294 



THE INHABITANTS OF THE SEA. 



Bulla. 



plate, resembling an upper jaw, and the tongue, by tri- 

 turating the food against this, gradually reduces substances 

 nowever hard. On opening the limpet, the tongue is found 

 doubled upon itself, and folded in a spiral manner beneath 

 the viscera. 



Many of the Gasteropods which live on coarse and refractory 

 materials are provided with several digestive cavities, re- 

 sembling in some degree the stomachs of the ruminating 

 quadrupeds; and frequently the triturating power of these 

 organs is still further increased by their being armed with teeth 

 variously disposed. 



In the Bulla, for instance, a genus belonging, like the sea- 

 hares, to the tectibranchiate order, the gizzard, or 

 second stomach, contains three plates of stony 

 hardness attached to its walls, and so disposed 

 that they perform the part of a most efficacious 

 grinding mill. 



On opening the gizzard 

 of the Scyllsea, it is found 

 to be still more formidably armed, for 

 in its muscular walls there are embedded 

 no less than twelve horny 

 plates (e), which are ex- 

 tremely hard and as sharp 

 as the blades of a knife. 



The Sea-hare, however, 

 furnishes us with the most 

 curious form of these 

 stomachal teeth, for here 

 we see not only the 

 gizzard (b) armed with horny pyramidal plates, whose tuber- 

 culated apices, meeting in the centre of the organ, must 

 necessarily bruise by their action whatever passes through 

 that cavity, but the third stomach (d) is also studded with 

 sharp-pointed hooks (c), resembling canine teeth, and ad- 

 mirably adapted to pierce and subdivide the tough leathery 

 fronds of the olive sea-weeds on which the animal feeds. Thus 

 these deformed and disgusting molluscs afford us one of the 

 most interesting examples of the adaptation of organs to their 



Gizzard of Bulla. 



Gizzard of Syllaaa 



