132 THE VALUE OF COLOUR 



of the species native to its second home, the 

 problem gains a special interest and fascination. 1 

 We are chiefly dealing with the fleeting and 

 changeable element of colour, and we expect to 

 find and we do find evidence of a comparatively 

 rapid evolution. The invasion of a fresh model 

 is for certain species an unusually sudden change 

 in the forces of the environment, and in some 

 instances we have grounds for the belief that the 

 mimetic response has not been long delayed. 



MIMICRY AND SEX 



Ever since Wallace's classical memoir on 

 Mimicry in the Malayan swallow-tail butterflies, 

 those naturalists who have written on the subject 

 have followed his interpretation of the marked 

 prevalence of mimetic resemblance in the female 

 sex as compared with the male. They have 

 believed with Wallace that the greater dangers of 

 the female, with slower flight and often alighting 

 for oviposition, have been in part met by the high 

 development of this special mode of protection. 

 The fact cannot be doubted. It is extremely 

 common for a non-mimetic male to be accom- 

 panied by a beautifully mimetic female and often 

 by two or three different forms of female, each 

 mimicking a different model. Indeed in these 

 latter cases the male is usually non-mimetic 

 (e. g. Papilio dardanus = merope), or if a mimic 



1 See pp. 159-77, which are devoted to the detailed considera- 

 tion of an example of this kind. 



