114 CAROLINE BURLING THOMPSON 



the reproductive type in figure 6 (cf. figs. 6, 8, 10). The com- 

 pound eyes of both types have increased in size, but are still 

 of about equal diameter, as seen in the who'e mounts. The 

 sex organs are also growing larger. 



Middle phases 



Phase S. Xymphs with fen antennary segments, the third seg- 

 ment gro ved: body length l.S to l.J/. mm., (figs. 10, 11, 38). The 

 greater bulk and relatively higher degree of differentiation of the 

 brain of the reproductive type is still to be observed in this 

 phase, but the mushroom bodies of the worker-soldier brain are 

 continuing to increase in size and complexity (figs. 10, 11). 



Fig. 3 Newly hatched nymphs of L. \'irginicus. ^4, reproductive type, male; 

 b, worker-soldier tj-pe, male; is, testis. Oc. 6, obj. 16, reduced one half. 



By actual measurement under the compound microscope the 

 head of the worker-soldier type is 2 niicra wider than that of the 

 reproductive type, (figs. 10, 11), table 1. It is therefore at this 

 point in the first stage of development — one-fifth of the way 

 between hatching and the fii'st molt — that the fii'st size differences 

 in the heads of the famous 'large headed' and 'smaL headed' 

 nymphs are to be noted. 



Within the head the mandibular muscles have increased in 

 bulk, spreading out as great fan shaped masses on each side of 

 the median fine. The tentorial invaginations of the hjT)odermis 

 are still ver}- conspicuous in this phase, and a thin cuticula. the 

 future tentorium, is forming on their inner, opposed, surfaces; 



