298 GENERAL ZOOLOGY 



Definition of Protozoa (Gr. protos, "first"; zoa, "ani- 

 mals"). The four members of the phylum described in this 

 chapter were selected as representatives of the four classes 

 that make up the phylum : Amoeba proteus, of the class Sar- 

 codi'na ; Euglena viridis, class Mastigoph'ora ; Paramecium 

 caudatum, class Cilia'ta; and Plasmodium malarise, class 

 Sporozo'a. 



Although in each class the genera differ widely, all the 

 members of the four classes agree in being composed of 

 single cells. Nearly all species are microscopic in size. 



Reproduction is brought about by division of the cell, and 

 in some cases by specialized germ cells, as in the higher 

 animals. 



In all the Protozoa discussed in this text, the body con- 

 sists of a single cell. However, in many species the cells, 

 after division, remain united in clusters. These groups, in 

 some instances, are only temporary and finally break apart 

 into entirely independent individuals. In other species, the 

 cells remain united permanently. Such groups, whether per- 

 manent or temporary, are called colonies. Division of labor 

 or specialization occurs in many of these colonies, for only 

 certain of the cells are capable of reproduction while the other 

 cells care for the nutrition and locomotion of the colony. 



