SHARKS 311 



and closely packed together. When the skin of a shark is 

 stroked from head to tail, it feels like a hair-cloth sofa, but 

 when stroked the other way, it is like the sharpest sand-paper. 

 For centuries shark-skin has been used for smoothing and 

 polishing wood and other substances; and when prepared for 

 that use it is called "shagreen." 



Instead of one very large gill-opening, as in typical fishes, 

 a shark has usually five small slits in the skin behind the 

 gills, which are capable of being tightly closed. In nearly all 

 species the mouth is situated underneath the head, and often 

 it is of enormous proportions. The jaws are composed of 

 cartilage, the teeth are usually triangular and set along the 

 edge of the jaw, in rows, crosswise with the edge of the mouth. 

 Behind each active and visible tooth there is a line of reserves, 

 from three to five in number, always growing outward and 

 crowding to the front, so that as soon as a tooth in the line 

 of battle becomes much worn, or in any way weakened or 

 broken, it is crowded off the jaw, and a new tooth is thrust 

 forward into its place. 



Many sharks bring forth their young alive; but others 

 (the majority, perhaps) lay eggs. Some of the egg cases are 

 of remarkable form. Some of them are rectangular, flat- 

 tened and provided at each corner with a long, threadlike 

 tendril with which to attach to any fixed object. 



Sharks very rarely exhibit color patterns, or bright colors 

 of any kind. As befits pirates and freebooters, they are 

 mostly ashy gray, or drab the most inconspicuous colors at 

 sea, both for sharks and men-of-war. The small Tiger Shark, 

 of Ceylon (Stegastoma tigrinum), is one of the few sharks of 



