A string of a dozen huge, spider-shaped robots of a totally new design were charging down at them, running swiftly along the sides of the rings of the Tube, through the tunnel. They carried no weapons, but the three soon saw why — from the ugly snouts of the egg-shaped bodies of the creatures protruded a black cone. A blinding flash came from the cone of the first of the new arrivals; the aim was bad, for overhead a section of the cement roof flared ghastly white and commenced to drip.

(Spider robot guards from 'Mars-Tube' by S.D. Gottesman)

Annamarie had her useless paralyzer out and firing before she realized its uselessness against metal beings with no nervous systems to paralyze. She hurled it at the nearest of the new robots in a highly futile gesture of rage.

But the two men had their more potent weapons out and firing, and were taking a toll of the spider-like monstrosities. Three or four of them were down, partially blocking the path of the oncoming others; another was missing all its metal legs along one side of its body, and two of the remainder showed evidence of the accuracy of the Earthmen’s fire.

But the odds were still extreme, and the built-in blasters of the robots were coming uncomfortably close.

Stanton saw that, and shifted his tactics. Holstering his heavy blaster, he grabbed Annamarie and shoved her into the Mars-Tube, crying to Josey to follow. Josey came slowly after them, turning to fire again and again at the robots, but with little effect. A quick look at the charge-dial on the butt of his heat-gun showed why; the power was almost exhausted.

He shouted as much to Stanton. “I figured that would be happening — now we run!” Stanton cried back, and the three sped along the Mars-Tube, leaping the hoops as they came to them.