Skirrl, on July 17 was evidently hungry and eager to locate food, but seemingly unable to select the right box. In trial 5 (765th) of the series, he was punished by confinement in box 8. When the doors were unlocked in order that the entrance door might be raised to release him, the lock-bar, sliding under the floor, made a slight grating noise, and the instant the entrance door was opened, he jumped out excitedly. _He made no outcry, but as soon as he was out of the box, sat down, and taking up his right hind foot, examined it for a few seconds._ Having apparently assured himself that nothing serious had happened, he went on unconcernedly about his task. The presumption is that the sound of the lock-bar, associated as it was with his painful experience in box 1, revived the strongly affective experience of stepping on the nail. Psychologically described, the sound induced an imaginal complex equivalent to the earlier painful experience. The behavior seems to the writer a most important bit of evidence of imagery in the monkey. Finally, on August 9, after ten hundred and seventy trials, Skirrl succeeded in choosing correctly in the ten trials of a series, and he was therefore considered to have solved the problem of the second door from the right end of the group. On the following day, he was given a control series with the settings which are presented on page 19 and also at the bottom of table 2. In this series he chose correctly five times,--in other words, as often correctly as incorrectly. An analysis of the choices indicates, however, that two of the five correct choices were made in box 8, which, as it happened, had proved a peculiarly easy one for him throughout the training, since from the first he tended to avoid door 9. Consequently, it is only fair to conclude, from the results for this control series and for those given on August 11 and 12, that the animal chose not on the basis of anything remotely resembling a general idea of secondness from the right end, but instead on the basis of gradually acquired modes of reaction to the particular settings. This conclusion is strengthened by the fact that he had failed to learn to react appropriately and readily to most of the settings of the regular series.