376 THE EVOLUTION OF THE METAZOA 



had adopted, for a long time, the sessile way of life. We have 

 also shown that there is no justification in a distinction between 

 the primarily two and three-layered Eumetazoa. We must 

 therefore cease to use this supposed difference in the taxonomy. 



There have been still other systematic attempts where a 

 bifurcation was suggested at the very root of the Eumetazoa. 

 Thus, for example, the Metazoa (s. 1.) were divided initially by 

 Hatschek into the Protaxonia and the Heteraxonia. This is 

 thus a classification on the basis of a supposed difference in 

 the axial conditions. Hatschek himself later abandoned 

 this classification because it was soon found that the axial 

 conditions are in reality very unreliable, that they have a role 

 similar to that of the symmetrical conditions in the phylogeny 

 and they are strongly changeable especially during the onto- 

 genies. 



A completely unacceptable classification was made by Colosi 

 (1956: 505). He divided the Eumetazoa into the Perineura and 

 the Epineura. It is only the Coelenterata that are included 

 among the Perineura while even Ctenophora do not appear in 

 this group. Colosi suggests that the Coelenterata consist 

 exclusively of the Cnidaria. He naturally believed in the 

 primary nature of the nerve-net system without a dorsal 

 brain ganglion. On the other hand, he inclines strongly 

 to a key-like dichotomy in the general classification of the 

 Eumetazoa which he pursues for not less than eight stages up 

 to the category of types (i.e. phyla). 



Furthermore, I should like to mention those classifications 

 which use the notion Coelomata while at the same time 

 omitting the opposite notion of Coelenterata. Thus, for ex- 

 ample, the groups Porifera, Ctenophora, Cnidaria and Planulo- 

 idea remain separate in the schematic survey which was made 

 by J. Meixner and published in the Handbuch derBiologie (edited 

 by L. von Bertalanffy and F. Gessner), Pt. Ill (The Genealogical 

 Tree of the Animal World). In the text, however, we hnd ne- 

 vertheless the word and the category of coelenterata used by 

 A. Remane (ibid: 85) and by other collaborators (e.g. by 



