go PROTOZOA. 
Paramecium can be seen, by the naked eye, to move 
with extreme rapidity through the water, and this move- 
ment is performed by the uniform layer of cilia covering its 
body. ‘There are also scattered all over the body a number 
of ¢richocysts or little oval bodies which, upon stimulation, 
Fig. 29.—PARAMG@CIUM CAUDATUM. 
Lateral view of entire animal from right side. x 60. (Ad nat.) 
Thread of Trichocyst. 
Food-vacuole. 
Micro-nucleus. 
Macro-nucleus. 
Contractile 
Vacuole. 
Trichocyst. 
Cilia. 
The anterior contractile vacuole is shown contracted into a star. 
eject from their interior long processes or stings. Lara- 
shiney macium not only has a definite shape, but as 
* it also has definite organs we can distinguish 
a symmetry in the arrangement of its parts. The animal, 
in fact, is plano-symmetric, and has a dorsal and ventral 
surface, two lateral surfaces and an anterior and a posterior 
end (page 23). 
Usually the anterior end is directed forwards in move- 
ment, but, when required, the animal is quite capable of 
“backing.” From about the middle third of the ventral 
