GALL-FLIES. 



383 



Woolly Gall of the Ouk caused by a cynips, and drawn from a 

 specimen. 



The woolly substance on the branch of the oak 

 which we have described was similarly constituted 

 with the tedeguar of the rose, with this difference, 

 that instead of the individual cells being diffused 

 irregularly through the mass, they were all arranged 

 at the off-goings of the leaf-stalks, each cell being 

 surrounded with a covering of the vegetable wool, 

 which the stimulus of the parent egg, or its gluten, 

 had caused to grow, and from each cell a perfect 

 fly had issued. We also remarked that there were 

 several small groups of individual cells, each of which 

 groups was contained in a species of calyx or cup 

 of leaf-scales, as occurs also in the well known gall 

 called the oak-apple. 



