XU INTRODUCTION 



their real nature. Though dogmas are characteristic for reli- 

 gious systems, yet the same can also be found in science. One 

 such dogma was, and it still is, the belief in the primary simp- 

 licity of Hydra, and even more so of Hydrozoa, and so too with 

 Cnidaria and Coelenterata. It is well known how diflficult it is 

 to fight against dogmas, particularly when they have been 

 accepted for so long, when they have been supported by re- 

 nowned scholars, and when they appear to be well founded. 

 My initial researches have shown that Hydra is in no way so 

 simply organized as the simple structure of its body would 

 seem to indicate when considered from a crudely anatomical 

 point of view. Soon I saw the first pillar of the proud struct- 

 ture of Coelenterata collapse. It has been almost generally ac- 

 cepted that Hjdra and its closest relatives are not primarily 

 soHtary animals but that, instead, they are derived from ances- 

 tors that were able to form cormi. Naturally, this discovery 

 alone could not suffice to make all Hydrozoa the secondarily 

 simplified Eumetazoa. Nevertheless, with this a good begin- 

 ning was made. 



