stimulation. The stinging capsules are very small and 

 cannot penetrate the human skin, so alcyonarians 

 can be handled with impunity. If we examine them 

 closely when the polyps are fully expanded we see 

 that the feeding polyps are all remarkably alike and 

 have a single circle of eight feathery tentacles. These 

 are widest at the tips and somewhat flattened, and 

 bear rows of side branchlets. The oval or elongate 

 mouth may have one ciliated groove at most, and it 

 opens into a gullet that has attached to it eight parti- 

 tions readily visible in transparent polyps. 



Many alcyonarians have a second kind of polyp 

 without tentacles, and these may be concerned with 

 circulation of water, which plays a large role in the 

 expansion and contraction of the colonies as well as 

 in respiration. Between the external covering layer 

 and the thin digestive lining is a thick jelly layer that 

 adds bulk to the body, and this is invaded by cells 

 that secrete the skeleton of calcium carbonate or of 

 horny material, either in little spicules of distinctive 

 shape or as amorphous substance. Even when loosely 

 scattered, the spicules give firmness to the flabby 

 body; and those alcyonarians in which the spicules 



are densely packed or fused may contribute no small 

 share to coral reefs. Also in the jelly are the digestive 

 canals that unite the many polyps. The sex cells de- 

 velop on the digestive partitions and are shed to the 

 outside through the mouth. 



THE SOFT CORALS 



The soft corals, or alcyonaceans (Plate 9) with 

 only scattered spicules stiffening the body, are 

 best known in temperate waters from the flesh-col- 

 ored, white, or orange-colored lobed masses called 

 "dead men's fingers'" in England and something less 

 mentionable in France. Akyoiiium digltatum, abun- 

 dant in European waters, lifts its spongy, gelatinous 

 lobes, like bloated fingers, as much as 8 inches high 

 from gravelly bottoms below low-tide mark. In duU 

 light the numerous and delicate transparent ends of 

 the polyps form a white furriness over the surface as 

 they project beyond the opaque lobes. At the slight- 

 est disturbance the little feeding disks are pulled in 

 by special muscles, and the rest of the delicate col- 

 umns follow, turning the formerly exposed parts of 

 the polyps inside out, like the fingers of a glove, and 



Dead men's fingers, Alcyonitim digitatum, a fleshy colony of .soft coral that extends delicate 

 polyps. (England. D. P. Wilson) 



