some Species o/" Madrepora. 191 



colony are made, one is impressed with the exceeding tough- 

 ness of the verj fragile-looking coral, and with the very 

 regularly concentric exogenous method of increase. Con- 

 centric circles of thin calcareous structure are seen separated 

 by radiating linear pillars ; the circles having been, in turn, 

 outside walls, and the radii either spinules or costee. 



If the coral is old, the circle of calcareous tissue immediately 

 around the septal cavities is dense, and so also may be a 

 second or a third circle ; but if the coral is growing rapidly, 

 the circles are less defined, of thinner substance, and less 

 regularly arranged. Moreover the nature and appearance of 

 the radiating structures differ according to the rapidity of 

 growth, and the original lamination or spinulation of the 

 costse. Some sections show very solid laminated costee pass- 

 ing up through the concentric mural circles and terminating 

 externally, in free costal edges, with or without spinules upon 

 them. Other sections exhibit a more confused radiation of 

 short, crooked, slender costee ; and near the surface of the coral 

 very distinct tall spinules are separate, conical, and support 

 the last produced film of mural tissue. 



There is always a quantity of concentric mural tissue around 

 the apical or terminal corallite, which is visible around its 

 calice. This structure may be mainly composed of costal 

 lamellse, united by fine, concentric, and often irregular plates; 

 or the tissue, may be so spongy in appearance that it is 

 difficult to make out any definite concentric and separately 

 radiating layers. 



Under both conditions, however, the deficiency of pores or 

 perforations in the costal structures is very much opposed to 

 the popular idea of a perforate coral. 



It is well known that when sections are made through a 

 moderately thick branch of a colony, several buds are cut 

 across at varying distances around the axial corallite. The 

 direction of the buds is outwards and forwards, and the in- 

 ference is very naturally drawn that the buds were continuous 

 with the axial corallite's cavity ; but transverse section after 

 transverse section may be made and yet no such conjunction 

 of young and old corallites be discovered. By using the 

 steel nippers carefully, and after making longitudinal sections, 

 the independence of the buds of the miscalled parent or axial 

 corallite can be well seen ; moreover, it then becomes appa- 

 rent that interstitial calcareous growth has diminished the 

 original area of the perforations, or vacuities, of the corallite- 

 wall. 



Besides, in this longitudinal view, the singularly imper- 

 forate condition of the septa is very visible. The principal 



