=Characteristic Arrangements of Nerve Cells Are as Subject to Inheritance as Other Structures of the Body.--=That the main features of the nervous system are inherited becomes obvious when we see that each kind of animal has its own distinctive numbers, arrangements and proportions of the various neural units. In man, for example, there are certain characteristics, types and groupings of nerve-cells which are reproduced generation after generation with remarkable fidelity. This means that in so far as these represent the mental make-up of the individual, his mentality is continuously linked with others which have gone before. The new-born child has all the nerve-cells in its brain that it will ever have but the ultimate linkages of the finer connectives between them, or at least the pathways of travel, remain in large measure to be made. As we have already seen, the cerebral cortex is the seat of the chief mental faculties of man or at least of the highest of these. Professor Lloyd Morgan, one of our greatest authorities on comparative psychology, is inclined to believe that the instincts are located in the subcortical material. In any event, the inheritance of mental ability resolves itself into the inheritance of a certain cerebral mechanism. =Different Parts of the Cortex Yield Different Reactions.--=The cerebral cortex, however, is not functionally homogeneous throughout. Certain regions have been shown to be motor, others sensory, and moreover, these regions are apparently further specialized so that a given one of them is associated with a specific type of sensory or motor response, not merely with responses in general. Thus by injuring one of the sensory areas we might destroy vision but not other sensations, or by stimulating one of the motor centers we would get a response in a corresponding motor organ but not in all such organs. Likewise, it is probable that still different areas, the so-called "association areas," relatively of much greater development in man than in any other animal, are the regions in which various perceptions and conceptions are synthesized and formed into organized knowledge. Here also are engendered the volitions which when flashed through the motor centers become expressed in activity or behavior.