REACTIONS OF AMCEBA PROTEUS TO FOOD. 419 



conditioned by the great chances afforded for the escape of the 

 prey. So after disturbing the prey twice and causing it to retreat 

 as often along the projected axis of the pseudopodium the Amceba 

 did not disturb the prey but sent about it pseudopodia which 

 eventually enclosed the quiet Chilomonas. This is of further 

 interest in demonstrating that the reaction of Amceba to food is 

 not a fixed one for twice the Chilomonas was rejected and the 

 third time deliberately accepted. 



In contrast with this reaction is that of the Amceba shown in 

 Fig. 3. Here a Chilomonas, after making contact with the ecto- 

 plasm of the Amceba, lay in between two pseudopodia, one of 

 which presented an inwardly directed surface and the other an 

 outwardly directed surface. If the disturbed prey were to strike 

 the former it would be deflected towards the fundus of the inter- 

 pseudopodial space, whereas if the disturbed prey were to strike 

 the latter it would be deflected away from the space which is 

 to form the basis of a food vacuole. Thus in this case the possible 

 retreat of the prey may be the chief condition to be met. 



When an object of prey entered a narrow angle between two 

 pseudopodia the possible retreat of the prey again became the 

 principal conditioning factor. If the Amceba had reacted at 

 the point of contact by sending out secondary pseudopodia 

 towards each side of the prey it would have crowded back the 

 prey and thus result in its escape. To prevent this escape the 

 Amceba sent secondary pseudopodia behind the Chilomonas 

 paramcecium as described for Fig. 4 on page 415. 



Further it is interesting to note that in this case the stimulus 

 was encountered at a and the reaction took place at b and c (Fig. 

 4). Thus we see that here it is not as Jennings ('06) says in 

 reference to locomotion that "it is primarily the part stimulated 

 that responds." For in this reaction 'it was not the part imme- 

 diately stimulated but the parts that could most advantageously 

 respond that did so. 



Where it was more advantageous for another part or parts to 

 respond we find that they responded. Take for example the 

 case in which the object of prey entered a broad angle between 

 two pseudopodia as described on page 415 for Fig. 5. If the 

 Amceba had reacted in the manner just described it would have 



