The so-called true Geese are aggregated into a subfamily (Anserinae), and number nine or ten genera and thirty or more species, but the limits of the group are not very satisfactorily fixed, and the lines separating certain of the genera are more or less arbitrary. They differ from the Swans in having a neck always shorter than the body, although it is longer than in most Ducks, and from most of the Ducks by having the front of the tarsus covered with small hexagonal instead of narrow scales, while they are distinguished from the last subfamily by the absence of a cere. They are birds of moderate size, with rather long legs, and although they swim well are also adapted for a terrestrial life, and being essentially vegetable feeders, are often seen away from water. They are almost cosmopolitan in distribution, but are most abundant in the Northern Hemisphere, rearing their young in many cases well within the Arctic Circle, and ranging south over wide areas in winter. They are all strong on the wing.