1^0 Asa Arthur Schae If er 



by itself. Some S ten tors from the beginning of the experiment 

 rejected carmine apparently only because food was also present. 

 The rejecting and the ingesting mechansism may therefore be 

 acted upon and their mode of action in consequence changed, 

 both by the physiological state as determined by the amount of 

 food in the animal, and by the condition of the stimulus-receiving 

 apparatus as influenced by the amount of previous stimulation. 



Whenever a particle possesses qualities that stimulate to a 

 greateror less extent both the ingesting and the rejecting mechan- 

 ism, the action of the cilia in the pouch and funnel are not thor- 

 oughly coordinated either for ingesting or for rejecting, and as a 

 consequence loops are formed in the path of the particle. It 

 seems from the experiments that the stimuli from the objectionable 

 features of a particle are summated more rapidly than the stimuli 

 from the desirable features; for 80 per cent of all the particles that 

 had loops in their paths were finally rejected. We also find that a 

 much larger number of loops occur when the Stentor is beginning 

 to be replete than when hungry or when almost satiated. At the 

 stage when the animal is just beginning to be replete, stimuli of 

 medium intensity are required to set off" either the ingesting or the 

 rejecting apparatus. The stimuli are more nearly of equal inten- 

 sity, or in other words, the mechanisms are set off more nearly 

 with equal readiness at this stage than at any other. This is 

 probably the reason for the larger number of loops at this stage. 



Selection between food and indigestible particles in Stentor 

 is an almost perfect adaptation. With very few exceptions only 

 particles (organisms) of food value are ingested. Indigestible 

 particles of many sorts which have for thousands of generations 

 not come in contact with Stentor are nevertheless rejected with 

 accuracy. 



SUMMARY 



I Stentor c.ieruleus exercises a selection among the particles 

 that are brought to its food pouch by the ciliary current. The 

 selection is brought about by changes in the beat of the cilia of the 

 pouch and funnel. Certain particles are rejected by a localized 



