140 ESSAY ON CLASSIFICATION. Part I. 



even the names of tribe and family have been apphed by some to what others 

 call sub-srenera ; some have called families what others have called orders ; some 

 consider 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, imder general heads, there is found the same diversity of opinion. It is, 

 nevertheless, possible, that under these manifold Biames, 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 wovild blame one another for calling them so, or otherwisa I can there- 

 fore no longer doubt that the controversy would be limited to definite ques- 

 tions, if naturalists could only be led to an agreement respecting the real nature 

 of each kind of grou2;)s. I am satisfied, indeed, that the most insuperable obstacle 

 to any exact appreciation of this suljject lies in the fact, that all naturalists, with- 

 out exception, consider these divisions, under whatever name they may designate 

 them, as strictly subordinate one to the other, in such a manner, that their differ- 

 ence is only dependent upon their extent; the class being considei'ed 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 exclu- 

 sion 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 j^rogress which has been 

 made in the philosophy of classification. 



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 categories of characters, genera would be called genera by all, whether 

 they differ much or little one from the other, and so would families be called fam- 

 ilies, orders be called orders, etc. Could, for instance, species be based upon absolute 

 size, genera upon the structure of some external parts of the body, families upon 

 the form of the body, orders upon the similarity of the internal structure, or the 

 like, it is plain that there could not be two opinions respecting these groups in 

 any class of the animal kingdom. But as the problem is not so simple in nature, 

 it was not until after the most extensive investigations, that I seized the clue to 



