GROWTH OF IDEAS 291 



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 Fhijlogeyiy : * 

 ^' 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 in- 

 vertebrate 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 

 ainphoridea and cystoidea in the Worh in Com- 

 memoration of Karl Gegenhaur^ 1896). 



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 philo- 

 sophy." i It was, he declared, his philosophical 

 testament. In a few months 10,000 copies of the 

 w^ork were sold, and a later cheap popular edition 



* It has not been translated into English. A recent re- 

 viewer in Nature pronounced it to be Haeckel's best work. 

 [Trans.] 



t Literally, the title is " World-Eiddles," or •' World- 

 Problems." [Trans.] 



