290 ELEMENTS OF COMPARATIVE ZOOLOGY. 



COMPAKISONS. 



With columns for sea-urchin and for starfish, answer 

 the following questions : 



(1) Of what is the skeleton composed ? 



(2) Are spines present upon the outside of the body ? 



(3) Can you speak of the parts as being radiately ar- 

 ranged ? 



(4) Can you also speak of them as bilateral ? 



(5) Do you find in both ampullae and ambulacra ? 



(6) Does the nervous system surround the mouth ? 



(7) Is there a body-cavity ? 



(8) Is there a madreporite and a stone-canal ? 



(9) Do you find radial canals ? 



