60 GENUS SYNERGUS. 



which oviposit in autumnal galls, leaving them early 

 in the spring; and those which live in the spring 

 galls, leaving them in July or about that time, the 

 latter species living in the galls only a short period 

 compared to those which winter. Whether all the 

 summer broods live in two distinct galls, a spring and 

 autumn one, is not clear. A species like 8. radiatus 

 might well live in the galls of Neuroterus baccarum in 

 May, come forth and oviposit in Andricus solitarius i 

 remaining in this gall to the following spring, if it were 

 not the fact that it issues from Andricus solitarius in 

 July of the same year. 



Our winter galls are — 



Synergus melanopus. 



— BeinJiardi. 



— apicalis. 



— incrassatus. 



— Tscheki. 



— pallicomis. 



— nervosus. 



— tristis. 



— vulgaris. 



— thaumacercb. 



The spring species are — 



Synergus albipes. 



— facialis. 



— radiatus. 



— thaumacera. 



The last-mentioned species is stated by Mayr to 

 winter in the galls of Biorhiza renum. 



It is difficult to find a group of Hymenoptera 

 wherein the separation of the species is more per- 

 plexing, or where the specific characters are more 

 plastic. There is hardly a single specific point 

 wherein we do not find extreme variability. Colour 

 we could hardly expect to find very stable in those 

 insects ; and, indeed, the amount of variation in this 

 respect in all the species is very great and often ex- 



