72
THE BIOLOGY OF F ISHES
«
separate from their“fellowsand race towards the heart.
It
is as if the heart were pulling them along, and to some
extent this is the case, a slight vacuum being formed in the
wake of the rhythmical contraction from before backwards.
This prOcess leads to channels being formed over the
—
surface of the yolk as fresh contingents of corpuscles are
’
drawn forward, until a complete network of vessels is formed
over the yolk. The corpuscles drawn through the heart
are forced along a ‘harrow space between the gut and’the
notochord into the still narrower spaces in the head and
between the muscle-bundles.
Then the channels over the
yolk extend inwards towards the body, rst of all in the
pectoral region then at the tail, and connect up with the
internal channels to form a complete circulation.
Denite blood—vessels are not formed, however, until
'
the circulating corpuscles become red, and the stage at
Which this occurs varies greatly.
Elasmobranch and
most of the Teleost .demersal eggs soon develop the red
blood; but the Herring and most of
'
the Teleost pelagic
eggs do not show any sign of red blood until the larvæ are
_
hatched.“ The Ganoids, except perhaps Polypterus, are like
_
the latærinthis reSpect._
Williamson (1897) has shown that the vitelline circula—
'
tion in the pelagic eggs of Teledsts is esSentially the same
;
_
as in the demersal forms, but the red blood (or rather
_
hæmoglobin) and denite walls to the channels are wanting.
Conseq_u‘ently, the embrÿos
these forms cannot receive
their
thrOugh the vascular System. Further, it is
and the Teleost
'
”
demersal embryoswfchred blobd have the gills developed
—
andthe,mouÏth
this is not the case
With th€ ;“H€Hig gr0uP and “the pelagic forms. For
"
considerable
hatching the"larmngerrihg has no
_
blood—Vessels in‘the'bodÿ eXCept-the dorsal
'
_
'The aer_ati6n of the
the pelagic
_: forme appearstç)-coïne through the gut and not çthrough the
,—
,”vitelline-circulation; _The'em‘bryon‘ic gut her'e communiCates
'
dir€Œlÿ_ ÎWithçthe ’p€ÎÏVitelli—nes_paceby means
in
,
“
THE BIOLOGY OF F ISHES
«
separate from their“fellowsand race towards the heart.
It
is as if the heart were pulling them along, and to some
extent this is the case, a slight vacuum being formed in the
wake of the rhythmical contraction from before backwards.
This prOcess leads to channels being formed over the
—
surface of the yolk as fresh contingents of corpuscles are
’
drawn forward, until a complete network of vessels is formed
over the yolk. The corpuscles drawn through the heart
are forced along a ‘harrow space between the gut and’the
notochord into the still narrower spaces in the head and
between the muscle-bundles.
Then the channels over the
yolk extend inwards towards the body, rst of all in the
pectoral region then at the tail, and connect up with the
internal channels to form a complete circulation.
Denite blood—vessels are not formed, however, until
'
the circulating corpuscles become red, and the stage at
Which this occurs varies greatly.
Elasmobranch and
most of the Teleost .demersal eggs soon develop the red
blood; but the Herring and most of
'
the Teleost pelagic
eggs do not show any sign of red blood until the larvæ are
_
hatched.“ The Ganoids, except perhaps Polypterus, are like
_
the latærinthis reSpect._
Williamson (1897) has shown that the vitelline circula—
'
tion in the pelagic eggs of Teledsts is esSentially the same
;
_
as in the demersal forms, but the red blood (or rather
_
hæmoglobin) and denite walls to the channels are wanting.
Conseq_u‘ently, the embrÿos
these forms cannot receive
their
thrOugh the vascular System. Further, it is
and the Teleost
'
”
demersal embryoswfchred blobd have the gills developed
—
andthe,mouÏth
this is not the case
With th€ ;“H€Hig gr0uP and “the pelagic forms. For
"
considerable
hatching the"larmngerrihg has no
_
blood—Vessels in‘the'bodÿ eXCept-the dorsal
'
_
'The aer_ati6n of the
the pelagic
_: forme appearstç)-coïne through the gut and not çthrough the
,—
,”vitelline-circulation; _The'em‘bryon‘ic gut her'e communiCates
'
dir€Œlÿ_ ÎWithçthe ’p€ÎÏVitelli—nes_paceby means
in
,
“