CCELENTERATA. l8l 



Many interesting experiments have been performed on 

 members of this group illustrating the power of regenerating 

 lost parts. Many of the polyps have been shown to have this 

 power and even the medusae may become perfect animals again 

 after having lost very considerable portions of their structure. 

 Hydra, one of the simplest members of the group, is most 

 famous for its power of regaining its original form, no mat- 

 ter to what sort of mutilation it has been subjected. As long 

 as there is a piece of the trunk of appreciable size containing 

 both ectoderm and entoderm it may regenerate the whole 

 animal, stalk, mouth, tentacles, and all, under favorable con- 

 ditions. 



Nothing about the Ccelenterates is more interesting to the 

 zoologist than the way in which the individuals in the poly- 

 morphic colonies (as in the Siphonophora) come to do the 

 work done by special organs in the higher Metazoa. 



226. Supplementary Studies, for field and library. 



1. Make a list of all the places where Hydra may be found 

 in your locality. 



2. Can you find an account of any other fresh- water 

 Coelenterata? 



3. What facts can you find concerning the power of re- 

 generation in Hydra or other Ccelenterates ? 



4. Coral reefs: kinds and mode of formation. Conditions 

 of life necessary to the reef-forming corals. 



5. Polyp colonies. Show, by reference to all the speci- 

 mens and figures you can find, where the newest bud appears 

 and how this helps determine the shape of the colony. 



6. Polymorphism and division of labor in polyp colonies. 



7. Corals in geological time. 



8. Sense organs among Ccelenterates. 



9. Alternation of generation in Obelia. In Aurelia. 



10. The symmetry of the Ccelenterates. 



