I am willing to trust these experimental results the more fully because during all the time I have had adult dancers under observation I have never once seen a reaction which could with any fair degree of certainty be referred to an auditory stimulus. Never once, although I have tried repeatedly, have I succeeded in arousing a dancer from sleep by producing noises or tones, nor have I ever been able to observe any influence of sounds on the dance movements. All of Cyon's signs have failed with my mice. Occasionally what looked like a response to some sound appeared, but critical observation invariably proved it to be due to some other cause than the auditory stimulus. A sound produced above the animal is very likely to bring about a motor reaction, as Cyon claims; but I have always found it to be the result of the currents of air or odors, which usually influence the animal when the experimenter is holding any object above it. I do not wish to maintain that Cyon's conclusions are false; I merely emphasize the necessity for care in the exclusion of other stimuli. The mice are extremely sensitive to changes in temperature, such, for example, as are produced by the breath of the experimenter, and one must constantly guard against the misinterpretation of behavior. In a single experiment with mice over a month old, I observed what might possibly indicate sensitiveness to sound. While holding a mouse, thirty- five days old, in my hand I pursed my lips and made a very shrill sound by drawing in air; the mouse seemed to start perceptibly according to the indications given by my sense of touch. I repeated the stimulus several times and each time I could see and feel the animal start slightly. With two other individuals which I tested the reaction was less certain, and with several others I failed to get any indication of response. This would seem to prove that the three individuals which responded happened to be sensitive to that particular tone at the age of five weeks. The test is unsatisfactory because the vibrations from my own body may have brought about the reaction instead of the air vibrations produced by my lips, and I therefore merely mention it in the enumeration of the various experimental tests which I have made.