THE ANATOMY OF PLEUROTOMARiA BEYRTOHII. 237 



the ventral and right half of the crop, while the right pouch 

 {Ip^.), which is somewhat smaller^ forms the dorsal and left 

 portion of the same. 



The non-papillate median dorsal and ventral areas remain 

 small, and are practically reversed in position. The position 

 of these folds and pouches is shown in figs. 10 and 11, the 

 latter being a diagrammatic transverse section of the crop, 

 from which it will be seen that the enlargement of the crop is 

 practically confined to the lateral pouches. 



Tracing the crop still further back it is found to gradually 

 diminish in size and complication, until it assumes the form 

 of a simple tube with rather thick walls, which we may speak 

 of as the oesophagus (fig. 7, o. e.). 



The Stomach. — The oesophagus extends back a little 

 behind the heart, and then suddenly debouches into the 

 stomach, which, as a large U-shaped cavity, lies below and 

 behind the right kidney (figs. 7 and 12, st.). The cavity of 

 the stomach is large and divided by a marked constriction 

 into a right and left portion, the former receiving the 

 oesophagus, while the latter receives the bile-duct (6. d.), and 

 gives origin to the intestine and the spiral caecum [sp. c). 

 The oesophageal aperture is very narrow and guarded by a 

 sphincter, while the intestinal orifice is large (fig. 12). The 

 bile-duct (6. d.) opens by a wide slit situated immediately to 

 the left of the semilunar fold which grows in from the floor 

 of the stomach and separates the two chambers. 



The spiral csecum {sp. c.) opens on the dorsal wall imme- 

 diately above the bile-duct, but the structure which may be 

 described as the columella of the spiral caecum is prolonged 

 down to the floor of the stomach, and forms the anterior lip 

 of the constriction between the two stomach-chambers. The 

 caecum itself forms a perfect helicoid spiral situated dorsally, 

 and overlying the two halves of the stomach. 



A spiral stomach-caecum is a very charactei'istic feature of 

 those Diotocardia possessed of a spiral shell, being specially 

 well marked in Trochus (fig. 13), Turbo, and Phasianella; 

 it is also developed in Haliotis, and in a very much modified 



