198 SEXUAL SELECTION: BIRDS. [Part IL 



the last class ; so that the cause of the difference, what- 

 ever it may have been, has acted on the females in the 

 present class cither less energetically or less persistently 

 than on the males in the last class. Mr. Wallace believes 

 that the males have had their colors rendered less conspic- 

 uous for the sake of protection during the period of incu- 

 bation ; 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 of less size, and have less strength. 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 or- 

 gans. Thus an almost complete transposition 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 w^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 im- 

 probable 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 

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



