THE PHYLUM CHORDATA 



41 



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

 The blood collects again in paired dorsal aortce, which unite back of 



eba da 



pc 



va 



FIG. 14. Diagram of the circulatory system of Amphioxus. aba, afferent 

 branchial artery; d, liver diverticulum; da, dorsal aortse; e, \efferent branchial 

 arteries; hp, hepatic portal system; pc, pharyngeal clefts; ph, pharynx; sv, 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. 



A B 



FIG. 15. A. Nephridium of Amphioxus with incurrent funnels crowned with 

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

 solenocytes. (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 



