PREVIOUS INTERPRETATIONS OF CNIDARIA 85 



guidance and supervision. Us (1932) succeeded in showing 

 that MetschnikoflF's results correspond fully to the actual 

 facts. In this way the difficulty has been removed, the Cteno- 

 phores have a mesoderm and this helps to prove the accuracy 

 of my hypothesis which tries to derive Ctenophora from the 

 planktonic polyclad larvae. 



Much later, I found that I was neither the first nor the only 

 person who formulated this idea about the origin of Cteno- 

 phora. Garstang developed his idea to explain the origin of 

 Ctenophora from the Miiller's larva of Polycladida by way 

 of neoteny; this idea was proposed in an ingenious poetical 

 w^ork whose form, however, did not correspond to that of a 

 serious scholarly interpretation. It was published by Hardy 

 in 1954. I have briefly mentioned this case in the introduction 

 to the present study. 



The origin of Turbellaria, and especially of Polycladida, 

 from the Ctenophora has been discussed much more than 

 the origin of Ctenophora. The reason for this can be found 

 in the large number of similarities that exist between Cteno- 

 phora and Polycladida; it has been much more obvious to 

 explain these similarities as being due to a development of 

 Polycladida with their compUcated genital mechanisms from 

 the simply built Ctenophora, than vice versa. This inter- 

 pretation has seemed to be supported by the discovery of 

 benthonic, and therefore flattened, species of Ctenophora, 

 e.g. Coeloplana, Platyctena, etc. Lang (1880) who had proposed 

 this theory, has been followed by numerous zoologists. 

 Nevertheless it soon became clear that these species of 

 benthonic Ctenophora cannot be anything but aberrant species 

 which can lead to no new forms except such as for example 

 the sessile Tjalfiella. In this way the Ctenophora must definitely 

 be excluded from the line of evolution of the so-called Coelo- 

 mata or Bilateria. They only represent a blindly ending side- 

 branch on the tree of the animal world. 



Finally, it should be mentioned that there have even been 

 some zoologists who have tried to find a solution of the 

 7 



