IV - BLOOD SYSTEM—RENAL ORGANS 125 
which runs backwards, lying between notochord and alimentary 
canal. This vessel gives off branches to the wall of the intestine, 
and these break up into capillary networks (Fig. 77, cp), from 
which the blood is collected by the median sub-intestinal vein. 
This then flows forwards to pass by the hepatic portal vein to 
the ventral edge of the saccular liver, in the wall of which it 
is distributed in a capillary network. The blood is collected 
on the dorsal edge of the liver by the hepatic vein, which 
runs posteriorly and then turns downwards and forwards to 
, 
d.ao dao 
Hh 
iC 
sccm 
cp 
; \\ ANN tné 
aaa Lean 
CEQAES To 
afbra’ Y2 vybzqg lr 
Fig. 77.—Diagram of the vascular system of Amphioxus. afbr.a, Afferent branchial 
arteries ; af.br.a’, similar vessels of the secondary (tongue) bars ; br.cl, gill-slits ; 
cp, intestinal capillaries ; d.ao, paired dorsal aortae ; d.ao’, median dorsal aorta ; 
ef.br.a, efferent branchial arteries ; hep.port.v, hepatic portal vein ; hep.v, hepatic 
vein ; int, intestine; Jr, liver; ph, pharynx; s.int.v, sub-intestinal vein; v.a0, 
ventral aorta. (From Parker and Haswell.) 
become continuous with the posterior end of the ventral aorta 
or “ heart.” 
It is clear that this course of the circulation agrees with that 
of a typical lower Vertebrate in all essential points:—(1) in 
having the main artery a dorsal aorta im which the blood flows 
backwards ; (2) in having a ventral vessel representing the heart, 
and sending impure blood forwards to the respiratory region of 
the alimentary canal to be aerated; and (5) in having a hepatic 
portal system consisting of the capillaries of the liver, through 
which the blood from the intestinal wall has to pass before reach- 
ing the ventral vessel (heart). 
Renal Excretory functions have been attributed to various 
organs in Amphioxus, and it is quite possible that, in addition to 
the true nephridia which are now known, other tracts of tissue 
in the body may be able to eliminate nitrogenous waste matters. 
Such are certain clumps of columnar epithelial cells on the floor 
of the atrium, and the single pair of large brown atrio-coelomic 
funnels lying on the dorsal edge of the posterior end of the 
