PART III 

 VERTEBRATA 



15. PISCES 



THE four chief orders of this class are the round-mouthed 

 fish (Cyclostomata), the cartilaginous fish (Elasmobranchii) , 

 the bony fish (Teleostomi), and lung fish (Dipnoi). 



FIG. 215. Ocean lamprey. Photograph one fourth natural size. The holes oi\ 

 the side behind the eyes are the gill openings. 



135 



