INTKODUCTION TO VOL. IV. 



In presenting the last volume of this work to my subscribers, it 

 may be well to draw attention to a few further incidental facts to 

 which the writing of the book has directed my attention. 



In the Introduction to Vol. I. I dealt with some of the " Probable 

 causes of variation," in that to Vol. II. with some thoughts on the 

 " Genetic Sequence in the Colours of Lepidoptera," and in Vol. III. 

 with those phases of variation connected with the sexes of Lepidop- 

 tera, generally known as " Secondary Sexual Characters." In the 

 present volume I propose dealing with matters which need explana- 

 tion, or have already had attention drawn to them, as well as a 

 general idea of the classification of our NOCTILEJ and their relation to 

 those of other countries. 



VARIETIES AND ABERRATIONS. Some entomologists lay great 

 stress on the distinction between " aberrations " and " varieties " and I 

 think very properly, although I have been unable to keep up so 

 artificial a distinction in this work. According to the distinction as 

 set up by Dr. Staudinger, " aberrations " are accidental forms, occurring 

 occasionally with the typical form, whilst " varieties " are local races 

 or modifications of the type, which they have supplanted in various 

 localities. It is very evident, that in a work based on exact study 

 rather than generalisations, the distinction to a great extent falls 

 through, and almost all the " varieties " so-called, would be in reality 

 "aberrations." But there is no real distinction in this direction. 

 Even in our own country the " varieties " or local races of one district 

 are " aberrations " in another and vice versa. Take for example 

 Cuspidia psi. In London, the pale type of this species is very rare, 

 and has been supplanted by a true variety or local race known as var. 

 suffusa. A few miles from London, the pale type generally occurs, 

 whilst a dark specimen of the variety svffma is very rare. In such a 

 locality, suffusa becomes purely an aberration in the Staudingerian 

 sense, and therefore within a few miles area, this form may be a 

 variety (local race) or an aberration (occasional form). Every 

 entomologist could give other examples Cuspidia leporina and its 

 var. bradyporina, Cymatopliora or and its var. scotica, Thera juniperata 

 and its var. scotica, Asphalia flavicornis and its vars. scotica and galbanus 

 and endless other species give parallel instances. It becomes clear, there- 

 fore, that such an arrangement is exceedingly artificial and indefinite, 

 and altogether unworkable, when the variation of most of our species 

 is closely and systematically worked out. 



Perhaps in another sense, almost all our British specimens of a 

 very large proportion of species are " varieties " in the Staudingerian 

 sense, i.e., if we compare them with the generally brighter and better 

 marked typical forms obtained in Central and Southern Europe, for 

 there are very few of our British species that do not differ from the 

 usual Continental forms of the same species, and that do not bear a 

 strong impress of the insular character of our fauna. In this way, 

 therefore, our most ordinary forms are often local races, and our own 



