C. Lloyd Morgan, "Instinct and Intelligence in Animals," Nature, February 3, 1898.
Essais, livre iii, ch. v.
Féré, "La Prédisposition dans l'étiologie des perversions sexuelles," Revue de médecine, 1898. In his more recent work on the evolution and dissolution of the sexual instinct Féré perhaps slightly modified his position by stating that "the sexual appetite is, above all, a general need of the organism based on a sensation of fullness, a sort of need of evacuation," L'Instinct sexuel, 1899, p. 6. Löwenfeld (Ueber die Sexuelle Konstitution, p. 30) gives a qualified acceptance to the excretory theory, as also Rohleder (Die Zeugung beim Menschen, p. 25).