n PHYLUM PROTOZOA 71 



the Euglena is in large measure saprophytic, the products of the 

 decay of organic matter dissolved in the water being absorbed 

 through the general surface. 



Sometimes the active movements cease, the animal becomes quies- 

 cent, numbers of them coming together and secreting a gelatinous 

 scum, in which they lie embedded, on the surface of the water. 

 Each animal surrounds itself with a cyst or cell-wall of cellulose (G), 

 from which, after a quiescent period, it emerges to resume active 

 life. It is during the resting condition that reproduction takes 

 place by the division of the body in a median plane parallel to 

 the long axis (G). Under certain circumstances multiple fission 

 takes place, and flagellulse are produced, which, sometimes after 

 passing through an amoeboid stage, develop into the adult form. 



2. CLASSIFICATION AND GENERAL ORGANISATION. 



The Mastigophora form a very extensive group, the genera and 

 species of which show a wonderful diversity in structure and habit. 

 The only character common to them all is the presence of one or 

 more flagella. Some approach plants so closely as to be claimed 

 by many botanists ; others are hardly to be distinguished from 

 Rhizopods ; while the members of one order present an interesting 

 likeness to certain peculiar cells found in Sponges. 



The class is divisible into four orders as follows : 



ORDER 1. FLAGELLATA. 



Mastigophora having one or more flagella at the anterior end 

 of the body. 



ORDER 2. CHOANOFLAGELLATA. 



Mastigophora having a single flagellum surrounded at its base 

 by a contractile protoplasmic collar. 



ORDER 3. DINOFLAGELLATA. 



Mastigophora having two flagella. one anterior, the other 

 encircling the body like a girdle. 



ORDER 4. CYSTOFLAGELLATA. 



Mastigophora having two flagella, one of which is modified 

 into a long tentacle, while the other is small and contained within 

 the gullet. 



Systematic Position of the Example. 



Eugelena viridis is one of several species of the genus Euglena, 

 and belongs to the family Euglenidce, sub-order Euglcnoidea, and 

 order Flagellata. 



The presence of an anterior flagellum and the absence of a 

 collar, transverse flagellum, or tentacle, indicate its position among 



