STAn-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 ]ircscntcd by the 

 sea-urchin, oi- Echinus ,Fig. 30). 



Fig 37.— A Brit'le-star. (From CasseH'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 l»een removed from the larger 

 portion of the specimen represented in Fig. 31i). In 

 the living animal these spines are fully movable 

 in all directions, each beino- mounted on a ball-and- 



