122 CAROLINE BURLING THOMPSON 



of cells has occurred. A slender bundle of fibers, the optic 

 nerve, issues from the inner surface of the eye 



The compound eyes of the reproductive castes (fig. 22) have 

 increased in diameter, the cells are highly differentiated and are 

 arranged in groups ; some of the optical cells are long and slender, 

 with axons which run toward the inner sm-face. 



Although it is probable that the ocelli are present in the repro- 

 ductive castes at this age I have so far been unable to distinguish 

 them. There is little change in the frontal gland of either type 

 since the last phases, except in size. 



The sex organs, and especially the ovaries, now show very 

 marked size differences between the two types and between the 

 two reproductive castes, which are correlated, as before, with 

 differences in the brains. The large brain and large ovaries of 

 the prototype of the female nymphs of the first form, the slightly 

 smaller brain and ovaries of the prototype of the female nymphs 

 of the second form, and the still smaller brain and ovaries of the 

 female worker-soldier type are very prominent and are dis- 

 tinguishable with a hand lens in stained specimens 2 mm. long. 



We have now examined all the phases of growth within the 

 first stage of development, or the period from the time of hatch- 

 ing to the first molt. It was found that at the time of hatching 

 two generalized types of nymphs are present, namely: the repro- 

 ductive type with large brain and large sex organs, and the worker- 

 soldier type with small brain and small sex organs. Shortly 

 after hatching — in the phase with ten antennary segments and 

 a body length of 1.3 mm. — the generalized reproductive type 

 differentiated into two groups of individuals, with large brain 

 and large sex organs, and with smaller brain and smaller sex 

 organs — which I have identified as the prototypes of the nymphs 

 of the first form, with long wing pads, and the nymphs of the 

 second form, with short wing pads, and hence of two adult 

 reproductive castes, the winged adults, and the 'neoteinic' 

 adults with short wing pads. 



Three kinds of individuals are therefore distinguishable at an 

 early phase: the prototypes of two of the adult reproductive 

 castes, and the still generalized worker-soldier individuals. 



