Gall-Flies. 401 



the curve of the belly, appears again near where it originates. 

 We copy from Reaumur his accurate sketch of this remark- 

 able structure. 



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 cir- 

 culation of the sap being thus interrupted, and thrown, by 

 the poison, into a fermentation that burns the contiguous 

 parts and changes the natural 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 introduces her egg " into a puncture 

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

 becomes surrounded with a fleshy chamber."! M. Virey 

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

 way as an inflamed tumor in an animal body, by the swell- 

 ing of the cellular tissue and the flow of liquid matter, which 

 changes the organization, and alters the natural external 

 form.J This seems to be the received doctrine at present in 

 France. 



Sprengel, speaking of the rose-willow, says, the insect in 

 spring deposits its eggs in the leaf buds. "The new 

 stimulus attracts the sap, the type of the part becomes 

 changed, and from the prevailing acidity of the animal 

 juice, it happens, that in the rose and stock-shaped leaves 

 which are pushed out, a red instead of a green colour is 

 evolved. "|| 



Without pretending positively to state facts which are, 

 perhaps, beyond human penetration, we may view the pro- 

 cess in a rather different light. (J. R.) Following the 

 analogy of what is known to occur in the case of the saw-flies, 



* Spectacle de la Nature, i. 119. 

 f Introduction, ii. 449. 

 J Hist, des Mceurs et. de 1'Instinct, vol. ii. 

 Entomologie, par R. A. E., p. 242. Pans, 1826. 

 | Elements of the Philosophy of Plants, Eng. Trans., p. 285. 



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