( xlvi ) 



of the ilrfiintioiis of irencra i\u<\ liis;her units. For the degree of exactness 

 (lejiends here (1) on the more or less intrinsic: stndy of a larger mitnber of 

 forms than in the ease of species and varieties, and (2) on the correctness of 

 the author's inductive reasoning. 



The dassificatory category coming in our system of classification next to 

 the species is the genus. Some authors interpolate between genus and species 

 a category they call subgenus. From a comparison of a number of subgenera 

 which have been defined, we are able to state that they had either no standing, 

 being groups of species quite arbitrarily put together, or they represented well- 

 dciiucd homogeneous groups—/.*;, were equal to a genus. We do not see any 

 possibility of distinguishing between a defined genus and a defined subgenus. 

 To call one defined group a genus and another defined group a subgenus is quite 

 arbitrary. As there is a gap betwceu every two species, and mostly between 

 the varieties as well, and, further, as the sjjecies fall into groups different in 

 extent or diflerent in composition, according to this or that organ being taken 

 as the basis of the grouping, the limitation of the genera would be entirely left 

 to the personal opinion and ability of each individual classifier, if there was no 

 general definition of what kind of dassificatory unit a genus is meant to be. 

 Systematists differ, indeed, very much in the extent given to genera, some 

 authors adhering to large unwieldy groups of the Linnean type, and others 

 erecting a genus- for almost every species, and sometimes even for subspecies. 

 In order to check arbitrariness, to escape uncertainty as far as possible, and 

 to make generic classification more stable, we think it advisable to define a 

 "■enns as a classijicatonj unit one cat«jorij higher than species comprising one 

 definable group of species. 



In many cases the group contains only one species by the other members 

 having become extinct, or by there being as yet only one species known, the 

 other species being still undiscovered. 



In the present llevision of the Sp/iingii/iie it has been our special endeavour 

 to give a solid foundation to the genera, supplementing and rectifying the vague 

 or faulty definitions with which the workers in this group of insects have 

 contented themselves. Though many genera hitherto considered to be valid 

 have been shown by us to have no standing, the number of genera of 

 Sphingidae has been much enlarged, owing to the closer examination of the 

 insects proving many groups of apparently similar species to be heterogeneous. 

 We have laid special stress upon the genera as conceived by us representing 

 stages in the evolution of the Sphingidae. 



There is nowadays a tendency among British Lepidopterists to imitate 

 some American leading spirits in Lepidopterology in shifting the term '' family " 

 (Jamilia ; designated by the ending -idae according to common consent) to 

 a lower category than that to which it was originally ap])lied. We do not 

 see what good it serves to call, for instance, all the Hawk Moths together 

 a snperfamily, and the next divisions of it families. It is an entirely 

 superfluous innovation, and only leads to confusion, like all shifting of 



