108 



CAROLINE BURLING THOMPSON 



that they constitute the two sharply defined types of individuals 

 which I have termed the reproductive type and the worker- 

 soldier type, which, as stated above, are the prototypes of the 

 ^small-headed' and 'large-headed' forms of Grassi, and also of 

 the future reproductive castes and the future workers and soldiers 

 (table 1 and figs. 6 to 17). The most striking differences between 

 these two types are the absolute size and degree of differentiation 

 of the brain, and the relative size of brain and head. 



Fig. 1 Newly hatched nymphs of L. flavipes. A, reproductive type, male; 

 b, worker-soldier type, female; is, testis; ov, ovary; n.c, nerve cord. Oc. 6, obj. 

 16, reduced one half. 



In the reproductive type (figs, la, 6,), the brain fills nearly 

 the entire head, and is separated from the hypodermis by a 

 very narrow area; the mushroom bodies, the optic lobes and the 

 antennary lobes are all large, prominent and well developed. 



In the worker-soldier type (figs, lb, 7, 39), the brain fills 

 only a portion of the head and is widely separated from the 

 hypodermis; the bulk of the brain is much less than that of the 

 reproductive type, and the mushroom bodies, the optic lobes, and 

 the antennary lobes are all smaller and less differentiated. 



Figure 2 a, in which the outlines of the two types of brains 

 are superimposed one upon the other, shows the relative size 



