DOMESTIC RABBITS.
DOMESTIC RABBITS DESCENDED FROM THE COMMON WILD RABBIT--ANCIENT
DOMESTICATION--ANCIENT SELECTION--LARGE LOP-EARED RABBITS--VARIOUS
BREEDS--FLUCTUATING CHARACTERS--ORIGIN OF THE HIMALAYAN BREED--CURIOUS
CASE OF INHERITANCE--FERAL RABBITS IN JAMAICA AND THE FALKLAND
ISLANDS--PORTO SANTO FERAL RABBITS--OSTEOLOGICAL
CHARACTERS--SKULL--SKULL OF HALF-LOP RABBITS--VARIATIONS IN THE SKULL
ANALOGOUS TO DIFFERENCES IN DIFFERENT SPECIES OF
HARES--VERTEBRAE--STERNUM--SCAPULA--EFFECTS OF USE AND DISUSE ON THE
PROPORTIONS OF THE LIMBS AND BODY--CAPACITY OF THE SKULL AND REDUCED
SIZE OF THE BRAIN--SUMMARY ON THE MODIFICATIONS OF DOMESTICATED
RABBITS.
All naturalists, with, as far as I know, a single exception, believe that
the several domestic breeds of the rabbit are descended from the common
wild species; I shall therefore describe them more carefully than in the
previous cases. Professor Gervais[247] states "that the true wild rabbit is
smaller than the domestic; its proportions are not absolutely the same; its
tail is smaller; its ears are shorter and more thickly clothed with hair;
and these characters, without speaking of colour, are so many indications
opposed to the opinion which unites these animals under the same specific
denomination." Few naturalists will agree with this author that such slight
differences are sufficient to separate as distinct species the wild and
domestic rabbit. How extraordinary it would be, if close confinement,
perfect tameness, unnatural food, and careful breeding, all prolonged
during many generations, had not produced at least some effect! The tame
rabbit has been domesticated from an ancient period. Confucius ranges
rabbits among animals worthy to be sacrificed to the gods, and, as he
prescribes their multiplication, they were probably at this early period
domesticated in China. They are mentioned by several of the classical
writers. {104} In 1631 Gervaise Markham writes, "You shall not, as in other
cattell, looke to their shape, but to their richnesse, onely elect your
buckes, the largest and goodliest conies you can get; and for the richnesse
of the skin, that is accounted the richest which hath the equallest mixture
of blacke and white haire together, yet the blacke rather shadowing the
white; the furre should be thicke, deepe, smooth, and shining; ... they are
of body much fatter and larger, and, when another skin is worth two or
three pence, they are worth two shillings." From this full description we
see that silver-grey rabbits existed in England at this period; and, what
is far more important, we see that the breeding or selection of rabbits was
then carefully attended to. Aldrovandi, in 1637, describes, on the
authority of several old writers (as Scaliger, in 1557), rabbits of various
colours, some "like a hare," and he adds that P. Valerianus (who died a
very old man in 1558) saw at Verona rabbits four times bigger than
ours.[248]
From the fact of the rabbit having been domesticated at an ancient period,
we must look to the northern hemisphere of the Old World, and to the warmer
temperate regions alone, for the aboriginal parent-form; for the rabbit
cannot live without protection in countries as cold as Sweden, and, though
it has run wild in the tropical island of Jamaica, it has never greatly
multiplied there. It now exists, and has long existed, in the warmer
temperate parts of Europe, for fossil remains have been found in several
countries.[249] The domestic rabbit readily becomes feral in these same
countries, and when variously coloured kinds are turned out they generally
revert to the ordinary grey colour.[250] The wild rabbits, if taken young,
can be domesticated, though the process is generally very troublesome.[251]
The various {105} domestic races are often crossed, and are believed to be
perfectly fertile together, and a perfect gradation can be shown to exist
from the largest domestic kinds, having enormously developed ears, to the
common wild kind. The parent-form must have been a burrowing animal, a
habit not common, as far as I can discover, to any other species in the
large genus Lepus. Only one wild species is known with certainty to exist
in Europe; but the rabbit (if it be a true rabbit) from Mount Sinai, and
likewise that from Algeria, present slight differences; and these forms
have been considered by some authors as specifically distinct.[252] But
such slight differences would aid us little in explaining the more
considerable differences characteristic of the several domestic races. If
the latter are the descendants of two or more closely allied species, all,
excepting the common rabbit, have been exterminated in a wild state; and
this is very improbable, seeing with what pertinacity this animal holds its
ground. From these several reasons we may infer with safety that all the
domestic breeds are the descendants of the common wild species. But from
what we hear of the late marvellous success in rearing hybrids between the
hare and rabbit,[253] it is possible, though not probable, from the great
difficulty in making the first cross, that some of the larger races, which
are coloured like the hare, may have been modified by crosses with this
animal. Nevertheless, the chief differences in the skeletons of the several
domestic breeds cannot, as we shall presently see, have been derived from a
cross with the hare.
There are many breeds which transmit their characters more or less truly.
Every one has seen the enormous lop-eared rabbits exhibited at our shows;
various allied sub-breeds are reared on the Continent, such as the
so-called Andalusian, which is said to have a large head with a round
forehead, and to attain a greater size than any other kind; another large
Paris breed is named the Rouennais, and has a square head; the so-called
Patagonian rabbit has remarkably short ears and a large round head.
Although I have not seen all these breeds, I feel some doubt about there
being any marked difference in the {106} shape of their skulls.[254]
English lop-eared rabbits often weigh 8 lbs. or 10 lbs., and one has been
exhibited weighing 18 lbs.; whereas a full-sized wild rabbit weighs only
about 31/4 lbs. The head or skull in all the large lop-eared rabbits examined
by me is much longer relatively to its breadth than in the wild rabbit.
Many of them have loose transverse folds of skin or dewlaps beneath the
throat, which can be pulled out so as to reach nearly to the ends of the
jaws. Their ears are prodigiously developed, and hang down on each side of
their faces. A rabbit has been exhibited with its two ears, measured from
the tip of one to the tip of the other, 22 inches in length, and each ear
was 5-3/8 inches in breadth. In a common wild rabbit I found that the
length of the two ears, from tip to tip, was 7-5/8 inches, and the breadth
only 1-7/8 inch. The great weight of the body in the larger rabbits, and
the immense development of their ears, are the qualities which win prizes,
and have been carefully selected.
The hare-coloured, or, as it is sometimes called, the Belgian rabbit,
differs in nothing except colour from the other large breeds; but Mr. J.
Young, of Southampton, a great breeder of this kind, informs me that the
females, in all the specimens examined by him, had only six mammae; and this
certainly was the case with two females which came into my possession. Mr.
B. P. Brent, however, assures me that the number is variable with other
domestic rabbits. The common wild rabbit always has ten mammae. The Angora
rabbit is remarkable from the length and fineness of its fur, which even on
the soles of the feet is of considerable length. This breed is the only one
which differs in its mental qualities, for it is said to be much more
sociable than other rabbits, and the male shows no wish to destroy its
young.[255] Two live rabbits were brought to me from Moscow, of about the
size of the wild species, but with long soft fur, different from that of
the Angora. These Moscow rabbits had pink eyes and were snow-white,
excepting the ears, two spots near the nose, the upper and under surface of
the tail, and the hinder tarsi, which were blackish-brown. In short, they
were {107} coloured nearly like the so-called Himalayan rabbits, presently
to be described, and differed from them only in the character of their fur.
There are two other breeds which come true to colour, but differ in no
other respect, namely silver-greys and chinchillas. Lastly, the Nicard or
Dutch rabbit may be mentioned, which varies in colour, and is remarkable
from its small size, some specimens weighing only 11/4 lb.; rabbits of this
breed make excellent nurses for other and more delicate kinds.[256]
Certain characters are remarkably fluctuating, or are very feebly
transmitted by domestic rabbits: thus, one breeder tells me that with the
smaller kinds he has hardly ever raised a whole litter of the same colour:
with the large lop-eared breeds "it is impossible," says a great
judge,[257] "to breed true to colour, but by judicious crossing a great
deal may be done towards it. The fancier should know how his does are bred,
that is, the colour of their parents." Nevertheless, certain colours, as we
shall presently see, are transmitted truly. The dewlap is not strictly
inherited. Lop-eared rabbits, with their ears hanging flat down on each
side of the face, do not transmit this character at all truly. Mr. Delamer
remarks that, "with fancy rabbits, when both the parents are perfectly
formed, have model ears, and are handsomely marked, their progeny do not
invariably turn out the same." When one parent, or even both, are oar-laps,
that is, have their ears sticking out at right angles, or when one parent
or both are half-lops, that is, have only one ear dependent, there is
nearly as good a chance of the progeny having both ears full-lop, as if
both parents had been thus characterized. But I am informed, if both
parents have upright ears, there is hardly a chance of a full-lop. In some
half-lops the ear that hangs down is broader and longer than the upright
ear;[258] so that we have the unusual case of a want of symmetry on the two
sides. This difference in the position and size of the two ears probably
indicates that the lopping of the ear results {108} from its great length
and weight, favoured no doubt by the weakness of the muscles consequent on
disuse. Anderson[259] mentions a breed having only a single ear; and
Professor Gervais another breed which is destitute of ears.
[Illustration: Fig. 5.--Half-lop Rabbit. (Copied from E. S. Delamer's
work.)]
The origin of the Himalayan breed (sometimes called Chinese, or Polish, or
Russian) is so curious, both in itself, and as throwing some light on the
complex laws of inheritance, that it is worth giving in detail. These
pretty rabbits are white, except their ears, nose, all four feet, and the
upper side of tail, which are all brownish-black; but as they have red
eyes, they may be considered as albinoes. I have received several accounts
of their breeding perfectly true. From their symmetrical marks, they were
at first ranked as specifically distinct, and were provisionally named _L.
nigripes_[260] Some good observers thought that they could detect a
difference in their habits, and stoutly maintained that they formed a new
species. Their origin is now well known. A writer, in 1857,[261] stated
that he had produced Himalayan rabbits in the following manner. But it is
first necessary briefly to describe two other breeds: silver-greys or
silver-sprigs generally have black heads and legs, and their fine grey fur
is interspersed with numerous black and white long hairs. {109} They breed
perfectly true, and have long been kept in warrens. When they escape and
cross with common rabbits, the product, as I hear from Mr. Wyrley Birch, of
Wretham Hall, is not a mixture of the two colours, but about half take
after the one parent, and the other half after the other parent. Secondly,
chinchillas or tame silver-greys (I will use the former name) have short,
paler, mouse or slate-coloured fur, interspersed with long, blackish,
slate-coloured, and white hairs.[262] These rabbits breed perfectly true.
Now, the writer above referred to had a breed of chinchillas which had been
crossed with the common black rabbit, and their offspring were either
blacks or chinchillas. These latter were again crossed with other
chinchillas (which had also been crossed with silver-greys), and from this
complicated cross Himalayan rabbits were raised. From these and other
similar statements, Mr. Bartlett[263] was led to make a careful trial in
the Zoological Gardens, and he found that by simply crossing silver-greys
with chinchillas he could always produce some few Himalayans; and the
latter, notwithstanding their sudden origin, if kept separate, bred
perfectly true.
The Himalayans, when first born, are quite white, and are then true
albinoes; but in the course of a few months they gradually assume their
dark ears, nose, feet, and tail. Occasionally, however, as I am informed by
Mr. W. A. Wooler and the Rev. W. D. Fox, the young are born of a very pale
grey colour, and specimens of such fur were sent me by the former
gentleman. The grey tint, however, disappears as the animal comes to
maturity. So that with these Himalayans there is a tendency, strictly
confined to early youth, to revert to the colour of the adult silver-grey
parent-stock. Silver-greys and chinchillas, on the other hand, present a
remarkable contrast in their colour whilst quite young, for they are born
perfectly black, but soon assume their characteristic grey or silver tints.
The same thing occurs with grey horses, which, as long as they are foals,
are generally of a nearly black colour, but soon become grey, and get
whiter and whiter as they grow older. Hence the usual rule is that
Himalayans are born white and afterwards become in certain parts of their
bodies dark-coloured; whilst {110} silver-greys are born black and
afterwards become sprinkled with white. Exceptions, however, and of a
directly opposite nature, occasionally occur in both cases. For young
silver-greys are sometimes born in warrens, as I hear from Mr. W. Birch, of
a cream-colour, but these young animals ultimately become black, The
Himalayans, on the other hand, sometimes produce, as is stated by an
experienced amateur,[264] a single black young one in a litter; but such,
before two months elapse, become perfectly white.
To sum up the whole curious case: wild silver-greys may be considered as
black rabbits which become grey at an early period of life. When they are
crossed with common rabbits, the offspring are said not to have blended
colours, but to take after either parent; and in this respect they resemble
black and albino varieties of most quadrupeds, which often transmit their
colours in this same manner. When they are crossed with chinchillas, that
is, with a paler sub-variety, the young are at first pure albinoes, but
soon become dark-coloured in certain parts of their bodies, and are then
called Himalayans. The young Himalayans, however, are sometimes at first
either pale grey or completely black, in either case changing after a time
to white. In a future chapter I shall advance a large body of facts showing
that, when two varieties are crossed both of which differ in colour from
their parent-stock, there is a strong tendency in the young to revert to
the aboriginal colour; and what is very remarkable, this reversion
occasionally supervenes, not before birth, but during the growth of the
animal. Hence, if it could be shown that silver-greys and chinchillas were
the offspring of a cross between a black and albino variety with the
colours intimately blended--a supposition in itself not improbable, and
supported by the circumstance of silver-greys in warrens sometimes
producing creamy-white young, which ultimately become black--then all the
above-given paradoxical facts on the changes of colour in silver-greys and
in their descendants the Himalayans would come under the law of reversion,
supervening at different periods of growth and in different degrees, either
to the original black or to the original albino parent-variety.
{111}
It is, also, remarkable that Himalayans, though produced so suddenly, breed
true. But as, whilst young, they are albinoes, the case falls under a very
general rule; for albinism is well known to be strongly inherited, as with
white mice and many other quadrupeds, and even with white flowers. But why,
it may be asked, do the ears, tail, nose, and feet, and no other part of
the body, revert to a black colour? This apparently depends on a law, which
generally holds good, namely, that characters common to many species of a
genus--and this, in fact, implies long inheritance in common from the
ancient progenitor of the genus--are found to resist variation, or to
reappear if lost, more persistently than the characters which are confined
to the separate species. Now, in the genus Lepus, a large majority of the
species have their ears and the upper surface of the tail tinted black; but
the persistence of these marks is best seen in those species which in
winter become white: thus, in Scotland the _L. variabilis_[265] in its
winter dress has a shade of colour on its nose, and the tips of its ears
are black: in the _L. tibetanus_ the ears are black, the upper surface of
the tail greyish-black, and the soles of the feet brown: in _L. glacialis_
the winter fur is pure white, except the soles of the feet and the points
of the ears. Even in the variously-coloured fancy rabbits we may often
observe a tendency in these same parts to be more darkly tinted than the
rest of the body. Thus, as it seems to me, the appearance of the several
coloured marks on the Himalayan rabbit, as it grows old, is rendered
intelligible. I may add a nearly analogous case: fancy rabbits very often
have a white star on their foreheads; and the common English hare, whilst
young, generally has, as I have myself observed, a similar white star on
its forehead.
When variously coloured rabbits are set free in Europe, and are thus placed
under their natural conditions, they generally revert to the aboriginal
grey colour; this may be in part due to the tendency in all crossed
animals, as lately observed, to revert to their primordial state. But this
tendency does not always prevail; thus silver-grey rabbits are kept in
warrens, and remain true though living almost in a state of nature; but a
{112} warren must not be stocked with both silver-greys and common rabbits;
otherwise "in a few years there will be none but common greys
surviving."[266] When rabbits run wild in foreign countries, under
different conditions of life, they by no means always revert to their
aboriginal colour. In Jamaica the feral rabbits are described as
"slate-coloured, deeply tinted with sprinklings of white on the neck, on
the shoulders, and on the back; softening off to blue-white under the
breast and belly."[267] But in this tropical island the conditions were not
favourable to their increase, and they never spread widely; and, as I hear
from Mr. R. Hill, owing to a great fire which occurred in the woods, they
have now become extinct. Rabbits during many years have run wild in the
Falkland Islands; they are abundant in certain parts, but do not spread
extensively. Most of them are of the common grey colour; a few, as I am
informed by Admiral Sulivan, are hare-coloured, and many are black, often
with nearly symmetrical white marks on their faces. Hence, M. Lesson
described the black variety as a distinct species, under the name of _Lepus
magellanicus_, but this, as I have elsewhere shown, is an error.[268]
Within recent times the sealers have stocked some of the small outlying
islets in the Falkland group with rabbits; and on Pebble Islet, as I hear
from Admiral Sulivan, a large proportion are hare-coloured, whereas on
Rabbit Islet a large proportion are of a bluish colour which is not
elsewhere seen. How the rabbits were coloured which were turned out on
these islets is not known.
The rabbits which have become feral on the island of Porto Santo, near
Madeira, deserve a fuller account. In 1418 or 1419, J. Gonzales Zarco[269]
happened to have a female rabbit on board which had produced young during
the voyage, and he turned them all out on the island. These animals soon
increased so {113} rapidly, that they became a nuisance, and actually
caused the abandonment of the settlement. Thirty-seven years subsequently,
Cada Mosto describes them as innumerable; nor is this surprising, as the
island was not inhabited by any beast of prey or by any terrestrial mammal.
We do not know the character of the mother-rabbit; but we have every reason
to believe that it was the common domesticated kind. The Spanish peninsula,
whence Zarco sailed, is known to have abounded with the common wild species
at the most remote historical period. As these rabbits were taken on board
for food, it is improbable that they should have been of any peculiar
breed. That the breed was well domesticated is shown by the doe having
littered during the voyage. Mr. Wollaston, at my request, brought home two
of these feral rabbits in spirits of wine; and, subsequently, Mr. W.
Haywood sent to me three more specimens in brine, and two alive. These
seven specimens, though caught at different periods, closely resembled each
other. They were full grown, as shown by the state of their bones. Although
the conditions of life in Porto Santo are evidently highly favourable to
rabbits, as proved by their extraordinarily rapid increase, yet they differ
conspicuously in their small size from the wild English rabbit. Four
English rabbits, measured from the incisors to the anus, varied between 17
and 173/4 inches in length; whilst two of the Porto Santo rabbits were only
141/2 and 15 inches in length. But the decrease in size is best shown by
weight; four wild English rabbits averaged 3 lb. 5 oz., whilst one of the
Porto Santo rabbits, which had lived for four years in the Zoological
Gardens, but had become thin, weighed only 1 lb. 9 oz. A fairer test is
afforded by the comparison of the well-cleaned limb-bones of a P. Santo
rabbit killed on the island with the same bones of a wild English rabbit of
average size, and they differed in the proportion of rather less than five
to nine. So that the Porto Santo rabbits have decreased nearly three inches
in length, and almost half in weight of body.[270] The head has not
decreased in length {114} proportionally with the body; and the capacity of
the brain-case is, as we shall hereafter see, singularly variable. I
prepared four skulls, and these resembled each other more closely than do
generally the skulls of wild English rabbits; but the only difference in
structure which they presented was that the supra-orbital processes of the
frontal bones were narrower.
In colour the Porto Santo rabbit differs considerably from the common
rabbit; the upper surface is redder, and is rarely interspersed with any
black or black-tipped hairs. The throat and certain parts of the under
surface, instead of being pure white, are generally pale grey or leaden
colour. But the most remarkable difference is in the ears and tail; I have
examined many fresh English rabbits, and the large collection of skins in
the British Museum from various countries, and all have the upper surface
of the tail and the tips of the ears clothed with blackish-grey fur; and
this is given in most works as one of the specific characters of the
rabbit. Now in the seven Porto Santo rabbits the upper surface of the tail
was reddish-brown, and the tips of the ears had no trace of the black
edging. But here we meet with a singular circumstance: in June, 1861, I
examined two of these rabbits recently sent to the Zoological Gardens, and
their tails and ears were coloured as just described; but when one of their
dead bodies was sent to me in February, 1865, the ears were plainly edged,
and the upper surface of the tail was covered, with blackish-grey fur, and
the whole body was much less red; so that under the English climate this
individual rabbit had recovered the proper colour of its fur in rather less
than four years!
The two little Porto Santo rabbits, whilst alive in the Zoological Gardens,
had a remarkably different appearance from the common kind. They were
extraordinarily wild and active, so that many persons exclaimed on seeing
them that they were more like large rats than rabbits. They were nocturnal
to an unusual degree in their habits, and their wildness was never in the
least subdued; so that the superintendent, Mr. Bartlett, assured me that he
had never had a wilder animal under his charge. This is a singular fact,
considering that they are descended from a domesticated breed; I was so
much surprised at it, that I requested Mr. Haywood to make inquiries on the
spot, {115} whether they were much hunted by the inhabitants, or persecuted
by hawks, or cats, or other animals; but this is not the case, and no cause
can be assigned for their wildness. They live on the central, higher rocky
land and near the sea-cliffs, and, being exceedingly shy and timid, seldom
appear in the lower and cultivated districts. They are said to produce from
four to six young at a birth, and their breeding season is in July and
August. Lastly, and this is a highly remarkable fact, Mr. Bartlett could
never succeed in getting these two rabbits, which were both males, to
associate or breed with the females of several breeds which were repeatedly
placed with them.
If the history of these Porto Santo rabbits had not been known, most
naturalists, on observing their much reduced size, their reddish colour
above and grey beneath, with neither tail nor ears tipped with black, would
have ranked them as a distinct species. They would have been strongly
confirmed in this view by seeing them alive in the Zoological Gardens, and
hearing that they refused to couple with other rabbits. Yet this rabbit,
which there can be little doubt would thus have been ranked as a distinct
species, has certainly originated since the year 1420. Finally, from the
three cases of the rabbits which have run wild in Porto Santo, Jamaica, and
the Falkland Islands, we see that these animals do not, under new
conditions of life, revert to or retain their aboriginal character, as is
so generally asserted to be the case by most authors.
_Osteological Characters._
When we remember, on the one hand, how frequently it is stated that
important parts of the structure never vary; and, on the other hand, on
what small differences in the skeleton, fossil species have often been
founded, the variability of the skull and of some other bones in the
domesticated rabbit well deserves attention. It must not be supposed that
the more important differences immediately to be described strictly
characterise any one breed; all that can be said is, that they are
generally present in certain breeds. We should bear in mind that selection
has not been applied to fix any character in the skeleton, and that the
animals have not had to support themselves under {116} uniform habits of
life. We cannot account for most of the differences in the skeleton; but we
shall see that the increased size of the body, due to careful nurture and
continued selection, has affected the head in a particular manner. Even the
elongation and lopping of the ears have influenced in a small degree the
form of the whole skull. The want of exercise has apparently modified the
proportional length of the limbs in comparison with the body.
[Illustration: Fig. 6.--Skull of Wild Rabbit, of natural size.]
[Illustration: Fig. 7.--Skull of large Lop-eared Rabbit, of natural
size.]
As a standard of comparison, I prepared skeletons of two wild rabbits
from Kent, one from the Shetland Islands, and one from Antrim in
Ireland. As all the bones in these four specimens from such distant
localities closely resembled each other, presenting scarcely any
appreciable difference, it may be concluded that the bones of the wild
rabbit are generally uniform in character.
_Skull._--I have carefully examined skulls of ten large lop-eared fancy
rabbits, and of five common domestic rabbits, which latter differ from
the lop-eared only in not having such large bodies or ears, yet both
larger than in the wild rabbit. First for the ten lop-eared rabbits: in
all these the skull is remarkably elongated in comparison with its
breadth. In a wild rabbit the length was 3.15 inches, in a large fancy
rabbit 4.30; whilst the breadth of the cranium enclosing the brain was
in both almost exactly the same. Even by taking as the standard of
comparison the widest part of the zygomatic arch, the skulls of the
lop-eared are proportionally to their breadth three-quarters of an inch
too long. The depth of the head has increased almost in the same
proportion with the length; it is the breadth alone which has not
increased. The parietal and occipital bones enclosing the brain are
less arched, both in a longitudinal and transverse line, than in the
wild rabbit, so that the shape of the cranium is somewhat different.
The surface is rougher, less cleanly sculptured, and the lines of
sutures are more prominent.
Although the skulls of the large lop-eared rabbits in comparison with
those of the wild rabbit are much elongated relatively to their
breadth, yet, relatively to the size of body, they are far from
elongated. The lop-eared rabbits which I examined were, though not fat,
more than twice as heavy as the wild specimens; but the skull was very
far from being twice as long. Even if we take the fairer standard of
the length of body, from the nose to the anus, the skull is not on an
average as long as it ought to be by a third of an inch. In the small
feral P. Santo rabbit, on the other hand, the head relatively to the
length of body is about a quarter of an inch too long.
[Illustration: Fig. 8.--Part of Zygomatic Arch, showing the projecting
end of the malar bone and the auditory meatus: of natural size. Upper
figure, Wild Rabbit. Lower figure, Lop-eared, hare-coloured Rabbit.]
This elongation of the skull relatively to its breadth, I find a
universal character, not only with the large lop-eared rabbits, but in
all the artificial breeds; as is well seen in the skull of the Angora.
I was at first much surprised at the fact, and could not imagine why
domestication should produce this uniform result; but the explanation
seems to lie in the circumstance that during a number of generations
the artificial races have been closely confined, and have had little
occasion to exert either their senses, or intellect, or voluntary
muscles; consequently the brain, as {117} we shall presently more fully
see, has not increased relatively with the size of body. As the brain
has not increased, the bony case enclosing it has not increased, and
this has evidently affected through correlation the breadth of the
entire skull from end to end.
In all the skulls of the large lop-eared rabbits, the supra-orbital
plates or processes of the frontal bones ere much broader than in the
wild rabbit, and they generally project more upwards. In the zygomatic
arch the posterior or projecting point of the malar-bone is broader and
blunter; and in the specimen, fig. 8, it is so in a remarkable degree.
This point approaches nearer to the auditory meatus than in the wild
rabbit, as may be best seen in fig. 8; but this circumstance mainly
depends on the changed direction of the meatus. The inter-parietal bone
(see fig. 9) differs much in shape in the several skulls; generally it
is more oval, or has a greater width in the line of the longitudinal
axis of the skull, than in the wild rabbit. The {118} posterior margin
of "the square raised platform" [271] of the occiput, instead of being
truncated, or projecting slightly as in the wild rabbit, is in most
lop-eared rabbits pointed, as in fig. 9, C. The paramastoids relatively
to the size of the skull are generally much thicker than in the wild
rabbit.
The occipital foramen (fig. 10) presents some remarkable differences:
in the wild rabbit, the lower edge between the condyles is considerably
and almost angularly hollowed out, and the upper edge is deeply and
squarely notched; hence the longitudinal axis exceeds the transverse
axis. In the skulls of the lop-eared rabbits the transverse axis
exceeds the longitudinal; for in none of these skulls was the lower
edge between the condyles so deeply hollowed out; in five of them there
was no upper square notch, in three there was a trace of the notch, and
in two alone it was well developed. These differences in the shape of
the foramen are remarkable, considering that it gives passage to so
important a structure as the spinal marrow, though apparently the
outline of the latter is not affected by the shape of the passage.
[Illustration: Fig. 9.--Posterior end of Skull, of natural size,
showing the inter-parietal bone. A. Wild Rabbit. B. Feral Rabbit from
island of P. Santo, near Madeira. C. Large Lop-eared Rabbit.]
[Illustration: Fig. 10.--Occipital Foramen, of natural size, in--A.
Wild Rabbit; B. Large Lop-eared Rabbit.]
In all the skulls of the large lop-eared rabbits, the bony auditory
meatus is conspicuously larger than in the wild rabbit. In a skull 4.3
inches in length, and which barely exceeded in breadth the skull of a
wild rabbit (which was 3.15 inches in length), the longer diameter of
the meatus was exactly twice as great. The orifice is more compressed,
and its margin on the side nearest the skull stands up higher than the
outer side. The whole meatus is directed more forwards. As in breeding
lop-eared rabbits the length of the ears, and their consequent lopping
and lying flat on the face, are the chief points of excellence, there
can hardly be a doubt that the great change in the size, form, and
direction of the bony meatus, relatively to this same part in the wild
rabbit, is due to the continued selection of individuals having {119}
larger and larger ears. The influence of the external ear on the bony
meatus is well shown in the skulls (I have examined three) of half-lops
(see fig. 5), in which one ear stands upright, and the other and longer
ear hangs down; for in these skulls there was a plain difference in the
form and direction of the bony meatus on the two sides. But it is a
much more interesting fact, that the changed direction and increased
size of the bony meatus have slightly affected on the same side the
structure of the whole skull. I here give a drawing of the skull of a
half-lop; and it may be observed that the suture between the parietal
and frontal bones does not run strictly at right angles to the
longitudinal axis of the skull; the left frontal bone projects beyond
the right one; both the posterior and anterior margins of the left
zygomatic arch on the side of the lopping ear stand a little in advance
of the corresponding bones on the opposite side. Even the lower jaw is
affected, and the condyles are not quite symmetrical, that on the left
standing a little in advance of that on the right. This seems to me a
remarkable case of correlation of growth. Who would have surmised that
by keeping an animal during many generations under confinement, and so
leading to the disuse of the muscles of the ears, and by continually
selecting individuals with the longest and largest ears, he would thus
indirectly have affected almost every suture in the skull and the form
of the lower jaw!
[Illustration: Fig. 11.--Skull, of natural size, of Half-lop Rabbit,
showing the different direction of the auditory meatus on the two
sides, and the consequent general distortion of the skull. The left ear
of the animal (or right side of figure) lopped forwards.]
In the large lop-eared rabbits the only difference in the lower jaw, in
comparison with that of the wild rabbit, is that the posterior margin
of the ascending ramus is broader and more inflected. The teeth in
neither jaw present any difference, except that the small incisors,
beneath the large ones, are proportionally a little longer. The molar
teeth have increased in size proportionally with the increased width of
the skull, measured across the zygomatic arch, and not proportionally
with its increased length. The inner line of the sockets of the molar
teeth in the upper jaw of the wild rabbit forms a perfectly straight
line; but in {120} some of the largest skulls of the lop-eared this
line was plainly bowed inwards. In one specimen there was an additional
molar tooth on each side of the upper jaw, between the molars and
premolars; but these two teeth did not correspond in size; and as no
rodent has seven molars, this is merely a monstrosity, though a curious
one.
The five other skulls of common domestic rabbits, some of which
approach in size the above-described largest skulls, whilst the others
exceed but little those of the wild rabbit, are only worth notice as
presenting a perfect gradation in all the above-specified differences
between the skulls of the largest lop-eared and wild rabbits. In all,
however, the supra-orbital plates are rather larger, and in all the
auditory meatus is larger, in conformity with the increased size of the
external ears, than in the wild rabbit. The lower notch in the
occipital foramen in some was not so deep as in the wild, but in all
five skulls the upper notch was well developed.
The skull of the _Angora_ rabbit, like the latter five skulls, is
intermediate in general proportions, and in most other characters,
between those of the largest lop-eared and wild rabbits. It presents
only one singular character: though considerably longer than the skull
of the wild, the breadth measured within the posterior supra-orbital
fissures is nearly a third less than in the wild. The skulls of the
_silver-grey_, and _chinchilla_ and _Himalayan_ rabbits are more
elongated than in the wild, with broader supra-orbital plates, but
differ little in any other respect, excepting that the upper and lower
notches of the occipital foramen are not so deep or so well developed.
The skull of the _Moscow_ rabbit scarcely differs in any respect from
that of the wild rabbit. In the Porto Santo feral rabbits the
supra-orbital plates are generally narrower and more pointed than in
our wild rabbits.
As some of the largest lop-eared rabbits of which I prepared skeletons
were coloured almost like hares, and as these latter animals and
rabbits have, as it is affirmed, been recently crossed in France, it
might be thought that some of the above-described characters had been
derived from a cross at a remote period with the hare. Consequently I
examined skulls of the hare, but no light could thus be thrown on the
peculiarities of the skulls of the larger rabbits. It is, however, an
interesting fact, as illustrating the law that varieties of one species
often assume the characters of other species of the same genus, that I
found, on comparing the skulls of ten species of hares in the British
Museum, that they differed from each other chiefly in the very same
points in which domestic rabbits vary,--namely, in general proportions,
in the form and size of the supra-orbital plates, in the form of the
free end of the malar bone, and in the line of suture separating the
occipital and frontal bones. Moreover two eminently variable characters
in the domestic rabbit, namely, the outline of the occipital foramen
and the shape of the "raised platform" of the occiput, were likewise
variable in two instances in the same species of hare.
_Vertebrae._--The number is uniform in all the skeletons which I have
examined, with two exceptions, namely, in one of the small feral Porto
Santo rabbits and in one of the largest lop-eared kinds; both of these
had as usual seven cervical, twelve dorsal with ribs, but, instead of
seven lumbar, both had eight lumbar vertebrae. This is remarkable, as
Gervais gives {121} seven as the number for the whole genus Lepus. The
caudal vertebrae apparently differ by two or three, but I did not attend
to them, and they are difficult to count with certainty.
In the first cervical vertebra, or atlas, the anterior margin of the
neural arch varies a little in wild specimens, being either nearly
smooth, or furnished with a small supra-median atlantoid process; I
have figured a specimen with the largest process (_a_) which I have
seen; but it will be observed how inferior this is in size and
different in shape to that in a large lop-eared rabbit. In the latter,
the infra-median process (_b_) is also proportionally much thicker and
longer. The alae are a little squarer in outline.
[Illustration: Fig. 12.--Atlas Vertebrae, of natural size; inferior
surface viewed obliquely. Upper figure, Wild Rabbit. Lower figure,
Hare-coloured, large, Lop-eared Rabbit. _a_, supra-median, atlantoid
process; _b_, infra-median process.]
_Third cervical vertebra._--In the wild rabbit (fig. 13, A _a_) this
vertebra, viewed on the inferior surface, has a transverse process,
which is directed obliquely backwards, and consists of a single pointed
bar; in the fourth vertebra this process is slightly forked in the
middle. In the large lop-eared rabbits this process (B _a_) is forked
in the third vertebra, as in the fourth of the wild rabbit. But the
third cervical vertebrae of the wild and lop-eared (A _b_, B _b_)
rabbits differ more conspicuously when their anterior articular
surfaces are compared; for the extremities of the antero-dorsal
processes in the wild rabbit are simply rounded, whilst in the
lop-eared they are trifid, with a deep central pit. The canal for the
spinal marrow in the lop-eared (B _b_) is more elongated in a
transverse direction than in the wild rabbit; and the passages for the
arteries are of a slightly different shape. These several differences
in this vertebra seem to me well deserving attention.
[Illustration: Fig. 13.--Third Cervical Vertebra, of natural size,
of--A. Wild Rabbit; B. Hare-coloured, large, Lop-eared Rabbit. _a, a_,
inferior surface; _b, b_, anterior articular surfaces.]
_First dorsal vertebra._--Its neural spine varies in length in the wild
rabbit; being sometimes very short, but generally more than half as
long as that of the second dorsal; but I have seen it in two large
lop-eared rabbits three-fourths of the length of that of the second
dorsal vertebra.
_Ninth and tenth dorsal vertebrae._--In the wild rabbit the neural spine
of the ninth vertebra is just perceptibly thicker than that of the
eighth; and {122} the neural spine of the tenth is plainly thicker and
shorter than those of all the anterior vertebrae. In the large lop-cared
rabbits the neural spines of the tenth, ninth, eighth, and even in a
slight degree that of the seventh vertebra, are very much thicker, and
of somewhat different shape, in comparison with those of the wild
rabbit. So that this part of the vertebral column differs considerably
in appearance from the same part in the wild rabbit, and closely
resembles in an interesting manner these same vertebrae in some species
of hares. In the Angora, Chinchilla, and Himalayan rabbits, the neural
spines of the eighth and ninth vertebrae are in a slight degree thicker
than in the wild. On the other hand, in one of the feral Porto Santo
rabbits, which in most of its characters deviates in an exactly
opposite manner to what the large lop-cared rabbits do from the common
wild rabbit, the neural spines of the ninth and tenth vertebrae were not
at all larger than those of the several anterior vertebrae. In this same
Porto Santo specimen there was no trace in the ninth vertebra of the
anterior lateral processes (see woodcut 14), which are plainly
developed in all British wild rabbits, and still more plainly developed
in the large lop-eared rabbits. In a half-wild rabbit from Sandon
Park,[272] a haemal spine was moderately well developed on the under
side of the twelfth dorsal vertebra, and I have seen this in no other
specimen.
[Illustration: Fig. 14.--Dorsal Vertebrae, from sixth to tenth
inclusive, of natural size, viewed laterally. A. Wild Rabbit. B. Large,
Hare-coloured, so called Spanish Rabbit.]
[Illustration: Fig. 15.--Terminal bone of Sternum, of natural size. A.
Wild Rabbit. B. Hare-coloured, Lop-eared Rabbit. C. Hare-coloured,
Spanish Rabbit. (N.B. The left-hand angle of the upper articular
extremity of B was broken, and has been accidentally thus
represented.)]
_Lumbar vertebrae._--I have stated that in two cases there were eight
instead of seven lumbar vertebrae. The third lumbar vertebra in one
skeleton of a wild British rabbit, and in one of the Porto Santo feral
rabbits, had a haemal spine; whilst in four skeletons of large lop-eared
rabbits, and in the Himalayan rabbit, this same vertebra had a
well-developed haemal spine.
_Pelvis._--In four wild specimens this bone was almost absolutely
identical in shape; but in several domesticated breeds shades of
differences {123} could be distinguished. In the large lop-eared
rabbits the whole upper part of the ilium is straighter, or less
splayed outwards, than in the wild rabbit; and the tuberosity on the
inner lip of the anterior and upper part of the ilium is proportionally
more prominent.
_Sternum._--The posterior end of the posterior sternal bone in the wild
rabbit (fig. 15, A) is thin and slightly enlarged; in some of the large
lop-eared rabbits (B) it is much more enlarged towards the extremity;
whilst in other specimens (C) it keeps nearly of the same breadth from
end to end, but is much thicker at the extremity.
[Illustration: Fig. 16.--Acromion of Scapula, of natural size. A. Wild
Rabbit. B, C, D; Large, Lop-eared Rabbits.]
_Scapula._--The acromion sends out a rectangular bar, ending in an
oblique knob, which latter in the wild rabbit (fig. 16, A) varies a
little in shape and size, as does the apex of the acromion in
sharpness, and the part just below the rectangular bar in breadth. But
the variations in these respects in the wild rabbit are very slight;
whilst in the large lop-eared rabbits they are considerable. Thus in
some specimens (B) the oblique terminal knob is developed into a short
bar, forming an obtuse angle with the rectangular bar. In another
specimen (C) these two unequal bars form nearly a straight line. The
apex of the acromion varies much in breadth and sharpness, as may be
seen by comparing figs. B, C, and D.
_Limbs._--In these I could detect no variation; but the bones of the
feet were too troublesome to compare with much care.
I have now described all the differences in the skeletons which I have
observed. It is impossible not to be struck with the high degree of
variability or plasticity of many of the bones. We see how erroneous the
often-repeated statement is, that only the crests of the bones which give
attachment to muscles vary in shape, and that only parts of slight
importance {124} become modified under domestication. No one will say, for
instance, that the occipital foramen, or the atlas, or the third cervical
vertebra is a part of slight importance. If the several vertebrae of the
wild and lop-eared rabbits, of which figures have been given, had been
found fossil, palaeontologists would have declared without hesitation that
they had belonged to distinct species.
_The effects of the use and disuse of parts._--In the large lop-eared
rabbits the relative proportional lengths of the bones of the same leg,
and of the front and hind legs compared with each other, have remained
nearly the same as in the wild rabbit; but in weight, the bones of the
hind legs apparently have not increased in due proportion with the
front legs. The weight of the whole body in the large rabbits examined
by me was from twice to twice and a half as great as that of the wild
rabbit; and the weight of the bones of the front and hind limbs taken
together (excluding the feet, on account of the difficulty of perfectly
cleaning so many small bones) has increased in the large lop-eared
rabbits in nearly the same proportion; consequently in due proportion
to the weight of body which they have to support. If we take the length
of the body as the standard of comparison, the limbs of the large
rabbits have not increased in length in due proportion by one inch, or
by one inch and a half. Again, if we take as the standard of comparison
the length of the skull, which, as we have before seen, has not
increased in length in due proportion to the length of body, the limbs
will be found to be, proportionally with those of the wild rabbit, from
half to three-quarters of an inch too short. Hence, whatever standard
of comparison be taken, the limb-bones of the large lop-eared rabbits
have not increased in length, though they have in weight, in full
proportion to the other parts of the frame; and this, I presume, may be
accounted for by the inactive life which during many generations they
have spent. Nor has the scapula increased in length in due proportion
to the increased length of the body.
The capacity of the osseous case of the brain is a more interesting
point, to which I was led to attend by finding, as previously stated,
that with all domesticated rabbits the length of the skull relatively
to its breadth has greatly increased in comparison with that of the
wild rabbit. If we had possessed a large number of domesticated rabbits
of nearly the same size with the wild rabbit, it would have been a
simple task to have measured and compared the capacities of their
skulls. But this is not the case; almost all the domestic breeds have
larger bodies than wild rabbits, and the lop-eared kinds are more than
double their weight. As a small animal has to exert its senses,
intellect, and instincts equally with a large animal, we ought not by
any means to expect an animal twice or thrice as large as another to
have a brain of double or treble the size.[273] Now, after weighing
{125} the bodies of four wild rabbits, and of four large but not
fattened lop-eared rabbits, I find that on an average the wild are to
the lop-eared in weight as 1 to 2.47; in average length of body as 1 to
1.41; whilst in capacity of skull (measured as hereafter to be
described) they are only as 1 to 1.15. Hence we see that the capacity
of the skull, and consequently the size of the brain, has increased but
little, relatively to the increased size of the body; and this fact
explains the narrowness of the skull relatively to its length in all
domestic rabbits.
In the upper half of the following table I have given the measurements
of the skulls of ten wild rabbits; and in the lower half of eleven
thoroughly domesticated kinds. As these rabbits differ so greatly in
size, it is necessary to have some standard by which to compare the
capacities of their skulls. I have selected the length of skull as the
best standard, for in the larger rabbits it has not, as already stated,
increased in length so much as the body; but as the skull, like every
other part, varies in length, neither it nor any other part affords a
perfect standard.
In the first column of figures the extreme length of the skull is given
in inches and decimals. I am aware that these measurements pretend to
greater accuracy than is possible; but I have found it the least
trouble to record the exact length which the compass gave. The second
and third columns give the length and weight of body, whenever these
measurements have been made. The fourth column gives the capacity of
the skull by the weight of small shot with which the skulls had been
filled; but it is not pretended that these weights are accurate within
a few grains. In the fifth column the capacity is given which the skull
ought to have had by calculation, according to the length of skull, in
comparison with that of the wild rabbit No. 1; in the sixth column the
difference between the actual and calculated capacities, and in the
seventh the percentage of increase or decrease, are given. For
instance, as the wild rabbit No. 5 has a shorter and lighter body than
the wild rabbit No. 1, we might have expected that its skull would have
had less capacity; the actual capacity, as expressed by the weight of
shot, is 875 grains, which is 97 grains less than that of the first
rabbit. But comparing these two rabbits by the length of their skulls,
we see that in No. 1 the skull is 3.15 inches in length, and in No. 5
2.96 inches in length; according to this ratio, the brain of No. 5
ought to have had a capacity of 913 grains of shot, which is above the
actual capacity, but only by 38 grains. Or, to put the case in another
way (as in column VII), the brain of this small rabbit, No. 5, for
every 100 grains of weight is only 4 per cent. too light,--that is, it
ought, according to the standard rabbit No. 1, to have been 4 per cent.
heavier. I have taken the rabbit No. 1 as the standard of comparison
because, of the skulls having a full average length, this has the least
capacity; so that it is the least favourable to the result which I wish
to show, namely, that the brain in all long-domesticated rabbits has
decreased in size, either actually, or relatively to the length of the
head and body, in comparison with the brain of the wild rabbit. Had I
taken the Irish rabbit, No. 3, as the standard, the following results
would have been somewhat more striking.
Turning to the Table: the first four wild rabbits have skulls of the
same length, and these differ but little in capacity. The Sandon rabbit
{126} (No. 4) is interesting, as, though now wild, it is known to be
descended from a domesticated breed, as is still shown by its peculiar
colouring and longer body; nevertheless the skull has recovered its
normal length and full capacity. The next three rabbits are wild, but
of small size, and they all have skulls with slightly lessened
capacities. The three Porto Santo feral rabbits (Nos. 8 to 10) offer a
perplexing case; their bodies are greatly reduced in size, as in a
lesser degree are their skulls in length and in actual capacity, in
comparison with the skulls of wild English rabbits. But when we compare
the capacities of the skull in the three Porto Santo rabbits, we
observe a surprising difference, which does not stand in any relation
to the slight difference in the length of their skulls, nor, as I
believe, to any difference in the size of their bodies; but I neglected
to weigh separately their bodies. I can hardly suppose that the
medullary matter of the brain in these three rabbits, living under
similar conditions, can differ as much as is indicated by the
proportional difference of capacity in their skulls; nor do I know
whether it is possible that one brain may contain considerably more
fluid than another. Hence I can throw no light on this case.
Looking to the lower half of the Table, which gives the measurements of
domesticated rabbits, we see that in all the capacity of the skull is
less, but in very various degrees, than might have been anticipated
according to the length of their skulls, relatively to that of the wild
rabbit No. 1. In line 22 the average measurements of seven large
lop-eared rabbits are given. Now the question arises, has the average
capacity of the skull in these seven large rabbits increased as much as
might have been expected from their greatly increased size of body. We
may endeavour to answer this question in two ways: in the upper half of
the Table we have measurements of the skulls of six small wild rabbits
(Nos. 5 to 10), and we find that on an average the skulls are in length
.18 of an inch shorter, and in capacity 91 grains less, than the
average length and capacity of the three first wild rabbits on the
list. The seven large lop-cared rabbits, on an average, have skulls
4.11 inches in length, and 1136 grains in capacity; so that these
skulls have increased in length more than five times as much as the
skulls of the six small wild rabbits have decreased in length; hence we
might have expected that the skulls of the large lop-eared rabbits
would have increased in capacity five times as much as the skulls of
the six small rabbits have decreased in capacity; and this would have
given an average increased capacity of 455 grains, whilst the real
average increase is only 155 grains. Again, the large lop-eared rabbits
have bodies of nearly the same weight and size as the common hare, but
their heads are longer; consequently, if the lop-eared rabbits had been
wild, it might have been expected that their skulls would have had
nearly the same capacity as that of the skull of the hare. But this is
far from being the case; for the average capacity of the two
hare-skulls (Nos. 23, 24) is so much larger than the average capacity
of the seven lop-cared skulls, that the latter would have to be
increased 21 per cent. to come up to the standard of the hare.[274]
{127}
------------------------------------------------+---------+-------------
| I. | II.
| |
| | Length
Name of Breed. | Length | of Body from
WILD AND SEMI-WILD RABBITS. | of | Incisors to
| Skull. | Anus.
------------------------------------------------+---------+-------------
| inches. | inches.
1. Wild rabbit, Kent | 3.15 | 17.4
2. " Shetland Islands | 3.15 | ..
3. " Ireland | 3.15 | ..
4. Domestic rabbit, run wild, Sandon | 3.15 | 18.5
5. Wild, common variety, small specimen, Kent | 2.96 | 17.0
6. Wild, fawn-coloured variety, Scotland | 3.1 | ..
7. Silver-grey, small specimen, Thetford warren| 2.95 | 15.5
8. Feral rabbit, Porto Santo | 2.83 | ..
9. " " | 2.85 | ..
10. " " | 2.95 | ..
Average of the three Porto Santo Rabbits | 2.88 | ..
| |
Domestic Rabbits | |
| |
11. Himalayan | 3.5 | 20.5
12. Moscow | 3.25 | 17.0
13. Angora | 3.5 | 19.5
14. Chinchilla | 3.65 | 22.0
15. Large lop-eared | 4.1 | 24.5
16. " " | 4.1 | 25.0
17. " " | 4.07 | ..
18. " " | 4.1 | 25.0
19. " " | 4.3 | ..
20. " " | 4.25 | ..
21. Large hare-coloured | 3.86 | 24.0
22. Average of above seven large lop-eared | |
rabbits | 4.11 | 24.62
------------------------------------------------+---------+-------------
23. Hare (_L. timidus_) English specimen | 3.61 |
24. " " German specimen | 3.82 |
------------------------------------------------+---------+-------------
----------+-------------+------------+-----------------+-----------
| III. | IV. | V. | VI.
| | | |
| | | Capacity |
| | | calculated | Difference
| | Capacity of| according to | between
| Weight | Skull | Length of | actual and
| of | measured by| Skull relatively| calculated
| whole Body.| Small Shot.| to that | capacities
| | | of No. 1. | of Skulls.
----------+-------------+------------+-----------------+-----------
| lbs. ozs. | grains. | grains. | grains.
1. | 3 5 | 972 | .. | ..
2. | .. | 979 | .. | ..
3. | .. | 992 | .. | ..
4. | .. | 977 | |
5. | 2 14 | 875 | 913 | 38
6. | .. | 918 | 950 | 32
7. | 2 11 | 938 | 910 | 28
8. | .. | 893 | 873 | 20
9. | .. | 756 | 879 | 123
10. | .. | 835 | 910 | 75
| | | |
(Average) | .. | 828 | 888 | 60
| | | |
11. | .. | 963 | 1080 | 117
12. | 3 8 | 803 | 1002 | 199
13. | 3 1 | 697 | 1080 | 383
14. | .. | 995 | 1126 | 131
15. | 7 0 | 1065 | 1265 | 200
16. | 7 13 | 1153 | 1265 | 112
17. | .. | 1037 | 1255 | 218
18. | 7 4 | 1208 | 1265 | 57
19. | .. | 1232 | 1326 | 94
20. | .. | 1124 | 1311 | 187
21. | 6 14 | 1131 | 1191 | 60
22. | 7 4 | 1136 | 1268 | 132
----------+-------------+------------+-----------------+-----------
23. | 7 0 | 1315 | |
24. | 7 0 | 1455 | |
----------+-------------+------------+-----------------+-----------
----+-----------------------------------
| VII.
|
| Showing how much per cent.
| the Brain, by calculation,
| according to the length of the
| Skull, is too light or too heavy,
| relatively to the Brain of the
| Wild Rabbit No. 1.
----+-----------------------------------
1. |
2. |
3. | ( [2 per cent. too heavy in
| ( comparison with No. 1.]
4. |
5. | 4 per cent. too light.
6. | 3 " "
7. | 3 " too heavy.
8. | 2 " "
9. | 16 " too light.
10. | 9 " "
|
Av. | 7 " "
|
11. | 12 " "
12. | 24 " "
13. | 54 " "
14. | 13 " "
15. | 18 " "
16. | 9 " "
17. | 21 " "
18. | 4 " "
19. | 7 " "
20. | 16 " "
21. | 5 " "
22. | 11 " "
----+-----------------------------------
23. |
24. |
----+-----------------------------------
{128}
I have previously remarked that, if we had possessed many domestic
rabbits of the same average size with the wild rabbit, it would have
been easy to compare the capacity of their skulls. Now the Himalayan,
Moscow, and Angora rabbits (Nos. 11, 12, 13 of Table) are only a little
larger in body, and have skulls only a little longer, than the wild
animal, and we see that the actual capacity of their skulls is less
than in the wild animal, and considerably less by calculation (column
7), according to the difference in the length of their skulls. The
narrowness of the brain-case in these three rabbits could be plainly
seen and proved by external measurement. The Chinchilla rabbit (No. 14)
is a considerably larger animal than the wild rabbit, yet the capacity
of its skull only slightly exceeds that of the wild rabbit. The Angora
rabbit, No. 13, offers the most remarkable case; this animal in its
pure white colour and length of silky fur bears the stamp of long
domesticity. It has a considerably longer head and body than the wild
rabbit, but the actual capacity of its skull is less than that of even
the little wild Porto Santo rabbits. By the standard of the length of
skull the capacity (see column 7) is only half of what it ought to have
been! I kept this individual animal alive, and it was not unhealthy nor
idiotic. This case of the Angora rabbit so much surprised me, that I
repeated all the measurements and found them correct. I have also
compared the capacity of the skull of the Angora with that of the wild
rabbit by other standards, namely, by the length and weight of the
body, and by the weight of the limb-bones; but by all these standards
the brain appears to be much too small, though in a less degree when
the standard of the limb-bones was used; and this latter circumstance
may probably be accounted for by the Limbs of this anciently
domesticated breed having become much reduced in weight, from its
long-continued inactive life. Hence I infer that in the Angora breed,
which is said to differ from other breeds in being quieter and more
social, the capacity of the skull has really undergone a remarkable
amount of reduction.
From the several facts above given,--namely, firstly, that the actual
capacity of the skull in the Himalayan, Moscow, and Angora breeds, is less
than in the wild rabbit, though they are in all their dimensions rather
larger animals; secondly, that the capacity of the skull of the large
lop-eared rabbits has not been increased in nearly the same ratio as the
capacity of the skull of the smaller wild rabbits has been decreased; and
thirdly, that the capacity of the skull in these same large lop-eared
rabbits is very inferior to that of the hare, an animal of nearly the same
{129} size,--I conclude, notwithstanding the remarkable differences in
capacity in the skulls of the small P. Santo rabbits, and likewise in the
large lop-eared kinds, that in all long-domesticated rabbits the brain has
either by no means increased in due proportion with the increased length of
the head and increased size of the body, or that it has actually decreased
in size, relatively to what would have occurred had these animals lived in
a state of nature. When we remember that rabbits, from having been
domesticated and closely confined during many generations, cannot have
exerted their intellect, instincts, senses, and voluntary movements, either
in escaping from various dangers or in searching for food, we may conclude
that their brains will have been feebly exercised, and consequently have
suffered in development. We thus see that the most important and
complicated organ in the whole organization is subject to the law of
decrease in size from disuse.
Finally, let us sum up the more important modifications which domestic
rabbits have undergone, together with their causes as far as we can
obscurely see them. By the supply of abundant and nutritious food, together
with little exercise, and by the continued selection of the heaviest
individuals, the weight of the larger breeds has been more than doubled.
The bones of the limbs have increased in weight (but the hind legs less
than the front legs), in due proportion with the increased weight of body;
but in length they have not increased in due proportion, and this may have
been caused by the want of proper exercise. With the increased size of the
body the third cervical vertebra has assumed characters proper to the
fourth cervical; and the eighth and ninth dorsal vertebrae have similarly
assumed characters proper to the tenth and posterior vertebrae. The skull in
the larger breeds has increased in length, but not in due proportion with
the increased length of body; the brain has not duly increased in
dimensions, or has even actually decreased, and consequently the bony case
for the brain has remained narrow, and by correlation has affected the
bones of the face and the entire length of the skull. The skull has thus
acquired its characteristic narrowness. From unknown causes the
supra-orbital processes of the frontal bones and the free end of the malar
bones have increased in breadth; and in the larger breeds {130} the
occipital foramen is generally much less deeply notched than in wild
rabbits. Certain parts of the scapula and the terminal sternal bones have
become highly variable in shape. The ears have been increased enormously in
length and breadth through continued selection; their weight, conjoined
probably with the disuse of their muscles, has caused them to lop
downwards; and this has affected the position and form of the bony auditory
meatus; and this again, by correlation, the position in a slight degree of
almost every bone in the upper part of the skull, and even the position of
the condyles of the lower jaw.
* * * * *
{131}