PHYLUM PROTOZOA 31 



only by a delicate thread, the rhizoplast. There is thus devel- 

 oped a system of centers associated with the base of the flagellum, 

 connected by fine protoplasmic fibers. The name kinetic ele- 

 ments has been applied to this system in the belief that it con- 

 trols or directs the activity of the flagellum. In most of the 

 parasitic, but lacking in the free-living flagellates, there occur 

 one or more masses of deeply staining substance known as the 

 parabasal body (Fig. 21) associated with the kinetic elements. 

 These are thought to be a store of material to be used by the 

 kinetic elements in their functioning. Kofoid and his followers 

 refer to this whole group of blepharoplast, nucleus, rhizoplasts, 

 and parabasal body as a neuromotor apparatus. 



Among the more characteristic Mastigophora, the flagella 

 occur at the anterior extremity. If they are directed forward 

 and by their movement pull the body along, they are called 

 trachella; if they are directed backward and by their movement 

 propel the body ahead, they are designated as pulsella. The 

 trachella are the more common type. In many Mastigophora, 

 flagella arising at the anterior extremity are directed backward 

 along the side of the body as trailing flagella. These may be 

 either free or fused with the side of the body as an undulating 

 membrane as in the Trypanosomes (Fig. 23). 



Even in some chlorophyll-bearing Mastigophora there is a 

 cytopharynx, though it is not always functional for ingestion of 

 solid food. Contractile vacuoles usually empty into the cyto- 

 pharynx, either directly or through communicating canals and 

 reservoirs. 



A single nucleus is usually present, though in some of the 

 parasitic forms there may be two (Giardia, Fig. 21) or many 

 nuclei, as in members of the family Calonymphidae, parasitic in 

 termites. 



On the basis of relationships and general methods of metabo- 

 lism, the Mastiogophora may be divided into two subclasses. 

 The distinctly plantlike forms are included within the Phytoma- 

 stigina, while the ones displaying more pronounced animal char- 

 acters are grouped within the subclass Zoomastigina. 



Subclass Phytomastigina 



Members of this subclass have one to four flagella located at 

 the anterior extremity. The cytoplasm is usually very finely 

 granular, not heavily vacuolated, and without distinct boundary 



