Gillespie points out that even in Freud's earliest formulations of a theory of female sexuality, he acknowledged the great influence that societal factors have on its development. Freud recognized that the clitoris serves an excitatory function in female sexual arousal; he insisted of course that a transformation of clitoral ('masculine') into vaginal sexuality was necessary. The author expresses the opinion that Freud overestimated the traumatic consequences that the visual perception of the anatomical difference between the sexes has for children of both sexes. The anatomic sex difference is significant as the index of an evolutionary readjustment. As mammals progressed to a terrestrial habitat, the female had to replace pleasure in extrusion with pleasure in the reception of the male sexual organ and products.