APA (7th ed.) Citation

Calkins, G. N. (1941). Protozoa in biological research. Hafner Publishing.

Chicago Style (17th ed.) Citation

Calkins, Gary N. Protozoa in Biological Research. New York: Hafner Publishing, 1941.

MLA (9th ed.) Citation

Calkins, Gary N. Protozoa in Biological Research. Hafner Publishing, 1941.