PREVIOUS INTERPRETATIONS OF CNIDARIA 225 



was repeated later by others with the same result). Not only as 

 a species but also as a genus, the green Hydra (Chlorohydra 

 vivridissima) is so closely connected with its green symbiont 

 that it is only with difficulty able to live without it. 



The fact may not be completely without significance that in 

 the lower Turbellaria the symbiotic algae appear everywhere in 

 their interior ("entomesoderm," or better archihiston, accord- 

 ing to Steinbock), clearly a sign of a lower level of develop- 

 ment. In Cnidaria we find, with a few exceptions, these algae 

 in the intestinal cells only. 



Thus the facts that can be observed in the symbiosis bet- 

 ween animals and the monocellular algae support my thesis 

 that this symbiosis had been developed as early as in Protozoa, 

 that it had been inherited from these by the lowermost Eume- 

 tazoa, then by Turbellaria, and that from these it was trans- 

 ferred to Cnidaria where it has been further evolved. 



With this we can conclude the second part of our present 

 study. In it I have endeavoured to make it at least more 

 probable that, contrary to the widely accepted opinion, the 

 phylogenetic development of Cnidaria followed the di- 

 rection Anthozoa— Scyphozoa— Hydrozoa, a direction which 

 also agrees with the generally accepted principle that the sessile 

 way of Hfe leads both to the radial symmetry and to the retro- 

 gression of the organization (especially inasmuch this is con- 

 nected with the free movement) with a simultaneous pro- 

 gressive development of new or of already present properties 

 that are connected with the sessile way of life, and that in this 

 way a new animal type is being developed. No well-warranted 

 facts are known to me which would be incompatible with 

 this new interpretation. On the contrary, I find that many 

 facts which could not be understood or which were obscure, 

 become understandable and clear if viewed from this stand- 

 point. 



