396 



THE EVOLUTION OF THE METAZOA 



yet they cannot be used in taxonomy. They only lead to an 

 unnecessary complication of the animal system and to diffe- 

 rentiations which are, we can say, personally biased. The case 

 of the antithetical pair Platyhelminthes : Aschelminthes where 

 these two groups are understood as two parallel taxons, or 



Polymer/a 



Amenta 



Nemertinea 



Entoprocta 



Kinorhyncha 



Gastrotricha 



Rotatoria 



MoUusca 



Priapuloidea ^\ 

 Acanthiocephala\ 

 Nematomorpha I 

 Nematoda 



Cestoda 

 Trematoda \ 

 Turbedaria \ 

 Ctenophora I 

 Cnidaria \ 

 f Hydrozoa \\ 

 Scypt)ozoaji 

 \ Anthozoa // 



Turbeltana 



Infusoria 

 (EucHiata) 



Fig. 54. Genealogical tree of the phylum: Ameria. 



as two taxons where one stands above the other, shows the 

 inadequacy of such a division because there is no real limit 

 between these two groups, because the Nemertinea stand in 

 the middle between them, and finally because not all the Tur- 

 bellaria are really flattened animals. We do not even know 

 which groups should be classified as Aschelminthes. Accord- 

 ing to Hyman the Aschelminthes consist of the follow- 

 ing classes: Rotifera, Gastrotricha, Kinorhyncha, Nematoda, 

 Nematomorpha, and Acanthocephala; yet they do not include 



