SPECIES AND THEIR ORIGIN 



303 



is often found that series of individuals from 

 different zoogeographical regions will differ markedly 

 in such characters. It then becomes a question 



FIG. 110. Polymorphism in ants (Cryptocerus varians) : a, soldier; 

 6, same in profile ; c, head of same from above ; d, worker ; e, female ; 

 /.male. (From Wheeler's "Ants," published by the Columbia Uni- 

 versity Press.) 



whether intermediate forms may be found which 

 will insensibly grade both ways into the two 

 types. If such are discovered, then we consider the 



