158 EVENINGS AT THE MICROSCOPE 



tip only bears saw-teeth, and these are directed backward, 

 but one side of the entire length presents a succession of 

 cutting edges, as if a number of short pieces of knife -blades 

 had been cemented on a rod, in such a manner as that the 

 cutting edges should be directed backward, and overlap 

 each other. The other lateral surface is plain, and both 

 are convex in their general aspect. The appearance of 

 these implements is very beautiful; for the texture is of a 

 clear pale amber, but the structure is strengthened by a 



OUTER SAW OP SAW-FLY. 



a, A portion more enlarged. 



band which runs along each edge, and by transverse bands 

 crossing at regular intervals, of a denser tissue; and these 

 are of a rich golden translucent brown. 



From the construction of this implement I should infer 

 that its force is exerted in pulling and not in pushing; the 

 direction of the teeth and of the cutting plates shows this. 

 The sharp horny point is probably thrust a little way into 

 the solid wood or bark, and then a backward pull brings 

 the teeth and cutting plates to act upon the material, and 

 so successively. And probably these points are the first 

 parts of the whole apparatus that come into operation; the 

 blunter saw of the sheath serving mainly to widen and 



