194 Prof. P. M. Duncan on the Hard Structures of 



correspond, the septa often arising from along other lines 

 than those of the direction of the costge, or. they may spring 

 from two spots and unite to form the trabecule along the line 

 of which arise the septal spinules. 



The junction of the opposite primaries may occur, or they 

 may only approximate towards the opening of the calice ; 

 very generally the inner ends of the septa have a few trabe- 

 culate processes joining them. 



When the new corallite is completed, the primaries are well 

 developed, and there are six small spinulose secondaries at the 

 calicular margin. The two opposite primaries are always the 

 largest, except in the apical corallites. Thickening of all the 

 mural structures then occurs, and in time budding will take 

 place from the new corallite-wall, and of course remotely 

 from the calicular margin. 



The secondary corallites never attain the dimensions of 

 mural, or fulness of septal, structure which characterize the 

 axial or apical corallite. The axial corallite has a margin 

 which is circular in outline and not nariform ; the mural struc- 

 ture is spongy in appearance, although formed of successive 

 exogenously growing layers. The septa are well developed, 

 there being six nearly equal primaries, some with slightly 

 spinulose inner edges, and six secondary septa which do not 

 reach the centre of the corallite and have spines on the free 

 inner edge. 



It will be of importance to study the soft parts of the two 

 kinds of corallites, for the impression left on the mind is that 

 the apical calices are much better suited for the presence of 

 mesenteries than the secondary corallites. 



In this species the budding is remote from the calicular 

 margin ; the wall of the bud is formed before the septa, which 

 are preceded by the costaj ; there is no special opening between 

 the cavity of the bud and the parent, and the bud may arise 

 from sclerenchyma remote from the wall of a corallite. 

 Finally the porosity of even the rapidly growing coral is 

 diminished by the comparative solidity of the costas and septa, 

 and by the calcareous deposition that occurs after a certain 

 stage of growth is passed. 



On the growth of " Immersed " Corallites. 



Second species : — 

 The species of Madrepora noticed above has a few immersed 

 calices, visible at the bases of the branchlets, which are the 

 openings of deeply seated corallites ; but their relations to the 

 surrounding structures are not well seen. It is therefore 

 necessary to seek a better example in an allied form. 



