214 AMPHIOXUS 



folds of the pharynx ; and is continued downwards 

 over the inner surfaces of the atrial folds, covering 

 the reproductive organs, and being thrown into folds 

 along the ventral wall of the atrial cavity. It also 

 forms an investment to the liver. 



4. The coelom is still more subdivided than in section B ; 



its main divisions are as follows : 



a. The dorsal coelomic canals are a pair of large 



spaces above the suspensory folds of the pharynx, 

 as in section B. 



b. The branchial coelomic canals are a series of cavi- 



ties in the primary branchial bars, as in section B. 



c. The endostylar coelomic canal is a median space in 



the endostyle. 



d. A space surrounding the liver, between its proper 



wall and the atrial epithelium, is part of the 

 ccelom. 



e. Paired spaces immediately surrounding the repro- 



ductive organs are also extensions of the coelom. 



5. A pair of large metapleural canals lie in the lateral fins. 



6. The circulatory system. 



a. The cardiac aorta, the dorsal aortse, and the aortic 



arches are as in section B. 



b. The portal veins he on the liver, in the coelomic 



space surrounding it. They are often difficult to 

 identify in transverse sections. 



c. The hepatic veins are three or four vessels lying 



side by side on the dorsal surface of the liver, 

 in the coelomic space between the liver and the 

 atrial membrane investing it. 



7. The reproductive organs occupy similar positions in the 



two sexes. They are masses, varying in size accord- 

 ing to the degree of ripeness of the ova or sperma- 

 tozoa, lying on the inner sides of the atrial folds, 

 and projecting into the atrial cavity. 



