136 EVENINGS AT THE MICROSCOPE. 



two inner lancets seem to be united in one, in Reaumur's 

 species, or else, which I think more probable, he did not 

 succeed in separating them. 



He describes the two curved spoon-shaped pieces as 

 finely indented on both sides with teeth, which are strong, 

 nine in number, arranged with great symmetry, increasing 

 in fineness towards the point. This instrument he de- 

 scribes as composed of three pieces, the two exterior, 

 which he calls the files, and another pointed, which he 

 compares to a lancet, which is not toothed. "The files 

 are capable of being moved forward and backward, while 

 the central one remains stationary ; and as this motion can 

 be effected by pressing a pin or the blade of a knife over 

 the muscles on either side at the origin of the ovipositor, it 

 may be presumed that those muscles are destined for 

 producing similar movements when the insect requires 

 them. By means of a finely-pointed pin carefully intro- 

 duced between the pieces, and pushed very gently down- 

 wards, they may be, with no great difficulty, separated in 

 their whole extent. 



" The contrivances by which those three pieces are held 

 united, while at the same time the two files can be easily 

 put in motion, are similar to some of our own mechanical 

 inventions, with this difference, that no human workman 

 could construct an instrument of this description so small, 

 fine, exquisitely polished, and fitting so exactly. We should 

 have been apt to form the grooves in the central piece, 

 whereas they are scooped out in the handles of the files, 

 and play upon two projecting ridges in the central piece, 

 by which means this is rendered stronger. M. Reaumur 

 discovered that the best manner of showing the play of 

 this extraordinary instrument is to cut it off with a pair of 

 scissors near its origin, and then, taking it between the 

 thumb and the finger at the point of section, work it gently 

 to put the files in motion. 



"Beside the muscles necessary for the movement of 



