142 ESSAY ON CLASSIFICATION 



almost inaccessible before, that I came to understand the meaning 

 of those divisions called types, classes, orders, families, genera, and 

 species, so long admitted in Natural History as the basis of every 

 system, and yet so generally considered as mere artificial devices to 

 facilitate our studies. For years I had been laboring under the im- 

 pression that they are founded in nature, before I succeeded in find- 

 ing out upon what principle they were really based. I soon perceived, 

 however, that the greatest obstacle in the way of ascertaining their 

 true significance lay in the discrepancies among different authors in 

 their use and application of these terms. Different naturalists do not 

 call by the same name groups of the same kind and the same extent: 

 some call genera what others call sub-genera; others call tribes or even 

 families what are called genera by others; even the names of tribe 

 and family have been applied by some to what others call sub-genera; 

 some have called families what others have called orders; some con- 

 sider as orders what others have considered as classes; and there are 

 even genera of some authors which are considered as classes by others. 

 Finally, in the number and limitation of these classes, as well as in 

 the manner in which they are grouped together under general heads, 

 there is found the same diversity of opinion. It is nevertheless possi- 

 ble that under these manifold names, so differently applied, groups 

 may be designated which may be natural, even if their true relation 

 to one another have thus far escaped our attention. 



It is already certain that most if not all investigators 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 call- 

 ing 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 group. I am satisfied indeed that the most insuperable ob- 

 stacle to any exact appreciation of this subject lies in the fact that 

 all naturalists without exception consider these divisions, under 

 whatever name they may designate them, as strictly subordinate one 

 to the other, in such a manner, that their difference is only depend- 

 ent upon their extent; the class being considered as the more com- 

 prehensive 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 



