CHAPTER III 



BEHAVIOR 



In broad perspective, multicellular animals enjoy periods of 

 relaxation or inactivity, but their constituent cells are ever active 

 as long as life maintains. Unicellular animals share with tissue 

 cells this unresting activity, and stentors are no exception. In their 

 reproduction, continual search for food, and avoidance if possible 

 of unfavorable surroundings, the abiding impression is that 

 stentors are always busy. Cessation of swimming and attachment 

 by the holdfast is only the prelude to active feeding. If we define 

 behavior as altered response to changing conditions, unresting 

 stentors are continually behaving. Observing them even briefly, 

 one is struck by the appearance that their activity is not mechan- 

 istically simple, though they may be high-grade automatons. If 

 we place ourselves in the position of early investigators, the 

 wonder is renewed that even in these minute and lowly forms of 

 life we can undertake to analyze behaviour. 



I. Food selection 



Food selection in Stentor seems to have been clearly demon- 

 strated in a nice series of experiments by Schaeffer (1910). He 

 recorded the uptake by coeruleus placed for a time in a prescribed 

 suspension of particles as well as observing what happened when 

 single particles were introduced one at a time with a capillary 

 pipette into the feeding vortex. In one of the "hand feeding" 

 tests, for example, 12 Phacus were ingested and only three rejected, 

 while 13 indigestible sulphur particles were rejected and only 

 three taken in. In another test all 50 Phacus presented were 

 ingested, while 18 starch grains were rejected and only one 

 accepted. Size was not determinative because the starch grains 

 were four to one-eighth times the size of Phacus. Again, 21 Phacus 

 and I starch grain were eaten, while 7 Phacus ^ 12 grains, and 11 

 glass particles were rejected. Euglena was preferred to Chilomonas. 



II 



