PALAEONTOLOGY. 385 



In addition to the Foraminifera, the Radiolarians with 

 siliceous or chitinous tests represent another class of Protozoa 

 which come under consideration in palaeontological researches. 

 The knowledge of the Radiolaria does not extend so far back 

 as that of Foraminifera. The earliest accounts of these micro- 

 scopically minute organisms were given by Tilesius (1806) 

 and by Meyer (1834); but Ehrenberg was the first investigator 

 who disclosed the wonderful variety and beauty of their sili- 

 ceous skeletons. In a series of special monographs and 

 magazine articles extended over a long period of years from 

 1838 to 1875, Ehrenberg described many hundred forms 

 belonging to this group, which he had called Polycystina. His 

 material had been collected from recent oozes on the ocean- 

 floor, and from the Tertiary marls of Sicily, Zante, Oran, 

 North America, and Barbadoes, the last-mentioned locality 

 alone providing 278 species. But Ehrenberg had very obscure 

 notions about the organisation of the Polycystina. 



The living structure and the systematic position of this 

 group were elucidated by Huxley in 1851. A fuller exposition 

 of the zoological aspects was given in 1855 by Johann Miiller, 

 who suggested the term of Radiolaria as better suited for the 

 group than Ehrenberg's name of Polycystina. The beautifully 

 illustrated monograph of the Radiolaria by Ernst Haeckel 

 erected a complete classificatory system for the Radiolaria, 

 and won universal admiration for the artistic representations of 

 the infinite diversity in the skeletal forms produced by these 

 simple organisms. 



Haeckel's works are chiefly devoted to recent Radiolaria, 

 and at that time, in 1862, science was only cognisant of the 

 occurrence of fossil Radiolaria in the Tertiary deposits. 

 Zittel, in 1876, described some older forms from Upper Cre- 

 taceous strata, and between 1885 and 1892 D. Riist carried 

 out a long series of researches, preparing microscopic sections 

 of siliceous rocks from all the geological formations ; he suc- 

 ceeded in demonstrating the presence of numerous Radio- 

 larian species from the Cambrian or oldest Palaeozoic 

 formation onwards to the present age. 



Brief mention must be made of a controversy that arose 

 regarding certain structures thought to represent the oldest 

 known animal organism. In the year 1858 MacCulloch col- 

 lected in the Laurentian gneiss of Canada curious aggregates 

 of serpentine and calcite, arranged in irregular alternate 



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