Nature seems to have a sameness on all inhabited worlds, tending toward the economy and simplicity of the human form. The upright carriage, freeing the hands, the opposable thumb, the color-sensitivity of retinal rods and cones, the development of language and of lengthy parental nurture--these things seem to be indispensable to the growth of civilization, and in the end they spell _human_. Except for minor variations depending on climate or foodstuff, the inhabitant of Megaera or Darkover is indistinguishable from the Terran or Sirian; differences are mainly cultural, and sometimes an isolated culture will mutate in a strange direction or remain, atavists, somewhere halfway to the summit of the ladder of evolution--which, at least on the known planets, still reckons homo sapiens as the most complex of nature's forms. The trailmen were a pausing-place which had proved tenacious. When the mainstream of evolution on Darkover left the trees to struggle for existence on the ground, a few remained behind. Evolution did not cease for them, but evolved _homo arborens_; nocturnal, nystalopic humanoids who lived out their lives in the extensive forests. The truck bumped over the bad, rutted roads. The wind was chilly--the truck, a mere conveyance for hauling, had no such refinements of luxury as windows. I jolted awake--what nonsense had I been thinking? Vague ideas about evolution swirled in my brain like burst bubbles--the trailmen? They were just the trailmen, who could explain them? Jay Allison, maybe? Rafe turned his head and asked, "Where do we pull up for the night? It's getting dark, and we have all this gear to sort!" I roused myself, and took over the business of the expedition again. But when the trucks had been parked and a tent pitched and the pack animals unloaded and hobbled, and a start made at getting the gear together--when all this had been done I lay awake, listening to Kendricks' heavy snoring, but myself afraid to sleep. Dozing in the truck, an odd lapse of consciousness had come over me ... myself yet not myself, drowsing over thoughts I did not recognize as my own. If I slept, who would I be when I woke? * * * * * We had made our camp in the bend of an enormous river, wide and shallow and unbridged; the river Kadarin, traditionally a point of no return for humans on Darkover. The river is fed by ocean tides and we would have to wait for low water to cross. Beyond the river lay thick forests, and beyond the forests the slopes of the Hellers, rising upward and upward; and their every fold and every valley was filled to the brim with forest, and in the forests lived the trailmen. But though all this country was thickly populated with outlying colonies and nests, it would be no use to bargain with any of them; we must deal with the Old One of the North Nest, where I had spent so many of my boyhood years.