upon its square of cloth.

"We--we had heard that this thing existed," Naida said presently, voice
hushed, "but no one except the holy men of our race has ever beheld
it."

"But, what is it?" Kirby asked. "Whence came it?"

However, when Naida would have answered, he interrupted.

"But wait! Tell me as we go. We could stay here for the rest of our
lives without much trouble, but we've got to cover the rest of the tower
and get back to the others."

* * * * *

It was after they had closed the door to the treasure room that Naida
told him the story.

"There is not so much to tell," she began. "The diamond itself is so
gorgeous that it is hard to talk about. But here is the story. A great
many ages ago one of the Ducas of our race found the diamond, decided to
carve it into a perfect likeness of the head of the Serpent God. All of
the craftsmen of the race helped him and when they were done, they took
their image to Quetzalcoatl himself, and showed him what they had done.

"Quetzalcoatl was pleased. So pleased, that he promised all of the wise
men that he would cease to prey upon them as he had in the past, and
henceforward would take his toll of sacrifice from the ape-men alone.
Them he hated and would continue to hate because they worshipped not him
but Xlotli.

"And so it came about," Naida went on slowly, looking up at Kirby as
they still mounted wide steps to the upper reaches of the tower, "that
our people gained immunity from a God which had always before harmed and
destroyed them. Our race presently began to build this castle here on
the high plateau, and Quetzalcoatl kept his compact with them. He still
comes out of his chasm at intervals and preys upon the ape-men, but no
one of our race has seen him for thousands of years, and he has always
let us alone. And there is the whole myth and explanation of why the
great diamond is revered among us as a holy of holies."

* * * * *

They had mounted to a new door which Kirby guessed might give entrance
to the Duca's living quarters. But he was in no mood to open it at
once.

"Wait a minute," he said as they all paused. "You say that, although
none of your race has seen Quetzalcoatl since the diamond head was
carved, he still comes out of his chasm and makes trouble for the
ape-men. Just what does that mean?"

"Why--" Naida looked at him wonderingly. "I mean what I have said. The
Serpent comes