18 BEHAVIOR OF THE LOWER ORGANISMS 



Amoebae moved in opposite directions and became completely separated. 

 The whole performance occupied about fifteen minutes. 



Such behavior is evidently complex. An analysis into simple re- 

 actions to simple stimuli is difficult if possible at all. We shall return 

 to this matter later. 



The method of food-taking illustrated in the behavior described is 

 characteristic for Amoebae of the proteus and Umax types. It is some- 

 times said that these Amoebae take food at the wrinkled posterior end. 

 This, if true at all, is certainly rare; the author has never observed it, 

 though he has seen food taken in dozens of cases. The essential fea- 

 tures of the food reaction seem to be the movement of the Amoeba 

 toward the food body (long continued, in some cases), the hollowing out 

 of the anterior end of the Amoeba, the sending forth of pseudopodia 

 on each side of and above the food, and the fusion of the free 

 ends of the pseudopodia, thus enclosing the food, with a quantity 

 of water. The reaction is thus complex; at times, as we have seen, 

 extremely so. 



In the process of taking food which we have just described there is 

 no adherence between the protoplasm and the food body. But in 

 A mceba verrucosa and its relatives foreign objects do adhere to the sur- 

 face of the body, and this adherence is of much assistance in obtaining 

 food. It partly compensates for the lack of pseudopodia in these species. 

 But it is not alone food substances that cling to the surface of the body. 

 Particles of soot and bits of debris of all sorts become attached in the 

 same way. Not all these substances are taken into the body as food, 

 so that adhesion to the surface does not account for food-taking. For 

 this an additional reaction is necessary. 



Food-taking in Amoeba verrucosa often occurs as follows: The ani- 

 mal in its progress comes in contact with a small food body, such as a 

 Euglena cyst. This adheres to the surface, and may pass forward on 

 the upper surface of the body to the anterior edge, in the way described 

 on a previous page. At the same time it begins to sink slowly into the 

 body, surrounded by a layer of ectosarc. When it has rounded the 

 anterior edge, the Amoeba passes over it ; then the food body passes up- 

 ward again at the posterior end and forward on the upper surface. It 

 is now sunk still more deeply into the protoplasm, and by the time it 

 reaches the anterior edge again it has usually passed completely into the 

 endosarc, together with the layer of ectosarc enveloping it. In this way 

 the author has seen Amoeba verrucosa ingest various algas, small flagel- 

 lates, Euglena cysts, and a small Amoeba of the proteus type. Indifferent 

 particles, such as bits of soot, which are attached to the surface at the 

 same time, are not taken in. 



