THE NEW GENEALOGICAL TREE 407 



emerged as a consequence of the fact that true meta- 

 morphosis had been introduced. The institution of teloblasts 

 and the introduction of zones of proliferation are two such 

 new elements of the ontogenetic process. 



The Problem of Justification of the High Taxons: 

 Protostomia-Deuterostomia 



Before we continue with our attempt to construct a new 

 animal classification we must first discuss the problem of a 

 justification of a division of the "Coelomata" into the two 

 high taxons, the Protostomia and the Deuterostomia. This 

 dichotomy has been widely accepted since the days of Hatschek 

 and Grobben as a consequence of a belief that there had been 

 a bifurcation of the two lines of evolution. There are few 

 systems only which did not incorporate such a dichotomy. 

 We therefore get an impression that this dichotomy must be 

 supported by solid basic facts and interpretations. As is well 

 known, the name itself has been given due to a phenomenon 

 which can be observed in the ontogenies of numerous Eume- 

 tazoa, and even among our Ameria, where a definitive oral 

 opening, i. e. the mouth of the adult form, appears as a con- 

 tinuation of the embryonic primitive mouth (gastrostoma). 

 We must add immediately that among the species or sub- 

 groups which are classified as Protostomia there is either no 

 mouth whatever, or a so-called primitive mouth only. During 

 the subsequent evolution the primitive mouth grows together 

 while at the same time a real "definitive" mouth is newly 

 formed, instead of the "primitive mouth" in the same place 

 more or less where the primitive mouth would be expected 

 if it had been preserved. In numerous other Eumetazoa we 

 can find a development which at first sight seems to be rather 

 surprising and where an embryonic primitive mouth does not 

 develop into a definitive mouth but rather into an anal open- 

 ing, while at the same time the actual mouth is newly developed 

 27* 



