46 



INTRODUCTION TO ZOOLOGY 



it grows, and making the body-wall hard and strong ; vertical 

 calcareous plates are also formed, alternating with the mesen- 

 teries or membranous septa described above. 



The Cup Coral is to be 

 found in many parts of Devon 

 and Cornwall between high 

 and low tide marks, but is more 

 plentiful in deeper water. 

 Reef- From such a 



building form as the Cup 

 Corals or Coral, it seems 

 Madrepores, ^^tural to pass on 

 directly to the reef-building 

 corals of warmer seas, the 

 Madrepores. In these forms, 

 the young polyps bud, and 

 the resulting individuals re- 

 main connected together, so 

 that colonies are formed as 

 in the Hydrozoa. 



Each polyp before it buds 

 produces its own stony sup- 

 port, having a form similar to 

 that described in Caryophyllia, 

 i.e. with a stony base, cup-like 

 wall, and vertical septa. When 

 it buds, this "skeleton" is 

 added to continuously, but the 

 living tissues at the base gradually die, the polyps only inhabit- 

 ing the ends of the branches. So the colony grows, year after 

 year, continually increasing in size, and in time consisting of 

 thousands of living polyps occupying the ends of branches 

 which have arisen in connection with, and still are attached 

 to, a mass of calcareous matter, representing the supports of 

 the ancestral polyps. Fig. 23 represents a small branch with 

 the cups of about 200 polyps attached to it. In this way 

 immense belts of solid calcareous rock have been constructed 

 by these minute soft-bodied animals, and it is such rock that 

 forms the banks known as ooral reefs. 



These colonial forms flourish best in water not deeper than 

 twenty fathoms, and of a temperature not lower than 68° F., 



Fig. 22. — The Devon Cup Coral 

 [Garyophyllia smithii). 



A, Live specimen with polyp intact. 

 B, Calcareous skeleton. 



