IN the vast majority of cases the relatively close resemblance between the Ducks, Geese, Swans, etc., is so plainly a mark of kinship that there is usually no question in associating them, but it is found, as already abundantly indicated in other groups, that where a more intimate study is made, certain members of the group show more or less marked divergences from what may be assumed to be the typical form. The question of the probable origin of the group as a whole, as well as that of its various members, has to be considered, and this of necessity leads to the employment of characters quite apart from mere external appearance. As in the order last reviewed, it has been found necessary to include birds that are very different from the central or typical form on account of their agreement in anatomical structure. The Anseriformes may be defined as lamellirostral swimming birds, with short legs and the front toes fully webbed, or else wading birds, with a short decurved bill and enormously developed feet. They agree with the Storks in having the bridge or band form of palate (desmognathous), but differ from them in having the basipterygoid processes, two pairs of tracheosternal muscles, and well-developed functional caeca. The young are “precocious,” that is, are able to swim or run about within a few hours after they are hatched, and are entirely covered with down. The combination of the last-mentioned characters with the bridged palate serves to separate them from all other birds, except possibly the Flamingos.
The order is divided into two suborders, the Palamedeae, or Screamers, and the Anseres, or Geese, Swans, Ducks, and their allies. Each embraces a single family, although the Anseres may be conveniently grouped into a number of fairly well marked subfamilies.