12 



BEHAVIOR OF THE LOWER ORGANISMS 



a reaction, while light falling from above or below on one side causes 

 none, this would seem to indicate that the direction of the rays in 

 passing through the body has something to do with determining the 

 direction of locomotion. But in the myxomycete plasmodium, which 

 resembles Amoeba in its movements and in many other respects, light 

 falling from above or below on a part of the body does produce a 

 negative reaction, — the withdrawal of the part affected. Probably 

 further experimentation will show the same thing to be true in Amoeba. 

 Reaction to Electricity. — Electric currents probably form no part of 

 the normal environment of Amoeba, yet the animal reacts in a very defi- 

 nite way when a continuous current is passed through the water con- 

 taining it. That side of the body which is directed toward the positive 

 pole or anode contracts as if the animal were strongly stimulated 

 here. Then a pseudopodium starts out somewhere on the side directed 



+ 



Fig. 17. — Reaction of Amoeba to the electric current. The arrows show the direction of 

 the protoplasmic currents; at 1 the direction of movement before the current acts is shown. 

 2, 3, 4, successive positions after the current is passed through the preparation. 



toward the negative pole or cathode, and the Amoeba creeps in that direc- 

 tion (Fig. 17). The reaction takes place throughout as if the Amoeba 

 were strongly stimulated on the anode side. If the electric current is 

 made very strong, the anode side contracts still more powerfully, and 

 the Amoeba bursts open on the opposite side. The current is thus very 

 injurious. 



C. How Amoeba gets Food 



In the water in which Amoeba lives are found many other minute 

 animals and plants. Upon these Amoeba preys, taking indifferently an 

 animal or a vegetable diet. Its behavior while engaged in obtaining 

 food is very remarkable for so simple an animal. 



Spherical cysts of Euglena are a common food with Amceba proleus. 

 These cysts are smooth and spherical, easily rolling when touched, so 

 that they present considerable difficulties to an Amoeba attempting to 



