What he was going back for he never said, for, at that instant, happening to look up at the hole in the roof, he gave a startled try:

"Here come the terrible bats!"

They all gazed upward. Through the opening they could see a great flock of the awful birds, headed for the temple, and they were led by one which seemed to fly with difficulty. It was the guardian of the treasure that Andy had wounded.

"Quick! We must get out of here!" shouted the old hunter. "They are big enough and strong enough to tear us all to pieces. Hurry!"

Down the centre of the temple they rushed, and not a moment too soon, for, ere they had pa.s.sed half way to the entrance, the opening in the roof was darkened by the coming of the bats, and soon the flapping of their wings awoke the thundering echoes in the ruined structure, while their shrill cries struck terror to the hearts of the travelers.

Up to the altar circled the bats, and then wheeling they flapped down the dim aisles toward the adventurers.

"Hurry! Hurry!" shouted Andy, who was in the rear.

He raised his rifle and fired several shots into the midst of the terrible creatures.

A number of the bats were wounded, and the others were so frightened by the sound of the shots and the flashes of fire that they turned back. This enabled the fleeing ones to gain the entrance to the temple, and soon they were outside.

"To the ship!" yelled Bill.

"There's little danger now!" called Andy, panting, for the run had winded him. "They will hardly attack us in the light!"

And he was right, for, though they could hear the bats flying about inside the temple, and uttering their cries, none came outside.

But no one felt like staying near the uncanny structure, and little time was lost in reaching the Mermaid. Then the doors were fastened, and the ship was sent high up into the air.

"Which way?" asked Jack, when Mr. Henderson told him to go to the conning tower and steer.

"Back to where we first met the giants," replied the professor. "We must prepare to start for our own earth again soon."

"I've almost forgotten how real sunlight looks," thought Jack, as he headed the ship around the other way. As he turned the levers a big diamond dropped from his pocket and rolled on the floor.

"This will be a good reminder of our trip though," he added.

The travelers, even including Mr. Henderson, were so taken up with their suddenly acquired riches that they hardly thought of meals. At the professor's suggestion they tied their gold and stones up in small packages convenient to carry.

"Better place them where you can grab them in a hurry in case of accident," the old scientist went on. "Of course if there should be too bad an accident they would never be of any use to us down here, but we'll look on the bright side of things."

"Do you antic.i.p.ate any accident?" asked Jack anxiously.

"No, Oh no," replied Mr. Henderson, but Jack thought the aged man had something weighing on his mind.

CHAPTER XXIX

BACK HOME--CONCLUSION

ON and on sped the Mermaid. Now that the travelers felt their journey accomplished they were anxious to begin the homeward trip. They made a straight course for the village where they had so nearly met with disaster, and where the king of the giants had saved them. They went in a direct line, and did not travel here and there, as they had after they left the town. Consequently they shortened the route by a great distance. Yet it was long enough, and when they finally came in sight of the place the dial registered a trip of five thousand miles underground.

It was one evening when they landed almost at the spot whence they had taken flight eventually to reach the temple of the treasure. Most of the giants had betaken themselves to their mound houses, but Hankos was walking in the fields, and, when he caught sight of the airship hovering above him he waved his great sword in welcome.

He rushed up to shake hands with the travelers when they came out of the ship, though to greet him it was only possible for the adventurers to grasp one of his immense fingers.

As soon as the greetings were over Hankos began to speak rapidly to the professor, at the same time going through many strange motions.

"It is as I feared!" suddenly exclaimed the scientist.

"What is the matter?" asked Mark.

"The worst has happened!" went on Mr. Henderson. "The great hole by which we came into this place has been closed by an earthquake shock!"

"The hole closed?" repeated Jack.

"An earthquake shock!" murmured Mark.

"Then how are we going to get back to earth?" asked old Andy.

A terrible fear entered the hearts of the travelers. The closing of the opening by which they had come to the strange world meant, in all probability that they would have to spend the rest of their lives in this underground place.

"What good did it do us to get all those diamonds and that gold?"

asked Mark in a sorrowful tone.

Hankos began to speak again, using his gestures which were almost as eloquent as words. The professor watched and listened intently. Then there seemed to come a more hopeful look to his face. He nodded vigorously as Hankos went on with what seemed to be an explanation.

"It's worth trying, at all events!" the scientist exclaimed. "It is our only hope!"

"What is?" asked Jack.

"Friends," began the professor in solemn tones. "I must admit our plight is desperate. At the same time there is a bare chance of our getting back to our own earth. As you remember, Hankos went from this place to the upper regions through the upward spouting column of water."

"If we had our submarine we might also," interrupted Jack. "But the Mermaid isn't built to sail in that fashion."

"Nor would the Porpoise have served us in this emergency," said the professor. "It would prove too heavy. But, nevertheless, I think I have a plan. Now, Mark, you are about to learn the secret of the storeroom. The real one, not the hiding of Hankos in there, which you imagined to be the cause of my desire to keep something hidden. When we planned a trip to this underground world I had a dim idea that we might meet with trouble. So I planned and made a cylinder lifeboat."

"A cylinder lifeboat?" repeated Mark.

"Yes," replied Mr. Henderson. "I have it in the storeroom. I did not want any of you to see it for fear you would have faint hearts. I thought there might be no necessity of using it. But, since there is, we must do our best. I will admit it may be a fearful ordeal, but we will have to risk something in order to escape.

"I have in the storeroom a large cylinder, capable of holding us all.

It will also contain food and drink for a month, but we will all have to go, packed almost like sardines in a box. My plan is to take the Mermaid to the place where the column of water shoots up. There we will get into the cylinder, close it, and trust ourselves to the terrible force that may bring us back to the upper world. What do you say? Shall we attempt it?"

For a few seconds no one spoke. Then Jack said slowly:

"I don't see that we can do anything else. I don't want to stay here all my life."

"I wants a chance t' wear some of them sparklers," put in Washington.