GREAT STEPS IN EVOLUTION 77 



labour and its structural aspect which we call 

 differentiation, the beginnings of sex and of 

 reproduction, the beginnings of a body and 

 of death. "Protozoology," as it is quaintly 

 called nowadays, is a fascinating study in 

 origins. 



The Protists. — It is useful to retain 

 Haeckel's term "Protists" for those simplest 

 of all living creatures, which lie at the base of 

 the V-shaped tree of life, showing no definite 

 bias towards distinctively plant or distinct- 

 ively animal characteristics. How far re- 

 moved even these simplest of the simple may 

 be from the first living creatures we do not 

 know, but they have remained, as it were, 

 in chronic indecision, neither clearly plants 

 nor animals. In studying them we are 

 brought face to face with one of the great 

 steps in evolution, and one of the earliest — a 

 dichotomy, like many other great steps — the 

 parting of the ways between plants and 

 animals. 



Plants and Animals. — We have all grown 

 up with our minds coloured by the childish 

 game of "Animal, Vegetable or Mineral.^" 

 and in too many schools they still teach that 

 there are three kingdoms of Nature. But 

 this is a surviving error of the alchemists, 

 continued by the early encyclopaedists of 

 nature, but broken down by Linnaeus, who 



