

SHALLOW-WATER FAUNA OF THE TROPICS. 57 



" insect" is used by zoologists as a general term 

 for certain air-breathing animals that are widely 

 distributed over the surface of the earth. Many 

 of them are extremely tiny, and hence the 

 natural mistake has arisen in the untrained 

 mind that all minute animals are insects. It 

 might clear the ground a little if the reader 

 would note at once that "insects" are very 

 rarely indeed marine in habit. If there is a 

 need for a popular word for the animals that 

 form coral, it should be Coral " polyps " or Coral 

 "anemones." The word "coral" has, from the 

 zoologist's point of view, a very indefinite mean- 

 ing, for it is applied to the hard skeleton of 

 carbonate of lime formed by certain Sea-weeds, 

 Sponges, and Worms, as well as to that of 

 Coral-anemones and other Polyps. In many 

 places on the British coasts the sea-bottom is 

 very largely composed of a branching Coral 

 formed by a true Sea-weed called Lithothamnion, 

 and in other places very large lumps of rock are 

 made by a Worm named Filograna. In the 

 Tropical regions, too, the well-known Nullipores, 

 which in many places play an important part in 

 the formation of Coral-reefs, are of vegetable, 

 and not animal origin. 



However, the greatest part of the Coral-reef 

 is made by animals closely related to the Sea- 

 anemones, living together in colonies ; and of all 

 the different kinds of Coral-polyps, by far the 

 most prolific as a reef-builder is one which will 

 be referred to in these pages as the Madrepore. 



Let us consider now the manner in which the 

 Polyps form the Coral. In a very old work on 



