ORIGIN OF CASTES OF TERMITES 87 



plants with the neuters of the same community. As with the varie- 

 ties of the stock, so with social insects, selection has been applied to 

 the family, and not to the individual, for the sake of gaining a service- 

 able end. 



Fritz Miiller ('73-'75), who devoted many years to the study 

 of termites, states that he, in accordance with Lespes, found the 

 young 'larvae' of the different castes all alike, but that, before 

 they have attained half the size of a worker, the future sexual 

 forms may be recognized by their wing buds, the future workers 

 and soldiers by their thicker heads and the absence of wing buds. 



The causes, phylogenetic as well as ontogenetic, of the castes 

 of the social Hymenoptera, are discussed by Weismann in 

 several of his works ('92, '93, '94, '02). In his famous contro- 

 versy with Herbert Spencer in the Contemporary Review during 

 the years '93-'94, Weismann held that food is merely a stimulus 

 acting upon predetermined units in the egg. In agreement with 

 Darwin, Weismann held that the castes of the social Hymenop- 

 tera arose phylogenetically by the action of natural selection 

 upon the fertile females, those which produced sterile offspring 

 as well as fertile having a greater selection value. For the 

 ontogenetic development of the castes Weismann assumed that 

 the eggs of the fertile female contain a set of 'determinants'' 

 for every caste. In the development of the egg one set of de- 

 terminants comes into activity, the others remaining inactive; 

 the stimulus which causes the development of one set of deter- 

 minants rather than another being the quality of the larval food. 



In Weismann's own words (The Germ Plasm): 



The individual is determined at the time of fertilization. The 

 germ plasm must contain double-determinants for certain parts of 

 the body of the queen and workers respectively. In the case of bees, 

 the factor that determines which of the two halves of the 'female' 

 determinants is to become active, seems to be the quaHty of the food 

 applied to the larva. 



It is well known of course that Weismann's theory is an argu- 

 ment for predetermination, but the complexity of his architecture 

 of the germ plasm forced him to postulate a selective stimulus in 

 the larval food. 



