Étienne Geoffroy St. Hilaire (April 15, 1772 - June 1, 1884) was a French naturalist. After the Reign of Terror he was appointed a professor of vertebrate zoology at the Musée National d'Histoire Naturelle. In 1794, he invited the young naturalist, Georges Cuvier, to come to Paris. Cuvier and Geoffroy collaborated on several research projects. Geoffroy accompanied Napoleon's invasion of Egypt in 1798, and brought back many animal specimens to Paris, notably mummified cats and birds, which Cuvier would later study and cite as proof that evolution had not occurred. In 1807 Geoffroy was named to the Academie des sciences. In 1809 he became a professor of zoology at the University of Paris.
While Cuvier founded the "functionalist" school of organismal biology, with his insistence on animals as functionally integrated wholes, Geoffroy continued the more "formalist" tradition of biology that had started with Buffon and was being continued by Goethe, Lamarck, and others. In his 1818 book Philosophie anatomique, Geoffroy saw all vertebrates as modifications of a single archetype, a single form.
Geoffroy spent much time drawing up rules for deciding when structures in two different organisms were variants of the same type -- in modern terminology, when they were homologous. His criterion was connections between parts: structures in different organisms were the same if their parts were connected to each other in the same pattern.