CHAPTER II 

 PHYLUM PROTOZOA 



The Protozoa (Gr. protos, first; zo'dn, an animal) are mostly 

 microscopic animals, although some of the commonest species, 

 like Paramecium (Fig. 33), are visible to the naked eye. They 

 are the simplest of all animals, consisting of but a single cell. 

 Nevertheless, most of the activities characteristic of the many- 

 celled, complex animals are exhibited by them, usually in a sim- 

 pler form. In many cases Protozoa are colonial; that is, a 

 number of individuals of one species are more or less intimately 

 associated into a colony (Fig. 29). 



The Protozoa are separated into classes according to the 

 presence or absence of locomotor organs and the character of 

 these when present. Four classes are usually recognized: 



elass I. Rhizopoda (Gr. rhiza, a root; pons, a foot), with 

 idopodia (Fig. 9, 3) ; 

 Class II. Mastigophora, (Gr. mastix, whip; phero, bear) 

 with flagella (Fig. 22); 



Class III. Sporozoa (Gr. spora, seed; zoon, animal), with- 

 out locomotor organs in adult stage (Fig. 32) ; and 



Class IV. Infusoria (Lat. infusus, poured into, crowded in), 

 with cilia (Fig. 7,3). 



1. Class I. Rhizopoda 



a. Ameba proteus 



The fresh-water Protozoon, Ameba proteus (Fig. 9), is usually 

 selected as a type of the class Rhizopoda. It is only about y^ 

 inch in diameter, and is therefore invisible to the naked eye. 



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