412 THE ALIMENTARY CANAL OF THE IMAGO. 
In transverse sections the cavity of this part of the intestine 
is diminished by the projection of four thick longitudinal folds 
of the intestinal wall into its interior (Pl. XXIV., Figs. 4and 5). 
The Proctodeum or rectum, as has been already stated, consists 
of three parts. The first part is dilated into a small sac lined 
with cubical cells, covered by a thin cuticular layer near the 
valve, but usually naked below. It is possible that the remains 
of the food are subjected to trituration as they pass through 
the distal portion of the distal intestine and the rectal valve, 
and that the residuum of nutritive matter is absorbed in this 
part of the rectum. 
The first part of the rectum is separated from the second 
part by a well-marked sphincter muscle. 
The second part of the rectum is a large pouch—the rectal 
pouch. It is lined bya single layer of flattened epithelium, 
and has a distinct cuticular intima. The rectal papille project 
into its cavity, which is usually occupied by the thick semi- 
fluid excrement which is not unlike the urine of birds and 
reptiles. 
The third portion of the rectum, the anal rectum, is tubular, 
narrowing towards the anus. It is lined by a thick cuticular 
intima continuous with the cuticular integument supported by 
pavement epithelium. The muscular coat is very thick. The 
lumen of this part of the intestine is reduced to a mere fissure 
except during the passage of excrement. 
b. The Malpighian Tubes. 
The Malpighian Tubes are four in number, two on each side ; 
they exhibit a moniliform appearance, and are usually of a 
bright yellowish-brown colour. The two tubes on either side 
unite at an acute angle and form a wide duct about 2 mm. in 
length, which opens into the lower extremity of the proximal 
intestine. 
The length of each of the Malpighian tubes is probably an 
inch or more, but they form such complex coils that I have 
found it impossible to unravel them. They lie on either side 
of and around the coils of the proximal intestine. 
