120 A STAE-FISH IN CHAIN ARMOR. 



stone plates united together at their edges by a sort of cartilage, so that 

 they can move in a slight degree; together they form the framework, 

 and act as a chain-armor to encircle and protect all the soft parts within. 

 Underneath, on the lower side of the star-fish, this framework terminates 

 in two series of larger plates, which are braced against one another like 

 rafters, and sustain the whole structure by a sort of arch. This armor is 

 sufficiently flexible to allow the star-fish to bend himself clumsily over or 

 around anything he is likely to wish to climb upon or grasp. 



Scattered everywhere upon the upper side are a large number of 

 blunt, short spines, which seem to have no special arrangement, and are 

 longest and thickest at the edges of the rays, and upon the plates border- 

 ing the lower side of each ray. Each one of these spines swells at its 

 base, where are fixed in a wreath several curious little appendages called 

 pedicellarice, whose odd forms and movements can only be understood 

 underneath a powerful microscope, on account of their diminutive size. 



Each of these consists of a little pedicel, bearing aloft a pair of dis- 

 proportionately large toothed jaws. The whole affair looks like the claw 

 of a miniature lobster, and waves about in a very threatening manner. 

 Now and then it happens that some little particle of food or sea-weed 

 will accidentally get caught by these valiant guardsmen of the spines 

 that tower up in their midst; but this appears to annoy rather than grat- 

 ify them, and their functions are not yet explained. They occur in some 

 form or other in all echinoderms, yet contribute no service to the animal 

 that we can detect. Outside of them, forming a second circle about each 

 spine, is a set of water-tubes, whose functions will be explained presently. 

 Notice near the centre of the disk, on the back, the madreporic body — a 

 small, smooth protuberance filled with openings, like a sprinkler, and then 

 turn the star-fish over. 



Though so tough and tuberculous above, on the under side it is soft 

 and almost white in tint, except where the strong spines along the edges 

 of each ray protect the soft parts between. In the very centre of the 

 disk is the opening of the mouth. It contains no teeth, but is surrounded 

 by an elastic tube and guarded by the hard edges of the skeleton-plates 

 which hem it in. From this centre run five furrows, one down each of 

 the arms. 



"Throughout all this branch of the Eadiates," observes Professor 

 Forbes, "the reigning number is five. Among the problems proposed 

 by that true-spirited but eceentric philosopher, Sir Thomas Browne, is 

 one, 'Why, among sea-stars, Nature chiefly delighteth in five points?' and 

 in his Garden of Cyrus he observes : ' By the same number (five) dotli 



