12 THE LAND SNAILS 
speaking, Helix albolabris. It is represented as crawling, 
and consequently extended fully from the shell. The two 
larger and two smaller “horns” projecting from the head, 
are respectively called the upper or superior, and lower 
or inferior tentacles. The superior tentacles are the long- 
est, and stand uppermost ; at the tips of these are found 
the eyes, little black specks, though large enough to be 
distinctly visible. The eyes are very simple in structure, — 
and probably serve no important use, as the snail in pro- 
gression, appears to depend entirely on the tentacles as 
. feelers to guide the way. While they crawl, the tentacles 
are continually in motion, and the tips oftentimes come in 
contact with various objects on the way. If the eyes 
were capable of ordinary vision, this occasional contact of 
the tentacles would be avoided. 
That the sense of smell is enjoyed by the snail has long 
been known, since they will oftentimes travel some dis- 
tance in quest of food for which they have a particular 
fondness ; the exact seat of this sense, however, has long 
been a disputed question. An eminent French Naturalist 
believes it to be seated at the extreme tip of the larger 
tentacles. A magnified drawing is given (Fig. 1, Plate 
1,) of the end of the larger tentacles to show the position 
of the nerves supposed to be the nerves of smell, or the 
olfactory nerves, (o, Fig. 1,) these are seen as minute 
threads or branches terminating at the extreme end of the 
bulb-like tentacle. In this figure the eye is also seen with 
the optic nerve. (e. eye, op. optic nerve. ) The larger 
tentacles are retractible, that is, they have the power ol 
withdrawing within the head, the eyes disappearing 
first, as a glove finger disappears as it is withdrawn 
over the hand, turning the glove wrong side out. The 
smaller, or inferior tentacles, have not this power of with- 
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