326 INSECT ARCHITECTURE. 



With this instrument the mother gall-fly pierces the part 

 of a plant which she selects, and, according to onr 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."t 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 jDushed 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. E.) Following the 

 analogy of what is k)ioicn to occur in the case of the saw-flies 

 (see page 137), after the gall-fly has made a pimcture and 

 pushed her egg into the hole, we may suppose that she 

 covers it over with some adhesive gluten or gum, or the 

 egg itself, as is usual among moths, &c., may be coated over 



* Spectacle de la Natui-e, i. 119. 



t Introduction ii. 449. 



X Hist, des Mceurs et do I'lnstinct, vol. ii. 



§ Entomologie par E. A. E, page 242. Paris, 1826. 



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



