STRUCTURE OF ALCYONIUM I — SPICULES. 



551 



sions arranged with a certain'regularity. But after being immersed 

 for a little time in a jar of Sea-water, the mass swells-out again, 

 and from every one of these depressions an eight-armed Polype is. 

 protruded, "which resembles a flower of exquisite beauty and 

 perfect symmetry. In specimens recently taken, each of the petal- 

 like tentacula is seen with a hand-glass to be furnished with a row 

 of delicately-slender pinnce or filaments, fringing each margin, and 

 arching outwards ; and with a higher power, these pinna? are seen 

 to be roughened throughout their whole length, with numerous 

 prickly rings. After a day's captivity, however, the petals shrink 

 up into short, thick, unshapely masses, rudely notched at their 

 edges" (Gosse). When a mass of this sort is cut-into, it is found 

 to be channelled-out, somewhat like a Sponge, by ramifying Canals ; 

 the vents of which open into the Stomachal cavities of the Polypes, 

 which are thus brought into free communication with each other, 

 — a character that especially distinguishes this Order. A move- 

 ment of fluid is kept-up within these Canals, as may be distinctly 

 seen through their transparent bodies, by means of Cilia lining 

 the internal surfaces of the Polypes ; but no cilia can be discerned 

 on their external surfaces. The tissue of this spongy Polypidom is 

 strengthened throughout, like that of Sponges (§ 406), with 

 Mineral spicules (always, however, Calcareous), which are remark- 

 able for the elegance of their forms ; these are disposed with great 

 regularity around the basis of the Polypes, and even extend part of 

 their length upwards on their bodies. In the Gorgonia or Sea-fan, 

 whilst the central part of the Polypidom is consolidated into a 

 horny Axis, the soft flesh 

 which clothes this axis is so 

 full of tuberculated spicules, 

 especially in its outer layer, 

 that, when this dries-up, 

 they form a thick yellowish 

 or reddish incrustation upon 

 the horny Stem ; this crust 

 is, however, so friable, that 

 it may be easily rubbed 

 down between the fingers, 

 and, when examined with 

 the Microscope, it is found 

 to consist of Spicules of 

 different shapes and sizes 

 more or less resembling 

 those shown in Figs. 283, 

 284, sometimes colourless, 

 but sometimes of a beautiful 

 crimson, yellow, or purple. 

 These Spicules are best seen 

 by the methods of Illumina- 



Fig. 283. 



Spicules of Alcyonium and Gorgonia. 



