x COLOURS AND ORNAMENTS CHARACTERISTIC OF SEX 275 



partners ; and Dr. Wallace of Colchester, who has largely bred 

 the fine Bombyx cynthia, confirmed this statement. Among 

 butterflies, several males often pursue one female, and Mr. 

 Darwin says, that, unless the female exerts a choice the 

 pairing must be left to chance. But, surely, it may be the 

 most vigorous or most persevering male that is chosen, not 

 necessarily one more brightly or differently coloured, and 

 this Avill be true "natural selection." Butterflies have been 

 noticed to prefer some coloured flowers to others ; but that 

 does not prove, or even render probable, any preference for 

 the colour itself, but only for flowers of certain colours, on 

 account of the more agreeable or more abundant nectar 

 obtained from them. Dr. Schulte called Mr. Darwin's atten- 

 tion to the fact, that in the Diadema bolina the brilliant blue 

 colour surrounding the white spots is only visible when we 

 look towards the insect's head, and this is true of many of 

 the iridescent colours of butterflies, and probably depends 

 upon the direction of the striae on the scales. It is suggested, 

 however, that this display of colour will be seen by the 

 female as the male is approaching her, and that it has been 

 developed by sexual selection. 1 But in the majority of cases 

 the males follow the female, hovering over her in a position 

 which would render it almost impossible for her to see the 

 particular colours or patterns on his upper surface ; to do so 

 the female should mount higher than the male, and fly 

 towards him — being the seeker instead of the sought, and this 

 is quite opposed to the actual facts. I cannot, therefore, 

 think that this suggestion adds anything whatever to the 

 evidence for sexual selection of colour by female butterflies. 

 This question will, however, be again touched upon after we 

 have considered the phenomena of sexual colour among the 

 vertebrata. 



Sexual Coloration of Birds. 



The general rule among vertebrates, as regards colour, is, 

 for the two sexes to be alike. This prevails, with only a few 

 exceptions, in fishes, reptiles, and mammalia; but in birds 

 diversity of sexual colouring is exceedingly frequent, and is, 

 not improbably, present in a greater or less degree in more 



1 Darwin in Nature, 1880, p. 237. 



