ON THE FEEDING HABITS OF AMEBA 553 



The behavior toward moving organisms varies greatly. For 

 instance, the pseiidopod may be transformed into a covering 

 sheet only and then thrown over the organism. Very slight 

 movements on the part of the food organism, a mild state of hun- 

 ger on the part of the ameba, or stimulation on the side of the 

 pseudopod, is likely to produce a food cup of this sort. Under 

 such conditions eating seems to be a side issue, for the main 

 stream is frequently not interrupted or changed in its direction 

 of flow. Sometimes a food organism is excreted undigested thirty 

 or more minutes after ingestion. This is especially true of large 

 objects such as desmids, when there is already a large amount of 

 undigested food in the body. The state of hunger is therefore 

 not directly determined by the digestive abilities of an ameba at 

 any given time. 



A small organism like chilomonas is apparently as acceptable a 

 food object as can be offered to an ameba, for it has been fre- 

 quently noted that when globulin or grain gluten or egg albu- 

 men, or other substance, was entirely and repeatedly disregarded, 

 a chilomonas would be ingested at once. 



Reactions to dead and to motionless organisms and to 

 parts of organisms 



A motionless organism whether living or dead does not usually 

 call forth a food cup before the ameba has come into physical 

 contact w^th it. This behavior is in strong contrast to that ob- 

 served when a living organism is eaten, where, as has been de- 

 scribed, a food cup is nearly always formed before the ameba has 

 come into contact with the prey. With the granular amebas 

 ingestion of immobile organisms or parts of organisms may be 

 frequently observed. Pieces of crabs or of worms are frequently 

 eaten. In many cases, however, they are avoided or left behind 

 when coming into contact with them the first time; but if the 

 pieces are shifted so as to lie again in the path of the ameba, they 

 may be eaten. 



Just what takes place in the ameba in such a case between the 

 first and second tests cannot be stated. When a higher animal 



THE JOCRXAL OF EXPERIMEXTAL ZOOLOGY, VOL. 20, NO. 4 



