Different
opinions are expressed by various authors as to the formation of this
product. Some insist that it is an unfruitful ovum ; others, that it is
a stone which covers a wound accidentally given by the animal to
itself; others, lastly, suppose that the bivalve covers with an animal
secretion some small extraneous body, which may have entered its shell
by chance, and this it does perhaps that it may not be injured by its
sharp edges. This opinion seems to us to be the most reasonable. We
can assert as a fact that, when any pearl is sawn in two, various
strata are seen to succeed each other, regularly, to the primitive nut
which occupies the centre, and is of quite a different nature from the
thin pearly layers.
Feuchtwanger
says that the Chinese string very small pearls on a thread, separating
them with knots ; then they put them inside bivalves, which are taken
at the suitable moment when they are open to enjoy the sun, placing
them so that they- do not touch the shell. They are afterwards put into
the sea, but in an enclosed place, whence they are withdrawn after many
years, when the pearls are found more or less enlarged, according to
the time passed, and without those spots which in others are produced
by adherence to the shell.
It
is thought that if a microscopic body of any form was put into a pearl
oyster purposely, and that it could remain without adhering to the
shell, it would serve as a nut for a pearl, which would retain its form
externally.
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