The layers of cells in an embryo, also known as germ layers, develop in stages to create all the parts of the living body. This image from 1874 illustrates exactly that. Showing the differing shapes of differing embryos, but matching the colors of each system across them, creates an effective tool.
For example, the yellow tube near the center of each figure is the neural tube, which will go on to become the central nervous system of the organism. Studying the development of the body in this way can be helpful as well pleasing to the eye.
|Illustration from Anthropogenie oder Entwickelungsgeschichte des menschen: gemeinverständliche wissenschaftliche Vorträge über die Grundzüge der menschlichen Keimes- und Stammes-Geschichte by Ernst Haeckel. 1874. Hagstromerbibloteket.|