774 



CRUSTACEA. 



Fig. 41 G. 



Fig. 417. 



Digestive canal of the Maja. 



a, Cardiac portion of the stomach. 



b, b, Upper portion of the frame-work of the 



stomach. 



c f Pyloric portion of the stomach. 

 d, The small intestine. 



c, Termination of the biliary ducts. 



f t Anterior appendages of the intestine. 

 g, Posterior appendages. 

 h, Rectum. 



and even in the several species of the same 

 genus. Still every one of them may be de- 

 monstrated with a little care, in the whole of 

 the Brachyura and of the Macroura. They 

 are less numerous, and are singularly modified 

 in proportion as we recede from these types. 

 In the Squilla mere vestiges only of the ap- 

 paratus are found in two semicorneous pieces 

 covered with rounded projections ; and its 

 functions are performed by a branch of each 

 mandible which penetrates even to the pyloric 

 orifice of the stomach. 



The intestine extends from the pylorus to 

 the anus without curve or convolution in its 

 course ( Jig. 4 1 6, d, h). In the superior Crustacea 



Liver of the Lobster. 



a, stomach ; b, intestine ; c, left lobe of the liver 

 in its natural state ; d, right lobe dissected, so 

 as to show its structure and the disposition of the 

 biliary ducts. 



it may be distinguished into two portions, one of 

 which may be named the duodenum, the other 

 the rectum. These two portions where they 

 occur vary extremely both in their nature and 

 in their relative lengths. Sometimes they are 

 separated by a valve (Lobster) corresponding 

 internally to a circular external elevation ; but 

 still more frequently their respective limits are 

 not obviously marked, and among the whole 

 of the inferior members of the family the 

 intestinal canal is entirely cylindrical, and per- 

 fectly identical in its constitution through its 

 whole length. The anus is constantly seated 

 in the last ring, and is closed by certain mus- 

 cular fibres which perform the office of a 

 sphincter. 



