Two comprehensive attempts have been made in recent years to study the inheritance of mental abnormality, one in England at the Eugenics Laboratory of the University of London, the other in this country under the leadership, more or less immediate, of the Eugenics Record Office. Both the English and the American school of workers agree that different grades of mental ability, mental defect and insanity are strongly inherited. But the two schools have reached very different conclusions as to the manner of inheritance of mental traits and mental defects. Each school entertains profound disrespect for the scientific methods and conclusions of the other and with the frankness and honesty which devotion to truth demand has freely criticised the other. By this criticism, at the bottom friendly though sometimes caustic, science has undoubtedly profited. The later work of each school begins to show the chastening influence of adverse criticism. The English school has leaned backward in its devotion to the inductive method of accumulating inheritance data, ostensibly without prejudice for or against any particular theory but in reality with an ill-concealed bias against anything savoring of "Mendelism." The American school recognizing in Mendelism a great advance and an important instrument for the discovery of new truth, has ignored the possibility that other undiscovered laws of heredity may exist and has cast aside as superfluous the valuable biometric tools wrought with much patient toil by Galton and Pearson. It will be the part of wisdom for students of genetics to imitate the hostile attitude of neither school, but to utilize the positive results of both. This is what Dr. Goddard has done in the work under review.