102 



PROBLEMS OF LAKE BIOLOOY 



100 150 

 Distance from water's edge. 



200 

 c-m. 



250 



300 



Fig. 6. Mean horizontal distribution of Eotatoria to a depth of 8 em. for four series of 10 ce sand samples 

 collected at a beach on the northeast shore of Muskellunge Lake, Vilas County, Wisconsin. 



in 1937 showed comparatively small num- 

 bers of psammophile rotifers (Fig-. 6), 

 with maxima of 25 and 24 per sample at 

 the and 100 cm stations. Psammobiotics 

 numbered 37 per sample at the edge of the 

 water and 59 at the 100 cm station. At the 



150 cm station the total number of rotifers 

 dropped sharply to only 15 per sample and 

 at the more distant stations less than five 

 were present. 



Fig. 7 shows the mean horizontal dis- 

 tribution of the rotifers for all samples col- 



o 



a 



50 



100 150 200 250 

 Distance from water's edge, em. 



300 



350 



Fig. 7. Mean horizontal distribution of Eotatoria to a depth of 8 cm for 49 series of 10 ce sand samples 



collected at 18 different beaches in Wisconsin. 



