In one of his more celebrated phrases, Guthrie once accused Tolman of leaving rats “buried in thought” as the creatures struggled to select among alternative paths to a goal in a multiple-choice-point maze (Guthrie, 1952, p. 143). Guthrie was, of course, referring to the question of how rats turned thought into action, a problem which is but one of many that have had their initial development in data that have come from the display of behavior in spatial mazes. The questions of place vs. response learning, and spatial memory [to which Chapters 12 (Olton) and 13 (Menzel) in this volume speak directly] are other cases in point, and so is the puzzle of how creatures manage to put things into some proper serial order. It is to the latter problem that this chapter is directed.