204 MINUTE MARVELS OF NATURE 



species prefer even to deposit their eggs within 

 the eggs of their victims. 



Another form of insect weapon one would hardly 

 expect to find is a saw for perforating the branches 



Fig. 137. The saw-fly's weapon 



of trees (Fig. 136). These tiny saws, the backs 

 of which work in grooves alternately, are used by 

 saw-flies for the same purpose as the weapon of 

 the ichneumon fly namely, for cutting inci- 

 sions in which to deposit eggs. The only differ- 

 ence between them is that in this case a saw is 

 used upon wood-tissue instead of a bayonet 



