THE PHYLA COELENTERATA AND CTENOPHORA 



193 



armed with nematocysts that can be used to reparalyze prey should it 

 recover after being swallowed. The radial canals are much branched. 



The sensory areas ol the bell margin in this class are concentrated 

 to form complex sense structures, the rhopalia (Fig. 10.12). These re- 

 spond to gravity, light, and chemicals in the water. Without them spon- 

 taneous activity of the medusa ceases. 



The gonads of scyphozoans develop in the gastrodermis of the 



R hop a.1 iu.Tn. 

 Mouth arra 



Gona.d in 

 ga.stric 



Ra.dial 



Figure 10.11. A, Ventral view of Aurelia. Compare with Pelagia on Figure 10.1, 

 which difters primarily in having larger tentacles. (After Hyman.) B, Left, Ephyra larva 

 of Aurelia. Right, Young Aurelia bell contracting (lateral view). (Courtesy Douglas P. 

 Wilson.) 



