Offprint from the Jen. Zeitschritft für Naturwissenschaft, Bd. XXII. Haeckel (1834-1919) studied with several naturalists, including Johannes Müller, before taking up the position of professor of zoology at the University of Jena in 1862 (a position he held until 1909). Haeckel’s many zoological monographs contained reports of nearly four thousand new species of lower marine animals, mainly radiolaria, medusae and sponges, for which he tried to establish phylogenetical natural systems. His article on the siphonophorae is based upon the collections made by the Challenger expedition under Wyville Thompson,, to which reference is made in the opening pages. The article preceded Haeckel’s monograph on the same subject, which appeared in 1888 as volume 28 of the scientific results of the voyage of H.M. S. Challenger; parts of Haeckels’ article appear in the Introduction to that report. Inscribed copies of Haeckel’s works are not common, this being a presentation to Johan Axel Palmén (1845-1919), professor of zoology at the University of Helsinki, Finland.