This image from Ernst Haeckel's 1874 The Evolution of Man shows comparisons between cross-sections of different animals and their embryos at different stages of development. For Haeckel the development of an embryo retraced the evolutionary history of the animal. The different colors represent the four types of tissues out of which all the organs formed.
Ernst Haeckel. Anthropogenie, oder, Entwickelungsgeschichte des Menschen. Leipzig: W. Engelmann. 1874.