568 



COMPARATIVE ANATOMY 



CHAP. 



The partitions between the consecutive gill -pouches are called 

 septa, and the edges of these which are turned to the intestine are 

 the septal edges. If a lateral wall of the branchial intestine be 

 viewed from the intestinal cavity, the septal edges and branchial 



Fig. 458. — Ptychodera minuta, transverse section through the branchi.il region, somewhat 

 diagrammatic (after Spengel). 1, Dorsal nerve cord ; 'i, dorsal hlood vessel ; 3, branchial furrow ; 

 4, body epithelium ; 5, gonad ; 6, longitudinal muscle layer of the integument ; V, ventral blood 

 vessel ; 8, ventral nerve cord ; 9, ccelom of the trunk ; 10, genital pore ; 11, branchial pore ; 12, 

 branchial tongue ; 13, dividing ridges ; 14, branchial septum ; 15, cavity of the branchial intestine ; 

 16, CBsophagus. 



tongues are seen regularly alternating. The septa, like the tongues, 

 are hollow, their cavities communicating with the ca>lom of the trurdv. 

 But whereas the septal edges are continued both dorsally and ventrally 

 into the wall of the intestine, the edges of the tongues turned towards 

 the intestine, the so-called backs of the tongues, are, of course, only 

 in connection with the intestinal wall dorsally. 



