ON THE FEEDING HABITS OF AMEBA 559 



certain that the change is not due to fatigue either of the sensing 

 mechanism or of the eating mechanism. The difference in the 

 behavior cannot be due only to the difference between the stimuli 

 in these experiments. 



But observe this ameba's further behavior. A piece of well 

 dried and nearly insoluble egg white was definitely avoided by 

 the ameba after having come into contact with it — 30. A piece 

 of debris was also avoided, but before coming into contact with 

 it — 32. But when a fresh grain of carmine of grade 2 was laid to 

 the left of the ameba's path, it was promptly ingested — 35. The 

 ameba became relatively quiet for about three minutes, then it 

 moved off in the original direction, excreting the carmine fifteen 

 minutes after ingestion. The grain of carmine seems to have 

 been regarded as possessing food qualities in a higher degree than 

 the first grain eaten ; for the water in the food vacuole persisted 

 for a longer time ; a period of rest followed ingestion ; the ameba 

 moved off in its previous direction ; and the carmine remained five 

 times as long in the ameba's body. 



Two minutes after it was excreted, the carmine grain was laid 

 directly in front of the ameba — 44. The carmine grain was rolled 

 around for four minutes and then left behind without any at- 

 tempt at ingestion. When laid in the ameba's path again — 57 — 

 side pseudopods were sent out under the carmine, but the ameba 

 did not change its direction of movement until the carmine lay 

 at the posterior end of the ameba. Then the tip of the ameba 

 broke up into several pseudopods, the one on the left becoming 

 the main one through which the ameba moved away. The ameba 

 again reacted less strongly in each of the successive tests with 

 this grain of carmine. 



A new grain of carmine of grade 2, laid on the ameba's right, 

 was again promptly ingested — 64. Six minutes after eating it the 

 carmine was egested, the ameba flowing off without a period of 

 rest intervening, 65° to the left, so that the carmine at once occu- 

 pied a position near the posterior end. Compared with the first 

 experiment where the direction of flow was reversed after inges- 

 tion, it may be noted that the carmine was retained twice as long 

 in this as in the first experiment; the stimulus causing excretion 



