74 THE EVOLUTION OF THE METAZOA 



Zoophjta had been created. It was much later that it has finally 

 become clear that these Zoophyta are really animals, and not 

 plants, or something that is between a plant and an animal. 

 It was not till 1723 that it was first suggested, by Peysonell, 

 that these are really the lowest or the most primitive 

 animals. The external forms of these animals, have always 

 been particularly emphasi^^ed and many zoologists have 

 become especially impressed by their radial symmetry. This 

 had been important when the first attempts were made to 

 construct a classification of the animal world on the basis of a 

 comparative method. In place of the name Zoophyta, the name 

 Radiata was introduced, with some simultaneous changes 

 of their spheres and of the subgroups they were supposed to 

 include: a possibly worse solution. The name Zoophyta itself 

 (this name was used for a long time) included all kind of ani- 

 mals, or, as this has been said by L. Hyman, "A variety of soft- 

 bodied animals, from sponges to ascidians." Under the banner 

 of Radiata, Cnidaria were again connected with completely 

 different types of animals, especially with the Echinodermata; 

 this was done because of their radial symmetry only (Cuvier). 

 Lamarck himself had tried to separate the medusae from po- 

 lyps. Many zoologists, especially the French scholars, adhered 

 strictly to this wrong concept of Radiata even a long time after 

 Darwinism had been firmly established and when attempts had 

 been made to create a natural animal system built on the 

 principles of evolution; the same mistakes can be partly en- 

 countered even to the present day. 



In the mean time great progress has been made in the field 

 of the fine morphology of the lower invertebrates. The prog- 

 ress made in the ontogenetics or in embryology— especially 

 of Vertebrata— has been of considerable importance for the 

 evaluation of Cnidaria; it was in this way that the theory 

 of germ layers was developed. Even the bodies of adult 

 animals have repeatedly been divided into layers: first there 

 was one stratum, then two, and finally three strata or dermas 

 (ecto-, ento-, and finally mesoderm). Even if it was likely that 



