198 



THE BEHAVIOR OF LOWER ORGANISMS. 



and many Euglena cysts it was not at all rare to find the animals 

 engaged in thus following a rolling ball of food. I have made full 

 notes and sketches of a number of other cases, but they show nothing 

 different in principle from that above described, so that it is not worth 

 while to enter into details. One further point is, however, worthy of 

 special note. Often a single pseudopodium comes in contact with such 

 a cyst and stretches out toward it, while the remainder of the Amceba 

 continues on its course, away from the cyst. The pseudopodium in 

 contact then stretches out as far as possible, keeping in contact with 

 the cyst and often pushing it ahead (Fig. 74), until it is finally pulled 

 bodily away by the movements of the whole Amceba. Apparently this 

 one pseudopodium reacts to the stimulus quite independently of the 

 remainder of the body. Again, two pseudopodia on opposite sides of 

 the body may each come in contact with a cyst. Each then stretches 



Fig. 74.* 



out, pulling a portion of the body with it, and follows its cyst, until the 

 body forms two lobes, connected only by a narrow isthmus. Finally, 

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

 substratum, and the entire Amceba follows the victorious pseudopodium. 

 Mechanical stimuli are, of course, involved in the above reactions; 

 perhaps also chemical stimuli from the cyst. It is important from the 

 theoretical standpoint to note that the movement of particles on the 

 surface of the Amoeba is toward the object causing the reaction. This 

 I have been so fortunate as to have opportunity of observing in several 

 cases. 



OTHER AMCEBa; AS FOOD. 



Amoebae frequently prey upon each other, as Leidy has already de- 

 scribed and figured (1879, p. 94 ; plate 7, Figs. 12-19) • ^i-'*^ the victim 

 does not always conduct itself so passively as in the case described by 

 Leidy, and sometimes finally escapes from its pursuer. A description 



*FiG. 74. — A single pseudopodium (x) reacts positively to a Euglena cjst, the 

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

 of the Amoeba moves in another direction ; 1—4, successive forms taken. At 4 the 

 reacting pseudopodium is pulled away from the cyst, and then contracts. 



