Every group of animals in the higher ranks has its own entailed property of innate reflexes, for example, the reflexes which subserve the reflex functions of the cord: those of locomotion, muscular and vascular tone, micturition, defæcation, impregnation and parturition. These exist in an animal of the spinal level whether or not it remains purely aquatic, partly aquatic, partly terrestrial, arboreal or terrestrial. As the progressive groups ascend the ladder of life they add to this inalienable heritage, gained we need not here ask how, fresh reflex-arcs by response to new initial stimuli, forging them by the incident of use. So, the original acquirements in the past levels serve as starting points for raising the degree of their nervous integration with growing control over their environments. The long story from the simple central nervous system of a fish, with a few or no association-areas, to that of man with his extensive frontal, parietal, parieto-occipital association-areas, could never be deciphered, even with the light of the laws of genetics turned on full, without a protracted process of construction of fresh arcs. A common illustration of such a series of changes and results may be seen in the building of a house. Bricks, foundation-stones, walls and a roof may serve some of the elementary requirements of a house and much less than these were of use to early man for his shelter. Without them we cannot call any structure a modern house; but also without floors, staircases, windows, chimneys, division into rooms, some degree of decoration by paint or paper, and a supply of water, we should refuse in these days the name of house to that rough structure, apart from beauty of design, decoration, within and without, and some addition of modern appliances of comfort and convenience. In the history of house-building the stages of supply of raw materials, adaptation to needs guided by selection, initiation, trial and error have their counterpart in the construction of higher animals. Evidence. It will be asked what evidence there is for the view here put forward that such is the order and method of the construction of the central nervous system. There are two classes of evidence. The first direct, and the second indirect and resting on inference. The well-known leads to the less-known and inferred. Direct evidence of the foundation of new reflex-arcs and their organization is of course small. The conditions, such as the duration of human life, preclude any extensive formation under experiment of new reflex-arcs, but enough is known to enable one to follow the backward way with some confidence. As to the inheritance of these, the evidence rests on opinion and tremendous probability, but as the only problem with which I am concerned here is that of initiative I think it better to leave the matter of transmission to a dispassionate consideration of the probability of its occurrence. Direct Evidence.