Franz Keibel studied the embryos of humans and other animals in Europe at the turn of the twentieth century. He lived and worked in several different parts of Germany and France. Keibel drew illustrations of embryos in many stages of development. Keibel used these illustrations, which he and others in the scientific community called normal plates, to describe the development of organisms in several species of vertebrates. His illustrations are published in the sixteen-volume text Normentafeln zur Entwicklungsgeschichte der Wirbelthiere (Normal Plates of the Developmental history of Vertebrates), published in 1895, and in the Manual of Human Embryology, which he edited with Franklin Paine Mall of the US, published in 1912. Keibel's plates showed human embryos in different stages of development between the twelfth day and the second month after fertilization.