THE CHARACTEKS OF GENERA. 127 



Genera proper. If the foregoing discussion upon 

 the nature of these groups is based upon trust- 

 worthy principles, we must admit that they are 

 all founded upon distinct categories of characters, 

 the primary divisions, or the Branches, upon 

 plan of structure, the Classes upon the manner 

 of its execution, the Orders upon the greater 

 or less complication of a given mode of execu- 

 tion, the Families upon form ; and it now re- 

 mains to be ascertained whether Genera also 

 exist in Nature, and by what kind of character- 

 istics they may be distinguished. 



Taking the practice of the ablest naturalists 

 in discriminating Genera as a guide in our esti- 

 mation of their true nature, we must, neverthe- 

 less, remember that even now, while their classi- 

 fications of the more comprehensive groups usu- 

 ally agree, they differ greatly in their limitation 

 of Genera, so that the Genera of some authors 

 correspond to the Families of others, and vice 

 versa. This undoubtedly arises from the absence 

 of a definite standard for the estimation of these 

 divisions. But the different categories of struct- 

 ure forming the distinctive criteria of the more 

 comprehensive divisions once established, the 

 question is narrowed down to an inquiry into the 

 special category upon which Genera may be de- 

 termined ; and if this can be accurately defined, 

 no difference of opinion need interfere hereaf- 

 ter with their uniform limitation. 



