THE CEPHALOCORDA 185 



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



D. 



Fig. 45 



A. Anterior portion of the nerve cord of Amphioxus, after Schneider. cn\, ctfi. 

 first and second pairs of " cranial " nerves ; rfV 1 , dorsal roots of the first pair, and 

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

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

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

 aorta ; br.a, branchial aorta ; ef, efferent branchial vessel ; hep, hepatic 

 diverticulum ; hv, hepatic vein ; nek, nptochord ; pb, primary bar ; tb, tongue- 

 bar ; si.7>, sub-intestinal vein. C. Section through a primary, and D, section 

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

 ca?, coelom ; s, skeletal rod ; v l , internal, z/ 2 , external, and z^ 3 , ccelomic 

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

 c, median cilia of endostyle ; coe, subendostylar coelom ; s, skeletal rods. 

 (C, D, and E after Benham.) 



should be noted that in Amphioxus the blood runs forwards in 



