Snails have an extraordinary power of re-producing any part which may be injured or cut off, even to the extent of the whole head, as has been observed to be the case; the reparation of injury done to the shell they can effect easily, as can all testaceous mollusks. Respecting the construction of the shell it may be observed that it is produced in the thickness of the mantle, or cloak-like covering which envelopes the body of the animal; the formation commences at the small end or spire, and gradually goes on, whorl upon whorl, as the still widening circles which give the ridgy appearance to most univalves, are called. Columella, or pillar, is the name given to the spire on which the cones are rolled; this is sometimes solid, and sometimes hollow; when the latter, the open end is called the Umbilicus, meaning the navel or centre. The opening at the bottom, from which the animal issues, is the last portion finished, and this is called the aperture, a Latin word adopted into the English dictionary. Some of these Helices are wide and flat, even hollow and cup-like, with the whorls rising above the pillar—these are called discoid shells; others which are long and narrow, with projecting spires, are termed turbinated shells; the former being more or less flat or disk-like, the latter twisted, whirling, like a spinning-top, from the Latin turbo—a whirling, a turning round.
If we take a Common Snail, and plunge it into boiling water, which will instantly kill it, so that it can be removed from the shell, we shall find the whole of that part of the body which was lodged in the upper whorls, or spiral part of the shell, is covered with a thin membrane or skin; this is called the mantle, and that portion of it which corresponds with what we may consider as the back of the mollusk, and which is considerably thickened, is termed the collar; here are situated the glands, which secrete the colouring and other matter of which the shell is mainly composed; although the substance called nacre, or mother-of-pearl, is secreted in the thinner part of the mantle; it is however from the collar that the growth or increase of the shell proceeds. It is in accordance with certain variations in the shape and disposition of this mantle and collar, that shells assume such very different shapes. Sometimes the whorls or spiral ridges, are projected or thrown far out, and this produces the turbinated shell. Sometimes they scarcely rise above each other, but rather spread towards the sides, and then we have the discoid shape. Generally speaking, the whorls of a shell take a direction from left to right, but occasionally an opposite one; they are then called sinistral, or left-handed shells: such are not common. If one of the twisted shells be divided length-ways, it will be seen that the inside of the whorls wind in an ascending direction, round the Columella, or central column, as the spiral staircases in the Crystal Palace.
But let us return to our Garden Snail, who has many near relatives in Britain, several of which have beautifully-marked and convoluted shells, as will be seen by a reference to our coloured illustrations, [Plate I]. We will introduce them in due order. Fig. 1, the Banded Snail, (Helix nemoralis,) from the Latin nemus—a wood or grove; the prettily-striped shells of this species may be found in great plenty among the roots and in the crevices of the rugged boles of old forest trees, as well as in hedge-rows and in mossy banks, and other situations near woods. Fig. 2, the Heath Snail, (H. ericetorum,) from erica, the Latin for heath; a small species with brown bands, remarkable for its large umbilicus, perforating the centre of the shell nearly through. Fig. 3, the Silky Snail, (H. sericea,) from the Latin sericus—silk-like; the shell of this species is covered with short slimy hairs, which give it a glistening appearance. Fig. 4, the Stone Snail, (H. lapicida,) from the Latin lapis—a stone: Linnæus called the species the Stone Cutter, probably on account of its habit of frequenting stony places, and the peculiar construction of the shell, which has a sharp edge running round each whorl; it is commonly found lodged in the cavities of loose-lying stones, but which it can scarcely be suspected of having hollowed out for its own accommodation.
Fig. 5, the Elegant Cyclostome, (Cyclostoma elegans.) On turning to the dictionary, we find that cyclostomous means having a circular mouth. This species is sometimes called Turbo elegans; the beautifully-marked shells are often found in chalk-hills covered with brushwood. This pretty mollusk has a curious mode of travelling; the under surface of the foot, which is long, is divided by a deep fissure, into two narrow strips, like ribbons; these take hold of whatever the creature may be moving on alternately; one keeping fast hold while the other advances, in like manner to fix itself, and drag the body forward. Fig. 6, the Undulated Plekocheilos, (P. undulatus;) the Latin plecto—to twist or twine, seems to be the root from which the generic name of this Snail is derived; the specific name will be easily understood; to undulate, is to flow like waves, and the lines on the shell it will be seen are undulating. This is not a British species, but is introduced here to give variety to the group; it is a West Indian Mollusk, and is found in immense numbers in the forests of St. Vincent; it glues its eggs to the leaves of a plant which holds water, and thus secures for them a damp atmosphere at all times. And here we must conclude our chapter of Land Snails, leaving unnoticed very many beautiful and interesting species, both British and Foreign.
Many poets have alluded to the Snail, but we can only find room for a few verses by Cowper:—
To grass, or leaf, or fruit, or wall,
The snail sticks close, nor fears to fall,
As if he grew there, house and all