86 INTRODUCTION TO CLASSIFICATION. 



between the Mollusca and the Molluscoida, the Annulosa and 

 the Annuloida, do I think it very improbable that, hereafter, 

 some common and distinctive characters may possibly be dis- 

 covered which shall unite these pairs respectively. But the 

 discoveries which shall effect this simplification have not yet 

 been made, and our classification should express not anticipa- 

 tions, but facts. 



. I have not thought it necessary or expedient, thus far, to 

 enter into any criticism of the views of other naturalists, or to 

 point out in what respect I have departed from my own earlier 

 opinions. But Cuvier's system of classification has taken such 

 deep root, and is so widely used, that I feel bound, in conclu- 

 sion, to point out how far the present attempt to express in a 

 condensed form the general results of comparative anatomy 

 departs from that embodied in the opening pages of the " Kegne 

 Animal." 



The departure is very nearly in the ratio of the progress of 

 knowledge since Cuvier's time. The limits of the highest 

 group, and of the more highly organized classes of the lower 

 divisions, with which he was so well acquainted, remain as he 

 left them ; while the lower groups, of which he knew least, and 

 which he threw into one great heterogeneous assemblage, the 

 Eadiata, have been altogether remodelled and rearranged. 

 Milne-Edwards demonstrated the necessity of removing the 

 Polyzoa from the radiate mob, and of associating them with the 

 lower Mollusks. Frey and Leuckart demonstrated the sub- 

 regnal distinctness of the Ccelenterata. Von Siebold and his 

 school separated the Protozoa, and others have completed the 

 work of disintegration by erecting the Seolecida into a primary 

 division, of Vermes, and making the Echinodermata into another. 

 Whatever form the classification of the Animal Kingdom may 

 eventually take, the Cuvierian Eadiata is, in my judgment, 

 effectually abolished : but the term is still so frequently used, 

 that I have marked out those classes which it denoted in 

 the diagram of the Animal Kingdom (p. 6), so that students 

 may not be at a loss to understand the sense in which it is 

 employed. 



