This masterpiece of scientific illustration was published by German biologist Ernst Haeckel (1834—1919) in 1904. Kunstformen der Natur (“Art Forms of Nature”) consists of 100 lithographs of various organisms, many which were first described by Haeckel himself. The book was highly influential in early 20th-century art. (Source: Wikipedia)
A high-res PDF of the book can be downloaded here (272 MB), digitized by Kurt Stüber at the Max Planck Institute for Plant Breeding Research. The license of this specific high-res version allows personal and educational use. The complete set of 100 tables can also be found over at Wikimedia Commons, where they are marked as Public Domain.