Altogether I remain unconvinced by Professor Ripley's arguments as to any large admixture of alien elements among contemporary Jews as unvouched for by history, and not necessarily postulated by anthropology. The broad skulls of the Jews, if they differ from those of earlier date (of which Professor Ripley has produced no evidence whatever), are due to the development of Jewish capacity, owing to their consistent attention to education and to the conditions under which they have pursued the struggle for existence. The persistence of Jewish features throughout the ages and the existence of an influential minority who are not allowed by Jewish law to marry outside their race is further proof of the position for which I have throughout contended. If there has been a tolerably large admixture of Jewish and alien blood throughout the Christian centuries it has been by conversions to Christianity or Islam, not by adoption of Judaism, and it is confirmed by history that the offspring have wandered away from the Jewish race and have not affected the more conservative remnant. The significance of this result for the science of anthropology can not be overrated. The great question of the science is that expressed by Dr. Galton as "the struggle between Nature and nurture"--the difference that social influences can produce on men of the same race. Jews afford the science almost the sole instance in which this problem can be studied in its least complex form. My own investigations have shown that social environment has a direct influence on such anthropometrical data as height and breathing capacity. The Jews of the West End of London, though of the same race as those of the East End, are superior in height and other external qualities, and this superiority can thus be shown to be due entirely to nurture. Similarly, if the argument I have previously adduced is correct, the brachycephalism of the Jew is a proof that intellectual development produces broad heads, and that, roughly speaking, the cephalic index is a key to intellectual capacity. I should rather reverse Professor Ripley's main contentions: breadth of skull is not a criterion of race, but of intellectual development; whereas features, which are not directly influenced by social or intellectual characteristics, are the true index to racial purity. SOME PRACTICAL PHASES OF MENTAL FATIGUE. BY PROF. M. V. O'SHEA. I.