Let us now consider examples of the instincts of self-preservation, subsistence, migration, and the continuation of the species. Most animals know their natural enemies prior to experience of any hostile designs upon themselves. A flight of young pigeons, even though they have no old birds with them, will become shy, and will separate from one another on the approach of a bird of prey. Horses and cattle that come from countries where there are no lions become unquiet and display alarm as soon as they are aware that a lion is approaching them in the night. Horses going along a bridle-path that used to leave the town at the back of the old dens of the carnivora in the Berlin Zoological Gardens were often terrified by the propinquity of enemies who were entirely unknown to them. Sticklebacks will swim composedly among a number of voracious pike, knowing, as they do, that the pike will not touch them. For if a pike once by mistake swallows a stickleback, the stickleback will stick in its throat by reason of the spine it carries upon its back, and the pike must starve to death without being able to transmit his painful experience to his descendants. In some countries there are people who by choice eat dog’s flesh; dogs are invariably savage in the presence of these persons, as recognising in them enemies at whose hands they may one day come to harm. This is the more wonderful inasmuch as dog’s fat applied externally (as when rubbed upon boots) attracts dogs by its smell. Grant saw a young chimpanzee throw itself into convulsions of terror at the sight of a large snake; and even among ourselves a Gretchen can often detect a Mephistopheles. An insect of the genius _bombyx_ will seize another of the genus _parnopæa_, and kill it wherever it finds it, without making any subsequent use of the body; but we know that the last-named insect lies in wait for the eggs of the first, and is therefore the natural enemy of its race. The phenomenon known to stockdrivers and shepherds as “das Biesen des Viehes” affords another example. For when a “dassel” or “bies” fly draws near the herd, the cattle become unmanageable and run about among one another as though they were mad, knowing, as they do, that the larvæ from the eggs which the fly will lay upon them will presently pierce their hides and occasion them painful sores. These “dassel” flies—which have no sting—closely resemble another kind of gadfly which has a sting. Nevertheless, this last kind is little feared by cattle, while the first is so to an inordinate extent. The laying of the eggs upon the skin is at the time quite painless, and no ill consequences follow until long afterwards, so that we cannot suppose the cattle to draw a conscious inference concerning the connection that exists between the two. I have already spoken of the foresight shown by ferrets and buzzards in respect of adders; in like manner a young honey-buzzard, on being shown a wasp for the first time,