CHAPTER XXIII 

 ONE-CELLED AND MANY-CELLED ANIMALS 



We move in a world populated by invisible live things 

 in great number and variety. Only powerful microscopes 

 can strengthen our sight sufficiently to enable us to dis- 

 cover and study some of them. 



Imagine a creature that moves about without legs, eats 

 without a mouth, and breathes without lungs, and that is 

 so tiny that countless thousands may inhabit a drop of old 

 milk. Small as they are, creatures like this may influence 

 our health for good or ill and may even destroy life itself. 



The protozoan, or one-celled animal, is the simplest form of 

 life. To know about it helps us to understand more complex forms. 

 The "slipper animal," or paramecium, is the one-celled animal 

 commonly studied. The amoeba is another form worth studying. 



The Paramecium. 1. Observe a living specimen, by use of a 

 compound microscope, and determine its shape, size, and how it 

 moves. 



2. Observe the parts of the cell as far 

 as possible. 



3. Using a prepared stained specimen, 

 observe the nucleus, and by use of a chart 



learn the position of the cilia, by which it A PARAMECIUM 



JTJ , t N Nucleus. 



moves. Observe the other parts. c Cilia. 



4. Make an enlarged labeled drawing 



of the animal, indicating the cell wall, the protoplasm, the nucleus, 

 the cilia, and the food vacuoles, or spaces containing food. 



Functions of a Paramecium. This small, one-celled animal, 

 without special organs, performs all the functions of larger organ- 

 isms. It is sensitive; it moves; it breathes; it takes, digests, 

 absorbs, circulates and assimilates food; excretes waste matter, 

 and it reproduces. 



Sensation. Although the animal has no nerves, or organs 

 equivalent to nerves, it responds to touch, light, chemicals or 



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