360 THE EVOLUTION OF THE METAZOA 



excluded in principle that the primarily heterotrophic orga- 

 nisms (in all probability micro-organisms)— thus the organisms 

 that had existed earlier than the eutrophic forms— had evolved 

 into the animal Protista, thus into the Protozoa; yet at the 

 same time such a suggestion cannot be made probable either. 

 It must be assumed, if such a deduction be right, that the 

 flagella had evolved at least twice, or we must suppose that 

 the Protophyta had evolved from the Protozoa which does 

 not seem to be probable at all. For all these reasons the inter- 

 pretation which believes in the priority of the Flagellata 

 appears to be more probable. The suggestion made by Grasse 

 has one purely formal advantage because it avoids the problem 

 which of the two groups should be given the priority. We 

 could justify such a unification from a factual point of view 

 only if w^e could prove that the common primitive form had 

 both flagella and pseudopodia and that the separation of forms 

 did not take place once only but several times. The suggestion 

 for such a unification has perhaps been made too early and it 

 is possible that in future it will be found that the suggestion 

 has been justified. It seems to us that the Flagellata represent 

 the central type of the Protozoa, that all the other types of 

 Protozoa up to the Ciliata had evolved from the Flagellata, and 

 that the Flagellata had played a role similar to the role of the 

 Turbellaria, among the Metazoa. 



Here we are not interested in any further and more detailed 

 taxonomy of the Protozoa inasmuch as it has no connection 

 with the evolution of the Metazoa. We would only Hke to 

 point to the fact that the polykaryonic (plasmodial) states can 

 be found developed by way of nuclear divisions— thus by way 

 of a polymerization of nuclei (which, however, is not identical 

 with the incomplete division!)— everywhere in all the large 

 groups of the Protozoa, even in such that lead an entirely 

 parasitic w^ay of Hfe; and that a process can afterwards be 

 observed in the personal development cycles which is very 

 similar to a cellularization. This process takes place in such a 

 way that either the "young cell" is, so to speak, excised from the 



