ceeding
layer of the pearl may be formed occasionally like another of the shell
sections though usually it is like the preceding one.
Marked
differences in the same skin occur more frequently in the pearl
formations of univalves. The skins of the abalone pearl especially, are
frequently nacreous in part only.
Pearl
oysters are found in immense numbers on banks having a calcareous
foundation. They are extraordinarily prolific, the spat of one oyster
being estimated at upwards of several hundred thousands to millions, so
that were it not for the natural enemies of their young and the
liability of being swept away and scattered by storms before they have
anchored, the banks would be overcrowded with the myriads produced.
Some idea of the numbers may be gained from the fact that during the
fishing season the Ceylon divers raise about one million each day.
The
oysters are seldom found in water with a temperature below 75 degrees
and they seem to thrive best in warm sheltered bays and inlets,
especially when the banks are situated far from the equator. They
attach themselves to the
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