TEE 8HABKS. 



147 



sharks owe their prosperity in life to their great size, great 

 Titality, and to the abundance of weaker animal life of all 

 descriptions which they can find in all situations; and when 

 their food at the bottom gives out, they rise to the surface 

 and chase schools of herring, mack- 

 erel, etc. Their home is the sea, 

 which has undergone little change 

 since the time when the first shark 

 lived. 



The eggs of sharks and rays are 

 very large compared with those of 

 bony fishes. The Cestracion (Fig. 

 153) is an old-fashioned form, which 

 inhabits the Australian seas. It 

 should be noticed that its mouth is 

 placed well forwards, near the end 

 of the head, and the teeth are round- 

 ed, while in the genus Carcharias 

 (Fig. 154) it is much larger and 

 placed further back under the head, 

 the teeth being sharp, flattened, and 

 conical. Nearly all the sharks are 

 bottom feeders, grubbing up the 

 shell-fish as well as flounders and 

 other fish which remain at the bot- 

 tom; when they rise near the sur- 

 face and chase the surface-swim- 

 ming fish, or try to seize a man over- 

 board, they have to turn upon their 

 backs in order to grasp their victim. 



Of the rays and skates, the saw- 

 fish (Pristis antiquorum) is most 

 like the sharks. Its snout is pro- 

 longed into a long, flat, bony blade, armed on each side 

 with large teeth (Fig. 155). The common sawflsh inhab- 

 its the Mediterranean Sea and the Gulf of Mexico; it is 

 viviparous. 



The genuine skates or rays have the body broad, flat, and 



Fig, 



_ 155— Beak of Sawflsh 

 seen from below, showing 

 its mouth, nostrils, and 

 lateral teeth. 



