"This book contains the results of my studies in the intelligence of Apes at the Anthropoid Station in Tenerife from the years 1913-1917. The original, which appeared in 1917, has been out of print for some time. I have taken this opportunity of making a few changes in the critical and explanatory sections, and have added as an Appendix some general considerations on the Psychology of Chimpanzees. With various recent books and essays on the subject I shall have an opportunity of dealing in a further contribution to the subject not yet completed"--Preface.