APA (7th ed.) Citation

Darwin, C. (1998). On the origin of species by Charles Darwin. Project Gutenberg Literary Archive Foundation.

Chicago Style (17th ed.) Citation

Darwin, Charles. On the Origin of Species by Charles Darwin. Salt Lake City: Project Gutenberg Literary Archive Foundation, 1998.

MLA (9th ed.) Citation

Darwin, Charles. On the Origin of Species by Charles Darwin. Project Gutenberg Literary Archive Foundation, 1998.

Warning: These citations may not always be 100% accurate.