NEW INTERPRETATION OF CNIDARIA 267 



this connection. The Endoprocta are not only an animal 

 group which lives on the sea bottom; they also show a strong 

 inclination to form cormi; they have not, however, developed, 

 a stage which would correspond to a medusa generation and 

 which would be able to live in plankton. Taken geologically, 

 Endoprocta may be younger than Cnidaria because they are 

 euproctous animals. Thus their phylogenetic root had reached 

 a higher level of evolution than the level that has been reached 

 by the aproctous Turbellaria. The Endoprocta, on the other 

 hand, have developed a planktonic larva whose organization 

 is even more highly developed than is the organization 

 of the adult animal form. Moreover, this differentation 

 had pursued its own direction which made it necessary 

 that a radical metamorphosis be introduced. This is a typical 

 example of a special evolution of a larva which leads 

 its own way of life. It would be completely wrong to see 

 a recapitulation in this kind of development, i.e. to conclude 

 on the basis of present conditions that the ancestors of Endo- 

 procta had lived in plankton and that they had the form and 

 the structure of a trochophore. It is even misleading to call 

 the larva of Endoprocta, a trochophore and to compare it in 

 any way with the larva of Ectoprocta in order to justify in 

 this way a systematic union of these two groups, as this 

 was done by Marcus (Hadzi, 1956). These are in reality 

 pure convergences only which were caused by very similar 

 ways of life, a fact which can also be observed, for example, 

 in all the sessile animal types. 



Since Endoprocta, as euproctous Ameria, are in all pro- 

 bability (as has already been emphasized) phylogenetically 

 younger than Cnidaria, it seems incomprehensible why the 

 older Cnidaria, which are equally sessile animals that form 

 cormi, had not developed a planktonic larva with a higher 

 level of organization. We have already tried to give an answer 

 to this problem, taking into consideration the formation of the 

 medusa generation which had taken over the role of plank- 

 tonic larvae. A medusa, however, cannot be considered to 



