I must emphasize as a character of this work of mine its intentional independence of biological investigation. I have carefully avoided the inclusion of the results of scientific investigation in general sex biology or of particular species of animals in this study of human sexual functions which is made possible by the technique of psychoanalysis. My aim was indeed to find out how much of the biology of the sexual life of man can be discovered by means of psychological investigation; I was able to point to additions and agreements which resulted from this examination, but I did not have to become confused if the psychoanalytic methods led in some points to views and results which deviated considerably from those merely based on biology.