106
1
f — THE BIOLOGY OF FISHES
',
»
'
,
'
level of the hyoid arch, it cannot be opened by the mechanism
‘
from that arch.The dilculty is increased at this time by
'
tWo things : the lower jaw ossies and a long rod of cartilage,
"
the preoperculum, forms along the posterior margin of the
"
suspensorium. The latter is then unable to- bend. It
may be drawn far backwards and thus allows an eno‘rmous
'
mouth to be formed, as in some deep—sea Teleosts, but in
many others it remains forward and then for a time the
mouth cannot be opened, and the postlarvæ have difculty
'
,
in obtaining food.
'
.
,
-
,
_
«
'. This remarkable condition has-now been revealed in a
large number of Tel€osts. ' What it leads to in the case of
the Flat-shes and the Pipe—shes will be describedglater.
But it seems clear that the little shes make violent efforts
to overcome the diiculty. Some elorigated forms work
their—mamies to such an extent that:the digestive tract is
forcedforwards right under the
;
In others the palatine
arCh- gives way, as :in the Pipe—shes;
form;
,
Styloph0rus, recently described ;by— Tate Régan_='
.
thewhole of the upper part
,awaÿfrbmtheskulh How the mouth is.-able then*td-ôp“e
or. close _isJStill afmySteiy.‘
Ï Insomeother forms, as in
Regalæùe—(Fig. 9)>a—nd Zeus (Fig. 22) the whole skull is
drawn doWnwards—; -—
.
'
_
.
'
,.
saves the Situation in most Teleosts.is the develop—
-
iatëfopsrèùlum:Œig4—25 , i)”-ê
,
_
'
: culum
It
"[ f0rmsalongthe0Ut€YSIdC0fthehy01darch(ceratohyal) and
,
; 1tsantenorend1sconnectedw1ththeouter face of the IOWer
'
=j- '
JaW,atrstümplybyskm,laterbÿdigament in which
'
developsasmallsesamœd
bone.
By this means
_
=
f
its joint, When the shbegins
.
original mechanismicontinües
‘
; 'LtOzfu‘rictio.
.Ç,::
:
_
f
_
'
"
The—_:‘changes =in>the Upper jaw are -,'eqùally
,
_
_.
'The
condition seems“ to be that shownÈby,the
”_.,_,E;Arthtodiràns, Protopterus (Fig. '26)—»and the H'olocephali
l
palato-quadrateÿ forms-part
f