THE NEW GENEALOGICAL TREE 365 



variant, i.e. whether evolution proceeded primarily by way of 

 a blastaea, or a planula, or a parenchymella. Certain charac- 

 teristics that are common both to the Spongiae and to the 

 "genuine" Metazoa (the Eumetazoa) do not disprove the 

 diphyletic origin of the two groups and the independent 

 evolution of the Spongiae. The same properties (these common 

 characteristics are generally the sexual phase and the ontogeny 

 which follows this sexual phase, with its initial phases, the 

 cleavage, the blastula, the gastrulation) can also be found in 

 the plant world during the transition of plants into the poly- 

 cellular forms, above all in the Phytomonadida or Volvocales. 

 These simiilarities are therefore clearly parallelisms. 



One more possibility can also be taken into consideration 

 which, however, can also be considered as a variant of the 

 pattern No. 3. This possibility is that all the Metazoa had 

 evolved from the colonial Choanoflagellata. According to such 

 an interpretation the Spongiae were the first which had 

 evolved, while the remaining Metazoa, the Eumetazoa had 

 developed from a very early phase of this phylogeny. We find 

 such a variant, w^hich can hardly be defended, quite unaccepta- 

 ble (Kemna has perhaps thought of some similar kind of 

 development?). 



Thus we find that contrary to the situation which exists in 

 plants it is comparatively easy to divide the animal world into 

 the Protozoa and the Metazoa inasmuch as we do not consider 

 that the Protozoa consists exclusively of the heterotrophic 

 monocellular (i.e. mononuclear) animal species. The Umit 

 between the Protozoa and the higher forms is also clear and 

 I dare maintain that no transitional forms between the Protozoa 

 and the Metazoa wdll ever be found among the recent species; 

 such forms had probably died out long ago. 



