PARAMECIUM AND ITS RELATIVES 173 



h. State the form and position of the cell nucleus. 

 3. Make a drawing of three of the cells described above, 

 each cell to be represented about an inch in diameter. 

 Label cell body and cell nucleus. 



4. (Optional.) Demonstrate by the use of prepared slides, 

 pictures, or charts that the blood, mtestine, and other 

 organs of the body of a frog or other higher animal are 

 composed of cells. Make a drawing of a single cell in 

 each ease. 



128. A comparison of Protozoa and the higher animals. — 



Our study thus far has shown that all animals, including the 

 Protozoa, perform the necessary functions of locomotion, 

 food getting, assimilation, respiration, and reproduction. 

 The adaptations for performing these functions, however, 

 are very diverse. 



All animals except the Protozoa consist of many cells and 

 the various functions of the higher animals are performed by 

 groups of cells known as organs. For example, certain com- 

 binations of cells carry on locomotion, others digestion, while 

 still others are set apart for breathing. All these functions 

 are performed in a Protozoan by a single cell. 



129. Economic importance of Protozoa. — Most of the 

 Protozoa serve as food for other animals that live in the 

 water and these in turn are fed upon by fish, which are eaten 

 by man. Thus the one-celled plants and animals are found 

 to be an important food-basis for human beings. 



Some of the Protozoa that live in the sea secrete tiny shells 

 (Fig. 122), and when the animals die the shells drop to the 

 bottom. As a result of heat, pressure, and other causes, 

 this bottom ooze is gradually solidified to form chalky 

 rocks, and in the upheavals that have taken place in ages 

 past these rocks have been forced above sea level. The 



