APA-referens (7:e uppl.)
Richards, R. J. (2008). The tragic sense of life: Ernst Haeckel and the struggle over evolutionary thought. University of Chicago Press.
Chicago-referens (17:e uppl.)
Richards, Robert J. The Tragic Sense of Life: Ernst Haeckel and the Struggle over Evolutionary Thought. Chicago: University of Chicago Press, 2008.
MLA-referens (9:e uppl.)
Richards, Robert J. The Tragic Sense of Life: Ernst Haeckel and the Struggle over Evolutionary Thought. University of Chicago Press, 2008.
Varning: dessa hänvisningar är inte alltid fullständigt riktiga.