516 HYMENOPTEEA, 



with the females are provided. These are lodged in a deep 

 chink under the hinder part of the body, like the blade of 

 a penknife in its handle, and are covered by two narrow, 

 scabbard-like pieces. The saws are two in number, placed 

 side by side, with their ends directed backwards, and are 

 so hinged to the under side of the body that they can be 

 withdrawn from the chink, and moved up and down when 

 in use. They vary in their form, and in the shape of their 

 teeth, in different kinds of saw-flies ; but they generally 

 curve upwards and taper towards the end, and are toothed 

 alone; the lower or convex edges. Each of the saws, like 

 a carpenter's fine saw, has a back to steady it ; the blade, 

 however, is not fastened to the back, but slides backwards 

 and forwards upon it. Moreover, the saw-blade is not only 

 toothed on the edge, but is covered, on one side, with trans- 

 verse rows of very fine teeth, giving to it the power of a 

 rasp, as well as that of a saw. 



The female saw-flies use these ingeniously contrived tools 

 to saw little slits in the stems and leaves of plants, wherein 

 they afterwards drop their eggs. Some, it appears, lay 

 their eggs in fruits ; for Mr. Westwood discovered their 

 young within apples that had fallen from the trees before 

 they had grown to the size of walnuts. The wounds made 

 in plants by some kinds of saw-flies swell, and produce galls 

 or knobs, that serve for habitations and for food to their 

 young. The eggs, themselves, of all these flies, are found 

 to grow, and increase to twice their former size after they 

 are laid, probably by absorbing the sap of the plant through 

 their thin shells. 



Most of the larvae or young of the saw-flies strikingly 

 resemble caterpillars, being usually of a cylindrical form, 

 of a greenish color, and having several pairs of legs. Hence 

 they are sometimes called false caterpillars. With the ex- 

 ception of such as belong to the genera Lyda and Cephus, 

 in which the legs are only six, and the prop-legs are entirely 

 wanting, these false caterpillars have a greater number of 



