LAND SNAILS. 
93 
like the finger of a tight glove; its protrusion, 
on the other hand, is effected by the alternate 
Fig. 7.—Structure of the tentacles in Helix, 
a, b, c, d, Tentacles in different states of protrusion l , brain mass; 
/, h, nerves of tentacles g, muscle of tentacle; n, eye. {Owen.) 
contraction of the circular bands of muscle 
which compose the walls of the tentacle. 
The mouth of the snail is armed with a horny 
semicircular jaw, which, by pressing against the 
floor of the mouth, cuts off the fragments of its 
vegetable food. The jaw presents various forms 
in the several species. The lingual ribbon com¬ 
prises a central inconspicuous row, and two 
lateral rows with numerous teeth. The teeth 
differ from those of the slugs (Limacidce ), in 
that the apices of the lateral teeth, as they ap¬ 
proach the margin, bifurcate and become ser¬ 
rated.. However, those of Vitrina and Helicella 
resemble those of Avion and Limax. 
Snails are vegetable-feeders, but some exhibit 
carnivorous propensities, the objects preyed upon 
