Saiv-Flies. 171 



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, how- 

 ever, not only all move upwards and downwards simulta- 

 neously, 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 a 

 saw with a wide set. 



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 saws requires. 

 According to Yallisnieri, 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 it 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 



Portion of a Saw- Fly's comb-toothed rasp, and saw. 



denticulated with fine teeth. The latter, also, combines at 

 the same time the properties of a saw and of a rasp or file. 

 So far as we are aware, these two properties have, never been 



