' ORIGIN OF CASTES OF TERMITES • 131 



able as the cause of sex has been. The cause of the sterihty 

 of the worker and soldier may also be explained by cytological 

 investigations. 



Lastly, I wish to emphasize the great need of investigation, 

 both experimental and cytological, of the eggs of all social 

 insects. If food is not the cause of differentiation in one group 

 of the social insects, why should it stand as a factor of unques- 

 tioned value for the other groups? 



SUMMARY OF RESULTS 



1. The newly hatched nymphs of L. flavipes and L. virginicus 

 are externally all alike, but internally there are marked structural 

 differences jvhich divide the nymphs into two sharply defined 

 types, ^he reproductive and the worker-soldier types, which 

 are respectively the prototypes of the 'small headed' and 'large 

 headed' nymphs of Grassi. Therefore, the fertile and sterile 

 types are predetermined at the time of hatching. 



2. The two types of newly hatched nymphs may be distin- 

 guished by the following characters: a, .the bulk of the brain; 

 h, the relative size of brain and head; c, the structure of the 

 compound eyes; and d, the size of the sex organs. 



3. The reproductive type of newly hatched nymph has a 

 large brain, in which the mushroom bodies, optic lobes and anten- 

 nary lobes are all large. The space within the hypodermis of 

 the head is nearly filled by the brain. The compound eyes are 

 slightly larger and more differentiated, and the sex organs are 

 larger than in the worker-soldier type. 



4. The worker-soldier type of newly hatched nymph has a 

 small brain, with small mushroom bodies, optic lobes and anten- 

 nary lobes. The space within the hypodermis of the head is 

 not nearly filled by the brain. The compound eyes are smaller 

 and simpler, and the sex organs are smaller than in the repro- 

 ductive type. 



5. The antennae of the newly hatched nymphs of both L. 

 flavipes and L. virginicus are composed of nine segments, the 

 third segment grooved and bare. 



