74
THE SEAS
when they begin to assume the adult form.
The young of
animals which live in very deep water would have difculty
'
in rising several miles to the surface for a oating existence
'
of perhaps only a few weeks or even days, and then dropping
back that great distance, and as a result we nd that the
development of deep—sea animals is “ direct,” i.e., there is
no
strange
“
larval ”
stage, when the young are free in
_the sea, between the egg and the xed adult, but the
latter develops_directly from the egg.
The advantage of
.
,
the former method in ensuring the wide distribution of
the
animal
concerned will be obvious.
The spawning
habits of bottom animals are many and various, but, .
as
with the shore animals, can be divided into three
main types, where the reproductive products are shed
_“
indiscriminately, where protected spawn is laid,
and
where the developing young are carried about by the
parent.
_
_
'
.
Bottom animals do net" make long migrations like the
*
'
'
sh.
This is impossible in the case of the many attached or_
rooted animals while a large number of the others are too
sluggish to move far.
Octopuses certainly mOVe from place
'
to place cau‘s‘ing, as we saw, great damage when they
_
'
suddenly invade new areas, but this is probably the result of
'
exceptional temperature conditions and not a seasonaï
occurrence.
Crustaceans, at any rate the larger ones, are
'
active beasts and can move about freely
many, like the
edible crab, coming inshorein the summer and then retiring
into deeper water in the winter.
In the summer the shore
waters are warmer than the deeper water, but in the winter
the reverse is true.
animal which -can
about is
the scallop, especially the smaller “
queen
”
-(Pe_cte‘zi operaulam‘s) which, by the continuous appingof its
shell valves, is able to swim about, hinge side hindm’œt
process which is reverséd‘ When*the animal is alarmed)
THE SEAS
when they begin to assume the adult form.
The young of
animals which live in very deep water would have difculty
'
in rising several miles to the surface for a oating existence
'
of perhaps only a few weeks or even days, and then dropping
back that great distance, and as a result we nd that the
development of deep—sea animals is “ direct,” i.e., there is
no
strange
“
larval ”
stage, when the young are free in
_the sea, between the egg and the xed adult, but the
latter develops_directly from the egg.
The advantage of
.
,
the former method in ensuring the wide distribution of
the
animal
concerned will be obvious.
The spawning
habits of bottom animals are many and various, but, .
as
with the shore animals, can be divided into three
main types, where the reproductive products are shed
_“
indiscriminately, where protected spawn is laid,
and
where the developing young are carried about by the
parent.
_
_
'
.
Bottom animals do net" make long migrations like the
*
'
'
sh.
This is impossible in the case of the many attached or_
rooted animals while a large number of the others are too
sluggish to move far.
Octopuses certainly mOVe from place
'
to place cau‘s‘ing, as we saw, great damage when they
_
'
suddenly invade new areas, but this is probably the result of
'
exceptional temperature conditions and not a seasonaï
occurrence.
Crustaceans, at any rate the larger ones, are
'
active beasts and can move about freely
many, like the
edible crab, coming inshorein the summer and then retiring
into deeper water in the winter.
In the summer the shore
waters are warmer than the deeper water, but in the winter
the reverse is true.
animal which -can
about is
the scallop, especially the smaller “
queen
”
-(Pe_cte‘zi operaulam‘s) which, by the continuous appingof its
shell valves, is able to swim about, hinge side hindm’œt
process which is reverséd‘ When*the animal is alarmed)