American Fisheries Society. 151 
this increase of thickness of the circulating part of the lake— 
not as fast, since, for reasons which I will not stop to go into, the 
oxygen follows a little behind the temperature. But the lower, 
cooler part of the lake is still devoid of oxygen. 
In October the temperature falls and becomes practically uni- 
form throughout the lake. Corresponding to this change the 

t1G. 8—Lake Mendota, Nov. 9, 1905. 
oxygen is found at the bottom of the lake in an amount quite 
sufficiently abundant to support.any sort of animal life. In 
November (Fig. 8) the temperature has still further fallen, 
having gone to about 7°., and with the cooling of the water the 
amount of oxygen which it can hold in solution is increased, the 
amount has risen to about 8 ce. per liter, and at this time and 
