246 TESTACEOUS FISHES. 



As we cannot defcribe the modes of the deep, and its peculiarities, to 

 giveexaft ideas of the manner in which fea-fhells are formed, wc mud 

 advert to an animal within our infpe6lion, with the formation of whofe 

 fhcll we are heft acquainted : fuch is the Garden-Snail, with whofe hif- 

 tory Swammerdam has taken endlefs pains. The fame manner of for- 

 mation extends to all animals having (hells, whether on land or in the 

 water. The young fnail, at learing the egg, carries its fhell on its back, 

 being arrived at a certain growth, and its little habitation fufficiently 

 hardened. This beginning of the fhell only equals a pin's head, but 

 grows rapidly, having at firft but two circumvolutions. As the animal 

 increafes in fize, thefe circumvolutions increafe alfo, until they be five 

 in number, which is never exceeded in land fnails, but. fea fnails fome- 

 times have ten. The animal enlarges its fhell at the mouth, with its 

 little teeth biting and clearing away the fcaly fkin from the edges, and 

 then adds another rim to its Ihell. Its whole body is furnifhed with 

 glands, from which flows out a kind of flimy fluid, like fmall fpiders 

 threads, which unite in one common furface, and by time condenfe into 

 a ftony hardnels. It is that gliftcning fubftance which it leaves after its 

 track. This fluid pafl^es through an infinite numiber of little glands till 

 it arrives at the pores of the flcin, but is there flopped by the fliell below ; 

 and therefore rifes to the mouth of the fliell, where enlargement is want- 

 ed. There the firft layer of flime foon hardens; then another is added, 

 which hardens alfo, till the fliell becomes as thick as is requifite. Thus 

 every fliell may be confidered as compofed of a number of layers of 

 "flime, which have entirely proceeded from the animal's own* body. If 

 the external coat be fcaled off, the inner fubftance will be found of one 

 Ample colouring ; which hints that the animal's own juices give only 

 one colour J whereas we fee fome fliells ftained with an hundred : fome- 

 times perhaps borrowed from furrounding objecls. Others think, that 

 as in the body of every one of thefe animals feveral ftreaks are difcerned 

 of a different colour, the juices flowing from thofe parts will be alfo of a 

 different hue, and will conformably tinge that part of the fliell which 

 their flime compofcs. 



Shells have generally a white ground, tindured with red, yellow, 

 brown, green, and other fliades and mixtures, but never blue ; for blue 

 is a colour which lea-water changes. 



Convolutions, prominences, and general form depend on the animal, 

 and ufually bear fome refemblance to the body on which they arc 



moulded. 



