LITERATURE OE THE SUB-KINGDOM C(ELEXTERATA. 417 



In comparing Zoological systems it is requisite, in the first place, 

 to select some well known classification which may serve for a con- 

 venient standard of comparison. For this purpose that of Cuvier 1 is 

 above all others to be preferred ; first, by reason of its intrinsic merits, 

 and, secondly, on account of its historical value, strongly contrasting, 

 as it did, with the arrangements of his predecessors, and forming, so 

 to speak, the basis on which the greater number of succeeding sys- 

 tems have been reared. "We shall, accordingly, proceed to indicate 

 the place which Ccelenterate animals held in the classification of 

 Cuvier, and then notice the gradual changes of opinion which have 

 led modern investigators to adopt the more accurate view of their 

 affinities now entertained. 



Of the four primary branches, or sub-kingdoms, into which the 

 entire animal kingdom was divided by Cuvier, the lowest, Zoophyta 2 

 or Eadiata, included five classes, viz. : — 



1. ECHINODERMATA. 



2. Intestina. 



3. Acaleph^:. 



4. Polypi. 



5. Infusoria. 



In thus bringing together a number of animal forms having few 

 characters in common save a certain vague resemblance in outward 

 aspect, and an inferiority, real or supposed, in the details of their 

 organization, Cuvier lost sight of the principle, so important in bio- 

 logical classification, which no one has more happily defined than its 

 first and clearest enunciator, Yon Baer. 3 In the year 1828 this most 

 philosophic of naturalists drew attention to the distinction between 

 the grade of development of an animal and the type of its organization. 

 The grade of development of an animal he denned as consisting " in 

 the greater or less heterogeneity of its elementary parts and of the 

 separate divisions of a complex apparatus ; in a word, in its greater 

 histological and morphological differentiation :" the type as " the 

 relative position of the parts." And since no real agreement in type, 

 or plan of structure, exists among the several divisions of Cuvier's 

 Zoophyta, it follows that this sub-kingdom can no longer be regarded 

 as constituting a truly natural group. 4 



1 Le Regne Animal. Nouvelle edition. Paris, 1829-30. 



2 For some account of the several senses hi which this term has heen used 

 see, especially, De Blainvillc, Manuel d' Aetinologic, p. 1; Johnston, History of 

 British Zoophytes, second edition, passim ; and Dana, Structure and Classification 

 of Zoophytes, p. 7. The word Phytozoa is of more modern construction, and may be 

 found in the work of Goldfnss, cited below. 



3 See the English translation (by Mr. Huxley) of selections from the works of 

 Von Baer, in Taylor's Scientific Memoirs, Natural History, 1853. p. 195. 



4 " We believe, in fact, (writes Von Baer^, that Cuvier has penetrated most 

 deeply into the relations of animal organisms. But he does not satisfy us in this ; 

 that he requires in the Mollusca and Articulata not oidy the type of their organiza- 



