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278
THE BIOLOGY OF FISHES
_
girdle. “Here a“sùpercialg bony plate serves as a drum, …
-
apparenÿ, and conveys differences in the external pressure
’
to theair—bladder.
At “any rate, shes like the Loaches, ; î
are provided with this apparatus, are very sensitive ;
to
changes in the atmospheric pressure and have been
’
called“ weather—shes.” But the most remarkable of the
air—bladder’s activities is that which has brought it into
:
communication with the statocyst or
“
ear.”
'
In many shes, like the Gadoids, the anteri0r end of the
bladder is continued by two solid cords which reach forward
—
'
to the head and are xed to the prootic, just outside the
,
labyrinth of the ear. Originally these were probably lled
with uid, and even though solid they are not merely
attaching structures but probably convey some impression
of the condition
bladder forward to the prootic,
which may serve as
:In'the Clupeids these anterior
prolongations penètfàte into the Semicircular canals and
_
expand into bullæ, with…”the lining membrane in contact
with the endolymph of the cahals. Thus, differences of
pressure in the air-bladder are conveyed to the endolymph
and thus to the nerve ampullæ within. It
formerly
thought that these prolongations were direct continuatios
of the air—bladder and lled with gas, but Thilo has shown
recently that they contain afliquid; probably Ïserous,uid,
and are. shut oÎ from
a membrana In
'
this
'serve as a manorétèrQr_bäromet<äñ _ Ê €:
_
A further stage of this remarkable_apparàtusÏisfôuiidfî_ti;_
_
Silurbid3;ÿetëi). Thegrowthm£f ;;
_
.
ufÏthégrSt-Ètwcf'or three r1bs in:rhædï@r:ñé has bei:aitëztfèrèd
'
'
means of the
'
processes of
'
the,
a most elaborate
_
mechanism conn_ecîcigÏ1tlwiththeÎ'stàtoCyst; ‘The accom—
‘
_panying
Will Show how the apparatus works. When
.
—
the air-bladder is loosean‘dcontracted, as in the rst gure,
_
the ossicles
hot-in -c0ntact with the statocyst ;' but
when therair-blàddet isdiste‘rided, the
becomes
'
';taùt and the front ossicle (c) closes like acap ona fenestra