Bird feather. Light micrograph of a small contour feather from the body of a bird. This feather, which is 6 millimetres long, is from a juvenile bird. The feather has no quill, a downy base (upper left), and barbs with crossed barbules, which do not interlock. The function of this feather is for insulation, as opposed to the different structure found on flight feathers. Magnification: x14 when printed at 10 centimetres across.