64 Annals Entomological Society of America [Vol. I, 



with sufficient frequency to maintain a representation of their 

 characters in the germ-plasm of the species. Conclusive evi- 

 dence of the presence or absence of such representation 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). 



In the foregoing discussion attention has been repeatedly 

 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 physio- 

 logical manifestation apart from the study of instinct. This has 

 been more or less distinctly perceived by nearly all writers on the 

 subject. However various their explanations, Spencer, Weis- 

 mann, 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 de- 

 ^■eloped except in a living environment consisting of the foster- 

 ing queen and workers which instinctively control the develop- 

 ment of the young in so far as this depends on external factors. 

 The worker caste may be regarded as a mutation comparable with 

 some of De Vries's CEnothera mutations, but able to repeat and 

 maintain itself for an indefinite series of generations in perfect sym- 

 Ijiosis with its parent form, the queen, because, notwithstanding 

 its relative infertility, it can be put to very important social use. 

 Among ants this social use not only pervades the activities of the 

 adult workers but extends even to the more inert larval stages. 

 Thus the latter represent a rich and ever-fresh supply of food that 

 can be devoured whenever a temporary famine o\'ertakes the 

 colony. In certain species, like the East Indian CEcophylla 

 smaragdina and the South American Camponotus senex, the larvas 

 are put to a more humane use as spinning machines for construct- 

 ing the silken nest inhabited by the colony. These exam- 

 ples also illustrate the purposive manner in which an organism 

 can satisfy definite needs by taking advantage of ever-present 

 opportunities and mechanisms. 



