550 ANTHON. [Vou. XIX. 
have very conspicuous nuclei. (Fig. 29.) There is a close 
resemblance in structure between the cells of the intestinal 
diverticulum and those of the Malpighian tubules. The cells 
are but loosely approximated to the muscle walls and in places 
the cells are separated by distinct canals. (Fig. 30.) The 
nuclei are very large, with deeply staining chromatic filaments. 
This large diverticulum, the presence of which characterizes 
the herbivorous Tipulids, is excretory in function, though it 
may also act as a sort of food reservoir. The similarity of 
cell structure with that of the urinary tubules would seem to 
point to this conclusion, but besides this there is the additional 
evidence of chemical tests. There is a strong uric reaction to 
the murexid test, which would seem to show conclusively that 
the diverticulum, as well as the Malpighian tubules, is excre- 
tory in function. 
The large intestine dilates gradually till it forms the rec- 
tum. In cross-sections the structure appears very similar to 
that of the cesophagus. The epithelial surface is thrown up 
into numerous irregular longitudinal folds. The cells are 
uniform in size, and show no signs of any activity in secretion. 
Within this epithelial layer there is a layer of chitin, which is 
thrown jnto irregular folds and laminz. Outside of the epithe- 
lial layer there is a series of striated annular muscles, which 
extends outwards for a distance equal to about one-fourth of 
the central cavity. (Fig. 31.) The structure of the rectum 
proper is very much like that of the colon, and the transition 
is imperceptible, but here the folds of the columnar epithelium 
extend much farther into the lumen and the chitinous layer 
is so thick that it almost obliterates the central cavity. The 
muscular ring is much thicker, extending out for a distance 
equal to the diameter of the lumen. (Fig. 32.) The heavy 
muscular walls serve, to retain the food in the absorptive por- 
tions of the digestive tract till all possible nutriment has been 
extracted. 
There is a much coiled salivary gland lying on each side 
of the esophagus. (Fig. 33.) Each consists of a greatly 
coiled tubule, with a slender collecting duct extending from 
