SWAN

Of the noble web-footed birds so called there are three British species — the Hooper or Bewick's, the wild and the tame swan. These form the type of the subgenus Cygnus. The wild swan and Hooper ought, perhaps, to be regarded as the only true native species. The tame swan (Cygnus olor) is superior in bulk to either of the wild species, and is at once distinguished by a large black callous knob on the base of the bill. Both the wild species are peculiarly characterized by convolutions of the windpipe, extending in the mature bird through the whole length of the keel of the sternum. These convolutions are horizontal in the Cygnus Bewickii, and vertical in the Cygnus fer us. [s. 1222]