POLYMORPHISM. 7 



of labor. It attains its clearest expression in the social insects, in 

 some of which, like the termites, we find both sexes equally polymor- 

 phic, while in others, like the ants, social bees, and wasps, the female 

 alone, with rare exceptions, is differentiated into distinct castes. This 

 restriction of polymorphism to the female in the social Hymenoptera, 

 with which we are here especially concerned, is easily intelligible if it 

 be traceable, as is usually supposed, to a physiological division .of 

 labor, for the colonies of ants, bees and wasps are essentially more or 

 less permanent families of females, the male representing merely a 

 fertilizing agency temporarily intruding itself on the activities of the 

 community at the moment it becomes necessary to start other colonies. 



\ 



FIG. 50. Males of Aphtrnogaster picca. (Photograph In- T. G. IIuMiartl and Dr. 



(). S. Stron.u. i 



\Vc may say, therefore, that polymorphism among social I lymcnoptera 

 is a physical expression of the high degree of social plasticity and 

 efficiency of the female sex among these insects. This is shown more 

 specifically in two characteristics of the female, namely the extra- 

 ordinary intricacy and amplitude of her instincts, which are thoroughly 

 representatiye of the species, and her ability to reproduce partheno- 

 genetically. This, of course, means a considerable degree of autonomy 

 even in the reproductive sphere. But parthenogenesis, while un- 

 doubtedly contributing to the social efficiency of the female, must be 

 regarded and treated as an independent phenomenon, without closer 

 connection with polymorphism, for the ability to develop from un- 

 fertilized eggs is an ancient characteristic of the Hymenoptera and 



