COfRAL-MAKERS AND JELLY-FISH 89 



uniform bright salmon-yellow colour or pure white. 

 When kept in an aquarium it fixes itself by its disk 

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

 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 



