24
.
—
THE SEAS
-
_
or' bony sh, with "the cartilage converted into bone by
,
the presence of limy matter, and the separate gill openings
,
.
covered—over with a ap known as the operculum.
"
'
All animals higher in the scale of evolution than the sh are
air breathers buta number have returned to the sea and
spend their'lives in it, some always near or on the surface
3
but others capable of diving to considerable depths though
«
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always compelled to return to the surface from time to time
,
_
toobtain air.
Among the REPTILIA are the water snakes
'
or HYDROPHIDÆ which have keeled bodies and tails attened
like those of_sh to aid them in swimming, and the turtles
'
which are aquatic tortoises with the limbs attened to
form swimmingpaddle's.
In the MAMMALIA there are the
‘
many kindsof whales, dolphins and porpoises which constitute the CetaCea and spend their entire lives in the sea,
'
an existence for which they are just as well equipped as the ‘
'
sh themselves, and also the strange sea cows (Sirenia),
—
sluggish,
beaSts which usually live in shallow
water
the 'mouths of rivers in tropical regions and
frequently sit on their tails With only their heads out of
Ÿ
_
water—the origin, probably, of all the stories about
'
mermaids ! Finally there is a group of the Carnivores
'
(which include the liens,: tigers and bears) the members
.of which,
exclusively marine, except in the breeding
.
season, are known as the Pinnipedia and include the Seals,
._
sea
liOns and malruses.
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‘
'
_
7
Plants
‘
The sea. is far poorer
types of plant life than the earth.
The owering plants have very few marine representatives;
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the best known being the eelgrass (Z ostéra marina) which is
widespread
in sheltered regions round our coasts.
The
.
great
et marine plants are
of simpler
structure
"than the owering plants and reproduCing ‘them—
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