1922] Branch: Internal Anatomy of Trichoptera 263 



Limnophilus indivisus Walker,* Plate XV, Figs. 1, 2, 3 and 5. 

 In this form the oesophagus passes from the buccal cavity into the head 

 region where it is a small tube and continues through the prothorax. 

 The crop is absent in this form and the oesophagus passes immediately 

 into the proventriculus. Here the chitinized "teeth" upon the lining 

 such as we find in H. analis are lacking. They are not needed, as the 

 form is strictly herbivorous and H. analis is semi-carnivorous. The 

 oesophagus begins to enlarge at the posterior edge of the prothorax to 

 form the proventriculus, which lies in the mesothorax. It is silvery in 

 appearance and dark colored, but not resistant to the needle owing 

 to the lack of chitinized teeth within. The proventriculus possesses 

 the six pairs of longitudinal muscles and the circular layer, but these 

 are not as heavy as in H. analis. At the posterior margin of the 

 mesothorax the proventriculus constricts slightly and passes over into 

 the mesenteron. This position is contrary to the usual division level 

 for these two portions of the alimentary canal, but the oesophageal 

 valve occurs here and the character of the wall changes to a light pale 

 color,, is thicker in cell depth and the six pairs of muscles from the 

 proventriculus form the characteristic layer around the new division. 

 From these characteristic markings there can be no doubt as to this 

 transition. The oesophageal valve is normal, Plate XV, Figs. 2 and 3 

 show it as a complete imagination of the wall, in a fold of eight pro- 

 jections 



The mesenteron takes its beginning in the mesothorax and increases 

 in diameter as it passes through the metathorax. It may be slightly 

 constricted in the first abdominal segment although it frequently 

 passes without any change of contour. It passes through the abdomen 

 at its diameter of one-third that of the abdomen and extends to the 

 sixth segment. Here the transition into the intestine occurs and the 

 juncture is marked by the presence of the six Malpighian tubules, 

 in the same arrangement as in H. analis. The tubes are longer, however, 

 and the first pair does not extend into the thorax, but turns backward 

 in the first abdominal segment and returns to the seventh. The 

 second pair frequently extends as far as segment three and then returns 

 to segment eight. The third pair may continue forward through 

 segment six before turning backward. The junction between mesenteron 

 and intestine is marked by a decided valve not found in H. analis 

 and similar to the oesophageal valve. A section showing this structure 

 is on Plate XV, Fig. 10. The intestine at its forward end is also cup- 

 shaped and, at the constriction between small and large intestine, 

 possesses a valve formed by the in vagina tion of the intestinal wall. 

 (Plate XV, Fig. 5). Along the intestine are six muscle bundles which 

 seem to control the initial position of the Malpighian tubules. Marchal, 

 1892, considers the tubules as being capable of motion and perhaps 

 these muscles have some part in that action. These muscles likewise 

 support the front edge of the rectum into which the large intestine 

 telescopes. 



* This species is selected for a comparison with H. analis, as the two rep- 

 resent widely divergent forms. 



