BVDER] LIFE-UISTOEY OF THE OYSTER. 325 



p ; it will be noticed that the ridges are wanting just a little below the 

 level of the mouth. The mouth m opens by way of a short gullet or 

 cesophagns into a very irregular cavity, which is the stomach. The in- 

 testine is continued from the posterior portion of the cavity of the 

 stomach as a wide, somewhat irregular tube i' compressed laterally. In 

 the lower part of this portion of the gut, and extending to its first bend, 

 a singular opalescent, hyaline cartilaginous rod, the crystalline style, is 

 lodged. Posteriorly, at the first bend of the intestine, a bluntly rounded 

 finger-like ventral process of the body-mass hm envelops the latter. 

 Beyond the first bend, the intestine i, as soon as it bends forwards again 

 towards the head, becomes more nearly cylindrical, and is continued 

 forwards over the gullet, bending down to the left side, and passes up- 

 wards, after making an open bend upon itself, obliquely backwards to 

 end at the vent v. 



The cavity of the intestine, along its narrow portion, is not really 

 cylindrical, as may be seen in Fig. 3, representing a cross-section of an 

 oyster, viewed from the anterior side, and taken from a specimen in a 

 plane corresponding very nearly to the line o in Fig. 2. In this section 

 the intestine is cut across twice, as shown at V above and at i below 

 the stomach. These sections show that the intestine proper has a pecu- 

 liar crescent-shaped cavity, when cut straight across, which arises from 

 the fact that one side of the wall of the intestine has been pushed in- 

 wards towards the other. This peculiarity characterizes the shape of 

 the cavity of the intestine from its first bend to its termination at the 

 vent. 



The only glandular appendage of the alimentary tract of the oyster 

 is the massive liver. It communicates with the stomach by means of 

 a number of wide ducts with somewhat folded or plicated walls. The 

 great ducts subdivide, and their ultimate ramifications terminate in a 

 multitude of minute oval follicles, which are the effective agents in 

 secreting the biliary and peculiar digestive juices. A thick stratum of 

 these follicles surrounds the stomach except at its back or dorsal side. 

 The extent or distribution of the liver I in the body-mass, and the way in 

 which it is imbedded in the connective tissue c around the stomach st, 

 may be inferred from Fig. 3. 



The function of the so-called liver of the oyster is evidently digestive, 

 and probably combines the action of a gastric, ijancreatic, and biliary 

 secretion. There are absolutely no triturating organs in the oyster for 

 the comminution of the food ; it is simply macerated in the glandular 

 secretion of the liver and swept along through the intestines by the 

 combined vibratory action of innumerable fine filaments with which 

 the walls of the stomach, hepatic ducts, and intestine are clothed. There 

 is no peristaltic action of the intestine and there are no annular muscles 

 in its walls. The nutritive matters of the food are acted upon in two 

 ways : first, a peculiar organic ferment or solvent derived from the liver 

 reduces it to a condition in which it may be absorbed ; secondly, in order 



