ON THE FEEDING HABITS OF AMEBA 537 



wanted without provoking negative reactions on the part of the 

 ameba. 



A single ameba was employed for as many experiments as was 

 possible, for in most cases the results of such experiments gain 

 added value on account of the comparisons which may be made. 

 But there is a limit to the value of such procedure in studying 

 feeding habits of ameba since an individual changes its behavior 

 to some extent on account of the food eaten and on account of 

 other previous reactions. Nevertheless, as many as twenty or 

 thirty experiments may be made in succession upon a single 

 specimen under the most favorable conditions. 



All the work was done while facing a north window to insure 

 constancy in the direction of light. As will be seen in a later 

 paper, amebas are verj^ sensiti\'e to light, particularly if there are 

 sharp gradations in intensity; and it will be desirable, therefore, 

 to bear this fact in mind while examining the figures. It does not 

 appear, however, that the light had any marked effect in their 

 general movements, for the amebas moved in all directions on 

 the slide, and they changed their direction of movement in al- 

 most every conceivable way, just as if the light came from all 

 possible directions with uniform intensity. The explanation of 

 this apparent contradiction regarding the effect of light on ameba 

 lies in the fact, experimentally determined, that amebas readily 

 become accustomed to light of relatively strong intensity; and 

 that they do not react to light of moderate intensity unless sharp 

 gradations of intensity come within sensing range. However 

 desirable it would be to have the light under controlled condi- 

 tions while testing feeding reactions, the experimental difficulties 

 involved in bringing such conditions about would result in greatly 

 limiting experimental latitude in other respects, for there must 

 always be sufficient light merely to see what is going on. In all 

 the experiments where north light was used I believe we may dis- 

 regard light as a factor affecting discrimination, as far as the 

 conclusions in this paper are concerned. 



Hitherto, however, the effect of continuous daylight has been 

 assumed to play a very important part in ameban behavior. 

 Thus Rhumbler ('98) expressed the opinion that light serves to 



THE JOURNAL OF EXPERIME>fTAL ZOOLOGY, VOL. 20, NO. 4 



