214 _
_THE ï’—_BIOLOGY .0F FISHE‘S
DevOniar‘r period, »,havè retained the primitive opercularj
cover, The posterior position of the gill—arches in the other
*
Elasmobranchs can be associated directly With the movements—' Ï
and mode of life of the embr'yos. In some Teleosts,as in the
Ï
',
Eels,the arches also retreat behind the head during development and the pectoral arch loses its connection With the skull.
,
The condition of the arches in the Cyclostomes cannot '
'_
therefore be considered as primitive. The place where the
-
gill—arches should form has been determined by the positi0n
of the heart and this by the pœition of the yolk—sac.
_
_
The superior
and renal systems
.
the Elasmobranchs-bÿ, comparison With those of the TeleostS,
,
…_î.
can also be referred to the
of reproduction. The
;LÏf5'
’
greater freedom alloWed to the embryo, owing to the absence Z
’
of;ahardened choriorï, and the elevationof the embryo above
theyolläesac,(Fig,f14)_have allowed more space for the
”
development'of the various tiSsues and organ‘s. , '
_
‘. , ,
: ' .
*
,
The mode of—reproduction Of the Teleosts has
been recognised as the _Simplest, and as it also prevailed
_
_
among the earliest Sharks as well as the Ganoids and Teleosts
:,5__it Can certainly be taken as, the mŒt’prîritive.
'
f
'
'
T he interpretati0n
structures of the mouth
_
alWays'beenzind still is a matter. of great difculty,and it
=
'
quite uncertain What, s0rt
some .of_the earliestl
=
,
shes
This
is
,
Stage of Îhe Clupeidsl ÉThéreëœn—fbè nodeubtthatmost1f
hŒ——âHæo£ theprmtweArthrodxranswereautestylæWith [ …?
: îge.1—19W6ffj_àv,ïhowever1tmayhavebænformedarüculaüng i>--Î:
d1recyw1ththeskullandthlsrsalsotheconcütmnm the
l'
?), and
-
baba cmmæaBuaBhfanhad that in the.
p5-i:
1tmadthfthantaa - jaw
h ugad ahaa «cha
.
adaptat10ntothehabsof LthŒeÿ shes.,
lt 5
cann0tbeignoredthattheAathmdarans had thlSpl”lllüve
,
:
: : aut°styhsmalongWhm soma
andp1e :
_THE ï’—_BIOLOGY .0F FISHE‘S
DevOniar‘r period, »,havè retained the primitive opercularj
cover, The posterior position of the gill—arches in the other
*
Elasmobranchs can be associated directly With the movements—' Ï
and mode of life of the embr'yos. In some Teleosts,as in the
Ï
',
Eels,the arches also retreat behind the head during development and the pectoral arch loses its connection With the skull.
,
The condition of the arches in the Cyclostomes cannot '
'_
therefore be considered as primitive. The place where the
-
gill—arches should form has been determined by the positi0n
of the heart and this by the pœition of the yolk—sac.
_
_
The superior
and renal systems
.
the Elasmobranchs-bÿ, comparison With those of the TeleostS,
,
…_î.
can also be referred to the
of reproduction. The
;LÏf5'
’
greater freedom alloWed to the embryo, owing to the absence Z
’
of;ahardened choriorï, and the elevationof the embryo above
theyolläesac,(Fig,f14)_have allowed more space for the
”
development'of the various tiSsues and organ‘s. , '
_
‘. , ,
: ' .
*
,
The mode of—reproduction Of the Teleosts has
been recognised as the _Simplest, and as it also prevailed
_
_
among the earliest Sharks as well as the Ganoids and Teleosts
:,5__it Can certainly be taken as, the mŒt’prîritive.
'
f
'
'
T he interpretati0n
structures of the mouth
_
alWays'beenzind still is a matter. of great difculty,and it
=
'
quite uncertain What, s0rt
some .of_the earliestl
=
,
shes
This
is
,
Stage of Îhe Clupeidsl ÉThéreëœn—fbè nodeubtthatmost1f
hŒ——âHæo£ theprmtweArthrodxranswereautestylæWith [ …?
: îge.1—19W6ffj_àv,ïhowever1tmayhavebænformedarüculaüng i>--Î:
d1recyw1ththeskullandthlsrsalsotheconcütmnm the
l'
?), and
-
baba cmmæaBuaBhfanhad that in the.
p5-i:
1tmadthfthantaa - jaw
.
adaptat10ntothehabsof LthŒeÿ shes.,
lt 5
cann0tbeignoredthattheAathmdarans had thlSpl”lllüve
,
:
: : aut°styhsmalongWhm soma
andp1e :