ALCYONOID POLYPS. 87 
are all from Hugorgia 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- 
nicellz 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- 
goniz 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 Muricea, 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, 
asin the Antipathus before described (p. 62). In the ordinary 
Aleyonoids that make no horny axis, the stolons, or budding 
stem or mass, creeps or spreads over the supporting body. 
But in these Gorgoniz, 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- 
