SOLDIER CASTE IN GENUS TERMOPSIS. 147 



of the soldier caste it is of importance to note that practically all 

 of our observations rest upon the study of small colonies which 

 never exceeded a hundred individuals. The size of the burrows 

 they inhabited also gave evidence of comparatively young com- 

 munities. Furthermore the brains of nearly two hundred in- 

 dividuals, chiefly in the first instar, were carefully measured and 

 the plotted results showed the same type of variation curve as did 

 the head width measurements. About fifty gonad measurements 

 were made which likewise showed the same type of variation as 

 width of head and brain. These facts, coupled with the entire 

 absence of any insect which showed even a trace of wing buds, 

 renders it perfectly certain that the following observations relate 

 solely to the soldier caste. 



The newly laid eggs of T. vcz'adensis are approximately 1.4 mm. 

 long by 0.57 mm. in greatest diameter, while those of T. anyusti- 

 collis average 1.55 mm. in length by 0.58 mm. Diameter. This 

 remains true even of those colonies where the royal pair is accom- 

 panied by hundreds of descendants, and doubtless are provided 

 with a relatively generous food supply. As development advances 

 all eggs increase in size at practically a uniform rate until at the 

 time of hatching the eggs of T. ncvadcnsis are approximately 

 1.5 mm. long by 0.6 mm. in diameter, and those of T. angusticollis 

 are on the average 1.7 mm. in length by 0.68 mm. in diameter. In 

 certain exceptional cases these lengths may be exceeded by as 

 much as thirteen per cent., though this is generally accompanied by 

 a proportional decrease in diameter. 



Recently hatched individuals of both species are found to have 

 the mid-gut filled with air. Whether this is swallowed or is se- 

 creted by the intestinal wall has not been determined, but it is 

 reasonably certain that the resulting increase in body size enables 

 the young insect to burst the egg membrane and escape. In a 

 relatively short time the air disappears, and in several cases it was 

 found that shortly after this stage the young are fed either by the 

 royal pair or by some of the attendant older offspring. 



Correlated with the fairly uniform size of the eggs of each 

 species there is a corresponding uniformity in the dimension of 

 the newly hatched young. This condition of affairs however 

 usually undergoes a rapid change with the distention of the ab- 



