448 THE EVOLUTION OF THE METAZOA 



the very specialized Pogonophora (together with the extinct 

 Graptolitha) as well as the Phoronidea. The only group which 

 therefore remains to be taken into consideration in connection 

 with our problem are the Enteropneusta. And even now 

 we can really find in the Enteropneusta the greatest number 

 of the so-called prophetic characteristics in spite of the repeated 

 specializations which they underwent "in the meantime." The 

 Enteropneusta move slowly yet they are nevertheless freely 

 moving animals, they usually burrow in the ground and they 

 have therefore an anterior part of the body which had evolved 

 much later in the Chordoma into the head of the Vertebrata 

 by way of a cephalization. 



It is possible that the process which had taken place in 

 the evolution of the Chordonia was similar to the process we 

 have presupposed in connection with the evolution of the 

 Polymeria from the Ameria, and of the Oligomeria from the 

 Polymeria. The evolution of the new type started in all 

 probability somewhere close to the root of the next lower 

 type. In its evolution it had followed Watson's rule; it was 

 due to a "fortunate" combination of several characteristics 

 that had existed scattered in the next lower type and to the 

 emergence of new characteristics which led to the formation 

 of the new type under a simultaneous radical change in the 

 environment and in the way of life. 



We must suppose (and we have good enough reasons to) 

 that something unusual had taken place in the period of 

 transition from the Oligomeria— from a primitive form of the 

 Oligomeria which is no longer preserved in recent animals 

 and which it seems had resembled most closely the present- 

 day Enteropneusta of all the recent Oligomeria— to the 

 Chordonia. The transition of an oUgomerous animal similar, 

 perhaps, to a Balanoglossus into a new animal form resembling 

 approximately the recent Amphioxus (Branchiostoma), or the 

 fossil Jamqytius, must have taken place in all probability in 

 the soft shallow ground of estuaries, or even in fresh water. 

 This supposition is based on the fact that Jamoytius, the most 



