Some species of birds live to a great age, longevity being more common than among mammals. Cases in which birds such as geese, swans, ravens, and some birds of prey, have been known to reach the age of fifty years,[289] are not uncommon, whereas such an event is very rare in the case of a mammal. Even small birds, such as canaries, may live as long as twenty years. Parrots are especially long-lived birds. Cockatoos have been known to reach the age of eighty years and more. I myself have had opportunities of observing a South American parakeet (_Chrysotis amazonica_) which lived more than eighty-two years, longer than is usual even with parrakeets. Several years before it died the bird showed unmistakable signs of old age. It became less lively, its plumage, although it did not whiten, lost much of its brightness, and the joints of the claws showed evidence of the presence of disease. In short, the parrakeet was obviously worn out and debilitated. Mammals show the signs of age even more plainly than do birds. A dog reveals old age by its slow movements, its white hairs, and worn teeth. The appearance of such an animal is never agreeable, while it is often dirty and ill-tempered. Brehm describes the old age of a dog as follows: “At twelve years of age a dog has grown old, and his gait and whole organisation show signs of age. The coat is no longer glossy; the forehead and muzzle are grey, the teeth are blunted or have fallen out. The animal is lazy and apathetic. Many such dogs are dumb and blind. Dogs may live for twenty, six and twenty, or even thirty years, but such cases are most unusual.” As the dog is a domesticated animal, it might be argued that its old age, with its manifest signs of decrepitude, is the result of the artificial conditions of its life. To decide on this point it is necessary to examine an instance of old age in a wild animal. This presents certain difficulties since wild animals when old and feeble become an easy prey to carnivorous enemies. It will best serve our present purpose to consider such information as has been collected regarding the period of old age in anthropoid apes. The natives of Borneo have observed “old orangs, which have not only lost their teeth, but being too feeble to climb, live on the fallen fruits and herbs.”[290] Gorillas, according to Savage, turn grey in their old age, from which has arisen the erroneous view that there are two species of the gorilla.