APA (7th ed.) Citation

Gaskell, W. H. (2013). The Origin of Vertebrates. Project Gutenberg.

Chicago Style (17th ed.) Citation

Gaskell, Walter Holbrook. The Origin of Vertebrates. Project Gutenberg, 2013.

MLA (9th ed.) Citation

Gaskell, Walter Holbrook. The Origin of Vertebrates. Project Gutenberg, 2013.

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