HYMENOPTERA. 407 



ptera which arc actually or seriously injurious to vegetation. 

 Those which I propose now to describe are not provided with 

 venomous stings, and, consequently, are to be included among 

 the Piercers. 



Such arc the saw-flies (Tenthredinid^), insects that arc 

 found on the leaves of plants, and live almost entirely on vege- 

 table food. They are the least active of the Hymenoptera, are 

 sluggish in their habits, fly heavily and but little, and do not 

 attempt to escape when touched. Most of them are rather 

 short and somewhat flattened. They have a broad head, 

 which, seen from above, appears transversely square. The 

 hind body is not narrowed to a point where it joins the tho- 

 rax, but is as broad as the latter, and is closely united to it. 

 The antenna? are generally short; but they vary much in form; 

 in many species they are threadlike and slightly tapering; in 

 some, thickened or knobbed at the end ; more rarely they end 

 suddenly with a few very small joints, much more slender than 

 the rest; they are feathered in some males, and notched in the 

 other sex ; and sometimes they are forked, or divided into long 

 branches. Their wings cross and overlap each other, and cover 

 the back horizontally when closed. But the most striking 

 peculiarity of these insects consists in the double saws where- 

 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 tsvo, naiTOw, scab- 

 bard-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 the under side of the body that they can be withdrawn from 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 transverse rows of very fine teeth, giving to 

 it the power of a rasp, as well as that of a saw. 



