Every one possesses a definite, individual taste of his own with regard to the other sex. If we compare the portrait of the women which some famous man has been known to love, we shall nearly always find that they are all closely alike, the similarity being most obvious in the contour (more precisely in the “figure”) or in the face, but on closer examination being found to extend to the minutest details, _ad unguem_, to the finger-tips. It is precisely the same with every one else. So, also, every girl who strongly attracts a man recalls to him the other girls he has loved before. We see another side of the same phenomenon when we recall how often we have said of some acquaintance or another, “I can’t imagine how that type of woman pleases him.” Darwin, in the “Descent of Man,” collected many instances of the existence of this individuality of the sexual taste amongst animals, and I shall be able to show that there are analogous phenomena even amongst plants. Sexual attraction is nearly always, as in the case of gravitation, reciprocal. Where there appear to be exceptions to this rule, there is nearly always evidence of the presence of special influences which have been capable of preventing the direct action of the special taste, which is almost always reciprocal, or which have left an unsatisfied craving, if the direct taste were not allowed its play. The common saying, “Waiting for Mr. Right,” or statements such as that “So-and-so are quite unsuitable for one another,” show the existence of an obscure presentiment of the fact that every man or woman possesses certain individual peculiarities which qualify or disqualify him or her for marriage with any particular member of the opposite sex; and that this man cannot be substituted for that, or this woman for the other without creating a disharmony. It is a common personal experience that certain individuals of the opposite sex are distasteful to us, that others leave us cold; whilst others again may stimulate us until, at last, some one appears who seems so desirable that everything in the world is worthless and empty compared with union with such a one. What are the qualifications of that person? What are his or her peculiarities? If it really be the case--and I think it is--that every male type has its female counterpart with regard to sexual affinity, it looks as if there were some definite law. What is this law? How does it act? “Like poles repel, unlike attract,” was what I was told when, already armed with my own answer, I resolutely importuned different kinds of men for a statement, and submitted instances to their power of generalisation. The formula, no doubt, is true in a limited sense and for a certain number of cases. But it is at once too general and too vague; it would be applied differently by different persons, and it is incapable of being stated in mathematical terms.