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 ef-tr.0. d 



cta.0 



afbr.a. 7 1 ^ 



af.br.a' vcu > qf bra 



e.ppor-1. v 



FIG. 77. Diagram of the vascular system of Amphioxus. af.br.a, Afferent branchial 

 arteries ; af.br.a', similar vessels of the secondary (tongue) bars ; br.d, gill-slits ; 

 cp, intestinal capillaries ; d.ao, paired dorsal aortae ; d.ao', median dorsal aorta ; 

 ef.br. a, efferent branchial arteries ; hep.port.r, hepatic portal vein ; hep.v, hepatic 

 vein; int, intestine; Ir, liver; ph, pharynx; s.int.v, sub -intestinal vein; v.ao, 

 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 in 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 (3) 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 



