16 MOLLUSCA. 



existence of a gullet is doubtful, as the food seems to enter 

 the stomach immediately ; while, in others, there is a por- 

 tion of the intestinal canal which has some claim to the de- 

 nomination. 



The stomach, in many instances, is membranaceous, and 

 can scarcely be distinguished from the remaining portion of 

 the intestinal canal. In some cases, however, it is strong 

 and muscular like the gizzard of a bird, and even fortified 

 with corneous knobs for the reduction of hard substances. 

 In some species, the stomach opens laterally into the py- 

 lorus, and, in a few instances, possesses a spiral caecum 

 attached to it. 



The liver is usually of very large dimensions, and seated 

 close to the stomach, which it, in many cases envelopes. 

 It is divided into many lobes, and receives numerous blood- 

 vessels. There is, however, nothing analogous to the vena 

 portarum of quadrupeds. The bile is poured, in some, into 

 the stomach, and, in others, into the pyloric extremity of 

 the intestine by different openings. There is no gall-blad- 

 der. 



There is no division of the canal into small and large in- 

 testines, as in the higher classes ; or rather, among the mol- 

 lusca, the relative size of the different parts is reversed. 

 Here the pyloric extremity is usually the largest, while the 

 anal is more slender. The intestine, as in fishes, is short 

 in proportion to the length of the body, and in its course, 

 is subject to few turns. The anus, is, in some, placed on 

 one side of the body ; in others it is terminal, while in a few 

 it opens on the back. 



The digestive system is thus more simple in its structure 

 than in the higher classes. It possesses neither pancreas, 

 spleen, nor mesentery. And, we may add, that the calls of 



