250 SEXUAL DIMORPHISM 



flies in which the female is more coloured, e.g. Colias edusa, 

 and in Pieris, it is stated by Professor Meldola that the 

 females support the males in the marriage flight, and Professor 

 Poulton has observed that in these cases the females were 

 the more ardent wooers, so that the males could exercise a 

 choice. There is, however, no evidence at all that the males 

 are affected by the colour of the females, and when we con- 

 sider that the difference consists in Pieris in the possession 

 by the female of one or two black spots, it is impossible to 

 believe that the male is determined in his affections by slight 

 variations of these. On the other hand, the very fact of the 

 female supporting the male in flight is a difference in her 

 exertions, and it is possible that, as in fishes, greater sexual 

 excitement may affect the secretion of pigment. 



There is every reason to believe that the sexual instincts 

 of Lepidoptera, and probably of insects generally, are exerted 

 chiefly through the sense of smell located in the antennas, 

 and that the sense of sight has little or nothing to do with 

 the matter. Therefore a theory based on ideas of beauty and 

 selection has very little foundation. Moreover, the dimorphism 

 does not always, or even generally, consist in differences of 

 beauty, nor are the most beautiful species generally the most 

 dimorphic. Professor Poulton 1 has maintained that the 

 dependence of bright colours and beauty in male moths on 

 sexual selection is strongly supported by the fact that the 

 more degenerate the female the less brightness and beauty 

 are seen in the males. His evidence for this argument is 

 taken from the Bombyces. In the family Saturniidse the 

 male Emperor moth is much more beautiful than the female, 

 and is in itself brilliantly coloured. In the Psychidae, on 

 the other hand, the female is much more degenerate, having 

 neither wings nor legs. In these the males, though well 

 developed and active, are less ornamented. The reason, 



1 Colours of Animals, Intern. Sci. Series, 1890, p. 294. 



