XVlll IXTKODUCTION 



Several interesting and informative papers on the 

 same subject have been piiTjlished in various Trans- 

 actions, etc. 



But the study of the causes of oak galls remained 

 greatly neglected, and although several British ento- 

 mologists worked out the life-history of some of the 

 Cj^nijudae it was not until Peter Cameron published 

 vol. iv of his excellent ' Monograph of the British 

 Phytophagous Hymenoptera ' (Ray Society, 1892) 

 that there was a comprehensive account in the English 

 language of the gall-producing species. 



in 1894 Charles R. Straton, M.D., translated from 

 the German Dr. Hermann Adler's ' Alternating 

 Generations ' (" A Biological Study of Oak Galls and 

 Gall Flies"), and himself added many pages of very 

 valuable information. 



In drawing up the descriptions of some of the galls 

 I have added extracts from these works ; the character- 

 istics of the specimens are so excellently described by 

 these authors that I feel sure the student will be 

 grateful for their reproduction. In addition I have 

 incorporated the results of fifteen years' practical 

 research in the field and in the study. I am also 

 glad to be able to describe several galls not mentioned 

 in any other English publication. 



AYith a very few exceptions the illustrations are 

 entirely new and original, and are my own production. 

 The specimens were collected expressly for this work, 

 and great care has been exercised in their selection 

 and arrangement that they may as far as possible be 

 representative. 



For several reasons it has been found desirable to 

 arrange the species in alphabetical order. In depart- 

 ing from the classification set forth in my other work, 

 ' British Vegetable Galls,' I have been animated with 

 the desire to present the subject in as simple a form 

 as possible. 



