NEW INTERPRETATION OF CNIDARIA 345 



the substratum) to a vertical attitude is sufficient to start a 

 trend towards radial symmetry (towards the polypoid form). 

 This change of symmetry can make a rapid progress regardless 

 of the original form of structure when this induction is sup- 

 ported by an attachment of the animal to its substratum. It is 

 obvious that the general type of structure nevertheless plays 

 a certain role in this development. It is enough if we refer 

 in this connection to the case of Aprocta-Euprocta. Radial 

 symmetry can develop much more easily and fully in the 

 aproctous type than in the Euprocta ; in the latter the anal 

 opening which was originally situated opposite to the oral 

 opening must be first transplaced, and finally abandoned, 

 before they are able to develop a perfect radial symmetry. 

 Recently, a significant tendency can be observed among 

 zoologists to use the highest categories, especially that of the 

 phylum, quite frequently w^hen they classify larger groups of 

 animals. Not infrequently, we can find systems w^hich propose 

 even up to forty different phyla, so that finally we could get 

 an impression that there were the same number of completely 

 different types of structures, and that the scholars are probably 

 too subjective when they use the category of a phylum. It 

 seems to me that in this way the true phyletic relationships 

 only become blurred. It may be better for us to use the 

 category "phylum" more carefully as long as w^e do not 

 dispose of more exact methods of determining the antiquity 

 of a certain structural form. The mistake will probably be 

 less significant if we exaggerate in the opposite direction, even 

 if in this way we expose ourselves to the accusation that we 

 would like to take refuge in the old notion of a "progressive 

 scale of all things," or of ^H'echelle animale.^' Such an accusation 

 is entirely unjustified as we will show later. We must pay 

 our main attention to the classes, to their peculiarities and 

 to their groupings which must not always be made from a 

 purely formaUstic point only. We can expect that in future 

 many such uncertain problems will be clarified by means of 

 biochemistry. 



