THE CEPHALOCORDA 185 



into the sub-intestinal vein, and so the circle is completed. It 



- 4^.... ./ &'^-imii--^/l^ 



Fig. 45 



A. Anterior portion of the nerve cord of Anfiphioxus, after Schneider, cn^, cn^, 

 first and second pairs of " cranial " nerves ; kr^, dorsal roots of the first pair, and 

 dr^, dorsal roots of the fourth pair of spinal nerves ; vr^, z/H, the correspond- 

 ing ventral roots; e, eyespot. B. Diagram illustrating the circulation in 

 Amphioxus. of. afferent branchial vessel with enlarged bulbil ; ao, dorsal 

 aorta ; l)r.a, branchial aorta ; eft efferent branchial vessel ; ke^, hepatic 

 diverticulum ; hv, hepatic vein ; nek, notochord ; />&, primary bar ; ib, tongue- 

 bar ; sz.T, sub-intestinal vein. C. Section through a primary, and V, section 

 through a tongue-bar. a.ep, atrial epithelium; b.ep^ branchial epithelium; 

 cce, ccelom ; s, skeletal rod ; v^, internal, v^, external, and v'^, coelomic 

 blood-vessels. E. Section through the endostyle. br.a, branchial aorta ; 

 c, median cilia of endostyle ; cce, subendostylar ccelom ; j, skeletal rods. 

 (C, D, and M after Benham.) 



should be noted that in Amphioxus the blood runs forwards in 



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