The _Lymnæa stagnalis_ is found in stagnant waters, particularly narrow
ditches, in great abundance. As it breathes air, it is necessary for
its existence that it should frequently resort to the surface of the
water; and consequently, we find these shells floating about in great
numbers, with the body partly out of the shell. The least appearance
of danger causes a Lymnæa to withdraw the whole of its body into
its shelly covering; and as this increases its specific gravity, it
instantly sinks to the bottom, where it remains in safety. In order
to reach the surface again, it is obliged to crawl to the side of the
ditch, and when it has reached the level of the water, it again trusts
its little bark to the mercy of the winds and stream, for it has very
little power to direct its own course.
During the Winter, these creatures remain at the bottom, buried in the
mud, and in a state of torpor. Although apparently useless to mankind,
they form part of the subsistence of many water-birds, and of fishes,
which are extremely fond of them. The species of this shell are not
easily decided, since they bear so great a resemblance to each other.