IMPORTANCE OF THE QUESTION OF 

 PRIMARY SEPTA. 



The ontogeny of the Tetracoralla has been the subject of a 

 great deal of investigation and debate. It is a difficult subject 

 because the group is extinct and any reasoning which involves 

 the soft parts of the polyps must be done by analogy with living 

 corals, while the part which is preserved as a fossil represents 

 merely a substructure, external and not readily modified by vital 

 changes in the function of the soft parts and yet at the same 

 time extremely impressionable by varying or accidental external 

 forces. 



Because of the importance of the primary septa in the discus- 

 sion of the phylogeny of the Tetracoralla the various papers 

 on this subject have been repeatedly summarized and only a short 

 account of them will be given here. Other summaries may be 

 found in Duerden (1902) and Faurot (1909). 



THEORIES OF PREVIOUS WRITERS. 



Milne-Edwards and Haime (1851) regarded the Tetracoralla 

 as having four primary septa to which the other (secondary) 

 septa were added. 



Ludwig (1861-66) insisted on the importance of the pinnate 

 arrangement of septa in four groups but considered this condition 

 to have been derived from an earlier grouping by six, and also 

 that there were six primary elements, only four of which were 

 involved in the formation of succeeding septa. 



Kunth (1869) also clearly described the pinnate manner of 

 addition of the secondary septa. 



Pourtales (1871) announced the discovery of an early stage 

 of growth with only six septa. The specimens used were of 

 Lopliophyllum proliferum and conclusions were reached similar 

 to those of Ludwig already stated. 



Quelch (1886) and Ogilvie (1897) paid much attention to the 

 microstructure, finding evidence of a close relationship between 

 Tetracoralla and Hexacoralla. 



Neumayr (1889 A and B) presented a strong argument for the 

 view that Hexacoralla are directly descended from the Paleozoic 



