32 THE STORY OF FISH LIFE. 



known as "denticles" or "odontoids" — little 

 teeth (p. 34). We shall show in the next chapter, 

 furthermore, that there is more than a resem- 

 blance in the likeness between the teeth and 

 scales ; that the two, in short, are really to all 

 intents and purposes identical. 



In some of the rays, or skates, as they are 

 more commonly called, and in the spinous shark 

 (Echinorhinus), these primitive scales are dis- 

 tributed unevenly over the body, sprinkled over, 

 we might almost say, and vary much in size. 

 But in the dog-fishes and sharks, where the 

 scales are very small, they are arranged more 

 definitely, generally running in oblique rows 

 from the middle of the back downwards and 

 backwards. It is this closely- packed mass of 

 tiny "scales" which furnishes us with w^iat is 

 known as "shagreen." 



In the Orkneys, Dr Gunther tells us, the 

 "larger" and "lesser spotted dog-fish" are 

 captured in large numbers. Their skins are 

 removed, spread on the rocks to dry, and used 

 for smoothing down cabinet-work — in place of 

 the more general sand-paper. 



There is yet a third form of scale, which we 

 may regard as intermediate between the horny 

 somewhat disc-like plates which are noticed in 

 the roach, and the spine-bearing nodular scale 

 which we have just described in the sharks and 

 rays. The third form is found in certain very 

 ancient types of fishes once very numerous, but 

 now represented by only a very few living forms. 

 It can best be studied in the " gar-pike " of the 

 fresh waters of North America, or in the 



