AT Mr. Lewis’s words, Bob and Joe stood mouth agape. They stared at the naturalist for several seconds in sheer surprise. Then they were overcome with joy.

“You’re not kidding, are you?” cried Bob, finally managing to utter the words.

“Not a bit,” said Mr. Lewis. “In fact, as soon as we put the proposed expedition before the museum heads, they were captivated by the idea. Said they greatly desired new specimens from Africa, and if we could get them it would be perfectly all right. They’re going to fix everything up for us.”

“Man alive!” cried Joe. “It’ll be a wonderful opportunity. Of course,” he went on, “there’s a chance that Bob and I may go with you, isn’t there?”

“Let’s not discuss that matter just now,” Mr. Holton said. “Of course, you know there are others besides Ben and I who have a say. But we’ll give it a thought, boys.”

“And now we’re off for the museum,” announced Joe’s father.

“Aren’t you going to stay for the circus performance?” asked Bob in some surprise.

“Really we haven’t the time, Son,” answered Mr. Holton. “With this African mission on our hands we’ll have to do some hustling. We just came down here to take a look at this big gorilla. Well, we’ll see you later, boys. Be good.”

With this the naturalists took their leave, while their sons glanced at each other.

“A trip to Africa!” cried Bob joyfully. He picked his chum up and danced around with him in happiness.

“Better cut this stuff out,” advised Joe. “As soon as you calm down a little you’ll lose some of that excess strength—and then maybe you’ll let me drop.”

Bob released his chum and stopped his dance of joy, as he noticed that people were beginning to trickle into the tent. But his face retained its look of exultation.

The boys still had some time before the performance was to start and amused themselves by looking about the grounds.

Later, in the main tent, the chums enjoyed the show immensely. Perhaps, however, as Bob said, they could have enjoyed it still more had they not been so absorbed in the coming expedition to Africa.

“We’ll just have to go with you,” pleaded Joe when the two had gone to the museum to join their fathers. “Why, you know it wouldn’t be complete without us.”

“Perhaps not,” came from Mr. Lewis, “although we hadn’t thought of it in that light.”

“You know we can take care of ourselves,” Bob defended himself and his friend. “And we’re both good shots. Remember the time when we potted off those gazelles on the Sahara?”

“Sure thing,” said Mr. Holton, nodding. “And you’ve brought us many other valuable specimens, too. But to tell the truth, boys, we’re not anxious for you to go with us this time. You see, we have orders to shoot some very dangerous game. Lions, rhinos, buffaloes, and the like.”

“Better and better!” exclaimed Bob, his eyes brightening still more. “Just where do you intend to explore?”

“In the middle of the Congo Basin,” returned his father. “Our ship will take us to Mombasa. From there we’ll take a train——”

“Train?” interrupted Joe, greatly puzzled. “Do they have trains in the heart of Africa?”

“Not exactly in the heart of Africa,” Mr. Holton answered. “But there is a railroad running from Mombasa to Lake Victoria. As I was saying, we’ll board a train and go as far as it will carry us. Then we’ll have to organize a safari.”

“Exactly what is that?” inquired Bob. “I’ve often heard the term, but never was quite clear about its meaning.”

“Safari means practically the same as expedition,” Mr. Lewis explained. “It is an Arabic term that is used quite frequently in Africa. A safari is composed of the explorers, the native police, bearers, and the like. It may vary from just a few people to several hundred. In our case, however, we won’t need a large number of carriers. If we do need more, we can engage them in the jungle to carry our specimens back to the coast. The money that they charge is only a very meager amount.”

“Just what animals do you want especially to bag?” asked Bob. “Of course, you want lions, don’t you?”

“Lions, yes,” returned his father. “And other dangerous game. But we also want to investigate reports of several strange animals that are at present generally unknown. Whether we’ll find them we have yet to see—if nothing with sharp teeth stops us,” he added with a smile.

“Nothing will,” said Bob conclusively. “But just what is the most dangerous game of Africa?”

The naturalists glanced at each other.

“Better not ask that question, or you’ll start a heated debate,” laughed Mr. Lewis. “Howard and I are very much in disagreement about it.”

“Why?” persisted Bob.

“You father is inclined to place the rhino as the most dangerous, while I would say the buffalo comes first. But to settle the argument, both are bad enough when they’re after you.”

“But what about the lion?” demanded Joe. “Isn’t he dangerous?”

“Very much so,” answered Mr. Holton. “However, he isn’t considered anything like the two animals that Ben mentioned. That doesn’t mean, though, that it’s advisable to go out and pick a quarrel with the king of beasts,” he added whimsically.

“Let me get a map of Africa, boys,” said Joe’s father, rising. “Then we can see exactly where we intend to explore.”

He went over to a bookcase in a corner of the office, returning a moment later with a large cloth map of the Dark Continent.

But at that moment the telephone rang, and Mr. Holton stepped over to answer it.

A few seconds later he uttered a cry of surprise. His brow wrinkled, and his face took on a look of dismay.

“Why, it can’t be!” he cried excitedly. “Stolen! Gone!”

At the scientist’s ominous words Mr. Lewis looked up in wonder. The boys too listened intently. They were growing impatient when Mr. Holton again spoke.

“Stay where you are,” he directed the person at the other end of the line. “We’ll meet you at once.”

With these words he hung up and turned to the others.

“Those specimens that we bought from Thompson in Chicago—they’ve been stolen!” he explained in a worried voice.

“What!” cried Mr. Lewis angrily. “Do you mean that?”

“Every word of it,” was the response. “We must go at once. If we get there in time we may be able to find the culprit.”

The naturalists grabbed their hats and dashed out of the office and through the building to the outside. Bob and Joe followed them, although without knowing where they were going.

All got in Mr. Holton’s car, which was parked near the museum.

“Now we must hurry,” Bob’s father said, starting the engine. “The robbery took place but a short time ago, and there is a chance that we can overtake the thief.”

“Weren’t the specimens covered by insurance?” inquired Joe.

Mr. Lewis shook his head.

“But even if they were,” the naturalist said, “this is a case where insurance could not replace the loss. Such rare birds and animals as those can be procured only with great patience and labor under a hot sun. You fellows know what a job it is to stalk wild animals. And it isn’t likely that we’ll find others like them in Africa.”

With a roar and a rush the automobile shot out into the street and was soon caught in the midst of heavy traffic. Although Mr. Holton greatly desired to travel at a rapid pace, he found it impossible to do so.

“Where are we going?” asked Bob. “We’ve been so interested in the robbery itself that Joe and I haven’t thought to inquire where the specimens were when they were stolen.”

“In a railroad freight yard,” returned his father. “The museum sent one of its trucks after them as soon as they arrived. I don’t have the details about the happening, but the box of specimens must have been stolen while the truck driver was not around. Apparently the robber was familiar with the contents of the box. Perhaps he had carefully planned the theft in advance. Heard us talking about the specimens, maybe.”

“Well, he won’t get away with it if we can help it,” said Bob with determination. “We’ll catch him somehow.”

“Let’s hope you’re right,” Mr. Holton said gravely as he pushed the accelerator still nearer to the floorboard.

After what seemed like hours they pulled up at their destination—a railroad freight yard.

Inside the main building they found the truck driver awaiting them, on his face a look of deep anxiety. His features relaxed a little as he caught sight of the two naturalists.

Mr. Lewis at once demanded an account of what had happened and urged the man to relate every detail.

The driver explained that he had loaded the box of specimens on the truck and, not doubting that they would be safe, had gone into the freight office for a brief stay. When he returned to the truck, he found, to his astonishment, that the box was gone. It was only then that he fully realized what had happened.

“If I’d only seen the guy that took them we might catch him,” he finished.

The scientists were greatly vexed at the driver for not taking better care of such valuable goods, but they managed to keep their temper.

They walked out to the truck to discover, if possible, the thief’s means of escape.

“He probably had another automobile waiting to take those specimens,” remarked Joe. “Maybe we can find its tracks. The ground here is soft after the recent rain.”

A careful survey of the roadway was not in vain, for soon they saw wide tracks of automobile tires which possessed a very odd tread.

“Here’s a clue, anyway,” said Mr. Holton. “Every little thing counts, you know.”

Bob had gone a piece toward the street. Now he came running toward the others.

“Look!” he cried excitedly. “I’ve found something. Let’s see what it is.”