126 ROBERT M. YERKES 



planned to test the ideational capacity of his subjects, and one 

 can not find a more stimulating discussion of ideation than 

 that contained in his " Mind in Evolution." The results of 

 his tests made with a P. rhesus monkey are similar to those 

 of Kinnaman, for almost all of them indicate the presence and 

 importance of ideas. 



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 ob- 

 tained by Haggerty (1909), in a much more extended investiga- 

 tion in which several species of monkey were used, obtained 

 more numerous and convincing evidences of ideation in imita- 

 tive behavior. Although this author wholly avoids the use of 

 psychological terms, seeking to limit himself to a strictly objec- 

 tive presentation of results, it is clear from an unpublished 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 evi- 

 dences of ideation are concerned, with that of Thomdike. 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 corres- 

 ponds to them. Satisfactory evidences of reasoning he failed 

 to obtain. 



Franz's (1907, 1911) studies of monkeys, unlike those rnen- 

 tioned above, have for their chief motive not the accurate de- 

 scription 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 con- 

 cerning 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 in- 



