i62 THE SEAS 



bud. This type of coral is best exemplified by the well- 

 known Meandrina or Brain-coral, so called because the 

 meandering depressions with which the surface is covered 

 resemble very closely the convolutions on the surface of 

 the human brain, as a result of which its surface, and so 

 the all-important grey matter, is greatly increased. 



There is a remarkable solitary coral, common on reefs, 

 which is worthy of a short description, so peculiar is its 

 manner of development. The swimming embryo settles 

 and develops into a little cup-shaped coral, but, on attaining 

 a certain size, this swells out at the top until it looks almost 

 exactly like a mushroom turned upside down so as to expose 

 the gills (hence the name of the coral, Fungia). After a 

 time this flattened upper portion falls off and drops on to 

 the sand, where it continues to grow until it is often six 

 inches across. The whitened skeletons of these stalkless 

 discs, consisting of a circular disc with radiating septal 

 plates (Plate 58), are common objects on coral shores and 

 in zoological museums. The original polyp does not die 

 when the flattened head falls away but starts again, as it 

 were, and grows a new one which, falling off in its turn, is 

 succeeded by an indefinite number of others. 



Corals grow like plants and they further resemble them in 

 that the form the colony finally assumes depends very largely 

 on the prevailing conditions. We know that plants grown 

 from identical seeds will vary a very great deal if one is 

 grown in a sheltered and otherwise favourable locality, 

 while the other is in an unfavourable situation. A plant 

 having a luxuriant growth in the valley may have a stunted 

 growth and quite a different appearance when grown on a 

 mountain top. In the case of corals, the chief factors 

 influencing growth form are the depth at which they live, 

 the degree of motion in the water, and the presence or 

 absence of sediment in the water. The common Madrepora 



