232 TOILERS IN THE SEA. 



except when young. Their outline is often discoid 

 or oval, but sometimes elongated elliptical, with the 

 plates on the upper surface radiating from a depressed 

 umbilicate centre, or from a central furrow, the outer 

 edges of the parallel plates being acute. 



The most important of the Actinoid l corals are 

 those which form compound groups, wherein a 

 number of polyps are connected together in a colony, 

 often as the result of the process of budding. These 

 colonies Professor Dana calls Zoothomes^ although 

 we prefer to avoid as much as possible the use of 

 technicalities of this description. Describing the 

 process of gemmation, or budding, he says, " the bud 

 commences as a slight prominence on the side of the 

 parent. The prominence enlarges, a mouth opens, 

 a circle of tentacles grows out around it, and increase 

 continues till the young family equals the parent in 

 size. Since in these species the young does not 

 separate from the parent, this budding produces a 

 compound group ; and the process continues until, in 

 some instances, thousands, or hundreds of thousands, 

 have proceeded from a single germ, and the colony 

 has increased to a large size, sometimes many feet, 

 or even yards, in breadth or height. In thecorallum, 

 -or dead skeleton, each stellate cavity, or prominence 



1 Actinoid, because resembling the Actinias, or Sea-ane- 

 mones. 



