XX INTRODUCTION. 



walkeri and tristiymata. This splitting up of the genus in America into 

 several very nearly related species is a distinct phase of variation and 

 merits particular attention. To separate the causes of variation, to 

 eliminate the factors, and correlate them with the resultant effects, may 

 bring us on the road to understand the reason for the diversity we find 

 in the animal kingdom " (in Hit. 1892). 



IDENTICAL JAPANESE AND EUROPEAN SPECIES. Many of the Japanese 

 and East Asiatic species appear at first sight, to differ as much from 

 our European specimens of the same species as do the American, but it is 

 rarely now that they are known by any other name than that of their 

 European types. Thus the normal condition of Viminia rumicis in 

 Corea, Japan and China, is to be of a deep brown coloration closely 

 approaching black, but the species is well recognised as rumicis. 

 Keferring to the ' Lepidoptera of Kiukiang,' we read Moma orion " agrees 

 exactly with specimens from Europe " ; Clisiocampa neustria, " identical 

 with European examples " ; Agrotis ypsilon, " includes most of the forms 

 occurring in Europe " ; Graphiphora (Noctua) dahlii, " several speci- 

 mens showing considerable variation in tone of colour. Among them 

 are examples identical with canescens, Butler ; " Dianthcecia compta, 

 " one example exactly like some European forms of this species," 

 and many similar entries are made of other species (Leach, "Lepi- 

 doptera of Kiukiang " in the ' Transactions of the Entomological 

 Society of London,' 1889, pp. 99-148). 



CLASSIFICATION. Another subject that has attracted niy attention 

 is that of classification. When I first commenced this work, in 

 common I suppose with almost all field naturalists in Britain, I knew 

 nothing of classification and cared to know less. A necessary alteration 

 in synonomy appeared in the light of an innovation, and as such, most 

 probably something to be resisted, but the study of variation soon 

 dispels such ideas, and shows that there is some relationship between 

 the various groups, some affinities more or less remote and some 

 superficial characters, which at first sight appear to bear relationships 

 to other similar forms, but which in fact have no such deep-seated 

 origin, the superficial resemblance being essentially due to similar 

 habits, developed by a similar environment, or by a commcn need for 

 protection and thus due to " protective resemblance." 



The naming of species is a minor matter, and the only purpose 

 served by a specific name is to make the particular species named 

 intelligible at once to all naturalists. 



Generic names serve to a limited extent the same purpose, but the 

 genera themselves are not only for this purpose but also serve a much 

 deeper one. Each genus usually now serves, not only as a means of 

 distinction of a group of certain species, but some relationship with 

 those genera around it. And not only " some relationship " but that of 

 the closest relationship is generally shown by allied genera. Beyond 

 these, we find that one group of genera exhibits certain characters in 

 connexion with another group, and yet, at the same time display 

 considerable differences. We then call each group of genera a Family, 

 and similarly by uniting allied families we get a series of sub- 

 classes. 



The whole of the sub-classes in the NOCTUJE were united by 

 Guenee into two great classes or groups, the larger called the NOCTIL&:- 

 TRIFID^E, the smaller the NOCTU^E-QUADRIFIDJE. These respectively 



