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THE HARMONIES OF NATURE. 



CHAPTER XV. 



SPONGES. 



Their Animal Nature Their remarkable Structure Their Skeleton Spicula 

 Sensibility and Spontaneous Movements Their Mode of Propagation Their 

 Importance in the Household of the Seas. 



THE Sponges, which were formerly supposed to belong to the 

 world of plants, have been proved by modern researches to 

 form a peculiar group of Protozoa. Attached to a solid base, 

 they revel like the polyps in every variety of shape and tint, 

 imitate like them every form of vegetation, and adorn like them 

 the submarine grounds with their fantastic shrubberies. More 

 than sixty different species have been discovered in the British 

 waters alone, and as they go on, increasing in number and 

 beauty until they attain their highest development along the 

 shores of the Tropical Ocean, they no doubt hold a conspicuous 

 rank among the living wonders of the sea. 



The first object that strikes 

 us in their organisation is 

 their skeleton, which is usually 

 composed of an irregular net- 

 work of tough horny fibres, so 

 arranged as to form a complex 

 aggregation of canals, the 

 flexibility of the fibres differ- 

 ing in different species of 

 sponge. Generally this fibrous 

 mass is interwoven with nu- 

 merous mineral spicules, which 

 serve to strengthen the fabric 

 Portion of a Sponge (Haiichondna) with and in some species entirely 



spicules projecting from the fibrous - ji r .ci i.i_ 



network. replace the horny fibre, though 



they are still so arranged as to preserve the reticulated 



