CCELENTERATA. 185 



7. Are the coelenterates strictly radially symmetrical? 



8 . What sense organs are described for the coelenterates ? 



9. What is the manner of action of the nettling cells? 



10. In what ways are the coelenterates more highly 

 organized than the sponges. 



1 1 . What arguments could you advance for the view 

 that Hydra is descended from marine hydroids and has 

 become adapted, in the course of time, to fresh water. 



1 2 . Why were these animals originally called zoophytes? 



