THE PROTOZOA 15 
permanent in form, constantly beats backward and forward 
with great rapidity in a general direction represented in 
the diagram (Fig. 6,c). The movement from a to 3 is 
much more rapid than the reverse, from b to a, which 
results, like the action of the human arm in swimming, in 
driving the organism forward. Not only does the flagel- 
lum serve the purpose of locomotion, but it also produces 
currents in the water which 
may serve to bear minute 
organisms down into the 
gullet, whence they read- 
ily pass into the soft pro- 
Fia. 6. — Flagellate Infusoria. <A, 
Euglena viridis; c¢, pulsating 
vacuole ; ¢, eye-spot; g, gullet ; 
n, nucleus ; ¢, flagellum. B, Co- Fie. 7.— Paramecium aurelia, a 
dosiga, with collar surrounding ciliate infusorian. ¢, cilia; c.v., 
the flagellum. C, diagram illus- pulsating vacuoles ; f, food 
trating the action of the flagel- particles ; g, gullet ; mm, buccal 
lum. All figures greatly enlarged. groove ; 7. nucleus. 
toplasm of the body, there to undergo the processes of di- 
gestion and assimilation. In some forms the protoplasm in 
the region of the flagellum is drawn out in the form ofa 
collar (Fig. 6, B), whose vibratory motion also aids in con- 
veying and guiding food into the body. 
18. The Slipper Animalcule——The second type of loco- 
motor organ may be understood from a study of the 
