vehicles, and for vessels. For walkers and vessels no people ever changed the custom, but especially the English, while preserving right-hand passing in foot-passengers and on the sea, anomalously developed left-hand passing for vehicles, and the same, of course, for double-track railroads. What everybody has failed to see is that right-handedness is necessarily bound up with right-footedness, and right-eyedness, because all closely united functions of the body must be correlated and their centers of motion located in contiguity and upon one side of the brain, in order to make effectual and rapid all responses of the organism to circumstance or environment. This works toward a necessary and desirable differentiation of function that makes the aims of the "ambidexterity" sillies more than resultless and foolish. Because whenever a center or congress of centers is developed in one half-brain, disuse and transfer to the other half is, according to age, either impossible, faulty, handicapping, or disease-producing. Coordinated functions of the body require coordinated and contiguous nerve-centers upon the same side of the brain, at least so far as is possible. If one or two dextral factors are in opposite cerebral hemispheres, responsive and quickly-acting coordinated functions will be slower and more inaccurate than if on a single side. The English left-hand passing of vehicles is probably due to the influence of the single-hand fights on foot, tourneyings and joustings of horseback riders, in which meeting and passing to the left was inevitable. The custom grew and continued directly into that of the wagon-drivers. In the United States there was a reversion to the right-hand passing of vehicles, because of the abeyance of left-hand passing of vehicles, and of vehicles themselves, for so long, with growth of the natural right-hand passing by walkers, horseback-riders, ox-teams, and wagons with drivers on the near-wheel horse, such as is found in the later prairie-schooner, and six-mule army-wagon. Three double-track railways in the United States still pass their trains to the left, an absurd and bad custom, expensive and productive of wrecks. But despite this the enginer sits upon the right of his cab, because he can in this place better observe the track and signals in front and to his right, and with the dominant right eye only outside of the cab-window, whereas, if sitting on the left, he would be compelled to put the entire head out in order to see with the right eye, and, even then, because of the boiler, not so well. Only right-eyedness will explain the long, doubtful, and varying custom in engine-building as to the position of the engineer in the beginning of history of railway construction and signaling.