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Tlie Protozoans — Representatives 

 or Unicellular Animals 



Living organisms are the centers of relationships that reach out and connect 

 with numberless other things, living and nonliving. These relationships have 

 muhiplied through the long past as they are still doing. This is evolution. 

 Learning about relationships is a universal and exciting occupation, whether 

 it occurs in telephone conversations, in political campaigns, in searching out 

 the what and wherefore of plants and animals and other things. Because of 

 this, protozoans have place and importance; no matter that they are little, 

 largely unknown, and hardly ever seen. Discoveries of their far-reaching rela- 

 tionships are the lively rewards of exploration into their daily lives. 



Protozoans — The Pioneer Animals 



The great advances in the evolution of animals occur in flights of steps on 

 the long stairway of living. The protozoans were the pioneers and dominating 

 animals on the first steps. Multicellular animals with innumerable complexities 

 dominated the second great flight of steps. Continuing their own evolution, 

 many protozoans moved into the bodies of the multicellular animals and be- 

 came successful parasites in these new surroundings. Others persisted in free 

 living, becoming adjusted for various conditions in the always-changing en- 

 vironment of the earth. 



Gradually many kinds of animals were gathered into communities, held by 

 bonds of food and shelter. Organized societies appear on the highest steps, 

 and are still continuing to change. Social insects became prominent, and after 

 long ages primitive human societies developed. The human groups became 

 divided; some scattered widely; others intermixed. They often came together 

 to eat, to fight, and to acclaim their works. All of this greatly benefited the 

 distribution of the protozoans; gave them new places to live and easy ways to 



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