Tom Swift looked deliberately around. It was characteristic of him that, though by nature he was prompt in action, he never acted so hurriedly as to obscure his judgment. So, though now Ned showed a trace of strange excitement, Tom was cool.

"What is it?" asked the young inventor. "What's the matter? What did you think you saw, Ned; another alligator?"

"Alligator? Nonsense! Up on shore? I saw a black shadow, and I didn't think I saw it, either. I really did."

Tom laughed quietly.

"A shadow!" he exclaimed. "Since when were you afraid of shadows, Ned?"

"I'm not afraid of ordinary shadows," answered Ned, and in his voice there was an uncertain tone. "I'm not afraid of my shadow or yours, Tom, or anybody's that I can see. But this wasn't any human shadow. It was as if a great big blob of wet darkness had been waved over your head."

"That's a queer explanation," Tom said in a low voice. "A great big blob of wet darkness!"

"But that just describes it," went on Ned, looking up and around. "It was just as if you were in some dark room, and some one waved a wet velvet cloak over your head--spooky like! It didn't make a sound, but there was a smell as if a den of some wild beast was near here. I remember that odor from the time we went hunting with your electric rifle in the jungle, and got near the den in the rocks where the tigers lived."

"Well, there is a wild beast smell all around here," admitted Tom, sniffing the air. "It's the alligators in the river I guess. You know they have an odor of musk."

"Do you mean to say you didn't feel that shadow flying over us just now?" asked Ned.

"Well, I felt something sail through the air, but I took it to be a big bird. I didn't pay much attention. To tell you the truth I was thinking about Beecher--wondering when he would get here," added Tom quickly as if to forestall any question as to whether or not his thoughts had to do with Beecher in connection with Tom's affair of the heart.

"Well it wasn't a bird--at least not a regular bird," said Ned in a low voice, as once more he looked at the dark and gloomy jungle that stretched back from the river and behind the little clearing where the camp had been made.

"Come on!" cried Tom, in what he tried to make a cheerful voice. "This is getting on your nerves, Ned, and I didn't know you had any. Let's go back and turn in. I'm dog-tired and the mosquitoes are beginning to find that we're here. Let's get under the nets. Then the black shadows won't get you."

Not at all unwilling to leave so gloomy a scene, Ned, after a brief glance up and down the dark river, followed his chum. They found Professor Bumper and Mr. Damon in their tent, a separate one having been set up for the two men adjoining that of the youths.

"Bless my fountain pen!" exclaimed Mr. Damon, as he caught sight of Tom and Ned in the flickering light of the smudge fire between the two canvas shelters. "We were just wondering what had become of you."

"We were chasing shadows!" laughed Tom. "At least Ned was. But you look cozy enough in there."

It did, indeed, look cheerful in contrast to the damp and dark jungle all about. Professor Bumper, being an experienced traveler, knew how to provide for such comforts as were possible. Folding cots had been opened for himself, Mr. Damon and the guide to sleep on, others, similar, being set up in the tent where Tom and Ned were to sleep. In the middle of the tent the professor had made a table of his own and Mr. Damon's suit cases, and on this placed a small dry battery electric light. He was making some notes, doubtless for a future book. Jacinto was going about the camp, seeing that the Indians were at their duties, though most of them had gone directly to sleep after supper.

"Better get inside and under the nets," advised Professor Bumper to Tom and Ned. "The mosquitoes here are the worst I ever saw."

"We're beginning to believe that," returned Ned, who was unusually quiet. "Come on, Tom. I can't stand it any longer. I'm itching in a dozen places now from their bites."

As Tom and Ned had no wish for a light, which would be sure to attract insects, they entered their tent in the dark, and were soon stretched out in comparative comfort. Tom was just on the edge of a deep sleep when he heard Ned murmur:

"I can't understand it!"

"What's that?" asked the young inventor.

"I say I can't understand it."

"Understand what?"

"That shadow. It was real and yet----"

"Oh, go to sleep!" advised Tom, and, turning over, he was soon breathing heavily and regularly, indicating that he, at least, had taken his own advice.

Ned, too, finally succumbed to the overpowering weariness of the first day of travel, and he, too, slept, though it was an uneasy slumber, disturbed by a feeling as though some one were holding a heavy black quilt over his head, preventing him from breathing.

The feeling, sensation or dream--whatever it was--perhaps a nightmare--became at last so real to Ned that he struggled himself into wakefulness. With an effort he sat up, uttering an inarticulate cry. To his surprise he was answered. Some one asked:

"What is the matter?"

"Who--who are you?" asked Ned quickly, trying to peer through the darkness.

"This is Jacinto--your guide," was the soft answer. "I was walking about camp and, hearing you murmuring, I came to your tent. Is anything wrong?"

For a moment Ned did not answer. He listened and could tell by the continued heavy and regular breathing of his chum that Tom was still asleep.

"Are you in our tent?" asked Ned, at length:

"Yes," answered Jacinto. "I came in to see what was the matter with you. Are you ill?"

"No, of course not," said Ned, a bit shortly. "I--I had a bad dream, that was all. All right now."

"For that I am glad. Try to get all the sleep you can, for we must start early to avoid the heat of the day," and there was the sound of the guide leaving and arranging the folds of the mosquito net behind him to keep out the night- flying insects.

Once more Ned composed himself to sleep, and this time successfully, for he did not have any more unpleasant dreams. The quiet of the jungle settled down over the camp, at least the comparative quiet of the jungle, for there were always noises of some sort going on, from the fall of some rotten tree limb to the scream or growl of a wild beast, while, now and again, from the river came the pig-like grunts of the alligators.

It was about two o'clock in the morning, as they ascertained later, when the whole camp-- white travelers and all--was suddenly awakened by a wild scream. It seemed to come from one of the natives, who called out a certain word ever and over again. To Tom and Ned it sounded like:

"Oshtoo! Oshtoo! Oshtoo!"

"What's the matter?" cried Professor Bumper.

"The vampires!" came the answering voice of Jacinto. "One of the Indians has been attacked by a big vampire bat! Look out, every one! It may be a raid by the dangerous creatures! Be careful!"

Notwithstanding this warning Ned stuck his head out of the tent. The same instant he was aware of a dark enfolding shadow passing over him, and, with a shudder of fear, he jumped back.