NEW INTERPRETATION OF CNIDARIA 253 



law " as it was formulated by Haeckel, and the hypothesis 

 that the polycellular animals had evolved from some colonies 

 of monocellular animals. In this situation it was most obvious 

 to think first of the Turbellaria. The Turbellaria have been in- 

 terpreted by almost all zoologists and above all by experts in 

 Turbellaria, as "Coelomata" with a primarily primitive struc- 

 ture. The zoologists who represent an exception here are 

 those who adhere to the enterocoele theory, i.e., those who, 

 like Sedgwick, try to deduce the metamery of Eucoelomata 

 from the cyclomery of anthopolyps. The typical Turbellaria, 

 however, i.e. the higher Turbellaria which stand above the 

 Acoela and which are usually taken into consideration by 

 zoologists when Turbellaria are mentioned, seem to be more 

 highly developed than Cnidaria because of their organization 

 and above all because of their extremely complex herm- 

 aphroditic genital apparatus. For all these reasons it appeared 

 as an alm.ost hopeless task to try to derive the Cnidaria from 

 the Turbellaria. 



This situation, however, changes quickly when we take 

 into consideration the frequently noticed fact that here we 

 have a case of a transition from the freely mobile to a sessile 

 way of life. Take for example Endoprocta (Kamptozoa), 

 Ectoprocta (Bryozoa), etc. Even among the Turbellaria 

 themselves the sexual apparatus shows a high degree of 

 variabiHty and there are some recent species of Turbellaria 

 with a very simple genital apparatus. We are therefore fully 

 justified in concluding that the possibilities of negative muta- 

 tions had existed at the time when the ancestors of Cnidaria 

 first evolved from the old forms of Turbellaria. It should 

 be mentioned in passing that a reduction of the genital 

 apparatus did not take place in individual cases of parasitism 

 (e.g. in Fecampia) that can be observed among the more 

 highly developed Turbellaria, but also in several cases of 

 Ameria whose development from Turbellaria can be considered 

 as more than probable (e.g. Nemertini, Gastrotricha, etc.). 

 Such a reduction took place even while free mobility was 



