220 



NATURAL HISTORY. 



ANATOMY OF THE COMMON GARDEN SNAIL. 



horny upper jaw, and is also provided with an odontophore, bearing an excellent set of lingual teeth. 

 (See p. 222.) 



The air-breathing Snails are, as a rule, vegetable feeders, and form two great divisions. 

 Division a. INOPERCULATA,* or Snails without an operculum. This division embraces a great 

 proportion 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 region*, where 

 vegetation is abundant, they are found even in very dry and arid regions, and are able to survive 

 under conditions which would at first sight appear fatal to any soft-bodied mollusc. 



Thus, for example, my 

 late colleague, Dr. Baird, 

 F.R.S., of the Zcological De- 

 partment, British Museum, 

 records (in the Annul* dm! 

 May. 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 25th March, 1846 ; 



, mouth: pp, foot: ee. Eyes; n. Orittcc opening into Pulmonarj -Cavity; m. Branchiae: tt. Tentacles: ' J ^' 



o, Position 01 Ovaries: the Shaded Tart is the Stomach and Intestines; the Single Lines are Nerves, f nnT1f ] fliflt tlio Snail Ivirl 

 the Dotted Lines Blood-vessels. 



out of his shell, and had dis- 

 coloured the tablet with his slime in his endeavours to free himself. Failing to do this, he had again 

 retired, closing the mouth of his shell with the glistening film which all Snails make during hiber- 

 nation (called an epiphragm f). This attracted attention, and Dr. Baird having immersed the Snail - 

 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 pests 

 of our gardens, the Limacidce, or Slugs (most of which are quite naked, though a few have a tiny 

 rudimentary shell, often internal). 



It also includes a family called Oncidiadce, another named Limncvidce (in which are many of 

 our Pond Snails), and a fifth family, the Aurlculidce, inhabiting 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 withdrawn.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 varied 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 

 countries 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 this temporary lid a small aperture is left to breathe 

 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 

 lias a strong horny upper mandible, and a broad oblong 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 irnperforate ; some are discoidal, or globosely depressed, or coiioidal. The aperture 

 also varies greatly in form. 



In Gibbus lyonetti, from Mauritius, the shell, after forming five ordinary convolutions, 

 suddenly makes a complete double in its growth, and remains hump-backed for the rest of its 

 * Latin, in, without ; operculum, a lid. f Greek, epi, upon ; phragma, a partition. 



