212 ESSAY ON CLASSIFICATION. 



agree in the limitation, of some groups at least, under 

 whatever name they may call them, and however much 

 they would blame one another for calling them so, or 

 otherwise. I can, therefore, no longer doubt that the 

 controversy would be limited to definite questions, if 

 naturalists could only be led to an agreement respecting 

 the real nature of each kind of groups. I am satisfied, 

 indeed, that the most insuperable obstacle to any exact 

 appreciation of this subject lies in the fact, that all na- 

 turalists, without exception, consider these divisions, under 

 whatever name they may designate them, as strictly sub- 

 ordinate one to the other, in such a manner that their 

 difference is only dependent upon their extent ; the class 

 being considered as the more comprehensive division, the 

 order as the next extensive, the family as more limited, 

 the genus as still more limited, and the species as the 

 ultimate limitation in a natural arrangement of living 

 beings; so that all these groups would differ only by the 

 quantity of their characters, and not by the quality, as if 

 the elements of structure in animals were all of the same 

 kind ; as if the form, for instance, was an organic element 

 of the same kind as the complication of structure, and as 

 if the degree of complication implied necessarily one plan 

 of structure to the exclusion of another. I trust I shall 

 presently be able to show, that it is to a neglect of these 

 considerations that we must ascribe the slow progress 

 which has been made in the philosophy of classifica- 

 tion. 



Were it possible to show that all these groups do not 

 differ in quantity, and are not merely divisions of a wider 

 or more limited range, but are based upon different cate- 

 gories of characters, genera would be called genera by all, 

 whether they differ much or little one from the other, and 



