BLOOD SYSTEM. 



37 



In the lowest of all fishes, if fish it may be called 

 viz., the lancelet (amphioxus), the enormously larg 



Fig. 252. — Anterior portion of a shark (CarcAartas), showing the five gil 

 openings. 



throat has many — twenty or more — slits, edged with im 

 perfect fringes (Fig. 255). 



Going up now the other way, in ganoids, such as th< 

 garfish or bony pike (Lepidosteus) of our American fresl 

 waters, and in the Polypterus of the Nile, we have ar 

 opercle and gills like the teleosts, but gill breathing i: 



Fig. 253. — Petromyzon marius, showing the seven branchial openings. 

 (After Cuvier.) 



supplemented by a little air breathing by means of aii 

 taken into a vascular air bladder (Fig. 256). 



Finally, in the most reptilian of all fishes, such as th( 

 protopterus of Africa, the lepidosiren of South America 



