16 



BRANCH CCELENTERATA. 



FIG. 22. 



FIG. 23. 



Cte nac'tis e chi nd'ta. Mushroom Coral. 



The co cy a' thus 



cy I'm dril' cH us. 



Cup Coral. 



smooth, hollow, and of a conical shape. They can be 

 extended or withdrawn at will, and are of use to the 

 animal as organs of touch. The number of tentacles is 

 usually six, or some multiple of six. 



The simple Mushroom and Cup Corals are little more 



than Anem- 

 ones. Between 

 the mesenterial 

 folds and at the 

 base of the ani- 

 mal, there is a 



deposit of lime. Some species measure over 

 a foot in diameter. 



If we examine a branching coral, we shall find extend- 

 ing through the axis, the remains of a single elongated 

 parent Actinia (ak tin'I a), or polyp (p61'ip), 

 from which others branch out in every 

 direction, all keeping a communication 

 with one another through the axial ca- 

 nals, and also through the external fleshy 

 investment. We thus see that the coral 

 is deposited not as a result of the industry 

 of the animals, but is merely, like our 

 skeletons, a support. The reef-forming 

 coral animals abound in tropical seas, 

 while solitary corals are found at depths, 

 even in the Arctic Ocean.* 



FIG. 24. 



Branching Coral. 

 A, Plan of single ani- 

 mal. 



* Dana, in describing the coral reefs of the Pacific, says : " The Actiniae 

 may well be called the asters, carnations, and anemones of the submarine garden ; 

 the tubipores are literally its pink beds ; the gorgoniae, its flowering twigs ; the 

 madrepores, its plants and shrubbery. Astraeas (star corals) often form domes 

 amid the grove, embellished with green or purple blossoms ; hemispheres of 

 meandrina (brain coral) appear as if enveloped in a net-work of flowering vines; 

 and vases of madrepores stand on a cylindrical base covered with branches, 

 spreading gracefully from the center and decked with sprigs of tinted polyps. 



