GALL-FLIES. 



325 



rest; but in others, not above a line or two of it is Tisible, 

 till the belly of the insect be gently pressed. When this is 

 done to the fly that produces the currant-gall of tlie oak, 

 the ovipositor may be seen issuing from a sheath in form of 

 a small curved needle, of a chestnut-brown colour, and of 

 a horny substance, and three times as long as it at first 

 appeared. 



Gall-fly, and mechanism of ovipositor, greatly magnilied. 



What is most remarkable in this ovipositor is, that it is 

 much longer than the whole body of the insect, in whose 

 belly it is lodged in a sheath, and, from its horny nature, it 

 cannot be either shortened or lengthened. It is on this 

 account that it is bent into the same curve as the body of 

 the insect. The mechanism by which this is effected is 

 similar to that of the tongue of the wood-peckers (^Picidce), 

 which, though rather short, can be darted out far beyond 

 the beak, by means of a forked bone at the root of the 

 tongue, which is thin and rolled up like the spring of a 

 watch. The base of the ovipositor of the gall-fly is, in a 

 similar way, placed near the anus, runs along the curvature 

 of the back, makes a turn at the breast, and then, following 

 the curve of the belly, appears again near where it origi- 

 nates. We copy from Reaumur his accurate sketch of this 

 remarkable structure. 



