A division of labour has now been established, and each organ, being in working order and fashioned for its own special use, performs its separate functions independently, although its activity is co-ordinated with that of all other organs in the structure. This far in the history of life on the earth sex has not been developed, or, more correctly stated, as the two sexes have not been separated, our animal is still androgynous or hermaphrodite—the reproductive functions being confined in one and the same individual. Within this little primeval animal, the progenitor of the human race, lay not only all the possibilities which have thus far been realized by mankind, but within it were embodied also the “promise and potency” of all that progress which is yet to come, and of which man himself, in his present undeveloped state, may have only a dim foreshadowing. From the time of the appearance of life on the earth to that of the separation of the sexes, myriads of centuries may have intervened. Only when through a division of labour these elements became detached, and the special functions of each were confided to two distinct and separate individuals, did the independent history of the female and male sexes begin. No fact is more patent, at the present time, than that sex constitutes the underlying principle throughout nature. Although it may not be said of the simplest forms of life that sexual difference has been established, yet we are assured that among the ciliated Infusorians “male and female nuclear elements have been distinguished.” This primitive condition, however, is supposed to be rather a state antecedent to sex than a union of sexes in one organism. Among all the higher orders of life, whether animal or vegetable, the sex elements, female and male, are recognized as the two great factors in creation. As, among all the animals in which there has been a separation of sexes, there has been established a division of labour, the consequent specialization of organs and the differentiation of parts form the true line of demarcation in the march of the two diverging columns. Doubtless in the future, when our knowledge of the history of life on the earth has become more extended, it will be found that it is only by tracing the processes of differentiation throughout the two entire lines of development that we may hope to unravel all the mysteries bound up in the problem of sex, or to understand the fundamental differences in character and constitution caused by this early division of labour. CHAPTER II THE ORIGIN OF SEX DIFFERENCES