Class II. GASTEROPODA. This term, derived from the Greek gaster, the belly, and pous, foot, signifies belly-walkers. THE COMMON SNAIL. The organ by which they move, as is shown in the common snail, consists of a broad, muscular, disk-like foot, attached to the ventral surface, upon which the animal creeps very slowly with a gliding motion. The muscular movements may be seen following each other in rapid waves, when a snail is climbing a pane of glass. There are numerous species, which greatly vary in form. All, however, have a distinct head; respiration is effected by branchiæ, or a pulmonary sac; the organs of the senses are tentacles of various forms; the eyes are usually placed at the ends of tentacles situated upon the head. No special organs of taste or smell have been detected, but there is good reason, from the discrimination these animals show in the selection of their food, for believing that they possess them. The general form of the body is characteristic of the class; from the preponderance of one side of the body, the whole, during growth, acquires a spiral form; it is only in some naked species that we find the body symmetrical. Most of the Gasteropoda close the aperture of their shell by a horny or calcareous plate, called the operculum. Most of the species are oviparous; a few are ovo-viviparous. The sexes are generally separate, but many are hermaphrodites. The young are always provided with a shell while in the egg. These animals are divided into three orders, the Pulmonifera, Branchifera, and Heteropoda. ORDER 1. PULMONIFERA. This term, from the Latin, pulmo, a lung, and fero, to bear, refers to the fact that the animals of this order breathe air by means of lungs, and not water by means of branchiæ. It includes several species popularly known under the name of Snails and Slugs. THE HELICIDE. Genus HELIX: Helix.-To this belongs the COMMON GARDEN-SNAIL, H. aspera. This is furnished with four tentacula, two of which are smaller than the others; at the end of these, which the animal pushes out or draws back like telescopes, are blackish knobs, which are the eyes. It lays eggs about the size of peas, which are of a soft transparent substance. By closely examining with a magnifying lens, the young snail may be seen in the egg, with its embryo shell on its back. The snail is extremely tenacious of life, in evidence of which numerous examples have been cited; among them is the following, which is furnished by Mrs. Loudon: a Mr. S. Simon, a merchant of Dublin, whose father, a Fellow of the Royal Society, and a lover of natural history, left him a small collection of fossils and other curiosities, had, among them, the shells of some snails. About fifteen years after his father's death, he gave to his son, a child of ten years old, some of these snail-shells to play with. The boy placed them in a flower-pot, which VOL. II.---64 Having occasion to use this, Mr. He examined the child respecting he filled with water, and the next day put them into a basin. But the most interesting example of resuscitation occurred to a specimen of the Desert-snail, from Egypt, chronicled by Dr. Baird. This individual was fixed to a tablet in the British Museum on the 25th of March, 1846, and on March 7th, 1850, it was observed that he must have come out of his shell in the interval, as the paper had been discolored, apparently in his attempt to get away; but finding escape impossible, he had again retired, closing his aperture with the usual glistening film; this led to his immersion in tepid water, and marvelous recovery. "He is now," says our authority, March 13th, 1850, "alive and flourishing, and has sat for his portrait." The reproduction of snails is most curious; at a certain time of the year, according to the account of Mrs. Loudon, they meet in pairs, and stationing themselves an inch or two apart, they launch at each other several little darts, not quite half an inch long. These are of a horny substance, and sharply pointed at one end. The animals, during the breeding season, are furnished with a little reservoir for them, situated in the neck, and opening on the right side. After the discharge of the first dart, the wounded snail immediately retaliates on its aggressor by ejecting at it a similar one; the other renews the battle, and in turn is again wounded. Thus are the darts of Cupid, metaphorical with all the rest of the creation, completely realized in snails. After the combat they embrace each other, and both lay eggs! The manner in which a snail increases the size of its shell and mends it in case of fracture, is thus described by Réaumur, and it is the more interesting, as it illustrates the mode of proceeding, in these cases, of many other mollusca: "When a testaceous animal is about to enlarge its shell, the common snail, for instance, and its body has become too large to be covered securely, it projects a portion of its body from the opening; it then attaches itself to a wall or other solid substance, and the naked part is soon covered with the fluids which are excreted from its surface; the pellicle, or covering, which they produce, when the fluid dries, is, at first, thin and elastic, but gradually assumes more consistence, and becomes at last similar to the whole part of the shell. If, in this stage of the process, a bit of the shell is broken off and removed without injuring the body of the animal, the skin of the snail is soon covered with a fluid which gradually thickens and becomes solid. In about twenty-four hours after the operation, a fine crust may be observed, which constitutes the first and external layer for repairing the breach that has been made; at the end of some days this layer becomes solid, and in ten or twelve days, under favorable circumstances, the new piece of shell has acquired the same thickness as that which was removed, but it never unites in the same way, being only as it were a plug. If, after the broken piece has been removed, particularly if the fracture is made near the edge of the opening, the animal is not supplied with a sufficient quantity of nourishment, its bulk is gradually diminished, and now finding what is left of the shell equal to completely cover its lessened body, no exertion takes place for the production of a new portion. It is obvious, snails, &c., cannot enlarge in volume but by the augmentation of the whorls, and that each previous turn of the spire remains the same in length; these make a great difference in the size of the shell, by the last and additional one, each being calculated to contain nearly double that of the preceding one; but in many shells, both marine and river, the last whorls of the spire, compared with the preceding ones, greatly exceed this proportion. In some, the external opening is twelve times greater, or from eight to twelve; this depends entirely on the increase of the animal's body, and the duration of that increase." The EDIBLE SNAIL, H. pomatia, grows to a large size, nearly that of a man's fist. highly prized by the ancient Romans, for the table; they fattened it with great care in a largebuilding, called a Cochlearia, where thousands of them were kept and fed with meal and new wine, boiled down. Varro says the shells of some of them would hold ten quarts. In Italy and France, at the present day, millions of these snails are fattened and brought to market, being used especially during lent, as they are not forbidden by "the Church." Another common European species is the BANDED SNAIL, H. memoralis. This was Snails are widely distributed over most parts of the world; sometimes, after a shower, they are so abundant in Europe, as to have given rise to the popular idea that it has rained snails. In some intertropical countries there are species with exceedingly beautiful shells. Snails are less numerous in this country than in Europe, though we have in the United States over sixty known species. One of the largest and most common among us is the H. albolabris ; this deposits its eggs in light mould by the side of rocks and logs; in twenty or thirty days the young snail issues forth with a shell containing one whorl and a half. In October this species cease to feed, close the aperture by secreting over it a thin membrane, place the operculum uppermost, and remain torpid till spring. Other American species are the H. alternata, abounding in ditches and moist places; H. monodon, usually living in pairs, and found in open fields under stones, or in rotten wood in forests, &c., &c. THE RED SLUG. THE LIMACIDE. Genus LIMAX: Limax.-This includes several species, called Siugs; these resemble snails in the form of the body, in the number and structure of the tentacles, and in their habits; but their shell is very small or rudimentary, and usually concealed in the interior of the mantle. Many of these species are very destructive in the gardens and fields, and a multitude of devices have been adopted for their destruction. The RED SLUG, L. rufus, is a very abundant species, and in Europe a broth made of it is used for diseases of the chest. The BLACK SLUG, L. nigrescens, and GRAY SLUG, L. griseus, are also common European species. The L. agrestis is an American species one and a half inches long, feeding on succulent leaves, and is often found on the under side of decayed leaves and trunks lying on the ground. Other species are L. flavus, two to two and a half inches long, and L. campestris, an inch long, &c. THE LIMNÆIDÆ. These, which are called POND SNAILS, inhabit fresh waters in all parts of the world: they feed chiefly on decaying leaves, and deposit their spawn, in the form of oblong, transparent masses, on aquatic plants and stones. There are several minute species in this country. ORDER 2. BRANCHIFERA. This order derives its name from the Latin branchia, gills, and fero, to bear, and is divided into two groups or sub-orders, the Prosobranchiata, and the Opisthobranchiata. THE PROSOBRANCHIATA. This term is compounded of the Greek proso, anterior, and branchia, gills, and includes a great number of species, all, however, possessing shells, usually spiral, within which they can retract themselves at pleasure. On account of the anterior position of the gills, the blood flows back toward the breast, and the auricle of the latter organ is placed in front of the ventricle. This division includes a great number of families, some of which we shall very briefly notice. THE CYPRÆIDE, OR COWRIES. In this family the shells are convolute, highly enameled, and many of them are beautifully colored. The animal has a broad foot, truncated in front, and a mantle expanded on each side. There are one hundred and fifty living species; they are found in all warm seas, except on the east coast of South America; they generally live in shallow water near the shore, and feed on zoophytes. Genus CYPRÆA: Cypræa, includes the C. annulus, used by the Asiatic Islanders to weight their fishing-nets and for barter. Mr. Layard found species of it in the ruins of Nimroud. The MONEY CowRY, C. moneta, is a native of the Pacific and Eastern seas, and is used as money by the natives on the coast of Western Africa. These are collected in immense quantities by the British and taken to Africa to be disposed of to the negroes. In 1849, three hundred tons of them were imported into Liverpool for this purpose. The MAP COWRY, 00 THE MAP COWRY. C. mappa, found in the Indian Ocean, is Besides the living ones, there are seventyeight known species of fossil Cypræidæ. THE CONIDÆ. These have the shell inversely conical; in the animal the head is produced, the tentacles far apart, and eyes on the tentacles. There are two hundred and sixty-nine known species, found in all tropical seas. They inhabit fissures and holes of rocks, and the warm and shallow pools inside of coral reefs. They move slowly, and sometimes bite when han dled. All are predacious. Some of the shells are beautiful, and have been sold for enormous prices. BISHOP'S MITRE SHELL. THE VOLUTIDÆ Genus VOLUTA: Voluta.-This includes numerous living as well as fossil species; among the former are the V. undulata, V. musica, V. vespertilio, V. Brasiliana, &c. Many of the Volutidæ are very beautifully marked. Genus MITRA: Mitra, includes the Mitre Shells, one of which, the BISHOP'S MITRE SHELL, M. episcopalis, is noted for a very long proboscis, sometimes twice the length of the shell. The latter is turretted, smooth, white, and spotted with light red. It is found in the seas of the East Indies and some of the Polynesian Islands. This is a very extensive family, some of the species being furnished with a long proboscis, with which they bore through the shells of other mollusca, and thus suck out the juices and destroy the animal within. The foot is broad, and adapted to crawling; the tentacles are short, and sometimes bear the eyes. All are marine and predatory; the shells are usually ornamented with spines; some assume very singular forms, and many are of very beautiful colors. The ancients obtained their purple dye from these animals; heaps of the shells may be still seen on the rocks of the Tyrian shores, and also on the coasts of the Morea, where it appears they were used in THE THORNY WOODCOCK. the same manner as by the Tyrians. One hundred and eighty living and one hundred and sixty fossil species are known. Genus MUREX: Murex.-This includes the STINGWINKLE OF HEDGE-HOG MUREX, M. erinaceus, common in the English Channel. The shell of the THORNY WOODCOCK, M. tribulus, sometimes called Venus's Comb, is much prized by collectors, if in a perfect state; it is often very delicate and beautiful. This is a native of the Moluccas and parts of the Indian Ocean. The M. regius is found on the west coast of Central America, and surpasses |