[260] ‘Bulletin de la Soc. Vaudoise des Sc. Nat.’ vol. x. 1869, p. 132. The young of the Polish swan, Cygnus immutabilis of Yarrell, are always white; but this species, as Mr. Sclater informs me, is believed to be nothing more than a variety of the Domestic Swan (Cygnus olor).
[261] I am indebted to Mr. Blyth for information in regard to this genus. The sparrow of Palestine belongs to the sub-genus Petronia.
[262] For instance, the males of Tanagra æstiva and Fringilla cyanea 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.) The 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 female when about three months old, but he does not acquire his full splendour until the end of the September in the following year.
[263] Thus the Ibis tantalus and Grus Americanus take four years, the Flamingo several years, and the Ardea Ludovicana two years, before they acquire their perfect plumage. See Audubon, ibid. vol. i. p. 221; vol. iii. p. 133, 139, 211.
[264] Mr. Blyth, in Charlesworth’s ‘Mag. of Nat. Hist.’ vol. i. 1837, p. 300. Mr. Bartlett has informed me in regard to gold pheasants.
[265] I have noticed the following cases in Audubon’s ‘Ornith. Biography. The Redstart of America’ (Muscicapa ruticilla, 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. 133). The Grus Americanus takes the same time, but breeds before acquiring its full plumage (vol. iii. p. 211). The adults of Ardea cærulea are blue and the young white; and white, mottled, and mature blue birds may all be seen breeding together (vol. iv. p. 58): but Mr. Blyth informs me that certain herons apparently are dimorphic, for white and coloured individuals of the same age may be observed. The Harlequin duck (Anas histrionica, Linn.) takes three years to acquire its full plumage, though many birds breed in the second year (vol. iii. p. 614). The White-headed Eagle (Falco leucocephalus, vol. iii. p. 210) is likewise known to breed in its immature state. Some species of Oriolus (according to Mr. Blyth and Mr. Swinhoe, in ‘Ibis,’ July, 1863, p. 68) likewise breed before they attain their full plumage.
[266] See the last footnote.
[267] Other animals, belonging to quite distinct classes, are either habitually or occasionally capable of breeding before they have fully acquired their adult characters. This is the case with the young males of the salmon. Several amphibians have been known to breed whilst retaining their larval structure. Fritz Müller has shewn (‘Facts and Arguments for Darwin,’ Eng. trans. 1869, p. 79) that the males of several amphipod crustaceans become sexually mature whilst young; and I infer that this is a case of premature breeding, because they have not as yet acquired their fully-developed claspers. All such facts are highly interesting, as bearing on one means by which species may undergo great modifications of character, in accordance with Mr. Cope’s views, expressed under the terms of the “retardation and acceleration of generic characters;” but I cannot follow the views of this eminent naturalist to their full extent. See Mr. Cope, “On the Origin of Genera,” from the ‘Proc. of Acad. Nat. Sc. of Philadelphia,’ Oct. 1868.
[268] Jerdon, ‘Birds of India,’ vol. iii. p. 507, on the peacock. Audubon, ibid. vol. iii. p. 139, on the Ardea.
[269] For illustrative cases see vol. iv. of Macgillivray’s ‘Hist. Brit. Birds;’ on Tringa, &c., p. 229, 271; on the Machetes, p. 172; on the Charadrius hiaticula, p. 118; on the Charadrius pluvialis, p. 94.