286 ESSAY ON CLASSIFICATION. 



forming natural, distinct groups, which he called Eadiata, 

 Articulata, Mollusca, and Vertebrata. 



It is true that the further subdivisions of these leading- 



o 



groups have undergone many changes since the publica- 

 tion of the " Kegne Animal." Many smaller groups, even 

 entire classes, have been removed from one of his " em- 

 branchments" to another; but it is equally true that the 

 characteristic idea winch lies at the bottom of these great 

 divisions was first recognized by him, the greatest zoolo- 

 gist of all time. 



The question which I would examine here in particular 

 is, not whether the circumscription of these great groups 

 was accurately denned by Cuvier, whether the minor 

 groups referred to them truly belong there or elsewhere, 

 nor how far these divisions may be improved within their 

 respective limits ; but whether there are four great funda- 

 mental groups in the animal kingdom based upon four 

 different plans of structure, and neither more nor less than 

 four. This question is very seasonable, since modern 

 zoologists, and especially Siebold, Leuckart, and Vogt, have 

 proposed combinations of the classes of the animal king- 

 dom into higher groups, differing essentially from those of 

 Cuvier. It is but justice to Leuckart to say that he has 

 exhibited, in the discussion of this subject, an acquaint- 

 ance with the wdiole range of Invertebrata, 1 which de- 

 mands a careful consideration of the changes he proposes, 

 as they are based upon a critical discrimination of differ- 

 ences of great value, though I think he overrates their 

 importance. The modifications introduced by Vogt, on 

 the contrary, appear to me to be based upon entirely un- 

 physiological principles, though seemingly borrowed from 

 that all important guide, Embryology. 



1 LEUCKART (R.), Ueber die Mor- haltnisse der wirbellosen Thiere ; 

 phologie uiid die Verwandtshaftsver- Braunschweig, 1848, 1 TO!. 8vo. 



