TEANSVERSE SECTIONS 193 



E. Transverse Section through the Anus. 



1. General characters. The section is much smaller than 



the preceding ones, and more symmetrical in shape. 

 It is oval, with median dorsal and ventral fins, and 

 the notochord occupies its centre. 



The section lies behind the atrial cavity, which is 

 therefore entirely absent. 



The skin and the skeletal, muscular, and nervous 

 systems are practically the same as in B, except that 

 the ventral muscles are absent. 



2. The intestine lies below the notochord, and the anus is 



on the left side of the ventral fin. 



3. The ccelom is a space surrounding the dorsal and lateral 



surfaces of the intestine. 



4. The dorsal aorta is a median vessel in the connective 



tissue below the notochord. 



