410 THE EVOLUTION OF THE META^^OA 



Oligomeria afterwards evolved from the Polymeria. It was 

 within the framework of the Oligomeria that a perfect deutero- 

 coelic-enterocoelic state had been reached. A perfect hypo- 

 neuria, however, did not develop earlier than in the Chordonia. 



It is even easier to pursue the enterocoelic type ot develop- 

 ment of the greatly reduced system of the perigastrocoele in 

 the Oligomeria than it is to study the deuterostomic state. It is 

 again a clear case of a rationalization of the ontogenetic 

 morphogeny, a simplification of its mechanism. The formation 

 of the perigastrocoele is brought closer to the Anlage of the 

 intestine. This takes place in such a way that first some cells 

 migrate from the epithelium of the primitive intestine into the 

 middle layer where they subsequently gather to form the 

 perigastrocoele sacks. This agrees well with the interpretation 

 which had already been suggested some time ago and which 

 considers the oligomerous state as a secondary phenomenon 

 which had evolved from the polymerous state by way of an 

 oligomerization. The deduction of the perigastrocoele from 

 the "lodges" of the anthopolyps which has been from the very 

 beginning a completely improbable suggestion, becomes 

 herewith superfluous. This is also true for the entirely artificial 

 construction of a bilaterogastrula and for many other similar 

 things. 



The fact that various Anlagen of the basic parts of the adult 

 organization begin to develop first in rather different ways 

 while finally they all become considerably uniformized (ration- 

 alized) can be considered as a general regularity of the onto- 

 genetic morphogeny. This can be clearly seen in connection 

 with the formation of the intestine (cf. the various modi that 

 occur in the Cnidaria alone), of the perigastrocoele, of the 

 segmentation, etc. 



Thus we come to the conclusion that the categories Pro- 

 tostomia-Deuterostomia do not exactly express the actual 

 facts, nor do they stand in agreement with the correct inter- 

 pretation of the same facts. This result is therefore similar 

 with our findings in connection with the high taxons the 



