Neitroferiis ostreus. 85 



October, in the same year. On the other hand, those 

 galls which mature in October do not yield their flies in 

 the same year, but these pass the winter in the pupa 

 state, and appear next March. 



Fly. Length 2-5-3 mm. ; black ; thorax dull, thinly 

 covered with whitish hairs, scutellum rugose ; antennae 

 black, pale at the base ; legs uniformly orange. 



Attempts at breeding with this fly have been made 

 without any results. I succeeded in getting some flies, 

 which were hatched in October, 1878, to prick the buds, 

 but no galls were formed. There can be no doubt, 

 however, judging by the formation of the gall, that a 

 generation alternating with this species does exist. The 

 flies emerging in October and March cannot directly pro- 

 duce the galls which appear in August ; and as these galls 

 spring from the midrib of a leaf late in the summer, it 

 is clear that another generation must have laid the ^^g. 

 I strongly suspect that the sexual generation belonging 

 to Neuroterus ostreus is to be sought for in Spathegaster 

 Aprilimis ^ The construction of the ovipositor which is 

 specially designed for boring the ribs of leaves, and a 

 certain general similarity in the flies, bear out this view. 



\} Professor Mayr informs me that this conjecture has since proved 

 to be correct. Beyerinck, howev^er, describes a sexual generation 

 inhabiting a small bark-gall growing on the bud-ring which he calls 

 Neuroterus farunctiliis, but he gives no details. {Bcob. lib. d. e. Entwick. 

 e. Cynipiden-Gallen, p. 37, note.) He also states that he bred Neuro- 

 terus Aprilinns from the galls oi Aphiloirix soUtaria (1. c. p. 138, note); 

 and Schlechtendal and Loew consider that Neuroterus Schlechtendali 

 is the agamous form of S. Aprilinus. Neuroterus Schlechtendali is 

 a small gall, i mm. in length, green at first, afterwards brown, 

 springing from a dilated part of the catkin in May on Quercus 

 pedunculata, Q. sessiliflora, and Q. pubescens. It emerges in July of 

 the second year.] 



