At first thought, the elimination of useless moves seems to tell the whole story of the rat's learning process; but careful study of his behavior reveals another factor. When the rat approaches a turning point in the maze, his course bends so as to prepare for the turn; he does not simply advance to the turning point and then make the turn, but several steps before he reaches that point are organized or coördinated into a sort of unit. {307} [Illustration: Fig. 48.--(From Watson.) Learning curve for the rat in the maze. This is a composite or average, derived from the records of four animals. The height of the heavy line above the base line, for any trial, indicates the number of minutes consumed in that trial in passing through the maze and reaching the food box. The gradual descent of the curve indicates the gradual decrease in time required, and thus pictures the progress of the animals in learning the maze.] The combination of steps into larger units is shown also by certain variations of the experiment. It is known that the rat makes little use of the sense of sight in learning the maze, guiding himself mostly by the muscle sense. Now if the maze, after being well learned, is altered by shortening one of the straight passages, the rat runs full tilt against the new end of the passage, showing clearly that he was proceeding, not step by step, but by _runs_ of some length. Another variation of the experiment is to place a rat that has learned a maze down in the midst of it, instead of at {308} the usual starting point. At first he is lost, and begins exploring, but, hitting on a section of the right path, he gets his cue from the "feel" of it, and races off at full speed to the food box. Now his cue could not have been any single step or turn, for these would all be too much alike; his cue must have been a familiar _sequence_ of movements, and that sequence functions as a unit in calling out the rest of the habitual movement. [Illustration: Fig. 49.--(From Watson.) A puzzle box. The animal must here reach his paw out between the bars and raise the latch, _L_. A spring then gently opens the door.] In short, the rat learns the path by _elimination_ of false reactions and by _combination_ of single steps and turns into larger reaction-units. The puzzle-box experiment.