Vol. XXXI ] ENTOMOLOGICAL NEWS 47 



differences in structure and in color pattern. Structural 

 characters are preferred, those of the genitalia often being 

 used; color is less reliable, for even strikingly different color 

 patterns may prove to intergrade when an abundance of ma- 

 terial is examined. 



Species though they may not intergrade with each other, each 

 may include a smaller or larger number of intergrading forms. 

 It is with reference to these that nomenclatorial practice var- 

 ies most. Entomologists will do well to profit by the experi- 

 ence of workers in ornithology and mammalogy, in which 

 sciences the problems connected with taxonomic categories 

 subordinate to the species have long received attention re- 

 sulting in a generally accepted usage. The subspecies is 

 freely used; it is a geographic race, a part of a species marked 

 by average differences in characters which intergrade w r ith 

 those of subspecies occupying different, though usually ad- 

 jacent parts of the general range of the species, along the com- 

 mon boundary of which intergradation is complete. 



It has sometimes been urged that the amount of difference 

 decides whether a form should be called a species or a sub- 

 species, but this is hardly true except in cases where the dif- 

 ferences are small and intergradation while not actually ob- 

 served is assumed to occur. In general practice, intergrada- 

 tion clearly is the criterion. Even minute differences known 

 to be non-intergrading are satisfactory for specific diagnosis, 

 while characters apparently more important which vary so 

 that intergradation is evident can be used only for the differ- 

 entiation of categories of lower than specific rank. 



These statements while in the form of dogmatic assertions 

 are not so intended; they merely epitomize the practice that 

 has grown up under the guidance of the Code of Nomencla- 

 ture of the American Ornithologists' Union, which may be 

 looked upon as a parent to the International Code. As a 

 matter of fact individual systematists differ widely in the im- 

 portance they attach to the various crtieria for the diagnosis 

 of species and subspecies, as intergradation or the contrary, 

 amount of difference, and geographical isolation or the re- 

 verse. Some discussion of these features may be profitable. 



