58 A. A. SCHAEFFER 



changes in protoplasmic streaming in the various pseudopods, 

 which were provoked by the giobuhn. Action was not unified 

 in 1624; the tendencies to move toward and away from the 

 giobuhn were equally strong. But after a few seconds of con- 

 tact with the giobuhn, the tendency to move away rapidly 

 became the stronger. At this same time a small pod was form- 

 ing at the posterior end, and it w^as doubtless this activity which 

 finally prevented the ameba from flowing away through the 

 right pseudopod, which appeared to become the main one. But 

 the protoplasm of the posterior half would have had to flow 

 toward the globulin to get into the pseudopod on the right. The 

 necessity of this may have caused the ameba to flow away 

 through the posterior end rather than through the pseudopod on 

 the right. 



The side pseudopods in figure 1623 illustrate graphically an 

 internal condition affecting behavior that is frequently observed 

 in amebas reacting indifferently toward food substances. When 

 an ameba that is not hungry encounters a food particle which 

 stimulates the ameba at the side of a pseudopod so that a new 

 pseudopod is formed toward the food object, there is formed 

 simultaneously or nearly so on the opposite side of the main 

 pseudopod a pseudopod of about the same size and flowing at 

 the same angle and at about the same rate as the one directed 

 toward the food. Opposite pseudopods of this character are not 

 formed by hungry amebas under otherwise similar conditions, 

 nor by any amebas toward indifferent objects (glass, sand, etc.) 

 nor toward objects producing usually negative behavior. There 

 are in these reactions two tendencies present, a positive and a 

 negative, judging from the objective behavior. The formation 

 of pseudopods is not directly determined by the stimulating 

 object as can be readily observed from the record of every ex- 

 periment. Then how is pseudopod formation controlled? This 

 question is of the profoundest interest. 



An unusual method of ingestion in which two pseudopods were 

 involved is shown in figures 939 to 950. The ameba was in Y-form 

 with the globulin lying nearer the right limb. Nevertheless, the 

 left hmb enlarged the more rapidly and came first into contact 



