PREVIOUS INTERPRETATIONS OF CNIDARIA 87 



as is the case in Ophiuroidea; while at the same time the 

 primarily aproctous Cnidaria usually have— with exceptions 

 that can be found above all in the Anthozoa— a pure radial sym- 

 metry. We have earlier pointed out that the radial symmetry 

 does not depend on a certain type of the structure and that it is 

 entirely and exclusively influenced by the type of the contact 

 with the environment. The sessile way of life will produce 

 the radial symmetry whatever the type of the structure may 

 be. In a natural system we are therefore not allowed to base 

 a taxonomic unit mainly on such a factor. The names, however, 

 of Radiata or Radialia have been widely compromised and so 

 it is better to avoid them altogether whenever we discuss 

 systematic categories, groups, or taxons. In the zoological 

 literature one can even find cases where Mesozoa, too, can 

 be found attributed to Radiata, either directly (D'Ancona 

 1955), or as a kind of an appendix to the latter (Biitschli 1921). 

 The Echinodermata, however, do not belong even near the 

 vicinity of Cnidaria; their true position is far away from the 

 latter, among the Oligomeria. 



It is interesting to see in this connection how a faithful 

 adherent to the taxon Radiata (E. Perrier) explains the origin 

 of the two groups of Metazoa: the Phytozoaires (i.e. Radiata) 

 and the Artozoaires : According to him the freely swimming 

 Gastraeadae were the first Metazoa. These began to settle on 

 the sea bottom where they grew larger and it was in this way 

 that the radially symmetric Radiata together with Echinoder- 

 mata developed; or they began to creep over the substratum, 

 and this was the way how the bilaterally symmetric "Artiozo- 

 aires" evolved. 



The Origin of Cnidaria 



Before we begin to discuss the main problem of the present 

 study, i.e. the true nature and the origin of Cnidaria, we 

 have first to touch on the question, **what is the primary or 

 fundamental form of Cnidaria?" It is weU known that 



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