so 



A ANATOMY OF AMPHIOXUS. 



the angle formed by the coecum with the alimentary canal, 

 where the vein bends sharply round into the branchial 

 artery, and so the cycle is completed (Fig, 20). According 

 to Johannes Muller, the time required for one complete 

 circulation of the blood in Amphioxus is one minute, and 

 in this time any given droplet of blood will have traversed 



the whole body. Con- 

 trary to what takes place 

 in the higher Verte- 

 brates, a single contrac- 

 tion of the heart {i.e. 

 branchial artery) in 

 r.a Amphioxus suffices for 

 a complete circulatory 

 cycle.2 



The right and left 

 dorsal aortae differ from 

 one another in respect 

 to the behaviour of their 

 anterior cephalic termi- 

 nations. At the front 



right aorta opens out 

 into a wide vascular ex- 



Fig. 22. — Transverse section through re- 

 gion of velum to show difference in behaviour end of the pharMlX, the 

 of right and left aorta?. (Altered from Lan'- 



GERHANS.) 



ch. Notochord. l.a. Left aorta. /;/. Meta- 

 pleur. V. Spinal cord. r.a. Right aorta, t.jn. 

 Transverse muscles ; the septum (raphe) which pansion which flanks the 

 divides these muscles into two halves is no ,,^i,,..„ ^^ ,-u., • r,*. -j 

 longer median, but shifted towards the right ' '^l"™ «" ^^C riffht Side 

 side in consequence of the fact, discovered by (Kio's, 

 VAN WlJHE.that the right transverse muscles 

 dwindle out and end in this region, while the JohaniieS Mliller, who 

 left transverse muscles are continued into the c », c i i.i ■ i. 



outer muscle of the oral hood. -..Velum. ^'^t figured this Struc- 



ture, took it for the an- 

 teriormost aortic arch connecting the branchial artery 

 directly with the dorsal aorta. 



However, according to the recent researches of Professor 



3 and 22, r.a). 



