1918] Alimentary Canal of Altica Larva 305 



At the proximal end of the rectum there is a pronounced 

 outpushing of the intima into the body-cavity; this serves as a 

 place for the attachment of the circular muscles of the colon, 

 and the origin of the circular muscles of the rectum. 



EpitheHum. The cells of the epithelium are much smaller 

 than those in the two sections immediately preceding the 

 rectum, and the cell divisions are much clearer. At the bases of 

 the chitinous folds referred to above, the epithelial cells are 

 thin and stretched out, but at the apices they are broadened 

 out and glandular in appearance. Because the cells are so thin 

 at their bases, they might readily be overlooked, and this 

 probably accounts for the fact that some writers have described 

 the epithelium as wanting in the case of similar structures. It 

 is, of course, evident that where there is an intima there must be 

 underlying cells to secrete it. The cytoplasm of these cells 

 stains deep pink with eosin, and is smooth, non-granular. The 

 nuclei are smaller than those of the ileum and colon, and are 

 not so chromatic. Posteriorly, the epithelium becomes more 

 and more glandular in appearance, and these gland-like cells 

 persist out into the otherwise unmodified hypodermis of the 

 body-wall, with which this layer is of course continuous. 



The epithelial cells elaborate a " molting-fluid " exactly as 

 was described in the case of the fore-intestine. In larvas fixed 

 just after a molt, or at the time of hatching, the cells of the 

 epithelium lie close against the intima; but they begin to secrete 

 a fluid very soon, and in a few days there is a fibrillar- vacuolar 

 area, which stains blue with Delafield's haematoxylin, separating 

 the intima and epithelium. This fibrillar area is always clearly 

 marked off from the true cytoplasmic cellular portion. The 

 presence of this fibrillar portion is characteristic of the rectum, 

 and is developed in all of the instars. The new cuticula is 

 formed ectad of this area just before each molt. The new 

 intima is formed not more than a day before the larva enters 

 the ground, and the secondary intima becomes apparent on the 

 fourth day of prepupal life. The fibrillar area extends out 

 beyond the proctodeal invagination between the hypodermis 

 and the cuticula in the body-wall, about to the point where 

 pigment appears in the primary cuticula, and glandular cells of 

 a type continuous with those of the rectum do not appear in the 

 hypodermis beyond this point. 



