Chap. XVI. THE YOUNG LIKE BOTH ADULTS. 213 



both sexes is perhaps the most probable. I may here 

 add that I have endeavoured, with little success, by 

 consultiug various works, to decide 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 sex, whilst those which occur early in life are 

 transmitted to both sexes), apparently hold good in 

 the first,^* second, and fourth classes of cases; but 

 they fail in an equal number, namely, in the third, 

 often in the fifth,^^ and in the sixth small class. 

 They hold good, however, as far as I can judge, with a 

 considerable majority of the species of birds. Whether 

 or not 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 

 period of variation, whether by the age in reference to 

 the duration of life, or to the power of reproduction, 

 or to the number of moults through which the species 

 passes. The moulting of birds, even within the same 

 family, sometimes differs much without any assignable 



2^ For instance, tlie males of Tanagra sestiva and Fringilla cijanea 

 require three years, the male of Fringilla ciris four years, to complete 

 their beautiful plumage. (See Audubon, ' Ornith. Biography,' vol. i. 

 p. 233, 280, 378.) Tiie Harlequin duck takes three years (ibid. vol. 

 iii. p. 614). The male of the Gold pheasant, as I hear from Mr. J. 

 Jenner Weir, can be distinguished from the femole when about three 

 months old, but he does not acquire his full splendour until the end 

 of the September in the following year. 



•^^ Thus the Ihis tantalus and Grus Americanus take four years, the 

 Flamingo several years, and the Ardea Ludovieana two years, before 

 they acquire their perfect plumage. See Audubon, ibid. vol. i. p. 221 ; 

 vol. iii. p. 133, 139, 211. 



