TYPE PROTOCHORDATA. 



611 



A blood system is present, probably communicating here 

 and there with these lacunae, and containing a colorless blood 

 in which float numerous colorless amcsboid corpuscles. The 

 system consists of a dorsal aorta, single throughout the 

 greater portion of its course, but divided into two trunks over 



Fig. 



279. — Tbansversb Section through the Branchial Kegion of 



Amphioxus (after Lankkstkr and Boveri from Hertwig). 

 a = descending aorta. 

 b = atrial chamber. 

 c = notochord. 

 CO — coelom. 



e = hypobranchial groove beneath 

 which is the ascending aorta. 

 g = reproductive organ 

 kb = branchial arches. 



kd — pharynx. 

 i^p = branchial clefts. 

 ' I = liver. 

 m = muscles. 

 n = nepbridium. 

 r = nerve-cord. 

 sn = nerves. 



the branchial region of the intestine. It sends off branches to 

 various regions of the body which, after breaking up into 

 capillaries, unite again to form the subintestinal or ventral 

 vein, which, passing forwards till it reaches a point in front of 

 the branchial region, becomes sinuous, and gives off a right 

 and left branch to the lips of the larval mouth (the velum), 

 and a third large vessel on the right side which passes dor- 



