The human family, according to most conservative authority, has been in existence for more than a half million years. During all the vast era of pleistocene time, with its recurrent glaciations and intervals of warmth, man's brain steadily grew. In volume, the cerebrum was slowly increasing. It developed gradual refinements in many of its structural details. Certain of its most recently acquired regions became still more highly specialized, until the brain of modern man has come to be a far more efficient organ than that possessed by the earliest of human kind. Several distinct races of primitive men already have been identified by means of fossilized bones from the body and cranium. The racial differentiations established in this manner have been utilized to reconstruct the outward appearance of these prehistoric peoples. In the reconstructions of Professor MacGregor the differences between them are striking (fig. 1). The apelike appearance of Pithecanthropus