In introductory notes the author discusses the high significance of hereditary tendency in the development of concomitant squint, the hereditary species character of binocular vision, the methods for exactly outlining the normal status of equilibrium and its anomalies and for proving the heredity of squint and its modification range, and finally the problems rising in those cases, where squint is combined with other psychical and somatical affections. He then divides his subject in three chapters, one dealing with sex and squint, a second with the results of twin research and a third with those of family stocks, which contain new data, collected by himself.