A little more than a year ago, my attention was called to this sign by the children who own the little Capuchin, Jack, in Charlestown. A number of times they said to him in my presence, "Jack, you must go to bed." At which he would shake his little black head, as if he really did not wish to comply. I watched this with great interest; but it was my belief at that time that he had been trained to do this, and that the sign did not really signify to him anything at all. The children, however, declared to me that he really meant "no." To believe that he meant this would presuppose that he understood the combination of words quoted; and this was beyond the limits of my faith, although it was certain that a repetition of the sentence always elicited from him the same sign, which indicated that he recognised it as the same sentence or combination of sounds, and gave it the same reply each time. I concluded that he had been taught to associate this sign with some sound--for instance, "bed" or "go"; but since that time I have found the sign to be almost universal with this species of monkey, and they use the sign to express negation. I have seen them use the sign in response to certain things which were wholly new to them, but where the idea was clear to them and they desired to express dissent. The fact that this sign is common to both man and Simian, I regard as more than a mere coincidence; and I believe that in this sign I have found the psycho-physical basis of expression. I have made scores of experiments on this subject, and I find this sign a fixed factor of expression. In one case, where I tried to induce a monkey to allow me to take him into my hands from the hand of his master, he would shake his head each time, and make a peculiar sound somewhat like a suppressed cluck. I would try to coax him with nuts, in response to which he would make the same sound and sign each time, and his actions showed beyond all controversy his intention. I had taught a monkey to drink milk from a bottle by sucking it through a rubber nipple, and after he had satisfied his thirst, when I would try to force the bottle to his lips, he would invariably respond by a shake of the head in the manner described, and at the same time utter a clucking sound. I tried many similar experiments with three or four other monkeys, and secured the same result in each case. In another instance, where a monkey was confined in a small cage so that I could easily catch him in order to tame him by handling, when I would put my hand into the cage to catch him, he would shake his head in this manner and accompany the act by a plaintive sound which was so touching, that I could not obtain my own consent to persecute the little prisoner by compelling him to submit to my caresses. I have found that the little rogue, McGinty, in Central Park does the same thing at times when I go into the cage and attempt to put my hands on him, and especially when he has taken refuge