. The coral Siderastrea radians and its postlarval development. Siderastrea radians Verrill. POSTLARVAL DEVELOPMENT. 103 The first two figures (a, b) correspond with plate 9, figs. 54-56, of the sections. The exoseptum is here simple, but bifurcated towards its periph- eral extremity. At first no mesenteries are included within the angle of bifurcation, but a pair has appeared in fig. 12, b. In relation to the mesen- teries the two limbs are clearly exoccelic, and may even at this stage be regarded as two individual exosepta. In fig. 12, c, one exoseptum has become distinct, and a short septum
. The coral Siderastrea radians and its postlarval development. Siderastrea radians Verrill. POSTLARVAL DEVELOPMENT. 103 The first two figures (a, b) correspond with plate 9, figs. 54-56, of the sections. The exoseptum is here simple, but bifurcated towards its periph- eral extremity. At first no mesenteries are included within the angle of bifurcation, but a pair has appeared in fig. 12, b. In relation to the mesen- teries the two limbs are clearly exoccelic, and may even at this stage be regarded as two individual exosepta. In fig. 12, c, one exoseptum has become distinct, and a short septum has appeared midway between the two older septa (c/. plate 9, fig. 57). Clearly this is a new entoseptum arising a little later than the new pair of mesen- teries. In fig. 12, d, the right exoseptum has also separated from the more central portion which is along the same radius as the entoseptum (cf. plate 9, fig. 58). The next figure, e, shows the exsert septa (cf. plate 9, fig. 59); the central part is becoming smaller, while it has disappeared in the last. FIG. la.—Series of diagrammatic figures illustrating figs 5t-6o on plate 9. figure, / (cf. plate 9, fig. 60), The entoseptum throughout extends the shortest vertical distance of the three, and so far as the development has pro- ceeded remains the smallest radially. Clearly when growth is completed the three septa will be related as shown in the six groups of fused septa in fig. io,/, p. 96, which is the usual relationship of the exosepta and entoseptum; the entoseptum in its further growth will have extended more centrally and fused with the central portion of the original exoseptum, and the two exosepta will turn inwardly to unite with it. The series of sections plainly demonstrates that a new entoseptum arises shortly after a new pair of mesenteries, not in advance of it, and the two peripheral limbs of a bifurcated exoseptum become distinct, so that each constitutes a new exoseptum. The new entoseptum takes the place
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