266 NATURE'S TEACHINGS. 



Skate, Saw-fish, &c. I have now before me a small, but perfect 

 example of the Saw-fish, the surface of which is covered 

 with flinty scales like those of the Dog-fish, but very much 

 smaller, requiring the aid of a magnifying lens to distinguish 

 them. Even to guess at the number of them is impossible, 

 for they cover the whole of the body, and extend to the very 

 end of the beak, in some places glittering in a strong light as if 

 pounded glass had been sprinkled all over the fish. One of the 

 most interesting points in their structure is the manner in 

 which they reach the rounded jaws, and there become con- 

 verted into teeth powerful enough to crush the animals on 

 which the fish live. The structure of these jaws will be 

 explained in a future chapter. 



Some of the skates and sharks have these scales of great 

 size, so as to show their formation almost without the aid of a 

 magnify ing- glass. This is the case with a species of skate, the 

 skin of which is used by the Japanese for wrapping round the 

 handles of their best swords, and which is greatly valued by that 

 nation, the sword being an almost sacred article in the eyes of 

 a Japanese. 



There is a well-known museum in which these swords are 

 labelled as having handles of "granulated ivory." Now, in 

 the first place, there is no such thing as granulated ivory ; and, 

 in the next, a mere glance ought to tell the observer that 

 the so-called ivory is a skin of some sort, worked upon the 

 handle while wet, and kept in its place by copper studs. Even 

 the junction of the edges is perceptible, and yet the authorities 

 of the museum in question, although they have been repeat- 

 edly corrected, still persist in calling the skate-skin by the 

 absurd title of granulated ivory. 



However, if ivory could be granulated, it would certainly 

 look very much like the skate- skin. When examined closely, 

 the scales, whether of Dog-fish, Skate, Shark, or Saw-fish, are 

 seen to resemble hexagonal cones, not coming quite to a 

 point, but truncated, so as to have an hexagonal flattened tip. 

 They are almost of a flinty hardness, especially at their tips, 

 and on inspection of them the observer is not surprised at the 

 use of Dog-fish skin in place of sand-paper. 



Perhaps the reader may ask why the Equisetum should be 

 taken as the prototype of the file, and the skin of the Dog-fish 



