116 ACQUIRED CHARACTERS sec. 



evolution, aud can be acquired and inherited in spite of all 

 panimixis. 



Experiments ox the Influence of Temperature 



ON Lepidoptera 



The direct influence of warmth on the modification of 

 animals is further shown by the experiments of Dorfmeister 

 and "Weismann on butterflies.^ 



Since the fourth decade of this century it has been known 

 that the two butterflies Vanessa Levana and Vanessa Prorsa, 

 formerly considered as different species, are really one and 

 the same. And, indeed, in these two forms of the same 

 butterfly we have two generations developed at different 

 seasons of the year. V. Levana is the winter form, V. 

 Prorsa the summer form. The chrysalis of Levana remains 

 dormant during the winter, the butterfly emerges in the 

 spring, breeds immediately, and its progeny go through their 

 whole development in tlie summer; from their chrysa- 

 lids emerge the V. Prorsa, whose progeny then pass the 

 winter as chrysalids, and in the spring produce the Levana. 

 These two forms of butterflies are differently coloured and 

 marked, and it is in complete agreement with many other 

 examples of the effect of warmth on the formation of pigment 

 in the integument, that the summer form (exposed to warmth), 

 Prorsa, is much more deeply coloured than the winter form 

 (exposed to cold), Levana. The former is deep black, the 

 latter brown-yellow in its ground colour. The characters of 

 the two also afford a very strong proof of the correctness of 

 my theory of the importance of correlation in the formation 



1 G. Dorfmeister, " On the Effect of Different Degrees of Warmth applied 

 during the Period of Development on the Colouring and Markings of Butterflies," 

 Mitt, des naturwiss. Vereins fur Steiermark, 1864 ; and A. Weismann, 

 Studien zur Descendenztheorie, I. Udier den Saison-DimorjMsmus der Schmet- 

 terlinge, 1875. 



