82 Bulletin American Museum of Natural History. [Vol. XXIII, 



"2. The social stage with but a single kind of male and female. The 

 peculiarities in nesting, caring for the brood, and the other instincts were 

 already developed during this stage. 



"3. The social stage with one kind of male and two or several kinds of 

 females, which were all fertile, but in consequence of the physiological divi- 

 sion of labor became more and more different in the course of generations. 

 The division of labor took place in such a manner that the sexual functions 

 passed over primarily to a group A, while the construction of the nest, 

 predatory expeditions and other duties devolved mainly on another group 

 of individuals (B) which on that account used their reproductive organs 

 less and less. 



"4. The present stage with one kind of male, a fertile form of female, 

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

 workers (group B). 



He thus assumes that the differentiation into sterile and fertile forms did 

 not take place till stage 3, and, if I understand him correctly, not till after 

 "the races had become differentiated morphologically." This view, as 

 Plate admits, resembles Spencer's (p. 59). 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 females of certain Formicce above men- 

 tioned, must have made their appearance in the fourth stage of Plate's 

 scheme. The view which I have advocated differs from Plate's in admit 

 ting 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 representa- 

 tion can be secured only by experimental breeding and especially by hybrid- 

 izing the male offspring of workers of one species (a), with females of another 

 (b) that has workers of a different character. Under these conditions some 

 of the characters of a should make their appearance in b. The most favor- 

 able genera for such experiments would probably be Myrmica, Formica, and 

 Lasius, in all of which there are species, subspecies, and varieties with dis- 

 tinctly characterized workers while the corresponding males and females 

 are sufficiently alike to make hybridization seem feasible. 



5. The Ethological and Psychological Aspects of Polymorphism. 



In the foregoing discussion attention has been repeatedly called to adap- 

 tation as the insurmountable obstacle to our every endeavor to explain poly- 

 morphism in current physiological terms. Of course, this is by no means a 

 peculiarity of polymorphism, for the same difficulty confronts us in every 



