608 CAROLINE B. THOMPSON. AND THOMAS E. SNYDER 
in the maturity of the sex organs. Specimens which are mature, 
or nearly so, are 6 mm. in length. The very small compound 
eyes are not visible in living or unstained specimens, the thorax 
is entirely wingless, and the color of the body almost white. 
Lateral ocelli are prominent in stained specimens. 
Investigation of the internal anatomy of the young third-form 
adult brings to light other characters which further distinguish 
this caste from the worker. The brain of the third-form adult 
(figs. 6, 9) is markedly smaller than that of the first or second 
form, but is slightly greater in bulk than in the worker (fig. 10), 
due to the greater number of cells in the mushroom bodies and 
optic lobes. The compound eyes are small and degenerate 
compared with those of the other reproductive forms, but, like 
their optic lobes, they are slightly larger than in the worker. 
Lateral ocelli, which are totally lacking in the worker, are present 
in the third form. The frontal gland is intermediate in size 
between that of the second form and of the worker; it is probably 
not glandular. The chitin covering the head is thin in all three 
reproductive castes; in the worker it is very thick and tough 
(figs. 31, 32). The mature sex organs are smaller than in either 
the first or second forms, though larger than those of the worker. 
The older adults of the third form. These forms differ externally 
from the similar phases of the other two reproductive castes 
chiefly in the absence of wings, the white or pale yellow body, 
and the less distended abdomen. Genital appendices are present 
on the ninth abdominal segment of the male, but are not visible 
in the female. The body length is from 7 to 9 mm. These 
older third-form adults, on account of the less enlarged abdomen, 
never lose their activity; the legs, in correlation with this activity, 
are, like those of the active older second form, stouter and more 
muscular than the legs of the greatly distended and more sluggish 
first form. The jaw muscles have undergone a degeneration 
similar to that already noted in the older first and second forms. 
Fewer males than females have been collected, perhaps on account 
of their greater activity, but probably because they are more 
readily confused with workers. 
The following table sets forth the chief structural differences 
between the third form and the worker of R. flavipes. 
