heel of the shell, and attaches it to the bottom ; in old shells however this byssus is completely wanting.
The
oyster is usually open an inch or two at the lips, to admit the sea
water and any organic substance that the tides and currents may bring
to serve as food. On being disturbed it immediately closes, and it_ is
no uncommon occurrence when the water is thick for a young diver to
come up with a shell fast on his fingers : in order to free him a knife
must be used to cut the muscle of the oyster, and thus allow the shell
to open. After being taken from its natural element, and exposed in a
boat to the tropical sun the shell opens, but it shuts tightly again on
being touched. The oysters do not generally live longer than twelve
hours after being taken from the water, and a dry wind off shore
hastens their death ; it is indeed a wonder, that, deriving their
oxygen from the water, they can live so long in our atmosphere.
Mother-of-Pearl
shells are taken as low down as 45 and 50 fathoms ; beyond this depth
the divers have hitherto been unable to explore, and hence their
extreme limit is unknown. One has, however, been brought up, when
splicing a cable, from a depth of 150 fathoms. The zones of all
submarine animal life are regulated by the pressure,
