252 THE EVOLUTION OF THE METAZOA 



evolution of freely moving animals could possibly have 

 reached the extent that Remane, and even more so 

 Jagersten, are obliged to construct. The problem of the 

 "mesoderm" becomes complicated beyond any solution (see 

 p. 100 in Jagersten's study, 1959). Jagersten will finally be 

 obliged to admit the existence of a coelenterate type, and 

 this in an even wider scope than was previously done by 

 Haeckel, who even classified Platyhelminthes among Coelen- 

 terata. This is more consistent since Platyhelminthes are 

 in reality not Coelomata in the usual sense of the word; 

 see in this connection Jagersten's discussion of Xenotur- 

 bella (1959:101). The uncertainty Jagersten finally feels can 

 be seen in the fact that in his diagram (1955: Fig. 8, p. 

 352) he does not use the notion and the category of 

 Coelenterata in opposition to Coelomata— he only mentions 

 Cnidaria and Ctenophora. In a more recent publication 

 (1959:101) he quite misleadingly classifies Xenoturbella among 

 Coelenterata, yet in the same paragraph he also speaks of the 

 "so-called coelenterates." 



It is not important that I have been the first neo-zoo- 

 logist who has (earlier and independently from Jagersten) 

 come to the conclusion, on the basis of a study of comparative 

 morphology, that the Anthozoa had evolved as the earliest 

 form of Cnidaria. The important thing is that I have come 

 to this conclusion by means of a study of comparative 

 morphology while taking into consideration the ecological 

 conditions. Because of this new situation it has become neces- 

 sary to try to find the probable origin of Cnidaria: it was 

 in this way that new problems arose and that a whole new 

 sphere of research has been opened. 



It was clear from the very beginning that the old concept 

 can be used no longer in this new situation, even if it has 

 been used so long without any reservations in spite of the 

 fact that there have been numerous well-known zoologists 

 who have expressed doubts about the foundations of the 

 same concept, such as is the so-called "fundamental biogenetic 



