Since 1927, the field here to be reviewed has opened up at an increasingly rapid rate. A good beginning can be made with Langdon-Davies' popular chapter on the " history of human ideas about sex differences " (79). Five factors are cited as causing the myth of the " female character," and a prophecy of the future of womankind is attempted. Sumner and Keller (124) present a vast amount of carefully gathered and documented data on the social side of sexual relations, especially in primitive man. Briffault (21), a British anthropologist, offers extensive and exhaustive documentation for his thesis that the basis of human culture lies in the primitive sentiments about woman in her reproductive capacity; his three volumes contain approximately 2,300 pages. Bauer (10,11), a Viennese gynecologist, tries to prove that sex determines all of woman's actions, no matter how trivial, from birth to death, citing many references in his study of the physical, mental, sexual, and erotic aspects of feminine life. Scheuer (113) offers a historical contribution to the psychology of sex. Heilbron (60) believes woman to be inferior, " above all in the central organ, the brain." A good bibliography of titles, from classical literature to modern experiment, is found in Weith-Knudson's popular book (128). The feministic note is represented in such studies as that by Kennedy (76), using a Japanese setting.Turning to bibliographical studies, it will be unnecessary to more than mention the following: Allen (2), Ellis (44), Lincoln (86), Louttit (88, 89), Scheuer (114,115), and Woody (135) ; these give the careful student the key to the better material. In addition, Goodenough's (54) statement of a program for future research, together with a short summary of some studies in this field, is important and stimulating. Current work on sex differentiation and sex determination in animals is reported in such periodicals as the /. of Exper. Zoology and the Biol. Bull, for 1928 and 1929 especially. II. Physical Differences. Anatomical studies may be passed over rapidly in favor of studies of behavior differences. Over one thou-