supposed transmission ok acquired characters 399 



3. Climatic Variation in Butterflies 

 Polyommatus phlceas, a butterfly belonging to the family 

 LyccenidcE, is distributed over the whole of the temperate and 

 colder parts of Europe and Asia. It also occurs on the shores 

 of the Mediterranean, in Maderia, the Canaries, and in part of 

 North America. Before the glacial epoch this species must 

 have inhabited the more northern circumpolar regions, and 

 have been driven southward during that epoch ; subsequently 

 it must have again migrated towards the north. In our lati- 

 tudes the upper surface of the wings of this form is of a beautiful 

 reddish-gold colour, and hence it has received the popular name 

 ' Feuerfalter ' (fire butterfly). Further south, the reddish-gold 

 colour is more or less thickly dusted with black, and specimens 

 from Sicily, Greece, or Japan often display only a few reddish- 

 gold scales, the general appearance being almost black. In 

 Germany this butterfly is double-brooded, and the two genera- 

 tions are similar ; but in certain districts of Southern Europe, 

 such as the Riviera di Levante, the first generation is 

 reddish-gold, — the second, which flies in midsummer, and is 

 know^n as the variety eleus^ having the wings well dusted with 

 black. As in Germany, during exceptionally hot summers, 

 individuals with a blackish tint have repeatedly been caught 

 together with the ordinary form, and as, moreover, in the extreme 

 southern limit of their range — so far as my experience extends 

 — both generations have a blackish colour, it would appear at 

 first sight that the modifications are merely due to the effect of 

 heat ; — the butterfly becomes red when exposed to a moderate 

 temperature, and black when the heat is greater. 



The following experiments, however, prove that this conclusion 

 cannot be a correct one. Caterpillars were raised from the eggs 

 of the German form of P. phlcEas^ and the pupas were then 

 exposed to a much higher temperature till the emergence of the 

 butterfly. The result was that many of the butterflies w^ere 

 slightly dusted with black, but ?ioHe of thon rese/nbled the 

 darkest forms of the southern variety eleus. I then made the 

 reverse experiment, subjecting caterpillars which had just en- 

 tered the pupal stage, and had been raised from the spring 

 generation of the Neapolitan form, to a very low temperature.* 



* I must take this opportunity of expressing my warmest thanks to Dr. 

 Schiemenz, of the Zoological Station at Naples, for the kind and generous 



