114 CLASS-BOOK OF ZOOLOGY. 



§ 469. How was the electric power of the Torpedo ascertained ? 



§ 470. What is the external character of the Shark ? 



§ 471. What do you know of the teeth of the Shark? 



§ 472. Why may Sharks be called the Tigers of the sea, and what * 

 the cause of their insatiable voracity ? 



§ 473. What do you know of the sense of smell in Sharks? 



§ 474. What is the size and weight of the Shark ; and where is it found 1 



§ 475. What do you know of the eggs of Sharks ? 



§ 476. What use is made of Sharks V 



§ 477. Why is the Saw-fish so called ? Describe its saw. 



§ 478. What is the length of a Saw-fish and its saw ? 



§ 479. What is said of the courage of the Saw-fish ? Where is this fish 

 found? 



§ 480. What do you know of the Hammer-headed Shark? 



SECTION XXVII. 



•2d Order — Cartilaginous Fishes with covered gills : 

 (BrancMostegi.) 



\ 481. Those cartilaginous fishes, the gills of which 

 -are covered with a membrane, belong to this Order ; as, 

 for instance, the Sturgeon. 



\ 482. The Sturgeon (Accipenser) has a cartilaginous 

 skeleton, covered with gills, and a mouth, like that of the 

 .Shark, placed far below, but without teeth. 



\ 483. Sturgeons are very large, some of them being 

 smore than twenty-five feet long ; but they are defenceless. 

 They feed on herring, mackerel, worms, and water-insects, 

 and are found in all the seas of the world. 



\ 484. The Sturgeon, towards spring, ascends the rivers 

 to deposit its roe, which is remarkable for its quantity and 

 the number of its eggs ; one hundred and fifty millions 

 having been found in a single roe. 



\ 485. These eggs are a considerable article of com- 

 merce with many people, but principally with the Cossacks 

 of the Don and the Black Sea, who salt and press them, 

 and export them in large cakes, like cheese ; in which form 

 they are known by the name of Caviar in all parts of the 

 world, and esteemed as an excellent article of food. 



