294 THE INHABITANTS OF THE SEA. 
plate, resembling an upper jaw, and the tongue, by tri- 
turating the food against this, gradually reduces substances 
however 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- 
7 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 Scyllea, it is found 
to be still more formidably armed, for 
in its muscular walls there are embedded 
no less than twelve horny 
plates (¢), 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 (¢), 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 
. 
iy / 
Gizzard of Syllea. 
Gizzard of Bulla. 
