CORAL-MAKERS AND JELLY-FISH 89 



uniform bright salmon-yellow colour or pure white. 

 I When kept in an aquarium it fixes itself by its disk 

 I on the glass wall, and often, as it slowly moves, allows 

 I pieces of the disk to become torn off and remain sticking 

 to the glass. These detached pieces develop tentacles 

 and a mouth, and grow to be small and ultimately full- 

 sized Weymouth anemones. 



If the disk were spread out and gave rise to little 

 anemones without tearing — so that they remained in 

 continuity with the parent — we should get a composite 

 or compound animal, made up of many anemones, all 

 connected at the base. This actually happens in a 

 whole group of polyps resembling the sea-anemones. 

 They grow into " stocks," " tree-like " or " encrusting " 

 masses, consisting of hundreds and even thousands of 

 individuals, each with its mouth and tentacles, but with 

 their inner cavities and bases united. These are the 

 " coral polyps," or " coral-insects " of old writers, of so 

 many varied kinds. One further feature of great import- 

 ance in a " coral " is the production of a hard deposit of 

 calcite, or limestone, which is thrown down by the sur- 

 face of the adhesive disk, and is also formed in deep, 

 radiating " pockets," pushed in to the soft animal from 

 the disk. The hard deposit of calcite is continuous 

 throughout the " stock," or " tree," and when the soft sea- 

 anemone-like animals die, the hard, white matter is left, 

 and is called " coral." Very commonly this white coral 

 shows star-like cups on its surface, which correspond to 

 the lower ends or disks of the soft sea-anemone-like 

 creatures which deposited the hard coral. In a less 

 common group (represented commonly on our coast by 

 the so-called " Dead men's fingers " found growing on 

 the overhanging edges of low-tide rocks) the hard coral 

 material does not form cups for the minute sea-anemones 



