WINGLESS REPRODUCTIVE TYPE OF TERMITES 621 
segment of both sexes. The gray color of the abdomen, due to 
the woody contents of the intestinal caecum, shows that for a 
time at least this caste feeds upon wood. 
The following internal structures are, in comparison with the 
second-form nymph, on a slightly smaller scale: the brain, i.e., 
mushroom bodies and optic lobes, the compound eyes and ocelli, 
the frontal gland, and the sex organs (figs. 16, 34). The plan 
of all these organs is the same in the two castes, but in the third- 
form nymph each part is composed of fewer cells. 
The young and enlarged third-form adults of P. simplex. In 
the young third-form adult the chief changes from the nymph 
are in the darker pigmentation of the body, the size, and the 
maturity of the sex organs. In the older adults of the third 
form the abdomen becomes distended and further changes take 
place; genital appendices are absent in the female. Within the 
abdomen there is an increase in the amount of fatty tissue as 
well as the growth of the sex cells. In the head the degeneration 
of the jaw muscles is accompanied by an increase in the masses 
of fat cells. 
In the table on page 619, the chief structural differences 
between the third form and the worker of P. simplex are given 
The worker of P. simplex. ‘The worker occurs in the nymphal 
and adult phases of development. 
The adult worker, 5 mm. (fig. 17), has a head and body smaller 
than any other caste, and has usually a grayish abdomen, the 
transparent abdominal wall, comparatively free from fat masses, 
permitting the woody contents of the intestinal sac to show 
through. The number of antennal segments is sixteen, two less 
than in the reproductive forms, the small compound eyes are 
seen best with a microscope, but are larger than those of the 
worker of R. flavipes. The thorax is wingless, the dorsal thoracic 
plates are small and their posterior margins are indented in the 
median line, whereas in the third form, these plates are larger and 
the posterior margins are not indented. 
Internal anatomy. The brain is absolutely smaller than that 
of the third form and the optic lobes are relatively reduced, in 
correlation with the smaller compound eyes and the very minute 
