AMERICAN PHILOSOPHICAL SOCIETY / SCIENCE PHOTO LIBRARY AMERICAN PHILOSOPHICAL SOCIETY / SCIENCE PHOTO LIBRARY
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Frank Rattray Lillie (1870-1947, right), American zoologist and embryologist. Lillie spent most of his career at the University of Chicago, USA, becoming Dean of Biological Sciences in 1931. He is best known for his work on fertilisation and sexual determination. He demonstrated that bovine freemartins (masculinised infertile females born when there are twins of each sex) were a result of male sex hormones in the blood and shared via the placenta.
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