It was useless to interfere. The horrified aviator knew it and watched with compassionate eyes while the condemned soldiers were ranged in a single, white faced line. They remained silent now, seeming to have found courage now that hope was dead. Upon brief command from a subaltern, the guards wheeled about and retreated perhaps twenty yards down the passage. There they halted, glittering eyes peering through the slots in their helmets to fix themselves upon the rigid prisoners who stood numbly resigned to death. With surprising speed each member of that weird firing squad detached a brazen grenade from his belt, then threw back his arm in exactly the same attitude as a bomb-throwing doughboy. Then there came a short, sharp command and some fifteen or twenty grenades bobbed through the air to crash on the stones at the feet of the victims. * * * * * His head swimming with repulsion at the slaughter, Nelson beheld a curious sight. It seemed that from the broken grenades appeared a yellowish green vapor which sprung _of its own accord_ upon the silent upright rank! In an instant it settled like falling snow upon the doomed soldiers. For a breathless fraction of a second they stood, eyes wide with horror, then collapsed, kicking and struggling as men do under the influence of gas. "Horrible!" gasped Nelson. "What was in the bombs?" "A vapor," explained Hero Giles shortly. "A fungus vapor which, falling upon exposed flesh, instantly invades the blood and multiplies by millions. See--" He pointed to the nearest dead man and Nelson, with starting eyes, watched a yellowish growth commencing to sprout from the dead man's nostrils. Swiftly the poisonous mould threw out tiny branches, spreading with astounding rapidity over the skin until, in less than a minute after the grenades had exploded, the whole tumbled heap of dead were covered with a horrible yellow green fungus growth. "Thou seest?" Hero Giles demanded. "Powerful, is it not? It is against the fungus vapor we wear this body armor made from the skin of a small lizard which inhabits our mountains." Shocked and appalled, Nelson watched the retreat of the solemn, silent execution party. Other soldiers fell to unconcernedly stripping their fallen comrades of equipment; then, to Nelson's horrified surprise, two hideous allosauri reappeared, shepherded by some six or eight keepers. Once the horrible creatures were released, they pounced upon the dead and, snarling horribly, commenced to rend and devour the corpses. * * * * * Too shaken to comment or to make the protest he knew to be futile, Nelson followed the stalwart English-speaking officer into a bronze door set in the cavern wall and up a short flight of stairs into what appeared to be a guard room, where food and wine were immediately set before the famished aviator.