The latest years in Haeckel’s constructive work are characterised mainly by _one_ idea. He had often been pressed to work up afresh the material of his _General Morphology_. He has not done so in the form that was expected, but chose a form of his own. In the first place he took the systematic introduction to the second volume, which had been the first able attempt to draw up the genealogical tree of the living world, branch by branch, and, with the material that had accumulated in the subsequent thirty-four years, built it up into a separate work. It had consisted formerly of 160 pages: now it formed three volumes of 1,800 pages. There were forty years of incessant study embodied in it. It had the title _Systematic Phylogeny_:[7] “a sketch of a natural system of organisms on the basis of their stem-history.” The first volume (dealing with the protists and plants) appeared in 1894; the second volume (dealing with the invertebrate animals) in 1896, and the third (dealing with the vertebrates) in 1895. Closely connected with it is his special systematic study of the stem-history of the echinoderms (star-fish, &c.), with particular reference to paleontology (_The Amphoridea and Cystoidea_ in the _Work in Commemoration of Karl Gegenbaur_, 1896). Footnote 7: It has not been translated into English. A recent reviewer in _Nature_ pronounced it to be Haeckel’s best work. [Trans.] His academic colleagues had hardly begun to master this new phylogeny when Haeckel once more roused a general agitation by working up the philosophic nucleus of the _Morphology_ in a more general form than he had done in the _History of Creation_. This new work was _The Riddle of the Universe_, “a popular study of the Monistic philosophy.”[8] It was, he declared, his philosophical testament. In a few months 10,000 copies of the work were sold, and a later cheap popular edition ran to more than 100,000 copies. It has also been translated into fourteen different languages. The controversy it excited has not yet died away. Already a supplementary volume, _The Wonders of Life_, has followed it (1904). Haeckel had been working in this department with great vigour for many years. He only made one appearance at a German scientific congress since the Virchow affair. That was on September 18, 1882, in quiet and uncontroversial form. A little excitement was caused amongst those who saw their salvation in keeping the gentle Darwin far apart from the impetuous Haeckel when he read a rather free philosophical confession of Darwin’s. Their tactics broke down as the deceased Darwin passed into an historical personality and disappeared from the struggle of contending parties. In 1892 Haeckel wrote with great vigour in the militant Berlin journal, the _Freie Bühne_, on the new alliance of the Church and political parties in Germany, criticising the political situation on general philosophical principles, and in opposition to Virchow’s spirit of compromise.