THE NEW GENEALOGICAL TREE 395 



case with Nemertinea, among the Ameria. This trend 

 towards polymerization and to an organization in the 

 direction of a polymerous type grew weaker and weaker 

 during the subsequent evolution of the Mollusca; an evolu- 

 tion which was generally progressive even if it went in a 

 special direction. The Mollusca must therefore be interpreted 

 as a side branch on the stem of the Ameria. The Cephalopoda 

 not only represent a climax in the evolution of the Mollusca, 

 but also of the evolution of the Ameria as a whole. It does not 

 seem that any new, higher animal type has ever evolved from 

 Mollusca. We will also find very similar conditions in other 

 main groups of the Eumetazoa. 



Turbellaria Cnidaria Gastrotricha 



Trem.atoda Ctenophora Kinorhyncha 



Cestoda Nemertinea Endoprocta 



Rotatoria Priapuloidea 



Nematoda Acanthocephala 



Nematomorpha Mollusca 



We can see if we make a survey of the fifteen classes* which 

 constitute the phylum Ameria that it is quite impossible to make 

 subdivisions ot this phylum where the classes that are more clo- 

 sely related with each other could be brought together into spe- 

 cial subphyla or superclasses (Fig. 54). This is also true for the 

 most widely accepted division into the Platyhelminthes and 

 the Coelhelminthes (Aschelminthes), or into the Scolecida and 

 the Aposcolecida, as well as for many other similar classifica- 

 tions which were suggested by various zoologists. Many of 

 these notions can prove quite useful here and in comparative 

 morphology — as is the case with the pair Aprocta : Euprocta — 



* In all probability a sixteenth class will have to be added to these, 

 i.e. that of the Orthonectoidea, as a side branch of the Trematoda (which 

 were called Mesozoa by Beklemischew (he divided the class Trematoda 

 into two groups: Monogenea and Digenea; in addition to these he also 

 created an independent class Udonelloidea). 



