MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES 569 



(fig. 79, 85). It nowhere becomes :i typical columnar epithelium, but remains highly granular, 

 with indistinct cellular divisions, and nuclei here and there The skeletogenic ectoderm, and 

 less so the mesogloea and endoderm, are much indented, corresponding with the granules on the 

 septal face (tie'. S4). 



The gastro-coelomrc cavities of the different polyps communicate with one another by means 

 of the perithecal continuation- of the mesenterial chambers. In retracted polyps the perithecal 

 chambers are deeply concave outwardly, the mesenteries being very short, hut the inner wall 

 against the theca is nearly Hat. 



In the upper sections of retracted polyps the twelve mesenterial chambers, separated from one 

 another by the septal invaginations, and each containing two mesenteries, are in communication 

 with the middle of the gastro-ccelomic cavity. But below, each chamber becomes divided into 

 two by an exoccelic septal invagination, so that twenty-four mesenterial chambers are formed, each 

 containing only one mesentery. These chambers are wholly distinct from one another in sections, 

 separated by the septa and columella; the exoseptal invaginations do not reach the columella, 

 but unite laterally with the entoseptal invaginations of the second order (lie-. 84). 



B.—F I SSI PAR ANTES. 



ASEXUAL REPRODUCTION- TAKES PLACE BY STOMOD.EAL FISSION, WITHOUT THE PRODUCTION 

 OF MORPHOLOGICALLY COMPLETE POLYPS. THE TENTACLES, MESENTERIES, AND SEPTA, AFTER 

 FlsSinN Is F.S1 ABLISHED, ARE NOT ARRANGED IN REGULAR HEXAMERAL CYCLES, AND NO NEW 

 DIRECTIVE MESENTERIES ARISE. 



Genus FAVIA Oken ". 



Polyps verrucose, usually distinct, slightly distant; occasionally two or more oral apertures are 

 inclosed within a single tentacular system; gastro-ccelomic cavity and mesenteries prolonged peri- 

 thecally; form convex, hemispherical, free, or incrusting colonies. Column cylindrical, oval, or irregular 

 in outline, on retraction almost completely folded over the disk; no sphincter. Tentacles irregularly 

 multicyclic, entoccelic and exoccelic, stem tuberculated, knobbed or rounded terminally. Stomodseal 

 ridges well developed, variable in number. 



Mesenteries irregularly multicyclic, all filamentiferous, directives present only in larval polyps. 

 Septal invaginations entoccelic and exoccelic, irregularly multicyclic, not wholly uniting centrally; 

 mesenterial loculi only partly distinct, obliquely truncated basally. 



Asexual reproduction by partial or complete fission. Polyps monoecious, viviparous. 



Example. — Faviafragvm (Esper). 



FA VI A FRAGTJM (Esper). 

 I Pis. XIII-XY, flgs. 92-116. | 



Exit rnal characters. — The colonies are usually small..", to lo cm. in diameter, sul .hemispherical 

 or irregularly shaped, attached by a narrow base to dead coral masses or other foreign objects, 

 and inhabit the shallow waters on the reefs. They are easily detached from their basal support. 

 The surface of the colony is approximately regular when the polyps are retracted, but becomes 

 uneven during full expansion, as some polyps extend higher than others, and otherwise vary 

 much in size. The polyps may he either round, oval, or triangular in outline, and on full 

 expansion are separated <i or 7 mm. from one another. In the majority of cases only one oral 

 aperture is surrounded by a tentacular system, hut sometimes there may he two or even three 

 apertures on a single disk, and all stages toward complete fission by the ingrowth of the lateral 

 wall of the caliee are to be met with on a colony. 



The polygonal lines of union of the column wall of contiguous polyps are not clearly indicated 

 by any smooth groove, but perithecal mesenterial attachments, alternating with the costae, are 



""Colony hemispherical, convex, lobed, rarely subplane, fixed, free or incrusting. Corallites united by their 

 costa? and by a cellular exotheca. Calioes variable in distance, with free margins, subcircular, oval, deformed in 

 outline. The columella is spongy. The septa are exsert, cross the wall, and the septo-costse unite with those of 

 other calices, or are separated by a groove. The septa are dentate, ami the inner teeth simulate pali. Endotheca 

 well developed. Epitheca often exists. Increase by fissiparity, the resulting corallites soon becoming separate." 

 Duncan, L885, p. 100. I 



