210 ESSAY ON CLASSIFICATION. Part I. 



I need not repeat here what I have ah-eady stated, in the first section, respecting 

 the primary divisions adopted by Siebold and Leuckart. As to the classes, I may 

 add that his three classes of Echinoderms exhibit only ordinal characters. Besides 

 Birds and Cephalopods, there is not another class so well defined, and so little 

 susceptible of being subdivided into minor divisions presenting any thing like class 

 characters, as that of Echinoderms. Their systems of organs are so closely homo- 

 logical, (compare p. 183,) that the attempt here made by Leuckart, of subdividing 

 them into three classes, can readily be shown to rest only upon the admission, as 

 classes, of groups which exhibit only ordinal characters, namely, different degrees of 

 complication of structure. With reference to the classes of Worms, the same is 

 equally true, as shown above. The arrangement of these animals jjroposed by Bur- 

 meister is certainly more correct than those of von Siebold and of Leuckart, inas- 

 much as he refers already correctly the Rotifera to the class of Crustacea, and does 

 not, like Leuckart, associate the Bryozoa with the Worms. I agree, however, with 

 Leuckart respecting the propriety of removing the Nemertini and Hirudinei from 

 among the true Annelides. Again, Burmeister appreciates also more correctly the 

 position of the whole type of Worms, in referring them, with de Blainville, to the 

 branch of Articulata. 



The common fault of all the anatomical classifications which have been proposed 

 since Cuvier consists, first, in having given up, to a greater or less extent, the funda- 

 mental idea of the plan of structure, so beautifully brought forward by Cuvier, and 

 upon which he has insisted with increased confidence and more and more distinct con- 

 sciousness, ever since 1812 ; and, second, in having allowed that of complication of 

 structure frequently to take the precedence over the more general features of plan, 

 which, to be correctly appreciated, require, it is true, a deeper insight into the struc- 

 ture of the whole animal kingdom than is needed merely for the investigation of 

 anatomical characters in single types. 



Yet, if we take a retrospective glance at these systems, and especially con- 

 sider the most recent ones, it must be apparent to those who are conversant with 

 the views now obtaining in our science, that, after a test of half a century, the 

 idea of the existence of branches, characterized by different plans of structure, as 

 expressing the true relations among animals, has prevailed over the idea of a 

 gradated scale including all animals in one progressive series. When it is con- 

 sidered that this has taken place amidst the most conflicting views respecting classi- 

 fication, and even in the absence of any ruling principle, it must be acknowl- 

 edged that this can be only owing to the internal truth of the views first pro- 

 pounded by Cuvier. We recognize in the classifications of Siebold, Leuckart, and 

 others the triumph of the great conception of the French naturalist, even though 

 their systems differ greatly from his, for the question whether there are four or 



