76 PROCEEDINGS OF THE ACADEMY OF [March, 



of segment eight, the longitudinal rectal folds begin to appear in 

 the epithelium. These folds become deeper and extend all through 

 segment eight and part of segment nine. Of the three folds, one is 

 dorsal, one may be called right latero-ventral and the third left 

 1 at ero- ventral (Fig. 1); in spite of their positions, shown in this 

 figure, they appear to correspond to folds 12, 4, and 8 of the clock 

 face. Between the folds there are thin pigmented areas. Toward 

 the posterior end of segment nine and continuing through segment 

 ten, the folds become gradually less pronounced until they form 

 merely three thickened areas of the rectal wall. Between these 

 areas of thickened epithelium, the rectal wall is extremely thin and 

 projects inward as a ridge. Since there are three areas of thickened 

 epithelium, of course there are three of these thin inwardly pro- 

 jecting ridges. All along through segments eight and nine tracheae 

 penetrate the thickened epithelium but no tracheae enter the thin 

 areas. Toward the middle of the ninth segment the thin epithelium 

 between the longitudinal folds becomes spongy. These spongy 

 masses continue through the ninth segment and into the tenth 

 segment. In the latter half of the ninth segment tracheae penetrate 

 these spongy masses. 



Tracheal System. 



There are two great dorsal longitudinal tracheae, called right 

 dorsal trachea, rdt, and left dorsal trachea, kit, and two longitudinal 

 lateral tracheae, rlt and lit. In the anterior part of segment eight 

 (Fig. 2), each lateral trachea gives off a visceral trachea, the right 

 visceral trachea, rvs, and the left visceral trachea, Ivs, respectively. 

 These extend ventrad, mesad and cephalad in the seventh segment. 

 For some distance there is no branching, but when the right visceral 

 trachea and the left visceral trachea change their course somewhat 

 and each takes up a lateral position a little farther forward, each 

 begins to branch. The branches of the right visceral trachea supply 

 the thickened epithelium on the right side of the alimentary canal, 

 divide and subdivide and finally the smallest tracheoles shown in 

 the diagram penetrate the epithelium. In like manner the branches 

 of the left visceral trachea supply the thickened epithelium of the 

 left side of the alimentary canal. The dorsal thickened epithelium 

 is supplied by small tracheae whose origin is from another branch 

 of the left visceral trachea. 



About the middle of the eighth segment each dorsal trachea gives 

 off a branch, the right dorsal rectal trachea, rdrt, and the left dorsal 



