OF TESTECEOUS FISHES. 
215 
arrived at a certain growth, when its little habitation is suf- 
ficiently hardened. This beginning of the shell is not much 
bigger than a pin’s head, but grows in a very rapid man- 
ner, having at first but two circumvolutions, for the rest are 
added as the snail grows larger. In proportion as the 
animal increases in size, the circumvolutions of the shell 
increase also, until the number of those volutes come to be 
live, which is never exceeded. 
The part where the animal enlarges its shell is at the 
mouth, to which it adds in proportion as it finds itself 
stinted in its habitation below. Being about to enlarge its 
shell, it is seen with its little teeth biting and clearing away 
the scaly skin that grows at the edges. It is sometimes seen 
to eat those bits it thus takes oil'; and at other times it only 
cleans away the margin when covered with films, and then 
adds another rim to its shell. 
lor the purposes of making the shell, which is natural to 
fhe animal, and without which it would not live three days, 
'ts whole body is furnished with glands, from the orifices of 
vvliich flows out a kind of slimy fluid, like small spiders 
threads, which join together in one common crust or surface, 
a nd i n tinjje condense and acquire a stony hardness- It is this 
s *hny humour that grows into a membrane and afterwards a 
stony skin, nor can it have escaped any who have observed 
the track of a snail ; that glistening substance which it leaves 
cm the floor or the wall is no other than the materials with 
■which the animal adds to its shell, or repairs it when broken. 
With respect to the figure of shells, Aristotle has divided 
them into three kinds ; and his method is, above all others, 
me most conformable to nature. These are, first, the uni- 
v alve, or turbinated, which consist of one piece, like the box 
0 , a snail ; secondly, the bivalve, consisting of two pieces, 
’niited by a hinge, like an oyster ; and thirdly, the multivahe , 
consisting of more than two pieces, as the acorn-shell, which 
'as not less than twelve pieces that goto its composition. All 
’hese kinds are found in the sea at different depths ; and are 
'aluable in proportion to their scarceness or beauty. All 
Shells are formed of an animal or calcareous earth, that 
cements with vinegar and other acids, and that burns into 
"ne, and will not easily melt into glass. 
Every shell, wherever it is found, is the spoil of someani- 
( a1 ’ that once found shelter therein. It matters not by what 
^"accountable means they may have wandered from the sea; 
m they exhibit all, and the most certain marks of their 
'gin. from their numbers and situation, we are led to 
bnjectuie, that the sea reached the places where they are 
’md ; and from their varieties we learn how little we know 
