\
.
_
,
-
_
,
,
ECONOMY OF THE BODY'—I
129
continuous
the auricle and the blood then passes into
the small, but muScular, ventricle (Fig.—34).
:
_
The ventricle is the rst portion of the heart _(indeed. of
the Whole vascular system) to be formed, and it forms just
where there is resistance .to the Circulation of: the blood or
lymphon entering the tissues of the embry0… .;It is; at rSt;
a simple tube through which the materials of {the
_
might pass in either direction.
,
In the
-
Teleo'stS generally the:yolk lies well forward under'the trunk
'
,
lit?
%
Ë
(:
,
_
6
é/k
.
_
heart ïi' n=:Ë—— A;," Eiàs‘mabfaach3; BArma
'
…
C., Teleost; a., auricle; ,Ïî-, bulbus aOrtæ ; c,, ,ÇOnUSgarteriœus; —s.,
sinus venosus ; k., semilunar valves ; v.,“ ventricle
faO‘rta.
(From Wiedersheim, after Boas.)
'
,
”
‘
'
_
"
‘
"
and head, in some even in front of the latter, so that the
,
heart deVelops beneath or even infront
of the head. .“ In the
,
_Elasmobranchs the yolk-sac lies more posteorly,
in
,
BdellÇst0ia still further back, and the heart and gillsÎthuS
the head.-_
'
_»
”As the?
the heart Or
itself£ÿand —fôrm8,a coil
its
1n
f
TeleostS.. ÏThe heart Of
Elasmobrançhs poss1b1y,that
,'
'
of the,Dipnoicertainly
'
"
;
to a greater
5Ë ”