6O ASA A. SCHAEFFER. 



came into contact with the dark spot a positive reaction. The 

 ameba then moved on through this pseudopod and partly over 

 the dark spot. The ameba was again shifted so that the dark 

 beam lay directly ahead 319. A pseudopod which was thrown 

 out toward the right led the ameba away, a definite negative 

 reaction. 



Another proteus was then brought into the field with the dark 

 spot directly ahead 322. The ameba turned to the right and 

 moved on, avoiding the dark beam. The ameba was then shifted 

 with the dark spot straight ahead 325. The ameba became 

 irregular in its streaming at the anterior end, indicating that the 

 ameba sensed the dark spot and that there was present a tendency 

 to react negatively; but the tendency to negative reaction was 

 weak, for the ameba started presently to move over the dark 

 area. The ameba, in irregular shape, was shifted again with the 

 dark spot directly ahead 329. When the ameba came into 

 contact with the outer edge, the tip of the main pseudopod forked, 

 the right prong becoming the main pseudopod through which 

 the ameba moved away. Negative behavior is again shown here. 

 The ameba was shifted with the dark spot directly ahead 333. 

 A pseudopod was thrown out on the left as the ameba moved into 

 contact with the dark spot 334 indicating a tendency to 

 negative reaction, but it was withdrawn as the tip of the ameba 

 proceeded for some distance beyond the further edge of the dark 

 area 336. The ameba was moved again so that the dark spot 

 lay slightly to the right 340. The ameba moved into contact 

 with the dark area, then sent out a pseudopod on the left, but it 

 was soon withdrawn and at the same time another was sent out 

 on the right. The ameba finally moved on in the original 

 direction. Here we have first positive behavior in the turning 

 of the ameba toward the dark spot; then negative behavior in the 

 formation of the pseudopod on the left; then again positive 

 behavior in the resumption of forward movement and the for- 

 mation of the pseudopod on the right. In the next trial the 

 ameba was moved with the dark spot slightly to the right 346. 

 The ameba turned slightly further to the left, then directly toward 

 the right and toward the dark spot 348. When the ameba 

 came into contact with the dark spot, a pseudopod was thrown 

 out on the left, but it was withdrawn as the ameba moved on. 



