202 ESSAY ON CLASSIFICATION. Part I. 



all animals are equal in the perfection of their organization, might be justified, if 

 it was qualified so as to imply a relative perfection, adapted in all to the end 

 of their special mode of existence. As no one observer has contributed more 

 extensively than Ehrenberg to make known the complicated structure of a host 

 of living beings, which before him were almost universally believed to consist of 

 a simple mass of homogeneous jelly, such a view would naturally be expected 

 of him. But this qualified perfection is not what he means. He does not wish 

 to convey the idea that all animals are equally perfect in their way, for he states 

 distinctly that "Infusoria have the same sum of systems of organs as Man," and 

 the whole of his system is intended to impress emphatically this view. The separa- 

 tion of Man from the animals, not merely as a class but as a still higher division, 

 is especially maintained upon that ground. 



The principle of classification adopted by Ehrenberg is purely anatomical ; the idea 

 of type is entirely set aside, as is shown by the respective position of his classes. 

 The Myeloneura, it is true, correspond to the branch of Vertebrata, and the 

 Sphygmozoa to the Articulata and MoUusca; but they are not brought together 

 on the ground of the typical plan of their structure, but because the first have 

 a spinal marrow and the other a heart or pulsating vessels with or without articular 

 tions of the body. In the division of Tubulata, it is still more evident how the 

 plan of their structure is disregarded, as that section embraces Radiata, (the 

 Echinoidea and the Dimorphaja,) Mollusca, (the Bryozoa,) and Articulata, (the 

 Turbellaria, the Nematoidea, and the Rotatoi'ia,) which are thus combined simply 

 on the ground that they have vessels which do not pulsate, and that their intestine 

 is a simple sac or tube. The Racemifera contain also animals constructed upon 

 different plans, united on account of the peculiar structure of the intestine, which 

 is either forked or radiating, dendritic or racemose. 



The limitation of many of the classes proposed by Ehrenberg is quite objec- 

 tionable, when tested by the principles discussed above. A large proportion of them 

 are, indeed, founded upon ordinal characters only, and not upon class characters. 

 This is particularly evident with the Rotatoria, the Somatotoma, the Turbellaria, the 

 Nematoidea, the Trematodea, and the Complanata, all of which belong to the branch 

 of Articulata. The Tunicata, the Aggregata, the Brachiopoda, and the Bryozoa are 

 also only orders of the class Acephala. Before Echinoderms had been so exten- 

 sively studied as of late, the separation of the Echinoidea from Asteroidea might 

 have seemed justifiable ; at the present day, it is totally inadmissible. Even 

 Leuckart, who considers the Echinoderms as a distinct bi'anch of the animal king- 

 dom, insists upon the necessity of uniting them as a natural group. As to the 

 Dimorphiea, they constitute a natural order of the class AcalephjB, which is generally 

 known by the name of Hydroids. 



