354 THE EVOLUTION OF THE METAZOA 



organisms. We consider them to be the first and phyloge- 

 netically the oldest type. It cannot be proved with certainty 

 that such organisms still exist. In view of the fact, how^ever, 

 that in the main evolution there was regularly one part 

 only that had further evolved while another part had remained 

 on the same old primitive level (certainly with some smaller 

 changes) we must admit the possibility that there still exist 

 essentially unchanged descendants from the primary heterotro- 

 phic organisms that were neither plants nor animals. We can 

 think here at once of viruses; it is even possible that not only 

 viruses can be placed into this group, and moreover not all 

 the organisms that are now known as viruses can be classified 

 into this group. In the meantime the viruses have become 

 strongly specialized, they live now mainly as endoparasites 

 with animals and plants. By way of a purely logical thinking 

 we can conclude that in the era of the primary heterotrophic 

 organisms the latter had lived freely, feeding mutually on 

 each other. Such an era, however, could not possibly have 

 been of along duration because under such conditions life 

 would necessarily soon come to an end if the producers of 

 the "living substance" had not evolved in the form of or- 

 ganisms which were capable of chemosynthesis; such forms 

 can already be classified among the bacteria. A new difficulty 

 emerges here of how to distinguish these primitive organisms 

 from the "younger" saprophytes which are usually classified as 

 plants. All these organisms can be considered as a special 

 group, and since it is necessary to name them, we could call 

 them Anucleata after Rothmiiller, or Monera after Barkley 

 (the latter name, however, does not mean the same thing 

 here as it was understood by Haeckel). 



The Anucleata which were capable of chemosynthesis 

 probably also evolved into the second main type of organisms 

 which feed autotrophically or by means of photosynthesis. 

 These organisms are plants (Phyta) regardless of whether they 

 are mono- or poly cellular forms. All plants can be divided 

 practically and roughly into Protophyta and Metaphyta; yet 



