The Relationship of the Tetracoralla to the Hexacoralla. 157 



Faurot (1909), using Duerden's method of grinding down the 

 coral tip and sketching each change in the arrangement of the 

 parts, obtained a very complete history of the septal sequence 

 in Cyathaxonia cornu. This led to an elaboration of Kunth's 

 law of pinnate arrangement. A short summary paper by the 

 same author (1914) gives his conclusion that in the case of the 

 hexacoral Turbinolia, and the tetracoral Cyathaxonia, there is 

 the same order of appearance and arrangement of the first twelve 

 septa. (See Fig. 3.) 



From the work of Lacaze-Duthiers, Von Koch, and others, 

 it has been known for a long time that among modern corals 

 some develop six primary septa, in others twelve septa appear 

 all at once. In Turbinolia it is reported, however, that there is 

 a stage with a ''single septum" of two septal elements, which is 

 succeeded by stages with four and six septa. Either the time of 

 the beginning of calcification is a stage easily retarded or accel- 

 erated, or the modern Hexacoralla must be considered as a 

 polyphyletic group. 



CONCLUSIONS. 



Although the ontogeny of corals, as far as septal sequence is 

 concerned, is now known for a considerable number of both 

 living and fossil genera, and is found to be quite uniform within 

 a group, the phylogenetic relations of the Tetracoralla and 

 Hexacoralla still are not wholly cleared up. Modern work on 

 the phylogeny of recent Anthozoa shows that the arrangement of 

 the mesenteries indicates most closely the various events in the 

 history of the phylum and therefore the most promising results 

 are apparently to be gained from a study of the arrangement 

 of septa in the two sub-classes. This method, as can be seen 

 from the above resume, has been applied by nearly all the recent 

 workers. It carries the assumption that the soft parts of the 

 polyp of the extinct Tetracoralla, of which nothing is known 

 except by analogy with modern forms, were essentially the 

 same as those of living Hexacoralla. This assumption is 

 considered to be justifiable by those who have studied both 

 groups. 



The results obtained by this method are divergent and those 

 relating to the results attained through ontogeny should be tested 

 in the light of chronogeny (geological appearance), and of the 



