FRESH- WATER RHIZOPODS 143 



For the present we wish to notice those creatures 

 that have shells and that live in fresh water. 



The ponds and lakes of all latitudes contain 

 rhizopods, and they are found at all levels, from that 

 of the sea to a height of ten thousand feet in the 

 Rocky Mountains. There need be no difficulty, 

 therefore, in obtaining specimens for examination. 



Whenever the ground is sufficiently damp for the 

 growth of algae there will also flourish the rhizopods. 

 They occur on the dead boughs of trees submerged 

 in water, and on the stems and leaves of aquatic 

 plants. They are found in profusion in bogs and 

 marshy ground, where bog- moss, or sphagnum, grows. 

 If the water squeezed out from spJiagmun be ex- 

 amined, it will be found to contain hosts of exquisite 

 specimens. Hence, if wet samples of this bog-moss 

 be collected in preserving pans, and renewed oc- 

 casionally with water, the supply of rhizopods may 

 be kept up for a considerable time. 



To examine rhizopods it is best to tease out the 

 mosses, and to press the water from the pulpy mass 

 into a watch glass. A drop of the sediment is then 

 sufficient for placing under the microscope. 



If we look at fig. 40 we shall see drawings of a set 

 of rhizopods known as Difflugia. 1 In each case the 

 material for the shell is obtained from external 

 sources, and is fashioned in a definite shape. The 

 first three on the top row, beginning from the left, 



1 Lat. diffluo, to flow. 



