DTSECTS : STINGS AND OVIPOSITORS. 147 



insect be gently pressed. When this is done to the fly 

 that produces the currant-gall of the oak, the ovipositor 

 may be seen issuing from a sheath in form of a small 

 curved needle, of a chesnut-brown colour, and of a 

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

 appeared. 



" "What is most remarkable in this ovipositor is, 

 that it is much longer than the whole body of the in- 

 sect, in whose belly it is lodged in a sheath, and, from 

 its horny nature, it cannot be either shortened or length- 

 ened. 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 tono-ue of 

 the woodpeckers {PicidcB), 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. Tlie 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 

 originates. 



" With' this instrument the mother gall-fly pierces 

 the part of a plant which she selects, and, according to 

 our older naturalists, ' ejects into the cavity a drop of 

 her corroding liquor, and immediately lays an egg or 

 more there ; the circulation of the sap being thus inter- 

 rupted, and thrown, by the poison, into a fermentation 

 that burns the contiguous parts and changes the na- 

 tural colour. The sap, turned from its proper channel, 

 extravasates and flows round the eggs, while its surface 

 is dried by the external air, and hardens into a vaulted 

 form.' Kirby and Spence tell us, that the parent-fly 



