xvii INTRODUCTION 
Several interesting and informative papers on the 
same subject have been published 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 
Cynipide 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 
IT have added éxtracts 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 
meorporated 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. 
With 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. 
