THE phenomenon of seasonal color change commonly seen in northern animals became of particular interest to the writer when it was found that primeness in all fur-bearing animals, save the albino, was solely dependent upon a blanching process of the hair-roots and entirely independent of dermal thickness or pigmentation. Subsequent investigation showed that the depigmentation process did not cease at the level of the epidermis, but that it was continued out into the proximal portion of the hair-shaft to a variable extent in different fur-bearing animals. The latter fact suggested the idea that the blanching of the jack-rabbit and Arctic white fox might merely be the outward evidence of an exaggerated state of this same physiological process. Examination of the literature gave a very wide range of opinion as to the cause and nature of the seasonal change of color in these mammals. One interpretation of the process is that expressed by Allen (1894), Anthony (1928), Seaton (1928), Nelson (1918), and Pennant (1784), who with one accord state that the autumnal change of color in variable mammals (Lepus americanus) is due to a shedding of the pigmented summer fur and the growth of a white (albinotic) winter coat. On the other hand, Richardson (1829), Hadwen (1929), Merriam (1884) and Welch (1869) suggest that the change is not due to a shedding of the summer pelage, but that the existing coat lengthens and undergoes a blanching process, thus providing the winter coloration. Both sides, with the exception of Hadwen and Merriam, apparently agree as to the manner in which the reversion to summer dress takes place, namely, that the