THE DEVELOPMENT OF FISHES
wanting. There is no pigment in the” body. The
_
"
is colourless (lymph) without hæmoglobin, and the vascular
system is not deVeloped.
-
,
…
'
;
'
,
From this ‘simplef= organism all other shes;, past br
present, can be derived, as Will- be seen from
.
pages.
'
_.
_,
_
The change from the larval to: the p0stlarval=_èondion
consiSts in the complete absorption of theyolk and the
deVelopment of the various Organs. The mouth
the head separàtes from the yolk ; the head continues to
swell, the yolk decreases and the
in "between
ruptures. , In the Elasmobranchs,
this occurs early,
the embryois anchored for a long time to,the heavy yolk—sac
and” the
takes the form of a crescent.
he head
can
only move from side to side and gradually_becomes
attened anjdfpointed- In the Teleosts, suCh1asth6*Herring,
-
Ï the head tilts _upwards, when released from the ij1k
connection and— the mouth then becomes narr0W2and'opens
nfouth grows Will be considered :in the
neXt'ëhapter.
__
,_
f
"
:
,
_'
The gills or breathing organe are forming
before the mouth OpenS; and
the outside
_
m‘embrane Connecting. the Shoulder=girdle with the head *”ijs
_
»
ruptured so that thegills are for a time
-
,
=
in}other cases the'membrane
has to be made, as in the
Eds.
These phenomena are connected
of the
‘
_-head on
_
-
,
As the yolk-di‘minishes, the liver“ cari
as-alarge
,
organ- lying ar'0undgthe
leadmg
_
f
from the yolk into the
; Ï _ ;
_
.ndi..æsthegubldd…lymphpBid;
”this there
anotherlobedorganSAmao’“hhVrbut ;;
_
’
slightly- lghtn1uthpnndmduP“th
twüdthbgnmgfthgwhhhplyd
-
,
.
a
veryImportantpætmthehfe°“heb‘mYShŒthealr
-.
‘
,
», Th13beginsasasllght swelhnghkea
”1
_
'
gthtpfthgt