insects: stings and ovipositors. 131 



of the edge of the instrument, on the contrary, is 

 towards the point somewhat concave, similar to a scythe, 

 while towards the base it becomes a little convex, the 

 whole edge being nearly the shape of an italic f. 



" The ovipositor-saw of the fly is put in motion in the 

 same way as a carpenter's hand-saw, supposing the 

 tendons attached to its base to form the handle, and the 

 muscles which put it in motion to be the hand of the 

 carpenter. But the carpenter can only work one saw at 

 a time, whereas each of these flies is furnished with 

 two, equal and similar, which it works at the same time 

 — one being advanced and the other retracted alternately. 

 The secret, indeed, of working more saws than one at 

 once is not unknown to our mechanics ; for two or three 

 are sometimes fixed in the same frame. These, however, 

 not only all move upwards and downwards simultane- 

 ously, but cut the wood in different places : while the 

 two saws of the ovipositor work in the same cut, and, 

 consequently, though the teeth are extremely fine, the 

 effect is similar to [that of] a saw with a wide set 

 [or course]. 



" It is important, seeing that the ovipositor-saws are 

 so fine, that they be not bent or separated while in 

 operation ; and this also nature has provided for by 

 lodging the backs of the saws in a groove, formed by 

 two membranous plates, similar to the structure of a 

 clasp-knife. These plates are thickest at the base, 

 becoming gradually thinner as they approach the point 

 which the form of the saw requires. According to 

 Valisnieri, it is not the only use of this apparatus to 

 form a back for the saws, he having discovered between 

 the component membranes two canals, which he sup- 

 poses are employed to conduct the eggs of the insect 

 into the grooves which she has hollowed out for them. 



" The teeth of a carpenter's saw, it may be remarked, 

 are simple, whereas the teeth of the ovipositor-saw are 



k 2 



