56 S. O. MAST AND L. C. PUSCH. 



clearly defined edges and furnished a band of intense light across 

 the field. The slide was adjusted so that the amoeba was within 

 a distance equal to approximately half its length from the light 

 with the pseudopod or pseudopods progressing towards it. If 

 the pseudopod did not stop when it came in contact with the 

 light the amoeba was discarded. If it stopped the behavior of 

 the amoeba was observed until it definitely moved away from the 

 light, and the number of pseudopods which made contact with 

 it was recorded. After this the light was shut off, and the amoeba 

 was left in darkness until the next trial was made. In this way 

 each individual was given twenty-seven trials. 



The interval between trials was approximately three minutes 

 except in the following as recorded in Table I: individual B, 

 trials 16-17 and 23-24, 24 hours; individual D, trials 15-16, 

 22 hours; individual E, trials 8-9 18 hours, 16-17, 48 hours, and 

 21-22, 24 hours; individual F, trials 8-9, 50 hours, and 20-21, 

 20 hours; individual G, trials 16-17, 16 hours, and 24-25, 3 hours. 

 During these intervals the amoebae were kept on their slides in 

 darkness undisturbed. 



The behavior of a typical individual is illustrated in Fig. I by 

 sketches representing all of the trials in the series. By referring 

 to this figure it will be seen that while during the first part of the 

 series there w r as something of a persistence on the part of the 

 amoeba to attempt to proceed in its original direction notably 

 7 attempts in trial 4 there was but little in the latter part of the 

 series a total of only 5 attempts during the last 14 trials. 



The results obtained in all of the tests are presented in Table I. 

 This table shows that the number of pseudopods which came in 

 contact with the light before the direction was changed decreased 

 in general as the number of trials increased in each series, that 

 there was a similar decrease in the total contacts of all amoeba! 

 for corresponding trials, and also in the totals of consecutive 

 groups of three trials. Amoeba B made 10 contacts with the light 

 in the first three trials; with trial 4 a general decrease begins. A 

 total of 20 pseudopods made contact in the first 14 trials of the 

 series, and a total of 9 in the last 13. In the series of amoeba D 

 there were 5 contacts in the first 6 trials but none at all in the 

 remaining 21 trials. Amoeba E made 21 contacts in the first 

 14 trials II of these were in the first 4 and 5 in the last 13 



