356 THE EVOLUTION OF THE METAZOA 



constitute a uniform and taxonomically fixed group, of the 

 so-called Mycetozoa (Myxomycetes, as they are called by 

 botanists), and of the problematic Xenophyophora. If we drop 

 the notion and the name of the systematic group Phyto- 

 flagellata then we are logically obliged to do the same with 

 the Zooflagellata (as a name of a group). Zoology as well 

 as the zoologists lose nothing if they transfer into the field 

 of botany (Phytology) a number of Protista that had second- 

 arily adopted the heterotrophic type of feeding. In fact they 

 can win in this way a great deal because by means of such 

 an exclusion a clear limit can be drawn between the world 

 of animals and the world of plants. Moreover, a majority 

 of "attempts" which were made by Nature to cross the 

 limit between the autotrophic and the heterotrophic organisms 

 soon came to a stop so that no new type of organism has ever 

 evolved in this way. This is best illustrated by the example 

 of the Cystoflagellata which consist of three monotypic genera 

 only (among these Noctiluca is best known). Other descend- 

 ants also have a completely isolated position from the typical 

 Dinoflagellata that adopted the parasitic way of life. 



Repeated attempts have been made to construct a system 

 of Protista on the basis of their cellular structures. The Pro- 

 tista have therefore been frequently divided into the sub- 

 cellular (without distinct cell nuclei: Protocytoidea, accord- 

 ing to Naef), primarily cellular (among these are a majority 

 of the monocellular Protophyta and Protozoa), hypercellular 

 (with polymerized parts of cells, the cell nucleus included), 

 and finally the poly cellular and secondarily cellular forms. 

 Such a classification does not seem to be very useful in our 

 systematic and taxonomic work. It is not useful in connec- 

 tion with the animal world because the animals do not include 

 any subcellular species; neither is it useful for the plant world 

 because there are no secondarily nuclear plant species. Such 

 a division, however, can be very good from a purely notional 

 point of view, and within the broader frame of a general 

 biology. Even the word "acellular," after Dobell, is usable 



