An interesting chapter on erotic aberrations, the demoniacal and the obscene, completes the third part of the book. There may be much in Lucka's theories which will rouse the scepticism of the monists; some of his deductions may appear to his readers a little strained, but no thinking man or woman can read his brilliant _Conclusion_ without denying him the tribute of sincere admiration. In this last chapter he applies Haeckel's biogenetic law to the domain of the spirit. As the human embryo passes through the principal stages of the development of the individual from lower forms of life, so the growing male must pass through the stages of psychical development through which the race has passed. The gynecocratic government of prehistoric time is revived in the nursery, where the mother rules supreme and the sisters dominate. The normal, healthy school-boy, preferring the company of his school-fellows to all others, shunning his mother and sisters, ashamed of his female relatives, is the modern individual representative of those early leagues and unions of young men who opposed matriarchy and finally brought about its overthrow and the establishment of male government. The promiscuous sexuality characteristic of adolescence reproduces the first, merely sexual, stage of the erotic life of the race in the life of the individual. As a rule this phase is followed by a period of woman-worship; love has conquered the sexual instinct and the latter is felt as base and degrading. Atavism is not so much the persistence of the earlier, as the absence of the later stages of psychical development. I need not emphasise the fact that the three stages are often intermingled and not traceable with equal clearness in the life of every individual. Many men never advance beyond the first stage and others are fragmentary and undeveloped; but certain phases are more or less distinguishable in every well-endowed male individual. Lucka finds a perfect illustration of his theory in the life and works of Richard Wagner, whose operas _The Fairies_ (based on Shakespeare's _Measure for Measure_), _Tannhauser_, and _Tristan und Isolde_, successively illustrate the three stages through which the great poet-composer and impassioned lover passed, and reflect the principal halting-places in the erotic evolution of the race. In _Parsifal_, Wagner's last and maturest work, he conjectures a potential fourth stage, divined by the genius of the great musician and thinker, a sublimation of our modern ideal, a stage when love will be freed from all sexual feeling (a conception not unlike Otto Weininger's), but to which we have not yet attained and which we are even unable fully to grasp.