The much-discussed question of the common education of the sexes (coeducation) is related to the mental hygiene of the sexual life of the child. I shall deal with this question only in so far as it bears upon our subject; and shall not consider whether other reasons, such as the different endowments of the sexes, are decisively opposed to coeducation. But coeducation has been opposed also for reasons of sexual education, on two grounds: that it leads to a premature awakening of the sexual life, and that it gives rise to immoral practices between the children. It is true that when boys and girls associate freely together the first sexual feelings of boys are directed towards girls. But a separation of boys and girls at school would here be of little use. Not only would some other person of the female sex be apt to take the place of a girl school-fellow, some person the boy often sees, it may be a grown woman, it may be a child (a school-friend of the boy's sister or of the family, a girl-cousin, or some girl employed about the house); but in many cases, if the sexes are separated in youth, both in boys and in girls the sexual impulse, when it awakens, may perhaps be directed towards a member of the same sex. I may refer, in this connexion, to what was said on page 60 about the undifferentiated sexual impulse. A further problem is that of the sexual practices which may result from the sexual impulse. It is an indisputable fact that many boys, when the contrectation impulse is intermingled with the detumescence impulse, readily take to sexual practices with others. Examples of this constantly occur in boarding-schools, and in all other kinds of educational institutions; even in day-schools, where the children live apart from one another, we may observe that occasionally they begin sexual practices very early in life (mutual masturbation, and intimate physical contact, especially contact involving the genital organs). We must always bear in mind the possibility that coeducation may lead to the more frequent occurrence of such practices between boys and girls. But we must avoid over-estimating this danger. In the first place, there are many institutions, higher schools and others, attended only by pupils of one sex, in which mutual sexual practices never take place, and in which neither boys nor girls, even though sexual inclinations arise in them, ever effect sexual intimacies with other children. Although mutual masturbation is fairly common in schools, it cannot be regarded as the general rule. Further, it may be pointed out that when boys and girls are educated in common, the girls' natural instincts of self-defence will in many cases lead them to repel improper sexual advances. This is proved by the actual experience of coeducation. Finck[134] gives reports regarding coeducation in the schools of the western states of the American Union, and informs us that there every girl has her beau of fourteen to seventeen years of age. Notwithstanding