which has made so prodigious an advance in the faculty of sign-making. In this greater reliance on the sense of sight, therefore, we probably have another among the many and complex conditions which determined the difference in respect of sign-making between the remote progenitors of man and their nearest zoological allies—a difference which would naturally become more and more pronounced the more that vision and gesticulation acted and reacted on one another. It appears to me that this suggestion of Geiger admits of being strikingly supported by certain facts which are known to obtain in the case of deaf-mutes. Even when wholly uneducated, the born mute, as we have previously seen, habitually invents articulate sounds as his own names of things. These sounds are, of course, unheard by the mute himself, and their use must be ascribed—as I have already ascribed it—to the hereditary transmission of an acquired propensity. But the point now is that, although the majority of these articulate sounds appear to be wholly arbitrary (_e.g._ _ga_ for “one,” _schuppatter_ for “two,” _riecke_ for “I will not”), a certain proportion are often clearly traceable to vocalizations incidental to movements of the mouth in performing the actions signified (_e.g._ _mumm_ for “eating,” _schipp_ for “drinking”).[307] Similarly, observation of a dog’s mouth, while in the act of barking, leads to an imitative action on the part of a mute as his sign for a dog, and this in turn may lead to the utterance of such an articulate sound as _be-yer_, which the mute afterwards uses as his name for a dog.[308] Now, if words may thus be coined even by deaf-mutes as a result of observing movements of the mouth, much more is this likely to have been the case among the “Urmenschen,” who were able not only to see the movements, but also to hear the sounds. * * * * *