98 THE EVOLUTION OF THE METAZOA 



riate), to the level of an organ and, finally, they disappear 

 without any trace when the animal adopts the colonial status. 



It would suffice to take into consideration only the unavoid- 

 able consequences of the sedentary way of life in order to 

 show the untenability of the concept which has been proposed 

 of a progressive evolution in Cnidaria. Further proofs of the 

 accuracy of our interpretation can be made by a morpholo- 

 gical comparison together wdth a simultaneous consideration 

 of the ecological condition. 



First we shall discuss here the symmetrical conditions; they 

 are the most conspicuous element and they have actually been 

 the first reason why scholars have begun to doubt the accuracy 

 of the idea of a progressive line of evolution in Cnidaria. 

 The palaeozoologists were the first who became aware of 

 this fact; in connection with a detailed analysis of the 

 internal skeleton of Madreporaria among Anthopolyps 

 they have discovered that the sclerosepta do not agree with 

 the radial symmetry of these animals as one would expect 

 particularly if we consider the Anthozoa as the most highly 

 developed Cnidaria. It was Otto H. Schindewolf (1930) 

 who has especially discussed this fact in great detail. We can 

 read in his book Gnindlagen der Palaontologie (1950, Stuttgart, 

 p. 179), "Die erste Anlage des Septalapparates bei den Ptero- 

 korallen ist bilateral; die sechs Protosepten wxrden ausge- 

 sprochen zweiseitig-symmetrisch herausgebildet. Erst nach 

 ihrer vollen Ausgestaltung tritt erstmal eine radiale Symmetrie- 

 form hervor, und zwar ist diese hexamer, sechszahlig." To 

 this he continues, "Die Radialitat beschrankt sich jedoch 

 nur auf ein voriibergehendes Stadium." Similar conditions can 

 be observed in numerous recent Anthozoa, particularly those 

 that live as soUtary animals. 



The palaeozoologist O. Kuhn (1939) has been lead by this 

 important fact to state, in spite of his reserved attitude with 

 regard to the "Wurzel der Coelenteraten," that the ancestral 

 form of Cnidaria must be imagined as a bilaterally built, 

 creeping, or freely swimming organism. 



