conchiolin zones distorted from their normal extension and action.
It
has also been suggested that the oyster deposits the nacreous layer in
a fluid state and then rests until the deposit hardens, when the
process is repeated. To a certain extent this may be true though
apparently it could not be a yearly process as pearls found in the
small varieties of the avicula which mature in four to six years and
die out in seven years, often contain a greater number of layers than
the years of the mollusk's life, and no pearl is ever found with a soft
exterior, though it seems possible that pearls with a dead white chalky
exterior are taken from the oyster at a period when the crystallization
of the outer skin has not been perfected, or that they have escaped
some action, chemical or of the animal, necessary for the formation of
the lustrous waves of nacre. Mr. Ludwig Stross, who has had much
experience at the pearl fisheries, says that he has frequently found
pearls of fair size in shells of the Lingah type which could not be
over twelve to fifteen months old. Some of these pearls weighed fully
three grains. As there are many apparent
166
