64 CORALS AND CORAL LSLANDS. 



3, 4, 5, are all from Eugorgia aiiraiitiaca V., the peculiar 

 kind shown in figure 3 occurring with the other more common 

 form, in species of this genus. In species of Plexaurella 

 many of the spicules are beautiful crosses of various fancy 

 shapes. In Eunicellae the cortex is covered with an out- 

 side layer, in which the spicules are club-shaped, though or- 

 nately so, and have the smaller end pointed inward. These 

 spicules afford valuable distinguishing characters also in all 

 Alcyonoids. 



The spicules are often brilliantly coloured, and sometimes 

 variously so in the same individual. Yellow, crimson, scarlet, 

 and purple are common colours, and they occur both of dark 

 and pale shades. Viewed under a compound microscope by 

 transmitted light, a group of these spicules from some species, 

 part bright yellow and part crimson, or of some other tints, 

 produces an exceedingly beautiful effect. It gives still greater 

 interest to this subject that all Gorgoniae owe the various 

 colours they present to the colours of their spicules. 



Spicules are usually wholly internal, or they only come to 

 the surface so as to make the exterior slightly harsh. But in 

 other cases, as in the genus Muricaea, they project and give a 

 somewhat bristly look to the coral. 



The calcareous spicules are internal secretions, like those of 

 ordinary coral, and the constitution is the same, — mere car- 

 bonate of lime. But the secretion of the axis of the branches 

 is epidermic^ from the inner surface of the cortex, as in the 

 Antipathus before described (page 42). In the ordinary Alcy- 

 onoids that make no horny axis, the stolons, or budding stem 

 or mass, creeps or spreads over the supporting body. But 

 in these Gorgonige, the budding cluster, which would make 

 a stolon if there were no horny secretions, has the form of 

 a tube about a horny axis ; and as this tube elongates and 

 secretes the axis within, it gives out buds externally; thus the 

 branch rises. New branches commence at intervals over the 

 sides of the rising stem or branch through the starting of 

 new budding centres, and so, finally, the Gorgonia zoophyte 

 is completed. 



