CHAPTER VIII 

 AMOEBOID PROTOZOA (Sarcodina) 



BY C. H. EDMONDSON 



Assistant Professor of Zoology, University of Oregon 



THE minute animals consisting of but a single cell throughout 

 their existence are commonly called Protozoa. They are world- 

 wide in their distribution, swarming the seas from the surface to 

 great depths and being found abundantly under almost all condi- 

 tions of moisture in fresh water as well as in the fluids and tissues 

 of other animals where many exist as parasites. 



The Protozoa may be grouped under the following subphyla: 



Subphylum I. Sarcodina. Moving by means of temporary 

 extensions of the protoplasm, called pseudopodia. 



Subphylum II. Mastigophora. Provided with one or more 

 whip-like processes, called flagella, as organs of locomotion or for 

 securing food. 



Subphylum III. Infusoria. Locomotor organs in the form of 

 fine hair-like structures, called cilia, present during the entire ex- 

 istence or during the embryonic stage only. 



Subphylum IV. Sporozoa. Without true organs of locomo- 

 tion; usually reproducing by spores. Parasitic. No free living 

 forms. 



It will be observed that the above grouping is based upon the 

 organs of locomotion. This basis has been found a convenient 

 one for classification and study, little difficulty arising except in 

 unusual cases where species are found to possess more than one 

 kind of motile organs or where species pass through distinct phases 

 during their life cycle. Of all the Protozoa those representing the 

 highest degree of simplicity of structure and the greatest general- 

 ization of life processes, if not the oldest in point of time, are to be 

 found in the group possessing pseudopodia. These fo/m the sub- 

 ject of the present chapter, the flagellate and ciliate forms are 

 considered in the next, and the parasitic Sporozoa do not properly 

 call for attention in this work. 



210 



