NATURAL HISTORY. 



Genus Achatina, "Agate-shell." The shell is like that of Bulimus in form, with a twisted 

 columella, truncated in front, with an oval aperture ; the lip is sharp. The great African Achatina 



is the largest land-shell knoAvn, being 

 eight inches in length; the eggs are 



^~^<:;: : :";^^-^;^^:^:::::^^:::::]-^ti more than an inch long; they have a 

 C-^J (J -0 C^^**"^'-^*^"^-'^ calcareous shell. They are found in all 



ft * * ^ " 



LINGUAL TEETH OF ACHATINA FULicA. (After s. P. Woodward.) quarters of the globe. One hundred 



n, Lateral ROWS; c, central uow. and twenty species are found living, 



and fourteen fossil. They are said to 



burrow in the earth, and to be found at roots of garden bulbs. An Achatina kept in confinement 

 refused vegetable food, but ate another Snail. 



In addition to the variously disposed jaws, or cutting-plates of a chitinous or calcareous substance 

 with which nearly all Land and Sea Snails and Cuttle-fishes are furnished, they possess a most charac- 

 teristic buccal, or mouth apparatus the "odontophore "* (tooth-bearer), commonly called the "tongue," 

 which is attached to the floor of the mouth. It is partly fibrous, and partly cartilaginous, and is 

 provided with special muscles. The external layer, called the radula, is armed with tooth-like 

 processes (see woodcuts), arranged in one or many series, and additions are being constantly made to 

 its posterior end, which is lodged in a sac. The teeth are thus replaced from behind as fast as they 

 are worn away by friction against the food which they rasp, at the anterior end of the tongue. The 

 muscles are so arranged as to cause this wonderful apparatus to travel, backwards and forwards, over 

 the ends of the supporting cartilages of the mouth, in the fashion of a chain-saw, and thus to rasp any 

 substance to which the teeth may be applied. The whole apparatus is also capable of being prot)-acted 

 or retracted, and may thus give to the extremity of the radii Ja a licking motion, which is quite 

 distinct from the chain-saw movement. Salivary glands are also generally present. (Huxley.) 



Genus Pupa, " Chrysalis-shell, "f The shells of this genus are very small, ovoid, Avith an obtuse 

 apex, whorls inflated, broadest in mid-growth, narrower in later growth ; the mouth is often con- 

 tracted, and sometimes thickened and toothed ; the surface of the shell is closely ribbed with straight 

 fine ridges. The foot is short and pointed behind, the lower tentacles short. Pupa has a world- 

 wide distribution ; it is common in Europe, North America, and Africa, under stones and in crevices 

 of rocks and trees, or among wet moss, chiefly in chalky districts. 



Genus Cylindrelki, Cylinder-shell. The shells of this genus are either pupiform or cylindrical, 

 many-whorled, sometimes left-handed ; in the adult shell the apex is usually lost, a septum or parti- 

 tion being formed within to cover the hole. Shells that have lost their apex are said to be 

 decollated. J The aperture is round and expanded. The animal is like Clausilia, with a short foot, 

 and the lower tentacles small. Fifty species are known in the West Indies and America. 



Genus Clausilia.^ These little shells are of a brown colour, with a tall spii'e swollen in 

 the middle ; the whorls are transversely striated ; the mouth has a thickened contracted lip, 

 with two shelly plates on the inner lip ; all the species are left-handed. Nearly 400 are known 

 in Europe and Asia. 



FAMILY XXVIII.-LIMACID^E (SLUGS). 



The Slugs have no true shell ; the head r.iid tentacles are retractile, the respiratory and visceral 

 organs being incorporated within the contractile body of the animal, which differs from the Snails in 

 being straight, not spiral. The first indication of a shell takes the form of a small shield-like plate, 

 coA^ering the breathing organs. This rudimentary shell is usually internal; in Testacella it is external. 



" The Limacirhe shun the light of day, rarely indulging their voracious appetites, except at night. 

 They inhabit gardens and roadside hedges in damp places, and congregate in cellars and outhouses and 

 under planks and stones, around old walls, pumps, and wells. These remarks apply chiefly to the 

 genera Arion, Geomalax, and Limax, which feed on vegetable matter, though not entirely abstaining 

 from flesh. Testacella burrows into the ground to the depth of from two to three feet, and feeds, or 



* Snails are hence called ODONTOPHOKA by some authors. 



t The oldest air-breathing snails have been found by Sir W. Dawson in the Coal Measures of Nova Scotia, viz., Pupa 

 vetusta and P. vermilionensis, Dawsonella meekie, and Zonites priscus. 



J Latin, de, without ; collis, a top. Latin, clausum, a closed place, in reference to the mouth of the shell. 



