Pvn H,i I'UitlS

42 ostreidjE.
case. In the Report of the British Association for
1856 Mr. Eyton has given some farther information as
to the appearance and habits of the oyster-fry. He
says, " The animal was semitransparent, with two
reddish elongated dots placed on each side behind the
cilia, which were in constant and rapid motion. They
were exceedingly tenacious of life, the cilia moving until
the water was dried up upon the glass. Some that I
placed
in a little salt and water were alive the next
day." After a short enjoyment of freedom they attach
themselves to a stone or some other object ;
the mantle
soon afterwards begins its work of secretion, and converts
the case into a shell ;
the latter becomes agglutinated
to some extraneous body ; the cilia and eye-like spots
disappear, and the permanent organs are developed.
This metamorphosis has its parallel in the Cirripedia
and other classes of invertebrate animals. The parent
oyster is slow in recovering from its long-continued parturition
; and it is not fit to eat until about the middle
of August. Indeed, it is not considered to be in full
flavour until September. The period of its longevity is
not known. It is said to be in prime condition from
the fourth to the seventh year, and rarely to live beyond
If the numerous laminse or plates of
its fifteenth year.
which the shell is composed denote the marks of annual
growth, some individuals must attain a very venerable
age; but these plates are formed inwardly,
outwardly
instead of
as is the case with the trunks of coniferous
trees, and the analogy therefore fails. A severe winter
causes great mortality among those which are laid in
park sor shore-beds, in consequence of the valves being
closed by ice during the recess of the tide. In all probability
the stock of sea- water, which had been taken
in before the oyster was laid bare, requires occasional