"You're witnessing the start of the Polar Cap's receding," Conley explained with a wry smile. "It does that twice a year, you know, getting smaller to about half its present size. "Receding!" Jim exclaimed. "The damn stuff's expanding, you mean." "It only looks that way. This is just the preliminary. Soon the extreme edges will vanish away and then the entire Cap will begin receding, for some strange reason. When that starts to happen, too bad for any man caught up here. Frankly, Jim, I should say that, if this continues tomorrow, we ought to head back." That struck an ominous note in Jim's heart, but he said nothing. To return now would mean they must wait several months before making another attempt. It was while helping to unroll the wide fabricoid mats that Jim felt the sharp, biting pain just above his knee. He ignored it at first. Then it came again, and he looked down. He saw a pale blue, tubular thing about four inches long. It had bitten through his clothing and into his flesh above the knee. Quiescent now, it clung there, and its transparent bluish tint was taking on a crimson flush as it fed upon his blood. * * * * * With a loathing horror Jim reached down and pulled the thing from him. It did not come away easily. He flung it to the ice and tried to crush it with his heel. It seemed amazingly rubbery, resilient, as it darted away from under his foot. Then he saw that others had attached to his fabricoid leggings, and were inching their way upward. Desperately he tried to brush them off, but they clung tenaciously. Another one bit through his trouser leg and into the flesh. It was cold and loathesome to the touch, but he tore it away with his fingers. Then he staggered back, as he saw that the ice was swarming with the things. "Your acid tube, man, use it!" he heard Conley cry. "That's all that'll stop 'em!" Already the men were up-ending the sleds, using them as a barricade from behind which they swept the ice with a thin misty spray. Not wishing to chance that acid on his own person, Jim tore the things from his legs one at a time and flung them out into the spray. They writhed and shrivelled and curled upon themselves, lifeless and blackened. Others were coming up from the crevices now. The ice was a thick, bluish writhing mass of them. Jim added his spray to the others, sweeping it low across the ice. The acid misted and clung there close to the surface, until gradually the greater mass of the bluish things retreated back into the depths. Kaarji opened a pouch he carried always with him, took out some _tsith_ stems and placed them in his mouth. He arose and stood gazing out to the north. Jim watched him. "Whew!" Conley gasped, wiping beads of cold perspiration from his brow. "Just in time! Let those things once get a foothold up here and there's no stopping them. I guess we've settled for most of them, though, they won't come again."