4 8 



ANATOMY OF AMPHIOXUS. 



direct communication between the vessels of the tongue- 

 bars and the branchial artery. 



At the base of the primary bars the lateral offshoots of 

 the branchial artery are found to be enlarged to form 

 vascular bulbils, which are also contractile. Furthermore, 

 at this point they divide into three branches of smaller 

 calibre, which constitute the vessels of the primary bar. 



La 



r.a 



Fig. 21. Diagram of a section through the pharynx involving a primary bar 

 (to the left), and a tongue-bar (to the right), to illustrate the circulation in the 

 branchial bars. (After SPENGEL.) 



br.a. Branchial artery, c. Ccelom ; outside of which is the atrial epithelium. 

 c.v. Coelomic vessel of primary bar. e. Endostyle. e.c. Endostylar ccelom. e.v. 

 External vessel, i.v. Internal vessel. La. Left aorta, r.a. Right aorta. /. Cavity 

 of pharynx, t.b. Tongue-bar. 



(Cf. Fig. 15.) One of these branches, as we have seen, 

 runs up between the coelomic and atrial epithelium, and 

 may be called after BOVERI the ccelomic vessel, of the primary 

 bar (Figs. 15 and 21). Another lies at the inner edge of 

 the skeletal rod, and is the so-called external vessel, while 

 a third lies immediately below the inner pharyngeal epi- 

 thelium of the bar, and forms the internal vessel. 



