MOLLUSC A. 171 



of which is armed with numerous pyramidal teeth, with ir- 

 regular summits, of a cartilaginous nature. The connection 

 between these teeth and the integuments is so slender, that 

 they are displaced by the application of the smallest force. 

 They, however, project ,so far into the cavity, as to offer re- 

 sistance to the progress of the food. There is yet another 

 stomach, armed on the one side with deflected, pointed, car- 

 tilaginous teeth. At the pyloric extremity are two mem- 

 branaceous ridges, between which are biliary orifices, and 

 the opening into a long narrow caecum, with simple walls, 

 which is contained within the liver. The intestine is sim- 

 ple, and after two turns ends in a rectum. The salivary 

 glands are very long, and, as usual, empty their contents 

 into the pharynx. The liver is divided into three portions 

 by the folds of the intestine, each of which consists of seve- 

 ral lobes. The biliary vessels are very large, and open at 

 the mouth of the caecum into the last stomach. The food 

 of the Aplysia consists of sea- weeds and minute shells. 



The circulating organs are remarkable. On each side 

 the body, in the region of the dorsal plate, there is a large 

 vessel, which receives blood from different parts of the body, 

 and which likewise, by various openings, has a free com- 

 munication with the cavity of the abdomen. In this respect 

 there is a resemblance to the spongy, glandular bodies of 

 the venae cavae of the Cephalopoda. These two vessels, or 

 vence cavce, unite posteriorly, and transmit their contents *o 

 the gills. The aerated blood is now conveyed to an auricle, 

 of large dimensions, and uncommonly thin walls, situate be- 

 neath and towards the front of the dorsal plate, and empty- 

 ing its contents through a valve, into the right side of the 

 ventricle. The aorta, which issues from the left and an- 

 terior side, divides into two branches, the smallest of which 



