120 ON CORAL AND CORAL REEFS 



nated with lime salts; and it is this dense skeleton 

 (usually turned red by a peculiar colouring matter) 

 cleared of the soft animal investment, as the hard wood 

 of a tree might be stripped of its bark, which is the red 

 coral. 



In the case of the red coral, the hard skeleton belongs 

 to the interior of the stem and branches only; but in 

 the commoner white corals, each polype has a complete 

 skeleton of its own. These polypes are sometimes soli- 

 tary, in which case the whole skeleton is represented by 

 a single cup, with partitions radiating from its centre 

 to its circumference. When the polypes formed by 

 budding or division remain associated, the polypidom 

 is sometimes made up of nothing but an aggregation of 

 these cups, while at other times the cups are at once 

 separated and held together, by an intermediate sub- 

 stance, which represents the branches of the red coral. 

 The red coral polype again is a comparatively rare 

 animal, inhabiting a limited area, the skeleton of which 

 has but a very insignificant mass ; while the white corals 

 are very common, occur in almost all seas, and form 

 skeletons which are sometimes extremely massive. 



With a very few exceptions, both the red and the 

 white coral polypes are, in their adult state, firmly ad- 

 herent to the sea-bottom; nor do their buds naturally 

 become detached and locomotive. But, in addition to 

 budding and division, these creatures possess the more 

 ordinary methods of multiplication ; and, at particular 

 seasons, they give rise to numerous eggs of minute size. 

 Within these eggs the young are formed, and they leave 

 the egg in a condition which has no sort of resemblance 

 to the perfect animal. It is, in fact, a minute oval body, 

 many hundred times smaller than the full grown crea- 

 ture, and it swims about with great activity by the help 



