25Q OF TURBINATED SHELL -FISH. 



refemble the garden fnail, in the fornaation of their (heWj in their her- 

 maphrodite natures, in the llimy fubftance with which they are covered, 

 in the formation 9f their inteftines, and in the difpofition and ufcsof the 

 hole on the right fide of the neck; yet there are one or two remarkable 

 diftindions : the Fresh-water Snail, and probably all fnails that live 

 in waterj. have a contrivance for rifing to the furface, or finking to the 

 bottooo. , -.This is by opening and fhutcing the orifice oh the right fide of 

 tHe neck, which is furniihed with mufcles for that purpofe, in order to 

 draw in or expel the air, as^it fiftds occafion. By dilating this it dfes ; 

 by compfeffing it, it finks. It is alfo viviparous, and brings forth its 

 young, not only alive, but with their fhells, in fome degree of perfection. 



*' March 12," fays Swammerdam, " I began my obfervations on this 

 fnail, and colle6l:ed a great number, which I put into a large bafon filled 

 with r^in-water, and fed for a, long time with potter's earth diflblved in 

 it. 1-opened one of thefe Ihails, . when I found nine living fnails in its 

 womb: the largeft were placed foremoft,; as the firil candidates for ex- 

 clufion. I put them into frefh- water, and they lived to the eighteenth of 

 the fame month, moving and fwimming, like fnails full grown." 



Of the fea k,inds alfo, fomq are viviparous, while other lay eggs. Such 

 are one or two of the Buccinums j within which living young have been 

 frequently found upcrn diffedion. In general the reft of this numer- 

 ous clafs bring forth egg§ j from whence the animal burfts at maturity, 

 completely equipped with an houfe, which the element where it refides 

 does not prevent from enlarging. 



Among fome of the fea kinds one impregnates the other; but is in- 

 capable of impregnation by the famie, and receives it from a third, which 

 is irfelf impregnated by a fourth. In this manner Mr. Adanfon has ken 

 vaft numbers of fea fnails united together in a chain. In the ^ulin and 

 the corei the orifices are feparate from each other : that which performs 

 the office of the male being at the origin of the horns ; the other farther 

 down on the neck. In general all that have this orifice on the 

 right fide, have their {hells turned from right to left; on the contrary, 

 t'hofe which have it on the "left fide, have their ihells turned from left to 

 right. 



Many fea fnails want horns, and none have above two. Eyes 

 are unnecefl'ary to creatures whole food is ufually concealed in the 

 dark'eft'placesi and who, poflfefled of very litde motion, are obliged to 

 grope for what they fubfift on. — Sea fnails are larger than land fnails. 



Tfee mouth, in the garden and the frellvwater fnails, is placed crolT- 

 I wife. 



