GENUS SYNERGUS. 59 



Genus Synergus. 



Synergus, Hartig, Germ. Zeit., ii, 186 ; Mayr, Genera, 3. 



Face with, coarse, oblique, radiating furrows. Petiole rugosely dis- 

 tinctly longitudinally striolate. Radial cellule closed. The second and 

 third abdominal segments connate. Cheeks without a furrow ; longer 

 than the eyes. Antennse, $ 14-, $ 15-jointed, the third joint in the 

 latter curved, sometimes enlarged; spindle-shaped. Parapsidal furrows 

 complete. Median segment with two parallel keels. Abdomen com- 

 pressed. Claws cleft. The front with a pair of keels which usually 

 reach near to the lateral ocelli. 



The sculpture of the thorax varies from alutaceous 

 to rugose ; the mesosternum is striolate ; the second 

 and third abdominal segments amalgamated, seldom 

 with the suture visible. 



The general features relating to the history of the 

 guest gall-flies have been already indicated. They 

 issue earlier into the fly state than the insects on 

 which they prey, a circumstance, indeed, rendered 

 necessary from their having to deposit their eggs in 

 the galls when these are very young. As a rule they 

 distort the galls to a more or less extent, and it is 

 probable that many of the abortive galls owe this fact 

 to the action of the inquilines. They may either 

 enlarge or reduce the gall. A well-marked example 

 of the former we have in Bhodites eglanterids ; of the 

 latter Neuroterus ostreus may be cited, but in this case 

 apparently only one larva has been in it, or at least 

 has come out of the gall. When several live in one 

 gall, say in DryopJianta divisa, they are separated from 

 each other by partitions apparently formed of the 

 substance of the gall and some secretion of the larva. 

 As has already been pointed out, the larger galls may 

 afford nourishment to the maker and to one or more 

 . inquilines, while it is of not uncommon occurrence for 

 a gall to yield inquilines and chalcid parasites, the 

 latter having preyed upon one of the inquiline larvas. 



The inquilines, as has been indicated by Mayr, 

 are divisible, as regards habits, into two groups, 

 namely, those which winter in the galls, i. e. those 



