NATURAL SAWS. 



241 



set along one side of a stick. It looks a rude and inefficient 

 affair enough, but it can cut better than might have been 

 thought, as I can testify from experiments on such a saw in 

 my collection. 



Many as are the varieties of the Saw, the principle is the 

 same in all, and the chief distinction lies in the shape and 

 arrangement of the teeth, according to the work which they 

 have to do. Watch-spring Saws, for example, which have to 

 cut metal, have their teeth so slight as to be hardly per- 

 ceptible, and arranged nearly in a line with each other. The 

 Fretwork Saws, which have to cut delicate patterns in wood, 



r — 'sa 



==7> 



SAW OP COMMON SAW-FLY (MAGNIFIED). 

 GROOVES CUT BY SAW IN BARK. 



HAND- SAW. 

 TENON SAW. 

 PIONEER'S SAW 



with the slightest possible waste of material, are of the same 

 character. Then we have the long curved teeth of the 

 Circular Saws, which tear their way savagely through great 

 tree-trunks, and fill the air with clouds of sawdust. There 

 are also the Tenon Saw, with its thin blade and broad back ; 

 the pioneer's saw for cutting green wood, with its double 

 array of teeth, so as to make a wide "kerf" in which it shall 

 not be clogged ; together with many others that we cannot 

 enumerate here. 



We will now examine some Saws as found in Nature. 



I need scarcely say that some of the best examples of natural 

 saws are furnished by those insects which are known to ento- 

 mologists as Tenthredinidae, and to the general world as Saw- 

 flies. These insects are supplied by Nature with a pair of 



R 



