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Show 280 THE PRINCIPLES OF PART 1II its own male and female sex to the hybrid offspring of both sexes. The same fact is likewise manifest, when characters proper to the male are occasionally developed in the female when she grows old or becomes diseased ; and so conversely with the male. Again, characters occasionally appear, as if transferred from the male to the female, as when, in certain breeds of the fowl, spurs regularly appear in the young and healthy females; but in truth they are simply developed in the female ; for in every breed each detail in the structure of the spur is transmitted through the female to her male offspring. In all cases of reversion, characters are transmitted through two, three, or many generations, and are then under certain unknown favourable conditions developed. This important distinction between transmission and development will be easiest kept in mind by the aid of the hypothesis of pan genesis, whether or not it be accepted as true. According to this hypothesis, every unit or cell of the body throws off gemmules or undeveloped atoms, which are transmitted to the offspring of both sexes, and are multiplied by selfdivision. They may remain undeveloped during the early years of life or during successive generations; their development into units or cells, like those from which they were derived, depending on their affinity for, and union with, other units or cells previously developed in the due order of growth. Inheritance at Corresponding Per£ods of Life.-This. tendency is '"ell established. If a new character appears in an animal whilst young, whether it endures throughout life or lasts only for a time, it will reappear, as a general rule, at the same age and in the same manne? in the offspring. If, on the other hand, a new character appears at maturity, or even during old. age, it tends CIJAP. Vlli. SEXUAL SELECTION. 281 to reappear in the offspring at the same advanced age. When deviations from this rule occur, the transmitted characters much oftener appear before than after the conesponding age. As I have discussed this subject at sufficient length in anotherwork,u1 I will here merely give two or three instances, for the sake of recalling the subject to the reader's mind. In several breeds of the Fowl, the chickens whilst covered with down, in their first true plumage, and in their adult plumage, differ greatly from each other, as well as from their common parent-form, the Gallus bankiva; and these characters are faithfully transmitted by each breed to their offspring at the corresponding period of life. For instance, the chickens of spangled Hamburghs, whilst covered with down, have a few dark spots on the head and rump, but are not longitudinally striped, as in many other breeds; in their first true plumage, "they "are beautifully pencilled," that is each feather is transversely marked by numerous dark bars; but in their second plumage the feathers all become spangled or tipped with a dark round spot.20 Hence in this breed variations have occurred and have been transmitted at three distinct periods of life. The Pigeon offers a more remarkable case, because the aboriginal parentspecies does not undergo with advancing age any change of plumage, excepting that at maturity the breast becomes more iridescent; yet there are breeds which do not acquire their characteristic colours until they 19 'The Variation of Animals and Plants under Domestication,' vol. ii. 1868, p. 75. In the la:.t chapter but one, the provisional hypothesis of pangenesis, nbove alluded to, is fully explained. 20 These facts are given on the high authority of a great breeclrr, 1\:Ir. Techny, in Tegetmcier's 'Poultry Book,' 1868, p. 158. On t.!Jo characters of chickens of different breeds, and on tile breeds of the pigeon, alluded to in the above paragraph, Eee 'Variation of Animals; &c., vol. i. p. 160, 249; vol. ii. p. 77. |