This plate, from a later book by Ernst Haeckel, shows a selection of vertebrate embryos from fish to human at three development stages. It was meant to illustrate the similarity between human and animal embryos. Haeckel explained that this is more complete at early stages and retained longer between more closely-related groups.
Haeckel’s scientific opponents accused him of drawing inaccurately to support his theories, and religious enemies taunted him with charges of forgery. His pictures were nevertheless very widely used in textbooks in the 20th century.