Lastly, I weighed the furculum, 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 had probably been caused by gradual disuse. Hence, during the earlier stages of the process of reduction, such birds would probably have resembled our domesticated ducks in the state of their organs of flight. 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 (8/19. 'Proc. Zoolog. Soc.' 1861 page 261.) 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. (8/20. 'Ceylon' by Sir J.E. Tennent 1859 volume 1 page 485; also J. Crawfurd on the 'Relation of Domest. Animals to Civilisation' read before Brit. Assoc. 1860. See also 'Ornamental Poultry' by Rev. E.S. Dixon 1848 page 132. The goose figured on the Egyptian monuments seems to have been the Red goose of Egypt.) 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. (8/21. Macgillivray's 'British Birds' volume 4 page 593.) A large majority of capable judges are convinced that our geese are descended from the wild Grey-leg goose (Anser ferus); the young of which can easily be tamed. (8/22. Mr. A. Strickland, 'Annals and Mag. of Nat. Hist.' 3rd series volume 3 1859 page 122, reared some young wild geese, and found them in habits and in all characters identical with the domestic goose.) This species, when crossed with the domestic goose, produced in the Zoological Gardens, as I was assured in 1849, perfectly fertile offspring. (8/23. See also Hunter 'Essays' edited by Owen volume 2 page 322.) Yarrell (8/24. Yarrell's 'British Birds' volume 3 page 142.) 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 sight 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 little flexible in its organisation under long- continued domestication, the amount of variation which it has undergone may be worth giving. It has increased in size and in productiveness (8/25. L. Lloyd 'Scandinavian Adventures' 1854 volume 2 page 413, says that the wild goose lays from five to eight eggs, which is a much fewer number than that laid by our domestic goose.); and varies from white to a dusky colour. Several observers (8/26. The Rev. L. Jenyns (Blomefield) seems first to have made this observation in his 'British Animals.' See also Yarrell, and Dixon in his 'Ornamental Poultry' (page 139), and 'Gardener's Chronicle' 1857 page 45.) 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 almost snow-white male of the Rock goose (Bernicla antarctica) standing on the sea-shore by his dusky partner is a sight well known to those who have traversed the sounds of Tierra del Fuego and the Falkland Islands. Some geese have top-knots; 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. (8/27. Mr. Bartlet exhibited the head and neck of a bird thus characterised before the Zoological Soc. February 1860.) 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. (8/28. W. Thompson 'Natural Hist. of Ireland' 1851 volume 3 page 31. The Rev. E.S. Dixon gave me some information on the varying colour of the beak and legs.) This latter fact deserves attention, because the colour of the legs and beak is highly serviceable in discriminating the several closely allied wild forms. (8/29. Mr. A. Strickland in 'Annals and Mag. of Nat. Hist.' 3rd series volume 3 1859 page 122.) At our Shows two breeds are exhibited; viz., the Embden and Toulouse; but they differ in nothing except colour. (8/30. 'Poultry Chronicle' volume 1 1854 page 498; volume 3 page 210.) Recently a smaller and singular variety has been imported from Sebastopol (8/31. 'The Cottage Gardener' September 4, 1860 page 348.), 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 that of 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 (8/32. 'L'Hist. de la Nature des Oiseaux' par P. Belon 1555 page 156. With respect to the livers of white geese being preferred by the Romans see Isid. Geoffroy St.-Hilaire 'Hist. Nat. Gen.' tome 3 page 58.) 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 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. The males of these japanned birds differ conspicuously from the common peacock in the colour of their secondary wing-feathers, scapulars, wing-coverts, and thighs, and are I think more beautiful; they are rather smaller than the common sort, and are always beaten by them in their battles, as I hear from the Hon. A.S.G. Canning. The females are much paler coloured than those of the common kind. Both sexes, as Mr. Canning informs me, are white when they leave the egg, and they differ from the young of the white variety only in having a peculiar pinkish tinge on their wings. These japanned birds, though appearing suddenly in flocks of the common kind, propagate their kind quite truly. 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. (8/33. Mr. Sclater on the black-shouldered peacock of Latham 'Proc. Zoolog. Soc.' April 24, 1860. Mr. Swinhoe at one time believed, 'Ibis' July 1868, that this kind of peafowl was found wild in Cochin China, but he has since informed me that he feels very doubtful on this head.)
On the other hand, Sir H. Heron states (8/34. 'Proc. Zoolog. Soc.' April 14, 1835.) 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 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, though a smaller and weaker bird, 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. Mr. Jenner Weir informs me that a peacock at Blackheath whilst young was white, but as it became older gradually assumed the characters of the black-shouldered variety; both its parents were common peacocks. Lastly, Mr. Canning has given a case of a female of this same variety appearing in Ireland in a flock of the ordinary kind. (8/35. 'The Field' May 6, 1871. I am much indebted to Mr. Canning for information with respect to his birds.) Here, then, we have seven well authenticated cases in Great Britain of japanned birds, having suddenly appeared within recent times in flocks of the common peafowl. This variety must also have formerly appeared in Europe, for Mr. Canning has seen an old picture, and another is referred to in the 'Field,' with this variety represented. These facts seem to me to indicate that the japanned peacock is a strongly marked variety or "sport," which tends at all times and in many places to reappear. This view is supported by the young being at first white like the young of the white breed, which is undoubtedly a variation. If, on the other hand, we believe the japanned peacock to be a distinct species, we must suppose that in all the above cases the common breed had at some former period been crossed by it, but had lost every trace of the cross; yet that the offspring of these birds 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 seven 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 bird as the P. nigripennis, when first imported, would have realised 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 be decisive in favour of the japanned or black-shouldered breed being a variation, induced by some unknown cause. On this view, the case is the most remarkable one 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.