It seems highly probable that just as the sensory and motor areas differ in kind from one another, so we must suppose there are qualitative differences in various parts of the association areas so that the different parts give different reactions in consciousness; that is, each special mental ability of the individual is more or less centered in a special part of the cortex. And just as there may be variations in other structures of the organism so there may be variations in these areas. The "gifted" person in some one direction, whether it be in mathematics, music, painting, or what not, is on this hypothesis one who has that particular area of his brain which forms the basis for the talent in question more highly developed than it is in the average individual. And since such talents are handed down to descendants, this can only mean that a similar grouping of the neurons in the region in question has occurred. =Skill Acquired in One Special Branch of Learning Probably Not Transferred to Another Branch.--=Such a differential arrangement of the brain-mechanism which presumably underlies the various mental abilities would lead to the inference that skill in one special branch of learning, in so far as it involves only certain centers of the cortex, would not be transferred to another branch based on different neural pathways and centers. Development of historical knowledge, for example, would not enhance one's mathematical ability, or vice versa. The testimony of various psychologists bears out this idea. In so far as certain factors of training, such as habits of industry, concentration, etc., are common to the study of either mathematics or history, the good effects of either discipline will probably be much the same, but the identity of effect vanishes as soon as the intrinsic characteristics of the subjects themselves are involved. Just how far we are warranted, however, in carrying this idea of localized functions as regards the association areas is a moot question. Our present attitude regarding the specificity of such localizations is largely a matter of inference based on analogy to conditions which obtain in other and better known parts of the brain, together with the indubitable differences in inborn abilities which exist between individuals. Some few brain physiologists maintain that the whole cortex operates more or less as a unit in all of the higher psychical activities.