192 INVERTEBRATE ZOOLOGY 
MASTIGOPHORA 
A FLAGELLATE (Euglena) 
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 proto- 
zoan, one end of which is pointed and the other blunt; in 
the latter end is a deep depression, from the bottom of which 
springs a long, thread-like, vibratile flagellum. The body is cov- 
ered by a very delicate cuticula; an oral groove and a mouth are 
not present. The animal is colored green by the presence of 
chlorophyll in its body. 
Mount a drop of water containing Euglena on a slide and 
study it under the microscope. Observe its shape and color; 
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. In some 
flagellates the flagellum is at the posterior end. Whether the 
flagellum in any species is at the anterior or the posterior end 
of the body depends upon the direction the vibratile motion of 
the flagellum takes. If the motion begins at the base of the 
flagellum and proceeds towards its tip, the animal’s body will be 
driven ahead with the flagellum at the rear, while 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 
alternate contraction and expansion of the body, like a worm. 
Bxercise 1. Draw a number of simple outlines of the body 
showing its shape at different times. 
