22 ZOOLOGY 
of the cortical layer has also rendered locomotion by pseudo- 
podia rare, and those Corticata which move about actively 
do so as a rule by means of rows of cilia or by a single or 
paired flagellum. 
Cuass I. Flagellata. 
The bodies of the members of this class are usually very 
minute, and always contain a nucleus; they are moved by the 
lashing of one, sometimes by two or three flagella, A mouth 
Fia. 17.—I. Typical form of Huglena viridis, Ehrb., after Sav. Kent. 
1. Contractile vacuole. 3. Gullet and origin of flagellum, 
2. Pigment spot. 4. Nucleus. 
Il. Il. IV. V. Four views of Huglena viridis, showing the change of shape 
consequent upon the euglenoid movement. 
may be present, but in those forms which live in nutritive 
fluids the nourishment is usually imbibed by the whole surface 
of the body. One or more contractile vacuoles occur, and 
sometimes a pigment spot is situated at one end of the body. 
Conjugation sometimes occurs, and is followed by the breaking 
up of the body into spores, reproduction also takes place by 
