WEMOIKS OF THE NATIONAL ACADEMY OF SCIENCES 569 



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

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

 less so the mesogkea and endoderDi, are much indented, corresponding with the granules on the 

 septal face (fig. 84). 



The gastro-ccelomic cavities of the ditl'erent polyps communicate with one another by means 

 of the perithecal continuations of the mesenterial chambers. In retracted polyps the perithecal 

 chambers are deeply concave outwardlj', the mesenteries being very short, liut the inner wall 

 against the theca is nearly flat. 



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 conniiunication 

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

 two by an exocoelic septal invagination, so that twenty-four mesenterial chambei's are formed, each 

 containing only one mesentery. These cham))ers are wholly distinct from one another in sections, 

 separated ])y the septa and columella; the exoseptal invaginations do not reach the columella, 

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



B.—F I SSI PAR ANTES. 



ASEXUAL REPRODUCTION TAKES PLACE BY STOMODjEAL FISSION, WITHOUT THE PRODUCTION 

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

 FISSION IS ESTABLISHED, ARE NOT ARRANGED IN REGULAR HEXAMEKAL 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; g-astro-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. Stomodeeal 

 ridges well developed, variable in number. 



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

 Septal invaginations entoccelic and exocoelic, 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. — Facia fragutn (Esper). 



FAVIA FRAGUM (Esper). 

 (Pis. XIII-XV, figs. 92-116.) 



External characters. — The colonies are usually small, .5 to 10 cm. in diameter, subhemispherical 

 or irregulai'ly shaped, attached b_v a narrow base to dead coral masses or other foreign objects, 

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

 The surface of the colony is appi'oximately regular when the polvps are retracted, but becomes 

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

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

 expansion are separated 6 or 7 mm. from one another. In the majority of cases onlj' one oral 

 aperture is surrounded by a tentacular system, but 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 calice are to be met with on a colonv. 



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 ccJstaj, are 



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

 cost* and by a cellular exotheca. Calices variable in distance, with free margins, subcircular, oval, deformed in 

 outline. The columella is spungy. - The septa are exaert, cross the wall, and the septo-fOstR> unite with those of 

 other calicea, or are separated by a groove. The sejita are dentate, and tlie inner teeth sinuilate pali. Endotheca 

 well develcipeil. Epitheca often exists. Increase by tissiparity, the resulting corallites soon becoming separate." 

 (Duncan, 188.5, p. 100. I 



