298 THE EVOLUTION OF THE META20A 



number of chromosomes which are, moreover, frequently 

 strongly polyploidal; yet a part of them, has become inactive. 

 The experiment which was made by Horv^th(1947) has shown 

 that this is really so. This Hungarian 2oologist suceeded in 

 separating the micronucleus by means of ultraviolet rays. The 

 animals remained alive. Parts of the old macronucleus which is 

 normally lost, developed during the conjugation into a new 

 micronucleus. I wish to mention in this connection that in 

 the Acoela no early separation of the Anlage of a gonad takes 

 place as far as we know about the early ontogeny of the Acoela. 

 This is also true for other Turbellaria. We must consider it 

 as a result of a secondary development if we find in other 

 groups of Eumetazoa, e.g. in Nematoidea, an early developed 

 "germ path." It seems to be very probable that in the primitive 

 Infusoria— which alone can be taken into consideration as 

 ancestors of the Acoela and which still have gametes that 

 become free — no early separation of the somatic and genera- 

 tive karyons had taken place, a situation that can still be 

 observed in the Opalinidae. 



The Point of Separation in the Evolution 

 of Infusoria and Eumetazoa 



This deviation from the straight line of argument which 

 investigates the origin of the Acoela, and thus of all 

 the Eumetazoa from their infusorian ancestors, has led 

 us to the more highly developed Infusoria whose comp- 

 lexity has been the main reason why it is so difficult to 

 get the right interpretation of acoela evolution. It has been 

 necessary to make this detour because wdth it we are en- 

 abled to determine with the greatest probability, the point 

 where the two diverging lines of evolution had separated. 

 I myself wavered initially on how^ to solve this question. 

 I was inclined to believe— in view of the numerous peculiari- 

 ties that are limited to the Infusoria only— that the Acoela 



