NEW INTERPRETATION OF CNIDARIA 275 



of the so-called "fundamental biogenetic law" as it was pro- 

 posed by Haeckel (even if recently an apology was written by 

 Remane (1960) in favour of the same law), but also with facts 

 that can be observed in the ontogenies; these facts show how 

 easily and radically the morphogenetic conditions of the onto- 

 genetic as well as of the embryonic and of postembryonic 

 stages can be changed. Such changes can even take place within 

 one and the same line of evolution (animal group). It should 

 be pointed out that during the development which takes place 

 under the protection of a husk or of the maternal body, thus 

 free of the direct influences of the environment, as well as 

 towards the close of an eventual larval life in another biotope 

 when a metamorphosis has become necessary, morphogenetic 

 processes can frequently be observed which would be im- 

 possible during an adult stage which leads an independent life 

 (e.g. the changes of the intestinal openings). Because of these 

 changes, zoologists are now divided into two opposite groups. 

 Unfortunately enough it must be repeated again and again: in 

 our phylogenetic conclusions we must take into consideration 

 the comparative morphology of the adult form (this should 

 above all be considered!) as well as the stages of the ontogene- 

 tic development; yet in the latter study we must proceed even 

 more carefully and critically, taking constantly into consider- 

 ation the peculiarities of the ontogenetic processes. 



In our case, i.e. in the study of the origin of Turbellaria we 

 consider that it agrees better with the given facts (we must not 

 forget that this is an opinion only, based on a probable 

 conclusion) when we do not take the easiest road by simply 

 supposing (this, too, is a supposition only, and nothing else) 

 that the most primitive Turbellaria had evolved from some 

 planuloid ancestors. Regardless of the fact that no planuloid 

 forms can be found now among the Hving animals (this is not 

 decisive because it is possible that such forms had formerly 

 existed and that they have now become extinct)— we cannot 

 consider the so-called Mesozoa to be such animals because they 

 are endoparasites — it is my opinion that no planuloid animal 



