It can hardly be said that inverted sexuality received a serious and sympathetic treatment until a German jurist, named Karl Heinrich Ulrichs, began his long warfare against what he considered to be prejudice and ignorance upon a topic of the greatest moment to himself. A native of Hanover, and writing at first under the assumed name of Numa Numantius, he kept pouring out a series of polemical, analytical, theoretical, and apologetical pamphlets between the years 1864 and 1870. The most important of these works is a lengthy and comprehensive Essay entitled "Memnon. Die Geschlechtsnatur des mannliebenden Urnings. Eine naturwissenschaftliche Darstellung. Schleiz, 1868." Memnon may be used as the text-book of its author's theories; but it is also necessary to study earlier and later treatises--Inclusa, Formatrix, Vindex, Ara Spei, Gladius Furens, Incubus, Argonauticus, Prometheus, Araxes, Kritische Pfeile--in order to obtain a complete knowledge of his opinions, and to master the whole mass of information he has brought together. The object of Ulrichs in these miscellaneous writings is twofold. He seeks to establish a theory of sexual inversion upon the basis of natural science, proving that abnormal instincts are inborn and healthy in a considerable percentage of human beings; that they do not owe their origin to bad habits of any kind, to hereditary disease, or to wilful depravity; that they are incapable in the majority of cases of being extirpated or converted into normal channels; and that the men subject to them are neither physically, intellectually, nor morally inferior to normally constituted individuals. Having demonstrated these points to his own satisfaction, and supported his views with a large induction of instances and a respectable show of erudition, he proceeds to argue that the present state of the law in many states of Europe is flagrantly unjust to a class of innocent persons, who may indeed be regarded as unfortunate and inconvenient, but who are guilty of nothing which deserves reprobation and punishment. In this second and polemical branch of his exposition, Ulrichs assumes, for his juristic starting-point, that each human being is born with natural rights which legislation ought not to infringe but protect. He does not attempt to confute the utilitarian theory of jurisprudence, which regards laws as regulations made by the majority in the supposed interests of society. Yet a large amount of his reasoning is designed to invalidate utilitarian arguments in favour of repression, by showing that no social evil ensues in those countries which have placed abnormal sexuality upon the same footing as the normal, and that the toleration of inverted passion threatens no danger to the well-being of nations. After this prelude, an abstract of Ulrichs' theory and his pleading may be given, deduced from the comparative study of his numerous essays.