COASTLINES 



among them all there are none more ingenious and 

 remarkable than the skeletons of sponges. 



Almost all of these are supported by loose or firmly 

 fused spicules of lime or silica, or (as in the case of the 

 common bath sponge) ''over-all" skeletons consisting of 

 interwoven horny fibres. 



Occurring in great profusion, from the shores of many 

 countries outwards and downwards into the great deeps, 

 sponges are such curious animals, in their manifold struc- 

 tures and strange habits, that they remained insoluble 

 puzzles for centuries. In early times they were thought to 

 be "worm-nests" ; in later centuries they were classed 

 with seaweeds ; and it was not until a little over a century 

 ago that our real knowledge of them began. Even today 

 they remain baffling and mysterious — life-forms which 

 are among the queerest of all the extraordinary creatures 

 to be found in the world's oceans. 



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