PRINCIPAL SYSTEMS OF ZOOLOGY 229 



the idea of simplicity of structure evidently prevails over that of plan, 

 as the subprovinces Radiaria, Entozoa, and Infusoria embrace, be- 

 sides true Radiata, the lowest types of two other branches, Mollusks 

 and Articulates. On the other hand, his three subprovinces corre- 

 spond to the first three types of von Siebold; the Infusoria^^ of Owen 

 embracing the same animals as the Protozoa of Siebold, his Entozoa'*^ 

 the same as the Vermes, and his Radiaria the same as the Zoophyta, 

 with the single exception that Owen refers the Annellata to the prov- 

 ince of Articulata, whilst Siebold includes them among his Vermes. 

 Beyond this the types of Mollusca and Articulata (Arthropoda) of 

 the two distinguished anatomists entirely agree. The position as- 

 signed by O^ven to the provinces Articulata and Mollusca, not one 

 above the other, but side by side with one another,^^ is no doubt 

 meant to express his conviction, that the complication of structure 

 of these two types does not justify the idea that either of them stands 

 higher or lower than the other; and this is perfectly correct. 



Several groups, established by previous writers as families or orders, 

 are here admitted as classes. His class Epizoa, which is not to be con- 

 founded with that established by Nitzsch under the same name, cor- 

 responds exactly to the family called Lernees by Cuvier. His class 

 Hydrozoa answers to the order Hydroia of Johnston and is identical 

 with the class called Dimorph/EA by Ehrenberg. His class Ccelelmin- 

 THA corresponds to the order of Intestinaux Cavitaires established 

 by Cuvier, with the addition of Gordius; while his class Sterelmin- 

 THA has the same circumscription as the order Intestinaux Paren- 

 CHYMATEux of Cuvicr. Generally speaking, it should not be under- 

 stood that the secondary divisions mentioned by the different authors, 

 whose systems I have analyzed here, were established by them. They 

 are frequently borro-wed from the results obtained by special inves- 

 tigators of isolated classes. But it would lead me too far to enter here 

 into a discussion of all these details. 



This growing resemblance of the modern systems of Zoology is a 



"■ The Rhizopoda are considered as a group coequal to Rotlfera and Polygastria, on 

 p. 16 of the Lectures (1855) but on p. 59, they stand as a suborder of Polygastria. 



*^The Turbellaria are represented as an independent group, in ibid., p. 16, and 

 referred as a suborder to the Trematoda, on p. 118. 



*^ From want of space, I have been compelled, in reproducing the classification of 

 Owen in the preceding diagram, to place his provinces Articulata and Mollusca one 

 below the other on my page; according to his views, they should stand on a level, side 

 by side with one another. 



