I>h'ixi<nt.<< of /,//<" and Time 



the people are arranged about the streets and 

 roads in such a manner that each can easily 

 appropriate his food from the water as it passes 

 along." 



Last and least are the single-celled organ- 

 isms grouped under the name of Protozoa, 

 making up in number of individuals what they 

 lack in size. Some, like the Infusoria, are soft, 

 and when dead leave behind no trace of their 

 existence, but others, belonging to the class 

 Rhizopoda, form beautiful shells of carbonate 

 of lime, or still more beautiful geometrical 

 skeletons of flint. The Forarninifera of to-day 

 dwell in the depths of the ocean, and in some 

 localities their minute shells accumulate to 

 form the most important constituent of the 

 soft ooze. In other places the flinty skeletons 

 of the Radiolarians predominate, and in the 

 past they have existed in such numbers as to 

 form considerable deposits of radiolarian lime- 

 stone. It gives one a vivid idea of time and 

 number to try and imagine how long it must 

 have taken and how many individuals it must 

 have required for their microscopic shells to 



51 



