1. Aristotle: Über Zeugung und Entwicklung der Tiere (On the Procreation and Development of Animals). Works in Greek and German. Vol. 3, pp. 149 and 736b. Leipzig, 1860;
2. Aristotle: Hauptwerke (Major Works). German translation by W. Nestle. p. 176. On the Soul. Stuttgart, 1953;
3. Aristotle: Physiognomik (Physiognomy). Heidelberg, 1929;
4. Aristotle: Naturgeschichte der Tiere (Natural History of Animals). German translation by Kersch. Vol. 3, 1, p. 119. Stuttgart, 1866.
5. Babkin, P. S.: Z. Nevropath. i psichiat. (Russian) 56, 22 (1956).