HABITS OF THE GORILLA 



225 



the low note and ending on the highest note or 

 pitch in each case, while the rise and fall of the 

 series of the beaten sounds was not measured by the 

 duration of the voice. The series each time began 

 with a soft note, but ended at any part of the srale at 

 which the voice ceased, and was not the same in 

 every case. 



I have no doubt that the gorilla beats upon his 

 breast : he has been seen to do so in captivity, but 

 the sounds described above were not so made. Since 

 the gorilla makes these sounds only at night, it is 

 not probable that any man ever saw him in the act. 

 It does not require a delicate sense of hearing to 

 distinguish a sound made by beating the breast from 

 that of dead wood or other similar substance. 



I have attributed the above sound to the gorilla, 

 because I have been assured by many white men 

 and scores of natives that it was made by him ; but 

 since my return from Africa I have had time to 

 consider and digest certain facts tabulated on 

 that trip, and as a result I am led to doubt whether 

 this sound is made by the gorilla or not. There are 

 good reasons to believe that it is made by the chim- 

 panzee instead, and I shall state them. 



I observed that my own chimpanzees made this 

 sound exactly the same as that I heard in the forest, 

 except that it was less in volume, which was due to 

 their age. I could induce them at any time to make 

 the sound, and frequently did so in order to study it. 

 On my arrival in New York I found that Chico, 

 the big chimpanzee belonging to Mr. Bailey,. 



