DEVELOPMENT OF CASTES OF TERMITES. 385 



The youngest nymphs of T. angusticollis that I have examined 

 2.2-2.5 mm - long, with eleven and twelve antennal segments 

 are all alike in external macroscopic appearance, but with 

 a lens the two types of fertile or reproductive nymphs and 

 sterile or soldier 1 nymphs may be seen. The heads are of simi- 

 lar size, but the large brain almost filling the head cavity of 

 the reproductive nymph (Fig. 3, a) is clearly distinguished from 

 the smaller brain of the soldier nymphs (Fig. 3, 6), and corre- 

 lated with the brain structure is the whiter denser abdomen of 

 the reproductive nymphs and the more transparent abdomen of 

 the soldier nymphs. In stained and mounted specimens the 

 larger sex organs of the reproductive nymphs are in marked 



FIG. 3. Termopsis angusticollis, young nymphs 1.8 mm. long, with twelve 

 antennal segments, a, head of reproductive nymph with large brain; b, head of 

 soldier nymph with small brain. Oc. 6, obj. 16, reduced one third. 



contrast to the smaller ones of the soldier nymphs. The brain 

 of all the adult castes of T. angusticollis has a very characteristic 

 form, as if it had been pulled out laterally, due to the lateral 

 extension of the optic lobes which extend out at right angles to 

 the long axis of the body. This peculiar form of the brain is 

 recognizable even in the youngest nymphs. 



Slightly older nymphs of Termopsis 2.8-3 mm -. witn tnir ~ 

 teen and fourteen antennal segments have the heads differen- 

 tiated in size so that the "small-headed," large-brained, repro- 

 ductive forms are easily distinguishable from the "large-headed," 

 small-brained, soldier nymphs. 



Cryptotermes cavifrons Banks. The egg of Cryptotermes, like 



1 The worker caste is lacking in the genus Termopsis. 



