228 ESSAY ON CLASSIFICATION 



Cl. Annellata. Ord. Suctoria, Terricola, Errantia, Tubicola. 

 Cl. Cirripedia. Ord. Thoracica, Abdominalia, and Apoda. 



Province. Mollusca. Heterogangliata. (Owen.) 



Cl. Cephalopoda. Ord. Tetrabranchiata and Dibranchiata. 



Cl. Gasteropoda. A. Monoecia: Ord. Apneusta (K611.), Nudibranchiata, Infero- 

 branchiata, Tectibranchiata, Pulmonata. B. Dioecia. Ord. Nucleobranchiata, 

 Tubulibranchiata, Cyclobranchiata, Scutibranchiata, and Pectinibranchiata. 



Cl. Pteropoda. Ord. Thecosomata and Gymnosomata. 



Cl. Lamellibranchiata. Ord. Monomyaria and Dimyaria. 



Cl. Brachiopoda. Only subdivided into families. 



Cl. Tunicata. Ord. Saccobranchiata and Taeniobranchiata. 



Subprovince. Radiaria.^ 



Cl. Echinodermata. Ord. Crinoidea, Asteroidea, Echinoidea, Holothurioidea, and 



Sipunculoidea. 

 Cl. Bryozoa. Only subdivided into families. 

 Cl. Anthozoa. Only subdivided into families. 

 Cl. Acalephae. Ord. Pulmograda, Ciliograda, and Physograda. 

 Cl. Hydrozoa. Only subdivided into families. 



Subprovince. Entozoa. 



Cl. Coelelmintha. Ord. Gordiacea, Nematoidea, and Onchophora. 



Cl. Sterelmintha. Ord. Taenioidea, Trematoda, Acanthocephala. — Turbellaria. 



Subprovince. Infusoria. 



Cl. Rotifera. Only subdivided into families. 



Cl. Polygastria. Ord. Astoma, Stomatoda. — Rhizopoda. 



The classification with which Owen^*' introduces his Lectures on 

 Comparative Anatomy is very instructive, as showing, more distinctly 

 than other modern systems, the unfortunate ascendancy which the 

 consideration of the complication of structure has gained of late over 

 the idea of plan. His provinces, it is true, correspond in the main to 

 the branches of Cuvier, with this marked difference, however, that 

 he does not recognize a distinct province of Radiata coequal with 

 those of Mollusca, Articulata, and Vertebrata, but only admits Ra- 

 diaria as a subprovince on a level with Entozoa and Infusoria. Here 



^°In the first edition of the work quoted above, published in 1843, the three sub- 

 provinces, Radiaria, Entozoa, and Infusoria are considered as one subkingdom called 

 Radiata, in contradistinction of the subkingdoms, Mollusca, Articulata, and Vertebrata, 

 and that subkingdom is subdivided into two groups, Nematoneura and Acrita. 



*" 1 have given precedence to the classification of Owen over those of von Siebold 

 and Stannius, Milne-Edwards, Leuckart, etc., because the first edition of the Lectures 

 on Comparative Anatomy was published in 1813; but in estimating its features, as 

 expressed in the preceding diagram, it should be borne in mind that in the first edition 

 the classes alone are considered, and that the orders and families were only added to 

 the second edition in 1855. I mention this simply to prevent the possibility of being 

 understood as ascribing to Owen all those subdivisions of the classes which he admits 

 and which do not appear in the systems considered before his. 



