CHAPTER LXII 



THE ORDER OF SHARKS 



SQVALI 



We have now reached the suljclass of Carti- 

 laginous Fislics. 



And what is a " car-ti-hig'i-nous fish? " 

 Cartilage is a bloodless tissue, commonly called 

 qriMc, fiexible but not elastic, ciuite colorless, of 

 the consistency of clieesc-rind, and of use in the 



1. MACKEREL SHARK, WITH HEIIDRA ATTACHED. 

 2. lIAlhMER-HEAU WHAKK. 



anatomy of animals for sustaming or connecting 

 softer parts. Tlie external ear of man consists 

 chicHy of a convoluted wing of cartilage covered 

 Willi skin. The so-called "breast-bone" of man 



is a tree-like development of cartilage designed 

 to bridge together the outer ends of the principal 

 ribs, protect with some firmness the ^'ital organs 

 within, and yet permit the rise and fall of the chest 

 in breathing. 



The Cartilaginous Fishes, embracing the .sharks, 

 rays, skates and intermediate forms, 

 are those whose skeletons are largely 

 composed of plates and stems of car- 

 tilage, or gristle and but little bone. 

 Instead of bony rays, the fins of 

 these creatures are supported by 

 cartilaginous rays so closely joined 

 together that they form plate-like 

 structures. 



General Characters of Sharks. — 

 With few exceptions, sharks ha^'e ex- 

 ternally the same general form as the 

 typical fishes. Instead of broad, flat 

 scales that overlap each other like 

 sliingles, their scales are very mi- 

 nute, horny, sharp-pointed 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 

 .sharj^est sand-paper. For centuries 

 shark-skin has been used for smooth- 

 ing and polishing wood and other 

 substances; and when prepared for 

 that use it is called "shagreen." 



Instead of one ^'cry large gill-open- 

 ing, as in typical fishes, a shark has 

 usually five small slits in the skin be- 

 hind the gills, whicli are capal)le of 

 feeing tightly closed. In nearly all 

 species the mouth is situated under- 

 neath 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 



432 



