Morphology of the Madreporaria. 393 



h. Larval polyps of fissiparous corals at first present a 

 regular cyclical hexameral arrangement of the mesenteries, 

 tentacles, and septa. The first fission partially or wholly 

 divides the polyp into two practically equal parts in an ento- 

 coelic plane at right angles to the directive plane, each 

 half having but one pair of directive mesenteries. In the 

 later growth new mesenteries arise in isocnemic pairs more 

 rapidly in some regions than in others, and thus destroy the 

 regularity of the cj^clical hexameral plan. Additional oral 

 apertures and stomoda3a, with which a variable number of 

 mesenteries are associated, arise at somewhat regular intervals. 

 The various stomoda3al systems may remain in continuity 

 with the common gastro-coelomic cavity, or partitions may 

 be formed in a greater or less number and lead to their 

 partial or complete separation. No new pairs of directives 

 ever arise, so that, however large the polypal system may 

 become, never more than the two primary pairs of directives 

 are present. 



c. Morphologically a fissiparous coral, whatever its size, 

 is to be regarded as only a single complex polyp, as contrasted 

 with a gemmiferous colony, which is made up of numerous 

 distinct individual polyps. 



References. 



1873. Lacaze-Duthiers, II. de. " Ddveloppemeut des Coralliaives. 

 Deux. M6m. Actiniaiies a Polypiers," Arcliiv. de Zool. Exp. et 

 G^n. torn. ii. 



1887. Bourne, G. C. " On the Anatomy of Mussa and Eujjhyllia 

 and the Morphology of the Madreporarian Skeleton," Quart. 

 Journ. Micr. Sci. vol. xxviii. 



1888. Fowler, G. H. " The Anatomy of the Madreporaria. — III.," 



Quart. Journ. Micr. Sci. vol. xxviii. 

 1888. Wilson, H. V. " On the Development of Manicina areolala," 



Journ. Morph. vol. ii. 

 1890. Obtmann, a. " Die Morphologie des Skelettes der Stein- 



korallen in Beziehung zur Kolouiebildung," Zeit. f. wiss. Zool. 



bd. 1. 



1896. VON Koch, G. ' Das Skelett der Steinkorallen.' Leipzig. 



1897. VON Koch, G. " Entwicklung von Caryophyllia cyathm" Mitt, 

 a. d. zool. Stat, zu Neapel, bd. xii. 



1897. Lac AZE-DuTHiBHS, Ii. DE. " Faune du Golfe du Lion. Coral- 

 liaires. Zoanthaires Sclerodermas," Archiv. de Zool. Exp. et 

 G^n. 3 S(5r., torn, v, 



1901. Vaughan, T. W. "The Stony Corals of the Porto Kican 

 Waters," U.S. Fish. Conim. Bull, for 1900, vol. ii. 



1901. Verhill, a. E. " Variations aud Nomenclature of Bermudian, 

 West Indian, and Brazilian Reef-Corals, with Notes on various 

 Indo-Pacific Corals," Trans. Coon. Acad. Science, vol. xi. 



1902. Duerden, J. E. " The Morphology of the Madreporaria. — II. 

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