58 CORALS AND CORAL ISLANDS. 



which grew, and multiplied its polyps as it grew, by this meth- 

 od. In such species some of the disks of the polyps will be 

 found to have two mouths. This is the first step in the pro- 

 cess. In others, the two mouths will be found to be partly 

 divided from one another by new-formed tentacles ; and finally 

 each will have its own circle complete and all else in polyp 

 perfection. 



Many of the Astrsea hemispheres of the Pacific, grown by 

 this method, have a diameter of ten to fifteen feet. 



In other Astrsea-like species, this spontaneous fission ends 

 in a complete separation of the two polyps formed ; and conse- 

 quently in a forking of an old branch. The figure annexed, 

 of a Caulastraea, from the Feejees, illustrates this mode of 



CATJLASTR^A FURCATA, J). 



branching. In the left hand polyp there are already two 

 mouths, and the work of subdivision is consequently begun ; 

 while in those to the right, which have a single mouth, the 

 subdivision has just been completed, and also the forking of 



