The origin of species :
by means of natural selection or the preservation of favored races in the struggle for life /
by Charles Darwin.

APA Citation

Darwin, C. (1900). The origin of species: by means of natural selection or the preservation of favored races in the struggle for life. 6th edition, with additions and corrections. London: J. Murray.

MLA Citation

Darwin, Charles, 1809-1882. The Origin of Species: by Means of Natural Selection Or the Preservation of Favored Races In the Struggle for Life. 6th edition, with additions and corrections. London: J. Murray, 1900.

Warning: These citations may not always be complete (especially for serials).