Much of the material for this volume was collected during the time that I was preparing for the press the Evolution of Woman, or while searching for data bearing on the subject of sex-specialization. While preparing that book for publication, it was my intention to include within it this branch of my investigation, but wishing to obtain certain facts relative to the foundations of religious belief and worship which were not accessible at that time, and knowing that considerable labor and patience would be required in securing these facts, I decided to publish the first part of the work, withholding for the time being that portion of it pertaining especially to the development of the God-idea.