34 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



Parasitic Protozoa. Because of their simple structure and 

 physiology the Protozoa easily adapt themselves to new modes 

 of life, when conditions are favorable. It was an easy step 

 from an existence in the water to life in the blood tissues of 

 some of the aquatic animals or in some of the higher animals, 

 and the Protozoa that have made this step have come to be 

 among the greatest scourges that affect mankind. These 

 parasitic Protozoa are so important that a later separate 

 chapter will be devoted to an account of them. (See Chapter 

 XXVIII.) 



Classification of the Protozoa. The branch Protozoa is 

 divided into five groups or classes, the divisions being based 

 principally on the manner in which the members of the different 

 groups move about. The Amceba, the Foraminifera and the 

 Radiolaria belong to the class Rhizopoda (Gr. rhiza, root; 

 pous, foot). Rhizopoda means "root-footed" and the name 

 is applied to those Protozoa which move about by means of 

 the extending or flowing out of the root-like processes called 

 pseudopodia, or false feet. 



Paramcecium and Vorticella belong to the class Infusoria 

 (L. infusus, infused), a name that was early used because 

 these organisms are so frequently found in infusions. Because 

 their body is furnished with minute hair-like organs called 

 cilia they are often called Ciliata. 



From an economic point of view the class Sporozoa (Gr. 

 spora, seed; zoon, animal) is the most important. The mem- 

 bers of this class are parasitic and cause some of the most 

 serious diseases of man and other animals, such as the various 

 malarial fevers, the spotted fever of man, and the Texas fever 

 of cattle. 



The whip-bearers (class Mastigophora, Gr. mastix, whip; 

 phero, bear) also include a number of important parasites, as 

 the trypanosomes that are the cause of the dreadful disease 

 which ends in sleeping sickness, and the Spirochatce, which are 

 the cause of certain relapsing fevers. The little green Euglena, 

 whose presence in standing pools often imparts a greenish 

 color to the water, and the wonderfully phosphorescent 

 Noctiluca of ocean waters, also belong to this class. The 



