450 THE EVOLUTION OF THE METAZOA 



The new type of movement of the primitive Chordoma 

 led to a formation of an elastic inner skeleton staff, the chorda 

 dorsalis. Numerous discussions have been conducted on 

 whether the so-called cephalochord of the Enteropneusta can 

 be considered as homologous to the genuine chorda dorsaUs^ 

 or not. I think that these discussions are completely super- 

 fluous. The anterior outgrowth of the intestine which can 

 be observed in the Enteropneusta is certainly not a "noto- 

 chord" s.str., it is certainly not a chorda dorsalis. It belongs 

 to a group ot forms that had been developed by the intestine 

 and which appear repeatedly even if in various ways in the 

 Eumetazoa. These are the intestinal diverticulae which originally 

 have a lumen and which function as a periphery of the intes- 

 tine. The lumen is later lost, the diverticulae become solid, 

 and they change at the same time their function by their 

 development towards an inner skeleton. The best known 

 instance of this development are the tentacles of the Cnidaria 

 which had secondarily evolved into solid forms. In some 

 species we can even find that some other parts of the intestine 

 also evolve into an elastic inner skeleton (theT^bu/aria species). 

 Forms similar to the "cephalochord" of the Enteropneusta 

 can occasionally be found in the Turbellaria (Ax, 1957), etc. 

 (Fig. 33). During the ontogenies we can see the chorda 

 dorsaln developed from the ''plafond^^ of the intestinal Anlage, 

 and this can be clearly observed in the low^er Chordonia. 

 The "notochord" of the Enteropneusta and the chorda dorsalis 

 of the Chordonia originate therefore in one and the same 

 trend of the intestinal tube to develop first some "hollow" 

 outgrowths, i.e. outgrowths which have a lumen that later 

 becomes solidified. Here we are not interested in the sub- 

 sequent destiny of the chorda dorsalis in spite of its interest- 

 ing character. This chorda is stubbornly preserved and it is 

 recapitulated down to the end of the evolution even if it 

 does not have any function in the adult animals. Its Anlage 

 must clearly have an important morphogenetic function dur- 

 ing the ontogenetic development. 



