ALGYONOID POLYPS. 87 



are all from Eugonjia aurantiaca V., the peculiar kind shown 

 in fig. 3 occurring with the other more common form, in species 

 of this genus. In species of Plexaurella many of the spi- 

 cules are beautiful crosses of various fancy shapes. In Eu- 

 nieellas the cortex is covered with an outside layer, in which 

 the spicules are club-shaped, though ornately so, and have the 

 smaller end pointed inward. These spicules afford valuable dis- 

 tinguishing characters also in all Alcyonoids. 



The spicules are often brilliantly colored, and sometimes 

 variously so in the same individual. Yellow, crimson, scar- 

 let and purple are common colors, and they occur both of 

 dark and pale shades. Viewed under a compound micro- 

 scope 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 Gor- 

 gonise owe the various colors they present to the colors 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 Muricsea, 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 

 carbonate 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 (p. 62). In the ordinary 

 Alcyonoids that make no horny axis, the stolons, or budding 

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

 But in these Gorgonise, 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 se- 



