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CLASS I. ECHINODERMATA.* 



IN these animals we find a thick skin, crustaceous 

 or leathery in its texture, and in many cases thickly 

 clothed with spines. They are all marine animals, 

 some of them swimming in the ocean, but the ma- 

 jority having a very peculiar apparatus for crawling, 

 consisting of a vast number of slender fleshy tubes, 

 protruded at will through round holes on the skin, 

 and terminating in flat suckers. Few, on compar- 

 ing that very singular animal called a Lily-stone 

 (Encrinus) with a Sea-urchin, (Echinus,} would be 

 able to discover the slightest resemblance between 

 them, or would suspect that these two creatures 

 could have been formed on one common plan. Yet 

 so it is ; the interval being filled by species ap- 

 proaching each other so gradually, that they form 

 an unbroken series. 



One of the most common species of this Order 

 on our own shores is the Eatable Sea-Urchin (Echi- 

 nus Esculentus). It much resembles in form and 

 size an orange, composed of five segments, like 

 the divisions visible in that fruit when the rind 

 is removed. On each segment are two rows of 

 half-round knobs, like little nipples, on each of 

 which a blunt spine is placed, working on it by a 



a hedgehog, and fy/tct, derma, the skin. 



