o races had no thought in common in the measure of time.

"One-half time of rotation of Great Planet upon axis?" flashed from
Czuv's brain, and "About five hours," King's mind flashed back.

"It will be about five hours before any steps can be taken, so that I
feel justified in using a brief period for explanation. In the evolution
of the various forms of life upon Callisto, two genera developed
intelligence far ahead of all others. One genus was the human, as you
and I; the other the hexan. This creature, happily unknown to you of the
planets nearer our common sun, is the product of an entirely different
evolution. It is a six-limbed animal, with a brain equal to our own--one
perhaps in some ways superior to our own. They have nothing in common
with humanity, however; they have few of our traits and fewer of our
mental processes. Even we who have fought them so long can scarcely
comprehend the chambers of horror that are their minds. Even were I able
to paint a sufficiently vivid picture with words, you of Earth could not
begin to understand their utter ruthlessness and inhumanity, even among
themselves. You would believe that I was lying, or that my viewpoint was
warped. I can say only that I hope most sincerely that none of you will
ever get better acquainted with them."

* * * * *

"Ages ago, then, the human and the hexan developed upon all four of the
major satellites of the Great Planet, which you know as Jupiter, and
upon the north polar region of Jupiter itself. By what means the two
races came into being upon worlds so widely separated in space we know
not--we only know it to be the fact. Human life, however, could not long
endure upon Jupiter. The various human races, after many attempts to
meet conditions of life there by variations in type fell before the
hexans; who, although very small in size upon the planet, thrived there
amazingly. Upon the three outer satellites humanity triumphed, and many
hundreds of cycles ago the hexans of those satellites were wiped out,
save for an occasional tribe of savages of low intelligence who lived in
various undesirable portions of the three worlds. For ages then there
was peace upon Callisto. Here is the picture at that time--upon Jupiter
the hexans; upon Io hexans and humans, waging a ceaseless and relentless
war of mutual extermination; upon the three outer satellites humanity in
undisturbed and unthreatened peace. Five worlds, each ign