542 MAN CONTROLS HIS ENVIRONMENT FOR WEALTH 



Direct use of protozoans. The protozoans have played an impor- 

 tant part in rock building. Chalk beds and limestone rocks are 

 made up to a large extent of the tiny skeletons of protozoans 

 called foraminifers. The skeletons of some species are used to 

 make a polishing powder. 



Sponges and coral. The sponges of commerce are the skeletons 

 of animals that live attached to the bottom of the sea, and are 

 composed of tough fibers of a material somewhat like that of a 

 cow's horn. This fiber is elastic and has the power to absorb 



water. The warm waters 

 of the Mediterranean Sea 

 and the West Indies fur- 

 nish most of our sponges. 

 The sponges are pulled up 

 from their resting places 

 on the bottom by means 

 of long-handled rakes 

 operated by men in boats, 

 or they are secured by 

 divers. They are then 

 spread out on the shore in 

 the sun, and the living 

 tissues allowed to decay. 

 Then after treatment con- 

 sisting of beating, bleach- 

 ing, and trimming, the 

 bath sponge is ready for 

 the market. 



Some forms of coral, the 

 skeleton of marine organ- 

 isms, are of commercial 

 value. The red or pre- 

 cious coral of the Mediter- 

 ranean Sea is highly prized 

 for ornamental purposes. 

 Pearls and mother-of-pearl. Pearls are prized the world over. 

 Most of the finest come from the oysters and clams in the waters 



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The pearl-like shells of fresh-water mussels are used 

 in button-making. These mussels are extensively 

 cultivated in the United States for this purpose. 



