cylindrical cells of the glandular epithelium nests of regenerative cells are 

 scattered; they replace cells lost during digestion; cells filled with secretion 

 are almost twice as long as normal cells sothatthe surface of the epithelium is 

 irregular. The epithelium of the midgut is followed by the thick basal membrane 

 which is first surrounded by circular, then by longitudinal musculature. 



The proctodaeum which is separated from the midgut by 

 a fold is divided into two parts: the small intestine and the 

 large intestine (Figure 27). The histological structure of 

 the intestine does not correspond with its division; it divides 

 the proctodaeum into the following parts; the pyloric sphinc- 

 ter, the small intestine (including the posterior sphincter), 

 the large intestine, and the rectum with the anus (Figure 34). 



The pyloric sphincter is situated at the boundary 

 between mesenteron and proctodaeum; the epithelium 

 of this part, like that of the whole proctodaeum, is covered 

 by an intima, but its cells are high, columnar; the walls 

 of the sphincter form six deep folds which project into 

 the lumen (Figure 35); the contraction of the musculature 

 closes the sphincter, separating the midgut from the 

 proctodaeum. 



Three pairs of malpighian tubes open in the anterior 

 part of the sphincter: two lateral pairs and one ventral 

 pair (Figure 36); the malpighian tubes of caddis fly 

 larvae are simple, long, curved tubes (Figure 2 7), lined 

 with reddish-brown glandular cells with large nuclei 

 (Branch, 1922:264-266). 



The epithelium of the small intestine is flat, resembling 

 the epithelium of the esophagus; the intima of its anterior 

 part is without denticles; however, there are denticles 

 more posteriorly, and the epithelium of the intestine is 

 folded. The lumen of the small intestine becomes 

 narrower posteriorly; this narrow part, which is 

 surrounded by circular musculature, is the posterior 

 sphincter of the small intestine. The structure of the 

 small intestine (Figure 37), with its wide lumen and 

 strong circular and longitudinal musculature, and the presence of sphincters 

 at both ends indicates that the food is subjected to the digestive juices of 

 the mesenteron and is retained here. 



The last part of the proctodaeum is the large intestine and rectum, 

 forming a visicle. The epithelium of the large intestine forms 6 folds 

 projecting into the lumen; the flat adsorbing cells of this epithelium which 

 are covered with a thin intima have large nuclei and a thick protoplasm; the 

 39 branching of tracheoles is richer in this part than in the preceding one; the 

 musculature consists of circular fibers and 6 groups of longitudinal fibers. 



The large intestine is followed by the rectum which does not form a 

 distinct division; the epithelium of the rectum is weakly developed and 

 covered with a thick intima; the folds of epithelium disappear near the anus 

 and the walls of the intestine are smooth; circular musculature forms the 

 weak anal sphincter. The posterior part of the rectum contains the rectal 

 gills (Figure 38) which have an osmoregulatory function. 



Circulatory system and fat body. The heart of the larvae 

 extends from the 1st to the 9th segment; the aorta extends from the posterior 

 margin of the thorax to the supraesophageal ganglion of the head (Figure 39); 



FIGURE 39. Diagram 

 of the circulatory 

 system of Limno- 

 philus sp. (after 

 Branch) 



34 



