DEVELOPMENT OF CASTES OF TERMITES. 393 



nymphs, with a smaller brain and smaller sex organs (Fig. 9, 

 b, d). The difference between the bodies of fixed specimens of 

 the two types is more marked in this termite than in any other 

 that I have examined; the body of the sterile worker-soldier 

 individuals is a very clear and transparent glistening white, 

 while that of the reproductive individuals is a dull opaque creamy 

 white. A long slender labrum is noticeable in all nymphs of 

 both types. 



No appreciable difference in the 'size of the heads is noted 

 until the nymphs have attained a length of about 2 mm., and 

 have twelve antennal segments. In this phase the "small- 

 headed" reproductive forms with large brain and creamy white 

 body are easily distinguishable with a hand lens from the "large- 

 headed" worker-soldier forms with small brain and transparent 

 glistening white body. 



In worker-soldier individuals about 2 mm. long and with 

 twelve antennal segments there is as yet no external differentia- 

 tion between the two sterile castes, but an internal differentiation 

 has already begun and may be observed in whole mounts of 

 stained individuals as well as in sections. The future soldiers 

 are distinguishable by the presence of the larger frontal gland 

 which appears, in frontal mounts of the head, as a small dense 

 spot posterior to the brain ; in whole mounts of the head of the 

 future worker no such spot is visible. After examining the 

 stained specimens in cedar oil to separate the future soldiers 

 from the future workers, the two kinds of individuals were 

 embedded and sectioned. In the soldier nymphs a large, al- 

 though embryonic, frontal gland opens to the exterior on the 

 frontal surface of the head. This gland was more than three 

 times the size of the vestigial gland found in the worker nymphs. 



The soldier caste of E. pilifrons is, therefore, not differentiated 

 by external characters at the time of hatching, but arises later 

 in the development, being first manifested in individuals about 

 2 mm. long with twelve antennal segments. The worker caste 

 is differentiated at the same time, and the two castes may be 

 recognized by the size and structure of the respective frontal 

 glands; although no external differentiations are yet present in 

 either caste. 



