HYMENOPTEllA — OAK GALLS. 139 



The imagines, apart from the salient features to be considered 

 under general anatomy, present very few interesting habits. They 

 are inactive, take no food, but are known to imbibe water, and a most 

 interesting point is the variation in the time of appearing. 



The males differ from the females in having longer antenniE, and 

 also have one or two more joints than in the case of the female (fig. 

 129, d). The female has a very large abdomen, and the precise shape 

 of the abdomen again differs according to species, which depends on 

 the form of the ovipositor (fig. 129, e). It is to be remembered that we 

 have two forms, the sexual and asexual or agamic, and that specific 

 characters are not very distinct ; therefore we have to rely on the 

 galls themselves for the most important points of discrimination of 

 species. 



The following are the most distinguishing features, according to 

 Cameron ^ : — 



" Cynipidse. — Abdomen petiolated — i.e., not attached by its entire 

 breadth to the thorax. 



"Abdomen pedunculated, trochanters biarticulate, antenntc 12 to 15 

 jointed and never elbowed, prothorax reaching to the insertion of 

 the wings ; wings Avithout a stigma, and with 1 radial and 1 to 3 

 cubital cellules, the second when ])resent being minute, usually 

 triangular ; the sub-costal cellule large, always present ; the other 

 cellules badly definqd or absent ; submarginal nervure absent ; abdo- 

 men compressed, ovipositor originating close to the base of the 

 abdomen, the borer usually semi-spiral, and with parts free ; larvae 

 apterous, never spinning a cocoon ; eggs stalked ; antennae in $ stouter 

 than $ ; legs, claws simple in Cynips, cleft in some species of Andri- 

 cus and Neuroterus. 



" Chalcididaj.- — Wings having a stigma; no radial or cubital 

 cellules ; antennce elbowed ; prothorax not reaching to insertion of 

 wings." 



The details of a wing of Cynips, fig. 129, /, should be carefully 

 studied, as the wings of the genuine oak-gall fly differ very much 

 from the various species of parasitic flies which are associated with 

 the Cynipidaj. 



1 Monograph of the British Phytophagous Hymenoptera, vol. iii. pp. 142, 

 147. Ray Society. 



^ This family contains many of the parasites found in oak galls, therefore it is 

 most important to recognise the contrasting points. 



