516 
HYMENOPTERA. 
witli 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withdrawn from the chink, and moved up and down when 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 
along 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 
Ik 
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 larvoe or young of the saw-flies strikingly 
resemble caterpillars, being usually of a cylindrical form, 
of a greenish color, and having seA^eral 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 
