142 ILLINOIS BIOLOGICAL MONOGRAPHS [142 



EXPLANATION OF PLATE XIII 

 Fig. 20. Showing the spawning period of the cisco in relation to the temperature of the water 

 and of the air. Data from Lake Mendota at Madison, Wisconsin, Nov. 15 to Dec. 16, 

 1916. This is typical of the conditions existing during the spawning period in the Wau- 

 kesha count}' lakes. 



