192 THE EVOLUTION OF THE METAZOA 



(Euciliata) among Protozoa; this property had obviously been 

 inherited by Turbellaria from the latter. This same property 

 has afterwards been inherited from Turbellaria by their nume- 

 rous descendants among Ameria that live a normal, i.e. a free 

 (and not a parasitic) life. It has even passed on (with few ex- 

 ceptions that can be easily explained) to the Polymeria and 

 Oligomeria and up to Chordata, even if here it has been pre- 

 served locally only and in the interior of their bodies, parti- 

 cularly during the transition from a wet to a dry environment. 



It may not be out of place to mention that the active or- 

 ganelles of cells that could practically be called undulipodia 

 appear phylogenetically first as single (per individual) flagella 

 which are later developed by way of polymerization into nu- 

 merous cilia; subsequently they can readopt, by way of oligo- 

 merization, the form of flagella. The possibility must also be 

 taken into consideration that such an ability to form un- 

 dulipodia which had been phylogenetically lost (by way of a 

 minus mutation) can again be restored (by way of a plus 

 mutation), perhaps with the limitation that not too long a 

 period had passed from the time of the minus mutation. 



Such minus mutations have also taken place in Turbellaria; 

 they have been supported by the natural selection when the 

 mechanism used for the movements develops in their muscular 

 system due to a change in their way of life. In this case, the 

 epidermal cells cease to form cilia and begin to develop a 

 protective organic cover, the cuticle. Among Turbellaria this 

 has been above all the case in Temnocephala. These are Tur- 

 bellaria that live as epizoic or even as ectoparasitic animals; 

 they are able to move easily (Matjasic, 1959) and they closely 

 resemble Trematoda so that some scholars have even included 

 them among Trematoda. The ciliation of the body surface 

 has been completely lost in Trematoda and in Cestoda that have 

 certainly developed from Turbellaria. 



The ciliation of the body surface has been preserved in all 

 small animals that move freely in water. All the young (larval) 

 freely moving stages of Cnidaria are covered with cilia. There 



