The emotion of love between the sexes has as yet received no thorough scientific treatment. No writer so far as I can find has treated it from a genetic standpoint. The literature upon the subject is therefore meager. In his recent treatise upon “The Psychology of the Emotions,” Ribot [2] remarks: “The sex-instinct, the last in chronological order with man and the higher animals, gives rise to the emotion of love with its numerous individual varieties.