THE GENETIC aspects of cancer in general have been carefully sifted and scrutinized in the search for clues to the origin of malignant neoplasia, with some significant results. Heredity is recognized as the motivating factor in the evolution of retinoblastoma, but at the opposite end of the scale is cancer of the lip, which has been shown to occur without any inherited predisposition.1 Between these two extremes is an intriguing array of data concerned with the role of heredity in the field of human cancer. These data are abundant in reference to some neoplasms, especially those occurring in "cancer families," but meager in regard to others, only the scantiest attention having been given to the hereditary features of malignant melanoma in humans. In succeeding paragraphs will be described first the hereditary aspects of malignant melanoma in animals, since these shed light on the problem as it involves