THE PHYLUM CHORDATA 



41 



blood forward and through the branchial arches, where it is aerated. 

 The blood collects again in paired doi^sal aortce, which unite back of 



eba da 



Fig, 14. — Diagram of the circulatory system of Amphioxus. aba, afferent 

 branchial artery; d, liver diverticulum; da, dorsal aorta;; e, efferent branchial 

 arteries; hp, hepatic portal system; pc, pharj'ngeal clefts; ph, pharynx; si>, sub- 

 intestinal vein; va, ventral aorta. (Modified after Parker and Haswell.) 



the pharnyx into a single dorsal aorta, that in turn carries the blood 

 to the various systems. The ventral vessel takes a loop about the 

 diverticulum and this loop is interpreted as a simple hepatic portal 

 system. 



J^ B 



Fig. 15. — A. Nephridium of Amphioxus with incurrent funnels crowned with 

 solenocytes. B. Enlarged view of a portion of one nephridial funnel, showing 

 Eolenocytes. (After Boveri and Goodrich.) 



The excretory system consists of paired nephridia (Fig. 15, A) with 

 ciliated nephrostomes from which protrude knobbed cells called soleno- 

 cytes (Fig. 15, B). The nephridia are true ccelomoducts, leading from 



