24O APES AND MONKEYS 



the first and second strokes the interval was slightly longer 

 than that between the second and third, and so on through 

 the scale. As the beating increased in loudness the inter- 

 val shortened in an inverse degree, while in descending the 

 scale the intervals lengthened as the beating softened, and 

 the author of the sound was conscious of the fact. 



I could trace no relation in time or harmony between the 

 sound of the voice and the beating, except that they began 

 at the same time and ended at the same time. The same 

 series of vocal sounds was repeated each time, beginning 

 on the low note and ending in each case with the note of 

 the highest pitch, while the rise and fall of the series of the 

 beaten sounds were not measured bv the duration of the 

 voice. The series each time began with a soft note, but 

 ended at any part of the scale at which it happened to be 

 at the time the voice ceased. The coinciding notes were 

 not the same in every case. 



Xo doubt the gorilla sometimes beats upon his breast. 

 He has been seen to do this 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 made by beating on 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 my first voyage, and, as a result of these 



