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ESSAY ON CLASSIFICATION.

it have now to be divided, and scattered, partly amongplants in the class of Algae , and partly among animals inthe classes of Acephala, (Yorticellae,) of Worms , (Para-mecium and Opalina,) and of Crustacea (Eotifera) ; theVorticellse being genuine Bryozoa , and therefore Acepha-lous Mollusks ; while the beautiful investigations of Danaand Leydig have proved the Eotifera to be genuineCrustacea, and not Worms .

The great type of Eadiata, taking its leading featuresonly, was first recognized by Cuvier , though he associatedwith it many animals which do not properly belong to it.This arose partly from the imperfect knowledge of thoseanimals at the time, but partly also from the fact that heallowed himself, in this instance, to deviate from his ownprinciple of classification, according to which types arefounded upon special plans of structure. With referenceto Eadiata, he departed, indeed, from this view, so far asto admit, besides the consideration of their peculiar plan,the element of simplicity of their structure as an essentialfeature in the typical character of these animals, in con-sequence of which he introduced five classes amongEadiata: the Echinoderms , Intestinal Worms , Acalephs,Polypi, and Infusoria. In opposition to this unnaturalassociation I need not repeat here what I have alreadystated of the Infusoria, when considering the case ofProtozoa ; neither is it necessary to urge again the pro-priety of removing the Worms from among the Eadiataand connecting them with the Articulata. There wouldthus remain only three classes among Eadiates,—Polypi,Acalephs, and Echinoderms, —which, in my opinion, con-stitute really three natural classes in this great division,inasmuch as they exhibit the three different ways inwhich the characteristic plan of the type, radiation, iscarried out, in distinct structures.