COMMON OBJECTS OF THE SHORE. 335 



unfit for domestic purposes. The sponges with 

 thorny framework belong mostly to the seas of 

 warmer zones, though even our common Turkey 

 sponge may be seen, on reducing it to ashes, to 

 contain a small portion of flint. The forms of the 

 spicula are invariable, and therefore constitute a 

 good characteristic of species. 



Our native sponges have not the grotesque 

 shape of the larger kinds belonging to tropical 

 seas, where balls, inverted cups, fans, and mosses 

 seem represented by them as they hang among 

 the fissures of the rock. Yet with us they fringe 

 the rock or sea cave, branching out like trees, or 

 grouping in rugged and irregular crusts, or clasp- 

 ing around the various olive-green sea-plants, or 

 forming a soft carpet on some rocky ledge. Their 

 brown or sandy-coloured branches lie about on the 

 beach, or sometimes we find them, as in the case 

 of the smallest of our native sponges (Sponyia 

 confervicola) , growing among the hair-like green 

 Arctic conferva on the rock, and contrasting its 

 brilliant white colour with the dark green tint of 

 that sea-weed. In some cases, as in a common 

 sponge (Spongiafluviatilis)) the colour varies from 

 bright green to pale brown, according to the action 

 of light, inducing many naturalists to think, that 

 though marine sponges are undoubtedly of an 

 animal nature, yet the fresh-water sponges may 

 belong to the vegetable kingdom. Many of our 

 native sponges grow within reach of the tide, 

 others down below in the deeper waters, where 

 they become of more compact structure, and are 

 less easily rent by wind or wave. 



Our figure will enable the reader to identify 

 one frequent object of our shores, the common 



