TREE-HOPPERS. 131 



metry, increasing in fineness towards the point, where 

 there are three or four very small ones, beside the nine 

 that are more obvious. The magnifier also shows that 

 the instrument itself, which appeared simple to the naked 

 eye, is, in fact, composed of three difi"erent pieces, two 

 exterior armed with the teeth before mentioned, denomi- 

 nated by Eeaumur files (limes), and another pointed like 

 a lancet, and not denticulated. The denticulated pieces, 

 moreover, are capable of being moved forwards and back - 

 wards, while the centre one remains stationary ; and as 

 this motion is 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 

 introduced between the pieces, and pushed very gently 

 downwards, they may be, with no great difiiculty, separated 

 in their whole extent. 



The contrivance by which those three pieces are held 

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

 put in motion, is 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 Ihe 

 files, and play upon two projecting ridges in the central 

 piece, by which means this is rendered stronger. M, 

 Reaumur discovered tliat 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 the 

 files, the handle of each is terminated by a curve of the 

 same hard horny substance as itself, which not only fur- 

 nishes the muscles with a sort of lever, but serves to press, 

 as with a spring, the tv/o files close to the central piece, as 

 is shown in the lower fio'ure. 



o 



