028 THE DESCENT OF MAN" 



ancient state of plumage; we can account by sexual selec- 

 tion for the summer or nuptial plumage of the adults, but 

 how are we to account for their distinct winter plumage? 

 If we could admit that this plumage serves in all cases as 

 a protection, its acquirement would be a simple affair; but 

 there seems no good reason for this admission. It may be 

 suggested that the widely different conditions of life during 

 the winter and summer have acted in a direct manner on the 

 plumage; this may have had some effect, but I have not 

 much confidence in so great a difference as we sometimes 

 see between the two plumages having been thus caused. A 

 more probable explanation is, that an ancient style of plu- 

 mage, partially modified through the transference of some 

 characters from the summer plumage, has been retained by 

 the adults during the winter. Finally, all the cases in our 

 present class apparently depend on characters acquired by 

 the adult males having been variously limited in their trans- 

 mission according to age, season, and sex; but it would not 

 be worth while to attempt to follow out these complex 

 relations. 



Class VI. The young in their first pluraage differ from 

 each other according to sex ; the young males resembling more 

 or less closely the adult males, and the young females more or 

 less closely the adult females.— ^h.e cases in the present class, 

 though occurring in various groups, are not numerous; yet 

 it seems the most natural thing that the young should at 

 first somewhat resemble the adults of the same sex, and 

 gradually become more and more like them. The adult 

 male blackcap {Sylvia atricapilla) has a black head, that 

 of the female being reddish brown; and I am informed by 

 Mr. Blyth that the young of both sexes can be distinguished 

 by this character even as nestlings. In the family of thrushes 

 an unusual number of similar cases have been noticed; thus, 

 the male blackbird {Turdus merula) can be distinguished in 

 the nest from the female. The two sexes of the mocking- 

 bird (Turdus polyglottus, Linn.) differ very little from each 

 other, yet the males can easily be distinguished at a very 

 early age from the females by showing more pure white.*' 

 The males of a forest-thrush and of a rock-thrush {Orocetea 

 erythrogastra and Petrocincla cyanea) have much of their 

 plumage of a fine blue, while the females are brown; and 



«« Audubon, "Ornith. Biography," vol. 1. p. 118. 



