150 



THE LANCELET 



(iii) The branchial coelomic canals in the gill-arches. 



(iv) The ventral or endostylar ccelomic canal, in the ventral region 



of the pharynx, 

 (v) The gonad sacs. 



(l) The right and the left dorsal aortse, one at each side of the epibranchial 

 groove. 

 (to) The ventral aorta lying beneath the endostyle. 

 (n) The hepatic veins of the liver. 



2. In a section taken through CD (the intestinal region) in Fig. 49, the 

 following parts may be seen : — 



(a) The section has the shape of an oval, the dorsal and ventral fins 



occupying the extremities of the long diameter. 

 The atrial cavity is absent, the section passing through behind it. 

 The integument, muscles, notochord, and spinal cord are the same as in 



the first section, except for the absence of the ventral muscles. 



(b) The intestine, l5ang just beneath the notochord, is a tube, oval in shape. 



(c) The ccelome, surrounding the intestine except dorsally. 



(d) The dorsal aorta between the notochord and the intestine. 



(e) The sub-intestinal vein below the intestine. 



-Dorsal fin 

 -Fin ray 



Connective tissue- 

 Ventral nerve' 

 Myotome 



Epibranchial 

 groove-- 



Dorsal 

 coelom--- 



Pharynx- 



Gonad 



Branchial 



coelom*- 

 Endostyle 

 with cilia—- 



Metapleural fold*' 



Ventral aorta 



—Atrium 

 -Tr:in3verse muscles 



Ventral tin-.-. 



A 



Endostylar coelom 



SubintcBtinal 

 vein 



Fig. 50. —Amphioxus. A. Transverse Section through the pharyngeal region of the body ; 

 B, Transverse Section through the intestinal region. A., after Shipley and MacBride; 

 B., after Wells and Davies. 



