Inasmuch as he could discover no structural basis for deafness, Panse (23 p. 140) expressed himself as unwilling to believe that the mice are deaf, and this despite the fact that he observed no responses to the sounds made by a series of tuning forks ranging from C5 to C8. He believes rather that they are strangely irresponsive to sounds and that their sensitiveness is dulled, possibly, by the presence of plugs of wax in the ears. Since another investigator, Kishi, has observed the presence of similar plugs of wax in the ears of common mice which could hear, there is but slight probability that Panse is right in considering the plugs of wax as the cause of the dancer's irresponsiveness to sounds. Far more thoroughgoing tests than those of Rawitz or Panse were made by Cyon (9 p. 218), who holds the unique position of being the only person on record who has observed the adult dancer give definite reactions to sounds. To a König Galton whistle so adjusted that it gave a tone of about 7000 complete vibrations per second, which is said to be about the pitch of the voice of the dancer, some of the animals tested by Cyon responded unmistakably, others not at all. In one group of four mice, two not only reacted markedly to the sound of the whistle but apparently listened intently, for as soon as the whistle was blown they ran to the side of the cage and pressed their noses against the walls as if attempting to approach the source of the stimulus. The remaining two mice gave not the slightest indication that the sound acted as a stimulus. By the repetition of this sound from eight to twelve times Cyon states that he was able to arouse the mice from sleep. When thus disturbed, the female came out of the nest box before the male. Similarly when the mice were disturbed by the whistle in the midst of their dancing, the female was first to retreat into the nest box. There is thus, according to Cyon, some indication of sex, as well as individual, differences in sensitiveness to the sound of the whistle. Cyon's statement that in order to evoke a response the whistle must be held above the head of the dancer suggests at once the possibility that currents of air or odors instead of sounds may have been responsible for the reactions which he observed. The work of this investigator justifies caution in the acceptance of his statements. Neither the conditions under which the auditory tests were made nor the condition of the animals is described with sufficient accuracy to make possible the comparison of Cyon's work with that of other investigators. As will appear later, it is of the utmost importance that the influence of other stimuli than sound be avoided during the tests and that the age of the mouse be known. The conclusion reached by Cyon is that some dancers are able to hear sounds of about the pitch of their own cries.