ACTINOZOA 



27 



is here inflected and forms a tube dipping down into the body 

 cavity, but not reaching the Ijottom of it. The lower end of this 

 tube or esophagus (which is really the beginning of the ali- 

 mentary tube of higher animals) corresponds to the mouth of 

 the Hydra, so that the tube is lined with ectoderm. The mouth 

 is the only external organ, and serves both for the entrance of 

 food and the ejection of waste. The body cavity about this 

 tube is divided by thin partitions into radiating spaces. 



No actinozoan is microscopic. All are long lived. One in an 

 English aquarium lived more than sixty years. ^ The sea-ane- 

 mones and all true corals producing reefs and islands have the 

 number of their tentacles in multiples of six. 



,-*«^ 



f.; 



Fig. 17. — Sea-anemone {Metrid'ium). (Emerton.) 



The Sea-anemones (Fig. 17). — As one gazes in wonder at 

 the sea-anemones in their marine home, he can scarcely persuade 

 himself that those beautifully colored objects, so flower-like — 

 hollow cups with their petals and sepals of such wonderful tints 

 — are else than flowers. But he touches one, the " sepals and 

 petals " close in upon his fingers, they tingle, and he finds that 

 this flower-like object is an animal and that the " sepals and 

 petals " are tentacles. A very different appearance it makes 

 when the body has been drawn down close to its attachment by 

 the longitudinal muscles, while the circular muscles shut in the 

 1" General Zoology," Dodge, p. 75. 



