ANATOMY OF AMPHIOXUS. 



n 



the angle formed by the ccecum 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 aortas differ from 

 one another in respect 

 to the behaviour of their 

 anterior cephalic termi- 

 nations. At the front 



Fig. 22. Transverse section through re- rut. 



gion of velum to show difference in behaviour end Of the pharynx, the 



m 



ch. Notochord. La. Left aorta, m. Meta- into a wide Vascular 6X- 

 pleur. n. Spinal cord. r.a. Right aorta, t.m. . . 



Transverse muscles ; the septum (raphe) which pailSlOn which f 



divides these muscles into two halves is no ypJjjjY) QJ-J the ri"ht side 

 longer median, but shifted towards the right 



side in consequence of the fact, discovered by (FigS. 3 and 22, I'.a.). 

 VAN WlJHE, that the right transverse muscles . T\T 11 u 



dwindle out and end in this region, while the Johannes Muller, Wh 



left transverse muscles are continued into the j-gj- fjo-ured this StrUC- 

 outer muscle of the oral hood. v. Velum. 



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 



