NEW INTERPRETATION OF CNIDARIA 329 



derm s. 1.), on the other hand, had taken over a large number 

 of functions and it had later even participated in the formation 

 of the skin and of the intestine (as a cutis layer of the skin or 

 as a muscularis). The final result of this is that in an adult 

 animal we can no longer find any sharply-limited system of 

 layers ; we only have a whole animal before us. 



Two Difficulties of the Theory of Polykaryons 



There are in the main two facts which seem to be the cause 

 of considerable difficulties in connection with our inter- 

 pretation, in spite of the fact that such a large number of 

 similarities can be observed in the Infusoria and in the Tur- 

 bellaria. One difficulty consists in the fact that I consider the 

 plasmodial-polykaryonic thesis as probably more valid for the 

 evolution of the Eumetazoa, while at the same time I admit 

 that the colonial thesis seems to be much more justified for 

 the evolution of the Metaphyta and of Spongiae. The second 

 difficulty consists in the fact that in the ontogenies of the 

 Eumetazoa as well as of Spongiae, the first steps are regularly 

 made by way of divisions of cells or of cleavages and not, as 

 one would expect, by way of a division or polymerization of 

 karyons, which would take place in a permanently uniform 

 cytoplasm, and by way of a subsequent cellularization. Or, 

 in other words, why is the supposedly primary morphogenetic 

 process not recapitulated at least in the lowest Eumetazoa, in 

 the acoelous Turbellaria? I have already partly shown that 

 it is possible to explain rationally both these difficulties. 



Above all it is comparatively easy to overcome the first 

 difficulty. I think that it is much more probable— in spite of 

 the recent attempts (A. A. Sachwatkin) to place the Rhizopoda 

 \^-ith their amoebae at the root of Protozoa— that the Flagellata 

 are the most primitive Protista (Protophyta -}- Protozoa). In the 

 recent Protista we can find active two trends to a higher 

 development, i.e. the development by way of a formation of 



