THE BEHAVIOR OF INFUSORIA; PARAMECIUM 107 



and retiring from those that are harmful. Its behavior is in principle 

 much like that of a blind and deaf person, or one that feels his way 

 about in the dark. It is a continual process of proving all things and 

 holding to that which is good. 



5. FEATURES OF GENERAL SIGNIFICANCE IN THE BEHAVIOR OF 



PARAMECIUM 



A. The Action System 



Passing in review the behavior of Paramecium, we find that the 

 animal has a certain set of actions, by some combination of which its 

 behavior under all sorts of conditions is made up. The number of 

 different factors in this set of actions is small, and they are combined 

 into a coordinated system, so that we may call the whole set taken 

 together the action system. The action system of Paramecium is based 

 chiefly on the spiral course, with its three factors of forward movement, 

 revolution on the long axis, and swerving toward the aboral side. The 

 behavior under most conditions is determined by variations in these 

 three factors. Such variations, combined in a typical manner, produce 

 what we have called the avoiding reaction. Other elements in the action 

 system are the resumption of forward movement, in response to stimula- 

 tion, and the coming to rest against solid objects in what we have called 

 the positive contact reaction. Subordinate activities, playing little part 

 in the behavior, are the contractions of the ectosarc and the discharge 

 of trichocysts. 



The action system thus includes only a small number of definite 

 movements. By one or another of these, or by some combination of 

 them, we may expect the organism to respond to any stimulus which 

 acts upon it. We cannot expect each kind of stimulation to have a 

 specific effect, different from that produced by other stimuli, for all 

 any stimulus can do is to set in operation certain features of the action 

 system. Many different stimuli acting on this one organism therefore 

 necessarily produce the same effect. Different organisms have different 

 action systems, so that the same agent acting on different organisms may 

 produce entirely different effects. The nature of the behavior under 

 given conditions depends as much (or more) on the action system of the 

 animal as on the nature of the conditions. In studying the behavior 

 of any organism the most important step is therefore to work out its 

 action system, — the characteristic set of movements by which its 

 behavior under all sorts of conditions is brought about. 



The most important features of the action system of Paramecium 



