Ortmaun.] 1 -^^ [May 15, 1896. 



The principle of constant difference is practically applied generally 'bj 

 systematists, and I hope I have given above a logical foundation of this 

 principle. In many cases, indeed, the constancy of dift'erence is the 

 only means by which species can be distinguished, if the former or the 

 actual separation of the respective forms cannot be made out with 

 certainty. But in all cases, where an actual separation is evident, we 

 should consider the respective forms, if morphologically distinct, as 

 species, not as varieties. Under the new definition of the term species 

 given here, many of the so-called local varieties become species, since 

 such are often distinguished only because the ditt'erences from "good " 

 species are only slight ones and are not considered as important enough 

 to create a distinct species. But this standpoint is not correct : any 

 dift'erence in characters, however slight, constitutes a distinct species, if 

 constant and due to separation. 



