516 CAEOLINE BURLING THOMPSON 



THE THIRD FORM OF T. ANGUSTICOLLIS 



Like the other reproductive castes, the third form of T. angusti- 

 colhs has the three developmental phases of nymph, young adult, 

 and older adult, but these phases are less marked, owing to the 

 negative structural characters of the caste, such as the lack of 

 wings, the paler body pigment, the less distended abdomen of 

 older individuals, etc. 



Like the other castes again, the third form is very variable, 

 the body length of mature third forms ranges from 9 to 17 mm. the 

 width of the head from 2.5 to 3.6 mm., the form of the abdomen 

 from flat to distended. The true color of the head and body is 

 light straw colored, or almost colorless, but the woody contents of 

 the intestine give the abdomen of most specimens a dark muddy 

 appearance. The compound eyes are small, 0.2 by 0.1 mm., 

 either colorless or pale pinkish with white rims. The number of 

 antennal segments is twenty-six or twenty-seven. The head 

 is much broader than in either first or second forms. The tho- 

 racic segments are either wholly wingless or, in many specimens 

 (fig. 8, wv), with narrow marginal thickenings which may be in- 

 terpreted as very minute vestiges of the ancestral wing pads 

 common to the species — another instance of variability. 



The legs are not relatively larger than in the first form, as might 

 be expected with the broader head and body. In some in- 

 dividuals (fig. 3, e) the legs are actually smaller, with slender 

 tibiae and tiny lateral tibial spines; in other larger individuals 

 (fig. 3, /) the legs slightly surpass the size of the larger first forms, 

 but the spines are smaller. Five tarsal segments and an ony- 

 chium are present as in the other castes. 



The abdomen is sometimes distended, though less so, relatively, 

 than in the first- and second-form adults; sometimes flat, as in 

 the soldier. It was at first thought that the third-form individual 

 with flattened abdomen might be sterile, or true workers, but a 

 careful dissection of many flattened specimens has proved that 

 the collapse of the abdomen frequently comes with age, after 

 many eggs have been laid, and after the fat-body deteriorates, 

 and that the rounded abdomen is usually, although not always, 

 characteristic of young individuals with large fat-masses and 



