JAWS OF FISHES. 1 13 



with folds, like lips, generally four in number, has 

 on the whole more the character of an organ for 

 suction, than of a cavity adapted to prehension and 

 mastication. The Gasteropoda, on the other hand, 

 being capable of locomotion, are enabled to seek 

 and to select food of a more solid kind ; and they 

 seize it with a mouth provided with moveable lips, 

 retain it by means of hooks, and masticate and 

 swallow it by the aid of a tongue and jaws ; but we 

 frequently tind them possessing a tubular organ. 



Most of the Mollusca which inhabit univalve 

 shells are provided with a tubular organ, of a cylin- 

 dric or conical shape, capable of elongation and 

 contraction, and of eversion and inversion, by cir- 

 cular and longitudinal muscular fibres, and serving 

 the purpose of a proboscis, or organ of prehension 

 for seizing and conveying food into the mouth. 

 These tubes exist in most of the testaceous gastero- 

 pods ; and they are of great size in the Succimim, 

 the Murex, and the Voluta ; as also in the Doris, 

 and other Nudibranchiate Gasteropods. In those 

 mollusca of this order which have not a proboscis, 

 as the Limax, or slug, the Helix, or snail, and the 

 Aplysia, or sea-hare, the mouth is furnished with 

 broad lips, and is supported by an internal carti- 

 lage, having several tooth-like projections, which 



270 assist in laying hold of the substances 

 taken as food. That of the snail is repre- 

 sented in Fig. 270. Most gasteropods 

 have also a tongue, which in the Patella, and the 

 Turbo pica, is of enormous length, and beset with 

 numerous spines, to enable them to act as a file 

 for rasping rocks and other hard bodies. 



All the Cephalopoda, or cuttle fish tribe, are fur' 



VOL. II. I 



