174 FOSSIL INFUSORIA. 



in the bodies of many species, which arc be- 

 Heved by Ehrenberg to be eyes." 



The least and simplest of these infusoria are 

 called monads^ which generally are spherical in 

 shape, and swim about with ease and rapidity. 

 It is not, however, the object of this notice to 

 trace the various families of infusoria, but by 

 a few general observations to show their most 

 prominent characteristics, and the singular 

 analogy between them and the minute fungi 

 brought before the reader in the foregoing- 

 parts of the volume. All geologists are ac- 

 quainted with the quantities of fossil infusoria 

 in chalk and other minerals, some of which 

 contain them to an extent per^ctly incredible, 

 until proved by ocular demo: stration. The 

 mineralised skeletons actually in many cases 

 have contributed to form solid strata of the 

 earth. There is a kind of siliceous stone from 

 Tripoli, which is comple.tely made up of skele- 

 tons or sheaths of infusoria. A single cubic 

 inch of bog iron ore contains about two mil- 

 lions of millions of microscopic animalculre. 

 Of the species of fossil infusoria thus disco- 

 vered half at least still exist. In their dead 

 state, and fossil condition, they doubtless con- 



