In a few species the genitalia appear to be in a plastic 

 condition, and we find considerable variations. Our 

 conclusion is that the species are actually in the process of 

 being differentiated into two or more. 



Epiblema pflugiana affords a good example. Here we 

 meet with at least three forms, very distinct externally; 

 (i) the large pale form with the smaller dark female 

 (scutulana); (ii) the middle form in which both sexes are 

 of the same size, and both have dark hind wings (circiana); 

 (iii) a small form taken in the Fens. This last appears most 

 closely allied to the first, but the genitalia give no constant 

 character on which to separate any of the three. 



Catoptria scopoliana and C. parvulana may be another 

 case of two species in process of differentiation. 



A valuable result of our work will be the practical aid 

 it affords in separating species of very similar and often 

 indistinguishable appearance; e.g., the Cnephasias. Often 

 it will be found possible to determine a specimen, without 

 mounting the abdomen, or in any way damaging it, by 

 means of the genitalia. It would much facilitate later 

 examination of any doubtful specimen, if at the time of 

 setting, a dorso- ventral squeeze were given to the end of 

 the abdomen with a pair of fine pointed forceps. This 

 would have the effect of extending the valvse of the male 

 genitalia. An example of this practical value of the 

 examination of the unmounted genitalia will be found in 

 the plate of the Cnephasias given in the Entomologist's 

 Eecord, Vol. 27, 1915, pi. iii.; another was given by Lord 

 Walsingham, E.M.M., Vol. 34, 1898, pi. ii. With the 

 help of the drawings given in this volume we think there 

 will be little difficulty in separating many other closely 

 allied species. 



Note. — The numbers placed in the text after the specific 

 names indicate the number of mounts, male and female 

 respectively, made of that species. 



