CHAPTER XVIII.

THE UNDERGROUND CITY.

Vasco Bilette's warning was received with ill humor by his men. They were angry because the kidnapping had not succeeded, and because the jaguar had alarmed the camp and put every one on guard.

"Come, let us give them battle now and take the boy!" suggested one.

"Do you want to be killed?" asked Vasco, angrily. "They are all armed now, and would shoot at the least suspicious sound. I, for one, don't care to have a bullet in me. Come, let us get out of this."

The Mexicans saw the force of Vasco's arguments. They did not care about being shot at like wild beasts, and they knew that the boys and the professor were ready for anything now.

"We will try to-morrow night," said Bilette, as, with Noddy and his men, he silently withdrew to where the horses and auto had been left. "Perhaps we'll have better luck then."

The men growled, but had to accept the situation. As for our friends, they were too excited to sleep any more that night, and so they sat around the camp-fire and talked until morning.

Breakfast over, camp was broken, and once more the auto started on the trip toward the hidden city. Professor Snodgrass got out the map made by his dead friend and studied it carefully.

"I believe we are on the right road," the naturalist said. "Here is a highway marked on the drawing that seems to correspond with the one we are on. And there is a place marked where two roads diverge. Only there is nothing said about the laughing serpent, though there is something here that might be taken for it," and he pointed to the map.

Every one was becoming quite anxious, and the boys, as well as the professor, kept close watch on each foot of the way to see if there were any indications that they were close to the underground town.

They stopped for dinner near a little brook, in which Bob caught several fish that made a welcome addition to the bill of fare.

"Now, if you boys don't object, I think I'll take a little stroll into the woods and see what I can find in the way of specimens," remarked the naturalist, as he finished the last of his fish and frijoles.

"Better take a gun along," called Ned. "A jaguar may get you."

"I'm not going very far," replied the professor. "All I want is my net and box," and with these only he started off.

It was about an hour later when Jerry observed:

"Doesn't it seem as if the monkeys were making more noise than usual?"

The boys listened for a few seconds. It was evident that something had disturbed these nimble inhabitants of the forest, for they were yelling and chattering at a great rate.

"Maybe another jaguar is after them," suggested Bob.

"No; it doesn't sound like that," said Jerry. "They seem to be yelling more in rage than in fear."

"Maybe they're having a fight," put in Ned.

Just then there came a crashing, as if several trees were being crashed down by a tornado. There was a crackling of the underbrush and a rustling in the leaves. Then, above this noise and the yells of the monkeys, sounded a single cry:

"Help, boys!"

"The professor's in trouble again!" cried Jerry. "I wonder what it is this time?"

Grabbing up a rifle, which example Bob and Ned imitated, Jerry ran in the direction of the voice. The noise made by the monkeys increased, and there were sounds as if a bombardment of the forest was under way.

"Where are you?" called Jerry. "We are coming!"

"Under this big rock!" called the professor, and the boys, looking in the direction his voice came from, saw the naturalist hiding under a big ledge of stone that jutted out of the side of a hill in a sort of a clearing.

"Can't you come out?" called Ned.

"I tried to several times, but I was nearly killed," replied the professor. "The monkeys are after me. Look at the ground."

The boys looked and saw, strewn in front of the shallow cave in which the professor had ensconced himself, a number of round, dark objects. As they looked there came a shower of others through the air. Several of them hit on the rock, broke, and a shower of white scattered all about.

"What in the world are they?" asked Bob.

He ran toward the professor. No sooner had he emerged out of the dense forest into the clearing than a regular hail of the round objects fell all about him. One struck him on the shoulder and the boy was glad enough to retreat.

"What's it all about?" asked Ned.

"The monkeys are bombarding the professor with cocoanuts," said Bob, gasping for breath after his run.

"Cocoanuts?"

"That's what they are. Here come some more."

He had scarcely spoken before the air was again dark with the brown nuts, which were much larger than those seen in market, being contained in their original husk. At the same time there was a chorus of angry cries from the monkeys.

It was evident now why the professor dared not leave his rock shelter. The minute he did so he would run the risk of being struck down and probably killed by a volley of the nuts. Nor could the boys go to his rescue, for the moment they crossed the clearing they would be targets for the infuriated animals.

"What's to be done?" asked Ned.

"Supposing we shoot some of the monkeys," suggested Bob.

"I don't think that would be a good idea," said Jerry. "In the first place if we kill any of the animals it will make the others all the angrier. And then we would have to keep shooting for several days to make much of an inroad on the beasts. There must be five thousand of them."

Indeed, the forest was full of the long-tailed and nimble-fingered monkeys, all perched in cocoanut or other trees, ready to resent the slightest movement on the part of their human enemies.

"I know a good trick," spoke Bob.

"What is it, Chunky?" asked Jerry.

"Take a big looking-glass and put it on a tree. The monkeys will be attracted by the shine of it; they will all go down to see what it is and when they see a strange monkey in the glass they will fight. That will make enough fuss so that the professor can escape."

"That might be a good trick if we had the big mirror, which we haven't," spoke Jerry. "You'll have to think of something else, Chunky."

But there was no need of this, for at that instant the cries of the monkeys ceased. The silence was almost oppressive in its suddenness and by contrast with the previous riot of noise. Then came unmistakable screams of fear from the simians.

"Now what has happened, I wonder?" said Ned.

"It's a jaguar!" cried Bob.

He pointed to a tree, on a limb of which one of the animals the monkeys dreaded so much was stretched out. The beast was stalking one of the chattering animals, but his presence had been discovered by the whole tribe.

So much in awe did the monkeys hold this scourge of the Mexican forests that his presence accomplished what the boys could never hope to. The apes trooped off with a rush, chattering in fright. With a howl of rage the jaguar took after them.

"You can come out now, Professor," called Ned. "The monkeys are gone."

In fear and trembling the naturalist came from his sheltering rock. He seemed in momentary fear lest he might be greeted with a shower of the nuts, but none fell. With rapid strides he crossed the clearing and joined the boys.

"How did it all happen?" asked Jerry, as soon as the professor had recovered his breath.

"It was all my fault," explained the naturalist. "I was collecting some butterfly specimens, when I happened to see some monkeys in the cocoanut trees. I had read that if any one threw something at the beasts they would retaliate by throwing down cocoanuts. I wanted to test it, so I threw a few stones at the monkeys. They returned my fire with interest, so I was forced to run under the rock for shelter.

"There were only a few monkeys at first, but more came until there were thousands. They kept throwing cocoanuts until the ground was covered. It's lucky you came when I called."

"It's luckier the jaguar came along when he did," said Jerry.

"Let's get back to the auto before I get into any more trouble," suggested the professor. "I do seem to have the worst luck of getting into scrapes."

Half an hour later the travelers were on their way. It was getting well along into afternoon and they were beginning to think of where they would spend the night.

They were getting deeper and deeper into the forest, and the way became more and more difficult to travel. But they would not turn back, for they felt they were on the right path.

At length they came to a place where creepers and vines were so closely grown across the path that nothing short of hatchets could make a way. The boys got out the small axes kept for such emergencies, and, after an hour's work, made a passage.

They started forward once more, and were going along at a pretty good clip, the road having improved in spots.

"I wonder when we'll get to that underground city?" said Ned, for perhaps the tenth time that day.

He had no sooner spoken than the earth trembled under the auto. The machine seemed to stand still. Then, with a sickening motion it plunged forward and downward.

A big hole had opened in the road and let the car and its occupants through the surface of the earth. The machine slid forward, revealing, near the top of a shaft, a brief glimpse of several ruined buildings.

"It is the underground city!" exclaimed the professor.

Then there came intense darkness.