APA (7th ed.) Citation

Darwin, C., & Darwin, F. (2007). The Foundations of the Origin of Species Two Essays written in 1842 and 1844. Project Gutenberg.

Chicago Style (17th ed.) Citation

Darwin, Charles, and Francis Darwin. The Foundations of the Origin of Species Two Essays Written in 1842 and 1844. Project Gutenberg, 2007.

MLA (9th ed.) Citation

Darwin, Charles, and Francis Darwin. The Foundations of the Origin of Species Two Essays Written in 1842 and 1844. Project Gutenberg, 2007.

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