128 EXPLANATION OF PLATES. 



and the independent character of the exoseptum on each side (c/. fig. 15). Synapticula now connect some 

 of the adjacent septa. The origin of part of the columella from nodular upgrowths, independent of the 

 inner septal edges, is very evident. The basal plate is thicker peripherally than centrallv, and the epitheca 

 is onlv feebly developed at the margin. Diameter of original, 2 mm. 



Fig. 29. The details presented are practically the same as in the previous figure, but the growth of 

 the three septa within the ventro-lateral sextants has reached the same stage as in the other sextants. 

 The epitheca is better developed than in fig. 28. 



Fig. 30. Double corallum produced by two polyps the larv* of which settled close together. Each 

 has an independent epithecal formation, the part common to boih bemg very irregular. The septa have 

 not preserved the regular hexameral plan. 



Plate 6. 



Fig. 31. Three fully expanded adult polyps, showing the forms assumed by the polyps and the 

 arrangement of the bilobed and simple tentacles. 



Fig. 32 Nearly mature polyp preserved in formalin in a partly expanded condition; surface view. 

 The tentacles over the third-cycle entosepta 'III) are still simple and resemble the exotentacles (X). 



Fig. 33. An isolated interseptal lamella from a decalcified polyp. The lower margin represents the 

 part of the lamella which rested upon a dissepiment, and about the middle nearly surrounded a synap- 

 ticulum. The apertures (.y) are the spaces formerly occupied by the synapticula. The column wall, 

 disc, a bifurcated tentacle, stomodjeum, and a mesenterial filament are shown. 



Fig. 34. Transverse section of a mature polyp, passing through the stomodsal region. The figure 

 shows the arrangement of the mesenteries, the septal invaginations, and synapticula. In this and other 

 figures the spaces occupied by the skeleton are represented by the dotted areas. 



Fig. 35. Transverse section through a portion of the calicinal ridge of two retracted polyps, showing 

 the continuity between the mesenterial chambers of adjacent polyps, and also the vertical free edge of the 

 mesenteries as they extend from the column wall to the skeletotrophic tissues. In the upper part the 

 septa are exsert, but below they are united with the calicinal wall {ex. sepi., e.xoseptum ; ert/. sept., 

 entoseptum). 



Fig. 36. Tangential section towards the periphery of a polyp. The column wall rests upon the septal 

 edges, and the mesenteries have a short vertical extent. 



Plate 7. 



Fig. 37. (7, fully expanded entotentacle ; b, fully expanded exotentacle. 



Fig. 38. Transverse section of the same polyp as in fig. 34, taken a little below the stomodaeal region. 



Fig. 39. Transverse section of a polyp towards its aboral region. The mesenterial loculi are alto- 

 gether isolated at this level, and appear further broken up by the synapticula stretching from one septum 

 to another. The mesenteries have almost disappeared and the middle of the section is occupied by the 

 columella. The skeletal ectoderm and endoderm are both represented. 



Fig. 40. Tangential section through the tentacular region. A single bilobed entocoelic tentacle is 

 almost resting upon a septal edge. In the septal invagination {sep. inv.) the calicoblast layer is repre- 

 sented. 



Fig. 41. Transverse section through a mesentery at the level represented in fig. 35. The meso- 

 glceal plaitings for the support of the retractor muscles are simple in character, the oblique musculture 

 is feebly seen, and also the desmoidal processes where the mesentery is attached to the skeletotrophic 

 layer {sk. I.). 



Fig. 42. Transverse section through a mesenterial filament immediately below the stomodieal region. 



Fig. 43. Transverse section of a mesentery some distance below the stomodreal region, showing the 

 form of the mesenterial filament, and also a single ovum; the peripheral end of the mesentery is under- 

 going resorption. 



Fig. 44. a, small nematocysts from the knob of the tentacle and column wall ; *, elongated form of 

 nematocysis from the knob of the tentacle and mesenterial filaments; c, large oval nematocyst from the 

 lower part of the mesenterial filaments. 



