276 .
THE BIOLOGY OF“
. Â
-
various times With? One another, Seeing that
’
can balancé;themselvesand rise and descend in thé” water
withoütit,we may take the air-bladder as another example
,
the organs and structures which have arisen without any
'
reference to their utility ; in fact, we may doubt if it has
been a useful organ in these two respects.
Its failure as a
balancing organ has been exemplied by the Flat—shes and
.
_
Pipe-SheS'. As a hydrostatic
it compels the sh to
keep to a certain level of pressure or bathymetric range,
even though an open duct may be.present; This duct or
9'f
communication from the ali‘mentary canal to the air-bladder
_
‘
-
allOWs air to enter, but not to leave apparently. OWing» to
this
the Clupeids havemade a
_
neW Opening—or “safety—valve
”
to the exterior, and it is
to thelattertha‘t' they ïowe _;their great verSa‘tility. Even
though pr.ovidedïivith”a
Pollan (Coregoims) Of; the
7
,
from deep water,have the“
,
air-bladder— —sWollen»to
they are unable
_to move, and soonPerish unless the air-bladderis pricked to
'
Ï
relieve the pressure (Semper),;
;
;
Ï
'—‘
.
The same phenomenon is more" freq'uentlyÿ seen“ in
shes, the majority of
,no openïduct; '_
A curious thing is that
'the;aiËf
'
Ï‘
E
bladder (oxygen and nitrogen
ag;sr}nall
'
:,
-carbonic àcid)- :Vary în
one. î'
?
Would, eXpèct. '—;.,Theépropar—iä;ofOxygenISleastmfresh
Wtershes : greateSt 1n deepsea shesThelatterhave
;
—f' Plessuf€0foxyg€nls0n1yab@utone°fthofan “atm08phere.
,
TheaCt1V1tyofthecellsrÏmstproducethæd1erence and
Ï
;_;it5sîoOn*ll‘SagamWlthgas,mostly OXygeii— (Pütter, 1911) =
_
; :l_
1nd1catethatthe sh is able to_,eXercise
»
;
* ;) i some
_‘andiî the f‘£fr.e_d “glands, _”, or retia
:
nubhfthPhy1t î6Videhyçusedï —f6r=this
:'ËÊÿîPôäêäï:iTheY
-Âïa*derisèë;c01nplex of glàndular