APA (7th ed.) Citation

Darwin, C. (1998). The Expression of the Emotions in Man and Animals. Project Gutenberg.

Chicago Style (17th ed.) Citation

Darwin, Charles. The Expression of the Emotions in Man and Animals. Project Gutenberg, 1998.

MLA (9th ed.) Citation

Darwin, Charles. The Expression of the Emotions in Man and Animals. Project Gutenberg, 1998.

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