94 .
THE "BIOLOGY o‘F FISHES
'
into
11—men1branc àndfÔrm various kindsof limb—like
_'
structûë's;gÿhilst the rays are little developed, as in the
Elasmdbrachs and Dipnoi.
Or the bases remain small and
the n-raÿèhre well developed under less mOvement, as__i‘n
'
rhost of the Teleosts.
In general, the stronger the move—
the n are, the longer it grows
and: the narrower,
?
that,i_âÿ;@ffhe central element or series of elements becomes
more prominent thaï—n the lateral ones—, and then the median
:
axis “may become segmented in the same Way as the vertebral
'
‘
With less mOvemét the bî'ead‘ch of the
n and nurher of rays increase, as in the Teleosfs.
°
CAUSES ÔF CHANGE IN THE
“
_
Iris perhaps' difculttorç:àliæ.that 'ShesÏ-arëäoÿ Well— -
jÏ
balanced ‘ The Pip‘easjhes and someothers swim
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lupwards, Centr1scus àd
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"sème-f of thè‘abn0r‘ràl Goldsheswi‘ch theirhead
:
,
_
Ribb‘on—shes, and…-even some of the
-»
Labroids lie on the one Side.
lower half of .the Clupeids
-
is
is heavier
-ih the specialised Tèle'osts' and
ThéÎbalanœ Of:
f.
'
the"ëhràÿthuâ be"irpérfŒti all
:
ff If
clôselÿ
{;
,
ndîà‘ç
really symmetrrcalThelohnDory
‘
,
a:
IntheSerranmds andpartmulaytheSparmdsthemebæl
'
CDiumandthePectoralarcharefrequenysotvmsted to the
EÉ
;
,
oneSIdethatonewondershowtheyhave managed to
‘,
= pbmngF1thAbut7op cent of the
.
conuenHaddockhavethesnoutbentto the-one side or the
—
to indicate the
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.
i
,
factor.
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old,
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‘
tehdto d;roop doWhWa-rd3
1
and toithe»ohe side, The'se"rhay seem
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exceptional,
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she'sg‘but if — '
Êff
Ïtâké the variations
into accoùh‘c, we
_
:;
o'fbalance has
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,