16 



Noctiiidcc of Temperate North America," Professor 

 John B. Smith says : — 



" The study of the primary sexual characters is 

 one of the most valuable guides in the recognition 

 of species. The structures are within my 

 experience absolutely invariable within specific 

 limits ; and species otherwise closely allied are 

 sometimes well separated by these characters. 

 They have proved invaluable in settling questions 

 of identity of American and European forms so 

 closely allied as to be considered races, and in 

 several instances they have proved the identity 

 or distinctness of species when superficial 

 characters left it in doubt. It has removed in- 

 dividual judgment as a factor in many cases, and 

 allows a final appeal in cases of difference." 



These remarks are obvious from our investigations 

 in recent years of the genus Aliana ; the genus 

 Oporahia ; the specific distinction of Coremia ferrugata 

 and C. iinidentaria ; of Retinea buoliana and R. pinicolana , 

 and of new species added to our British list, or even 

 to Science, Zygcena achillcca ; Hydroecia crinanensis ; 

 H. lucens and H.paludis; Cidaria concmnata ; Nonagria 

 edlesteni; N. nenrica and N . arundineta. The recognition 

 of all of which is mainly due to examination of the 

 genitalia. 



When I first took up the work, one of the 

 great difficulties was to convince entomologists that 

 species did not differ inter se, or alter with drying. 

 This is generally accepted now, and it would be useless 

 entering into the arguments brought forward to lessen 

 the value of my observations, all of which were found to 

 be groundless. At the same time it must not be taken 

 for granted that there is no variation in the organs. To 

 a certain extent there must always be some. Dr. T. A. 

 Chapman in a plate in the " Entomologist," vol. XL. 

 (1907) May, shows several slight variations in Acronycta 

 tridens, some of which may be errors in interpretation. 

 Generally, however, the organs are remarkably constant. 



