456 J. F. ILLING WORTH, 



in one row on each side of the radula and are shorter than the re- 

 curved theeth (Med) which follow. These are in several rows. Their 

 distal curved ends show a row of small, pointed projections on each 

 side when viewed under a high-power lens. The third kind (En) are 

 the largest and strongest of all. They occupy the inner row on each 

 side of the radula and are greatly curved when viewed from the 

 side. These large teeth usually have two points, one down on the 

 outside edge much shorter than the terminal point. 



The pharynx (Fig. 6) supports the great, brown digestive 

 glands (Dg), the lobes of which open freely into it. Food passing 

 into the pharynx inevitably lodges in these pockets for a time and 

 is neutralized by the acid secretion, the food of these animals being 

 mainly sea-weed, which contains an abundance of alkaline salts. 



The oesophagus extends back between the liver and the genital 

 organs in the groove between the latter (Fig. 2), thence around the 

 posterior side of the liver to the ventral side of the stomach, which 

 lies imbedded in the liver. Its hning (Oe) is greatly folded longi- 

 tudinally, producing a great increase in its surface. 



The stomach lies diagonally across the posterior end of the vis- 

 ceral cavity (Fig. 1) with the large end, entered by the oesophagus, 

 the farthest back and the small end forward and to the left. The 

 liver surrounds the stomach ventrally and posteriorly, being in close 

 connection with it. When viewed from the inside after the contents 

 have been washed out, the stomach shows numerous folds in the 

 smaller end, and in the larger part, where the oesophagus enters, 

 there is a crenated ring (Fig. F Oe) formed by the walls of the 

 oesophagus extending a short distance into the stomach. This acts 

 as a valve to prevent anything returning into the oesophagus, the 

 edge folding in from all sides and completely closing the opening. 

 To the right of this opening there is a pocket of considerable size 

 usually filled with food in the bottom of which is one of the three 

 great hepatic ducts (Fig. F Hd). The other two ducts are situated 

 near the entrance of the oesophagus. All are of about equal size, and 

 apparently have no connection with each other. 



The liver (Fig. 1 Liv) is a thick glandular organ of a dark 

 brownish color, crowded closely between the bends of the alimentary 

 canal. There are three indistinctly marked lobes, each sending a great 

 duct into the stomach. The posterior lobe lies parallel to the back 

 wall of the stomach and is wedged in between the genital mass and 

 the stomach. Its upper surface may be seen by removing the dorsal 



