Zoologist, biologist (1868-1938).
Félix Étienne Pierre Mesnil (Omonville-la-Petite, La Manche department, 12 December 1868 – 15 February 1938, Paris) was a French zoologist, biologist, botanist, mycologist and algologist. He was a student of Alfred Giard at the École Normale Supérieure and a classmate of Maurice Caullery. From 1892 he worked at the Pasteur Institute, initially as an associate demonstrator. He was an assistant of Louis Pasteur, and in the meantime, performed studies on cellular immunity, physiology and comparative pathology in the laboratory of Ilya Ilyich Metchnikov (1845–1916). He founded the Pasteur Institut