108 DIATOMS 



diatoms are attached to the stems of other 

 plants under water, it is best to remove the 

 stem with its specimens. Very frequently, 

 however, they are only entangled in the 

 meshes of confervse, and can be obtained by 

 the usual ring net employed by microscopists. 

 The surface mud of ponds generally contains 

 large supplies of beautiful representatives of 

 this remarkable family. To separate them 

 from the sand, &c., the contents of the 

 bottles should be placed in distilled water 

 and allowed to remain for a time, when 

 the sand, being the heavier, will collect at 

 the bottom, and the diatoms may be 

 skimmed off. 



A few words more as to the markings 

 which the surfaces of the diatoms exhibit. 

 Some of them are arranged in lines, parallel 

 or radiating, or assume the outline of the 

 individual specimen. Some markings appear 

 as dots, others as if crossing each other. 

 Many naturalists believe that the markings 

 are depressions, but as different effects may 

 be obtained by different methods of illumina- 



