Introduction Difficulties have been experienced in classifying a large group of tumors, the common feature of which is the presence of melanin pigment (melanomas). These hardships in classification are attributable, in large measure, first to an attempt on the part of earlier observers to trace the origin of the tumor to one type of cell; second, to the existence of multiple and conflicting concepts throughout the literature on pigmented tissues; third, to the indiscriminate use of such terms as chromatophore, melanophore, melanoblast, mole, nevus, lentigo, café au lait spots, chromatophoroma, melanoma, etc. According to the modern usage, there are recognized three types of melanoblasts, one derived from epithelium, one from connective tissue, and one whose origin cannot be definitely stated. The first is the commonly known basal cell of the epithelium and hair follicle. The second is illustrated well by the cells comprising the blue nevus of Jadassohn or the choroid of the eye. The third is that cell which is commonly found in clusters beneath the epithelium of the skin, surrounding the dendrites of peripheral nerves. In addition to these three types, there is a group of cells which has no melanoblastic function but contains pigment by virtue of its power to phagocytose melanin. These are called chromatophores and are usually connective-tissue cells, but may in certain instances be of epithelial origin. There are several methods available for distinguishing the melanoblast from the chromatophore. One is a specific staining reaction; another, embryologic and comparative anatomic study; a third, the study of cellular morphology in conjunction with one of the first two modes of investigation.