APA (7th ed.) Citation

Hertwig, O., & Mitchell, P. C. (2011). The Biological Problem of To-day Preformation Or Epigenesis? The Basis of a Theory of Organic Development. Project Gutenberg.

Chicago Style (17th ed.) Citation

Hertwig, Oscar, and P. Chalmers Mitchell. The Biological Problem of To-day Preformation Or Epigenesis? The Basis of a Theory of Organic Development. Project Gutenberg, 2011.

MLA (9th ed.) Citation

Hertwig, Oscar, and P. Chalmers Mitchell. The Biological Problem of To-day Preformation Or Epigenesis? The Basis of a Theory of Organic Development. Project Gutenberg, 2011.

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