508 



MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



The phenomena presented by the early divisions of ^[((n'loiiKi clearly prove that fission actually 

 takes place in a phme at rio-ht angles to the long- axis of the mouth and stomodauun; otherwise 

 the regular distribution to each daug'hter stomodajum of six complete pairs of mesenteries, 

 derived from the primary twelve pairs, with one pair of directives only at opposite extremities, 

 would be iucouceival)le. Although among the many living colonies whicli have been examined, 

 examples in which the oral aperture or stomodseum was in the actual process of division have 

 not been observed, yet fre(|uently two small luouths are found in close proximity, suggesting 

 that they have arisen from the splitting of a single larger aperture. 



The later divisions in Mauiclna reveal that the tission of the stomodreum, along with its 

 associated mesenteries, is not always median, or results in the production of equal halves. 

 Sometimes in living pol^'ps a very small aperture will be found, as if cut off from a larger, and 

 only a few mesenteries are associated with it compared with the number united with the latter. 



FISSION IN FAVIA. 



Favia fragum occurs in some abundance on the I'eefs throughout the West Indies, forming 

 small, convex, hemispheroidal or irregular colonies, usually four to five centimeters in diameter. 



m 



EI 



m 



in 



cL. 



Fig. 15 (a-d). 

 Favia fragum.— Figs. 15. Diagrammatic, figures illustrating the mesenterial seijuenco and fission in iarrfe. a, Larva with three pairs of 

 protocnemes, of which only one pair is comijletc (<■/. PI. XIV. fig. 112). b. Larva with three protoenemic pairs, of which two are 

 complete (c/. PI. XV, tig. 113). r. Larva with five pairs of protocnemes, of which three pairs are complete and two pairs incomplete 

 (c/. PI. XV, fig. 115). (/, Larva at stage of li.tation, with Edwardsian mesenteries complete and fifth and sixth pairs incomplete. 



New polyps are added to the colony Ijy division of the older polyps, apparentl}' never by bud- 

 ding. A polyp sometimes exhibits two or three oral apertures on a single elongated or ti-iangu- 



