During the daytime silence and solitude prevail over the open plains. It is the hour when most animals seek, under the foliage of the trees, among the tall rank grasses, in the bosom of the waters or under the surface of the earth, a shelter against the swift burning arrows of the sun, and repose immovable in their different lairs. But when the great orb of day sinks towards the horizon, all Nature seems to awake. More imperious needs succeed to those of rest and slumber; hunger and thirst stimulate the most sluggish into exertion. Then the reptile begins to stir in the mud where he lay embedded; the herbivora return to their fresh pastures, and move towards the rivers and ponds in whose waters they may slake their thirst; the carnaria take the same road; they know that in the open plain they will find victims for their murderous jaws. The Desert is astir with strange sounds and mysterious voices; the air re-echoes the thousand discordant cries which ring from the mountains and the rocks; black shadows pass, re-pass, and flit to and fro, in every direction; terror, rage, agony, voracity, all these instincts obtain expression in the dreadful concert; it is the orgie of the appetites, the grand "Witches' Sabbath" of Nature, whose furious animation slackens towards the middle of the night, until, at sunrise, the lively accents and joyous melodies of the birds, and the peaceful pastimes of the other animals of the day, succeed to the lamentations and sinister invocations of the prowlers of the darkness. [Illustration: HIPPOPOTAMUS AND CROCODILE OF THE RIVER NILE.]