PREFACE. 



The cordial reception extended to the " Genitalia 

 of the British Noctuida," published in 1909, has induced 

 me to launch on the sea of scientific literature a second 

 volume dealing with the interesting and important study 

 of the genitalia of the Lepidoptera. The former volume, 

 I believe, has been the means of directing attention to the 

 difficult family of the Diptera, and Prof. Newstead is 

 now doing good work among the Tse Tse flies, while the 

 genitalia of other groups are being studied. 



In presenting this account of the genitalia of 

 the Geometridce, I have had the advantage of the 

 criticisms passed on the previous work, and thus have 

 been enabled to make good the omissions that it contained, 

 and, I trust, also to make the present volume more 

 complete. 



The publication in the "Noetuidse" of names for the 

 different parts of the genitalia has produced a good deal 

 of interest in this department of our study, particularly 

 with reference to the standing of the names under the 

 law of priority, and as a result several employed in the 

 above work have had to fall before others previously 

 given. Dr. J. McDonnough, in the " Canadian Entomo- 

 logist," for June, 1911, vol. xliii., No. 6, has attempted 

 the difficult ask of unravelling the nomenclature and of 

 giving a complete list of the names which for the future 

 should be employed. With many of his conclusions I 

 agree, and, so far as our present knowledge will permit, I 

 have tried to make use, in the descriptions of the parts, of 

 all now established names. I would here like to impress 

 upon those working on the genitalia the necessity of using 



