On the Seasonal Dimorphism of Butterflies. 73 



from the fact that hibernation takes place in the 

 caterpillar stage in many species of the sub-family 

 Satyridce which are now digoneutic, as well as in 

 the remaining monogoneutic species of the same 

 sub-family. But we cannot expect seasonal dimor- 

 phism to appear in all digoneutic butterflies the 

 winter generation of which hibernates in the 

 caterpillar form, since the pupal stage in these 

 species experiences nearly the same influences of 

 temperature in both generations. We are hence 

 led to the conclusion that seasonal dimorphism 

 must arise in butterflies whenever the pupae of 

 the alternating annual generations are exposed 

 throughout long periods of time to widely 

 different regularly recurring changes of tem- 

 perature. 



The facts agree with this conclusion, inasmuch 

 as most butterflies which exhibit seasonal dimor- 

 phism hibernate in the pupa stage. Thus, this 

 is the case with all the Pierince^ with Papilio 

 Machaon, P. Podalirius, and P. Ajax, as well as 

 with Araschnia Lev ana. Nevertheless, it cannot 

 be denied that seasonal dimorphism occurs also in 

 some species which do not hibernate as pupae but 

 as caterpillars ; as, for instance, in the strongly 

 dimorphic Plebeius Amyntas. But such cases can 

 be explained in a different manner. 



Again, the formation of a climatic variety and 

 as such must we regard seasonally dimorphic 

 forms by no means entirely depends on the 



