Pigmented malignant neoplasms are among the most serious tumors afflicting mankind. They are fortunately rare, which fact has militated against a clearer conception of their origin and nature. Ewing1 stated: "The peculiar and obscure conditions of its origin, the remarkable physiologic properties of the chromatophores (melanoblasts—author) in the animal kingdom, the eccentricities of its clinical course and its interesting history as a field of debate render this tumor one of the most notable topics in oncology." Many authors have written on this subject, more recently Dawson2 and Miescher.3 Difficulties in interpretation on solely morphologic grounds have been partially overcome by the functional approach to the problem of melanin pigmentation, which phase of biologic activity lends itself well to study, since it furnishes a visible end-point.
Consideration of the pigment problem may be found in recent publications.4 The salient features may be briefly summarized. Cutaneous