Tissue Interactions in Scale and Feather Development as Studied in Dermal-epidermal Recombinations.

T H E foot of developing embryos of scalefooted varieties of the common domestic fowl (Silver Campine, White Leghorn and others) frequently exhibits feather primordia emerging from the scales of various regions. Many of the feather germs are rudimentary and disappear by the time of hatching, but some persist and differentiate into normal feathers. Such feathers are often inconspicuous and easily overlooked (Plate 1, figs. I-M). Scales bearing feathers by no means represent an unusual phenomenon. Indeed, they were clearly identified by many of the earlier workers, particularly those interested in homologizing these two specialized epidermal derivatives (Jefferies, 1883; Davies, 1889; Bornstein, 1911; Blaszyk, 1935). More recently, the frequent association of feathers with the scales of those pedal components (digits) which arise from the wing ectoderm, after implantation of mesoderm from the prospective foot region, has been noted by Saunders, Cairns & Gasseling (1957) working with White Leghorns. Although scales are the most common integumentary covering of the foot (tarsometatarsus, digits and plantar surface) and, often, adjacent portions of the tibiotarsus, they are not uniquely avian structures and do not distinguish birds from other vertebrates as does the possession of feathers. There are many birds in which the foot is partly or completely covered with feathers throughout life (Rawles, 1960). Even in closely related species, either the feathered or the scaled condition may predominate. Such observations strongly suggest that the prospective skin of the foot, unlike that of other body regions, is not irrevocably committed to the formation of one type of specialized epidermal derivative; rather, it is potentially capable