ORIGIN OF CASTES OF TERMITES 115 



the cuticula on the outside of the head is slightly thicker, and 

 especially on the edges of the mandiVjles. 



The frontal gland of both types consists of a small anterior 

 hypodermal invagination and a posterior cup shaped basement 

 membrane. The hypodermal invagination at this age extends 

 only through three or four sections in the anterior or frontal 

 part of the brain. The cup shaped basement memh>rane, how- 

 ever, extends backward through about ten more sections to the 

 point where the fontanelle nerve will enter the posterior part of 

 the brain, namely: between the posterior roots of the mushroom 

 bodies. At this age, therefore, the frontal gland of both types 

 of individuals consists of two different regions, the anterior 

 formed h)y the hypodermal invagination resting on the basement 

 membrane; the posterior, into which the hypodermal invagina- 

 tion has not yet grown, consisting only of the cup shaped base- 

 ment membrane, partly filled by loose mesenchyme cells, and 

 to the sides of which a pair of muscles, the m. retractor fonten- 

 ellae are attached, The hypodermal invagination is slightly 

 larger in individuals of the reproductive than in the worker- 

 soldier type. 



The compound eyes of the worker-soldier type have not in- 

 creased in size to any extent ; indeed, in surface views of the head, 

 (figs. 10, 11), they appear of the same diameter as in the last phase. 

 The eyes of the reproductive type, however, are cortsiderably 

 larger. 



Another and a still more important differentiation has now 

 manifested itself. The individuals of the reproductive type 

 with a body length of 1.3 to 1.4 mm. are divisible into two 

 groups: d) forms with a more highly differentiated brain, as 

 shown by the mushroom bodies, and large sex organs (fig. 4 a); 

 (2) forms with a less highly differentiated brain, as shown by 

 the mushroom bodies, and sex organs that are smaller, (fig. 4 h), 

 although not so small as those of the worker-soldier individual 

 drawn in figure 4 c. 



Figure 5 a is a male of the reproductive type, 1.3 mm. long, with 

 large brain and large sex organs. The male of the reproductive 

 type with smaller brain and sex organs has not been figured, 



