THE BEHAVIOR OF PROTOZOA 83 



rhythmical manner. To contact stimuli Stentor responds 

 in a variety of ways dependent on the strength of the 

 stimuli and the number of times they have been repeated. 

 A moderately strong stimulus causes the Stentor to contract 

 violently, but after a number of repetitions the contractions 

 diminish in vigor and finally disappear. Jennings found 

 that when Stentor is stimulated by a quantity of fine par- 

 ticles of India ink or carmine which were poured upon the 

 disk by a capillary pipette, a regular series of responses 

 was given. Frequently the Stentor would not respond at 

 first, but would sweep the particles into its gullet con- 

 tinuously. Sooner or later, however, the organism would 

 respond by bending to the aboral side. This may be 

 repeated several times, but if it fails to afford relief from 

 the stimulation another reaction is "tried." There is a 

 sudden reversal of the action of the cilia and the par- 

 ticles are then thrown off the disk. The response is but 

 momentary, however, and then the usual movements are 

 resumed. If these two reactions are fruitless the Stentor 

 contracts strongly, thus drawing its body out of the re- 

 gion of the impending particles. After a little it slowly 

 extends again, and if the particles still fall on the disk the 

 contraction may be repeated. If the stimuli still come 

 after a number of such attempts to avoid them the Sten- 

 tor makes several violent contractions in quick succession 

 and breaks loose from its attachment and swims away. 

 We have a series of reactions to the same external stimulus. 

 If one reaction is unsuccessful another is tried until the 

 organism finally obtains relief. These reactions are all of an 

 adaptive character, so we can say that 'the creature is pro- 

 vided with a number of ways of meeting a given situation. 

 The external stimulus remaining the same, the particular 

 reaction that is given obviously depends upon the condition 



