90 



PROTOZOA. 



Paratnoecium 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 trichocysts or little oval bodies which, upon stimulation, 



Fig. 29. — Paramgecium Caudatum. 



Lateral view of entire animal from right side. X 60. {Ad nat.) 



Thread of Trichocyst. 



Trichocyst. 



Cilia. 



The anterior contractile vacuole is shown contracted into a star. 



eject from their interior long processes or stings. Fara- 

 moecium not only has a definite shape, but as 

 ymme ry. .^ ^^^ ^^^ definite organs we can distinguish 

 a symmetry in the arrangement of its parts. The animal, 

 in fact, is plano-sy?mnetric, 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 



