oe. 



diq. di. 



cr 3. 



Centimeters 



Figure 197. — Digestive system of the oyster, C. virginica, drawn from the dissected preparation after the injection of 

 latex. The right outer labial palp was cut off to expose the esophagus. The parenchymal tissues over the stomach and 

 intestine were removed, an. — anus; cl. — cloaca; cr.s. — crystalline style sac; dig. div. — digestive diverticula; int. — 

 intestine (mid-gut); oe. — esophagus; r. — rectum; st. — stomach. 



Three groups of wide ducts emerging from the 

 wall of the stomach lead to the digestive diver- 

 ticula. Two of them (fig. 199. di, d2) originate 

 at the anterior chamber and one (da) from the 

 posterior chamber. 



The internal lining of the anterior chamber 

 forms a number of irregular ridges and furrows 

 covered with ciliated epithelium. A broad ridge 

 separates the anterior from the posterior chamber 

 and apparently directs the food particles. The 

 left ventral wall of the posterior chamber is 

 covered by a translucent meml)rane, the gastric 

 shield (fig. 200), which lies directly opposite the 



opening of the long sac occupied by the crystalline 

 style (cr.s.). 



Ciliary tracts of the stomach lining are very 

 complex. Detailed observations on the course 

 followed by food particles after they enter the 

 stomach were made for 0. edulis and Mya arenaria 

 by Yonge (1923, 1926a), who studied them by 

 carefully cutting off the wall and adding fine 

 powdered carborundum or aquedag to the exposed 

 surface. In general the pattern of ciliary move- 

 ments in the stomach of the American oyster is 

 similar to that of 0. edulis. The direction of 

 ciliary beat along different ridges and channels 



220 



FISH AND WILDLIFE SERVICE 



