320 THE EVOLUTION OF THE METAZOA 



Instead of the vague and indefinite statement that the 

 Eumetazoa evolved first as the Acoela, among the Turbellaria, 

 from some Infusoria-like ancestors, we can now state with 

 better justification that the Eumetazoa evolved first — 

 contrary to the evolution of sponges and of all the polycellular 

 plants— as polymerized Protozoa, thus as Protozoa that were 

 equipped with a larger number of karyons and of kinetids 

 (cilia); during that state they were no longer typical FlageUata, 

 neither had they yet reached the state of the typical Infusoria; 

 yet their ancestors stood closer to the Infusoria than to the 

 FlageUata mainly because of the fact that their diploid and 

 polykaryonic vegetative generation (the "indifferent" gener- 

 ation, according to Dogiel) had also become the bearer of 

 the sexual, i.e. hermaphroditic, generation. These ancestors can 

 therefore be called the "Urciliata" (Protociliata) (the primitive 

 Ciliata). 



The gamontized generation therefore also includes the 

 sexual generation which had remained cellularized (it has by 

 now already changed into a phase). This sexual generation deve- 

 lops its maturity in the interior of the maternal animal and it 

 becomes free in the form of gametes after or during 

 pairing. The zygotes which are formed in this way, the ferti- 

 lized &gg cells, develop during ontogeny into a new genera- 

 tion. Thus the progamic subphase of the sexual phase has been 

 internalized and this has led to the formation of gonads. These 

 gonads represent therefore from the very beginning a corpus 

 separatum in the body of the Eumetazoa and they cannot be 

 considered as a genuine gland. 



The earliest Eumetazoa have taken over all the organelles as 

 well as the finer and specialized cytoplasmatic structure of 

 their protozoan ancestors. For reasons that are so far un- 

 known, the direction of division changed just at this moment 

 from a longitudinal to a transverse division via an oblique 

 division. This change occurred during a transition which 

 is at the same time one of the most crucial transitions in the 

 whole evolution of the living world. The change may perhaps 



