Chap. XI. Butterflies and Moths. 321 



We are led to this conclusion by cases, even within the same 

 genus, of gradation from an extraordinary amount of difference 

 to identity in colour between the two sexes. 



But it may be asked whether the differences in colour between 

 the sexes may not be accounted for by other means besides 

 sexual selection. Thus the males and females of the same 

 species of butterfly are in several cases known 26 to inhabit 

 different stations, the former commonly basking in the sunshine, 

 the latter haunting gloomy forests. It is therefore possible that 

 different conditions of life may have acted directly on the two 

 sexes ; but this is not probable, 27 as in the adult state they are 

 exposed to different conditions during a very short period ; and 

 the larvae of both are exposed to the same conditions. Mr. 

 Wallace believes that the difference between the sexes is due 

 not so much to the males having been modified, as to the females 

 having in all or almost all cases acquired dull colours for the 

 sake of protection. It seems to me, on the contrary, far more 

 probable that it is the males which have been chiefly modified 

 through sexual selection, the females having been comparatively 

 little changed. We can thus understand how it is that the 

 females of allied species generally resemble one another so much 

 more closely than do the males. They thus shew us ap- 

 proximately the primordial colouring of the parent-species of 

 the group to which they belong. They have, however, almost 

 always been somewhat modified by the transfer to them of some 

 of the successive variations, through the accumulation of which 

 the males were rendered beautiful. But I do not wish to deny 

 that the females alone of some species may have been specially 

 modified for protection. In most cases the males and females of 

 distinct species will have been exposed during their prolonged 

 larval state to different conditions, and may have been thus 

 affected ; though with the males any slight change of colour 

 thus caused will generally have been masked by the brilliant 

 tints gained through sexual selection. When we treat of Birds, 

 I shall have to discuss the whole question, as to how far tho 

 differences in colour between the sexes are due to the males 

 having been modified through sexual selection for ornamental 

 purposes, or to the females having been modified through 

 natural selection for the sake of protection, so that I will here 

 say but little on the subject. 



In all the cases in which the more common form of equal 



28 H. W. Bates, 'The Naturalist »* On this whole subject see « The 



in the Amazons,' vol. ii. 1863, p. Variation of Animals and Plants 



~28. A. R. Wallace, in 'Transact. under Domestication,' 18G8. vol. ii 



uan. Soc' vol. xxv. 1865, p. 10. chap, xxiii. 



15 



