1922] Branch: Intoiial Anatomy of Trichoptem 261 



heavy and thick that they give the canal the appearance of having 

 great rings around it. The stomodeum is composed of four parts, 

 namely: buccal cavity, oesophagus, crop and proventriculus. The buccal 

 cavity is large, including half the depth of the head capsule, it narrows 

 rapidly and passes over into a slender tube which passes beneath the 

 supra-oesophageal ganglia as the oesophagus. The oesophagus extends 

 backward through the head and prothorax with only slight expansion. 

 At the posterior margin of the prothorax it begins to enlarge and extends 

 through the length of the mesothorax with a diameter one-third that 

 of the thorax and four times the diameter of the oesophagus in the 

 prothorax. This is the crop. At the posterior margin of the meso- 

 thorax the stomodeimi is suddenly constricted to about half its width 

 and within a longitudinal distance of .5 mm. suddenly enlarges to form 

 a cylindrical structure, the wall of which becomes resistant to dissecting 

 instruments and is very hard. The circular muscles are larger and 

 heavier in this region and inside the tube are chitinized teeth. This 

 portion is the proventriculus, which functions as a grinding organ 

 and possibly as a straining device. 



The cylindrical shape ends suddenly at the posterior margin of the 

 metathorax and the transition into the mesenteron is well indicated by 

 change in color, texture and stmcture of the wall and by a deep fold. 

 The proventriculus pushes into the forward end of the mesenteron and 

 forms there an cesophageal valve. The mesenteron folds up over the 

 proventriculus and causes a distinct line to appear between the two 

 portions. The silvery tone of the wall is lost at this juncture; the 

 longitudinal muscles break up to form a layer of muscles around the 

 mesenteron and this layer extends the full length of the mesenteron. 

 Beneath these muscles can be seen the very thin layer of circular muscles. 

 The mesenteron enlarges at its beginning to at least a third the diameter 

 of the abdomen of the larva and increases slightly toward the fourth 

 segment and then returns to its width at the beginning before it reaches 

 its length. This division arises at the posterior end of the metathorax 

 and extends through the length of the abdomen as an almost straight 

 tube, varying only as above in diameter, circular in cross section, and 

 possessed of an extremely thick wall, but one that is easily torn apart. 

 In the sixth segment the mesenteron becomes about two-thirds the 

 diameter at its beginning and passes over into the proctodeum. The 

 proctodeum is composed of intestine, both large and small, and the 

 rectum. The mesenteron pushes into the intestine in much the same 

 manner that the proventriculus pushes into the mesenteron, but the 

 distance is not as great and the valve formed is not a distinct one in this 

 species, although the division between the two main divisions of the 

 canal is clearly marked. At the point where these two portions meet, 

 the Malpighian tubules, of which there are six, make their appearance 

 upon the surface. These tubules are situated upon the lateral and 

 ventral faces of the alimentary canal and the dorsal face is void of them; 

 however, the first pair may be easily seen from a dorsal view, each mem- 

 ber of this pair lies upon the upper portion of the lateral face and 

 extends forward through the abdomen and into the metathorax. Slightly 



