THE SIMPLEST, OR ONE-CELLED ANIMALS 121 



protoplasmic network outside of the shell. In some cases 

 there is a complete layer of protoplasm— part of the body 

 protoplasm of the Protozoan — ^surrounding the cell externally. 

 When these tiny animals die their hard shells sink to 

 the bottom of the ocean, and accumulate slowly, in incon- 

 ceivable numbers, until they 

 form a thick bed on the 

 ocean floor. Large areas of 

 the bottom of the Atlantic 

 Ocean are covered with 

 this slimy ooze, called Fora- 

 minifera ooze or Radiolaria 

 ooze, depending on the kinds 

 of animals which have form- 

 ed it. Nor is it only in 

 present times that there has 

 been a forming of such 

 beds by the marine Pro- 

 tozoa. All over the world 

 there are thick rock strata 

 composed almost exclusively 

 of the fossil shells of these 

 simplest animals. The chalk- 

 beds and cliffs of England, Fig. 47. Stenlor sp.; a Protozoan 



which may be fixed, like Vorti- 

 cella, or free-swimming, and 

 which has the nucleus in the 

 shape of a string or chain of 

 bead-like bodies. The figure 

 shows a single individual as it 

 appeared when fixed, with elon- 

 gate stalked body, and as it ap- 

 peared when swimming about, 

 with contracted body. (From life.) 



and of France, Greece, 

 Spain, and America, were 

 made by Foraminifera. 

 Where now is land were 

 once oceans the bottoms of 

 which have been gradually 

 lifted above the water's sur- 

 face. Similarly the rock 

 called Tripoli found in Sicily and the Barbadoes earth 

 from the island of Barbadoes are composed of the shells 

 of ancient Radiolaria. 



