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Oblique section of a newly developing feather of a Muscovy Duck (Cairina moschata) (HE)
Feathers are replaced periodically. A new feather is produced by the same follicle; it is the initiation of this new growth that normally â€˜pushes the old feather outâ€™.
Feather development is an extremely complex process in which many elements happen at the same time:
- The development of a â€˜columnâ€™ of epidermis out of the epidermal collar and the differentiation of this outer epidermis consecutively into barb ridges, barbs and barbules, rachis and calamus;
- The formation and regression of an inner pulp and pulp caps out of the dermal papilla and the covering epidermis;
- Keratinisation and pigmentation of the feather.
At the micrograph above, the blastema is just becoming active: regeneration of a new feather has begun with the lengthening of the dermal papilla. In the epidermal collar, a basilar and intermediate layer can be differentiated from each other.