BIRDS. 551 



prevailed throughout the present class of cases. That the males 

 varied while young and transmitted their variations to their offspring 

 of both sexes is the most probable. I may here add that 1 have, 

 with little success, endeavored, by consulting various works, to 

 decide how far the period of variation in birds has generally deter- 

 mined 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, while those which occur 

 early in lite are transmitted to both sexes), apparently hold good in 

 the first,* second, and fourth classes of cases; but they fail in the 

 third, often in the fifth, f and in the sixth small class. They apply, 

 however, as far as I can judge, to a considerable majority of the 

 species; and we must not forget the striking generalization by Dr. 

 W. Marshall with respect to the protuberances on the heads of 

 birds. Whether or not the two rules generally hold good, we may 

 conclude from the facts given in the eighth chapter that the period 

 of variation is 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, some 

 times differs much without any assignable cause. Some birds moult 

 so early that nearly all the body-feathers are cast off before the first 

 wing-feathers are fully grown; and we cannot believe that this was 

 the primordial state, of things. When the period of moulting has 

 been accelerated the age at which the colors of the adult plumage 

 are first developed will falsely appear to us to be earlier than it 

 really is. This may be illustrated by the practice followed by some 

 bird-fanciers, who pull out a few feathers from the breast of nestling 

 bullfinches, and from the head or neck of young Gold pheasants, in 

 order to ascertain their sex; for in the males, these feathers are 

 immediately replaced by colored ones4 The actual duration of life 

 is known in but few birds, so that we can hardly judge by this 

 standard. And with reference to the period at which the power of 

 reproduction is gained, it is a remarkable fact that various birds 

 occasionally breed while retaining their Immature plumage. 



* For instance, the males of Tanagra cestiva and Fringilla o/anea require 

 three years, the male of JFringffla ciiis four years, to complete their beautful 

 plumage, (See Audubon, " Ornith. Biography," vol. i, pp. 233, 280, 378). The 

 Harlequin duck takes three years (ibid, vol. iii, p. 614). The male of the Gold 

 pheasant, as I hea- from Mr. Jenner Weir, can be distinguished from the 

 female when about three months old, but he does not acquire his full splendor 

 until the end of September in the following year. 



t Thus the Ibis tantalus and &nis americanus take four years, the Flamingo 

 several years, and the Ardea ludovicanc two years, before they acquire their 

 perfect plumage. See Audubon, ibid, vol. i, p. 2^1; vol. iii, pp. 133, loi*. zn. 



$Mr. Blyth, in Charlesworth's "Mag. of Nat. Hist,," vol. i, 1837, p. 300. 

 Mr. Bartlett has informed me in regard to Gold pheasants. 



I have noticed the following cases in Audubon's " Ornith. Biography:" 

 The /edstart of America (Mvscapica rt'tidUa^ vol. i, p. 203. The Ibis tantalus 

 takes four years to come to full maturity, but sometimes breeds in the second 

 year (vol. iii, p. 138). The tirus americanvt takes the same time, bat breeds be- 

 fore acquiring its full plumage (vol. iii, p. 211). The adults of Ardea ccerulw 



