found
here, bound- together like a cluster of grapes, showing that even
within this muscle these Pearls receive further accretions. In course
of time such Pearls as avoid passing into this muscle find their way
downwards to the lowest part of the oyster, and according to their
position therein, may or may not find their way out of the tissues of
the oyster into the sheil.
Up
to this time the Pearl has received regular layers all over its
surface, but rings, and other marks of lesser brightness frequently
occur, the result probably, of contact with the coarser tissues of the
oyster. For a short time the Pearl is loose in the shell, and it falls
into the same category as a stone, or any other intruder. It is
encircled by the growing layer of shell, and proceeds on its downÂward
course through the shell, like an ordinary " blister," the upper
portion receiving further layers, until it is hidden beneath the shell
which by degrees, resumes its natural shape. This process is well
illustrated by Figs. 2 and 3, p. 95.
The
shell, as stated in the last chapter, is worn away from the outside at
the same rate that it is renewed within, so that m time, the Pearl with
its surrounding tomb yields to. the general
