314 The Study of Animal Life PART iv 



to advantageous white. Not a few animals vary slightly 

 with the changing seasons. Thus many cases are known 

 where a butterfly produces in a year more than one brood, 



iter form 

 larcellus)* 



y v 



FIG. 67. Seasonal dimorphism of Papilio ajax ; to the left the win 

 (variety Telamonides\ to the right the summer form (variety Ma 

 (From Chambers's Encyclop. ; after Weismann.) 



of which the winter forms are so different from those born 

 in summer that they have often been described as different 

 species. It is possible that this is a reminiscence of past 

 climatic changes, such as those of the Ice Ages, as the 



FIG. 68. Seasonal changes of the bill in the puffin (Fratcrcuta arctictt)\ to the 

 left the spring form, to the right .the winter form, both adult males. (After 

 Bureau.) 



result of which a species became split up into two varieties. 

 Thus Araschnia levana and Araschnia prorsa are respect- 

 ively the winter and summer forms of one species. In the 



