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SYSTEMATIC ZOOLOGY. 



Sponges are largely marine, only a few forms, and 

 these of no economic importance, occurring in fresh water. 

 The sponges of commerce come from the Mediterranean, 

 the Red Sea, and Florida and the West Indies. They are 

 brought up by divers or by hooks which are dragged over 

 the bottom. The fleshy portions are allowed to decay, 

 then the skeleton is washed, and the sponges are packed 



FIG. 11. Sponge (Dactyocalyx). From Lutken. 



in bundles for the market. There are different grades of 

 elasticity and fineness of fibre and consequently different 

 values. The finest sponges come from the eastern part 

 of the Mediterranean. Sponges occur as fossils, espe- 

 cially in the Cretaceous rocks. 



There are two great groups of sponges. In the first, 

 called CALCAREA, the skeleton is composed of carbonate of 

 lime; in the second, SILICEA, there is sometimes a skeleton 

 consisting of silica (quartz), sometimes of horny fibres 

 (here belong the sponges of commerce), sometimes of 

 both horny fibres and siliceous spicules; and again, there 

 are a few forms which have no skeleton. 



