681 



A HISTORY OF 



multiplication of snails at some years, that 

 gardeners imagine they burst from the earth. 

 A wet season is generally favourable to their 

 production ; for this animal cannot bear very 

 i:ry seasons, or dry places, as they cause too 

 great a consumption of its slime, without 

 plenty of which it cannot subsist in health and 



vigour. 



Such are the most striking particulars in 

 the history of this animal ; and this may serve 

 as a general picture, to which the manners 

 and habitudes of the other tribes of this class 

 may be compared and referred. These are, 

 the sea-snail, of which naturalists have, from 

 the apparent difference of their shells, mention- 

 ed fifteen kinds ; a the fresh-water snail, of 

 which there are eight kinds ; and the land- 

 snail, of which there are five. These all bear 

 a strong resemblance to the garden-snail, in 

 the formation of their shell, in their hermaphro- 

 dite natures, in the slimy substance with which 

 they are covered, in the formation of their in- 

 testines, and the disposition of the hole on the 

 right side of the neck, which serves at once 

 for the discharge of the faeces, for the lodging 

 the instruments of generation, and for respira- 

 tion, when the animal is under a necessity of 

 taking in a new supply. 



But in nature, no two kinds of animals, 

 however like each other in figure or confor- 

 mation, are of manners entirely the same. 

 Though the common garden-snail bears a very 

 strong resemblance to that of fresh -water, and 

 that of the sea, yet there are differences to be 

 found, and those very considerable ones. 



If we compare them with the fresh-water 

 snail, though we shall find a general resem- 

 blance, yet there are one or two remarkable 

 distinctions : and first, the fresh-water snail, 

 and, as I should suppose, all snails that live in 

 water, are peculiarly furnished with a contri- 

 vance by nature, for rising to the surface, or 

 sinking to the bottom. The manner in which 

 this is performed, is by opening and shutting 

 the orifice on the right side of the neck, which 

 is furnished with muscles for that purpose. 

 The snail sometimes gathers this aperture 

 into an oblong tube, and stretches or protends 

 it above the surface of the water, in order to 

 draw in or expel the air as it finds occasion. 

 This may not only be seen, but heard also by 



D'Argenville's Concliylioligie. 



the noise which the snail makes in moving 

 the water. By dilating this it rises, by com- 

 pressing it the animal sinks to the bottom. 

 This is effected somewhat in the manner in 

 which little images of glass are made to rise 

 or sink in water, by pressing the air contained 

 at the mouth of the tubes, so ihat it shall drive 

 the water into their hollow bodies, which be- 

 fore were filled only with air, and thus make 

 them heavier than the clement in which they 

 swim. In this manner does the fresh-water 

 snail dive or swim, by properly managing the 

 air contained in its body. 



But what renders these animals far more 

 worthy of notice is. that they are viviparous, 

 and bring forth their young not only alive, but 

 with their shells upon their backs. This 

 seems surprising : yet it is incontestably true f 

 the young come to some degree of perfection 

 in the womb of the parent; there they receive 

 their stony coat ; and from thence are ex- 

 cluded, with a complete apparatus for subsis- 

 tence. 



"On the twelfth of March," says Swam- 

 merdam, " I began my observations upon this, 

 snail, and collected a great number of the 

 kind, which I put into a large basin filled with 

 rain-water, and fed for a long time with pot- 

 ter's earth, dissolved in the water about them. 

 On the thirteenth of the same month I opened 

 one of these snails, when I found nine living 

 snails in its womb : the largest of these were 

 placed foremost, as the first candidates for ex- 

 clusion. I put them into fresh-water, and 

 they lived till the eighteenth of the same 

 month, moving and swimming, like snails full 

 grown ; nay, their manner of swimming was 

 much more beautiful." Thus, at whatever 

 time of the year these snails are opened, they 

 are found pregnant with eggs, or with living 

 snails ; or with both together. 



This striking difference between the fresh- 

 water and the garden-snail, obtains also in 

 some of the sea kind ; among which there are 

 some that are found viviparous, while others 

 lay eggs in the usual manner. Of this kind 

 are one or two of the Buccinums ; within 

 which living young have been frequently 

 found, upon their dissection. In general, 

 however, the rest of this numerous class bring 

 forth eggs ; from whence the animal bursts at 

 a proper state of maturity, completely equip- 

 ped with a house, which the moistness of the 



