464 THE EVOLUTION OF THE METAZOA 



symmetric Cnidaria whose radial symmetry is actually a second- 

 ary phenomenon; the Ctenophora finally do not show a radially 

 symmetric structure at all. For reasons which we do not 

 wish to repeat here we should also abandon the division of the 

 "Bilateria" into the Protostomia and the Deuterostomia. This 

 is the change which will be least easily accepted and which 

 is at the same time also the most important one that has to 

 be made. All the remaining changes that must be made in 

 the diagram as proposed by Hyman have a minor character 

 only and they are actually "quite painless." First of all wx 

 must cancel in this system larval names (planula, dipleurula, 

 trochophore) because they do not belong in such a diagram 

 for reasons which we have sufficiently discussed. Furthermore 

 we must also omit the Mesozoa, a group w^hich is already 

 now accompanied by a question mark. This especially must be 

 done because we do not find indicated in the same diagram 

 the adequate categories of the Protozoa, Metazoa, and the 

 Eumetazoa, even if these groups are used in the linear 

 enumerations. 



The "primitive medusa" which has really no justification, 

 must be abandoned as the initial form of the Coelenterata. 

 Neither should the Coelenterata be indicated as such (in the 

 enumeration they can appear together wdth the name Cnidaria, 

 thus with the exclusion of the Ctenophora!). We must also 

 cease to divide (this is actually not even done in the diagram 

 here discussed) the Eumetazoa (they are indicated here as a 

 "branch") into the Acoelomata, Pseudocoelomata, and the 

 Eucoelomata (they are all written with capital letters only); 

 the same should also be made with the division of the Eucoelo- 

 mata into the Schizocoela and the Enterocoela, a division 

 which is indicated once only ("other Schizocoela") and w^hich 

 is represented in the linear survey with numbers only. Such 

 a division does not correspond to the well know^n relationship 

 connections, a fact which is particularly true for the group 

 Schizocoela, yet it is also valid for the group Enterocoela 

 (e.g. the separation of the Brachiopoda from the Chaetognatha, 



