3484 



CCELENTERA TES 



longitudinal furrows become visible at the upper pole, where the mouth sinks 

 deeper. At the ends of these furrows the twelve tentacles appear. The three illus- 

 trations on p. 3483 show the stages which follow in rapid succession, resulting in 

 a form almost exactly like a young sea anemone. It has, however, already com- 

 menced to secrete its calcareous skeleton. This is not formed as a connected whole, 

 but begins as a number of separate centres of secretion between the polyp and the 

 substance to which it is fixed. These meet and fuse, till gradually the skeleton is 

 produced. The polyp commences to bud, and the buds develop their skeletons, the 

 whole together forming a stock like that shown in the illustration. 



The star corals, which are some of the principal reef builders, do not branch, 



but form great solid mounds; 

 the polyps being all cemented 

 together, and the budding so 

 arranged that the whole colony 

 forms a thin, living layer or 

 covering to the mass it and its 

 parents have built up; all but 

 this thin layer on the surface 

 being dead coral. The illustra- 

 tion given is of Astrcea pallida, 

 a species which appears as a 

 rounded mass, with flat base, and 

 the individuals being quite dis- 

 tinct from one another, although their outer walls are in contact. Those on 

 the top and to the right of the figure are represented in a contracted condition, 

 and the rest with expanded tentacles. None of the individuals here seen are in 

 the act of dividing; and the genus is characterized by the fact that the budding 



A ^ftara-Ba^ 



B 



A STAR CORAL, Astrcza (one-half natural size). 



A BRAIN CORAI,. 



A. Stock with the soft parts; B. Skeleton. (Natural size.) 



polyps separate from one another completely, forming so many distinct individual 

 polyps. 



In the brain corals, or Meandrina, we have animals budding, but not com- 

 pletely separating. No hard wall grows between the bud and its parent, although 

 such separate the polyps less closely related. We thus get a system of valleys 



