Doors No. of No. of Settings open doors open right door 1..................5.6........................2..................5 2..................5.6........................2..................6 3..................4.5.6.7.8.9................6..................4 4..................4.5.6.7.8.9................6..................9 5..................1.2.3.4.5..................5..................1 6..................1.2.3.4.5..................5..................5 7..................2.3.4.5.6.7................6..................2 8..................2.3.4.5.6.7................6..................7 9..................3.4.5.6.7.8................6..................3 10..................3.4.5.6.7.8................6..................8 PROBLEM 4. Middle Doors No. of No. of Settings open doors open right door 1..................4.5.6.7.8..................5..................6 2..................1.2.3......................3..................2 3..................1.2.3.4.5.6.7.8.9..........9..................5 4..................2.3.4.5.6..................5..................4 5..................6.7.8......................3..................7 6..................3.4.5.6.7.8.9..............7..................6 7..................7.8.9......................3..................8 8..................1.2.3.4.5.6.7..............7..................4 9..................2.3.4......................3..................3 10..................3.4.5.6.7..................5..................5 It was my aim so far as possible to present to a given subject each day the ten settings under a given problem in order, without interruption. If for any reason the series of observations had to be interrupted, it was resumed at the same point subsequently. Occasionally it was found desirable or necessary to present only five of the series of ten settings in succession and then to interrupt observations for an interval of a few minutes or even several hours. But as a rule it was possible to present the series of ten settings. All things being considered, it proved more satisfactory to give only ten trials a day to each subject. Frequently twenty and rarely thirty trials were given on the same day. In such cases the series of settings was simply repeated. The only pause between trials was that necessary for resetting the entrance doors and replenishing the food which served as a reward for success. III RESULTS OF MULTIPLE-CHOICE EXPERIMENTS 1. Skirrl, _Pithecus irus_ _Problem 1. First at the Left End_ Systematic work with the multiple-choice apparatus and method described in the previous section was undertaken early in April with Skirrl, Sobke, and Julius. The results for each of them are now to be presented with such measure of detail as their importance seems to justify.