CCELENTERATA 189 



Many interesting experiments have been performed on mem- 

 bers of this group illustrating the power of regenerating lost 

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

 and even the medusa 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 matter 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 conditions. 



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. 



231. 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 Ccelen- 

 terata ? 



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

 eration in Hydra or other coelente rates ? 



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 specimens 

 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 Amelia. 



10. The symmetry of the ccelenterates. 



11. The structure, position and uses of the nettling cells in 

 the phylum. 



12. Study the polyp of Aurelia (Scypkistoma) from descrip- 

 tions and cuts, and show in what respects it seems to stand 

 intermediate between the Hydrozoa and the Actinozoa. 



