112 Asa Arthur Schaeffer 



change from a condition of surfeit to one of only partial satiety 

 was caused by the impinging of five Trachelomonas on the Sten- 

 tor's disk. 



This decrease in the condition of satiety does not represent a 

 similar rate of decrease of food in the Stentor's body. We see 

 therefore that a particular state of hunger in a Stentor does not 

 directly nor necessarily accurately represent the amount of food 

 in the Stentor at the given moment. What the state of hunger 

 actually represents is the condition of the organ for receiving stim- 

 uli from external food particles. This is influenced: (i) by the 

 past history of the amount and kind of stimulation from external 

 particles; (2) by the amount of food in the Stentor's body. 



Other peculiarities of behavior attendant upon the condition 

 of satiety are the following: 



1 Extension is always sub-maximal. Instead of being ex- 

 tended as fully as possible with the disk spread so as to present 

 the greatest area to the base of the vortex set up by the membran- 

 ellae, the Stentor is only partially extended and the disk is smaller. 

 The animal does not extend perpendicularly upward or horizon- 

 tally from its base of attachment, but generally hangs downward, 

 or frequently lies upon some debris, etc., if possible. 



2 The aboral side is more strongly convex when replete than 

 when hungry. This posture may be related in some way to the 

 voiding of excrementa, though no evidence could be obtained to 

 show that this is true. 



3 There is a marked decrease in the activity of the membran- 

 ellae. This may have much to do with the degree of extension in 

 Stentor. Strong action of the membranellae tends to pull the 

 disk away from the foot, and therefore full extension may be 

 partly due to the strong beat of the membranellae. If the mem- 

 branellae beat only in a weak manner there is no such pull upon 

 the Stentor, and as a result it lies prone or hangs downward from 

 its point of attachment. This is made still more probable by 

 the fact that hungry, free-swimming S ten tors are seldom as fully 

 extended as attached ones. 



4 Satiated Stentors are very irritable to stimuli affecting the 

 swallowing or rejecting mechanisms. In hungry Stentors one 



