316 



LECTURE XV. 



the common simple type of the intestine in Crustacea, by having that 

 canal disposed in one or two spiral coils. In the Stomapods or 

 Squillae the stomach bends forwards in advance of the cardiac orifice ; 

 a bi-articulate plate extends from that orifice backwards through the 

 pylorus into the intestine, and regulates the passage of the alimentary 

 substances into that tube ; they are previously subjected to the action 

 of four lateral dentated pyloric processes. 



In the higher Crustacea the stomach {Jig. 132, c) is of a globular 



132 



Cancer pagurus. 



form, more capacious tlaan in the Limulus, and its walls are connected 

 with a calcareous frame-work supporting dense tubercles, which 

 project into the interior of the stomach around the pylorus, and are 

 so situated and moved with relation to each other as to divide and 

 bruise the alimentary matters before they pass into the intestine. In 

 the common lobster these gastric teeth are three in number, the middle 

 one serving as a kind of anvil upon which the two larger lateral pieces 

 work.* This complex kind of gizzard is sometimes found to be everted 

 and protruded from the mouth, the gastric teeth being then external, 

 like those of the anterior muscular segment or proboscis of the alimen- 

 tary canal in the Anellides. The inner tunic of the stomach is com- 

 posed of chitine, and is beset with groups of hair-like processes in most 

 Decapoda. 



The intestine in almost all Crustacea is continued to the vent with- 

 out convolutions ; a terminal portion, or rectum, is sometimes, as in 

 the lobster, indicated by a slight circular valve ; the vent is situated 



♦ Preps. Nos. 407, 408. 



