BIOPSYCHOLOGTCAL 595 



that the animals have been studied in conditions of comfort and 

 along with their fellows. Thus Kohler, primarily a psychologist, 

 made his observations and experiments in Teneriffe, where the 

 climate suits the chimpanzee, and under conditions where the 

 animals lived together cheerfully. As that observer remarked, a 

 solitary chimpanzee is no longer a chimpanzee. What Kohler has 

 done is to show that chimpanzees often solve problems in an 

 intelligent way, appreciating the significance and relatedness of 

 different links in a chain of acts, and apparently making perceptual 

 inferences in reference to visible situations. Thus they would put 

 one box on the top of another, even making four-storied erections, 

 in order to reach a banana suspended from the roof. They learned 

 to join two pieces of bamboo rod together in order to make a length 

 sufficient to reach a prize outside their cage. One of them bit at the 

 end of a piece of stick, reducing the end till it was of a size suitable 

 for insertion into a bamboo rod that had to be lengthened to reach 

 a desired object. There are many such examples, well documented 

 and well criticised. It is true that chimpanzees must have the factors 

 for the solution of the problem within their visual range, for they 

 seem to have a very limited capacity of working with mental images ; 

 but the outstanding fact is that they are far more intelligent than 

 was suspected. 



Noteworthy is Dr. Homaday's account of an orang that dis- 

 covered the effectiveness of a lever, and then proceeded to find 

 other levers of various sizes, including the heavy trapeze-bar with 

 which it was possible to prize asunder the vertical bars of the cage, 

 thus allowing the orang to gratify his long-cherished desire of 

 looking round the comer at his neighbour in the next cage. 



Kohler records some interesting facts in regard to the ape's 

 appreciation of a mirror. He gave a hand-mirror to one of the 

 female chimpanzees, and it at once became a source of delight. 

 It was passed from one to another, and the reflection was evidently 

 recognised as that of a chimpainzee. But in every case and in diverse 

 ways the chimpanzees made attempts, while holding the mirror in 

 one hand, to catch the other chimpanzee "behind the looking- 

 glass". Very rapid surprise movements were made over and over 

 again, and the futility of the attempt did not suffice to dislodge the 

 fixed idea. Even more interesting, however, as indicative of an 

 active brain, was that the chimpanzees proceeded to discover new 

 mirrors for themselves, pieces of polished tin and the like, into which 

 they would gaze intently. A striking situation which Kohler pictures 

 is that of chimpanzees gazing abstractedly at their reflection in a 

 rain-puddle! May this not have been reflection in another sense — 

 even the dawn of self -consciousness ! 



Prof. R. M. Yerkes, well known for his careful study of the 

 "dancing mouse", made an intimate study of two young chimpan- 



