THE CANADIAN ENTOMOLOGIST. 87 



gence is the lighter. Take, for instance, the genus Pieris. The vernal 

 broods of P. napi and P. protodice are distinctly more dusky than those 

 which have undergone their whole metamorphosis in a single season ; but, 

 on the other hand, the spring emergences of P. rapoe and P. brassicce are 

 wont to be pale, and the spring-emerging P. virginiensis is pale, and as 

 Mr. W. H. Edwards remarks ( " Papilio," 1881, p. 97), more like the 

 summer than the winter form of its progenitor P. napi. In Japan, it would 

 appear ("Entomologist," 1888, p. 24,) that the vernal form of P. napi 

 is less dusky than the summer emergence. 



Hitherto it has been held by the majority of Entomologists that 

 the darkening of vernal forms was due to the cold to which the pupa? were 

 subjected during the winter, and this view seemed to receive ample con- 

 firmation when Mr. W. H. Edwards proved experimentally that cold 

 applied to pupa? did produce darkening of the forms. 



Supposing, then, that cold is the sole cause of the darkness of vernal 

 broods, why are not all vernal broods dark, since they have all been 

 subjected to a greater amount of cold in the pupa-stage than the summer 

 ones ? 



It seems to me that this question is unanswerable on the supposition 

 that duskiness is the simple effect of cold, and I have therefore been led 

 to seek another explanation of the phenomenon. 



On one occasion, I bred a specimen of the European Geometra 

 papilionaria Linn., and paid particular attention to the appearance of the 

 pupa before emergence. I noted that although there could be no doubt 

 that the vital organs of the body were gradually formed during a consider- 

 able period before emergence, the wing-pigments did not begin to be 

 developed until the last few days. First of all the pigment appeared 

 brown, and only just before emergence did it assume the vivid green 

 characteristic of the insect. 



Now suppose that G. papilionaria were a species hybernating in the 

 pupa-state, how would cold effect the formation of the wing-pigment ? 

 Obviously, not at all, since the pigment is not called into existence until a 

 short time before emergence, that is to say, not until the warm spring sun 

 has wakened the sleeping pupa into new life. 



I have not had the opportunity of making careful observations of a 

 similar kind with the pupae of Rhopalocera since I began to pay special 

 attention to the subject, but I think it will generally be accepted as a fact 



