390 HISTORY OF GEOLOGY AND PALEONTOLOGY. 



Milaschewitsch, D'Archiardi; and Duncan's book on British 

 fossil corals has enjoyed a wide circulation. Quenstedt alone 

 adheres both in his text-books and Mis Paleontology of Germany 

 (vol. vii., 1889) to the old system of Ehrenberg, and continues 

 to group the Bryozoa along with the corals. 



A short but very important paper was published in 1869 

 by A. Kunth. This observer pointed out the fundamental 

 difference in the method according to which new septa had 

 developed in the Palaeozoic group of the Rugosa, as compared 

 with the order of intussusception of the septa in the younger 

 corals; and he showed how with this difference was associated 

 the bilateral symmetry of the Rugose corals on the one hand, 

 and the radial symmetry of the younger corals. After the 

 publication of Kunth's memoir, the Rugose corals, also known 

 under the synonyms of " Tetracorallia " or " Pterocorallia," 

 were treated as an independent group in the classification of 

 corals, distinct from the younger group of " Hexacorallia," for 

 which Milne-Edwards' and Haime's observations still held good. 

 Kunth's work gave a new impulse to the study of the Rugose 

 group of Palaeozoic corals, and was followed by a number of 

 special memoirs, those of Dybowski, Nicholson, Schliiter, 

 Lindstrom, and Freeh, among many others. 



In 1872, Lacaze-Duthiers made known his valuable embryo- 

 logical investigations, which necessitated a new revision of the 

 laws of septal symmetry enunciated by Milne-Edwards and 

 Haime. The discoveries made by L. Agassiz and Moseley 

 regarding the zoological relationship of Millepora and Helio- 

 pora entirely overthrew the group of Tabulata as it had been 

 defined in the system of Milne-Edwards and Haime. And 

 Dybowski, Roemer, Nicholson, and other leading authorities 

 on Palaeozoic corals then endeavoured by the most detailed 

 investigations of the growth-relations, the organisation, and 

 finer structure, to explain the remarkable diversity of forms 

 comprised in this group. 



The microscopic structure of the calcareous skeleton had 

 been little taken into consideration by Milne-Edwards and 

 Haime. In 1865, Kolliker first directed attention to it; in 

 1882, there followed almost simultaneously the works of Pratz 

 and Koch, showing illustrations of microscopic sections, and 

 a similar method was followed by Nicholson, Freeh, Volz, 

 Felix, Struve, and others. The most comprehensive investiga- 

 tion into the microscopic structure of the skeleton of living and 



