CONTENTS 



Page 



I. Interests, opportunity and materials 1 



II. Observational problems and methods 8 



III. Results of multiple-choice experiments: 



1. Skirrl, Pithecus irus 21. 



2. Sobke, Pithecus rhesus 43 



3. Julius, Pongo pygmaiis 63 



IV. Results of supplementary tests of ideational behavior: 



1. Julius, Pongo pygmaus: 



Box "stacking experiment 88 



Box and pole experiment 99 



Draw-in experiment 102 



Lock and key test 102 



2. Skirrl, Pithecus iriis: 



Box stacking experiment 104 



Box and pole experiment 106 



Draw-in experiment 107 



Hammer and nail test 108 



Other activities 110 



3. Sobke, Pithecus rhesus: 



Box stacking experiment Ill 



Draw-in experiment 114 



Box and pole experiment 114 



Other activities 115 



V. Miscellaneous observations: 



1. Right- and left-handedness 116 



2. Instinct and emotion: 



Maternal instinct 118 



Fear 120 



Sympathy 121 



VI. Historical and critical discussion of ideational behavior in monkeys and 

 apes: 



1. Evidences of ideation in monkeys 125 



2. Evidences of ideation in apes 128 



VII. Provision for the study of the primates and especially the monkeys and 



anthropoid apes 133 



VIII. Bibliography 144 



