ORIGIN OF CASTES OF TERMITES 107 



(2) the size and structure of the compound eyes; (3) the size 

 of the sex organs. 



In the whole mounts from which figures 6 to 17 are drawn, 

 the eyes of the reproductive and worker-soldier types appear 

 equal in size, but figures 18 to 23, drawn from sections with 

 high magnification, show that from the beginning there are 

 marked, although slight, differences in the two types of eyes. 



I wish to emphasize the value of well stained and cleared whole 

 mounts, for without them this work could hardly have been 

 accomplished. It is possible, however, to distinguish the two 

 types of nymphs in unstained alcoholic specimens, the size of 

 the brain making a good criterion in a well preserved individual. 

 These specimens also show that the abdomen of the worker- 

 soldier type is frequently more translucent than that of the 

 reproductive type, owing to the difference in the amount of 

 fatty tissue. 



Early phases 



Phase 1. The newly hatched nymphs of L. fiavipes. (figs. 1, 

 6, 7, 39.) A newly hatched living nymph of L. fiavipes is 

 pure white and about one millimeter long; in well preserved 

 specimens the length, after fixation, is 1.1 mm. 



The antennae consist of nine segments, eight of which are 

 hairy; the third segment is without hairs, and its surface is 

 slightly grooved, so that the later number ten is indicated, but 

 the interior of the third segment is wholly undivided. 



The heads of all the newly hatched nymphs are about equal 

 in size (figs. 6, 7), the slight differences which may be noted in 

 some specimens being due to individual contraction or expansion ; 

 the thorax and abdomen are also similar in specimens that are 

 not contracted. The newly hatched nymphs of L. fiavipes are 

 therefore externally all alike. 



This, however, is by no means true of the internal structure, 

 as seen in the stained whole mounts and in sections, since very 

 striking differences are to be observed within the head and in 

 the posterior part of the abdomen, namely, in the brain and in 

 the sex organs. These differences are so great and so constant 



