THE PROTOZOA 233 



another; that is, the germ cells of one generation, the parent 

 colony, survive to produce the body and germ cells of the 

 daughter colonies. A distinction between germ cells and body 

 cells can be made in all the higher animals including man, and, 

 as in Volvox, the parents produce germ cells (eggs and sper- 

 matozoa) which give rise to the body and germ cells of the young. 



Characteristics and Classification. — Protozoa are one-celled 

 animals which in many cases form colonies. They live in fresh 

 water, salt water, damp earth, and as parasites in or on the 

 bodies of other animals. They vary in shape from the shapeless 

 Ameba to the highly organized Vorticella. Locomotion takes 

 place by means of cilia and pseudopodia. The various physio- 

 logical processes occur in Protozoa just as they do in higher or- 

 ganisms, but within a single cell and without definite organs. 



The Protozoa are separated into classes according to the pres- 

 ence or absence of locomotor organs and the character of these 

 when present. Four classes are usually recognized: — 



Class 1. Rhizopoda. — With pseudopodia, as in Ameba. 



Class 2. Mastigophora. — With flagella, as in Euglena. 



Class 3. Sporozoa. — Without locomotor organs in adult 

 state. Produce spores, as in malarial parasite. 



Class 4. Infusoria. — With cilia, as in Paramecium. 



REFERENCES 



The Protozoa, by G. N. Calkins. — The Macmillan Co., N. Y. City. 

 Protozoology, by G. N. Calkins. — Lee, Febiger and Co., Philadelphia. 

 Introduction to the Study of the Protozoa, by E. A. Minchin. — Edward 

 Arnold, London, England. 



