A serious difficulty in understanding how to educate and regulate the relations of sex arises from the fact that it is the relation of two equal but distinct halves of the human race, and exists in the dual form--male and female. Unless the distinctive characteristics and requirements of each of these equal halves are fully understood, the relation between them cannot be satisfactory. The physiological meaning of the differences in organization between the sexes is at present very imperfectly understood. The most striking distinction, however, in the manifestation of the sexual faculties exists between man and the brute creation, and is found in the mental or moral aspects which it assumes in man. The general structural resemblance between man and the lower animals affords no guidance to the education of this human faculty, for the differences between man and the lower animals are radically greater than the resemblance between them. The most evident form of this mental difference shows itself as a sentiment of self-consciousness which is not observed in the brute. If an animal is not frightened by human beings it never hesitates in carrying on sexual congress in their presence, and neither before nor after the special act does it exhibit the smallest approach to shame in relation to it. In man, however, from the earliest dawn of the approaching faculty, self-consciousness is intense. This is not only observed in well brought-up boys and girls, who shrink from indecency of word or action, but it is never entirely extinguished in the most corrupt man or woman; and even the poor little waifs of our streets, blighted from earliest infancy, exhibit marked consciousness in their infantile depravity. All the vast difference between the gregariousness of the lower animals and the highest human civilization indicates the mental difference which moulds the human form of the sexual relations. Permanent parental care of offspring, mutual respect between the sexes, reverence for these faculties as typifying the mighty Creative Power of the universe, are stages of social progress based upon this mental difference in human and brute sex. It is the mental or moral aspect of our sexual powers which, as society grows, shapes so much of the literature of every civilized country. In the popular ballads of a people, songs of love are even more abundant than patriotic songs; and as education spreads amongst the masses, romances and novels form the bulk of popular reading. The subject of love is always of the most absorbing interest to the younger and more active portion of a people; sexual passion, in its ennobling or debasing form, exercises irresistible attraction.