THE DE^rxRTIAN OF SPECIES. 517 



of that monograph expressing the difficulties he encountered 

 in assigning to some or many of the previously-recorded species 

 their proper places, in consequence of the insufficient descrip- 

 tions of the authors who had characterized them. c As a 

 knowledge of species is a necessary basis on which a more 

 scientific structure must be raised, and as every writer on 

 species wishes his labours to result in the instruction of those 

 for whose information they were directed, it becomes important 

 that the descriptions employed should be so accurate, and 

 drawn with such care, that the entomologist may gain, with 

 certainty and facility, an acquaintance with those objects he 

 desires to recognize, and understand fully the distinctions that 

 separate the species of a genus from each other. Whoever, 

 therefore, undertakes to write a monograph, or to describe 

 species, ought to be perspicuous and simple in his descrip- 

 tions, employing terms generally received and understood, and 

 defining such characters only as will at once distinguish the 

 individual from which they are drawn from each and all of 

 its congeners. If he separates his insects, and raises them to 

 the rank of species on trifling differences, which it requires 

 " an empirical tact to discover," it will no doubt be difficult for 

 him to express, in definite terms, such slight modifications of 

 variation ; indeed a very fair question will be raised, how far 

 he is warranted in assigning to such slight differences an 

 amount of value sufficient to determine that they are specific ; 

 but if, uninfluenced by the paltry desire of detecting new spe- 

 cies, he has proceeded with caution, and has divided one insect 

 from another on intelligible appearances of dissimilarity of 

 form, sculpture, size, or colour, he can with accuracy define in 

 words what those visible differences are, and thus convey to 

 his reader a clear idea of the peculiar distinctive characters 

 which mark each supposed species. B will then be easily 

 recognized from A, — C from A and B, — D from E, — F, G, 

 and H from each other, and from A, B, C, D and E. The 

 business of a describer is, I conceive, to " define differences," 

 and that so clearly, that if an entomologist has but a single 

 species in his collection belonging to the genus described, he 

 may be enabled, on referring to the monograph, to identify it, 

 or to satisfy himself it is unnoticed. It not unfrequently 



c See F.ntoai. Mag. Vol. II., pp. 2')i— '2M. 



