It became intensely cold. Breathing was difficult. The girl, Phaidor, and the black pirate kept their eyes glued upon me. At length the girl spoke.

"Unconsciousness comes quickly at this altitude," she said quietly. "Unless you are inviting death for us all you had best drop, and that quickly."

There was no fear in her voice. It was as one might say: "You had better carry an umbrella. It is going to rain."

I dropped the vessel quickly to a lower level. Nor was I a moment too soon. The girl had swooned.

The black, too, was unconscious, while I, myself, retained my senses, I think, only by sheer will. The one on whom all responsibility rests is apt to endure the most.

We were swinging along low above the foothills of the Otz. It was comparatively warm and there was plenty of air for our starved lungs, so I was not surprised to see the black open his eyes, and a moment later the girl also.

"It was a close call," she said.

"It has taught me two things though," I replied.

"What?"

"That even Phaidor, daughter of the Master of Life and Death, is mortal," I said smiling.

"There is immortality only in Issus," she replied. "And Issus is for the race of therns alone. Thus am I immortal."

I caught a fleeting grin passing across the features of the black as he heard her words. I did not then understand why he smiled. Later I was to learn, and she, too, in a most horrible manner.

"If the other thing you have just learned," she continued, "has led to as erroneous deductions as the first you are little richer in knowledge than you were before."

"The other," I replied, "is that our dusky friend here does not hail from the nearer moon-he was like to have died at a few thousand feet above Barsoom. Had we continued the five thousand miles that lie between Thuria and the planet he would have been but the frozen memory of a man."

Phaidor looked at the black in evident astonishment.

"If you are not of Thuria, then where?" she asked.

He shrugged his shoulders and turned his eyes elsewhere, but did not reply.

The girl stamped her little foot in a peremptory manner.

"The daughter of Matai Shang is not accustomed to having her queries remain unanswered," she said. "One of the lesser breed should feel honoured that a member of the holy race that was born to inherit life eternal should deign even to notice him."

Again the black smiled that wicked, knowing smile.

"Xodar, Dator of the First Born of Barsoom, is accustomed to give commands, not to receive them," replied the black pirate. Then, turning to me, "What are your intentions concerning me?"

"I intend taking you both back to Helium," I said. "No harm will come to you. You will find the red men of Helium a kindly and magnanimous race, but if they listen to me there will be no more voluntary pilgrimages down the river Iss, and the impossible belief that they have cherished for ages will be shattered into a thousand pieces."

"Are you of Helium?" he asked.

"I am a Prince of the House of Tardos Mors, Jeddak of Helium," I replied, "but I am not of Barsoom. I am of another world."

Xodar looked at me intently for a few moments.

"I can well believe that you are not of Barsoom," he said at length. "None of this world could have bested eight of the First Born single-handed. But how is it that you wear the golden hair and the jewelled circlet of a Holy Thern?" He emphasized the word holy with a touch of irony.

"I had forgotten them," I said. "They are the spoils of conquest," and with a sweep of my hand I removed the disguise from my head.

When the black's eyes fell on my close-cropped black hair they opened in astonishment. Evidently he had looked for the bald pate of a thern.

"You are indeed of another world," he said, a touch of awe in his voice. "With the skin of a thern, the black hair of a First Born and the muscles of a dozen Dators it was no disgrace even for Xodar to acknowledge your supremacy. A thing he could never do were you a Barsoomian," he added.

"You are travelling several laps ahead of me, my friend," I interrupted. "I glean that your name is Xodar, but whom, pray, are the First Born, and what a Dator, and why, if you were conquered by a Barsoomian, could you not acknowledge it?"

"The First Born of Barsoom," he explained, "are the race of black men of which I am a Dator, or, as the lesser Barsoomians would say, Prince. My race is the oldest on the planet. We trace our lineage, unbroken, direct to the Tree of Life which flourished in the centre of the Valley Dor twenty-three million years ago.

"For countless ages the fruit of this tree underwent the gradual changes of evolution, passing by degrees from true plant life to a combination of plant and animal. In the first stages the fruit of the tree possessed only the power of independent muscular action, while the stem remained attached to the parent plant; later a brain developed in the fruit, so that hanging there by their long stems they thought and moved as individuals.

"Then, with the development of perceptions came a comparison of them; judgments were reached and compared, and thus reason and the power to reason were born upon Barsoom.

"Ages passed. Many forms of life came and went upon the Tree of Life, but still all were attached to the parent plant by stems of varying lengths. At length the fruit tree consisted in tiny plant men, such as we now see reproduced in such huge dimensions in the Valley Dor, but still hanging to the limbs and branches of the tree by the stems which grew from the tops of their heads.

"The buds from which the plant men blossomed resembled large nuts about a foot in diameter, divided by double partition walls into four sections. In one section grew the plant man, in another a sixteen-legged worm, in the third the progenitor of the white ape and in the fourth the primaeval black man of Barsoom.

"When the bud burst the plant man remained dangling at the end of his stem, but the three other sections fell to the ground, where the efforts of their imprisoned occupants to escape sent them hopping about in all directions.

"Thus as time went on, all Barsoom was covered with these imprisoned creatures. For countless ages they lived their long lives within their hard shells, hopping and skipping about the broad planet; falling into rivers, lakes, and seas, to be still further spread about the surface of the new world.

"Countless billions died before the first black man broke through his prison walls into the light of day. Prompted by curiosity, he broke open other shells and the peopling of Barsoom commenced.

"The pure strain of the blood of this first black man has remained untainted by admixture with other creatures in the race of which I am a member; but from the sixteen-legged worm, the first ape and renegade black man has sprung every other form of animal life upon Barsoom.

"The therns," and he smiled maliciously as he spoke, "are but the result of ages of evolution from the pure white ape of antiquity. They are a lower order still. There is but one race of true and immortal humans on Barsoom. It is the race of black men.

"The Tree of Life is dead, but before it died the plant men learned to detach themselves from it and roam the face of Barsoom with the other children of the First Parent.

"Now their bisexuality permits them to reproduce themselves after the manner of true plants, but otherwise they have progressed but little in all the ages of their existence. Their actions and movements are largely matters of instinct and not guided to any great extent by reason, since the brain of a plant man is but a trifle larger than the end of your smallest finger. They live upon vegetation and the blood of animals, and their brain is just large enough to direct their movements in the direction of food, and to translate the food sensations which are carried to it from their eyes and ears. They have no sense of self-preservation and so are entirely without fear in the face of danger. That is why they are such terrible antagonists in combat."