108
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THE BIOLOGY OF FISHES
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Way—through the water they might be horizontal at a given
if moving faster they would tend to rise, if slower‘ the
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head or the tail might sag. The acquiremént of an airfjp
bladder might seem to be a remedy for this state of mattets,Ï {?
but a great deal depends on its position and how it growS.'
The Clupeids are able to do without an air—bladder for
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time, and when it appears, it pushes rapidly alOng the Wh018* =
length of the abdominal cavity, so that the greater part of
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the body is supported by its means. «This arrangement
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also has its disadvantages, however, and the,Clupeids had
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to make
otherregulati0ns, but for the moment we,
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are more concerned With cases in which
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the air—bladder
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is,—crit short; as it were, in its growth and does not extend
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The little sh, supple and
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has thentobalance itself on’a knife—edge.
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condition is seen in the larV,a 0f«
Fistul—aria recently. described by Delsmah
It is 111
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every way…a’ Clu£peid larVa, but within a short timé:*its '
appearance ';completely alters; The
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air—bladder remains
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about the middle of
3;)andwe can follÔW'
the_sigs:0f an,alternatingse€—saw movement of
headand …
“rst £the, tail end
«The'—>£headÎ.äiË-Ïî* *
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plate (or parasphenoid axiS) is bentûpwardsïfelave ..to
the ,
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mici—line of the body (Fgz73>ndthfbnbœ
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PushedbackwardbetweentheeyesApefmanemslgn°f ":
ÿ thlseaycompresswnlsmsomecasesfoundmthefuæon
E shownabovetobeall—lmp0rtamlnthe formation of the
: ':Ï mouth,1sendeavourmgtocounteractthm upward tendency.
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from the head by the
_:musclese;
ar”,ch»is__strongly .retraeted
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on _theîlower;jaw,. upwardS and back—f
Well Jason—the” gill—arches.
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,
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; fl
lower
closes andthe critical Stage is reached. , '
appearance of the Ïbodÿ:ahdthei :
;_narrovvÿàgutindicate that the little sh
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