Chap. XYL] THE YOUNG LIKE BOTH ADULTS. 199 



birds, the greater size and strength and the extraordinary 

 pugnacity of the females of the Turnix and Emu, must 

 mean that they endeavor to drive away rival females, in 

 order to gain possession of the male ; and on this view, 

 all the facts become clear ; for the males would probably 

 be most charmed or excited by the females which were 

 the most attractive to them by their brighter colors, other 

 ornaments, or vocal powers. Sexual selection would then 

 soon do its work, steadily adding to the attractions of the 

 females ; the males and the young being left not at all, or 

 but little modified. 



Class III. — When the adult male resembles the adult 

 female, the young of both sexes have a peculiar first plu- 

 mage of their own. — In this class both sexes when adult 

 resemble each other, and differ from the young. This 

 occurs with many birds of many kinds. The male robin 

 can hardly be distinguished from the female, but the 

 young are widely different with their mottled dusky-olive 

 and brown plumage. The male and female of the splen- 

 did scarlet Ibis are alike, while the young are brown ; and 

 the scarlet color, though common to both sexes, is appar- 

 ently a sexual character, for it is not well developed with 

 birds under confinement, in the same manner as often oc- 

 curs in the case of brilliantly-colored male birds. With 

 many species of herons the young differ greatly from the 

 adults, and their summer plumage, though common to both 

 sexes, clearly has a nuptial character. Young swans are 

 slate-colored, while the mature birds are pure white ; but it 

 would be superfluous to give additional instances. These 

 differences between the young and the old apparently de- 

 pend, as in the last two classes, on the young having 

 retained a former or ancient state of plumage, which lias 

 been exchanged for a new plumage by the old of both 

 sexes. When the adults are brightly colored, we may 

 conclude from the remarks just made in relation to the 



