Cassell's natural history (1896) (20352872250)

Title: Cassell's natural history
Identifier: cassellsnaturalh05dunc (find matches)
Year: 1896 (1890s)
Authors: Duncan, P. Martin (Peter Martin), 1821-1891; Metcalf Collection (North Carolina State University). NCRS
Subjects: Animals; Animal behavior
Publisher: London (etc) Cassell & Company, Limited
Contributing Library: NCSU Libraries
Digitizing Sponsor: NCSU Libraries



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XJJ'!\ 11 jij.-^/ojn: lioniv upper jvw, and is also provided witli an o:/2.) " ._ " The air-bi-e; thing Si.ails are, as a rule, vegetable feeders, and form two greiit divisions. Division a. Imoperculata,* or Snails without an operculum. This division embraces a great projwrtion of the terrestrial Snails. They usually have well-developed shells, sufficiently large to conceal the entire animal; and although, as a rule, they flourish most in warm humid regions, where \egetation is abundant, they are found even in very dry and arid regions, and are able to .sur\-ive under conditions which would at first sight aj>peai- fatal to any soft-bodied mollusc. Thus, for examjile, my late colleague. Dr. Baird, F.R.S., of the Zco^.ogical De- partment, British Museum, records (in the Annah and ' Mmj. Nat. Hist for 1850) that, having received some specimens of the " Desert Snail" from Egypt, he fixed them with gum mastic to a tablet on i.Hli -March, 1846; ^. on 7th Jlareh, 1850, it was '• fcund that the Snail had come out of his shell, and had dis- Failing to do this, he had again 1 all Snails make during hiber- unl liavim; immersed the Snail-
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coloured the tablet with his slime in his endeavours to free himself, retired, closing the mouth of his shell with the glistening film whie nation (called an ejiiphragm f). This attracted attention, and Dr. B; shell in tepid water, the desert wanderer crawled out and walked about, and partook of a lettuce- leaf, and was for a long time the cynosure of an admiring circle of visitors. In this division are also placed those apparently helpless, but exceedingly wide-awake jiests of our gai'dens, tlie Liiiiiieid(i\ or Slugs (most of which are quite naked, though a few have a tiny rudimentary shell, often iutfrual). It aLso includes a family called Oncidiadw, another named Limnwida; (in which are many of our Pond Snails), and a fifth family, the Aurindidce, inhaljitiug salt marshes in the tropics. FAMILY XXVII.—HELICID.E. The Land Snails have a well-developed external shell, into which the entire animal can be withdrawn. These " snail-houses " are exceedingly vaiied in the form of their spirals, and the whorls are frequently decorated with bright bands of colour ; the mouth is often curiously twisted and toothed within. Some show periodic growths. In cold countries Snails hibernate in winter ; in hot countiies they sleep during the dry season, coming out with the first rain. In both cases the Snail (having no operculum to his shell) makes an epiphragm of hardened mucus, sometimes strengthened with a thin deposit of lime. In tliis temporary lid a small aperture is left to lireathe through, the rest being carefully closed. The Snail has a head with four cylindrical, retractile tentacles, of which the upper pair are the longest, and have the eyes at their summits. The breathing opening is on the right side, beneath the margin of the shell. The foot is very distinct, and usually elongated. The mouth has a strong horny upper maudiljle, and a broad oWong tongue armed with numerous rows of small teeth. Genus Helix. The shells of the Helices vary in form, but are mostly either umbilicated, (perforate or imperforate ; some are discoidal, or globosely depressed, or conoidal. The aperture also varies greatly in form. In Gibbiis hjonmi, from JNlauritius, the shell, after forming five ordinary convolutions, suddenly makes a complete double in its gi'owth, and remains hump-backed for the rest of its * Latin, in, without; ojxrculum, .i lid. f Greek, epi, upon; pkrayma, a partition.