RCHIXOIDS. 



447 



great number of curious little organs called Pedicillarive. 

 They look like a stem ending in a knob ; but the knob is 

 composed of three pieces or blades, which open and shut 

 tightly, thus forming a sort of pincers. The uses of 



FIG. 676. 



--^^m 



f> 



Small portion of a cross section of a spine of a Sea-urchin. 



FIG. 677. 



Embryonic development of a Sea-urchin. 



A, Pluteus larva; a, mouth; 6, stomach; c, echinoid disk; d, arms of the plnteua 

 larva; g, ciliated processes of the proboscis; BCD, disk in progressive stageg of de- 

 velopment. 



