266 THE SOCIAL LIFE OF ANIMALS 



nuptial flight, second form reproductives with wing 

 buds, and third form, which are wingless; and there 

 are the sterile workers and soldiers in which both 

 sexes are also represented equally. The colony is 

 usually composed of reproductives of some one sort, 

 and the two sterile castes (Plate V). 



The controversy as to whether caste formation is 

 a result of heredity or of the social environment has 

 been as intense with students of termites as among 

 students of ants. The trend of present information 

 tends to support the theory of control by the environ- 

 ment. (27, 75) A certain California termite called 

 Zootermopsis has reproductives and soldiers in its 

 colonies, but no workers in the accepted sense of the 

 term. Their place is taken by the younger nymphs, 

 all of which have the possibility of developing into 

 one of the reproductive grades or into soldiers. 

 When Dr. Castle of the University of California (27) 

 set up experimental colonies of nymphs alone, he ob- 

 tained in due time one or more pairs of reproduc- 

 tives. If the small experimental colony lacked a fer- 

 tile male, one of the nymphs developed into that; if 

 a fertile female was lacking and a male was placed 

 in the colony, a nymph developed into a fertile fe- 

 male. If the nymphs in a colony that lacked both 

 males and females were fed on filter-paper which 

 contained an extract of fertile females made with 



