ANATIDAE I I 3 



to horizontal. Anseranas shews a double loop in this organ. 1 and 

 in the males of many Ducks an enlargement is found at its junc- 

 tion with the bronchial tubes, consisting of a round bony structure, 

 termed the bulla ossea or "labyrinth." Similar structures have been 

 noticed in Chenalopex, Dendrocycna, Chloepliaga, Plectropterus, and 

 Sarcidiornis ; and in the Fuligulinae they shew apertures with 

 membranous coverings ; Metopiana peposaca, Mergus merganser, M. 

 serrator, Tadorna cornuta, Oedemiafusca, and (doubtfully) Oe.per- 

 spicillata 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, 2 though modified by subsequent discoveries, 

 give a good idea of the distribution. He assigns as residents 

 about seventy-seven species to the Northern Kegions, 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. 



The Anatidae are for the most part of similar habits, and 

 frequent seas, lakes, rivers, and watery spots generally, being found 

 to a great extent in winter on the shore, especially where mud- 

 flats are exposed by the ebbing tide, and beds of such food-plants 

 as Zostera (grass-wrack) are uncovered. Large flocks, which 

 include many migrants, are formed at that season, and in spring 

 the ganders and drakes commonly collect into parties while the 

 female is incubating, which she does during twenty-one to forty-two 

 days. Later in summer the majority of the Family shed their quills 

 simultaneously, and conceal themselves until again capable of flight, 

 the males then becoming dull in colour for several weeks, and re- 

 sembling the other sex. 3 Merganetta is found only on the torrents 

 of the Andes ; Hymenolaemus and Salvadorina being also residents 

 on mountain streams. The noisy flight is extremely powerful, and 

 much swifter than it appears, the wedge-shaped formation which 

 Geese affect being especially noticeable ; some forms, however, are 

 practically flightless, such as Nesonettc^ and the adult Steamer-Duck 

 ( Tachyeres). All the Anatidae swim exceptionally well, diving being 

 carried to its perfection in the marine Fuligulinae ; while the parti- 



1 W. A. Forbes, P.Z.S. 1882, p. 350. 

 2 P.Z.S. 1880, p. 533. 3 Supra, p. 4. 



VOL. IX I 



