We must therefore now briefly but adequately consider the argument of the remarkable book published by the Scottish biologists in 1889, and presented in a new edition in 1900. The latter date is of interest, because it coincides with the re-discovery of the work of Mendel, published in 1865, to which we must afterwards more than once refer; and the work of the Mendelians during the subsequent decade very substantially modifies much of the authors' teaching upon the determination of sex, and the intimate nature of the physiological differences between the sexes. We have learnt more about the nature of sex in the decade or so since the publication of the new edition of the "Evolution of Sex" than in all preceding time. Such, at least, is the well-grounded opinion of all who have acquainted themselves with the work of the Mendelians, as we shall see: and therefore that book is by no means commended to the reader's attention as the last word upon the subject. The rather would one particularly direct him to the following prophetic and admirable passage in the preface of 1900:-- "Our hope is that the growing strength of the still young school of experimental evolutionists may before many years yield results which will involve not merely a revision, but a recasting of our book." --a passage which may well content the authors to-day, when its fulfilment is so signal. Yet assuredly the main thesis of the volume stands, and profoundly concerns every student of womanhood in any of its aspects. It will continue to stand when the brilliant foolishness of such writers as poor Weininger, the author of that evidently insane product "Sex and Character," is rightly estimated as interesting to the student of mental pathology alone. There has lately been a kind of epidemic citation from Weininger, whose book is obviously rich in characters that make it attractive to the ignorant and the many; and it is high time that we should concern ourselves less with the product of a suicidal and much-to-be-pitied boy, and more with the sober and scientific work for which daily verification is always at hand. We cannot do better than have before us at the outset the authors' statement of their main proposition, in the preface to the new edition of their work:--