INTESTINE. 



25 



sally the skeletal rods of both bars bifurcate and arch over the 

 clefts to join the branches of the adjacent bars. Below the 

 endostyle are some flat plates of skeletal tissue, which partially 

 overlap one another. They correspond in number with the 

 primary slits at the lower end of which they are placed, 



FIG. 11. Transverse sections at right angles to the length of the pharyngeal bars of Amphioxus 

 lanceolatm, A of a tongue bar, B of a primary bar (after Benham slightly altered). The 

 relative sizes of the two bars is maintained. 1 endoderm epithelium on the pharyngeal end 

 of a bar ; 2 pigment cells ; 3 coelom of the primary bar in B, coelom or external blood- 

 vessel contained in the skeletal rod of the tongue bar in A (coelom according to Lankester 

 and Benham) ; 4 external blood-vessel of the primary bar f'5 atrial epithelium ; 6 skeletal 

 rod ; 7 somatic blood-vessel ; 8, 9 septal membrane ; 10 visceral blood-vessel. 



The pharynx opens posteriorly into the intestine which' runs 

 straight back to open by the anus placed a little to the left 

 of the median line at the level of the septum between the 51st 

 and 52nd myotome. The anus is provided with a sphincter of 

 striated muscular fibres. The intestine is lined by a columnar 

 ciliated epithelium. The anterior part of the intestine is slightly 

 dilated and called the stomach. It gives off a forwardly directed 



