STAR-FISH AND SEA-URCHINS. 263 
sea-cucumbers and lily-stars (Fig. 38). Without, 
however, waiting to consider these, I shall go a 
little more particularly into the modification of 
Star-fish structure which is presented by the 
sea-urchin, or Echinus (Fie. 39). 
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Fig. 37.—A Brittle-star. (From Cassell’s “Nat. Hist.’’) 
Externally, the animal presents the form of an 
orange, and is completely covered with a large 
number of hard calcareous spines, on which account 
it derives its scientific name of Echinus, or hedge- 
hog (the spines have been removed from the larger 
portion of the specimen represented in Fig. 39). In 
the living animal these spines are fully movable 
in all directions, each being mounted on a ball-and- 
