301 



end/ ^- ^- sub. end. coeL ^metapi. 



Fig. 226. — Transverse section through Branchiostoma in the region of the 

 pharynx. — After Krause. Young, The Life of Vertebrates, 1950. The 

 Clarendon Press, Oxford.. 



atr., atrium ; d.a., dorsal aorta ; d.coel., dorsal portion of coelom ; div., intestinal diverticulum ; d.nA, and 

 rf.n.2, branches of the dorsal nerve root ; end., endostyle ; ep.gr., epipharyngeal groove ;/., lin-ray box ; 

 g., gonad; 1y.b., primary gill bars containing coelom; my., myotome; metapl., metapleural fold; 

 n., notochord ; n.c, nerve cord ; ph., pharynx ; sub. end. coeL, subendostylar coelom ; t.b., tongue bar ; 

 v.a., ventral aorta ; v.n., ventral nerve root. 



GENERAL ANATOMY 



The skin has an outer epidermis, consisting of a single layer of 

 columnar epithelium, ciHated only within the oral hood and in 

 parts of the atrium, and two layers of a fibrous cutis. The con- 

 nective tissue is scanty, and consists of fibrillated ground substance 

 with some cells. There is a thick muscular body-wall, divided, 

 as we have seen, into segments, which are V-shaped and fit into 



