the open doors yawning. This happened even when he was extremely hungry
and evidently eager enough for food.

From July 12 on the hunger motive was increased by feeding the monkey
only in the apparatus and by so regulating the amount of food given in
each trial that he should obtain barely enough to keep him in good
physical condition. An increase in the number of correct choices
promptly resulted, and continued until on July 14 the ratio of choices
was 1 to .54. It appeared from these data that a relatively small number
of choices, say not more than ten a day, the rewards in connection with
which supplied the only food received by the animal, yielded most
favorable results.

On July 16, the period of confinement in wrong boxes was increased to
sixty seconds, and it was so continued for a number of days. But in the
end, it became clear that the period of thirty seconds, combined with a
liberal reward in the shape of desired food and a single series of ten
trials per day, was most satisfactory. The detailed data of table 2
indicate that at this time Skirrl was making his choices by memory of
the particular setting.

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