Abdul said the ants used the yellow earth below the black soil on the surface. Their first move was to swallow it, and thus mix it with an albuminous matter from their bodies, so as to give it the character of cement. Then the substance was formed into the mound which rose above the level of the highest floods. When the river is low the black soil is uncovered, and the ants roam in the vicinity of the mounds; but at the time of the inundation the entire country is under water, with the exception of the mounds, which stand out like small islands. [Illustration: A HERD OF ANTELOPE.] From this point the ant-hills were numerous, and at the next halting-place a group of antelopes was seen, with one of its number stationed on a mound as a sentry. Finding the boat would be there a sufficient time to permit the experiment, Doctor Bronson determined to capture the sentinel, as an addition to the table of the steamer. Armed with his rifle, he started on foot, carefully keeping several ant-hills in range of the one where the sentry was standing, and never allowing himself more than a glimpse of the creature's horns. The sentinel did his duty thoroughly, and gave the Doctor no little trouble to approach without being discovered. Creeping slowly from hill to hill, he at last reached one about two hundred yards from that where the sentinel stood. The animal was motionless, with the exception of his head, which he turned from side to side occasionally, so as to take in the entire horizon. His side was toward his enemy, so that he offered an excellent mark. The rest of the herd was grazing near; but as the sentinel was larger and a better prize than any of his companions, the Doctor made no change of intention, and took aim at the one he had first marked as his own. The shot had its effect. As the smoke cleared away the antelope sunk to its knees for an instant, and then rolled to the ground, where it lay, quite dead. The balance of the herd fled, and the hunter, after reloading his rifle, ran forward to survey the effect of his shot. Mounting to the summit of the ant-hill, he waved his handkerchief three times, which had been agreed upon to announce a successful shot. As soon as the signal was seen four men were sent from the boat to carry away the game. The boys walked out to meet the Doctor and congratulate him on his morning's work, and also to see the dead antelope. Frank pronounced him "a beauty," and Fred said he was the finest animal of the kind he had ever seen.