DIGESTIVE ORGANS OF MOLLUSCA. 219 



both in length and width* : the shortening of 

 the intestine not being in proportion to that of 

 the whole body, requires its being folded upon 

 itself for a certain extent. In the moth, (Fig. 

 328), the contraction of the stomach has pro- 

 ceeded much farther ; and an additional cavity, 

 which may be considered as a species of crop, 

 or gizzard (g), is developed : the small intestine 

 takes a great many turns during its course ; 

 and a large pouch, or caecum, has been formed 

 at the part where it joins the large intestine. 



The hepatic vessels are exceedingly numer- 

 ous in the Crustacea, occupying a very large 

 space in the general cavity ; and they compose 

 by their union an organ of considerable size, 

 which may be regarded as analogous in its 

 functions to the Liver of the higher classes 

 of animals. This organ acquires still greater 

 size and importance in the Mollusca ; where it 

 frequently envelopes the stomach, pouring the 

 bile into its cavity by numerous ducts. t As the 

 structure and course of the intestinal canal 

 varies greatly in different tribes of Mollusca, 

 they do not admit of being comprised in any 



* Carus states that he found the stomach of a pupa, twelve 

 days after it had assumed that state, scarcely half as long, and 

 only one-sixth as wide as it had been in the caterpillar. 



t Transparent crystalline needles, the nature and uses of which 

 are quite unknown, are frequently found in the biliary ducts of 

 this class of animals. 



