180 AMPHIOXUS 



beneath the notochord one on each side of the hyper- 

 branchial groove, and project into the dorsal ccelomie 

 canals. 



The dorsal aortee carry the arterialised blood back- 

 wards : they unite at the hinder end of the pharynx 

 to form a single vessel, which runs back along the 

 dorsal surface of the intestine. 



4. The portal veins are vessels running, in the coelom, along 



the ventral surface of the intestine : they collect the 

 blood from the intestine and carry it forwards to the 

 liver, where they break up into capillaries. 



5. The hepatic veins are vessels which collect the blood 



from the liver and carry it backwards along the 

 dorsal surface of the liver. On reaching the junc- 

 tion of the liver and intestine, they unite to form a 

 single vessel, which turn forwards along the ventral 

 surface of the pharynx and becomes the cardiac 

 aorta. 



6. A longitudinal vessel runs along the inner side of each 



atrial fold, and supplies the myotomes and reproctuc- 

 tive organs. 



G. The Excretory System. 



It is not yet certain whether Amphioxus has any definite 

 excretory organs. 



The pigfmented canals discovered by Lankester are possibly 

 excretory. These are a pair of short tubes, with deeply pig- 

 mented walls, placed ia the twenty-seventh segment of the 

 body, opposite the hinder end of the 'pharynx. They lie, one 

 at each side of the body, in the dorsal coelomic canals above 

 the suspensory folds of the pharynx. Each tube is attached 

 along its outer side to the body- wall, and opens behiad iato the 

 atrial cavity : in front it is considerably contracted, but appears 

 to open into the coelomic canal. 



Hatschek regards as a kidney' a ciliated canal which lies 

 on the left side of the anterior end of the body. It extends 

 from the anterior border of the mouth to immediately behind 

 the velum, and is believed to open behind into the pharynx. 



