682 
.T. DAVIDSON. 
intestine increases in size, and lies transversely across the 
median line above the anterior end or the stomach, turning 
abruptly on the left of the median line in a posterior dii’ec- 
tion beneath that structure. About the third abdominal 
segment it narrows considerably, and passes beneath the 
stomach towards the thorax, where it again bends at right 
angles across the median line, and leads into the rectum (r.), 
which continues in a postero-median direction towards the 
anus. 
The coils of the alimentary canal lie beneath the large 
ovarian crnca, near the ventral surface of the body, and are 
held in position by strands of connective tissue and fine rami- 
fying trachem. 
The Rectum. — The rectum or posterior chamber of the 
hind-gut continues in a post-median direction as a thin- 
walled tube, and passing between the two oviducts, extends 
upwards above the vagina to the anus. In some individuals 
it is distended in a sac-like manner, but attenuates towai-ds 
the anus. 
The structure of the wall of the rectum (fig.- 37) differs 
from that of the mid-gut. It is composed of an irreg’ular 
epithelium which bounds the lumen. The cell walls are not 
clearly defined, but conspicuous nuclei are embedded through- 
out the epithelium. A delicate, chitinous intima, continuous 
with the body integument, extends for some distance along the 
rectum. 
Two bands of divaricator muscles are attached to the 
rectum near the anus, and pass to the body-wall. 
Malpighian tubes are absent in S.lanigera. Kowalevsky 
(1889), as cited by Mordwilko (1895, p. 353) and other 
authors, has shown that in insects which have no Malpigdiian 
tubules, the cells of the rectum wall may have an excretory 
function. 
B. The Nervous System (figs. 35 and 36). 
The nervous system is concentrated in the head and thorax. 
It consists of a pair of fused supra-oesophageal ganglia (s. g.), 
