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GALLER\.J 
NATURAL HISTORY. 
49 
secreted by certain glands on the surface of the body, by means of 
chalky matter, which is also secreted by similar glands. The unhatched 
animal, very shortly after it is formed, begins to construct its shell; and 
when the animal is hatched, it deposits on the edge of the mouth of the 
little shell which covered its body in the egg, a small quantity of mucous 
secretion. This dries, and is then lined with other mucous matter, in¬ 
termixed with calcareous particles, and when this becomes hardened, 
the animal again places on its edge another thin layer of the mucous 
secretion, and again lines it as before. The mucous secretion first de¬ 
posited, called periostraca , forms the outer coat of the shell, and is of 
use in protecting it from injury, while the mucous matter mixed with 
lime, which is placed within, forms the substance of the shell itself. 
This alternate deposition of mucus, and of mucus mixed with calcareous 
matter, goes on as the animal grows, and feels, from its increasing size, the 
want of a larger shell for its protection. The shell is, in fact, moulded 
on the body of the animal itself as the body grows, and for this reason, 
any inequality or irregularity of the body is reproduced on the shell. 
If the irregularity or inequality is of a permanent character, such as a 
canal, tubercles, &c., it causes a permanent groove or ridge, running 
from the apex to the mouth of the shell, or even produced beyond it as 
far as the canal of the mantle extends. But besides these permanent 
inequalities, which are generally necessary for the functions of the ani¬ 
mal, the Mollusca, like most other animals, appear to have seasons of 
activity, or developement, and of rest; and in the season of activity there 
are often expanded from the edge of their mantle leaf-like, thread-like, 
or variously shaped appendages; w T hich appendages, as soon as they are 
formed, generally secrete on the edge of the shell, shelly leaf-like ex¬ 
pansions, tubular spines, &c., for their protection; these fleshy expansions 
are after a time gradually contracted until the period of rest recurs, and 
the part of the shell that is formed during this period is destitute of such 
appendages on its surface. Thus the marks produced by the permanent 
projections from ribs, grooves, &c., run from the apex to the edge of 
the mouth of the shell; while those produced by the alternations of 
the periods of rest and growth are always in concentric lines parallel 
with the edge of its mouth. This method of formation and enlargement 
allows only the inner surface and the edge of the mouth of the shell, 
which is immediately applied to the surface of the animal, to be within 
its influence, as each deposition of new matter removes the part which 
it covers from the animal’s control; consequently all the shelly append¬ 
ages, &c., on the surface, except those on the immediate edge, which 
were used by the animal to protect its fleshy expansions, are no longer 
of any use to it, though they often add greatly to the beauty of the 
shell. 
The animal has the faculty also of mending any break or injury that 
its shell may receive, if it is not of such a magnitude as to derange all 
the functions of the animal itself; and it mends them in the same man¬ 
ner as it forms its shell, that is to say, by depositing first a coat of ani¬ 
mal matter, which is moulded on the body until it is dry, and then 
lining it with mucous matter mixed with chalk to harden it. But as 
the animal is usually very desirous of getting the repairs done as quickly 
as possible, and is most probably damaged by the injury the shell has 
received, and also wants the support that the already formed shell gives 
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