156 PHYLUM PROTOZOA 



Class : Mastigophora 

 A FLAGELLATE {EUGLENA VIRIDJS) 



This single-celled organism, which combines the characters of 

 animals and plants, is often so plentiful in pools and ditches that 

 it makes the water green. It is a minute, elongated protozoan, one 

 end of which is pointed and the other blunt ; in the latter end is 

 the mouth, which leads into a depression called the gullet, from 

 which springs a long, threadlike, vibratile flagellum. The body 

 is covered by a very delicate cuticula. The animal is colored green 

 by the presence of chlorophyll bodies in it. 



Mount a drop of water containing Euglena on a slide and study 

 it under the microscope. Observe its shape and color ; observe 

 also its swimming motions and the motions of the flagellum. 

 The latter organ will be seen to be at the anterior end of the 

 body ; it is always in advance as the animal swims. The animal 

 revolves on its long axis as it swims and describes a spiral path 

 in its progress from one spot to another. In some flagellates the 

 flagellum is at the posterior end. Whether the flagellum in any 

 species of flagellate is at the anterior or the posterior end of the 

 body depends upon the direction the vibratile motion of the fla- 

 gellum takes. If the motion begins at the base of the flagellum 

 and proceeds toward its tip, the animal's body will be driven 

 ahead with the flagellum at the rear, whereas if the motion 

 begins at the tip of the flagellum, the body will be drawn after 

 it. Note the extreme plasticity of the body. It can assume a 

 variety of shapes, and will often be seen swimming by the alter- 

 nate contraction and expansion of the body, like a worm. 



Exercise 1. Draw a number of simple outlines of the body showing 

 its shape at different times. 



Study the structure of the body. The protoplasm composing 

 it is clear, its surface often showing delicate striations. Note the 

 cuticula. In the middle of the body is a large, spherical nucleus. 

 At the anterior end near the gullet is a clear space called the reser- 

 voir; find it. It receives the discharges of the pulsating vacuoles. 



