PREVIOUS INTERPRETATIONS OF CNIDARIA 79 



blastica or Radiata— which consist of Spongiae and Coelente- 

 rata— and Triploblastica (Bilateria). The influence of the histo- 

 rical moment (or of conservatism?) can be seen in the fact 

 that the old notion of Radiata reappears again and again 

 to be used for systematic-taxonomic purposes, even if in the 

 mean time it has become clear that it is not in Cnidaria 

 only that radial symmetry can be found (in Cnidaria this 

 symmetry is not even completely developed), and that it is 

 arbitrary (even if correct) to exclude Echinodermata from Radi- 

 ata. It was due to this influence that it has not been perceived 

 that the radially symmetric distribution of various parts (the 

 formation of antimeres) is not connected with any definite type 

 of structure, and that instead it can appear at any level of 

 organization, even if the more or less perfect development of 

 this symmetry can vary: the only condition for it is the adoption 

 of a sessile way of life. Exactly as it has finally become necessary 

 to accept the fact that, phyletically, Cnidaria have nothing in 

 common with Echinodermata even if they are both (secon- 

 darily!) more or less radially symmetric, it will be necessary 

 to get used to the fact that Ctenophora must be separated from 

 Cnidaria— like Echinodermata— even if they are not widely 

 different from them: each has developed out of its own "root" 

 and it was the ancestors only of these two groups which were 

 closely related to each other; in both cases the ancestors were 

 turbellarians, yet of different subtypes. The same is naturally 

 true— yet to a considerably greater degree— for the mutual 

 connections between Porifera and Cnidaria. 



For historical reasons and because of their external ap- 

 pearance Cnidaria have always been— justly, as it has seemed— 

 connected with Ctenophora. The latter are occasionally called 

 Acnidaria (Biitschli) in order particularly to emphasize in this 

 way their close connection with Cnidaria. The names of these 

 animals have been repeatedly changed in the more distant past 

 as this can be seen in Krumbach (1928); frequently they were 

 called Acalepha, i.e. medusae. Their jelly like, even watery, 

 consistency, their life in plankton, the strong contractility of 



