.
THE SEA SHORE
'
53
‘
.
snell by adding to the free edges, or the sea urchins, which
increase theirs by adding new plates in between these
already formed, the crustaceans are unable to add to the
shell and have to cast it and form a new one (Plate 16).
These moults take place at regular intervals, depending on
the particular beast and on the prevailing conditions, the
-
entire shell being cast—not only that which protects the
body but the covering of the limbs and even the lining of
.
the stomach and hinder part of the gut!
The animal
withdraws itself, often with obvious difculty, from its old
shell and is then left soft and completely defenceless,
until the new one has_formed and hardened ; this, however,
takes place very quickly, for the substances Of Which it is
'
formed have been stored up in the skin beforehand.
The
_new
shell is always larger than the old one, the animal
seizing this opportunity to “
grow
to the size it would
have
if the hard shell had not
_
prevented its
increase.
_
'
This must end our brief survey of the animals and plants
of the sea shore.
,
'