HYMENOPTERA. TEREBRANTIA. 167 



while in the ovipositor we find the chief character which 

 divides the present from the former family. The antennae 

 are thread-like, or very slender and bristle-like. They 

 possess from ten to twenty-five joints, and the number of 

 joints sometimes varies in the sexes. 



The difference between the ovipositor of the Sawfly 

 and that of the Woodborer presents an instance of the 

 modification of structure to serve an especial end. It 

 is impossible to examine this instrument in the two in- 

 sects without perceiving that correspondence between 

 them which would be looked for in animals so nearly 

 connected, but the appearance of the two instruments is 

 widely different, that of the Sawfly consisting chiefly of 

 two thin and gracefully curved serrated blades, while 

 that of the Borer is apparently a single strong boring 

 implement. This auger, however, is found upon micro- 

 scopic examination to be a kind of sheath, embracing, 

 though not entirely enclosing two stiff serrated bristles 

 which play, as it were, within the borer, and can be 

 partially protruded. These latter are in fact the parts 

 corresponding with the blades of the saws in the Sawfly, 

 while their cylindrical case represents the backs of the 

 saws in that insect. These backs, which in one case 

 strengthen and support two independent saws, in the 

 other, soldered together, form the principal part of the 

 boring instrument. 



The purpose of the variation in the ovipositor requires 

 no explanation when the habit of the Woodborer is 

 known. Not as with the Sawfly, in tender leaves, frnit, 

 or the soft stems of plants, are the eggs of the Sirex to be 

 deposited, but in the substance of sound and solid wood. 

 Indeed, an account is given in the "Zoologist" (5829), 

 taken from some French papers, in which numbers of 



