Influence of Environment on AnixMals 211 



h) Changes in the color of butterflies produced through the 

 influence of temperature.— The experiments of Dorfnicister, 

 Weismann, Merrifield, Standfuss, and Fischer on seasonal 

 dimorphism and the aberration of color in butterflies have so 

 often been discussed in biological literature that a short refer- 

 ence to them will suffice. By seasonal dimori)hism is meant 

 the fact that species may appear at different seasons of the year 

 in a somewhat different form or color. Vanessa prorsa is the 

 summer form, Vanessa levana the winter form oi tlie same 

 species. By keeping the pupae of Vanessa prorsa several 

 weeks at a temperature of from 0° to 1° Weismami succeeded 

 in obtaining from the summer chrysalids specimens which 

 resembled the winter variety, Vanessa levana. 



If we wish to get a clear understanding of the causes of 

 variation in the color and pattern of butterflies, we must direct 

 our attention to the experiments of Fischer, who worked with 

 more extreme temperatures than his predecessors, and fomid 

 that almost identical aberrations of color could be produced 

 by both extremely high and extremely low temperatures. This 

 can be seen clearly from the following tabulated results of his 

 observations. At the head of each colunm the temperature 

 to which Fischer submitted the pupae is given, and in the 

 vertical column below are found the varieties that were pro- 

 duced. In the vertical column A are given the normal forms : 



