60 



COLLEGE ZOOLOGY 



24°C-28°C 

 Selects the optimum temperature 



Figure 28. Behavior of the paraniecium to various conditions in its environment. 



Reactions to stimuli 



The Paramecium not only reacts to chem- 

 icals, but to contact, to changes in tem- 

 perature, to light, to electric current, and 

 to other stimuli. If the anterior end of a 

 Paramecium, which is more sensitive than 

 the other parts of the body, is touched with 

 a glass rod, the avoiding reaction is given. 

 Frequently, a paramecium when swimming 

 slowly comes to rest with its cilia in contact 



with an object; this positive response often 

 brings it into an environment rich in food. 

 Paramecia do not respond in any way to 

 ordinary visible light, but give the avoiding 

 reaction when ultraviolet rays are thrown 

 upon them. 



The optimum temperature for the Para- 

 mecium lies, under ordinary conditions, be- 

 tween 24° C. and 28° C. A number of ani- 

 mals placed on a slide which is heated at 



