ANTIPATHARIAN CORALS 137 



the larger branches are frequently without thorns, and 

 present a hard, smooth, and often highly polished jet-black 

 surface. The axis of the Gorgoniidae and Plexauridae is 

 never provided with thorns, and although it may be grooved, 

 always feels smooth to the touch, and the same is true of 

 the genus Gerardia, which is described at the end of this 

 chapter. 



In transverse sections of a stem or thick branch of an 

 Antipatharian coral there is usually found a central circular 

 cavitv around which the horny matter is arranged in a 

 number of concentric layers. It has, therefore, some re- 

 semblance to a section of a tree stem, the central cavity 

 corresponding with the pith and the concentric layers of 

 keratin with the annual rings of wood. 



In the axis of the Gorgonacea there is usually no central 

 cavity, the texture is more fibrous than in the Antipatharia, 

 and the concentric lamellae, if present, much less well 

 defined. 



In the large thick stems of the black coral some- 

 times used by the Japanese for making their elaborately 

 carved netsukes, the central cavity and the arrangement in 

 concentric layers may be entirely obscured, although this 

 coral is undoubtedly Antipatharian in origin, and conse- 

 quently no single character is left by which the exact 

 nature of black coral can be determined with certainty. 



The soft living tissue which covers and secretes the horny 

 axis of the Antipatharia is absolutely different from that of 

 any of the Alcyonarian flexible corals. It forms only a thin 

 white or purple coloured transparent film, and is entirely 

 devoid of spicules or any other kind of calcareous structures. 

 This character of the soft tissues of the Antipatharia was 

 recognised by Rumphius, Pallas, and other writers of the 

 eighteenth and early part of the nineteenth centuries.^ They 

 called it slime or mucus in contrast to the coenenchym of 

 the Alcyonaria, which they called " bark." 



The polyps are small, and, with a few exceptions, are 



^ " Cortex autem, quo Antipathes vivit, non calcareus est ; sed 

 gelatinosum tegumentum in extremis ramis crassius, inque polypos efflor- 

 escens " (P. S. Pallas, Elenchus Zoophytoruni, 1766, p. 206). 



