“HOW long will it take us to get to this Forest of Mystery?” inquired Bob Holton, as he and his chum followed the naturalists over the grassy plain.

“Many, many days,” answered Mr. Lewis. “It is in the very heart of the vast Belgian Congo and is inaccessible by way of roads and railways.”

“So much the better for us,” laughed Joe. “We’ll probably find things there that no one else has seen. At least, no other white men.”

“Let’s hope you’re right, Son,” came from his father. “Howard and I would like to discover some totally unknown animals. But,” he added significantly, “we’ll have to watch our step. Who knows what perils may be hidden in that mysterious forest?”

The afternoon was rapidly wearing on, and although the explorers were still on the open plain, Noko announced that he desired to get beyond it before nightfall. In the distance they could see a dark jungle, through which they would soon be passing.

The grass under their feet was tough and wiry and yielded reluctantly. Occasionally small animals darted out before them and disappeared under cover of the grass. None of the large cats, however, showed itself.

“Wish we could get a look at a lion,” remarked Bob, tightening his grip on his rifle. “What I’ll do to one if I see one!”

The naturalists looked back and smiled.

“Maybe it would work the other way around,” chuckled Mr. Holton. “What would the lion do to you?”

“Oh, I don’t know, Dad. I’m not a bad shot. You know that. And I’ve met wild animals before.”

“True, Bob,” came from his father. “But none happened to be as ferocious as old felis leo——”

“I thought the lion is called simba,” interrupted Joe.

A burst of laughter followed.

“It’s very apparent,” said Mr. Lewis, “that you need to brush up on your natural history.”

“Why?” inquired Joe, somewhat surprised. “What was funny?”

“Still don’t get the point, huh?” laughed Mr. Holton. “Well, we’d better tell you before you spring that one before some of our naturalist friends. Felis leo, boys, is the lion’s scientific name. Simba is the name given to him by the natives.”

The boys laughed also when Mr. Holton had finished.

“Simba fits him better,” mused Joe. “Of course, it’s less distinguished, but, just the same, it’s easier to say.”

At last they found themselves nearing the jungle, after having left the long stretch of veldt behind. As it was almost sundown, the naturalists greatly desired to stop for the night. Noko, however, for some reason wanted to plunge into the jungle without delay. Perhaps he feared the invasion of wild beasts if camp should be made on the grassland.

Before long they plunged into the woodland, and their rate of travel was necessarily reduced somewhat. For with all the many sharp-pointed thorns, low bushes, tangled vines, and other obstacles, the adventurers found it difficult to maintain a rapid pace.

“Keep a sharp lookout,” cautioned Mr. Holton, glancing back for a moment. “This region shouldn’t be particularly dangerous, but you never can tell.”

“Only thing I’m especially afraid of,” began Joe, “is poisonous snakes. Can’t tell just when you might step on one.”

“Leopards are also dangerous,” put in his father. “At any minute one might leap down from a tree and make for us. Still, the animals are likely to be frightened by such a large safari as ours.”

At frequent intervals Bob and Joe took turns in “shooting” the country with the motion-picture cameras. These latter were not the type that require a tripod, but were relatively simple in design and easy to operate, it being necessary only to press a button as the lens was focused.

The jungle was becoming more tangled with every passing minute. Huge forest trees were everywhere, many of them having parasitic vines wound tightly around their trunks. Strange, odd plants grew about in profusion. Bright-colored flowers were everywhere and often diverted the youths’ attention from the path.

Many varieties of butterflies, frequently beautifully marked, fluttered about. Once Joe was lucky enough to catch one with his hand and at once passed it to Mr. Holton, who was nearest him.

They had trekked for over an hour when suddenly there arose a commotion in the rear ranks of the line of carriers.

“What’s that?” burst out Bob, turning on the instant. “Sounds like something’s the matter.”

Mr. Holton ran back down the path, followed by Bob, Joe, and the latter’s father.

Then they saw the cause of the disturbance. A veritable army of tiny red ants was attacking the bare feet of the bearers and was doing the job right. There must have been tens of thousands of the little creatures, for they were crawling about in great masses.

Noko shouted something in the native language, motioning and frowning indignantly. What he said the Americans never knew.

“Look at them,” said Joe excitedly. “Isn’t there anything they can do to beat them off?”

The natives were becoming frantic with fear and discomfort. They jumped about wildly in attempts to escape from the countless menacing hordes. Despite the seriousness of the matter, Bob and Joe could not help laughing at the actions of the natives.

“This ought to be a swell scene,” laughed Bob, focusing the movie camera on the dancing mob. “And it’s all genuine, too. No acting about it.”

The filming was shortly interrupted, as the attacked bearers rushed madly up the path, apparently intent upon running from the red ants. Bob and Joe took to their heels with the rest and at last were sufficiently far from the scene to be out of danger. All were panting and perspiring after the short but tiring run.

“Are we rid of them?” inquired Bob. He had not seen a red ant since he had started running.

Noko nodded.

“They gone,” he said, stopping for a moment and facing Bob. “Heap bad. Bites hurt.”

“I shouldn’t imagine it is very pleasant to be bitten by them,” said Joe.

“The natives steer clear of them,” put in Mr. Lewis, as the cavalcade again took up the journey. “Not infrequently red ants invade villages and drive the entire population to some place of refuge. Howard and I have often come upon deserted villages that had been left for that very reason.”

Just before nightfall the party came to a wide stream of muddy water, which wound itself through the dense jungle. From all appearances the stream was very deep.

The chums saw that fifty feet farther along there was a log spanning the creek, probably placed there by natives.

“Wonder if we’ll have to cross that?” mused Joe, looking with distrust at the improvised bridge.

“Looks like it,” his friend responded. “The path quits off there, you know, and continues from the other side.”

The words were scarcely spoken when Noko stopped and turned to the naturalists.

“Cross here,” he told them, indicating the log. “Must be care. Not slip.”

“Wow!” cried Bob suddenly.

“What’s the matter?” asked Joe.

For answer, Bob pointed to the stream.

There, lurking sluggishly on a flat shelf, was a huge crocodile which looked as if it were waiting for one of the adventurers to plunge into the dark water.