THE PHYLUM PROTOZOA 140 



Tl^gzll 



Mouth 



Nucleu-S 



Tentacles 



D E 



Figure 8.1. Classes of the phylum Protozoa. A, Flagellata. B, Sarcodina. C, Ciliata. 

 D, Suctoria. E, Sporozoa. 



tion or feeding; (4) Suctoria, in which the young have ciha but the aduUs 

 have tentacles; and (5) Sporozoa, parasitic forms that reproduce by 

 multiple fission (division into more than two daughter cells) and in 

 which adult forms lack obvious locomotor structures. 



47. Organelles 



Each protozoan cell must carry on all the life processes of its species. 

 These include the cellular activities described in Chapter 4, and also 

 the physiologic activities described in Chapter 5. The metazoa have 

 capitalized upon a division of labor among cells: some are nutritive, 

 others excretory, and still others muscular. In the protozoa these various 

 activities are accomplished by specialized structures within the single 

 cell. Such structures, whose functions are comparable with those of the 

 organs of higher animals, are called organelles. A few of these will be 

 described as examples of intracellular differentiation. 



Cilia and Flagella. Obvious in many protozoa are the locomotor 

 organelles. Many ciliates are rapid swimmers, propelling themselves by 

 the concerted action of their many cilia. Flagellates may also move 

 rapidly, pulling themselves forward by lashing the anteriorly located 

 flagella. Each flagellum (Fig. 8.2) is a long, supple filament containing 

 an axial fibril. Although this fibril resembles the contractile fibrils of 



