The principles of biological science forbid us to assume a permanent stability of bodily form. Our whole modern concept of the development of varieties and of species is based on the assumption of cumulative or sudden variation. The variations that have been found in the human body are quite in accordance with this view, and I may quote here a few words from Wiedersheim’s admirable treatise on the structure of man as an index of his past history: “In the course of Phylogeny the body of Man has undergone a series of modifications which still in part find expression in his ontogeny. There are indications that changes in his organization are still continuing, and that the Man of the future will be different from the Man of to-day.” The best illustrations of those changes are found in the forms of organs which are undergoing reduction. Thus we may observe that in modern man the little toe is often two-jointed, a phenomenon presumably due to lack of functional use. This condition has been observed in races going barefooted as well as in those wearing shoes, so that it cannot be ascribed to artificial causes. The teeth also show a tendency to gradual reduction, especially in the variable size of the molars and of the upper outer incisors. The third molar, or wisdom tooth, is often retained, and is in most races considerably reduced in size. Retention or slight development of the upper outer incisor is also of frequent occurrence. A similar reduction may be observed at the lower end of the thorax, where the development of ribs and sternum shows great variations. The significance of these phenomena lies in the fact that in the evolutionary series the abnormal occurrences, which are found in different races in varying frequency, appear as new developments, which, if they should become normal, would increase the differentiation between man and the lower forms. The actual proof of increasing frequency of these features, and of their becoming permanent characteristics, has not been given, but seems more than plausible. This inference is strongly supported by the occurrence of rudimentary, functionless organs, and by the temporary appearance of lower features during ontogenetic development.