To men of to-day this jungle would have been impenetrable, except by the incessant use of axe or machete. But Grom and his party were Cave-Men, and had not yet forgotten all the instincts and capacities of their tree-dwelling ancestors. Sometimes, where it seemed easiest, they forced their way along the ground, or followed the trodden trail of some great jungle beast, so long as it led in the right direction. But here they had to be ceaselessly on the watch against surprise by creatures whose monstrous tracks were unlike any that they had ever seen before. Whenever possible, therefore, they preferred to journey, after the fashion of their apish ancestors, by way of the high branches and the liana bridges. Hampered as they were by their weapons, their progress by this aerial way was slow. But it was comparatively secure. And it was also comparatively cool; while down at the ground-level the steaming heat and the stinging insects were almost beyond endurance. Yet before the end of that first day's journey they learned that even in tree-tops it was necessary to be always on the watch. Once the little hairy scout, Loob, who traveled always on the outskirts of the party, was struck at suddenly by a huge black leopard, which lay ambushed in the crotch of a tree. Loob, however, who was so quick-sighted that he seemed to see things before they actually happened, leapt to a higher branch in time to escape the deadly paw. In the next instant he struck down furiously with his spear, catching his assailant between the shoulder-blades and driving the stroke home with all his strength. With a screech, the beast stiffened out, and then, somewhat slowly, collapsed. As Loob wrenched his weapon free, the great animal slumped limply from its branch. For a moment or two it hung by the fore-paws, coughing and frothing at the mouth. Then this last hold relaxed and it fell, bumping with a curious deliberation from branch to branch. It vanished through a floor of thick leafage, and struck the ground with a dull crash. It must have fallen under the very jaws of an unseen waiting monster; for there arose at once a strange, hooting roar, followed by the sound of rending flesh and cracking bone. Loob grinned over his feat, and Grom, glancing at A-ya, muttered quietly: "It is better to be up here than down there." As he spoke, and they all peered downwards, a dreadful head, with the limp body of the leopard gripped like a rat between its long jaws and dripping yellow fang, thrust itself up through the floor of leafage and stared at them with round eyes as cold and black as ice. Grom itched to shoot an arrow into one of those unwinking, devilish eyes. But arrows were too precious to be wasted.