The diadem in the center of the circlet of gold upon the brow of Lakor proclaimed him a Holy Thern, while his companion, not thus adorned, was a lesser thern, though from his harness I gleaned that he had reached the Ninth Cycle, which is but one below that of the Holy Therns.

As I stood for a moment looking at the gruesome havoc Woola had wrought, there recurred to me the memory of that other occasion upon which I had masqueraded in the wig, diadem, and harness of Sator Throg, the Holy Thern whom Thuvia of Ptarth had slain, and now it occurred to me that it might prove of worth to utilize Lakor's trappings for the same purpose.

A moment later I had torn his yellow wig from his bald pate and transferred it and the circlet, as well as all his harness, to my own person.

Woola did not approve of the metamorphosis. He sniffed at me and growled ominously, but when I spoke to him and patted his huge head he at length became reconciled to the change, and at my command trotted off along the corridor in the direction we had been going when our progress had been interrupted by the therns.

We moved cautiously now, warned by the fragment of conversation I had overheard. I kept abreast of Woola that we might have the benefit of all our eyes for what might appear suddenly ahead to menace us, and well it was that we were forewarned.

At the bottom of a flight of narrow steps the corridor turned sharply back upon itself, immediately making another turn in the original direction, so that at that point it formed a perfect letter S, the top leg of which debouched suddenly into a large chamber, illy lighted, and the floor of which was completely covered by venomous snakes and loathsome reptiles.

To have attempted to cross that floor would have been to court instant death, and for a moment I was almost completely discouraged. Then it occurred to me that Thurid and Matai Shang with their party must have crossed it, and so there was a way.

Had it not been for the fortunate accident by which I overheard even so small a portion of the therns' conversation we should have blundered at least a step or two into that wriggling mass of destruction, and a single step would have been all-sufficient to have sealed our doom.

These were the only reptiles I had ever seen upon Barsoom, but I knew from their similarity to the fossilized remains of supposedly extinct species I had seen in the museums of Helium that they comprised many of the known prehistoric reptilian genera, as well as others undiscovered.

A more hideous aggregation of monsters had never before assailed my vision. It would be futile to attempt to describe them to Earth men, since substance is the only thing which they possess in common with any creature of the past or present with which you are familiar-even their venom is of an unearthly virulence that, by comparison, would make the cobra de capello seem quite as harmless as an angleworm.

As they spied me there was a concerted rush by those nearest the entrance where we stood, but a line of radium bulbs inset along the threshold of their chamber brought them to a sudden halt-evidently they dared not cross that line of light.

I had been quite sure that they would not venture beyond the room in which I had discovered them, though I had not guessed at what deterred them. The simple fact that we had found no reptiles in the corridor through which we had just come was sufficient assurance that they did not venture there.

I drew Woola out of harm's way, and then began a careful survey of as much of the Chamber of Reptiles as I could see from where I stood. As my eyes became accustomed to the dim light of its interior I gradually made out a low gallery at the far end of the apartment from which opened several exits.

Coming as close to the threshold as I dared, I followed this gallery with my eyes, discovering that it circled the room as far as I could see. Then I glanced above me along the upper edge of the entrance to which we had come, and there, to my delight, I saw an end of the gallery not a foot above my head. In an instant I had leaped to it and called Woola after me.

Here there were no reptiles-the way was clear to the opposite side of the hideous chamber-and a moment later Woola and I dropped down to safety in the corridor beyond.

Not ten minutes later we came into a vast circular apartment of white marble, the walls of which were inlaid with gold in the strange hieroglyphics of the First Born.

From the high dome of this mighty apartment a huge circular column extended to the floor, and as I watched I saw that it slowly revolved.

I had reached the base of the Temple of the Sun!

Somewhere above me lay Dejah Thoris, and with her were Phaidor, daughter of Matai Shang, and Thuvia of Ptarth. But how to reach them, now that I had found the only vulnerable spot in their mighty prison, was still a baffling riddle.

Slowly I circled the great shaft, looking for a means of ingress. Part way around I found a tiny radium flash torch, and as I examined it in mild curiosity as to its presence there in this almost inaccessible and unknown spot, I came suddenly upon the insignia of the house of Thurid jewel-inset in its metal case.

I am upon the right trail, I thought, as I slipped the bauble into the pocket-pouch which hung from my harness. Then I continued my search for the entrance, which I knew must be somewhere about; nor had I long to search, for almost immediately thereafter I came upon a small door so cunningly inlaid in the shaft's base that it might have passed unnoticed by a less keen or careful observer.

There was the door that would lead me within the prison, but where was the means to open it? No button or lock were visible. Again and again I went carefully over every square inch of its surface, but the most that I could find was a tiny pinhole a little above and to the right of the door's center-a pinhole that seemed only an accident of manufacture or an imperfection of material.

Into this minute aperture I attempted to peer, but whether it was but a fraction of an inch deep or passed completely through the door I could not tell-at least no light showed beyond it. I put my ear to it next and listened, but again my efforts brought negligible results.

During these experiments Woola had been standing at my side gazing intently at the door, and as my glance fell upon him it occurred to me to test the correctness of my hypothesis, that this portal had been the means of ingress to the temple used by Thurid, the black dator, and Matai Shang, Father of Therns.

Turning away abruptly, I called to him to follow me. For a moment he hesitated, and then leaped after me, whining and tugging at my harness to draw me back. I walked on, however, some distance from the door before I let him have his way, that I might see precisely what he would do. Then I permitted him to lead me wherever he would.

Straight back to that baffling portal he dragged me, again taking up his position facing the blank stone, gazing straight at its shining surface. For an hour I worked to solve the mystery of the combination that would open the way before me.

Carefully I recalled every circumstance of my pursuit of Thurid, and my conclusion was identical with my original belief-that Thurid had come this way without other assistance than his own knowledge and passed through the door that barred my progress, unaided from within. But how had he accomplished it?

I recalled the incident of the Chamber of Mystery in the Golden Cliffs that time I had freed Thuvia of Ptarth from the dungeon of the therns, and she had taken a slender, needle-like key from the keyring of her dead jailer to open the door leading back into the Chamber of Mystery where Tars Tarkas fought for his life with the great banths. Such a tiny keyhole as now defied me had opened the way to the intricate lock in that other door.