THE NEW GENEALOGICAL TREE 373 



intestine), according to Ulrich, which have also been suggested 

 for the Eumeta2oa are therefore very suitable. 



We must not be led astray by the types of formation of the 

 "body layers" which can be observed during the ontogenies ; 

 these types are mutually different and they change more and 

 more during their subsequent development. These ontogenetic 

 types of formation can even become identical in the two lines 

 of evolution which are basically different (in the phylogenetic 

 sense !) ; on the one hand in the evolution of the Metaphyta 

 and of the Spongiae which alone are without an intestine, and 

 on the other hand in the evolution of the Eumetazoa. We must 

 Uberate ourselves from the belief that the ontogenetic morpho- 

 genesis via blastula-gastrula were identical with the phyletic 

 morphogenesis via blastaea-gastraea, as if the ontogenetic type 

 of development were identical with a recapitulation of the 

 phyletic (i.e. of the fully developed forms) development. 



A digestive plasmodium existed even before there was any 

 ontogeny of the Eumetazoa ; it had been a substratum of the 

 subsequent intestine in the interior of the proeumetazoon 

 where the cyclosis of the digestive vacuoles had been stopped. 

 There w^as no need of a gastrulation by w^ay of a transference 

 of the blastula epitheUum into the interior of the animal. It was 

 only due to the introduction of the ontogenetic morpho- 

 genesis (which finally became necessary) combined with an 

 initial cleavage that the gastrulation processes finally began to 

 take place. We can therefore still continue to use the notions 

 gastrula and gastrulation even in this new situation, yet 

 without any parallel idea of a blastaea or a gastraea. No Blastae- 

 adae or Gastraeadae had in reality ever existed and no such 

 forms can be found among the recent animals either, at least 

 as regards the Eumetazoa. 



Quite frequently we can see in some Cnidaria and Endopro- 

 cta how an intestine (the entoderm) develops from the "skin" 

 (the ectoderm) during the ontogenies or during the so-called 

 atypical budding. Experimental embryology, however, has 

 shown that these processes are an instance only of an 

 25 



