Neuroterns lenticularis. 13 



thirty-four buds pricked between March 28 and April 6. 

 Of these buds only nineteen developed, and as they 

 unfolded and their leaves became visible I examined 

 their surfaces with the greatest care for any sign of the 

 eggs which had been deposited in the bud. I was at 

 first unsuccessful, but after a long search I discovered 

 at last five of the young shoots exhibiting traces of gall 

 formation on their leaves. They were small round 

 excrescences, rich in sap, which grew tolerably quickly, 

 and were soon recognizable as the galls oi SpatJicgaster 

 baccarum. 



Thus in spite of taking every precaution to ensure 

 that the buds were pricked by Neuroterits lenticularis, 

 a perfectly different gall had been formed from the one 

 out of which this Neuroterus had emerged. I did not 

 rest satisfied with this one attempt, but continued for 

 many years to make experiments with this and many 

 othfer species of Nem'oteriis. 



It is remarkable in experimental breeding how small 

 is the number of galls that actually develop compared 

 with that of the eggs deposited in the buds. Many of 

 the buds themselves come to nothing, but even in those 

 which grow there are a great number in which the galls 

 do not form. For example in 1877 I made an experi- 

 ment in which the results were particularly unfavourable. 

 An oak was pricked abundantly by Neuroterus lenticu- 

 laris, and yet only a single Spathegaster baccarum gall 

 was formed. In such experiments it very probably 

 happens that the conditions of life natural to the flies 

 have not been successfully reproduced, and consequently 

 many of the eggs laid fail to develop. I have, however, 



