3. co. 



Fig, 18. Diagram illustrating the anatomy of the pharyngeal region 

 of Amphioxus. A segment has been cut out of the pharyngeal 

 region, and a portion of the right wall removed to show the atrial 

 cavity, the pharynx and its gill-slits, and the dorsal coelom 

 ao. dorsal aorta ; atr. atrium; d.co. dorsal coelom; en. endostyle 

 ep. epipleur;/r. fin-ray; go. gonads; hy. hyperbranchial groove 

 mp. metapleur; mpc. metapleural canal; my. myotomes; nch. 

 notochord ; nph. nephridium ; nt. neural tube ; p.b. primary gill- 

 bar ; tb. tongue-bar; S.co. sub-endostylar coelom. (From G. C. 

 Bourne.) 



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