CHAPTER XXVII 



AMOEBA AND SOME ALLIES: PROTOZOA 



Gradual, from these what numerous kinds descend, 



Evading even the microscopic eye! 



Full nature swarms with life, — one wondrous mass 



Of animals, or atoms organized. 



James Thomson, Summer 



Protozoa. There are untold millions of animals which 

 are so very small that most people are not aware of their 

 existence, for they may be seen only with a microscope. 

 The simplest and many of the smallest of these are called 

 Protozoa. They exist under every conceivable condition 

 that will support life, and some even have the power, though 

 dried up completely and blown with the dust, of coming 

 to active life again if they get into suitable surroundings. 

 Stagnant pools teem with these minute forms. Even most 

 drinking water is populated with them, though fortunately 

 most of them are harmless. Some inhabit the soil, and many 

 species live as parasites in the bodies of other animals. In 

 spite of their microscopic size each of these organisms carries 

 on the same functions of life that are characteristic of the 

 higher animals. In the higher animals there are special 

 organs for metabolism, for reproduction, for movements, 

 and for the various other functions performed by living 

 animals. In the Protozoa all the functions of life are car- 

 ried on by the parts of the smallest unit of living matter — 

 a single cell. This cell feeds, moves, and produces other in- 

 dividuals like itself just as effectively as does man with his 

 complicated organization. Thus, in spite of its minute size, 

 each cell is a complete individual. 



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