With the ever-present belief that animals could talk to each other, I observed from year to year certain things which tended to confirm it. About sixteen years ago an instance occurred which forever removed from my mind all doubt or wavering. Prior to that time I had observed that animals of the higher orders appeared to have the better types of speech and, concurrent with this belief, I tabulated many facts. In 1884 I made a visit to the Cincinnati Zoölogical Garden, where I was deeply impressed with the conduct of a school of monkeys occupying a cage which also contained a large mandrill. This savage baboon was an evident source of terror to the smaller inmates of the cage. A brick wall separated the cage into two compartments. The one was intended for summer and the other for winter occupancy. Through this wall was a small doorway, large enough to admit the passage of the occupants. I observed that two or three of the monkeys kept continual watch over the conduct of the baboon and reported to the other monkeys every movement that he made. When he was lying still, the monkeys passed back and forth without fear, but the instant he rose to his feet or gave any sign of disquiet the fact was promptly reported by the monkeys on watch to those in the adjoining compartment, and they acted in accordance with the warning. I was not able to determine the exact thing they reported, but the nature of the report was evident, and I resolved to learn more fully its meaning. After spending some hours watching their conduct and listening to the sound which controlled it, I became convinced that what they said was sufficiently definite to guide the actions of those to whom it was addressed. In fact I should have been willing to intrust my own safety to those warnings. After a brief study of those sounds I was able to understand the attitude of the baboon towards his neighbors; and while the warning contained no elaborate detail that I could understand, the nature of his actions was made evident. I observed that a certain sound of warning caused them to act in a certain way, and a certain other sound caused them to act differently. From this start I determined to learn the speech of monkeys. I did not suspect that the task would be so great as it has proved to be. I did not foresee the difficulties that have since become apparent. Year by year, as new ideas came to me, new barriers arose and the horizon continually widened. Yet I was not discouraged at the poor success of my first efforts. From time to time I visited the various collections of monkeys in this country and even availed myself of those found with traveling shows, hand organs, and elsewhere.