Exoskeleton and Feathers

The pigeon's exoskeleton, derived from the epidermis, appears as horny claws (used for walking and perching), scales on the legs and feet, a horny toothless beak (used for feeding, fighting and preening), and, over almost the whole body, feathers - the arrangement of which on the body is called pterylosis. Three kinds of feather occur: large quill feathers on the wings and tail used for flight, contour feathers that form the smooth outer body covering, and hair-like filoplumes lying between the contour feathers; young nestlings are instead covered in soft down feathers, which resemble filoplumes. A single quill feather has a central stem or scapus made of a lower, hollow calamus (quill), whose base has an opening (the inferior umbilicus) that once received a nutrient- and pigment-supplying dermal papilla, and an upper, solid rachis; a second opening, the superior umbilicus, sits where the calamus meets the rachis, next to a small tuft of soft after-shaft feathers. Along the rachis, numerous fine barbs are fringed with still finer barbules bearing tiny hooklets (ba …