THE SUB-KINGDOM CCELENTEEATA. 



oval in form, and containing a fluid in their 

 interior. Tlie outer wall of the sac is entire and 

 very delicate ; the inner one is much stronger, having 

 its open extremity produced into a stout, rather 

 fusiform, sheath, which terminates in a long thread, 



Fig. I. 



Urticating organs of CffiLEXTERATA-.—fl-, e, and/, thread-cells of 

 Caryophyllia Smithii ; b, tliread-cell of Corynactis Allmani ; c, 

 portion of the marginal canal of WiUsia stdlata, with pecuKar 

 receptacle, containing thread-cells, arising therefrom ; d, a single 

 thread-cell of the same ; g, thread-cell of Actinia (or Bunodes) 

 crassicornis. (All magnified.) 



or ^ecthorseum.' A number of barbs or hooks are 

 sometimes disposed spirally around the sheath, 

 the ecthoragum itself being often delicately ser- 

 rated. In the ordinary condition of the thread- 



