CNIDARIA AS THE ONLY COELENTERATA 31 



are not yet fully developed. In the future we can with certainty 

 expect more important results from this method. My invitation 

 to biochemists to check, by means of the serum method, my 

 hypothesis of the closer relationship between Cnidaria and 

 Turbellaria has remained, to the best of my knowledge, so 

 far without any response in the international literature on 

 the subject. 



It has been already mentioned that we cannot expect to 

 find fossil remains of the early stages in the evolution of 

 Cnidaria, since possibly no species belonging to them had 

 existed at that time which could have left some fossilized 

 traces. Yet even those traces w^hich go back to more recent 

 times arenotunimportantfor our purposes. Somewhat doubt- 

 ful kinds of remains belonging to Cnidaria are known, that 

 date from the Middle Cambrian. They belong to the now 

 extinct Tetracoralla. No remains that can with certainty be 

 attributed to Hydrozoa can be found earlier than in the 

 Upper Triassic; some partly uncertain forms that resemble 

 the present-day Campanulariae date from the Silurian. Impres- 

 sions of Scyphomedusae that can be easily identified go back 

 to the JVIiddle Cambrian. 



According to Schindewolf (1950), who in his studies paid 

 special attention to the evolution of corals, the earliest remains 

 that can with certainty be attributed to Madreporaria, and 

 thus to Anthozoa, belong to the Upper Ordovician (which 

 was formerly usually called Silurian). They evolved rapidly 

 and differentiated into numerous species, some lived a solitary 

 life (this is very important in our connection!), and some 

 which formed colonies or cormi and which began to build 

 coral reefs. Similar earUer reefs had been built by the Archaeo- 

 cyathidae, which are now considered to have been a kind 

 of silicious sponges. Fortunately enough, we find sclerosepta 

 even in the earliest stone-corals; this enables us to study 

 their internal structures, i.e. the distribution of the sarcosepta. 

 It has even been possible to trace the ontogenetical develop- 

 ment of their septal apparatus. In this way Schindewolf 



