Hoatzin chick climbing back up to its nest
As a feather develops it requires a flow of blood. The shaft or calamus is a direct link to the blood supply and the feather grows out something like a flower. Once the feather is fully developed the blood source dries up and is closed. The shaft then hardens and the feather becomes functional.
The calamus is still visible in the primary feathers of this hoatzin.
Tropical Wild Life in British Guinea. William Beebe, 1917.
A Lunar Mosaic
Image Credit: Carlo Muccini
Photo by Cornell Capa, 1947
Olive by the Australian painter Norman Lindsay (1879-1969).
Sculpture by Jean Antoine Injalbert. Chappaz hotel,Béziers, France.