ON GASTEROPODA. Som 
whether they have not a peculiar office. The latter appears 
probable. Some writers are of opinion that the anterior pair 
may serve as olfactory organs. Others have imagined that 
the entire skin of these mollusca, was, as it were, pituitary, 
z.e. that it could transmit the sensation of odours, but from 
analogy, this appears to be extremely improbable. Be this, 
however, as it may, it is certain that snails can smell extremely 
well, for they are easily attracted by many plants, the odour 
of which pleases them. 
The black points at the extremities of the last pair of ten- 
tacula already mentioned, all authors have agreed to consider 
as eyes, and very probably, with great justice. Swammer- 
dam has even anatomized them, and declares that he has 
found there all the parts which compose a true eye. It must, 
however, be very imperfect, since, when we oppose a body to 
the first or second pair of the tentacula of these animals, they 
do not seem to perceive it more with one than the other. 
There is no trace of any special organ of hearing in the 
snails, and in fact these animals do not seem to perceive noise, 
unless it be so considerable and so near them as to produce 
a sensible agitation in the circumambient air. 
The apparatus of locomotion in the helices is general or 
partial. It is general in so much as the muscular or con- 
tractile fibre is not distinct from the skin of which it forms 
the internal stratum, directed in all ways. This is only 
more thick, and takes a more determined direction, when it 
belongs to the foot, where the muscular fibres are divided into 
little bundles, and disposed lengthwise. It is by means of 
this foot the animal moves, and very promptly, contracting 
and elongating successively each of these little bundles. 
There is a muscle which penetrates from one of the muscular 
bundles of the pillar, (another of these serves to retract the 
foot within the shell) into the interior of the tube of each 
