DUCKS--GOOSE--PEACOCK--TURKEY--GUINEA-FOWL--CANARY-BIRD--GOLD-FISH--
HIVE-BEES--SILK-MOTHS.
DUCKS, SEVERAL BREEDS OF--PROGRESS OF DOMESTICATION--ORIGIN OF, FROM
THE COMMON WILD-DUCK--DIFFERENCES IN THE DIFFERENT BREEDS--OSTEOLOGICAL
DIFFERENCES--EFFECTS OF USE AND DISUSE ON THE LIMB-BONES.
GOOSE, ANCIENTLY DOMESTICATED--LITTLE VARIATION OF--SEBASTOPOL BREED.
PEACOCK, ORIGIN OF BLACK-SHOULDERED BREED.
TURKEY, BREEDS OF--CROSSED WITH THE UNITED STATES SPECIES--EFFECTS OF
CLIMATE ON.
GUINEA-FOWL, CANARY-BIRD, GOLD-FISH, HIVE-BEES.
SILK-MOTHS, SPECIES AND BREEDS OF--ANCIENTLY DOMESTICATED--CARE IN
THEIR SELECTION--DIFFERENCES IN THE DIFFERENT RACES--IN THE EGG,
CATERPILLAR, AND COCOON STATES--INHERITANCE OF CHARACTERS--IMPERFECT
WINGS--LOST INSTINCTS--CORRELATED CHARACTERS.
I will, as in previous cases, first briefly describe the chief domestic
breeds of the duck:--
BREED 1. _Common Domestic Duck_.--Varies much in colour and in
proportions, and differs in instincts and disposition from the
wild-duck. There are several sub-breeds:--(1) The Aylesbury, of great
size, white, with pale-yellow beak and legs; abdominal sack largely
developed. (2) The Rouen, of great size, coloured like the wild-duck,
with green or mottled beak; abdominal sack largely developed. (3)
Tufted Duck, with a large top-knot of fine downy feathers, supported on
a fleshy mass, with the skull perforated beneath. The top-knot in a
duck which I imported from Holland was two and a half inches in
diameter. (4) Labrador (or Canadian, or Buenos Ayres, or East Indian);
plumage entirely black; beak broader, relatively to its length, than in
the wild-duck; eggs slightly tinted with black. This sub-breed perhaps
ought to be ranked as a breed; it includes two sub-varieties, one as
large as the common domestic duck, which I have kept alive, and the
other smaller and often capable of flight.[436] I presume it is this
latter sub-variety which has been described in France[437] as flying
well, being rather wild, and when cooked having the flavour of the
wild-duck; nevertheless this sub-variety is polygamous, like other
domesticated ducks and unlike the wild duck. These black Labrador ducks
breed true; {277} but a case is given by Dr. Turral of the French
sub-variety producing young with some white feathers on the head and
neck, and with an ochre-coloured patch on the breast.
BREED 2. _Hook-billed Duck_.--This bird presents an extraordinary
appearance from the downward curvature of the beak. The head is often
tufted. The common colour is white, but some are coloured like
wild-ducks. It is an ancient breed, having been noticed in 1676.[438]
It shows its prolonged domestication by almost incessantly laying eggs,
like the fowls which are called everlasting layers.[439]
BREED 3. _Call-Duck_.--Remarkable from its small size, and from the
extraordinary loquacity of the female. Beak short. These birds are
either white, or coloured like the wild-duck.
BREED 4. _Penguin Duck_.--This is the most remarkable of all the
breeds, and seems to have originated in the Malayan archipelago. It
walks with its body extremely erect, and with its thin neck stretched
straight upwards. Beak rather short. Tail upturned, including only 18
feathers. Femur and meta-tarsi elongated.
Almost all naturalists admit that the several breeds are descended from the
common wild duck (_Anas boschas_); most fanciers, on the other hand, take
as usual a very different view.[440] Unless we deny that domestication,
prolonged during centuries, can affect even such unimportant characters as
colour, size, and in a slight degree proportional dimensions and mental
disposition, there is no reason whatever to doubt that the domestic duck is
descended from the common wild species, for the one differs from the other
in no important character. We have some historical evidence with respect to
the period and progress of the domestication of the duck. It was
unknown[441] to the ancient Egyptians, to the Jews of the Old Testament,
and to the Greeks of the Homeric period. About eighteen centuries ago
Columella[442] and Varro speak of the necessity of keeping ducks in netted
enclosures like other wild fowl, so that at this period there was danger of
their flying away. {278} Moreover, the plan recommended by Columella to
those who might wish to increase their stock of ducks, namely, to collect
the eggs of the wild bird and to place them under a hen, shows, as Mr.
Dixon remarks, "that the duck had not at this time become a naturalised and
prolific inmate of the Roman poultry-yard." The origin of the domestic duck
from the wild species is recognised in nearly every language of Europe, as
Aldrovandi long ago remarked, by the same name being applied to both. The
wild duck has a wide range from the Himalayas to North America. It crosses
readily with the domestic bird, and the crossed offspring are perfectly
fertile.
Both in North America and Europe the wild duck has been found easy to tame
and breed. In Sweden this experiment was carefully tried by Tiburtius; he
succeeded in rearing wild ducks for three generations, but, though they
were treated like common ducks, they did not vary even in a single feather.
The young birds suffered from being allowed to swim about in cold
water,[443] as is known to be the case, though the fact is a strange one,
with the young of the common domestic duck. An accurate and well-known
observer in England[444] has described in detail his often repeated and
successful experiments in domesticating the wild duck. Young birds are
easily reared from eggs hatched under a bantam; but to succeed it is
indispensable not to place the eggs of both the wild and tame duck under
the same hen, for in this case "the young wild ducks die off, leaving their
more hardy brethren in undisturbed possession of their foster-mother's
care. The difference of habit at the onset in the newly-hatched ducklings
almost entails such a result to a certainty." The wild ducklings were from
the first quite tame towards those who took care of them as long as they
wore the same clothes, and likewise to the dogs and cats of the house. They
would even snap with their beaks at the dogs, and drive them away from any
spot which they coveted. But they were much alarmed at strange men and
dogs. Differently from what {279} occurred in Sweden, Mr. Hewitt found that
his young birds always changed and deteriorated in character in the course
of two or three generations; notwithstanding that great care was taken to
prevent any crossing with tame ducks. After the third generation his birds
lost the elegant carriage of the wild species, and began to acquire the
gait of the common duck. They increased in size in each generation, and
their legs became less fine. The white collar round the neck of the mallard
became broader and less regular, and some of the longer primary
wing-feathers became more or less white. When this occurred, Mr. Hewitt
always destroyed his old stock and procured fresh eggs from wild nests; so
that he never bred the same family for more than five or six generations.
His birds continued to pair together, and never became polygamous like the
common domestic duck. I have given these details, because no other case, as
far as I know, has been so carefully recorded by a competent observer of
the progress of change in wild birds reared for several generations in a
domestic condition.
From these considerations there can hardly be a doubt that the wild duck is
the parent of the common domestic kind; nor need we look to distinct
species for the parentage of the more distinct breeds, namely, Penguin,
Call, Hook-billed, Tufted, and Labrador ducks. I will not repeat the
arguments used in the previous chapters on the improbability of man having
in ancient times domesticated several species since become unknown or
extinct, though ducks are not readily exterminated in the wild state;--on
some of the supposed parent-species having had abnormal characters in
comparison with all the other species of the genus, as with hook-billed and
penguin ducks;--on all the breeds, as far as is known, being fertile
together;[445]--on all the breeds having the same general disposition,
instinct, &c. But one fact bearing on this question may be noticed: in the
great duck family, one species alone, namely, the male of {280} _A.
boschas_, has its four middle tail-feathers curled upwardly; now in every
one of the above-named domestic breeds these curled feathers exist, and on
the supposition that they are descended from distinct species, we must
assume that man formerly hit upon species all of which had this now unique
character. Moreover, sub-varieties of each breed are coloured almost
exactly like the wild duck, as I have seen with the largest and smallest
breeds, namely Rouens and Call-ducks, and, as Mr. Brent states,[446] is the
case with Hook-billed ducks. This gentleman, as he informs me, crossed a
white Aylesbury drake and a black Labrador duck, and some of the ducklings
as they grew up assumed the plumage of the wild duck.
With respect to Penguins, I have not seen many specimens, and none were
coloured precisely like the wild duck; but Sir James Brooke sent me three
skins from Lombok and Bali, in the Malayan archipelago; the two females
were paler and more rufous than the wild duck, and the drake differed in
having the whole under and upper surface (excepting the neck, tail-coverts,
tail, and wings) silver-grey, finely pencilled with dark lines, closely
like certain parts of the plumage of the wild mallard. But I found this
drake to be identical in every feather with a variety of the common breed
procured from a farm-yard in Kent, and I have occasionally elsewhere seen
similar specimens. The occurrence of a duck bred under so peculiar a
climate as that of the Malayan archipelago, where the wild species does not
exist, with exactly the same plumage as may occasionally be seen in our
farm-yards, is a fact worth notice. Nevertheless the climate of the Malayan
archipelago apparently does tend to cause the duck to vary much, for
Zollinger,[447] speaking of the Penguin breed, says that in Lombok "there
is an unusual and very wonderful variety of ducks." One Penguin drake which
I kept alive differed from those of which the skins were sent me from
Lombok, in having its breast and back partially coloured with
chestnut-brown, thus more closely resembling the Mallard.
From these several facts, more especially from the drakes of all the breeds
having curled tail-feathers, and from certain sub-varieties in each breed
occasionally resembling in general {281} plumage the wild duck, we may
conclude with confidence that all the breeds are descended from _A.
boschas_.
I will now notice some of the peculiarities characteristic of the
several breeds. The eggs vary in colour; some common ducks laying
pale-greenish and others quite white eggs. The eggs which are first
laid during each season by the black Labrador duck, are tinted black,
as if rubbed with ink. So that with ducks, as with poultry, some degree
of correlation exists between the colour of the plumage and the
egg-shell. A good observer assured me that one year his Labrador ducks
laid almost perfectly white eggs, but that the yolks were this same
season dirty olive-green, instead of as usual of a golden yellow, so
that the black tint appeared to have passed inwards. Another curious
case shows what singular variations sometimes occur and are inherited;
Mr. Hansell[448] relates that he had a common duck which always laid
eggs with the yolk of a dark-brown colour like melted glue; and the
young ducks, hatched from these eggs, laid the same kind of eggs, so
that the breed had to be destroyed.
The hook-billed duck has a most remarkable appearance (see fig. of
skull, woodcut No. 39); and its peculiar beak has been inherited at
least since the year 1676. This structure is evidently analogous with
that described in the Bagadotten carrier pigeon. Mr. Brent[449] says
that, when hook-billed ducks are crossed with common ducks, "many young
ones are produced with the upper mandible shorter than the lower, which
not unfrequently causes the death of the bird." A tuft of feathers on
the head is by no means a rare occurrence; namely, in the true tufted
breed, the hook-billed, the common farmyard duck, and in a duck having
no other peculiarity which was sent to me from the Malayan archipelago.
The tuft is only so far interesting as it affects the skull, which is
thus rendered slightly more globular, and is perforated by numerous
apertures. Call-ducks are remarkable from their extraordinary
loquacity: the drake only hisses like common drakes; nevertheless, when
paired with the common duck, he transmits to his female offspring a
strong quacking tendency. This loquacity seems at first a surprising
character to have been acquired under domestication. But the voice
varies in the different breeds; Mr. Brent[450] says that hook-billed
ducks are very loquacious, and that Rouens utter a "dull, loud, and
monotonous cry, easily distinguishable by an experienced ear." As the
loquacity of the Call-duck is highly serviceable, these birds being
used in decoys, this quality may have been increased by selection. For
instance, Colonel Hawker says, if young wild-ducks cannot be got for a
decoy, "by way of make-shift, _select_ tame birds which are the most
clamorous, even if their colour should not be like that of wild
ones."[451] It has been {282} falsely asserted that Call-ducks hatch
their eggs in less time than common ducks.[452]
The Penguin duck is the most remarkable of all the breeds; the thin
neck and body are carried erect; the wings are small; the tail is
upturned; and the thigh-bones and metatarsi are considerably lengthened
in proportion with the same bones in the wild duck. In five specimens
examined by me there were only eighteen tail-feathers instead of twenty
as in the wild duck; but I have also found only eighteen and nineteen
tail-feathers in two Labrador ducks. On the middle toe, in three
specimens, there were twenty-seven or twenty-eight scutellae, whereas in
two wild ducks there were thirty-one and thirty-two. The Penguin when
crossed transmits with much power its peculiar form of body and gait to
its offspring; this was manifest with some hybrids raised in the
Zoological Gardens between one of these birds and the Egyptian
goose[453] (_Anser AEgyptiacus_), and likewise with some mongrels which
I raised between the Penguin and Labrador duck. I am not much surprised
that some writers have maintained that this breed must be descended
from an unknown and distinct species; but from the reasons already
assigned, it seems to me far more probable that it is the descendant,
much modified by domestication under an unnatural climate, of _Anas
boschas_.
[Illustration: Fig. 39.--Skulls, viewed laterally, reduced to
two-thirds of the natural size. A. Wild Duck. B. Hook-billed Duck.]
_Osteological Characters._--The skulls of the several breeds differ
from each other and from the skull of the wild duck in very little
except in the proportional length and curvature of the premaxillaries.
These latter bones in the Call-duck are short, and a line drawn from
their extremities to the summit of the skull is nearly straight,
instead of being concave as in the {283} common duck; so that the skull
resembles that of a small goose. In the hook-billed duck (fig. 39)
these same bones as well as the lower jaw curve downwards in a most
remarkable manner, as represented. In the Labrador duck the
premaxillaries are rather broader than in the wild duck; and in two
skulls of this breed the vertical ridges on each side of the
supra-occipital bone are very prominent. In the Penguin the
premaxillaries are relatively shorter than in the wild duck; and the
inferior points of the paramastoids more prominent. In a Dutch tufted
duck, the skull under the enormous tuft was slightly more globular and
was perforated by two large apertures; in this skull the lachrymal
bones were produced much further backwards, so as to have a different
shape and to nearly touch the post. lat. processes of the frontal
bones, thus almost completing the bony orbit of the eye. As the
quadrate and pterygoid bones are of such complex shape and stand in
relation with so many other bones, I carefully compared them in all the
principal breeds; but excepting in size they presented no difference.
[Illustration: Fig. 40.--Cervical Vertebrae, of natural size. A. Eighth
cervical vertebra of Wild Duck, viewed on haemal surface. B. Eighth
cervical vertebra of Call Duck, viewed as above. C. Twelfth cervical
vertebra of Wild Duck, viewed laterally. D. Twelfth cervical vertebra
of Aylesbury Duck, viewed laterally.]
_Vertebrae and Ribs._--In one skeleton of the Labrador duck there were
the usual fifteen cervical vertebrae and the usual nine dorsal vertebrae
bearing ribs; in the other skeleton there were fifteen cervical and ten
dorsal vertebrae with ribs; nor, as far as could be judged, was this
owing merely to a rib having been developed on the first lumbar
vertebra; for in both skeletons the lumbar vertebrae agreed perfectly in
number, shape, and size with those of the wild duck. In two skeletons
of the Call-duck there were fifteen cervical and nine dorsal vertebrae;
in a third skeleton small ribs were attached to the so-called fifteenth
cervical vertebra, making ten pairs of ribs; but these ten ribs do not
correspond, or arise from the same vertebrae, with the ten in the
above-mentioned Labrador duck. In the Call-duck, which had small ribs
attached to the fifteenth cervical vertebra, the haemal spines of the
thirteenth and fourteenth (cervical) and of the seventeenth (dorsal)
vertebrae corresponded with the spines on the fourteenth, fifteenth, and
eighteenth vertebrae of the wild duck: so that each of these vertebrae
had acquired a structure proper to one posterior to it in position. In
the twelfth cervical vertebra of this same Call-duck (fig. 40, B), the
two branches of the haemal spine stand much closer together than in the
wild duck (A), and the descending haemal processes are much shortened.
In the Penguin duck the neck from its thinness and erectness falsely
appears (as ascertained by measurement) to be much elongated, but the
cervical and dorsal vertebrae present no difference; the posterior
dorsal vertebrae, however, are more completely anchylosed to {284} the
pelvis than in the wild duck. The Aylesbury duck has fifteen cervical
and ten dorsal vertebrae furnished with ribs, but the same number of
lumbar, sacral, and caudal vertebrae, as far as could be traced, as in
the wild duck. The cervical vertebrae in this same duck (fig. 40, D)
were much broader and thicker relatively to their length than in the
wild (C); so much so, that I have thought it worth while to give a
sketch of the eighth cervical vertebra in these two birds. From the
foregoing statements we see that the fifteenth cervical vertebra
occasionally becomes modified into a dorsal vertebra, and when this
occurs all the adjoining vertebrae are modified. We also see that an
additional dorsal vertebra bearing a rib is occasionally developed, the
number of the cervical and lumbar vertebrae apparently remaining the
same as usual.
I examined the bony enlargement of the trachea in the males of the
Penguin, Call, Hook-billed, Labrador, and Aylesbury breeds; and in all
it was identical in shape.
The _Pelvis_ is remarkably uniform; but in the skeleton of the
Hook-billed duck the anterior part is much bowed inwards; in the
Aylesbury and some other breeds the ischiadic foramen is less
elongated. In the sternum, furcula, coracoids, and scapula, the
differences are so slight and so variable as not to be worth notice,
except that in two skeletons of the Penguin duck the terminal portion
of the scapula was much attenuated.
In the bones of the leg and wing no modification in shape could be
observed. But in Penguin and Hook-billed ducks, the terminal phalanges
of the wing are a little shortened. In the former, the femur and
metatarsus (but not the tibia) are considerably lengthened, relatively
to the same bones in the wild duck, and to the wing-bones in both
birds. This elongation of the leg-bones could be seen whilst the bird
was alive, and is no doubt connected with its peculiar upright manner
of walking. In a large Aylesbury duck, on the other hand, the tibia was
the only bone of the leg which relatively to the other bones was
slightly lengthened.
_On the effects of the increased and decreased Use of the Limbs._--In
all the breeds the bones of the wing (measured separately after having
been cleaned) relatively to those of the leg have become slightly
shortened, in comparison with the same bones in the wild duck, as may
be seen in the following table:--
+--------------------+-----------------+-------------------+-----------+
| | Length of Femur,| Length of Humerus,| |
| Name of Breed. | Tibia, and | Radius, and | |
| | Metatarsus | Metacarpus | Or as |
| | together. | together. | |
+--------------------+-----------------+-------------------+-----------+
| | Inches. | Inches. | |
|Wild mallard | 7.14 | 9.28 | 100 : 129 |
|Aylesbury | 8.64 | 10.43 | 100 : 120 |
|Tufted (Dutch) | 8.25 | 9.83 | 100 : 119 |
|Penguin | 7.12 | 8.78 | 100 : 123 |
|Call | 6.20 | 7.77 | 100 : 125 |
+--------------------+-----------------+-------------------+-----------+
| | Length of same | Length of all the | |
| | Bones. | Bones of Wing. | |
| +-----------------+-------------------+ |
| | Inches. | Inches. | |
|Wild duck | | | |
|(another specimen) | 6.85 | 10.07 | 100 : 147 |
|Common domestic duck| 8.15 | 11.26 | 100 : 138 |
+--------------------+-----------------+-------------------+-----------+
{285}
In the foregoing table we see that, in comparison with the wild duck,
the reduction in the length of the bones of the wing, relatively to
those of the legs, though slight, is universal. The reduction is least
in the Call-duck, which has the power and the habit of frequently
flying.
In weight there is a greater relative difference between the bones of
the leg and wing, as may be seen in the following table:--
+--------------------+-----------------+-------------------+-----------+
| | Weight of Femur,| Weight of | |
| Name of Breed. | Tibia, and | Humerus, Radius, | |
| | Metatarsus | and Metacarpus | Or as |
+--------------------+-----------------+-------------------+-----------+
| | Grains. | Grains. | |
|Wild mallard | 54 | 97 | 100 : 179 |
|Aylesbury | 164 | 204 | 100 : 124 |
|Hooked-bill | 107 | 160 | 100 : 149 |
|Tufted (Dutch) | 111 | 148 | 100 : 133 |
|Penguin | 75 | 90.5 | 100 : 120 |
|Labrador | 141 | 165 | 100 : 117 |
|Call | 57 | 93 | 100 : 163 |
+--------------------+-----------------+-------------------+-----------+
| |Weight of all the| Weight of all the | |
| | Bones of the | Bones of the | |
| | Leg and Foot. | Wing. | |
| +-----------------+-------------------+ |
| | Grains. | Grains. | |
|Wild duck | | | |
|(another specimen) | 66 | 115 | 100 : 173 |
|Common domestic duck| 127 | 158 | 100 : 124 |
+--------------------+-----------------+-------------------+-----------+
In these domesticated birds, the considerably lessened weight of the
bones of the wing (_i.e._ on an average, twenty-five per cent. of their
proper proportional weight), as well as their slightly lessened length,
relatively to the leg-bones, might follow, not from any actual decrease
in the wing-bones, but from the increased weight and length of the
bones of the legs. The first of the two tables on the next page shows
that the leg-bones relatively to the weight of the entire skeleton have
really increased in weight; but the second table shows that according
to the same standard the wing-bones have also really decreased in
weight; so that the relative disproportion shown in the foregoing
tables between the wing and leg bones, in comparison with those of the
wild duck, is partly due to the increase in weight and length of the
leg-bones, and partly to the decrease in weight and length of the
wing-bones.
With respect to the two following tables, I may first state that I
tested them by taking another skeleton of a wild duck and of a common
domestic duck, and by comparing the weight of _all_ the bones of the
leg with _all_ those of the wings, and the result was the same. In the
first of these tables we see that the leg-bones in each case have
increased in actual weight. It might have been expected that, with the
increased or decreased weight of the entire skeleton, the leg-bones
would have become proportionally heavier or lighter; but their greater
weight in all the breeds relatively to the other bones can be accounted
for only by these domestic birds having used their legs in walking and
standing much more than the wild, for they never fly, and the more
artificial breeds rarely swim. In the second {286} table we see, with
the exception of one case, a plain reduction in the weight of the bones
of the wing, and this no doubt has resulted from their lessened use.
The one exceptional case, namely, in one of the Call-ducks, is in truth
no exception, for this bird was constantly in the habit of flying
about: and I have seen it day after day rise from my grounds, and fly
for a long time in circles of more than a mile in diameter. In this
Call-duck there is not only no decrease, but an actual increase in the
weight of the wing-bones relatively to those of the wild duck; and this
probably is consequent on the remarkable lightness and thinness of all
the bones of the skeleton.
+--------------------+-------------------+-----------------+-----------+
| | Weight of entire | Weight of | |
| Name of Breed. | Skeleton. | Femur, Tibia, | |
| | (N.B. One | and Metatarsus. | Or as |
| | Metatarsus and | | |
| | Foot was | | |
| | removed from each | | |
| | skeleton, as it | | |
| | had been | | |
| | accidentally lost | | |
| | in two cases.) | | |
|--------------------+-------------------+-----------------+-----------+
| | Grains. | Grains. | |
|Wild mallard | 839 | 54 | 1000 : 64 |
|Aylesbury | 1925 | 164 | 1000 : 85 |
|Tufted (Dutch) | 1404 | 111 | 1000 : 79 |
|Penguin | 871 | 75 | 1000 : 86 |
|Call (from Mr. Fox) | 717 | 57 | 1000 : 79 |
+--------------------+-------------------+-----------------+-----------+
| |Weight of Skeleton | Weight of | |
| | as above. | Humerus, | |
| | | Radius and | |
| | | Ulna, and | |
| | | Metacarpus. | |
| +-------------------+-----------------+ |
| | Grains. | Grains. | |
|Wild mallard | 839 | 97 |1000 : 115 |
|Aylesbury | 1925 | 204 |1000 : 105 |
|Tufted (Dutch) | 1404 | 148 |1000 : 105 |
|Penguin | 871 | 90 |1000 : 103 |
|Call (from | | | |
| Mr. Baker) | 914 | 100 |1000 : 109 |
|Call (from Mr. Fox) | 717 | 92 |1000 : 129 |
+--------------------+-------------------+-----------------+-----------+
Lastly, I weighed the furcula, coracoids, and scapula of a wild duck
and of a common domestic duck, and I found that their weight,
relatively to that of the whole skeleton, was as one hundred in the
former to eighty-nine in the latter; this shows that these bones in the
domestic duck have been reduced eleven per cent. of their due
proportional weight. The prominence of the crest of the sternum,
relatively to its length, is also much reduced in all the domestic
breeds. These changes have evidently been caused by the lessened use of
the wings.
It is well known that several birds, belonging to different Orders, and
inhabiting oceanic islands, have their wings greatly reduced in size and
are incapable of flight. I suggested in my 'Origin of Species' that, as
these birds are not persecuted by any enemies, the reduction of their wings
has probably been caused by gradual disuse. Hence, during the earlier
stages of the {287} process of reduction, such birds might be expected to
resemble in the state of their organs of flight our domesticated ducks.
This is the case with the water-hen (_Gallinula nesiotis_) of Tristan
d'Acunha, which "can flutter a little, but obviously uses its legs, and not
its wings, as a mode of escape." Now Mr. Sclater[454] finds in this bird
that the wings, sternum, and coracoids, are all reduced in length, and the
crest of the sternum in depth, in comparison with the same bones in the
European water-hen (_G. chloropus_). On the other hand, the thigh-bones and
pelvis are increased in length, the former by four lines, relatively to the
same bones in the common water-hen. Hence in the skeleton of this natural
species nearly the same changes have occurred, only carried a little
further, as with our domestic ducks, and in this latter case I presume no
one will dispute that they have resulted from the lessened use of the wings
and the increased use of the legs.
THE GOOSE.
This bird deserves some notice, as hardly any other anciently domesticated
bird or quadruped has varied so little. That geese were anciently
domesticated we know from certain verses in Homer; and from these birds
having been kept (388 B.C.) in the Capitol at Rome as sacred to Juno, which
sacredness implies great antiquity[455]. That the goose has varied in some
degree, we may infer from naturalists not being unanimous with respect to
its wild parent-form; though the difficulty is chiefly due to the existence
of three or four closely allied wild European species[456]. A large
majority of capable judges are convinced that our geese are descended from
the wild Grey-lag goose (_A. ferus_); the young of which can easily be
tamed,[457] and are domesticated by the Laplanders. This species, when
crossed with the domestic goose, produced in the Zoological Gardens, as I
was assured in {288} 1849, perfectly fertile offspring.[458] Yarrell[459]
has observed that the lower part of the trachea of the domestic goose is
sometimes flattened, and that a ring of white feathers sometimes surrounds
the base of the beak. These characters seem at first good indications of a
cross at some former period with the white-fronted goose (_A. albifrons_);
but the white ring is variable in this latter species, and we must not
overlook the law of analogous variation; that is, of one species assuming
some of the characters of allied species.
As the goose has proved so inflexible in its organization under
long-continued domestication, the amount of variation which can be detected
is worth giving. It has increased in size and in productiveness;[460] and
varies from white to a dusky colour. Several observers[461] have stated
that the gander is more frequently white than the goose, and that when old
it almost invariably becomes white; but this is not the case with the
parent-form, the _A. ferus_. Here, again, the law of analogous variation
may have come into play, as the snow-white male of the Rock-Goose
(_Bernicla antarctica_) standing on the sea-shore by his dusky partner is a
sight well known to all those who have traversed the sounds of Tierra del
Fuego and the Falkland Islands. Some geese have topknots; and the skull
beneath, as before stated, is perforated. A sub-breed has lately been
formed with the feathers reversed at the back of the head and neck.[462]
The beak varies a little in size, and is of a yellower tint than in the
wild species; but its colour and that of the legs are both slightly
variable.[463] This latter fact deserves attention, because the colour of
the legs and beak is highly serviceable in discriminating the several
closely allied wild forms.[464] At our {289} Shows two breeds are
exhibited; viz. the Embden and Toulouse; but they differ in nothing except
colour.[465] Recently a smaller and singular variety has been imported from
Sebastopol,[466] with the scapular feathers (as I hear from Mr. Tegetmeier,
who sent me specimens) greatly elongated, curled, and even spirally
twisted. The margins of these feathers are rendered plumose by the
divergence of the barbs and barbules, so that they resemble in some degree
those on the back of the black Australian swan. These feathers are likewise
remarkable from the central shaft, which is excessively thin and
transparent, being split into fine filaments, which, after running for a
space free, sometimes coalesce again. It is a curious fact that these
filaments are regularly clothed on each side with fine down or barbules,
precisely like those on the proper barbs of the feather. This structure of
the feathers is transmitted to half-bred birds. In _Gallus sonneratii_ the
barbs and barbules blend together, and form thin horny plates of the same
nature with the shaft: in this variety of the goose, the shaft divides into
filaments which acquire barbules, and thus resemble true barbs.
Although the domestic goose certainly differs somewhat from any known wild
species, yet the amount of variation which it has undergone, as compared
with most domesticated animals, is singularly small. This fact can be
partially accounted for by selection not having come largely into play.
Birds of all kinds which present many distinct races are valued as pets or
ornaments; no one makes a pet of the goose; the name, indeed, in more
languages than one, is a term of reproach. The goose is valued for its size
and flavour, for the whiteness of its feathers which adds to their value,
and for its prolificness and tameness. In all these points the goose
differs from the wild parent-form; and these are the points which have been
selected. Even in ancient times the Roman gourmands valued the liver of the
_white_ goose; and Pierre Belon[467] in 1555 speaks of two varieties, one
of which was larger, more fecund, and of a better colour than the other;
and he expressly states that good managers {290} attended to the colour of
their goslings, so that they might know which to preserve and select for
breeding.
THE PEACOCK.
This is another bird which has hardly varied under domestication, except in
sometimes being white or piebald. Mr. Waterhouse carefully compared, as he
informs me, skins of the wild Indian and domestic bird, and they were
identical in every respect, except that the plumage of the latter was
perhaps rather thicker. Whether our birds are descended from those
introduced into Europe in the time of Alexander, or have been subsequently
imported, is doubtful. They do not breed very freely with us, and are
seldom kept in large numbers,--circumstances which would greatly interfere
with the gradual selection and formation of new breeds.
There is one strange fact with respect to the peacock, namely, the
occasional appearance in England of the "japanned" or "black-shouldered"
kind. This form has lately been named on the high authority of Mr. Sclater
as a distinct species, viz. _Pavo nigripennis_, which he believes will
hereafter be found wild in some country, but not in India, where it is
certainly unknown. These japanned birds differ conspicuously from the
common peacock in the colour of their secondary wing-feathers, scapulars,
wing-coverts, and thighs; the females are much paler, and the young, as I
hear from Mr. Bartlett, likewise differ. They can be propagated perfectly
true. Although they do not resemble the hybrids which have been raised
between _P. cristatus_ and _muticus_, nevertheless they are in some
respects intermediate in character between these two species; and this fact
favours, as Mr. Sclater believes, the view that they form a distinct and
natural species.[468]
On the other hand, Sir R. Heron states[469] that this breed suddenly
appeared within his memory in Lord Brownlow's large stock of pied, white,
and common peacocks. The same thing occurred in Sir J. Trevelyan's flock
composed entirely of the {291} common kind, and in Mr. Thornton's stock of
common and pied peacocks. It is remarkable that in these two latter
instances the black-shouldered kind increased, "to the extinction of the
previously existing breed." I have also received through Mr. Sclater a
statement from Mr. Hudson Gurney that he reared many years ago a pair of
black-shouldered peacocks from the common kind; and another ornithologist,
Prof. A. Newton, states that, five or six years ago, a female bird, in all
respects similar to the female of the black-shouldered kind, was produced
from a stock of common peacocks in his possession, which during more than
twenty years had not been crossed with birds of any other strain. Here we
have five distinct cases of japanned birds suddenly appearing in flocks of
the common kind kept in England. Better evidence of the first appearance of
a new variety could hardly be desired. If we reject this evidence, and
believe that the japanned peacock is a distinct species, we must suppose in
all these cases that the common breed had at some former period been
crossed with the supposed _P. nigripennis_, but had lost every trace of the
cross, yet that the birds occasionally produced offspring which suddenly
and completely reacquired through reversion the characters of _P.
nigripennis_. I have heard of no other such case in the animal or vegetable
kingdom. To perceive the full improbability of such an occurrence, we may
suppose that a breed of dogs had been crossed at some former period with a
wolf, but had lost every trace of the wolf-like character, yet that the
breed gave birth in five instances in the same country, within no great
length of time, to a wolf perfect in every character; and we must further
suppose that in two of the cases the newly produced wolves afterwards
spontaneously increased to such an extent as to lead to the extinction of
the parent-breed of dogs. So remarkable a form as the _P. nigripennis_,
when first imported, would have realized a large price; it is therefore
improbable that it should have been silently introduced and its history
subsequently lost. On the whole the evidence seems to me, as it did to Sir
R. Heron, to preponderate strongly in favour of the black-shouldered breed
being a variation, induced either by the climate of England, or by some
unknown cause, such as reversion to a primordial and extinct condition of
the species. On the view that the black-shouldered {292} peacock is a
variety, the case is the most remarkable ever recorded of the abrupt
appearance of a new form, which so closely resembles a true species that it
has deceived one of the most experienced of living ornithologists.
THE TURKEY.
IT seems fairly well established by Mr. Gould,[470] that the turkey, in
accordance with the history of its first introduction, is descended from a
wild Mexican species (_Meleagris Mexicana_) which had been already
domesticated by the natives before the discovery of America, and which
differs specifically, as it is generally thought, from the common wild
species of the United States. Some naturalists, however, think that these
two forms should be ranked only as well-marked geographical races. However
this may be, the case deserves notice because in the United States wild
male turkeys sometimes court the domestic hens, which are descended from
the Mexican form, "and are generally received by them with great
pleasure."[471] Several accounts have likewise been published of young
birds, reared in the United States from the eggs of the wild species,
crossing and commingling with the common breed. In England, also, this same
species has been kept in several parks; from two of which the Rev. W. D.
Fox procured birds, and they crossed freely with the common domestic kind,
and during many years afterwards, as he informs me, the turkeys in his
neighbourhood clearly showed traces of their crossed parentage. We here
have an instance of a domestic race being modified by a cross with a
distinct species or wild race. F. Michaux[472] suspected in 1802 that the
common domestic turkey was not descended from the United States species
alone, but likewise from a southern form, and he went so far as to believe
that English and French {293} turkeys differed from having different
proportions of the blood of the two parent-forms.
English turkeys are smaller than either wild form. They have not varied in
any great degree; but there are some breeds which can be distinguished--as
Norfolks, Suffolks, Whites, and Copper-coloured (or Cambridge), all of
which, if precluded from crossing with other breeds, propagate their kind
truly. Of these kinds, the most distinct is the small, hardy, dull-black
Norfolk turkey, of which the chickens are black, with occasionally white
patches about the head. The other breeds scarcely differ except in colour,
and their chickens are generally mottled all over with brownish-grey.[473]
The tuft of hair on the breast, which is proper to the male alone,
occasionally appears on the breast of the domesticated female.[474] The
inferior tail-coverts vary in number, and according to a German
superstition the hen lays as many eggs as the cock has feathers of this
kind.[475] In Holland there was formerly, according to Temminck, a
beautiful buff-yellow breed, furnished with an ample white topknot. Mr.
Wilmot has described[476] a white turkey-cock with a crest formed of
"feathers about four inches long, with bare quills, and a tuft of soft
white down growing at the end." Many of the young birds whilst young
inherited this kind of crest, but afterwards it either fell off or was
pecked out by the other birds. This is an interesting case, as with care a
new breed might probably have been formed; and a topknot of this nature
would have been to a certain extent analogous to that borne by the males in
several allied genera, such as Euplocomus, Lophophorus, and Pavo.
Wild turkeys, believed in every instance to have been imported from the
United States, have been kept in the parks of Lords Powis, Leicester, Hill,
and Derby. The Rev. W. D. Fox procured birds from the two first-named
parks, and he informs me that they certainly differed a little from each
other in the shape of their bodies and in the barred plumage on their
wings. These birds likewise differed from Lord Hill's stock. Some of the
latter kept at Oulton by Sir P. Egerton, though precluded from {294}
crossing with common turkeys, occasionally produced much paler-coloured
birds, and one that was almost white, but not an albino. These half-wild
turkeys in thus slightly differing from each other present an analogous
case with the wild cattle kept in the several British parks. We must
suppose that the differences have resulted from the prevention of free
intercrossing between birds ranging over a wide area, and from the changed
conditions to which they have been exposed in England. In India the climate
has apparently wrought a still greater change in the turkey, for it is
described by Mr. Blyth[477] as being much degenerated in size, "utterly
incapable of rising on the wing," of a black colour, and "with the long
pendulous appendages over the beak enormously developed."
THE GUINEA FOWL.
The domesticated guinea-fowl is now believed by naturalists to be descended
from the _Numida ptilorhynca_, which inhabits very hot, and, in parts,
extremely arid districts in Eastern Africa; consequently it has been
exposed in this country to extremely different conditions of life.
Nevertheless it has hardly varied at all, except in the plumage being
either paler or darker-coloured. It is a singular fact that this bird
varies more in colour in the West Indies and on the Spanish Main, under a
hot though humid climate, than in Europe.[478] The guinea-fowl has become
thoroughly feral in Jamaica and in St. Domingo,[479] and has diminished in
size; the legs are black, whereas the legs of the aboriginal African bird
are said to be grey. This small change is worth notice on account of the
often-repeated statement that all feral animals invariably revert in every
character to their original type.
{295}
THE CANARY BIRD.
As this bird has been recently domesticated, namely, within the last 350
years, its variability deserves notice. It has been crossed with nine or
ten other species of Fringillidae, and some of the hybrids are almost
completely fertile; but we have no evidence that any distinct breed has
originated from such crosses. Notwithstanding the modern domestication of
the canary, many varieties have been produced; even before the year 1718 a
list of twenty-seven varieties was published in France,[480] and in 1779 a
long schedule of the desired qualities was printed by the London Canary
Society, so that methodical selection has been practised during a
considerable period. The greater number of the varieties differ only in
colour and in the markings of their plumage. Some breeds, however, differ
in shape, such as the hooped or bowed canaries, and the Belgian canaries
with their much elongated bodies. Mr. Brent[481] measured one of the latter
and found it eight inches in length, whilst the wild canary is only five
and a quarter inches long. There are topknotted canaries, and it is a
singular fact, that, if two topknotted birds are matched, the young,
instead of having very fine topknots, are generally bald, or even have a
wound on their heads.[482] It would appear as if the topknot were due to
some morbid condition which is increased to an injurious degree when two
birds in this state are paired. There is a feather-footed breed, and
another with a kind of frill running down the breast. One other character
deserves notice from being confined to one period of life and from being
strictly inherited at the same period: namely, the wing and tail feathers
in prize canaries being black, "but this colour is retained only until the
first moult; once moulted, the peculiarity ceases."[483] Canaries differ
much in disposition and character, and in some small degree in song. They
produce eggs three or four times during the year.
{296}
GOLD-FISH.
Besides mammals and birds, few animals belonging to the other great classes
have been domesticated; but to show that it is an almost universal law that
animals, when removed from their natural conditions of life, vary, and that
races can be formed when selection is applied, it is necessary to say a few
words on gold-fish, bees, and silk-moths.
Gold-fish (_Cyprinus auratus_) were introduced into Europe only two or
three centuries ago; but it is believed that they have been kept in
confinement from an ancient period in China. Mr. Blyth[484] suspects from
the analogous variation of other fishes that golden-coloured fish do not
occur in a state of nature. These fishes frequently live under the most
unnatural conditions, and their variability in colour, size, and in some
important points of structure is very great. M. Sauvigny has described and
given coloured drawings of no less than eighty-nine varieties.[485] Many of
the varieties, however, such as triple tail-fins, &c., ought to be called
monstrosities; but it is difficult to draw any distinct line between a
variation and a monstrosity. As gold-fish are kept for ornament or
curiosity, and as "the Chinese are just the people to have secluded a
chance variety of any kind, and to have matched and paired from it,"[486]
we may feel nearly confident that selection has been largely practised in
the formation of new breeds. It is however a singular fact that some of the
monstrosities or variations are not inherited; for Sir R. Heron[487] kept
many of these fishes, and placed all the deformed fishes, namely those
destitute of dorsal fins, and those furnished with a double anal fin, or
triple tail, in a pond by themselves; but they did "not produce a greater
proportion of deformed offspring than the perfect fishes."
Passing over an almost infinite diversity of colour, we meet with the most
extraordinary modifications of structure. Thus, out of about two dozen
specimens bought in London, Mr. Yarrell observed some with the dorsal fin
extending along more than {297} half the length of the back; others with
this fin reduced to only five or six rays; and one with no dorsal fin. The
anal fins are sometimes double, and the tail is often triple. This latter
deviation of structure seems generally to occur "at the expense of the
whole or part of some other fin;"[488] but Bory de Saint Vincent[489] saw
at Madrid gold-fish furnished with a dorsal fin and a triple tail. One
variety is characterized by a hump on its back near the head; and the Rev.
L. Jenyns[490] has described a most singular variety, imported from China,
almost globular in form like a Diodon, with "the fleshy part of the tail as
if entirely cut away; the caudal fin being set on a little behind the
dorsal and immediately above the anal." In this fish the anal and caudal
fins were double; the anal fin being attached to the body in a vertical
line: the eyes also were enormously large and protuberant.
HIVE-BEES.
Bees have been domesticated from an ancient period; if indeed their state
can be considered one of domestication, for they search for their own food,
with the exception of a little generally given to them during the winter.
Their habitation is a hive instead of a hole in a tree. Bees, however, have
been transported into almost every quarter of the world, so that climate
ought to have produced whatever direct effect it is capable of producing.
It is frequently asserted that the bees in different parts of Great Britain
differ in size, colour, and temper; and Godron[491] says that they are
generally larger in the south than in other parts of France; it has also
been asserted that the little brown bees of High Burgundy, when transported
to La Bresse, become large and yellow in the second generation. But these
statements require confirmation. As far as size is concerned, it is known
that bees produced in very old combs are smaller, owing to the cells having
become smaller from the {298} successive old cocoons. The best
authorities[492] concur that, with the exception of the Ligurian race or
species, presently to be mentioned, distinct breeds do not exist in Britain
or on the Continent. There is, however, even in the same stock, some
variability in colour. Thus Mr. Woodbury states[493] that he has several
times seen queen bees of the common kind annulated with yellow like
Ligurian queens, and the latter dark-coloured like common bees. He has also
observed variations in the colour of the drones, without any corresponding
difference in the queens or workers of the same hive. The great apiarian
Dzierzon, in answer to my queries on this subject, says[494] that in
Germany bees of some stocks are decidedly dark, whilst others are
remarkable for their yellow colour. Bees also seem to differ in habits in
different districts, for Dzierzon adds, "If many stocks with their
offspring are more inclined to swarm, whilst others are richer in honey, so
that some bee-keepers even distinguish between swarming and honey-gathering
bees, this is a habit which has become second nature, caused by the
customary mode of keeping the bees and the pasturage of the district. For
example; what a difference in this respect one may perceive to exist
between the bees of the Lueneburg heath and those of this country!"...
"Removing an old queen and substituting a young one of the current year is
here an infallible mode of keeping the strongest stock from swarming and
preventing drone-breeding; whilst the same means if adopted in Hanover
would certainly be of no avail." I procured a hive full of dead bees from
Jamaica, where they have long been naturalised, and, on carefully comparing
them under the microscope with my own bees, I could detect not a trace of
difference.
This remarkable uniformity in the hive-bee, wherever kept, may probably be
accounted for by the great difficulty, or rather impossibility, of bringing
selection into play by pairing particular queens and drones, for these
insects unite only during {299} flight. Nor is there any record, with a
single partial exception, of any person having separated and bred from a
hive in which the workers presented some appreciable difference. In order
to form a new breed, seclusion from other bees would, as we now know, be
indispensable; for since the introduction of the Ligurian bee into Germany
and England, it has been found that the drones wander at least two miles
from their own hives, and often cross with the queens of the common
bee.[495] The Ligurian bee, although perfectly fertile when crossed with
the common kind, is ranked by most naturalists as a distinct species,
whilst by others it is ranked as a natural variety: but this form need not
here be noticed, as there is no reason to believe that it is the product of
domestication. The Egyptian and some other bees are likewise ranked by Dr.
Gerstaecker,[496] but not by other highly competent judges, as geographical
races; and he grounds his conclusion in chief part on the fact that in
certain districts, as in the Crimea and Rhodes, the hive-bee varies so much
in colour, that the several geographical races can be closely connected by
intermediate forms.
I have alluded to a single instance of the separation and preservation of a
particular stock of bees. Mr. Lowe[497] procured some bees from a cottager
a few miles from Edinburgh, and perceived that they differed from the
common bee in the hairs on the head and thorax being lighter coloured and
more profuse in quantity. From the date of the introduction of the Ligurian
bee into Great Britain we may feel sure that these bees had not been
crossed with this form. Mr. Lowe propagated this variety, but unfortunately
did not separate the stock from his other bees, and after three generations
the new character was almost completely lost. Nevertheless, as he adds, "a
great number of the bees still retain traces, though faint, of the original
colony." This case shows us what could probably be effected by careful and
long-continued selection applied exclusively to the workers, for, as we
have seen, queens and drones cannot be selected and paired.
{300}
SILK-MOTHS.
These insects are in several respects interesting to us, more especially
because they have varied largely at early periods of life, and the
variations have been inherited at corresponding periods. As the value of
the silk-moth depends entirely on the cocoon, every change in its structure
and qualities has been carefully attended to, and races differing much in
the cocoon, but hardly at all in the adult state, have been produced. With
the races of most other domestic animals, the young resemble each other
closely, whilst the adults differ much.
It would be useless, even if it were possible, to describe all the many
kinds of silk-worms. Several distinct species exist in India and China
which produce useful silk, and some of these are capable of freely crossing
with the common silk-moth, as has been recently ascertained in France.
Captain Hutton[498] states that throughout the world at least six species
have been domesticated; and he believes that the silk-moths reared in
Europe belong to two or three species. This, however, is not the opinion of
several capable judges who have particularly attended to the cultivation of
this insect in France; and hardly accords with some facts presently to be
given.
The common silk-moth (_Bombyx mori_) was brought to Constantinople in the
sixth century, whence it was carried into Italy, and in 1494 into
France.[499] Everything has been favourable for the variation of this
insect. It is believed to have been domesticated in China as long ago as
2700 B.C. It has been kept under unnatural and diversified conditions of
life, and has been transported into many countries. There is reason to
believe that the nature of the food given to the caterpillar influences to
a certain extent the character of the breed.[500] Disuse has apparently
aided in checking the development of the wings. But the most important
element in the production of the many now existing, much modified races, no
doubt has {301} been the close attention which has long been applied in
many countries to every promising variation. The care taken in Europe in
the selection of the best cocoons and moths for breeding is notorious,[501]
and the production of eggs is followed as a distinct trade in parts of
France. I have made inquiries through Dr. Falconer, and am assured that in
India the natives are equally careful in the process of selection. In China
the production of eggs is confined to certain favourable districts, and the
raisers are precluded by law from producing silk, so that their whole
attention may be necessarily given up to this one object.[502]
The following details on the differences between the several breeds are
taken, when not stated to the contrary, from M. Robinet's excellent
work,[503] which bears every sign of care and large experience. The
_eggs_ in the different races vary in colour, in shape (being round,
elliptic, or oval), and in size. The eggs laid in June in the south of
France, and in July in the central provinces, do not hatch until the
following spring; and it is in vain, says M. Robinet, to expose them to
a temperature gradually raised, in order that the caterpillar may be
quickly developed. Yet occasionally, without any known cause, batches
of eggs are produced, which immediately begin to undergo the proper
changes, and are hatched in from twenty to thirty days. From these and
some other analogous facts it may be concluded that the Trevoltini
silkworms of Italy, of which the caterpillars are hatched in from
fifteen to twenty days, do not necessarily form, as has been
maintained, a distinct species. Although the breeds which live in
temperate countries produce eggs which cannot be immediately hatched by
artificial heat, yet when they are removed to and reared in a hot
country they gradually acquire the character of quick development, as
in the Trevoltini races.[504]
_Caterpillars._--These vary greatly in size and colour. The skin is
generally white, sometimes mottled with black or grey, and occasionally
quite black. The colour, however, as M. Robinet asserts, is not
constant, even in perfectly pure breeds; except in the _race tigree_,
so called from being marked with transverse black stripes. As the
general colour of the caterpillar is not correlated with that of the
silk,[505] this character is disregarded {302} by cultivators, and has
not been fixed by selection. Captain Hutton, in the paper before
referred to, has argued with much force that the dark tiger-like marks,
which so frequently appear during the later moults in the caterpillars
of various breeds, are due to reversion; for the caterpillars of
several allied wild species of Bombyx are marked and coloured in this
manner. He separated some caterpillars with the tiger-like marks, and
in the succeeding spring (pp. 149, 298) nearly all the caterpillars
reared from them were dark-brindled, and the tints became still darker
in the third generation. The moths reared from these caterpillars[506]
also became darker, and resembled in colouring the wild _B. Huttoni_.
On this view of the tiger-like marks being due to reversion, the
persistency with which they are transmitted is intelligible.
Several years ago Mrs. Whitby took great pains in breeding silkworms on
a large scale, and she informed me that some of her caterpillars had
dark eyebrows. This is probably the first step in reversion towards the
tiger-like marks, and I was curious to know whether so trifling a
character would be inherited; at my request she separated in 1848
twenty of these caterpillars, and having kept the moths separate, bred
from them. Of the many caterpillars thus reared, "every one without
exception had eyebrows, some darker and more decidedly marked than the
others, but _all_ had eyebrows more or less plainly visible." Black
caterpillars occasionally appear amongst those of the common kind, but
in so variable a manner, that according to M. Robinet the same race
will one year exclusively produce white caterpillars, and the next year
many black ones; nevertheless, I have been informed by M. A. Bossi of
Geneva, that, if these black caterpillars are separately bred from,
they reproduce the same colour; but the cocoons and moths reared from
them do not present any difference.
The caterpillar in Europe ordinarily moults four times before passing
into the cocoon stage; but there are races "a trois mues," and the
Trevoltini race likewise moults only thrice. It might have been thought
that so important a physiological difference would not have arisen
under domestication; but M. Robinet[507] states that, on the one hand,
ordinary caterpillars occasionally spin their cocoons after only three
moults, and, on the other hand, "presque toutes les races a trois mues,
que nous avons experimentees, ont fait quatre mues a la seconde ou a la
troisieme annee, ce qui semble prouver qu'il a suffi de les placer dans
des conditions favorables pour leur rendre une faculte qu'elles avaient
perdue sous des influences moins favorables."
_Cocoons._--The caterpillar in changing into the cocoon loses about 50
per cent. of its weight; but the amount of loss differs in different
breeds, and this is of importance to the cultivator. The cocoon in the
different races presents characteristic differences; being large or
small;--nearly spherical with no constriction, as in the _Race de
Loriol_, or cylindrical with either a deep or slight constriction in
the middle;--with the two ends, or with one end alone, more or less
pointed. The silk varies in fineness and quality, and in being nearly
white, of two tints, or yellow. Generally the colour of {303} the silk
is not strictly inherited: but in the chapter on Selection I shall give
a curious account how, in the course of sixty-five generations, the
number of yellow cocoons in one breed has been reduced in France from
one hundred to thirty-five in the thousand. According to Robinet, the
white race, called Sina, by careful selection during the last
seventy-five years, "est arrivee a un tel etat de purete, qu'on ne voit
pas un seul cocon jaune dans des millions de cocons blancs."[508]
Cocoons are sometimes formed, as is well known, entirely destitute of
silk, which yet produce moths; unfortunately Mrs. Whitby was prevented
by an accident from ascertaining whether this character would prove
hereditary.
_Adult stage._--I can find no account of any constant difference in the
moths of the most distinct races. Mrs. Whitby assured me that there was
none in the several kinds bred by her; and I have received a similar
statement from the eminent naturalist M. de Quatrefages. Captain Hutton
also says[509] that the moths of all kinds vary much in colour, but in
nearly the same inconstant manner. Considering how much the cocoons in
the several races differ, this fact is of interest, and may probably be
accounted for on the same principle as the fluctuating variability of
colour in the caterpillar, namely, that there has been no motive for
selecting and perpetuating any particular variation.
The males of the wild Bombycidae "fly swiftly in the day-time and
evening, but the females are usually very sluggish and inactive."[510]
In several moths of this family the females have abortive wings, but no
instance is known of the males being incapable of flight, for in this
case the species could hardly have been perpetuated. In the silk-moth
both sexes have imperfect, crumpled wings, and are incapable of flight;
but still there is a trace of the characteristic difference in the two
sexes; for though, on comparing a number of males and-females, I could
detect no difference in the development of their wings, yet I was
assured by Mrs. Whitby that the males of the moths bred by her used
their wings more than the females, and could flutter downwards, though
never upwards. She also states that, when the females first emerge from
the cocoon, their wings are less expanded than those of the male. The
degree of imperfection, however, in the wings varies much in different
races and under different circumstances; M. Quatrefages[511] says that
he has seen a number of moths with their wings reduced to a third,
fourth, or tenth part of their normal dimensions, and even to mere
short straight stumps: "il me semble qu'il y a la un veritable arret de
developpement partiel." On the other hand, he describes the female
moths of the Andre Jean breed as having "leurs ailes larges et etalees.
Un seul presente quelques courbures irregulieres et des plis anomaux."
As moths and butterflies of all kinds reared from wild caterpillars
under confinement often have crippled wings, the same cause, whatever
it may be, has probably acted on {304} silk-moths, but the disuse of
their wings during so many generations has, it may be suspected,
likewise come into play.
The moths of many breeds fail to glue their eggs to the surface on
which they are laid,[512] but this proceeds, according to Capt.
Hutton,[513] merely from the glands of the ovipositor being weakened.
As with other long-domesticated animals, the instincts of the silk-moth
have suffered. The caterpillars, when placed on a mulberry-tree, often
commit the strange mistake of devouring the base of the leaf on which
they are feeding, and consequently fall down; but they are capable,
according to M. Robinet,[514] of again crawling up the trunk. Even this
capacity sometimes fails, for M. Martins[515] placed some caterpillars
on a tree, and those which fell were not able to remount and perished
of hunger; they were even incapable of passing from leaf to leaf.
Some of the modifications which the silk-moth has undergone stand in
correlation with each other. Thus the eggs of the moths which produce
white cocoons and of those which produce yellow cocoons differ slightly
in tint. The abdominal feet also of the caterpillars which yield white
cocoons are always white, whilst those which give yellow cocoons are
invariably yellow.[516] We have seen that the caterpillars with dark
tiger-like stripes produce moths which are more darkly shaded than
other moths. It seems well established[517] that in France the
caterpillars of the races which produce white silk, and certain black
caterpillars, have resisted, better than other races, the disease which
has recently devastated the silk-districts. Lastly, the races differ
constitutionally, for some do not succeed so well under a temperate
climate as others; and a damp soil does not equally injure all the
races.[518]
From these various facts we learn that silk-moths, like the higher animals,
vary greatly under long-continued domestication. We learn also the more
important fact that variations may occur at various periods of life, and be
inherited at corresponding periods. And finally we see that insects are
amenable to the great principle of Selection.
* * * * *
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