This mutation, which, in one case quoted by Darwin, increased among a flock of peafowl until the black-winged supplanted the ordinary kind, is so distinct in appearance in all stages that it was formerly supposed to be a true species (_Pavo nigripennis_), of which the wild habitat was unknown. The Golden Pheasant (_Chrysolophus pictus_) produces, in domestication, the dark-throated form (_C. obscurus_), in which the cock has the throat sooty-black instead of buff, and the scapulars or shoulder feathers black instead of red. Moreover, the two middle-tail-feathers are barred with black and brown like the lateral ones, while in the ordinary form they are spotted with brown on a black ground. The hens have a chocolate-brown ground-colour instead of yellow-ochre as in the normal type. The chicks are likewise darker. The common duck, in domestication, when coloured like the wild mallard, sometimes produces a form in which the chocolate breast and white collar of the drake are absent, the pencilled grey of the abdomen reaching up to the green neck. In this mutation the duck has the head uniformly speckled black and brown, and lacks the light eye-brow and cheek-stripes found in the normal duck. Both sexes have the bar on the wing dull black instead of metallic blue. The ducklings which ultimately bear this plumage are sooty-black throughout, not black and yellow like normal ones. The phenomenon of mutation is not confined to animals in a state of domestication. The common Little Owl of Europe (_Athene noctua_) has produced the mutation _A. chiaradiæ_ in the wild state. In this the irides are dark, instead of yellow as in the normal type, and the plumage of the back of the wings is longitudinally streaked with white instead of barred. Several examples of this form were found, along with normal young, in the nest of one particular pair of little owls in Italy, but the whole family were foolishly exterminated by local ornithologists. The reed bunting (_Emberiza schœniclus_) exists in two distinct forms—one having a much stouter bill than the other (_E. pyrrhuloides_). This probably is an example of a mutation. The rare yellow-rumped Finch (_Munia flaviprymna_), of Australia, has displayed a tendency to change into the allied and far commoner chestnut-breasted Finch (_M. castaneithorax_) during the lifetime of the individual (_Avicultural Magazine_, 1907). Conversely, the male of the common Red-billed Weaver (_Quelea quelea_) of Africa has been found in its old age to assume the characters of the comparatively rare _Q. russi_, its black throat becoming pale buff as in that form. Everyone is familiar with the chequered variety of the common blue-rock pigeon, in which the wings are regularly mottled with black instead of being barred. This form sometimes occurs among wild birds, so that it has been described as a distinct species. It is important to note that there are red, dun, and silver chequers as well as blue ones.