82 THE BEHAVIOR OF PROTOZOA 



ahead in another direction. To a degree unusual among 

 infusoria Stentor has the power of changing the form of 

 its body. It may extend into the form of a very long slender 

 trumpet, or contract almost into a sphere. The ability 

 to undergo these changes is due to the presence of numerous 

 contractile threads or myonemes which extend for the most 

 part longitudinally just beneath the outer layer of ecto- 

 plasm. Food taking in Stentor is accomplished with the aid 

 of the cilia at the anterior end of the body and the membran- 

 ellse leading to the oral opening. The currents set up by 

 the beating of these organs carry bodies to the mouth 

 which has the power of taking in comparatively large ob- 

 jects, for one often sees rotifers, diatoms, alga3, and various 

 protozoans in the endoplasm of the animal. 



While swimming freely in the water the behavior of 

 Stentor is in general similar to that of Paramoecium. The 

 spiral swimming and the motor reflex in response to chemical, 

 mechanical, thermal and electrical stimuli are much the 

 same* in both organisms. Stentors as a rule react to light 

 which has little effect on Paramoecia. In Stentor cceruleus, 

 which is negatively phototactic, sudden illumination evokes 

 the motor reflex which after one or more trials enables the 

 animal to reach a more shaded region. The anterior end is 

 the region most sensitive to light and when the organism 

 is pointed toward the light it gives the motor reflex, and 

 swims in a different direction. If still pointing obliquely 

 toward the light it may repeat the motor reflex and continue 

 to do so until its anterior end is directed away from the 

 source of stimulation, when the Stentor swims off in the 

 direction of the rays. 



When Stentor is attached it exhibits several peculiar types 

 of activity. It may contract or extend the body, and it 

 often sways about in various directions in a more or less 



