At his request she sang again as they continued their way along the winding tunnel, which was now lighted by occasional bulbs which appeared to be similar to the radium bulbs with which she was familiar and which were common to all the nations of Barsoom, insofar as she knew, having been perfected at so remote a period that their very origin was lost in antiquity.  They consist, usually, of a hemispherical bowl of heavy glass in which is packed a compound containing what, according to John Carter, must be radium.  The bowl is then cemented into a metal plate with a heavily insulated back and the whole affair set in the masonry of wall or ceiling as desired, where it gives off light of greater or less intensity, according to the composition of the filling material, for an almost incalculable period of time.

As they proceeded they met a greater number of the inhabitants of this underground world, and the girl noted that among many of these the metal and harness were more ornate than had been those of the workers in the fields above.  The heads and bodies, however, were similar, even identical, she thought.  No one offered her harm and she was now experiencing a feeling of relief almost akin to happiness, when her guide turned suddenly into an opening on the right side of the tunnel and she found herself in a large, well lighted chamber.

CHAPTER V

THE PERFECT BRAIN

The song that had been upon her lips as she entered died there—­frozen by the sight of horror that met her eyes.  In the center of the chamber a headless body lay upon the floor—­a body that had been partially devoured—­while over and upon it crawled a half a dozen heads upon their short, spider legs, and they tore at the flesh of the woman with their chelae and carried the bits to their awful mouths.  They were eating human flesh—­eating it raw!

Tara of Helium gasped in horror and turning away covered her eyes with her palms.

“Come!” said her captor.  “What is the matter?”

“They are eating the flesh of the woman,” she whispered in tones of horror.

“Why not?” he inquired.  “Did you suppose that we kept the rykor for labor alone?  Ah, no.  They are delicious when kept and fattened.  Fortunate, too, are those that are bred for food, since they are never called upon to do aught but eat.”

“It is hideous!” she cried.

He looked at her steadily for a moment, but whether in surprise, in anger, or in pity his expressionless face did not reveal.  Then he led her on across the room past the frightful thing, from which she turned away her eyes.  Lying about the floor near the walls were half a dozen headless bodies in harness.  These she guessed had been abandoned temporarily by the feasting heads until they again required their services.  In the walls of this room there were many of the small, round openings she had noticed in various parts of the tunnels, the purpose of which she could not guess.