Dr Munro maintained in this paper that, by the attainment of the erect posture and the consequent conversion of his limbs into hands and feet, man became homo sapiens, and inaugurated a new phase of existence, by means of which the manipulative organs became correlated with the progressive development of the brain. In the evolutionary career of man two stages were therefore to be recognised. First, that during which his physical transformation had been effected, so as to adapt him to bipedal locomotion; second, that during which his mental organisation had become a new governing force in the universe. The one, being readily effected in accordance with the laws of morphological adaptation, had a short duration. The other, an extremely slow process, consisted of small increments to his knowledge, acquired by repeated experiences of reasoning from causes to effects and from means to ends. The one was merely an adjustment of physical contrivances to physical ends, comparable to that by which the bird, the bat, and the whale had converted their limbs to their special purposes. The other had to be relegated to the mystic laboratory, where thought was converted into its material equivalent in the form of increased brain substance. The transition from the semierect to the erect posture could not, in point of duration, be at all paralleled with the ages during which this erect being had lived on the globe. It was also probable that this transformation took place in a limited area, so that the chances of finding the intermediary links of this stage were very small.