384 THE EVOLUTION OF THE METAZOA 



which do not appear here under this name, the Platyhelmin- 

 thes and the Bryozoa evolve almost together from one and 

 the same point (we cannot speak here of a root or of a stem) 

 which is also the starting point for the evolution of the 

 Chaetognatha. The Annelida are placed above the Brachiopoda, 

 Mollusca, Crustacea, and Arachnoidea, etc. It is really comple- 

 tely unnecessary to discuss here this system. The point of the 

 bifurcation of the Eumetazoa can be found placed equally 

 deeply in the system which was proposed by Steiner (1956). 

 This survey does not include all the attempts which have 

 been made so far to find the correct position of the Cnidaria 

 in the animal classification. Yet even this should suffice to 

 show how many different opinions have been proposed so far 

 and how little all these attempts are able to survive earnest 

 examination. I suggest on the basis of the plasmodial theory 

 of the origin of the Eumetazoa that the Cnidaria should not 

 be separated from the remaining lower Eumetazoa. The 

 dichotomy Coelenterata : Coelomata has in this way become 

 superfluous. The same is also true for the two similar di- 

 chotomies, Diploblastica : Triplobastica (because there are no 

 primary Diploblastica), and Radiata (Radialia) : Bilateria. All 

 the Eumetazoa have a primarily bilaterally symmetric struc- 

 ture, the radial symmetry being a secondary element caused 

 by the transition to, and a longer preservation of, the sessile 

 state. In this w^ay we also achieve a simplification of the 

 general system and of the genealogical tree. 



The Coelomata as a Taxonomic Unit 



On the basis of our study of the Cnidaria and of Cteno- 

 phora wx have come to conclusion that the large taxon of 

 Coelenterata has really no justification. The question neces- 

 sarily arises in this connection what should be the destiny 

 of its "counterpart," of the Coelomata, as that of a special 

 taxon. The name itself indicates that those animal groups are 

 included in this taxon which show a coelom in their internal 



