Darwin, Origin of Species, Chap. V, p. 166. New York, 1895.
R. Virchow, Rassenbildung und Erblichkeit, Bastian Festschrift,pp. 14, 43, 44. Berlin, 1896.
Darwin, Descent of Man, pp. 34-35. New York, 1899.
Darwin, Origin of Species, Chap. I, pp. 8-9. New York, 1895.
P. Ehrenreich, Die Urbewohner Brasiliens, p. 30. Braunschweig, 1897.
Ratzel, Die Erde und das Leben, Vol. I, pp. 364, 365. Leipzig and Vienna, 1901.
W.Z. Ripley, Races of Europe, pp. 79-86, 96, 100. New York, 1899.
T. Waitz, Anthropology, pp. 57-58. Edited by J.F. Collingwood. London, 1863.
Schoolcraft, Indian Tribes of the United States, Vol. I, pp. 198-200, 219. Philadelphia, 1853.