APA (7th ed.) Citation

Darwin, C. (1999). On the origin of species by Charles Darwin (6th edit.). Project Gutenberg Literary Archive Foundation.

Chicago Style (17th ed.) Citation

Darwin, Charles. On the Origin of Species by Charles Darwin. 6th edit. Salt Lake City: Project Gutenberg Literary Archive Foundation, 1999.

MLA (9th ed.) Citation

Darwin, Charles. On the Origin of Species by Charles Darwin. 6th edit. Project Gutenberg Literary Archive Foundation, 1999.

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