RESPIRATORY AND VASCULAR SYSTEMS. 471 



victim, and adheres like a vacuum sucker ; the toothed 

 " tongue " works like a piston ; both flesh and blood are 

 thus obtained. From the floor of the pharynx a groove is 

 constricted off (cf. p. 450). 



From the gullet of the young larva seven gill pouches 

 open directly to the exterior ; but in the adult this larval 

 gullet becomes wholly a respiratory tube. - It is closed 

 posteriorly, and opens anteriorly into the gullet of the adult, 

 which is a new structure. At the junction of the re- 

 spiratory tube with the gullet of the adult, lie two flaps 

 or vela. 



The rest of the gut is straight and simple, with a single- 

 lobed liver, but without a pancreas. There is a slight fold 



FIG. 152. Longitudinal vertical section of anterior end 

 of larval lamprey. (After BALFOUR). 



w., Mouth ; th., thyroid ; g*p>, one of the gill pouches ; v.a.0., ven- 

 tral aorta ; h., heart ; N., notochord ; S.C., spinal cord ; ., audi- 

 tory vesicle; cb., cerebellum; /.., pineal body; ch., cerebral 

 hemispheres ; olf., olfactory involution. 



in the intestine, which may be compared with the spiral 

 valve of Elasmobranchs. 



Respiratory System. 



Seven gill pouches with plaited walls open directly to the 

 exterior on each side, and communicate indirectly with the 

 gullet as already described. 



When the lamprey is sucking a victim, and perhaps at 

 other times, water passes in as well as out by the external 

 openings of the gill pouches. In the larva there is an eighth 

 most anterior pouch which does not open to the surface. It 

 corresponds to the spiracle of Elasmobranchs. 



