41 



F.V. 



and in front of the heart which lies between the nephridium and the pancreas. 



The rectum lies just beneath the skin of the lower surface of the visceral 

 mass. Its upper surface is next to the ventral part of the nephridium and to the 

 ink sac which separates it from the anterior vena cava. The rectum is about half 

 as long as the liver and it extends 

 from the level of the hinder end of 

 the liver to the middle of the same. 

 The forward end of the rectum is 

 attached to the liver case by a mesen- 

 tery-like fold of skin. It ends in a small 

 anal chamber from which it is separated 

 by an anal sphincter. The ink sac opens 

 into the anal chamber and the cham- 

 ber opens into the mantle cavity through 

 the transversely oval anus which is 

 bounded by an upper and 

 a lower lip. A pair of 

 ovate leaf-like processes, 

 the rectal valves , sup- 

 ported on short round 

 stalks are attached at 

 each side of the anus. 



The wall of the 

 intestine and rectum has 

 the usual circular and 

 longitudinal muscles and, 

 with the exception of the 

 distal part of the rectum, 

 is lined by a ciliated 

 columnar epithelium in 

 which are scattered go- 

 blet cells. The epithelium of the middle of the rectum is non-ciliated and contains 

 a large number of goblet cells while that of the ventral end is palisadal , non- 

 ciliated , and contains a large number of characteristic cells (Text figure 13). 

 Each of these cells has a single process from one to four times as long as the 

 cell and one half or less the breadth of the cell. The majority of the processes 

 are blunt , but some of them taper out into fine points while a few are knobbed 

 or contain a vacuole in the free end. The processes vary in size from mere 



Fig. 13. 



