The peculiar organic distinction of the Swan is the great length of the neck, consisting of twenty-three vertebræ, and the cavity in the sternum for the reception of the trachea, which is admirably described by Mr. Yarrell as descending the passage between the two branches of the forked bone called the merrythought to a level with the keel of the breast-bone, which is double, and receives the tube of the trachea between its two sides, which here turns upon itself after traversing the whole length of the keel, and passes upwards and forwards, and again backwards, till it ends in the vertical bone where the two bronchial tubes go off, one to each lobe of the lungs. This is the apparatus through which the cry is produced, which is variously described as a whistle, a whoop, or a song, according to the fancy of the writer. They fly at a great height when on a migratory journey, and in a wedge-like figure, uttering this note as they proceed, and when heard at a distance it is not unmusical. Mr. McGillivray listened to a flock of Wild Swans coming in from the Atlantic after a gale: their clear, loud, and trumpet-like cries delighted him as they sped their way in lengthened files; but they were too far off for him to decide whether or not they were of this species. From six to eight eggs, of a greenish white, the female lays, and the incubation lasts about six weeks. The cygnets are at first covered with a grey down, and do not put on their adult plumage until the third year. Swans care but little for concealing their broods, as they feel confident of their power to protect them against every enemy. They will fight even with the Eagle itself, harassing it with beak and wings, until the marauder is glad to make a more or less honourable retreat. In the protection of their young they display extraordinary courage. On one occasion a female Swan was sitting on the bank of a river, when she perceived a fox swimming towards her from the opposite bank. Thinking that she would be better able to defend herself in her natural element, she took to the water and went to meet the enemy which was threatening her brood. She soon reached him, and, springing upon him with much fury, gave him such a violent blow with her wing that the fox was disabled, and consequently drowned.