REPRODUCTION, RESPIRATION 



51 



as in the amoeba ; but there are two contractile vacuoles, 

 one at either end, and the food and water vacuoles are 

 more numerous than in amoeba. 



33. Locomotion and Defense. — The animal moves by the 

 action of the cilia, the direction bein^ due to the angle at 

 which the cilia are held. It can 



be observed that the animals 

 move backward and forward, 

 and that they also rotate on the 

 long axis. Paramoecia defend 

 themselves by discharging the 

 trichocysts. This discharge 

 occurs either as a result of cer- 

 tain strong artificial stimuli, 

 such as electric currents or 

 chemicals, or naturally because 

 of collision with certain other 

 Protozoa. If attacked by some 

 animal which feeds upon them, 

 they discharge the trichocysts in the region of the attack 

 (Figure 49). 



34. Reproduction, Respiration. — Paramoecia reproduce by 

 fission, i.e., an animal divides, producing two; these 

 divide and produce two more. The process of fission 



goes on indefinitely (Figure 50). Like 

 the amoeba these forms can encyst win mi 

 conditions of life become unfavorable. 

 They can then be blown about in dust. 

 As in amoeba?, the oxygen which is 

 necessary to respiration is obtained 

 from the water. Excretory waste is 

 cast from the body by the contractile 



vacuoles, which force it through the ectoplasm, (iases 



escape from the entire surface. 



Figure 49. — Paramecium. 



Being attacked by another 

 Protozoan that feeds upon 

 it. The trichocysts are dis- 

 charged, and they force 

 the foe away. 



Figure 50. — Para 

 mcecium reproduc 

 ing by Fission. 



