NEW INTERPRETATION OF CNIDARIA 335 



Can Egg Cleavage Be Really Considered 

 as a Proof of the Colonial Theory? 



We can now return to the question: can we conclude on 

 the basis of the fact that the ontogenies of a majority of 

 Eumetazoa begin with a cleavage, i.e. without a polykaryonic 

 state, that the Eumetazoa also evolved (similarly as Metaphyta 

 and Spongiae) from some colonies of the Flagellata? Those 

 who adhere to the old colonial theory find this situation 

 considerably simpler, especially if they believe in the validity 

 of the "fundamental biogenetic law" and if they consider 

 that the evolution proceeded in the direction Mono-, Di- and 

 Triploblastostoidea. In this case one could expect in advance 

 that the Eumetazoa also develop as postgamous individuals 

 by way of polytomous or repeated divisions of cells, and 

 secondarily and under special conditions plasmodially. This is 

 the case when their zygote is overloaded with a reserve food 

 while at the same time it is possible that a change in the type 

 of breathing also plays an important role in this connection. 



I think, in spite of the apparently greater probabiHty of a 

 generally colonial evolution of all the metabionts, that the 

 Eumetazoa evolved from a plasmodial or polykaryonic state 

 and that they adopted their cleavage as a result of a secondary 

 development at a period when the older stages and the adult 

 animal form had already become cellularized, even if we 

 are well aw^are that we cannot offer any strict proof for 

 this interpretation. We can make our interpretation only 

 probable, and that on the basis of two "indications." The 

 first indication w^hich has already been mentioned could be 

 the physiological necessity of the parcelling or of the cellula- 

 rization just during the earUest ontogenetic stages because of 

 the great consumption of oxygen and because of the need of 

 large free surfaces which is a consequence of the increased 

 consumption of oxygen. 



The following objection can be made against this indication. 

 If the cellularization had appeared at such early stages of the 



