52
.
THE SEAS
'
fragments, each” of which grows into a new individual.;
,
The anemones, although some kinds habitually reproducé
‘
themselves
sexuall'y, often divide (a process which is '
highly developed in the reef building corals, as described
in Chapter VII-), or break off small fragments near the base. ' '
;
The little syllid Worms break up in a periectly denite
-
way into fragments of a few segments, each of which grdws
a new head at one end and a new tail at the other, and so
:
develops into a full—sized worm.
The hydroids have a
complicated history.
They produce not eggs
little
jellysh, called medusæ, whichswim about near the surface
‘
of the sea and, when fully developed, produce eggs which
_
develop into the hydroids which produce the med;usæ.
This, in” common with the production of swimming young
:
by various shore animals, is"of great importance in seCuring
'
the distribution of animals which, because of their slowness
—
of movement or xed mode of life, would not otherwise be
_
able to spread far from their original home.
'
j
.
GROWTH'
.
_
Length of life in —shore' animals varies within the widest
limits.
Some animals, such as many sponges , and. sea
squirts; are annuals or even go through several generations
in a single summer, Whilst on the otherhand aneniones may
live to—.a great age ; there are some in captivity known to
F
be over sixty years-old.
After the early embryOnic or, in
—
the case» of animals with swimming young quite unli—ke
their parents;
"" larval ” Stages, most animals assume the '
adult ”shape changing in size only as time goes by:.
Growth
"
is usually 'a steady process, varying in speed according_.-to
,
,
the time et theyear, being generally slowér in winterä and
quicker in summer when it is warmer and there is more food.
In the erustaceans, however, growth takes place by -a
series of jumps.- ‘ Unlike the molluscs, which increase the
.
THE SEAS
'
fragments, each” of which grows into a new individual.;
,
The anemones, although some kinds habitually reproducé
‘
themselves
sexuall'y, often divide (a process which is '
highly developed in the reef building corals, as described
in Chapter VII-), or break off small fragments near the base. ' '
;
The little syllid Worms break up in a periectly denite
-
way into fragments of a few segments, each of which grdws
a new head at one end and a new tail at the other, and so
:
develops into a full—sized worm.
The hydroids have a
complicated history.
They produce not eggs
little
jellysh, called medusæ, whichswim about near the surface
‘
of the sea and, when fully developed, produce eggs which
_
develop into the hydroids which produce the med;usæ.
This, in” common with the production of swimming young
:
by various shore animals, is"of great importance in seCuring
'
the distribution of animals which, because of their slowness
—
of movement or xed mode of life, would not otherwise be
_
able to spread far from their original home.
'
j
.
GROWTH'
.
_
Length of life in —shore' animals varies within the widest
limits.
Some animals, such as many sponges , and. sea
squirts; are annuals or even go through several generations
in a single summer, Whilst on the otherhand aneniones may
live to—.a great age ; there are some in captivity known to
F
be over sixty years-old.
After the early embryOnic or, in
—
the case» of animals with swimming young quite unli—ke
their parents;
"" larval ” Stages, most animals assume the '
adult ”shape changing in size only as time goes by:.
Growth
"
is usually 'a steady process, varying in speed according_.-to
,
,
the time et theyear, being generally slowér in winterä and
quicker in summer when it is warmer and there is more food.
In the erustaceans, however, growth takes place by -a
series of jumps.- ‘ Unlike the molluscs, which increase the