ON THE FEEDING HABITS OF AMEBA 551 



organisms, flagellates and diatoms, are generally more numerous 

 and therefore easier to obtain, than other classes of protozoa and 

 protophyta. 



As far as my observations go, it happens very seldom that one 

 ameba attempts to eat another when two come near each other. 

 Nor do the small amebas of the radiosa type call forth the feed- 

 ing reaction except in very few cases. Other food : coleps, chilo- 

 monas, spathidium, etc., is taken readily while ameban forms 

 are refused. If however an ameba is cut into several pieces, and 

 a fragment placed in the path of an ameba, the feeding reaction 

 is frequently started, but very seldom is the fragment ingested 

 unless it is agitated by means of a glass needle. 



Another organism that is much less readily eaten than might 

 be expected, is the motile Euglena viridis. In a number of cases 

 these were passed by without any attempt at ingestion, although 

 their rate of movement was slow enough to permit of the forma- 

 tion of a food cup over them. In one instance a euglena was 

 ingested by a raptorial ameba but the euglena could not be kept 

 inside of the ameba's body. After the food cup was closed up 

 the euglena made its way into the endoplasm which was quite 

 thoroughly churned up by the vigorous movements of the eu- 

 glena as it moved from one part of the ameba to another. The 

 ameba nevertheless kept on moving forward slowly, apparently 

 not much disturbed b}^ the wrigglings of the euglena within its 

 body. The ameba's digestive juices did not seem to have any 

 effect on the euglena except perhaps to stimulate it to greater 

 activity. Just fifteen minutes after ingestion the ectoplasm 

 broke and the euglena wriggled out of the ameba as an earth- 

 worm might wriggle out of a lump of soft clay. The water taken 

 in with the euglena disappeared in this case, in less than a 

 minute. 



From the general acceptance of chemotaxis as the most im- 

 portant factor in the general movement and feeding reactions of 

 the lower organisms, it might be assumed that a quiet organism 

 would be eaten as readily as a moving one, but this is not the 

 case. I shall therefore speak first of 



