290 THE EVOLUTION OF THE METAZOA 



of zygotes which occur frequently en masse. The postgamous 

 divisions of the still enclosed zygote (the zygote karyon) are 

 strongly reduced in the conjugating Ciliata because of their 

 general oligomerization; yet there still occur regularly, special 

 divisions of the zygote karyon which succeed each other 

 quickly and which are also followed by the divisions of the 

 whole body. Numerous experiments have shown that the 

 exconjugants divide more rapidly. This shows that during 

 the conjugation the animals also become reorganized (or, as 

 we frequently hear, rejuvenated). An essential difference 

 between the genuine Ciliata and all the Eumetazoa lies in the 

 fact that in the latter each zygote is regularly developed by way 

 of divisions into a new polykaryonic individual which finally 

 leads to an embryonic development. It is worth mentioning 

 that much later this situation finally evolves in numerous 

 animal groups, including man himself, into the phenomenon 

 where simultaneously, or even generally, one gynogamete only 

 is developed while the number of androgametes remains very 

 large, a situation which can be easily understood if we take 

 into consideration the function of the spermatozoa. 



Other facts that have been observed and described under 

 various names in connection with the sexual karyons of In- 

 fusoria, such as endomixis, hemimixis, reorganization, etc., can 

 not only be compared with the similar developments in the 

 "normal" Protozoa if we view the organization of Infusoria 

 from our point of view; they can even be declared as simply 

 homologous to self-fertilization and to parthenogenesis. A 

 detailed study of these problems, however, would pass the 

 limits of our present task. 



A sexualization of the generation of gamonts takes place 

 also elsewhere among the Protozoa as this can be seen in the 

 case of Eugregarinida where the syzygy can be observed; from 

 the Protozoa it was clearly transferred to the Eumetazoa. The 

 question arises whether something similar could not also be 

 found among the Acoela? As far as I know no sexualization 

 of the vegetative phase has yet been observed in the Acoela. 



