Pisces. 



169 



The gill openings are separate. The teeth are flat, three- 

 cornered, and sharp. There is a constant succession of 

 teeth, so that as those of the front row are lost, others take 

 their place from behind. Though sharks are very vora- 

 cious, it does not follow that they always attack human 



FIG. 103. SHARK (DOGFISH). 



Showing separate gill slits. Tail heterocercal. 



beings. For instance, on the coast of North Carolina sharks 

 are abundant and of large size ; yet they do not attack man. 

 This is probably because fishes are abundant and the 

 sharks have an ample supply of food. But in some parts 

 of the world sharks are exceedingly dangerous. 



The Rays. The skates and rays have a broad body, 

 partly due to the merging of the body into the large, 

 horizontally flattened pectoral fins. The bo'dy is usually 



A 



FIG. 104. SHARK (DOGFISH), VENTRAL VIEW. 



Showing nostrils, mouth, gill slits, and anus. 



rhomboidal, often wider than long. One form is called 

 the "barn-door skate." They live on the bottom, feeding 

 on mollusks, and have pavement teeth. Some have sharp 



