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274
THE BIOLOGY‘ ”OF FISHES
in the water (Plate XIII,»
The tail is sefving as a
.breathing organ. All breathing membranes, whether gills‘
Ï
or lungs, require to be moistened
given'the moisture in
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sufcient quantity many shes can live out of the: water
…
for quite a long time. ”Whether the skin of any sh, like
_.
that of the frogs, can serve as- a respiratorÿ:organ, we do
n0t know with certainty, but it is
that this is
the
in the Lung—shes and Bel—like shes. (Amphipnous') which can. live away from the water;
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.
»
addition to the principal breathing apparatus or ’gills,
certain
subsidiary and accessory parts are frequently
developed. If a sh like the —Wrasse or Cod is watched in
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an aquarium, particularly when at rest, it Will be observed
=
that justinside themouth two aps or folds of skin “are
automatically heating backwards and forwards. These — ‘ ‘
the so—'calledzbreathing—valves, withdrawing as the oral
Cavitÿwidens and
drawn in, returning when the
cavity c0ntracts- and the gin—arches and cover open to let
the water pass behind through the clefts and over thè’gills.
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These folds of skin have probably arisen
constant regurgitation of the
and there
;no f—doubt
that they must save thesh a great dealinmusèubr energy.
The Wrasse breathes only at the rate of fteen respirations
in the minute; but the-'Stick1eback needs almost ten times
_
Many sheS, eSpecially'thè
=“=
organization and
greater
,
,
Êi
“need 'for —
oxygen than lothersi When the Mlnn0Ws comeup
to the surface,Ë}itÏis….not{onlytocatchfhes,there is”{;1ore“
Oxygen
thÏeÿfaréîkei d0wn below,
by ‘
a—:—_ net —ofrî other
'The Dipnoi,
“though
müst;i also
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have free access
to— the air.
_
Other shes Cofe regularly t_o
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the surface and
—
take -in=_gulpsof air,}anjd- from this habit several important
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,
.
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—
Inthes1mplest cases, (Some Clupeids and the Ophioce—
:
-;
the ordinary(
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gill‘s‘
lininzg
the cavity {becomes “highly-f“ Vascular