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SNAIL

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Originally appearing in Volume V25, Page 285 of the 1911 Encyclopedia Britannica.
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SNAIL. In England the word " snail " in popular language is associated with Gasteropods which inhabit land or fresh water, and which possess large conspicuous spiral shells; terrestrial Gasteropods, in which the shell is rudimentary and concealed, are distinguished as " slugs." In Scotland the word " slug " is absent from the vernacular vocabulary, both shell-bearing and shell-less inland molluscs being known as snails. Marine Gasteropods are occasionally termed " sea-snails," and the compounds " pond-snails," " river-snails," " water-snails " are in common use. The commonest land-snails are those species which constitute the family Helicidae, order Pulmonalaf ii;iib order Stylommatophora. The families Limacidae, Arionidae and Oncidiidae of the same sub-order, include nearly all the slugs. The Oncidiidae are entitled to the name " sea-slugs," as they are shell-less Pulmonates living on the seashore, though not actually in the sea. The term " water-snails " includes the whole of the remaining sub-order of the Pulmonata, namely, the Basommatophora, in which the eyes are sessile, with the exception of the Auriculidae. The latter are terrestrial and occur mostly near the seashore. Thus the whole of the Pulmonata (which breathe air, are destitute of gill-plumes and operculum and have a complicated hermaphrodite reproductive system) are either snails or slugs. But there are a considerable number of snails, both terrestrial and aquatic, which are not Pulmonates. The land-snails which have no gill-plume in the mantle-chamber and breathe air, but have the sexes separated, and possess an operculum, belong to the orders Aspidobranchia and Pectinibranchia, and constitute the families Helicinidae, Proserpinidae, Hydrocenidae, Cyclophoridae, Cyclostomatidae and Aciculidae. The fresh-water snails which are not Pulmonates are the Paludinidae, Valvatidae and Ampullaridae, together with Neritina, a genus of the Neritidae. These all possess a fully developed gill-plume and are typical Pectinibranchs of the sub-order Taenioglossa, most of the members of which are marine. The family Helicidae has a world-wide distribution. In Helix the spire forms a more or less obtuse-angled cone; there are above 1200 species, of which 24 are British. Helix nemoralis, L., of which H. hortensis is a variety, is one of the commonest forms. Helix pomatia, L., is the largest species, and is known as the edible snail "; it is commonly eaten in France and Italy, together with other species. It was formerly believed to have been introduced into Britain by the Romans, but there is no doubt that it is a native. In Succinea the cone of the spite is acute-angled; three species are British. In Farina the spire is very flat and the surface glassy. In Bulimus the spire is elongated with a pointed apex. Pupa is named from its resemblance to a chrysalis, the apex being rounded. The shell of Clausilia is sinistral and its aperture is provided with a hinged plate. The commoner European slugs of small size all belong to the genus Limax, in which the opening of the mantle-chamber is posterior. L. flavus is the cellar slug. L. agrestis, L. arborum, L. maximus occur in gardens and fields. The larger black slugs are species of Arion, of which two are British, A. ater and A. hortensis. Testacella haliotidea is common in Great Britain and throughout Europe. The species of Helix are all herbivorous, like the Pulmonata generally; snails and slugs are well-known enemies to the gardener. The animals being hermaphrodite copulate reciprocally, The eggs of Helix are laid separately in the earth, each contained in a calcified shell; those of Limax are also separate, but the shell is gelatinous. Helix hibernates in a torpid condition for about four months, and during this period the aperture of the shell is closed by a calcareous membrane secreted by the foot. The Limnaeidae occur in all parts of the world. Limnaeus contains the largest species. L. pereger, Muller, is ubiquitous in Great Britain and common all over Europe. All the species are usually infested with Cercariae and Rediae, the larval forms of Trematode parasites of vertebrates. L. truncatulus harbours the Cercaria of Fasciola hepatica, the liver-fluke, which causes, rot in sheep. Ancylus, which occurs in rivers, has a minute limpet-like shell. Planorbis has the spire of the shell in one plane. Physa is smaller than Limnaeus and has the upper part of the spire much shorter. In the Auriculidae the aperture is denticulated. Auricula is confined to the East Indies and Peru. Carychium minimum is British. Of the Cyclostomidae only one species, Cyclostoma elegans, Muller, is British; it hides under stones and roots. The Helicinidae are exotic, ranging from the West ladies to the Philippines: Of the Aciculidae, which are all minute, Acicula lineata is British. The Ampullaridae are confined to the tropics. Ampullariahas very long tentacles and a long siphon formed by the mantle. Valvata is common in fresh waters throughout Britain; the gill when the animal is expanded is protruded beyond the mantle-chamber. The Paludinidae are common in the N. hemisphere. Paludirtii 'and Bithynia are both British genera. In Paludinathe whorls of the spiral are very prominent ; the genus is viviparous. Bithynia is smaller and the shell smoother. Neritina has a very small spire, the terminal portion of the shell containing nearly the whole animal. For the morphology and classification of snails, see GASTROPODA. A history of the British forms is given in Gwyn Jeffreys's British Conchology (1862), and by Forbes and Hanley in British Mollusca. For speciegraphical details, see Woodward's Manual of the Mollusca (1875), and Bronn's Tierreich (Weichtiere). For Fasciola hepatica, see Thomas, Quart. Journ. Mic. Sci. (1802). SNAKE-BIRD (the " darter " of many authors, and the Plolus anhinga 1 of ornithology), the type of a small but very well-marked genus of birds, Plotus, belonging to the family Phalacrocoraeidae which contains the 'cormorants and shags. The name commonly given to it by the English in N. America was derived from its "long slender head and neck," which, its body being submerged as it swims, " appears like a snake rising erect out of the water " (J. Bartram's MS., quoted by G. F. Ord in A. Wilson's Am. Ornithology, ix. 81). Snake-birds bear a general resemblance both outwardly and in habits to Cormorants (q.v.), but are much more slender in form and have both neck and tail much elongated. The bill also; instead of being tipped with a maxillary hook, has its edges beset with serratures directed backwards, and is sharply pointed—in this respect, as well as in the attenuated neck, likening the Snake-birds to the Herons; but the latter do not generally. transfix their prey as do the former. The male of the American species, which ranges from Illinois to the S. of Brazil, is in full breeding-plumage a very beautiful bird, with crimson irides, the bare skin round the eyes apple-green and that of the chin orange, the head, neck and most part of the body Indian Snake-Bird (from S. R. Tickell's Drawing in the Library of the Zoological Society). clothed in black glossed with green; but down each side of the neck runs a row of long hair-like white feathers, tinged with pale lilac. The much elongated scapulars, and the small upper wing-coverts bear each a median white mark, which on the former is a stripe pointed at either end, and on the latter a broad ovate patch.' The larger wing-coverts are dull white, but the quill-feathers of the wings and tail are black, the last broadly tipped with brownish-red, passing into greyish-white, and forming a conspicuous band when the tail is spread in form of a fan, as it often is under water.' The ben differs much in appearance from the cock, having the head, neck and breast of a more or less deep buff, bounded beneath by a narrow chestnut band; but otherwise her plumage is like that of her mate, only not so bright in colour. The Snake-bird frequents the larger rivers or back-waters connected with them, where it may be seen resting motionless on some neighbouring tree, generally choosing a dead branch, or on a " snag " projecting from the bottom, whence it plunges beneath the surface, in pursuit of its prey, to emerge, in the manner before related, showing little more than its slender head and neck. Its speed and skill under water are almost beyond exaggeration, and it exhibits these qualities even in captivity, taking—apparently without effort—fish after fish, however rapidly they may swim and twist, and only returning to its perch when its appetite is appeased or its supply of food exhausted. At liberty it will indulge in long flights, and those of the male at the breeding- " Anhinga," according to Marcgrav, who first described this bird (Hist. rer. nat. Brasiliae, p. 218), was the name it bore among the natives. 2 These feathers are very characteristic of each species of the genus, and in India, says Jerdon,are among the Khasias a badge of royalty. 3 This peculiarity, first pointed out to the writer by A. D. Bartlett, who observed it in birds in the Zoological Society's possession, doubtless suggested the name of " Water-Turkey " by which in some places Rotas anhinga is said to be known. season are ostentatiously performed in the. presence of his mate, vast majority of snakes are further characterized by having the right and left halves of the under-jaws connected by an elastic band; a median, longitudinal furrow in the skin below and behind the chin; the. whole palatal apparatus is but loosely connected with the skull, nowhere articulating with it. The quadrate is indirectly articulated with the skull, first by the horizontal, movable squamosal, secondly by the columella auris. The quadrato-mandibular joint is placed in a level far behind the occiput: around whom he plays in irregular zigzag courses. The nest is almost always in trees or bushes overhanging the water's edge, and is a large structure of sticks, roots and moss, in which are laid four eggs with the white chalky shell that is so characteristic of most Steganopodous birds. Not infrequently several or even many nests are built close together, and the locality that suits the Snake-bird suits also many of the herons.' The African snake-bird, P. congensis (or levaillanti of some authors), inhabits the greater part of that continent N. from Natal; but, though met with on the White Nile, it is not known to have occurred in Egypt; a fact the more remarkable seeing that Canon Tristram found it breeding in considerable numbers on the Lake of Antioch, to which it is a summer visitor, and it can hardly reach its home without passing over the intervening country. The male bird is easily distinguishable from the American species by its rufous coronal patch, its buff throat and its chestnut greater wing-coverts. A third species, P. inelanogaster, ranges from Madagascar to India, Ceylon, Borneo, Java and China. This so closely resembles the last-mentioned that the differences between them cannot be briefly expressed. The Australian region also has its snake-bird, which is by some regarded as forming a fourth species, P. novae-hollandiae; but others unite it to that last mentioned, which is perhaps somewhat variable, and it would seem (P.Z.S.; 1877, p. 349) that examples from New Guinea differ somewhat from those inhabiting Australia itself. The anatomy of the genus Flatus has been dealt with more fully than that of most forms. Beside the excellent description of the American bird's alimentary canal furnished to Audubon by Macgillivray, other important points in its structure have been well set forth by A. H. Garrod and W. A. Forbes in the Zoological Proceedings (1876, pp. 335-345, pls. xxvi.-xxviii.: 1878, pp. 679-681; and 1.882, pp. 208-212), showing among other things that there is an appreciable anatomical difference between the species of the New World and of the Old; while the osteology of P. melanogaster has been admirably described and illustrated by A. Milne-Edwards in A. Grandidier's great Oiseaux de Madagascar (pp. 691-695, pls. 284, 285). In all the species the neck affords a feature which seems to be unique. The first seven of the cervical vertebrae form a continuous curve with its concavity forward, but the eighth articulates with the seventh nearly at a right angle, and, when the bird is at rest, lies horizontally. The ninth is directed downwards almost as abruptly, and those which succeed present a gentle forward convexity. The muscles moving this curious framework are as curiously specialized, and the result of the whole piece of mechanism is to enable the bird to spear with facility its fishy prey. . (A. N.) SNAKE-FLY, the name given to neuropterous insects of the genus Raphidia, closely allied to the alder-flies, remarkable for the elongation of the head and prothorax to form a neck and for the presence in the female of a long ovipositor. The larva, which is active and carnivorous, is terrestrial, and lives in rotten timber. SNAKE-ROOT. In most countries where snakes abound some root or herb is used by the natives as an antidote for the bitesof venomous species, and many herbs have consequently received the name of snake-root. Botanically speaking, the name properly belongs to Ophiorrhiza Mungos, the Mungoose plant, a plant of the natural order Rubiaceae, used in the E. Indies loathe purpose above indicated. In medicine, however, the roots of Aristolochia Serpenlaria, Polygala Senega and Cimicifuga racemosa were understood by this name, being distinguished as the Virginian, seneca and black snake-roots. The root of Aristolochia reticulates is known in the United States as Red river or Texan snake-root. The roots or rhizome of Liatris spicata, Eryngium aquaticum and Eupatoriurn altissimum have all been used in N. America for snake-bites, the first two being known as button snake-root and the last as white snake-root. The rhizome of Asarum canadense passes under the name of Canadian snake-root. All of these contain acrid or aromatic principles which, when a warm decoction of the drug is taken, exercise a powerfully diaphoretic or, in some cases, diuretic action, to which any benefit that may be derived from their use must be attributed.
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SIR WARINGTON WILKINSON SMYTH (1817-1890)
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