with them to the world from which they had come.
But all such considerations were quite remote from his thoughts as he and Tar-gash were crossing a rolling, tree-dotted plain in their search for the tribe of men to which the Sagoth was guiding him. By comparison with other plains they had crossed, this one seemed strangely deserted, but the reason for this was evident in the close- cropped grass which suggested that great herds had grazed it off before moving on to new pastures. The absence of life and movement was slightly depressing and Tarzan found himself regretting the absence of even the dangers of the teeming land through which they had just come.
They were well out toward the center of the plain and could see the solid green of a great forest curving upward into the hazy distance when the attention of both was attracted by a strange, droning noise that brought them to a sudden halt. Simultaneously both turned and looked backward and up into the sky from which the sound seemed to come.
Far above and just emerging from the haze of the distance was a tiny speck. 'Quick!' exclaimed Tar-gash. 'It is a thipdar,' and motioning Tarzan to follow him he ran swiftly to concealment beneath a large tree.
'What is a thipdar?' asked Tarzan, as the two halted beneath the friendly shade.
'A thipdar,' said the Sagoth, 'is a thipdar;' nor could he describe it more fully other than to add that the thipdars were sometimes used by the Mahars either to protect them or to hunt their food.
'Is the thipdar a living thing?' demanded Tarzan.
'Yes,' replied Tar-gash. 'It lives and is very strong and very fierce.'
'Then that is not a thipdar,' said Tarzan.
'What is it then?' demanded the Sagoth.
'It is an aeroplane,' replied Tarzan.
'What is that?' inquired the Sagoth.
'It would be hard to explain it to you,' replied the ape-man. 'It is something that the men of my world build and in which they fly through the air,' and as he spoke he stepped out into the opening, where he might signal the pilot of the plane, which he was positive was the one carried by the O-220 and which, he assumed, was prosecuting a search for him.
'Come back,' exclaimed Tar-gash. 'You cannot fight a thipdar. It will swoop down and carry you off if you are out in the open.'
'It will not harm me,' said Tarzan. 'One of my friends is in it.'
'And you will be in it, too, if you do not come back under the tree,' replied Tar-gash.
As the plane approached, Tarzan ran around in a small circle to attract the pilot's attention, stopping occasionally to wave his arms, but the plane sped on above him and it was evident that its pilot had not seen him.
Until it faded from sight in the distance, Tarzan of the Apes stood upon the lonely plain, watching the ship that was bearing his comrade away from him.
The sight of the ship awakened Tarzan to a sense of his responsibility. He realized now that someone was risking his life to save him and with this thought came a determination to exert every possible effort to locate the O-220.
The passage of the plane opened many possibilities for conjecture. If it was circling, which was possible, the direction of its flight as it passed over him would have no bearing upon the direction of the O-220, and if it were not circling, then how was he to know whether it was traveling away from the ship in the beginning of its quest, or was returning to it having concluded its flight.
'That was not a thipdar,' said Tar-gash, coming from beneath the tree and standing at Tarzan's side. 'It is a creature that I have never seen before. It is larger and must be even more terrible than a thipdar. It must have been very angry, for it growled terribly all the time.'
'It is not alive,' said Tarzan. 'It is something that the men of my country build that they may fly through the air. Riding in it is one of my friends. He is looking for me.'
The Sagoth shook his head. 'I am glad he did not come down,' he said. 'He was either very angry or very hungry, otherwise he would not have growled so loudly.'
It was apparent to Tarzan that Tar-gash was entirely incapable of comprehending his explanation of the aeroplane and that he would always believe it was a huge, flying reptile; but that was of no importance—the thing that troubled Tarzan being the question of the direction in which he should now prosecute his search for the O-220, and eventually he determined to follow in the direction taken by the airship, for as this coincided with the direction in which Tar-gash assured him he would find the tribe of human beings for which they were searching, it seemed after all the wisest course to pursue.
The drone of the motor had died away in the distance when Tarzan and Tar-gash took up their interrupted journey across the plain and into broken country of low, rocky hills.
The trail, which was well marked and which Tar-gash said led through the hills, followed the windings of a shallow canyon, which was rimmed on one side by low cliffs, in the face of which there were occasional caves and crevices. The bottom of the canyon was strewn with fragments of rock of various sizes. The vegetation was sparse and there was every indication of an aridity such as Tarzan had not previously encountered since he left the O-220, and as it seemed likely that both game and water would be scarce here, the two pushed on at a brisk, swinging walk.
It was very quiet and Tarzan's ears were constantly upon the alert to catch the first sound of the hum of the motor of the returning aeroplane, when suddenly the silence was shattered by the sound of hoarse screeching which seemed to be coming from a point further up the canyon.
Tar-gash halted. 'Dyal,' he said.
Tarzan looked at the Sagoth questioningly.
'It is a Dyal,' repeated Tar-gash, 'and it is angry.'
'What is a Dyal?' asked Tarzan.
'It is a terrible bird,' replied the Sagoth; 'but its meat is good, and Tar-gash is hungry.'
That was enough. No matter how terrible the Dyal might be, it was meat and Tar-gash was hungry, and so the two beasts of prey crept warily forward, stalking their quarry. A vagrant breeze, wafting gently down the canyon, brought to the nostrils of the ape-man a strange, new scent. It was a bird scent, slightly suggestive of the scent of an ostrich, and from its volume Tarzan guessed that it might come from a very large bird, a suggestion that was borne out by the loud screeching of the creature, intermingled with which was a scratching and a scraping sound.
Tar-gash, who was in the lead and who was taking advantage of all the natural shelter afforded by the fragments of rock with which the canyon bed was strewn, came to a halt upon the lower side of a great boulder, behind which he quickly withdrew, and as Tarzan joined him he signalled the ape-man to look around the corner of the boulder.
Following the suggestion of his companion, Tarzan saw the author of the commotion that had attracted their attention. Being a savage jungle beast, he exhibited no outward sign of the astonishment he felt as he gazed upon the mighty creature that was clawing frantically at a crevice in the cliffside.
To Tarzan it was a nameless creature of another world. To Tar-gash it was simply a Dyal. Neither knew that he was looking upon a Phororhacos of the Miocene. They saw a huge creature whose crested head, larger than that of a horse, towered eight feet above the ground. Its powerful, curved beak gaped wide as it screeched in anger. It beat its short, useless wings in a frenzy of rage as it struck with its mighty three-toed talons at something just within the fissure before it. And then it was that Tarzan saw that the thing at which it struck was a spear, held by human hands—a pitifully inadequate weapon with which to attempt to ward off the attack of the mighty Dyal.
As Tarzan surveyed the creature he wondered how Tar-gash, armed only with his puny club, might hope to pit himself in successful combat against it. He saw the Sagoth creep stealthily out from behind their rocky shelter and move slowly to another closer to the Dyal and behind it, and so absorbed was the bird in its attack upon the man within the fissure that it did not notice the approach of the enemy in its rear.
The moment that Tar-gash was safely concealed behind the new shelter, Tarzan followed him and now they were within fifty feet of the great bird.
The Sagoth, grasping his club firmly by the small end arose and ran swiftly from his concealment, straight toward the giant Dyal, and Tarzan followed, fitting an arrow to his bow.
Tar-gash had covered but half the distance when the sound of his approach attracted the attention of the
