BIRDS. 547 



their colors rendered less conspicuous for the sake of pro- 

 tection during the period of incubation; but the difference 

 between the sexes in hardly any of the foregoing cases 

 appears sufficiently great for this view to be safely accepted. 

 In some of the cases the brighter tints of the "female are 

 almost confined to the lower surface, and the males, if thus 

 colored, would not have been exposed to danger while 

 sitting on the eggs. It should also be borne in mind that 

 the males are not only in a slight degree less conspicuously 

 colored than the females, but are smaller and weaker. 

 They have, moreover, not only acquired the maternal 

 instinct of incubation, but are less pugnacious and 

 vociferous than the females, and in one instance have 

 simpler vocal organs. Thus, an almost complete transposi- 

 tion of the instincts, habits, disposition, color, size, and of 

 some points of structure, has been effected between the two 

 sexes. 



Now, if we might assume that the males in the present 

 class have lost some of that ardor which is usual to their 

 sex, so that they no longer search eagerly for the females; 

 or, if we might assume that the females have become much 

 more numerous than the males and in the case of one 

 Indian Turnix the females are said to be " much more 

 commonly met with than the males " * then it is not 

 improbable that the females would have been led to court 

 the males, instead of being courted by them. This indeed 

 is the case to a certain extent with some birds, as we have 

 seen with the peahen, wild turkey, and certain kinds of 

 grouse. Taking as our guide the habits of most male 

 birds, the greater size and strength, as well as the extraor- 

 dinary 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 bright colors, other orna- 

 ments, or vocal powers. Sexual selection would then 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 



* Jerdon, "Birds of India," vol. iii, p. 598. 



