Watson (1908) in tests of the imitative ability of _P. rhesus_ saw relatively little evidence of other than extremely simple forms of ideation. But in contrast with his results, those obtained by Haggerty (1909), in a much more extended investigation in which several species of monkey were used, obtained more numerous and convincing evidences of ideation in imitative behavior. Although this author wholly avoids the use of psychological terms, seeking to limit himself to a strictly objective presentation of results, it is clear from an unpublished manuscript (thesis for the Doctorate of Philosophy, deposited in the Library of Harvard University) that he would attribute to monkeys simple forms of ideational experience. Witmer (1910) reports, in confirmation of Haggerty's results, intelligently imitative behavior in _P. irus_. The work of Shepherd (1910) agrees closely, so far as evidences of ideation are concerned, with that of Thorndike. He obviously strives for conservatism in his statements concerning the adaptive intelligence of his monkeys, all of which belonged to the species _P. rhesus_. At one point he definitely states that they exhibit ideas of a low order, or something which corresponds to them. Satisfactory evidences of reasoning he failed to obtain. Franz's (1907, 1911) studies of monkeys, unlike those mentioned above, have for their chief motive not the accurate description of various features of behavior but instead knowledge of the functions of various portions of the brain. His results, therefore, although extremely interesting and of obvious value to the comparative psychologist, throw no special light upon the problem of ideation. The investigation by Hamilton (1911) of reactive tendencies in _P. rhesus_ and _irus_ yielded preeminently important data concerning complex behavior. For the ingenious quadruple-choice method devised by this observer showed that mature monkeys exhibit fairly adequate types of response. As Hamilton's interest centered in behavior, he did not discuss ideation, but this does not prevent the comparison of his data with those of the present report, and the agreement of his findings with my own is obvious. My work contrasts sharply with that briefly mentioned above in that I applied systematically and over a period of several months an experimental method suited to reveal problem solving ability. Previously, the so-called problem or puzzle-box method had been used as a means of testing for the presence of ideas. For this I substituted the multiple-choice method. One of the chief advantages of this new method is the possibility of obtaining curves of learning for the solution or attempted solution of relational problems of varying difficultness. I am confident that these curves of learning will prove far more valuable than such data as are yielded by the puzzle-box method.