1922] Branch: Internal Anatomy of Trichoptera 265 



Oesophagus: The cells of the epithelium are cubical and the whole 

 epithelium is lined with a chitinous intima. The basement membrane 

 is distinct between the epithelium and the muscles surrounding the 

 oesophagus. 



Crop: Conditions the same as in the oesophagus. 



Proventriculus: The cells of the epithelium do not vary from those 

 of the oesophagus but the wall itself is thrown into folds and the intima 

 becomes thick and dense and forms the stomachic teeth, the number of 

 which is about thirty-six. A cross section of this region shows them 

 surrounding the cavity. At the posterior margin of the proventriculus 

 is the oesophageal valve which in this form is of peculiar plan. It is 

 practically double with a strongly chitinized invagination into the pro- 

 ventriculus and an extremely deep but narrow invagination into the 

 mesenteron This valve does not completely surround the constriction 

 between the two divisions. For further details see Noyes 1915. This 

 valve in L. indivisus is normal and complete. It extends into the mesen- 

 teron in a fold, the upper part of which is composed of cubical cells with 

 an extremely heavy intima, while the under portion of the fold although 

 the cells are cubical become somewhat flattened and the intima reduced 

 to a thin membrane. The wall changes suddenly into the columnar 

 structure of the mesenteron with its striated border. At the point 

 where the intima ceases the peritrophic membrane arises. This is sep- 

 arated from the epithelial wall of the mesenteron and surrounds the 

 food in the canal, Plate XV, Fig. 6. 



Mesenteron: The epithelium here is similar to that at the posterior 

 end of the oesophageal valve except that the cells become more col- 

 umnar. The conditions in function accord with those described in the 

 dragonfly nymph, Needham, 1907, and need no further discussion 

 here_ The wall of the mesenteron is folded as mentioned in the dis- 

 cussion of the gross anatomy of the canal to produce more assimilative 

 surface and this condition prevails the entire length of the mesenteron 

 to the sixth segment. In this same segment the Malpighian tubules 

 show upon the surface and the mesenteron passes over into the intestine 

 Plate XV, Fig. 10 at dep. 



Malpighian tubules: At the posterior end of the mesenteron where 

 the cells are still columnar, the ventral pair of Malpighian tubules may 

 be seen breaking through the epithelial wall on their way to the surface, 

 Plate XVI, Fig. 7. Patten, 1884, in his embryological investigation of 

 the Trichoptera shows that these tubules are evaginations of the proc- 

 todeum before the wall of the forming mesenteron is joined with that 

 of the proctodeum. Further evidence of this is seen in sections of the 

 intestine further back where the tubules may be seen forming within 

 the epithelial tissue of the intestinal walls. The cells are still columnar 

 but the presence of intima and the loss of the striated border indicate 

 that this is no longer mesenteron, Plate XVI, Fig. 6. The Malpighian 

 tubules are composed of large cells, glandular in appearance, with a 

 large nucleus in the center of the cell. The pigment so noticeable in 

 gross structure now becomes more evident and stains darker than the 

 nucleus and is not confined to a given region of the cell. There are three 



