ANEMONES AND CORALS 53 



others thin pieces of carbonate of lime cross them, more or less, 

 cutting off the lower parts from the upper. These dissepiments, 

 as they are called, are secreted by the animal, which lives above 

 the upper one. Outside the cup are a series of longitudinal ridges, 

 or ribs, in relation to the septa within, and they may be united 

 by cross-bars. 



While some Corals remain as solitary and separate individuals 

 throughout their life, others, and particularly the reef-builders, 

 become compound ; that is to say, they propagate or increase 

 by a process of budding from the parent, and then these first buds 

 in turn give rise to a succession of buds. First a little projection 

 appears on the side of the parent cup, and soon a few tentacles are 

 formed, until by its outward and upward growth the little bud 

 resembles the parent. Other buds now arise, and all grow upwards 

 in a bush-like form, fresh successions of buds constantly being 

 produced. As the growth progresses, either the bush shape remains, 

 or else structures composed of layers of hard tissue arranged in 

 cellular compartments or cross-bars, so as to give both lightness 

 and strength, are grown between the buds and parent, connecting 

 the whole into a solid mass, or exotheca. Thus an individual 

 Coral perfect in itself, like the little Devonshire Coral and the 

 Mushroom Coral, is called a Corallum ; while a member or an indi- 

 vidual which has budded or divided off, and yet still remains as 

 part of a whole, is called a Corallite. 



Ova are produced by all the Corals, and escaping from the 

 mouth of the parent become long, ciliated planulae, which soon 

 fix themselves to a base and become like the parent in appear- 

 ance. The growth of the individual is accompanied by an increase 

 in the number of mesenteries within the body, and of solid septa 

 between each pair of mesenteries. 



The little Corals to be found on the southern coasts of England 

 are simple, and do not form reefs, for the temperature of the sea 

 around our coasts to-day is not sufficiently high to support the 

 life of the reef-building Corals, although there is abundant evidence 

 from the fossil remains of reef-building Corals preserved in vari- 

 ous strata to show that in the geological past our shores were 

 lapped by the waves of a tropical sea. The reef-building Corals can 

 only flourish in a warm sea where the temperature is never lower 

 than 68 F., and may rise to 86. Moreover, the sea-water must 



