14 



HISTORICAL GEOLOGY 



Fig. 1 

 A Protozoan (Amoeba) without a 

 shell. Greatly enlarged. (From 

 Shimer's "Introduction to the 

 Study of Fossils," courtesy of 

 The Macmillan Company.) 



Fig. 2 

 Shelled Protozoans (Foramin- 

 ifers). (From Shimer's "In- 

 troduction to the Study of 

 Fossils," courtesy of The 

 Macmillan Company.) 



I. Protozoans are the simplest of all animals. They consist 

 of single cells of protoplasm and are without distinct organs. Rhi- 

 zopods are the only Protozoans which are encased in shells, the 



Fig. 3 



Sponges on a shell. (Courtesy of the American 



Museum of Natural History.) 



