“But the sun, Perry!” I urged. “How in the world can the sun shine through five hundred miles of solid crust?”

“It is not the sun of the outer world that we see here. It is another sun—an entirely different sun—that casts its eternal noonday effulgence upon the face of the inner world. Look at it now, David—if you can see it from the doorway of this hut—and you will see that it is still in the exact center of the heavens. We have been here for many hours—yet it is still noon.

“And withal it is very simple, David. The earth was once a nebulous mass. It cooled, and as it cooled it shrank. At length a thin crust of solid matter formed upon its outer surface—a sort of shell; but within it was partially molten matter and highly expanded gases. As it continued to cool, what happened? Centrifugal force hurled the particles of the nebulous center toward the crust as rapidly as they approached a solid state. You have seen the same principle practically applied in the modern cream separator. Presently there was only a small super-heated core of gaseous matter remaining within a huge vacant interior left by the contraction of the cooling gases. The equal attraction of the solid crust from all directions maintained this luminous core in the exact center of the hollow globe. What remains of it is the sun you saw today—a relatively tiny thing at the exact center of the earth. Equally to every part of this inner world it diffuses its perpetual noonday light and torrid heat.

“This inner world must have cooled sufficiently to support animal life long ages after life appeared upon the outer crust, but that the same agencies were at work here is evident from the similar forms of both animal and vegetable creation which we have already seen. Take the great beast which attacked us, for example. Unquestionably a counterpart of the Megatherium of the post-Pliocene period of the outer crust, whose fossilized skeleton has been found in South America.”

“But the grotesque inhabitants of this forest?” I urged. “Surely they have no counterpart in the earth’s history.”

“Who can tell?” he rejoined. “They may constitute the link between ape and man, all traces of which have been swallowed by the countless convulsions which have racked the outer crust, or they may be merely the result of evolution along slightly different lines—either is quite possible.”

Further speculation was interrupted by the appearance of several of our captors before the entrance of the hut. Two of them entered and dragged us forth. The perilous pathways and the surrounding trees were filled with the black ape-men, their females, and their young. There was not an ornament, a weapon, or a garment among the lot.