ORGANS OF DIGESTION. 3/3 



directed to that side, as in reverse shells where a similar 

 transposition is seen in all the viscera. The higher car- 

 nivorous proboscidian gasteropods, armed with an operculated 

 turbiiiated shell, and for the most part pectinibranchiate 

 and with the sexes separate, have generally sharp teeth 

 placed on a divided tongue at the end of the long muscular 

 proboscis. These teeth, like maxillse, are supported by two 

 long stiliform cartilaginous pieces, like the gastric carti- 

 laginous dart of conchifera, and are moved like jaws by 

 powerful muscles, as seen in the buccinum undatum (Fig. 66. 

 a.) Through the axis of this muscular tube passes the 

 oesophagus, and between them run the long ducts of the 

 salivary glands to the mouth at the free extremity. The 

 oesophagus is therefore of great length in these predaceous 

 animals, and is sometimes provided with a small crop on 

 entering the abdominal cavity. The stomach is small, simple, 

 and membranous, and the short intestine forms a wide colon 

 in advancing along the right side of the body to terminate 

 near the neck, on that side, under the mantle. 



XVII. Pteropoda. These small swimming mollusca ap- 

 pear to feed, like conchifera, on minute animals or organic 

 particles suspended in the waters they inhabit, and their 

 digestive apparatus is formed on a plan nearly as simple 

 as that of the inhabitants of bivalved shells or of the lowest 

 gasteropods. No teeth are perceptible in the triangular 

 fleshy mouth of the clio borealis, but long follicular salivary 

 glands open into the sides of the buccal cavity, as in the 

 pneumodermon, and the oesophagus, after passing through 

 the usual cerebral or ganglionic ring, dilates into a long 

 wide membranous stomach surrounded by the lobes of a 

 large liver and perforated by their ducts. From this length- 

 ened stomach the short intestine, still destitute of me- 

 sentery, turns upwards in a slightly convoluted direction, 

 on the left side, to terminate on the neck under the left 

 gill, the mantle of the pteropods being closed above, and 

 there being here no median open funnel for the excre- 

 tions as in the cephalopods. The oesophagus is generally 

 lengthened in the pteropods as in the gasteropods, while it 

 is very short in the conchifera and tunicata. The stomach 

 is perforated by the biliary ducts, and the intestine is en- 

 veloped in the hepatic lobes in the pneumodermon, as in 

 the clio. In the stomach of the cimbulia there are dense 



