Gall-Flies 411 



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 nourish- 

 ment. 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. 



Hoot Galls of the Oak, produced by Cynips quercus iwfcrus f drawn from a specimen. 



Reaumur says the perfect insects (Cynips 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 description, from galls formed on 

 the bark or wood of the oak, at the line of junction between 

 the root and the stem. These galls are precisely similar in 

 structure to the oak-apple, and are probably formed at a 

 season when the fly perceives, instinctively, that the buds 

 of the young branches are unfit for the purpose of nidifica- 

 tion. 



There is another oak-gall, differing little in size and 

 appearance from the oak-apple, but which is very different 

 in structure, as, instead of giving protection and nourish- 

 ment to a number of grubs, it is only inhabited by one. 

 -This sort of gall, besides, is hard and woody on the outside, 



