THE NEW GENEALOGICAL TREE 389 



slits and cavities filled with the "cell fluid." This is the case, 

 for example, with the gonocoele of the Turbellaria with its 

 different canals, side cavities, and not infrequently with a 

 secondary polymerization (of gonads, of the terminal organs 

 of nephridia). This is how a rich morphological differentiation 

 became possible. It seems to me, however, that they do not 

 represent a sound basis to be used in classification. These 

 various coeloms and the morphological peculiarities which 

 are connected with them enter into such a variety of combina- 

 tions that it is impossible to develop on this basis any 

 principle which could be used in the classification. For- 

 tunately enough there have been only few attempts w^hich 

 have tried to construct a system on the basis of the conditions 

 that can be observed in these coeloms. Among these we must 

 mention above all the high taxons the Acoela and the Pseudo- 

 coela, or the Acoelomata and the Pseudocoelomata. To these 

 we must add the Eucoelomata as the third subseries (accord- 

 ing to Schimkewitsch, 1891). This classification was accepted 

 by Hyman (1940) and by the AAA'S) (Zoo logical Names ^ edited 

 by A. S. Pearse, 1949), obviously under the influence of 

 Hyman. The category Acoelomata has only sense if we 

 consider only the perigastric coelom as a genuine coelom; 

 yet if we accept the broader definition and if we consider 

 the coelom to be any body cavity which can be found in the 

 middle body layer of the Eumetazoa and which is surrounded 

 by its own cells, we see that the category Acoela becomes 

 completely senseless because in this case there are no genuine 

 and primary Acoela among the Eumetazoa. The notion of the 

 Pseudocoelomata is even less justified and useful. There do 

 not exist any Pseudocoelomata at all. A body cavity can 

 either be a primary cavity, i.e. without a coelothelium; or 

 it can be a genuine coelom if it has a coelothelium. The 

 category Pseudocoelomata consists, according to Hyman, 

 of the Aschelminthes and of the Endoprocta only. 

 These Endoprocta are actually Aschelminthes that had adopted 

 the sessile way of life but they do not differ essentially 

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