INSECTS : STINGS AND OVIPOSITORS. 131 



instrument, on the contrary, is towards the point some- 

 what concave, similar to a scythe, while towards the base 

 it becomes a little convex, the whole edge being nearly 

 the shape of an italic /. 



" 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 simultaneously, 

 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 Yalisnieri, 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 supposes 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 

 themselves denticulated with fine teeth. The latter also 

 K 2 



