350 THE EVOLUTION OF THE METAZOA 



In order to avoid any misunderstandings I wish to mention 

 that I think here of large groups only. We can see, if we make 

 a survey of almost innumerable attempts to construct the 

 genealogical tree of the animal world, that almost all these 

 genealogical trees are based on the principle of the oligophyly. 

 This is also true for my attempt. If we observe the best-known 

 case of the Vertebrata, where we are not obliged to work 

 with special phyla, we can see that in these evolution had 

 proceeded concordantly with the principle of the oligophyly, 

 and not of the polyphyly and there had been probably only 

 one diphyly when the reptilian type evolved on the one hand 

 into birds, and in the other into mammals. Yet even these two 

 highest groups did not evolve in all probability from a com- 

 mon initial point as can be understood if w^e view the extremely 

 schematized sketches of the genealogical tree. 



G. S. Carter who sees in my attempt a similarity to 'U'echelle 

 aniwale^' has in his own attempt taken into consideration the 

 diphyletic development only of his superphyla which cor- 

 respond roughly to my phyla. The "radiation" of his super- 

 phylum Annelida, however, does not issue from a single 

 point, or from a single root, but rather from a very prolonged 

 curve. 



The example of the evolution of the Protozoa shows that 

 we are not alw^ays able to use the concept of monophyly 

 only. Here polyphyly seems to be the most probable 

 form of the evolution. Yet even here the w^ord polyphyly 

 sounds an exaggeration because it seems that there were only 

 two to three separate lines of evolution. The word oligophyly 

 appears therefore to be more suitable also in this case. The 

 same is true for the evolution of the Metazoa from the Pro- 

 tozoa; it is quite improbable that in the evolution of the Metazoa 

 there were more than two separate roots or points of separa- 

 tion, i.e. besides those of the Parazoa and the Eumetazoa, 

 that of the Mesozoa also, as the third root. 



The question also arises of how those cases can be evaluated 

 and named where two or several subtypes had probably evolv- 



