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THE PEARL
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breaking of the ears, which would enable sand to get into the interior.
Pearls,
or pearly excrescences on the interior of the shell, were due to the
intrusion of leuco-dore, clione and other borers. Pearls found in the
mussels, especially at the levator and pallial insertions, were formed
around calcospherules, minute calcareous concretions produced in the
tissues. But most of the fine pearls found free in the body of the
Ceylon oyster, contained the remains of platyhelminthian parasites.
These observations agree with the opinions formed, after careful study,
by several eminent con-chologists.
The
action of the mollusk results differently as the object to be covered
is free within the folds of the creature's mantle or, rising above the
surface of the nacreous lining, presses upon it. If free, the intruder
is enveloped by the animal's exudations and the deposits become
concentric instead of level, or nearly so, as in the construction of
the shell. It is said that the foreign substance acts as an irritant,
causing the fish to exude its secretions abnormally in order to protect
itself, and thereby creating a diseased
154
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