The Influence of Environment 303 



turned out to be connected with the temperature co- 

 efficient. The experiments of Dorfmeistcr, Weismann, 

 Merrifield, Standfuss, and Fischer, on seasonal dimor- 

 phism and the aberration of colour in butterflies have 

 so often been discussed in biological literature that a 

 short reference to them will suffice. By seasonal 

 dimorphism is meant the fact that species may appear 

 at different seasons of the year in a somewhat different 

 form or colour. Vanessa prorsa is the summer form, 

 Vanessa levana the w^inter form of the same species. 

 By keeping the pupae of Vanessa prorsa several 

 weeks at a temperature of from 0° to 1° Weismann 

 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 colour and pattern of butterflies, 

 we must direct our attention to the experiments of 

 Fischer, who worked with more extreme temperatures 

 than his predecessors, and found that almost identical 

 aberrations of colour could be produced by both ex- 

 tremely high and extremely low temperatures. This can 

 be seen clearly from the following tabulated results of 

 his observations. At the head of each column the 

 reader finds the temperature to which Fischer sub- 

 mitted the pupae, and in the vertical column below are 

 found the varieties that were produced. In the vertical 

 column A are given the normal forms: 



