ON THE FEEDING HABITS OF AMEBA 539 



But shortly after Rhumbler published the paper from which 

 the above extract was taken, Harrington and Learning ('00) 

 showed that amebas quickly become accustomed to even strong 

 light; that after they had been exposed to strong white or mono- 

 chromatic light for a few seconds, which causes retardation or 

 cessation of movement, they begin to move normally again as if 

 the light was without further effect. Ameba seems therefore to 

 be affected by light only when its intensity suddenly changes; 

 uniform moderate intensity is without effect in changing 

 behavior. 



The explanation of Rhumbler's observations where an Amoeba 

 verrucosa ejected a partly ingested alga filament when strong 

 light was turned on lies in the sudden change in light intensity. 

 It is more than likely that no ejection would have occurred if 

 the change had been made very gradually. 



Regarding the notion that amebas eat only or chiefly at night, 

 owing to the assumed preventive effect of strong light in the day- 

 time, it may be said that previous observations of ameban be- 

 havior have not been protracted enough. This may readily be 

 granted in view of the large number of successful cases of feeding 

 recorded in this paper. 



GENERAL DESCRIPTION OF THE FEEDING PROCESS 



Before taking up the detailed behavior of ameba toward the 

 various test substances, it may be advisable to insert here a gen- 

 eral description of the usual feeding process together with some 

 previous observations by other investigators, in order that the 

 detailed account which is to follow may be clear from the outset. 



One of the first students of ameban behavior to describe the 

 feeding habits of this animal was the geologist-naturalist P. M. 

 Duncan, who gives in his Studies amongst Amoebae ('77) a very 

 interesting, if anthropomorphic, interpretation of the general 

 behavior of amebas. With regard to their feeding habits, Dun- 

 can leaves the impression that food is taken only at the posterior 

 end of the ameba. 



The large end ever in advance moves over every obstacle around and 

 under it, l3ut the most tempting food never sinks in or is caught bv it 

 (p. 230). 



