THE LANCELET 



327 



the left side of the ventral fin where it passes into the 

 caudal. Behind it is a region of the body of some length 



^^ssgS 



Fig. 233. — Amphioxus, from the left side, with the atrial floor 

 contracted. 



at.fl. 

 Fig. 234. — The same, from the ventral side. 



m.f. ,ph. est. at.fl. 



' I I . s J 



Fig. 235. — The same, from the ventral side, after the floor of the atrium 

 has been cut open. 



an., Anus ; at.fl., floor of atrium ; at.fl'., the same cut through and turned back ; 

 atfi.. atriopore ; atp' ., line indicating position of same in side view ; c.f., caudal 

 fin; d.f.r., rays of dorsal fin; est., endostyle ; gon. , gonads; Ir. , liver; m.J., 

 metapleural fold ; mym., myomeres; myc, myocommata or septa of connective 

 tissue between the myomeres; n.p., nerve cord; nek., natochord ; or.c, oral 

 cirri ; or.h., oral hood ; ph., pharynx ; v.f.r., rays of ventral fin. 



which does not contain any part of the alimentary canal. 

 Such a region is known as a tail. At the end of the flat 

 region of the belly is a mid-ventral opening known as the 

 atriopore, through which a current of water escapes. The 



