ON THE FEEDING HABITS OF AMEBA 557 



the mere spreading out of the newly formed pseudopod, and the 

 carmine was then speedily ingested with a considerable amount 

 of water. In about a minute the water was absorbed, and the 

 ameba flowed off in the opposite direction. Three minutes later 

 the carmine was excreted. 



One of the most interesting features of this behavior, not hith- 

 erto described, is the sensing of the carmine at a distance and 

 the movement toward it. The explanation of the reaction at a 

 distance that at once suggests itself is based, of course, upon the 

 diffusion of the dissolving carmine. Another item of behavior 

 that calls for an explanation is this : Why did the main pseudopod 

 resume forward movement after turning toward the carmine, 

 and after the pseudopod was projected toward it, but was re- 

 tracted after the ameba came into contact with the carmine? 

 Still another feature of behavior, should be noticed at this time, 

 for it will recur again and again. Why should the ameba reverse 

 its. direction of movement after eating the carmine? Why did 

 it not move on in the original direction? The direction of move- 

 ment after eating an object as compared with the previous direc- 

 tion of movement, is not a matter of chance but is fairly well 

 resolvable into two or three factors. If an object is eaten which 

 seems not to be wanted after it has been eaten (which may be 

 inferred from its hasty excretion) the ameba is liable to move 

 away in such a direction as will bring the object soonest near the 

 new posterior end. This experiment also brings out strikingly 

 the contrast between the evacuation of the carmine by the ameba 

 before ingestion and after it has come into contact with the in- 

 ternal protoplasm; or between reactions of ectoplasm and endo- 

 plasm to the same object; or between organismal and histonic 

 selection of food. It is at present impossible to state the case 

 satisfactorily because not all the factors determining 'selection' 

 are known. But it seems that an ameba sometimes eats what 

 it does not want. 



About eleven minutes after excreting the grain of carmine as 

 above described, another grain of carmine of grade 4 (containing 

 a considerable amount of egg white) was placed slightly to the 

 right of the ameba's path — 8. The ameba moved into contact 



