MIMETIC TENDENCY OF FEMALE 245 



diverge in all directions after the species which serve 

 them for models. Furthermore, the females, by rever- 

 sion, are in rare instances brought back towards the 

 ancestral type represented by the males. 



It is hardly necessary to point to examples, for these 

 general principles will probably be at once conceded by 

 any who have made a study of the subject. I may, 

 however, allude to the non-mimetic Papilio meriones of 

 Madagascar and the related forms with similar males but 

 widely different mimetic females on various parts of the 

 mainland of Africa ; to the general resemblance between 

 the males of so many forms of Hypolimnas of the bolina 

 group to each other and to those of H. misippus, &c. ; 

 to the varying degrees of reversion towards the appear- 

 ance of the male presented by occasional females of 

 Hypolimnas bolina. 



These relationships are the reverse of those which 

 usually obtain. Outside the category of Mimetic Resem- 

 blances it is the rule, when any difference between the 

 sexes exists, for the female to show us the ancestral type, 

 the male the more modern development ; and the male 

 in growth from youth to maturity generally passes through 

 the condition permanently retained by the female. 



No probable interpretation of the unusual relationship 

 has been offered by any theory except Natural Selection. 

 The theory of External Causes demands the improbable 

 hypothesis, for which no evidence can be found, that the 

 female of certain mimetic species (but not of others) is 

 constitutionally more ready to respond to the direct action 

 of external forces than the male, and that the difference 

 is commonly great enough for the female to have given 

 a complete and detailed response, when the male, subject 

 to the same direct forces, does not exhibit the faintest 

 trace of the operation of any such influence. 



The facts are equally inexplicable by the theory of 

 Internal Causes and not inexplicable only, but the 

 reverse of what we should expect ; for, as I have already- 

 stated, it is the female which, outside these resemblances, 

 tends to retain the ancestral form. 



The theory of Sexual Selection also fails to account 



