72 THE WOODPECKERS 



tip ? Can the bird pick as well as he could 

 with a sharp point? The bird and the mason 

 reap the same benefit from this form of tool. 

 A sharp-pointed drill would bind in the hole 

 and could neither be driven ahead nor removed 

 without difiiculty, but the sharp-edged tool cuts 

 a hole as wide as the instrument. There is, of 

 course, some difference between working in stone 

 and in wood, but the principle is the same. The 

 mason strikes his drill with his hammer and cuts 

 a crease in the stone ; then lifts and turns the 

 drill, cutting a crease in another direction ; and 

 so by continually changing the direction of the 

 cuts until they radiate from a centre like the 

 spokes of a wheel, he finally reduces a little 

 circle of stone to a powder fine enough to be 

 blown out of the hole. In drilling for a grub 

 the woodpecker must do much the same thing. 

 He wishes to keep his hole small at the top so 

 as to save work, yet it must be large enough 

 at the bottom to admit the borer when nipped 

 between his mandibles ; therefore he needs an 

 instrument that, like a drill or a chisel, will cut 

 a straight-sided hole. Indeed, we might call it 

 a chisel just as well if it were not a double- 

 wedge instead of a single wedge and if it did 

 not move when it is struck instead of being 

 held stationary beneath the blows. 



