84 CAROLINE BURLING THOMPSON 



throw light upon the greater question whether the heritable 

 bodily structure is determined by extrinsic factors, such as food 

 and environment, or by intrinsic factors within the germ plasm. 

 The related problems of polymorphism and the meaning of the 

 castes of social insects may also be better understood when the 

 question of caste origin is settled. 



Two views of the origin of termite castes, both based upon 

 observation and experiment, are held today. According to the 

 first view, the young are all alike and undifferentiated at the 

 time of hatching, but differentiate into the various adult castes 

 through the influence of external factors, such as food, the pres- 

 ence of parasites, the care received from the older workers, etc. 



According to the second view, the young are not all alike at 

 the time of hatching; some, if not all, of the different castes are 

 distinguishable from the beginning, and the castes are therefore 

 predetermined in the egg or embryo by intrinsic factors. 



The first view has the authority of age and of the number of 

 its supporters; its weakness lies in the fact that it is based upon 

 assumptions which either have not been proved or which can 

 be disproved. For example, there is no experimental proof that 

 food is the cause of differentiation in the young nymphs, nor 

 even exact knowledge of what their food is, and the present writer 

 has evidence to disprove the statement that the newly hatched 

 nymphs are all alike. 



The second view was regarded as possible by a few of the older 

 naturalists; the evidence for it is to be found in the recent writings 

 of Bugnion ('12, '13), and in the work of the present writer, to 

 be presented in this paper. The observations of Knower ('94) 

 and Snyder ('13, '15) on the origin of the soldier caste furnish 

 additional evidence, and important arguments in favor of this 

 view may be found in certain studies upon other social insects, 

 notably, von Ihering ('03), upon the development of the stingless 

 South American bees, and Wheeler ('07), upon polymorphism 

 in ants. j 



