CHAPTER IV
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Swimming Animals
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OVER the sea bottom lie the waters of the ocean extending
—
for miles in all directions.
Above the surface of the land
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the air is the medium through which birds and insects, and
'
even‘man, can make their way with great speed.
In the
,
same way the sea water forms a medium through which »
certain animals can travel rapidly from place to place by
_
swimming.
Although many minute animals can swim (in
the true meaning of the word), that is, make…their way
through the water, it is usually agreed that the real's‘wim—
thing animals of the sea are those only who can make heàd- '
.way with sufcient speed to move from place to -pT挀
-
against any current they may meet.
Those smaller
_
creatures that'can swim without sufcient strength to stem
the currents, and are drifted to and fro by them, are usually
classed under the heading of drifting life, and will be dealt
with at length in the next chapter.
The true swimmers are to be found in only a few groups
'
of the animal kingdom, and are the shes, the Whales and
seals, and the squids or cuttlesh.
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_
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FÏSHES
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Most sea shes can be divided into two main groups,
the
,
Cë£Ëilaginous shes or Elasmobranchs, and the
'
or 'Telé6ätë
In‘ ”the group of cartilaginouS shés
be
'
_found
all the shark family—dog—sh,_ tôè, sharks, raY5
'
and
skates.
These ”are…characterized‘ by the fact that no