Ernst Haeckel was one of the great biologists of the 19th century, and he contributed greatly to the study of protozoan diversity, especially of the large marine actinopods - the radiolaria (at that time, this group included the polycystines, phaeodarea and acantharea). He carried out many of his key observations as part of a major scientific cruise organized by the British scientific establishment, that of the HMS Challenger, and his results were published in the (massive) reports from that cruise. Ernst Haeckel is also remembered for improving'on what he saw. He contributed to von Baer's concepts that ontogeny recapitulates phylogeny by showing similarities in comparable developmental stages in embryos of different vertebrates. His contributions are now criticized because he embellished his observations to overemphasize similarities. Despite this, and some strange views on humanity, his contributions to protistology have been massive. This is his first major synthesis of work on the radiolaria. The Challenger report, published 25 years later, is an even more massive account of the same organisms. Image from the cover of the book. Image out of copyright.