PIIYTIVOROUS MOLLUSCA. 381 



weed bit by bit, and nips away a portion from a larg-e frond 

 as easily as the Tritonia can be supposed to do. It is not 

 unlikely, however, that those jawless species which possess 

 the spinous tongue may take their food by rasping it oiF the 

 surface by aid of the prickles ; for it may be remarked that 

 the Patellje and the j)eriwinkles, when active, are constantly 

 protruding the anterior portion of the tongue between the 

 lips, and withdrawing it in rapid succession. 



The liver appears to be proportionally greater in these 

 tribes, in relation to the other viscera, than in the zoopha- 

 gous mollusca ; and, unlike that of the acephalous mollusca, 

 it rarely envelopes the stomach. It occupies, very generally, 

 a backward position among the viscera, filling the U2)per 

 convolutions of the shell ; and it is composed of lobes and 

 lobules,* of which the ultimate are in the form of hollow 

 globules, in each of which a biliary vessel originates. These 

 vessels, by successive reunions, contribute to form one, 

 three, or four large canals, which open directly into the 

 stomach, and pour in, we may presume, a large quantity 

 of bile ; essential, apparently, to the rapid digestion and 

 assimilation of the food. Sometimes the biliary pores, as 

 in Doris, are so large, that Cuvier wonders by what means 

 the food is prevented entering them ;■]- but, according to 

 Professor Grant, it actually does enter and fill them. 

 " UjDon opening the cavity of the stomach," says this dis- 

 tinguished naturalist, " we see, as in the tunicated animals, 

 and in the inhabitants of bivalve shells, the large perfora- 

 tions leading from the cavity into the substance of the liver. 

 Here, again, we observe the short, wide hepatic ducts, bear- 

 ing the same general character which they have from the 

 lowest of the mollusca up to the class of fishes. Baron 

 Cuvier remarks, that it is surprising the vegetable food 

 does not gain admission from the stomach into the cavities 

 and substance of the liver. I have collected many of those 

 animals upon our coasts, and have opened them in all con- 

 ditions as regards food taken into their stomach, and I have 

 found the stomach often completely filled with minutely 

 divided portions of coarse marine plants ; but I never found 

 them with their stomach thus filled, without finding that 

 the hepatic ducts were also filled with the food. These 



* Swammcrdam says it is diviilcd into lol)cs, "according to tlic ditiercnt 

 course of tlie intestines, vvliich make as many divisions in it as they have 

 turnings and windings." Our description of tlie liver is derived from 

 Blainville, Man. de JVIalacologic, p. 123. See also Lambron's description 

 of tlie liver of Helix pomatia in Edin. Med. Surg. Journ., vol. liv. p. 505. 



t Mem. sur h; Doris, p. 15. 



