THE GENEALOGY OF FISHES
209
highly organised sh adapted to living under more varied
'_conditions of depth, pressure,and salinity than any other
form.
.
'
,
'The conclusion that the earliest -sheS were pelagic and
‘
like the Clupeidlarva leads us to picture them as Îelongated
and muscular bodies divided into uniformee‘gments“.
!
consequence of their free movements the body
pressed or attened fromside to side, n0t rounded as in the
Cyclostomes. This attened’ shape of a muscular
led to the originand development of the ns, in the
caudal, dorsal, and then either anal or—pfairedns,whichardse
in the rst place where, themuscles hadfreest 'm0vement,
near/che tail.
That the earliest known forms had the Same
asymetrÿ: of the ns as we nd in the Clupeid larva,
indicates that they also had difculties in maintaining a
horizontal level, the head tending to droop downwards.
_
Given a fairly sti notoohord, however, the .movements Of
,
such a caudal region would bring the-sh up to the surface,
where they could —takein air directly. The Ganoids and
Dipnoi were cert—airin provided with air—Sacs, probably
'
-
also the Arthrodiràns, =to judge
Shapeoftheir ,
,
column, and, perhaps all the eàrliest shes; This »
,
the
of respiration,:sifrlàr
Ÿ to
the
,
f
:
Teleosts of the present day:(Chap,—. IV). ::It- is not yetzcertain ‘
'
whether the earliest shes (ag. Birkeniidæ) had
gills,
and these organs do not develop in the Clupeids until One
to three days after the larva is hatched.
This comparison of the Clupeid larva with the earliest
known shes may be carried a step further when we take
"
ihtOÿaccount = the enigmatical Palæospondyius, which was
£oùd.iri
Lower Old Red Sandstone of Scotland, thus
,
same layers as the earliest shes mentioned
;
Traquair, who described it, thought it was the
,
‘
desired ' evidence of a pri1itive;Cyclostdïne, and ÇheÏ WaS'
*
supported by A. Smith,…Woodward, both ;acknoWl'edged
experts
',But
'
:
a. long time [With
*’ “
209
highly organised sh adapted to living under more varied
'_conditions of depth, pressure,and salinity than any other
form.
.
'
,
'The conclusion that the earliest -sheS were pelagic and
‘
like the Clupeidlarva leads us to picture them as Îelongated
and muscular bodies divided into uniformee‘gments“.
!
consequence of their free movements the body
pressed or attened fromside to side, n0t rounded as in the
Cyclostomes. This attened’ shape of a muscular
led to the originand development of the ns, in the
caudal, dorsal, and then either anal or—pfairedns,whichardse
in the rst place where, themuscles hadfreest 'm0vement,
near/che tail.
That the earliest known forms had the Same
asymetrÿ: of the ns as we nd in the Clupeid larva,
indicates that they also had difculties in maintaining a
horizontal level, the head tending to droop downwards.
_
Given a fairly sti notoohord, however, the .movements Of
,
such a caudal region would bring the-sh up to the surface,
where they could —takein air directly. The Ganoids and
Dipnoi were cert—airin provided with air—Sacs, probably
'
-
also the Arthrodiràns, =to judge
Shapeoftheir ,
,
column, and, perhaps all the eàrliest shes; This »
,
the
of respiration,:sifrlàr
Ÿ to
the
,
f
:
Teleosts of the present day:(Chap,—. IV). ::It- is not yetzcertain ‘
'
whether the earliest shes (ag. Birkeniidæ) had
gills,
and these organs do not develop in the Clupeids until One
to three days after the larva is hatched.
This comparison of the Clupeid larva with the earliest
known shes may be carried a step further when we take
"
ihtOÿaccount = the enigmatical Palæospondyius, which was
£oùd.iri
Lower Old Red Sandstone of Scotland, thus
,
same layers as the earliest shes mentioned
;
Traquair, who described it, thought it was the
,
‘
desired ' evidence of a pri1itive;Cyclostdïne, and ÇheÏ WaS'
*
supported by A. Smith,…Woodward, both ;acknoWl'edged
experts
',But
'
:
a. long time [With
*’ “