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CHAPTEK IX. 



ECHINODERMATA. 



" Ultra magis pisces et Echinos sequora celent." Hor. Ep. 



IN their " Natural History of the Echinodermata," Messrs. Hupe and 

 Dujardin divide this vast natural group into five orders or families, 

 namely: 1, Asteroid as, which includes the true star-fishes; 2, Orinotdas, 

 stone lilies, calcareous, stem composed of movable pieces ; 3, Opliiurse, 

 having the disk much depressed, the rays simple, and furnished with 

 short stems ; 4, Echinidw, comprehending the animals known as sea- 

 eggs, or sea-urchins, distinguished by their rounded form and absence 

 of arms; 5, HolotJiuroidse, with soft lengthened cylindrical body, 

 covered with scattered suckers. 



The Echinodermata, from the Greek words e^Iix)?, rough, and Se'/o/m, 

 skin ; indicating an animal bristling with spines like the hedgehog's. 

 They are animals sometimes free, sometimes attached by a stem, 

 flexible or otherwise, and radiating, that is, presenting an appearance 

 more or less regular in all its parts, after the manner of a circle or 

 star, its form being globular, egg-shaped, cylindrical, or like a pen- 

 tagonal plate; or, lastly, like a star, with more or less elongated 

 branches, which secrete either in all their tissues or only in the in- 

 tegument very numerous symmetrical calcareous plates of solid matter, 

 sometimes forming an internal skeleton or regular shell covered with 

 a more or less consistent skin, often pierced with holes, from which 

 the feet or tentacula issue; they are frequently furnished with 

 appendices of various kinds, such as prickles, scales, &c. 



The organization of the Echinodermata is the most perfect of all 

 the zoophytes, serving as a transition between them and animals of more 



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