ORIGIN OF CASTES OF TERMITES 119 



^neoteinic' enlarged queens with short wing pads Since, there- 

 fore, the adults with wing stubs possess larger sex organs in the 

 final, post-adult, stage of development than the 'neoteinic' 

 forms with short wing pads, it is clear that the larger sex organs 

 of the nearly mature nymphs of the second form represent not 

 a morpho ogical, but merely a physiological phase, due to the 

 earlier ripening of the sex cells in a caste that never swarms and 

 does not leave the nest. 



It is now evident that the first variety of the reproductive type, 

 with large brain and large sex organs, is the prototype of the 

 nymphs of the first form, and hence of the winged adult caste ; 

 the second variety of the reproductive type, with smaller brain 

 and smaller sex organs, is the prototype of the nymphs of the 

 second form, and hence of the 'neoteinic' reproductive caste 

 with short wing pads. Two adult reproductive castes are there- 

 fore distinguishable in L. flavipes in nymphs with ten antennary 

 segments and a body length of 1.3 to 1.4 mm. It is possible 

 that with more careful study and better material these castes, 

 might be distinguished at an even earlier age. 



Phase 4' Nymyhs with eleveyi antennary segments, ihe third 

 either entire or grooved; body tength 1.4 to 1.6 mm. (figs. 12, 13). 

 One change to be observed under the microscope, although not 

 yet visible to the unaided eye, is the greater size of the head of 

 the worker-soldier type, which is now very evidently 'large 

 headed' as compared with the 'small headed' reproductive type, 

 (figs. 12, 13). 



The mandibular muscles are stouter and larger; the greater 

 increase of these muscles in the worker-soldier type is evidently 

 related to the enlargement of the head. 



The brain of the reproductive castes shows an increased bulk 

 and a higher degree of differentiation in the various parts, es- 

 pecially in the mushroom bodies and optic lobes. A similar, 

 although relatively smaller, increase in the worker-soldier brain 

 will be noted in figure 2 h, where the superimposed outlines of 

 the two types of brain are shown. In sections of individuals 

 of the reproductive castes with a body length of 1.6 mm., the 

 nerve cells in the different parts of the brain have begun to 



