small and curved, but are long and sharp in _Anseranas_, _Dendrocycna_, _Nettopus_, and _Plectropterus_. The wings vary considerably, but are usually ample and rather long, though short in _Cosmonetta_, _Erismatura_, and _Tachyeres_; the number of primaries is eleven, and of secondaries from fifteen to twenty-eight, a horny spur being developed on the pollex, or even on the index, in _Plectropterus_, _Sarcidiornis_, _Chenalopex_, and _Merganetta_. The tail is, generally speaking, short, and may be narrow and pointed, as in _Anas_, _Dafila_, and _Harelda_; in _Aex_, _Querquedula_, _Tadorna_, and so forth, it is rounded; in _Chenalopex_ squarer; and in _Sarcidiornis_ and _Asarcornis_ more cuneate. In _Tachyeres_ the two median rectrices are long and recurved, and in the males of _Harelda_ and _Dafila_, they are inordinately produced; while all the feathers have spiny shafts and narrow webs in the Erismaturinae and Merganettinae. The number varies from twelve to twenty-four, with even more in Swans. In _Eunetta_ the upper and under tail-coverts exceed the tail itself. The formation and disposition of the trachea[109] are of great importance. _Cygnus musicus_, _C. buccinator_, _C. bewicki_, and _C. columbianus_ have a peculiar cavity in the sternum, while the windpipe, entering in front of the clavicles, traverses and retraverses the swollen keel, which in old birds it penetrates to its furthest extremity, the direction being changed in the two last from vertical {113}to horizontal. _Anseranas_ shews a double loop in this organ,[110] and in the males of many Ducks an enlargement is found at its junction with the bronchial tubes, consisting of a round bony structure, termed the _bulla ossea_ or "labyrinth." Similar structures have been noticed in _Chenalopex_, _Dendrocycna_, _Chloëphaga_, _Plectropterus_, and _Sarcidiornis_; and in the Fuligulinae they shew apertures with membranous coverings; _Metopiana peposaca_, _Mergus merganser_, _M. serrator_, _Tadorna cornuta_, _Oedemia fusca_, and (doubtfully) _Oe. perspicillata_ are stated to have an additional bulb, but _Oe. nigra_ has none. _Clangula glaucion_ and the Merginae have a swelling in the middle of the trachea. The headquarters of the Family are in the north, while Dr. Sclater's calculations,[111] though modified by subsequent discoveries, give a good idea of the distribution. He assigns as residents about seventy-seven species to the Northern Regions, forty-one to the Neotropical, twenty-nine to the Australian, twenty-two to the Ethiopian, and twelve to the Indian; twenty Geese out of thirty-three, seven Swans out of ten, and twenty-six Sea-Ducks out of thirty-one belonging to the first. Polynesia is especially poor.