"Haeckel was evidently just as fascinated with the protozoa, enough to write and illustrate a substantial monograph. Die Radiolarien (Rhizopoda radiaria): Eine Monographie (1862) is available at the Biodiversity Heritage Library and the Internet Archive in a mammoth four-volume set, a large portion of which is explanatory text. There’s also a separate volume with a … Continue reading Haeckel’s Radiolaria