450 



EVOLUTION OF ANIMALS 



Part V 



FRONT END 



Coniractile 

 vacuole 



Small nucleus 

 Large nucleus 



Top view of 

 surface cilia 

 and network 

 of coordinat- 

 ing fibrils 



Food vacuole 



Contractile 

 vacuole 



Clear outer 

 layer 



Cilium 



Stiff outer 

 covering 



Trichocysts 



Oral groove 



Mouth 

 pore 



Gullet 



Food vacuole 

 forming 



Anal pore 



Cilia 



REAR END 



Fig. 21.17. Paramecium, a general view, with its main structures and functions 

 indicated. Gullet, food vacuole, and other organelles are embedded in the proto- 

 plasm. (Courtesy, Gerard: Unresting Cells. New York, Harper & Bros., 1940.) 



Fig. 21.18. Diagram of an avoiding reaction, the basic pattern of behavior in 

 paramecia {Paramecium caiuiatiim) . A is the source of stimulation; 1-6 are suc- 

 cessive positions of the animal. The habitual rotation on the long axis of the body 

 is not shown. (Courtesy, Jennings: Behavior of Lower Organisms. New York, 

 Columbia Univ. Press, 1906.) 



