128 SOME WONDERS OF THE SEA. 



Flowers, because in many of the species the tentacles 

 have so floral an aspect, that for many centuries they 

 were considered to be flowers of the sea, having, like the 

 sensitive plants, the habit of contracting when touched. 



It is only with those Anthozoa which deposit a solid 

 skeleton that we have at present to deal, and so we 

 will proceed at once to the Madrephylles, the best- 

 known example of which is that which has been already 

 mentioned. 



If we look at the upper surface of the Madrepore, we 

 shall see that it presents a curiously striking resemblance 

 to the under surface of the common mushroom, a num- 

 ber of thin laminse, or stony plates, radiating from a 

 common centre, just as do the vegetable " gills " of the 

 mushroom. 



Turn it over, and a number of rounded ridges are seen 

 on the concave under-surface, each being covered with 

 thorny projections, and having between each pair of 

 ridges a variable number of the small thin laminae. 



If we could re-invest this mass of stony plates with 

 the creature that formed them, we should find that 

 there would be nothing but a thin film of gelatinous 

 matter, apparently without any more appearance of a 

 living structure than if it were so much glue washed 

 over the lamina? with a brush. 



Yet, if touched, the membranous film will withdraw 

 itself between the lamina?, and not return to its place 

 until some time after the irritating cause has been 

 removed. 



