“Nonsense!” exclaimed the professor. “There may be things as bad, but there are no such things as ghosts. Have your gun ready, Andy.” With every sense on the alert, the old hunter advanced. Every one was a bit nervous, and, as Mark and Jack afterward admitted, they half expected some terrible beast to rush out at them. But nothing of the kind happened, and they went into the interior of the temple. At first it was so dark they could see nothing. There were vast dim shapes on every side, and from the hollow echo of their footsteps they judged the roof must be very high and the structure big in every way. Then, as their eyes became used to the darkness, they could make out, up front, something like an altar or pulpit. “Perhaps that’s where they offered up the gold and diamonds as a sacrifice to their gods,” spoke Mark in a whisper. “Sacrifice to their gods!” came back a hundred echoes and the sound made every one shudder. “Oh!” said Washington, in a low voice. “Oh! Oh! Oh!” repeated the echoes in voices of thunder. “Well, this is pleasant,” spoke Andy, in his natural tones, and, to the surprise of all there was no echo. It was only when a person whispered or spoke low that the sound was heard. After that they talked naturally. “You stay here, and Andy and I will go up front and see what there is,” said Mr. Henderson. “Be on your guard, and if you hear us coming back in a hurry, run!” It was with no little feeling of nervousness that the boys, Bill, Tom and Washington watched the two men move off in the darkness. They could hear their footsteps on the stone flags and could dimly see them. “They must be almost to the altar by this time,” said Mark, after a long pause. Hardly had he spoken than there came a loud sound from where Mr. Henderson and Andy had gone. It was as if some giant wings were beating the air. Then came shrill cries and the voice of the old hunter could be heard calling: “Kneel down, Professor! Let me get a shot at the brute!” Those waiting in the rear of the temple huddled closer together. What terrible beast could have been aroused? The next instant the place seemed illuminated as if by a lightning flash, and a sound as of a thousand thunder claps resounded. “I think I winged him!” cried Andy’s voice, and the boys knew he had fired at something. Then there came a crash, and from the roof of the old temple a dozen stones toppled off to one side, letting in a flood of colored light. By this illumination could be seen, flapping through the big space overhead, an enormous bat, as large as three eagles. And, as it flew about in a circle it gave utterance to shrill cries. “Bang!” Andy’s gun spoke again, and the bat with a louder cry than before, darted through the hole in the roof made by the falling stones, which had been loosened by the concussion from the rifle. “Come on!” cried the old hunter. “That was the guardian of the treasure! We are safe now!”