Snail

a term employed to designate the species of terrestiial Gasteropod a (q.v.) which have well formed spiral shells. The more typical snails Fig. — Common 1. Snail (Helix aspers a) 6ggs; b, appearance when newly hatched c, slightly advanced stage d, mature snail.;; belong to the genus Helix, of the family Helicidse, and have the shell of many whorls, globose, depre ed, or conical. The aperture or mouth of the shell is more or le encroached upon by the last wlioil but one, it is often strengthened by an internal thickened rib, its edges are usually more or le reflexed, and there are sometimes calcareous tooth-like prominences known as the denticles or apertural lamellte. The animal progre es upon a foot or sole, which is flattened beneath, and fringed at the edge. There are four retractile tentacles, the two upper ones the largest, and bearing the eyes. There is a crescent-sliaped jaw, whicli is usually strongly ribbed. The tongue or lingual membrane bears very many teeth arranged in transverse rows. Thiis, the Common Garden Snail has 135 rows of 105 teeth = 14,175 in all. Snails are hermaphrodite, but mutual impregnation takes place. They are provided with calcareous styles or darts, which are secreted within a sac, the dartsac, from which they are protruded during copulation. The forms of these darts are veiy various, and sometimes. ^ offer excellent characters for the separation of allied species. The eggs of /| fij snails are round or oval, and are de- )/ ))osited in damp places or in the earth. 1 Those of the Edible Snail are nearly I as large as a pea. At the approach of winter, or in very dry weather, snails ® close the mouth of the shell with a membrane epiphragm formed by the ( ) drying of the mucous substance whicb, and become inactive and ‘ vt ’ of secrete, toipid. Some, as the Edible Snail, Snails- '‘lake a succe ion of such membranes, o, Helix aspers a; Helix arb us the outer one of which is also strength- 'b. torum. ened by a quantity of calcareous matter, the secretion being at first a white viscid fluid, but quickly hardening like plaster of Paris. When this is to be removed a fresh secretion of fluid mucus softens it at the edges. The Common Garden Snail is to some extent gregarious when in the torpid state many individuals: may frequently be found closely packed together in cracks in walls, under logs or stones, and in other sheltered places. Snails delight in warm moist weather, and are active chiefly at night and during or after rain. They are also more abundant on limestone soils than elsewhere the kinds found; in districts where there is little or no lime have frequently very thin shells, owing to the deficiency of calcareous matter to strengthen them. Snails feed chiefly on vegetable substances, although they are very indiscriminate in their appetite, and even devour the dead of their own kind. The mischief which they do to garden crops is too well known; and gardeners are constantly on the alert to desti'oy them. Thrushes and blackbirds devour great quantities of snails they select a suitable stone against; whicli they break the shells. These ‘ breaking stones ’ may often be found in fields and by roadsides surrounded by fragments of shells. Snails po e in a very high degree the power of repairing injuries, and specimens may not rarely be found in which part of the shell has been broken and repaired again. Snails are found in nearly every part of the globe, some you sands of species having been described by authors. Seventy species are found in the British Islands, of which twenty two belong to the genus Helix. The Edible or Roman Snail {H. pomatia), much esteemed as an article of food on the Continent, is regularly bred on large and prosperous snail-farms in canton Zurich, Bavaria, and elsewhere, being fed on salad, greens, kitchen-waste, meal, . It is a large tawny species, not rare in parts of the south of England (especially Kent and Surrey), and is sold for food in London. The Common Garden Snail H. the most { aspers a), destructive species in Britain, is too abundant in most places, but rare in parts of Scotland and north-west England. It is also used for culinary purposes, notably in the Newcastle, Bristol, anil Swindon districts. The Striped Snail (H. nenioralis) is smaller than the Garden Snail, and of various colours, usually red or yellow, ornamented with one to five spiral dark-brown bands. The rim or lip of the aperture in this species is dai k brown, but in a closely allied species, H. hoi-teyisis, it is white. Both these species are very common, and it is a fa\ ourite custom for collectors to obtain large series showing the \ ariation, their beauty and interest being very great. Taking variations in the banding alone, already eighty-nine of H. nemoral is and fifty of H. hortensis have been found within the British Islands, while very many others are known from abroad. H. nemoral is, when introduced into Virginia, produced many band-variations which are not known in Europe. H. a rhus to rum is a species about the same size as H. nemoral is, but brown, mottled with pale yellowish, and usually encircled by a single dark band. The Kentish Snail (H. can tian a) is smaller, whitish, more or le tinged with rufous. The Hairy Snail {H. hispid a) is a small horn-coloured or brown species found in hedges, among mo , . its shell is clothed with minute; hairs or bristles. H. virgata is a species rather over J-incl i in diameter, found very abundantly in chalky places, on downs, and by the sea. It is usually white with one or more dark-brown bands, thougli some of the varieties are blackish or yellowish. On the South Downs this and an allied but smaller species (H. caper at a) are so abundant that the sheep, when feeding upon the short gra , can scarcely avoid devouring them and the excel- Down; lency of the South and Dartmoor mutton has in part been attributed to the nutritive qualities of the snails. H. ericetorum is another species allied to H. virgata, and found in similar places, but it is larger and has the shell much flattened above. H. jndcliella is a minute but very beautiful species, found abundantly both in Europe and North America. Hyalin i a (often called Zonites) is a genus of small snails in which the jaw is without ribs, and the shell smooth and shiny. There are eleven British species. Some of them emit a garlic odour, especially H. all i aria. H. crystal lin a is a small species of a clear white colour. The genus Pupa consists of brown cylindrical shells, resembling small seeds. Some of them, which are placed in the sub-genus Vertigo, are exceedingly minute. P. anti vertigo has the aperture of the shell so barred by long calcareous proce es (denticles) that it is a wonder how the animal can emerge from it. Clausilia is somewhat similar to Pupa, but longer both actually and in proportion to the width the aperture is turned to the; left (sinistral) instead of to the right (as is the case with the majority of snails), and is provided with a very curious spiral, shelly plate (clausium). A south European snail (Stenogyra decollata) of is a cylindrical shape, and sheds its upper whorls when it becomes adult, the aperture so formed being covered by a shelly plate. Adult specimens thus appear truncate, presenting a very singular appearance. See Rimmer’s Land and Fresh-water Shells of the British Islands ( 1880).