------------------------------------------------------------------------ =Transcriber’s Notes= Some inconsistencies in spelling, hyphenation, and punctuation have been retained. This file uses _underscores_ to indicate italic text. Two charts have been omitted from the text version of this eBook. They were too complex to render into text. They are included as images in the other versions. 1. “STANDARD SCHEME OF DESCENT” just after the Table of Contents 2. “Illustrations of the Herbert Spencer Lecture 1907.” on p. 72. Other charts were rendered as text. Some of them are wide.