84 EVOLUTION 



myxa and Myxomycetes, we get a new light 

 on our classification. For in these life- 

 histories we find, for instance, that amoeboid 

 forms become encysted, that the encysted stage 

 gives rise to active flagellate spores, and that 

 these sink down again into amoebae. The 

 three chapters in the life-history of the 

 simplest forms are, as it were, prophecies of 

 each of the three groups Infusorians, Rhizo- 

 pods, and Gregarines. In other words, the most 

 primitive organisms pass through a cycle of 

 three phases, one of which is accented by each 

 of the three main groups of Protozoa. And 

 while each main group is characterized by one 

 dominant phase of cell-life flagellate, amoe- 

 boid or encysted there are often transient 

 hints of other phases. An infusorian may 

 have its encysted chapter, a gregarine its 

 amoeboid stage, and a rhizopod may begin as 

 a mobile flagellate spore; for each group, 

 while accenting one phase of the cycle, retains 

 reminiscences of the others. 



The conviction that the triple division really 

 means much, grows stronger when we pass 

 from the unicellulars to the cells that compose 

 the higher animals. For they, too, may be 

 rationally classified along the three great lines, 

 There are active ciliated or flagellate cells in 

 most animal types the flagellate cells of 



