Geoffroy Saint-Hilaire, Étienne (ātyĕnˈ zhôfrwäˈ săNtēlĕrˈ) [key], 1772–1844, French zoologist. He was professor at the Museum of Natural History (1793–1840) and also at the Faculty of Sciences (from 1809), both in Paris, and was a member (1798–1801) of Napoleon's scientific staff in Egypt. He expressed in his Philosophie anatomique (2 vol., 1818–22) and in other works the theory that all animals conform to a single plan of structure. This attracted many supporters but was strongly opposed by Cuvier, who had been his friend, and in 1830 a widely publicized debate between the two took place. Some of Geoffrey Saint-Hilaire's ideas have been confirmed by modern developmental biologists. His son, Isidore Geoffroy Saint-Hilaire, 1805–61, also a zoologist, was an authority on deviation from normal structure. He succeeded to his father's professorships.
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