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Show 52 INHERITANCE. C II AI'. XIII. again; the comb, wattles, and spurs do not grow to their full size; and the hackles assume an intermediate appearance between true hackles and the feathers of the hen. Cases are recorded of confinement alone causing analogous results. But characters properly confined to the female ~re li!i:ewise ac~uired; the capon takes to sitting on eggs, and w1ll brmg up chickens ; and what is more curious, the utterly sterile male hybrids from the pheasant and the fowl act in the same manner, " their delight being to wateh when the hens leave their nests, and to take on themselves the office of a sitter." 54 That admirable observer Reaumur 55 asserts that a cock, by being long confined in solitude and darkness, can be taught to take charge of young chickens; he then utters a peculiar cry, and retains during his whole life this newly acquired maternal instinct. rrhe many :veil-ascertained cases of various male mammals giving mi.lk, show that their rudimentary mammary glands retain this capacity in _a latent condition. We thus see that in many, probably in all cases, the secondary characters of each sex lie dormant or latent in the opposite sex, ready to· be evolved under peculiar cil:cumstances. Vve can thus understand how, for instance, it is possible for a good milking cow to transmit her good qualities through her male offspring to future generations ; for we may confidently believe that these qualities are present, though latent, in the males of each generation. So it is with the game-cock, who can transmit his superiority in courage and vigour through his female to his male offspring; and with man it is known 56 that diseases, such as hydrocele, necessarily confined to the male sex, can be transmitted through the female to the grandson. Such cases as these offer, as was remarked at the commencement of this chapter, the simplest possible examples of reversion; and they are intelligible on the belief that characters common to the grandparent and grandchild of the same sex are present, though latent, in tl;le intermediate parent of the opposite sex. The subject of latent characters is so important, as we shall see in a future chapter, that I will give another illustration. M 'Cottage Gardener,' 1860, p. 379. ss 'Art de fau·e Eclorre,' &c., 1749, tom. ii. p. 8. os Sir H. Holland, 'Medical Notes and Reflections,' Srd edit., 1855, J· 31. C HAP. XIII. REVERSION. 53 Many animals have the right and left sides of their body unequally developed: this is well known to be the case with flat-fish, in which the one side differs in thickness and colour and in the shape of the fins from the other· and durino- the' ' ' 0 growth of the young fi sh one eye actually travels, as shown by Steenstrup, from the lower to the upper surface.57 In most flatfi shes the left is the blind side, but in some it is the right; though in both cases "wrong fishes," which are developed in a reversed manner to what is usual, occasionally occur, and in Platessa jlesus the right or left side is indifferently developed, the o~e as often as the other. vVith gasteropods or shell-fish, the n ght and left sides are extremely unequal; the far greater number of species are dextral, with rare and occasional reversals of development, and some few are normally sini stral; but certain species of Bulimus, and many ·Achatinellre/8 are as often sini~tral as ~ extral. I will give an analogous case in the great Articulate kmgdom : the two sides of Verruca 59 are so wond~ rfully unlike, th~t without careful dissection it is extremely d.1fficult to recogmse the corresponding parts on the opposite sides of the body; yet it is apparently a mere matter of chance whether it be the right or the left side that undergoes so singular an amount of change. One plant is known to me 60 in which the flower, according as it stands on the one or other side of the spike, is unequally developed. In all the foregoing cases the two. sides of the animal are perfectly symmetrical at an early pen od of growth. Now, whenever a species is as liable to be ~n equa1ly develope~ on the one as on the other side, we may mfer th.at the capac1ty for such development is present, though latent, m t~e undeveloped side. And as a reversal of development occaswnall y occurs in animals of many kinds, this latent capacity is probably very common. rrhe best yet simplest instances of characters lying dormant are, perhaps, those previously given, in which chickens and "7 Prof. Thomson on Steenstrup's Views on the Obliquity of Flounders : 'Annals and Mag. of Nat. Hist.,' May, 1 86~ ~ 361. • 59 Dr. E. von Martens, in 'Annals and Mag. of Nat. Hit.,' March, 1866, p. 209. 59 Darwin, 'Balanidm,' Ray Soc., 1854, p. 499 : see also the appended remarks on the apparently capricious development of the thoracic limbs on the right and left sides in the higher crustaceans. 60 Mormodes ignea: Darwin,' F ertilization of Orchids,' 1862, p. 251. |