Darwin, after a most comprehensive and searching investigation of the phenomena of life and variation, came to the conclusion that “man is the co-descendant with the other mammals of a common progenitor,” and still “bears in his bodily frame the indelible stamp of his lowly origin.” With the immense and varied ancestry man has had, and the infinitude of his connections with the rest of the animal world, “atavism,” i.e., inheritance of characteristics from remote, not from the more immediate ancestors, is a very interesting subject of study. The presence of supernumerary nipples in man may be cited as an example of atavism. This abnormality has been noticed by me in four patients during five years' observations in the hospitals in this country. In some parts of Central and Eastern Europe a very high percentage of men is said to possess this abnormality. This characteristic is absent in apes, baboons, and monkeys, who are men's immediate successors, but is found in lemurs, an order of mammals lower in order. The rare occurrence of multiple births in women is a characteristic which is reversion, or atavistic towards the condition normal in lower vertebrates.