CORAL 603 



there may be noticed also small pits no larger tlian a pin-prick. These, which are frequently 

 absent in perfectly fresh coral, have been caused by marine oi'ganisms, such as boring- 

 sponges and boring-worms. Dead coral is frequently so much bored and eaten away by 

 such creatures that it is useless for commercial purposes. 



A piece of coral which has not been attacked by boring animals appears perfectly 

 homogeneous, compact, and solid, and free from internal cavities. It may occasionally 

 enclose foreign bodies of various kinds, which have by some chance found themselves in such 

 a position as to become enveloped by the calcareous material secreted by the colony, of 

 which the piece of coral formed the axis. The fractured surface of a piece of fresh coral is 

 uneven and splintery. In many cases, when a transversely fractured surface is examined 

 with the naked eye or with a lens, it becomes obvious that the piece of coral is built up of 

 thin, concenti'ic layers, the whole mass, indeed, consisting, as it were, of a number of hollow 

 tubes fitting closely one inside another. This structure is more clearly demonstrated by the 

 examination under the compound microscope of thin, transverse sections ; and one can make 

 out, in addition, the fact that each concentric layer is built up of numberless fine fibres, the 

 general direction of which is radial, that is to say, they i"un outwards from the common 

 centre towards the periphery. These fibres have an extraordinary power of double refrac- 

 tion, in which respect, and in others to be mentioned presently, they agree «'ith the mineral 

 species calcite, to which they are probably to be referred. The concentric structure of a 

 piece of coral is also demonstrated very clearly when the latter is ignited, the concentric 

 layers separating from each other and peeling off. 



The observation of thin, transverse sections of coral under the microscope also discloses 

 the fact that the concentric layers are coloured alternately bright red and white. In very 

 thin sections the red colour is scarcely apparent at all, only appearing in slices of a certain 

 thickness. The precise shade of colour of coral is different in different specimens. That 

 from which the coenosarc has been newly stripped ranges in colour from pure white to the 

 brilliant tint of red lead. Pure white coral is rare, and the absence of colour is said to be 

 the consequence of a diseased condition of the organism. Yellow coral is also rare. In 

 Italy, the home of the coral industry, special terms are used to distinguish coral of different 

 shades of colour. Thus, first comes pure white (bianco), next a fresh, pale, flesh-red {pelle 

 cfangeld), then pale rose {rosa pallida), then bright rose (rosa vivo), which is followed by 

 " second colour " {secondo coloro), red {rosso), dark red (rosso scuro), and finally the darkest 

 red of all {carbonetto or arciscuro). It is unusual to find diff^erent colours or different shades 

 of colour in the same piece of coral, this being usually of one uniform tint in all its 

 branches. 



Red coral when reduced to a fine powder is pale reddish in colour, the shade being 

 more pronounced the deeper the colour of the piece, and vice versa. 



The death and decay of the living -portion of a coral-colony is accompanied by a. change 

 in colour of the skeleton, thab is to say, of the red substance commonly known as coral. 

 Coral which has lain at the bottom of the sea in muddy water for any considerable length 

 of time is almost sure to assume a more or less dark brown or black colour, and is said by 

 the Italians to be "burnt" (bruciato). Some of the black coral of commerce is, however, 

 something quite different, and will be considered later. In exceptional cases dead coral, 

 instead of beconiing black, turns white or yellow. An immense amount of dead coral is 

 rendei'ed useless for industrial and ornamental purposes by the attacks of boring worms, 

 sponges, and other marine organisms. 



The black or brown colour of a piece of dead coral does not always extend over the 

 whole of its surface nor penetrate to its innermost layers. There may be black patches and 



