One still night on the Amazon Jack Bosworth got out a map and turned a flashlight on it. Frank and Harry stood looking over his shoulder.

"Right here," Jack said, presently, "is where we leave the main stream of the Amazon and take to the Madeira."

"How do you know that stream is the Madeira?" asked Frank. "We have passed so many large tributaries that I'm all mixed up."

"And why not try some other stream?" Harry questioned. "I've heard that the Madeira is full of falls and rapids."

"Anyway," Jack insisted, "it takes us away up into the Andes, almost to Lake Titicaca, and that's all any stream will do. As for the falls and rapids, do you expect any stream to creep down from that great plateau without jumping off occasionally?"

"All right," Frank cut in. "Go your own way to destruction! But how do you know that rippling sheet of water off there," swinging an arm to the south, "is the Madeira river? It looks like a lake to me."

"I found out while you were asleep this morning," Jack replied. "A chap came along in a launch and I asked him all about it. He said he had just come from the Andes, and advised me to turn back."

"Kind-hearted little fellow, eh?" laughed Harry.

"He wasn't very little," answered Jack. "He was six feet two, and was coming out with a finger off and a cut across a cheek bone which will last him for a spell, I guess. He cut his finger off because a poisoned arrow struck it."

"Cannibals?" asked Harry, with a laugh.

"The same," replied Jack. "Said they chased him for miles."

"We'll curb their appetites with lead," Harry observed.

"If we see them first," added Jack.

So the Black Bear was turned into the Madeira river, which is something like seven hundred miles long, and drains the wooded country where the black sheep of the land of Brazil live. Away up in the hills it is fed by the Beni river, which has its source in the mountains east of Lake Titicaca.

More than once the boys were obliged to haul their motor boat out on a rocky "bench," take it to pieces, carry it and most of the stock around rapids, and then put it together and load up again. Still, they made good time, and on the evening of the third day found themselves at the junction with the Beni river.

They were now in a wild and dangerous country. The forests swarmed with wild game, the thickets were full of serpents, and the trees were often crowded with monkeys. For two days they had seen no natives. This was suspicious as it was certain that they had penetrated to the home of the cannibal tribes so greatly dreaded by hunters and explorers.

It was on the evening of the 21st of August that Jack sent the Black Bear into a little creek, shut off the power, and turned to put up the panels. It was not very warm, but the atmosphere was sticky and heavy with the breath of the woods.

"We'll smother in there tonight," Frank said, observing the actions of the other. "Why not leave some of 'em out?"

"If you want a poisoned arrow nestling in your ribs you can sleep outside," Jack answered. "For my part, I want to wake up in this good old world in the morning."

"I don't think there's any danger yet," Frank said.

But the panels were put up and supper prepared. By this time the lads had become accustomed to preparing their own meals, as well as providing the fish from the river, and the repast was soon over. Then Jack lay back and gazed through the one glass panel of the top of the Black Bear.

It was a dark, lowering night. The wind is usually from the east in that part of Brazil. Blowing over the Atlantic it gathers up moisture to dump on the eastern slope of the Andes. The summits drain the clouds and makes Peru a dry country. It was murky now, and the clouds hung low.

"What do you see up there, Jack?" asked Frank. "Trying to study astronomy, with not a star in sight?"

"There you are wrong," Jack replied. "There is at least one star in sight."

"With that mass of clouds drifting over the sky?" laughed Harry. "I reckon you must be seeing things not present to the senses!"

"Come and look, then," Jack invited. "Look straight up, and you'll see a star."

Frank placed himself under the glass panel and looked up.

"Well?" Jack demanded, in a tone of triumph.

"It's something," Frank exclaimed, "but I don't believe it is a star."

"It may be a reflector at the top of the Flatiron building," grinned
Jack. "What is it, if it isn't a star?"

"Look yourself!" cried Frank.

The boys were all looking now. They saw the light which Jack had mistaken for a star flashing to and fro under the clouds like a firefly. It rushed earthward with amazing speed for an instant, then spiraled upward again. Once it came directly over the Black Bear, and seemed about to drop down.

Jack threw a couple of panels open, and then the whirr of motors reached their ears. Frank sprang outside and turned a flashlight upward.

"There's your star!" he shouted to Jack.

"Quick!" Harry cried. "Wigwag with that light. It is the Nelson!
They may be able to see us!"

"Yell, every soul of you!" directed Frank. "Yell! She is going away!"

The boys waved their lights frantically and shouted at the top of their voices, but the light in the sky crept away to the west and soon disappeared, evidently passing above the clouds which lay like a black blanket over the Brazilian forests.

"Great heavens!" Jack sighed. "If we could only have made them hear! I'll bet they've been to Paraguay and released Lyman. Now they're going back home! Fine show we now stand of having any fun with them!"

"They went west," Harry corrected. "That isn't the way home!"

"I'd like to know just what success they have had," Jack went on. "Say," he continued, "can't we do something to attract their attention? Why not set fire to some big dry tree and let her blaze up?"

"I just can't have it this way!" Harry said. "I can't stand it to have them come so close to us and then go away without knowing we are here. We've got to bring them down in some way."

"But they've gone!" Frank declared, gravely.

"If we make a big blaze," Jack hastened to say, "the reflection on the clouds will attract their attention, and they'll come back. They won't be able to see the fire itself, of course, but they'll see the reflection, and that will bring them down to investigate. Then we'll fire our revolvers and wigwag with blazing sticks until they see who we are."

"It may not be the Nelson," Harry suggested.

"I don't believe there's any other aeroplane sailing about the roof of the world," Frank replied. "Of course it is the Nelson!"

"Perhaps the Nelson was followed," Harry went on. "I've heard of such things. The chap in that machine may be looking for Ned. Anyway," he added, "it won't do any harm to let the aviator, whoever he is, know that we are here. Come on, let's go ashore and build a big fire."

"I certainly would give a year's growth to know whether that is the Nelson," Harry said, as the boys sought the shore and began gathering dry wood, which, it may be well to add, was not easy to find, as there had been quite a shower during the day. "For all we know," he continued, "there may be another aeroplane here. If the people who are trying for the Lyman concession are as active here as they seem to have been in Paraguay, they may have half a dozen airships out after the Nelson."

Finally a quantity of wood which was fairly dry was secured, and Jack bundled it up against a dead tree which seemed to run straight up into the sky until it touched the clouds. But when the boys came to apply matches they discovered that the wood was not dry enough to be ignited in that way.

"I'll get a gallon of gasoline and pour over it," Frank explained.
"Then we can run like blazes when we touch her off. What?"

The gasoline was brought, and the blaze started with a mighty concussion of the air. A portion of the highly inflammable fluid had entered a great crevice in the dead tree, with the result that there was an explosion which resounded through the forests for miles. Then the flames mounted the tree, which was soon blazing like a great torch.

"I guess that will attract their attention!" Jack said, shielding his face from the intense heat.

"Yes," Frank replied, "and I'm afraid it will attract the attention of others, too. You know we were told to sneak through this country like little mice!"

"It is too late now!" Jack said, a shadow of anxiety coming over his face. "We are in for it, I guess. What shall we do?"

Above the crackling of the flames, above the drawing and sighing of the wind, there now came a strange sound which seemed to proceed from the fire-tinted clouds above. Now and then branches of the nearby trees stirred mysteriously, and at times a wild shriek rose above the monotonous chattering.

"Monkeys!" cried Jack. "They've come out to help us bring the airship to earth. Good little beasts!"

"Don't be in too much of a hurry to give the little devils a certificate of good character!" Harry answered. "They may make trouble for us."

After a time the foolish, wrinkled faces of the monkeys were seen peering from trees. Then, above the din they made, above the crackling of the fire, constantly mounting higher, came a scream almost like that of a child.

"That's a jaguar!" Harry declared, "a South American tiger, and we'd better be getting toward the boat."

"The animals won't come near the fire," Frank said. "We may as well remain here and see the menagerie."

Directly it seemed to the excited lads that all the wild animals in South America were assembled about their signal. Harry declared that he heard the call of the red wolf, the scream of the tiger cat, the wail of the puma, the vicious snarling of the wild dog.

While the boys listened to the chorus their efforts to attract the attention of the aeroplane had produced, there came into the discord another sound—the hissing of a monster serpent. Heretofore the boys had little to do with Brazilian forms of animal life, for they had kept near the middle of the main stream of the Amazon, and also about in the center of the Madeira and the much smaller Beni, which was only a creek when compared with the other rivers.

Occasionally they had seen a monster cayman nosing against the current, and at times their progress had been retarded by turtles, but they had never before seen anything like this. Their fire had certainly brought out a combination in nature which would have been decidedly interesting if it hadn't been so threatening.

"Me for the boat!" Jack said, with a shiver, as the serpent launched his head and a third of his body from the tree and swept about in widening circles. "I never could endure snakes!"

"I'm going to take a shot at it," Frank said. "I'd like to see him take a tumble into the fire."

"Better let him alone," Harry advised.

Frank was about to fire when Jack caught his arm and held up his hand in a listening attitude.

"What is it?" Frank asked.

"Human voices!" was the quick reply.

"Inhuman voices, I should say," Harry observed, after a second of silence.

A chant unlike anything the boys had ever heard before undulated through the forest. It rose and fell with the gusts of wind, and always nearer to the fire.

"This is a new one on me!" Jack cried. "It is also another reason for getting to the boat! Come on, fellows!"

"I'm not going to run until I find out what that is," insisted
Frank. "I'm going to write a newspaper story about this menagerie!"

"If you want your story published in this world," Jack cried, "you'd better get under cover, for that's the chant of the head hunters!"

"Wow!" cried Frank, and he beat both his chums to the boat.

"I guess we've started something!" Jack said, as he busied himself putting up the few panels which had been removed when they went ashore. "Now, some one push that button, and I'll get the Black Bear out of this creek. A good old scout like the Black Bear has no business associating with the wild animals on shore."

"Right you are!" shouted Harry, and the propellers began moving.
Still, the boat made no progress to the rear, the reverse being on.

"What's doing?" demanded Jack. "You'd better hurry, for the head hunters are coming right along. See that big chief over there? He's got a club that would level the Singer building at a blow!"

"I can't make her back," Harry complained. "There's something the matter below her in the stream. It was all clear when we came in."

In an instant all was intense excitement on board the motor boat. There was only one way in which the savages could reach them, and that was to block their passage out and starve them to death! Had this system been resorted to? Had the cunning savages obstructed the little stream while the lads were busy building their fire and observing their menagerie, as they called it?

These questions were in the minds of all as efforts to back the Black Bear were redoubled. Finally Jack opened a panel at the rear and looked out, a thing he should have done at first.

What he saw was a large log blocking the channel. The propellers were pounding against it, and one of them was broken.

"I guess the little brown men have got us good and plenty," he said, slowly, as he reached forward and shut off the power. "While we were playing about the blaze they plugged the river."

"They can't get in here, anyway!" Frank consoled.

"No; they'll wait for us to get good and hungry and go out!" Jack replied.

The situation was a serious one. The head hunters now appeared in the open space about the blazing tree and shook their spears and their clubs at the boat. Now and then an arrow with a poisoned tip struck the side of the Black Bear.

"They'll never leave until they get us!" Jack said, presently, "and so we may as well get a few of them. Get your guns, boys."

"Just you wait, old hard luck prophet," Frank exclaimed. "Look up through the glass panel above your head and tell me what you see."

"Well," Jack replied, "it looks like we had established communication with the Nelson at last. And also with the Greatest Show on Earth!" he added, as a mighty roar went up from the shore.

The other boys crowded the panel and looked out. The clouds above were red with the reflection of the blazing tree, yet against the mass a different light blazed out. This light moved about, from north to south and back again, as if searching out the reason for the strange happenings below.

The popping of her motors could be plainly heard, and so it was probable that those on the airship could hear the wild animal concert which was going on in the woods. Harry pushed a panel aside and fired three quick shots. The aeroplane wavered above the river a moment and then drifted away.

"They must know there's somebody down here in trouble!" said Harry. "Why don't they throw down dynamite? That would give the savages all the heads they wanted for a time, I guess."

The boys fired again and again, flashed their lights in wigwag signals, but the aeroplane did not come nearer. Instead it whirled swiftly about in a circle for a moment and then shot out of sight beyond the clouds.

And every moment the circle of savage faces gathered closer about the Black Bear, effectively blocked in the narrow stream.