"It's going to be like this from now on," he remarked to the shaken Gunga. "All these things wouldn't bother us as long as the machinery kept the building dry and cool. They couldn't live in here. But it's getting damp and hot. Look at the moisture condensing on the ceiling!" Gunga gave a guttural cry of despair. "It knows, Boss; look!" Through one of the round, heavily framed ports it could be seen, the lower part of its large, shapeless body half-floating in the lashing water that covered their rocky shelf to a depth of several feet, the upper part spectral and gray. It was a giant amoeba, fully six feet in diameter in its present spheroid form, but capable of assuming any shape that would be useful. It had an envelope of tough, transparent matter, and was filled with a fluid that was now cloudy and then clear. Near the center there was a mass of darker matter, and this was undoubtedly the seat of its intelligence. The Earth man recoiled in horror! A single cell with a brain! It was unthinkable. It was a biological nightmare. Never before had he seen one--had, in fact, dismissed the stories of the Inranian natives as a bit of primitive superstition, had laughed at these gentle, stupid amphibians with whom he traded when they, in their imperfect language, tried to tell him of it. They had called it the Ul-lul. Well, let it be so. It was an amoeba, and it was watching him. It floated in the downpour and watched him. With what? It had no eyes. No matter, it was watching him. And then it suddenly flowed outward until it became a disc rocking on the waves. Again its fluid form changed, and by a series of elongations and contractions it flowed through the water at an incredible speed. It came straight for the window, struck the thick, unbreakable glass with a shock that could be felt by the men inside. It flowed over the glass and over the building. It was trying to eat them, building and all! The part of its body over the port became so thin that it was almost invisible. At last, its absolute limit reached, it dropped away, baffled, vanishing amid the glare of the lightning and the frothing waters like the shadows of a nightmare. * * * * * The heat was intolerable and the air was bad. "Haw, we have to open vent'lator, Boss!" gasped the Martian. Forepaugh nodded grimly. It wouldn't do to smother either. Though to open the ventilator would be to invite another invasion by the black mold, not to mention the amoebae and other fabulous monsters that had up to now been kept at a safe distance by the repeller zone, a simple adaptation of a very old discovery. A zone of mechanical vibrations, of a frequency of 500,000 cycles per second, was created by a large quartz crystal in the water, which was electrically operated. Without power, the protective zone had vanished. "We watch?" asked Gunga. "You bet we watch. Every minute of the 'day' and 'night.'"