a^ap. j^ 



^ .. , 10 



Centimeters 



Figure 198. — Latex cast of the stomach, crystalline style 

 sac, and esophagus of a large C. virginica, viewed from 

 the left side. Upper part of the esophagus is slightly 

 distended by injection. The visceral mass was dissected 

 and the injected parts left in their natural position. 

 Drawn from a preparation preserved in 5 percent for- 

 malin, a. — anterior chamber; a.ap. — anterior appendix 

 of the caecum; b. — posterior chamber; c. — caecum; 

 cr.s. — crystalline style sac; d.p. — dorsal pouch; d. — 

 group of ducts of the digestive gland; m.g. — midgut; 

 p.ap. — posterior appendix of the caecum; p.c. — pyloric 

 caecum. 



Centimeters 



Figure 199. — Latex cast of the stomach, crystalline style 

 sac, and esophagus of a large C. virginica viewed from 

 tlie right side. The visceral mass was dissected, and the 

 injected parts were left in their natural position. Drawn 

 from a preparation preserved in 5 percent formalin, 

 a. — anterior chamber; b. — posterior chamber; cr.s. — 

 crystalline style sac; di, d2, da — ducts leading to the diges- 

 tive diverticula; m.g. — midgut; oe. — esophagus. 



brings the food from the esophagus to the caecuiii 

 where the food materials are separated according 

 to size. Some of the larger particles entering the 

 midgut may be voided without being digested 

 while the smaller particles are pushed toward 

 the gastric shield. Other groups of cilia conduct 

 the particles toward the ducts leading to the 

 digestive diverticula. The ducts branch out into 

 a large number of smaller passages that ramify and 

 extend deep into the mass of diverticula. 



Nearly the entire inner surface of the stomach 



ORGANS OF DIGESTION AND FOOD OF THE OYSTER 

 733-S51 O— 64 15 



is covered by ciliated epithelium; only the areas 

 imder the gastric shield and near the posterior 

 end of the stomach are nonciliated. The epithe- 

 lium is of columnar type with very long cilia, 

 which are particularly prominent on the ridges 

 (fig. 201). The height of the cells gradually 

 decreases toward the caecum. Mucous cells are 

 abundant, particularly near the junction with the 

 midgut, and phagocytes are numerous between 

 the epithelial cells and in the underlying connec- 

 tive tissue. There is no well-developed muscular 

 layer under the epithelial lining, but a few smooth 



221 



