MORPHOLOGY OF THE MADREPORARIA. IO3 



those between the entotentacles and exotentacles. The law of 

 substitution, first discovered by Lacaze-Duthiers for the tentacles 

 of Hexactinias, is thus found to hold also for the septa. 



8. Where the cyclic hexamerism of a corallite is incomplete 

 the ordinary cyclic formula does not express the true relation- 

 ships of the septa ; the entosepta and exosepta vary in the same 

 degree, so that the true morphological septal formula for a cor- 

 allite with three cycles and part of another is 6; 6, X, 6 -f 6 + A' 

 where X may be any number from i to 12. 



9. The cycles of septa and mesenteries represent so many dis- 

 tinct recurring phases of growth at intervals all round the polyp, 

 not a continuous increase from one extremity to the other as in 

 metameric animals. With the exception of the first the mem- 

 bers of each cycle follow a dorso-ventral succession, display a 

 bilateral symmetry for some time, and ultimately assume an 

 approximate radial plan. The succession for the third cycle of 

 entosepta is two-fold. 



REFERENCES. 



Delage, Y., and Herouard, E. 



'01 Les Ccelenteres. Traite de Zoologie Concrete, torn. II., Pt. 2. Paris. 



Duerden, J. E. 



'02 West Indian Madreporarian Polyps. Mem. Nat. Acad. Sciences, vol. VIII., 

 7th Mem. 



Faurot, L. 



'95 Etudes sur 1'anatomie, 1'histologie et le developpement des Actinies. Arch, 

 de Zool. Exp. et Gen., ser. 3, vol. III. 



Gardiner, J. S. 



'02 South African Corals of the Genus Flabellum, with an account of their Anat- 

 omy and Development. Marine Investigations in South Africa. Vol. II., 

 Cape Town. 



von Koch, G. 



'81 Mittheilungen iiber das Kalkskelet der Madreporaria. I. Das Vermehr- 

 ungsgesetz der Septen. Morphl. Jahrb. , bd. VIII. 



von Koch, G. 



'82 Ueber die Entwickelung des Kalkskeletes von Astroides calvcularis und 

 dessen morphologischer Bedeutung. Mitt. a. d. Zool. Stat. zu Neapel, bd. 

 III. 



von Koch, G. 



'97 Entwickelung von Caryophyllia cyathus. Mitt. a. d. Zo5l. Stat. zu Neapel, 

 bd. XII. 



