156 THE MALAYAN PAPILIONIDJE A3 



sexual selection. For instance, in most polygamous 

 animals the males fight for the possession of the 

 females, and the victors, always becoming the pro- 

 genitors of the succeeding generation, impress upon 

 their male offspring their own superior size, strength, 

 or unusually developed offensive weapons. It is thus 

 that we can account for the spurs and the superior 

 strength and size of the males in Gallinaceous birds, 

 and also for the large canine tusks in the males of 

 fruit-eating Apes. So the superior beauty of plumage 

 and special adornments of the males of so many birds 

 can be explained by supposing (what there are many 

 facts to prove) that the females prefer the most beau- 

 tiful and perfect-plumaged males, and that thus, slight 

 accidental variations of form and colour have been 

 accumulated, till they have produced the wonderful 

 train of the Peacock and the gorgeous plumage of 

 the Bird of Paradise. Both these causes have no 

 doubt acted partially in insects, so many species 

 possessing horns and powerful jaws in the male sex 

 only, and still more frequently the males alone re- 

 joicing in rich colours or sparkling lustre. But there 

 is here another cause which has led to sexual differ- 

 ences, viz., a special adaptation of the sexes to diverse 

 habits or modes of life. This is well seen in female 

 Butterflies (which are generally weaker and of slower 

 flight), often having colours better adapted to con- 

 cealment; and in certain South American species (Pa- 

 pilio torquatus) the females, which inhabit the forests, 

 resemble the JEneas group of Papilios which abound 



