22 



KHANCH ECHIXODKHMATA. 



FIG. 31. 



Stron gy lo c?n'fr5 tus dro bach- 

 i en' sis. Sea urchin, the am- 

 bulacral suckers appearing as 

 the long filaments, far out- 

 reaching the protective spines. 



The common Urchin of the North 

 Atlantic coast is of about the size 

 and shape, and has the general ap- 

 pearance of a chestnut bur. It moves 

 about on the rocks, gathering vege- 

 table incrustations from their surface 

 by means of its five sharp teeth, or- 

 gans with which we have not hith- 

 erto met. These are worked by thirty- 

 five powerful muscles. 



ORDER CLYPEASTRIDEA (klip e as trid'e a). 



The Sea-otter departs 

 somewhat from the five-rayed 

 structure of the previous mem- 

 bers of this branch. While 

 an imaginary line might be 

 drawn across the Star-fish, 

 through the coral-plate and 

 the arm which in Fig. 27 is 

 toward the right, dividing the 

 animal into two equal por- 

 tions; the Sea -otter has a 

 more obvious right side equal- 

 ing a left side, a structure 

 characterized by the term "bi- 

 lateral symmetry." 



FIG. 32. 



Schiz as' ter. Sea-otter, viewed from the 

 lower side. O, Mouth. S, Openings 

 through which are thrust the ambulacral 

 suckers. 



CLASS HOLOTHUBOIDEA (hoi o thu roid'e a). 



The HOLOTHURIANS (hoi o ti-m'ri anz), called Sea-cucu 1 1 1 -- 

 bers because of their peculiar form, are regarded as the 

 highest of the Echinoderms. Though they depart con- 



