I N A series of transplantation experiments, reported earlier (Rawles i940b), in which the embryonic coelom of the White Leghorn fowl was used with considerable success as a site for testing the pigment-forming potency of various portions of mouse embryos of a potentially pigmented (black) strain, evidence was obtained which suggested that the migratory pigment-forming cells, the melanophores, take their origin from the neural crest, as in other vertebrates, e.g., amphibians and birds.The results of grafting a variety of embryonic mouse tissues, such as skin ectoderm plus the underlying mesoderm, somites with and without the adjacent neural tube, limb buds and prospective limb buds, from various body levels, showed that between 81/2 and I2 days of gestation the capacity of the grafted embryonic tissue to produce melanophores spreads rather rapidly in both an anteroposterior and a mediolateral direction. It was found, for example, that grafts of skin ectoderm and mesoderm from somites of the anterior-trunk levels, including the level of the forelimb, of embryos of approximately io days gestation age, produced hairs fully pigmented (black), while similar grafts farther posteriorly, i.e., at the hind-limb level, produced only unpigmented (white) hairs. Later, by the IIth day, grafts from all body levels, including the posterior-limb level, produced hairs fully pigmented. 'All the illustrations were prepared by my husband, Mr. John Spurbeck. It is with deep appreciation that I acknowledge my indebtedness to him.

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NINE WQURESThis investigation was begun with the idea of locating the areas in the chick blastoderm of the head-process stage which possess the capacity to produce heart and liver. The frequent duplication of these organs which was observed in transplants of the entire pellucid area to the chorio-allantois (Willier and Rawles, '31 a ) would seem to indicate that the material from which they take their origin is bilaterally placed in the early blastoderm. To acquire some definite knowledge as to the extent of this material in antero-posterior and medio-lateral directions, it was planned to divide the blastoderm into a number of median and lateral pieces, each of which could be transplanted to the highly vascularized chorio-allantoic membrane of older host embryos in order to test their potencies. Obviously, in effecting such an analysis, data relative to the location not only of heart and liver but of many other embryonic organs would be obtained, and it was therefore considered perhaps preferable at this time to construct first of all a general map showing the position, as far as possible, of the various organ-forming areas in the blastoderm as a whole, and then to follow this analysis further by the use of appropriate cuts designed to show the limits of any one of these areas.