CURIOSITIES OF STAR-FISH LIFE. 



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uppermost rays to it, and then, letting go its other attachments, swing 

 from the old support to the new. The activity and co-ordination mani- 

 fested in these acrobatic movements, says Dr. Romanes, are surprising, 

 and give to the animal an almost intelligent appearance. 



The feet of astropecten are partly rudimentary, having lost their 

 terminal suckers, and these star-fish assist themselves in locomotion by 

 the muscular movements of their rays. The brittle-stars are still fur- 

 ther removed in the same direction from the common star-fish ; their 

 tubular feet are of no use for crawling, while their rays are so long, 

 flexible, and muscular, as to enable them to shuffle quite rapidly over 

 horizontal surfaces. Two opposite arms are used upon the floor with 

 the motion of swimming, the animal leaping forward about two inches 

 at each stroke, and, as these leaps follow one another quickly, the star- 

 fish is able to travel at the rate of six feet a minute. A common star- 

 fish can crawl only two inches a minute. Some of the Comatulce, in 

 which the muscularity of the rays has proceeded still further, are able 

 actually to swim by the co-ordinated movements of their rays. 



The sea-urchin, or echi- 

 nus, is a modification of 

 the star-fish structure, hav- 

 ing the form of a flattened 

 sphere, and is covered with 

 hard spines (Fig. 6). In 

 the living animal these 

 spines are movable in all 

 directions, each being 

 mounted on a ball-and- 

 socket joint, and provided 

 with muscles at its base. 

 Like the star-fish, the echi- 

 nus has a madreporic tu- 

 bercle, pedicellariae, and 

 feet. If we shave off the 

 spines and pedicellariae, we 

 come down to a hard shell, which is hollow and filled with liquid. 

 The liquid resembles sea-water, but is richly corpusculated, and co- 

 agulates when exposed to the air. Five double rows of holes extend 

 symmetrically from pole to pole of the shell. It is through these 

 holes that the feet are thrust out, so that in its main features an 

 echinus is merely a star-fish with its five rays curved into the shape 

 of a hollow spheroid, and then converted into a rigid box, with 

 holes left for its feet to come through. The urchin crawls in the 

 same way as the common star-fish, but makes use of its spines also to 

 help push itself along. The suckers, moreover, in being protruded 

 from all sides of a globe instead of from the under side of a flat organ- 

 ism, are of much more use as feelers than they are in the star-fish. If 



Fig. 6. An Echtntts partly denuded of its Spines. 

 (From CasseH's "Natural History.") 



