106 



PROBLEMS OF LAKE BIOLOGY 



abundant and in liard-water lake beaches 

 great concentrations of diatoms were found 

 as far back as 250 cm from the edge of the 

 water. Needless to say, the psammolittoral 

 presents many interesting j)roblems for the 

 algologist. 



Except in the early spring, the remains 

 of zooplankton organisms such as Cycloids, 

 Diapi omits, Keratella, and Pohjarthra were 

 negligible. 



In conclusion we make this statement : If 

 an '' average" 10 cc sand sample be taken 

 from the surface of a beach at a distance of 



150 cm from the edge of the water, it will 

 be found to contain 4,000,000 bacteria, 8,000 

 Protozoa, 400 Rotatoria, 40 Copepoda, 20 

 Tardigrada, and small numbers of other 

 microscopic Metazoa. The sample will be 

 found to contain from 2 to 3 cc of water. 

 In this small volume of water, then, is 

 concentrated a great population, finding all 

 conditions necessary for a flourishing exist- 

 ence. So far as the author has been able tt) 

 discover, there is no other environment 

 which is capable of supporting such a diver- 

 sified and dense population of microscopic 

 organisms. 



