NEW IXTERPRETATIOX OF CXIDARIA 299 



had separated from the Une of evolution that had been pursued 

 by Infusoria even before the true Infusoria had developed, 

 i.e. that the separation had taken place on the level of poly- 

 karyonic and polymastigous Flagellata (Hadzi, 1944:160). I 

 thought that this stage of the phylogenetic development 

 should replace the planula as proposed by v. Graff. Later 

 (Hadzi, 1953 : 149)1 became convinced that we must place this 

 important point somewhat higher, and so I spoke of the 

 "infusorial-like ancestors" of the Acoela. Due to a recent 

 restudy of the whole problem I have now come to the conclu- 

 sion—I will soon return to this point— that the separation 

 of these two lines of evolution had taken place on the level 

 of very primitive Infusoria which on the other hand had 

 already ceased to be genuine typical Flagellata. These very 

 primitive Infusoria had later developed on one hand into 

 the typical Infusoria, and on the other into the Eumetazoa. 

 It is much more probable that the definitive and total in- 

 corporation and internaUzation of gametes had taken place 

 after the Une of Eumetazoa had already separated from the 

 line Infusoria. In the latter the development had led to con- 

 jugation as it is now known. This means that in the Eu- 

 metazoa the gametocytes have never lost their independence 

 and that they have never united their own cytoplasm with 

 the cvtoplasm of the progamont. Xo cellularization of gametes 

 has therefore in aU probabiHty been necessary. The sexual 

 phase had become internalized; it was just at this point and 

 in its transition to the hermaphroditism that this primitive 

 infusorian— which was the ancestor of Eumetazoa— had dif- 

 fered from its equally polvkarvonic and hypermastigous 

 flagellate ancestors. 



It should be mentioned in this connection when we refer 

 to the Flagellata as direct antecedents of Eumetazoa that 

 in this way we are easily able to understand, \^ithout being 

 obliged to take refuge in the thesis of flagellate colonies, the 

 numerous cvtological peculiarities that can also be found in 

 the Eumetazoa, and not only in sponges. 



