Formation of ‘Polyhedral’ Cell Cavities in Cloudy Media of Bird Feathers

Abstract

SynopsisIn feathers of a wide variety of unrelated birds non-iridescent blue and related shades are produced by structures. In these, each colour-producing cell of a barb medulla contains a cavity whose outline tends to parallel the cell-boundaries (‘polyhedral’ cavity).This contrasts with the situation in some other birds with corresponding colour structures where each medullary cell contains a smaller ‘spheroidal’ cavity left by the pycnotized nucleus.Three different processes of moulding polyhedral cavities are described which modify the thickness of the colour-producing cloudy medium and possibly represent independent evolutionary trends.