in
guinea-pigs it is found only in the later coat.

It is difficult to formulate a satisfactory definition of an albino mammal. \
Absence of pigment is the most obvious characteristic of albinos ; yet, as /
we have seen, many albinos possess a considerable amount of pigment.
Furthermore, experiment shows that black-eyed white cavies, which
produce no pigment whatever in the coat, nevertheless transmit very dif-^
ferent hereditary pigment potentialities from those of albinos. Accord-
ingly the amount of pigment produced in the coat is not distinctive^
between albinos and other animals ; neither is the absence of pigment
from the eyes distinctive, for Darbishire ( : 04) has experimented with
a race of pink-eyed mice which when crossed with albinos behave
every way like ordinary pigmented ones.

Without attempting a complete analysis of the matter, for which J
present knowledge does not suffice, I would suggest the following as /
criteria which, so far as observed, separate albino mammals sharply/
from all others. An albino is an animal with unpigmented eyes and\
with little or no pigment in its coat. The pigment, if present, is found/
in greatest amount at the extremities of the body. In a word, the pig-\
mentation of an albino is essentially centrifugal. When by selection OB/
cross-breeding the pigmentation is reduced, it is reduced centrifugally.

But in animals not albinos, the pigmentation is centripetal. Reduc-\
tion of the pigmented areas takes place in this case toward well- '
marked centers, as has been pointed out by Allen ( : 04) in the case of
mice. From a study of spotted mice Allen was led to recognize for that
animal five paired pigment centers situated dorso-laterally, as follows :
(i) genal or cheek center, (2) nuchal or neck center, (3) scapular or
shoulder center, (4) pleural or side center, and (5) sacral or rump cen-

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

ter. It is possible that we should recognize as a sixth distinct center
the retina of the eye. These same centers are recognizable with great
clearness in the guinea-pig, for in many cases adjacent patches, when
not separated by unpigmented areas, contain elementary pigments whose
limits are marked by sharp color contrasts. Thus a cheek patch may
be black and the adjacent shoulder patch red (fig. 5) ; * or the side patch
black and the sacral patch red, or vice versa (figs, i and 3) ; or again, the
right patch of a pair black, the left red, or vice versa (figs. 3 and 6).
As compared with the mouse, the guinea-pig shows slight differences
in the location and extent of the pigment patches, as one might expect

FIG. i.— Diagram showing the coat pattern of

973. Cheek, side, and rump patches are
present, though much reduced in extent.

FIG. 2.— Coat pattern of O 3166, a daughter of <j>
973 (fig. i). Cheek and rump patches
are present, but no shoulder or side

Each pair is of a different color. patches.

in forms structurally so different. The side patch of the guinea-pig lies
chiefly posterior to the middle of the body and frequently extends well
back, covering the greater part of the hip and hind leg, while the
sacral patches may be so small and closely approximated that they seem
to form an unpaired area at the extreme posterior end of the body (figs.
i, 5, and 7). The pigment patches are apparently not correlated with
internal structures, such as the distribution of blood vessels or nerves.
They are epidermal in origin and subject to more or less apparent asym-
metry and mutual displacement, as if they were derived from distinct
groups of ectodermal cells endowed in many cases with distinct pig-

*In fig*. 1-8, solid black indicates black coat; black stipple, red coat; white
stipple on black ground, red and black hairs interspersed.

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

ment potentialities, which by unequal cell multiplication come to cover
areas which may or may not be symmetrical in arrangement.

Sometimes one or both of a pair of patches is wanting altogether;
in other cases a patch apparently gets displaced from its normal posi-
tion, so that it lies across the median plane ; frequently when a right
or left patch is wanting, its mate extends somewhat beyond the median
plane (fig. 3). Nevertheless, when one examines a number of spotted
animals it is clear that there is a strong tendency for the pigmented
areas to occur in the general body regions indicated, each of the ten
recognizable patches being a unit in the composition of the coat.

FIG. 3. — Coat pattern of ^ 1358, a son of Cj 973
(fig. i). The right cheek patch is black,
the left one red. There is a left side
patch of black, but no right side patch.
The fused rump patches are red.

FIG. 4. — Coat pattern of J* 1360, a son of ^ 97;
(fig. i). There are cheek patches of red.
and a right neck (ear) patch of black,
No others of the typical patches arc
present.

This unity may be obscured if it happens that two pigments, as black
and red for example, are both present in the same patch. Neverthe-
less, in such cases one can often still identify the typical patches either
by the occurrence of unpigmented areas between them, or by the
occurrence of mixed pigments in one patch and of unmixed pigments
in adjacent patches.

At one time I thought that I had obtained an explanation of the
difference in behavior of the centrifugal and centripetal types of pigmen-
tation. It seemed that the centrifugal pigmentation was of dermal
origin, the centripetal of epidermal origin ; but more careful examina-
tion of sections of the skin indicates that both sorts of pigmentation are
similar in origin, arising within cells of the epidermis.

COAT CHARACTEKS IN GUINEA-PIGS AND RABBITS.

SPOTTED.

The five principal color varieties of the cavy which have thus far
been described are alike known as self-colored (*. «., colored alike all
over), in distinction from the spotted or pied varieties, which will next
be noticed. Each of the four varieties, agouti, black, chocolate, and
yellow (including red), may become spotted with white either by
reduction in the extent of the pigment patches (as already explained), so
that they no longer meet and cover the entire body, or by the entire
absence of one or more of the typical color patches. The first-named
process produces such familiar manifestations of partial albinism as (i)

FIG. 5.— Coat pattern of J 2698. The cheek patches
are of black, the combined neck and right
shoulder patches red ; in the correspond-
ing area of the left side are a few black
hairs mixed with the red ; the side patches
are black, the minute rump patch mixed
red and black.

Fie. 6.— Coat pattern of <j> 1920. The left cheek
patch is black, the right one red and
black mixed. The right side and rump
patches are red, the left ones black. A
sharp line of division separates them
along the median plane both dorsally
and ventrally.

a white spot or a longitudinal white streak on the belly of the animal,
where the side or shoulder patches fail to meet below, or (2) a white
throat, where the cheek patches fail to meet below, or (3) a white
blaze (forehead stripe) where they fail to meet above (fig. 5), or (4)
white feet, to which the shoulder and rump patches do not quite extend.
Dropping out of one or more entire pigment patches may produce an
asymmetrical white spotting, such as a white cheek, shoulder, or side.
The two processes, reduction in extent of the pigment patches and
dropping out altogether of certain pigment centers, usually progress
simultaneously, and when they occur symmetrically may result in such

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

forms as the much admired Dutch-marked varieties, in which the two
cheek patches are distinct (not united) above and below, the shoulder
patches are wanting altogether, leaving a broad white girdle around the
animal, and the rump patches fail to reach below the middle of the
hind leg, though united dorsally (compare fig. 6, which shows an
approximation to the Dutch-marked type).

A mottling similar in pattern, but with different color effects, is pro-
duced when the various patches are differently colored. Thus in one
strain which I have bred from the beginning of my experiments, some of
the pigment patches are usually pure black, others pure red, though

FIG. 7. — Color pattern of O 2427. The color
patches are of very limited extent.
They consist of a red eye patch and a
black neck (ear) patch in the right half
of the body, and a median (paired, but
fused?) rump patch.

FIG. 8.— Color pattern of Cj 2928. The left cheek
patch is red, the adjacent neck (ear)
patch black. The fused right cheek
and ear patches are black. The fused
shoulder patches are of mixed red and
black.

occasionally a patch contains hairs of both colors intermingled. (See
figs. 1-8.) Further, the patches in this strain frequently fail to cover
the whole body, so that the animals are mottled with large clear areas
of black, red, and white, a condition which undoubtedly has been
common among domesticated cavies since their introduction into Europe
from South America some three or more centuries ago. (See Cum-
berland, p. n.)

BRINDLED.

In brindled animals black and red hairs are interspersed in the same
pigment patches. The latter may or may not be continuous with each
other ; if they are not continuous, white mottling results, associated
with the brindled character.

14 COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

RUAN, AND SILVERED.

In roan animals white hairs are interspersed with red ones. A simi-
lar modification may occur in the coat of black animals also, which are
then said to be " silvered." I have never seen a cavy with an entire
coat of this character ; usually certain patches only are affected, or
more often the ventral part only of a patch. I have noticed, however,
the transmission of this character from generation to generation and
have no doubt that a roan race or a silvered one could be established
if desired.

RESULTS OF CROSSING THE ELEMENTARY COLOR VARIETIES.
ALBINOS AND PIGMENTED ANIMALS.*

These two types are very distinct. Each by itself breeds true, and
cross-breeding between them fails to produce intermediates ; it results
invariably in the production of young of the centripetally pigmented
type. Thus in the course of these experiments, (i) albino parents
mated inter se have produced 156 young, all albinos; (2) pure pig-
mented parents (/. e., animals altogether devoid of the albino charac-
ter) mated inter se have produced 261 young, all pigmented ; and (3)
albinos mated to pure pigmented animals have produced 314 young,
all pigmented. The young produced by this last sort of mating,
though similar in appearance to those produced by (2), are not pure
pigmented animals, for they possess the potentiality to form albino
young, which the young of the two pure pigmented parents do not.
In Mendelianf terminology the pigmented character is dominant, the
albino character is recessive, and cross-breds between a dominant and
a recessive parent are hybrid dominants. The hybrids form gametes
(/. e., spermatazoa and eggs ready for fertilization), half of which, ap-
proximately, transmit the pigmented character, half the albino character.

Students of heredity at the present time are giving earnest attention
to testing the two principles which make up Mendel's law, viz, (i)
the principle of dominance, and (2) the principle of segregation. In
the case under consideration there can be no question of the validity of
both . The centripetal type of pigmentation invariably domi nates over the
albino, as the statistics already given clearly indicate. This is in harmony
with numerous observations on mice, rats, rabbits, and other mammals
made by Haacke ('95), Von Guaita ('98, :oo), Cuenot (103,: 04),

^r * Although, as we have seen, the albino guinea-pig regularly develops a cer-
/ tain amount of pigment in its coat, it will be convenient to use the term
"albino" in contrast to "pigmented," the latter term referring only to the
y dark-eyed centripetally pigmented animals.

X t For a brief statement of Mendel's law, see Castle ( : 03, or : 03*) ; for a fuller
one tee Bateson (: 02).

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

Darbi shire ( : 04) , Castle & Allen ( : 03), Bateson ( : 03) , Allen ( : 04) ,
and others. The evidence that segregation of the dominant and
recessive characters occurs when the cross-bred pigmented animals
form gametes is not less clear. The matter can be conveniently tested in
two ways : (i) By mating a cross-bred with an albino animal, when
half the young should be pigmented, the other half albino, if segre-
gation occurs as demanded by Mendel's law ; (2) by mating hybrids
inter se, when we should expect three-fourths of the young to be
pigmented, one-fourth albino. The first sort of mating has in these
experiments produced 211 pigmented and 214 albino young, where
the expectation is 212.5 °f eacn sort, which certainly is a very close
approximation. The second sort of mating has produced 264 pig-
mented and 112 albino young, the expectation being 282 pigmented and
94 albino young, i. e., there are 18 more than the expected number of
albinos in a total of 376 young, a fairly close approximation, but not
so close as that observed in the first case.

Combining the results of all matings which are expected to produce
albinos, we get the following :

Pigmented.

Albino.

Expected

Observed

^26

This shows an excess over expectation of 19.5 albinos in a total of
801 young, or about 2.5 per cent.

$7.1C(.P)

7.3a

$7.3*

?207(?)

FIG. 9.— A genealogical table showing the character, as regards recessive albinism, of the young pro-
duced by three matings between a pure pigmented (f) and a hybrid pigmented animal.

Matings of hybrid pigmented with pure pigmented animals have, as
expected, produced only pigmented offspring, which number 35 1 . The
Mendelian expectation is that half the young so produced will be pure
in character, half hybrid. Since the two sorts look alike, only indi-
vidual breeding tests will suffice to distinguish them. In certain cases
such tests have been made, the results showing that the expectation
based on theory is realized.

Fig.9 shows the results of three different matingsof this sort in a single

l6 COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

family of guinea-pigs. The animals enumerated were all pigmented ;
those marked (/*), when mated with albinos, produced only pigmented
young showing that they were pure; the others produced some albino
offspring, when mated with albinos (or with other hybrid pigmented
animals), showing themselves to be hybrid in character. In the case
of one animal only (9 207) no test was made as to the production of
albino gametes. This animal was paired with pure pigmented mates
only, and the young were, of course, invariably pigmented.

It will be observed from fig. 9 that pure 9 7 was mated with two
different hybrid males, viz, c? R and cf A. By cf R she had four
daughters (9 7.1", 9 7.1", 9 7.1% and 9 7.1*), two of them pure (/>),
two hybrid in character. By cf A she had two daughters (9 7.3*
and 9 7.3b),both hybrid in character. In the next generation, hybrid
cf A was mated with pure 9 7.1°, producing in three different litters
seven pigmented young, which were used as breeders. One of these
(9 207) was not tested for recessive albinism, as already stated. Of the
others, four proved to be pine, two hybrid in character. Altogether
there were among the young indicated in the table six pure individuals,
six hybrids, and one of uncertain character.

f So far as observed, there are no intermediate conditions between pure
[ and hybrid pigmented animals. If an animal forms albino gametes at
i all, half its gametes are of that character. Of course in individual
litters, or when only small numbers of offspring are dealt with, con-
siderable deviations from the Mendelian ratios are likely to be encoun-
tered. This is to be expected on the theory of probabilities, as Allen
(rcxj, p. no) has clearly pointed out. But when more extensive tests
are made the expected ratios are more closely approximated.

ALBINISM AND THE "LAW OF ANCESTRAL HEREDITY."
The foregoing results show very clearly that albinism conforms
in its mode of inheritance to Mendel's law of heredity. The fact,
however, must not be overlooked that a somewhat different explanation
of its inheritance has recently been given, based on Gallon's " law of
ancestral heredity." I shall not at this time enter into a detailed dis-
cussion of Gallon's hypothesis, which was an entirely rational one in the
form in which it was originally proposed, and quite in harmony with the
phenomena of gametogenesis as then interpreted. I have shown else-
where (Castle, :o3h) by a specific test in the case of mice, based on the
observations of Von Guaita ('98, :oo), that Gallon's law fails to account
for the observed facts concerning the inheritance of albinism, but that
Mendel's law does this perfectly. Nevertheless Darbishire ( : 04), like-
wise dealing with albinism in mice, though admitting that certain of
his results are not in disagreement with Mendel's law, is inclined rather

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

to interpret the phenomena on some such hypothesis as that of Galton.
He states the matter very clearly (p. 24) as follows :

It is well known that according to this [MendelianJ view the hybrid contains
equal numbers of germ-cells which produce the dominant character, and of those
which produce the recessive; and this is said to be true of the hybrids however
far the individual is removed from the original cross, whether it is the result of
the cross (*'. «., the hybrid) or the great-great-grandchild of this. This is the
ground on which the doctrine of the purity of the germ-cells and the law of
ancestral heredity flatly contradict one another; the former asserting that DR x
DR will produce 25 per cent DD, 50 per cent DR, and 25 per cent RR for a
very great if not an indefinite number of generations ; the latter maintaining that
the further the individual hybrid under consideration happens to be removed from
the cross the less albinos will it produce ; and that two hybrids whose mothers were
albinos will produce more albinos than would two hybrids wM have no albinos
in their pedigree later than their great-great-great-grandmother. This seems to
me to afford a case in which experiment could provide a decisive answer.

In this statement I heartily concur.

The experiment which Darbishire made was this. He made three
different kinds of matings between animals which, we are told, were
hybrids, (i) In one case each of the two animals mated had one albino
and one pigmented parent. (2) In the second case, one animal was of
the parentage just described, the other was born of two pigmented par-
ents. (3) In the third case, the parents of both animals were pig-
mented. In brief, there were two albino grandparents in case (i), one
albino grandparent in case (2), and no albino grandparents in case (3).
The ancestry back of the grandparents was the same in all three cases.
The conditions are thus very simple and should, as Darbishire suggests,
give a decisive test. Darbishire states that —

Number of
young.

Number of
albinos.

Albinos
(percent.).

121

io7

18 69

Q->

IO 7?

This is a seemingly conclusive demonstration of the correctness of
Darbishire's contention ; but in fact Darbishire's results, when carefully
analyzed, prove just the opposite of his deduction.

Fortunately he has recorded in an appendix the various litters from
which the totals given are made up. An examination of these records
makes it evident that his so-called " hybrids " were not all hybrids.
In mating (i) the animals used undoubtedly were hybrids, since each
had, as stated, one albino and one pigmented parent. It is noteworthy
that in that case the Mendelian expectation of 25 per cent albinos is

l8 COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

realized as perfectly as is possible in an odd number of young, there
being 30 albinos in a total of 121 young. In cases (2) and (3) Darbi-
shire gives us no evidence that the animals which he mated were
really hybrids in the sense that they contained recessive albinism. He
calls them " extracted hybrids" because they had dark eyes, as did all
his primary hybrids obtained by crossing pink-eyed with albino mice.
The latter unquestionably were hybrids in the sense that they con-
tained recessive albinism, for in every case one of the parents was an
albino. The former may or may not have contained albinism recessive ;
Darbishire's experiments indicate that in some cases they did, and in
other cases they did not. Darbishire himself has shown that there is
in his mice (contrary to an erroneous prediction of Castle & Allen,
: 03, p. 612) no necessary correlation on one hand between recessive
albinism and dark eyes, and on the other hand between freedom from
albinism and the pink-eyed pigmented-coat condition. He calls especial
attention to the fact (p. 22) that in five different families of his mice
there occurred altogether seven pink-eyed pigmented animals, which
in each case had one albino and one pigmented parent, and which
accordingly must have been hybrids. In an earlier paper (Darbishire,
: 03, p. 285) he showed that a pink-eyed mouse of this kind does pro-
duce albino offspring when mated to albinos, a thing which his original
(pure) stock of pink-eyed mice never did. If, then, pink-eyed pigmented
animals may contain recessive albinism, is it improbable that dark-
eyed animals may in some cases fail to contain it ?

Accordingly, in what have been called Darbishire's matings (2) and
(3), we may reasonably ask for evidence that the animals mated were
really hybrids. A pair which has produced albino offspring consists
unmistakably of two hybrid animals. Pairs which fail to do this are
questionably hybrid and maybe provisionally left out of consideration.
In mating (i) where both parents were unquestionably hybrid, since
each had an albino parent, Darbishire gets the precise Mendelian
proportion (one-fourth) of albinos. The question is, are fewer albinos
produced by hybrids in matings (2) and (3), in which the albino ances-
try was less.

Omitting only pairs which failed to produce any albinos in matings
(2) and (3), Darbishire's observations may be summarized as follows :

Pigmented
young.

Albino
young.

Albinos
(per cent).

Mating (i)

Mating (2)

24-79

3I-35

Mating* (a) and (3) together.

27.52

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 19

Instead of producing less than 25 per cent of albinos, as Darbishire
supposes them to do, matings (2) and (3) really produce more than
that proportion of albinos. Considered separately they produce, one
somewhat more than 25 per cent, the other somewhat less, as we
should expect to be the chance result where small numbers of young
are considered.

In further evidence that Darbishire's " extracted hybrids " did not in
all cases contain recessive albinism, his matings of such animals with .
albinos are instructive (see his Table F, p. 36). Five out of nineteen /
such matings failed to produce any albinos whatever, though they pro- /
duced a total of 19 young, all pigmented. If the pigmented parents in
these matings had really been hybrids, half their young should have been
albinos. Such was precisely the proportion of albinos produced by the
fourteen matings in which the pigmented parent, though of the same
ancestry as in the foregoing cases, showed itself to be really a hybrid,
for these fourteen matings produced 36 pigmented young and 36 albinos.

Darbishire designates the cases just discussed " the most conclusive
results which I have obtained " [in favor of the law of ancestral hered-
ity]. Careful examination of these results, however, as we have seen,
makes them seem far from conclusive in favor of that hypothesis. I
have, therefore, thought it worth while to apply a further experimental
test to Darbishire's hypothesis, in the case of guinea-pigs. »

In doing so I class as a hybrid pigmented animal (i) any pigmented \
animal known to have had an albino parent, or (2) any pigmented I
animal born of pigmented parents which has produced one or more j
albino young. In Tables A and B are summarized the results of all of
the matings between two animals known to be hybrids, or between a
hybrid and an albino, which have been made in my later experi-
ments. Matings from my earlier experiments are not included for
the reason that the ancestry of the animals at that time used is
too imperfectly known. The Mendelian expectation is, as Darbishire
states, that all hybrids alike, whether they have few or many albino
ancestors, will form gametes approximately half of which bear the
albino character, half the pigmented character. Darbishire's con-
tention, on the other hand, based on the hypothesis of Gallon, is
that the more albino ancestors a hybrid animal has, the more albino
offspring will it produce. To test these alternative hypotheses I have
tabulated the matings which have been made in these experiments
according to the amount of albino ancestry involved in each, this amount
being greatest in the first part of each table. Table A includes matings
between two hybrids, Table B matings between a hybrid and an albino.

COAT CHARACTERS 1* GUINKA-PIGS AND RABBITS.

TABLE ^.—Proportions of albino young productd by hybrid pigmented parents
of different amounts of albino ancestry.

Albino
grand-
parents.

Albino
great-
grand-
parents.

Albino
young.

Pigmented
young.

Remarks.

a
a

"1 Two albino grandpar-
ents, 43 albino to 124

\ pigmented young,

2§

or 25.9 percent, al-

1 binos.

4
3

5
3

One albino grandpar-
\ ent, 16 albino to 18

[

5
3

pigmented young.

(No albino grandpar-
- cuts. 6 albino to 16

( pigmented young.

...

158

TABLE B. — Proportions of albino young produced by matings between albinos
and hybrid pigmented animals, both with varying amounts of albinism in
their ancestry.

Albino
grand-
parents.

Albino
great-
grand-
parents.

Albino
young.

Pigmented
young.

Remarks.

Three albino grand-

parents, 55 albino

to 64 pigmented

young.

5
4
3

8
16

Two albino grandpa-
rents, 63 albino to 56
pigmented young.

2
I
O

3
3
3
9

One albino grandpar-
ent, 13 albino to 18
pigmented young.

0
0

(No albino grandpar-
•< ents, 5 albino to 10
( pigmented young.

...

'36

148

Throughout Table A we find the expected Mendelian ratio (i : 3) of
albino to pigmented young approximated, quite irrespective of the
amount of albino ancestry back of the parents mated. Of course, there
are marked deviations in individual cases where the number of young

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 21

is small, as we expect on the theory of probabilities, but we find no
falling off in production of albinos as the amount of albino ancestry
decreases.

Similarly throughout Table B we find the expected Mendelian equality
of albino and pigmented young approximated, irrespective of the num-
ber of albino grandparents and great-grandparents. Thus the proportion
of albinos is actually higher when there are only two than when there
are three albino grandparents, though on Darbishire's hypothesis we
should expect this relation to be reversed ; for the young produced in
cases where there are three albino grandparents aggregate 55 albino to
64 pigmented animals, an excess of 4.5 pigmented ; but the young pro-
duced in cases where there are only two albino grandparents (in the same
total number of young) aggregate 63 albino to 56 pigmented animals, an
excess of 3.5 albinos. The deviations from equality are in the two cases
opposite in character and almost equal. Undoubtedly it is merely a
chance outcome that they are opposite in nature to what Darbishire's
hypothesis demands. The tables as a whole, however, do give an
emphatic negative to Darbishire's position. They lend support to the
alternative (Mendelian) hypothesis, that any pigmented animal which
forms albino gametes forms approximately 50 per cent of such gametes.

In what precedes I have made no mention of what has been called
Pearson's modification of Galton's law of ancestral heredity. Else-
where (Castle, : 03") I have discussed this briefly in applying a statis-
tical test to the laws of Galton and Mendel in the case of albinism in
mice. Galton's law I applied generation by generation to Von Guaita's
('98, : oo) mouse records, as Galton ('97) himself had applied his law
to the Basset hound records. The test thus made showed the complete
failure of Galton's law as applied to the heredity of albinism. No such
detailed test was made in the case of Pearson's law, but the statement
was made : " Comparing Pearson's series with that of Galton we see
that the parental influence is reckoned as substantially the same by both
Galton and Pearson, but that Pearson assigns a much greater influence
to the more remote ancestors than does Galton." For which reason
it was concluded, " The discrepancies noted between observed and cal-
culated [in testing Galton's law] will remain and even be accentuated
if we replace Galton's series with one of those suggested by Pearson.
For the result will be unchanged [I should have said similar, rather
than unchanged] in Generation II, but the calculated numbers will in
most cases diverge still more from the observed ones, in the later gener-
ations, because Pearson attaches more weight to the remoter ancestors
than does Galton." To these conclusions Pearson (: 04) takes exception,
maintaining that neither of the two series which I took from his writ-
ings was quoted in a form comparable with that of Galton's series.

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

He gives a series of his own and that of Galton in comparable form.
They are, he says, " if we measure parental influence by intensity of
correlation " .*

Influence.

Pearson's
series.

Gallon's
series.

}

Great-great-grandparental . ...

Even when they are given thus, it seems to me still, as I stated
before, that " Pearson attaches more weight to the remoter ancestors
than does Galton," and if so, that " the discrepancies noted between
observed and calculated [in testing Galton's law] will remain and even
be accentuated if we replace Galton's series with one of those suggested
by Pearson." That Pearson himself had not contemplated such a test
of his law would not affect in the slightest degree the outcome of the
test. Further, it seems to me an admission very damaging to a law of
heredity when Pearson says: " Personally I have no means of deter-
mining whether the law of ancestral heredity holds or does not hold for
coat color in mice. The theory has not yet been worked out in a form
covering Von Guaita's cases." Yet in Von Guaita's material we have
a full record of the coat color of every animal in seven successive gen-
erations, and we know that back of this for an indefinite number of
generations all the ancestors on one side of the ancestry were albinos,
on the other side spotted black-and-white. That is sufficient basis on
which to make very reliable predictions as to the character of the off-
spring, under Mendel's law, as I have elsewhere shown.

In fact, it seems to me that Pearson's law, as he now explains it, is
not a law of heredity at a//, but one of variability in successive gen-
erations, for he says (p. no) : "So far as I can understand the Law of
Ancestral Heredity as I have myself enunciated it, the produce of a
grey mouse and a fawn mouse might be on the average a green mouse
without that Law having anything to say on the point. From it you
can not possibly deduce what number of the offspring of any generation
will be like this or that ancestor. It is not a law of types, but of the
distribution of deviations from type, and this is a very different thing
indeed." But from a genuine law of heredity, such as that of Mendel,
one is enabled, as I have shown, to predict with great accuracy what
color types will prevail among the offspring in successive generations.
Since Pearson's law, as now interpreted by its author, though dealing
with alternative color types in successive generations, gives no informa-

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

tion whatever as to what color types will prevail in one as compared
with another, nor as to what proportion of the young will be de-void of
color, it would seem desirable, to avoid confusion, that the law be re-
named as something other than a law of heredity.

ALBINISM AND SEXUAL PREPOTENCY.

Gallon ('97), on purely empirical grounds, was inclined to think
the male sex prepotent in the transmission of black spots in the case of
Basset hounds. Though I have elsewhere (Castle, : 03") shown that
the conclusions which he drew from that study were probably erroneous
because they rested on false assumptions, it may be worth while in
this connection to test the idea of sexual prepotency in regard to
albinism. This may be done by comparing the results of reciprocal
matings, as shown in Table C, which contains a summary, as regards
the production of albino young, of most of the matings made up to this
time. Only matings between pigmented parents of undetermined j
character as regards recessive albinism have been omitted from this
summary. These omitted matings produced several hundred young, all
pigmented, as was to be expected if either one or both pigmented parents /
were free from recessive albinism. From Table C it is evident that, (i)
when a mating is made between a hybrid pigmented and a pure pig-
mented animal the result is the same whether the hybrid be father or
mother ; in every case the young are pigmented ; (2) when a mating
is made between a hybrid pigmented animal and an albino, hybrid
pigmented and albino young are produced in approximately equal

TABLE C. — Proportions of pigmented (p.) and albine (a.) young produced by
matings of various sorts.

Mothers.

Father pure
pigmented.

Father hy-
brid pig-
mented.

Father
albino.

Young.

261 : o
136 : 0
109 : o

p, a,

215 : 0
264 : 112
91 : 98

/. a.

205 : o
120 : 116
o: 156

Hybrid pigmented

Albino

numbers, viz, 120 pigmented to 116 albino young when the albino
parent was a male, 91 pigmented to 98 albino young when the albino
parent was a female. The deviations from equality are very slight
and unquestionably the result of chance. In the one case the deviation is
2 individuals in a total of 236 ; in the other, it is 3.5 in a total of 189
young. There is, accordingly, in this case no evidence of prepotency
in the transmission of albinism on the part of either sex.

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

ALBINISM AND LATENT PIGMENT CHARACTERS.

Although, as we have seen, (i) albinism is a condition recessive in
heredity with respect to ordinary or centripetal pigmentation, and (2)
albinos produce only albino offspring, irrespective of their ancestry, it
is not true, as might be supposed, that one albino breeds like another
when crossed with the same centripetally pigmented type. This mat-
ter has. been very fully discussed by Allen ( : 04, p. 130), but may be
illustrated by some simple examples, (i) My albino guinea-pig,
cf 2002, when mated with red females, invariably produces offspring
marked with black as well as with red pigment. (2) Albino c? 635,
when mated with the very same or with similar red females, produces
young about half of which are pigmented with black and red, like the
offspring of $ 2002, the other half being pigmented only with red or
yellow, not with black. (3) Albino <$ 1999, when mated with red
females, produces only red (or yellow) pigmented offspring, never
black pigmented ones. From an inspection of these three albino males
or of their offspring by albino females, one would get no inkling of the
existence among them of the differences revealed by the experiment
described. This experiment shows that in the gametes produced by
^ 2002, the capacity to form black pigment is latent. This capacity is
exercised whenever such a gamete unites with one bearing the centri-
petal type of pigmentation. In J1 635 only about half the gametes
formed contain latent black ; in tf 1999 none of the gametes formed
contain latent black. The idea underlying this explanation is that a
recessive character (in this case albinism) may contain the dominant
one (centripetal pigmentation) in a state of inactivity which nothing
but cross-breeding with the pigmented type will disturb. Further evi-
dence in support of this idea will be adduced when we come to discuss
coat characters other than those of pigmentation.

Meanwhile, let me say a word concerning the term latency. In com-\
mon with others I have frequently in earlier papers used this word I
loosely as synonymous with recessive. This usage was, I believe, an j
unfortunate one ; accordingly, in what follows I shall use the two
terms for conditions quite distinct, which my experiments show to
have a real existence and to require names, (i) Recessive I shall \
use as Mendel used it, to designate a character which disappears when *
brought by fertilization into the same (hybrid) individual with a con- 1
trasted " dominant" character, but which is transmitted, distinct from/
the dominant character, in half of the gametes formed by the hybrid/
individual. (2) Latency, as I shall use it, is a condition of inactivity \
in which a normally dominant character may exist in a recessive indi- j
vidual or gamete. It is questionable whether a recessive character

COAT CHARACTERS IN GUINKA-PIGS AND RABBITS. 25

may ever be latent. Future investigations alone can'decide this point.
A recessive character apparently reappears pure in half the gametes
formed by the hybrid dominant individual, and is present in all the
gametes formed by a recessive individual ; a latent character apparently
never regains its existence apart from the recessive (i. e., becomes
active) until cross-breeding brings this about. Future investigations
may require further modification or even entire abandonment of these
definitions, but for the present I find them useful to express the results
of my experiments.

Latency of pigment characters in albinos is particularly clear in
mice, as shown by the investigations of Cu^not ( : 03), Darbishire
( : 04) , and especially of Allen ( : 04). For albino mice are, so far as
known, wholly unpigmented, yet they ordinarily, perhaps always,
transmit latent pigment characters, either singly or in combinations
identical with those occurring in pigmented mice. Alike in guinea-
pigs and in mice, a clew to what pigment characters are latent in the
individual may often, though not always, be learned from a mere
knowledge of its parentage. Thus, in guinea-pigs, an albino born of
two red or yellow parents does not transmit latent black in any of its
gametes ; but one born of two black parents may or may not form
gametes transmitting red apart from black pigment. The reason for
this difference will be apparent when we come to consider the relation
of red and black to each other in cross-breeding. For the present I
would merely call attention to this case as showing that it is not the
ancestry of the albinos which governs the behavior of their gametes in
cross-breeding, as Darbishire ( .-04) maintains, but rather the existence
of pigment characters as distinct entities, though latent, in the gametes
formed by albinos. In certain cases we can, with confidence, predict
the absence of a pigment character, even in a latent condition, from
the gametes of an albino, viz, in cases where we know the pigmented
parents to have been free from that character. Thus an albino born of
red or yellow parents does not transmit black, because red or yellow
animals do not contain the black character either active or latent, and
so can not transmit it to their albino offspring. Where the parentage
is unknown, suitable breeding tests show with equal certainty (often the
production of as few as two young indicates clearly) what latent pigment
characters are transmitted by the albino. A particular pigment charac-
ter, when present latent in the gametes formed by an albino, appears
to be regularly present either (i) in all the gametes formed, or (2) in
half those formed, as suggested by the cases of albino cfc? 2002 and
635 already cited. No evidence exists of the occurrence of a latent
pigment character in other proportions of the gametes, as should be
the case on the "ancestry " idea of Darbishire.

> COAT CHAKACTEHS IN GUINEA-PIGS AND RABBITS.

INTERCROSSING OF DIFFERENT PIGMENT TYPES.
Intercrossing of elementary pigment types other than albino results
not in perfect dominance of one and complete disappearance (recessive-
ness) of the other, but in coexistence of the two in the offspring, though
one pigment character from its nature may be much more in evidence
than the other. Thus black animals mated with red ones ordinarily
produce black offspring, though of a shade different from that of the
black parent, the more intense black pigment masking to a great extent
the presence of red. True Mendelian dominance, then, is wanting in
such crosses; nevertheless the other Mendelian principle, segregation,
is here realized.

THE AGOUTI TYPE.

An agouti animal, as we have seen, is one which bears the three pig-
ments— black, chocolate, and red-yellow — in a particular regional distri-
bution on the same hair. It is the original or wild type of pigmentation
and might be expected to show superior potency in crosses. My ex-
periments, which, however, are far from complete, indicate that this
type of pigmentation as transmitted in the gametes of a wild animal
really is potent over other types. Thus, a male Cavia aperea, which
was captured wild in southern Brazil, has produced by two different
domesticated albino females (neither of which was of agouti-colored
parentage) 15 young, all agouti-colored, but in some cases at least of a
somewhat lighter shade than the wild parent. I can not speak very
emphatically as to the exact shade of pigmentation in several cases,
because all but four of the hybrids were born dead, and their coats have
been examined as yet only in a wet condition. This matter will be
discussed more fully in a subsequent paper.

The agouti type of pigmentation, when borne by gametes of a domes-
ticated guinea-pig, likewise shows a strong tendency to dominate over
other types of pigmentation, the only possible exception thus far ob-
served being black.

Agouti x agouti. — It goes without saying that pure agoutis, like
pure* animals of any other type, breed true. Thus, agouti <$ 2017
mated with agouti 9 9 2019 and 2021 produced 6 young, all of the same
(golden) agouti type as the parents.

Agouti x black. — Agouti 9 2018 mated with black cT 2053 (known

by test to be pure) produced 3 young, of which one was an agouti, the

I other two black. This outcome indicates that the black type of pig-

1 mentation may in some cases at least have equal potency with the

• The term pure is here used, as throughout this paper, in the Mendelian sense,
referring to the character of the gametes which an animal forms. Thus a pure
agouti animal is one which forms gametes all of which transmit the agouti type
of pigmentation.

COAT CIIARACTEHS IN GU1NKA-P1GS AND RABBITS. 27

agouti, showing alternative dominance with respect to it. When this/
result was obtained I at once questioned the purity of 9 2018, suspect-
ing that she might contain recessive black, but her purity has since been
established with considerable probability by a mating with albino cf 635,
neither of whose pigmented parents was an agouti. This mating
produced 4 young, all agouti or agouti spotted with red. Previously
9 2018 had been mated with agouti c? 2017, producing 3 agouti young.

Further support for the idea that agouti and black may show alter-
native dominance is afforded by matings of hybrid agouti (albino)*
9 2020. This animal contained recessive albinism in which black
apparently was latent. For, when mated witli agouti c? 2017, she
produced 2 agouti and 2 black young, indicating that at least half her
gametes bore the black character, and that this dominated over agouti in
at least two out of four cases. When mated with albino c? 2039 she pro-
duced i albino, i spotted white >f red-black, and i spotted red-black
young. Mated with hybrid red (albino) c? 1019, she produced 2 black
> red young. Manifestly only part, if any, of this female's gametes
bore the agouti character, though all apparently bore the character
black, either in the agouti combination or in the segregated state.

Again, an agouti daughter of 9 2020 by agouti c? 2017, viz, agouti
(black?) 9 IO35> when mated with albino <$ 2059, produced 2 agouti >
red, and 2 black > red young. This result indicates that 9 1035,
like her mother, formed gametes, half only of which bore the agouti
character, half the black character. But the black character is appar-
ently present in 9 1035 as a simple recessive, not latent in recessive
albinism as in her mother ; for the mating of 9 1035 with albino
cT 2059, though it produced 4 young, gave no albino offspring ; and
a subsequent mating with white > red-black (albino) cf 1631 like-
wise gave no albino offspring, but i agouti and i black-red young.
This 9 1035 undoubtedly arose from the union of an agouti gamete fur-
nished by the father (since he was shown by breeding tests to be pure)
with a gamete bearing the black character furnished by the mother,
9 2020. But if 9 1035 does not contain recessive albinism, the gamete
furnished at her formation by 9 2020 can not have been an albino
gamete. It would seem then that 9 2020 furnished certain gametes
bearing black, not latent in association with albinism, but active. If so,
she must have borne two different pairs of contrasted pigment poten-
tialities, viz, (i) centripetal pigmentation -vs. albinism; (2) agouti
pigmentation vs. black pigmentation ; and she must have transmitted

* A character indicated thus in parentheses is present in a recessive condition.

tThis symbol is used to indicate inequality in the extent of body areas of
different character as regards pigment. Thus, white > red means an animal
with more white than red fur on its body.

28 COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

centripetal pigmentation associated either with agouti or with black
pigmentation (for the latter combination 9 1035 is specific evidence) ,
and albinism associated probably either with agouti or with black pig-
mentation (these of course being in a latent condition). It seems from
I this and other similar cases that the regional distribution of pigments
I on the body (centripetal vs. albino) is something inherited independ-
\ ently of the specific character of the pigments formed. Albinism
vs. centripetal pigmentation forms one pair of alternative (Mendelian)
characters ; agouti vs. black pigmentation forms another pair. An
animal like 9 2020, then, is a dihybrid as regards pigment characters,
and should form in equal number gametes of four different sorts, viz,
albino [black latent],* albino [agouti latent], centripetal agouti, and
centripetal black. This idea is supported by Allen's ( : 04) observations
on mice, and finds frequent illustrations in these experiments.

Agouti x red. — I have made this mating between pure parents only
once. Agouti 9 2019, mated with red cT 2054, produced 4 young, 3 of
them agouti > red, I red > agouti > white. This result indicates a
tendency of agouti to dominate over red, or at least to mask the presence
of red. In this experiment, the mother, 9 2019, had a red hip patch.
The occurrence of red and of white spots on the young was probably
due to a mosaic character of certain of her gametes rather than to
some peculiarity of the father, a self red.

One of the young produced by this cross, viz, agouti > red 9 1294,
when mated with her red father, c? 2054, produced 6 young, 2 agouti
> red, i red > agouti, 2 red-black, and i red, indicating segregation of
the respective agouti > red, and red characters brought together in the
previous generation, so as to allow of the formation of pure red gametes.
The occurrence of two red-black young indicates that in some cases
the agouti character may break up into isolated black and red under
the influence of the cross.

/" Agouti x albino. — Pure agoutis mated with albinos of spotted or of

I unknown ancestry have produced only animals predominantly agouti-

l colored, though the offspring have in some cases had one or more of

V the typical color patches red or white, but never black or chocolate.

The spotting with red or white was inherent in the agouti stock used.

It is probable that in no case did the albino parent in these crosses

transmit latent agouti. This statement is based on the results of

other crosses made with these same albino animals, as well as on an

examination of their pedigrees. If this assumption is correct, there is

I seen in this experiment a strong tendency for the agouti character to

I dominate over other pigment characters contained latent in albino gam-

\ etes; for every one of the 17 young was agouti-pigmented.

•Brackets will be used to indicate latent characters, just as parentheses to
indicate recessive ones.

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 29

The matings made and their results are :

Parents.

Young.

Gold, agouti.

Albino.

Agouti.

Agouti-
red.

Agouti
red-
white.

Silver
agouti-
yellow-
white.

Agouti 9 1030
Agouti > red 9 IO29
Agouti rf 2017
Agouti ¥ 2018

rf 2059...
$785

3
i

3
3

Agouti > red $ 202 1.
Total

^63S

That an albino may transmit latent agouti is shown unmistakably by
the following case. Albino c? 2060 was purchased from a breeder and
his ancestry is wholly unknown to me. But I found on mating him
with spotted females not of agouti parentage that a large proportion
of his young were agouti-marked, and this proportion proves to be
almost exactly one-half. Thus he has produced by 15 different females,
which were spotted with black and red (and in some cases also with
white), 19 young marked with agouti (in no case with solid black hairs
on the body, though frequently with red or white ones) and 18 young
marked with black but not with agouti. By the red or red-white
females he has produced 3 agouti-marked and 3 black-marked young.
The total pigmentecl young produced by matings with the spotted
females are 22 agouti-marked and 21 black-marked, an approximation to
equality as close as is possible with an odd number of young. The
matings with red and red-white females show that all the gametes
formed by c? 2060 bear the latent character black pigmentation, but
that half his gametes transmit it in the agouti combination with red,
half in the form of solid or segregated black.

If this interpretation is correct it should be possible by suitable mat-
ings of cJ1 2060 with his descendants, or of the latter inter se, to obtain
albinos all of whose gametes would transmit latent agouti. This mat-
ter, it is hoped, can soon be given an experimental test.

In the foregoing case it seems necessary to assume the dominance of
agouti pigmentation over the intermingled condition of black and red
spots ; indeed, all my experiments support that idea, except possibly
those mentioned in discussing the agouti x black cross (p. 26). The
alternative dominance which may have occurred in those cases is
apparently exceptional, the rule being that agouti pigmentation domi-
nates over black or black-red. Alternative dominance can scarcely be
invoked to explain the results obtained from the matings of c? 2060,
for it would fail to account for the black-red offspring in the matings
with red or red-white females.

3O COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

The following experiment likewise bears upon the point which is
under discussion. Agouti <? 2017, mated with albino 9 785, produced
3 agouti and i agouti > red young (as stated on p. 29). The albino
9 785 was born of albino parents, but part of her grandparents
and great-grandparents were spotted black-red-white, part of them
albinos; none were agouti-marked. It seems probable, therefore,
that the pigment characters latent in the gametes of 9 785 were in
everv case black-red. If so, her agouti young should contain recessive
white with which black-red had been introduced as a latent constit-
uent, and should, as explained on page 28, form in equal numbers
gametes of four sorts, viz, agouti, black-red, albino [agouti latent],
albino [black- red latent]. If two such sets of gametes be combined
(as in mating these hybrid young) , and all gametic unions prove equally
fertile, their young should be, on the hypothesis that agouti is dominant
over black-red, in the proportions 9 agouti to 3 black-red to 4 albino;
but on the hypothesis that agouti and black-red are alternatively domi-
nant, the young should be in the proportions 6 agouti to 6 black-red to 4
albino. That is, on one hypothesis, agouti young should be three
times as numerous as black-red ; on the other hypothesis, both sorts
should be equally numerous. The result observed is 7 agouti to 3 black-
red to 3 white, which certainly favors the hypothesis that agouti domi-
nates over black-red, though the number of young is undesirably small.

The details of the experiment follow :

Young.

Agouti.

Black-red.

Albino.

Agouti cf 1509 X Agouti 2 1508
Agouti $ 1509 X Agouti 9 1 507 • ••

Agouti cf 1509 X Agouti > red 9 1510..

Total

Other matings of agouti cf 1509 support the hypothesis that agouti
gametes dominate over black-red ones. Thus he was mated with three
different albino females derived from the same black-red-white spotted
stock as his mother. The gametes of these females undoubtedly trans-
mitted the black-red, never the agouti character. On the hypothesis
that agouti is dominant over black-red, the young produced by these
matings should be in the proportions, 2 agouti to 2 black-red to 4 albino ;

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 3!

on the hypothesis of alternative dominance between agouti and black-
red, the young should be in the proportions, i agouti to 3 black-red to 4
albino. The numbers observed are 2 agouti to 3 black-red to 5 albino —
too few to be conclusive, but favoring the former hypothesis. On the
whole it seems highly probable that agouti as a rule dominates over
all other pigment combinations, but in the case of exceptional animals
like ? 2020, page 27, black or black-red gametes may be formed which
have a potency equal to that of agouti. This is an indication of indi-
vidual prepotency like that discussed further on, under the heading,
" Prepotency and Dominance."

Agouti synthetically produced. — An occasional animal with an ex-
cellent agouti coat may result from mating a red with a black individual.
One such animal, $ 1178, tested as to the character of its gametes, ap-
parently forms pure red and pure black gametes in approximately equal
numbers, for mated with red females he has produced 3 red, 2 black,
and i agouti young. His red gametes uniting with those furnished by
the red females should produce red offspring, while his black gametes
forming similar unions should produce either black or agouti young.
Hence the result observed is exactly what we should expect, on the
hypothesis that black and red have formed merely a temporary, not a
permanent union in the agouti parent, and that the gametes formed by
it contain either red or black, but not the two united in the agouti com-
bination. What conditions, if any, can bring about a permanent union
between segregated red and black my experiments do not as yet indicate.

THE BLACK TYPE.

My original black animals were obtained from Miss Soule. Bred
inter se they produce only black offspring, though a few red hairs
may usually be found by careful search somewhere on the body. The
relation of black to agouti has already been discussed, so that we
may pass immediately to its relations with red and with albinism.

Black X red. — The young produced by this cross have ordinarily
a black coat, but of a reddish shade, as if the pigmentation of the black
parent had been diluted with that of the red one ; in other words, the
characters of both parents show their influence in the offspring, which
are not intermediate, only because black pigment is so much more
opaque than red that the latter is scarcely visible. In other cases the
weakening of the black pigmentation is seen in a restriction of the
black pigmented areas, which then fall into the series of pigmented
patches described on page 9, while red, or red and white together, fill
up the intervening spaces. This results in the production of a black-
red or black-red-white spotted animal. Or, thirdly, and less often
still, the black and red may have the characteristic distribution which
produces the agouti coat.

COAT CHARACTERS IN GUINKA-PIGS AND RABBITS.

In detail, the matings which I have made under this category and
their results are as follows :

Young.

Parents.

Reddish
black.

Black >
red.

Agouti.

$ 2053 (black, but with a few red hairs)

y 2013 (very deep black, without red

Total

Hybrids of all three sorts show segregation in forming gametes, though
as yet not exactly in the expected Mendelian proportions. Thus the
two reddish-black young of 9 2013 by J* 2054, viz, 9 1 179 and cT 1 180,
have given the following results when mated with red animals :

Young.

Parents.

Red.

Yellow.

Black-
red.

Black-
yellow.

Agouti.

Black 9 "79 X red $ 2054
Cfatherof $ 1179)

Black 9 1179 x red <^ 2004.

...

Black cP ubo x red P 1073.

...

Black c? 1180 X red 9 1278-

...

Black rfj 1180 X red V 1279-

Black J1 1180 X red 9 1286.

...

...'

Black cf 1180 X red Q n°7-

...

Black <$ 1 180 x red 9 2026.

Black g 1180 x red 9 2027.

...

Total

•

It will be observed that 9 1 179 has given by two different red males
as close an approximation as is possible to the expected equality of
red young on one hand and of black or agouti young on the other
hand. But her brother, c? 1180, has produced a most astonishing
excess of red individuals, more than three times as many red young
being recorded as black ones. It would seem to be a peculiarity of
this animal to form red gametes either more numerous or more vigorous
than his black ones, for red young are in excess in all his matings

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

except one, that with 9 1073. Another unexpected result is the pro-
duction of weakly pigmented animals of the red type, i. e., of yellows,
and of one yellowish-black (or blue) individual, where we expect only
red and reddish-black offspring. The first mentioned peculiarity of
cT nSo is possibly shared by other cross-breds between the black and
red types. Thus black > red 9 1156, a daughter of black cf 2053 by
red 9 755, gave the following result :

Parents.

Young.

Red.

Agouti.

9 1156
9 1156

X red c
X red c

f' 2054

i
4

P 2004

Again, reddish-black 9 3OI7' a daughter of the similarly pigmented
9 1 179 by red J1 2054, gave by red c? 2004, three young, all red. The
results thus far obtained by mating with red females the agouti d" 1178
(produced by the cross of black with red) have been previously given.
Thev indicate that this hybrid forms red and black gametes in num-
bers approximately equal. Combining the results of all the matings
made between an animal whose parents were red and black respec-
tively, and red animals, we get 37 red (or yellow) to 14 black, blue, or
agouti, where we should expect an equal number in each of the two
general classes. Further^ experiments are needed to show whether
the inequality thus far observed is a chance result which will disap-
pear with larger numbers, or whether it is significant and will remain.

Several other black-red animals, which evidently contain recessive
red, have produced, when mated with red animals, 8 black-red and 13
red young. The matings making up this total are as follows :

Parents.

Young.

Black-red.

Red.

Black-red.

Red.

cf 23
c? 23

9 4

o
o

4
i
i
i

9 1227... .
9 1288... .
9 1448-. -
5 1482... .
9 1607... .
cT "65... .

Total....

$ 1140 . ..

CJ" 1140. ..
$ 1140. ..

3 1140 ..

qf 1140. ..
9 1262. ..

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

Again, black-red pigmented animals which contain recessive red
(or else latent red, see p. 25) when mated inter sc have produced
young as follows :

Younj

I-

Black-
red.

Red.

Albino.

Black-red cf 23 x black red (albino) 9 i A

Black-red (albino) d" 89. i" x black-red (albino) $ i A.
Black-red rf 23 x black red-white 9 51 2b

•

Black-red (albino) j* 89.1* x black-red-white 9 51.2*.
Black-red (albino; cf 89. I* X black-red (albino) 9 89. 3s.
Black-red c? 23 x black-red (albino) 9 §9 3b

i
6

•

Black-red c? 23 x black-red-white 9 2°9

Total

I I

We should expect the black-red young to be three times as numerous
as the red ones, but we find them only twice as numerous, yet the
numbers involved are small, and the precise proportion observed
probably not significant. Combining the results of all matings of
black pigmented animals which are expected to produce red young
we get a total of 105 young :*

Black pig-
mented.

Red pig-
mented.

Observed

Expected

Black X albino. — As elsewhere stated, few, if any, of my black
animals are entirely free from red pigmentation, and my albinos, so far
as determined, always possess latent red. Accordingly, more often
than otherwise, the young produced by this cross show more or less
red pigmentation, though in my experiments it has never amounted to
more than a few red hairs, or one or two small red spots situated at the
border of one of the typical pigment patches. The blackest young
produced in this series of experiments resulted from matings between
a very heavily black pigmented female (9 2012) and an albino male
(c? 635) part of whose gametes, as stated on page 24, entirely lacked
the black character.

* Further experiments made since the foregoing was written continue to give
a steady excess of red animals and a corresponding deficiency of black ones.

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 35

In detail, the matings made are as follows :

Young.

Mating.

Parents.

Black.

Black *>
red.

Black >
white.

(i)

Black 9 2O12 x albino (^635

(2)

Black Q 2012 x albino $ 2002...

(3)

Black V 2014 x albino ^2039....

...

(4)

Black 9 2014 x albino $ 2059....

...

fsb

Black >red $ 2053 x albino 9 807

...

(6)

Black >red tf 2053 x albino 9 ?66

...

Total

•j

The relation existing between the characters combined in this cross
is one of simple Mendelian dominance, followed by segregation in the
next generation, as is clear from the following matings :

Mating.

Parents.

Young.

Black.

Black >
red.

Black >
white.

Albino.

(7)
(8)
(9)

Black>white J* 1 1 1 1 [born
of mating (2) above] X
albino 9 9

4
3

4
6

Black>red $ I256 [born
of mating (6) above] x
albino 9 9

Black $ 1570 [born of mat-
ing (i) above] X albino

Q O

Total

6 -

The hybrid males, it is evident, form in approximately equal num-
bers albino gametes and those bearing the centripetal type of pigmen-
tation, and the latter transmit essentially the same kind of pigmentation
as was possessed by the pigmented parent and the pigmented grand-
parent. This conclusion is further supported by the result of matings
of hybrids inter se, as shown on the following page.

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

ParenU.

Young.

Black.

Black>
red.

Black >
white.

Albino.

Black>red <? I2s6 [mating (6)1 x

black>red ? 1194 [mating (5)]

...

Black>red $ 1256 [mating (6)J X

black>red 9 "96 [mating (5/j

...

Black>red $ 1256 [mating (6)] X
black>red9i255 [mating (6)]
Black rf 1570 [mating (i)] x black>
red 9 1194 [mating (5)]
Black rf 1570 [mating(i)]x black >
red y UQ7 [mating (5)] .

2
j

...

Black tf 1570 [mating (i)x black >

Black tf 1570 [mating (i)] X black>

Total .

The result observed is in exact agreement with the expected Men-
delian ratio, 3:1.

From what was said on page 24 concerning the transmission of pig-
ment characters by albino gametes, we should expect that the charac-
ter of the albino used in a cross with black would in some measure
influence the result of the cross. That this is actually so is indicated
by comparing results of matings (i) and (2), page 35, the black parent
being the same in both matings, but the albinos markedly different.
One of the albino males (<$ 635) forms gametes about half of which
are entirely free from black ; the other (c? 2002) always transmits black
pigmentation, frequently with a tendency to spotting. By the former
were produced nine young, all but two of which were self-colored black ;
by the latter were produced four young, all spotted with red or black.

THE RED TYPE.

Red (including its dilute forms known as yellow and cream) is the
only one of the three pigments of the coat which I have been able to
obtain unquestionably free from the other two. Red and yellow ani-
mals not only form no black pigment in their hair, but appear to be
incapable of transmitting the capacity to form black coat pigment. Red
animals mated inter se ordinarily produce only red offspring, but reds
obtained by cross-breeding with black may produce yellows when bred
inter se. This case will receive further attention presently. Yellow
mated with yellow produces, in my experience, only yellow offspring.

The relations of red to agouti and to black have already been dis-
cussed, and in part also that of red to albinism. Accordingly it remains
only to consider in greater detail the last-named topic.

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 37

Red X albino* — The result of this cross depends upon what latent
pigment characters are borne by the albino, and this in turn may in
some cases be inferred from the ancestry of the albino, though in other
cases not. Most of the albinos with which I have experimented contain
latent black as well as red, and when mated with red or yellow animals
produce invariably black-pigmented offspring. The matings indicated
in Table D fall into this category of cases.

TABLE D. — Matings of albinos (all of -whose gametes transmit latent black) -with
red or yellow animals. The pigmented offspring all have black pigment

in (heir coats.

Parents.

Young.

Albino.

Pure red or
yellow.

Black-
red.

Black-
yellow.

Gold
agouti-
red.

Silver
agouti-
yellow.

Albino 9 644.. .
Albino S 76i
Albino 9 778
Albino 9 778.. .
Albino $ 779
Albino 9 1216 ...
Albino 9 1649 •••
Albino cf 2002
Albino $ 2002...
Albino <-f 2002...
Albino ,-^ 2039...
Albino ^ 2039...

Total

Red (^ 2004

I
4
3

2
I

••

Red cf 2004

Red $ 2004
Red $ 2054 •
Yellow J* 1347- •
Red 9 755
Red 9 784
Yellow 9 2001...
Red 9 753
Red 9 830

Albino.

Hybrid red or
cream (albinism
recessive).

Black-
red.

Black-
yellow.

Gold
agouti-
red.

Silver
agouti-
yellow.

2
<

i
4

Albino 9 "Him-
alayan."
Albino 9 766....
Albino 9 1027...
Albino 9 1028...
Albino 9 I544---
Albino <$ 2002 ...
Albino (^ 2039...
Albino tf 2060 ..
Albino 3" 2060...
Albino (^ 2060...

Total

Cream ^ 1147....
Cream $ 1147....

...

Red (j* 1019

...

Red 9 683

Red Q 1020
Red Q i"*cc

I
2

'.'.'.

2
I
2

Red 9 1442
Red 9 1476

...

Sixteen different albinos mated, as indicated in the table, with red,
yellow, or cream animals, produced 59 pigmented young, all bearing
black pigment.

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

/ Seven of my albino animals contain latent black, but transmit it appa-
/ rently to only about half of their offspring. Matingsof such albinos with
I red or yellow animals are enumerated in Table E.

The pigmented young produced by these matings are 41 black pig-
mented, 37 free from black pigment («. e., bearing only red or yellow
pigment in their coats). The obvious explanation is that only one of
the two gametes which united to form each of these albino parents
contained latent black, the other being free from it ; consequently only
half the gametes formed by the albinos contain latent black.

TABLE E. — Matings of albinos {part only of whose gametes transmit latent black)
•with red or yellow animals. Approximately half of the figmented offspring
have black pigment in their coats.

Voung

red-white, or yellow animal.

Black-
red.

Black-
yellow.

Red.

Yellow.

Albino.

Albino cf 635 x red-white $ 43...
Albino r? 635 X red 9 47°

...

Albino r? 635 X red Q 575

Albino r$ 635 X red 9 610

Albino cf 635 X red $ 610 and
red 2 7<i

Albino r? 635 x red 2 755

Albino (^ 635 x red 9 830

Albino c? 635 X red 9 1073. .
Albino <J 635X red-white 91093.
Albino r? 635 X red 9 2008

i
I

Albino r? 635 x yellow 9 2001...
Albino 9 815 X yellow $ 2061..
Albino 9 i222 X red <? 2004
Albino 9 "22 X red J* 2054

Albino 9 i224Xyellow <5" 1347....
Albino J* 1516 x red-white 9
i ^87

! (agouti-
red.)

2
I

i
3

...

Total

Parents an albino and a red, red-

Young

white, or yellow animal with
recessive albinism.

Black-
red.

Black-
yellow.

Red.

Yellow.

Albino.

Albino c? 635 X red-white 9 690 •
Albino tf 1516 x red-white 9 1344-
Albino <£ I5i6xyellow 9 1346...
Albino cf isi6xyellow 9 1348....
Albino rf 1516 X red-white 9 1434-
Albino y 1216 x red $ 1386

2
2

i
i

Albino 9 i224Xred cf 1386
Albino 9 1236 x red rf* 1386

I
2

...

Total

V V

COAT CHARACTERS IN GUIXEA-PIGS AND RABBITS.

A means of testing the validity of this explanation has been suggested
by Allen ( : 04) for the similar case of chocolate pigmentation in mice.
If the albino gametes which contributed to the production of the red or
yellow offspring in the matings last mentioned were really free from
black, then two of these hybrid red animals (containing recessive albin-
ism) when mated should produce albino offspring not any of whose gam-
etes contain latent black. Experiment has shown this to be the actual
result. Albino $ 1999 was produced by mating two hybrid yellow
animals containing recessive albinism. He has been several times
mated with yellow females (see Table F) and has produced 13 pig-
mented offspring, all yellow. As a control he was mated also with a
black female containing recessive albinism. This mating produced
3 albinos and i black pigmented young. Another albino tested,
g 2059, is apparently similar in nature to ^ 1999, for when mated
with red 9 610, he produced 3 young, all red pigmented (see Table F) .
The ancestry of this albino is unknown to me, as I obtained him from
a breeder, and as no other test of this sort was made in his case, the
result can not be considered conclusive, because of the small number of
young produced ; but it is probable that all his gametes were free from
latent black, for four of his albino daughters by albino mothers con-
taining latent black form albino gametes free from black, as well as
other gametes containing black. They are 99 1216, 1222, 1224,
and 1236, Table E. Each of these four daughters of c? 2059, all that
have been tested, must have received from the father albinism free
from latent black, for the mothers, as stated, did not form gametes
containing latent black.

TABLE F. — Matings of albinos (not any of -whose gametes transmit latent black)
with red or yellow animals. Not any of the offspring are black pigmented.

Parents.

Young.

Albino.

Pure red or yellow.

Red.

Yellow.

Albino.

Yellow 9 3105
Yellow 9 32oo ....
Yellow Q 3085
Red 9 610

3
5

...

Total

Albino.

Yellow (albinism
recessive).

Red.

Yellow.

Albino.

O 174.6

2
I

9 1348

9 9 2063 and 3°36-

...

Total

40 COAT CHARACTERS IN GUINEA-PIGS AND KABBITS.

Although the discovery of the differences among albinos, as regards
matings with red animals, was made by mere accident while comparing
the matings of ef 635 with those of other albino males, I have since
found it possible to produce at will albinos free from latent black (like
cf 1999) by beginning with matings between ordinary albinos (all of
whose gametes transmit latent black) and red or yellow animals. The
following case illustrates the method used : Albino cf 2002 is shown by
matings recorded in Table D to form only gametes transmitting latent
black. For by red or yellow females he has produced to pigmented
young, all with more or less black in their coats. From the mating
with yellow 9 2001 there resulted 3 black-yellow young, 9 9 2033-
2035. Each of these, according to the hypothesis offered, received
from one parent albinism with latent black, and from the other yellow
free from black. In forming gametes the yellow-black hybrids should
produce gametes of four different kinds, all equally numerous (on the
hypothesis that albinism is inherited independently of specific pigments,

alb. o 20°2 x yel. ? Z001

bL-yel °° 2033-3035 yel. O 2061

yet. $1346 yel.^1347 yel. $1348 yel. °. 1349 yel.? 1350 yel.-wh.$ 1351 3bl.-yel.youn$
(alb. recessive) (pure) (alb. recessive) (pure) (pure) (alb. recessive)

FIG. jo.— A genealogical table ; for description, see text.

as previously explained, viz, (i) yellow, (2) black, (3) albinism [yellow
latent], (4) albinism [black latent]. Accordingly, when a mating
of such a hybrid is made with a pure yellow animal, such as cf 2061
(see fig. 10), gametic unions of four different sorts should occur with
equal frequency, viz, (i) yellow -f yellow, producing pure yellow
young ; (2) black -f- yellow, producing black-yellow young free from
recessive albinism ; (3) albinism [yellow latent] + yellow, producing
yellow young (with albinism recessive) ; (4) albinism [black latent] +
yellow, producing black-yellow young (with albinism recessive). That
is, half the young should be yellow, half should be black-yellow ; and
of each sort half again should contain recessive albinism, half should be
free from it. In the case under discussion (see diagram, fig. 10) there
were produced 6 yellow and 3 black-yellow young, but in a series of
matings equality of the two classes would undoubtedly have been more
closely approximated, as Table E indicates. The yellow young alone
were tested for the presence of recessive albinism, and it was found in
exactly half of them, viz, 9 9 1346, 1348, and 1351, the test indicating
that the other three yellow young are pure. The method by which

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

albinos free from latent black may be obtained from red or yellow
hybrids, like 9? *346, 1348, and 1351, has already been explained.
It is simply to mate the hybrids inter se, when there should be produced
albino young, approximately one-fourth of all the young produced, and
these albinos should be free from latent black. A number of albinos
have been so produced in these experiments, but only one of them, viz,
c? 1999, Table F, has yet been tested. It is evident that his gametes
are, as expected, free from latent black.

This experiment indicates methods of practical utility to the breeder
who desires either albinos as free as possible from peripheral pigment

TABLE G. — Matings inter se of red or yellow animals having albinism recessive.
None of the young- black-pigmented. Expected proportion of albinos i in 4.

Young.

Parents.

Red or
red-white.

Yellow
or yellow-
white.

Albino.

Yellow $ 1147 x yellow 9 ^32

Yellow $ 1*47 X yellow 9 1487

Yellow^ 1147 x vellow 9 1786

Red $ 1433 X red 9 ^43

Red (^ 1453 x red 9 1291

Red (^ 1453 X red 9 I297

Red $ 1453 X red 9 ?

Red (^ 1477 X red 9 1292

Yellow (^ I998X yellow $ 9 I35I an^ I535--

Total

or animals of various shades of red or yellow. For (i) albinos free
from latent black have much less peripheral (chocolate or chocolate
and black) skin pigment than others, and (2), when mated with red
or yellow animals they frequently produce young of a lighter shade of
red or yellow than that of the pigmented parent. He who mates
ordinary albinos with red animals in hope of obtaining yellows will
be sorely disappointed, for the young will be mottled with black
(received latent from the albino parent) ; but he who employs albinos,
such as I have described, in matings with red or yellow animals, may
doubtless with patience realize his fondest hopes. By this method I
have been able to produce cream-colored animals of a much lighter
shade than any I ever saw before. Theoretically it should be possible
by following up this method to produce animals practically white, but

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

with dark eyes. Time will show whether this is possible. It is not
improbable that practical difficulties may be encountered. Experi-
enced breeders say that the " purest" albino guinea-pigs (/. e., those
most free from peripheral pigmentation) incline to sterility. Two
cases which have occurred in my own experiments make me think
there is some truth in this idea. Further, albinos free from latent
black have not yet been mated inter se, but I shall not be surprised

TABLE H. — Mat ittgs of males mentioned in Table G -with animals black pig-
menttd, but having albinism recessive. The expected proportion of albinos
is i in 4.

Young.

Parents.

Black-
red.

Black-
yellow.

Yellow.

Agouti-
yellow.

Albino.

Red /-? IOIQ x agouti 9 2020....

Yellow $ 1147 X black-yellow

91 IAQ

Yellow $ 1147 X silver agouti-
yellow 9 1252

Yellow (^ 1147 X black-yellow
$20-14.

Total

TABLK I. — Matings of males mentioned in Table G -with albino females, ft is
expected that half the offspring -will be albinos.

Parents.

Young.

Black-
red.

Black-
yellow.

Agouti-
red.

Albino.

4
i

Yellow (^ 1 147 X albino 9 " Himalayan "

Yellow r? 1147 x albino 9 815

Red ^ I433X albino 9 *544

ToUl

^_ 4

-• — — -V1 — '

to find them relatively unproductive when this is done, for the hybrids
bred inter sc have in certain cases produced fewer albino young than
they should produce on the Mendelian hypothesis. Thus, an exami-
nation of Table G shows that only 8 albinos have been produced in a
total of 54 young, where 13.5 are expected. Nevertheless, this may
be only a chance deviation from the expected proportion of albinos
which will disappear as larger numbers are produced. Tables H and
I indicate that the hybrid males employed in the matings enumerated

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 43

in Table G really produce a full quota of albino gametes, and that
these are entirely fertile when they meet gametes transmitting black,
either active or latent.*

It is a question of much interest, theoretical as well as practical,
whether animals of a particular type, when produced by cross-breed-
ing, form the same sort of gametes as are produced by pure-bred
animals of the same type. In the case of albinos this evidently is not
always true. From an albino which forms gametes all of which trans-
mit latent black, there may be produced, as we have seen, by cross-
breeding with a red animal and then interbreeding the hybrids, albinos
of three different sorts as regards the transmission of latent black
pigment. Again, the character of a red race which breeds true may
be modified by cross-breeding with black, resulting in the production of
yellow young. Thus two red animals, young of black (red recessive)
red&? red? 2007

redo 2004 red ? 2026 bl.? 2013 red £ 2054 red £ ? red $ 2007

I I

red? 1307 bl.(red recessive) 5 1180

red ? 309S red £ 3082

(
3 yellow young

FIG. ii. — A genealogical table showing how cross-breeding between red and black may cause variation
in the intensity of the red.

tf 1180, by two different pure-bred red females, when mated together,
produced a litter of 3 yellow young. The relationships involved will
perhaps be more readily understood from the above diagram (fig. n).
Apparently the cross with black induced variation in the intensity of
the pigmentation transmitted by the gametes bearing red, so that some
of the zygotes which were formed bore the dilute form of red, viz,
yellow.

BLACK-EYED WHITE.

Guinea-pigs of this sort have hair and skin very free from pigment,
indeed in the integument of the living animal I can detect no pigment
at all, yet the eyes are black pigmented. Two animals of this sort
have been born in the course of my experiments, and I have likewise
experimented with two others obtained by purchase. They are not
albinos and do not contain recessive albinism, at least those which I
have had do not. They are of spotted parentage and may be considered
spotted animals in which the typical pigment patches show an extreme

* Experiments made since the foregoing was written show that albinos free
from latent black are entirely fertile inter se. Further, the deficiency of albinos
observed at first is now disappearing.

44 COAT CHARACTERS IN GUINKA-PIGS AND RABBITS.

condition of reduction. The successive steps by which the pigmenta-
tion of guinea-pigs undergoes reduction are about as follows: (i) The
pigment centers are all functional, but the pigment areas do not quite
meet along the middle of the ventral surface, or in the forehead. Per-
haps the pigment fails to reach one or more of the feet also. (2) One
or both shoulder patches are wanting, producing the Dutch-marked
type (compare fig. 6, p. 12). (3) The side patches are also wanting; only
the rump and sides of the head are pigmented (fig. 2, p. 10). (4) The
rump patch disappears ; only the sides of the head are pigmented, and
here the patches are small, or one or more of them may be wanting
(fig. 4, p. n). An extreme condition of this sort is represented by
c? 721 , whose coat was entirely unpigmented except for a small patch of
black about 5 mm. square on the outer surface of his right ear. (5)
The skin is wholly unpigmented, though the eyes are as in all the fore-
going stages dark. One can by selection progress in either direction
through this series of changes, either increasing or decreasing the
number and extent of the pigment patches, but it is impossible without
long-continued selection to fix the color pattern at any particular stage in
the series ; perhaps it is wholly impossible to do so, as Cu6not ( : 04, p. LV)
asserts on the basis of his studies on mice, but this I very much doubt.
I doubt it first, because we do find color patterns of this sort firmly fixed
in many wild species, such as antelopes, skunks, etc. ; secondly, and still
more, I doubt it because of what we see accomplished in domesticated
animals. Take the case of cattle alone. Different breeds of cattle have
often distinctive color patterns, as well as specific pigments in their
coats. Holstein cattle are white, marked with large but more or less
irregular black spots, the color pattern being apparently not definitely
fixed. Dutch belted cattle, probably derived from the same general
source as the Holstein, have for a long time been subjected to a rigid
selection for a more definite color pattern, viz, an animal wholly black
except for a broad white belt around the middle of the body. To this
type the breed is said to keep very true.

Pure-bred Hereford cattle as kept at the present time in America
are red over the greater part of the body, but are invariably white-
faced ; a longitudinal white stripe extends down the middle of the
back, and the belly and flanks are more or less extensively marked
with white. The white face, though now rigidly insisted upon and
always seen in pure-bred herds, has not always been so common in the
breed. A half century or more ago, according to Shaw ( : 03), rival
breeders advocated white-faced and mottled-faced Herefords, but the
former prevailed, and by continued selection the mottled-faced con-
dition has now apparently been eliminated from the breed.

These cases indicate that certain of the typical color patches, as, for
example, the cheek patches of cattle, can by continued selection be

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 45

eliminated altogether, while others are kept at their maximum inten-
sity. How this is possible we could understand better if we knew in
what condition pigment characters are transmitted in the germ. From
the experimental evidence alone it would seem probable that the dif-
ferent color patches are represented in the germ by different elements
separately heritable, possibly in different chromosomes — though of this
we know absolutely nothing — and that as a result of long selection
these separately heritable elements may become firmly associated with
particular body regions. From the mode of development of the hair
pigments as described by Leo Loeb ('97) and confirmed by observa-
tions of Mr. Howard and myself, it is clear that the pigments are
formed in the Malpighian layer of the epidermis. A pigment patch,
then, is, morphologically, simply the pigmented epidermis of a particular
body region, and its character is determined by whatever determines the
character of the epidermis in that body region.

That black-eyed white animals are essentially animals of the centrip-
etally pigmented type is shown by breeding them inter se or by mat-
ing them with albinos. In every case thus far I have obtained only
young with one to several, or even with a//, of the typical pigment
patches. The task of establishing a black-eyed white race which will
breed true is similar to that of establishing a Dutch-marked race which
will breed true, or in cattle a white-faced race like the Hereford. It
is not to be accomplished in a single generation, but I doubt not its
possibility. When guinea-pigs have been bred to a particular color
pattern for many generations, we can form a better estimate of the
magnitude of the task involved, and possibly meantime may learn
something1 about the mechanism of transmission of the color patches.

The specific pigments transmitted by black-eyed white animals are
probably determined by the same rules that govern in the latent pig-
mentation of albinos. These pigments probably differ according to the
parentage in different cases, or more correctly according to the latent
pigmentation which each individual received from its parents. Indeed,
it is not impossible that vanished pigment patches are merely latent
pigment patches, and that the reason why these keep reappearing in
such a seemingly erratic fashion is that they keep emerging from
latency under the influence of cross-breeding. In the black-eyed white
animals with which I have experimented, red as well as black spots
are apparently transmitted in the gametes formed, but I should expect
that in animals different in origin red might be transmitted apart from
black or vice versa.

I have not examined with the microscope the eye-pigments of the
different self-colored varieties of the guinea-pig. From a superficial
examination, however, I should say that black pigment is present in

46 COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

every case except that of the albino. Yet we have seen that red and
yellow animals, which have no black pigment in their coats, do not
transmit black coat-pigment to their offspring, though they do transmit
black eye-pigment. We might conclude that eye-pigment is something
altogether different from and independent of coat-pigment, but two
considerations negative this idea : (i) Black-eyed white animals mated
with albinos produce animals with coat-pigment in the typical patches,
a thing which neither parent possessed ; (2) in mice, animals with coat
patches but devoid of eye-pigment, when mated with unrelated albinos,
produce offspring with pigmented eyes, again a character which neither
parent possessed (Darbishire, 104). From these facts we see that a cer-
tain connection does exist between eye-pigmentation and coat-pigmenta-
tion, though apparently it is less close than that between one coat-patch
and another coat-patch. The disappearance of eye-pigmentation, like
the disappearance of coat- pigmentation, is probably due, in the case of
ordinary albinos, to latency in the germ of a particular hereditary unit.
This condition of latency, it is evident, can be made to disappear by
cross-breeding with any animal of the centripetally pigmented type.
But in centripetally pigmented animals, as we shall see, disappearance
of eye-pigment, when once it has occurred, is apparently beyond recall,
at least by cross-breeding with albinos. This is indicated by the instruc-
tive experiments of Darbishire ( : 04), which we shall presently examine
more in detail.

A condition which might be described as semi-latency of a coat-
• pigment was observed in the case of a red-white animal, 9 915, which
\ was mated with red cf 1019. To my great surprise she produced in
two successive litters four young having black-reft coats. This was
contrary to any previous experience (compare Table G), and I at once
sought for an explanation. Upon looking the animal over carefully
I found, what I had before overlooked, that she had a sacral patch of
black skin, though not a single hair of her body, so far as I could dis-
cover, was black pigmented. The capacity to form black integumen-
tary pigment was evidently present in the animal, though its influence
extended only to the epidermis proper, not to the hair-follicles. One
often sees in dogs, for example in fox-terriers, black skin spots of this
sort in body regions where the coat is entirely white. The character
semi-latent in 9 915 came into full activity in four of her offspring
by a male devoid of that character.

Black skin is not infrequently seen on the feet of red guinea-pigs,
but such animals do not produce young with black hairs when they
are mated with other red animals. A comparison of this result with
that described in the case of 9 915 serves to emphasize the distinction
which has been made between centrifugal and centripetal pigmentation

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 47

(see p. 9). The black-footed guinea-pig has the former, which it
transmits to its offspring ; it does not possess the latter and its offspring
never do, unless a mating has been made with an animal having pig-
mentation of that sort. The black-footed red guinea-pig, as regards
black pigmentation, is in exactly the same condition as an albino with
clark-pigmented extremities ; centripetal black pigmentation is fully
latent in it.

Black-eyed white animals, of the sort which I have had, and ani-
mals like £ 9I5» are centripetallv pigmented animals in which the
capacity to form black pigment in the typical central patches is semi-
latent, /. <?., they may apparently transmit the character in a fully active
condition, when mated inter se, across with animals having a different
type of pigmentation being unnecessary for this purpose.

Darbishire's pink-eyed but centripetally pigmented mice, if they
possessed at all the capacity to form eye-pigment, must have possessed
it in a more than latent condition, for they bred true inter se, and though
a cross with albinos brought the character into full activity, there are
strong reasons for believing, as we shall presently see, that the capacity
to form eye-pigment was recovered, not from the pink-eyed animal,
but from the albino with which it was mated. It is to be expected
that continued selection and inbreeding of black-eyed white guinea-
pigs would establish a condition of the coat-pigment patches similar
to that of the character eye-pigmentation in Darbishire's pink-eyed
mice, a condition which goes beyond the latency of centripetal pig-
mentation in albinos, and may, for all we at present know, amount to
elimination of the character in question from the germ. This question
offers an attractive field for further investigation.

Comparison 'with pink-eyed mice. — The dark-eyed mice obtained
by Darbishire ( : 04) upon mating pink-eyed spotted mice with albinos,
yielded an interesting result when bred inter se. Approximately one-
fourth of the young were, as we should expect, albinos ; one-half were
dark-eyed, like their parents, the primary hybrids ; and one-fourth
were pink-eyed and spotted. We should naturally expect the dark-eyed
young (like their parents) to contain recessive albinism, and the pink-
eyed spotted ones to be free from it, like their pink-eyed grandparents.
While in many cases this was undoubtedly true, in others it was not
true ; for Darbishire's breeding experiments show that some of the
dark-eyed animals did not contain recessive albinism, and that some of
the pink-eyed ones did. Further, the "extracted" albino young in
some cases behaved differently from their albino grandparents in
crosses with pink-eyed spotted animals. They produced pink-eyed
as well as dark-eyed hybrids, the two sorts being approximately equal
in number (7 pink-eyed to 6 dark-eyed, Darbishire, : 04, Table D, p. 24).

48 COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

From this it is clear that the five albino parents which gave the result
just described transmitted in approximately half their gametes the
pink-eyed and in half the dark-eyed condition. These albinos are com-
parable in the matter of the pink-eyed character with my albino guinea-
pigs of Table E in the matter of black coat-pigment. A close parallel
exists throughout the two cases. Darbishire's original albinos all con-
tained latent the character pigmented eye. This character was invaria-
bly brought into activity by across with the centripetally pigmented but
pink-eyed race. That race would seem not to have possessed the
character eye-pigmentation, even in a state of latency which a cross
with albinos would bring into activity ; for half the gametes formed
by the hybrids apparently lacked the character eye-pigmentation, and
that character was as often associated latent with the albino character,
as it was associated active with the alternative character, standing for
centripetal pigmentation. If so, the hybrids must have formed with
equal frequency gametes of these four sorts: (i) pigmented coat,
pink-eye,* (2) pigmented coat, dark-eye, (3) albinism [pigmented coat
and pink-eye latent], (4) albinism [pigmented coat and dark-eye latent].

Hybrids forming sets of gametes like these, when mated inter sc,
should produce young visibly of three classes in the proportions, 9
dark-eyed pigmented to 3 pink-eyed pigmented to 4 albino. The num-
bers observed by Darbishire are 287 (or 284?) dark-eyed pigmented,
131 (or 134?) pink-eyed pigmented, and 137 albino young.

On the hypothesis which I have suggested, these young, though
visibly of only three different sorts, should really fall into nine classes,
whose numerical proportions are theoretically as follows :f

Class (5),
Class (\),^Pd(Ap) "I Class (6) ,

Class (2), 2 Pd(p) i 9 pigmented
Class (3), 2 Pd(A <t) f dark-eyed. Class (7),
Class (4), i Pd Class (8),

Class (9),

PP (A P)\ 3 pigmented
Pp > pink-eyed.

A [.dp] )

A[dd~\ ^ 4 albinos.

Alt A )

This classification rests on the assumption that eye-pigmentation may
be inherited apart from coat-pigmentation, /. £., that the primary
hybrids are really ^/-hybrids in the Mendelian sense. It involves the
further hypothesis that eye-pigmentation was invariably latent in the
original albino stock used, and as invariably absent from the pink-eyed

* Although the pink eye is due merely to absence of pigment from the eye,
just as albinism to absence of pigment from the eye and coat, it is convenient
in both cases to speak of the negative character as if it were positive. This can
be done, I trust, without confusion to the reader.

* EXPLANATION.— A = albino; P = pigmented; d = dark-eyed; / = pink-
eyed; ( ) indicate recessive characters, [ ] latent characters. The relative
frequency of occurrence of individuals of each class is indicated by a coefficient.

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

pigmented animals (at least in a state capable of becoming active as a
result of matings with albinos).

Let us now inquire whether Darbishire's experiments indicate the
existence of these various hypothetical classes or not. Darbishire gives
in the first part of his Table E, page 35, the results of mating inter se
dark-eyed pigmented animals of generation F2.* On the "ancestry"
hypothesis these should all breed much alike, for their ancestry is sim-
ilar in all cases ; on the hypothesis which I have stated, they include
the four distinct sorts of individuals which I have called classes (i) to
(4), page 48, and these will breed very differently one from another.
An examination of Darbishire's table shows that in fact the various
pairs of pigmented dark-eyed animals gave results of four different sorts.

I. The following pairs gave young of three sorts — dark-eyed, pink-
eyed, and albino :

ifoung

Pd.

Pp.

2H 48

2H <;2

•j

2H Q-? . .

Total

On the Mendelian hypothesis each of the parents in these three fami-
lies must have furnished gametes bearing the pink-eyed character as
well as gametes bearing the albino character. If so, and if each of these
characters was represented in half the gametes formed, and the two
characters were independent of each other, then the parents were of
class ( i) , page 48, and the young should be as 9 P d to 3 P p to 4 A,
which approximates roughly the observed 7 to 4 to 4.

II. The following pairs gave only dark-eyed and pink-eyed young,
without albinos :

Pair.

Young.

Pd.

Pp.

2H 390

5
4
4

2
I
I

I
2

2H 70/9

2H ci/3

2H I7Q.

2H 142

Total

* I adopt here and in the following pages Bateson's convenient notation for
the successive " filial " generations following a cross, viz, Ft, F8, F8,etc.

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

A result of this sort can have followed either from matings inter se
of animals of class (2), page 48, or from matings of such animals with
those of class (i). In either case the young should be 353 Pdto i Pp,
a ratio closely approximated in the observed 23 P d to 7 Pp.

III. The following pairs gave only dark-eyed and albino young,
without pink-eyed pigmented ones :

Pair.

Young.

Pd.

2H y>a.

4
4
7
6
3

i
i

zH ejoS

2H 96

2H QQ

Total

Such a result would be produced either by mating inter se individ-
uals of class (3), page 48, or by mating individuals of that class with
those of class (i). In either case the young should be as 3 Pdto i A.
The observed numbers, 2410 6, are not greatly at variance with this ratio,
considering the small number of young produced.

IV. The following pairs produced only dark-eyed pigmented young,
without either albinos or pink-eyed pigmented young ;

Pair.

Young.
Pd

21136

•7

aH 40 . .

2H5i

aHgz

•3

Total

Such a result should follow mating inter se two individuals of class
(4), page 48, or mating an individual of that class with one from any
of the other three classes, (i) to (3), or from a mating between classes
(2) and (3).

Accordingly, in the eighteen pairs which Darbishire formed of dark-
eyed pigmented mice of this second filial generation (omitting only
one pair which gave but a single young), we get evidence of the
probable existence of all four of the hypothetical classes of dark-eyed
individuals. If the pairs were taken quite at random without regard
to the recessive characters present in the different animals (and this
was evidently the case, since Darbishire does not admit the existence

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

of such characters) , we should expect from the theoretical numerical
frequencies of classes (i) to (4) that pairs giving the four sorts of results
described would be as follows. The observed frequencies are for con-
venience in comparison given in a parallel column.

Group.

Expected
frequency.

Approxi-
mately.

Observed

frequency.

•>

-?8

Ill

c->

The agreement between expected and observed frequencies, it will
be noticed, is as close as could reasonably be expected in so small a
number of pairs.

Again, Darbishire mated dark-eyed animals, like those whose mat-
ings we have been discussing, with dark-eyed animals of different
parentage, one of the parents having been a hybrid, the other an albino.
In all such cases the albino parent evidently possessed and transmit-
ted to its offspring the dark-eyed character, for none of the pigmemted
young were pink-eyed. But the hybrid parent, according to our hypoth-
esis, transmitted the pink-eyed character to half its offspring, forming
gametes as follows (see p. 48) : P d + Pp + A \_d] + A [>].

Union of the gametes of the albino parent, all A [«T] , with gametes
like these would produce young as follows :

Pd(Ad) + Pd (Ap) + A [dd] + A [_dp~\.

But as Darbishire utilized in the experiment under discussion only
pigmented animals, we are concerned at present only with the first two
classes of young. They are identical in character with individuals of
classes (3) and (i), respectively (p. 48), but occur in equal numbers,
whereas in a group of hybrids like that described on page 48, class
(i) is twice as abundant as class (3).

The question now before us is, if individuals of classes (i) and
(3) be taken with equal frequency to mate with individuals taken at
random from a mixture of classes (i) to (4) in the proportions indi-
cated on page 48, what sorts of offspring are to be expected and in what
proportions in the various pairs formed. Making the calculations by
the methods already explained, we find that pairs should occur giving
the same four sorts of results as in the previous case (pp. 49 and 50, 1
to IV) ; but these pairs should occur in frequencies somewhat different.

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

The pairs recorded by Darbishire (p. 35, Table E, middle section)
which fall into these respective groups are as follows (omitting only
one pair which produced 3 albinos and which might fall into either
Group I or Group III) :

GROUP I.

GROUP II.

Pair.

Young.

Pair.

Young.

Pd.

Pp.

Pd. Pp.

2H 23

3
i

2
I
I
I

2H 28

4 l
5 *
5 3
3 3

2H 74.

2H 77. .

21138

2H4t

2H44« ..

2H 107 ....

Total

17 8

Expected

3 i

GROUP III.

GROUP IV.

Pair.

Young.

Pair.

Young.

Pd.

2 II 2O

3
4
3
5

4
3

2
2
2
2
2

2H 32

5
3
5
5

2H 41

2H 4O

2H 440

2H 103

,, Vr

2H 118

2H I06

Total

2H I IQ

2H i4C

Total

12
I

18
all Pd.

Expected

The expected relative frequencies of these four sorts of pairs are as
follows, the frequencies observed being given in a parallel column :

Group.

Expected
frequencies.

Observed
frequencies.

Ill

IV .

From this experiment we get additional evidence of the existence of
the four hypothetical classes of dark-eyed pigmented individuals, (i) to
(4), page 48, and of their occurrence in something like the theoretical
proportions. Still further support for this view is afforded by the third
section of Darbishire's Table E, page 35, which includes matings of

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

dark-eyed animals, each having one albino and one hybrid parent.
Half of these animals should have the character of class (i), p. 48, and
half that of class (3) . Pairs established by random selection of indi-
viduals should, therefore, be in the proportions, i mating within class (i)
to 2 matings between classes (i) and (3) to i mating within class (3).
Pink-eyed pigmented young should be produced only in matings of the
first sort, but albinos should result from all three sorts of matings.
The matings which produced pink-eyed young are as follows :

Pair

ifoung.

Pd,

PP>

2H 18

2H 27

2H III

...

2H 716

2Hi43

2H 146

2H 14.7

aH 148

Total

Expected

The remaining matings are as follows :

Pair.

Young.

Pd.

2H 10

4
5
4
i

4
3
3

4
3

2
-I

3
3

3
i

2H 20

2H 22

2H 25

2H 26

2H T7....

2H 4C

2H IIO .

2H 112 .. .

2H 113

2H 114

2H 115

2H 144 ...

Total

48
3

21
I

Expected

The evidence from the group of matings contained in these two lists
is less clear than that from the two groups previously examined.
There is a considerable excess of pink-eyed young in most of the mat-

54 COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

ings which produced offspring of that character, and a deficiency,
almost as great, of albinos. If these deviations from the expected pro-
portions indicate anything other than a chance result, it is an increase in
the proportion of gametes bearing the character pink-eye associated
with pigmented coat, and a corresponding diminution in the propor-
tion of albino gametes. Yet such a change is of very doubtful occur-
rence ; more probably the outcome is a chance one, for the deficiency
of albinos produced by the eight pairs which had pink-eyed young is
more than offset by an excess of albinos produced by the other thirteen
pairs, the total young produced being 121 pigmented to 30 albinos.

The fact, too, that certain pairs of this category produced no albinos
must not be taken as conclusive evidence that the animals mated did
not contain recessive albinism. The expectation is that only i in 4 of
the young produced will be albinos, and it is not surprising that, as a
chance result, no albinos should be found among as few as the 3 to 9
young produced by a pair. More extensive tests, or the simpler test
of mating with albinos, would without doubt have shown the forma-
tion of albino gametes by each of the parents in question, if they really
were of the parentage indicated in Darbishire's table.

The foregoing considerations indicate that the correctness of the
classification of pairs in the cases previously examined is not estab-
lished beyond question. For example, a pair which in a total of 6 or
8 young has produced only those of two sorts, might in subsequent lit-
ters produce young of the third sort, which would place the parents in

different category. Only in the cases where young of all three sorts
'have been produced is the character of a pair conclusively estab-
lished. In other cases the probability of correctness in the classifica-
tion made increases with the number of young produced. Whatever
errors are involved tend to increase the magnitude of Group IV (pp.
50 and 52) at the expense of Groups I to III, and that of II and III at
the expense of I. Making all allowance for such possible errors, there
would still seem to be little reason to question the existence, among
Darbishire's dark-eyed mice of generation F,, of all the four classes
designated (i) to (4) on page 48.

The existence of the two classes of pink-eyed pigmented mice (5)
and (6), page 48, is strongly indicated by matings inter se of pink-
eyed mice belonging to generation F,, as recorded by Darbishire in his
Table H, page 37. According to our hypothesis, the pink-eyed mice
of this generation are in character either Pp or Pp (Ap), individuals
of the latter sort being twice as numerous as those of the former. Not
any of them contain the dark-eyed character ; consequently they should
produce only pink-eyed young or albinos, when bred inter se. The

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

seven pairs tested by Darbishire produced 31 pink-eyed and i albino
young, with no -dark-eyed ones — conclusive evidence against the
" ancestry" hypothesis of Gallon and Darbishire, for all four grand-
parents were dark-eyed. The number of young produced by a pair
in this experiment ranged from 2 to 6, the single albino occurring in a
litter of 5. This one albino gives conclusive evidence that its parents
both contained recessive albinism and so were of class (5). We should
on the theory of probabilities expect the occurrence of three such pairs
in seven taken at random. It is possible that more extensive tests would
actually have shown the occurrence of more than this one, but it is a
probability which amounts almost to a certainty that not all the seven
pairs would have given albinos, had they been more extensively
tested. If not, then the occurrence of individuals of class (6), i. e., P ' p,
would be fully established by the experiment. But the absence of
recessive albinism from certain of the pink-eyed mice of this genera-
tion is shown in a simpler way, viz, by matings with albinos. Nine-
teen such matings are recorded by Darbishire in his Table G, page 36.
The number of young produced by a pair ranges from 2 to 8. Five of
the nineteen pairs produced albino young, showing that they contained
recessive albinism and transmitted it in approximately half their
gametes, for the young produced by these pairs are 12 pigmented to 12
albino. Since the remaining fourteen pairs produced not a single
albino in a total of 74 young, it is certain that many if not most of
them did not form albino gametes, for had they done so half their
young should have been albino. The albino parents used in this
test evidently all transmitted latent the black-eyed character, for every
one of the nineteen pairs produced dark-eyed young, showing that the
albino parent was either of class (8), page 48, or possibly of class (7).
The occurrence of an albino of this latter class (one which transmits
latent in half its gametes the dark-eyed character, but in the other half the
pink-eyed character) is shown beyond question, in Darbishire's Table
G, by a mating (2/7 120) which produced 2 dark-eyed and i pink-eyed
young. The occurrence of albinos which may have been either of
class (7), page 48, or of class (9) (/. £., which transmitted the pink-
eyed character either in half or in *11 of their gametes) is indicated by
three pairs in Darbishire's Table F, page 36, as follows :

Voung

Pd.

Pp.

K 10

K ii

K ic

56 COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

In this experiment the parents both belonged to generation F;, and
were respectively a dark-eyed animal — which might be taken from any
of the classes (i) to (4), p. 48 — and an albino — which might be taken
from any of the three classes (7) to (9). We should, on the theory
of probabilities, expect half the eighteen pairs enumerated in Darbi-
shire's Table F as producing pigmentcd young to produce pink-eyed
offspring. Only three, as stated, gave this result, instead of the expected
nine. But the number of young produced by several of the pairs
was very small, being in four cases 3, and matings which should pro-
duce less than I in 4 of pink-eyed young (viz, 3 in 16) may well have
failed to produce any in litters of 4 or less. In the three matings cited
it is evident that both parents formed gametes bearing the pink-eyed
character, since pink-eyed young were produced. Accordingly the
dark-eyed parent must have belonged either to class (i) or to class (2),
and the albino parent either to class (7) or to class (9). In mating
K 10, the dark-eyed parent was probably of class (2), since no albino
young were produced, though the small number of young, three, leaves
this uncertain ; but in matings K 1 1 and K 15, it is clear that the dark-
eyed parent was of class (i ) , since albino young were produced in both
cases. There is nothing to indicate whether the albino parents in these
three matings were pure or hybrid as regards the pink-eyed character,
except the large proportion of pink-eyed young produced, which would
indicate that they were probably of class (9), i. e., pure.

Accordingly, in Darbishire's experiments, we lack strong evidence
by breeding test of the occurrence of this class (9) only of all those in-
dicated on page 48. Yet I doubt not that the single albino born of pink-
eyed parents, as recorded in Darbishire's Table H, page 37, if tested
would prove to be of this sort, i. e., lacking entirely the dark-eyed
character, so that when mated with pink-eyed animals only pink-eyed
offspring would be produced. This result would be parallel with what
in mice Allen ( : 04) observed to be the relation of chocolate and choco-
late-yellow pigmentation to albinism, and what I, in guinea-pigs, have
shown to be the relation of red and of yellow pigmentation to albinism.

HEREDITY OF ROUGH COAT.

In certain varieties of the domesticated guinea-pig the hair has a very
peculiar arrangement, sloping away in all directions from certain points,
which are situated for the most part symmetrically along the sides of
the body, nearly coinciding with the centers of the typical pigment
patches. As a consequence the animal seems covered with cowlicks or
rosettes, between which the hair, sloping in opposite directions, forms a
series of ridges or crests. These are best seen in the so-called Abys-
sinian (the short-haired but rough) variety. (See PI. 2, figs. 3 and 4.)

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 57

When the rough coat character is best developed, rosettes are seen
around the following paired centers: (i) The eye, (2) a point immedi-
ately behind the ear, (3) the shoulder, (4) a point dorso-lateral on the
side of the body about midway between shoulder and hip, (5) the hip,
(6) the groin, (7) each of the single pair of mammae; and from two
unpaired centers, viz, (8) the middle of the forehead, and (9) the navel.
The direction of the hair is also reversed on the toes.

In crosses between pure rough individuals and smooth ones, the rough
character is dominant, all the young being rough and ordinarily having
the rough character as fully developed as in the rough parent. jBut
certain smooth animals, which may properly be described as prepotent,
produce offspring which show a weakened condition of the rough char-
acter, some of the typical rosettes being either less well developed than
in the rough parent or wanting altogether (see PI. 6, fig. 12). Such
offspring may be called partial rough. They frequently transmit the
rough character in its full intensity to their offspring, as we shall pres-
ently see, though they themselves are only partially rough.

Repeated crossing of rough animals with prepotent smooth ones
results in further weakening of the rough character until it is almost
eliminated. Successive stages in this weakening process may be recog-
nized, which are about as follows :

Condition A: The fully developed rough character as above de-
scribed (see PI. 2, figs. 3 and 4).

Condition B : Forehead and shoulder rosettes have disappeared, hip
and side rosettes either fuse into an obliquely longitudinal dorso-lateral
part sloping downward posteriorly, or the hip center disappears entirely.

Condition C (PI. 6, fig. 12) : The only conspicuous rosettes are the
side rosettes, though the ear rosettes may usually be found by careful
examination ; between the ear and side rosettes a ridge runs obliquely
downward and backward across the body from the shoulder ; there is
likewise a median dorsal crest ; the hair is reversed in direction on the
hind feet, and turned laterally but not reversed on the front feet.

Condition D : Only a single pair of rosettes, the side rosettes, persist ;
a mid-dorsal crest extends from the head back to the rump ; hair on the
feet as in Condition C, or that of the front feet straight.

Condition E : No rosettes, a mid-dorsal crest from the head back-
ward, perhaps half the length of the body ; hair of toes reversed on
hind feet only or not at all.

Condition F : No rosettes or crest. Hair reversed on hind feet only. \

It must not be understood that these steps are necessarily taken one \
at a time. The original cross between rough and smooth may lead I
directly from Condition A to Condition D, when the smooth parent it /
very prepotent.

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

The matings which have been made between pure rough parents
and smooth ones may be summarized as follows :

Parentage.

Young, in appearance.

PR.

Sm.

R c? 1516 x Sm. 9 9

8
"3

2
3'

166

5
ii

1" —

R c? 1586 X Sm 9 9

R tf 2002 x Sm. 9 9

R. 9 2040 x Sm. cf 2060
R C? 2°59 X Sm 9 9

Total

[Abbreviations : tf. - rough ; PR. = partial rough ; .S'wr. = smooth.]

It will be observed that every one of the 186 young produced by this
experiment bears the rough character, all but 20 of them having it fully
developed (Condition A) ; the character of the exceptional 20 partial-
rough animals varies from Condition B to Condition D.

PREPOTENCY AND DOMINANCE.
The matings which produced the 20 partial-rough young are of par-
ticular interest. In detail they are as follows :

Young.

PR.

5m.

Sm. 9 ao8 (or 996?) X R . cf 2002
Sm. 9 2005 X R- (jf 2002

Sm. 9 2005 X R. tf 2059

Sm. 9 2056 X R. tf 2002

Sm. 9 2056 x R. cT 2059

Sm. 9 1344 x /?. cf 1516

Sm. 9 1499 X R. tf 1516

The partial rough young, it will be noticed, were all produced by
five (or possibly six) mothers. Unfortunately, there is some uncertainty
as to the mother of the first of the lots of young enumerated. The two
females (9 208 and 9 996) had 6 young together at the same time, and
so it was impossible to separate the young by litters, but from the color-
ation and size of the young I think it probable that 9 208 was the
mother of the 4 partial-rough young. But 9 996 was of the same
smooth stock as 9 208, and it would not be surprising if her gametes
had a similar potency. Unfortunately, no further tests with these
mothers could be made, for they both died soon after producing the
young enumerated. The two females, 9 2005 and 9 2056, were both
mated with the same rough males (d* 2002 and d1 2059). The former
produced only partial-rough young by both males ; the latter produced

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 59

some fully rough and some partial-rough young by both males. From
these cases it seems clear that the production of partial- rough young
was due to some unusual potency of the gametes bearing the smooth
character, and that this potent character was inherent in all the gametes
formed by 9 2005, but in only about half of those formed by 9 2056.
If 9 208 was, as supposed, the mother of the 4 young, all partial-rough in
character, then she probably formed only potent gametes, as did 9 2005
apparently ; but if 9 208 and 9 996 each produced some of the partial-
rough and some of the fully-rough young, then they were both similar in
character to 9 2056, as regards the formation of potent gametes. It
would seem probable, accordingly, that potency of the sort under consid-
eration is a function of the gametes ; that while most smooth females form
no potent gametes, some form 50 per cent and some 100 per cent of such
gametes ; or, in other words, that some smooth animals are purely potent,
others hybrid, as regards potency, but a majority «o»-potent.

;The question now arises, is this potency handed on from generation
o generation, /. e., do the gametes remain pure as regards potency, or
s their potency affected by a cross with the alternative and dominant
character, rough coat. There is some evidence in favor of both these
ideas. On one hand there is a manifest tendency for gametes to retain
from generation to generation any abnormal potency which they may
possess ; but on the other hand cross-breeding probably does frequently
alter the potency of recessive gametes.

The first of the two ideas just mentioned receives support from the
admirable experiments of Coutagne ( : 02) with silk-moths, which
seem to have received less attention than is warranted by their great
richness in results and the care with which they have been executed.
Coutagne crossed two distinct races of silk-moths, one of which pro-
duced only white cocoons, the other only yellow cocoons. Dominance
apparently was alternative between the two characters, which seem to
have been nearly equal in potency, so that sometimes one, sometimes
the other dominated. The cocoons were 219 white in character, 340
yellow, without intermediates. Images hatching from either sort of
cocoon, when mated inter se, produced the other sort of cocoon, as
well as that from which they hatched, and approximately in the pro-
portions 3 of their own sort to i of the other. Thus, moths hatch-
ing from white cocoons mated inter se, and moths hatching from yel-
low cocoons mated inter se, produced in different lots —
From white cocoons : TOTAL.

White 339 87 180 606

Yellow 140 36 109 285

From yellow cocoons :

White 120 34 80 334.

Yellow 44i 89 236 766

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

Evidently there is a strong tendency for white, when it dominates in
a first cross, to behave as a dominant also among the progeny of that
cross ; and likewise for yellow, when it dominates in a first cross, to
behave as a dominant among the progeny of that cross. This indicates
clearly the persistence from generation to generation of relative poten-
cies of gametes of a particular sort. As regards the relative proportions
of white and of yellow cocooned young, it is noteworthy that there is
throughout the experiment a slight excess of yellows over the expected,
indicating a somewhat superior potency of that character, which, in
matings between other white-cocooned and yellow-cocooned races, was
found to be uniformly dominant.

That cross-breeding may modify the relative potencies of gametes
seems highly probable, yet the evidence for this idea at present avail-
able is inconclusive. It consists principally in an observed excess of
partial-rough young over the expected proportion in certain matings,
which will presently be described, but the numbers of young as yet
produced in these experiments are too small to be at all conclusive.

One mating of pure rough animals (/?. cT 2002 X /?. 9 2003) Pr°-
duced, as expected, only rough young, five in number (see p. 63).

Hybrid rough animals, R. (Sm.), when mated with pure rough
animals, have produced, as expected, only rough young, 57 being fully
rough (Condition A, p. 57) and" i partial-rough (Condition B or C).

The one partial-rough animal occurred in a litter of three young borne
by R. 9 2040 mated with hybrid R. (Sm.) tf 994. This female had
previously borne two fully rough young by Sm. d* 2060 (see p. 58).
It is probable, therefore, that the hybrid c? 994 did form some smooth
gametes of unusua?- potency, though, unfortunately, he was not tested by
other matings with rough females.

Hybrid rough animals, R. (Sm.) in character, when mated with
smooth ones, have produced 127 rough young and 146 smooth ones,
equality of the two classes being expected on the Mendelian hypothesis
of segregation. Of the 1 27 rough young, all except 6 have Condition
A, the fully rough coat. The 6 partial-rough young were produced in
four different litters, each by a different pair. They were as follows :

Parentage.

Young,
in appearance.

PR.

Sm.

R. (Sm.) $ mi X Sm 9 644 .

3
i

R. (Sm. ) cT 1178 X Sm. Q 1661

R. (Sm.) rf 1332 X Sm. 9 1338

R. (Sm.) 9 2034 X Sm. ^ 1147 ...

...

COAT CHARACTERS IN GUINEA PIGS AND RABBITS. 6l

The smooth animals used in these matings were all pure-bred except
9 1338, which had a hybrid, R. (Sm.), father, but a pure-bred smooth
mother. We can not assume, however, that these hybrid rough ani-
mals formed in general weak rough gametes, for R. (Sm.) cJ1 1111 had
in all, by smooth females, 13 rough offspring, but only in the mating
with 9 644 was a partial-rough individual produced ; again R. (Sm.)
c? 1 178 had rough offspring (6 in all) by three different smooth females,
but only in the mating with $ 1661 did he produce a partial-rough
animal. It would seem that the degree in which dominance is realized^
in the zygote is dependent upon the relative potency of the gametes]
uniting, and that potency is apt to be more variable in the gametes oi/
cross-bred than in that of pure-bred animals. If so, hybrid rough ani-
mals bred inter se, or with cross-bred rough or smooth individuals,
should produce an especially large proportion of partial-rough young.
The experiments made are as yet hardly extensive enough to give a
decisive answer to this question.

Fully rough hybrid, R. (-Szw.), animals bred inter se, have produced
in all 32 rough young, only one of which is a partial-rough. This one
was produced by the following mating :

R. (Sm.} J1 mi X R. (Sm.) 9 1438, produced i R., i PR., 2 Sm.

This same male, it will be remembered, produced a partial-rough indi-
vidual by the smooth female 644.

We may return now to the question whether the condition of unusual
potency in the smooth gametes of animals producing partial-rough
young is handed on to the posterity of those animals. If the partial-
rough character of hybrid animals is due simply to :mperfectly realized
dominance of the character borne by the dominant gamete, and if the
characters united in the zygote maintain their distinctness and segre-
gate with the same relative potencies, when gametes are formed by
the hybrid as they possessed before, then we should expect to get fully
rough, as well as partial-rough offspring, by mating partial-rough
animals either inter se or with rough animals. The result of mating
partial-rough with smooth animals would depend upon the relative
potency of the gametes formed by the smooth mates ; if none of their
gametes were unusually potent, then the offspring should be half fully
rough and half smooth, without partial-rough young. But if half
the gametes formed by the smooth animals are unusually potent, then
the offspring should be visibly as i R. to i PR. to 2 Sm.

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

Matings of these three sorts show the following results. The " ex-
pected " results are calculated on the hypothesis of persistent relative
potencies and full segregation of the rough and smooth characters.

Parentage.

Young, in appearance.

Observed.

Expected.

7?.

PR.

Sm.

It.

/Ve.

£M.

I.— PR. (Sm.} x PR. (Sm.} :

2
3

...

r? 1987 X 9 1268

Total

10
2

\\.-PR. (Sm.) X /?. (Sm.):

rP Il6o X Q OQI

...

Total

6
i

2
2

III.— PR. (Sm.*) X (Sm.):

...

;

o 'j™ ^ * *->w

i
i

...

Total

Si-"*

o-5*

10}

The agreement between the observed and the expected proportions
of fully rough (/?.) and partial-rough (PR.) offspring is sufficiently
close to lend support to the hypothesis of persistent gametic potency
from generation to generation. For on the alternative hypothesis, that
partial-rough hybrid animals form only partial-rough gametes and
smooth ones, no animals with the fully developed rough character
should be formed either in Group I or Group III of the foregoing
matings, but we see that young of this sort were produced in all these
groups. Yet it is probable that cross-breeding must be recognized as
an element which may modify the potencies of gametes, causing those
of a cross-bred individual to be less uniform in potency than those of
an animal not so crossed. Further experiments are needed to throw
light on this question.

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 63

Leaving out of consideration the degree in which the rough character
is developed in the coat of hybrid offspring, we may inquire how nearly
the Mendelian proportions of rough and smooth young are approxi-
mated. This will be plain from an examination of the following table :

Nature of mating.

Young.

Observed.

Expected.

Rough.

Smooth.

Rough.

Smooth.

Rough x rough

'35

^_437
6:

»9
159

~78~

54
H7

450

...

is
M7

~65~

Rough x rough (smooth). ..... . .

Rough x smooth

Rough (smooth) x rough (smooth).
Rough (smooth) x smooth

Total

6i5

As in the case of albinism, there are a few more recessive individuals
than are expected. This may be purely a chance result, or it may be
due to superior fertility of the recessive gametes ; but a different expla-
nation is suggested by an observation which will presently be stated.
The suggested explanation is that the excess of recessive individuals
may be due to latency of the rough character in certain individuals
apparently smooth. That such latency is possible is shown by the
sudden appearance in one of my families of smooth animals of a partial
rough individual, 9 969, having a well-marked crest extending from
the head to the middle of the back and conspicuous though imperfectly
developed side rosettes. The ancestors of this female for at least three
generations had been ordinary smooth individuals, though it is possible
that one or more of these may have had a slight crest in the region of
the shoulders; for I found that a brother of 9 969, viz, c? 971, had
such a crest, though it could be detected only by very careful examina-
tion. Unfortunately most of the ancestors had died before my attention
was called to this case. The father's skin, which I have, shows no
indication of a crest, though possibly it might have done so before it
was dried. The partial-rough 9 969 had by the brother mentioned,
c? 971, four young, one of which was a partial-rough like herself, the
others being smooth. Clearly, then, she both possessed the rough
character in a state of partial activity and was able to transmit it in
this condition to her offspring, though in her ancestors it must have
been present in a state of almost, if not quite complete latency. Very
likely suitable matings of the mother would restore the rough character
in certain of her offspring to a condition of full activity. Further
experiments with this animal are now in progress.

64 COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

If I have interpreted correctly the partial-rough animals obtained in
my experiments, they may be similar in nature to centripetally pig-
mented animals which lack some of the typical pigment patches, or
have only the eyes pigmented. A cross with albinos in which cen-
tripetal pigmentation is latent may serve to call the full set of coat spots
into activity, producing fully pigmented young, as we have already seen.
Similarly we may expect that crossing a partial-rough animal with a
smooth animal in which the rough character is fully latent would call the
rough character into full activity in the offspring. It remains, however,
to demonstrate the existence of smooth animals contain mgfu/ly latent
the rough character. I have as yet no evidence of their existence other
than the slight excess of smooth animals over the expected proportion.

HEREDITY OF LONG COAT.

The longest or contour hairs of ordinary domesticated guinea-pigs,
like those of the wild Cavia aperea, do not exceed a length of about 4
centimeters, but domesticated varieties with hair many times that length
are now well known. Where or when they originated is unknown ;
according to Cumberland they would seem to have been introduced into
England from France ; our American stocks probably came from Eng-
land. Long-haired smooth animals are commonly called "Angoras,"
and long-haired rough ones " Peruvians." But the two sets of charac-
ters (long vs. short, and smooth vs. rough) are entirely independent of
each other, as we shall see, so that for the present we shall consider only
the length of the coat, irrespective of whether it is rough or smooth.

My first experience with long-coated guinea-pigs was wholly un-
premeditated. In a family of short-haired guinea-pigs with which I
was experimenting and was practicing close-breeding, there appeared
several animals whose contour hairs were about twice as long as those
of their parents. These animals were all descended from a single pair
of short-haired guinea-pigs which had been purchased from a breeder,
but which I have no doubt had numbered among their ancestors a
long-haired animal. I found that the long-haired young bred true
inter se, which indicated that the long-haired character was recessive
in nature in relation to normal or short coat. This idea has been fully
confirmed by subsequent experiments, which were systematically insti-
tuted with the longest haired animals which I could secure.

In studying the inheritance of this character, it is necessary to rear
the young to an age of about two months before one can be sure
whether they are to have a normal coat, or one of more than normal
length. For at birth guinea-pigs of all sorts have hair of about the
same length (2 cm.). The coat of short-haired guinea-pigs reaches its
maximum length (about 4 cm.) not far from the age of one month, and

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 65

is then gradually shed. On the other hand, the hair of long-coated ani-
mals apparently is not shed at this period, but keeps on growing.
At two months of age it is 5 to 7 cm. long, at three months it is 6 to
9 cm. long. In the period from three to four months of age is another
critical stage. Animals which begin to shed their longest hair at this
period apparently do not acquire a longer coat at any period of their
subsequent life, but continue to have one whose maximum length is about
8 cm. But animals which pass the age of about four months without
shedding their longest hairs increase the length of their coat rapidly,
so that they may have a coat of 10 to 12 cm. maximum length when four
to five months old, and one of 14 to 16 cm. at six to seven months.

The acquisition of an abnormally long coat is due, accordingly, not
to unusually rapid growth of the hair, but to a peculiar mode of growth.
The hairs of a normal animal are thick and stiff in the middle, but taper
toward either end, somewhat like the quills of a porcupine. In the
middle of the hair the medulla is very thick, but it diminishes gradually
toward either end, where it is wanting altogether. A hair of this sort,
then, is the result of a definite growth cycle in the hair follicle, this
cycle covering apparently about two months' time, though my observa-
tions on this point are yet imperfect. When a hair is completed, after
attaining a length of about 4 cm. , a new one apparently is formed below
it and crowds the old one out. But in the long-haired animal, the
termination of a two-months growth cycle is frequently, if not regularly,
omitted. The hair is more nearly of uniform thickness throughout its
length, and is not narrowed to a base at the end of a single period of
two months, but grows without interruption during two, three, or four
such periods.

For this reason, as I have observed, hair measurements of long-
coated animals do not form a continuous series, but tend to group
themselves about mean maximal lengths as follows:

(1) 8 cm., double the length of normal or short coat, not attained
under three months of age.

(2) 12 cm., three times the length of short coat ; not attained under
five months of age.

(3) 16 cm., four times the length of short coat; not attained under
seven months of age.

Coats longer than this I have not had an opportunity to study, though
such are said to occur.

That long-haired animals bred inter sc produce only long-haired 1
young is shown by the following experiment : Six different long-haired
males (viz, 955, 1586, PI. 5, fig. 9, 1709, 2002, PI. I, fig. i, and 2060, /
pl- 3i %• 5) nave been mated with 19 different long-haired females, /
producing 49 young, all long-haired. There were produced also

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

ral young which died before their coat-character could be determined,
but all those which survived had hair much longer than that of the
ordinary short-haired animal.

Further evidence of the recessive nature of long coat is afforded by
matings between long-haired and short-haired animals. Long-haired
c? 2002 (PI. i, fig. i), whose coat measures 14-17 cm., according to
condition, has been mated with 14 different short-haired females, pro-
ducing 58 young, all of which have hair under 5 cm. in length.
Nevertheless, the influence of the long-haired parent is frequently seen
in increased softness of the coat, though this is, as a rule, not longer

rthan in the short-haired parent.

When two long-haired animals are mated, one of which has longer
hair than the other, the offspring have a coat like that of the shorter-
haired parent, usually without, though sometimes with, interspersed
hairs of greater length (PI. 6, fig. 1 1 ) . In other words there is a strong
tendency for the shorter coat to dominate in all cases over the longer one.
Accordingly, evidence for the dominance of short coat in crosses
with long coat is fairly complete ; the evidence for the occurrence of
segregation in the next generation is less satisfactory, for, though there
occur among the offspring good long-coated and good short-coated
individuals, others show a poor development of the long coat, and the
whole number of long-coated animals exceeds that expected. Thus
hybrids, Sh. (.£•)* in character, mated inter se^ have produced thus far
13 Sh. to 7 Z., where 3 Sh. to i L. are expected, and long-haired animals
when mated with hybrids, Sh. (Z.), for the most part children of <?
2002 (see PI. i, fig. i) have produced 36 Sh. to 65 Z,., or nearly twice
as many long-haired as short-haired young, where equality of the two
sorts is expected. These young have been born to seven different long-
haired parents, and the excess of long-haired offspring appears among
the young of all except two of them, as follows :

Parents.

Young.

Long-haired.

Short-haired {Long).

Short.

Long.

J» 206

<?73^-
c? 1586.

99
9 9
0 iGoS

5
5
o

9
o

»5

S
9

18
3
25

(? I7OQ

O 1770

C? 2002
O 2O4O. ..

9 9

d* 206?.. ..::::::::::::

Total

9 9

* L. = long-haired, Sh. = short-haired.

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 67

The departure here from the expected equality of the two classes is
too great and too uniform to be referable to chance. It would seem
probable, rather, that fewer gametes are formed bearing the character
short-coat than are expected. This maybe due either to failure of con-
trasted characters to segregate at gamete formation in certain cases, or
possibly to partial latency of the character short-hair in gametes which
transmit active the character long-hair, the resultant being an interme-
diate condition. Further experiments are needed to show which of these
two ideas is correct, though at present the former seems more probable.

Short-haired females obtained by mating a primary hybrid, Sh. (£.),
with a pure short-haired animal have, in several cases, been mated
with the long-haired males, 2002 (PL i, fig. i) and 2060 (PI. 3, fig. 5).
It is expected that half of such females will contain recessive the charac-
ter long-coat, and that half will be free from it, z'. e., will produce only
short-haired young. The outcome shows that 9 out of 12 females
tested contain recessive the character long-coat, for they produce long-
coated young. This is another bit of evidence that segregation
occurred less often than expected in the gametes of the primary hybrids,
though it throws no doubt on the uniformly dominant character of
short-coat. Again, the nine extracted hybrids, which contain reces-
sive the character long-coat, should, when mated with long-haired
animals, produce short-haired and long-haired young in equal numbers
if segregation occurs in every case where it is expected. In the mat-
ings in question there have been produced 10 short-haired young and 16
long-haired ones — further evidence that segregation is less frequent than
expected. It is true that these numbers are yet small, but their uniform
deviation in one direction from the expected result indicates that they are
significant. If so, we must recognize in this pair of characters full
Mendelian dominance, attended, however, with only partial Mendelian
segregation.

CORRELATION AMONG COAT-CHARACTERS.

In the preceding pages we have discussed separately the heredity of
three different pairs of alternative coat-characters which we have found
to conform more or less closely with Mendel's law of heredity. It
remains to inquire whether there is any correlation between one of
these pairs of characters and another, /. e., whether rough coat is
more often associated with white or with pigmented coat, with long
or with short coat, etc. An inquiry of this sort may be based upon ex-
periments made with the albino male 2002 (PI. i,fig. i), which possessed
the recessive members of two of the pairs of characters (viz, albinism
and long-coat), but the dominant member of the third pair (viz, rough
coat). It goes without saying that he was pure as regards albinism

68 COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

and long-coat, for all long-haired albinos are pure in these characters,
and as the result of experiment it may be stated that he was likewise
pure as regards the third or dominant character, rough coat. He was
mated with nine different pure pigmented, short-haired, and smooth
females, producing 29 young, all pigmented, short-haired, and rough
(see PI. 2, figs. 3 and 4), but, presumably, all containing the three cor-
responding recessive characters — albinism, long coat, and smooth coat.
He was likewise mated with three other pigmented short-haired,
smooth females, which differed from those previously mentioned only
in this, that they contained recessive albinism. They produced by
this mating 15 young, of which all, of course, were short-haired and
rough, but 9 were albinos and 6 pigmented. The latter should be
similar in nature to the 29 young of the matings previously described,
making in all, from matings of cT 2002, 35 young bearing the three
dominant characters, but supposed to contain the corresponding reces-
sives, /. e., to be hybrid in all three pairs of characters. A number of
these young which were tested by suitable matings proved to be of the
character expected. They have produced by different matings all the
eight possible visibly different combinations of characters, viz :

(i.) Pigmented rough short, P. R. Sh. (compare PI. 2, fig. 4).
(2.) Pigmented rough long, P. JR. L. (compare PI. 5, fig. 9).
(3.) Pigmented smooth short, P. Sm. Sh. (compare PI. 3, fig. 6).
(4.) Pigmented smooth long, P. Sm. L. (compare PI. 5, fig. jo).
(5.) Albino rough short, A. R. Sk. (compare PI. 2, fig. 3).
(6.) Albino rough long, A. JR. L. (compare PI. i, fig. i).
(7.) Albino smooth short, A. Sm. Sh. (compare PI. 4, fig. 7).
(8.) Albino smooth long, A. Sm. L. (compare PI. 4, fig. 8).

This result shows clearly that there is no necessary correlation be-
tween either character of one pair and either character of another pair.
On the hypothesis that each pair of characters is, in its transmission,
•wholly independent of the others, i. £., that no correlation whatever
exists among the pairs, we should expect triple hybrids, like the 35
young of c? 2002 already described, to produce, when mated inter se,
young visibly of the eight different sorts just enumerated in the following
proportions : 27 P. R. Sh., 9 P. R. L., 9 P. Sm. -SV&., 3 P. Sm. L.,
9 A. R. Sh., 3 A. R. L., 3 A. Sm. Sh., i A. Sm. L. It will be
noticed that at least 64 young must be reared to an age at which all
three coat-characters can be determined before we may expect all these
classes to be represented among the offspring. As yet only 8 young
have been reared to such an age, so that the results are scarcely signifi-
cant quantitatively, yet they indicate that the classes which are expected
to be largest will really be so, for the eight young are distributed thus :
4 P. R. Sh., 3 P. R. L., i P. Sm. Sh.

Certain of the triple-hybrid offspring of c? 2002 were mated in ways

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 69

other than inter se, which should give some indication of whether any
correlations exist among the three pairs of coat-characters. Thus
triple hybrids were mated with several pure pigmented, smooth, and
short-haired individuals, P. Sm. Sh., as follows:

Parents.

Young.

P. (A.) R (Sm.)
SA. (L).

P. Sm. Sh.

Rough.

Smooth.

cT 2036....
c? 2036 ...

9 972
9 973

3
3

2
I

CT 2O?7

9 906

c?2037

9 9 907 and 922

9QIC

O Q-I-I

c? 2°37

J 933"

9 9 2033-5
Total

c? 2061

»5

»3

All the young were, as expected, pigmented and short-haired. It is
expected, further, that half will be rough, half smooth, and this result
is approximated in the observed 15 rough to 13 smooth. The young,
though visibly of only two sorts, should be — on the hypothesis that no
correlations exist among the pairs of coat-characters— of eight different
sorts, all equally numerous. For the gametes of the triple hybrids
should be as follows : P. R. Sh. + P. R. L. + P. Sm. St. + P. Sm.
L. + A. R. Sh. + A. R. L. + A. Sm. Sh. + A. Sm. L. But the
gametes of the pure mates used should all be P. Sm. Sh., and the
zygotes formed (i. e., the characters present in the young) should be
with equal frequency of these eight sorts, parentheses indicating reces-
sives not visible :

5. P.(A.)R. (Sm.) SA.

6. P. (A.) R. (Sm.) SA. (L.)

7. P. (A.) Sm. SA.

8. P. 04.) Sm. SA. (L.)

1. P. R. (Sm.) SA.

2. P. R. (Sm.) SA. (L.)

3. P. Sm. SA.

4. P. Sm. SA. (L.)

The tests to determine what recessives each of the young possesses
are not yet complete, but thus far show the following distribution :

Class i. i (or 2) individuals. Class 5. i individual.

Class 2. i (or 2) individuals. Class 6. 2 (or 3) individuals.

Class 3. i individual. Class 7. None.

Class 4. None. Class 8. 4 individuals.

Considering that only ten individuals have as yet been fully tested,
their distribution among the classes is sufficiently wide to indicate the
probable absence of correlation among the three pairs of coat-characters.
The full details of the several tests on which this classification of indi-
viduals is based will be given in a subsequent report when a larger
number of tests has been completed.

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

EXPERIMENTS WITH RABBITS.

Certain experiments with rabbits, while less extensive than those
made with guinea-pigs, serve to confirm and extend some of the con-
clusions already reached.

CROSS BETWEEN TWO DIFFERENT TYPES OF ALBINOS.

Particularly instructive are the experiments with two different types
of albinos, the pure or wholly unpigmented type, and the Himalayan
or peripherally pigmented type.

A pair of Himalayans purchased of a dealer produced in two succes-
sive litters only good Himalayan young, 12 in number. Presumably,
therefore, they were pure.

A pure white female rabbit born of pigmented parents, but herself
wholly unpigmented, was likewise found to breed true when mated to
animals like herself. Crosses were now made between the two breeds,
as follows :

Parents.

Young.

Pure white.

Himalayan.

Dark

Himalayan.

Inter-
mediate.

Mosaic.

9 i
9 i

Total

C?6
<?7

i
3

All the young had pigmented extremities ; some were nearly or quite
as heavily pigmented as those of the Himalayan parent, but others had
pigmentation less heavy than that of the Himalayan parent ; these we
may call intermediate. Still others bore pigment on part only of the
areas which are pigmented in a pure Himalayan ; thus the foot might
be pigmented, but its toes pure white, or the center of the nose white,
with a sooty band lying above and to either side of it. Individuals such
as this we may call mosaics. Dominance of the peripheral pigmentation
was, accordingly, very imperfectly realized in the hybrid offspring.
Nevertheless, segregation of the two types of albino character involved
in this cross takes place with great regularity when the hybrids form
gametes, and this is true alike of all three sorts of young, the dark
Himalayan, the intermediate, and the mosaic, as the following matings
show.

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

Parents.

Young.

Hybrid.

Pure white.

Dark
Hima-
layan.

Inter-
mediate
mosaic.

Inter-
mediate.

Pure
white.

Dark HimaPn 9 24.

<? 56

0 i

2
2

Intermediate c? 19 ..
Total

9 SI

The observed result approximates equality of the pigmented and
unpigmented classes of albinos, as expected on the hypothesis that
segregation occurs in all cases. The one good Himalayan produced by
the intermediate cf 19 is noteworthy as showing that the full Himalayan
character was present in the hybrid and capable of segregation, though
seen in a partially dominated condition in the hybrid himself. Similar
cases occur in the matings enumerated below. Apparently cases of
this sort are like those of the imperfect rough guinea-pigs produced by
certain smooth animals in crosses with rough ones, which nevertheless
were capable of transmitting the rough character in its full intensity.

Further evidence of segregation of the Himalayan and pure white
types of albino character in the gametes of the hybrids is afforded by
mating these inter se, as the following experiments show.

Young.

Himalayan type.

Hybrid.

D. M.

I. M.

I. C? 19

I. 9 21

...

I. c? 19

D. 9 23

...

I. d1 19

D. 9 24

...

D. M. c? 20

I. 9 21

...

D. M. cT 20

I. 9 22

D. M. cT 20

D. 9 23

D. M. c? 20

I. 9 21

I. M. c?45

D. M. 9 108....

I. M. c?45

D. 9 109

Totals observer!

Totals expec

ted

4°*

13*

Explanation.— D. = fully pigmenttd or dark Himilayan ; D. M. = dark mosaic ; /. M. = inter-
mediate mosaic ; /. = intermediate ; P. = pure white.

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

The observed numbers of Himalayan and pure white young, it will
be noticed, approximate fairly well the numbers expected on the hy-
pothesis of complete segregation.

The possibility of transmuting the Himalayan type into the pure
white type by cross-breeding is suggested by an interesting experiment
performed by Raspail ( : 02). He set at liberty in a park frequented
by wild gray rabbits, a Russian female rabbit, which variety has
the Himalayan type of peripheral pigmentation. The female was
presumably fertilized by wild males, certainly by pure pigmented
animals, as the outcome indicates. In three successive litters she pro-
duced only self colored gray or black young, in numbers approxi-
mately equal, as follows :—

Gray.

Black.

Litter i .. .

Litter 2

Litter 3 . ...

Total

Certain of the gray hybrids bred inter se produced 5 gray young, 3
white ones [apparently Himalayan], and I pure white. Two of the
[Himalayan] whites, when mated inter se produced a litter of 4 [Hima-
layan] white young. Two of these in turn interbred produced 5 pure
white offspring.

This experiment I attempted to repeat, substituting for the wild
pigmented parent a pure reddish gray pigmented animal of the breed
known as the Belgian hare. A female Belgian hare was mated with
Himalayan cf 6, the original male employed in the experiments already
described. Three young were reared, a male and two females, of a
gray color somewhat darker than that of the mother, since it contained
more black pigment. The hybrids bred inter se have produced young
as follows : —

Young.

Parents.

Gray.

Black.

Hima-
layan.

<J 48 x 9 49

(A?)*

c?48 x $ 50
cT 48 x 9 5°

5
5

Total

' Gray or black, died early.

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 73

It is expected that one-fourth of the young will be albinos, and this
proportion is approximated. But all six of the albinos thus far ob-
tained have pigmented extremities, as did their Himalayan grand-
father. No pure whites have been produced. In this respect my
results differ from those of Raspail. It is true that the intensity of
pigmentation of these extracted Himalayans varies considerably, as
does that of the pigmented young. There are dark and light Hima-
layans, just as there are dark and light grays, among the offspring.
Cross-breeding has in this case, as in others, been the cause of variation
within the types of the parents, but I have no evidence as yet that it
can completely remove the pigmentation from the Himalayan albino
type, thus converting it into a pure albino. Nevertheless further ex-
periments may lead to this result, yet I hardly expect it in view of the
distinctness shown by the Himalayan and the pure albino types in the
experiments already described. I suspect, rather, that the Russian
female, with which Raspail began his experiments, was in reality a
hybrid, like those which I have described on page 70, in which pure
albinism was recessive. Raspail says concerning her, page 172 :

La femelle de Lapin russe qui m'a servi pour mes experiences, n'e*tait pas de
race pure : le museau, I'extre'mit^ des pattes, les oreilles et le dessus de la queue
e*taient d'un noir moins franc et moins veloute'; sa taille etait notablement plus
forte et ses yeux rouges indiquaient qu'elle tournait a Palbinisme.

This explicit statement and description certainly favors the idea that
she was a cross-bred with a pure albino race, which, if true, would
fully explain the occurrence of pure albinos in her offspring of genera-
tion F2, without necessitating the conclusion that the peripherally
pigmented type of albino had been transmuted into the unpigmented
type by cross-breeding.

HEREDITY OF LONG OR "ANGORA" COAT.

This character is in rabbits, as in guinea-pigs, a recessive Mendelian
character. Dominance and segregation both appear to be complete in
crosses between normal (or short-haired) and angora (or long-haired)
rabbits. I have observed in this case neither formation of intermediates,
i. <?., of inferior long-haired specimens, nor deviation from the expected
proportions of long-haired and short-haired individuals, of which con-
ditions there were some indications in guinea-pigs. But in one or two
cases I have thought that 1 could recognize in hybrids a greater soft-
ness of the coat, just as in guinea-pigs which are cross-breds between
long-haired and short-haired races.

The numbers of young thus far reared are small, and not much
weight is to be attached to them, so far as quantitative results are con-
cerned.

74 COAT CHARACTERS IN GUIVKA-PIGS AND RABBITS.

In detail the matings made are as follows :

Parents.

Young.

Long.

Short.

Long.

c?N .

$ 9 17, 18, and 28..
6 Lop

10
8

:::

tf 4C

Total

18*

...

Short (LJ

Short (L.)

Short.

Long.

9 i

Brother

2
2

9 i ....

C? 20 (son)

921

Total

(? 20

15+

Long.

Short (L.)

Short.

Long.

r? 4<C

9 108

O 4o
r? -jc

9 IOQ...

Total

• Expected, all short. t Expected, 3 short : i long. t Expected, i short : i long.

EXPLANATION — L. = long-haired or angora. Parentheses indicate recessive characters not visible.

HEREDITY OF LOP-EARS.

Some experiments are likewise in progress with the inheritance of
the large or lop-eared character in rabbits, but these are hardly far
enough advanced to make their outcome certain. The young produced
by a cross between two breeds having ears of different relative size
themselves have ears of an intermediate size. In other words, there is
no evidence of dominance. A second generation of young has been
obtained, but is not yet fully grown ; apparently they too will have ears
of an intermediate character. If so, we may conclude that segregation
as well as dominance is wanting in this case, which would seem to be
one of blended or non-Mendelian inheritance, similar to that of the
willow-hybrids studied by Wichura and that of the Hieracium hybrids
of Mendel ('70).

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 75

SUMMARY.

(1) There occur among domesticated guinea-pigs three pairs of alter-
native coat-characters which conform in their inheritance to Mendel's
law of heredity. These are (i) albinism, which is recessive with respect
to pigmented coat ; (2) smooth coat, which is recessive with respect to
rough coat ; and (3) long coat, which is recessive with respect to short
coat. Two of the recessive characters, viz, albinism and long coat, are \
doubtless characters of comparatively recent origin, which have made 1
their appearance since the guinea-pig was domesticated. The third
recessive character, smooth coat, is undoubtedly ancestral, and curiously
enough is regularly dominated by rough coat, a character probably of
recent origin, for a cavy bearing rosettes like those of the " Abyssinian "
guinea-pig is unknown in a wild state. This indicates that ancestral
characters are not necessarily dominant over new characters in heredity.
The three pairs of characters are probably wholly uncorrelated.

(2) In rabbits occur two of the three pairs of alternative coat-charac»
ters which are found in guinea-pigs. Here, too, albinism and long or
" angora" coat are recessive characters. A resetted or rough coat is
unknown in rabbits.

(3) A sharp distinction must be made between characters which
are recessive and those which are latent. Recessive characters dis-
appear from an individual in which they are associated with the
corresponding dominant character, yet they reappear distinct in half
the gametes formed by that individual ; latent characters are characters
normally dominant, which have disappeared in recessive gametes
beyond hope of recall, except under conditions of cross-breeding which
are in most cases not entirely clear. Albino gametes transmit in a
latent condition both specific pigment characters and specific color-
patterns. These latent characters can be brought into activity only by

cross-breeding with a pigmental animal. The rough coat-character \
I may likewise become almost completely, if not quite completely, latent |
y in smooth animals. These facts indicate a possible explanation of the
observed slight excess of recessives over the Mendelian expectation in
cases involving one or the other of these two pairs of characters. In
the case of the long -vs. short pair of characters, an excess of recessives .
and the occurrence simultaneously of intermediates in generation F,,
but not in Fn are more probably due to imperfect segregation than to
latency of the dominant character. It is possible, however, that/ar/tf£
latency and imperfect segregation are related, if not identical phenomena.

76 COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

/ (4) Some recessive individuals are prepotent, for their gametes,

' when united with those of ordinary dominants, produce young of an

intermediate character. These intermediates, however, have the power

/ to transmit the full dominant character in matings with recessive incli-

/ viduals. There is reason to believe, accordingly, that the dominant

V character is in such cases, not partially latent, but partially dominated.

If so, we have in cases if this sort something remotely resembling

the alternative dominance seen in certain of the crosses among silk

moths made by Coutagne ( : 02).

/ (5) The lop-eared condition in rabbits is probably a non-Mendelian
/character in its relation to normal ear; for the children and grand-
ychildren produced by crosses are apparently alike intermediate in
character.

(6) A cross between two different types of albino rabbits, Himalayan \
and pure white, shows imperfect dominance of the Himalayan character^/
in the offspring, but complete segregation among their gametes.

(7) Cross-breeding between dominant and recessive individual*
may lead to the production of new sorts of individuals in a variety of
ways, e. £., (i) by producing new combinations among different pairs
of alternative characters, as among the children of triple-hybrid guinea-
pigs ; (2) probably by causing a complex character, like the agouti coat
of guinea-pigs, to break up into its elements — black, chocolate, and yel-
low— one or more of the elementary pigment characters either becoming
latent or passing bodily out of the gamete ; (3) by the coming into
activity of elements of the dominant character which were latent in
recessive gametes, as black latent in albino guinea-pigs or in Himalayan
rabbits (see next report) ; (4) by inducing variability in the intensity of
characters, quite aside from resolution and recombination of characters,
as when red cross-bred with black produces a very light shade of red,
e. g., yellow or cream.

COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 77

BIBLIOGRAPHY.

Allen, G. M.

: 04. The heredity of coat color in mice. Proc. Amer. Acad. Arts and

Sci., vol. 40, no. 2, pp. 61-163, 7 figs.
Bateson, W.

:o2. Mendel's principles of heredity, a defence. With a translation of
Mendel's original papers on hybridisation, xiv -+• 212 pp. Cam-
bridge. [England. Contains bibliography and portrait of Mendel.]
Bateson, W.

: 03. The present state of knowledge of colour-heredity in mice and rats.

Proc. Zool. Soc. London, 1903, vol. 2, pp. 71-99.
Castle, W. E.

103. Mendel's law of heredity. Proc. Amer. Acad. Arts and Sci., vol. 38,

no. 18, pp. 535-548.
Castle, W. E.

103^. Mendel's law of heredity. Science, n. s., vol. 18. No. 456, pp.
396-406, September 25, 1903. [A reprint of the foregoing, with
some additions and corrections.]
Castle, W. E.

:o3b. The laws of heredity of Gallon and Mendel, and some laws gov-
erning race improvement by selection. Proc. Amer. Acad. Arts
and Sci., vol. 39, no. 8, pp. 223-242.
Castle, W. E.

1030. The heredity of " Angora" coat in mammals. Science, n. s., vol.

1 8, no. 467, pp. 760-761, December n, 1903.
Castle, W. E., and Allen, G. M.

103. The heredity of albinism. Proc. Amer. Acad. Arts and Sci., vol. 38,

pp. 603-622.
Coutagne, G.

: 02. Recherches exp6rimentales sur 1'he're'dite' chez les vers a soie. Bull.

Sci. France et Belg. , torn. 37, pp. 1-194, P'S- I-9-
Cuenot, L.

-.03. L'he're'dite de la pigmentation chez les souris. (2m* note.) Arch.
Zool. Expdr. et Ge"n., se"r. 4, torn, i, Notes et Revue, pp. xxxiii-xli.
Cuenot, L.

-.04. L'he're'dite' de la pigmentation chez les souris. (3me note.) Arch.

Zool. Expe"r. et Ge"n., ser. 4, torn. 2, Notes et Revue, pp. xlv -Ivi.
Cumberland, C.

[Date?] The guinea-pig, or domestic cavy, for food, fur, and fancy. 100 pp.,

illus., London. L. Upcott Gill.
Darbishire, A. D.

103. Third report on hybrids between waltzing mice and albino races.

Biometrika, vol. 2, pt. 3, pp. 282-285.
Darbishire, A. D.

: 04. On the result of crossing Japanese waltzing with albino mice. Biome-
trika, vol. 3, pt. i, pp. 1-51, 8 figs.

'97'. The average contribution of each several ancestor to the total heritage
of the offspring. Proc. Roy. Soc., London, vol. 61, pp. 401-413.

Guaita, G. von.

'98. Versuche mit Kreuzungen von verschiedenen Rassen des Hausmaus.
Ber. naturf. Gesellsch. zu Freiburg, Bd. 10, pp. 3I7-332-

78 COAT CHARACTERS IN GUINEA-PIGS AND RABBITS.

Guaita, G. von.

:oo. Zweite Mittheilungiiber Versuche mit Kreuzungen von verschiedenen
Rassen des Hausmaus. Ber. naturf. Gesellsch. zu Freiburg, Bd. n,
pp. 131-138, 3 Taf.
Haacke, W.

'95. Ueber Wesen,Ursachen und Vererbung von Albinismus und Scheckung,
und iiber deren Bedeutung fur vererbungstheoretische und entwick-
lungs-mechanische Fragen. Biol. Centralbl., Bd. 15, pp. 44-78.
Loeb, L.

'97. Ueber Transplantation von weisser Haul auf einem Defect in schwarzer
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Mech., Bd 6, pp. 1-44, 3 Taf., 2 Fig.
Mendel. G.

'66. Versuche iiber Pflanzenhybriden. Verh. Naturf. Vereins in Briinn,

Bd. 4, Abh., pp. 3-47. [Translation in Bateson, :o2.]
Mendel, G.

'70. Ueber einige aus kiinstlicher Befruchtung gewonnenen Hieracium-
Kastarde. Verh. Naturf. Vereins in Briinn, Bd. 8, Abh., pp. 26-31.
[Translation in Bateson. :o2.]
Pearson, K.

104. A Mendelian's view of the law of ancestral inheritance. Biometrika,

vol. 3, pt. i, pp. 109-112.
Raspail. X.

: 02. Note surune race de lapins albinos issue du croisement d'une femelle
tie lapin russe et d'un male garenne (Lepus cuniculus). Bull. Soc.
Nat. d'Acclimatation de France, 49me ann6e, pp. 170-175.
Shaw, T.

103. The study of breeds in America. Cattle, sheep, and swine, xvi -)•
371 pp., illus. Orange Judd Co., N. Y.

PLATE 1.

FIG. 1.— A LONG-HAIRED, ROUGH, ALBINO GUINEA-PIG, C? 2002.

Pure (*'. e., homozygous) as regards all three coat-characters, two of which are recessive
in nature, one dominant. Fanciers' name for all animals of this appearance, whether
homozygous or heterozygous in character, White Peruvian.

FIG. 2.— A SHORT-HAIRED, SMOOTH, RED GUINEA-PIG, 9 1355.

Pure in respect to two of its coat-characters, viz, smooth coat and pigtnented coat, but
heterozygous as regards the third, since it contains recessive long coat, though its own
coat is no longer than that of most pure short-haired animals. Toes of right fore foot whUe.
Fanciers' name for animals of this appearance, whether or not homozygous, Red Enghsh.

PLME 2.

FIG. 3.— A SHORT-HAIRED, ROUGH, ALBINO GUINEA-PIG, C? 1095.
Son of c? 2002 (fig. 1, pi. 1) and of Red English $ 3, which contained recessive
albinism, but was otherwise homozygous (compare fig. 2, pi. 1). This animal is a double
heterozygote, containing recessive the two characters, long coat and smooth coat. As
regards albinism, it is, of course, pure. Fanciers' name for all animals of this appearance,
White Abyssinian.

FIG. 4.— A SHORT-HAIRED, ROUGH, BLACK-RED PIGMENTED GUINEA-PIG, O 2037.

Son of cf 2002 (fig. 1, pi. 1) and of pure Red English ? 755 (compare fig. 2, pi. 1).
A triple heterozygote containing recessive the three characters, long coat, smooth coat,
and albino coat. The^black pigment seen in this animal's coat was inherited, not from
the red pigmented mother, but from the albino father. Unfortunately black areas are
scarcely distinguishable from red ones in the figure. Fanciers' name for all animals of
this appearance, Tortoise-shell Abyssinian.

PLATE 3.

FIG. 5.— A LONG-HAIRED, SMOOTH, ALBINO GUINEA-PIG, $ 2060.

From inspection alone of this animal, one may know that it is pure as regards coat-
characters, since it manifests the three which are by nature recessive. Fanciers tiutnt ,
White Angora.

FIG. 6.— A SHORT-HAIRED, SMOOTH, RED-BLACK PIGMENTED GUINEA-PIG.

The parents were both triple heterozygotes (compare fig. 4, pi. 2). This animal is. of
course, pure as regards smooth coat, but whether it contains the two recessive characters
which it does not manifest, can be determined only by breeding tests. In this figure, as
in fig. 4, black areas unfortunately are indistinguishable from red ones. Fanciers' name
for all animals of this appearance, whether pure or heterozygous, Tortoise-shell English.

PLATE 4.

FIG. 7.— A SHORT-HAIRED, SMOOTH, ALBINO GUINEA-PIG, * 1499.

Daughter of two albino parents, viz, 9 991, a double heterozygote like •$ 1095 (fig. 4,
pL 2), and $ 635, a pure short-haired, smooth animal. We know without experimental
test that this animal is pure as regards the two recessive characters which it manifests,
smooth coat and albinism, but breeding tests are necessary to show whether or not it con-
tains recessive the character long coat. This animal has been found to form prepotent
smooth gametes. Fanciers' name for all animals of this appearance, White English.

FI3. 8.-A LONG-HAIRED, SMOOTH, ALBINO GUINEA-PIG, * 1756.
Daughter of 3 2060 (fig. 5. pi. 3) and of ? 993, which was a double heterozygote like
C? 1095 (fig. 3. pi. 2). This animal, like C? 2060, being a triple recessive, is pure as regards
all three coat-characters. Fanciers' name. White Angora.

PLATE 6.

FIG. 11. — * PARTIALLY LONG-HAIRED, ROUGH, AND SPOTTED GUINEA-PIG, 9 2258.

Daughter of two triple-heterozygotes (compare fig. 4, pi. 2). The long-haired dial-
acter is imperfectly developed in this animal, only part of the hair being long as in the
Peruvian grandparent, cJ* 2002 (fig. 1, pi. 1).

FIG. 12.— A TRIPLE HETEROZYGOTE, C?1989a.

(Compare fig. 4, pi. 2.) Son of cf 2002 (fig. 1, pi. 1) and of black-eyed white 9
2005, which is also a prepotent smooth animal. The coat is in part pigmented; the
rough character is imperfectly developed, showing only one pair of the rosettes which are
typically formed (compare figs. 3 and 4, pi. 2).

VSV9HV9 V1NVS o

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