120 CAROLINE BURLING THOMPSON 



differentiate, especially those of the mushroom bodies, antennary 

 lobes, and the intercerebral region. The large rounded masses 

 of cells which form the central cellular group of the mushroom 

 bodies, known as cell group I, (Thompson '16) are now clearly 

 defined, although mitotic figures still occur among the cells 

 of this group.' The cell groups II and III, or the nerve cells 

 which forni the peripheral part of the mushroom bodies are 

 less clearly defined, but may be recognized. 



The compound eyes of both types with a body length of 1.6 

 mm., are slightly larger, (figs. 20, 21); the worker-soldier eye 

 still retains its simple undifferentiated condition, but that of the 

 reproductive castes shows that the differentiation and the group- 

 ing of cells is proceeding rapidly. 



In the frontal gland of the reproductive castes the hypodermal 

 invagination has grown farther back and appears as a large 

 prominent mass of epithelial cells lying somewhat above the 

 cup shaped basement membrane (fig. 36, /.s'., b.m.); and not yet 

 completely filling it, A very delicate but distinct fontanell 

 nerve (f.n.), the former median ocellar nerve (Thompson, '16), 

 runs from the basement membrane of the posterior part of the 

 frontal gland into the brain, entering the protocerebral lobes 

 in exactly the same position as in the older forms described in 

 pt. I, namely: between the posterior roots of the mushroom bodies 

 (p.r. m.b.). The hypodermal invagination of the frontal gland 

 is smaller in the worker-soldier type, and doeb not extend so 

 far backward. In figure 37, the empty basement membrane, 

 (b.m.) and the fontanelle nerve (f.n.), are shown. 



No further changes except those of growth are to be noted 

 in this phase. 



End phases 



Phase 6. Nymphs with twelve antennary segments, the third 

 segment entire and not hairy; body length 1.7 to 1.8 mm. (figs. 14, 

 15). The head of the worker-soldier type is still slightly larger 

 by actual microscopic measurement than that of the reproductive 

 types and this difference is readily noticed with a lens (figs. 

 14, 15, and table 1). Both types of brains are becoming more 



