ITS COLOURS. 118 



not certainly say. It is not visible, at any time, 

 much below the level at which the individuality of 

 the plates is lost in the rough surface. You would 

 suppose that it is pushed out from between the plates, 

 but in reality, the plates are clothed with it, as the 

 bones of a vertebrate animal are with muscles and 

 skin. When the soft parts are withdrawn, the film of 

 flesh that invests the plates is indeed extremely thin, 

 so attenuated that it is not appreciable by the senses ; 

 but, it is there, as you will perceive if you exactly 

 watch the process of protrusion. I think I have 

 before mentioned that the interior of an Actinia con- 

 sists of a number of perpendicular veils of membrane, 

 stretched from the skin to the centre, where thev all 

 meet; and if you imagine that every one of these 

 membranes is turned to stone, or, which is more 

 correct, that stony particles are deposited in the inter- 

 spaces of such veils, — you will understand the for- 

 mation of the Madrepore's skeleton, and its relation 

 to the soft investing flesh : a knowledge of the more 

 importance, since the structure of all the vast variety 

 of corals that swarm in the tropical seas will be 

 understood at the same time. 



The colours of our native Madrepore vary con- 

 siderably ; but they are always beautiful. The mouth 

 is a transverse slit, the edges or lips of which are 

 white, and minutely notched. The mouth is always 

 more or less prominent, and it can be protruded and 

 expanded to an astonishing extent. A space sur- 

 rounding the lips is commonly fawn-colour or rich 

 chestnut-brown ; then there is a star or vandyked 

 circle of vivid colour, on which the beauty of the 



