instinct, modified by experience, a natural mode of accounting for the unexpected features of Skirrl's behavior. _Sympathy_ The instinctive playfulness of the young monkey Tiny contrasted most strikingly with the more serious, if not more sedate, modes of behavior of the older individuals. During the greater part of my period of observation Tiny was cage-mate of Scotty, the most calm and apparently lazy of all the monkeys. Tiny delighted in teasing Scotty, and her varied modes of mildly tormenting him and of stirring him to pursuit or to retaliation were as interesting as they were amusing. Her most common trick was to steal up behind him and pull the hair of his back, or seize his tail with her hands or teeth. Often when he was asleep she would suddenly run to him, give a sudden jerk at a handful of hairs, and leap away. He was surprisingly patient, and I never saw him treat her roughly in retaliation. Another of Tiny's favorite forms of amusement was that of trying to stir up the other monkeys to attacks on one another. She very cleverly did this by pretending that she herself was being attacked. The instant the older animals began to show hostility toward one another she would leap out of the way and watch the disturbance with evident satisfaction. It was this mode of behavior in the little animal which ultimately provided opportunity for the observations which I wish now to report as indicative of sympathetic, possibly I may say altruistic, emotions. Tiny was confined with Scotty in a cage adjoining the one in which Jimmie and Gertie were being kept. The cages were separated by wire netting of half-inch mesh.