On the Seasonal Dimorphism of Butterflies. 45 



II. 



SEASONAL DIMORPHISM AND CLIMATIC 

 VARIATION. 



IF, as I have attempted to show, seasonal dimor- 

 phism originates through the slow operation of a 

 changed summer climate, then is this phenomenon 

 nothing else than the splitting up of a species into 

 two climatic varieties in the same district, and we 

 may expect to find various connexions between 

 ordinary simple climatic variation and seasonal 

 dimorphism. . Cases indeed occur in which sea- 

 sonal dimorphism and climatic variation pass into 

 each other, and are interwoven in such a manner 

 that the insight into the origin and nature of 

 seasonal dimorphism gained experimentally finds 

 confirmation. Before I go more closely into this 

 subject, however, it is necessary to come to an 

 understanding as to the conception " climatic 

 variation," for this term is often very arbitrarily 

 applied to quite dissimilar phenomena. 



According to my view there should be a sharp 

 distinction made between - climatic and local 

 varieties. The former should comprehend only 

 such cases as originate through the direct action 



