GALL-FLIES. 385 



oak-apple is commonly as large as a walnut or small 

 apple, rounded, but not quite spherical, the surface 

 being irregularly depressed in various places. The 

 skin is smooth, and tinged with red and yellow, like a 

 ripe apple; and at the base there is, in the earlier 

 part of the summer, a calyx or cup of five or six small 

 brown scaly leaves ; but these fall off as the season 

 advances. If an oak-apple be cut transversely, there 

 is brought into view a number of oval granules, each 

 containing a grub ; and embedded in a fruit-looking 

 fleshy substance, having fibres running through it. As 

 these fibres, however, run in the direction of the stem, 

 they are best exhibited by a vertical section of the gall ; 

 and this also shows the remarkable peculiarity of each 

 fibre terminating in one of the granules, like a foot- 

 stalk, or rather like a vessel for carrying nourishment. 

 Reaumur, indeed, is of opinion that these fibres are 

 the diverted nervures of the leaves, which would have 

 sprung from the bud in which the gall-fly had inserted 

 her eggs, and actually do carry sap-vessels throughout 

 the substance of the gall. 



Reaumur says the perfect insects (Cyrrips quercus) 

 issued from his galls in June and the beginning of 

 July, and were of a reddish-amber colour. We have 

 procured insects, agreeing with Reaumur's descrip- 

 tion, from galls formed on the bark or wood of the 



Root-Galls of the Oak, proilucat by Cynips querent inform t 

 drawn from a specimen. 



oak, at the line of junction between the root and the 

 seem. These galls are precisely similar in structure 



