300 



CHORD ATA. 



however, the atrium is not continued round the dorsal 

 line of the pharynx. In Ascidia it was the mid-ventral 

 portion which was incomplete. The atrium is continued 

 backwards behind the pharynx and along the intestine 

 until it terminates in the atriopore, through which the water 

 has exit. 



Fig. 214. — Transverse Section through Amphioxus in the 

 Pharyngeal Region. 



(After Lankester, Boveri and others.) 



Dorsal Fin-skeleton. 



Nerve Cord. 



Notochord, 



, The dark shading is the connective tissue and the light outside is the simple 

 ectoderm. The myomeres and pharyngeal clefts are cut across as they run 

 diagonally. The section is taken across C D in Fig. 213. 



Lying on the right side of the pharynx in the atrium is 

 a long hollow sac, the liver^ which opens into the alimentary 

 canal at the junction of pharynx and intestine. The intes- 

 tine is produced backwards as a long tube to the anus. 



The muscular system is well developed. The longitudinal 

 muscles consist of a dorsal longitudinal system of muscles,' 

 called the myomeric muscles, extending through- 

 out the length of the body. The muscle-fibres 

 extend between numerous connective-tissue septa which are 



