Now the spinning wheels of light began to merge, and the spokes fused into luminous bars that slowly receded into the distance, rotating on their axes as they did so. They split into pairs and the resulting sets of lines started to oscillate across one another, slowly changing their angles of intersection. Fantastic, fleeting geometrical patterns flickered in and out of existence as the glowing grids meshed and unmeshed; and the man-apes watched, mesmerized captives of the shining crystal. They could never guess that their minds were being probed, their bodies mapped, their reactions studied, their potentials evaluated. At first, the whole tribe remained half crouching in a motionless tableau, as if frozen into stone. Then the man-ape nearest to the slab suddenly came to life. He did not move from his position, but his body lost its trancelike rigidity and became animated as if it were a puppet controlled by invisible strings. The head turned...