Because, with the ever further evolution of Form and Faculty as organisms have risen higher in the scale of life, the bodies of living creatures are seen to have become further differentiated into two sides; a right and a left. Anatomically, these two sides appear identical in structure and in function, although contrary in incidence to one another. Each is incomplete and impotent without the other. Nevertheless, paralysis and other diseases show that each is, as it were, an entity totally distinct from the other. One side may be wholly helpless and insensitive while its fellow remains sound and efficient. Complementary and supplementary each to the other, both are, in a sense, complete. Further and closer comparison of function shows, however, that although they co-operate in action, they are by no means identical in power or aptitude. The right half of the body is, for both sexes, the active and executive half; quicker and stronger, and in all ways more efficient on the plane of physics. The left half is, relatively, passive and inert, is _responsive_, mainly, to the initiative and requirements of the right half, by which its powers are overshadowed in every form of direct activity. As with the two sides of the body, so it is with the two halves of the brain, which are at the same time the agencies of mentality and the centres for recording the sensations and for directing the movements of the two sides of the body. The brain-half which controls the right side is known as "the Leading half." It is the agent in concrete intellection, as in physical activity. While, so far as biologists and psychologists have been able to discover, the other half of the brain is negative in function--a blank, as regards concrete intelligence and nervous or muscular initiative. In disease, it has sometimes been found to undertake, and to perform feebly and imperfectly, sundry of the duties of its active "Leading" partner. But inert and inadequate in muscular action, it is negative in intellection. It has been observed, however, that patients in whom this brain-half is diseased show signs of moral deterioration. Yet whatsoever its functions--and the fact that it does not atrophy nor degenerate in the marvellous structure and complexity which characterise brain-constitution shows that it functions duly--its operations are totally dissimilar to, and are, moreover, wholly overshadowed by those of its active, intelligent partner. Here again, as in the two sides of the body, appear, surely, the factors of Dominance and Recessiveness--in other words of Maleness and Femaleness; of strength and activity upon material planes, and of inhibition upon these.