528 THE DESCENT OF MAN. 



CHAPTER XVI, 



BIRDS concluded. 



The immature plumage in relation to the character of the plumage in 

 both sexes when adult Six classes of cases Sexual differences 

 between the males of closely allied or representative species 

 The female assuming the characters of the male Plumage of 

 the young in relation to the summer and winter plumage of the 

 adults On the increase of beauty in the birds of the world 

 Protective coloring Conspicuously colored birds Novelty appre- 

 ciated Summary of the four chapters on birds, 



WE must now consider the transmission of characters as 

 limited by age, in reference to sexual selection. The truth 

 and importance of the principle of inheritance at corre- 

 sponding ages need not here be discussed, as enough has 

 already been said on the subject. Before giving the several 

 rather complex rules or classes of cases under which the 

 differences in plumage between the young and the old, as 

 far as known to me, may be included, it will be well to 

 make a few preliminary remarks. 



With animals of all kinds, when the adults differ in color 

 from the young, and the colors of the latter are not, as far 

 as we can see, of any special service, they may generally 

 be attributed, like various embryological structures, to the 

 retention of a former character. But this view can be 

 maintained with confidence only when the young of several 

 species resemble each other closely, and likewise resemble 

 other adult species belonging to the same group; for the latter 

 are the living proofs that such a state of things was formerly 

 possible. Young lions and pumas are marked with feeble 

 stripes or rows of spots, and as many allied species both 

 young and old are similarly marked no believer in evolution 

 will doubt that the progenitor of the lion and puma was a 

 striped animal, and that the young have retained vestiges 

 of the stripes like the kittens of black cats, which are not 

 in the least striped when grown up. Many species of deer, 



