168 ORGANS OF DIGESTION. 



the esophagus now runs a short course, and near the sto- 

 mach dilates into a small crop, opening into a round mem- 

 branous stomach, surrounded or imbedded in the substance 

 of the liver; the length of the intestine is considerably 

 less than that of the esophagus ; it describes a turn, di- 

 lates into a wide colon, and terminates on the right side, 

 under the open mantle ; the liver is of considerable size, occu- 

 pying the spiral turns of the shell, and, as in the preceding 

 classes, pours its secretion by numerous ducts into the sto- 

 mach. The digestive organs of other gasteropoda are formed 

 after the same type. 



The Patella (or limpet) feeds on marine vegetables, and is 

 always found in situations -where they are most abundant. It 

 is deprived of a proboscis, but the mouth is armed with a 

 long, slender, convoluted tongue, studded with rows of sharp, 

 silicious recurved teeth (fig. 194), by which it exercises a filing 

 process on its vegetable food. The wide sacculated esopha- 

 gus opens into a large stomach of a lengthened form, sur- 

 rounded by the liver; the long convoluted intestinal canal 

 makes several turns through the structure of this organ, and 

 finally opens into a dilated rectum ; the long salivary vessels 

 empty themselves into the esophagus. 



The Helix (snail) and Limax (slug) have large lips, which may 

 be regarded as the rudiments of a proboscis ; the upper jaw 

 of the garden snail (Helix aspera) is furnished with sharp 

 teeth, which perforate and file down the leaves of plants. The 

 short esophagus, having passed through the nervous collar, di- 

 lates into a large membranous stomach, contracted in the centre, 

 into the posterior half of which the biliary ducts enter ; the in- 

 testine, having made a turn through the liver, passes up along 

 the right side of the body, and opens by a small orifice at the 

 margin of the respiratory sac. 



In the Pleuro-branchus the digestive organs are remarkable 

 for their complex structure, and for the resemblance the stomach 

 bears to the compound stomach of ruminating quadrupeds. 

 The esophagus is dilated into a membranous bag, or paunch, 

 into which the biliary ducts open ; to this succeeds a globular 

 muscular organ, analogous to the second or honeycomb sto- 

 mach of ruminants; this leads to a membranous organ, provided 

 internally with longitudinal folds of the lining membrane, the 

 analogue of the leaflet, or manyplies, and, lastly, into a fourth, 



