Four problems which had previously been presented to other organisms were in precisely the same form presented to the three primates. These problems may be described, briefly, by definition of the right reaction mechanism, thus: problem 1, the first mechanism at the subject's left; problem 2, the second mechanism at the subject's right (that is, from the end of the series at the subject's right); problem 3, alternately, the first mechanism at the subject's left and the first at its right; problem 4, the middle mechanism of the group.

It was my intention to present these four problems, in order, to each of the three animals, proceeding with them as rapidly as they were solved. But as it happened, only one of the three subjects got as far as the fourth problem. When observations had to be discontinued, Sobke was well along with the last, or fourth problem; Skirrl was at work at the third problem; and Julius had failed to solve the second problem.

For each of the problems, a series of ten different settings of the doors was determined upon in advance. These settings differ from those employed in a similar investigation with the pig only in that the numbering of the doors is reversed. In the present apparatus, the boxes as viewed from the front (entrance) are numbered from the left to the right end, whereas those of the pig apparatus were numbered from the right end to the left end.

Below are presented for each of the several problems (1) the numbers of the settings presented in series; (2) the numbers of the doors open; (3) the number of doors open in each setting and for the series of ten settings; and (4) the number of the right door.

PROBLEM 1. First mechanism at left of group

Doors No. of No. of
Settings open doors open right door
1………………1.2.3………………….3………………1
2………………8.9……………………2………………8
3………………3.4.5.6.7………………5………………3
4………………7.8.9………………….3………………7
5………………2.3.4.5.6………………5………………2
6………………6.7.8………………….3………………6
7………………5.6.7………………….3………………5
8………………4.5.6.7.8………………5………………4
9………………7.8.9………………….3………………7
10………………1.2.3………………….3………………1
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Total 35

PROBLEM 2. Second mechanism from the right end of group

Doors No. of No. of
Settings open doors open right door
1………………7.8.9………………….3………………8
2………………1.2.3.4………………..4………………3
3………………2.3.4.5.6.7…………….6………………6
4………………1.2.3.4.5.6…………….6………………5
5………………4.5.6.7.8………………5………………7
6………………1.2.3………………….3………………2
7………………2.3.4.5………………..4………………4
8………………1.2.3.4.5.6.7.8.9……….9………………8
9………………1.2.3.4………………..4………………3
10………………3.4.5.6.7.8…………….6………………7
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Total 50

PROBLEM 3. Alternately the first mechanism at the left and the
first at the right end of the group

Doors No. of No. of
Settings open doors open right door
1………………5.6.7………………….3………………5
2………………5.6.7………………….3………………7
3………………1.2.3.4.5.6…………….6………………1
4………………1.2.3.4.5.6…………….6………………6
5………………4.5.6.7.8………………5………………4
6………………4.5.6.7.8………………5………………8
7………………2.3.4.5………………..4………………2
8………………2.3.4.5………………..4………………5
9………………3.4.5.6.7.8.9…………..7………………3
10………………3.4.5.6.7.8.9…………..7………………9
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Total 50