Island and Reef Builders. 



grow out in the most graceful branches, fans, and 

 arborescent forms, or become compact, rounded masses 

 like the " Brain " corals, or grow into large, solid masses 

 of many tons weight. No matter what the final size 

 and shape of the colony, it had its origin in a single 

 individual. First a little projection appeared on the 

 side of the parent cup, and soon a few tentacles were 

 formed, until by its outward and upward growth the 

 little bud became like its parent in appearance. Other 

 buds then arose, and all grew upwards in a bushlike 

 form, fresh successions of buds constantly appearing. 

 As this growth progresses, either the bushy shape 

 remains, or else structures composed of layers of hard 

 material, arranged in cellular compartments or cross- 

 bars so as to give both strength and lightness, are 

 formed between the buds, connecting the whole into 

 a compact and solid mass. While these reef-building 

 corals are comparatively shallow-water forms, and are 

 restricted to the warm, sunlit waters of the Tropics, 

 the solitary corals have a far wider distribution, and 

 some have been dredged up from very great depths. 

 Besides the process of budding just described, corals 

 also have a true sexual method of propagation. The 

 oval-shaped young escape from the mouth of the 

 parent, and swimming by means of delicate threads, 

 or cilia, soon fix themselves to a base, and become 

 like the parent in appearance. 



The work of the reef-building corals comes under 

 three headings : (i) Shore reefs, which fringe the shores 

 of continents and islands ; (2) barrier or encircling 

 reefs, which rise from deep water at a greater distance 

 than the fringing reefs from land, so that there is a 



21 



