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happened to come open. She never clearly perceived why a button or a hook kept her from opening the box. An animal of higher intelligence would have comprehended the cause of the difficulty and performed the appropriate act without wasting so much time and effort in random biting and clawing. Lizzie was very impatient to obtain her objectives. If she could not see quickly and intuitively what course should be followed, she did not spend time in devising new methods of attack. She seemed quite incapable of exercising what we might call conscious deliberation over means of attaining ends.

I have dwelt upon Lizzie's intellectual aptitudes and limitations because they indicate a stage of mental development that is in many respects intermediate between what is found in ordinary mammals and the higher type of mentality possessed by the anthropoid apes. The recent studies of Köhler and Yerkes have added much to our knowledge of the ape mind. These studies had the great merit, as compared with older observations, of putting the animals through experimental tests in order to ascertain the character and extent of their intellectual powers. It has been shown quite clearly that the apes employ means to ends in a way that indicates a faculty of inferring what will happen if the proper conditions are fulfilled. In several experiments performed by Köhler with chimpanzees a piece of fruit was suspended beyond the reach of the animals (Fig. 2). When given boxes to mount upon, the apes quickly learned to pull them into position and climb upon them to reach the fruit. After one of the chimpanzees. Sultan, had learned to use the box the fruit was suspended still higher and two boxes were placed at his disposal some distance away from the objective. His behavior under these conditions was as follows: "Sultan drags the bigger of the two boxes towards the