122 THE GENUS MONTICULIPORA. 



adjoining tubes being recognisable. The actual orifices of the 

 corallites are surrounded by a fibrous and laminated ring, and 

 the intervening spaces between them are occupied by structure- 

 less sclerenchyma perforated by numerous minute thick-walled 

 apertures, belonging to the interstitial tubuli of the colony. 

 Some of these interstitial tubes are of comparatively large size, 

 and show a well-defined central cavity; others are much smaller, 

 and show only a very limited lumen, or none at all, appearing 

 in the latter case merely as dark spots. In any case, numer- 

 ous as are these interstitial tubes, they normally form only a 

 single row between adjacent corallites, and there can be no 

 doubt but that the surface-spines which surround the margins 

 of the calices are really their upper terminations. 



Longitudinal sections (PI. III. figs. \e and \f) show that 

 the corallites are vertical in the centre of the stems, bending 

 outwards at a considerable ancrle to reach the surface. In the 

 axial part of their course they are provided with thin and 

 delicate walls, but their visceral cavities are considerably con- 

 tracted in the outer portion of their course by a secondary 

 deposit of laminated sclerenchyma, by which the walls be- 

 come greatly thickened. I am, however, not able to confirm 

 M 'Coy's statement that this thickening is periodic, and gives 

 rise to a moniliform structure of the wall, such as is charac- 

 teristic of the genus Stcnopora, properly so called — all my 

 observations going to prove that the thickening of the walls 

 of the corallites is effected continuously, and leads to results 

 precisely similar to those observed in many other species of 

 Monticulipora {e.g., J\I. gracilisy James). Longitudinal sec- 

 tions also show that complete horizontal tabulae are developed 

 in moderate numbers, both in the axial and circumferential 

 portions of the corallites. There is therefore no reason to 

 accept the views of those who are disposed to think that 

 tabulae are wanting in this species ; while I have found no 

 evidence of the perforated tabulae which M'Coy states he 

 has observed closing the mouths of the corallites in this 

 species. The interstitial " spiniform corallites " are only 



