Selection of Food in Stentor Caruleus [Ehr.) 87 



of indigestible particles is very effective. Very few particles ever 

 get into the pouch so long as this mode of ciliary action takes place. 

 This modification of behavior appears gradually and also disap- 

 pears gradually; and during the transitions the action is imperfect, 

 some particles passing into the pouch while others are carried 

 to the right before dropping into the pouch. This phenomenon 

 is interesting in that the discal cilia, which act usually in a certain 

 definite coordinated way, are able to change their behavior so as to 

 act in an entirely different but still coordinated way. What is 

 more remarkable still perhaps is that some of the cilia beat in the 

 same direction in both cases, while some others beat in an exactly 

 opposite direction, the rest of them beating in every conceivable 

 direction between their usual direction of beat and its direct oppo- 

 site. This is a very good example of the extreme plasticity of 

 behavior of such an organism as Stentor. 



Under the same conditions in which the foregoing change of 

 behavior was observed there was found another method by means 

 of which the Stentor made its ingesting apparatus ineffective. 

 This was done hy contracting and staying contracted. Contrac- 

 tions for more than several minutes have not heretofore been 

 recorded, but in one set of Stentors I observed continuous contrac- 

 tion for more than two and three-quarter hours. There was not 

 a single relaxation during all this time and it is possible that this 

 state of continuous contraction lasted longer than two and three- 

 quarter hours, for the observation was not continued until relaxa- 

 tion occurred. The body cilia remained constantly reversed in 

 this case, but the membranellse frequently alternated between 

 the usual and the reversed beat. Both groups of these cilia beat 

 less vigorously than when relaxed or free swimming. The pouch 

 and funnel were closed and no particles whatever were ingested. 



Still other Stentors under similar circumstances differed in 

 behavior from all the above. Under stimulation of dense clouds 

 of carmine some Stentors swam with the foot ahead continuously 

 for Over three hours. The membranellae were sometimes beat 

 in the ordinary and sometimes in the reversed way, but always 

 with a less vigorous beat than when the Stentor is fully extended 

 attached, and in water with few particles present. There was no 



