TNSECT ARCHITECTURE. 



stand a little to the right, and the other half a little 

 to the left. The distance of the two parallel lines 

 thus formed is called the course of the saw, and it 

 is only the portion of wood which lies in the course 

 that is cut into sawdust by the action of the instru- 

 ment. It will follow, that in proportion to the thin- 

 ness of a saw there will be the less destruction of 

 wood which may be sawed. When cabinet-makers 

 have to divide valuable wood into very thin leaves, 

 they accordingly employ saws with a narrow course ; 

 while sawyers who cut planks, use one with a broad 

 course. The ovipositor-saw being extremely fine, does 

 not require the teeth to diverge much, but from the 

 manner in which they operate, it is requisite that they 

 should not stand like those of our saws in a straight 

 line. The greater portion of the edge of the instru- 

 ment, on the contrary, is towards the point some- 

 what cancave, similar to a scythe, while towards the 

 base it becomes a little convex, the whole edge being 

 nearly the shape of an Italic /. 



Mpositurmw of Saw-fly, with ratpi shtwn in tht erott '' 



