Those who are now working at these problems experimentally, actually seeing what happens in given cases, and whom we may for convenience call Mendelians after the master who gave them their method and their key, have latterly obtained results the main tenour of which must be stated here, as they indicate the lines of a portion of the succeeding argument. The task was to attack experimentally the determination of sex--a fascinating problem for which so many solutions that failed to hold water have been found, but hitherto no others. In finding the answer to it, as they appear certainly to have done so far as the higher animals are concerned, the Mendelians are also beginning to ascertain, as we shall see, certain basal facts as to the composition or constitution of the individual; and to us, who wish to know exactly what a woman is, and what she is as distinguished from a man, this discovery is of the most vital importance. The experimental facts are not yet numerous, and if they were not consonant with facts of other orders, it would be rash to proceed; but it will be evident, in the sequel, that common experience is well in accord with the experimental evidence. It appears that, amongst at any rate the higher animals, the sex of offspring is determined by the nature of the mother's contribution. The cell derived from the father is always male--as goes without saying, we might add, if we knew little of the subject. But the ovum, the cell derived from the mother, may carry either femaleness or maleness. When an ovum bearing maleness meets the invariably maleness-bearing sperm, the resultant individual is a male, of course, and he is male all through. But when an ovum bearing femaleness meets a sperm, the resulting individual is female, femaleness being a Mendelian "dominant" to maleness; if both be present, femaleness appears. The female, however, is not female all through as the male is male all through. So far as sex is concerned, he is made of maleness _plus_ maleness; but she is made of femaleness _plus_ maleness. In Mendelian language the male is homozygous, so-called "pure" as regards this character. But the female is heterozygous, "impure" in the sense that her femaleness depends upon the dominance of the factor for femaleness over the factor for maleness, which also is present in her. In the Mendelian terminology, she is an instance of impure dominance. The observed practical equality in the numbers of the two sexes is in exact accord with this interpretation of the facts, this proportion being the expected and observed one in many other cases which doubtless depend upon parallel conditions of the reproductive cells. Surely there is great enlightenment here: for the discovery of the factors determining sex is a very small affair compared with the suggestive inference as to the constitution of womanhood. Let us compare man and woman on the basis of this assumption.