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Show 212 SEXUAL SELECTION : BIRDS. PAI~l' H. and legs, which nearly resembled the same parts in tho adults. 32 It may bo worth while to illustrate the above throe modes by which, in the present class, tho two sexes and the young may have come to resemble each other, by the curious case of the genus Passet:-33 In the house-sparrow (P. domestious) the male differs much from the female and from the young. These resemble each other, and likewise to a large extent both sexes and the young of the sparrow of Palestine (P. braohydaotylus ), as well as of some allied species. W o may therefore assume that tho female and young of the house-sparrow approximately shew us the plumage of the pro.genitor of the genus. Now with tho tree-sparrow (P. montanus) both sexes and the young closely resemble tho male of the house-sparrow ; so that they have all been modified in the same manner, and all depart from tho typical colouring of their early progenitor. This may have been effected by a male ancestor of the treesparrow having varied, firstly, when nearly mature, or, secondly, whilst quite young, having in either case transmitted his modified plumage to the females and the young; or, thirdly, he may have varied when adult ~ncl transmitted his plumage to both adult sexes, and, ow~ng to the failure of the law of inheritance at correspondmg ages, at some subsequent period to his young. It is impossible to decide which of these three modes has generally prevailed throughout the present class of cases. The belief that the males varied whilst young, and transmitted their variations to their offspring of 32 • Bulletin de b Soc. Vaudoisc des So. Nat.' vol. x. 1869, p. 132. 'l'he young of the Polish swan, Cygnus immutabilis of Y_ancll_, arc always white; but this species, as 1\ir. Sclatcr informs me, 1s bol10ved to be nothing more than a variety of the Domestic Swan (Cygnus ol01)· 33 I am indebted to Mr. Blyth for information in regard to tlns. genus. The sprurow of Palestine brlongs to the sub-genus Petronia .. ·<.:uAP. XVI. THE YOUNG LIKE BOTTI ADULTS. 213 .1oth sexes is perhaps the most probable. I may here add th~t I h~ve endeavoured, .with little success, by consultwg varwus works, to deCJde how far with birds the period of variation has generally determined the transmission of characters to one sex or to both. The two rules, often referred to .(namely, that variations occurring late in life are transmitted to one and the same ~ex, whilst those which occur early in life are transmitted to both sexes), apparently hold good in the :first,3 4o second, and fourth classes of cases· but they f~il in an equal number, namely, in the third, ~ften m the :fifth, 35 and in the sixth small class. The~ hold good,. h~wever, as far as I can judge, with a considerable ma;Jonty of the species of birds. Whether o~· no~ this be so, we may conclude from the facts :given In the eighth chapter that the period of variation has been one important element in determining the form of transmission. With birds it is difficult to decide by what standard we _ought to judge of the earliness or lateness of the perwd of variation, whether by the age in reference to the duration of life, or to the power of reproduction or to the number o~ moults. through which the specie~ pas~es. The moulting of buds, even within the same family, sometimes differs much without any assignable 34 F . t . . . or ms ance, the males of Tanagra mst'iva and F1·ingilla cyanea ~~q~_11 e thr~e years, the male of Fringilla ciris four years, to complete ) eu beautiful plumage. (See Audubon, 'Ornith. Biography,' vol. i. L 233, 280, 378.) 'l'he Harlequin duck takes three years (ibid. vol. J · P· 614).. The male of the Gold pheasant as I hear from Mr J enner Wmr, can be distinguished from the f~male when about th.rc~ ~~o~tb~ old, but ~e does not acquire his full splendour until the end ' Je eptember m the following year. ' 15 Thus th Ib" ta z • Fl . e ts nta us and G1·us Americanus take four years the thea mm.g o .s ever a.1 years, aucl t h c A1·dea Ludovicana two years, be•f ore tVol Y.. ~ cqui1r3c theu perfect plumage. See Audubon, ibid vol i p 221 . . lll. p. 3, 139, 211. . . . . • |