366 ESSAY ON CLASSIFICATION. 



CL. 12. ACEPHALA. Sulcl. 1. BRACHIOPODA ; Ord. Rudista, Brachi- 

 opoda. Sulcl. 2. LAMELLIBRANCHIA ; Ord. Pleurochoncha, 

 Orthoconcha, Inclusa. 



CL. 13. TUNICATA. Ord. Ascidirc, Biphora. 'i 



CL. 14. CTENOPHORA. Ord. Only subdivided into familes. > 

 CL. 15. BRYOZOA. Ord. Stelrnatopoda, Lophopoda. 



V. VERMES. Organs bilateral. 



CL. 16. ANNELIDA. Ord. Hirudinea, Gephyrea, Scoleina, Tubicola, 



Errantia. 



CL. 1 7. ROTATORIA. Ord. Sessilia, Natantia. 

 CL. 18. PLATYELMIA. 1. Ord. Cestoidea, Trematoda. 2. Ord. Pla- 



narida, Nemertina. 

 CL. 19. NEMATELMIA. Ord. Gregarinea, Acanthocephala, Gordiacei, 



Nematoidei. 



VI. RADIATA. Organs radiate. 



CL. 20. ECHINODERMATA. Ofd. Crinoidca, Stellerida, Echinida, Ho- 



lothurida. 



CL. 21. SIPHONOFIIORA. Only subdivided into families. 

 CL. 22. HYDROMEDUSYE. Not clearly subdivided into orders. 

 CL. 23. POLYPI. Ord. Hexactinia, Pentactinia, Octactinia. 



No ECJCJ. 



VII. PROTOZOA. 



CL. 24. INFUSORIA. Ord. Astoma and Stomatoda. 



CL. 25. RUIZOPDA. Ord. Monosomatia and Polythalamia. 



The classification of Vogt (Zoologisclie Briefe, q. a., 

 p. 288) presents several new features, one of which is 

 particularly objectionable. I mean the separation of the 

 Cephalopoda from the other Mollusks, as a distinct primary 

 division of the animal kingdom. Having adopted the 

 fundamental distinction introduced by Kolliker between 

 the animals in which the embryo is developed from the 

 whole yolk, and those in which it arises from a distinct 

 part of it, Vogt was no doubt led to this step in conse- 

 quence of his interesting investigations upon Acteeon, in 

 which he found a relation of the embryo to the yolk dif- 

 fering greatly from that observed by Kolliker in the Ce- 

 phalopods. But, as I have already shown above, this can 

 no more justify their separation as branches, than the total 



