228
,
THE BIOLOGY OF FISHES
!
'
_;
'
the branchioStegal rays and covering bones Which extended
-
forward to the symphysiS of the lower jaw. These forms
'
represent, therefore, an early stage in the development of
==
the Clupeid type.
-
’
:
5- f
With regardto the Squamation, some of these ancient ::
,
.
Clupeids had small rhombic or somewhat square-shaped
_.—
scales which tted into one another, usually with a peg-and—. _”
'
socket joint, so that the whole body was encased in a sheath;
:
If we regard the deposit of calcareous substances in the skin
as an excretion, it is probable that these shes had an even ,
_
m0re imperfect excretory system than the modern Clupeids,
_
ÏÎ
and With this we can associate the lack Of exibility in the ’
;
rhombic squamation. In other words, the earlier pelagic
_
:
_
forms were less mobile and less active and their internal
’Ï:
organs less developed.
.
'
_Î
_In sorewhat ‘ later forms of the same type there is a
gradual transition ï from the rhombic to the cycloid scales
even on the same sh, the trunk having the former, the more
[ Ï
;
exible tail the latter.
As Ryder and Smith Woodward
) ;,gilj
have indicated, these changes—as, irideed, the whole forma;gÏ
tion of"the= scaleS—Can be associated With the working of
:Ë
On the skin and dermis.— The faster the sh
moves, the more the skin is wrinkled and tends to form [;
cycloid, overlapping scales. The rhombic squamation
practicallyV disappeared during the
period :and
only persistS atthe present time inthe
and on the tail of the
' ï_Ÿ
_
tion» to therhombic .arrangement'can st111 beSeeninsome of
'
*
.
the—çpelagic,slow—“moving
that some of
of the earliest
Ïï
*
__
Ganoids had
their’paddle—shaped paired '
;»
forms of thefreshwaærsnotmamæ
,
—
1
Â
.
ï Wecanfollowthrspelagrctype, its distribution and =eVen
1
:
_'
thechangesrn 1tsmeuth and squamation, down to .1;hejÿ__…
present day.} Durlngthe
'
Mesozûic . period —_
’
_it ; Was» reprÇæ; _.
’
:
sentednotonlybyäÂthe Palæohisoidæbut also by. the large
;". groupof ‘iïÿrotospondyli: (Smith ‘ 1_ Woodward). »Soi{rieÏ of '
,
THE BIOLOGY OF FISHES
!
'
_;
'
the branchioStegal rays and covering bones Which extended
-
forward to the symphysiS of the lower jaw. These forms
'
represent, therefore, an early stage in the development of
==
the Clupeid type.
-
’
:
5- f
With regardto the Squamation, some of these ancient ::
,
.
Clupeids had small rhombic or somewhat square-shaped
_.—
scales which tted into one another, usually with a peg-and—. _”
'
socket joint, so that the whole body was encased in a sheath;
:
If we regard the deposit of calcareous substances in the skin
as an excretion, it is probable that these shes had an even ,
_
m0re imperfect excretory system than the modern Clupeids,
_
ÏÎ
and With this we can associate the lack Of exibility in the ’
;
rhombic squamation. In other words, the earlier pelagic
_
:
_
forms were less mobile and less active and their internal
’Ï:
organs less developed.
.
'
_Î
_In sorewhat ‘ later forms of the same type there is a
gradual transition ï from the rhombic to the cycloid scales
even on the same sh, the trunk having the former, the more
[ Ï
;
exible tail the latter.
As Ryder and Smith Woodward
) ;,gilj
have indicated, these changes—as, irideed, the whole forma;gÏ
tion of"the= scaleS—Can be associated With the working of
:Ë
On the skin and dermis.— The faster the sh
moves, the more the skin is wrinkled and tends to form [;
cycloid, overlapping scales. The rhombic squamation
practicallyV disappeared during the
period :and
only persistS atthe present time inthe
and on the tail of the
' ï_Ÿ
_
tion» to therhombic .arrangement'can st111 beSeeninsome of
'
*
.
the—çpelagic,slow—“moving
that some of
of the earliest
Ïï
*
__
Ganoids had
their’paddle—shaped paired '
;»
forms of thefreshwaærsnotmamæ
,
—
1
Â
.
ï Wecanfollowthrspelagrctype, its distribution and =eVen
1
:
_'
thechangesrn 1tsmeuth and squamation, down to .1;hejÿ__…
present day.} Durlngthe
'
Mesozûic . period —_
’
_it ; Was» reprÇæ; _.
’
:
sentednotonlybyäÂthe Palæohisoidæbut also by. the large
;". groupof ‘iïÿrotospondyli: (Smith ‘ 1_ Woodward). »Soi{rieÏ of '