Tissue Interactions in Scale and Feather Development as Studied in Dermal-Epidermal Recombinations
Authors: Rawles Mary E. 
Published: April 2021

The present report is based on an experimental analysis of interactions of epidermis and dermis in the formation of the scale and its homologue, the feather. The method used consists of reciprocal exchange of epidermis and dermis from prospective scaled and feathered regions (tarsometatarsus and mid-dorsum), at stages before and during primordia formation. The recom-bined tissue-layers were grown on the chorioallantoic membrane. Results of examination of over 500 grafts have shown that both the inductive capacity of the dermis and the competence of the epidermis vary with developmental stage and with location on the body. Dermis from the tarsometatarsus acquires specific inductive capacity late in ontogeny; not until approximately the 13th day does the inductive stimulus reach a level of intensity sufficiently high to elicit scale formation in overlying ‘foreign’ epidermis. Feathers develop regularly in association with scales induced in the grafts. Dermis from the prospective spur region of the tarsometatarsus is excep-tional in that it possesses intense inductive capacity at 9 days, the earliest stage tested. The spur scale induced in ‘foreign’ epidermis of the graft is always free of associated feathers, as in the normal chick. Dermis from the mid-dorsum, like that of the spur region, is strongly inductive at the earliest stage tested (5 days) and continues strong throughout the entire age span used ( days). The inductive capacity of this feather-inducing dermis is not of short duration. The competence of epidermis from the mid-dorsum changes within a brief period of time between and days. This change can be detected only when the epidermis is brought into contact with tarsometatarsal dermis that has developed specific inductive capacity (13 – 15 days). At this time, the later -day epidermis, unlike that of earlier stages, produces no typical scales but continues to differentiate in a feather direction. The feathers, however, are not entirely normal. Epidermis from the tarsometatarsus exhibits a change in competence between 12 and 13 days. This change can be detected only in the structural aberrance of the resulting feathers. Those produced from 13-day epidermis are extremely aberrant. (Scales are never produced from tarsometatarsal epidermis in contact with mid-dorsal dermis, irrespective of the stage of either tissue component.) The change in competence with age, noted above for both mid-dorsal and tarsometatarsal epidermis, can be entirely masked if each is brought in contact with a stronger inductor, such as the dermis of the beak. Dermis from the beak ( days) induces a perfect beak in both -day mid-dorsal epidermis and 13-day tarsometatarsal epidermis. The remarkable ability of the epidermis to alter its course of differentiationat relatively late stages suggests that the morphological similarities between scale and feather may be more than superficial. Since tarsometatarsal dermis is capable of inducing both scales and feathers in the normal chick and in grafts, it appears to be bipotential. The possibility exists, however, that the epidermis of birds possesses inherent feather-forming tendencies which, in certain regions, become modified second-arily by the underlying dermis.