THE BEHAVIOR OF AMCEBA 



15 



sees it for the first time. The Amoeba conducts itself in its efforts to 

 obtain food in much the same way as animals far higher in the scale. 

 In cultures containing many Amcebae and many Euglena cysts it is not 

 at all rare to find specimens thus engaged in following a rolling ball of 

 food. Sometimes the chase is finally successful; sometimes it Is not. 



Many of the cysts are attached to the substratum. Amceba often 

 attempts to take such cysts as food, sending pseudopodia on each side 

 of and above them, in the usual way, then covering them completely 

 with its body. But it finally gives up the attempt and passes on. 



Sometimes when a single pseudopodium comes in contact with a 

 cyst, this pseudopodium alone reacts, stretching out and pushing the 

 cyst ahead of it and keeping in contact with it as long as possible. Mean- 

 while the remainder of the Amceba moves in some other direction (Fig. 

 20). Finally the pseudopodium is pulled by the rest of the body away 



Fig. 20. — A single pseudopodium (.v) reacts positively to a Euglena cyst, its protoplasm 

 flowing in the direction of the cyst and pushing it forward, while the remainder of the Amceba 

 moves in another direction. 1-4, successive forms taken. At 4 the reacting pseudopodium 

 is pulled away from the cyst, whereupon it contracts. 



from the cyst. Again, two pseudopodia on opposite sides of the body 

 may each come in contact with a cyst. Each then stretches out, pull- 

 ing a portion of the body with it, and follows its cyst. Soon the body 

 comes to form two halves connected only by a narrow isthmus. Finally 

 one half succeeds in pulling the other away from its attachment to the 

 bottom. The latter, half then contracts* and the entire Amceba follows 

 the victorious pseudopodium. 



Amcebae frequently prey upon each other. Sometimes the prey is 

 contracted and does not move; then there is no difficulty in ingesting 

 it. Such a case has been described and figured by Leidy (1879, p. 94, 

 and PI. 7, Figs. 12-19). But the victim does not always conduct itself 

 so passively as in this case, and sometimes finally escapes from its 

 pursuer. This may be illustrated by a case observed by the present 

 writer (Fig. 21). 



