180 ESSAY ON CLASSIFICATION. Part I. 



The question which I would examine here in particular, is not whether the 

 circumscription of these great groups was accurately defined by Cuvier, whether 

 the minor groups referred to them truly belong there or elsewhere, nor how far 

 these divisions may be improved within their res^jective limits, but whether there 

 are four great fundamental groups in the animal kingdom, based upon four differ- 

 ent 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 kingdom into higher groups, 

 differing essentially from those of Cuvier. It is but justice to Leuckart to say 

 that he has exliibited, in the discussion of this subject, an acquaintance with the 

 whole rancce of Invertebrata,' which demands a careful consideration of the changes 

 he proposes, as they are based upon a critical discrimination- of differences of great 

 value, though I think he overrates their importance. The modifications intro- 

 duced by Vogt, on the contrary, appear to me to be based upon entirely unphysio- 

 logical principles, though seemingly borrowed from that all important guide. Em- 

 bryology. 



The divisions adopted by Leuckart are : Protozoa, (though he does not enter 

 upon an elaborate consideration of that group,) Coelenterata, Echinodermata, Vermes, 

 Arthropoda, MoUusca, and Vertebrata. The classification adopted, many years before, 

 by Siebold, in his text-book of comparative anatomy, is nearly the same, except 

 that Mollusks follow the Worms, that Coelenterata and Echinoderms are united 

 into one group, and that the Bryozoa are left among the Polyps. 



Here we have a real improvement upon the classification of Cuvier, inasmuch 

 as the Worms are removed from among the Eadiates, and brought nearer the 

 Arthropods, an improvement however, which, so far as it is correct, has already 

 been anticipated by many naturalists, since Blainville and other zoologists long 

 ago felt the impropriety of allowing them to remain among Radiates, and have 

 been induced to associate them more or less closely with Articulates. But I 

 believe the union of Bryozoa and Rotifera with the Worms, projjosed by Leuckart, 

 to be a great mistake ; as to the separation of Coelenterata from Echinoderms, I 

 consider it as an exaggeration of the difference which exists between Polyps and 

 Acalephs on the one hand, and Echinoderms on the other. 



The fundamental groups adopted by Vogt,^ are : Protozoa, Radiata, Vermes, Mol- 

 lusca. Cephalopoda, Articulata, and Vertebrata, an arrangement which is based solely 

 upon the relations of the embryo to the yolk, or the absence of eggs. But, as 



* Leuckart, (R.,) Ueber die Morpholojjie und die ' Vogt, (Carl,) Zoologische Briefe. Naturge- 



Verwandtshaf'tsverhiiltnisse der wirbellosen Thiere, schichte der lebenden und untergegangenen Thiere. 

 Braunseliweig, 1848, 1 vol., 8vo. Frankfurt a. M., 1851 ; vol. 1, p. 70. 



