Variation of animals and plants under domestication, v.2

Page 47

76 INHERITANCE CHAP. XIV. grown plants differ but little. Cabbages on the other hand differ greatly in foliage and manner of growth, but hardly at all in their seeds ; and generally it will be found that the differences between cultivated plants at different periods of growth are not necessarily closely connected together, for plants may differ much in their seeds and little when full-grown, and conversely may yield seeds hardly distinguishable, yet differ much when full­grown. In the several breeds of poultry, descended from a single species, differences in the eggs and chickens, in the plumage at the first and subsequent moults, in the comb and wattles during maturity, are all inherited. With man peculiarities in the milk and second teeth, of which I have received the details, are inhe­ritable, and with man longevity is often transmitted. So again with our improved breeds of cattle and sheep, early maturity, including the early development of the teeth, and with certain breeds of fowl the early appearance of secondary sexual cha­racters, all come under the same head of inheritance at corresponding periods. N umel'ous analogous facts could be given. The silk-moth, perhaps, offers the best instance ; for in the breeds which transmit their characters truly, the eggs differ in size, colour, and shape ;-the caterpillars differ, in moulting three or four times, in colour, even in having a dark-coloured mark like an eyebrow, and in the loss of certain instincts ;-the cocoons differ in size, shape, and in the colour and quality of the silk; these several differences being followed by slight or barely distin­guishable differences in the mature moth. But it may be said that, if in the above cases a new pecu­liarity is inherited, it must be at the corresponding stage of development; for an egg or seed can resemble only an egg or seed, and the horn in a full-grown ox can resemble only a horn. The following cases show inheritance at corresponding periods more plainly, because they refer to peculiarities which might have supervened, as far as we can see, earlier or later in life, yet are inherited at the same period at which they first ap­peared. In the Lambert family the porcupine-like excrescences appeared in the father and sons at the same age, namely, about nine weeks after CHAP. XIV. AT CORRESPONDING PERIODS. 77 birth.29 In the extraordinary hairy family described by Mr. Crawfurd,30 children were produced during three genemtions with hairy ears; in the father the hair began to grow over his body at six years old; in his daughter somewhat earlier, namely, at one year; and in both generations the milk teeth appeared late in life, the permanent teeth being afterwards singularly deficient. Greyness of hair at an unusually early age bas been· transmitted in some families. These cases border on diseases inherited at corresponding periods of life, to which I shall immediately refer. It is a well-known peculiaTity with almond-tumbler pigeons, that the full beauty and peculiaT chaTacter of the plumage does not appear until the bird has moulted two or three times. Neumeister describes and figures a breed of pigeons in which the whole body is white except the breast, neck, and head; but before the first moult all the white feathers acquire colomed edges. Another breed is more remark~ble : its first plumage is black, with Tusty-red wing-baTS and a crescent-shaped mark on the breast; these marks then become white, and remain so during three or fom moults ; but after this period the white spreads over the body, and the bird loses its beauty.31 Prize canary-birds have their wings and tail black: "this colouT, however, is only retained lmtil " the first moult, so that they must be exhibited ere the change takes place. " Once moulted, the peculiarity has ceased. Of comse all the birds emanating "from this stock have black wings and tails the first year."32 A curious and somewhat analogous account bas been given 33 of a family of wild pied rooks which were :first observed in 1798, near Chalfont, and which every year from that date up to the peTiod of the published notice, viz. 1837, "have several of their brood particolomed, black and white. Tpis "variegation of the plumage, however, disappears with the first moult; "but among the next young families there are always a few pied ones." These changes of plumage, which appear and are inherited at various corresponding periods of life in the pigeon, canary-bird, and rook, are remarkable, because the parent-species undergo no such change. Inherited diseases afford evidence in some respects of less value than the foregoing cases, because diseases are not necessarily connected with any change in structure; but in other 1·espects of more value, because the periods have been more carefully observed. Certain diseases are com­municated to the child apparently by a process like inoculation, and the child is from the :first affected; such cases may be here passed over. Large classes of diseases usually appear at certain ages, such as St. Vitus's dance in youth, consumption in early mid-life, gout later, and apoplexy still later ; and these are naturally inherited at the same period. But even in diseases of this class, instances have been recorded, as with St. Vitus's 29 Prichard, 'Phys. Hist. of Mankind,' 1851, vol. i. p. 349. 30 'Embassy to the Court of Ava,' vol. i. p. 320. The third generation is described by Capt. Yule in his 'Narra­tive of the Mission to the Court of Ava,' 1855, p. 94. 31 • Das Ganze der Taubenzucht,' 1837, s. 21, tab. i., fig. 4; s. 24, tab. iv., fig. 2. 32 Kidd's ' Treatise on the Canary,' p. 18. 33 Charlesworth,' Mag. of Nat. Hist.,' vol. i., 1837, p. 167.