The Great War, which has changed so many things, has nowhere effected a greater change than in the sphere of women's activities. In all the belligerent countries women have been called upon to undertake work which they had never been offered before. Europe has thus become a great experimental laboratory for testing the aptitudes of women. The results of these tests, as they are slowly realised, cannot fail to have permanent effects on the sexual division of labour. It is still too early to speak confidently as to what those effects will be. But we may be certain that, whatever they are, they can only spring from deep-lying natural distinctions. The differences between the minds of men and the minds of women are, indeed, presented to all of us every day. It should, therefore, we might imagine, be one of the easiest of tasks to ascertain what they are. And yet there are few matters on which such contradictory and often extravagant opinions are maintained. For many people the question has not arisen; there are no mental differences, they seem to take for granted, between men and women. For others the mental superiority of man at every point is an unquestionable article of faith, though they may not always go so far as to agree with the German doctor, Mobius, who boldly wrote a book on "The Physiological Weak-mindedness of Women." For others, again, the predominance of men is an accident, due to the influences of brute force; let the intelligence of women have freer play and the world generally will be straightened out. In these conflicting attitudes we may trace not only the confidence we are all apt to feel in our intimate knowledge of a familiar subject we have never studied, but also the inevitable influence of sexual bias. Of such bias there is more than one kind. There is the egoistic bias by which we are led to regard our own sex as naturally better than any other could be, and there is the altruistic bias by which we are led to find a charming and mysterious superiority in the opposite sex. These different kinds of sexual bias act with varying force in particular cases; it is usually necessary to allow for them. Notwithstanding the fantastic divergencies of opinion on this matter, it seems not impossible to place the question on a fairly sound and rational base. In so complex a question there must always be room for some variations of individual opinion, for no two persons can approach the consideration of it with quite the same prepossessions, or with quite the same experience.