This book expands the symbols of the phallus and vagina into cosmic symbols, not by reference to myths but by his interpretations of embryonic, physiological, psychological facts. It develops the view that the whole of life is determined by a tendency to return to the womb, equating the process of birth with the phylogenetic transition of animal life from water to land, and linking coitus to the idea of "thalassal regression": "the longing for the sea-life from which man emerged to primeval times".