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 
