The detailed results for this problem are given in table 7.  Reactive tendencies which appear are:  (a) persistent choice of the end boxes followed, subsequently, by (b) the tendency to locate the middle box directly.  This proved fairly easy when the number of boxes involved was only three as in settings 1, 4, 7, and 10.  Setting 4 was most difficult of all, because box 9 was avoided or ignored.  When the number of open boxes was as great as five, as in settings 2 and 8, the task was obviously more difficult, but whereas success in setting 2 appeared early, in setting 8 it failed to appear during the course of experimentation.  For the settings 3, 6, and 9, involving either seven or nine open boxes, the direct choice of the middle box was next to impossible, and Sobke tended to choose, first of all, a particular box toward one end of the series, for example, box 2, in setting 3, and box 7 in setting 9.  To the experimenter, as he watched the animal’s behavior, it looked as though effort each time were being made to locate the middle member of the group.  This appeared relatively easy for groups of three boxes, extremely difficult for as many as five boxes, and almost impossible for seven or nine.

3.  Julius, Pongo pygmaeus

Problem 1.  First at the Left End

The orang utan, Julius, was gentle, docile, and friendly with the experimenter throughout the period of investigation.  He at no time showed inclination to bite and could be handled safely.  As contrasted with Skirrl and even with Sobke, he adapted himself to the multiple-choice apparatus very promptly, and only slight effort on the part of the observer was necessary to prepare him, by preliminary trials, for the regular experiments.  But in order to facilitate work, he was familiarized with the apparatus by means of regular route training and feeding in the several boxes from April 5 to April 9.

On April 10 the apparatus was painted white as has been stated previously, and on the following Monday, April 12, Julius when again introduced to it gave no indications of fear, uneasiness, or dislike, but worked as formerly, making his round trips quickly and eagerly entering any box which happened to be open, in order to obtain the reward of food.

The regular experimentation was undertaken on April 13, and the results of the first series of trials with Julius are sharply contrasted with those obtained with the monkeys in that fewer choices were necessary.  Instead of the expected ratio of right to wrong first choices, 1 to 2.5, the orang utan gave a ratio of 1 to 1.  An additional markedly different result from that obtained with the monkeys is indicated below in the total time required for a series of trials.  As examples, the data for the first, second, fifth, and tenth series are presented.

TIME FOR SERIES OF TRIALS