STAR-FISH AND SEA-URCIUNS. 



265 



which occur in the Star-fish, though considerably 

 larger, and the ambulacial system is constructed 



Fig. 39.— A.n Echinus, partly denuded of its spines. (From Cassell's "Nat. 

 Hist.") 



upon the same plan. If we shave off the spines 

 and pedicellari'ce (Fig. 39), w^e find that we come to 



Fig. 40.— Showing iiit> lior ul Echinus shell. (From Cassell's " Nat. Hist.") 



a hard shell, which, if we break, we find to be 

 hollow^ and filled with fluid (Fig. 40\ The fluid 



