INSECTS 243 



possible that the different conditions of life may have acted 

 differently on the two sexes, but that this is improbable 

 because the period of exposure, i.e. of the life of the imago, is 

 short and the larvae are exposed to the same conditions. 

 Now the colours of the imago, it is well known, do not 

 depend directly on those of the larva, and as the imago 

 varies independently there is no reason why its variations 

 should not be influenced by its special conditions. It is very 

 obvious that there is no evidence of real importance to show 

 that female butterflies exert a choice in their sexual relations, 

 or that the brilliant colours of one sex in dimorphic species 

 have any influence in exciting the sexual instincts of the 

 other sex. Indeed, the fact that such a high degree of 

 coloration and ornamentation can exist in one sex only of 

 many species of Lepidoptera affords good reason for rejecting 

 the view that the brilliant plumage of male birds is chiefly 

 due to the choice of the female among competing suitors. 

 On the other hand, if we assume that variations in definite 

 directions are excited by external conditions, in this case 

 principally by light of different colours, the facts become 

 intelligible in general, although it is not possible in the 

 present state of knowledge to explain all particular cases. 



On the other hand, Darwin quotes the evidence of Mr. 

 Bates that in the case of the South American genus, Fpicalia, 

 there is in many species an extreme difference between the 

 sexes, although they haunt the same stations. I can only 

 suggest in this case that the two sexes may be influenced by 

 different conditions in some way of which Mr. Bates was not 

 aware. It must be remembered that, according to the views 



exceptions all the individuals of these various species (about 80 in number) 

 thus sporting in sunny places were of the male sex, their partners, which 

 are much more soberly dressed and immensely less numerous than the males, 

 being confined to the shades of the woods. Every afternoon, as the sun was 

 getting low, I used to notice these gaudy, sunshine-loving swains trooping off 

 to the forest, where I suppose they would find their sweethearts and wives." 



