isn’t the chief aim of the expedition, is it?”

“No. It is being sent out by the division of ethnology at the museum in Washington. The scientists in that field have in mind mainly to study the ruins of the vanished Inca civilization. Those Indians, you know, that built so many marvelous works of architecture. That’s about as much as I know about them, though,” he laughed. “My line runs straight through the field of natural history and zoölogy, and incidentally anatomy, histology, taxonomy, embryology, ecology——”

“That’s enough!” interrupted Bob, smiling sheepishly. “You don’t expect Joe and me to be acquainted with all those subjects, do you? We’re pretty good shots, but as scientists we’re as yet a complete flop.”

A general laugh ensued, after which the naturalist again pointed to the map.

“We are to explore the region northwest of Lake Titicaca,” he continued. “I understand there are some very high peaks in this range, all the way from ten to twenty thousand feet in altitude.”

“These Incas,” started Joe, “when did they live? It hasn’t been so very long ago, has it?”

“Not as time is usually thought of. The sixteenth century witnessed their downfall. This was at the time of the Spanish South American explorations, you know.”

“Those Spaniards sure saw something unusual and unexpected,” remarked Bob. “This mountainous region was chock-full of architectural wonders, all built by the Incas.”

“Something tells me we’ll see sights, all right,” said Joe. “It will be good to get away from home again—into the unknown, I mean. And that reminds me. Would it be possible for you to lend us enough money to get back to Washington?”

“Why—of course. How much do you need?”

“Fifty dollars will pull us through. Perhaps we can get along on less than that,” was the answer from Bob.

“All right. I’ll see that you get it. But wait! I expect to go day after tomorrow with a friend, who is driving East on business. There will be plenty of room for two more. You fellows don’t have to get home at once, do you?”

“No, we don’t have to,” returned Joe. “We——”

“Suppose you be my guests until then. I’ll be only too glad to have you. In the meantime we can be discussing the coming expedition.”

“We’d sort of hate to do that,” Bob said. “It will mean a lot of trouble to you.”

“Forget it! I’ll be only too glad to have you.”

“Well, all right, if you——” Joe began.

“We’ll call it settled,” Mr. Wallace said. “And now, since my day is practically over, we may as well go to the house. That is, if you’re ready.”

“We’re ready any time,” Bob told him.

The three went outside, to a place where the naturalist’s automobile was parked. All got inside and drove through the city till they came to a beautiful suburb.

“Here’s my place,” said Mr. Wallace, pointing to a large house of rather costly design.

Inside, the youths were introduced to Mrs. Wallace, who made them feel perfectly at home.

“I hate to see Mr. Wallace leave on an expedition,” she said, “but I can appreciate his interest in science. In fact, I have often wished I could accompany him. Be a sort of Mrs. Martin Johnson, you know.”

“I wish our mothers were like that,” laughed Bob. “If they were, perhaps Joe and I wouldn’t have so much difficulty in getting their consent to go with our dads.”

A bountiful dinner was soon served, Bob and Joe eating heartily.

“And now I have a surprise for you,” Mr. Wallace said, when the meal was over. “It is something I know we all will enjoy, especially in view of what is to come.”

The young men looked inquiring.