118 A NATUBALIST IN CELEBES ch. vi 



describe the varieties that are found. The hard and 

 complicated calcareous structures we see in our museums 

 under the heading Zoantharia are the shells, or skeletons 

 as they are more generally called, secreted by and sup- 

 porting a number of small anemone-like animals called 

 the polypes. The polypes are not ' insects ' nor anything 

 like insects ; they are simply sea-anemones, provided with 

 an elongated slit-like mouth surrounded by a crown of 

 simple tentacles. 



The reason that one hears so many people talk about 

 coral insects is that until quite modern times a perfectly 

 erroneous doctrine had been current about the relation of 

 the coral polypes to their shells. Many people supposed that 

 the relation between them was the same as that between the 

 bees and the honeycomb, that the coral was of the nature of 

 a hive or nest in which the coral ' insects ' could take refuge. 

 If we must make any comparison at all with other orders of 

 the animal kingdom, we might say that the coral skeleton 

 is like the shell of a whelk, with this difference, that whereas 

 every whelk has its own separate and independent shell, the 

 coral shell is very often a colonial one, being formed by 

 and giving shelter to a multitude of polypes, each of which, 

 though housed in its own compartment, is to a degree con- 

 nected with its neighbours. The hard parts of the coral, it 

 must be understood, are formed outside the body of the 

 polypes like a mollusc shell, not inside like a vertebrate 

 skeleton, and this is why it might perhaps be more consis- 

 tent to call them coral ' shells ' instead of coral ' skeletons,' 

 as is more generally done. 



Here, again, it is possible a misunderstanding may arise. 

 Although the calcareous shell is truly formed outside the 

 coral polypes, it very frequently has the appearance of being 

 inside and enclosed by them. This is entirely due to the 

 overlapping of the soft parts over the complex ridges of the 



