248 SEXUAL DIMORPHISM 



might be different. In some cases the males might be more 

 numerous in proportion to the females than in others. In 

 some cases the males might fight, in others compete by the 

 beauty of their wings, in others again the individuals with 

 the most acute sense of smell might succeed. Male Lepi- 

 doptera certainly do not fight very fiercely, and I do not know 

 of any structures possessed by them which are specialised 

 for offence or defence. What evidence is there of the com- 

 petition in beauty ? Is there any reason to believe that the 

 colour or markings of the male serve as in birds to gain the 

 consent of the female. Dr. A. G-. Butler 1 some years ago 

 discussed the shaded marginal spots in Brahmsea, one of the 

 Heterocera or moths of West Africa, and suggested that 

 their evolution was due to the same principle as that of the 

 ocelli of the Argus pheasant, according to Darwin. He states 

 that many moths when approaching the female swing up 

 and down with a pendulum motion behind her, so that at 

 each swing the ocelli on the wings of one side would be seen 

 correctly shaded. But it is by no means clear that this 

 movement on the part of the male is intended to exhibit the 

 wings to the female, or indeed that the eyes of the Lepidop- 

 terous insect have any appreciation of beauty at all. In 

 birds there is no doubt that males display their specialised 

 plumage, and that the females are sexually excited by the 

 display. But in butterflies I find no reason to believe that 

 anything of the kind takes place. Birds erect their sexual 

 plumes, and in most cases the beauty and the colour are 

 scarcely visible except when the bird is showing off. The 

 beauty of a butterfly's wing is equally visible whenever the 

 insect flies ; there is no special attitude of display exhibited 

 in courtship, nor any evidence of the male inviting the 

 female by showing his beauty. In illustration of this subject 

 I may refer to Skertchly's observation of the courtship and 



1 Lepidoptera Exotica, London, 1874, p. 78. 



