Aphilotrix fecundatrix. 49 



larva does not proceed ; it may remain alive in the galls 

 for several years, but at length it dies. In what wa}'- 

 the alteration of the environment acts it is difficult to 

 tell, but the operation of such atmospheric influences 

 as cold, damp and heat appears to be absolutely 

 necessary to secure the regular progress of meta- 

 morphosis. The flies emerge in April. 



Fly. Size 4-5 mm. The whole fly dark, almost 

 black ; thorax dull, rugose, with white silky hairs ; 

 abdomen black and shining, but the sides more or 

 less reddish brown ; legs dark as a rule, the knees 

 distinctly reddish brown, front legs at the widest part 

 sometimes bright reddish brown, the upper part of the 

 femur dark. 



Experimental breeding. In conducting experiments 

 with this species I have had some difficulty because the 

 fly only lays its eggs in male catkin buds. As the 

 little oak trees which I planted in pots produced no 

 flowers, there was nothing to be done but to watch the 

 flies ovipositing in the open air. I succeeded, on 

 April 14, 1878, in accurately observing several of them 

 while in this act, but to be quite clear about their 

 manner of ovipositing, I allowed some flies reared by 

 myself to pierce branches which I had cut off" and 

 brought indoors for the purpose. I found that the fly 

 directed its ovipositor under the bud-scales until it 

 pierced an anther, when it laid the &^% in it. It was 

 therefore certain that the gall would be formed on the 

 anther. During my observations made in the open air, 

 several buds were pierced under my own eyes, and 

 I marked these by tying a thread around them. When 



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