82 AN INTRODUCTION TO ZOOLOGY 



Class 4. Sporozoa. 1 Type: Plasmodium vivax. Parasitic Pro- 

 tozoa; no motile organs. 



Order Hemosporidia. Blood-dwelling Sporozoa. 

 Genus Plasmodium. 

 Species vivax (lively). 



2. EUGLENA 



(Euglena viridis Ehrbg.) 



Euglena viridis is the animal usually selected in preparatory 

 courses to represent the Class Mastigophora. It is found in 

 fresh-water ponds and may appear in cultures prepared as de- 

 scribed on page 38. It is green in color, and, though a single 

 animal cannot be seen with the naked eye, when a great many are 

 massed together they impart a green tint to the water. 



Anatomy. Euglena (Fig. 39) is a single elongated cell pointed 

 at the posterior, and blunt at the anterior end. Two kinds of 

 cytoplasm may be distinguished in Euglena as in Ameba and 

 Paramecium, a dense outer layer, the ectosarc, and a central mass, 

 the endosarc, which is more fluid. A thin cuticle is present, as in 

 Paramecium, covering the entire surface of the body. Parallel 

 thickenings of this cuticle run obliquely around the animal, 

 making it appear striated (B). A little to one side of the center 

 of the anterior blunt end of the body is a funnel-shaped depres- 

 sion known as the mouth (A, m.). At the bottom of this depres- 

 sion is an opening which leads into a short duct called the gullet. 



1 Only one of the protozoan types (Plasmodium vivax) discussed in this 

 book is parasitic. There are, however, parasitic species in each of the classes 

 of Protozoa. For example, the Rhizopod, Entameba histolytica, is held re- 

 sponsible for amebic dysentery ; the Flagellate, Trypanosoma gambiense, is a 

 blood parasite which causes sleeping sickness in Africa ; and the Ciliate, 

 Balantidium coli, which is found in the alimentary canal of man, is supposed 

 to play a part in catarrhal inflamation of the intestine. Each class of Pro- 

 tozoa contains many other parasites of both man and the lower animals, some 

 being apparently harmless, whereas others are dangerous and frequently fatal. 



