A correspondent writes me that he has a cock which is passionately fond of the sound of the violin. This bird always flies to the window of the music-room as soon as he hears the sound of the violin, where he will quietly remain perched as long as the music continues. As soon as the music ceases, he flies down from the window. Horses very frequently show an appreciation for musical sounds, especially when they are produced by a band of brasses. Amusement and pastime are, unquestionably, æsthetic psychical characteristics, hence, when we see evidences of these mental operations, we must acknowledge the presence of æstheticism in the animals in which they are to be noticed. I propose to show that animals low in the scale of life--animals so low and so minute that it takes a very high-power lens to make them visible, have their pastimes and amusements. Also, that many insects and even the slothful snail are not so busily engaged in the struggle for existence that they cannot spare a few moments for play. In our researches in this field of animal intelligence we must not attribute the peculiar actions of the males in many species of animals when courting the females, to simple pastime, for they are the outward manifestations of sexual desire, and are not examples of psychical amusement. I have seen, in actinophorous rhizopods, certain actions, unconnected with sexual desire or the gratification of appetite, which lead me to believe that these minute microscopic organisms have their pastimes and moments of simple amusement. On several occasions while observing these creatures, I have seen them chasing one another around and around their miniature sea. They seemed to be engaged in a game of tag. This actinophrys is not very agile, but when excited by its play, it seems to be an entirely different creature, so lively does it become. These actions were not those of strife, for first one and then another would act the pursuer and the pursued. There were, generally, four or five actinophryans in the game. One of the rotifers frequently acts as if engaged in play. On several occasions I have observed them perform a kind of dance, a _pas seul_, for each rotifer would be alone by itself. Their motions were up and down as if exercising with an invisible skipping-rope. They would keep up this play for several minutes and then resume feeding or quietly remain at rest. This rotifer goes through another performance which I also believe to be simply a pastime. Its tail is armed with a double hook or forceps. It attaches itself to a piece of alga or other substance by this forceps, and then moves its body up and down in the water for several minutes at a time.