

PHYLUM PROTOZOA 65 



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 otherwise unique 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 en- 

 circling 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. 



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

 and belongs to the Family Euglenidcv, sub-order Euglenoidea, and 

 order Flagellata. 



The presence of an anterior flagellum and the absence of a 

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

 the Flagellata. It is placed among the Euglenoidea in virtue of 

 possessing a single flagellum and a small gullet into which the 

 contractile vacuole opens. The genus Euglena is distinguished 

 by its centrally placed nucleus, green chromatophore, red stigma, 

 and euglenoid movements. E. viridis is separated from other 

 species of the genus by its spindle-shaped body with blunt ante- 

 rior and pointed posterior end, and by the flagellum being somewhat 

 longer than the body. 



ORDER 1. FLAGELLATA. 



The cell-body is usually ovoid or flask-shaped (Fig. 47, 6, 7, 9, 

 &c.), but may be almost globular (1\ or greatly elongated (3). 



