The undifferentiated stage begins at very various ages. I have known instances in which it could be traced back to the fifth, year of life. I regard it as probable, however, that it may begin even earlier than this. But more commonly it begins somewhat later; not infrequently at the age of seven or eight, and very often at the age of nine or ten years. As previously mentioned, I do not maintain that an undifferentiated stage is of universal occurrence. When such a stage is absent, the symptoms of the differentiated sexual impulse often make their appearance at the age at which in other cases the undifferentiated stage of the impulse usually begins. In the case of a large number of men, inquiry will show that at the age of nine or ten they began to experience an inclination towards persons of the female sex; in a good many this occurs even at the age of eight, and in a few yet earlier; as regards women, _mutatis mutandis_, the same conditions obtain. In cases in which an undifferentiated stage is well marked, its duration is likewise very variable. In isolated instances it lasts until the age of twenty, or even a few years longer. Ordinarily, however, the differentiation of the impulse becomes manifest at an earlier age--between the ages of fifteen and seventeen years. Beyond question, in the great majority of cases, the "perverse" sentiments of childhood subsequently disappear spontaneously. But when I come to discuss sexual perversions in detail, I shall point out that this disappearance, in certain circumstances, fails to occur.