DIATOMACE&. 137 



DlATOMACE^E. This probably has been the most attrac- 

 tive class to nearly all microscopists. Diatoms are a family 

 of Confervoid Algae, in which the protoplasm is enclosed in 

 silicious valves, generally covered with very fine markings, 

 the nature of which has not yet been satisfactorily made 

 out. They are found in fresh, brackish, and salt water, 

 adhering to plants and stones, or scattered amongst peat, 

 water mosses, or Oscillatoriae, and even upon damp ground. 

 Nothing is easier than their collection, but of course it is 

 not always possible to meet with the specimens desired. 



Diatoms are often found in the stomachs of fish, especially 

 crustaceans and molluscs, and several species have been 

 found in the internal arrangements of Noctiluca miliaris, a 

 small exceedingly transparent organism of the size of a 

 grain of mustard seed, causing a phosphorescence in the 

 sea. 



A little experience will enable any one to find and to 

 gather all he may desire. Those living in the city can 

 easily procure many beautiful varieties by simply fastening 

 a muslin bag like an umbrella cover to the hydrant. After 

 securing a quantity of the sediment, empty it into a large 

 fruit jar or other receptacle nearly filled with water, and let 

 it settle. 



The green, brown, or fawn-coloured scum on the surface 

 of pools, bogs, and marshes, is mostly diatoms, and it may 

 be taken up by means of a spoon or bottle and preserved, 

 always in alcohol and water, or dried upon paper. The 

 living weeds should be taken carefully from their location 

 without much compressing or washing. The finer water 

 plants yield the richest harvest. Fresh-water forms are 

 sometimes found hanging in green-coloured masses from 

 drains, sluices, and water-pipes. To gather from the lake, 

 a net of fine muslin, having an opening in the bottom in 

 which a wide-mouthed phial is tied, may be towed at the 



