Gall-Flies. 



405 



sharp mandibles through the walls of their little cells, which 

 are now so hard as to be cut with difficulty by a knife. 

 (J. R.) 



Another structure, similar in principle, though different 

 in appearance, is very common upon oak-trees, the termina- 

 tion of a branch being selected as best suited for the purpose. 

 This structure is rather larger than a filbert, and is composed 

 of concentric leaves diverging from the base, and expanding 

 upwards, somewhat like an artichoke. Whether this leafy 



Artichoke Gall of the Oak-bud, with Gall-fly (Cynips quercus gemmce), natural size, 

 and its ovipositor (a) magnified. 



structure is caused by a superinduced disease, as the French 

 think , or by the form of the pores in the pellicle of gluten 

 surrounding the eggs, or rather by the tendency of the 

 exuding sap of the oak to form leaves, has not been ascer- 

 tained ; but that it is intended, as in the case of the bedeguar, 

 to afford an efficient protection against the weather to the 

 included eggs or grubs, there can be no doubt. 



From the very nature of the process of forming willow- 

 galls, bedeguar, and the artichoke of the oak, whatever 



