The production of robin pigment in White Leghorn feathers by grafts of embryonic robin tissue

Summary

1. Small pieces (0·6 × 0·3 mm.) of skin from the postero-lateral head region of robin embryos of developmental stages equivalent to 90–96 hr. chicks, were grafted (as free as possible of underlying mesenchyme) to the developing right wing bud of 72 hr. White Leghorn host embryos.

2. At hatching, the hosts showed areas of coloured down, varying from pale cinnamon brown to blackish brown, covering a part or all of the right wing and even contiguous body regions.

3. In one case which attained sexual maturity the coloured down was replaced by juvenile contour feathers of mosaic coloration—the distal portions tawny, the proximal grey—as in the breast feathers of the robin and of identical colour. In addition white basal areas (host-coloured) appeared on the remiges and larger coverts. After moulting the entire graft region became host-coloured (white).

4. Microscopic study of the four types of pennaceous barbules and the typical down barbules from the robin-coloured feathers growing on the White Leghorn showed unmistakably that the structure was identical with that of the Leghorn host and not like that of the robin donor.

5. The pigment rodlets in the down of the robin-coloured feathers of the graft area were found to be identical in shape, size, and colour with those of the normal robin control but they were scattered throughout the cells with the typical distribution of the pigmented fowl, instead of being massed at the nodes as in the robin.

6. The data have proved that (1) the robin-coloured feathers growing on the White Leghorn host arose from host (Leghorn) feather germs and (2) the pigmenet was produced by donor (robin) melanophores which migrated from the grafted tissue into the epidermal “collar” of the developing host feather germs.