4 GIANT FISHES 



denticles in situ, are used by carpenters and cabinet-makers, 

 as well as by metal-workers and others, while the dyed skins, 

 suitably prepared, provide a handsome shagreen for ornamental 

 purposes. With the denticles removed, and after undergoing 

 a special tanning process, the skins of certain Sharks and Rays 

 provide a strong and durable leather, and there is nowadays 

 a brisk demand for shoes, bags and other articles made from 

 this commodity. 



All the existing Sharks are grouped into a single order, the 

 Pleurotremata (literally " side openings "), and may be readily 

 distinguished from the Rays, which form the second order of 

 existing Selachians, the Hypotremata (literally " under 

 openings "), by the position of the external gill-clefts, which 

 are placed on the sides of the head ; by the free front edges 

 of the pectoral fins, which are never joined to the sides of the 

 body or head ; and by the distinct margins of the eyes. The 

 order Pleurotremata includes a number oi genera and species, 

 ranging from veritable monsters 50 feet or more in length to 

 comparative dwarfs scarcely more than 2 feet long. Sharks 

 are to be found in nearly all the seas of the world, and at most 

 depths ; a few even ascend rivers beyond the influence of the 

 tides, and at least one lives permanently in fresh water. The 

 great majority are active animals, chasing and hunting down 

 their prey, aided by a very well-developed sense of smell. All 

 have a carnivorous diet, but the food taken varies from shellfish 

 and tiny shrimp-like creatures to fishes, marine mammals and 

 even man himself, and includes also a good deal of carrion 

 and garbage. Most of the larger Sharks are viviparous, that is 

 to say the eggs hatch within the body of the mother and 

 the young are brought forth alive, but many of the smaller 

 kinds produce large yolky eggs, which are deposited in horny 

 protective cases. 



COMB-TOOTHED OR COW-SHARKS. 



(Family Hexanchid^e.) 



Sharks with a comparatively long body and a long unequally 

 lobed tail. The snout is pointed and overhangs the mouth, 

 which is large and not connected by grooves with the nostrils. 



