"But what the devil are they?" Jim asked. "And how can they subsist in this barren country?" "It's not so barren. Far below the ice are green growing things, at least this far south there is. Those blue tube-things ride down with the ice twice a year, feed, and then migrate back to the north. "Vegetarians, eh?" Jim grunted. "Then what were those two chewing on me for?" "Blood's something comparatively new to them, and it seems to drive them wild. They can sense it for amazing distances. They come flocking beneath the ice to wherever anyone stops. There's a story of an Earthman who was lost up here once, and--Well, never mind. Anyway we'll take turns on guard tonight." * * * * * Jim slept fitfully. There were fragmentary nightmares of the ice opening to spew hordes of bluish tube creatures up at him. He was glad when Kaarji awakened him for his turn at guard. But Kaarji did not return to sleep either. He seemed restless and brooding. He sat beside Jim against one of the sleds, and for a long time there was silence as he stared far out to the north with troubled eyes. "Jim Landor," he broke the silence at last, "there is one thing I did not tell you." "I thought there was." "Frank Landor and I found something. The body of a man in the ice far to the north of here. It had been there a long time." Jim merely waited for him to go on. "In his clothing we found some of these." Kaarji fumbled in his pocket, and handed something to Jim. It was a piece of metal, flat, round and amazingly light. It seemed to have once been part of some ornamentation. What interested Jim, however, was not what it might have been, but rather the metal itself. It was a dull greenish-gray in color and strangely different to the touch from any metal he had ever known. It was somehow reminiscent of radite, but only faintly. In it was a subtle suggestion of--yes, of fabulous strength and power! In the dim grayness of that Polar night Jim looked at Kaarji and said in a voice he did not recognize as his own: "Kaarji, do you realize what this means? Up here somewhere there is a city, a former civilization--a M'Tonak! That man you found dead--_he_ reached M'Tonak and was coming back with the news when disaster overtook him! But that might have been many years ago.... "Tell me something, Kaarji. Why have you come up here three times before? Are you seeking M'Tonak?" "I do not know. Something calls me. Something inside. And I only know that I must go." "Is that all, just something calling you?" "That is all. Except that this time it is different. This time I know that I shall reach--whatever is calling me, and I shall not return. I am sure of it."