SNAILS AND SLUGS, names restricted in their original application to gasteropodous mol lusks typifying the families Helicidce and Limacidce respectively, but now used in a much wider sense. The terrestrial and fresh-water snails and slugs represent the order Pulmonata, characterized by the presence of a lung-sac for the respiration air formed by a fold of the man tle and opening by a conspicuous pore situated at the mantle border, usually on the left side. They are always asymmetrical, but have the visceral loop of the nervous system straight and the ganglia concentrated in a ring about the oesophagus. All are hermaphroditic, though the structure of the complex genital organs varies greatly. A shell is generally present, though absent or rudimentary in the slugs, and is usually dextral. Except in the brackish water Amphibolidce of New Zealand there is no oper culum. Within the mouth is the jaw, usually single and placed just behind the upper lip, but in some forms there are accessory pieces and in others the jaw is absent. Both the jaws and the teeth on the lingual ribbon or odontophore present an astonishing variety of form which is characteristic of genera and species. With these organs the food, usually vegetable, is cut and rasped. Scarcely any of the Pulmonata are marine, and very few live in even brack ish water, though a large number inhabit fresh water and some the depths of lakes, from which they never come to the surface to breathe air, but take water into the lung, which has, there fore, secondarily assumed the function of a gill. The great number of species are arranged in two sub-orders: the Basommatophora, which have non-retractile tentacles with the eyes sit uated at their bases and male and female or gans opening separately, and the Stylommato phora, with retractile and often invaginable tentacles, two of which bear the eyes at their tips, and the genital orifices generally united. Each suborder includes numerous families, upon the exact number and arrangement of which au thorities are not yet fully agreed.
As examples of the sessile-eyed snails the following may be selected, the generic names employed being in most cases in the less re stricted sense. Alelampus lineatus represents the family Auriculidce, and is one of the few marine species, inhabiting the salt marshes along the coast in great numbers. Th° shell is solid and sub-oval, with a polished surface of a handsome brown color marked with reddish bands. The Limpuridw are the common pond snails, which have a very delicate fragile shell and the orifice of the lung protected by a special lobe. The species are very numerous and abound everywhere in sluggish fresh waters. Planorbis has the shell rolled in a flat spiral and thicker than usual in the family. A num ber of species are common in the sluggish rivers and streams of the United States, where they may be found attached to stones along with masses of their eggs. Limnea is the type genus and is known by its rather slender, dextrally spiral, delicate shell with a large aperture. L. stagnalis is abundant in ponds, and other species are particularly well repre sented in the northern States and Canada.
Their eggs may be found imbedded in little packets of transparent jelly attached to aquatic plants throughout the summer. During sea sons of drought these and other water snails burrow into the mud or close the aperture of the shell by a membrane formed of secreted mucus. They are strictly vegetarian and make
useful and interesting inmates of aquaria. Physa heterostropha is equally common and has similar habits, but the very delicate shell is sinis tral. Ancylus includes the fresh-water limpets, our species being very small, with flattened con ical shells, which are found attached limpet-like to stones and plants in ponds. This group in cludes no slugs.
The stalked-eyed snails are more numerous and important. Glandina truncata of fresh water swamps of the southern States belongs to the family Testacellide, which are remarkable because of their carnivorous habits and the ab sence of a jaw. This species has a well-de veloped shell, but the related genus Testacella of Europe is a slug, bearing the small disc-like shell at the posterior end of the body. It at tacks and devours earthworms and slugs, but also eats decaying animal matter. The true slugs belong to the family Limacide in which the shell, if present, is usually buried in the mantle or else is a plate covering only a small portion of the animal. The visceral hump of the snails is absent or little developed in the slugs. The body is generally oval or oblong, elongated, from one to three inches in length. The creeping disc, or sole of the foot, extends the whole length of the animal, but, like snails, slugs frequently raise their heads and move their tentacles in search of objects above them. They often climb trees, and can lower them selves to the ground by the accumulation of mucus at the extremity of the tail hardening into a thread, and as they crawl they leave a slimy track. They oviposit in moist places in spring and summer, often at roots of grass; the eggs are laid in strings, each in a separate gelatinous envelope. Slugs are found in moist places in the woods, damp cellars, etc., and are especially partial to decaying wood, upon which they in part feed. But their chief food consists of the tender leaves and shoots of plants. and the garden species often inflict considerable damage upon lettuce, celery, etc.; but much less in this country than in Europe. They may be checked by sprinkling wood ashes, lime or soot about young and tender plants or in cellars by sprinkling salt about their haunts. They are active at night and conceal themselves by day. During the winter they hibernate. Among the genera are Anion, Agriolimax, Limax and its numerous subdivisions. Several of our com mon garden and cellar species are European importations. Limax maximus is very common and four or five inches long, of an ashy gray color with black stripes and spots. It is some times eaten in England. L. campestris is very common in woods and meadows. It is much smaller and uniform pale gray or brown. Anion fuscus, a European species, has been in troduced into this country in the neighborhood of Boston. The shell is concealed and very imperfect and there is a large triangular mucous pore near the posterior end. The eggs are said to be phosphorescent. Philomycus carolinensis is a large slug found under logs and bark in woods and which is often placed in a distinct family. There is no trace of a shell and the mantle covers the entire back.