358 THE EVOLUTION OF THE METAZOA 



the "hypercellular forms") should consist of an independent 

 cladus of Ciliata. Hatschek also united the two phyla into 

 the division Cyto2oa. In spite of the fact that Hatschek was 

 the first 20ologist who suggested such a classification we now 

 find the same division generally used, yet under other names 

 which were coined (quite unnecessarily) by Doflein (1901) 

 as the Plasmodroma and the Ciliophora. 



In many respects the Ciliata represent in fact an isolated 

 group among other groups of Protozoa. The standpoint can 

 also be defended that the climax of the progressive evolution 

 of the Protozoa had been reached in the Ciliata. In spite of 

 this it seems to be rather problematic that we should separate 

 the Ciliata so thoroughly from the Flagellata by means of 

 such a strict division into two large groups because it is quite 

 certain that the Ciliata evolved from the latter. It may be 

 better and more in agreement with the genetic conditions 

 if for the present we avoid dividing the main groups of the 

 Protozoa taxonomically into subgroups. In morphological 

 practice, however, the notional pair Cytoidea and Cyto- 

 morpha may prove useful, as is also the case with the notion 

 of the Undulipodia (Hadzi, 1944) which includes the FlageUata 

 and the Ciliata because of their undulipodia (flageUa and cilia). 

 In the literature we can frequently find that the division of 

 Protozoa into two large subgroups has not been accepted 

 (cf. Hall's Proto^oolog)}). 



Some protozoologists, e.g. Belar and others, may be right 

 when they suggest that the taxon "phylum" should be given 

 to those groups of Protozoa which have been given the taxon 

 "class" so far, even if in the Protozoa the morphological 

 differences (the structural forms) are not so conspicuous, 

 owing to their acellularity and small dimensions, as in the 

 geologically younger Metazoa. We must take into considera- 

 tion here the fact that the Protozoa had at their disposal a 

 much longer period for their evolution than the Metazoa. 

 This circumstance has perhaps also been the reason why 

 protozoologists are still so uncertain regarding the relation- 



