152 EVENINGS AT THE MICROSCOPE 



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 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 cor- 

 roding liquor, and immediately lays an egg or more there; 

 the circulation of the sap being thus interrupted, and 

 thrown, by the poison, into a fermentation that burns the 

 contiguous parts and changes the natural color. 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 introduces her egg 'into a punc- 

 ture made by her curious spiral sting, and in a few hours 

 it becomes surrounded with a fleshy chamber.' M. Yirey 

 says the gall-tubercle is produced by irritation, in the 

 same way as an inflamed tumor in an animal body, by 

 the swelling of the cellular tissue, and the flow of liquid 

 matter, which changes the organization, and alters the 

 natural external form." ' 



1 "Ins. Arch.," 371. 



