POLYMORPHISM. "7 



female, which arose from group A, and one or several kinds of 

 sterile females, or workers (group B)." 



Plate assumes that the differentiation into sterile and fertile forms 

 did not take place until stage 3, and if I understand him correctly, not 

 till after " the races had become differentiated morphologically." This 

 view, as he admits, resembles Spencer's (p. 100). The two views, in 

 fact, differ merely in degree, for the underlying contention is the same, 

 namely that sterility is one of the most recently developed characters 

 among the social insects. There can be little doubt, however, that the 

 smaller adaptive characters, for example those of the families of certain 

 species of Formica above mentioned, must have made their appearance 

 in the fourth stage of Plate's scheme. The view which I have advocated 

 differs from Plate's in admitting that even in this stage the workers 

 are fertile with sufficient frequency to maintain a representation of 

 their characters in the germ-plasm of the species. Conclusive evidence 

 of the presence or absence of such representation can be secured only 

 by experimental breeding, and especially by hybridizing the male off- 

 spring of workers of one species (a), with females of another (b ) 

 that has workers of a different character. 



In the foregoing discussion attention has been repeatedjy called to 

 adaptation as the insurmountable obstacle to our every endeavor to 

 explain polymorphism in current physiological terms. Of course, this 

 is by no means a peculiarity of polymorphism, for the same difficulty 

 confronts us in every biological inquiry. As the type of polymorphism 

 with which we are dealing has been developed by psychically highly 

 endowed social insects, it cannot be adequately understood as a mere 

 morphological and physiological manifestation apart from the study of 

 instinct. This has been more or less clearly perceived by nearly all 

 writers on the subject. However various their explanations, Spencer, 

 Weismann, Emery, Forel, Marchal and Plate all resort to instinct. 

 Emery especially has seen very clearly that a worker type with its 

 peculiar and aberrant characteristics could not have been developed 

 except by means of a worker-producing instinct. In other words, this 

 type is the result of a living environment consisting of the fostering 

 queen and workers which instinctively control the development of the 

 young in so far as this depends on external factors. Only under such 

 conditions could a worker caste arise and repeat itself generation after 

 generation. This caste may be regarded as a mutation comparable with 

 some of De Yries's (Enothera mutations, but able to repeat and maintain 

 itself for an indefinite series of generations in perfect symbiosis with its 

 parent form, the queen, because, notwithstanding its relative infertility, 

 it can be put to very important social use. Among ants this social 



