xii PHYLUM CHORDATA 361 



true Fishes. In the Lamprey each of these communicates 

 with the exterior by the corresponding gill-slit, and inter- 

 nally opens into a common passage the respiratory tube 



oes.cl.d 



FIG. 208. Head of Myxine glutinosa (A) and of Bdellostoma forsteri (B), from 

 beneath, br. np. branchial aperture ; br. cl.i, first branchial cleft ; inth. mouth ; 

 no.. af>. nasal aperture ; as. ct. d. cesophageo-cutaneous duct. The smaller 

 openings in A are those of the mucous glands. (After W. K. Parker.) 



(Fig. 209, r. /.) which leads in front into the buccal cavity. 

 In Bdellostoma each gill-pouch has its own internal 

 opening through a narrow tube into the pharynx, as 



