160 HALF AN HOUR WITH SEA-URCHINS 



the sea-urchin along. Long though the spines are, 

 the sucking feet can be thrust forth further still, 

 and, as the animal can put them forth at will in 

 any direction, and retract them in the same easy 

 way, it follows that it can crawl or warp itself 

 along over the sea-bottom wherever it chooses ! Even 



Fig. 82. 



Ambulacral Disc, x 180. 



these suckers have a calcareous skeleton, which forms 

 a beautiful microscopical object, as may be seen in 

 Fig. 82. 



The mouth of the sea-urchin is very peculiar, and 

 well adapted for trituration. Just within it may be 

 seen five conical teeth, which are formed of lime, 

 and all come to a point so as to form a cone. Their 



