The Snail (_Helix_) is an animal well-known in every part of the globe,
and its species are still extremely numerous, although many shells
which belonged to this tribe, under the Linnæan arrangement, have been
placed in other divisions. The head of the Snail is furnished with
two pair of tentacula, or feelers; these, unlike similar appendices
in other Mollusca, are retractile; that is, they can be withdrawn
into the body at the will of the animal. The use of these tentacula
is uncertain. At the top of each of the longest pair we find a black
spot; these spots have been supposed to be the eyes of the animal,
and a celebrated anatomist says, that he has discovered in them all
the component parts of perfect eyes. However this may be, the animal
appears to use them rather as organs of touch than of sight. Some
writers suspect that the sense of smell resides in one or both pairs of
these appendages.
The uses to which Snails are applied are not many; some of the larger
kinds, however, are, in some countries, employed as food. The Romans,
according to Pliny, consumed large quantities, and considered them in
the light of delicacies, and considerable pains were taken in fattening
them for the table. Those from Sicily and the Balearic Islands were in
great request, and attained a very large size. Some authors say they
are still used as food in several parts of the Continent.
[Illustration: _Helix nemoralis._]
In Paris, London, and many large towns, great numbers of Snails are
frequently brought to market; but these are not employed as food, but
used medicinally by persons suffering under consumption, and other
diseases of the chest.
It was already known that polypi, and some species of worms, could have
portions of their body cut off, and that the parts removed would be
afterwards reproduced; and as these animals had no well distinguished
extremities, such as heads or limbs, the fact, although singular, was
not disputed; but, when it was asserted by Spallanzani, that Snails,
which have a very well defined series of parts, could, after the head
was removed, reproduce that portion of the body, the scientific world
became naturally incredulous, and numerous experiments were made,
and thousands of Snails slaughtered, to ascertain the fact. No one,
however, for a length of time, could succeed;—it was then suspected
that Spallanzani had only removed a portion of the head. At length,
it would appear, from the experiments of M. G. Tarenne (an account of
which appeared in 1808), that these creatures could actually reproduce
a complete head. He gives as a reason of the want of success of others,
the little precaution taken to provide the mutilated Snails with proper
nourishment. The new head, according to him, is perfect in about two
years after the old head has been removed.
M. Tarenne says, that after having cut off the heads of two hundred
Snails, he threw them all into a moist spot at the end of his garden,
that they might obtain the nourishment most fitted for them (how they
could eat without their heads he does not say); at the end of the
Summer he examined all the mutilated Snails he could find, and he
discovered that they all had a new head, about the size of a grain
of coffee; they had four small tentacula, a mouth, and lips; at the
end of the following Summer, the heads were perfectly reproduced, and
like the original head, with the exception of the skin, which was more
delicate. “After this experiment,” says a French author, “we cannot
doubt that the entire head of a Snail can be regenerated after it has
been removed; however, I cannot disguise the fact, that I have a kind
of repugnance at admitting the matter to be entirely beyond dispute.”
If the advantages bestowed on man by Snails are not numerous, the
disadvantages, or rather inconveniences, produced by them are very
considerable; they are particularly destructive in orchards and
kitchen-gardens. On this account, many methods have been recommended
for the purpose of destroying them. Although many of these are
tolerably successful, there is no plan more likely to keep the breed
of Snails under, particularly in enclosed gardens, than that of early
rising and gathering them, if we may so express ourselves, while the
dew is yet on the grass: if the shells are then broken, they become
excellent food for poultry. Ducks may sometimes be allowed to wander
in the garden, as they do but little damage to the vegetation, and are
great destroyers both of Snails and slugs.
A singular account of the instinct of Snails is, perhaps, worth
recording.
The garden of a small house, by the side of one of the roads leading
into London, was much infested by a colony of Snails; the proprietor of
this house, desirous of getting rid of the pest, and yet unwilling to
kill the Snails, collected them, and threw them unharmed into the road;
but still, he every morning discovered as many Snails among his pinks
and tulips as he had removed the previous day; this somewhat puzzled
him, until once, on leaving his house early, he perceived the Snails
which he had but an hour before thrown into the dusty road, moving, not
in a body, but each from the spot on which it was thrown, in a direct
line from that spot to the low wall which encompassed the garden, as
if they comprehended the mathematical fact that, “a straight line is
the nearest way from one given point to another.” How were these Snails
aware that by moving in that direction, they should arrive at a green
spot? From the road nothing could be visible to them but dust,—from
the path, nothing but the wall in front,—but still, although the
whole of their path was covered with dust, they proceeded steadily on,
until they had surmounted the wall, and reached their old quarters. By
what other faculty were they guided but that instinct which supplies
the place of the higher powers of the mind, and which is imparted with
so liberal a hand to the meanest creature in nature?
_ORDER GASTEROPODA._
The Gasteropods are so called from two Greek words, meaning belly and
foot, because the foot, or organ of motion of the animals of which
this order consists, is attached to the whole of the under part of the
creature, or rather, the belly or under part is itself the foot, and is
for that purpose broad and flat. The Gasteropods are also distinguished
from the last order by having a straight body, in no case spiral,
and never possessing a shell capable of enclosing the whole body; in
some cases, the body is completely naked, and without the protecting
covering of any shell whatever.