THE LIFE OF THE SIMPLEST ANIMALS 



19 



It is 



traced far back in the geologic history of the world, 

 an ancient type of animal structure. 



The Eadiolaria, too, which live abundantly in the pres- 

 ent oceans, especially in the marine waters of the tropical 

 and temperate zones, are found as fossils in the rocks from 

 the time of the coal age on. The siliceous shells of the 



PIG. \\.-Heliosphaera actinota (after HAECKEL) ; a radiolarian with symmetrical 



shell. 



Kadiolaria sinking to the sea bottom and accumulating 

 there in great masses form a radiolaria-ooze similar to the 

 globigerinae-ooze ; and just as with the Globigerinae, the 

 remains of the ancient Radiolaria formed thick layers on 

 the floor of the ancient oceans, which have since been up- 

 lifted and now form certain rock strata. That kind of 

 rock called Tripoli, found in Sicily, and the Barbados 

 earth from the island of Barbados, both of which are used 



