Spawning Ground by Lester Del Rey - They weren't human. They were something more—and something less—they were, in short, humanity's hopes for survival!

The Starship Pandora creaked and groaned as her landing pads settled unevenly in the mucky surface of the ugly world outside. She seemed to be restless to end her fool's errand here, two hundred light years from the waiting hordes on Earth. Straining metal plates twanged and echoed through her hallways.

Captain Gwayne cursed and rolled over, reaching for his boots. He was a big, rawboned man, barely forty; but ten years of responsibility had pressed down his shoulders and put age-feigning hollows under his reddened eyes. The starlanes between Earth and her potential colonies were rough on the men who traveled them now. He shuffled toward the control room, grumbling at the heavy gravity.

Lieutenant Jane Corey looked up, nodding a blonde head at him as he moved toward the ever-waiting pot of murky coffee. "Morning, Bob. You need a shave."

"Yeah." He swallowed the hot coffee without tasting it, then ran a hand across the dark stubble on his chin. It could wait. "Anything new during the night?"

"About a dozen blobs held something like a convention a little ways north of us. They broke up about an hour ago and streaked off into the clouds." The blobs were a peculiarity of this planet about which nobody knew anything. They looked like overgrown fireballs, but seemed to have an almost sentient curiosity about anything moving on the ground. "And our two cadets sneaked out again. Barker followed them, but lost them in the murk. I've kept a signal going to guide them back."