The line A C is drawn as a straight line joining A and C--but if the skull is accurately posed it corresponds to the edge of the plane at right angles to the sagittal plane of the skull--which traverses both bregma (C) and ophryon (A)--and where it ‘cuts’ the skull marks off the prefrontal area or boss. (See for the full-face view of this area in the two skulls--Figs. 1 and 2.) The line _d_ is a perpendicular let fall from the point of greatest prominence of the prefrontal area on to the prefrontal plane. It indicates the depth of the prefrontal cerebral region. Drawn on both sides on the surface of the bone and looked at from in front (the white dotted line in Figs. 1 and 2) it gives the maximum breadth of the prefrontal area. By dividing the ophryo-tentorial line into 100 units, and using those units as measures, the depths of the brain cavity in the regions plumbed by the lines _d_, _e_, and _f_, can be expressed numerically and their differences in a series of skulls stated in percentage of the ophryo-tentorial length. CONTENTS PAGE CHAPTER I.--NATURE’S INSURGENT SON 1 CHAPTER II.--THE ADVANCE OF SCIENCE, 1881-1906 66 CHAPTER III.--NATURE’S REVENGES: THE SLEEPING SICKNESS 159 LIST OF ILLUSTRATIONS FRONTISPIECE:--Profile views of the Cranial Dome of _Pithecanthropus erectus_, the ape-like man from an ancient river gravel in Java, and of a Greek skull. FIG. 1.--Frontal view of the Cranial Dome of _Pithecanthropus_ 16 FIG. 2.--Frontal view of the same Greek skull as that shown in the frontispiece 16 FIG. 3.--Eoliths, of ‘borer’ shape, from Ightham, Kent 18 FIG. 4.--Eoliths of trinacrial shape, from Ightham, Kent 20 FIG. 5.--Brain casts of four large Mammals 23 FIG. 6.--_Spironema pallidum_, the microbe of Syphilis discovered by Fritz Schaudinn 37 FIG. 7.--The Canals in Mars 43 FIG. 8.--The Canals in Mars 44 FIG. 9.--Becquerel’s shadow-print obtained by rays from Uranium Salt 73 FIG. 10.--Diagrams of the visible lines of the Spectrum given by incandescent Helium and Radium 76 FIG. 11.--The transformation of Radium Emanation into Helium (spectra) 83 FIG. 12.--Dry-plate photograph of a Nebula and surrounding stars 90 FIG. 13.--The Freshwater Jelly fish, _Limnocodium_ 97 FIG. 14.--Polyp of _Limnocodium_ 97