On the Seasonal Dimorphism of Butterflies. 5 5 



by gaining an insight into the mysterious chemico- 

 physiological processes by which the butterfly is 

 formed in the chrysalis ; and indeed only by such 

 a complete insight into the most minute details, 

 which are far beyond our scrutiny, could we arrive 

 at, or even approximate to, an explanation of the 

 development of any living organism. Neverthe- 

 less an important step can be taken towards the 

 solution of this problem, by establishing that the 

 change does not depend essentially upon the 

 action of warmth, but upon the organism itself, 

 as appears from the nature of the change in one 

 and the same species. 



If we compare the Italian summer form of Poly- 

 ommatus Phlceas with its winter form, we shall find 

 that the difference between them consists only in 

 the brilliant coppery red colour of the latter being 

 largely suffused in the summer form with black 

 scales. When entomologists speak of a " black 

 dusting" of the upper side of the wings, this state- 

 ment must not of course be understood literally'; 

 the number of scales is the same in both forms, 

 but in the summer variety they are mostly black, 

 a comparatively small number being red. We 

 might thus be inclined to infer that, owing to the 

 high temperature, the chemistry of the material 

 undergoing transformation in Phlczas is changed 

 in such a manner that less red and more black 

 pigment is produced. But the case is not so 

 simple, as will appear evident when we consider 



