234 ESSAY ON CLASSIFICATION 



IV. Arthropoda. 

 Cl. 10. Crustacea. Ord. Entomostraca (Neusticopoda Car.) and Malacostraca. 

 Cl. 11. Insecta. Ord. Myriapoda, Arachnida (Accra, Latr.,) and Hexapoda. 



V. MoLLUSCA, Cuv. (Palliata, Nitzsch.) 



^ Leuckart is somewhat inclined to consider the 



Cl. 12. Tunicata. Ord. AsCldiae (Tethyes I Tunicata not simply as a class, but even as another great 



Sav.) and Salpas (Thalides Sav.) | type or branch, intermediate between Echinoderms 



J and Worms. 



Cl. 13. Acephala. Ord. Lamellibranchiata (Cormopoda Nitzsch, Pelecypoda Car.) and 



Brachiopoda. 

 Cl. 14. Gasteropoda. Ord. Heterobranchia (Pteropoda, Inferobranchia, and Tecti- 



branchia), Derraatobranchia (Gymnobranchia and Phlebenterata), Heteropoda, Cteno- 



branchia, Pulmonata, and Cyclobranchia. 

 Cl. 15. Cephalopoda. 



VI. Vertebrata. (Not considered.) 



I need not repeat here what I have already stated, in the first sec- 

 tion, respecting the primary divisions adopted by Siebold and Leuck- 

 art. 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 char- 

 acters as that of Echinoderms. Their systems of organs are so closely 

 homological, that the attempt here made by Leuckart, of subdivid- 

 ing them into three classes, can readily be shown to rest only upon 

 the admission, as classes, of groups which exhibit only ordinal char- 

 acters, 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 proposed by Burmeister is 

 certainly more correct than those of von Siebold and of Leuckart, in- 

 asmuch 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 Anne- 

 lides. 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 fundamental 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- 



