THE GEODP OF GALL MAKERS. 185 



and in centre of face. Legs marked with black at the 

 base ; claws brownish. It feeds on the leaves of the 

 common hazel, eating them along the edge. The 

 cocoon is spun in the earth. Found in September in 

 Scotland, in July in Prussia. 



Very rare. Arran. 



Prussia is the only continental country from which 

 ifc has been recorded. 



XX. THE GROUP OF GALL MAKERS. 



fipecies of from 1^ to 2J or 3 lines in lengthy with black 

 bodies, white legs (entirely white, or the femora may be 

 more or less blade) ; hyaline wings, with white, fuscous, 

 or white and fuscous, stigmata. Olypeus incised. 



The preceding section borders so closely on the 

 present that it is impossible to draw any clear line of 

 demarcation between the two. N. vesicator is a gall- 

 maker and might be included here ; but it is so closely 

 related to non-gall-making species, and as it has the 

 legs, abdomen, and stigma yellow, it is best kept out 

 of the present section, which, as above defined, contains 

 only species with white, or at least testaceous legs, and 

 with the stigma fuscous or white. Some of the species 

 resemble those of the group of Ruficornis, and perhaps 

 it might be more natural to place these latter in the 

 vicinity of the present section. 



As the third volume of this work deals more par- 

 ticularly with the gallflies, it is unnecessary to enter 

 here into the various theories and facts connected with 

 the origin of galls. It is necessary, however, to point 

 out certain peculiarities wherein sawfly gall-makers 

 differ from the Cynipidce. Unlike what happens with 

 a Gynips, the sawfly gall is fully formed before the 

 larva leaves the egg, so it is clear that the larva can 

 have nothing to do in setting the gall-growth in motion ; 

 while in the Gynipidce no gall commences to form until 



