I shall now give a summary of the contents of this chapter. Living beings cannot be described bluntly as of one sex or the other. The real world from the point of view of sex may be regarded as swaying between two points, no actual individual being at either point, but somewhere between the two. The task of science is to define the position of any individual between these two points. The absolute conditions at the two extremes are not metaphysical abstractions above or outside the world of experience, but their construction is necessary as a philosophical and practical mode of describing the actual world. A presentiment of this bisexuality of life (derived from the actual absence of complete sexual differentiation) is very old. Traces of it may be found in Chinese myths, but it became active in Greek thought. We may recall the mythical personification of bisexuality in the Hermaphroditos, the narrative of Aristophanes in the Platonic dialogue, or in later times the suggestion of a Gnostic sect (Theophites) that primitive man was a “man-woman.” CHAPTER II MALE AND FEMALE PLASMAS The first thing expected of a book like this, the avowed object of which is a complete revision of facts hitherto accepted, is that it should expound a new and satisfactory account of the anatomical and physiological characters of the sexual types. Quite apart from the abstract question as to whether the complete survey of a subject so enormous is not beyond the powers of one individual, I must at once disclaim any intention of making the attempt. I do not pretend to have made sufficient independent investigations in a field so wide, nor do I think such a review necessary for the purpose of this book. Nor is it necessary to give a compilation of the results set out by other authors, for Havelock Ellis has already done this very well. Were I to attempt to reach the sexual types by means of the probable inferences drawn from his collected results, my work would be a mere hypothesis and science might have been spared a new book. The arguments in this chapter, therefore, will be of a rather formal and general nature; they will relate to biological principles, but to a certain extent will lay stress on the need for a closer investigation of certain definite points, work which must be left to the future, but which may be rendered more easy by my indications. Those who know little of Biology may scan this section hastily, and yet run little risk of failing to understand what follows.