MONOCELLULAR ANIMALS-THE PROTOZOA 



109 



told, rather than the details concerning the 

 individual animals. Of course you must 

 know certain specific points about repre- 

 sentative animals, but the whole picture 

 is more important than the isolated facts, 

 no matter how fascinating they may be. 



PHYLUM PROTOZOA 



The Protozoa display the full potentiali- 

 ties of protoplasm within the confines of a 

 single cell. With a few exceptions, they are 

 all unicellular, yet with so little they have 

 done as much exploring with possible vari- 

 ations in pattern and function as have the 

 multicellular animals. As a consequence, we 

 see a vast array of sizes, shapes, and habi- 

 tats among some 30,000 different species 

 of these tiny animals. They range in size 

 from 3 to 15,000 microns and live in almost 

 any environment, from soils to the red 

 blood cells of vertebrates. 



Physiological and pharmacological re- 



Fig. 7-2. This is a photograph (photomicrograph) of a 

 living amoeba taken through the light microscope. 

 Note the highly granular nature of the protoplasm 

 in the main body of the cell and the clear regions 

 where the pseudopods are forming. 



Fig. 7-1. This ciliated protozoan, Tetrahymena geleii, has 

 many of the nutritional requirements of higher ani- 

 mals, including mammals, and for that reason has 

 become valuable in research. The study of micro- 

 organisms has become an important field of research 

 where the fundamental workings of protoplasm are 

 under investigation. 



search has and will continue to employ 

 Protozoa for experimentation to find out 

 about the effect of various substances, in- 

 cluding poisons, on the animal cell. Tetra- 

 hipnena geleii (Fig. 7-1) is a particularly 

 valuable laboratory animal for many kinds 

 of protozoan research. Before an under- 

 standing can be had of the more complex 

 Metazoa it is essential that more knowledge 

 be accumulated concerning the single- 

 celled forms. 



In order to understand the Protozoa as 

 a group let us first study two representa- 

 tives in detail, and later in more cursory 

 fashion a few additional forms to gain some 

 notion of diversity. We have selected 

 amoeba as a simple form and Paramecium 

 as one of the most complex protozoans. 

 Both of these are ubiquitous in their distri- 

 bution and because they are easily handled 

 have been classic material for biology 

 classes for many years. 



