286 THE EVOLUTION OF THE METAZOA 



little is known about the sexual phase of other polykaryonic 

 Flagellata. It was even thought that they have completely lost 

 their sexual phase, a supposition which has now been proved 

 wrong. 



It could perhaps be expected that some transitional forms 

 might be found among the Euciliata, a possibility which cannot 

 be completely excluded. Thus the case of the Glaucoma (Dalla- 

 sia) front ata Stokes was described some time ago by G. N. 

 Calkins and by R. Bowling (1941). It has been reported that 

 a copulation as well as a typical conjugation can be observed 

 in this species of holotrichous Infusoria. Yet the very fact 

 that the copulation and a simultaneous conjugation have been 

 observed makes it improbable that we really have a copula- 

 tion here. It is supposed that here two individuals which 

 consist of two nuclei each, encyst with each other which finally 

 leads to copulation. The true gametes, however, consist of one 

 nucleus only and they must pass through one or two meioses. 

 I believe that the case of the Glaucoma frontata can be set aside. 



The Zooflagellata (with strongly polymerized and equiva- 

 lent kinetids and nuclei which were gonochoristic and repro- 

 duced asexually, yet which propagated during the sexual phase 

 by way of oogamy producing greatly unequal free gametes 

 that copulated mutually, creating one zygote each time) can be 

 imagined as the initial form for the evolution of the typical 

 Euciliata as well as of the primitive Eumetazoa. These gametes 

 were haploid, and the zygote as well as the vegetative genera- 

 tion diploid. It should be mentioned in passing that in this they 

 differed greatly from Volvox w^hich is frequently mentioned 

 as a pattern of the ancestor of Metazoa: the zygote of the Vol- 

 vox undergoes a reduction, a fact which was particularly 

 stressed by E. D. Hanson (1958 : 27). 



There were in all probability two processes which played 

 a major role during the transition from the polymastigous and 

 polykaryonic Zooflagellata that had thus been developed by 

 way of polymerization: (1) the emergence of the hermaphrodi- 

 tism, and, (2) the internalization of gametogenesis. The inter- 



