I discussed first the problem of selecting scientific facts for boys because there is little dispute as to the advisability of giving them as much scientific information as may possibly replace the vulgar knowledge that the average boy is likely to possess. I know that there are a few men and many women who will disagree with this because they believe in the absolute ignorance of their boys; but I doubt whether one healthy adolescent boy in a hundred belongs in the "innocent" class. So we need not worry much concerning any supposed danger of treating facts too frankly, provided that they are given a dignified, scientific setting. In the case of numerous adolescent girls there is certainly dense ignorance, and so there must be more difficulty in getting approval of parents and teachers concerning facts proposed for girls. Often when talking with groups of parents I have heard them say that they would like to have their boys learn the scientific truth regarding certain facts, but they feel that it would be too startling and unnecessary for their daughters. Such is the widespread feeling which must be seriously considered in all planning of advanced sex-instruction for girls. No doubt there will be much honest disagreement with the suggestions here offered. The biological introduction based on plants and animals should be the same as for boys (Sec. 27). [Sidenote: Structure and names.] An adolescent girl of fourteen to sixteen should know the general plan of her own sexual structure. She should know the scientific names of her organs, not because there are many vulgar names as in the case of boys, but because dignified names help attitude. Ovaries, uterus (womb), vagina, Fallopian tubes, and vulva will be sufficient. Detailed description of the external organs (vulva) might arouse curiosity that leads to exploration and irritation, and hence many women physicians think that a girl under sixteen or possibly eighteen needs only the name vulva for the external parts surrounding the entrance to the vagina. [Sidenote: An ancient belief.] Some books for girls perpetuate the ancient but absurd emphasis on the virginal significance of the hymen; and a recent book from a prominent publisher goes so far as to try to frighten girls into remaining chaste by stating that a physician could discover if they have been unchaste. This is far from being always true, for the structure may be congenitally absent, may sometimes remain after sexual union, or may be accidentally destroyed in childhood; and reliable physicians have stated that proving unchastity by the hymen is by no means easy. Hence, the less said about the ancient belief, the better for young women. The truth is that the hymen is a worse-than-useless relic of embryological development, and it is neither an indicator nor a dictator of morality. [Sidenote: Physiology of women.]