INTRODUCTION. XXV 



stomach itself contains a very remarkable apparatus, con- 

 sisting of several hard calcareous pieces, which may be 

 termed gastric teeth. These are attached to horny or 

 calcareous levers fixed in the parietes of the stomach ; 

 they are moved by a complicated system of muscles, and 

 are admirably adapted to complete the thorough breaking- 

 down of the aliment, which had already been to a con- 

 siderable extent effected by the buccal appendages. 

 These gastric teeth may be readily seen and examined in 

 the larger species of the Decapoda, as in the large eatable 

 crab and the lobster; and it will be readily perceived how 

 perfectly the different pieces are made to act upon each 

 other, and to grind the food interposed between them. 

 Analogous structures, but of less complexity, are found 

 in the Edriophthalma. The single and simple intestine 

 extends in a direct line from the stomach, and terminates 

 at the last segment of the abdomen. Immediately from 

 its origin at the pyloric opening of the stomach, a notable 

 enlargement is observed, but the rest of the canal is 

 of uniform size. The enlarged portion is, in some cases, 

 very short ; in others, it occupies the larger portion of 

 the total length. 



The liver is of considerable volume in most of the 

 families of Crustacea, and occupies in the Decapoda the 

 greater portion of the visceral cavity. It consists of a 

 mass of caecal vesicles, ordinarily more or less elongated, 

 and pouring the secretion into a system of membranous 

 canals, the union of which forms ultimately a large trunk 

 on each side, which opens into the pyloric portion of the 

 stomach. Such is the structure of this important gland 

 in the highest forms ; but in the larger Stomapoda its 

 structure is apparently granular, and it forms two series 



