The Riddle of the Universe (Barnes & Noble Digital Library): At the Close of the Nineteenth CenturyErnst Haeckel
Freedom in Science and Teaching. from the German of Ernst Haeckel: Advancing Knowledge Through Unrestricted Inquiry and EducationErnst Haeckel
The Riddle of the Universe at the close of the nineteenth century: Exploring Evolution, Cosmos, and Life in the 19th CenturyErnst Haeckel
The Wonders of Life: A Popular Study of Biological Philosophy: Exploring Nature's Marvels: A Philosophical Journey through Biological WondersErnst Haeckel
The Last Link: Our Present Knowledge of the Descent of Man: Unveiling the Origins of Humankind: A Evolutionary Journey through TimeErnst Haeckel