^^"^ THE NEW EVOLUTION '^^'^ 



mon blue. In all of these cases the latest individuals 

 of the spring brood closely resemble the individuals 

 of the summer brood in those species in w^hich there 

 is a summer brood. 



In certain butterflies the individuals of the spring 

 brood may be the same, or nearly the same, through- 

 out the range, while the individuals of the summer 

 brood or broods differ very w^idely in different regions. 

 This is well illustrated by the common little copper 

 butterfly as it occurs in Europe, North America 

 and Asia. 



Some butterflies are at all times very highly variable 

 in both sexes in color or in wing form or in both 

 features. Thus one of our common western swallow- 

 tails may be either predominantly yellow or predomi- 

 nantly black, or of any intermediate type. But the 

 yellow form does not occur in Arizona, while the 

 black form does not occur in Oregon or northward. 

 Great diversity of color in one region, but the occur- 

 rence of only a single color type in the same species 

 in another region, is a common phenomenon in the 

 insects. In South America some of those curious but- 

 terflies called heliconians are so very variable that 

 scarcely any two individuals can be found which are 

 quite alike. 



In most wide-ranging species there is more or less 

 extensive variation in color, size, and wing form from 

 one region to another. The different forms taken by 

 the species in the different regions are recognized as 

 subspecies or geographical varieties. These sub- 

 species may grade imperceptibly into the correspond- 



[^36] ' 



