Presidential Address. 41 



coloured than the male, and in the last two species she is fur- 

 ther distinguished by what in most birds is emphatically a mascu- 

 line property, though its use here is unknown, namely- — a com- 

 plex trachea — while the male has that organ simple. He is 

 also believed to undertake the duty of incubation."*. It has 

 been shewn that the cases in which female birds are more con- 

 .spicuously coloured than the males are not numerous, though 

 thev are distributed among various orders. The amount of 

 difference, also, between the sexes is incomparably less than that 

 which occurs in those classes where the male is superior to the 

 female : — " So that the cause of the difference, whatever it may 

 have been, has here acted on the females either less energetically 

 or less persistently. "'' Charles Darwin does not accept the 

 suggestion of A. R. Wallace that the colours of the male are less 

 conspicuous for the sake of protection during the period of 

 incubation. He continues : — " It should also be borne in mind 

 that the males are not only in a slight degree less con.spicuously 

 coloured than the females, but are smaller and weaker in 

 strength. They have, moreover, not only acquired the maternal 

 instinct of incubation, but are less pugnacious and vociferous 

 than the fftnales, and in one instance have simpler vocal organs. 

 Thus an almost complete transposition of the instincts, habits, 

 disposition, colour, size, and of some points of structure, has been 

 effected between the two sexes. Now if we might assume that 

 .the males [in the class where the male is superior to the female] 

 have lost some of that ardour \\''hich 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. Taking as 

 our guide the habits of most male birds, the greater size and 

 strength as well as the extraordinarypugnacity of the females of the 

 Turnix, must mean that they endeavour 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 colours, other ornaments, or vocal powers. 

 Sexual selection would then soon do its work, steadilv adding to 



