iv CHANGES IN GENERAL COLORATION 135 



these other cases we have the formation of new characters by 

 the influence of external conditions. This is proved by the 

 conversion of Levana into Prorsa, and that of Bryonise into 

 Napi. In both cases the cold-form is the original, the warmth- 

 form the new. Warmth has evidently in Levana -Prorsa 

 gradually produced a darker, more simply marked form, 

 which in its extreme stages hitherto occurs but rarely. Arti- 

 ficial warmth can easily produce this extreme stage. Retarded 

 development depending on cold can also produce the cold-form 

 nothing indicates any necessity to explain the origin of 

 either form by reversion. 



FURTHER PtEMARKS ON THE CAUSES WHICH CHANGE THE 

 GENERAL COLOURING OF ANIMALS 



I must here make some further remarks on another ques- 

 tion, namely, that of the effect of external agents, particularly 

 of light and warmth, on the total coloration. 



Dorfmeister would of course say that in Lepidoptera also 

 warmth produces more vivid, more brilliant colours, while dull 

 shades predominate under the influence of cold. This agrees 

 perfectly with my assumptions, and does not contradict the 

 facts brought forward by Weismann, provided that we consider 

 the part that light plays in certain cases (e.g. in high regions, 

 Pieris Bryoniae), and when we further reflect that lighter 

 general coloration can be obtained by distribution of the 

 dark pigment without any necessary diminution thereof. 



But the case also occurs in which the colours under the- 

 influence of warmth and light undoubtedly become lighter. 

 Thus by rearing the caterpillar of Xanthia Cerago in a higher 

 temperature up to the pupa stage, Dorfmeister obtained the 

 variety flavescens Esp., which occurs also in natural con- 

 ditions, and which is lighter coloured than the principal form. 

 Exceptional cases of this kind, in which warmth actually 



