There are five primary types (bottom row) of pigment-filled sacks, called melanosomes, within the nanostructure (left)` of iridescent feathers. Thick rods are found in birds with weak iridescent ...

but they lacked outer feathers with a central 'rachis', the distinctive structure of feathers. By the 49th day of life, however, these chickens molted, and the new feathers that emerged developed ...