ORIGIN OF CASTES OF TERMITES 125 



A thorough study of the second stage of development, or the 

 period between the first and second molts has not yet been com- 

 pleted, but some whole mounts have been made and a number 

 of stained individuals of the large headed worker-soldier type 

 of this stage have been examined in cedar oil, with low magni- 

 fication. It w^as hoped that this study might reveal differences 

 in the size of the frontal gland, which should be small in the 

 future worker, large and prominent in the future soldier nymphs. 



Of two large headed worker-soldier individuals so examined, 

 with fourteen antennary segments and a body length of about 

 3.75 mm., one had a clear space in the frontal gland region, be- 

 tween the mushroom bodies, the other a dark dense spot, which 

 was evidently a mass of cells. These two individuals were 

 labeled tentatively worker and soldier, and w^ere embedded and 

 sectioned. 



The sections showed that the so-called worker individual had 

 a frontal gland- resembling that of the adult worker and also 

 of the worker-soldier individuals of the preceding stage, in being 

 small and delicate, and very primitive in appearance. The so- 

 called soldier individual, however, had a large stout frontal 

 gland of hypodermal origin, still widely open to the exterior at 

 its anterior end, and composed of tall columnar cells with rounded 

 distal ends. The high degree of differentiation as well as the 

 size of this soldier frontal gland seems good evidence that it had 

 not just appeared but that it had been forming for some time, 

 and would therefore be distinguishable at an earlier age than 

 3.75 mm. Several other soldier nymphs of this age were dis- 

 tinguished from worker nymphs by the size of the frontal gland. 



The prototypes of the worker and soldier castes therefore, 

 although externally alike, are distinguishable by internal struc- 

 tural differences at the end of the second stage of development, in 

 individuals with a body length of 3.75 mm., table 2. With further 

 study I hope to find the complete series of phases, leading back 

 to the generalized worker-soldier type, and forward to the 

 workers and soldiers which are recognizable by external characters. 



