“Quick!” cried Bob, his voice cool but determined. “Fire at them before they get us!”

A moment later he took careful aim and pulled the trigger.

His rifle cracked, and the foremost camel went down, sending its rider sprawling over the ground.

Bang! came the sound of Mr. Lewis’s gun, and another camel fell.

The eight Arabs who were still mounted wheeled about and galloped back hurriedly. As quickly as possible they formed a wide line, one beside the other, until it stretched several rods.

“They’re going to charge!” observed Dr. Kirshner. “Have your rifles in position, and make every shot count.”

When the bandits were confident of their formation, their leader gave the command, and bending low over their camels, they dashed with all speed toward the explorers.

Shots rang out from the Arabs’ pistols, but they were too unsteady to cause any damage.

The explorers’ rifles spoke out, and those of Bob and the naturalists found their marks.