I. Two sets of interests lead us to test the intelligence of the higher apes. We are aware that it isa question of beings which in many ways are nearer to man than to the other ape species ;in particular it has been shown that the chemistry of their bodies, in so ~ar as this may be perceived in the quality of the blood, and the structure of their most highly developed organ, the brain, are more closely related to the chemistry of the human body and human brain-structure than to the chemical nature of the lower' apes and thelr brain development. These beings show so many human traits in their "everyday" behaviour that the question was quite automatically suggested whether the animals do not behave with intelligence and insight under conditions which require such behaviour. This question expresses the first, one may say, naive, interest in the intellectual capacity of animals. We wished to ascertain the degree of relationship between anthropoid apes and man in a field which seems to us particularly important, but on which we have as yet little information.