They broke open the door into Wimpolo's private room, and Don showed them the secret exit. The traffic sphere was gone. Only a blank, empty hole faced them.
CHAPTER II
To Selketh
DON, the Professor, several Martians and the animals raced along the traffic tunnel. The gradient was steep and the tile-covered floor slippery. They reached the general system of traffic tunnels with its many forks. An alarm had been given, and many spheres were hunting for the Princess.
Before long word came that the Princess' sphere had been found. It had been abandoned in the tunnels close to a jagged hole in a wail. Looking into the hole they saw a rough, rocky cavern with floor so steep and so littered with loose stones that it would have been almost impossible for a man of Mars to climb down it. The ape-men and the little Earthlings, however, had little difficulty. To the snake and the zekolo, of course, the jagged, slipping rocks were their natural home.
Don and Winterton threw over their shoulders luminous capes that filled the cave with blue light. Switches on their breasts turned the light on and off. On their heads were searchlights. Cautiously they picked their way over loose stones.
After the polished perfection of the tiled traffic tunnels it seemed strange to be in the rugged grandeur of these enormous natural holes. They performed climbing feats that looked absolutely impossible, and that would have been impossible on Earth.
"Are you sure we are going the right way?" Winterton panted. "Remember that the ape-men were carrying Princess Wimpolo. She is a terrific weight. Could even they, with their enormous strength, have carried a Martian girl down these treacherous rocks?"
"They used a rope," Don answered. "See the marks of the rope in the dust and slime. And here is the imprint of the Princess' shoe in the moss of a crevice."
They were certainly on the right trail, but it was slow going, A loose stone rattled past them. Don looked up, lifting his deathray box to his shoulder, ready to reply to any attack from above. But it was not necessary. A group of Wimpolo's guards were following them, using snakes as natural ropes.
Don blinked. He felt that he would never accustom himself to the innumerable uses the Martians made of their uncanny pets. He spoke the word of command to the snake and the zekolo.
At once Winterton and he were picked up and carried forward on their journey with great speed. They sat on the back of the zekolo, the natural configurations of its shell making a good seat, and one octopus-like arm coiled round them for added security. Like a spider the zekolo raced down the rocks, the snake squirming sinuously after.
The crack they were following opened into the roof of a large cavern. Three hundred feet below was the floor. There was no way of climbing down, even for the animals.
"We shall have to wait until long ropes can be brought," Don thought.
The zekolo, however, did not hesitate. Still holding them on its back it hung by two of its arms into the vast hole. Don was amazed to see the arms stretch like elastic rubber. Another pincer let go. The zekolo hung by one arm only. That last arm stretched beyond belief, until the creature hung like a spider on
