CORALS 149 
GEenus Madrepora 
Some species of these corals appear like branches, while others 
have flat, low surfaces or fronds; all of them are covered with 
innumerable small cylindrical cups. Each cup is the home of a 
polyp, which secretes calcareous matter around its column, and 
septa between its radial partitions. The corallum, when ex- 
amined with a glass, looks like meshwork. Through the fine 
openings of the porous surface, the polyps of the colony are 
connected by interlacing tubes of animal substance (ccenosare). 
The polyps of the madrepore colonies are small in comparison 
with the connecting structure, which becomes very massive; but, 
although large, the corallum is fragile, on account of its perfo- 
rated character and the exceeding delicacy of its parts. . 
In species which form incrustations, new polyps arise from 
tissue which spreads beyond the corallites. In some species cer- 
tain polyps and corallites increase in length, growing longitudi- 
nally, and continually form buds around the base. This manner 
of growth leads to the formation of branches, while the former 
manner gives lateral extension. Both of these forms of budding 
may take place at the same time in the same colony. The mad- 
repores are among the most common of the reef-builders. They 
form reefs which extend for miles around the Florida Keys. 
M, cervicornis, the stag-horn coral. This is a branching species 
which attains large size. Its manner of growth is as follows: At the tip 
of each branch is an individual polyp, which is larger than those which 
surround the branch. This is the original animal which started the 
branch, and is the parent from which all the others on the branch have 
budded. The large terminal polyp buds around the base; a surplus of 
lime also collects at the base and clogs its tissues, so that it no longer 
can perform the functions of life, and after a certain period the base 
becomes dead matter. The polyp on the upper end continues to live 
and rises above the excess of solid matter. At the same time it con- 
tinues to form new buds. The buds become independent corallites and 
secrete an excess of calcareous matter at their bases, which cements them 
to the parent stock and increases the thickness of the branch. Thus, as 
the original polyp constantly rises and buds, the colony assumes a stem- 
like form, covered with numerous individuals. Certain polyps on the 
main stem have the attributes of the parent animal. These start 
branches, and so the process goes on, and in time the colony becomes 
much branched and arborescent in form. In the living coral each little 
polyp is like a minute sea-anemone, having a colored cylindrical body 
surrounded on its upper disk with numerous tentacles. (Plate XLV.) 
