Comparative embryology by von Baer. 19th-century illustration of the theories of German scientist Karl Ernst von Baer (1792-1876) on the comparative anatomy of different animal embryos. Across top are an embryo and yolk developing in a chicken's egg (from the ovary to 24 hours after incubation starts). The middle four diagrams show aspects of an idealised vertebrate embryo. At lower left are annelid (worm) and arthropod (figure 8) and jellyfish (figure 9) embryos. Figures 11 to 14 show the directions of development of four types of embryos: 'radiates', 'molluscs', 'articulates' and vertebrates. Von Baer studied the development of animal embryos and compared them (a science known as comparative embryology), giving insights into animal evolution. His work led to Baer's laws of embryology. This page is the third plate from von Baer's 'Uber Entwickelungsgeschichte der Thiere' (On the evolutionary history of animals, 1828).