[180] D. Ferrier: The Functions of the Brain, p. 111, London, 1886.
[181] A. Hill: Can Birds Smell? Nature, vol. 71, pp. 318, 319, 1905.
[182] W. Mills: The Nature and Development of Animal Intelligence, pp. 248, 250, New York, 1898.
[183] Hachet-Souplet: Examen Psychologique des Animaux, pp. 33-38, Paris, 1900. See also Riverside Natural History, vol. 4, pp. 240, 241, Cambridge, 1888.
[184] Orientation chez le pigeon-voyageur, Revue Scientifique, vol. 13, pp. 352-359, 1900.
[185] Orientation du pigeon-voyageur, Revue Scientifique, vol. 2, pp. 417-420, 453-457. 1904.
[186] Grundlinien zur Erforschung des Helligkeits- und Farbensinnes der Tiere, p. 102, Prague, 1888.
[187] Some Notes on the Psychology of Birds, Seventh Annual Report of the New York Zoölogical Society, p. 154, 1902.
[188] Ueber die Begleiterscheinungen psychischer Vorgänge in Athem und Puls, Philosophische Studien, vol. 18, pp. 7-14, 1901.
[189] Animal Intelligence, pp. 8-12, 31-36, 51-55, New York, 1898.